Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
1999-11-12
2001-10-02
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
C384S480000, C384S482000, C384S484000
Reexamination Certificate
active
06296396
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a strut bearing comprising two bearing races, roll bodies arranged between these races, and a seal which seals the space between said two races.
Strut bearings of this type serve for supporting strut-type wheel suspensions for the steerable wheels of automotive vehicles on the vehicle body. The strut-type suspension is essentially formed by a shock absorber and a helical spring surrounding the same. The head of the shock absorber is connected to the vehicle body and is surrounded by the strut bearing. The casing of the strut bearing must, accordingly, have a relatively large internal diameter. A member rigidly connected to the vehicle body is supported on the upper race of the bearing, whereas the lower race is supported on a spring collar which forms an engagement surface for the upper end of the helical spring. Thus, the bearing must be capable of absorbing a high axial load which corresponds to the portion of the weight of the vehicle acting upon the associated wheel. In addition, the bearing is subject to relatively high radial forces, because the strut is normally inclined relative to the vertical.
Known strut bearings of this type comprise a casing formed by two annular casing halves made of synthetic resin and snap-fastened to one another, which accommodate the races of the bearing and on which the seal is formed. In view of the relatively high load, a comparatively hard synthetic resin material must be used for the casing. The seal is formed by sealing lips formed integrally with the casing halves or by labyrinth profiles and has the purpose to protect the races and roll bodies accommodated in the casing against mud and water.
When the vehicle wheel is steered, the bearing is expected to allow for a smooth rotation of the strut about its longitudinal axis.
In conventional strut bearings, it may however happen during a steering operation that the bearing becomes locked, so that the rotation of the spring collar is stopped and the helical disk is subject to a torsional force. When the torsional force exceeds the locking force of the spring collar, the spring collar makes an abrupt rotation, and the torsional bias of the helical spring is released, until the bearing locks again. This effect which is also termed “spring jumping” is perceptible to the driver as a slight vibration and a disturbing noise during the steering operation.
It is an object of the invention to provide a strut bearing which can avoid the phenomenon of spring jumping.
SUMMARY OF THE INVENTION
According to the invention, this object is achieved by providing a strut bearing comprising two bearing races, a space formed between the two races, roll bodies arranged in the space between the two races, and a seal which seals the space between the two races, wherein said seal comprises an elastic, soft material molded to the races or to parts of a casing accommodating the races.
This solution is based on an analysis which has shown that, in conventional strut bearings, the phenomenon of spring jumping is mainly due to the fact that the sealing lips or labyrinth profiles of the seal are made of the same hard synthetic resin material as the rest of the casing halves. Due to the above-mentioned radial forces and the lacking resiliency of the seal, the frictional forces occurring on the sealing surfaces which come into engagement with each other may become so large that they resist a rotation of the casing halves relative to one another and lead to a stick-slip effect which, as the case may be, is still enhanced by resonances of the helical spring and causes the above-mentioned vibration and noise. According to the invention, the use of a softer material for the seal or at least for parts of the seal leads to a higher resiliency, so that this effect is largely suppressed. On the other hand, since the seal is still directly molded to the main part of the casing half, it is still possible to manufacture the casing halves as one-piece bodies, and it is still possible to employ compact sealing structures in view of the restrained mounting space.
In the manufacturing process, the casing half of the bearing can be molded from synthetic resin in two steps. In this case, the main body of the casing half is molded in a first step from a hard resin material, and subsequently the seal is molded in a second step from a softer material. Alternatively, a two-component molding process can be employed in which the harder main body of the casing half and the softer seal are molded in one operation.
In a modified embodiment of the invention it is also possible to dispense with one or both of the casing halves and to mold the seal structures directly to the bearing races.
In general, it is sufficient when the sealing lip which effectively closes the sealing gap is connected to the main body of the casing half or to the bearing race by a bridge portion made of said softer material, so that the required resiliency of the seal is achieved. The sealing lip itself could be made of a harder material. In a preferred embodiment, however, the seal or, more precisely, the sealing lip is in its entirety made of a soft material, e.g. soft synthetic resin or rubber having a friction coefficient as small as possible.
If the seal is structured as a labyrinth, then there is normally no frictional engagement between surfaces of the sealing structures. The feature according to the invention becomes effective when the radial forces lead to a deformation of at least one of the two casing halves and/or to a shift of the casing halves or the bearing races relative to one another, with the result that surfaces of the sealing structures come into frictional engagement with one another. In a preferred embodiment, however, the seal is formed by a sealing lip, and this sealing lip is constantly engaged with an associated counter surface of the other casing half or the other race of the bearing.
As in conventional strut bearings, the seal in the strut bearing according to the invention may also be configured such that it can be used for snap fastening the two casing halves together, so that the bearing can conveniently be handled as a single unit until it is built into the vehicle.
REFERENCES:
patent: 4274655 (1981-06-01), Lederman
patent: 23 29 910 (1975-01-01), None
patent: 26 58 748 (1978-06-01), None
patent: 42 27 474 (1994-02-01), None
patent: 42 29 199 (1994-03-01), None
patent: 0 390 331 (1990-10-01), None
patent: 2 145 781 (1985-04-01), None
Burns Doane , Swecker, Mathis LLP
Footland Lenard A.
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