Chapter 12 Electronic Control Systems 281 Copyright by Goodheart-Willcox Co., Inc. AFL AFL Filter (49) Lo/1st Sig A AFL Sol A N.O. on Sol B N.O. on D3 1-2 shift valve 3-4 shift valve 2-3 shift valve 2-3 shuttle D4 3-2 25 26 29 28 27 AFL AFL Example A: Park/reverse/neutral/& first gear 2nd AFL AFL Filter (49) Lo/1st Sig A AFL Sol A N.O. off Sol B N.O. off D3 1-2 shift valve 3-4 shift valve 2-3 shift valve 2-3 shuttle D4 3-2 25 26 29 28 27 AFL AFL Example B: Third gear 2nd Figure 12-25. Multi-shift solenoids. Although there are only two solenoids, their sequence of operation causes three shifts in drive. (General Motors) Figure 12-26. Possible solenoid position sequences for a trans- mission with two multi-shift solenoids. Frame Spring Armature Variable bleed orifice Exhaust Torque signal fluid Actuator feed limit fluid Spool valve spring Fluid screens Spool valve Spool valve sleeve Damper spring Coil assembly Push rod Restrictor Figure 12-27. Pressure control solenoids pulse on and off many times per second. The length of the pulses is called the duty cycle. The length of the duty cycle determines the pres- sure output of the valve. (General Motors) Electronic Transmission and Transaxle Operation The following sections cover the operation of electronic transmissions and transaxles. Emphasis is on the opera- tion of the solenoids and related hydraulic system parts. Remember that the holding members and many hydraulic control system parts are similar to those used on hydrauli- cally controlled transmissions. Sensor Inputs and Computer Operation The transmission solenoids cannot operate unless the ECM tells them what to do. In turn, the ECM is helpless unless it receives input from the sensors. In its most basic operation, the ECM compares the vehicle speed with the throttle opening and tells the solenoids when to shift the transmission into the next gear. For example, assume that while accelerating from stop, the vehicle speed sensor indicates that the vehicle is traveling 12 mph (kph) and the throttle position sensor indicates a small throttle opening (light acceleration). The ECM will command the appropri- ate solenoid to shift the transmission from first to second. However, if the speed sensor indicates that the vehicle is traveling 12 mph (kph) and the throttle position sensor indicates a large throttle opening (heavy acceleration), the ECM will not energize the solenoid until a higher speed is reached. Figure 12-29 shows how this simple arrange- ment works. Note how this compares to the action of the Solenoid A Solenoid B on on off off on off off on Sig A 4th sig 3-4 sig Ex Ex Ex Ex Ex Ex Ex Ex Orun D3 D2 2nd 3-4 acc 3-4 sig Servo feed D4 Lo Sig A 4th sig 3-4 sig Ex Ex Ex Ex Ex Ex Ex Ex Orun D3 D2 2nd 3-4 acc 3-4 sig Servo feed D4 Lo