JP2013003037A - Torque sensor and electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a torque sensor with high torque detection accuracy and an electric power steering device.SOLUTION: When an input shaft 2a and an output shaft 2b are coupled by a torsion bar 2c, for example, recessed portions 13 and projecting portions 14 continuing in an axial direction are alternately formed on an outer peripheral surface of the input shaft 2a so as to be adjacent to each other in a circumferential direction. A high magnetic permeability portion 15 is provided on the outer side in a diametrical direction of the projecting portions 14, and a cylindrical member 16 made of a conductive and non-magnetic material is arranged so as to cover the recessed portions 13 and the projecting portions 14, and fixed to the output shaft 2b. A window 17 of which the exposure amount of the high permeability portion 15 changes according to relative rotations of the input shaft 2a and the output shaft 2b is formed on the cylindrical member 16. A coil 18 is arranged on an outer periphery of the cylindrical member 16 so as to cover the window 17. Steering torque T generated on the input shaft 2a and the output shaft 2b is calculated from the induced electromotive force of the coil 18.

Description

  The present invention relates to a torque sensor and an electric power steering apparatus, and is suitable, for example, for detecting torque generated in an input shaft and an output shaft of an electric power steering apparatus for a vehicle.

  As such a torque sensor, there exists a thing described in the following patent document 1 which this applicant proposed previously, for example. In Patent Document 1, when the first rotating shaft and the second rotating shaft are connected by a torsion bar, the first portion covered with the conductive and nonmagnetic material and the second portion covered with the magnetic material are, for example, For example, a cylindrical member made of a conductive and non-magnetic material is formed on the outer peripheral surface of the first rotating shaft alternately in the circumferential direction and is disposed so as to cover the first and second portions of the first rotating shaft. A window is formed on the cylindrical member that is fixed to the two rotation shafts, and the exposure amount of the first and second portions changes according to the relative rotation of the first rotation shaft and the second rotation shaft, and the cylinder is covered to cover the window. A coil is arranged on the outer periphery of the member. An alternating current is supplied to the coil, an induced electromotive force generated in the coil is detected, and a torque is calculated from the induced electromotive force. When relative rotation occurs between the first rotating shaft and the second rotating shaft, the exposure amounts of the first part and the second part exposed to the window change. Since the first part is covered with a conductive and non-magnetic material, when the exposure amount of the first part facing the coil increases, the inductance of the coil decreases and the induced electromotive force also decreases. On the other hand, since the second part is covered with a magnetic material, when the exposure amount of the second part facing the coil increases, the inductance of the coil increases and the induced electromotive force also increases. From the change in the induced electromotive force, the torque generated in the first rotating shaft and the second rotating shaft can be calculated. For example, if the first part and the second part are alternately formed in the circumferential direction on the outer periphery of the first rotating shaft, the exposure amount of the second part decreases when the exposure amount of the first part increases, and the first part When the exposure amount decreases, the exposure amount of the second part increases, so that the change in the induced electromotive force with respect to the relative rotation of the first rotating shaft and the second rotating shaft becomes steep.

JP-A-8-240492

However, for example, in an electric power steering apparatus, a more accurate torque sensor is required.
The present invention has been made paying attention to the above-described problems, and an object thereof is to provide a torque sensor and an electric power steering apparatus with high torque detection accuracy.

  In order to solve the above problems, a torque sensor according to the present invention includes a first rotating shaft, a second rotating shaft disposed coaxially with the first rotating shaft, the first rotating shaft and the second rotating shaft. A torsion bar, a recess and a projection that are formed along the axial direction of the first rotating shaft and are adjacent to each other in the circumferential direction of the first rotating shaft, and a first rotating shaft diameter of the protruding portion A high magnetic permeability portion provided on the outer side in the direction, and a cylindrical member made of a conductive and nonmagnetic material, disposed so as to cover the concave portion and the convex portion of the first rotating shaft, and fixed to the second rotating shaft A window formed in the cylindrical member so that an exposure amount of the high magnetic permeability portion changes according to relative rotation between the first rotating shaft and the second rotating shaft, and the cylinder so as to cover the window A coil disposed on the outer periphery of the member; and an electromotive force detection unit that detects an induced electromotive force of the coil; Is characterized in that a torque calculation unit for calculating a torque generated in the first rotary shaft and second rotary shaft from the induced electromotive force of the coil which is detected by the electromotive force detecting portion.

  The electric power steering apparatus according to the present invention is characterized in that the torque sensor is attached to an input shaft and an output shaft connected by a torsion bar, and torque generated in the input shaft and the output shaft is detected.

Thus, according to the torque sensor of the present invention, the exposed area of the high permeability portion of the convex portion facing the coil changes according to the relative rotation between the first rotating shaft and the second rotating shaft. The inductance and the induced electromotive force change, and the torque can be detected with high accuracy by calculating the torque generated in the first rotating shaft and the second rotating shaft from the induced electromotive force.
In addition, according to the electric power steering apparatus of the present invention, more accurate assist torque control can be performed using torque detected with high accuracy by a torque sensor.

It is a lineblock diagram showing one embodiment of an electric power steering device using a torque sensor of the present invention. It is a block diagram of the torque sensor of the electric power steering apparatus of FIG. It is a longitudinal cross-sectional view of the torque detection part of the torque sensor of FIG.

Next, an embodiment of a torque sensor and an electric power steering device of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of the electric power steering apparatus of the present embodiment. Reference numeral 1 in the drawing denotes a steering wheel attached to the rear end portion of the steering shaft 2 in the vehicle. The steering shaft 2 includes an input shaft (first rotating shaft) 2a to which the steering wheel 1 is attached, and an output shaft (second rotating shaft) 2b connected to the input shaft 2a via a torsion bar 2c (see FIG. 2). It is prepared for.

  A lower shaft 5 is connected to the lower end portion of the output shaft 2 b of the steering shaft 2 via the universal joint 4, and a pinion shaft 7 is connected to the vehicle front end portion of the lower shaft 5 via the universal joint 6. A pinion 8a is connected to the pinion shaft 7, the pinion 8a meshes with a rack 8b, and a tie rod 9 is connected to the rack 8b. The pinion 8a and the rack 8b constitute a rack-and-pinion type steering gear mechanism 8, and the rotational movement associated with the steering transmitted from the steering wheel 1 to the steering shaft 2, the lower shaft 5, and the pinion shaft 7 is the linear movement of the tie rod 9. Convert to

  The output shaft 2b of the steering shaft 2 is provided with an assist torque mechanism 10 that applies assist torque (steering assist force). The assist torque mechanism 10 includes a reduction gear mechanism 11 connected to the output shaft 2b, and an electric motor 12 connected to the reduction gear mechanism 11 and generating assist torque. For example, a brushless electric motor or the like is employed as the electric motor 12.

  The steering shaft 2 is provided with a torque sensor 31 that will be described in detail later. A motor drive unit 34 in the controller 33 is based on the steering torque T detected by the torque sensor 31 and the traveling speed V detected by the traveling speed sensor 32. The assist torque current command value is calculated by calculating the voltage command value by, for example, proportional-derivative control of the difference value between the calculated assist torque current command value and the motor drive current, and the motor drive voltage is calculated based on the calculated voltage command value. As a result, the motor current is supplied to the electric motor 12 to generate assist torque. The assist torque is transmitted to the output shaft 2b of the steering shaft 2 via the reduction gear mechanism 11, and the steering wheel 1 can be lightly steered.

  FIG. 2 is a configuration diagram of a torque detection unit provided in the torque sensor 31 and the controller 33. The torsion bar 2c is connected to the input shaft 2a at the right end of the figure, and is connected to the output shaft 2b at the left end of the figure, and many parts of the torsion bar 2c are built in the input shaft 2a. Yes. On the outer periphery of the end of the output shaft 2b side of the input shaft 2a that houses this torsion bar 2c, spline-like or serrated recesses 13 and projections 14 are alternately arranged adjacent to each other in the circumferential direction as shown in the longitudinal sectional view of FIG. Are evenly distributed. Since the concave portion 13 and the convex portion 14 are splined or serrated, they are continuous in the axial direction of the input shaft 2a. Furthermore, a high magnetic permeability portion 15 made of a high magnetic permeability member such as permalloy is provided on the outer side of the convex portion 14 in the radial direction of the input shaft 2a. In this embodiment, the concave portion 13 and the convex portion 14 are integrally formed on the outer peripheral surface of the input shaft 2a. However, the concave portion 13 and the convex portion 14 may be separate from the input shaft 2a, for example. However, it is necessary to rotate in synchronization with the input shaft 2a. Moreover, you may provide the recessed part 13 and the convex part 14 in the output shaft 2b. However, in that case, it is necessary to fix a cylindrical member to be described later to the input shaft 2a.

  A cylindrical member 16 disposed on the outer periphery of the input shaft 2a is fixed to an end of the output shaft 2b on the input shaft 2a side so as to cover the concave portion 13 and the convex portion 14 of the input shaft 2a. The cylindrical member 16 is made of a conductive and nonmagnetic material. Further, two coils 18 separated in the axial direction are provided on the outer periphery of the cylindrical member 16. A plurality of windows 17 are formed in a portion of the cylindrical member 16 facing the coil 18. 3a is, for example, a longitudinal section of a portion of the left coil 18 shown in FIG. 2, and FIG. 3b is, for example, a longitudinal section of a portion of the right coil 18 shown in FIG. The pitch is the same as the pitch of the concave portion 13 or the convex portion 14, but the phase of each coil 18 is shifted.

  2a shown in FIG. 2 shown in FIG. 3a and the right coil 18 shown in FIG. 3b shown in FIG. 3b, the individual heights provided on the radially outer side of the projection 14 in the drawing. The magnetic permeability portion 15 is exposed to the window 17 by half of the entire outer peripheral surface. In this state, when the cylindrical member 16, that is, the output shaft 2b is fixed and the concave portion 13 and the convex portion 14, that is, the input shaft 2a is rotated in the clockwise direction, the convex portion 14 in the window 17 of the cylindrical member 16 shown in FIG. The exposed area (exposure amount) of the high magnetic permeability portion 15 is reduced, and the exposed area (exposure amount) of the convex portion 14, that is, the high magnetic permeability portion 15 is increased in the window 17 of the cylindrical member 16 shown in FIG. On the other hand, when the output shaft 2b is fixed and the input shaft 2a is rotated in the counterclockwise direction, the exposed area (exposure amount) of the convex portion 14, that is, the high magnetic permeability portion 15 in the window 17 of the cylindrical member 16 shown in FIG. In the window 17 of the cylindrical member 16 shown in FIG. 3B, the exposed area (exposure amount) of the convex portion 14, that is, the high magnetic permeability portion 15, is reduced.

  Since the high magnetic permeability portion 15 exposed to the window 17 faces the coil 18, as described in Patent Document 1, when the exposure amount of the high magnetic permeability portion 15 facing the coil 18 increases, the coil 18. And the self-induced electromotive force when an alternating current is supplied also increases. Conversely, when the exposure amount of the high magnetic permeability portion 15 facing the coil 18 is reduced, the self-inductance of the coil 18 is reduced, and the self-induced electromotive force when an alternating current is supplied is reduced. Since the relative rotation of the output shaft 2b and the input shaft 2a is generated almost equally in the two coils 18, the more the input shaft 2a is rotated in the clockwise direction with respect to the output shaft 2b, that is, the torque in that direction is increased. The larger the coil 18 shown in FIG. 3a, the smaller the self-induced electromotive force, and the coil 18 shown in FIG. 3b has a larger self-induced electromotive force. Further, as the input shaft 2a is rotated in the counterclockwise direction with respect to the output shaft 2b, that is, as the torque in the direction increases, the self-induced electromotive force of the coil 18 shown in FIG. The coil 18 has a small self-induced electromotive force.

  A torque detection unit that detects torque from the self-induced electromotive force of each coil 18 rectifies and smoothes the self-induced electromotive force of each of the oscillation units 19 that simultaneously supply alternating currents having a predetermined frequency to the two coils 18. Rectifying / smoothing circuit 20 that outputs the difference, two differential amplifiers 21 that amplify and output the differential value of the outputs of the two rectifying / smoothing circuits 20, and noise that removes high-frequency noise components from the outputs of the individual differential amplifiers 21 A torque calculating unit 23 for calculating torque generated in the input shaft 2a and the output shaft 2b based on, for example, an average value of the outputs of the removal filter 22 and the two noise removal filters 22, that is, a steering torque T; The unit 34 drives the electric motor 12 so that an assist torque based on the steering torque T calculated by the torque calculation unit 23 is generated. To. As a method of calculating the steering torque T, for example, based on the average value of the outputs of the two noise removal filters 22, for example, the concave portion 13 and the convex portion, that is, the input shaft 2a and the cylindrical member 16, that is, the output shaft 2b The direction and size can be calculated, and the result can be obtained by multiplying the result by, for example, a predetermined proportional constant.

  In this torque detector, as described above, the differential rotation of the difference between the self-induced electromotive forces of the two coils 18 that change in the opposite directions depending on the relative rotation of the input shaft 2a and the output shaft 2b, that is, the direction of the steering torque. Therefore, the output of the differential amplifier 21 changes linearly according to the direction and magnitude of the steering torque. Further, since the differential amplifier 21 obtains the difference value of the rectifying / smoothing circuit 21, the change in self-inductance due to temperature or the like is cancelled.

  In the torque sensor described in Patent Document 1, when the sensitivity as a sensor is not sufficient as performance, it is necessary to amplify to the optimum value according to the conditions in the signal processing circuit section at the subsequent stage. As a negative effect, not only the sensor sensitivity but also the influence on the electrical signal due to disturbances (magnetism, radio waves, environment, etc.) to the torque detection unit is amplified, and there is a concern about the decrease in detection accuracy. There is a problem that the sensor sensitivity itself must be improved without relying on amplification.

  In the present embodiment, by disposing the high magnetic permeability portion 15 on the convex portion 14 of one rotating shaft, the spontaneous magnetization of the rotating shaft is enhanced and the torque detection sensitivity is improved. Further, the amount of spontaneous magnetization of one rotating shaft can be increased without increasing the amount of eddy current flowing through the cylindrical member 16 generated by the magnetic flux generated in the coil 18, that is, a conductive and nonmagnetic member, and the coil can be efficiently produced. Therefore, the torque sensor sensitivity can be improved, the torque sensor accuracy can be improved, the noise resistance can be improved, and the environment resistance can be improved.

Moreover, since only the convex part 14 should just be made into a magnetic body, the restrictions on a design reduce and the optimal material can be selected from the surface of a specification and cost as a structure, such as a part to which a load is applied.
As described above, in this embodiment, the high permeability portion 15 of the convex portion 14 facing the coil 18 is exposed in accordance with the relative rotation between the input shaft (first rotation shaft) 2a and the output shaft (second rotation shaft) 2c. Since the area changes, the inductance of the coil 18 and the induced electromotive force change, and the steering torque T generated in the input shaft (first rotating shaft) 2a and the output shaft (second rotating shaft) 2c is calculated from the induced electromotive force. Thus, the steering torque T can be detected with high accuracy.

In addition, more accurate assist torque control can be performed using the steering torque T detected with high accuracy by the torque sensor.
As described above, the cylindrical member 16 may be provided on the input shaft 2a, and the concave portion 13, the convex portion 14, and the high magnetic permeability portion 15 may be provided on the output shaft 2b. That is, any of the input shaft 2a and the output shaft 2b may be the first rotating shaft and the second rotating shaft of the present invention.

Further, as described above, even if there is only one coil 18, the self-induced electromotive force is changed by the relative rotation of the first rotating shaft and the second rotating shaft, so that the torque can be calculated even if only one coil 18 is used.
Further, as described above, the convex portion 13 and the concave portion 14 may be separate from the first rotating shaft or the second rotating shaft. However, it is necessary to rotate synchronously with the provided rotation shaft.

1 is a steering wheel 2 is a steering shaft 2a is an input shaft (first rotating shaft)
2b is an output shaft (second rotating shaft)
2c is a torsion bar 4 and 6 is a universal joint 5 is a lower shaft 7 is a pinion shaft 8 is a steering gear mechanism 9 is a tie rod 10 is an assist torque mechanism 11 is a reduction gear mechanism 12 is an electric motor 13 is a recess 14 is a protrusion 15 is high Permeability unit 16 is a cylindrical member 17 is a window 18 is a coil 19 is a starting unit 20 is a rectifying / smoothing circuit 21 is a differential amplifier 22 is a noise elimination filter 23 is a torque calculation unit 31 is a torque sensor 32 is a running speed sensor 33 is a controller 34 is a motor drive unit

Claims (2)

  A first rotating shaft, a second rotating shaft disposed coaxially with the first rotating shaft, a torsion bar connecting the first rotating shaft and the second rotating shaft, and an axial direction of the first rotating shaft A concave portion and a convex portion that are continuous along the circumferential direction of the first rotating shaft, a high permeability portion that is provided on the outer side in the radial direction of the first rotating shaft of the convex portion, and conductive and A cylindrical member made of a non-magnetic material and disposed so as to cover the concave and convex portions of the first rotating shaft and fixed to the second rotating shaft, and a relative relationship between the first rotating shaft and the second rotating shaft A window formed in the cylindrical member so that an exposure amount of the high magnetic permeability portion changes according to rotation; a coil disposed on an outer periphery of the cylindrical member so as to cover the window; and induction of the coil An electromotive force detection unit for detecting an electromotive force, and an induced electromotive force of the coil detected by the electromotive force detection unit. Torque sensor is characterized in that a torque calculation unit for calculating a torque generated in the first rotary shaft and second rotary shaft.   An electric power steering apparatus, wherein the torque sensor according to claim 1 is attached to an input shaft and an output shaft connected by a torsion bar, and torque generated in the input shaft and the output shaft is detected.

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