JP3779743B2 - Electric power steering device - Google Patents

Description

【Technical field】
[0001]
The present invention relates to an electric power steering device that generates an auxiliary steering force for assisting a manual steering force in a vehicle, and more particularly to an improvement in a power transmission mechanism that transmits a driving force of an electric motor to a rack shaft.
[0002]
[Prior art and its problems]
In a vehicle such as an automobile, although the steered wheel by the driver are steered by steering the steering wheel, the electric power steering in order to reduce the steering force of Ru size kuna handle in time like Ri据切A device is added. In order to apply an auxiliary steering force to the rack shaft by the electric power steering device, the rack shaft and the electric motor must be connected by a power transmission mechanism.
Various inventions have been made so far for the coupling mechanism between the electric motor and the rack shaft depending on the type and size of the vehicle. For example, in Japanese Patent Laid-Open No. 60-25854, a ball screw type power transmission mechanism is arranged such that an electric motor is coaxial (coaxial) with a rack shaft, while in Japanese Patent Laid-Open No. 60-25854, an electric motor is mounted on a rack shaft. They are arranged in parallel.
In any case, when a large steering assist force is required for the electric power steering device, a larger electric motor is used, a reduction ratio between the electric motor and the ball screw mechanism is increased, It is necessary to devise measures such as reducing the lead of the ball screw groove.
[0003]
However, if the electric motor is made larger, the steering body becomes larger, and if the reduction ratio between the electric motor and the ball screw mechanism is made larger, the speed reduction mechanism becomes larger. In either case, the manufacturing cost increases.
In addition, when the ball screw mechanism and the electric motor are parallel, it is necessary to dispose an idle gear, a belt, and the like between them, which complicates the structure and increases the manufacturing cost. If the lead of the ball screw groove is further reduced, the diameter of the ball is inevitably reduced, and it is necessary to increase the number of turns of the ball screw groove in order to withstand a large load applied to the ball. At the same time, the manufacturing cost increases.
[0004]
The present invention solves the above-described problems in the prior art, that is, without increasing the size of the electric motor, increasing the reduction ratio between the electric motor and the ball screw mechanism, or reducing the lead of the ball screw groove. The object of the present invention is to provide an electric power steering device capable of obtaining a large auxiliary steering force.
[0005]
[Means and Actions for Solving the Problems]
In order to achieve the above object, in the present invention, the output shaft 54 of the electric motor 50 and the ball nut 30 of the ball screw mechanism 35 are crossed at a predetermined acute angle, neither coaxial nor parallel. For this purpose, the bevel gears 58 and 31 are fixed to the output shaft and the ball nut of the electric motor and meshed with each other.
Thus, the driving force of the electric motor disposed obliquely with respect to the rack shaft is transmitted to the ball nut through the pair of bevel gears, and the rack shaft is moved by the rotation of the ball nut.
[0006]
【Example】
Hereinafter, a first embodiment of the present invention will be described with reference to FIG.
In FIG. 1, a longitudinal rack shaft 20 is movably accommodated in a cylindrical housing 10 extending in the left-right direction of the vehicle, and each end thereof is connected to a steered wheel (not shown) via a ball joint 22. Has been. The joint 22 is covered with a boot 24. A steering shaft 16 is disposed obliquely with respect to the rack shaft 20, and a steering wheel (not shown) is attached to the upper end thereof. The lower end of the steering shaft 1 6 is connected to the rack shaft 20 by the rack-pinion mechanism 18, a rack-pinion mechanism 18 motion direction is converted by the rack shaft 20 by rotating the steering wheel is moved in the lateral direction.
The housing 10 has a cylindrical ball screw mechanism housing portion 12 to the left part, and now pinion rack mechanism saucer-shaped projecting obliquely at a predetermined acute angle to 18-side electric motor mounting portion 14, a ball screw A ball screw mechanism 35 is disposed in the mechanism housing portion 12, and an electric motor 50 is attached to the electric motor attachment portion 14.
[0007]
Next, the relationship among the rack shaft 2 0 , the ball screw mechanism 35 and the electric motor 50 will be described.
The outer peripheral surface of the left half of the rack shaft 2 0 and ball screw groove 26 is formed in a spiral shape, a cylindrical ball nut 30 which is loosely fitted on the outside thereof to the ball screw mechanism housing portion 12 by a pair of bearings 38 And is rotatably supported. A ball screw groove 34 is spirally formed on the inner peripheral surface of the ball nut 30. The rack shaft 2 0 of the ball screw groove 26 and the spiral annular space formed by the ball screw groove 34 of the ball nut 30 number of balls 40 is filled. A ball return pipe 42 is disposed outside the ball nut 30 to return the ball 40 that has progressed in the axial direction as it rotates to the rear. The ball screw mechanism 35 is configured by the ball screw groove 26, the ball nut 30, the ball 40, and the like.
The ball nut 30 is held in a predetermined state by a lid member 44 and a fastening member 46 inserted into the ball screw mechanism accommodating portion 12.
[0008]
Electric motor 50 is attached by bolts 52 to the electric motor mounted only parts 14 are located in the immediate vicinity of the rack-pinion mechanism 18. The output shaft 5 4 of the electric motor 50 is rotatably supported by a pair of bearings 56, a small bevel gear 58 of the radius is fixed at its tip. A bevel gear 31 having a large radius is attached to one end of the ball nut 30 and meshes with the bevel gear 58. The axis of the rack shaft 2 0 i.e. the axis electric motor 50 of the ball nut 30 forms a relatively small acute angle (e.g. 30 ° before and after).
[0009]
Next, the operation of this embodiment will be described.
As described above, the manual steering the steering shaft 1 6 is rotated by the driver to turn the steering wheel, is achieved by this rotation is converted into axial movement of the rack shaft 20 by the rack-pinion mechanism 18 .
On the other hand, steering force assistance by the electric motor 50 is performed as follows.
The rotation of the output shaft 54 of the electric motor 50 causes the ball nut 30 to rotate around the rack shaft 20 via the pair of bevel gears 58 and 31. As a result, the rack shaft 20 is moved in the axial direction by the action of a known ball nut mechanism, and a steered wheel (not shown) is steered.
[0010]
In this embodiment, the axes of the electric motor 50 of the rack shaft 20 at a relatively small acute angle of 30 degrees before and after, moreover the electric motor 50 are disposed inclined to the rack-pinion mechanism 1 8 side. As a result of reducing the crossing angle, the entire electric motor 50 is closer to the rack shaft 20 and the rack and pinion mechanism 18, and the dimensions of the steering device, particularly in the direction perpendicular to the axis of the rack shaft 20 (vertical direction in FIG. 1). The width could be made as small as possible.
Further, only a pair of bevel gears 58 and 31 having different radii are disposed between the ball nut 30 and the output shaft 54 of the electric motor 50, and power transmission members such as belts and idle gears are not disposed at all. Not. As a result, a relatively large reduction ratio can be obtained with an extremely simple structure, and the structure around the power transmission section can be made extremely compact. Further, since an extra power transmission member is not required between the rack shaft 20 and the electric motor 50, the ball screw mechanism housing portion 12 and the electric motor mounting portion 14 of the housing 10 can be integrated.
[0011]
Incidentally, the crossing angle formed by the axes of the electric motor 50 of the rack shaft 2 0, it can be easily changed by changing the radius or cone angle of the bevel gears 31,58.
[0012]
Next, a second embodiment of the present invention will be described with reference to FIG.
The second embodiment differs from the first embodiment in that the angle of intersection between the axis of the electric motor 60 and the axis of the rack shaft 20, the position of the electric motor 60 relative to the rack and pinion mechanism 18, and the motor output. It is a support method of the 2nd bevel gear of a shaft.
That is, the axis of the electric motor 60 forms a relatively large acute angle (for example, around 50 °) with respect to the axis of the rack shaft 20 and is disposed on the opposite side to the rack and pinion mechanism 18. In this connection, the housing 10 is formed with a cylindrical ball screw mechanism accommodating portion 11 and a saucer-like electric motor mounting portion 13, and the axial length of the ball nut 30 is relatively long so that its left end and middle The part is supported by a bearing 38. A bevel gear 15 including a flange portion 15 a and a conical portion 15 b is attached to the right end portion of the ball nut 30. The output shaft 54 of the motor 60 is supported by bearings 61 and 63 on both sides of the bevel gear 64.
[0013]
In this embodiment, in addition to the effects in the first embodiment, although the electric motor 60 projects upward slightly than the first embodiment, the radial space outside the ball nut 30 is more effectively utilized effective.
[0014]
【The invention's effect】
As described above, according to the present invention, the axis of the rack shaft and the axis of the electric motor are arranged to form a predetermined acute angle. The electric motor was brought close to the rack shaft 20 by crossing them at an acute angle, not coaxial or parallel. As a result, the size of the steering device (in particular, the direction perpendicular to the axis of the rack shaft) can be reduced. In addition, there is no power transmission member such as a belt or idle gear between the ball nut and the output shaft of the electric motor, so a relatively large reduction ratio can be obtained with an extremely simple structure, and power transmission The structure around the part can be made extremely compact. In connection with this, the effect that the ball nut mechanism accommodation part and electric motor attachment part of a housing can be made into an integral structure is acquired.
[Brief description of the drawings]
FIG. 1 is a front view (partially broken) showing a first embodiment of the present invention.
FIG. 2 is a front view (partially broken) showing a second embodiment of the present invention.
[Explanation of symbols]
10: Housing
11, 12: Ball screw mechanism housing
13, 14: Electric motor mounting portion 18: Rack and pinion mechanism 20: Rack shafts 26, 34, 35: Ball screw groove 30: Ball nut 31, 58: Bevel gear 40: Ball 50: Electric motor 54: Output shaft

Claims (3)

In a vehicle, a steering shaft to which a manual steering force is input is connected via a rack and pinion mechanism to a rack shaft that is movable in the axial direction to steer the steered wheels, and is coaxial with the rack shaft. In the electric power steering device in which a ball screw mechanism is arranged and the ball nut fitted to the rack shaft is rotated by an electric motor to move the rack shaft to assist manual steering force.
The electric power steering apparatus, wherein the rack shaft and the electric motor are arranged such that an axis of the rack shaft and an axis of the electric motor form a predetermined acute angle. The ball nut and the electric motor are connected to each other by meshing a first bevel gear fixed to the ball nut and a second bevel gear fixed to the output shaft of the electric motor. The electric power steering apparatus according to claim 1. The electric power steering apparatus according to claim 1, wherein the rack shaft, the ball nut, and the electric motor are accommodated in a common housing.

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