Valve timing control apparatus and method for setting minimum torque

A method for setting a minimum torque for a biasing mechanism of a valve timing control apparatus for an engine, the valve timing control apparatus comprising:

• a drive rotational member synchronously rotated with a crankshaft;
• a driven rotational member provided coaxially with the drive rotational member and rotated with a camshaft;
• a fluid pressure chamber provided in one of the drive rotational member and the driven rotational member;
• a vane dividing the fluid pressure chamber into an advanced angle chamber and a retarded angle chamber;
• a relative rotational phase-controlling mechanism for supplying or discharging an working fluid to or from one or both of the advanced angle chamber and the retarded angle chamber, for changing a relative position of the vane to the fluid pressure chamber, and for controlling a relative rotational phase between the drive rotational member and the driven rotational member within a range from a most retarded angle phase at which a volume of the retarded angle chamber becomes maximum to a most advanced angle phase at which a volume of the advanced angle chamber becomes maximum;
• a locking mechanism for restraining the relative rotational phase at an intermediate phase between the most advanced angle phase and the most retarded angle phase;
• and
• a biasing mechanism for applying a torque to the drive rotational member relative to the driven rotational member so that the relative rotational phase advances toward the most advanced angle phase, wherein
• a larger one of a first torque which is a minimum torque required for changing the relative rotational phase from the most retarded angle phase to the intermediate phase in a case where a fluid pressure is discharged from both of the advanced angle chamber and the retarded angle chamber and cranking is performed at a first temperature before warming up of the engine and a second torque which is a minimum torque required for changing the relative rotational phase from the most retarded angle phase to the intermediate phase in a case where hydraulic pressure remains in the advanced angle chamber and the retarded angle chamber and cranking is performed at a second temperature which is a minimum temperature at which the relative rotational phase is controlled by the relative rotational phase-controlling mechanism is selected as the minimum torque.