EP0967028B1 - Hydraulic press - Google Patents

Description

The invention relates to a hydraulic press, in particular a press brake, with at least one double-acting hydraulic working cylinder with different effective areas on both sides of the piston, the side of the larger effective area being connected to the hydraulic tank via an additional suction line and a suction valve being switched into this suction line. which is closed during the working stroke and opened during the rapid strokes (see, for example, US Pat. No. 4,307,654).

During the working cycle of hydraulic presses, different demands are usually made regarding press force and speed. During the actual working stroke or travel, large forces are usually required at low speeds, whereas in the case of press retraction (rapid stroke up) and also during a rapid movement in the pressing direction (rapid stroke down), the highest possible speeds with low required forces are usually desired. In order to meet these requirements in a simple and cost-effective manner, hydraulic cylinders with a large difference in effective area between the piston surface and the annular surface (remaining cross-sectional area on the side of the piston rod between the latter and the cylinder inner wall) are usually used in such presses today. The ratio of these active areas reaches 16: 1 and more, for example.

If the available pump delivery volume is used to act on the annular space side for the above-mentioned rapid-up movement, the amount of oil multiplied by the ratio of the effective areas from the piston-side cylinder space is directly via an additional one in the constructions customary in this context on the opposite side of the piston Connection (suction line) pushed out into the hydraulic tank. With the rapid down movement in the pressing direction, however, a corresponding amount of oil must be returned from the tank to the piston-side cylinder space. Especially in this so-called suction of the piston-side cylinder interior due to the weight of the upper press beam and the atmospheric pressure in the It is important for the tank to keep the pressure losses in the suction line from the tank to the piston side of the cylinder to a minimum, as this could otherwise lead to outgassing and the formation of bubbles in the hydraulic medium.

For the actual working stroke or travel, it is of course necessary in the above context to interrupt the connection between the tank and the piston-side cylinder interior, which is now to be pressurized, preferably without leakage oil, which is accomplished by a so-called refill or fill valve, which is used in the Known presses of the type mentioned are usually simply designed as a 2/2-way seat valve and are opened during the rapid movements for a particularly low-loss connection (large cross sections) between the piston-side interior and the tank and are closed during the working stroke. Such valves are usually controlled hydraulically and are used either open in the basic position or closed in the basic position.

A disadvantage of the known presses of the type mentioned is particularly the fact that during the retraction movement (rapid-up movement) due to the relatively small annular surface on the rod side of the respective cylinder with a correspondingly large mass of the upper cheek of the press and in particular also in connection With long hydraulic connecting lines between the respective actuator (e.g. proportional directional control valve) and the cylinder, the natural frequency of the hydraulic system may be very low, which leads to stability problems in the synchronization or speed control of the press cylinders.

The object of the present invention is to improve a hydraulic press of the type mentioned at the outset in such a way that the disadvantages mentioned of the known presses of this type are avoided and in particular that the internal system rigidity is increased in a simple and cost-effective manner and corresponding stability problems in the press retraction are largely eliminated.

This object is achieved according to the present invention in a press of the type mentioned in that a switchable throttle is additionally arranged in the suction line, which is effective during the extension of hydraulic medium from the cylinder side with a larger effective area to the hydraulic tank. This simple throttling of the hydraulic medium flowing out of the piston-side cylinder space during the rapid upward movement of the press upper beam to the tank results in an increase in the system rigidity and a damping effect against speed peaks when the upper beam accelerates. This eliminates the stability problems mentioned in the retreat and also increases the loop gain of the machine control in the retreat by orders of magnitude. There is a practically constant throttling effect on the amount of oil ejected from the piston-side working area of the cylinder, which is effective over the entire retraction of the press.

Although, in principle, the switchable throttle could also be connected upstream or downstream of the suction valve, in addition to or in addition to the suction valve, a further embodiment of the invention is preferred, according to which the suction valve itself has at least one in addition to the open and closed position Has throttle position. Thus, for the reasons described at the beginning with regard to the suctioning of the tank during the rapid-down movement, the shortest possible or unthrottled connections between the piston-side working space of the cylinder and the tank can also remain as short and unthrottled without further or additional elements - in any case Existing suction valve is simply designed so that it also has a throttle position in which the flow is weakened in the desired manner compared to the full cross section. If necessary, several throttle positions with different strengths can also be provided in order to allow different influences on the outflowing hydraulic medium.

In a further embodiment of the invention it is provided that the suction valve has a preferably hydraulically operable additional mechanical valve stop, which allows only partial opening with a constant throttling effect on the hydraulic medium flowing through. This is a very simple mechanical configuration, which ensures reliable functioning of the arrangement without additional complicated adjusting elements or the like having to be provided.

According to another preferred embodiment of the invention, a continuously open connection with the pump pressure of the hydraulic press control can be provided for the hydraulic control of the additional valve stop, with the result that further switching valves or the like are also superfluous for this additional throttle position.

According to a particularly preferred further embodiment of the invention, the throttle is designed to be adjustable, which enables easy and simple adaptation, for example to different presses or operating conditions.

The invention is explained in more detail below with reference to the partially schematic drawings. FIG. 1 shows a partial circuit diagram of a hydraulic press designed according to the invention, and FIG. 2 shows an exemplary embodiment of a suction valve for use in a press designed, for example, according to FIG. 1.

From the actual hydraulic press, only a part of the upper beam 1, which is displaceable relative to the lower beam, not shown, on which the piston rod 2 of a double-acting hydraulic working cylinder 3 engages can be seen in FIG. 1. Usually, a further working cylinder of the same design is arranged at the left end of the upper beam, not shown here, whereby these two (or also further working cylinders) are usually controlled jointly via a synchronous control, but also, for example, for an intended inclination of the upper beam 1 some can be operated separately.

The supply of the working rooms 4, 5 of the working cylinder or cylinders 3 with hydraulic working medium takes place from a control unit 6, which is supplied via line 7 from a motor-operated pump 8 with pressure medium. The control unit 6 has control elements designed and arranged in the usual way, such as pressure limiters, pressure compensators, switching valves, proportional directional valves, setbacks and the like. on, which are not shown as essential in connection with the present invention neither described nor further described. To connect the piston-side working chamber 4 or the rod-side working chamber 5 of the working cylinder 3 to the control unit 6, lines 9 are provided, which are connected in a sealed manner to the corresponding connections in a manner which is also known and is of no further interest here.

In order to be able to achieve the highest possible speeds with the available pump delivery rate for the rapid retraction of the upper cheek 1 (movement in the illustration according to FIG. 1), the working cylinders 3 in such arrangements are today mostly with a large effective area difference between the cross-sectional area of the cylinder interior formed on the top of the piston and the ring surface remaining between the piston rod 2 and the inner wall of the working cylinder 3 on the rod side, this area ratio being 16: 1. If, for example, the rod-side working chamber 5 is acted upon with the available pump delivery rate for the rapid upward movement of the upper cheek 1 in the direction of arrow 10 in FIG. 1, the piston 11 moved from the piston-side working chamber 4 must immediately understand this by the aforementioned area ratio, a multiple amount of hydraulic medium can be pushed out via the suction valve. Around the piston-side working space 4, which is acted upon by the pump pressure during a normal working stroke (relatively slow movement of the upper cheek 1 with a large force - counter to arrow 10 in FIG. 1) To be able to close off the tank 13 as leak-free as possible, a suction valve 14 is switched into the suction line 12, which is closed during the working stroke and opened during the rapid strokes. The required volume compensation between the two working spaces 4 and 5 can thus take place in the described manner in the rapid upward movement of the upper cheek 1 in the rapid downward movement (for the rapid delivery of a tool or the like) can usually be as short as possible and with Low losses (large diameter) designed suction line 12, the additional volume required for filling the piston-side working space 4 can be supplied from the tank 13 without outgassing and bubble formation in the hydraulic medium.

As a result of the mentioned differences in effective area on both sides of the piston, there is a relatively small annular area of the working space 5, which with a correspondingly large mass of the upper beam 1 of the press and in particular in connection with long hydraulic connecting lines between the actual actuators (e.g. proportional directional control valve in the control unit 6) and the cylinder may have a very low natural frequency of the hydraulic system and may lead to stability problems in synchronism or speed control. In order to prevent this and to increase the internal hydraulic rigidity of the system, a switchable throttle 15 is additionally arranged in the suction line 12, which throttle 15 only has the larger effective area to the hydraulic tank when the hydraulic medium is being pushed out from the cylinder side (i.e. during the rapid opening). Movement) is effective. For this purpose, the suction valve 14 itself is designed in the embodiment shown so that, in addition to the open position shown and the symbolically visible closed position on the left, it also has a throttle position indicated in the middle. By simple hydraulic adjustment of the suction valve 14 via lines 16, which are also connected to the central control unit 6, it can thus be ensured that the piston-side working space 4 as desired during the normal working stroke compared to the Tank 13 is completed, the required additional volume can be sucked out of the tank 13 practically unthrottled during the rapid down movement (fast delivery) and with the rapid upward movement (rapid retraction), the system volume is only reduced accordingly by increasing the system rigidity Tank 13 can derive.

According to FIG. 2, the suction valve 14 is provided with a hydraulically actuated additional mechanical valve stop 16, which allows only partial opening with a constant throttling effect on the hydraulic medium flowing through (corresponding to the central position in FIG. 1). According to FIG. 2, the suction valve 14 essentially consists of a valve sleeve 17, a valve piston 18 which is axially movable therein, a sealing part connected to the valve sleeve 17 and part of the spring chamber 19 and a side control connection SA 1, a screwed part into the middle part and sealed stop sleeve 20 and a stop piston 21 guided axially movably therein. Furthermore, valve spring 22 including spring plate 23 and stop ring 24 arranged in spring chamber 19 and biasing valve piston 18 into the position shown, as well as connection or Refer to locking parts on the control connections SA 1 and SA 2. A union nut securing the screwed-in stop sleeve 20 is designated by 25. Finally, various sealing rings are not identified in the drawing in order to ensure pressure tightness with regard to the usually relatively high press pressures.

The structure and mode of operation of the suction valve 14 are explained in more detail below with regard to the essential press functions:

Rapid down movement (fast tool delivery):

The connection SA 1 is relieved at the top dead center of the hydraulic press. The pump pressure which is present constantly and unswitched at the control connection SA 2 corresponds to the circulating pressure which is usually in the control unit 6 provided three-way pressure balance or the basic pressure of the proportional pressure relief valve provided there. The effective area of the stop piston 21 is dimensioned such that the valve spring 22 moves the stop piston 21 against this minimum pressure over its entire stroke, so that the valve piston 18 of the suction valve 14 opens completely in the manner shown in FIG. 2 and only on the stop surface 26 in the fully open position is stopped. The closing edge 27 on the valve piston 18 is lifted at most from the associated seat surface 28 on the inside of the valve sleeve 17, so that the unrestricted backflow of hydraulic medium along the arrows 29 from the tank 13 to the piston-side working chamber 4 can take place.

Working stroke (presses):

The control connection SA 1 shown in FIG. 2 below is now acted upon by the pump pressure. Due to the large effective area of the valve piston 18 (corresponding to its largest diameter), which in any case is at least slightly larger than the diameter of the closing surface between the closing edge 27 and the seat surface 28, the valve piston 18 moves into the left end position, not shown, or Closed position, with which the suction valve 14 is closed and the pump pressure in the piston-side working chamber 4 causes the press movement.

Rapid-up movement (rapid withdrawal of the press):

The control connection SA 1 is relieved of pressure to the tank. The effective surface of the stop piston 21 is designed so that when the upper cheek 1 is withdrawn, the pump pressure required for this moves the stop piston 21 (and thus also the valve piston 18) against the valve spring 22 up to its stop via SA 2. The valve stop 16 is thus formed here by the interaction of the annular surface 30 on the stop piston 21 with the annular surface 31 in the stop sleeve 20, the maximum stroke of the stop piston 21 designated 32 in the illustration according to FIG. 2 being of course smaller than that designated 33 Maximum stroke of the valve piston 18, which should not now be moved into the closed position but must still have an open gap to the seat surface 28 in the throttle position. The amount of hydraulic medium displaced from the piston-side working chamber 4 into the tank 13 in this state against the direction of the arrows 29 is thus throttled, as a result of which the rigidity of the hydraulic system is increased and speed peaks are damped when the upper beam is accelerated.

To enable the function of the suction valve 14 to be adapted to other presses or other operating conditions, the throttling effect could also be adjustable, for which purpose a maximum stroke length 32 of the stop piston 21 that could be adjusted from the outside or by exchanging the stop piston 21, for example, could be provided in the construction shown and discussed ,

Apart from the illustrated and discussed embodiment with a suction valve 14 having an additional throttle position, this could also be designed, for example, as a simple 2/2-way valve and a separate or upstream separate throttle element can be provided, which can be switched into the suction line if necessary.

Claims (5)

1. A hydraulic press, in particular a bending press, having at least one hydraulic working cylinder (3) acting on two sides and having effective areas of differing sizes on either side of the piston (11), the side of the larger effective area being connected via an additional equalizing line (12) to the hydraulic tank (13) and an equalizing valve (14), which is closed during the working stroke and open during rapid strokes, being incorporated in this equalizing line (12),
   characterised in that a switchable throttle (15) is also arranged in the equalization line (12), and is effective when hydraulic medium is being discharged to the hydraulic tank (13) from the cylinder side having the larger effective area.
2. The press according to Claim 1, characterised in that the equalization valve (14) itself has at least one throttle position in addition to the open and closed positions.
3. The press according to Claim 2, characterised in that the equalization valve (14) has a preferably hydraulically actuatable additional mechanical valve stop (16), which allows only partial opening with constant throttle action on the hydraulic medium as it flows through.
4. The press according to Claim 2, characterised in that a constantly open connection to the pump pressure of the hydraulic press control is provided for hydraulic control of the additional valve stop (16).
5. The press according to one or more of claims 1 to 4, characterised in that the throttle (15) is configured to allow adjustment.