FR2841978A1 - Power assisted car steering rotation parameter detection coder having distance between rotation support center and peripheral outer surround varying progressively/continuously following angular offset - Google Patents

Abstract

The coder mechanism (8) has a support portion (13) with a circular slide section and a radial portion (14). The distance between the rotation center of the support and the exterior peripheral surround varies progressively and continuously as a function of the spatial angle considered.

Description

Encoder device for detection of rotation parameters, bearing at

  instrumented bearing and electric motor so equipped.

  The invention relates to the field of detection of parameters of rotation of an element with respect to another, for example a rolling bearing in which a rotating member of the bearing carries an encoder and a non-rotating member of the bearing carries a sensor in the purpose of determining the speed of rotation of the rotating element supporting the encoder. Such devices find their application in many fields, such as electric motors in which they are made to operate under severe temperature conditions, servomotors, angular detection devices used in

  power steering for automobiles.

  Document FR-A-2 754 903 discloses a rolling bearing comprising a sensor secured to the non-rotating ring, of the Hall effect probe type, and an encoder secured to the rotating ring scrolling in rotation with a small air gap by relative to the sensor while being capable of producing in the sensor a periodic signal of frequency proportional to the speed of rotation of the rotating ring. The encoder comprises an annular active part made with a plasto-magnet and provided with an active zone arranged opposite the sensor, supplemented by a reinforcing part composed of two annular elements arranged in contact with the active part, on each side of the active area. Such a bearing generally gives

  satisfaction, particularly in the field of electric motors.

  However, this type of encoder cannot operate at high temperatures, of the order of 1200. The sensor and the encoder do not function satisfactorily if they are subjected to strong external magnetic fields. Finally, the axial compactness of the

  rolling bearing thus instrumented is not optimal.

  In synchronous electric motors, motor control requires detection of the motor rotation parameters. It is indeed necessary to know the position of the rotor relative to the stator in order to be able to adapt the frequency, the intensity and the direction of the current entering the coils of the stator. The use of an encoder of the multipolar type associated with a Hall effect probe, can only be suitable for applications in which the power and the requirements of piloting precision are relatively low, and which do not require

  no absolute position information for motor control.

  The invention aims to remedy these drawbacks.

  The invention proposes an encoder for an instrumented rolling bearing, very axially compact, capable of operating at high temperatures while allowing precise detection, including

  understood when subjected to strong magnetic fields.

  The encoder device, according to one aspect of the invention, is intended for the detection of rotation parameters, in particular the absolute angular position of a rotating element. The encoder device includes a support portion having a circular bore, and a radial portion. The radial distance between the center of rotation of the support portion and the outer peripheral periphery of the radial portion opposite the circular portion varies gradually and continuously as a function of the angular position considered. It is thus possible to detect the angular position and the direction of rotation. In one embodiment, the support portion is a

axial portion.

  In one embodiment, the peripheral contour of the radial portion is circular, the geometric center of the circle defining said contour being located on an axis parallel to the axis of

rotation of the support portion.

  In one embodiment, the peripheral contour of the

  radial portion is oval and the radial portion is balanced in rotation.

  The rolling bearing, according to one aspect of the invention, comprises a rotating part and a non-rotating part, the rotating part comprising an encoder to allow detection, of rotation parameters, in particular the absolute angular position of the rotating part. The encoder includes a support portion having a circular bore, and a radial portion. The radial distance between the center of rotation of the support portion and the peripheral periphery of the radial portion opposite the circular portion varies gradually and continuously as a function of the angular position of the encoder relative to a reference of the non-rotating part. In one embodiment, the support portion is

  fitted onto a support belonging to the rotating part.

  In one embodiment, the bearing comprises a sensor provided with at least one radial planar micro-coil arranged opposite

of the encoder.

  In one embodiment, the coil is arranged on a support of a processing circuit mounted in a sensor block of the

non-rotating part.

  In one embodiment, the sensor is provided with at least one pair of micro-coils connected to a processing circuit capable of

generate a differential signal.

  In one embodiment, the encoder is arranged in

  the space between the bearing rings.

  In one embodiment, the sensor is arranged axially

  opposite the radial portion of the encoder.

  The electric motor, according to one aspect of the invention, comprises a rotor, a stator, at least one bearing for supporting the rotor, and a sensor assembly comprising an encoder and a sensor. The encoder includes a portion of the support having a circular bore, and a radial portion. The radial distance between the center of rotation of the circular portion and the peripheral periphery of the radial portion opposite the circular portion varies progressively and continuously as a function of a relative angular position of the encoder relative to

a fixed part.

  The motor can be of the synchronous type, in which one wishes to achieve fine control by precisely measuring the rotation parameters. In one embodiment, the device comprises a plurality of substantially co-planar receiving microbins

  radials. The sensor can thus perform precise detection.

  In another embodiment of the invention, the device comprises a plurality of receiving microbins arranged in a plurality of parallel radial planes. It is thus possible to have a higher number of reception coils ensuring increased precision. The coils can be produced in printed circuit technology. The support can be a printed circuit board or a

resin plate.

  Advantageously, the device comprises a plurality of microbools associated in pairs and angularly offset in order to generate a differential signal. Such a differential signal is less sensitive to electromagnetic fields. Detection accuracy

  rotation parameters is therefore increased.

  The encoder can be made in one piece. The encoder can

be made of stamped sheet metal.

  For reasons of compactness, it is wise to provide that the encoder is arranged in the space between the bearing rings, that is to say radially between the cylindrical surfaces of the rings which extend between the raceways and the frontal surfaces delimiting said rings, and axially in line with said cylindrical surfaces, between the rolling elements and the radial surfaces

of the bearing rings.

  In one embodiment of the invention, the sensor block is annular. In another embodiment of the invention, the blocker occupies an angular sector of less than 180, for example of

around 1200.

  In one embodiment of the invention, the data processing circuit is a chip produced specifically

(ASIC).

  The term “microbool” is understood here to mean a winding coil formed on a circuit, for example a copper coil on a printed circuit board. The thickness of the card and the micro-coil is

around 1 mm.

  The invention will be better understood on studying the description

  detail of some embodiments taken by way of non-limiting examples and illustrated by the appended drawings, in which: FIG. 1 is a view in axial section of an instrumented rolling bearing, according to an embodiment of the invention ; FIG. 2 is a partial view of the sensor of FIG. 1 — FIG. 3 is a front elevation view of the encoder of FIG. 1; FIG. 4 is a graph of the curves of the output signals of two coils; and

  FIG. 5 is an electrical diagram of the sensor.

  As illustrated in Figure 1, the rolling bearing 1 comprises an outer ring 2, an inner ring 3, a row of rolling elements 4, here balls, arranged between the outer ring 2 and the inner ring 3 and held by a cage 5, a seal 6 on one of its sides, and on the opposite side a speed sensor 5 secured to the outer ring 2 and an encoder 8 secured to

the inner ring 3.

  In the embodiment shown, the outer ring is non-rotating and the inner ring is rotating. However, the

  reverse arrangement is perfectly possible.

  The sensor 7 comprises a detection part 9 illustrated in more detail in FIG. 2, a support block 10 made of synthetic material, and a metal element 11 fitted on a surface of the outer ring 2, here in the groove usually used for the fixing of the seal provided in non-instrumented bearings. A cable 12 connected to the detection part 9 makes it possible to transmit speed information, or more generally rotation parameters, to other units able to use such data and which

were not represented.

  The metallic element 11 is completed by a short radial portion directed outwards from the portion 11a and in contact on one side with the radial end surface 2c of the outer ring 2, and on the other side with the support block 10 of the sensor 7, and by an axial portion lic extending from the free end of the radial portion llb which radially surrounds the support block 10, with the exception of the exit zone of the cable 12 o it is intended that the support block 10 extends outwards, forming a protuberance 21 surrounding the

cable 12 and protecting its output.

  The support block 10 is made of synthetic material and has a generally annular shape with the protrusion 21 projecting from its periphery and an axial recess from its radial face on the side of the bearing which constitutes a housing for the detection part 9 in covering it on its face opposite to the bearing and on its thickness in the radial direction. The support block 10 and the part of

detection 9 are interdependent.

  The encoder 8, see FIGS. 1 and 3, comprises a support part 13 and an operational part 14. The support part 13 is of tubular shape fitted on a cylindrical surface 3a of the inner ring 3 formed between the rolling track 3b which is in contact with the rolling elements 4 and a radial surface 3c which forms the end of the inner ring 3 in the axial direction on the side of the sensor. The operational part 14 is radial and has a periphery whose radial distance h relative to the support part 13 varies gradually and continuously as a function of the angular position cc relative to a reference. By "varies gradually and continuously" is meant the fact that the radial distance h is continuous and that the derivative of the radial distance h with respect to the angle cc which is written d is continuous. Here, the periphery 15 of the operational part 14 is circular and centered on an axis parallel to the axis of the support portion 13. In other words, the operational part 14 has a variable radial height h without

  present discontinuities of material in the circumferential direction.

  This variable radial height h can be expressed as a function of the angle by the relation h = e cos cc - r + R12- (e sincx) 2, see Figure 3. E is the eccentricity between the axis of rotation of the encoder and the geometric axis of the circle of radius Rd defining the periphery of the encoder; r is the radius of the circle defining the base of the operational part of the encoder. Furthermore, we have R = r + h. As a variant, the operational part 14 can be of oval circumference coaxial with the support part 13 or have a certain

number of lobes.

  The operational part 14 and the support part 13 are made in one piece, resulting in an economical and particularly robust construction. The encoder 8 can be produced from a

  sheet metal by means of stamping steps.

  It will be noted that the operational part 14 is slightly set back relative to the radial surface 3c of the inner ring 3. The encoder 8 is therefore particularly compact and is located in the space defined radially between the rings 2 and 3 of the bearing and axially between the rolling elements 4 and the radial plane through which

  pass the end surfaces 2c, 3c of said rings 2 and 3.

  The detection part 9 of the sensor 7 comprises a support 17 on which are mounted an integrated circuit 18, for example of the ASIC type, and which is intended for data processing, four microbools 19 to 22 offset by 900 two by two and four capacitors 23 to 26 (see FIG. 5), each arranged parallel to the microbools 19 to 22, in particular for filtering. Two microbools 19 and 21, 20 and 22 offset by 90 are arranged in series. Advantageously, the capacitors 23 to 26 are integrated in

circuit 18.

  The detection part 9 is disposed axially at a small distance from the operational part 14 of the encoder 8 and occupies an angular sector of the order of 1200, while being inserted in the support block 10 which is itself circular. The detection part 9 has a face not covered by the material of the support block 10 and oriented in

look of the encoder 8.

  The microbools 19 to 22 are of the planar winding type perpendicular to the axis of rotation and can be of the printed circuit type. The flatness of the windings provides excellent axial compactness to the sensor 7. In addition, the coils 19 to 22 have a square external contour and are arranged two on one side and the other of the data processing circuit 18 on the arc of circle formed by the support 17. The coils 19 to 22 and the capacitors 23 to 26 are connected to the data processing circuit 18, itself connected so

not shown on cable 12.

  The metal element 11 comprises a hook part 11a folded back in the groove of the outer ring 2 usually serving for the attachment of a sealing element which, in an uninstrumented bearing, is conventionally symmetrical to the seal

sealing 6.

  The operating mode of the sensor-encoder assembly is as follows. The coils 19 to 22 supplied with electrical energy, for example by a DC voltage, create a magnetic field whose field lines, which tend to pass through the operational part 14 of the encoder 8, are modified according to the radial height of the operational part 14. The rotation of the encoder therefore causes a linear variation of current in the coils, this constituting the basis of the signal.

  which will then be adequately processed by circuit 18.

  Each coil 19 to 22 is associated with a capacitor 23 to 26

  which contributes to the linearity of the signal.

  As the operational part 14 of the encoder 8 has a height varying sinusodally over one revolution, the output signal is an analog signal of simple sinusodal form which is interesting.

  for processing downstream of the sensor.

  The encoder can be made of a magnetic metallic material, such as steel, or non-magnetic, such as

aluminum or copper.

  It is advantageous to produce the encoder 8 from a nonmagnetic and electrically conductive material, in particular if use of the instrumented bearing in intense magnetic fields is planned. This prevents the intense magnetic field S outside the instrumented bearing from disturbing the measurement, for example

by saturation of the encoder.

  Microbools 19 to 22 operate in pairs 27, 28 to provide a differential signal. When the encoder scrolls in rotation in front of the sensor, the variation in radial height of the operational part 14 causes a variation in the metal mass which is located opposite the microbools 19 to 22. The pairs of coils 19 to 22 are angularly offset. The coils of the pair 27 are therefore arranged opposite a portion of the operational part 14 of radial height different from that of the portion of the operational part 14 opposite which the coils of the pair 28 are located. This results variations in different induced currents which generate a phase difference in the currents at the output of the coils. In FIG. 4, the waveforms of the signal at the output of each of the pairs 27, 28 of coils 19 to 22 are illustrated. This phase shift can then be processed and extracted adequately by the processing circuit 18, in order to obtain the desired information, such as absolute angular position, direction of rotation, speed, etc. Preferably, the pairs of coils are offset by 900 and output a sine signal and a cosine signal representative of the same angle O. The absolute angular position can then be calculated uniquely by 0 = Arctan (sinO / cosO), from causes the system to generate a single sine / cosine value per mechanical revolution of the encoder 8. This calculation can be performed by circuit 18

  or by another circuit mounted downstream and not shown.

  The generation of the electronic signal therefore does not depend on the level or direction of a magnetic field picked up by the microbobins, but on the modification of the currents induced in it in the presence of variations in the metallic masses passing past said microbobins. The coils 19 to 22 are distributed on the support 17 with a radial position and an adequate angular pitch to cooperate with the operational part 14 of the encoder 8 and supply the desired signals. It is possible, if necessary, to increase the number of coils 19 to 22 in the circumferential direction, or alternatively to use a stack of several coils in the axial direction, in order to obtain

stronger signals.

  Since the thickness of the microbrobes is extremely small, as is that of the processing circuit 18, the sensor 7 has extremely reduced axial dimensions, allowing integration into a sensor block 10 which itself has very small axial dimensions. Similarly, the encoder can, by its structure, have a very small axial thickness and be integrated without problem in the space between the rings of the bearing, so that said encoder does not affect the external dimensions of the bearing.

instrumented.

  In FIG. 5, the electrical functions of the system are illustrated in more detail. It can be seen that the coils 19 to 22 are grouped in two pairs referenced 27 and 28 and represented by a

frame in broken lines.

  The coils 19 to 22 and the capacitors 23 to 26 are connected to the processing circuit 18, which contributes to the linearity of the signals of the coils. The processing circuit 18 comprises two phase demodulators 29 and 30 connected to the output of each of the coils 19 to 22. The circuit 18 also comprises two interpolator comparators 31, 32,

  mounted respectively at the output of the phase demodulators 29 and 30.

  At output, the processing circuit 18 emits a digital signal representative of at least one parameter of rotation of the bearing, such as the absolute angular position, the direction of rotation, the speed, the acceleration, etc. This produces an instrumented bearing that can be easily integrated into a mechanical assembly due to its small size, capable of operating at high temperatures, such as those prevailing in an electric motor, and capable of operating in an environment.

  subjected to strong magnetic fields.

  These qualities confer on the instrumented bearing, according to the invention, advantageous aptitudes for its use in a high-power synchronous electric motor, the instrumented bearing being able to fulfill both the mechanical bearing function and the electronic detection functions necessary for piloting. of the motor. The instrumented bearing according to the invention can therefore be used in many industrial fields and applications, such as robots, steering columns for motor vehicles, handling vehicles, etc.

Claims (8)

  1-Encoder device (8) for detection of rotation parameters, in particular the absolute angular position of a rotating element, comprising a support portion (13) having a circular bore, and a radial portion (14), characterized by the fact that the radial distance between the center of rotation of the support portion (13) and the outer peripheral periphery (14a) of the radial portion (14) opposite the circular portion varies gradually and continuously as a function of the angular position considered.   2-Device according to claim 1, characterized in that   the support portion (13) is an axial portion.   3-Device according to claim 1 or 2, characterized in that the peripheral contour (15) of the radial portion is circular, the geometric center of the circle defining said contour being located on an axis parallel to the axis of rotation of the portion of support (13).   4-Rolling bearing (1) comprising a rotating part and a non-rotating part, the rotating part comprising an encoder (8) to allow detection of rotation parameters and in particular the absolute angular position of the rotating part, said encoder comprising a support portion (13) having a circular bore (13), and a radial portion (14), characterized in that the radial distance between the center of rotation of the support portion (13) and the peripheral periphery (15 ) of the radial portion (14) opposite the circular portion varies progressively and continuously as a function of the angular position of the encoder relative to a   reference of the non-rotating part.   -Stair according to claim 4, characterized in that the support portion (13) is fitted on a support belonging to the rotating part.   6-bearing according to claim 4 or 5, characterized in that it comprises a sensor (7) provided with at least one micro-coil   radial plane (19) arranged opposite the encoder.   7-bearing according to claim 6, characterized in that the coil (19) is disposed on a support (17) of a processing circuit   (18) mounted in a sensor block (10) of the non-rotating part.   8-bearing according to claim 6 or 7, characterized in that the sensor (7) is provided with at least one pair (24) of microbrobes connected to a processing circuit (18) capable of generating a signal differential.   9-bearing according to any one of claims   previous, characterized in that the encoder is arranged in   the space between the bearing rings (2, 3).   -Palier according to any one of the claims   previous, characterized in that the sensor (7) is arranged   axially opposite the radial portion (14) of the encoder (8).   il-Electric motor comprising a rotor, a stator, at least one bearing (1) for supporting the rotor, and a sensor assembly comprising an encoder (8) and a sensor (7), said encoder comprising a portion of the support (13) having a circular bore, and a radial portion (14), characterized in that the radial distance between the center of rotation of the circular portion (13) and the peripheral periphery (15) of the radial portion (14) at the opposite of the circular portion varies gradually and continuously depending on a   relative angular position of the encoder with respect to a fixed part.