System and method for direct liquid cooling of electric machines

A system is provided for cooling a stator coil of a rotating machine. In one embodiment, and by way of example only, the system includes a stator core, a radial core opening, and a sleeve. The stator core has an axially extending slot formed therein, an outer circumferential surface, and an inner circumferential surface. The radial core opening extends from the stator core outer circumferential surface to the axially extending slot. The sleeve is disposed within the axial slot and configured to surround the stator coil. The sleeve has a cooling fluid supply port formed therein that is aligned with the radial core opening.

TECHNICAL FIELD

The present invention relates to rotating electrical machines and, more particularly, to a cooling system for a stator of a rotating electrical machine.

BACKGROUND

Aircraft systems include various types of rotating electrical machines, such as alternating current (AC) motors and generators of various designs. Generally, an AC machine includes a rotor and a stator. If the machine is operated as a motor, electrical power is supplied to the stator to develop a rotating electrical field. This rotating electrical field generates a torque in the rotor causing it to rotate. If the machine is operated as a generator, electrical power is supplied to the rotor to generate a magnetic field. A prime mover is coupled to the rotor causing it, and thus the generated magnetic field, to rotate. This rotating magnetic field induces a voltage into the stator, which supplies electrical power to a load.

A stator for AC machines may typically include a stator core having a plurality of wire coils wound around it. The stator core is generally formed by laminating a plurality of ring plates. The ring plates include an inner circumference that together form a main axial opening through the stator core for housing rotating components. A plurality of slots is formed in the inner circumference, and each of the slots extends along the axis of the main axial opening. Each slot includes an axial slit that allows communication between the slot and the main axial opening. The wire coils typically include ends that are inserted into the slots.

The wire coils may produce heat during machine operation and may, consequently, undesirably transfer the heat to the core. To prevent such a consequence, thermal insulating and/or cooling schemes are typically included in AC machines. In one example, a portion of each coil is wrapped with a thermally insulating liner that isolates coils from the stator core, and inhibits heat transfer to the core. Although this is adequate for small rotating machines, it typically does not sufficiently inhibit heat transfer in rotating machines that include larger sized cores. In other examples, cooling fluid or gas is directed into the stator slots and contacted with the coils. However, because the slots are typically designed to open into the main axial opening, the fluid or gas may leak through the opening and contact the rotating components causing the components to become inoperable.

Hence, there is a need for a cost-efficient, effective system for cooling an electrical rotating machine of any size. Additionally, it is desirable for the system to be capable of being retrofitted into existing electrical rotating machines. Moreover, it is desirable for the system to operate without affecting the rotating components of the machine.

BRIEF SUMMARY

The present invention provides a system for cooling a stator coil of a rotating machine. In one embodiment, and by way of example only, the system includes a stator core, a radial core opening, and a sleeve. The stator core has an axially extending slot formed therein, an outer circumferential surface, and an inner circumferential surface. The radial core opening extends from the stator core outer circumferential surface to the axially extending slot. The sleeve is disposed within the axial slot and configured to surround the stator coil. The sleeve has a cooling fluid supply port formed therein that is aligned with the radial core opening.

In another embodiment, and by way of example only, a system is provided for cooling a rotating machine having a plurality of stator coils disposed therein. The system includes a stator core, an axial slot, a radial core opening, a sleeve, a cooling fluid supply port, and cooling fluid. The stator core has an outer circumferential surface, an inner circumferential surface, and a length. The axial slot is formed in the stator core and extends the stator core length and configured to house at least a portion of the stator coil therein. The radial core opening is formed in the stator core and extends from the stator core outer circumferential surface to the axial slot. The sleeve is disposed within the axial slot and is configured to surround the stator coil portion. The cooling fluid supply port is formed in the sleeve and is aligned with the radial core opening. The cooling fluid is disposed in the rotating machine and flows through the radial core opening and the cooling fluid supply port to cool the stator coil.

In another embodiment, and by way of example only, a method is provided for cooling a rotating machine including a stator core having a radial opening extending there through, an axial slot formed in the stator core having a channel and an outlet therein that communicate with the radial opening, and a sleeve disposed in the axial slot and having a cooling fluid supply port in direct communication with the radial opening. The method comprises the steps of flowing cooling fluid through the rotating machine, directing the cooling fluid through the stator core radial opening, and flowing the cooling fluid through the cooling fluid supply port and axial slot channel.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A simplified mechanical schematic representation of a generalized embodiment of an AC machine100is depicted inFIG. 1. The machine100may be either an AC motor or an AC generator, and includes a shaft102, a rotor104, and a stator106. A device108is coupled to the shaft102. If the AC machine100is a generator, the device108is a prime mover for rotating the shaft102and the electrical power generated in the stator106is delivered to a load via a set of leads110that are coupled to each of the stator windings. If the AC machine100is a motor, the device108is a load to be rotated by the shaft102and power is supplied to the stator106from a source (not shown) via the leads110. In either case, the AC machine100is preferably bathed in a fluid that may be contained therein or supplied thereto that is used to cool the machine100. The cooling fluid may be a lubricant, such as oil, that supplied to the AC machine100by the prime mover or other oil contained in the AC machine100.

Turning now toFIG. 2, a perspective view of the stator106is provided. As shown in the figure, the stator106includes a stator core202, a plurality of sleeves204(shown inFIGS. 3-5), and a plurality of stator coils206The stator core202is perferably formed from a plurality of laminations, and is preferably cylindrically shaped. It will be appreciated that the stator core202may alternatively be formed as a single, cast piece. It is noted that the stator core202may be formed of any one of numerous known materials known in the art including, but not limited to, electrical-grade steels such as cobalt-iron and silicon-iron. However, in a perferred embodiment the stator core202is formed of cobalt-iron.

The stator core202has a first end208, a second end210, an outer circumferential surface212, and an inner circumferential surface214. The inner circumferential surface214defines a main axial opening216and includes a plurality of slots218. A plurality of radial openings220are formed between the inner and outer circumferential surfaces212,214.

As briefly alluded to above, each of the slots218is formed on the inner circumferential surface214. The slots218preferably extend axially between the first and second ends208,210of the stator core202, and are preferably evenly spaced around the inner circumferential surface214. As shown inFIG. 2, the slots218each include a slit222that provides communication between the slot218and the main axial opening216. In addition, each of the slots218is radically sized to receive at least a portion of two stator coils206, one in an inner slot position and another in an outer slot position. It will be appreciated that this slot configuration is merely exemplary of a preferred embodiment and that other slot configurations may alternatively be used.

The radial openings220are configured to provide a passage through which cooling fluid flows. To allow the cooling fluid to travel through most of the length of the slot218, the radial openings220are preferably formed proximate one end of the core202. Most preferably, the radial openings220are proximate the forward end of the core202, shown inFIG. 2as the first end208. Additionally, the radial openings220are preferably formed in a circular pattern around the circumference of the core202; however it will be appreciated that the openings220may alternatively be formed around the core202circumference in any one of numerous other suitable patterns.

With reference toFIGS. 3-5, as briefly mentioned above, the stator106also includes a plurality of sleeves204. The sleeves204are configured to receive the cooling fluid supplied to the radial openings220and to direct the cooling fluid into contact with the coils206. In this regard, each sleeve204is disposed, one each, in the slots218, and may be placed, inserted, or alternatively molded into the slots218. Each sleeve204includes a channel224and a cooling fluid supply port226and may be constructed from a material that will maintain structural integrity upon exposure to a temperature within the temperature range of an operating coil206. For example, the sleeve204may be constructed of plastic or any other similar material, or may be made from thermally insulating materials, such as Nomex® or Kapton® (both available from E.I. du Pont de Nemours and Co. of Delaware).

The channel224is preferably configured to provide space for the insertion of one or more stator coils206therein and includes a stator coil inlet228and a stator coil outlet230. In the embodiment depicted inFIGS. 3-5, two coil ends206are inserted into the channel224via the stator coil inlet228and extend out the stator coil outlet230. The channel224may have any suitable radial cross-section shape, such as, for example, circular or rectangular, and may be any suitable size. For example, the channel224may be sized as large as the slot218and may have the same shape as the slot218. Each cooling fluid supply port226communicates with the channel224and is formed such that when the sleeve204is appropriately disposed within the slot218, the cooling fluid supply port226aligns and directly communicates with one of the radial openings220of the core202.

Returning back toFIG. 2, the stator coils206are wound around the stator core202and each coils206includes two legs302,304that are each inserted into two sperate slots218. Accordingly, the legs302,304are inserted into two sperate sleeves204. Perferably, each leg302,304is inserted into non-adjacent slots218, though it will be appreciated that the present invention is not limited to this scheme. Each stator coil206is made from a conductive metal, such as copper, and is perferably rectangular in cross section. However, it will be appreciated that the coils206could be constructed of other conductive metals, such as aluminum, gold and silver, and could have other cross sectional shapes, such as round or square. Moreever, each coil206other cross sectional shapes, such as round or square. Moreover, each coil206could be constructed of a single conductor, or a purality of conductors.

Since the coils206are made of conductive metal, the temperature of the coils206may reach an undesirable range during stator106operation. To cool the coils206, cooling fluid supplied to the rotating machine100is directed into and through the radial openings220of the core202, through the sleeve openings226, into the channel224, until it reaches the corresponding coil206. The cooling fluid then exits the sleeve204via the channel inlet228or the channel outlet230.

A system has now been provided that inexpensively and efficiently cools stator coils206. Additionally, the system may be easily implemented into existing stators. Moreover, the system isolates the cooling fluid from the rotating components of the electrical rotating machine.