Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-11-02
2001-09-25
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S052000
Reexamination Certificate
active
06294853
ABSTRACT:
RIGHTS OF THE GOVERNMENT
The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
BACKGROUND OF THE INVENTION
The present invention relates generally to electrical control devices and more specifically to an electromechanical actuator including a passive cooling system.
There is a growing trend in the design of modern aircraft control systems to replace the well known control surface hydraulic actuators with localized, dedicated electromechanical actuating devices. The overall aim is to eliminate the aircraft hydraulic system in order to enhance simplicity, reduce operating costs, reduce aircraft weight and avoid loss of aircraft control situations due to hydraulic system failure. Military aircraft are perhaps especially vulnerable to hydraulic system failure from flight critical battle damage received during combat. Both military and civilian aircraft, however, would benefit from the elimination of the hydraulic control systems in favor of dedicated, individual electromechanical control devices.
As is well known, electromechanical actuators are inefficient during operation. The waste heat generation of the electromechanical actuators average 10-25% of their power, which must be removed in order to assure continuous, reliable operation. While hydraulic actuators also generate waste heat, this heat is removed by the central hydraulic system and discharged at a remote location. While it would be possible to provide a central cooling system to cool the electromechanical actuators, much of the benefit otherwise gained by the utilization of the individual electromechanical actuators would be lost because one centralized system is simply substituted for another. Moreover, the increased complexity of such a central cooling system including the attendant pumps, valves, plumbing, etc. serves to eliminate this as a choice of a viable, alternative system.
One recent approach to providing a self cooling electromechanical device is found in U.S. Pat. No. 5,770,903 to Bland et al. disclosing a reflux-cooled electromechanical device including a housing surrounding the stator defining a sealed boiling chamber. The boiling chamber contains a fluid for transferring heat and a condenser for removing the heat externally from the boiling chamber. While this device does provide a degree of heat transfer from the electromechanical actuator, a need for improvement exists. More specifically, because of the boiling chamber design, the heat transfer characteristics of this device change dramatically with changes in G loading forces as would be encountered by modern military aircraft in flight.
A need exists therefore for an improved self cooled electromechanical actuator Such a device would be capable of providing independent, reliable operation in a range of operating conditions from <<1 G to 10 G.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention to provide an improved, passively cooled electromechanical actuator overcoming the limitations and disadvantages of the prior art.
Another object of the present invention is to provide a passively cooled electromechanical actuator that is self contained and capable of operation in a range of G loading conditions from <<1 G to 10 G.
Yet another object of the present invention is to provide a passively cooled electromechanical actuator having a sealed cooling system requiring no coolant replenishment.
Still another object of the present invention is to provide a passively cooled electromechanical actuator that includes a thermally activated phase change material for absorbing or releasing heat during transient high heat flux operating conditions.
Additional objects, advantages and other novel features of the invention will be set forth, in part, in the description that follows and will, in part, become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects and in accordance with the purposes of the present invention as described herein, a passively cooled electromechanical actuator incorporates sealed thermosyphons to provide effective, passive cooling of the actuator during operation.
The preferred embodiment of the passively cooled electromechanical actuator selected to illustrate the invention includes a pair of closed thermosyphons in thermal communication with the stator. The thermosyphons receive heat from the stator and transmit it to a pair of mounting platforms to direct the heat away from the actuator. For aircraft applications, the mounting platforms are attached to the inner surfaces of the wings, so as to direct the heat into the atmosphere, away from the aircraft.
According to an important aspect of the present invention, the passively cooled electromechanical actuator includes a pair of inner supports in thermal communication with the actuator stator. Received within each support is a quantity of phase change material. This phase change material, normally solid, has a melting temperature just above the expected range of operating temperatures encountered by the passively cooled electromechanical actuator during normal aircraft operation. During transient conditions, when a greater than normal heat flux is encountered either internally by actuator operation or externally by aircraft high mach dashes, the phase change material melts, and in so doing, temporarily absorbs this additional heat. The thermosyphons, being in thermal communication with the phase change material, will remove this additional, stored heat when operating conditions return to normal. The phase change material will re-solidify in readiness for the next transient cycle.
Accordingly, the passively cooled electromechanical actuator of the present invention can also effectively operate in unexpected, high heat flux transient conditions both internal and external, assuring reliable, independent operation over a wide range of aircraft operating conditions.
REFERENCES:
patent: 4063122 (1977-12-01), Kullmann
patent: 4358937 (1982-11-01), Okamoto
patent: 4797588 (1989-01-01), Capion
patent: 5642987 (1997-07-01), Taricco
patent: 5770903 (1998-06-01), Bland et al.
patent: 5939808 (1999-08-01), Adames
patent: 5952748 (1999-09-01), Boldlehner
Leland John E.
Lin Lanchao
Ponnappan Rengasamy
Kundert Thomas L.
Lambert Richard A.
Scearce Bobby D.
Tamai Karl
The United States of America as represented by the Secretary of
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