EP0515608B1 - Hydraulic system - Google Patents

Abstract

Disclosed is a hydraulic system in which several consumers (5', 5''; 5''') are powered by a common pump (1). The pump (1) is controlled as a function of the difference between the pump pressure (Delta P) and the maximum load pressure. This pressure difference (Delta Pmax) is compared with a minimum pressure difference (Delta Pmin) and the signal resulting from this comparison process used in a control unit (21) to adjust the reference-value signals (S1, S2, S3) with which the individual valves (6'; 6''; 6''') are controlled.

Description

The invention relates to a hydraulic system according to the preamble of the claim.

This hydraulic system is known from WO-A-9002882.

In this hydraulic system, the position of the control valves is always readjusted when there is a deviation between the pressure difference between the load pressure and the pump pressure and the specified pressure difference. The regulation provided there thus serves to regulate the pressure difference from the load pressure and the pump pressure as precisely as possible to the predetermined pressure difference, as a result of which the control circuit must constantly readjust the positions of the control valves. This makes this hydraulic system susceptible to vibration, since when the pump flow is sufficient to supply all consumers, the control valves are readjusted, which means that from a certain position the control valves would have to be regulated in the opposite direction, etc.

Another hydraulic system is known from DE 26 51 325 C2. A control valve is notified on the one hand of the pressure at the pump and on the other hand of the highest load pressure. If the pump can no longer deliver the volume flow required by the control valves and the associated consumers, the pressure difference between the pressure of the pump and the highest load pressure is reduced. The control valve consequently reduces the supply to the control pressure transmitter, by means of which the valves assigned to the consumers are actuated. This limits the flow of the valves. However, this limitation only becomes effective if there is already an excessive demand. If this limitation comes into effect, the consumers can no longer be controlled by means of their control valves.

In the system known from patent 35 46 336, the electrical control signals of the controlled directional valves are added. The volume flow, which corresponds to the sum of the control signals, is compared with the maximum possible pump flow. If the total of the control signals exceeds the possible pump current, the control signals are reduced. With this system, all control signals must be recorded. In addition, the dependence of the valve flows on the control signals correctly taken into account by means of a computer.

The object of the invention is to design the hydraulic system so that it is not susceptible to vibration and that any weighting and adaptation of the individual consumer flows to the operating parameters of the pump is also possible.

The solution results from the characterizing part of claim 1. The solution has the advantage that it does not affect the response range of the setpoint generator. Therefore, the individual consumers remain controllable even when the consumption is high, while in the known system the speed of the individual consumers can no longer be controlled if the maximum predetermined pump current is exceeded. There is also the advantage that not only the pressure difference, but preferably also the change in the pressure difference and the direction of change of the pressure difference can be detected. In this way, the reduction in consumption can already begin if a deficiency (i.e. the sum of the set consumer flows exceeds the maximum pump flow specified (maximum pump flow)) is heralded by the size and direction of the rate of change of the pressure difference.

If the sum of the consumer flows, which is required by appropriate setting of the valves assigned to the consumers, rises above the maximum pump current, the control signals of the valves are reduced. The reduction of consumer currents can take place proportionally. However, a reduction according to priorities is also possible if, for. B. an individual consumer should not reduce his speed in contrast to the others.

However, the control circuit, which is the subject of this invention, intervenes only in exceptional cases, namely when the pumpable pump flow is not sufficient for the consumer flows set on the respective valves, which add up to the current production volume. In this case, the current flow rate is reduced by reducing the respective consumer flows supplied.

The adjustment of the consumer flows to the maximum pump flow is done by adjusting the valves, which are assigned to the consumers. Basically, it can be assumed that these valves are adjusted electromagnetically or hydraulically from the outside, that is, by hand or by external input parameters. According to this invention, however, an adjustment signal for reducing the actuation of the valve piston by multiplication is superimposed on these input signals (setpoint signals) when it is determined in the hydraulic system by measuring the pressure difference that the pumpable pump current has been exceeded.

The maximum pump current does not necessarily correspond to the maximum pump current that can be pumped. Rather, a lower limit, e.g. B. 80% of the maximum conveyable pump flow. This ensures that the hydraulic system does not fall out of its control range due to an absolute overload of the pump. The same applies to the specified minimum pressure difference.

The adaptation of the consumer flows to the specified pump flow that can be conveyed when the minimum limit value of the pressure difference is exceeded is basically achieved by reducing the sum of the consumer flows to the specified limit value. In the simplest case, this can be done by reducing all consumer flows by the same percentage. However, it is also possible to weight the control signals, by means of which the consumer currents are reduced, differently for each consumer. This allows individual consumers to be given priority over other consumers. It can e.g. B. ensure that such consumers for security reasons always have to be loaded with a certain consumer current, e.g. B. hydraulic brakes have priority over other consumers. This will be discussed later.

The particular importance of the invention according to claim 1 is that the adaptation of the consumer currents to a predetermined limit value (maximum pump current) by monitoring the minimum pressure difference to be observed only functions when the predetermined limit value is reached. So several control loops are superimposed. An internal control circuit uses the pressure difference Delta P between the pump pressure and the highest load pressure as a measured variable, the specified minimum pressure difference as a control variable and the control position of the control pump as a control variable.

The superimposed outer control loop uses the currently measured pressure difference minus the minimum pressure difference in order to reduce the consumer flows and increase the pressure difference again in the event of a deficiency (consumption exceeds the maximum pump current) and the resulting drop below the limit value of the pressure difference (minimum pressure difference).

In addition, the adaptation of the consumer flows of the individual consumers to the specified maximum pump current can also be achieved by superimposing the measurement signal obtained from the measurement of the current delivery volume (deflection = control position of the control pump) with the pump output or the pump torque (delivery volume x delivery pressure) and / or Delivery pressure. This has the advantage that a desired weighting of the delivery rate, the delivery torque and the delivery pressure of the control pump can be predetermined when the valve position is adapted to the maximum pump flow. Here, the delivery capacity or the torque of the pump, which is currently determined from the respective control position of the pump and the delivery pressure of the pump by multiplication, is compared with a target torque, and the output signal obtained from the difference is compared selectable function is superimposed, for example in such a way that the position and adjustability of the valves assigned to the individual consumers is influenced only when a predetermined drive torque is exceeded, but not below this limit value. Likewise, the position and adjustability of the valves assigned to the individual consumers can be influenced when a certain pressure is exceeded by superimposing the delivery pressure after a certain function, but not below this pressure or only with a certain percentage. As a result, the maximum external load is also taken into account when influencing the valves assigned to the consumers, in particular directional valves.

The influencing of the pump current supplied to each consumer and the total of the consumers takes place, for. B. electrically or hydraulically in that the entered setpoints of the valves assigned to the individual consumers are influenced as a function of the pressure difference between the highest consumer pressure and the pump pressure of the control pump.

For special applications of the hydraulic system according to the invention, a setpoint processing is expedient. The setpoints are the manually or automatically specified control signals for the valves assigned to the consumers. These externally entered setpoints can be fed to the system via attenuators (ramps). This specifies the rates of change at which the consumer currents can change if the setpoints entered change suddenly. It is thereby achieved that the adjustment speed of the pump or pressure differential balance is sufficient in any case to follow the change in the consumer flows over time. There can therefore be no shortage of consumers for a short time. Furthermore, the consumer flows requested by the entered target values can be roughly adapted to the maximum flow rate that can be supplied by the pump. For this purpose, those entered from outside Setpoints are brought into dependence on the sum of the entered setpoints and, in addition, on the specified pump flow that can be pumped or the minimum pressure difference. On the one hand, this leads to a weighting of the individual consumers and ensures that B. for safety reasons - important consumers always have an adequate oil flow. On the other hand, the setpoints are reduced in advance if the specified pump flow that can be conveyed is expected to be exceeded on the basis of the input setpoint signals.

In the following, exemplary embodiments of the invention are illustrated using the circuit diagrams described below.

Fig. 1

einen Schaltplan für ein Hydrauliksystem mit Regelpumpe;

Fig. 2

einen Schaltplan mit Einzelheiten nach Figur 1;

Fig. 3

einen Schaltplan für die Sollwert-Aufbereitung.

Show it:

Fig. 1

a circuit diagram for a hydraulic system with control pump;

Fig. 2

a circuit diagram with details of Figure 1;

Fig. 3

a circuit diagram for the setpoint processing.

Several consumers 5 ', 5˝, 5 ‴ are fed by a common control pump 1. The control pump 1 can be adjusted hydraulically by means of a control valve 2. The control valve 2 is controlled by a magnet via an amplifier 3 and has a feedback 4 to the control position of the control pump 1.

The individual consumers 5 ', 5˝, 5 ‴ are controlled by directional valves 6', 6˝, 6 ‴, which are actuated by electromagnets a1-a3, b1-b3. Each directional control valve 6 ', 6˝, 6 ‴ is preceded by a pressure control valve 7', 7˝, 7 ‴. Each of the pressure control valves 7 ', 7˝, 7 ‴ is acted on the one hand with the pressure in front of the directional control valve 6', 6˝, 6 ‴ and on the other hand with the consumer pressure behind the directional control valve 6 ', 6˝, 6 ‴. As a result, the volume flow supplied to the consumers 5 ', 5˝, 5 ‴ is load-independent. The one in front of each Pressure control valves 7 ', 7˝, 7 ‴ resulting pump pressure and the highest consumer pressure detected via a shuttle valve chain 8 is given to a differential encoder 9 together. Its output signal represents the pressure drop Delta P between the pump 1 and the highest consumer pressure. This pressure difference is given, together with its differentiation (differentiating element 12), on the one hand, to a delta-p controller 10, which controls the control valve 2 via the amplifier 3 already mentioned. On the other hand, the two signals are given via a weighting block 13 to comparison blocks 14 ', 14˝, 14 ‴, which are each assigned to the individual actuators 16', 16˝, 16 ‴ of the directional control valves 6 ', 6˝, 6 ‴. The comparison blocks 14 ', 14˝, 14 ‴ have a second input, to which a desired setpoint from setpoint generator 15', 15˝, 15 ‴ can be specified. The comparison blocks 14 ', 14˝, 14 ‴ influence the actuators 16', 16˝, 16 ‴ in such a way that the adjustment of the valves 6 ', 6˝, 6 ‴ is adapted and reduced such that the maximum Pump 1 flow rate cannot be exceeded.

At the same time, torque can also be superimposed, in that the pump pressure and, on the other hand, the already mentioned pressure drop are recorded in a multiplier 17 and the output signal of this multiplier 17 is fed to the weighting module 13 via a comparator 18.

FIG. 2 is a functional diagram in which the control unit 21 is shown with the functional modules contained therein.

2 and with reference to FIG. 1, the processing of the entered setpoints in control unit 21 into manipulated variables for the directional control valves 6 is described below.

The pressure difference delta P is input to a module 23 in the control unit 21. At the same time, a limit value Delta P _{min is} specified for module 23. This limit value can be specified constantly if only the input of the pressure difference is connected to the control unit 21. If the pump pressure P is also connected, further processing of the value Delta P follows, which will be discussed later.

In block 23, the measured or further processed pressure difference and the limit value Delta Pmin are weighted. The output signal of the block 23 is given to the weighting block 13. This contains a function block 25, which gives the positive constant output signal A equal to 1, as long as the limit value of the pressure difference Delta Pmin is smaller than the measured or further processed pressure difference Delta P. If the pressure difference Delta P falls below the limit value, the output signal A of the function block becomes 25 smaller than 1. It decreases from 1 based on a time-dependent function until an equilibrium is reached by increasing the measured or further processed pressure difference. This will be discussed later.

The pressure difference signal Delta P continues to be applied to the Delta P controller 10. The setpoint value of the pressure difference is also given to the delta-P controller 10. The output signal of the delta-P controller 10 leads via amplifier 3 to the control valve 2 shown in FIG. 1, by means of which the control position of the pump 1 is adjusted. For this purpose, the solenoid of the control valve 2 is acted upon by the output current of the amplifier 3. This results in an adjustment of the control valve 2 in the sense that the two sides of the control piston are equally loaded and the control pump 1 is adjusted in the sense of a reduction in the flow rate (pump flow, pump flow) (adjustment piston moves to the left). As a result, the spring acting on the other side of the valve is loaded by the return 4 and it takes place an adjustment of the piston of the control valve 2 in the sense that the pressure on the spring side of the adjusting piston is relieved. As a result, the control pump 1 is adjusted in the sense of increasing the delivery rate. A reverse effect results when the output signal of the amplifier 3 is reduced. In any case, an equilibrium is set at the control valve 2, so that the output signal of the delta-P controller forms the regulated setpoint for the control position of the control pump 1 and therefore - at given speed - is also a measure of the current delivery rate of pump 1.

The output signal of the delta-P controller 10 is applied to the multiplication module 17 at the same time as the pump pressure P tapped via the pressure converter 11. The output signal of the multiplication module 17 represents the current torque M of the pump 1, since the input signal to the amplifier 3 represents the current delivery quantity of the pump 1. This output signal is related in block 18 (comparator) to a maximum possible limit value of the torque. The output signal of the comparator 18 is given to the weighting module 13. In the weighting block 13, the output signal of the comparison block (comparator) 18 is processed in a function block 26 so that it emits a compensation signal = 1 when the current torque M is less than the limit value of the torque, and that it emits a decreasing output signal as long as the currently determined torque M is greater than the predetermined constant limit value M _max . In the latter case, the output signal from 1 is reduced according to a time-dependent, continuous function until the torque M of the pump 1 has decreased so far that the equilibrium is established by feedback of the setpoints (which will be discussed later).

For this purpose, the output signal of the function block 26 is a multiplication block 24 together with the pressure difference Delta P abandoned. The pressure difference and the output signal, which has been obtained from the torque comparison, are multiplied in the multiplication module 24. The output signal of this multiplication module 24 represents the measured but further processed pressure difference and is given to the weighting module 23 already mentioned and described. The output signal of the function block 26 is thus used to process the pressure difference in the multiplication block 24, as has already been indicated. In the event of an overload, the weighting module 23 is supplied with a constantly reduced delta P signal. Therefore, the output signal of the weighting module 23 will also decrease continuously and, in the function module 25, the output signal A will be reduced if the overload P P / Delta P _min continues.

In order to also take the pump pressure P into account, in a further comparator 28 (comparison module) a permanently entered limit value of the pump pressure P _{max is} related to the currently measured pump pressure P.

The module 13 also contains a function module 29 which is controlled by the output signal of the comparator 28 and additionally by a limit value which represents the maximum target value S _max . These entered variables are processed in the function block 29 in such a way that the function block 29 gives an output signal B which is equal to one as long as the measured pump pressure P is less than the limit value P _{max of} the pressure and which is equal to the limit value S _{max of} the desired values when the measured pump pressure P exceeds the limit value P _{max of} the pump pressure.

The weighting block 13 with its two output signals A of the function block 25 and B of the function block 29 then controls comparison elements 14 ', 14˝, 14 ‴, each one of the valves 6', 6˝, 6 ‴ for the individual Consumers 5 ', 5˝, 5 ‴ are assigned. Each of these comparison elements 14 is given a different setpoint S1, S2, S3 via the setpoint generator 15 ', 15˝, 15 15. In the comparators, these output signals A and B are superimposed on the entered target values. The outputs then go via the actuators 16 ', 16˝, 16 ‴ to the respective magnets a1, b1; a2, b2; a3, b3 of the respective valves 6 ', 6˝, 6 ‴. As a result, after a preset function and a preset setpoint value S1, S2, S3, the volume flow supplied to the individual consumer 5 ', 5˝, 5 ‴ can be reduced to such an extent that the total amount that can be pumped by the pump 1 is not exceeded. Through the simultaneous detection and direct input of the adjustment path alpha or the swivel angle of the control pump 1, it can simultaneously be ensured in the weighting module 13 that for the adaptation of the measured maximum pressure difference Delta P _max to the minimum pressure difference Delta P _min an adaptation to the current torque M at the same time Pump 1 takes place. The current pump pressure P or other operating parameters of the hydraulic system can also be included in the weighting.

For this purpose, the comparison elements 14 - as shown in FIG. 2 - are divided into a multiplication module 31 ', 31˝, 31 ‴ and a limitation module 32', 32˝, 32 ‴. The output signal A of the function block 25 and the setpoint value S1, S2, S3 are given to the multiplication block. This sets the setpoint S in relation to the currently measured maximum pressure difference Delta P _max when the sum of the consumer currents exceeds the limit value of the pump current P _max . The setpoints S1, S2, S3 are reduced accordingly. The output signal of the multiplication module 31 is given to the limiting module 32 together with the output signal B of the function module 29, which establishes the relationship to the measured pump pressure P. If the specified limit value of the pump pressure P _max is exceeded, the output signal of the limiting _module becomes 32 limited to the entered limit value Smax of the setpoint. In each of the blocks 32 ', 32˝, 32 ‴, a further evaluation of the limit value Smax can be carried out in the sense that either there is no limit at all or the limit value S _{max is} reduced or increased. As a result, individual consumers 5 ', 5˝, 5 ‴ priorities can be granted. Other consumers can be shut down or treated subordinately if the setpoint specifications S1, S2, S3 would lead to the limit value of the pump current being exceeded.

In Fig. 3, a setpoint processing is now additionally shown, which can be used optionally. For this purpose, a setpoint generator 33 can be arranged upstream of the control unit 21. The setpoint generator 33 has a first component 34 for each input setpoint S1, S2, S3, which is referred to below as ramp 34. This ramp means that an abruptly entered setpoint only changes over time. This has the effect that the signal processing and adaptation of the hydraulic system can follow in time even when the setpoint input is erratic and there is no temporary undersupply of the consumers 5 ', 5˝, 5 ‴. The output signals of the ramps 34 are then multiplied in multiplication modules 35 by input limit values G1 to G3. These limit values represent a certain percentage of the limit value of the pump delivery flow. This results in a weighting of the entered target values S1, S2, S3 in the multiplication modules 35. The output signals of the multiplication modules 35 are fed to a summing element 36 with the output signal e2, which represents the sum of the output signals of the multiplication modules.

The signal e2 is given to a function block 37 together with a signal e1. The signal e1 represents the maximum predetermined pump delivery flow in a form that is comparable to the signal e2. In function block 37, the two input signals e1 and e2 connected. The output signal A is equal to 1 as long as the predetermined limit value of the pump delivery flow e1 is greater than the set and weighted sum e2 of the setpoints S1, S2, S3. The output signal A is equal to the quotient of the limit value el and the weighted sum e2 if the weighted sum e2 is greater than the limit value e1.

The output signal A of the function block 37 is now given to the multiplication blocks 38 ', 38˝, 38 ‴. In each of the multiplication modules 38, the respective setpoint S1, S2, S3 is multiplied after it has preferably first been passed over the ramps 34 ′, 34˝, 34 ‴. The output signal of the multiplication modules 38 represents the respective setpoint given to the comparison module 14. This setpoint processing ensures that the setpoint values S1, S2, S3 do not lead to a consumption which does not contribute to the predetermined limit value of the pump delivery flow e1 far exceeds. However, this is only a rough precaution. The inventive superimposition of the adaptation of the consumer flows to the measured pump flow ensures that each consumer 5 ', 5˝, 5 ‴ remains functional in the frame assigned to it.

The particular importance of the invention lies in the fact that on the one hand the pump torque M is corrected, but that a torque control can be superimposed on this torque control by simultaneously also detecting the speed of the pump 1 or its delivery rate.

REFERENCE SIGN LISTING

1

Control pump

2nd

Control valve

3rd

amplifier

4th

Feedback device

5

consumer

6

Control valve, directional valve

7

Pressure control valve, differential pressure balance

8th

Shuttle valve

9

Differential encoder

10th

Delta P controller

11

Pressure transducer

12th

Differentiator

13

Weighting module, function module

14

Comparison module, comparison element

15

Setpoint generator

16

Amplifiers, actuators, actuators

17th

Multiplier block, multiplication block

18th

Comparator (M / M _max )

20th

Pump pressure line

21

Control unit

23

Block, weighting block

24th

Multiplication module

25th

Function block

26

Function block

28

Comparator (P / P _max )

29

Function block

31

Multiplication module

32

Limiting block

33

Setpoint generator

34

Building block, ramps

35

Multiplication module

36

Summer

37

Function block

38 ′

)

38˝

Multiplication module

38 ‴

)

• Legend to Fig. 2

  Legend 10

  Δp controller

  Legend 17

  multiplication

  Legend 24

  multiplication

  Legend 25

  if Δp / Δp _Min ≧ 1 ↝ A = 1;
  if Δp / Δp _Min <1 ↝ A decrease to Δp / Δp _Min = 1;

  Legend 26

  if M / M _Max ≦ 1 ↝ a = 1;
  if M / M _Max > 1 ↝ a decrease to M / M _{Max = 1;}

  Legend 29

  if P / P _Max ≦ 1 ↝ B = 1;
  if P / P _Max > 1 ↝ S1 - S3 limit to S _Max;

  Legend 31

  multiplication

  Legend 32

  Limitation; Limitation

  S1, S2, S3

  Setpoint

• Legend to Fig. 3

  Legend 35

  multiplication

  Legend 37

  if e1 - e2 ≧ 0 ↝ a = 1;
  if e1 - e2 <0 ↝ a = $\frac{\text{e1}}{\text{e2}}$

  

  ;

  Legend 38

  multiplication

Claims (5)

1. Hydraulic system in which a plurality of consumer units (5′ ; 5˝ ; 5‴) are fed by a common regulating pump (1), in which the pressure difference between the consumer units (5′ ; 5˝ ; 5‴) is measured at the maximum load pressure and the pump pressure and is stabilized by adjusting the regulating pump (1) and is simultaneously used for influencing the actuating signals (a1, b1; a2, b2; a3, b3) for the control valves (6′; 6˝; 6‴) associated with the individual consumer units (5′ ; 5˝ ; 5‴) in such a way that the pump flow delivered to all the consumer units (5′ ; 5˝ ; 5‴) can be adapted to the maximum preset pump conveying flow, the pressure difference Delta P measured being placed in a function block in relation to a preset pressure difference and an output signal A being generated therefom with respect to which the actuating signals (a1, b1; a2, b2; a3, a4) presetting the control valves (6′ ; 6˝ ; 6‴) are varied with respect to the input nominal values (S1, S2, S3), characterized in that a minimum pressure difference Delta P min is preset as the preset pressure difference, the output signal A is equal to 1 provided the pressure difference measured is equal to or greater than this minimum pressure difference, and is continuously decreased from a value equal to 1 provided the pressure difference measured is smaller than this minimum pressure difference.
2. Hydraulic system according to Claim 1, characterized in that the regulating setting of the regulating pump (1) is measured and its displacement (alpha) is multiplied by the additionally measured pump pressure and the product (M) is additionally used for adapting the consumer unit flows.
3. Hydraulic system according to Claim 1 or 2, characterized in that the pump pressure is additionally used for adapting the consumer unit flows.
4. Hydraulic system according to any one of the preceding Claims, characterized in that the nominal value signals (S1, S2, S3) are reduced in dependence on the preset conveyable pump flow and on the sum of the nominal value signals set before the nominal value signals (S1, S2, S3) are multiplied by the reducing factor.
5. Hydraulic system according to Claim 4, characterized in that before the summation of the input nominal value signals (S1, S2, S3) each nominal value signal is multiplied by a limiting value Gv which is preset for the respective consumer unit

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