Connection unit, electric motor, and valve timing change device

A connection unit for transmitting a rotation force to a rotation body the connection unit comprising:

• a rotation shaft including a width across flat portion arranged at a first end of the rotation shaft;
• and
• a core including:
• a rectangular portion defining a rectangular opening portion configured to slidably receive the width across flat portion,
• two protrusions which protrude in a direction perpendicular to the width across flat portion, the two protrusions configured to engage the rotation body, and
• a cut-out formed, on a radial outer edge of each protrusion;
• and
• a regulation guide portion arranged on the rotation shaft at the width across flat portion, the regulation guide portion configured to limit a movement of the core in an axial direction of the rotation shaft and to guide a two-dimensional movement of the core with respect to the width across flat portion as the core rotates integrally with the rotation shaft,
• wherein the rectangular portion includes longitudinal ends with circular arc surfaces, and two straight sides that connect the circular arc surfaces,
• wherein each of the two protrusions defines a tapered surface with a thickness dimension in the axial direction that gradually decreases towards the radial outer edge,
• wherein axially-facing end surfaces of the core are opposed convex surfaces each defined by a radius of curvature having a respective center disposed along an axis of the rotation shaft, and
• wherein the regulation guide portion comprises a step portion defining a boundary of the width across flat portion, and a stopper fixed to the rotation shaft so as to cooperate with the step portion in clamping the core.