Drive device

1. A drive device comprising:

a reduction drive that reduces a speed of rotation produced by a motor, wherein the reduction drive includes at least two resin helical gears meshed with each other;

an accommodation portion that accommodates the reduction drive, wherein the accommodation portion includes rotation supports that respectively support the at least two helical gears in a rotatable manner; and

an output unit that outputs the rotation, of which the speed has been reduced by the reduction drive, to an outer side, wherein

the accommodation portion includes a gear housing, which includes a gear accommodation portion capable of accommodating the at least two helical gears, and a housing cover, which closes an opening of the gear accommodation portion,

the at least two helical gears include an output-side helical gear and another helical gear,

the output-side helical gear is located closer to the output unit than the other helical gear in a power transmission path of the reduction drive,

the rotation supports include a rotation support that supports the output-side helical gear and includes a first center axis and a rotation support that supports the other helical gear and includes a second center axis,

the housing cover includes at least one restriction portion disposed so as to intersect a straight line intersecting the first center axis and the second center axis,

the at least two helical gears are configured so that a thrust force, which directs from a bottom of the gear accommodation portion toward the housing cover, acts on a meshed portion of the at least two helical gears,

the restriction portion projects from the housing cover toward the bottom of the gear accommodation portion,

the output-side helical gear includes a first axial end surface facing toward the housing cover, and a second axial end surface facing toward the bottom of the gear accommodation portion, and

the restriction portion is configured to allow for slidable contact with the first axial end surface of the output-side helical gear, which has received the rotation from the other helical gear, to restrict axial bending of the output-side helical gear caused by the thrust force acting on the meshed portion.

2. The drive device according to claim 1 , wherein

the output-side helical gear includes a tubular inner circumferential surface parallel to a rotation axis of the output-side helical gear, and

the restriction portion is configured to allow for slidable contact with the inner circumferential surface of the output-side helical gear.

3. The drive device of claim 1 , wherein the restriction portion is located adjacent to a portion where the two helical gears are meshed with each other.

4. The drive device of claim 1 , wherein

the housing cover includes a first cover that covers the other helical gear, and a second cover that covers the output-side helical gear, and

the restriction portion is located at a boundary between the first cover and the second cover.

5. The drive device according to claim 1 , wherein the restriction portion is configured to allow for slidable contact with the output-side helical gear at least when a load is applied to the output unit.

6. The drive device of claim 5 , wherein the restriction portion is configured to avoid slidable contact with the output-side helical gear when a load applied to the output unit is smaller than a rated load.

7. The drive device according to claim 1 , wherein the restriction portion is configured to allow for slidable contact over an entire circumference of the output-side helical gear to restrict axial bending of the output-side helical gear over the entire circumference.

8. The drive device of claim 7 , wherein the restriction portion includes restriction portions arranged in a circumferential direction of the output-side helical gear.