EP1174620B1 - Dynamic pressure control - Google Patents

Description

The invention relates to a dynamic pressure circuit with a hydraulic pump for conveying a pressurized fluid.

From DE 196 53 165 C1 an adjusting device for adjusting the delivery volume of a hydraulic pump is known. In this case, a part of the pumped pressure fluid is removed from the high pressure line of the hydraulic pump for the operation of the adjustment. However, if the hydraulic pump is pivoted to its zero position, so that no more pressurized fluid is conveyed, then the hydraulic pump can not be swung solely because of the removed pressure fluid. Therefore, a spring element is provided in the known adjusting device, which causes the pump can swing out of a once reached zero position automatically again.

The adjusting device known from DE 196 53 165 C1 of DE 3541750 A1 has several disadvantages. If the hydraulic pump is in its zero position, d. H. to vanishing delivery volume, pivoted, then the residual pressure in the high pressure line drops to zero, so that there is damage to the pump due to lack of lubrication. This case also occurs when the hydraulic pump is running in open circuit without load, i. H. if z. B. the pump due to Wegschaltung the consumer from the fluid tank directly back into the fluid tank.

The invention is therefore an object of the invention to provide a dynamic pressure circuit which generates a non-disappearing back pressure in the high-pressure or delivery line of a hydraulic pump, even if the pump promotes zero or the pump quantity is switched to circulation.

The object is solved by the features of claim 1. Advantageous developments are possible by the measures specified in the dependent claims.

The dynamic pressure circuit according to the invention has the advantage that when the pump is switched to circulation, z. Example, when the consumer is switched off, the delivery pressure is limited to a predetermined residual pressure, and a drop in the delivery pressure of the hydraulic pump is prevented by these by the biasing valve. This prevents that the pump runs without residual pressure in the delivery line, so that there is always adequate lubrication of the pump. In addition, a pivoting of the hydraulic pump from its zero position can take place due to the residual pressure by the delivery volume control device.

It is advantageous that the preload valve is connected between the pump and the control valve. Thereby, the biasing valve is arranged as close to the high-pressure outlet of the hydraulic pump, so that an at least partial closing of the biasing valve is prevented, which takes place due to a pressure drop across the control valve, the consumer or the like. In addition, thereby the residual pressure can be cut off by the bias valve already before the control valve.

It is advantageous that the biasing valve has a first measuring surface, which is acted upon by a pressure of the pressure fluid on the pump side, and at least a second measuring surface, which is acted upon by the consumer side with a pressure of the pressure fluid. From the pressure of the pressure fluid and the first measuring surface results in a compressive force which must be overcome with the biasing valve closed to open the biasing valve, which defines the back pressure. When the biasing valve is open, the pressure of the pressurized fluid on the one hand, ie from the side of the pump, acts on the first measuring surface and on the other hand, ie from the side of the consumer, on the second measuring surface. Thus results from the pressure of the pressure fluid and the two measuring surfaces a compressive force that holds the biasing valve in the open position. Because of the greater effective area, therefore, a lower pressure of the pressurized fluid is required to hold the biasing valve in its open position than for opening the biasing valve from its closed position. This ensures that the preload valve when opening already at least substantially completely opens to prevent losses on the preload valve.

Advantageously, the biasing valve on a valve body which cooperates with the valve housing of the biasing valve to a sealing seat, wherein the measuring surfaces are formed on the valve body and separated from each other by the sealing seat. In this case, the surface of the valve body comprises the two measuring surfaces, wherein a subdivision of the surface takes place in the measuring surfaces through the sealing seat.

Advantageously, the valve body is biased for acting on the sealing seat with a biasing force by means of a biasing spring against the valve housing, wherein the pressure is adjustable by the bias of the biasing spring, opens from which the biasing valve. The pressure from which the preload valve opens is given by the biasing force of the biasing spring and resulting from the first measuring surface effective area, wherein the effective area results from the projection of the first measuring surface in the opening direction of the valve body.

It is advantageous that the biasing valve has a vent line for venting an interior of the biasing valve, in which the biasing spring is arranged. Thereby, a pressure fluid intruding into the internal space can be discharged, so that pressurized fluid accumulated in the internal space is prevented from damping the movement of the biasing valve upon opening. By urging through the gap between the valve body and the valve housing Pressure fluid is thereby achieved an advantageous lubrication, which ensures easy displacement of the valve body.

It is advantageous that the valve body has a circumferential groove in which a sealing ring for sealing the interior, in which the biasing spring is arranged, is provided. As a result, in the case of an outer smooth-running valve body and / or in the case of a very high delivery pressure, excessive leakage of the pressurized fluid through outflow via the said gap can be prevented.

It is advantageous that the delivery volume control means comprises a controllable changeover valve, that in the position of the control valve in which the pump is switched to circulation in the pressure fluid tank limits the delivery pressure to the predetermined residual pressure and in another position of the control valve in the the load is switched on, limiting the delivery pressure to a maximum delivery pressure that is greater than the predetermined residual pressure. This prevents valve leakage that occurs when the pump is pumping pressurized fluid through the preload valve.

It is advantageous that the controllable changeover valve is electromagnetically actuated in order to achieve fast response times of the delivery volume control device.

Fig. 1

einen axialen Schnitt durch ein Ausführungsbeispiel des steuerbaren Umschaltventils der Fördervolumenregelungseinrichtung der erfindungsgemäßen Staudruckschaltung; und

Fig. 2

ein Ausführungsbeispiel der erfindungsgemäßen Staudruckschaltung mit dem in Fig. 1 beschriebenen steuerbaren Umschaltventil.

The invention will be described below with reference to an embodiment with reference to the drawings. In the drawing show:

Fig. 1

an axial section through an embodiment of the controllable switching valve of the delivery volume control device of the dynamic pressure circuit according to the invention; and

Fig. 2

An embodiment of the dynamic pressure circuit according to the invention with the controllable changeover valve described in Fig. 1.

1 shows an exemplary embodiment of a controllable changeover valve 1 of the delivery volume control device of the dynamic pressure circuit according to the invention. The controllable changeover valve 1 is used in particular for switching between two pressure-carrying lines in the context of a delivery volume control of a hydraulic pump. It can be switched with the controllable changeover valve 1 to the higher pressure line to adjust the idle operation of the hydraulic pump to a minimum delivery volume or to achieve a reduction in pressure to a predetermined residual pressure.

The controllable changeover valve 1 has a first input line 2, a second input line 3 and an output line 4. The lines 2, 3, 4 are formed by bores formed in the valve body 5 of the controllable diverter valve 1 and optionally suitable connection means to which high-pressure lines can be connected. The valve body 5 has a cavity 6, which comprises a first inner space 7, a second inner space 8 and a control space 9. The first inner space 7 is connected to the first input line 2, the second inner space 8 is connected to the second input line 3 and the control chamber 9 is connected via a throttle 10 to the first input line 2. In the cavity 6, a valve piston 11 is at least partially arranged, which is a collar 12, on the one hand adjacent to the second interior 8, a collar 13, which on the one hand adjacent to the second interior 8 and the other to the first inner space 7, and a collar 14th has, on the one hand adjacent to the first inner space 7 and on the other hand to the control chamber 9.

In a vented by means of a vent line 15 in a fluid tank 16 interior 17, a first spring element 18 is arranged, which is acted upon by an adjustable bias, which is on the one hand to the contact surface 19 of the valve body 5 and on the other hand to the contact surface 20 of the collar 12 of the valve piston 11 is supported, so that is acted upon by the bias of the first spring member 18 of the valve piston 11 with a pointing in the direction 21 to the control chamber 9 biasing force. The second interior space 8 is filled with a pressurized fluid acted upon by the pressure P _{E2 of} the second input line 3, wherein the pressure forces acting on the valve piston 11 via the collar 12 and the collar 13 in the opposite direction, due to the surface equality of the at the collars 12, 13 effective areas, cancel each other. Accordingly, the first inner space 7 is filled with a pressurized fluid, which is acted upon by the pressure P _{E1 of} the first input line 2, wherein the pressure forces acting on the valve piston 11 via the collars 13, 14, because of the same effective areas formed on these , also cancel each other. The control space 9 is limited in the direction of movement of the valve piston 11, which is parallel to the direction 21, on the one hand by the collar 14 of the valve piston 11 and on the other hand by the surface 22 formed on the projection 23 of the valve body 5. In this case, the control chamber 9 is limited in the lateral direction at least substantially by an at least partially formed by the cavity 6 inner surface of the valve body 5.

The prevailing in the control chamber 9 pressure P _E1 , which is equal to the pressure P _E1 in the first input line 2, therefore acts on the valve piston 11 against the direction 21, which is equal to the direction of the valve piston 11 acting on the first spring element 18 generated Biasing force is, with a compressive force resulting from the formed on the collar 14 of the valve piston 11 effective side surface 24. The prestressed first spring element 18 in this case provides a switching pressure, which, if no further forces acting on the valve piston 11, must be exceeded by the pressure P _E1 of the pressure fluid in the control chamber 9, so that the valve piston 11 moves counter to the direction 21 to the Releasing connection between the first input line 2 and the output line 4 by means of the control edge 25 of the collar 13 of the valve piston 11. If the pressure P _E1 of the pressure fluid in the control chamber 9 falls below the switching pressure predetermined by the first spring element 18, then by operating the valve piston 11 in the direction 21 of the biasing force of the first spring element 18, the connection between the second input line 3 and the output line 4 released by means of the formed on the collar 13 of the valve piston 11 control edge 26. In the case in question, ie when no additional forces acting on the valve piston 11, therefore, the second input line 3 is at least partially connected to the output line 4, when the pressure P _E1 in the first input line is smaller than the maximum switching pressure predetermined by the first spring element 18 is, and the output line 4 is at least partially connected to the first input line 2 when the pressure P _E1 exceeds said maximum switching pressure.

In quasi-static operation, that is, when the pressure drop caused by the outflow of pressurized fluid from the output line 4 is negligible and sufficient pressurized fluid flows through the input lines 2, 3, the following can be noted with respect to the pressure P _A in the output line 4: When the pressure P _E1 in the first input line 2 is smaller than the predetermined by the first spring element 18 maximum switching pressure, then the pressure P _A in the output line 4 is equal to the pressure P _E2 in the second input line 3. However, if the pressure P _E1 in the first input line. 2 is greater than the maximum switching pressure, then the pressure P _A in the Output line 4 equal to the pressure P _E1 in the first input line. 2

In addition, the controllable switching valve 1 has a switching pressure reduction device 30 for reducing the switching pressure predetermined by the first spring element 18 to a reduced switching pressure. The switching pressure reduction device 30 comprises a second spring element 31 and an actuatable by an electromagnetic actuator 32 control member 33. The actuation of the control member 33 may also be otherwise, for example electromechanically via a instead of the electromagnetic actuator 32 to be provided electric motor. Upon actuation of the control member 33, which is opposite to the direction 21 of the first spring element 18 generated biasing force, the second spring element 31 is tensioned so that a biasing force of the first spring element 18 at least partially compensating clamping force is generated, in addition to that of the pressure force generated in the control chamber 9 under the pressure P _E1 pressure against the direction 21 of the biasing force of the first spring element 18 acts on the valve piston 11. Therefore, the switching pressure is reduced, starting from the predetermined by the first spring element 18 maximum switching pressure to a reduced switching pressure, which is to be reached by the pressure P _E1 in the first input line 2 to switch the switching valve in the sense that the output line 4 with the first input line 2 instead of the second input line 3 is connected.

By using a proportional solenoid for the electromagnetic actuator 32, the operation of the control member 33 can be made stepless. In the operation of the control member 33 is an adjustment available, which is limited by a formed on a stop element 35 stop surface 34, whereby a maximum stroke h is specified. The stopper member 35 has a relation to the direction of movement of the control member 33, which is parallel to the direction 21 of the biasing force, inclined adjusting surface 36, against which a chamfered region 42 of a screwed by means of a thread in the valve body 5 adjusting screw 37, wherein an adjustment of the adjusting screw 37 an adjustment of the stop element 35 in one Direction, which is parallel to the direction 21 of the biasing force of the first spring element 18, can be made adjustable. By adjusting the stop element 35 by means of the adjusting screw 37, the maximum stroke h of the control member 33 can be adjusted, whereby the maximum achievable by a maximum actuation of the control member 33 voltage of the second spring element 31, that is, the maximum resulting reduction of the switching pressure, pretend ,

Thus, the stop element 35 is always applied to the chamfered portion 42 of the adjusting screw 37, the stop element 35 is acted upon by a retaining spring 38 which is supported on the one hand on the stop element 35 and on the other hand on a closure plate 39 of the valve body 5, against the adjusting screw 37 with a bias , This also bouncing the control member 33, which may occur when the control member 33 abuts against the stop surface 34, is prevented or damped. This is particularly advantageous when the operation of the control member 33 is two-stage, i. the actuator 32 is turned on or not, takes place, since then a rebound would occur with each actuation of the control member 33.

By the adjusting screw 37, the axial position of the stop element 35, that is, the position which results by moving the stop element 35 in a direction parallel to the direction 21, are given exactly, so that the bias of the second spring element 31, which occurs when striking of the control member 33 adjoins the abutment surface 34 of the abutment element 35, is precisely defined by the spring constant of the second spring element 31. This defined pretension corresponds while a certain amount by which the switching pressure is then reduced compared to the maximum switching pressure. Thereby, the minimum required switching pressure, which is to be achieved by the pressure P _E1 in the first input line 2 for switching the switching valve, can be set precisely.

To possibly in the interior 40 of the valve body 5, in which the second spring element 31, the stop element 35, the retaining spring 38 and at least partially the control member 33 are arranged to discharge penetrating pressure fluid, the inner space 40 is connected through the vent line 41 to the fluid tank 16 ,

Fig. 2 shows an embodiment of the dynamic pressure circuit according to the invention with the controllable changeover valve 1 described in Fig. 1. Already described elements are provided with matching reference numerals, whereby a repetitive description is unnecessary. Furthermore, reference is made to the description of FIG. 1 with regard to the detailed description of the controllable changeover valve 1.

In FIG. 2, the first input line 2 of the controllable changeover valve 1 is connected to the high-pressure outlet 51 of the hydraulic pump 50. As a result, pressurized fluid is conveyed from the fluid tank 16 into the first inlet line 2 by the hydraulic pump 50 via the low-pressure inlet 52, wherein the delivery in this embodiment takes place indirectly via the high-pressure line 53. In this case, the first input line 2 branches off at a connection node 54 from the high-pressure line 53.

The second input line 3 is connected to a proportional valve 55 designed as a throttled 3/3-way valve. The input line 56 of the proportional valve 55 is connected to the first input line 2 of the controllable changeover valve 1, ie, indirectly connected to the high pressure output 51 of the hydraulic pump 50. The Proportional valve 55 is further connected by the vent line 57 to the fluid tank 16.

The proportional valve 55 has the following three switching positions, between which, since the proportional valve 55 is a throttled directional control valve, a continuous transition takes place. In the first position, the second input line 3 of the controllable switching valve 1 is connected by means of the vent line 57 to the fluid tank 16, while the input line 56 with respect to the passage through the proportional valve 55 is disconnected, ie blocked. In this position, therefore, the second input line 3 is depressurized. In the second position, ie in the center position of the proportional valve 55, the second input line 3 is connected via a throttle with the vent line 57 to the fluid tank 16 and via another throttle with the input line 56 of the proportional valve 55 to the first input line 2 of the controllable switching valve 1 connected. Therefore, in the second position of the proportional valve 55, the second input line 3 is subjected to a pressure between the pressure in the vent line 57 and the pressure in the input line 56, wherein in quasi-static operation, the pressure in the second input line 3 is preferably equal to half the pressure in the Input line 56 is. In the third position of the proportional valve 55, the input line 56 is connected to the second input line 3, while the vent line 57 is switched off, that is blocked. As a result, the input line 56 is preferably connected to the second input line 3 almost unthrottled. As a result, in the second input line 3 of the controllable changeover valve 1, at least in quasi-static operation, and at least substantially the same pressure as in the input line 56 of the proportional valve 55, ie, as in the first input line 2 and in the high pressure line 53, a.

The proportional valve 55 has a controllable magnetic adjusting device 58, which acts on the proportional valve 55 for adjusting with an adjusting force. In addition, acts on the proportional valve 55 connected to a cylinder piston 59 adjusting 60 via a power control unit 61 a. In this embodiment, the power control unit 61 comprises two adjustable springs 62, 63, wherein up to a certain adjustment only the spring 63 is actuated and from there the springs 62 and 63 are operated in parallel, so that there is a spring constant equal to the sum the spring constant of the springs 62, 63 is. As a result, a power control is provided in a simple manner in which the delivery volume of the hydraulic pump 50 decreases approximately hyperbolic with the delivery pressure of the hydraulic pump 50, if the hydraulic pump 50 is switched in the working mode, as will be explained in more detail in the following description.

The cylinder piston 59 is disposed in a cylinder bore 64 which is connected to the input line 2 and the high pressure line 53, so that the cylinder bore 64 is filled with pressurized fluid acted upon by the pressure of the high pressure outlet 51 of the pump 50. The cylinder piston 59 is displaceable in the cylinder bore 64 parallel to a displacement direction 65 and connected by a rigid transmission element 66 with the swash plate 67 of the hydraulic pump 50, wherein upon movement of the cylinder piston 59 in the direction of displacement 65, the hydraulic pump 50 pivots in the direction of decreasing delivery volume becomes. In addition, the swash plate 67 is connected to a further transmission element 68 with a cylinder bore 69 displaceable in a direction parallel to the displacement direction 71 cylinder piston 70, wherein upon displacement of the cylinder piston 70 in the direction of displacement 71, the pump 50 is pivoted in the direction of decreasing delivery volume. Here, the displacement of the cylinder piston 59, 70 in the directions 65, 71 in particular by the Transmission elements 66, 68 and the swash plate 67 linked together so that adjusts the inclination of the swash plate 67 and thus the delivery volume of the hydraulic pump 50 in response to the pressure of the pressurized fluid in the cylinder bore 64 and the pressure of the pressurized fluid in the cylinder bore 69 as the equilibrium state. When looking at the torques generated by the pressures acting on the swashplate 67, the effective surfaces 72 and 73 formed on the cylinder pistons 59, 70 and the distances in which the adjusting forces on the swashplate 67 act with respect to their axis of rotation are also shown. to take into account, further by the proportional valve 55 and the power control unit 61, an additional torque is applied. In the extreme positions of the hydraulic pump 50, ie at maximum or minimum delivery volume, the case may also occur that an at least small change in the pressure of the pressure fluid in at least one of the cylinder bores 64, 69 has no effect on the inclination of the swash plate 67.

In working operation of the hydraulic pump 50, as described above, in particular in connection with Fig. 1, the pressure P _A in the output line 4 equal to the pressure P _E2 in the second input line 3, depending on the position of the proportional valve 55 between the pressure in the vent line 57, ie, preferably almost vanishing pressure, and the discharge pressure of the pump 50, which is equal to the pressure P _E1 in the first input line 2, moves, if the pressure P _E1 in the first input line 2 from that of the first spring element 18 of the controllable switching valve 1 does not exceed predetermined maximum switching pressure. The operation of the pump 50 is then performance-controlled. If the pressure P _E1 in the first input line 2 exceeds the predetermined maximum switching pressure, then the controllable switching valve 1 switches, so that the pressure P _A in the output line 4, equal to the pressure of the pressure fluid in the cylinder bore 69 is equal to the pressure P _E1 in the first input line 2, ie equal to the delivery pressure of the pump 50. In the described embodiment, the adjusting forces transmitted from the cylinder pistons 59, 70 to the swashplate 67 act on the swashplate 67 at points substantially equidistant from the pivot point of the swashplate 67, thereby increasing the size due to the surface 72 of the cylinder piston 59 Surface 73 of the cylinder piston 70, the cylinder pistons 59, 70 are moved in the displacement directions 65, 71 for pivoting the swash plate 67 in the direction of minimum delivery volume.

The result is an approximated by the spring assembly 62, 63 power control, which limits the delivery pressure generated by the pump 50 by reducing the delivery volume to a preferably approximately vanishing delivery volume to the predetermined by the first spring element 18 maximum switching pressure.

The pump 50 is connected via a designed as a 4/3-way valve control valve 80 to a consumer 81. The consumer 81 may be, for example, a hydraulic motor. The control valve 80 is connected on the one hand by the high pressure line 53 to the pump 50 and on the other hand by the lines 82, 83 to the load 81. For adjusting the control valve in one of its three positions, electromagnetic switches 84, 85 are preferably provided. The three positions of the control valve 80 are described in more detail below. In the first position, the high-pressure line 53 is connected to the line 82 to convey pressurized fluid by means of the pump 50 to the consumer 81, and the line 83 is connected to the vent line 86 to that of the consumer 81, in particular for the production of labor, recycled pressurized fluid into the fluid tank 16. In the third position of the control valve 80, the connection of the lines 53, 86 with the lines 82, 83 vice versa, ie the high pressure line 53 is connected to the line 83 and the line 82 is connected to the line 86. Thereby, the pressurized fluid from the pump 50 is conveyed into the conduit 83, while the return of the pressurized fluid into the fluid tank 16 via the lines 82, 86 takes place. In this way, for example, the direction of rotation of a consumer designed as a hydraulic motor 81 can be changed.

In the second position of the control valve 80, the high pressure line 53 is switched to the vent line 86, which leads into the fluid tank 16, d. H. the connection of the high-pressure line 53 with the line 82 or 83 is interrupted and the hydraulic pump 50 is switched to circulation, d. H. bypassing the consumer 81 connected to the pressure fluid tank 16. Further, in the second position of the control valve 80, the lines 82, 83 are switched off and closed at their ends of the control valve 80. Thus, in the second position of the control valve 80, the pump 50 is disconnected from the consumer 81 and the consumer 81 is disconnected from the oil circuit of the pump 50.

In the second position of the control valve 80, d. H. If the pump 50 is switched to circulation, the hydraulic pump 50 would initially continue to promote in principle, so that pressurized fluid from the fluid tank 16 via the control valve 80 is fed back into the fluid tank 16. If the pump 50 while working, d. H. in an operating state, as when the load 81 is switched on, further promotes high valve losses occur at the control valve and other components or lines and the components and lines are unnecessarily burdened. In addition, the problem would arise that the pressure in the high pressure line 53 due to the connection of the high pressure line 53 to the fluid tank 16 drops to zero, so that it comes to the lack of lubrication of the hydraulic pump 50.

In addition to the delivery volume control device, the controllable switching valve 1, the proportional valve 55, the Power control unit 61 and guided in the cylinder bores 64, 69 cylinder piston 59, 70, and the control valve 80 is therefore connected according to the invention, a biasing valve 100 for generating a back pressure in the high-pressure line 53 between the hydraulic pump 50 and the control valve 80. The biasing valve 100 connects a pump-side part 101 of the high-pressure line 53 to a consumer-side part 102 of the high-pressure line 53. The pump-side part 101 of the high-pressure line 53 is connected to an inflow space 103 of the preload valve 100 and the consumer-side part 102 of the high-pressure line 53 is provided with a discharge space 104 of the biasing valve 100.

The biasing valve 100 has a valve housing 105 and a guided in the valve housing 105 valve body 106. Between the valve housing 105 and the valve body 106, a gap 107 is provided, flows through the pressurized fluid from the discharge chamber 104 into the interior 108 of the valve housing 105 of the biasing valve 100 for lubricating the guide of the valve body 106 in the valve housing 105 in small quantities to ensure that there is always the same response of the biasing valve 100. In order to prevent larger amounts of pressurized fluid from accumulating in the interior space 108 of the biasing valve 100, the interior space 108 is connected to the fluid tank 16 via the venting line 109, thereby ensuring that the interior space 108 is vented.

In order to reduce the leakage rate, which is formed by the outflow of pressure medium through the gap 107 formed between the valve body 106 and the valve housing 105 into the interior 108 of the biasing valve 100, a circumferential groove 117 is provided on the valve body 106 into which a sealing ring 118 is introduced, which cooperates with the wall 119 of the valve housing 105 to a seal.

In the interior 108 of the biasing valve 100, a biasing spring 110 is arranged, on the one hand on the Valve housing 105 and on the other hand supported on the valve body 106. To make the biasing valve 100 compact and to reduce the mass of the valve body 106, the valve body 106 has a recess 111 in which the biasing spring 110 is partially disposed. When opening the biasing valve 100 by moving the valve body 106 in the direction 112, the biasing spring 110 is increasingly compressed by the valve body 106, wherein in a position in which the biasing valve 100 is opened to the maximum, the biasing spring 110 is fully disposed in the recess 111 of the valve body 106 is.

The biasing spring 110 is biased, whereby the valve body 106 is pressed against a formed on the valve housing 105 valve seat body 113, whereby a sealing seat is formed. The sealing seat side part of the valve body 106 forms a valve closing body 114, which is at least partially conical and on which a first measuring surface 115 and a second measuring surface 116 are formed. The sealing seat is formed on the abutment surface against which the valve closing body 114 rests against the valve seat body 113 of the valve housing 105 of the preload valve 100 in the closed state of the preload valve 100. At the sealing surface of the sealing seat, the surface of the valve closing body 114 of the valve body 106 is divided into the first measuring surface 115 and the second measuring surface 116. The first measuring surface 115 of the valve closing body 114 adjoins the inflow space 103 of the biasing valve 100 and is therefore dependent on the pressure of the pressure fluid in the pump-side part 101 of the high pressure line 53, that is, by the delivery pressure of the hydraulic pump 50, acted upon. The second measuring surface 116 of the valve closing body 114 of the valve body 106 adjacent to the discharge chamber 104 of the biasing valve 100, so that this acts on the pressure of the pressure fluid in the consumer-side part 102 of the high-pressure line 54.

The biasing valve 100 is opened by displacing the valve body 106 in the direction 112 with respect to the valve housing 105, thereby opening the sealing seat formed by the valve closing body 114 of the valve body 106 and the valve seat body 113 of the valve housing 105. The bias of the biasing spring 110 is a pressure to be exceeded by the pressure fluid in the pump-side portion 101 of the high pressure line 53, so that the biasing valve 100 opens. The pressure of the pressure fluid in the pump-side part 101 of the high-pressure line 53 acts on the valve closing body 114 of the valve body 106 at the first measuring surface 115, wherein the effective area of the first measuring surface 115, that is the projection of the first measuring surface 115 in the direction 112, and the pressure of the pressure fluid in the pump-side part 101 of the high-pressure line 53 results in a pressure force acting on the valve body 106, which acts against the biasing force of the biasing spring 110 on the valve body 106. Exceeds the said compressive force, the biasing force, then the biasing valve 100, whereby pressurized fluid from the pump-side portion 101 of the high-pressure line 53 via the inflow space 103 in the discharge chamber 104 of the biasing valve 100 and in the consumer-side portion 102 of the high-pressure line 53 is promoted.

In the first position and in the third position of the control valve 80, that is, when the consumer 81 is connected in the delivery circuit of the hydraulic pump 50, the pressure of the fluid flow generated by the pump 50 drops substantially at the consumer 81 from. The pressure in the consumer-side part 102 of the high-pressure line 53 then corresponds at least substantially to the pressure in the pump-side part 101 of the high-pressure line 53, so that the first measuring surface 115 and the second measuring surface 116 are acted upon at least approximately the delivery pressure generated by the pump 50. This increases the effective area over which the pressure of the pressure fluid in the high pressure line 53 to the valve closing body 114 of the Valve body 106 acts on the projection of the first measuring surface 115 and the second measuring surface 116 in the direction 112. At constant delivery pressure of the pump 50 thereby increases the force acting on the valve closing body 114 of the valve body 106 compressive force, which is directed against the biasing force of the biasing spring 110 with respect to the pressing force which arises for opening the biasing valve 100 by the action of the pressure of the pressurized fluid in the pump-side part 101 of the high-pressure line 53 on the first measuring surface 115. Thereby, after the sealing seat formed between the valve closing body 114 and the valve seat body 113 has been slightly opened, the biasing valve 100 opens, as a rule, at least almost completely, thereby avoiding friction losses on the biasing valve 100. In addition, it is prevented that at a delivery pressure, which substantially corresponds to the pressure for opening the biasing valve 100 or to this oscillates, a swinging of the biasing valve 100 occurs.

If the consumer 81, by the control valve 80 is placed in its second position, disconnected from the delivery circuit of the pump 50 and the pump 50 switched to circulation, then the discharge chamber 104 and the consumer-side portion 102 of the high-pressure line 53 is connected to the fluid tank 16, so that they are depressurized. As a result, the delivery pressure generated by the pump 50 is substantially only at the first measurement surface 115, so that there is a reduced pressure force. Therefore, the biasing valve 100 immediately completely closes when the discharge pressure drops below the opening pressure of the biasing valve 100 required for keeping the biasing valve 100 open.

By the biasing valve 100 is therefore achieved that in the consumer-side part 102 of the high-pressure line 53, a back pressure is maintained, the amount is limited by the bias of the biasing spring 110. By the biasing spring 110 is adjustable biased, the amount limit can be set arbitrarily. However, there are several disadvantages if, when switching off the consumer 81, the pump 50 is only switched to circulation and otherwise the delivery volume control device does not provide the inventive limitation of the delivery pressure to a predetermined residual pressure. In this case, the pump 50 further conveys pressure fluid, so that due to the back pressure generated by the biasing valve 100, the pressure in the pump-side portion 101 of the high-pressure line 53 increases until the predetermined by the bias of the biasing spring 110 maximum dynamic pressure is exceeded, whereby the biasing valve 100 opens. By the pressure drop generated by the opening, the biasing valve 100 closes again, so that then in turn builds the back pressure in the consumer-side portion 102 of the high-pressure line 53 to the said maximum back pressure. The alternating operation of the biasing valve 100 results in significant valve losses

Therefore, the delivery volume control means of the dynamic pressure circuit limits the discharge pressure of the pump 50 in a position in which the pump 50 is switched to circulation to a predetermined residual pressure which is lower than the pressure from which the biasing valve 100 opens due to the bias of the biasing spring 110. In other words, the delivery volume control device limits the delivery pressure to a predetermined residual pressure if the pump 50 is switched to circulation, wherein the biasing valve 100 opens to generate a dynamic pressure from a pressure which is greater than the predetermined residual pressure. For limiting the discharge pressure to a predetermined residual pressure, in the event that the pump 50 is switched to circulation, the controllable changeover valve 1 of the delivery volume control device is used.

By the controllable switching valve 1, the disadvantages mentioned are avoided as follows. When the control valve 80 in the second position, ie in the position in which the Consumers 81 is switched off, is also controlled the controllable switching valve 1 by means of the electromagnetic actuator 32 to, as already described with reference to FIG. 1, to reduce the predetermined by the first spring element 18 maximum switching pressure. For example, at a stroke h of the anchor 33 of 2 mm, the pressure limit can be lowered by 300 bar. As a result of the pressure reduction, the changeover valve 1 switches the first input line 2 onto the output line 4 already at a reduced switchover pressure P _{E1 of} the first input line, which is considerably lower than the maximum switchover pressure given by the first spring element 18, so that the hydraulic pump 50 is already off the reduced switching pressure is pivoted in the direction of minimum flow. That is to say, the pressure limitation within the power regulation predetermined by the power control unit 61 already takes place from the reduced switchover pressure.

As a result, the hydraulic pump 50 only delivers the power required by the load 81 as a result of the power control 61, when the load 81 is switched on by the control valve 80. As a result, the load on the components and lines can be significantly reduced.

The result is therefore the following operation of the dynamic pressure circuit: First, it is assumed that the consumer 81 is switched on and is supplied by the pump 50 with pressurized fluid. If the consumer 81 is switched off by means of the control valve 80, ie the control valve 80 is switched to the second position, and the pump 50 is switched to circulation, then the controllable changeover valve 1 of the delivery volume control device is simultaneously activated to adjust the delivery pressure of the pump 50 to the reduced switchover pressure to limit. In addition, since the high pressure line 53 is vented via the control valve 80, the pressure in the high pressure line 53 drops sharply in a short time. However, once the pressure of the pressurized fluid under the from the preload valve 100 predetermined maximum back pressure falls, this closes, so that the hydraulic pump 50 can build a delivery pressure even at extremely low flow. The delivery volume control device limits the back pressure generated by the pump 50 to a pressure that is less than the pressure required to open the biasing valve 100. As a result, a predetermined residual pressure is maintained in the pump-side portion 101 of the high-pressure line 53, which ensures adequate lubrication of the pump 50 in idle mode and for the operation of the delivery volume control device, especially when switching the load 81 to swing out the swash plate 67 of the pump 50 again Available.

In the embodiment described with reference to FIG. 2, the pump 50 recirculates pressurized fluid from the fluid tank 16 via the low-pressure inlet 52 through the high-pressure line 53 and the vent line 86 into the fluid tank 16. Alternatively, when switching the hydraulic pump 50 into circulation, the vent line 86 may be directly connected to the low pressure input 52 of the hydraulic pump 50.

Claims (11)

1. A dynamic pressure circuit having a hydraulic pump (50) for delivering a hydraulic fluid, a delivery volume regulating device (61, 1) which regulates the delivery volume of the pump (50) depending on its delivery pressure, and a control valve (8) which is connected between the pump (50) and a consumer (81), in which the delivery volume regulating device (61, 1) restricts the delivery pressure to a specified residual pressure when the control valve (80) is in a position in which the pump (50) is switched to direct circulation by-passing the consumer (81), characterised by a prestressed valve (100) which is connected downstream of the pump (50) and only opens to generate a dynamic pressure when the pressure is greater than the specified residual pressure.
2. A dynamic pressure circuit according to Claim 1, characterised in that the prestressed valve (100) is connected between the pump (50) and the control valve (80).
3. A dynamic pressure circuit according to Claim 2, characterised in that the prestressed valve (100) has a first measuring face (115), which is acted upon on the pump side by the pressure of the hydraulic fluid, and at least one second measuring face (116) which is acted upon on the consumer side by the pressure of the hydraulic fluid.
4. A dynamic pressure circuit according to Claim 3, characterised in that the prestressed valve (100) has a valve body (106) which cooperates with the valve housing (105) of the prestressed valve (100) to form a sealing seat, the measuring faces (115, 116) being constructed on the valve body (106) and being separated from one another by the sealing seat.
5. A dynamic pressure circuit according to Claim 4, characterised in that the valve body (106) has a conical portion on which the measuring faces (115, 116) are constructed.
6. A dynamic pressure circuit according to Claim 4 or 5, characterised in that the first measuring face (115) adjoins a feed space (103) and the second measuring face (116) adjoins a discharge space (104), the feed space (103) being separated from the discharge space (104) by the sealing seat.
7. A dynamic pressure circuit according to one of Claims 4 to 6, characterised in that the valve body (106) is prestressed against the valve housing (105) by means of a prestressed spring (110) for acting upon the sealing seat with a prestress force, with the pressure from which the prestressed valve (100) opens being adjustable by the prestress of the prestressed spring (110).
8. A dynamic pressure circuit according to Claim 7, characterised in that the prestressed valve (100) has a ventilation line (109) for ventilating an interior space (108) of the prestressed valve (100) in which the prestressed spring (110) is arranged.
9. A dynamic pressure circuit according to Claim 8, characterised in that the valve body (106) has a circumferential groove in which a sealing ring (118) is provided for sealing the interior space (108) in which the prestressed spring (110) is arranged.
10. A dynamic pressure circuit according to one of Claims 1 to 9, characterised in that the delivery volume regulating device (61, 1) has a controllable change-over valve (1) which restricts the delivery pressure to the specified residual pressure when the control valve (80) is in the position in which the pump (50) delivers directly into the hydraulic fluid tank (16), and restricts the delivery pressure to a maximum delivery pressure which is greater than the specified residual pressure when the control valve (80) is in another position, in which the consumer (81) is connected.
11. A dynamic pressure circuit according to Claim 10, characterised in that the controllable change-over valve (10) is electromagnetically actuable.

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