GB2175648A - Pressure intensifier hydraulic cylinder system - Google Patents

Abstract

A pressure intensifier hydraulic system provided with four coaxially aligned piston and cylinder units, the piston 3 of the first unit being operable to move a common piston rod 6 in a working stroke direction when acted upon by a primary fluid pressure, the second unit having its piston 4 rigidly connected to the piston rod 6 and provided with predetermined pressure flow-by 18, 19 so that the piston 4 will move continuously in the working stroke direction when primary fluid pressure is applied to the piston 3 of the first unit to produce a stepped up pressure on a working fluid medium. The third piston and cylinder unit 13 constituted by the thicker part of piston rod 6 and cylinder 23 providing, at a predetermined location in the working stroke, a further step up in pressure on the working fluid medium and the fourth unit comprises a floating piston 21 and a cylinder 1(b) in fluid medium communication with the second and third unit cylinders during the working stroke prior to reaching the predetermined location. Valve 14 is used to apply primary fluid pressure through conduit 12 to the fourth piston for a period of time prior to application of the primary fluid pressure through conduit 13 to the first piston and cylinder unit. <IMAGE>

Description

SPECIFICATION Pressure intensifier hydraulic cylinder system The present invention relates to a pressure intensifier hydraulic cylinder arrangement suitable for use in a punch press and analogous machines. This invention more particularly relates to a pressure intensifier system utilizing a plurality of piston and cylinder arrangements capable of supplying, for instance, three different levels, or steps of pressure to a working pressure fluid medium.

Pressure intensifier systems providing two levels or steps of pressure to a working fluid medium are know from Canadian patents 1,052,234 and 1,132,441 issued to the present applicant.

The known pressure intensifier systems utilize a coaxial arrangement of three piston and cylinder units, the pistons of which move in unison by virtue of the fact they are all mounted on a unitary piston-rod. A first piston and cylinder arrangement, operated by pressure, for instance air, from a primary source, is effective to move the pistons of all three coaxial units in a working stroke direction, to act on a working fluid medium contained in the second and third cylinders which are provided with fluid medium communication during, at least, the initial part of the working stroke.

The second piston-cylinder unit of the arrangement is provided with flow-by means, by means of a loose piston cylinder fit or bleed holes provided through the second piston. The second piston-cylinder arrangement provides a first pressure level in the working fluid medium, and due to leakage in this unit the unitary piston rod moves in a working stroke direction so that the third piston-cylinder unit becomes active and produces the second pressure level, i.e. the final power stroke pressure.

In operation of the know systems the first level is generally used for claimping the workpiece to the press table by means of a stripper plate and the second level is utilized for the punching action.

Although the known systems are eminently satisfactory it is desirable to provide a pressure intensifier system, possible combined with an integral ram system, with a longer working stroke so that, for instance, work pieces may be more readily inserted or removed from the punching location. This can, of course, be accomplished by the known systems by lengthening the working stroke.

However this results in a waste of power and, generally, larger than desirable pressure intensifier units.

The present invention provides a pressure intensifier which will provide three levels of pressure to a working fluid.

The present invention also provides a pressure intensifier which is capable of a longer than normal working stroke or a greater movement of working fluid with a minimum use of extra power (energy).

According to the present invention there is provided a multiple step fluid pressure intensifier system comprising first, second and third operative piston and cylinder units arranged in coaxial alignment, the pistons of the second and third units being rigidly fixed to a common piston rod, the first piston having a greater effective working area than the second, a working fluid chamber, located between the cylinders of the first and second units, through which the piston rod passes, the cylinder of the second unit being provided with a fluidic connection between it and the fluid chamber, the fluid chamber and the cylinder of the second unit containing a common working fluid, the piston rod being provided with a reduced cross-section portion between the first and second units, the reduced crosssection portion residing with the fluidic connection when the piston rod is at the unactuated position of a working cycle, in order that there be fluidic communication between the chamber and the cylinder of the second unit, the third piston and cylinder unit being constituted by the unreduced cross-section portion of the piston rod and the fluidic connection respectively, the third piston and cylinder unit only becoming operative as such at a predetermined position of the piston rod in the working stroke direction, from the unactuated position, the second piston and cylinder unit being provided with limited working fluid flowby during a working stroke to allow continued movement of the piston rod, in the working stroke direction, under impetus of a primary fluid pressure supplied to the first piston and cylinder unit to provide a working stroke cycle, and wherein a fourth piston and cylinder unit is provided between the first and second piston and cylinder units with the piston of the fourth unit being a floating piston encircling the common piston rod in the area of the reduced cross-section at the beginning of a working stroke and axially moveable therealong, valving means adjustable to provide, at the start of a working stroke, primary fluid pressure to the flating piston to move it in a working stroke direction to force the common working fluid through the fluidic connection into the second cylinder, the valve being thereafter actuable to supply primary fluid pressure to the first piston to move that piston in the working stroke direction and provide a first step-up in pressure of the working fluid in the cylinder of the second unit by unison movement of the piston of the second unit in the working stroke direction and after movement of the piston rod a greater distance, in the working stroke direction, than the predetermined position, the pressure of the working fluid in the cylinder of the second unit being further increased primarily solely by the third piston and cylinder unit, and means provided to utilize the pressurized working fluid.

In the present invention a fourth piston cylinder unit is added to the known coaxial arrangement, the fourth unit being provided with a, so called, floating piston which is effective initially, by switched primary pressure application thereto, to move working fluid medium from the fourt cylinder, which, at the beginning of the working stroke, is in fluid communication with the second cylinder (and the third cylinder), into the second and third cylinders to apply thereto a first pressure level equal to that of the primary source. Thi first pressure level is sufficient to take up the slack, i.e. move the ram over a free travel distance to bring it against a workpiece on a work-table.

Thereafter, primary pressure is applied to the piston of the first piston-cylinder unit of the coaxial arrangement to move the piston rod, in conjunction with the second and third pistons, in the working stroke direction. A stepped-up pressure is applied to the working fluid medium by the second piston-cylinder unit. Due to the bypass leakage of this unit, the pistons and rod continue to move in the working stroke direction to subsequently close off communication between the second and fourth cylinders by means of the third piston entering the third cylinder which acts as a seal between the second and fourth cylinders.

Thereafter the pressure on the working fluid medium is determined by the third piston-cylinder unit and the final pressure step is achieved. The effective working areas of the second and third pistons are selected so that the final pressure step is the highest, both being greater than that produced by the primary pressure source by means of the floating piston. In this manner a three step pressure intensifier is provided with the facility of a long stroke at low pressure to conserve power and simultaneously allow for greater clearance between a working ram and a press table.

An embodiment of the invention will now be described by way of an example, with reference to the accompanying drawing, in which: Figure 1 is a longitudinal section through the pressure intensifier showing the parts prior to the initiation of a working stroke, Figure 2 shows the pressure intensifier with primary pressure applied to the floating piston thereof, and Figures 3 and 4 show the pressure intensifier in intermediate and final positions in the working stroke direction of movement of the pistons.

Referring to Fig. 1 the pressure intensifier apparatus is shown in its position of rest from which a working stroke movement begins.

The apparatus comprises a multi piston-cylinder arrangement comprising a housing 1, 2, shown stepped, although this is essential only with regard to material and weight savings.

The larger upper portion 1 of the housing comprises a primary pressure source (air) actuated piston-cylinder arrangement 1 a, 3 (first piston-cylinder unit), with a pressure inlet port 13 connected to a primary pressure source conduit 15 via a control valve 14. A return spring 7 is located between the piston 3 and the lower wall 1 C of the piston-cylinder unit la, 3. Piston 3 is -mounted on a piston rod 6, having a part 20 of reduced diameter which extends downwardly into the cylinder 2.

A fourth piston-cylinder unit 21, 1 b is located immediately below the first piston-cylinder unit 3, 1a. Piston 21 is a "floating piston" slideable on a slide bearing 5 which encircles the piston rod 6. Bearing 5 could be dispensed with but its use facilitates a shortened apparatus overall since the reduction in diameter of the rod 6 has to be taken care of to prevent binding between the piston 21 and the rod 6. Cylinder 1 b is provided with a primary source pressure inlet part 12, via valve 14, whereby primary pressure is applied to the upper side of piston 21. Cylinder 1 b, beneath piston 21 is filled with working fluid in communication, via port 22, around the reduced rod section 20, and bleeder holes 18, 19 in piston 4, with the working fluid 11 in cylinder 2.

A second piston-cylinder arrangement 4, 2, is located below cylinder 1 b. Piston 4 is fixed rigidly to the reduced portion 20 of rod 6.

Piston 4 is provided with a metered bleeder hole 18 and two further bleeder holes 19 which may be closed off by a valve plate 16, moveable axially on a reduced diameter portion of piston 4. Valve plate 16 is secured on rod portion 20 by a stop washer means 17.

A third piston-cylinder unit is constituted by piston rod 6 (piston) and cylinder 2 including the piston rod 6 aperture 23 in partition 1 d.

In a preferred embodiment of the invention the lower end of the cylinder 2 incorporates a ram member 9 and a ram operating piston 8 connected thereto. A ram return spring is provided as shown at 10 so that when a working stroke is completed the ram 9 will return to its upper limit thus clearing a workpiece for removal. Air pressure may be used for the ram return, replacing the spring 10.

It should be noted that rather than using an integral ram system the working medium 11 could be tapped off so that the medium, under working pressure could be supplied to a ram system at a remote location.

In operation of the system primary pressure, normally air, is supplied through conduit 15 and at the start of a working stroke, initiated by an operator or automatically, as desired, to the upper side of floating piston 21 which immediately moves downward, at a predetermined rate, dependent on the air pressure and port 22, to force working medium 11 through the port 22, around reduced portion 20 of piston rod 6, ports 19 in piston 4 to quickly move ram piston 8 downward under a reduced pressure.

After a time delay, which may be built into the valve 14, sufficient to allow full downward movement of the floating piston 21, air pressure is supplied to the upper side of the piston 3 which moves the piston rod 6 downward carrying with it the piston 4. Piston 4, having a reduced working area with respect to the piston 3 supplies a stepped up pressure to the working medium 11. After a predetermined downward movement of the pistons 3 and 5, the unreduced diameter portion of the piston rod 6 enters the aperture 23 in partition 1 d and the pressure on working medium 11, as applied to ram piston 8, is again stepped up by the ratio of the working areas of the pistons 3 and 6 (rod 6 cross-sectional areas so that full working pressure is available for the final workpiece operation.

Thereafter valve 14 is operated to release air pressure from pistons 3 and 21. Piston 3 is returned to its starting location by the return spring 7 whereas ram return spring 10 exerts return pressure on ram piston 8 which forces oil through return ports 19 of piston 4 to return floating piston 21 to its starting position. It will be understood that pistons 3 and 8 do not necessarily move in unison on the return stroke since each is operated by a separate return spring.

It should now be obvious that the pistoncylinder arrangement, according to the invention, supplies pressures to the working medium 11 and, consequently, the ram piston 8 in three steps, i.e. primary pressure (air), first stepped-up pressure due to the ratio of the effective working areas of pistons 3 and 4 and the final stepped-up high pressure due to the ratio of the effective working areas of piston 3 and piston rod 6.

Although a preferred embodiment of the invention has been described it will be obvious that varius embodiments of the invention will occur to those skilled in the art, which embodiments fall within the invention as defined in the appended claims.

Claims (6)

1. A multiple step fluid pressure intensifier system comprising first, second and third operative piston and cylinder units arranged in coaxial alignment, the pistons of the second and third units being rigidly fixed to a common piston rod, the first piston rod having a greater effective working area than the second, a working fluid chamber, located between the cylinders of the first and second units, through which the piston rod passes, the cylinder of the second unit being provided with a fluidic connection between it and the fluid chamber, the fluid chamber and the cylinder of the second unit containing a common working fluid, the piston rod being provided with a reduced cross-section portion between the first and second units, the reduced crosssection portion residing within the fluidic connection when the piston rod is at the unactuated position of a working cycle, in order that there be fluidic communication between the chamber and the cylinder of the second unit, the third piston and cylinder unit being constituted by the unreduced cross-section portion of the piston rod and the fluidic connection respectively, the third piston and cylinder unit only becoming operative as such at a predetermined position of the piston rod in the working stroke direction, from the unactuated position, the second piston and cylinder unit being provided with limited working fluid flowby during a working stroke to allow continued movement of the piston rod, in the working stroke direction, under impetus of a primary fluid pressure supplied to the first piston and cylinder unit to produce a working stroke cycle, and wherein a fourth piston and cylinder unit is provided between the first and second piston and cylinder units with the piston of the fourth unit being a floating piston encircling the common piston rod in the area of the reduced cross-section at the beginning of a working stroke and axially moveable therealong, valving means adjustable to provide, at the start of a working stroke, primary fluid pressure to the flating piston to move it in a working stroke direction to force the common working fluid through the fluidic connection into the second cylinder, the valve being thereafter actuable to supply primary fluid pressure to the first piston to move that piston in the working stroke direction and provide a first step-up in pressure of the working fluid in the cylinder of the second unit by unison movement of the piston of the second unit in the working stroke direction and after movement of the piston rod a greater distance, in the working stroke direction, than the predetermined position, the pressure of the working fluid in the cylinder of the second unit being further increased primarily solely by the third piston and cylinder unit, and means provided to utilize the pressurized working fluid.

2. A system as claimed in claim 1, wherein flow-by is provided by a loose fit between the piston and cylinder of the second unit.

3. A system as claimed in claim 1, wherein the flow-by is provided by a pressure bleed hole through the piston of the second unit.

4. A system as claimed in any one of claims 1 to 3, wherein the second piston and cylinder unit is provided with a pressure relief valve which becomes operative during the re turn stroke of the working cycle.

5. A system as claimed in any one of claims 1 to 3, wherein the valving means has a built in delay to automatically apply primary fluid pressure to the first piston a predetermined time after application of pressure to the fourth piston.

6. A multiple step fluid pressure intensifier system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.