Electric motor-attached speed reducer
An electric motor-attached speed reducer includes a first member, an electric motor, a speed reduction mechanism, and a second member. The electric motor is arranged to produce rotational motion with respect to the first member. The speed reduction mechanism is arranged to transfer the rotational motion obtained from the electric motor while reducing the speed thereof. The second member is arranged to rotate relative to the first member at a rotation rate resulting from the speed reduction. A first bearing is arranged between the first and second members. A second bearing is arranged between the first member and a rotor of the electric motor. The speed reduction mechanism includes a flexible third bearing arranged between a non-perfect circular cam and a flexible external gear. The second bearing is arranged to radially overlap with a rotor holder at a first axial position. The third bearing is arranged to radially overlap with the rotor holder at a second axial position different from the first axial position.
1. An electric motor-attached speed reducer comprising:
a first member;
an electric motor arranged to produce rotational motion with respect to the first member;
a speed reduction mechanism arranged to transfer the rotational motion obtained from the electric motor while reducing a speed thereof;
a second member arranged to rotate relative to the first member at a rotation rate resulting from the speed reduction;
a first bearing arranged to support the first and second members such that the first and second members are rotatable relative to each other;
a second bearing arranged to support the first member and a rotor of the electric motor such that the first member and the rotor are rotatable relative to each other, the rotor including a rotor magnet, and a rotor holder arranged to hold the rotor magnet; and
a grease; wherein
the speed reduction mechanism includes:
a non-perfect circular cam including an outer circumferential surface being at different distances from a rotation axis of the electric motor at different circumferential positions;
a flexible external gear arranged to be deformed in accordance with rotation of the non-perfect circular cam;
a third bearing being flexible and arranged between the non-perfect circular cam and the flexible external gear; and
an internal gear arranged in the second member;
the flexible external gear and the internal gear are arranged to have different numbers of teeth, mesh with each other, and rotate relative to each other because of the different numbers of teeth;
the second bearing is arranged to radially overlap with the rotor holder at a first axial position;
the third bearing is arranged to radially overlap with the rotor holder at a second axial position different from the first axial position;
at least a portion of the second bearing and at least a portion of the third bearing are arranged axially opposite to each other;
the rotor holder includes:
a first holder portion being cylindrical;
a second holder portion being cylindrical and smaller in distance from the rotation axis than the first holder portion; and
an annular plate portion arranged to extend radially to join the first and second holder portions to each other;
the first holder portion is arranged radially outside of the second bearing; and
the second holder portion is arranged radially outside of the rotor magnet and radially inside of the third bearing.
2. The electric motor-attached speed reducer according to claim 1 , wherein
the flexible external gear includes:
a tubular portion arranged to extend in an axial direction; and
a flange portion arranged to extend radially outward from the tubular portion; and
the flange portion is fixed to the first member.
3. The electric motor-attached speed reducer according to claim 2 , wherein
the tubular portion is arranged to extend in the axial direction so as to span a range between the first and second axial positions;
the flange portion is arranged to extend radially outward from an end portion of the tubular portion on a side closer to the first axial position; and
the third bearing is arranged to support an end portion of the tubular portion on a side closer to the second axial position.
4. The electric motor-attached speed reducer according to claim 1 , wherein the first bearing is a cross-roller bearing.
5. The electric motor-attached speed reducer according to claim 1 , wherein the rotor holder and the non-perfect circular cam are defined by a same member.
6. The electric motor-attached speed reducer according to claim 1 , wherein the annular plate portion includes a shoulder portion.
7. The electric motor-attached speed reducer according to claim 1 , wherein
the first member includes:
a base portion arranged to extend perpendicularly to the axial direction; and
a through hole arranged to pass through the base portion in the axial direction; and
a portion of the second bearing is arranged to axially overlap with the through hole.
8. The electric motor-attached speed reducer according to claim 1 , further comprising a cover member arranged to extend perpendicularly to the axial direction, and fixed to the second member, wherein
the cover member is arranged axially opposite to both the rotor holder and the third bearing; and
the grease is arranged between the cover member, the rotor holder, and the third bearing.