Assist mechanism and electric power steering device

An electric power steering device comprising an assist mechanism, wherein

• the assist mechanism comprises:
• an electric motor in which a rotor has a magnet and a stator has a winding;
• a shaft-shaped member in which a worm engaged with a worm wheel is formed;
• and
• a coupling that couples an output shaft of the electric motor and the shaft-shaped member to each other,
• a smallest rotation order among rotation orders of the electric motor and a rotation order of the worm are prime to each other,
• the rotation order of the electric motor is n times a larger natural number of two natural numbers other than 1 when a multiplication of the two natural numbers expresses the number of poles of a magnet in the rotor,
• n is a natural number of 1 or greater,
• the rotation order of the worm is the number of teeth of the worm wheel that advance in response to one rotation of the shaft-shaped member,
• the worm wheel is provided to an output shaft of a steering wheel,
• the electric power steering device is a column assist power steering device,
• the first transmission member and the second transmission member have the same number of projections,
• the rotation order of the coupling is equal to the number of the projections,
• a first elastic member is provided between the first transmission member and the third transmission member,
• a second elastic member is provided between the second transmission member and the third transmission member, and
• the third transmission member has higher rigidity than the first elastic member and the second elastic member.

An electric power steering device comprising an assist mechanism, wherein:

• the assist mechanism comprises:
• an electric motor;
• a shaft-shaped member in which a worm engaged with a worm wheel is formed;
• and
• a coupling that couples an output shaft of the electric motor and the shaft-shaped member to each other, wherein
• a smallest rotation order among rotation orders of the electric motor and a rotation order of the coupling are prime to each other,
• the rotation order of the electric motor is n times a larger natural number of two natural numbers other than 1 when a multiplication of the two natural numbers expresses the number of poles of a magnet or a commutator in a rotor,
• n is a natural number of 1 or greater,
• the coupling includes
• a first transmission member fixed to the output shaft;
• a second transmission member fixed to the shaft-shaped member;
• and
• a third transmission member engaged with a predetermined number of projections of each of the first transmission member and the second transmission member to couple the first transmission member and the second transmission member to each other,
• the worm wheel is provided to an output shaft of a steering wheel,
• the electric power steering device is a column assist power steering device,
• the first transmission member and the second transmission member have the same number of projections,
• the rotation order of the coupling is equal to the number of the projections,
• a first elastic member is provided between the first transmission member and the third transmission member,
• a second elastic member is provided between the second transmission member and the third transmission member, and
• the third transmission member has higher rigidity than the first elastic member and the second elastic member.