Electronic control device for automatic power transmission mechanism

Claim 1

In an automatic power transmission for a motor vehicle driven by an engine wherein said automatic power transmission has a driven shaft, the improvement of an electronic protection device comprising a vehicle speed sensor connected to said driven shaft of said automatic power transmission to sense vehicle speed and to generate a negative voltage signal which negatively increases in its magnitude as the vehicle speed increases; a comparator cirCuit electrically connected to said vehicle speed sensor for comparing said negative voltage signal with predetermined positive voltage levels for thereby selectively generating three different electric signals when said negative voltage signal exceeds said predetermined positive voltage levels; a command circuit electrically connected to said comparator circuit and responsive to said electric signals for generating first, second and third speed gear ratio command signals, and a hydraulic control device electrically connected to said command circuit and responsive to said first, second and third speed gear ratio command signals for automatically controlling said automatic power transmission; said comparator circuit including a bus line of a predetermined positive voltage, a first transistor connected at its base to said bus line and said vehicle speed sensor to receive said predetermined positive voltage and said negative voltage; a first resistor connected between the base of said first transistor and said bus line; a second resistor connected between the base of said first transistor and said vehicle speed sensor, the resistance values of said first and second resistors being adjusted within a first range to render said first transistor conductive when the vehicle speed is below a first predetermined level; a second transistor connected at its base to the collector of said first transistor and connected at its collector to said bus line, said second transistor being further connected at its collector to said command circuit through a line on which said electric signal appears, said first transistor being conductive when the potential at the base of said first transistor exceeds a predetermined upperlimit level thereby rendering said second transistor non-conductive to generate said first electric signal at the collector thereof; a third transistor connected at its base to said bus line and said vehicle speed sensor, a fourth resistor connected between the base of said third transistor and said bus line, the resistance values of said third and fourth resistors being adjusted within a second range to render said third transistor conductive when vehicle speed is in a range between the first predetermined level and a second predetermined level; a fourth transistor connected at its base to the collector of said second transistor and the collector of said third transistor, said fourth transistor being also connected at its collector to said command circuit through a second line at which said second electric signal appears, said fourth transistor being nonconductive when said third transistor is conductive for thereby generating said second electric signal at the collector thereof; a fifth transistor connected at its collector to said bus line, and a sixth transistor connected at its base to the collector of said fifth transistor, said sixth transistor being also connected at its collector to said bus line and said command circuit through a third line on which said third electric signal appears, said fifth transistor being rendered conductive when the vehicle speed exceeds the second predetermined level to cause said third transistor to become nonconductive thereby to render said sixth transistor nonconductive for thereby generating said third electric signal at the collector thereof.