Patent GB-1505935-A (GB)
Title: Clutch-brake steering mechanisms
IPC: B62D11/08
Filed: 1976-03-19
Abstract: 1505935 Steering endless track vehicles INTERNATIONAL HARVESTER CO 19 March 1976 [24 March 1975] 11158/76 Heading B7H A clutch-brake steering system for an endless track vehicle comprises a spring-applied brake 108B and a spring-released clutch 110C for controlling rotation of a right hand track drive sprocket 22, an hydraulic brake cylinder 90B for acting in opposition to brake springs 92 to release the brake, an hydraulic clutch cylinder 96C for acting in opposition to clutch springs 98 to engage the clutch, and a control valve assembly 40 having flow restricting valves which control the pressure at a common inletoutlet port 202 connected to both cylinders 90B, 96C. When the control valve assembly 40 is actuated to reduce the pressure at the inletoutlet port 202, the springs 98 first disengage the clutch 110C and the springs 92 then apply the brake 108B, brake application being in a cushioned manner because of a slowing of the fall in pressure due to fluid flowing out of the clutch cylinder 96C as the springs 98 continue to collapse the clutch cylinder after complete disengagement of the clutch 110C. Engagement of the clutch 110C is cushioned in similar manner when the control pressure at the inletoutlet port 202 rises because of continued expansion of the brake cylinder 90B against the resistance of the springs 92 after release of the brake. The control valve assembly 40 includes a metering valve 200 which permits restricted communication through metering slots 284, 286 between the inlet-outlet port 202 and either a high pressure groove 18 connected to a pressure supply line 56 or a low pressure groove 186 connected to a drain line 198, the position of the valve 200 establishing the control pressure at the port 202 at a level which is set by a hydropotentiometer valve 44 linked to a right hand steering lever 42. One end of the metering valve 200 is subjected to control pressure at the port 202 and the other end is subjected to a signal pressure prevailing at a signal pressure port 266 on the hydropotentiometer valve 44 which communicates through double helical grooves 262, 264 with a high pressure port 184 connected to the pressure supply line 56 and with a low pressure space 224 connected to a drain line 226. The relative effective lengths of the respective helical grooves 262, 264 and the pressure drops therein determine the value of the signal pressure acting on the metering valve 200 in dependence on the axial position of the valve 44. A second hydropotentiometer valve 44-2 linked to a left hand steering lever 42-2 has associated therewith a second metering valve 200-2 which determines the control pressure at a second inlet-outlet port connected to brake and clutch cylinders 90B-2, 96C-2 for controlling rotation of a left hand track drive sprocket. A brake valve 48 linked to a brake pedal 46 can be actuated to progressively release the pressure in the left and right brake cylinders 90B, 90B-2 to apply both brakes regardless of the position of the steering valves and without affecting the state of engagement of the clutches. The steering system can be pressurized to release the brakes 108B, 108B-2 so that the vehicle can be towed when there is no pressure in the supply line 56 by pumping grease into the system through a one-way valve 170, engagement of the clutches 110C, 110C-2 being prevented by a towing valve 232 which automatically blocks communication between the control valve assembly 40 and the clutch cylinders 96C, 96C-2 when there is no supply line pressure.