JP2589314Y2 - Electric power steering system - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an electric power steering apparatus for an automobile or the like, and more particularly, to a power steering apparatus having a rack shaft formed with a rack engaged with a pinion of a pinion shaft connected to a steering shaft. The present invention relates to a power steering device that moves a rack shaft by a driver's steering force and an auxiliary steering force of an electric motor corresponding to the steering force.

[0002]

2. Description of the Related Art Conventionally, as this type of electric power steering apparatus, a ball screw shaft parallel to the housing is mounted on a housing so as to rotate with respect to the housing but not move in the axial direction. A ball nut having an axis parallel to the rack shaft is screwed around the circulation shaft through the circulation ball, and the rack shaft and the ball nut are connected so that the ball nut can move in the axial direction but does not rotate. The rotation of the ball screw shaft is caused by the rotation force of the ball screw shaft, and the rotation of the ball screw shaft causes the ball nut to move in a direction parallel to the axial direction of the rack shaft, thereby moving the rack shaft in the axial direction. Are known (for example, Japanese Utility Model Laid-Open No. 62-146678, Japanese Utility Model Laid-Open No. 63-195974,
No.).

[0003]

However, in the conventional electric power steering apparatus, when an external force is applied from the wheel side and the rack shaft is bent, the following problem occurs. That is, when bending occurs in the rack shaft, the ball nut connected to the rack shaft also tilts with respect to the ball screw shaft. When the rack shaft and the ball nut are connected to each other, in this connection portion, the distance between the axis of the inclined ball nut and the axis of the ball screw shaft in the direction orthogonal to the ball screw axis is equal to that portion. It becomes equal to the amount of deflection of the rack shaft and becomes relatively large. Therefore, even if there is a gap between the ball nut and the ball screw shaft and the circulating ball, the rotation of the ball screw shaft by the electric motor is not smoothly transmitted to the ball nut, and as a result, the auxiliary steering force is reliably transmitted to the rack shaft. Does not reach.

An object of the present invention is to provide an electric power steering apparatus which solves the above problem.

[0005] The electric power steering apparatus according to the present invention provides a rack shaft formed with a rack supported by the housing and engaged with a pinion of a pinion shaft connected to a steering shaft, and applies an auxiliary steering force to the rack shaft. A ball screw axis parallel to the rack axis is attached to the housing so that it can move in the axial direction but does not rotate, and one end of the ball screw axis is connected to the rack axis.
, A ball nut is screw-fitted around a portion on the other end side of the ball screw shaft via a circulating ball, and the ball nut is attached to the housing so that it can rotate but does not move in the axial direction. Is mounted on the housing and the rotor is fixed to the outer periphery of the ball nut.

[0006]

[Function] When the brushless motor is started, its rotational force is low.
The ball screw is transmitted to the ball nut via the rotor and the ball nut is rotated, thereby moving the ball screw shaft in the axial direction. As a result, the rack shaft connected to the ball screw shaft moves in the same direction as the ball screw shaft. The auxiliary steering force is given by being moved.

[0007] If the bending when an external force is applied from the wheel to the rack shaft occurs, but also bending the ball screw shaft connected to the rack shaft occurs, one end of the ball screw shaft rack
Around the other end of the ball screw shaft.
The ball nut is screwed into the enclosure via the circulation ball
Therefore, the ball nut is screwed into the ball screw shaft via the circulating ball at a position relatively far away from the connection between the ball screw shaft and the rack shaft ,
The amount of deflection of the ball screw shaft at the portion where the ball nut is screwed is smaller than the amount of deflection of the ball screw shaft at the portion connected to the rack shaft .

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a portion of an electric power steering apparatus for an automobile, and FIG. 2 shows details of a main portion thereof. In the following description, the left and right of the drawing are referred to as left and right.

In FIG. 1 and FIG. 2, a housing 1 long in the left-right direction is fixed to the body of an automobile. A rack shaft 2 extending in the left-right direction in this housing 1 does not rotate, but is rotated left and right. It is supported so that it can move in the direction (axial direction). Near the right end of the housing (1), a pinion shaft (3) connected to the steering wheel
Pinion (4) meshes with the rack (2a) of the rack shaft (2). At the left and right ends of the rack shaft (2) protruding from the housing (1), tie rods are inserted via ball joints (5) and (6).
(7) and (8) are linked.

A bulging portion (1a) bulging radially outward is formed on the left side portion of the housing (1), and the bulging portion (1a)
Inside, a ball screw shaft (9) parallel to the rack shaft (2) is arranged so as to be movable in the left-right direction. Ball screw shaft (9)
Has a left end protruding from the housing (1), and is connected to the left end of the rack shaft (2) via a bracket (10). The left end of the ball screw shaft (9) is fixed to the bracket (10) so as not to rotate.

A ball nut (11) is screwed on the right side of the ball screw shaft (9) via a number of circulating balls (12). Ball nut (11) is rotated left and right pair of bearings (13) as it can not move in the lateral direction through the (14) that is supported on the housing (1).

A brush is provided in the bulging portion (1a) of the housing (1).
An electric motor (20) is built in. That is, Bourna
The rotor (21) of the brushless motor (20) is
The brushless motor (20) is fixed to the housing (1).
The data (22) is attached. In addition, housing (1)
Rotation using a rotary encoder etc. at an appropriate position
A position sensor (23) is installed, and this sensor (23)
The gear (24) and ball nut formed integrally with the input shaft (23a)
Gear (25) formed integrally with the outer periphery of the left end of the gear (11).
I'm right. The rotation of the ball nut (11)
(25) Decelerated or accelerated by (24) and transmitted to sensor (23)
The ball nut (11), i.e.
The rotational position of the motor (21) is detected. And brushless
The rotational force of the motor (20) is transmitted to the ball nut via the rotor (21).
(11) to rotate the ball nut (11). It is supposed to.

In such a configuration, when the driver turns the steering wheel to rotate the steering shaft, the rotation is transmitted to the pinion (4), and the rotation of the pinion (4) causes the rack shaft (2) to move left and right. Direction and the wheels are steered. At this time, the brushless electric motor (20) is driven based on the direction and magnitude of the steering torque detected by a torque sensor (not shown ) , whereby the rotational force of the brushless electric motor (20) is reduced by the ball nut (11) and the ball screw (20). It is transmitted to the rack shaft (2) via the shaft (9). As a result, the rack shaft (2) is moved in the same direction as by the pinion (4).

When an external force is applied to the rack shaft (2) from the wheel side and the bending occurs, the ball screw shaft (9) connected to the rack shaft (2) also bends. However, the rack shaft
(2) and the ball screw shaft (9) are connected to each other at the left end, and the ball nut (11) is connected to the right side of the ball screw shaft (9) via the circulating ball (12). 9), the amount of deflection of the ball screw shaft (9) at the ball nut (11) is at the left end, which is the connection between the ball screw shaft (9) and the rack shaft (2). Is smaller than the deflection amount. Therefore, this bending is absorbed by the gap between the ball nut (11) and the ball screw shaft (9) and the circulating ball (12), and the rotation of the ball nut (11) by the brushless electric motor (20) causes the ball screw (11) to rotate. Smoothly transmitted to the shaft (9), the auxiliary steering force of the electric motor (20) is transferred to the rack shaft.
(2) Reliable transmission.

[0016]

According Effect of invention] The power steering apparatus of this invention, as described above, deflection of the ball screw shaft at a portion where the ball nut is I Flip fitted through the circulation ball, La
The amount of deflection of the ball screw shaft at the connection with the lock shaft is smaller than that of the ball screw shaft. Therefore, this bending is absorbed by the gap existing between the ball nut and the ball screw shaft and the circulating ball, and the rotation of the ball nut due to the rotating force of the motor is smoothly transmitted to the ball screw shaft. Is reliably transmitted to the rack shaft.

Also, by using a brushless motor,
Therefore, a failure due to abrasion of the brush can be eliminated. I
In fact, brushless motors are less expensive than brushed motors.
The moment of inertia of the motor
Good, no delay in steering assistance.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a part of an electric power steering apparatus showing an embodiment of the present invention.

FIG. 2 is an enlarged view showing a main part of FIG. 2;

[Explanation of symbols]

Reference Signs List 1 housing 2 rack shaft 3 pinion shaft 4 pinion 9 ball screw shaft 11 ball nut 12 circulation ball 20 brushless electric motor 21 rotor 22 stator

Claims (1)

(57) [Scope of request for utility model registration] 1. A rack shaft having a rack supported by a housing and having a rack meshing with a pinion of a pinion shaft connected to a steering shaft, and a brushless electric motor for applying an auxiliary steering force to the rack shaft. A ball screw shaft parallel to the shaft is mounted on the housing so that it can move in the axial direction but does not rotate .
One end is connected to the rack shaft, and the other
A ball nut is screwed around the end portion through a circulating ball, the ball nut is mounted on the housing so that the ball nut can rotate but does not move in the axial direction, and the stator of the brushless motor is mounted on the housing and the rotor is mounted on the rotor. Is an electric power steering device fixed to the outer periphery of the ball nut.