Hydraulic control system of a transport vehicle

A hydraulic control system for hydraulically actuating a servomotor in first and second directions in proportion to a manual input, comprising:

• a source of pressurized fluid;
• double-acting servomotor;
• a manual input controlled first three-position valve having an input for said pressurized fluid and a fluid return line;
• said first three-position valve having a first position which it assumes in the absence of a manual input, a second position which it assumes in the absence of a manual input requiring said servomotor to move in said first direction and a third position which it assumes in the presence of a manual input requiring said servomotor to move in said second direction;
• first and second outputs of said first three-position valve;
• said first three-position valve being effective to apply fluid pressure from said source to said first output in proportion to said manual input when said first three-position valve is in its second position;
• said first three-position valve being further effective to apply fluid pressure from said source to said second output in proportion to said manual input when said first three-position valve is in its third position;
• a second three-position valve having first, second and third positions, first and second control fluid pressure inlets and a single actuation fluid pressure inlet;
• said first and second outputs being connected to said first and second control fluid pressure inlets, respectively;
• said second three-position valve including means for assuming its first position in the absence of fluid pressure in either of its first and second control fluid pressure inlets, means for assuming its second position in the presence of fluid pressure in its first control fluid pressure inlet, and means for assuming its third position in the presence of fluid pressure in its second control fluid pressure inlet;
• said second three-position valve having first and second actuating fluid outlets connected to corresponding inlets of said servomotor;
• a control fluid throttling member having a first throat area;
• an actuating fluid throttling member having a second throat area;
• an inlet of said actuating fluid throttling member being connected to said source;
• outlets of said control fluid throttling member and said actuating fluid throttling member being combined and applied to said actuation fluid pressure inlet of said second three-position valve;
• pressure responsive means for selecting the higher pressure acting in one of said first and second inlets from said first and second outputs, respectively, and applying said higher pressure to said control fluid throttling member;
• said second three-position valve being effective to block the combined control and actuating fluid from said first and second actuating fluid outlets when in its first position, to apply said combined control and actuating fluid to said first actuating fluid outlet when in its second position and to apply said combined control and actuating fluid to said second actuating fluid outlet when in its third position whereby said servomotor is enabled to remain motionless, move in said first direction and move in said second direction, respectively.