UNDERDRIVE Clutch

The underdrive clutch operates in 1st, 2nd, and 3rd gears and transmits driving force from the input shaft to the underdrive sun gear (A).

The components comprising the under clutch are as illustrated below.

Hydraulic pressure acts in the piston pressure chamber (B) (between the piston (c) and retainer) and thus pushes the piston (C). In turn, the piston depresses the clutch discs and thereby transmits driving force from the retainer (D) to the hub (E) side.

Fig 1: Identifying Piston Pressure Chamber

Courtesy of KIA MOTORS AMERICA, INC.

At high speed, fluid remaining in the piston pressure chamber is subjected to centrifugal force and attempts to push the piston.

However, fluid in the balance fluid chamber (A) (the space between the piston and return spring retainer (B)) is also subjected to centrifugal force.

Thus, the hydraulic pressure on one side of the piston cancels out the hydraulic pressure on the other side, and the piston does not move.

Fig 2: Identifying Fluid Chamber And Return Spring Retainer

Courtesy of KIA MOTORS AMERICA, INC.