JPH09104352A - Motor-driven power steering device with ball screw mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To certainly prevent a lubricating oil from leaking by enclosing a ball returning means furnished at a ball nut of a ball screw mechanism to be rotated by a motor, and thereby preventing the oil in the ball screw mechanism from leaking to the outer surface of the ball nut. SOLUTION: A power steering device includes a ball screw mechanism 30 having a ball nut 32, with which the steering motion is assisted by operating a motor 20, rotating the ball nut 32, and moving a rack shaft 10 in the axial direction. To return back the balls 42 which have advanced between grooves 34, 36, two tubes 50 having a U-shape as a whole are mounted on the periphery of the ball nut 32. These ball returning tubes 50 are held by a tube holder 54 having approx. channel-shaped section, and thereover a seal cap 54 is attached as an oil leak preventing means, and the two members 52, 54 are secured by fastening to the ball nut 32 with bolt 56. Thereby the oil is precluded from leaking at the peripheries of the tubes 50.

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 device using a ball screw mechanism, and more particularly to a device capable of favorably preventing leakage of lubricating oil in the ball screw mechanism.

[0002]

2. Description of the Related Art A type of electric power steering that assists a manual steering force in a vehicle is one type of an electric power steering system that converts a rotational force of an electric motor into an axial movement of a rack shaft. There is a device using a ball screw mechanism arranged in parallel with an electric motor. This is to connect a rotating member (rotor) of an electric motor and a ball nut of a ball screw mechanism, rotate the ball nut by the rotation of the electric motor, and to rotate the ball nut. The rack shaft is moved in the axial direction.

As a conventional example, Japanese Patent Application Laid-Open No. 7-165089 is known. In this conventional example, the rotor of the electric motor and the ball screw mechanism are integrated with each other, and a so-called ball-type ball circulating portion is used. Here, since a through hole is formed in the ball nut in the outer diameter direction for mounting the top, the ball nut is supplied into a spiral ball screw groove formed between the ball nut and the ball screw shaft. The lubricating oil may leak from the clearance of the through hole to the outer surface of the ball nut as the ball rolls. Since the above-mentioned conventional example does not take any positive preventive measures against this leakage of the lubricating oil, the lubricating oil leaked from the through hole enters the electric motor through the ball nut and the rotor, which causes a bad effect. Was sometimes caused. This situation is the same when a tube type ball circulating unit is used. This is because a through hole for inserting the tip of the ball return tube is formed in the ball nut.

The present invention has been made for the purpose of solving the above-mentioned problems in the prior art. In the ball circulating portion, the lubricating oil inside the ball screw mechanism is outside the ball nut regardless of whether it is a top type or a tube type. Leaking on the surface,
It is possible to prevent the flow toward the electric motor,
An electric power steering device using a ball screw mechanism is provided.

[0005]

In order to achieve the above object, in the present invention, a rack shaft movably supported by a housing in the axial direction and connected at both ends to steered wheels of a vehicle, and the rack shaft. And a ball screw mechanism arranged coaxially with the rack shaft and in parallel with the electric motor, wherein the ball nut of the ball screw mechanism is rotated by the rotor of the electric motor. In the electric power steering apparatus having the ball screw mechanism for moving the rack shaft in the axial direction, the ball returning means provided in the ball nut of the ball screw mechanism is covered, Lubricating oil leakage preventing means for preventing the lubricating oil from leaking to the outer surface of the ball nut is provided.

[0006]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, a rack shaft 10 is housed in a housing 12 extending in the left-right direction of the vehicle, and both ends thereof are connected to front wheels via universal joints (not shown). A rack and pinion type manual steering unit 14 for inputting a manual steering force is provided on the right side portion 12a of the housing 12. This is to rotate the pinion shaft 16 by rotational steering of a steering wheel (not shown) and convert this rotation into axial movement of the rack shaft 10. However, since this is a known technique, it will not be described in detail here.

An electric motor (motor unit) 20 is arranged in the central portion 12b of the housing 12, and a left portion 12c is provided.
A ball screw mechanism 30 is provided in each. The electric motor 20 includes a sleeve 22 that is loosely fitted to the rack shaft 10.
And a cylindrical rotary member (rotor) 24 fitted to the sleeve 22, and a stator 28 fixed to the central portion 12b and including an electromagnetic coil 26. One end (right end) of the sleeve 22 is rotatably supported by the bearing 25 with respect to the central portion 12b.

One end (right end) of the ball screw mechanism 30 is telescopically fitted to the other end (left end) of the sleeve 22, a spiral ball screw groove 34 is formed on the inner peripheral surface of the intermediate portion, and the other end ( Cylindrical ball nut 32 whose left end) is rotatably supported by the bearing 35 with respect to the left portion 12c.
A ball screw shaft 38 having a spiral ball screw groove 36 formed in the middle of the rack shaft 10, a large number of balls 42 interposed between the ball screw grooves, and between the ball screw grooves 34, 36. And two ball return tubes (tubes) 50 for returning the ball 42, which has moved forward in the axial direction, to the rear side.

As shown in FIGS. 1 and 2, the ball return pipe 5
0 has a U shape as a whole and is attached to the outer peripheral surface of the ball nut 32, and after the openings of the respective ends are inserted into the through holes formed in the ball nut 32, the adjacent ball screw grooves 34 , 36. After pressing the ball return tube (tube) 50 with a tube retainer 54 having a U-shaped cross section, and attaching a seal cap 52 so as to cover the top,
The tube retainer 54 and the seal cap 52 are fixed to the ball nut 32 with bolts 56.

In this embodiment, when an auxiliary steering force is applied to the rack shaft 10 from the electric motor 20, the rotor 24 and the sleeve 22 are integrally rotated by a predetermined electric signal,
The ball nut 32 integrated with the sleeve 22 rotates. When the ball nut 32 rotates, the ball screw shaft 38, that is, the rack shaft 10 is moved through the ball 42 by a known operation.
Moves in the axial direction. Lubricating oil is supplied to the ball screw grooves 34 and 36 of the ball screw shaft 38 and the ball nut 32 to facilitate the operation of the ball screw mechanism 30, and the end of the ball return pipe 50 is inserted into the ball nut 32. Although there is a through hole for this purpose, there is no concern that this lubricating oil will leak outside from the periphery of the ball return pipe 50. This is because the ball return pipe 50 is covered with the seal cap 52 and attached to the ball nut 32. Therefore, there is no concern that the lubricating oil will flow from the ball nut 32 through the rotor 24 and into the electric motor 20.

Further, the seal cap 52 and the tube retainer 54 can be easily made from a synthetic resin plate, a metal plate or the like, and it is easy to attach them to the ball nut 32. Moreover, even if the tube cap 52 or the like is attached, it is not necessary to change the configuration of the ball screw mechanism 30, and the ball screw mechanism 30 does not become large.

Next, a second embodiment of the present invention will be described with reference to FIGS. 3 and 4. This embodiment is different in that a plurality of ball returning pieces 60 are adopted instead of the ball returning tube 50 of the first embodiment. Ball return piece 60
It is publicly known and has an elongated shape and is curved with the same curvature as the ball nut 32. Ball return piece 6
A ball rake groove 62 is formed on the inner peripheral surface of 0, and both ends thereof extend between the adjacent ball screw grooves 34, 36. A thin cylindrical nut cover 64 is attached so as to cover the ball nut 32 and the ball return piece 60.

In the present embodiment, even if the lubricating oil leaks out from the clearance of the through hole for mounting the ball returning piece formed in the ball nut 32, the nut cover 64 prevents the lubricating oil from flowing to the periphery. . Further, even when the top 60 is poorly attached (bonded) to the ball nut 32, the cover 64 can prevent the top 60 from falling off. It is needless to say that the above is only the embodiment of the present invention, and the present invention can be appropriately modified and improved within a range not impairing the gist thereof.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing a first embodiment of the present invention.

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

FIG. 3 is a front sectional view showing a second embodiment of the present invention.

FIG. 4 is a cross-sectional view of the main parts of FIG.

[Explanation of symbols]

 10: rack shaft 12: housing 20: electric motor 30: ball screw device 32: ball nut 50; 60: ball returning means 52, 54, 56; 64: lubricating oil leak prevention means

Claims (1)

[Claims] 1. A rack shaft movably supported in the axial direction by a housing and connected at both ends to steered wheels of a vehicle, and an electric motor coaxially arranged with the rack shaft.
A ball screw mechanism arranged coaxially with the rack shaft and arranged in parallel with the electric motor, wherein a ball nut of the ball screw mechanism is rotated by a rotor of the electric motor, whereby the rack shaft is axially moved. In an electric power steering device having a ball screw mechanism for moving, a ball returning means provided on a ball nut of the ball screw mechanism is covered, and lubricating oil inside the ball screw mechanism leaks to an outer surface of the ball nut. An electric power steering device equipped with a ball screw mechanism, characterized in that it is provided with a lubricating oil leak prevention means for preventing the oil from leaking out.