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Electric power steering system

a technology of electric power steering and steering shaft, which is applied in the direction of electric steering, power driven steering, vehicle components, etc., can solve the problems of increasing the man-hours required to manufacture the electric power steering system, the inability to apply assist force to the rack shaft, and the increase in production costs. , to achieve the effect of convenient assembly

Inactive Publication Date: 2014-07-08
JTEKT CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0010]The invention provides an electric power steering system in which the connection between a motor shaft and a ball screw nut is maintained even if an impact load acts on a rack shaft, which requires less manufacturing man-hours, and which is more easily assembled.
[0011]According to a feature of an example of the invention, in an electric power steering system that applies assist force that assists an operation of a steering system of a vehicle to a rack shaft, there is provided a restricting member that restricts a distance that a motion conversion mechanism is able to move relative to a motor shaft in such a direction that engagement of an engaging portion is cancelled, to a predetermined distance, and a length of the engaging portion is set longer than the predetermined distance. This structure makes it possible to maintain connection between the motor shaft and a ball screw nut even if an impact load acts on the rack shaft. In addition, this structure makes it possible to reduce man-hours required to manufacture the electric power steering system, and to facilitate assembly of the electric power steering system.

Problems solved by technology

If it becomes impossible to transmit the driving force of the motor to the rack shaft 90 due to the loosening in the fastening structure, it may be not possible to apply assist force to the rack shaft 90.
This leads to an increase in man-hours required to manufacture the electric power steering system, and consequently causes an increase in production cost.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

first embodiment

[0025]An electric power steering system according to the invention will be described with reference to FIG. 1 to FIG. 4.

[0026]As shown in FIG. 1, the electric power steering system is formed of a steering mechanism 1 and an assist mechanism 2. The steering mechanism 1 changes the steered angle of steered wheels of a vehicle in response to a driver's operation of a steering wheel. The assist mechanism 2 assists the driver in performing a steering operation. In the electric power steering system, the steering mechanism 1 and the assist mechanism 2 are covered with a housing 3 to be protected from the external environment.

[0027]The housing 3 is structured such that a second housing 3b is connected via an O ring Or1 to one end portion of a first housing 3a that covers the radially outer side of the assist mechanism 2 and a third housing 3c is connected via an O ring Or2 to the other end portion of the first housing 3a. In this way, by forming the housing 3 as a splittable body formed of...

second embodiment

[0055]In the above-described embodiment, the engaging portion 43 of the ball screw nut 40 is fastened to the motor shaft 21 through thread fastening. Alternatively, as shown in FIG. 5A, a leaf spring (tolerance ring) 60 may be interposed between the engaging portion 43 of the ball screw nut 40 and the inner periphery of the open end 21b of the motor shaft 21 and the ball screw nut 40 and the motor shaft 21 may be engaged with and coupled to each other by the tension of the leaf spring 60 (second embodiment). In this case, as shown in FIG. 5B that shows the enlarged structure of the ball screw nut 40 and its surrounding portions, the length of the engaging portion 43 is the length S in the drawing.

third embodiment

[0056]In the above-described embodiment, the bearing 51 is arranged on the outer periphery of the ball screw nut 40. Alternatively, as shown in FIG. 6A, a bush 53 may be interposed between the ball screw nut 40 and the first housing 3a (third embodiment). When the bush 53 is used, if the bush 53 contacts the end portion 3d of the third housing 3c as the ball screw nut 40 moves in the direction indicated by the arrow a2, the bush 53 and the third housing 3c are brought into plane contact with each other. Therefore, friction force is generated between the bush 53 and the third housing 3c, and the rotation of the ball screw nut 40 and the axial movement of the rack shaft 11 may be hindered. To avoid this problem, for example, sticking a low-friction sheet (low μ sheet), or the like, onto a surface of the third housing 3c, which the bush 53 of the third housing 3c contacts, is effective. In this way, it is possible to reduce friction force generated between the bush 53 and the third hou...

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PUM

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Abstract

Assist force that assists an operation of a steering system of a vehicle is applied to a rack shaft by transmitting driving force of a motor to the rack shaft via a motor shaft and a ball screw nut. A step is formed on the outer periphery of the ball screw nut. An end portion of a third housing is arranged to face a bearing such that the distance that the ball screw nut is able to move relative to the motor shaft in axial direction and the relative movable length is longer than a predetermined length.

Description

INCORPORATION BY REFERENCE / RELATED APPLICATION[0001]This application claims priority to Japanese Patent Application No. 2011-214995 filed on Sep. 29, 2011 the disclosure of which, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The invention relates to an electric power steering system that assists an operation of a steering system of a vehicle by applying assist force to a rack shaft of the vehicle.[0004]2. Discussion of Background[0005]A conventional electric power steering system of this type is described in, for example, Japanese Patent Application Publication No. 2011-51387 (JP 2011-51387 A). FIG. 9 shows the structure of the electric power steering system described in JP 2011-51387 A. In a vehicle in which the electric power steering system is mounted, a rack shaft 90 in FIG. 9 makes a reciprocal motion in its axial direction (direction indicated by arrows a1...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): B62D5/04
CPCB62D5/0448B62D5/0442
Inventor ASAKURA, TOSHIHIRONAKAYAMA, TAKUYAKANEKO, TETSUYA
Owner JTEKT CORP