EP2118500A1

EP2118500A1 - Method for operating a hydraulic system, and hydraulic system

Info

Publication number: EP2118500A1
Application number: EP07818902A
Authority: EP
Inventors: Winfried RÜB
Original assignee: Hydac Fluidtechnik GmbH
Current assignee: Hydac Filtertechnik GmbH
Priority date: 2006-12-07
Filing date: 2007-10-11
Publication date: 2009-11-18
Anticipated expiration: 2027-10-11
Also published as: EP2118500B1; US8661809B2; JP2010511842A; WO2008067866A1; DK2118500T3; EP2118500B8; US20100043421A1; DE102006057699A1

Abstract

A method for operating a hydraulic system having at least one supply device, in particular a hydraulic pump (39)), which supplies different hydraulic consumers is characterized in that a synchronizing device (33, 35) ensures that, if at least one hydraulic consumer is not supplied sufficiently, the deficit in volumetric flow for said consumer is compensated for in such a way that all the consumers compensate for the deficit equally.

Description

Method for operating a hydraulic system and hydraulic system

The invention relates to a method for operating a hydraulic system with at least one supply device, in particular a hydraulic pump, which supplies various hydraulic consumers. In addition, the invention relates to a hydraulic system operable by the method according to the invention.

For motor-driven systems and devices with hydraulic systems, such as loader and excavator-type construction machines, it is usually forced for cost reasons, interpret the power of the diesel engine to drive the hydraulic pump without reserves. Also for cost reasons, the hydraulic pump is not designed in many cases so that at the same time maximum volume flow requirement of all consumers an adequate supply of all consumers would be guaranteed.

In the working mode, this leads to the fact that on the one hand the diesel engine is operated at its power limit and on the other hand that the pump delivery volume in the case of parallel operation of hydraulic consumers is not suitable for the Wish maximum working speeds sufficient. It is therefore necessary to use priority valves in safety functions, which initially supply the preferred consumers, before the supply line is released to the other consumers. All other consumers have to share the residual current.

In implements such as the construction machines mentioned, it is state of the art to provide consumers with directional valves with upstream pressure compensators, the spool valves of the directional control valves determine the opening size of the metering orifices for the supply of consumers. Due to the functional principle of the upstream pressure compensators, which copy the pressure of the external loads in front of the orifices and increase them by the amount of the force of their control spring, there are a number of different high resistances from the pump. If the pump delivery volume is insufficient, the Pump pressure and the working fluid flows the path of least resistance. The consumer with the highest load can thereby come to a standstill. Its "saved" volume flow is thus available to all other consumers.

For the machine operator, this system procedure is unacceptable, because the typical machine control with cross lever operates several functions at the same time. If a consumer stops unintentionally, the operator gets into trouble with the controller.

Attempting to solve these problems by using valves with pressure gauges downstream of the metering orifice does not lead to the desired result, although downstream pressure compensators do not provide the load pressure in front of the metering orifice but the highest load pressure in the system copy behind the metering orifice, whereby all resistances remain the same even when the pump pressure drops from the pump. Disadvantageously, in such systems, however, a quantity cut-off must take place before the metering orifice, which is not readily possible. Another particular disadvantage is that the load reporting system of directional valves with downstream pressure compensator causes a constant Ausspeisestrom from the regulated volume flow of the highest-load consumer, which represents an energy loss.

In view of this problem, the invention has the object to provide a method for operating a hydraulic system available, since it is characterized by an overburden of the supply device by a comparatively improved performance.

According to the invention this object is achieved by a method having the features of claim 1 in its entirety.

Accordingly, the peculiarity of the invention is that in the case of an undersupply of a consumer, all consumers located in the hydraulic system are used to compensate for the volumetric flow deficit of the underserved consumer. While in the prior art in systems with upstream pressure compensator in the case of an undersupply standstill of the highest load can occur whose savings volume flow then benefits the other consumers, the invention provides contrast, that in the case of undersupply all consumers a correspondingly reduced flow to Is made available. There is therefore no danger that a machine operator who simultaneously controls several consumers in order to drive several functions at the same time, confronts the situation. that one consumer comes to a standstill while the other consumers are still active (on the move).

In embodiments in which from each pump via an associated, adjustable metering orifice a dependent of their opening size volume flow of pressure fluid is supplied, wherein the respective aperture with the opening size and the pump delivery flow related pressure difference is generated at the orifices, can in an advantageous manner The procedure is such that when the pressure difference at at least one metering orifice drops below a target value, a correction signal is generated, whose signal value is used to reduce the opening size of all metering orifices synchronously, the correction signal being maintained until the desired value of the pressure difference is reached again becomes. The correction signal is therefore generated as a function of the fact that, when the hydraulic pump is over-charged, its pump delivery flow is no longer sufficient to generate the necessary dynamic pressure at the metering orifice of the highest-load consumer, whereby the pressure difference at this diaphragm drops below a specified nominal value.

As a correction signal, a synchronizing pressure is preferably generated in a synchronous channel. Since the correction signal is thus in the form of a pressure signal, it can advantageously be brought into effect directly in the valve system.

In particularly preferred embodiments, the synchronous pressure is generated via a synchronous pressure compensator, which is acted upon on the one hand with the pump pressure and on the other hand with the highest load pressure of the system, plus the force of its control spring, and on the undershoot their control pressure difference, a pressure source is connected to the synchronous channel.

In embodiments in which the control of the supply to the consumer by proportional directional valves takes place, the spool for the change of the metering orifices by encoder pressure is hydraulically actuated, the synchronous pressure is supplied to the not controlled by the encoder pressure end face of the spool. The synchronizing pressure generated in operating conditions of the undersupply therefore causes the control spool of all directional valves to be reset against the respective sensor pressure by an amount dependent on the synchronous pressure and therefore all consumers for the compensation of the undersupply are supplied with a correspondingly reduced volume flow.

In particularly advantageous embodiments, the pressure difference at the metering orifices of the directional control valves is regulated by an associated individual pressure compensator and the system pressure by a system pressure compensator.

Preferably, in this case, the differential pressure of the synchronous pressure compensator is set to a slightly lower value than the differential pressure of the system pressure compensator. This ensures that during normal operation of the system the differential pressure in the system is clearly determined by the system pressure compensator.

The pressure difference of the synchronous pressure compensator is preferably set to the pressure difference of the individual pressure compensators or higher. In particularly preferred embodiments, the valve and pump system is dimensioned so that at maximum possible volume flow requirement of the maximum synchronous pressure does not exceed the biasing force of the centering springs of the spool. This ensures that in the event of a shortage of the system, the spools can not be reset to their neutral position by the synchronous pressure.

In systems with consumers, which, for example, for security reasons, are particularly preferred, the supply of the correction signal to the respective preferred consumer can be prevented in the manner of a priority circuit.

The invention also provides a hydraulic system which is operable according to the method of any one of claims 1 to 10 and having the features a) to c) of claim 11.

Further features of the hydraulic system are specified in the subclaims 12 to 14.

The invention is explained in detail below with reference to the drawing. Show it:

1 is a hydraulic circuit diagram of a prior art hydraulic system for supplying two hydraulic

Consumer;

Figures 2 and 3 are hydraulic circuit diagrams of two different system pressure regulators for use in hydraulic systems of the type shown in Figure 1; Fig. 4 is a flow chart illustrating the operation principle of the invention;

FIG. 5 shows a hydraulic circuit diagram similar to FIG. 1, but of a hydraulic system according to the invention intended for carrying out the method according to the invention; FIG.

Fig. 6 is a circuit diagram of a directional control valve for the synchronous control method according to the invention and with a logic circuit for the control with synchronous pressure and

Fig. 7 is a schematically simplified sectional view of a synchrondruckwaage.

In the illustration of Fig. 1, which shows a prior art hydraulic system for the supply of two consumers (not shown), a pump line 1 upstream system pressure regulator is omitted. Figures 2 and 3 show two embodiments of system pressure regulators which may be used in hydraulic systems of the type shown in Figure 1 to maintain the pressure difference between pump pressure P _P u and maximum load pressure LSmax constant. 2 is a hydraulic pump in the form of a constant displacement pump 3, whose pressure side is connected to a three-way pressure compensator 5, which on the one hand with the pump pressure P _P u and on the other hand with LSmax, plus the force of a control spring 7, is acted upon and how a pilot-operated pressure relief valve that keeps the pressure difference between the pump line 1 and LSmax constant. On the other hand, FIG. 3 shows the use of a variable displacement pump 9, the regulator of which is formed by a directional control valve 1 1, which regulates the required delivery flow within the control loop "adjusting mechanism of the pump". The supply of the consumers not shown in FIG. 1 via the supply lines A1, B1 and A2, B2 via proportional directional control valves 13, define the control slide 15 with its control edges, the opening size of Zumessblenden 17. The directional control valves 13 are each preceded by an individual pressure compensator 19 which, in the usual manner with upstream pressure compensators on the one hand with the pending at the respective metering orifice 17 of the directional valve 13 back pressure pT or p2 'and on the other hand with the load pressure of the associated consumer LSi or LS2, plus the force of their control spring 21, are acted upon. An exchange valve 23, to which the load pressures LSi and LS2 are supplied, decides which load pressure as LSmax is supplied to the system pressure regulator, not shown in FIG. For the control of the volume flows which are supplied to the consumers via the supply lines A1, B1 and A2 and B2, the control valves 13 are hydraulically controlled by a donor pressure Xai or Xa2 to one end of the spool 15 or to the opposite end a donor pressure Xt »I or Xb2 is supplied.

If, during operation of the system shown in FIG. 1, the pump pressure drops when the pump power is exceeded, only a reduced pressure difference is available at the individual pressure balance 19 with the highest load pressure as excess pressure for regulating the pressure difference at the relevant metering orifice 17. If this dynamic pressure at the highly loaded directional control valve 13 drops to the load pressure or below, then this consumer remains stationary while the low-loaded ones continue to move.

Fig. 4 illustrates the different state, which results from the inventive method. During operation of the system, the directional control valves 13 are opened so far that the pump delivery flow is no longer sufficient to throttle the necessary dynamic pressure in front of the metering orifices 17, then the dynamic pressure decreases according to a quadratic function, see box 25 (first box from below). In the box 27 above, the control law of a synchronous pressure compensator (33 in FIG. 5) ensures that the volumetric flow demanded by the consumers is taken back to the possible pump delivery rate by a correction signal in the form of a synchronous pressure Xs _yn , a compensation to the Control valves 15 is applied control pressures. The compensating synchronous pressure X _syn counteracts the actuation pressures X, see box 29, and thus reduces the opening cross-sections of all metering orifices 17. This takes place until the setpoint differential pressure set on the synchronous pressure compensator 33 is reached again, see box 31.

5 illustrates the method according to the invention with reference to a hydraulic system with three-way valves 13 for the supply of three consumers, wherein the supply lines omitted and the directional control valves 13 are shown simplified for clarity. Of the directional control valves 13, an individual pressure compensator 19, in a similar arrangement as shown in FIG. 1, are connected upstream, while the directional control valve 13 for the consumer N without an individual pressure compensator is integrated into the system. The system pressure control is carried out in accordance with the example of FIG. 2 by a three-way pressure compensator 5 connected to the pump line 1 at the outlet of the fixed-displacement pump 3.

The synchronous pressure compensator 33 serving to generate a synchronizing pressure Xsyn in a synchronous channel 35 is acted upon on the one hand by the pump pressure P _Pu and on the other hand by the maximum control block load pressure LSTB, plus the force of a control spring 37. The selection, which Load pressure as the maximum load pressure LSTB is supplied to both the synchronous pressure compensator 33 and the system pressure compensator 5 occurs, as in the system of Fig. 1, by shuttle valves 23rd

The synchronous pressure compensator 33 operates as the pump controller in a control loop in which also the spool 15 all directional control valves 13 participate. The basic principle is a sensor circuit which monitors the level of the current pressure difference at the control block (directional control valve 13). If this pressure difference is in the specified range, the synchronous pressure compensator 33 remains passive, ie. H. it is pressed by the desired pressure difference against its control spring 37 and relieves the synchronous channel 35 to tank 39. In the other case, the synchronous pressure compensator 33 goes into an open position and feeds from a supply line 41 volume flow in the synchronous channel 35 to produce a synchronizing pressure Xsyn. The synchronous channel 35 is connected in parallel with each end face of all spool 15, wherein the decision - supply of control pressure / pressure sensor - is made in each case by a shuttle valve 43, the one hand, encoder pressure X ... and on the other hand, the synchronous pressure Xsyn is supplied.

When the synchronous pressure Xsyn increases and penetrates to the end face of a spool 15, it can be assumed that it is the side of the spool 15 which is opposite to the side controlled by the sensor pressure. If, for example, a directional control valve 13 is actuated at 7 bar and delivers 50 l / min and then the synchronizing pressure rises from 0 to 2 bar, then the slide 15 deflected by 7 bar is reset by 2 bar back pressure to a slide position corresponding to 5 bar control pressure, whereby the the volume flow supplied to the consumer is reduced. The same applies to the spool 15 of the directional control valves 13 of the other consumers. The synchronous pressure is built up so long, ie the Synchronous pressure compensator 33 remains in the open position until the desired pressure difference at the control block has again reached the desired value.

The differential pressure of the synchronous pressure compensator 33 is set slightly lower than the differential pressure of the system pressure regulator, so that the differential pressure in the system is uniquely determined by the system pressure regulator in normal, saturated operation. The differential pressure of the individual pressure compensators 19 is ideally set to the value of the pressure difference of the synchronous pressure compensator 33. Then the synchronous pressure compensator 33 detects an incipient undersaturation of the system pressure compensator 5, while the individual pressure compensators 19 are still saturated. As a result, even when incipient undersupply fails, there is no error in the synchronous control because, before the individual pressure compensators 19 would completely open due to incipient undersaturation and then could no longer regulate, the synchronous pressure compensator 33 already begins to generate a compensating synchronizing pressure Xsyn, and thus all deflected control valves 15 to put back.

As an alternative to the use of change valves 43, a logic circuit on the spool 15 of the directional control valves 13 can make a selection as shown in FIG. 6, to which end side donor pressure or synchronous pressure is supplied.

Fig. 7 shows a sectional view of the synchronous pressure compensator 33, the slider 45 is shifted by the load pressure LS and the force of the control spring 37 so far in the figure to the left that a control edge 47 begins to connect the supply line 41 with the synchronizing channel 35, while the connection to the tank 39 is prevented. When the pressure P _pu increases until the desired differential pressure is reached and the spool 45 is reset to the right, the synchronous channel 35 is relieved again to tank 39.

If in the present text of orifices, such as Zumessblenden is spoken, the pertinent statements also apply to chokes, such as metering orifices. Likewise, the pertinent statements apply to nozzles used.

Claims

Patent claims

1. A method for operating a hydraulic system with at least one supply device, in particular hydraulic pump (39) which supplies various hydraulic consumers, characterized in that it is ensured by a synchronizer (33, 35) that at a low supply of at least one hydraulic consumer that Volume flow deficit is balanced for this consumer so that all consumers compensate for the deficit alike.

2. The method according to claim 1, characterized in that from a pump delivery flow to each consumer via an associated, adjustable metering orifice (17) a dependent of their opening size volume flow of pressure fluid is fed to the diaphragm (17) each with its opening size and the Pump flow in relation pressure difference is generated, and that when a decrease in the pressure difference at least one metering orifice (17) below a setpoint, a correction signal (Xsyn) is generated, the signal value of which depends on the opening size of all orifices

(17) is reduced synchronously, and that the correction signal is maintained until the target value of the pressure difference is reached again.

3. The method according to claim 2, characterized in that a synchronizing pressure (Xsyn) in a synchronous channel (35) is generated as a correction signal.

4. The method according to claim 3, characterized in that the synchronous pressure (Xsyn) via a synchronous pressure balance (33) is generated, on the one hand with the pump pressure (P _pu ) and the other with the highest load pressure (LSTB) of the system, plus the force of their Regelfeder (37), is acted upon and connected to the falling below their control pressure difference, a pressure source (Pv) with the synchronous channel (35).

5. The method according to claim 4, characterized in that the control tion of the supply of the consumer by proportional directional control valves

(13) takes place, the control slide (15) for the change of the metering orifices (17) by encoder pressure (X.) Is hydraulically controllable, and that the synchronous pressure (Xsyn) to the not with the encoder pressure (X.) Controlled end face of the spool ( 15) is supplied.

6. The method according to claim 5, characterized in that the pressure difference at the metering orifices (17) of the directional control valves (13) are regulated by an associated individual pressure compensator (19) and the system pressure by a system pressure compensator (5).

7. The method according to claim 6, characterized in that the differential pressure of the synchronous pressure compensator (33) is set to a slightly lower value than the differential pressure of the system pressure compensator (5).

8. The method according to claim 6 or 7, characterized in that the pressure difference of the synchronous pressure compensator (33) is set to the pressure difference of Indivdualdruckwaagen (19) or higher.

9. The method according to any one of claims 5 to 8, characterized in that the valve and pump system is dimensioned so that at maximum possible volume flow requirement of the maximum synchronous pressure (Xsyn) does not exceed the biasing force of the centering springs of the control slide (15) ,

10. The method according to any one of claims 2 to 9, characterized in that the supply of the correction signal (Xsyn) is suppressed to preferred consumers.

1 1. A hydraulic system operable according to the method of any one of claims 1 to 10 and comprising:

a) at least one supply device, in particular hydropump (3, 9), which supplies various hydraulic consumers; b) each one associated with each consumer, adjustable metering orifice (17) to supply a dependent on their opening size volume flow of pressure fluid, and c) a synchronizer (33, 35) to a drop of the pressure difference at least one metering orifice (17) under one

Reference value to generate a correction signal (Xsyn), from whose signal value depending on the opening size of all orifices (17) is synchronously reduced.

12. Hydraulic system according to claim 1 1, characterized in that a synchronous pressure (Xsyn) as a correction signal generating synchronous pressure compensator (33) is provided, on the one hand with the pump pressure (P _P u) and on the other hand with the highest load pressure (LSTB) of the system, plus the force of its control spring (37) is applied.

13. Hydraulic system according to claim 12, characterized in that for the control of the supply of the consumer proportional directional control valves (13) are provided whose control slide (15) for the change of the metering orifices (17) by encoder pressure (X.) Is hydraulically controllable, and that the synchronous pressure (Xsyn) via a synchronous channel (35) in parallel with each end face of the spool (15) of all directional control valves (13) is connectable.

14. A hydraulic system according to claim 13, characterized in that each directional control valve (13) changeover valves (43) or a hydraulic logic circuit (Fig. 6) are assigned, via which the respective end faces of the spool (15) a transmitter pressure (X.) Or a Synchronous pressure (Xsyn) can be fed.