GB2276220A

GB2276220A - Piston and piston rod assembly

Info

Publication number: GB2276220A
Application number: GB9305379A
Authority: GB
Inventors: Keith Oates
Original assignee: Kinetic Engineering & Design L
Current assignee: Kinetic Engineering & Design L
Priority date: 1993-03-16
Filing date: 1993-03-16
Publication date: 1994-09-21
Anticipated expiration: 2013-03-16
Also published as: GB9305379D0; GB2276220B

Abstract

A piston and piston rod assembly in which the piston rod member (12) is secured in a cylindrical bore of the piston member (10) by a plurality of rolling elements (14) located in an annular cavity (20) formed between the piston member (10) and the piston rod member (12). The rolling elements (14) can be inserted via an aperture in the piston member (1). <IMAGE>

Description

Piston and piston rod assembly The invention relates to a piston and piston rod assembly.

A common method of mounting a piston on a piston rod involves the machining of the piston rod to produce a reduced diameter cylindrical portion terminating in an abutment shoulder, the forming of a screwthreaded end length of smaller diameter than said cylindrical portion, the fitment of the piston on said cylindrical portion with a sealing ring between the two, and the securement of said piston by means of a washer and nut fitted to the screwthreaded end length of the rod. However, since it involves considerable machining, this method is expensive.

According to one aspect of the invention, a method of mounting a piston member on a piston rod member includes the steps of forming a groove in one of said members at what is to be one of two cylindrical mating surfaces between the two members; forming a groove or two or more spaced cavities in the other of said members at what is to be the other of said two cylindrical mating surfaces; sliding said piston along the piston rod to bring the groove in the one member into register with the groove or spaced cavities in the other member; and feeding two or more rolling elements into the space formed by said grooves or by the one groove and the two or more spaced cavities through an aperture in one of the members leading to said space.

According to a further aspect of the invention, there is provided a piston and piston rod assembly in which the piston rod member is secured in a cylindrical bore of the piston member by a plurality of rolling elements located in a space formed by a groove in one of said members, at cylindrical mating surfaces between the two members, and a groove or two or more spaced cavities in the other of said members at said cylindrical mating surfaces.

In order that the invention may be fully understood and readily carried into effect, the same will now be described, by way of example only, with reference to the accompanying drawings, of which Figure 1 is a part sectional side view of a piston and piston rod assembly embodying the invention, Figure 2 is a section on the line 2-2 in Figure 1, Figure 3 is a diagrammatic perspective view which illustrates the steps in the mounting of said piston on said piston rod, Figures 4 and 5 are views similar to Figure 1 which illustrate possible modifications, and Figures 6 and 7 are views similar to Figure 2 which illustrate further possible modifications.

Referring now to Figures 1 and 2 of the drawings, the assembly there illustrated includes a piston member 10 mounted on a piston rod member 12 in a manner such that axial force can be transmitted from one to the other.

The means by which axial force can be transmitted from one to the other of said piston member and piston rod member comprise a plurality of rolling elements 14 which are located in an annular cavity 16, the latter being formed by a flat bottomed groove 18 in the piston rod member 12 and a groove 20 of the same width and similar depth in the piston member 10. It will be understood that axial forces will be transmitted to the piston rod member through the areas of the rolling elements shown shaded in Figure 2. Axial forces transmitted to the piston member will be through the remaining areas of said rolling elements.

A radial aperture 22, through which the rolling elements have been fed into the annular cavity 16, communicates with the undercut groove in the piston member. Said aperture is closed by a screwthreaded plug 24 which abuts against a flat bottomed surface of said aperture and the outer end of which is beneath the periphery of the piston member.

At the periphery of the piston member there is a circumferential groove 26 for the reception of a seal 27 for sealing the piston member in a cylinder in which it will in use be located. The bore of the piston member is provided with a groove accommodating an 0-ring seal 28 to prevent the escape of high pressure fluid along the cylindrical mating surfaces of the piston member and piston rod member.

In Figure 3 there is illustrated diagrammatically the steps in the mounting of the piston member on the piston rod member, these steps being the sliding of the piston member along the piston rod member to bring the groove 20 in the piston member into register with the groove 18 in the piston rod member; the feeding of the rolling elements 14 into the annular cavity formed by said grooves through the radial aperture 22 so that said rolling elements have their axes running in generally the same direction as the piston rod member; and the closure of said aperture by the screwthreaded plug 24.

When the piston member has been mounted on the piston rod member in the manner just described, the assembly is very secure and is completely safe against accidental detachment of the piston member from the rod member. If the rolling elements fit the annular cavity without any measurable end play the piston member will be without axial movement on said piston rod member. Furthermore whatever the axial force applied to the piston rod member by the piston member, or vice versa, there will be no radially acting bursting force applied by the rolling elements to the wall of the piston member as there would be if the rolling elements were replaced by spherical ball members located in a toroidal cavity.

Various modifications may be made. For example, in Figure 4 there is illustrated a piston member and piston rod member assembly similar to that of Figure 1 except that the piston member has a closed end which abuts against the end of the piston rod member and there is therefore no longer any need for a resilient seal between the cylindrical mating surfaces of the piston member and piston rod member.

In Figure 5 there is illustrated a variation on the arrangement just described, in which, instead of the radial aperture 22 for the feeding of the rolling elements into the annular cavity, there is provided a longitudinally extending feed hole 30 in the end of the piston member, said feed hole extending also through a peripheral part of the end of the piston rod member to communicate with the annular cavity 16. A resilient sealing washer 25 is located beneath the screwthreaded plug which closes the feed hole 30, the sealing washer preventing the leakage of fluid under pressure through the piston member.

Referring now to Figure 6, this illustrates the fact that the space into which the rolling elements 14 are introduced need not necessarily be an annular space. The rolling element accommodating space in Figure 6 is formed by a groove 20 in the piston member 10 and a series of spaced cavities 19 in the piston rod member 12. It will be understood that on assembly of the piston and piston rod members in this case, the feed hole 30 will be brought into register with one of the cavities 19 of the piston rod member, a rolling element will be fed into position therewith, and the piston member will then be rotated on the piston rod member to bring the feed hole into register with the next cavity 19 and so on until the entire compliment of elements have been fed into position whereupon the feed hole will be blanked off by the screwthreaded plug 24.

A similar arrangement is illustrated in Figure 7, except that in this case the rolling element accommodating space is formed by a circumferential groove 18 in the piston rod member and a series of spaced cavities 19 in the bore of the piston member.

When mounting a metal piston member on a metal piston rod member, the rolling elements employed can for convenience be the hardened and ground rollers used in roller bearings or can be pieces of metal rod cut to the required length. However, the invention can equally well be used for the mounting of a plastics piston member on a metal or plastics piston rod member or of a metal piston member on a plastics piston rod member. In this case, the rolling elements could be made either of metal or of plastics. If made of plastics with either a metal piston member or a metal piston rod member, or with both the piston member and piston rod member made of metal, the rolling elements could constitute shearable members serving to limit the maximum axial loading capable of being transmitted by the assembly.

Claims

CLAIMS:

1. A piston and piston rod assembly in which the piston rod is secured in a cylindrical bore of the piston member by a plurality of rolling elements located in a space formed by a groove in one of said members, at cylindrical mating surfaces between the two members, and a groove or two or more spaced cavities in the other of said members at said cylindrical mating surfaces.

2. An assembly according to claim 1, in which said piston member includes an aperture through which said rolling elements can be inserted into said space.

3. An assembly according to claim 2, further comprising a removable plug for closing said aperture.

4. An assembly according to claim 2 or claim 3, in which said aperture extends radially through said piston member.

5. An assembly according to claim 2 or claim 3, in which said aperture is part of a longitudinally extending feed hole which further extends through a peripheral part of the end of the piston rod to communicate with said space.

6. An assembly according to any preceding claim, in which said rolling elements are cylindrical rollers, the longitudinal axis of each of which is substantially parallel to that of the piston member.

7. An assembly according to any preceding claim, in which the rolling elements are shearable, and thereby limit the maximum axial loading capable of being transmitted by the assembly.

8. An assembly according to any preceding claim, in which the rolling elements fit into the said space without end play.

9. An assembly according to any preceding claim, in which said bore of said piston member is blind.

10. A method of mounting a piston member on a piston rod comprising the steps of: forming a groove in one of said members at what is to be one of two cylindrical mating surfaces between the two members; forming a groove or two or more spaced cavities in the other of said members at what is to be the other of said two cylindrical mating surfaces; sliding said piston member along said piston rod to bring the groove in the one member into register with the groove or spaced cavities in the other member; and feeding two or more rolling elements into the space formed by said grooves or by the one groove and the two or more spaced cavities through an aperture in one of the members leading to said space.

11. A piston and piston rod assembly substantially as described herein with reference to the accompanying drawings.

12. A method of mounting a piston member on a piston rod, substantially as described herein with reference to the accompanying drawings.