JPS60261777A - Power steering device - Google Patents

Abstract

PURPOSE:To obtain a great steering aiding force without the need of increasing the dimensions of a power steering unit by forming a female-screw engaging part in such a manner that the axis thereof is displaced from the center axis of the external diameter of a piston in the direction opposite to a sector gear. CONSTITUTION:A piston 12 has the female-screw engaging part 16 formed on the internal peripheral face thereof in the position to have the axis of said part displaced by the specified distance S from the center of the external diameter in the reverse direction (that is, in the upper position in the drawing) with respect to the position of a sector gear 20. Therefore, without the needs of displacing the turning center O of the sector gear 20 into the lower position in the drawing and reducing the thickness of the piston 12, the radius R of the pitch circle of the sector gear 20 can be set to a value greater than that by the specified dimension and the steering aiding force can also be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) This invention relates to a power steering device, and particularly to a recirculating pole type (hereinafter referred to as RB type) power steering device that can generate a larger steering assist force.

(Prior art) As a conventional RB type power steering device, for example, the one shown in Fig. 2 is known.
7-171966, etc.). As shown in the figure, a piston 12 is slidably fitted into a gear housing 11, defining two fluid chambers 13a and 13b connected to a control valve (not shown). The piston 12 is
It has a substantially cylindrical shape with an opening at one end closed by a plug 14, a rack 15 is formed on the outer circumferential surface, and a female screw-shaped engagement part 16 concentric with the outer circumferential surface is formed on the inner circumferential surface. The female threaded meshing portion 16 of the piston 12 is connected to a male threaded meshing portion 18 formed on the worm shaft 17 via a large number of glue circulating balls 19, and a rack 15 is provided on a sector shaft (not shown). It meshes with the sector gear 20 that is rotated. The worm shaft 17 is rotatably supported by the gear housing 11, connected to a steering wheel (not shown), and rotates integrally with the steering wheel. The sector gear 20 is provided on a sector shaft (not shown) connected to a steering wheel (not shown) via a steering linkage or the like.

In such a power steering device, when the steering wheel is steered and pressure fluid of different pressures is supplied from the control valve to the two fluid chambers 13a and 13b according to the steering of the steering wheel, this pressure is Piston 12 is pressed according to the difference, and piston 1
2 is displaced to drive the sector gear 20. As a result, the sector gear 20 rotates with a torque (hereinafter referred to as steering assist force T) approximately as shown in the following equation (1).

T=(π/4)・D2・ΔP−R---(1) However,
D: Outer diameter of piston 12 (see diagram) ΔP: Fluid chamber 13a
, 13b; Pitch circle radius of sector gear 20 (see figure) In other words, when the steering wheel is steered, the worm shaft 17 rotates together with the steering wheel, and the steering torque applied to the steering wheel (
The piston 12 is displaced in accordance with the manual steering force) and the rotational displacement of the steering wheel. Therefore, the sector gear 20 rotates with a torque obtained by adding the steering assist force <T) to the manual steering force transmitted via the worm shaft 17 etc., and steers the steering wheels.

However, in such a conventional power steering device, as shown in equation (1) above, if the outer diameter of the piston 12, that is, the pressure receiving area of the piston 12 is fixed, the fluid chambers 13a, 13b Fluid pressure difference Δ between
The configuration is such that the magnitude of the auxiliary torque T when P is constant is determined by the pinch circle radius R of the sector gear 20. Therefore, when trying to obtain a larger auxiliary torque T, in order to increase the pinch circle radius R of the sector gear 20, the rotation center 0 of the sector gear 20 is shifted in the direction opposite to the pitch 12 (downward in the figure) to make the sector gear 20 larger. The problem is that it turns into something.

On the other hand, in order to solve this problem, it may be possible to form the rack 15 of the piston 12 at a position shifted toward the central axis Cp of the piston 12 to increase the pitch circle radius R of the sector gear 20. , in this case piston 12
Because the wall thickness of the piston 12 is reduced,
There was a problem in that the diameter of the female screw 6 had to be reduced, and the strength of the female thread-shaped engaging portion 16 was reduced.

(Object of the invention) This invention was made by focusing on such conventional problems, and it is possible to solve the problem without increasing the size or reducing the strength.
It is an object of the present invention to provide a power steering device that can generate a larger steering assist force.

(Structure of the Invention) The present invention provides a worm shaft that has a male thread-like meshing portion, is rotatably supported by a gear housing and rotates integrally with a steering wheel, and a worm shaft that meshes with the male thread-like meshing portion of the worm shaft. A threaded engagement portion is formed on the inner circumferential surface and a rank is formed on the outer circumferential surface, and the gear housing is fitted into the gear housing so as to be displaceable in the axial direction as the worm shaft rotates, thereby defining two fluid chambers. A sector shaft is provided with a cylindrical piston and a sector gear that engages with a rank of the piston and rotates as the piston is displaced, and is connected to a steering wheel. In a power steering gear mechanism in which pressurized fluids of different pressures are supplied in response to steering to generate a steering assisting force in accordance with the pressure difference between the pressure fluids, the piston has the female thread-shaped meshing portion at a diameter of the outer circumference of the piston. It is formed at a position eccentric in the opposite direction to the sector gear with respect to the central axis.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention. In addition,
The same parts as those of the power steering device shown in FIG. 2 described above will be described with the same reference numerals.

First, to explain the structure, in the same figure, 11 is a gear housing fixed to the body of an automobile, and inside the gear housing 11, a substantially cylindrical piston 12 with a hollow hole 12a formed therein is displaced in the direction of the axis C1. The fluid chambers 13a and 13b are defined by the fluid chambers 13a and 13b. These fluid chambers 13a, 13b are connected to control valves (not shown), and pressure fluids of different pressures are supplied from the control valves to each of the fluid chambers 13a, 13b in accordance with the steering of the steering wheel. The piston 12 has a female thread-like engagement part 16 formed on a part of the circumferential surface of the hollow hole 12a, which engages with a male thread-like engagement part of a worm shaft, which will be described later. A rack 15 is formed that meshes with a sector gear to be described later. This piston 12 has a female thread-like engagement part 16 of the hollow hole 12a formed at a position eccentric to the outer circumferential surface by a predetermined dimension, so that the female thread-like engagement part 16, that is, the center axis C2 of the hollow hole 12a and the center axis of the piston outer circumference. C1 is at a position shifted in parallel by a predetermined distance S, and its rank 15 is at a position shifted in the direction of the central axis C□ of the piston 12 (upward in the figure) corresponding to the dimension (eccentricity) S. It is formed. Note that 14 is a plug that closes one end opening of the hollow hole 12a of the piston 12.

The female threaded engagement portion 16 of the piston 12 has a large number of male threaded engagement portions 18 formed on the worm shaft 17.
9-1"L/-5-x 7f*-tLt19'c 1
- Jointed for free rotation. The worm shaft 17 is connected to a steering wheel (not shown) via a steering shaft or the like so as to rotate integrally with the steering wheel.

Further, a sector gear 20 whose number is attached to a sector shaft (not shown) meshes with the rack 15 of the piston 12. The sector gear 20 is supported by the gear housing 11 so as to be rotatable about the rotation center 0, and rotates as the piston 12 is displaced. Note that the sector shaft is connected to the steering wheel via a steering linkage (not shown) or the like, rotates together with the sector gear 20, and transmits steering force to the steering wheel.

Next, the effect will be explained.

In this power steering device, as is well known, when the steering wheel is steered, pressure fluids of different pressures are supplied from the control valve to the two fluid chambers 13a and 13b, respectively. ,
The piston 12 is pressed by the pressure difference between these fluid chambers 13a and 13b. At the same time, the manual steering force applied to the steering wheel is transmitted to the screw I/N 12 from the worm shaft 17 via the externally threaded engagement section 18 and the internal threaded engagement section 16. Therefore, the piston 12 is displaced in the direction of the axis C8 to drive and rotate the sector gear 20, and the steering wheels to which the rotation of the sector gear 20 is transmitted are steered.

Here, the piston 12 has a female thread-shaped engagement portion 16 on the inner circumferential surface.
is a predetermined dimension S in the direction opposite to the sector gear 20 with respect to the outer peripheral surface.
A rack 15 is formed at an eccentric position and meshes with the sector gear 20 on its outer circumferential surface, and is formed at a position offset in the opposite direction (upward in the figure) from the sector gear 20, corresponding to the predetermined dimension S. Therefore, the sector gear 20 does not shift its rotation center 0 downward in the figure, and without reducing the wall thickness of the piston 12, its pitch radius R is smaller than that of the one in FIG. 2 described above. The predetermined dimension X can be set to a larger value, and the steering assist force T can also be increased as shown in the following equation (2).

T-(π/4)-D・ΔP・(Rx)---(2
1 However, X is a value corresponding to the dimension S mentioned above.

That is, without moving the rotation center of the sector gear 20 (without increasing the size of the gear housing 11),
Further, the rack 15 of the piston 12 and the female thread-shaped engaging portion 16
The sector gear 20 is enlarged to increase the pinch circle radius R without reducing the wall thickness between the sector gear 20 and the steering assist force T.
can be made larger.

Furthermore, in this power steering device, it is possible to increase the rigidity near the steering neutral position without reducing its gear ratio, and its steering response can also be improved. That is, in the RB type power steering device, generally speaking, the piston 12 and the worm shaft 17 are connected to the curing ball 19.
It is difficult to maintain the rigidity near the steering neutral position due to elastic deformation of the parts that come into contact with the piston I2.In order to maintain this rigidity, it is necessary to
8. It is known that it is effective to increase the pitch l of the externally threaded meshing portion 18 of the worm shaft I7. However, since the gear ratio K of the RB type power steering gear mechanism is expressed as shown in the following equation (3), a problem arises in that the gear ratio K becomes smaller when the pitch β is increased. However, in the power steering device according to the present invention, the pitch Tado IR can be increased even if the pitch l is increased, so the pitch e is increased without decreasing the gear ratio K, and the steering neutral Rigidity in position can be ensured.

K=2πR/ 1 --(31 However, l: Pitch of the female thread-shaped engaging portion 16 of the piston 12 (effects of the invention) As explained above, in the power steering device according to the present invention, it is difficult to increase the size. without doing anything, and
A larger steering assist force can be obtained without reducing the strength, and furthermore, it is possible to increase the rigidity near the neutral position without reducing the gear ratio.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a steering device according to an embodiment of the present invention, and 2rXJ is a sectional view showing a conventional steering gear mechanism. 11--Gear housing, 12--Piston, 122-m-hollow hole, 13a, 13 b--fluid chamber, 15-R, 16--Female threaded meshing part, 17--worm shaft, 18--male thread-like meshing portion, 20--sector gear, C8--central axis of piston outer diameter, C2-- central axis of hollow hole. Agent Patent Attorney Arigagun Part

Claims (1)

[Claims] A worm shaft having a male threaded meshing part and rotatably supported by the gear housing to rotate integrally with the steering wheel, and a female threaded meshing part that meshes with the male threaded meshing part of the worm shaft on the inner peripheral surface. a generally cylindrical piston having a rank formed on its outer circumferential surface and fitted into the gear housing so as to be displaceable in the axial direction as the worm shaft rotates, thereby defining two fluid chambers; a sector shaft connected to a steering wheel and provided with a sector gear that meshes with the rank and rotates in accordance with the displacement of the piston, and the two fluid chambers have different pressures depending on the steering of the steering wheel. In a power steering gear mechanism that is supplied with fluid and generates a steering assist force in accordance with a pressure difference between the pressure fluids, the piston is configured such that the female thread-shaped engagement portion is connected to the sector gear with respect to the center axis of the piston's outer circumferential diameter. A power steering device characterized by being formed at an eccentric position in the opposite direction.