Leak diagnosis method and leak diagnosis device for blowby gas treatment device of internal combustion engine

An internal combustion engine blowby gas treatment device leak diagnosis device comprising:

• an internal combustion engine including a compressor in an intake passage for supercharging;
• a blowby gas treatment device including:
• a fresh air induction pipe structured to induce fresh air into a crank case from a section of the intake passage downstream of an air flow meter;
• a pressure control valve disposed in a section of the intake passage upstream of a throttle valve and upstream of the compressor;
• a first blowby gas pipe structured to induce blowby gas from the crank case into a section of the intake passage between the compressor and the pressure control valve;
• a second blowby gas pipe structured to induce blowby gas from the crank case into a section of the intake passage downstream of the compressor and downstream of the throttle valve;
• a shutoff valve structured to block the fresh air induction pipe;
• a one-way valve structured to allow only a gas flow in the first blowby gas pipe from the crank case to the intake passage;
• and
• a PCV valve disposed in the second blowby gas pipe;
• and
• a control section configured to diagnose leaking of the blowby gas treatment device, wherein the control section is configured to:
• perform a first diagnosis to close the shutoff valve under a supercharging condition and determine whether falling of a pressure in the crank case after the closing of the shutoff valve is normal or abnormal;
• perform a second diagnosis to control the pressure control valve into an open-side state and a closed-side state under a non-supercharging condition and determine whether or not an open-side state intake air quantity is equal to a closed-side state intake air quantity, wherein the open-side state intake air quantity is a quantity of intake air measured when the pressure control valve is in the open-side state, and wherein the closed-side state intake air quantity is a quantity of intake air measured when the pressure control valve is in the closed-side state;
• determine presence of a leak to an outside of a system of the blowby gas treatment device, in response to a condition that the first diagnosis determines the falling of the pressure as abnormal and the second diagnosis determines the open-side state intake air quantity as unequal to the closed-side state intake air quantity;
• and
• determine presence of a failure within the system of the blowby gas treatment device, in response to a condition that the first diagnosis determines the falling of the pressure as abnormal and the second diagnosis determines the open-side state intake air quantity as equal to the closed-side state intake air quantity.