WO2011026759A1

WO2011026759A1 - Bump stop device and macpherson strut

Info

Publication number: WO2011026759A1
Application number: PCT/EP2010/062297
Authority: WO
Inventors: Richard Corbett; Jérôme DUBUS; Samuel Viault
Original assignee: Aktiebolaget Skf
Priority date: 2009-09-01
Filing date: 2010-08-24
Publication date: 2011-03-10
Also published as: FR2949524A1

Abstract

The bump stop device for motor vehicles comprises a rolling bearing (22) forming an axial stop and provided with a top ring (24), a bottom ring (26) and at least one row of rolling elements (28) arranged between the rings, a bearing cap (18) in contact with the top ring, and a support cap (20) in contact with the bottom ring. Each ring (24, 26) of the rolling bearing comprises a sealing gasket (32, 34) comprising a bead (32a, 34a) covering the free end of a radial portion (24c, 26c) of said ring and at least one dynamic sealing lip (32b, 34b) projecting outward from the bead and in friction contact with a substantially radial surface of one of said caps.

Description

Bump stop device and MacPherson strut

The present invention relates to the field of the bump stop devices used in particular on motor vehicles in the MacPherson struts of the steered wheels.

The invention relates more particularly to a bump stop device comprising a ro lling bearing forming an axial stop and comprising a top ring and a bottom ring between which is arranged at least one row of rolling elements, for examp le balls or rollers. The top and bottom rings are usually mounted in contact with bottom and top bearing or support pieces, such as cups or caps. The top and bottom caps form a housing for the rings o f the rolling bearing and provide the interface between said rings and the nearby elements .

The bump stop device is arranged in the top part of the MacPherson strut between the bodywork of the vehicle and a suspension spring . The spring is installed about a damping piston rod, the end o f which is linked to the bodywork of the vehicle via an elastic blo ck for filtering the vibrations. The suspension spring bears axially, directly or indirectly, on the bottom support cap . The top bearing cap is fixed relative to the bodywork of the vehicle.

Such a bump stop device transmits axial forces between the suspension spring and the bodywork of the vehicle while allowing a rotation movement between the bottom support cap and the filtering elastic block deriving from a turn of the steered wheels of the vehicle and/or from the compression o f the suspension spring.

The interior of the rolling bearing of the device, namely the space that exists between the rings, usually contains a lubricant. For the bearing to work correctly, it is important both to retain the lubricant within this space and to prevent the ingress of pollutant particles, solids or liquids . To this end, seals can be arranged between the rings o f the bearing.

The Japanese Patent Application JP 2008-248950 disclo ses a bump stop provided with a bottom support cap, a top bearing cap and a rolling bearing mounted axially between said caps. The top ring of the rolling bearing comprises, at each end, a sealing lip in friction contact with the bottom support cap . More specifically, a first lip rubs against an axial portion of the support cap and a second lip rubs against a substantially radial portion of said cap .

This so lution is difficult to implement given that, in a relative radial misalignment of the caps due, for example, to manufacturing tolerances, the friction torque of the rolling bearing is different from that predicted in the unmounted state.

This spurious friction, which is non-uniform over the circumference of the rolling bearing, may cause an undesirable noise to be generated and premature wear of the sealing lips .

Furthermore, in case o f significant radial misalignment between the bottom and top caps, the sealing can no longer be assured on the first sealing lip .

The present invention aims to remedy these drawbacks .

More particularly, the present invention aims to provide a bump stop device in which the friction torque is substantially the same according to the relative radial positioning of the bottom and top caps, and in which the ingress o f any water droplets or pollutant particles is limited.

Another aim o f the present invention is to provide a device that is particularly reliable over time, of simple design and cost-effective.

In one embodiment, the bump stop device for motor vehicles comprises a ro lling bearing forming an axial stop and provided with a top ring, a bottom ring and at least one row of rolling elements arranged between the rings, a bearing cap in contact with the top ring, and a support cap in contact with the bottom ring. Each ring of the rolling bearing comprises a sealing gasket comprising a bead covering the free end o f a radial portion of said ring and at least one dynamic sealing lip projecting outward from the bead and in friction contact with a substantially radial surface of one of said caps .

The expression "dynamic sealing" should be understood to mean a seal-tightness between two pieces having relative movement. In one embodiment, the bottom ring comprises an external dynamic sealing lip in friction contact with the support cap . The top ring can also comprise an internal dynamic sealing lip in friction contact with the bearing cap . The expression "external lip" should be understood to mean the lip oriented towards the outside of the device and the expression "internal lip" should be understood to mean the lip extending towards the inside.

The dynamic sealing lips can radially delimit an impervious space containing the bottom and top rings and the rolling elements o f the rolling bearing.

In one embodiment, at least one of the rings of the rolling bearing comprises a static sealing lip in friction contact with one o f the bearing or support caps or with the other ring of said rolling bearing. Each ring of the rolling bearing can comprise at least one static sealing lip . The dynamic and static sealing lips of at least one o f the rings are advantageously produced in a single piece . The dynamic and static sealing lips of at least one of the rings can be in friction contact with two surfaces axially facing one another.

The invention also relates to a MacPherson strut comprising a damper and a bump stop device as defined previously.

The present invention will be better understood from studying the detailed description o f embodiments taken as non-limiting examples and illustrated by the appended drawings in which Figures 1 and 2 are axial cross-sectional views o f bump stop devices according to two embodiments of the invention.

Figure 1 shows a bump stop device, designated by the general numeric reference 10, designed to be mounted between an element o f the chassis of a motor vehicle and a helical-type suspension spring 12. The device 10 is arranged about a damping rod 14, of an axis 1 6 assumed to be overall vertical, said rod being axially elongate in the form o f a cylinder of revolution. The suspension spring 12 is mounted about the damping rod 14.

The device 10, of axis 16, comprises a top bearing cap 1 8 designed to bear against a filtering elastic block interposed between the device and the chassis of the vehicle, a bottom support cap 20 forming bearing means for the suspension spring 12, and a rolling bearing 22 arranged axially between said caps and forming an axial stop .

The bearing cap 1 8 , of axis 16, may consist of a single-piece part produced by moulding a thermoplastic material, for example a polyamide PA 6.6 , with or without glass fibre reinforcement. It comprises an annular top radial surface 1 8a intended to come into contact with the filtering elastic block, an axial bore 1 8b extending downwards from a small-diameter edge of the radial surface 1 8a, and an axial external surface 1 8c. The bearing cap 1 8 also comprises an annular bottom radial surface 1 8 d extending radially towards the inside from the bottom end of the external surface 1 8c, which is itself prolonged by a toroidal surface 1 8e. A bottom edge of the toroidal surface 1 8 e is prolonged radially towards the inside by an annular radial surface 1 8f, the small-diameter edge of which is connected to the bottom end o f the bore 1 8b .

The support cap 20 , of axis 16, can also consist of a single- piece part produced by moulding a thermoplastic material, for examp le a po lyamide PA 6.6 , with or without glass fibre reinforcement. It comprises a cylindrical axial external surface 20a, the bottom end o f which is pro longed towards the inside by an annular radial surface 20b, which is in turn pro longed towards the inside and downwards by a rounded surface fo llowed by an axial surface 20c. The radial surface 20b provides a bearing surface for the top end turn of the suspension spring 12, the axial surface 20c enabling it to be centred.

From the bottom end o f the axial surface 20c there extends towards the inside an annular radial surface 20d which is prolonged from a small-diameter edge axially upwards by a bore 20e . The top end of the bore 20e o f the support cap 20 is prolonged radially towards the outside by an annular radial surface 20f axially facing the radial surface 1 8 f of the bearing cap 1 8. On the radial surface 20f, there is provided an annular groove 22 axially oriented upwards in the direction of the bearing cap . The groove 22 is prolonged towards the outside by a toroidal surface 20g, the top edge of which is prolonged radially towards the outside by an annular radial surface 20h axially facing the radial surface 1 8 d of the bearing cap 1 8.

The ro lling bearing 22, o f axis 1 6, comprises a top ring 24 and a bottom ring 26, between which is housed a row of rolling elements 28 , in this case produced in the form of balls. A cage could also be provided to enable a regular circumferential spacing to be maintained between the rolling elements 28. The rolling elements 28 are arranged between the raceways formed by the top 24 and bottom 26 rings . Advantageously, said rings can be obtained from one and the same steel blank by cutting and stamping, by virtue of the fact that the external diameter of the top ring 24 is substantially equal to the internal diameter of the bottom ring 26.

The top ring 24 comprises a toroidal portion 24a in contact with the toroidal surface 1 8e of the bearing cap 1 8 of complementary shape, said toroidal portion 24a being prolonged towards the inside by a toroidal portion 24b of opposite concavity which is pro longed radially towards the inside by a short radial portion 24c extending in the vicinity o f the radial surface 1 8 f of the bearing cap 1 8. The external surface of the toroidal portion 24a has, in cross section, a quarter-circle concave internal profile and forms a toric raceway for the rolling elements 28. The radial portion 24c is axially situated between said radial surface 1 8f and the groove 22 o f the support cap 20 while remaining at a distance from the latter.

The bottom ring 26 also comprises a toroidal portion 26a in contact with the toroidal surface 20g of the support cap 20 of complementary shape, said toroidal portion being prolonged towards the outside by a toroidal portion 26b of opposite concavity, itself prolonged towards the outside by a radial portion 26c extending in the vicinity o f the radial surfaces 20h and 1 8 d of the support 20 and bearing 1 8 caps while remaining at a distance from the latter. The internal surface o f the toroidal portion 26a has, in cross section, a quarter-circle concave internal profile and forms a toric raceway for the rolling elements 28. The free end of the radial portion 26c is radially offset towards the inside of the device relative to the external surfaces 1 8c, 20a of the bearing and support caps .

To ensure its protection against the ingress of pollutant particles and to avoid leaks of lubricant towards the outside, the rolling bearing 22 comprises internal 32 and external 34 sealing gaskets respectively provided on the top 24 and bottom 26 rings. Advantageously, said sealing gaskets are obtained by overmoulding a flexible material, for example an elastomer such as rubber or even polyurethane or elastomer thermoplastic, on the rings .

The internal sealing gasket 32 comprises an annular bead 32 a covering the free end of the radial portion 24c of the top ring 24, and two relatively thin annular internal sealing lips 32b, 32c proj ecting towards the inside from the bead 32a. The bead 32a is axially situated at a distance from the bearing 1 8 and support 20 caps .

The sealing lip 32b proj ects obliquely towards the inside and downwards and comes into friction contact with the radial bottom o f the groove 22 of the support cap 20. The sealing lip 32c proj ects obliquely upwards and towards the inside and comes into friction contact with the radial surface 1 8 f of the bearing cap 1 8. The sealing lips 32b, 32c are separated from one another and form a split lip, the axial section o f which is in the form o f a V oriented radially towards the inside.

The sealing lip 32b fulfils a dynamic sealing function with the support cap 20, the sealing lip 32c fulfilling a static sealing function with the bearing cap 1 8. The free ends of the sealing lips 32b, 32c are arranged in one and the same axial plane which is axially offset towards the inside relative to the radial portion 24c of the top ring 24. Advantageously, these ends have, in cross section, a rounded shape so as to reduce the friction torque that exists between them and the corresponding cap .

Similarly, the external sealing gasket 34 comprises an annular bead 34a covering the free end o f the radial portion 26c of the bottom ring 26, and two relatively thin annular external sealing lips 34b, 34c proj ecting towards the outside from the bead 34a. The bead 34a is axially situated at a distance from the bearing 1 8 and support 20 caps .

The sealing lip 34b extends obliquely towards the outside and upwards and comes into friction contact with the radial surface 1 8d o f the bearing cap 1 8 in the vicinity o f the external surface 1 8c. The sealing lip 34c extends obliquely downwards and towards the outside and comes into friction contact with the radial surface 20h of the support cap 20. The sealing lips 34b, 34c are separated from one another by being distanced from the bead 34a and form a sp lit lip whose axial section is in the form o f a V radially oriented towards the outside .

The sealing lip 34b fulfils a dynamic sealing function, the sealing lip 34c fulfilling a static sealing function. The free ends of the sealing lips 34b, 34c are arranged in one and the same axial plane which is radially offset towards the outside relative to the radial portion 26c while, however, remaining retracted relative to the external surfaces 1 8c and 20a of the bearing 1 8 and support 20 caps. The free ends o f the sealing lips 34b, 34c can advantageously have, in cross section, a rounded shape so as to reduce the friction torque between said lips and the caps.

The dynamic sealing lips 32b, 34b are in sealing contact, via an annular surface, respectively with the radial bottom o f the groove 22 of the support cap 20 and with the radial surface 1 8 d of the bearing cap 1 8 , that is to say surfaces whose normal is parallel to the axis 16 of the rolling bearing. The static sealing lips 32c, 34c are also in sealing contact, via an annular surface, respectively against the radial surface 1 8 f of the bearing cap 1 8 and the radial surface 20h of the support cap 20, the normal o f which is parallel to the axis 16.

The sealing lips 32b, 32c and 34b, 34c are flexible in the axial direction. Said lips are mounted between the bearing 1 8 and support 20 caps while being deformed or compressed in the axial direction. On each lip, the seal-tightness is assured by an annular friction surface, more specifically a surface in the form of a flat ring, the normal o f which is parallel to the axis 16. In case of radial misalignment of the bearing 1 8 and support 20 caps relative to one another, the annular area o f contact of the lips is slightly displaced without changing surface or orientation, the forces that exist between the lips and their area o f application then varying almo st not at all. Thus, in the event of such a misalignment, the friction torque of the device 10 remains substantially the same and there is no break in the contact seal- tightness produced by the lips 32b, 32c and 34b, 34c.

The internal 32 and external 34 sealing gaskets radially delimit between the bearing 1 8 and support 20 caps an impervious space 36 containing the top ring 24, the bottom ring 26 and the rolling elements 28. This space is axially delimited by the bearing cap 1 8 and by the support cap 20. The impervious space 36, sealed by the annular contact areas o f the sealing lips 32b, 32c and 34b, 34c with the bearing 1 8 and support 20 caps, prevents leaks towards the outside of the lubricant contained in the ro lling bearing 22 and the ingress o f po llutant particles.

Inside the impervious space 36, the rings 24, 26 of the rolling bearing are entirely protected from chemical attack (corrosion) or mechanical attack (abrasion) from the medium external to the rolling bearing 22. The lubricant present in the space 36 provides them with sufficient protection in the absence of surface treatments . This configuration is o f particular interest from the cost-effectiveness point of view because it makes it possible to avoid the need, on the rings 24, 26, for relatively costly surface treatments that are pollutant to implement. The lifetime o f the bump stop device 10 is thus protected and the risk o f noisy operation which could be due to internal corrosion of the rolling bearing is reduced.

Moreover, the downward curvature in the direction of the support cap 20 of the sealing lips 32b, 34c and the upward curvature in the direction of the bearing cap 1 8 of the sealing lips 32c, 34b is advantageous because it increases their ability to repel any splashes o f water or pollutant particles. The sealing lips therefore form particularly effective deflectors. Furthermore, in the event of such splashes, the contact pressure between the lips and the corresponding cap increases, which further increases their effectiveness.

The embodiment illustrated in Figure 2 in which identical elements are given the same references differs from the preceding embodiment in that the sealing gaskets 32 , 34 comprise only the dynamic sealing lips 32b , 34b and are not provided with static sealing lips . In this embodiment, the bead 32a of the sealing gasket 32 rubs via an annular surface against the radial surface 1 8 f of the bearing cap 1 8 and the bead 34a o f the sealing gasket 34 rubs via an annular surface against the radial surface 20h of the support cap 20. The beads 32a, 34a each fulfil a static sealing function with the associated cap .

In the embo diments illustrated, the sealing lips rub against strictly radial bearing surfaces, the normal of which is parallel to the axis o f the ro lling bearing so that, in the case of relative radial displacement of the bearing and support caps, the annular contact area on each lip is displaced without changing surface or orientation, the forces that exist between the lips and the caps then varying almo st not at all. As a variant, it could, however, be possible to provide, for at least one of the sealing lips, a bearing on a substantially radial surface, the normal o f which forms an angle of less than 30° with the axis 16 o f the ro lling bearing.

It could also be possible to provide, on one of the caps, a circularly discontinuous or continuous radial hook able to cooperate with a radial rib provided on the other cap so as to obtain, through diametral interference, a relative axial retention of said caps .

The bump stop device of the invention makes it possible to obtain a good protection o f the elements forming the ro lling bearing and to reduce the manufacturing costs by reducing the number of parts to be assembled by virtue of the integration o f the sealing lips in the rings of said ro lling bearing. The rings of the rolling bearing constitute or form cups supporting the sealing lips . The rings therefore simultaneously provide the functions o f support for the lips and the raceways for the ro lling elements . Furthermore, since the sealing lips are mounted between the bearing and support caps while being axially stressed or compressed, any possible wear of the lips will be compensated by their elastic deformation. Moreover, bearing of the lips on radial or substantially radial surfaces makes it possible to obtain a device with a good tolerance to the misalignment of the bearing and support caps relative to their common axis.

Claims

1 . Bump stop device for motor vehicles comprising a rolling bearing (22) forming an axial stop and provided with a top ring (24), a bottom ring (26) and at least one row of rolling elements (28) arranged between the rings, a bearing cap ( 1 8) in contact with the top ring, and a support cap (20) in contact with the bottom ring, characterized in that each ring (24, 26) of the rolling bearing comprises a sealing gasket (32, 34) comprising a bead (32a, 34a) covering the free end of a radial portion (24c, 26c) of said ring and at least one dynamic sealing lip (32b, 34b) projecting outward from the bead and in friction contact with a substantially radial surface of one of said caps .

2. Device according to Claim 1 , in which the bottom ring (26) comprises an external dynamic sealing lip (34b) in friction contact with the support cap (20) .

3. Device according to Claim 1 or 2, in which the top ring

(24) comprises an internal dynamic sealing lip (32b) in friction contact with the bearing cap ( 18) .

4. Device according to any one of the preceding claims, in which the dynamic sealing lips (32b, 34b) radially delimit an impervious space (36) containing the bottom ring, the top ring and the rolling elements of the rolling bearing.

5. Device according to any one of the preceding claims, in which at least one of the rings (24, 26) of the rolling bearing comprises at least one static sealing lip (32c, 34c) in friction contact with one o f the caps or with the other ring of said rolling bearing.

6. Device according to Claim 5 , in which each ring of the rolling bearing comprises at least one static sealing lip .

7. Device according to Claim 5 or 6, in which the dynamic and static sealing lips (32b, 34b, 32c, 34c) of at least one of the rings are produced in a single piece.

8. Device according to any one of Claims 5 to 7, in which the dynamic and static sealing lips (32b, 34b, 32c, 34c) of at least one o f the rings are in friction contact with two surfaces axially facing one another.

9. MacPherson strut comprising a damper and a bump stop device according to any one of the preceding claims .