JPH11268660A - Electric power steering unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To permit quick assist in accordance with the steering direction without changing the direction of rotation of the electric motor. SOLUTION: A screw shaft 2 onto which screws a cylindrical nut 3 is provided in a rack shaft 1 of a steering mechanism parallel to the rack shaft 1. A first roller 8 which rotates by an electric motor 4 and a second roller 9 which contacts this first roller and rotates in the opposite direction are provided. The first roller 8 or the second roller 9 switch, pressing against the nut 3 by an actuator 11 in accordance with the steering. Rotation is transmitted to the nut 3, rotating the rack shaft 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus for assisting a steering force of a steering wheel.

[0002]

2. Description of the Related Art Detecting torque applied to a steering wheel,
An electric power steering apparatus in which an assist motor corresponding to the torque is obtained by an electric motor is well known.

A conventional electric power steering apparatus includes an input shaft for transmitting rotation from a steering wheel, and an output shaft having a gear connected to the input shaft and the input shaft via a torsion bar so as to be relatively rotatable. A torque sensor that detects the rotational torque of the torsion bar as a relative rotational displacement between the input shaft and the output shaft, a rack shaft of a steering mechanism that meshes with a pinion provided on the output shaft, and a motor shaft. An electric motor provided with a reduction gear meshing with the gear of the input shaft, wherein the rotation of the electric motor is transmitted to a rack shaft via a pinion provided on the output shaft.

[0004]

The above-described conventional electric power steering apparatus assists by changing the rotation direction of the electric motor according to the steering direction. Therefore, when changing the steering direction, the steering assist may be slightly delayed due to the inertia of the rotor of the electric motor.

[0005] It is an object of the present invention to provide an electric power steering apparatus which enables quick assist according to a steering direction without changing the rotation direction of an electric motor.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is directed to a screw in which a cylindrical nut is screwed into a rack shaft of a steering mechanism in which rotation of a handle is transmitted via a pinion. A first roller having an axis provided in parallel with the rack shaft and rotating by an electric motor, and a second roller rotating in the opposite direction in contact with the first roller;
Pressing means for pressing the first roller or the second roller against the nut to transmit rotation to the nut, and controlling means for controlling the pressing means in accordance with a steering state to axially move the rack shaft It is characterized by having.

[0007] The pressing means in the above-mentioned structure supports the first roller and the second roller at both ends of the V-shaped arm, and swings the V-shaped arm by an actuator according to a steering state. The first roller or the second roller is switched and pressed against the nut.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3, reference numeral 1 denotes a rack shaft of a steering mechanism. This rack shaft 1 is shown in FIG.
As shown in FIG. 2, an input shaft (not shown) for transmitting rotation from the handle 12 and a pinion 13 provided on an output shaft rotatably connected via a torsion bar mesh with the input shaft and the output shaft. The torque applied to the steering wheel 12 is detected by a torque sensor 14 that detects the relative rotational displacement with respect to the steering wheel 12, and an assist force corresponding to the torque is obtained by an electric motor 4 described later.

A screw shaft 2 (ball screw) is fixed to the rack shaft 1 along an axis parallel to the rack shaft 1, and a cylindrical nut 3 (ball nut) is screwed to the screw shaft 2. The rotation of the nut 3 causes the screw shaft 2 to rotate.
The rack shaft 1 is axially moved by the screw lead.

Reference numeral 4 denotes an electric motor. This electric motor 4
And a flywheel 6 rotating at a position offset from the output shaft of the electric motor 4 by a belt 7.

The flywheel 6 has a first roller 8
(A driving roller) is directly connected, a second roller 9 (a driven roller) is always in contact with the first roller 8, and the rotation of the electric motor 4 drives the first roller 8 to rotate.
The rotation of the first roller 8 causes the second roller 9 to rotate in the opposite direction to the first roller 8.

The first roller 8 and the second roller 9 are switched and pressed against the nut 3 by a pressing means described later.
The nut 3 is rotated. Therefore, when the first roller 8, the second roller 9 and the nut 3 are in contact with each other, the rotation transmission is ensured and the axial movement of the nut 3 is restrained. However, it is desirable to engage with this annular tooth profile.

As shown in FIG. 4, the pressing means for switching and pressing the first roller 8 or the second roller 9 against the nut 3 is such that the first roller 8 and the second roller 9 The shafts are respectively supported on the tips 10a and 10b,
An actuator 11 for swinging the V-shaped arm 10 is connected to a base end 10c of the V-shaped arm 10.

The actuator 11 detects the steering direction of the steering wheel 12 at the same time as the torque applied to the steering wheel 12 by the torque sensor 14, and rotates the V-arm 10 left or right according to the detection signal of the steering direction. By swinging to the right, the first roller 8 or the second roller 9 is pressed against the nut 3. Accordingly, the rotation of the actuator 11 is restricted when the first roller 8 or the second roller 9 presses against the nut 3.

The operation of the apparatus of the present invention having the above configuration will be described. When the rack shaft 1 in a straight running state in which the handle 12 is not turned left or right is near the neutral position, the first roller 8
Neither of the second roller 9 nor the second roller 9 contacts the nut 3. As a result, a sense of neutral rigidity that is important for the steering feel can be obtained.

When the steering wheel 12 is turned left or right, the steering direction is determined by a torque sensor 14 on the steering wheel 1.
At the same time, the electric motor 4 is rotated. The rotation direction of the electric motor 4 is always constant, and the rotation output from the electric motor 4 is transmitted to the flywheel 6 via the pulley 5 and the belt 7, and the first roller 8 is rotationally driven by the flywheel 6, The second roller 9 which is always in contact with the first roller 8 is driven to rotate in a direction opposite to the first roller 8.

Therefore, the first motor rotationally driven by the electric motor 4 is used.
In the rotation direction of the roller 8, the rack shaft 1 is axially moved leftward via the nut 3 and the screw shaft 2, and the nut 3 and the screw shaft 2 are rotated in the rotation direction of the second roller that rotates in contact with the first roller 8. When the rack shaft 1 is axially moved rightward through the shaft, when the torque sensor 14 detects the right steering direction of the steering wheel 12, the V-arm 10 is moved leftward in FIGS. 1 and 4 by the actuator 11. To press the second roller 9 against the nut 3.

As a result, the nut 3 is rotated by the second roller 9 in the direction opposite to the rotation direction of the second roller 9, and the rack shaft 1 is axially moved rightward by the screw lead of the screw shaft 2 to increase the steering force. Assist. In the left steering direction of the handle 12, the V-shaped arm 10 is swung rightward in FIGS. 1 and 4 by the actuator 11, the first roller 8 is pressed against the nut 3, and the screw shaft 2 is rotated by the rotation of the nut 3. The rack shaft 1 is axially moved to the left by the screw lead of (1) to assist the steering force.

Therefore, according to the present invention, the assist is performed according to the left and right steering directions in a state where the rotation direction of the electric motor 4 is fixed. As a result, there is no assist delay due to inertia of the electric motor 4 when changing the steering direction, and quick assist according to the steering direction can be obtained.

In the above configuration, when the steering angle is extremely small as in a normal traveling, the assisting force is obtained by the rotational energy stored in the flywheel 6, but when the steering is stationary or the steering angle is large, The electric motor 4 outputs a necessary rotational force to assist a corresponding steering force.

The rotation of the electric motor 4 and the first roller 8 is transmitted through the pulley 5, the belt 7 and the flywheel 6, and the first roller 8 and the second roller 9 are swung left or right by the first roller 8. Although the displacement of the axis of the roller 8 and the second roller 9 is absorbed, the rotation of the output shaft of the electric motor 4 and the rotation of the first roller 8 is transmitted by a gear, and the first roller 8 and the second roller 8 are rotated. The first roller 8 and the second roller 8 are swung to the left or right of the roller 9.
It is also possible to absorb the displacement of the shaft center of the roller 9 so that the gear of the rotating shaft of the first roller 8 revolves around the gear of the output shaft of the electric motor 4.

In the above embodiment, the switching pressing of the first roller 8 or the second roller 9 to the nut 3 is made to swing left and right with the base end 10c of the V-shaped arm 10 as a fulcrum. In a configuration in which the motor 4 and the first roller 8 are rotationally transmitted to the first roller 8 via the pulley 5, the belt 7 and the flywheel 6, the rotation between the shafts of the first roller 8 and the second roller 9 is restricted. It is also possible to move the first roller 8 or the second roller 9 to the nut 3 by switching linearly to the left and right by a linear actuator such as a solenoid.

[0023]

As described above, according to the present invention, the rotation direction of the electric motor assisting the steering force of the steering wheel is not changed in accordance with the steering direction, but is changed in the fixed direction according to the left and right steering directions. Since assisting is performed, there is no delay in assisting due to inertia of the electric motor when changing the steering direction, and there is an advantage that quick assist according to the steering direction can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of the apparatus of the present invention.

FIG. 2 is a specific structural view of the apparatus of the present invention.

FIG. 3 is an enlarged view of a main part of the apparatus of the present invention.

FIG. 4 is a sectional view taken along line AA of FIG. 3;

[Explanation of symbols]

 Reference Signs List 1 rack shaft 2 screw shaft 3 nut 4 electric motor 8 first roller 9 second roller 10 V-arm 11 actuator

Claims (2)

[Claims] A first roller rotated by an electric motor is provided with a screw shaft in which a cylindrical nut is screwed into a rack shaft of a steering mechanism to which rotation of a handle is transmitted via a pinion. A second roller that rotates in the opposite direction by contacting the first roller; pressing means for pressing the first roller or the second roller against the nut to transmit rotation to the nut; Control means for controlling the pressing means in accordance with the condition and for axially moving the rack shaft. 2. The pressing means supports the first roller and the second roller at both ends of a V-shaped arm, and swings the V-shaped arm by an actuator in accordance with a steering state, thereby allowing the V-shaped arm to be attached to the nut. The electric power steering apparatus according to claim 1, wherein the first roller or the second roller is switched and pressed against the first roller or the second roller.