Patent GB-1502418-A (GB)
Title: Gearboxes for vehicles
IPC: F16H61/02
Filed: 1975-03-27
Abstract: 1502418 Change-speed control AUTOMOTIVE PRODUCTS Ltd 27 March 1975 [27 March 1974 31 Jan 1975] 13569/74 and 4363/75 Heading F2D  A vehicle gear-box of the planetary type with controllable friction elements for establishing the various ratios has electronic control means so arranged that selection of a ratio for moving the vehicle from rest results in the friction element(s) of a higher ratio being operated, for a predetermined period before the selected ratio is engaged. The arrangement, which may apply to reverse as well as forward drive, reduces shock as parts in the gear system, rotating due, e.g. to drag in a torque converter or hydraulic coupling between the engine and gear-box, are brought to rest. The control means is responsive to vehicle speed and degree of throttle opening for actuating solenoid valves which control application of fluid pressure to the friction elements, and includes a manually operable switch for selecting reverse. In the embodiment described the gear-box has four forward and two reverse ratios and the manually operable switch is effective also to enable first, second or third ratio to be held until vehicle speed exceeds the automatic upshift speed at full throttle opening. Also included is means operative in response to large throttle openings when vehicle speed is low to apply an increased fluid pressure to the friction elements. Gear arrangement.-An input shaft 40, Fig. 2, which may be driven through a torque converter, is connectible by a forward clutch 41 with a bevel wheel 48, and by a top and reverse clutch 43 with a bevel wheel 50. Planetary pinions 49, 52 on a carrier 58 mesh respectively with the two wheels 48, 50 and with a wheel 53 on the output shaft 45 and a wheel 51. A sprag clutch engages the carrier so that low ratio is established when the forward clutch 41 is engaged. With the clutch 41 remaining engaged, second and third ratios are established by application of respective brake bands 55, 56, and top by engagement of the clutch 43. Normal reverse is established by the clutch 43 and a brake band 57, and highratio reverse, employed only for the predetermined period before normal reverse, is engaged by the clutch 43 and brake band 55. Automatic control circuit.-A signal of which the frequency varies with gear-box output speed is supplied to a terminal 110, Fig. 3a, whence it passes through a shaping circuit 112, 114 &c., producing a square wave output, to an amplifier 116, 117, &c., and thence from a resistor 118 to three transistor pump circuits 120, 121, 122, each of which produces an output voltage proportional to the frequency of the input signal and feeds it to a respective voltage divider 138, 139, 140. Also fed to each voltage divider is a signal indicative of throttle opening derived from a potentiometer 150, so that a signal representing a combination of vehicle speed and throttle opening appears on each of lines 157, 158, 159. Diodes 161, 162, 163 prevent unwanted gear changes at small throttle openings, as described in Specification 1,420,307. Each line 157, 158, 159 connects with a respective amplifier trigger 170, 171, 172 comprising four transistors 174, 175, 176, 177 &c. Tho trigger circuits control, respectively, ratio changes between first and second, second and third, and third and top. The emitter of the transistor 175 is connected through a resistor 200 and a transistor 201 to a delay circuit 202 comprising three transistors, and the emitter of the transistor 176 is connected through a resistor 208 and transistors 209, 210 to an output stage 212 of which a line 216 leads to a solenoid of a valve controlling the reverse brake band 57. The emitter of the transistor 205 of the delay circuit 202 connects through a summing junction 218 with a second output stage 219 having line 221 leading to a solenoid valve for the second ratio brake band 55. The emitter of the transistor 180 in the trigger circuit 171 also connects with the summing junction 218 through a transistor 236 and a delay circuit 237, whilst the transistor 179 connects through a transistor 226, a delay circuit 227 and summing junction 230 with an output stage 231 leading to a solenoid valve of the third ratio brake band 56. The transistors 184, 183 of the trigger circuit 172 are similarly connected through delay circuits 241, 240 with summing junction 230 and with an output stage 243, the latter stage controlling a solenoid valve of the top and reverse clutch 43. In the automatic mode of operation (position D of the manual selector switch 280) first ratio is operative until vehicle speed and throttle opening are such that the trigger circuit 170 switches to cause the transistor 220 to become conductive and engage the second ratio brake 55. At a higher value of the combined speed and throttle signal the trigger circuit 171 switches and causes instantaneous energization of the third ratio brake 56 through the output stage 231, and delayed reduction, due to the capacitor in the delay circuit 237, of the potential at the summing junction 218, thereby causing delayed switching of the output transistor 220 to the non-conducting state. This provides some overlap of the brake applications to promote smother ratio change. Shift between third ratio and top is similarly controlled with overlap, by the trigger circuit 172 connected to the summing junction 230 and a further output stage 243. Each output stage is connected through a resistor 250, 251, 252, 253 to a common line 254 which is assocated with a protective circuit (Fig. 4, not shown) operative to deenergize all of the friction elements in the event of a malfunction giving rise to simultaneous energization of more than one of the reverse, second and third brakes, and the top and reverse clutch. Manual control.-A first wafer 281 in the manual selector switch 280 has connections such that when it is in any of positions P, R, N the speed signal is inhibited. It has connections also such that when it is positioned at 3, 2 or 1 it renders conductive a transistor 288, transistors 289 and 288, or transistors 290, 289 and 288 to increase the shift speeds as indicated above. A second wafer 282 is connected to prevent energization of the reverse brake whenever P, N, D, 3 or 2 is selected. The D, 3, 2, 1 positions of a third wafer 283, and the R position of a fourth wafer 284 are connected between resistors 300, 301 of a circuit which receives a speed signal from the transistor 116 and includes various transistors &c. and flip-flops 321, 322 each comprising four NAND gates. One NAND gate 330 is connected to an output circuit 335 including a transistor 338 of which the emitter is connected to control the forward clutch, and another NAND gate 331 is connected to the input of the trigger circuit 170 through transistors 341, 343, 344, a delay circuit 350 and a diode 353. The transistor 343 is connected to the output stage 243 to engage the top and reverse clutch when an appropriate signal appears at its collector. This arrangement prevents both engagement of reverse when the vehicle is travelling forwards at more than, e.g. 2 or 3 m.p.h., and engagement of a forward ratio when the vehicle is in reverse. The emitter of the transistor 338 is also connected to the input of the trigger circuit 172 by a delay circuit 245 and diode 248 so that when the selector switch is moved to select forward drive a signal appearing at the transistor 338 for engaging the forward clutch also causes the triger circuit 172 (and also, due to diodes 349, 349<SP>1</SP>, the trigger circuit 170, 171) to change state so that the top and reverse clutch is engaged. After an interval, depending on the delay circuit 245, the trigger circuit returns to its original state so that the top and reverse clutch is released and the vehicle can move off in first ratio. Similarly, when the selector is moved to position R, a signal from the transistor 344 to the trigger circuit 170 causes the second ratio brake band to be engaged to provide high reverse ratio for a limited period. A line 312 from the emitter of a transistor 310 leads to a circuit (Fig. 5, not shown) controlling a solenoid valve which increases the pressure of fluid supplied to the friction elements at low vehicle speeds and large throttle openings. Reference is made to a modification using a single-wafer selector switch controlling a semi-conductor circuit to perform the functions of the multiwafer switch described. Reference has been directed by the Comptroller to Specification 1,421,329.