Operation control device and operation control method for multi-cylinder internal combustion engine

Abstract

When the cut-off cylinder operation execution condition of a multi-cylinder internal combustion engine is fulfilled, the temperature of the catalytic converter provided in the exhaust passage linked to the cylinders that are made inoperative during the cut-off cylinder operation is estimated, and when this temperature is less than the predetermined preliminary heating requiring temperature, a catalyst preliminary heating operation is executed by which the ignition timing of the cylinders is delayed and the temperature of the catalytic converter is raised. Then, the cut-off cylinder operation is started after the temperature of the catalytic converter becomes equal to or higher than the preliminary heating requiring temperature.

1 . An operation control device for a multi-cylinder internal combustion engine which is provided with a first catalyst provided in a first exhaust passage linked to at least one cylinder from among a plurality of cylinders and a second catalyst provided in a second exhaust passage linked to other cylinders, and in which the at least one cylinder is made inoperative by cut-off cylinder operation when a predetermined cut-off cylinder operation execution condition is fulfilled, comprising:
 a catalyst temperature recognition portion that detects or executes a temperature of the first catalyst; and   a catalyst preliminary heating operation execution portion that executes a catalyst preliminary heating operation for increasing a temperature of the first catalyst to a temperature equal to or higher than a preliminary heating requiring temperature, which is higher than a lower limit of activation temperature of the first catalytic converter by a predetermined amount, before the cut-off cylinder operation is executed in a case where the temperature of the first catalyst that has been detected or estimated by the catalyst temperature recognition portion is less than the predetermined preliminary heating requiring temperature when the cut-off cylinder operation execution condition is fulfilled,   wherein the catalyst preliminary heating operation delays an ignition timing of a spark plug of the at least one cylinder that becomes inoperative during the cut-off cylinder operation prior to executing the cut-off cylinder operation and gradually increases a delay amount of the ignition timing, thereby gradually decreasing an amount of kinetic energy participating in torque generation in the internal combustion engine and gradually increasing an amount of thermal energy participating in the catalyst preliminary heating, from among an energy generated by combustion of an air-fuel mixture,   and wherein, while the cut-off cylinder operation execution condition is being fulfilled, when the temperature of the first catalyst becomes equal to or higher than the preliminary heating requiring temperature due to the catalyst preliminary heating operation, the catalyst preliminary heating operation is stopped and the cut-off cylinder operation is started.   
     
     
         2 - 4 . (canceled) 
     
     
         5 . The operation control device for a multi-cylinder internal combustion engine according to  claim 1 , wherein
 in a case where the temperature of the first catalyst has decreased to a predetermined full-cylinder operation restoration temperature during the cut-off cylinder operation, switching is made from the cut-off cylinder operation to the full-cylinder operation, and   the full-cylinder operation restoration temperature is set to a temperature that is higher than the lower limit of activation temperature of the first catalyst at which the air-fuel mixture can burn inside the first catalyst and to a temperature that is lower than the preliminary heating requiring temperature.   
     
     
         6 . The operation control device for a multi-cylinder internal combustion engine according to  claim 1 , wherein the predetermined amount is 150° C. 
     
     
         7 . An operation control method for a multi-cylinder internal combustion engine which is provided with a first catalyst provided in a first exhaust passage linked to at least one cylinder from among a plurality of cylinders and a second catalyst provided in a second exhaust passage linked to other cylinders, and in which the at least one cylinder is made inoperative by cut-off cylinder operation,
 the method comprising:
 determining whether a predetermined cut-off cylinder operation execution condition is fulfilled; 
 detecting or estimating a temperature of the first catalyst; 
 executing a catalyst preliminary heating operation for increasing a temperature of the first catalyst to a temperature equal to or higher than a preliminary heating requiring temperature, which is higher than a lower limit of activation temperature of the first catalytic converter by a predetermined amount, before the cut-off cylinder operation is executed in a case where the temperature of the first catalyst that has been detected or estimated is less than the predetermined preliminary heating requiring temperature when the cut-off cylinder operation execution condition is fulfilled, wherein the catalyst preliminary heating operation delays an ignition timing of a spark plug of the at least one cylinder that becomes imperative during the cut-off cylinder operation prior to executing the cut-off cylinder operation and gradually increases a delay amount of the ignition timing, thereby gradually decreasing an amount of kinetic energy participating in torque generation in the internal combustion engine gradually increasing an mount of thermal energy participating in the catalyst preliminary heating, from among an energy generated by combustion of an air-fuel mixture; and 
 ceasing the catalyst preliminary heating operation and starting the cut-off cylinder operation, when the temperature of the first catalyst becomes equal to or higher than the preliminary heating requiring temperature due to the catalyst preliminary heating operation, while the cut-off cylinder operation execution condition is being fulfilled.