Valve timing control system of internal combustion engine

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 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 having a first toothed gear 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 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 having a second toothed gear 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 the first speed reducer of the intake valve timing control device is configured to transmit torque by repeated relocations of each of rolling elements rolling and relocating from one of two adjacent teeth of the first toothed gear to the other, and the second speed reducer of the exhaust valve timing control device is configured to transmit torque by meshed-engagement of the second toothed gear with another toothed gear.

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 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 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 cogging torque of the first electric motor of the intake valve timing control device is set to be less than a cogging torque of the second electric motor of the exhaust valve timing control device.

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 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 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 the first electric motor of the intake valve timing control device is constructed by a brushless motor, and the second electric motor of the exhaust valve timing control device is constructed by a brush-equipped direct-current motor.