Patent Description:
<CIT>), <CIT>), <CIT> (SHANGHAI JIWU TECH CO LTD) and <CIT>) describe examples of the related art.

The sideways rolling motion of a boat can create safety problems for passengers and crew on boats, as well as cause discomfort to passengers not accustomed to the rolling motion of the boat. A number of technologies currently exist to reduce the sideways rolling motion of a boat. One technology currently in use is active fin stabilization. Stabilizer fins are attached to the hull of the boat beneath the waterline and generate lift to reduce the roll of the boat due to wind or waves. In the case of active fin stabilization, the motion of the boat is sensed and the angle of the fin is controlled based on the motion of the boat to generate a force to counteract the roll. Fin stabilization is most commonly used on large boats and is effective when the boat is underway. Fin stabilization technology is not used frequently in smaller boats and is generally not effective when the boat is at rest. Stabilizer fins also add to the drag of the hull and are susceptible to damage.

Gyroscopic boat stabilization is another technology for roll suppression that is based on the gyroscopic effect. A control moment gyroscope (CMG) is mounted in the boat and generates a torque that can be used to counteract the rolling motion of the boat. The CMG includes a flywheel that spins at a high speed. A controller senses the attitude of the boat and uses the energy stored in the flywheel to "correct" the attitude of the boat by applying a torque to the hull counteracting the rolling motion of the boat. CMGs work not only when a boat is underway, but also when the boat is at rest. CMGs are also typically less expensive than stabilizer fins, do not add to the drag of the hull, and are not exposed to risk of damage from external sources.

Although CMGs are gaining in popularity, particularly for smaller fishing boats and yachts, this technology has some limitations. The energy used to counteract the rolling motion of the boat comes from the angular momentum of the rotation of the flywheel at a high rate of speed. Consequently, heat builds up in the bearings supporting the flywheel and bearing failure can result if the operational temperature of the bearings is exceeded. The flywheel is typically mounted inside an enclosure for safety reasons. In order to obtain the high spin rate, the flywheel is typically contained in a vacuum enclosure, which makes heat dissipation problematic.

Another problem with existing CMGs is that it takes a significant amount of time for the flywheel to "spin up", i.e., to obtain its desired operating speed. In some CMGs currently on the market, it can take as long as seventy minutes before the CMG is ready for use. The long "spin up" period means that the CMG cannot be used for trips of short duration, which comprises a majority of boating occasions. It also takes a long time for the flywheel to "spin down," typically in the order of several hours. While the flywheel is spinning down, it may continue to make a whining noise, which can be disruptive to the enjoyment of the occupants after the boat has arrived at its destination on the water or returned to the docks following a day of boating.

Thus, there remains a need for alternative approaches to gyroscopic boat stabilization, advantageously approaches that allow for better cooling of the bearings and/or motor, so that performance can be improved.

The present disclosure as claimed relates to a gyroscopic roll stabilizer for a boat. In an aspect, the gyroscopic roll stabilizer includes an enclosure mounted to a gimbal for rotation about a gimbal axis and configured to maintain a below-ambient pressure, and a flywheel assembly including a flywheel and flywheel shaft, with the flywheel assembly rotatably mounted inside the enclosure for rotation about a flywheel axis. The gyroscopic roll stabilizer also includes a motor operative to rotate the flywheel assembly and disposed inside the enclosure. A motor cooling circuit is configured to transfer heat away from the motor. The motor cooling circuit has a closed fluid pathway for recirculating cooling fluid therein. The fluid pathway includes a fluid channel jointly defined by the motor and the enclosure and having the cooling fluid therein. The gyroscopic roll stabilizer is configured to transfer heat away from the motor to the cooling fluid. The enclosure comprises an integrally formed boss for mounting the motor, and the inner face of the boss, facing the motor, comprises a groove. The groove defines at least a portion of the fluid channel.

Other aspects of the disclosure relate to methods of operating a gyroscopic roll stabilizer for a boat. The method includes maintaining a below ambient pressure within an enclosure surrounding a flywheel assembly, the flywheel assembly including a flywheel and a flywheel shaft; spinning the flywheel assembly about a flywheel axis via a motor mounted internal to the enclosure; dissipating heat from the motor by transferring the heat by conduction and convection to a cooling fluid flowing through a fluid channel jointly defined by the motor and the enclosure; cooling the cooling fluid by removing heat from the cooling fluid external to the portion of the enclosure maintained at the below-ambient pressure; and recirculating the cooling fluid through a closed fluid pathway that includes the fluid channel. The enclosure comprises an integrally formed boss for mounting the motor, and the inner face of the boss, facing the motor, comprises a groove. The groove defines at least a portion of the fluid channel wherein the dissipating comprises routing the cooling fluid through the groove.

The features, functions and advantages that have been discussed above, and/or are discussed below, can be achieved independently in various aspects or may be combined in yet other aspects, further details of which can be seen with reference to the following description and the drawings.

Referring now to the drawings, <FIG> illustrate a control moment gyroscope (CMG) <NUM> mounted in a boat <NUM> for roll stabilization. Multiple embodiments of the CMG <NUM> are described. For convenience, similar reference numbers are used in the following description of the embodiments to indicate similar elements in each of the embodiments.

Referring now to <FIG> and <FIG>, the main functional elements of the CMG <NUM> comprise a single-axis gimbal <NUM>, an enclosure <NUM> mounted to the gimbal <NUM> for rotation about a gimbal axis G, a flywheel assembly <NUM> mounted by bearings <NUM> inside the enclosure, a motor <NUM> to rotate the flywheel assembly <NUM>, and a torque control system <NUM> (<FIG>) to control precession of the flywheel assembly <NUM> so that the energy of the flywheel assembly <NUM> is transferred to the hull of the boat <NUM> to counteract rolling motions. Each of the embodiments further comprises a bearing cooling system <NUM> (<FIG>) to cool the flywheel bearings <NUM>. Various designs of the bearing cooling system <NUM> may be employed.

The gimbal <NUM> comprises a support frame <NUM> that is configured to be securely mounted in the boat <NUM>. Preferably, the gimbal <NUM> is mounted along a longitudinal axis L of the boat <NUM> with the gimbal axis G extending transverse to the longitudinal axis L. Conventionally, the gimbal <NUM> is mounted in the hull of the boat <NUM>, but could be mounted at any location. The support frame <NUM> of the gimbal <NUM> comprises a base <NUM> and two spaced-apart supports <NUM>. A bearing <NUM> is mounted on each support <NUM> for rotatably mounting the enclosure <NUM> to the supports <NUM>. For this purpose, the enclosure <NUM> includes two gimbal shafts <NUM> projecting from diametrically opposed sides of the enclosure <NUM>. The gimbal shafts <NUM> are rotatably journaled in the gimbal bearings <NUM> to allow the enclosure <NUM> and flywheel assembly <NUM> to rotate or precess about the gimbal axis G in the fore and aft directions.

The basic elements of enclosure <NUM> are the same in the various embodiments described herein but vary in some details depending on the design of the bearing cooling system <NUM>. The enclosure <NUM> is generally spherical in form and comprises two main housing sections <NUM> and two cover plates <NUM>. The two main housing sections <NUM> join along a plane that typically bisects the spherical enclosure <NUM>. The cover plates <NUM> join the main housing sections <NUM> along respective planes closer to the "poles" of the spherical enclosure <NUM>. All joints in the enclosure <NUM> are sealed to maintain a below-ambient pressure within the enclosure <NUM> to reduce aerodynamic drag on the flywheel assembly <NUM>. Typical below-ambient pressures should be in the range of <NUM>-<NUM> torr (<NUM>-<NUM> Pa, <NUM>-<NUM> psi). Although the construction of the enclosure <NUM> is generally the same in the embodiments herein described, the details of the housing sections <NUM> and cover plates <NUM> vary as described more fully below depending on the design of the bearing cooling system used.

Referring to <FIG>, the flywheel assembly <NUM> comprises a flywheel <NUM> and flywheel shaft <NUM> that is mounted for rotation inside the enclosure <NUM> of the gimbal <NUM> so that the axis of rotation F of the flywheel assembly <NUM> is perpendicular to the gimbal axis G. Thus, when the boat <NUM> is level such that gimbal axis G is horizontal, the axis of rotation F of the flywheel shaft <NUM> will be in the vertical direction, typically perpendicular to the deck of the boat. The flywheel <NUM> and shaft <NUM> may be formed as a unitary piece, or may comprise two separate components. In one exemplary embodiment, the diameter and the flywheel <NUM> is approximately <NUM> (<NUM> inches) and the flywheel assembly <NUM> has a total weight of about <NUM> (<NUM> lbs). The flywheel assembly <NUM> has a moment of inertia of about <NUM> m<NUM> (<NUM>,<NUM> Ibm in<NUM>). When rotated at a rate of <NUM> rpm, the angular momentum of the flywheel assembly <NUM> is about <NUM> m<NUM>/s (<NUM>,<NUM> Ibm ft<NUM>/s).

The flywheel assembly <NUM> is supported by upper and lower bearing assemblies inside the enclosure <NUM>. Each bearing assembly comprises a bearing <NUM> mounted within a bearing block <NUM>. Each bearing <NUM> comprises an inner race <NUM> that is affixed to and rotates with the flywheel shaft <NUM>, an outer race <NUM> that is mounted inside the bearing block <NUM>, and one or more ball bearings <NUM> disposed between the inner and outer races <NUM>, <NUM>. The bearing blocks <NUM> are secured to the interior of the enclosure <NUM>. Seals (not shown) are disposed on the top and bottom of the bearings <NUM> to contain lubricant in the bearings <NUM>.

The motor <NUM> rotates the flywheel assembly <NUM> at a high rate of speed (e.g., <NUM> rpm). The motor <NUM> includes a rotor <NUM> that connects to the flywheel shaft <NUM> and a stator <NUM> that this secured to the enclosure <NUM> by any suitable mounting system. Although the motor <NUM> is shown mounted inside the enclosure <NUM>, it is also possible to mount the motor <NUM> on the exterior of the enclosure <NUM>. In one embodiment, the motor <NUM> operates on <NUM> Volt single phase AC power (or could be three-phase AC power, or AC or DC battery power, such as from a lithium ion battery pack) and is able to accelerate a flywheel assembly with a moment of inertia of about <NUM> m<NUM> (<NUM>,<NUM> Ibm in2) from rest to a rotational speed of <NUM> rpm preferably in about <NUM> minutes or less for an average acceleration of about <NUM> rpm/s, and more preferably in about <NUM> minutes or less for an average acceleration of about <NUM> rpm/s, and even more preferably in about <NUM> minutes or less for an average acceleration of about <NUM> rpm/s (or <NUM> radians/s2).

The torque control system <NUM>, shown in <FIG>, controls the rate of precession of the flywheel assembly <NUM> about the gimbal axis G. The rolling motion of a boat <NUM> caused by wave action can be characterized by a roll angle and roll rate. The rolling motion causes the flywheel <NUM> to precess about the gimbal axis G. Sensors <NUM>, <NUM> measure the roll angle and roll rate respectively, which are fed to a controller <NUM>. The controller <NUM> generates control signals to control an active braking system or other torque applying device <NUM> that controls the rate of precession of the flywheel assembly <NUM>. By controlling the rate of precession, the flywheel assembly <NUM> generates a torque in opposition to the rolling motion. This torque is transferred through the gimbal <NUM> to the boat <NUM> to dampen the roll of the boat <NUM>. An example of the active braking system <NUM> is described in <CIT>, entitled "Braking System For Gyroscopic Boat Roll Stabilizer".

When the flywheel assembly <NUM> rotates at high speed, the bearings <NUM> and motor <NUM> will generate a substantial amount of heat, which could lead to bearing and/or motor failure. Conventional air and liquid cooling techniques are not suitable for bearings <NUM> or other heat generating components contained within a vacuum or significantly below ambient pressure environment. Various embodiments of the bearing cooling system <NUM> are disclosed herein allow cooling of bearings <NUM> and other heat generating components contained within the enclosure without direct contact of the recirculated oil or liquid coolant with the bearings <NUM> or other moving heat generating components, which would result in high frictional losses. In general, heat is transferred by solid and/or liquid conduction to a heat sink that is cooled by oil, glycol, or other liquid coolant. Oil or liquid cooling enables more heat to be dissipated compared to air cooling or gaseous convection and conduction. Reliance on gaseous convection and conduction in existing CMGs imposes limitations on the amount of heat that can be dissipated because the interior of the enclosure <NUM> is typically maintained at a below ambient pressure. The limited heat transfer capacity in conventional CMGs imposes limitations on the size of the electric motor that is used, which in turn limits the time to engage and use the conventional CMG. Because the electric motor in conventional CMGs is undersized to avoid heat generation, conventional CMGs require significant time to accelerate the flywheel assembly <NUM> to a speed that provides the desired counter-torque and roll stabilization. Providing more efficient cooling of the bearings <NUM> and/or motor <NUM> as herein described enables use of a larger and more powerful motor <NUM> and faster acceleration of the flywheel assembly <NUM> so that the benefits of using the CMG <NUM> can be obtained in significantly shorter time periods.

<FIG> is a schematic diagram of a cooling circuit <NUM> for circulating the liquid coolant. A fluid reservoir <NUM> contains the liquid coolant which is circulated in a "closed" circuit by a fluid pump <NUM>. The fluid reservoir <NUM> may include a heat exchanger <NUM> to cool the liquid coolant in the fluid reservoir <NUM>. After leaving the fluid reservoir <NUM>, the liquid coolant passes through the heat exchanger <NUM> where it adsorbs and carries away heat generated by the bearings <NUM>, as described more fully below. In some embodiments, heat is transferred from the flywheel shaft <NUM> to a heat sink and then by solid and liquid conduction to the heat exchanger <NUM>. In other embodiments, heat is transferred from the flywheel shaft <NUM> to the liquid coolant which is circulated through a cavity <NUM> in the flywheel shaft <NUM>. Accordingly, the heat transfer to the liquid coolant occurs within the cavity <NUM> of the flywheel shaft <NUM> so the heat exchanger <NUM> is not required. In some embodiments, a scavenging circuit <NUM> is provided to collect liquid coolant that may seep into the interior of the enclosure <NUM> and return the liquid coolant to the fluid reservoir <NUM>.

<FIG> illustrates one embodiment of a bearing cooling system <NUM> using a heat sink to dissipate heat generated by the bearings <NUM> and/or motor <NUM>. While the present discussion of the bearing cooling system <NUM> is generally in the context of cooling the upper bearing <NUM>, it should be noted that the upper and lower bearings <NUM> may be cooled in similar ways, if desired. For the upper bearing <NUM>, the upper portion of the flywheel shaft <NUM> is secured within bearing <NUM> that is, in turn, secured within the enclosure <NUM>. Each bearing <NUM> includes an outer race <NUM>, one or more ball bearings <NUM>, and an inner race <NUM> that engages the flywheel shaft <NUM> and rotates therewith. The flywheel shaft <NUM> includes a cavity <NUM> at each end thereof. The cavity <NUM> in each end of the flywheel shaft <NUM> is open at one end and includes a side wall and a bottom wall.

A heat transfer member <NUM> that functions as a heat sink is suspended in the cavity <NUM>. The heat transfer member <NUM> does not directly engage the side or bottom walls of the cavity <NUM>. Rather, the outer surface of the heat transfer member <NUM> is spaced from the side and bottom walls of the cavity <NUM>. In one embodiment, the spacing between the heat transfer member <NUM> and the walls of the cavity <NUM> is approximately <NUM>"-<NUM>". Various materials can be used for the heat transfer member <NUM> discussed herein. Preferably, copper, aluminum, or alloys thereof are used because of their relatively high thermal conductivity.

A heat transfer medium is contained in the gap between the heat transfer member <NUM> and the walls of the cavity <NUM>. As one example, the heat transfer medium comprises a low vapor pressure fluid that is suitable for the low pressure environment in the enclosure <NUM>. A low vapor pressure fluid is a liquid, such as oil, that has a relatively low boiling point compared to water and is suitable for employment in a vacuum environment. For example, aerospace lubricants, such as perfluoropolyether (PFPE) lubricants, designed for vacuum environments can be used as the heat exchange medium. The low vapor pressure fluid enables transfer of heat from the flywheel shaft <NUM> to the heat transfer member <NUM> by liquid conduction and liquid convection. A labyrinth seal <NUM> extends around the heat transfer member <NUM> and effectively seals the cavity <NUM> such that the heat transfer medium is maintained within the cavity <NUM>. The labyrinth seal <NUM> is preferably fixed to the heat transfer member <NUM>, which means that the flywheel shaft <NUM> rotates around the labyrinth seal <NUM>.

As seen in <FIG>, heat transfer member <NUM> projects from cavity <NUM>, through an opening in a cover plate <NUM> forming a part of the enclosure <NUM>, and into a heat exchanger <NUM>. Seals <NUM> located in corresponding grooves in the cover plate <NUM> maintain vacuum within the enclosure <NUM>. The heat exchanger <NUM> is mounted to the exterior surface of the cover plate <NUM>. The heat exchanger <NUM> comprises a housing <NUM> and a heat exchange plate <NUM> confined within the housing <NUM>. The heat transfer member <NUM> is secured by a fastener <NUM> to the heat exchange plate <NUM> so that the heat transfer member <NUM> is effectively suspended in the cavity <NUM> formed in the flywheel shaft <NUM>. More particularly, the heat exchange plate <NUM> includes a recess in the bottom surface thereof that receives the end of the heat transfer member <NUM>. The surface contact between the end of the heat transfer member <NUM> and the heat exchange plate <NUM> facilitates the efficient transfer of heat by solid conduction from the heat transfer member <NUM> to the heat exchange plate <NUM>.

A liquid coolant, such as a glycol coolant, is circulated through the heat exchanger <NUM> to absorb and carry heat away from the heat exchange plate <NUM> as shown in <FIG>. The upper surface of the heat exchange plate <NUM> can be provided with fluid channels and/or cooling fins to increase surface area of the heat exchange plate <NUM> and to facilitate heat transfer from the heat exchange plate <NUM> to the liquid coolant.

Heat is generated in the inner and outer races of the bearing assemblies <NUM> due to the high side loads generated from the CMG's torque as the enclosure <NUM> rotates about the gimbal axis G. The outer race <NUM> has a continuous heat conductive path through the enclosure <NUM> which permits the heat associated with the outer race <NUM> to be conveyed into the atmosphere. The inner race <NUM> requires a heat sink path through parts of the enclosure <NUM>. In this embodiment, heat from the inner race <NUM> of the bearing assembly <NUM> is transferred by solid conduction to the flywheel shaft <NUM>. The heat is then transferred by liquid conduction from the flywheel shaft <NUM> to the heat transfer member <NUM>, and by solid conduction through the heat transfer member <NUM> to the heat exchange plate <NUM> that continuously conveys the heat into surrounding liquid coolant. In some embodiments, the heat exchanger <NUM> could employ air or gas cooling rather than liquid cooling.

Alternative approaches to bearing cooling systems <NUM> for cooling the bearing assemblies <NUM> may be employed, including the use of heat transfer members <NUM> that are internally cooled via circulation of cooling fluid internally through the heat transfer member <NUM>. The various bearing cooling systems <NUM> may be used alone, or in combination with the motor cooling systems (e.g., motor cooling circuit <NUM>) described herein. Just by way of example, the CMG <NUM> may include the motor cooling system(s) of <FIG>, and the bearing cooling system(s) described above, or just the bearing cooling system(s) described above, or just the motor cooling system(s) of <FIG>.

<FIG> show a motor cooling system for cooling the motor <NUM> when the motor <NUM> is mounted inside the enclosure <NUM>. In general, the motor cooling system includes a motor cooling circuit <NUM> that includes a closed fluid pathway <NUM>. The fluid pathway <NUM> extends through a fluid channel <NUM> disposed in close proximity to the motor <NUM>. Cooling fluid <NUM> flows through the fluid pathway <NUM> (including through the fluid channel <NUM>), and absorbs heat from the motor <NUM> and transfers that heat away from the motor <NUM>.

As shown in <FIG>, the enclosure <NUM> includes a boss <NUM> that is integrally formed with enclosure <NUM>, and is configured to receive the motor <NUM> for mounting the motor <NUM> in the enclosure <NUM>. The boss <NUM> extends inwardly into the interior of the enclosure <NUM>, and toward the flywheel <NUM>, generally parallel to the flywheel axis F. The boss <NUM> includes a chamber <NUM> generally aligned with the flywheel axis F, and advantageously peripherally surrounds the flywheel axis F. The chamber <NUM> is sized and shaped to receive the motor <NUM>. The chamber <NUM> is bounded by an inner face <NUM> on the boss <NUM> which faces the motor <NUM>. The stator <NUM> of the motor <NUM> advantageously abuts the inner face <NUM> or is at least very closely spaced therefrom. A plurality of seals <NUM> are advantageously abutting the stator <NUM> and the inner face <NUM>, so that a fluid-tight seal is maintained. One or more retention plates <NUM> may be used to secure the motor in the boss <NUM>.

The motor cooling circuit <NUM> is schematically shown in <FIG>. The motor cooling circuit <NUM> includes the fluid pathway <NUM>, which in turn includes the fluid channel <NUM>. The fluid channel <NUM> is jointly defined by the motor <NUM> and the enclosure <NUM>, meaning for a given section of the fluid channel <NUM>, the motor <NUM> forms a part of the channel wall for that section, and the enclosure <NUM> forms another part of the channel wall of that section that overlaps (along the path of the channel) with the part of the channel wall formed by the motor <NUM>. In <FIG>, the fluid channel <NUM> is formed at the interface between the stator <NUM> and the inner face <NUM> of boss <NUM> of enclosure <NUM>. The inner face <NUM> includes one or more grooves <NUM>. See <FIG>, <FIG>. Such groove(s) <NUM> are conceptually closed off, to form the fluid channel <NUM>, by the outer face of stator <NUM>. Note that seals <NUM> may be used to trap any cooling fluid <NUM> that escapes fluid channel <NUM>. Alternatively and/or additionally, the stator <NUM> may include one or more grooves <NUM> (not shown) on its outer face that face the inner face <NUM> of the boss <NUM>. Such stator groove(s) <NUM> are conceptually closed off, to form the fluid channel <NUM>, by the inner face <NUM> of the boss <NUM>. Note that the groove(s) <NUM> may be oriented perpendicular to the flywheel axis F, or may advantageously spiral around the flywheel axis F, such as by being helical or other spiral shape. Alternatively, the groove(s) may wind around the interface of the boss <NUM> and the stator <NUM> in any suitable fashion, such as in a sinusoidal shape, or a zig-zag shape, whether regular or irregular. Advantageously, the fluid pathway <NUM> peripherally surrounds the flywheel axis F, such as by circumnavigating motor. The flow direction in the fluid pathway <NUM> may be in any suitable direction, such as clockwise or counter-clockwise, or both as appropriate. When the fluid channel <NUM> is spiral (e.g., helical), the cooling fluid advantageously flows through the fluid channel <NUM> spirally (e.g., helically) either outward away from the flywheel <NUM>, or inward toward flywheel <NUM>.

As shown in <FIG>, the motor cooling circuit <NUM> optionally also includes a reservoir <NUM> for the cooling fluid <NUM> flowing through the motor cooling circuit <NUM>, and a fluid pump <NUM> operative to recirculate the cooling fluid <NUM> through motor cooling circuit <NUM>. Thus, the fluid pathway <NUM> for the cooling fluid <NUM> optionally extends through the fluid reservoir <NUM>, the fluid channel <NUM>, and the fluid pump <NUM>. Thus, the pump <NUM> is operatively connected to the fluid channel <NUM> and configured to recirculate the cooling fluid <NUM> through the fluid channel <NUM> to remove heat from the motor <NUM>. The presence of the motor cooling circuit <NUM> in the gyroscopic roll stabilizer <NUM> allows the gyroscopic roll stabilizer <NUM> to be configured to transfer heat away from the motor <NUM> to the cooling fluid <NUM>. Note that a heat exchanger, such as heat exchanger <NUM>, is operatively connected to closed fluid pathway <NUM> and configured to remove heat from the cooling fluid <NUM> to ambient after the cooling fluid <NUM> has passed through the fluid channel <NUM>.

In some respects, the fluid pathway <NUM> also includes an inlet port <NUM> and an outlet port <NUM>, such as on the enclosure <NUM>. The inlet port <NUM> is operatively disposed between the pump <NUM> and the fluid channel <NUM>, and operative to allow passage of the cooling fluid <NUM> into the enclosure <NUM> toward the fluid channel <NUM>. The outlet port <NUM> is operatively disposed between the fluid channel <NUM> and the heat exchanger <NUM>, and operative to allow passage of the cooling fluid <NUM> out of the enclosure <NUM> toward the heat exchanger <NUM>.

For the <FIG> arrangement, the heat flow for dissipating heat from the motor <NUM> is from the stator <NUM> to the cooling fluid <NUM> in the fluid channel <NUM>, then to external to the CMG <NUM> via the heat exchanger <NUM>. Note that the heat is transferred by conduction and convection to the cooling fluid <NUM>.

In an alternative design shown in <FIG> (not according to the invention, present for illustration purposes only), the fluid channel <NUM> is not jointly defined by the motor <NUM> and the enclosure <NUM>, but is instead formed in a separate element that is disposed between the stator <NUM> and the enclosure <NUM>. For example, a separate cooling ring <NUM> may surround (e.g., be disposed immediately outside of) the stator <NUM>, between the stator <NUM> and the enclosure <NUM> in a lateral direction as shown in <FIG>. The cooling ring <NUM> should be fluid-tight, and may have one or more internal passages that define the fluid channel <NUM>. There may be one or more fins <NUM> internal to the cooling ring <NUM> that form the internal passages. The internal passages may be substantially circular, or may advantageously spiral around the flywheel axis F, such as by following a helical path. The fluid channel <NUM> may be connected, via suitable connections and seals, with the inlet port <NUM> and outlet port <NUM>. Cooling fluid <NUM> may circulate through the fluid channel <NUM> in the cooling ring <NUM> to extract heat from the motor <NUM> and move that heat away from the motor <NUM>. Care should be taken to properly secure the cooling ring <NUM> inside the enclosure <NUM>, such as by suitable screws, to avoid possible damage to the rapidly spinning flywheel <NUM>. Because use of such a cooling ring <NUM> results in the cooling fluid <NUM> being separated from the stator <NUM> by the wall of the cooling ring <NUM>, this approach is believed to be functional, but less efficient than other approaches disclosed herein.

In some aspects, the CMG <NUM> includes both the bearing cooling system <NUM> and the motor cooling system (e.g., motor cooling circuit <NUM>) described herein, and the two systems may optionally use a common reservoir <NUM>, pump <NUM>, and heat exchanger <NUM> so as to share the cooling fluid <NUM>.

A method (<NUM>) of operating a gyroscopic roll stabilizer <NUM> that includes a motor cooling circuit <NUM> as discussed above is shown in <FIG>. The method (<NUM>) includes maintaining (<NUM>) a below ambient pressure within an enclosure <NUM> surrounding a flywheel assembly <NUM>, with the flywheel assembly <NUM> including a flywheel <NUM> and a flywheel shaft <NUM>. The method also includes spinning (<NUM>) the flywheel assembly <NUM> about the flywheel axis F via motor <NUM> mounted internal to the enclosure <NUM>. In addition, the method includes dissipating (<NUM>) heat from the motor <NUM> by transferring the heat by conduction and convection to a cooling fluid <NUM> flowing through a fluid channel <NUM> jointly defined by the motor <NUM> and the enclosure <NUM>. During the dissipating, the cooling fluid <NUM> optionally flows through the fluid channel <NUM> helically in an outward direction away from the flywheel <NUM>. Further, the method includes cooling (<NUM>) the cooling fluid <NUM> by removing heat from the cooling fluid <NUM> external to the portion of the enclosure <NUM> maintained at the below-ambient pressure. In addition, the method includes recirculating (<NUM>) the cooling fluid <NUM> through closed fluid pathway <NUM> that includes the fluid channel <NUM>. Note that the recirculating (<NUM>) optionally includes routing (<NUM>) the cooling fluid <NUM> from the fluid channel <NUM> to reservoir <NUM>, and pumping (<NUM>) the cooling fluid <NUM> from the reservoir <NUM> to the fluid channel <NUM>, and the cooling (<NUM>) the cooling fluid <NUM> comprises cooling the cooling fluid <NUM> via a heat exchanger <NUM> disposed external to the enclosure <NUM>. Note that the various steps of method may be carried out in any suitable order, including in whole or in part in parallel. For example, at least the maintaining (<NUM>), the spinning (<NUM>), and the dissipating (<NUM>) are advantageously carried out simultaneously.

The bearing cooling systems <NUM> and/or motor cooling systems as herein described allow much greater heat dissipation compared to current technology, which enables use of a larger motor <NUM>, and advantageously lower operating temperature even with the larger motor <NUM>. The larger motor and lower operating temperature enable rapid spin up and spin down of the flywheel assembly <NUM>, and a significantly lower time to engage as discussed further below.

In use, the gimbal <NUM> is normally locked during spin up, i.e., while the flywheel assembly <NUM> is being accelerated, to prevent precession of the flywheel <NUM> until a predetermined rotational speed is achieved. The CMG <NUM> can be locked to prevent rotation of the enclosure <NUM> by the active braking system <NUM>. When the CMG <NUM> is unlocked, precession of the flywheel <NUM> will place side loads on the bearings <NUM>. The bearing friction from the side loading of the bearings <NUM> generates heat. In addition, the bearing friction from the side loading also adds drag, which must be overcome by the motor <NUM> in order to continue acceleration of the flywheel's rotation. Thus, the frictional losses of side loading the bearings <NUM> have two impacts: generating heat and increasing the load on the motor <NUM>.

Conceptually, there are two main sources of heat in the CMG: heat generated by the motor inside the enclosure <NUM> and heat generated by bearing friction. A large percentage of the heat budget is needed to dissipate heat from the bearings in order to prevent bearing failure. The remaining portion of the heat budget, after accounting for bearing cooling, determines the size of the motor that can be used inside the enclosure.

One conventional approach to bearing cooling for a CMG maintained in a vacuum environment uses interwoven fins and relies primarily on gaseous conduction between the interwoven fins to dissipate the heat. See, e.g., <CIT> and <CIT>. The reliance on gaseous conduction as the primary mode of heat transfer severely limits the amount of heat that can be dissipated since gaseous conduction is less efficient than liquid or solid conduction. The heat transfer capacity of the interwoven fins is also limited by the surface area of the interwoven fins. Less surface area means less heat transfer capacity. As the enclosure of CMGs shrink in size, there is less space available for the interwoven fins. These factors place severe limits on the heat budget for conventional CMGs, which in turn limits motor size. Thus, conventional CMGs using interwoven fins for heat dissipation are limited in the size of their motor. The limitation on the motor size results in a poor acceleration profile for the flywheel in conventional CMGs, which in turn means a long waiting period before the conventional CMG can be used. Further, if the gimbal <NUM> in a conventional CMG is unlocked too early, the frictional losses will prevent the smaller motors used therein from accelerating the flywheel assembly <NUM>, or will greatly diminish the acceleration of the flywheel assembly <NUM> resulting in a much longer spin up period. In conventional CMGs, the gimbal <NUM> is typically locked until the flywheel assembly <NUM> reaches <NUM>-<NUM>% or more of the nominal operating rotational speed. Conventional CMGs currently on the market may take thirty minutes or longer to reach the minimum operating speed at which the flywheel can be allowed to precess. However, many boat trips, particularity on smaller boats, are thirty minutes or less. This means the waiting period before the time to engage (unlock the flywheel assembly for precessing) is reached is longer than many boat trips for conventional CMGs.

Further, the size of the motor in conventional CMGs places a floor on the minimum operating speed at which the conventional CMG can be engaged (i.e., unlocked). The bearing friction from the side loading of the bearings when the conventional is engaged dramatically decreases the already slow acceleration rate of conventional CMGs. In some cases, the frictional load may be too much for the motor to overcome so that the further acceleration of the flywheel assembly becomes impossible and the normal operating speed cannot be reached.

Another consideration is that the power to the motor is at its maximum when the flywheel is being accelerated, and is reduced when the flywheel reaches its normal operating speed. Thus, more heat is generated by the motor when it is accelerating. The additional heat generated by the motor also limits the time to engage because the additional heat from the motor may exceed the design limits of the bearing cooling system in conventional CMGs.

The bearing cooling systems <NUM> and/or motor cooling circuits <NUM> as described herein enable more efficient heat transfer, which enables a far greater heat transfer capacity and an increased heat budget. The increased heat budget means that larger and more powerful motors <NUM> that generate more heat can be used without causing bearing failure. With a larger and more powerful motor <NUM>, the improved CMG <NUM> of the present disclosure is able to achieve greater acceleration of the flywheel assembly <NUM> and lower time to engage than a conventional CMG. In addition to the higher rates of acceleration, which naturally lead to lower times to engage assuming the same minimum operating speed, a larger motor <NUM> enables the flywheel assembly <NUM> to be engaged at a lower operating speed (e.g., a lower percentage of nominal operating speed), which further reduces the time to engage, because the larger motor <NUM> is able to overcome the additional friction from the loading of the bearings <NUM>. In some embodiments, the motor <NUM> is configured to enable the CMG <NUM> to be unlocked in under twenty minutes, and preferably in under ten minutes and more preferably in under five minutes. By combining higher acceleration with lower operating speeds at the time of engagement, a time to engage can be reduced to a few minutes. For example, a motor <NUM> rated at <NUM>,<NUM> to <NUM>,<NUM> watts could potentially achieve a time to engage rates in the order of a few minutes.

As one example, the flywheel assembly <NUM> described above with a moment of inertia equal to about <NUM> m<NUM> (<NUM>,<NUM> Ibm in2) can be accelerated from rest to <NUM> rpm in about <NUM> minutes or less, which equates to an average acceleration of about <NUM> rpm/s or more, and preferably in about <NUM> minutes or less, which equates to an average acceleration of about <NUM> rpm/s or more, and even more preferably in about <NUM> minutes or less, which equates to an average acceleration of about <NUM> rpm/s or more. Additionally, the time to engage for the CMG <NUM> as herein described is much shorter because the motor <NUM> is powerful enough to overcome the frictional losses when the gimbal <NUM> is unlocked. For example, in a flywheel assembly <NUM> with a moment of inertia equal to about <NUM> m<NUM> (<NUM>,<NUM> Ibm in2), the time to engage (assuming <NUM>% of operating speed) is less than about <NUM> minutes, and more preferably less than about <NUM> minutes, and even more preferably less than <NUM> minutes. The rapid spin up and shorter time to engage enables beneficial use of the CMG <NUM> even for short trip times, which makes up a majority of boating trips. Thus, the rapid spin-up enables the CMG <NUM> to be used on a greater number of boating occasions.

Similarly, the spin down is in the order of minutes rather than hours compared to the current technology. Cooling systems with interleaved fins that rely on gaseous conduction and convection operate at a high temperature (e.g., <NUM> °F) and dissipate heat relatively slowly. In such systems, if the flywheel is stopped too fast, the heat may cause components to warp, which in turn may cause bearing life to be shortened. The bearing cooling systems <NUM> and/or motor cooling circuits <NUM> as herein described enables the CMG <NUM> to operate at a lower temperature (e.g., <NUM> °F) and be more efficient at removing heat. Consequently, the spin down time is cut from <NUM>-<NUM> hours to a few minutes (such as five to twenty minutes). This reduced running temperature as well as the rapid cooldown period prevents the well balanced rotating components from warping and thus the spin down time can be reduced. The short spin down time also eliminates the annoying hum and vibration from the spinning flywheel sooner and allows enjoyment of the peace and serenity after returning from a day of boating to begin sooner.

Claim 1:
A gyroscopic roll stabilizer (<NUM>) for a boat (<NUM>), the gyroscopic stabilizer (<NUM>) comprising:
an enclosure (<NUM>) mounted to a gimbal (<NUM>) for rotation about a gimbal axis (G) and configured to maintain a below-ambient pressure;
a flywheel assembly (<NUM>) including a flywheel (<NUM>) and flywheel shaft (<NUM>); the flywheel assembly (<NUM>) rotatably mounted inside the enclosure (<NUM>) for rotation about a flywheel axis (F);
a motor (<NUM>) operative to rotate the flywheel assembly (<NUM>) and disposed inside the enclosure (<NUM>);
a motor cooling circuit (<NUM>) configured to transfer heat away from the motor (<NUM>); the motor cooling circuit (<NUM>) having a closed fluid pathway (<NUM>) for recirculating cooling fluid (<NUM>) therein;
characterized in that:
the fluid pathway (<NUM>) includes a fluid channel (<NUM>) jointly defined by the motor (<NUM>) and the enclosure (<NUM>) and having the cooling fluid (<NUM>) therein;
wherein the gyroscopic roll stabilizer (<NUM>) is configured to transfer heat away from the motor (<NUM>) to the cooling fluid (<NUM>);
wherein the enclosure (<NUM>) comprises an integrally formed boss (<NUM>) for mounting the motor (<NUM>);
wherein an inner face of the boss (<NUM>), facing the motor (<NUM>), comprises a groove (<NUM>); and
wherein the groove (<NUM>) defines at least a portion of the fluid channel (<NUM>).