Secondary air supply device for internal combustion engine

A secondary air supply device for an internal combustion engine, the secondary air supply device comprising:

• a secondary air supply passage configured to supply secondary air to an exhaust gas passage of the internal combustion engine provided with exhaust gas purifying catalyst;
• an air pump configured to supply the secondary air to the secondary air supply passage;
• a control valve arranged on a downstream side of the air pump, the control valve being configured to open/close the secondary air supply passage;
• a pressure sensor arranged between the air pump and the control valve, the pressure sensor being configured to detect a pressure within the secondary air supply passage;
• and
• an electronic control unit operatively connected to the air pump and the control valve, the electronic control unit configured to:
• (a) control the air pump to maintain driving of the air pump and control the control valve to close so as to close the secondary air supply passage when the control valve is opened so that the secondary air supply passage is opened and the air pump is driven;
• (b) detect progresses of a fluctuation in the pressure within the secondary air supply passage since just after the secondary air supply passage is closed, by the pressure sensor;
• (c) calculate a differential pressure between a maximum pressure and a convergence pressure of the pressures within the secondary air supply passage since just after the secondary air supply passage is closed;
• (d) calculate a flow amount of the secondary air supplied from the secondary air supply passage to the exhaust gas passage based on the differential pressure;
• and
• (e) control the air pump and the control valve in response to the calculated flow amount of the secondary air supplied from the secondary air supply passage to the exhaust gas passage.