Valve drive system of an internal combustion engine

A valve drive system of an internal combustion engine, comprising:

• a first rotating member which rotates in association with a crankshaft of the internal combustion engine;
• a second rotating member rotatable relatively to the first rotating member;
• a cam provided on said second rotating member and rotating integrally with the second rotating member, thereby opening and closing a valve of said internal combustion engine, in cooperation with a valve spring;
• and
• a connecting unit which connects said first rotating member and said second rotating member while permitting a relative rotation therebetween, said connection unit having a transmission unit which transmits the rotary force of said first rotating member to said second rotating member, and a varying unit which changes a rotation speed of said second rotating member with respect to said first rotating member in conjunction with a restoring force of said valve spring in accordance with an operational state of said internal combustion engine to determine a time of termination of said valve opening with respect to the rotational phase of said crankshaft, said connecting unit including a fluid coupling connecting said first and second rotating members, said fluid coupling including,
• a fluid chamber defined between said first and second rotating members, said fluid chamber having a viscous fluid sealed therein,
• a first plate located in said fluid chamber and fixed to said first rotating member, and
• a second plate located opposite said first plate in said fluid chamber and fixed to said second rotating member.