The article deals with the development of the transmission of caterpillar bulldozers with a thrust class of 10 ... 15 tons on a caterpillar.

To start, a little history. The very concept of "bulldozer" arose at the end of the 19th century. and meant a powerful force that overcomes any barriers. This concept began to be attributed to caterpillar tractors in the 1930s, figuratively characterizing the power of a caterpillar vehicle with a metal shield fixed in front that moves the soil. Initially, an agricultural tractor was used as a base, with the main feature being a caterpillar track that provides maximum grip on the ground. A caterpillar is defined as an endless rail. Russian scientists were involved in its invention, as well as in all key fundamental discoveries. One of the first patents was registered in Russia around 1885.

One of the features of the caterpillar track is the ability to turn by turning off one of the tracks, or blocking it, or turning it into a counter move. On fig. 1 shows a typical mechanical transmission scheme, which was used on the first crawler bulldozers and is still used today.

Advantages of this scheme- simplicity of the design of the units, efficiency more than 95%, low cost and minimal time spent on repairs.

During the period of rapid growth of the world economy in 1955-1965. and the development of machining technologies and the chemical industry, in parallel, several manufacturers of crawler bulldozers have applied hydromechanical transmission (HMT). It was built on the basis of a torque converter (GTR), which by that time had become widespread on diesel locomotives. GMT on bulldozers was in demand primarily in the heavy class: more than 15 tons of thrust, and is characterized by the ability to obtain maximum torque at zero speed, i.e. with maximum grip of the caterpillar with the ground and maximum resistance of the moved soil mass. The only and critical drawback, in addition to technological complexity, was high mechanical losses - 20 ... The scheme of hydromechanical transmission is shown in fig. 2.

Advantages of this scheme- the maximum possible traction on the tracks, simpler control compared to a mechanical transmission, elastic connection between the engine and the caterpillar.

The need to use expensive planetary gearboxes and final drives is caused by the transfer of higher torque than in a mechanical transmission - up to two times. The GMT scheme is currently used by the leading manufacturers of caterpillar bulldozers Komatsu and Caterpillar. Only the Chelyabinsk Tractor Plant provides a significant share of mechanical transmissions, producing a virtually unchanged copy of the 1960s Caterpillar for more than 50 years.

The next technological step in the development of the transmission of caterpillar bulldozers was the use of the “hydraulic pump (HP) - hydraulic motor (GM)” scheme under the general term “hydrostatic transmission” (HST). The beginning of the widespread use of GN-GM was laid by the military when improving the drives of artillery pieces, which required a high speed of movement of moving parts with a considerable inertial mass, which excluded the use of a rigid mechanical connection.

A transmission of this type is today predominantly common on medium and heavy class special equipment: hydrostatic transmission is used by all leaders in the excavator equipment market. The use of HTS in excavators is associated with the performance of their main work by actuators with hydraulic force transfer. The spread of HTS was also facilitated by the improvement of machining technologies and the widespread use of synthetic oils produced for predetermined use parameters, as well as the development of microelectronics, which made it possible to implement complex HTS control algorithms. The scheme of hydrostatic transmission is shown in fig. 3.

Advantages of this scheme:

• high efficiency - more than 93%;
• the maximum possible thrust on the tracks is higher than that of the GMT, due to lower losses;
• better maintainability due to the minimum number of units and their unification by different manufacturers, mainly not producing ready-made crawler bulldozers;
• it also ensures the minimum cost of the units;
• the simplest control with one joystick, which allows you to implement remote control without modifications, including by means of radio communication;
• elastic connection engine-caterpillar;
• small overall dimensions, which allows you to use the freed up space for attachments;
• the possibility of macro-control of the state of the entire transmission by one parameter - the temperature of the working fluid;
• maximum possible maneuverability - zero turning radius due to anti-travel tracks;
• the possibility of 100% power take-off for hydroficated attachments from a regular hydraulic pump;
• the possibility of cheap software and technological modernization in the near future due to an elementary transition to a working fluid with new properties obtained on the basis of nanotechnology.

An indirect confirmation of such advantages is the choice of GTS by Liebherr, the leader of German manufacturers of special equipment, as the base in the design of all special equipment, including crawler bulldozers. A table of all the advantages, disadvantages and features of the operation of various types of transmissions, including the “new” for Caterpillar and the electromechanical transmission actually implemented back in 1959 by the ChTZ plant on the DET-250 bulldozer, is given on the website www.TM10.ru of the DST- Ural".

Of course, readers paid attention to the preferences of the authors of the article. Yes, we are making our choice in favor of the GTS and we believe that such a solution will make it possible to overcome the technological backlog of the leaders in the production of special equipment in Russia and break away from the eastern neighbor - China, which claims to easily absorb our bulldozer market. The new TM bulldozer with a transmission based on Bosch Rexroth components with a thrust class of 13…15 tons will be presented by DST-Ural in July. The working weight of the new bulldozer will remain 23.5 tons, power - 240 hp. and maximum thrust - 25 tons, which, with a 5% lag, corresponds to the Liebherr PR744 analogue (24.5 tons, 255 hp). Once again, let us recall the existing possibilities of domestic mechanical engineering. For example, we were the first in the world practice to apply the scheme of bogies on swing carriages in the 10th class of caterpillar bulldozers in serial production. Prior to this, manufacturers could afford it only in the heavy class of these machines weighing more than 30 tons, where prices are several times higher. The market price of the TM10 bulldozer on swing carriages with hydrostatic transmission is planned to be no more than 4.5 million rubles.

PUMP adjustable MOTOR fixed

1 – booster pump safety valve; 2 – Check Valve; 3 – boost pump; 4 - servo cylinder; 5 - hydraulic pump shaft;
6 - cradle; 7 - servo valve; 8 - servo valve lever; 9- filter; 10 - tank; 11 - heat exchanger; 12 - hydraulic motor shaft; 13 - emphasis;
14 – valve box spool; 15 – overflow valve; 16 – high pressure safety valve.

Hydrostatic transmission GTS

The HST hydrostatic transmission is designed to transmit rotational motion from the drive motor to the executive bodies, for example, to the chassis of self-propelled machines, with stepless regulation of the frequency and direction of rotation, with an efficiency close to unity. The main GST set consists of an adjustable axial piston hydraulic pump and an unregulated axial piston hydraulic motor. The pump shaft is mechanically connected to the output shaft of the drive motor, the motor shaft - to the actuator. The speed of the output shaft of the motor is proportional to the angle of deflection of the lever of the control mechanism (servo valve).

The hydraulic transmission is controlled by changing the speed of the drive motor and changing the position of the handle or joystick associated with the pump servo valve lever (mechanically, hydraulically or electrically).

When the drive motor is running and the control handle is in neutral position, the motor shaft is stationary. When the position of the handle is changed, the motor shaft starts to rotate, reaching maximum speed at the maximum deflection of the handle. To reverse, the lever must be moved away from neutral.

Functional diagram of the GTS.

In general, a volumetric hydraulic drive based on HST includes the following elements: an adjustable axial piston hydraulic pump assembly with a make-up pump and a proportional control mechanism, an unregulated axial piston motor assembly with a valve box, a fine filter with a vacuum gauge, an oil tank for the working liquids, heat exchanger, pipelines and high pressure hoses (HPR).

Elements and nodes of the GTS can be divided into 4 functional groups:

1. The main circuit of the HTS hydraulic circuit. The purpose of the main circuit of the HTS hydraulic circuit is to transfer the power flow from the pump shaft to the motor shaft. The main circuit includes the cavities of the pump and motor working chambers and the high and low pressure lines with the working fluid flowing through them. The magnitude of the flow of the working fluid, its direction is determined by the revolutions of the pump shaft and the angle of deviation of the lever of the proportional control mechanism of the pump from the neutral. When the lever deviates from the neutral position in one direction or another, under the action of the servo cylinders, the angle of inclination of the swash plate (cradle) changes, which determines the direction of flow and causes a corresponding change in the working volume of the pump from zero to the current value, with a maximum deviation of the lever, the working volume of the pump reaches its maximum values. The working volume of the motor is constant and equal to the maximum volume of the pump.

2. Suction (feed) line. Appointment of the suction line (feed):

· - supply of working fluid to the control line;

· - replenishment of the working fluid of the main circuit to compensate for leaks;

· - cooling of the working fluid of the main circuit due to replenishment with fluid from the oil tank that has passed through the heat exchanger;

· - ensuring the minimum pressure in the main circuit in different modes;

· - cleaning and indicator of contamination of the working fluid;

· - compensation for fluctuations in the volume of the working fluid caused by temperature changes.

3. Purpose of control lines:

· - transmission of pressure to the executive servo-cylinder of the cradle rotation.

4. Purpose of drainage:

· - removal of leaks to the oil tank;

· - removal of excess working fluid;

· - heat removal, removal of wear products and lubrication of friction surfaces of hydraulic machine parts;

· - cooling of the working fluid in the heat exchanger.

The operation of the volumetric hydraulic drive is provided automatically by valves and spools located in the pump, boost pump, valve motor box.

Hydrostatic transmission is a hydraulic drive with a closed (closed) circuit, which includes one or more hydraulic pumps and hydraulic motors. Designed to transfer the mechanical energy of rotation from the motor shaft to the executive body of the machine, by means of a stepless flow of the working fluid regulated in magnitude and direction.

The main advantage of a hydrostatic transmission is the ability to smoothly change the gear ratio over a wide range of rotational speeds, which allows much better use of the machine's engine torque compared to a stepped drive. Since the output speed can be brought to zero, a smooth acceleration of the machine from a standstill is possible without the use of the clutch. Low speeds are especially needed for various construction and agricultural machines. Even a significant change in load does not affect the output speed, since there is no slip in this type of transmission.

The great advantage of hydrostatic transmission is the ease of reversing, which is provided by a simple change in the inclination of the plate or hydraulically, by changing the flow of the working fluid. This allows for exceptional maneuverability of the vehicle.

The next major advantage is the simplification of mechanical wiring around the machine. This allows you to get a gain in reliability, because often, with a heavy load on the machine, the cardan shafts do not withstand and you have to repair the machine. In northern conditions, this occurs even more often at low temperatures. By simplifying the mechanical wiring, it is also possible to free up space for auxiliary equipment. The use of a hydrostatic transmission can make it possible to completely remove the shafts and bridges, replacing them with a pumping unit and hydraulic motors with gearboxes built directly into the wheels. Or, in a simpler version, hydraulic motors can be built into the bridge. Usually it is possible to lower the center of gravity of the machine and more rationally place the engine cooling system.

Hydrostatic transmission allows you to smoothly and ultra-precisely adjust the movement of the machine or smoothly adjust the speed of the working bodies. The use of electro-proportional control and special electronic systems allows achieving the most optimal power distribution between the drive and actuators, limiting the engine load, and reducing fuel consumption. Engine power is used to the maximum even at the lowest speeds of the machine.

The disadvantage of hydrostatic transmission can be considered a lower efficiency compared to a mechanical transmission. However, compared to mechanical transmissions that include gearboxes, hydrostatic transmission is more economical and faster. This happens due to the fact that at the time of manual gear shifting, you have to release and press the gas pedal. It is at this moment that the engine spends a lot of power, and the speed of the car changes jerkily. All this negatively affects both speed and fuel consumption. In a hydrostatic transmission, this process is smooth and the engine runs more economically, which increases the durability of the entire system.

The most common application of a hydrostatic transmission is in the propulsion of tracked machines, where the hydraulic drive is designed to transfer mechanical power from the drive motor to the track sprocket, by controlling the pump flow and the tractive power output by controlling the hydraulic motor.

A hydrostatic transmission is a hydraulic drive with a closed (closed) circuit, which includes one or more hydraulic pumps and motors. The most common application of hydrostatic transmission is the drive of machines on wheels or caterpillars, where the hydraulic drive is designed to transfer mechanical energy from the drive motor to the executive body.

A hydrostatic transmission is a hydraulic drive with a closed (closed) circuit, which includes one or more hydraulic pumps and motors. In Russian and Soviet literature, a different name is used for such hydraulic drives - hydrostatic transmission. The most common application of a hydrostatic transmission is in the propulsion of wheeled or tracked machines - where the hydraulic drive is designed to transfer mechanical power from the drive motor to the axle, wheel or sprocket of the tracked vehicle, by controlling the pump flow and tractive power output by controlling the hydraulic motor.

Hydrostatic transmission has many advantages over mechanical transmission. One of the advantages is the simplification of the mechanical wiring around the machine. This allows you to get a gain in reliability, because often, under a heavy load on the car, the cardans do not withstand and you have to repair the car. In northern conditions, this occurs even more often at low temperatures. By simplifying the mechanical wiring, it is also possible to free up space for auxiliary equipment. The use of a hydrostatic transmission can make it possible to completely remove the shafts and bridges, replacing them with a pumping unit and hydraulic motors with gearboxes built directly into the wheels. Or, in a simpler version, hydraulic motors can be built into the bridge.

The first of the mentioned schemes, where hydraulic motors are built into the wheels, can be applicable for wheeled vehicles, but a variant of such a hydraulic drive for tracked vehicles is more interesting. For such machines, Sauer-Danfoss has also developed a control system based on hydraulic pumps and hydraulic motors of the 90 series, H1 series and 51 series -. Microcontroller control allows for comprehensive control of the machine, starting from diesel engine control. During operation, the system ensures the synchronization of the sides for the rectilinear movement of the machine and the side turn of the machine using the steering wheel or electric joystick.

The second scheme mentioned above is used for tractors or other wheeled vehicles. This is a hydraulic drive, in which there is one hydraulic pump and one hydraulic motor built into the drive axle. To control the hydraulic drive, both mechanical or hydraulic control, as well as the most advanced electrical control technologies using the controller built into the hydraulic pump, can be used. The program for controlling such a hydraulic drive can also be in the MC024 microcontroller installed separately. As well as for “Dual Path”, it allows you to control not only the hydrostatic transmission, but also the engine via the CAN bus. Electric control allows for even smoother and more precise control of the speed of movement and traction power of the machine.

The disadvantage of the hydrostatic transmission can be considered a low efficiency, which is much lower than that of a mechanical transmission. However, compared to mechanical transmissions that include gearboxes, hydrostatic transmission is more economical and faster. This happens due to the fact that at the time of manual gear shifting, you have to release and press the gas pedal. It is at this moment that the engine spends a lot of power, and the speed of the car changes jerkily. All this negatively affects both speed and fuel consumption. In a hydrostatic transmission, this process is smooth and the engine runs more economically, which increases the durability of the entire system.

For hydrostatic transmission, Sauer-Danfoss develops several series of hydraulic pumps and hydraulic motors. The most common in both Russian and foreign technology are adjustable axial piston. Their production began back in the 90s of the last century and now it is a fully debugged line of equipment that has a lot of advantages over the so-called GTS 90, produced by many domestic and foreign companies. The advantages include the compactness of the units, the possibility of making tandem pump units and all control options from mechanical to electro-hydraulic based on the microcontroller control of the PLUS+1 system.

In conjunction with the hydraulic pumps of the 90 series, adjustable axial piston pumps are often used. They may also have different ways of regulating the working volume. Proportional electric control allows you to smoothly adjust the power over the entire range. Discrete electric control allows you to work in low and high power modes, which is used either for various types of soil, or for driving on flat or hilly terrain.

The latest development of Sauer-Danfoss are the H1 series. The principle of their operation is similar to the hydraulic pumps of the 90 series and the motors of the 51 series, respectively. But compared to them, the design was worked out using the latest technology. The number of parts was reduced, which ensures greater reliability, and the dimensions were reduced. But the main difference from the old series can be considered the presence of only one control option - electric. This is a modern trend - to use systems based on complex electronics, controllers. And the H1 series is completely designed for these modern requirements. One of the signs of this is the version of hydraulic pumps with an integrated controller mentioned above.

There are also axial piston hydraulic pumps and hydraulic motors of the 40 and 42 series, which are applicable in low power hydrostatic transmission, where the working volume of the hydraulic pump does not exceed 51 cm 3. Such hydraulic drives can be found in small utility harvesters, skid steer loaders, mowers and other small-sized equipment. Often, gerotor hydraulic motors can be used in such a hydraulic drive. So in Bobcat loaders they are used. For other equipment, gerotor hydraulic motors of the OMT, OMV series are applicable, and for very light equipment.

The GST–90 hydraulic drive (Figure 1.4) includes axial-plunger units: an adjustable hydraulic pump with a make-up gear pump and a hydraulic distributor; non-adjustable hydraulic motor assembly with valve box, fine filter with vacuum gauge, pipelines and hoses, as well as a tank for working fluid.

Shaft 2 The hydraulic pump rotates in two roller bearings. A cylinder block is mounted on the shaft spline 25 , in the holes of which the plungers move. Each plunger is connected by a spherical hinge to the heel, which rests on a support located on a swash plate. 1 . The washer is connected to the hydraulic pump housing by means of two roller bearings, and due to this, the inclination of the washer relative to the pump shaft can be changed. The change in the angle of the washer occurs under the action of the efforts of one of the two servo cylinders 11 , the pistons of which are connected to the washer 1 with the help of traction.

Inside the servo cylinders are springs that act on the pistons and set the washer so that the support located in it is perpendicular to the shaft. Together with the cylinder block, the attached bottom rotates, sliding along the distributor mounted on the rear cover. Holes in the distributor and attached bottom periodically connect the working chambers of the cylinder block with the lines connecting the hydraulic pump with the hydraulic motor.

Figure 1.4 - Scheme of the hydraulic drive GTS-90: 1 - washer; 2 - output shaft of the pump; 3 - reversible adjustable pump; 4 - hydraulic control line; 5 - control lever; 6 - spool for controlling the position of the cradle; 7 8 - make-up pump; 9 - check valve; 10 - safety valve of the make-up system; 11 - servo cylinder; 12 - filter; 13 - vacuum gauge; 14 - hydraulic tank; 15 - heat exchanger; 16 - spool; 17 - overflow valve; 18 - main high pressure safety valve; 19 - low pressure hydraulic line; 20 - high pressure hydraulic line; 21 - drainage hydraulic line; 22 - unregulated motor; 23 - hydraulic motor output shaft; 24 - inclined washer of the hydraulic motor; 25 - cylinder block; 26 - connection thrust; 27 - mechanical seal

The spherical hinges of the plungers and the heels sliding along the support are lubricated under pressure by the working fluid.

The inner plane of each unit is filled with a working fluid and is an oil bath for the mechanisms operating in it. Leaks from the junctions of the hydraulic unit also enter this cavity.

A recharge pump is attached to the rear end surface of the hydraulic pump 8 gear type, the shaft of which is connected to the shaft of the hydraulic pump.

The make-up pump draws the working fluid from the tank 14 and submits it:

- into the hydraulic pump through one of the check valves;

- to the control system through the hydraulic distributor in quantities limited by the jet.

On the feed pump housing 8 safety valve located 10 , which opens when the pressure developed by the pump increases.

hydraulic valve 6 serves to distribute the fluid flow in the control system, that is, to direct it to one of the two servo cylinders, depending on the change in the position of the lever 5 or blocking fluid in the servo cylinder.

The hydraulic distributor consists of a body, a spool with a return spring located in a glass, a control lever with a torsion spring, and a lever 5 and two pulls 26 that connect the spool to the control lever and swash plate.

Hydraulic motor device 22 similar to the pump device. The main differences are as follows: the heels of the plungers slide along the swash plate when the shaft rotates 24 , which has a constant angle of inclination, and therefore there is no mechanism for its rotation with a hydraulic distributor; instead of the charge pump, a valve box is attached to the rear end surface of the hydraulic motor. A hydraulic pump with a hydraulic motor is connected to two pipelines (hydraulic pump-hydromotor lines). On one of the lines, the flow of working fluid under high pressure moves from the hydraulic pump to the hydraulic motor, on the other, it returns back under low pressure.

The valve box housing contains two high pressure valves, an overflow valve 17 and spool 16 .

Make-up system includes make-up pump 8 , as well as inverse 9 , safety 10 and overflow valves.

The make-up system is designed to supply the control system with working fluid, ensure minimum pressure in the hydraulic pump-motor lines, compensate for leaks in the hydraulic pump and hydraulic motor, constantly mix the working fluid circulating in the hydraulic pump and hydraulic motor with the fluid in the tank, and remove heat from parts.

High pressure valves 18 protect the hydraulic drive: from overloads, bypassing the working fluid from the high pressure line to the low pressure line. Since there are two lines and each of them can be a high-pressure line during operation, there are also two high-pressure valves. overflow valve 17 must release excess working fluid from the low pressure line, where it is constantly supplied by the boost pump.

spool 16 in the valve box, connects the overflow valve to the “hydraulic pump-hydraulic motor” line in which the pressure will be less.

When the valves of the make-up system (safety and overflow) are activated, the outflowing working fluid enters the internal cavity of the units, where, mixed with leaks, it enters the heat exchanger through drainage pipelines 15 and on to the tank 14 . Thanks to the drainage device, the working fluid removes heat from the rubbing parts of hydraulic units. A special mechanical shaft seal prevents leakage of the working fluid from the internal cavity of the unit. The tank serves as a reservoir for the working fluid, has a partition inside that separates it into a drain and suction cavity, and is equipped with a level indicator.

Fine filter 12 with a vacuum gauge retains foreign particles. The filter element is made of non-woven material. The degree of contamination of the filter is judged by the readings of the vacuum gauge.

The engine rotates the hydraulic pump shaft, and, consequently, the cylinder block and feed pump shaft associated with it. The make-up pump sucks the working fluid from the tank through the filter and supplies it to the hydraulic pump.

In the absence of pressure in the servo cylinders, the springs located in them install the washer so that the plane of the support (washer) located in it is perpendicular to the axis of the shaft. In this case, when the cylinder block rotates, the heels of the plungers will slide along the support without causing axial movement of the plungers, and the hydraulic pump will not send working fluid to the hydraulic motor.

From an adjustable hydraulic pump during operation, you can get a different volume of liquid (feed) supplied per revolution. To change the flow of the hydraulic pump, it is necessary to turn the hydraulic distributor lever, which is kinematically connected to the washer and spool. The latter, having moved, will direct the working fluid coming from the feed pump to the control system into one of the servo cylinders, and the second servo cylinder will be connected to the drain cavity. The piston of the first servo cylinder, under the influence of the pressure of the working fluid, will begin to move, turning the washer, moving the piston in the second servo cylinder and compressing the spring. The washer, turning to the position set by the hydraulic distributor lever, will move the spool until it returns to the neutral position (in this position, the outlet of the working fluid from the servo cylinders is closed by the spool bands).

When the cylinder block rotates, the heels, sliding along the inclined support, will cause the plungers to move in the axial direction, and as a result, the volume of the chambers formed by the holes in the cylinder block and the plungers will change. Moreover, half of the chambers will increase their volume, the other half will decrease. Thanks to the holes in the attached bottom and the distributor, these chambers are connected in turn to the “hydraulic pump-hydromotor” lines.

In the chamber, which increases its volume, the working fluid comes from the low-pressure line, where it is supplied by a feed pump through one of the check valves. By a rotating block of cylinders, the working fluid in the chambers is transferred to another line and forced into it by plungers, creating high pressure. Through this line, the liquid enters the working chambers of the hydraulic motor, where its pressure is transferred to the end surfaces of the plungers, causing them to move in the axial direction and, due to the interaction of the heels of the plungers with the swash plate, causes the cylinder block to rotate. After passing through the working chambers of the hydraulic motor, the working fluid will exit into the low-pressure line, through which part of it will return to the hydraulic pump, and the excess will flow through the spool and overflow valve into the internal cavity of the hydraulic motor. When the hydraulic actuator is overloaded, the high pressure in the “hydraulic pump-hydraulic motor” line can increase until the high pressure valve opens, which transfers the working fluid from the high pressure line to the low pressure line, bypassing the hydraulic motor.

The GST-90 volumetric hydraulic drive allows stepless change of gear ratio: for each revolution of the shaft, the hydraulic motor consumes 89 cm 3 of working fluid (excluding leaks). The hydraulic pump can produce such an amount of working fluid in one or more revolutions of its drive shaft, depending on the angle of the washer. Therefore, by changing the flow of the hydraulic pump, you can change the speed of the machines.

To change the direction of movement of the machine, it is enough to tilt the washer in the opposite direction. A reversible hydraulic pump, with the same rotation of its shaft, will change the direction of the flow of the working fluid in the "hydraulic pump-hydromotor" lines to the opposite (that is, the low pressure line will become a high pressure line, and the high pressure line will become a low line). Therefore, to change the direction of movement of the machine, it is necessary to turn the control valve lever in the opposite direction (from the neutral position). If, however, the force is removed from the hydraulic distributor lever, then the washer will return to the neutral position under the action of the springs, at which the plane of the support located in it will become perpendicular to the axis of the shaft. The plungers will not move in the axial direction. The supply of working fluid will stop. The self-propelled vehicle will stop. In the "hydraulic pump-hydromotor" lines, the pressure will become the same.

The spool in the valve box, under the action of the centering springs, will take a neutral position, in which the overflow valve will not be connected to any of the lines. All fluid supplied by the boost pump will drain through the safety valve into the internal cavity of the hydraulic pump. With uniform movement of a self-propelled machine in the hydraulic pump and hydraulic motor, it is only necessary to compensate for leaks, so a significant part of the working fluid supplied by the boost pump will be redundant and will have to be released through valves. In order to use the excess of this liquid for heat removal, the heated liquid that has passed through the hydraulic motor is released through the valves, and the cooled liquid is released from the tank. For this purpose, the overflow valve of the feed system, located in the valve box on the hydraulic motor, is set to a slightly lower pressure than the safety valve on the feed pump housing. Due to this, when the pressure in the make-up system is exceeded, the overflow valve will open and release the heated liquid that has left the hydraulic motor. Further, the liquid from the valve enters the internal cavity of the unit, from where it is sent through the drainage pipelines through the heat exchanger to the tank.