US 5,660,247 AGranted

Rack servo-steering, particularly for motor vehicles

AssigneeZF Friedrichshafen AG

InventorArmin Lang

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Abstract

In a servo-steering unit provided for motor vehicles, one pinion (2) supported in a steering housing (1) meshes with a rack (6). A steering valve (8) which serves to control the pressurized fluid for the servo-steering unit has two inlet seat valves (10, 11) and two outlet seat valves (12, 13) the closing members of which are movable via actuating tappets depending upon rotation of a steering spindle. The outlet seat valves (12, 13) are open in the neutral position of the steering valve. The inlet seat valves (10, 11) are actuatable in a closing direction by the force of pressure springs and are opened only after closing of the respective outlet seat valve (12, 13). A limiting piston (31) is provided for each side of the steering valve (8). Each limiting piston (31) is actuated on one side by one of the centering springs (30) and by a first pressure prevailing in a working chamber of a servo-motor and on the other side by a limiting force. In the neutral position of the steering valve (8) the limiting force is stronger than the force of the centering spring (30) so that the limiting piston (31) abuts against a stop shoulder in the neutral position of the steering valve (8). An "interception" or "actuating torque limitation" is obtained with such an arrangement.

Claims11

Dependent claims

A servo-steering unit having a steering valve, a housing receiving a steering spindle, and two steering valve components located within the housing, each of said two steering valve components comprising:

a respective inlet seat valve having a respective first closing member;
a respective outlet seat valve having a respective second closing member;
a respective actuating tappet controlling movement, depending on rotation of said steering spindle, of said respective first and said respective second closing members to one of an opened and a closed position;
a respective centering spring biasing said respective actuating tappet toward a neutral position of said steering valve in which said respective first closing member of said respective inlet seat valve is in said closed position and said respective second closing member of said respective outlet seat valve is in said opened position;
and said respective first closing member being movable from the closed position to the opened position only once said respective second closing member has moved to the closed position;
wherein each steering valve component has a respective limiting piston, each said limiting piston is actuated, on one side, by one said respective centering spring and by a first pressure prevailing in a respective working chamber of a servo-motor and, on the other side, by a respective limiting force;
and said respective limiting force, in said neutral position of said steering valve, is greater than a force of said respective centering spring;
and
each said limiting piston, in said neutral position of said steering valve, abuts against a respective stop shoulder of said steering housing.

6 more elements

Dependencies are inferred from the claim text.