Patent GB-1103052-A (GB)
Title: Automatic gear changing apparatus
IPC: F16H59/08
Filed: 1963-08-20
Abstract: 1,103,052. Change speed control. TRENT MOTOR TRACTION CO. Ltd., and J. A. ACRAMAN. 11 Nov., 1964 [20 Aug., 1963], No. 32921/63. Heading F2D. [Also in Division H3] In an automatic control for a public service vehicle change-speed gear, such as an epicyclic gear having ratios established by pneumatically or hydraulically actuated friction band brakes controlled by electromagnetic valves, forward ratio-shift is controlled by transistor switches responsive to vehicle speed. Function summary.-The gear provides 4 Forward gears and 1 Reverse and, alternatively, automatic control (speed responsive only) for all forward gears together with manual override, and purely manual control. Fuel is cut off by a valve FC during upshifts only. 4-3, 3-2 downshifts are effected at lower vehicle speeds than the corresponding upshifts. Means are provided to ensure non-engagement of 2nd or 1st gear when engine speed is reduced by braking; to prevent operation of the fuel cut-off and consequent engine cut-out should the brake be applied when the vehicle, in 1st gear, is stationary or moving slowly; to disable the circuit and prevent damaging engagement of 1st gear in the event of loss of signal from a speed-responsive means; and to provide for resumption of automatic control after a manual override. Circuit components include electromagnetic valve coils GA1 ... GA4 and GAR respectively for establishment of 1st ... 4th and Reverse gears; a manual shift lever switch GCS selectively connecting a positive supply PS to terminals T1 ... T4 and TR; a rectifier MR which receives an A.C. input from a device SG generating an output voltage dependent on vehicle speed and delivers a D.C. output which is smoothed by a large capacity capacitor C1; a switching circuit including NPN transistors VT3, VT4; NPN transistors VT1, VT2; a PNP transistor VT5; and relays BL1 ... RL8 switching contacts RL1A, RL1B ... RL8A. Operation - automatic. -For automatic operation, switches SW1, SW2 are set to positions A and the switch GCS connects the supply PS to the terminal T4. The relay RL5 is thereby energized through the contacts RL6B to connect the rectifier MR output to the bases of transistors VT1, VT2 and VT3 through the contacts RL5A and potentiometers RV1, RV2 and a variable resistor VR3 respectively, and to connect the supply PS to the collectors of transistors VT1, VT2 through the contacts RL5C and the transistors VT3, VT4 through the contacts RL5C, RL2C, RL1A. The transistors VT1 and VT2 are non-conductive, and the transistor VT3 is non-conductive whereby the transistor VT4 conducts. The relay RL7 is thereby energized to energize the coil GA1 through a diode D4 and the contacts RL7A, to disconnect the relay RL5 from the contacts RL5C by opening the contacts RL7B, and to charge a capacitor C4 through the contacts RL7C. The energization of the coil GA1 engages 1st gear. 1-2 Upshift.-On increase in vehicle speed to, say, 6-7 m.p.h., the transistor VT3 becomes conducting and blocks the transistor VT4. The relay RL7 is thereby de-energized to switch the contacts RL7A to de-energize the coil GA1 to disengage 1st gear and energize the coil GA2 through a microswitch AS and the contacts RL1C to engage 2nd gear. The relay RL4 is energized from the capacitor C4 through the contacts RL7C, a diode D5 and the transistor VT5 thereby energizing the fuel cut-off valve FC from a supply PSA through the contacts RL4A for the discharge period of the capacitor C4, say 2 seconds. The contacts RL7B then provide a path parallel to that through the contacts RL6B. 2-3 Upshift.-On. further increase in vehicle speed to say 18 m.p.h., the transistor VT1 becomes conducting. The relay RL1 is thereby energized to switch the contacts RL1C to disengage 2nd gear and energize the relay RL3 through an electrically conductive link LK and a network comprising an adjustable resistor VR1 and a capacitor C2 to energize the fuel cutoff valve FC through the contacts RL3A for the charging period of the capacitor C2, say 4 seconds. During this period the contacts RL3C are open. After said charging period the coil GA3 is energized through the contacts RL2C, RL1A and RL3C to engage 3rd gear. The switching of the contacts RL1B connects to the negative line the slider of a potentiometer RV3 across the transistor VT1 base-emitter path. 3-4 Upshift.-On further increase in vehicle speed, to, say, 28 m.p.h., the transistor VT2 becomes conducting. The relay RL2 is thereby energized to switch the contacts RL2C to disengage 3rd gear and energize the relay RL4 through a network comprising an adjustable resistor VR2 and capacitor C3 and a diode D7 to energize the fuel cut-off valve FC for the charging period of the capacitor C3, say 2 seconds. The switching of the contacts RL2A energizes the coil GA4 to engage 4th gear. The switching of the contacts RL2B connects to the negative line the slider of a potentiometer RV4 across the transistor VT2 base-emitter path. The switching of the contacts RL1B and RL2B on 2-3, 3-4 upshifts is effected so that 4-3, 3-2 downshifts occur at lower speeds than the corresponding upshifts, say at 22, 13 m.p.h. respectively. To ensure non-engagement of 2nd or 1st gear when engine speed is reduced by braking, so as to avoid lurching of the vehicle, release of the accelerator when applying the foot brake opens the switch AS to prevent energization of the coil GA2, and application of the foot brake operates a switch, not shown, to close a brake warning circuit BWL and apply a positive bias to the base of the transistor VT3, a diode D8 isolating the signal from the rectifier MR, to maintain said transistor conducting and preventing energization of the coil GA1. Applying the foot brake also lights a brake warning light BS and applies a positive reverse bias to the base of the transistor VT5 to block said transistor and isolate the relay RL4 from the capacitor C4 to prevent operation of the fuel cut-off valve FC and consequent engine cut-out should the brake be applied when the vehicle, in 1st gear, is stationary or moving slowly. In the event of loss of output from the generator SG due to generator failure or emergency halting braking, with the vehicle travelling under automatic control in 3rd or 4th gear, the relays RL1, RL2 and RL7 revert to their normal conditions, i.e. relays RL1, RL2 de-energized and RL7 energized, in the order RL2, RL1, RL7, this sequence being permitted by the large capacity of the capacitor C1. When the relay RL1 becomes de-energized, the relay RL6 is disconnected from the positive supply by the switching of the contacts RL1C, but due to discharge of a capacitor C5 the relay RL6 remains energized until after the relay RL7 has reverted to an energized state. When the relay RL7 reverts thus the contacts RL7B open and since the contacts RL6B remain held open the relay RL5 is de-energized to open the contacts RL5C to disable the gear change circuit and prevent damaging engagement of 1st gear. De-energization of the relay RL5 provides a holding current for the relay RL6 from the supply PSA through contacts RL5B, RL8A and RL6A to prevent re-energization of the relay RL5 over the contacts RL6B on termination of the capacitor C5 discharge. In order that the apparatus may resume its normal function, the supplies PS and PSA may be switched off for a short period. When, for manual overriding gear selection, with the vehicle travelling in 3rd or 4th gear, the switch GCS is moved from the automatic position, i.e. the terminal T4, the relay RL5 is de-energized whereby the contacts RL5B close to hold the energized relay RL6 and the contacts RL5A switch the D.C. output of the rectifier MR to energize the relay RL8 through the closed contacts RL6C. The contacts RL8A then open and the relay RL6 is de-energized, whereupon the contacts RL6A, RL6C open and the contacts RL6B close to complete the line between the switch SW1 and the relay RL5 so that on re-connection of the switch GCS and the terminal T4 the relay is again energized for resumption of the normal function of the apparatus. Operation-manual.-For manual operation, the switches SW1, SW2 are set to M respectively for direct selective energization of the valve coils and for isolation of the automatic control by breaking the hold current of the relay RL6. A variable resistor VR6 in series with a speedometer is adjusted to give correct speedometer readings during automatic control, and a further variable resistor VR5 is adjusted, after the resistor VR6 is set, to give correct speedometer readings under manual control. Main clutch.-With a centrifugal main clutch incorporated in the vehicle the link LK is present to provide a sufficient period of fuel cutoff during 2-3 upshift; however, if a fluid flywheel is incorporated the large reduction of engine speed afforded by energization of the relay RL3 is not necessary and the link LK is removed to disable this relay.