Patent Publication Number: US-2016238066-A1

Title: Rolling bearing and a mechanical system comprising such a rolling bearing

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a Non-Provisional Patent Application, filed under the Paris Convention, claiming the benefit of Europe (EP) Patent Application Number 15305227.9, filed on 16 Feb. 2015 (16.02.2015), which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD OF THE INVENTION 
     The invention concerns a rolling bearing, adapted for mounting on a balancing shaft. The invention also concerns a mechanical system, for example a vehicle engine, comprising a balancing shaft and such a rolling bearing. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 3,384,429 discloses an example of needle rolling bearing, comprising an outer ring, a cage and needles mounted in pockets of the cage. The rolling bearing also comprises thrust rings detachably secured on both sides of the outer ring. The rolling bearing is mounted on a shaft, with the thrust rings disposed in bearing contact against a thrust collar and a shoulder of the shaft. 
     In practice, downsizing of a mechanical system allows to reduce its weight and cost. In some applications, for example when the mechanical system includes a balancing shaft, it is interesting to further reduce friction and power losses. 
     SUMMARY OF THE INVENTION 
     The aim of the invention is to provide an improved rolling bearing, providing the advantages here-above. 
     To this end, the invention concerns a rolling bearing, adapted for mounting on a balancing shaft and comprising: an outer ring having a cylindrical outer surface and a cylindrical inner surface centered on a central axis, and two annular lateral surfaces extending radially to the central axis and defining a ring width parallel to the central axis; a cage having pockets distributed around the central axis and two annular lateral surfaces extending radially to the central axis and defining a cage width parallel to the central axis; and rolling members mounted in the pockets of the cage and disposed in rolling contact with the inner surface of the outer ring. According to the invention, the cage width is superior or equal to the ring width. 
     Thanks to the invention, the radial load capacity of the rolling bearing is increased. The cage protrudes axially on at least one side of the outer ring, preferably on both sides of the outer ring. The cage can be centered between radial parts belonging or mounted on the shaft, reducing the shocks and vibrations due to axial cage displacements. Thus, the rolling bearing mounted on a balancing shaft allows a reduction of weight, friction and power losses, while providing a robust arrangement. 
     According to further aspects of the invention which are advantageous but not compulsory, such a rolling bearing may incorporate one or several of the following features:
         The cage width is superior to the ring width.   The cage width is equal to the ring width.   The cage protrudes axially beyond at least one lateral surface of the outer ring.   The cage protrudes axially beyond both lateral surfaces of the outer ring.   An axial overstepping is defined parallel to the central axis on at least one side of the outer ring, from the lateral surface of the outer ring up to the lateral surface of the cage, the axial overstepping being comprised between 0.2 and 3 millimeters, and preferably between 0.2 and 0.5 millimeter.   Axial oversteppings are defined on both sides of the outer ring.   The rolling members are needles or rollers extending parallel to the central axis.       

     The invention also concerns a mechanical system, for example a vehicle engine, comprising: a balancing shaft having a axial part centered on the central axis and at least one radial part extending radially to the central axis; a second member secured to the balancing shaft; a housing which is located between the radial part and the second member and which comprises two annular lateral surfaces extending radially to the central axis and defining a housing width parallel to the central axis; and a rolling bearing as defined here-above, the outer ring being mounted in the housing, the rolling members being disposed in rolling contact with the axial part of the balancing shaft, the radial part and the second member forming axial guidance means for the cage disposed therebetween, the cage width being superior to the housing width. 
     According to further aspects of the invention which are advantageous but not compulsory, such a mechanical system may incorporate one or several of the following features:
         The ring width is superior or equal to the housing width.   The ring width is equal to the housing width.   The ring width is superior to the housing width.   An axial clearance is defined parallel to the central axis on at least one side of the cage, from the lateral surface of the cage up to the lateral surface of the radial part or of the second member, the axial clearance being inferior or equal to 0.5 millimeters, preferably equal to 0.3 millimeters.   Axial clearances are defined on both sides of the cage.   The second member is another radial part formed integral with the balancing shaft.   The second member is an unbalanced part, for example a cam or a flying arm, which is formed eccentric relative to the central axis.   The radial part is an unbalanced part, for example a cam or a flying arm, which is formed eccentric relative to the central axis.   The balancing shaft is a camshaft and the unbalanced parts are cams.   The balancing shaft is a crankshaft and the unbalanced parts are flying arms supporting crankpins.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be explained in correspondence with the annexed figures, and as an illustrative example, without restricting the object of the invention. In the annexed figures: 
         FIG. 1  is a sectional view of a mechanical system according to the invention, equipped with a rolling bearing also according to the invention; 
         FIG. 2  is a sectional view, at a larger scale, showing detail II of  FIG. 1 ; 
         FIG. 3  is a sectional view similar to  FIG. 1 , showing a mechanical system according to the invention, equipped with a second embodiment of a rolling bearing according to the invention; and 
         FIG. 4  is a sectional view, at a larger scale, showing detail IV of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF SOME EMBODIMENTS 
       FIGS. 1 and 2  partly show a mechanical system  1  according to the invention, for example a vehicle engine. 
     System  1  comprises a balancing shaft  2  including an axial part  3  and a radial part  4 , a gear  6  secured to shaft  2  by a screw  7 , and a housing  8  located between radial part  4  and gear  6 . In the present case, radial part  4  is a counterweight or unbalanced mass. A lateral surface  43  of radial part  4  and a lateral surface  64  of gear  6  are facing each other. Housing  8  comprises a cylindrical inner bore  82  and two lateral surfaces  83  and  84  defining a housing width w 8 . 
     Moreover, system  1  comprises a rolling bearing  10  also defined according to the invention. Rolling bearing  10  is mounted on axial part  3  of shaft  2  and in bore  82  of housing  8 , between surface  43  of radial part  4  and surface  64  of gear  6 . Rolling bearing  10  is centered on a central axis X 10  and comprises rolling members  12 , an outer ring  20  and a cage  30 . Rolling members  12  are needles or rollers extending parallel to axis X 10 . Part  4  and gear  6  form axial guidance means for rolling bearing  1 , in particular axial guidance means for cage  30  disposed therebetween. 
     As shown on  FIG. 1 , constitutive elements of system  1  are also centered on axis X 10 . In the context of the invention, “axially” means parallel to axis X 10 , while “radially” means perpendicular to axis X 10 . 
     Outer ring  20  has a cylindrical outer surface  21  and a cylindrical inner surface  22  centered on axis X 10 . Surface  21  is fitted in bore  82 , while surface  22  is in rolling contact with rolling members  12 . Outer ring  20  also has two annular lateral surfaces  23  and  24  extending radially to axis X 10 . Outer ring  20  has a ring width w 20  defined parallel to axis X 10  between lateral surfaces  23  and  24 . 
     Cage  30  is radially spaced from outer ring  20 . Cage  30  is in contact with axial part  3  and with a corner  45  formed between parts  3  and  4  of shaft  2 . Cage  30  has an inner surface  32  in contact with axial part  3 . Cage  30  has two annular lateral surfaces  33  and  34  extending radially to axis X 10 . Surface  33  faces surface  43 , while surface  34  faces surface  64 . Part  4  and gear  6  form axial guidance means for cage  30  disposed therebetween. Cage  30  comprises pockets  38  distributed around axis X 10 . Cage  30  has a cage width w 30  defined parallel to axis X 10  between lateral surfaces  33  and  34 . Rolling members  12  are mounted in pockets  38  and disposed in rolling contact, on the one hand, with inner surface  22  of outer ring  20  and, on the other hand, with axial part  3  of shaft  2 . 
     As shown on  FIGS. 1 and 2 , cage width w 30  is superior to ring width w 20 . More precisely, cage  30  protrudes axially on both sides of outer ring  20 . 
     Besides, in the example of  FIGS. 1 and 2 , widths w 8  and w 20  are substantially equal. Surface  23  is aligned with surface  83 , while surface  24  is aligned with surface  84 , radially to axis X 10 . 
     Parallel to axis X 10 , several distances a 3 , b 3 , c 3  are defined on a first side of bearing  10  near surfaces  23 ,  33  and  43 , while several distances a 4 , b 4 , c 4  are defined on a second side of bearing  10  near surfaces  24 ,  34  and  64 . An axial overstepping a 3  is defined from surface  23  up to surface  33 . An axial clearance b 3  is defined from surface  23  up to surface  43 . An axial clearance c 3  is defined from surface  33  up to surface  43 . An axial overstepping a 4  is defined from surface  24  up to surface  34 . An axial clearance b 4  is defined from surface  24  up to surface  64 . An axial clearance c 4  is defined from surface  34  up to surface  64 . 
     Axial oversteppings a 3  and a 4  are for example comprised between 0.2 and 3 millimeters, and preferably between 0.2 and 0.5 millimeter. In other words, cage  30  protrudes axially beyond at least one lateral surface  23  or  24  of outer ring  20  and beyond corresponding lateral surface  83  or  84  of housing  8 . Preferably, as shown on  FIGS. 1 and 2 , cage  30  protrudes beyond both lateral surfaces  23  and  24  of outer ring  20  and beyond both corresponding lateral surfaces  83  and  84  of housing  8 . 
     Axial clearances c 3  and c 4  are inferior or equal to 0.5 millimeters, preferably equal to 0.3 millimeters. The cage is centered between part  4  and gear  6 , thus reducing the shocks and vibrations due to axial cage displacements. In operation, the axial movement of cage  30  is stopped either by surface  43  of radial part  4  on one side or by surface  64  of gear  6  on the other side. 
       FIGS. 3 and 4  show mechanical system  1  equipped with a second embodiment of a rolling bearing  10  according to the invention, comprising an outer ring  120  having a ring width w 120  substantially equal to cage width w 30 . Surface  23  is aligned with surface  33 , while surface  24  is aligned with surface  34 , radially to axis X 10 . Otherwise, mechanical system  1  and rolling bearing  10  are similar to the first embodiment and their constitutive elements have the same numerical references. 
     Besides, ring width w 120  is superior to housing width w 8 . Outer ring  120  and cage  30  protrude axially on both sides of housing  8 . 
     Parallel to axis X 10 , several distances b 3 , c 3 , d 3  are defined on a first side of bearing  10  near surfaces  23 ,  33  and  43 , while several distances b 4 , c 4 , d 4  are defined on a second side of bearing  10  near surfaces  24 ,  34  and  64 . An axial clearance b 3  is defined from surface  23  up to surface  43 . An axial clearance c 3  is defined from surface  33  up to surface  43 . An axial overstepping d 3  is defined from surface  83  up to surface  23 . An axial clearance b 4  is defined from surface  24  up to surface  64 . An axial clearance c 4  is defined from surface  34  up to surface  64 . An axial overstepping d 4  is defined from surface  84  up to surface  24 . 
     In the examples of  FIGS. 3 and 4 , axial clearances b 3  and c 3  are equal to each other, while axial clearances b 4  and c 4  are equal to each other. Axial clearances b 3 , c 3 , b 4  and c 4  are inferior or equal to 0.5 millimeters, preferably equal to 0.3 millimeters. In operation, the axial movement of cage  30  is stopped either by surface  43  of radial part  4  on one side or by surface  64  of gear  6  on the other side. 
     Axial oversteppings d 3  and d 4  are for example comprised between 1.5 and 10 millimeters, and preferably between 2 and 5 millimeters. In other words, outer ring  120  and cage  30  protrude axially beyond at least one lateral surface  83  or  84  of housing  8 . Preferably, as shown on  FIGS. 3 and 4 , axial overstepping d 3  and d 4  are defined on both sides of housing  8 . In other words, outer ring  120  and cage  30  protrude beyond both lateral surfaces  83  and  84  of housing  8 . 
     Other non-shown embodiments can be implemented within the scope of the invention. In particular, shaft  2 , housing  8  and rolling bearing  10  can have different shapes or arrangements within the scope of the invention. 
     According to a non-shown embodiment, member  6  can be a radial part formed integral with shaft  2 . 
     According to another non-shown embodiment, part  4  and/or member  6  is an unbalanced part, for example a cam or a flying arm, which is formed eccentric relative to axis X 10 . 
     According to a particular embodiment, shaft  2  is a camshaft and unbalanced parts  4  and  6  are cams. 
     According to another particular embodiment, shaft  2  is a crankshaft and unbalanced parts  4  and  6  are flying arms supporting crankpins. 
     According to another non-shown embodiment, an axial overstepping a 3  or a 4  is defined on only one side of cage  30 . 
     According to another non-shown embodiment, an axial overstepping d 3  or d 4  is defined on only one side of housing  8 . 
     Whatever the embodiment of the invention, the cage width w 30  is superior or equal to the ring width w 20 /w  120 . 
     In addition, technical features of the different embodiments can be, in whole or part, combined with each other. Thus, the mechanical system  1  and/or the rolling bearing  10  can be adapted to the specific requirements of the application.