Control system for variable valve timing apparatus

Abstract

When a cam shaft phase is changed during engine operation is stopped, a power supply increase control to an electric motor is carried out, according to which a power-supply duty ratio to the electric motor is increased to a predetermined power increase value which is necessary for moving a VVT apparatus during the stop of the engine operation. Then, the power-supply duty ratio is feedback controlled so that an actual changing speed of the cam shaft phase becomes equal to a target changing speed. As a result, the cam shaft phase can be surely changed and operating sound can be reduced by preventing the changing speed of the cam shaft phase from becoming too fast.

1 . A control system for a variable valve timing apparatus of an electrically-driven type for an internal combustion engine comprising:
 a phase variable mechanism having an input portion connected to a crank shaft, an output portion connected to a cam shaft, and a control portion connected to an electric motor, for changing a rotational phase of the cam shaft with respect to the crank shaft by controlling rotation of the electric motor; and   an electronic control unit for controlling the rotation of the electric motor,   wherein, in a case the rotational phase of the cam shaft is changed during the engine operation is stopped, the electronic control unit carries out a power supply increase control in order to increase power supply amount to the electric motor to a target power increase amount at a beginning of the power supply to the electric motor, and   wherein, after the power supply increase control, the electronic control unit carries out a feedback control in order that an actual changing speed of the rotational phase of the cam shaft is controlled to be equal to a target changing speed.   
     
     
         2 . The control system for the variable valve timing apparatus according to the  claim 1 , wherein
 the electronic control unit sets, during the feedback control for the changing speed of the rotational phase, at least one of a gain for the feedback control for the changing speed of the rotational phase and an initial value for the power supply increase control, depending on the actual changing speed of the rotational phase of the camshaft during the power supply increase control.   
     
     
         3 . The control system for the variable valve timing apparatus according to the  claim 1 , wherein
 during the feedback control for the changing speed of the rotational phase, the power supply amount is feedback controlled by use of an integral term.   
     
     
         4 . A control system for a variable valve timing apparatus for an internal combustion engine comprising:
 a phase variable mechanism for transmitting rotational force of an electric motor to a can shaft of the engine to thereby change a rotational phase of the cam shaft with respect to a crank shaft; and   an electronic control unit for controlling rotation of the electric motor,   wherein the electronic control unit has a target value control portion for controlling the rotational phase of the camshaft to a target value after engine operation is stopped,   wherein the electronic control unit has a locked condition detecting portion for detecting whether a locked condition, in which a change of the rotational phase is stopped or close to a stopped condition, has occurred during an operation of the target value control portion for controlling the rotational phase of the cam shaft to the target value, and   wherein the electronic control unit has a phase control portion for temporarily reversing a direction of changing the rotational phase of the cam shaft, so that the direction is temporarily changed to an opposite direction of changing the rotational phase of the camshaft to the target value, when the locked condition is detected.   
     
     
         5 . The control system for the variable valve timing apparatus according to the  claim 4 , wherein
 the phase control portion temporarily reverses direction of power supply to the electric motor, so that the direction of changing the rotational phase of the cam shaft is temporarily reversed.   
     
     
         6 . The control system for the variable valve timing apparatus according to the  claim 4 , wherein
 the electronic control unit further has a phase-changing amount setting portion for setting a phase-changing amount when controlling the rotational phase of the cam shaft in the reversed direction, and   the phase control portion carries out the control of the rotational phase of the cam shaft in the reversed direction based on the phase-changing amount set by the phase-changing amount setting portion.   
     
     
         7 . The control system for the variable valve timing apparatus according to the  claim 4 , wherein
 in a case that the rotational phase of the cam shaft is controlled to the target value after the rotational phase of the camshaft has been temporarily controlled in the reversed direction by the phase control portion, the electronic control unit carries out a power supply increase control for the power supply to the electric motor for a predetermined time period at starting the power supply increase control, so that the power supply amount to the electric motor is increased to a predetermined power increase value.   
     
     
         8 . The control system for the variable valve timing apparatus according to the  claim 4 , wherein
 the electronic control unit has a memory portion for storing information relating to occurrence of the locked condition and release of the locked condition, and   the phase control portion controls the rotational phase of the cam shaft in the reversed direction based on the information relating to the occurrence and/or release of the locked condition.