Homogenous charge compression ignition engine and controlling method of the engine

A homogeneous charge compression ignition (HCCI) engine, wherein the HCCI engine allows a combustion mode to be switched between an HCCI combustion and a spark ignition combustion, the HCCI engine comprising:

• a combustion chamber;
• a piston that reciprocates in the combustion chamber, the piston defining an exhaust top dead center of the combustion chamber;
• an intake valve;
• an exhaust valve;
• an intake variable valve mechanism for changing an intake lift amount, which is a lift amount of the intake valve, wherein the intake lift amount is set to a first intake lift amount in the spark ignition combustion and to a second intake lift amount in the HCCI combustion, wherein the intake variable valve mechanism is capable of controlling an intake opening timing, which is the opening timing of the intake valve;
• an exhaust variable valve mechanism for changing an exhaust lift amount, which is a lift amount of the exhaust valve, wherein the exhaust lift amount is set to a first exhaust lift amount in the spark ignition combustion and to a second exhaust lift amount in the HCCI combustion, wherein the exhaust variable valve mechanism is capable of controlling an exhaust closing timing, which is the closing timing of the exhaust valve, and wherein a reference exhaust closing timing to be used in the HCCI combustion is set;
• a controller for controlling the intake variable valve mechanism and the exhaust variable valve mechanism,
• wherein the controller sets an internal EGR amount, which includes the amount of burned gas that remains in the combustion chamber at the time of the HCCI combustion, by setting a negative valve overlap period, during which both of the intake valve and the exhaust valve are closed, such that not all the burned gas is discharged from the combustion chamber,
• wherein, when switching the combustion mode from the spark ignition combustion to the HCCI combustion, the controller executes following operations:
• a) switching the intake lift amount from the first intake lift amount to the second intake lift amount, such that the intake opening timing is delayed relative to the exhaust top dead center, so that intake is started while the interior of the combustion chamber is under negative pressure during an intake stroke, causing the intake air to spurt into the combustion chamber and an adiabatic compression effect of the combustion chamber is enhanced, so that the temperature of the combustion chamber is raised and the HCCI combustion is thus carried out;
• b) switching the exhaust lift amount from the first exhaust lift amount to the second exhaust lift amount;
• and
• c) temporarily delaying the exhaust closing timing relative to the reference exhaust closing timing corresponding to the HCCI engine load and speed in the HCCI combustion, such that the internal EGR amount is generated less than the internal EGR amount generated by the reference exhaust closing timing after the operation a) to suppress an excessive increase of the temperature in the combustion chamber to prevent the occurrence of a state where the spark ignition combustion and the HCCI combustion are simultaneously carried out and abrupt changes of the torque are suppressed, and then advancing the exhaust closing timing to the reference exhaust closing timing.