US 6,148,947 AGranted

Power assisted steering unit for motor vehicles

AssigneeTRW Fahrwerksysteme GmbH & Co. KG

InventorsEugen Eberhart, Lars Hampe

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Abstract

To provide a particularly simple and cost effective design of a power-assisted steering unit for motor vehicles for supplying a servo-cylinder (3) with a hydraulic fluid as a function of the travelling speed and the steering rate, comprising a steering valve (1) by means of which the left and right chambers (16, 17) of the servo-cylinder (3) can be pressurized with hydraulic fluid via a pump (2) when there is a steering movement, and a bypass valve (10) connected in parallel to the servo-cylinder (3), by means of which a portion of the hydraulic fluid for pressurizing the servo-cylinder (3) that is directed past the servo-cylinder (3) is controlled, a throttling unit (26) is connected in series with the bypass valve (10). The hydraulic fluid inflow or return flow of the servo-cylinder (3) flows through this throttling unit (26) depending on the steering direction. The throttling unit (26) automatically throttles the flow of hydraulic fluid that is directed through the bypass valve (10) starting from a predetermined value of such volume flow. Furthermore defined is an assisted-power unit for motor vehicles for supplying hydraulic fluids to a servo-cylinder (3) as a function of the travelling speed, wherein the bypass valve (10) is designed as a proportional valve to achieve a particularly compact and cost effective form of construction.

Claims14

Dependent claims

An assisted-power steering unit for a motor vehicle wherein power assistance is dependent upon the vehicle's speed and rate of steering, the unit comprising:

a servo-cylinder (3) having two chambers (16, 17);
a steering valve (1) for directing pressurized hydraulic fluid from a pump (2) to the respective chambers (16, 17) of the servo-cylinder (3) when there is steering movement;
a bypass valve (10) being connected in parallel with the servo-cylinder (3), the bypass valve (10) providing means for controlling a portion of the hydraulic fluid that bypasses the servo-cylinder (3);
and
a throttle unit (26) being connected in series with the bypass valve (10), the throttle unit (26) automatically throttling hydraulic fluid flow directed through the bypass valve (10) after a predetermined hydraulic fluid flow through the bypass valve (10) is reached, the throttle unit (26) having a cylinder tube (27) that is closed by cylinder heads (28, 29) to form a working chamber, the working chamber being divided into two parts by an axially displaceable piston (30) whereby a first part (31) is hydraulically connected with the servo-cylinder (3) by openings (33) arranged in a corresponding cylinder head (28) and a second part (32) is connected with the steering valve (1) by openings (34) in the wall of the cylinder tube (27), and whereby the piston (30) is provided with at least one orifice type opening (35) in an axial direction.

2 more elements

Dependencies are inferred from the claim text.