Patent GB-1439675-A (GB)
Title: Electrical systems for automatically controlling the gear changes  of road vehicles
IPC: F16H59/44
Filed: 1973-05-29
Abstract: 1439675 Change-speed control FERRANTI Ltd 28 May 1974 [29 May 1973] 25545/73 Heading F2D An electronic control for gear shift of a transmission 9 on a motor road or other vehicle, or other purpose, comprises a reversible binary counter 21, which issues an upshift or downshift signal on the basis of a comparison between the number of pulses of a repetitive series produced by an output-driven pulser 22 controlled by a timer 24 triggered by a control 16, and a desired shift speed up or down, also in the form of a repetitive series of pulses from a store 14 receiving a digital signal from an analoguedigital converter 13 representing engine throttle opening, together with a signal from a select curve circuit 17 which stores shift curves of preset desired shift speeds at particular throttle openings (Fig. 2, not shown), selection of the appropriate curve being controlled by the control stage 16 and by a transducer 15 representing the ratio actually established in the gear 9. The timer 24 is a monostable triggered at fixed intervals by the control stage 16 from a stable negative to an unstable positive state. During the latter it opens an AND gate 23 to deliver a timed stream of positive pulses representing actual output speed from an output speed pulser 22 to the counter 21. The timer 24 also selects between desired upshift and downshift comparison by issuing the positive signal to the select curve 17 for selection of an upshift speed-throttle curve and a negative for down, this signal also appearing on a line 27 to condition AND gates 31, 35 for up or down shift respectively. In operation, during the stable negative interval, the store 14 scans first the upshift curve corresponding to the established ratio, the scan proceeding as far as the throttle-opening signalled at 13, thus supplying to the counter 21 a series of pulses corresponding in number to the critical speed requiring upshift at that throttle opening. The counter 21 stores this upwardly counted pulse number, and when the control 16 changes the timer 24 to its unstable positive state, is counted downwardly towards zero by the pulses received from the actual speed pulser 22. If zero is reached before the end of the timing interval this indicates that actual road speed is too high for the prevailing gear ratio and throttle opening, and the zero in the counter 21 causes a zero detector 25 to issue a positive signal on a line 26, which, together with the positive signal from the timer on the line 27, opens the upshift AND gate 31, to energize electromechanical servos producing upshift in the gear 9. If zero is not reached in the counter 21 before the end of the timing interval upshift is not required, downshift does not occur since the timer 24 reverts to its stable negative state at the end of the interval, thereby selecting the corresponding downshift curve for sampling, and changing the line 27 to downshift negative, closing the upshift gate 31. During the next positive interval of the timer 24, the countdown of output speed pulses 22 is repeated against the pulses of the downshift curve stored during the preceding negative interval. If zero is not reached during this countdown, the zero detector 25 maintains a normal negative signal on the line 26, which together with negative signals at 27 and the timer 24, both produced at the end of the positive interval when the timer 24 reverts to its negative state, are all negated at 33, 34, 36, to produce positive signals opening the downshift gate 35 to produce a downshift signal 37. Should neither upshift nor downshift signals be produced the count is resumed without shift. Curve selection and store.-The store 14, Fig. 3, comprises six rows of transistors each row representing a predetermined speed-throttle shift curve (Fig. 3, not shown), the rows corresponding respectively to the three downshifts 4-3; 3-2 and 2-1 and three upshifts 1-2; 2-3 and 3-4. Each row has a number of transistors arranged in columns with their bases connected in common to lines 43 connected to incremental stages of a decoder 44 the stages of which represent percentage throttle openings from zero to one hundred as measured by the throttle transducer 12. The transistor collectors are all connected through a line 61 to the counter 21, whilst a low switching potential is applied to all the emitters of a selected row through respective gates 53 . . . 58 selectively opened by ratioestablished signals from the ratio-transducer 15 and from a bi-stable 46 changed in state by the upshift positive and downshift negative signals generated by the timer 24. The decoder 44 repetitively scans all the rows, going from zero to the prevailing throttle opening, and as it does so the transistors of the selected row are switched on in sequence to supply a series of pulses to the counter 21, the number of such pulses defining the desired critical shift speed, up or down, for the prevailing throttle opening, for comparison with the actual speed pulses in the counter as above described. Where the speed-throttle shift curves do not start at the origin, pulses corresponding to the starting speed are injected into the counter by supplementary stores controlled by monostables (Fig. 5, not shown). The slope of the shift curves can be predetermined by varying the number of transistors in the particular row. Upshift and downshift curves are spaced by the usual hysteresis zone.