Abstract:
An instrumented bearing, in particular for an electric steering wheel ( 12 ), comprises an outer element ( 1 ) and an inner element ( 6 ) whereof one is mobile relative to the other which is fixed, via at least a row of rolling elements ( 14 ) arranged between the elements, and by detection ( 22, 23, 31 ) of rotational parameters of the rotating element. The bearing further comprises electronic elements ( 34 ) for processing signals emitted by the detecting elements and electronic elements ( 35 ) for controlling at least an actuator electrically connected to the device, advantageously arranged on a printed circuit plate ( 33 ) fixed in rotation.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This is the 35 USC 371 national stage of international application PCT/FR01/03373 filed on 30 Oct. 2001, which designated the United States of America. 
   The object of the present invention is an instrumented bearing device which can be used in particular in association with an electric steering wheel, for example for a fork lift truck or public works machinery. 
   FIELD OF THE INVENTION 
   The bearing is of the type comprising an external element and an internal element, between which at least a row of rolling elements is provided. One of these elements remains fixed relative to a structure, while the other can be rotated by the steering wheel. The instrumented bearing comprises detection means of the rotation parameters of the revolving element, so as to control an electric or electro-hydraulic solenoid. 
   An electric direction control is used more and more currently in conveyors, for example fork lifts or certain public works machinery. The steering wheel, rotated by the driver, is mounted on a support fixed by means of one or two bearings to which is added a rotation detection system, integrated or not into the bearings. This detection system emits a signal representative of the rotation of the steering wheel (angle, direction and angular speed) which is directed to a signal processing system, then to an electronic pilot logic system which in turn sends signals appropriate to electric or electro-hydraulic solenoids causing orientation of the vehicle wheels according to orders given by the driver. 
   An example of such a device is illustrated in French patent application 2 782 970, in which a system for braking the steering wheel has also been provided in order to generate a load moment favouring driving precision and reliability of the vehicle. 
   These already known devices, though technically satisfactory, nevertheless have certain disadvantages, especially in terms of compactness and ease of assembly on the vehicle or on the machine. 
   In conventional devices, for example those using Hall effect sensors cooperating with a multipolar magnetised ring, it is difficult to obtain absolute coding allowing the absolute angular position of the revolving part relative to a predetermined reference “zero” to be known, with the quality of measurement depending on the number and precision of the realisation of poles of the magnetised ring. 
   On the other hand, obtaining absolute coding by a multipolar ring supposes that the latter comprises additional information permitting identification of a reference pole, which occurs detrimentally to simplicity, cost and spatial requirement. 
   European patent application 0 932 01 9 describes a sensor comprising a rotating disc equipped with a magnetised rod capable of moving in front of a sensor comprising a magnetoresistor. This device utilised for determining angular position does not however comprise any bearing capable of ensuring suitable support of the revolving part. In addition, nothing is provided for integrated and reliable processing of the signal put out by the sensor. 
   BACKGROUND OF THE INVENTION 
   The object of the present invention is to eliminate the difficulties of previous devices and to create an instrumented bearing which is particularly compact and reliable, and which also allows precise determination of the absolute angular position. 
   The instrumented bearing according to the present invention, which can be used especially for an electric steering wheel of a conveyor fitted with an electric direction control system, comprises an external element and an internal element whereof one is mobile in rotation about an axis relative to the other which is fixed, by means of at least a row of rolling elements disposed between said elements. The device also comprises means of detection of rotation parameters of the revolving element which comprise a sensor sensitive to magnetism arranged on a fixed part and a permanent magnet arranged on a revolving part, opposite the sensor, with its polar parts on either side of the axis of rotation. 
   The permanent magnet is mounted on a front face of the revolving element, on the side opposite the steering wheel. 
   In this way, absolute coding of the angular displacement of the revolving part is attained very simply and thus economically. 
   In a preferred embodiment, the sensor sensitive to magnetism comprises a plurality of cells of Hall effect distributed around a point corresponding to the axis of rotation of the revolving part equipped with the permanent magnet. 
   The sensor sensitive to magnetism can be advantageously created in the form of an integrated circuit chip and may comprise a plurality of contact pins enabling an electric current supply, where the output of the signal and programming of a predetermined angular position from the fixed part define a zero reference angle. 
   In another embodiment, the sensor sensitive to magnetism comprises a magnetoresistor centred on the axis of rotation. 
   The sensor sensitive to magnetism is preferably fixed on a printed circuit board mounted fixed in rotation in a space defined between the bearing and a closing cover which can have a connector. In this way, the support means of the steering wheel and the ensemble of electric processing means of the signal are integrated in the form of a unit. Once this unit is fixed on a vehicle or a machine, it suffices to mount the steering wheel and to connect an electric cable on the connector to make the ensemble function. 
   The electronic means for processing the signals and the electronic pilot means are preferably disposed oh the printed circuit board which already houses the sensor sensitive to magnetism. In this case, a simple change of printed circuit easily allows the device to be adapted to another application. 
   The link between the connector borne by the cover and the printed circuit board is preferably done by contact means, thus avoiding any connection cable. 
   Preferably, the sensor supplies a signal of absolute angular position relative to a zero reference position. 
   In a preferred embodiment, the permanent magnet is mounted in a recess on the revolving element so as not to project outside said front face. The axial bulkiness of the device is thus reduced to the maximum. 
   In a variant, the permanent magnet can be supported by a piece solid with a rotating ring of the bearing or even can be supported directly by the rotating ring of the bearing. 
   In an advantageous embodiment, the revolving part bearing the permanent magnet and a part at least of the steering wheel, indeed all the steering wheel, form a single monobloc piece. Assembly is accordingly particularly simple. 
   In a variant, the rotating ring of the bearing directly supports the steering wheel. 
   The permanent magnet can be a bipolar magnetised rod or a cylindrical element whose poles are situated on either side of the axis of rotation of the revolving part. 
   SUMMARY OF THE INVENTION 
   The invention will be better understood from two particular embodiments described by way of non-limiting example and illustrated by the accompanying diagrams, in which: 
     FIG. 1  is an axial section of an embodiment of an instrumented bearing device according to the present invention, 
     FIG. 2  diagrammatically illustrates a position taken up by the permanent magnet relative to the sensor sensitive to magnetism of the device in  FIG. 1 , and 
     FIG. 3  diagrammatically illustrates a position taken up by a permanent magnet of cylindrical shape, according to a second embodiment, relative to an ensemble of cells of Hall effect. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the embodiment illustrated in  FIG. 1 , the instrumented rolling bearing device comprises an external element  1 , of annular shape, made of pressed sheet in the example illustrated, comprising a tubular portion  2  and a radial portion  3  extending outwards at one end of the tubular portion. The radial portion  3  is provided with a plurality of fixing holes  4  for taking up screws for attaching to a fixed structure  5 , illustrated diagrammatically. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The bearing device further comprises an internal element  6  centred on the same axis  7  as the external element  1 . The internal element  6  is in the form of a solid cylindrical piece having an external cylindrical span  8 . A plurality of holes  10  is provided at one end of the revolving internal element  6  for taking up screws illustrated at  11 , for example intended for attaching a rotating steering wheel  12 , illustrated diagrammatically in dotted lines. The steering wheel  12  is fixed on an axial end of the revolving part supporting a magnet at its other end. The internal element  6  exhibits a radial face  6   b  from which the holes  10  are formed. 
   In the embodiment illustrated, a ball bearing  13  is mounted between the external element  1  and the internal element  6 . The ball bearing  13  comprises a row of balls  14  disposed between an external ring  15  mounted in the bore of the tubular portion  2  of the external element  1 , and an internal ring  16  mounted on the cylindrical span  8  of the internal element  6 . 
   In a variant, it could well be that the rolling elements such as the balls  14  or rollers, needles, etc., are mounted directly in contact with the external elements  1  and internal elements  6  by means of races machined on said external and internal elements. 
   The external ring  15 , embedded in the bore of the tubular portion  2  of the external element  1 , is provided with a race  15   a  for the rolling elements  14 . The internal ring  16 , embedded on the cylindrical span  8  of the internal element  6 , is provided with a race  16   a  for the rolling elements  14 . The external ring  15  is also provided with two symmetrical grooves  18  and  19  embedded into its bore, on either side of the race  15   a , enabling sealing elements  20 , which rub against a span of the internal ring  16 , to be attached. 
   The internal revolving element  6  comprises a permanent magnet  21  made in the form of a bipolar magnetised rod which is, in the illustrated example, lodged in a recess  22  machined on the front face  6   a  of the revolving internal element  6  so as not to project from this front face  6 , faces  6   a  and  6   b  forming the opposite ends of the internal element  6 . The permanent magnet  21  is arranged on the revolving internal element  6  opposite the steering wheel  12 . The polar parts north and south of the permanent magnet  21  are arranged on either side of the axis of rotation  7 . 
   The sensor sensitive to magnetism here is in the form of a magnetoresistor  23  disposed opposite the permanent magnet  21 , slightly offset from the latter by an air gap, the magnetoresistor  23  being fixed on a printed circuit board  24  disposed in a radial plane and fixed on the fixed external element  2  by any appropriate means such as screws, adhesion etc. The printed circuit board  24  simultaneously comprises electronic means  25  for processing signals emitted from the magnetoresistor  23  and electronic means  26  constituting pilot logic for a solenoid, for example of the electro-hydraulic type, designated by reference numeral  44  and illustrated in  FIG. 1  in dotted lines. 
   In the embodiment shown, the magnet  21  and the sensor are directly opposite one another. In a variant, the sensor can be mounted on the side opposite the board  24 , that is, on the side of the electronic means  25  and  26 . The magnet  21  and the sensor are then separated by the board  24 , apart from the air gap. 
   The device in its entirety is formed on the side of the printed circuit board  24  by a radial partition in the form of closing cover  27  made of a synthetic material, for example, affixed by any suitable means to the external edges of the tubular portion  2  of the fixed external element  1 . A radial partition originating directly from the tubular portion  2  could also be provided. 
   In the embodiment illustrated, the cover  27  also comprises a connector  28  whereof the pins  29  are connected electrically directly to the output of the pilot electronics provided on the printed circuit board  24 . The connection is made in a fairly direct manner, without connection cable, with considerable compacity and by eliminating any deterioration risk. Transmission to the solenoid  44  of pilot orders resulting from rotation of the steering wheel  12  is done via the cable  30  which connects directly on the connector  28 . 
     FIG. 2  illustrates in plan view and schematically the magnetoresistor  23  and the permanent magnet  21  shown in a particular relative position. By way of example, the respective axes of symmetry  23   a  and  21   a  of the magnetoresistor  23  and of the permanent magnet  21  make up between them an angle α which corresponds to rotation of the steering wheel  12 . 
   The magnetoresistor  23  is in the form of a chip comprising two resistive conductor elements  31  and  32 , each constituted in the form of resistive wires disposed in meanders elongated along an axis. The meanders of the resistive element  31  are disposed parallel to the longitudinal axis  23   a , while the meanders of the resistive element  32  are disposed perpendicularly to the axis  23   a . One of the ends of the resistive element  31  is connected to a supply terminal  33 , while the other end is connected to an output terminal  34 . Under the same conditions, the resistor element  32  is connected at one of its ends to an input terminal  35  and at its other end to the output terminal  34  which thus constitutes a terminal common to the two resistive elements  31  and  32 . 
   Considering the disposition of the meanders making up the resistive elements  31  and  32 , the variation in magnetic field to which the magnetoresistor  23  is subjected, for a determined angular position of the permanent magnet  21 , generates in the magnetoresistor a variation in resistance, supplying an electric signal in the form of a current whose voltage is representative of the value of the angle α between the permanent magnet  21  and the magnetoresistor  23 . 
     FIG. 3  illustrates a second embodiment in which the sensor sensitive to magnetism used, designed by  36  in its entirety, comprises a plurality of cells of Hall effect  37  numbering five in the illustrated example and distributed evenly around an imaginary point  38  through which the axis of rotation of the revolving part of the device passes. The cells of Hall effect  37  are integrated into a very small integrated circuit chip  39 , having sides of a few millimetres and approximately 1 mm in thickness. The integrated circuit chip  39  advantageously comprises a pre-processing signal circuit, not shown in the figure, as well as a plurality of contact pins  40 , here numbering six in the example illustrated, ensuring supply of electric current, with the output of the signal giving the absolute angular position as well as the programming of the position of the zero reference angle. 
   The permanent magnet  41  used in the embodiment illustrated in  FIG. 3  is a cylindrical element whereof each demisector defines a pole magnetised north or south, as illustrated in the figure. The axis of the cylindrical element  41  is confused with the artificial point  38 . Rotation of the magnet  41  in front of the different cells of Hall effect  37  causes in each cell  37  variations in electric output current in response to variations in the magnetic field. Integration of the variations in electric output current of each of the cells  37  supplies a signal representative of the angular position α of the magnet, the angle α being defined between the axis  42  which represents the zero reference position and the axis  43  joining the two poles north and south of the permanent magnet  41 . 
   The device can thus be advantageously utilised to obtain coding supplying the absolute angular position of the revolving part relative to a determined zero position of the fixed part. 
   A braking element, not illustrated in the figure, can also be provided so as to generate a friction moment between the organs mobile in rotation and the fixed organs and thus improve the precision in rotation movements of the steering wheel. By way of example of such a braking element, reference can be made to French patent application no. 2 782 970. 
   The device according to the present invention thus makes it possible to obtain, with minimal bulkiness, in particular in the axial direction, absolute coding of the angular displacement of the rotating part. 
   The structure of the device allows use of a standard bearing comprising a suitable sealing device on each of its sides. 
   The compact structure of the device makes it possible to increase the reliability while the bearing is being handled by eliminating any risk of losing pieces, the sensitive elements also being perfectly well protected. 
   Even though in the embodiment described by way of example, the permanent magnet has been mounted on a revolving internal element, it is understood that in a variant the permanent magnet can be attached directly to the rotating ring of the bearing or again to another piece solid with this rotating ring. 
   In an advantageous embodiment it could also be envisaged to constitute the revolving internal element bearing the permanent magnet in the form of a monobloc piece with all or part of the steering wheel, thus further simplifying assembly and disassembly. 
   In another variant, the steering wheel could on the other hand be fixed directly on the rotating ring of the bearing. 
   Even though the description has been made in the illustrated example with an external element fixed to a revolving internal element, it is understood that the invention can also be applied without major modification to a structure in which the external element would be turning while the internal element would be fixed. 
   The invention offers a multi-use system in the form of a module which can be mounted on a fixed structure and which can be connected to different types of solenoids (electric solenoids for a road vehicle, a boat equipped with a “steer-by-wire” system, for example).