Background to the Invention Pistons used in, for example, diesel and high-compression gas engines are generally provided with a plurality of compression rings at an upper end (or crown) of the piston, i e. at the end located closest to the combustion chamber of the engine. The function of the compression rings is to seal the space between the piston and the cylinder liner in which the piston moves, thereby inhibiting combustion gases from traveling down the liner during the compression stroke.

Pistons are generally also fitted with one or more oil-control rings located below the compression rings. These rings are used to scrape off a large portion of the lubricating oil splashed into the cylinder by the crankshaft and connecting rod on the down stroke of the piston and to ride over the remaining oil on the up stroke.

This inhibits surplus oil from being carried up into the combustion chamber where it would bum incompletely and form carbon as well as allowing sufficient oil to be carried to the upper region of the liner during the up stroke to lubricate the piston surface and compression ring.

Due to the compression and frictional forces exerted on both the compression and oil-control rings during use, they wear quickly and have to be replaced regularly.

The inventor therefore believes that a need exists for piston rings (specifically oil and control rings) that fulfill all the functions of conventional piston rings whilst wearing slower than conventional rings.

Summary of the Invention According to the invention there is provided an oil-control ring including : - -two spaced apart scraping edges for aiding distribution of oil on an outer surface of a piston on which the ring is fitted and an inner surface of a cylinder in which the piston is located, during the interval when the piston is displaced so as to decrease the working volume of the cylinder and which aid in removing oil from the inner surface of the cylinder during the interval when the piston is displaced so as to increase the working volume of the cylinder, and -two faces, at least a portion of each face extending angularly from one of the scraping edges towards a central region of the ring.

The oil-control ring may include one or more drainage passages extending from a region at which the faces meet across the width of the ring to a back portion of the ring for draining oil away from the scraping edges.

The oil-control ring may be of unitary construction.

Altematively, the oil-control ring may include an upper and a lower portion, each portion including one scraping edge and one face or the oil-control ring may include an upper and a lower portion, each portion including one scraping edge, one face and a portion of the drainage passages.

One of either the upper or the tower ring portions may include a male member configured to engage a female member on the other ring portion.

The oil-control ring may be jointed. The joint may be any suitable joint selected from the group including a butt joint, an angle joint or a lap joint.

Both the upper and lower ring portions may be jointed.

The cross-sectional shape of the drainage passages may be selected from the group including : round, oval, elliptical, square and rectangular.- The oil-control ring may be manufactured from any suitable material having a suitable hardness, for example cast iron or steel.

The intemal diameter of the oil-control ring may be dimensioned cornplementally to a piston groove located on the outer surface of the piston to facilitate a snug fit thereof.

The oil-control ring may act as a compression ring.

According to a second aspect of the invention there is provided a compression ring having an inner and an outer diameter with inner and outer faces respectively, wherein the inner face is beveled along at least a portion thereof.

The outer face may be generally arcuate.

The outer face may be substantially flat.

The outer face may be beveled along at least a portion thereof.

The ring may be of unitary construction.

The ring may be the jointed. The joint may be any suitable joint selected from the group including a butt joint, an angle joint or a lap joint.

The ring may be manufactured from any suitable material having a suitable hardness, for example cast iron or steel.

The inner diameter of the ring is dimensioned complementally to a piston groove located on an outer surface of a piston to facilitate a snug fit thereof.

The invention extends to s set of piston rings including an oil-control ring and at least one compression ring as described above.

The inventor believes that the design of the oil-control ring as described above results in a longer lifespan of the oil-control ring. This is believed to be due to the configuration of the scraping edges and faces of the oit-control ring that cause rough portions on the cylinder liner to wear off gradually, so that good contact is then achieved between the scraping edges and the cylinder liner without excess friction that may cause accelerated wear of the scraping edges.

Use of the oil-control ring furthermore results in a deposition of a very thin film of oil on the outer surface of the piston, the film being considerably thinner than when conventional oil-control rings are used. The scraping edges of the oil- control ring increase in area as the ring begins to wear, thereby ensuring good oil distribution and therefore a reduction is wear of the oh-control ring.

The inventor believes that the design of the compression ring further aids good lubrication of the outer surface of the piston by virtue of oil becoming trapped between and then expelled from the piston groove housing the compression ring and the beveled portion (s) of the ring.

Detailed Description of the invention The invention will now be described by way of the following non-limiting examples with reference to the accompanying drawings (drawings are not to scale).

In the drawings:- Figure 1 shows a partial cross-section through a piston and cylinder arrangement wherein an embodiment of an oil-control ring in accordance with the present invention is fitted to the piston ; Figure 2 shows a partial cross-section through a piston and cylinder arrangement wherein a first embodiment of a compression ring in accordance with the present invention is fitted to the piston; and Figure 3 shows a partial cross-section through a piston and cylinder arrangement wherein a second embodiment of a compression ring in accordance with the present invention is fitted to the piston.

In the drawings, reference numeral 10 generally indicates an embodiment of an oil-control ring in accordance with the present invention.

An oil-control ring 10 includes two spaced apart scraping edges 12 and 14 for aiding distribution of oil (not shown) on an outer surface 16 of a piston 18 on which the ring 10 is fitted and an inner surface 20 of a cylinder 22 in which the piston 18 is located, during the interval when the piston 18 is displaced so as to decrease the working volume of the cylinder 22 and which aid in removing oil from the inner surface 20 of the cylinder 22 during the interval when the piston 18 is displaced so as to increase the working volume of the cylinder 22 and two faces 24 and 26, at least a portion of each face 24 and 26 extending angularly from one of the scraping edges 12 and 14 towards a central region (not shown) of the ring 10.

The oil-control ring 10 includes a plurality of drainage passages 28 extending from a region 30 at which the faces 24 and 26 meet across the width of the ring 10 to a back portion 32 of the ring 10 for draining oil away from the scraping edges 12 and 14.

In the embodiment shown, the oil-control ring 10 includes an upper 34 and a lower 36 portion, each portion 34 and 36 including one scraping edge 12 or 14, one face 24 or 26 and a portion of the drainage passages 28.

The upper portion 34 includes a male member in the form of a protrusion (not shown) configured to engage a female member in the form of an indentation (not shown) on the lower portion 36. In use, the two portions 34 and 36 are placed on top of each other and aligned so that the protrusion and indentation engage, thereby aligning the portions of the drainage passages 28 in the upper 34 and lower 36 portions.

Both the upper 34 and lower 36 ring portions are jointed. Typically, the joints are angle joints (not shown).

The cross-sectional shape of the drainage passages 28 is typically round and the oil-control ring 10 is typically manufactured from steel.

The intemal diameter of the oil-control ring 10 is dimensioned complementally to a piston groove 38 located on the outer surface 16 of the piston 18 to facilitate a snug fit thereof.

The dimensions of the oil-control ring 10 are typically as follows : Scraping edge height h : 0, 666 mm Face height f : 0,8 mm

Drainage passage diameter: 1,6 mm Width w of oil-control ring: 4 mm Thickness t of oil-control ring : 4 mm Length I of drainage passage: 2 mm The width w of the oil-control ring is preferably double the length of the drainage passage.

The dimensions of the oil-control ring naturally vary with the size of the piston that the ring is to be fitted to.

Referring now to Figure 2 there is shown a first embodiment of a compression ring 40 in accordance with the present invention.

The compression ring 40 has an inner and an outer diameter with inner 42 and outer 44 faces, wherein the inner face 42 is beveled along at least a portion thereof as shown in Figure 2. The outer face 44 is generally arcuate.

Referring now to Figure 3 there is shown a second embodiment of a compression ring 40 in accordance with the present invention.

The compression ring 40 has an inner and an outer diameter with inner 42 and outer 44 faces, wherein both the inner 42 and outer 44 faces are beveled along at least a portion thereof as shown in Figure 3. The outer face 44 is substantially flat.

The ring 40 is of unitary construction and is jointed by means of an angle joint (not shown).

The ring 40 is typically manufactured from steel.

The inner diameter of the ring 40 is dimensioned complementally to a piston groove 38 located on the outer surface 16 of the piston 18 to facilitate a snug ftt thereof.

The dimensions of the compression ring 40 shown in Figure 2 are typically as follows : Thickness t: 2 mm Width w of ring : 4 mm Height h of beveled portion : 0, 333 mm The dimensions of the compression ring naturally vary with the size of the piston that the ring is to be fitted to.

The dimensions of the compression ring 40 shown in Figure 3 are typically as follows : Thickness t : 2 mm Width w of ring : 4 mm Height h of beveled portions: 0, 333 mm.

The dimensions of the compression ring naturally vary with the size of the piston that the ring is to be fitted to.

Typically, an oil-control ring 10, a compression ring 40 as shown in Figure 2 and compression ring 40 as shown in Figure 3 are mounted together on a piston 16.

The oil-control ring 10 is mounted closest to the skirt portion of the piston 16.

Compression ring 40 as shown in Figure 2 is mounted closest to the crown portion of the piston 16 and compression ring 40 as shown in Figure 3 is mounted intermediate the oil-control ring 10 and the other compression ring 40.

It is to be appreciated, that the invention is not limited to any specific embodiment or configuration as hereinbefore generally described or illustrated.