Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
2003-01-24
2004-08-10
Wolfe, Willis R. (Department: 3747)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
C060S276000
Reexamination Certificate
active
06775608
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a controller for controlling an air-fuel ratio of an internal combustion engine, and more particularly, to a controller for controlling an air-fuel ratio of an internal combustion engine to optimally reduce oxygen excessively absorbed by a catalyst converter.
A catalyst converter for purifying exhaust gas is provided in an exhaust system of an internal combustion engine of a vehicle. When the air-fuel ratio of air-fuel mixture introduced to the engine is lean, the catalyst converter oxidizes HC and CO by excessive oxygen included in the exhaust gas. When the air-fuel ratio is rich, the catalyst converter reduces Nox by HC and CO. When the air-fuel ratio is in the stoichiometric air-fuel ratio region, HC, CO and Nox are simultaneously and effectively purified.
On the other hand, a method for stopping fuel supply when a vehicle is decelerating (for example, when engine braking is used) is known. Such stopping of fuel supply is generally called a “fuel cut”. The fuel cut allows fuel efficiency to be improved. The fuel cut is performed, for example, when a throttle valve is totally closed over a predetermined period or longer and the engine rotational speed is greater than a predetermined rotational speed. If the engine rotational speed is below the predetermined rotational speed, or if the throttle valve is opened, fuel supply is resumed.
Since fuel is not supplied during the fuel cut, a large amount of oxygen is introduced and absorbed by the catalyst converter. If the catalyst converter absorbs excessive oxygen, the performance of the catalyst, especially the capability of reducing Nox deteriorates. In order to remove the oxygen absorbed by the catalyst converter, a method for making the air-fuel mixture rich when the fuel supply is resumed is proposed.
Japanese Patent Application Unexamined Publication No. 9-72235 describes a method for feedforward controlling the air-fuel ratio after a fuel cut or lean state is returned to a normal fuel supply state. More specifically, the mass of substances absorbed by the catalyst converter is estimated during the fuel cut or lean state based on output of an air-fuel ratio sensor provided upstream of the catalyst converter. When the fuel cut or lean state is cancelled, the air-fuel ratio is feedforward-controlled to reduce the estimated mass of the absorbed substances.
Japanese Patent Publication No.2913282 discloses a method for determining a target air-fuel ratio for making the fuel mixture rich and a period during which the target air-fuel ratio is maintained. The determination is performed based on the duration of the lean state or fuel cut, and an engine load and engine rotational speed during the lean state or fuel cut. After the lean state or fuel cut is cancelled, the air-fuel ratio is controlled so that the target air-fuel ratio is maintained for the determined period.
Furthermore, a scheme for providing an O2 sensor (exhaust gas sensor) downstream of the catalyst converter is known. When the fuel cut is cancelled, the target air-fuel ratio is set to be rich. A reduction process for the catalyst is started. When the output of the O2 sensor is inverted from a value indicative of lean to a value indicative of rich, the reduction process for the catalyst is stopped.
The mass of substances absorbed by the catalyst varies depending on operating conditions of the engine. If a load of the engine varies, the mass of the absorbed substances also varies. Therefore, it is difficult to precisely determine the mass of the absorbed substances during the fuel cut or lean state.
If the catalyst deteriorates with time, the capability of absorbing oxygen is degraded. After the fuel cut or lean state is cancelled, if the air-fuel mixture is made rich under such degradation, the air-fuel mixture may be made excessively rich. Such an excessive rich state increases HC and CO emissions.
Thus, the feedforward control of the air-fuel ratio is unstable against variations in operating conditions of the engine and variations in degradation of the catalyst. The feedforward control may degrade the purification performance of the catalyst.
There exists dead time in combustion cycles of the engine and transportation through the exhaust system. It takes some time from adjustment of an amount of fuel injection based on a target air-fuel ratio determined from the output of an O2 sensor until the result of the fuel injection is reflected in the output of the O2 sensor. Therefore, if a process for making the air-fuel ratio rich is stopped in synchronization with the inversion of the O2 sensor provided downstream of the catalyst from lean to rich, the catalyst may be excessively reduced. As a result, the amount of HC and CO emissions is increased.
Therefore, there is a need for air-fuel ratio control that performs a reduction process that is stable against variations in a load of the engine after a lean state or fuel cut is cancelled. Furthermore, there is another need for air-fuel ratio control that performs a reduction process in accordance with deterioration of the catalyst. There is yet another need for air-fuel ratio control that prevents the air-fuel ratio from being made excessively rich after a lean state or fuel cut is cancelled.
SUMMARY OF THE INVENTION
According to one aspect of the invention, an exhaust gas sensor is provided between an upstream catalyst disposed upstream of an exhaust manifold and a downstream catalyst disposed downstream of the exhaust manifold. A virtual exhaust gas sensor is virtually provided downstream of the downstream catalyst. When a lean state is cancelled or when a fuel cut is cancelled, the controller estimates an output of the virtual exhaust gas sensor based on a gas amount that contributes to reduction of the upstream and downstream catalysts, and an output of the exhaust gas sensor. First air-fuel ratio control controls the air-fuel ratio of the internal combustion engine in accordance with the estimated output.
According to the invention, it is possible to control a purification atmosphere (oxidation atmosphere and reduction atmosphere) of the downstream catalyst that can not be directly observed by the exhaust gas sensor provided between the upstream and downstream catalysts. The reduction process for the downstream catalyst is appropriately and stably performed based on the estimated output of the virtual exhaust gas sensor. Thus, the purification rate of Nox after the lean state or fuel cut is cancelled can be quickly returned to an optimal rate.
According to another aspect of the invention, the gas amount that contributes to reduction of the upstream and downstream catalysts is determined based on an operating condition of the engine. Therefore, a variation in the load of the engine after a lean state or fuel cut is cancelled, a variation in the duration of a lean state or fuel cut, a variation in the air-fuel ratio during a lean state or fuel cut, and a variation in deterioration of the catalysts are compensated. As a result, the purification rate of Nox after a lean state or fuel cut is cancelled can be stably returned. Furthermore, the air-fuel ratio is prevented from being made excessively rich caused by an excessive reduction process, avoiding increasing the amount of HC and CO emissions.
According to another aspect of the invention, when a lean state is cancelled or when a fuel cut is cancelled, the controller changes a target air-fuel ratio to a predetermined rich value. The gas amount that contributes to the reduction of the upstream and downstream catalysts is determined based on the amount of the change in the target air-fuel ratio. According to one embodiment, the target air-fuel ratio is controlled to change from a stoichiometric state (stoichiometric air-fuel ratio) to a predetermined rich state. In this case, the gas amount that contributes to the reduction of the upstream and downstream catalysts is determined based on a difference between the target air-fuel ratio and the stoichiometric air-fuel ratio. Since the air-fuel ratio t
Hoang Johnny H.
Honda Giken Kogyo Kabushiki Kaisha
Squire Sanders & Dempsey L.L.P.
Wolfe Willis R.
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