Patent GB-716134-A (GB)
Title: Improvements in power transmission mechanisms for vehicles and control systems thereof
IPC: F16H61/02
Filed: 1951-12-04
Abstract: 716,134. Hydro-mechanical variable-speed gearing; friction clutches. GENERAL MOTORS CORPORATION. Dec. 4, 1951 [Dec. 8, 1950], No. 28352/51. Class 80 (2) [Also in Group XXXIV] A control system, for a valve - controlled, servooperated, stepped-ratio transmission for a vehicle, includes a delay valve in the fluid circuit of one servo-mechanism having a pressure responsive element exposed to the fluid pressure in another servomechanism to displace the valve to reduce its throttling action so as to delay operation of the one servomechanism until the other Servo-mechanism has been fully operated. As shown, a gear giving four forward and one reverse ratio comprises a front epicyclic reduction unit, an intermediate fluid coupling, a rear epicyclic reduction unit and a reversing epicyclic unit, torque-splitting occuring in the third and fourth ratios. In reverse the rear epicyclic unit is interconnected with the reversing epicyclic unit. In the first and lowest ratio the engine shaft 1, Fig. 1, drives, through a vibration damper 4 and a hollow shaft 6, the annulus 10 of the front unit, the planet carrier 20, a hollow shaft 21 an impeller 22 and runner 23 of a fluid coupling, a shaft 25 carrying the sun gear 26, Fig. 2, of the rear unit, the planet carrier 30 of which is attached to the output shaft 50. Brake bands 170, 40 hold drums 14, 31 stationary together with the sun wheel 11 and annulus 27 respectively attached thereto. For the second ratio the brake 170 is released and a clutch 165, 166 is engaged to connect the sun 11 to the carrier 20, the front unit then transmitting a direct drive to the rotor 22 and thereafter as in the first ratio. For the third ratio the tront unit is made operative by releasing the clutch 165, 166 and re-applying the brake 170, the rear unit brake 40 is released and a clutch 167, 168 engaged to connect the annulus 27 to the shaft 21 thereby transmitting a split torque drive through the rear unit. For the fourth and highest ratio the brake 170 is disengaged and the clutch 165, 166 re-engaged to allow the front unit to transmit a direct drive to the shaft 21, the rear unit functioning as in the third ratio. The reversing gear comprises a sun 55 splined to a plate 51 attached to the annulus 27 of the rear unit, a planet carrier 52 splined to the output shaft 50 and an annulus 57 which is normally free to rotate on a sleeve 59 but may be braked by a piston 129 and a stationary ring 132 acting on a conical extension 130 of the annulus 57. For reverse drive the front and rear units function as in the first ratio except that the brake 40 is disengaged and the annulus 57 is braked by applying fluid pressure at 133 behind the piston 129. The piston 129 is prevented from rotating by pins 65 and is urged by springs 66 to the inoperative position. The clutches 165, 166 and 167, 168 are engaged by fluid pressure acting on pistons 41, 36 in cylinders 42, 37 formed in the drums 14, 31 respectively and are disengaged by springs 19, 332. The resilient brake band 170, Fig. 3, normally clear of its drum 14, is supported at one end by an adjustable anchor 280 and is engaged at the other end by the rod 282 of a piston 160 which slides in a cylinder 159 to apply the brake when oil is admitted through a passage 158. Additional oil may be supplied through a passage 392 to act on a piston 296, attached to the rod 282, and augment the brake applying force. The brake is disengaged by supplying oil under pressure to the chamber 285 through the line 139 and thence, through ports 291, channel 292 and ports 294 in the rod 282, to a chamber 285<SP>1</SP>. Springs 287, 297 maintain the band out of engagement when no oil pressure is applied. The resilient brake band 40, Fig. 4, is adjustably anchored at one end 302 and is normally maintained engaged with the drum 31 by springs 313, 314 which act on the other end of the band through a piston rod 305, a bell crank lever 304 and thrust rod 303. The band is disengaged by supplying oil under pressure to the chambers 310, 311 through the lines 121, 121a, and a check valve 307. The engaging force of the springs 313, 314 may be augmented by oil under pressure supplied through a line 392 to a chamber 317 and thence by way of a hollow piston rod 316 to a chamber 318. The oil pressure in the chamber 317 acts on a plunger 308 to lift the check valve 307 and allow a free exhaust of oil from the chamber 311 thereby reducing the time required for application of the brake. A spring 322 opposes the release of the band 40 after a certain travel of the piston 301. A gear pump P driven from the shaft 6 supplies oil through a passage 185 to the working space W of the fluid coupling and, through a spring- loaded valve 91, to lubrication passage 96, Fig. 1, and 98, 98<SP>1</SP>, 197, 198, Fig. 2. A gear 56 on the output shaft 50 drives a gear-type oil pump Q and a governor G of the kind described in Specification 522,881 which is supplied from a line 116, Fig. 5, with oil under pressure and delivers oil to lines 178, 179 at pressures dependent upon the governor speed. Oil is delivered to the lines 115, 116 from the pump P through a line 196 and from the rear pump Q through a check valve 111. A driver's lever having "R" "L" "D" and "N" positions actuates a valve 100 which is shown in Fig. 5 in the reverse gear position " R ". When the engine is running with the lever in this position the pump P delivers oil under pressure via the lines 115, 117, valve 100 and line 121 to the chambers 310, 311 to hold of the brake hand 40. Oil under pressure is also supplied via a line 125 to the cylinder 133 of the reverse brake piston 129, to a line 134 leading to a " timing " valve 150, and to the regulator valve 180 of the pump P. A further supply of oil under pressure is also taken via a line 123 to valves 143, 144 which control the changes from first to second and second to third gear ratios respectively, these valves being then held in the inactive position shown against any operating forces transmitted from the governor G. A branch 122 of the line 121 conveys oil under pressure to a chamber 131 beneath a "double transition " valve 250 which is thereby raised to interrupt the supply from a line 149 to a line 139 which conveys oil under pressure to disengage the front brake 170 and engage the front clutch 165, 166. A line 120 connects the supply 117 to the timing valve 150 which valve is also connected to the front brake operating chamber 286 by a line 158. When the cylinder space 133 is full and the piston 129 tightly seated the pressure rises in the lines 125 and 134, the valve 150 being moved to the left against its spring 151 and allowing oil under pressure to flow into the line 158 and apply the front brake band 170. Movement of the driver's lever to the " R " position is arranged to cause a spring 253, Fig. 11, to bias a parking pawl 236, Fig. 12, toward engagement with teeth 62 on the annulus 57 of the reverse gear unit but actual engagement is prevented by a piston 240 which is moved outwardly of its cylinder 247, against a spring 241, by oil under pressure derived from the line 116. A second piston 255 is movable by oil under pressure supplied via a line 256 from the governor against a spring 257 to engage a lever 251 which acts on the spring 253. The lever 251 is operated when the driver's lever is placed in its " R " position and is acted on by a tension spring 262 which passes through a dead centre position as the parking pawl 236 moves from the " parking " to the " released " position. The parking pawl 236 cannot therefore be set for or moved into engagement until the vehicle and engine are stopped to remove the rear and front pump pressures. A check valve 136 in the line 125 operates at a given pressure to allow a greater flow of oil to the cylinder 133. This ensures that the timing valve 150 does not operates to allow oil to be supplied to the front brake operating chamber 286 until the cylinder 133 is filled, and also prevents an initial pressure drop in the line 116 sufficient to allow engagement of the pawl 236. The rise of pressure in the line 125 is applied to a regulator valve 180 in the pump P to prevent its regulating action and ensure full pump pressure for maximum applying force on the brakes 170, 130. The valve 150 tends to reduce the pressure on the front brake actuator and ensures that any slip will be taken by the band 170 rather than by the cone 130. If the vehicle is decelerated in reverse the reaction of the band 170 may raise the pressure in the line 158, move the valve 150 to vent that line to exhaust and prepare the band 170 for soft reengagement on further rearward movement. When the driver's lever is placed in the neutral position "N" the valve 100 is lifted to its highest position, oil under pressure is supplied by the pump P via lines 196, 115, 121 to the chambers 310, 311 to disengage the rear brake band 40. No drive is then transmitted to the output shaft 50. When the driver's lever is placed in the drive position "D" the line 121 is exhausted by way of ports 104 105 of the valve 100, (Fig.5a), lines 216<SP>1</SP>, 216 and the exhaust port 217 of the valve 144, the brake band 40 then being applied by springs 313, 314. Oil is also supplied under pressure via ports 107, 106 of the valve 100, line 120, valve 150 and line 158 to apply the brake band 170, the vehicle then moving, forward in the first gear ratio. The governor G then begins to impose control pressure on the chambers 202, 209, 210 under plungers 203, 221, 211 of the valves 143, 145, 144, Fig. 5b. Springs 220, 204, 212 and 142 bias the valves 145, 143, 144 downwardly and their strengths are such that valves will rise in sequence at predetermined governor pressures to select the appropriate ratio change. As the vehicle speed rises the increasing pressure in the line 178 and chamber 202 lifts the valves 143 allowing oil to flow from the line 118 via ports 225, 226, line