Electrical unit and attachment method

1 . An electrical unit including a casing-shaped first electrical device having one surface provided with an engagement recess, and a second electrical device configured to be attached to the one surface and having an engagement portion configured to slide over the one surface and engage with the engagement recess, the electrical unit comprising:

a slit formed in the one surface and configured to guide sliding of the engagement portion to the engagement recess; and

a rib provided on the engagement portion and configured to be inserted into the slit during sliding of the engagement portion; and

wherein the second electrical device is casing-shaped and has a contact surface configured to come into contact with the one surface,

the engagement portion protrudes from a side surface adjacent to the contact surface,

the engagement portion has a first surface and a second surface that are parallel to the contact surface and the side surface, and a curved surface connecting the first surface and the second surface to each other, and

the rib protrudes from the first surface and the curved surface.

2 . The electrical unit according to claim 1 ,

wherein the slit has a widened portion at an end portion farther from the engagement recess.

3 . The electrical unit according to claim 1 , wherein the rib is tapered toward a protruding end.

4 . The electrical unit according to claim 1 , further comprising

a blocking wall continuous with the one surface and configured to stop sliding of the engagement portion inside the engagement recess,

wherein the slit extends from the one surface to a position on the blocking wall, and

the rib extends from the first surface to a position on the second surface.

5 . The electrical unit according to claim 2 , wherein the rib is tapered toward a protruding end.

6 . An attachment method for attaching a second electrical device to a first electrical device, the second electrical device is casing-shaped and has a contact surface and an engagement portion, the first electrical device is casing-shaped and includes one surface having a side surface adjacent to the one surface to define an engagement recess, the method comprising:

providing the engagement portion with a first surface and a second surface that are parallel to the contact surface and the side surface, and a curved surface connecting the first surface and the second surface to each other;

providing a rib on the engagement portion, the rib protruding from the first surface and the curved surface;

inserting the rib into one end portion out of two end portions of a slit provided in the one surface and extending to the engagement recess, the one end portion being farther from the engagement recess;

sliding the engagement portion over the one surface along the slit; and

engaging the engagement portion with the engagement recess at another end portion of the slit.