Abstract:
A rolling bearing cage provides a circumferential spacing of a row of rolling elements and comprises first pockets configured to accommodate first rolling elements of the row of rolling elements. The first pockets are provided with axial retention portions configured to retain the rolling bearing cage on the first rolling elements. Second pockets are configured to accommodate second rolling elements of the row of rolling elements and not provided with axial retention portions configured to retain the cage on the second rolling elements. Separation portions are provided which between the separation portions delimit the first and second pockets. Each of the separation portions delimiting one of the first pockets comprises a notch open in an axial direction and open in opposing radial directions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a United States Non-Provisional Utility Patent Application claiming the benefit of French Patent Application Number 1257937 filed on Aug. 22, 2012, which is incorporated herein in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to the field of rolling bearings, notably rolling bearings used in motor vehicle electric power steering systems. The invention relates more particularly to the retaining cages that provide the circumferential spacing between the rolling elements of the rolling bearings. 
     BACKGROUND OF THE INVENTION 
     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 perform 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 rolling bearing, either directly or via a ball-screw system. 
     The rolling bearing generally comprises an inner ring, an outer ring and a row of rolling elements, generally balls, arranged between the rings. 
     A retaining cage for a rolling bearing comprising a plurality of pockets for housing balls each of which is defined in part by two claws arranged on the opposite side to a heal of the cage is known from document FR-A1-2 911 934. Such cages are completely satisfactory in a great many applications. However, in applications involving a low rotational speed, or in applications in which the direction of rotation reverses sharply, this kind of cage runs into various difficulties. Specifically, under the effects 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. 
     In addition, when the direction in which the load is applied to the bearings changes, for example when the wheels of a vehicle equipped with an electric power steering as described above are turned as the driver manoeuvres to the left and to the right when parking the vehicle, the cage is likewise severely deformed, or even destroyed. Moreover, it may prove difficult to fit such a cage over the balls. 
     A cage for a rolling bearing and comprising first pockets for the balls provided with axial retention claws for retaining the cage on the balls, and second pockets not provided with axial retention claws and dimensioned so that the associated balls are offered a relatively large degree of play so that they can move radially and circumferentially with respect to the second pockets is also known, from document FR-A1-2 883 941. 
     With such a cage, the interaction between the balls housed in the second pockets and the cage is reduced. In addition, the balls are able to move relative to one another, limiting the risk of deformation in the event of antagonistic movements of two adjacent balls. Moreover, it is easier to fit the cage over the balls in so far as only part of the pockets is equipped with the axial retention claws. 
     However, clipping the claws onto the balls when fitting the cage may cause small cracks to appear on the cage, and this may cause more rapid deterioration in service. 
     One aim of the present invention is to overcome these drawbacks. 
     More particularly, the present invention seeks to provide a cage for a rolling bearing that is easy to fit and that offers good reliability. 
     The present invention also seeks to provide a cage of small size, limited weight and which is not very deformable in service. 
     In one embodiment, the rolling bearing cage intended to provide the circumferential spacing of a row of rolling elements comprises first pockets for first rolling elements of the row, these pockets being provided with axial retention means for retaining the cage on the rolling elements, second pockets for second rolling elements of the row and not provided with axial retention means for retaining the cage on the rolling elements, and separation portions which between them delimit first and second pockets. Each separation portion delimiting one of the first pockets comprises a notch which is open axially and opens radially onto each side of the separation portion. 
     Advantageously, the notch leaves remaining at the separation portion a tab connected to the wall of the associated first pocket. 
     In one embodiment, the notch is open axially on the opposite side to the pockets. 
     The cage may comprise an axial portion from which the separation portions project. The notches of the separation portions may be open axially in the direction of an end face of the axial portion which is on the opposite side to the axial retention means. 
     In one embodiment, the first pockets comprise a spherical wall of constant thickness. 
     Each separation portion delimiting one of the first pockets may comprise a claw extending circumferentially towards the claw of the adjacent separation portion and forming the axial retention means. 
     In one embodiment, the separation portions delimiting the second pockets each comprise a cavity open axially on the opposite side to the pockets and radially towards the inside. Alternatively, or as a combination, the separation portions each comprise a cavity open axially on the opposite side to the pockets and radially towards the outside. 
     In another embodiment, each separation portion delimiting one of the second pockets comprises a cavity open axially on the opposite side to the pockets and opening radially on each side of the separation portion. 
     Each separation portion delimiting one of the second pockets may comprise a notch open axially on the same side as the pockets and opening radially on each side of the separation portion. The second pockets may have substantially cylindrical lateral walls. 
     The cage may, for example, be made as a single piece in a synthetic material, preferably, in a polymer material. 
     A second aspect of the invention relates to a rolling bearing comprising an outer ring, an inner ring, at least one row of rolling elements which are arranged between the rings, and a cage as defined hereinabove. 
     A third aspect of the invention relates to a motor vehicle electric power steering comprising at least one rolling bearing as defined hereinabove. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention and its advantages will be better understood by studying the detailed description of specific embodiments given by way of non-limiting examples and illustrated by the appended drawings on which: 
         FIG. 1  is a perspective view of a rolling bearing according to a first example of the invention, 
         FIGS. 2 and 3  are perspective views of the cage of the bearing of  FIG. 1 , and 
         FIGS. 4 to 6  are perspective views of a cage according to second, third and fourth exemplary examples of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As can be seen in  FIG. 1 , the rolling bearing  10  comprises an outer ring  12 , an inner ring  14 , a plurality of rolling elements  16 , here produced in the form of balls, and a cage  18  that maintains an even circumferential spacing of the rolling elements. The outer ring  12  and inner ring  14  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. 
     The outer ring  12  comprises, in the region of its bore, a deep groove raceway which, in cross section, has a concave internal profile tailored to the rolling element  16 , the raceway facing radially inwards. The inner ring  14  also comprises, in its cylindrical exterior surface, a deep groove raceway which, in cross section, has a concave internal profile tailored to the rolling elements  16 , the raceway facing radially outwards. The cage  18  is arranged radially between the outer surface of the inner ring  14  and the bore of the outer ring  12 . 
     As illustrated more visibly in  FIGS. 2 and 3 , the cage  18  comprises an annular axial portion  20  designed to be arranged axially on one side of the rolling elements and forming a heel, and separation portions  22  or separation fingers extending axially from the axial portion  20  on the opposite side to a radial end face  20   a  of the portion. The separation portions  22  are of one piece with the axial portion  20  and between them delimit pockets  24  in which the rolling elements are arranged. 
     The separation portions  22  take the form of pegs projecting axially from the axial portion  20 , the portions being delimited radially by an inner surface aligned with the bore of the axial portion  20  and by an outer surface aligned with the outer surface of the axial portion. The separation portions  22  are delimited in the circumferential direction by substantially cylindrical axial lateral walls which define the pockets  24 . The diameter of the cylinder defining the walls of each pocket  24  is greater than that of the rolling elements so that the rolling elements can be offered some clearance to move radially and circumferentially with respect to the pockets  24 . Each pocket  24  is open radially towards the inside and towards the outside and open axially on the opposite side to the axial portion  20  in order to allow the cage  18  to be fitted. The pockets  24  have an axial opening provided with cylindrical edges or walls so as to reduce the friction of the rolling elements rubbing against the cage. 
     Each separation portion  22  comprises a notch  26  formed at its free end and open axially on the opposite side to the axial portion  20 . The notches  26  open radially towards the inside and towards the outside of the cage. In other words, each notch  26  opens radially on each side of the associated separation portion  22 . Each notch  26  delimits on the associated separation portion  22  two axial protrusions  28  of substantially cylindrical shape which are situated axially on the opposite side from the axial portion  20  and which axially extend the lateral walls of the separation portion. The protrusions  28  are not suitable for providing axial retention of the cage on the rolling elements. The pockets  24  are not provided with such axial retention means. 
     The cage  18  also comprises the hybrid separation portions  30  defining pockets  32  provided with axial retention means for retaining the cage on the rolling elements. As will be described hereinafter, the hybrid separation portions  30  have a hollowed structure to promote the flexibility of the pockets  32 . 
     In the embodiment illustrated, the cage  18  comprises six hybrid separation portions  30  which in pairs define three pockets  32 , whereas the pockets  24  are nine in number and the separation portions  22  are six in number. The pockets  32  have a spherical overall shape that tends to envelop the associated rolling elements. The pockets  32  are evenly distributed in the circumferential direction in order to provide even axial retention of the cage  18  on the rolling elements. 
     The hybrid separation portions  30  take the form of fingers or pegs projecting axially from the axial portion  20  and are delimited radially by inner and outer surfaces respectively aligned with the bore and with the outer surface of the axial portion  20 . Each hybrid separation finger  30  has, on one side in the circumferential direction, a substantially cylindrical lateral wall so that with an adjacent separation portion  22  it forms one of the pockets  24  adjacent to the pocket  32 , and on the other side has a spherical wall which connects with the spherical wall of the adjacent hybrid separation portion  30  to form the actual pocket  32  proper. The wall of each pocket  32  is spherical and forms a cup of constant thickness to accommodate the associated rolling element. This means that pockets  32  offering good flexibility can be obtained. 
     Each separation finger  30  comprises a claw  34  extending axially on the opposite side to the axial portion  20  and the free end of which extends in the circumferential direction towards the opposite claw  34  of the adjacent hybrid separation portion  30  to delimit the same pocket  32 . The concave inner surface of each claw  34  forms part of the spherical wall of the pocket  32 . The two claws  34  associated with a pocket  32  extend towards one another, their free ends being spaced apart by a distance that is smaller than the diameter of the rolling elements. The claws  34  of a pocket are capable of axially retaining the cage  18  by clipping onto the rolling element arranged in the pocket. The cage  18  is retained axially on the row of rolling elements by the claws  34 . 
     Each hybrid separation portion  30  also comprises an axial protrusion  36  of cylindrical shape extending axially in the opposite direction from the axial portion  20 . The protrusion  36  of each hybrid separation portion  30  delimits, in part, with the protrusions  28  of the adjacent separation portion  22 , one of the pockets  24  that is not provided with axial retention means. Each protrusion  36  is unable to provide axial retention of the cage with respect to the rolling element arranged in the pocket  24  adjacent to the pocket  32 . 
     The claw  34  and the protrusion  36  of each hybrid separation portion  30  are separated in the circumferential direction by a cavity  38  so that the claw  34  has a relatively small circumferential thickness and a certain degree of flexibility allowing the cage  18  to be clipped onto the rolling elements via a circumferential parting of the claws  34  when axial thrust is applied on the axial portion  20  of the cage in the direction of the rolling elements. Each cavity  38  is formed at the free end of the associated hybrid separation portion  30  and is open axially on the opposite side to the axial portion  20 . Each cavity  38  extends axially towards the end face  20   a  and opens radially towards the inside and towards the outside of the cage. In other words, each cavity  38  opens radially on each side of the associated hybrid separation portion  30 . Each pocket  32  is open radially towards the inside and towards the outside and is also open axially on the opposite side to the axial portion  20  so as to allow the cage  18  to be installed. 
     Each hybrid separation portion  30  further comprises a notch  40  extending axially from the end face  20   a  of the axial portion. The notch  40  extends axially up to close to the cavity  38  formed between the claw  34  and the protrusion  36  leaving remaining axially between them a tab  42  of small thickness which connects to the spherical wall of the associated pocket  32 . The notch  40  of rectangular overall shape is situated axially in the continuation of the cavity  38 . The notch  40  is open axially on the opposite side to the pockets  24 ,  32 . The notch  40  opens radially on each side of the associated separation portion  30 . The notch  40  opens radially towards the inside in the bore of the axial portion  20  of the cage and radially towards the outside at the outer surface of the separation finger. The open-ended notch  40  passes through the thickness of the separation portion  30 . The notch  40  is delimited in the circumferential direction by the hybrid separation portion  30  and by the spherical wall of the pocket  32 . The notch  40  is situated in the circumferential direction between the pocket  32  and the adjacent pocket  24 . 
     The adjacent hybrid separation portions  30  between them defining one of the pockets  32  comprise, on each side of the pocket, two notches  40  which are open axially towards the end face  20   a  of the axial portion and radially on the inside and on the outside, and two flexible tabs  42  delimited by the notches. Each pocket  42  is axially offset toward the end face  20   a  of the axial portion with respect to the claw  34 . The notches  40  form, on the cage  18 , zones in which the mechanical strength of the cage is locally weakened to encourage deformation of the tabs  42  axially on the side of the axial portion  20  and flexibility of the pocket  32 . Further, the notches  40  form cavities which lighten the cage  18  by reducing the amount of material used. The cage  18  is advantageously made as a single piece by moulding a polymer material such as polyamide for example, notably PA 66 or PA 46,or alternatively a polyetheretherketone (PEEK). 
     The alternative form of embodiment illustrated in  FIG. 4 , in which identical elements bear the same references, differs only in that each separation portion  22  of the cage comprises, on its inner surface, a cavity  50  extending axially from the end face  20   a  of the axial portion into the vicinity of the notch  26 . The cavity  50  is open axially on the opposite side to the pockets  24  and  32  towards the end face  20   a,  opens radially towards the inside into the bore of the axial portion of the cage, and is delimited radially towards the outside by the separation portion  22 . Each cavity  50  is of rectangular overall shape. 
     As an alternative, as illustrated in  FIG. 5 , in which identical elements bear the same references, each separation portion  22  of the cage comprises, on its outer surface, a cavity  52  extending axially from the end face  20   a  of the axial portion into the vicinity of the notch  26 . The cavity  52  is open axially on the opposite side to the pockets  24  and  32 , opens radially towards the outside and is delimited radially towards the inside by the separation portion  22 . Each cavity  52  is of rectangular overall shape. 
     In another alternative form of embodiment illustrated in  FIG. 6 , in which identical elements bear the same references, each separation portion  22  of the cage comprises a cavity  54  extending axially from the end face  20   a  of the axial portion into the vicinity of the notch  26 . The cavity  54  is open axially on the opposite side to the pockets  24  and  32  and opens radially towards the inside into the bore of the axial portion  20  of the cage and radially towards the outside in the region of the outer surface of the separation finger. Each cavity  54  is of rectangular overall shape. 
     By virtue of the invention, the cage pockets equipped with the means of retention on or of clipping onto the rolling elements have greater flexibility in the axial direction, making it possible to avoid the appearance of cracks when the cage is fitted onto the rolling elements by axial thrust. The notches allow the flexibility of the cage to be locally increased.