Mounting structure for electric motor

1 . A mounting structure for an electric motor, the electric motor comprising:

a stator core having a cylindrical shape about an axis and having a plurality of teeth in an inner peripheral portion of the stator core and eight holes formed on an outer peripheral portion of the stator core, the eight holes being located at equal angular intervals about the axis; and

a case housing the stator core, the case including a cylindrical wall and a bottom part that closes one axial end of the case, the bottom part having a mounting surface on an inner side thereof, wherein:

the stator core is fastened to the case by three bolts inserted through a first hole, a second hole, and a third hole among the eight holes, the three bolts are fastened at corresponding three fastening positions on the mounting surface of the case;

symmetry of radial rigidity of the stator core about the axis in a state in which the stator core is mounted to the case is broken due to at least one of (i) different fastened states between the stator core and the case at the three fastening positions; and (ii) different rigidities of the case at the three fastening positions;

a polygon formed by connecting the first hole, the second hole, and the third hole as viewed in the direction of the axis includes the axis;

among the remaining five holes of the eight holes other than the first hole, the second hole, and the third hole, a first pair of two holes are provided between the first hole and the second hole, one hole is provided between the second hole and the third hole, and a second pair of two holes are provided between the third hole and the first hole;

the bottom part includes thick regions at each of the three fastening positions, the thick regions having a thickness in the direction of the axis greater than a thickness of an adjacent radially inward region of the bottom part; and

the thick regions have different thicknesses from each other.

2 . The mounting structure according to claim 1 , wherein the symmetry of the radial rigidity of the stator core about the axis in the state in which the stator core is mounted to the case is broken due to either or both of the following: the fastened states between the stator core and the case by the three bolts are different from each other; and the rigidities of the case at the fastening positions are different from each other.

3 . The mounting structure according to claim 1 , wherein the fastened states between the stator core and the case by the three bolts are different from each other due to either of both of the following: outside diameters of the three bolts inserted through the first hole, the second hole, and the third hole are different from each other; and axial forces on the three bolts inserted through the first hole, the second hole, and the third hole are different from each other.

4 . The mounting structure according to claim 1 , wherein the rigidities of the end case at the fastening positions are different from each other due to radial lengths of the thick regions of the case at the fastening positions are different from each other.

5 . The mounting structure according to claim 1 , wherein at least one of the thick regions projects outward in the direction of the axis.

6 . The mounting structure according to claim 1 , wherein the three holes are configured as fastening holes into which the three bolts are inserted to fasten the stator core and the case, and the remaining five holes are configured as non-fastening holes which are distinct from the fastening holes.

7 . The mounting structure according to claim 1 , wherein the three bolts include a first bolt inserted into the first hole, a second bolt inserted into the second hole, and a third bolt inserted into the third hole, and

a thickness of the thick regions at a fastening position of the first bolt is smaller than a thickness of the thick regions at a fastening position of the third bolt.