Hydraulic system. Types of hydraulics: general classifications Design, operating principle of the hydraulic system

February 10, 2016

A hydraulic system is a device designed to convert small forces into large ones by using a fluid to transmit energy. There are many varieties of nodes operating according to this principle. The popularity of systems of this type is explained primarily by their high efficiency, reliability and relative simplicity of design.

Scope of use

This type of system is widely used:

1. In industry. Very often, hydraulics are an element of the design of metal-cutting machines, equipment intended for transporting products, loading/unloading them, etc.
2. In the aerospace industry. Similar systems are used in various kinds controls and chassis.
3. IN agriculture. It is through hydraulics that the attachments of tractors and bulldozers are usually controlled.
4. In the field of cargo transportation. Cars often have a hydraulic braking system.
5. In ship equipment. Hydraulics in in this case used in steering, included in the design of turbines.

Operating principle

Any hydraulic system operates on the principle of a conventional fluid lever. The working medium supplied inside such a unit (in most cases, oil) creates the same pressure at all its points. This means that by applying a small force on a small area, you can withstand a significant load on a large one.

Next, we will consider the principle of operation of such a device using the example of such a unit as the hydraulic brake system of a car. The design of the latter is quite simple. Its circuit includes several cylinders (main brake, filled with liquid, and auxiliary). All these elements are connected to each other by tubes. When the driver presses the pedal, the piston in the master cylinder moves. As a result, the liquid begins to move through the tubes and enters the auxiliary cylinders located next to the wheels. After this, the braking is applied.

Design of industrial systems

The hydraulic brake of a car - the design, as you can see, is quite simple. Used in industrial machines and mechanisms liquid devices more complicated. Their design may be different (depending on the scope of application). However, the basic design of an industrial-style hydraulic system is always the same. Typically it includes the following elements:

1. Liquid reservoir with neck and fan.
2. Filter rough cleaning. This element is designed to remove various types of mechanical impurities from the liquid entering the system.
3. Pump.
4. Control system.
5. Working cylinder.
6. Two filters fine cleaning(on the supply and return lines).
7. Distribution valve. This structural element is designed to direct fluid to the cylinder or back to the tank.
8. Reverse and safety valve s.

Hydraulic system operation industrial equipment also based on the fluid lever principle. Under the influence of gravity, the oil in such a system enters the pump. It is then directed to the control valve and then to the cylinder piston, creating pressure. The pump in such systems is not designed to suck in liquid, but only to move its volume. That is, the pressure is created not as a result of its work, but under the load from the piston. Below is a schematic diagram of the hydraulic system.

Advantages and disadvantages of hydraulic systems

The advantages of units operating on this principle include:

• The ability to move large-sized and weighted loads with maximum precision.
• Virtually unlimited speed range.
• Smooth operation.
• Reliability and long term services. All components of such equipment can be easily protected from overloads by installing simple pressure relief valves.
• Economical in operation and small in size.

In addition to the advantages, hydraulic industrial systems, of course, also have certain disadvantages. These include:

• Increased risk of fire during operation. Most fluids used in hydraulic systems ah, they are flammable.
• Sensitivity of equipment to contamination.
• The possibility of oil leaks, and therefore the need to eliminate them.

Hydraulic system calculation

When designing such devices, many of the most important factors are taken into account. various factors. These include, for example, the kinematic coefficient of viscosity of the liquid, its density, the length of pipelines, rod diameters, etc.

The main goals of performing calculations for a device such as a hydraulic system are most often to determine:

• Pump characteristics.
• The stroke values ​​of the rods.
• Working pressure.
• Hydraulic characteristics of lines, other elements and the entire system as a whole.

The hydraulic system is calculated using various arithmetic formulas. For example, pressure losses in pipelines are determined as follows:

1. The estimated length of the highways is divided by their diameter.
2. The product of the density of the liquid used and the square average speed streams are divided into two.
3. Multiply the resulting values.
4. Multiply the result by the travel loss coefficient.

The formula itself looks like this:

• ∆p i = λ x l i(p) : d x pV 2: 2.

In general, in this case, the calculation of losses in highways is carried out approximately according to the same principle as in such simple designs like hydraulic heating systems. Other formulas are used to determine pump characteristics, piston stroke, etc.

Types of hydraulic systems

All such devices are divided into two main groups: open and closed type. The schematic diagram of the hydraulic system we considered above belongs to the first type. Open design They usually have devices of low and medium power. More complex closed-type systems use a hydraulic motor instead of a cylinder. The liquid enters it from the pump and then returns to the main line.

How the repair is carried out

Since the hydraulic system in machines and mechanisms plays a significant role, its maintenance is often entrusted to highly qualified specialists from companies engaged in this particular type of activity. Such companies usually provide a full range of services related to the repair of special equipment and hydraulics.

Of course, these companies have all the equipment necessary to carry out such work. Hydraulic system repairs are usually performed on site. Before carrying it out, in most cases, various kinds of diagnostic measures must be carried out. To achieve this, hydraulic service companies use special installations. Employees of such companies also usually bring the components necessary to fix problems with them.

Pneumatic systems

In addition to hydraulic ones, pneumatic devices can be used to drive components of various types of mechanisms. They work on approximately the same principle. However, in this case the energy is converted into mechanical compressed air, not water. Both hydraulic and pneumatic systems cope with their task quite effectively.

The advantage of devices of the second type is, first of all, the absence of the need to return the working fluid back to the compressor. The advantage of hydraulic systems compared to pneumatic ones is that the environment in them does not overheat or overcool, and therefore, there is no need to include any additional components or parts in the circuit.

2015-11-15

Hydraulic drive(volumetric hydraulic drive) is a set of volumetric hydraulic machines, hydraulic equipment and other devices designed to transmit mechanical energy and convert motion through fluid. (T.M Bashta Hydraulics, hydraulic machines and hydraulic drives).

The hydraulic drive includes one or more hydraulic motors, fluid energy sources, control equipment and connecting lines.

The operation of the hydraulic drive is based on the principle

Let's consider the system.

In this system, the force created on piston 2 can be determined by the dependence:

It turns out that force depends on area ratio, the larger the area of ​​the second piston, and the smaller area first, the greater the difference between the forces F1 and F2. Thanks to the hydraulic lever principle, you can get a lot of force with little effort.

Gaining in effort on a hydraulic lever, you will have to sacrifice movement, having moved the small piston by the amount l1, we obtain the movement of piston 2 by the amount l2:

Considering that the area of ​​the piston S2 is greater than the area of ​​S1, we obtain that the displacement l2 is less than l1.

The hydraulic drive would not be so useful if the loss in movement could not be compensated, but this was done thanks to special hydraulic devices -.

A check valve is a device for blocking flow moving in one direction, and allowing the return flow to pass freely.

If in the example considered, install at the output of the chamber with piston 1 check valve , so that the liquid can leave the chamber, but cannot flow back. The second valve must be installed between the chamber with piston 1 and the additional tank with liquid, so that the liquid can enter the chamber with, and cannot flow from this chamber back into the tank.

The new system will look like this.

By applying a force F1 to the piston and moving it a distance l1, we obtain the movement of the piston with a force F2 at a distance l2. Then we move piston 1 to the initial distance; liquid will not be able to flow back from the chamber with piston 2 - the check valve will not allow it - piston 2 will remain in place. Liquid from the tank will flow into the chamber with piston one. Then, you need to again apply force F1 to piston 1 and move it by distance l1, as a result of which piston 2 will again move to distance l2 with force F2. And in relation to the initial position, in two cycles piston 2 will move a distance of 2*l2. By increasing the number of cycles, it is possible to obtain a larger displacement of piston 2.

It was the ability to increase movement by increasing the number of cycles that allowed the hydraulic lever to get ahead of the mechanical lever in terms of the possible force developed.

Drives where it is necessary to develop enormous forces are usually hydraulic.

The unit with the chamber and piston 1, as well as with check valves in hydraulics is called pump. Piston 2 with chamber - hydraulic motor, in this case - .

Distributor in hydraulic drive

What to do if in the system under consideration it is necessary to return piston 2 to its initial position? With the current configuration of the system, this is impossible. The liquid from under piston 2 cannot flow back - the check valve will not allow it, which means a device is needed that allows the liquid to be sent to the tank. You can use a simple tap.

But in hydraulics there is a special device for directing flows - distributor, allowing you to direct fluid flows according to the desired direction.

Let's get acquainted with the operation of the resulting hydraulic drive.

Devices in hydraulic drives

Modern hydraulic drives are complex systems, consisting of many elements. The design of which is not simple. In the presented example there are no such devices, because they are generally intended to achieve required characteristics drive.

The most common hydraulic devices

• Safety valves
• Reducing valves
• Flow regulators
• Chokes

You can get information about hydraulic devices on our website in the - section. If you have any questions, ask them in the comments to this article.

Hydraulic systems are used in a variety of equipment, but each operates on a similar principle. It is based on the classical Pascal's law, discovered in the 17th century. According to him, pressure that is applied to a volume of liquid creates force. It is transmitted evenly in all directions and creates the same pressure at each point.

The basis of any type of hydraulics is the use of fluid energy and the ability, with little effort, to withstand an increased load over a large area - the so-called hydraulic multiplier. Thus, hydraulics can include all types of devices that operate using hydraulic energy.

Special equipment with hydraulic units
Hydropowered robots at the Kamaz plant

Types of hydraulics by area of ​​application

Despite the common “foundation,” hydraulic systems are striking in their diversity. From basic hydraulic designs consisting of a few cylinders and tubes, to those that combine hydraulic elements and electrical solutions, they demonstrate the breadth of engineering and bring practical benefits to a wide variety of industries:

• industry - as an element of foundry, pressing, transportation and loading and unloading equipment, metal-cutting machines, conveyors;
• in agriculture - the attachments of tractors, excavators, combine harvesters and bulldozers are controlled by hydraulic units;
• automotive production: a hydraulic braking system is a “must have” for modern passenger cars and trucks;
• aerospace industry: systems, independent or combined with pneumatics, are used in chassis, control devices;
• construction: almost all special equipment is equipped with hydraulic units;
• marine technology: hydraulic systems are used in turbines, steering;
• oil and gas production, offshore drilling, energy, logging and storage, housing and communal services and many other areas.

Hydraulic station for lathe

In industry (for metal-cutting and other machine tools), modern productive hydraulics are used due to its ability to provide optimal mode work using stepless regulation, obtaining smooth and precise movements of the equipment and ease of automation.

Systems with automatic control, and in construction, landscaping, road and other works - excavators and other tracked or wheeled vehicles with hydraulic units. The hydraulic system operates from a vehicle motor (ICE or electric) and ensures the functioning of attachments - buckets, booms, forks, and so on.

Hydraulic backhoe loader

Types of hydraulics with different hydraulic drives

In equipment for different areas hydraulic drives of one of two types are used - hydrodynamic, operating primarily on kinetic energy, or volumetric. The latter use the potential energy of liquid pressure and provide high pressure and, thanks to technical excellence, are widely used in modern cars. Systems with compact and efficient volumetric drives are installed on heavy-duty excavators and machine tools - their operating pressure reaches 300 MPa or more.

An example of a technique with a volumetric hydraulic drive
Hydraulic turbine impeller for hydroelectric power station

Volumetric hydraulic drives are used in most modern hydraulic systems installed in presses, excavators and construction equipment, metalworking machines, and so on. Devices are classified by:

• the nature of the movement of the output links of the hydraulic motor - it can be rotational (with a driven shaft or housing), translational or rotary, with movement at an angle of up to 270 degrees;
• regulation: adjustable and unregulated in manual or automatic mode, throttle, volumetric or volumetric throttle method;
• circulation circuits of working fluids - compact closed, used in mobile equipment, and open, which communicates with a separate hydraulic tank;
• sources of liquid supply: with pumps or hydraulic drives, mainline or autonomous;
• engine type - electric, internal combustion engines in cars and special equipment, ship turbines, and so on.

Siemens turbine with hydraulic drive

Design of different types of hydraulics

In industry, they use machines and mechanisms with a complex structure, but, as a rule, the hydraulics in them work according to the general schematic diagram. The system includes:

• a working hydraulic cylinder that converts hydraulic energy into mechanical movement (or, in more powerful industrial systems, hydraulic motor);
• hydraulic pump;
• a tank for working fluid, which contains a neck, a breather and a fan;
• valves - non-return, safety and distribution valves (directing liquid to the cylinder or into the reservoir);
• fine filters (one each on the supply and return line) and rough cleaning - to remove mechanical impurities;
• a system that controls all elements;
• circuit (pressure tanks, piping and other components), seals and gaskets.

Classic scheme of a separate hydraulic system

Depending on the type of hydraulic system, its design may differ - this affects the scope of application of the device and its operating parameters.

Standard hydraulic brake cylinder for the Niva SK-5 combine harvester

Types of hydraulic system structural elements

First of all, the type of drive is important - the part of the hydraulics that converts energy. The cylinders are of the rotary type, and can direct fluids to only one end or both (single or double action, respectively). Their effort is directed rectilinearly. Open-type hydraulics with cylinders that impart reciprocating motion to the output links are used in low- and medium-power equipment.

Special equipment with hydraulic motor

In complex industrial systems, instead of working cylinders, hydraulic motors are installed, into which liquid flows from the pump and then returns to the main line. Hydraulic motors impart rotational motion to the output links with an unlimited rotation angle. They are driven by hydraulic fluid supplied by the pump, which in turn causes them to rotate. mechanical elements. In equipment for different areas, gear, blade or piston hydraulic motors are installed.

Radial piston hydraulic motor

The flows in the system are controlled by hydraulic valves - throttling and guide valves. Based on their design features, they are divided into three types: spool, valve and valve. Hydraulic distributors of the first type are most in demand in industry, engineering systems and communications. Spool models are easy to use, compact and reliable.

Hydraulic pump- another fundamentally important element of hydraulics. Equipment that converts mechanical energy into pressure energy is used in closed and open hydraulic systems. For equipment operating in “harsh” conditions (drilling, mining, etc.), dynamic type models are installed - they are less sensitive to pollution and impurities.

Hydraulic pump
Sectional view of a hydraulic pump
Hydraulic pump-hydraulic motor pair

Pumps are also classified according to their action - forced or non-forced. In most modern hydraulic systems that use high pressure, pumps of the first type are installed. Based on their design, the following models are distinguished:

• gear;
• lobed;
• piston - axial and radial types.
• and etc.

Hydroficated manipulators for 3D printing

There are ways to use the laws of hydraulics - manufacturers come up with new models of machinery and equipment. Among the most interesting are hydraulic systems installed in 3D printing manipulators, collaborative robots, medical microfluidic devices, aviation and other equipment. Therefore, any classification cannot be considered complete - scientific progress supplements it almost every day.

pi4 workerbot - an ultra-modern industrial robot that reproduces facial expressions

3D printed hydraulic manipulator

Hydraulic equipment on aircraft plant lines

HYDRAULIC DRIVE

DRIVE TYPES

To transfer mechanical energy from the internal combustion engine to the actuators of the working equipment, a hydraulic drive (hydraulic drive) is used, in which the mechanical energy at the input is converted into hydraulic energy, and then on exiting again into the mechanical, driving the mechanisms of the working equipment. Hydraulic energy is transmitted by a fluid (usually mineral oil), which serves as the working fluid of the hydraulic drive and is called the working fluid.

Depending on the type of transmission used, the hydraulic drive is divided into volumetric and hydrodynamic.

In a volumetric hydraulic drive Volumetric hydraulic transmission is used. In it, energy is transferred by static pressure (potential energy) of the working fluid, which is created by a positive displacement pump and is realized in a hydraulic motor of the same type, for example in a hydraulic cylinder.

In a volumetric hydraulic drive, a volumetric pump serves as a converter of mechanical energy at the input to the hydraulic transmission. Displacement of liquid from the working chambers of the pump and filling of the suction chambers with it occurs as a result of a decrease or increase in the geometric volume of these chambers, hermetically separated from each other. The work of displacement and suction is performed by the working body of the pump - a plunger, piston, plate, gear, depending on the type of pump . The reverse energy converter in the volumetric hydraulic transmission is a hydraulic motor, the working stroke of which is carried out as a result of an increase in the volume of the working chambers under the influence of liquid entering them under pressure.

Energy converters in a hydraulic drive (pumps and an engine are called hydraulic machines. The operation of a hydraulic machine is based on a change in the volume of the working chambers as a result of the supply of mechanical energy (pump) or as a result of the supply of hydraulic energy by a flow of working fluid under pressure (engine).

Energy is transmitted through pipelines, including flexible hoses, to any location on the machine. This feature of the hydraulic drive is called remoteness. Using a hydraulic drive, it is possible to drive several actuator motors from one pump or a group of pumps, and it is possible to switch on the motors independently.

The principle of operation of the hydraulic drive is based on the use of two main properties of the working fluid of the hydraulic transmission - the working fluid. The first property is that the liquid is an elastic body and is practically incompressible; second, in a closed volume of liquid, a change in pressure at each point is transmitted to other points without change. Let's consider the operation of a hydraulic drive using the example of a hydraulic jack (Fig. 56). The volumetric hydraulic drive includes a pump, tank and hydraulic motor. The volumetric pump is formed by a cylinder /, a plunger 2 s earring 3 and handle 4. The progressive hydraulic motor includes a cylinder 7 and a plunger 6. These components are connected by pipelines called hydraulic lines. The hydraulic lines are equipped with reverse

Rice. 56. Hydraulic jack:

/, 7 - cylinders, 2, 6 - plunger, 3 - earring, 4 - handle, 5 - tank, 8 - hydraulic line, 9 - valve, 10, 11 - valves

valves 10 And //. Valve 10 allows liquid to pass only in the direction away from the cylinder cavity 1 to the cylinder cavity 7, and the valve 11 - from tank 5 to cylinder /. The cavity of the cylinder 7 is connected by an additional hydraulic line to the tank 5. A shut-off valve is installed in this hydraulic line 9, which closes this line when the pump is running.

By swinging the handle 4 plunger 2 reciprocating motion is reported. When moving upward, the plunger sucks working fluid from the tank 5 through the valve // ​​into the cylinder cavity /. Liquid fills the cylinder cavity under the action atmospheric pressure and the liquid is in the tank. When entering downward, liquid from the cylinder cavity / is forced into the cylinder cavity 7 through the valve 10. Due to incompressibility, the volume of liquid displaced from the cylinder cavity completely enters the cylinder cavity 7 and raises the plunger to a certain height.

Plunger stroke 2 the downward stroke of the pump is working, and the upward stroke is idle; the hydraulic line connecting the tank to the pump is called suction; the hydraulic line connecting the pump to the hydraulic motor is called pressure. Multiple valves act as flow distributors and ensure continuity of pump operation.

Plunger 6 When the pump is running, it moves only in one direction - up. In order for the plunger 6 lower down (under

influence of external load or gravity), it is necessary to open the valve and release liquid from the cavity of the cylinder 7 into the tank.

Let's look at the main technical characteristics of the pump. When the pump plunger moves from one extreme position to another, the volume of the cylinder 1 change the value equal toVi = Fi* Si, where Fi and Si - respectively, the area and stroke of the plunger. This volume determines theoretical presentation pump in one stroke and is called working volume a. In pumps where the input link does not reciprocate, but performs continuous rotational motion, the displacement is called the flow rate per shaft revolution. The working volume is measured in dm 3, l, cm 3.

The product of the working volume and the number of working strokes or revolutions of the pump shaft input per unit of time - theoretical pump flow Q , measured in l/min, determines the speed of the actuators.

The liquid, enclosed in a closed volume between the plungers of the pump and the actuator cylinder, at rest acts on their working areas with the same pressure. This pressure also acts on the walls of cylinders and pipelines. It depends on the magnitude of the external load. Fluid pressure, or working pressure hydraulic drive, is called the force per unit of the working surface of the plungers, cylinder walls and pipelines, etc. Exceeding the pressure above the working one, for which the parts and mechanisms of the hydraulic drive are designed, leads to their premature wear and can cause rupture of pipelines and other breakdowns.

Since the fluid pressure is transmitted uniformly in all directions and the forces are balanced by this pressure, then, provided that the friction of the plungers and their seals is neglected, the working pressure Pi == pF- i; Pg == pFs, where p is the working pressure.

This inverse proportionality relationship represents the gear ratio of a hydraulic drive with translational hydraulic machines. It is similar to the gear ratio of a simple lever. Indeed, if to the long end of the handle 4 apply force R, then with this lever you can overcome the force P, which is so many times greater d R[, how many times is the short arm of the lever less than the long one, and the path S 1 is so much less than the path S2, how many times the short arm of the lever is less than the long one. This leverage is also represented in the form of inverse proportionality.

In hydraulic drive mechanical energy sources, internal combustion engines and electric motors, the output link is a rotating shaft, from which one or more hydraulic pumps are driven, which also have a rotating shaft as an input link. The rotary hydraulic drive (Fig. 57) includes, for example, a pump and motor of the same design.

The pump consists of a stationary housing (stator), a rotating rotor 3, in longitudinal grooves 4 which slide gates 5 and 6. ( The rotor is shifted relative to the stator axis (to the left in the figure), therefore, when rotating, its outer surface either approaches or moves away from the inner surface of the housing. The gates 5, rotating together with the rotor and sliding along the walls of the stator, simultaneously move into the grooves or move out of the grooves of the rotor. If you rotate the rotor in the direction indicated by the arrow, then between its wall, the housing wall and the gate 5 a continuously expanding crescent-shaped cavity is formedAi, into which the working fluid will be sucked from tank 1. CavityBiat this time it will continuously decrease in volume and the liquid in it will be forced out of the pump body through the tap 8 and feed to the motor.

In the valve position shown in the figure 8 liquid will fill the cavity Ai and apply pressure on the gate 11, forcing it along with the rotor 10 turn clockwise. From cavity 5.2 liquid through the tap 8 will be forced into the tank. With further rotation of the rotor 3 pump ta- __________

Fig. 57, Rotary hydraulic drive:

1 - tank, 2, 13 - housings, 3, 10 - rotors. 4 - groove, 5, 6, 9, II - gates, 7 - valve, 8 - tap, A i, Bi- pump cavities, A i, B i - motor cavities

what kind of work will the gates do? 6 pump and gate 9 motor, and the process of rotation of the rotor will proceed continuously.

In order to rotate the motor rotor in the opposite direction, you need to switch the tap 8. Then the cavity B1 the pump will communicate with the cavity B2 motor and into this cavity the working fluid will flow under pressure, and from the cavity Lz the liquid will drain into the tank. If the motor is overloaded, its rotor will stop while the pump will continue to supply liquid. As a result, the pressure in the cavity of the pump, hydraulic motor and pressure pipeline will increase until safety valve 7 opens, releasing liquid into the tank and thereby protecting the hydraulic transmission from damage.

Rotational motion is transmitted in the same way as in a belt drive. In the latter, mechanical energy is transmitted through a belt, in hydraulic transmission - by the flow of working fluid. In a belt drive, the number of revolutions of the driving and driven pulleys is inversely proportional to the ratio of their radii. With the same amount of passing fluid, the rotation speed of the pump and motor rotors is inversely proportional to their working volumes. These relationships are valid in the absence of volumetric losses in transmissions.

The power transmitted through a belt drive can be increased by increasing the width of the belt while keeping the rotation speed constant. Obviously, in hydraulic transmission this can be achieved (at constant pressure) by increasing the working volume of the pump by, for example, expanding the housing and rotor with plates.

For a hydraulic drive that includes a drive pump and a hydraulic motor on an actuator, the overall efficiency is the ratio of the power removed from the hydraulic motor shaft to the power supplied to the pump shaft.

The hydraulic drive of loaders includes components inherent in any hydraulic drive: a pump, hydraulic motors and devices for controlling the flow and protecting the hydraulic system from overloads.

Rice. 58. Block diagram of the hydraulic drive:

1, 2, 3, 4. 5. 6 - hydraulic lines; ICE - internal combustion engine, N - pump, B - tank, P - safety valve, M - pressure gauge, R- distributor;

D1, D2, D3 - hydraulic motors. N - supplied energy, N 1, N 2, N 3 - energy consumed

rice. Figure 58 shows a typical block diagram of a hydraulic drive. ut yes internal combustion engine ICE energy goes to the pump N can be expended through hydraulic motors D1, D2 and D3 a drive of the working mechanisms of the machine. The working fluid enters the pump from the tank B via suction hydraulic line 1 and supplied through a pressure hydraulic line 2 to the distributor R, in front of which a safety valve is installed P. Distributor R connected to each hydraulic motor by executive hydraulic lines 4, 5 And 6. A pressure gauge is installed in the pressure line M to control pressure in the hydraulic system.

When the hydraulic motors are turned off, the working fluid of the hydraulic drive - liquid - is pumped over by a pump N from the tank B to distributor R 0 back to tank B. The suction, pressure and drain lines form a circulation circuit. Coming from ICE energy is spent to overcome mechanical and hydraulic losses in the circulation circuit. This energy is mainly used to heat the fluid and hydraulic system.

The hydraulic motor is activated by the distributor R, at the same time, it performs the functions of regulating the flow both in terms of flow rate (at the moment of switching on) and in the direction of fluid movement (reversal) to the engines. Reversible hydraulic motors are connected to the distributor by two executive lines, which in turn are connected alternately to the pressure line 2 or drain 3 circulation circuit lines depending on the required direction of engine movement.

During operation of the hydraulic motor, the circulation circuit turns on the engine and its executive hydraulic lines; when stopped, for example, when the hydraulic cylinder rod approaches the extreme position, the circulation circuit is interrupted and a state of overload of the hydraulic system occurs, since the pump N continues to receive energy from the engine ICE. In this case, the pressure will begin to increase sharply and as a result, the engine will either stop ICE, or one of the hydraulic system mechanisms fails, for example, a hydraulic line breaks 2. To prevent this from happening, a safety valve is installed on the pressure hydraulic line. P and pressure gauge M. The valve is adjusted to a pressure higher than the operating pressure, usually 10-15%. When this pressure is reached, the valve is activated and connects

pressure hydraulic line 2 with drain 3, restoring the fluid circulation circle.

In some cases, to reduce the speed of the hydraulic motor, a throttle is installed in one executive line, limiting the supply of fluid to the motor at a given pressure. If the pump performance turns out to be greater than the specified value, the valve releases part of the liquid to be drained into the tank. Pressure gauge M designed to control pressure in the hydraulic system.

Hydraulic systems of machines usually include additional devices: controllable check valves (hydraulic locks), rotating joints (hydraulic joints), filters; distributors with o built-in safety and check valves. Loaders use power steering, which also belongs to the hydraulic drive, but has its own characteristics devices and work.

In hydrodynamic drive hydrodynamic transmission is used, in which energy is also transferred by a liquid, but the main importance is not the pressure (pressure energy), but the speed of movement of this liquid in its circle of circulation, i.e. kinetic energy.

In a hydromechanical transmission, the clutch and gearbox are eliminated, and the vehicle’s driving mode is changed without disconnecting the transmission from the engine by changing its rotation speed, which made it possible to reduce the number of controls.

Rice. 59. Hydrodynamic transmission:

1 - axis, 2, 16 - shafts, .3 - coupling, 4, 5, 9 - wheels. 6 - ring gear, 7 - flywheel, 8 - oil indicator, 10, 22, 23 - gears, II, 14- T op mosa. 12, I3 - blockgears, 15 - drum, 17 - lid, 18 - distributor, 19 - screw, 20 - n aco With 21 - filter, 24 - crankcase

The hydrodynamic transmission (Fig. 59) contains a torque converter located in one crankcase and two planetary gears. The torque converter is designed to change the torque on the output shaft, replacing the clutch and gearbox, and planetary gears are used to change the direction of movement of the machine, replacing the reverse mechanism.

The torque converter consists of a pump 9, turbine 5 and reactor 4 wheels The pump wheel is connected to the flywheel 7 of the engine, the turbine wheel is connected to the shaft 2, reactor wheel via overrunning clutch 3 connected to the axis / mounted on the crankcase 24. Planetary block gear 13 fixed on the output shaft 16 and interacts on one side with the satellite gears of the block gear 12, s the other is the brake drum sun gear 15. Block gear 12 freely mounted on the crankcase shaft, meshes with the block gear pinions 13, and the outer surface forms a brake pulley interacting with the brake 11. Pump wheel 9 contains gear 10, which is connected to the gear through the wheel 22 hydraulic pump 20.

The pump, turbine and reactor wheels are made with blades located at an angle to the plane of rotation.

Band brakes are actuated by hydraulic cylinders using a distributor 18, which is controlled by a handle on the control panel. When moving forward, the drum brakes 15, at the rear - block 12. Pump 20 Designed to pump oil to the torque converter, planetary gears and brake control cylinders.

When the engine is running, the oil between the blades of the pump wheel, under the action of centrifugal forces, is pressed to the periphery of the wheel and directed to the blades of the turbine wheel, and then towards the stationary blades of the reactor wheel.

At low engine speeds, the oil rotates the reactor wheel, while the turbine wheel remains stationary. As the speed increases, the overrunning clutch 3 jams on the shaft and the turbine wheel begins to rotate, transmitting engine torque through planetary gears to the output shaft 16. The direction of rotation of this shaft depends on which brake is applied. As the engine speed increases, the torque on the shaft 16 decreases and the rotation speed increases. Between input shaft 16 and the drive axle is equipped with a single-stage gearbox with a gear ratio of 0.869.

Under operating conditions, monitor the oil level and its cleanliness. Filter 21

washed systematically. Frequent clogging indicates the need to change the oil.

WORKING FLUIDS

The working fluid of hydraulic systems is considered as component hydraulic drive, since it serves as the working fluid of the hydraulic transmission. At the same time, the working fluid cools the hydraulic system, lubricates rubbing parts and protects parts from corrosion. Therefore, the performance, service life and reliability of the hydraulic drive depend on the properties of the fluid.

Forklifts operate outdoors in many different areas of the country. In the cold season, the machine and working fluid can be cooled to -55 ° C, and in some areas of the Middle Asia In summer, during operation, the liquid heats up to 80 °C. On average, the fluid should ensure the hydraulic drive operates within those temperatures from -40 to +50 "C. The fluid must have a long service life, be neutral to the materials used in the hydraulic drive, especially rubber seals, and also have good heat capacity and at the same time thermal conductivity in order to cool the hydraulic system.

Mineral oils are used as working fluids. However, there are no oils that are suitable for all operating conditions at the same time. Therefore, depending on their properties, oils are selected for specific operating conditions (climatic zone in which the machine is used and time of year).

The reliability and durability of the hydraulic system largely depend on the correct selection of the working fluid, as well as on the stability of the properties.

One of the main indicators by which they select and evaluate

oils, this is the viscosity. Viscosity characterizes the ability of a working fluid to resist shear deformation; measured in centistokes (cSt) at a given temperature (usually 50 °C) and in conventional units - degrees Engler, which are determined using a viscometer and express the ratio of the time a liquid of a given volume (200 cm 3) flows through a calibrated hole to the time the same volume flows water. The ability of a hydraulic drive to operate at low and low temperatures primarily depends on viscosity. high temperatures. As the machine operates, the viscosity of the working fluid decreases and its lubricating properties deteriorate, which shortens the service life of the hydraulic drive.

During oxidation, resinous deposits fall out of the oil, forming a thin hard coating on the working surfaces of parts that are destructive to rubber seals and filter elements. The intensity of oil oxidation increases sharply with increasing temperature, so it should not be allowed to increase pace oil temperature above 70 °C.

Typically, working fluids are completely replaced in spring and autumn.

If all-season oil is used, it must be replaced after 300-1000 hours of hydraulic drive operation, depending on the type (the replacement period is indicated in the instructions), but at least once a year. In this case, the system is washed with kerosene Idling. The frequency of replacement depends on the brand of liquid, the operating mode of the system volume and the tank in relation to the pump supply. The larger the system capacity, the less frequently the oil needs to be changed.

The durability of the hydraulic system is affected by the presence of mechanical impurities in the oil, therefore filters are included in the hydraulic system cleaning oil from mechanical impurities, as well as magnetic plugs.

The basis for choosing oil for the hydraulic system is the temperature of the limit of use of this fluid, depending on the type of hydraulic drive pump. The lower temperature limit of use is determined not by the pour point of the working fluids, but by the pumpability limit of the pump, taking into account losses in the suction hydraulic line. for gear pumps, this limit is a viscosity of 3000-5000 cSt, which corresponds to the pumpability limit during short-term (start-up) operation. The lower temperature limit of stable operation is determined by filling the working chamber of the pump, at which the volumetric efficiency reaches its greatest value, which approximately for gear pumps corresponds to a viscosity of 1250-1400 cSt.

The upper temperature limit for the use of the working fluid is determined by the lowest viscosity value, taking into account its heating during operation. Exceeding this limit causes an increase in volumetric losses, as well as sticking of the surfaces of mating friction pairs, their intense local heating and wear due to deterioration of the lubricating properties of the oil.

The basis for the use of a particular type of oil is the recommendation of the manufacturer of the hydraulic drive machine.

Before adding or changing oil, check the neutrality of the mixed oils. The appearance of flakes, sedimentation and foaming indicate that mixing is unacceptable. In this case, the old oil must be drained and the system flushed.

When filling the system, measures are taken to ensure the purity of the oil being poured. To do this, check the serviceability of the filling filters, the cleanliness of the funnel and the filling container.

HYDRAULIC MACHINES

In a volumetric hydraulic drive, hydraulic machines are used: pumps, pump motors and hydraulic motors, the operation of which is based on alternately filling the working chamber with working fluid and displacing it from the working chamber.

Pumps convert the mechanical energy supplied to them from the engine into the energy of fluid flow. Rotational motion is imparted to the pump input shaft. Their input parameter is the shaft rotation speed, and the output parameter is the fluid supply. The liquid moves in the pump due to its displacement from the working chambers by pistons, gates (blades), gear teeth, etc. In this case, the working chamber is a closed space, which during operation alternately communicates with either the suction hydraulic line or the pressure line.

In hydraulic motors, the energy of the working fluid flow is converted back into mechanical energy at the output link (hydraulic motor shaft), which also performs rotational motion. Based on the nature of the movement of the output link, a distinction is made between rotary motion engines - hydraulic motors and translational motion engines - hydraulic cylinders.

Hydraulic motors and pumps are divided according to the possibility of regulation, the possibility of changing the direction of rotation, according to the design of the working chamber and other design features.

Some designs of pumps (hydraulic motors) can perform the functions of a hydraulic motor (pump); they are called pump-motors.

Loaders use unregulated (non-reversible) pumps of various designs: gear, vane, axial piston. Adjustable hydraulic motors (pumps) have a variable volume of working chambers.

A gear pump (Fig. 60) consists of a pair of interlocking gears, placed in a housing that tightly encloses them, having channels on the input and output sides of the mesh. Pumps with external spur gears are the simplest and are characterized by reliability in operation, small overall dimensions and weight, compactness and others. positive qualities. Maximum pressure of gear pumps 16-20 MPa, flow up to 1000 l/min, rotation speed up to 4000 rpm, service life

Rice. 60. Scheme of operation of a gear pump

average 5000 hours

During rotation, the gear fluid contained in the cavity of the teeth is transferred from the suction chamber along the periphery of the housing to the discharge chamber and further into pressure hydraulic line. This occurs due to the fact that when the gears rotate, the teeth drive more fluid than can fit in the space vacated by the meshing teeth . The difference in volumes described by these two pairs of teeth is the amount of liquid that is displaced into the discharge cavity. As it approaches the discharge chamber, the fluid pressure increases, as shown by the arrows. In hydraulic systems, pumps NSh-32, NSh-46, NSh-67K are used, their modifications are NSh-32U and NSh-46U.

The NS pump (Fig. 61) contains 12 master and slave 11 gears and bushings 6. The housing is closed with a cover 5, screwed on 1. Between the body 12 and cover 5 is sealed with an O-ring 8. The drive gear is made as one piece ts splined shaft, which is sealed with a cuff 4, installation of cover 5 in the bore using support 3 and spring 2 rings The front bushings 6 are placed in the bores of the cover 5 and sealed with rubber rings. They can move along their axes. The pump's discharge cavity is connected by a channel to the space between the ends of the said bushings and the cover. Under fluid pressure, the front bushings together with the gears are pressed against the rear which, in turn, are pressed against the body 12, providing automatic sealing of the ends of the bushings and gears.

In the pump discharge cavity near the elbow 13 the pressure on the ends of the bushings is many times greater than on the opposite side. At the same time, the pressure on the ends of the covers from the side of the body tends to press the bushings against cover 5. Together, this can cause the bushings to skew towards the suction cavity, one-sided wear of the bushings and increased oil leaks. In order to reduce the uneven loading of the bushings, part of the area of ​​the ends of the bushings is covered with a relief plate 7, sealed along the contour with a rubber ring. This ring is tightly clamped between the ends of the body and the cover, and as a result, relative equality of forces acting on the bushings is created.

The bushings wear out as the pump operates, and the distance between the ends and the cover increases. In this case, the ring of the relief plate 7 expands, maintaining the necessary seal between the cover and the bushings. The tightness of this ring determines the reliable and long work pump

Rice. 61. NSh gear pump:

/ - screw, 2, 3, 8 - rings. 4 - cuff, 5 - cover, 6 - gear bushing, 7 - plate, 9 - cotter pin, 10, II - gears, 12 - frame, 13 - square

During assembly, a gap of 0.1-0.15 mm is left between the mating bushings. After assemblies this gap is forced. To do this, the bushings are unfolded and fixed with spring pins, which are installed in the holes of the bushings.

NSh pumps produce right and left rotation. On the pump body, the direction of rotation of the drive shaft is indicated by an arrow. For a left-hand rotation pump (as viewed from the cover side), the drive shaft rotates counterclockwise, and the suction side is on the right. A right-hand rotation pump differs from a left-hand rotation pump in the direction of rotation of the drive gear and its location.

When replacing a pump, if the new and replaced pumps differ in the direction of rotation, the direction of inlet and outlet of fluid into the pump must not be changed. Pump suction pipe ( large diameter) must always be connected to the tank. Otherwise, the pinion seal will be under high pressure and be damaged.

If necessary, the left-hand rotation pump can be converted into a right-hand rotation pump. In order to assemble a right-hand rotation pump (Fig. 62, A, b), it is necessary to remove the cover, remove the front bushings / from the body, 2 complete with spring cotter pins 4, rotate 180° and reinstall. In this case, the line of junction of the bushings will be rotated, as shown in Fig. 62. Then the driving and driven gears are swapped and their pins are inserted into the previous bushings. The front bushings are rearranged in the same way as the rear ones. After this, install unloading plate 7 (see Fig. 61) with an o-ring in the same place 8, a then the roofs are previously rotated 180°.

Pumps NSh-32 and NSh-46 are unified in design; their rods differ only in tooth length, which determines the working volume of the pumps.

NShU pumps (index U means “unified”) differ from NSh the following features. Instead of unloading plate and ring 8 a solid rubber plate is installed 12 (Fig. (Sandwiched between the cover 3 and body 1. At the point where the bushing journals pass through the plate 12 holes are made into which sealing rings are installed 13 with thin steel washers adjacent to the lid. Arc-shaped channels are made on the ends of the bushings adjacent to the gears 14. Guide spring pins 9 (see Fig. 61) are removed, and on the suction side a segment-shaped rubber seal is inserted into the housing bore 15 (see Fig. 63) and aluminum liner 16.

Rice. 62. Assembly of NSh pump bushings:

a - left rotation, b - right rotation; I, 2- bushings, 3 - well, 4 - cotter pin, 5 - body

Rice. 63. NShU gear pump:

/ - frame, 3, 4 - gears, 9 - cover 5, 6 - bushings, 7, 9, 13 - rings, 8 - cuff, 10 - bolt, // - washer, 12 - plates 14 - bushing channels, 15 - compaction 16 - inserts; A - space under the pump cover

When the NShU pump operates, oil from the discharge chamber enters the space above the front bushings and tends to press these bushings against the ends of the gears. At the same time, oil pressure acts on the bushing from the side of the teeth, entering the arc-shaped channels 14v As a result of the action of pressure on the gear bushings, the operating time of the pump is under a certain force directed from the cover into the depths of the pump housing. This design ensures automatic preloading and, consequently, end wear of gears and bushings and affects the sealing properties of the plate 12. Rubber seal 15 necessary to ensure that oil from the space above the bushings does not penetrate into the suction cavity.

A number of loader models use NSh-67K and HUJ -100K (Fig. 64). These pumps consist of a housing/cover 2, clamp 7 and bearing 5 races, driven 3 and leading 4 gears, centering sleeves, seals and fasteners.

Rice. 64. Hydraulic pump NSh-67K(NSH-100K):

/ - frame, 2 - lid, 3, 4- gears, 5, 7, - cages, 6. 11, 14, 15 - cuffs, 8 - bolt, 9 - washer, 10 - ring, 12 - plate,I3 - platiki

Bearing race 5 is made in the form of a half-cylinder with four bearing seats, in which the driven 3 and presenter 4 gears. The clamping ring 7 provides a radial seal; it rests on the gear journals with its supporting surfaces. The collar also serves as a radial seal. 13, in which creates a force to press the holder against the gear teeth. Support plate 12 designed to bridge the gap between the body and the clamping holder. The clamping ring 7 compensates for the radial gap between its own sealing surface and the gear teeth as the supporting surfaces wear out.

The ends of the gears are sealed using two plates 13, which rise by force from the pressure in the cavity sealed by the cuffs 14. The force created in the chambers of the clamping ring, sealed with cuffs 15, balances the clip 7 from the force that is transmitted from the chambers through the cuffs 14. The drive shaft is sealed using cuffs that are held in the housing by support and locking rings. The pumping element (gears assembled with cages and plates) is secured against rotation in the housing by a centering sleeve.

Ring 10 seals the connector between the body and the cover, connected to each other by bolts.

Proper operation and durability of pumps are ensured by compliance with technical operation rules.

It is necessary to fill the hydraulic system with clean oil of appropriate quality and the appropriate grade, recommended for a given pump when operating in a given temperature range; Monitor the serviceability of the filters and the required oil level in the tank. In the cold season, you cannot immediately turn on the pump to the working load.

It is necessary to let the pump idle for 10-15 minutes at medium engine speed. During this time, the working fluid will warm up and the hydraulic system will be ready for operation. It is not allowed to give the pump maximum speed when warming up.

Cavitation is dangerous for the pump - local release of gases and steam from the liquid

(liquid boiling) followed by destruction of released vapor-gas bubbles, accompanied by local hydraulic microshocks high frequency and pressure surges. Cavitation causes mechanical damage to the pump and can damage the pump. To prevent cavitation, it is necessary to eliminate the causes that can cause it: foaming of the oil in the tank, which causes a vacuum in the suction cavity of the pump, air leakage into the suction cavity of the pump through the shaft seal, clogging of the filter in the suction line of the pump, which worsens the conditions for filling its chambers, separation of air from liquid in receiving filters (as a result, the liquid in the tank is saturated with air bubbles and this mixture is sucked in by the pump), high degree rarefaction in suction line along the following reasons: high speed liquids, high viscosity and increased lifting height of the liquid,

The operation of the pump largely depends on the viscosity of the working fluid used. There are three operating modes depending on the viscosity Sliding mode characterized by significant volumetric losses due to internal leaks and external leaks, which decrease with increasing viscosity. In this mode, the volumetric efficiency of the pump sharply decreases, for example, for the NSh-32 pump with a viscosity of 10 cSt it is 0.74-0.8, for NPA it is 0.64-0.95. Stable operation mode characterized by stability of volumetric efficiency in a certain viscosity range, limited by the upper limit of viscosity at which the working chambers of the pump are completely filled. Feed failure mode - disruption due to insufficient filling of the working chambers.

Gear pumps are characterized by the widest range of stable operation depending on viscosity. This property of the pumps has made them effective for use on machines operating outdoors, where, depending on the time of year and day, the ambient temperature varies within significant limits.

Due to wear of gear pumps, their performance deteriorates. The pump does not develop the required operating pressure and reduces flow. In NSh pumps, due to wear of the end mating surfaces of the bushings, the tension of the sealing ring covering the unloading plate decreases. This leads to oil circulation inside the pump and a decrease in its flow. The same consequences are caused by the misalignment of the gears and bushings together in the vertical plane due to uneven wear of the bushings on the side of the pump suction cavity.

A vane pump (Fig. 65) is used on some models of loaders to drive power steering, and the power steering pump of a ZIL-130 car is used. Rotor 10 pump, freely sitting on the splines of shaft 7, has grooves in which the gates move 22. Stator working surface 9, attached to the body 4 The pump has an oval shape, due to which two suction and discharge cycles are provided per one revolution of the shaft. Distribution disc // in the cover cavity 12 at. is pressed by oil pressure entering the cavity from the injection zone. Oil is supplied to the suction zones from both sides of the rotor through two windows at the end of the housing.

Piston pumps and hydraulic motors are made of various types and purposes; depending on the location of the pistons in relation to the axis of the cylinder block or the axis of the shaft, they are divided into axial piston and radial piston. Both types can operate with both pumps and hydraulic motors. A piston hydraulic motor (pump), in which the piston axes are parallel to the axis of the cylinder block or make angles with it of no more than 40°, is called an axial piston. A radial piston hydraulic motor has piston axes perpendicular to the axis of the cylinder block or located at an angle of no more than 45°,

Axial piston motors are made with an inclined block (Fig. 66, A), in them, movement is carried out due to the angle between the axis of the cylinder block and the axis of the output link or with an inclined washer (Fig. 66, b), when the movement of the output link is carried out due to the connection (contact) of the pistons with the flat end of the disk, inclined to the axis of the cylinder block.

Hydraulic motors with an inclined washer are usually manufactured unregulated (with a constant displacement), and hydraulic motors (pumps) with an inclined block are made unregulated or adjustable (with a variable displacement). I regulate the working volume by changing the angle of inclination of the block. When the ends of the cylinder block) washers are parallel, the pistons do not move in the cylinders and the flow to coca stops, at the greatest angle of inclination - the feed is maximum.

b) d)

Rice. 66. Piston hydraulic motors:

A -axial piston with an inclined block, b - also with an inclined washer. 9 - radial piston cam, G - Same. crank; / - block. 2 - connecting rod. 3 - piston, 4 - rotor, 5-body, 6 - washer

Radial piston hydraulic motors are cam and crank motors. In the cams (Fig. 66, V) the transmission of motion from the pistons to the output link is carried out by a cam mechanism, in crank-rod ones (Fig. 66, G) - crank mechanism.

Hydraulic cylindersAccording to their purpose, they are divided into main and auxiliary. The main hydraulic cylinders are an integral part of the actuator, its engine, and the auxiliary cylinders ensure the operation of the control, monitoring system or activate auxiliary devices.

There are single-acting cylinders - plunger and double-acting - piston (Table 4). For the first, the extension of the input link (plunger) occurs due to the pressure of the working fluid, and movement in the opposite direction is due to the force of a spring or gravity, for the second, the movement of the output link; (rod) in both directions is produced by the pressure of the working fluid.

The plunger cylinder (Fig. 67) is used to drive the load lifter. It consists of a welded body 2, plunger 3, bushings 6, nuts 8 and sealing elements, cuffs, sealing 5 and wiper rings.

Sleeve 6 serves as a guide for the plunger and at the same time limits its upward stroke. It is secured in the body with a nut 8. The cuff seals the interface between the plunger and the sleeve, and ring 5 seals the interface between the sleeve and the body. To the plunger using a pin 10 the traverse is attached. Air periodically accumulates in the cylinder. A plug is used to release it into the atmosphere. 4. The surface of the plunger has a high surface finish. To ensure that it is not damaged during operation, a wiper ring is installed to prevent dust and abrasive particles from getting into the plunger interface 3 and bushings 6; bushing 6 made of cast iron so that the steel plunger does not ride up; the cylinder is supported on the movable and stationary parts of the lift through spherical surfaces so that bending loads are eliminated.

Rice. 67, Plunger cylinder:

/ - pin, 2 - frame; 3 - plunger, 4 - cork, 5, 9 - rings, 6 - sleeve,- 7 - sealing device, 8 - screw, 10- hairpin

Oil is supplied to the cylinder through a fitting at the bottom of the housing 2. At the extreme upper position the plunger 3 the shoulder rests against the bushing 6.

Piston cylinders (Fig. 68) have a variety of designs. For example, a forklift tilt cylinder consists of a housing 12, including a sleeve and a rod bottom welded to it // with a piston 14 and O-rings 13. Piston 14 secured to the stem shank 11 with a nut 3 co cotter pin 2. The shank has a groove for an O-ring 4. At the front of the cylinder there is a cylinder head 5 with a bushing. The rod in the head has a seal in the form of a cuff 9 with thrust ring 10. The head is secured in the cylinder with a threaded cap 6 with wiper 7.

A necessary condition for the operation of a hydraulic cylinder is the sealing of the rod (plunger) at the point where it exits the cylinder body, and in a piston cylinder - sealing of the rod and piston cavities. Most designs use standard rubber rings and cuffs for sealing. Fixed sealing is carried out using rubber O-rings.

Rubber O-rings or cuffs are installed on the pistons as seals. The service life of the round ring is significantly increased if it is installed in conjunction with one (for single-sided seal) or two (for double-sided seal) rectangular Teflon rings.

The rod caps are equipped with one or two seals, as well as a wiper to clean the rod as it is retracted into the cylinder. Plastic seals at smaller overall dimensions They have a significantly longer service life compared to rubber ones.

Rice. 68. Piston cylinder:

1 - plug, 2 - cotter pin, 3 - screw, 4, 10, 13 - rings.S - cylinder head, 6 - cover, 7 - wiper, 8 - oiler 9 - cuff, // - stock, 12 - body, 14 - piston

During the technical operation of hydraulic cylinders, the following basic rules should be observed. When working, do not allow dirt to get on the working surface of the rod and protect this surface from mechanical damage; even a scratch breaks the seal of the cylinder.

If the machine has been standing for a long time with the working surface of the rod open, then before work, clean the rod with a soft cloth soaked in oil or kerosene.

Failure of the seal between the piston and rod cavities while the cylinder is under significant load can result in damage to the housing or breakout of the rod cover due to rod effect,

The pressure difference produced at a given flow rate at which the valve moves to throttle the flow is determined by adjusting the spring using the nut. The more the spring is tightened, the greater the load the valve will operate. Spring is adjustable So to ensure stable lowering of the forklift without a load.

Installing a back-throttle valve ensures a constant lowering speed, but does not exclude lowering of the load and loss of liquid in the event of a sudden break in the supply hydraulic line, which is a disadvantage of the described design. The ability to regulate the lowering speed by changing the pump flow is realized yc by installing the lift cylinder valve block, which you attach directly to the cylinder.

The valve block performs four functions: it allows the entire fluid flow into the cylinder with minimal resistance and locks the fluid in the cylinder when the distributor spool is in the neutral position, and if the supply hydraulic line is damaged, it regulates the fluid flow leaving the cylinder using a controlled throttle valve, while the flow rate from the cylinder is proportional to the pump performance ; provides emergency lowering of cargo in case of failure of the hydraulic drive (hydraulic pump, pipelines) of the engine.

The valve block (Fig. 74) consists of a body 10, which houses the check valve 4 with rod 5 and spring 6, controlled valve / spring 2, fittings 3 and 9, covers, valve seats and seals. In the fitting 9 a damper nut with a calibrated hole is attached.

By turning on the distributor to lift liquid through the fitting 3 directed to the end of the valve 4, compressing the spring with pressure force, opens it and enters the cavity A cylinder. Spring force 2 valve / is pressed tightly against the seat. In the cavity B there is no pressure.

Rice. 74. Valve block:

1,4 - valves, 2, 6 - springs. 3,9 - fittings. 5 - rod, 7 - lock nut; 8 - cap, 10 - frame

In the neutral position of the distributor spool, the pressure of the liquid in the cylinder and the force of the valve spring 4 pressed tightly to the saddle; also pressed to its seat by a valve / spring 2, eliminating fluid leakage from the cylinder. By switching the distributor to lower, the pressure hydraulic line from the pump is connected to the cavity B and through the throttle washer with drain IN, and the cavity D communicates with the drain. The higher the pump performance, the greater the pressure created in the cavity B, as the pressure drop across the throttle plate increases. Fluid pressure causes the valve / to move to the left, communicating with the cavity And with cavity D, and the liquid is transferred through the annular gap into the tank.

When the valve moves, spring compression and pressure in the cavity increase IN, because the hydraulic resistance drain

the line increases with increasing flow proportionally to the opened valve, and the pressure in the cavity is balanced B. The valve movement will also decrease and the valve will move to the right under the action of the spring 2 and pressure in the cavity IN, partially blocking the annular gap. If at the same time we reduce the pump flow and thereby the pressure in front of the damper nut, then the pressure in the cavity B will also decrease and, with the force of spring 2, the valve will move to the right, partially closing the annular gap.

Smooth and reliable operation controlled valve, spring selection is ensured 2, valve diameter 1 and the angle of its conical part, the volume of the cavity and the diameter of the calibrated hole in the damper nut. In this regard, any change in the controlled valve is unacceptable, since it can lead to disruption of its proper operation, for example, to the occurrence of self-oscillations, which is accompanied by impacts of the valve on the seat and noise.

If the drive fails, the emergency lowering of the lift is carried out in the following sequence: the distributor handle is set to the neutral position, the protective cap is removed 8; rod 5 is kept from turning by inserting a screwdriver into the slot and unscrewing locknut 7; rod 5 is turned with a screwdriver counterclockwise by 3-4 turns (counting the turns along the slot); The distributor handle is set to the “descent” position and the load lifter is lowered. If the load lifter does not lower, then set the distributor handle to the neutral position and additionally unscrew rod 5.

After lowering, the rod must be returned to its original position by rotating clockwise and the lock nut and protective cap must be replaced.

If, when the distributor handle is set to the neutral position, the load drops under the influence of gravity, this indicates incomplete closing of the valves. The reasons may be: leakage at the interface between the seats and conical surfaces due to contact with particulate matter; jamming of one of the valves as a result of solid particles entering the gap between the body and the valves; the controlled valve does not rest against the seat due to clogging of the calibrated hole in the damper nut (liquid in the cavity B turns out to be locked).

If, when moving the handle to the “descent” position, the forklift does not c repents, this indicates that the calibrated hole is clogged.

To ensure safety when changing the tilt of the forklift, an adjustable throttle with a check valve is installed in the hydraulic lines to the tilt cylinders. The latter is installed in the hydraulic line to the piston cavity of the tilt cylinder.

A throttle with a check valve (Fig. - 75) consists of a housing. which houses valve 7, spring 6, nut 5, plunger with seal 2, screw 4 and a locknut. When the forklift is tilted back, the liquid passes into the cylinder through the check valve 7; during the reverse stroke, the liquid from the cylinder cavity is forced out to drain through the annular gap between the side hole of the housing and the plunger cones and the inclined hole in the housing. By rotating the nut, a gap is established that ensures a safe speed for tilting the forklift forward.

Forklifts typically use two separate pumps to drive the power steering implement. If one pump is used to supply consumers, a flow divider is installed in the hydraulic system. It is designed to divide the fluid flow into the drive of the working equipment and into the hydraulic booster, while a constant speed of rotation of the wheels must be ensured at different pump flows.

The flow divider (Fig. 76) has a housing 1 with a hollow plunger 5, safety valve 4, spring 2, cork 3 and fitting 7. A diaphragm is fixed in the plunger 6 s hole. From the pump, liquid enters the cavity A and through the hole in the diaphragm into the cavity B to the hydraulic booster (or hydraulic steering). The diameter of the hole in the diaphragm is chosen so that the cavity B 15 l/min flows at low engine speeds. As the pump performance increases, the pressure in the cavity A increases, plunger 5 rises, compressing the spring 2, and through the side holes in the plunger, part of the liquid flow enters the distributor. At the same time, the fluid flow into the cavity increases B, the pressure in it increases and excess fluid passes through the safety valve 4 goes into the cavity IN and then into the tank. Plunger movement 5 and valve operation 4 ensure constant fluid flow to power the hydraulic booster.

Rice. 75. Throttle with check valve:

/ - housing, 2 - seal, 3 - plunger,

4, 5 - screw, 6 - spring, 7 - valve

Rice. 76. Flow divider:

/ - frame. 2 - spring. 3 - cork, 4 - valve, 5 - plunger, 6 - diaphragm, 7 - fitting; A, B, C, D - cavities

In other divider designs, an adjustable throttle is installed instead of a diaphragm with a hole.

By turning the valve handle, the siphon is connected to the atmosphere, preventing liquid from flowing out of the tank under the influence of gravity.

If the valve is opened and the pump starts, the liquid will foam, the pump will operate noisily and will not develop pressure in the hydraulic system. Therefore, you should always check the closure of the valve before starting work, before starting the engine.

A shut-off valve is installed in the hydraulic system of the loader to disconnect the pressure gauge. To measure the pressure, you need to unscrew the tap one or two turns, after measuring, turn off the distributor and turn on the tap. Working with the pressure gauge constantly on is not allowed.

HYDRAULIC TANK, FILTERS, PIPELINES

Hydraulic tankdesigned to accommodate and cool the working fluid of the hydraulic system. Its volume, depending on the pump flow and the volume of the hydraulic cylinders, is equal to 1-3 minute pump flow. The hydraulic tank includes a filler neck with a mesh filter and a valve connecting its cavity to the atmosphere, a liquid level indicator, and a drain plug. The tank reservoir is welded, with a transverse partition. The suction and drain tubes in the form of siphons are placed on different sides of the partition, which allows you to dismantle the hydraulic lines suitable for the hydraulic tank without draining the liquid. 10-15% of the tank volume is usually air.

Filtersserve to clean the working fluid in the hydraulic system.

Filters are built into the tank or installed separately. The filter in the filler neck of the hydraulic tank ensures cleaning during refueling. He made of wire mesh; its filtering qualities are characterized by the cell size in the light and the cross-sectional area of ​​the cells per unit surface area. In some cases they use mesh filters with 2-3 layers of filter mesh, which increases cleaning efficiency.

A drain filter with a bypass valve is installed on the drain hydraulic line of domestic loaders (Fig. 77). The filter consists of a housing 6 with lid 10 and fitting 1, in which filter elements are placed on tube 5 4 with felt rings 7 at the ends, tightened with a nut 16. The housing is fixed on top of the tube 14 bypass valve. Ball 13 pressed by a spring /5, which is held in the tube using brackets 17, 18. The filter is installed on the return hydraulic line from the power steering.

The liquid enters the outer side of the filter elements and, having passed through the cells of the elements and through the slot in tube 5, enters the central channel connected to the drain hydraulic line. By As the hydraulic system operates, the filter elements become dirty, the filter resistance increases, when the pressure reaches 0.4 MPa, the bypass valve opens and the liquid is drained into the tank unpurified. The passage of liquid through the valve is accompanied by a specific noise, which indicates the need to clean the filter. Cleaning is done by partially disassembling the filter and washing the filter elements. Installing a filter on the drain from the hydraulic booster, operating at lower pressure, does not cause pressure loss in the hydraulic system of the working equipment.

On Balkankar loaders, the filter is installed in the suction hydraulic line (suction filter) and is placed in the hydraulic tank. The suction filter (Fig. 78) contains a housing /,

Rice. 77. Drain filter with bypass valve:

/ - union, 2, 7, 11, 12 - rings, 3 - pin, 4 - filter element, 5 - a tube, 6 - frame, 8 - cap. 9, 15 - springs, 10 - lid, 13 - ball. 14 - body, valves, 16 - screw, 17, I8 - staples

Rice. 78. Suction filter:

/ - frame, 2 - spring, 3 - lid, 4 filter element, 5 - valve

between the covers 3 which the filter element is placed 4. The covers and the element are pressed against the body by a spring 2. The filter element is made of brass mesh, which has 6400 holes per 1 cm 2, which ensures a cleaning accuracy of 0.07 mm. If the mesh is clogged, the liquid is sucked in by the hydraulic pump through the bypass valve. 5. The setting of the bypass valve made at the factory should not be violated during operation - this can cause backwater on the drain if the filter is installed on the drain hydraulic line, or cavitation of the hydraulic pump if the filter is installed in the suction line.

Pipelineshydraulic drive is made of steel pipes, high and low pressure hoses (suction hydraulic line). Sleeves are used to connect parts of hydraulic systems that move relative to each other.

For installation of parts of pipelines, connections with an internal cone are used (Fig. 79, a). The tightness of the connection is ensured by tight contact of the surface of the steel ball nipple with the conical surface of the fitting / using a nut 2. The nipple is butt welded to the pipe.

Rice. 79. Pipeline connections:

a - with an inner ring, b - with a flared ring, c - with a cutting ring;

1 - union, 2 - screw, 3, 5 - nipples, 4 - pipe, 6 - cutting ring

Pipes of small diameter (6.8 mm) are connected with a flaring (Fig. 79, b) or with a cutting ring (Fig. 79, b) V). In the first case, the pipe 4 it is pressed to the fitting by a conical nipple 5 with the help of a nut, in the second - the seal is made by the sharp edge of the ring when screwing the union nut.

When installing hoses, they must not be bent at the embedment site or twisted along their longitudinal axis. It is necessary to provide a length reserve to reduce the length of the hose under pressure. The hoses must not touch the moving parts of the machine.

HYDRAULIC DIAGRAMS FOR LOADER

Schematic hydraulic diagrams show the design of hydraulic systems using graphic symbols (Table 5),

Let's look at a typical hydraulic diagram of a 4045P loader (Fig. 80). It includes two independent hydraulic systems with a common tank 1. The tank is equipped with a filling filter 2 with a ventilation valve-prompter, and the suction hydraulic line coming from the tank has a jet break valve 3. Two hydraulic pumps are driven from a common shaft, small 5 - for driving the hydraulic booster and large 4 - for driving working equipment. From the large pump, fluid is supplied to a monoblock distributor, which includes a relief valve and three spools: one to control the lift cylinder, one to control the tilt cylinder, and the third to operate additional attachments. From the spool 6 the fluid is directed through one hydraulic line to the block 12 valves and into the cavity of the lift cylinder, and through another parallel to the control cavity of the valve block and into the drain line through the throttle 13.

The operating hydraulic lines of spool 7 are connected in parallel to the tilt cylinders of the forklift: one with the piston cavities, the other with the rod cavities. Throttles are installed at the entrance to the cavities. The third spool is a reserve one. 1

When the distributor is in the neutral position, liquid from the pump is supplied to each distributor spool and is drained into the tank through an open channel in the spools. If the spool is moved to one or another working position, then the drain channel is locked and through another channel that opens, the liquid enters the executive hydraulic line, and the opposite hydraulic line communicates with drain

In the “Lift” position of the lift cylinder spool, the liquid passes into the cylinder cavity through the check valve of the valve block and lifts the forklift. In the indicated and neutral positions of the spool, reverse flow of fluid is excluded, i.e., the forklift cannot lower. In the spool position " Ha lowering" the pressure line from the pump communicates with the drain through the throttle and at the same time enters the control cavity of the valve block. At low engine speeds, the pressure in the cavity of a small controlled valve will open slightly, the flow from the cylinder cavity will be small and the speed of lowering the load will be limited.

To increase the lowering speed, it is necessary to increase the engine speed, the pressure in front of the throttle will increase, controlled, the valve will open by a larger amount and the flow from the cylinder cavity will increase.

Throttles are installed in the hydraulic lines to the cavities of the tilt cylinders, which limit the tilt speed of the forklift.

The hydraulic system of the Balkankar loaders (Fig. 81) uses

Rice. 80. Hydraulic diagram of the loader 4045Р:

I -tank, 2 -filter, 3 - valve, 4, 5 - hydraulic pumps, 6, 7 - spools. 8 - tap, 9 - pressure gauge 10, II - cylinders, 12 - valve block, 13 - throttle, 14, - filter, 15 - hydraulic booster

one pump. The working fluid to the pump comes from the tank / through the filter 2 s bypass valve and is supplied to the flow divider, which directs part of the fluid to the hydraulic steering wheel 17, and the rest of the flow - to the sectional distributor // containing four spools and safety valve 5. From the spool 9 k lift cylinder cavity 13 via check valve 12 there is only one hydraulic line. When rising, the entire fluid flow will be directed into the cylinder cavity, and when lowering, the flow rate is limited by the flow area of ​​the throttle. Also via check valve ,

Rice. 81. Hydraulic system of the Balkankar loader: I

1 - tank, 2- filter. 3 - pump, 4, 5, 10, It, 15 - valves, 6-9 - spool valves, 11 - distributor. 13, 14, 16 - cylinders, 16 - flow divider, 17 - hydraulic steering wheel

Oil is directed to the rod end of the tilt cylinders, allowing the forklift to slowly tilt forward for safety.

Spools b and 7 are designed for attachments. The fluid pressure in the actuating hydraulic cylinders of the attachments is regulated by a separate safety valve.

A hydraulic drive is a system in which the transfer of energy from a source (usually a pump) to a hydraulic motor (hydraulic motor or hydraulic cylinder) is carried out through a drop of liquid.

Structurally, the hydraulic drive consists of a pump(s), control and distribution equipment, a hydraulic motor(s), a working fluid, a container (tank) for its contents and means (filters and coolers) that preserve its quality, as well as connecting and sealing fittings.

In Fig. 2.1. shows a diagram of the studied volumetric hydraulic drive consisting of a pump 1, a safety valve 2, distributors 3 and 4, hydraulic motors - a hydraulic motor 5 and a hydraulic cylinder 6, a retarding device 7 for lowering a load 8, a tank and a filter 9 installed in the drain hydraulic line, interlocked with a valve 10.

Rice. 2.1 Diagram of the hydraulic drive being studied.

The pump 1 is designed to convert the mechanical energy flow coming from the primary energy source 11 (electric or fuel engine) into a hydraulic energy flow, i.e. into the flow of working fluid under pressure, which, depending on the positions (positions) of the valve valves 3, 4, can be directed directly (idle mode) or through one or both hydraulic motors 5, 6 (operating mode) into the tank. In this case, the pressure at the outlet of the pump depends on the totality of resistance encountered by the flow of working fluid on the path from the pump to the tank. In cases where distributors 3, 4 are in positions “A” (see Fig. 2.1), the flow of working fluid from pump 1 passes into the tank through the mentioned distributors, hydraulic lines and filter 9 (idle mode). The pressure at the pump outlet is:

Where
– the pressure values ​​necessary for the flow of working fluid to overcome the resistance, respectively, of the sections of the gyrolines, distributors and filter.

In cases where, upon an external command, one or both distributors 3, 4 are moved to any position “B” or “C”, one or both hydraulic motors are (are) switched on, respectively. The direction of movement of the hydraulic motors depends on the position “B” and “C” of their distributors. When only one hydraulic motor is turned on, for example hydraulic motor 5, the operating pressure at the outlet of the pump will be:

Where
– pressure loss to overcome the resistance of the distributor 3, 4

– pressure loss on the drive of hydraulic motor 5, depending on the load to be overcome on its shaft.

In the case when the hydraulic motor 5 and the hydraulic cylinder 6 are simultaneously activated, their joint operation is possible only at the same required pressures. If one of them has a lower required pressure than the other, then their joint work is impossible, since the fluid flow will mainly go in the direction of less resistance and disrupt normal work hydraulic drive as a whole.

If the required pressure in the hydraulic drive exceeds the permissible pressure, safety valve 2 is activated and diverts the flow of working fluid from pump 1 into the tank (overload mode), thereby limiting the pressure in the hydraulic drive and protecting its elements from destruction.

To ensure the smoothness of lowered loads (working bodies), hydraulic drives use retarding devices (see Fig. 2.1, item 7), usually consisting of a check valve and a throttle. When lifting the load (working body), the working fluid enters the cylinder through a check valve and a throttle. When lowering the load, the liquid from the cylinder cavity enters the tank only through the throttle, which provides resistance to it, the value of which depends on the magnitude of its flow and thereby ensures the smoothness of its lowering. In this case, the opposite cavity of the hydraulic cylinder is filled with liquid supplied by the pump. If there is an excess amount of liquid supplied by the pump, part of it will be drained through safety valve 2.

To visually monitor the pressure in the hydraulic drive, pressure gauge 12 is used. To ensure the cleaning of the working fluid from solid contaminants (abrasives, wear products), filters of various designs are used in hydraulic drives.

Hydraulic machines

Hydraulic machines (hydraulic machines) are mechanical devices designed to transform types of energy flows using droplet liquid as an energy carrier.

Hydraulic machines are divided into pumps and hydraulic motors.

Pumps are hydraulic machines designed to convert mechanical energy flow into hydraulic energy flow.

Hydraulic motors are hydraulic machines designed to convert hydraulic energy flow into mechanical energy flow.

Hydraulic motors, the output links of which perform linear reciprocating movements, are called hydraulic cylinders (hydraulic cylinders).

Hydraulic motors, the output links of which perform rotational movements called hydraulic motors (hydraulic motors).

Depending on the angle of rotation of the output link, hydraulic motors are divided into full-
and part-rotary
.

Hydraulic machines in which the working process is based on the use of the kinetic energy of the fluid are called dynamic, and those machines in which the working process is based on the use of the potential energy of the fluid are called volumetric.

The main feature of volumetric hydraulic machines is that they contain at least one working chamber, the volume of which varies
during the working cycle. Moreover, each working chamber contains a movable element designed to change its volume. Usually the moving element of the working chamber is called a displacer. Displacers can be pistons, plungers, gear teeth, balls, rollers, plates, membranes, etc.

During the operation of a volumetric hydraulic machine, each of its chambers alternately communicates with the low and high pressure line, i.e. the working chambers of the pump alternately communicate with the suction and discharge lines, and for engines - with the high pressure output line and with the drain line.

The amount of pressure developed (realized) by the pump depends on the resistance of the consumer (usually a hydraulic motor) and the connecting hydraulic fittings.

The amount of working fluid pressure consumed by a hydraulic motor depends on the amount of load it implements on the output link.

Based on the type of displacers, hydraulic machines are divided into piston, plunger, ball, roller, gear (gear), plate, membrane, etc., and based on the number of working chambers, into single- and multi-chamber ones.

Hydraulic machines in which the working chambers together with the displacers perform rotational movements are called rotary.

The size of the changing volume of the working chambers of a hydraulic machine is called its working volume. The working volume of hydraulic machines is usually expressed in cubic centimeters.

The amount of working fluid supplied by the pump to the system per unit of time is called its supply.

If the working volume is known
pump and operating cycle frequency , then its ideal feed can be determined by the formula

.

Due to the fact that there are leaks of working fluid between the moving elements of the pump, the actual flow will always be less than ideal, i.e.

Where
– the amount of leakage through the gaps;

– volumetric efficiency of the pump.

The ideal hydraulic motor rotation speed is determined by the formula

,

and the actual one is

,

Where
– the value of the input flow of working fluid;

– working volume of the hydraulic motor;

– volumetric efficiency of the hydraulic motor.

The volumetric efficiency of a hydraulic motor can be determined by the formula

Where
– the amount of working fluid flow usefully used in the hydraulic motor;

– the amount of leakage through the gaps in the hydraulic motor.

The driving power of the pump can be determined by the formula

Where
– power of the working fluid flow at the outlet of the pump;

– total efficiency of the pump;

– pressure value at the pump outlet;

– hydraulic efficiency of the pump;

– the pressure value in the working chamber(s) of the pump;

– mechanical efficiency of the pump.

The energy quality of a hydraulic motor is characterized by its total efficiency, which can be defined as the ratio of the amount of power on its output shaft
to the power of the input fluid flow
, i.e.

Where
– torque;

– angular velocity;

– pressure drop in the hydraulic motor.

Most positive displacement hydraulic machines are reversible, i.e. they are capable of operating both as pumps and as hydraulic motors.

In hydraulic drives of construction and road machines, gear (Fig. 2.2) and axial (Fig. 2.3) hydraulic machines are most widely used as pumps, and axial (Fig. 2.3) and radial (Fig. 2.4) are used as hydraulic motors.

Due to the fact that in rotary pumps the working chambers with liquid move from the suction cavity to the discharge cavity, they differ from simple piston (plunger) pumps in the absence of valve distribution of liquid, which in turn increases their speed to 85 s -1 and ensures high uniformity of supply and pressure. All rotary hydraulic machines can only operate on clean, non-aggressive fluids that have good lubricating properties and are intended for hydraulic drives.

Gear hydraulic machines

Gear machines are rotary hydraulic machines with working chambers formed by the surfaces of gear wheels, housing and side covers.

Gear hydraulic machines are made with external (see Fig. 2.2, a) or internal (see Fig. 2.2, b) gears. Such a hydraulic machine is a pair of (most often identical) gears 1 and 2, meshed and placed in a housing with small radial clearances (usually 10...15 µm).

Rice. 2.2 Schemes of gear (gear) hydraulic machines.

The working process of an external gear pump is as follows. Drive gear 1 (see Fig. 2.2, a) drives driven gear 2 into rotation. When the gears rotate in opposite directions in chamber “A,” their teeth disengage, which leads to an increase in the volume of the working chamber and a decrease in the pressure of the working fluid to vacuum value. Due to the resulting pressure difference between the reservoir (tank) and the suction chamber “A”, the working fluid from the tank will flow into the chamber “A” and fill the cavities between the teeth of gears 1 and 2. With further movement of the gears, the working fluid in the cavities between the teeth is transferred from the zone suction (from chamber “A”) to the discharge zone (to chamber “B”). In the injection zone, the gear teeth mesh and push the liquid out of the depressions into the injection hydraulic line under pressure, the magnitude of which depends on the resistance of the consumer and the connecting hydraulic fittings.

In pumps with internal gears (see Fig. 2.2, b), the drive is most often the internal gear 1 with external teeth. The suction “A” and discharge “B” windows are made on the end side of the gear teeth in the side cover or pump housing. The female gear 2 with internal teeth rotates in the cylindrical bore of the housing. Between the gears there is a separating crescent element 3, through which the suction cavity “A” is separated from the discharge cavity “B”.

IN Lately in hydraulic power steering machines, hydraulic machines with internal gears with a special tooth profile are widely used (see Fig. 2.2, c), in which there is no separating element of cavities with different pressure levels. Such hydraulic machines are called gerotor or birotor, i.e. with two rotors. The annular rotor (wheel) 1 has one more tooth than the internal one (gear) 2. Their axes are shifted relative to each other by an amount , forming the meshing of gears in the area of ​​the upper dividing bridge. The contact of the teeth as they pass over the lower dividing bridge ensures the separation of the high and low pressure cavities. The inlet and outlet hydraulic lines with the interdental cavities are connected through crescent-shaped windows “A” and “B”.

Gerotor hydraulic machines are used as pumps operating at working fluid pressures of up to 14 MPa and a shaft rotation speed of 30 s -1 . They can be used as high-speed low-torque hydraulic motors. In some cases, gerotor hydraulic machines are capable of operating at pressures of 30 MPa at rotation speeds of up to 60 s -1.

The working process (suction and discharge) in internal gear pumps occurs in the same way as in external gear pumps.

The overall dimensions and weight of pumps with internal gearing are significantly less than pumps with external gearing with equal working volumes.

The spur gearing of pump gears is characterized by straight-line contact of the working surfaces (profiles) of the teeth along their entire width (length), inaccurate manufacturing of which causes uneven movement of the driven gear and noise, and rapid wear of the working surfaces is observed.

These shortcomings are eliminated in helical (spiral) and chevron gears (see Fig. 2.2, d and e). Entry into and exit from the teeth meshing in these gears occurs gradually, due to which errors in the tooth profile are reduced and smooth and relatively silent operation of the hydraulic machine is achieved.

In helical gear pumps, flow and torque pulsation and fluid trapping in the cavities are significantly lower than in spur gear pumps. To reduce pressure pulsations, it is necessary to ensure that the product
equaled
etc., where - angle of inclination of teeth; - gear width; - tooth pitch. Corner are chosen so that the shift of the teeth along the circumference at the ends of the gears is half the pitch. In practice, this angle usually does not exceed 7...10.

When pumps with helical gears operate, axial forces arise that press the gears against the ends of the housing (covers). This drawback is eliminated in pumps with herringbone gears (Fig. 8.2, e). Tooth angle chevron gears used in pumps is usually 20...25.

Axial hydraulic machines

Axial hydraulic machines are characterized by the fact that the axes of their cylinders are parallel to the axis of rotation of the cylinder block or make an angle with it of no more than 45°.

The positive qualities of axial hydraulic machines include:

high working pressure (35...70MPa);

speed (80…550 s -1);

low metal consumption (0.5…0.6 kg/kW);

wide range of hydraulic motor shaft speed control 1:100 at variable and 1:1000 at constant loads;

possibility of operating hydraulic motors on low frequencies rotation (up to 0.01 s -1);

greater durability (up to 12,000 hours);

high speed (feed change from zero to maximum and vice versa in 0.04...0.08 s);

low operating costs and quick payback.

Axial hydraulic machines come with an inclined cylinder block (see Fig. 2.3, a, b) or with an inclined washer (see Fig. 2.3, c, d). They can be piston (see Fig. 2.3, a, b) or plunger (see Fig. 2.3, c, d) with a variable (adjustable) or constant (unregulated) working volume. In axial piston hydraulic machines there is: a small radial load on the piston, a large angle of inclination of the cylinder block (up to 45), as well as a higher (2...3%) efficiency than that of a hydraulic machine with an inclined washer.

In Fig. 2.3, a shows a diagram of an axial piston adjustable hydraulic machine with an inclined block. It consists of a shaft 1, a cylinder block 2, a mechanical distributor 3, a central axis 4, pistons 5, connecting rods 6 and a cardan 8.

The described hydraulic machine functions as a pump as follows. The rotation of the drive shaft through the cardan 7 and connecting rods 6 is transmitted to the cylinder block 2. With the coaxial arrangement of the shaft 1 and the cylinder block 2, the pistons 5 do not perform reciprocating motion and, therefore, the pump flow is 0. The deviation of the axis of the cylinder block from the axis of the drive shaft leads to reciprocating movement of the pistons.

For one revolution, each piston completes one working cycle. The magnitude of the piston strokes depends on the angle of inclination of the cylinder block. When the angle of inclination of the cylinder block changes in the opposite direction from zero, the direction of pump flow changes, i.e. The hydraulic machine ensures reversal of the hydraulic drive.

Axial hydraulic machines with an inclined washer are characterized by the following advantages compared to hydraulic machines with an inclined cylinder block: the ability to operate at higher high pressures(up to 70 MPa); low noise level; small dimensions; low cost; simplicity of design and its manufacturability.

Rice. 2.3 Schemes of axial hydraulic machines.

In Fig. 2.3, c shows a simplified diagram of an axial plunger hydraulic machine with an inclined washer. In the cylinders of its block 1, plungers 2 are installed, which by means of springs 6 through shoes 3 are kinematically connected to the swash plate 4.

The described hydraulic machine functions as a pump as follows. Shaft 5 rotates cylinder block 1. In this case, plungers 2 perform reciprocating movements in the cylinder block. The stroke of the plungers, corresponding to the pump flow, is determined by the angle of inclination of the washer 4. When the plungers, under the influence of the springs 6, move out of the cylinder block, the process of suction of the working fluid occurs, and when they return, the pumping occurs.

Axial plunger hydraulic machines with an inclined washer are often used in the functions of adjustable and unregulated hydraulic motors, the operating principle of which is similar to the principle of operation of axial hydraulic machines with an inclined cylinder block.