R Position (Reverse Inhibition Control): Outline

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The driving force of the input shaft is transmitted to the reverse and high clutch drum, and then to the front sun gear through the reverse clutch, causing the front sun gear to rotate counterclockwise.
None of the low and reverse brake are operating, however, so this force is not transmitted to the output gear.

Fig 1: Identifying Reverse Inhibition Control Driving Force
Courtesy of MAZDA MOTORS CORP.