Torque transmission apparatus and a collar

An axle assembly comprising:

• an electric motor module;
• a gear reduction module that is operatively connected to the electric motor module, the gear reduction module including a planetary gear set that has a sun gear that is operatively connected to the electric motor module, a planetary ring gear, a planet gear that meshes with the sun gear and the planetary ring gear, and a planet gear carrier that rotatably supports the planet gear and has a first set of teeth;
• a drive pinion having a first shaft that is rotatable about a first axis;
• a second shaft that is rotatable about the first axis and is spaced apart from the first shaft;
• and
• a shift collar that is moveable along the first axis and that is selectively couplable to the first shaft or the second shaft, the shift collar having a collar gear having a collar tooth having a concave collar tooth side surface centered about a transverse collar tooth plane;
• wherein the sun gear has a second set of teeth and the shift collar couples the second shaft to the second set of teeth such that the sun gear and the second shaft are rotatable together about the first axis when the shift collar is in a first position;
• wherein the sun gear has a third set of teeth and the shift collar couples the first shaft to the third set of teeth such that the sun gear and the first shaft are rotatable together about the first axis when the shift collar is in a second position;
• wherein the shift collar is decoupled from the first shaft, the second shaft, the sun gear, and the planet gear carrier when the shift collar is in a first neutral position that is axially positioned between the first position and the second position, wherein the collar gear is axially positioned between the second set of teeth and the third set of teeth when the shift collar is in the first neutral position;
• and
• wherein the sun gear has a tooth that has a convex lateral side surface centered about a transverse tooth plane and the concave collar tooth side surface cooperates with the convex lateral side surface to align the transverse collar tooth plane to the transverse tooth plane when the convex lateral side surface engages the concave collar tooth side surface.