JP5108482B2 - Magnetostrictive torque sensor and electric power steering apparatus equipped with magnetostrictive torque sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize further the detection accuracy of a torque sensor comprising magnetostrictive sections and coils. <P>SOLUTION: A electric power steering apparatus 10 includes a magnetostrictive torque sensor 41. The magnetostrictive torque sensor comprises a rotating shaft 24 of which one end 24a is a free end, and an intermediate part 24d and the other end 24b are supported by a housing 51 through bearings 55-57, two magnetostrictive sections 81, 82 which are arranged on the surface between one end and the intermediate part and of which magnetostrictive characteristics vary with torque, and coils which are arranged close to the magnetostrictive sections and detect magnetostrictive effects produced in the magnetostrictive sections. One end of the rotating shaft is connected to a universal coupling 23 and a steering wheel. The other end 24b of the rotating shaft is connected to steer wheels through a rack and pinion mechanism 25. The rotating shaft is supported by a bearing 61 at the part between two magnetostrictive sections. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a magnetostrictive torque sensor and an electric power steering apparatus equipped with the magnetostrictive torque sensor.

Some electric power steering apparatuses steer a steering wheel with a rack shaft by a combined torque obtained by adding an auxiliary torque of an electric motor to a steering torque of a driver. In such an electric power steering device, when the driver steers the steering handle, the steering torque is transmitted from the rotating shaft to the rack shaft through the rack and pinion mechanism, and the steering torque detected by the magnetostrictive torque sensor is used. The auxiliary torque generated accordingly is also transmitted to the rack shaft, and various types are known (for example, see Patent Document 1).
JP 2004-245636 A

FIGS. 7A and 7B are schematic views of a conventional electric steering apparatus.
As shown in FIG. 7A, a conventional electric power steering apparatus 100 according to Patent Document 1 connects one end 102a of a rotating shaft 102 to a steering handle (not shown) via a steering shaft and a universal shaft joint 101, A rack shaft 104 is connected to the other end 102 b of the rotating shaft 102 via a rack and pinion mechanism 103, and a steering wheel is connected to the rack shaft 104. The rotating shaft 102 is supported by a housing 107 through two bearings 105 and 106 except for one end 102a. That is, only the both ends of the pinion 108 of the rack and pinion mechanism 103 in the rotating shaft 102 are supported by the two bearings 105 and 106.

  Furthermore, the electric power steering apparatus 100 includes a magnetostrictive torque sensor 110. The magnetostrictive torque sensor 110 detects the steering torque of the steering system applied to the steering handle. The magnetostrictive films 111 and 112 provided on the surface of the one end portion 102a of the rotating shaft 102, and the magnetostrictive films 111, It consists of coils 113 and 114 arranged in the vicinity of 112. Since the magnetostrictive characteristics of the magnetostrictive films 111 and 112 change according to the torque acting on the rotating shaft 102, the torque can be detected magnetically by detecting this with the coils 113 and 114.

When the steering handle is steered, a reaction force F1 (see FIG. 7B) corresponding to the steering torque acts on the pinion 108. As shown in FIG. 7B, the reaction force F1 causes a bending moment to act on the rotating shaft 102, so that the rotating shaft 102 bends as indicated by an imaginary line.
In this case, the one end 102a of the rotating shaft 102 bends due to the influence of the bending angle α generated by the action of the bending moment due to the reaction force F1.

Incidentally, as shown in FIG. 7A, the center line CL12 of the universal joint 101 is inclined by an angle θ2 (hereinafter referred to as “inclination angle θ2”) with respect to the center line CL11 of the rotating shaft 102. The inclination angle θ2 is determined by the arrangement relationship between the steering handle and the housing 107, and the constant speed of the steering handle and the pinion 108, that is, the rotational speed of the pinion 108 is made equal to the steering speed of the steering handle. Is set to approximately 10 ° to 30 °.
Moreover, the universal shaft joint 101 is connected to the one end 102a of the rotating shaft 102, so that the movement of the rotating shaft 102 in the axial direction is restricted.

  When the center lines CL11 and CL12 coincide with each other, that is, when the inclination angle θ2 is 0 (θ2 = 0), the universal joint 101 follows to some extent even if the one end 102a of the rotating shaft 102 is bent. .

  However, when the center line CL12 of the steering shaft and the universal joint 101 is inclined with respect to the center line CL11 of the rotating shaft 102, there is a limit to follow the bending of the one end 102a of the rotating shaft 102. For this reason, the universal shaft joint 101 performs a pulling action when the one end portion 102a of the rotating shaft 102 is about to bend, and functions to suppress the bending action of the one end portion 102a by the pulling force. As a result, the force F <b> 2 that suppresses the bending, that is, the suppression force F <b> 2 acts on the one end portion 102 a. This restraining force F2 increases according to the steering torque.

  For example, when the rack shaft 104 is slid to the slide end position by the steering handle, the rack shaft 104 cannot slide any further. Still, when the steering wheel is steered, the steering torque is further increased. As a result, since the suppression force F2 increases, a large bending moment acts on the one end portion 102a of the rotating shaft 102.

  An object of the present invention is to provide a technique that can further stabilize the detection accuracy of a torque sensor including a magnetostrictive portion and a coil.

According to the first aspect of the present invention, two magnetostrictive portions are provided on the surface of the rotating shaft and at a predetermined interval in the longitudinal direction of the rotating shaft, and the magnetostrictive characteristics change according to torque, and the two magnetostrictive portions. disposed in the vicinity of the section, Do and a coil for detecting a magnetostrictive effect occurs in the two magnetostrictive portions Ri, a magnetostrictive torque sensor that is housed in the housing, the rotary shaft is located between the two magnetostrictive portions There is supported by a bearing, both end faces in the axial direction of the inner ring of the bearing surface der that is not in contact either directly or indirectly with respect to the rotation axis is, not the torque is added to the rotational axis in absence, the bearing holding member relative to the housing, characterized that you have been arranged with a gap.

According to a second aspect of the present invention, in the first aspect, the one end portion of the rotating shaft is a free end that is not supported in the radial direction.
According to a third aspect of the present invention, in the second aspect of the present invention, in the second aspect, the rotary shaft is positioned in a position opposite to the one end with respect to the two magnetostrictive portions by a bearing different from the bearing in the axial direction. It is characterized in that it is supported so as to be rotatable while its displacement is restricted.

In the invention according to claim 4 , the magnetostrictive torque sensor according to any one of claims 1 to 3 is used as a steering torque sensor for detecting a steering torque of a steering system generated by a steering handle. And mounted on an electric power steering device for steering a steering wheel by driving an electric motor based on the steering torque, and one end of the rotating shaft is connected to a universal shaft joint and a steering shaft. It is a shaft end portion connected to the steering handle, and the other end portion of the rotating shaft is a shaft end portion connected to the steering wheel via a rack and pinion mechanism.

In the invention according to claim 1, the position between the two magnetostrictive portions of the rotating shaft is supported by the bearing. For this reason, even if a bending load acts on a rotating shaft, the bending of the position between the two magnetostrictive parts in a rotating shaft can be controlled. As a result, the bending of the positions of the two magnetostrictive portions on the rotating shaft is also restricted. Therefore, an excessive bias does not occur in the gap (air gap) between the two magnetostrictive portions and the coil.
In addition, the two magnetostrictive portions include a portion where tensile stress is generated and a portion where compressive stress is generated due to the rotation shaft being bent by a bending load. However, since the bending of the rotating shaft due to an excessive bending load is restricted, the difference between the magnetostrictive property of the portion where the tensile stress occurs in the magnetostrictive portion and the magnetostrictive property of the portion where the compressive stress occurs can be suppressed as much as possible. .
For this reason, the rotating shaft and the two magnetostrictive portions can suppress the influence of the bending load acting on the rotating shaft. Accordingly, the detection accuracy of the torque sensor including the magnetostrictive portion and the coil can be further stabilized, so that stable torque control can be performed.

  Furthermore, since the position between the two magnetostrictive portions of the rotating shaft is supported by the bearing, when a bending moment acts on the rotating shaft, a substantially equal bending moment acts on the two magnetostrictive portions. For this reason, the influence of the bending moment which each acts on two magnetostriction parts can be made substantially equivalent. As a result, the magnetostriction characteristics of the two magnetostrictive portions can be made substantially equal. Accordingly, the detection accuracy of the torque sensor including the magnetostrictive portion and the coil can be further stabilized, so that stable torque control can be performed.

In the invention which concerns on Claim 2, the one end part of a rotating shaft is made into the free end. For this reason, when a bending load is applied to a position closer to the other end than the bearing supporting between the two magnetostrictive portions of the rotating shaft, only a relatively small bending moment acts on the magnetostrictive portion. That's okay. As a result, the influence of the bending moment acting on the magnetostrictive portion can be further reduced. Accordingly, the detection accuracy of the torque sensor including the magnetostrictive portion and the coil can be further stabilized, so that stable torque control can be performed.
In the invention according to claim 3, the rotating shaft is rotatable at a position opposite to the one end with respect to the two magnetostrictive portions while being restricted in displacement in the axial direction by a bearing different from the bearing. It is supported.

In the invention according to claim 4 , when the driver steers the steering handle and the steering torque is transmitted to one end of the rotating shaft via the universal shaft joint, the universal shaft joint is inclined with respect to the rotating shaft. Therefore, a bending load acts from the universal shaft joint to one end of the rotating shaft.

  Since the position between the two magnetostrictive portions on the rotating shaft is supported by the bearing, even if an excessive bending load acts on one end portion of the rotating shaft, the bending of the rotating shaft can be restricted. Therefore, an excessive bias does not occur in the gap (air gap) between the two magnetostrictive portions and the coil.

  In addition, the magnetostrictive portion includes a portion where tensile stress is generated and a portion where compressive stress is generated because the rotating shaft is bent by the bending load. However, since the bending of the rotating shaft due to an excessive bending load is restricted, the difference between the magnetostrictive property of the portion where the tensile stress occurs in the magnetostrictive portion and the magnetostrictive property of the portion where the compressive stress occurs can be suppressed as much as possible. .

  For this reason, the rotating shaft and the magnetostrictive portion can suppress the influence of the bending load acting on the rotating shaft from the universal joint regardless of the magnitude of the steering torque. Accordingly, the detection accuracy of the torque sensor including the magnetostrictive portion and the coil can be further stabilized, so that stable torque control can be performed.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. Hereinafter, an example in which the torque sensor is mounted on the electric power steering apparatus will be described.

  FIG. 1 is a schematic diagram of an electric power steering apparatus according to the present invention. The electric power steering apparatus 10 includes a steering system 20 that extends from a steering handle 21 of a vehicle to steering wheels (front wheels) 29 and 29 of the vehicle, and an auxiliary torque mechanism 40 that applies an auxiliary torque to the steering system 20.

The steering system 20 is connected to the steering handle 21 via the steering shaft 22 and the universal shaft joints 23 and 23, one end 24 a of the pinion shaft 24 (that is, the rotating shaft 24), and racked to the other end 24 b of the pinion shaft 24. A rack shaft 26 is connected via an and pinion mechanism 25, and left and right steering wheels 29, 29 are connected to both ends of the rack shaft 26 via left and right tie rods 27, 27 and knuckles 28, 28.
The rack and pinion mechanism 25 includes a pinion 31 formed on the pinion shaft 24 and a rack 32 formed on the rack shaft 26.

  According to the steering system 20, when the driver steers the steering handle 21, the steering wheels 29 and 29 can be steered via the rack and pinion mechanism 25 by the steering torque.

The auxiliary torque mechanism 40 detects the steering torque of the steering system 20 applied to the steering handle 21 with the torque sensor 41, generates a control signal with the control unit 42 based on this detection signal, and responds to the steering torque based on this control signal. The auxiliary torque is generated by the electric motor 43, the auxiliary torque is transmitted to the pinion shaft 24 via the worm gear mechanism 44, and the auxiliary torque is transmitted from the pinion shaft 24 to the rack and pinion mechanism 25 of the steering system 20. Mechanism.
According to the electric power steering apparatus 10, the steering wheels 29 and 29 can be steered by the rack shaft 26 by a combined torque obtained by adding the auxiliary torque of the electric motor 43 to the steering torque of the driver.

FIG. 2 is an overall configuration diagram of the electric power steering apparatus according to the present invention, in which the left end portion and the right end portion are cut away. This figure shows that the rack shaft 26 of the electric power steering apparatus 10 is accommodated in a housing 51 extending in the vehicle width direction (left-right direction in FIG. 2) so as to be slidable in the axial direction.
The rack shaft 26 is a shaft in which tie rods 27 and 27 are connected to both longitudinal ends protruding from the housing 51 via ball joints 52 and 52. 53 and 53 are dust seal boots.

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2 and shows a vertical cross-sectional structure of the electric power steering apparatus 10. FIG. 4 is an enlarged view around the torque sensor shown in FIG.
As shown in FIG. 3, the electric power steering apparatus 10 houses a pinion shaft 24, a rack and pinion mechanism 25, a torque sensor 41 and a worm gear mechanism 44 in a housing 51, and the upper opening of the housing 51 is closed by an upper housing 54. It is a thing. Hereinafter, the term “housing 51” includes the upper housing 54.

  The electric motor 43 has a motor shaft that extends horizontally from the other side of the paper into the front housing 51. The motor shaft is an output shaft connected to the worm shaft 46 of the worm gear mechanism 44. The worm shaft 46 includes a worm 47 formed integrally. The housing 51 rotatably supports both ends of the worm shaft 46 extending horizontally through bearings.

  The worm gear mechanism 44 is configured to transmit torque from the worm 47 to the load side via the torque transmission worm wheel 48 by meshing the drive side worm 47 with the torque transmission worm wheel 48. Further, the worm gear mechanism 44 includes an auxiliary worm wheel 49 in addition to the torque transmitting worm wheel 48. The auxiliary worm wheel 49 is an auxiliary gear provided to remove backlash between the worm 47 and the torque transmitting worm wheel 48.

As shown in FIGS. 1 and 3, one end portion 24 a of the pinion shaft 24 (rotating shaft 24) is a shaft end portion connected to the steering handle 21 via the universal shaft joints 23 and 23 and the steering shaft 22. The one end 24a has a serration 24c for connecting the universal shaft joint 23 to the shaft end. The center line CL2 of the universal shaft joint 23 connected to the one end portion 24a of the pinion shaft 24 is inclined with respect to the center line CL1 of the pinion shaft 24 by an angle θ1 (hereinafter referred to as “inclination angle θ1”). .
On the other hand, the other end 24 b of the pinion shaft 24 is a shaft end portion connected to the steering wheel 29 via the rack and pinion mechanism 25.

  As shown in FIG. 3, the pinion shaft 24 is supported by the housing 51 only through the three bearings 55 to 57 except for the one end 24 a. In other words, the pinion shaft 24 has one end 24 a as a free end, and the intermediate portion 24 d and the other end 24 b are supported by the housing 51 via the bearings 55 to 57.

  More specifically, the pinion shaft 24 is provided with a torque transmitting worm wheel 48 at the shaft longitudinal central portion 24d (intermediate portion 24d), and the magnetostriction of the torque sensor 41 at one end side (one end portion 24a) from the shaft longitudinal central portion 24d. Portions 81 and 82, and a pinion 31 on the other end side (the other end portion 24b) with respect to the shaft longitudinal center portion 24d.

The shaft end position of the other end 24 b of the pinion shaft 24 is rotatably supported by the housing 51 via the first bearing 55. In the intermediate portion 24 d of the pinion shaft 24, the position between the pinion 31 and the torque transmission worm wheel 48 is rotatably supported by the housing 51 via the second bearing 56. In the intermediate portion 24 d of the pinion shaft 24, the position between the torque transmitting worm wheel 48 and the magnetostrictive portions 81 and 82 is rotatably supported by the housing 51 via the third bearing 57. These three bearings 55 to 57 are rolling bearings such as ball bearings.
The pinion shaft 24 is restricted from moving in the axial direction with respect to the housing 51 by, for example, the second bearing 56 being constituted by a four point contact bearing.

  Here, the one end portion 24 a of the pinion shaft 24 means the serration 24 c side with respect to the magnetostrictive portions 81 and 82. Since the one end 24a is not supported by the three bearings 55 to 57, it can be said that it is basically a free end.

  3 and 4, the pinion shaft 24 is supported by a free end bearing 61 in the vicinity of the magnetostrictive portions 81 and 82, that is, between the one end portion 24a and the intermediate portion 24d. . The free end bearing 61 is referred to as a free end bearing because it is a bearing that supports the space 24e between the one end 24a and the intermediate portion 24d, which are free ends. The support structure by the free end bearing 61 will be described below.

  5 (a) and 5 (b) are a sectional view and an operation view around the free end bearing and the elastic body shown in FIG. As shown in FIGS. 4 and 5A, the free end bearing 61 is a rolling bearing such as a ball bearing. The free end bearing 61 is supported by the housing 51 via an elastic body 63.

More specifically, the two magnetostrictive portions 81 and 82 of the pinion shaft 24 are fitted into the free end bearing 61 so that the free end bearing 61 has a gap 24e between the one end 24a and the intermediate portion 24d. It can be rotatably supported.
The free end bearing 61 is mounted in an annular bearing holding member 62 with its relative rotation and axial movement restricted. The bearing holding member 62 has an annular groove 62b on the outer peripheral surface 62a, and an annular elastic body 63 is attached to the groove 62b by fitting. The elastic body 63 is made of a material having a predetermined flexibility such as rubber, and is made of, for example, an O-ring.

  Such a bearing holding member 62 is housed in the housing 51 with its axial movement restricted. The outer diameter D2 of the bearing holding member 62 is set smaller than the inner diameter D1 of the housing 51. For this reason, a gap Ag having a dimension δ is provided between the inner surface 51 a of the housing 51 and the outer peripheral surface 62 a of the bearing holding member 62. When the bearing holding member 62 is fitted into the housing 51, the outer peripheral surface of the elastic body 63 is in a state of being substantially in contact with the inner surface 51 a of the housing 51.

  The space 24e between the one end 24a and the intermediate portion 24d of the pinion shaft 24 can be displaced in the radial direction by the dimension δ of the gap Ag. That is, when the pinion shaft 24 is bent, the elastic body 63 can be elastically deformed according to the force acting in the radial direction. As a result, as shown in FIG. 5B, the bearing holding member 62 can be displaced until the outer peripheral surface 62 a contacts the inner surface 51 a of the housing 51. At this time, the center line CL1 of the pinion shaft 24 is eccentric by the dimension δ. In this way, the housing 51 can support the portion 24e between the one end portion 24a and the intermediate portion 24d of the pinion shaft 24 so as to be eccentric to some extent, so-called floating support.

  As shown in FIG. 3, the housing 51 includes an oil seal 58 and a rack guide 70. The rack guide 70 includes a guide portion 71 that contacts the rack shaft 26 from the opposite side of the rack 32, an adjustment bolt 73 that pushes the guide portion 71 through the compression spring 72, a contact member 74 that slides the back surface of the rack shaft 26, It consists of a lock nut 75 for positioning the adjustment bolt 73.

As shown in FIGS. 3 and 4, the torque sensor 41 is provided on the surface of the pinion shaft 24 and a portion 24e between the one end portion 24a and the intermediate portion 24d of the pinion shaft 24, and the magnetostriction characteristics change according to the torque. The magnetostrictive torque sensor includes a pair of upper and lower magnetostrictive portions 81 and 82 and coils 85 and 85 that are disposed in the vicinity of the magnetostrictive portions 81 and 82 and detect the magnetostrictive effect generated in the magnetostrictive portions 81 and 82. .
In other words, the torque sensor 41 includes a pair of magnetostrictive portions 81 and 82 provided on the pinion shaft 24 and a pair of detection portions 83 and 83 provided around the magnetostrictive portions 81 and 82.

  As shown in FIG. 4, the magnetostrictive portions 81 and 82 are made of a magnetostrictive film in which residual strains in opposite directions are given to the longitudinal direction of the pinion shaft 24. The magnetostrictive films 81 and 82 are films made of a material having a large change in magnetic flux density with respect to a change in strain. is there. The thickness of this alloy film is desirably about 5 to 20 μm. The thickness of the alloy film may be less than or greater than this. The magnetostriction direction of the second magnetostrictive film 82 is different from the magnetostriction direction of the first magnetostrictive film 81 (having magnetostriction anisotropy). The two magnetostrictive films 81 and 82 are arranged with a predetermined interval in the axial longitudinal direction.

  Ni-Fe-based alloy films tend to increase the magnetostriction effect when the Ni content is approximately 20% by weight and approximately 50% by weight, so that the magnetostriction effect tends to increase. Is preferably used. For example, as the Ni—Fe-based alloy film, a material containing 50 to 60% by weight of Ni and the rest being Fe is used. The magnetostrictive films 81 and 82 may be ferromagnetic films, such as permalloy (Ni; about 78 wt%, Fe; remaining) or supermalloy (Ni; 78 wt%, Mo; 5 wt%, Fe; remaining). ). Here, Ni is nickel, Fe is iron, and Mo is molybdenum.

  As shown in FIG. 4, the pair of detection units 83 and 83 electrically detect the magnetostriction effect generated in the magnetostriction units 81 and 82 and output the detection signal as a torque detection signal. It is stored in.

The detection unit 83 includes a pair of upper and lower cylindrical coil bobbins 84 and 84 passed through the pinion shaft 24, coils 85 and 85 wound around the coil bobbins 84 and 84, and a coupler 86 provided in the coil bobbins 84 and 84, It consists of coil bobbins 84 and 84 and a yoke 87 having magnetism for accommodating the coils 85 and 85. The coil bobbins 84 and 84 and the coils 85 and 85 can be surrounded by the yoke 87.
The coil 85 is disposed so as to surround the pinion shaft 24. The coupler 86 is a terminal portion that takes out the detection signals of the pair of coils 85 and 85 to the outside.

  The yoke 87 is a magnetic shielding back yoke (coil yoke forming a magnetic path) surrounding the pair of coils 85 and 85, and is made of a magnetic material. The yoke 87 includes a pair of upper and lower yoke bodies 88, 88 and a yoke bottom plate 89 that closes the openings of the yoke bodies 88, 88. The yoke 87 is housed in the housing 51 with its radial movement and axial movement restricted.

  As shown in FIG. 4, a leaf spring 91 is interposed between the lower end of the bearing holding member 62 and the yoke body 88 in the detection unit 83 below the bearing holding member 62. The leaf spring 91 is a member for removing the backlash by absorbing the axial clearance between the bearing holding member 62 and the detection portions 83 and 83 housed in the housing 51. It consists of an annular spring, for example a disc spring.

The above description is summarized as follows.
In the present invention, the free end bearing 61 is supported by the housing 51 (including the upper housing 54; the same applies hereinafter) via the elastic body 63, so that the free end bearing 61 is elastically deformed. It can be displaced in the radial direction as much as possible. Therefore, by supporting the vicinity of the magnetostrictive portions 81 and 82 of the rotating shaft 24 (pinion shaft 24) with such a free end bearing 61, the portion of the rotating shaft 24 near the magnetostrictive portions 81 and 82 is The free end bearing 61 can be displaced in the radial direction by the amount displaceable. Moreover, since the rotating shaft is supported by the free end bearing 61, the rotating shaft 24 can be elastically supported while the rotating shaft 24 is smoothly rotated, and the vibration of the rotating shaft 24 can be attenuated.
Here, the radial force necessary to elastically deform the elastic body 63 is referred to as “elastic reaction force”.

  When the driver steers the steering handle 21 and the steering torque is transmitted to the one end 24 a of the rotary shaft 24 via the universal shaft joint 23, the universal shaft joint 23 is inclined with respect to the rotary shaft 24. A bending load acts on the one end portion 24a of the rotary shaft 24 from the universal shaft joint 23 by the amount. With respect to this bending load, the one end portion 24a of the rotating shaft 24 can be gently bent by the elastic reaction force. As a result, it is possible to suppress a sudden change in the magnetostrictive characteristics due to a sudden stress generated in the magnetostrictive portions 81 and 82 such as a magnetostrictive film. Therefore, since the detected value of the torque sensor 41 including the magnetostrictive portions 81 and 82 and the coils 85... Does not change suddenly, stable torque control can be performed.

  In addition, the free end bearing 61 can be directly supported by the housing 51 when the elastic body 63 exceeds the deformation range. For this reason, even if an excessive bending load acts on the one end part 24a of the rotating shaft 24, the bending of the rotating shaft 24 can be regulated. Therefore, an excessive bias does not occur in the gap (air gap, gap) Ag between the magnetostrictive portions 81 and 82 and the coils 85.

  Further, when the rotating shaft 24 is bent by a bending load, the magnetostrictive portions 81 and 82 have a portion where tensile stress is generated and a portion where compressive stress is generated. However, since the bending of the rotary shaft 24 due to an excessive bending load is restricted, the difference between the magnetostrictive characteristics of the magnetostrictive portions 81 and 82 where the tensile stress is generated and the magnetostrictive characteristics of the portion where the compressive stress is generated is suppressed as much as possible. can do.

  For this reason, the rotating shaft 24 and the magnetostrictive portions 81 and 82 can suppress the influence of the bending load acting on the rotating shaft 24 from the universal shaft joint 23 regardless of the magnitude of the steering torque. Therefore, since the detection accuracy of the torque sensor 41 composed of the magnetostrictive portions 81 and 82 and the coils 85... Can be further stabilized, stable torque control can be performed.

  By the way, the pinion shaft 24 shown in FIGS. 1 to 5 transmits steering torque to the rack shaft 26 to steer the steering wheels 29 and 29, so that high mechanical strength is required. For example, the pinion 31 needs to have sufficient mechanical strength such as wear resistance and fatigue strength (fatigue strength). Therefore, the pinion shaft 24 is often subjected to heat treatment such as carburizing and induction hardening in order to ensure sufficient strength necessary for high load torque transmission.

However, various heat effects such as bending deformation may occur in the pinion shaft 24 subjected to the heat treatment. This tendency is greater as the pinion shaft 24 is longer.
A pinion shaft manufacturing method for correcting such bending deformation will be described with reference to FIG.

6A to 6D are explanatory views for explaining the outline of the method for manufacturing a pinion shaft according to the present invention. The manufacturing procedure of the pinion shaft 24 will be described as follows.
First, as shown in (a), the pinion shaft 24 is machined to form the pinion 31 and the like.
Next, in the pinion shaft 24, in order to increase the mechanical strength of the pinion 31, etc., heat treatment such as carburizing treatment or induction hardening is performed. The pinion shaft 24 may be slightly bent and deformed under the influence of heat treatment. At this time, the center line of the pinion shaft 24 is CLb.
Next, as shown in (b), the both ends of the pinion shaft 24 are set on the jig Ji, and the correction load Fc is applied from the direction perpendicular to the axis to perform the bending correction process. In this way, the bending deformation of the pinion shaft 24 is corrected to obtain the pinion shaft 24 with the least bending deformation as shown in FIG.
Next, as shown in (d), a predetermined position of the pinion shaft 24 is plated to provide the magnetostrictive films 81 and 82, thereby completing the operation.
The bending correction process may be performed after the plating process.

  Thus, by correcting the bending deformation of the pinion 31, a gap (air gap) is formed between the magnetostrictive films 81 and 82 provided on the surface of the pinion 31 and the coils 85 shown in FIG. It is possible to suppress the occurrence of excessive bias.

In the embodiment of the present invention, the electric power steering apparatus 10 is configured to add auxiliary torque generated according to the steering torque detected by the magnetostrictive torque sensor 41 to the rotating shaft 24 (pinion shaft 24). It is not limited, For example, the structure added to the rack axis | shaft 26 may be sufficient.
The intermediate portion 24d of the pinion shaft 24 may be supported by only the second bearing 56 without providing the third bearing 57.
The presence or absence of the bearing holding member 62 is arbitrary, and for example, the elastic body 63 may be directly attached to the free end bearing 61.

  The electric power steering device of the present invention is configured to transmit the steering torque generated by the steering handle to the rotating shaft via the steering shaft and the universal shaft joint, and further to the steering wheel from the rotating shaft via the rack and pinion mechanism. The steering torque transmitted to the rotating shaft is detected by a magnetostrictive torque sensor, and the electric motor generates auxiliary torque according to the detection signal of the magnetostrictive torque sensor, and this auxiliary torque is added to the steering system. Therefore, it is suitable for an electric power steering device for a vehicle.

1 is a schematic diagram of an electric power steering apparatus according to the present invention. 1 is an overall configuration diagram of an electric power steering apparatus according to the present invention. FIG. 3 is a sectional view taken along line 3-3 in FIG. 2. FIG. 4 is an enlarged view around a torque sensor shown in FIG. 3. FIG. 5 is a cross-sectional view and action diagram of the free end bearing and the elastic body shown in FIG. 4. It is explanatory drawing explaining the outline | summary of the manufacturing method of the pinion shaft which concerns on this invention. It is a schematic diagram of the conventional electric steering device.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus, 20 ... Steering system, 21 ... Steering handle, 22 ... Steering shaft, 23 ... Universal shaft joint, 24 ... Rotating shaft (pinion shaft), 24a ... One end of rotating shaft, 24b ... Rotating shaft Other end portion, 24c ... serration, 24d ... intermediate portion, 24e ... between one end portion and intermediate portion of the rotating shaft, 25 ... rack and pinion mechanism, 29 ... steering wheel, 41 ... magnetostrictive torque sensor, 51 ... housing, 55 to 57 ... bearings, 61 ... bearings for free ends, 62 ... bearing holding members, 63 ... elastic bodies, 81 and 82 ... magnetostrictive portions (magnetostrictive films), 84 ... coil bobbins, 85 ... coils, CL1 ... centerlines of rotating shafts .

Claims (4)

Two magnetostrictive portions that are provided on the surface of the rotating shaft and at a predetermined interval in the longitudinal direction of the rotating shaft, and the magnetostrictive characteristics change according to torque;
Disposed in the vicinity of the two magnetostrictive portions, Do and a coil for detecting a magnetostrictive effect occurs in the two magnetostrictive portions Ri, a magnetostrictive torque sensor that is housed in the housing,
The rotating shaft is supported by a bearing at a position between the two magnetostrictive portions,
The end faces of the inner ring in the axial direction of the bearing, Ri surface der that is not in contact either directly or indirectly to said rotary shaft,
The bearing located between the two magnetostrictive portions is a bearing whose outer peripheral surface is held by a bearing holding member;
In a state where no said torque is applied to the rotary shaft, the bearing holding member, the magnetostrictive torque sensor relative to said housing, and characterized that you have been arranged with a gap.   The magnetostrictive torque sensor according to claim 1, wherein one end of the rotating shaft is a free end that is not supported in a radial direction.   The rotary shaft is rotatably supported at a position opposite to the one end with respect to the two magnetostrictive portions, while being restricted in axial displacement by a bearing different from the bearing. The magnetostrictive torque sensor according to claim 2. The magnetostrictive torque sensor according to any one of claims 1 to 3 is used as a steering torque sensor for detecting a steering torque of a steering system generated by a steering handle, and based on the steering torque. It is mounted on an electric power steering device that steers steering wheels by driving an electric motor,
One end portion of the rotating shaft is a shaft end portion connected to the steering handle via a universal shaft joint and a steering shaft,
An electric power steering apparatus equipped with a magnetostrictive torque sensor, wherein the other end of the rotating shaft is a shaft end connected to the steering wheel via a rack and pinion mechanism.

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