Controlling device for internal combustion engine equipped with turbocharger

A controlling device for an internal combustion engine equipped with a turbocharger, that has a first actuator that changes an amount of air that is taken into a cylinder, a second actuator that supplies fuel into the cylinder, and a third actuator that ignites a mixture gas in the cylinder, and is configured to be capable of selecting an operation by a first air-fuel ratio and an operation by a second air-fuel ratio that is leaner than the first air-fuel ratio, comprising:

• requested torque reception means for receiving a requested torque;
• target air amount calculation means for calculating a target air amount for achieving the requested torque from the requested torque by using a parameter that gives a conversion efficiency of an air amount into torque;
• parameter value changing means for changing a value of the parameter to a value that reduces the conversion efficiency in response to a decrease of the requested torque to a reference value or smaller;
• target air-fuel ratio switching means for switching a target air-fuel ratio from the first air-fuel ratio to the second air-fuel ratio, after the value of the parameter is changed to the value that reduces the conversion efficiency;
• first actuator control means for determining an operation amount of the first actuator based on the target air amount, and operating the first actuator in accordance with the operation amount;
• second actuator control means for determining a fuel supply amount based on the target air-fuel ratio, and operating the second actuator in accordance with the fuel supply amount;
• and
• third actuator control means for determining an ignition timing for achieving the requested torque based on a torque that is estimated from the operation amount of the first actuator and the target air-fuel ratio, and the requested torque, and operating the third actuator in accordance with the ignition timing,
• wherein the target air amount calculation means includes
• target first air amount calculation means for calculating the target first air amount for achieving the requested torque from the requested torque by using a first parameter that gives a conversion efficiency of an air amount into torque, and
• target second air amount calculation means for calculating a target second air amount for achieving the requested torque from the requested torque by using a second parameter that gives a conversion efficiency of the air amount into torque,
• the parameter value changing means includes
• first parameter value changing means for changing a value of the first parameter to a value that reduces the conversion efficiency in response to the requested torque being reduced to a first reference value or smaller, and
• second parameter value changing means for
• starting to change a value of the second parameter in a direction to reduce the conversion efficiency in response to the requested torque being decreased to a second reference value or lower, the second reference value larger than the first reference value, and
• gradually changing the value of the second parameter in the direction to reduce the conversion efficiency in accordance with the requested torque further decreasing from the second reference value to the first reference value,
• the target air-fuel ratio switching means includes means for switching the target air-fuel ratio from the first air-fuel ratio to the second air-fuel ratio, after the value of the first parameter is changed to a value that reduces the conversion efficiency,
• the first actuator includes
• an intake property variable actuator that changes an intake property of air that is taken into the cylinder in an intake passage at a downstream side of the turbocharger, and
• a turbocharging property variable actuator that changes a turbocharging property of the turbocharger, and
• the first actuator control means includes
• intake property variable actuator control means for determining an operation amount of the intake property variable actuator based on the target first air amount, and operating the intake property variable actuator in accordance with the operation amount, and
• turbocharging property variable actuator control means for determining an operation amount of the turbocharging property variable actuator based on a target turbocharging pressure that is calculated from the target second air amount, and operating the turbocharging property variable actuator in accordance with the operation amount.