JP2007261408A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of consistently realizing the detection accuracy of a torque sensor consisting of a magnetostrictive unit and a coil. <P>SOLUTION: The electric power steering device 10 has a magnetostrictive torque sensor 41. A magnetostrictive torque sensor comprises a rotary shaft 24 with one end 24a being a free end, and an intermediate part 24d and the other end 24b being supported by a housing 51 via bearings 55-57, magnetostrictive units 81, 82 which are provided on a surface between the one end and the intermediate part of the rotary shaft with its magnetostrictive characteristic being changed according to the torque, and a coil which is arranged in a vicinity of the magnetostrictive unit to detect the magnetostrictive effect generated in the magnetostrictive unit. The one end of the rotary shaft is connected to a universal joint 23 and a steering wheel. The other end 24b of the rotary shaft is connected to steered wheels via a rack-and-pinion mechanism 25. A portion of the rotary shaft in a vicinity of the magnetostrictive unit is supported by a bearing 61 for the free end. The bearing for the free end is supported by the housing via an elastic body 63. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an electric power steering apparatus including a 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 via 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

9A and 9B are schematic views of a conventional electric steering apparatus.
As shown in FIG. 9A, 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. 9B) corresponding to the steering torque acts on the pinion 108. As shown in FIG. 9B, 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. 9A, 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.

In the invention which concerns on Claim 1, one end part is a free end, and the intermediate part and the other end part are supported by the housing via the bearing, On the surface between the one end part and intermediate part of this rotary shaft Electric power steering equipped with a magnetostrictive torque sensor, which is provided with a magnetostrictive portion that changes in magnetostriction characteristics according to torque, and a coil that is disposed in the vicinity of the magnetostrictive portion and detects a magnetostrictive effect generated in the magnetostrictive portion A device,
One end portion of the rotating shaft is a shaft end portion connected to the steering handle via the universal shaft joint and the steering shaft, and the other end portion of the rotating shaft is a shaft connected to the steering wheel via the rack and pinion mechanism. In the electric power steering device that is the end part,
The vicinity of the magnetostrictive portion of the rotating shaft is supported by a free end bearing, and the free end bearing is supported by a housing via an elastic body.

In the first aspect of the invention, since the free end bearing is supported by the housing via the elastic body, the free end bearing can be displaced in the radial direction by the elastic deformation of the elastic body. Accordingly, by supporting the vicinity of the magnetostrictive portion of the rotating shaft with such a free end bearing, the portion of the rotating shaft near the magnetostrictive portion is radially displaced by the amount that the free end bearing can be displaced. Can be displaced. In addition, since the rotating shaft is supported by the free end bearing, the rotating shaft can be elastically supported while smoothly rotating the rotating shaft, and the vibration of the rotating shaft can be attenuated.
Here, the radial force necessary to elastically deform the elastic body is referred to as “elastic reaction force”.

  When the driver steers the steering handle and the steering torque is transmitted to one end of the rotary shaft via the universal shaft joint, the universal shaft joint is tilted relative to the rotary shaft. A bending load acts on one end portion of the rotating shaft from. With respect to this bending load, one end of the rotating shaft can be gently bent by the amount of 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 portion such as the magnetostrictive film. Accordingly, since the detected value of the torque sensor composed of the magnetostrictive portion and the coil does not change suddenly, stable torque control can be performed.

  In addition, when the elastic body exceeds the deformation range, the free end bearing can be directly supported by the housing. For this reason, even if an excessive bending load acts on the one end part of a rotating shaft, the bending of a rotating shaft can be controlled. Therefore, an excessive bias does not occur in the gap (air gap) between the magnetostrictive portion 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 characteristic of the part where the tensile stress is generated and the magnetostrictive characteristic of the part where the compressive stress is generated 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 24a of the pinion shaft 24 is inclined by an angle θ1 (hereinafter referred to as “inclination angle θ1”) with respect to the center line CL1 of the pinion shaft 24. .
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. For example, the magnetostrictive films 81 and 82 are Ni—Fe alloy films formed on the outer peripheral surface of the pinion shaft 24 by vapor phase plating. 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 pinion shaft 24 (rotating shaft 24) may be configured so that the vicinity of the magnetostrictive portions 81 and 82 is supported by the free end bearing 61 in the space 24e between the one end portion 24a and the intermediate portion 24d. For example, it can be set as the structure of the modification shown in following FIG.6 and FIG.7.

FIG. 6 is a cross-sectional view showing a longitudinal cross-sectional structure of an electric power steering device (modification). FIG. 7 is an enlarged view around the torque sensor shown in FIG.
As shown in FIGS. 6 and 7, the electric power steering apparatus 10 according to the modification has a free end bearing between the serration 24 c (that is, one end portion 24 a) and the magnetostrictive portions 81 and 82 in the pinion shaft 24. It is the structure supported by 61, It is characterized by the above-mentioned. The free end bearing 61 is supported by the housing 51 via a bearing holding member 62 and an elastic body 63 in the same manner as in the configuration shown in FIGS.
Other configurations are the same as the configurations shown in FIGS. 3 to 5 described above, and thus the same reference numerals are given and description thereof is omitted.

As described above, the electric power steering device 10 according to the modified example is configured such that the position of the pinion shaft 24 near the one end 24a (position on the serration 24c side) from the magnetostrictive portions 81 and 82 is the free end bearing 61 and the elastic body 63. It is the structure supported by. For this reason, the dimension δ of the clearance Ag between the housing 51 and the bearing holding member 62 shown in FIG. 5 can be set larger than in the case of the embodiment shown in FIGS.
Therefore, the allowable range in which the one end 24a is displaced (deflected) in the radial direction can be increased by an amount corresponding to the increase in the dimension δ. Therefore, even if accuracy such as processing accuracy and assembly accuracy is loosened, the same effect as in the case of the embodiment shown in FIGS. 3 to 5 can be achieved.

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 rotating 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 7 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.

8A to 8D 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 sectional drawing which shows the longitudinal cross-section of an electric power steering apparatus (modification). FIG. 7 is an enlarged view around a torque sensor shown in FIG. 6. 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 (1)

One end is a free end and an intermediate part and the other end are supported by a housing via a bearing;
A magnetostrictive portion that is provided on a surface between one end portion and an intermediate portion of the rotating shaft, and whose magnetostrictive characteristics change according to torque;
An electric power steering device including a magnetostrictive torque sensor, which is disposed in the vicinity of the magnetostrictive portion and includes a coil for detecting a magnetostrictive effect generated in the magnetostrictive portion,
One end of the rotating shaft is a shaft end portion connected to a steering handle via a universal shaft joint and a steering shaft,
In the electric power steering apparatus, the other end portion of the rotating shaft is a shaft end portion connected to a steering wheel via a rack and pinion mechanism.
The vicinity of the magnetostrictive portion of the rotating shaft is supported by a free end bearing,
The free-end bearing is supported by the housing via an elastic body, and is an electric power steering device.

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