Control apparatus for an a.c. generator for automobile

Claim 1

A voltage control apparatus for an a.c. generator for an automobile, which comprises: an a.c. generator having an armature winding (101) and a field winding (102), a rectifier (2) for rectifying the output of the a.c. generator to charge a battery (12) containing an electrolyte, a voltage detection circuit (8,9) for detecting the voltage of the battery, a constant voltage circuit (5) for generating a constant voltage on the basis of the voltage of the battery through the operation of a key switch (6), a reference voltage circuit (4) comprising: (i) a first voltage divider including two resistors (401,402) connected in series and defining a first junction point (413) therebetween, (ii) a second voltage divider including a resistor (403) and a diode (405,406) connected in series and defining a second junction point (414) therebetween, (iii) a third voltage divider including a diode (409,410) and a resistor (408) connected in series and defining a third junction point (415) therebetween, (iv) the second junction point having a negative voltage-temperature characteristic with respect to the electrolyte temperature, the third junction point having a positive voltage-temperature characteristic with respect to the electrolyte temperature, and the first, second and third voltage dividers being connected between said constant voltage circuit and ground, (v) a first coupling diode (411) connected to the second junction point for supplying a potential thereof to the first junction point, and (vi) a second coupling diode (412) connected to the third junction point for supplying a potential thereof to the first junction point and having a polarity opposite that of the first coupling diode, and a voltage control circuit (3) for comparing the voltage of the voltage detection circuit with the voltage of the first junction point of the reference voltage circuit and controlling a field current to the field winding depending on a difference in the comparison to render the voltage of the battery constant, wherein: (a) the voltage at the first junction point remains constant below a first predetermined electrolyte temperature (t1). (b) the voltage at the first junction point decreases with an electrolyte temperature increase at a first reduction rate between said first temperature and a second, higher predetermined electrolyte temperature (t2), and (c) the voltage at the first junction point decreases with an electrolyte temperature increase at a second lower reduction rate above said second temperature.