Info - New Product Information - Adaptive Control Feature of Allison 1000 Series Transmission

The Allison 1000 Series transmission consists of five (5) clutches labeled C1 to C5. A combination of two (2) clutches is required to be engaged to attain a torque path from the input to the output of the transmission. The following chart indicates the clutch combinations for each range:

This transmission utilizes clutch to clutch shift control to achieve range changes. In every case (except shifts to or from Neutral), one clutch is exhausted and another applied to make a range shift. The handoff between exhausting and applying clutches is very precisely controlled, by use of two PPC (Pressure Proportional to Current) solenoids. These solenoids are labeled "A" and "B" in the transmission, and are referred to as "trim" solenoids. For example, to make a 1-2 shift, A solenoid is used to trim pressure off C5 clutch, and B solenoid is used to trim pressure on C4 clutch.

The transmission control module (TCM) modulates the current to both A & B solenoids, which translates to a proportional level of pressure to the clutch. In order to make a shift, the TCM uses software and calibration settings of several program parameters to determine the level of current sent to the respective trim solenoids. These parameters are referred to as "adaptive values". With a new transmission and TCM calibration, the adaptive values are set to base calibration level. The transmission uses the base calibration to perform the first of each type of shift. However, once it has performed a shift, the TCM evaluates the actual shift and compares it to an ideal shift in the TCM's memory. Based on that comparison, the TCM changes the settings of the adaptive values to a level that it believes will result in a shift closer to the ideal shift the next time it makes that type of shift. This is referred to as "adaptive shifting".

When the transmission/TCM calibration is new, the TCM is in fast adaptive mode. In other words, the TCM is allowed to make relatively large changes in the adaptive values after each shift. Once the TCM determines that a given shift is close to its ideal level, it switches to slow adaptive mode. In slow adaptive, the TCM still is evaluating shifts and changing adaptive values, but is only allowed to do so in smaller increments. When a shift switches from fast to slow adaptive mode, it is described as "converged".

The TCM is programmed to try to switch from fast to slow adaptive mode in as many as 15 to 20 shifts. It is important to understand that there are many different distinct shifts recognized by the TCM, and each of these shift have its own adaptive values. For example, there are upshift and downshifts to and from each range, as well as unique adaptive values for several different throttle regions for each upshift and downshift. The point is, it may take a significant amount of time before most of the shifts converge from fast to slow adaptive, and thus it is not unusual to experience somewhat harsh or unpleasant shift quality until these shifts are adapted.

TCC engagement is accomplished by a separate pulse-width modulated (PWM) solenoid labeled "F" in the transmission. There are adaptive values for this as well, and thus it will also require some driving for TCC engagement to converge.