An assist mechanism includes: 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. The smallest rotation order among rotation orders of the electric motor and a rotation order of the worm are prime to each other. The smallest rotation order among the rotation orders of the electric motor and a rotation order of the coupling are prime to each other. The rotation order of the worm and the rotation order of the coupling are prime to each other. The rotation order of the worm is 3. The rotation order of the coupling is 5 or 7.

An assist mechanism includes: 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. The smallest rotation order among rotation orders of the electric motor and a rotation order of the worm are prime to each other. The smallest rotation order among the rotation orders of the electric motor and a rotation order of the coupling are prime to each other. The rotation order of the worm and the rotation order of the coupling are prime to each other. The rotation order of the worm is 3. The rotation order of the coupling is 5 or 7.

A system and method for increasing a tooth shear strength without also increasing a torsional rigidity of a flexible spline disposed between two hubs of a flexible coupling for transmitting mechanical motion between two shafts includes attaching a stiffening cap to an end of a flexible spline, between the flexible spline and the hubs and inserting a plurality of dowels into the teeth of the flexible spline to reinforce the flexible spline.

A driving-side concave-convex portion of a driving-side transmission member is engaged with an elastic member. The driving-side concave-convex portion is engaged with an intermediate concave-convex portion of an intermediate transmission member with a circumferential gap being interposed therebetween. A driven-side concave-convex portion of a driven-side transmission member is engaged with the elastic member. The driven-side concave-convex portion is engaged with the intermediate concave-convex portion with a circumferential gap being interposed therebetween. Both axial side surfaces and a periphery of the intermediate transmission member are covered by a side surface covering portion and a periphery covering portion of the elastic member.

Provided is a torque transmission joint that is able to suppress occurrence of noise when reversing the direction of rotation of the drive shaft. The first transmission member 17 fixed to the output shaft 12a which is a drive shaft is engaged with the first elastic member 20 in a state where the first gap in the circumferential direction is interposed, as well as with the intermediate transmission member 19 in a state where a gap in the circumferential direction which is larger than the first gap is interposed. The second transmission member 18 fixed to an end portion of the worm 8 is engaged with the second elastic member 21 in a state where the second gap in the circumferential direction is interposed, as well as with the intermediate transmission member 19 in a state where a gap in the circumferential direction which is larger than the second gap. The first annular convex portion 54 is pressure fitted to the first annular concave portion 38, and the second annular convex portion 60 is pressure fitted to the second annular concave portion 45 so as to prevent separation of the first, second elastic members 20, 21 with respect to the intermediate transmission member 19.

A first concave-convex portion of a first transmission member is engaged with an intermediate concave-convex portion of an intermediate transmission member with a circumferential gap being therebetween. A second concave-convex portion of a second transmission member is engaged with the intermediate concave-convex portion with a circumferential gap being therebetween. A first elastic member and a second elastic member are engaged with a first engagement portion and a second engagement portion of the intermediate transmission member such that separation between the intermediate transmission member and the first elastic member and the second elastic member can be prevented.

Provided is a torque transmission joint that makes it possible to transmitting torque continuously between a pair of end section transmission members even when the torque transmission function of an intermediate transmission member is deteriorated.

The torque transmission joint includes an intermediate transmission member 19, and a first transmission member 17 and a second transmission member 18 that are arranged with one each on both side sections in the axial direction of the intermediate transmission member 19, with the outer side sections in the radial direction of each engaging with the inside section in the radial direction of the intermediate transmission member 19. The first transmission member 17 and the second transmission member 18 have a first preliminary engagement section 63 and a second preliminary engagement section 66 at the end sections in the axial direction on sides close to each other. The first preliminary engagement section 63 and the second preliminary engagement section 66 engage with each other with a circumferential gap interposed therebetween that does not disappear when torque transmission is performed between the first transmission member 17 and the second transmission member 18 via the intermediate transmission member 19.

An assist mechanism includes: 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. The smallest rotation order among rotation orders of the electric motor and a rotation order of the worm are prime to each other.

The driven-side concave-convex part is engaged to the second coupling-side concave-convex part, and the driven-side concave-convex part is engaged to a part, which is located further toward the other axial side than the partition wall part, of the third coupling-side concave-convex part in a state where a circumferential gap, which is greater than a circumferential gap provided to an engagement part between the driven-side concave-convex part and the second coupling-side concave-convex part, is interposed therebetween. At least a part of the partition wall part is arranged between axial end faces of the drive-side transmission member and the driven-side transmission member.

Circumferential rigidity of both axial end portions of each coupling-side convex portion is lower than circumferential rigidity of an axially intermediate portion of each coupling-side convex portion. The drive-side concave-convex portion is engaged with a half portion on the other axial side of the coupling-side concave-convex portion. The driven-side concave-convex portion is engaged with a half portion on one axial side of the coupling-side concave-convex portion.