Shaft coupling

1. A shaft coupling that couples a first shaft to which a torque is input and a second shaft configured to output the torque, the shaft coupling comprising:

a first coupling member fixed to an end of the first shaft on a side of the second shaft, the first coupling member including a plurality of first protrusions provided at predetermined intervals in a circumferential direction of the first shaft, the first protrusions protruding toward the second shaft;

a second coupling member fixed to an end of the second shaft on the side of the first shaft, the second coupling member including a plurality of second protrusions provided at predetermined intervals in a circumferential direction of the second shaft to protrude between the first protrusions; and

a cushioning member including a plurality of radiating portions extending radially, each of the radiating portions being disposed between the first protrusion and the second protrusion, wherein

when the first coupling member and the second coupling member are disposed coaxially and the first coupling member and the second coupling member are in an unloaded state, predetermined paired facing surfaces have a minimum clearance angle present on a radially outer side with respect to a center of the radiating portion in a radiating direction, the predetermined paired facing surfaces being at least one of first paired facing surfaces and second paired facing surfaces,

the first paired facing surfaces are facing surfaces of the first protrusion and the radiating portion,

the second paired facing surfaces are facing surfaces of the second protrusion and the radiating portion,

the clearance angle is an angle of two intersections of an imaginary concentric circle and the predetermined paired facing surfaces about a connection axis, the imaginary concentric circle being defined about the connection axis on which the first coupling member and the second coupling member are disposed,

the facing surface of the radiating portion in the predetermined paired facing surfaces is located in a first plane that is (i) extending in a direction parallel to a second plane defined by the radiating direction and the connection axis and (ii) spaced from the second plane, and

the facing surface of the first protrusion or of the second protrusion in the predetermined paired facing surfaces is not parallel to the second plane and is inclined, relative to the second plane, such that a distance between the predetermined paired facing surfaces decreases from a radially inner side toward the radially outer side in the radiating direction so as to have the minimum clearance angle present on the radially outer side.

2. The shaft coupling according to claim 1 , further comprising a maintaining member softer than the cushioning member, the maintaining member being configured to maintain, in the unloaded state, a predetermined clearance as at least one of a clearance between each of the first protrusions and each of the radiating portions and a clearance between each of the second protrusions and each of the radiating portions.

3. The shaft coupling according to claim 2 , wherein each of the radiating portions is divided into a plurality of layers in a direction along the connection axis, and the maintaining member is disposed between the layers of each of the radiating portions.