Patent ID: 7044093

Claim:
A method of operating a four-stroke internal combustion engine, said engine comprising a cam and an engine valve actuator, both of which are operably connected to an intake valve, said valve actuator comprising an actuator cylinder having an actuator piston reciprocatingly positioned in the actuator cylinder, an electrorheological fluid contained in the actuator cylinder, an electromagnetic coil proximate to the electrorheological fluid, and a biasing mechanism connected with a control surface of the actuator piston, the method comprising the steps of: opening the intake valve with the cam to let air flow into an engine cylinder during an intake stroke; energizing the electromagnetic coil to hold open the intake valve during a portion of a compression stroke; de-energizing the electromagnetic coil to close the intake valve during the compression stroke; injecting fuel into the engine cylinder during the compression stroke and after the intake valve is closed; and combusting the fuel during the compression stroke and an expansion stroke.