Precision steer wheel control system with internal solenoid

An apparatus for holding at a center position at least one steerable member mounted on a frame means for movement to either side of the center position, said apparatus comprising linkage means of variable length extending between said steerable member and said frame means, the length of said linkage means defining said center position, and accumulator means for holding a supply of fluid and means for pressurizing the fluid held in said accumulator means;

• wherein said linkage means comprises centering means for providing a resistance force resisting steering forces tending to move said steerable member to either side of the center position, and trim means for transmitting said steering forces to said centering means;
• wherein said trim means comprises:
• a trim piston,
• trim cylinder means providing a portion of said linkage means and cooperating with said trim piston to form first and second trim chambers one on each side of said trim piston,
• and trim fluid means for providing a flow of trim fluid between said accumulator means and each of said trim chambers and comprising trim valve means operable between a closed position for preventing said trim fluid flow so that said trim piston is held in a locked position, and an open position for allowing said trim fluid flow so that said trim piston is free to move away from said locked position in said trim cylinder, said trim piston movement causing trim fluid flow to one of said trim chambers and trim fluid flow from the other of said trim chambers to permit trimming movement of said steerable member to another center position by changing the length of said linkage means in response to said steering forces;
• wherein said centering means comprises:
• centering cylinder means providing a portion of said linkage means,
• centering piston means cooperating with said centering cylinder means to form first and second centering chambers, and being arranged for movement in a first direction for compressing a fluid within said first centering chamber and for movement in a second direction for compressing a fluid within said second centering chamber,
• centering rod means providing a portion of said linkage means and arranged for movement with said centering piston means to either side of a neutral position corresponding to said center position,
• and centering fluid means for providing a pressurized centering fluid in each of said first and second centering chambers so that fluid pressure provides said resistance force by biasing said centering piston means toward said neutral position upon movement of said steerable member toward either side of said center position;
• wherein said trim cylinder means and said centering cylinder means are interconnected by an intermediate head member and said trim valve means is located in said intermediate head member;
• and wherein said trim fluid means further comprises:
• conduit means for providing fluid communication between said accumulator means and said centering chambers,
• a first supply passage in said intermediate head member for communicating with at least one of said centering chambers to supply trim fluid to said first trim chamber,
• a second supply passage in said intermediate head member for communicating with at least one of said centering chambers to supply trim fluid to said second trim chamber,
• a first return passage in said intermediate head member for communicating with one of said trim chambers to return trim fluid to said conduit means,
• a second return passage in said intermediate head member for communicating with the other of trim chambers to return trim fluid to said conduit means,
• a first supply valve for preventing reverse fluid flow in said first supply passage,
• a second supply valve for preventing reverse fluid flow in said second supply passage,
• a first return valve for preventing reverse fluid flow in said first return passage,
• and a second return valve for preventing reverse fluid flow in said second return passage;
• and wherein said apparatus further comprises operating means activatable from a remote location for operating said trim valve means between said closed and open positions.