EP0514748B1 - Device for restricting the stroke of a hydraulic cylinder - Google Patents

Description

The invention relates to a device for limiting the stroke of a hydraulic cylinder according to the preamble of claim 1.

From DE-OS 23 23 522 a stroke-dependent valve device for limiting the working movement of the piston is known for an auxiliary power steering device. When a stroke end position is reached, opening a valve causes a pump short circuit between the pressure and suction side of the pressure medium pump. To actuate the valve, control cams are provided which are connected to the working piston and which, when the predetermined stroke end position is reached, switch off a pressure force which holds the control slide together with a spring in the rest position blocking the pump short circuit. Valve and line expenditure for switching off the working pressure are relatively high in this known device.

The invention has for its object to provide a particularly simple and inexpensive device for limiting the stroke of the piston of a working cylinder, which can be combined with the working cylinder to form a unit in a compact design that requires structurally simple actuating elements and in which with simple means a hydromechanical Position control loop can be represented. In addition, the device should be such that the stroke limitation with respect to the point in time or piston position can subsequently be easily adjusted within limits.

This object is achieved by the characterizing features a) to f) of claim 1.

Thereafter, the stroke limitation is brought about by the mechanical actuation of a single valve before the predetermined end position is reached, by branching off from the pressure medium supply line such an amount of pressure medium that the working piston, which on the opposite side is exposed to the action of a constant pressure of an accumulator, in the specified end position is held hydraulically. It is particularly advantageous that the mechanical action on the shut-off valve is not always effective, but only starts before the predetermined stroke end position of the working piston is reached. For the feedback from the working piston to the shut-off valve, only a relatively short distance of the entire stroke is required. It corresponds to the path from the contact closure of the towing bar with the working piston to the occurrence of the regulated state, d. H. until such a position of the slide piston is reached, in which the entire delivery of the pressure source can flow off via the branch to the tank. In this state, a hydromechanical position control loop has stabilized without the need for an external circuit.

Advantageous developments of the device according to claim 1 are described in the subclaims. To simplify assembly and to facilitate maintenance, the shut-off valve is designed as a detachable component of the working cylinder.

The shut-off valve is essentially designed as follows. In the housing bore for the slide piston, two ring grooves lying axially one behind the other are provided, to which on the one hand the branch line and on the other hand the tank line are connected, while the slide piston has a circumferential groove adapted to the ring grooves in its axial length. In the starting position, the first circumferential groove, to which the supply line is connected, is covered by the slide piston. After leaving the starting or basic position of the slide piston, the circumferential groove increasingly also covers the previously blocked circumferential groove, so that an increasing proportion of the delivery quantity supplied by the pressure source can flow off via the branch to the tank. Due to the fact that the diverted delivery rate does not increase suddenly, but rather over a certain period of time up to the maximum value, a sudden limitation or switching off of the working stroke of the piston is avoided.

The return movement of the working piston is brought about by a further reduction in the pressure on the piston bottom side of the working piston. For this purpose, the slide piston is moved independently of the working piston by external action in the sense of a further opening of the branch line in the direction of the tank. This can be done hydraulically by mechanical actuation or by actuating pistons. For hydraulic actuation, an attachment is advantageously attached to the housing of the shut-off valve at the free end, in which two actuating pistons are mounted, by means of which the slide piston can be moved into its fully open position against the constantly acting restoring shaft. The river Oder the actuating pistons are advantageously controlled with the aid of a solenoid valve.

In order to be able to subsequently change the time of the stroke limitation, the stop at the inner end of the towing bar is advantageously designed as an adjustable stop.

An advantageous solution of an adjustable stop provides that the stop is mounted with an internal thread on a threaded section of the tow bar, the rear end of the tow stands protruding from the device and is provided with a suitable profile for the execution of a rotating adjustment movement. The stop for its part is secured against twisting in this embodiment in the hollow piston position, but is guided in an axially slidable manner.

Fig. 1

einen Hydraulikzylinder mit Abschaltventil in einem Axialschnitt in Verbindung mit einem hydraulischen Schaltschema, wobei der Arbeitskolben in der Ruhestellung steht,

Fig. 2

eine der Fig. 1 entsprechende Darstellung, in der jedoch der Arbeitskolben in der Abschaltstellung steht, und

Fig. 3

eine der Fig. 1 entsprechende Darstellung, die den Arbeitskolben während des Rückhubes zeigt.

The invention is explained in more detail below using an exemplary embodiment which is illustrated schematically in the drawing. It shows:

Fig. 1

a hydraulic cylinder with a shut-off valve in an axial section in connection with a hydraulic circuit diagram, the working piston being in the rest position,

Fig. 2

a representation corresponding to FIG. 1, but in which the working piston is in the switch-off position, and

Fig. 3

a representation corresponding to FIG. 1, which shows the working piston during the return stroke.

The exemplary embodiment shown in the drawing includes a hydraulic cylinder (1) with a working piston (2) in the form of a differential piston, from which a hollow piston rod (3) closed at the end, which ends outside the cylinder (1).

At the other end, the cylinder (1) is closed by a head plate (4) which delimits the working pressure chamber (5) on the piston crown side.

The housing (6) of a shut-off valve (7) is detachably connected to the top plate (4). A slide piston (9) is slidably mounted in a bore (8) concentric with the cylinder axis, and a return spring (10) acts on its inner end face. Fig. 1 shows the slide piston (9) in its basic position, in which it is connected with its outer end face to a stop ring (11).

The slide piston (9) is penetrated in a central bore (12) by a towing rod (13) which extends through a bore (14) in the piston (2) into the hollow piston rod (3). At its inner end, a ring stop (15) sits on the threaded rod (13) on a threaded section, which is guided in the longitudinal bore (16) of the piston rod (3) in a slidable manner, but secured against rotation. Recesses (17) in the lateral surface of the stop (15) create a connection between the spaces on the two sides of the ring stop (15).

A support ring (18) is fastened to the tow bar (13) in the area of the working pressure chamber (5), which rests on the head plate (4) in the basic position and thus limits the axial mobility of the towing bar (13) in the opposite direction to the working movement of the piston (2). Furthermore, in the vicinity of the rear end of the towing bar (13), a driving ring (19) is fastened on the towing bar (19), which comes into contact with the stop ring (11) when the towing bar (13) is towing.

A circumferential groove (20) is incorporated on the circumference of the slide piston (9), which cooperates with two annular grooves (21, 22) in the housing (6) and is dimensioned in its axial length so that it is in the open position of the slide piston (9 ) both ring grooves (21, 22) completely covered (Fig. 3). In the opposite closed position of the slide piston (9), the circumferential groove (20) lies outside the inner annular groove (21), which in this position is blocked by the annular piston (9).

With the housing (6) at its free end, an approach (23) is connected, the housing for z. B. forms two piston tappets (24) which can act on the stop ring (11) when pressurized. With E₁ a device for indicating the position of the towing bar (13) is indicated, which triggers a signal when the end piece (25) of the towing bar (13) is at the same level with the device E₁.

For the connection of the pressure medium supply line A₁ to carry out the working stroke of the piston (2) on the housing (6), a bore (26) and for the connection of the tank line T, a bore (27) is provided. On the one hand, a channel leads from the bore (26) to Pressure medium chamber (5) and on the other hand a channel to the annular groove (21). The bore (27) is only connected to the annular groove (22). Furthermore, a bore (28) is provided on the cylinder (1) for connecting a pressure medium line P₂, from which a channel leads to the pressure medium space on the ring side of the piston (2). Finally, the approach (23) contains a bore (30) for connecting a line (31) through which the pressure medium for acting on the tappet pistons (24) is supplied or removed.

The components also provided for the operation of the hydraulic cylinder are explained below in connection with the description of the mode of operation.

Initial position:

The working piston (2) is in the retracted position. The spool (9) of the shut-off valve (7) assumes the closed position under the action of the return spring (10). The pressure medium chamber (29) can be supplied with the pressure medium from a pressure source (32) via a check valve (33). On the feed line P₂ is an adjustable pressure relief valve (34) on the one hand and a hydraulic pressure accumulator (35) on the other hand via a directional control valve Y₂ behind the check valve. Also indicated are a pressure measuring device (36) and safety accessories (37).

After switching on the directional control valve Y₂, the hydraulic pressure accumulator (35) is loaded, for. B. to a pressure of 60 bar. This pressure is in the pressure medium chamber (29) and holds the working piston (2) in the retracted position.

Working stroke (Fig. 1):

Another pressure source (38) is connected via line A₁ to the bore (26) and supplies the pressure medium for the application of the working pressure chamber (5). A check valve (39) prevents backflow through line A 1. At the outgoing from the pressure source (38) line, a switchable pressure relief valve Y₃ is connected. If the valve Y₃ is connected to voltage, the pressure medium flows from the pressure source (38) into the working pressure chamber (5). Since the shut-off valve (7) is closed, pressure can build up, which causes the working piston (2) to extend.

The extension speed depends on the delivery rate of the pressure source (38), while the pressure in the pressure medium chamber (5) (excluding external forces) depends on the area ratio of the effective piston areas and the operating pressure in the pressure medium chamber (29).

Stroke cut-off in the end position (Fig. 2):

If the extending working piston (2) comes into contact with the ring stop (17) shortly before reaching its end position with a support surface (40) provided for this purpose (start of mechanical feedback), the now moving drag rod (13) dragged along the driving ring (19) of the slide piston (9) in the opening direction. The circumferential groove (20) reaches the area of the annular groove (21) and thus establishes a (branch) connection from the feed line A 1 to the tank line T. As a result, part of the delivery of the pressure source (38) can flow to the tank; the extension speed of the working piston (2) is reduced because a defined counterforce is effective on the ring side of the piston (2).

In this way, a hydromechanical position control loop is created without the need for an external circuit, which is stabilized as follows:

The opening stroke of the slide piston (9) adjusts itself automatically so that the flow rate flowing in via A 1 can flow off completely via the line T.

• eine externe Kraft auf die Kolbenstange (3) einwirkt und/oder
• die Fördermenge der Druckquelle (38) verändert wird.

Of course, a change occurs in the open position of the spool (9), provided that

• an external force acts on the piston rod (3) and / or
• the delivery rate of the pressure source (38) is changed.

However, if nothing is changed, the working piston (2) of the hydraulic cylinder remains "regulated" in this position. The working piston has thus reached the end position of the working stroke without the action of a mechanical lock.

As soon as the tow bar (13) is towed by the working piston (2), the device E 1 signals this state.

As is clear from these explanations, the mechanical feedback takes up only a very small part of the total length of the working stroke of the working piston (2). It corresponds essentially to the overlap of the circumferential groove (20) with the annular groove (21).

Return stroke (Fig. 3):

The plunger pistons (24) are expediently operated with the pressure medium from the pressure source (30). For this purpose, the line (31) is connected to the line P₂ via a switchable 4/2-way valve Y₁. The connection T of the valve Y₁ is, as usual, connected to a line leading to the tank; port A is blocked.

If the solenoid valve Y 1 is connected to voltage, the plunger slide (9) is moved further out of its regulated position in the opening direction by extending the tappet piston (24), whereby the overlap of the circumferential groove (20) with the annular groove (21) is further increased. The associated reduction in the throttle function of the shut-off valve (7) causes the pressure in the working pressure chamber (5) to drop so much that the prevailing pressure on the ring side of the working piston (2) retracts it until the starting position is reached. The pressure medium that was stored in the hydraulic pressure accumulator (35) when it was extended is used for this.

During the return stroke, it is immaterial whether the flow rate of the pressure source (38) either flows back to the tank via line A 1 or is passed directly to the tank via the switchable pressure relief valve Y 3.

If the hydraulic cylinder (1) is to be operated continuously, it is advisable not to switch off the pressure relief valve Y₃ during operation and only to realize the switching point of the working piston (2) with the solenoid valve Y₁.

Claims (8)

1. Arrangement for limiting the stroke of a hydraulic cylinder, more especially for presses of the like, with a bilaterally operable power piston in the form of a differential piston, from which a hollow piston rod (3) emanates on the one side, characterised by the following features:

   a) the operating pressure space (5) on the piston head side is filled with the pressure means of a pressure source (38) via an inflow line (A₁), and is emptied into the tank with the aid of a shut-off valve (7), which is connected on the piston head side of the power cylinder (1) coaxially to the latter,

   b) the space (29) on the ring side of the power piston (2) is constantly supplied with pressure means by the action of a pressure store (35), and

   c) the shut-off valve (7) contains a slide valve piston (9) which is retained in the closing position by elastic restoring force, e.g. of a spring (10), and by means of which a branch from the inflow line (A1) to the power cylinder (1) to a line (T) leading to the tank can be controlled,

   d) in the slide valve piston runs a tow rod (13), which extends with one end through the power piston (2) to the inside (16) of the hollow piston rod (3) of the power piston (2), and with a front-ended stop (15), before the limit position of the working movement of the power station (2) is reached, comes into contact closure with the latter,

   e) on the tow rod (13) there is contained at the opposite end an annular shoulder (19), by means of which, upon contact closure, the slide piston (9) is moved in the direction of the open position until a regulated-out state is reached in which the power piston (2) is hydraulically retained in its limit position,

   f) with the shut-off valve (7) is coordinated at least one operating piston (24) driven by pressure means, which, after termination of the working movement of the power piston (2), can act upon the slide valve piston in the sense of a further opening movement, by which the latter leaves the previous regulated-out position, and by further opening of the connection from the inflow line (A1) to the tank line (T), reduces the pressure of the pressure means on the piston head side to such an extent that the power piston (2), because of the overweight of the counter-pressure on the ring side, can be moved back into its initial position.
2. An arrangement as claimed in Claim 1, characterised in the that pressure source (38) for the working stroke is connected, on the one hand, via a non-return valve (39) to the inflow line (A₁), and on the other hand, via a controllable pressure-limiting valve (Y₃) to an outflow valve.
3. Arrangement as claimed in Claim 1 or Claim 2, characterised in that the shut-off valve (7) forms a detachable component of the operating cylinder (1).
4. Arrangement as claimed in one of the Claims 1 to 3, characterised in that in the housing bore (8) for the slide valve piston (9) are provided two annular grooves (21 and 22) situated axially one behind the other, to which, on the one hand, the branch line, and on the other hand, the tank line (T) are connected, and that the slide valve piston (9) has a circumferential groove (20) which, after the slide piston has left the initial position, also increasingly covers the second axially rear annular groove (21).
5. Arrangement as claimed in one of Claims 1 to 4, characterised in that there is fixed to the housing (6) of the shut-off valve (7) at the free front end, an attachment (23), in which two operating pistons (24) are mounted, by which the slide valve piston (9) can be moved into its fully open position against the restoring force.
6. Arrangement as claimed in one of Claims 1 to 5, characterised in that the operating piston of pistons (24) can be controlled with the aid of a solenoid valve (Y₁).
7. Arrangement as claimed in one of Claims 1 to 6, characterised in that the stop (15) of the tow rod (13) is axially adjustable from outside.
8. Arrangement as claimed in Claim 7, characterised in that the stop (15) is mounted with an inner thread on a threaded section (13₁) of the tow rod (13) and that the rearward end of the tow rod (13) projects from the attachment (23) and is provided with a suitable profile or the like for carrying out a rotating movement in order to adjust the stroke limitation.

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