Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1998-06-02
2001-01-30
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250
Reexamination Certificate
active
06181129
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of detecting parameters of the rotation of a steering column, for example of a motor vehicle. The rotation parameters which need to be known are, in general, the angular position, the rate of rotation and the direction of rotation.
BACKGROUND OF THE INVENTION
Instrumented rolling bearings which are intended to be mounted on a shaft and which require the steering column to be dismantled when a defective element of a rolling bearing of this kind has to be changed are known from the prior art.
Equipment for detecting the rate of rotation and direction of a steering column shaft is known from document EP-A-0,443,940. The steering column shaft is fitted with a rolling bearing comprising an elongate inner race and an outer race which is also elongate, with rolling bodies arranged between the two races. The inner race is secured to the shaft and the outer race is secured to the steering column casing. An encoder is mounted on the inner race. A sensor is secured to a removable sensor block and supported by the stationary outer race.
This type of equipment has certain drawbacks. The removable sensor block is clipped to the outer race of the rolling bearing of one of the steering column bearings, which means that this race has a shape specially adapted to receive the said block. The encoder ring is fixed to the rotating race of the same rolling bearing, which requires a race shape and dimensions adapted to receive the said encoder. The result of these two requirements is that use is made of non-standard bearings, which leads to an additional cost.
As only the sensor is removable, replacing a defective detection unit (sensor and encoder) therefore involves operations on the steering column mechanism in order to remove the rolling bearing fitted with the encoder.
As the sensor block is mounted on the steering column bearing, the variations of the loads applied to the said bearings may cause variations in the size of the radial air gap between the sensor and the encoder, and this detracts from the detection accuracy. In the event of a failure of the steering column bearing, and of this bearing being changed, the encoder cannot be recovered. The protection of the sensor and of the encoder against external contaminants is not entirely satisfactory. The detection equipment can be fitted only at the end of a steering column in so far as it is fixed to one of the rolling bearings that form the steering column bearing.
Other devices of the prior art propose detection systems in which the encoder is fixed to the rotating shaft of the steering column and in which the sensor is secured to the column casing.
In this case, the air gap between sensor and encoder is generally factory-preset at the time of fitting.
Apart from the problems already mentioned earlier, it is difficult to guarantee a precise air gap that gives a good signal when changing a defective sensor/encoder unit.
BRIEF SUMMARY OF THE INVENTION
The object of the invention is to solve all of these problems by proposing a removable detection device that it is independent of the steering column bearings, the said removable device combining the sensor means and the encoder means.
The detection device according to the invention is intended for measuring parameters of the rotation of a shaft that rotates with respect to a stationary element, there being at least one bearing between the shaft and the stationary element so that the shaft can be mounted to rotate with respect to the stationary element. The detection device comprises an encoder means rotated by the rotating shaft, and a sensor means secured to a stationary element and arranged facing and a small air gap away from the encoder means whose passage during rotation is detected by the sensor means. The encoder means and the sensor means are supported by a removable unit independent of the bearing, the said unit being capable of being mounted on the stationary element and having a stationary part supporting the sensor means and a rotating part supporting the encoder means, the rotation of the rotating part being connected to that of the rotating shaft. Thus, the detection device is not affected by mechanical operations on the steering column and, from the other point of view, any changing of the detection device does not involve operations on the mechanical part of the steering column. The detection device is not mechanically connected to a rolling bearing. The rotating part can be arranged radially on one side of the shaft.
In one embodiment of the invention, the removable unit comprises at least one rolling bearing arranged between the stationary part and the rotating part.
Advantageously, the removable unit is radially adjacent to the rotating shaft and is fixed into an opening made in a tubular casing of the stationary element, the said removable unit comprising a cover closing the said opening. The sensor means and the encoder means are thus perfectly protected.
In one embodiment of the invention, the removable unit comprises an elastic pad arranged between the cover and the stationary part.
In another embodiment, the stationary part comprises an elastic sleeve.
In another embodiment of the invention, the stationary part and the cover are produced as one piece, being connected by an elastic portion which may have a meandering shape. In these three instances, the pad, the sleeve or the elastic portion have the purpose of absorbing any excessive radial preload which may occur directly or indirectly between the rotating part supporting the encoder means and the rotating shaft.
Such a radial preload could be due, for example, to defects in the relative positioning of the rotating shaft and of the rotating part supporting the encoder means or alternatively to radial deformation of the rotating shaft.
This elastic device also makes it possible to reduce or eliminate play between the sets of teeth.
Advantageously, the removable unit comprises a means of taking movement off the rotating shaft.
In one embodiment of the invention, the means of taking movement off the rotating shaft comprises a pinion secured to the rotating shaft, and a crown of teeth arranged on an exterior surface of the rotating part of the removable unit and capable of interacting with the pinion. The pinion may be formed directly on the rotating shaft.
In these embodiments, the pad, the sleeve or the elastic portion make it possible, while avoiding the risks of excessive preload, to make the sets of teeth mesh with no clearance or with a very small clearance, and therefore to obtain a signal that is perfectly representative of the rotation of the rotating shaft.
In another embodiment of the invention, the means of taking movement off the rotating shaft comprises a roller made of an elastic material arranged on an exterior surface of the rotating part of the removable unit and capable of interacting by friction with the rotating shaft.
It may be anticipated for the encoder means to be driven with a step-down ratio other than unity, something which may be highly advantageous in terms of compatibility with the processing system, and as far as the exploiting of the signal provided by the sensor means are concerned. Thus a step-down ratio greater than unity makes it possible to use a magnetic encoder but has a lower number of poles than would be needed if the said encoder were mounted directly on the steering column shaft.
In one embodiment of the invention, the rotating part is of approximately tubular shape, the movement take-off means being arranged approximately in the same radial plane as the rolling bearing.
The encoder means may be arranged on an exterior surface or on a bore of the rotating part.
The invention thus makes available a complete and compact removable detection unit including the sensor and the encoder. The removable unit is not affected by the load applied to the steering column bearings. The rolling bearing used for mounting the encoder so that it can rotate with respect to the sensor experiences no appreciable load likely to cause a va
Landrieve Franck
Lhote Pascal
Message Olivier
Thoumieux Jean-Luc
SKF France
Smith , Gambrell & Russell, LLP
Snow Walter E.
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