Patent GB-926518-A (GB)
Title: Change-speed transmissions
IPC: F16H47/06
Filed: 1961-07-26
Abstract: 926,518. Change-speed epicyclic gear and control ; differential gear. GENERAL MOTORS CORPORATION. July 26, 1961 [Aug. 15, 1960], No. 27065/61. Class 80 (2). In an hydraulic control for a combined change-speed epicyclic and differential steering gear for endless track vehicles, speed-responsive means comprising an output pump 176 and control valves 181, 196 is operative, on movement of a manual selector valve 161 from High to Low gear position, to prevent Low gear establishment until the vehicle speed has fallen to a predetermined value. Other speed-responsive means comprising the pump 176 and a control valve 206 is operative on movement of the valve 161 to Reverse position, to prevent Reverse gear establishment until the forward vehicle speed has fallen to predetermined value. Gear arrangement.-The change-speed epicyclic gear comprises parallel trains, viz. a twospeed forward sun-ring train 31, 33, 36 and a reverse sun-ring train 43, 46, 47, serially arranged behind an hydrodynamic torque converter comprising an impeller 18 driven from an input shaft 10 through spur increasing and bevel gears 14, 16, respectively, a turbine 21 driving, through a shaft 23, the two-speed forward and reverse train suns 31, 43, respectively, and twin reactors 24 reacting to the casing through one-way detents 26. An output cross-shaft 34 is connected to the two-speed forward train carrier 33 and the reverse train ring 47. For Low and High gear forward and Reverse drives respectively the ring 36 is friction braked at 37, the sun 31 and ring 36 are friction clutched together at 41 for forwardtrain lock-up, and the carrier 46 is friction braked at 49. The brakes 37, 49 and the clutch 41 are respectively actuated by hydraulic servomotors 38, 51 and 42. The output crossshaft 34 is connected to rings 61, 56 of left-hand and right-hand epicyclic sun-ring trains, the carriers 63, 58 of which are connected to track output shafts 64, 59 and the reaction suns 72, 66 of which are connected through gears 73, 74, 82 and 68, 69, 77 to externally and internally toothed rings 83, 78 which mesh interengaging planets 87, 88 carried by the turbine driven shaft 23 and are friction brakable at 86, 81; this differential arrangement, when both brakes 86, 81 are released, providing equal reaction at the suns 72, 66 for straight drive, and, when one of the brakes is engaged, retarding or holding one sun and driving the other at an increased speed for steering. Hydraulic control system.-Front and rear pumps 12, 91, respectively, driven from the input shaft 10 through increasing gears 11 and from the left-hand track output shaft 64 through gears 93, 92, draw from a sump 96 through strainers 97, 98 and lines 101, 106, and feed a pressure main 104 through lines 102, 107 and an oil filter 103. A regulator valve 111 in the main 104 comprises an exhaust port to a converter feed line 118, a spring-loaded ball safety valve 125 exhausting to a lubrication line 127 and a spring-loaded valve member 112 which has large and small diameter lands a, b and which, to damp the valve action, comprises a passage 121, a spring-loaded ball check valve providing free downward and restricted upward flow, and a headed piston closing the passage 121. When the selector valve 161 is in High, pressure oil acts on the base of the land b through a signal line 126 to regulate main pressure to a lower value. Oil flows from the converter through a line 131, coolers 133, 136 and a converter pressure regulator valve 141 to the lubrication line 127. The valve 141 comprises, in parallel with a permanent restricted by-pass 148, a spring-loaded valve member 142 which has equal diameter lands a, b and is subjected to control pressure from the converter feed line 118 acting on the top of the land a through a signal line 146 having a damping orifice 147. Lubrication line pressure is limited by a spring- loaded relief valve 151. Relief valves 153 and 155 respectively maintain the desired small pressure difference between the converter inlet and outlet and protect the coolers and converter against excessive pressure due to cold oil particularly in the lubrication system. The manual selector valve 161 comprises a fourlanded valve member 161 movable into four positions, viz.: Neutral, Low, High and Reverse, in which the pressure main 104 is respectively blocked, and connected to Low, High and Reverse servomotor lines 168, 171, 166, the lines not under pressure exhausting. The pump 176, also driven from the left-hand track output shaft 64 through the gears 93, 92 and drawing through the line 106, feeds a governor line 178, the pressure in which is rendered proportional to vehicle speed by a vent orifice 179 and is limited by a relief valve 180. The control valve 181 is arranged in the line 168 and comprises a valve member 182 which is spring-urged downwardly to connect the line 168 to the Low gear servomotor 38 and is urged upwardly by pressure in the governor line 178 to exhaust the servomotor 38 and connect the line 168 to a line 189 to the control valve 196. The latter comprises a valve member 197 which is spring-urged upwardly to connect the line 171 to the High gear servomotor 42 and is urged downwardly by pressure in the line 189 to connect the latter to the High gear servomotor 42 through a line 203 and to block the line 171. A land a in the valve member 182 of the valve 181 has a passage 187 therethrough to reinforce the downward spring loading during Low gear engagement to prevent automatic upshifting due to increasing vehicle speed; however, as a safety measure, the relief valve 180 may be set to permit a governor line pressure great enough to overcome the spring force and the oil pressure on the upper side of the land a and so upshift into high gear to prevent excessive drive train and engine speeds. Large and small diameter lands b, c of the valve member 182 are so arranged that when the line 168 is connected to the main 104, pressure on the unbalanced area between the lands b, c prevents the valve member 182 from being spring-urged downwardly until the speed has fallen below that at which it is upwardly moved by governor line pressure when the selector valve is in High gear position. The control valve 206 is arranged in the line 166 and has a valve member 207 which has equal diameter lands a, b, is spring-urged downwardly to connect the line 166 to the Reverse servomotor 51, and is urged upwardly by governor line pressure to exhaust the servomotor 51 and block the line 166. Operation.-When in High gear with the selector valve set to High, if the vehicle speed exceeds 12 m.p.h. governor line pressure forces the valve member 182 upwardly. If the selector valve is now moved to Low, Low gear is not established but the line 168 is connected between the lands b, c to the line 189 to maintain the High gear engaged, this occurring before the High gear clutch 41 is disengaged by servomotor 42 exhaust. When the vehicle speed drops to, say, 10 m.p.h., the valve member 182 is spring-urged downwardly to connect the line 168 to the Low gear servomotor 38, to establish Low gear, and to exhaust the line 189. When the forward vehicle speed exceeds 5 m.p.h., governor line pressure blocks the Reverse servomotor line 166.