DE1576140B1 - Process for controlling a hydraulic system and control system for carrying out the process - Google Patents

Description

The invention relates to a method for regulating a hydraulic system with a displacement pump with variable flow rate and with a distributor valve with closed center position for the pressure medium supplied by the displacement pump to a hydraulic motor, in which the delivery flow is changed and the delivery pressure is limited to a predetermined maximum value, as well as a control system for carrying out the procedure.

In known hydraulic systems it has already been shown like a hydraulic motor from a positive displacement pump with variable flow rate Pressure medium is supplied, its delivery flow changed and its delivery pressure to a maximum value is limited. The regulation carried out is a pure power regulation in which the Delivery rate decreases with increasing delivery pressure. If the flow rate is reduced here by a slide or completely interrupted, then the delivery pressure must rise very sharply, so that the output power remains constant. This high oil pressure in front of the valve and in the lines between the Slide valve and the pump leads to large leakage losses and heating of the oil and thus a waste of energy. If the flow rate flowing to the hydraulic motor is due to a Adjustment of the slide increases, then a large pressure drop occurs at the slide, which also contributes to an increase in leakage losses.

The invention is based on the object of providing a control method of the type specified at the beginning through which the disadvantages that have occurred up to now, such as energy waste and leakage losses, can be eliminated or reduced in a simple manner.

According to the invention this is achieved in that the delivery flow of the positive displacement pump at open distributor slide and a delivery pressure below the maximum value as a function of is regulated by the pressure drop across the distributor slide so that this pressure drop increases is kept a substantially constant value, and that the flow rate is closed The distributor slide is regulated as a function of the delivery pressure in such a way that the delivery pressure is essentially is kept constant at a value well below the maximum value.

Considerable advantages result from this arrangement according to the invention. While the slide, which determines the flow rate, with the known control systems in the closed state a very is exposed to high pressure, the pressure is now at a value in front of the closed distributor slide held, which is considerably below the value that is regulated for constant output power Systems occurs. The ever-present leakage losses that still occur to a small extent, thus occur in the case of the system regulated according to the new type of procedure with a very small one Pressure on, so that heating of the oil and thus energy losses are greatly reduced. Even at the opened distributor slide occurs in the system regulated according to the new type of procedure no longer the large pressure drop familiar with known control systems, but a constant one small pressure drop, so that in this case, too, the leakage losses and those caused by the heating of the The energy losses resulting from oil can be reduced. Thus, based on the invention, there is a control method created for a hydraulic system that is essential compared to previously known control systems Has merits.

The invention is described by way of example with reference to the hydraulic system shown schematically in the drawing.
The arrangement includes a positive displacement pump 1

ίο with variable displacement and a distributor slide 2 with closed center position. The arrangement is used to operate a double-acting Motor 3 used. The motor 3 itself can be used to carry a wide variety of loads, such as

z. B. to move the boom or the container of a loading machine or the shovel of a road construction machine. The distributor slide 2 contains an inlet chamber 4, which is connected via the delivery line 5 to the outlet opening la of the displacement

ao pump 1 is connected, two motor chambers 6 and 7, which are connected via lines 8 and 8 a and 9 and 9 a with the rod and head ends of the motor 3 g , two outlet chambers 11 and 12, which f continuously with one Reservoir 13 are in communication and a movable slide piston 14. The slide piston 14 is provided with a central ring groove 15 and with two control surfaces 16 and 17, in which many V-shaped throttle notches 16 a and 17 a are cut. In the illustrated neutral position of the spool 14, the control surfaces 16 and 17 separate the inlet chamber 4 from the other chambers, while the throttle notches 16 a and 17 a connect the motor chambers 6 and 7 with the outlet chambers. The slide piston 14 can be displaced in opposite directions by actuation of the lever 18 from the neutral position, whereby one of the motor chambers 6 and 7 is connected to the inlet chamber 4 and is separated from the outlet chamber adjacent to it.

This also restricts the flow from the other motor chamber to its adjacent outlet chamber decreased.

The lines 8, 8 a and 9, 9 a are provided with conventional controlled check valves 19 and 21 (which prevent the motor 3 from moving in any direction under the action of the load. The check valves 19 and 21 are provided with control motors 19 a or equipped 21a, which are connected to the lines 9 and 8 by branch lines 9b and 8 connected b. in this manner, the supply pressure opens in one of the lines 8 and 9, which supplies the distributor slide 2 pressure medium, directly, the check valve in this conduit and The non-return valve in the other line indirectly via one of the control motors.

The positive displacement pump 1 can be constructed in any desired manner and is driven by a motor (not shown). It is supplied by the reservoir 13, with which its inlet opening 1 b is connected. The displacement of the positive displacement pump 1 is controlled by a lever 22 which is pressed by the pressure forces of the pump pistons and by a helical compression spring 23 into the position shown with the displacement zero. It is also set by a double-acting control motor 24, which in turn is controlled by a manually operated servo slide 25, a compensating control slide 25 a and a

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Slide switch 25 b is controlled. The servo slide let, motor and outlet openings 58, 59 and 61 25 has a housing with a control chamber 26, and with a displaceable slide piston 62 two motor chambers 27 and 28, which see with the opposite, through which the motor opening 59 optionally with overlying working chambers 24 a and 24 b of the two other openings can be connected. Control motor 24 are connected and two with the 5 The inlet opening 58 receives via the line 63 oil reservoir 13 connected outlet chambers 29 from a jointly with the displacement pumps 1 and 31. in the displacement, the output pressure of which is limited by a back and forth movable slide piston 38 pressure valve 64 a. The motor opening 59 is located. The slide sleeve 32 is connected with five of one is connected by a line 65 to the control opening 49 on the other separate radial openings 33 to 37 ver of the compensating control slide 25a, which lead to the chambers 29, 27, 26, 28 and 31 respectively the outlet opening 61 are permanently aligned with the VorauEgs. The slide piston 38 is connected to a storage tank 13. The spool 62 annular groove 39 and with two so dimensioned is provided by a helical compression spring 66 in the Darge control surfaces 41 and 42 that each of the radial inlet position is pressed, in which the openings len openings 34 and 36 with both the radial 58 and 59 are connected to one another via the annular groove 67 and to one of the radial openings, while the control surface 68 is connected to the outlet channels 33 and 37 when the slide opening 61 closes. In order to move the sliding piston 38 with respect to the sliding sleeve 32 in the darber piston into the outlet position in which the control-controlled zero position is located. The sliding sleeve 20 surface 68 closes the opening 58, while it connects the 32 is connected to each other by a helical compression spring 43 to the openings 59 and 61, a right is pressed. It can also be attached by a piston engine 69. The slide piston 62 44 a rotatably mounted follower lever 44 in which, in addition to the two positions just mentioned, is displaced in opposite directions. From an overlapping position in which the control surface 68 starting from the position shown, the slide 25 can separate the motor opening 59 from the two openings 58 and piston 38 also by means of the manually operated 61. The working chamber 69 a of the motor 69 operating lever 45 can be moved to the left. is continuously via the branch lines 5 a and 5 b. The control chamber 26 of the servo slide 25 is connected to the delivery line 5. As indicated by the line 46 with the motor opening 47 of the following description of the mode of action-compensating control slide 25 a, which goes with 30, the slide switch 25 b is provided by a slide piston 48, which is used to push the displacement pump 1 the Pressure in the connection between this opening, the control of the delivery line 5 to one of the adjustment opening 49 and the outlet opening 51 to control. The maximum value determined by the spring 66.
Slide piston 48 is pressed to the left into an inlet position by a helical compression spring 54, 35 mode of operation
in which the openings 47 and 49 via the annular groove 52

When the operating levers 18 and 45 close the opening 51 in their surface 53. Located through a neutral position shown, the double-acting servomotor 55 can take the slide valve 25, 25 α and 25 b their actuating piston 48 shown in the opposite direction in a 40 gene. The displacement of the positive displacement pump 1 outlet position can be pushed at which this displacement is equal to zero. A connection from the control pump 64 is interrupted and the opening 47 with the supplied oil is connected to the control chamber 26 of the servo opening 51. It can be seen that the slide valve 25 via the line 63, the inlet opening, the opening 47 is wider than the control surface 53. 58, the annular groove 67, the motor opening 59, the line Therefore, the spool 48 passes through at its 45 65, the control opening 49, the annular groove 52, the motor movement between the inlet and outlet opening 47 and the line 46 is supplied. From there a control area in which the motor opening 47 returns the oil on two parallel paths into the reservoir 13 with both the opening 49 and the opening, one of which is in communication with the ra-51. The left working chamber Diene implementation 35, the annular groove 39, the radial

55 a of the servomotor 55 is connected via the branch line 5 a 50 passages 34 and 33 and the outlet chamber permanently to the delivery line 5, while 29 includes, while the other via the radial the right working chamber 55 b with the help of the line passage 35, the annular groove 39, the radial diameter

56 and the pressure sensitive shuttle valve 57 guides 36 and 37 and the outlet chamber 31 optionally with that of lines 8 and 9. The control surfaces 41 and 42 throttle the oil collars in which the higher pressure is present. Out of the current on these paths, so that the engine came down the following description of the mode of operation mern 27 and 28 are exposed to a backwater, the it can be seen that the compensating control slide 25 a, the working chambers 24 a and 24 & of the control motor the displacement of the positive displacement pump 1 thus keeps 24 filled with liquid. This backwater is controls that the difference between the in the For- but not so great that the control motor 24 den derleitung 5 and either the adjustment lever 22 in the line 8 or 60 from its position with the twist in the line 9 prevailing pressure normalization zero moves.

sometimes always essentially constant. The operator increases the displacement

is held when the distributor slide 2 that of the displacement pump 1 by an adjustment

Motor 3 supplies oil in precisely dosed quantities. of the slide piston 38 of the servo slide 25 according to The control opening 49 of the compensating control slide 65 on the left, so that the control surface 41 the connection between

25 a will see the radial passages 33 and 34 and according to the pressure in the conveyor

line 5 from slide switch 25 & relieves or under the control surface 42 the connection between the ra-

Pressure set. The slide switch 25 b is interrupted by single-dial passages 35 and 36. Of the

5 6

Pressure in the working chambers 24 α and 24 & rises the drive machine of the displacement pump 1, or falls now. and the control motor 24 begins to rise, the servomotor 55 pushes the slide piston adjusting lever 22 to its maximal displacement position 48 to move either to the right within its control area. When the adjusting lever 22 moves richly into a new position in which the backwater moves in the direction in which the displacement of the motor opening 47 is only reduced or in which it is increased, the follower lever 44 pushes the slide outlet position, if the pressure rise suddenly erbüchse 32 to the left. If now the adjusting lever 22 follows. The pressure acting on the adjusting lever 22 has reached the position that forces the selected position can now move it into its displacement control lever 45, the straight direction is located. In this case, a slide bushing 32 takes place again relative to the slide piston oil displacement from the working chamber 24 a to ben 38 in a zero position, and the control motor 24 reservoir 13 along one of the motor chambers stops. Since the control motor is not held in place with hydraulic means 27, radial passage 34, annular groove 39, or hydraulic means, the pressure forces acting on radial passage 35, control chamber 26 and adjusting lever 22 try to get it into line 46, the motor opening 47 and the out of the position with the displacement zero back to 15 let opening 51 leading path. If the change ren. However, since a movement of the adjusting lever 22 of the displacement, which is caused by a movement of the Ver in this direction with a right shift of the adjusting lever 22, the change in the sliding sleeve 32 relative to the spool 38 is caused by the increase in the drive speed , the working chamber 24 α under pressure th outflow cancels, the system pressure drops as soon as the adjusting lever 22 leaves the position set by the operating 20 to the desired amount of 14 at, and the spring actuating lever 45, whereupon 54 leads the spool 48 in a position in the adjusting lever returns to this position. back within its control range, in which the servo slide 25 basically controls the position control motor 24 due to the back pressure in the motor f. It should be noted, however, that the servo opening 47 operates the slide 25 acting on the adjusting lever 22 only as long as 25 can compensate for pressure forces. On the other hand, the control chamber 26 pushes oil at a pressure supplied to the spring 54, which becomes the spool 48 into its inlet, which is large enough to order the control motor 24 and thus increases the pressure of the actuating device. Control motor 24 supplied oil when the drive-When the adjusting lever 22 falls out of its position speed of the displacement pump 1 and moves with the displacement zero, the pressure in the delivery line 5 begins to drop below 14 at. When the displacement pump 1 supplies oil to the delivery line 5 under these conditions, the control motor 24 moves the valve, and since the distributor slide 2 is in its adjustment lever 22 in the displacement-increasing neutral position, the pressure in this direction in the line determined by the operating lever 45 rises immediately . This pressure becomes the working position. When the system pressure again passed the chamber 55 a of the servomotor 55, where 35 has reached the desired size, the servomotor moves it develops a force that tries to move the spool 48 55 the spool 48 into a position within to the right. Since the working of its control area back, in which the control motor chamber 55 & at this point in time via the line 24 the pressure 56 acting on the adjusting lever 22, the pendulum valve 57, the motor chamber 6, the forces are balanced. From the above explanation he throttle notches 16 a and the outlet chamber 11 to 40 one knows that the compensating control slide 25 α is open towards the reservoir 13, the pressure in the delivery line 5 constantly moves the slide piston 48 on an adjustment motor 55 into a position proportional holds low value as long as the Verin of the motor opening 47 is closed by the control surface 53 divider slide 2, and that the slide is projected and in which the bushing 32 in the motor opening 47 with respect to the spool ( formed back pressure is reduced so that it 45 38 to the right of the zero position is sufficient for the control motor 24 to hold the adjusting lever in its respective position if the operator cannot hold a very small 22. If displacement is selected by the displacement pump 1, this pressure reduction of the oil that the servo has.

slide 25 is supplied, then takes place when the So that the motor 3 drives the load to the right, Control motor 24 pushes adjusting lever 22 straight into position 50, the operator pushes slide piston 14 from the operating lever 45 brings the position required, the distributor slide 2 to the left, so that the cam remains the adjusting lever 22 close to this position mern 4 and 6 on the piston groove 15 with each other stand, and he sets a delivery rate to be connected to the displacement and the throttling of the flow supply pump 1, which reduces the leakage losses of the system through the throttle notches 17 α. That just balances. In the illustrated arrangement 55 pressurized oil in the delivery line 5 can it is assumed that the pressure in the reservoir is now via the inlet chamber 4, the piston groove 15, the ter is 3.5 at and that the spring 54 designed motor chamber 6, the line 8, the check valve is that a pressure difference of 1.5 at between 19 and the line 8 a to the rod end of the motor 3 the working chambers 55 a and 55 & is required, flow. The supply pressure in the line 8 opens with it the servomotor 55 the slide piston 48 in the 60 net by its action on the control motor 21a Bring it to the middle of the control area and hold it there- the check valve 21 so that the oil is held in the head can. When the distributor slide 2 is closed, the motor 3 via the line 9 a, the back is, the servo slide 25 cannot have any further check valve 21, the line 9, the motor chamber 7, increase the pump displacement effect more, the throttle notches 17 a and the outlet chamber 12 when the pressure in the delivery line 5 can flow back approximately 65 to the storage container 13. if at reached. the pendulum valve 57 is not yet in its position shown. When the pressure in the delivery line 5 over 14 at, it moves into this position as soon as the for example, as a result of an increase in speed of the distributor slide 2 is opened, so that the actuating

motor 55 to the pressure difference between the For- This means that the servo slide 25 can control the adjustment line 5 and the line 8 responds. lever 22 in the by the operator if the distributor slide 2 is open, the selected position increases. The slide sleeve 32 is located Pressure in line 8, so that the servomotor 55 is relative to the spool 38 in a zero position and the spring 54 the spool 48 of the development when between the positions of the variable displacement control spool 25 a instantly in its hebeis 22 and the operating lever 45 match inlet position push. The control motor 24 starts mung has been reached.

If the motor 3 has brought the load in the desired position increasing direction in the direction of the operating lever 45, the operator brings the selected position to push. When between io divider slide 2 back into its illustrated neutral to the pressures in lines 5 and 8 again one position back, whereby the working chamber 55 & the difference of 10.5 at has been established, the servomotor 55 is opened and the servomotor is turned away 55 the slide piston 48 of the equalizing control slide 25 a is made possible to reduce the compensation control slide 25 a to a position within the displacement pump 1 half of its control range, so that the return 15 and so in the delivery line 5 again build up a pressure of the motor opening 47 decreased and that of about 14 at.
Control motor 24 is prevented from increasing the displacement of the displacement pump 1 by shifting the slide piston 14. to the right is a movement of the motor 3 to It is assumed that the distributor slide reaches 2 on the left. As a result, on the one hand, oil is precisely dosed via the KoI to the engine 3, that is, the ao bennut 15 establishes a connection between the chambers 4 distributor slide 2, the flow to the engine 3 and 7 and, on the other hand, the throttling of an amount that is lower is, as the out flow through the notches 16 a diminished. The selected displacement of the positive displacement pump 1. At the head end of the motor 3, the pressure medium is now produced, the adjusting lever 22 remains close to the position established by the delivery line 5, the inlet chamber 4 and the operating lever 45. The 25 piston groove 15, the motor chamber 7, the line 9, the compensating control slide 25 a and the adjusting lever the check valve 21 and the line 9 α supplied-22 now remain at rest until the operator leads. The rod end of the motor stands over person the position of the distributor slide 2 changes. the line 9 a, the check valve 19, the lei-When the operator closes this slide for processing 8, the motor chamber 6, the throttle notches 16 a slowing the movement of the motor 3 slightly 30 and the outlet chamber 11 with the reservoir, the pressure rises in the delivery line 5, 13 in connection. During this operating state whereupon the servomotor the slide piston 48 after working the slide 25 and 25 a shifts in the same way to the right, so that the pressure in the working as in the case of the right shift of the motor 3, chamber 24 a decreases. As a result, the pressure forces acting on the lever 22, with the exception that the compensating control slide, can now move this in the 35 25 a direction to the pressure difference between the Leitunverdrängungsverhresserverringerung direction. When gene 5 and 9 responds instead of lines 5 and 8, as a result, the pressure in the delivery line 5 drops because the pendulum valve 57 is in its left position.
If the desired pressure difference of 10.5 at. If the pressure in has ever been reached again during operation, the spring 54 moves that of the delivery line 5 to the maximum (that in the spool 48 into a position within its 40 shown embodiment with 210 at assumed control range back, in which the adjustment is increased), for which the system is designed, lever 22 pushes acting opposing forces again balanced the piston motor 69 the slide piston 62 of the. If, on the other hand, the operator moves the slide valve 25 & into its overlapping position, distributor slide 2 to increase the speed at which the control surface 68 opens the motor opening 59 from the speed of the motor 3, the compensation 45 causes the two openings 58 and 61 to be separated, whereby the control slide 25 a automatically a corresponding the oil supply to the slides 25 a and 25 with enlargement of the displacement of the displacement breaches. If this state occurs when the pump 1. In this way, the compensating displacement pump 1 changes below its maximum tax slide 25a in the entire metering range of the pressure, this interruption of the distributor slide 2 prevents the displacement of the displacement oil supply the operator from operating the displacement pump 1 in inverse proportion to the movement of the pump through a shift in the operating amount of the throttling in the distributor slide, as a result of which actuation lever 45 has to be increased further. If the pressure, the pressure drop across this slide, should rise further, the piston motor 69 pushes it constantly at 10.5 at. Since the absolute value of the spool 62 in its outlet position and pressure in the system depends on the size of the load moved by the motor 3 55 opens an outlet path from the working chamber 24 α, and as changes in this load via the motor chamber 27, the radial passage load changes the pressures in The 34, the annular groove 39, the radial passage 35, the working chambers 55 a and 55 & cause the control chamber 26, the line 46, the motor opening control effect of the compensating control slide 25 a un- 47, the annular groove 52, the control opening 49, the Line depending on the size of the load. 60 65, the motor opening 59 and the outlet opening 61 When the distributor slide 2 in a position to the reservoir 13. The opening of this path is moved outside of its metering range, reduces the pressure in the working chamber 24 a that is, if there is a greater flow to the motor 3 and enables the pressure forces on the adjusting lever 22, as required by the operating lever 45, to move it into the displacement direction, the pressures in the lines 5 and 8 will move 65 decreasing direction. The spring 66 pushes essentially the same, whereupon the slide piston moves the slide piston 62 back into its overlapping 48 of the compensating control slide 25 α by the spring and closes the just mentioned 54 into its illustrated inlet position. Outlet path if the displacement of the displacement

supply pump 1 has been reduced enough that a system pressure with the desired maximum of 210 at is restored. Since the follower lever 44 has then moved the slide sleeve 32 with respect to the slide piston 38 from a zero position to the right, the control surface 41 now separates the radial passage 34 from the radial passage 33. In this way, the control motor 24 is hydraulically locked and holds the Adjusting lever 22 in its position with reduced displacement when the compensating control slide 25 ″ is in the inlet position when the switch slide 25 ″ returns to its overlapping position. If, on the other hand, the slide piston 48 of the equalization control slide 25 a takes a position within its control range at the time when the slide switch 25 & moves back into its overlapping position, the working chamber 24 α is via the openings 47 and 51 of the equalization control slide with the storage container 13 in Link. The control motor is not blocked hydraulically. In this case, the pressure in the working chamber 24 α becomes smaller, and the pressure forces acting on the adjusting lever 22 try to move it in the displacement-reducing direction as soon as the slide switch 25 & moves into its overlapping position. However, as soon as the adjusting lever 22 moves away from the displacement position in which the pressure is stabilized at 210 atm, the pressure in the delivery line 5 drops, whereupon the spring 66 pushes the slide piston 62 into its inlet position. As a result of this process, the pressure in the working chamber 24 α is increased and the control motor 24 causes the adjusting lever 22 to be withdrawn from the position into which it tried to move.

The spring 66 of the slide valve 25 & is designed so that a system pressure of 210 atm is required so that the spool 62 is held in its overlapping position. Therefore, the slide switch 25 b, as long as the pressure in the Förderleirung 5 is so great, a predominant control effect and brings the adjusting lever 22 in a position with less displacement than is required of each of the slides 25 a and 25 &. Under extreme load conditions, the servo slide 25 can even cause the adjusting lever 22 to move into its position with the displacement of zero. When the load on the line system has dropped to an amount at which the pressure in the delivery line 5 is less than 210 at and even when the displacement pump 1 works with a displacement selected by the operator through the servo slide 25, moves the slide piston 62 of the slide switch 25 b back into its illustrated inlet position, while the slide 25 and 25 a control the pump displacement in the usual manner described above. When the system is in operation and the distributor slide 2 is only closed for a relatively short time, the operator leaves the operating lever 45 in its selected position so that the displacement pump 1 continues to supply liquid to the delivery line 5. Under these conditions, the compensating control slide 25 a, as described above, keeps the outflow pressure at a low value, whereby the energy losses are brought to a minimum. In periods of prolonged inactivity or when the lines 5, 5 a or Sb have to be opened, the operator moves the operating lever 45 back into its position with the displacement zero. The slide piston 38 is displaced to the right from a zero position against the slide bushing 32, as a result of which the control surface 41 separates the radial passage 34 from the radial passage 35 and the control surface 42 separates the radial passage 36 from the radial passage 37. The pressures in the working chambers

24 & and 24 a of the control motor 24 rise or fall now, so that the control motor 24, supported by the pressure forces acting on the adjusting lever 22, works and moves the adjusting lever 22 to the position with the displacement zero. When the lever this Has reached position, the slide piston 38 is with respect to the housing of the servo slide

25 in a neutral position. The follower lever 44 then has the slide sleeve 32 with respect to the slide piston moved back to a zero position.

The servo control by the servo slide 25 has been created in the illustrated embodiment, so that the operator can limit the pump displacement to a value below its pre d viewed maximum on the one hand and on the other hand, in longer periods of time in which the system is idle, the pump displacement to the value zero can decrease. In designs in which these properties are not required, the servo slide 25 can be omitted. The working chamber 24a can then be connected directly to the line 46. In this case, the working chamber 24 b is permanently open to the storage container 13, so that the control motor 24 is a single-acting motor.

Claims (5)

Patent claims: 1. A method of controlling a hydraulic system with a positive displacement pump with variable Flow rate and with a distributor slide valve with closed center position for the pressure medium supplied by the positive displacement pump to a hydraulic motor, in which the delivery flow changes and the delivery pressure is limited to a predetermined maximum value is, characterized in that the delivery flow of the displacement pump (1) with the distributor slide valve (2) open and with one delivery pressure below the maximum value depending on the pressure drop at the distributor slide (2) is controlled so that this pressure drop is at a substantially constant Value is held, and that the flow rate of the displacement pump (1) when the Distributor slide (2) is regulated as a function of the delivery pressure in such a way that the delivery pressure substantially constant at a value well below the maximum value is held. 2. The method according to claim 1, characterized in that the delivery flow of the positive displacement pump (1) for every position of the distributor slide (2) depending on the pressure drop at the distributor slide (2) is regulated in such a way that this pressure drop on a substantially is kept constant. 3. Control system for performing the method according to claim 1 or 2, characterized through a line (8 or 9) which, when the distributor slide (2) is open, the load pressure of a Motor (3) is exposed and with the distributor slide (2) closed with a storage container (13) communicates, one on the pressure difference between that in the line (8 or 9) and the pressure prevailing in the delivery line (5) of the displacement pump (1) Servomotor (55) and by a compensating control slide operated by the servomotor (55) (25 a) to control the pressure in an auxiliary pressure circuit for applying a to Change in the flow rate of the displacement pump (1) used control motor (24) a variable restoring force acts against the pressure of the auxiliary pressure circuit. 4. Control system according to claim 3, characterized in that the compensating control slide (25 a) is located in the connection between a switching slide (25 b) which limits the maximum pressure and the control motor (24). 5. Control system according to claim 4, characterized in that a manually operated servo slide (25) switched between the compensation control slide (25a) and the control motor (24) with which the position of the control motor can be controlled. 1 sheet of 5OFY drawings