Internal-combustion engines – Spark ignition timing control – Electronic control
Reexamination Certificate
2004-01-12
2004-11-23
Mohanty, Bibhu (Department: 3747)
Internal-combustion engines
Spark ignition timing control
Electronic control
C123S090150
Reexamination Certificate
active
06820591
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. 2003-028625 filed on Feb. 5, 2003, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a control apparatus and method for an internal combustion engine.
2. Description of the Related Art
An engine mounted in a vehicle such as an automobile has been known which is provided with a valve characteristic varying mechanism that varies a valve characteristic of at least one of an intake valve and an exhaust valve. In this engine, a valve overlap amount of the intake valve and the exhaust valve is adjusted by driving the valve characteristic varying mechanism based on the engine operating state, i.e., the engine speed and engine load, so that an internal EGR amount appropriate for that engine operating state is obtained. That is, by adjusting the valve overlap amount, the internal EGR amount is able to be adjusted, for example, to a value that gives priority to engine output or a value that gives priority to exhaust emissions and fuel efficiency, depending on the engine operating state.
Also, in a spark ignition engine mounted in a vehicle, the ignition timing is retard-corrected based on a correction amount which is increased or decreased depending on the presence or absence of knock. Retard-correcting the ignition timing inhibits an increase in the temperature of the combustion chamber, thereby suppressing knock. In this case, an increase in the combustion chamber temperature is able to be suppressed by retard-correcting the ignition timing because when the ignition timing is retarded, the timing at which the combustion of the mixture in the combustion chamber takes place is delayed, such that some of the mixture is expelled as exhaust into an exhaust passage while still at the high combustion temperature. As a result, the amount of heat transferred to the combustion chamber walls during combustion of the mixture is less by the amount of heat of the expelled mixture.
If the ignition timing is retard-corrected to suppress knock, however, the optimum value for the valve overlap amount (internal EGR amount) may decrease according to the amount of retard, depending on the operating state of the engine. This kind of change in the optimum value occurs, for example, when the ignition timing is retard-corrected in order to suppress knock when the engine is in an operating state where priority should be given to exhaust emissions and fuel efficiency, for example. In this operating state, the actual internal EGR amount is adjusted to the maximum value to improve exhaust emissions and fuel efficiency, but as the ignition timing is retarded this maximum value decreases. Therefore, the valve overlap amount, which is a parameter that controls the internal EGR amount, needs to be reduced so the optimum value for the valve overlap amount is reduced when there is a retard-correction of the ignition timing.
If the optimum value for the valve overlap amount were to be reduced in this way, the valve overlap amount would be higher than the optimum value. As a result, the amount of internal EGR in the engine would become excessive and adversely effect fuel efficiency and torque fluctuation. JP(A) 11-125126 proposes technology for reducing the valve overlap amount based on a correction amount used in the retard-correction of the ignition timing in order to suppress the adverse effects from this excessive amount of internal EGR. The amount of decrease in the valve overlap amount at this time is set to a value that differs for each operating range, defined according to engine speed and fuel injection quantity.
Reducing the valve overlap amount in this way makes it possible to suppress the adverse effects on fuel efficiency and torque fluctuation due to an excessive amount of internal EGR following a retard-correction of the ignition timing in order to suppress knock. However, when the ignition timing is retard-corrected only an amount corresponding to the correction amount in order to suppress knock, there may not be much change in the optimum value for the valve overlap amount depending on the operating state of the engine. If the valve overlap amount were to be reduced in this case, the amount of internal EGR would end up being reduced more than is necessary.
For example, when the engine is in an operating state where priority should be given to engine output, a value less than the value for obtaining the maximum amount of internal EGR for that engine operating state is set as the optimum value for the valve overlap amount. This is because the amount of (exhaust) gas which does not contribute to combustion, but which is in the combustion chamber during combustion, increases as the amount of internal EGR increases. So if the amount of internal EGR were to be set to the maximum value, there is a possibility that engine output would drop. Also, when the engine is in an operating state where priority should be given to engine output, in particular, when the throttle valve is close to fully open, priority is given to increasing the intake air amount as much as possible rather than to obtaining a given amount of internal EGR. Accordingly, a value with which the maximum amount of intake air can be obtained is set as the optimum value for the valve overlap amount. The optimum value for the valve overlap amount at this time is a value less than the value with which the maximum amount of internal EGR is obtained.
When the valve overlap amount is adjusted to the optimum value in this way, even if a retard-correction of the ignition timing is performed, the actual internal EGR amount is already a value less than the maximum value so the internal EGR amount will not become excessive with that retard-correction. Therefore, the valve overlap amount, which is a parameter that controls the internal EGR amount, does not need to be reduced so the optimum value for the valve overlap amount does not change following the retard-correction of the ignition timing.
In this case, if the valve overlap amount were to be reduced based on the correction amount used in the retard-correction of the ignition timing, the valve overlap amount would become much smaller than the optimum value. As a result, the amount of internal EGR would be reduced more than is necessary. In JP(A) 11-125126, the amount of decrease in the valve overlap amount at this time is set to a value that differs for each operating range. However, because the fact that the valve overlap amount is still reduced remains unchanged, the internal EGR amount would inevitably be reduced more than is necessary.
SUMMARY OF THE INVENTION
In view of the foregoing problems, this invention thus provides a control apparatus and method for an internal combustion engine, capable of suppressing an amount of internal EGR from becoming excessive, while suppressing a valve overlap amount from being reduced more than is necessary when a retard-correction of an ignition timing is performed to suppress knock.
A first aspect of the invention relates to a control apparatus for an internal combustion engine, which suppresses knock by retard-correcting an ignition timing based on a correction amount that is increased or decreased depending on the presence or absence of knock, while controlling a valve overlap amount of an intake valve and an exhaust valve to a value appropriate for the operating state of the engine. The control apparatus is provided with a guard controller which applies an upper limit guard to limit the valve overlap amount using an upper limit guard value according to the correction amount and the operating state of the engine.
Depending on the operating state of the engine, a value such as one prioritizing engine output or one prioritizing exhaust emissions and fuel efficiency is made the optimum value, and the valve overlap amount is then adjusted so as to become that optimum value. Therefore, depending on the operating state of the engine, when a retard-correction of th
Kaneko Rihito
Kishi Hirohisa
Takagi Isao
Tanei Katsutoshi
Yoshimi Masashi
Mohanty Bibhu
Toyota Jidosha & Kabushiki Kaisha
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