Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
1999-10-12
2001-07-31
Kwon, John (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S305000
Reexamination Certificate
active
06267095
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an internal combustion engine control apparatus and control method, and more particularly to the control of the equivalent ratio when switching is done between stratified combustion and homogeneous combustion in an internal combustion engine capable of switching between these combustion modes in accordance with the driving condition.
In the Japanese laid-open patent application publication 10-331696, there is disclosure of the setting of the lower limit value of the equivalent ratio, in accordance with driving conditions, such as the engine speed, the load and the EGR ratio, immediately before switching from the stratified combustion to the homogeneous combustion.
SUMMARY OF THE INVENTION
According to an investigation by the inventors, in a spark-ignited internal combustion engine, such as one in which fuel is directly injected into a combustion chamber, in the low and medium load regions, fuel is injected during the compression stroke, with a stratified combustible gas mixture being produced in only the region of the spark plug, leading to the possibility of an extremely lean air-to-fuel ratio, which is an advantage with regard to fuel consumption and cleanliness of emissions.
In the above-noted internal combustion engine, because there is an intrinsic limitation in the cylinder volume, in a high-load region, in which there is a demand for a large engine torque, rather than perform the stratified combustion, it is preferable to form a gas mixture having a homogeneous mixture, by injecting fuel during the intake stroke, so that the homogeneous combustion is done. It is therefore preferable that the engine be switchable between the stratified combustion and the homogeneous combustion in accordance with driving conditions.
While it is also preferable that exhaust gas recirculation (EGR) be done for the purpose of reducing NO
x
in the exhaust emissions resulting from the stratified combustion, with the homogeneous combustion because it is possible to make the air-to-fuel ratio extremely lean, EGR is not essential and in fact, when EGR is done there is a worsening of combustion, making it preferable that EGR be prohibited.
In an internal combustion engine configured so that the above-noted switching is done between the stratified combustion and the homogeneous combustion, if we consider the case of switching from the stratified combustion to the homogeneous combustion, it is preferable that EGR be stopped at the time of the switching. However, even if EGR itself is stopped, because exhaust gas remains in the exhaust system, this residual exhaust gas causes a tendency to unstable combustion or miss fire of combustion.
On the other hand, if we consider the switch from the homogeneous combustion to the stratified combustion, while it is preferable at the time of this switching to start EGR, because exhaust gas is not instantaneously supplied to the combustion chamber, there is a time delay in the amount of EGR. However, this time lag in the amount of EGR is cancelled out by a time delay in the amount of intake, so there is no particular influence.
In view of the above, it is preferable that, when a switch is made from the stratified combustion to the homogeneous combustion, the lower limit value of the target equivalent ratio be set, in accordance with driving conditions, such as the engine speed, the load, and the EGR ratio immediately before the switching of combustion modes. The above-noted equivalent ratio is a value that is proportional to the reciprocal of the air-to-fuel ratio.
In the above-noted case of setting the equivalent ratio lower limit value, however, if this is taken as simply a fixed value, a torque that is larger than the demanded torque can be generated, the engine speed can increase and there can be an increase in the amount of NO
x
emitted in the exhaust.
In accordance with the current investigation of the inventors, the above-noted phenomenon is thought of as occurring because, whereas after switching from the stratified combustion to the homogeneous combustion, there is a reduction in the residual exhaust gas, because the equivalent ratio is limited by the lower limit value, gas that is richer than an appropriate value is combusted.
The present invention was made in consideration of the above-noted phenomenon, and has as an object the provision of an internal combustion engine control apparatus, which, by setting the target equivalent ratio lower limit value so that the equivalent ratio is an appropriate value after a switch from the stratified combustion to the homogeneous combustion, thereby eliminating combustion instability, such as miss fire of combustion, this control apparatus further enabling the prevention of the blow-up of the engine speed caused by an increase in torque, and the reduction of the amount of NO
x
exhaust emissions. It is a further object of the present invention to provide a method for performing the above-noted control of an internal combustion engine.
In order to achieve the above-noted object, a control apparatus and control method for an internal combustion engine according to the present invention is applied to an internal combustion engine that enables switching of the combustion mode between the stratified combustion and the homogeneous combustion, that is provided with an EGR apparatus, and that prohibits EGR in the EGR apparatus immediately after switching from the stratified combustion to the homogeneous combustion.
More specifically, a control apparatus for an internal combustion engine according to the present invention comprises: transient condition detection section detecting a transient condition in switching the combustion mode from the stratified combustion to the homogeneous combustion; a residual EGR ratio calculation section calculating, when the transient condition is detected, a residual EGR ratio of EGR gas remaining in an intake system of the internal combustion engine; a lower limit value setting section variably setting a lower limit value of a target equivalent ratio immediately after switching the combustion mode from the stratified combustion to the homogeneous combustion, in accordance with the residual EGR ratio; and a limiter limiting the target equivalent ratio to the lower limit value immediately after switching the combustion mode from the stratified combustion to the homogeneous combustion.
Stated in other terms, a control apparatus for an internal combustion engine according to the present invention comprises: means for detecting a transient condition in switching the combustion mode from the stratified combustion to the homogeneous combustion; means for calculating, when the transient condition is detected, a residual EGR ratio of EGR gas remaining in an intake system of the internal combustion engine; means for variably setting a lower limit value of a target equivalent ratio immediately after switching the combustion mode from the stratified combustion to the homogeneous combustion, in accordance with the residual EGR ratio; and means for limiting the target equivalent ratio to the lower limit value immediately after switching the combustion mode from the stratified combustion to the homogeneous combustion.
On the other hand, a method for controlling an internal combustion engine according to the present invention detects a transient condition in switching the combustion mode from the stratified combustion to the homogeneous combustion calculates a residual EGR ratio of EGR gas remaining in an intake system of the internal combustion engine when the transient condition is detected; variably sets, in accordance with the residual EGR ratio, a lower limit value of the target equivalent ratio immediately after switching the combustion mode from the stratified combustion to the homogeneous combustion; and limits the target equivalent ratio to the lower limit value immediately after switching from the stratified combustion to the homogeneous combustion.
REFERENCES:
patent: 6024069 (2000-02-01), Yoshino
patent: 6041757 (2000-03-01), Kadota
paten
Fujimori Ichirou
Ikeda Munetoyo
Takahashi Tomohiko
Foley & Lardner
Kwon John
Nissan Motor Co,. Ltd.
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