EP1701042B1 - Hydraulic control device - Google Patents

Abstract

The hydraulic control device has a pressure regulator (32) pressurized by a constant force (Px) in the opening direction, lower pressure in closing direction downstream of the inlet metering orifice (40,44) and upstream of outlet metering orifice (42,46). The discharge flow of the pump (8) is adjustable as a function of larger of the two pressures.

Description

The invention relates to a hydraulic control arrangement for controlling a consumer according to the preamble of patent claim 1.

From the DE 100 45 404 C2 a control arrangement is known in which a hydraulic consumer, for example a double-acting cylinder for moving a load via a continuously adjustable directional control valve with pressure medium can be supplied. In the pressure medium inlet to the cylinder and in the drain from the cylinder each unlockable check valves are provided, wherein the inlet-side check valve is brought by the pressure downstream of the directional control valve in an open position. The drain-side check valve can be moved by pressing a poppet into an open position, which allows the drainage of the pressure fluid from the consumer to the directional control valve. In this solution, via the drain-side blocking block is a flow control by feedback of the discharge pressure before the flow-determining slide control edge of the continuously adjustable directional control valve on the topping piston of the blocking block.

In the DE 199 31 142 C2 a control arrangement is disclosed in which a supply control via an upstream of the control valve individual pressure compensator. This is acted upon in the opening direction by the force of a spring and the pressure in the inlet to the consumer.

The DE 36 39 174 C2 shows a control arrangement for a single-acting hydraulic consumer, wherein a LS-pressure compensator is connected upstream of a continuously adjustable directional control valve which is acted upon in the closing direction by the force of a spring and by the individual load pressure and in the opening direction by the pressure between the pressure compensator and the directional control valve. The known control arrangement further has a load-compensated unlockable check valve, via which a sequence control can be performed.

In the DE 102 16 958 a hydraulic control arrangement is shown, in which upstream of a Zulaufmessblende an LS-pressure compensator is provided, which is acted upon in the opening direction by the force of a spring and the highest pressure downstream of the Zulaufmessbrende and upstream of a drain metering orifice. In the closing direction, the LS pressure compensator acts on the pressure upstream of the inlet orifice plate.

All vorbeschiebenen embodiments have the common drawback that the inlet cross-section and the flow cross-section of the metering orifices controlling control edges (inlet control edge, flow control edge) must be extremely precisely coordinated.

Another disadvantage of these solutions is that in each case only either the pressure medium volume flow flowing to the consumer or the volume flow flowing from the consumer can be controlled independently of the load. In addition, especially in the control of double-acting cylinders at so-called pulling loads - ie at loads where the pressure in the flow is higher than in the inlet - the risk of undersupply of the inlet-side cylinder chamber. Such undersupply can lead to cavitations, by which the consumer or the associated hydraulic switching elements are damaged. Such a Operating conditions can occur, for example, in a downhill or then when a load is first raised, then overcomes a dead center and then pulling on the hydraulic consumer acts.

To avoid such underpayments of the consumer, for example, suction valves can be used. Due to the comparatively low differential pressure between the suction side and the tank pressure during the suction, however, these valves must have a very large cross-section.

An alternative possibility is to provide biasing valves in the pressure fluid outlet. However, such bias valves are associated with a high energy loss, since the inlet pressure, especially at low loads, must be greatly increased.

Another possibility is to use brake valves. However, these also require a comparatively high pressure on the inlet side in order to control the volume flow on the outlet side and thus to avoid an undersupply of the inlet.

D. h., These known ways to avoid a shortage (Nachsaugventil, preload valve, lowering brake valve) require a considerable circuit complexity and are also associated with energy losses.

In contrast, the invention has for its object to provide a hydraulic control arrangement for controlling a consumer, by which a deficiency can be avoided with little effort and in the pressure medium flow to the consumer and the running of the consumer pressure medium flow rate can be controlled independently of the load.

This object is achieved by a hydraulic control arrangement having the features of patent claim 1.

The hydraulic control arrangement according to the invention is designed with an adjustable inlet and an adjustable flow meter, wherein a pressure in the forward flow pressure compensator is acted upon in the opening direction by a constant force and in the closing direction of the lower of the pressures downstream of the inlet orifice and upstream of the drain orifice. In the pressure fluid outlet a lockable block is provided, which acts as a check valve in the inlet direction and regulates the drainage pressure medium flow rate in the pressure fluid outlet.

Through the interaction of the pressure compensator and the load-compensated blocking block, both the consumer-flowing and the consumer-running pressure medium volume flows can be kept constant independently of the load pressure. In addition, the load can be biased by the pressure compensator and the blocking block of the consumer in all operating conditions, so that the above-mentioned undersupply in the pressure medium inlet is safely avoided.

The bias of the load can be easily adjusted by adjusting the force acting on the pressure compensator in the opening direction constant force to the system.

The solution according to the invention can be realized with very little effort, the additional valve arrangements described above, such as suction valves, Preload valves, lowering brake valves, etc. are not required. Due to the bias of the consumer, air leakage on the suction side can be reliably avoided.

It was further found that in the hydraulic control arrangement according to the invention a lower increase in the inlet pressure is required, so that over conventional solutions, an energy saving is possible.

In a particularly preferred embodiment of the invention, a delivery rate of a pump of the hydraulic control assembly is controlled in response to the greater of the pressures downstream of the metering orifice and upstream of the downcomer orifice. This flow rate is regulated so that in the pump line by a certain pressure difference .DELTA.p above the load pressure lying pump pressure is present (LS system).

The inlet and outlet orifice plates are preferably formed by a continuously adjustable directional control valve whose working connections are connected to an inlet and a drain line and the pressure connection is connected to a flow line and the tank connection to a return line.

The solution according to the invention makes it possible to carry out the feed cross section opened by an inlet control edge greater than the flow cross section opened by a flow control edge or to control the flow cross section later, so that the coordination of the two control edges is simplified due to the lower demands on the inlet control edge. The speed of the consumer is then always determined by the flow cross-section.

The force acting on the pressure compensator constant force is applied in a variant of the invention by acting on a control surface of a pressure compensator piston control pressure. Alternatively, the constant force can also be applied to the pressure compensator piston via a spring or the like.

The adjustment of the bias voltage of the consumer can then be easily changed by adjusting the constant pressure. This can also be lowered by suitable circuit to zero, so that the pressure medium can flow from the consumer, without the pressure medium is conveyed to the inlet.

When controlling a double-acting consumer, such as a differential cylinder unlockable blocking blocks are preferably provided both in the inlet and in the process, each having an actuatable by a control pressure topping piston. The structure of the control arrangement is particularly simple if this control pressure corresponds to the constant control pressure which acts on the pressure compensator in the opening direction.

The smaller pressure downstream of the inlet orifice and upstream of the drain orifice can be tapped via an inverse shuttle valve.

Other advantageous developments of the invention are the subject of further subclaims.

In the following, a preferred embodiment of the invention will be explained with reference to a single figure. This shows a circuit diagram of a hydraulic control arrangement for controlling a double-acting consumer.

Such control arrangements are used in particular for controlling the consumers of a mobile implement, for example in a forklift or a tractor. In the illustrated embodiment, the consumer is designed as a differential cylinder 2, which is connectable via a valve assembly 4 with a pressure medium supply 6.

The pressure medium supply 6 has in the illustrated embodiment, a constant displacement pump 8, is sucked via the pressure medium from a tank T and conveyed into a pump line 10. From the pump line 10 branches off a bypass line 12, in which an inlet pressure compensator 14 is arranged, which is acted upon in the opening direction by the pressure in the pump line 10 and in the closing direction of the highest load pressure of all consumers and the force of a spring 16. This highest load pressure is tapped in a known manner via a shuttle valve cascade of all consumers of the system and is connected via a load reporting line 18 to the inlet pressure compensator 14. The pump 8 can be designed as a fixed displacement pump with speed-controlled drive or as a variable displacement pump.

The flowing back from the cylinder 2 pressure fluid flows depending on the direction of movement of the cylinder 2 via a return line 20 or a return line 22 back to the tank T.

The valve assembly, which is designed for example as a valve disc of a mobile control block, has a pressure port P, a LS port LS, two return ports R and two working ports A, B, the latter via working lines 24, 26 with a bottom-side cylinder chamber 28 and a piston rod side annulus 30 are connected.

As can also be seen from the figure, the two return lines 20, 22 are connected to the two return connections R, the pump line 10 to the pump connection P and the load-signaling line 18 to the LS connection LS. The valve arrangement consists essentially of a pressure compensator, referred to below as individual pressure compensator 32, a continuously adjustable directional valve 34 indicated by dot-dash lines and two unlockable blocking blocks 36, 38. The continuously adjustable directional control valve 34 usually has a directional part prescribing the pressure medium flow direction and a speed part, respectively is formed by an inlet and a drain measuring aperture. In the circuit diagram shown four measuring orifices are shown schematically, but depending on the setting of the directional part only two orifices are effective. D. h., At a pressure medium flow to the working port A, the measuring orifice provided with the reference numeral 40 acts as a metering orifice, while the drain orifice plate is provided with the reference numeral 42, which is effective at a pressure medium flow from the working port B to the tank T. Upon rotation of the flow direction, the measuring orifices, which are furthermore illustrated, then become effective as inlet orifice 44 and as drain orifice 46. The two drain orifices 42, 46 are each arranged in a return channel 48 and 50, which are each connected to one of the return ports R.

The directional valve has two working ports A 'and B', which are connected via a supply line 52 and a drain line 54 to the working ports A, B. The structure of the blocking blocks 36, 38 is known per se, so that detailed explanations are unnecessary. These blocking blocks 36, 38 can be adjusted by means of a poppet piston 56 or 58 from a spring-biased basic position, in each case they act as a check valve in a flow position, which allows a return flow of the pressure medium from the cylinder 2. The actuation of the poppet 56, 58 via a constant control pressure p _x , which is tapped from a suitable control pressure supply. In the opposite direction acts on an annular surface of the poppet piston 58, the pressure (seen in the outflow direction) downstream of the respective blocking block 36, 38 which is tapped via a channel 60 and 62 from the inlet channel 52 and the drain channel 54. As a result of this feedback of the load pressure in the sequence, the blocking block 36, 38 works load-compensated and regulates the pressure in the respectively assigned line, which then acts as a discharge channel independent of the load to a constant value. The blocking block, which is in each case in the inlet, then works as a check valve.

In a connected to the pressure port P of the valve assembly 4 feed channel 64, the individual pressure compensator 32 is arranged, which is acted upon in the opening direction by the constant control pressure p _x and in the closing direction by the force of a pressure compensator spring 66 and a pressure in a message channel 68. This pressure is the lesser of the pressures in the inlet channel 52 and the outlet channel 54, ie, the smaller of the pressures downstream of the inlet metering orifice 40 and upstream of the metering orifice 42 (at a pressure medium flow toward the working port A and from the working port B to the tank T). This pressure is tapped from the inlet channel 52 and from the outlet channel 54 via a respective tapping channel 70, 72, each leading to an input of an inverse shuttle valve 74. Its output is connected to the signaling channel 68.

Of the pickup channels 70, 72 branches off in each case an LS branch channel 76, 78, each with an input of a Shuttle valve 80 are connected, the output of which is connected to the input of another LS shuttle valve 82 of the aforementioned LS Wechselventilkasskade, via which the highest load pressure of all supplied by the pump 8 consumers is tapped. This highest load pressure is then in the load reporting line 18 and acts on the slide of the inlet pressure compensator 14 in the closing direction.

For a better understanding of the invention, the function of the control arrangement according to the invention will now be explained with reference to the extension of the cylinder 2, d. h., The pressure medium is conveyed by the pump 8 via the working port A in the cylinder chamber 28 and displaced back from the annular space 30 via the working port B to the tank T. In this case, the metering orifice 40 acts as an inlet metering orifice and the metering orifice 42 as a drainage metering orifice, the metering orifices 44, 46 are closed.

Principle function

For extending the cylinder 2, the directional control valve 34 is adjusted so that an inlet control edge of the directional control valve 34 opens the cross section of the inlet orifice 40 and accordingly a flow control edge opens the cross section of the drain orifice 42. The directional control valve 34 is designed so that the opening cross-section of the inlet metering orifice 40 is greater than that of the drain metering orifice. The pressure medium then flows via the pressure compensator 32, the function of which will be explained in more detail below, the up-flow meter orifice 40, the inlet channel 52 and the check block 36 acting as a check valve, via the working port A and the working line 24 into the cylinder chamber 28 Pressure medium displaced from the annular space 30 and flows through the working line 26, the working port B and from the constant control pressure p _x opened blocking block 38, the drain passage 54, the open-drain orifice 42, the return passage 50, via the return port R and the return line 22 back to the tank. The pressures in the inlet channel 52 and in the outlet channel 54 are compared via the inverse shuttle valve 74 and the shuttle valve 80. The larger of the two pressures is guided via the shuttle valve 80 as a LS signal to the LS shuttle valve 82 and from there (if no other higher load pressure is present) to an effective in the closing direction control surface of the inlet pressure compensator 14. The smaller of the two pressures is reported via the inverse shuttle valve 74 and the message channel 68 to the individual pressure compensator 32 and compared there with the constant control pressure p _x . By means of this arrangement, the pressure medium volume flow through the inlet channel 52 via the inlet metering orifice 40 is adjusted so that a constant pressure is maintained in the drainage channel 54 before the drainage orifice 42 aufsteuernden flow control. If the smaller pressure tapped via the inverse shuttle valve is greater than the constant pressure p _x (less the force of the compression balance spring 66), then the pressure balance slide of the individual pressure balance 32 restricts the pressure fluid flow more strongly. If the tapped over the inverse shuttle valve 74 smaller pressure is too low, the flow opening of the individual pressure compensator 32 is extended and performed according to more pressure medium to the inlet orifice 40.

Driven load

When the load is driven, the pressure in the inlet channel 52 is greater than the pressure in the outlet channel 54. Apart from the pressure loss via the check block acting as a check valve 36 in the inlet of this larger pressure is passed as LS signal and the inlet pressure compensator 14 so set that the pressure in the pump line 10 by a predetermined pressure difference Ap over this highest load pressure is. The lower pressure on the discharge side is reported to the individual pressure compensator 32 and is about 0 bar when the directional control valve 34 is not actuated. The individual pressure compensator 32 is then fully opened by the constant control pressure p _x . When operated directional control valve 34 as long as pressure medium in the cylinder chamber 28 of the cylinder 2 is promoted until the pressure on the discharge side, ie in the drain passage 54, the value of the constant pressure p _x (minus the force of the pressure compensator spring 66). The pressure compensator slide of the individual pressure compensator 32 reduces the opening cross section of the individual pressure compensator so that the pressure in front of the outflow measuring diaphragm 42 is kept constant.

When the drain metering orifice 42 is opened, the pressure in the discharge passage 54 initially drops, so that the individual pressure compensator 32 opens slightly and the pressure medium volume flow increases via the inlet metering orifice 40 until the pressure in the discharge passage 54 reaches the regulating pressure of the individual pressure compensator again. The pressure medium volume flow on the inlet side is accordingly regulated so that the pressure in front of the drain measuring orifice 42 remains constant at the regulating pressure of the individual pressure compensator 32. The opening cross section of the drain metering orifice 42 thus determines, in conjunction with the control pressure of the individual pressure compensator 32, the pressure medium volume flow. The cylinder 2 is clamped, wherein this clamping force is adaptable by a suitable choice of the control pressure p _x .

Pulling load

When the load is pulled, the pressure in the outlet channel 54 is greater than the pressure in the inlet channel 52. This pressure in the outlet channel 54 is transmitted via the load-compensated blocking block 38 held constant, this value is relatively low. This control pressure of the blocking block 38 is delivered as LS signal via the shuttle valves 80, 82 to the pressure medium supply 6 - the pressure in the pump line 10 is set to a relatively low stand-by pressure.

On the inlet side, i. in the inlet channel 52 initially prevails at a pulling load only a very low or no pressure. This lower pressure is reported via the inverse shuttle valve 74 to the individual pressure compensator 32. This is completely open when the directional control valve 34 is not actuated. If now the directional control valve 34 is actuated and the inlet orifice plate 40 is opened, the pump pressure is sufficient to raise the pressure in the inlet channel 52 to the point where the individual pressure compensator 32 is moved into a control position. If the pressure in the inlet reaches the control pressure of the individual pressure compensator 32, it is controlled. In this way, the inlet-side pressure can be kept at a constant value, which corresponds to the control pressure of the individual pressure compensator 32.

When opening the process control edge, i. when controlling the drain metering orifice 42, the pressure in the drainage passage 54 is throttled by the load compensated locking block 38 from the load pressure in the annulus 30 or in the working line 26 to a constant level in the drainage passage 54 and kept constant. Thus, the moving speed of the cylinder is determined even when pulling load through the opening cross-section of the drain metering orifice 42 in conjunction with the control pressure of the load-compensated blocking block 38.

When the cylinder 2 is moved faster, the pressure in the inlet channel 52 initially drops when the load is pulled, and the pressure in the inlet channel 52 drops accordingly Individual pressure compensator 32 reduces acting pressure, so that this increases its opening cross-section until the pressure in the inlet (inlet channel 52) again the control pressure of the individual pressure compensator 32 is reached. The cylinder 2 thus remains clamped even with pulling load with this control pressure.

By switching off the two blocking blocks 36, 38 and the individual pressure compensator 32 acting in the opening direction constant control pressure p _x , a safety function can be realized, since the two locking blocks 36, 38 act as check valves and the individual pressure compensator 32 is controlled. This safety function can be realized for example by a separate switching valve, via which the constant control pressure p _x can be switched off. This safety function can also be made possible by suitable design of the control edge of the directional control valve 34.

If the constant control pressure is switched off only for the individual pressure compensator 32, then a method of the cylinder 2 is possible without pressure medium being conveyed into the inflow chamber.

The constant control pressure p _x can be varied in order to adapt the pressure gradient across the control edges of the directional control valve 34 and thus the pressure medium volume flow to different operating conditions for a given orifice.

Instead of the constant control pressure p _x and the pressure compensator spring 66, a spring can also be mounted on the left side (view according to the single FIGURE), via which a substantially constant force is applied to the pressure compensator piston of the individual pressure compensator 32 becomes. Other means can be used to keep this force constant.

Disclosed is a hydraulic control arrangement for controlling a hydraulic consumer with an adjustable inlet and an adjustable drain metering and arranged in a pressure medium flow pressure compensator. The control arrangement further has a releasable locking block, which acts as a check valve in the inlet direction and in the drain direction by means of a control pressure can be unlocked. According to the invention, the pressure compensator is acted upon in the opening direction by a constant force and in the closing direction by the lower of the pressures downstream of the inlet metering orifice and upstream of the outflow metering orifice.

LIST OF REFERENCE NUMBERS

2

cylinder

4

valve assembly

6

Pressure medium supply

8th

fixed displacement pump

10

pump line

12

bypass line

14

Inlet pressure

16

feather

18

Load-sensing line

20

Return line

22

Return line

24

working line

26

working line

28

cylinder space

30

annulus

32

Individual pressure compensator

34

way valve

36

locking block

38

locking block

40

Supply measuring orifice

42

Drain measuring orifice

44

Supply measuring orifice

46

Drain measuring orifice

48

Return channel

50

Return channel

52

inlet channel

54

drain channel

56

topping

58

topping

60

channel

62

channel

64

forward channel

66

Compensator spring

68

signaling channel

70

Abgreifkanal

72

Abgreifkanal

74

inverse shuttle valve

76

Zweigkanal

78

Zweigkanal

80

shuttle valve

82

LS shuttle valve

Claims (10)

1. A hydraulic control arrangement for controlling a hydraulic consumer 8"9, comprising an adjustable supply measuring orifice and an adjustable drain measuring orifice (40, 42; 44, 46), a pressure compensator (32) arranged in a pressure medium delivery for controlling the pressure medium volume flow across the supply measuring orifice (40, 42) and comprising at least one releasable cut-off block (36, 38) that acts as a check valve in direction of supply and is releasable by means of a control pressure (p_x) in the direction of drain, characterized in that the pressure compensator (32) is subjected to a constant force (p_x) in the opening direction and to the lower one of the pressures downstream from the supply measuring orifice (40, 44) and upstream from the drain measuring orifice (42, 46).
2. The control arrangement in accordance with claim 1, wherein a flow rate of a pump (8) is adjustable in dependence on the higher one of the two pressures.
3. The control arrangement in accordance with claim 1 or 2, wherein the drain measuring orifice and supply measuring orifice (40, 42; 44, 46) are formed by a continuously adjustable directional control valve (34) .
4. The control arrangement in accordance with claim 3, wherein the supply cross-section controlled open by a supply control edge is larger than the drain cross-section controlled open by a drain control edge.
5. The control arrangement in accordance with any one of the preceding claims, wherein the constant force is applied by a control pressure (p_x) acting on a control surface of the pressure compensator (32) and/or by a spring.
6. The control arrangement in accordance with claim 5, first alternative, wherein the constant pressure (p_x) may be varied or reduced to Zero.
7. The control arrangement in accordance with any one of the preceding claims, wherein in the supply and in the drain a respective releasable cut-off block (36, 38) is arranged which includes a topping piston (56) adapted to be actuated by a control pressure.
8. The control arrangement in accordance with claim 7, wherein the topping piston (56) is subjected to the pressure in the drain in the direction opposite to the control pressure.
9. The control arrangement in accordance with claim 7 or 8, wherein the control pressure corresponds to the constant control pressure (p_x).
10. The control arrangement in accordance with any one of the preceding claims, wherein the lower pressure is tapped via an inverse shuttle valve (74).

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