BACKGROUND OF THE INVENTION As shown in Fig. 7, a typical prior art oil control ring of combined three piece type comprises a spacer expander 1, and a pair of side rails 2,3 positioned above and below the spacer expander 1. As illustrated in Fig. 11, the spacer expander 1 is formed of a metallic strip into a radially corrugated ring which comprises a plurality of outer arcuate segments la ; a plurality of inner arcuate segments lb ; and a plurality of connecting segments 1c for connecting the outer and inner arcuate segments la, lb. A pair of protrusions 4 are integrally formed at upper and lower edges of each outer arcuate segment la in alignment with each other in the axial direction of piston so that the protrusions 4 are in contact with side rails 2,3 to retain them in a spaced relation to each other. In other words, the protrusions 4 upward and downward project from each outer arcuate segment la to vertically support the side rails 2,3. A pair of lugs 5 are integrally formed at upper and lower edges of each inner arcuate segment lb in axial alignment with each other so that the lugs 5 are in contact with each inner side of the side rails 2,3 to resiliently push the side rails 2,3 in the radial and outward direction. In other words, the lugs 5 upward and downward project from each inner arcuate segment lb to contact each inner side of the upper and lower side rails 2,3. Each lug 5 has an inclined abutment surface by approximately 15 degrees with respect to an axial direction of piston so that the abutment surface elastically pushes the side rails 2,3 in the radial and outward direction toward a cylinder bore surface when the abutment surfaces of the lugs 5 are in contact with the side rails 2, 3, and simultaneously the abutment surfaces push the side rails 2,3 toward radial and horizontal upper and bottom surfaces of an annular groove formed in piston.

Each connecting segment Ic is formed into a substantially S-shape or with an inclination to the radial direction of the spacer expander 1 between the outer and inner arcuate segments la, lb. The connecting segment lc has an opening 1d through which oil scraped by the side rails 2, 3 is discharged.

In another three piece type of a prior art oil control ring shown in Fig. 12, a spacer expander 1 is formed of a metallic strip into an axially corrugated ring.

Similarly to the three piece type oil control ring shown in Fig. 11, the oil control ring shown in Fig. 12 comprises upper arcuate segments le ; and a plurality of lower arcuate segments If connected alternately to each other to extend in a circumferential direction with axial corrugations; protrusions 4 formed in an outer side 7 of the spacer expander 1 for supporting the side rails 2,3; lugs 5 formed in an inner side 8 of the spacer expander 1 for resiliently pushing the side rails 2, 3 in the radial and outward direction; and connecting segments le for connecting upper and lower arcuate segments le and If to form axial corrugations. Each connecting segments 1c is formed into a substantially S-shape or with an inclination to the axial direction of the piston between the upper and lower arcuate segments le, If so that the connecting segment le has an opening ld to discharge scraped oil therethrough. The protrusions 4 upward and downward project from each outer arcuate segment la to vertically support the side rails 2,3. Also, the lugs 5 upward and downward project from each inner arcuate segments lb to contact respectively upper and lower side rails 2,3. The spacer expander 1 made of steel possesses elasticity or spring force so that the lugs 5 can push the metallic side rails 2,3 in the radial and outward direction toward an inner surface of the cylinder bore for sliding movement of the side rails 2,3 on the cylinder bore.

During operation of engine, carbon is accumulated in a combustion chamber and it tends to enter into an annular groove formed in a piston to which a top piston ring is attached. Existence of carbon in the annular groove temporarily increases frictional force between a lower side surface of the top piston ring and the lower side surface of the annular groove so that it generates a disadvantageous resistance against a slapping of piston occurring when the piston swings from an anti-thrust direction to a thrust direction after passing the top dead center (TDC) of combustion. Accordingly, the frictional resistance holds up or delays movement of the piston to the thrust direction to increase impact energy of the piston on the cylinder bore, thus resulting in louder slapping noise.

In addition, prior art oil control rings have lugs 5 formed on all upper and lower edges of inner arcuate segments 1b of the spacer expander 1 to push the side rails 2,3. Accordingly, when one of the upper and lower side rails 2,3 inwardly pushes one of the lugs 5 of the spacer expander 1 due to the slapping of the piston or thermal deformation of the cylinder, adjacent lug or lugs 5 of the spacer expander 1 are concurrently inwardly moved under an effect of the movement of the lug 5 pushed by the side rails 2,3. Accordingly, the latter involved or associated lug 5 is prevented from sufficiently outwardly pushing the side rails 2,3 due to the concurrent inward movement of the lugs 5 with reduction of the contact pressure by the side rail 2,3 on the cylinder bore surface, resulting in deterioration of the oil sealing or scraping function by the side rail 2,3 and increase in oil consumption.

In accordance with an analysis by the inventors, it has been found that the rigidity of the lugs 5 in the spacer expander 1 of prior art oil control ring is so high as to bar each independent movement of the lugs 5, and each movement of the lugs 5 has a large effect on movement of adjacent lugs 5 and an ill effect on the side rail 2,3 which tends to move away from the cylinder bore surface. In particular, the movement of the lug 5 of the spacer expander 1 exerts a strong influence on the opposite lug 5 in the axial direction of piston for pushing the side rails 2,3. For example, when the piston inclines due to the slapping, radial and inward force is applied on the lug 5 of the spacer expander 1 through side rail 2 or 3 so that the opposite lug 5 in the axial direction of piston slightly moves radially inwardly with reduction of the force by the lug 5 for pushing the side rail 2 or 3 toward the cylinder bore surface. For that reason, the pushing pressure of each outer side of the side rail 2 or 3 on the cylinder bore is decreased with lowering of oil sealing performance. In this way, as the lugs 5 are formed in upper and lower sides of the corrugation in the spacer expander 1, movement of a lug 5 exerts a dynamic effect on the other side lug 5 through the spacer expander 1, resulting in reduction of the side rail pressure of the other side on the cylinder bore surface.

An object of the present invention is to provide a three piece type oil control ring wherein lugs in a spacer expander can certainly push side rails on a cylinder bore surface.

DISCLOSURE OF THE PRESENT INVENTION A three piece type oil control ring according to the present invention, comprises a spacer expander (1) formed of a metallic strip into a radially or axially corrugated ring, and a pair of side rails (2,3) supported by the spacer expander (1).

The spacer expander comprises an outer side (7); protrusions (4) axially protruded from the outer side (7) to support the side rails (2,3); an inner side (8); and lugs (5) axially protruded from the inner side (8) to radially outwardly push the side rails (2, 3). Since the lugs (5) are formed on the inner segments every other corrugation or every three or more corrugations, the distance between the adjacent lugs (5) is longer than that of a prior art spacer expander (1), resulting in reduction of the rigidity or stiffness. Accordingly, each lug (5) is easy to perform the independent movement with less dynamic influence by adjacent lugs (5) and with improvement in motion performance of each lug (5) which therefore always pushes the side rails (2,3) on the inner surface of the cylinder bore at a constant pressure along the whole circumference of the spacer expander (1).

In an embodiment of the present invention, the spacer expander (1) is formed with a plurality of inner arcuate segments (lb) and a plurality of outer arcuate segments (la) connected alternately to each other to extend in a circumferential direction with radial corrugations. The lugs (5) are formed in every other inner arcuate segments (lb) or every three or more inner arcuate segments (lb), in other words, at plural intervals or in a zigzag pattern. No lug is formed on an edge of the inner arcuate segments (lb) in axial alignment with the edge formed with the lug (5). In another embodiment of the invention, the spacer expander (1) is formed with a plurality of upper arcuate segments (le) and a plurality of lower arcuate segments (If) connected alternately to each other to extend in a circumferential direction with axial corrugations so that the lugs (5) are formed in every other upper or lower arcuate segments or every three or more upper or lower arcuate segments (le, lf).

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view of a piston to which the three piece type oil control ring according to the present invention is attached.

Fig. 2 is a plan view of a spacer expander for the oil control ring according to the present invention.

Fig. 3 is a partial perspective view of the spacer expander shown in Fig. 2.

Fig. 4 is a development of the spacer expander shown in Fig. 2.

Fig. 5 is a sectional view of a piston showing another embodiment of the present invention.

Fig. 6 is a perspective view of the spacer expander shown in Fig. 5.

Fig. 7 is a sectional view of a prior art oil control ring.

Fig. 8 is a sectional view showing a test condition for measuring movement of lugs in oil control rings.

Fig. 9 is a graph showing strains of a pair of axially spaced lugs produced when an external force is applied to each side rail of the oil control rings shown in Figs. 1 and 11.

Fig. 10 is a graph showing strains of a pair of axially spaced lugs produced when an external force is applied to each side rail of the oil control rings shown in Figs. 5 and 12.

Fig. 11 is a perspective view of a spacer expander in a prior art oil control ring.

Fig. 12 is a perspective view showing a spacer expander of another type in a prior art oil control ring.

BEST MODE OF EMBODIMENT OF THE INVENTION Embodiments of the oil control ring according to the present invention are described hereinafter in connection with Figs. 1 to 6 wherein same symbols are applied to similar portions to those shown in Figs. 7 to 12 with omission of the detailed explanation thereon.

As shown in Fig. 1, the oil control ring according to the present invention is attached in an annular groove 11 formed in a piston 10. An upper side rail 2 is supported on protrusions 4 formed on each upper edge of outer arcuate segments la of the spacer expander 1. The upper side rail 2 is pushed toward an inner surface 13 of a cylinder bore 12 by lugs 5 formed on upper edges of the spacer expander 1 while the upper side rail 2 is kept in contact with an upper wall lla of the annular groove 11. Similarly, a lower side rail 3 is in contact with protrusions 4 formed on each lower edge of the outer arcuate segments la of the spacer expander 1. The lower side rail 3 is pushed toward the inner surface 13 of the cylinder bore 12 by the lugs 5 formed on lower edges of the spacer expander 1 while the lower side rail 3 is retained in contact with a bottom wall lib of the annular groove 11. The spacer expander 1 is formed with a plurality of inner arcuate segments lb and a plurality of outer arcuate segments la connected alternately to each other to extend in a circumferential direction with radial corrugations. As shown in Fig. 4, slits 5a may be formed in both sides of each lug 5 to provide the lug 5 with necessary resiliency or weakened rigidity.

As shown in Fig. 4, the lugs 5 are formed in every other inner arcuate segments lb, and no lug is formed on an edge of the inner arcuate segments lb in axial alignment with the edge formed with the lug 5. Otherwise, the lugs 5 may be formed every three or more inner arcuate segments 1b in other words at plural intervals or in a zigzag pattern. Since the lugs 5 are formed on the inner segments every other corrugation or every three or more corrugations, the distance between the adjacent lugs 5 is longer than that of a prior art spacer expander, resulting in reduction of the rigidity. Accordingly, each lug 5 is easy to independently move with less dynamic influence by adjacent lugs 5 and with improvement in separate motion performance of each lug 5 which always pushes the side rails 2,3 on the inner surface of the cylinder bore at a constant pressure along the whole circumference of the space expander 1. For example, when a piston slapping occurs and the piston inclines with decrease of a clearance between the piston 10 and the inner surface 13 of the cylinder bore 12, the side rail 2,3 inwardly pushes the lugs 5 of the spacer expander 1. In this case, the spacer expander 1 of the oil control ring according to the present invention allows each lug 5 to move independently from each other because the lug 5 is provided in sufficiently spaced relation to each other for independent motion. Accordingly, each lug 5 can fully push the side rails 2,3 toward the cylinder bore 12 without mutual dynamic influence of the adjacent lugs 5. The lugs 5 of the spacer expander 1 always exert the pushing force on the side rails 2,3 which are surely supported on three points of the lug 5 and a pair of the protrusions 4 for a longer period of time so that the side rails 2,3 is kept in position with improvement in the operational stability.

Figs. 5 and 6 illustrate another embodiment of the present invention wherein the spacer expander 1 is formed with a plurality of upper arcuate segments le and a plurality of lower arcuate segments 1f connected alternately to each other to extend in a circumferential direction with axial corrugations. In this embodiment, the lugs 5 are formed in every three upper or lower arcuate segments le or If to keep the independent motion of each adjacent lug 5 similarly to the first embodiment shown in Figs. 1 to 4. In this way, the adjacent lugs 5 can be formed in every other upper or lower arcuate segments or every three or more upper or lower arcuate segments le or lf.

To test the effect of the present invention, spacer expanders were made including two kind shown in Figs. 1 and 5 with the configuration of upper and lower lugs 5 provided in the zigzag pattern. As shown in Fig. 8, an external force was radially inwardly applied to a lower side rail 3 of three-piece oil ring of the diameter: 87.5 mm to measure movement of a lower lug 5b of the spacer expander with a dial gauge 6b and also measure movement of an upper lug 5a with a dial gauge 6a. Measurements of the lower and upper lugs 5b and 5a are shown as Strain Sl and Strain S2. Here, Strain S2 in the present invention indicates the movement of a nearest upper lug because no lug exists in a just upper position of the lower lug 5. Fig. 9 indicates the measured result of S1 and S2 in the oil control ring according to the present invention shown in Fig. 1 and prior art oil control ring shown in Fig. 11. Fig. 10 indicates the measured result of S1 and S2 in the oil control ring according to the present invention shown in Fig. 5 and prior arts oil control ring shown in Fig. 12. As understood from Figs. 9 and 10, the invention's oil control rings demonstrate that the attended movement of the lug 5 affected by movement of the other side lug 5 is approximately only 40 to 60 percents of the attended movement of the lug 5 in prior art oil control rings.

The above embodiments and mode of the present invention may be varied in various ways. For example, Figs. 1 to 4 illustrate the lugs 5 formed every other corrugation, otherwise the lugs 5 may be formed every three or more corrugations. Also, in the embodiment shown in Figs. 5 and 6, the lugs 5 may be formed every other corrugation, every two, four or more corrugations. The spacer expander is not limited to the illustrated shapes so long as it is formed into a ring with corrugations.

As mentioned above, in the oil control ring according to the present invention, each lug is easy to perform the independent movement with less dynamic influence by adjacent lugs and with a constant pressure of the side rails on the inner surface of the cylinder bore. Therefore, the side rails can maintains the excellent oil sealing performance on the cylinder bore to prevent increase of oil consumption by oil leakage. In addition, as the side rails are surely supported on three points of the lug and a pair of the protrusions, the outer side of the side rails always makes the sliding movement on and in the closely contact with the cylinder bore surface with the stabilized operation and restricted vibration of the side rails.

Accordingly, the side rails can scrape oil on the cylinder bore surface with less oil leakage between the side rails and cylinder bore surface.