When the engine is idling and the transmission is in park or neutral, what is happening inside the torque converter regarding component speeds?

When the engine is idling and the transmission is in park or neutral, what is happening inside the torque converter regarding component speeds?

• A. Both the impeller and the turbine are stopped, and the stator is turning.
• B. The impeller, the stator, and the turbine are all turning at close to the same speed.
• C. The impeller is turning; the stator is locked; and the turbine is stopped.
• D. Both the impeller and the turbine are turning, and the stator is locked.

Answer: (B)

At idle with the transmission in Park or Neutral, the torque converter behaves like a light fluid coupling because there’s little load on the drivetrain. The engine drives the impeller, pushing transmission fluid toward the turbine. Since there’s almost no resistance on the output side, the turbine speeds up with the flowing fluid, and the impeller and turbine come to about the same speed. The stator, which redirect fluid flow to boost torque, is allowed to rotate freely by its one-way clutch in this light-load condition, so it also turns at roughly the same rate. In this situation there’s minimal slip, so the impeller, stator, and turbine all rotate at close to the same speed. If a load were applied (in drive), more slip would occur and torque multiplication would come into play.

At idle with the transmission in Park or Neutral, the torque converter behaves like a light fluid coupling because there’s little load on the drivetrain. The engine drives the impeller, pushing transmission fluid toward the turbine. Since there’s almost no resistance on the output side, the turbine speeds up with the flowing fluid, and the impeller and turbine come to about the same speed. The stator, which redirect fluid flow to boost torque, is allowed to rotate freely by its one-way clutch in this light-load condition, so it also turns at roughly the same rate. In this situation there’s minimal slip, so the impeller, stator, and turbine all rotate at close to the same speed. If a load were applied (in drive), more slip would occur and torque multiplication would come into play.