Apparatus for controlling engine

Abstract

An engine has variable-valve mechanisms. An engine control system has an engine control unit for executing automatic stop and start control. At an automatic-stop, the variable-valve mechanisms are controlled to obtain a valve operation characteristic suitable for a restart of the engine. When a catalyst is in an inactivated state, the variable-valve mechanisms are controlled to reduce the amount of residual gas leaking out from cylinders. At an automatic-start, the control of the variable-valve mechanism is prohibited and an intake air is adjusted by using a throttle valve. At an automatic-stop, the engine speed is abruptly reduced so that the engine speed passes through a resonant revolution speed area in a short period of time. When the voltage of a battery is low, the control of the variable-valve mechanism may be prohibited.

What is claimed is:  
     
         1 . A control apparatus for an internal combustion engine, comprising: 
 variable-valve control means for controlling at least an intake airflow by adjusting valve operation characteristics of the intake valve, exhaust valve or both the intake and exhaust valves of the engine;    an automatic-stop control means, which is used for automatically stopping the engine when a predetermined automatic stop condition is satisfied in the course of an operation of the engine; and    an automatic-stop valve control means, which is used for computing target valve operation characteristics for an automatic-stop time on the basis of present states of the engine and/or a vehicle employing the engine and for controlling the valve operation characteristics to the target valve operation characteristics for an automatic-stop time right after the automatic-stop control means automatically stops the engine.    
     
     
         2 . A control apparatus for an internal combustion engine according to  claim 1 , further comprising: 
 an automatic-start control means, which is used for automatically starting the engine when a predetermined automatic-start condition is satisfied in an automatic-stop state of the engine; and    an automatic-start valve control means, which is used for computing target valve operation characteristics for an automatic-start time on the basis of present states of the engine and/or the vehicle and for controlling the valve operation characteristics to the target valve operation characteristics for an automatic-start time when the automatic-start control means automatically starts the engine.    
     
     
         3 . A control apparatus for an internal combustion engine according to  claim 1 , wherein the automatic-stop valve control means computes valve operation characteristics presumed to be proper for the next automatic start as the target valve operation characteristics for an automatic-stop time.  
     
     
         4 . A control apparatus for an internal combustion engine according to  claim 1 , wherein the automatic-stop valve control means computes valve operation characteristics, which sets valve lift quantities at 0 or minimum values, as the target valve operation characteristics for an automatic-stop time.  
     
     
         5 . A control apparatus for an internal combustion engine according to  claim 1 , wherein the automatic-stop valve control means computes the target valve operation characteristics for an automatic-stop time on the basis of at least one of an automatic-stop count, a cooling-water temperature, an intake-air temperature, an oil temperature and information having correlations with any one of the automatic-stop count, the cooling-water temperature, the intake-air temperature, and the oil temperature.  
     
     
         6 . A control apparatus for an internal combustion engine, comprising: 
 a variable-valve control means for controlling at least an intake airflow by adjusting valve operation characteristics of the intake valve, exhaust valve or both the intake and exhaust valves of the engine;    an automatic-start control means, which is used for automatically starting the engine when a predetermined automatic-start condition is satisfied in an automatic-stop state of the engine; and    an automatic-start valve control means, which is used for computing target valve operation characteristics for an automatic-start time on the basis of present states of the engine and/or a vehicle employing the engine and for controlling the valve operation characteristics to the target valve operation characteristics for an automatic-start time when the automatic-start control means automatically starts the engine.    
     
     
         7 . A control apparatus for an internal combustion engine according to  claim 6 , wherein the automatic-start valve control means computes the target valve operation characteristics for an automatic-start time on the basis of at least one of an automatic-stop count, an automatic-stop time, a cooling-water temperature, an intake-air temperature, an oil temperature and information having correlations with the automatic-stop count, the automatic-stop time, the cooling-water temperature and the oil temperature.  
     
     
         8 . A control apparatus for an internal combustion engine according to  claim 6 , wherein, in the event of an engine stall caused by a failure of an automatic start of the engine, the automatic-start valve control means controls the valve operation characteristics to increase the intake airflow and the automatic-start control means restarts the engine.  
     
     
         9 . A control apparatus for an internal combustion engine, comprising: 
 a variable-valve control means for controlling at least an intake airflow by adjusting valve operation characteristics of the intake valve, exhaust valve or both the intake and exhaust valves of the engine;    an automatic-start control means, which is used for automatically starting the engine when a predetermined automatic-start condition is satisfied in an automatic-stop state of the engine;    a variable-valve control prohibition means for fixing the valve operation characteristics at predetermined conditions during a variable-valve control prohibition period, which is a predetermined period after the automatic start of the engine carried out by the automatic-start control means; and    a throttle-valve control means for controlling the intake airflow during the variable-valve control prohibition period by adjusting the opening of a throttle valve provided on an intake path of the engine.    
     
     
         10 . A control apparatus for an internal combustion engine according to  claim 9 , wherein, during the variable-valve control prohibition period, the variable-valve control prohibition means fixes the valve operation characteristics each at a target valve operation characteristic for an automatic start of the engine.  
     
     
         11 . A control apparatus for an internal combustion engine according to  claim 9 , wherein the variable-valve control prohibition means sets the variable-valve control prohibition period at a value dependent on the automatic-stop count or automatic-start count of the engine.  
     
     
         12 . A control apparatus for an internal combustion engine, comprising: 
 a variable-valve mechanism for varying valve operation characteristics of the intake valve, exhaust valve or both the intake and exhaust valves of the engine in control of an intake airflow by; and    an automatic-stop control means, which is used for adjusting the intake airflow by controlling the variable-valve mechanism and/or controlling a throttle valve so as to gradually reduce a torque output by the engine and stop the engine when a predetermined automatic-condition is satisfied during an operation of the engine,    wherein, in a process to gradually reduce a torque output by the engine and stop the engine, the automatic-stop control means executes torque abrupt reduction control to abruptly reduce the intake airflow by controlling the variable-valve mechanism so as to abruptly reduce the torque output by the engine with a timing with which an engine speed is about to pass through a predetermined revolution speed range.    
     
     
         13 . A control apparatus for an internal combustion engine according to  claim 12 , wherein the predetermined revolution speed range is set to include a resonant revolution speed zone in which vibration of the engine is resonant with vibration of a vehicle-driving system.  
     
     
         14 . A control apparatus for an internal combustion engine according to  claim 12 , wherein the automatic-stop control means controls the variable-valve mechanism so as to put the intake valve in a completely closed state during the torque abrupt reduction control.  
     
     
         15 . A control apparatus for an internal combustion engine according to  claim 12 , wherein the automatic-stop control means controls the variable-valve mechanism and completely closes the throttle valve so as to minimize the intake airflow during the torque abrupt reduction control.  
     
     
         16 . A control apparatus for an internal combustion engine according to  claim 12 , wherein the automatic-stop control means terminates injection of fuel during the torque abrupt reduction control.  
     
     
         17 . A control apparatus for an internal combustion engine according to  claim 12 , wherein, in a process to gradually reduce a torque output by the engine and stop the engine, the automatic-stop control means controls a fuel injection volume so as to sustain an air-fuel ratio at a target air-fuel ratio till the engine speed is reduced to the predetermined revolution speed range.  
     
     
         18 . A control apparatus for an internal combustion engine, comprising: 
 a variable-valve control means for by varying valve operation characteristics of the intake valve and/or exhaust valve of the engine in accordance with a voltage output by a battery mounted on a vehicle employing the engine and controlling at least an intake airflow into a combustion chamber of the engine;    an automatic-start control means, which is used for automatically starting the engine when a predetermined automatic-restart condition is satisfied in an automatic-stop state of the engine;    a battery-voltage detection means for detecting a voltage output by the battery; and    a variable-valve control prohibition means, which is used for prohibiting variable control executed by the variable-valve control means on the intake valve and/or the exhaust valve in dependence on the voltage of the battery detected by the battery-voltage detection means after the engine is automatically started by the automatic-start control means.    
     
     
         19 . A control apparatus for an internal combustion engine according to  claim 18 , wherein the variable-valve control prohibition means prohibits the variable control executed by the variable-valve control means on the intake valve and/or the exhaust valve till the voltage of the battery detected by the battery-voltage detection means reaches a predetermined level.  
     
     
         20 . A control apparatus for an internal combustion engine according to  claim 18 , wherein the variable-valve control means is a means for setting valve lift quantities of the intake valve and/or the exhaust valve by utilizing a voltage output by the battery.