Importance

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Abstract

A semi-automatic power shift transmission for use in a forklift truck includes a manual shift lever with first and second gear positions, a hydraulically shifted transmission gear mechanism operable in one of first and second gear ratios corresponding to the first and second gear positions, a plurality of solenoids for, when energized, causing the transmission gear mechanism to be either up-shifted from the first to the second gear ratio or down-shifted from the second to the first gear ratio, a transmission speed sensor for detecting the output speed of the transmission gear mechanism to generate a transmission speed signal, an engine speed sensor for picking up the speed of a vehicle engine to produce an engine speed signal, a steering wheel angle sensor for measuring the steering wheel angle to issue a wheel angle signal, and a transmission control unit responsive to the transmission speed signal, the engine speed signal and the wheel angle signal for selectively energizing the solenoids to thereby carry out the up-shifting operation in the event that a load ratio calculated by dividing the transmission speed with the engine speed is greater than a preselected reference load ratio, with the transmission speed larger than a preselected reference up-shift speed and the steering wheel angle smaller than a preselected reference angle. Also disclosed is a novel shift control method of the power shift transmission noted above.

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First Claim