GB1492523A - Electrical control means for changespeed gearing - Google Patents

Abstract

1492523 Change speed control THOMAS ELECTRONICS Ltd 27 Nov 1974 [30 Aug 1973] 40943/73 Heading F2D An electronic speed-ratio control on a motor vehicle responds to an output speed signal 22, 24 and to two switches 16, 20 operated respectively at full-closed and full-open positions of the engine throttle control, such that, on closed throttle, upshift (e.g. on a downgrade) is prevented and speed-responsive downshift is still permitted, whilst the open throttle position raises the shift speeds, producing kickdown, and there is an additional manual switch 18 in parallel with the throttle-closed switch 16 to produce the same upshift prevention function as that switch. During upshift the engine fuel is cut-off; during downshift a neutral interval appropriate to the selected ratio is established; means, sensed by current overload prevents simultaneous establishment of two ratios; emergency downshift to second ratio is produced by failure of the service brakes; alternative manual selection of individual ratios is provided. Manual selector switch 10 has an automatic position A and four manually selected positions in which the switch supplies current directly to the ratio-establishing devices, including reverse E, in an electro-pneumatic valve unit EP when contacts CG are moved to their upper position by closure of the upper contacts of a switch 12 energizing a relay RLG, for manual operation. Speed signal is derived at 22, 24 from the A.C. generator of the vehicle speedometer, amplified in three transformer stages TR1, TR2, TR3, which switch transistors T21 ... T23, introducing power from the main circuit to produce a signal of speed-responsive frequency, which is rectified at RC1, smoothed by a capacitor C15, and applied through diodes D11...14 and individual resistors R65...68, to the shift circuits as a speed-responsive D.C. voltage. Automatic operation.-With the upper contacts 12c of switch 12 open, its lower contacts 12a closed, and the manual selector in A setting the contacts CG are in their lower position shown with the automatic circuit lines connected to the EP unit. Ratios one to four are then established by closure of respective contacts CA, CB, CC, CD by energizing relays RLA ... RLD in the respective shift circuits sequencing as follows. Positive voltage, stabilized by a diode ZD1 is fed through a diode D24, fuse F1, closed switch 14, and conducting transistor T25 to a relay RLE, the energizing circuit through which is completed as a transistor T24 is rendered conductive as a capacitor C7 charges. The relay RLE then closes contacts CE supplying a common positive line to all the shift-circuits, which switches on transistors T1, T2, energizing the relay RLA to close the first ratio contacts CA introducing first ratio in the unit EP and also switching on hold-on transistors T16, T17 for the relay RLE. 1-2 upshift.-At a predetermined speed, determined by the resistor R68 the speed signal through R68 switches on transistors T4, T5, causing a voltage to appear across a resistor R14 and a thermistor TH1, which switches on a transistor T6 energizing the relay RLB, closing contacts CB to establish second gates in the EP unit. At the same time voltage appearing across a resistor R78 feeding the contacts CB switches on a transistor T3, de-energizing the relay RLA and thereby opening the first ratio contacts CA. At successively higher speeds the speed signal, through the resistors R67, R66, transistor circuits T8 ... 11, and T12 ... 14, relays RLC, RLD and their contacts CC, CD, produces 2-3 and 3-4 upshifts. Downshift is the reverse of upshift, except that the establishment of the on-going ratio is delayed after release of the off-going ratio by the time taken for respective capacitors C8, C9, C10, to discharge and thereby switch off respective transistors T3, T7, T11 to permit energization of the respective relays RLA, RLB, RLC, thereby producing a neutral pause. Kickdown.-Full throttle opening closes a switch 20, which inserts resistors R62 ... 64 in parallel with respective resistors R10, 24, 38 between the speed signal and the negative line in each of the second, third and fourth ratio shift circuits, thereby reducing the bias effect of the speed signal and thus raising upshift speeds. Upshift prevention, e.g. on a downgrade, is produced by closing either of two switches, one, 18, manual, the other, 16, by accelerator release, to energize a relay RLF, closing contacts CF which, in the case of first ratio being established, through a diode D9, switch on the transistor T7, preventing switch on of T6 to establish second ratio. Similarly transistors T11, T15, switched on in second and third ratios respectively, prevent upshift therefrom, downshift being unaffected. Throttle close during upshift.-Capacitors C11, C12, C13 are provided across the respective relay contacts CB, CC, CD of second, third and fourth ratios respectively and, when these close on upshift, the capacitor begins to charge and switches on a respective transistor T18, 19 or 20 for a predetermined time period, thereby energizing a relay RLH which closes contacts CH energizing a fuel cut off circuit 26 (not shown). Diode circuits D18, D16 &c. prevent this action on downshift. Safety arrangements.-Loss of speed signal from the resistor 65 causes loss of bias and hence switch off of the hold-on transistor T16, deenergizing the relay RLE and opening its contacts CE to switch off the supply to the shift circuits and establish neutral. Current overload causes the voltage across a resistor 81 to be diffident to switch off a transistor T25, also breaking the shift supply circuit and establishing neutral. This also prevents simultaneous establishment of two ratios. Emergency second ratio.-A switch 14, placed beneath the source brake pedal, closes on brake failure and directly establishes second ratio in the EP unit. Signal lamps L2 and L1 respectively indicate automatic operation and energization of the upshift prevention relay RLF.