Patent GB-1354718-A (GB)
Title: Overdrive electronic control system
IPC: F16H63/02
Filed: 1971-10-11
Abstract: 1354718 Change-speed control BORGWARNER CORP 11 Oct 1971 [12 Nov 1970] 47186/71 Heading F2D An electronic circuit automatically controlling overdrive, in a motor-vehicle equipped also with a manual or automatic transmission, responds to an analogue signal 16 representing vehicle speed, and fed to a comparator 30 only in a low to medium engine load range L1, as determined by a low vacuum switch 20, responding to engine intake depression, the reference voltage 46 against which the speed signal 16 is compared being changed from a high R1 value, effective in the L1 load range, to a low R2 value when a second engine load signal, representing a low load L2, is issued by a high vacuum switch 40. Thus in the L1 load range overdrive cuts in at 28 m.p.h. and drops out at a lower speed, but if overdrive is established and the low load range L2 is entered, e.g. at zero throttle, overdrive persists to a much lower speed of 5 m.p.h. Further, in this L2 range, overdrive will not drop out even if switched out by a manual selector switch 50 or kickdown switch 55, both of which are effective at all other loads. Both these switches 50, 55 are normally closed, the former being opened for overdrive lock-out, the latter opened for temporary downshift by depression of the accelerator pedal or a separate push-button. Included also is a temperature switch preventing establishment of overdrive at low oil temperatures. In the block diagram, Fig. 1, assuming that overdrive is not established, and that one signal input 66 of a final AND circuit 70 is supplied through an OR circuit 65 and AND circuit 60 by the manual and kickdown switches, 50, 55, both being closed, the other input signal 31 of the final AND circuit 70, which energizes the line 71 of the overdrive solenoid 75, is derived from the comparator 30, at engine loads under L1, when the signal 21 operates the gate 25 to supply the speed signal 16 to the comparator 30. In the absence of an under L2 load signal 41, the gate 145 applies the high reference voltage signal R1 to the comparator and upshift to overdrive occurs at 28 m.p.h. The upshift signal 71 is fed back to the OR circuit 200, causing the gate 25 to cut-off the speed signal 16 from the comparator 30. The overdrive signal 71, fed back to the OR gate 200 latches the gate 25, maintaining the speed signal source 15 coupled to the comparator 30 and keeping the L1 load signal ineffective until overdrive is cut out. As long as engine load is above L2 level overdrive will be maintained until vehicle speed falls below the R1 speed reference level, whereupon the comparator 30 will cut out the overdrive. At engine loads under L2, the signal 41 appears, and together with the feedback signal 71, shifts the gate 145 to substitute low reference voltage R2 for R1 so that, under that condition, overdrive persists down to 5 m.p.h., whether or not the manual switch 50 or kickdown switch 55 is opened. The transistor circuit, Fig. 2, not shown, details the block diagram, Fig. 1. The speed signal 16 is derived from an A.C. generator the output of which, rectified by a diode (D1) feeds the base of a transistor (Q1), providing a square-wave output, rectified to a D.C. voltage by a pair of diodes (D2, D3) and a resistancecapacity (R5, R6, C2). The gate 25 is a second transistor (Q2), triggered by the L1 load switch 20 or the feedback line 71; the comparator 30 a bi-stable multi-vibrator with two transistors (Q3, Q4), the speed signal 16 input and a voltage divider (R15, R13) providing the R1 reference, and a transistor (Q5) triggered by the L2 load switch 40 to short one resistor (R13) to provide the R2 reference. The gate 70 is a sixth transistor (Q6) with output and power transistors (Q7, Q8) feeding the overdrive solenoid line 71, which includes the temperature switch (80). An indicator lamp (85) is in parallel with the solenoid (75).