GB2046682A

GB2046682A - Rack-type Power Steering Cylinder Device

Info

Publication number: GB2046682A
Application number: GB8006994A
Authority: GB
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1979-03-03
Filing date: 1980-02-29
Publication date: 1980-11-19
Also published as: FR2450734A1; DE3007813A1

Abstract

A rack-type power steering cylinder device includes a manually operable and hydraulically assisted rack shaft (2) axially slidably supported by bearings (9, 8) and has a piston (30) in a cylinder (7). The piston (30) is radially movably supported by the rack shaft (2) and/or at least one bearing is radially movably supported in the cylinder (7), so as to permit radial displacement or deflection of the rack shaft (2) caused by reaction of a rough surface without accompanying interference between the cylinder and the piston and/or between the rack shaft and the bearing. The piston (30) comprises a piston ring (12) surrounding the rack shaft (2) with clearance, two guide rings (16, 17) slidably contacting the side surface of the piston ring (12) and forming clearances between their outer periphery and the cylinder (7), a first seal disposed between one of the guide rings (16, 17) and the shaft (2), a second seal between one of the guide rings and the piston ring (12), and snap rings (22, 23) axially retaining the guide rings (16, 17) on the shaft. The bearing (9) comprises a bearing ring (34) slidably supporting the rack shaft (2) and disposed with clearance in the cylinder (7), a first seal (35) between the bearing ring and the rack shaft, a second, deformable seal (36) between the bearing ring and the cylinder, and guide rings (38, 39) axially retaining the bearing ring in the cylinder. <IMAGE>

Description

SPECIFICATION Rack-type Power Steering Cylinder Device The present invention relates to a rack-type power steering cylinder which assists the steering force of a vehicle by hydraulic pressure.

Conventional rack-type power steering cylinders are shown in Figs. 1 and 2. The power steering cylinder shown in Fig. 1 comprises a pinion a connected with a steering wheel, not shown, which is operated by a driver. The pinion a meshes with a rack c formed on a rack shaft b which is axially slidably supported in a housing d.

A cylinder e is secured to the housing dto slidably support the rack shaft b through a bearing i. A bearing mounted at one end of the housing d also supports the rack shaft b. A piston fis axially slidably mounted in the cylinder e, and is supported by the rack shaft b. Snap rings h fitted around the rack shaft b axially retain the piston f through guide rings g at both sides of the piston f.

Oil seals k seal both ends of the cylinder e against leakage of the working fluid along the outer surface of the rack shaft b.

When a vehicle equipped with the power steering cylinder of Fig. 1 is driven along a rough road, external force caused by the uneven surface of the road is applied to tires of the vehicle, and a portion of the reaction force is applied to the rack shaft t as a force F shown in Fig. 1. Since the pinion a meshes with the rack c, the force F produces a vertical component P. The force P is approximately 70 kg at the maximum, which deflects the rack shaft b vertically by about 2 mm.

When such a vertical load is applied to the rack shaft b, vertical pressures are applied between the piston fand the cylinder e as well as between the rack shaft b and the bearings i, j or the oil seals k.

Thus, the relatively sliding surfaces tend to bind on each other. Such a binding action results in unevenness of the steering force, reduction of effective hydraulic force, and deterioration of the sealing performance.

Frequently, the hydraulic assisting force of conventional power steering apparatus may be reduced by mis-alignment of the apparatus caused by an accident, other than the normal 'kick-back, even when the apparatus is apparently serviceable.

Another known rack-type power steering cylinder is disclosed in the U.S. Patent No.

3,817,155, which eliminates the above mentioned disadvantage. As shown in Fig. 2, the cylinder has a floating type bearing of the rack shaft b adjacent the housing d. A relatively thin tube /which is secured to the right hand end of the housing d projects into the cylinder e as a cantilever, and the free end of the tube I is provided with a bearing m which supports the rack shaft b.

The power steering cylinder shown in Fig. 2 absorbs radial displacement of the rack shaft b by a resilient deformation of the tube A However, the twisting force between the bearing m and the rack shaft b, and between an oil seal n at the end of the bearing m and the rack shaft b cannot be effectively absorbed. Thus, the service lives of the bearing m and the oil seal n are still not improved.

Also, the power steering cylinder requires the deformable tube which must extend into the cylinder e to form a double tube construction.

Further, the sealing device between the tube land the housing d must be complicated. As the cylinder e must be long, the power steering cylinder shown in Fig. 2 necessarily becomes bulky and heavy.

Accordingly, a primary object of the present invention is to provide a rack type power steering cylinder device in which the rack shaft slides smoothly along the cylinder even when the rack shaft is radially moved or deflected, without accompanying interference between the cylinder and the piston and/or between the rack shaft and the bearing supporting the rack shaft.

According to one aspect of the present invention, the piston comprises a piston ring adapted to receive hydraulic pressure in the cylinder and forming a first clearance between the rack shaft and the piston ring, guide rings slidably contacting both side surfaces of the piston ring and forming second clearances between the cylinder and the guide rings, a first seal means disposed between at least one of the guide rings and the rack shaft, a second seal means disposed between said at least one of the guide rings and the piston ring, and means axially retaining the guide rings on the rack shaft, said first and second clearance permitting radial movement of the rack shaft.

According to another aspect of the present invention, at least one of the bearings supporting the rack shaft comprises a bearing ring supporting the rack shaft and forming a clearance between the cylinder and the bearing ring, a first seal means disposed between the bearing ring and the rack shaft and slidably engaging the rack shaft, a second deformable seal means disposed between the cylinder and the bearing ring, and means axially retaining the bearing ring in the cylinder, said deformable seal means permitting radial movement of the bearing ring.

By thus forming sufficient clearances between the rack shaft and the piston, and/or between at least the rack side bearing and the cylinder, the radial displacement or deflection caused by the reaction component transmitted from the vehicle tire during driving along a rough road is effectively absorbed. Thus, binding or twisting is prevented and the rack shaft slides smoothly along the cylinder under all adverse operating conditions.

In the accompanying drawings:- Figure 1 is a longitudinal sectional view of a conventional rack-type power steering cylinder device; Figure 2 is a longitudinal sectional view of a portion of another conventional rack-type power steering cylinder device; Figure 3 is a longitudinal sectional view of a rack-type power steering cylinder device according to one embodiment of the present invention; Figure 4 is an enlarged sectional view of a portion of Fig. 3; Figures 5 to 7 are sectional views of three modifications of the device shown in Fig. 4; Figure 8 is an enlarged sectional view of another portion of Fig. 3; and Figures 9 and 10 are sectional views of two modifications of the device shown in Fig. 8.

Referring to Fig. 3, a rack-type power steering cylinder device according to a first embodiment of the present invention comprises side rods 1 of a vehicle steering apparatus, which are connected with a rack shaft 2 through ball joints 3, respectively. The rack shaft 2 is formed with a rack 4 which meshes with a pinion 5 connected to a steering wheel, not shown. A housing 6 encloses the rack shaft 2 and is secured coaxially to a cylinder 7. The rack shaft 2 is axially slidably supported in the cylinder by a floating bearing 9 which is accommodated in the housing 6 near one end thereof which faces the cylinder 7, and by a fixed bearing 8 located at the other end of the cylinder 7. Ports 10 are formed at both ends of the cylinder 7, which are connected through a control valve device, not shown, with a hydraulic oil source and a drain, respectively.Rubber boots 11 are provided at both ends of the cylinder device to seal the ball joints 3.

A piston 30 is mounted on the rack shaft 2 to receive hydraulic assisting force in the cylinder 7.

The piston 30, according to the embodiment shown in Fig. 4, comprises a piston ring 12 which forms a clearance S, between the inner periphery thereof and the outer periphery of the rack shaft 2. An annular groove 13 is formed on the outer periphery of the piston ring 12 and contains a back-up O-ring 14 and a plastics seal ring 1 5 which is arranged radially outwardly of the O-ring 14 and slides along the inner periphery of the cylinder 7.

Guide rings 16 and 1 7 are fitted around the rack shaft 2 on both sides of the piston ring 12, to form clearances S2 between the outer periphery of each of the guide rings 16 and 17 and the inner periphery of the cylinder 7. At least one of the guide rings 1 6 and 17, e.g. the guide ring 16 shown in Fig. 4, supports an O-ring 1 9 which engages with the right side surface of the piston ring 12, and an O-ring 1 8 which engages with the outer periphery of the rack shaft 2. Both of the 0rings 18 and 1 9 are arranged in corresponding annular grooves formed on the inner and left side surfaces of the guide ring 1 6.As the piston ring 12 is radially movable relative to the guide rings 16 and 17, the O-ring 19 may preferably be formed of wear resisting material, such as that used for the O-ring 14 and the seal ring 1 5.

Annular grooves 20 and 21 are formed on the outer periphery of the rack shaft 2 to receive snap rings 22 and 23 which retain the end surfaces of the guide rings 16 and 17. Thus, the piston 30 is axially retained.

Figs. 5 to 7 show other embodiment of the arrangement shown in Fig. 4. The same reference numerals are used to show similar parts or portions with those shown in Figs. 3 and 4, and only the differences will be described hereinafter.

In the embodiment shown in Fig. 5, the O-ring 18 is supported in a groove formed on the outer periphery of the rack shaft 2, while the O-ring d 9 is supported in an annular recess formed on a side surface of the piston ring 12.

In the embodiment shown in Fig. 6, an external thread 24 is formed on the outer periphery of the rack shaft 2, and a nut 25 is threaded on the external thread 24 to regulate the sliding contact pressure between the piston ring 12 and the guide rings 16 and 17.

In the embodiment shown in Fig. 7, a stepped portion 26 is formed on the outer periphery of the rack shaft 2 to retain the outer side surface of the guide ring 1 7. That is, serrations 27 are partially rolled on circumferentially spaced portions of the rack shaft 2, and projections of the serrations 27 are machined to form the stepped portions 26 on the rack shaft 2.

In the embodiments shown in Figs. 4 to 7, when the vehicle is driven along a rough road and a reaction force component is transmitted by the tires of the vehicles to the rack shaft 2 to radially displace or deflect the rack shaft 2, the clearance St between the rack shaft 2 and the piston ring 12, as well as the clearance S2 between the guide rings 1 6 and 1 7 and the cylinder 7 effectively absorb the radial displacement or deformation of the rack shaft 2. During the operation, the piston ring 12 slides radially relative to the surfaces of the guide rings 1 6 and 17, and the O-ring 19 allows such relative movement by sliding on the side surface of the piston ring 12 shown in Figs.

3, 4, 6 and 7, or on the side surface of the guide ring 16 shown in Fig. 5.

Consequently, no radial force is applied to the piston ring 12 even when the rack shaft 2 is radially displaced or deformed. Thus, undesirable binding or twisting between the cylinder and the piston is effectively prevented. Further, unevenness of the steering force and reduction of the hydraulic assisting force are avoided.

Fig. 8 illustrates the detailed arrangement of the floating bearing 9 located between the housing 6 and the cylinder 7 as shown in Fig. 3.

The bearing 9 comprises a bearing ring 34 which axially slidably supports the rack shaft 2, and which forms a clearance S3 between the outer periphery of the bearing ring 34 and the inner periphery of an enlarged portion of the cylinder 7.

An oil seal 35 prevents leakage of the working fluid along the rack shaft 2. A resilient O-ring 36 is inserted between the cylinder 7 and the bearing ring 34 to resiliently support the bearing ring 34 in the radial direction.

A stepped portion 37 is formed in the cylinder 7, and a guide ring 38 fitted in the enlarged portion of the cylinder 7 contacts the stepped portion 37. A guide ring 39 is also fitted in the enlarged portion and contacts the housing 6. The guide rings 38 and 39 retain the bearing ring 34 axially, and clearances S4 are formed between the inner periphery of the guide rings 38 and 39 and the outer periphery of the rack shaft 2.

In the embodiment shown in Fig. 8, the oil seal 35 and the O-ring 36 are axially offset with each other such that the oil seal 35 faces the inner space of the cylinder 7 while the O-ring 36 is positioned adjacent to the housing 6.

Figs. 9 and 10 show other embodiments of the arrangement shown in Fig. 8. The same reference numerals represent the same parts or portions, and differences only will be described hereinafter.

In the embodiment shown in Fig. 9, the O-ring 36 covers all the axial length of the bearing ring 14 to resiliently support the bearing ring 14 and the rack shaft 2 in the radial direction. In this case, the- clearance S3 shown in Fig. 8 is not formed so that all the radial displacement of the rack shaft 2 is absorbed by the resilient deformation of the 0 ring 36.

In the embodiment shown in Fig. 10, the cylinder 7 is not formed with an enlarged portion 37. The guide rings 38 and 39 at both sides of the bearing ring 34 is axially retained by snap rings 40 which are engaged with annular grooves 41 formed on the inner periphery of the cylinder 7.

The O-ring 36 is inserted between the enlarged portion of the bearing ring 14 and the cylinder 7.

The clearance S3 is formed between the cylinder 7 and the bearing ring 14. In this embodiment, the axial position of the bearing 9 is not limited to the end surface of the housing 6.

In the embodiments shown in Figs. 8 to 10, when the vehicle is driven along a rough road and a reaction force component transmitted from the tires displaces or deflects the rack shaft 2 radially as described before, the bearing ring 34 of the bearing 9 which supports the rack shaft 2 adjacent the housing 6 moves with the rack shaft 2 due to the presence of the clearance S3 between the cylinder 7 and the bearing ring 34, and by the resiliently.supporting O-ring 36 which is inserted between the cylinder 7 and the bearing ring 34. Also, the clearances S4 between the guide ring 38 and the rack shaft 2 as well as between the guide ring 39 and the rack shaft 2 allow radial displacement of the rack shaft 2.

Consequently, when the rack shaft 2 is radially displaced, this displacement is absorbed by relative sliding movement between the side surfaces of the bearing ring 34 and the opposite surfaces of the guide rings 38 and 39. The displacement of the bearing ring 34 is substantially in parallel with the side surfaces of the guide rings 38 and 39. Thus, substantially no twisting force is applied between the rack shaft 2 and the bearing ring 34, as well as between the rack shaft 2 and the oil seal 35.

It will be apparent that the housing side bearing of the rack type power steering cylinder device, according to the present invention, does not interfere with the rack shaft, and undesirable binding or twisting is substantially eliminated.

Consequently, the power steering cylinder device is free from unevenness of the steering force, and reduction of hydraulic assisting force.

Further, the power steering cylinder device -shown in Figs. 8 to 10 eliminates the flexible tube extending into the cylinder of the conventional device shown in Fig. 2. Thus, a simple and compact device as compared with the conventional device can be obtained.

By combining the piston 30 shown in Figs. 4 to 7 and the bearing 9 shown in Figs. 8 to 10, in the rack type power steering cylinder device, radial displacement or deflection of the rack shaft is completely absorbed by the clearances Sg and S2 of the piston 30 and the clearances S3 and S4 of the bearing 9, so that smooth axial sliding of the piston along the cylinder 7 and smooth axial relative sliding of the bearing 9 along the rack shaft 2 are maintained.

Claims

1. A hydraulically operated rack-type power steering cylinder device including a cylinder, a manually operable rack shaft slidably supported in the cylinder, a piston supported by the rack shaft and axially slidable in the cylinder, and bearings at both ends of the cylinder and supporting the rack shaft; said piston comprising a piston ring adapted to receive hydraulic pressure in the cylinder and forming a first clearance between the rack shaft and the piston ring, guide rings slidably contacting both side surfaces of the piston ring and forming second clearances between the cylinder and the guide rings, a first seal means disposed between at least one of the guide rings and the rack shaft, a second seal means disposed between said at least one of the guide rings and the piston rings, and means axially retaining the guide rings on the rack shaft, whereby said first and second clearances permit radial movement of the rack shaft.

2. A hydraulically operated rack-type power steering cylinder device including a cylinder, a manually operable rack shaft slidably supported in the cylinder, a piston supported by the rack shaft and axially slidable in the cylinder, and bearings at both ends of the cylinder and supporting the rack shaft; at least one of said bearings comprising a bearing ring supporting the rack shaft and forming a clearance between the cylinder and the bearing ring, a first seal means disposed between the bearing ring and the rack shaft and slidably engaging with the rack shaft, a second deformable seal means disposed between the cylinder and the bearing ring, and means axially retaining the bearing ring in the cylinder, whereby said deformable seal means permits radial movement of the bearing ring.

3. A hydraulically operated rack-type power steering cylinder device including a cylinder, a manually operable rack shaft slidably supported in the cylinder, a piston supported by the rack shaft and axially slidable in the cylinder, and bearings at both ends of the cylinder and supporting the rack shaft; said piston comprising a piston ring adapted to receive hydraulic pressure in the cylinder and forming a first clearance between the rack shaft and the piston ring, guide rings slidably contacting both side surfaces of the piston ring and forming second clearances between the cylinder and the guide rings, a first seal means disposed between said at least one of the guide rings and the rack shaft, a second seal means disposed between said one of the guide rings and the piston ring, and means axially retaining the guide rings on the rack shaft, said first and second clearances permitting radial movement of the rack shaft; and at least one of said bearings comprising a bearing ring supporting the rack shaft and forming a third clearance between the cylinder and the bearing ring, a third seal means disposed between the bearing ring and the rack shaft and slidably engaging with the rack shaft, a fourth deformable seal means disposed between the cylinder and the bearing ring, and means axially retaining the bearing ring in the cylinder, said deformable seal means permitting radial movement of the bearing ring.

4. A hydraulically operated rack-type power steering cylinder device, substantially as described with reference to, and as illustrated in Figs. 3, 4 and 8, or Figs. 3, 4 and 8 as modified by any of Figs.5 to 7, or 9 and 10 of the accompanying drawings.