Cage for a rolling bearing, in particular for a bearing of an electric power steering system of a motor vehicle

Abstract

Cage (18) for a rolling bearing (10), wherein the cage (18) is provided to ensure the spacing of a row of rolling elements (16) in the circumferential direction, and with first pockets (28) for first rolling elements (16) of the row, wherein the pockets (28) are provided with axial retaining means for axially retaining the cage (18) on the rolling elements (16), and with second pockets (30) for the second rolling elements (16) of the row, wherein the pockets (30) do not have axial retaining means for retaining the cage (18) on the rolling elements (16), wherein the distribution of the first pockets (28) is non-uniform over the circumference of the cage (18), characterized in that the cage (18) is provided with at least two pairs of first pockets (28), wherein the pockets (28) of each pair are adjacent, and with at least one additional first pocket (28) which in the circumferential direction is spaced from the pairs of at least one second pocket (30).

Description

The present invention relates to the field of rolling bearings, in particular rolling bearings used in electric power steering systems of motor vehicles.In particular, the invention relates to the retaining cages which ensure a spacing between the rolling bodies of the rolling bearings in the circumferential direction.An electric power steering system of a motor vehicle generally includes an electromechanical actuator disposed on the steering column or on the lower assembly having mechanical components provided to provide angular adjustment of the steering wheels of the vehicle. The electromechanical actuating element comprises an electric rotary motor, the axis of which is mounted by at least one rolling bearing either directly or via a ball screw.The rolling bearing generally comprises an inner ring, an outer ring and a series of rolling elements, generally balls, arranged between the rings.U.S. Pat. No. 4,040,687 A discloses a rolling bearing according to the preamble of claim 1.From document FR 2 911 934 A1 a retaining cage for a rolling bearing is known, which has several pockets for receiving the balls and each of which is partially fixed by two claws arranged opposite a foot of the cage. Such cages are completely adequate in many applications. However, in applications where a low speed is encountered or in applications where the direction of rotation is abruptly reversed, various difficulties are encountered with this form of cage. In particular, the cage may undergo a considerable deformation under the action of the balls and come into contact with the inner ring, causing it to be damaged or even destroyed.Moreover, when the direction in which a load acts on the rolling bearing changes, as is the case, for example, when the wheels of a vehicle equipped with an electric power steering as described above are steered, because the driver maneuvers left and right when parking the vehicle, the cage is also largely deformed or even destroyed. In addition, it may be difficult to place such a cage on the balls.There are also known cages for rolling bearings which have, for the balls, both first pockets provided with axial retaining claws for retaining the cage on the balls and second pockets not provided with axial retaining claws. The first and second pockets are distributed alternately in the circumferential direction to allow balanced axial retention of the cage on the balls.However, in certain applications referred to herein as quarter turn applications, in which the rolling bearing does not rotate but oscillates, such a cage is subjected to severe radial and axial stress in an angular range referred to as the stress range. In this zone, the cage does not give the rolling elements sufficient freedom of movement and this leads to a strong local cage deformation.An object of the present invention is to overcome this drawback.In particular, the present invention seeks to provide a cage for a rolling bearing which is suitable for a quarter turn application and provides a high operational safety.To this end, the invention provides a cage for a rolling bearing according to independent claim 1. The dependent claims relate to advantageous embodiments of the present invention.In one embodiment, the cage for a rolling bearing intended to ensure circumferential spacing of a row of rolling elements comprises first pockets for first rolling elements of the row, the pockets being provided with axial retaining means for axially retaining the cage on the rolling elements, and second pockets for the second rolling elements of the row, the pockets having no axial retaining means for retaining the cage on the rolling elements. The distribution of the first pockets over the circumference of the cage is non-uniform.The cage comprises at least two pairs of first pockets, the pockets of each pair being adjacent, and at least one additional first pocket spaced circumferentially from the pairs of at least one second pocket.The circumferential distance between the pairs of first pockets may be greater than the circumferential distance between one of the pairs and the additional pocket. Preferably, the circumferential distance between one of the pairs of first pockets and the additional first pocket is equal to the circumferential distance between the other pair of first pockets and the additional pocket.In one embodiment, the cage includes an annular foot and cut-off portions extending from the foot and defining between them the first and second pockets.The cage may include: a first group of partition members each having at least one pawl extending in a circumferential direction and forming the axial retaining means; and a second group of partition members having no pawls. Suitably, the first group comprises separation parts each having two claws extending in the circumferential direction toward each other, and hybrid separation parts each having a single claw and a cylindrical protrusion. Each partition part of the first group may have a recess formed in the thickness of the partition part and opening axially on the side opposite to the pockets. In one embodiment, the recess in each cut-off part opens into the recess of the adjacent cut-off part. The cage can be manufactured, for example, in one piece from a synthetic material, preferably a polymer.According to a second embodiment, the invention relates to a rolling bearing comprising an inner ring, an outer ring, at least one row of rolling elements arranged between the rings, and a cage according to the above definition.According to a third embodiment, the invention relates to an electric power steering system of a motor vehicle, which has at least one rolling bearing according to the above definition.The present invention will be better understood from reading the detailed description of some embodiments given by way of example, which is not intended to be limiting in any way, and which is illustrated by the accompanying drawings, in which:FIG. 1 is a perspective view of a rolling bearing according to a first embodiment of the invention; andFIGS. 2 and 3 are perspective views of the cage of the bearing of FIG. 1.As can be seen from FIG. 1, the rolling bearing 10 comprises an outer ring 12, an inner ring 14, a plurality of rolling elements 16 which are here produced in the form of balls, and a cage 18 which maintains a constant spacing of the rolling elements in the circumferential direction. The outer ring 12 and the inner ring 14 are compact. By a "compact ring" is meant a ring whose shape has been obtained by machining (turning, grinding) from tubes, rod material, forged and / or rolled blanks.The outer ring 12 has, in the region of its bore, a deep raceway groove which, in cross section, has a concave inner profile which is cut to size on the rolling bodies 16 which are radially opposite the raceway toward the inside. The inner ring 14 also has in its cylindrical outer surface a deep raceway groove which has in cross section a concave inner profile cut to the rolling element 16 radially opposite the raceway outwards. The cage 18 is radially disposed between the outer surface of the inner ring 14 and the bore of the outer ring 12.As shown more clearly in Figures 2 and 3, the cage 18 has an annular axial portion 20 which is adapted to be axially disposed on one side of the rolling elements and which forms a root and first and second separator portions 22, 24 or separator fingers and hybrid separator portions 26 which extend axially from the axial portion 20 on the side opposite a radial end face 20a of the portion. The separator members 22-26 are integral with the axial member 20 and bounded therebetween are the first and second pockets 28, 30 in which the rolling elements are disposed, as will be described in more detail below.The first partition members 22 take the form of castellations projecting axially from the axial member 20, the members being bounded radially by an inner surface aligned with the bore of the axial member 20 and an outer surface aligned with the outer surface of the axial member. The partition members 22 are bounded in the circumferential direction by substantially cylindrical side walls that at least partially define the pockets 30. The diameter of the cylinder defining the sidewalls of each pocket 30 is greater than that of the rollers, so that some clearance can be left for the rollers to move radially and circumferentially with respect to the pockets 30. Each pocket 30 is radially open toward the inside and the outside, and is axially open on the side opposite to the axial part 20 so as to allow the cage 18 to be fitted. The pockets 30 have an axial opening provided with cylindrical walls or edges so as to reduce the friction of the rolling bodies that rub against the cage.Each partition 22 has a notch 32 formed at its free end and opening axially on the side opposite to the axial part 20. The notches 32 open radially toward the inside and the outside of the cage. Each notch 32 delimits, on the associated separating part 22, two axial protrusions 34 of substantially cylindrical shape, which are arranged axially on the side opposite the axial part 20 and which axially widen the side walls of the separating part. The projections 34 are not suitable for providing axial retention of the cage on the rolling bodies. The pockets 30 are not provided with such axial retaining means.Each partition 22 has a recess 36 formed in the thickness of the part and extending from the face 20a of the foot to the nearest vicinity of the notch 32. Each recess 36 is axially open on the side opposite the pockets 26, 28 towards the end face 20a and is radially delimited by the inner and outer surfaces of the associated partition part.The second separator members 24 and the hybrid separator members 26 define the pockets 28 which are provided with axial retaining means to retain the cage on the rollers. The pockets 28 have a spherical overall shape that is adapted to encompass the associated rolling elements. Each hybrid separation portion 26 defines a pocket 30 with the adjacent first separation portion 22. In the illustrated embodiment, the cage 18 includes six hybrid cut-off members 30, two of which define one of the pockets 28, and four of which, paired with the cut-off members 24, define four other pockets 28. The number of the first and second partition members 22, 24 is four and two, respectively, and there are seven pockets 26.The pockets 28 are distributed non-uniformly in the circumferential direction. The circumferential distance between two successive pockets 28 is not constant over the circumference of the cage. In the illustrated embodiment, the cage 18 includes four pockets 28 arranged in pairs, the pockets of each pair being immediately adjacent, and a fifth pocket 28 spaced from each pair by two successive pockets 30. Between the two pairs of pockets 28 there are three pockets 30. The fifth pocket 28 is formed by two adjacent hybrid cut-off parts 26, and the other four pockets 28 are formed by one hybrid cut-off part 26 and one second cut-off part 24, respectively, which are adjacent. Six of the seven pockets 30 are defined by a hybrid separator 26 and an adjacent first separator 22, respectively, the seventh pocket 30 being defined by two adjacent separators 22.The hybrid separator members 26 take the form of fingers or castellations which extend axially from the axial member 20 and which are radially bounded by the inner and outer surfaces which mate with the bore and outer surface of the axial member 20, respectively. Each hybrid cut-off portion 26 has a side wall on one side in the circumferential direction which is substantially cylindrical so as to form one of the pockets 30 with an adjacent cut-off portion 22, and has a wall on the other side which spherically adjoins the spherical wall of the adjacent hybrid cut-off portion 26 to form the pocket 28 which is adjacent to the pocket 30.Each hybrid separator 26 has a claw 38 that extends axially on the side opposite the axial part 20 and whose free end extends in a circumferential direction to delimit the associated pocket 28. In the case of the pocket 28 formed by the two adjacent hybrid cut-off members 26, the claw 38 extends from one of the cut-off members toward the claw belonging to the other cut-off member to define the pocket 28. The concave inner surface of each pawl 38 forms part of the spherical wall of the pocket 28. The dogs 38 of the pocket 28 are capable of axially retaining the cage 18 by pressing it onto the rolling element disposed in the pocket. The cage 18 is partially axially retained on the row of rolling elements by the claws 38.Each hybrid separating part 26 also has an axial protrusion 40 of cylindrical shape, which extends axially in the direction opposite the axial part 20. The protrusion 40 of each hybrid separator 26 partially defines with the protrusion 34 of the adjacent separator 22 one of the pockets 30 that is not provided with axial retention means. Each protrusion 40 is incapable of providing axial retention of the cage with respect to the roller disposed in the pocket 30 adjacent the pocket 28.The pawl 38 and the protrusion 40 of each hybrid cut-off portion 26 are separated from each other in the circumferential direction by a notch 42 such that the pawl 38 has a relatively small thickness in the circumferential direction and a certain degree of resiliency, which allows the cage 18 to be pressed onto the rolling element by pushing the pawls 38 apart in the circumferential direction when an axial pushing force is applied to the cage axial portion 20 in the direction of the rolling elements. Each pocket 28 is radially open to the inside and the outside, and is also axially open on the side opposite the axial part 20 so as to allow the cage 18 to be installed.Each hybrid separator 26 further includes a recess 44 formed in the thickness of the part and extending from the face 20a of the foot to the vicinity of the notch 42. Each recess 44 is axially open on the side opposite the pockets 26, 28 toward the end face 20a and is radially defined by the inner and outer surfaces of the associated partition member. In the case of the pocket 28 formed by the two adjacent cut-off parts 26, the recesses 44 open in the circumferential direction with respect to one another.The two separating parts 24 are in the form of fingers or castellations projecting axially with respect to the axial part 20 and are bounded radially by the inner and outer surfaces which are aligned with the bore and the outer surface of the axial part 20, respectively. Each partition 24 has a spherical wall on each side in the circumferential direction, which connects to the spherical wall of the adjacent hybrid partition 26 to form the associated pocket 28.Each separator 24 has two claws 46 which extend axially on the side opposite the axial part 20 and which are identical in construction to the claws 38 of the hybrid separator members 26 and extend circumferentially in opposite directions. Each jaw 46 extends in the direction of the jaw 38 of the adjacent hybrid separator 26 to define the associated pocket 28. The free ends of the adjacent two claws 38, 46 are separated from each other by a distance which is smaller than the diameter of the associated rolling element. The claws 38, 46 of the pocket 28 are capable of providing axial retention of the cage 18 by pressing on the rolling element which is arranged in the pocket. The cage 18 is axially retained on the row of rolling elements by the claws 38, 46. The dogs 46 of each separator 24 are circumferentially separated by a notch 48 such that they all have a relatively small circumferential thickness and a certain degree of compliance which allows the cage 18 to be pressed onto the rollers.Each partition portion 24 also includes a recess 50 formed in the thickness of the portion which extends from the face 20a of the foot to the vicinity of the notch 48. Each recess 50 is axially open on the side opposite the pockets 26, 28 toward the end face 20a and is radially defined by the inner and outer surfaces of the associated partition member. Each circumferential end of each recess 50 is open to the recess 44 of the adjacent hybrid separator 26.The cut-outs 36, 44, 50 of the separating parts form regions of local weakening of the mechanical strength of the cage in the cage 18, which promotes its bending. In addition, the recesses reduce the weight of the cage by reducing the amount of material used. Conveniently, the cage 18 is made in one piece by compression moulding a polymeric material such as polyamide, in particular PA 66 or PA 46, or alternatively a polyether ether ketone (PEEK).Thanks to the circumferentially non-uniform distribution of the pockets equipped with the retaining means or means for clip fastening on the rolling elements, it is possible, especially in a quarter-revolution application, to provide a cage alignment such that in the most heavily loaded area of the bearing, the number of pockets equipped with retaining means is limited, so as to facilitate the radial and circumferential movement of the rolling elements present in this area and to avoid cage deformation.

Claims

Cage (18) for a rolling bearing (10), the cage (18) being intended to ensure the circumferential spacing of a row of rolling elements (16), and having first pockets (28) for first rolling elements (16) of the row, the pockets (28) being provided with axial retaining means for the axial retaining of the cage (18) on the rolling elements (16), and having second pockets (30) for the second rolling elements (16) of the row, the pockets (30) not having axial retaining means for the retaining of the cage (18) on the rolling elements (16), the distribution of the first pockets (28) being non-uniform over the circumference of the cage (18), characterized in that the cage (18) is provided with at least two pairs of first pockets (28), the pockets (28) of each pair being adjacent, and at least one additional first pocket (28) spaced circumferentially from the pairs of at least one second pocket (30).The cage (18) of claim 1, wherein the circumferential distance between the pairs of first pockets (28) is greater than the circumferential distance between one of the pairs and the additional first pocket (28).The cage (18) of claim 1 or 2, wherein the circumferential distance between one of the pairs of first pockets (28) and the additional first pocket (28) is equal to the circumferential distance between the other pair of first pockets (28) and the additional pocket (28).A cage (18) as claimed in any preceding claim, including an annular foot and partition members (22, 24, 26) extending from the foot and defining between them the first and second pockets (28, 30).The cage (18) of claim 4 including a first group of separator members (24, 26) each having at least one pawl (38, 46) extending in a circumferential direction and forming said axial retaining means, and a second group of separator members (22) having no pawls (38, 46).The cage (18) of claim 5, wherein the first group comprises cut-off members (24) each having two prongs (46) extending circumferentially toward each other and hybrid cut-off members (26) each having a single prong (38) and a cylindrical protrusion (40).A cage (18) according to claim 5 or 6, wherein each partition (24, 26) of the first group has a recess (44, 50) formed in the thickness of the partition (24, 26) and opening axially on the side opposite the pockets (28, 30).A cage (18) according to claim 7, wherein the recess (44, 50) in each partition (24, 26) opens into the recess (44, 50) of the adjacent partition (24, 26).Rolling bearing (10) comprising an inner ring (14), an outer ring (12), at least one row of rolling elements (16) arranged between the rings, and a cage (18) according to any one of the preceding claims.Electric power steering system of a motor vehicle, which has at least one rolling bearing (10) according to Claim 9.

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