A POWER ASSISTED VEHICLE STEERING MECHANISM

Abstract: A power assisted vehicle steering mechanism having a rack and pinion assembly, the pinion being mounted to be displaceable by reaction with the rack on the application of steering torque, including a lever (4) mounted for pivotal movement in response to displacement of the pinion, movement of said lever actuating both an hydraulic valve for directing hydraulic fluid to augment steering torque and electrical sensor means (11) for energising a motor which drives a pump to supply hydraulic fluid to said valve.

Description: This invention relates to a power assisted vehicle steering mechanism having a rack and pinion assembly, such as defined in the preamble of claim 1 and known for example from GB-A-1 111 565. There are many examples in the prior art of power assisted vehicle steering with rack and pinion assemblies in which a pivoted lever is used to actuate the power assistance means and in which movement of the lever is caused by the reaction of the pinion with the rack when steering torque is applied. In prior British Patent GB-A-1,111,565 (Hydrosteer), pivotal movement of a lever, caused by lateral movement of the pinion on steering torque being applied, will effect actuation of a valve assembly through a rod, the valve assembly causing hydraulic power assistance to by applied to augment the manually applied steering torque. In prior Japanese Patent Publication No JP-A-61-171665, a lever is moved by the reaction of the pinion on the rack and this movement of the lever causes actuation of an electrical device for the purpose of augmenting steering torque. OBJECT OF THE INVENTION It is the main object of this invention to provide a power assisted rack and pinion vehicle steering mechanism of low cost construction. STATEMENTS OF INVENTION According to the present invention there is provided a power assisted vehicle steering mechanism having a rack and pinion assembly, the pinion being mounted to be displaceable by reaction with the rack on the application of steering torque, including a lever mounted for pivotal movement in response to displacement of the pinion, movement of said lever actuating both an hydraulic valve for directing hydraulic fluid to augment steering torque and electrical sensor means for energising a motor which drives a pump to supply hydraulic fluid to said valve. The position of the operating connection of the electrical sensor means may be further away from the pivot point of the lever than the operative connection of the hydraulic valve. DRAWING The Figure is a part sectional view through a power assistance vehicle steering mechanism according to the invention. SPECIFIC DESCRIPTION The mechanism of the invention may be used with any type of conventional rack and pinion steering assembly in which the pinion is mounted so that the reaction of manual steering torque will cause displacement of the pinion. A pinion shaft 1 enters a housing 2 and is supported by bearings one of which is shown at 3. The pinion shaft 1 is mounted to be displaceable on the application of steering torque. A lever 4, pivoted at 5, is rotated (in the plane of the drawing) by displacement of the pinion shaft 1 either clockwise or counter-clockwise dependent on the direction of steering. The lever 4 has an extension portion 6 with a bulbous portion 7 operating in an aperture 8 at one end of a spool valve 9 and a plate 10 for actuating an electrical sensor means 11. The lever 4 has a hole 12 through which a pin may be inserted into a recess in the casing for setting up the assembly during manufacture. The spool valve is of conventional construction with a centralising mechanism 13 incorporating a spring 14 to return the valve to its neutral position. The electrical sensor means 11 is carried by a bracket 15 and comprises electrical micro-switches 16 and 17 alternately operated by movement of plate 10. The electrical sensor means 11 is connected to an electric motor so that, regardless of which micro-switch is actuated, the motor will be energised. The motor rotates an hydraulic pump for supplying hydraulic fluid to the spool valve 9 for distribution to the power assistance means. It will be noted that the connection of the electrical sensor means 11 with the lever 4 is further away from the pivot point 5 of lever 4 than is the connection 7, 8 of the lever with the spool valve 9. This feature has the advantage that the movement of the lever, for a given angular rotation thereof, is greater the further from the point of rotation and actuation of the electrical micro-switches can be made so as to cause the electric motor to be energised and rotate the hydraulic pump in advance of any significant movement of the spool valve. This configuration minimises the size of the mechanism and yet gives adequate operating movement.

Claims: A power assisted vehicle steering mechanism having a rack and pinion assembly, the pinion being mounted to be displaceable by reaction with the rack on the application of steering torque, including a lever (4) mounted (5) for pivotal movement in response to displacement of the pinion, movement of said lever (4) actuating an hydraulic valve (9) for directing hydraulic fluid to augment steering torque, CHARACTERISED IN THAT movement of the lever (4) also actuates electrical sensor means (11) for energising a motor which drives a pump to supply hydraulic fluid to said valve (9). A power assisted vehicle steering mechanism as claimed in claim 1, in which the position of the operating connection of the electrical sensor means (11) is further away from the pivot point (5) of the lever than the operative connection of the hydraulic valve (9).

Inventors: ADAMS, FREDERICK JOHN
Applicants: TRW CAM GEARS LIMITED
Application year: 1988
Main classification: B62D5
IPC codes: B62D5