Abstract:
The present invention prevents anchoring between a space expander and a side rail of a combination oil ring. A combination oil ring ( 10 ) is provided with a vertical pair of side rails ( 11, 12 ) and a space expander ( 13 ) arranged therebetween, the space expander ( 13 ) includes a plurality of upper pieces ( 14 ) and lower pieces ( 15 ) alternately arranged in the peripheral direction and spaced apart in the axial direction and the peripheral direction, a coupling piece ( 16 ) coupling the adjacent upper pieces ( 14 ) and lower pieces ( 15 ), and flange sections ( 17, 18 ) that press against the side rails ( 11, 12 ) and are formed upright on an inner peripheral side end of the upper pieces ( 14 ) and the lower pieces ( 15 ), and a through hole ( 19 ) is formed in the flange sections ( 17, 18 ), wherein side rail supporters ( 14   a,    15   a ) which project out in the axial direction are formed at one portion, in the peripheral direction, of the outer peripheral side end of the upper pieces ( 14 ) and the lower pieces ( 15 ) of the space expander ( 13 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a three-piece combination oil ring. 
       BACKGROUND ART 
       [0002]    When a three-piece combination oil ring including a pair of upper and lower side rails and a spacer expander arranged therebetween is used, sludge such as unburned carbon or carbon produced from a product of combustion of lubricant oil tends to be deposited between the spacer expander and the side rails. With a progression of deposition, the side rails and the spacer expander stick to each other due to deposits, and the side rails cannot follow the shape of a cylinder bore, so that the oil ring may not be able to exert predetermined performance as an oil ring. 
         [0003]    Meanwhile, in Patent Literature 1, a hole large enough to cause sludge to pass therethrough is formed in a center portion between convex and concave portions of an expander each having a substantially flat surface. 
         [0004]    Also, in Patent Literature 2, a groove is formed in a surface that is close to a side rail of an upper piece and a surface that is close to a side rail of a lower piece of a spacer expander, and the groove communicates with a through hole formed in a flange portion for pressing the side rails in a combination oil ring. Also, since the groove extends radially and is open on an outer circumferential side, oil flows in from the opening portion to form a flow of oil from the outer circumferential side to an inner circumferential side, so that the oil containing sludge is easily discharged from the through hole in the flange portion, thereby making it difficult for deposits to accumulate. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: Japanese Utility Model Publication No. 2-31559 
         Patent Literature 2: Japanese Patent Laid-Open No. 2011-185383 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    In Patent Literature 1, however, since the hole is formed in the center portion between the convex and concave portions each having a substantially flat surface of the expander, the expander may lack rigidity. 
         [0008]    Also, although Patent Literature 2 further proposes the technique for preventing the side rails and the spacer expander of the combination oil ring from sticking to each other, there is a demand for a further improvement in the performance of discharging the oil containing sludge. 
         [0009]    It is an object of the present invention to prevent side rails and a spacer expander of a combination oil ring from sticking to each other. 
       Solution to Problem 
       [0010]    The present invention is a combination oil ring including a pair of upper and lower side rails and a spacer expander arranged therebetween, the spacer expander including a plurality of upper pieces and lower pieces alternately arranged in a circumferential direction with the pieces axially and circumferentially apart from each other, a coupling piece coupling an upper piece and a lower piece adjacent to each other, and a flange portion formed standing at an inner circumferential-side end portion of each of the upper pieces and the lower pieces so as to press the side rails, and a through hole being formed in the flange portion, 
         [0011]    wherein a side rail support portion that projects axially is formed at a portion in the circumferential direction of an outer circumferential-side end portion of each of the upper pieces and the lower pieces of the spacer expander. 
         [0012]    The side rail support portion of the spacer expander may preferably be formed at an end portion in the circumferential direction of the outer circumferential-side end portion of each of the upper pieces and the lower pieces, or at a portion including the end portion. 
         [0013]    The side rail support portion of the spacer expander may preferably be formed at a position of an intermediate portion in the circumferential direction of the outer circumferential-side end portion of each of the upper pieces and the lower pieces. 
         [0014]    A portion other than the side rail support portion in the circumferential direction of the outer circumferential-side end portion of each of the upper pieces and the lower pieces of the spacer expander may preferably have a flush surface continuous from an inner circumferential side. 
         [0015]    A portion other than the side rail support portion in the circumferential direction of the outer circumferential-side end portion of each of the upper pieces and the lower pieces of the spacer expander may preferably project to an axially opposite side from the side rail support portion. In this case, the portion other than the side rail support portion in the circumferential direction of the outer circumferential-side end portion of each of the upper pieces and the lower pieces of the spacer expander may preferably have a radial through hole on an inner circumferential side. 
         [0016]    Each of gaps between the upper and lower pieces of the spacer expander and the side rails may preferably be continuously or discontinuously widened radially inward from an inner circumferential side of the side rail support portion to a base portion of the flange portion. 
         [0017]    Preferably, a groove may be formed in a surface that is close to the side rail of at least the upper piece out of the upper and lower pieces of the spacer expander, and the groove may communicate with the through hole in the flange portion. Preferably, in this case, the groove may extend radially, and may be open on an outer circumferential side. 
         [0018]    The side rail support portion of the spacer expander is formed in a trapezoidal shape, a semi-elliptical shape, or a rectangular shape as viewed from the radial direction. 
         [0019]    Although a side rail support surface of the side rail support portion of the spacer expander may be a flat surface, the present invention is not limited thereto, and, for example, the side rail support surface may preferably be radially formed as a tapered surface or an arc surface so as to support the side rails at the outer circumferential-side end portion. 
         [0020]    The side rail support portion of the spacer expander may preferably be formed by plasticity processing. 
       Advantageous Effects of Invention 
       [0021]    In accordance with the present invention, since the side rail support portion is formed at a portion in the circumferential direction of the outer circumferential-side end portion of the spacer expander, a space is formed between the spacer expander and the side rails at the portion other than the side rail support portion in the circumferential direction of the outer circumferential-side end portion of the spacer expander. As a result, oil flows in from the space to form a flow of oil from the outer circumferential side to the inner circumferential side, and the oil containing sludge is easily discharged from the through hole in the flange portion of the spacer expander, so that the side rails and the spacer expander can be prevented from sticking to each other due to deposits. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0022]      FIG. 1  is a vertical sectional view illustrating a state in which a piston to which a combination oil ring is mounted is inserted into a cylinder according to one embodiment of the present invention. 
           [0023]      FIG. 2  is a perspective view illustrating a portion of a spacer expander. 
           [0024]      FIG. 3  is a vertical sectional view illustrating a state in which a piston to which a combination oil ring is mounted is inserted into a cylinder according to another embodiment of the present invention. 
           [0025]      FIG. 4  is a perspective view illustrating a portion of a spacer expander. 
           [0026]      FIG. 5  is a vertical sectional view illustrating a state in which a piston to which a combination oil ring is mounted is inserted into a cylinder according to yet another embodiment of the present invention. 
           [0027]      FIG. 6  is a perspective view illustrating a portion of a spacer expander. 
           [0028]      FIG. 7  is a perspective view illustrating a portion of yet another spacer expander of the present invention. 
           [0029]      FIG. 8  is a perspective view illustrating a portion of yet another spacer expander of the present invention. 
           [0030]      FIG. 9  is a perspective view illustrating a portion of yet another spacer expander of the present invention. 
           [0031]      FIG. 10  is a vertical sectional view illustrating a state in which a piston to which a combination oil ring is mounted is inserted into a cylinder according to yet another embodiment of the present invention. 
           [0032]      FIG. 11  is a perspective view illustrating a portion of a spacer expander. 
           [0033]      FIG. 12  is a vertical sectional view illustrating a state in which a piston to which a combination oil ring is mounted is inserted into a cylinder according to yet another embodiment of the present invention. 
           [0034]      FIG. 13  is a perspective view illustrating a portion of a spacer expander. 
           [0035]      FIG. 14  is a vertical sectional view illustrating a state in which a piston to which a combination oil ring is mounted is inserted into a cylinder according to yet another embodiment of the present invention. 
           [0036]      FIG. 15  is a perspective view illustrating a portion of a spacer expander. 
           [0037]      FIG. 16  is a vertical sectional view illustrating a state in which a piston to which a combination oil ring is mounted is inserted into a cylinder according to yet another embodiment of the present invention. 
           [0038]      FIG. 17  is a perspective view illustrating a portion of a spacer expander. 
           [0039]      FIG. 18  is a perspective view illustrating a portion of yet another spacer expander of the present invention. 
           [0040]      FIG. 19  is a perspective view illustrating a portion of yet another spacer expander of the present invention. 
           [0041]      FIG. 20  is a view of a side rail support portion as viewed from a radial direction. 
           [0042]      FIG. 21  is a view of a side rail support portion as viewed from a radial direction. 
           [0043]      FIG. 22  is a vertical sectional view illustrating a portion of a combination oil ring. 
           [0044]      FIG. 23  is a vertical sectional view illustrating a portion of a combination oil ring. 
           [0045]      FIG. 24  is a view for explaining a dimensional relationship of a side rail support portion. 
           [0046]      FIG. 25  is a view for explaining a dimensional relationship of a side rail support portion. 
           [0047]      FIG. 26  is a view illustrating an axial distance c between a flange portion base position of a spacer expander and a side rail, and an axial width d of an outer circumferential-side end portion of the spacer expander. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0048]    In the following, one embodiment of the present invention will be described based on  FIGS. 1 and 2 . 
         [0049]    In  FIG. 1 , a combination oil ring  10  is mounted to an oil ring groove  4  formed in an outer circumferential surface  3  of a piston  2  within a cylinder  1 . The combination oil ring  10  is a three-piece combination oil ring made of steel, and includes a pair of upper and lower side rails  11  and  12 , and a spacer expander  13  arranged therebetween. 
         [0050]    The side rails  11  and  12  are annular plate-like rails each provided with a gap. 
         [0051]    The spacer expander  13  (see  FIGS. 1 and 2 ) is composed of a plurality of axially-corrugated periodic elements lying in series in a circumferential direction. In the spacer expander  13 , a plurality of horizontal upper and lower pieces  14  and  15  are alternately arranged in the circumferential direction with the pieces axially and circumferentially apart from each other, and an upper piece  14  and a lower piece  15  adjacent to each other are coupled together with a coupling piece  16 . Flange portions  17  and  18  for pressing the side rails  11  and  12  are formed standing in an arched shape at inner circumferential-side end portions of each of the upper pieces  14  and each of the lower pieces  15 , and a through hole  19  is formed in each of base portions of the flange portions  17  and  18 . 
         [0052]    In outer circumferential-side end portions of each of the upper pieces  14  and each of the lower pieces  15 , end portions in the circumferential direction project axially outward to form support portions  14   a  and  15   a  for the side rails  11  and  12 . That is, one end portion in the circumferential direction of the outer circumferential-side end portion of the upper piece  14  projects upward to form the support portion  14   a  for the side rail  11 , and one end portion in the circumferential direction of the outer circumferential-side end portion of the lower piece  15  projects downward to form the support portion  15   a  for the side rail  12 . Portions  14   b  and  15   b  other than the side rail support portions in the circumferential direction of the outer circumferential-side end portions of the upper piece  14  and the lower piece  15  have horizontal surfaces continuous from the inner circumferential side. 
         [0053]    Accordingly, in the upper piece  14  and the lower piece  15 , the end portions in the circumferential direction of the outer circumferential-side end portions project axially to constitute projecting surfaces that form the side rail support portions  14   a  and  15   a , and the other portions (the portions other than the side rail support portions)  14   b  and  15   b  constitute the horizontal surfaces continuous from the inner circumferential side. 
         [0054]    The spacer expander  13  is mounted in the oil ring groove  4  of the piston  2  in a compressed state with both gap end portions abutted against each other so as to generate a radially-outward expansion force, and brings an outer circumferential surface of each of the side rails  11  and  12  into close contact with an inner wall of the cylinder  1  by holding the upper and lower side rails  11  and  12  vertically (axially) apart from each other by the side rail support portions  14   a  and  15   a  of the upper and lower pieces  14  and  15 , and pressing inner circumferential surfaces of the upper and lower side rails  11  and  12  by the upper and lower flange portions  17  and  18 , respectively. Accordingly, the outer circumferential surfaces of the upper and lower side rails  11  and  12  come into press contact with the inner wall of the cylinder  1 , and thereby scrape oil off the inner wall of the cylinder  1 . 
         [0055]    As described above, in the combination oil ring  10  according to the present embodiment, the side rail support portions  14   a  and  15   a  of the spacer expander  13  are formed at the end portions in the circumferential direction of the outer circumferential-side end portions of the upper piece  14  and the lower piece  15 , so that spaces are formed between the upper piece  14  of the spacer expander  13  and the upper side rail  11 , and between the lower piece  15  of the spacer expander  13  and the lower side rail  12 , at the portions  14   b  and  15   b  other than the side rail support portions in the circumferential direction of the outer circumferential-side end portions. As a result, oil flows in from the spaces to form a flow of oil from the outer circumferential side to the inner circumferential side, and the oil containing sludge is easily discharged from the respective through holes  19  in the flange portions  17  and  18  of the spacer expander  13 , so that the side rails  11  and  12  and the spacer expander  13  can be prevented from sticking to each other due to deposits. 
         [0056]      FIGS. 3 and 4  show another embodiment of the present invention. The combination oil ring  10  according to the present embodiment differs from the combination oil ring according to the aforementioned embodiment in the configuration of the portions  14   b  and  15   b  other than the side rail support portions in the circumferential direction of the outer circumferential-side end portions of the upper piece  14  and the lower piece  15  of the spacer expander  13  as described below, and the other configurations are the same as those in the aforementioned embodiment. 
         [0057]    In the present embodiment, in the outer circumferential-side end portions of the upper piece  14  and the lower piece  15  of the spacer expander  13 , the end portions in the circumferential direction also project axially outward to form the support portions  14   a  and  15   a  for the side rails  11  and  12 . That is, the end portion in the circumferential direction of the outer circumferential-side end portion of the upper piece  14  of the spacer expander  13  projects upward to form the support portion  14   a  for the side rail  11 , and the end portion in the circumferential direction of the outer circumferential-side end portion of the lower piece  15  projects downward to form the support portion  15   a  for the side rail  12 . 
         [0058]    However, in the present embodiment, the portions  14   b  and  15   b  other than the side rail support portions in the circumferential direction of the outer circumferential-side end portions of the upper piece  14  and the lower piece  15  of the spacer expander  13  are configured as follows. That is, the portions  14   b  and  15   b  other than the side rail support portions in the circumferential direction of the outer circumferential-side end portions of the upper piece  14  and the lower piece  15  project to axially opposite sides from the side rail support portions  14   a  and  15   a , and a radial through hole  20  is formed in each of the inner circumferential sides. That is, the portion  14   b  other than the side rail support portion in the circumferential direction of the outer circumferential-side end portion of the upper piece  14  of the spacer expander  13  projects downward to be formed one-step lower than the horizontal surface portion on the inner circumferential side, with the radial through hole  20  formed on the inner circumferential side, and the portion  15   b  other than the side rail support portion in the circumferential direction of the outer circumferential-side end portion of the lower piece  15  projects upward to be formed one-step higher than the horizontal surface portion on the inner circumferential side, with the radial through hole formed on the inner circumferential side. 
         [0059]    As described above, in the combination oil ring  10  according to the present embodiment, the side rail support portions  14   a  and  15   a  of the spacer expander  13  are formed at the end portions in the circumferential direction of the outer circumferential-side end portions of the upper piece  14  and the lower piece  15 , so that spaces are formed between the upper piece  14  of the spacer expander  13  and the upper side rail  11 , and between the lower piece  15  of the spacer expander  13  and the lower side rail  12 , at the portions  14   b  and  15   b  other than the side rail support portions in the circumferential direction of the outer circumferential-side end portions. As a result, oil flows in from the spaces to form a flow of oil from the outer circumferential side to the inner circumferential side, and the oil containing sludge is easily discharged from the respective through holes  19  in the flange portions  17  and  18  of the spacer expander  13 , so that the side rails  11  and  12  and the spacer expander  13  can be prevented from sticking to each other due to deposits. Moreover, in the present embodiment, the portions  14   b  and  15   b  other than the side rail support portions project to the axially opposite sides from the side rail support portions  14   a  and  15   a , and the radial through hole  20  is formed in each of the inner circumferential sides, so that the oil passes through the portions  14   b  and  15   b  other than the side rail support portions to be discharged to the inner circumferential side from the radial through holes  20 , thereby making it difficult for the sludge to accumulate between the spacer expander  13  and the side rails  11  and  12 . 
         [0060]      FIGS. 5 and 6  show yet another embodiment of the present invention. The combination oil ring  10  according to the present embodiment differs from the combination oil ring according to the first embodiment described using  FIGS. 1 and 2  in the configuration of portions on the inner circumferential side from the side rail support portions  14   a  and  15   a  of the upper piece  14  and the lower piece  15  of the spacer expander  13  as described below, and the other configurations are the same as those in the first embodiment. 
         [0061]    In the present embodiment, in the outer circumferential-side end portions of the upper piece  14  and the lower piece  15  of the spacer expander  13 , the end portions in the circumferential direction also project axially outward to form the support portions  14   a  and  15   a  for the side rails  11  and  12 . That is, the end portion in the circumferential direction of the outer circumferential-side end portion of the upper piece  14  of the spacer expander  13  projects upward to form the support portion  14   a  for the side rail  11 , and the end portion in the circumferential direction of the outer circumferential-side end portion of the lower piece  15  projects downward to form the support portion  15   a  for the side rail  12 . 
         [0062]    However, in the present embodiment, the portions on the inner circumferential side from the side rail support portions  14   a  and  15   a  of the upper piece  14  and the lower piece  15  of the spacer expander  13  are configured as follows. That is, a groove  21  that extends linearly in the radial direction is formed in the portion on the inner circumferential side from the side rail support portion in each of a surface that is close to the side rail  11  of the upper piece  14  and a surface that is close to the side rail  12  of the lower piece  15  of the spacer expander  13 . The grooves  21  are formed by deforming predetermined portions of the upper piece  14  and the lower piece  15  into an arc shape in section by plasticity processing. Inner circumferential-side end portions of the grooves  21  in the upper piece  14  and the lower piece  15  communicate with the through holes  19  in the base portions of the flange portions  17  and  18 , respectively, and outer circumferential-side end portions are open to an external space so as to communicate with the external space. Reference numeral  22  denotes the opening. Although the sectional shape of the groove  21  is shown as an arc shape, the present invention is not limited thereto, and, for example, an inverted trapezoidal shape or a V shape may be also used. 
         [0063]    As described above, in the combination oil ring  10  according to the present embodiment, the side rail support portions  14   a  and  15   a  of the spacer expander  13  are formed at the end portions in the circumferential direction of the outer circumferential-side end portions of the upper piece  14  and the lower piece  15 , so that spaces are formed between the upper piece  14  of the spacer expander  13  and the upper side rail  11 , and between the lower piece  15  of the spacer expander  13  and the lower side rail  12 , at the portions  14   b  and  15   b  other than the side rail support portions in the circumferential direction of the outer circumferential-side end portions. As a result, oil flows in from the spaces to form a flow of oil from the outer circumferential side to the inner circumferential side, and the oil containing sludge is easily discharged from the respective through holes  19  in the flange portions  17  and  18  of the spacer expander  13 , so that the side rails  11  and  12  and the spacer expander  13  can be prevented from sticking to each other due to deposits. Moreover, in the present embodiment, the grooves  21  are formed in the upper piece  14  and the lower piece  15  of the spacer expander  13 , so that the sizes of the through holes  19  provided at the base portions of the flange portions  17  and  18  and facing the space portions between the side rails  11  and  12  and the spacer expander  13  can be formed larger by sizes corresponding to the grooves  21  than those of the flat surfaces with no groove; therefore, the deposits between the upper and lower pieces  14  and  15  of the spacer expander  13  and the side rails  11  and  12  are easily discharged from the through holes  19  in the flange portions  17  and  18  of the spacer expander  13 , and the side rails  11  and  12  and the spacer expander  13  can be prevented from sticking to each other due to the deposits. Also, since the grooves  21  extend in the radial direction and are open to the external space so as to communicate with the external space without being closed on the outer circumferential side, the oil flows in from the openings  22  to form a flow of oil from the outer circumferential side to the inner circumferential side; therefore, the deposits become difficult to accumulate and easily discharged from the through holes  19  in the flange portions  17  and  18 , so that the side rails  11  and  12  and the spacer expander  13  can be further prevented from sticking to each other due to the deposits. 
         [0064]    The structure of the grooves  21  described in the aforementioned embodiment may be also applied to the combination oil ring according to the embodiment described using  FIGS. 3 and 4 . 
         [0065]    Also, although the side rail support portions  14   a  and  15   a  formed at the end portions in the circumferential direction of the outer circumferential-side end portions of the upper piece  14  and the lower piece  15  of the spacer expander  13  are formed at the end portions circumferentially opposite to each other of the outer circumferential-side end portions in the aforementioned embodiments, the side rail support portions  14   a  and  15   a  may be, of course, formed on the same side. Accordingly, the rigidity of the spacer expander  13  is increased. 
         [0066]    The above example is shown in  FIGS. 7 to 9 . 
         [0067]      FIG. 7  corresponds to the first embodiment shown in  FIGS. 1 and 2 , in which the side rail support portions  14   a  and  15   a  of the outer circumferential-side end portions of the upper piece  14  and the lower piece  15  of the spacer expander  13  are formed at the end portions on the same side in the circumferential direction. The other configurations are the same as those in the first embodiment shown in  FIGS. 1 and 2 . In the present embodiment, the same effects as those in the embodiment shown in  FIGS. 1 and 2  are produced, and the rigidity of the spacer expander  13  can be also improved. 
         [0068]      FIG. 8  corresponds to the embodiment shown in  FIGS. 3 and 4 , in which the side rail support portions  14   a  and  15   a  of the outer circumferential-side end portions of the upper piece  14  and the lower piece  15  of the spacer expander  13  are formed at the end portions on the same side in the circumferential direction. The other configurations are the same as those in the embodiment shown in  FIGS. 3 and 4 . In the present embodiment, the same effects as those in the embodiment shown in  FIGS. 3 and 4  are produced, and the rigidity of the spacer expander  13  can be also improved. 
         [0069]      FIG. 9  corresponds to the embodiment shown in  FIGS. 5 and 6 , in which the side rail support portions  14   a  and  15   a  of the outer circumferential-side end portions of the upper piece  14  and the lower piece  15  of the spacer expander  13  are formed at the end portions on the same side in the circumferential direction. The other configurations are the same as those in the embodiment shown in  FIGS. 5 and 6 . In the present embodiment, the same effects as those in the embodiment shown in  FIGS. 5 and 6  are produced, and the rigidity of the spacer expander  13  can be also improved. 
         [0070]      FIGS. 10 and 11  show yet another embodiment of the present invention. The combination oil ring  10  according to the present embodiment differs from the combination oil ring according to the first embodiment described using  FIGS. 1 and 2  in the configuration of the side rail support portions  14   a  and  15   a  of the outer circumferential-side end portions of the upper piece  14  and the lower piece  15  of the spacer expander  13  as described below, and the other configurations are the same as those in the first embodiment. 
         [0071]    In the present embodiment, in the outer circumferential-side end portions of the upper piece  14  and the lower piece  15  of the spacer expander  13 , center portions in the circumferential direction project axially outward to form support portions  14   a  and  15   a  for the side rails  11  and  12 . That is, the center portion in the circumferential direction of the outer circumferential-side end portion of the upper piece  14  projects upward to form the support portion  14   a  for the side rail  11 , and the center portion in the circumferential direction of the outer circumferential-side end portion of the lower piece  15  projects downward to form the support portion  15   a  for the side rail  12 . Portions  14   b  and  15   b  other than the side rail support portions in the circumferential direction of the outer circumferential-side end portions of the upper piece  14  and the lower piece  15 , that is, both side portions  14   b  and  15   b  of the side rail support portions  14   a  and  15   a  have horizontal surfaces continuous from the inner circumferential side. 
         [0072]    Accordingly, in the upper piece  14  and the lower piece  15  of the spacer expander  13 , the center portions in the circumferential direction of the outer circumferential-side end portions project axially to constitute projecting surfaces that form the side rail support portions  14   a  and  15   a , and the other portions (the portions other than the side rail support portions)  14   b  and  15   b  constitute the horizontal surfaces continuous from the inner circumferential side. 
         [0073]    As described above, in the combination oil ring  10  according to the present embodiment, the side rail support portions  14   a  and  15   a  of the spacer expander  13  are formed at the center portions in the circumferential direction of the outer circumferential-side end portions of the upper piece  14  and the lower piece  15 , so that spaces are formed between the upper piece  14  of the spacer expander  13  and the upper side rail  11 , and between the lower piece  15  of the spacer expander  13  and the lower side rail  12 , at the both side portions  14   b  and  15   b  of the side rail support portions  14   a  and  15   a  in the circumferential direction of the outer circumferential-side end portions. As a result, oil flows in from the spaces to form a flow of oil from the outer circumferential side to the inner circumferential side, and the oil containing sludge is easily discharged from the respective through holes  19  in the flange portions  17  and  18  of the spacer expander  13 , so that the side rails  11  and  12  and the spacer expander  13  can be prevented from sticking to each other due to deposits. 
         [0074]      FIGS. 12 and 13  show yet another embodiment of the present invention. The combination oil ring  10  according to the present embodiment differs from the combination oil ring according to the aforementioned embodiment described using  FIGS. 10 and 11  in the configuration of portions on the inner circumferential side from the side rail support portions  14   a  and  15   a  of the upper piece  14  and the lower piece  15  of the spacer expander  13  as described below, and the other configurations are the same as those in the aforementioned embodiment. 
         [0075]    In the present embodiment, in the outer circumferential-side end portions of the upper piece  14  and the lower piece  15  of the spacer expander  13 , the center portions in the circumferential direction also project axially outward to form the support portions  14   a  and  15   a  for the side rails  11  and  12 . That is, the center portion in the circumferential direction of the outer circumferential-side end portion of the upper piece  14  of the spacer expander  13  projects upward to form the support portion  14   a  for the side rail  11 , and the center portion in the circumferential direction of the outer circumferential-side end portion of the lower piece  15  projects downward to form the support portion  15   a  for the side rail  12 . 
         [0076]    However, in the present embodiment, the portions on the inner circumferential side from the side rail support portions  14   a  and  15   a  of the upper piece  14  and the lower piece  15  of the spacer expander  13  are configured as follows. That is, a groove  21  that extends linearly in the radial direction is formed in the portion on the inner circumferential side from the side rail support portion in each of a surface that is close to the side rail  11  of the upper piece  14  and a surface that is close to the side rail  12  of the lower piece  15  of the spacer expander  13 . The grooves  21  are formed by deforming predetermined portions of the upper piece  14  and the lower piece  15  into an arc shape in section by plasticity processing. Inner circumferential-side end portions of the grooves  21  in the upper piece  14  and the lower piece  15  communicate with the through holes  19  in the base portions of the flange portions  17  and  18 , respectively, and outer circumferential-side end portions are open to an external space so as to communicate with the external space. Reference numeral  22  denotes the opening. Although the sectional shape of the groove  21  is shown as an arc shape, the present invention is not limited thereto, and, for example, an inverted trapezoidal shape or a V shape may be also used. 
         [0077]    As described above, in the combination oil ring  10  according to the present embodiment, the side rail support portions  14   a  and  15   a  of the spacer expander  13  are formed at the center portions in the circumferential direction of the outer circumferential-side end portions of the upper piece  14  and the lower piece  15 , so that spaces are formed between the upper piece  14  of the spacer expander  13  and the upper side rail  11 , and between the lower piece  15  of the spacer expander  13  and the lower side rail  12 , at the both side portions  14   b  and  15   b  of the side rail support portions  14   a  and  15   a  in the circumferential direction of the outer circumferential-side end portions. As a result, oil flows in from the spaces to form a flow of oil from the outer circumferential side to the inner circumferential side, and the oil containing sludge is easily discharged from the respective through holes  19  in the flange portions  17  and  18  of the spacer expander  13 , so that the side rails  11  and  12  and the spacer expander  13  can be prevented from sticking to each other due to deposits. Moreover, in the present embodiment, the grooves  21  are formed in the upper piece  14  and the lower piece  15  of the spacer expander  13 , so that the sizes of the through holes  19  provided at the base portions of the flange portions  17  and  18  and facing the space portions between the side rails  11  and  12  and the spacer expander  13  can be formed larger by sizes corresponding to the grooves  21  than those of the flat surfaces with no groove; therefore, the deposits between the upper and lower pieces  14  and  15  of the spacer expander  13  and the side rails  11  and  12  are easily discharged from the through holes  19  in the flange portions  17  and  18  of the spacer expander  13 , and the side rails  11  and  12  and the spacer expander  13  can be prevented from sticking to each other due to the deposits. Also, since the grooves  21  extend in the radial direction and are open to the external space so as to communicate with the external space without being closed on the outer circumferential side, the oil flows in from the openings  22  to form a flow of oil from the outer circumferential side to the inner circumferential side; therefore, the deposits become difficult to accumulate and easily discharged from the through holes  19  in the flange portions  17  and  18 , so that the side rails  11  and  12  and the spacer expander  13  can be further prevented from sticking to each other due to the deposits. 
         [0078]      FIGS. 14 and 15  show yet another embodiment of the present invention. The combination oil ring  10  according to the present embodiment differs from the combination oil ring according to the aforementioned embodiment shown in  FIG. 7  in the configuration of portions on the inner circumferential side from the side rail support portions  14   a  and  15   a  of the upper piece  14  and the lower piece  15  of the spacer expander  13  as described below (also slightly differs in the configuration of the flange portions  17  and  18 ), and the other configurations are the same as those in the aforementioned embodiment. 
         [0079]    In the present embodiment, a gap between the upper piece  14  of the spacer expander  13  and the side rail  11 , and a gap between the lower piece  15  and the side rail  12  are continuously widened radially inward from the inner circumferential sides of the side rail support portions  14   a  and  15   a  to the base portions of the flange portions. 
         [0080]    That is, in the present embodiment, the upper piece  14  of the spacer expander  13  has an inclined piece portion  14   c  that separates away from the side rail  11  radially inward from the inner circumferential side of the side rail support portion  14   a  to the base portion of the flange portion  17 . Similarly, the lower piece  15  of the spacer expander  13  has an inclined piece portion  15   c  that separates away from the side rail  12  radially inward from the inner circumferential side of the side rail support portion  15   a  to the base portion of the flange portion  18 . 
         [0081]    Each of surfaces that are close to the side rails  11  and  12  of the flange portions  17  and  18  is composed of a lower end surface that stands vertically, and an inclined surface that extends upward therefrom so as to be inclined inward. 
         [0082]    The combination oil ring  10  according to the present embodiment further provides following effects in addition to the effects produced by the embodiment shown in  FIG. 7 . That is, since the gap between the upper piece  14  and the side rail  11  and the gap between the lower piece  15  and the side rail  12  of the spacer expander  13 , are continuously widened radially inward from the inner circumferential sides of the side rail support portions  14   a  and  15   a  to the base portions of the flange portions, sticking of the side rails  11  and  12  and the spacer expander  13  due to deposits can be suppressed. Also, since the upper piece  14  has the inclined piece portion  14   c  that separates away from the side rail  11  radially inward, oil containing sludge flows on the inclined surface of the upper piece  14  to be easily discharged from the through hole  19  in the flange portion  17 , so that the sticking of the side rail  11  and the spacer expander  13  due to the deposits can be suppressed. 
         [0083]      FIGS. 16 and 17  show yet another embodiment of the present invention. The combination oil ring  10  according to the present embodiment differs from the combination oil ring according to the aforementioned embodiment shown in  FIG. 7  in the configuration of portions on the inner circumferential side from the side rail support portions  14   a  and  15   a  of the upper piece  14  and the lower piece  15  of the spacer expander  13  as described below (also slightly differs in the configuration of the flange portions  17  and  18 ), and the other configurations are the same as those in the aforementioned embodiment. 
         [0084]    In the present embodiment, a gap between the upper piece  14  and the side rail  11  and a gap between the lower piece  15  and the side rail  12  of the spacer expander  13 , are discontinuously widened radially inward from the inner circumferential sides of the side rail support portions  14   a  and  15   a  to the base portions of the flange portions. 
         [0085]    In the present embodiment, the upper piece  14  of the spacer expander  13  has a stepped piece portion  14   d  that separates away from the side rail  11  radially inward from the inner circumferential side of the side rail support portion  14   a  to the base portion of the flange portion  17 . Similarly, the lower piece  15  of the spacer expander  13  has a stepped piece portion  15   d  that separates away from the side rail  12  radially inward from the inner circumferential side of the side rail support portion  15   a  to the base portion of the flange portion  18 . 
         [0086]    Each of surfaces that are close to the side rails  11  and  12  of the flange portions  17  and  18  is composed of a lower end surface that stands vertically, and an inclined surface that extends upward therefrom so as to be inclined inward. 
         [0087]    The combination oil ring  10  according to the present embodiment further provides following effects in addition to the effects produced by the embodiment shown in  FIG. 7 . That is, since the gap between the upper piece  14  and the side rail  11 , and the gap between the lower piece  15  and the side rail  12  of the spacer expander  13 , are discontinuously widened radially inward from the inner circumferential sides of the side rail support portions  14   a  and  15   a  to the base portions of the flange portions, sticking of the side rails  11  and  12  and the spacer expander  13  due to deposits can be suppressed. Also, since the upper piece  14  has the stepped piece portion  14   d  that separates away from the side rail  11  radially inward, oil containing sludge flows on the stepped piece portion  14   d  of the upper piece  14  to be easily discharged from the through hole  19  in the flange portion  17 , so that the sticking of the side rail  11  and the spacer expander  13  due to the deposits can be suppressed. 
         [0088]      FIG. 18  shows yet another embodiment of the present invention. The combination oil ring  10  according to the present embodiment differs from the combination oil ring according to the aforementioned embodiment shown in  FIGS. 14 and 15  in the configuration of portions on the inner circumferential side from the side rail support portions  14   a  and  15   a  of the upper piece  14  and the lower piece  15  of the spacer expander  13  as described below, and the other configurations are the same as those in the aforementioned embodiment. 
         [0089]    In the present embodiment, a groove  21  that extends linearly in the radial direction is formed in each of the inclined piece portions  14   c  and  15   c  from the inner circumferential sides of the inclined piece portions  14   c  and  15   c  to the base portions of the flange portions in the surface that is close to the side rail  11  of the upper piece  14  and the surface that is close to the side rail  12  of the lower piece  15  of the spacer expander  13 . The grooves  21  are formed by deforming predetermined portions of the inclined piece portions  14   c  and  15   c  of the upper piece  14  and the lower piece  15  into an arc shape in section by plasticity processing. Inner circumferential-side end portions of the grooves  21  in the upper piece  14  and the lower piece  15  communicate with the through holes  19  in the base portions of the flange portions  17  and  18 , respectively, and outer circumferential-side end portions are open to an external space so as to communicate with the external space. Reference numeral  22  denotes the opening. Although the sectional shape of the groove  21  is shown as an arc shape, the present invention is not limited thereto, and, for example, an inverted trapezoidal shape or a V shape may be also used. 
         [0090]    The combination oil ring  10  according to the present embodiment further provides following effects in addition to the effects produced by the aforementioned embodiment shown in  FIGS. 14 and 15 . That is, the grooves  21  are formed in the upper piece  14  and the lower piece  15  of the spacer expander  13 , so that the sizes of the through holes  19  provided at the base portions of the flange portions  17  and  18  and facing the space portions between the side rails  11  and  12  and the spacer expander  13  can be formed larger by sizes corresponding to the grooves  21  than those of the flat surfaces with no groove; therefore, the deposits between the upper and lower pieces  14  and  15  of the spacer expander  13  and the side rails  11  and  12  are easily discharged from the through holes  19  in the flange portions  17  and  18  of the spacer expander  13 , and the sticking of the side rails  11  and  12  and the spacer expander  13  due to the deposits can be suppressed. Also, since the grooves  21  extend in the radial direction and are open to the external space so as to communicate with the external space without being closed on the outer circumferential side, the oil flows in from the openings  22  to form a flow of oil from the outer circumferential side to the inner circumferential side; therefore, the deposits become difficult to accumulate and easily discharged from the through holes  19  in the flange portions  17  and  18 , so that the sticking of the side rails  11  and  12  and the spacer expander  13  due to the deposits can be further suppressed. 
         [0091]      FIG. 19  shows yet another embodiment of the present invention. The combination oil ring  10  according to the present embodiment differs from the combination oil ring according to the aforementioned embodiment shown in  FIGS. 16 and 17  in the configuration of portions on the inner circumferential side from the side rail support portions  14   a  and  15   a  of the upper piece  14  and the lower piece  15  of the spacer expander  13  as described below, and the other configurations are the same as those in the aforementioned embodiment. 
         [0092]    In the present embodiment, a groove  21  that extends linearly in the radial direction is formed in each of the stepped piece portions  14   d  and  15   d  from the inner circumferential sides of the side rail support portions  14   a  and  15   a  to the base portions of the flange portions in the surface that is close to the side rail  11  of the upper piece  14  and the surface that is close to the side rail  12  of the lower piece  15  of the spacer expander  13 . The grooves  21  are formed by deforming predetermined portions of the stepped piece portions  14   d  and  15   d  of the upper piece  14  and the lower piece  15  into an arc shape in section by plasticity processing. While inner circumferential-side end portions of the grooves  21  in the first stepped piece portions  14   d  and  15   d  of the upper piece  14  and the lower piece  15  are open, and outer circumferential-side end portions are open to an external space so as to communicate with the external space, inner circumferential-side end portions of the grooves  21  in the second stepped piece portions  14   d  and  15   d  communicate with the through holes  19  in the base portions of the flange portions  17  and  18 , respectively, and outer circumferential-side end portions are open to the external space so as to communicate with the external space. Reference numeral  22  denotes the respective openings. Although the sectional shape of the groove  21  is shown as an arc shape, the present invention is not limited thereto, and, for example, an inverted trapezoidal shape or a V shape may be also used. 
         [0093]    The combination oil ring  10  according to the present embodiment further provides following effects in addition to the effects produced by the embodiment shown in  FIGS. 16 and 17 . That is, the grooves  21  are formed in the upper piece  14  and the lower piece  15  of the spacer expander  13 , so that the sizes of the through holes  19  provided at the base portions of the flange portions  17  and  18  and facing the space portions between the side rails  11  and  12  and the spacer expander  13  can be formed larger by sizes corresponding to the grooves  21  than those of the flat surfaces with no groove; therefore, the deposits between the upper and lower pieces  14  and  15  of the spacer expander  13  and the side rails  11  and  12  are easily discharged from the through holes  19  in the flange portions  17  and  18  of the spacer expander  13 , and the sticking of the side rails  11  and  12  and the spacer expander  13  due to the deposits can be suppressed. Also, since the grooves  21  extend in the radial direction and are open to the external space so as to communicate with the external space without being closed on the outer circumferential side, the oil flows in from the openings  22  to form a flow of oil from the outer circumferential side to the inner circumferential side; therefore, the deposits become difficult to accumulate and easily discharged from the through holes  19  in the flange portions  17  and  18 , so that the sticking of the side rails  11  and  12  and the spacer expander  13  due to the deposits can be further suppressed. 
         [0094]    Although the shape of the side rail support portions  14   a  and  15   a  is shown as a trapezoidal shape (e.g., see  FIG. 20 ) as viewed from the radial direction in the aforementioned embodiments, the present invention is not limited thereto, and the side rail support portions  14   a  and  15   a  may be also formed in, for example, a semi-elliptical shape (e.g., see  FIG. 21 ) or a rectangular shape. 
         [0095]    Also, although the side rail support surfaces of the side rail support portions  14   a  and  15   a  are formed as flat surfaces in the aforementioned embodiments, the present invention is not limited thereto. A behavior during engine operation is stabilized by radially forming the side rail support surfaces as, for example, tapered surfaces (e.g., see  FIG. 22 ) or arc surfaces (e.g., see  FIG. 23 ), and supporting the side rails  11  and  12  at the outer circumferential-side end portions. 
         [0096]    Also, as shown in  FIG. 24 , when a circumferential width of the side rail support portion  14   a  of the upper piece  14  is X and a circumferential width of the upper piece  14  is Y, it is preferable to satisfy the relationship of 0&lt;X/Y≦0.7. The same applies to the lower piece  15 . 
         [0097]    Also, as shown in  FIG. 25 , when an axial projecting height of the side rail support portion  14   a  of the upper piece  14  is “a” and an axial width on the side of the flange portions  17  and  18  of the spacer expander  13  is “b”, it is preferable to satisfy the relationship of 0.02&lt;a/b≦0.2. The same applies to the lower piece  15 . 
         [0098]    Also, as shown in  FIG. 26 , when an axial distance from the base positions of the flange portions  17  and  18  of the spacer expander  13  to the side rails  11  and  12  is “c” and an axial width of the outer circumferential-side end portion of the spacer expander  13  is “d”, it is preferable to satisfy the relationship of c≧0.1 mm and c/d=0.04 to 0.3. 
         [0099]    If c/d is less than 0.04, the oil containing sludge becomes difficult to discharge from the through holes in the flange portions. If c/d is more than 0.3, the thickness of the spacer expander around the through holes in the flange portions becomes small. 
         [0100]    The spacer expander  13  described above is formed by plasticity processing. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  . . . Cylinder 
           2  . . . Piston 
           3  . . . Piston outer circumferential surface 
           4  . . . Oil ring groove 
           10  . . . Combination oil ring 
           11 ,  12  . . . Side rail 
           13  . . . Spacer expander 
           14  . . . Upper piece 
           15  . . . Lower piece 
           14   a ,  15   a  . . . Side rail support portion 
           14   b ,  15   b  . . . Portion other than the side rail support portion 
           14   c ,  15   c  . . . Inclined piece portion 
           14   d ,  15   d  . . . Stepped piece portion 
           16  . . . Coupling piece 
           17 ,  18  . . . Flange portion 
           19  . . . Through hole 
           20  . . . Through hole 
           21  . . . Groove 
           22  . . . Opening