| 摘要 |
An improved method of operation for an electromechanical purge valve of a vehicle evaporative emission control system reduces the activation level of the purge valve below a nominal minimum level by a variable offset amount under specified operating conditions to lower purge flow. Specifically, the low flow control is permitted when the fuel in the purge vapor being drawn into the engine exceeds a calibrated percentage of the engine fuel requirement and the activation level of the purge valve has been reduced to the nominal minimum, provided that the system voltage level is at or above a specified value. When low flow control is permitted, the offset amount is incrementally increased so long as the engine fuel control is able to maintain the air/fuel ratio error at or below a calibrated amount, and incrementally decreased when the low flow control is no longer permitted or the air/fuel ratio becomes lean enough to potentially degrade combustion stability.
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