GB2192690A - Piston oil control ring - Google Patents

Abstract

An oil control ring for a piston in an i.c. engine comprising an expander ring 21 and two lamellar rails 24 which scrape the oil from the cylinder wall. The expander ring 21 is formed from a flat strip 11 and has two series of lugs 19 arranged alternately on each side, which support the rails 24. The expander ring has two series of notches 12, 14 in its outer and inner circumference and is bent into a circular form. Its free ends form a butt joint. The material between the notches 14 of one series and the outer edge of the strip has fold zones 17 so that the strip is displaced from its plane alternately to each side of the plane. <IMAGE>

Description

SPECIFICATION Multiple part oil-control ring for piston.

The present invention relates to a multiple-part oil control ring for a piston e.g. in an internal combustion engine, or a compressor.

A known construction of a ring of this type comprises an expander or spring ring and one or more lamellar rings or rails supported by the expander.

The composite ring is located in a groove in the piston and the expander is arranged to urge the rails both radially outwards against the cylinder wall and axially against the walls of the groove.

The expander may take many forms though one form frequently encountered comprises an expander formed by folding a flat strip with a series of alternate cut-outs along each edge to form a U-shaped channel section and subsequently bending the channel section into a generally U-sectioned ring.

In the motor industry, engine designers wish to reduce engine dimensions to improve car body profiles and to reduce engine weight.

One way of achieving this is to reduce the engine block dimension in the direction of the engine cylinders, however, it is generally preferable to do so without affecting the cylinder capacity and compression parameters. This can be done by reducing the compression height of the piston, and indeed this is frequently an objective sought by piston designers. The compression height is the distance between the top of the piston and the axis of the gudgeon pin connecting the piston to the connecting rod.

One of the drawbacks of the folded-strip form of expander described above resides in the fact that its minimum axial thickness, in practice, tends to be quite large if it is to perform its spring/support function effectively.

It is therefore an object of the present invention to provide an oil control ring having a comparatively small dimension in the axial direction of the piston, in order to reduce the piston compression height.

According to the invention, there is provided a multiple-part oil-control ring for a piston which comprises an expander ring and at least one lamellar rail supported by the expander, the expander being formed from a flat strip of spring material lying generally in a plane and having a first series of notches along one edge and a second series of notches alternating with the first series along the other edge, the material between the notches of the second series and the one edge of the strip being deformed whereby the notches of the first series are displaced out of the plane of the strip alternately to each side of the plane, the material between adjacent notches of the second series being deformed to provide support means, the strip being bent to form the expander ring with the one edge at the outer circumference of the ring and the other edge at the inner circumference of the ring, whereby the support means provide a series of (axial) supports for the lamellar rail.

The fact that the expander ring is not folded in the axial sense means that its axial thickness may be less than that of a comparable expander of the known type described above.

Preferably, the material between the notches of the first series and the other edge of the strip is deformed to provide lugs standing proud of the surface of the strip. These lugs would then constitute rail location and support means. Preferably the lugs extend away from the plane of the strip.

Preferably, the material between the notches of the second series and the one edge of the strip is deformed by the provision of fold zones or kinks which extend from the base of the notches to the one edge.

Preferably, the control ring includes two rails, one on either side of the expander ring, in which case the support means or lugs should protrude on both sides of the expander ring to support the two rails. Preferably, the lugs are punched from the strip material to protrude alternately from each surface of the expander ring.

The alternate displacement of the notches of the first series (and therefore also the material defining these notches) serves to space the rails from the expander ring, thereby improving oil drainage from between the rails to the piston groove, by providing free space between the expander and rails. Further more, the spacing between the rails is determined by the extent of this displacement and can therefore be set to the desired value by adjustment of this displacement.

Alternatively, there may be only one rail associated with the expander ring, this rail preferably being on the top or piston crown side of the expander ring. In such a construction, the support means or lugs on the expander ring preferably extend on one side only of the expander ring.

There may be extensions on the inner circumference of the expander ring, particularly if the piston groove is comparatively deep, in order to help ensure that the composite ring is correctly located, and in order to help prevent "popping out" of the uncompressed composite ring out of the groove as the piston is inserted into the cylinder. The extensions may be formed integrally at the inner circumference of the expander ring, or may be separately attached. They may be present at spaced intervals between the notches of the second series, or may be present between each and every notch in which case each extension should take up a part only of the space between the notches.

In order to adjust or regulate the resilience of the expander ring, cut-away portions may be provided at the inner circumference of the expander ring at positions corresponding to positions of the notches of the first series.

The expander ring may be of stainless steel preferably with a hardness in the range HV300-350 or may be of a suitably tempered carbon steel to give the required spring properties. It will be appreciated that the strip from which the expander ring is formed may be stamped out and subsequently deformed by bend punching.

It has been found that a strip thickness of 0.020 inches (0.51mm) is preferable though this may be as low as 0.015 inches (0.38) or as high as 0.025 inches (0.64mm). The rails used may be 0.018 (0.46mm) or 0.020 inches (0.51mm) in thickness though they may have thicknesses in the range 0.015 inches (0.38mm) to 0.025 inches (0.15mm). The lugs may protrude from the surface of the expander ring by from 0.0075 inches (0.19mm) to 0.023 inches (0.58mm). The displacement of the notches of the first series and the surrounding material may be from 0 inches (0 mm) to 0.012 inches (0.3 mm) preferably 0.008 inches (0.2 mm).In a preferred embodiment, the strip thickness is 0.020 inches (0.51mm), the rails are 0.020 inches (0.51 mm) in thickness, the lugs protrude by 0.018 inches (0.46 mm) and the notches of the first series are displaced by 0.007 inches (0.17 mm); this gives an overall composite ring thickness of 0.075 inches (1.9 mm)t The invention may be carried into practice in various ways and some embodiments will now be described by way of example with reference to the accompanying drawings in which:: FIGURE 1 is an elevation of a portion of a strip according to the invention, prior to its being bent into a ring, FIGURE 2 is a front view of the strip of FIGURE 1; FIGURE 3 is a section on the line Ill-Ill of FIGURES 1 and 2; FIGURE 4 is an isometric sketch of the strip of FIGURES 1 to 3; FIGURE 5 is a section through a composite oil control ring in position in a piston; and FIGURE 6 is an isometric cutaway sketch of the compisite oil control ring.

The strip 11 shown in FIGURES 1 to 4 is formed from a basic spring steel strip 3.6 mm wide and 0.504 mm thick. It is formed with a first series of notches 12 3.23 mm wide extending from one edge 13 and a second series of notches 14 2.81 mm wide alternating with the first series and extending from the other edge 15.

The strip 11 is deformed out of its general plane alternately one way and then the other so that, effectively, alternate notches 12 of the first series, and the material defining these notches 12, are displaced to one side and then to the other side. This is achieved by bend-punching the strip 11 to cause bend zones 16 along lands 17 defined between the second series of notches 14 and the first edge 13.

Lands 18 defined between the first series of notches 12 and the second edge 15 are punched to define lugs 19 which protrude from the surface of the strip in the same general direction as the material from which it protrudes itself is displaced.

To form an expander ring, the formed strip 11 is bent into a ring, the external diameter being formed by the first edge 13 and the internal diameter being formed by the second edge 15. Thus, the lugs 19 present a series of support surfaces, alternately on one side then the other side of the ring.

Referring now to FIGURE 5, an expander ring 21 is shown located within a groove 22 of a piston 23. A pair of rails 24 are located by the expander ring, these being located radially by the lugs 19 and axially between the groove wall and the material of the ring 21 on each side of the respective notch 12 of the first series. Thus, as can be visualised from a consideration of FIGURE 4, a considerable amount of free space will be present between the two rails 24 as a result of the first series of notches 12 and their displacement, this being indicated for example by the reference numeral 25 in that figure.

The lugs 19 actually provide an arcuate support which, in conjunction with the internal diameter of the rails 24, has the effect of causing a small axial force on the rails 24, at their inner peripheries. This provides side sealing so that angling of the flat base is not necessary although an angle of 2" to 10 may be provided by some pressing means, should this be required to provide additional side sealing force.

The outward load on the rails 24 which enables them to scrape oil from the cylinder wall is obtained by compressing the expander ring 11 when the composite ring, mounted in the piston groove 22 is forced into the cylinder bore. Drainage for oil scraped from the cylinder wall between the rails 31, 32 is provided by the free spaces 25 which communicate with drainage passages in the groove 22.

Claims (7)

1. A multiple-part oil-control ring for a piston which comprises an expander ring and at least one lamellar rail supported by the expander, the expander being formed from a flat strip of spring material lying generally in a plane and having a first series of notches along one edge and a second series of notches alternating with the first series along the other edge, the material between the notches of the second series and the one edge of the strip being deformed whereby the notches of the first series are displaced out of the plane of the strip alternately to each side of the plane, the material between adjacent notches of the second series being deformed to provide support means, the strip being bent to form the expander ring with the one edge at the outer circumference of the ring and the other edge at the inner circumference of the ring, whereby the support means provides a series of supports for the lamellar rail.

2. A control ring as claimed in Claim 1 in which the material between the notches of the first series and the other edge of the strip is deformed to provide lugs standing proud of the surface of the strip, thereby providing rail location and support means.

3. A control ring as claimed in Claim 2 in which the lugs extend away from the plane of the strip.

4. A control ring as claimed in any preceding claim in which the material between the notches of the second series and the one edge of the strip is deformed by the provision of fold zones extending from the base of the notches to the one edge.

5. A control ring as claimed in any preceding claim in which the strip is deformed from both sides to provide lugs protruding from both axial surfaces of the ring, and in which two annular rails are provided, one supported by the lugs associated with one surface of the expander ring and the other supported by the lugs associated with the other surface of the expander ring.

6. A control ring a claimed in claim 5 in which the lugs are punched from the strip material to protrude alternately from each surface of the expander ring.

7. A multiple-part oil control ring for a piston constructed and arranged substantially as herein specifically described with reference to and as shown in FIGURES 1 to 5 of the accompanying drawings.