GB Patent 951036 - Improvements relating to fluid pressure power steering mechanisms for motor vehicles

Description

PATENT SPECIFICATION

DRAWINGS ATTACHED 951,036 :'/47Fak Date of Application and filing Complete Specification: Sept. 6, 1962.

_1 Yg f sNo. 34216/62.

Application made in United States of America (No. 137893) on Sept. 13, 1961.

Complete Specification Published: March 4, 1964.

Crown Copyright 1964.

Index at acceptance:-B7, H(27A1, 27A3B, 27A4E, 27DX, 27E).

International Classification:-B 62 d.

COMPLETE SPECIFICATION

Improvements relating to Fluid Pressure Power Steering Mechanisms for Motor Vehicles We, GENERAL MOTORS CORPORATION, a Company incorporated under the laws of the State of Delaware, in the United States of America, of Grand Boulevard, in the City of Detroit, State of Michigan, in the United States of America (Assignees of DONALD ERNEST DEFORD, ROBERT PAUL RORDE, and WILLIAM BLAIR THOMPSON) do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: -

This invention relates to fluid pressure power steering mechanisms for motor vehicles, and is concerned more particularly with a steering linkage booster which include a piston and cylinder servomotor and a control valve therefor and is arranged to be fitted into the steering linkage, preferably a parallelogramtype steering linkage, as a component thereof with the servomotor piston connected by way of a piston rod to the vehicle frame.

Clearance and other problems have hitherto arisen in the mounting of steering linkage boosters. According to the present invention an adaptor portion rigidly interconnects the servo cylinder and a housing for the control valve, and at least one connecting member projects from the adaptor portion for connection to at least one link member adapted to transmit steering movement to the vehicle wheels.

Preferably such connection is effected by means of a pair of ball studs mounted in the adaptor portion with their shanks projecting for connection to a pair of tie rods (track rods) respectively pivotally connected to knuckle arms (steering arms) to transmit steering movement to the steerable wheels of the vehicle.

The scope of the monopoly is defined by the appended claims; the invention and how it may be performed are hereinafter particularly described with reference to the accompanying drawings, in which:

Figure 1 is a plan view of the front portion of the chassis of a motor vehicle equipped with one embodiment of a steering linkage booster according to the invention, the engine of the vehicle being omitted and certain parts being shown broken away; Figure 2 is a section taken on the line 2-2 of Figure 1; and Figure 3 is a section taken on the line 3-3 of Figure 2.

As shown in Figure 1, side rail components 10 of a vehicle frame are interconnected by a cross frame member 12. Independent suspension assemblies for the dirigible wheels 14 are secured to the cross frame member:

each such suspension assembly comprises upper and lower control arms 16 and 18. The lower control arms are pivotally connected to the cross frame member 12; the upper arms are pivotally supported by a bracket member 20 itself supported by the cross frame member. The upper and lower control arms 16, 18 of each pair are interconnected near the corresponding dirigible wheel by means of a steering knuckle support 24.

The dirigible wheels 14 are steered through knuckle arms 26 which have pivotal connections 28 to tie rods 30 and 32. Each of the tie rods incorporates a turnbuckle device 34 whereby the rod may be lengthened or shortened as required. As shown, the tie rods are disposed at a lower level than the frame side rails 10 and are pivotally inter-connected by means of an integrated, in-line control valve and fluid servomotor assembly 36, the two connections being made through an adaptor (Figure 2) which is disposed between and rigidly interconnecting the control valve and the servo cylinder of the assembly.

The control valve, which is denoted by the reference numeral 42, is of the axial spool type including a housing 46 and a valve spool (valve member) 48 slidable within the housing.

c:The servomotor includes a servo cylinder 44 of double-wall construction and a piston having a piston rod 52 extending through the end of the cylinder for connection to the frame of the vehicle at 54.

The valve spool 48 is actuated by a pitman arm 56 which is responsive to steering effort and terminates in a ball stud 58 accommodated within the adaptor 40 between a pair of seats 60 housed by a sleeve 66, the seats being held in close engagement with the ball stud by the force of a spring 62. One end of the spring is seated on a plug 64 threaded into the sleeve 66. The sleeve 66 is also formed with an annular shoulder 68 forming an abutment for the right hand one of the pair of seats 60.

The sleeve 66 and all that it contains move as a unit with the spool valve 48. To this end the plug 64 is a split-flanged construction (Fig 3), and is threaded into the sleeve 66 into abutting engagement with flats 72 at the inner end of the valve spool 48. The plug 64 accommodates a locking spider 74 which prevents loosening of the plug, the body of the spider 74 abutting a washer 76 which in turn abuts a land 78 integral with the valve spool 48. This land it located within a chamber 80 provided by the valve housing 46. A spacer washer 82 surrounds the washer 76, and provides a shoulder 88 engaging a composite seal and spring seat 90. A spring 92 which seats on the spring seat 90 with one of its ends at its other end reacts against a washer 94 abutting flush shoulder 96.

The spring 92 tends to maintain the valve spool 48 and the sleeve 66 in their positions shown, such positions corresponding to the straight-ahead position of the dirigible wheels 14. Axial displacement of these parts in either direction relatively to the housing 42 is marked by compression of the spring. When the parts are moved to the right, the land 78 slides within the composite seal and spring seat 90, which is prevented from partaking of this movement to the right by the spacer washer 82. On movement of the valve spool and sleeve to the left, however, the valve spool and the part 90 are carried along by the washer 76, causing compression of the spring 92.

As shown in Figure 2, the complete power steering system includes a pump 100 drawing fluid from a reservoir 102. Pressure fluid from the pump enters the control valve through a passage 104 which opens to an annular groove 106. In addition to such groove the valve comprises annular grooves 108 and communicating with a common passage 112 opening to a return line to the reservoir.

At the two sides of a central valve land 114, which is centrally located with respect to the pressure fluid passage 104, are passages 115 and 116, which communicate respectively with conduits 118 and 120. The conduit 118 opens to a left-hand chamber 122 of the servo cylinder 44, the conduit 120 opens to a port 124 in the outer wall of the servo cylinder 44 from which port fluid can enter the space between the two walls of the servo cylinder and hence the right-hand chamber of the servo cylinder via a port 128 in the inner wall of the cylinder.

In addition to the ports previously mentioned, the valve housing has a port 129 which interconnects the annular groove 106 and the chamber 80, and which with the pump operation is thus at all times open to the ingress of fluid at system pressure.

The adaptor 40 houses, in addition to the sleeve 66 and the parts therein contained, seats 130 for ball studs 30 A and 32A. The shank portions of the ball studs are connected to the tie rods 30 and 32. The tie rod 32 is substantially longer than the tie rod 30, in order that the interconnection between the two tie rods may be made as shown. Contrary to what might be exepected, the use of tie rods of different lengths does not adversely affect the steering geometry.

The control valve shown is of the "opencentre" type, that is, when the valve spool 48 is in its neutral position the lands thereof do not fully close the corresponding ports. In other words, with the valve spool in the said neutral position pressure fluid supplied by the pump 100 circulates to the valve and back to the reservoir 102 against the static pressure of the fluid in the servo cylinder 44.

In operation, for a right turn, the valve spool is displaced axially to the left by the pitman arm 56, thereby fully or substanially fully opening the annular groove 106 to allow pressure fluid to flow through the conduit 118 to the left-hand chamber 122 in the servo cylinder 44. Such displacement of the valve spool closes off the conduit 120 from the source of pressure fluid but opens the conduit to exhaust via the passage 112. Accordingly, the entire control valve and servo cylinder unit is displaced to the left, thereby turning the dirigible wheels to the right as desired.

Correspondingly, for a left turn rightward displacement of the control valve is marked by the creation of a pressure differential across the piston 50 in favour of the right-hand chamber 126, resulting in axial displacement of the control valve and servo cylinder unit to the right, thereby turning the dirigible wheels to the left.

Irrespective of the direction of displacement of the valve spool 48, the effort imposed to achieve the displacement must overcome not only the resistance of the spring 92 but also the resistance of the pressure fluid contained in the chamber 80. Such fluid reacts during rightward displacement of the valve spool, against the shoulder 96, and during leftward displacement of the valve spool, against the composite seal and spring seat 90.

951,036 5. A steering linkage booster according to claim 4, wherein the sleeve accommodates a ball stud formed at the end of a pitman arm.

6. A steering linkage booster according to claim 5, wherein the centre of the ball stud lies on the common axis of the control valve and the servo cylinder.

7. A steering linkage booster for a power steering mechanism for motor vehicles, comprising a servo cylinder containing a piston connectible to the frame of the vehicle, a control valve housing spaced coaxially from the servo cylinder and containing a valve member adapted to be moved relatively to the housing by means of an actuating member which is connectible to an arm responsive to steering effort, and an adaptor portion which rigidly interconnects the servo cylinder and the control valve housing and accommodates a pair of ball studs the shank portions of which project from the adaptor portion for connection to respective tie rods through which steering movement may be transmitted to the vehicle wheels.

8. A steering linkage booster according to claim 7, wherein the control valve is a slide valve.

9. A steering linkage booster according to claim 8, wherein the actuating member comprises a sleeve retaining a plug which contacts the valve members.

10. A steering linkage booster according to claim 9, wherein the sleeve accommodates a ball stud formed at the end of a pitman arm.

11. A steering linkage booster according to claim 10, wherein the centre of the ball stud lies on the common axis of the control valve and the servo cylinder.

E. WILLIAMSON, Chartered Patent Agent.

These reaction areas are controlled by design to compensate for the diameter of the piston shaft 52, thereby to obtain a balance as well understood in the art. The advantage of the fluid pressure resistance resides in the fact that an artificial steering " feel " is given the driver. This resistance is directly proportional to the actual steering resistance, the pressure in the chamber 80 at any time being the same as prevails in the working chamber of the power cylinder.