Patent Application
20180361842
This disclosure related to the field of hybrid electric vehicles. More particularly, the disclosure relates to a structure of a permanent magnet rotor.
Many vehicles are used over a wide range of vehicle speeds, including both forward and reverse movement. Some types of engines, however, are capable of operating efficiently only within a narrow range of speeds. Consequently, transmissions capable of efficiently transmitting power at a variety of speed ratios are frequently employed. When the vehicle is at low speed, the transmission is usually operated at a high speed ratio such that it multiplies the engine torque for improved acceleration. At high vehicle speed, operating the transmission at a low speed ratio permits an engine speed associated with quiet, fuel efficient cruising.
In order to reduce fuel consumption, some vehicles include hybrid powertrains which utilize energy storage to supplement the power produced by the internal combustion engine. These powertrains permit the vehicle to operate a portion of the time with the engine off and the remainder of the time at torque levels at which the engine is more efficient. Hybrid powertrains also enable the capture and later use of energy that would otherwise be dissipated by the braking system.
In some embodiments, a motor includes a stator, a rotor, and a plurality of permanent magnets. The rotor is supported for rotation with respect to the stator and defines a plurality of magnet pockets. Each magnet of the plurality of permanent magnets has a non-cuboid parallelepiped form and has a net magnetization direction that is not perpendicular to any surface of the magnet. The magnets may be arranged in an inner row and an outer row. An outer surface of each magnet may be oriented diagonally or perpendicular to a radial of the rotor.
In some embodiments, a motor includes a stator, a rotor, and a plurality of permanent magnets. The rotor is supported for rotation with respect to the stator and defines a plurality of magnet pockets. Each magnet of the plurality of permanent magnets has a non-cuboid form and has a net magnetization direction that is parallel to a sideward surface and not perpendicular to an outwards surface of the magnet. The magnets may be arranged in an inner row and an outer row. An outer surface of each magnet may be oriented diagonally or perpendicular to a radial of the rotor.
A vehicle includes a rotor and a plurality of permanent magnets. The rotor defines a plurality of magnet pockets into which the permanent magnets are inserted. The magnets have a non-cuboid parallelepiped form and have a net magnetization direction that is not perpendicular to any magnet surface. The net magnetization direction may be parallel to a sideward surface of the magnet. The vehicle may also include an inverter configured to induce alternating currents in windings in a stator to establish magnetic fields that cause the rotor to rotate with respect to the stator. The vehicle may also include an internal combustion engine selectively coupled to the rotor by a clutch. The vehicle may also include a multi-speed transmission configured to driveably connect the rotor to vehicle wheels.
As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.
Torque converter 22 includes an impeller fixedly connected to the transmission input shaft 20 and a turbine fixedly connected to the input of gearbox 24. Torque converter 22 transmits power from the impeller to the turbine whenever the impeller rotates faster than the turbine. Torque converter 22 may also include a stator which multiplies the torque such that the torque on the turbine is greater than the torque on the impeller. Torque converter 22 may also include a lockup clutch that selectively couples the impeller to the turbine for more efficient power transfer when the slip associated with the hydrodynamic power transfer between the impeller and turbine is not required.
Gearbox 24 includes several clutches and brakes that establish various power flow paths from the gearbox input shaft to the transmission output shaft. These power flow paths have different speed ratios. The transmission shifts from one power flow path to another power flow path by disengaging one or more clutches or brakes and engaging other clutches or brakes. A neutral mode is established in which no power flow path between the gearbox input and the transmission output exists. Gearbox 24 may also include a parking pawl that may be engaged to hold the transmission output stationary when the vehicle is unoccupied.
The transmission output shaft is connected to differential 26 which divides the power between left and right driven wheels 28 and 30. The differential permits slight speed differences between the wheels such as when the vehicle turns a corner.
Internal combustion engine 32 is selectively coupled to transmission input shaft 20 by clutch 32. Note that transmission input shaft 20 extends through traction motor 10. When clutch 32 is engaged, engine 30 and traction motor 10 rotate at the same speed and the torque on transmission shaft 20 is equal to the sum of the torque produced by engine 30 and the torque produced by traction motor 10. In some operating modes, engine 30 may provide all power for propulsion by setting the traction motor torque to zero. In other operating modes, the motor may draw power from battery 12 to assist in propelling the vehicle. In still other operating modes, the engine may produce more power than required for propulsion with the motor diverting some of the power to charge battery 12. When clutch 32 is disengaged, all propulsion is provided by traction motor 10.
The powertrain is controlled by controller 34. Controller 34 may be a single micro-processor or multiple communicating micro-processors. Controller 34 accepts commands from the driver via the accelerator pedal position, the brake pedal position, the position of the shift selector (PRNDL), etc. The controller also uses signals from various sensors. The controller controls engagement and disengagement of clutch 32, the torque converter lockup clutch, and the clutches and brakes within gearbox 24. The controller also sends commands to the engine 30 and to inverter 14 to control the torque of motor 10.
Current in the windings 42 create magnetic fields in the stator poles 40. Magnetic forces between the stator poles and the rotor exert torque on the rotor. The magnitude of the torque depends upon the current in the windings and the location of the stator magnetic field relative to the rotational position of the rotor. Inverter 14 adjusts the voltage applied to the stator windings to achieve a desired current magnitude and adjusts the current phase angle to locate the stator magnetic field relative to rotor position. During generation, inverter 14 converts AC power from the machine into DC power to be stored in battery 12.
In some circumstances, the magnetic field produced by the stator may act to demagnetize the permanent magnets. Any demagnetization of the permanent magnets reduces the motor performance in the future.
The inventors have discovered that demagnetization is less likely to occur when the net magnetization direction is not perpendicular to the outward magnet surface. Use of this magnetization direction permits use of thinner magnets for a given application without experiencing demagnetization. Having the magnetization direction parallel to a sideward surface permits the magnets to be cut from a bar magnet, simplifying manufacture.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.
