EP1987256B1 - Control device and hydraulic pilot control - Google Patents

Abstract

A control device for controlling a hydraulic consumer, is equipped with a distributing valve having a control pressure chamber and a control slide that can be displaced against the force of a spring by the build-up of a control pressure in the control pressure chamber. A pilot control valve controls the supply and discharge of control fluid into and out of the control pressure chamber. A release device is used to drive the control fluid out of the control pressure chamber, bypassing the pilot control valve.

Description

The invention relates to a control device for controlling a hydraulic consumer with a hydraulically actuated directional control valve according to the preamble of patent claim 1.

Such a control device is off DE 4137963 A1 known.

Hydraulic control devices with hydraulically actuated directional control valves are used, inter alia, in vehicle hydraulic systems. Appropriately, several directional control valves in the form of valve disks are linked in a so-called control block. With such a hydraulic control device lifting devices of a lift truck or a tractor, loading cranes, the blade of a wheel loader, but also driving and steering functions of a vehicle are operated hydraulically. In the case of a demand-current-controlled (load-sensing) control, individual valve disks have a pressure compensator for controlling the hydraulic pressure medium flow flowing through the valve.

As hydraulic fluid or pressure medium is used in industrial and mobile hydraulics mostly mineral oil. For certain applications, however, a water-based pressure medium is used. In the following, the term fluid is used for hydraulic fluids.

A hydraulic control device is for example from the DE 197 15 020 A1 known. In various valve disks directional control valves for controlling hydraulic consumers are arranged. The directional control valves have valve pistons for controlling pressure medium connections and two spring chambers each. In a spring chamber, a control pressure is built up to actuate the valve piston against the spring preload. The respective control pressure is generated by an electrically operated pressure control valve. For a valve disc two pressure control valves are each provided as pilot valves. This allows the valve piston to deflect in two opposite directions. The electrical control of the pressure control valves is usually carried out by means of a control element.

In rare cases, electrically controlled pressure control valves fail because the control piston of the pressure control valve jams and can no longer be operated electrically. One reason for this may be dirt particles entrained in the fluid flow. The control piston is just in the control position, in which the output of the pressure control valve is shut off against the control fluid supply port and the tank port, so can no longer displace control fluid from the corresponding spring chamber of the directional control valve. The directional control valve is thus blocked in the activated position and the movement executed by the hydraulic consumer can not be stopped. Even by countermeasures (Kontem) on the control element, whereby the opposite spring chamber is acted upon by the corresponding pressure control valve with control pressure, such a blockade can not solve because of the shut-off spring chamber, as I said, no fluid can be displaced.

The DE 103 08 910 A1 deals with a safety valve, which is integrated in the supply line of pilot valves. The described, electromagnetically actuated 3/2-way valve can connect the supply line of the pilot valves either with a Druckmitteiquelle or with a container. The valve spool of the 3/2-way valve has a discharge channel from the outlet connection to the spring chamber. When the magnet is actuated, the discharge channel is shut off by the magnetic plunger. With unactuated magnet, the discharge channel to the spring chamber and thus to the container is open, unless the valve slide does not follow the magnetic plunger. A disadvantage of this valve is the complex construction. The design can not be readily transferred to trained as a pressure reducing valves pilot valves. In addition, the supply line can not be relieved, if there is a continuous operation by a fault in the control electronics of the 3/2-way valve.

It is the object of the present invention to provide an improved control device for controlling a hydraulic consumer, which reliably allows the valve piston of a pilot-operated directional control valve to be returned from an actuation position to a neutral position and which is characterized in particular by a simple, cost-effective design.

This object is achieved by a control device with the feature of claim 1.

The control device according to the invention for controlling a hydraulic consumer is equipped with a directional control valve, which has a control pressure chamber and a spool, which is adjustable by establishing a control pressure in the control pressure chamber against the force of a spring. A pilot valve controls the inflow and outflow of control fluid into and out of the control pressure chamber. It is the peculiarity of the present invention that a relief device is provided, by means of which the control fluid can be displaced from the control pressure chamber, bypassing the pilot valve.

In this way, the control device according to the invention reliably allows the return of the spool from the actuated position. In normal operation, the directional control valve is controllable like a conventional directional control valve. In a disturbance of the pilot valve, wherein the outflow of control fluid is blocked from the control pressure chamber via the pilot valve, the spool can still be moved from the actuated position. Thus, such a control device on a high reliability. Not only with a jamming of the control piston of the pilot valve but even with a continuous operation of the pilot valve by an error in its electrical drive circuit, the spool of the directional control valve can be returned to the neutral position or even operated in a reverse direction. The control device according to the invention is also easy and inexpensive to implement. The bypass of the pilot valve is in particular by means of cheap standard components, such as check valves or pressure relief valves, representable.

In addition, according to the present invention, a hydraulic pilot control device has a control fluid supply port and at least one pressure control valve that generates a regulated control pressure at a control pressure output. Between the control pressure output and the control fluid supply port, a check valve opening toward the control fluid supply port is provided.

Such a pilot control device allows the reliable displacement of control fluid from a control pressure chamber, bypassing the pressure control valve. As a result, the reliability of a hydraulic control device can be increased. In addition, such a pilot control device is particularly simple and requires compared to a conventional pilot control device only a few additional components.

The relief device comprises a relief line and a check valve, via which control fluid from the control pressure chamber can be displaced into the relief line. As a result, a particularly uncomplicated design relief device is specified. The behavior of the discharge device can be easily controlled by means of a pressure prevailing in the discharge line pressure.

Further advantageous embodiments are specified in the subclaims.

Preferably, the discharge line via a pressure relief valve with a tank can be connected. Thus, a pressure necessary to bypass the pilot valve can be easily adjusted at the pressure relief valve. This pressure is further adjustable independently of the pressure of the control fluid supply line. If the pressure limiting valve can be actuated manually, a venting of the control pressure chambers can be carried out in a simple manner.

According to a further preferred embodiment, the discharge line is in fluid communication with a control fluid supply line of the pilot valve. Such a designed control device allows a particularly simple and efficient protection of a control pressure chamber against blocking of the fluid drain. In addition, corresponds to the circumvention of the Pilot valve pressure always the supply pressure of the control fluid supply line, so that it does not have to be set separately.

Preferably, the pressure in the discharge line can be limited to a value which is equal to or higher than the pressure that the pilot valve can set at its output at most. This ensures that in a normal control of the directional control valve no displacement of control fluid in the discharge line takes place.

According to a further preferred embodiment, the pressure in the discharge line is limited to a value which is less than the sum of the maximum control pressure and a pressure corresponding to a biasing force of the spring. In this way, the force required to return the spool from the actuated position can be applied by the hydraulic action of the spool, e.g. by pressurizing an oppositely arranged control pressure chamber. If the same pressure prevails in both control pressure chambers, the control spool returns to a neutral position with the aid of its counteracting springs.

If the relief line is relieved by a switching valve to a tank, the spool returns without further action and very quickly in a neutral position. It can be deflected by pressurizing an oppositely arranged control pressure chamber even in a reverse direction.

Preferably, the directional control valve has two control pressure chambers, through which the spool can be acted upon in mutually opposite directions. Further, from the two control pressure chambers control fluid via a separate check valve in two different branches of the discharge line displaced, the two different branches of the discharge line are fluidly separated from each other, and there are two switching valves available over the branches of the discharge line independently relieved to a tank are. As a result, the different branches of the discharge line and thus the connected control pressure chambers can be relieved independently of each other in the event of a defect of the pilot valve. This is an important prerequisite for the realization of a safe drive, which allows not only to stop a hydraulic motor in case of failure of the pilot valve but also to perform a retraction movement. In particular, a defective pilot valve can be bypassed or the one control pressure chamber can be relieved, and by a further pilot valve, the oppositely disposed control pressure chamber are pressurized, so that a hydraulic valve controlled by the directional control valve executes a retraction movement.

Preferably, control fluid from two different branches of the discharge line to a pressure relief valve via a respective check valve, which opens to the pressure relief valve, fed. Thus, by a simple, efficient design of the control device oppositely arranged Steuerdruckkammem the directional control valve to prevent blocking of the pilot valves. By pressurizing an opposing control pressure chamber can also control fluid from a control pressure chamber, the pilot valve fails to be displaced. Thus, it is possible to stop a hydraulic load in case of failure of a pilot valve by counter-controlling the control. In addition, the branches of the relief line may additionally be separated from each other by e.g. a switching valve are relieved, so that a return movement of a hydraulic motor is executable despite a defect of the pilot valve.

Preferably, a plurality of directional control valves are provided, wherein from each control pressure chamber of the various directional valves control fluid via a respective separate check valve in a discharge line - or a branch of the discharge line can be displaced. In this way, the control pressure chambers can be efficiently protected against failure of the pilot valves even for several directional control valves.

Hereinafter, the present invention and its advantages will be explained with reference to the embodiments illustrated in the figures.

Fig. 1

eine Seitenansicht einer Wegeventilscheibe eines Hydrauliksteuer- blocks -teilweise als Schnittbild - mit einer zusätzlichen Fluidleitung, über die Steuerfluid aus den Steuerdruckkammem verdrängbar ist,

Fig. 2

ein Schaltbild einer hydraulischen Steuervorrichtung mit zwei Wege- ventilen, die auf die in Fig. 1 dargestellten Weise gegen ein Blockieren des Fluidabflusses aus den Steuerdruckkammem abgesichert sind und die zusätzlich eine manuell betätigbare Entiüftungsfunktion auf- weisen,

Fig. 3

ein Schaltbild einer hydraulischen Steuervorrichtung mit zwei Wege- ventilen, und zwei Zweigen einer Entiastungsleitung, die unabhängig voneinander durch Schaltventile entlastbar sind, und die außerdem über ein Druckbegrenzungsventil Steuerfluid zum Tank abführen kön- nen,

Fig. 4

ein Schaltbild einer hydraulischen Steuervorrichtung, bei der Steu- erfluid aus den Steuerdruckkammern in die Steuerfluidversorgungs- leitung verdrängbar ist, und

Fig. 5

eine Seitenansicht einer Wegeventilscheibe eines Hydrauliksteuer- blocks - teilweise als Schnittbild - in einer dem Schaltbild der Fig. 4 entsprechenden Ausführung.

Show it:

Fig. 1

a side view of a directional control valve disk of a Hydrauliksteuer- block -partially as a sectional view - with an additional fluid line, via the control fluid from the Steuerdruckkammem is displaceable,

Fig. 2

a circuit diagram of a hydraulic control device with two-way valves, on the in Fig. 1 are secured against blockage of the fluid outflow from the control pressure chambers and additionally have a manually actuatable ventilation function,

Fig. 3

a circuit diagram of a hydraulic control device with two-way valves, and two branches of Entiastungsleitung which are relieved of pressure independently by switching valves, and also can dissipate via a pressure relief valve control fluid to the tank NEN,

Fig. 4

a circuit diagram of a hydraulic control device, wherein the control fluid is displaceable from the control pressure chambers in the control fluid supply line, and

Fig. 5

a side view of a directional valve disk of a Hydrauliksteuer- block - partly as a sectional image - in a circuit diagram of Fig. 4 corresponding execution.

The present invention will now be described with reference to FIG. 1 using a directional control valve disc as used in a hydraulic control block. However, the invention is not limited to this specific type of hydraulic control device but can be used in hydraulic control devices of almost any type.

In the Fig. 1 illustrated valve disc 1 has a base body 3 with a valve bore 25 within which a spool 26 is movably guided. Through the valve bore 25 and the spool 26 different control edges are formed, can be controlled by the fluidic connections between a fluid supply port 10 and the terminals 22, 23 for a hyraulische consumer. Likewise, connections between the consumer connections 22, 23 and tank connections 12. 13 are controllable.

The illustrated valve disc is designed using load-sensing technology. Thus, the load applied to the load terminals 22 and 23 load pressure is detected and fed to a load pressure signaling line 16. The details of the load-sensing technique are not relevant to the present invention and are therefore not described in detail. However, the skilled person is familiar with the load-sensing technique.

The valve bore 25 is covered on the right side and left side of the main body 3 by control cover 30, 31. In the control covers 30, 31 spring chambers 32 and 33 are formed, in each of which a prestressed spring 34 and 35 is located. The springs 34, 35 are supported on spring plate 28, 29 on the base body 3. By the action of the biased springs 34, 35 and the spring plate 28, 29 of the spool 26 is centered in a central position.

The spring chambers 32, 33 also form Steuerdruckkammem, which can be acted upon by a control pressure. By being in a spring chamber - e.g. 32 - acting control pressure, the spool 26 experiences a force in the direction of the other spring chamber -. 33 - opposite to the bias of the spring 35 disposed therein overcomes the force exerted by the control pressure on the spool 26 force the bias of the spring 35, the spool 26 moves from its centered position.

In the left side attached to the valve disc 1 control cover 30 also pressure control valves 38 and 40 are used. The pressure control valves 38, 40 are both connected via the fluid passage 42 with a control fluid supply line 18. Another fluid channel 43 connects the pressure control valves 38, 40 with a control fluid return line 20.

The pressure control valve 38 can be actuated via a (not shown) electromagnet and generates at its output a proportional to the magnetic force control pressure. The control pressure generated by the pressure control valve 38 is propagated via a fluid channel 39 into the spring chamber 33. This control pressure causes the control spool 26 a leftward force. The likewise equipped with an electromagnet pressure control valve 40 communicates with the spring chamber 32 via the fluid passage 41 in connection. The one by the Pressure control valve 40 generated control pressure is thus in the spring chamber 32 and causes the control spool a rightward force.

Furthermore, the spring chamber 32 is connected to a check valve 46, which opens toward a fluid line 48. To the spring chamber 33, a check valve 47 is also connected, which opens to the fluid line 48 back. The fluid line 48 leads via a pressure relief valve 50 to a fluid tank. In the illustrated directional valve disc this is conveniently accomplished by connection to the control fluid return line 20. However, the output of the pressure relief valve 50 may also be connected to a drain port or other fluid return line. The pressure relief valve 50 is set to a pressure corresponding to at least the highest of the pressure control valves 38, 40 can be generated control pressure.

The pressure control valves 38, 40 each have a control piston, which can flow control fluid from the control fluid supply line 18 in the respective spring chamber 32 and 33, respectively, until the predetermined by the magnetic force pressure is reached. If the pressure in the spring chamber is higher than this preselected pressure, the control piston allows control fluid to flow via the respective pressure control valve 38, 40 into the control fluid return line 20.

The control piston has a positive overlap with respect to the valve housing of the pressure control valve 38 or 40. This means that after reaching the preset pressure in the spring chamber, the spring chamber is shut off both against the Steuerfluidversorgungsieitung 18 ais and against the control fluid return line 20. Blocked the control piston in such a control position, it can be displaced via the pressure control valve no more control fluid from the corresponding spring chamber.

As an example, the case is considered that the spool 26 is deflected due to the pressure prevailing in the spring chamber 32 pressure from the centered position to the right. Now blocks the pressure control valve 40 so that no more control fluid can flow out of the spring chamber 32 above it, the spool 26 initially maintains the deflected position. Once by a leftward actuation of the spool 26, the pressure in the spring chamber 32 is increased, corresponds to a pressure of at least the pressure set on the pressure relief valve 50, control fluid flows bypassing the pressure control valve 40 via the check valve 46 in the fluid line 48 and the pressure relief valve 50 to the tank. Thus, it is possible to return the spool 26 to a centered position despite the blocked pressure control valve 40. Since the pressure set at the pressure limiting valve 50 is above the highest control pressure which the pressure regulating valves 38, 40 can generate, there is no impairment of the normal operation.

The leftward actuation of the spool 26, to bypass the blocked pressure control valve 40, can be done in particular by.Druckbeaufschlagung the spring chamber 33. A machine operator who realizes that the pressure control valve 40 is blocked - for example because the hydraulic consumer does not stop despite a completed operation - can counteract the control element. Thus, the pressure control valve 38 generates a control pressure in the spring chamber 33 and causes a leftward force on the spool 26. In addition, acts on the part of the spring 35, a force corresponding to the control pressure generated in the spring chamber 32 generated before blocking on the deflected to the right Spool 26. The force exerted by the spring 35, however, corresponds to at least the spring preload.

If the pressure in the spring chamber 32 - due to the tension of the spring 35 and the control pressure in the spring chamber 33 - reaches a value which corresponds at least to the pressure set at the pressure limiting valve 50, then the control fluid flows in the spring chamber 32 via the check valve 46 and the pressure relief valve 50 off. Thus, the spool 26 returns to the centered position.

So that the displacement of the control fluid from the spring chamber 32 by pressurizing the spring chamber 33 is possible, the pressure set at the pressure limiting valve 50 may correspond at most to the sum of the pressure equivalent of the spring preload and the highest producible control pressure. Then also a little deflected spool 26 are returned under the displacement of control fluid via the check valve 46 and the pressure relief valve 50 in the centered position.

Common pressure control valves are able to generate a control pressure of 30 bar. The bias of the springs 34 and 35, which center the spool 26, each corresponding to a pressure of 5 bar, which acts on the side surface of the spool 26. Preferably, accordingly, the pressure limiting valve 50 is set to a pressure between 32 bar and 35 bar. In this way, the spool 26 can be reliably returned to the centered position, even if one of the valves 38, 40, which generate the control pressure blocked. The return of the spool 26 is possible without mechanical intervention in the valve disc 1 - alone by hydraulic actuation.

The mechanisms described for the displacement of control fluid from the left-hand spring chamber 32 naturally also apply analogously to the right-hand spring chamber 33, in particular with respect to a displacement of control fluid via the check valve 47 and the pressure-limiting valve 50.

In the example described, an undesirable deflection of the spool 26 was corrected by means of an opposite operation by the machine operator. However, a return of the spool, bypassing a pilot valve is also feasible by an automatic electronic control. For this purpose, first the position of the spool 26 is detected. Does the spool 26 does not return to the centered position, although at any of the pressure control valves, a target pressure is given, so applied to the electronic control by operating a pressure control valve, the spool 26 in one of its deflection opposite direction. In this case, it is possible to bypass a blocked pressure regulating valve via the fluid line 48.

Instead of detecting the position of the spool 26, can be closed by detecting the operating state, such as a speed, a hydraulic load on the position of the spool 26.

Instead of using two pressure control valves 38, 40, a pilot-operated directional control valve can also be actuated hydraulically via a pilot control valve which is likewise designed as a directional control valve. If, according to the invention, a fluid line is provided by means of which control fluid can be displaced from the control pressure chambers while bypassing the pilot valve, the control slide of the pilot operated valve can be returned from an actuated position even if the pilot valve fails. The pressure required for this can e.g. be built by manual operation. Alternatively, a hydraulic emergency operation of the spool can be provided.

The FIG. 2 shows the diagram of a hydraulic control device 52, which is equipped with two continuously variable, pilot operated directional valves 54 and 55 for controlling hydraulic consumers. The directional valves 54 and 55 can analogously to the in FIG. 1 be constructed directional control valve disc. The respective spool of the directional control valves 54 and 55 are centered by springs. To the (not shown) Steuerdruckkammem the directional control valves 54 and 55 are each an electrically operated pressure control valve 60, 61, 62 and 63 connected to produce a predetermined control pressure. The pressure control valves 60, 61, 62 and 63 are supplied with a control fluid via a control fluid supply line 18. The control fluid supply pressure is established by a pump 56 and is determined by the pressure relief valve 57. Further, a control fluid return line 20 is connected to each pressure control valve 60, 61, 62, 63 to return control fluid to a tank 58.

The Steuerdruckkammem each way valve are connected via a respective check valve 64, 65, 66 and 67 to a fluid line 68. The check valves 64, 65, 66 and 67 open in the direction of the fluid line 68. The fluid line 68 leads via a pressure relief valve 70 to the tank. The pressure relief valve 70 can be opened by manual operation. A suction valve 71 is connected in parallel to the pressure limiting valve 70 and opens to the fluid line 68 back. The suction valve 71 may also be integrated in the pressure limiting valve 70.

The functional principle of in FIG. 2 shown control device substantially corresponds to the operating principle of in FIG. 1 shown control device that has been extended to two-way valves.

From each control pressure chamber of the two-way valves 54 and 55 is under a pressure corresponding to the set pressure of the pressure control valve 70, control fluid, bypassing the pressure control valves 60, 61, 62, 63 displaceable. The control fluid flows in this case via the corresponding check valve 64, 65, 66, 67 via the fluid line 68 and the pressure relief valve 70 to the tank 58. The set pressure of the pressure relief valve 70 is above the highest by the pressure control valves 60, 61, 62, 63 can be generated control pressure , The set pressure is also not above a pressure corresponding to the spring preload plus the highest by the pressure control valves 60, 61, 62, 63 can be generated control pressure.

Thus, the spool of each directional valve 54 and 55 can be reliably returned to the spring-centered position, even if one of the pressure control valves fails. In particular, the return of the spool can be done by hydraulic actuation.

Particularly advantageous at the in FIG. 2 is shown that from each control pressure chamber of the directional control valves 54, 55 control fluid into a single common fluid line 68 is displaceable. In addition, only a single pressure relief valve 70 is required to secure the Steuerdruckkammem. In the FIG. 2 shown control device can be easily extended by further directional valves. Their control pressure chambers are connected to the fluid line 68 for protection via a non-return valve opening toward the fluid line 68.

The response pressure of the pressure relief valve 70 can be adjusted independently of the supply pressure of the control fluid supply line 18. The control fluid supply line 18 may be set at a higher pressure than the pressure limiting valve 70 or at a pressure higher than the highest control pressure that can be generated by the pressure regulating valves 60, 61, 62, 63 supply more control fluid consumers or to ensure shorter control times.

In the FIG. 2 shown control device 52 additionally allows the Steuerdruckkammem the directional control valves 54, 55 and the control fluid system in a simple way to vent. For this purpose, the pressure relief valve 70 can be opened by manual operation. In the Steuerdruckkammem flowing control fluid can flow freely through the check valves 64, 65, 66, 67 and the open pressure relief valve 70 to the tank 58. Trapped air is discharged to the tank 58 together with the control fluid.

The FIG. 3 FIG. 12 illustrates a circuit diagram of another hydraulic control device 72. The control device 72 differs from that in FIG Fig. 2 illustrated control device 52 as set forth below. The same components are assigned the same reference numerals.

The control pressure spaces of the directional control valves 54 and 55 are connected via check valves 64, 66 and 65, 67 to two separate branches 68a and 68b of a fluid line. The fluid line 68a and 68b serves as a relief line in the event of failure of one of the pilot valves 60, 61, 62 and 63. In the FIG. 3 On the left, control pressure chambers of the directional control valves 54 and 55 are connected via the check valves 64 and 66 to the line branch 68a. The line branch 68a leads on the one hand via a further check valve 78 to the pressure relief valve 74. On the other hand, the branch 68a is connected via a switching valve 76 directly to a tank. In the FIG. 3 right arranged Steuerdruckkammem are connected via the check valves 65 and 67 to the line branch 68b. This leads via the check valve 77 to the pressure relief valve 74. In addition, a switching valve 75 is provided, through which the line branch 68b is connectable to a tank. The switching valves 75 and 76 are each configured to connect the respective leg 68a and 68b to the tank in an unactuated position and to interrupt communication between the leg 68a and 68b and the tank in an actuated position.

As with the in FIG. 2 control device 52 shown in the case of blockage of a pilot valve - in the following example, the pilot valve 60 - control fluid from the controlled control pressure chamber of the directional control valve 54 via the check valve 64, the line branch 68a, the check valve 78 and the pressure relief valve 74 to the tank 58 displace. Thus, by driving the pilot valve 61 and by the action of the return springs on the spool of the directional control valve 54 control fluid from the left control pressure chamber are displaced via the check valve 64 until the spool has returned to its neutral position.

In addition, the line branches 68a and 68b can be relieved independently of each other through the switching valve 75 and 76 towards the tank. In normal operation, the switching valves 75 and 76 are actuated, i. they interrupt the. Connection between the branches 68a and 68b and the tank. In the event of a blockage, e.g. of the pilot valve 60, one can switch the switching valve 76 in the unactuated position, so that the line branch 68a is depressurized. Then control fluid from the left control pressure chamber of the directional control valve 54 via the check valve 64 to flow towards the tank. The spool of the directional control valve 54 then returns to its neutral position. If one generates a control pressure by operating the pilot valve in the right control pressure chamber of the directional control valve 54, the spool can be deflected even beyond the neutral position in the direction of a reduction of the left control pressure chamber. This makes it possible not only to stop a hydraulic load / motor controlled by the directional control valve 54 but also to allow it to perform a retraction or return movement. Thereby important, e.g. For hydraulic drive actuators met relevant safety requirements.

The fluidic separation of the line branches 68a and 68b through the check valves 77 and 78 allows the line branches to be relieved independently of each other through the switching valves 75 and 76, respectively. Only in this way can an actuation of a directional control valve 54 or 55 for exerting a return movement take place during one of the line branches 68a or 68b is relieved. In addition, the hydraulic consumer controlled by the directional control valve can in any case be stopped by counteracting (control) on the operating element, even if the switching valves 75 and 76 are left in the actuated position. For the supply of control fluid from the line branches 68a and 68b to the pressure relief valve 74, a shuttle valve can be used instead of the check valves 77 and 78 shown.

In case of failure of the control electronics, the switching valves 75 and 76 returned to an unactuated position in which the line branches 68a and 68b are relieved. As a result, the hydraulic consumers controlled by the directional valves 54 and 55 are stopped.

In FIG. 4 a circuit diagram of another hydraulic control device 80 is shown. The control device 80 is equipped with a pilot operated, continuously variable directional control valve 82. The spool of the directional control valve 82 is spring-centered. The hydraulic control of the directional control valve 82 is effected by two pressure control valves 38 and 40 which are each connected to a spring chamber of the directional control valve 82. A pump 56 provides via the control fluid supply line 18, the supply of the pressure control valves 38 and 40 with control fluid. The pressure in the control fluid supply line 18 is predetermined by a pressure relief valve 84. Via control fluid return lines 20, the pressure control valves 38 and 40 are connected to the tank 58.

Parallel to the pressure regulating valve 38, a check valve 85 opening toward the control fluid supply line 18 is connected between the outlet of the pressure regulating valve 38 and the control fluid supply line 18. Another check valve 86 is connected in parallel to the pressure control valve 40 between its output and the control fluid supply line 18. Also, the check valve 86 opens in the direction of the control fluid supply line 18th

From the pressure chamber connected to the pressure control valve 38 Stsuerdruckkammer thus control fluid can be displaced via the check valve 85 in the control pressure supply line 18. Likewise can be from the with the Pressure control valve 40 connected control pressure chamber control fluid via the check valve 86 in the control pressure supply line 18 displace.

The pressure required to displace fluid from a control pressure chamber via the check valve 85 or 86 into the control fluid supply line 18 corresponds to the supply pressure of the control fluid supply line 18. The supply pressure is set to the highest control pressure to be generated by the pressure control valves 38 and 40 or slightly higher , Thus, the displacement of the fluid from a control pressure chamber by hydraulic loading of the spool on the part of the opposite control chamber is possible, the supply pressure in the control fluid supply line 18 may not be higher than the sum of a pressure corresponding to the spring bias of Zentrierfedem, and the highest by the pressure control valves 38 and 40 can be generated control pressure.

If e.g. the pressure control valve 40 is stuck and the left control chamber of the directional valve 82 shuts off while the spool is deflected to the right, by means of the pressure control valve 38, a control pressure in the right control pressure chamber can be generated. By the action of the control pressure generated in the right control pressure chamber and by the force of the spring in the right spring chamber on the spool in the left control pressure chamber, a pressure which allows the displacement of the control fluid via the check valve 86 in the control fluid supply line 18. The control fluid displaced from the left control pressure chamber flows either via the check valve 84 to the tank 58 or via the pressure control valve 38 into the right control pressure chamber.

Thus, even with a failure of a pressure control valve, the spool of the directional control valve 82 can be reliably returned to the centered position. The control device according to FIG. 4 Achieves the protection of Steuerdruckkammem against blocking the drain with a very low cost of additional components. Only check valves 85 and 86 are connected in parallel to the pressure control valves 38, 40.

The FIG. 5 represents a valve disc 90 of a control block, which after the in FIG. 4 illustrated circuit diagram is constructed. Der.Uufbau of the valve disc 90 corresponds in essential parts to the structure of in FIG. 1 The same valve components are provided with the same reference numerals and not described again below.

In particular, the main body 3 of the valve disc 90 correspond with its components and connections and the right-hand control cover 31 den.in FIG. 1 represented respective components. The left control cover 93 has a spring chamber 32 as the left control pressure chamber. Therein is the prestressed spring 34 and the spring plate 28. In the left control cover 93, the pressure control valves 38 and 40 are still used. The pressure regulating valve 40 generates the control pressure in the control pressure chamber 32. The pressure regulating valve 38 generates the control pressure applied in the control pressure chamber 33. Via the fluid channels 42 and 43, the pressure control valves 38 and 40 are connected to the control fluid supply line 18 and the control fluid return line 20, respectively.

In the control cover 93, the check valves 85 and 86 are additionally arranged. The check valve 85 leads from the fluid channel 39, which is connected to the output of the pressure regulating valve 38, to the fluid channel 42, which is connected to the control fluid supply line 18. It opens in the direction of the control fluid supply line 18. The check valve 86 leads from the output of the pressure control valve 40 - the fluid passage 41 - also on the fluid passage 42. The check valve 86 opens in the direction of the control fluid supply line 18th

Thus, a valve disc can be specified in a particularly simple manner, the in FIG. 4 shown circuit corresponds. Compared to a conventional valve disc only the left control cover is extended by two check valves. Although the valve disc 90 has a safeguard against blocking the pressure control valves 38 and 40, it builds only slightly more expensive than a conventional valve disc.

LIST OF REFERENCE NUMBERS

1

valve disc

3

body

10

Fluid supply port

12

tank connection

13

tank connection

16

Load pressure signaling line

18

Control fluid supply line

20

Control fluid return line

22

consumer connection

23

consumer connection

25

valve bore

26

spool

28

spring plate

29

Spring plate 30 Control cover

31

control cover

32

left spring chamber / control pressure chamber

33

right spring chamber / control pressure chamber

34

feather

35

feather

38

Pressure control valve

39

fluid channel

40

Pressure control valve

41

fluid channel

42

fluid channel

43

fluid channel

46

check valve

47

check valve

48

fluid line

50

Pressure relief valve

52

Hydraulic control device

54

Constantly adjustable directional control valve

55

Constantly adjustable directional control valve

56

pump

57

Pressure relief valve

60

Pressure control valve

61

Pressure control valve

62

Pressure control valve

63

Pressure control valve

64

check valve

65

check valve

66

check valve

67

check valve

68

fluid line

68a

Fluid line branch

68b

Fluid line branch

70

Pressure relief valve with manual override

71

cavitation valve

72

Hydraulic control device

74

Pressure relief valve

75

switching valve

76

switching valve

77

check valve

78

check valve

80

Hydraulic control device

82

way valve

84

Pressure relief valve

85

check valve

86

check valve

90

valve disc

93

control cover

Claims (9)

1. A control device for the control of a hydraulic consumer comprising a directional valve (1; 54; 90) which has a control pressure chamber (32) and a control slider (26) which is adjustable against the force of a spring (35) by building up a control pressure in the control pressure chamber (32) and comprising a pilot control valve (40, 60) for the control of the inflow and outflow of control fluid into and out of the control pressure chamber (32); and having a relief device (46, 48, 50; 68a, 76; 86) is present by which the control fluid can be displaced from the control pressure chamber (32) while bypassing the pilot control valve (40; 60), wherein the relief device includes a relief line (48) and a check valve (46) via which control fluid can be displaced from the control pressure chamber (32) into the relief line (48),
   characterized in that
   the pressure in the relief line (48) can be restricted to a value which is as high or higher than the pressure which the pilot control valve can set as a maximum at its outlet.
2. A control device in accordance with claim 1, characterized in that the relief line (48) can be connected to a tank via a pressure relief valve (50).
3. A control device in accordance with claim 2, characterized in that the pressure relief valve (70) can be actuated manually to exert a bleeding function.
4. A control device in accordance with claim 1, characterized in that the relief line is in fluid communication with a control fluid supply line (18) of the pilot control valve (38,40).
5. A control device in accordance with one of the claims 1 to 4, characterized in that the pressure in the relief line (48) can be restricted to a value which is lower than the sum of the maximum control pressure and a pressure corresponding to a bias force of the spring (35).
6. A control device in accordance with one of the claims 1 to 5, characterized in that the relief line (68a) can be relieved into a tank by a switching valve (76).
7. A control device in accordance with claim 6, characterized in that the directional valve (54) has two control pressure valves by which the control slider can be acted on in mutually opposite directions; in that control fluid can be displaced from the two control pressure chambers via a respective separate check valve (64, 65) into two different branches (68a, 68b of the relief line); in that the two different branches (68a, 68b) of the relief line are fluidly separated from one another; and in that two switching valves (75, 76) are present via which the branches (68a, 68b) of the relief line can be relieved to a tank independently of one another.
8. A control device in accordance with either of the claims 2 and 7, characterized in that control fluid can be supplied from the two different branches (68a, 68b) of the relief line to the pressure relief valve (74) via a respective check valve (77, 78) which opens toward the pressure relief valve (74).
9. A control device in accordance with one of the claims 1 to 8, characterized in that a plurality of directional valves (54, 55) respectively having at least one control pressure chamber are provided; and in that control fluid can be displaced from each of the control pressure chambers of the different directional valves (54, 55) via a respective separate check valve (64, 66) into the relief line (68) or a branch of the relief line (68a, 68b).

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