This invention relates to an electric machine, and more particularly, to a hybrid electric machine which generates flux by way of a plurality of permanent magnet poles, a plurality of consequent poles, and a selectively controllable field current, and which provides a relatively constant output power or voltage over a relatively wide range of operating speeds.
Electric machines such as generators and motors generally utilize a plurality of rotating magnets and/or rotating magnetic members in order to generate electrical power and/or torque.
One common type of electric machine, known as an electromagnetic motor or generator, generally includes a rotor having a plurality of pole fingers in the form of north and south ferromagnetic members or consequent poles and one or more electric xe2x80x9cfield coilsxe2x80x9d which are selectively and electrically energized, thereby selectively producing a flux within the rotating members or xe2x80x9cpolesxe2x80x9d of the rotor. In these types of electromagnetic machines, electric power is supplied to the rotating field coils by way of one or more brushes, slip rings, and/or other devices. The output of these electromagnetic machines (e.g., the output torque, power, and/or voltage) can be relatively easily controlled by varying the amount of current supplied to the xe2x80x9cfield coilsxe2x80x9d. In this manner, these types of electric machines provide a relatively consistent output voltage, torque, or power over a relatively wide range of operating speeds and temperatures. While these electromagnetic machines are effective to generate a relatively consistent output voltage, torque, or power, they suffer from some drawbacks.
For example and without limitation, the brushes, slip rings, and/or other devices, which are required within these machines to provide an electrical connection to the rotating field coils, undesirably add to the cost, complexity, and size of the machines, and undesirably xe2x80x9cwearxe2x80x9d or degrade over time, thereby resulting in diminished performance and/or failure of the machine.
A second type of electric machine, known as a permanent magnet motor or generator, generally includes a rotor having a plurality of permanent magnets which form or create poles and selectively produce a flux within the machine. Due to the presence of permanent magnets within the rotor, these types of machines do not typically require field coils to produce magnetic flux. Therefore, these systems do not require the brushes, slip rings or other devices which are necessary in the previously described electromagnetic machines. As such, these permanent magnet machines are typically smaller, less complex, more efficient, and less costly than the previously described electromagnetic machines. These permanent magnet type machines do, however, suffer from some other drawbacks.
For example and without limitation, because the flux generated within these electric machines is provided by permanent magnets, the flux remains substantially constant and is relatively difficult to substantially alter or vary by the use of electric field coils. Thus, the output of these machines (e.g., the output power or voltage) is almost solely and completely dependent upon the operating speed of the machine. As such, these machines are only able provide a relatively consistent or constant output voltage, torque, or power over a relatively narrow and limited range of operating speeds. Therefore, these electric machines cannot be utilized in applications where the operating speed is provided by a relatively xe2x80x9cvariablexe2x80x9d or fluctuating source, such as the engine of a vehicle.
There is therefore a need for a new and improved electric machine which overcomes many, if not all, of the previously delineated drawbacks of such prior electric machines.
It is a first object of the invention to provide an electric machine which overcomes at least some of the previously delineated drawbacks of prior electric machines.
It is a second object of the invention to provide an electric machine which provides a relatively consistent output power and/or voltage over a relatively wide range of operating speeds.
It is a third object of the invention to provide an electric machine having an output torque, power, and/or voltage which may be substantially and selectively controlled by way of a stationary field coil.
It is a fourth object of the invention to provide an electric machine having a rotor which includes poles generated from both permanent magnets and xe2x80x9csoftxe2x80x9d magnetic members.
According to a first aspect of the present invention, an electric machine is provided and includes a generally cylindrical ferromagnetic housing; first and second stator assemblies which are fixedly disposed within the housing and which each include a plurality of pole portions and a winding; a rotor which is rotatably disposed between the first and the second stator assemblies, the rotor having a plurality of permanent magnet poles which collectively generate a first magnetic flux and a plurality of consequent poles which cooperatively generate a second magnetic flux; and a coil which is fixedly coupled to the housing and is disposed in relative close proximity to the rotor. The coil is selectively energizable, and effective to controllably vary the second magnetic flux.
According to a second aspect of the invention a method for providing an electric machine having a controllable output voltage is provided. The method includes the steps of providing a ferromagnetic housing; providing a rotor having a plurality of permanent magnet poles which selectively generate a first magnetic flux and a plurality of consequent poles which selectively generate a second magnetic flux; disposing the rotor within the housing; providing a stator having winding; disposing the stator within the housing and in relative close proximity to the rotor; providing a field coil; fixedly disposing the field coil in relative close proximity to the rotor; selectively energizing the winding effective to produce torque between the rotor and the stator, the torque having a magnitude; and selectively energizing the field coil, effective to vary the second magnetic flux, thereby controlling the magnitude of the torque.
These and other features, aspects, and advantages of the invention will become apparent by reading the following specification and by reference to the following drawings.