JP2003002219A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rack assist type electric power steering device realizing a securement of rigidity and a prevention of noises in a power transmission system. SOLUTION: An idler gear 38 is turnably supported to an idler gear shaft 63 secured to a gear housing 31 and a ball screw housing 33 through a pair of bearings 61. Both bearing 61 are arranged at the inside of the idler gear 38 in an axial direction and are preloaded by a pair of nuts (double nut) 65, 67. The respective gears 37-39 comprise helical gears.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball screw type rack assist type electric power steering device, and more particularly to a technique for ensuring rigidity and preventing abnormal noise in a power transmission system.

[0002]

2. Description of the Related Art In a steering system of an automobile, a so-called power steering device is widely used, which assists steering by using an external power source. Conventionally, a vane type hydraulic pump has been used as a power source for a power steering device, and many of these hydraulic pumps are driven by an engine. However, this type of power steering device has a large engine drive loss due to the constant drive of the hydraulic pump (several horsepower to 10 horsepower at maximum load), so it is recommended to be used in light vehicles such as small displacement vehicles. It was difficult and it was unavoidable that the running fuel consumption could not be neglected even in a car with a relatively large displacement.

To solve these problems, an electric power steering device using an electric motor as a power source (Electric Power Steering, hereinafter referred to as EPS)
Has been attracting attention in recent years. Since the EPS uses an on-vehicle battery as a power source of the electric motor, there is no direct engine drive loss, and since the electric motor is started only during steering assist, reduction in running fuel consumption is suppressed and electronic control is performed. It has features such as extremely easy operation.

On the other hand, as a steering gear for passenger cars, a rack and pinion type is now predominant because of its high rigidity and light weight. As the EPS for the rack and pinion type steering gear, in addition to the column assist type in which an electric motor is arranged on the side of the column to drive the steering shaft and the pinion itself, the rack shaft is driven by an electric ball screw mechanism. Ball screw type rack assist type is also used. In the ball screw type rack assist type EPS (hereinafter, simply referred to as a rack assist type EPS), the assist force does not act on the meshing surface between the pinion and the rack, so that the contact surface pressure between both members that causes wear and deformation. Becomes relatively small.

In the rack assist type EPS, the male screw groove of the ball screw shaft formed on the rack shaft and the female screw groove formed on the ball nut are engaged with each other through a plurality of circulating balls (steel balls). The rack shaft moves in the axial direction by rotationally driving the ball nut with an electric motor. As a method of transmitting power between the electric motor and the ball nut, there is a timing belt type disclosed in Japanese Utility Model Publication No. 6-49489 or the like, but Japanese Patent Publication No. 6-504 (first related art) or Kaihei 10-16799 (second prior art), Japanese Patent Application No. 10-532733 (3rd)
The gear type described in (Prior Art) is generally used.

[0006]

Conventionally, when the gear type power transmission method is adopted in the rack assist type EPS, there have been various problems as described below. For example, in the above-mentioned first conventional technique, the drive gear fixed to the output shaft of the electric motor is in mesh with the driven gear formed on the outer periphery of the ball nut.
In this case, the outer diameters of the drive gear and the driven gear become large due to the relationship between the shaft distances of the electric motor and the ball nut, and it is inevitable that the steering gear case becomes large and the device weight increases. On the other hand, in the second conventional technology and the third conventional technology, this problem is solved by interposing an idler gear between the drive gear and the driven gear. However, the gear shaft that holds the idler gear does not move with respect to the steering gear case. Since it is held and supported, there is a possibility that the idler gear may tilt (fall over) when a large steering reaction force is input. Further, in the above-mentioned conventional technique, since a spur gear (spur gear) is used for each gear, it is inevitable that a so-called gear noise is generated during driving. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rack-assist type electric power steering device that secures rigidity in a power transmission system and prevents abnormal noise.

[0007]

According to a first aspect of the present invention, in order to solve the above-mentioned problems, an electric motor is connected to the electric motor via a gear train including an idler gear and is used for driving a rack shaft. An electric power steering apparatus having a ball screw mechanism and a steering gear case having the rack shaft and the ball screw mechanism built therein, wherein the idler gear is rotated by an idler gear shaft having both ends fixed to the steering gear case. It is proposed that a pair of bearings, which are freely supported and are preloaded by preloading means, are interposed between the idler gear shaft and the idler gear. In this invention, since the idler gear shaft is supported by the steering gear case on both sides, the idler gear is prevented from falling down due to the steering reaction force. Further, since the bearing is preloaded by the preload means, the support rigidity of the idler gear is increased, and rattling of the idler gear and abnormal noise are less likely to occur during steering reversal.

Further, the invention of claim 2 proposes the electric power steering device of claim 1 in which the idler gear is a helical gear or a double helical gear. According to the present invention, since the idler gear and the other gear are continuously meshed with each other, generation of gear noise is suppressed and smooth power transmission is realized.

[0009]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a vehicle compartment side portion of an electric power steering apparatus according to an embodiment.
A member indicated by reference numeral 1 in the figure is a steering column, and rotatably supports the upper steering shaft 3. A steering wheel 5 is attached to an upper end of the upper steering shaft 3, and a lower steering shaft 9 is connected to a lower end of the upper steering shaft 3 via a universal joint 7. Lower steering shaft 9
A steering gear 11 including a rack and pinion mechanism, a power assist mechanism, and the like is further connected to the lower end of the steering gear 11. In FIG. 1, reference numeral 13 indicates a column cover that covers the steering column 1, and reference numeral 15 indicates the steering gear 1.
The tie rod connected to the left and right ends of 1 is shown.

FIG. 2 is a longitudinal sectional view of a main part of the steering gear 11, FIG. 3 is a sectional view taken along the line AA in FIG. 2, and FIG. 4 is an enlarged sectional view of a portion B in FIG. The member indicated by reference numeral 21 in FIG. 2 is a rack & rack forming a steering gear case.
The pinion housing holds a rack shaft 23 and a pinion (not shown) that form a rack and pinion mechanism. The rack shaft 23 has a rack 25 that meshes with a pinion on the left side in the drawing, and a spherical joint 27 that swingably supports the tie rods 15 is fixed to the left and right ends thereof.

The power assist mechanism includes a gear housing 31 formed at the right end of the rack and pinion housing 21 in the figure, and a ball screw housing which is bolted to the gear housing 31 and constitutes a steering gear case together with the rack and pinion housing 21. The outer contour is 33. The front end of the electric motor 35 is bolted to the lower portion of the gear housing 31. In addition, between the ball screw housing 33 and a drive gear 37 fixed to a motor shaft (not shown) of the electric motor 35,
A driven gear 39 that meshes with the drive gear 37 via an idler gear 38 is stored. A ball nut 41 having a driven gear 39 spline-fitted to the outer periphery thereof is rotatably held in the ball screw housing 33 via a double-row angular ball bearing 43. In the case of the present embodiment, each gear 37 to 39 is a helical gear (helical gear).

A male screw groove 51 is formed on the rack shaft 23, while a female screw groove 53 is formed on the ball nut 41. Between the male screw groove 51 and the female screw groove 53, a large number of steel balls 55 serving as circulating balls are formed. Is installed. Further, the ball nut 41 is equipped with a circulating top (not shown) for circulating the steel balls 55.

As shown in FIG. 4, the idler gear 38
Is a pair of bearings (both deep groove ball bearings in this embodiment) 6
1 is rotatably supported by an idler gear shaft 63 fixed to the gear housing 31 and the ball screw housing 33. Both bearings 61 are arranged inside the idler gear 38 in the axial direction and are preloaded by a pair of nuts (double nuts) 65 and 67. In the figure, a member indicated by reference numeral 69 is a shim interposed between the nut 67 and the ball screw housing 33, and a member indicated by reference numeral 71 is a bearing for supporting the drive gear 37.

The operation of this embodiment will be described below. When the driver rotates the steering wheel 5, the upper steering shaft 3 and the lower steering shaft 9
The rotational force is transmitted to the steering gear 11 via. Since the rack and pinion mechanism for converting the rotational input into the linear motion is built in the steering gear 11, the rack shaft 23 moves in either the left or right direction, and the steering angle of the wheels is changed via the left and right tie rods 15. The steering fluctuates. At this time, in the power assist mechanism, the electric motor 35 rotates in a forward or reverse direction with a predetermined rotational torque based on the output of a steering torque sensor (not shown), and the rotation thereof is the drive gear 37, the idler gear 38, and the driven gear 39. Is reduced and transmitted to the ball nut 41 via. When the ball nut 41 rotates, a thrust force acts on the male screw groove 51 of the rack shaft 23 via the steel balls 55 engaged with the female screw groove 53, and thereby steering assist is realized.

In this embodiment, the idler gear shaft 6
Since the gear 3 is supported by the gear housing 31 and the ball screw housing 33 on both sides, the idler gear 38 does not fall due to a steering reaction force from the rack shaft 23 or the like. Further, since the bearing 61 is preloaded, the gears 37 to 39 are helical gears, and therefore, there is almost no abnormal noise at the time of steering reversal. Further, since the bearing 61 is disposed in the idler gear 38, the inertia of the idler gear 38 is reduced, so that the inertia of the power transmission system is reduced and the bearing 61 and the bearing 71 do not interfere with each other. The miniaturization with the ball screw housing 33 is also realized.

The description of the specific embodiment is completed above.
Aspects of the present invention are not limited to the above embodiment.
For example, in the above embodiment, the idler gear or the like is a helical gear, but it may be a spur gear or a double helical gear. Further, in the above embodiment, the idler gear is supported by the idler gear shaft via the deep groove ball bearing, but an angular ball bearing or a taper roller bearing may be adopted. Further, the overall configuration of the steering gear, the structure of the power assist mechanism, and the like are not limited to the examples in the above-described embodiment, and are required in terms of design or specifications as long as they do not depart from the gist of the present invention. Can be changed as appropriate.

[0017]

As described above, according to the electric power steering apparatus of the present invention, the electric motor is connected to the electric motor through the gear train including the idler gear and is used for driving the rack shaft. An electric power steering apparatus having a ball screw mechanism and a steering gear case having the rack shaft and the ball screw mechanism built therein, wherein the idler gear is rotated by an idler gear shaft having both ends fixed to the steering gear case. Since a pair of bearings, which are freely supported and are preloaded by preloading means, are interposed between the idler gear shaft and the idler gear, the idler gear does not easily fall due to the steering reaction force, and steering Rattling of the idler gear and abnormal noise are less likely to occur during reversing.

[Brief description of drawings]

FIG. 1 is a perspective view showing a vehicle compartment side portion of a steering device according to the present invention.

FIG. 2 is a vertical cross-sectional view of a main part of a steering gear according to the embodiment.

3 is a cross-sectional view taken along the line AA in FIG.

FIG. 4 is an enlarged sectional view of a B part in FIG.

[Explanation of symbols]

21 ... Rack and pinion housing 23 ... Rack shaft 31 ... Gear housing 33 ... Ball screw housing 35 Electric motor 37 ... Drive gear 38 ... idler gear 39: Driven gear 41 ... Ball nut 61 ... Bearing 63 ... idler gear shaft 65, 67 ... Nuts

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshihiro Fukuda             78 Toba-cho, Maebashi-shi, Gunma Nippon Seiko Co., Ltd.             In the company (72) Inventor Jun Okada             78 Toba-cho, Maebashi-shi, Gunma Nippon Seiko Co., Ltd.             In the company F-term (reference) 3D033 CA02 CA04 CA16 CA21                 3J009 DA11 EA04 EA05 EA11 EA12                       EA13 EA21 EA32 EB23 EC05                       FA08                 3J062 AA07 AB22 AC07 BA26 CD04                       CD23                 3J063 AA02 AB02 AC01 BA09 BB11                       BB12 BB21 BB41 CA01 CB14                       CB41 CC23 CC35 CD02 CD42                       CD43 CD53 XB06

Claims (2)

[Claims] An electric motor, a ball screw mechanism connected to the electric motor via a gear train including an idler gear, and used for driving a rack shaft, and a steering wheel including the rack shaft and the ball screw mechanism. An electric power steering device having a gear case, wherein the idler gear is rotatably supported by an idler gear shaft whose both ends are fixed to the steering gear case, and between the idler gear shaft and the idler gear, An electric power steering apparatus comprising a pair of bearings preloaded by a preload means. 2. The electric power steering apparatus according to claim 1, wherein the idler gear is a helical gear or a double helical gear.