Transmission, and powered actuator using the same

A transmission, comprising :

• a transmission case provided with an internal gear an inner wall thereof;
• a multistage planetary gear mechanism housed in the transmission case, each stage of the multistage planetary gear mechanism comprising a retainer, a sun gear and a plurality of planetary gears mounted on the retainer, the planetary gears of each stage of the multistage planetary gear mechanism respectively meshed with the corresponding sun gear and the internal gear;
• wherein the plurality of the planetary gears in the last planetary gear stage of the multistage planetary gear mechanism comprises four planetary gears annularly arranged between the corresponding sun gear and the inner gear in an uneven manner, two of the four planetary gears at intervals are symmetrically arranged on opposite sides of the sun gear with a connection line, defined as line d connecting the rotation axes thereof, the other two of the four planetary gears are symmetrically arranged on opposite sides of the sun gear with a connection line, defined as line p, connecting the rotation axes thereof, the line d and line p satisfy the following conditions:
• θ
• 1
• =
• K
• ⁢
• ▯
• ⁢
• 360
• Z
• a
• +
• Z
• c
• ;
• θ
• 2
• =
• (
• K
• +
• 1
• )
• ⁢
• ▯
• ⁢
• 360
• Za
• +
• Zc
• ⁢
• and
• ,
• K
• =
• Z
• a
• +
• Z
• c
• 4
• -
• 0
• .5
• ,
• wherein θ1 is first included angle formed between the line p and one side of the line d, θ2 is a second included angle formed between the line p and the other side of the line d, which is not equal to θ1, Za is a teeth number of the sun gear, Zc is a teeth number of the internal gear.