Patent ID: 12261501

DETAILED DESCRIPTION

Electric motors typically generate heat during operation. While heat can be generated from various locations through the system, a major source of heat can be from the ends of the stator wires. A casing surrounding an electrical motor typically includes a cylindrical portion that connects with a circular flat top portion and a circular flat bottom portion. The ends of the stator wires are the portions of the stator wires which run along the flat top and bottom portions of the casing that surround the cylindrical portion of the casing. Generation of heat in electric motors can cause electric motors to fail. Typically, in order to mitigate failure from over-heating, a larger electric motor is used than is desirable so that the motor runs cooler and does not overheat. Cooling the electric motor can allow a smaller motor to run a larger load and not overheat. Various electric motor cooling systems have focused on cooling the outside of a casing surrounding the stator and the rotor, such as a water jacket. These cooling systems have been ineffective because of poor heat transfer to the casing from main heat sources such as the stator. Accordingly, it would be advantageous to be able to cool the electric motor by directly cooling the stator and, in particular, the ends of the stator wires.

Various embodiments disclosed herein relate to an electric motor with a cooling system. The electric motor can include a rotor which is connected to an output shaft and a stator which is disposed about the rotor. A casing can be at least partially disposed about the stator and the rotor. The cooling system includes a cooling assembly which can include one or more inlets configured to deliver coolant into the casing and onto the stator to cool the stator. The stator can be a major source of heat when operating the electric motor. Therefore, by delivering coolant directly onto the stator, the cooling system can effectively cool the electric motor which can allow for a larger load to be mechanically powered by a smaller electric motor.

In some embodiments, the inlet can be configured to flow coolant directly onto the ends of the stator wires in order to cool the ends of the stator wires which can be a major source of heat within the electric motor. The inlet can comprise multiple inlets which flow coolant onto different locations of the stator. The distance from the inlet to the stator wires can vary depending upon the size of the motor. When the electric motor is running, the motor can splash and swirl the coolant within the engine so as to prevent the coolant flowing from the inlet from reaching the ends of the stator wires. The gap between each inlet to the ends of the stator wires may be close enough so as to adequately flow the coolant from the inlet to the ends of the stator wires. In some embodiments, the ends of the inlets can be 2 mm to 10 mm away from the ends of the stator wires.

FIG.1is a schematic cross sectional view of an electric motor100. The electric motor100includes stator102that surrounds a rotor104which is attached to an output shaft106. The stator102includes metal cores103each with one or more stator wires105wrapped around the metal cores103. The metal cores103can be made of steel or other suitable material. The metal cores103of the stator102can comprise a hollow generally rectangular shape with the stator wires105wrapped around the metal cores103. In some embodiments, the stator wires105can be copper wires or wires made of other suitable conductive materials. The rotor104can comprise a magnetic material which can be a permanent magnet or an induced magnet. The rotor104fits into the middle of the stator102with an air gap107between the rotor104and the stator102. When a current is run through the stator wires105of the stator102a magnetic field is created which interacts with the magnetic material of the rotor104to impart rotation to the rotor104. Thus, the stator102can be stationary while the rotor104rotates within the stator102. The rotor104can be mechanically connected to an output shaft106by way of any suitable type of mechanical connection, such as a press-fit or interference connection. Therefore, the shaft106also rotates when the rotor104rotates. The shaft106can be connected to various types of movable devices, such as wheels or gears in order to impart mechanical force on these devices. A casing108can be provided to encapsulate both the stator102and the rotor104. The shaft106can protrude from the casing108. The casing108can comprise one unitary piece or can be segmented into multiple pieces.

Heat is produced during the operation of the electric motor100. Specifically, it has been discovered that the most intense heat in the electric motor100is generated at the ends of the stator wires105wrapped around each of the metal cores103. Thus, it can be advantageous to be able to stream coolant directly onto the ends of the stator wires.

FIG.2is a schematic cross sectional view of an exemplary embodiment of an electric motor200. The electric motor200shares many features of the electric motor100ofFIG.1. Unless otherwise noted, reference numerals ofFIG.2may represent components that are the same as or generally similar to like-numbered components ofFIG.1. The electric motor200ofFIG.2includes a cooling system which includes one or more inlets204for streaming liquid coolant into the electric motor200, e.g., directly onto the stator wires204. The casing108includes one or more side segments202which has been adapted for use with one or more inlets204. The side segments202can be integrally formed with the casing108or can be separate pieces which has been adapted to fit with the rest of the casing108. In some embodiments, the side segments202can be retrofitted for use with an existing casing. Beneficially, retrofitting the side segments202for use with an existing casing can allow an existing conventional electric motor to be cooled using the embodiments disclosed herein, which can improve performance and efficiency of the existing electric motor. The ends of the stator wires204are located near the side segments and therefore, the inlets204can be placed on the side segments202in such as location as to directly stream coolant onto the ends of the stator wires.

In some embodiments, the end of the inlets204can be 2 mm to 10 mm away from the ends of the stator wires of the stator102. The distance from the inlet to the stator wires can vary depending upon the size of the motor. When the electric motor is running, the motor can splash and swirl the coolant within the engine so as to prevent the coolant flowing from the inlet from reaching the ends of the stator wires. The gap between each inlet to the ends of the stator wires may be close enough so as to adequately flow the coolant from the inlets204to the ends of the stator wires. In various embodiments, the inlet204can be configured to direct a liquid jet or other liquid stream of coolant directly onto the stator wires. The liquid stream can have a momentum along or substantially parallel to a pathway or vector of the stream, such that the liquid stream is not a stagnant liquid pool but rather a liquid stream directed along a pathway to hot spot(s) of the stator wires. The liquid stream can be directed on to the ends of the stator wires105as explained above. The liquid coolant can comprise any suitable type of coolant, such as an Automatic Transmission Fluid (ATF; e.g. Dextron VI). The liquid coolant can be electrically inactive such that the coolant does not short out the stator wires upon contact.

Depicted inFIG.2, the one or more side segments202are two side segments202that are on both sides of the motor and therefore can stream coolant onto multiple circumferential locations along the stator102. However, the one or more side segments can also be on only one side of the engine and therefore stream coolant onto only one side of the stator102.

InFIG.2, while the motor200is depicted in a vertical orientation, the motor200can also be run in a horizontal orientation since the ends of the inlets204are positioned to stream coolant directly onto the ends of the stator wires105. As discussed previously, the ends of the stator wires105are the hottest portions of the motor200and therefore streaming coolant directly onto the ends of the stator wires105will continually keep these components cool. With other cooling systems where the coolant floods the motor, the orientation of the motor will affect flow of the coolant which will affect the cooling within the motor.

FIG.3is a side view of an exemplary embodiment of a segment202of the casing108of the electric motor200illustrated inFIG.2. As shown, the one or more inlets204comprises multiple inlets204which are located at multiple locations near the outer periphery of segment202. There can be also inlets204located radially inward which can stream coolant to cool other portions of the stator102. The Inlets204can be placed such that they directly stream coolant onto the ends of the stator wires. There can be more or fewer inlets204and the number of inlets204can depend on a variety of factors such as the size of the electric motor200, the number of metal cores103and the amount of cooling desired. In some embodiments, the end of each of the inlets can be 2 mm to 10 mm away from the ends of the stator wires105of the stator102.

Further shown inFIG.3is a first outlet304and a second outlet302. The size of the first outlet304and the second outlet302may be larger than the inlets204. The inlets204can operate under pressure whereas the first outlet304and the second outlet302operate under a vacuum source. Coolant flowing under pressure may flow faster than coolant flowing under a vacuum and the size of the first outlet304and the second outlet302can be adjusted to accommodate the different in flow rate. Also, while only a first outlet304and a second outlet302shown inFIG.3, it should be appreciated that there can instead be more or fewer outlets. For example, one of the first outlet304and the second outlet302can be omitted. The size of the outlets302/304and inlets204can be adjusted based on number of outlets302/304and inlets204. The electric motor200further includes a sight gauge306which can allow a user to visually estimate the amount of coolant within the electric motor200without opening the electric motor200.

When the electric motor200is operating, the turning rotor can circulate coolant within the casing108. When the coolant rotates within the casing108, the liquid coolant can be centrifugally forced outward through the first outlet304and/or the second outlet302. The second outlet302can be positioned near the bottom of the stator102and the first outlet304can be positioned above the second outlet302. Thus, a first portion of liquid coolant can absorb heat from the stator102and can be directed centrifugally outward from the motor200through the first outlet304. The positioning of the first outlet304and the second outlet302can be varied based on the orientation of the motor200.FIG.3depicts the first outlet304and second outlet302based on the motor200in a vertical orientation.

The second outlet302can operate as a scavenge port to remove liquid coolant that falls to the bottom of the casing108due to gravity. Thus, a second portion of the coolant can absorb heat, fall to the bottom of the casing108due to gravity, and can exit the electric motor200through the second outlet302. By having the second outlet302located near the bottom of the stator, the second outlet302keeps coolant from remaining in the electric motor200. The low volume of coolant that remains in the motor200minimizes drag on the rotor104as it spins, which increases performance. However, by keeping a low volume of coolant within the motor200, the coolant does not pool within the motor200and therefore does not continually contacts of the motor200. As discussed previously, the ends of the stator wires105are the portions of the motor200that produce the most heat. By positioning the inlets such that coolant is streamed or jetted directly onto the ends of the stator wires105, the motor200can be adequately cooled even when the volume of the coolant remaining within the motor200remains low. Further, by keeping the volume of the coolant within the motor200low, the inlet delivers fresh coolant directly onto the outer surface of the stator without mixing with other coolant within the system.

FIG.4illustrates a schematic view of the cooling system400for the electric motor200. Coolant flow is represented by the arrows. The coolant can be non-electrically conductive. The coolant can be a low viscosity oil or other suitable cooling fluid. The coolant can have anti-foaming characteristics such that the coolant does not easily absorb air. The cooling system400includes the segment202of the casing108of the electric motor200which was described above inFIG.3. The features of segment202described above in connection withFIG.3are not repeated in detail. The cooling system400includes piping that connects the elements of the system. The piping can be metal, plastic, or a material suitable for withstanding high temperatures of the coolant of the system. As shown, the first outlet304can be in fluid connection with an accumulator tank402through a valve404. The valve404can comprise a one way valve such as a check valve. The valve404can be configured to allow coolant to flow into the accumulator tank402while blocking passage of the coolant and/or system pressure back into the electric motor200. Beneficially, the valve404keeps hot coolant from flowing back into the electric motor200.

The accumulator tank402can comprise an expansion tank. During operation, the fluid pressure may change within the electric motor200. The air volume within the accumulator tank402can absorb the pressure changes in the electric motor200which can decrease the chance of a coolant leak. Further, the accumulator tank402can collect the coolant expelled from the first outlet304, which may be relatively frothy due to the high velocity rotational motion of the coolant within the motor200. The frothy coolant includes air dissolved in the liquid. The accumulator tank402can permit the air to separate from the liquid coolant at the top of the accumulator tank402and the liquid coolant to settle at the bottom of the accumulator tank402. The accumulator tank402can also act as the system's coolant reservoir which can minimize the amount of volume of coolant kept in the electric motor200. Advantageously, lower coolant levels within the electric motor200can decrease resistance within the electric motor200and increase performance. The accumulator tank402can be placed slightly lower than the level of the electric motor200which can decrease the amount of static coolant within the electric motor200. In some embodiments, the amount of coolant within the accumulator tank402is one third the level of the accumulator tank402.

Further, the accumulator tank402and the second outlet302can be in fluid connection with a pump406. The pump406can be activated to draw liquid coolant from the accumulator tank402and from the second outlet302. In some embodiments, the second portion of the liquid coolant from the second outlet302can be entrained with the first portion of liquid coolant from the accumulator tank402(and the first outlet304). For example, a fluid joint412can be provided at the intersection of the fluid pathways from the accumulator tank402and the second outlet302. The pump406can comprise an electric pump that can be powered by a battery or another power source. In some embodiments, the pump406can include a brass impeller that can safely run dry. The pump406can further be run with frothy aerated coolant or pure liquid coolant without aeration. The pump406can also tolerate heat from heated coolant. Alternatively, the pump406can be omitted and the coolant may be circulated by the movement of the electric motor200. Depending on the size of the electric motor200and the amount of coolant in the system, the centrifugal force generated by the electric motor200may be sufficiently high so as to drive the coolant without use of the pump406.

The pump406can be in fluid connection with a heat exchanger408. The heat exchanger408can transfer heat to the outside environs from the hot coolant which flows through the heat exchanger408. The heat exchanger408can include fins and/or coils and outside air may flow onto the fins and/or coils in order to cool the heat exchanger408and thereby further cool the hot coolant. After the coolant exits the heat exchanger408, the coolant is cooler than when the coolant enters the heat exchanger408. Other components of the system such as the piping and the electric motor200can transfer heat to the outside from the coolant. The heat exchanger408can be omitted if the heat transferred from the coolant to the outside from the other components of the system is adequate.

With continued reference toFIG.4, the heat exchanger408can be in fluid connection with one or more connectors410. The connectors410can serve as a manifold to spread out the coolant into multiple streams which can connect into the inlets204. The manifold can be positioned relative to the segment202so as to direct multiple streams of liquid coolant onto the stator102. The number of streams can be the same as the number of inlets204. The connectors410can be one or more connectors or the number of connectors chosen to adequately divide the coolant into the inlets204. As shown, each connectors410has a separate fluid connection with the heat exchanger408. Also, each connector410can have separate fluid connections with a number of inlets. For example, each connectors410can be connected to one to six different inlets. In some embodiments, each connectors410is connected to three different inlets. Also, different connectors410can be in fluid connection with a different number of inlets. For example, one connector can be connected to three inlets while another connector can be connected to four inlets. While inFIG.4connection to only six different inlets are shown, it is understood that the connectors410are in fluid connection with all of the inlets.

FIG.5is a schematic view of an example accumulator tank402shown inFIG.4. The coolant flow is represented by arrows and a coolant reservoir level is represented by wavy line510. As shown, the accumulator tank402includes both a tank inlet504and a tank outlet506. The tank inlet504can be located above the tank outlet506. The tank inlet504can be located above or below the coolant reservoir level. The tank inlet504can be in fluid communication with the first outlet304. The tank outlet506can be located at or near the bottom of the accumulator tank402. The tank outlet506can also be located in other locations but should be located below the coolant reservoir level. In some embodiments, the pump406can draw the settled liquid coolant from the accumulator tank402by way of the tank outlet506. The accumulator tank508can further include a sight gauge508which can display the current coolant level without having the visually open the accumulator tank508. A breather502can be located at the top of the accumulator tank508. The breather502can also be located at other locations however should be above the coolant reservoir level. The breather allows air to escape the accumulator tank402while keeping particles and other contaminates from entering the accumulator tank402. Alternatively, the breather502can be omitted and replaced with an opening. The breather502can be removable in order to allow a user to add or remove coolant from the system.

FIG.6is an image of an exemplary implementation of the electric motor200ofFIG.2with the segment202ofFIG.3.FIG.7. is an image of an exemplary implementation of the electric motor200ofFIG.2with the accumulator tank402ofFIG.5. The features in the images ofFIGS.6and7are the same as or generally similar to like-numbered components ofFIGS.2-5, and the description of these components is not repeated. As also shown, the electric motor200can be housing in a housing702and connected to a chain704, which can drive a movable device, such as a wheel. The housing can also accommodate the accumulator tank402. Further components of the cooling system400can also be housed by the housing.

Although this invention has been disclosed in the context of certain embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while several variations of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the invention. It should be understood that various features and aspects of the disclosed embodiments can be combined with, or substituted for, one another in order to form varying modes of the disclosed invention. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.