AU2003203976A1 - Improvements in automotive power steering systems - Google Patents

Description

53711 GEH:PAB:PFB P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE

SPECIFICATION

FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: COOPER-STANDARD AUTOMOTIVE (AUSTRALIA) PTY LTD Name of inventor: ANDREW DAVID MARSH Address for Service: COLLISON CO.,117 King William Street, Adelaide, S.A. 5000 Invention Title: IMPROVEMENTS IN AUTOMOTIVE POWER STEERING SYSTEMS Details of Associated Provisional Applications: AUPS2144 Dated 7 th May 2002 The following statement is a full description of this invention, including the best method of performing it known to us: This invention relates to improvements in automotive power steering systems, more particularly to modifications to attenuate steering shudder.

Power steering systems are commonly installed in motor vehicles to assist the driver by reducing the effort required to steer the vehicle while still retaining a degree of feel on the steering wheel. The power steering system includes a hydraulic pump to supply fluid under pressure from a reservoir to a control valve which directs the oil to either side of a piston rack piston. The rack is moved by a pinion on the steering column, the rack piston assisting in the movement.

The pump delivers high pressure oil to the control valve through a high pressure line. A low pressure line is connected to the outlet of the control valve, the low pressure line returns the oil to the reservoir through an oil cooler heat exchanger loop.

However a problem exists in many power steering systems. At the time of sudden steering movements the rapid opening and closing of the control valve creates large pressure pulses and fluctuations in the hydraulic system. This creates shudder in the vehicle and can be quite severe to such an extent the vehicle is un-drivable.

Various attempts have been made to overcome the problem and examples of these are referred to below.

JP 11321681 describes a system whereby the low pressure oil from the control valve passes through the oil cooler to the reservoir. An electromagnetic valve selectively bypasses the oil cooler under the control of sensors detecting the turning of the wheels in a steering movement.

JP 11115782 provides a hydraulic hose adapted for elastic deformation in a radial direction to absorb pressure variations in a power steering system.

JP 53002825 discloses a pair of pistons in a vibration absorbing chamber to prevent chatter phenomenon at the initial time of steering.

JP 10287256 describes a branch line on the lower pressure line from the control valve. The branch line is plugged at its end and consists of material having extensibility to absorb the pressure pulses.

In JP 02274659 the reservoir is divided into two separate chambers. The pump is fed from one chamber, the return from the control valve exhausts into the second chamber. From the second chamber the oil passes through an oil cooler back to the first chamber. The surge pressure from the valve is absorbed in the second chamber.

JP 60143181 and JP 60143182 each describe a reaction chamber which exhibits a damper function to suppress vibration of the valve spool.

US Nos 6119728, 5941283, 5539164, 6338363,4285534 and 4794955 describe various forms of attenuation hoses.

US 4203287 describes an expansible chamber in a power steering system.

US 5193885 describes a power braking system in which pressure pulsations are absorbed in an accumulator.

It is an object of the invention to provide a modification to a power steering system to attenuate steering shudder.

A further object of the invention is to provide a device to attenuate fluid borne pulsations that lead to power steering pump noise and shudder.

Thus there is provided according to the invention an attenuating device positioned in the interior of a line or hose of the power steering circuit to break up pressure waves which may exist in the system.

In a preferred form of the invention, the device may comprise a baffle positioned in either the pressure or return hoses.

In a preference, the baffle may be positioned in the hose or pipe such that the entire fluid flow passes through the baffle, or alternately some of the fluid may pass around the outer surface of the baffle.

In a preferred form of the invention, the baffle comprises a tube having baffle plates restricting the fluid flow spaced along the tube to interrupt and reflect pressure pulsations.

In preference, each baffle plate is semi-circular, adjacent baffle plates being oriented 180 degrees from its adjacent baffle.

In a preferred form of the invention, the baffle mar comprise a spiral wound tuner cable within a tube, whereby the fluid can pass not only through the tube, but bypass around the outside of the tube.

In order to more fully describe the invention reference will now be made to the accompanying drawings in which:- Figure 1 is a diagrammatic sketch of a typical power steering system, and Figures 2a and 2b are views of one form of the baffle.

Referring to Figure 1 the hydraulic pump 1 delivers pressurised fluid to the steering control valve 2 through line 3. The hydraulic fluid then passes through line 4 including an oil cooler 5 back to the oil reservoir 6 supplying the pump through line 7.

Figure 2 shows one form of attenuator, in the form of a cylindrical tube 8. In this embodiment the tube has four baffle plates 9, each baffle plate being orientated at 180 degrees. Each baffle plate is semi-circular and thus obstructs one half of the interior of the tube. In the embodiment shown there are four baffle plates, but it is to be realised other numbers of baffle plates can be used. In the particular installation in which the baffle was tested four baffle plates gave a satisfactory result. If there are more baffle plates, there is an increase in back pressure.

The baffle can be positioned in either the pressure line 3 or the return line 4.

More specifically the baffle may be mounted as part of a spiral wound tuner cable arrangement located within the pressure or return hoses. In this instance it may be installed such that fluid not only passes through the baffle but provides also a fluid path around the outside of the baffle tube. Alternately the baffle can be clamped into the hose allowing fluid to pass only through the baffle tube itself.

Thus there has been described an attenuation device in the form of a baffle tube inserted in the hydraulic circuit of a power steering system, and although various forms of the invention have been described the invention is not to be limited hereto but can include modifications and variations falling within the spirit and scope of the invention.

Claims (7)

1. A device for attenuating shudder in vehicle power steering systems, the device being positioned in the interior of a line or hose of the power steering hydraulic circuit to break up pressure waves which may exist in the system.

2. The device for attenuating shudder in vehicle power steering systems of Claim 1, wherein the device may comprise a baffle positioned in either the pressure or return hoses.

3. The device for attenuating shudder in vehicle power steering systems of Claim 2, wherein the baffle may be positioned in the hose or pipe that the entire fluid flow passes through the baffle, or alternately some of the fluid may pass around the outer surface of the baffle.

4. A device for attenuating shudder in vehicle power steering systems as defined in Claims 2 or 3, the baffle comprising a tube having baffle plates restricting the fluid flow spaced along the tube to interrupt and reflect pressure pulsations.

A device for attenuating shudder in vehicle power steering systems as defined in claim 4 wherein each baffle plate is semicircular, adjacent baffle plates being oriented 1800 from its adjacent baffle.

6. A device for attenuating shudder in vehicle power steering systems as defined in Claims 1 or 2 wherein the baffle may comprise a spiral wound tuner cable within a tube, whereby the fluid can pass not only through the tube but by-pass around the outside of the tube. 7

7. A device for attenuating shudder in vehicle power steering systems substantially as described in the specification with reference to, and as illustrated by the accompanying illustrations. Dated this 2nd day of May 2003 COOPER STANDARD AUTOMOTIVE (AUSTRALIA) PTY LTD By their Patent Attorneys, COLLISON CO.