Control device for a vehicular ac generator

A voltage regulator 3 for controlling the output voltage of the AC generator 1 includes two voltage dividers having junction points J1 and J2 coupled to the zener diode 306 controlling the ON/OFF of the controlling transistor 309 and the power transistor 310. The voltage level at the junction point J1 is varied by means of the short-circuiting transistor 313 in response to the output of control transistor 401. Usually, the voltage at the junction point J1 is higher than the voltage at the junction point J2, and the output voltage of the AC generator 1 is controlled on the basis of the voltage at the junction point J1 to a normal and a reduced level in accordance with the output at the target voltage change-over terminal B. When quick charging is needed, however, the control transistor 402 is turned on to ground the junction point J1, such that the output voltage of the AC generator 1 is controlled to a higher level on the basis of the voltage at the junction point J2.

BACKGROUND OF THE INVENTION 
This invention relates to a control device for a vehicular AC generator and 
a method of controlling the same, and more particularly to such a control 
device and method by which the battery can be charged quickly when 
necessary. 
FIG. 7 is a circuit diagram showing a conventional control device for a 
vehicular AC generator, which is disclosed, for example, in Japanese 
Utility Model Publication (Kokoku) No. 62-30480. The circuit of FIG. 7 
includes an AC generator 1, a full-wave rectifier 2 for rectifying the 
output of the AC generator 1, and a voltage regulator 3 for regulating the 
output voltage of the AC generator 1 to several distinct predetermined 
levels in accordance with the operation condition. The target voltage to 
which the voltage regulator 3 regulates the output voltage the AC 
generator 1 is adjusted to two distinct target levels in accordance with 
the output of an engine control unit 4. Further, the target voltage is 
adjusted to a third level when the battery terminal voltage detector 
terminal A is disconnected from the battery 5. 
The AC generator 1 includes a three-phase armature coil 101 mounted on the 
stator (not shown) of the AC generator 1, and a field coil 102 mounted on 
the rotor (not shown) of the AC generator 1. The full-wave rectifier 2 
coupled to the output of the three-phase armature coil 101 consisting of 
six main and three auxiliary diodes includes a main rectifier output 
terminal 201, an auxiliary output terminal 202, and a grounded terminal 
203. 
The voltage regulator 3 coupled to the auxiliary output terminal 202 and 
the field coil 102 includes a first series of voltage divider resistors 
301, 302, and 303 coupled across the battery terminal voltage detector 
terminal A and the ground, and a second series of voltage divider 
resistors 304 and 305 coupled across the auxiliary output terminal 202 and 
the ground. The voltage divider resistors 301, 302, and 303 constitute the 
first voltage detector circuit and the voltage divider resistors 304 and 
305 constitute the second voltage detector circuit. The junction point J1 
of the first voltage divider resistors 301, 302, and 303 and the junction 
point J2 of the second voltage divider resistors 304 and 305 are coupled, 
through a zener diode 306 and a diode 307 and a diode 308, respectively, 
to the base of a controlling transistor 309, which is coupled in series 
with a resistor 311 across the auxiliary output terminal 202 and the 
ground. The collector of the controlling transistor 309 is coupled to the 
base of a power transistor 310 coupled in series with a surge absorber 
diode 312 across the auxiliary output terminal 202 and the ground. 
Further, a short-circuiting transistor 313 is coupled across the two 
terminals of the voltage divider resistor 303. The target voltage 
change-over terminal B of the engine control unit 4 is coupled to the 
auxiliary output terminal 202 through a resistor 314 and to the base of 
the short-circuiting transistor 313. 
The engine control unit 4 includes a control transistor 401, the base of 
which is coupled to a control signal representing, for example, the 
vehicle speed, idling state, and the battery voltage. A serial connection 
of a key switch 6 and a charging state display lamp 7 is coupled across 
the battery 5 and the auxiliary output terminal 202 of the full-wave 
rectifier 2. Further, an electric load 8 is coupled across the main 
rectifier output terminal 201 and the ground through a load switch 9. The 
battery 5 is coupled across the main rectifier output terminal 201 and the 
ground. 
Normally (i.e., if the battery terminal voltage detector terminal A is not 
disconnected), the voltage regulator 3 regulates the output voltage of the 
AC generator 1 to two distinct target voltage levels in accordance with 
the output of the engine control unit 4. When the control transistor 401 
of the engine control unit 4 is turned off and hence the voltage at the 
target voltage change-over terminal B is at the high level H, the 
short-circuiting transistor 313 is turned on to short-circuit the voltage 
divider resistor 303, the voltage is controlled to the normal target level 
(e.g., 14.4 V) determined by the resistance ratio of resistor 302 with 
respect to the sum of the resistors 301 and 302. When, on the other hand, 
the control transistor 401 of the engine control unit 4 is turned on and 
hence the voltage at the target voltage change-over terminal B is at the 
low level L, the voltage is controlled to the reduced target level (e.g., 
12.8 V) determined by the resistance ratio of the resistors 301 through 
303. More particularly, the reduced target level is determined by the 
resistance ratio of the serial connection of the resistors 302 and 303 
with respect to the serial connection of the resistors 301, 302 and 303. 
Next, the operation of the circuit is described in greater detail. 
When the key switch 6 is closed to start the engine, the base current is 
supplied from the battery 5 to the power transistor 310 through the key 
switch 6, the charging state display lamp 7, and the resistor 311. The 
power transistor 310 is thus turned on, such that the field current is 
supplied from the battery 5 to the field coil 102 through the key switch 6 
and the charging state display lamp 7. Thus, the charging state display 
lamp 7 is turned on to indicate that the battery 5 is not currently 
charged. At the same time, the base current is supplied to the 
short-circuiting transistor 313 from the battery 5 through the resistor 
314. The short-circuiting transistor 313 is thus turned on, to 
short-circuit the voltage divider resistor 303. Thus, the first voltage 
detector circuit is constituted only of the voltage divider resistors 301 
and 302. 
When the engine is started under this circumstance, an AC voltage 
corresponding to the rpm of the engine is induced across the three-phase 
armature coil 101, and the output of the AC generator 1 is full-wave 
rectified by the full-wave rectifier 2. Assume that the full-wave 
rectified output voltage of the AC generator 1 is still less than a 
predetermined level, 14.4 V, and that the control transistor 401 of the 
engine control unit 4 is turned off and hence the voltage at the target 
voltage change-over terminal B is at the high level H. Then the voltage at 
the junction point J1 is still insufficient to cause the break-down of the 
zener diode 306, and hence the zener diode 306 is kept turned off. The 
controlling transistor 309 is thus also kept turned off, and the power 
transistor 310 continues to be turned on to supply the field current to 
the field coil 102. As the rpm of the AC generator 1 increases with the 
increase of the rpm of the engine, the output voltage thereof rises. When 
the output voltage of the AC generator 1 thus exceeds the predetermined 
level, 14.4 V, the voltage at the junction point J1 rises above the level 
to cause the break-down of the zener diode 306. The zener diode 306 is 
thus turned on, thereby turning on the controlling transistor 309. The 
power transistor 310 is thus turned off. The supply of the current to the 
field coil 102 is thus interrupted, to reduce the output voltage of the AC 
generator 1. When the output voltage level of the AC generator 1 falls to 
or below the predetermined level, 14.4 V, the zener diode 306 and hence 
the controlling transistor 309 are again turned off, thereby turning on 
the power transistor 310. The supply of the field current to the field 
coil 102 is resumed, to raise the output voltage of the AC generator 1. 
By repeating the above operations, the output of the AC generator 1 is 
controlled to the predetermined normal target level, 14.4 V. The battery 5 
is charged by the output of the AC generator 1 and the electric load 8 is 
supplied with power. When the voltage across the battery 5 thus rises to a 
level substantially equal to the output voltage of the AC generator 1 
supplied from the auxiliary output terminal 202, the charging state 
display lamp 7 is turned off to indicate that the charging of the battery 
5 is now complete. 
The base of the control transistor 401 of the engine control unit 4 
receives a signal based on the information supplied from various sensors 
(e.g., the information upon the vehicle speed, the idling state, and the 
battery voltage). Thus, when the engine is under normal operating 
condition and not in the idling state, the base of the control transistor 
401 is at the low level, and the control transistor 401 is turned off. The 
short-circuiting transistor 313 is thus turned on to short-circuit the 
voltage divider resistor 303. As a result, the output voltage of the AC 
generator 1 is controlled to the predetermined normal target level. 
When, on the other hand, the engine control unit 4 determines, based on the 
information from various sensors, that the engine is in the idling state 
and the battery voltage is above a predetermined level, the control 
transistor 401 is turned on, to reduce the voltage at the target voltage 
change-over terminal B to the low level L. The short-circuiting transistor 
313 is thus turned off, and the voltage at the junction point J1 now rises 
to a higher level determined by the resistors 301, 302 and 303. The 
regulation target voltage is thus adjusted to the reduced predetermined 
level, 12.8 V. When the engine is idling, the output voltage of the AC 
generator 1 is thus regulated to the reduced target level, to reduce the 
load upon the engine and to improve the mileage per gallon of the fuel of 
the vehicle. 
Furthermore, when the battery terminal voltage detector terminal A is 
disconnected from the battery 5, the output voltage of the AC generator 1 
is regulated to a quick-charging voltage, 15.6 V, determined by the 
voltage at the junction point J2 between the voltage divider resistors 304 
and 305. The over-charging of the battery 5 is thereby prevented. 
It is noted that the three target voltage levels are determined by the 
resistance ratios of the resistors 301 through 305. 
As described above, the above conventional control device for a vehicular 
AC generator controls the output voltage of the AC generator 1 to the 
normal level, 14.4 V under the normal operation condition. When the engine 
is in the idling state, however, the target voltage is switched to the 
reduced level lower than the normal. The mileage of the vehicle is thereby 
improved. However, in the case of the above conventional control device, 
even when a rapid charging of the battery is needed, no measure can be 
taken other than raising the target output voltage of the AC generator 1 
from the reduced to the normal level. The quick charging capacity of the 
control device is thus insufficient. 
SUMMARY OF THE INVENTION 
It is therefore an object of this invention to provide a control device for 
a vehicular AC generator and a method of controlling the same by which the 
battery can be charged quickly when necessary. 
The above object is accomplished in accordance with the principle of this 
invention by a control device for controlling an output voltage of a 
vehicular AC generator which includes: first voltage detector circuit 
means, electrically coupled to an output of the AC generator, for 
outputting a first voltage level proportional to an output voltage of the 
AC generator; second voltage detector circuit means, electrically coupled 
to the output of the AC generator, for outputting a second voltage level 
proportional to the output voltage of the AC generator, the second voltage 
level being lower than the first voltage level output from the first 
voltage detector circuit means; voltage regulation means, coupled to the 
first and second voltage detector circuit means, for controlling a current 
supply to the coil of the AC generator thereby adjusting the output 
voltage of the AC generator to a target level, wherein the voltage 
regulation means regulates the current supply to the coil of the AC 
generator in response to a higher one of the first and second voltage 
levels output from the first and second voltage detector circuit means; 
target regulation voltage change-over means for selectively disabling the 
first voltage detector circuit means to reduce the first voltage level to 
a level substantially lower than the second level output from the second 
voltage detector circuit means such that the voltage regulation means 
controls the output voltage of the AC generator to a target level 
corresponding to the second voltage level output from the second voltage 
detector circuit means when the target regulation voltage change-over 
means disables the first voltage detector circuit means. 
Preferably, the first and second voltage detector circuit means consist of 
a first and a second voltage divider circuit, respectively, the first and 
second voltage divider circuit being electrically coupled to the output of 
the AC generator, the first and second voltage level being provided at a 
first junction point of the first voltage divider circuit and a second 
junction point of the second voltage divider circuit, respectively. It is 
further preferred that the voltage regulation means includes: reference 
voltage detector means coupled to the junction points of the voltage 
dividers of the first and second voltage detector circuit means, the 
reference voltage detector means being turned on when the higher one of 
the first and second voltage level exceeds a predetermined reference 
level; and a switching element coupled serially with the coil of the AC 
generator, the switching element being turned on and off as the switching 
element is turned off and on, respectively. 
Furthermore, the target regulation voltage change-over means may include: 
short-circuit means for short-circuiting the first junction point in 
response to a control signal representing a need for a quick charging of a 
battery electrically coupled to the AC generator. Alternatively, the 
target regulation voltage change-over means may include: disconnector 
means for electrically disconnecting the first voltage divider from the 
output of the AC generator in response to a control signal representing a 
need for a quick charging of a battery electrically coupled to the AC 
generator. 
Preferably, the first voltage detector circuit means is coupled to a 
terminal of a battery electrically coupled to the AC generator and the 
second voltage detector circuit means is coupled to an output of the AC 
generator. It is also preferred that the target regulation voltage 
change-over means includes means for changing the first voltage level 
output by the first voltage detector circuit means to two distinct levels 
in response to a first control signal. Further, the target regulation 
voltage change-over means may disable the first voltage detector circuit 
means in response to a second control signal, the target regulation 
voltage change-over means further including a logical circuit means for 
determining a consistency of the first and second control signals, wherein 
the target regulation voltage change-over means changes the first voltage 
level and disables the first voltage detector circuit on the basis of an 
judgment of the logical circuit means. 
The target regulation voltage change-over means may includes: means for 
generating at least two two-level signals; judgment means for determining 
a consistency of the two-level signals; and fail-safe circuit means for 
preventing the target regulation voltage change-over means from disabling 
the first voltage detector circuit means when the judgment means detects 
an inconsistency in the two-level signals.

In the drawings, like reference numerals represent like or corresponding 
parts or portions. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the 
accompanying drawings, the preferred embodiments of this invention are 
described. 
FIG. 1 is a circuit diagram showing a control device for a vehicular AC 
generator according to a first embodiment of this invention. In FIG. 1, 
the parts 1 through 3 and 5 through 9 are identical to those of FIG. 7. 
The engine control unit 4A, however, includes two transistors 401 and 402. 
The control transistor 401 is similar to the control transistor 401 of 
FIG. 7. Thus, the control transistor 401 is coupled across the target 
voltage change-over terminal B and the ground, the base thereof receiving 
the signal based on the information upon the idling state of the engine, 
etc. More specifically, the collector of the control transistor 401 is 
coupled to the target voltage change-over terminal B while the emitter 
thereof is grounded. On the other hand, the collector of the control 
transistor 402 is coupled to the junction point J1 through another target 
voltage change-over terminal C, the emitter thereof being grounded 
together with the emitter of the control transistor 401. 
As in the case of the circuit of FIG. 7, provided that the control 
transistor 402 is kept turned off, the output voltage of the AC generator 
1 is controlled to a normal and a reduced target voltage level, 14.4 V and 
12.8 V, in response to to the signal level at the target voltage 
change-over terminal B. In addition, the output voltage of the AC 
generator 1 is controlled to a third target level, 15.6 V, when the 
battery terminal voltage detector terminal A is disconnected. The 
operation under such circumstances is identical to tile operation of the 
circuit of FIG. 7. 
When, however, the control transistor 402 is turned on to reduce the 
voltage at the target voltage change-over terminal C to the low level L, 
the target regulation voltage is switched to the third or the 
quick-charging level, 15.6 V, even if the battery terminal voltage 
detector terminal A is not disconnected. Namely, assume, for example, that 
the discharge of the battery 5 is conspicuous during a time the vehicle is 
driven, and hence it is necessary to charge the battery 5 quickly, or 
that, for example, the engine is being decelerated and hence the AC 
generator 1 does not constitute an undue load upon the engine. Then, upon 
receiving an external signal from various sensors, the engine control unit 
4A raises the signal level at the base of the control transistor 402 and 
turns it on. Consequently, the voltage level at the target voltage 
change-over terminal C falls to the low level L. Namely, the junction 
point J1 between the voltage divider resistors 301 and 302 is grounded 
through the target voltage change-over terminal C and the control 
transistor 402, and the first voltage detector circuit consisting of the 
voltage divider resistors 301, 302, and 303 is disabled. Thus, the output 
voltage of the AC generator 1 is controlled to the third or quick-charging 
level determined by the voltage divider resistors 304 and 305 constituting 
the second voltage detector circuit. 
Namely, the ON/OFF of the controlling transistor 309 and the power 
transistor 310 is controlled by the ON/OFF of the zener diode 306. The 
zener diode 306 is turned on when the voltage at the cathodee (the 
terminal coupled to the diodes 307 and 308) rises above the break-down 
level thereof. Thus, the power transistor 310 is turned on to supply the 
field current to the field coil 102 when the voltage at the cathode of the 
zener diode 306 falls below the predetermined level (the break-down of the 
zener diode 306). The power transistor 310 is turned off to interrupt the 
field current to the field coil 102 when the voltage at the cathode of the 
zener diode 306 rises above the predetermined level. The cathodee of the 
zener diode 306 is coupled, through the diodes 307 and 308, respectively, 
to the junction point J1 and the junction point J2. Thus, the ON/OFF of 
the power transistor 310 is controlled in response to the higher one of 
the voltages at the junction point J1 and junction point J2. As described 
above, the voltage level at the junction point J1 is controlled to a first 
and a second level proportional to the voltage at the battery terminal 
voltage detector terminal A by turning on and off the short-circuiting 
transistor 313. Namely, when the short-circuiting transistor 313 is turned 
on to short-circuit the voltage divider resistor 303, proportion of the 
voltage at the junction point J1 with respect to the voltage at the 
battery terminal voltage detector terminal A is determined by the 
resistance ratio of the voltage divider resistors 301 and 302. When, on 
the other hand, the short-circuiting transistor 313 is turned off, the 
proportion of the voltage at the junction point J1 with respect to the 
voltage at the battery terminal voltage detector terminal A is determined 
by the resistance ratio of sum of the resistances of the voltage divider 
resistors 302 and 303 with respect to the resistance of the serial 
connection of the voltage divider resistors 301, 302, and 303. 
When the voltage at the junction point J1 is reduced to the ground level, 
the ON/OFF of the zener diode 306 and hence the controlling transistor 309 
and the power transistor 310 are determined exclusively by the voltage 
level at the junction point J2 between the voltage divider resistors 304 
and 305. Proportion of the voltage at the junction point J2 with respect 
to the voltage at the auxiliary output terminal 202 is determined by the 
resistance ratio of the resistance of the voltage divider resistor 305 
with respect to the sum of the resistances of the voltage divider 
resistors 304 and 305. The output voltage of the AC generator 1 is thus 
controlled to the third or the quick-charging level determined by the 
resistance ratio of the resistors 304 and 305. The battery 5 can thus be 
charged quickly when necessary. 
FIG. 2 is a circuit diagram showing a control device for a vehicular AC 
generator according to a second embodiment of this invention. The circuit 
of FIG. 2 is similar to that of FIG. 1, except for the engine control unit 
4B. The engine control unit 4B includes, in addition to the control 
transistor 401 coupled across the target voltage change-over terminal B 
and the ground, a control transistor 403 coupled in series with a resistor 
404, and an ON/OFF transistor 405 coupled in series with the first voltage 
detector circuit (the voltage divider resistors 301, 302, and 303) for 
connecting and disconnecting the voltage supply thereto from the battery 
5. The collector of the control transistor 403 is coupled to the base of 
the ON/OFF transistor 405 through the resistor 404, while the emitter of 
the control transistor 403 is coupled to the ground together with the 
emitter of the control transistor 401. The emitter of the ON/OFF 
transistor 405 is coupled to the positive terminal of the battery 5 
through the battery terminal voltage detector terminal A, while the 
collector thereof is coupled to a terminal of the first voltage detector 
circuit (i.e., to the terminal of the voltage divider resistor 301 
opposite to that coupled to the junction point J1). 
Usually, the control transistor 403 is kept turned on to ground the base of 
the ON/OFF transistor 405, and hence the ON/OFF transistor 405 is also 
kept turned on. Under such circumstances, the output voltage of the AC 
generator 1 is controlled to a normal and a reduced target voltage level, 
14.4 V and 12.8 V, in response to the voltage level at the target voltage 
change-over terminal B. This operation is similar to that of the circuits 
of FIGS. 1 and 7. The output voltage of the AC generator 1 is controlled 
to a third level, 15.6 V, when the battery terminal voltage detector 
terminal A is disconnected. 
Further, the quick charging operation of the circuit of FIG. 2 is similar 
to that of FIG. 1, except for some details as described below. Namely, 
assume that quick charging is necessary or the engine is decelerating 
under the condition where output voltage of the AC generator 1 is 
controlled to the normal or the reduced target level. Then, an external 
signal indicating the necessity of the quick charging or the deceleration 
of the engine is supplied from the various sensors to the engine control 
unit 4B. In response thereto, the engine control unit 4B turns off the 
control transistor 403 to raise voltage level at the base of the ON/OFF 
transistor 405. Thus, the ON/OFF transistor 405 is turned off, to 
disconnect the first voltage detector circuit (consisting of the resistors 
301, 302, and 303) electrically from positive terminal of the battery 5. 
Thus, the voltage level at the junction point J1 is reduced to the ground 
level through the resistors 302 and 303, and the ON/OFF of the zener diode 
306 and the controlling transistor 309 determined exclusively by the 
voltage level at the junction point J2 between the voltage divider 
resistors 304 and 305. The output voltage of the AC generator 1 is thus 
controlled to the third or the quick-charging level determined by the 
resistance ratio of the resistors 304 and 305. The battery 5 can thus be 
charged quickly when necessary. 
FIG. 3 is a circuit diagram showing a control device for a vehicular AC 
generator according to a third embodiment of this invention. The circuit 
of FIG. 3 is similar to that of FIG. 1 except for the following points. In 
addition to the parts 301 through 314 corresponding to those of FIG. 1, 
the voltage regulator 3A of FIG. 3 includes: a short-circuiting transistor 
315 coupled in parallel with the serial connection of the voltage divider 
resistors 302 and 303; and a resistor 316 coupled across the auxiliary 
output terminal 202 and the base of the short-circuiting transistor 315. 
Further, a fail-safe regulation voltage change-over circuit 10 including 
an OR gate 111 and a NOR gate 112 is inserted between the engine control 
unit 4A and the voltage regulator 3A. The bubbles at the terminals of the 
OR gate 111 and the NOR gate 112 indicate the logical negation (i.e., the 
inversion). The non-inverting input terminal and the inverting input 
terminal of the OR gate 111 are coupled to the collector of the control 
transistor 401 and the control transistor 402, respectively. The output 
terminal of the OR gate 111 is coupled to the base of the short-circuiting 
transistor 313 of the voltage regulator 3A. The inverting input terminal 
and the non-inverting input terminal of the NOR gate 112 are coupled to 
the collector of the control transistor 401 and the control transistor 
402, respectively. The output terminal of the NOR gate 112 is coupled to 
the base of the short-circuiting transistor 315 of the voltage regulator 
3A. It is assumed that the gates 111 and 112 are operated in accordance 
with the positive logic. Namely, the high level H corresponds the logical 
1 and the low level L corresponds to the logical 0. The output of the OR 
gate 111 corresponds to the OR of the signal level at the target voltage 
change-over terminal B and the negation of the signal level at the target 
voltage change-over terminal C. The output of the NOR gate 112, on the 
other hand, corresponds to the AND of the negation of the signal level at 
the target voltage change-over terminal B and the signal level at the 
target voltage change-over terminal C. The short-circuiting transistor 313 
and the short-circuiting transistor 315 are turned on and off in response 
to the outputs of the OR gate 111 and the NOR gate 112, respectively. 
The input to the base of the control transistor 401 represents the idling 
state of the engine, etc., and is rises to the high level H when the 
target level is to be reduced. On the other hand, the input to the base of 
the control transistor 402 represents the need for the quick charge of the 
battery 5. Thus, the two signals applied upon the base of the transistors 
401 and 402 are complementary in character and should not rise to the high 
level H simultaneously. The signals levels B and C at the terminals B and 
C coupled to the collector of the transistors 401 and 402 are the inverse 
of the signals applied on the base thereof, respectively. The output of 
the OR gate 111 is the logical OR of the signal B and the negation of the 
signal C. Thus, the output of the OR gate 111 is reduced to the low level 
L to turn off the short-circuiting transistor 313 (thereby adjusting the 
target voltage to the reduced level) if and only if the signal B is at the 
low level L and the signal C is at the high level H. On the other hand, 
the output of the NOR gate 112 is rises to the high level H to turn on the 
short-circuiting transistor 315 (thereby disabling the first voltage 
detector circuit and raising the target voltage to the third or the quick 
charging level), if and only if the signal B is at the high level H and 
the signal C is at the low level L. 
The relationship among the outputs B and C of the transistors 401 and 402, 
the outputs of the fail-safe regulation voltage change-over circuit 10, 
and the regulate voltage levels may be is shown in TABLE 1. 
TABLE 1 
______________________________________ 
In. In. 
of of 
B C B C OR111 NOR112 Reg. V. St. 
______________________________________ 
L(ON) L(ON) H H H L 14.4 V S1 
L(ON) H(OFF) H L L L 12.8 V S2 
H(OFF) L(ON) L H H H 15.6 V S3 
H(OFF) H(OFF) L L H L 14.4 V S4 
______________________________________ 
In the above TABLE 1, the states S1 through S4 are as follows. In state S1, 
both the transistors 401 and 402 are turned on to ground the terminals B 
and C. The engine control unit 4A is in failure. In state S2, the target 
voltage is adjusted to the reduced level and the load on the torque of the 
engine is minimized to reduce the fuel consumption. In state S3, the quick 
charging of the battery is performed. State S4 corresponds to the normal 
operation state of the engine, or the state where the terminals B and C 
are disconnected. 
Further, in the above TABLE 1, the leftmost columns B and C indicate the 
signal levels at the terminals B and C coupled to the collector of the 
transistors 401 and 402, respectively. The next two columns are the 
inversions of the signal levels at the terminals B and C, and the columns 
OR 111 and NOR 112 indicate the output signal levels of the OR gate 111 
and the NOR gate 112, respectively. 
Normally, the control transistor 401 and the control transistor 402 of the 
engine control unit 4A are turned off (state S4 in TABLE 1). The output of 
the OR gate 111 is thus at the high level H, and hence the 
short-circuiting transistor 313 is turned on. On the other hand, the 
output of the NOR gate 112 is at the low level L, and hence the 
short-circuiting transistor 315 is turned off. Thus, among the voltage 
divider resistors 301, 302, and 303, only the voltage divider resistor 303 
is short-circuited. The output voltage of the AC generator 1 is thus 
controlled to the normal target level 14.4 V determined by the resistance 
ratio of the resistors 301 and 302. 
When, on the other hand, the discharge of the battery 5 is conspicuous and 
the battery 5 must be charged quickly, or when the engine is decelerating, 
the control transistor 402 is turned on in response to the external signal 
(state S3 in TABLE 1). The output of the NOR gate 112 of the fail-safe 
regulation voltage change-over circuit 10 thus rises to the high level H 
to turn on the short-circuiting transistor 315. The junction point J1 is 
thus grounded through the short-circuiting transistor 315. Hence the 
ON/OFF of the zener diode 306 and the controlling transistor 309 is 
determined exclusively by the voltage level at the junction point J2 
between the voltage divider resistors 304 and 305. The output voltage of 
the AC generator 1 is thus controlled to the third or the quick-charging 
level 15.6 V determined by the resistance ratio of the resistors 304 and 
305. The battery 5 can thus be charged quickly. 
Further, when, for example, the engine is in the idling state and the load 
on the torque of the engine due to the AC generator 1 is to be reduced to 
improve the mileage per gallon of the fuel of the vehicle, the control 
transistor 401 is turned on and the control transistor 402 is turned off, 
in response to external signals applied upon the bases thereof (state S2 
in TABLE 1). The outputs of the OR gate 111 and the NOR gate 112 of the 
fail-safe regulation voltage change-over circuit 10 are both reduced to 
the low level L. The short-circuiting transistors 313 and 315 are thus 
both turned off. The output voltage of the AC generator 1 is controlled to 
the reduced target level, 12.8 V, determined by the voltage level at the 
junction point J1. Proportion the voltage level at the junction point J1 
with respect to the voltage at the battery terminal voltage detector 
terminal A is determined by the resistance ratio of: the serial connection 
of the resistors 302 and 303; and the serial connection of the resistors 
301 through 303. 
When both the target voltage change-over terminal B and C are disconnected 
(state S4) or when the engine control unit 4A is in failure to turn on 
both the control transistors 401 and 402 and the terminals B and C are 
both grounded (state S1), the output of the OR gate 111 is at the high 
level H while the output of the NOR gate 112 is at the low level L. Thus, 
the short-circuiting transistor 313 is turned on while the 
short-circuiting transistor 315 is turned off. As a result, the output 
voltage of the AC generator 1 is controlled to the normal target level 
14.4 V. The fail-safe regulation voltage change-over circuit 10 thus 
provides the fail-safe capacity. 
FIG. 4 is a circuit diagram showing a control device for a vehicular AC 
generator according to a fourth embodiment of this invention. The circuit 
of FIG. 4 is similar partly to that of FIG. 2 and partly to that of FIG. 
3. Namely, a fail-safe regulation voltage change-over circuit 10 similar 
to that of FIG. 3 is inserted in the middle portion of the engine control 
unit 4B of FIG. 2. The voltage regulator 3B includes: a resistor 317 
corresponding to the resistor 404 of FIG. 2; and an ON/OFF transistor 318 
corresponding to the ON/OFF transistor 405 of FIG. 2. On the other hand, 
the engine control unit 4C does not include the resistor 404 and the 
ON/OFF transistor 405 of FIG. 2. The parts 1, 2, 5 through 10 are similar 
to those of FIG. 2. 
As in the case of the circuit of FIG. 3, the logic of gates 111 and 112 are 
in accordance with the positive logic. Namely, the high level H 
corresponds the logical 1 and the low level L corresponds to the logical 
0. The output of the OR gate 111 corresponds to the OR of the signal level 
at the target voltage change-over terminal B and the negation of the 
signal level at the target voltage change-over terminal D. The output of 
the NOR gate 112, on the other hand, corresponds to the AND of the 
negation of the signal level at the target voltage change-over terminal B 
and the signal level at the target voltage change-over terminal D. The 
short-circuiting transistor 313 and the ON/OFF transistor 318 are turned 
on and off in response to the outputs of the OR gate 111 and the NOR gate 
112, respectively. Thus, the relationship among the outputs B and D of the 
transistors 401 and 403, the outputs of the fail-safe regulation voltage 
change-over circuit 10, and the regulate voltage levels may be summarized 
as shown in TABLE 2. 
TABLE 2 
______________________________________ 
In. In. 
of of 
B D B D OR111 NOR112 Reg. V. St. 
______________________________________ 
L(ON) L(ON) H H H L 14.4 V S1 
L(ON) H(OFF) H L L L 12.8 V S2 
H(OFF) L(ON) L H H H 15.6 V S3 
H(OFF) H(OFF) L L H L 14.4 V S4 
______________________________________ 
In the above TABLE 2, the states S1 through S4 are similar to those in 
TABLE 1. In state S1, both the transistors 401 and 403 are turned on to 
ground the terminals B and D. The engine control unit 4C is in failure. In 
state S2, the target level is reduced and the load on the torque of the 
engine is minimized to reduce the fuel consumption. In state S3, the quick 
charging of the battery is effected. State S4 corresponds to the normal 
operation state of the engine, or the state where the terminals B and D 
are disconnected. 
Further, in the above TABLE 2, the leftmost columns B and D indicate the 
signal levels at the terminals B and D coupled to the collectors of the 
transistors 401 and 403, respectively. The next two columns are the 
inversions of the signal levels at the terminals B and D, and the columns 
OR 111 and NOR 112 indicate the output signal levels of the OR gate 111 
and the NOR gate 112, respectively. 
Normally, the control transistor 401 and the control transistor 403 of the 
engine control unit 4C are turned off (state S4 in TABLE 2). The output of 
the OR gate 111 is thus at the high level H, and hence the 
short-circuiting transistor 313 is turned on. Thus, the voltage divider 
resistor 303 is short-circuited. On the other hand, the output of the NOR 
gate 112 is at the low level L, and hence the ON/OFF transistor 318 is 
turned on. The output voltage of the AC generator 1 is thus controlled to 
the normal target level 14.4 V determined by the resistance ratio of the 
resistors 301 and 302. 
When, on the other hand, the discharge of the battery 5 is conspicuous and 
the battery 5 must be charged quickly, or when the engine is decelerating, 
the control transistor 403 is turned on in response to the external signal 
applied upon the base thereof (state S3 in TABLE 2). The output of the NOR 
gate 112 of the fail-safe regulation voltage change-over circuit 10 thus 
rises to the high level H to turn off the ON/OFF transistor 318. The 
terminal of the battery 5 is thus electrically disconnected from the first 
voltage detector circuit consisting of the voltage divider resistors 301, 
302, and 303. Hence the ON/OFF of the zener diode 306 and the controlling 
transistor 309 is determined exclusively by the voltage level at the 
junction point J2 between the voltage divider resistors 304 and 305. The 
output voltage of the AC generator 1 is thus controlled to the 
quick-charging level 15.6 V determined by the resistance ratio of the 
resistors 304 and 305. The battery 5 can thus be charged quickly. 
Further, when, for example, the engine is in the idling state and the load 
on the torque of the engine due to the AC generator 1 is to be reduced to 
improve the mileage per gallon of the fuel of the vehicle, the transistors 
401 is turned on and the control transistor 403 is turned, respectively, 
in response to external signals (state S2 in TABLE 2). The outputs of the 
OR gate 111 and the NOR gate 112 of the fail-safe regulation voltage 
change-over circuit 10 are both reduced to the low level L. The 
short-circuiting transistor 313 is thus turned off and the ON/OFF 
transistor 318 is turned on. The output voltage of the AC generator 1 is 
thus controlled to the reduced target level, 12.8 V, determined by the 
voltage level at the junction point J1. Under this circumstance, the 
proportion of the voltage level at the junction point J1 with respect to 
the voltage at the battery terminal voltage detector terminal A is 
determined by the resistance ratio of the serial connection of the 
resistors 302 and 303 with respect to the serial connection of the 
resistors 301 through 303. 
When both the target voltage change-over terminal B and D are disconnected 
(state S4) or when the engine control unit 4C is in failure to turn on the 
control transistors 401 and 403, and the terminals B and D are both 
grounded (state S1), the output of the OR gate 111 is at the high level H 
while the output of the NOR gate 112 is at the low level L. Thus, the 
short-circuiting transistor 313 and the ON/OFF transistor 318 are both 
turned on. As a result, the output voltage of the AC generator 1 is 
controlled to the normal target level 14, 4 V. Thus, the fail-safe 
regulation voltage change-over circuit 10 provides the fail-safe capacity. 
FIG. 5 is a circuit diagram showing a control device for a vehicular AC 
generator according to a fifth embodiment of this invention. The parts 1, 
2, and 5 through 9 are identical to those of FIG. 1. The voltage regulator 
3C is distinguished from the voltage regulator 3 of FIG. 1 in that the 
voltage regulator 3C does not include the voltage divider resistor 303, 
the short-circuiting transistor 313, and the resistor 314 of FIG. 1. A 
fail-safe regulation voltage change-over circuit 10A consist of a single 
OR gate 113. The engine control unit 4D includes a control transistor 406 
and a resistor 407. The emitter of the control transistor 406 is grounded. 
The collector of the control transistor 406 is coupled to the 
non-inverting input terminal of the OR gate 113 through the target voltage 
change-over terminal C1. The resistor 407 is coupled across the inverting 
input terminal of the OR gate 113 and the base of the control transistor 
406. The output of the OR gate 113 of the fail-safe regulation voltage 
change-over circuit 10A is coupled to the junction point J1 between the 
voltage divider resistors 301 and 302. 
In the case of the circuit of FIG. 5, the output voltage of the AC 
generator 1 is controlled to two target levels: a reduced level, 14.4 V 
and a normal level, 15.6 V. The reduced target level is determined by the 
resistance ratio of the voltage divider resistors 301 and 302. The normal 
target level is determined by the resistance ratio of the voltage divider 
resistors 304 and 305. When the output of the OR gate 113 is at the high 
level H, the output voltage of the AC generator 1 is controlled to the 
normal level determined by the voltage divider resistors 301 and 302, 
When, on the other hand, the output of the OR gate 113 is at the low level 
L, the output voltage of the AC generator 1 is controlled to the second 
level determined by the voltage divider resistors 304 and 305. 
The input signal applied via the resistor 407 to the base of the control 
transistor 406 represents the need for the quick charging of the battery 
5. This signal is supplied to the inverting input terminal of the OR gate 
113 through the target voltage change-over terminal C2. If the operation 
of the control transistor 406 is normal, the target voltage change-over 
terminal C1 is grounded through the control transistor 406 only when the 
signal at the C2 is at the high level. The output of the OR gate 113 is 
the logical OR of C1 and the negation of C2. Thus the output of the OR 
gate 113 is at the low level L if and only if the signal C2 representing 
the need for quick charging rises to the high level H and, in response 
thereto, the control transistor 406 is turned on. The low level L output 
of the OR gate 113 disables the first voltage detector circuit consisting 
of the voltage divider resistors 301 and 302, such that the voltage at the 
junction point J2 provided by the second voltage detector circuit 
consisting of the voltage divider resistors 304 and 305 determines the 
ON/OFF of the zener diode 306, and hence the target level of the output 
voltage of the AC generator 1. The OR gate 113 of the fail-safe regulation 
voltage change-over circuit 10A thus provides the fail-safe function. 
The following TABLE 3 shows the relationship among: the input signal to the 
base of the control transistor 406 (the rightmost column Tr406); the 
voltage levels at the target voltage change-over terminal C1 and C2; the 
inversion of the C2; the output of the OR gate 113; the target regulation 
voltage, and the corresponding state. 
TABLE 3 
______________________________________ 
Tr406 C1 C2 Inv. of C2 
OR 113 Reg. Volt 
State 
______________________________________ 
grounded 
L L H H 14.4 V S1 
open H H L H 14.4 V S2 
H(ON) L H L L 15.6 V S3 
L(OFF) H L H H 14.4 V S4 
______________________________________ 
In the normal state, or when the engine control unit 4D fails (state S4), 
input signal to the base of the control transistor 406 of the engine 
control unit 4D is at the low level L, and hence the control transistor 
406 is turned off. Thus, the input signal C1 to the non-inverting input 
terminal of the OR gate 113, the input signal C2 to the inverting input 
terminal thereof, and the inversion of the signal C2 are at the high level 
H, at the low level L, and at the high level H, as shown in the TABLE 3. 
The output of the OR gate 113 is thus at the high level H, and the output 
voltage of the AC generator i is controlled to the normal level determined 
by the resistance ratio of the voltage divider resistors 301 and 302. 
When on the other hand, the discharge of the battery 5 is conspicuous and 
the battery 5 must be charged quickly, or when the engine is decelerating, 
the input signal to the base of the control transistor 406 is raised to 
the high level H, thereby turning on the control transistor 406. The 
output of the OR gate 113 thus falls to the low level L, to reduce the 
voltage level at the junction point J1 substantially to the ground level. 
The first voltage detector circuit consisting of the voltage divider 
resistors 301 and 302 is thus disabled and can no longer detect the 
terminal voltage of the battery 5. The output voltage of the AC generator 
1 is now controlled to the quick charging level determined by the 
resistance ratio of the voltage divider resistors 304 and 305, coupled to 
the auxiliary output terminal 202 of the AC generator 1. The battery 5 is 
thus quickly charged. 
When the target voltage change-over terminal C1 and C2 are opened or 
disconnected (state S2 in TABLE 3), or when target voltage change-over 
terminal C1 and the C2 are grounded (state S1), the output of the OR gate 
113 is kept at the high level H, and the voltage at the junction point J1 
is proportional to the voltage at the battery terminal voltage detector 
terminal A, the proportionality factor being determined by the resistance 
ratio of the voltage divider resistor 302 with respect to the sum of the 
resistors 301 and 302. The output voltage of the AC generator 1 is thus 
controlled to the normal level based on the terminal voltage level of the 
battery 5. 
FIG. 6 is a circuit diagram showing a control device for a vehicular AC 
generator according to a sixth embodiment of this invention. In FIG. 6, 
the parts 1, 2, and 5 through 9 are identical to those of FIG. 1. The 
engine control unit 4D, on the other hand, is identical to that of FIG. 5. 
The voltage regulator 3D of FIG. 6 is distinguished from the voltage 
regulator 3B of FIG. 4 in that the voltage regulator 3D does not include 
the short-circuiting transistor 313 and the resistor 314. 
A fail-safe regulation voltage change-over circuit 10B consists of a single 
NOR gate 114. The engine control unit 4D includes a control transistor 406 
and a resistor 407. The emitter of the control transistor 406 is grounded. 
The collector of the control transistor 406 is coupled to the 
non-inverting input terminal of the NOR gate 114 through the target 
voltage change-over terminal C1. The resistor 407 is coupled across the 
inverting input terminal of the NOR gate 114 and the base of the control 
transistor 406. The output of the NOR gate 114 of the fail-safe regulation 
voltage change-over circuit 10B is coupled to the base of the ON/OFF 
transistor 318 through the resistor 317. 
The operation of the circuit of FIG. 6 is similar to that of the circuit of 
FIG. 5. However, in response to the high level H output of the NOR gate 
114, the ON/OFF transistor 318 is turned off to disconnect the terminal of 
the battery 5 from the first voltage detector circuit consisting of the 
resistors 301 and 302. The output of the NOR gate 114 is the logical AND 
of the negation of the signal C1 and the signal C2. Thus the output of the 
NOR gate 114 rises to the high level H to disable the first voltage 
divider resistors 301 and 302 if and only if the signal representing the 
need for quick charging is applied on the base of the control transistor 
406 and, further, the control transistor 406 is turned on in response 
thereto. 
The following TABLE 4 shows the relationship among: the input signal to the 
base of the control transistor 406 (the rightmost column Tr406); the 
voltage levels at the target voltage change-over terminal C1 and C2; the 
inversion of the C2; the output of the NOR gate 114; the target regulation 
voltage, and the corresponding states. 
TABLE 4 
______________________________________ 
Tr406 C1 C2 Inv. of C2 
OR 114 Reg. Volt 
State 
______________________________________ 
grounded 
L L H L 14.4 V S1 
open H H L L 14.4 V S2 
H(ON) L H L H 15.6 V S3 
L(OFF) H L H L 14.4 V S4 
______________________________________ 
In the normal state, or when the engine control unit 4D fails (state S4), 
input signal to the base of the control transistor 406 of the engine 
control unit 4D is at the low level L, and hence the control transistor 
406 is turned off. Thus, the input signal C1 to the non-inverting input 
terminal of the NOR gate 114, the input signal C2 to the inverting input 
terminal thereof, and the inversion of the signal C2 are at the high level 
H, at the low level L, and at the high level H, as shown in the TABLE 4. 
The output of the NOR gate 114 is thus at the low level L, and the ON/OFF 
transistor 318 is turned on. The output voltage of the AC generator 1 is 
controlled to the normal level determined by the resistance ratio of the 
voltage divider resistors 301 and 302. 
When on the other hand, the discharge of the battery 5 is conspicuous and 
tile battery 5 must be charged quickly, or when the engine is 
decelerating, the input signal to the base of the control transistor 406 
is raised to the high level H, thereby turning on the control transistor 
406. The output of the NOR gate 114 thus rises to the high level H, to 
turn off the ON/OFF transistor 318 and disconnect electrically the first 
voltage divider resistors 301 and 302 from the battery terminal voltage 
detector terminal A coupled to the battery 5. The first voltage detector 
circuit consisting of the voltage divider resistors 301 and 302 is thus 
disabled and can no longer detect the terminal voltage of the battery 5. 
The output voltage of the AC generator 1 is now controlled to the quick 
charging level determined by the resistance ratio of the voltage divider 
resistors 304 and 305, coupled to the auxiliary output terminal 202 of the 
AC generator 1. The battery 5 is thus quickly charged. 
When the target voltage change-over terminal C1 and C2 are opened or 
disconnected (state S2 in TABLE 4), or when target voltage change-over 
terminal C1 and the C2 are grounded (state S1), the output of the NOR gate 
114 is kept at the low level L, and the voltage at the junction point J1 
is proportional to the voltage at the battery terminal voltage detector 
terminal A, the proportionality factor being determined by the resistance 
ratio of the voltage divider resistor 302 with respect to the sum of the 
resistors 301 and 302. The output voltage of the AC generator 1 is thus 
controlled to the normal level based on the terminal voltage level of the 
battery 5.