Patent GB-1432568-A (GB)
Title: Steering system control assemblies for track-laying vehicles
IPC: B62D11/08
Filed: 1972-05-04
Abstract: 1432568 Steering tracked vehicles INTERNATIONAL HARVESTER CO OF GREAT BRITAIN Ltd 12 April 1973 [4 May 1972] 20703/72 Heading B7H An endless tracked vehicle is provided with an hydraulically actuated brake and clutch for steering each track, and the fluid flow to each brake and clutch actuating cylinder 16, 16<SP>1</SP> and 15, 15<SP>1</SP> is controlled by a spool valve control unit 17 comprising two spool valves 35, 35<SP>1</SP> and two relief valves 36, 36<SP>1</SP>, each valve 35, 35<SP>1</SP> controlling the brake and clutch of one track and having three operative positions in which, (a) the clutch is engaged while the brake is released, (b) the brake and clutch are disengaged and (c) the clutch is disengaged while the brake is engaged. Each brake cylinder 16, 16<SP>1</SP> is connected to a fluid supply pump 20 by lines 18, 18<SP>1</SP> and via lines 21, 21<SP>1</SP> to the control unit 17, the brake cylinders contain differential pistons which are balanced when a pressure of 240 p.s.i. is applied to the piston rod side and 150 p.s.i. is applied to the head side. Each side of the clutch actuating cylinders is connected via lines 22, 22<SP>1</SP> or 23, 23<SP>1</SP> to the outlet parts 75, 75<SP>1</SP> and 76, 76<SP>1</SP> of the control unit. The control unit has an inlet part 48 and an exhaust part 46, and each spool valve has chambers 29, 29<SP>1</SP> and 27, 271 respectively connected thereto. With spool 37 in the first position, Figs. 3 and 6, fluid passes via part 48 and chamber 29 to a further chamber 30 and then via line 23 to the rod side of the piston in the clutch actuating cylinder 15. The other side of the cylinder is connected via line 22 to a valve part 75 which connects with the exhaust part 46 via a channel 80, orifice 81 and chamber 27, hence the clutch actuating piston is moved to the right to engage the clutch. At the same time the brake actuating piston is moved to the right to disengage the brake. In the second piston of the spool valve, see spool 37<SP>1</SP> in Fig. 3, pressure fluid passes via chamber 29<SP>1</SP> to chamber 28<SP>1</SP> and thence via orifice 81<SP>1</SP> and passage 80<SP>1</SP> to part 75<SP>1</SP>. Fluid applied via line 22<SP>1</SP> to clutch piston in cylinder 15<SP>1</SP> causes the clutch to disengage Fluid from the rod side of the piston is passed via line 23 to part 76<SP>1</SP> and then via chamber 30<SP>1</SP> and a bore 40<SP>1</SP> in the spool to chamber 27<SP>1</SP>. The passage 80 is connected via a line 83<SP>1</SP> to a chamber 52<SP>1</SP> closed by a member 66<SP>1</SP> of the relief valve 36<SP>1</SP> urged home by a spring 69<SP>1</SP>. This relief valve opens when a pressure of 150 p.s.i. is applied thereto to spill fluid back to the exhaust port 46 via a bore 60, so limiting the pressure in lines 22<SP>1</SP>, 21<SP>1</SP> to 150 p.s.i. Hence in the second position of the spool valve the brakes remain disengaged. On moving the spool 37<SP>1</SP> further to the left to its third position the spring 69<SP>1</SP> is compressed and the pressure in lines 22<SP>1</SP>, 21<SP>1</SP> may increase above 150 p.s.i. thus causing the brakes to engage.