Electronic control for transmissions

A third-generation transmission electronic control system developed by Allison primarily for mobile equipment applications will be phased into all of its off-highway transmissions.

In 1971, electronic controls were introduced for automatic shifting of Allison Transmission's off-highway transmissions. The system's controller was a discrete logic device called a shift-pattern generator (SPG). The SPG received inputs from an engine-throttle-position sensor, a transmission-output-speed sensor, and a shift selector to make decisions on when to shift the transmission and then send a signal to the control valve to execute the shift (Figure 1). The SPG system provided some logic to protect the transmission from making an unacceptable shift-one that could potentially result in an overspeed of mechanical components in the transmission or engine.

Second-generation electronic controls were introduced in 1986 on Allison off-highway transmissions, identified as CEC1 (Commercial Electronic Controls 1). The CEC1 electronic control unit (ECU) was a special microcomputer developed from the basic General Motors Custom Microprocessor that was used for automotive applications (Figure 2). A major enhancement of the CEC1 system over the first-generation SPG system was that it contained a removable, erasable, read-only memory chip (EPROM) that was programmed to provide shift calibration information. Another significant enhancement with the CEC1 system was its built-in diagnostic capability.