HIGH EFFICIENCY, LOW COOLANT FLOW ELECTRIC MOTOR COOLANT SYSTEM

A fluid-cooled electric motor includes a generally tubular-shaped motor housing having a plurality of channels through which a coolant can flow. The channels are spaced apart from each other in an annular arrangement around the housing and extend through the housing in an axial direction. Each of the channels is surrounded by a portion of the housing defining walls of the channel forming a cooling surface area.

DETAILED DESCRIPTION

Various embodiments disclosed herein are directed to a coolant system for an electric motor. The coolant system efficiently removes heat from the electric motor by providing a unique path for liquid coolant to flow through extruded channels in the motor's outer shell or housing. The channels are connected in a way that exposes a greater surface area that coolant is in contact with. Consequently, there is an increased rate of heat removal per unit motor volume. Additionally, the coolant channels are designed to provide minimal flow restriction, thus maximizing flow rates and cooling performance.

In addition, the coolant system simplifies manufacturing because the coolant channels are integral with the motor housing or casing, which comprises a single part that can be made of extruded metal. The extruded motor housing contains only a small number of internal cavities, which improves “extrudability”, while generally maximizing the cooling surface area of the channels. (The internal cavities comprise the cooling channels and the bore. The bore supports the motor stator and the endplates, which support the motor and the rotating rotor.) The design is scalable to generally any motor length by simply cutting the extrusion to the required length. All other components simply attach to the extrusion in the same or similar way, resulting in a cooling system that is highly and easily configurable.

As discussed below, heat extraction from an electric motor depends on several factors including the available surface area on the motor surface to conduct the heat transfer, the temperature of the liquid coolant flowing on the surface of the motor, and the flowrate of the coolant. Other factors such as the thermal conductivities for all materials used are also important, but not addressed as they are considered constants when comparing with other heat extraction methods.

Various types of coolant can be used in the coolant system including, e.g., water, oil, aqueous coolant mixtures (ethylene or propylene glycol +distilled water), and phase change coolants.

FIG. 1is a cross-section view of a typical water-cooled electric motor10in accordance with the prior art. A water-tight sleeve12surrounds the motor10. The sleeve12forms a seal that keeps the liquid coolant next to the motor, and has an inlet14(to pump the water into the sleeve), and an outlet16(which sends the heated water to a radiator or other heat exchanger). Water enters from the inlet14and runs through the coolant sleeve12on both sides of the motor10. During this time, heat exchange takes place where the water absorbs heat from the motor10. The water takes a circumferential path around the motor, and then exits through outlet16at the opposite side of the sleeve12.

As the water flows within the water-cooled sleeve12, the cross-sectional area in which the water is allowed to flow varies greatly. It is at its smallest within the inlet hose14, then transitions to a much larger area once entering the cooling jacket12. Because the water is incompressible and the total flowrate through the motor is unchanged, the water has reduced velocity when flowing within the jacket12. It is a well understood effect of nature that convective cooling performance diminishes as flow velocity decreases. Convection performance is at a minimum when the flow is laminar (non-mixing stream lines), and increases as turbulence starts to occur as the flow speeds up (mixing streamlines).

In the design shown inFIG. 1, it is difficult to maintain non-laminar (turbulent) flow conditions due to the slowing of the flow velocity, and convective cooling performance is accordingly typically poor.

FIG. 2shows an exemplary electric motor100in accordance with one or more embodiments. The motor100includes a motor housing102, which surrounds a stator108and rotor104.FIGS. 3 and 4separately show the stator/rotor assembly and the motor housing102, respectively. InFIGS. 2 and 4, a portion of the motor housing has been cut away to illustrate channels formed therein.

In accordance with one or more embodiments, the motor housing102is made from a single piece of extruded metal. By way of example, the extrusion can be made from aluminum alloys (6061,6005A,6063). A plurality of channels110A-F are formed within the housing102and spaced apart in an annular arrangement around the housing102as shown inFIGS. 5-7. The channels110A-F are designed to carry coolant lengthwise (i.e., axially) along the motor.

Liquid coolant is forced to flow through channels110A-F, which are connected to each other. The channels110A-F can be connected in series, in parallel, or in a combination of the two.

FIG. 6illustrates how heat is conducted radially from the interior of the motor into the housing102(as indicated by arrows120). Heat is first transferred to the radially inner side122of the housing102, and then is conducted along the walls124between the channels110A-F (as indicated by arrows128) to the radially outer side126of the housing102. As metal is an excellent heat conductor, both the inside122and outside126of the motor housing102will be heated. Because the channels110A-F are surrounded by portions of the housing102, the heat transfer surface area around the coolant is significantly increased. Accordingly, regardless of whether the flow through the channels110A-F is in series or in parallel, the convective cooling performance of the motor housing102is significantly improved because of the increased heat transfer surface area provided by the channels110A-F.

By contrast, in common coolant-cooled electric motors as shown inFIG. 1, cooling is accomplished by using a sleeve12that encapsulates the motor and allows coolant to flow around the motor from one side to the other. Heat transfer takes place only on the inner (i.e., motor side) of the sleeve12; the opposite outer side of the sleeve12is used for retaining the coolant next to the motor, but is not connected to the motor itself. Accordingly, very little or no heat transfer is contributed by the outer side of the coolant sleeve12.

The exemplary motor housing102illustrated inFIG. 5contains six channels110A-F. It should be understood that the number of channels can be varied depending on particular applications.

FIG. 7schematically shows how the coolant flows from one channel to the next when the channels110A-F are connected in series. For purposes of illustration, only the first three channels are shown inFIG. 7. Coolant is received by the motor through an inlet. The coolant enters the first channel110A and flows lengthwise across the motor to the opposite end, where it is re-directed into the adjacent channel110B where it now flows in the opposite direction across the length of the motor. When the coolant reaches the end of channel110B, it is re-directed into the next channel110C where it flows lengthwise along the motor, and is then redirected into the next channel110D (not shown inFIG. 7). This process continues until all the channels110A-F are used, and then the coolant exits through an outlet and is sent to a heat-exchanger such as a radiator.

By connecting the channels110A-F in series, a higher flow velocity is achieved (with increased flow restriction), resulting in improved convective cooling performance. If the channels are connected in parallel (not shown), there is decreased flow restriction resulting in decreased flow velocity, which thereby reduces convective cooling performance.

The routing of coolant from one channel to the next is performed by the end-cap assemblies200and220shown inFIGS. 8 and 9, respectively, which are provided at opposite ends of the motor housing102. Each end-cap assembly200,220comprises a single cast end-cap202,204and a single flat diverter plate206,208, respectively. Each end-cap202,204is bolted to a flat diverter plate206,208, and then the assemblies are each bolted to one end of the motor. The parts are sealed using gasketing sealant. By simply bolting each end-cap to each end, adjacent cooling channels in the housing102can be connected either in series or parallel while also supplying structural mounts for the rotor and wiring. Different end-cap configurations are needed for series or parallel coolant routing. The end-cap assemblies comprise relatively simple mechanisms with few parts for coolant routing.

If the motor is required to be longer or shorter (e.g., to obtain more or less power, respectively), the housing extrusion can be cut longer or shorter as needed. The endplate assemblies and mechanism of connecting adjacent channels and sealing remain unchanged.

FIG. 10shows an alternate configuration of the housing extrusion300with two sets of channels302,304that are radially spaced apart. This structure results in additional coolant distribution within the housing and increased cooling power as a result of the increased heat transfer surface area provided by the additional channels in the housing. This design is also achievable using the integrated channel extrusion design shown in other exemplary embodiments disclosed herein.

FIG. 11shows another alternative configuration of the housing extrusion320. In this embodiment, the channels322each include internal ribs324on the inside channel wall. The ribs324increase the channel surface area, thereby increasing the rate of heat transfer to the coolant. The ribs324can be provided on the radially inner side of the channel (as shown inFIG. 11), the opposite side, or on both sides to further increase the channel surface area. The ribs increase the surface area presented to the coolant, thus increasing the total heat transfer.

The electric motor coolant system in accordance with various embodiments has several advantages. The system can be easily manufactured and assembled. The motor housing can be extruded as a single piece. The coolant channels do not have to be cut or attached to the motor, as the channels are integrally formed within the motor housing during extrusion.

In addition, changing the length of motor (to increase or decrease output power) requires the modification of only one part to adjust length of the motor housing.

The system also has less complexity and is less likely to leak as a result since the main portion of the cooling system is contained within a single piece of extruded metal. Because fewer parts are used in the assembly, the chances of leakage due to part failure is reduced.

The system provides higher efficiency in heat extraction. The surface area that the coolant comes in contact with is increased. The greater the surface area available for contact with a liquid coolant, the quicker and more efficient the heat removal becomes.

Lower flows for liquid cooling can be used, which allows for use of smaller pumps, reduced energy usage in pumping the coolant, and a simplified mechanical design.

Furthermore, because the cooling system is an integral structural part of the motor, a more reliable and robust design is possible as it comprises a single piece. It is less likely to be leak, break, or crack as a result of thermal stress, usage over time, or an accidental puncture.

The system can be made at a lower cost due to its reduced design complexity and part count. Parts can be manufactured using high volume manufacturing methods, and require minimal machining.

Having thus described several illustrative embodiments, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to form a part of this disclosure, and are intended to be within the spirit and scope of this disclosure. While some examples presented herein involve specific combinations of functions or structural elements, it should be understood that those functions and elements may be combined in other ways according to the present disclosure to accomplish the same or different objectives. In particular, acts, elements, and features discussed in connection with one embodiment are not intended to be excluded from similar or other roles in other embodiments.

Additionally, elements and components described herein may be further divided into additional components or joined together to form fewer components for performing the same functions.

Accordingly, the foregoing description and attached drawings are by way of example only, and are not intended to be limiting.

What is claimed is: