Patent ID: 8677848

Claim:
A speed reduction device for a power seat adapted to be fixed to a seat frame, the speed reduction device comprising: a worm gear coaxially and integrally rotating with an output shaft of a motor: a helical gear meshed with the worm gear and coaxially and integrally rotating with a drive shaft driving a movable portion of the power seat; and a casing accommodating the worm gear and the helical gear to be rotatable; wherein the casing includes: a casing body rotatably supporting the worm gear and including a circular-shaped opening portion through which the helical gear is inserted; a casing cover tightened to the casing body and closing the opening portion of the casing body, such that contact surfaces of the casing body and the casing cover are engaged with each other; annular fitting portions formed at contact surfaces of the casing body and the casing cover respectively and fitted to each other; a first engagement portion formed at an outer circumferential side of the annular fitting portion of the casing body, the first engagement portion projecting from one of the contact surfaces of the casing body in an engaging direction towards the casing cover; a second engagement portion formed with the casing cover and engaging with the first engagement portion, the second engagement portion including a hole shaped opening provided at the contact surface configured to receive the projecting first engagement portion; and a tightening means tightening the casing cover to the casing body, wherein the casing body and the casing cover are mounted to the seat frame by the tightening means via each of the first engagement portion and the second engagement portion in a state where the casing body and the casing cover contact each other at the respective contact surfaces, wherein the casing body includes a plurality of first assembly portions while the casing cover includes a plurality of second assembly portions assembled on the respective first assembly portions, the second assembly portions each including a region that projects away from the contact surfaces and having a through hole with a larger diameter than a diameter of the hole shaped opening provided at the contact surface, and wherein the casing body and the casing cover are tightened by the tightening means extending through the through holes of the second assembly portions and into the first assembly portions.