Patent ID: 7987664

Claim:
A secondary air supply system that supplies secondary air to an exhaust passage of an engine, comprising: a supply source of the secondary air; a supply passage through which the secondary air is supplied from the supply source to the exhaust passage; an engine state determination device arranged to determine a state of the engine; a storage device arranged to store a target air-fuel ratio set in advance depending on the state of the engine; and an air flow adjustment device arranged to adjust, based on the state of the engine determined by the engine state determination device and the target air-fuel ratio stored in the storage device, an amount of the secondary air to be supplied from the supply passage to the exhaust passage so that an air-fuel ratio in the exhaust passage is the target air-fuel ratio; wherein the state of the engine includes a first state and a second state set in advance based on an amount of nitrogen oxide exhausted from a combustion chamber of the engine, and a third state set in advance based on a load applied on the engine; the amount of the nitrogen oxide exhausted in the first state is smaller than the amount of the nitrogen oxide exhausted in the second state, and the load applied on the engine in the third state is higher than a load applied on the engine in the first and second states; and the target air-fuel ratio includes a first air-fuel ratio corresponding to the first state, a second air-fuel ratio corresponding to the second state, and a third air-fuel ratio corresponding to the third state, the first air-fuel ratio is leaner than the second air-fuel ratio, and the second air-fuel ratio is leaner than the third air-fuel ratio.