Exhaust heating device for internal combustion engine and control method therefor

Abstract

An internal combustion engine in which first and second turbochargers are incorporated in series has first and second bypass passages bypassing exhaust turbines of the first and second turbochargers and two opening/closing valves for opening/closing the first and second bypass passages respectively. An exhaust gas heating device for heating exhaust gas being led to an exhaust purifying device from the engine is disposed in an exhaust passage so as to be located upstream of a confluent portion of the exhaust passage and the second bypass passage and downstream of the turbine of the second turbocharger. A valve capable of regulating the flow rate of exhaust gas flowing in the exhaust passage is disposed in the exhaust passage so as to be located downstream of a branched portion of the exhaust passage and the second bypass passage and upstream of the turbine of the second turbocharger.

1 - 6 . (canceled) 
     
     
         7 . An exhaust heating device for heating exhaust gas being led to an exhaust purifying device from an internal combustion engine having a first bypass passage bypassing an exhaust turbine of a first exhaust turbocharger, a second bypass passage bypassing an exhaust turbine of a second exhaust turbocharger, and two opening/closing valves for opening or closing the first and second bypass passages independently of each other, the first exhaust turbocharger and the second exhaust turbocharger that is disposed in an exhaust passage so as to be located upstream of the first turbocharger and is used in mainly a lower speed range of the internal combustion engine, the first and second turbochargers being incorporated in series on the exhaust passage,
 wherein the exhaust heating device is disposed in the exhaust passage so as to be located upstream of a confluent portion of the exhaust passage and the second bypass passage and downstream of an exhaust turbine of the second turbocharger; and   a valve capable of regulating the flow rate of exhaust gas in the exhaust passage is disposed in the exhaust passage so as to be located downstream of a branched portion of the exhaust passage and the second bypass passage and upstream of the exhaust turbine of the second exhaust turbocharger.   
     
     
         8 . The exhaust heating device for the engine as claimed in  claim 7 , wherein the exhaust heating device includes a fuel supply valve for supplying fuel to the exhaust passage, and ignition means for igniting and conflagrating the fuel supplied from the fuel supply valve to the exhaust passage. 
     
     
         9 . The exhaust heating device for the engine as claimed in  claim 8 , wherein an oxidation catalytic converter is provided in the exhaust passage between the ignition means and the exhaust purifying device. 
     
     
         10 . The exhaust heating device for the engine as claimed in  claim 8 , wherein when the fuel is ignited by using the ignition means, the opening of the valve is regulated in such a manner that the flow rate of the exhaust gas passing the exhaust turbine of the second turbocharger becomes smaller than that of the exhaust gas in the second bypass passage. 
     
     
         11 . The exhaust heating device for the engine as claimed in  claim 9 , wherein when the fuel is ignited by using the ignition means, the opening of the valve is regulated in such a manner that the flow rate of the exhaust gas passing the exhaust turbine of the second turbocharger becomes smaller than that of the exhaust gas in the second bypass passage. 
     
     
         12 . A control method for the exhaust heating device as claimed in  claim 7 , comprising the steps of:
 determining whether or not the exhaust purifying device is activated;   detecting an engine speed of the engine;   setting the opening of the valve based on the detected engine speed of the engine; and   driving the valve in such a manner as to achieve a set opening when it is determined that the exhaust purifying device is not activated so as to lead the exhaust gas to the turbine of the second turbocharger at a predetermined flow rate and actuate the exhaust heating device.   
     
     
         13 . A control method for the exhaust heating device as claimed in  claim 8 , comprising the steps of:
 determining whether or not the exhaust purifying device is activated;   detecting an engine speed of the engine;   setting the opening of the valve based on the detected engine speed of the engine; and   driving the valve in such a manner as to achieve a set opening when it is determined that the exhaust purifying device is not activated so as to lead the exhaust gas to the turbine of the second turbocharger at a predetermined flow rate and actuate the exhaust heating device.   
     
     
         14 . The control method as claimed in  claim 12 , wherein the step of driving the valve in such a manner as to achieve the set opening when it is determined that the exhaust purifying device is not activated so as to lead the exhaust gas to the turbine of the second turbocharger at a predetermined flow rate and actuate the exhaust heating device includes a step of driving the second opening/closing valve in such a manner as to turn the second bypass passage into a fully open state. 
     
     
         15 . The control method as claimed in  claim 13 , wherein the step of driving the valve in such a manner as to achieve the set opening when it is determined that the exhaust purifying device is not activated so as to lead the exhaust gas to the turbine of the second turbocharger at a predetermined flow rate and actuate the exhaust heating device includes a step of driving the second opening/closing valve in such a manner as to turn the second bypass passage into a fully open state.