Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Reexamination Certificate
2000-05-22
2001-08-21
Nguyen, Tan (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C477S154000
Reexamination Certificate
active
06278927
ABSTRACT:
TECHNICAL FIELD
This invention relates to an electronically controlled motor vehicle powertrain including a multi-range automatic transmission and a multi-range transfer case, and more particularly to a control for indicating the range of the transfer case.
BACKGROUND OF THE INVENTION
A significant aspect of electronic transmission control involves monitoring powertrain parameters to determine if the controlled friction elements (clutches, brakes, etc.) of the transmission have properly engaged or disengaged. For example, a proper engagement state of the transmission clutches may be verified by computing the transmission speed ratio (input speed/output speed) and comparing it with the several possible discrete speed ratios of the transmission. As a practical matter, however, only a limited number of parameters can be economically measured, and the monitored data is frequently ambiguous. For example, in certain powertrain configurations where the transmission drives the vehicle wheels through a multi-range transfer case (as in four-wheel-drive applications), the output speed measurement is based on the transfer case output speed instead of the transmission output speed. Since the transfer case provides two different speed ranges, the transmission ratio cannot be unambiguously determined unless the transfer case speed ratio is known. While some transfer cases are equipped with a speed range indicator switch, a failure of the indicator switch is also possible. Accordingly, what is needed is a diagnostic control for enabling reliable determination of proper transmission operation in powertrain configurations of the above type.
SUMMARY OF THE INVENTION
This invention is directed to an improved diagnostic control method for a motor vehicle powertrain including an electronically controlled multi-range transmission and a multi-range transfer case, wherein a default determination of transfer case range enables reliable evaluation of transmission ratio, for powertrain configurations with or without a transfer case range indicator switch. According to the invention, an overall speed ratio is computed according to a ratio of the transmission input speed and the transfer case output speed, and the computed ratio is monitored to identify a period of stable operation at the conclusion of transmission shifting and in steady state operation during which the rate of change of the computed ratio is stable over a predefined interval. If the computed ratio is also deemed to be stable, it is compared with an expected overall ratio based on an assumed speed range (low or high) of the transfer case. In configurations having a transfer case indicator switch, the switch state determines the assumed speed range, whereas in configurations not having an indicator switch, a low range of the transfer case is assumed. A default condition of the transfer case is determined based on the ratio comparison, and transmission diagnosis is carried out based on the default conditions.
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Fox Christopher Ray
Gleason Sean E
Mundy Scott E
Runde Jeffrey Kurt
General Motors Corporation
Hargitt Laura C.
Nguyen Tan
Tran Dalena
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