Engine exhaust purification device

Abstract

An engine exhaust purification device includes a filter, a burner, and a control unit. The filter is arranged in an engine exhaust pipe. The burner burns fuel injected from a fuel injection nozzle and heats exhaust to increase the temperature of the filter at an upstream side of the filter in the exhaust pipe. A period including a single fuel injection period and a single injection stop period is set as a single injection cycle. The fuel injection period is a period injecting fuel a number of times at a predetermined frequency. The injection stop period is a variable period that stops fuel injection. The control unit controls the fuel injection nozzle so that the fuel injection nozzle injects the fuel according to the injection cycle. The control unit is configured to lengthen the injection stop period as the temperature of the filter increases.

1 . An engine exhaust purification device comprising:
 a filter that is arranged in an exhaust pipe of an engine and traps fine particles that are suspended in an exhaust passing through the exhaust pipe;   a burner including a fuel injection nozzle and arranged at a position located at an upstream side of the filter in the exhaust pipe, wherein the burner burns fuel injected from the fuel injection nozzle and heats the exhaust to increase the temperature of the filter and remove the fine particles trapped in the filter; and   a control unit that controls a fuel injection mode of the fuel injection nozzle, wherein   a period including a single fuel injection period and a single injection stop period is set as a single injection cycle,   the fuel injection period is a period in which fuel is injected for a number of times at a predetermined frequency;   the injection stop period is a variable period in which the injection of fuel is stopped,   the control unit controls the fuel injection nozzle so that the fuel injection nozzle injects fuel in accordance with the injection cycle, and   the control unit is configured to lengthen the injection stop period as the temperature of the filter increases.   
     
     
         2 . The engine exhaust purification device according to  claim 1 , wherein the control unit is configured to shorten the injection stop period as an exhaust flow rate increases in the exhaust pipe. 
     
     
         3 . The engine exhaust purification device according to  claim 1 , wherein
 the fuel injection period is a first fuel injection period,   a period of one of a number of injections repeated at the predetermined frequency in the first fuel injection period is a second fuel injection period,   the engine includes an intake pipe that supplies air to the burner, and   the control unit is configured to lengthen the second fuel injection period as the air amount supplied to the burner increases in the first fuel injection period.   
     
     
         4 . The engine exhaust purification device according to  claim 3 , wherein the control unit is configured to set the second fuel injection period so that a ratio of a total amount of fuel injected in the first fuel injection period and an air amount supplied to the burner in the first fuel injection period conforms to the stoichiometric air-fuel ratio. 
     
     
         5 . The engine exhaust purification device according to  claim 3 , wherein the control unit sets the injection stop period and the second fuel injection period in the injection cycle. 
     
     
         6 . The engine exhaust purification device according to  claim 1 , wherein the control unit sets the frequency to 100 Hz or greater and 200 Hz or less. 
     
     
         7 . The engine exhaust purification device according to  claim 1 , wherein
 the control unit sets a unit injection amount, which is an injection amount of fuel per unit time in the fuel injection cycle, based on a map of which parameters are the exhaust flow rate in the exhaust pipe and the temperature of the filter; and   the control unit calculates and sets the injection stop period from the total amount of fuel injected in the fuel injection period and the unit injection amount.