Hybrid vehicle and control method therefor

Details Hybrid vehicle and control method therefor Hybrid vehicle and control method therefor

2002-12-09

2003-10-07

Tso, Edward H. (Department: 2838)

Electricity: battery or capacitor charging or discharging

One cell or battery charges another

Vehicle battery charging

C320S150000, C307S010100

Reexamination Certificate

active

06630810

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hybrid vehicle comprising a vehicle driving engine, and a motor, which can drive the engine or generate electric power. In particular, the present invention relates to a hybrid vehicle comprising a control device for controlling a DC/DC converter, used for supplying electric power to auxiliary machines of the vehicle in response to energy generated by the motor.
2. Description of the Related Art
Conventionally, various vehicles such as an EV (Electric Vehicle) or an HEV (Hybrid Electric Vehicle) acquire electric energy by rotating a three-phase alternating current motor for generating the three phase alternating current electric power by use of an inverter deriving the electric energy from a high voltage main battery (electric power storage cell). In, addition, vehicles are provided with a DC/DC converter for converting a high voltage (for example, 144V) of the main battery to 12V for supplying electric power to a control computer actuated by 12V or auxiliary machines (such as the cooling fan, air conditioner, fuel pump and so on), and an auxiliary battery for storing an electric power obtained by converting by a DC/DC converter.
However, in the above-described conventional vehicles, the DC/DC converter is always operated deriving energy from the main battery in order to actuate the auxiliary machines, and a problem arises in that the energy of the main battery cannot always be sufficiently utilized for rotating the motor for driving. In order to solve such a problem, a control device has been proposed in Japanese Unexamined Patent Application, First Publication No. Hei 7-79505. This control device comprises a vehicle travel detect signal generating device for generating a vehicle travel detect signal while the vehicle travels (vehicle is driving) and when the vehicle travels, the control device sets the output voltage of the DC/DC converter at a lower voltage (a voltage that cannot charge the auxiliary battery) which is lower than the output voltage at the time of vehicle stop. Consequently, a part of the electric power supplied to the DC/DC converter at the vehicle stop can be used for rotating the motor during the vehicle travels.
However, since the conventional control device merely distributes the electric power of the main battery, the conventional control device cannot cope with the output voltage drop of the battery caused by the rush current flowing in the auxiliary machines at the time of starting the DC/DC converter.
The above effect will be explained with reference to FIG.
6
. As shown by line b in
FIG. 6
, for example, when the DC/DC converter is actuated, the output current of the DC/DC converter is rapidly increased due to the rush current to the auxiliary machines, as shown by line d in FIG.
6
. The internal resistance of the main battery is normally in a range of 0.1 to 0.3 &OHgr;, but the resistance increases at a level of 10 &OHgr; when the main battery is placed in a low temperature atmosphere. In addition, when a current flows rapidly in the DC/DC converter when the internal resistance is high, the output voltage of the main battery may cause a large voltage drop, as shown by line e in FIG.
6
.
As a result, depending upon the increased internal resistance, the output voltage of the main battery may be reduced to below the lower limit voltage, shown by line e in
FIG. 6
, of the main battery (power storage cell). Excessive reduction of the output voltage causes an overdischarge of the battery, degradation of the battery, and deterioration of the service life of the battery. The control battery voltage, shown by line c in
FIG. 6
, represents the voltage applied to the auxiliary battery. As shown by line d in
FIG. 6
, even when the output current from the DC/DC converter increases rapidly, since the rapid increase is caused by the rush current, the voltage applied to the auxiliary battery increases gradually.
In order to solve the aforementioned problem, a technique to prevent the excessive voltage drop of the main battery has been proposed in the hybrid vehicle comprising a travel driving engine and a motor which drives the engine or which can generate electric energy. The technique to prevent the excessive voltage drop in the hybrid vehicle is carried out such that by using the motor as a motor generator, the discharge from the main battery is reduced to be as low as possible by controlling generation of the motor-generator driven by the engine in response to the input current to the DC/DC converter.
However, the above-described technique encounters a limit. This is, associated with the late response of the secondary air valve used for stabilizing the engine rotation when the engine is in the idle state, even when it is desired to compensate for the electric energy consumed by the DC/DC converter by one time generation by the motor generator, the engine output does not follow the increase of the generation torque of the motor generator, which results in causing the engine encountering stall or rotation fluctuation. When the generation torque of the motor generator is slowly increased so as to meet the late response of the secondary air valve, it will take time to convert the energy generated by the motor generator to the output voltage of the DC/DC converter, and, as a result, insufficient power will be compensated by the discharge of the battery, causing further voltage drop of the main battery.
SUMMARY OF THE INVENTION
The present invention has been made to solve the aforementioned problems, and it is the object of the present invention to provide a hybrid vehicle and a control method therefor which, while maintaining the stabilized idle rotation of the engine, is capable of preventing the temporary voltage drop of the battery by controlling the discharge of the battery at the time of starting the DC/DC converter at low temperatures.
The first aspect of the present invention provides a hybrid vehicle comprising an engine (for example, an engine
7
in the embodiment) for driving the vehicle, and a motor (for example, a motor generator
6
in the embodiment) for driving the engine or for generating electric energy, a battery (for example, a high voltage battery
1
in the embodiment), a DC/DC converter (for example, a output variable DC/DC converter
2
in the embodiment) for supplying energy to the auxiliary machines (for example, a controller computer and auxiliary machines
3
in the embodiment), a temperature detecting device (for example, a temperature sensor
11
in the embodiment), and an output voltage increasing device (for example, motor controllers
8
and
21
in the embodiment), when the temperature of the battery is below a predetermined temperature, the output voltage increasing device sets the output voltage at a predetermined voltage and starting the DC/DC converter, and, after starting the DC/DC converter, and gradual increases the output voltage of the DC/DC converter from the predetermined voltage.
By constituting the hybrid vehicle as described above, when the engine is in the idle state and the electric energy generated by the motor is low, and when the temperature of the battery is below a predetermined temperature, the DC/DC converter is activated at a low output voltage, and the output voltage of the DC/DC converter is increased gradually from the voltage at the time of activation so that the electric power consumed by the DC/DC converter can be increased gradually.
According to the second aspect of the present invention, the hybrid vehicle comprising an engine (for example, an engine
7
in the embodiment) for driving the vehicle and a motor (for example, a motor generator
6
in the embodiment) for driving of the engine or for generating electric power, and a battery (for example, a high voltage battery
1
in the embodiment), which is charged by electric power generated by the motor, a DC/DC converter (for example, a output variable DC/DC converter
2
in the embodiment), capable of outputting a variable output voltage, and outputting

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