Electricity: single generator systems – Automatic control of generator or driving means – Speed or frequency of generator
Reexamination Certificate
2000-03-29
2001-08-07
Mullins, Burton S. (Department: 2834)
Electricity: single generator systems
Automatic control of generator or driving means
Speed or frequency of generator
C322S025000
Reexamination Certificate
active
06271649
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a control apparatus for a vehicle-onboard AC generator.
BACKGROUND ART
FIG. 3
is a circuit diagram showing a structure of a control apparatus for a conventional vehicle AC generator which is disclosed, for example, in Japanese Utility Model Registration Application No. 34900, 1989.
Operation of the conventional apparatus will be described by reference to this circuit diagram.
When a key switch
8
is closed upon starting of an engine, a base current flows to a power transistor
308
from a battery
7
by way of the key switch
8
, a reverse-current blocking diode
11
, a resistor
12
for initial excitation and a base resistor
309
of the power transistor
308
, as a result of which the power transistor
308
is turned on, i.e., turned to a conducting state.
When the power transistor
308
is turned on, a field current flows to a field coil
102
from the battery
7
by way of the key switch
8
, the reverse-current blocking diode
11
, the resistor
12
for initial excitation, the field coil
102
and the power transistor
308
, whereby an electric generator
1
is set to the state capable of generating electricity.
When engine operation is started, the generator
1
is rotationally driven, whereby generation of electricity is started. In this state, a divided voltage obtained by dividing a generated voltage of the generator
1
with voltage dividing resistors
301
and
302
is compared with a reference voltage derived from voltage division of a constant voltage supplied from a constant-voltage power source A with voltage dividing resistors
303
and
304
by means of a comparator
305
of a voltage regulator
3
. When the divided voltage resulting from the division of the voltage generated by the generator
1
is equal to or lower than the preset reference voltage value resulting from the voltage division of the voltage of the constant-voltage power source A, the comparator
305
assumes a conducting or on-state from a non-conducting or off-state, which results in that a transistor
306
is turned off from the conducting state or on-state.
When the power transistor
308
is turned on, then the field current tends to flow through the field coil
102
. However, because the comparator
305
is in the conducting state, the voltage smoothed by a smoothing circuit
4
is discharged to a discharging resistor
405
from a capacitor
404
.
In this conjunction, it is noted that the discharging time constant determined by the capacitor
404
and the discharging resistor
405
is large. Consequently, the output of a comparator
601
assumes on- and off-state periodically at a predetermined interval until it is detected that the generated voltage of the generator
1
reaches a predetermined value through comparison of a triangular waveform voltage outputted from a triangular waveform generator
5
with the discharge voltage of the smoothing circuit
4
.
As a result of this, a transistor
602
is turned on and off in response to the output of the comparator
601
, whereby the power transistor
308
is turned on and off with a predetermined duty ratio to thereby control the field current flowing through the field coil
102
such that generation of the output current of the generator
1
is retarded.
When the output current of the generator
1
has reached a current level equivalent to a load current of a vehicle electric load
9
with the generated voltage of the generator
1
reaching a predetermined value, the output of the comparator
601
assumes on/off levels with such a duty ratio to produce the on/off control of the field current demanded for the output current of the generator
1
.
The transistor
602
is turned on/off in response to the output of the comparator
601
to thereby control the power transistor
308
and hence the field current flowing through the field coil
102
, as a result of which the generated voltage of the generator
1
is regulated to the predetermined value.
As is apparent from the above, in the case of the conventional apparatus, the resistance value of the charging resistor
402
for the capacitor
404
constituting a part of the smoothing circuit
4
is selected to be small while that of the discharging resistor
405
is selected large. Thus, the value of the time constant for electric charging is set short or small (e.g. not greater than 0.5 sec.), whereas the time constant for electric discharge is set long or large (e.g. not smaller than 0.5 sec.), whereby such operation is ordinarily realized that the output of the comparator
601
becomes substantially equivalent to the output of the comparator
305
which constitutes a part of the voltage detecting circuit.
FIG. 4
shows changes in the generator output voltage waveform in the state where the vehicle-onboard electric load (e.g. headlight) is turned on in response to the turning-on or closing of a switch
10
and changes in the conducting rate of the power transistor
308
in consideration of the discharge characteristic.
In the conventional apparatus such as described above, the charging time constant of the smoothing circuit is set short while the discharging time constant is set long, wherein each of the time constants mentioned above is always set to a fixed value. Consequently, the ration of conduction of the power transistor
308
increases progressively or gradually in dependence on the magnitude of the discharging time constant which is effective when the electric load
9
is turned on and finally reduces a predetermined conducting rate after lapse of a predetermined time. Thus, the generator output voltage falls once temporarily to &Dgr;V
1
upon turning-on electric energizing of the electric load
9
and thereafter gradually increases in conformance with the conducting rate of the power transistor
308
.
The conventional apparatus is certainly effective for minimizing a decrease of the engine rotation number (rpm) by gradually increasing the output power of the generator when the engine, by which the generator is driven, is in the idling state. However, because the operation of gradually increasing the generator output is effective equally in a high-speed rotation state where the engine output allows a margin, the output voltage of the generator always falls every time the electric load is turned on, which in turn brings about variation in the output states of the loads already set to the on-state such as variation in luminance of lamps installed on instrumentation panels, room lamps, etc. which is of course uncomfortable for the driver, giving rise to a problem.
DISCLOSURE OF THE INVENTION
The present invention has been made with a view to solving the problem as mentioned above, and thus as object of the present invention is to provide a control apparatus for a vehicle AC generator which is capable of lengthening a time period during which the field duty (i.e., duty ratio of the field current) gradually increases, to thereby minimize a reduction of the engine rotation number upon turning-on of an electric load, while shortening a time period during which the field duty (i.e., duty ratio of the field current) is gradually increased, to thereby minimize reduction of the generator output voltage when the electric load is turned on.
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Mitsubishi Denki & Kabushiki Kaisha
Mullins Burton S.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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