During closed-loop control, the TCU is controlling shift quality by doing which of the following?

During closed-loop control, the TCU is controlling shift quality by doing which of the following?

• A. Using the fixed ramp rate
• B. Applying full-line pressure to the on-coming clutch
• C. Varying the on-coming clutch application pressure using pulse-width modulation
• D. None of the above is correct.

Answer: (C)

In closed-loop control, the system uses feedback to adjust how the shift actually occurs, aiming for a target shift quality. The transmission control unit does this by fine-tuning the hydraulic pressure applied to the on-coming clutch. It uses pulse-width modulation to vary that clutch pressure in small, rapid on/off cycles, which lets the average pressure rise smoothly as needed. This controlled modulation lets the system manage clutch slip and torque transfer precisely during a shift, resulting in smoother engagement and better shift quality.

Using a fixed ramp rate would be an open-loop approach that doesn’t respond to real-time conditions, so it can’t adapt to changes in engine torque, vehicle speed, or transmission temperature. Applying full-line pressure to the on-coming clutch would produce a harsh, abrupt engagement with little opportunity to control slip. Therefore, varying the on-coming clutch pressure with PWM is the method that best achieves the desired, responsive control over shift quality.