US 4,553,389 AGranted

Hydrostatic auxiliary steering apparatus

AssigneeZahnradfabrik Friedrichshafen AG

InventorsWerner Tischer, Karl-Heinz Liebert, Rolf Fassbender

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Abstract

In a hydrostatic auxiliary power steering apparatus, a short-circuit passage of a control valve establishes a restricted flow path from a pump pressure line to a reservoir return line in the neutral position of the control valve wherein all other flow paths are blocked. A fixed flow restrictor in the pump pressure line conducts a continuous flow from one of two pumps connected to the pressure line for regulation of the fluid power steering circuit by the pressure drop across the flow restrictor. If one of the pumps is of the variable volume type, the pressure downstream of the flow restrictor is utilized to regulate pump flow adjustment. If fluid under operating pressure is supplied to both the fluid power steering circuit and another fluid operating circuit, a flow dividing valve controlled by the pressure differential across the flow restrictor distributes pressurized fluid between the two fluid circuits.

Claims10

Dependent claims

In a hydrostatic auxiliary power steering apparatus having a metering pump, a servomotor, a main pump, a reservoir from which fluid is drawn by the main pump and a fluid power steering circuit including a control valve displaceable from a neutral position in which flow through the metering pump is blocked;

short-circuit passage means for recirculating the fluid from the main pump to the reservoir with increasing flow restriction in response to displacement of the control valve from the neutral position, a second constant volume pump, and a pressure passage to which the fluid pressurized by the main pump is conducted to the control valve, the improvement comprising a flow restrictor (26) disposed within the pressure passage (22) which has a fixed flow area less than that of the short-circuit passage means (23) in the neutral position of the control valve (16), branch passage means (27) connected to the pressure passage upstream of the flow restrictor for conducting the pressurized fluid to the servomotor (17) through the metering pump (7) in response to said displacement of the control valve from the neutral position, means responsive to a reduction in flow through the flow restrictor for unloading the main pump and means (31) connecting the second pump (29) to the pressure passage in parallel with the main pump (18, 32) for continuously conducting the pressurized fluid through the flow restrictor to the short-circuit passage means.

Dependencies are inferred from the claim text.