Internal combustion engine and control method of internal combustion engine

1. An internal combustion engine comprising:

an engine body including cylinders;

an intake manifold for supplying air into the cylinders;

an exhaust manifold for discharging exhaust gas from the cylinders;

a fuel injection valve configured to directly inject fuel into a combustion chamber of the internal combustion engine;

a spark plug, an electrode portion of the spark plug being disposed in one of the inside of a fuel injection path and the vicinity of the fuel injection path;

a characteristic switching mechanism configured to switch a lift characteristic between a first lift characteristic and a second lift characteristic, the first lift characteristic being a lift characteristic of an exhaust valve of opening the exhaust valve in an exhaust stroke, the second lift characteristic being a lift characteristic of the exhaust valve of opening the exhaust valve in the exhaust stroke and an intake stroke; and

an electronic control unit having a non-transitory computer-readable memory storing executable instructions:

to control the fuel injection valve and the spark plug such that fuel is combusted by one of pre-mixture compression ignition combustion and flame propagation combustion;

to switch the lift characteristic of the exhaust valve to the second lift characteristic using the characteristic switching mechanism in a predetermined first operation range, the predetermined first operation range including at least a part of a compression ignition operation range, the compression ignition operation range being a range in which fuel is combusted by the pre-mixture compression ignition combustion;

to switch the lift characteristic of the exhaust valve to the first lift characteristic using the characteristic switching mechanism in a predetermined second operation range, the predetermined second operation range including at least a flame ignition operation range, the flame ignition operation range being a range in which fuel is combusted by the flame propagation combustion;

to determine whether switching failure has occurred, the switching failure being failure in which the lift characteristic of the exhaust valve is not switchable from the second lift characteristic to the first lift characteristic using the characteristic switching mechanism;

to control the spark plug to ignite fuel to perform homogeneous combustion in the flame ignition operation range when the electronic control unit determines that the switching failure has not occurred;

wherein the homogeneous combustion is a combustion in which fuel homogeneously diffused into the combustion chamber is ignited by the spark plug and is combusted by the flame propagation combustion; and

to control the fuel injection valve to perform spray-guided stratified combustion in the second operation range when the electronic control unit determines that the switching failure has occurred;

wherein with the spray-guided stratified combustion is a combustion in which fuel in the fuel injection path is ignited by the spark plug and is combusted by the flame propagation combustion.

2. The internal combustion engine according to claim 1 , further comprising:

a throttle valve disposed in an intake air passage;

wherein the electronic control unit further includes executable instructions to control an opening degree of the throttle valve such that the opening degree becomes a target opening degree based on an engine load; and

when the electronic control unit determines that the switching failure has occurred, the electronic control unit is configured to control the opening degree of the throttle valve to become at least one of a maximum opening degree and an opening degree greater than the target opening degree in the second operation range.

3. The internal combustion engine according to claim 1 , further comprising:

an exhaust turbocharger disposed in an exhaust gas passage; and

an exhaust gas adjuster configured to adjust a flow rate of exhaust gas flowing into a turbine of the exhaust turbocharger;

wherein the exhaust gas adjuster is one of a waste gate valve and a variable nozzle;

wherein the electronic control unit further includes executable instructions to control an opening degree of the exhaust gas adjuster such that the opening degree becomes a target opening degree based on an engine load; and

wherein when the electronic control unit determines that the switching failure has occurred, the electronic control unit is configured to control the opening degree of the exhaust gas adjuster to become at least one of a maximum opening degree and an opening degree greater than the target opening degree in the second operation range.

4. The internal combustion engine according to claim 1 , further comprising:

a variable exhaust phase mechanism configured to change an exhaust phase;

wherein the exhaust phase is a phase of an exhaust cam shaft with respect to a crank shaft;

wherein the electronic control unit further includes executable instructions to change the exhaust phase such that a valve opening timing of the exhaust valve in an intake stroke is a predetermined timing in the second operation range when the electronic control unit determines that the switching failure has occurred;

wherein the predetermined timing is a timing at which a rate of change in volume of the combustion chamber in the intake stroke is relatively small.

5. The internal combustion engine according to claim 4 , wherein

the electronic control unit further includes the executable instructions to change the exhaust phase such that the valve opening timing of the exhaust valve in the intake stroke is an initial stage of the intake stroke when the electronic control unit determines that the switching failure has occurred.

6. The internal combustion engine according to claim 4 , wherein

the electronic control unit further includes the executable instructions to change the exhaust phase such that the valve opening timing of the exhaust valve in the intake stroke is a final stage of the intake stroke when the electronic control unit determines that the switching failure has occurred.

7. The internal combustion engine according to claim 1 , further comprising:

a variable intake phase mechanism configured to change an intake phase;

wherein the intake phase is a phase of an intake cam shaft with respect to a crank shaft;

wherein when the electronic control unit determines that the switching failure has occurred, the electronic control unit further includes executable instructions to change the intake phase in the second operation range such that a valve closing timing of an intake valve is changed by one of the following controls at least one of:

(i) the valve closing timing being advanced in a direction which the valve closing timing moves away from an intake bottom dead center in comparison with a case in which the electronic control unit determines that the switching failure has not occurred; and

(ii) the valve closing timing being retarded in a direction which the valve closing timing moves away from the intake bottom dead center in comparison with a case in which the electronic control unit determines that the switching failure has not occurred.

8. The internal combustion engine according to claim 1 , wherein the electronic control unit further the executable instructions to control the fuel injection valve to perform the spray-guided stratified combustion in all the operation ranges when the electronic control unit determines that the switching failure has occurred.

9. The internal combustion engine according to claim 1 , wherein

the electronic control unit further includes the executable instructions to determine whether the switching failure has occurred in the flame ignition operation range; and

the electronic control unit further includes the executable instructions to prohibit an operation in a predetermined area and to combust fuel by the pre-mixture compression ignition combustion in the first operation range when the electronic control unit determines that an engine operating state transitions from the second operation range to the first operation range after the switching failure has occurred;

wherein the predetermined area is at least one of the second operation range on a higher load side than the first operation range and the second operation range on a higher rotation speed side than the first operation range.

10. A control method of an internal combustion engine, the internal combustion engine including an engine body including cylinders, an intake manifold for supplying aft into the cylinders, an exhaust manifold for discharging exhaust gas from the cylinders, a fuel injection valve, a spark plug, a characteristic switching mechanism, and an electronic control unit, the fuel injection valve being configured to directly inject fuel into a combustion chamber of the internal combustion engine, an electrode portion of the spark plug being disposed in one of the inside of a fuel injection path and the vicinity of the fuel injection path, the characteristic switching mechanism being configured to switch a lift characteristic between a first lift characteristic and a second lift characteristic, the first lift characteristic being a lift characteristic of an exhaust valve of opening the exhaust valve in an exhaust stroke, the second lift characteristic being a lift characteristic of the exhaust valve of opening the exhaust valve in the exhaust stroke and an intake stroke, the control method comprising:

controlling, by the electronic control unit, the fuel injection valve and the spark plug such that fuel is combusted by one of pre-mixture compression ignition combustion and flame propagation combustion;

switching, by the electronic control unit, the lift characteristic of the exhaust valve to the second lift characteristic in a predetermined first operation range;

switching, by the electronic control unit, the lift characteristic of the exhaust valve to the first lift characteristic in a predetermined second operation range;

determining, by the electronic control unit, whether switching failure has occurred;

wherein when the electronic control unit determines that the switching failure has not occurred, controlling the spark plug to ignite fuel, by the electronic control unit, to perform homogeneous combustion in the flame ignition operation range; and

wherein when the electronic control unit determines that the switching failure has occurred, controlling the fuel injection valve, by the electronic control unit, to perform spray-guided stratified combustion in the second operation range;

wherein the predetermined first operation range includes at least a part of a compression ignition operation range, the compression ignition operation range is a range in which fuel is combusted by the pre-mixture compression ignition combustion;

wherein the predetermined second operation range includes at least a flame ignition operation range, the flame ignition operation range is a range in which fuel is combusted by the flame propagation combustion;

wherein the switching failure is failure in which the lift characteristic of the exhaust valve is not switchable from the second lift characteristic to the first lift characteristic by the electronic control unit, the homogeneous combustion is combustion in which fuel homogeneously diffused into the combustion chamber is ignited by the spark plug and is combusted by the flame propagation combustion; and

wherein the spray-guided stratified combustion is combustion in which fuel in the fuel injection path is ignited by the spark plug and is combusted by the flame propagation combustion.