Prime-mover dynamo plants – Electric control – Engine control
Reexamination Certificate
2000-10-26
2004-03-02
Ponomarenko, Nicholas (Department: 2834)
Prime-mover dynamo plants
Electric control
Engine control
C180S065100
Reexamination Certificate
active
06700213
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control system for a hybrid vehicle with an engine and a motor, and in particular, to a control system for a hybrid vehicle which determines whether the output from the engine is assisted by the motor with reference to an air-fuel ratio of an air-fuel mixture which is supplied to the engine.
This application is based on Japanese Patent Application No. Hei 11-310348, the contents of which are incorporated herein by reference.
2. Description of Related Art
Conventionally, hybrid vehicles which carry electric motors as power sources for driving vehicles in addition to engines are known. One kind of conventional hybrid vehicle is a parallel hybrid vehicle which uses a motor as an assisting driving source for assisting the output from the engine. In the parallel hybrid vehicle, for example, when the vehicle accelerates the output from the engine is assisted by the motor, a battery is charged by deceleration regeneration when the vehicle decelerates, and various controls are performed while maintaining electric energy of the battery (which is hereinafter called the “state of charge (remaining battery charge)”) in response to the driver's demands (as disclosed in, for example, Japanese Unexamined Patent Application, First Publication, No. Hei 7-123509).
In an example of the above-described conventional hybrid vehicle, when an air-fuel ratio of an air-fuel mixture which is supplied to the engine is frequently shifted between the air-fuel ratio for the lean state, which is lower than the theoretical air-fuel ratio (a stoichiometric state), and the air-fuel ratio for the rich state, which is higher than the theoretical air-fuel ratio, in response to the running condition of the engine, an assist determination threshold value (a standard value which determines whether the output from the engine by the motor is assisted) is changed. Accordingly, the engine output assistance by the motor may be started or stopped.
When the air-fuel ratio of the air-fuel mixture which is supplied to the engine, is set at the lean state in which the air-fuel ratio is lower than the theoretical air-fuel ratio, that is, a lean-burn control is performed, the amount of nitrogen oxide (NOx) exhaust tends to increase. As an example of a conventional art which prevents the amount of NOx exhaust from increasing, an exhaust gas control device which includes an NOx absorbent which absorbs or adsorbs NOx and which is provided in the exhaust system of the engine to purify the exhaust gas is known.
When the air-fuel ratio of the exhaust gas is lower than the theoretical air-fuel ratio, that is, the air-fuel ratio of the exhaust gas is set at the lean state, and the oxygen concentration in the exhaust gas is relatively high, the NOx absorbent absorbs or adsorbs NOx. When the air-fuel ratio of the exhaust gas is in the vicinity of or higher than the theoretical air-fuel ratio, that is, when the air-fuel ratio is set at the rich state, and the oxygen concentration in the exhaust gas is relatively low and the concentration of hydrocarbons (HC), carbon monoxide (CO), and the like included in the exhaust gas is high, then NOx absorbed or adsorbed in the NOx absorbent is deoxidized and converted to nitrogen gas and emitted.
When the engine output assistance by the motor is repeatedly started and stopped, problems arise such that drivability decreases and drivers feel discornfort.
NOx is accumulated in the NOx absorbent, so that the purification efficiency of NOx is reduced, therefore, it is necessary to emit NOx accumulated in the NOx absorbent at a suitable time. The air-fuel ratio of the exhaust gas flowing into the NOx absorbent is temporarily set at the rich state, which is higher than the theoretical air-fuel ratio and NOx is emitted from the NOx absorbent Simultaneously, HC, CO, and the like, which are contained in the exhaust gas of the rich state, are used to control the reduction and purification of NOx emitted (hereinafter called a “rich spike”), so that the NOx absorbent is regenerated (as is disclosed, for example, in Japanese Unexamined Patent Application, First Publication, No. Hei 10-276267).
In the control system of hybrid vehicles according to the example of the above conventional art, when the standard which determines whether to start the engine output assistance by the motor is changed depending on whether the air-fuel ratio of the air-fuel mixture which is supplied to the engine is set at the lean state, that is, the air-fuel ratio is lower than the theoretical air-fuel ratio, or at the rich state, that is, the air-fuel ratio is higher than the theoretical air-fuel ratio, the running condition of the vehicle may change whenever a rich spike control is executed.
For example, since the output from the engine is relatively low when the lean-burn control is performed, the driver may depress the accelerator pedal to maintain the drivability. If the rich spike control is executed in this condition, the engine output assistance by the motor may be suddenly started. Therefore, an unexpected acceleration or the like may be experienced by the driver.
Additionally, if such a rich spike is, for example, repeatedly executed at predetermined intervals, the vehicle's running condition will be jerky and the vehicle will not run smoothly, and the drivability deteriorates.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a control system for a hybrid vehicle which can prevent the jerky feeling in the running condition of the vehicle and can improve the drivability, even if the air-fuel ratio of the exhaust gas compared with the theoretical air-fuel ratio is temporarily changed from the lean state to the rich state, in order to regenerate the exhaust gas control device used for deoxidizing and purifying nitrogen oxide in the exhaust gas.
To achieve the above object, the control system is provided in a hybrid vehicle of the present invention with a combustion engine (E) for outputting a driving force, an electric motor (M) for generating a force for assisting the output from the engine, depending on the driving conditions, a power storage unit (battery
22
) for storing electric energy generated by the motor acting as a generator using the output from the engine and electric energy regenerated by the motor when the vehicle decelerates. The control apparatus comprises: an output assist detenination means (steps S
122
and S
135
) for determining, based on a determination threshold value (the throttle assist trigger threshold value MTHAST, the air intake passage pressure assist trigger threshold value MAST, or the air intake passage pressure assist trigger threshold value MASTTH) as the standard, whether to assist the output from the engine by the motor, depending on the driving condition of the vehicle; an air-fuel controller (FIECU
12
) for changing the air-fuel ratio of the mixture, which is to be supplied to the engine, to a condition leaner or richer than the stoichiometric air-fuel ratio; a determination threshold value changing means (steps S
251
and S
301
) for changing the determination threshold value, depending on whether the air-fuel ratio of the mixture is leaner or richer than the stoichiometric air-fuel ratio; and a determination threshold value change prohibiting means (steps S
254
and S
304
) for prohibiting the operation of the determination threshold value changer when the air-fuel controller changes the air-fuel ratio of the mixture from a condition leaner than the stoichiometric air-fuel ratio to a condition richer than the stoichiometric air-fuel ratio.
According to the above control system for a hybrid vehicle, even in the case where the air-fuel ratio of the air-fuel mixture supplied to the engine is temporarily set richer than the stoichiometric air-fuel ratio by the air-fuel ratio controller, for example, in order to recover the absorption capacity of NOx absorbent when the absorbent is degraded, because the determination threshold value change prohibiting means fo
Iwamoto Takashi
Izumiura Atsushi
Kumagai Katsuhiro
Nakaune Kan
Ukai Asao
Armstrong Westerman & Hattori, LLP
Gonzalez Julio C.
Honda Giken Kogyo Kabushiki Kaisha
Ponomarenko Nicholas
LandOfFree
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