Patent Application
20140001901
The present disclosure relates generally to electric motors, and specifically to a sealing configuration within an electric motor.
Conventional electric motors, such as those used on board an aircraft, use a rotor/stator configuration in which electric power passing through the stator generates an electromagnetic field, which in turn causes a physical rotation of the rotor. The rotor is coupled to an output shaft and allows rotational power to be translated to a mechanical system connected to the output shaft. In some conventional designs, the rotor cavity includes a fluid that is used to cool and lubricate the rotor. This fluid is referred to as a working fluid. The working fluid is pumped throughout the aircraft by the motor. In these designs, a seal is positioned between the rotor cavity and the stator cavity to prevent the working fluid from leaking into the stator cavity and damaging or destroying the stator components.
It is understood that the material used to construct the seal will gradually corrode, resulting in the eventual failure of the seal. When the seal fails, the working fluid is introduced into the stator cavity and will rapidly corrode the stator components. When this occurs motor failure is imminent. Furthermore, conventional motor designs provide no indication that the seal is leaking, and often the first sign of a problem is when the motor has become inoperable and irreparable.
Disclosed is an electric motor having a rotor in a rotor cavity; a stator in a stator cavity, wherein the stator is arranged circumferentially about the rotor; a stator sleeve isolating the stator cavity from the rotor cavity; a first primary seal within the rotor cavity, wherein the first primary seal is operable to prevent a working fluid within the rotor cavity from exiting the rotor cavity; and a first secondary seal within the stator cavity, wherein the secondary seal is operable to prevent a working fluid within the rotor cavity from entering the stator cavity.
Also disclosed is, a method for repairing an electric motor including the steps of identifying the presence of a leaking seal within the motor by identifying a working fluid leaking from at least one weep hole; removing at least one of an end cap and a mounting plate of the motor; replacing the leaking seal; and reattaching the at least one of the end cap and the mounting plate.
These and other features of this application will be best understood from the following specification and drawings, the following of which is a brief description.
Each of the end cap 30 and the motor housing 20 includes a weep hole 40, 42. The weep holes 40, 42 allow a working fluid that has leaked through an internal rotor cavity seal to exit the motor 10 without damaging the stator components. The weep holes 40, 42 are aligned axially, thereby allowing gravity to pull the working fluid out of the weep hole 40, 42. In alternate motor mounting configurations, the weep holes 40, 42 can be oriented in another direction, thereby allowing gravity to drain the working fluid out of the motor housing 20 and the end cap 30.
Turning now to
Between each of the primary seals 150 and their corresponding secondary seals 160 is a gap 180 defined by the stator sleeve 170 and the end cap 30 or the mounting plate 50. Each of the gaps 180 is similarly connected to a corresponding weep hole 40, 42. In this way, a working fluid that leaks through the primary seal 150 from the rotor cavity 130 is blocked by the secondary seal 160 and accumulates in the gap 180. After accumulating, the working fluid is drawn out the weep hole 40, 42 and exits the motor 10. Due to the orientation of the weep holes 40, 42, and the mounting orientation of the motor 10, gravity provides the force required to draw the working fluid out of the weep holes 40, 42.
The weep hole 40, 42 arrangement further facilitates repair and maintenance of the motor 10 by providing a visual indication of a failing internal primary seal 150 without requiring the motor 10 to be disassembled. As the weep holes 40, 42 on the motor 10 are visible during an inspection, an inspector will notice working fluid leaking out of the weep holes 40, 42 when the primary seal 150 has begun to fail. The inspector can then note the leaking working fluid and the motor 10 can be scheduled for replacement before the motor 10 has been rendered inoperable.
Alternatively, the motor 10 can be scheduled for repair, thereby allowing the life span of the motor 10 to be extended. To repair a leaking primary seal 150, the end cap 30 or the mounting plate 50 corresponding to the weep hole 40, 42 weeping working fluid is removed from the motor 10. As the primary seal 150 is located between the stator sleeve 170 and the end cap 30 or between the stator sleeve 170 and the mounting plate 50, removal of the end cap 30 or the mounting plate 50 provides access to the seal 150 without requiring a complete reconstruction of the motor 10.
In some example motors 10, such as the illustrated example motor 10, the stator sleeve 170 is glued or epoxied in place. In alternate examples, the stator sleeve is not glued and the secondary seal 160 can be accessed by the additional removal of the stator sleeve 170. Motors built according to the alternate example can include replacing the secondary seal 160 as part of the maintenance.
Each of the primary seals 150 and the secondary seals 160 in the illustrated example motor 10 are O-ring type seals. Alternatively, any stiff non-rotating seal type can be used to similar effect. In further alternative embodiments, additional weep holes 40, 42 can be used in place of the singular weep holes 40, 42 on each axial end of the motor 10, as illustrated in the example embodiment. Additional weep holes can allow working fluid to be drained from the gap 180 quicker in the case of a leaking primary seal 150, thereby lengthening the operational time of the motor 10 after the primary seal 150 has begun to leak and increasing a repair/replace time window before the motor 10 fails.
Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
