Abstract:
Instrumented rolling bearing device of the type including a non-rotating race, a rotating race, at least one row of rolling elements arranged between two raceways of the rotating and non-rotating races, and an assembly for detecting rotation parameters including a non-rotating sensor assembly and a rotating encoder, and an elastic member intended for axially prestressing the rolling bearing, retained axially on the sensor, the elastic member being of annular shape and having a diameter smaller than or equal to that of the outer race of the bearing, the elastic member including a supporting surface designed to be in contact with an element outside the bearing device in order to exert, directly or indirectly, by reaction, an axial force on the non-rotating race in a direction opposite to the detection assembly.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to the field of instrumented rolling bearings fitted with an assembly for detecting rotation parameters, such as angular position, direction of rotation, speed and acceleration. The invention relates more particularly to an instrumented rolling bearing comprising a sensor secured to a non-rotating race and an encoder secured to a rotating race. 
   2. Description of the Relevant Art 
   Instrumented rolling bearings are used, for example, for controlling synchronous electric motors. The indexing of the sensor makes it possible to know, in particular, the speed of rotation and the angular position of the poles of the rotor in relation to the poles of the stator. 
   Document EP-A-1037051 discloses an instrumented rolling bearing device in which an encoder member is secured to a shaft, a sensor unit being secured to a rotating race. The non-rotating race is mounted in a bore in a fixed part to allow an axial displacement relative to the fixed part, conical washers exerting an axial force on the non-rotating race in order to keep it in position. 
   Because such a device uses a plurality of prestressing washers that are independent of the rolling bearing and of the detection system, the motor maker must thus manage, handle and assemble a large number of components. 
   SUMMARY OF THE INVENTION 
   Described herein is an instrumented rolling bearing that is economical and easy to install in a machine for which it is intended, for example, in an electric motor. 
   The instrumented rolling bearing device, in one embodiment, is of the type including a non-rotating race, a rotating race, at least one row of rolling elements arranged between two raceways of the rotating and non-rotating races, and an assembly for detecting rotation parameters comprising a non-rotating sensor assembly and a rotating encoder. The device includes an elastic member intended for axially prestressing the rolling bearing, retained axially on the sensor assembly. The elastic member is of an annular shape and has a diameter smaller than or equal to that of the outer race of the bearing. The elastic member includes a supporting surface designed to be in contact with an element outside the device in order to exert, directly or indirectly, by reaction, an axial force on the non-rotating race in a direction opposite to the detection assembly. 
   The axial retention of the elastic member on the detection assembly prior to mounting the detection assembly on the rolling bearing for which it is intended makes it possible to reduce the number of components to be procured and to be fitted. Manufacturing errors resulting from forgetting the elastic member are thus avoided. The detection assembly has a small radial bulk because of the elastic member, the outside diameter of which is smaller than or equal to that of the outer race of the bearing. The axial force may be exerted by direct contact of the elastic member on the non-rotating race. Alternatively, the axial force may be exerted by way of another element, for example a printed-circuit board. 
   In one embodiment, the elastic member is a corrugated washer. In another embodiment, the elastic member is a conical washer. In one embodiment, the elastic member is a washer provided with elastic tongues. 
   Advantageously, the sensor assembly includes a body or sensor unit fitted with means for retaining the elastic member. The retaining means includes at least one finger. 
   In one embodiment, the sensor assembly includes a printed circuit and a sensor element supported by the printed circuit, the elastic member being in contact with the printed circuit on an opposite side to the sensor element. The elastic member may be arranged axially between the printed circuit and means for retaining the elastic member forming part of the sensor assembly, the printed circuit taking part in transmitting the axial force between the non-rotating race and the elastic member. Apart from its radial compactness, the device may have satisfactory axial compactness. 
   In one embodiment, the rolling elements transmit said axial prestress from one race of the rolling bearing to the other. 
   In one embodiment, the elastic member for axially prestressing the rolling bearing pushes the non-rotating race away from said assembly for detecting rotation parameters. 
   Also described is an assembly for detecting rotation parameters including a non-rotating sensor assembly and a rotating encoder, and including an axially prestressing elastic member retained axially on the sensor assembly. The elastic member is of annular shape and has a diameter smaller than or equal to that of the sensor assembly. The elastic member comprises a supporting surface designed to be in contact with an element outside the device in order to exert, directly or indirectly, by reaction, an axial force on the detection assembly. 
   In one embodiment, the elastic member includes a washer. 
   Also described is an electric motor comprising a rotor, a stator, a rolling bearing and an instrumented rolling bearing device comprising a non-rotating race, a rotating race, at least one row of rolling elements arranged between two raceways of the rotating and non-rotating races, an assembly for detecting rotation parameters comprising a non-rotating sensor assembly and a rotating encoder, and an elastic member intended for axially prestressing said rolling bearing. The elastic member is retained axially on a sensor assembly while at the same time having an annular shape and a diameter smaller than or equal to that of an outer race of the rolling bearing. The elastic member includes a supporting surface designed to be in contact with an element outside the device in order to exert, directly or indirectly, by reaction, an axial force on the non-rotating race in a direction opposite to the detection assembly. 
   Advantageously, the elastic member is arranged axially between the sensor assembly and non-rotating part of the motor, for example a part of the casing or an added part coupled to the casing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings in which: 
       FIG. 1  depicts an axial cross-section view of an instrumented rolling bearing; 
       FIG. 2  depicts a perspective view of the rolling bearing of  FIG. 1 ; 
       FIG. 3  depicts an axial cross-section view of an electric motor; and 
       FIG. 4  depicts an alternate axial section of the electric motor of  FIG. 3 . 
   

   While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawing and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 1 , the instrumented rolling bearing, denoted in its entirety by reference  1 , is designed to be mounted on the end of a rotating shaft of an electric motor (not shown). The bearing  1  includes an outer race  2  provided with a raceway  3 , an inner race  4  provided with a raceway  5 , a row of rolling elements  6 , in this case balls, arranged between the raceways  3  and  5 , a cage  7  for maintaining the circumferential spacing between the rolling elements  5 , and a seal  8  fitted in a groove  9  in the outer race  2  on one side of the row of rolling elements  6 . The bearing  1  is, furthermore, equipped with a detection assembly  10  composed of an encoder  11  and of a sensor assembly  12 . 
   The encoder  11  comprises an annular support  13  having an S-shaped cross section, with a cylindrical portion push-fitted onto an outer bearing surface of the rotating inner race  4 , an outwardly directed radial portion and another cylindrical portion directed away from the rolling elements  6 , and an active part  14  in the form of a multi-pole ring made of plastoferrite or of elastoferrite overmolded onto the support  13 , the active part  14  being arranged axially so as to project relative to the radial frontal surfaces bounding the outer race  2  and inner race  4  of the bearing  1 . 
   The sensor assembly  12  includes a sensor unit  15  made of synthetic material and rigidly secured to the outer race  2 . The sensor unit  15  comes into contact with the frontal radial surface of the outer race  2  on the opposite side of the seal  8  and is fixed in a groove  16  that is symmetrical to the groove  9  relative to a plane passing through the center of the rolling elements  6 . The sensor unit  15  includes a substantially radial part  17  arranged axially between the rolling elements  6  and the radial part of the support  13  of the encoder  11 , and radially between the groove  16  and the cylindrical part of the support  13  push-fitted onto the outer bearing surface of the inner race  4 , and a substantially tubular part  18  having an outside diameter that is slightly smaller than the outside diameter of the outer race  2  and extending axially away from the rolling elements  6 . The tubular part  18  includes a bore  19  provided with a shoulder  20 . The tubular part  18  radially surrounds the active part  14  of the encoder  11 . 
   The sensor assembly  12  also includes a printed-circuit or integrated-circuit board  21  of annular shape that is fitted into the bore  19  until it comes into contact with the shoulder  20  arranged approximately at the center of the tubular part  18 , one or more sensor elements  22  supported by the board  21  on the side on which the encoder  11  is, and a ribbon connector  23 . The board  21  has a bore allowing a shaft of the motor to pass through. The sensor element or elements  22  may be of the Hall-effect type. The ribbon connector  23  is connected to the board  21  on the opposite side to the sensor elements  22  and comprises a plurality of conductors  24  that can transmit power and/or electrical signals. The sensor element or elements  22  are arranged with a slight axial gap with respect to the active part  14  of the encoder  11 . 
   As shown in  FIG. 2 , the bearing  1  additionally includes an axially prestressing member  25 , here taking the form of a corrugated washer, this member being arranged in the bore  19  and being in contact with the board  21  by way of a surface  25   a  on the same side as the ribbon connector  23 . Formed at the free end of the tubular part  18  of the sensor unit  15  are a plurality of fingers, of which three fingers  26  ensure that the board  21  is retained axially such that it is immobilized axially between the shoulder  20  and the fingers  26 . The fingers  26  project radially inward with respect to the bore  19 . 
   Also provided are three other retaining fingers  27 , likewise distributed circumferentially, for retaining the axially prestressing member  25 , these likewise projecting inward with respect to the bore  19 . The retaining fingers  27  are in contact with a surface  25   b  of the axially prestressing member  25  on the opposite side to the surface  25   a . The axially prestressing member  25  forms, with the bearing  1 , a pre-assembled subassembly that may be assembled economically with the other constituents of an electric motor. 
   As can be seen in  FIG. 3 , the instrumented rolling bearing  1  is mounted in a motor  28  of which only an end part is shown. The bore of the inner race  4  is fitted tightly on a shaft  29  secured to a rotor  30 . The outer race  2  is fitted in a motor casing  31  generally including a plurality of elements and of which only part is shown. The outer race  2  is installed with a sliding fit in a tubular portion  32  of the casing  31 . The casing  31  also has a radial part  33  that is arranged at the opposite end of the tubular part  32  to the rotor  30  and has an annular shape with a bore  34  through which the end of the shaft  29  and the ribbon connector  24  pass. The surface  25   b  of the axially prestressing member  25  bears on the inner radial face of the radial part  33  of the casing  31 . In this way, the axially prestressing member  25  tends to push the outer race  2  toward the rotor  30  by way of the board  21  and of the sensor unit  15 , and this allows the bearing  1  to be axially preloaded. 
   In  FIG. 4 , the motor  28  is partially represented schematically. The opposite end of the shaft  29  to the rolling bearing  1  is equipped with a non-instrumented conventional type of rolling bearing  35  with a row of rolling elements, comprising an outer race  36 , a row of rolling elements  37 , in this case balls, an inner race  38  secured to the shaft  29  with a tight fit, and a sealing element  39  secured to the outer race  36  and forming a narrow passage with the inner race  38 . The outer race  36  is mounted in the casing  31  of the motor, which includes a tubular part  40  and a radial part  41  arranged at the opposite end of the tubular part  40  to the rotor  30 , leaving a central passage open through which the shaft  29  projects. The outer race  36  of the rolling bearing  35  may be force-fitted into the tubular part  40 . Of course, the various parts  32 ,  33 ,  40  and  41  of the casing  31  are firmly connected together in a way that has not been shown. 
   The axial prestress exerted by the axially prestressing member  25  is transmitted from the outer race  2  of the rolling bearing  1  to the inner race  4  by way of the rolling elements  6 , then to the shaft  29 , to the inner race  38  of the rolling bearing  35 , to the rolling elements  37  and to the outer race  36 . It will be understood that the presence of a single axially prestressing member  25  allows the rolling bearing  1  and the rolling bearing  35  to be axially preloaded while accommodating different expansions of the shaft, generally made of steel, and of the casing, generally based on aluminum, the rolling bearing  1  being able to slide axially with respect to the casing supporting it. 
   The rolling bearing  1  is assembled as follows. The board  21  is positioned in the bore  19  of the sensor unit  15  until it comes into abutment with the shoulder  20 . The axially prestressing member  25  is then positioned in the bore  19  against the board  21 . Studs emanating from the free end of the tubular part  18  of the sensor  15  are then deformed by heating in order to form the retaining fingers  26  and  27  that determine the final position of, and axially retain, the board  21  and the axially prestressing member  25 . 
   The axially retaining member  25  thus bears against a part of the motor outside the rolling bearing and exerts, by reaction, an axial prestress on the non-rotating race, the rolling elements and the rotating race. The rolling bearing is preloaded axially. In the embodiment shown, the preload is transmitted by the board  21  and the sensor unit  15 ; however, it is also possible to provide direct contact of the axially prestressing member  25  with the sensor unit  15  or, alternatively, with the non-rotating race. 
   Of course, it would be possible to provide a rotating outer race and a non-rotating inner race according to the machine for which the rolling bearing is intended. The expressions “rotating” and “non-rotating” are to be understood in relative terms. 
   The assembly thus obtained is particularly compact, it may be transported and handled with complete safety without any risk of loss of the elastic washer. The motor manufacturer has one less component to procure, manage and fit. The assembly may be fitted in the motor particularly easily without requiring any special precautions. There are thus provided, with a single rolling bearing assembly, the bearing function, an electronic detection function, for example speed detection or angular-position detection, and the mechanical function of axially prestressing the rolling bearings of the motor. 
   Further modifications and alternative embodiments of various aspects of the invention may be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description to the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims. In addition, it is to be understood that features described herein independently may, in certain embodiments, be combined.