Speed reducer and actuator
View Patent ↗A speed reducer includes a sun gear, planetary gears, a fixed part, an output part, a first bearing, and a second bearing. The sun gear rotates relative to the fixed part at a first rotation speed. The planetary gears are disposed around the sun gear to engage with the sun gear. The output part includes an annular internal gear engaging with the planetary gears. The output part rotates relative to the fixed part at a second rotation speed lower than the first rotation speed. The first bearing is interposed between the fixed part and the output part at a position closer to an input side with respect to the planetary gears. The second bearing is interposed between the fixed part and the output part at a position closer to an output side with respect to the planetary gears. The second bearing is smaller in radial size than the first bearing.
1. A speed reducer for converting rotational motion about a rotation axis extending between an input side and an output side, at a first rotation speed into rotational motion at a second rotation speed being lower than the first rotation speed, the speed reducer comprising:
a fixed part;
a sun gear that rotates relative to the fixed part about the rotation axis at the first rotation speed;
a plurality of planetary gears that are disposed around the sun gear to engage with the sun gear;
an output part that includes an internal gear having an annular shape and engaging with the plurality of planetary gears and rotates relative to the fixed part at the second rotation speed;
a first bearing that is interposed between the fixed part and the output part at a position closer to the input side with respect to the plurality of planetary gears; and
a second bearing that is interposed between the fixed part and the output part at a position closer to the output side with respect to the plurality of planetary gears, wherein
a radial size of the second bearing is smaller than a radial size of the first bearing.
2. The speed reducer according to claim 1 , further comprising a plurality of support pins that axially extend from the fixed part and respectively support the planetary gears in a rotatable manner,
wherein
at least a part of the second bearing overlaps each of the support pins as seen in axial view.
3. The speed reducer according to claim 2 , wherein
a radial length from the rotation axis to an inner peripheral face of the second bearing is shorter than a radial length from the rotation axis to a radially inner edge of each of the support pins.
4. The speed reducer according to claim 2 , wherein
a radial length from the rotation axis to an outer peripheral face of the second bearing is longer than a radial length from the rotation axis to a radially outer edge of each of the support pins.
5. The speed reducer according to claim 1 , wherein
a section of the second bearing is larger than a section of the first bearing, the sections being perpendicular to a circumferential direction.
6. The speed reducer according to claim 1 , wherein
an axial dimension of the second bearing is larger than an axial dimension of the first bearing.
7. The speed reducer according to claim 1 , wherein
a radial dimension from an inner peripheral face to an outer peripheral face of the second bearing is larger than a radial dimension from an inner peripheral face to an outer peripheral face of the first bearing.
8. The speed reducer according to claim 1 , wherein
the fixed part includes:
a gear holder that holds the plurality of planetary gears; and
a protrusion that axially protrudes from the gear holder and has an outer peripheral face formed in a cylindrical shape and being smaller in diameter than an outer peripheral face of the gear holder, and
the second bearing has an inner ring fixed to the outer peripheral face of the protrusion.
9. The speed reducer according to claim 1 , further comprising a wheel that rotates together with the output part.
10. The speed reducer according to claim 9 , wherein
the second bearing is placed radially inward of the wheel.
11. The speed reducer according to claim 1 , wherein
the output part includes:
the internal gear; and
a bearing holder that is separate from the internal gear and is fixed to the internal gear, and
the second bearing has an outer ring fixed to an inner peripheral face of the bearing holder.
12. The speed reducer according to claim 11 , wherein
a material for the internal gear is higher in strength than a material for the bearing holder.
13. The speed reducer according to claim 1 , further comprising
a lubricating oil that is applied to surfaces of at least some of the members; and
an oil receiving cover that is placed closer to the output side with respect to the second bearing.
14. The speed reducer according to claim 13 , wherein
the oil receiving cover is disposed perpendicularly to the rotation axis and is fixed to the fixed part.
15. An actuator comprising:
the speed reducer according to claim 1 ; and
a motor that is directly or indirectly coupled to the sun gear,
wherein
the sun gear rotates at the first rotation speed when the motor is driven.