EP0628730B1 - Hydraulic system, particularly for a power brake - Google Patents

Description

The invention relates to a hydraulic system which is used in particular in connection with a press brake and which has the features from the preamble of claim 1.

Press brakes have a top beam, which can usually be moved up and down by two synchronized differential cylinders. A piston in each differential cylinder separates its interior into a piston chamber and an annular chamber and is connected to the upper cheek of the press via a piston rod. Starting from an upper end point of the movement, the upper cheek first falls during a press cycle due to its weight in rapid traverse, with oil being metered out of the annular spaces of the differential cylinder. At a short distance from the sheet to be machined, the top beam is switched to creep speed, during which the sheet is moved and the sheet is deformed. After a decompression phase, the upper cheek is finally moved up again in rapid traverse.

Known hydraulic systems for press brakes include, in addition to the differential cylinders, a proportional directional control valve for each differential cylinder, with which the pressure medium paths between a pump and a tank on the one hand and the differential cylinder on the other hand can be controlled and which has a valve piston which can be moved from a rest position to a working position . The position of the valve piston and thus also the rest position can usually be detected by a position transmitter in order to be able to react quickly and precisely to the respective differential cylinder. In order not to have to use a separate valve for the metered outflow of oil from the annular space of a differential cylinder, the annular space and the piston space of a differential cylinder can be connected to one another via the proportional directional control valve while the upper beam is moving downwards. With this so-called differential circuit, the oil flowing out of the annulus flows through the proportional directional control valve in the piston chamber of the differential cylinder. The differential circuit can be maintained not only in rapid and creep speed before touching the sheet, but also during the deformation of the sheet. The ratio of the piston surface facing the annular space to the piston surface facing the piston space is namely very small and is approximately in the range of 1:10, so that at the same pressure in the annular space and in the piston space, the pressing force is only slightly smaller than in the case in which of the pressing process in the annulus tank pressure prevails (see for example FLUID, Vol. 22, September 1988, pages 37-39, "endurance run with prop technology").

When the upper cheek stops, the annular space of the differential cylinder should be blocked off from the tank for safety reasons by two safety valves located in the blocking position, in particular monitored. A monitored safety valve is understood to mean a valve whose status is determined by a sensor, e.g. by an electrical limit switch, can be detected. With lower safety requirements, a single valve can be sufficient to shut off the annulus. Monitoring can then also be dispensed with. If only one of the two safety valves is in its blocking position during a stop, this can be indicated optically or acoustically. In addition, the machine cannot be started until the defect in the safety valve or in the electrical control has been remedied.

The invention has for its object to provide a hydraulic system with the features from the preamble of claim 1 so that the desired control of a differential cylinder and the safety requirements can be met with a few valves.

This object is achieved by a hydraulic system which has the features from the preamble of claim 1 and in which, according to the characterizing part of this claim, the annular space of the differential cylinder in the rest position of the proportional directional control valve can be shut off by this against the pump and against the tank. In an inventive hydraulic system with a differential circuit during the downward movement of the upper beam of the press, the proportional directional control valve is used as a safety valve.

Advantageous embodiments of a hydraulic system according to the invention can be found in the subclaims.

The proportional directional control valve has a first outlet for lifting the upper beam, which can be connected to the annulus of the differential cylinder. According to claim 2, the use of the proportional directional control valve as a safety valve is now possible in a simple manner in that the first output in the working position of the valve piston, which it assumes for the downward movement of the upper beam, can be connected to the connection between the pressure side of the pump and the piston chamber of the differential cylinder and can be shut off in the rest position of the valve piston.

A proportional directional control valve normally has a first chamber which can be connected to the pressure side of the pump and a second chamber which can be connected to the piston chamber of the differential cylinder. The connection of the first output of the proportional directional control valve to the pressure side of the pump or to the piston chamber of the differential cylinder can now be established indirectly via a third chamber, which is permanently connected only to the first or only to the second chamber and which in the working position of the valve piston with the is connected to the first output and is blocked in the rest position towards the first output. Preferably, the third chamber is permanently connected to the first chamber or the third chamber within a housing of the proportional directional control valve, so that no additional output of the proportional directional control valve is necessary, which is outside the housing with the input connected to the pressure side of the pump or with the second output of the proportional directional control valve connected to the piston chamber would have to be connected.

A direct connection of the first outlet to the first or the third chamber can also be favorable. This is how known from conventional directional valves, a first chamber connectable to the pressure side of the pump and a second chamber connectable to the piston chamber of the differential cylinder and a chamber connected to the first outlet, the latter being connected directly to the first or through the valve piston in the working position connected to the second chamber and locked in the rest position. It is advantageous here that it is possible to fall back on a common housing manufactured in large quantities, with which only a valve piston already known from practice is used. However, a larger nominal size of the directional control valve could be necessary in a configuration according to claim 5 than in an embodiment according to claims 3 or 4.

In principle, it is conceivable to detect the rest position of the valve piston of the proportional directional control valve by means of a limit switch, which functions in particular on an inductive basis and which changes its state as soon as the valve piston has left the rest position. As already indicated, a proportional directional control valve for a fast-reacting and precise control is usually provided with a displacement sensor with which every actual position of the valve piston can be detected. Advantageously, this displacement sensor is now used as a position sensor for the rest position of the valve piston.

There are accident prevention regulations that state that the annular space must be blocked by two successive monitored safety valves to prevent an abrupt downward movement of the upper cheek of a press. According to the invention, one of these safety valves is the proportional directional valve. In principle, a 2/2-way valve can be used as the second safety valve, which blocks in the rest position and is open when actuated. Since a slow downward movement of the upper cheek is permissible up to a certain speed, this second safety valve does not have to be leak-free, so that its valve element can be a slide piston. However, in addition to the currently applicable accident prevention regulations, most press manufacturers want the upper cheek remains at rest when the hydraulic system is switched off. Therefore, the second safety valve is advantageously designed so that in the rest position it acts as a check valve opening towards the annular space and is open in the actuated position.

In order to avoid accidents, it is also desired that the pump can only build up pressure in the annular space or in the piston space if two, in particular, monitored safety valves have been brought from a rest position into a working position. One of these two safety valves can in turn be the proportional directional control valve. The other is advantageously, in particular, a pilot-controlled pressure relief valve, which is connected to the pressure side of the pump and the condition of which can be monitored. When the top beam stops and the pump is running, it pumps to the tank via the pressure relief valve switched to circulation. Because of the volume delivered, this pressure relief valve is usually a pilot operated valve with a main piston and with a pilot valve. Such a pressure relief valve can be easily switched to circulation in a manner known per se in that the main piston can be relieved to the tank via a directional valve with a movable valve element. According to claim 9, the position of the movable valve element of this directional control valve can now be monitored, thereby achieving the desired high safety standard. It is particularly advantageous here that regardless of the size of the press brake and the desired speeds of the upper cheek and the resulting different amounts of oil flowing into and out of the cylinder rooms, the same monitored safety valve can always be used. A safety valve upstream of the piston space or annular space would have to be adapted to the respective oil quantities.

According to claim 10, there is only one pressure relief valve and thus only one further safety valve for several differential cylinders.

An exemplary embodiment of a hydraulic system according to the invention for a press brake and various directional control valves that can be used in such a system and are shown with their circuit symbols are shown in the drawings. The invention will now be explained in more detail with reference to the figures of these drawings.

Figur 1

ein Schaltschema einer erfindungsgemäßen hydraulischen Anlage mit einer ersten Ausführung eines Proportionalwegeventils, bei dem in einer Arbeitstellung ein mit dem Ringraum eines Differentialzylinders verbindbarer erster Ausgang direkt an einer Verbindung zwischen dem Pumpenanschluß und einem zweiten Ausgang anschließbar ist,

Figur 2

das Proportionalwegeventil nach Figur 1 in etwas ausführlicherer Darstellung,

Figur 3

ein anderes Proportionalwegeventil, bei dem der erste Ausgang indirekt über einen zusätzlichen Kanal im Ventilgehäuse mit dem Pumpenanschluß verbindbar ist

Figur 4

ein dem Proportionalwegeventil aus Figur 2 ähnliches Proportinalwegeventil, bei dem jedoch außerhalb des Ventilgehäuses eine Verbindung zwischen dem zusätzlichen Kanal und dem Pumpenanschluß besteht,

Figur 5

ein Proportionalwegeventil, das demjenigen aus Figur 2 ähnelt, bei dem jedoch der zusätzliche Kanal innerhalb des Gehäuses mit dem zweiten Ausgang verbunden ist, und

Figur 6

ein letztes Proportionalwegeventil, bei dem der zusätzliche Kanal und der zweite Ausgang außerhalb des Gehäuses miteinander zu verbinden sind.

Show it

Figure 1

1 shows a circuit diagram of a hydraulic system according to the invention with a first embodiment of a proportional directional control valve, in which, in a working position, a first output which can be connected to the annular space of a differential cylinder can be connected directly to a connection between the pump connection and a second output,

Figure 2

the proportional directional control valve according to Figure 1 in a somewhat more detailed representation,

Figure 3

another proportional directional control valve, in which the first output can be connected indirectly to the pump connection via an additional channel in the valve housing

Figure 4

a proportional directional control valve similar to the proportional directional control valve from FIG. 2, but with a connection between the additional channel and the pump connection outside the valve housing,

Figure 5

a proportional directional control valve which is similar to that of Figure 2, but in which the additional channel within the housing is connected to the second outlet, and

Figure 6

a last proportional directional valve, in which the additional channel and the second outlet are to be connected outside of the housing.

To move the upper cheek of a press brake, two differential cylinders 10 are provided in the exemplary embodiment shown, each of which houses a piston 11, which is fixed with one emerging from an end face of the differential cylinder Piston rod 12 is connected. The upper cheek of the press brake is attached to the piston rods 12. The piston 11 separates the inside of a differential cylinder 10 into an annular space 13 on the piston rod side and into a cylindrical pressure space 14 away from the piston rod, the circular area of the piston 11 facing the pressure space 14 being approximately ten times as large as the annular area facing the annular space 13.

Each differential cylinder 10 is assigned a control block 20 which is identical to the control block of the other differential cylinder and which has a pressure connection P, a tank connection T and two control connections X1 and X2. The control connection X1 is connected to the pressure chamber 14 and the control connection X2 to the annular space 13. A proportional directional control valve 25 is placed on the control block 12, which is a 4/3-way valve and whose valve piston 26 can assume a spring-centered central rest position and work positions on both sides of this rest position. In one working position, the valve piston 26 is brought into operation by actuating one of two electromagnets 27. Even if there is talk of one working position on each side of the middle rest position, since the valve 25 is a proportional valve, one must always keep in mind that in principle an infinite number of lateral positions of the valve piston are possible, which differ through different distinguish large flow cross-sections, but in which the same inputs and outputs of the valve 25 are always connected. The valve 25 has four connections, of which a pump connection P is connected to this pump connection of the control block via a check valve 28 which blocks the pump connection of the control block 20, a tank connection T to the tank connection T of the control block and a consumer output A to the control output X1 of the control block 20 is. A consumer connection B of the valve 25 can be connected to the control connection X2 of the control block 20. As can be seen from the circuit symbols from FIG. 1 and from FIG. 2, all four connections of the valve 25 are blocked in the rest position of the valve piston 26. In one working position, the tank connection T is still blocked while the pump connection P and the two consumer outputs A and B are interconnected. In the other working position, however, the consumer outlet B is connected to the pump connection P and the consumer outlet A to the tank connection T.

The position of the valve piston 26 can be monitored with a displacement sensor 29 which is arranged on one side of the valve piston 26. In particular, a displacement sensor is used which is based on the principle of changing an inductance and which, in a manner known per se, consists of several coils and an iron core, the axial position of which changes within the coils with the position of the valve piston. With the help of the displacement sensor 29, it can also be determined whether the valve piston 26 is in the rest position or not. The rest position of the valve piston 26 can also be monitored by a limit switch to comply with safety regulations.

Between the consumer outlet B of the valve 25 and the control connection X2 of the control block 20 there is a check valve 31 which can be unlocked with the aid of an electromagnet against the force of a spring and which, in its rest position, blocks the consumer outlet B of the valve 25. The rest position of the valve element of the check valve 31 is monitored by a limit switch 32. By designing the valve 31 as a seat valve, the annular space 13 is shut off without leakage oil when the valve 31 is in the rest position.

Between the valve 31 and the control port X2 of the control block 20 on the one hand and the tank port T of the control block 20 on the other hand, a pressure relief valve 33 is inserted, which has no function in normal operation, but is only intended to prevent an excessively high pressure in the annular space 13 during commissioning of the system .

The two pressure connections P of the two control blocks 20 are connected to a common pressure line 38, in which an oil filter 39 is installed and which is fed by a hydraulic pump 40, which sucks in oil from a tank 41. The pressure line 38 is through a pilot-controlled proportional pressure relief valve 42 is secured, which is connected on the input side to the pressure connection of the hydraulic pump 40 and on the output side to the tank 41 and which is also provided with a maximum pressure protection. A main piston 49 of the pressure relief valve 42 can be relieved by a 2/2-way valve 43, via which a control port X of the pressure relief valve 42 is connected to the tank 41 in the rest position. If the directional control valve 43 has been actuated with the aid of an electromagnet 44, the control connection X is shut off. The rest position of a movable valve element 48 of the directional control valve 43 can be detected with a limit switch 45 assigned to the valve 43.

A suction valve 46 is placed on the control block 20 and is connected on the one hand to the control connection X1 of the control block and on the other hand to a tank line 47 leading from the tank connection of the control block 20 to the tank 41. The suction valve 46 can be unlocked by pressurizing a control line 48. Both control lines 48 are connected to an output of a directional valve 50, which is connected to the common pressure line 38 in the rest position of the valve 50 and is relieved towards the tank in the actuated position of the valve 50.

When the pistons 11 and with them the upper cheek of a press brake rest, the valves assume the positions shown in FIG. 1. The annular space 13 of the differential cylinder 10 is blocked off from the tank by the two valves 25 and 31, which are monitored and can thus serve as safety valves. A pressure build-up in the annular space 13 is not possible even when the pump is running, since in the rest position of the valve 25 all connections of this valve are blocked and since the main piston of the pressure relief valve 42 is relieved by the directional control valve 43. Against a build-up of pressure in the annular space 13, the valve 25 and the valve 43 are used together with the valve 42 as safety valves. Both valves also serve as safety valves against pressure build-up in the pressure chamber 14.

Starting from the position of the pistons 11 shown, they may now be moved downwards in rapid traverse. The valve 31 is switched to flow. The valve 25 is actuated so that the consumer outlet B is connected to the connection between the pressure connection P and the consumer outlet A. The amount of oil that flows out of the annular space 13 and via the valve 25 to the pressure space 14 is now metered with the valve 25. The still missing amount of oil for the pressure chamber 14 is sucked out of the tank 41 via the valve 46. During the rapid traverse, the valve 43 is open, so that the pump 40 circulates via the pressure relief valve 42.

The upper cheek is stopped just above the sheet to be machined by resetting the valve 25. It should now be moved slowly to the sheet metal and then deform the sheet metal. The directional valve 43 is now actuated so that the pump 40 can generate a pressure. The proportional directional control valve 25 is adjusted in the same direction as during the rapid traverse so that oil conveyed by the pump 40 reaches the piston chamber 14 in a metered manner. In the annular space 13, the pressure is initially e.g. about ten times as high as in the piston chamber 14 before the upper cheek hits the sheet to be deformed and a pressure determined in the pressure chamber 14 is determined by the deformation work to be performed.

The valve 50 was actuated during the downward movement of the upper cheek. During the subsequent upward movement, the valve 50 returns to its rest position, so that the suction valves 47 are unlocked. The proportional directional control valve 25 is brought from the rest position in the other direction into a working position in which the outlet B is connected to the pressure inlet P and the outlet A is connected to the tank connection T. The flow cross section between P and B can now be used to determine the speed at which the piston 11 moves upwards. Oil, which is displaced from the pressure chamber 14 and cannot flow to the tank via the valve 25, reaches the tank via the suction valve 46.

In FIGS. 2 to 6, the housing 60 of a proportional directional control valve 25 that can be used in the system according to FIG. 1 is to be indicated by the dash-dotted line. The usual switching symbol for a valve is only intended to identify the valve piston 26. Such a valve piston 26 is usually located in a bore in the housing 60, this bore being provided with various annular chambers which are connected to the externally visible connections of the valve. These annular chambers are symbolized in FIGS. 2 to 6 by the U-shaped characters between the valve pistons and the housings 60.

It can be seen in the valve according to FIG. 2, which is the same valve as in FIG. 1, that a total of four valve chambers are present. A first valve chamber 61 is connected to the pressure connection P, a second valve chamber 62 to the outlet A, a third valve chamber 63 to the outlet B and a fourth valve chamber 64 to the tank connection T. It can be seen that in one working position of the valve 25, the chamber 63 is connected directly to the chamber 61 or the chamber 62 via the valve piston 26.

In the valve 25 according to FIG. 3, in addition to the valve chambers 61 to 64, there is a further valve chamber 65 which has a connection to the valve chamber 61 within the housing 60. In one working position, the chamber 63 is connected via the piston 26 to the chamber 65 and via this to the chamber 61.

The embodiment according to FIG. 4 is very similar to that from FIG. 3. However, the chambers 61 and 65 are connected to one another outside the housing 60.

In the embodiments according to FIGS. 5 and 6, in addition to the valve chambers 61 to 64, there is also a further valve chamber 65 which, in the embodiment according to FIG. 5, is connected inside the housing 60 and in the embodiment according to FIG. 6 outside the housing 60 with the valve chamber 62 is.

Claims (10)

1. A hydraulic system for a press, in particular for a power brake, with a differential cylinder (10) comprising a piston (11) separating a piston chamber (14) and an annular chamber (13) from each other and connected to an upper jaw of the press capable of travelling upwards as well as, in fast approach and press mode, downwards, and with a proportional directional valve (25) permitting control of the pressure fluid passages between a pump (40), a tank (41) and the chambers (13, 14) of the differential cylinder (10) and incorporating a valve spool (26) that can be shifted from a rest position, in particular monitored by a position sensor (29), into a work position, whereby, while the upper jaw is in fast approach mode, the pump (40) delivers to tank (41) in recirculation mode, and pressure fluid can be displaced at a controlled rate from the annular chamber (13) of the differential cylinder (10) into the piston chamber (14) of the differential cylinder (10) via the proportional directional valve (25) in its work position and replenished from the tank (41) into the piston chamber (14) of the differential cylinder (10) via an anti-cavitation valve (46), and whereby, while the upper jaw is in press mode, the pressure fluid delivered by the pump (40) and displaced from the annular chamber (13) of the differential cylinder (10) can be routed at a controlled rate to the piston chamber (14) of the differential cylinder (10) via the proportional directional valve (25), characterized in that the annular chamber (13) of the differential cylinder (10) can be isolated from the pump (40) and from the tank (41) by the proportional directional valve (25) in its rest position.
2. A hydraulic system according to Claim 1, characterized in that a first outlet port (B) of the proportional directional valve (25) that can be connected to the annular chamber (13) of the differential cylinder (10) can also be connected to the passage linking the pressure side of the pump (40) and the piston chamber of the differential cylinder (10) when the valve spool (26) is in work position or isolated when the valve spool (26) is in rest position.
3. A hydraulic system according to Claim 2, characterized in that the proportional directional valve (25) comprises a first valve chamber (61) that can be connected to the pressure side of the pump (40), a second valve chamber (62) that can be connected to the piston chamber (14) of the differential cylinder (10), and a third valve chamber (65) that is permanently connected either exclusively to the first valve chamber (61) or exclusively to the second valve chamber (62), and that the third valve chamber (65) is connected to the first outlet port (B) when the valve spool (26) is in work position and isolated from the first outlet port (B) in rest position.
4. A hydraulic system according to Claim 3, characterized in that the third valve chamber (65) within a housing (6) of the proportional directional valve (25) is permanently connected either to the first valve chamber (61) or to the second valve chamber (62).
5. A hydraulic system according to Claim 2, characterized in that the proportional directional valve (25) comprises a first valve chamber (61) that can be connected to the pressure side of the pump (40), and a second valve chamber (62) that can be connected to the piston chamber (14) of the differential cylinder (10), and a valve chamber (63) connected to the first outlet port (B), the latter chamber being directly connected either to the first valve chamber (61) or to the second valve chamber (62) when the valve spool (26) is in work position and isolated in rest position.
6. A hydraulic system according to any of the preceding Claims, characterized in that the proportional directional valve (25) is equipped with a position sensor (29) for the valve spool (26) and that this position sensor (29) is used to indicate the rest position of the valve spool (26).
7. A hydraulic system according to any of the preceding Claims, characterized in that between the proportional directional valve (25) and the annular chamber (13) of the differential cylinder (10) is situated a valve (31), in particular one that is monitored, which in its rest position acts as a check valve blocking the passage from the annular chamber (13) to the proportional directional valve (25) and is open when in an actuated position.
8. A hydraulic system according to any of the preceding Claims, characterized in that a pressure relief valve (42), in particular a pilot operated one whose condition can also in particular be monitored, is connected with the pressure side of the pump (40).
9. A hydraulic system according to Claim 8, characterized in that the pilot operated pressure relief valve (42) comprises a main spool (49) that can be relieved by means of a directional control valve (43) with a movable valve element (48), and that in particular the position of the valve element (48) can be registered by a position sensor (45), and that the directional control valve (43) is open in the rest position.
10. A hydraulic system according to Claims 8 and 9, characterized in that it comprises two synchronously operated differential cylinders (10) that can be connected to a common pressure line (38), and that the pressure relief valve (42) is connected to this common pressure line (38).

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