GB2129091A

GB2129091A - Oil-scavenging piston ring

Info

Publication number: GB2129091A
Application number: GB08307399A
Authority: GB
Inventors: Yukihiko Kubo
Original assignee: Teikoku Piston Ring Co Ltd
Current assignee: Teikoku Piston Ring Co Ltd
Priority date: 1982-10-26
Filing date: 1983-03-17
Publication date: 1984-05-10
Also published as: JPH0329979B2; JPS6145172A; GB2129091B; GB8307399D0; JPS5966063U

Abstract

An oil-scavenging piston ring comprises an oil-scraper ring (1) having a generally I-shaped cross- section providing the ring (1) with upper and lower side rails (3A and 3B) and a thin inter-connecting web (5) defining an outer peripheral oil- collecting channel (15) and an inner peripheral groove (17) which communicate with each other through vent holes (21) in the web (5). The piston ring also comprises an annular expander coil (40) which is seated in the inner peripheral groove (17) for expanding the scraper ring (1) so that the radially outer surfaces (9A, 9B) of the upper and lower side rails are pressed against the cylinder wall (61). The radially inner surfaces (11A, 11B) of the side rails defining the inner peripheral groove (17) are flat when viewed in a radial plane and are tangential to the expander coil (40) so that there is substantially point contact between the coil (40) and each surface (11A, 11B) in a radial plane. Also, there is a slight gap (19) between the expander coil (40) and the web (5) of the scraper ring (1). <IMAGE>

Description

SPECIFICATION Oil-scavenging piston ring This invention relates to an oil-scavenging piston ring for an internal combustion engine and, in particular, to such a ring having an oil scraper ring and an expander coil for pressing the scraper ring against the cylinder wall. In general, each piston of an automobile engine will be provided with at least one oil-scavenging piston ring for scraping excess oil from the corresponding cylinder wall.

The oil scraper ring usually consists of upper and lower side rails and an inter-connecting web which provide the scraper ring with an outer peripheral channel for receiving oil scraped from the cylinder wall, and an inner peripheral groove for receiving the annular expander coil. The web is provided with a plurality of elongated oil vent holes for allowing oil to pass from the outer peripheral channel into the inner peripheral groove. In use, the oil passes from the inner peripheral groove into the piston through oil drain holes provided in the peripheral groove of the piston housing the piston ring, and is then returned to the oil sump of the engine.

In the known forms of such oil-scavenging piston rings, the inner peripheral groove of the oil scraper ring, which is usually made of cast iron, usually has an arcuate cross-sectional shape complementary to the circular cross-sectional profile of the expander coil. As a result, the expander coil comes into considerable surface contact with the inner peripheral groove. Too much surface contact between the expander coil and the oil ring, however, closes the oil vent holes to a large extent, thus preventing the smooth passage of the scavenged oil from the outer peripheral channel to the inner peripheral groove for return through the piston to the engine sump. In some cases, the oil vent holes can become completely clogged with oil siudge, consequently reducing the oil scrapping effect of the piston ring and resulting in increased oil consumption by the engine.

Further, as the oil scraper ring is usually made of cast iron, it cannot be made particulariy light in weight because the relatively low strength of cast iron means that the thickness of the web cannot be decreased below a certain minimum. Furthermore, in the case of a cast iron oil scraper ring having an expander coil which comes into considerable surface contact with the arcuate inner periphery of the scraper ring, the coil may be thrust totally into the inner peripheral groove of the scraper ring due to wear of the ring.

With the aim of avoiding the above disadvantages, according to the present invention an oil scavenging piston ring comprises an oil scraper ring having a generally I-shaped cross-section whereby the scraper ring comprises upper and lower side rails and a thin interconnecting web defining an outer peripheral oil receiving channel and an inner peripheral groove, the web including a series of oil vent holes through which the outer peripheral channel communicates with the inner peripheral groove, and an annular expander coil seated in the inner peripheral groove, the expander coil engaging each of the upper and lower side rails in substantially point contact when viewed in a radial plane and being spaced from the web so that there is a slight gap between the coil and the web.

Preferably the radially inner surfaces of the upper and lower side rails which define the inner peripheral groove and which are engaged by the expander coil are flat when viewed in a radial plane and are inclined with respect to the axis of the ring, preferably converging towards a peripherally extending centre line of the web.

With the arrangement in accordance with the invention, different sizes of expander coil can be stably held by and between the walls of the inner peripheral groove of the scraper ring because of the radial plane point contact between the coil and each wall, which effectively forms a two-point contact.

However, this radial plane point contact would normally increase the wear of the oil scraper ring in comparison with that produced by the substantial surface contact in the conventional form of oil scavenging piston ring, since the pressure acting on the scraper ring by the expander coil is inversely proportional to the area of contact between the two elements. In order to prevent such increased wear, the oil scraper ring of the piston ring in accordance with the invention may be made of steel or the like instead of the usual cast iron. Furthermore, the surfaces of the oil scraper ring contacting the expander coil, and the surface of the expander coil contacting the scraper ring may be treated for wear resistance.

Also, when the expander coil comprises a helically wound coil or wire, the wire may have a crosssection with a flat surface which faces radially outwards and engages the surfaces of the side rails defining the inner peripheral groove. This will increase the contacting surface area between the expander coil and the oil scraper ring, and thereby help to decrease the wear of the scraper ring, and to prevent the expander coil from thrusting into the inner periphery of the scraper ring.

By making the oil scraper ring of steel, the web can be made thinner in comparison with a cast iron scraper ring, which contributes to increasing flexibility of the scraper ring. The side rails, which are relatively rigid are connected to the inner web and, accor.dingly, the oil scraper ring can follow the inner peripheral profile of the cylinder wail to obtain a high oil scraping effect. The rigid side rails prevent the scraper ring from deforming and provide a predetermined contact pressure against the cylinder wall.

Examples of the piston ring in accordance with the invention will now be described with reference tozthe accompanying drawings, in which: Figure 1 is a radial section through one example located in a peripheral groove in a piston and projecting into contact with the wall of the cylinder in which the piston reciprocates; Figure 2 is a partial perspective view of the piston ring shown in Figure 1 Figure 3A is a perspective view of the oil scraper ring of the piston ring shown in Figure 1; Figure 3B is an enlarged view of the part of the oil scraper ring shown at A in Figure 3A; Figure 4 is a radial section through the oil scraper ring of an alternative form of the piston ring shown in Figure 1;; Figure 5 is a schematic radial sectional view of a piston ring similar to that of Figure 1 and identifying the dimensions thereof; Figure 6 is a diagram showing the amount of wear experienced by the oil scraper ring of an example of the piston ring in accordance with the present invention, in comparison with the scraper ring of an oil scavenging piston ring of known construction; and, Figure 7 is a diagram showing the oil consumption of an engine fitted with oil scavenging piston rings in accordance with the present invention, in comparison with an engine fitted with conventional oil scavenging piston rings.

Figures 1 and 2 show an oil-scavenging piston ring having an oil scraper ring 1 (hereinafter called an oil ring) and a coil expander 40 for use in a diesel engine. The oil ring 1 with the coil expander 40 is located in a peripheral groove 51 of a piston 50 of the engine. The piston 50 reciprocates in a cylinder bore 63 of a cylinder 60. The oil ring 1 is made in one piece and has an upper rigid side rail 3A, a lower rigid side rail 38, and a thin, preferably straight, web 5 connecting the side rails 3A and 3B, so that the oil ring 1 has a substantially I-shaped section.The side rails 3A and 38 have peripheral radially outer ends 7A and 7 B which bear upon and slide against the inner wall 61 of the cylinder 60 when the piston 50 reciprocates, and these outer ends 7A and 7B are preferably provided with surface treated layers 9A and 9B to decrease wear thereof.

The layers 9A and 9B may be formed, for example, by chrome plating, or composite plating having a base of nickel, chrome, or iron having boride, carbide, nitride, or the like dispersed therein, or a plasma sprayed single or mixed layer of molybdenum, self fluxing alloy, stainless steel, orferrochrome alloy, or the like. Nickel, chrome, or iron having boride, carbide, nitride or the like dispersed therein can be added to the plasma layer, if necessary, provided that the layers prevent wear of the corresponding cylinder wall. When the plasma sprayed layer is provided on the outer peripheral ends 7A, 7B, an undercoat made of Ni-Al (nickel-aluminide) or the like is preferably applied to the plasma sprayed layer.

Alternatively, the layers 9A and 9B can be treated by quenching or nitriding or sulfurizing-nitriding. The quenching includes induction hardening or laser hardening. The nitriding includes ion-nitriding or soft nitriding in gas or in a salt bath.

Alaternatively, as shown in Fig. 4, the peripheral outer ends 7A and 7B can be provided with grooves 30A and 308 which are filled with wear resistance materials 31 A and 31 B similar to those of the surface treatment layers 9A and 98.

Preferably, the peripheral outer ends 7A and 78 have a trapezoidal shape in section, as shown in Fig. 1. The trapezoidal shape has a narrow flat bearing surface 8A (or 8B) with sharp edges ensuring the outer ends 7A and 7B scrape the oil on the cylinder wall 61. The surface area of the flat bearing surfaces 8A and 8B can be considerably decreased and the flexibility of the oil ring is totally increased because of the thinner web 5, so that the flat bearing surfaces having a decreased surface area ensure a required and uniformly distributed surface pressure against the cylinder wall. When the outer ends 7A and 7B have the wear-resistance layers 9A and 9B, the flat bearing surfaces 8A and 8B are, of course, provided on the layers 9A and 9B.

The oil ring 1 has an outer peripheral channel 1 5 which is defined by the side rails 3A, 3B and the web 5 and which is adapted to receive the oil scraped by the outer ends 7A and 7B. The oil ring 1 also has an inner peripheral groove 1 7 which is defined by the side rails 3A, 38 and web 5. The opposed walls of the side rails 3A and 3B that define the groove 17 are made of inclined flat surfaces 1 A and 118, according to bne embodiment of the invention.Extensions of the inclined surfaces 1 A and 1 1 B intersect at an angle of 60 to 1 200, preferably 90 . The inclined surfaces 1 A and 11 B, which rub against the coit expander 40 due to the elasticity or flexibility of the latter, can be treated for wear resistance at areas 1 3A and 138, respectively. The wear resistance surface treatment can be, for example, chrome plating or nitriding (including sulfurized-nitriding).

The oil ring 1 is provided with a number of small round or rectangular oil vent holes 21 arranged side by side along the peripheral direction of the web 5, as shown in Fig. 3A. In case of steel oil ring, the number of the oil vent holes can be considerably increased in comparison with cast iron oil ring, because of a large strength of the steel material. The oil vent holes 21 connect the outer peripheral channel 1 5 and the inner peripheral groove 1 7 so that the scraped oil received in the outer peripheral channel 1 5 can flow into the inner peripheral groove 1 7. The large number of oil vent holes ensures a smooth passage of the scraped oil. The oil then passes through spaces between turns of coil expander 40 and comes into the piston 50 through oil drain holes (not shown) provided therein. The oil ring is preferably, of a symmetrical shape with respect to the peripherally extending center line L (Fig. 3) of the web 5.

The coil expander 40 consists of a wound coil of round wire 43 having a sectional shape presenting a part of a circle, as shown in Fig. 1. The wire 43 has advantageously a flat contacting surface 45 which comes in surface contact with the inclined flat surfaces 1 A and 1 8 of the oil ring, for the purpose of increasing the contact surface area, thus decreasing the pressure acting on the oil ring at the two contact points, as mentioned before. Alternatively, the wire 43 can be of rectangular or square or the like. The coil expander 40 is located in the groove 1 7 of the oil ring 1 and bears against the oil ring 1 at two points. The coil expander 40 presses the oil ring against the cylinder wall 61.

According to the present invention, the coil expander 40 comes into contact with the inclined surfaces 1 A and 11 B of the oil ring at two points, rather than considerable surface contact as in the prior art.

According to the present invention, the coil expander 40 does not contact the web 5 of the oil ring 1, but is spaced therefrom by a slight gap 19. The web 5 is, preferably, provided with a recess 1 8 which provides the gap 19 and which has round corner edges 1 8'. The round edges 1 8' are more preferable than angular or sharp edges, since the angular or sharp edges tend to crack due to concentration of internal stress. The outer periphery of the coil expander 40, i.e., of the coil, is preferably treated for wear resistance, such as by chrome plating or nitriding (including sulfurized-nitriding), shown at 41 in Fig. 1.

By the presence of the gap 1 9, the scraped oil can easily flow into the inner groove 1 7 through the oil vent holes 21.

Preferably, the oil ring 1 of the present invention is made of steel, such as SWRS, SWRH, SWOSC, -SWOCV, SK, SUP, or SUS (which are represented by Japanese Industrial Standard). The oil ring can be easily manufactured from a steel strip or a steel wire, bar, or rod having a uniform sectional shape by a usual drawing or rolling method. The blank drawn or roiled into a predetermined shape corresponding to that shown in Fig. 1 is hardened by heat treatment. The oil vent holes 21 can be formed by a punching process, usually before the blank is hardened. Alternatively, punching of the oil vent holes can be effected even after the blank is hardened, since the thickness of the web of a steel oil ring is smaller than that of the web of cast iron oil ring. After the oil vent holes 21 are punched, the blank is rolled and is then cut at a predetermined iength to form annular oil rings.

As is well known, if the oil vent holes are formed by milling, as in case of a cast iron oil ring, burrs tend to be produced at edges of the holes and it is difficult to obtain a uniform thickenss of the web because the thickness of the portions of the web adjacent to the holes tend to be larger than that of the remaining portions due to non-uniform internal stress. The burrs easily detach during the operation of the engine and enter between the cylinder wall and the piston ring, which results in engine trouble.

Punching of oil vent holes is, however, free from these disadvantages.

The present invention offers the following additional advantages, listed hereinbelow by way of reference.

1. Thinner web, resulting in a lighter weight oil ring, due to greater strength of steel.

2. Greater flexiblity and followability of oil ring with respect to cylinder wall, due to thinner web.

3. Larger diameter coil expander, due to two-point contact, rather than considerable surface contact, and due to the thinner web.

4. Smaller spring factor of coil expander, due to larger diameter coil expander, resulting in small extent of decrease of the spring pressure in use.

5. Greater resistance to deformation and distortion both during installation into piston and use, due to decreased internal stress, resulting from punching of oil vent holes rather than milling.

6. Overall greater resistance to wear and easy attainment of circularity of oil ring and flatness of upper and lower surfaces of the side rails, difficult with cast iron oil rings, by milling of oil vent holes, due to thinner web and single punching process of oil vent holes, thus preventing increased oil consumption.

7. Easy obtainment of a higher precision sectional profile of oil ring, due to drawing or rolling of steel oil ring.

8. Smaller flat bearing surface of side rails sufficient to obtain a required unit pressure against the cylinder wall, due to use of steel.

9. Overall smaller size of oil ring, resulting in possible wider use, for example even to a smaller piston as in a two-wheeled vehicle, such as a motorcycle.

The coil expander can be replaced by a so-calied web type equalizer spring in the present invention. In such an alternative, the equalizer spring is provided with flat surfaces which come into contact with the inclined flat surfaces 1 A and 11 B.

The following table shows three examples of actual sizes of the product for gasoline, diesel, or other multipurpose engines according to the present invention. The marks used in the table connotes as follows (see Fig. 5).

D+. . . outer diameter of the oil ring B . . . width of the oil ring T . . . radial thickness of the oil ring in section b . . . width of the outermost bearing surface of side rails t . . . thickness of web .. diameter of the coil expander 2 x . . . bottom length of trapezoid of the side rails y . .. length of the bottom of inclined flat surfaces (unit: mm)

13 T T b t Df | x | y 1 2 1st 68 3.5 2.2 0.30 0.45 2.5 0.93 1.04 2nd 90 4.0 2.4 0.30 0.45 2.8 0.89 1.29 3rd 150 5.0 2.8 0.35 0.55 3.8 1.15 1.49 Usually, the thickness of a web of a cast iron oil ring cannot be below 0.8 mm. According to the present invention, the thickness t of the web is below 0.8 mm, which increases flexibility and followability of the piston ring with respect to the cylinder wall, as mentioned before.The thickness t of the web must be larger than a certain value tb provide a necessary strength of the oil ring. It has been experimentally confirmed that "t" is preferably within the range of 0.3 mm < t < 0.8 mm. Further, it has been also experimentally confirmed that relationships of 2.5 < x/b < = 8.0 and 2.0 < y/t < 5.5 gave a good result with respect to the amount of the flat bearing surfaces of the side rails of the oil ring and to the oil consumption.

Figures 6 and 7 show experimental results of the amount of wear of the oil ring and the oil consumption in the present invention and prior art. In Fig. 6, as prior art, an oil ring which is made of cast iron and which has an archwise inner peripheral surface with which a coil expander is brought into contact without a gap between the inner peripheral surface and the coil expander was used. As a product of the present invention, the second example of the table mentioned before was used.

As can be seen from Fig. 6, the amount of wear in the present invention is smaller than that of prior art.

In Fig. 7, the oil consumption of a combination of piston rings having first (top) and second compression rings and one oil ring was measured. The same top and second compression rings were used for the present invention and prior art. The oil rings used in the experiments shown in Fig. 7 are the same as those used in Fig. 6. The measurements before the endurance run and during a 100 hour endurance run, 200 hour endurance run, and 300 hour endurance run are mean values. As can be seen from Fig. 7, oil consumption can be decreased in the present invention, in comparison with prior art.

The particulars of the engines used in the experiments were as follows; four-cycle diesel engine having a displacement of 2188 cc cylinder bore . . . 900 (mm) horsepower. . .72 stroke. .. 86 (mm)

Claims

1. An oil-scavenging piston ring comprising an oil scraper ring having a generally I-shaped crosssection whereby the scraper ring comprises upper and lower side rails and a thin interconnecting web defining an outer peripheral oil receiving channel and an inner peripheral groove, the web including a series of oil vent holes through which the outer peripheral channel communicates with the inner peripheral groove, and an annular expander coil seated in the inner peripheral groove, the expander coil engaging each of the upper and lower side rails in substantially point contact when viewed in a radial plane and being spaced from the web so that there if a slight gap between the coil and the web.

2. A piston ring according to claim 1, in which the oil scraper ring is made of steel.

3. A piston ring according to claim 2, in which the web of the oil scraper ring has a large number of oil vent holes.

4. A piston ring according to any one of claims 1 to 3, in which the radially outer portion of each of the upper and lower side rails has a substantially trapezoidal cross-section providing a narrow flat bearing surface for engaging a cylinder wall and sharp edges for scraping oil from the wall.

5. A piston ring according to any one of the preceding claims, in which the radially inner surfaces of the upper and lower side rails which define the inner peripheral groove and which are engaged by the expander coil are flat when viewed in a radial plane and are inclined with respect to the axis of the ring.

6. A piston ring according to claim 5, in which the inclined radially inner surfaces converge towards a peripherally extending centre line of the web.

7. A piston ring according to claim 5 or claim 6, in which the included angle defined by extensions of the inclined radially inner surfaces is from 600 to 1200.

8. A piston ring according to claim 7, in which the included angle is 900.

9. A piston ring according to any one of the preceding claims, in which the radially outer ends of the side rails are treated for wear-resistance.

1 0. A piston ring according to any one of clains 1 to 8, in which the radially outer end of each side rail is provided with a groove which is filled with a wear-resistant material.

11. A piston ring according to any one of clams 5 to 8, in which the inclined radially inner surfaces of the side rails are treated for wear-resistance at least in the regions where they are engaged by the expander coil.

12. A piston ring according to any one of preceding claims, in which the expander coil comprises a helically wound coil of wire having a cross-section with a flat surface which faces radially outwards and engages the surfaces of the side rails defining the inner peripheral groove.

1 3. A piston ring according to claim 12, in which the outer surface of the expander coil is treated for wear resistance.

14. A piston ring according to any one of the preceding claims, in which the slight gap between the expander coil and the web is formed by a recess in the web.

1 5. A piston ring according to claim 1, substantially as described with reference to Figures 1 to 3, Figure 4, or Figure 5 of the accompanying drawings.