Patent ID: 6278927
Filing Date: 2001-08-21
Classification: B60K,F16H,Y10T

Abstract:
A diagnostic method for verifying that a speed ratio provided by a motor vehicle multi-speed ratio automatic transmission corresponds to a commanded speed ratio, where the transmission has an input coupled to an engine and an output coupled to a transfer case providing first or second speed ratios, and the transfer case has an output coupled to drive the vehicle, the method comprising the steps of:measuring an input speed corresponding to a rotational speed of the transmission input and an output speed corresponding to a rotational speed of the transfer case output;computing an overall speed ratio provided by said transmission and transfer case based on the measured input and output speeds;determining if the transmission satisfies predetermined stability criteria;determining if the computed overall ratio is stable over a given time interval;comparing the computed overall ratio to a window of ratios based on the commanded speed ratio and an assumed speed ratio of said transfer case, once it is determined that the transmission satisfies the predetermined stability criteria and that the computed ratio is stable over the given time interval;indicating the speed ratio provided by the transfer case based on the comparison of said computed overall ratio to said window of ratios; andverifying that the speed ratio provided by the transmission corresponds to the commanded speed ratio based on the computed overall speed ratio and the indicated speed ratio of said transfer case.