JPS6015818B2 - Control device for hydrostatic transmissions - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The invention relates to a hydrostatic transmission in which a drive engine drives a main pump which is connected via a line system to a hydromotor and which is adjustable by an adjustment unit. A control device for the machine, in which a pressure related to the rotation speed is generated using an auxiliary pump driven by a drive engine and a control pressure signal generator, and the control unit is a hydraulic type. actuated by a regulating motor, to which pressurized liquid is supplied via a servo-valve, which servo-valve is regulated by a piston arrangement, the piston arrangement being arranged to Oppositely acting control pressure surfaces are loaded with a control pressure that can be supplied via a directional valve for determining the direction of delivery of the main pump, said piston device being connected to the main pump. For each direction of delivery, in addition to the control pressure surfaces, there is a corresponding pressure surface which acts in each case opposite to these control pressure surfaces, and these two corresponding pressure surfaces are connected to each conduit of the working circuit. Concerning things that are connected to one side.

In known control systems of this type from the prior art (cf. DE 282 355 y), the piston arrangement has a piston, which acts as a control pressure surface. It has two annular surfaces and two circular surfaces smaller in diameter than these control pressure surfaces.

This piston is centered by two springs and connected to the first valve member of the servo valve. With such an arrangement, the pressure of the main pump that develops in the line of the working circuit during heavy loads acts against the respective control pressure and thus immediately reduces the output of the main pump during heavy loads. This means that no undesirable suppression of the drive engine occurs. However, during braking operation, if the pressure ratios in the two conduits of the working circuit are exchanged, the servovalve is adjusted to increase the output of the main pump, resulting in a higher vehicle speed and an insufficient braking effect. . Control devices for hydrostatic transmissions are also known (German Patent Application No. 195
940y specification). In this control device, the piston device for regulating the servovalve is regulated solely by a control pressure, which itself is regulated by a discharge throttle controlled by high pressure. For this purpose, the throttle control piston is connected via a switching valve to one or the other line of the working circuit. In this case, when the high pressure is transferred from one conduit of the working circuit to the other during braking operation, the control pressure does not drop, so that a control pressure proportional to the rotational speed acts on the piston device. However, since the high pressure does not act directly on the piston arrangement of the servovalve, adjustment of the main pump due to changes in the high pressure takes place with a certain delay. Problems to be solved by the present invention The problem to be solved by the present invention is to use a control device of the type mentioned at the beginning to suppress the engine, that is, to suppress the drop in the drive engine rotation speed to a relatively small amount when a strong load is applied to the hydromotor. The object of the present invention is to provide a brake system that can be used without interfering with braking operation.

SUMMARY OF THE INVENTION The invention provides that the piston arrangement has two separate pistons each with a control pressure surface and a corresponding pressure surface assigned to a respective discharge direction. and these two pistons are operatively connected to the servo-valve in such a way that they each transmit a force to the servo-valve in mutually opposed directions of action.

By dividing the working piston arrangement into two pistons and operatively connecting these two pistons to the servo valve in such a way that the force is transmitted to this servo valve, one piston can be used for the normal load of the hydromotor. The same relationship is obtained as in the piston system equipped with the machine, and moreover, during braking operation, the parts of the piston system loaded by high pressure are separated from the servo valve, so that the high pressure that builds up during operation does not act on the servo valve. do not have.

Servovalves are regulated exclusively by control pressure. Vehicles equipped with such a hydrostatic transmission are therefore controlled by the usual accelerator pedal even during braking operation. A particularly simple construction is obtained if the piston of the piston arrangement is constructed as a differential piston, as claimed in claim 2.

According to claim 3, the force acting on the piston device is also compared with the spring force of the servo valve.

This results in significantly smaller valve movements compared to stroke-controlled servo valves, so that the entire control device can be constructed in a small size. Embodiment Next, the structure of the present invention will be specifically explained with reference to an embodiment shown in the drawings.

A drive engine 1 in the form of a diesel engine, adapted to be controlled via an accelerator pedal 2, has on its output shaft 3 a main pump 4, a first auxiliary pump 6 and a second auxiliary pump 6a.
The discharge amount of the main pump 4 is changed by an adjustment unit 5.

This main pump 4 supplies hydraulic pressure via a line system 7 to a hydromotor 8, which is used, for example, to drive the wheels of a vehicle. The first auxiliary pump 6 is
It is used to operate a lifting or working device 48, which is connected to the auxiliary pump 6 by means of a conventional switching valve 49. The auxiliary pump 6a has multiple functions. That is, by using the control pressure signal generator 10 having the measuring orifice 11 and the conversion unit 12, the control pressure Pst, which is approximately proportional to the discharge base discharged from the auxiliary pump 6a and thus to the rotation speed of the drive engine 1, is determined. Output conduit 1
It is produced by 3.

'o) Pressurized liquid is fed into the line system 7 via the line 14, which is protected by the overpressure valve 15, so that leakage losses occurring there can be compensated.

The two check valves 16 and 17 reliably prevent pressure liquid from being delivered to the respective low pressure side of the conduit system 7.

Via the conduit 18 and the servo valve 19, a two-part hydraulic adjusting motor 20, 21 is supplied with pressure liquid for adjusting the actuating element 22 of the adjusting unit 5.

In this embodiment, each adjusting motor part 20, 21 has a piston 23 which is loaded by a spring 24 and has an end stop 25.

When the operating member 22 is adjusted, the shaft 26 that adjusts the main pump 4 is pivoted, and the discharge amount is changed by this adjustment. For example, in an axial type piston pump, the inclination angle of the rotating disk on the end face side is changed, and in a radial type piston pump, the eccentric position of the rolling ring is changed. The operating member 22 may be constructed integrally with these rotating disks or rotating rings. A pivoting movement in the direction of the arrow 27 causes one valve member 29 of the servovalve 19 to be adjusted relative to the other valve member 30 by means of a feedback mechanism 28 against the forces of the two springs 31 and 32. . The valve member 30 is controlled using a piston device 33.

The piston device 33 has two differential pistons 34 and 3
5, and these rhombic pistons 34 and 35
The three valve members abut each other so as to transmit force via one piston rod 36 or 36' respectively. Via the directional valve 47, a control pressure Fst is supplied selectively to the larger pressure face 37 of the rhombic piston 34 or to the larger pressure face 38 of the differential piston 35. The smaller pressure surface 39 of the tread piston 34 is connected via a line 40 to a point 41 of the line system 7;
The smaller pressure side 42 of the differential piston 35 is connected via a line 43 to a point 44 of the line system 7 . This piston device 33 uses a control pressure Pst to control the sardine piston 34.
The design is such that pressurized liquid is delivered to the delivery side 45 of the main pump 4 when the main pump 4 is loaded.

In this case, high pressure PH. occurs. If, on the other hand, differential piston 35 is loaded with control pressure Pst, pressure fluid is delivered to main pump 4 via delivery side 46 . In this case, depending on the load on the hydro motor 8, this discharge side 4
6, a high pressure PH2 is generated. Accordingly, a corresponding pressure PH or PH2 acts on the piston arrangement 33 in a direction opposite to the control pressure Pst acting in each case, which corresponds to the line system on the delivery side of the main pump 4. equal to the pressure generated within the
As a result, as the load on the hydromotor 8 increases, the effect of the control pressure Pst on the servo valve 19 is significantly weakened.

Therefore, when the load on the hydromotor 8 increases, the regulating unit 5 is directly adjusted so that the output of the main pump 4 is relatively low. Therefore, until a new balance condition is obtained, it is only necessary to reduce the speed of the drive engine 1 less significantly than before, so that the auxiliary pump 6 also maintains its normal speed, and therefore the working device 48 is connected. This working device 48 can be operated at full speed even when the vehicle is in use. Therefore, if the hydromotor 8 is rotated faster than the speed corresponding to the delivery by the main pump 4, for example when descending a slope, a high pressure will be generated from the delivery side of the main pump to the connection opposite to this delivery side. Movement and braking functions are obtained.

For example, a control pressure Pst acts on the inset piston 34, and accordingly a high pressure Pst is applied to the discharge side 45 during normal operation.
When H, occurs, the high pressure during braking operation moves to the delivery side 46 opposite this delivery side 45, so that the writing piston 34 is no longer loaded with high pressure, whereas , the differential piston 35 is loaded with a high pressure PH2, and the piston shaft 36' moves away from the valve village 30. The valve member 30 is therefore loaded on the left side only by the control pressure Pst. Therefore, during braking operation, the rotation speed can be adjusted using the accelerator pedal 2 in the same way as during normal operation. The structure of the control pressure signal generator 10 is arbitrary, and various variants are known for this purpose. What is desired for this purpose is for the control pressure to follow the rotational speed of the drive engine 1 as precisely as possible. The servo-valve may have two additional neutral position springs supported in position to define the inactive position of the servo-valve. Effects As described above, according to the present invention, when a strong load is applied to the hydromotor, a control device can be obtained which can suppress the drop in the drive engine rotational speed to a relatively small amount and does not interfere with braking operation. Ta.

[Brief explanation of drawings]

The drawing is a schematic circuit diagram showing one embodiment of a control device according to the present invention. DESCRIPTION OF SYMBOLS 1... Drive engine, 2... Accelerator pedal, 3... Output shaft, 4... Main pump, 5... Adjustment unit, 6.6
a... Auxiliary pump, 7... Conduit system, 8... Hydro motor, 9... Wheels, 10... Control pressure signal generator, 11... Measurement orifice, 12... Conversion unit ,1
3... Output conduit, 14... Conduit, 15... Overpressure valve, 16, 17... Check valve, 18... Conduit, 19... Servo valve, 20, 21... Adjustment motor, 22... Operating member, 23... Piston, 24... Spring, 25... End stopper, 26... Shaft, 27... Arrow, 28... Feedback mechanism, 23, 30... Valve member, 31, 32・
...Spring, 33... Piston Soma, 34, 35...
Differential piston, 36, 36'... Piston rod, 37,
38, 39, 42...pressure surface, 40,43...conduit, 4
1, 44...point, 45, 46...discharge side, 47...direction switching valve, 48...lifting or working device, 49...
・Switching valve.

Claims (1)

Claims: 1. Control device for a hydrostatic transmission in which a drive engine drives a main pump which is connected to a hydromotor via a line system and is adjustable by means of a regulating unit, which also includes: A pressure dependent on the rotational speed is generated using an auxiliary pump driven by a drive engine and a control pressure signal generator, the regulating unit being actuated by a hydraulic regulating motor and controlling the regulating unit. The motor is supplied with pressure fluid via a servo valve, the servo valve being regulated by a piston arrangement, the control pressure surfaces of which act opposite each other. The piston arrangement is adapted to be loaded with a control pressure that can be supplied via a directional valve for determining the direction of delivery of the main pump, and the piston arrangement is adapted to control the control pressure surface for each direction of delivery of the main pump. In addition, these control pressure surfaces each have a corresponding pressure surface acting on the opposite side, and these two corresponding pressure surfaces are each connected to one of the conduits of the working circuit, Said piston arrangement 33 comprises two separate pistons 34, each with a control pressure surface 37, 38 and a corresponding pressure surface 39, 42, assigned to the respective delivery direction;
35, and these two pistons 34,
35 actuate the servo valves 19 in opposite directions of action.
A control device for a hydrostatic transmission, characterized in that it is operatively connected to this servo valve 19 for transmitting force to the servo valve 19. 2. The pistons 34, 35 of the piston arrangement 33 are configured as differential pistons, the larger surfaces of which form control pressure surfaces 37, 38, and the smaller surfaces form corresponding pressure surfaces 39, 38. 42, the differential piston being operatively connected to the axially movable valve member 30 of the servo valve 19 so as to transmit force from mutually opposite sides;
A control device according to claim 1. 3. the servo valve 19 has two valve members 29, 30, the first valve member 30 of these two valve members 29, 30 being adjustable by the piston device 33; A second valve member 29 is connected to the regulating unit 5 via a feedback mechanism 28, said first valve member 30 being connected to the two pistons 3 of said piston arrangement 33.
3. The control device according to claim 1, wherein the control device is loadable by means of springs 31, 35 and connected to the second valve member 29 via springs 31, 32.