GB2043832A

GB2043832A - Piston Seal Assembly

Info

Publication number: GB2043832A
Application number: GB8006868A
Authority: GB
Original assignee: Festo Maschinenfabrik Gottlieb Stoll Firma
Current assignee: Festo Maschinenfabrik Gottlieb Stoll Firma
Priority date: 1979-03-03
Filing date: 1980-02-29
Publication date: 1980-10-08
Also published as: GB2043832B; DE2908292B1; DE2908292C2

Abstract

A piston (10) has a pair of grooves (18, 20) in which are located thrust rings (28, 28') and meander-shaped (zig-zag) sealing rings (36, 36'), biassed radially outwardly for contact with an inner wall of a cylinder. The sealing rings have guide lips (40) in nesting engagement and supported by the web (22), and are formed from plastics material having good sliding properties, e.g. a polyamide or PTFE. <IMAGE>

Description

SPECIFICATION Piston Ring Assembly The invention is concerned with improvements in or relating to a piston ring assembly.

A known assembly has a piston ring comprising an elastic inner ring and a continuous outer ring made of a plastics material having good sliding properties, such as polyamide, polytetrafluorethylene etc., and having band sections extending in axial and circumferential directions. The outer edge of the band sections can slide in close contact along a cylinder wall, while the inner edge is installed into a retaining groove of a piston, within which the outer ring is pressed outwards against the inner cylinder wall by the elastic inner ring, the outer ring being provided with a guide lip extending in the direction of the longitudinal cylinder axis.

The outer ring is prepared from solid T-section strip material.

The elastic inner ring is represented by a spring plate U-section provided with axial flanges. In order to facilitate the resilience of the inner ring, the axial flanges are provided with cutouts and axial slots, thus creating discrete axial spring tongues.

Even if such an outer ring were continuous, there is the disadvantage of the need for a piston ring holder in order to install the outer ring without significant radial expansion, which would be made impossible by the lack of elasticity of polytetrafluorethylene. This involves a mechanically complicated design and relatively long assembly times.

The invention therefore aims to provide an improved piston ring assembly with the object of maintaining an essentially continuous plastics surface area hving good sliding properties on the one hand, whilst ensuring a perfectly continuous piston ring assembly, which is easily installed, on the other hand.

According to the present invention there is provided a piston ring assembly comprising a piston having a piston ring, the latter comprising a resilient, radially inner annular member and continuous, radially outer annular member formed of a plastics material having good sliding properties, the outer annular member being defined by a pair of meander-shaped annular sealing sections extending in axial and circumferential directions and nesting in each other, with radially outer edges of the sealing sections being capable of sliding in close contact along an inner wall of a cylinder, and radially inner edges of the sealing sections located in a retaining groove of the piston to be biased radially outwardly against the inner cylinder wall by the inner annular member, the meanders of the sealing sections being axially arranged and the sealing sections having axially extending guide lips which are wedge-shaped and are arranged to face and engage with each other.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Fig. 1 is an axial section through one half of a piston with a piston ring arrangement comprising two sealing rings engaging each other; and Fig. 2 is a developed view of part of the lateral piston surfuce and the piston ring arrangement.

Fig. 1 illustrates a piston 10 fitted to a reduced end section 12 of a piston rod 14 and secured to the latter by a nut 1 6. This nut is threaded onto a threaded section of the piston rod 14.

The piston 10 is provided with two deep ring grooves 1 8, 20 of rectangular cross-section, which extend in the circumferential direction and are arranged at an axial spacing from each other, and, a web 22 between these grooves, with a shallow groove 24 extending in the circumferential direction. In the groove 24, an 0ring 26 is installed. Arranged in the ring grooves 1 8 and 20 are thrust rings 28, 28' respectively, made of soft rubber, which, as is shown, may be represented by conventional lip seals. Each of the rings 28, 28' has an essentially U-shaped crosssection, a thick outer leg 30, an inner leg 32 tapering towards the free end and, joining the two legs, a base 34. The base 34 is adjacent to the web 22.

The thrust rings 28, 28' radially prestress respective sealing rings 36 and 36' made of polyamide. Each of the sealing rings 36, 36' has a meander-shaped main body 38 and, supported by this, a wing-shaped axial guide lip 40. Each guide lip 40 has bevelled edges 42, 44 tapering towards a free end, thus resembling a trapezium if viewed from above. The width of the guide lip 40 at the free end is identical to, or a little smaller than, the clearance between two axial meander sections 46 of the main body 38 (in the stressfree state). The axial meander sections 46 are joined by a circumferential meander section 48 on the side adjacent to the guide lip 40 and by a circumferential meander section 50 on the side remote from the guide lip 40. The meander sections 46, 48 and 50 are identical in thickness.

The guide lips 40 of the sealing rings 36, 36' are supported by the O-ring 26 and the web 22 lying beneath the O-ring and thus held in elastic contact with the inner wall of a cylinder not illustrated here. The guide lips 40 of the two sealing rings engage each other like the teeth of two combs and together form a virtually unbroken guiding surface for the piston.

The meander sections 46, 48, 50 of one sealing ring and the guide lips 40 of the otter sealing ring together with the O-ring 26 form enclosed pockets 52, which may be packed with grease for permanent lubrication.

The piston does not present any problems in manufacture of fitting. The ring grooves 18, 20 and the groove 24 are produced on the piston 10 by turning. The soft rubber thrust rings 28, 28' are radially expanded and fitted into the ring grooves 18, 20. The O-ring is similarly expanded and easily fitted into the groove 24. The sealing rings 36, 36' are also easily expanded radially, since the guide lips 40 are separated and the meander sections 46 and 50 only subjected to bending stress during expansion. The circumferentially perfectly continuous and lapped sealing rings 36, 36' are therefore easily installed on top of the thrust rings 28, 28' in the ring grooves 18, 20.

Before the piston is installed, there remains a small clearance between the edges 42 and 44 of the mutually engaging guide lips 40 of the sealing rings 36 and 36'. When the piston is inserted into the cylinder, the sealing rings are further compressed and then held in elastic contact with the inner cylinder wall by the thrust rings 28, 28'.

Various modifications may be made without departing from the invention.

The overall result is a piston ring which, owing to the plastics material from which it is made and owing to its continuous design, is wear resistant and has good sliding and sealing properties. A further advantage lies in the fact that a ring designed in this way does not require much force to be radially expanded since the meander sections extending in the circumferential direction are only subjected to bending, not to tensile stresses. This ensures simple and quick assembly.

The mutual engagement of the guide lips of the two sealing rings further results in an outer ring with a large surface area and thus is good guidance for the piston, eliminating the risk of canting due to different pressures acting on the piston faces.

This piston ring of the known assembly is made of one or more layered metal bands, having a meandering sealing lip extending along its circumference. This meander design was chosen to aid lubrication. It does not achieve a secure and reliable guidance of the piston along the inner wall of the cylinder.

Claims

1. A piston ring assembly comprising a piston having a piston ring, the latter comprising a resilient, radially inner annular member and a continuous, radially outer annular member formed of a plastics material having good sliding properties, the outer annular member being defined by a pair of meander-shaped annular sealing sections extending in axial and circumferential directions and nesting in each other, with radially outer edges of the sealing sections being capable of sliding in close contact along an inner wail of a cylinder, and radially inner edges of the sealing sections located in a retaining groove of the piston to be biased radially outwardly against the inner cylinder wall by the inner annular member, the meanders of the sealing sections being axially arranged and the sealing sections having axially extending guide lips which are wedge-shaped and are arranged to face and engage with each other.

2. A piston ring assembly in accordance with claim 1, wherein the guide lips are supported by a central web in the retaining groove.

3. A piston ring assembly in accordance with claim 2, wherein each sealing section comprises a meander-shaped main body and the guide lips are moulded on to circumferential meander sections, the central web in the retaining groove defining a pair of ring grooves, and the inner annular member comprising a pair of thrust rings located in respective ones of the ring grooves the main body engaging in a respective one of the pair of ring grooves, and the mutually engaging guide lips of the sealing sections being supported on the web, which carries an O-ring.

4. A piston ring assembly in accordance with any of claims 1 to 3, wherein the outer annular member is formed of a plastics material such as polya mide or polytetrafluorethylene.

5. A piston ring assembly substantially as herein before described with reference to the accompanying drawing.

6. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.