Field of the invention

The present invention relates to a hydraulic press, especially a hy- draulic deep drawing press, and further especially a single action hydraulic deep drawing press, comprising a frame; a press table supported by the frame; a ram member opposite the press table; and at least one hydraulic cylinder. Background of the invention

Fig. 1 shows schematically a prior art, single action, hydraulic press e.g. for deep drawing. The press comprises a frame 1 in which a press table 3 is supported. Opposite the press table 3 a ram member 5 is positioned. The ram member 5 is movable towards the press table 3 by means of a ram cylin- der 7. Beneath the press table 3 i.e. on the opposite side of the press table 3 relative to the ram member 5, a cushion table 9 is provided. The cushion table 9 is provided with cushion pins 11 extending slidably through the press table 3 towards the ram member 5. The cushion table 9 with the cushion pins 11 is movable towards the ram member 5 by means of a cushion cylinder 13. The ram member 5 and the cushion table 9 are movable back and forth in direc tions of and along a press axis 15.

Fig. 2 illustrates deep drawing by means of the hydraulic press shown in Fig. 1. A lower inner tool 17 is positioned on the press table 3 and a number of the cushion pins 11 have been removed as such cushion pins would otherwise collide with the lower inner tool 17. The remaining cushion pins 11 are carrying a lower outer tool 19 which has an aperture 21 substan tially corresponding to a cross section perpendicular to the press axis 15 of the lower inner tool 17. A blank 23, such as a steel plate, is positioned above the lower tools 17, 19 to be supported by the lower outer tool 19. On the ram member 5, on a lower side thereof, an upper tool 25 is attached. The upper tool 25 has an aperture 27 substantially corresponding to the cross section perpendicular to the press axis 15 of the lower inner tool 17. In operation the ram member 5 with the upper tool 25 will be lowered by means of the ram cylinder 7 the latter being pressurized to exert a pres sure at a force of e.g. approx. 500 tons (approx. 5000 kN). The cushion cylin der 13 is pressurizes to exert a counter pressure at a counter force of e.g. approx. 300 tons (approx. 3000 kN).

In a starting position shown in Fig. 2 the top of the lower inner tool 17 is positioned at a level slightly below an upper surface of the lower outer tool 19 and the blank 23. Due to the pressurization of the ram cylinder 7, the ram member 5 with the upper tool 25 is lowered to initially contact the blank 23 with a lower surface of the upper tool 25, thereby pinching the blank 23 be tween the upper surface of the lower outer tool 19 and the lower surface of the upper tool 25 by a ‘pinching force’ substantially equal to the counter force. Subsequently, due to the larger pressure or force exerted by the ram member 5, i.e. the difference between the force of the ram cylinder and the counter force, which herein is designated ‘the work force’, the upper tool 25 together with the lower outer tool 19 is moved downwards, the lower inner tool 17 mov ing relatively through the aperture 21 of the lower outer tool 19 and penetrat ing into the aperture 27 of the upper tool 25 carrying along the blank 23. Thereby peripheral parts of the blank are sliding between the surfaces of the upper and lower outer tool 25, 19, said peripheral parts thereby being drawn towards the press axis 15, and the material of the peripheral parts of the blank 23 are thereby being deformed by compression and stretching in a plane of the blank 23, whereby the peripheral parts of the blank 23 become respectively thicker and thinner in a direction perpendicular to the plane of the blank 23. Gradually, parts of the blank 23 that were initially pinched between the upper tool 25 and the lower outer tool 19 are mowed towards the lower inner tool 17 for a part of the blank 23 to assume the shape of the lower inner tool 17 and the aperture 27.

During the process, the lower outer tool 19, the cushion pins 11 and the cushion table 9 are moved downwards, the cushion cylinder 13 being compressed and hydraulic fluid pressurizing the cushion cylinder 13 being expelled through a pressure control valve, not shown. From an energetic point of view this represents a loss of energy.

Fig. 3 shows schematically parts of a prior art embodiment of a hy draulic circuit for operating a hydraulic press, such as the hydraulic press shown in Figs. 1 and 2. Thus Fig. 3 shows the ram member 5, the ram cylin der 7, the press table 3, the cushion table 9, the cushion pins 11, and the cushion cylinder 13. The ram cylinder 7 comprises an upper cylinder chamber 7’ and an annular lower cylinder chamber 7” on either side of a two-sided pis ton 8 having a major piston area A4 in the upper cylinder chamber 7’ to be pressurized to lower the ram member 5 and perform a deep drawing process, and an opposite annular minor piston area A5 in the annular lower cylinder chamber 7” to be pressurized to raise the ram member 5 with an upper tool to complete a deep drawing process by releasing a processed blank.

A hydraulic line 29 is connected to and provided for feeding (and re lieving) the upper cylinder chamber 7’ with hydraulic fluid pressurized by a hydraulic pump 31 driven by a motor 33. The hydraulic line 29 passes a box 35 intended to indicate that any components, that the person skilled in the art will appreciate as being necessary or appropriate, may be connected and at tached to the hydraulic line 29 such as e.g. a pressure gauge, a pressure control valve, a pressure relief valve, a directional valve, etc.

A hydraulic line 37 is connected to and provided for relieving and feeding the annular lower cylinder chamber 7”. To provide for relieving the annular lower cylinder chamber 7”, as will be explained below, the hydraulic line 37 is provided with pressure control valve 39 with a drain to a reservoir 39’, and as indicated by the box 35, which the hydraulic line 37 is shown to pass, the hydraulic line 37 may comprise or be attached to any such compo nents as the person skilled in the art will appreciate as being necessary or appropriate such as e.g. a pressure gauge, a pump for feeding hydraulic fluid from a source, a pressure control valve, a directional valve, etc.

The cushion cylinder 13 is connected by a hydraulic line 41 to a pressure control valve 43 with a drain to a reservoir 43’ and further to a box 45 indicating that further components, that the person skilled in the art will appreciate as being necessary or appropriate such as a source for supplying and initially pressurizing the cushion cylinder, a pressure gauge, a pressure relief valve, a directional valve, etc. may be included.

The cushion cylinder 13 has a piston 14 with a major piston area A2 in a lower cylinder chamber 13’ to which the hydraulic line 41 is connected to provide fluid connection between the lower cylinder chamber 13’ and the pressure control valve 43.

The cushion cylinder 13 is shown to comprise an annular upper cyl inder chamber 13” connected through a hydraulic line 47 to a reservoir 47’ through the box 45 indicating the any such components that the person skilled in the art will appreciate as being necessary or appropriate may be included.

In a deep drawing operation, during an initial lowering of the ram el ement 5 from the position shown in Fig. 2 to a position in which the upper tool 25 abuts on the blank 23, i.e. during the so-called approach movement, hy draulic fluid is fed to the upper cylinder chamber 7’ of the ram cylinder 7 by the pump 31 and hydraulic fluid is expelled from the annular lower cylinder chamber 7” of the ram cylinder 7 through the pressure control valve 39 to the reservoir 39’ which is not pressurized. Subsequently, during the common lowering of the ram element 5 and the cushion table 9 with the cushion pins 11 , hydraulic fluid is further, as also indicated above, expelled from the lower cylinder chamber 13’ of the cushion cylinder 13 through the pressure control valve 43 to the reservoir 43’ which is not pressurized, i.e. the reservoir is held at ambient pressure.

The pressurized hydraulic fluid that is expelled through the pressure control valves 39 and 43 represents losses of energy.

Summary of the invention

It is an object of the present invention to avoid or reduce at least some of the losses of energy found in prior art hydraulic presses like the hy draulic press described above.

This is obtained by a hydraulic press as mentioned by way of intro duction, comprising a hydraulic pressure recipient for receiving hydraulic pressure from said at least one hydraulic cylinder, said at least one hydraulic cylinder being connected, at least during operation, through a hydraulic pres sure transmission to the hydraulic pressure recipient. Hereby is obtained that energy loss due to pressurized hydraulic fluid being expelled to ambient pres sure is avoided at least to a certain degree.

Further the press comprises a cushion table positioned on an oppo site side of the press table relative to the ram member, and the at least one cylinder comprises a hydraulic cushion cylinder configured to actuate the cushion table in a direction towards the ram member. Hereby is obtained that a loss of energy due to pressurized hydraulic fluid being expelled from the cushion cylinder during operation of the press is avoided.

Further the hydraulic cushion cylinder is connected through a hydrau lic line to the hydraulic pressure recipient, and said hydraulic line preferably comprises a hydraulic shut off valve. Hereby a simple construction is ob tained.

Further the hydraulic press further comprises a primary ram cylinder. Hereby is obtained a possibility of adjusting the pinching force and the work force individually.

Still further the hydraulic pressure recipient is a secondary ram cylin der, a piston area of the hydraulic cushion cylinder is smaller than a piston area of the secondary ram cylinder, and the press comprises a pressurized source of hydraulic liquid, such as a hydraulic accumulator, connected by a conduit connection, e.g. a pipe, a hose, a bore, etc., to the hydraulic cushion cylinder and the secondary ram cylinder. Hereby is obtained that all hydraulic fluid expelled from the cushion cylinder is used for assisting driving the ram member, thereby minimizing loss and providing a better economy, and any lack of sufficiency of the hydraulic fluid supplied by the cushion cylinder for the secondary ram cylinder is compensated for by the pressurized source.

In a practical embodiment the hydraulic pressure transmission com prises one or more elements selected from a group comprising: a hydraulic line; a hydraulic shut off valve; a hydraulic motor; a hydraulic pump; and a hydraulic motor/pump. It should be understood that the hydraulic pressure transmission may comprise one or more of each of said elements.

In a practical embodiment the secondary ram cylinder and the prima ry ram cylinder are separate cylinders.

In another practical embodiment the secondary ram cylinder and the primary ram cylinder are built together in a single element comprising more separate cylinder chambers each comprising a piston.

In an embodiment the at least one cylinder comprises ram lifting cyl inder connected by a hydraulic line to a hydraulic accumulator. Hereby is ob tained that the pressure of hydraulic expelled from the ram lifting cylinder, e.g. during a deep drawing process such as during an approach movement, is not lost but is retained at least partially for later use in the accumulator.

In a practical embodiment the ram lifting cylinder is connected to the accumulator through a hydraulic motor/pump, whereby it is possible to use a relatively small electric motor.

In other examples of hydraulic presses: the hydraulic pressure recipient is selected from a group comprising: a hydraulic cylinder and a hydraulic accumulator, it should be understood that the hydraulic pressure recipient may comprise one or more hydraulic cylin ders and/or hydraulic accumulators; the hydraulic pressure recipient comprises a ram cylinder or a sec ondary ram cylinder configured to actuate the ram member in a direction to wards the press table, whereby is obtained that the pressure of hydraulic fluid expelled from the cushion cylinder during e.g. a deep drawing process is in stantly used for assisting in driving the ram member; a piston area of the hydraulic cushion cylinder is larger than a piston area of the secondary ram cylinder, the hydraulic press further comprising a primary ram cylinder, and a pressure control valve is connected to the hy draulic cushion cylinder and the secondary ram cylinder, whereby is obtained a possibility of adjusting the pinching force and the work force individually, and the presence of a pressurized source for compensating an insufficiency of supply of hydraulic fluid for the secondary ram cylinder is not necessary; the hydraulic pressure transmission comprises a hydraulic motor and a hydraulic pump, the hydraulic motor being in driving connection with the hydraulic pump, preferably at least one of said hydraulic motor and hydraulic pump being a hydraulic motor/pump, whereby it is possible to use a single ram cylinder for lowering the ram element during a deep drawing process thus providing a solution i.a. suitable for retrofit to an existing hydraulic press; the hydraulic press further comprises a second motor in driving con nection with the hydraulic pump; a fluid outlet of the hydraulic motor is connected by a hydraulic line to the ram cylinder, whereby is obtained that a relatively small electric motor may be used thus lowering production costs; a fluid outlet of the hydraulic motor is connected by a hydraulic line to a reservoir, preferably at substantially atmospheric pressure, which provides for using a relatively simple hydraulic motor and a relatively small electric mo tor, which per se may be beneficial to production costs.

Embodiments of the invention

In the following the invention will be explained in further detail by way of examples having reference to the schematic drawing showing non-limiting examples of embodiments of the invention. In the drawing:

Fig. 1 shows a prior art, single action, hydraulic press e.g. usable for deep drawing;

Fig. 2 illustrates a deep drawing process performed by means of the hydraulic press of Fig. 1 ;

Fig. 3 illustrates parts of a hydraulic system of a prior art hydraulic press;

Figs. 4 to 9 illustrates 1 ^st to 6 ^th embodiment of a part of a hydraulic system for a hydraulic press according to the present invention; and

Fig. 10 illustrates an embodiment of another part of a hydraulic sys tem for a hydraulic press according to the present invention.

The present invention relates to energy saving in hydraulic presses. In the following a number of embodiments are presented as non-limiting ex- amples.

In the different embodiments, similar elements and elements similar to elements of the prior art embodiments of Figs. 1 to 3, are indicated by the same reference numeral. As used herein by “hydraulic cylinder” is mainly intended an actuator element comprising a cylinder chamber with a piston attached to or integral with a piston rod, the piston having at least one active surface that in use is subject to hydraulic pressure to move the piston and actuate the piston rod to exert a force. As used herein by “cushion table” with “cushion pins” is intended a supporting tool that provides for supporting a lower outer tool for said lower outer tool to be pressed against a blank from an opposite side relative to an upper tool to pinch the blank between said lower outer tool and upper tool. No special embodiment of such supporting tool is intended. As used herein by “pressure control valve” is mainly intended a valve that opens when subject to a certain level of an upstream pressure of a liquid being controlled by the valve to maintain said upstream pressure below said level and that closes when the upstream pressure is below said level to pre vent the fluid from passing the valve. As used herein “hydraulic line” is mainly intended to mean a hydrau lic conduit providing a conduit connection for transferring a fluid. Thus “hy draulic line” may include e.g. a pipe, a hose, a bore, etc.

As used herein “piston area” is intended to mean the effective sur face area that will effectively drive the piston when subject to fluid pressure, i.e. an area of a projection of the surface of the piston in the direction of travel of the piston, as it will be appreciated by those skilled in the art.

As used herein the term “hydraulic motor/pump” indicates a device that is capable of converting hydraulic pressure and flow into torque and an gular displacement, and vice versa in accordance with conditions to which the device is subjected. Non-exclusive examples of a hydraulic motor/pump are a gear motor/pump; a vane motor/pump; and a gerotor motor/pump. Other ex amples are known to those skilled in the art. It should be noted that terms like “up”; “upper”; “down”; “lower”; etc. are used to indicate mutually different directions and are used as appropriate having reference to the embodiments shown in the drawings, but said terms are not intended to limit the invention to a specific orientation of a hydraulic press.

Figs. 1 and 2, as described above in the opening part of the descrip tion, show the main features of a hydraulic press. Figs. 4 to 9 show different embodiments of a part of a hydraulic circuit for activating e.g. such hydraulic press and especially Figs. 4 to 9 show such parts of the hydraulic circuit that allow utilizing the pressure of hydraulic fluid expelled from the cushion cylin der 13 for driving the ram cylinder 7.

It is noted that for simplicity, the frame is not shown in Figs. 4 to 10.

In the embodiments shown in Figs. 4 to 7 the ram cylinder 7 shown in the prior art embodiment of Figs. 1 and 2 is substituted by one (or more) sec ondary ram cylinder 7.1, 7.1a and one or more primary ram cylinders 7.3’, 7.3a.

In general, the cylinders may respectively be constituted as a single cylinder or as more cylinders working in parallel.

Thus, in the embodiments of Figs. 4 and 5, the primary ram cylinder is shown to be configured as two primary ram cylinders 7.3’ working in paral lel. In general, and as the person skilled in the art will appreciate, it is benefi cial to design the press in such a way that the forces provided by the work cylinders, and respectively by the first cylinder for that sake, are mainly sym metrical in relation to the press axis 15, see Figs. 1 and 2. The secondary ram cylinder 7.1 has a two-sided piston 48 with a major piston area AT and an opposite annular minor piston area A5. Each of the two primary ram cylinders 7.3’ comprises a piston 49 with a piston area A3’ summing up to a total piston area A3. The major piston area AT faces an upper cylinder chamber 48’; the opposite annular minor piston area A5 faces an annular cylinder chamber 48”; and each of the piston areas A3’ faces a cylinder chamber 49’.

In the embodiments of Figs. 6 and 7 the secondary ram cylinder 7.1a and the primary ram cylinder 7.3a are built together in a single element 51 comprising more separate cylinder chambers each comprising a piston. Thus, the element 51 comprises a stationary upper part 51.1 and a movable lower part 51.2, the latter providing an inner cylinder chamber 52 housing a piston 53 with a piston area A3, the piston 53 being part of the upper part 51.1 and thus being stationary. The stationary upper part 51.1 provides an annular up per cylinder chamber 5T housing a two-sided annular piston 55 with an upper major piston area A1, the latter being part of the movable lower part 51.2 and further the latter comprises a lower or opposite annular minor piston area A5 facing a lower annular cylinder chamber 51”.

In all of the embodiments shown in Figs. 4 to 10 a cushion cylinder 13 comprises a piston 14 with a major piston area A2 like the prior art embod iments shown in Figs. 1 to 3. Thus, the cushion cylinder 13 of Figs. 4 to 10 comprises the lower cylinder chamber 13’, which the major piston area A2 faces, and the upper cylinder chamber 13” that is connected through the hy draulic line 47 to a box 47” indicating the any such components that the per son skilled in the art will appreciate as being necessary or appropriate, includ ing a drain to a reservoir, may be included. Further, like in the prior art em bodiment of Fig. 3, box 45 is connected to the lower cylinder chamber 13’ of the cushion cylinder 13 through hydraulic line 41 indicating that further com ponents, that the person skilled in the art will appreciate as being necessary or appropriate such as a source for supplying and initially pressurizing the cushion cylinder, a pressure gauge, a pressure relief valve, a directional valve, etc. may be included.

In the embodiments of Figs. 4 to 7 the lower cylinder chamber 13’ of the cushion cylinder 13 is connected respectively to the upper cylinder cam ber 48’ of the secondary ram cylinder 7.1 or the annular upper cylinder cham ber 5T of the secondary ram cylinder 7.1a through a hydraulic line 57 includ ing a shut off valve 59. Thus, in the embodiments of Figs. 4 to 7 the hydraulic cylinder 7.1; 7.1a, respectively, constitutes a hydraulic pressure recipient for receiving hydraulic pressure directly from the cushion cylinder 13, i.e. from the lower cylinder chamber 13’ thereof, through a hydraulic pressure trans mission comprising the hydraulic line 57 and the shut off valve 59. In the embodiments of Figs. 4 and 6 the major piston area A2 of the cushion cylinder 13 is larger, albeit possibly only slightly larger, than the major piston area A1’ of the secondary ram cylinder 7.1 and the upper major piston area A1 of the secondary ram cylinder 7.1a, respectively; and these embodi ments comprise, like the prior art of Fig. 3, pressure control valve 43 with drain to reservoir 43’ at ambient pressure, that is connected to the cushion cylinder 13, i.e. to the lower cylinder chamber 13’ thereof, through hydraulic line 41. In operation, when the ram member 5 and accordingly the cushion table 9 with the cushion cylinder 13 are lowered, hydraulic fluid will be ex pelled from the lower cylinder chamber 13’ and because the major piston area A2 is larger than the major piston area A1’ and the upper major piston area A1, respectively, an excess of hydraulic fluid is expelled relatively to what can me accommodated by the upper cylinder chamber 48’ or the annular upper cylinder chamber 51’, respectively. This excess amount of hydraulic fluid and the accompanying hydraulic pressure may be relieved through the hydraulic control valve 43. The relieving of pressure through a pressure control valve represents a loss of energy which however is much smaller than what is known from the prior art as described in the introductory part of the descrip tion. An advantage of this embodiment is that due to the larger major piston area A2 of the cushion cylinder a risk of shortage of hydraulic fluid in the sys tem comprising the cushion cylinder and the secondary ram cylinder is avoid ed.

In the embodiments of Figs. 5 and 7 a pressure control valve 61a is attached to the hydraulic line 57 and has a drain to the reservoir 6T. Further a pressurized source of hydraulic fluid in the form of a hydraulic accumulator 63 is connected to the hydraulic line 57 through the pressure control valve 61a.

In the embodiments of Figs. 5 and 7 the major piston area A2 of the cushion cylinder 13 is smaller than the major piston area A1 ’ of the secondary ram cylinder 7.1 or the upper major piston area A1 of the secondary ram cyl inder 7.1a, respectively. Accordingly, when during operation hydraulic fluid is expelled from the cushion cylinder 13 to be transferred to the secondary ram cylinder 7.1; 7.1a a shortage of hydraulic fluid may occur that would imply a drop of pinching force as will explained below. Such shortage will however be automatically and instantly replenished from the hydraulic accumulator 63. Further a box 65 is connected to a hydraulic line 63’ connecting the hydraulic accumulator 63 with the pressure control valve 61a to indicate that further components, that the person skilled in the art will appreciate as being neces sary or appropriate such as a source for supplying and initially pressurizing the accumulator, a pressure gauge, a pressure relief valve, etc. may be in cluded.

In all of the embodiments of Figs. 4 to 7 a box 67 is connected to an upper part 57’ of the hydraulic line 57 to indicate that further components, that the person skilled in the art will appreciate as being necessary or appropriate such as a source for supplying and initially pressurizing the upper cylinder chamber 48’ of the secondary ram cylinder 7.1 or the annular upper cylinder chamber 51’ of the secondary ram cylinder 7.1a, respectively, a pressure gauge, a pressure relief valve, a directional valve, etc. may be included.

Further, in the embodiments of Figs. 4 to 7, a box 69 is connected through a hydraulic line 71 to the cylinder chambers 49’ of the primary ram cylinders 7.3’ or the inner cylinder chamber 52 of the primary ram cylinder 7.3a, respectively, to indicate that further components, that the person skilled in the art will appreciate as being necessary or appropriate such as a source for supplying and pressurizing the primary ram cylinders, a pressure gauge, a pressure relief valve, a directional valve, etc. may be included.

Still further, in the embodiments of Figs. 4 to 7 a box 73 is connected though a hydraulic line 75 to the annular cylinder chamber 48” of the second ary ram cylinder 7.1 or the lower annular cylinder camber 51” of the second ary ram cylinder 7.1a, respectively, to indicate that the features presented below with reference to Fig. 10 may be applied to the embodiments of Figs. 4 to 7.

In operation, corresponding to the procedure indicated with reference to Fig. 2, of the embodiments of Figs. 4 to 7, initially the shut off valve 59 is closed and the cushion cylinder 13 is supplied and pressurized from the box 45 to be adjusted to a position as indicate in Fig. 2; and the upper cylinder chamber 48’ of the secondary ram cylinder 7.1 or the annular upper cylinder chamber 51’ of the secondary ram cylinder 7.1a, respectively, are supplied and pressurized from box 67 for the ram member 5 with an upper tool like the upper tool 25 to be brought into contact with a blank like the blank 23 to pinch the blank by a pinching force provided by pressure of the secondary ram cyl inder 7.1 ; 7.1a and counter pressure of the cushion cylinder 13. The blank thus being in a pinched condition, the connections to the hydraulic fluid sourced of boxes 45 and 67 are shut off and the shut off valve 59 is opened. Subsequently, the primary ram cylinders 7.3’ ad 7.3a, respectively are pres surized to lower the ram member 5 with the upper tool to conduct the deep drawing process while pressurized hydraulic fluid is expelled from the cushion cylinder 13 to be transferred to the secondary ram cylinders 7.1 ; 7.1a as de scribed above.

During the deep drawing process, the pinching force is controlled and maintained by the action of the pressure control valve 43 or 61a, respectively.

It should be noted that the pressure control valves 43 and 61a are adjustable to provide for adjusting the pinching force, e.g. in accordance with parameters of a specific deep drawing process such as the kind of the mate rial of the blank, the thickness of the blank, the size of the item to be pro duced by the process, etc.

It is noted that the designations “primary ram cylinder” and “second ary ram cylinder” are chosen to indicate that the primary ram cylinder is con nected to the box 69 to be pressurized during operation to lower the ram member, whereas the secondary ram cylinder is connected to the cushion cylinder 13 to contribute in providing the pinching force. Further it is noted that though in the embodiments shown, the cylinders comprising the cylinder chambers 49’ and 52, respectively, are set up as primary ram cylinders, and the cylinders comprising the cylinder chambers 48’ and 5T, respectively, are set up as secondary ram cylinders, it is possible by, amending the connec tions of the hydraulic lines 57’ and 71 to the cylinders, to change this set up, so that the cylinders comprising the cylinder chambers 49’ and 52, respective ly, would be set up as secondary ram cylinders, and the cylinders comprising the cylinder chambers 48’ and 51’, respectively, would be set up as primary ram cylinders. In the embodiments of Figs. 8 and 9 the lower cylinder cham ber 13’ of the hydraulic cushion cylinder 13 is connected to a hydraulic motor 77 through the hydraulic line 41. The hydraulic motor 77 is drivingly connect ed to a hydraulic pump 79, and a second motor 81, e.g. an electric motor, is likewise drivingly connected to the hydraulic pump 79 for the latter to be driv en by the hydraulic motor 77 and the second motor 81.

In the embodiments of Figs. 8 and 9 the ram member 5 is driven by a single ram cylinder 7, similar to the ram cylinder 7 disclosed in and describer with reference to Fig. 3. To lower the ram member 5, such as during a deep drawing process, the upper cylinder chamber 7’ of the ram cylinder 7 is fed with pressurized hydraulic fluid through the hydraulic line 29.

It should be noted that the major piston area A2 of the cushion cylin der 13 is substantially smaller than the major piston area A4 of the ram cylin der 7. This provides for the pressure in the upper cylinder chamber 7’ of the ram cylinder 7 being substantially lower than the pressure in the lower cylin der chamber 13’ of the cushion cylinder 13 during operation, while the ram cylinder 7 is still exerting a substantially larger force than the cushion cylinder 13, namely both a pinching force, like the cushion cylinder, and a work force.

Like in the embodiments of Figs. 4 to 7, the box 73 is connected though the hydraulic line 75 to the lower cylinder chamber 7” of the ram cylin der 7 to indicate that the features presented below with reference to Fig. 10 may be applied to the embodiments of Figs. 8 and 9.

In the embodiment of Fig. 8 a fluid inlet or first hydraulic port 77’ is connected to the hydraulic line 41 and a fluid outlet or second hydraulic port 77” is connected to the hydraulic line 29. A fluid inlet or first hydraulic port 79’ of the hydraulic pump 79 is connected to a reservoir 80 and a fluid outlet or second hydraulic port 79” of the hydraulic pump 79 is connected to the hy draulic line 29.

During operation of the embodiment of Fig. 8, hydraulic fluid expelled from the lower cylinder chamber 13’ is led to the hydraulic motor 77 which transforms a part of the pressure of the hydraulic fluid into torque that drives the hydraulic pump 79. The hydraulic fluid that has entered the first hydraulic port 77’ exits the second hydraulic port 77” at pressure generally similar to the pressure driving the ram cylinder 7 in the upper cylinder chamber 7’. Since the piston area A4 of the upper cylinder chamber 7’ is larger than the piston area A2 of the lower cylinder chamber 13’ the amount of hydraulic fluid driving the ram cylinder 7 need to be supplemented which is provided for by the hy draulic pump 79 which pumps hydraulic fluid from the reservoir 80 to the hy draulic line 29. The driving effect for the hydraulic motor 77 is supplemented by the second motor 81 in so far as the driving effect provided by the hydrau lic motor 77 does not suffice to provide the amount of hydraulic fluid at the pressure needed for driving the ram cylinder 7.

In the embodiment of Fig. 9 the fluid outlet or second hydraulic port 77” of the hydraulic motor 77 is connected by a hydraulic line 78 to a reservoir 78’, preferably at substantially atmospheric or ambient pressure.

During operation of the embodiment of Fig. 9, hydraulic fluid expelled from the lower cylinder chamber 13’ is led to the hydraulic motor 77 which transforms the pressure of the hydraulic fluid into torque that drives the hy draulic pump 79. The hydraulic fluid that has entered the first hydraulic port 77’ exits the second hydraulic port 77” at generally ambient or atmospheric pressure. In this embodiment the hydraulic pump 79 basically delivers the amount of hydraulic fluid needed to drive the ram cylinder 7 and at the pres sure needed to drive the ram cylinder 7. The driving effect provided by the hydraulic motor 77 is supplemented by the second motor 81 in so far as the driving effect provided by the hydraulic motor 77 does not suffice to provide the amount of hydraulic fluid at the pressure needed for driving the ram cylin der 7.

It is seen that in the embodiments of Figs. 8 and 9 the hydraulic mo tor 77 and the hydraulic pump 79 provides a hydraulic pressure transmission transmitting pressure from the lower cylinder chamber 13’ of the cushion cyl inder 13 to the upper cylinder chamber 7’ of the ram cylinder 7.

Providing for using a single ram cylinder like the prior art, the embod iments of Figs. 8 and 9 provide solutions suitable for retrofit to an existing hy- draulic press.

For the embodiments of Figs. 8 and 9, like in the prior art embodi ment of Fig. 3, box 45 is connected to the lower cylinder chamber 13’ of the cushion cylinder 13 through hydraulic line 41 indicating that further compo- nents, that the person skilled in the art will appreciate as being necessary or appropriate such as a source for supplying and initially pressurizing the cush ion cylinder, a pressure gauge, a pressure relief valve, etc., may be included.

Further a box 83 is connected to the hydraulic line 29 indicating that further components, that the person skilled in the art will appreciate as being necessary or appropriate such as a source for supplying and initially pressur izing the ram cylinder, a pressure gauge, a pressure relief valve, a directional valve, etc., may be included.

Fig. 10 shows an embodiment of a different part of a hydraulic sys tem for a hydraulic press according to the present invention. Thus, Fig. 10 shows, similar to Fig. 3, the ram member 5 attached to the ram cylinder 7; the press table 3; and the cushion table 9 supported by the cushion cylinder 13.

As indicated, the ram cylinder 7 comprises the piston 8 and the upper cylinder chamber 7’ that is connected through the hydraulic line 29 to a box 85.

As further indicated, the cushion cylinder 13 comprises the upper cyl inder chamber 13” connected through hydraulic line 47 to the box 47”; the piston 14; and the lower cylinder chamber 13’ connected through the hydrau lic line 41 to a box 87. It should be understood that the boxes 85 and 87 indicates that fur ther components may be included in possibly interconnected hydraulic net works as may be envisaged by those skilled in the art. E.g. the boxes 85 and 87 may together comprise the elements disclosed with reference to Fig. 8 or 9 to interconnect pressure-wise the lower cylinder chamber 13’ of the cushion cylinder 13 with the upper cylinder chamber 7’ of the ram cylinder 7.

The ram cylinder 7 comprises the lower cylinder chamber 7” from which hydraulic fluid is expelled during the lowering of the ram member 5 and which is pressurized when the ram member 5 should be raised. The lower cylinder chamber 7” is through the hydraulic line 75, according to the present invention, connected to a hydraulic accumulator 89 through a hydraulic mo tor/pump 91 which is in driving connection with a motor, preferably an electric motor 93.

The hydraulic motor/pump 91 is shown to be connected to the accu mulator 89 through an extension 75’ of the hydraulic line 75 and a box 95 is connected to the extension 75’ to indicate that any such components that the person skilled in the art will appreciate as being necessary or appropriate may be included or attached, such as e.g. a pressure gauge, a source for replen ishing hydraulic fluid, a pressure control valve, a directional valve, etc.

The upper cylinder chamber 7’ has the major piston area A4 and the annular lower cylinder chamber 7” has the opposite annular minor piston area A5 which is much smaller that the major piston area A4. Accordingly, when the ram member 5 is lowered during e.g. a deep drawing process or during approach movement, hydraulic fluid is expelled from the lower cylinder cham ber 7” to the hydraulic accumulator 89 in which pressure accordingly is build ing up especially during the approach movement. As a non-limiting example the pressure in the hydraulic accumulator may thus vary between 20 bar (2 MPa) and 80 bar (8 MPa). When the ram member 5 is to be raised again the motor 93 may assist to raise the pressure provided to the lower cylinder chamber 7” to e.g. 150 bar (15 MPa).

It is seen that in this embodiment, the hydraulic pressure of the lower cylinder chamber 7” is transferred to the hydraulic accumulator 89 as a recipi ent for said pressure to be reused later in the overall process of the press.

The embodiment of Fig. 10 may be used together with any of the embodiments shown in Figs. 4 to 9, as the elements 89, 91, 93, and 95 to gether may correspond to the box 73 of those embodiments.