CHAPTER 46 Electronically Controlled Automatic Transmissions
programmable read-only memory (PROM) chip A memory chip particular to the application of the vehicle in which it is found. pulse-width modulation The ability of a solenoid electric circuit to control pressure buildup in a clutch by turning on and off the flow of current at a fixed frequency. ramp-off rate The specific reduction in clutch apply pressure for the clutch that is being released during a shift in the World Transmission (WT). range verification tests Tests constantly being performed by the Allison World Transmission (WT) control system whenever there is no shift in progress the test compares turbine times the gear ratio to the output speed to ensure the transmission is not slipping. ratio test A test performed at the beginning and end of a shift in process. retarder Any system used to slow a vehicle’s momentum and augment the service brake. secondary modulation (sub-modulation) A very high-frequency pulse-width modulation of the current flowing through the primary modulated circuit of a World Transmission (WT) solenoid. The secondary modulation occurs at between 12000 and 19000 Htz and is used to fine tune the solenoid function. SensoTop A system used by Voith that senses topography and adapts the shifting schedule accordingly. shift logic The logical process created by the transmission controller using data gained from the vehicle to determine when and how shifting should occur. shift solenoid 1 (SS1) The solenoid used in fourthgeneration and later World Transmissions (WTs) to control the position of the C-1 and C-2 latch valves. slow adaptive A type of adaptive control that involves making small changes to the shifts as a way to mitigate the effects of clutch wear and solenoid drive and degradation. synchronous speed The point at which the on-coming clutch has applied and there is no more slippage. Turbine shaft seed times the gear ratio equals output shaft speed.
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time to full apply (TFA) The point after synchronous speed has been detected at which the solenoid controlling the on-coming clutch in a World Transmission (WT) is commanded to full pressure (that is, to fully apply the clutch). torque converter control (TCC) A control solenoid used in fourth-generation and later World Transmissions (WTs). transmission control module (TCM) The electronic controller that issues commands to the solenoids inside the transmission to obtain the desired range. Also known as the transmission electronic control unit (ECU). transmission electronic control unit (ECU) The electronic controller that issues commands to the solenoids inside the transmission to obtain the desired range. Also called the transmission control unit (TCU). trimmer An accumulator used in the ATEC/CEC systems to smoothen out the shift process. turbine pull down A decrease in turbine speed as a shift is in progress that results from the on-coming clutch starting to control its gear train component; the signal for the transmission to enter closed-loop control of the shift in progress. variable-bleed solenoid (VBS) Hydraulic solenoids used in late-model Allison World Transmissions (WTs), which control application by allowing some of the pressure going to a device to bleed off to exhaust. vehicle speed sensor (VSS) An inductive pick-up sensor that reads the speed of the transmission output shaft. World Transmission Electronic Control (WTEC) Allison’s original electronic transmission control system for the World Transmission.
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