Patent GB-1368580-A (GB)
Title: Gear changing system for motor vehicles
IPC: B60W10/10
Filed: 1972-09-18
Abstract: 1368580 Change-speed control FIAT SpA 18 Sept 1972 [25 Sept 1971] 43225/72 Heading F2D Ratio-selecting clutches 446, 448, in a countershaft-type change-speed gear in a motor-vehicle, are synchronized during shift by an electronic control unit 462, receiving signals from input and output speed sensors 452, 454, and sensors of position of a main clutch 414 and the ratio clutches, and issuing signals to operate the main and ratio clutches and synchronizers hydraulically. On receipt of a shift command signal from a shift lever 470, operated manually or automatically in response to engine speed and load, the electronic unit controls the engine fuel supply and releases the main clutch; shifts into reduction ratio or vice versa as required an auxiliary direct-reduced two-speed range gear 424..426 arranged in series ahead of the main four speed gear 428 ... 432, and synchronized either by conventional mechanical means or electronically; neutralizes the off-going ratio: re-engages the main clutch; under control of the speed sensors for upshift decelerates the engine and applies a brake 460 to the engine shaft, gear input shaft, or countershaft, or for downshift accelerates the engine with or without engagement of an optional disc clutch 474 between the final output shaft 420 and the lowest speed wheel 428, meshing the countershaft cluster; and on attainment of synchronism engages the on-going ratio clutch. Fluid circuit, Figs. 2a, 2b.-A single enginedriven pump 100 supplies an accumulator 110 and the system, which includes a single-acting actuator 112 for releasing the main clutch; a  double-acting actuator 118 for the engine fuel control, normally spring-held in an inactive central position and increasing or decreasing fuel supply only at its two end positions; a singleacting actuator 124 for the input brake 460; a double-acting actuator for the direct-reduced range gear clutch 444; a double-acting actuator 138 selecting neutral and reverse; and two three-position actuators 148, 150 and 184, 186 for respectively actuating the 1-2 and 3-4 selector clutches 446, 448. The latter each comprise pair of large and small cylinders, the large pistons 166, 174 freely abutting on one side a selector rod 176 and, on the other, rods 162 attached to the smaller pistons 158, 172 the inward movement of which beyond the central position is limited by stops 160. All the actuators are controlled by solenoid valves, action of the three-position actuators being as follows. To move the selector rod 176 from the central neutral position shown to the left for first ratio or right for second, valve 152 or 154 respectively is operated and, on completion of the selected movement is returned to exhaust position, shown, by position sensing microswitches 178 ... 182. For neutral both valves are actuated together and subsequently returned to exhaust.  Electronic circuit, Fig. 3.-The speed-frequency signals provided by the input and output speed sensors 52, 54 are processed to speedvoltage analogues 214, 228, applied, after inversion of the signal 214, in summators 232, 234, the outputs of which are negative or positive according to whether input speed exceeds or is less than that of output when the time constants of the monostable multivibrators 208, 222 are equal. To introduce the required speed ratio factor the time constant of 222 is varied by a ratio signal 238 from the gate circuit 244. The outputs of the summators 232, 234 pass to the gating circuits 244 through triggers 240, 242, which have negative and positive thresholds respectively for operation of the acceleration or deceleration of the engine, input brake 460, and, if provided, the output clutch 474, under control of the various positional micro-switches 116 &c., Figs. 2a, 2b. To accelerate the response and compensate for inertial delays, the speed signals 214, 228 are also referred to a differential amplifier 258 which signals the gate circuits 244 through triggers 260, 262, having positive and negative thresholds respectively, their values being set to define a tolerance interval for synchronizing, whereby between these values the summator triggers 240, 242 are interdicted and a shift consent signal issued. Gear preselection with the vehicle stationary is provided by a zero speed signal 268 from the output speed sensor 54.