Control device for diesel engine

Abstract

A control device for a diesel engine has a valve timing switching mechanism capable of selectively switching between first opening/closing timing and second opening/closing timing for an exhaust valve. The first opening/closing timing is set such that the period for which the exhaust valve is open overlaps the period for which an intake valve is open, and that opening start timing for the exhaust valve is after bottom dead center of expansion stroke of a piston. The second opening/closing timing is set such that opening start timing for the exhaust valve is advanced compared with the opening start timing according to the first opening/closing timing. A control unit controls the valve timing switching mechanism so that the exhaust valve is opened and closed according to the first opening/closing timing, at least when the diesel engine is operating in a predetermined cold condition.

1 . A control device for a diesel engine, comprising:
 a valve timing switching mechanism capable of selectively switching between first opening/closing timing and second opening/closing timing for an exhaust valve of the diesel engine;   an exhaust after-treatment device for purifying exhaust gas discharged from the diesel engine; and   a control means for controlling the valve timing switch mechanism so that the exhaust valve is opened and closed according to the first opening/closing timing, at least when the diesel engine is operating in a predetermined cold condition, wherein   the first opening/closing timing is set such that the period for which the exhaust valve is open overlaps the period for which an intake valve associated with the same cylinder that the exhaust valve is associated with is open, and that opening start timing for the exhaust valve is after bottom dead center of expansion stroke of a piston in the cylinder, and   the second opening/closing timing is set such that opening start timing for the exhaust valve is advanced compared with the opening start timing according to the first opening/closing timing.   
   
   
       2 . The control device for a diesel engine according to  claim 1 , wherein
 the opening start timing for the exhaust valve according to the first opening/closing timing is set to a predetermined crank angle of the piston between 40° and 70° after bottom dead center.   
   
   
       3 . The control device for a diesel engine according to  claim 1 , wherein
 the exhaust valve is opened and closed according to the second opening/closing timing when a working oil is supplied to the valve timing switching mechanism, and the exhaust valve is opened and closed according to the first opening/closing timing when the working oil is not supplied to the valve timing switching mechanism.   
   
   
       4 . The control device for a diesel engine according to  claim 3 , wherein
 when the control means is controlling the valve timing switching mechanism so that the exhaust valve is opened and closed according to the first opening/closing timing, the control means prohibits the valve timing switching mechanism from switching from the first opening/closing timing to the second opening/closing timing until determining that the temperature of the working oil has risen to a predetermined oil temperature or above.   
   
   
       5 . The control device for a diesel engine according to  claim 1 , wherein
 when the control means determines that the diesel engine is operating in a predetermined condition that causes a decrease in the temperature of the exhaust gas, the control means controls the valve timing switching mechanism so that the exhaust valve is opened and closed according to the first opening/closing timing.   
   
   
       6 . The control device for a diesel engine according to  claim 5 , wherein
 the diesel engine is mounted on a vehicle as a power source; and   when the vehicle is decelerating, the control means determines that the diesel engine is operating in the predetermined condition that causes a decrease in the temperature of the exhaust gas.   
   
   
       7 . The control device for a diesel engine according to  claim 5 , wherein
 when the diesel engine is decelerating, the control means determines that the diesel engine is operating in the predetermined condition that causes a decrease in the temperature of the exhaust gas.   
   
   
       8 . The control device for a diesel engine according to  claim 5 , wherein
 when the diesel engine is operating in a predetermined low-speed low-load condition, the control means determines that the diesel engine is operating in the predetermined condition that causes a decrease in the temperature of the exhaust gas.   
   
   
       9 . The control device for a diesel engine according to  claim 5 , wherein
 when the temperature of the exhaust gas of the diesel engine is below a predetermined exhaust temperature, the control means determines that the diesel engine is operating in the predetermined condition that causes a decrease in the temperature of the exhaust gas.