Patent ID: 8402749

Claim:
A control method of a spark-ignition engine which comprises a spark plug to supply a spark to ignite an air-fuel mixture within a combustion chamber and a catalyst for purifying exhaust gas which is provided in an exhaust passage, the control method comprising: executing a normal combustion control in case an engine operating condition is in a specified operating area including a low engine-speed and low engine-load area and a temperature of the catalyst is a specified temperature or higher, the normal combustion control including setting an excess air ratio λ at a first specified ratio which is between two and three and setting an ignition timing at a timing of MBT to provide the maximum torque; and executing a catalyst-temperature-related combustion control in case the engine operating condition is in said specified operating area and the temperature of the catalyst is lower than said specified temperature, the catalyst-temperature-related combustion control having at least a first control which is executed when the catalyst temperature is within a first temperature range and a second control which is executed when the catalyst temperature is lower than the first temperature range, the first control including setting the excess air ratio λ at two or greater and retarding the ignition timing from the timing of MBT, the second control including setting the excess air ratio λ to one or smaller and maintaining the ignition timing at the timing of MBT.