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 hydrostatic transmission is the ability to smoothly change the gear ratio over a wide range of 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.
Hydraulic transmission- a set of hydraulic devices that allow you to connect a source of mechanical energy (engine) with the actuators of the machine (wheels of a car, machine spindle, etc.). Hydraulic transmission is also called hydraulic transmission. As a rule, in a hydraulic transmission, energy is transferred through a fluid from a pump to a hydraulic motor (turbine).
In the presented video, a translational hydraulic motor is used as the output link. The hydrostatic transmission uses a rotary motion hydraulic motor, but the principle of operation is still based on the law. In a rotary hydrostatic drive, the working fluid is supplied from pump to motor. In this case, depending on the working volumes of hydraulic machines, the torque and frequency of rotation of the shafts can change. Hydraulic transmission has all the advantages of a hydraulic drive: high transmitted power, the possibility of implementing large gear ratios, the implementation of stepless regulation, the possibility of transferring power to moving, moving elements of the machine.
Methods of regulation in hydrostatic transmission
The speed control of the output shaft in the hydraulic transmission can be carried out by changing the volume of the working pump (volumetric control), or by installing a throttle or flow controller (parallel and sequential throttle control). The illustration shows a hydraulic transmission with closed loop volume control.
Closed Loop Hydraulic Transmission
Hydraulic transmission can be realized according to closed type(closed circuit), in this case there is no hydraulic tank connected to the atmosphere in the hydraulic system.
In hydraulic systems of a closed type, the speed of rotation of the shaft can be controlled by changing the working volume of the pump. Most often used as pump motors in hydrostatic transmission.
Open loop hydraulic transmission
open called a hydraulic system connected to a tank that communicates with the atmosphere, i.e. the pressure above the free surface of the working fluid in the tank is equal to atmospheric pressure. In open-type hydraulic transmissions, it is possible to implement volumetric, parallel and sequential throttle control. The following figure shows an open loop hydrostatic transmission.
Where are hydrostatic transmissions used?
Hydrostatic transmissions are used in machines and mechanisms where it is necessary to realize the transmission of large powers, to create a high torque on the output shaft, to carry out stepless speed control.
Hydrostatic transmissions are widely used in mobile, road-building equipment, excavators, bulldozers, in railway transport - in diesel locomotives and track machines.
Hydrodynamic transmission
Hydrodynamic transmissions also use turbines to transmit power. The hydraulic fluid in hydraulic transmissions is supplied from the dynamic pump to the turbine. Most often, hydrodynamic transmission uses paddle pump and turbine wheels located directly opposite each other, so that fluid flows from the pump wheel directly to the turbine wheel, bypassing the pipelines. Such devices that combine the pump and turbine wheels are called fluid couplings and torque converters, which, despite some similar elements in the design, have a number of differences.
fluid coupling
hydrodynamic transmission consisting of pump and turbine wheel installed in a common crankcase are called fluid coupling. The moment on the output shaft of the hydraulic clutch is equal to the moment on the input shaft, that is, the hydraulic clutch does not allow changing the torque. In a hydraulic transmission, power can be transmitted through a hydraulic clutch, which will provide smooth running, a smooth increase in torque, and a reduction in shock loads.
torque converter
Hydrodynamic transmission, which includes pump, turbine and reactor wheels placed in a single housing is called a torque converter. Thanks to the reactor torque converter allows you to change the torque on the output shaft.
Hydrodynamic transmission in an automatic transmission
The most famous example of hydraulic transmission application is car automatic transmission, in which a fluid coupling or torque converter can be installed. Due to the higher efficiency of the torque converter (compared to the fluid coupling), it is installed on most modern cars with automatic transmission.
Hydrostatic transmissions, made according to a closed hydraulic circuit, have found wide application in the drives of special equipment. These are mainly machines in which movement is one of the main functions, for example, front loaders, bulldozers, backhoe loaders, agricultural combines,
logging forwarders and harvesters.
In the hydraulic systems of such machines, the regulation of the flow of the working fluid is carried out in a wide range both by a pump and a hydraulic motor. Closed hydraulic circuits are often used to drive working bodies of rotational motion: concrete mixers, drilling rigs, winches, etc.
Let's consider a typical structural hydraulic diagram of the machine and select the contour of the hydrostatic drive transmission in it. There are many versions of enclosed hydrostatic transmissions in which the hydraulic system includes a variable displacement pump, usually a swash plate, and a variable displacement hydraulic motor.
Hydraulic motors are mainly used radial piston or axial piston with an inclined block of cylinders. Small-sized machines often use constant-displacement swashplate axial piston hydraulic motors and gerotor hydraulic machines.
The displacement of the pump is controlled by a proportional hydraulic or electro-hydraulic pilot system or by direct servo control. To automatically change the parameters of the hydraulic motor depending on the action of an external load in the pump control
controllers are used.
For example, the power regulator in hydrostatic drive transmissions allows the machine to slow down without operator intervention in the event of increasing driving resistance, and even stop the machine completely without allowing the engine to stall.
The pressure regulator provides a constant torque of the working body in all operating modes (for example, the cutting force of a rotating cutter, auger, drilling rig cutter, etc.). In any pump and hydraulic motor control stages, the pilot pressure does not exceed 2.0-3.0 MPa (20-30 bar).
Rice. 1. Typical scheme of hydrostatic transmission of special equipment
On fig. 1 shows a common diagram of a hydrostatic drive transmission for a machine. The pilot hydraulic system (pump control system) includes a proportional valve controlled by the accelerator pedal. In fact, this is a mechanically controlled pressure reducing valve.
It is powered by the auxiliary pump of the leakage replenishment (make-up) system. Depending on the degree of depression on the pedal, the proportional valve regulates the amount of pilot flow entering the cylinder (in the real design, the plunger) for controlling the tilt of the washer.
The pilot pressure overcomes the resistance of the cylinder spring and turns the washer, changing the pump displacement. Thus, the operator changes the speed of the machine. Reversal of the power flow in the hydraulic system, i.e. change of the direction of movement of the machine is carried out by the solenoid "A".
Solenoid "B" controls the hydraulic motor regulator, which sets the maximum or minimum displacement of the motor. In the transport mode of the machine, the minimum working volume of the hydraulic motor is set, thanks to which it develops the maximum shaft speed.
During the period when the machine performs power technological operations, the maximum working volume of the hydraulic motor is set. In this case, it develops maximum torque at minimum shaft speed.
Upon reaching the level of maximum pressure in the power circuit of 28.5 MPa, the control cascade will automatically reduce the angle of the washer to 0° and protect the pump and the entire hydraulic system from overload. Many mobile machines with hydrostatic transmission are subject to stringent requirements.
They must have a high speed (up to 40 km/h) in the transport mode and overcome large resistance forces when performing power technological operations, i.e. develop maximum traction. Examples are wheel loaders, agricultural and forestry machines.
The hydrostatic travel transmissions of these machines use adjustable tilt motors. As a rule, this regulation is relay, i.e. provides two positions: maximum or minimum displacement of the hydraulic motor.
However, there are hydrostatic transmissions that require proportional control of the displacement of the hydraulic motor. At maximum displacement, torque is generated at high pressure in the hydraulic system.
Rice. 2. Scheme of the action of forces in the hydraulic motor at maximum working volume
On fig. 2 shows a diagram of the action of forces in the hydraulic motor at maximum displacement. The hydraulic force Fg is decomposed into axial Fo and radial Fр. The radial force Fr creates a torque.
Therefore, the larger the angle α (the angle of inclination of the cylinder block), the higher the force Fp (torque). The arm of action of the force Fp, equal to the distance from the axis of rotation of the shaft to the point of contact of the piston in the hydraulic motor cage, remains constant.
Rice. 3. Scheme of the action of forces in the hydraulic motor when moving to the minimum working volume
When the angle of inclination of the cylinder block decreases (angle α), i.e. the working volume of the hydraulic motor tends to its minimum value, the force Fp, and consequently, the torque on the hydraulic motor shaft also decreases. The diagram of the action of forces in this case is shown in Fig. 3.
The nature of the change in torque is clearly visible from the comparison of vector diagrams for each angle of inclination of the hydraulic motor cylinder block. Such control of the working volume of a hydraulic motor is widely used in hydraulic drives of various machines and equipment.
Rice. 4. Scheme of typical control of the hydraulic motor of the power winch
On fig. 4 shows a diagram of a typical power winch hydraulic motor control. Here, channels A and B are the working ports of the hydraulic motor.
Depending on the direction of movement of the power flow of the working fluid, they provide direct or reverse rotation. In the position shown, the hydraulic motor has the maximum displacement. The working volume of the hydraulic motor changes when a control signal is applied to its port X.
The pilot flow of the working fluid, passing through the control spool, acts on the cylinder block displacement plunger, which, turning at high speed, quickly changes the displacement of the hydraulic motor.
Rice. 5. Characteristics of hydraulic motor control
On the graph in fig. 5 shows the control characteristic of the hydraulic motor, it is linear in nature of the inverse function. Often in complex machines, separate hydraulic circuits are used to drive the working bodies.
At the same time, some of them are made according to an open hydraulic circuit, others require the use of hydrostatic transmissions. An example is a full-revolving single-bucket excavator. In it, the rotation of the turntable and the movement of the machine are provided by hydraulic motors with
valve group.
Structurally, the valve box is installed directly on the hydraulic motor. The power supply of the hydrostatic transmission circuit from the hydraulic pump operating according to the open hydraulic circuit is carried out using a hydraulic distributor.
Rice. 6. Diagram of the hydrostatic transmission circuit, fed from an open hydraulic system
It provides the power flow of the working fluid to the hydrostatic transmission circuit in the forward or reverse direction. A diagram of such a hydraulic circuit is shown in Fig.6.
Here, the change in the working volume of the hydraulic motor is carried out by a plunger controlled by a pilot spool. The pilot spool can be acted upon by both an external control signal transmitted via the X channel, and an internal control signal from the “OR” selective valve.
As soon as the power flow of the working fluid is supplied to the pressure line of the hydraulic circuit, the selective “OR” valve opens access to the control signal to the end face of the pilot spool and, opening the working windows, directs a portion of the fluid to the plunger of the cylinder block drive.
Depending on the amount of pressure in the discharge line, the displacement of the hydraulic motor changes from its normal position towards its decrease (high speed / low torque) or increase (low speed / high torque). In this way, the management
movement.
If the spool of the power hydraulic distributor has moved to the opposite position, the direction of movement of the power flow will change. The selective OR valve will move to a different position and send a control signal to the pilot spool from the other line of the hydraulic circuit. The regulation of the hydraulic motor will be carried out in a similar way.
In addition to the control components, this hydraulic circuit contains two combined (anti-cavitation and anti-shock) valves tuned to a peak pressure of 28.0 MPa, and a working fluid ventilation system designed for its forced cooling.
The principle of operation of hydrostatic transmissions (HST) is simple: a pump connected to the prime mover creates a flow to drive a hydraulic motor that is connected to the load. If the pump and motor volumes are constant, the HTS simply acts as a gearbox to transfer power from the prime mover to the load. However, most hydrostatic transmissions use variable displacement pumps or variable displacement motors, or both, so that speed, torque, or power can be adjusted.
Depending on the configuration, the hydrostatic transmission can control the load in two directions (forward and reverse) with stepless speed change between the two maximums at constant optimal speed of the prime mover.
GTS offer many important advantages over other forms of power transmission.
Depending on the configuration, hydrostatic transmission has the following advantages:
- high power transmission in small dimensions
- small inertia
- works effectively in a wide range of torque-to-speed ratios
- maintains speed control (even when reversing) regardless of load, within design limits
- Precisely maintains the set speed under passing and braking loads
- can transfer power from one prime mover to different locations, even if their position and orientation change
- can handle full load without damage and with little power loss.
- Zero speed without additional blocking
- provides faster response than manual or electromechanical transmission.
Fig.2
Whatever the task, hydrostatic transmissions must be designed for optimal matching between engine and load. This allows the engine to run at the most efficient speed and the GTS to match the operating conditions. The better the match between input and output characteristics, the more efficient the entire system.Ultimately, a hydrostatic system must be designed to strike a balance between efficiency and productivity. A machine designed for maximum efficiency (high efficiency) tends to have a sluggish response that reduces productivity. On the other hand, a machine with a fast response usually has a lower efficiency, since the power reserve is available at any time, even when there is no immediate need for work.
Four functional types of hydrostatic transmissions.
Functional types of HTS differ in combinations of adjustable or unregulated pump and motor, which determines their performance.
The simplest form of hydrostatic transmission uses a fixed displacement pump and motor (Figure 3a). Although this GTS is inexpensive, it is not used due to low efficiency. Since the pump displacement is fixed, it must be calculated to drive the motor at the maximum set speed at full load. When maximum speed is not required, some of the working fluid from the pump passes through the relief valve, converting energy into heat.
Fig.3
The use of a variable displacement pump and a fixed displacement motor in a hydrostatic transmission can provide constant torque transmission (fig. 3b). The output torque is constant at any speed as it depends only on fluid pressure and motor displacement. Increasing or decreasing the pump flow increases or decreases the speed of the hydraulic motor, and hence the drive power, while the torque remains constant.
A HTS with a constant displacement pump and a variable hydraulic motor provides constant power transmission (Fig. 3c). Since the amount of flow entering the hydraulic motor is constant, and the volume of the hydraulic motor varies to maintain speed and torque, the transmitted power is constant. Reducing the volume of the hydraulic motor increases the speed of rotation, but reduces the torque and vice versa.
The most versatile hydrostatic transmission is the combination of a variable displacement pump and a variable displacement hydraulic motor (Figure 3d). Theoretically, this circuit provides infinite ratios of torque and speed to power. With the hydraulic motor at maximum volume, by changing the pump power, directly adjust the speed and power while the torque remains constant. Reducing the volume of the hydraulic motor at full pump flow increases the motor speed to a maximum; torque varies inversely with speed, power remains constant.
The curves in fig. 3d illustrate two adjustment ranges. In range 1, the volume of the hydraulic motor is set to the maximum; pump volume increases from zero to maximum. The torque remains constant as the pump volume increases, but the power and speed increase.
Band 2 starts when the pump reaches its maximum displacement, which is held constant while the motor displacement is reduced. In this range, torque decreases as speed increases, but power remains constant. (Theoretically, the speed of a hydraulic motor can be increased to infinity, but from a practical point of view, it is limited by dynamics.)
Application example
Assume that a hydraulic motor torque of 50 Nm is to be achieved at 900 rpm with a fixed displacement HTS.
The required power is determined from:
P = T × N / 9550Where:
P - power in kW
T - torque N * m,
N is the speed of rotation in revolutions per minute.Thus, P \u003d 50 * 900 / 9550 \u003d 4.7 kW
If we take a pump with a nominal pressure
100 bar, then we can calculate the flow:
Where:
Q - flow in l / min
p - pressure in barHence:
Q= 600*4.7/100=28 l/min.
Then we select a hydraulic motor with a volume of 31 cm3, which at this rate will provide a speed of approximately 900 rpm.
We check according to the formula of the torque of the hydraulic motor index.pl?act=PRODUCT&id=495
Figure 3 shows the power/torque/speed characteristics for the pump and motor, assuming the pump is running at a constant flow rate.The pump flow is maximum at rated speed and the pump delivers all the oil to the hydraulic motor at a constant speed of the latter. But the inertia of the load makes it impossible to accelerate instantaneously to the maximum speed, so that part of the pump flow is drained through the relief valve. (Figure 3a illustrates power loss during acceleration.) As the motor speeds up, more flow from the pump enters the motor and less oil escapes through the relief valve. At rated speed, all oil passes through the motor.
The torque is constant, because determined by the setting of the safety valve, which does not change. The power loss on the safety valve is the difference in the power developed by the pump and the power coming to the hydraulic motor.
The area under this curve represents the power lost when the movement starts or ends. It also shows low efficiency for any operating speed below the maximum. Fixed displacement hydrostatic transmissions are not recommended in drives requiring frequent starts and stops, or where full torque is often not needed.
Torque/speed ratio
Theoretically, the maximum power transmitted by a hydrostatic transmission is determined by flow and pressure.
However, in transmissions with constant power output (non-variable pump and variable displacement motor), the theoretical power is divided by the torque/speed ratio, which determines the power output. The highest transmit power is determined by the minimum output rate at which this power must be transmitted.
Fig.4
For example, if the minimum speed represented by point A on the power curve in Fig. 4 is half of the maximum power (and the moment of force is maximum), then the ratio of moment - speed is 2: 1. The maximum power that can be transmitted is half the theoretical maximum.
At less than half the maximum speed, the torque remains constant (at its maximum value), but the power decreases in proportion to the speed. The speed at point A is the critical speed and is determined by the dynamics of the hydrostatic transmission components. Below critical speed, power decreases linearly (with constant torque) to zero at zero rpm. Above critical speed, torque decreases as speed increases, providing constant power.
Design of a closed hydrostatic transmission.
In the descriptions of closed hydrostatic transmissions in fig. 3 we focused only on the parameters. In practice, additional functions should be provided for in the GTS.Additional components on the pump side.
Consider, for example, a constant torque HTS, which is most commonly used in power steering systems with a variable pump and a non-variable hydraulic motor (Fig. 5a). Since the circuit is closed, leaks from the pump and motor are collected in one drain line (Fig. 5b). The combined drain stream flows through the oil cooler to the tank. An oil cooler in a hydrostatic drive is recommended to be installed at a power of more than 40 hp.
One of the most important components in a closed hydrostatic transmission is the boost pump. This pump is usually built into the main one, but can be installed separately and serve a group of pumps.
Regardless of location, the booster pump performs two functions. First, it prevents main pump cavitation by compensating for pump and motor fluid leaks. Secondly, it provides the oil pressure required by the disc displacement control mechanisms.
On fig. 5c shows relief valve A which limits the boost pump pressure, which is typically 15-20 bar. Check valves B and C installed opposite each other provide a connection between the suction line of the make-up pump and the low pressure line.
Rice. 5
Additional components on the hydraulic motor side.
A typical closed-type HTS should also include two safety valves (D and E in Fig. 5d). They can be built into both the motor and the pump. These valves perform the function of protecting the system from overloading that occurs during sudden changes in load. These valves also limit the maximum pressure by diverting the flow from the high pressure line to the low pressure line, i.e. perform the same function as a safety valve in open systems.
In addition to the safety valves, the system has an "or" valve F, which is always pressure switched so that it connects the low pressure line to the low pressure safety valve G. Valve G directs excess priming pump flow to the motor housing, and then this flow through the drain line and heat exchanger returns to the tank. This contributes to a more intensive oil exchange between the working circuit and the tank, cooling the working fluid more efficiently.
Cavitation control in hydrostatic transmission
The stiffness in GTS depends on the compressibility of the fluid and the suitability of the system of components, namely pipes and hoses. The effect of these components can be compared to the effect of a spring-loaded accumulator if it were connected to the discharge line through a tee. With a light load, the battery spring is compressed a little; under heavy loads, the battery is subjected to significantly more compression and contains more liquid. This additional volume of liquid must be supplied by the boost pump.
The critical factor is the rate of pressure buildup in the system. If the pressure rises too quickly, the rate of growth of the high side volume (flow compressibility) can exceed the capacity of the charge pump and cavitation occurs in the main pump. It is possible that systems with variable pumps and automatic control are the most sensitive to cavitation. When cavitation occurs in such a system, the pressure drops or disappears altogether. Automatic controls may try to respond, resulting in an unstable system.
Mathematically, the rate of pressure rise can be expressed as follows:dp/dt =B eQcp/V
B e – effective volume modulus of the system, kg/cm2
V is the liquid volume on the high pressure side cm3
Qcp - performance of the booster pump in cm3 / s
Let us assume that the HTS in Fig. 5 is connected with a steel pipe 0.6 m, diameter 32 mm. Neglecting the pump and motor volumes, V is about 480 cm3. For oil in steel pipe, the effective bulk modulus is about 14060 kg/cm2. Assuming the boost pump delivers 2 cm3/s, the rate of pressure rise is:
dp/dt= 14060 × 2/480
= 58 kg/cm2 / sec.
Now consider the effect of a system with 6 m of 32 mm three-wire braided hose. Hose manufacturer gives data B e about 5906 kg/cm2.Hence:
dp/dt\u003d 5906 × 2 / 4800 \u003d 2.4 kg / cm2 / sec.
It follows from this that an increase in the performance of the boost pump leads to a decrease in the likelihood of cavitation. As an alternative, if sudden loads are not frequent, a hydraulic accumulator can be added to the swap line. Indeed, some GTS manufacturers make a port for connecting the battery to the swap circuit.
If the rigidity of the GTS is low and it is equipped with automatic control, then the transmission should always be started with zero pump flow. In addition, the speed of the disc tilt mechanism must be limited to prevent abrupt starts, which in turn can cause pressure surges. Some GTS manufacturers provide damping holes for smoothing purposes.
Thus, system stiffness and rate of buildup control may be more important in determining priming pump performance than simply internal pump and motor leaks.
______________________________________
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.
