Electricity: battery or capacitor charging or discharging – Battery or cell charging – Time control
Reexamination Certificate
2001-10-22
2003-02-18
Toatley, Jr., Gregory J. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell charging
Time control
82
Reexamination Certificate
active
06522105
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to a battery charging apparatus for charging a high-voltage battery and a low-voltage battery which are installed in, for instance, a hybrid vehicle.
2. Related Art
With a view to environmental preservation and reduction of energy consumption, attention is recently being given to a hybrid vehicle which is fitted with a power system combining an engine and an electric motor. In this hybrid vehicle, the output of the engine is efficiently supplemented in various ways, e.g. the electric motor supplements the output of the engine when accelerating, and the battery is charged by deceleration regeneration and the like when decelerating. The hybrid vehicle is fitted with a high-voltage (e.g. 36 V) battery for supplying electrical energy to the electric motor for driving, and a low-voltage (e.g. 12 V) battery for supplying power to various types of supplementary devices, and a battery charging apparatus for charging both batteries having different voltage specifications is required.
This type of conventional battery charging apparatus will be explained using
FIG. 1
, described later.
The field-effect transistors Q
4
to Q
6
shown in
FIG. 1
comprise one of the characteristic features of the battery charging apparatus according to the present invention, described below. In the conventional battery charging apparatus explained below, a rectifier (diode) is used instead of the field-effect transistors; together with diodes D
1
to D
3
and diodes D
4
to D
6
, this diode forms an all-wave rectifier.
In
FIG. 1
, the ac output of a generator ACG is distributed via a system (open regulator) comprising the diodes D
1
to D
3
and field-effect transistors Q
1
to Q
3
to a low-voltage system battery BL, and in addition, is distributed via the diodes D
4
to D
6
to a high-voltage system battery BH. The ac output of the generator ACG is distributed by controlling the conduction of the field-effect transistors Q
1
to Q
3
, provided in the low-voltage system, in synchronism with the phases of the ac output (U-phase, V-phase, and W-phase) of the generator ACG. That is, as shown in
FIG. 4
, during the period P
1
when the U-phase voltage generated by the generator ACG is high, the field-effect transistor Q
1
switches on and becomes conductive, whereby the U-phase output is supplied via the field-effect transistor Q
1
to the low-voltage system battery BL.
At this time, the U-phase voltage decreases as it is pulled by the terminal voltage of the low-voltage system battery BL, but the high-voltage system battery BL does not discharge since the rectifer D
4
in the high-voltage system is reverse-biased. Thereafter, when the U-phase is inverted in period P
2
and the output voltage decreases, the diode D
1
becomes reverse-biased. In the conventional apparatus, the battery BL is recharged via an unillustrated diode corresponding to the field-effect transistor Q
4
.
In period P
3
, during which the U-phase voltage increases, the field-effect transistor Q
1
switches off and becomes nonconductive. This shuts off the power supply to the low-voltage system battery BL, increasing the U-phase voltage from the generator ACG. As a result, the diode D
4
becomes sequence-biased, and the power output from the generator ACG is supplied via the diode D
4
to the high-voltage system battery BH.
The battery is charged by the V-phase and W-phase outputs in the same manner.
By controlling the field-effect transistors Q
1
to Q
3
on the low voltage side in this way, it is possible to supplementarily charge the low-voltage and high-voltage systems, enabling both batteries to be charged by a single generator.
Incidentally, the distribution of the phase output of the generator and the like for charging the low-voltage and high-voltage systems is determined as appropriate in accordance with the charge status of the batteries in these systems.
The torque required to rotate the input axis of the generator during charging (hereinafter abbreviated as “input torque”) is determined by the output voltage and output current of the generator, and there is a correlative relationship between the input torque of the generator and the power consumed in charging. When the output voltage of the generator is constant, the greater the charge current, the greater the input torque of the generator; when the output current of the generator is constant, the greater the charge voltage, the greater the input torque of the generator. Applying the rotatory power (e.g. rotary output of an engine), which is generated by the input torque, to the input axis of the generator from the outside generates power comprising electrical energy. Therefore, ideally, when the rotatory power applied to the input axis of the generator is constant, the output voltage and output current should be set so that the output power is constant.
However, in reality, even when a constant rotatory power is applied to the generator, fluctuation in the load changes the output voltage, and consequently, due to the characteristics of the generator, the output current cannot make the output power constant and the output power becomes liable to change. For this reason, as shown in
FIG. 4
, the size of the input torque T in the period P
1
, when the low-voltage side battery is being charged, is different from that in the period P
3
, when the high-voltage side battery is being charged, and the input torque T fluctuates when the output of the generator is distributed to the batteries. As a consequence, the generator produces noise and vibrates, adversely affecting its quietness and durability.
According to the conventional apparatus described above, when for example switching from charging the low-voltage system battery to charging the high-voltage system battery, the output current waveform of the generator becomes distorted. When the current waveform is distorted, the torque required to rotate the input axis of the generator (hereinafter abbreviated as “input torque”) fluctuates. The input torque is determined by the output voltage and output current of the generator, and power comprising electrical energy is generated by applying the rotatory power (e.g. rotary output of an engine), which is generated by the input torque, to the input axis of the generator. Therefore, when the waveform of the output current becomes distorted during charging, the input torque fluctuates, whereby the generator produces noise and vibrates, adversely affecting its quietness and durability.
In
FIG. 1
, the input axis of the generator ACG is coupled to the output axis of the engine, and the input axis of the generator ACG is rotated by the output of the engine, generating ac output.
According to one method for charging, when the output voltage of the generator is insufficient due to the low number of rotations of the engine, the output of the generator is boosted to obtain the voltage required for charging, and, when the number of rotations of the engine has increased, boosting stops and the battery is charged directly. However, as explained below, according to the battery charging apparatus which uses this type of charging method, when starting and stopping the boosting, the torque required to rotate the input axis of the generator (hereinafter abbreviated as “input torque”) abruptly changes, creating allophones.
The mechanism which generates this type of torque fluctuation will be explained.
FIG. 13
shows characteristics of the input torque and output current (charge current) of the generator with respect to the number of rotations of the input axis. The number of rotations of the generator varies in accordance with the number of rotations of the engine. As shown in
FIG. 13
, when the output of the generator is increased before charging (boost charging), the voltage required for charging the battery is maintained in the region of low rotation, and the output current of the generator is consumed as charge current, generating input torque in the generator. As the number of rotations increases, the output current of the gener
Fujiwara Tadashi
Kaneko Masaharu
Kodama Koji
Kubo Kazuyuki
Arent Fox Kintner & Plotkin & Kahn, PLLC
Shindengen Electric Manufacturing Co. Ltd.
Toatley , Jr. Gregory J.
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