Automatic Shift Control for Heavy Duty Transmissions

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Automatic Shift Control for Heavy Duty Transmissions

Schmidt, J. W.

Through the years, changes have occurred in vehicle design that have necessitated a re-evaluation of transmission shift systems. Vehicle trends have been towards increased size, articulation, and multi-power usage. Mechanical linkages for these vehicles have become costly to design and build, and are troublesome to maintain due to wear, improper adjustment, and damage.In 1968 an electric shift control concept was introduced for the off-highway heavy duty transmission market to eliminate the problems associated with mechanical, hydraulic, and air linkages. This system consisted primarily of three components: shift tower, wiring harness, and range selector control valve body.Now a new electronic shift control has been developed which enables the transmission with electric shift to achieve the optimum in fully automatic operation. The electronic control ensures that all shifts occur at optimum speeds, eases driver operation, and provides a unit that is precise, reliable, maintenance-free, and adaptable to large and complex vehicles.The new shift control is of significant interest, as described in this paper, because of the complexity of combining electronics and hydraulics to automate the shifting of the heavy duty transmission.