Ball spline with lubrication passage

A ball spline comprising:

• a spline shaft having a first rolling groove at an outer surface thereof;
• an outer sleeve slidably sleeved on the spline shaft and having a second rolling groove at an inner surface thereof, the second rolling groove of the outer sleeve and the first rolling groove of the spline shaft forming a load channel, the outer sleeve having a non-load channel and an oil guide channel inside, two ends of the non-load channel and two ends of the oil guide channel passing through two opposite end surfaces of the outer sleeve;
• two circulation elements mounted to the two end surfaces of the outer sleeve and penetrated by the spline shaft, the circulation elements each having a circulation groove with two ends thereof connected with the load channel and the non-load channel to form a circulation channel, an oil filling hole, an oil storage tank communicating with the oil filling hole, the load channel, and the oil guide channel of the outer sleeve, and an oil guide portion disposed in the oil storage tank and corresponding to the oil filling hole and protruding towards the oil guide channel;
• and
• a plurality of balls disposed in the circulation channel.