Home Chassis Hydraulic car transmission. What is a hydrostatic transmission applied to mini tractors. GST hydrostatic transmission

Chassis

Hydraulic car transmission. What is a hydrostatic transmission applied to mini tractors. GST hydrostatic transmission

Hydrostatic transfers

During the first two decades of existence automotive industry A number of hydraulic studies were proposed, in which the fluid under pressure generated by the pump operated by the engine flows through the hydraulic engine. As a result of moving, under the action of fluid, the working bodies of the hydromotor to its shaft is supplied. The liquid, of course, carrys some kinetic energy supply, however, since it comes out of the hydromotor at the same speed with which it enters it, the magnitude of the kinetic energy does not change and, therefore, does not participate in the transmission of power.

A single type of hydraulic studies appeared somewhat later, in which both rotating elements are placed in one crankcase - and the wheel of the pump, leading the fluid, and the turbine, in the blades of which the moving liquid is hidden. In such transmissions, the liquid comes out of the channels between the blades of the slave element with a much smaller absolute speed than enters them, and the power is transmitted through the liquid in the form of kinetic energy.

Thus, two types of hydraulic arms should be distinguished: hydrostatic or volume transmissions in which the energy is transmitted to the fluid pressure acting on moving pistons or blades, and hydrodynamic transmissions in which the energy is transmitted by increasing the absolute fluid velocity in the pump wheel and reduce absolute speed in turbine

Transmission of motion or power using fluid pressure with great success is used in a number of regions. An example of the successful use of similar gears are hydraulic systems of modern machines. Other examples are the hydraulic drives of the steering mechanisms of the courts and the management of gun tower towers of combat boxes. From the point of view of applying on cars, the most favorable property of the hydrostatic transmission is the possibility of stepless change of gear ratio. To do this, only a pump is needed, in which the volume described by the pistons in one turnover of the shaft can be smoothly changed during operation. Another advantage of the hydrostatic transmission is the simplicity of receiving the reverse. In most constructions, the movement of the control organ further corresponding to the zero speed, and the transfer ratio, equal to infinity, causes rotation in the opposite direction with gradually increasing speed.

Use of oil as a working "fluid. Translated the term "hydraulic" means the use of water as working fluid. However, in practice, using this term, usually imply the use of any fluid for transmitting motion or power. In hydraulic transmissions of all types are used mineral oilsSince they protect the mechanism from corrosion and simultaneously provide its lubricant. Usually use low-viscosity oils, since the internal losses increase with an increase in viscosity. However, the less viscosity, the harder it is to prevent the leakage of the working fluid.

The use of hydrostatic gears on cars has never come out of the experiment stage. However, some successes were achieved in the field of using these broadcasts on rail transport. At the exhibition vehicle In the German city of Seddin, held in the mid-20s, on seven of the eight demonstrated maneuver diesel locomotives were installed. These transmissions are very convenient to manage. Since they allow you to get any gear ratio, the engine can always work with the number of revolutions per minute, which corresponds to the highest to. P. D.

One of the serious shortcomings that prevent the use of hydrostatic gears on vehicles is the dependence of them to. P. D. From speed. The literature published data according to which the maximum to. P. D. Similar gear reaches 80%, which is quite acceptable. However, it is necessary to keep in mind that the maximum to. P. D. Is always achieved at low operating speeds.

Dependence to. P. D. From speed. In the hydrostatic gears, turbulent fluid flow occurs, and with a turbulent movement of the loss (heat release), the third degree of speed is directly proportional to the third degree of speed, while the power transmitted power changes directly in proportion to the flow rate. Therefore, with an increase in the flow rate to. P. D. Quickly falls. Most of the well-known data on the C. P. hydrostatic gear refers to the speed of rotation, significantly less than 1000 rpm (usually 500-700 rpm); If you use similar transmissions to work with the engine, the normal speed of rotation crankshaft which is over 2000 rpm, then to. p. d. will be unacceptable low. Of course, a gear gearbox can be installed between the engine and the hydrostatic transmission pump. However, this transmission would complicate another unit, and the low-speed pump and the hydraulic motor would be overhaul. Another disadvantage is to use in hydrostatic transmissions of high pressures that reach up to 140 kg! CM2, in which, naturally, is very difficult to prevent leakage of the working fluid. Moreover, all parts that are exposed to such pressures must be very durable.

Hydrostatic transmissions did not get distribution in cars by no means because they did not pay attention to them. A number of American and European firms who have sufficient technical and cash, engaged in the creation of hydrostatic gears, in most cases, having to use the transmission on vehicles. However, as far as the author is known, cargo cars with hydrostatic gears did not enrolled in production. In cases where firms produced hydrostatic transmissions for some time, they found them sales in other engineering industries, where high speed of rotation and low weight are not mandatory applications. Several ingenious designs of hydrostatic transmissions were proposed, two of which are described below.

Transmission of Manley. One of the first car hydrostatic gears created in the United States is Mainie's transfer. It was invented by Charles Manley, a Pioneer Employee of the Langlei Aid and Chairman of the Society of American Automotive Engineers. The transfer consisted of a five-cylinder radial piston pump with variable strokes of pistons and a five-cylinder radial piston hydromotor with a constant piston running; The pump connected with the hydraulic motor two pipelines. When the direction of rotation changes, the injection pipe has become sucking, and vice versa; With a decrease in the stroke of the pump piston to zero, the hydraulic engine operated the role of the brake. To prevent damage to the mechanism from excessive pressure, a safety valve opened at a pressure of 140 kg / cm2 was used.

The longitudinal section of the transfer of Mainie is presented in Fig. 1. The pump and the hydraulic motor were located coaxially next to each other, forming a single compact unit. On the left is the incision of one of the pump cylinders. The gap between the piston and the cylinder was very small, and the pistons did not have sealing rings. The lower heads of the rods did not cover the crank, but had the form of sectors and retained with two rings located on both sides of the connecting rod. The change in the stroke of the pump piston was carried out with the help of the eccentrics installed on the crankshaft shaft. During the operation of the aggregate, the crankshaft and the eccentrics remained fixed, and the cylinder block rotated around the axis of Eccentric E. On the figure, the mechanism is shown in a position corresponding to the maximum move of the piston equal to the amount of radius of crank and eccentricity of its eccentric; The cylinders rotate around the axis E, and the pistons of the pump - around the axis R. to reduce the stroke of the pistons, the eccentric turns around the axis E in one direction, and the crank is around the axis in the opposite direction; Due to this, the angular position of the crank remains unchanged, and the distribution mechanism continues to work as before. Management is carried out with the help of two worm wheels installed on the eccentric, one of which is planted freely, the second is fixed. A freely sitting worm wheel is associated with a crankshaft by means of a gear that is reinforced on the colleague shaft, which engages with internal teeth, made on a worm wheel. Wormwood wheels are in engaging with worms connected by two cylindrical gears. Thus, the worms are always rotated in opposite directions, and the transmission was designed so that the angular movements of the eccentric and the crank were equal in the absolute value are opposite to the direction. If the eccentric and crank rotated at an angle of 90 °, the course of the piston of the pump became zero. Eccentric distribution mechanism was installed at an angle of 90 ° to the shoulder of the crank. The hydromotor differs from the pump only by the fact that it does not have a mechanism for changing the piston running. Both the pump and the hydromotor have spool valves, controlled by eccentric.

Fig. 1. Hydrostatic transfer Mainie:
1 - pump; 2 - hydromotor.

Fig. 2. Eccentric management of Menley's transfer.

Transmission of Mainic, intended for use on a cargo car with a carrying capacity of 5 g gasoline engine With a capacity of 24 liters. from. At 1200 rpm, there was a pump with cylinders with a diameter of 62.5 mm and the maximum stroke of the pistons of 38 mm. The pump worked for two hydromotors (one for each leading wheel). With the working volume of the five-cylinder pump, equal to 604 cm3 to transmit 24 liters. from. At 1200 rpm, at the maximum progress, the pistons required a pressure of 14 kg / cm2. When driving, Mainic in the laboratory, it was found that peak to. P. D. Took place at 740 rpm of the pump shaft and amounted to 90.9%. With a further increase in the speed of rotation to. P. D. Dropped sharply and already at 760 rpm amounted to only 81.6%.

Fig. 3. Hydrostatic gear gear.

Transmission of Jenna. Jenny's hydraulic frame has long been built by Waterbury Tul Company for various industries; In particular, she was also installed on trucksAvtomotris and locomotives. This transfer consists of a multi-cylinder porseless pump with a swinging washer and variable stroke and the same hydraulic transmission, but with a constant piston. The longitudinal section of the aggregate is presented in Fig. 144. The difference in the pump and hydrometer device is only that in the first slope of the swinging washer can change, and in the second - cannot. Pump and hydromotor shafts perform each from one end. Each shaft relies on the sliding bearing in the crankcase and on the roller bearing in the camshaft. A cylinder block is attached to the inner end of each shaft, which has nine holes forming cylinders. The axes of these cylinders are parallel to the axis of rotation and are at an equal distance from it. When the cylinder heads are rotated, the cylinder head slide across the camshaft. The holes in the head of each cylinder are periodically communicated with one of the two windows in the distribution plate, made on the circle arc; Thus, the supply and production of the working fluid is carried out. The length of each window on the arc is about 125 °, and since the cylinder message with the channel in the stove begins from the moment when the hole in the cylinder head begins to combine with the window, and continues until the window in the stove is blocked by the edge of the opening, then The discovery phase is about 180 °.

The springs installed on the shafts are used to press the cylinder blocks to the distribution plate at a time when the load is not transmitted. When transferring the load, the contact is provided by fluid pressure. Cylinder blocks are installed on the shafts in such a way that they can slide and slightly swing on them. This provides a dense adjacent of the cylinder block to the distribution plate even with some inaccuracies of manufacture, as well as in the case of wear.

The gap between the piston and the cylinder is 0.025 mm, and the piston do not have any sealing devices. Each piston is connected to a hinged ring by means of a rod with spherical heads. The body of the connecting rod has a longitudinal hole, and the hole is also made in the bottom of each piston. Thus, the connecting rod heads are lubricated by oil from the main flow of fluid and the pressure under which the oil is supplied to the support surfaces, in proportion to the load. Each swinging washer is attached to the shafts by driven hinges in such a way that when it rotates with the shaft, its rotation plane can be any angle with the axis of the shaft. In the pump, the angle of inclination of the swinging washer can vary in the range from 0 to 20 ° in any direction. This is achieved using the control handle associated with the rotating bearing jack. In the hydraulic engine, the bearing nest is rigidly attached to the Carder at an angle of 20 °.

In cases where the swinging washer is a straight angle with the shaft, when the cylinder block rotates, the piston will not move in the cylinders; Accordingly, there will be no oil supply. But as soon as the angle between the swinging washer and the axis of the shaft will be changed, the piston will begin to move in the cylinders. Throughout one half of the turnover, the oil is suused through the hole in the distribution plate; During the second half of turnover, the oil is injected through the injection hole in the camshaft.

The oil supplied under pressure in the hydraulic motor causes the piston of the hydromotor to move, and the forces acting on the swinging washer through the connecting rods are caused to rotate the cylinder block and its shaft. In the case when the angle of inclination of the pumping washer of the pump is equal to the angle of inclination of the swinging washer of the hydraulico, the latter shaft will rotate at the same speed as the shaft 'of the pump; Reducing the rotational speed of the hydraulic shaft can be achieved by reducing the angle between the pumping of the pump and the shaft.

In the transmission built for automotive engine with a capacity of 150 l., E., K. P. D. At 25% load and maximum speed rotation was 65%, and when maximum load - 82%. The transfer of this type has a significant weight; The unit given as an example had a proportion of 11.3 kg per 1 liter. from. Transmitted power.

TO Manager: - Automotive clutch

Hydraulic transmission - Collapse hydraulic devicesallowing to connect the source of mechanical energy (engine) with executive mechanisms Machines (car wheels, machine spindle, etc.). The hydrotransmission is also called hydraulic transmission. As a rule, in hydraulic transmission, energy is transmitted by fluid from the pump to hydromotor (turbine).

In the presented video, a hydraulic motion was used as a output level. In the hydrostatic transmission, the hydraulic motor of the rotational motion is used, but the principle of operation is still based on the law. In the hydrostatic drive of rotational action, the working fluid is supplied from the pump to the motor. At the same time, depending on the working volumes of hydromachins, the moment of rotation of the shafts may change. Hydraulic transmission It has all the advantages of the hydraulic drive: high power transmitted, the possibility of implementing large gear ratios, implementation of stepless regulation, the possibility of transmitting power to movable, moving machine elements.

Methods for regulation in hydrostatic transmission

Adjusting the speed of the output shaft in the hydraulic transmission can be carried out by changing the volume of the working pump (volumetric control), or by setting the choke or the flow controller (parallel and consistent throttle). The figure shows a hydrotransmission with a volumetric control with a closed circuit.

Hydrotransmission with closed contour

Hydraulic transmission can be implemented by closed type (closed loop), in this case there is no hydraulic tank in the hydraulic system connected to the atmosphere.

In the hydraulic systems of a closed type, the regulation of the rotational speed of the shaft can be carried out by changing the pump working volume. As a pump-motors in the hydrostatic transmission most often used.

Open contour hydrotransmission

Open Call hydraulic system connected to the tank, which is reported to the atmosphere, i.e. The pressure over the free surface of the working fluid in the tank is equal to the atmospheric. In the hydrotransissions of the open type it is possible to implement volumetric, parallel and consistent throttle. The following figure shows a hydrostatic transmission with an open circuit.

Where hydrostatic transmissions are used

Hydrostatic transmissions are used in machines and mechanisms where it is necessary to implement the transfer of large capacities, create a high moment on the output shaft, to carry out stepless speed control.

Hydrostatic transmissions are widely used. In mobile, road construction equipment, excavators of bulldozers, on railway transport - in locomotives and traveling machines.

Hydrodynamic transmission

In hydrodynamic transmissions for power transmission, turbines are used. The working fluid in hydraulic transmissions is supplied from the dynamic pump to the turbine. Most often in the hydrodynamic transmission, blade pumping and turbine wheel are used, located directly opposite each other, in such a way that the fluid comes from the pumping wheel immediately to the turbine percentage of pipelines. Such devices combining the pump and turbine wheel are called hydromefts and torque converters, which, despite some similar elements in the design, have a number of differences.

Hydromefta

Hydrodynamic transmission consisting of pumping and turbine wheelinstalled in the general crankcase called hydromuft. The moment on the outlet shaft of the hydraulic clutch is equal to the moment on the input shaft, that is, the hydromefta does not allow you to change the torque. In the hydraulic transmission, power transmission can be carried out through a hydraulic coupling, which will ensure the smoothness of the stroke, the smooth increase in the torque, reduced shock loads.

Hydrotransformer

Hydrodynamic transmission, which includes pumping, turbine and reactor wheels, placed in a single housing is called a torque converter. Thanks to the reactor, hydrotector Allows you to change the torque on the output shaft.

Hydrodynamic transmission in a tetatic gearbox

The most famous example of the use of hydraulic transmission is automatic car gearboxin which hydromefta or hydrotransformer can be installed. Due to the higher efficiency of the hydrotransformer (compared to hydromefta), it is installed on most modern cars from automatic box Transmissions.

Hydrostatic transfer B. passenger cars So far does not apply, since it is the road and its efficiency relatively low. Most often it is used in special machines and vehicles. At the same time, the hydrostatic drive has many opportunities for use; It is particularly suitable for transmissions with electronic control.

The principle of hydrostatic transmission is that the source of mechanical energy, for example, the engine internal combustionThe hydraulic pump leads oil to the traction hydraulic engine. Both of these groups are interconnected by a high-pressure pipeline, in particular, flexible. It simplifies the design of the machine, there is no need to use many gears, hinges, axes, since both groups of aggregates can be located independently of each other. The drive power is determined by the volumes of hydraulic pump and hydraulic motor. Changing the gear ratio in the hydrostatic drive stepless, its reversing and hydraulic lock is very simple.

In contrast to the hydromechanical transmission, where the connection of the traction group with the torque converter is rigid, in the hydrostatic drive, the transfer of force is performed only through the liquid.

As an example of the work of both transmissions, consider moving the car with them through the folds of the area (Damb). At the entrance to the dam in a car with a hydromechanical transmission arises, as a result of which, with a constant frequency of rotation, the vehicle speed is reduced. When descending from the vertex of the dam, the engine begins to act as a brake, but the direction of the bucking of the torque converter is changing and since the torque converter has low brake properties with this direction of the bucking, the car accelerates.

At the hydrostatic transmission during the descent from the vertex of the dam, the hydraulic motor performs the function of the pump and the oil remains in the pipeline connecting the hydraulic motor with the pump. The compound of both drive groups occurs through a pressure under pressure, which possesses the same degree of rigidity as the elasticity of shafts, clips and gears in a conventional mechanical transmission. The acceleration of the car, so it will not happen during the descent from the dam. Hydrostatic gear is particularly suitable for high-pass vehicles.

The principle of the hydrostatic drive is shown in Fig. 1. The hydraulic pump drive 3 from the internal combustion engine is performed through the shaft 1 and the inclined washer, and the regulator 2 control the angle of inclination of this washer, which changes the fluid supply by hydraulic pump. In the case shown in Fig. 1, the washer is installed rigidly and perpendicular to the axis of the shaft 1 and instead of it, the housing of the pump 3 in the casing 4 is tilted. The oil is supplied from hydraulic pump through the pipeline 6 to the hydraulic motor 5, having a constant volume, and from it - again returns to the pipeline 7 into the pump.

If the hydraulic pump 3 is located coaxially shaft 1, then the supply of oil is zero and the hydraulic motor in this case is blocked. If the pump is tilted down, it serves oil in the pipeline 7 and it returns to the pump on the pipeline 6. With a constant frequency of rotation of the shaft 1, provided, for example, a diesel regulator, the speed control and the direction of the vehicle movement is made by only one knob of the regulator.

In the hydrostatic drive, you can use several regulatory schemes:

the pump and the engine have unregulated volumes. In this case, we are talking about "hydraulic shaft", the gear ratio is constant and depends on the ratio of the volume of the pump and the engine. Such a transmission for use in the car is unacceptable;
the pump has an adjustable, and the engine is unregulated volume. This method is most commonly applied in vehicles, as it provides a large range of regulation with a relatively simple design;
the pump has an unregulated, and the engine is adjustable. This scheme is unacceptable for car drive, because it cannot be braked by car through transmission;
the pump and the engine have adjustable volumes. Such a scheme provides best opportunities regulation, but very complex.

The use of hydrostatic transmission allows you to adjust the output power up to the output shaft stop. At the same time, even on cool descent You can stop the car by moving the knob of the regulator to the zero position. In this case, the transmission is hydraulically blocked and the need to apply brakes disappears. To move the car, it is enough to move the handle forward or backward. If several hydraulic motigaves are used in the transmission, then their regulation can be achieved by the operation of the differential or blocking it.

In the hydrostatic transmission there is no whole range of units, for example, gearbox, clutch, cardan shafts with hinges, home gear, etc. It is beneficial from the position of the mass and cost of the car and compensates for a sufficiently high cost hydraulic equipment. All of the above, first of all, refers to special transport and technological means. At the same time, from the point of view of energy savings, the hydrostatic transmission has great advantages, for example, for use in buses.

Above mentioned the feasibility of accumulating energy and the energy gain received when the engine operates with a constant rotational speed in the optimal zone of its characteristic and its rotational speed does not change when switching gear or change the vehicle. It also noted that the rotating masses connected to the leading wheels should be as small as possible. It was also said, in addition, the advantages of a hybrid drive, when the highest engine power is used during acceleration, as well as the power accumulated in the battery. All these advantages can be easily implemented in a hydrostatic drive, if high pressure hydroaccumulator is located in its system.

The scheme of such a system is presented in Fig. 2. Motor-driven 1 pump 2 with a constant volume supplies oil into battery 3. If the battery is filled, the pressure regulator 4 gives the pulse to the electronic regulator 5 of the engine stop. From the battery, the pressure oil is fed through the central control device 6 to the hydraulic motor 7 and is reset from it to the oil tank 8, from which the pump is again closed. The battery has a branch 9, intended for nutrition additional equipment car.

In the hydrostatic drive, the opposite direction of movement of the fluid can be used to brake the car. In this case, the hydraulic motor takes oil from the tank and serves it under pressure in the battery. In this way, you can accumulate braking energy for further use. The disadvantage of all batteries is that any of them (liquid, inertial or electric) has limited capacity, and if the battery is charged, it can no longer accumulate energy, and its excess must be reset (for example, transformed into warmth) As in the car without accumulating energy. In the case of a hydrostatic drive, this problem is solved by the use of a reduction valve 10, which, with a filled battery, is bypassing the oil into the tank.

Urban bus buses Thanks to the accumulation of the braking energy and the possibility of charging the liquid battery during stops, the engine could be adjusted to less power and at the same time ensure compliance with the necessary accelerations when overclocking the bus. Such a drive scheme allows economically to realize traffic in the urban cycle, previously described and depicted in Fig. 6 in the article.

The hydrostatic drive can be conveniently combined with conventional gear. As an example, we give a combined vehicle transmission. In fig. 3 Dana scheme of such a transmission from engine flywheel 1 to gearbox 2 of the main transmission. Torque through cylindrical gear 3 and 4 is supplied to the piston pump 6 with a constant volume. The gear ratio of the cylindrical transmission corresponds to IV-V transmissions mechanical box Transmissions. When rotating the pump begins to feed the oil into the traction hydraulic motor 9 with an adjustable volume. The inclined hydraulic motor controller 7 is connected to the lid 8 of the transmission housing, and the hydraulic motor body 9 is connected to the main transmission shaft 5.

When the car is accelerated, the hydrodial washer has the highest angle of inclination and oil injected by the pump, creates a large moment on the shaft. In addition, the pump is also valid for the shaft. As the car is accelerated, the tilt of the washer decreases, therefore, the torque of the hydraulic motor body is reduced, but the oil pressure supplied by the pump increases and, consequently, the jet momentum of this pump will increase.

With a decrease in the angle of inclination of the washer to 0 °, the pump is hydraulically blocked and the transmission of torque from the flywheel to the main program will be carried out only by a pair of gears; The hydrostatic drive will be turned off. This improves the efficiency of the entire transmission, as the hydraulic motor and the pump are disabled and rotate in a locked position along with the shaft, with an efficiency equal to one. In addition, wear and noise of hydraulic units disappear. This example is one of many showing the possibilities of using a hydrostatic drive. The mass and dimensions of the hydrostatic transmission are determined by the magnitude of the maximum fluid pressure, which currently reached 50 MPa.

The principle of operation of hydrostatic transmissions (GST) is simple: the pump connected to the primary engine creates a stream for the drive of the hydraulic motor that is connected to the load. If the pump volumes and motor are constant, the GTS simply acts as a gearbox for transmitting power from the primary motor to the load. However, in most hydrostatic transmissions, adjustable pumps or hydraulic motors with variable volume or both types are immediately, so that the speed, torque, or power can be adjusted.

Depending on the configuration, the hydrostatic transmission can control the load in two directions (direct and reverse) with a stepless change in the speed between two maxima with constant optimal turnover of the primary motor.

GTS offer many important advantages compared to other forms of energy transmission.

Depending on the configuration, the hydrostatic transmission has the following advantages:

transmission of high power at small sizes
- small inertia
- effectively works in a wide range of torque ratios to speed
- supports speed control (even during reverse), regardless of the load, at the calculated limits
- accurately supports the specified speed during passing and braking loads
- can transmit energy from one primary engine in different places, even if their position and orientation changes
- it can hold full load without damage and low power losses.
- Zero speed without additional lock
- provides a faster response than a mechanical or electromechanical transmission.
There are two constructive types of hydrostatic transmissions: integrated and separate. The separate type is used most often, as it allows you to transmit power over long distances and in hard-to-reach places. In this type, the pump is connected to the primary engine, the engine is connected to the load, and the pump itself and the engine are connected by pipes or RVD, fig. 2.
Fig.2
Whatever tasks, hydrostatic transmissions should be developed for optimal conformity between the engine and the load. This allows the engine to work at the most efficient speed and GTS to meet the operating conditions. The better the correspondence between the input and output characteristics, the more effective the entire system.
Ultimately, the hydrostatic system should be calculated on the balance between efficiency and productivity. A machine designed to achieve maximum efficiency (high efficiency), as a rule, has a sluggish reaction that reduces performance. On the other hand, the quick reaction machine usually has an efficiency below, since the power supply is available at any time, even when there is no direct need for work.
Four functional types of hydrostatic transmissions.
Functional types of GTS differ in combinations of an adjustable or unregulated pump and motor, which determines their operational characteristics.
In the simplest form of hydrostatic transmission, a pump and a motor with fixed volumes are used (Fig. 3a). Although this GTS is inexpensive, it is not applied due to low efficiency. Since the volume of the pump is fixed, it must be designed to drive a motor with a maximum set speed at full load. When the maximum speed is not required, part of the working fluid from the pump passes through the safety valve, turning the energy to heat.
Fig. 3.
Use in the hydrostatic transmission of the pump with an adjustable feed and hydraulic transmission with a constant volume can be transferred to the transmission of a constant torque (Fig. 3b). The output torque is constant at any speed, as it depends only on the pressure of the fluid and the volume of the hydromotor. An increase or decrease in pump feed increases or reduces the speed of rotation of the hydraulic motor, and therefore the drive power, while the torque remains constant.
The GTS with a constant volume pump and the adjustable hydraulic motor ensures the transmission of a constant power (Fig. 3B). Since the value of the flow entering the hydraulic motor is constant, and the volume of the hydromotor changes, to maintain the speed and torque, then the transmitted power is constant. Reducing the volume of the hydromotor increases the speed of rotation, but reduces the torque and vice versa.
The most universal hydrostatic transmission is the combination of an adjustable pump and a variable hydrometer (Fig. 3D). Theoretically, this scheme provides infinite torque ratios and power speeds. With a hydraulic motor at a maximum volume, changing the power of the pump, directly adjust the speed and power, while the torque remains constant. Reducing the volume of the hydromotor with a complete supply of the pump increases the speed of the motor to the maximum; The torque varies inversely proportionately, the power remains constant.
Curves in fig. 3D illustrate two adjusting bands. In the range 1, the volume of the hydraulic motor is set to maximum; The volume of the pump increases from zero to maximum. The torque remains constant with increasing the volume of the pump, but power and speed increase.
The range 2 begins when the pump reaches the maximum volume, which is supported constant, while the volume of the hydraulic motor is reduced. In this range, the torque decreases as the speed increases, but the power remains constant. (Theoretically, the hydrometer speed can be increased to infinity, but from a practical point of view, it is limited to dynamics.)
Example application
Suppose that the torque of the hydraulic motor 50 H * M should be achieved at 900 revolutions per minute with the GTS fixed volume.
The required power is determined from:
P \u003d T × N / 9550
Where:
P - Power in kW
T - torque N * m,
N - speed of rotation in revolutions per minute.
Thus, p \u003d 50 * 900/9550 \u003d 4.7 kW
If we take a pump with nominal pressure
100 bar, then the feed can calculate:
Where:
Q - Feed in l / min
P - Pressure in the bar
Hence:
Q \u003d 600 * 4.7 / 100 \u003d 28 l / min.
Then we select the hydraulic vapor of 31 cm3, which, with such a feed, will provide an approximately 900 rpm.
We check the index.pl?Act\u003dProduct&id\u003d495 in the torque formula

Figure 3 shows the characteristics of power / torque / velocity for the pump and motor, provided that the pump is working with a constant feed.
The pump feed is maximum at rated speed, and the pump serves all oil into the hydraulic engine at a constant speed of the latter. But the inertia of the load makes the instantaneous acceleration instantly to the maximum speed, so that part of the pump flow is merged through the safety valve. (Fig. 3a illustrates power loss during acceleration.) As the hydraulic motor increases the speed of rotation, more and more flow from the pump comes into it, and less oil goes through the safety valve. At rated speed, all oil passes through the motor.
Torque constant, because Determined by the adjustment of the safety valve that does not change. Power loss on the safety valve is the difference in the power of the developed pump and the power coming to the hydraulic engine.
The area under this curve is a lost power, when the movement begins or ends. Also visible low efficiency for any operating speed below the maximum. Hydrostatic transmissions with fixed volumes are not recommended in drives requiring frequent starts and stops, or when there is often no need for full torque.
Moment / speed ratio
Theoretically, the maximum power transmitted by the hydrostatic transmission is determined by consumption and pressure.
However, in transmissions with constant power transmitted (unregulated pump and hydraulic motor with variable volume) theoretical power is divided into a moment / speed ratio, which determines the output power. The largest transmit power is determined at a minimum output speed at which this power must be transmitted.
Fig.4
For example, if the minimum speed, represented by the point A on the power curve of Fig. 4 is half the maximum power (and the moment of force is maximum), then the ratio of the moment is the speed of 2: 1. The maximum power that can be transmitted is half the theoretical maximum.
At a speed of less than half of the maximum, the torque remains constant (on its maximum value), but the power decreases in proportion to the speed. Speed \u200b\u200bat point A is a critical rate and is determined by the dynamics of the components of the hydrostatic transmission. Below the critical speed, the power decreases linearly (with constant torque) to zero at zero revs per minute. Above the critical speed, the torque decreases as the speed increases, which ensures constant power.
Designing a closed hydrostatic transmission.

In the descriptions of closed hydrostatic transmissions in Fig. 3 We concentrated only on the parameters. In practice, additional functions should be provided in the GTS.
Additional components from the pump side.
Consider, for example, the GTS with a constant torque, which is most commonly used in the steering servos of the steering with an adjustable pump and an unregulated hydraulic motor (Fig. 5a). Since the contour is closed, leaks from the pump and the motor are collected in one drainage line (Fig. 5b). The combined drainage flow enters the oil cooler to the tank. The oil cooler in the hydrostatic drive is recommended to be installed at a capacity of more than 40 hp.
One of the most important components in the hydrostatic transmission of the closed type is the pump paging pump. This pump is usually embedded in the main, but can be installed separately and maintain a group of pumps.
Regardless of the location, the pump pump performs two functions. Firstly, it prevents cavitation of the main pump, compensating for the leakage of the fluid of the pump and hydrometer. Secondly, it provides oil pressure desired disk offset control mechanisms.
In fig. 5C shows a safety valve A, which limits the pressure pump pressure, which is usually 15-20 bar. Check valves in and from installed towards each other provide the connection of the suction line of the feed pump with the line low pressure.
Fig. five
Additional components from the hydromotor.
The typical GTS of the closed type should also have two safety valves in its composition (D and E in Fig. 5d). They can be built into both the motor and the pump. These valves perform the system protection function from overload arising from sharp load changes. These valves also limit the maximum pressure, the bypass flow from the high pressure line in the low line, i.e. Perform the same function as the safety valve in open systems.
In addition to the safety valves, the system "or" F valve is installed in the system, which pressure is always switched in such a way that connects the low pressure line with low pressure G safety valve. The valve G sends an excess flow of pump pump to the housing of the hydromotor, and then this flow through the drainage line and the heat exchanger returns to the tank. This contributes to a more intensive oil exchange between the working outline and the tank, more efficiently cool the working fluid.
Cavitation control in hydrostatic transmission
The rigidity in the GTS depends on the compressibility of the liquid and the correspondence of the component system, namely pipes and hoses. The effect of these components can be compared with the effect of the spring-loaded battery, if it were connected to the injection line through a tee. With a small load, the battery spring is slightly compressed; With large loads, the battery is exposed to significantly greater compression and there is more liquid in it. This additional volume of fluid must be supplied using a feeding pump.
Critical factor is the rate of increase in pressure in the system. If the pressure rises too quickly, the growth rate on the high pressure side (stream compressibility) may exceed the performance of the feed pump, and cavitation occurs the main pump. Possible schemes with adjustable pumps and automatic control The most sensitive to cavitation. When cavitation occurs in such a system, the pressure drops or disappears at all. Automatic controls can try to respond, which leads to an unstable system.
Mathematically, the pressure growth rate can be expressed as follows:
dP./dt. =B E.Q CP./V.
B. E. – efficient System System Module, kg / cm2
V - the volume of liquid on the side of the high pressure cm3
QCP - Paddock pump performance in cm3 / s
Suppose that the GTS in Fig. 5 is connected by a steel pipe of 0.6 m, a diameter of 32 mm. Neglecting the volumes of the pump and the engine, V is about 480 cm3. For oil in steel pipe, an effective volumetric modulus of elasticity is about 14060 kg / cm2. Assuming that the feed pump is supplied 2 cm3 / sec., Then the rate of increases of pressure:
dP./dt. \u003d 14060 × 2/480
\u003d 58 kg / cm2 / s.
Now consider the influence of the system with a length of 6 m hose with a three-wire braid with a diameter of 32 mm. Plant manufacturer of the hose gives data b E. About 5 906 kg / cm2.
Hence:
dP./dt. \u003d 5906 × 2/4800 \u003d 2.4 kg / cm2 / s.
It follows from this that increasing the performance of pump pump leads to a decrease in the likelihood of cavitation. As an alternative, if sharp loads are not frequent, you can add a hydroaccumulator into the punch line. In fact, some GTS manufacturers make the port for connecting the battery to the paging circuit.
If the rigidity of the GTS is low, and it is equipped with automatic control, then the transmission start should always be carried out with zero pump feed. In addition, the speed of the disk tilt mechanism must be limited to prevent sharp starts, which, in turn, can cause pressure jumps. Some GTS manufacturers provide damping holes for smoothing.
Thus, the stiffness system and control speed control can be more important to determine the performance of pump pump than simply internal leaks of pump and hydraulic motors.
______________________________________

Hydraulics, hydraulic drive / pumps, hydraulic machines / What is hydraulic transmission

Hydraulic transmission - A combination of hydraulic devices that allow you to connect the source of mechanical energy (engine) with the actuators of the machine (car wheels, the spindle of the machine, etc.). The hydrotransmission is also called hydraulic transmission. As a rule, in hydraulic transmission, energy is transmitted by fluid from the pump to hydromotor (turbine).

Depending on the type of pump and motor (turbine) distinguish hydrostatic and hydrodynamic transmission.

Hydrostatic transmission

Hydrostatic transmission It is a bulk hydraulic engine.

In the presented video, a hydraulic motion was used as a output level. In the hydrostatic transmission, the hydraulic motion of the rotational motion is used, but the principle of operation is still based on the law of the hydraulic lever. In the hydrostatic drive of rotational action, the working fluid is supplied from the pump to the motor. At the same time, depending on the working volumes of hydromachins, the moment of rotation of the shafts may change. Hydraulic transmission It has all the advantages of the hydraulic drive: high power transmitted, the possibility of implementing large gear ratios, implementation of stepless regulation, the ability to transmit power to movable, moving machine elements.