Patent Application
20160261169
The present invention relates generally to an electric motor assembly and, more particularly, to an efficient motor cooling system that can be used to cool the rotor of a motor assembly.
In response to the demands of consumers who are driven both by ever-escalating fuel prices and the dire consequences of global warming, the automobile industry is slowly starting to embrace the need for ultra-low emission, high efficiency cars. While some within the industry are attempting to achieve these goals by engineering more efficient internal combustion engines, others are incorporating hybrid or all-electric drive trains into their vehicle line-ups. To meet consumer expectations, however, the automobile industry must not only achieve a greener drive train, but must do so while maintaining reasonable levels of performance, range, reliability, safety and cost.
The most common approach to achieving a low emission, high efficiency car is through the use of a hybrid drive train in which an internal combustion engine (ICE) is combined with one or more electric motors. While hybrid vehicles provide improved gas mileage and lower vehicle emissions than a conventional ICE-based vehicle, due to their inclusion of an internal combustion engine they still emit harmful pollution, albeit at a reduced level compared to a conventional vehicle. Additionally, due to the inclusion of both an internal combustion engine and an electric motor(s) with its accompanying battery pack, the drive train of a hybrid vehicle is typically much more complex than that of either a conventional ICE-based vehicle or an all-electric vehicle, resulting in increased cost and weight. Accordingly, several vehicle manufacturers are designing vehicles that only utilize an electric motor, or multiple electric motors, thereby eliminating one source of pollution while significantly reducing drive train complexity.
In order to achieve the desired levels of performance and reliability in an electric vehicle, it is critical that the temperature of the traction motor remains within its specified operating range regardless of ambient conditions or how hard the vehicle is being driven. A variety of approaches have been used to try and adequately cool the motor in an electric car. For example, U.S. Pat. No. 6,191,511 discloses a motor that incorporates a closed cooling loop in which the coolant is pumped through the rotor shaft. A stationary axial tube mounted within the hollow rotor shaft injects the coolant while a series of blades within the rotor assembly pump the coolant back out of the rotor shaft and around the stator. Heat withdrawal is accomplished using fins integrated into the motor casing that allow cooling via ambient air flow.
U.S. Pat. No. 7,156,195 discloses a cooling system for use with the electric motor of a vehicle. The refrigerant used in the cooling system passes through an in-shaft passage provided in the output shaft of the motor as well as the reduction gear shaft. A refrigerant reservoir is formed in the lower portion of the gear case while an externally mounted cooler is used to cool the refrigerant down to the desired temperature.
U.S. Pat. No. 7,489,057 discloses a rotor assembly cooling system utilizing a hollow rotor shaft. The coolant feed tube that injects the coolant into the rotor shaft is rigidly coupled to the rotor shaft using one or more support members. As a result, the rotor and the injection tube rotate at the same rate. The coolant that is pumped through the injection tube flows against the inside surface of the rotor shaft, thereby extracting heat from the assembly.
While there are a variety of techniques that may be used to cool an electric vehicle's motor, these techniques typically only provide limited heat withdrawal. Accordingly, what is needed is an effective cooling system that may be used with the high power density, compact electric motors used in high performance electric vehicles. The present invention provides such a cooling system.
The present invention provides a motor assembly with an integrated rotor cooling system, where the motor assembly is comprised of (i) a stator contained within a motor enclosure; (ii) a rotor shaft passing between the first end cap and the second end cap of the motor enclosure; and (iii) a rotor assembly mounted to the rotor shaft. The rotor assembly is comprised of a plurality of lamination discs assembled into a rotor stack, where each of the lamination discs include a plurality of slots co-aligned within the rotor stack and through which pass a plurality of conductive rotor bars, and a plurality of coolant apertures aligned within the rotor stack to form a plurality of coolant passageways that pass through the rotor stack between a first end surface and a second end surface of the stack.
The plurality of coolant passageways that pass through the rotor stack may be configured such that each coolant passageway (i) runs parallel to the rotor stack's cylindrical axis; (ii) is in a right-handed or a left-handed helical pattern centered about the rotor stack's cylindrical axis; (iii) is in a right-handed or a left-handed spiral pattern about the rotor stack's cylindrical axis; or (iv) pass directly through the rotor stack in a non-helical and a non-spiral pattern, where the distance between each of the coolant passageways and the rotor stack's cylindrical axis increases between the first and second end surfaces of the rotor stack.
In another aspect, each of the lamination discs may be stamped from metal and coated with an electrically insulating coating. The plurality of coolant apertures corresponding to each of the lamination discs may be formed by a stamping or a boring process.
In another aspect, the assembly further includes a coolant pump for injecting a coolant into the motor assembly and through the coolant passageways within the rotor stack. The coolant, which may be comprised of either oil or air, may be pressurized.
In another aspect, the assembly may further include first and second bearing assemblies, where the first bearing assembly is interposed between a first portion of the rotor shaft and the first end cap, and where the second bearing assembly is interposed between a second portion of the rotor shaft and the second end cap.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.
It should be understood that the accompanying figures are only meant to illustrate, not limit, the scope of the invention and should not be considered to be to scale. Additionally, the same reference label on different figures should be understood to refer to the same component or a component of similar functionality.
As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises”, “comprising”, “includes”, and/or “including”, as used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” and the symbol “/” are meant to include any and all combinations of one or more of the associated listed items. Additionally, while the terms first, second, etc. may be used herein to describe various steps or calculations, these steps or calculations should not be limited by these terms, rather these terms are only used to distinguish one step or calculation from another. For example, a first calculation could be termed a second calculation, similarly, a first step could be termed a second step, similarly, a first component could be termed a second component, all without departing from the scope of this disclosure.
The motor and cooling systems described and illustrated herein are generally designed for use in a vehicle using an electric motor, e.g., an electric vehicle (EV), and may be used with a single speed transmission, a dual-speed transmission, or a multi-speed transmission. In the following text, the terms “electric vehicle” and “EV” may be used interchangeably and may refer to an all-electric vehicle, a plug-in hybrid vehicle, also referred to as a PHEV, or a hybrid vehicle, also referred to as a HEV, where a hybrid vehicle utilizes multiple sources of propulsion including an electric drive system.
At one end of rotor shaft 113 is a drive gear 117. Although not shown in this figure, drive gear 117 is contained within a gearbox (i.e., gear housing). The gearbox may be separate from motor 100; alternately, the gearbox or at least one wall of the gearbox may be integral with front motor housing member 103. An exemplary configuration utilizing an integrated motor/gearbox housing is shown in co-assigned U.S. patent application Ser. No. 14/503,683, filed 1 Oct. 2014, the disclosure of which is incorporated herein for any and all purposes.
Each disc 401 (or each disc 401 and each interposed spacer disc) includes a plurality of peripherally spaced openings or slots 403 through which conductive bars 303 are inserted or cast. Conductive bars 303 are typically fabricated from aluminum or copper. Slots 403, all of which have substantially the same shape and dimensions, have a shape that is complementary to the cross-sectional shape of conductive bars 303. At either end of the rotor assembly an end ring 201 is formed by mechanically and electrically joining together the ends of the conductive bars that extend beyond the stack. A containment ring 203 may be fit over end rings 201, thus helping to prevent end ring creep due to centripetal forces.
Preferably slots 403 have an approximately rectangular shape. Slots 403 may align such that they extend axially through stack 301, thus allowing each of the conductive bars 303 to be aligned in parallel with the rotor shaft. Alternately, slots 403 may be slightly skewed, thereby causing the conductive bars 303 within the rotor assembly to be oblique to the axis of the rotor shaft. It will be appreciated that the rotor assembly of the present invention is not limited to lamination discs that utilize a specific number of slots 403, nor is it limited to a specific shape for bars 303/slots 403, nor is it limited to a specific slot alignment configuration, rather the number, shape and alignment of the bars and slots in the figures are only meant to illustrate, not limit, the invention.
As shown in
In accordance with the invention, each disc 401 of stack 301 includes at least one aperture 409, and preferably a plurality of apertures 409, that allow coolant to flow through the lamination stack, thereby helping to cool the rotor assembly. A plurality of coolant apertures 409, preferably evenly spaced about the stack's central axis, insure that rotor balance is maintained. Rotor balance is especially important for a high speed motor, such as those commonly used in an electric vehicle. Additionally, the use of a plurality of evenly spaced coolant apertures in stack 301 helps to provide more efficient, as well as more uniform, cooling of the rotor assembly. In the embodiment illustrated in
As each lamination disc 401 includes a set of coolant apertures 409, the relative locations of each of these apertures from disc to disc will determine the coolant passageways through the lamination stack. In general, the pattern of coolant flow passageways through the lamination stack is selected to achieve optimal heat transfer out of the rotor assembly. Factors that may influence the selection of a specific configuration of coolant apertures, and thus a particular coolant flow pattern, include the intended coolant, e.g., air versus a liquid coolant, as well as the intended application for the motor, e.g., a motor in a hybrid vehicle versus primary propulsion motor in an all-electric vehicle versus a non-vehicle motor.
While the configuration shown in
While helical coolant passageways provide efficient and balanced use of the space between the conductor slots and the central bore, it should be understood that other coolant passageway configurations may also be used with the invention. For example, each coolant passageway of a four passageway configuration is shown individually in
It will be appreciated that the invention may utilize coolant passageways other than those described above. For example and as illustrated in
There are a variety of techniques that may be used to form the coolant passageways that pass through the lamination stack. For example, the passageways may be bored after the lamination stack is assembled. The inventor has found, however, that the preferred fabrication approach is to incorporate the requisite number of coolant apertures into each lamination disc, for example using the same stamping process used to fabricate the discs. Then during assembly of the lamination stack, the laminates are positioned to achieve the desired coolant passageways. While a typical lamination stack utilizes a large number of discs, the eight discs shown in
The lamination discs shown in
As previously described, either air or a liquid coolant can be forced through the coolant passageways formed within an electric motor's rotor assembly configured in accordance with the invention. Furthermore, any of a variety of cooling systems may be used to pump coolant through the coolant passageways. An exemplary cooling system is shown in
In the exemplary cooling system illustrated in
Rotor shaft 113 includes one or more intake thru-holes 1215 immediately adjacent to the region defined by rotor shaft 113, the bore of end cap 103, and seals 1211/1213. Intake thru-hole(s) 1215 allows coolant passing through coolant passageway 1207 to flow into the central, hollow region 1201 of rotor shaft 113. The coolant within region 115 is then forced out of shaft 113 through multiple thru-holes 1217, this coolant flowing throughout region 1219 of the motor enclosure. The coolant within the motor enclosure then flows through the coolant passageways 1221 integrated into the rotor stack in accordance with the invention, and as described above. After passing through the rotor stack coolant passageways 1221, the coolant flows into area 1223 of the motor enclosure prior to passing through one or more output apertures 1225 before being collected into coolant reservoir 1227. Reservoir 1227 is coupled to coolant pump 1205. The heat absorbed by the coolant can be transferred to the ambient environment or to another thermal system (e.g., refrigeration system) using any of a variety of well-known techniques.
The embodiment described above provides efficient heat removal via multiple thermal passageways. Specifically, circulating the coolant throughout the system allows heat to be removed via direct transfer between the coolant and the rotor shaft (e.g., via region 1201 within shaft 113), between the coolant and rotor 111 via coolant passageways 1221, and between the coolant and the stator 115. This approach also effectively cools the motor bearings.
Systems and methods have been described in general terms as an aid to understanding details of the invention. In some instances, well-known structures, materials, and/or operations have not been specifically shown or described in detail to avoid obscuring aspects of the invention. In other instances, specific details have been given in order to provide a thorough understanding of the invention. One skilled in the relevant art will recognize that the invention may be embodied in other specific forms, for example to adapt to a particular system or apparatus or situation or material or component, without departing from the spirit or essential characteristics thereof. Therefore the disclosures and descriptions herein are intended to be illustrative, but not limiting, of the scope of the invention.
