EP0771949A1 - Control device with hydraulic centering mechanism - Google Patents

Control device with hydraulic centering mechanism Download PDF

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Publication number
EP0771949A1
EP0771949A1 EP96112820A EP96112820A EP0771949A1 EP 0771949 A1 EP0771949 A1 EP 0771949A1 EP 96112820 A EP96112820 A EP 96112820A EP 96112820 A EP96112820 A EP 96112820A EP 0771949 A1 EP0771949 A1 EP 0771949A1
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EP
European Patent Office
Prior art keywords
control
pressure
centering
piston
pressure chambers
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Granted
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EP96112820A
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German (de)
French (fr)
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EP0771949B1 (en
Inventor
Wilhelm Appel
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Brueninghaus Hydromatik GmbH
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Brueninghaus Hydromatik GmbH
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Publication of EP0771949A1 publication Critical patent/EP0771949A1/en
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B49/00—Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00
    • F04B49/002—Hydraulic systems to change the pump delivery
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B49/00—Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00
    • F04B49/10—Other safety measures

Definitions

  • the invention relates to an adjusting device for adjusting an adjusting piston acting on the displacement volume of a hydrostatic machine.
  • Such an adjustment device is e.g. Known from DE-OS 41 25 706 and comprises a spring-centered control device which hydraulically displaces the actuating piston for adjusting the displacement volume of the hydrostatic machine.
  • the control device is operated manually using a hand lever.
  • a corresponding spring centering is provided to ensure that the control device controls the hydrostatic machine via the adjusting piston to zero displacement volume without actuating the hand lever.
  • a control device for a radial piston machine emerges from DE-OS 29 25 236.
  • the present invention is therefore based on the object of providing an adjusting device for adjusting the displacement volume of a hydrostatic machine, in which the return of the actuating piston to its neutral position, in which the hydrostatic machine works without displacement volume, is reliably ensured even in the event of a fault.
  • the invention is based on the finding of providing an additional hydraulic centering device which is only activated when both control lines do not or no sufficient control pressure.
  • the solution according to the invention provides for the combination of a switching valve with a centering valve, the switching valve activating the centering valve when the control pressure disappears in both control pressure lines. This relieves Centering valve in the event of unequal pressures in the signal pressure chambers, the signal pressure chamber to which the higher pressure is applied.
  • the switching valve can be provided between the centering valve and a pressure medium tank. It is only opened if the control lines do not have or no sufficient control pressure, and then connects the centering valve to the pressure medium tank. To ensure that the switching valve is only opened when both control lines do not have sufficient control pressure, the switching valve is preceded by a shuttle valve according to claim 3, which connects the control line which carries the higher control pressure with the switching valve.
  • the centering valve has a spring-centered centering piston which is arranged between two centering pressure chambers connected to the actuating pressure chambers.
  • the centering piston is designed according to claim 5 so that it blocks the connection between the control pressure chambers and the switching valve in a neutral position which the centering piston assumes when there is no pressure difference between the control pressure chambers.
  • the connection between the signal pressure chamber to which the higher pressure is applied is released with a pressure medium tank when there is an imbalance between the pressures in the two signal pressure chambers.
  • control device can have a feedback element which connects the actuating piston to the control piston in order to return the control piston to its neutral position when the actuating piston is adjusted in the direction.
  • the feedback element then takes over the centering. If the control device fails, e.g. By breaking the return spring, the necessary centering and thus the pivoting back of the hydrostatic machine is ensured by the hydraulic centering device.
  • FIG. 1 shows a hydraulic circuit diagram of the adjusting device according to the invention for adjusting the adjusting piston 3 arranged between the actuating pressure chambers 1 and 2 works without displacement.
  • control pressure chambers 1, 2 are connected to a control device 8 via control pressure lines 6 and 7.
  • the control device 8 serves to selectively apply the control pressure chambers 1, 2 and a predetermined control pressure in order to move the control piston 3 into a position corresponding to the displacement volume of the hydrostatic machine to be set.
  • the control unit 8 is controlled via two control lines 9 and 10, which act on the control pressure chambers 11 and 12 of the control unit 8 with corresponding control pressures y 1 and y 2 .
  • the control pressure chambers 11 and 12 are connected to the associated control lines 9 and 10 via corresponding connections 13 and 14. Between the control pressure chambers 11, 12, a control piston 16 is provided in the control unit 8, which is displaced as a function of the pressure difference between the control pressure chambers 11, 12 from a neutral position shown in FIG. 1 and one of the two control pressure lines 6 or 7 with this displacement connects the feed line 15, which leads the feed pressure p sp . As a result, the actuating pressure chamber 1 or 2 connected to the corresponding actuating pressure line 6 or 7 is acted upon by an appropriate actuating pressure, as a result of which the actuating piston 3 is moved into the desired position.
  • a return device In order to cause the actuating piston 3 to be reset, a return device, generally designated 17, is provided.
  • a return lever 18 engages in a corresponding groove in the actuating piston 3.
  • the return lever 18 is operatively connected to the control piston 16, which will be described in more detail later with reference to FIGS. 2A and 2B.
  • a restoring force proportional to the adjustment of the actuating piston 3 from its neutral position is applied to the control piston 16 exercised, which counteracts the actuating force exerted by the control pressure y 1 or y 2 on the control piston 16.
  • the pressure in the actuating pressure chambers 1 and 2 does not continue to increase and the position of the actuating piston proportional to the control pressure y 1 or y 2 is reached.
  • the arrangement described above also causes the actuating piston 3 to be returned to the neutral position shown in FIG. 1 via the reset device 17 described above if the control pressures y 1 and y 2 in the two control lines 9 and 10 are controlled to zero.
  • a difficulty arises, however, when a fault occurs in the control device 8. In practice it has been shown that such a fault is often associated with a break in the return spring 20 of the return device 17. Since a break in the return spring 20 causes the actuating piston 3 to no longer be positively connected to the control piston 16, the return of the actuating piston 3 to its neutral position corresponding to the zero displacement volume of the hydrostatic machine is no longer guaranteed.
  • the hydrostatic machine also works in the uncontrolled state, ie with control pressures y 1 and y 2 switched off, completely uncontrolled. Because of the now freely movable control piston 16 of the actuating piston 3 may be p sp assume any desired position and is also in the absence of supply pressure sp p in the feed line 15 due to the slow flowing actuating medium only slowly over the centering 4, 5 in the neutral position when still present feed pressure returned. In the meantime, the hydrostatic machine works with an uncontrolled displacement and can cause considerable damage.
  • the hydraulic centering device 21 comprises a centering valve 22 and a switching valve 23.
  • the centering valve 22 has two centering pressure chambers 24, 25 shown in FIG. which are each connected to one of the signal pressure lines 6 and 7 via centering lines 26 and 27.
  • a centering piston 28 is movably arranged between the centering chambers 24 and 25.
  • the centering piston 28 is centered in its neutral position shown in FIG. 1 by centering springs 29, 30, it being possible for at least one of the centering springs 29, 30 to be adjustable.
  • centering springs 29, 30 In the exemplary embodiment shown in FIG.
  • the centering piston 28 has a central region, the diameter of which is adapted to the surrounding cylinder and blocks a connecting line 34 in the neutral position shown in FIG. 1, and two tapered regions 32, 33 arranged laterally therefrom.
  • the tapered areas 32, 33 are each connected to one of the centering lines 26 and 27, respectively.
  • the central region 28 blocks the connection between the centering lines 26 and 27 with the connecting line 34 to the switching valve 23.
  • the centering piston 28 is shifted laterally accordingly , so that the centering line 26, 27, which carries the higher pressure, is connected to the connecting line 34.
  • the switching valve 23 is arranged between the pressure medium tank 35 and the connecting line 34, which leads to the centering valve 21.
  • the switching valve 23 comprises a switching piston 37 which is movable against a return spring 36 and is acted upon by the pressure of a switching pressure chamber 38 and blocks the connection between the centering valve 21 and the pressure medium tank 35 above a switching pressure which can be set by means of the return spring 36.
  • the switching pressure chamber 38 of the switching valve 23 is connected to the two control lines 9, 10 via a shuttle valve 39.
  • the shuttle valve 39 operates in such a way that the control line 9 or 10 carrying the higher pressure is connected to the switching pressure chamber 38 of the switching valve 23.
  • the operation of the hydraulic centering device according to the invention is as follows: As long as there is a predetermined minimum control pressure in at least one of the control lines 9 or 10, the hydraulic centering device 21 is not activated since the switching pressure chamber 38 of the switching valve 23 via the shuttle valve 39 with the higher of the two control pressures y 1 prevailing in the control lines 9 and 10 or y 2 is acted upon and thus shifts the switching piston 37 into a position in which the connection between the centering valve 22 and the pressure medium tank 35 is interrupted. However, as soon as the control lines 9 and 10 carry no or insufficient control pressure, the switching valve 23 is opened and the connecting line 34 is connected to the pressure medium tank 35.
  • the signal pressure chamber 1 or 2 to which the higher signal pressure is applied becomes via the associated signal pressure line 6 or 7 and the corresponding centering line 26 or 27 Pressure medium tank 35 relieved. The relief takes place until a pressure equilibrium between the actuating pressures in the actuating pressure chambers 1 and 2 has been restored and thus the pressures guided by the centering lines 26 and 27 match and the centering piston 31 is returned to its neutral position.
  • the hydraulic centering device 21 according to the invention described above brings about a swift and safe return of the adjusting piston 3 to its neutral position, in which the hydraulic machine works without displacement, even if a fault, in particular a break in the return spring 20, occurs in the control device 8.
  • the arrangement also works reliably if the feed pressure p sp of the feed pressure line 15 is omitted, since after centering springs 4, 5 have relieved the pressure on pressure chambers 1 and 2.
  • the hydraulic centering device 21 according to the invention which only requires a small amount of construction, prevents damage due to overloading of the otherwise uncontrolled working hydrostatic machine on the system.
  • control device 8 is briefly described below with reference to FIGS. 2A and 2B.
  • FIG. 2A shows a section through an exemplary embodiment of the control device 8.
  • the control piston 16 is designed as a stepped piston and, when shifted from the neutral position shown in FIG. 2A, gives the connection between the ones shown in FIG. 1 at the control edges 50, 51 Signal pressure lines 6 and 7 with the feed line 15 free.
  • the return lever 18 of the return device 17 already described is pivotally mounted about an axis 52.
  • a pin 54 is formed on the extension 53 of the return lever 18, which pin deflects one of the two rocker arms 55 and 56 when the return lever 18 is pivoted .
  • the return spring 20 is arranged between the hook-shaped end regions 57 and 58 of the rocker arms 55 and 56.
  • the rocker arms 55 and 56 are in engagement with the control piston 16 in order to exert the restoring force already described with reference to FIG. 1.
  • the return spring 20 effects the centering of the control piston 16 after switching off the control pressures y 1 and y 2 acting on the control piston 16 via the control pressure chambers 11 and 12.
  • a break in the return spring 20, as already described, has the consequence that the centering of the control piston 16 and thus of the actuating piston 3 actuated by the latter is not guaranteed.
  • the above-described hydraulic centering device 21 counteracts this disadvantage.
  • the switching valve 23 can also be easily inserted into the centering lines 26 and 27 and with the control pressure y 1 and y 2 present interrupt the centering lines 26 and 27. It is also conceivable to connect the switching valve 23 to the control pressure lines 9 and 10 by means of appropriate throttles instead of a shuttle valve 39. Of course, the design of the centering valve 22 and the switching valve 23 can be varied while maintaining the function.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Fluid-Pressure Circuits (AREA)

Abstract

A control unit (8) has two control pressure chambers (11,12), each connected to a control line (9,10), and a control piston (16) between the chambers. The piston is moved from a neutral position dependant upon the pressure differential between the chambers, to connect one chamber to a feed pressure line (15). The piston is moved into neutral by a spring. A hydraulic centering device (21) has a switching valve (23) connected to the control lines, and a centering valve (22) connected to the chambers. Switching piston (37) and centering piston (28) are moved into end positions, when the control pressure in the lines has dropped, but a differential remains in the chambers. The chamber with the higher pressure is relieved via the valves, and the adjusting piston pressure is returned to neutral.

Description

Die Erfindung betrifft eine Verstellvorrichtung zum Verstellen eines auf das Verdrängungsvolumen einer hydrostatischen Maschine einwirkenden Stellkolbens.The invention relates to an adjusting device for adjusting an adjusting piston acting on the displacement volume of a hydrostatic machine.

Eine derartige Verstellvorrichtung ist z.B. aus der DE-OS 41 25 706 bekannt und umfaßt eine federzentrierte Ansteuereinrichtung, die den Stellkolben zum Einstellen des Verdrängungsvolumens der hydrostatischen Maschine hydraulisch verschiebt. Die Betätigung der Ansteuereinrichtung erfolgt manuell über einen Handhebel. Um sicherzustellen, daß die Ansteuereinrichtung ohne Betätigung des Handhebels die hydrostatische Maschine über den Stellkolben auf Null-Verdrängungsvolumen steuert, ist eine entsprechende Federzentrierung vorgesehen.Such an adjustment device is e.g. Known from DE-OS 41 25 706 and comprises a spring-centered control device which hydraulically displaces the actuating piston for adjusting the displacement volume of the hydrostatic machine. The control device is operated manually using a hand lever. A corresponding spring centering is provided to ensure that the control device controls the hydrostatic machine via the adjusting piston to zero displacement volume without actuating the hand lever.

Eine Ansteuereinrichtung für eine Radialkolbenmaschine geht aus der DE-OS 29 25 236 hervor.A control device for a radial piston machine emerges from DE-OS 29 25 236.

In der Praxis hat sich gezeigt, daß ein Bruch der Rückstellfeder nicht ausgeschlossen ist. Bei bekannten Verstellvorrichtungen hat dies zur Folge, daß der Stellkolben nicht oder nicht sicher bei dieser Störung in seine Neutralstellung, in der die hydrostatische Maschine ohne Verdrängungsvolumen arbeitet, zurückgeführt wird. Dies ist höchst unerwünscht, da die hydrostatische Maschine dann ohne jegliche Steuerung mit einem nicht definierten Verdrängungsvolumen weiterläuft.In practice it has been shown that breakage of the return spring cannot be ruled out. In known adjusting devices, this has the consequence that the actuating piston is not, or not reliably, returned to its neutral position, in which the hydrostatic machine works without displacement volume, in the event of this malfunction. This is highly undesirable since the hydrostatic machine then continues to run without any control with an undefined displacement.

Der vorliegenden Erfindung liegt daher die Aufgabe zugrunde, eine Verstellvorrichtung zum Verstellen des Verdrängungsvolumens einer hydrostatischen Maschine zu schaffen, bei der auch bei einer Störung die Rückführung des Stellkolbens in seine Neutralstellung, in der die hydrostatische Maschine ohne Verdrängungsvolumen arbeitet, sicher gewährleistet ist.The present invention is therefore based on the object of providing an adjusting device for adjusting the displacement volume of a hydrostatic machine, in which the return of the actuating piston to its neutral position, in which the hydrostatic machine works without displacement volume, is reliably ensured even in the event of a fault.

Die Aufgabe wird durch die Merkmale des Anspruches 1 gelöst.The object is achieved by the features of claim 1.

Der Erfindung liegt dabei die Erkenntnis zugrunde, eine zusätzliche hydraulische Zentriereinrichtung vorzusehen, die lediglich dann aktiviert wird, wenn beide Steuerleitungen keinen oder keinen ausreichenden Steuerdruck führen. Die erfindungsgemäße Lösung sieht die Kombination eines Schaltventils mit einem Zentrierventil vor, wobei das Schaltventil das Zentrierventil aktiviert, wenn der Steuerdruck in beiden Steuerdruckleitungen verschwindet. Dabei entlastet das Zentrierventil bei ungleichen Drücken in den Stelldruckkammern diejenige Stelldruckkammer, die mit dem höheren Druck beaufschlagt ist.The invention is based on the finding of providing an additional hydraulic centering device which is only activated when both control lines do not or no sufficient control pressure. The solution according to the invention provides for the combination of a switching valve with a centering valve, the switching valve activating the centering valve when the control pressure disappears in both control pressure lines. This relieves Centering valve in the event of unequal pressures in the signal pressure chambers, the signal pressure chamber to which the higher pressure is applied.

Die Ansprüche 2 bis 6 betreffen vorteilhafte Weiterbildungen der Erfindung.Claims 2 to 6 relate to advantageous developments of the invention.

Gemäß Anspruch 2 kann das Schaltventil zwischen dem Zentrierventil und einem Druckmitteltank vorgesehen sein. Es wird nur geöffnet, wenn die Steuerleitungen keinen oder keinen ausreichenden Steuerdruck führen, und verbindet dann das Zentrierventil mit dem Druckmitteltank. Um sicherzustellen, daß das Schaltventil nur dann geöffnet wird, wenn beide Steuerleitungen keinen ausreichenden Steuerdruck führen, ist dem Schaltventil ein Wechselventil entsprechend Anspruch 3 vorgeschaltet, das die Steuerleitung, die den höheren Steuerdruck führt, mit dem Schaltventil verbindet.According to claim 2, the switching valve can be provided between the centering valve and a pressure medium tank. It is only opened if the control lines do not have or no sufficient control pressure, and then connects the centering valve to the pressure medium tank. To ensure that the switching valve is only opened when both control lines do not have sufficient control pressure, the switching valve is preceded by a shuttle valve according to claim 3, which connects the control line which carries the higher control pressure with the switching valve.

Entsprechend Anspruch 4 weist das Zentrierventil einen federzentrierten Zentrierkolben auf, der zwischen zwei mit den Stelldruckkammern verbundenen Zentrierdruckkammern angeordnet ist. Dabei ist der Zentrierkolben nach Anpruch 5 so ausgebildet, daß er in einer Neutralstellung, die der Zentrierkolben dann einnimmt, wenn keine Druckdifferenz zwischen den Stelldruckkammern herrscht, die Verbindung zwischen den Stelldruckkammern und dem Schaltventil sperrt. Andererseits wird die Verbindung zwischen derjenigen Stelldruckkammer, die mit dem höheren Druck beaufschlagt ist, mit einem Druckmitteltank dann freigegeben, wenn ein Ungleichgewicht zwischen den Drücken in den beiden Stelldruckkammern herrscht.According to claim 4, the centering valve has a spring-centered centering piston which is arranged between two centering pressure chambers connected to the actuating pressure chambers. The centering piston is designed according to claim 5 so that it blocks the connection between the control pressure chambers and the switching valve in a neutral position which the centering piston assumes when there is no pressure difference between the control pressure chambers. On the other hand, the connection between the signal pressure chamber to which the higher pressure is applied is released with a pressure medium tank when there is an imbalance between the pressures in the two signal pressure chambers.

Entsprechend Anspruch 6 kann die Ansteuereinrichtung ein Rückführungselement aufweisen, das den Stellkolben mit dem Steuerkolben verbindet, um den Steuerkolben bei Verstellen des Stellkolbens in Richtung auf seine Neutralstellung zurückzuführen. Im Normalbetrieb ohne Störung übernimmt dann das Rückführungselement die Zentrierung. Bei einem Ausfall der Ansteuereinrichtung, z.B. durch Bruch der Rückstellfeder, wird die notwendige Zentrierung und damit das Zurückschwenken der hydrostatischen Maschine durch die hydraulische Zentriereinrichtung sichergestellt.According to claim 6, the control device can have a feedback element which connects the actuating piston to the control piston in order to return the control piston to its neutral position when the actuating piston is adjusted in the direction. In normal operation without a fault, the feedback element then takes over the centering. If the control device fails, e.g. By breaking the return spring, the necessary centering and thus the pivoting back of the hydrostatic machine is ensured by the hydraulic centering device.

Die Erfindung wird nachfolgend anhand eines bevorzugten Ausführungsbeispiels unter Bezugnahme auf die Zeichnung näher beschrieben. Es zeigen:

Fig. 1
einen hydraulischen Schaltplan eines Ausführungsbeispiels der erfindungsgemäßen Verstellvorrichtung,
Fig. 2A
einen Schnitt durch ein Ausführungsbeispiel einer Ansteuereinrichtung, die bei der Erfindung verwendet wird,
Fig. 2B
einen Schnitt entlang der Linie A-A in Fig. 2A.
The invention is described below with reference to a preferred embodiment with reference to the drawing. Show it:
Fig. 1
a hydraulic circuit diagram of an embodiment of the adjusting device according to the invention,
Figure 2A
3 shows a section through an exemplary embodiment of a control device used in the invention,
Figure 2B
a section along the line AA in Fig. 2A.

Fig. 1 zeigt einen hydraulischen Schaltplan der erfindungsgemäßen Verstellvorrichtung zum Verstellen des zwischen den Stelldruckkammern 1 und 2 angeordneten Stellkolbens 3. Durch Verstellen des Stellkolbens 3 wird das Verdrängungsvolumen einer nicht dargestellten hydrostatischen Maschine verändert, wobei in der in Fig. 1 dargestellten Neutraistellung die hydrostatische Maschine ohne Verdrängungsvolumen arbeitet.1 shows a hydraulic circuit diagram of the adjusting device according to the invention for adjusting the adjusting piston 3 arranged between the actuating pressure chambers 1 and 2 works without displacement.

Der Stellkolben 3 ist in dieser Neutralstellung durch die lediglich schematisch dargestellten Zentrierfedern 4 und 5 zentriert. Die Stelldruckkammern 1, 2 sind über Stelldruckleitungen 6 und 7 mit einer Ansteuereinrichtung 8 verbunden. Die Ansteuereinrichtung 8 dient der gezielten Beaufschlagung der Stelldruckkammern 1, 2 und einem vorgegebenen Stelldruck, um den Stellkolben 3 in eine dem einzustellenden Verdrängungsvolumen der hydrostaischen Maschine entsprechende Position zu verschieben. Die Ansteuerung der Ansteuereinheit 8 erfolgt über zwei Steuerleitungen 9 und 10, die die Steuerdruckkammern 11 und 12 der Ansteuereinheit 8 mit entsprechenden Steuerdrücken y1 und y2 beaufschlagen.In this neutral position, the adjusting piston 3 is centered by the centering springs 4 and 5, which are only shown schematically. The control pressure chambers 1, 2 are connected to a control device 8 via control pressure lines 6 and 7. The control device 8 serves to selectively apply the control pressure chambers 1, 2 and a predetermined control pressure in order to move the control piston 3 into a position corresponding to the displacement volume of the hydrostatic machine to be set. The control unit 8 is controlled via two control lines 9 and 10, which act on the control pressure chambers 11 and 12 of the control unit 8 with corresponding control pressures y 1 and y 2 .

Die Steuerdruckkammern 11 und 12 sind über entsprechende Anschlüsse 13 und 14 mit den zugeordneten Steuerleitungen 9 bzw. 10 verbunden. Zwischen den Steuerdruckkammern 11, 12 ist in der Ansteuereinheit 8 ein Steuerkolben 16 vorgesehen, der in Abhängigkeit von der Druckdifferenz zwischen den Steuerdruckkammern 11, 12 aus einer in Fig. 1 dargestellten Neutralstellung verschoben wird und entsprechend dieser Verschiebung eine der beiden Stelldruckleitungen 6 oder 7 mit der Speiseleitung 15 verbindet, die den Speisedruck psp führt. Dadurch wird die mit der entsprechenden Stelldruckleitung 6 bzw. 7 in Verbindung stehende Stelldruckkammer 1 bzw. 2 mit einem entsprechenden Stelldruck beaufschlagt, wodurch der Stellkolben 3 in die gewünschte Position bewegt wird.The control pressure chambers 11 and 12 are connected to the associated control lines 9 and 10 via corresponding connections 13 and 14. Between the control pressure chambers 11, 12, a control piston 16 is provided in the control unit 8, which is displaced as a function of the pressure difference between the control pressure chambers 11, 12 from a neutral position shown in FIG. 1 and one of the two control pressure lines 6 or 7 with this displacement connects the feed line 15, which leads the feed pressure p sp . As a result, the actuating pressure chamber 1 or 2 connected to the corresponding actuating pressure line 6 or 7 is acted upon by an appropriate actuating pressure, as a result of which the actuating piston 3 is moved into the desired position.

Um eine Rückstellung des Stellkolbens 3 zu bewirken, ist eine allgemein mit 17 bezeichnete Rückführeinrichtung vorgesehen. Im dargestellten Ausführungsbeispiel greift ein Rückführhebel 18 in einen entsprechende Nut im Stellkolben 3 ein. Der Rückführhebel 18 steht mit dem Steuerkolben 16 in Wirkverbindung, was später anhand der Fig. 2A und 2B noch detaillierter beschrieben wird. Dadurch wird eine der Verstellung des Stellkolbens 3 aus seiner Neutralstellung proportionale Rückstellkraft auf den Steuerkolben 16 ausgeübt, die der von dem Steuerdruck y1 bzw. y2 auf den Steuerkolben 16 ausgeübten Stellkraft entgegenwirkt. Nach Erreichen des Kräftegleichgewichts zwischen der Stellkraft und der Rückstellkraft wächst der Druck in den Stelldruckkammern 1 bzw. 2 nicht weiter an und die dem Steuerdruck y1 bzw. y2 proportionale Stellung des Stellkolbens ist erreicht.In order to cause the actuating piston 3 to be reset, a return device, generally designated 17, is provided. In the exemplary embodiment shown, a return lever 18 engages in a corresponding groove in the actuating piston 3. The return lever 18 is operatively connected to the control piston 16, which will be described in more detail later with reference to FIGS. 2A and 2B. As a result, a restoring force proportional to the adjustment of the actuating piston 3 from its neutral position is applied to the control piston 16 exercised, which counteracts the actuating force exerted by the control pressure y 1 or y 2 on the control piston 16. After the equilibrium of forces between the actuating force and the restoring force has been reached, the pressure in the actuating pressure chambers 1 and 2 does not continue to increase and the position of the actuating piston proportional to the control pressure y 1 or y 2 is reached.

Die vorstehend beschriebene Anordnung bewirkt auch das Rückführen des Stellkolbens 3 in die in Fig. 1 dargestellte Neutralstellung über die vorstehend beschriebene Rückstelleinrichtung 17, wenn die Steuerdrücke y1 und y2 in den beiden Steuerleitungen 9 und 10 auf Null gesteuert werden. Eine Schwierigkeit ergibt sich jedoch dann, wenn eine Störung in der Ansteuereinrichtung 8 auftritt. In der Praxis hat sich gezeigt, daß eine solche Störung häufig mit einem Bruch der Rückstellfeder 20 der Rückführeinrichtung 17 verbunden ist. Da ein Bruch der Rückstellfeder 20 bewirkt, daß der Stellkolben 3 nicht mehr kraftschlüssig mit dem Steuerkolben 16 in Wirkverbindung steht, ist die Rückführung des Stellkolbens 3 in seine dem Null-Verdrängungsvolumen der hydrostatischen Maschine entsprechende Neutralstellung nicht mehr gewährleistet. Die hydrostatische Maschine arbeitet vielmehr auch im nicht angesteuerten Zustand, d.h. mit abgeschalteten Steuerdrücken y1 und y2 vollkommen unkontrolliert. Aufgrund des nunmehr frei beweglichen Steuerkolbens 16 kann der Stellkolben 3 bei noch vorhandenem Speisedruck psp jede beliebige Position einnehmen und wird auch bei fehlendem Speisedruck psp in der Speiseleitung 15 aufgrund des nur langsam abfließenden Stellmediums nur langsam über die Zentrierfeder 4, 5 in die Neutralstellung zurückgeführt. Währenddessen arbeitet die hydrostatische Maschine mit unkontrolliertem Verdrängungsvolumen und kann einen erheblichen Schaden verursachen.The arrangement described above also causes the actuating piston 3 to be returned to the neutral position shown in FIG. 1 via the reset device 17 described above if the control pressures y 1 and y 2 in the two control lines 9 and 10 are controlled to zero. A difficulty arises, however, when a fault occurs in the control device 8. In practice it has been shown that such a fault is often associated with a break in the return spring 20 of the return device 17. Since a break in the return spring 20 causes the actuating piston 3 to no longer be positively connected to the control piston 16, the return of the actuating piston 3 to its neutral position corresponding to the zero displacement volume of the hydrostatic machine is no longer guaranteed. Rather, the hydrostatic machine also works in the uncontrolled state, ie with control pressures y 1 and y 2 switched off, completely uncontrolled. Because of the now freely movable control piston 16 of the actuating piston 3 may be p sp assume any desired position and is also in the absence of supply pressure sp p in the feed line 15 due to the slow flowing actuating medium only slowly over the centering 4, 5 in the neutral position when still present feed pressure returned. In the meantime, the hydrostatic machine works with an uncontrolled displacement and can cause considerable damage.

Dem wirkt die im folgenden zu beschreibende erfindungsgemäße hydraulische Zentriereinrichtung, die allgemein mit 21 bezeichnet ist, entgegen.Die hydraulische Zentriereinrichtung 21 umfaßt ein Zentrierventil 22 und ein Schaltventil 23. Das Zentrierventil 22 weist im Fig. 1 dargestellten Ausführungsbeispiel zwei Zentrierdruckkammern 24, 25 auf, die mit jeweils einer der Stelldruckleitungen 6 bzw. 7 über Zentrierleitungen 26 bzw. 27 verbunden sind. Zwischen den Zentrierkammern 24 und 25 ist ein Zentrierkolben 28 beweglich angeordnet. Der Zentrierkolben 28 wird in seine in Fig. 1 dargestellte Neutralstellung durch Zentrierfedern 29, 30 zentriert, wobei zumindest eine der Zentrierfedern 29, 30 justierbar ausgeführt sein kann. Im in Fig. 1 dargestellten Ausführungsbeispiel weist der Zentrierkolben 28 einen mittleren Bereich, dessen Durchmesser an den umgebenden Zylinder angepaßt ist und in der in Fig. 1 dargestellten Neutralstellung eine Verbindungsleitung 34 sperrt, sowie zwei davon seitlich angeordnete, verjüngte Bereiche 32, 33 auf. Die vejüngten Bereiche 32, 33 stehen jeweils mit einer der Zentrierleitungen 26 bzw. 27 in Verbindung.This is counteracted by the hydraulic centering device according to the invention to be described below, which is designated generally by 21. The hydraulic centering device 21 comprises a centering valve 22 and a switching valve 23. The centering valve 22 has two centering pressure chambers 24, 25 shown in FIG. which are each connected to one of the signal pressure lines 6 and 7 via centering lines 26 and 27. A centering piston 28 is movably arranged between the centering chambers 24 and 25. The centering piston 28 is centered in its neutral position shown in FIG. 1 by centering springs 29, 30, it being possible for at least one of the centering springs 29, 30 to be adjustable. In the exemplary embodiment shown in FIG. 1, the centering piston 28 has a central region, the diameter of which is adapted to the surrounding cylinder and blocks a connecting line 34 in the neutral position shown in FIG. 1, and two tapered regions 32, 33 arranged laterally therefrom. The tapered areas 32, 33 are each connected to one of the centering lines 26 and 27, respectively.

In der in Fig. 1 dargestellten Neutralstellung sperrt der mittlere Bereich 28 die Verbindung zwischen den Zentrierleitungen 26 und 27 mit der Verbindungsleitung 34 zu dem Schaltventil 23. Sobald sich jedoch zwischen den Zentrierleitungen 26 und 27 eine Druckdifferenz einstellt, wird der Zentrierkolben 28 entsprechend seitlich verschoben, so daß diejenige Zentrierleitung 26, 27, die den höheren Druck führt, mit der Verbindungsleitung 34 in Verbindung gebracht wird.In the neutral position shown in FIG. 1, the central region 28 blocks the connection between the centering lines 26 and 27 with the connecting line 34 to the switching valve 23. However, as soon as a pressure difference occurs between the centering lines 26 and 27, the centering piston 28 is shifted laterally accordingly , so that the centering line 26, 27, which carries the higher pressure, is connected to the connecting line 34.

Das Schaltventil 23 ist im in Fig. 1 dargestellten Ausführungsbeispiel zwischen dem Druckmitteltank 35 und der Verbindungsleitung 34, die zu dem Zentrierventil 21 führt, angeordnet. Das Schaltventil 23 umfaßt einen gegen eine Rückstellfeder 36 beweglichen Schaltkolben 37, der vom Druck einer Schaltdruckkammer 38 beaufschlagt wird und oberhalb eines mittels der Rückstellfeder 36 einstellbaren Schaltdrucks die Verbindung zwischen dem Zentrierventil 21 und dem Druckmitteltank 35 sperrt. Die Schaltdruckkammer 38 des Schaltventil 23 steht über ein Wechselventil 39 mit den beiden Steuerleitungen 9, 10 in Verbindung. Das Wechselventil 39 arbeitet in der Weise, daß jeweils die den höheren Druck führende Steuerleitung 9 oder 10 mit der Schaltdruckkammer 38 des Schaltventlls 23 in Verbindung gebracht wird.In the exemplary embodiment shown in FIG. 1, the switching valve 23 is arranged between the pressure medium tank 35 and the connecting line 34, which leads to the centering valve 21. The switching valve 23 comprises a switching piston 37 which is movable against a return spring 36 and is acted upon by the pressure of a switching pressure chamber 38 and blocks the connection between the centering valve 21 and the pressure medium tank 35 above a switching pressure which can be set by means of the return spring 36. The switching pressure chamber 38 of the switching valve 23 is connected to the two control lines 9, 10 via a shuttle valve 39. The shuttle valve 39 operates in such a way that the control line 9 or 10 carrying the higher pressure is connected to the switching pressure chamber 38 of the switching valve 23.

Die Wirkungsweise der erfindungsgemäßen hydraulischen Zentriereinrichtung ist dabei folgende:
Solange in zumindest einer der Steuerleitungen 9 oder 10 ein vorgegebener Mindest-Steuerdruck herrscht, ist die hydraulische Zentriereinrichtung 21 nicht aktiviert, da die Schaltdruckkammer 38 des Schaltventils 23 über das Wechselventil 39 mit dem höheren der beiden in den Steuerleitungen 9 und 10 herrschenden Steuerdrücke y1 oder y2 beaufschlagt ist und somit den Schaltkolben 37 in eine Position verschiebt, in der die Verbindung zwischen dem Zentrierventil 22 und dem Druckmitteltank 35 unterbrochen ist. Sobald die Steuerleitungen 9 und 10 jedoch keinen oder keinen ausreichenden Steuerdruck führen, wird das Schaltventil 23 geöffnet und die Verbindungsleitung 34 wird mit dem Druckmitteltank 35 verbunden. Sofern bei Aktivierung des Zentrierventils 22 ein Ungleichgewicht zwischen den Drücken in den beiden Stelldruckkammern 1 und 2 herrscht, wird diejenige Stelldruckkammer 1 oder 2, welche mit dem höheren Stelldruck beaufschlagt ist, über die zugeordnete Stelldruckleitung 6 oder 7 und die entsprechende Zentrierleitung 26 oder 27 zum Druckmitteltank 35 hin entlastet. Die Entlastung erfolgt so lange, bis sich ein Druckgleichgewicht zwischen den Stelldrücken in den Stelldruckkammern 1 und 2 wieder eingestellt hat und somit auch die von den Zentrierleitungen 26 und 27 geführten Drücke übereinstimmen und der Zentrierkolben 31 in seine Neutralstellung zurückgeführt ist.The operation of the hydraulic centering device according to the invention is as follows:
As long as there is a predetermined minimum control pressure in at least one of the control lines 9 or 10, the hydraulic centering device 21 is not activated since the switching pressure chamber 38 of the switching valve 23 via the shuttle valve 39 with the higher of the two control pressures y 1 prevailing in the control lines 9 and 10 or y 2 is acted upon and thus shifts the switching piston 37 into a position in which the connection between the centering valve 22 and the pressure medium tank 35 is interrupted. However, as soon as the control lines 9 and 10 carry no or insufficient control pressure, the switching valve 23 is opened and the connecting line 34 is connected to the pressure medium tank 35. If there is an imbalance between the pressures in the two signal pressure chambers 1 and 2 when the centering valve 22 is activated, the signal pressure chamber 1 or 2 to which the higher signal pressure is applied becomes via the associated signal pressure line 6 or 7 and the corresponding centering line 26 or 27 Pressure medium tank 35 relieved. The relief takes place until a pressure equilibrium between the actuating pressures in the actuating pressure chambers 1 and 2 has been restored and thus the pressures guided by the centering lines 26 and 27 match and the centering piston 31 is returned to its neutral position.

Die vorstehend beschriebene erfindungsgemäße hydraulische Zentriereinrichtung 21 bewirkt dabei ein zügiges und sicheres Zurückführen des Stellkolbens 3 in seine Neutralstellung, in der die hydraulische Maschine ohne Verdrängungsvolumen arbeitet, auch dann, wenn in der Ansteuereinrichtung 8 eine Störung, insbesondere ein Bruch der Rückstellfeder 20, auftritt. Die Anordnung arbeitet auch dann zuverlässig, wenn der Speisedruck psp der Speisedruckleitung 15 entfällt, da nach Entlastung der Stelldruckkammern 1 bzw. 2 die Zentrierung durch die Zentrierfedern 4, 5 bewirkt wird. Durch die erfindungsgemäße hydraulische Zentriereinrichtung 21, die lediglich einen geringen konstruktiven Aufwand erfordert, werden Schäden infolge einer Überlastung der ansonsten unkontrolliert arbeitenden hydrostatischen Maschine am System vermieden.The hydraulic centering device 21 according to the invention described above brings about a swift and safe return of the adjusting piston 3 to its neutral position, in which the hydraulic machine works without displacement, even if a fault, in particular a break in the return spring 20, occurs in the control device 8. The arrangement also works reliably if the feed pressure p sp of the feed pressure line 15 is omitted, since after centering springs 4, 5 have relieved the pressure on pressure chambers 1 and 2. The hydraulic centering device 21 according to the invention, which only requires a small amount of construction, prevents damage due to overloading of the otherwise uncontrolled working hydrostatic machine on the system.

Um das Verständnis der Erfindung zu erleichtern, wird nachfolgend die Ansteuereinrichtung 8 anhand der Fig. 2A und 2B kurz beschrieben.In order to facilitate understanding of the invention, the control device 8 is briefly described below with reference to FIGS. 2A and 2B.

Fig. 2A zeigt einen Schnitt durch ein Ausführungsbeispiel der Ansteuereinrichtung 8. Der Steuerkolben 16 ist im dargestellten Ausführungsbeispiel als Stufenkolben ausgebildet und gibt bei Verschiebung aus der in Fig. 2A dargestellten Neutralstellung an den Steuerkanten 50, 51 die Verbindung zwischen den in Fig. 1 dargestellten Stelldruckleitungen 6 bzw. 7 mit der Speiseleitung 15 frei. Der bereits beschriebene Rückführhebel 18 der Rückführeinrichtung 17 ist um eine Achse 52 schwenkbar gelagert. Wie aus der in Fig. 2B dargestellten Schnittdarstellung entlang der Linie A-A in Fig. 2A besser zu erkennen ist, ist an der Verlängerung 53 des Rückführhebels 18 ein Zapfen 54 angeformt, der bei Verschwenken des Rückführhebels 18 einen der beiden Kipphebel 55 bzw. 56 auslenkt. Zwischen den hakenförmig ausgeformten Endbereichen 57 und 58 der Kipphebel 55 und 56 ist die Rückstellfeder 20 angeordnet. Die Kipphebel 55 und 56 stehen mit dem Steuerkolben 16 in Eingriff, um die bereits anhand von Fig. 1 beschriebene Rückstellkraft auszuüben. Die Rückstellfeder 20 bewirkt die Zentrierung des Steuerkolbens 16 nach Abschalten der über die Steuerdruckkammern 11 und 12 auf den Steuerkolben 16 einwirkenden Steuerdrücke y1 und y2. Ein Bruch der Rückstellfeder 20 hat, wie bereits beschrieben, zur Folge, daß die Zentrierung des Steuerkolbens 16 und somit des von diesem angesteuerten Stellkolbens 3 nicht sicher gewährleistet ist. Diesem Nachteil wirkt die vorstehend beschriebene erfindungsgemäße hydraulische Zentriereinrichtung 21 entgegen.2A shows a section through an exemplary embodiment of the control device 8. In the exemplary embodiment shown, the control piston 16 is designed as a stepped piston and, when shifted from the neutral position shown in FIG. 2A, gives the connection between the ones shown in FIG. 1 at the control edges 50, 51 Signal pressure lines 6 and 7 with the feed line 15 free. The return lever 18 of the return device 17 already described is pivotally mounted about an axis 52. As can be seen better from the sectional illustration along the line AA in FIG. 2A shown in FIG. 2B, a pin 54 is formed on the extension 53 of the return lever 18, which pin deflects one of the two rocker arms 55 and 56 when the return lever 18 is pivoted . The return spring 20 is arranged between the hook-shaped end regions 57 and 58 of the rocker arms 55 and 56. The rocker arms 55 and 56 are in engagement with the control piston 16 in order to exert the restoring force already described with reference to FIG. 1. The return spring 20 effects the centering of the control piston 16 after switching off the control pressures y 1 and y 2 acting on the control piston 16 via the control pressure chambers 11 and 12. A break in the return spring 20, as already described, has the consequence that the centering of the control piston 16 and thus of the actuating piston 3 actuated by the latter is not guaranteed. The above-described hydraulic centering device 21 counteracts this disadvantage.

Es ist ohne weiteres erkennbar, daß die Erfindung nicht auf das dargestellte Ausführungsbeispiel begrenzt ist. So kann das Schaltventil 23 ohne weiteres auch in die Zentrierleitungen 26 und 27 eingefügt sein und bei vorhandenem Steuerdruck y1 und y2 die Zentrierleitungen 26 und 27 unterbrechen.Ferner ist es denkbar, das Schaltventil 23 anstatt mit einem Wechselventil 39 durch entsprechende Drosseln mit den Steuerdruckleitungen 9 und 10 zu verbinden. Selbstverständlich kann die konstruktive Ausgestaltung des Zentrierventils 22 und des Schaltventils 23 bei Erhaltung der Funktion variiert werden.It is readily apparent that the invention is not limited to the exemplary embodiment shown. Thus, the switching valve 23 can also be easily inserted into the centering lines 26 and 27 and with the control pressure y 1 and y 2 present interrupt the centering lines 26 and 27. It is also conceivable to connect the switching valve 23 to the control pressure lines 9 and 10 by means of appropriate throttles instead of a shuttle valve 39. Of course, the design of the centering valve 22 and the switching valve 23 can be varied while maintaining the function.

Claims (6)

Verstell-Vorrichtung zum Verstellen eines zwischen zwei Stelldruckkammern (1, 2) angeordneten, auf das Verdrängungsvolumen einer hydrostatischen Maschine einwirkenden Stellkolbens (3) mit
einer Ansteuereinrichtung (8),
die zwei mit je einer Steuerleitung (9, 1O) verbundene Steuerdruckkammern (11, 12) und einen zwischen den Steuerdruckkammern (11, 12) angeordneten Steuerkolben (16) aufweist, der in Abhängigkeit von der Druckdifferenz zwischen den Steuerdruckkammern (11, 12) aus einer Neutralstellung verschoben wird und dadurch eine der Stelldruckkammern (1, 2) mit einer Speisedruckleitung (15) verbindet,
und mit einer hydraulischen Zentriereinrichtung (21),
die ein mit den Steuerleitungen (9, 1o) verbundenes Schaltventil (23) und ein mit den Stelldruckkammern (1, 2) verbundenes Zentrierventil (22) aufweist, wobei das Schaltventil (23) bei verschwindendem Steuerdruck in beiden Steuerleitungen (9, 1o) das Zentrierventil (22) so schaltet, daß dieses bei einer Druckdifferenz zwischen den Stelldruckkammern (1, 2) die mit höherem Druck beaufschlagte Stelldruckkammer (1, 2) entlastet, um den Stellkolben (3) in seine Neutralstellung, in der die hydrostatische Maschine ohne Verdrängungsvolumen arbeitet, zurückzuführen.Adjusting device for adjusting an adjusting piston (3) arranged between two adjusting pressure chambers (1, 2) and acting on the displacement volume of a hydrostatic machine
a control device (8),
which has two control pressure chambers (11, 12) each connected to a control line (9, 10) and a control piston (16) which is arranged between the control pressure chambers (11, 12) and which, depending on the pressure difference between the control pressure chambers (11, 12) is shifted to a neutral position and thereby connects one of the signal pressure chambers (1, 2) to a feed pressure line (15),
and with a hydraulic centering device (21),
which has a switching valve (23) connected to the control lines (9, 1o) and a centering valve (22) connected to the control pressure chambers (1, 2), the switching valve (23) doing this in both control lines (9, 1o) when the control pressure disappears Centering valve (22) switches so that when there is a pressure difference between the actuating pressure chambers (1, 2), the actuating pressure chamber (1, 2), which is pressurized with higher pressure, is relieved to move the actuating piston (3) into its neutral position, in which the hydrostatic machine has no displacement volume works, attributed. Verstell-Vorrichtung nach Anspruch 1,
dadurch gekennzeichnet,
daß das Schaltventil (23) zwischen dem Zentrierventil (22) und einem Druckmitteltank (35) angeordnet und nur geöffnet ist, wenn die Steuerleitungen (9, 1O) keinen oder keinen ausreichenden Steuerdruck führen.Adjusting device according to claim 1,
characterized by
that the switching valve (23) is arranged between the centering valve (22) and a pressure medium tank (35) and is only open when the control lines (9, 10) do not or no sufficient control pressure. Verstell-Vorrichtung nach Anspruch 1 oder 2,
dadurch gekennzeichnet,
daß ein mit beiden Steuerleitungen (9, 10) und dem Schaltventil (23) verbundenes Wechselventil (39) vorgesehen ist, das die den höheren Steuerdruck führende Steuerleitung (9, 10) mit dem Schaltventil (23) verbindet.Adjustment device according to claim 1 or 2,
characterized by
that a with two control lines (9, 10) and the switching valve (23) connected shuttle valve (39) is provided which connects the higher control pressure control line (9, 10) with the switching valve (23). Verstell-Vorrichtung nach einem der Ansprüche 1 bis 3,
dadurch gekennzeichnet,
daß das Zentrierventil (22) einen federzentrierten Zentrierkolben (28) aufweist, der zwischen zwei mit jeweils einer der Stelldruckkammern (1, 2) verbundenen Zentrierdruckkammern (24, 25) angeordnet ist.Adjusting device according to one of claims 1 to 3,
characterized by
that the centering valve (22) has a spring-centered centering piston (28) which is arranged between two centering pressure chambers (24, 25) connected to one of the actuating pressure chambers (1, 2). Verstell-Vorrichtung nach Anspruch 2 und 4,
dadurch gekennzeichnet,
daß der Zentrierkolben (28) so ausgebildet ist, daß er in seiner Neutralstellung, in der keine Druckdifferenz zwischen den Zentrierdruckkammern (24, 25) herrscht, die Verbindung zwischen den Stelldruckkammern (1, 2) und dem Schaltventil (23) sperrt und bei Verschiebung aus der Neutralstellung durch eine Druckdifferenz zwischen den Zentrierdruckkammern (24, 25) die Verbindung der mit dem höheren Druck beaufschlagten Stelldruckkammer (1, 2) über das Schaltventil (23) zum Druckmitteltank (35) hin freigibt.Adjustment device according to claim 2 and 4,
characterized by
that the centering piston (28) is designed so that in its neutral position, in which there is no pressure difference between the centering pressure chambers (24, 25), the connection between the actuating pressure chambers (1, 2) and the switching valve (23) is blocked and upon displacement from the neutral position by a pressure difference between the centering pressure chambers (24, 25) releases the connection of the actuating pressure chamber (1, 2) with the higher pressure via the switching valve (23) to the pressure medium tank (35). Verstell-Vorrichtung nach einem der Ansprüche 1 bis 5,
dadurch gekennzeichnet,
daß die Ansteuereinrichtung (8) ein Rückführelement (17) aufweist, das den Stellkolben (3) mit dem Steuerkolben (16) verbindet, um den Steuerkolben (16) nach Verstellen des Stellkolbens (3) in Richtung auf seine Neutralstellung zurückzuführen.Adjustment device according to one of claims 1 to 5,
characterized by
that the control device (8) has a feedback element (17) which connects the control piston (3) with the control piston (16) in order to return the control piston (16) after adjusting the control piston (3) in the direction of its neutral position.
EP96112820A 1995-10-31 1996-08-08 Control device with hydraulic centering mechanism Expired - Lifetime EP0771949B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19540654A DE19540654C1 (en) 1995-10-31 1995-10-31 Adjusting device for adjusting piston of hydrostatic engine
DE19540654 1995-10-31

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EP0771949B1 EP0771949B1 (en) 2001-05-09

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DE102013110568A1 (en) * 2013-09-24 2015-03-26 Claas Selbstfahrende Erntemaschinen Gmbh Drive system for hydraulically driven working members of a working machine
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EP0771949B1 (en) 2001-05-09
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