EP0515608A1

EP0515608A1 - Hydraulic system.

Info

Publication number: EP0515608A1
Application number: EP92900271A
Authority: EP
Inventors: Otwin Eich; Franz-Peter Salz
Original assignee: Barmag AG; Barmag Barmer Maschinenfabrik AG
Current assignee: Oerlikon Barmag AG
Priority date: 1990-12-15
Filing date: 1991-12-13
Publication date: 1992-12-02
Anticipated expiration: 2011-12-13
Also published as: WO1992010684A1; US5297381A; EP0515608B1; DK0515608T3; JPH05504819A; DE59105057D1

Abstract

Dans un système hydraulique, plusieurs consommateurs (5'; 5'';5''') sont alimentés par une pompe commune à débit variable (1). La pompe à débit variable (1) est mise en fonction pour une pression située entre une pression de pompe (Delta P) et une pression de charge maximale. Cette différence de pression (Delta Pmax) est mise en relation avec une différence de pression minimale (Delta Pmin), et le signal de comparaison est utilisé dans un dispositif de commande (21) afin d'influer sur des signaux de valeur de consigne (S1, S2, S3) avec lesquels les différentes soupapes (6'; 6''; 6''') sont pilotées.In a hydraulic system, several consumers (5 '; 5' '; 5' '') are supplied by a common variable flow pump (1). The variable displacement pump (1) is activated for a pressure between a pump pressure (Delta P) and a maximum load pressure. This pressure difference (Delta Pmax) is related to a minimum pressure difference (Delta Pmin), and the comparison signal is used in a control device (21) in order to influence setpoint signals ( S1, S2, S3) with which the various valves (6 '; 6' '; 6' '') are controlled.

Description

DESCRIPTION hydraulic system

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

This hydraulic system is known from DE 26 51 325 C2. A control valve becomes the pressure at the pump and the highest load pressure

reported. 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 will only apply to existing ones

Effective excess demand. If this limitation comes into effect, the consumers are no longer using their control valves

controllable.

In the system known from patent 35 46 336, the electrical control signals of the controlled directional valves

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 dependency of the valve flow on the Stellsi gnalen be 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 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. You also have the

Advantage that not only the pressure difference, but preferably also the change in the pressure difference and the change direction 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 loop intervenes, the

The subject of this invention is 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

happen that all consumer flows are reduced 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 special meaning of the invention according to claim 1 is that the adaptation of the consumer flows to one

specified limit value (maximum pump current) by monitoring the minimum pressure difference to be observed only functions when the specified limit value is reached. So several control loops are superimposed. An internal control loop 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 controlled variable and the

Control position of the control pump as a manipulated variable.

The superimposed outer control loop uses the currently measured pressure difference minus the minimum pressure difference in order to increase the consumer flows 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)

reduce and increase the pressure difference again.

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 quantity (deflection = control position of the control pump) with the pump output or the pump torque

(Delivery volume × delivery pressure) and / or the delivery pressure

respectively. This has the advantage that a desired weighting of the delivery rate, the delivery torque and the delivery pressure of the control pump when adapting the valve position to the

maximum pump current can be specified. 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 superimposed, such that only at

Exceeding a predetermined drive torque influencing the position and adjustability of the individual

Valves assigned to consumers take place, but not below this limit. Likewise, the position and adjustability of those assigned to the individual consumers can be superimposed on the delivery pressure according to a specific function

Valves are affected when a certain pressure is exceeded, 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 those specified manually or automatically

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. This means that consumers may not be under-supplied 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 for the - z. B. for safety reasons - important consumers always have an adequate oil flow

is ready. On the other hand, there is one in advance

Reduction of the setpoints if the

given pump flow can be expected based on the input setpoint signals.

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

Show it:

Figure 1 is a circuit diagram for a hydraulic system with a control pump.

2 shows a circuit diagram with details according to FIG. 1;

Fig. 3 is a circuit diagram for the setpoint conditioning.

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 valve 6 ', 6'',6''' is a pressure control valve 7 ', 7'',7''' upstream. Each of the pressure control valves 7 ', T', 7 '''is on the one hand with the pressure upstream of the directional control valve 6', 6 '', 6 '''and on the other hand the consumer pressure behind the directional control valve 6', 6 '', 6 '''. This means that the volume flow supplied to the consumers 5', 5 '', 5 '''is independent of the load respective Pressure regulating valves 7 ', 7'',7''' resulting pump pressure and the highest detected via a shuttle valve chain 8

Consumer pressure is common to a differential encoder 9

given up. 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 sent via a weighting module 13 to comparison modules 14 ', 14' ', 14' '', which each give the individual actuators 16 ', 16' ', 16' '' of the directional control valves 6 ', 6' ', 6 ''' assigned. The comparison modules 14 ', 14' ', 14' '' have a second one

Input to which a desired setpoint can be specified from setpoint generator 15 ', 15' ', 15' ''. Through the

Comparison modules 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 in this way that the maximum flow rate of pump 1 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.

With reference to FIG. 2 and with reference to FIG. 1, the processing of the entered target values is shown in FIG

Control unit 21 described for manipulated variables for the directional control valves 6. 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. The magnet of the

Control valve 2 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 one

Torque M of pump 1, since the input signal to amplifier 3 represents the current delivery rate of 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 the

Weighting block 13 abandoned. The output signal of the comparison module is now in the weighting module 13

(Comparator) 18 processed in a function block 26 so that it emits a compensation signal = 1 when the current

Torque M is smaller 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 based on a time-dependent, continuous function until the torque M of the pump 1 has decreased so much that the equilibrium is established by feedback of the setpoints (this 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

Reduce the weighting block 23 continuously and, in the function block 25, lead to a reduction in the output signal A 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 such 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 that

Limit value P _{max of} the pressure, and that is equal to the limit value S _{max of} the target values if the measured pump pressure P exceeds the limit value P _{max of} the pump pressure.

The weighting module 13 with its two output signals A of the function module 25 and B of the function module 29 then controls comparison elements 14 ', 14 ", 14'", each of which 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'". 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, according to a preset function and a preset setpoint S1, S2, S3, the individual

Consumers 5 ', 5 ", 5'" supplied volume flow are reduced so far that the pumpable by the pump 1

Total amount 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, in order to adapt the measured maximum pressure difference Delta P _max to the minimum pressure difference Delta P _min, an adaptation to the

current torque M of pump 1 takes place. The current pump pressure P or others can also be included in the weighting

Include the operating parameters of the hydraulic system.

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 limitation construction Stone 32 limits the entered limit value Smax of the setpoint. In each of the modules 32 ', 32 ", 32"', a further evaluation of the supplied limit value Smax can take place in the sense that either there is no limit at all or the limit value S _{max is} reduced or increased.

This allows individual consumers 5 ', 5 ", 5"' to be given priorities. Other consumers can be shut down or treated subordinately if the set

Setpoint specifications S1, S2, S3 to exceed the

Limit value of the pump current would lead.

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 ensures that the signal processing and adaptation of the hydraulic system can follow in time even when the setpoint value is entered suddenly and does not result in a temporary one

Undersupply of consumers 5 ', 5 ", 5' '' comes

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 el 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 el and e2 connected. The output signal A is 1 as long as the specified one

Limit value of the pump delivery flow el 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 applied to the multiplication blocks 38 ', 38 ", 38'". In each of the multiplication modules 38, the respective

Setpoint S1, S2, S3, after it has preferably first been passed over ramps 34 ', 34 ", 34"'. The output signal of the multiplication blocks 38 represents the respective setpoint value given to the comparison block 14. This setpoint value preparation ensures that the setpoint values S1, S2, S3 do not lead to a consumption which contributes to the predetermined limit value of the pump delivery flow el far exceeds. However, this is only a rough precaution. The inventive superimposition of the adaptation of the consumer flows to the measured pump delivery flow ensures that each consumer 5 ', 5 ", 5'" in it

assigned frame remains functional.

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 CHARACTERISTICS

1 control pump

2 control valve

3 amplifiers

4 feedback device

5 consumers

6 control valve, directional control valve

7 pressure control valve, pressure differential balance

8 shuttle valve

9 differential encoder

10 Delta P controllers

11 pressure transducers

12 differentiator

13 weighting block, function block

14 comparison module, comparison element

15 setpoint adjuster

16 amplifiers, actuators, actuators

17 multiplier module, multiplier module 18 comparator (M / M _max ) 20 pump pressure line

21 control unit 23 component, weighting component

24 multiplication block

25 function block

26 function block 28 comparator (P / P _max )

29 Function block 31 Multiplication block 3 Limiting block 33 Setpoint generator

34 building block, ramps

35 multiplication module 36 summator

37 Function block

38 ')

38 "multiplication module 38 '")

File number PCT / DE 91/00967

Legend to Fig. 2

Legend 10 ..... Δp controller

Legend 17. . . .. multiplication

Legend 24 ..... multiplication

Legend 25 ..... if 4P / ΔP _Min ≥1 ↝A = 1;

if Δp / Δ p _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≥ O↝a = 1.

Legend 38 ..... multiplication

Claims

PATENT CLAIMS

1. hydraulic system,

in which several consumers (5 '; 5 "; 5'") are fed by a common control pump (1),

in which the pressure difference between the consumer (5 '; 5 "; 5"') is measured with the highest load pressure and the pump pressure and adjusted by adjusting the control pump (1) and at the same time to influence the control signals (a1, b1; a2, b2; a3, b3) is used for the control valves (6 '; 6 "; 6'") which are assigned to the individual consumers (5 '; 5 "; 5'"),

that the pump current supplied to the entirety of the consumers (5 '; 5 "; 5'") to the maximum predetermined

Pump flow is adjustable,

characterized in that

the measured pressure difference Delta P in a function block is related to a given one

Minimum pressure difference Delta P _min and an output signal A is generated,

which A is equal to 1 as long as the measured pressure difference is greater than or as large as the predetermined minimum pressure difference and

which is continuously reduced from A equal to 1 as long as the measured pressure difference is less than the specified minimum pressure difference,

and that the control signals (6 '; 6 "; 6'") predetermined control signals (a1, b1; a2, b2; a3, b3) compared to the

entered setpoints (S1, S2, S3) can be changed in proportion to the output signal A.

2. Hydraulic system according to claim 1,

characterized in that

the control position of the control pump (1) is measured and its deflection (alpha) is multiplied by the additionally measured pump pressure and the product (M) is also used to adapt the consumer flows.

3. Hydraulic system according to claim 1 or 2,

characterized in that

the pump pressure is also used to adjust the consumer flows.

4. Hydraulic system according to one of the preceding claims, characterized in that

the setpoint signals (S1, S2, S3) are reduced as a function of the specified pump flow that can be pumped and the sum of the setpoint signals set before the setpoint signals (S1, S2, S3) are multiplied by the reduction factor.

5. Hydraulic system according to claim 4,

characterized in that

Before the sum of the input setpoint signals (S1, S2, S3), each setpoint signal with a limit value Gv

is multiplied, which is specified for the respective consumer.