Variable valve timing control apparatus

A variable valve timing control apparatus, comprising:

• a driving side rotation member synchronously rotating with a crankshaft of an internal combustion engine;
• a driven side rotation member positioned to be coaxially rotatable relative to the driving side rotation member about a common rotational axis, synchronously rotating with a camshaft for opening and closing a valve of the internal combustion engine, and including a rotation peripheral surface;
• a fluid pressure chamber formed between the driving side rotation member and the driven side rotation member;
• an advanced angle chamber and a retarded angle chamber formed by dividing the fluid pressure chamber by a dividing portion provided at least one of the driving side rotation member and the driven side rotation member;
• a phase control portion for controlling a rotational phase of the driven side rotation member relative to the driving side rotation member by supplying a pressurized fluid to the advanced angle chamber or to the retarded angle chamber;
• an intermediate lock mechanism including a lock fluid passage allowing an inflow of the pressurized fluid and a lock member allowing a switching of a locked state where the rotational phase of the driven side rotation member is locked at an intermediate phase between a most retarded angle phase and a most advanced angle phase and an unlocked state where the locked state is released by a fluid pressure of the pressurized fluid flowing in from the lock fluid passage;
• the driven side rotation member including an advanced angle fluid passage, which is in communication with the advanced angle chamber, a retarded angle fluid passage, which is in communication with the retarded angle chamber, and the lock fluid passage;
• a fixed member formed with a fixed peripheral surface facing the rotation peripheral surface of the driven side rotation member in a standstill state, positioned coaxially to an axis of the driven side rotation member, and including a plurality of fluid passages opening to the fixed peripheral surface to allow a supply of the pressurized fluid to an advanced angle fluid passage, a retarded angle fluid passage, and a lock fluid passage;
• a plurality of seal rings each formed in an annular shape and positioned between the rotation peripheral surface of the driven side rotation member and the fixed peripheral surface of the fixed member, the seal rings positioned spaced apart from each other by a predetermined distance;
• the advanced angle fluid passage, the retarded angle fluid passage, and the lock fluid passage are in communication with the corresponding fluid passages via a communication portion for advanced angle, a communication portion for retarded angle, and a communication portion for lock formed by annularly defining a void between the rotation peripheral surface and the fixed peripheral surface by the corresponding seal rings, respectively;
• wherein
• the seal ring sandwiched between two of the communication portion for advanced angle, the communication portion for retarded angle, and the communication portion for lock in a direction of the rotational axis among said plurality of seal rings includes a communication passage which establishes constant communication between both sides thereof in association with the direction of the rotational axis when temperature of the pressurized fluid is within a temperature range which allows a control of the rotational phase of the driven side rotation member;
• and
• a length of the seal ring at an outer portion in a radial direction is shorter than a length of the seal ring at an inner portion in a radial direction, and a void corresponding to a difference in the length corresponds to the communication passage.