Internal combustion engine control apparatus and control method

An internal combustion engine control apparatus, the engine being capable of switching a combustion mode between a stratified combustion and a homogeneous combustion, and being prevented from performing EGR immediately after switching the combustion mode from the stratified combustion to the homogeneous combustion, the apparatus comprising:

• 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, an actual 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, the lower limit value calculated as a function of the actual 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.

A method of controlling an internal combustion engine capable of switching a combustion mode between a stratified combustion and a homogeneous combustion, and prevented from performing EGR immediately after switching the combustion mode from the stratified combustion to the homogeneous combustion, the method comprising:

• detecting a transient condition in switching the combustion mode from the stratified combustion to the homogeneous combustion;
• calculating an actual residual EGR ratio of EGR gas remaining in an intake system of the internal combustion engine when the transient condition is detected;
• variably setting, 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, wherein the lower limit value is calculated as a function of the actual residual EGR ratio;
• and
• limiting the target equivalent ratio to the lower limit value immediately after switching from the stratified combustion to the homogeneous combustion.