What is meant by synchronous speed as it relates to the Allison World Transmission TCU?

What is meant by synchronous speed as it relates to the Allison World Transmission TCU?

• A. Turbine shaft speed equals output shaft speed times the gear ratio of the oncoming clutch.
• B. The turbine speed equals the output shaft speed.
• C. The engine speed times the gear ratio equals the turbine speed.
• D. The output shaft speed times the gear ratio equals the engine speed.

Answer: (A)

Synchronous speed means the turbine and the output shaft are rotating at speeds that line up according to the oncoming clutch’s gear ratio, so the clutch can engage without slipping. In the Allison World Transmission TCU, the oncoming clutch connects the turbine to the output, and its gear ratio sets how the turbine speed relates to the output speed. When the turbine speed equals the output speed multiplied by that gear ratio, there is zero relative motion across the clutch plates, allowing a clean, smooth engagement. For example, if the oncoming clutch has a gear ratio of 2:1, synchronous speed occurs when the turbine turns twice for every one turn of the output shaft. The TCU watches turbine and output speeds and waits for this match before engaging the clutch to shift. This concept isn’t about engine speed or simply equal speeds elsewhere; it’s about the correct relationship between turbine speed and output speed dictated by the clutch’s gear ratio to prevent slip during engagement.

Synchronous speed means the turbine and the output shaft are rotating at speeds that line up according to the oncoming clutch’s gear ratio, so the clutch can engage without slipping. In the Allison World Transmission TCU, the oncoming clutch connects the turbine to the output, and its gear ratio sets how the turbine speed relates to the output speed. When the turbine speed equals the output speed multiplied by that gear ratio, there is zero relative motion across the clutch plates, allowing a clean, smooth engagement.

For example, if the oncoming clutch has a gear ratio of 2:1, synchronous speed occurs when the turbine turns twice for every one turn of the output shaft. The TCU watches turbine and output speeds and waits for this match before engaging the clutch to shift.

This concept isn’t about engine speed or simply equal speeds elsewhere; it’s about the correct relationship between turbine speed and output speed dictated by the clutch’s gear ratio to prevent slip during engagement.