Compression ignition engine

Abstract

In a compression ignition engine employing a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of an intake valve lift and an intake valve closure timing, a control system operates to temporarily lower an effective compression ratio of the engine by controlling the intake valve characteristic during a cranking period of cold starting operation. At a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise, the effective compression ratio is risen by controlling the intake valve characteristic. After combustion of the engine has been stabilized, the intake valve characteristic is brought closer to a desired value determined based on engine operating conditions by way of closed-loop control.

1 . A compression ignition-engine comprising: 
 sensors that detect engine operating conditions;    a variable valve operating system comprising at least a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve and actuated by an actuator; and    a control unit configured to be electrically connected to the sensors and the actuator for controlling the variable valve actuation mechanism via the actuator to bring the intake valve characteristic closer to a desired value determined based on the engine operating conditions detected by the sensors; said control unit comprising a processor programmed to perform the following, 
 (a) temporarily lowering an effective compression ratio of the engine by controlling the intake valve characteristic during a cranking period of cold starting operation;  
 (b) rising the effective compression ratio by controlling the intake valve characteristic at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise; and  
 (c) bringing the intake valve characteristic closer to the desired value determined based on the engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.  
   
   
   
       2 . The compression ignition engine as claimed in  claim 1 , wherein: 
 the variable valve actuation mechanism of the variable valve operating system is able to vary the intake valve characteristic, before cranking operation of the engine is started or simultaneously with the engine cranking operation; and    the variable valve operating system further comprises a sensor that is able to detect information regarding an operating state of the intake valve from a substantially zero engine speed value.    
   
   
       3 . The compression ignition engine as claimed in  claim 1 , further comprising: 
 a sensor that is able to detect information regarding an operating state of the intake valve from a substantially zero engine speed value; and    a sensor that detects information regarding a quantity of air charged into an engine cylinder,    wherein the processor is further programmed for: 
 (d) compensating for, based on at least one of the information regarding the intake valve operating state and the information regarding the quantity of air charged into the cylinder, at least one of a fuel injection amount and a fuel injection timing, both determined based on the engine operating conditions including engine speed and engine load.  
   
   
   
       4 . The compression ignition engine as claimed in  claim 1 , further comprising: 
 a sensor that is able to detect information regarding an operating state of the intake valve from a substantially zero engine speed value,    wherein the processor is further programmed for: 
 (e) gradually controlling the intake valve operating state including at least an actual intake valve closure timing, to a normal intake valve operating state, when restarting the engine by either one of a starter and a motor generator.  
   
   
   
       5 . The compression ignition engine as claimed in  claim 1 , wherein the processor is further programmed for: 
 (f) generating a control command signal to the actuator for controlling at least the intake valve closure timing to a desired standby timing spaced apart from a piston bottom dead center position during a stopping period of the engine; and    (g) generating an engine stop signal after generating the control command signal.    
   
   
       6 . The compression ignition engine as claimed in  claim 1 , wherein the processor is further programmed for: 
 (h) temporarily shutting off or reducing electric power supply to either one of a glow plug and an electric heater, during the cranking period of cold starting operation.    
   
   
       7 . A compression ignition engine ( 1 ) comprising: 
 sensors that detect engine operating conditions;    a variable valve operating system comprising at least a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve and actuated by an actuator;    a decompression device provided to operate an exhaust valve in a decompression mode corresponding to a constantly-opened valve operating state during a cranking period of cold starting operation; and    a control unit configured to be electrically connected to the sensors and the actuator for controlling the variable valve actuation mechanism via the actuator to bring the intake valve characteristic closer to a desired value determined based on the engine operating conditions detected by the sensors; said control unit also configured to be electrically connected to the decompression device for switching the exhaust valve to the decompression mode during the cranking period; and said control unit comprising a processor programmed to perform the following, 
 (a) temporarily lowering an effective compression ratio of the engine by maintaining the exhaust valve in the decompression mode corresponding to the constantly-opened valve operating state during the cranking period;  
 (b) inhibiting the decompression mode and returning the exhaust valve to a normal operating state at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise;  
 (c) rising the effective compression ratio by controlling the intake valve characteristic substantially at the point of time when the predetermined cranking speed threshold value has been reached owing to the cranking speed rise; and  
 (d) bringing the intake valve characteristic closer to the desired value determined based on the engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.  
   
   
   
       8 . A compression ignition engine comprising: 
 sensor means for detecting engine operating conditions;    a variable valve operating system comprising at least a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve and actuated by an actuator; and    a control unit configured to be electrically connected to the sensor means and the actuator for controlling the variable valve actuation mechanism via the actuator to bring the intake valve characteristic closer to a desired value determined based on the engine operating conditions detected by the sensor means; said control unit comprising 
 (a) means for temporarily lowering an effective compression ratio of the engine by controlling the intake valve characteristic during a cranking period of cold starting operation;  
 (b) means for rising the effective compression ratio by controlling the intake valve characteristic at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise; and  
 (c) means for bringing the intake valve characteristic closer to the desired value determined based on the engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.  
   
   
   
       9 . A compression ignition engine comprising: 
 sensor means for detecting engine operating conditions;    a variable valve operating system comprising at least a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve and actuated by an actuator;    a decompression device provided to operate an exhaust valve in a decompression mode corresponding to a constantly-opened valve operating state during a cranking period of cold starting operation; and    a control unit configured to be electrically connected to the sensor means and the actuator for controlling the variable valve actuation mechanism via the actuator to bring the intake valve characteristic closer to a desired value determined based on the engine operating conditions detected by the sensor means; said control unit also configured to be electrically connected to the decompression device for switching the exhaust valve to the decompression mode during the cranking period; and said control unit comprising 
 (a) means for temporarily lowering an effective compression ratio of the engine by maintaining the exhaust valve in the decompression mode corresponding to the constantly-opened valve operating state during the cranking period;  
 (b) means for inhibiting the decompression mode and returning the exhaust valve to a normal operating state at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise;  
 (c) means for rising the effective compression ratio by controlling the intake valve characteristic substantially at the point of time when the predetermined cranking speed threshold value has been reached owing to the cranking speed rise; and  
 (d) means for bringing the intake valve characteristic closer to the desired value determined based on the engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.  
   
   
   
       10 . A method for controlling a compression ignition engine employing a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve, the method comprising: 
 (a) temporarily lowering an effective compression ratio of the engine by controlling the intake valve characteristic during a cranking period of cold starting operation;    (b) rising the effective compression ratio by controlling the intake valve characteristic at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise; and    (c) bringing the intake valve characteristic closer to a desired value determined based on engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.    
   
   
       11 . A method for controlling a compression ignition engine employing a variable valve actuation mechanism variably adjusting an intake valve characteristic including at least one of a valve lift of an intake valve and a valve closure timing of the intake valve and a decompression device provided to operate an exhaust valve in a decompression mode corresponding to a constantly-opened valve operating state during a cranking period of cold starting operation, the method comprising: 
 (a) temporarily lowering an effective compression ratio of the engine by maintaining the exhaust valve in the decompression mode corresponding to the constantly-opened valve operating state during the cranking period;    (b) inhibiting the decompression mode and returning the exhaust valve to a normal operating state at a point of time when a predetermined cranking speed threshold value has been reached owing to a cranking speed rise;    (c) rising the effective compression ratio by controlling the intake valve characteristic substantially at the point of time when the predetermined cranking speed threshold value has been reached owing to the cranking speed rise; and    (d) bringing the intake valve characteristic closer to the desired value determined based on the engine operating conditions by way of closed-loop control, after combustion of the engine has been stabilized.