Patent GB-1374089-A (GB)
Title: Power transmission
IPC: F16H45/00
Filed: 1971-11-04
Abstract: 1374089 Clutch control CATERPILLAR TRACTOR CO 4 Nov 1971 [4 Nov 1970] 61402/71 Headings F2C F2L F2D and F2W  A control system for a continuously slippable friction clutch 21 controlling the torque transmitted between an input shaft 12 and an output shaft 18 of a motor vehicle comprises a speed responsive valve 31 controlling clutch engagement and supplied with pressure liquid from a pump 27 through a regulating valve 28 which adjustably determines the maximum pressure supplied to the valve 31 and thus the maximum clutch engaging pressure. As shown the clutch 21 connects a second pump element 23 of a torque converter 14 to a driving casing 24. The torque converter additionally includes a continuously driven first pump element 22, a turbine element 17 and a reactor 16. As the clutch 21 is progressively engaged the speed of the second pump 23 increases to increase the torque transmitted by the torque converter 14. Centrifugal clutch control.-The valve 31 comprises a valve spool 91 slidable in a bore 92 of the input driven casing 24 between a radially inner position in which it connects a clutch engaging servo chamber 62 to exhaust and a radially outer position in which it connects the servo chamber 62 to the pressure supply line 29. The valve spool 91 is biased radially inward by a spring 93 and by clutch engaging pressure acting in a chamber 98 and is moved outward against the bias by centrifugal force. The disengaging effect of torque converter working circuit pressure acting on the clutch engaging servo piston 61 is compensated for by supplying working circuit pressure to a chamber 103 of the valve 31. Pressure regulation.-The valve 28 comprises a valve spool 66 which meters pressure liquid from the pump supply line 42 to the control pressure supply line 29. The spool 66 is biased to a closed (low pressure in the line 29) position by a spring 71 and by supply line pressure acting in a chamber 72. The valve spool 66 is moved, in opposition to the bias, to an open position by torque converter working circuit pressure acting on the left end of the valve spool 66 and by a pneumatic servo piston 83. A manually controlled valve 46 controls the air pressure supplied to the servo piston 83 and thus the maximum pressure in the line 29. Other features.-A transmission control valve 41 cuts off the supply of pressure liquid to the regulator valve 42 when a ratio shift is effected in a change-speed gear driven by the shaft 18. A pump 48 driven by the input shaft 12 supplies pressure liquid to ancillary equipment on the vehicle. Operation.-When the input shaft speed is below 1600 r.p.m. the clutch 21 is disengaged and the torque converter 14 absorbs minimum power to provide additional power to the ancillary equipment. As the input speed rises above 1600 r.p.m. the clutch 21 is progressively engaged to increase the torque supplied to the output shaft 18. If the supply pressure 29 is the maximum possible the clutch 21 is fully engaged at an input speed of 1800 r.p.m. If the supply pressure 29 is limited to a value below the maximum the clutch 21 slips continuously. Alternate embodiments.-In Fig. 5 (not shown) the clutch (21<SP>1</SP>) directly connects input and output shafts (211, 212) and the controls responsive to torque converter working circuit pressure are omitted. An additional relay shutoff valve (214) is provided between the transmission control valve (41<SP>1</SP>) and the regulator valve (28<SP>1</SP>). The pneumatic servo control of the regulator valve (28<SP>1</SP>) is replaced by a direct manual control. Fig. 6 (not shown) is similar to Fig. 1, but the torque converter working circuit pressure control of the clutch control and regulator valves is omitted. In Figs. 7 and 8 (not shown) the torque converter has a single pump element and the slippable clutch is provided between the input shaft and the pump element. In Fig. 8 the centrifugal valve controls the exhaust from the clutch servo chamber which is connected directly to the supply line (29<SP>11</SP>).