COMBINED OIL CONTROL RING

Abstract

To provide a combined oil control ring for an automobile engine which is capable of maintaining an outstanding oil control function without causing the occurrence of firm sticking between the spacer expander and the side rails even when the engine is operated over an extended period of time, the crest and the trough of the spacer expander are each provided with a seating tab for pressing an inner peripheral surface of the side rail, a projection for supporting the side rail, and a middle part between the seating tab and the projection, and a ratio (S.sub.min/S.sub.0) is 1.9% or greater, where S.sub.min is a minimum axial cross-sectional area of a space formed between the middle part and the side face of the side rail opposed thereto, and S.sub.0 is an axial cross-sectional area from a groove bottom of an oil ring groove of a piston, to which the combined oil control ring is attached, to an inner wall of a cylinder liner.

Claims

1. A combined oil control ring comprising a pair of side rails and a spacer expander with crests and troughs formed in an axial waveform, wherein the crest and the trough of the spacer expander are each provided with a seating tab for pressing an inner peripheral surface of the side rail, a projection for supporting the side rail, and a middle part between the seating tab and the projection, and a ratio (S.sub.min/S.sub.0) is 1.9% or greater, where S.sub.min is a minimum axial cross-sectional area of a space formed between the middle part and the side face of the side rail opposed thereto, and S.sub.0 is an axial cross-sectional area from a groove bottom of an oil ring groove of a piston, to which the combined oil control ring is attached, to an inner wall of a cylinder liner.

2. The combined oil control ring according to claim 1, wherein the ratio (S.sub.min/S.sub.0) is 4.5% or less.

3. The combined oil control ring according to claim 1 or 2, wherein the seating tab has a seating tab height (a10) which is 28.9 to 34.2% of an expander radial thickness (a9) of the spacer expander.

4. The combined oil control ring according to claim 1, wherein the projection has a projection height (C) which is 5.3 to 26.3% of an expander radial thickness (a9) of the spacer expander.

5. The combined oil control ring according to claim 1, wherein the projection has a projection width (A) which is 6.7 to 13.9% of an expander width (h9) of the spacer expander.

6. The combined oil control ring according to claim 1, wherein the middle part has a height (B) which is 39.5 to 55.3% of an expander radial thickness (a9) of the spacer expander.

7. The combined oil control ring according to claim 1, wherein a projection width (A) of the projection is 0.12 to 0.25 mm.

8. The combined oil control ring according to claim 1, wherein the middle part opposed to the side rail is tilted substantially in a circumferential direction.

9. The combined oil control ring according to claim 8, wherein the middle part opposed to the side rail is convexed substantially in the circumferential direction.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0024] FIG. 1 is a cross-sectional view illustrating an example of an oil ring of the present invention which is a combination of a pair of side rails and a spacer expander.

[0025] FIG. 2 is a cross-sectional view illustrating an oil ring groove of a piston inserted into a cylinder liner.

[0026] FIG. 3(a) is a perspective view illustrating part of another example of a spacer expander that constitutes the oil ring of the present invention.

[0027] FIG. 3(b) is a cross-sectional view illustrating an oil ring of the present invention which is a combination of the spacer expander of FIG. 3(a) and side rails.

[0028] FIG. 4(a) is a perspective view illustrating part of still another example of a spacer expander that constitutes an oil ring of the present invention.

[0029] FIG. 4(b) is a cross-sectional view illustrating an oil ring of the present invention which is a combination of the spacer expander of FIG. 4(a) and side rails.

[0030] FIG. 5(a) is a diagram showing the relation between S.sub.min/S.sub.0 and an abutment joint gap ratio (m2/m1).

[0031] FIG. 5(b) is a diagram showing the relation between S.sub.min/S.sub.0 and the amount of oil sludge adhesion.

[0032] FIG. 6(a) is a perspective view illustrating part of a conventional spacer expander.

[0033] FIG. 6(b) is a cross-sectional view illustrating a conventional oil ring.

DESCRIPTION OF EMBODIMENTS

[0034] A description will now be given of oil rings according to embodiments of the present invention with reference to the drawings.

[0035] FIG. 1 shows an embodiment of an oil ring of the present invention. Like the conventional spacer expander, a spacer expander (11) is configured such that crests and troughs are each configured from a seating tab (12a, 12b), a projection (13a, 13b), and a middle part (14a, 14b), and there is formed a space (15a, 15b) between the middle part (14a, 14b) and the side face of a side rail (20a, 20b) opposed thereto. The axial cross-sectional area of the space (15a, 15b) (Sa, Sb, where Sa=Sb because the areas are vertically symmetric), and in particular, the minimum axial cross-sectional area (S.sub.min) affects the flow rate of oil flowing through the space (15a, 15b) and serves as a critical parameter in preventing firm sticking. As a result of experimental studies based on an axial cross-sectional area (S.sub.0) illustrated in FIG. 2 from the groove bottom of an oil ring groove to a cylinder liner inner wall, it was found that a ratio (S.sub.min/S.sub.0) of 1.9% or greater allows the firm sticking between the side rail and the spacer expander to be avoided with reliability, but conversely, a ratio (S.sub.min/S.sub.0) of less than 1.9% allows the firm sticking to be avoided with difficulty. The ratio (S.sub.min/S.sub.0) may not be provided with a particular upper limit, but the ratio (S.sub.min/S.sub.0) is preferably 4.5% or less.

[0036] Furthermore, the oil ring of the present invention is also preferably configured such that the trackability of the side rails is improved, and to reduce oil consumption, the width size (a1) of the side rails are relatively reduced. In that case, the corresponding spacer expander is preferably configured such that the seating tab height (a10) of the seating tab (12a, 12b) is 28.9 to 34.2% of the expander radial thickness (a9) of the spacer expander.

[0037] As described above, when an adjustment of the seating tab height (a10) leads to a decrease in the radial thickness (a1) of the side rail (20, 20), the angle of the seating tab (12a, 12b) is preferably adjusted from the viewpoints of the sealing function of the upper and lower surfaces of the oil ring groove, and in the case of the oil ring of the present invention, is preferably 10 to 30, more preferably 15 to 25.

[0038] Furthermore, to make the ratio (S.sub.min/S.sub.0) 1.9% or greater, the oil ring of the present invention may be preferably configured such that the projection (13a, 13b) of the spacer expander is increased in the projection width (A), and the middle part (14a, 14b) is also increased in the middle part height (B). In that case, the projection height (C) of the associated projection (13a, 13b) is preferably 5.3 to 26.3% of the expander radial thickness (a9) of the spacer expander, more preferably 5.3 to 15.8%.

[0039] Furthermore, the projection (13a, 13b) of the spacer expander preferably has a projection width (A) of specifically 0.12 to 0.25 mm, more preferably 0.15 to 0.20 mm. Furthermore, the projection width (A) is preferably 6.7 to 13.9% of the expander width (h9) of the spacer expander, more preferably 8.3 to 11.5%.

[0040] FIGS. 3(a) and 3(b) illustrate a spacer expander (21) according to another embodiment. The middle part (24a, 24b) is tilted substantially in the circumferential direction so as to allow the oil in the middle part to readily flow in one circumferential direction. The inclination angle of the adjacent middle parts may either plus (upward) or minus (downward) substantially in the circumferential direction, or may be repeatedly plus (upward) and minus (downward) in an alternate manner. Therefore, the minimum axial cross-sectional area (S.sub.min) of the space (25a, 25b) that is formed between the middle part (24a, 24b) and the side face of the opposed side rail (20a, 20b) is the axial cross-sectional area of an end portion of the space (25a, 25b).

[0041] FIGS. 4(a) and 4(b) illustrate a spacer expander (31) according to still another embodiment. The middle part (35a, 35b) exhibits an inverse V-shaped and convexed substantially in the circumferential direction, allowing the oil in the middle part to readily flow in both circumferential directions. The axial cross-sectional area at the position corresponding to the convex-shaped top is the minimum axial cross-sectional area (S.sub.min) of the space (35a, 35b).

[0042] The aforementioned spacer expander may be formed by plastic working of wire material.

EXAMPLES

Examples 1 to 10 (E1 to E10) and Comparative Examples 1 to 4 (C1 to C4)

[0043] A combined oil ring was produced in which the spacer expander was formed of a rolled strip (SUS304) of 1.90 mm0.25 mm (whereas 1.60 mm0.25 mm for Comparative Example 1) using a forming method utilizing a gear, and the side rails were formed of a rolled strip (SUS440B) of 1.62 mm0.35 mm by coiling (whereas 1.72 mm0.35 mm for Examples 2 to 3, 5 to 6, and 8 to 10, and 1.37 mm0.35 mm for Comparative Example 1). The combined oil ring had a nominal diameter (d1) of 87 mm, a combined width (h1) of 2.0 mm, and a combined radial thickness (a6) of 2.2 mm (whereas 1.9 mm for Comparative Example 1). Here, the spacer expander had a crest (trough) to crest (trough) pitch of 2.7 mm, and a tab angle of 20 (whereas 25 for Comparative Example 1), and the middle part was a plane substantially parallel to the side face of the side rail. Note that with a tension value of 23 N employed as a target value, the developed length of the spacer expander was adjusted. For each of Examples 1 to 10 and Comparative Examples 1 to 4, the detailed sizes of the spacer expander are shown in Table 1, and the sizes of the width and radial thickness of the side rail are shown in Table 2.

TABLE-US-00001 TABLE 1 SPACER EXPANDER DIMENSIONS SEATING MIDDLE OVERALL PROJECTION TAB PART WIDTH HEIGHT WIDTH HEIGHT HEIGHT HEIGHT h9, mm a9, mm A, mm C, mm a10, mm B, mm E1 1.8 1.9 0.12 0.3 0.65 0.95 E2 1.8 1.9 0.12 0.3 0.55 1.05 E3 1.8 1.9 0.12 0.1 0.55 1.05 E4 1.8 1.9 0.15 0.3 0.65 0.95 E5 1.8 1.9 0.15 0.3 0.55 1.05 E6 1.8 1.9 0.15 0.1 0.55 1.05 E7 1.8 1.9 0.2 0.5 0.65 0.75 E8 1.8 1.9 0.2 0.3 0.55 1.05 E9 1.8 1.9 0.2 0.1 0.55 1.05 E10 1.8 1.9 0.25 0.3 0.55 1.05 C1 1.8 1.6 0.05 0.4 0.6 0.6 C2 1.8 1.9 0.05 0.5 0.65 0.75 C3 1.8 1.9 0.12 0.65 0.65 0.6 C4 1.8 1.9 0.12 0.5 0.65 0.75

TABLE-US-00002 TABLE 2 SIDE RAIL DIMENSIONS RADIAL WIDTH THICKNESS mm a1, mm E1 0.35 1.62 E2 0.35 1.72 E3 0.35 1.72 E4 0.35 1.62 E5 0.35 1.72 E6 0.35 1.72 E7 0.35 1.62 E8 0.35 1.72 E9 0.35 1.72 E10 0.35 1.72 C1 0.35 1.37 C2 0.35 1.62 C3 0.35 1.62 C4 0.35 1.62

[1] Engine Test

[0044] The combined oil rings according to Examples 1 to 4 were attached to No. 1 to No. 4 cylinders of a 2.4-liter four-cylinder engine. The test was conducted, using a degraded oil collected from the market as an engine oil, in a condition that a pattern operation was conducted for a predetermined time (predetermined number of cycles) in which continuously repeated are the operation condition from a stop state to the maximum output RPM and the oil water temperature condition from lower temperatures to higher temperatures. After a predetermined period of time elapsed, the evaluation method below was followed to measure the abutment joint gap of the side rail and measure the amount of oil sludge adhesion. Here, the top ring and the second ring used had the following specifications.

(1) Top Ring

[0045] Material: SWOSC-V, the outer peripheral surface processed by nitride chromium ion plating

[0046] Sizes: d1=87.0 mm, h1=1.2 mm, a1=3.1 mm

(2) Second Ring

[0047] Material: SWOSC-V, the outer peripheral surface processed by chrome plating

[0048] Sizes: d1=87.0 mm, h1=1.2 mm, a1=3.4 mm

[0049] For the combined oil rings according to Examples 5 to 10 and Comparative Example 1 to 4, engine tests were conducted using the 2.4-liter 4-cylinder engine mentioned above in the same manner as for a combination of Examples 1 to 4 on the combinations of Examples 5 to 8, Examples 9 to 10 and Comparative Examples 1 to 2, Comparative Examples 3 to 4 and Examples 1 to 2, Examples 3 to 6, Examples 7 to 10, and Comparative Examples 1 to 4. Therefore, the number of times of the tests was two times for each example and comparative example.

[2] Measurement of Side Rail Abutment Joint Gap

[0050] After the engine tests, the abutment joint gap (m2) of the upper and lower side rails of the oil ring was measured with the pistons taken away from the cylinders so as to determine the ratio (m2/m1) of the abutment joint gap (m2) to the abutment joint gap (m1) with the oil ring being attached to the piston before the engine test (which is equal to the abutment joint gap in a free state before the engine test). For each of the pair of side rails, m2/m1 was determined so as to compute the average value of the two engine tests.

[3] Method for Measuring the Amount of Oil Sludge Adhesion

[0051] After the engine test was ended, the oil rings were taken away from the pistons, dried at 200 C. in an electric furnace for one hour, and cooled in a desiccator down to the room temperature; and subsequently, the mass of the oil rings was measured. The difference between the resulting mass and the mass of the oil ring measured in advance before the engine test was conducted, so that the average value of the two engine tests was determined as the amount of oil sludge adhesion.

[0052] The results of the engine tests according to Implementation Examples 1 to 10 and Comparative Examples 1 to 4 are shown in Table 3. Each test result is shown in relative values, e.g., the abutment joint gap is shown with the m2/m1 of Example 1 defined as 100, and the amount of oil sludge adhesion is shown with the amount of adhesion according to Example 1 defined as 100.

TABLE-US-00003 TABLE 3 ABUTMENT JOING RATIO OF AMOUNT OF GAP RATIO OIL SLUDGE m2/m1 ADHESION E1 100 100 E2 117 83 E3 124 81 E4 100 101 E5 126 82 E6 120 83 E7 101 107 E8 113 84 E9 108 101 E10 104 103 C1 27 359 C2 40 255 C3 53 203 C4 58 169

[0053] As can be seen from Table 3, the abutment joint gap ratio (m2/m1) after the engine test is 100 to 126 for Examples 1 to 10 while being reduced to 27 to 58 for

[0054] Comparative Examples 1 to 4, and the amount of oil sludge adhesion is 81 to 107 for Examples 1 to 10 while being increased to 169 to 359 for Comparative Examples 1 to 4. That is, it is considered that for Comparative Examples 1 to 4, the constraint of the side rail due to the deposition of oil sludge caused the abutment joint to be returned (expanded) to the original state with difficulty even when the piston was drawn out of the cylinder, whereas for Examples 1 to 10, a reduction in adhesion/deposition of oil sludge led to a reduction of the degree of constraint of the oil ring, thereby allowing the abutment joint to be returned (expanded) to the original state with ease.

[0055] To consider the aforementioned evaluation results, Table 4 shows the minimum axial cross-sectional area (S.sub.min) of the space formed between the middle part determined by each size of the spacer expander and the side face of the side rail opposed thereto, the axial cross-sectional area (S.sub.0) from the groove bottom of the oil ring groove of the piston to the inner wall of the cylinder liner, the ratio (S.sub.min/S.sub.0), the ratio (a10/a9) of the seating tab height (a10) to the expander radial thickness (a9), the ratio (C/a9) of the projection height (C) to the expander radial thickness (a9), the ratio (A/a9) of the projection width (A) to the expander radial thickness (a9), and the ratio (B/a9) of the middle part height (B) to the expander radial thickness (a9).

TABLE-US-00004 TABLE 4 PARAMETERS OF SPACER EXPANDER S.sub.min S.sub.0 mm.sup.2 mm.sup.2 S.sub.min/S.sub.0 % a10/a9 % C/a9 % A/h9 % B/a9 % E1 0.119 6.2 1.9 34.2 15.8 6.7 50.0 E2 0.131 6.2 2.1 28.9 15.8 6.7 55.3 E3 0.155 6.2 2.5 28.9 5.3 6.7 55.3 E4 0.149 6.2 2.4 34.2 15.8 8.3 50.0 E5 0.164 6.2 2.6 28.9 15.8 8.3 55.3 E6 0.194 6.2 3.1 28.9 5.3 8.3 55.3 E7 0.160 6.2 2.6 34.2 26.3 11.1 39.5 E8 0.220 6.2 3.5 28.9 15.8 11.1 55.3 E9 0.260 6.2 4.2 28.9 5.3 11.1 55.3 E10 0.277 6.2 4.5 28.9 15.8 13.9 55.3 C1 0.033 6.2 0.5 37.5 25.0 2.8 37.5 C2 0.041 6.2 0.7 34.2 26.3 2.8 29.5 C3 0.074 6.2 1.2 34.2 34.2 6.7 31.6 C4 0.095 6.2 1.5 34.2 26.3 6.7 39.5

[0056] FIG. 5(a) shows the relation between S.sub.min/S.sub.0 and the abutment joint gap ratio (m2/m1), while FIG. 5(b) shows the relation between S.sub.min/S.sub.0 and the ratio of the amount of oil sludge adhesion. It can be seen that the abutment joint gap ratio (m2/m1) abruptly increases for S.sub.min/S.sub.0 from 1.5% to 1.9%, and for 1.9% or greater, the constraint of the side rail occurs with difficulty. On the other hand, it can be seen that since the amount of oil sludge adhesion is monotonously reduced for S.sub.min/S.sub.0 up to 1.9% and not changed for 1.9% or greater, the adhesion/deposition of oil sludge is inhibited for S.sub.min/S.sub.0 of 1.9% or greater.

Example 11 (E11)

[0057] A combined oil ring was produced in the same manner as that in Example 1 except that the spacer expander with the middle part that was tilted substantially in the circumferential direction as shown in FIGS. 3(a) and 3(b). The projection width Al of one end of the projection in the circumferential direction was 0.12 mm and the projection width A2 of the other end was 0.15 mm. Therefore, S.sub.min is the same as that of Example 1.

Example 12 (E12)

[0058] A combined oil ring was produced in the same manner as that in Example 1 except that the spacer expander with the middle part that was convexed substantially in the circumferential direction as shown in FIGS. 4(a) and 4(b). The projection width A3 at the center of the projection in the circumferential direction was 0.12 mm, and the projection width A4 at both ends in the circumferential direction was 0.15 mm. Therefore, S.sub.min is the same as that of Example 1.

[0059] The same engine test as that for Example 1 was also conducted for Example 11 (E11) and Example 12 (E12). Here, the combined oil ring according to Example 11 was attached to No. 1 cylinder and No. 3 cylinder of the 2.4-liter 4-cylinder engine, and the combined oil ring according to Example 12 was attached to No. 2 cylinder and No. 4 cylinder. The test results are shown in Table 5.

TABLE-US-00005 TABLE 5 ABUTMENT JOINT RATIO OF AMOUNT OF GAP RATIO OIL SLUDGE m2/m1 ADHESION E11 110 87 E12 114 83

REFERENCE SIGNS LIST

[0060] 1 piston

[0061] 2 cylinder

[0062] 3 piston ring groove

[0063] 11, 21, 31, 101 spacer expander

[0064] 12a, 12b, 22a, 22b, 32a, 32b, 105a, 105b seating tab

[0065] 13a, 13b, 23a, 23b, 33a, 33b, 106a, 106b projection

[0066] 14a, 14b, 24a, 24b, 34a, 34b, 107a, 107b middle part

[0067] 15a, 15b, 25a, 25b, 35a, 35b, 108a, 108b space

[0068] 20a, 20b, 120a, 120b side rail

[0069] a1 radial thickness of side rail

[0070] a6 combined radial thickness of combined oil ring

[0071] a9 expander radial thickness of spacer expander

[0072] a10 seating tab height of spacer expander

[0073] h1 combined width of combined oil ring

[0074] h9 expander width of spacer expander

[0075] A projection width of spacer expander

[0076] B middle part height of spacer expander

[0077] C projection height of spacer expander

[0078] tab angle of spacer expander

[0079] S.sub.min minimum axial cross-sectional area of space

[0080] S.sub.0 axial cross-sectional area of oil ring groove to cylinder liner inner wall in axial direction

[0081] m1 abutment joint gap of side rail before engine test

[0082] m2 abutment joint gap of side rail after engine test