Patent GB-1424216-A (GB)
Title: Override control system for a controlled slippable clutch
IPC: F16D48/04
Filed: 1973-03-22
Abstract: 1424216 Clutch control CATERPILLAR TRACTOR CO 22 March 1973 [23 March 1972] 13918/73 Headings F2L and F2W In a control system for a slippable friction clutch 16 controlling the torque transmitted between an input shaft 20 and an output shaft 24 of a motor vehicle wherein a speed responsive valve 34 controlling clutch engagement is supplied with pressure liquid from a pump 36 through a first regulating valve 48 which determines the maximum pressure which may be supplied to the valve 34 and a second manually adjustable regulating valve 50 which adjustably determines the actual pressure supplied to the valve 34, actuation of a manually controlled override valve 58 overrides the second regulating valve 50 to supply the maximum pressure to the valve 34.  Power transmission elements.-As shown the slippable clutch 16 directly connects an engine driven input shaft 20 to an output shaft 24 which drives a change-speed gear 14. The clutch 16 is progressively engaged as the input speed rises by the speed responsive valve 34. In Fig. 2 (not shown) the slippable clutch connects the input shaft to a second pump element of a torque converter having a continuously driven first pump element, a turbine element and a reactor. Pressure regulation.-The first pressure regulating valve 48 comprises a valve spool 60 which meters pressure liquid from the pump supply line 52 to a maximum pressure supply line 82. Pump supply pressure 52 initially acts through ducts 76, 78 on a plug 74 to move the valve spool 60 right against the bias of springs 66, 68 to a metering position. Thereafter pressure in the line 82 acts through a duct 86 on the lefthand end of the valve spool 60 to maintain a predetermined pressure in the line 82. When the valve 60 is metering the duct 76 is closed and the pressure in the duct 78 is exhausted through an orifice 89. The valve 48 also provides a priority function in that a drop in pressure in the pump supply line 52 due to a fluid pressure demand from a change speed gear control 40 causes the valve spool 60 to move left and block the pump supply line 52. The leftward movement of the valve spool 60 additionally connects the maximum pressure line 82 to exhaust at 96 and thus reduces clutch engagement during ratio shift. The manually adjustable pressure regulating valve 50 comprises a valve spool 102 which meters pressure liquid from the maximum pressure line 82 to a control pressure supply line 54 feeding the speed responsive valve 34. The spool 102 is biased to an open (high pressure in line 54) position by a spring 114 and is moved towards a closed position by the pressure in the line 54 acting in a chamber 110 on a plug 112. The loading of the spring 114 and thus the pressure in the line 54 is adjusted manually by a lever 56 which acts through a cable 100 and plunger 98 on the spring. The override valve 58 selectively closes the chamber 110 or connects it to vent at 148. When the chamber 110 is vented the spring 114 moves the spool 102 fully left whereupon the maximum pressure is supplied to the line 54 for maximum clutch engagement. The override valve 58, as shown, comprises a rotary valve spool 132 which selectively connects the chamber 110 to the vent 148. The valve 58 is actuated by depression of a plunger (122), Fig. 4 (not shown), which acts through a lever 122 to oscillate a shaft 128. Rotation of the shaft 128 in one direction is transmitted to the valve spool 132 through a one-way clutch 134. The valve spool 132 is held in its open and closed positions by spring pressed detents 136. The valve spool 132 additionally actuates a switch 150 in circuit with an indicating lamp 152. The switch 150 is closed when the valve 58 vents the chamber 110 to indicate that maximum pressure is being supplied to the line 54. In Figs. 6-12 (not shown) the override valve comprises an axially slidable valve spool (212) fast with a plunger and the valve spool is held in its open or closed positions by a detent (196). Other features.-A pump 38 driven by the input shaft 20 supplies pressure liquid to ancillary equipment on the vehicle. Operation.-When the input shaft speed is below 1800 r.p.m. the clutch 16 slips to provide additional power to the ancillary equipment. As the input speed rises the clutch 16 is progressively engaged to increase the torque supplied to the output shaft 24. If the supply pressure 54 is the maximum the clutch 16 is fully engaged at an input speed of 1800 r.p.m. If the supply pressure 54 is limited by the regulating valve 50 to a value below the maximum the clutch 16 slips continuously. During operation with the supply pressure 54 below the maximum and the clutch 16 slipping actuation of the override valve 58 increases the supply pressure 54 to the maximum without altering the manual setting of the regulator valve 50. The clutch 16 thus provides additional torque to the output shaft 24. Subsequent closure of the override valve 58 returns the pressure in the supply line 54 to the value which previously prevailed and thus re-establishes the previously existing slipping condition in the clutch 16.