Combined oil control ring

Abstract

To provide a combined oil control ring comprising a pair of upper and lower side rails and an axially corrugated spacer expander having upper and lower portions for automobile engines, which is capable of keeping an excellent oil-controlling function without sticking between a spacer expander and side rails even in a long period of engine operation, the upper and lower portions of the spacer expander have tabs pushing inner peripheral surfaces of the side rails, projections supporting the side rails, and intermediate portions between the tabs and the projections; and each intermediate portion opposing the side rail has a center-raised bottom having a center-raised shape when viewed along a substantially circumferential direction center-raised shape and a radial direction.

Claims

1. A combined oil control ring comprising a pair of upper and lower side rails, and an axially corrugated spacer expander having upper and lower portions; said upper and lower portions of said spacer expander having tabs pushing inner peripheral surfaces of said side rails, projections supporting said side rails, and intermediate portions between said tabs and said projections; each intermediate portion opposing said side rail having a bottom which is center-raised when viewed along a substantially circumferential direction and a radial direction.

2. The combined oil control ring according to claim 1, wherein the height p of said center-raised bottom is 0.5-20% of the combined width h1.

3. The combined oil control ring according to claim 1, wherein each center-raised bottom is constituted by curved surfaces.

4. The combined oil control ring according to claim 1, wherein each center-raised bottom is constituted by pluralities of flat planes.

5. The combined oil control ring according to claim 3, wherein each center-raised bottom has a domed or conical shape.

6. The combined oil control ring according to claim 4, wherein each center-raised bottom has a pyramid or truncated pyramid shape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1(a) is a perspective view partially showing an example of spacer expanders constituting the oil ring of the present invention.

(2) FIG. 1(b) is a cross-sectional view showing the oil ring of the present invention, in which the spacer expander of FIG. 1(a) is combined with side rails.

(3) FIG. 2 is a perspective view partially showing another example of spacer expanders constituting the oil ring of the present invention.

(4) FIG. 3(a) is a perspective view partially showing a conventional spacer expander.

(5) FIG. 3(b) is a cross-sectional view showing a conventional oil ring.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) The examples of the oil ring of the present invention will be explained below referring to the drawings.

(7) FIGS. 1(a) and 1(b) show an example of spacer expanders constituting the oil ring of the present invention. Like a conventional spacer expander, the spacer expander 11 comprises upper and lower portions each having a tab 12a, 12b, a projection 13a, 13b and an intermediate portion 14a, 14b. Each intermediate portion opposing the side rail has a bottom which is center-raised both in a substantially circumferential direction and in a radial direction. In this structure, each center-raised bottom is constituted by curved surfaces. With this shape, oil surely flows from the intermediate portion in a circumferential or radial direction of the intermediate portion. Accordingly, spaces 15a, 15b between the intermediate portions of the spacer expander and the side rails need not be expanded, but the height p of the center-raised bottom (height of a top of the center-raised bottom from a boundary of the intermediate portion and the tab or projection) is preferably 0.5-20% of the combined width h1. Specifically, the height p is preferably 0.05 mm or more, and its upper limit is preferably not more than 0.5 mm.

(8) Though each intermediate portion may have pluralities of the above center-raised bottoms, it preferably has one center-raised bottom to make sure the flow of oil from the intermediate portion, and the intermediate portion is more preferably entirely occupied by the center-raised bottom. Specifically, the center-raised bottom is preferably in a domed or conical shape. Each center-raised bottom may have a flat plane on the top, though the flat plane should have a smaller area than that of the entire center-raised bottom.

(9) FIG. 2 shows another example of spacer expanders 21. The intermediate portion has a bottom raised in a quadrangular pyramid shape.

(10) The above spacer expander can be formed by plastically working the wire.

Example 1

(11) A SUS440 wire of 0.35 mm1.72 mm was formed into side rails, and a SUS304 wire of 0.25 mm1.9 mm was formed into a spacer expander, to produce a combined oil ring having a nominal diameter d1 of 71 mm, a combined nominal width h1 of 2.0 mm, and a combined thickness a1 of 2.3 mm. The spacer expander had a pitch of 2.7 mm from an upper portion (lower portion) to an upper portion (lower portion), and each center-raised bottom in the intermediate portion had a curved surface shape with a height p of 0.1 mm as shown in FIGS. 1(a) and 1(b). There were spaces 15a, 15b of 0.1 mm between the highest points of the center-raised bottoms and the side rails.

Example 2

(12) As shown in FIG. 2, a combined oil ring was produced in the same manner as in Example 1, except for changing each center-raised bottom in the intermediate portion of the spacer expander to a square-pyramid-shaped bottom. The height p of each center-raised bottom was 0.1 mm. Space 15a, 15b between the highest point of each center-raised bottom and each side rail was as wide as 0.1 mm.

Comparative Example 1

(13) As shown in FIGS. 3(a) and 3(b), a combined oil ring was produced in the same manner as in Example 1, except for using a conventional spacer expander having flat intermediate portions with no center-raised bottoms. The distance between a side-rail-supporting surface of each projection and each intermediate portion was 0.1 mm.

Example 3

(14) A SUS304 wire for a spacer expander used in Example 1 was provided with a Ni plating comprising a half-luster Ni plating layer and a bright Ni plating layer using a sulfamate solution, and subjected to a softening heat treatment at 600 C. for 30 seconds. The resultant Ni plating had a thickness of 5 m and hardness of 226 HV0.01. A combined oil ring was produced in the same manner as in Example 1 except for using this Ni-plated wire.

Example 4

(15) A combined oil ring was produced in the same manner as in Example 2 except for using the Ni-plated wire in Example 3.

(16) [1] Actual Engine Test

(17) Each combined oil ring of Examples 1 and 2 and Comparative Example 1 was mounted to each of first to third cylinders in a one-liter, three-cylinder engine. This engine was repeatedly subjected to a predetermined operation pattern for an actual engine test. According to the following evaluation methods after 250 hours, the gaps of side rails and the amount of oil sludge deposited were measured. Each measurement was conducted three times in each Example and Comparative Example. Top and second rings used had the following specifications.

(18) (1) Top Ring

(19) Material: SWOSC-V,

(20) Outer peripheral surface: ion-plated with chromium nitride,

(21) Size: d1=71 mm, h1=1.0 mm, and a1=2.3 mm.

(22) (2) Second Ring

(23) Material: SWOSC-V,

(24) Entire surface: treated with zinc phosphate,

(25) Size: d1=71 mm, h1=1.0 mm, and a1=2.3 mm.

(26) Using the above one-liter, three-cylinder engine, the combined oil rings of Examples 3 and 4 and Comparative Example 1 were subjected to the actual engine test in the same manner as in Examples 1 and 2 and Comparative Example 1.

(27) [2] Evaluation Method

(28) The following evaluations were conducted after the actual engine test.

(29) (1) Measurement of Side Rail Gap

(30) After the actual engine test, the piston was withdrawn from the cylinder to measure the gaps S.sub.2 of upper and lower side rails in the oil ring. Before the actual engine test, the gaps S.sub.1 of upper and lower side rails when the oil ring was assembled to the piston, which were equal to gaps in a free state, were also measured to determine a ratio S.sub.2/S.sub.1. S.sub.2/S.sub.1 was determined in both upper and lower side rails, and averaged in three actual engine tests (six actual engine tests in Comparative Example 1).

(31) (2) Measurement of Amount of Oil Sludge Deposited

(32) After the actual engine test, the oil ring was detached from the piston, dried at 200 C. for 1 hour in an electric furnace, cooled to room temperature in a desiccator, and then measured with respect to its mass. Difference between the masses of the oil ring measured before and after the actual engine test was calculated, and averaged in three actual engine tests (six actual engine tests in Comparative Example 1) to determine the amount of oil sludge deposited.

(33) The actual engine test results of Examples 1-4 and Comparative Example 1 are shown in Table 1. The gap is expressed by a relative value, assuming that S.sub.2/S.sub.1 in Comparative Example 1 is 100, and the amount of oil sludge deposited is expressed by a relative value, assuming that the amount of carbon sludge deposited in Comparative Example 1 is 100.

(34) TABLE-US-00001 TABLE 1 Amount of Oil No. S.sub.2/S.sub.1 Sludge Deposited Example 1 285 61 Example 2 235 64 Example 3 330 41 Example 4 290 46 Com. Ex. 1 100 100

(35) Table 1 indicates that as compared with the gap and the amount of oil sludge deposited after the actual engine test in Comparative Example 1, the gaps were as large as about 2.3-2.8 times in Examples 1 and 2 and 2.9-3.3 times in Examples 3 and 4, and the amounts of oil sludge deposited were as small as 61-64% in Examples 1 and 2 and 41-46% in Examples 3 and 4. In Comparative Example 1, the accumulated oil sludge constrained the side rails, so that the gap did not easily return to an original one, even when the piston was withdrawn from the cylinder. On the other hand, in Examples 1-4, the attachment and accumulation of oil sludge were so reduced that constraint to the oil ring was lowered, closer to a state before the operation than in Comparative Example 1. It was observed that the amount of oil sludge deposited was extremely reduced, particularly when combined with a sticking-preventing Ni coating.

DESCRIPTION OF REFERENCE NUMERALS

(36) 11, 21, 31: Spacer expander 12a, 12b, 32a, 32b, 105a, 105b: Tab 13a, 13b, 33a, 33b, 106a, 106b: Projection 14a, 14b, 34a, 34b, 107a, 107b: Intermediate portion 15a, 15b, 35a, 35b, 108a, 108b: Space 102: Upper portion 103: Lower portion 104: Leg portion 120a, 120b: Side rail