JP2001122136A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a cylindrical rotor of a motor for steering assistance constituted inside a housing of a steering shaft to be displaced in accordance with deflection of the steering shaft, and to prevent obstruction of motion converting action of a ball screw mechanism constituted by the steering shaft and a ball nut constituted on one side of the rotor. SOLUTION: This device is constituted so that the cylindrical rotor 52 of the motor 5 for steering assistance is radially supported by a radial bearing 6 inside a rack housing H1 supporting a rack shaft 1 and a motor housing H3, an annular spring 9 wound around a recessed groove 9a provided in a relevant position of the rotor 52 is elastically contacted to an inside of the radial bearing 6, and the rotor 52 is displaceable inside a fitting gap with the radial bearing 6 in a position of support by the radial bearing 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor for assisting steering in a housing supporting a steering shaft such as a rack shaft in a rack and pinion type steering device, coaxially with the steering shaft, and rotation of the motor. And a ball screw mechanism that converts the linear motion into linear motion and transmits the linear motion to the steering shaft.

[0002]

2. Description of the Related Art A steering assist electric motor (hereinafter referred to as a motor) is driven based on a detection result of a steering torque applied to a steering wheel for steering, and the torque of the motor is transmitted to a steering device to perform steering. The assisted electric power steering device controls the assist force characteristics according to the traveling state, such as the speed of the vehicle, the frequency of the steering, and the like, as compared with the hydraulic power steering device using the hydraulic actuator as the source of the steering assist force. In recent years, there is an advantage that the applicable range can be expanded.

[0003] Various types of steering devices for automobiles have been put into practical use, one of which is a rack and pinion type steering device. That is, a rack shaft (steering shaft) having rack teeth formed over a predetermined length in the axial direction extends in the left-right direction of the vehicle body, and both ends of the rack shaft are steered via tie rods. And a pinion shaft meshing with the rack teeth is connected to a steering wheel via a column shaft, and the operation of the steering wheel for steering is transmitted to the rack shaft via the pinion shaft. The steering is performed by moving the rack shaft in the axial direction.

When such a rack-and-pinion type steering device is configured as an electric power steering device, the rotation of a steering assist motor is directly transmitted to a rack shaft, and the rack shaft is moved in the axial direction. Is reasonable. For this purpose, it is necessary to dispose a steering assist motor around the rack shaft.However, around the position where the rack shaft is arranged, a motor capable of generating sufficient rotational force for steering assist is provided. There is a problem that it is difficult to secure an occupied space.

In order to solve this problem, the applicant of the present invention has a steering assist motor coaxially formed inside a cylindrical housing for supporting a rack shaft so that the generated force of the motor is transmitted to the rack shaft. The proposed electric power steering device. FIG. 5 is a partially cutaway front view showing a configuration of a main part of the electric power steering device.

[0006] intermediate portion of the movably supported by the rack shaft 1 to the inside in the axial direction of the as shown in the cylindrical rack housing H _1, the rack teeth 11 are formed over a predetermined length, pinion housing Pinion shaft 4 at the intersection with H ₂
Meshed with a pinion 40 integrally formed at the lower end of the
The rotation of the pinion shaft 4 in response to the operation of a steering wheel (not shown) is converted into the axial lengthwise movement of the rack shaft 1 at the meshing portion between the pinion 40 and the rack teeth 11, and this movement is transmitted to the left and right steered wheels. This constitutes a rack-and-pinion type steering device that performs steering.

[0007] motor 5 for assisting the steering operation performed by the movement of the thus rack shaft 1, cylindrical configured integrally intermediate portion with enlarged diameter over a suitable length of the rack housing H ₁ motor housing H ₃ , a stator 51 fixed to the inner peripheral surface of the motor housing H ₃ , and a cylindrical rotor 52 supported on both left and right sides by a pair of bearings 54, 55 and rotating inside the stator 51. It is comprised including.

On one side of the rotor 52, a ball screw mechanism 2 that converts the rotation of the rotor 52 into a linear motion and transmits it to the rack shaft 1 is formed. The ball screw mechanism 2, the coaxially connected to one end of the rotor 52, the ball nut 20 supported to the rack housing H ₁ by a bearing 56
, And a screw rail 21 formed on the outer periphery of the rack shaft 1 including a portion inserted into the ball nut 20 are screwed together via a large number of balls 22, 22.

With the above construction, the ball nut 20 rotates integrally with the rotation of the motor 5, that is, the rotation of the rotor 52 upon energization of the stator 51, about the axis. 22 ... are the screw rails 21 on the outer circumference of the rack shaft 1
, The rack shaft 1 is mounted on each of the balls 22, 22.
Is pressed by the axial component of the acting force applied to the screw rail 21 and is moved in the axial direction, and this movement assists the steering performed as described above.

In the electric power steering apparatus constructed as described above, the steering assist motor 5 is provided with the rack housing H ₁ for supporting the rack shaft 1 as a steering shaft.
Some are constructed in the interior of the motor housing H ₃ formed by diameter and can be arranged without the need for large becomes occupied space around the rack shaft 1. As a motion conversion mechanism for converting the rotation of the motor 5 into the movement of the rack shaft 1, a ball screw mechanism 2 using screw advancement is used, and the motion conversion process involves deceleration (increase). Therefore, the size of the motor 5 can be reduced, and the occupied space can be further reduced.

[0011]

In the above arrangement, the ball screw mechanism 2 used as a motion converting mechanism is used to reliably transmit the power from the steering assist motor 5 to the rack shaft 1. High accuracy is required for each part, and in particular, it is necessary to enhance concentricity between the ball nut 20 and the rack shaft 1. Therefore,
The ball nut 20 is fitted to one side of the rotor 52 rigidly by press-fitting, and the concentricity between the two is increased, and the processing of these support portions by the bearings 54, 55, 56 is performed with high accuracy. A desired concentricity is ensured between the ball nut 20 and the rack shaft 1.

Thus, the rack shaft 1 at the time of assembly is
Although it is possible to secure concentricity between the rack shaft 1 and the ball nut 20, the rack shaft 1 being steered may be bent by the action of the road surface reaction force applied to the steered wheels connected to both ends thereof. In addition, the deflection causes the concentricity secured at the time of assembly to be deviated, and the screw thread 21 of the outer periphery of the rack shaft 1 and the ball nut 20 prevent the ball screw mechanism 2 for motion conversion constituted as described above from being screwed badly. In addition, there is a problem that smooth rolling of the balls 22, 22,... Along the screw rails 21 is hindered, and uneven torque due to this is perceived by the driver as a sense of being caught, resulting in deterioration of the steering feeling. There was a problem of doing.

[0013] The above-mentioned construction is similar to the rack shaft 1 in the rack and pinion type steering device described above, and various types of steering devices having a steering shaft that is steered according to the movement in the axial direction can be provided by an electric power steering. The present invention can be applied to a case where it is configured as a device, and the above-described problem similarly occurs in such an electric power steering device.

The present invention has been made in view of such circumstances, and has a cylindrical rotor for a steering assist motor formed inside a housing of a steering shaft, and a ball nut connected to one side thereof. Between the screw rail formed on a part of the steering shaft and the ball nut due to concentric misalignment such as deflection of the steering shaft. It is an object of the present invention to provide an electric power steering device that prevents the occurrence of a steering motion and reduces the impediment to the motion conversion operation of the ball screw mechanism, thereby preventing deterioration of the steering feeling.

[0015]

An electric power steering apparatus according to a first aspect of the present invention is rotatably supported coaxially with the steering shaft inside a cylindrical housing for supporting the steering shaft. A steering assist motor having a cylindrical rotor, and a ball screw mechanism having a ball nut connected to one side of the rotor, wherein the rotation of the rotor is converted into linear motion by the ball screw mechanism, An electric power steering device configured to transmit to a steering shaft and assist the steering by moving the steering shaft in the axial direction, wherein the electric power steering device is interposed between a bearing that radially supports the rotor and the rotor or the housing. And an elastic body having elasticity in a radial direction.

In the present invention, when the steering shaft is bent during steering, a bearing for radially supporting the rotor of the steering assist motor is deformed by an elastic body interposed between the rotor and the housing. Displaced in the radial direction following the deflection, the concentricity between the ball nut connected to one side of the rotor and the steering shaft is maintained, and the operation inhibition of the ball nut mechanism is prevented.

An electric power steering apparatus according to a second aspect of the present invention is characterized in that the elastic body is formed by an annular spring wound around the outer periphery of the rotor, projecting radially outward and elastically contacting the inner surface of the bearing. The electric power steering apparatus according to the third invention, wherein the elastic body is wound around an inner periphery of the housing,
The bearing is characterized by being constituted by an annular spring projecting inward in the radial direction and elastically contacting the outer surface of the bearing.

In these inventions, an annular spring wound around an inner surface or an outer surface of a bearing for radially supporting the rotor is wound around the outer periphery of the rotor or the inner periphery of the housing to elastically displace the rotor in the radial direction. Is simply and reliably realized.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 1 is a partially broken front view showing a configuration of a main part of an electric power steering device according to the present invention (hereinafter referred to as the present device).

[0020] figure 1 is a rack shaft, the interior of the rack housing H ₁ forming the lateral direction extending in-cylinder-shaped body, not shown, it is constrained to rotate about its axis by a rotation restraining means which is not shown, is slidably supported in the axial direction, the rack shaft 1 respectively protrude on both sides of the rack housing H ₁ both ends, left and right of the steering wheel (typically, not shown, via a respective tie rods Front wheel).

[0021] an intermediate portion of the rack housing H ₁ causes the cross it and the shaft center and the pinion housing H ₂ is continuously provided, the inside of the pinion housing H _2, rotatable at about its axis A pinion shaft 4 is supported on the shaft.
Pinion shaft 4, Yes by suitable lengths projecting on top of the pinion housing H _2, the protrusion is connected to a steering wheel via a column shaft (not shown), about an axis in response to operation of a steering wheel for steering It is designed to rotate.

[0022] The lower part of the pinion housing of H ₂ pinion shaft 4 which extends inside, as shown by the dashed line in the figure, the pinion 40 is formed integrally. Further, the bearing has been to the rack shaft 1 in the rack housing H _{in. 1} are formed rack teeth 11 over the axial direction to a predetermined length range, the pinion shaft at the intersecting position between the pinion housing H ₂ 4 In the lower part of the pinion 40.

When the steering wheel is operated for steering, the pinion shaft 4 is rotated in accordance with the operation, and the rotation is converted by the engagement of the pinion 40 and the rack teeth 11 and the rack is rotated. The shaft 1 moves in the axial direction, and this movement is transmitted to left and right steering wheels via tie rods at both ends, and these steering wheels are steered according to the operation of the steering wheel. Is configured.

In the apparatus of the present invention, the motor 5 for assisting the steering performed as described above is provided by the rack housing H.
₁ of the intermediate portion in the interior of a suitable cylindrical constituted by enlarged diameter over a length motor housing H _3, the stator 51 and the rotor 52
And a three-phase brushless motor comprising:

The rotor 52 is a cylindrical body having an inner diameter larger than the outer diameter of the rack shaft 1, is inserted through a middle part of the rack shaft 1 so as to surround the outer side, and the motor housing H
It is supported rotatably around the axis of ₃ . Also, the stator 51 is fixed to the inner circumferential surface of the motor housing H _3, Yes is opposed through a slight gap between the magnetic pole 53 held on the outer periphery of the rotor 52, depending on the energization of the said stator 51 Thus, the rotor 52 is configured to rotate in both forward and reverse directions.

The above as the motor 5 for steering assist which is configured, the stator 51 based on the detection result of the torque sensor (not shown) configured in the interior of the pinion housing H ₂
Is driven to generate a rotational force corresponding to the magnitude of the steering torque in the direction of the steering torque applied to the steering wheel, and the rotation is performed by a movement provided on one side of the rotor 52. The linear motion is converted by the ball screw mechanism 2 for conversion and transmitted to the rack shaft 1.

The ball screw mechanism 2 is fitted in an enlarged diameter portion 52a extending to one side of the rotor 52, and the enlarged diameter portion 52a
And a cylindrical ball nut 20 inserted around the outside of the rack shaft 1 so as to surround the middle of the rack shaft 1, and the rack shaft 1 including a portion inserted into the ball nut 20. And a screw rail 21 formed over a predetermined length on the outer periphery of the ball screw, and screwed together via a large number of balls 22, 22,.

With the above structure, the ball nut 20 connected to one side of the rotor 52 rotates integrally with the rotation of the motor 5, that is, the rotation of the rotor 52 when the stator 51 is energized. Then, according to this rotation, the balls 22,
Are rolled along the screw rails 21 on the outer periphery of the rack shaft 1. As described above, the rack shaft 1 restrained from rotating around the shafts is rotated by the balls 22, 22,.
Pressed by the axial component of the acting force applied to 21,
The steering performed as described above is assisted by the movement of the rack shaft 1 in the axial direction.

In the apparatus of the present invention, the rotor 52 of the motor 5 for assisting steering and the ball nut 20 integrally connected to one side of the motor 52, as shown in FIG. If, by the other side of the radial thrust combined bearing 7 of the rotor 52, it is rotatably supported in the motor housing H ₃ while maintaining concentricity between the rack shaft 1. The feature of the device of the present invention lies in the configuration of a support portion formed by the radial bearing 6 that supports the connection side with the ball nut 20.

FIG. 2 is an enlarged cross-sectional view showing the vicinity of a support portion on one side of the rotor 52 by the radial bearing 6. As shown in the figure, the radial bearing 6 has an inner ring
52 along with the tightening of the lock nut 60 screwed on the outer surface to sandwiched and fixed between the end surface of the enlarged diameter portion 52a of the outer ring which is fitted into the motor housing H _3, screw on the inner surface of the motor housing H ₃ This is a ball bearing configured to abut against the mating lock nut 61 to mainly bear a radial load acting on the rotor 52.

On the outer peripheral surface of the rotor 52, a concave groove 9a is formed over the entire circumference at the outer fitting position of the radial bearing 6 as described above, and a leaf spring is annularly formed inside the concave groove 9a. An annular spring 9 formed and wound is wound around and elastically contacts the inner surface of the radial bearing 6.

FIG. 3 is a perspective view of the annular spring 9. As shown in the figure, the annular spring 9 is formed by forming a thin strip made of a material having a high elasticity such as spring steel into a portion having a suitable width at one place in the circumferential direction.
It is formed into an annular shape with an excess of 90, for the force acting radially inward with the reduced width of the notch 90, and for the force acting radially outward with the widening of the notch 90 On the other hand, it is configured to generate a spring force against each of them.

As shown in FIG. 2, the annular groove 9a formed on the outer periphery of the rotor 52 is mounted in an annular spring whose inner diameter d (see FIG. 3) in the natural state is larger than the outer diameter of the bottom of the groove 9a. 9, the annular spring 9 is reduced in diameter along with the reduced width of the notch portion 90 and is housed in the concave groove 9a, and the radial bearing outwardly projecting outward is fitted at the corresponding position. 6 is restrained by the inner surface.

With the above configuration, the rotor 52 can be displaced in the radial direction at the position supported by the radial bearing 6 within the range of the fitting gap between the rotor 52 and the spring force of the annular spring 9. Accordingly, the ball nut 20 integrally connected to the same side can also be displaced in the radial direction. Here, in the middle part of the rack shaft 1 which constitutes the ball screw mechanism 2 together with the ball nut 20, bending occurs due to the effect of the road surface reaction force applied to the steered wheels connected to both ends in accordance with the aforementioned steering. However, at this time, in the device of the present invention, the ball nut 20 is displaced as described above following the bending of the rack shaft 1, and the concentricity between the two is maintained.

Therefore, the balls 22, 22,... Between the screw rail on the inner periphery of the ball nut 20 and the screw rail 21 on the outer periphery of the rack shaft 1 are formed.
Is smoothly performed without being affected by the bending of the rack shaft 1, the operation of the ball nut mechanism 2 is not hindered by the bending, and the rotation from the rotation of the motor 5 to the movement of the rack shaft 1 is prevented. Motion conversion can be performed favorably.

FIG. 4 is an enlarged sectional view showing another embodiment in the vicinity of the support portion of the radial bearing 6 on one side of the rotor 52. In this view, the annular spring 9 is wound around the motor housing H ₃ of the inner surface of the corresponding position in the formed recess groove 9b,
The inner surface of the annular spring 9 projecting inward is elastically contacted with the radial bearing 6. The configuration of the other parts is the same as the configuration of the support part shown in FIG. 2 described above, and the same reference numerals as those in FIG. 2 are assigned and the detailed description is omitted.

The mounting of the annular spring 9 to the motor housing H ₃ of the inner surface which is formed in the groove 9b in the inner diameter D in the natural state (see FIG. 3), the groove 9b bottom small annular spring than the inner diameter of 9 and the annular spring 9 is connected to the missing portion.
The diameter is increased with the width of 90 and is accommodated in the concave groove 9b, and the radially inward protrusion is restrained by the outer surface of the radial bearing 6 fitted in the corresponding position.

With the above construction, the rotor 52 and the ball nut 20 are displaced in the radial direction against the spring force of the annular spring 9 within the range of the fitting gap between them at the position supported by the radial bearing 6. The screw rail on the inner circumference of the ball nut 20 and the screw rail 21 on the outer circumference of the rack shaft 1
Are caused to engage with each other via the balls 22, 22, and the ball nut mechanism 2 is operated without being hindered by the bending of the rack shaft 1, and from the rotation of the motor 5 to the movement of the rack shaft 1. Can be satisfactorily performed.

In the above embodiment, the annular spring 9 is used as an elastic body interposed between the bearing for radially supporting the rotor of the steering assist motor and the rotor or the housing. An elastic body such as a spring or hard rubber may be used.

Further, in the above-described embodiment, the configuration in which the rotation of the steering assist motor is transmitted to the rack shaft of the rack and pinion type steering device has been described. In another type of steering device having a steering shaft that performs steering by moving to the steering shaft, it can be applied to convert the rotation of the steering assist motor to linear motion and transmit it to the steering shaft, and in these cases also, Needless to say, the effect is obtained.

[0041]

As described in detail above, in the device of the present invention, the bearing for supporting the rotor of the steering assist motor, which is coaxial with the steering shaft, is radially supported by the housing of the steering shaft, and the rotor or the housing. Since the elastic body is interposed, the rotor may be displaced in the radial direction with deformation of the elastic body together with the ball nut connected to one side, following the deflection generated on the rack shaft during steering. As a result, the concentricity of the ball nut and the steering shaft is maintained, and a proper threaded state is always obtained in the motion converting ball screw mechanism formed by the two, realizing a good motion converting operation, Sensation can be prevented from deteriorating.

Further, since the elastic body is constituted by an annular spring which is wound around the outer periphery of the rotor or the inner periphery of the housing and elastically contacts the inner periphery or the outer periphery of the bearing, the elastic member in the radial direction of the rotor follows the deflection of the steering shaft. The present invention has excellent effects such that the displacement can be realized simply and surely, and the motion conversion operation by the ball nut mechanism can always be appropriately performed.

[Brief description of the drawings]

FIG. 1 is a partially cutaway front view showing a configuration of a main part of a device of the present invention.

FIG. 2 is an enlarged sectional view of the vicinity of a support portion on one side of a rotor.

FIG. 3 is a perspective view of an annular spring used as an elastic body in the device of the present invention.

FIG. 4 is an enlarged sectional view showing another embodiment in the vicinity of a support portion on one side of a rotor.

FIG. 5 is a partially cutaway front view showing a configuration of a main part of a conventional electric power steering device.

[Explanation of symbols]

1 rack shaft 2 ball screw mechanism 4 the pinion shaft 5 motor 6 radial bearing 9 annular spring 9a groove 9b groove 20 ball nut 21 screw rail 51 stator 52 rotor H ₁ rack housing H ₂ pinion housing H ₃ motor housing

Claims (3)

[Claims] 1. A steering assist motor having a cylindrical rotor rotatably supported coaxially with the steering shaft inside a cylindrical housing supporting the steering shaft, and one side of the rotor. A ball screw mechanism having a ball nut connected to the steering wheel, the rotation of the rotor is converted into linear motion by the ball screw mechanism and transmitted to the steering shaft, and the steering shaft is moved in the axial direction to perform steering. An electric power steering apparatus having an auxiliary configuration, comprising an elastic body which is interposed between a bearing for radially supporting the rotor and the rotor or the housing and has elasticity in a radial direction. Power steering device. 2. The electric power steering apparatus according to claim 1, wherein the elastic body is formed of an annular spring wound around the outer periphery of the rotor, projecting radially outward and elastically contacting the inner surface of the bearing. 3. The electric power steering apparatus according to claim 1, wherein the elastic body is formed by an annular spring wound around an inner periphery of the housing, protruding radially inward, and elastically contacting an outer surface of the bearing. .