Apparatus for controlling a steering-by-driving system

An apparatus for controlling propelling rotation of at least two driven wheels of a vehicle in response to movement of a steering member, said apparatus comprising:

• a fluid source;
• a hydraulic motor associated with each driven wheel for, when pressurized with fluid, rotating the respective wheel in a particular propelling rotational direction dependent upon the direction of fluid flow through the hydraulic motor;
• means for generating a first electrical signal having a value responsive to the position of the steering member, each position of the steering member resulting in a different first electrical signal value;
• control means for controlling the fluid flow rates from said fluid source to the hydraulic motors and for controlling the directions of fluid flow through said hydraulic motors, the fluid flow rate and direction of fluid flow through each hydraulic motor varying as a function of said value of said first electrical signal, the vehicle being steering as a result of the rotational speed and direction of rotation of the driven wheels, said control means including means for permitting fluid flow to the hydraulic motors in opposite directions so as to cause the motors to rotate in opposite propelling rotational directions and selection means operable by a vehicle operator for selecting the functional relationship between fluid flow rates to the hydrualic motors and the position of the steering member so as to provide a selectable steering ratio.

An apparatus for controlling at least two driven wheels of a vehicle, said apparatus comprising:

• a source of pressurized fluid;
• hydraulic motors, each driven wheel having an associated hydraulic motor for, when pressurized with said pressurized fluid, driving such motor's associated wheel in propelling rotation;
• an operator controlled speed input device for generating an electrical control signal, the input device being movable from an initial position to a first location in one direction and to a second location in another direction, said electrical control signal having a value that is functionally related to the position of the input device;
• means for separately controlling fluid flow rate from the source of pressurized fluid to each of the hydraulic motors in response to the value of said electrical control signal, said vehicle (i) remaining stationary when the input device is in said initial position, (ii) moving in a first direction when the input device is moved toward said first direction, and (iii) moving in a second direction when the input device is moved toward said second direction;
• and
• means for establishing a maximum limit and a minimum limit on the value of said electrical control signal, means for comparing the value of said electrical control signal against said established maximum and minimum limits and providing a signal indicative of whether the value of said electrical control signal is within said established limits, and means for preventing said pressurized fluid from pressurzing said hydraulic motors when said signal provided from said means for comparing indicates said electrical control signal is not within said established minimum and maximum limits.

An apparatus for controlling a steering-by-driving system of a vehicle having an engine and hydraulically driven motors for driving wheels or the like of the vehicle, said apparatus comprising:

• a load sense piston pump driven by the engine for providing pressurized fluid, the amoutn of pressurized fluid being responsive to engine RPM's;
• means for valving pressurized fluid from said pump to said motors in response to an electrical control signal, said driving wheels rotating at a speed which is functionally related to the valving of the pressurized fluid from the pump;
• and
• means for establishing a maximum value of said electrical control signal in resposne to said sensed engine speed so as to limit the rotational speed of the driving wheels and thereby prevent improper operation of said load sense piston pump.