EP1588057B1 - Hydraulic system for linear drives controlled by a displacer element - Google Patents

Abstract

The invention concerns a hydraulic system for linear drives with a differential cylinder, in particular for mobile machines which through the use of displacement-control of the drives avoids the many and diverse disadvantages of the state of the art and renders possible a precise and energy-efficient control of linear drives with differential cylinders, and which is economical and simple to maintain and which can be well integrated into the total hydraulic system of such machines.

Description

The invention relates to a hydraulic system for displacer-controlled linear drives, in particular for mobile machines with at least one differential cylinder, at least one high pressure circuit, which includes at least one pump with adjustable flow and is connected by at least two unlockable check valves with a low pressure system.

Hydraulic systems for mobile machines today rely predominantly on valve-controlled principles. In this case, the various hydraulic consumers, such as drives of the working hydraulics, steering, braking u.a. controlled. Usually, one or more central pressure supplies, often in the form of load-sensing pumps, are used for this purpose, which provide pressure medium flows which are influenced by single or multi-stage valve arrangements in accordance with the desired behavior of the hydraulic consumers.

A disadvantage of these valve-controlled hydraulic systems is in particular the poor energy efficiency. In order to achieve the required pressure fluid flows, pressure differences are required at the throttle edges of the valves, which in principle leads to high energy losses in hydraulic valve controls. It is not possible to use energy surpluses at a consumer of the system in the form of potential energy or braking energy for other consumers in the system and thereby improve the system efficiency, which further deteriorates the heat generation in the system. A central pressure medium supply also has the disadvantage that in the case that several consumers must be operated simultaneously, the volume flows are divided, which complicates the precise control and operation of the individual components. Safety-relevant circuits in which it must be ensured that individual consumers, such as the steering or brake, always have enough pressure fluid available, for example, must always be implemented on complicated priority valve arrangements. A simultaneous movement of several consumers in the system leads to a different system behavior compared to single movements. All this leads to very complex and thus cost and maintenance-intensive valve arrangements whose possibilities are limited in terms of controllability and energy utilization.

Occasionally, displacement-controlled systems for rotary drives are also used, in which a pump adjustable in the displacement volume is used to control or regulate the movement of the hydraulic motor (s). The consumer is thus controlled solely by the volume flow provided by the pump, without the use of a control valve or the like in the main circuit. In the transmission of this control principle to linear actuators with differential cylinder, the problem arises that the cylinder volume is different on both sides of the cylinder piston and thereby occur in the movement of differential flow, which must be compensated by different known solutions.

However, the previously known such displacement-controlled systems are extremely inflexible, have a large number of additional components or displacement units and do not provide the functional scope and system simplicity that is necessary for use in mobile machines (eg DE 40 08 792 A1, DE 27 06 091 A1, CA 605 046, DT 23 49 351 so-Rahmfeld and Ivantysynova 2000, energy-saving controlled linear drive with differential cylinder, 2nd IFK, p 191-205, Dresden).

The object of the invention is therefore to provide a hydraulic system for linear drives with differential cylinder, especially for mobile machines, which avoids the manifold disadvantages of the prior art by the use of a displacement control of the drives and allows precise energy-efficient control of linear drives with differential cylinders, cost and easy to maintain and integrate well into the overall hydraulic system of such machines.

This object is solved by the characterizing features of claim 1.

The check valves are located between the two high-pressure lines, which lead from the adjustable in their flow pump to the differential cylinder, and the common low-pressure system. If a volume flow is generated by the adjustable pump and thereby the differential cylinder is moved, the occurring depending on the direction of movement of the piston, positive or negative differential flow can flow into the low-pressure system and be sucked out of this. In the case of the intake of volume flow from the low pressure system, the corresponding check valve opens automatically. In the case of outflow from the flow to the low pressure system, the corresponding check valve is released from the system high pressure.

For the realization of a floating position, the two sides of the Differential cylinder hydraulically connected to each other, whereby a free movement of the piston is made possible. For this purpose, the check valves are unlocked, so that pressure medium can flow through them regardless of the pump volume flow in both directions. The differential volume flow is compensated in this case also by the low pressure system.

According to the invention, the hydraulic system provides that the electronic Control device for controlling the check valves has an electro-hydraulic 4/2-way valve. By such a valve, the Entsperr- connection of the check valves can be alternately connected to one or the other side of the high pressure circuit, which corresponds to a switching between the normal differential volume compensation and the floating position of the differential cylinder. This results in the valve position of the check valves according to the direction of movement and the applied load and thus the pressure conditions in the cylinder. This creates a secure possibility to change the operating states, whereby the risk of pressure surges is minimized.

Alternatively, two electro-hydraulic 3/2-way valves can be used.

The use of an electronic control for switching the check valves allows the valves unlock, for example, at the request of the operator and thus the floating position is realized. In addition, however, it offers the advantage that such switching occurs only when certain pressure conditions prevail in the high-pressure circuit, so that shocks or other undesirable conditions are prevented and supporting the load present on the differential cylinder is always safely avoided. Such a control device also allows further functions of such a displacement-controlled circuit, which are described in more detail in the following subclaims.

Thus it can be provided that the control device for controlling the pump delivery rate is electronically formed. The flow rate of adjustable pumps is usually controlled electro-hydraulically. Therefore, it is particularly advantageous if this control is applied integrated with the control device of the check valves, so that a safe and accurate control of the complete circular behavior is possible. Thus, for example, prevent the pump promotes a volume flow when unlocking the check valves, which would then be closed by the unblocked check valves short.

A particular embodiment of the hydraulic system provides that a controllable shut-off valve is provided on at least one connection of the differential cylinder. By such a shut-off valve, a connection of the cylinder can be shut off leak-free, which is useful in particular for the realization of a holding function. In this case, the cylinder is brought by the volume flow of the pump in a certain position and then shut off the high-pressure port of the differential cylinder, so that this remains in its position, even without the pump maintains the pressure. If a shut-off valve is also provided at the second port of the differential cylinder, the cylinder can be completely disconnected from the hydraulic circuit while remaining in position. By the pump and the connected hydraulic circuit, a further differential cylinder can be operated in this state, which is then also separable via shut-off valves from the circuit. This can be easily and inexpensively another function in the Implement working machine, which can be operated alternatively by the other existing cylinders.

Advantageously, it may be that the low pressure system is designed as a storage charging circuit with a storage charging valve, a pump with hydraulic accumulator and a pressure relief valve. Such a design of the low-pressure side is characterized by a particularly high energy efficiency. The pump only delivers to the low-pressure system when it falls below a set minimum pressure value. The storage charging circuit ensures that a low pressure level is maintained between adjustable limits. Such a low-pressure system can be designed centrally for the entire hydraulic system and supply all displacer-controlled hydraulic circuits according to the invention.

A further embodiment of the hydraulic system according to the invention is characterized in that the controllable shut-off valve is designed as a seat valve with 3/2-way pilot control. In addition, it may be useful that the controllable shut-off valve is designed as a continuous valve. With such a valve, it is easy to realize the corresponding blocking function of the connection without the valve opening or closing being too jerky. This can prevent unwanted pressure peaks in the system.

Advantageously, it may be that further optionally controllable shut-off valves are provided for alternative and / or simultaneous control of additional differential cylinders. As described above, can be realized by such valves further functions on the same high-pressure circuit, which are always alternatively to each other in operation. The shut-off valves are switched so that the pump with the associated protection and compensation valves each connected to a differential cylinder or more parallel connected the same function and supplies them with pressure medium.

A further embodiment of the invention provides that at the Hochdruckkeis connections are provided for a passive vibration damping system. Such damping systems consist of a hydraulic circuit with memory, which reduces the vibrations of the implement occurring, for example, when driving with a raised load. For this purpose, the vibration damping system is connected directly to at least one connection on one side of the high-pressure circuit and can be switched on and off in order to suppress the undesirable vibration states in desired operating situations.

In one embodiment of the invention it is provided that the electronic control device, the controllable valves and possibly further existing hydraulic system components are formed with the adjustable pump as an integrated component.

Such integration of the pump with a number of the valves and the controller offers the advantage of an extremely compact design, which may be useful because these components are necessary for any hydraulic function driven by differential cylinder systems. The integration reduces the number of individual components, reduces the complexity of the overall system, reduces the installation effort and thus reduces the cost of such a system compared to conventional systems.

It may be advantageous for the control and regulation concepts that sensors for detecting the system states, in particular the differential cylinder position and the hydraulic pressures, are provided.

In addition, it may be useful that an electronic control device is provided for controlling the controllable system components depending on the measured system status and user preferences.

By measuring the system states and processing the data obtained in a control device, the linear cylinders can be operated in a closed loop, which significantly improves the positioning accuracy and the stability of the system.

The drive system according to the invention can also be controlled, i. operate in an open chain.

The invention is also directed to a mobile work machine having at least one hydraulic system as described above. In one embodiment of such a work machine several high-pressure circuits are provided with a common low-pressure circuit. This has, as already explained, the advantage of additional cost savings, since a single low pressure circuit with a pump and the other components to supply all hydraulic systems of the invention is sufficient.

Fig. 1:

eine schematische Grundschaltung eines Hydrauliksystems nach der Erfindung,

Fig. 2:

eine Schaltung eines erfindungsgemäßen Hydrauliksystems in einer erweiterten Ausführung,

Fig. 3:

eine weitere Ausführung,

Fig. 4:

noch eine weitere Ausführung,

Fig. 5 :

ein Gesamtsystem für eine mobile Arbeitsmaschine und in

Fig. 6:

ein weiteres Gesamtsystem für eine mobile Arbeitsmaschine.

The invention is explained in more detail below with reference to the drawings by way of example. These show in:

Fig. 1:

a schematic basic circuit of a hydraulic system according to the invention,

Fig. 2:

a circuit of a hydraulic system according to the invention in an expanded version,

3:

another version,

4:

yet another version,

Fig. 5:

a complete system for a mobile work machine and in

Fig. 6:

another overall system for a mobile work machine.

A generally designated 1 hydraulic system is used to control a hydraulic differential cylinder. 2

A pump 3 with adjustable delivery volume and reversal of the conveying direction is connected via two lines 4 and 5 with the two terminals of the differential cylinder 2.

A volume flow delivered by the pump 3 in one direction or the other leads to a movement of the piston 6 of the differential cylinder 2. Since the two chambers of the hydraulic differential cylinder 2 have a different volume due to the asymmetrical design of the piston 6 and the piston rod, respectively on a movement of the piston 6, a different amount of the pressure medium is discharged on one side than is absorbed by the other side. In order to compensate for this difference in volume flow in the actually closed circuit between the pump 3 and cylinder 2, this high-pressure circuit is connected via two pilot-operated check valves 7 and 8 to a low-pressure system 9.

In the stationary case, the opposing check valve 7 or 8 between the high pressure line and low pressure system 9 is unlocked by the higher pressure, in one of the two lines 4 and 5, so that always the low pressure side of the hydraulic differential cylinder 2 is connected to the low pressure system 9. If a volume flow to the differential cylinder 2 is conveyed by the adjustable pump 3, this leads to a movement of the piston 6 of the differential cylinder 2. The positive or negative differential volume flow dependent on the direction of movement is compensated via one of the two non-return valves 7 or 8 with respect to the low-pressure system 9. For this basic position is one with the check valves 7 and 8 connected electro-hydraulic 4/2-way valve 10 is switched so that the unlocking of the check valves 7 and 8 are each connected to the opposite part of the high pressure circuit. As a result, a takeover of the differential flow compensation by the other valve without pressure spikes is guaranteed even with a change of the load condition on the differential cylinder 2, since the check valves 7 and 8 always switch exactly when it rests on both sides of the check valve about low pressure.

The electronically controllable 4/2-way valve 10 also serves to realize a floating position function. If the valve 10 is switched over (floating position function), the unlocking connections of the check valves 7 and 8 are no longer connected to the opposite, but with the lying in the direction of their passage side. As a result, the check valves 7 and 8 open as soon as in one of the two lines 4 or 5, a pressure is applied, which is slightly higher than the low pressure in the low pressure system 9. Thus, the piston 6 in the differential cylinder 2 can move freely. It makes sense, when switching the 4/2-way valve 10 in the floating position, the pump 3 is set so that it does not promote flow, since this would also be compensated by the quasi-short circuit through the check valves 7 and 8 respectively.

At a connection of the differential cylinder 2, a controllable shut-off valve 11 is provided. Thus, this side of the differential cylinder 2 can be shut off without leakage, whereby the piston 6 is fixed in this position and a load located thereon is held. As a rule, this is the more heavily loaded piston side of the differential cylinder. 2

The system contains pressure sensors 12 which are used to detect the conditions in serve the high pressure lines. At the hydraulic differential cylinder 2 is a displacement sensor 13 or an angle sensor in the kinematics of the working equipment, which detects the piston position. The signals of the sensors 12 and 13 are processed by an electronic control device 14 together with predetermined by user controls corresponding 15 user requests and determines the corresponding manipulated variable, which is forwarded to the electronic control device 16. This then controls the adjustable pump 3 in its displacement volume and thus the funded volume flow and possibly the switching states of the electronic valves 10 and 11 respectively.

An extension of this basic principle is shown in Fig. 2 in more detail. In this case, a hydraulic differential cylinder 2 is again connected substantially directly with an adjustable pump 3. The differential flow is compensated in promotion by the two pilot operated check valves 7 and 8, the Entsperranschlüsse of an electro-hydraulic 4/2-way valve 10 are each alternately connected to the opposite or adjacent sides of the high pressure circuit.

To protect the system from overpressure two Hochdruckabsicherungen 27 are provided. The integrated electronic control device 14 controls the control of the individual components, such as the adjustable pump 3, taking into account the measured system states and the user preferences 15th

In addition to the electronically controllable shut-off valve 11, the second side of the differential cylinder 2 can also be shut off by an electronically controllable shut-off valve 17. In addition, two additional electronically controllable shut-off valves 18, an additional differential cylinder 19 on High pressure circuit connected.

During operation of the second differential cylinder 19, the first differential cylinder 2 is separated by the two shut-off valves 11 and 17 from the hydraulic circuit and thereby held in position. Subsequently, the two shut-off valves 18 are opened so that a volume flow delivered by the pump 3 moves the second differential cylinder 19. The difference volumes occurring are compensated again via the two pilot-operated check valves 7 and 8 in the low-pressure circuit 9. The controllable shut-off valves 11, 17 and 18 may be formed in some cases as a continuous valves, so that they can be controlled continuously in particular situations during operation and thus a simultaneous operation of the two differential cylinders 2 and 19 is possible.

The low pressure in the low-pressure system 9 is realized with a storage charging circuit. In this case, a fixed displacement pump 20 with a storage charging valve 21 and a hydropneumatic accumulator 22 is used. A pressure relief valve 23 protects the system against overload. In this case, the accumulator charging valve 21 ensures that the constant displacement pump 20 promotes into the low-pressure system 9 only when a set minimum value of the pressure is reached. Since the accumulator charging valve 21 ensures pure printer maintenance, the system can be implemented in an energy-efficient manner. But other combinations for the realization of the low-pressure system 9 are possible, for example via a simple combination of fixed displacement pump, memory and pressure relief valve or by means of a variable. This low pressure is also used behind the port 24 of the variable displacement pump 3 to operate the electro-hydraulic adjustment system of this pump. The terminals 25 and 26 serve to connect a passive vibration damper system on the differential cylinder 2.

In Fig. 3, a first modification of the basic principle is shown, in which instead of the electro-hydraulic 4/2-way valve two 3/2-way valves 28, 29 are used to realize the floating position by switching the Entsperranschlüsse the pilot-operated check valves 7, 8 , Furthermore, the low pressure is now impressed via a constant displacement pump 20 with a hydropneumatic accumulator 22 and a pressure relief valve 23. 4, a further modification of the basic principle is shown. The floating position is realized via a bypass by two valves 30, 31, i. when energizing the valves, the two cylinder chambers are connected to the low pressure and the differential cylinder 2 can move freely. The low pressure is impressed here via a variable displacement pump 20 'with a hydropneumatic accumulator 22 and secured via a pressure relief valve 23. In addition, this scheme also shows another way to provide the third function with the pump 3. Two 3/2-way valves 32, 33 at ports 34, 35 can simply switch the pump 3 to the third function when activated.

Fig. 5 shows an overall system for a mobile work machine (here wheel loader) with displacement-controlled working hydraulics according to the above-described displacement-controlled linear drive principle (valveless principle) and hydrostatic drive. The simple coupling of several actuators via the low pressure and with the hydrostatic drive reduces the system complexity again.

In Fig. 6, another overall system (here wheel loader) is shown, in which case there is a hydrostatic drive in the 2- engine concept with decoupled adjustment and the low pressure for all displacement-controlled Main functions is impressed by the return of the hydrostatic fan and a memory. An accumulator charging valve connects the return of the fan to the low pressure only when low pressure volume flow is needed.

By electrohydraulic control of the adjustable pump 3, all other functionalities that are backed by software, can be realized, such as fork parallel guide, automatic return, Hubendabschaltung, variable blade stop, variable damping cylinder (soft dust), shaking or distribution functions on the blade for agricultural Inserts, etc. The respective variable displacement pump is addressed directly via the controller of the device. In this case, the displacer-controlled actuator can be operated both in position control and in speed control (example: parallel tool guide) or also in open-loop control. The controller processes the input of the operator (eg via a joystick).

Of course, the invention is not limited to the above example, but in many ways modifiable without departing from the spirit. Thus, a variety of designs for the pumps, valves, etc. are conceivable as long as they fulfill the functions claimed. The separation of the functions of individual valves on several components is conceivable and may make sense. It is also possible to operate additional cylinders via shut-off valves on the same high-pressure system.

LIST OF REFERENCE NUMBERS

1

hydraulic system

2

differential cylinder

3

pump

4

management

5

management

6

piston

7

check valve

8th

check valve

9

Low pressure system

10

4/2-way valve

11

controllable shut-off valve

12

pressure sensor

13

displacement sensor

14

electronic control device

15

operating element

16

electronic control device

17

shut-off valve

18

shut-off valve

19

differential cylinder

20

fixed displacement pump

20 '

variable

21

Accumulator charging valve

22

hydropneumatic storage

23

Pressure relief valve

24

connection

25

connection

26

connection

27

High pressure protection

28

3/2-way valve

29

3/2-way valve

30

Valve

31

Valve

32

3/2-way valve

33

3/2-way valve

34

connection

35

connection

Claims (14)

1. A hydraulic system for displacer-controlled linear drives, in particular for mobile working machines, comprising at least one differential cylinder which is arranged in a closed high pressure circuit with at least one pump with an adjustable delivery amount and with reversal of the delivery direction, wherein to compensate for the differential volume flow the high pressure circuit is connected to a low pressure system by at least two openable non-return valves, wherein the respective non-return valve which is opposite to the high pressure side of the high pressure circuit is opened by the high pressure,
   characterised in that the non-return valves (7, 8) are connected to an electronic control device (16) in such a way that switching surge-free change-over between retraction or extension of the differential cylinder (2) and a floating position is possible, and that to provide that floating position of the differential cylinder (2) an electrohydraulic 4/2-way valve (10) or a respective electrohydraulic 3/2-wave valve (28, 29) is arranged between the high pressure circuit and the openable non-return valves (7, 8).
2. A hydraulic system according to claim 1 characterised in that the low pressure system (9) is in the form of a storage device charging circuit with a storage device charging valve (21), a pump (20) with a hydraulic storage device (22) and a pressure limiting valve (23).
3. A hydraulic system according to claim 1 characterised in that the low pressure system (1) is provided with a pump (20) with a hydraulic storage device (22) and a pressure limiting valve (23).
4. A hydraulic system according to claim 1, claim 2 or claim 3 characterised in that the electronic control device (16) is adapted to regulate the delivery amount and the delivery direction of the pump (3) of the high pressure circuit.
5. A hydraulic system according to one of the preceding claims characterised in that a controllable shut-off valve (11) is provided at at least one connection of the differential cylinder (2).
6. A hydraulic system according to claim 5 characterised in that the controllable shut-off valve (11) is in the form of a seat valve with 3/2-way pilot control.
7. A hydraulic system according to claim 5 characterised in that the controllable shut-off valve (11) is in the form of a continuous valve.
8. A hydraulic system according to one of the preceding claims characterised in that there are provided further, optionally continuously controllable shut-off valves (17, 18) for alternative and/or simultaneous actuation of further differential cylinders (19).
9. A hydraulic system according to one of the preceding claims characterised in that provided on the high pressure circuit are connections (25, 26) for a passive oscillation damping system.
10. A hydraulic system according to one of the preceding claims characterised in that the electronic control device (16), the 4/2-way valve (10) and the shut-off valve (11) and optionally further hydraulic system components that may be present are in the form of an integrated unit with the pump (3) of the high pressure circuit.
11. A hydraulic system according to one of the preceding claims characterised in that there are provided sensors (12, 13) for detecting the system conditions, in particular the differential cylinder position and the hydraulic pressures.
12. A hydraulic system according to claim 11 characterised in that there is provided an electronic regulating device (14) for regulating the controllable system components in dependence on the measured system condition and user presettings.
13. A mobile working machine comprising at least one hydraulic system according to one of claims 1 to 12.
14. A mobile working machine according to claim 13 characterised in that there are provided a plurality of high pressure circuits with a common low pressure system.

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