Importance

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Abstract

An electronically controlled transmission system includes an engine driven torque converter driving a planetary gear transmission. The torque converter is lockable by a lockup solenoid valve to provide a direct through drive and the planetary gear transmission is shiftable among a plurality of gear ratios by selected operation of solenoid operated valves which control power to clutch- and brake-selected transmission gears. An automatic electronic control provides for a 'work' mode of transmission operation wherein a shift control provides for manual shifting over a first set of selected gear ratios and for automatic, speed dependent shifting over a second set of selected gear ratios while torque converter lockup inhibition is provided for both sets of ratios. The automatic electronic control further provides for a 'transport' mode of transmission operation wherein the shift control provides for manual shifting over a third set of selected gear ratios and for automatic, speed dependent shifting over a fourth set of selected ratios while automatic torque converter lockup is provided for the upper speeds of each of the gear ratios in the third and fourth sets of ratios. The automatic electronic control still further incorporates hysteresis and time delay automatic shifting to prevent speed related hunting for the proper gear ratios as well as the downshift control to prevent manual downshifting at excessive speeds. A manual override and a hold for holding any automatically selected gear ratio is provided for greater operator control.

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First Claim