Variable valve actuating mechanism with magnetorheological fluid lost motion device

A valve actuating mechanism for opening and closing an engine valve with controlled variable lift of the actuated valve, said mechanism comprising:

• an actuator;
• a valve driven by the actuator in opening and closing motions;
• a support carrying both the actuator and the valve;
• and
• a lost motion device containing magnetorheological (MR) fluid disposed in the mechanism between the actuator and one of the valve and the support for controlling the transmission of valve opening forces between the actuator and the valve, the device including magnetic means operative to controllably increase shear strength of the fluid to limit the degree of lost motion and vary the range of valve lift between minimum and maximum limits;
• wherein at least some of the fluid is maintained between closely opposing surfaces of the lost motion device and the magnetic flux is applied to the maintained fluid to control the shear strength of the fluid and thereby control the resistance of the fluid to shearing action between the surfaces, thus controlling the amount of lost motion between the surfaces and the stroke of the driven member during opening of the valve.