Patent ID: 8220250
Filing Date: 2012-07-17
Classification: F02D,F02M

Abstract:
1. An internal combustion engine comprising: a plurality of cylinders divided into at least two cylinder groups; a plurality of exhaust branch pipes, joined near downstream ends, each connected to a cylinder group of the at least two cylinder groups; a common exhaust pipe connected to the downstream ends, which are joined, of the plurality of exhaust branch pipes; an exhaust gas purifying catalyst disposed in the common exhaust pipe; at least one first air-fuel ratio sensor disposed in each of the exhaust branch pipes; a second air-fuel ratio sensor disposed in the common exhaust pipe upstream from the exhaust gas purifying catalyst; and a controller that is configured to usually perform normal operation, which causes combustion in each cylinder group with a prescribed air-fuel ratio, wherein when there is a need to supply a reducing agent and air to the exhaust gas purifying catalyst, the controller is configured to perform rich-lean operation, which causes combustion with an air-fuel ratio richer than a stoichiometric air-fuel ratio in a first cylinder group and causes combustion with an air-fuel ratio leaner than the stoichiometric air-fuel ratio in a second cylinder group so that exhaust gas having the prescribed air-fuel ratio flows into the exhaust gas purifying catalyst, wherein when a prescribed condition is established, the controller is configured to perform purge control introducing a gas including a fuel vapor into an intake passage leading to all of the plurality of cylinders, and determines and records an amount of fuel vapor introduced into the intake passage during the purge control as a learned value, wherein, during normal operation, when determining the fuel vapor amount introduced into the intake passage during purge control, the controller is configured to determine the fuel vapor amount using an output value of the at least one first air-fuel ratio sensor and a fuel vapor amount determined and recorded as a learned value of fuel vapor amount during normal operation, wherein, during rich-lean operation, when determining the fuel vapor amount introduced into the intake passage during purge control, the controller is configured to determine the fuel vapor amount using an output value of the second air-fuel ratio sensor and a fuel vapor amount determined and recorded as a learned value of fuel vapor amount during rich-lean operation, and wherein the learned value of the amount of fuel vapor introduced into the intake passage during the purge control is reset to zero when the internal combustion engine switches from the normal operation to a sulfur poisoning recovery operation or switches from the sulfur poisoning recovery operation to the normal operation.