Power plants – System having plural motors or having diverse types of... – Having condition responsive control
Reexamination Certificate
1999-12-13
2001-04-17
Nguyen, Hoang (Department: 3748)
Power plants
System having plural motors or having diverse types of...
Having condition responsive control
C180S193000, C180S065310
Reexamination Certificate
active
06216465
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a control system for a hybrid vehicle, and in particular, to a control system for a hybrid vehicle which reduces a shock when the vehicle shifts from a cruise mode for generating electric power without assisting the driving shaft of the engine to an acceleration mode for assisting the engine.
This application is based on Japanese Patent Application No. Hei 10-359831, the contents of which are incorporated herein by reference.
2. Background Art
Conventionally, hybrid vehicles which carry motors as power sources for driving the vehicles in addition to engines are known. Hybrid vehicles are divided into series hybrid vehicles and parallel hybrid vehicles. In series hybrid vehicles, the engine drives a generator, which outputs electric power to the motor, and the motor drives the wheels.
Because the engine and the wheels are not mechanically connected, the engine constantly runs within a rotational range which reduces fuel consumption and emissions, as compared with conventional engine vehicles.
In parallel hybrid vehicles, the motor connected to the engine assists the rotation of the drive shaft of the engine while charging a battery using a generator which is separate from the motor or is the motor itself.
Although the engine and the wheels are mechanically connected, the parallel hybrid vehicle can reduce the load to the engine. Thus, the parallel hybrid vehicle also has reduced fuel consumption and emissions as compared with conventional engine vehicles.
In the parallel hybrid vehicle, the motor for assisting the output of the engine is directly connected to the output shaft of the engine, and acts as a generator for charging the battery when the vehicle speed is reduced. Alternatively, either or both of the engine and the motor may generate the drive power, and the generator may be provided separately.
When a hybrid vehicle accelerates, the engine is assisted by the motor, and, when it decelerates, various operations are performed, such as charging the battery by deceleration regeneration, so as to maintain sufficient electric energy in the battery (hereinafter referred to as the “state of charge (remaining charge)”) to meet the driver's demands (as disclosed in, for example, Japanese Patent Application, First Publication No. Hei 7-123509).
In conventional hybrid vehicles, particularly, in parallel hybrid vehicles, when the vehicle is cruising, the motor does not perform the torque assist for the driving shaft of the engine, while the motor acts as a generator for generating electric energy to increase the remaining charge.
However, when the generation is started during the cruising, the driver may depress an accelerator pedal so that the vehicle enters the acceleration mode, which may cause a shock.
When the vehicle enters the acceleration mode, the motor normally performs the torque assist, that is, adds a torque to the torque from the engine. When the motor as the generator generates, i.e., 2 kW during the cruising and performs the assist of 2 kW in the acceleration mode, a variation of 4 kW in total occurs in the output. This variation in the output causes a shock greater than anticipated when the vehicle accelerates, and the driver may feel uneasy.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a control system for a hybrid vehicle which reduces a shock when the vehicle shifts from the cruise mode to the acceleration mode.
The control system is provided for a hybrid vehicle with an engine (E) for producing a driving force for the vehicle, a motor (M) for producing an assist driving force to assist the output from the engine, and a power storage unit (capacitor
3
) for supplying electric energy to the motor and storing regenerated energy produced by regeneration of the motor when the vehicle decelerates. This control system comprises: an assist trigger threshold value setting device (step S
121
) for setting a throttle opening state when the motor starts assist for the output from the engine; a throttle opening state lower limit setting device (step S
314
) for setting a lower limit (MASTFL) by subtracting a predetermined value (&Dgr;TH for the throttle opening state TH) from the threshold value (final threshold value MASTF for assist trigger) obtained by the assist trigger threshold value setting device; and a generation reduction device (step S
316
) for gradually reducing the generation by the motor between the lower limit and the threshold value so that the generation finally becomes zero when the present throttle opening state reaches the threshold value, when the vehicle shifts from a generation state, in which the motor acts as a generator and the output is supplied only from the engine, to an output assist state in which the motor assists the output.
When the driver depresses the accelerator pedal in the generation state so that the throttle opening state reaches the lower limit, the generation reduction device gradually reduces the generation until the throttle opening state reaches the threshold value for the assist trigger, at which point the generation becomes zero, thereby allowing the vehicle to enter the output assist state.
According to the present invention, when the vehicle shifts from a generation state to an output assist state to allow the motor to assist the output, the generation becomes zero at the starting of the motor assist. Therefore, the invention prevents a shock due to the disappearance of the negative torque produced by the generation, thus minimizing discomfort for the driver.
The generation state, in which the motor acts as a generator, may correspond to a cruise mode (step S
8
), and the output assist state, in which the motor assists the output from the engine, may correspond to an acceleration mode (step S
7
). In this configuration, when the driver depresses the accelerator pedal in the cruise mode so that the throttle opening state reaches the lower limit, the generation reduction device gradually reduces the generation until the throttle opening state reaches the threshold value for the assist trigger, at which point the generation becomes zero, thereby allowing the vehicle to enter the output assist state.
The threshold value for the assist trigger may be corrected, based on the atomospheric pressure (PA). When the vehicle runs in the rarefied air in a low atomospheric pressure area such as highlands, the threshold value for the assist trigger may be increased, thus providing an improved riding comfort, taking into consideration the atomospheric pressure.
REFERENCES:
patent: 5806617 (1998-09-01), Yamaguchi
patent: 6054844 (2000-04-01), Frank
Kitajima Shinichi
Kuroda Shigetaka
Matsubara Atsushi
Nakamoto Yasuo
Sawamura Kazutomo
Armstrong Westerman Hattori McLeland & Naughton LLP
Honda Giken Kogyo Kabushiki Kaisha
Nguyen Hoang
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