Method and apparatus for controlling temperature of catalyst and engine system having the apparatus

Abstract

An HC absorption combustion catalyst is provided in the exhaust pipe of an internal combustion engine and shifts from an HC absorption phase to an HC purification phase through an HC release phase as a temperature of the HC absorption combustion catalyst increases from a low value to a high value. The temperature of the HC absorption combustion catalyst is controlled in accordance with the HC absorption phase, the HC release phase and the HC purification phase.

1 . A catalyst temperature control apparatus for controlling a temperature of an HC absorption combustion catalyst which is provided in an exhaust pipe of an internal combustion engine and which shifts from an HC absorption phase to an HC purification phase through an HC release phase as a temperature of the HC absorption combustion catalyst increases from a low value to a high value, wherein 
 a temperature of the HC absorption combustion catalyst is controlled in accordance with the HC absorption phase, the HC release phase and the HC purification phase.    
   
   
       2 . A catalyst temperature control apparatus according to  claim 1 , wherein 
 a temperature of the HC absorption combustion catalyst is controlled by switching the temperature increasing rate of the HC absorption combustion catalyst in accordance with the HC absorption phase, the HC release phase and the HC purification phase.    
   
   
       3 . A catalyst temperature control apparatus according to  claim 1 , wherein 
 a temperature of the HC absorption combustion catalyst is controlled in a manner that a temperature increasing rate of the HC absorption combustion catalyst at a time of the HC absorption phase of the HC absorption combustion catalyst is made smaller than a temperature increasing rate of the HC absorption combustion catalyst at a time of the HC release phase of the HC absorption combustion catalyst.    
   
   
       4 . A catalyst temperature control apparatus according to  claim 1 , comprising: 
 a temperature gentle increase control unit which increases a temperature of the HC absorption combustion catalyst at a first increasing rate;    a temperature rapid increase control unit which increases a temperature of the HC absorption combustion catalyst at a rate larger than the first increasing rate;    a temperature gentle/rapid increase control determination unit for determining one of the temperature gentle increase control unit and the temperature rapid increase control unit which performs temperature control of the HC absorption combustion catalyst; and    a temperature gentle/rapid increase control switching unit which switches between the temperature gentle increase control unit and the temperature rapid increase control unit in accordance with determination result of the temperature gentle/rapid increase control determination unit.    
   
   
       5 . A catalyst temperature control apparatus according to  claim 4 , wherein 
 the temperature gentle/rapid increase control determination unit is constituted by a lapse time measuring unit for measuring a time period lapsed after start of the engine, and a determination unit for determining whether or not the lapse time after the start of the engine measured by the lapse time measuring unit exceeds a predetermined value.    
   
   
       6 . A catalyst temperature control apparatus according to  claim 4 , wherein 
 the temperature gentle/rapid increase control determination unit is constituted by a catalyst temperature detecting unit for detecting temperature of the HC absorption combustion catalyst and a determination unit for determining whether or not the temperature of the HC absorption combustion catalyst detected by the catalyst temperature detecting unit exceeds a predetermined value.    
   
   
       7 . A catalyst temperature control apparatus according to  claim 4 , wherein 
 the temperature gentle/rapid increase control determination unit is constituted by an air flow rate detecting unit for detecting a flow rate of air flowing into the engine and a determination unit for determining whether or not the air flow rate detected by the air flow rate detecting unit exceeds a predetermined value.    
   
   
       8 . A catalyst temperature control apparatus according to  claim 4 , wherein 
 the temperature gentle increase control unit includes a circulation pipe for circulating exhaust gas from the engine to a suction side of the engine, a circulation valve for adjusting circulation rate of the exhaust gas and a circulation valve control means for controlling the circulation valve.    
   
   
       9 . A catalyst temperature control apparatus according to  claim 4 , wherein 
 the temperature rapid increase control unit controls so as to retard an ignition timing.    
   
   
       10 . A catalyst temperature control apparatus according to  claim 4 , wherein 
 the temperature rapid increase control unit controls so that air fuel ratios of respective cylinders of the engine are differentiated in rich and lean states respectively.    
   
   
       11 . A catalyst temperature control apparatus according to  claim 4 , wherein 
 the temperature rapid increase control unit controls so as to burn unburned HC within the exhaust pipe by introducing air or O2 within the exhaust pipe.    
   
   
       12 . A catalyst temperature control method for controlling a temperature of an HC absorption combustion catalyst which is provided in an exhaust pipe of an internal combustion engine and which shifts from an HC absorption phase to an HC purification phase through an HC release phase as a temperature of the HC absorption combustion catalyst increases from a low value to a high value, comprising the step of: 
 controlling a temperature of the HC absorption combustion catalyst in accordance with the HC absorption phase, the HC release phase and the HC purification phase.    
   
   
       13 . A catalyst temperature control method according to  claim 12 , wherein 
 a temperature of the HC absorption combustion catalyst is controlled by switching the temperature increasing rate of the HC absorption combustion catalyst in accordance with the HC absorption phase, the HC release phase and the HC purification phase.    
   
   
       14 . A catalyst temperature control method according to  claim 12 , wherein 
 a temperature of the HC absorption combustion catalyst is controlled in a manner that a temperature increasing rate of the HC absorption combustion catalyst at a time of the HC absorption phase of the HC absorption combustion catalyst is made smaller than a temperature increasing rate of the HC absorption combustion catalyst at a time of the HC release phase of the HC absorption combustion catalyst.    
   
   
       15 . A catalyst temperature control method according to  claim 13 , wherein 
 the temperature increasing rate of the HC absorption combustion catalyst is switched in accordance with a time period lapsed after start of the engine.    
   
   
       16 . A catalyst temperature control method according to  claim 13 , wherein 
 the temperature increasing rate of the HC absorption combustion catalyst is switched in accordance with a temperature of the HC absorption combustion catalyst.    
   
   
       17 . An engine system comprising: 
 an internal combustion engine; 
 an HC absorption combustion catalyst which is provided in an exhaust pipe of the engine and which shifts from an HC absorption phase to an HC purification phase through an HC release phase as a temperature of the HC absorption combustion catalyst increases from a low value to a high value; and  
 a catalyst temperature control apparatus for controlling a temperature of the HC absorption combustion catalyst in accordance with the HC absorption phase, the HC release phase and the HC purification phase.  
   
   
   
       18 . An engine system according to  claim 17 , wherein 
 the engine is a lean burn engine in which combustion is performed with air fuel mixture having an air fuel ratio thinner than a stoichiometric air-fuel ratio, and wherein    the catalyst temperature control apparatus includes    a lean combustion allowance unit which determines to allow lean combustion for the lean burn engine,    a target ignition timing calculation unit for calculating a target ignition timing based on the determination result of the lean combustion allowance unit,    a target fuel injection value/fuel injection timing calculation unit for calculating a target fuel injection amount and a target fuel injection timing based on the determination result of the lean combustion allowance unit,    a target air flow rate calculation unit for calculating a target air amount based on the determination result of the lean combustion allowance unit,    an ignition timing control device for controlling an ignition timing based on the calculation result of the target ignition timing calculation unit,    fuel injection valves for controlling fuel injection value and fuel injection timing based on the calculation result of the target fuel injection value/fuel injection timing calculation unit, and    an air flow rate control device for controlling an air flow rate based on the calculation result of the target air flow rate calculation unit.    
   
   
       19 . An engine system according to  claim 17 , wherein 
 the catalyst temperature control apparatus is arranged in a manner that the HC absorption combustion catalyst is disposed at such a position that the temperature of the HC absorption combustion catalyst is the temperature of the HC absorption phase during a predetermined time period after start of the engine in which HC can be absorbed within the HC absorption combustion catalyst.    
   
   
       20 . An engine system according to  claim 17 , further comprising: 
 a three way catalyst provided on an upstream side of the HC absorption combustion catalyst, wherein    the catalyst temperature control apparatus is arranged in a manner that the HC absorption combustion catalyst is disposed at such a position that the temperature of the HC absorption combustion catalyst is the temperature of the HC absorption phase until the temperature of the three way catalyst reaches a temperature at which purification function of the three way catalyst starts.