and the second wall 22 b are arranged with a first bulge 221 and a second bulge 222 the receiving space 22 is for mounting a control device 5 the control device 5 includes a pivot part 52 with a pivot hole 521 a first holding part 51 a and a second holding part 51 b formed by extension of the pivot part 52 a platform part 53 between the first holding part 51 a and the second holding part 51 b and a groove 54 set on the platform part 53 refer to fig2 a support body 6 made from metal includes a connection part 61 with a pivot hole 611 a back part 62 formed by extension of the connection part 61 and a hook part 63 formed by extension of one end of the back part 62 the pivot hole 611 of the support body 6 is aligned with and assembled with the pivot hole 521 of the pivot part 52 the shape of the connection part 61 is matched with the shape of the groove 54 the horizontal surface of the back part 62 and the horizontal surface of the platform part 53 are on the same plane while the hook part 63 is projecting from the platform part 53 after the support body 6 being.