GB2271149A

GB2271149A - Hydraulic press

Info

Publication number: GB2271149A
Application number: GB9220003A
Authority: GB
Inventors: Alan Brian Durston
Original assignee: PJ Hare Ltd
Current assignee: PJ Hare Ltd
Priority date: 1992-09-22
Filing date: 1992-09-22
Publication date: 1994-04-06
Anticipated expiration: 2012-09-22
Also published as: GB2271149B; GB9220003D0

Abstract

A hydraulic press includes a piston chamber which is divided into a first sub-chamber 16 and a second sub-chamber 18 by a piston 2. The piston actuates a press member and is controlled by a hydraulic circuit. The press has a regeneration valve 32, opposite sides of which are connected directly to the sub-chambers 16, 18 respectively. Flow is permitted between the two sub-chambers 16, 18 during a fast advance mode, but flow is prohibited by the regeneration valve 32 between the two sub-chambers 16, 18, during a pressing mode of the press. There are no restrictions in the ducts between the regenerative valve and the sub-chambers. <IMAGE>

Description

HYDRAULIC PRESS This invention relates to a hydraulic press, and in particular to a hydraulic press having regenerative cycles which enable rapid movement of a press member to and from a work piece.

Hydraulic presses commonly comprise a piston disposed within a piston chamber, the movement of which effects movement of a press member towards and away from a work piece. A hydraulic circuit controls the movement of the piston within the chamber, and such a hydraulic circuit commonly comprises a hydraulic pump and a fluid tank, in combination with a selection of control members. When the piston moves within the piston chamber, fluid must be expelled from the piston chamber on one side of the piston and fluid must enter the chamber on the other side of the piston.

Regeneration is a known technique which involves the step of passing the discharged fluid from one side of the piston into the expanding chamber on the other side of the piston without the fluid passing through the pump. Using this technique a relatively small capacity pump can be used to effect a relatively high speed of the piston. The pump need only supply a quantity of fluid which relates to the change in volume of the piston chamber as a result of the movement of the piston. The smaller the difference in pressure areas on either side of the piston the higher the speed that can theoretically be effected by a pump of a given size. In practice the ratio of regenerative flow to pump flow is limited due to inefficiencies caused by mechanical and fluid friction.A known hydraulic press uses two hydraulic pumps when the piston is to be moved rapidly within the piston chamber, because, although the principle of regeneration is employed, inefficiencies mean that only a small ratio of regenerative flow to pump flow can be used.

Hereafter the expression "directly connected to", in the context of fluid connections, is taken to mean connected to without any intermediate flow restrictions (such as open valves), other than normal pipe connections.

According to a first aspect of the present invention, there is provided a hydraulic press including a piston chamber and a piston which divides the piston chamber into first and second sub-chambers, the piston being capable of actuating a press member and being controlled by a hydraulic circuit, the hydraulic circuit comprising a fluid reservoir and pressurizing means, the circuit effecting the selection between operative modes of the press, these operative modes including (i) a fast advance mode, in which the piston is moved at a relatively high rate to effect rapid movement of the press member in an operative direction, and (ii) a pressing mode, in which a relatively high force is applied to the press member in the operative direction, the circuit further comprising a regeneration valve, disposed in close proximity to the piston chamber, the regeneration valve having two ports, which communicate with opposite sides of the valve, the two ports being directly connected to the first and second sub-chambers respectively, the arrangement of the hydraulic circuit being such that, during the fast advance mode flow is permitted across the regeneration valve to transfer fluid from one subchamber to the other sub-chamber and such that, during the pressing cycle, flow across the regeneration valve is prohibited.

Preferably a third sub-chamber is defined within the piston chamber, such that fluid in the third subchamber acts on a surface of the piston so as to move the press member in a direction opposite to the operative direction.

The operative modes will then preferably include a fast return mode, in which the piston operates to move the press member rapidly in the direction opposite to the operative direction. During the fast return mode, flow across the regeneration valve is permitted.

The operative modes may further include a decompressive mode, during which pressure built up during the pressing mode is controllably released, and a high force return mode, during which a relatively high force is applied to the press member in a direction opposite to the operative direction. During the high force return mode, flow across the regeneration valve is prohibited, to enable a large pressure difference to be maintained between the first and second sub-chambers.

The hydraulic circuit may comprise a plurality of multi-positional flow selectors, the positions of which are controlled by solenoids, which in turn are controlled by electronic control circuitry. The positions of these selectors may then determine the operative modes of the press.

According a second aspect of the present invention, there is provided a hydraulic piston and cylinder unit comprising a regeneration valve which is operable to provide fluid communication between the cylinder on opposite sides of the piston, or to prevent such communication, the regeneration valve having ports which are directly connected, respectively, to opposite end regions of the cylinder.

In a preferred embodiment the regeneration valve comprises a valve body which is mounted rigidly on the cylinder.

For a better understanding of the present invention and to show how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows, in schematic form, one embodiment of a hydraulic press and regeneration valve system according to the present invention; Figure 2 shows a hydraulic circuit for the press of Figure 1, in a fast advance mode; Figure 3 shows the hydraulic circuit of Figure 2 in a pressing mode; Figure 4 shows the hydraulic circuit of Figure 2 in a decompressive mode; Figure 5 shows the hydraulic circuit of Figure 2 in a fast return mode; Figure 6 shows the hydraulic circuit of Figure 2 in a high force return mode; and Figure 7 shows, in more detail, the construction of the piston and piston chamber assembly.

The hydraulic press shown in Figure 1 comprises a piston 2 disposed within a piston chamber having an outer wall 4. The piston chamber is substantially cylindrical and has an inwardly projecting sealing rim 6 disposed around an inner circumference of the chamber. The piston 2 is elongate, extending along the same axis as the axis of the piston chamber. The outer circumference of the piston is stepped such that the piston 2 may be considered to be divided into different regions. Thus, it has an upper region 8, the diameter of which is sized for engagement with the inner surface of the piston chamber. The piston further has an intermediate region 10, the diameter of which is sized for engagement with the inner surface of the rim 6.

The piston further has a lower region 12 of smaller outer diameter and which extends, sealingly, through a bore 14 provided in a lower region of the piston chamber wall 4. A first sub-chamber (the top chamber) 16 is defined above the upper region of the piston 8.

A second sub-chamber 18 (the bottom chamber) is defined below the intermediate region and it is, at least in part, annular and disposed around the lower portion of the piston. A third sub-chamber 20 (the middle chamber) is defined around the intermediate region 10 of the piston, this sub-chamber also being annular.

The top end of the middle chamber 20 is limited by a lower face of the upper region of the piston and the bottom end is limited by the tongue 6. Sealing engagement is provided between all cooperating surfaces of the piston with the piston chamber.

The piston 2 further has a cylindrical recess 21 which is formed about the longitudinal axis of the piston. A lip 24 extends inwardly above the cylindrical recess 21 and this lip defines an orifice in the top surface of the piston 2 which communicates with the recess 21. A stop 22 is provided, which is housed within the recess 21 and which limits longitudinal movement of the piston within the piston chamber. The lip 24 provides an abutment for the stop 22. An adjustment member 26, in the form of a handwheel, is provided to enable adjustment of the position of the stop, thereby to vary the stroke of the piston. The adjustment member is connected to the stop by means of a shaft 28 having a threaded portion 30 which engages with a threaded portion of the piston chamber wall 4.

The effective area, A, upon which fluid pressure acts in the top chamber is equal to the cross-sectional area of the chamber less the cross-sectional area of the cylindrical recess 21 (pressure on opposite sides of the lip 24 cancel). The effective area B, upon which fluid acts in the bottom chamber is equal to the area of the circle defined by the rim 6 less the crosssectional area of the lower region 12 of the piston.

Area A is chosen to be slightly greater than area B.

A regeneration valve 31 is attached directly onto the piston chamber 4, the valve 32 having a valve member 31, the position of which determines whether the valve is opened or closed. One side of the regeneration valve communicates, through a bore in the piston chamber 4, with the bottom chamber 18. A fluid pipe connects the other side of the regeneration valve to the top chamber 16. Thus, the top and bottom chambers are directly connected to the regeneration valve. Further fluid lines 34 are used for the control of the regeneration valve. The regeneration valve 32 forms part of a hydraulic circuit which further comprises a fluid reservoir 36, in the form of a tank, and a hydraulic pump 38 driven by a motor.

The construction of the piston and piston chamber assembly is shown in more detail in Figure 7, where similar components to those in Figure 1 are denoted by the same references. The stop 22 does not move with the piston, and this facilitates control of the adjustment of the stop. As shown in Figure 7, the shaft 28 is turned through a worm and wheel arrangement, 37 and 39 respectively. The handwheel 26 (not shown in Figure 7) turns a spindle 41 upon which the worm 37 is carried. The shaft 28 is thus rotated through gearing thereby to reduce the torque required to turn the handwheel. The wheel 39 is pressed on to a sleeve mounted in ball bearings, and turns the shaft 28 through a Woodruff key.

The handwheel 26 is conveniently located, and a digital read-out may be implemented to indicated the position of the stop. This read-out may be in the form of a counter, which counts the number of revolutions of the spindle 41. Alternatively, a motor and an encoder may be fitted to the spindle, to enable electronic control of the position of the stop.

In the embodiment shown in Figure 7, a second spindle 43 is turned by the handwheel 46 to effect rotation of a knockout rod 45, This rod 45 extends through the centre of the piston 10. Rotation of the handwheel 26 alters the height of the knockout rod with respect to the spindle 43, as a result of the engagement of an internally threaded portion of the rod 45 with a corresponding externally threaded portion of the spindle 43. The function of the knock-out rod is to eject components that get stuck in the top press tool.

The hydraulic circuit which operates the press is shown schematically in Figure 2. The hydraulic press has five operative modes which are put into effect by the hydraulic circuit. These five modes are: (1) a fast advance mode, in which the piston is moved at a high rate to effect rapid movement of the press member in an operative direction; (2) a pressing mode, in which a relatively high force is applied to the press member in the operative direction; (3) a decompressive mode, in which the pressure built up during the pressing mode is controllably released; (4) a fast return mode, in which piston operates to move the press rapidly in the direction opposite to the operative direction; and (5) a high force return mode, in which a relatively high force is applied to the press member in the direction opposite to the operative direction.

The hydraulic circuit comprises the hydraulic pump 38 which delivers fluid to the hydraulic circuit. The hydraulic circuit has first, second and third fluid path connection units 40, 42, 44 respectively. These units are in the form of multi-positional valves. They comprise a spool, the position of which determines which fluid connections are made between two inlet ports and two outlet ports of each unit. Four solenoids are provided S1, S2, S3, S4, two of which are associated with the first connection unit, the first connection unit having three distinct positions for the spool. The remaining two connection units have two positions for the spool and each have one solenoid associated with them.As can be seen in Figure 2, each connection unit has a spring or springs associated with it to bias the spool into a certain position when the respective solenoid (or solenoids) is not activated.

In the case of the first connection unit, the two springs at each end of the spool bias the spool into the central position when neither solenoid S1 nor solenoid S2 is activated.

An electronic circuit (not shown) controls the operation of the solenoids to create the desired operative cycle.

The circuit further comprises a valve 46, one side of which communicates with the middle chamber 20 of the piston chamber 4. The valve 46 has a control port 47, to enable controlled closure of the valve.

Fluid connections interconnect each of the above components, also effecting connection to the three subchambers of the piston chamber.

The hydraulic circuit further comprises a reservoir filter 48 which filters the fluid from the reservoir prior to being pumped by the motor 38. A second filter 50 also filters the fluid that is returned to the tank. A check valve 52 is provided which operates in the event of the second filter 50 becoming blocked. A heat exchanger 54 is also present to dissipate the excess heat produced by prolonged operation of the circuit, for example. A relief valve 56 is connected between the output of the motor 38 and the reservoir 36 and is preset to impose a maximum pressure limit within the circuit.

A monitoring arrangement 58 is provided to monitor the pressure in the top chamber of the piston chamber to provide a signal, once a predetermined pressure limit has been reached. This pressure limit is set by a variable relief valve 60.

The regeneration valve 32 has two control ports which enable a force to be applied to the valve member 31 so as to open or close the valve. A first control port leads to a control area 33 which may be put under pressure to exert a closing force on the valve. Also, a piston 35 is operated by means of a second control port to enable the valve to be opened, against the action of a spring.

The operation of the hydraulic circuit will now be explained in greater detail with reference to the particular operating modes of the circuit. In these circuits, the flow of fluid around the hydraulic circuit is represented by arrows. A solid arrow indicates that the fluid in that particular pipeline has undergone pressurization through the pump. The hollow arrows indicate that these fluid lines then follow a path back to the reservoir.

During an idle state of operation, the pump 38 draws oil from a reservoir through the reservoir filter 48. The spool of the first connection unit 40 is in the central position so that the pump is connected through the unit 40 to the top chamber 16, and to the reservoir through both the first and second connection units 40, 42. The oil in the middle chamber is trapped by valve 46 as well as by the first connection unit.

The same pressure acts on the control port 47 as on the inlet of the valve 46; consequently, regardless of whatever pressure is exerted on the inlet of the valve from the middle chamber, the valve will always remain closed. The piston is thus supported by two valves in series and the top chamber is vented to the reservoir by two valves in parallel. The oil returns to the reservoir through the heat exchanger 54 and the oil filter 50.

The fast advance mode is shown in detail in Figure 2. Solenoids S1, S3, and S4 are energised. Unit 40 connects the pump to the top chamber 16 and connects the middle chamber 20, through the unit 40 to tank (via valve 46). The third unit 44 connects the pump to the bottom annulus. The second unit 42 connects the control port 47 of valve 46 to the reservoir.

Consequently, the seat of the valve 46 is not forced closed and, as a result, flow is permitted from the middle chamber 20 through the valve 46.

A regenerative flow is induced from the bottom chamber 18 through the regeneration valve 32 to the top chamber. The pressure at the pump P1 is exerted on the control area 33 of the regeneration valve 32. The pressure P2 in the first sub-chamber 16 will be slightly less than P1 due to losses through the first connection unit 40 and the oil passageways. Also, the pressure P3 in the second sub-chamber 18 must be greater than P1 to open the regeneration valve.

However, the differential between P2 and P3 must be very small otherwise there will be no net driving force to urge the piston downwards. The physical design of the piston and piston chamber and of the regeneration valve is therefore crucial to the success of the device.

The piston extends at a speed which is a function of the difference in effective areas upon which fluid acts within the first and second sub-chambers (i.e.

between A and B), and the pump flow.

The pressing mode is shown in detail in Figure 3.

Solenoid 4 is de-energised, leaving solenoids S1 and S3 energised. The first connection unit 40 connects the pump to the top chamber and connects the middle chamber, through valve 46, to the reservoir 36. The control port of the valve 46 is connected to the reservoir and consequently the valve is not forced closed and fluid from the middle chamber can be urged to pass through the valve. The third connection unit 44 connects the bottom chamber to the reservoir 36.

The forces acting on the regeneration valve 32 hold it firmly shut since the net force closing the valve is much greater than that trying to open it, as can be seen in Figure 3. The piston extends at a speed which is a function of the effective area upon which fluid acts in the top chamber and the pump flow. This is a pressing cycle, since the pressure differential across the piston is maintained, through closure of the regeneration valve 32.

The load applied to the workpiece is controlled and limited by relief valve 60. Flow monitor 58 generates an electronic signal when the set pressure is reached. Relief valve 60 is connected downstream to the second sub-chamber so that it does not open during the Fast Advance movement, since during the fast advance mode, a small pressure differential is experienced between the first and second sub-chambers.

The decompression mode then follows as shown in Figure 4. Thus, on completion of the pressing stroke solenoid S3 is de-energised leaving only solenoid S1 energised. The release of solenoid S3 opens a flow path to the reservoir but the path is restricted by a control orifice. This therefore controls the rate of decompression of the top chamber.

The configuration of the hydraulic circuit during the fast return mode is shown in Figure 5. Solenoid S2 is energised. The first connection unit 40 connects the pump flow through valve 46 to the middle chamber.

The pump 38 is also connected to the second control port of the regeneration valve. This therefore physically forces the regeneration valve to open. This measure is necessary, since the other pressures acting on the regeneration valve would otherwise cause it to close. The first connection unit 40 also connects the first sub-chamber to the reservoir as does the second connection unit 42.

The piston rises at a speed which is a function of the annular area of the piston upon which fluid in the middle chamber acts, and the pump flow. The bottom chamber is filled by oil from the top chamber flowing through the regeneration valve. The balance of the flow returns to the reservoir through the first and second connection units-40, 42.

High force return is shown in Figure 6. Solenoids S2 and S4 are energised. The first connection unit 40 connects the pump flow through valve 46 to the third sub-chamber. Since there must be a pressure drop across the valve 46, it is evident that the pressure acting on the control port is less than the input pressure. Consequently, the valve opens. The pump 38 is also connected to the bottom chamber by connection unit 44. The first connection unit 40 connects the top chamber to the reservoir as does the second connection unit. Both sides of the piston 35 of the regeneration valve 32, together with the first control area 33, experience pump pressure so that the regeneration valve is held shut.

The piston returns at a speed that is a function of the sum of the areas of the piston upon which fluid acts within the second and third sub-chambers, and the pump flow.

Redundancy and monitoring play an important role in the specific embodiment of the press shown in the drawings.

When all the solenoids are de-energised the top chamber is connected to the reservoir by two parallel flow paths, via units 42 and 44, i.e. if either connection unit fails to take up its correct de-energised position the main cylinder will still be connected to tank via the other.

The piston is supported by oil trapped in the third sub-chamber annulus by both the valve 46 and the connection unit 40 connected in series, i.e. if either valve fails to take up its de-energised position (valve 46 is controlled by unit 42) the piston will still be supported by the other. Connection unit 40 is monitored by function, i.e. it has to work correctly or the press will not work. Valve 46 is monitored by a linear transducer and this also monitors the function of the second connection unit 42 because, if unit 42 fails to take up its de-energised position, the control area of valve 46 will remain connected to the reservoir and the valve will not close.

The system according to the present invention has advantages in terms of efficiency of design, cost and in the speed at which the piston can be made to move during the regeneration cycles, owing to the minimized pressure losses in this cycle.

Claims

1. A hydraulic piston and cylinder unit comprising a regeneration valve which is operable to provide fluid communication between end regions of the cylinder on opposite sides of the piston, or to prevent such communication, the regeneration valve having ports which are directly connected, respectively, to the opposite end regions of the cylinder.

2. A unit as claimed in claim 1, in which the regeneration valve comprises a valve body which is mounted rigidly on the cylinder.

3. A unit as claimed in claim 1 or 2 in which the piston is operable in a high speed mode, in which the piston is moved at a relatively high rate and in which the regeneration valve provides fluid communication between the end regions of the cylinder, and a pressing mode, in which the piston is moved under a relatively high force and in which the regeneration valve prevents communication between the end regions of the cylinder.

4. A hydraulic press including a piston chamber and a piston which divides the piston chamber into first and second sub-chambers, the piston being capable of actuating a press member and being controlled by a hydraulic circuit, the hydraulic circuit comprising a fluid reservoir and pressurizing means, the circuit effecting the selection between operative modes of the press, these operative modes including (i) a fast advance mode, in which the piston is moved at a relatively high rate to effect rapid movement of the press member in an operative direction, and (ii) a pressing mode, in which a relatively high force is applied to the press member in the operative direction, the circuit further comprising a regeneration valve, disposed in close proximity to the piston chamber, the regeneration valve having two ports, which communicate with opposite sides of the valve, the two ports being directly connected to the first and second sub-chambers respectively, the arrangement of the hydraulic circuit being such that, during the fast advance mode flow is permitted across the regeneration valve to transfer fluid from one sub-chamber to the other sub-chamber and such that, during the pressing cycle, flow across the regeneration valve is prohibited.

5. A press as claimed in claim 4 in which a third sub-chamber is defined within the piston chamber, such that fluid in the third sub-chamber acts on a surface of the piston for movement in a direction opposite to the operative direction.

6. A press as claimed in claim 5 in which the operative modes include a fast return mode, in which the piston operates to move the press member rapidly in the direction opposite to the operative direction, in which operative mode flow across the regeneration valve is permitted.

7. A press as claimed in claim 6, in which, during the fast return mode, pressure is applied to the third sub-chamber.

8. A press as claimed in any one of claims 4 to 7 in which the operative modes include a decompressive mode, during which pressure built up during the pressuring mode is controllably released.

9. A press as claimed in any one of claims 4 to 8 in which the operative modes include a high force return mode, during which a relatively high force is applied to the press member in a direction opposite to the operative direction, in which operative mode flow across the regeneration valve is prohibited.

10. A press as claimed in any one of claims 4 to 9 in which the hydraulic circuit comprises a plurality of multi-positional flow selectors, the positions of which are controlled by solenoids which in turn are controlled by electronic control circuitry.

11. A press as claimed in claim 10 in which the positions of the flow selectors determine the operative modes of the press.

12. A hydraulic press as claimed in any preceding claim substantially as described herein with reference to and as shown in the accompanying drawings.