Abstract:
A combined oil control ring for automobile engines capable of keeping an excellent oil-controlling function without suffering sticking between a spacer expander and side rails for a long period of operation comprises upper and lower two side rails, and an axially corrugated spacer expander having upper and lower portions; a leg portion connecting each upper portion and each lower portion of the spacer expander having a portion having an inclination angle θ of 15° or more from the axial direction.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a combined oil control ring mounted to a piston for an internal combustion engine, particularly to a combined oil control ring comprising two upper and lower side rails, and an axially corrugated spacer expander having upper and lower portions. 
     BACKGROUND OF THE INVENTION 
     In automobile engines, a lubricating oil is heated and exposed to a blowby gas during a long period of operation, so that the lubricating oil is contaminated with unburned hydrocarbons and degenerated oil additives (called “oil sludge” as a whole). The oil sludge includes oil sludge precursors having relatively high viscosity. The oil sludge attached to and accumulated on engine parts likely wears the parts and clogs lubricating oil paths, causing troubles in the functions of engine parts such as combined oil control rings (called “oil rings” unless otherwise mentioned). In the oil rings, spacer expanders and side rails are stuck to each other in the worst case, hindering the movement of separate side rails, and thus failing to exhibit a sufficient oil-controlling function. 
     As shown in  FIGS. 6( a )-6( c ) , a conventional combined oil ring  101  comprises a pair of annular side rails  120   a ,  120   b  arranged with a gap, and a spacer expander  101  supporting the side rails  120   a ,  120   b . The spacer expander  101  in an axially corrugated form has upper portions  102 , lower portions  103 , and leg portions  104  connecting the upper portions  102  and the lower portions  103 . It has tabs  105   a ,  105   b  on the inner side of the upper portions  102  and the lower portions  103 , projections  106   a ,  106   b  supporting the side rails  120   a ,  120   b  on the outer side, and dented intermediate portions  107   a ,  107   b  between the tabs  105   a ,  105   b  and the projections  106   a ,  106   b . When the spacer expander  101  is combined with the side rails  120   a ,  120   b , each space  108   a ,  108   b  is defined by each tab  105   a ,  105   b , each projection  106   a ,  106   b , each intermediate portion  107   a ,  107   b , and each side rail  120   a ,  120   b.    
     In the oil ring, the side rails  120   a ,  102   b  are pressed by radial and axial components of a force due to the inclination angle of the tabs  105   a ,  105   b  of the spacer expander  101 , thereby exhibiting a function of sealing a cylinder wall and side surfaces of ring grooves of a piston. Particularly, a small-width oil ring having a small axial width h1 has good followability to a cylinder sidewall with a side-sealing function, resulting in reduced friction loss without increasing oil consumption even if it is a low-tension type. However, in the oil ring, oil sludge is easily accumulated in a space  108   a ,  108   b  between the spacer expander and the side rails as described above. Particularly in the case of a small-width oil ring with extremely narrow space  108   a ,  108   b , the side rails  120   a ,  120   b  are highly likely stuck to the spacer expander  101  by the accumulated oil sludge. The accumulation of oil sludge extremely reduces the followability of side rails  120   a ,  120   b  to a cylinder wall, resulting in drastically increased oil consumption. 
     To prevent the attachment and accumulation of oil sludge to an oil ring, the surface coating of a spacer expander and a side rail, and the structure of a spacer expander avoiding the accumulation of oil sludge are disclosed. 
     For example, JP 2002-310299 A and JP 2003-254155 A disclose a fluororesin coating and a fluororesin-containing resin coating, JP 2000-027995 A discloses a coating containing fluoroalkyl-substituted alkoxide, JP 2006-258110 A discloses a hydrophilic prepolymer coating containing inorganic polysilazane, WO 2011/043364 A1 discloses a method for forming a metal coating having low surface free energy and hydrogen bonding force. These coatings are water-repellant, oil-repellant, or oppositely hydrophilic coatings, or those formed based on methods of preventing the attachment of oil sludge. 
     As a structural measure, JUM 59-127856 A discloses an oil ring comprising a spacer expander having upper and lower portions, sufficiently large holes permitting foreign materials such as lead compounds to pass being formed in intermediate portions of the upper and lower portions, such that they do not reach uprising portions of corrugation. U.S. Pat. No. 5,195,758 and JP 2011-185383 A disclose spacer expanders having structures preventing the accumulation of oil sludge, which comprise radial grooves in intermediate portions, and oil-exiting holes communicating with the grooves in tabs. 
     However, the coating methods of JP 2002-310299 A, JP 2003-254155 A, JP 2000-027995 A, JP 2006-258110 A, and WO 2011/043364 A1 suffer excess steps leading to cost increase, and the hole-forming method of JUM 59-127856 A need difficult working, making the oil rings expensive. Also, oil resides in the grooves formed in intermediate portions in U.S. Pat. No. 5,195,758 and JP 2011-185383 A during the stop of engines, likely suffering the accumulation of oil sludge. As a result, sufficient durability is not obtained in such an operation pattern as undergoing repeated stop of engines. 
     OBJECT OF THE INVENTION 
     To solve the above problems, an object of the present invention is provide a combined oil control ring for automobile engines capable of keeping an excellent oil-controlling function without suffering sticking between a spacer expander and side rails for a long period of operation. 
     SUMMARY OF THE INVENTION 
     It has been found that the accumulation of oil sludge can be prevented even in a small-width, low-tension, combined oil control ring, by having a basic structure making oil easily flowable from intermediate portions of a spacer expander toward both circumferential sides. 
     Thus, the combined oil control ring of the present invention comprises two upper and lower side rails, and an axially corrugated spacer expander having upper and lower portions; a leg portion connecting each upper portion and each lower portion of the spacer expander having a portion with an inclination angle θ of 15° or more from the axial direction. The inclination angle θ is preferably in a range of 25° or more. 
     Each of the upper and lower portions is preferably constituted by a tab pressing an inner peripheral surface of the side rail, a projection supporting the side rail, and an intermediate portion between the tab and the projection; at least the intermediate portion comprising a substantially flat pad portion; and a ratio L/P of the circumferential length L of the flat pad portion to a corrugation pitch P being 40% or less. The ratio L/P is more preferably 30% or less, further preferably 20% or less. 
     Each of the upper and lower portions is preferably constituted by a tab pressing an inner peripheral surface of the side rail, a projection supporting the side rail, and an intermediate portion between the tab and the projection; at least the intermediate portion being curvedly projecting toward the opposing side rails. The radius of curvature R of the projection is more preferably in a range of 0.3-3 mm, further preferably in a range of 0.5-1.5 mm. 
     The intermediate portion is preferably inclined such that it becomes more distant from the opposing side rail as it nears the tab. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing from outside part of an example of spacer expanders constituting the combined oil control ring of the present invention. 
         FIG. 2  is a view showing from outside part of another example of spacer expanders constituting the combined oil control ring of the present invention. 
         FIG. 3  is a view showing from outside part of a further example of spacer expanders constituting the combined oil control ring of the present invention. 
         FIG. 4  is a view showing from outside part of a still further example of spacer expanders constituting the combined oil control ring of the present invention. 
         FIG. 5  is a cross-sectional view showing a still further example of the combined oil control rings of the present invention, wherein the view is sectioned axially through a tab. 
         FIG. 6( a )  is a perspective view showing part of a conventional spacer expander. 
         FIG. 6( b )  is a view showing from outside part of a conventional spacer expander. 
         FIG. 6( c )  is a cross-sectional view showing a conventional combined oil control ring. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Examples of the combined oil control ring of the present invention will be explained in detail referring to the drawings below. The spacer expander  11  shown in  FIG. 1  comprises leg portions  14  having an inclination angle θ of 15° or more to the axial direction, which is larger than in conventional spacer expanders. Accordingly, the spacer expander  11  comprises intermediate flat pad portions  17   a ,  17   b  with a relatively short circumferential length L, between upper portions  12  and lower portions  13 . Of course, in place of the flat pad portions  17   a ,  17   b , curved intermediate portions  27   a ,  27   b  projecting toward opposing side rails with a curvature of 1/R may be used as shown in  FIG. 2 . With such a shape, oil sludge unlikely resides in a space between the spacer expander and the side rail, thereby avoiding the accumulation of oil sludge and the adhesion of the spacer expander to the side rail. The circumferential length L of the flat pad portions  17   a ,  17   b  has a close relation to the inclination angle θ of the leg portions  14  of the spacer expander. A larger inclination angle θ tends to reduce the circumferential length L of the flat pad portions  17   a ,  17   b . The inclination angle is preferably in a range of 25° or more. A ratio of the circumferential length L of the flat pad portions to the corrugation pitch P of the spacer expander is preferably 40% or less, more preferably 30% or less, further preferably 20% or less. When the intermediate portions  27   a ,  27   b  are in the form of an upward projecting curve, their radius of curvature R is preferably 0.3-3 mm, more preferably 0.5-1.5 mm. 
     From the aspect of the dischargeability (less residence) of oil sludge, a larger effectively is obtained by flat pad portions with smaller circumferential length L, projections with a smaller radius of curvature R, or leg portions with a smaller inclination angle θ. However, in the embodiment shown in  FIGS. 1 and 2 , shorter flat pad portions need leg portions with a larger inclination angle θ, making it impossible to expect the improvement of the dischargeability of oil sludge by reducing the inclination angle θ of the leg portions. In the embodiment shown in  FIGS. 3 and 4 , the leg portions have a small inclination angle θ only in portions near the upper portions and the lower portions, and a large inclination angle θ in middle portions between the upper and lower portions of the leg portions. With such a shape, the dischargeability of oil sludge is remarkably improved by reducing the circumferential length L of the flat pad portions  37   a ,  37   b  ( FIG. 3 ) or the radius of curvature R of the projections ( FIG. 4 ), or by drastically increasing the inclination angle of the leg portions from the flat pad portions. 
     In the combined oil control ring shown in  FIG. 5 , the spacer expander is inclined, such that the intermediate portions become more distant from the opposing side rails as they near the tabs. Of course, the spacer expander may be inclined oppositely, such that the intermediate portions become more distant from the side rails as they near the projections. With this inclination, the residence of oil sludge is further prevented. 
     Examples 1-5 and Comparative Example 1 
     An spacer expander of SUS304 having a nominal diameter d1 of 71 mm, a combined nominal width h1 of 1.5 mm, and a combined thickness a1 of 1.9 mm, and a side rail of SUS440 having a width of 0.4 mm were formed for a combined oil ring. The spacer expander having a pitch of 2.7 mm between adjacent upper portions (lower portions), as well as the inclination angle θ of leg portions and the circumferential length L of flat pad portions shown in Table 1, was produced by axially corrugating a SUS304 ribbon by local bending with gears, shearing it to form tabs, rolling it to provide tabs with a predetermined tab angle of 20°, and finally coiling it to form a truly circular spacer expander. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Inclination 
                 Circumferential 
                   
               
               
                   
                   
                 Angle 
                 Length L of Flat 
                 L/P* 
               
               
                   
                 No. 
                 θ (°) 
                 Pad Portions (mm) 
                 (%) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Example 1 
                 35 
                 0.7 
                 26 
               
               
                   
                 Example 2 
                 20 
                 1.2 
                 44 
               
               
                   
                 Example 3 
                 25 
                 1.0 
                 37 
               
               
                   
                 Example 4 
                 40 
                 0.6 
                 22 
               
               
                   
                 Example 5 
                 45 
                 0.3 
                 11 
               
               
                   
                 Comparative 
                 10 
                 1.6 
                 59 
               
               
                   
                 Example 1 
               
               
                   
                   
               
               
                   
                 Note: 
               
               
                   
                 *P: 2.7 mm. 
               
             
          
         
       
     
     [1] Actual Engine Test 
     Combined oil control rings of each of Examples 1-3 were attached to first to third cylinders of a 1-liter, 3-cylinder engine. The operation of this engine under the conditions of a predetermined pattern was repeated as an actual engine test. After 250 hours, a side rail gap and the amount of oil sludge attached were measured by the following evaluation methods. Further, an actual engine test was conducted on cylinders having combined oil control rings of each of Examples 4-5 and Comparative Example 1 under the same operation conditions as in Examples 1-3. Each test was conducted three times in each Example and Comparative Example. Top rings and second rings used had the following specifications. 
     (1) Top Ring 
     Material: SWOSC-V, 
     Peripheral surface: Ion-plated with chromium nitride, and 
     Size: d1=71 mm, h1=1.0 mm, and a1=2.3 mm. 
     (2) Second Ring 
     Material: SWOSC-V, 
     Entire surface: Coated with zinc phosphate, and 
     Size: d1=71 mm, h1=1.0 mm, and a1=2.3 mm. 
     [2] Evaluation Method 
     The following evaluation was conducted after the actual engine test. 
     (1) Measurement of Side Rail Gap 
     After the actual engine test, the piston was withdrawn from the cylinder, and a gap S 2  of each of upper and lower side rails in each combined oil control ring was measured, to determine a ratio S 2 /S 1 , wherein S 1  represents the gap of each side rail mounted to the piston before the actual engine test. S 2 /S 1  was determined on each of the upper and lower side rails in three actual engine tests, and averaged. 
     (2) Measurement of the Amount of Attached Oil Sludge 
     After the actual engine test, each combined oil control ring was removed from the piston, and cleaned with acetone. Thereafter, it was dried at 120° C. for 1 hour in an electric furnace, cooled to room temperature in a desiccator, and then measured with respect to its mass to determine its difference from the mass of the combined oil control ring measured in advance before the actual engine test. Differences determined in three actual engine tests were averaged to obtain the amount of oil sludge attached. 
     The actual engine test results in Examples 1-5 and Comparative Example 1 are shown in Table 2. The side rail gap and the amount of attached oil sludge are shown by relative values, with S 2 /S 1  in Comparative Example 1 as 100, and the amount of attached carbon sludge in Comparative Example 1 as 100. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                   
                 Amount of 
               
               
                   
                   
                   
                 Attached Carbon 
               
               
                   
                 No. 
                 S 2 /S 1   
                 Sludge 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Example 1 
                 170 
                 34 
               
               
                   
                 Example 2 
                 148 
                 80 
               
               
                   
                 Example 3 
                 162 
                 40 
               
               
                   
                 Example 4 
                 168 
                 35 
               
               
                   
                 Example 5 
                 165 
                 32 
               
               
                   
                 Comparative 
                 100 
                 100 
               
               
                   
                 Example 1 
               
               
                   
                   
               
             
          
         
       
     
     Table 2 indicates that Examples 1-5 had as large gaps as about 1.5-1.7 times and the amounts of attached oil sludge reduced to 32-80% after the actual engine test, as compared with those of Comparative Example 1. It is considered that in Comparative Example 1 in which the leg portions of a spacer expander had an inclination angle of 10°, the accumulation of oil sludge constrained the side rails, so that the gaps were not returned to the original one (did not expand) even after the pistons were withdrawn from the cylinders, while in Examples 1-5, the attachment and accumulation of oil sludge were reduced, resulting in reduced constraint of the oil rings, and thus expanding the gaps more closely to those before the operation than in Comparative Example 1. It was observed in Example 3 that when the leg portions of the spacer expander had an inclination angle of 25° or more, an extremely smaller amount of oil sludge was attached. 
     Example 6 
     Combined oil control rings were produced in the same manner as in Example 1, except that intermediate portions of each spacer expander had curved shapes having a radius of curvature of 1 mm and projecting toward opposing side rails in place of the flat pad portions, and mounted to each cylinder of a 3-cylinder engine to carry out the same actual engine test as in Example 1. The measurement results of all cylinders were averaged. As compared with Comparative Example 1, the gap was 1.6 times, and the amount of attached oil sludge was 32%. 
     Example 7 
     Combined oil control rings were produced in the same manner as in Example 1, except that each spacer expander was formed to have leg portions with an inclination angle of 18° only in portions near the upper and lower portions and 50° in middle portions between the upper and lower portions, with intermediate flat pad portions having a circumferential length of 0.5 mm, and mounted to each cylinder of a 3-cylinder engine to carry out the same actual engine test as in Example 1. The measurement results of all cylinders were averaged. As compared with Comparative Example 1, the gap was 1.7 times, and the amount of attached oil sludge was 35%. 
     Examples 8-10 
     Combined oil control rings were produced in the same manner as in Example 1, except that each spacer expander was formed to have not only leg portions with an inclination angle of 18° only in portions near the upper and lower portions and 50° in middle portions between the upper and lower portions, but also curved shapes having the radius of curvature shown in Table 3 and projecting toward opposing side rails in place of the intermediate flat pad portions, and mounted to each cylinder of a 3-cylinder engine to carry out the same actual engine test as in Example 1. The measurement results of the actual engine test conducted 3 times were averaged, and are shown in Table 3. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                 Radius of 
                   
                   
               
               
                   
                   
                 Curvature R of 
                   
                 Amount of 
               
               
                   
                 Inclination 
                 Intermediate 
                   
                 Attached Oil 
               
               
                 No. 
                 Angle θ* (°) 
                 Portions (mm) 
                 S 2 /S 1   
                 Sludge 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Example 8 
                 50 
                 0.5 
                 165 
                 36 
               
               
                 Example 9 
                 50 
                 1.5 
                 168 
                 34 
               
               
                 Example 10 
                 50 
                 2.0 
                 155 
                 41 
               
               
                   
               
               
                 Note: 
               
               
                 *Inclination angle of the leg portions in middle portions between the upper and lower portions. 
               
             
          
         
       
     
     Examples 8-10 were excellent in both of the side rail gap and the amount of attached oil sludge. This reveals that extremely high dischargeability of oil sludge is achieved by the leg portions having as large an inclination angle θ as 50° in middle portions between the upper and lower portions, and as small an inclination angle as 18° only in portions near the upper and lower portions, as well as a drastically increased inclination angle from the intermediate portions, the intermediate projections having a small radius of curvature R. 
     Example 11 
     Combined oil control rings were produced in the same manner as in Example 2 (inclination angle θ: 20°, circumferential length L of flat pad portions: 1.2 mm, and L/P: 44%), except that each spacer expander was formed to have intermediate portions inclined by 3° such that they became more distant from opposing side rails as they neared the tabs, and mounted to each cylinder of a 3-cylinder engine to carry out the same actual engine test as in Example 2. The measurement results of all cylinders were averaged. As compared with Comparative Example 1, the gap was 1.61 times, and the amount of attached oil sludge was 33%, which were much improved than in Example 2. 
     Effects of the Invention 
     In the combined oil control ring of the present invention comprising an axially corrugated spacer expander having upper and lower portions connected via leg portions which have an inclination angle θ of 15° or more from the axial direction, namely having upper and lower portions having short circumferential length, oil sludge is less accumulated in a space between the intermediate portions of the spacer expander and side rails, thereby preventing the side rails from sticking to the spacer expander. When the intermediate portions are curvedly projecting toward opposing side rails, oil sludge easily flows in both circumferential directions of the intermediate portions. Also, when the intermediate portions are inclined such that they become more distant from the side rails as they near the tabs, oil sludge easily flows inward. In both cases, a higher effect of preventing the accumulation of oil sludge is obtained, making it possible to prevent the accumulation of oil sludge even in a small-width, low-tension, combined oil control ring. Further, the spacer expander constituting the combined oil control ring of the present invention can be formed by usual gears without needing additional steps such as coating and drilling. Because of such structure, of course, oil does not reside in a space between the spacer expander and the side rails while the engine is not operated, resulting in sufficient durability even in an operation pattern having repeated stops of the engine.