Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1996-04-30
1998-09-01
Dougherty, Thomas M.
Electrical generator or motor structure
Dynamoelectric
Rotary
310114, 310166, 310168, 310218, 310254, 310258, 310266, 310268, H02K 112, H02K 118, H02K 1700, H02K 1712
Patent
active
058014730
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to an electric machine. In particular, the invention concerns an open stator axial flux electric (OSAF) motor.
The invention will be described by way of example with reference to a preferred application or use of the motor. This preferred use or application employs the motor of the invention as a traction motor for driving a railway bogie. It should be appreciated that this is by way of example only and that the motor of the invention may be employed in other applications and for other purposes.
BACKGROUND OF THE INVENTION
Traction motors for rail bogies in recent times typically are three phase asynchronous motors powered by an inverter controlled bridge providing a three phase AC voltage of about 750 to 2000 VAC depending upon the particular traction system used.
Such traction motors have a stator and a rotor with the rotor operating at relatively high speeds.
Electronic converters/inverters (e.g. pulse width modulation) are used to develop the variable frequency traction drive three phase supply to power and control the motor. The motor is typically of a squirrel cage design. The high speed range is necessary to take advantage of the high torque characteristic at high rotational speed of conventional three phase machines.
High motor speed over 4000 rpm and up to 6500 rpm requires special bearing design and lubrication attention for heavy engineering, marine and traction applications. Difficulties arise with low starting speed, lubricant film levels and over-lubrication and heating at the high speed. Shorter bearing life and shorter maintenance periods for bearing lubrication are a reality.
High motor speed requires expensive drive train and gear box design. It is time consuming and expensive to change an element of a drive system e.g. wheel or motor in a rail traction system.
Traction motor construction is such that there is no stator case or housing and the stator laminations form the body of the motor. A catastrophic rotor failure or a stator winding failure may require complete replacement of the motor.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved electric motor for use as a drive system, e.g. a traction motor for railway bogies.
According to one aspect the invention provides an open stator axial flux asynchronous induction electric motor including:
an open stator including two spaced insulating supports with a slot extending from a periphery of each of the supports to an inner location thereof, a plurality of poles with pole pieces extending between the supports and secured thereto, the pole pieces being made of magnetically permeable material and arranged along a circular path around the supports, the stator having either distributed windings or salient phase pole windings associated with at least some of the pole pieces with an opening between adjacent pole pieces in the region of the slots in the supports;
a rotor having a shaft locatable in and extending through the slots and extending at right angles to the supports, two spaced rotor discs on the shaft with a respective said disc located on the shaft and either side of the stator, each disc being constructed of magnetically permeable material and having either an inner face of electrically conductive material or an inner face with conductive paths providing rotor windings, the shaft being supported for rotation relative to the rotor.
The shaft which forms part of the rotor is preferably made from a non-magnetically permeable material. In this way the flux linkage paths from one of the rotor discs to the other of the rotor discs are minimised and the magnetic paths are contained within the discs and the stator poles. Fringing and losses may be reduced by such a choice of shaft material. In one embodiment the shaft is made from an austenitic stainless steel although other non-magnetically permeable materials may also be used e.g. the relative permittivity of about 1.03 for austenitic stainless steel is particularly preferred.
As mentioned, the rotor discs may
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Dougherty Thomas M.
Queensland Rail
Tamai Karl
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