Governor Shift Schedules

The electronic governor has several governor curves possible as opposed to a conventional governor, which has a single governor curve with the 2 stages. These transmissions are mechanically and hydraulically the same as the ones they replace.

As with all-hydraulic transmissions, the vehicle shift speeds are determined by throttle position (called throttle pressure). The four curves are used during the following operating conditions.

• Low Transmission Fluid Temperature -  When the transmission fluid is cold at or below 30°F, the conventional governor can delay shifts, resulting in higher than normal shift speeds and harsh shifts. The electronically controlled low temperature governor pressure curve is higher than normal to make the transmission shift at normal speeds and sooner. The PCM uses a temperature sensor in the transmission oil sump to determine when low temperature governor pressure is needed.
• Transfer Case Low-Range Operation -  On four-wheel drive vehicles operating in low range, the engine can accelerate to its peak more rapidly than in the Normal range, resulting in delayed shifts and undesirable engine "flare". The low range governor pressure curve is also higher than normal to initiate upshifts sooner. The PCM compares the electronic vehicle speed signal to the transmission output shaft speed signal to the transmission output shaft speed signal to determine when the transfer case is in low range.
• Wide-Open Throttle Operation -  In wide-open throttle (WOT) mode, adaptive memory in the PCM assures that up-shifts occur at the preprogrammed optimum speed. WOT operation is determined from the throttle position sensor, which is also a part of the emission control system. The initial setting for the WOT upshift is below the optimum engine speed. As WOT shifts are repeated, the PCM learns the time required to complete the shifts by comparing the engine speed when the shifts occur to the optimum speed. After each shift, the PCM adjusts the shift point until the optimum speed is reached. The PCM also considers vehicle loading, grade and engine performance changes due to high altitude in determining when to make WOT shifts. It does this by measuring vehicle and engine acceleration and then factoring in the shift time.
• Normal Operation -  Normal operation is refined through the increased computing power of the PCM and through access to data on engine operating conditions provided by the PCM. This facilitated the development of a load adaptive shift strategy - the ability to alter the shift schedule in response to vehicle load conditions. One Manifestation of the capability is grade "hunting" prevention - the ability of the transmission logic to delay an upshift of a grade if the engine does not have sufficient power to maintain speed in the higher gear. The 3-2 downshift and the potential for hunting between gears occurs when a heavily loaded vehicle or on steep grades. When hunting occurs, it is very objectionable because shifts are frequent and accompanied by large changes in noise and acceleration.