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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 th

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.

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1. 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 i

1. 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. 2. The improvement as defined in claim 1, wherein the main pump (18) is of the variable volume type having flow volume adjusting means (46), and control passage means (28) connecting the pressure passage (22) downstream of the flow restrictor (26) to the flow volume adjusting means of the main pump for adjustment thereof. 3. The apparatus as defined in claim 1, wherein the fluid power steering circuit further includes an inlet port (21) through which the pressure passage (22) is connected to the main pump, and an outlet port (24) through which the short-circuit passage means (23) is connected to the reservoir (19) to which the fluid is exhausted from the servomotor. 4. In combination with the apparatus as defined in claim 3, an additional fluid operating circuit (34), and flow dividing valve means (36) connecting the main pump to the additional fluid operating circuit and to the inlet port (21) of the fluid power steering circuit for priority supply of the pressurized fluid thereto. 5. The combination as defined in claim 4 wherein the dividing valve means (36) includes a valve member displaceable in opposite directions to positions in which the pressurized fluid from the main pump (18, 32) is supplied exclusively to one of the circuits (33 and 34), a spring (39) biasing the valve member in one of said opposite directions to one of said positions in which the pressurized fluid is supplied exclusively to the power steering circuit (33), said pump unloading means (38) being connected to the pressure passage (22) downstream of the flow restrictor (26) for urging the valve member in said one of the opposite directions, and fluid actuating means (37) connected through the inlet port (21) to the pressure passage upstream of the flow restrictor (26) for urging the valve member in the other of said opposite directions against the bias of the spring (39). 6. The combination as defined in claim 5, wherein the main pump (32) is of the constant volume type. 7. In combination with the apparatus as defined in claim 1, an additional fluid operating circuit (34) to which fluid under an operating pressure is supplied, and flow dividing valve means (36) interconnecting the main pump (18, 32) with both of the circuits (33 and 34) for supply thereto of the fluid under said operating pressure with priority to the fluid power steering circuit (33). 8. The combination as defined in claim 7, including fluid actuating means (37, 38) for applying a differential valve adjusting pressure to the flow dividing valve means that is a function of the pressure drop across the flow restrictor (26). 9. The combination as defined in claim 8, wherein the main pump (18) is of the variable volume type having flow volume adjusting means (46). 10. The combination of claim 9, including two-way valve means (40) connecting the flow volume adjusting means of the main pump (18) to one of the circuits (33, 34) for supply of the fluid under the higher of the operating pressures to the volume adjusting means through pressure control lines (38, 38A or 41, 41A).