2000-01-0545 Unconventional Approach to Achieving a Default Throttle Position

Motorized throttle valves on conventional spark-ignited engines are designed to have a default position such that when unpowered they go to a fixed position which is between closed-in-bore and wide open. This position allows some, albeit limited, vehicle function in the event of a throttle positioning fault. Described here is a new default positioning mechanism attained by rotating the valve past the conventional operating arc (between closed-in-bore and wide open) through wide open to a partially open position. This default throttle position concept eliminates control difficulties and an undesirable failure mode. The advantages and disadvantages are discussed. Further, the required valve geometry is derived.