Washing machine driving system and a washing machine with the same

A washing machine driving system comprising:

• a motor comprising a rotor frame;
• and
• a planetary gear assembly comprising:
• a gear housing,
• a carrier comprising (i) a carrier flange disposed inside the gear housing and (ii) a carrier shaft that extends from the carrier flange in an axial direction and protrudes toward a front side of the gear housing, the carrier shaft being connected to a drum shaft and configured to rotate with the drum shaft,
• a sun gear having (i) a front end that is rotatably coupled to the carrier and spaced apart from a back end of the drum shaft and (ii) a back end that protrudes toward a back side of the gear housing and is coupled to the rotor frame,
• a key bolt that couples the sun gear to the gear housing, the key bolt comprising (i) a bolt head coupled to the front end of the sun gear and (ii) a bolt shaft that extends backward along the axial direction and passes through the sun gear,
• a plurality of pinion gears coupled to the carrier flange and tooth-coupled to the sun gear, and
• a ring gear that is tooth-coupled to the plurality of pinion gears,
• wherein the key bolt further comprises a coupling protrusion that protrudes backward from the bolt head toward the back end of the sun gear along the axial direction, and
• wherein the sun gear defines a protrusion insertion groove that receives the coupling protrusion of the key bolt.