Patent claim: The electric power steering apparatus according to claim 1 wherein a circumferential side surface of the center arm portion is configured to protrude toward the engagement space side with respect to a circumferential side surface of the first cover arm portion and a circumferential side surface of the second cover arm portion.

Related passage: As described above according to the shaft coupling mechanism 1 the intermediate interposed member 8 disposed between the rotation transmitting members 6 and 7 has the projecting portions 73 each of which is disposed between the respective ones of the projecting portions 33 and 53 of the rotation transmitting members 6 and 7 in the A direction and has the larger width D2 in the R direction than the width D1 of each of the projecting portions 33 and 53.Each projecting portion 73 of the intermediate interposed member 8 has a smaller rigidity than the rigidity of each of the projecting portions 33 and 53 of the rotation transmitting members 6 and 7.As a result the transmission of the rotation of the rotating shaft 2 in the R direction to the steering shaft 4 is effected through the elastic deformation of the projecting portions 73 of the intermediate interposed member 8.Therefore the transmission of very small rotationof the rotating shaft 2 in the R direction to the steering shaft 4 can be reduced or prevented by the elastic deformation of the projecting portions 73 of the intermediate interposed member 8 while the transmission to the steering shaft 4 of large relative rotation of the rotating shaft 2 in the R direction with respect to the steering shaft 4 can be effected as it is through the rotation transmitting members 6 and 7 having a greater rigidity than the projecting portions 73 of the intermediate interposed member 8.Moreover in the relative rotation of the rotating shaft 2 in the R direction by more than a fixed degree with respect to the steering shaft 4 the large elastic deformation of the projecting portions 73 of the intermediate interposed member 8 can be prevented by the rotation transmitting members 6 and 7 having a greater rigidity so that even if a flexible resin material having a small rigidity is used for the intermediate interposed member 8 the permanent deformation of the intermediate interposed member 8 due to creep can be reduced.Moreover since the pair of rotation transmitting members 6 and 7 are coupled to each other through the coupling means 9 the assembling efficiency can be improved and the mutual separation in the A direction between the pair of rotation transmitting members 6 and 7 due to the elastic deformation of the intermediate interposed member 8 can be eliminated thereby making it possible to suppress the expansion of the pair of rotation transmitting members 6 and 7 in the A direction to a fixed degree.Thus it is possible to reduce the transmission to the steering wheel of the impact at the time of the reversing of the electric motor and the brush vibration.Furthermore it is possible to eliminate backlash in the R direction between the rotating shaft 2 and the steering shaft 4.Hence the steering feel can be prevented from becoming uncomfortable and the shaft coupling mechanism can be made to excel in durability and can be provided with stable characteristics.