Adjustment device for a hydrostatic machine and hydrostatic machine

Abstract

Adjusting device for a hydrostatic machine, with an adjusting piston (16) for adjusting a displacement volume (delivery / displacement volume) of the machine, which delimits an adjusting chamber (18) which can be connected to high pressure and low pressure via an electrically or electro-hydraulically adjustable control valve (24), wherein a fail-safe valve (44) via which the adjusting piston (16) can be adjusted to a predetermined position in the fail-safe function, characterized in that the fail-safe valve (44) has an inlet connection (P) connected to high pressure, a tank connection (T) connected to low pressure and a connection (B) which is connected or connectable to an inlet connection (P) of the control valve (24), wherein the fail-safe valve (44) is designed to be continuously adjustable and is acted upon by a return spring (20) in one direction and by a fail-safe spring (50) in the opposite direction.

Description

[0001] The invention relates to an adjusting device for a hydrostatic machine according to the preamble of patent claim 1 and to a hydrostatic machine designed with such an adjusting device.

[0002] Such a hydrostatic machine can, for example, be a variable displacement pump with an axial piston design, in which a delivery volume flow is adjusted by changing the swivel angle of a swash plate. The basic structure of such an adjustment device for electro-proportional swivel angle control is shown in DE 10 2008 038 435 A1. The swash plate is acted upon by a control piston of a control cylinder in the direction of increasing the swivel angle and by a counter-piston of a counter-cylinder in the direction of decreasing the swivel angle. The counter-piston is always pressurized with high pressure, while control oil can be supplied to a control chamber of the control cylinder or discharged from it to the tank via an electrically controlled, proportionally adjustable control valve. The swivel angle can thus be controlled in a higher-level control circuit via a proportional magnet of the control valve.A valve spool of the control valve is operatively connected to the control piston via a return spring. This return spring represents a disturbing force that reduces the power reserve of the proportional solenoid. To achieve high adjustment dynamics, it is necessary to override the valve spool of the control valve, which is generally only possible to a limited extent, so the adjustment dynamics are negatively influenced by the return spring.

[0003] In this solution, the adjustment device is designed with a fail-safe function, in which the swash plate is pivoted to a predetermined position in the event of a malfunction, for example, a cable break on the control valve. In the conventional solution, this is achieved via the return spring and an opposing counter spring, which, in a force equilibrium, move the valve spool to a fail-safe position, thus establishing a corresponding control pressure in the control chamber.

[0004] When the power supply is switched off and the adjustment system is depressurized, the swash plate swings out in the direction of the maximum flow rate due to spring force.

[0005] DE 197 24 870 discloses an adjustment device that enables electrohydraulic control of the pressure and flow rate of an axial piston pump. This type of control is also referred to as a DFE control. The basic mechanical design of such an adjustment device corresponds to that of the previously described embodiment. The swivel angle is also adjusted via a control valve, whereby in the event of a malfunction, a fail-safe control system regulates the axial piston pump to a specific pressure and not, as in the embodiment described above, to a predetermined swivel angle. Such a solution requires considerable equipment and control technology complexity, and in the event of a cable break, fail-safe pressure control is not always guaranteed.

[0006] DE 11 2010 004 755 T5 discloses an adjustment device for a hydrostatic machine adjustable beyond zero displacement. This device is equipped with a rigid feedback device that actuates a return valve in the form of a 4 / 3-way valve. This takes into account on which side of zero displacement the hydrostatic machine is operating. A return spring, with which the set displacement can be regulated in the form of a spring force in the force equilibrium at a pressure compensator, is not provided. If the power supply to the hydrostatic machine fails, the two actuating cylinders are fluidly blocked by a fail-safe valve, so that the currently set displacement remains set. This can lead to a dangerous situation.

[0007] A pressure relief safety valve with an auxiliary valve is known from DE 1 120 830 B.

[0008] In contrast, the object of the invention is to provide an adjusting device and a hydrostatic machine designed with such an adjusting device, which can be adjusted with high dynamics and with little device-technical expenditure.

[0009] This object is achieved by an adjusting device having the features of patent claim 1 and a hydrostatic machine having the features of patent claim 12 9.

[0010] Advantageous further developments of the invention are the subject of the subclaims.

[0011] According to the invention, the adjustment device for a hydrostatic machine has a control piston for directly or indirectly adjusting a displacement (the delivery volume when operating as a pump, the displacement when operating as a motor) of the hydrostatic machine. This control piston defines a control chamber in which a control pressure can be adjusted via an electrically or electrohydraulically adjustable control valve. According to the invention, in addition to the control valve, a fail-safe valve is provided, via which the control piston can be reset to a predetermined position in the event of a malfunction, preferably mechanically, in other words without electrical assistance.During normal operation, the control valve regulates the control pressure in the control chamber and thus the swivel angle of the hydrostatic machine, while in the event of a fault, for example in the event of a cable break, the control piston and thus also the swash plate of the hydrostatic machine are reset to a predetermined position.

[0012] The control valve is designed to optimize its control behavior and the required adjustment dynamics, while the reset in the event of a fail-safe condition is achieved via the appropriately designed fail-safe valve. This type of solution is characterized by minimal hardware complexity and high control dynamics.

[0013] In one embodiment of the invention, the fail-safe valve has an inlet port connected to high pressure, a tank port connected to low pressure, and an outlet port connected to an inlet port of the check valve.

[0014] According to the invention, the fail-safe valve is designed as a continuously adjustable valve and is preloaded into a home position by a return spring and a fail-safe spring. The return spring, which determines the control dynamics of the control valve, is integrated into the fail-safe valve in the inventive solution and thus no longer determines the control behavior during normal operation.

[0015] In one embodiment of the invention, it is provided that the control valve is designed with a fail-safe position which is assumed in the event of a fault and in which the output connection of the fail-safe valve is connected to the actuating chamber, so that a pressure is regulated in the actuating chamber via the fail-safe valve in order to adjust the swash plate to its predetermined fail-safe position.

[0016] A valve piston of the fail-safe valve can be acted upon by the pressure in the actuating chamber in the direction of action of the return spring. As explained above, the control valve establishes a control oil connection between the actuating chamber and the high-pressure or low-pressure (tank), so that control oil is supplied to or discharged from the actuating chamber.

[0017] In one embodiment, the fail-safe valve has a control chamber that is pressurized with high pressure in the control valve's control position. In the fail-safe function, the movable valve body of the fail-safe valve is pressure-equalized. This can be achieved, in principle, by introducing high pressure into another control chamber, and this pressure compensates for the force exerted by the pressure in the first control chamber. However, in the fail-safe position of the control valve, the control chamber of the fail-safe valve, which was previously pressurized with high pressure, is preferably pressurized with low pressure.

[0018] In such a variant, it is preferred if the control chamber is connected to high pressure via a nozzle or the like.

[0019] The fail-safe valve can be designed with a stop against which the valve piston of the fail-safe valve runs during normal operation of the control valve.

[0020] In a preferred embodiment, the adjustment device has a counter-cylinder whose counter-piston acts counter to the actuating piston to adjust the delivery / displacement volume of a hydrostatic machine. The return spring is operatively connected to the counter-piston. Accordingly, the return spring is tensioned or relaxed depending on the movement of the counter-piston.

[0021] In a further embodiment of the invention, the control valve is also designed with a return spring, which is also operatively connected to the counter piston in the manner described above, thus enabling reliable return of the control valve with a minimal overall length. In this variant, a single-acting solenoid actuator is sufficient to adjust the control valve.

[0022] The design is particularly simple if both return springs are supported on a common spring plate.

[0023] According to a further embodiment, an auxiliary valve is provided which functionally switches off the fail-safe valve in one position and switches it on in the fail-safe function so that it can exert the described effect.

[0024] In one variant, the auxiliary valve can be designed such that it is acted upon in one direction by the pressure in an auxiliary chamber and in the opposite direction by a spring. In a fail-safe position of the control valve, the auxiliary chamber is relieved to a tank or low pressure, so that a control oil connection between the fail-safe valve and the control valve is then opened. In a control position of the control valve, the auxiliary chamber is pressurized with high pressure, so that the control oil connection between the control valve and the fail-safe valve is interrupted, and the latter is deactivated.

[0025] The auxiliary valve is ideally designed as a seat valve so that the leakage between high pressure and low pressure is very low in the control state.

[0026] As explained above, a hydrostatic machine equipped with such an adjustment device is characterized by improved control dynamics and reduced device-related expenditure and thus comparatively low manufacturing costs.

[0027] This hydrostatic machine is preferably designed as an axial piston machine that can be pivoted beyond zero. In a preferred embodiment of the invention, the hydrostatic machine is pressure and flow controlled (DFE control).

[0028] Preferred embodiments of the invention are explained in more detail below with reference to schematic drawings.

[0029] It shows Fig. 1 a circuit diagram of a first embodiment of a hydrostatic machine according to the invention with an adjusting device according to the invention, Fig. 2 a second embodiment of a hydrostatic machine, Fig. 3 a concrete design of an adjusting device according to a third embodiment, Fig. 4 a section through a main axis of the adjustment device according to Fig. 2, Fig. 5 a concrete solution of a variant of the embodiment according to Fig. 2, Fig. 6 a circuit diagram for the third embodiment, Fig. 7 a circuit diagram of a fourth embodiment, Fig. 8 a fifth embodiment with an auxiliary valve and Fig. 9 a concrete solution of the fifth embodiment according to Fig. 8.

[0030] Fig. Figure 1 shows a circuit diagram of a hydrostatic machine, more specifically, an axial piston pump 1 that can be pivoted above zero, the pivot angle of which is adjustable via an adjustment device 2 according to the invention. This device has a counter cylinder 6 that acts on a pivoting cradle 4 of the axial piston pump in one adjustment direction, and an actuating cylinder 8 with an actuating piston 9 that acts on the pivoting cradle 4 in the opposite direction.

[0031] The counter cylinder 6 has a counter piston 10, which is acted upon by a counter spring 12 in order to reduce the size of a pressure chamber 14. As explained in more detail below, this pressure chamber 14 is acted upon by the pressure at an output connection P of the axial piston pump 1. The actuating cylinder 8, whose effective cross-section is considerably larger than the corresponding cross-section of the counter cylinder 6, has an actuating piston 16 which delimits an actuating chamber 18 and which is acted upon by a return spring 20 in order to enlarge the pressure chamber 18 and thus reduce the pivot angle (displacement flow rate) of the axial piston pump 1. In the opposite direction, an actuating spring 22 acts on the actuating piston 16 and thus acts on the actuating piston 16 in order to increase the pivot angle of the pivoting cradle 4.The described spring arrangement (springs 12, 18, and 22) is designed such that when the electrohydraulic adjustment device 2 is de-energized and there is no pressure at the output port P of the axial piston pump 1 (pump not driven), the swivel angle 8 is adjusted to a predetermined value (zero-stroke operation), which can be approximately in the range of 4 percent to 8 percent of the maximum swivel angle. When the pump is driven, the pump pressure acts in the pressure chamber 14, and the swivel cradle 4 is swiveled out.

[0032] During normal operation of the axial piston pump 1, pressure medium is supplied to the control chamber 18 via a control valve 24 and discharged from the control chamber 18. The control valve 24 is designed as a continuously adjustable proportional valve, with a valve spool 26 being adjustable via a proportional magnet 28 against the force of a control spring 30. The control valve 24 has an output port A, a pressure port P and a tank or low-pressure port T. The output port A is connected to the control chamber 18 via a control line 32. The tank port T is connected to a tank 34. The pressure port P is connected via a pressure line 36 to a pump line 38 connected to the pressure port P of the axial piston pump 1. This pump line also opens into a high-pressure accumulator 40, which can thus be charged by the axial piston pump 1.The high-pressure accumulator 40 is designed so that even if the pressure connection of the axial piston pump 1 is shut off, sufficient pressure is still available to pivot the swivel cradle 4 back to its target position. Instead of a high-pressure accumulator 40, the pump 1 can also deliver pressure medium to another hydraulic consumer, for example, to a hydraulic cylinder or a hydraulic motor.

[0033] A line 42 branches off from the pressure line 36 and opens into the pressure chamber 14 of the counter cylinder 6, so that the pressure prevailing in the pressure line 36 or in the pump line 38, i.e. the pump pressure, always acts therein.

[0034] The adjustment device 2 is designed with a second valve axis, which is referred to below as the fail-safe valve 44 and is designed as a proportional directional control valve. This has an output port B, which is connected via a line section 46 to a fail-safe port FS of the control valve 24. The fail-safe valve 44 also has a pressure port P connected to the pressure line 36 and a tank port T connected to the tank 34. The return spring 20 acts on a valve body 48 of the fail-safe valve 44 in the direction of the positions marked (a), while a control spring 50 acting in the opposite direction acts on the valve body 48 in the direction of the positions marked (b).

[0035] When the proportional solenoid 28 is de-energized, the valve spool 26 of the control valve 24 is in a Fig. 1 is preloaded in the position marked (c), which is referred to below as the fail-safe position. In this fail-safe position (c), the FS port is connected to port A of the control valve, so that the actuating chamber 18 of the actuating cylinder 8 is connected to the output port B of the fail-safe valve 44. The valve is in its control position when there is a balance of forces with regard to the forces exerted on the valve body 48 by the return spring 20 and the control spring 50. In the event that the force of the return spring 20 is too high, the fail-safe valve 44 is adjusted towards its position marked (a), so that pressure medium flows to the actuating chamber 18 from the pressure port P of the fail-safe valve 44, thus resetting the pivot angle of the pivoting cradle 4 and correspondingly reducing the spring force exerted by the return spring 20.Conversely, when the force applied by the return spring 20 is less than the force applied by the control spring 50, the fail-safe valve 44 is moved toward its positions marked (b), thereby connecting the output port B to the tank port T, so that the control chamber 18 is connected to the tank and pressure medium is accordingly expelled from it. The pivoting cradle 4 pivots out, tensioning the return spring 20 accordingly until the fail-safe valve 44 is in its control position, thus creating a force equilibrium between the springs 20 and 50.

[0036] As explained above, this fail-safe control only occurs when the control valve 24 is moved to its fail-safe position (c). This is the case, for example, if a cable break occurs on the control valve 24 and adjustment via the proportional solenoid 28 is therefore no longer possible. In normal operation, when the control of the control valve 24 is functioning properly, it is moved towards its positions marked with the letters (d) and (e). The control position, in which there is zero overlap or a small positive or negative overlap between ports P, T and A, is achieved when there is a force balance between the force applied by the proportional solenoid 28 and the control spring 30.In the event of deviations from this equilibrium of forces, the valve spool 26 is either adjusted in the direction of the positions marked (d), in which the pressure port P is connected to the output port A and thus the pivoting angle of the pivoting cradle 4 is reduced. When adjusted in the direction of the positions marked (e), the output port A is connected to the tank port T in the opposite direction, so that the pivoting angle increases accordingly until equilibrium of forces is achieved. Thus, by appropriately energizing the proportional magnet 28, the pivoting angle of the pump 1 can be increased (magnetic force greater than spring force in the middle position between position (d) and position (e)), reduced (magnetic force less than spring force in the middle position) or maintained (magnetic force equal to spring force in the middle position).

[0037] The fail-safe valve 44 moves during this normal operation due to the change in the spring force of the return spring 20. Since the fail-safe port FS is blocked in positions (d) and (e) of the control valve 24, this movement of the fail-safe valve 44 has no hydraulic effect during normal operation. This continuous movement of the fail-safe valve 44 has the advantage that it does not "freeze" if the fail-safe function is not used for an extended period.

[0038] An essential aspect of the invention is that in the described normal operation, the dynamics of the control valve 24 are not influenced by the return spring 20, so that an adjustment of the pivot angle of the pivoting cradle 4 is possible with high dynamics.

[0039] Fig. Figure 2 shows an embodiment in which the continuous adjustment of the fail-safe valve 44 is prevented during normal operation. The basic structure of the embodiment according to Fig. 2 largely corresponds to that of the previously described embodiment, so that essentially only the differing components will be discussed. As in the previously described embodiment, the hydrostatic machine is designed as an axial piston pump 1, the pivoting cradle 4 of which is adjustable via the adjustment mechanism 2 with an actuating cylinder 8 with an actuating piston 16 and a counter-cylinder 6 with a counter-piston 10. As indicated, the axial piston pump 1 can be pivoted over a displacement of zero, whereby it operates as a motor at pivot angles less than zero and can therefore also be more generally referred to as an axial piston machine or axial piston unit. The pressure chamber 14 of the counter-cylinder 6 is pressurized with high pressure.The pressure in the actuating chamber 18 of the actuating cylinder 8, which has a significantly larger cross-section than the counter-cylinder 6, is adjusted during normal operation according to the pressure medium supplied and discharged via the control valve 24 in accordance with the instantaneous load. As in the previously described embodiment, the control valve 24 has a pressure port P, a fail-safe port FS and an output port A as well as an additional tank port T'. The control valve 24 can be adjusted via the proportional magnet 28 in the direction of the positions marked (d) and (e), whereby in position (d) the connection between A and T is opened, while in position (e) the pressure port P is connected to the output port A.In the event of a cable break, the control valve 24 is moved into its fail-safe position (c) by the force of the control spring 30, in which the pressure port P is connected to the working port A and the ports FS and T' are connected to one another. The fail-safe valve 44, which is implemented via a separate valve axis, has a pressure port P, a tank port T and an output port B and is acted upon by the return spring 20 in the direction of the positions marked (a) and by the control spring 50 in the direction of the positions marked (b). A control pressure also acts in this direction in a control chamber 52, which is connected on the one hand to the FS port of the control valve 24 via a control line 56 and on the other hand to the pressure line 36 via a nozzle 54. The return spring 20 is clamped between the control piston of the valve 44 and the counter piston 10.In positions (d), (e) of the control valve 24, the pressure medium connection from the FS port to the tank port T' is shut off, so that the pump pressure (high pressure) acts accordingly in the control chamber 52 and thus the fail-safe valve 44 is preloaded toward its position (b) against a stop 58. This means that during normal operation of the adjustment device 2, the fail-safe valve 44 remains in its contact position against the stop 58 in position (b).

[0040] In the event of a fault, such as a cable break, the control valve 24 is moved into its fail-safe position (c) by the force of the control spring 30. The pressure in the pressure chamber 52 is released to the tank T', so that the valve body 48 of the fail-safe valve 44 lifts off the stop 58 and, via the force balance between the springs 20, 50, a predetermined position of the counter piston 10 and thus of the actuating piston 16 is set, which corresponds to the intended swivel angle in the event of a fault. The nozzle 54 ensures, in this fail-safe function, that the pressure in the control chamber 52 is reduced. In the embodiment according to Fig. 2, the valve body 48 of the fail-safe valve 44 is urged in the direction of positions (a) by the return spring 20, which is connected to the counter piston 10.

[0041] Fig. 3 shows a design solution of the control valve, as for example in the variant according to Fig. 2 can be used. The valve slide 26 of the control valve 24 is guided axially displaceably in a valve bore 88 of a housing 90 of the control valve 24 (main axis) and is preloaded against a tappet 92 of the proportional magnet 28 via the control spring 30. The above-described connections P, A, T are formed in the housing and open radially into the valve bore 88. Also indicated is the connection FS, which in the embodiment according to Fig. 2 is connected via the control line 56 to the control chamber 52 of the fail-safe valve 44. As also Fig. 3, the central control collar 64 with the control edges 70, 72 and the two end collars 66, 68 are formed on the valve slide 26. The left end collar 66 rests with its front side on the tappet 92. On the front surface of the Fig. 3 right-hand end collar 68 engages the control spring 30, so that the valve slide 26 moves without current into the Fig. 3, in which the control edge 70 opens the pressure medium connection between the connections A, P - the control valve 24 is thus in the fail-safe position (c) according to Fig. 2. A spring chamber 94 for the control spring 30 in front of the end face of the valve spool 26 facing away from the electromagnet 28 and a chamber 98 in front of the other end face of the valve spool are each pressurized with low pressure, i.e. with tank pressure, wherein the chamber 98 is connected to tank connection T via a tap hole 100 in the housing 90. The spring chamber 94 is connected to the tank in a corresponding manner. The connection FS opens into the spring chamber 94. Since this is connected to the tank, the tank pressure is applied to the connection FS in the illustrated fail-safe position of the control valve 24, so that the control chamber 52 is correspondingly depressurized.

[0042] When the proportional solenoid 28 is actuated, the valve spool 26 is displaced to the right by the tappet 96, so that the pressure medium connection between the FS port and the tank (spring chamber 94) is closed by the end collar 98, which also forms a control edge, and high pressure builds up in the pressure chamber 52 of the fail-safe valve 44. The control valve 44 is then moved against its stop 58 (position (b) of the fail-safe valve 44), so that the pump pressure is applied to the pressure port P of the control valve 24.

[0043] At the beginning of the adjustment of the valve spool 26, the swivel angle is set to its fail-safe position: Depending on the magnetic force applied to the valve spool 26 via the tappet 96, a corresponding control pressure is then regulated in the control chamber 18 in the resulting control position of the control piston 26. In the event of a cable break or the like, the valve spool 26 is returned to the position indicated in Fig. 4 shown basic position (c).

[0044] In the Fig. In the embodiment shown in Figure 3, the tank pressure in chamber 98 is tapped via the tap hole 100. An alternative solution is also indicated, according to which the tank pressure in chamber 98 can be tapped via a radial bore 102, an axial bore section 104, and an inclined bore 106 of the valve spool 26. In this case, no complex housing machining is required to form the tap hole 100.

[0045] Fig. Figure 4 shows a simplified diagram of the previously described embodiment. It shows the control valve 24 actuated by the proportional solenoid 28, the valve spool 26 of which is pressure-balanced on its front side, with both front surfaces being pressurized, for example, with tank pressure and being in pressure communication with each other via the axial bore 104. Here, the valve spool 26 is shown in its control position, in which the output port A is completely covered. The fail-safe valve 44 is also shown in its control position, in which, during the fail-safe function, the pressure at port B of the fail-safe valve 44 is mechanically regulated depending on the force balance between the return spring 20 and the control spring 50. In normal operation, i.e., when controlling the swivel angle via the control valve 24, the pump pressure tapped via the nozzle 54 is present in the control chamber 52, so that the valve body 48 moves from its Fig. 5 shown control position to the left. In the spring chamber of the return spring 20 is located as shown in Fig. 5 Tank pressure.

[0046] In the event of a cable break or other malfunction, as already explained, the valve slide 26 is moved from the illustrated control position to the left, so that the control chamber 52 is relieved towards the tank and the valve body 48 is adjusted accordingly to its illustrated control position.

[0047] In the example according to the Fig. In Figure 5, the valve spool 26 of the control valve 24 and the valve body 48 of the fail-safe valve 44 are each shown in their control position, which, however, is not possible in principle, as explained above. In normal operation, only the valve spool 26 is in its control position, while in the fail-safe function, only the valve body 48 operates in its control position. Fig. Figure 6 shows valve 24 in the fail-safe position and valve 44 in the normal operation position.

[0048] According to the presentation in Fig. 5, the valve spool 26 of the control valve 24 is adjusted via a tappet 62 of the proportional magnet 28 against the force of the control spring 30. The valve spool 26 has a central control collar 64, which is spaced from two end collars 66, 68 by two annular grooves. The control spring 30 engages the end collar 66, while the tappet 62 acts on an end face of the end collar 68. In the control position shown, the control collar 64 blocks the pressure medium connection between the control line 32 and the control line 56, which opens into the control chamber 52 of the fail-safe valve 44. This is connected via the nozzle 54 to the pressure line 36 carrying the pump pressure. When the valve spool 26 is adjusted from the position shown in Fig. 5 shown control position to the left, a pressure medium connection between the pressure line 36 and the control line 32 is opened via a control edge 70 of the control collar 64. When the valve slide 26 is moved in the illustration according to Fig. 5 to the right, a pressure medium connection between a channel 74 connected to the tank connection T via the fail-safe valve 44 in its position (b) and the control line 32 is opened in a corresponding manner via a further control edge 72. These actuating movements of the valve slide 26 correspond to the positions (e) and (d) in the illustration according to Fig. 6.

[0049] In the control position of the control valve 24, the control collar 64 blocks the control line 56 both to the channel 74 and to the control line 32, so that the pressure in the pressure line 36 is present in the control chamber 52 and thus the valve body 48 of the fail-safe valve 44 is moved from the control position according to Fig. 5 is moved to the left until it hits the stop 58. This adjustment in the fail-safe function occurs against the force of the return spring 20, which acts on an end section of the valve body 48 via a spring plate 76. In this construction, the control spring 50 also acts on this end section and acts on the valve body 48 in the opposite direction, that is, in the direction of an enlargement of the control chamber 52. In this position, the channel 74 is connected to tank T via the connection B of the valve 44. The return spring 20 is supported in the embodiment according to the Fig. 5 and Fig. 6 also on the actuating piston 16.

[0050] In the fail-safe function, the valve spool 26 of the control valve 24 is shown in the illustration according to Fig. 5 is shifted to the right by the force of the control spring 30, so that the control line 32 is connected to the channel 74 via a control edge 72 and thus the output B of the fail-safe valve 44 is connected to the output port A of the control valve 24 via the channel 74 and the cross-section opened up by the control edge 72. The displacement of the valve spool 26 is so great that the channel 56 and thus the port FS of the valve 24 is also connected to the port A.

[0051] In this exemplary embodiment, two control edges 82, 84 of the valve body 48 are also formed via two annular grooves 78, 80, which, in the illustrated control position, determine the pressure medium connection of the channel 74 to the tank connection T or to the pressure line 36, which opens into the valve bore of the fail-safe valve 44 in the region of the annular groove 78. The pressure medium connection between the pressure line 36 and the channel 74 is controlled via the control edge 82, and the pressure medium connection between the tank connection T and the channel 74 is controlled via the control edge 84.

[0052] In contrast to the embodiments according to the Fig. 1 and the Fig. 2 and Fig. 3 is in the embodiment according to the Fig. 5 and Fig. 6, the valve spool 48 of the fail-safe valve 44 is subjected to the pressure prevailing in the actuating chamber 18 of the actuating cylinder 8 and in a spring chamber 86 on an end face opposite the pressure chamber 52, over an area of ​​the same size as the pressure chamber 52. As explained above, in the fail-safe function, the valve spool 26 of the control valve 24 is moved into a position in which the port FS and thus also the pressure chamber 52 are connected to port A. In the fail-safe position of the control valve 24, the valve spool 48 is thus pressure-balanced. Thus, only the springs 20 and 50 act on the valve spool 48. In the fail-safe case, the fail-safe valve 44 regulates such a pivoting angle of the axial piston unit 1 that, in the control position of the valve spool 48, the force of the return spring 20 is equal to the force of the control spring 50.

[0053] Out of Fig. 5 it can be seen that the pressure line 36 leads directly to the valve bore for the valve spool 26, bypassing the valve bore in which the valve spool 48 is located. The circuit diagram according to Fig. 6, on the other hand, is drawn as if the pressure line 36 passes through the bore for the valve spool 48. Functionally, there is no difference between the two versions, as long as the valve spool 48 is not influenced by the pressure directly in the pressure line 36, but only by the pressure in the line 56.

[0054] In normal operation, the fail-safe valve is in position (b) because the FS connection is blocked by the control valve 24, which is in positions (d) and (e9). The pump pressure is then present in the pressure chamber 52, while the actuating pressure prevailing in the actuating chamber 18 of the actuating cylinder 8 is present in the spring chamber 86, which actuating pressure is considerably smaller than the pump pressure because the actuating chamber 18 of the actuating cylinder 8 is considerably larger than the pressure chamber 14 in the counter cylinder 6. The control valve 24 can then allow pressure medium to flow from P via A to the actuating chamber 18 or can displace pressure medium from the actuating chamber 18 from A to T.

[0055] In the previously described embodiments, the hydrostat, i.e., the axial piston unit, is controlled to the desired swivel angle position via a target / actual comparison. This requires a swivel angle sensor (not shown in detail), which records the current swivel angle of the swivel cradle 4 so that a corresponding signal can then be sent via the control unit to the control valve 24, or more precisely, its proportional magnet 28. In the event of a fault, for example, a cable break at the proportional magnet 28, the actuating chamber 18 is then connected via the control valve 24 to the output of the fail-safe valve 44. This then controls the axial piston unit to the desired fail-safe swivel angle position, which is essentially predetermined by the force of the fail-safe spring 50.A disadvantage of this solution is that if the swivel angle sensor fails, emergency operation is no longer possible - the axial piston machine then becomes torque-free and a vehicle operated with it stops or rolls to a stop.

[0056] This disadvantage is eliminated in the embodiment according to Fig. 7 overcome. Fig. 7 shows a circuit diagram of an adjustment device 2, the basic structure of which corresponds to that shown in Fig. 2. Accordingly, the pivot angle of a pivoting cradle 4 is adjusted via an actuating cylinder 8 and a counter-cylinder 6, wherein a control oil connection between the actuating chamber 18 of the actuating cylinder 8 and the high-pressure pressure line 36 or the tank T can be established via the control valve 24 in order to adjust the pivot angle α. The fail-safe valve 44 is assigned to the control valve 24, which is acted upon on the one hand by the pressure in the control chamber 52 and the force of the fail-safe spring 50 and on the other hand by the force of the return spring 20. The preload of the return spring 20 depends on the pivot angle and is coupled to the counter-piston 10, for example, via a suitable mechanism.

[0057] During normal operation of the swivel cradle adjustment, the control valve 24 assumes its described control position, in which the pressure in the pressure line 56 is applied in the control chamber 52, so that the fail-safe valve is preloaded into its illustrated position (b). In the event of a cable break, the control valve 24 is moved into its fail-safe position (c) by the force of the control spring 30, so that the control chamber 52 is relieved of pressure and a swivel angle of the swivel cradle 4 is set, which approximately corresponds to the force equilibrium of the return spring 20 with the fail-safe spring 50. A special feature of the Fig. The embodiment shown in Figure 7 is that the control valve 24 is also supported, counter to the force of the control spring 30, via a return spring 108 on the mechanism 110 that transmits the pivot angle of the pivoting cradle 4. In the specific solution, both the return spring 108 and the return spring 20 are supported on a common spring plate 112. Accordingly, in the event of a cable break, the control valve 24 is adjusted to a position that depends on the force balance between the control spring 30 and the return spring 108. In the variant shown, the proportional magnet 28 is designed as a pulling magnet.

[0058] One advantage of such a solution is that only a single-acting proportional magnet 28 needs to be used, so that the device-related complexity is significantly reduced compared to solutions that use a double-acting proportional magnet or single-acting proportional magnets on both sides. A further advantage is that if the swivel angle sensor fails, the axial piston machine can continue to operate with slightly lower control accuracy. The solution according to Fig. 7 enables the same control during normal operation as in the previously described embodiments via the electronic swivel angle control loop with swivel angle sensor. If the swivel angle sensor fails, redundancy is provided, and electroproportional operation can continue, although electrically overlaid control is obviously not possible.

[0059] In the Fig. 2, as explained above, the fail-safe valve 44 is essentially displaced by the high pressure acting in the control chamber 52 into the position marked (b), in which position the connection of the pressure line 36 to the inlet of the control valve 24 is switched through. In the fail-safe case, this control chamber 52 is relieved via a control edge of the control valve 24 towards the tank T, so that the pivoting cradle 4 is regulated via the fail-safe valve 44 into a pivot position dependent on the force equilibrium between the return spring 20 and the fail-safe spring 50. The pressure relief of the control chamber 52 takes place via the control valve 24 and is not completely successful, since there is always a slight pressure difference across the additional fail-safe control edge of the control valve 24.Accordingly, a small residual force from the control chamber 52 still acts on the valve body 48 of the fail-safe valve 44, which thus also acts as a disturbance variable on the control valve 24. This disturbance variable, in turn, depends on the volume flow through the nozzle 54 and thus on the high pressure in the pressure line 56. The basic position of the swivel cradle 4 in the fail-safe position is thus dependent on the high pressure level and may be negatively influenced by high pressure pulsation.

[0060] This disadvantage is overcome by the Fig. 8 and Fig. 9. In this embodiment, an auxiliary valve 114 is provided, which activates the fail-safe valve 44 in the fail-safe function and, so to speak, "switches it off" during normal operation of the adjustment device. According to the Fig. In the circuit diagram shown in Figure 8, the basic structure of the adjustment device 2 essentially corresponds to that of the previously described embodiments, with control positions (f) and (g) of the fail-safe valve 44 and the control valve 24 being indicated in the circuit symbols. A further difference is that the valve body 48 of the fail-safe valve 44 is not acted upon by a control pressure but only by the force of the return spring 20 and the fail-safe spring 50, so that in the fail-safe position, only the spring forces are effective and the disturbance variable mentioned above cannot occur. Also shown is a blocking position (s) of the control valve 24.

[0061] In the illustrated embodiment, the additional auxiliary valve 114 is designed as a continuously adjustable 3-way valve. In principle, however, it can also be designed as a switching valve.

[0062] A pressure branch line 36' branches off from the pressure line 36 and leads to a pressure port P of the auxiliary valve 114. A port T is connected to the output port B of the fail-safe valve. An output port C of the auxiliary valve 114 is in control oil communication with a port P of the control valve 24. As in the previously described embodiments, the output port A of the control valve 24 is connected to the actuating chamber 18, while the pressure chamber 14 of the counter-cylinder 6 is directly connected to the pressure branch line 36'.

[0063] The latter is also connected to the port FS of the control valve 24 via the nozzle 54.

[0064] In the representation according to the Fig. 8 and Fig. 9, the valves 44, 114 and 24 are each shown in their control position - as explained, this representation does not correspond to reality but merely serves to simplify the readability of the drawing.

[0065] The auxiliary valve 114 has a control chamber 116, which is connected to the pressure branch line 36', so that the high pressure is effective in this control chamber 116. This control pressure acts against the force of an auxiliary spring 118. The force of this spring and the effective area of ​​the control chamber 116 are coordinated such that, during normal operation of the adjustment device 2, the auxiliary valve 114 is adjusted to its position marked (h), in which the port P of the auxiliary valve 114 is connected to the pressure port P of the control valve 24. In this position, the pressure medium connection to the output port B of the fail-safe valve 44 is blocked, so that the valve is deactivated. Fig. 8 also shows a control position (i) of the auxiliary valve 114 and a switching position (j) set in the fail-safe case, in which the output port C of the auxiliary valve 114 is connected to the port T and thus a control oil connection to the output port B of the fail-safe valve is established.

[0066] In the fail-safe case, as already explained, the valve spool of the control valve 24 is moved into its fail-safe position (c) by the force of the control spring 30, so that the control chamber 116 is connected to the tank connection T' of the control valve and is thus relieved of pressure. This pressure relief is possible because the control chamber 116 is arranged downstream of the nozzle 54. During this pressure relief, the auxiliary valve 118 is then switched to position (j), so that the output connection A of the control valve 24 is connected via its pressure connection P, the output connection C of the auxiliary valve 114 and its connection T to the output B of the fail-safe control valve 44, via which a position of the pivoting cradle 4 is set, which depends on the force balance of the springs 20, 50.

[0067] In contrast to the previously described embodiments, the fail-safe axis is activated via the separate auxiliary valve 114, which is immune to pulsations in the high-pressure range. A specific pre-load pressure can be set via the auxiliary spring 118, at which point the fail-safe valve 44 is activated. This pre-load pressure preferably lies between the tank pressure level and the minimum high pressure during normal operation. The functions "activation of fail-safe mode" and "control in fail-safe mode" are separate in this embodiment. Such a control concept is largely immune to pressure pulsations.

[0068] Ideally, the auxiliary valve 114 is placed near the fail-safe valve 44 to minimize the pressure loss in the connecting line between ports B and T. However, due to the aforementioned low pre-pressure in the auxiliary valve 114, this is not absolutely necessary. In this embodiment, a single-acting proportional solenoid 28 can also be provided for the control valve 24.

[0069] Fig. 9 shows a concrete solution of the embodiment according to Fig. 8, whereby the structure of the control valve 24 is largely the same as that of Fig. 5 illustrated embodiment. Accordingly, the control valve 24 has a valve spool 26 with the two end collars 66, 68 and the middle control collar 64, on which the two control edges 70, 72 are formed. In the illustrated control position of the control valve 24, the two control edges 70, 72 throttle the pressure medium connection between the ports A, P and A, T. The control oil connection to the port T is via the axial bore section 104, which opens into the annular space between the control collar 64 and the end collar 68. Alternatively, a relief bore to the tank can open directly into the valve bore with the valve spool 24, as shown in Fig. 9 is indicated by dashed lines.

[0070] The auxiliary valve 114 has a slide 120 with two end collars 122, 124 and an approximately central control collar 126, which has two control edges 128, 130. As explained, in the illustrations according to the Fig. 8 and Fig. 9 also shows the auxiliary valve 114 in a control position, in which the two control edges 128, 130 connect the output port C of the auxiliary valve 114 with the pressure port P and the tank port T in a throttled manner. The pressure port P is in pressure medium connection with the pressure line 36, the tank port T is connected via a short channel to the port B of the fail-safe valve 44. Similar to the Fig. The embodiment shown in Figure 5 has two annular grooves 78, 80, between which a control collar with two control edges 82, 84 remains. The end collar 124 defines the control chamber 116, which is in pressure medium communication with the connection FS of the control valve 24. This control chamber 116 is connected to the pressure line 36 via the nozzle 54. The auxiliary spring 118, which is accommodated on one end face of a spring chamber 132, acts on the opposite end face of the slide 120.

[0071] The valve body 48 of the fail-safe valve 44 is also shown in its control position, in which the two control edges 82, 84 control a throttled connection of the output port B with the tank port T and the pressure port P, which is connected to the pressure line 36.

[0072] As explained, the valve body 48 is acted upon on the one hand by the return spring 20 via the spring plate 76 and on the other hand by the fail-safe spring 50,

[0073] During normal operation of the adjustment device, as explained, high pressure is present in the control chamber 116, so that the slide 120 is moved against the force of the auxiliary spring 118 into its end position, in which the pressure medium connection from the outlet of the fail-safe valve 44 to the inlet of the control valve 24 is closed via the control edge 128 and its inlet connection P is connected to the pressure line 36 via the control edge 130 of the auxiliary valve 114 - the fail-safe valve is thus practically ineffective.

[0074] In the fail-safe case, the valve slide 26 of the control valve 24 is actuated by the control spring 30 in the illustration according to Fig. 9 is shifted to the right, so that the control edge 70 opens the control oil connection between the ports A and P and the control edge formed by the end collar 68 opens the pressure medium connection of the port FS to the tank T. As explained, the control chamber 116 is then connected to the tank T, so that the slide 120 of the auxiliary valve 114 is moved by the force of the auxiliary spring 118 from the position shown in Fig. 9, in which the control edge 128 opens the pressure medium connection between the input port P of the control valve 24 and the output port B of the fail-safe valve 44. At the same time, the pressure medium connection between the output port C of the auxiliary valve 114 and the pressure line 36 is controlled via the control edge 130. As explained, the pivoting cradle 4 is then adjusted to a pivot position that is essentially determined by the force balance of the springs 20 and 50.

[0075] The invention explained using the exemplary embodiments enables virtually uninterrupted control during normal operation through the electronic swivel angle control circuit, whereby the swivel cradle can be equipped with a swivel angle sensor. The disruptive force of the return spring 20, which is common in conventional solutions, acts only on the fail-safe valve 44, which is hydraulically separated from the actuating chamber of the actuating cylinder during normal operation. This makes it possible to adjust the swivel cradle with increased dynamics at a lower magnetic force level.

[0076] The invention is particularly applicable in so-called hybrid vehicles, for example, in a passenger car, with an internal combustion engine and a hydraulic drive train including a hydraulic pump, hydraulic accumulator, and / or hydraulic motor between the internal combustion engine and an axle. The hydraulic units can be equipped with an adjustment device according to the invention.

[0077] Disclosed are an adjustment device for a hydrostatic machine and a hydrostatic machine equipped with such an adjustment device. According to the invention, in addition to a control valve, a fail-safe valve is provided, via which the hydrostatic machine is adjusted to a predetermined displacement / displacement volume in the fail-safe function.

Claims

[1] Adjustment device for a hydrostatic machine, with an adjusting piston (16) for adjusting a displacement (discharge / sucking volume) of the machine, which delimits an adjusting chamber (18) which can be connected to high pressure and low pressure via an electrically or electro-hydraulically adjustable control valve (24), wherein a fail-safe valve (44), via which the adjusting piston (16) can be adjusted to a predetermined position in the fail-safe function, characterized by in that the fail-safe valve (44) has an inlet connection (P) connected to high pressure, a tank connection (T) connected to low pressure and a connection (B) which is connected or connectable to an inlet connection (P) of the control valve (24), wherein the fail-safe valve (44) is designed to be continuously adjustable and is acted upon by a return spring (20) in one direction and by a fail-safe spring (50) in the opposite direction. [2] Adjustment device according to claim 1, wherein the control valve (24) has a fail-safe position (c) which it assumes in the fail-safe function and in which the connection (B) of the fail-safe valve (44) is connected to the control chamber (18). [3] Adjustment device according to claim 2, wherein a valve body (48) of the fail-safe valve (44) is subjected to low pressure or the control pressure in the direction of action of the return spring (20). [4] Adjustment device according to claim 2 or 3, wherein the fail-safe valve (44) has a control chamber (52) which is pressurized with high pressure in the control position of the control valve (24) and is relieved to low pressure in the fail-safe function. [5] Adjusting device according to claim 4, wherein the control chamber (52) is connected to high pressure via a nozzle (54). [6] Adjustment device according to claim 4 or 5, wherein the fail-safe valve (44) is designed with a stop (58). [7] Adjusting device according to one of the preceding claims, with a counter-cylinder (6), the counter-piston (10) of which acts counter to the adjusting piston (16) in the sense of adjusting the delivery / absorption volume, wherein a return spring (20) is operatively connected to the counter-piston (10) or to another component adjusted as a function of the pivot angle. [8] Adjusting device according to claim 7, wherein a return spring (108) of the control valve (24) is also in operative connection with the counter-piston (10) or the other component adjusted as a function of the pivot angle. [9] Adjusting device according to claim 8, wherein both return springs (20, 108) are supported on a common spring plate (112). [10] Adjusting device according to one of the preceding claims, with an auxiliary valve (114) which activates the fail-safe valve (44) in the fail-safe function. [11] Adjustment device according to claim 10, wherein the auxiliary valve (114) has a slide (120) which is acted upon in one direction by the pressure in a control chamber (116) and in the opposite direction by an auxiliary spring (118), wherein the control chamber (116) is connected to a tank or low pressure in a fail-safe position and is acted upon by high pressure in a control position of the control valve (24), so that in the fail-safe position of the control valve (24) a control oil connection between the fail-safe valve (44) and the control valve (24) is opened and in the control position of the control valve (24) is blocked or at least throttled. [12] Hydrostatic machine with an adjusting device according to one of the preceding claims. [13] Hydrostatic machine according to claim 12, wherein it is designed as an axial piston machine which can be pivoted above zero and which is preferably pressure and volume flow controlled.

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