Control device for internal combustion engine

1. A control device for an internal combustion engine comprising:

an internal combustion engine having a lean burn capability and/or an external EGR capability;

an intake variable valve train capable of switching between a dual valve variable control state, in which the operating angles of a first intake valve and a second intake valve provided for each cylinder of the internal combustion engine are both variable, and a single valve small operating angle state, in which the operating angle of the second intake valve is smaller than the operating angle of the first intake valve;

operating region setup means for setting up at least a high load region, a low load region in which the load is lower than in the high load region, and an extremely low load region in which the load is lower than in the low load region, as a operating region for the internal combustion engine; and

operating mode control means for using, in the high load region and the extremely low load region, a stoichiometric dual valve variable control mode to provide combustion at a theoretical air-fuel ratio in the dual valve variable control state, and using, in the low load region, a lean single valve small operating angle mode to provide a lean burn in the single valve small operating angle state or an EGR single valve small operating angle mode to provide external EGR in the single valve small operating angle state,

wherein the low load region is a region in which the lean single valve small operating angle mode or the EGR single valve small operating angle mode exhibits a lower specific fuel consumption than the stoichiometric dual valve variable control mode, and

the extremely low load region is a region in which the stoichiometric dual valve variable control mode exhibits a lower specific fuel consumption than the lean single valve small operating angle mode or the EGR single valve small operating angle mode.

2. The control device for an internal combustion engine according to claim 1 , further comprising:

temperature acquisition means for detecting or estimating a representative temperature of the internal combustion engine or of a catalyst installed in an exhaust path of the internal combustion engine;

wherein, when the representative temperature is lower than a predetermined temperature, the operating mode control means uses the stoichiometric dual valve variable control mode in the low load region as well.

3. The control device for an internal combustion engine according to claim 1 , further comprising:

temperature acquisition means for detecting or estimating an EGR gas temperature or an intake temperature;

wherein, when the EGR gas temperature or the intake temperature is higher than a predetermined temperature, the operating mode control means uses the stoichiometric dual valve variable control mode in the low load region as well.

4. A control device for an internal combustion engine comprising:

an internal combustion engine having a lean burn capability and/or an external EGR capability;

an intake variable valve train capable of switching between a dual valve variable control state, in which the operating angles of a first intake valve and a second intake valve provided for each cylinder of the internal combustion engine are both variable, and a single valve small operating angle state, in which the operating angle of the second intake valve is smaller than the operating angle of the first intake valve;

an operating region setup device for setting up at least a high load region, a low load region in which the load is lower than in the high load region, and an extremely low load region in which the load is lower than in the low load region, as a operating region for the internal combustion engine; and

an operating mode control device for using, in the high load region and the extremely low load region, a stoichiometric dual valve variable control mode to provide combustion at a theoretical air-fuel ratio in the dual valve variable control state, and using, in the low load region, a lean single valve small operating angle mode to provide a lean burn in the single valve small operating angle state or an EGR single valve small operating angle mode to provide external EGR in the single valve small operating angle state,

wherein the low load region is a region in which the lean single valve small operating angle mode or the EGR single valve small operating angle mode exhibits a lower specific fuel consumption than the stoichiometric dual valve variable control mode, and

the extremely low load region is a region in which the stoichiometric dual valve variable control mode exhibits a lower specific fuel consumption than the lean single valve small operating angle mode or the EGR single valve small operating angle mode.

5. The control device for an internal combustion engine according to claim 4 , further comprising:

a temperature acquisition device for detecting or estimating a representative temperature of the internal combustion engine or of a catalyst installed in an exhaust path of the internal combustion engine;

wherein, when the representative temperature is lower than a predetermined temperature, the operating mode control device uses the stoichiometric dual valve variable control mode in the low load region as well.

6. The control device for an internal combustion engine according to claim 4 , further comprising:

a temperature acquisition device for detecting or estimating an EGR gas temperature or an intake temperature;

wherein, when the EGR gas temperature or the intake temperature is higher than a predetermined temperature, the operating mode control device uses the stoichiometric dual valve variable control mode in the low load region as well.