Zahnradfabrik Friedrichshafen, Ag.

Erich Jablonsky

Dieter Elser

A transfer valve assembly controls the change-over in the supply of pressurized fluid to a steering servomotor from engine driven and vehicle driven pumps. The outflow rate of fluid from the engine driven pump is metered to control shift of the transfer valve assembly between its two operating positions preventing any delay or overlap in the change-over between pumps because of low or residual output pressure from the engine driven pump.

Auxiliary power steering for motor vehicles

Means for adjusting automatically for backlash caused by wear between the teeth of a steering nut gear rack on a steering shaft worm and the teeth of a steering mechanism gear sector which engages the rack teeth. The invention utilizes a resiliently biased, e.g., spring pressed pin carried either by the steering nut member or the gear sector member and pressing against a tooth of the other to maintain a constant torque bias of the steering nut maintaining it to a rotated position on the steering shaft. Thus, the teeth of the two members will always effect engagement with no backlash when such members are positioned with respect to each other for straight-ahead steering. When steering is initiated the response is immediate and there is no play due to looseness between steering nut rack and gear sector teeth.

Steering gear for motor vehicles

The invention provides a steering assembly comprising a gear rack actuated by a pinion shaft rotated by a steering spindle wherein misalignment of the teeth of the gear rack and of the teeth of the pinion shaft can be readily adjusted for the entire flanks of both sides of the teeth so as to eliminate play and maintain constant engagement. A two part housing having relative pivotal motion on a spherical juncture is utilized as a bearing means between the housing members.

Rack and pinion steering, especially for motor vehicles

A steering control valve and worm nut centering device for a power steering booster mechanism control valve is provided comprising a flexure rod carried either by the double-acting piston member or the worm nut member and extending between those members or into the valve spool. The overall construction is conventional and well known, the particular feature of the invention being a flexure rod which is adjustable translationally or rotatively, in various modifications, to center the valve spool of the control valve and to center the worm nut. The flexure rod can be predetermined as to length, taper, alloy, and other design factors so as to flex to give a desired increase in road resistance feel substantially over and above that afforded by the usual size of reaction chambers and centering spring conventionally associated with the valve spool. Thus, a flexure characteristic curve of extent of flexure versus degree of steering provides a sharp increase in road resistance simulation as the steering spindle is turned.

Power steering mechanism control valve

A dual hydraulic circuit arrangement is provided each comprising essential elements of an independent booster steering system, each having valving mechanisms for steering control wherein the valving mechanisms pressurize and exhaust the power cylinder of the respective circuit. The valving mechanisms are operable in a sequential order so that initially and ordinarily one power cylinder effects steering, but in the event of failure or very heavy requirement the second power cylinder is capable of operating the steering mechanism or of assisting in such operation. It is contemplated that the pump of the initially operative circuit is engine driven and the pump of the other or emergency circuit is driven by the vehicle wheels. Thus, in the event of vehicle engine failure, the emergency power circuit can effect steering as long as the vehicle is moving. On the other hand, when heavy steering load is encountered, as in parking, both circuits are operative.

A dual hydraulic system comprising two independent power steering hydraulic circuits is provided wherein a first hydraulic circuit is used primarily for normal steering and a second hydraulic circuit is used where increased steering power is needed as in rough terrain driving or in parking a vehicle. The arrangement provides for each circuit carrying about half the increased load. Respective valve mechanisms under operator control via a steering wheel controls pressure and exhaust of the double acting power cylinders of the respective circuits. Actuation of the two valve mechanisms is effected in a sequential order so that ordinarily the first hydraulic circuit is operative, followed by the operation of the second hydraulic circuit responsive to increase in steering load as would be occasioned in cross country rough terrain driving or in a vehicle parking situation.

A bypass vavle arrangement extends fixedly from the end wall of a double acting cylinder through the radial wall of a booster piston with a sliding sealed fit to block bypass flow between the pressure chambers at opposed faces of the piston between desired limits of piston travel. Bypassing of such flow from one chamber to another effects a pressure drop from the pressurized chamber to the chamber being exhausted to limit the pressure driving force on the piston and thus effect a desired limit or extent of piston travel and of the connected steering mechanism. The invention provides for such bypass flow by means of flow passages spaced on opposite sides of a central valve body portion which passages are of a length to span the radial wall through which the valve body has passed when the piston has reached a certain point of its travel in either direction. A particular point of novelty resides in the adjustability of the bypass valve means so as to predetermine the point at which bypass effect takes place so that desired limits of travel of the piston are thus determined, such adjustment being made from the exterior of the cylinder at one end thereof. A further feature resides in the provision of a bushing having axial play through which the valve body passes and which bushing is pressure actuated to cut off bypass flow at either limit of piston travel so that rapid reversed direction steering under pressure can be effected with no need for manual force at the steering wheel to effect pressure build up.

Adjustable bypass valve to effect steering limits in booster power

A double acting power boost cylinder comprising a movable servo piston for vehicle steering purposes is provided with means comprising a fixed piston protruding into a bore of the servo piston so as to reduce the effective end surface pressure receiving areas of the servo piston. Thus, the total forces acting to drive the servo piston are reduced to avoid overload or damage to a steering mechanism driven by the servo power piston. The invention has its utility in vehicles where a common hydraulic source is used for various purposes such as steering, brakes, vehicle level and the like where pressures required may vary and where the pressure required for steering is not as great as required for other purposes. Usually accumulators are used and the invention is of particular utility since it permits the use of small pumping devices. In particular, however, the conventional booster steering gear arrangements comprising double acting power cylinders have dimensions and diameters determined by the geometry of gear sectors, within the housing, engaging rack teeth cut into the surface of the servo piston, as well as various other mechanical parts in the housing. Accordingly, the invention permits the reduction in the overall driving force of the servo piston without need for redesign of the overall dimensions of a conventional double acting cylinder arrangement.

Auxiliary power steering gear for motor vehicles having a common

A fluid power steering system for motor vehicles in which a reaction force is generated to resist manual movement of a control valve piston through which pressurized fluid is supplied to a servomotor. The reaction force is limited by displacement of force limiting valve pistons in response to excessive pressure in reaction chambers. When displaced from its normal position, a force limiting valve sequentially blocks supply of pressurized fluid to one of the reaction chambers and then relieves the pressure in said chamber.

Auxiliary power steering system

The steering wheel controlled valve operator in a fluid power steering system, is mechanically held in a neutral position by centering springs associated with fluid pressure controlled reaction pistons yieldably resisting movement of the control valve by the valve operator. Check valves opened in response to suction pressure, conduct fluid in by-pass relation to the control valve between a servo motor chamber and a return fluid line, the control valve connecting both servo motor chambers to the return line in the neutral position.

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Boebingen, Germany

Erich Jablonsky