Variable system of internal combustion engine and method for controlling the same

A variable system of an internal combustion engine:

• wherein the variable system is used for an internal combustion engine including a turbocharger equipped with a waste gate valve, a variable actuation valve mechanism configured to control a closing timing of an intake valve, and a variable compression ratio mechanism configured to control a mechanical compression ratio and a mechanical expansion ratio;
• wherein the variable system further includes a control unit configured to control the waste gate valve, the variable actuation valve mechanism, and the variable compression ratio mechanism;
• wherein the control unit controls the variable actuation valve mechanism and the variable compression ratio mechanism at least in a region where an engine torque is an intermediate level and a region where the engine torque is higher than the region of the intermediate level;
• and
• wherein, further, the control unit reduces the mechanical expansion ratio to a predetermined mechanical expansion ratio according to an increase in the engine torque and also sets the closing timing of the intake valve from an advance-angle side to a retard-angle side of an intake bottom dead center according to the increase in the engine torque in the region where the engine torque is the intermediate level, and increases the predetermined mechanical expansion ratio and controls the waste control valve to open it according to the increase in the engine torque and also sets the closing timing of the intake valve to the advance-angle side advanced from the intake bottom dead center according to the increase in the engine torque in the region where the engine torque is higher than the region of the intermediate level.

A method for controlling a variable system of an internal combustion engine, the variable system including a control unit configure to control

• a variable actuation valve mechanism configured to control a closing timing of an intake valve and
• a variable compression ratio mechanism configured to control a mechanical compression ratio and a mechanical expansion ratio, the control method comprising:
• keeping the mechanical expansion ratio at a first mechanical expansion ratio and also setting the closing timing of the intake valve to an advance-angle side advanced from an intake bottom dead center in a first region where an engine torque is low;
• reducing the first mechanical expansion ratio to a second mechanical expansion ratio according to the increase in the engine torque and also setting the closing timing of the intake valve from the advance-angle side to a retard-angle side of the intake bottom dead center according to the increase in the engine torque in a second region where the engine torque is an intermediate level;
• and
• increasing the second mechanical expansion ratio to a third mechanical expansion ratio according to the increase in the engine torque and also setting the closing timing of the intake valve to a retard-angle side further retarded from the retard-angle side in the case of the second region according to the increase in the engine torque in a third region where the engine torque is high.