CN113315313A

CN113315313A - A circulative cooling system that is used for outer rotor brushless motor of unmanned ship

Info

Publication number: CN113315313A
Application number: CN202110142743.2A
Authority: CN
Inventors: 和浩楠; 高雷; 陈岳夫; 贾杰
Original assignee: Shanghai Rainbowfish Ocean Technology Co ltd
Current assignee: Shanghai Rainbowfish Ocean Technology Co ltd
Priority date: 2021-02-02
Filing date: 2021-02-02
Publication date: 2021-08-27

Abstract

The application relates to a circulating cooling system of an outer rotor brushless motor for an unmanned ship. In order to improve the heat radiation performance of an outer rotor brushless motor installed on an unmanned ship, a circulation heat radiation system is provided, which includes: a hydronic cooling system for an outer rotor brushless motor for an unmanned boat, comprising: an inner drive shaft for delivering heat-carrying coolant to the distal end for cooling; an outer drive shaft coupled to the inner drive shaft for receiving the cooled coolant from the inner drive shaft; a storage chamber communicating with the inner drive shaft and the outer drive shaft for containing a coolant; and a motor rotation mechanism for powering the above components, wherein the motor rotation mechanism includes an outer rotor and an inner stator. The application also provides a corresponding circulating cooling method.

Description

A circulative cooling system that is used for outer rotor brushless motor of unmanned ship

Technical Field

The application relates to the field of circulating cooling of unmanned ship power devices, in particular to a circulating cooling system of an unmanned ship outer rotor brushless motor.

Background

An electric motor (motor for short) is a device that converts electrical energy into mechanical energy. The electromagnetic power generating device generates a rotating magnetic field by utilizing an electrified coil (namely a stator winding) and acts on a rotor (such as a squirrel-cage closed aluminum frame), so as to form a magnetoelectric power rotating torque. The motor may be divided into a dc motor and an ac motor according to the power source used. The electric motors in the power system are mostly ac motors, which may be synchronous motors or asynchronous motors.

Due to various losses, the temperature of the motor body can rise continuously during use, and if the motor body cannot be cooled well, the service life of the motor can be seriously affected. The high-voltage motor generally has a large power, and the absolute value of the power loss is also large. In order to be able to use the motor normally and prolong the service life of the motor, it is important to cool the motor in time.

For a closed motor (i.e., the motor and compressor are mounted in the same housing), the flow of air in the enclosure is relatively similar to an open motor (i.e., the enclosure is not fully enclosed, heat dissipation holes are left in the body, front and rear end caps, no heat dissipation fan is provided, and self-cooling is achieved). The biggest difference between the cooling methods of the closed motor and the open motor is that the heat exchange between the hot air in the casing and the external cold medium is required when the closed motor is cooled. The cooling medium most commonly used in the art is typically air, followed by water.

When air is used as the cooling medium, an external fan coaxial with the motor is generally used to generate wind pressure to drive the outside air; when water is used as the cooling medium, a dedicated water pump is required to drive the circulating refrigerant water to circulate in the cooling water tank so as to cool the hot air inside the cabinet. However, when the cooling device is used, an external circulating cooling system is additionally required. This may not be a limiting factor for systems where space is not a limitation, but for more space-constrained installations such as ships, boats, etc., such external hydronic systems are generally at a disadvantage in space installations. Because it occupies too much space and the cooling effect is also poor, the predetermined cooling effect is often not achieved. Particularly, in the case of an apparatus having a small closed space such as an unmanned ship, in which an internal motor is used, the cooling effect is further deteriorated.

For open-drive motors, ambient air is typically directed into the motor interior for cooling, and the cool air carries the motor heat directly away and out into the surrounding environment. There are two main routes of air travel within the motor.

The first is axial, with cool air entering at one end of the motor and exiting at the other end. Because only one end of the iron core is required to be provided with the fan, the fan with a larger diameter can be arranged, the cooling effect is better, and the iron core structure is more compact. However, this cooling method has disadvantages of large ventilation loss and uneven temperature distribution in the axial direction of the motor, and is generally used for motors having a small capacity.

The second is radial, which requires many heat-conducting fins to be installed to increase the heat-dissipating area. Then cold air enters from both ends and is exhausted from the radial ventilation channels of the iron core. The disadvantage of this cooling method is that only fans with an outer diameter smaller than the diameter of the rotor can be installed because fans are installed at both ends.

The motors can be divided into dc motors and ac motors according to the types of their operating power sources, wherein the dc motors can be divided into two types, namely brushless dc motors (brushless motors for short) and brushed dc motors according to the structure and operating principle.

The brushless motor is one of the most common power devices of the unmanned surface vehicle. The brushless motor is generally classified into an outer rotor brushless motor and an inner rotor brushless motor. As the name implies, an inner rotor brushless motor refers to a motor in which the working rotating part is designed on the inside and the static part is designed on the outside. It is further understood that the outer rotor brushless motor refers to a motor in which the rotating part is designed on the outside and the static part is designed on the inside.

Brushless motors release a significant amount of heat during operation due to the current passing through the motor coils, which have electrical resistance. If this heat cannot be released in a timely manner, the brushless motor may be damaged by overheating. At present, a 'motor water cooling shell' is generally adopted for cooling on an unmanned surface vehicle. The principle is that under the suction effect, the water around the unmanned boat is sucked from the outside of the boat and is guided into the water cooling shell, and the heat generated by the motor is continuously taken away by taking water as a medium, so that the motor is cooled.

However, the above method has various problems in practical use. The most common problems are: foreign matters doped in the external water body, such as but not limited to, water plants, nylon ropes and other filamentous garbage, even plastic cloth and the like, easily block the water inlet, so that the water cooling effect of the 'motor water cooling shell' is ineffective. The unmanned ship is relatively small in size, the water inlet is correspondingly very small, and the water inlet is easily blocked due to the fact that the motor is cooled by water cooling, so that the water cooling is ineffective.

For example, chinese utility model patent No. CN2634717Y discloses a heat dissipation system for an electric motor. The motor mainly comprises a hollow conducting bar on a motor rotor and a heat dissipation cavity communicated with the conducting bar. The electric heat generated on the rotor is transferred to the heat dissipation cavity to dissipate heat by utilizing a fluid convection method, so that the temperature of the motor is controlled in a lower range, and the purposes of improving the running performance of the motor and improving the conversion efficiency of the motor are achieved. The system transmits heat into the heat dissipation cavity for heat dissipation, but the heat dissipation cavity is still inside the motor, so that the heat dissipation efficiency is slightly low. In addition, the external rotor motor has no use value, and has certain limitation on the use range.

For example, chinese utility model patent with publication number CN103219833B discloses a motor heat dissipation structure, including: motor housing, heat dissipation tooth, heat pipe and supplementary heat dissipation mechanism, the first end of heat pipe is installed motor housing's surface, the second end of heat pipe extends to motor housing's afterbody, the supplementary heat dissipation mechanism of second end installation of heat pipe, it is a plurality of the heat dissipation tooth cladding is in motor housing's surface. This heat radiation structure has utilized cooling tube, heat dissipation tooth to dispel the heat to the motor, nevertheless heat dissipation tooth and cooling tube still install inside the motor, and this has very big influence to heat radiation structure's the radiating efficiency. In practical use, the heat dissipation efficiency is still low.

Therefore, until today, no cooling means other than the "motor water-cooled shell" exists for unmanned boats having a small volume. The method can avoid the problem that sundries in water block the cooling water inlet and can realize good cooling effect.

Therefore, there is a great need in the art for a hydronic cooling system for an outer rotor brushless motor for an unmanned boat.

Disclosure of Invention

The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

According to a first aspect of the present application, there is provided a circulative cooling system of an outer rotor brushless motor for an unmanned boat, comprising:

an inner drive shaft for delivering heat-carrying coolant to the distal end for cooling;

an outer drive shaft coupled to the inner drive shaft for receiving the cooled coolant from the inner drive shaft; a storage chamber communicating with the inner drive shaft and the outer drive shaft for containing a coolant; and

and the motor rotating mechanism is used for providing power for the components, and comprises an outer rotor and an inner stator.

According to a preferred embodiment of the present application, the outer drive shaft has a reverse internal thread and the inner drive shaft has a forward internal thread, whereby the two are nested one inside the other and have a uniform wall thickness in the circumferential direction.

According to a preferred embodiment of the present application, the outer drive shaft and the inner drive shaft are integral with the outer rotor.

According to a preferred embodiment of the present application, the distal ends of the inner and outer drive shafts are submerged in the cooling medium.

According to a preferred embodiment of the present application, the inner drive shaft communicates with the storage chamber through an opening.

According to a preferred embodiment of the application, the communication of the inner drive shaft with the storage chamber is achieved by axially perforating the wall thereof.

According to a preferred embodiment of the application, the cooled cooling liquid flows back to the storage chamber via a groove on the inner wall of the outer drive shaft.

According to a second aspect of the present application, there is provided a method for cooling an unmanned surface vehicle outer rotor brushless motor using the above-mentioned circulation cooling system according to the present application, comprising the steps of:

s1: the heat-carrying coolant stored in the storage chamber is pumped out via the inner drive shaft;

s2: cooling the heat-carrying coolant to a distal end via an internal drive shaft;

s3: the cooled cooling liquid flows back to the storage cavity from an external driving shaft;

s4: the cooled coolant cools the brushless motor.

The circulating heat radiation system of the invention drives the heat generated by the motor to be gradually conducted to the outside by the circulating flow of the cooling liquid in the device. When the rotor rotates, the forward thread on the inner shaft drives the cooling liquid to flow from the bottom to the upper part, the heat generated under the working state of the motor is transmitted to the outside to be dissipated, and compared with a heat dissipation device arranged on the outside, the heat dissipation efficiency of the device is greatly improved, and any outside device is not needed to be matched. The rotor is adopted to drive the shaft to rotate, so that the threads rotate to drive the cooling liquid to flow, and the integrated structure ensures that the rotation of the shaft and the rotor has consistency, and increases the efficiency of the whole work. The cooling liquid is transferred to the part extending out of the outer side of the shaft, and the shaft at the outer side is in contact with cold water, so that a certain temperature difference exists, and the brought heat is dissipated.

To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed and the present description is intended to include all such aspects and their equivalents.

Drawings

So that the manner in which the above recited features of the present application can be understood in detail, a more particular description of the disclosure briefly summarized above may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this application and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects.

In the drawings:

fig. 1 shows a schematic overall structural diagram of a hydronic cooling system 100 for an unmanned boat outer rotor brushless motor, according to an embodiment of the present application;

FIG. 2 is a schematic diagram illustrating the flow direction of the cooling fluid in the operation state of the hydronic cooling system 100 according to an embodiment of the present application, wherein the components of the hydronic cooling system are specifically shown;

FIG. 3 illustrates an enlarged view of the structure at the slot of the inner drive shaft 102 according to an embodiment of the present application;

FIG. 4 illustrates a schematic structural diagram of a composite driveshaft according to an embodiment of the present application;

FIG. 5 shows a flow diagram of a method of cycle cooling according to an embodiment of the present application; and

fig. 6 shows a graph of a temperature test of the circulation cooling system 100 in an operating state according to an embodiment of the present application.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the following detailed description of the present application is provided in connection with exemplary embodiments and with reference to the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the described exemplary embodiments. It will be apparent, however, to one skilled in the art that the described embodiments may be practiced without at least some of these specific details. In some exemplary embodiments, descriptions of well-known structures, method steps, technical means, and the like, are simplified or omitted so as to not obscure the novel and inventive aspects of the present inventive concept.

It is to be noted, that while exemplary embodiments of the present application are illustrated in the accompanying drawings, those skilled in the art will appreciate that the embodiments can be implemented in various forms and modifications equivalent to the described exemplary embodiments, and not necessarily limited to the described exemplary embodiments. In other words, these exemplary embodiments are provided only to enable those skilled in the art to better understand the application concepts and to correspondingly fully convey the scope of the application to those skilled in the art and the public.

It is also to be noted that, unless otherwise specified, technical or scientific terms used herein shall have the meaning and meaning commonly understood by those skilled in the art. In the context of the present application, when technical or scientific terms used deviate from the meaning and meaning commonly understood in the foregoing, the present application controls.

It will be further appreciated that, throughout the present application, when directional words such as "upper," "lower," "left," "right," "front," and "rear" are referred to, they are intended to describe the arrangement and orientation of the associated components relative to one another in the corresponding figures, and are not intended to constitute limitations on the arrangement and orientation of the associated components.

Referring to fig. 1, there is shown a schematic diagram of an overall configuration of a hydronic cooling system 100 for an unmanned marine outer rotor brushless motor according to an embodiment of the present application. As shown in fig. 1, the hydronic cooling system 100 is largely divided into an inner stator structural part and an outer rotor structural part.

Fig. 2 is a schematic diagram illustrating the incoming flow direction of the cooling liquid in the working state of the circulation cooling system according to the embodiment of the application, wherein the components of the circulation cooling system are specifically shown.

As shown, the circulation cooling system includes an outer drive shaft 101, an inner drive shaft 102, an outer rotor 103, a yoke 104, a permanent magnet pole 105, an inner stator 106, an excitation winding 107, a bearing 108, a storage chamber 109, and an inner stator core 110.

The inner stator structure part mainly comprises: an inner stator 106, an excitation winding 107, a bearing 108, a storage chamber 109, and an inner stator core 110.

The field winding 107 is wound around the inner stator core 110, and the inner stator core 110 and the field winding 107 are sealed with glue. The watertight bearing 108 is mounted at the interface of the storage chamber 109. For example, at the inner stator core 110, a space having a diameter of 28mm and a depth of 50mm is dug as the storage chamber 109. Of course, as those skilled in the art will appreciate, the above dimensions are merely illustrative dimensions for a particular brushless motor. It is within the scope of the present application for a person skilled in the art to be able to design different sizes of the secondary storage chamber for storing cooling liquid in accordance with different sizes of the brushless motor and different cooling requirements.

The storage chamber 109 is used to store the cooling fluid and forms an internal circulation structure with the outer drive shaft 101 and the inner drive shaft 102. The reservoir 109 is connected to the inner drive shaft 102 by a watertight bearing 108. This ensures both good rotation of the inner drive shaft 102 and that no leakage of coolant occurs during normal operation of the motor arrangement.

The outer rotor structure portion mainly includes: outer drive shaft 101, inner drive shaft 102, outer rotor 103, yoke 104, permanent magnet poles 105. The inner drive shaft 102 is nested inside the outer drive shaft 101, and the permanent magnet poles 105 are fitted into the yokes 104. In the embodiment of the present application, the yoke 104 and the permanent magnet pole 105 inside the motor apparatus are fixed to each other by a glue seal. The combined

drive shafts

101, 102 and yoke 104 are integrated via metal 3D printing.

At the connection with the outer rotor 103, the inner spaces of both the outer drive shaft 101 and the inner drive shaft 102 are connected to each other. This is achieved, for example, by: the inner drive shaft 102 is axially outwardly opened with 3 holes spaced 120 ° from each other and having a depth of 25mm without interfering with the threaded holes, and the outer drive shaft 101 is axially outwardly opened with 3 holes spaced 120 ° from each other and surrounding the shaft at 10mm from the outside, and having a length of 15mm and a width of 2.5 mm. Thereby interconnecting the space inside the outer drive shaft 101 and the inner drive shaft 102.

Fig. 3 shows an enlarged view of the structure at the slot of the inner drive shaft 102 according to an embodiment of the present application.

After the heat-carrying coolant flows from the storage chamber 109 to the distal end via the inner drive shaft 102 to be cooled, it returns to the storage chamber 109 again via the outer drive shaft 101. This is achieved by providing slots in the outer wall of the inner drive shaft 102 which allow clearance between the inner and outer drive shafts to facilitate the flow of cooling fluid.

In the specific embodiment of the present application, by way of example but not limitation, in a specific size of the outer rotor brushless motor, the wall thickness of the inner drive shaft 102 is 0.4mm at a position of up to 40mm from the bottom surface; the wall thickness was 0.8mm from 40mm up to the top. A circular groove with the length of 30mm and the width of 0.3mm is cut upwards from the position 40mm above the bottom end, and the depth from the inner wall of the circular groove to the outer wall of the inner shaft is 0.1 mm. At the bottom end 50mm upwards, 3 holes which are spaced by 120 degrees and are 15mm long and 2.5mm wide are arranged inwards on the surface of the inner driving shaft to connect the circular ring grooves. Thus, the coolant flowing back through the outer drive shaft 101 enters the annular groove through the three holes formed in the inner drive shaft 102, and then flows through the annular groove into the storage chamber 109.

Fig. 4 shows a schematic structural view of a composite drive shaft according to an embodiment of the present application.

In the embodiment of the present application, the combined

drive shafts

101, 102 are combined by the outer drive shaft 101 and the inner drive shaft 102 in an inside-outside nested manner, and have a uniform wall thickness. In addition, the inner surfaces of the outer driving shaft 101 and the inner driving shaft 102 are both provided with threads, the inner part of the outer driving shaft 101 is provided with reverse threads, the inner part of the inner driving shaft 102 is provided with forward threads, and the threads are used for providing power for outputting the cooling liquid outwards under the driving of the outer rotor 103. And the combination of screw thread can provide bigger contact surface to increase heat radiating area, improve the radiating efficiency.

In the embodiment of the present application, the material of the outer driving shaft 101 and the inner driving shaft 102 may be various metals, alloys, depending on the requirements of the working environment for the material, and is easily appreciated by those skilled in the art. The internal threads of the outer and

inner drive shafts

101, 102 may be referenced to the cross-sectional view of the combination drive shaft shown in fig. 4.

FIG. 5 shows a flow diagram of a method of circulating cooling according to an embodiment of the present application.

As shown in fig. 5, in normal operation, when the motor is energized, the outer rotor 103 rotates the outer drive shaft 101 and the inner drive shaft 102 at a high speed, and the combination of the threads provides power for the coolant to enter and exit the combined drive shaft. The high temperature coolant in the reservoir 109 flows from the reservoir 109 outwardly along the inner drive shaft 102 (by opening, e.g., perforating, the inner drive shaft 102) to the distal end, i.e., the portion of the outer drive shaft 101 and the inner drive shaft 102 that is submerged in the cooling medium, such as water. At this time, the high-temperature coolant is rapidly cooled due to a temperature difference between the outer drive shaft 101 and the inner drive shaft 102, which are immersed in the cooling medium.

After cooling, the cooling fluid is then transported by the outer drive shaft 101 back to the storage chamber 109 inside the motor, cooling the motor which generates heat. This is achieved by grooving the outer wall of the inner drive shaft. A circulation is formed, thereby forming a heat dissipation structure based on the internal circulation of the motor as a whole.

By adopting the mode to cool the brushless motor with the outer rotor, the temperature of the motor can be controlled within a reasonable range, so that the long-time continuous and stable work of the motor is ensured.

FIG. 6 shows a graph of temperature testing in an operating state according to an embodiment of the present application.

An outer rotor brushless motor with 24V, 138W power and 3000r/min rotation speed is adopted on the unmanned ship, the motor is firmly fixed on the ship, and the watertight structure is well formed at the contact position between the output shaft of the motor and the shell of the ship; and meanwhile, a temperature sensor is arranged on the motor shell so as to record the real-time temperature condition of the motor.

After the power is switched on, the temperature is tested for 20 minutes in a river, the temperature is recorded every 2 minutes, the test is carried out for three times, the temperature condition of the motor is monitored in real time, and the abnormal temperature of the motor is prevented so as to facilitate rescue. The results of the experiment are shown in FIG. 6.

The operation of the external rotor circulation cooling system 100 according to the present application will be further described with reference to the above-mentioned drawings.

After the external stator 106 and the internal rotor 103 are properly assembled, power is applied, the motor is turned, and the hydronic cooling system 100 begins to operate. When the inner rotor 103 starts to rotate, it is brought into rotation by virtue of being integral with the combined

drive shafts

101, 102. At this point, the coolant in the reservoir 109 is directed by the attractive force created by the high speed rotation of the forward threads within the inner drive shaft 102 to move the higher temperature coolant toward the distal end of the composite drive shaft until it reaches the distal most portion of the composite drive shaft. The shortest end portion is immersed in a cooling medium such as water. Because the coolant and the water flowing in the shaft have larger temperature difference, the heat carried by the coolant can be transmitted to the cooling medium by taking the driving shaft as the medium, thereby achieving the cooling effect.

The cooled coolant flows into the motor by attraction force generated by the high-speed rotation of the reverse screw in the outer drive shaft 101. Cooling of the primary motor is accomplished by passing through the interior of the inner drive shaft 102 to the storage chamber 109 via a slot provided in the inner drive shaft 102 (as shown in fig. 3). Then the cooling liquid absorbs the high temperature again and is conveyed to the outer end to be cooled repeatedly.

The circulating cooling system for the unmanned ship outer rotor brushless motor has the following advantages:

firstly, the influence of sundries in water on the circulating cooling system is completely avoided, and the reliability of the circulating cooling system is improved;

secondly, any external cooling device or equipment is not required to be added, so that the manufacturing cost is greatly reduced, and the system reliability is improved;

thirdly, the internal structure of the existing motor is completely based, the internal space is saved, and the motor cooling device is particularly suitable for cooling the space-limited motor.

Aspects are described with reference to one or more components and one or more methods that may perform the actions or functions described herein. In an aspect, the terms "component," "part," and "component" as used herein may be one of the parts that make up a system, may be hardware or software, or some combination thereof, and may be divided into other components. While the operations described below in the figures are presented in a particular order and/or as performed by example components, it should be understood that the order of the actions and the components performing the actions may vary depending on the implementation. Further, it should be understood that the following acts or functions may be performed by a specially programmed processor, a processor executing specially programmed software or computer readable media, or by any other combination of hardware components and/or software components capable of performing the described acts or functions.

It is to be understood that the specific order or hierarchy of steps in the methods disclosed is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the methods or system of methods described herein may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented unless specifically recited herein.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean "one and only one" (unless specifically so stated) but rather "one or more". Unless specifically stated otherwise, the term "some" means one or more. A phrase referring to "at least one of a list of items refers to any combination of those items, including a single member. By way of example, "at least one of a, b, or c" is intended to encompass: at least one a; at least one b; at least one c; at least one a and at least one b; at least one a and at least one c; at least one b and at least one c; and at least one a, at least one b and at least one c. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.

Claims

1. A hydronic cooling system for an outer rotor brushless motor for an unmanned boat, comprising:

an outer drive shaft coupled with the inner drive shaft for receiving the cooled coolant from the inner drive shaft;

a storage chamber communicating with the inner drive shaft and the outer drive shaft for containing the coolant; and

2. The hydronic cooling system according to claim 1, wherein the outer drive shaft has a reverse internal thread and the inner drive shaft has a forward internal thread, whereby the two are nested within each other and have a uniform wall thickness in the circumferential direction.

3. The hydronic cooling system of claim 1, wherein the outer drive shaft and the inner drive shaft are integral with the outer rotor.

4. The hydronic cooling system according to any one of claims 1 to 3, wherein an exterior of the inner drive shaft and the outer drive shaft is immersed into a cooling medium.

5. A circulating cooling system as claimed in any one of claims 1 to 3, wherein the inner drive shaft communicates with the storage chamber through an opening.

6. The hydronic cooling system according to claim 5, wherein the communication of the inner drive shaft with the storage chamber is achieved by axially perforating the wall thereof.

7. A circulating cooling system as claimed in any one of claims 1 to 3, wherein the cooled cooling liquid flows back to the storage chamber via a groove in the inner wall of the outer drive shaft.

8. A method of cooling an unmanned surface vehicle outer rotor brushless motor using the hydronic cooling system of any one of claims 1 to 7, comprising the steps of:

s1: the heat-carrying coolant stored in the storage chamber is drawn out via the inner drive shaft;

s2: the heat-carrying coolant flows to a distal end via the internal drive shaft for cooling;

s3: the cooled coolant flows back to the storage cavity by the external drive shaft;

s4: the cooled coolant cools the brushless motor.

9. The method of claim 8, wherein the cooled coolant flows back to the storage chamber via a groove in an inner wall of the outer drive shaft.