Patent Application
20100264768
The present invention generally relates to permanent magnet machines, and more particularly relates to systems and methods for extending the range and torque of such machines.
Permanent magnet machines are used in a variety of contexts, including hybrid cars, traditional automobiles, and the like. In general, typical permanent magnet machine includes a rotor having set of permanent magnets attached to or embedded within its exterior, and is configured to rotate axially with respect to a stator. The stator and rotor are generally concentric such that a fixed air gap is formed therebetween.
Currently known permanent magnet machines are unsatisfactory in a number of respects. For example, it is known that for any given rotational speed, the air gap necessary to achieve maximum torque is not a constant. Thus, traditional fixed air-gap machines typically provide optimum torque over a narrow range of speeds.
Furthermore, the back-EMF produced by a permanent magnet machine is a function of air-gap magnitude. During a fault condition, this back-EMF voltage can be significant enough to cause failure of the inverter switch. It would be desirable therefore to increase the air-gap under certain conditions to reduce back-EMF, thereby reducing the voltage requirements of the inverter switch.
Accordingly, it is desirable to provide improved permanent magnet machines with optimized torque characteristics. Additional desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
A permanent magnet machine in accordance with one embodiment includes a stator, a rotor configured to coaxially rotate with respect to the stator and having a plurality of permanent magnets coupled thereto, and an air gap between the stator and the rotor having a magnitude that is continuously adjustable to optimize torque, reduce back-EMF, and the like.
A more complete understanding of the present invention may be derived by referring to the detailed description and claims when considered in conjunction with the following figures, wherein like reference numbers refer to similar elements throughout the figures.
The following discussion generally relates to a permanent magnet machine with a tapered or conical stator (and matching rotor) that can be displaced axially to achieve a variable air gap. In that regard, the following detailed description is merely illustrative in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. For the purposes of conciseness, conventional techniques and principles related to magnetism, permanent magnet machines, motors, and the like need not and are not described herein.
Referring to the lateral cross-sectional views shown in
Air gap 115 is formed between the outer surface of rotor 120 and the inner surface of stator 110. In accordance with the present invention, the magnitude of air gap 115 is continuously adjustable, thereby allowing the operation of machine 100 to be optimized in accordance with any desired criteria.
Stator 110 and rotor 120 each have a generally tapered inner surface. That is, the diameter monotonically increases or decreases along the z-axis (the rotational axis 102). In the illustrated embodiment, the inner surface of stator 110 and the outer surface of rotor 120 are both generally conical and concentric. Thus, a consistent gap 115 having a magnitude d1 is formed between the two surfaces.
As illustrated in
As air gap 115 is continuously adjustable during rotation, it may be altered during rotation while monitoring a property of the permanent magnet machine, thereby allowing that property to be optimized. In one embodiment, the torque of machine 100 may be maximized while, for example, minimizing back EMF for any particular conditions. Such adjustments may be open loop (setting a particular air gap magnitude to achieve a corresponding empirically determined torque) or closed loop (providing a control system that continually monitors a characteristic and iteratively changes the air gap magnitude to optimize that characteristic).
The present inventors have found that the adjustable air gap system described above results in a permanent magnet machine with highly desirable characteristics. For example, by varying the air gap as a function of rotational speed, greater power output can be achieved within any given space constraints. At the same time, as the air gap is increased, the EMF voltage is reduced. During a fault condition, such EMF voltage can result in failure of any associated inverter switch. Reducing the EMF voltage therefore reduces the voltage requirements of the inverter switch.
While at least one example embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the example embodiment or embodiments described herein are not intended to limit the scope, applicability, or configuration of the invention in any way. The foregoing detailed description provides those skilled in the art with a convenient and edifying road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention and the legal equivalents thereof.
