JPH0613300B2 - Power steering device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a power steering apparatus, and more particularly to a cross shaft disposed orthogonal to the axis of a piston that operates axially in response to an operation of a steering shaft. The present invention relates to a ball screw type power steering device in which a sector gear integrally provided with the cross shaft is meshed with a rack of the piston.

<Prior Art> In the conventional power steering apparatus of this type, a preload is applied in the axial direction of the cross shaft to remove rattling between the rack and the sector gear on the piston and to make the handle heavy near the neutral position of the handle. However, it has a structure that imparts steering stability.

<Problems to be Solved by the Invention> However, according to such a conventional device, when there is a gear manufacturing error, it is impossible to apply an accurate preload between both gears. For example, as shown in FIG. As described above, a so-called double-peak phenomenon occurs in which the handle torque increases at a position deviating from the vicinity of the neutral position of the handle, which may cause the handle to sway during steering in a straight line, or the gear may wear due to long-term use. A rattling occurs between both gears, which causes a phenomenon of preload loss near the neutral position of the steering wheel as shown in FIG. 7 (B), which causes a problem of impairing steering stability.

<Means for Solving the Problems> The present invention has been made to solve the above-mentioned conventional problems, and is arranged by displacing the position from the center of the screw shaft and rotating force around the screw shaft on the piston. The preload giving means for giving a preload between the rack and the sector gear is composed of a chevron-shaped cam portion and an abutting member biased by a spring in the direction of abutting the cam portion, and the cam portion is a piston. Alternatively, it is disposed on one of the members that move relative to this, and the contact member contacts the piston or the other member that moves relative to this on the top of the cam portion at the neutral position of steering, and as the cam portion deviates from the neutral position, It is arranged such that it is separated from the top and a maximum preload is applied at the neutral position of steering.

<Operation> Since the present invention has the above configuration, when the handle is in the neutral position, the contact member is in contact with the top of the cam portion.

This contact causes the spring to be compressed, and the repulsive force of the spring causes the piston to rotate clockwise around the screw shaft, resulting in the piston rack being in close contact with the small end image side of the sector gear and the gap between the two. Are removed. This contact phenomenon of the gears increases the handle torque near the neutral position of the handle, and sets the handle to an appropriate weight.

When the steering wheel is further steered and the fixer is further moved from the vicinity of the neutral position, the contact between the contact member and the cam portion is released, and the repulsive force of the sprig stops acting.

<Examples> Examples of the present invention will be described below with reference to the drawings. As shown in FIGS. 1 and 2, the power steering apparatus of the present invention is
It is composed of a power cylinder 1 and a valve device 2 for controlling the pressure fluid supplied to the power cylinder 1. In the power cylinder 1, a piston 5 is fitted in a cylinder portion 4 of a housing 3 so as to be slidable along its axial direction, and a rack 16 is formed on a part of an outer peripheral surface of the piston 5.

A male screw 9a of a screw shaft 9 is screwed into a female thread 5a formed at the axial center of the piston 5 via a number of circulating balls 8. One end of the screw shaft 9 is rotatably supported by the partition wall 10a of the valve housing 10 and is connected to the steering shaft 12 via a torsion bar 11.
The steering shaft 12 is connected to a steering handle (not shown). The valve housing 10 contains a normally open type servo valve which is operated by the relative relationship between the steering shaft 12 and the screw shaft 9.

The housing 3 accommodates a cross shaft 13 which is orthogonal to the axial direction of the piston 5. A sector gear 15 is formed on the cross shaft 13 as a dislocation tooth surface by inclining at a predetermined angle, and the sector gear 15 and the rack 16 of the piston 5 are meshed with each other.

As shown in FIG. 2, one end of the cross shaft 13 projects outward from the housing 3, and the projecting end is connected to a steering wheel through a link mechanism. The other end of the cross shaft 13 has an end cover. It is rotatably supported by the roller bearing rig 40.

Further, a preload applying means 30 is provided between the piston 5 and the cross shaft 15. The preloading means 30 is slidably fitted into a cam portion 31 integrally formed on the cross shaft 13 and a guide hole 33 formed in the piston 5 at a position displaced from the center of the screw shaft 9. The contact member 32 is included. The contact member 32 is repelled by the spring 34 toward the cam portion 31, and the repulsive force imparts a rotational force to the piston 5 in the clockwise direction about the screw shaft 9 to allow the rack to move. 16
Is closely meshed with the small end portion of the sector gear 15.

Further, the cam portion 31 has the sector gear 15 as shown in FIG.
Has a mountain shape with an apex 31a having an angular phase corresponding to the center tooth bottom, and the abutting member 32 increases the preload corresponding to the apex 31a at the neutral position of the steering, and steering from the neutral position to the left and right. Accordingly, the contact member 32 is gradually separated from the top portion 31a to reduce the preload.

Reference numeral 32a is a locking flange that abuts against the end of the guide hole 33 and regulates the protrusion amount of the abutting member 32.

Next, the operation of the power steering apparatus having the above configuration will be described.
First, when the steering handle is operated to the right, the road surface resistance from the steering wheel side (not shown) acts on the screw shaft 9, so that the torsion bar 11 is twisted and the relative rotation occurs between the screw shaft 9 and the steering shaft 12. Occurs, the valve device 2 operates and the pressure fluid from the pump is introduced into the right chamber 4a of the power cylinder.

As a result, the piston 5 moves in the direction of arrow A in FIG. 1, and the fluid in the left chamber 4b of the power cylinder flows out to the tank through the valve device 2. With the movement of the piston 5 in the direction of arrow A, the linear movement of the piston 5 is converted into rotational movement by the engagement between the rack 16 and the sector gear 15, and is transmitted to the cross shaft 13. As a result, the steering force applied to the steering wheel is assisted by the power of the power cylinder 1, and the steering wheel (not shown) connected to the cross shaft 13 is lightly deflected.

In this operation, when the piston 22 is in the neutral position, the contact member 32 corresponds to the top 31a of the cam portion 31,
The repellency of the spring 33 is applied to the top portion 31a. As a result, the repulsive force of the spring 33 causes the piston 5 to rotate clockwise about the screw shaft 9, and the rack 1
6 closely meshes with the small end of the sector gear 15. As a result, the steering wheel torque becomes heavy in the vicinity of the steering wheel neutral, and the steering stability is improved when the vehicle goes straight ahead.

Further, when the steering wheel is deviated from the neutral position and steered to the right or left, the abutting member 32 is gradually released from the abutting state with the apex 31a of the cam portion 31, because the piston 5 moves in the axial direction. As a result, the pressure is gradually reduced by the spring 33, and finally it stops working. As a result, the engagement between the rack 16 and the sector gear 15 becomes a normal engagement state, and a large preload such as when the steering wheel is neutral does not work.

In the above embodiment, the contact member 32 is provided on the piston 5 and the cam portion 31 is formed on the cross shaft 13. However, the present invention is not limited to this, and FIGS.
As shown in the drawing, the contact member 32 may be slidably fitted on the power cylinder 1 to form the cam portion 31 on the piston 5. In this case, as the supporting structure of the abutting member 3, as shown in FIGS. 4 and 5, the abutting member 3 is slidably fitted in a direction perpendicular to the axis of the cross shaft 13 or as shown in FIG. Cross shaft 13
It may be slidably fitted in any direction parallel to the axis of the.

In the above embodiment, the cam portion having a middle-height shape is used. However, the shape of the cam portion may be set according to the required preload, for example, by forming a small recess in the center of the top portion 31a. Good.

<Effects of the Invention> As described above, according to the present invention, the preload is provided by displacing the position from the center of the screw shaft and applying a rotational force around the screw shaft to the piston to provide a preload between the rack and the sector gear. The means is a Yamagata cam part,
The contact member is urged by a spring in the direction of contacting the cam portion, and the cam portion is disposed on one of the piston and the member that moves relative to the piston, and the other of the piston and the member that moves relative to the piston. The contact member abuts on the top of the cam at the neutral position of the steering wheel, separates from the top of the cam as it deviates from the neutral position, and is arranged in such a positional relationship that the maximum preload is applied at the neutral position of the steering wheel. Therefore, the preload can be surely applied only when the handle is operated in the neutral state without being affected by the manufacturing error of the gear tooth surface, and the double-peak phenomenon occurs like the conventional device. It is also possible to prevent the occurrence of preload loss even when the gear is worn during long-term use without causing rattling between the gears.

Further, in the present invention, since the contact member is brought into contact with the cam portion, there is no limitation due to the number of teeth unlike in the case where the contact member is brought into contact with the center tooth of the sector gear.
The present invention can be applied to those with four teeth and has an advantage that the optimum preload characteristic set by the cam shape of the cam portion can be obtained without being affected by the tooth shape.

[Brief description of drawings]

FIG. 1 is a partial sectional view of a part of a power steering apparatus showing an embodiment of the present invention, FIG. 2 is a sectional view taken along the line II-II of FIG. 1, and FIG. 3 is FIG. III-III sectional view taken along the line of FIG. 4, FIG. 4 is a sectional view taken along the line II-II of FIG. 1 showing a second embodiment of the present invention, and FIG. 5 is a sectional view taken along the line VV of FIG. FIG. 6 is a sectional view taken along the line II-II of FIG. 1 showing the third embodiment of the present invention.
7A and 7B are graphs showing the relationship between the steering angle and the steering wheel torque in the conventional device. 1 ... Power cylinder, 5 ... Piston, 5a ... Female screw, 8 ... Ball, 9 ... Screw shaft, 9a ... Male screw, 1
2 ... Steering shaft, 13 ... Cross shaft, 15 ... Sector gear, 16 ... Rack, 30 ... Preloading device, 31 ... Cam part, 32 ... Abutment member, 33 ... Guide hole, 34 ……spring.

Claims (1)

[Claims] 1. A power cylinder, a piston fitted to the power cylinder, and a screw shaft connected to a steering handle and screwed through a large number of balls circulating in an internal thread provided on the piston. A cross shaft that is connected to the wheel side and that has a sector gear that meshes with a rack provided on the piston; and a cross shaft that is displaced from the center of the screw shaft and that applies rotational force about the screw shaft to the piston. In a power steering apparatus including a preload imparting means for imparting a preload between a rack and a sector gear, the preload imparting means is a chevron-shaped cam portion and a spring biased in a direction of abutting the cam portion. A contact member, and the cam portion is provided on one of the piston and a member that moves relative to the piston, The abutting member abuts on the other of the members that relatively move with the apex of the cam portion at the neutral position of the steering wheel, and is separated from the top portion of the cam portion as it deviates from the neutral position, and the maximum preload at the neutral position of the steering wheel. A power steering apparatus, wherein the power steering apparatus is arranged in a positional relationship that imparts