Abstract:
A cage for a bearing for electric steering for a motor vehicle. The cage is designed to provide circumferential spacing of a row of roller elements, including an annular heel axially extended by separating portions that define cavities for the roller elements therebetween. The cavities radially extending from either side of the cage. The inner diameter of the separating portions is greater than the inner diameter of the annular heel.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a National Stage Application claiming the benefit of International Application Number PCT/EP2013/066981 filed on 14 Aug. 2013 (14.08.2013), which claims the benefit of French Patent Application Serial Number 1257933, filed on 22 Aug. 2012 (22.08.2012), both of which are incorporated herein by reference in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to the field of rolling bearings, notably the rolling bearings used in motor vehicle electric power steering. 
         [0003]    More specifically, the invention relates to the retention cages which ensure a circumferential spacing between rolling elements of rolling bearings. 
       BACKGROUND OF THE INVENTION 
       [0004]    A motor vehicle electric power steering generally comprises an electromechanical actuator situated on the steering column or on the lower assembly which comprises mechanical components intended to ensure the angular positioning of the steered wheels of the vehicle. The electromechanical actuator comprises a rotary electric motor the shaft of which is supported by at least one four-point contact ball bearing device either directly, or via a ball screw system. 
         [0005]    The rolling bearing generally comprises an inner ring, an outer ring and a row of rolling elements, generally balls, which is arranged between the rings. 
         [0006]    Rolling-bearing ball-retaining cages made of synthetic material, comprising pockets to house the balls, are known from document FR 2 921 451. The pockets are separated by claws arranged in pairs, on the opposite side to a heel extended axially by a dividing portion having an inside diameter substantially equal to the inside diameter of the heel, so that in cross-section it forms an L-shape. Such retaining cages are entirely satisfactory in many applications. However, in applications involving low rotational speed or those in which the direction of rotation reverses sharply, this kind of cage runs into various difficulties. Specifically, under the effect of the loading of the balls, the cage may suffer extensive deformation and come into contact with the inner ring, causing it to become damaged or even destroyed. 
         [0007]    In addition, when the direction in which the load is applied to the rolling bearing changes, as it does for example when the wheels of a vehicle equipped with an electric power steering system as described hereinabove are turned as the driver maneuvers to the left and to the right in order to park the vehicle, the cage is likewise severely deformed, or even destroyed. 
         [0008]    Finally, the centrifugal force as the rolling bearing rotates throws the lubricant contained in the rolling bearing outward. Such cages are unable to retain the lubricant. 
         [0009]    Reference may also be made to documents FR 2 900 996 and FR 2 911 934 which describe a rolling-bearing cage for high-speed applications, the dividing portion of which is likewise L-shaped. However, when the rolling bearing is used at low speed, the L shape of the dividing portion would come into contact with the inner ring and this would cause it to become damaged or even destroyed. 
         [0010]    This is because when a cage is used at low speed, the cage deforms inward when it comes into a zone of axial and radial load. The cage is therefore subjected to torsion forces and severe banking, notably when the rolling bearing slows down suddenly, causing the rolling element to press suddenly against the pocket in which it is housed. 
         [0011]    The present invention therefore seeks to overcome these disadvantages. 
         [0012]    More particularly, the present invention seeks to provide a rolling bearing cage for low-speed applications that is not very deformable, is of restricted size, and provides good distribution of stress across the cage. 
         [0013]    The present invention also seeks to provide a cage that allows the lubricant present in the rolling bearing to be recovered. 
       SUMMARY OF THE INVENTION 
       [0014]    One subject of the invention is a motor vehicle electric power steering rolling bearing cage intended to ensure the circumferential spacing of a row of rolling elements, comprising an annular heel extended axially by dividing portions between them defining pockets for the rolling elements opening radially on either side of the cage. 
         [0015]    The inside diameter of the dividing portions is greater than the inside diameter of the annular heel. 
         [0016]    Thus, as the dividing portions have an inside diameter greater than the inside diameter of the heel they are not made to come into contact with the inner ring, as the rolling bearing rotates. The cage therefore has an extended life. In addition, the lubricant present in the rolling bearing is recovered by the dividing portions so that it can be distributed to the rolling elements. 
         [0017]    Advantageously, the outside diameter of the dividing portions is less than or equal to the outside diameter of the annular heel. Thus, the cage in cross section has a gamma “Γ” or “T” shape. 
         [0018]    According to one embodiment, the cage comprises at least one first pocket provided with axial retention means for retention of the cage on a rolling element. 
         [0019]    The dividing portions situated between two adjacent first pockets may comprise two claws the free end of which extends in the circumferential direction toward the claw of the adjacent dividing portion to form one of the first pockets. 
         [0020]    According to another embodiment, the cage comprises a plurality of second pockets that do not have axial retention means for retention of the cage on a rolling element. 
         [0021]    Advantageously, the dividing portions situated between a first pocket and a second pocket comprise a claw the free end of which extends in the circumferential direction toward the claw of the adjacent dividing portion to form one of the first pockets and a cylindrical protuberance forming, with the cylindrical protuberance of the adjacent dividing portion, one of the second pockets. 
         [0022]    According to one embodiment, the dividing portions comprise a recess made on the internal face of the dividing portion. 
         [0023]    The annular heel may have an opening in the thickness of the heel opening axially between a face of the heel which is the opposite face to the rolling elements, and the recess of the dividing portions. 
         [0024]    The presence of an opening in the heel and in the dividing portion allows the cage to be mounted more easily on the rolling elements, thanks to the increase in the flexibility of the dividing portions. In addition, the weight and the cost of manufacture are less. 
         [0025]    The first pockets are, for example, provided with substantially spherical walls and the second pockets are, for example, provided with substantially cylindrical walls. 
         [0026]    The cage may be made of synthetic material, preferably a polymer material. 
         [0027]    A second aspect of the invention relates to a rolling bearing comprising an outer ring, an inner ring each one comprising at least one raceway, a row of rolling elements which are arranged between the raceways and a cage as described hereinabove. 
         [0028]    The rolling elements may be balls. 
         [0029]    A third aspect of the invention relates to an electric power steering comprising at least one rolling bearing as described hereinabove. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    The present invention will be better understood from reading the description of some embodiments which are given by way of entirely nonlimiting examples and illustrated by the attached drawings in which: 
           [0031]      FIG. 1  is a perspective view of a rolling bearing according to a first embodiment of the invention; 
           [0032]      FIG. 2  is a view in cross section of the rolling bearing according to  FIG. 1 ; 
           [0033]      FIG. 3  is a perspective view of a cage according to  FIG. 1 ; 
           [0034]      FIG. 4  is a perspective view of a cage according to a second embodiment of the invention; 
           [0035]      FIG. 5  is a perspective view, from the rear, of the cage according to  FIG. 4 ; 
           [0036]      FIG. 6  is a view in cross section of a rolling bearing according to a third embodiment of the invention; 
           [0037]      FIG. 7  is a perspective view of a cage according to a fourth embodiment of the invention; and 
           [0038]      FIGS. 8 and 9  are views in section of a rolling bearing comprising a cage according to  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0039]    The rolling bearing, of axial axis X-X, referenced  1  overall in  FIGS. 1 and 2 , is intended to be mounted in a motor vehicle steering column. 
         [0040]    As  FIGS. 1 and 2  illustrate, the rolling bearing  1  comprises an outer ring  2 , an inner ring  3 , a row of rolling elements  4 , in this instance produced in the form of balls, a cage  5  for maintaining the even circumferential spacing of the rolling elements  4 . 
         [0041]    The outer ring  2  and inner ring  3  are solid, what is meant by a “solid ring” is a ring the shape of which is obtained by machining with the removal of chips (turning, grinding) from tubes, bar stock, forged and/or rolled blanks. 
         [0042]    The outer ring  2  comprises, at its bore, a deep-groove raceway  2   a  having, in cross section, a concave internal profile suited to the rolling elements  4 , the raceway  2   a  facing radially inward. The inner ring  3  also comprises, on its cylindrical outer surface, a deep-groove raceway  3   a  which in cross section has a concave internal profile suited to the rolling elements  4 , the raceway  3   a  being directed radially outward. The cage  5  is arranged radially between the outer surface of the inner ring  3  and the bore of the outer ring  2 . 
         [0043]    The inner and outer rings  3 ,  2  have radial frontal surfaces  3   b,    3   c,    2   b,    2   c  that are substantially aligned and may each be produced as one by machining from a piece of steel. 
         [0044]    As visibly illustrated in  FIGS. 2 and 3 , the cage  5  comprises an annular portion  6  designed to be positioned axially on one side of the rolling elements  4  and that forms an annular heel, and dividing portions  7  or dividing fingers extending axially from the annular heel  6 . The dividing portions  7  are as one with the annular heel  6  and between them delimit pockets  8  in which the rolling elements  4  are positioned and have a spherical overall shape that tends to envelop the associated rolling elements. 
         [0045]    The dividing portions  7  take the form of pegs projecting axially with respect to the annular heel  6 . The dividing portions  7  are delimited in the circumferential direction by lateral walls which define the pockets  8 . The diameter of the cylinder defining the walls of each pocket  8  is greater than that of the rolling elements so that the rolling elements can be offered clearance in which to move radially and circumferentially with respect to the pockets  8 . Each pocket  8  is open radially toward the inside and toward the outside and open axially on the opposite side to the annular heel  6  in order to allow the cage  5  to be fitted. 
         [0046]    In the example illustrated in  FIGS. 1 to 3 , the dividing portion  7  has an inside diameter greater than the inside diameter of the annular heel  6 , and an outside diameter substantially equal to the outside diameter of the annular heel  6 , having in cross section the shape of an omega. Thus, at high levels of banking, the dividing portion  7  deforming toward the inside does not come into contact with the inner ring  3 . In addition, the lubricant that has a tendency to flow toward the outside of the rolling bearing is retained radially by the dividing portion  7  of the cage  5 . 
         [0047]    Each dividing portion  7  comprises a claw  8   a  directed radially away from the annular heel  6  and the free end of which extends in the circumferential direction toward the claw  8   a  of the adjacent dividing portion  7  in order to form one of the substantially spherically shaped pockets  8  that tend to envelop a ball  4 . The claws  8   a  form means of axial retention of the cage  5  on the rolling elements  4 . The cage  5  comprises a connection  5   a  situated at the base of the dividing portion  7  and forms an interface between the annular heel  6  and the dividing portion  7 . The connection  5   a  in cross section has a rounded profile. 
         [0048]    The embodiment illustrated in  FIGS. 4 and 5 , in which the same elements bear the same references, differs from the embodiment illustrated in  FIGS. 1 to 3  through the presence of a recess  7   a  made on the internal face of the dividing portion  7 , not opening radially to the outside. As an alternative, provision could be made for the recess  7   a  to open radially on each side of the cage  5 . The annular heel  6  has an opening  6   a  in the thickness of the heel  6 , opening axially between a face of the heel  6  which is the opposite face to the rolling elements  4 , and the recess  7   a  of the dividing portions  7 . As illustrated, the opening  6   a  is circumferential and is delimited radially between an outer part  6   b  of the heel  6  and an inner part  6   c  of the heel  6 . As an alternative, the opening could be situated locally so as to open into the recess  7   a  of each dividing portion  7 . 
         [0049]    The embodiment illustrated in  FIG. 6 , in which the same elements bear the same references, differs from the embodiment illustrated in  FIGS. 1 to 5  through the shape of the cage. 
         [0050]    The cage  10  illustrated in  FIG. 6  comprises an annular portion  11  arranged axially on one side of the rolling elements  4 , forming an annular heel, and dividing portions  12  or dividing fingers extending axially from the annular heel  11 . The dividing portions  12  are of one piece with the annular heel  11  and between them delimit pockets  13  in which the rolling elements  4  are arranged. The dividing portion  12  has an inside diameter greater than the inside diameter of the annular heel  11 , and an outside diameter smaller than the outside diameter of the annular heel  11 , in cross section having the shape of “T”. Thus, under steep banking, the dividing portion  12  deforming toward the inside does not come into contact with the inner ring  3 . In addition, the lubricant, which has a tendency to flow toward the outside of the rolling bearing, is retained radially by the dividing portion  12  of the cage  10   
         [0051]    Each dividing portion  12  comprises a claw  12   a  directed radially away from the annular heel  11  and the free end of which extends in the circumferential direction toward the claw  12   a  of the adjacent dividing portion  12  to form one of the pockets  13  of substantially spherical shape that tend to envelop a ball  4 . The claws  12   a  form axial retention means for the axial retention of the cage  10  on the rolling elements  4 . The cage  10  comprises a connection  10   a  situated at the base of the dividing portion  12  and forms an interface between the annular heel  11  and the dividing portion  12  and in cross section has a rounded profile. 
         [0052]    The embodiment illustrated in  FIGS. 7 to 9 , in which the same elements bear the same references, differs from the embodiment illustrated in  FIGS. 1 to 5  through the shape of the cage. 
         [0053]    The cage  15  comprises a plurality of first pockets  16  provided with axial retention means for the axial retention of the cage  15  on a rolling element  4  and a plurality of second pockets  17  which do not have axial retention means for the axial retention of the cage  15  on a rolling element  4 . Each first pocket  16  is separated from a first pocket  16  by a second pocket  17 . As an alternative, provision could be made for a plurality of first pockets  16  to follow on in succession and for the plurality of first pockets  16  to be separated from a first pocket  16  by a plurality of second pockets  17 . The first pockets  16  are provided with substantially spherical walls and the second pockets  17  are provided with substantially cylindrical walls. A first pocket  16  is separated from an adjacent second pocket by a hybrid dividing portion  18  extending axially from an annular heel  19  arranged on one side of the rolling elements  4 . The first pockets  16  are evenly distributed in the circumferential direction to ensure even axial retention of the cage  15  on the rolling elements  4 . 
         [0054]    The hybrid dividing portions  18  take the form of fingers or pegs projecting axially from the annular heel  19  and each having on one side in the circumferential direction a lateral wall  16   a  that is substantially spherical in order with an adjacent hybrid dividing portion  18  to form one of the first pockets  16  near a second pocket  17  and on the other side has a cylindrical wall  17   a  connecting to the cylindrical wall of the adjacent hybrid dividing portion  18  in order to form a second pocket  17 . 
         [0055]    Each hybrid dividing finger  18  comprises a claw  18   a  extending axially away from the annular heel  19  and the free end of which extends in the circumferential direction toward the opposite claw  18   a  of the adjacent hybrid dividing portion  18  to delimit the same first pocket  16 . The concave interior surface of each claw  18   a  forms part of the spherical wall  16   a  of the pocket  16 . The two claws  18   a  associated with a first pocket  16  extend toward one another, their free ends being spaced apart by a distance smaller than the diameter of the rolling elements  4 . The claws  18   a  of a pocket  16  are capable of ensuring the axial retention of the cage  15  by clip-fastening onto the rolling element  4  arranged in the pocket  16 . The cage  15  is retained axially on the row of rolling elements by the claws  18   a.    
         [0056]    Each hybrid dividing portion  18  also comprise an axial protuberance  18   b  of cylindrical shape extending axially away from the annular heel  19 . The protuberance  18   b  of each hybrid dividing portion  18  delimits in part, with the protuberance  18   b  of the adjacent dividing portion  18 , one of the second pockets  17  that does not have axial retention means. Each protuberance  18   b  is unable to provide axial retention of the cage  15  in relation to the rolling element  4  arranged in the second pocket  17  next to the first pocket  16 . The cylindrical interior surface of the cylindrical protuberance  18   b  forms part of the cylindrical surface  17   a  of the second pocket  17 . 
         [0057]    The claw  18   a  and the protuberance  18   b  of each hybrid separation portion  18  are separated in the circumferential direction by a recess  18   c  so that the claw  18   a  has a relatively small circumferential thickness and a certain degree of flexibility allowing the cage  15  to be clip-fastened onto the rolling elements  4  through a circumferential parting of the claws  18   a  when an axial thrust is applied to the annular heel  19  of the cage  5  in the direction of the rolling elements  4 . Each first pocket  16  is open radially toward the inside and towards the outside and is also open axially on the opposite side to the annular heel  19  in order to allow the cage  15  to be fitted. 
         [0058]    As an alternative, when two first pockets  16  are adjacent, a first dividing finger comprising two claws  18   a  extending in opposite circumferential directions could be provided and when two second pockets  17  are adjacent, a second dividing finger comprising two cylindrical protuberances  18   b  could be provided. 
         [0059]    As illustrated in  FIGS. 8 and 9 , the dividing portion  18  in cross section has the shape of a gamma the outside diameter of which is substantially identical to the outside diameter of the annular heel  19  and the inside diameter of which is greater than the inside diameter of the annular heel  19 . 
         [0060]    In all the embodiments illustrated, the cage is advantageously made as a single piece, for example made of a synthetic material, preferably a polymer material, such as for example PA66, PA46, polyetheretherketone (PEEK), or a glass fiber reinforced polymer material. As an alternative, the cage is made of a metallic material such as brass, steel that is cast, sintered, machined, or by injection molding. 
         [0061]    By virtue of the invention, the dividing portions, which have an inside diameter greater than the inside diameter of the heel, are not made to come into contact with the inner ring as the rolling bearing rotates. The cage therefore has an extended life. 
         [0062]    In addition, the lubricant present in the rolling bearing is recovered by the projecting parts so that it can be distributed to the rolling elements.