GB1316365A - Electronic protection device for an automatic power transmission of a motor vehicle - Google Patents

Abstract

1316365 Change-speed control NISSAN MOTOR CO Ltd 9 Oct 1970 [13 Oct 1969] 48162/70 Heading F2D An electronic protection circuit to prevent unsafe overspeeding of the engine of a motorvehicle provided with an automatic transmission with manual downshift potential, comprises a sensor 14 generating a voltage signal proportional to vehicle speed, a comparator circuit 16 comparing that voltage with fixed voltage levels corresponding respectively to each ratio, and generating signals W1, W2, corresponding to the first and second of the three ratios of the transmission, to indicate that a safe downshift to the particular ratio is possible without causing overspeeding of the engine, and a command circuit 17 responsive to the comparator signals to generate signals applied to the hydraulic control of the transmission to prevent downshift or produce upshift. Only the comparator circuit 16 is described, and this comprises two Schmidt-triggers including six transistors 20 ... 25. The speed sensor 14 generates a negative voltage which increases with vehicle speed increase, is compared with a constant 10-volt positive signal 27, and applied through resistors, adjusted to suit the particular gear ratios, to the bases of first and third transistors 20, 22, causing them to become successively non-conductive with speed increase. Thus over a lowest speed range, safe for first ratio, the first transistor 20 remains conductive, causing the second transistor 21 to be non- conductive so that a safe first speed signal W1 is produced. Above this speed range the first transistor 20 becomes non-conductive, 21 conductive and the safe signal W1 disappears. At the same time the fifth transistor 24 is rendered non-conductive by a connection to the collector of conducting transistor 21, so that a safe second ratio signal W2 is now produced. At 2-3 upshift speed the third transistor 22 is rendered non-conductive the fifth, 24, conductive, cancelling the second-ratio signal W2, whilst the fourth transistor 23 is rendered conductive causing the sixth, 25, to become non- conductive producing a third ratio signal W3. The signals W1, W2, W3 control the hydraulic transmission through the command circuit 17, not described. As an example, at high speed the signal W3 only appears, and if mannal 2 is then selected the signal W3 enforces upshift to or maintains third ratio.