EP0216776B1 - Pressure-adjusting system for a hydraulically-operated clutch and/or brake for the drive shaft of a press - Google Patents

Abstract

The pressure-adjusting system for controlling and damping the starting and braking operations, which is adapted to the requirements of press operation by means of an electric control system (37, 38, 39) according to the travel, time or angle, prevents at each cycle restrictions in the feed line (3) between the safety valve (4) of the press and the actuation cylinder (5) and allows an optimum pressure pattern by a parallel line (15) which is inserted therein, through which, depending on the setting position of a distribution valve (23) fitted inside, the pressure can be decreased or increased to a pre-selected degree without a considerable loss of time. A pressure-maintaining system, which is itself independent of the position of the safety valve of the press together with a storage unit (19) and topping-up system permits not only the pressure relief to the tank (1), but also the additional pressure or a removal from the supply line (3) directly after the switching over of the magnetic setting elements (31, 33, 35) controlling the valves (4, 23), which are triggered by signal emitters (39), which mark the various partial strokes of the press.

Description

The invention relates to Druckbeeinflussungsein- _T ichtungen for hydraulically actuated clutch-brake combination or separately arranged clutches and brakes for the drive shaft of a press.

Devices of this type or efforts to absorb shock and reduce noise on presses that work with partial pressure or maximum pressure phases have become known in many different ways.

According to EP-A-00 51 684 z. B. suggested that the actuating cylinder be preceded by a program-controlled proportional valve in the feed line and that the press stroke be started with an intermediate pressure that was greatly increased compared to a partial pressure and then to set the desired speed by switching over to a lower partial pressure before the max. Working pressure is released for the actual work process. Not only is a sudden start associated with high mechanical loads on the drive elements, but the arrangement of a throttle in the feed line also slows down the oil flow to and from the actuating cylinder, so that longer switching times also result with increased damping. This reduces the parts output. There is also no influence on the pressure reduction or braking phase at the end of the press stroke. In addition, safety concerns against the arrangement of a damping valve in the main pressure line itself appear justified.

Other solutions also make use of the possibility of achieving damping by means of a throttle element arranged at the input or output of the actuating cylinder of the press.

According to DE-A-1 502 319 and 1 577 264 for compressed air controls, it is known for the throttle bodies of the feed line to only release a partial pressure below the maximum pressure after starting and only then to release the maximum pressure, but this is still undesirable hard speed transitions and there is also no influence on the emptying speed or braking after passing through the press work area. This method is therefore unsuitable for hydraulic systems.

According to DE-A-2 321 117, a pressure damper is provided for a hydraulic application, which consists of a pressure-dependent locking slide in a pressure relief line branching off the line carrying the hydraulic fluid, in which throttle channel cross sections, which are variable as a function of the differential pressure, differ by a locking member provided with a preselectable cone Pressure relief effects should cause automatically depending on the position of the press ram. This variant also makes it difficult to fill up the actuating cylinder quickly and makes it impossible to make major changes to the setting without dismantling the damper locking element, e.g. B. for the purpose of using a truncated cone with other slopes. The viscosity influences are also of particular importance here. In addition, with higher damping effects, temporal extensions of the entire press stroke due to the expansion of the travel path due to the slower inflowing oil cannot be ruled out, so that the partial output of the press can also decrease.

A separate influencing of the emptying or braking phase after passing through the working area of the press is also not provided here or is not possible.

Starting from this hydraulic device according to DE-A-23 21 117, the object of the invention is seen in further developing the pressure influencing devices for hydraulic actuation in such a way that, while avoiding damping valves in the feed line downstream of the press safety valve and also highly viscosity-dependent, only pressure medium-actuated switching elements, both for coupling or the pressure build-up as well as for braking or pressure reduction shock-absorbing and quickly functioning pressure modulation is achieved, which, however, z. B. for adjustment work, quickly cancel or change without internal intervention and then repeats easily identically.

The solution is achieved with the characterizing features of claim 1 essentially by using a directional control valve that can be electrically adjusted to a blocking position and a plurality of pressure relief stages with return to the tank, each with differently throttling pressure relief conditions between the press safety valve linked to it and the actuating cylinder in exact association with the respective The press ram position is driven and can be adjusted sensitively, without interference from flow obstacles in the main path to or from the actuating cylinder having to be accepted. Due to the adjustability of different pressure levels in parallel branches of the pressure relief line when it can be activated via a single common directional valve and its electrical function linkage with the press safety valve, the movement of the locking elements is so reliable that the selected operating conditions can be maintained exactly and can be easily found again after changes in operation are.

It is not necessary to change the valve (e.g. by using a plug with a different inclination) to change the respective setting, and both pressure and quantity values as well as activation times can be varied within wide limits or adapted to requirements without the individual work cycles the press strokes are more necessary wise to stretch in time.

It can be mastered with the same device even extreme operating conditions without hydraulic changes, such as z. B. with one-stroke operation and when setting up new production processes. Since no special mechanical blocking elements are used and standard valves are available for this device, the effort is very inexpensive and reliable.

In addition, the device, which can preferably be implemented in the cartridge principle, is free of space problems, since the control elements can be inexpensively installed outside the area of the actuating cylinder. The control electronics also enable various automatic safety checks for each individual operating phase and rapid error detection. Thanks to flow obstacles such. B. throttle valves, free main feed line of the actuating cylinder, a very fast filling of the cylinder, i.e. short cycle times with soft starting, clutching and braking, and thus a reduction in noise and wear in all engagement and disengagement processes of the entire press stroke is achieved without wasting time.

The precise change of the working pressure even in the extremely short phases of the transition to the operating speed or at a standstill allows the torque to be briefly reduced in the phases outside the working area, i.e. to reduce the kinetic energy, as long as it is not outside the press working area anyway is fully needed. In this way, the occurrence of vibration resonances and impacts can also be prevented on the entire circulation. By means of the proportional technology known per se, the damping effect can be automatically adapted to a wide variety of speed requirements in an advantageous manner.

In addition, the device can be used almost identically for any type of press, since neither, e.g. B. in the clutch or brake of the press, special spring or surface adjustments made even valve inserts in special damper valves for different operating conditions must be replaced. Once set values have been changed even after interim changes, e.g. B. for single stroke, identifiable quickly, and changing a pressure phase of the partial strokes does not necessarily result in a change in the following partial strokes. In clutch-brake combinations, neither springs nor piston surfaces need to be different, so that simple manufacturing conditions also arise in this regard.

Further refinements of the invention are specified in the subclaims.

According to claim 2, an advantageous for 2 partial pressure levels and a maximum pressure embodiment with a refill option from a parallel to the feed line of the actuating cylinder pressure line from the pump of the system or from a memory is proposed, which contributes with a special automatic shutoff valve that both pressure build-up and Depressurization takes place quickly and always under the same preselected conditions. In the event that even more pressure stages are to be operated, only correspondingly more branches of the pressure relief line and corresponding valve connections would have to be provided.

According to claim 3, a precaution is taken to automatically switch off interference from the parallel pressure line into the feed line with certainty.

According to claim 4, the automatic refill option for the memory is also provided for situations in which the shut-off valve is closed and at the same time the shut-off valve is kept free of differential pressure influences.

According to claim 5, the two line branches of the pressure limitation stage are protected by a separate pressure damping device against interference from the feed line.

According to claim 6, the starting phase is started with a reduced pressure by a predetermined amount in a branch of the pressure relief line of the pressure fluid in the feed line can first be discharged into the tank via the pressure relief line or the directional control valve.

According to claim 7, high pressure is brought about in the feed line by blocking the pressure relief line, but residual damping from the damping valve can be maintained.

According to claim 8, a further damping phase is initiated towards the end of a press stroke in that the braking torque for the press ram is reduced to a level that is just required by a further relief position of the directional valve.

According to claim 9, the press stroke is ended quickly and clearly after the previous braking by opening the drain opening of the press safety valve and closing the pressure relief line via the directional valve.

The invention also offers the possibility of connecting the electrical connection between the press safety valve and the directional control valve to a safety circuit (not shown), which reports any deviation from the desired state and also the source of the fault, or switches off the press when or as soon as the damping does not work according to the setting. According to the principle of the same effect, appropriate signal transmitters and further directional valves can be used to arrange any number of pressure stages in the same way without having to provide any flow regulators in the actual feed line from the press safety valve to the actuating cylinder.

• Fig. 1 ist ein Schaltschema einer Druckbeeinflussungseinrichtung für eine Kupplungs-Brems-Kombination einer Presse.
• Fig. 1A stellt die Anschlußmöglichkeit des gleichen Systems für eine getrennte Kupplung und eine getrennte Bremse einer Presse dar.
• Fig. 2 ist das die Druckbeeinflussungsphasen bestimmende Umlaufdiagramm eines Pressenhubes.
• Fig. 3 ist eine zugehörige Schaltstellungstabelle der Magnetstellglieder an Pressensicherheitsventil und Wegeventil.
• Fig. 4 ist ein Arbeitsdiagramm eines Pressenhubes mit der erfindungsgemäßen Druckbeeinflussungseinrichtung.

The invention is explained in more detail with reference to the schematic exemplary embodiment shown in the drawings:

• Fig. 1 is a circuit diagram of a pressure leg Flow device for a clutch-brake combination of a press.
• Fig. 1A shows the possibility of connecting the same system for a separate clutch and a separate brake of a press.
• 2 is the circulation diagram of a press stroke which determines the pressure influencing phases.
• Fig. 3 is an associated switching position table of the magnetic actuators on press safety valve and directional control valve.
• 4 is a working diagram of a press stroke with the pressure influencing device according to the invention.

In Fig. 1, the most important elements of the hydraulic system and the most important electrical connections with the signal or position sensors on the press or on its plunger or drive shaft are shown in the position which they are at top dead center (zero position) of the press ram Take home position 0.

From the tank 1, the pump 2 takes hydraulic fluid into the feed line 3, which finally opens via the press safety valve 4 into the actuating cylinder 5 of the brake 6 or the clutch 7 of the clutch-brake combination. In the actuating cylinder 5, an actuating piston 8 is supported against a clutch-side return spring 9. Depending on the switching position, the piston rod 10 can rest on the brake 6 or clutch 7. In the zero position 0, the brake 6 is activated because the press safety valve 4 is relieved of pressure to the tank 1, so that the return spring 9 can press the piston 8 and its rod 10 against the brake 6, whereby the press ram, not shown, is locked. A total of four end take-off lines branch off from the feed line 3, three of which 12, 13, 14 in front of the press safety valve 4, one -15 - between the same and the actuating cylinder 5. A pressure cut-off valve 16 is connected via line 12, which uses a check valve 51 to control the feed pressure in front of the press safety valve 4, irrespective of its position and any previous withdrawals, and, with the appropriate setting, allow excess fluid to flow back into the tank 1. The line 13 has a check valve 17 that prevents backflow and is a pressure compensation line for a further pressure-maintaining system. It ends in a differential pressure-dependent shut-off valve 18 in line 14 or 20, which connects the shut-off valve 18 via a throttle 21 to a reservoir 19, which from line 20 via a further line 22 with an outlet of a 4/3-way valve 23 facing away from the press communicates. This directional control valve 23 is the termination of the pressure relief line 15, which branches off the current after the press safety valve 4 and whose outputs, depending on the position, either turn to the tank 1 or into the aforementioned connection line 22. In the pressure relief line 15 located upstream of the directional control valve 23, there is initially a damping valve 24, seen downstream, in whose spring-loaded floating piston an internal throttle is arranged downstream and which can release an outlet to the tank 1 if the pressure is too sudden or too high. The pressure relief line 15 then branches into two branches 25, 26, each of which has its own adjustable and pressure-dependent pressure relief valve 27, 28. One branch 25 then opens into a first press-side connection 29 of the 4/3-way valve 23, while the second branch 26 opens into a second press-side connection 30 there. Both connections 29, 30 are in the initial position shown in FIG Zero position 0 of the press in locked position, d. that is, there is no pressure relief. - The accumulator 19 releases volume via the check valve 53 when engaging. The directional control valve 23 is switched again after a start phase 41, 42, as a result of which the accumulator 19 can then only be filled via the throttle 54. After the shut-off valve 18 is closed, the accumulator 19 is only connected to the feed line 14 via the throttle 52.

The press safety valve 4 is shown here in a simplified manner so that it is provided on one side with magnetic actuators 31 for opening a passage position, which work against return springs 32 on the other side. The directional valve 23 has magnetic actuators and return _- springs 33, 34 and 35, 36, which are opposite each other and separately operable are an electrical control system 37 which is coupled together via a switch box 38 to the solenoid actuator 31 of the press safety valve 4 and its switching commands both from Hand as well as one or more signal generator (s) 39 can receive the z. B. from path, time or angle encoders on the press, in the press ram or the drive shaft, etc., may exist.

In Fig. 1A, the feed line 3 with a separate arrangement of the brake 6 and clutch 7 is only divided into their separate actuating cylinder 5, without the need for separate switching elements.

2 shows the initial position (zero position) 0 at 360 ° of the press flywheel 40. After the start phase 41, 42, a first changeover position is generally arranged at approximately 10 to 20 ° after the initial position 0. According to the invention, there is only then an increase in pressure for the clutch, which leads to the working area 43A of the tappet being reached at approximately 120 to 150 °. This is followed by a constant pressure zone 43B. This is followed by a pressure reduction area 44 to low pressure from a second switching point at approximately 270 to 320 °. The actuating piston 8 is then pushed back into its initial position in the region 44 and the braking is carried out in the region 45 until the valves 4 and 23 are brought back to the initial position, that is to say in the pressure relief position, at the third switchover point at approximately 340 to 350 ° . Valves 4 and 23 are located in area 46 back to the starting position.

In Fig. 3 the positions of the magnetic actuators 31, 33, 35 or the valves 4 and 23 corresponding to the above sequence are shown in a table. The full points mean excitation of the respective magnetic actuator, the open circles the rest position and the crossings the blocking of the valve passage in question.

At 0 or 360 °, all actuators are in the initial position, that is, the magnetic actuators 31, 33 and 35 are not energized, and the press safety valve 4 in the pressure relief position and the directional control valve 23 in the blocking position.

At the start, the magnetic actuator 31 is energized, so that the press safety valve 4 releases inlet to the actuating cylinder 5. At the same time, however, the first pressure relief position of the directional control valve 23 is activated by excitation of the first magnetic actuator 33, that is to say a filling pressure deviating from the pump pressure is driven.

At a press stroke of approx. 10 to 20 °, press safety valve 4 or magnetic actuator 31 remains activated, however directional control valve 23 or its magnetic actuator 33 returns to the blocking position and thus causes the full pump pressure to be available as filling pressure on actuating cylinder 5 for work area 43.

At approximately 270 to 320 °, the press safety valve 4 or the magnetic actuator 31 remains activated, however, the magnetic actuator 35 or its directional control valve 23 now opens via another pressure relief outlet and thus brings about a pressure reduction which does justice to the reduced torque in the braking phase 45 .

At approx. 340 to 350 °, the press stroke ends with the deactivation of the press safety valve 4 by the return of the magnetic actuator 31 to the pressure relief position and the magnetic actuator 35 to the blocking position.

4, the various pressures in the actuating cylinder 8 are shown schematically with continuous lines 47, the torque curve at the clutch M _K with dashed lines 48 and the speed curve n with dash-dotted lines 49 over the time t of a press stroke. In practice, there are naturally smooth and rounded transitions between the different values. In the start phase 41, in which a low pressure is built up in the brake cylinder 8, the same must first reach the response pressure PA, that is, for. B. overcome the spring resistance and static friction before the pressure PK sufficient to close the clutch is reached. Then, using a further acceleration pressure AE P _ee, the pressure increases up to the value of the so-called switch-on pressure P _E , at which the clutch retains torque M _K until the clutch engagement is complete and then the actual press work area 43A with the pressure rising to the nominal pressure P _N begins. After a constant pressure zone 43B, the pressure runs out after a pressure reduction area 44, in which the pressure fluid is pushed out of the brake cylinder 8, with a brake area 45 reduced by the hydraulic counter pressure P _H. The speed change is initiated smoothly by the braking effect of the braking pressure APg _r . A braking torque M _{B can be switched} until the speed n has completely dropped to 0.

The filling pressure in the brake cylinder 8 is thus reduced to low pressure before the end of the phase in order to avoid shock, and in the region 46 the valves 4 and 23 are again in the starting position.

The press speed n only begins at the point of engagement of the clutch at the end of the start phase 41, reaches its maximum before the end of the pressure build-up area 42, remains at this value during the work area 43A and the constant area 43B. With the beginning of the pressure reduction area 44, it drops to a low pressure and towards the end of the press stroke with a reduced braking area 45 quickly returns to 0 in the starting position 46. The continuously increasing or decreasing gradual acceleration and deceleration in the shortest possible time cause shocks when tearing loose in the starting phase just as avoided or greatly reduced as when braking after the end of the pressing work. The difference compared to a previously customary type of pressure influencing by means of a throttle section after the press safety valve 4 according to the prior art mentioned at the beginning of the description is indicated by the pressure curve 50, which is also shown in FIG. 4 with a dotted line.

The functional sequence begins at top dead center in zero position 0 with the press ram stationary, in the start phase 41, 42 with the downward stroke and the excitation of the magnetic actuator 31 of the press safety valve 4 and of the first magnetic actuator 33 on the directional control valve 23, which has a pressure compensation preselected on the pressure limiting valve 27 brings about the first branch 25 of the pressure relief line 15. The accumulator 19 delivers oil via the check valve 53 or line 14 into the main feed line 3, as long as the shut-off valve 18 is relieved on the spring side via line 14A and line 22 via directional valve 23 to tank 1. The throttle 21 prevents oil from flowing back into the line 14A from there, and that the shut-off valve 18 would thereby close again too soon. Thus, oil flows here with both the pressure of the pump 2 and the accumulator 19 in the high pressure phase via the line 3 to the actuating cylinder 5, without having to pass through a further throttle element other than the press safety valve 4. The piston rod 10 of the clutch / brake combination 6/7 has previously been in the braking position on the brake 6 due to the pressure of the spring 9. As soon as the hydraulic pressure in the brake cylinder 5 corresponds to the spring pressure P _F , the piston 8 contacts the clutch 7 .

The pressure in the actuating cylinder 5 initially rises in accordance with the spring characteristic at maximum delivery rate (without throttling effect in FIG. 3) Line quickly up to the spring pressure P _F , then further due to the spring characteristic of the clutch 7 up to the clutch closing pressure P _K. Only now that no more compression volume is needed, the pressure corresponding to the total delivery rate from pump 2 and accumulator 19 increases rapidly to a value preselected at pressure relief valve 27, which is above the closing pressure P _{K of} the clutch and which acts as switch-on pressure P _E. With the same, the damper valve 24 is relieved on the spring side and can release excess pressure to the tank 1, so that the pressure in the actuating cylinder 5 remains constant at a reduced value during this phase. The acceleration of the drive shaft of the press is thus controlled with the differential pressure which results from the value set on the pressure relief valve 27 and the closing pressure P _{K of} the clutch. With this relatively low acceleration pressure dP _ae he therefore follows the speed change on the shaft from 0 to operating speed with a much lower pressure surge than at full pump pressure, that is to say in a short time period. A coordinated with the reaching of the operating speed n setting a signal transmitter 39 on the press, not shown, then causes the de-energization of the magnetic actuator 33 and thus the decrease of the directional control valve 23 in the blocking position, so that no pressure reduction takes place and the maximum, with the corresponding position of the press ram Pressure from the pump 2 would build up quickly, which is only limited by the pressure shut-off valve 16 directly adjacent to the pump 2, because due to its area ratio, the damper valve 24 then also closes its drain to the tank 1. This switchover from low pressure to high pressure takes place in good time after the end of the acceleration process that in the working area 43 of the press, before reaching bottom dead center at 180 ° of the press stroke in the feed line 3, the nominal pressure P _{μ is} available and thus the torque required for the nominal pressing force M _"stands. By de-energizing the solenoid actuator 33 and the shut-off valve 18 is closed again, due to its area ratio is available. Once the memory 19 is filled, thus there is only a connection via the throttle 52 to the line 3, as well as the pressure equalization line 13 via the valve 17 blocks the connection from the accumulator 19 to the feed line 3. At the same time, the oil from the pump 2 can flow via the lines 13, 14 and 20 only via the throttle 54 to the accumulator 19, so that it is automatically refilled until the next starting process , and the nominal pressure in the feed line 3 is immediately available while there is no pressure relief via the directional valve 23. When a further stop of the signal generator 39 is reached in the subsequent upward stroke of the press ram (preferably at approximately 270 to 320 °), the magnetic actuator 35 is then energized and the line branch 30 is thus switched to pressure relief in the direction of tank 1. The nominal pressure present before and after the damper valve 24 thus opens the pressure limiting valve 28, which is adjusted to a value set below the spring pressure P _F. The relevant stop point of the signal transmitter 39 is placed so that the excitation of the magnetic actuator 35 is adjusted electrically so that the press ram comes to exactly at top dead center, in the starting position 0. As soon as the pressure in line 26 drops, the damper valve 24 can open on the spring side, relieve the pressure on the actuating cylinder 5, so that the piston rod 10 is pressed back under spring force away from the clutch 7 to the brake 6. This is then effective under spring pressure. However, since a preselectable hydraulic back pressure is generated via the pressure relief valve 28, the brake does not stop hard, but rather with shock absorption. The pressure drop in the valves 24 and 28 and the directional control valve 23 is maintained via the press safety valve 4 from the supply quantity of the accumulator 19 via the throttle 52, so that the effective braking pressure ΔP _{Br is} derived from the spring pressure P _F minus the hydraulic counter pressure at the pressure relief valve 26 corresponds. Both the magnetic actuator 31 on the press safety valve 4 and the magnetic actuator 35 on the directional control valve 23 are switched off shortly before reaching the starting position 0 at top dead center at about 340 to 350 ° of the press stroke, so that the actuating cylinder 5 of the press is neither via the main feed line 3 nor via the parallel lines 22, 15 can be pressurized. This guarantees a safe total shutdown. - Thanks to the parallel connection of the pressure compensation system to the feed line, the entire process takes place almost as quickly as without damping when coupling and braking.

Reference numerals

• 0 zero position
• 1 tank
• 2 pump
• 3 feed line
• 4 press safety valve
• 5 actuating cylinders
• 6 brake
• 7 clutch
• 8 actuating pistons
• 9 return spring
• 10 piston rod
• 11 -
• 12 pressure relief line
• 13 pressure equalization line
• 14 refill line
• 15 pressure relief line
• 16 pressure cut-off valve
• 17 non-return valve
• 18 Shut-off valve dependent on differential pressure 19 Accumulator
• 20 storage connection line
• 21 choke
• 22 connecting line from 19 to 15
• 23 4/3 • Directional valve
• 24 damping valve
• 25 First branch of 15
• 26 Second branch of 15
• 27 pressure relief valve of 25
• 26 pressure relief valve of 26
• 29 First connection of 23
• 30 Second connection of 23
• 31 magnetic actuator of 4
• 32 return springs of 4
• 33 First magnetic actuator from 23
• 34 First return spring from 23
• 35 Second magnetic actuator from 23
• 36 Second return spring from 23
• 37 Electrical control system
• 38 switch box of 37
• 39 signal transmitter to press etc.
• 40 press flywheel
• 41 Start phase with low pressure
• 42 Pressure build-up area
• 43 Working range of the ram at maximum pressure
• 44 Pressure relief area
• 45 braking area
• 46 Ready to start
• 47 Pressure in the actuating cylinder 8
• 48 moment on the press ram
• 49 Speed of the press
• 50 Pressure curve in the prior art 51 check valve
• 52 throttle
• 53 check valve
• 54 throttle
• 55
• P _A or P _F response or spring pressure
• P _H Hydraulic back pressure
• P _K clutch closing pressure
• P _E switch-on pressure
• P _N nominal pressure
• DP _Be acceleration pressure
• ΔP _Br brake pressure
• M _K clutch torque
• M _N nominal torque
• n speed
• t time

Claims (9)

1. Pressure-adjusting system for an hydraulically-operated clutch and/or brake for the drive shaft of a press,

a) in which a press safety valve (4) within a feed line (3) terminating at an actuating cylinder (5) works together with an adjustable distributor valve (23) with settings for pressure reduction and locking, to provide damping against shock by combining partial pressure phases with main pressure ones, characterized in that

b) the distributor valve (23) is located in a pressure relief line (15) branching out of the feed line (3) downstream beyond an externally. adjustable pressure-limiting or proportional pressure stage (27, 28),

c) both the press safety valve (4) and the distributor valve (23) are provided with magnetic actuating elements (31,33,35) which are linked to the press by an electrical program control device (37, 38) equipped with rotational-movement or time sensors (39),

d) and the electrical control device (37, 38) and/or the magnetic actuating elements (31, 33, 35) are fitted with a preselection device for adjusting the operating pressure in the actuating cylinder when pressure is either rising (clutch action) or falling (braking).

2. Device according to Claim 1, characterized in that

a) the distributor valve (23) is a 4/3-way valve,

b) pressure-limiting or proportional pressure valves (27, 28) are located ahead of its two connections (29, 30) on the press side in parallel branches (25, 26) of the pressure relief line (15), and

c) its connections (22, 1) on the side furthest from the press are connected by their own pressure equalizing line (22) to a pressure-dependent shut-off valve (18) on a storage unit (19) or a tank (1).

3. Device according to Claim 2, characterized in that

a) one end of the shut-off valve (18) is connected to the feed line (3) before the press safety valve (4), and the other end to the storage unit (19), and

b) the surface of its closing element is such that the shut-off valve (18) is held in the closed position by the differential pressures prevailing when the distributor valve (23) is in its initial position.

4. Device according to Claims 2 or 3, characterized in that the pressure in the storage unit (19) can be equalized by means of a pressure equalizer line (13) fitted with a non-return valve (17) which closes towards the feed line (3).

5. Device according to one of the Claims 1 to 4, characterized in that a damping valve (24) with its own pressure-dependent discharge circuit is fitted to the pressure relief line (15) upstream from the pressure-limiting stages (27, 28).

6. Device according to one of the Claims 1 to 5, characterized in that whenever a press stroke is commenced from the 0 position, the press safety valve (4) is open and the distributor valve (23) is in the discharge position relative to the tank (1) via its first connection (29) on the press side.

7. Device according to Claim 6, characterized in that approximately 10 to 20° after the 0 position, the discharge position of the distributor valve (23) is closed again via its first connection (29), while the press safety valve (4) remains open.

8. Device according to either Claim 6 or 7, characterized in that approximately 270 to 320° after the 0 position, the distributor valve (23) reaches its discharge position relative to the tank (1) by way of its second connection (30), while the press safety valve (4) continues to remain open.

9. Device according to one of Claims 6 to 8, characterized in that approximately 340 to 350° after the 0 position the press safety valve (4) reaches its pressure relief position and the distributor valve (23) its closed position.

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