Patent GB-1162058-A (GB)
Title: A Drive Control System
IPC: F16H61/40
Filed: 1967-10-20
Abstract: 1,162,058. Controlling hydrostatic transmissions. INTERNATIONAL HARVESTER CO. 20 Oct., 1967 [20 Oct., 1966], No. 47842/67. Heading F2D. Fluid supply to a two-speed hydraulic motor is controlled by a two-position selector valve having a position corresponding to each motor speed, the valve being biased towards its lower speed position and having a latch which is engageable to hold the valve in its higher speed position and is released when the difference between the motor inlet and outlet pressures exceeds a predetermined value, so that the motor is switched to low-speed operation to prevent stalling of a prime mover. As shown, two fixed swashplate motors 20, 22 driving wheels on opposite sides of a vehicle are selectively supplied with fluid from an engine-driven pump 30 drawing from a reservoir 32 for speed and steering control by a reversing valve 26 and a two-position speed selector valve 24. Fluid supplied to the motor ports 29, 31 drives the motors at high speed forward, to motor ports 29, 25 and 31, 27 drives the motors at low speed forward, and to ports 21, 23 drives the motors at low speed in reverse. The reversing valve 26, described in Specification 1,065,346, has two rotatable spools 38, 40 for the motors 20, 22 respectively, movable by respective levers 74, 75 acting through sector and pinion gearing 72, 70 and 73, 71. Forward settings of spools 38, 40 (corresponding to full line positions of levers 75 (74) in Fig. 1) connect the pump 30 outlet to ports 80, 82 and a return line 36 to the reservoir 32 to ports 81, 83. In reverse (broken line position in Fig. 1) the pump outlet is connected to ports 81, 83 and return line 36 to ports 80, 82. The levers 74, 75 have central neutral positions. The speed selector valve 24 has a single spool 84 movable axially by a lever 86, 87 having a fixed pivot 88. For low speed, port 80 is connected to lines 22b, 22c and thus to motor ports 31, 27, port 82 is connected to lines 20b, 20c and thus to motor ports 29, 25, post 81 is connected to line 22a and thus to motor port 23, and port 83 is connected to line 20a and thus to port 21. For high speed, ports 80 and 31; 82 and 29; 81 and 23, 27 ; and 83 and 21, 25; are connected. Latch and interlocking.-A latch 100 pivoted to the lever 86 is engageable in a recess 106 of the valve 24 body to hold the lever 86 in its high-speed position. A spring 110 holds the latch engaged, and, when the latch is released, moves the lever 86 to its low-speed position. Manual release of the latch is by gripping a lever 114 to the lever 86, to raise the latch via a link 120. When either of the levers 74, 75 is moved to its reverse position, it carries with it a bar 130 on a lever 132 rigid with a lever 138, to act via a link 142 to move lever 114 and release the latch if the lever 86 is in its high-speed position. Thus selection of reverse of one or both motors automatically ensures that low speed is selected. Supply and return pressures are conveyed via lines 44p, 54p and 44r, 54r respectively to opposite sides of a differential piston 58 in a bore 56 of the valve 24 block, a spring reinforcing the action of the return pressure. When the difference between these two pressures exceeds a predetermined value, the piston 58 moves upwardly (Fig. 2) so that its end pushes the latch 100 out of the recess 106 if high speed is engaged, or prevents the latching of the lever 86 in its high-speed position.