"行星齿轮变速箱" can be translated into English as "planetary gear transmission" or "planetary gearbox".
"Planetary gear transmission" emphasizes the functional aspect of the mechanism, indicating that it is a type of transmission system that utilizes planetary gears.
"Planetary gearbox" is more specific, referring to the entire assembly or box that contains the planetary gear system, often used in the context of machinery or vehicles.
Both terms are widely accepted and understood in the field of mechanical engineering and automotive technology.