Patent Application
20080142284
The invention relates generally to a double-sided electrical machine for vehicles, and more particularly to a double-sided electrical machine designed to drive the vehicle wheels, and to a method for operating such machines.
Electrical machines that transform electrical energy into mechanical energy are used for various motion and drive applications. Electrical machines may include direct current (DC) motors or alternating current (AC) motors. Both DC and AC motors typically provide high performance in motion and drive applications, and both may be used in adjustable speed adjustable drive applications, although under different control regimes. For example, DC motors may be driven by variable voltage or current drives, such as by pulse-width modulation, while AC motors are typically driven by inverter drives or other variable frequency controls. AC motors may be designed for use with either polyphase or single-phase power systems. Such AC motors may include permanent magnet, switched reluctance, synchronous, and induction motors.
In certain applications such as vehicle drives, wind generators, ship propulsion system, or the like, double-sided electrical machines may be used to provide a high torque density. Such double-sided machines typically include a rotor having an inner rotor core and an outer rotor core and a double-sided stator having an inner stator side and an outer stator side. The inner rotor core and the outer rotor core are coupled to a common shaft. The double-sided stator is concentrically disposed between the inner rotor core and the outer rotor core. The double-sided stator is configured to enable at least a portion of magnetic flux to be shared between the inner stator side and the outer stator side. However, such known double-sided electrical machines are not well suited for applications such as wheel drive systems of vehicles, for example, off-highway vehicle, where wheels are required to rotate at different speeds during turning conditions of the vehicle.
In certain vehicle motion and drive applications, high-speed motors in combination with a gearbox may be used to drive the wheels of the vehicle. However, the gearbox may need maintenance and replacement at frequent intervals. Moreover, such arrangements can add significantly to the overall cost, size and weight of the motor drive system.
There is a need for improved double-sided electrical systems, and for method for driving wheels of vehicles, in which wheels coupled to opposite sides of the systems can be rotated at different speeds. Also, there is a need for a double-sided electrical system which may be used in combination with a gearbox system to drive wheels of the vehicle, or without a gearbox, as the application dictates.
In accordance with one exemplary embodiment of the present invention, a double-sided electrical machine includes a stator disposed between the inner rotor and the outer rotor. The stator core includes a plurality of inner stator coils disposed adjacent to the inner rotor for driving the inner rotor. A plurality of outer stator coils disposed adjacent to the outer rotor for driving the outer rotor.
In accordance with another exemplary embodiment of the present invention, a vehicle includes a pair of wheels configured to support the chassis. A double-sided machine is coupled to the pair of wheels. The machine includes a stator disposed between the inner rotor and the outer rotor. The stator includes a plurality of inner stator coils disposed adjacent to the inner rotor for driving the inner rotor. A plurality of outer stator coils disposed adjacent to the outer rotor for driving the outer rotor.
In accordance with yet another exemplary embodiment of the present invention, a double-sided electrical machine includes an inner rotor and an outer rotor supported to the stator housing via one or more bearings. A stator is provided inside the stator housing and disposed between the inner rotor and the outer rotor. The stator includes a plurality of inner stator coils disposed adjacent to the inner rotor for driving the inner rotor. A plurality of outer stator coils disposed adjacent to the outer rotor for driving the outer rotor.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
As discussed in detail below, embodiments of the present invention provide a double-sided electrical machine with a stator disposed between an inner rotor and an outer rotor. The stator includes a plurality of inner stator coils disposed adjacent to the inner rotor for driving the inner rotor. The stator also includes a plurality of outer stator coils disposed adjacent to the outer rotor for driving the outer rotor. The inner rotor is coupled to a first rotor shaft. The outer rotor is coupled to a second rotor shaft. The stator is also enclosed within an outer stator housing. The inner rotor and the outer rotor are rotatably supported with respect to the outer stator housing via one or more bearings. The plurality of inner stator coils and outer stator coils are provided in such a way that inner stator coils and outer stator coils are separated and controllable independently. As a result, the first and second rotor shafts are rotatable at different speeds.
The double-sided machine in accordance with certain exemplary embodiments of the present invention may be desirable for certain applications such as wheel drives in off-highway vehicle in which two rotor shafts are desirable. In such applications, wheels are rotatable at different speeds, such as when the vehicle is turning. In certain applications the two rotor shafts are rotatable in different directions. The exemplary double-sided machine facilitates greater flexibility in terms of driving and turning.
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Further, the machine 10 includes a first power converter 30 coupled to the inner stator coils 26 and configured to drive the inner stator coils 26. A second power converter 32 is coupled to the outer stator coils 28 and configured to drive the outer stator coils 28. In certain embodiments, the converters 30, 32 may be coupled to a DC power source such as a battery, or to any other DC or AC power source, such as a vehicle engine generator (not shown). The converters 30, 32 are configured to convert a power signal transmitted from the DC or AC power source to a controllable AC power source to the inner and outer stator coils 26, 28. As appreciated by those skilled in the art, the converters 30, 32 may include a single-phase inverter, a multi-phase inverter, a multi-level inverter, a parallel configuration or a combination thereof. A control circuit 34 is coupled to the converters 30, 32 and is configured to control various characteristics such as frequency, and magnitude of control signals applied to the converters for producing the appropriate drive signals for the motors. The control circuit 34 facilitates to control speed and direction of rotation of the inner rotor core 20 and the outer rotor core 22 by proper application of controlled frequency signals to the stator windings. It should noted herein that the illustrated configuration of double-sided machine 10, power converters 30, 32 and the control circuit 34 is intended to be an exemplary embodiment, and not limiting in nature. The actual configuration of such drive components may vary depending on the application.
In certain other exemplary embodiments, the converters 30, 32 are coupled to an AC power source via a power source rectifier. The AC power source may comprise either a single phase AC source or a multi-phase AC source. The power source rectifier is configured to convert an AC power signal transmitted from the AC power source to a DC power signal. Similarly any number of configurations of the converters and the power sources are envisaged. In the illustrated embodiment, the inner and outer rotor cores 20, 22 are separated and controlled independently. As result, the speed and direction of rotation of the rotor cores 20, 22 are also controlled independently. Certain presently contemplated configurations of machine 10 are explained in greater detail with reference to subsequent figures.
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An air gap 42 is formed between an inner stator side portion 44 of the stator core 24 and the inner rotor core 20. Another air gap 46 is formed between an outer stator side portion 48 of the stator core 24 and the outer rotor core 22. The inner stator side portion 44 and the outer stator side portion 48 include a double-sided lamination stack 50 axially bolted to an outer stator housing 52 via axial bolts 54. The lamination stack 50 is disposed between the two core plates 56. The core plates 56 and head portions of the axial bolts 54 provide uniform compression of the stack 50. The inner stator coils 26 and the outer stator coils 28 provide magnetic flux to the inner stator side portion 44 and the outer stator side portion 48. In certain exemplary embodiments, seals, such as labyrinth or brush-type seals are provided for sealing between stator and rotor components. Other methods to hold laminations together may, of course, be used, as may other mechanisms for holding core elements together, such as welded or riveted rods, and so forth.
In the illustrated embodiment, the inner rotor core 20 is coupled to a first rotor shaft 58 and the outer rotor core 22 is coupled to a second rotor shaft 60. The first rotor shaft 58 is arranged co-axially relative to the second rotor shaft 60. As illustrated, the first rotor shaft 58 is oriented along a first direction 62 and the second rotor shaft 60 is oriented along a second direction 63 opposite to the first direction 62. The resulting structure provides high torque density (i.e., output torque per unit mass). Morever, the exemplary machine 10 in accordance with the aspects of the present invention, provides the first rotor shaft 58 rotatable independently of the second rotor shaft 60. The inner rotor core 20 is rotatably supported to the outer stator frame 52 via a first bearing 61 and the outer rotor core 22 is rotatably supported to the frame 52 via a second bearing 64. Although in the illustrated embodiment, two bearings are illustrated, alternative bearing configurations such as more than two bearings are also envisaged.
As noted above, in accordance with certain exemplary embodiments of the present invention, the inner rotor core 20 and the outer rotor core 22 are separated and are rotatable at different speeds. The inner stator coils 26 are coupled together to form one multi-phase winding and the outer stator coils 28 are coupled together to form another multi-phase winding. The two sets of multi-phase windings are driven by the power converters in such a way that each set of windings is driven independently. In one exemplary embodiment, the rotor shafts 58, 60 are rotatable along the same direction but at different speeds. In another exemplary embodiment, the shafts 58, 60 are rotatable along the same direction and at same speed. For applications such as off-highway vehicle, the first rotor shaft 58 is coupled to one wheel and the second rotor shaft is coupled to the other wheel. The exemplary machine 10 facilitates flexibility in terms of driving and turning of the wheels of the vehicle. That is, the drive signals may cause both shafts to rotate at the same speed when the vehicle is being propelled in a straight line, and at different speeds to account for different turning radii, thereby avoiding significant wear on the wheels by dragging and sliding, and improving drive traction in turns.
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While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
