GB2095367A - Piston/cylinder devices - Google Patents

Abstract

A piston and cylinder device which requires a reduced quantity of working fluid comprises a piston rod (12) having one region 14, of larger cross-sectional area than a second region 13. A second piston rod (18) may be detachably securable to the piston (11). The second piston rod (18) is automatically released from the piston (11) when the piston (11) is moved to one end of the cylinder (10) by a releasing device (28) provided at that end wall of cylinder (10). <IMAGE>

Description

SPECIFICATION Piston/cylinder devices This invention relates to piston/cylinder devices for use with hydraulic or pneumatic systems.

When a fluid is introduced into or is pumped from a cylinder at a side of the piston having no piston rod, or having only a small diameter piston rod relative to the diameter of the piston, a relatively large quantity of fluid must be displaced if the piston is to travel through a large distance. If the fluid is oil this means that a large quantity of oil must be incorporated in the hydraulic system and this adds to the cost of providing the system. Furthermore if a large quantity of fluid is to be displaced the time taken for such displacement must be relatively large, thus creating problems in connection with use of the system for certain high speed applications.

To overcome or avoid the abovementioned problems and disadvantages it is known to provide a piston rod having a diameter only slightly smaller than that of the piston, thus reducing the volume of the cylinder available for the working fluid. Also a piston rod may be provided on both sides of the piston.

However in such cases the operating pressure acts on only a narrow annulus of the piston and must be increased considerably in comparison with the previously described arrangements in order to provide a comparable thrust on the piston. Such large pressures, in particular the large dynamic pressures which may be involved, can introduce problems in the construction of the apparatus and require that the apparatus is both heavy and bulky. Hence such constructions may be unsuitable for certain applications or alternatively are costly to produce.

It is an object of the present invention to provide piston/cylinder devices in which the above disadvantages are avoided or at least mitigated to an appreciable extent.

The invention provides a piston/cylinder device comprising a piston disposed within a cylinder for relative sliding movement longitudinally therebetween, said piston being mounted on a piston rod extending axially of said cylinder, characterised in that said piston rod comprises two axially adjacent longitudinally extending regions, one of said regions being of small cross-sectional area relative to the other of said regions.

Preferably said region of relatively small crosssectional area extends between said piston and said region of relatively large cross-sectional area.

By means of the invention the quantity of fluid required in a hydraulic system is reduced in comparison with an arrangement in which the piston rod has a small cross-sectional area relative to the piston. Also it has been found that for a given piston thrust the maximum dynamic fluid pressure required in the cylinder of the invention is reduced in comparison with an arrangement in which the piston rod is of uniform relatively large cross-sectional area.

Preferably the interface between the two regions is non-planar and may be substantially hemispherical.

The invention also provides a piston/cylinder device comprising a piston disposed within a cylin der for relative sliding movement longitudinally therebetween, said piston being mounted on a first piston rod extending axially of said cylinder, characterised in that a second piston rod extends axially of said cylinder and is detachably securable to a face of said piston opposed to the face thereof at which said piston is mounted on said first piston rod. Said piston and said second piston rod may comprise cooperable interengageable parts thereon.

At least one of said piston rods may comprise two axially adjacent longitudinally extending regions, one of said regions being of small cross-sectional area relative to the other of said regions.

The second piston rod may extend through an end wall of said cylinder and releasing means may be provided at said end wall adapted upon operation to release said piston from engagement with said second piston rod.

By means of the invention the apparatus is suitable for use with the second piston rod engaged for high speed, low fluid volume applications in which the piston thrust required is relatively low, or alternatively with the second piston rod disengaged for high or low speed applications in which the piston thrust required is relatively large. In the latter case there is still only a low fluid volume required on the attached piston rod side of the piston.

One embodiment of the invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a sectional side elevation with the second piston rod engaged by the piston; Fig. 2 is a scrap sectional side elevation with the second piston rod retained at the end of the cylinder and disengaged from the piston.

Referring now to Fig. 1, there is shown a cylinder 10 in which a piston 11 is disposed for relative sliding movement therebetween. Piston 11 is mounted on a piston rod 12 which comprises two axially adjacent longitudinally extending regions 13, 14. The cross-sectional area of region 13 is small relative to that of region 14, the dimensions of region 14 being such that there is only a relatively small annular space 15 between region 14 and the cylinder 10. The interface between regions 13 and 14 is formed as a hemispherical surface 16 thus facilitating fluid flow between the annular space 15 and the larger annular space 17 surrounding region 13. Apart from the manner of attachment to the piston 11, second piston rod 18 is constructed in a similar mannerto piston 12.

Piston rod 18 is releasably attached to piston 12 as follows. Atapered recess 19 is provided in piston 12 and an annular groove 20 is provided in the wall of recess 19. The end 21 of piston rod 18 is tapered to correspond with the taper of recess 19 so as to be receivable therein. Balls or plungers 22 are located in radial bores 23 in the tapered end 21 of piston rod 18 and are pushed outwardly by cam insert 24so as to engage annular groove 20 in piston 11.

The piston rod 18 is attached to and detached from piston 11 in the following manner. The piston 11 is moved to the end of cylinder 10 which is uppermost as shown in Fig. 1, in which position the piston 11 will abut shoulder 25 and the enlarged part 26 of piston rod 18 will be withdrawn into the enlarged end region 27 of cylinder 10 as shown in Fig. 2. Pis tons 28 in the enlarged region 27 are then actuated by pressure means (not shown) so as to move radially inwardly, thus in turn moving radially inwardly plungers 29 which are located in radial bores 30 in the enlarged part 26 of piston rod 18. The plungers 29 are in contact with a tapered section 31 of cam insert 24 which is caused to move axially of the piston rod 18 from the position shown in Fig. 1 to the position shown in Fig. 2 against the reaction of spring 32.Spring 32 is disposed between the end of cam insert 24 and an end cap 33 secured in the end 21 of piston rod 18 and biases the cam insert 24 towards the position shown in Fig. 1.

When cam insert 24 is moved by the plungers 29 to the position shown in Fig. 2, the balls or plungers 22 are able to move radially inwardly into a groove or recesses 34 provided in the periphery of cam insert 24, thus being disengaged from groove 20 in the piston 11. Movement of the piston 11 downwardly is then achieved whilst the piston rod 18 is retained within the end 27 of the cylinder 10.

If the piston 11 is subsequently brought into contact with the end 21 of piston rod 18 and the pistons 28 are allowed to move radially outwardly, the spring 32 will cause cam insert 24 to move to the position shown in Fig. 1. Balls or plungers 22 will be pushed radially outwardly by cam insert 24 so as to re-engage groove 20 and thus piston rod 18 and piston 11 will be mutually secured.

By means of the invention the piston rod 18 may be secured to piston 11 when the apparatus is to be used for high speed, low fluid volume, low piston thrust applications. The apparatus can also be used for lower speed, larger fluid volume, higher piston thrust applications if required, in which case piston rod 18 is detached from piston 11.

As an example a cylinder of 1 1/s inch (28.57 mm) internal diameter, with a piston to which a piston rod having a uniform diameter of 1 inch (25.4 mm) was secured, had oil introduced therein at that side of the piston to which the piston rod was attached. A load of 42 Ibis wit (19.05 kg) was suddenly applied to the piston and a maximum oil pressure of 120 psi (8436 grm/cm2) was recorded. The same test was performed upon apparatus which was the same as that above except in that the piston rod has a first region adjacent the piston of < inch (12.7 mm) diameter. The remainder of the piston rod was of 1 inch (25.4 mm) diameter as before and the interface between the two regions of the piston rod was substantially hemispherical. A maximum oil pressure of 36 psi (2531 grm/cm2) was recorded.

It will be seen therefore that a considerable reduction in maximum pressure may be achieved by means of the invention, thus reducing the design strength of apparatus required to withstand such maximum pressures. In this way considerable cost and weight savings can be achieved in comparison with previously known arrangements. Also the power required to perform a given amount of work may be reduced, thus saving further costs and energy. The reduction of the cross-sectional area of the piston rods adjacentthe piston will provide for a cushioning effect as the piston reaches the ends of its travel, thus obviating the need for providing other cushioning means.

Alternatively, for double acting piston/cylinder devices which are to be used solely for high speed, low fluid volume, low piston rod thrust applications, a piston rod 12 may be secured to each of the two opposed faces of piston 11 instead of there being one detachable piston rod 18 as in the Fig. 1 embodiment.

Piston/cylinder devices in accordance with this latter embodiment were tested and the power requirements compared with manufacturers published figures relating to correspondingly sized piston/cylinder devices having parallel piston rods, the results of such tests being as follows.

Piston Stroke Strokes Max Stall PowerRequirementskg-misec dia (cm) (cm) permin Pressure necked manufacturers grmlcm2 pistons figures 22.86 22.86 30 10545 494 1140 22.86 22.86 40 10545 661 1140 30.48 22.86 34 10545 912 1900 35.56 30.48 28 8787 1140 1900 45.72 38.10 28 8787 1900 3800 It can be seen from the above figures that by means of the present invention, power savings of about 50% may be achieved.

Claims (16)

1. A piston and cylinder device comprising a piston disposed within a cylinder for relative sliding movement longitudinallytherebetween, said piston being mounted on a first piston rod extending axially of said cylinder, characterised in that said first piston rod comprises two axially adjacent longitudinally extending regions, one of said regions being of small cross-sectional area relative to the other of said regions.

2. A device according to claim 1 wherein said one region extends between said piston and said other region.

3. A device according to claim 1 or claim 2 wherein the interface between said regions is nonplanar.

4. A device according to claim 3 wherein said interface is substantially hemispherical.

5. A piston and cylinder device comprising a pis ton disposed within a cylinder for relative sliding movement longitudinally therebetween, said piston being mounted on a first piston rod extending axially of said cylinder, characterised in that a second piston rod extends axially of said cylinder and is detachably securable to one face of said piston opposed to the face thereof at which said piston is mounted on said first piston rod.

6. A device according to any one of claims 1 to 4 wherein a second piston rod extends axially of said cylinder and is detachably securable to one face of said piston opposed to the face thereof at which said piston is mounted on said first piston rod.

7. A device according to claim 5 or claim 6 wherein said piston and said second piston rod comprise cooperable interengageable parts thereon.

8. A device according to claim 7 wherein said second piston rod comprises two axially adjacent longitudinally extending regions, one of said regions being of small cross-sectional area relative to the other of said regions.

9. A device according to claim 8 wherein said one region of said second piston extends between said interengageable part thereof and said other region of said second piston rod.

10. A device according to any one of claims 5 to 9 wherein said second piston extends through an end wall of said cylinder and releasing means are provided at said end wall adapted upon operation to release said piston from engagement with said second piston rod.

11. A device according to claim 10 wherein said piston has a tapered recess in said one face thereof adapted to receive a tapered end of said second piston rod.

12. A device according to claim 11 wherein an annular groove is provided within said recess adapted to receive retaining means mounted in said tapered end of said second piston rod.

13. A device according to claim 12 wherein said second piston rod has an axial bore therein, in which is slidably received a cam insert adapted upon sliding in a first direction to move said retaining means radially outwardly of said second piston rod to engage said annular groove.

14. A device according to claim 13 wherein said releasing means comprise means adapted to slide said cam insert axially of said second piston in a second direction opposed to said first direction to release said retaining means.

15. A device according to claim 14 wherein said releasing means comprise at least one piston adapted to apply pressure to the surface of a tapered section of said cam insert.

16. A piston and cylinder device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.