Valve timing control system of internal combustion engine

Abstract

In a valve timing control system of an internal combustion engine employing both an electric-motor-driven intake valve timing control device (VTC) and an electric-motor-driven exhaust VTC having similar fundamental configurations, a maximum drive-efficiency motor-speed range of a first electric motor of the intake VTC and a maximum drive-efficiency motor-speed range of a second electric motor of the exhaust VTC are set to differ from each other depending on two different working ranges respectively suitable for the intake VTC and the exhaust VTC such that the maximum drive-efficiency motor-speed range of the intake VTC is set higher than that of the exhaust VTC. A reduction ratio of a first speed reducer configured to reduce a rotational speed of the first electric motor is set higher than that of a second speed reducer configured to reduce a rotational speed of the second electric motor.

What is claimed is: 
     
         1 . A valve timing control system of an internal combustion engine, comprising:
 an electric-motor-driven intake valve timing control device installed on an intake camshaft and having a first electric motor provided to generate torque by energizing the first electric motor; and   an electric-motor-driven exhaust valve timing control device installed on an exhaust camshaft and having a second electric motor provided to generate torque by energizing the second electric motor,   wherein a maximum drive-efficiency motor-speed range of the first electric motor of the electric-motor-driven intake valve timing control device and a maximum drive-efficiency motor-speed range of the second electric motor of the electric-motor-driven exhaust valve timing control device are set to differ from each other depending on a first working range suitable for the electric-motor-driven intake valve timing control device and a second working range suitable for the electric-motor-driven exhaust valve timing control device.   
     
     
         2 . The valve timing control system as recited in  claim 1 , wherein:
 the maximum drive-efficiency motor-speed range of the first electric motor of the electric-motor-driven intake valve timing control device, whose working range is wider than the working range of the electric-motor-driven exhaust valve timing control device, is set higher than that of the second electric motor of the electric-motor-driven exhaust valve timing control device.   
     
     
         3 . The valve timing control system as recited in  claim 1 , wherein:
 each of the first electric motor of the electric-motor-driven intake valve timing control device and the second electric motor of the electric-motor-driven exhaust valve timing control device is a brush-equipped direct-current motor.   
     
     
         4 . A valve timing control system of an internal combustion engine, comprising:
 an electric-motor-driven intake valve timing control device installed on an intake camshaft, the electric-motor-driven intake valve timing control device comprising:
 a first electric motor provided to generate torque by energizing the first electric motor; and 
 a first speed reducer configured to reduce a rotational speed of the first electric motor, and transmit the reduced rotational speed to the intake camshaft for changing intake valve timing; and 
   an electric-motor-driven exhaust valve timing control device installed on an exhaust camshaft, the electric-motor-driven exhaust valve timing control device comprising:
 a second electric motor provided to generate torque by energizing the second electric motor; and 
 a second speed reducer configured to reduce a rotational speed of the second electric motor, and transmit the reduced rotational speed to the exhaust camshaft for changing exhaust valve timing, 
   wherein a reduction ratio of the first speed reducer for a reduction in the rotational speed of the first electric motor and a reduction ratio of the second speed reducer for a reduction in the rotational speed of the second electric motor are set to differ from each other.   
     
     
         5 . The valve timing control system as recited in  claim 4 , wherein:
 the reduction ratio of the first speed reducer of the electric-motor-driven intake valve timing control device is set to be greater than the reduction ratio of the second speed reducer of the electric-motor-driven exhaust valve timing control device.   
     
     
         6 . The valve timing control system as recited in  claim 4 , wherein:
 each of the first speed reducer of the electric-motor-driven intake valve timing control device and the second speed reducer of the electric-motor-driven exhaust valve timing control device is a cycloid speed reducer employing a plurality of rollers.   
     
     
         7 . A valve timing control system of an internal combustion engine, comprising:
 an electric-actuator equipped intake valve timing control device installed on an intake camshaft, the electric-actuator equipped intake valve timing control device comprising:
 a first electric actuator provided to generate torque by energizing the first electric actuator; and 
 a first speed reducer configured to reduce a rotational speed of the first electric actuator, and transmit the reduced rotational speed to the intake camshaft for changing intake valve timing; and 
   an electric-actuator equipped exhaust valve timing control device installed on an exhaust camshaft, the electric-actuator equipped exhaust valve timing control device comprising:
 a second electric actuator provided to generate torque by energizing the second electric actuator; and 
 a second speed reducer configured to reduce a rotational speed of the second electric actuator, and transmit the reduced rotational speed to the exhaust camshaft for changing exhaust valve timing, 
   wherein a reduction ratio of the first speed reducer for a reduction in the rotational speed of the first electric actuator and a reduction ratio of the second speed reducer for a reduction in the rotational speed of the second electric actuator are set to differ from each other.