Zahnradfabrik Friedrichshafen, Ag.

Werner Tischer

Karl-Heinz Liebert

Rolf Fassbender

Kurt Leberfinger

Christoph Deppenbrock

Josef Deppenbrock

All-wheel steering system for motor vehicles

Control mechanism for two hydraulic adjustment devices supplied via one,

A hydrostatic steering device is provided with a pump connected with a reservoir, a steering valve, a controlled-volume pump that is capable of being activated by a steering wheel and with a steering cylinder. The steering mechanism has a variable working flow and a constant pilot flow, with the pilot stream flowing through a constant throttle and the pressure drop through the constant throttle serving as a control signal for the conveying flow in a pressure delivery line. The controlled-volume pump is coupled mechanically with an adjustment throttle through which the pilot flows. Between the constant throttle and the adjustment throttle lies a pressure compensator that is controlled by the adjustment throttle's differential pressure. To receive the load signal, a control line branches off between the constant throttle and the pressure compensator and leads to the pump or, in the case of a fixed displacement pump with a rear-position flow-dividing valve, to the flow-dividing valve.

Hydrostatic steering device

In a flow divider valve for pressure feed to a hydraulic circuit for auxiliary power steering and to a hydraulic circuit for a power take-off the interior of a hollow regulator piston receives pressure feed for distribution to the hydraulic circuits. For one such circuit, preferably the power take-off, flow passes via multiple bores and coacting flow control grooves of the regulator piston and a housing in which it reciprocates. Accordingly, a desired flow quantity and pressure advantages are achieved, in comparison with use of a single flow control bore which would require a larger piston traverse causing delays in pressure build-up as well as oscillations and strong flow pulses and energy loss.

Flow divider valve

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.

Hydrostatic auxiliary steering apparatus

A hydrostatic steering system having a hand operated metering pump and steering control valve regulating and distributing fluid flow from a servo pump to a piston servomotor of the differential pressure surface type. A compensation valve disposed in the pressure line leading to one of the opposed chambers of the piston servomotor, is actuated by a differential pressure surface dimensioned to establish a constant ratio of pressures prevailing in the opposed pressure chambers in the neutral steering position while the metering pump is ineffective to produce any differential pressure. During active steering, the compensation valve is bypassed through a check valve.

Hydrostatic steering arrangement

A control valve for booster power steering has a back pressure check valve openable by pressure caused by wheel jolting, which check valve connects between a servopump pressure passage of the control valve through the inner bore of a valve sleeve operable within a housing bore to the inlet of a metering pump. Such valve ensures that the steering is 'closed' under all circumstances including during steering to prevent pressure jolts being transmitted from the vehicle wheels due to road roughness. However, after completion of a steering operation high pressure can build up within the valve sleeve causing expansion of the valve sleeve and jamming within the housing bore, making operation difficult. Accordingly, a pressure limiting valve is provided connected to relieve the pressure within the valve sleeve bore.

Booster power steering

A flow regulating channel in a servo steering valve controls exhaust flow with varying restriction from a fluid operating motor while controlling operation of a separate steering servo motor on a priority basis. An operational control valve for the fluid operating motor has a valve passage that is open only in the neutral position to complete a recirculating flow path from a common servo pump through the flow regulating channel that is fully open in the neutral position of the steering valve.

Hydraulic servo steering for vehicles

A flow control valve for a power steering system of the kind having a metering pump is provided with a leaf spring device stressed upon rotation of a hand steering wheel to operate a valve sleeve and the metering pump. The spring device provides a force for returning the valve sleeve to neutral position after a steering operation and comprises curved or arched springs between pressure plates. The convex sides are back-to-back between pressure plates and have curved ends supported on and shaped to slide on the pressure plates with minimum friction as the springs are compressed. The pressure plates are uniquely shaped in the central areas for providing flexibility to compensate for manufacturing inaccuracies. The spring device is assembled in a carrier with the pressure plates under initial compression and an actuating sleeve within the valve sleeve is rotated by a manual force on a steering wheel to stress the springs and to rotate the metering pump and, via a coarse threaded connection, shift the valve sleeve axially for flow control to a servomotor. The springs are elongated in the axial direction of the valve sleeve and operated by stressing their margins between the actuating sleeve and a spring assembly carrier, the arrangement being such that no direct contact between the springs or pressure plates acts against the valve sleeve. However, the initial compression of the springs ensures a force for maintaining the valve sleeve in neutral position.

Hydrostatic power steering system with curved valve return springs

Maximum angular displacement between the rotatable valve elements of a steering control valve is governed solely by the circular pitch of the piston gear associated with the metering gear pump in a hydrostatic fluid power steering system. A pair of fluid collecting manifolds in the control valve respectively communicate with the expanding and contracting pockets in the gear pump to form part of the flow paths between the gear pump and the fluid power steering motor.

Hydrostatic steering system for motor vehicles

Passage bridging cavities formed in a steering gear housing communicate with annular grooves in a cylindrical valve element through recesses in the cavities at limited, and angularly spaced valve edge locations to control distribution of pressurized fluid in a hydrostatic power steering system in response to axial and rotational movement of the valve element.

Hydrostatic steering system

Axially spaced and aligned longitudinal distributor grooves are formed in the radially outer surface of a thin-walled tubular valve element in angularly spaced relation to internal grooving of the valve element for conducting pressurized fluid and establishing a torsional coupling in a hydrostatic controller associated with a power steering system. Obliquely orientated bores in the valve housing establish fluid communication between the longitudinal grooves adjacent opposite axial ends of the housing and axial passages in the housing.

Rotatable controller system

Axially spaced distributor grooves externally formed on a rotatable controller valve element conduct pressurized fluid to a servomotor in response to axial displacement of the valve element within a housing enclosing pressurized spaces to which opposite axial ends of the valve element are exposed. Flow of the pressurized fluid through the grooves is controlled by slide valve surfaces on the valve element axially between the pressurized spaces and the grooves.

Rotatable controller valve

In a steering control valve device of the kind utilizing a metering pump and a torsional stress means for returning the flow control valve sleeve to a neutral position, there is provided a coupling sleeve between the manually operable steering spindle and the valve sleeve. Such coupling sleeve is for the purpose of providing an intermediate actuating member between the steering spindle and the valve sleeve to overcome errors in alignment and other disadvantages which can occur in conventional constructions where the steering spindle directly actuates the valve sleeve wherein rotation of the steering spindle effects axial shift of the valve sleeve for flow control purposes. The invention is particularly advantageous where the means of translating rotary motion of the steering spindle to axial movement of the valve sleeve is effected by threaded coaction.

Hydrostatic auxiliary power steering

An auxiliary steering flow control device having known features of a rotatable steering spindle which initially effects axial shift of a valve sleeve through a torsional stressing device acting on a pair of compressibly arched leaf springs longitudinally disposed on the axis of the steering spindle and carried in a holder within the steering spindle. The leaf springs have contiguous contacting arched surfaces on the steering spindle axis and the arched configuration effects a back to back pretensing that augments the potential energy that can be stored in the springs, particularly in arched surface contiguity with each other.

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Bobingen, Germany

Werner Tischer