A speed reducer comprises a transmission shaft, an eccentric wheel, a first wheel assembly, a rotating wheel and a second wheel assembly. The first wheel assembly comprises a first wheel disc and at least one first roller. The at least one first roller is disposed on the inner wall of first wheel disc. The rotating wheel comprises a main body comprising an outer ring structure and a concave structure. The outer ring structure comprises at least one first tooth. The at least one first tooth is in contact with the corresponding first roller. At least one second roller is disposed within the concave structure. The second wheel assembly comprises a second wheel disc and at least one second tooth. The at least one second tooth is disposed on an outer periphery of the second wheel assembly. The at least one second tooth is in contact with the corresponding second roller.

A reduction gear configured to decelerate and output rotation of a motor includes two-stage planetary gear mechanisms that are provided side by side in an axial direction of the motor and are each configured of helical gears, and a case made of resin and formed into a cylindrical shape, the case incorporating the two-stage planetary gear mechanisms. At least one of an inner engagement ratio of a sun gear and a pinion gear of the planetary gear mechanism in a first stage and an outer engagement ratio of the pinion gear and a ring gear of the planetary gear mechanism in the first stage is 3.0 or more, and both the inner engagement ratio and the outer engagement ratio are larger than an engagement ratio of the planetary gear mechanism in a second stage.

A reduction gear configured to decelerate and output rotation of a motor includes two-stage planetary gear mechanisms that are provided side by side in an axial direction of the motor and are each configured of helical gears, and a case made of resin and formed into a cylindrical shape, the case incorporating the two-stage planetary gear mechanisms. At least one of an inner engagement ratio of a sun gear and a pinion gear of the planetary gear mechanism in a first stage and an outer engagement ratio of the pinion gear and a ring gear of the planetary gear mechanism in the first stage is 3.0 or more, and both the inner engagement ratio and the outer engagement ratio are larger than an engagement ratio of the planetary gear mechanism in a second stage.

An apparatus and method for reducing edge contact stress concentrations in a press-fit. The apparatus and method of the present disclosure specifically provide for a press-fit collar having a channel circumscribing a collar axis. The channel having an asymmetrical cross-sectional profile in a radial face. The asymmetrical cross-sectional profile being configured to reduce an edge contact pressure.

An apparatus and method for reducing edge contact stress concentrations in a press-fit. The apparatus and method of the present disclosure specifically provide for a press-fit collar having a channel circumscribing a collar axis. The channel having an asymmetrical cross-sectional profile in a radial face. The asymmetrical cross-sectional profile being configured to reduce an edge contact pressure.

Disclosed herein are actuator, planetary-gear apparatus, and structural-unit embodiments configured to reduce noise and vibration caused by operation of planetary gears. An embodiment may include a ring gear having an outer peripheral surface that extends in the axial direction. A first raised portion may be formed on said outer peripheral surface; and a housing having an inner peripheral surface that is provided facing, and with a gap from, the outer peripheral surface of the ring gear. A second raised portion may be formed on said inner peripheral surface. Movement of the ring gear in the circumferential direction is limited by linear contact or point contact between the first raised portion and the second raised portion, for example. The outer peripheral surface and/or the inner peripheral surface may be a surface of a crowned shape that is bowed in the outer radial direction, according to some further embodiments.

Disclosed herein are actuator, planetary-gear apparatus, and structural-unit embodiments configured to reduce noise and vibration caused by operation of planetary gears. An embodiment may include a ring gear having an outer peripheral surface that extends in the axial direction. A first raised portion may be formed on said outer peripheral surface; and a housing having an inner peripheral surface that is provided facing, and with a gap from, the outer peripheral surface of the ring gear. A second raised portion may be formed on said inner peripheral surface. Movement of the ring gear in the circumferential direction is limited by linear contact or point contact between the first raised portion and the second raised portion, for example. The outer peripheral surface and/or the inner peripheral surface may be a surface of a crowned shape that is bowed in the outer radial direction, according to some further embodiments.

A brake device of the present invention includes: a wheel brake unit for braking a wheel; an electric motor for driving the wheel brake unit; a speed reducer for decelerating rotation of the electric motor; a rotation-linear motion converter for converting a rotational output of the speed reducer into a linear motion; and a braking force transmission member for transmitting the linear motion produced by the rotation-linear motion converter to the wheel brake unit.

A brake device of the present invention includes: a wheel brake unit for braking a wheel; an electric motor for driving the wheel brake unit; a speed reducer for decelerating rotation of the electric motor; a rotation-linear motion converter for converting a rotational output of the speed reducer into a linear motion; and a braking force transmission member for transmitting the linear motion produced by the rotation-linear motion converter to the wheel brake unit.

A power transmission device includes a pin gear having a plurality of power transmission pins that are relatively moved corresponding to a tooth shape formed on an outer gear, a motor arranged in a direction crossing a rotation axis of the pin gear, and generating power to rotate the pin gear, and a motion transfer unit connected to the pin gear and the motor between the pin gear and the motor, and transferring a rotational motion of the motor to a rotational motion of the pin gear.