A speed reducer includes a planetary gear, a first ring gear and a second ring gear. The planetary gear is a helical gear and has planetary gear teeth each of which is tilted relative to an axis of the planetary gear. The first ring gear is a spur gear and has first ring gear teeth which extend in parallel with an axis of the first ring gear and are configured to mesh with the planetary gear teeth. The second ring gear is a spur gear and has second ring gear teeth which extend in parallel with an axis of the second ring gear and are configured to mesh with the planetary gear teeth.

A planetary gear has: a first planetary gear annular surface formed at one axial end of the planetary gear and a second planetary gear annular surface formed at another axial end of the planetary gear. A sun gear has a sun gear annular surface that is opposed to the first planetary gear annular surface. A second ring gear has an output-side annular surface that is opposed to the second planetary gear annular surface. A relative movement of a carrier subassembly relative to a housing in an axial direction is limited when the first planetary gear annular surface abuts against the sun gear annular surface or when the second planetary gear annular surface abuts against the output-side annular surface.

A housing is placed at an inside space of a case to be installed on a vehicle. The housing includes: a housing plate portion configured to contact a case plate portion of the case; and a receiving space located on one side of the housing plate portion which is opposite to the case plate portion. An electric motor is placed at the receiving space and is configured to output a torque. The housing includes: a housing ventilation hole that extends through the housing plate portion and communicates between an outside space of the housing and the receiving space; and a breathable filter that is placed on a side of the housing ventilation hole, at which the case plate portion is placed, to cover the housing ventilation hole, while the breathable filter is configured to perm it a gas to pass through the breathable filter.

A housing is placed at an inside space of a case to be installed on a vehicle. The housing includes: a housing plate portion configured to contact a case plate portion of the case; and a receiving space located on one side of the housing plate portion which is opposite to the case plate portion. An electric motor is placed at the receiving space and is configured to output a torque. The housing includes a housing protrusion and a housing recess. The housing protrusion protrudes from a surface of the housing plate portion located on another side of the housing plate portion at which the case plate portion is placed, and the housing protrusion is configured to fit into a case recess of the case. The housing recess is recessed from another surface of the housing plate portion which is opposite to the housing protrusion.

A transmission for a vehicle includes a transmission unit for receiving a transmission command for a vehicle, a driving unit for generating a driving force for switching a posture of the transmission unit, and a control device for controlling the driving unit to switch the posture of the transmission unit based on whether a preset condition is satisfied. The driving unit includes a first stator for generating magnetic flux, a first rotor having a first inner permanent magnet and a second inner permanent magnet axially arranged at a predetermined spacing along a rotation axis, and configured to be rotated by the magnetic flux transferred to the first inner permanent magnet, an outer permanent magnet, and a second rotor configured to rotate along a magnetic force path between the second inner permanent magnet and the outer permanent magnet.

A deceleration mechanism is provided with first and second gears, a first tooth part arranged in the first gear and extending spirally in an axial direction of the first gear, an engagement projected part arranged on the first tooth part, second tooth parts arranged on the second gear, and an engagement recessed part arranged between the adjacent second tooth parts. The engagement projected part is formed in an arc shape in a direction orthogonal to the axial direction of the first gear and has a curvature center eccentric from a rotation center of the first gear. The second tooth parts are inclined with respect to the axial direction of the first gear and arranged in a circumferential direction of the second gear. The engagement projected part is formed in an arc-shape in a direction orthogonal to the axial direction of the first gear and engaged with the engagement projected part.

An axial flux magnetic geared machine includes a high speed magnetic rotor and a low speed magnetic rotor maintained in a spaced relationship from the high speed magnetic rotor. A modulating structure is disposed between the high speed magnetic rotor and the low speed magnetic rotor. A stator is disposed in a radially central bore of one or more of the high speed magnetic rotor, the low speed magnetic rotor, and the modulating structure.

An axial flux magnetic geared machine includes a high speed magnetic rotor and a low speed magnetic rotor maintained in a spaced relationship from the high speed magnetic rotor. A modulating structure is disposed between the high speed magnetic rotor and the low speed magnetic rotor. A stator is disposed in a radially central bore of one or more of the high speed magnetic rotor, the low speed magnetic rotor, and the modulating structure.

An electrical machine comprising: a first rotor, the first rotor producing a first magnetic field having a first number of pole pairs; a second rotor comprising a plurality of pole pieces, the plurality of pole pieces being arranged to modulate the first magnetic field to produce a second magnetic field having a second number of pole pairs; a stator Comprising one or more windings arranged to produce a third magnetic field arranged to interact with the first number of pole pairs and the second number of pole pairs; wherein the interaction of the third magnetic field with the first number of pole pairs and the second number of pole pairs changes a torque ratio between the first rotor and the second rotor.

An electrical machine comprising: a first rotor, the first rotor producing a first magnetic field having a first number of pole pairs; a second rotor comprising a plurality of pole pieces, the plurality of pole pieces being arranged to modulate the first magnetic field to produce a second magnetic field having a second number of pole pairs; a stator Comprising one or more windings arranged to produce a third magnetic field arranged to interact with the first number of pole pairs and the second number of pole pairs; wherein the interaction of the third magnetic field with the first number of pole pairs and the second number of pole pairs changes a torque ratio between the first rotor and the second rotor.