Electromechanical actuator having an oil and water thermal system

A cooling system of an electromechanical actuator is provided. The cooling system includes a housing and a stator located within the housing and defining a central bore. A first body including a sleeve portion is configured to extend into the central bore of the stator, with the first body defining a first chamber including a first cavity within the sleeve portion and a second cavity fluidly connected to the first cavity. A heat sink is provided in thermal communication with the second cavity.

BACKGROUND OF THE INVENTION

The embodiments herein generally relate to electromechanical actuators and more particularly to thermal cooling systems for electromechanical actuators.

The demands to actuate the ailerons and flaps of an aircraft during the extreme conditions of take-off, flight, and landing require powerful actuators. Traditional actuators were hydraulic actuators. Hydraulic actuators are relatively large in terms of volume and weight. The high surface area and mass provided by the structure combined with the cooling effects of the hydraulic fluid flow of the relatively large hydraulic actuators allowed for sufficient heat absorption and dissipation to prevent overheating of the hydraulic actuators during operation.

However, the trend in modern aircraft is toward a thin-wing design which limits the amount of space and weight of actuators that can be installed in and on wings of the aircraft. Due to the limited volume permitted with the wings of thin-wing aircraft, actuators must have reduced sizes as compared to the former hydraulic versions, both to fit within the wings and to reduce weight. Accordingly, electromechanical actuators have been proposed as a means of providing actuation for thin-wing aircraft in a more compact configuration.

The electromechanical actuators of thin-wing aircraft are smaller but the small size results in a higher power density. The increased power density increasing the production of heat which must be removed from the stator of the electromechanical actuator to prevent overheating and reduced motor performance.

BRIEF DESCRIPTION OF THE INVENTION

According to one embodiment, a cooling system of an electromechanical actuator is provided. The cooling system includes a housing and a stator located within the housing and defining a central bore. A first body including a sleeve portion is configured to extend into the central bore of the stator, with the first body defining a first chamber including a first cavity within the sleeve portion and a second cavity fluidly connected to the first cavity. Further, a heat sink is provided in thermal communication with the second cavity.

According to another embodiment, a method of manufacturing a cooling system of an electromechanical actuator is provided. The method includes providing a housing of an actuator and installing a stator defining a central bore within the housing. Further, the method includes installing a first body including a sleeve portion into the housing, wherein the sleeve portion of the body extends into the central bore of the stator and wherein the first body defines a first chamber including a first cavity within the sleeve portion and a second cavity fluidly connected to the first cavity. The method further includes providing a heat sink in thermal communication with the second cavity.

Technical effects of embodiments of the invention include providing an improved electromechanical actuator that is small in volume and provides an efficient thermal cooling system to remove heat from a stator of the actuator thus enabling high power density actuators for use in thin-wing aircraft.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, a cross-sectional exemplary illustration of a thin wing100of an aircraft housing an actuator112in accordance with embodiments of the invention is shown. Wing100defines a leading edge102, which is to the right inFIG. 1, and a trailing edge104, which is to the left inFIG. 1. Located at the trailing edge of the wing100is an aileron106. Aileron106is rotationally or hingedly attached to the trailing edge104of wing100. Aileron106provides a flight control surface that can be controlled to assist in the flight of an aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement around the aircraft's longitudinal axis), which normally results in a change in flight path due to the actuation of the aileron106.

The aileron106is configured to be actuated or rotated upward in direction108and downward in direction110, as shown inFIG. 1. The actuation of aileron106is provided and controlled by the actuator112, which operationally connects the aileron106to the trailing edge104of wing100. Actuator112provides a hinged attachment between the aileron106and the wing100. Actuator112connects to the wing100by means of a housing arm114which connects to a wing spar of wing100, and connects to the aileron106by means of an output arm116that connects to an aileron spar of aileron106. Actuator112is configured to allow aileron106to rotate about an axis of rotation118.

The actuator112is an electromechanical actuator with an external rotor and an internal stator. Because the stator is configured internally (seeFIGS. 2A and 2B) heat cannot be easily dissipated, such as by passing a cool fluid (e.g., ambient air) over the actuator112. As the heat rises in the actuator112, the performance of the stator of the actuator112decreases. Accordingly, an efficient means of thermal energy dissipation must be provided to remove the heat from the internally located stator.

Turning now toFIGS. 2A and 2B, an electromechanical actuator motor200in accordance with an exemplary embodiment of the invention is shown.FIG. 2Ashows a cut-away isometric view of actuator200andFIG. 2Bshows a cross-sectional view of the actuator200along the line A-A inFIG. 2A.

Actuator200includes a front housing202and a rear housing204which are configured to enable actuator200to be mounted within and/or to a wing of an aircraft. Within the housing202,204is a servo motor, or more specifically a motor stator214. The stator214is provided to enable the actuator200to rotate and/or move an aileron (seeFIG. 1). InFIGS. 2A and 2B, the stator214provides the motive force to the rotor causing the rotational movement, or actuation, of an output arm216that is operatively connected to an aileron (not shown inFIGS. 2A and 2B). Located between the stator214and the output arm216are one or more bearings218, such as roller bearings, which further enable the rotational movement and actuation of the output arm216and thus the aileron connected thereto.

During operation of the actuator200, the stator214produces heat that must be dissipated or removed in order to prevent overheating and/or damage to the stator214. In order to prevent overheating of the stator214, fluids may be contained within the actuator200to enable heat dissipation and/or thermal energy transfer away from the stator214.

Accordingly, within the housing202,204are first and second bodies206,208configured as fluid vessels. In the exemplary embodiment shown inFIGS. 2A and 2B, the second body208is configured to act as the rotor with permanent magnets attached thereto. For example, each body/vessel may be defined as a shell or wall with an interior hollow volume or chamber for containing a fluid. The fluids stored or contained within the bodies may be one or more cooling mediums or fluids configured to absorb and remove thermal energy from the stator214, i.e., enable heat dissipation from the stator214. As an example, fluids, as used herein, may be air, water, oil, or other similar liquids and/or gases that absorb thermal energy. The first and second bodies206,208may be formed, at least in part, of thermally conductive materials such that thermal energy can between transferred between fluids contained in the fluid vessels. Examples of thermally conductive materials that may be used in various embodiments of the invention are steel, silver, copper, aluminum, and other similar thermally conductive materials and/or composites, and may include magnets attached thereto. However, those skilled in the art will appreciate that other materials may be used without departing from the scope of the invention.

The first body206includes a first portion205and a second portion207. The first portion205of the first body206defines a reduced diameter sleeve that passes through an interior portion or central bore of the stator214and includes a first subchamber220. The second portion207defines a larger diameter with a second subchamber222located therein, the second subchamber222fluidly connected to the first subchamber220. As shown, the second portion207has a conical shape, starting at a reduced diameter, and expanding to a larger diameter as the second portion extends away from the first portion205. The first and second cavities220,222of the first body206are fluidly connected and define a first chamber210that is configured to contain a first fluid.

The first fluid is in thermal contact with the stator214by means of the first portion205(the sleeve within the bore of the stator214). During operation of the stator214, the first fluid within the first subchamber220will be heated by the heat from stator214. The thermally conductive material of the first portion205of the first body206enables thermal transfer from the stator214to the first fluid in the first subchamber220. As the first fluid is heated it will move into the second subchamber222by means of convection, thermal expansion, or other process, and then cool down. Once cooled, the first fluid will return to the first subchamber220, and repeat the process, thus providing a cyclical cooling mechanism within actuator200.

To further enable the cooling process provided by the first fluid, the first body206includes a heat sink224at an end thereof, opposite the first portion205. The heat sink224may, in part, define an end cap226of the first body206and also form part of the front housing202. Heat sink224includes one or more nodes or fins228to provide additional surface area on the heat sink224, improving the efficiency thereof. Thus, when the first fluid contacts the heat sink224, the thermal energy contained in the first fluid may be transferred to the heat sink224and removed from the actuator200.

Additionally, as shown inFIGS. 2A and 2B, the end cap226houses or contains a condenser230that is thermally connected to the heat sink224. Condenser230may be any condenser known in the art, and may be one that is relatively small and light such that minimal weight is added to the actuator200. Condenser230enables the first fluid to more efficiently transfer thermal energy away from the stator214. For example, the first fluid, when located in the first subchamber220may be heated to a temperature that causes a phase-change of the fluid, such as from liquid to gas, i.e., the first fluid, in liquid form, is heated to a temperature above its boiling point.

The first fluid, in gas form, will expand and/or flow from the first subchamber220into the second subchamber222. When the first fluid contacts the condenser230, the gas will again change phase (from gas to liquid). The cooled liquid will then flow back into the first subchamber220to repeat the cycle. Moreover, in addition to removing thermal energy (heat) from the stator214through the process of fluid convection, the first fluid also consumes a portion of the thermal energy during the phase change from liquid to gas, thus further reducing the heat within actuator200.

The first portion205further includes structural components to increase the efficiency of thermal energy transfer from the stator214to the first fluid within the first subchamber220. For example, as shown inFIGS. 2A and 2B, baffling232may be included within the first portion205to increase the surface area that the first fluid contacts when in the first subchamber220. In alternative embodiments, the additional surface area may be provided by metallic sponges, metallic foams, phase change materials, and/or similar structures or materials or combinations thereof.

In some embodiments, the volume of the first fluid may be configured to not fill the entire first chamber210when in liquid form. This allows for the phase change of the first fluid, from liquid to gas, without compromising the physical structure of the actuator200as a result of the volume expansion during the phase change. Further, in some embodiments, a predetermined amount or volume of the first fluid may be provided in liquid form in the first chamber210. The predetermined liquid volume may be determined by the volume requirements for gas/liquid transitions and/or determined based on the need to have sufficient fluid to remove heat, even if the phase change does not occur. Thus, in some embodiments, a sufficient volume of liquid of the first fluid is stored within the first chamber210such that at least a portion of the first fluid, in liquid form, is present in the first subchamber220at all times.

For example, even if a phase change does not occur, the first fluid, in liquid form, may increase in temperature but not boil. The heated liquid will then flow toward the condenser230and the heat sink224to dissipate the thermal energy contained therein. When applied in the aircraft setting, high transient loads are present during extreme flight conditions, such as take-off and landing, and thus the thermal energy production by the stator214may be at its highest leading to boiling of the first fluid. However, during low transient loads, such as when cruising or on the ground, the first liquid may only warm but not reach temperatures at or above the boiling point. However, heat dissipation is still required to prevent overheating of the stator214. Thus, the predetermined volume or liquid ensures proper cooling for all operating conditions.

Turning now to the second body208, a second chamber212is defined therein and is configured to house a second fluid that is in thermal contact with the stator214. The second body208is larger than the first body206and is configured to contain both the stator214and at least a portion of the first body206within the second chamber212. The second chamber212is fluidly isolated from the first chamber210by one or more walls of the first body206such that the first and second fluids cannot intermix. Further, as shown, the bearings218are fluidly isolated from the second chamber212by a wall or portion of the second body208. However, those skilled in the art will appreciate that it is not required for the bearings218to be fluidly isolated from the second chamber212. In some embodiments, the second chamber212may be in fluid communication with the bearings218. In these embodiments, the second fluid may be a lubricating and/or working fluid for bearings218, such as oil.

The second fluid located within the second chamber212provides another means for heat dissipation. The second fluid surrounds the stator214and is in direct contact therewith. Accordingly, thermal energy will be absorbed by the second fluid directly and the second fluid flows toward the heat sink224to dissipate heat. As shown inFIGS. 2A and 2B, an exterior surface of the first body206may include fins234or other similar heat transfer surfaces that extend into the second chamber212. The fins234enable an improved thermal energy transfer from the second fluid, through the first body206, and into the first fluid. The thermal energy may then dissipate through the heat sink224and/or be consumed during phase transitions of the first fluid.

As noted, the exemplary actuator of the embodiments disclosed herein is configured for actuating an aileron of an aircraft. Due to the conditions of high altitude flight the actuator may not be used regularly or consistently when cruising at altitude. However, at cruising altitudes, the ambient temperature may be sufficient to freeze the fluid(s) within the actuator and lack of operative of the actuator may not provide sufficient heat to prevent freezing. Thus, in some embodiments, a heater (not shown) may be included internally or externally to the actuator to heat the fluids contained therein. Those of skill in the art will appreciate that heaters are known and any suitable heater or heating mechanism can be used without departing from the scope of the invention. Alternatively, the stator of the actuator may be dithered to maintain a temperature that is above the freezing point of the fluid(s). Further, in some embodiments, thermocouples and/or other temperature determining/monitoring mechanisms may be used to monitor and/or control the temperature of the fluid(s) within the actuator.

Advantageously, embodiments of the invention provide an efficient means to remove thermal energy produced by a stator of an electromechanical actuator during operation and thus prevent overheating. This is provided, in part, by the inclusion of a fluid chamber that extends through a central bore of the stator and allows for a fluid to absorb thermal energy and transfer it away from the stator. Additionally, thermal energy is removed from the stator through phase change of the fluid that is in the vessel that passes through the central bore of the stator. Furthermore, embodiments of the invention provide additional means of thermal cooling by inclusion of a second fluid that is provided in a second chamber of the actuator that is external to the first chamber, as described above.

Moreover, advantageously, embodiments of the invention enable an actuator with a high power density to be used under high transient loads because the thermal energy may be efficiently and effectively removed from the stator/motor of the actuator. Thus smaller and lighter actuators may be used on thin-wing aircraft. Moreover, advantageously, in accordance with some embodiments, different fluids may be used to cool a stator of an actuator, such that one fluid may be water and the other fluid may be an oil for lubricating bearings of the actuator.

Moreover, advantageously, high power density electric motors benefit from the cooling systems provided herein. The cooling systems provide heat dissipation mechanisms to the motor/stator and the bearings during transient thermal loads. This allows actuators to be sized according to peak characteristics such that a smaller motor could be used to complete the same job as a larger motor that was sized for continuous characteristics.

For example, although described herein as an actuator that is configured to actuate an aileron of an aircraft, the actuators described herein may be used for any actuation on a thin-wing aircraft. Moreover, actuators as described herein are not limited to aircraft, but may be used for any actuation, wherein an electromechanical actuator may be employed.

Moreover, although shown and described with the first and second cavities of first chamber as a single, compact unit in the first body, with the condenser proximate to the first subchamber, this is not a limiting example. For example, the condenser and/or heat sink could be located remote from the actuator and the first fluid may be conveyed to the condenser and/or heat sink through a fluid pipe or connector. This alternative embodiment may further reduce the size and weight of the actuator. Further, although shown with the inclusion of the condenser within the first body, the condenser is an optional feature, and those skilled in the art will appreciate that the thermal systems described herein may omit the condenser without departing from the scope of the invention.

Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.