The present disclosure relates to improving efficiency of an electronic machine, particularly to thermal management in and around the electronic circuitry of the electronic machine.
Rotary electric machines include electric motors, alternators, electric generators, and devices that selectively operate as either an electric motor or generator. An alternator is a type of generator that includes a stationary stator and a rotor that rotates about an axis, and in which, during machine operation, a regulated direct current passes through the field winding of the rotor to induce an alternating current in the stator windings. Rectifier circuitry rectifies the alternating current to generate a direct current voltage that is compatible with the electrical system of a vehicle, most notably the vehicle battery.
Typically, rectifier circuits employ two diodes per stator phase to convert the alternating current flowing through the stator winding associated with a stator phase to a direct current voltage; the rectified DC voltage typically includes a corresponding voltage ripple. See generally, Bradfield, M., Improving Alternator Efficiency Measurably Reduces Fuel Costs, pgs. 9-12, http://www.delcoremy.com/documents/high-efficiency-white-paper.aspx, © DelcoRemy, 2008.
Some rectifier circuits provide active rectification, also referred to as synchronous rectification, which employs MOSFET-based rectifier bridges integrated into a discrete electronic module or block to generate the direct current voltage. Although the MOSFET-based rectifier circuits minimize the high voltage drop and power consumption experienced with conventional diode rectifiers, resistive losses in the stator wires and the switching losses in the MOSFET-based electronic rectifier modules generate heat that, left unabated, can thermally stress and/or result in eventual failure of the electric machine. As a related problem, active rectifier circuits may include additional control circuitry which increases the overall package size of the discrete electronic blocks. Challenges arise in fitting such MOSFET-based rectifier circuits in smaller sized alternators.
Electric machines typically include a fan that generates airflow over or about the rectifier circuitry. In alternators, this airflow is commonly constrained by the air inlet size and shape, the size of the MOSFET-based electronic modules, and/or the rectifier bridge heat sinking arrangement, which typically funnels the airflow over a heat sink surface. The air exchange efficiency often suffers due to uneven loading caused by non-uniformly distributed air inlets. Also, air inlets located near the exhaust air outlets draw in and recirculate exhaust air through the electric machine, which increases the bulk temperature of cooling air passing over the rectifier circuitry. The net effect is to increase the operating temperature of the electronic machine, which may thermally stress components and decrease power efficiency. Id., pg. 23.
Accordingly, there is a need for an improved electric machine design that reduces thermal stress, increases the power efficiency of electric machines, and addresses machine electronic component considerations, particularly regarding space, power efficiency, and thermal issues associated with MOSFET-based active rectifiers in alternators.
The present disclosure addresses the above thermal management issues and shortcomings of prior electrical machines in connection therewith.
The present disclosure provides a rotary electric machine through which cooling air is passed during machine operation. The machine includes a stator, and a rotor operably coupled with and surrounded by the stator. A frame is connected to the stator, and has a frame air inlet, a frame air outlet, and a first airflow space located between the frame air inlet and the frame air outlet into which a first portion of cooling air is receivable through the frame air inlet and from which the first portion of cooling air is expelled through the frame air outlet. A cover overlies the frame. The cover has a cover air inlet and defines a second airflow space having a cover air outlet. The second airflow space is located between the cover air inlet and the cover air outlet, and is receivable of a second portion of cooling air through the cover air inlet. The second portion of cooling air is drawn from the second airflow space through the cover air outlet and expelled with the first portion of cooling air through the frame air outlet. During machine operation cooling air in the first airflow at a location proximate the cover air outlet is at a first speed and a first pressure and cooling air in the second airflow space at a location proximate the cover air outlet is at a second speed and a second pressure. The first speed is greater than the second speed, and the first pressure is less than the second pressure. Consequently, a venturi effect induces movement of the second portion of the cooling air through the second airflow space and the cover air outlet in response to movement of the first portion of cooling air past the cover air outlet.
A further aspect of this disclosure is that a portion of the cover air outlet is defined by the frame air outlet.
A further aspect of this disclosure is that the frame defines a portion of the second airflow space.
A further aspect of this disclosure is that the cover air inlet and the frame air inlet are both receivable of the first portion of cooling air.
An additional aspect of this disclosure is that the stator and rotor are coaxial relative to a central axis about which the rotor is rotatable relative to the stator and the cover, and the frame air inlet and the cover air inlet are aligned in a direction parallel with the central axis.
Furthermore, an aspect of this disclosure is that the machine includes a fan rotatable in unison with the rotor, the fan adapted to draw a flow of cooling air through the cover air inlet during machine operation.
An additional aspect of this disclosure is that the stator and rotor are coaxial relative to a central axis about which the rotor is rotatable relative to the stator and the cover, and both the cover air inlet and the frame air inlet are disposed at respective locations that are radially inward of both the cover and frame air outlets.
An additional aspect of this disclosure is that the stator and the rotor are coaxial relative to a central axis along which is provided a reference point axially inward of the frame air outlet, the frame air outlet and the cover air outlet are respectively located at a first distance and a second distance from the reference point in a direction parallel with the central axis, and the second distance is greater than the first distance.
Furthermore, an aspect of this disclosure is that the frame air inlet and the cover air inlet are respectively located at a third distance and a fourth distance from the reference point in a direction parallel with the central axis, and the fourth distance is greater than the third distance.
Further still, an aspect of this disclosure is that the fourth distance is greater than either of the first distance and the second distance.
A further aspect of this disclosure is that the stator and the rotor are coaxial relative to a central axis, the frame air inlet is radially inward of the frame air outlet, and the frame includes a frame wall portion located between the first airflow space and second airflow space and extending between the frame air inlet and the frame air outlet.
An additional aspect of this disclosure is that the frame wall portion is oriented at an acute angle relative to the central axis.
Furthermore, an aspect of this disclosure is that, relative to the central axis, the cooling air receivable into the first airflow space and the second airflow space is guided in directions axially towards the rotor and radially outwardly.
An additional aspect of this disclosure is that the cover includes a wall portion located between the cover air inlet and outlet and is substantially parallel with and spaced from the frame wall portion.
Furthermore, an aspect of this disclosure is that the frame wall portion defines a heat sink, and further comprising at least one heat source in conductive thermal communication with the heat sink and located in the second air flow space.
A further aspect of this disclosure is that the stator and rotor are coaxial relative to a central axis about which the rotor is rotatable relative to the stator and the cover, the frame air outlet is one of a plurality of frame air outlets, and the cover air outlet is one of a plurality of cover air outlets, each cover air outlet paired with and defined by a frame air outlet, the paired cover air outlets and frame air outlets distributed about the central axis.
An additional aspect of this disclosure is that the cover has a cover edge extending about the central axis, the cover edge sealably engaging the frame at locations between adjacent frame air outlets, whereby cooling air expelled from the frame air outlets is prevented from entering the second airflow space along the cover edge.
Furthermore, an aspect of this disclosure is that the machine includes an insulator disposed between the cover edge and the frame, whereby the cover edge sealably engages the frame at locations between circumferentially adjacent frame air outlets through the insulator, and wherein the insulator defines each of the plurality of cover air outlets.
The present disclosure also provides a method of moving cooling air through a rotary electric machine. The method includes: drawing a first portion of cooling air through a frame air inlet and into a first airflow space located between the frame air inlet and a frame air outlet; directing the first portion of cooling air within the first airflow space towards the frame air outlet and past a cover air outlet at a first speed and first pressure; inducing a second portion of cooling air to flow through a second airflow space located between a cover air inlet and the cover air outlet at a second speed and second pressure respectively lower than the first speed and higher than the first pressure; drawing the second portion of cooling air from the second airflow space through the cover air outlet and into combination with the first portion of cooling air flowing past the cover air outlet; and expelling the combined first portion of cooling air and second portion of cooling air through the frame air outlet.
The present disclosure also provides another method of moving cooling air through a rotary electric machine. This method includes: drawing a first portion of cooling air into a first airflow space located between a frame air inlet and a frame air outlet; directing the first portion of cooling air to flow past a cover air outlet of a second airflow space that is located between a cover air inlet and the cover air outlet; inducing a second portion of cooling air to flow through the second airflow space as a function of the flow of the first portion of cooling air that passes the cover air outlet; and expelling the first portion of cooling air and the second portion of cooling air through the frame air outlet.
The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of the disclosed device and method, the drawings are not necessarily to scale or to the same scale and certain features may be exaggerated in order to better illustrate and explain the present disclosure. Moreover, in accompanying drawings that show sectional views, cross-hatching of various sectional elements may have been omitted for clarity. It is to be understood that any omission of cross-hatching is for the purpose of clarity in illustration only.
The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention.
Each exemplary electric machine described herein is an alternator or AC generator, but it is to be understood that the teachings of the present disclosure may also be applied to other types of electric rotary machines, such as electric motors or DC generators, for example.
Electric machine 20 includes housing 22, frame assembly 24 including frame end member 26 which is attached to housing 22 by fasteners 28, and cover 30 having central air inlet 32. Central air inlet 32 of cover 30 includes a plurality of cover air inlet openings 34. Frame end member 26 may be cast, molded, or otherwise formed of a rigid, thermally conductive material such as an aluminum alloy. Cover 30 is injection molded from a suitably rigid but somewhat pliable, thermally stable thermoplastic.
Cover 30 is secured to frame end member 26 in a suitable, well-known manner, such as by screws (not shown) or elastically deformable interlocking tabs (not shown). Cover 30 engages frame assembly 24 to form a plurality of cover air outlets 36, and cover airflow space 38 which is located between cover air outlets 36 and cover air inlet 32. Frame end member 26 defines central airflow space or passage 40 having frame air inlet 42, a plurality of frame air outlets 44, and frame airflow space 46 located between frame air inlet 42 and frame air outlets 44.
Machine 20 further includes annular stator 50 fixed to surrounding housing 22, and generally cylindrical rotor 52 surrounded by stator 50. Stator 50 includes stator core 54 having stator teeth (not shown) between which are received longitudinal segments (not shown) of stator windings 60 which have end turnings 62 located axially outside of stator core 54, as shown in
Axial and radial directions mentioned herein are relative to central axis 66, i.e., axial directions are parallel, and radial directions are perpendicular, to axis 66. Moreover, characterizations as top or bottom are arbitrary, but defined with respect to the orientation of machine 20 (e.g., alternator 20) as shown in
Referring to
As best seen in
Within frame airflow space 46 is centrifugal fan 104 disposed about driveshaft 64 between bearing support 70 and rotor 52. Fan 104 rotates in unison with rotor 52 and driveshaft 64, and may be rotatably coupled directly to driveshaft 64 or to rotor 52. As can be understood from
Fan 104 draws air into cover air inlet 32 and through central airflow passage 40. Fan 104 is generally circular, and includes a plurality of fan blades 110 integrally attached to fan face 112, which may be substantially planar as shown, or generally frustoconical. Fan blades 110 generally extend to circular outer edge 114 of fan face 112. Cooling air moves towards fan 104 generally along the axial direction, and is expelled from rotating fan 104 in radial directions, in a manner well-known in the art. Fan blades 110 may be curved, as shown in
Cover 30 has interior surface 130 and exterior surface 132 which define generally cylindrical cover side wall 134. Cover side wall 134 extends between generally circular, axially inner rim 136 and generally frustoconical portion 138 of cover 30. Cover frustoconical portion 138 extends between cylindrical side wall 134 and cover top wall 98 which, as mentioned above, includes central air inlet 32 and top wall central portion 96. As discussed further below, cover rim 136 sealably engages portions of frame end member 26 to form cover air outlets 36. Cover 30 also includes axially outwardly projecting collar 140 located in frustoconical portion 138 that defines an opening through which projects alternator B+ terminal 142, which is externally accessible for connection to the vehicle battery (not shown) in a well-known manner.
The interior of bearing support 70 is substantially enclosed at its axially outer end by cover 30. The portion of cover interior surface 130 defined by top wall central portion 96 is provided with axially inwardly projecting annular collar 144 that continually surrounds the open, axially outer end of cylindrical bearing support neck portion 76, which is covered by top wall central portion 96. Top wall central portion 96 is joined to the surrounding portion of cover top wall 98 a plurality of radially extending connecting members 146 that define the plurality of cover inlet openings 34, as shown in
Alternative electric machine embodiments having respectively different cover configurations are now described with reference to
Except as described herein or depicted in the drawings, second embodiment machine 20B, a portion of which is shown in
Except as described herein or depicted in the drawings, third and fourth embodiment machines 20C and 20D, portions of which are shown in
In applications of machine 20C or 20D wherein cover central air inlet 32 is ducted, it is preferable that the inlet (not shown) of the cooling air duct connectable to cover air inlet 32 be remote from frame air outlets 44 and other heat sources. The cooling air duct may extend from cover 30C, 30D to a location at which the duct inlet is provided with a source of cooling air that is distant from frame air outlets 44 and other sources of heat, and also protected against direct road splash, thereby better protecting against cooling air recirculation and the ingestion of water and other contaminants such as road salt into the machine's airflow spaces 38, 46. Other than its inlet opening(s) 34C, 34D, cover 30C or 30D is preferably bereft of voids through which air may be drawn into machine 20C, 20D, particularly air that has previously been exhausted from frame air outlets 44 and might otherwise be recirculated through the machine.
Except as described herein or depicted in the drawings, fifth embodiment machine 20E, a portion of which is shown in
In each of machines 20, 20B, 20C, 20D, and 20E, the respective cover central air inlet 32 is located about and near central axis 66 to maximize its distance from frame air outlets 44. Thus, the management of cooling air in accordance with the present disclosure reduces the possibility of cooling air recirculation, and facilitates a minimal average bulk temperature of cooling air entering the cover air inlet 32.
Returning now to machine 20 in describing other, common aspects of machines 20, 20B, 20C, 20D, and 20E,
Bearing support 70 is joined to frustoconical portion 170 through a plurality of circumferentially spaced support members 172, as best seen in
Frame end member 26 is provided with a circumferentially distributed arrangement of elongate slots 174 each having a first end 176 located in frame cylindrical portion 168 and a second end 178 located in frame frustoconical portion 170. Slots 174 may be of substantially uniform size and shape, and symmetrically located about the periphery of frame end member 26. Slots 174 each extend between opposite first and second ends 176, 178 and completely through the thickness of frame end member 26, i.e., between its exterior and interior surfaces 160, 162. Both cover air outlets 36 and frame air outlets 44 are defined by slots 174, as discussed further below.
Generally frustoconical frame exterior surface 160 includes above-mentioned regulator heat sink portion 92, which is provided with mounting surface 180 radially aligned with the omitted portion of cylindrical bearing support neck portion 76. Brush holder/regulator assembly 84 is affixed to mounting surface 180 such that regulator master 90 and mounting surface 180 are in thermally conductive contact. Heat conductively transferred from brush holder/regulator assembly 84 through mounting surface 180 is absorbed by heat sink portion 92, and generally by frame end member 26, and is convectively transferred to the cooling airflow through machine 20, as described herein.
Frame exterior surface 160 also includes a plurality of heat sink portions 182 (e.g., three, as shown), each defining a mounting surface 184. Each mounting surface 184 is generally planar, and has an electronics module 186 affixed thereto in thermally conductive contact, as by threaded fasteners (not shown) that extend through clearance holes 188 in modules 186 and are received in threaded holes 190 of each heat sink portion 182. Heat transferred conductively from modules 186 to mounting surfaces 184 is absorbed by heat sink portions 182, and generally by frame end member 26, and is convectively transferred to the cooling airflow through machine 20, as described herein.
Referring to
Preferably, baffle 200 is located between cover axially inner rim 136 and frame end member frustoconical portion 170. Baffle 200 may be similar to the phase lead insulator referred to in above-mentioned U.S. patent application Ser. No. 13/801,908, entitled PHASE LEAD INSULATOR, filed Mar. 13, 2013, the disclosure of which is incorporated herein by reference. Baffle/phase wire insulator 200 (identified by reference numeral 48 in the incorporated reference) is a circumferential ring formed of a flexible, electrically insulative, compressible material. On frame exterior surface 160, between adjacent slots 174, are baffle ledge portions 202 positioned on frustoconical portion 170 between ends 176, 178 of circumferentially arranged slots 174. Baffle 200 extends continuously about the radially outer periphery of frame frustoconical portion 170, with its bottom surface alternatingly traversing slots 174 and abutting ledge portions 202. Cover rim 136 is placed in abutting contact with the top surface of baffle 200 and, with cover 30 secured to frame end member 26, baffle 200 is compressed between cover rim 136 and baffle ledge portions 202.
Each elongate slot 174 has first and second portions 204, 206 that are respectively defined by opposite first and second slot ends 176, 178. First slot portions 204 are in fluid communication with frame airflow space 46 and define frame air outlets 44. Second slot portions 206 are in fluid communication with both frame airflow space 46 and cover airflow space 38 and define cover air outlets 36. The separation between first and second slot portions 204, 206 is defined by baffle 200. With regard to most slots 174, this occurs at the juncture of cover axially inner rim 136 and frame end member exterior surface 160, which is located along those slots 174 between their respective slot ends 176, 178, where baffle 200 traverses the respective slot 174. Thus, baffle 200 is disposed between cover 30 and frame exterior surface 160, and cover 30 sealably engages frame end member 26 through baffle 200 at baffle ledge portions 202. Accordingly, cover 30 operatively engages the top surface of baffle 200 to form cover airflow space 38, which is located between cover interior surface 130 and frame exterior surface 160.
Baffle 200, the edges of first slot portions 204, and cover 30 which engages frame end member 26 through baffle 200, define frame air outlets 44 through which cooling air is radially exhausted from frame airflow space 46 to ambient space outside of machine 20. Baffle 200, the edges of second slot portions 206, and cover 30 which engages frame end member 26 through baffle 200, define cover air outlets 36 through which cooling air is drawn from cover airflow space 38 into frame airflow space 46. Thus, cover 30 sealably engages frame end member 26 to form cover air outlets 36 and frame air outlets 44, with each cover air outlet 36 paired with a respective one of frame air outlets 44 through their common slot 174. The passage of cooling air from cover airflow space 38 is thus limited to entry into frame airflow space 46, and the sealed engagement of cover rim 136 to baffle ledge portions 202 helps to prevent the recirculation of cooling air exhausted through frame air outlets 44, back into cover airflow space 38 at locations along the interface between cover rim 136 and baffle ledge portions 202. Notably, as shown in
Reference point 208 may be chosen along central axis 66 axially inward of frame end member 26, and therefore axially inward of slot first ends 176. For example, reference point 208 may be located at first end 68 of driveshaft 64 or perhaps, near the center of rotor 52. From the axial position of reference point 208, in an axially outward direction parallel to central axis 66, frame air outlets 44 are located at first distance d1; cover air outlets 36 are located at second distance d2; frame air inlet 42 is located at third distance d3; and cover air inlet 32 is located at fourth distance d4. The relative locations of cover air inlet 32, cover air outlets 36, frame air inlet 42, and frame air outlets 44 may thus be described with reference to
Referring to
Projecting axially inwardly from the bottom of baffle 200 and extending radially inwardly relative to baffle radially inner surface 216 are protrusions 218 adapted to be received into cooperating slots 174. In the depicted embodiment, these cooperating slots 174 are axially aligned with wire guide apertures 210. As shown in
Referring still to
Baffle 200 may have radially outwardly extending air vectoring walls 228 projecting from its radially outer surface 230 at locations substantially radially aligned with the positions of electronic modules 186. Air vectoring walls 228 guide the flow of cooling air once exhausted from frame air outlets 44 radially outwardly and forward, in directions away from cover 30 and cover inlet 32, to help ensure that cooling air exhausted from frame air outlets 44 is not recirculated back into cover and frame airflow spaces 38, 46, and to help ensure that the heat of the exhausted air is not transferred through cylindrical cover side wall 134 to regions of cover airflow space 38 proximate to modules 186.
As described above, frame airflow space 46 is located between frame air inlet 42 and frame air outlets 44, and cover 30 overlies and engages frame end member 26, preferably through baffle 200, to form air outlets 36 from cover airflow space 38. During machine operation, cooling air in frame airflow space 46 downstream of fan 104, flowing under the influence of fan 104 at high speed (relative to air movement through cover airflow space 38) towards frame air outlets 44, passes second portions 206 of slots 174 (i.e., cover air outlets 36) and interacts with relatively slower moving air in cover airflow space 38 to produce a venturi effect and draw the slower moving air into combination with the faster moving air through cover air outlets 36.
Those of ordinary skill in the relevant art well-understand the venturi effect, which is employed in machine 20 as a function of fluid pressure and flow velocity differences between cooling air located on opposite sides of cover air outlets 36. Particularly, a first portion of cooling air enters frame airflow space 46 through frame air inlet 42 and is expelled radially from frame airflow space 46, under force imparted by fan 104, through frame air outlets 44. Meanwhile, a second portion of cooling air is received into cover airflow space 38 from cover air inlet 32 and is caused to be drawn, under a venturi effect, through cover air outlets 36 and into frame airflow space 46 by the first portion of cooling air being directed past cover air outlets 36 within frame airflow space 46. The second portion of cooling air is combined with the first portion, and the combined first and second cooling air portions are expelled from machine 20 through frame air outlets 44.
More particularly, the first portion of cooling air flowing through frame airflow space 46 and directed towards frame air outlets 44 is at a first pressure and a first velocity as it passes across the exit from cover air outlets 36. The second portion of cooling air at the entrance to cover air outlets 36 within cover airflow space 38 is at a second pressure comparatively greater than the first pressure and a second velocity comparatively less than the first velocity. These relative pressure and velocity conditions induce a venturi effect across cover air outlets 36, which causes the second portion of cooling air to be drawn through cover air outlets 36 and into combination with the first portion of cooling air. The combined first and second portions of cooling air are together exhausted from machine 20 through frame air outlets 44.
As will also be understood by one of ordinary skill in the relevant art, movement of the second portion of cooling air from cover airflow space 38 through cover air outlets 36 reduces the pressure of cooling air within cover airflow space 38 near the entrances to cover air outlets 36. This pressure reduction induces the flow of cooling air from inside of cover air inlet 32 into and through cover airflow space 38 on a continual basis during operation of machine 20, creating the airflow within cover airflow space 38.
It is to be understood that while preferably to include baffle 200 in machine 20 to seal cover 30 to frame end member 26, control the flow of cooling air within and from cover airflow space 38, and from frame air outlets 44, and to insulate and wires of stator winding 60 and route them to module terminals 194, 196, it is envisioned that baffle 200 may be omitted from certain non-depicted embodiment of machine 20. In such embodiments, cover axially inner rim 136 may operably engage external surface 160 of frame end member 26 directly, for example at the sites of its baffle ledge portions 202, with a venturi effect inducing airflow from cover airflow space 38 to frame airflow space 46 through cover air outlets 36 remaining substantially as described above.
The second portion of cooling air flowing through cover airflow space 38 is convectively warmed by relatively warmer surfaces within cover airflow space 38 (e.g., by surfaces of frame end member 26, electronics modules 186, and regulator master 90). The continuous flow of cooling air through cover airflow space 38, which may be controlled as described above, flushes the warmed air from about those surfaces and from cover airflow space 38. The first portion of cooling air received into frame airflow space 46 convectively cools bearing support 70, interior surface 162 of frame end member 26, and the end turns 62 of stator windings 60 that are enclosed by frame end member 26.
In this regard, the advantage of machine 20 over prior rotary electric machines is readily apparent.
Cover 30P, having central cover air inlet 32P and side air inlet 232 is sealably engaged with frame end member 26P to define cover airflow space 38P between the interior surface of the cover 30P and backface portion exterior surface 160P. Alternator 20P includes frame air inlet 42P formed between the outer cylindrical surface of bearing support portion 72P and radially inner rim 164P of backface portion 170P. Frame airflow space 46P is defined between frame air inlet 42P and frame air outlets 44P. During operation of machine 20P, its fan draws cooling air though both central cover opening 32P and side air inlet 232, and through frame air inlet 42P. Frame air inlet 42P is defined by a radial gap of distance D1P between the outer cylindrical surface of bearing housing portion 72P and annular radially inner rim 164P of backface portion 170P.
Notably, air ingested into frame airflow space 46P is previously warmed by a part of it having been circulated through cover airflow space 38P, about the electronics packaged therein, and across backface portion exterior surface 160P. In other words, frame air inlet 42P also serves as the outlet from cover airflow space 38P. Cooling airflow drawn into machine 20P through central air inlet 32P and side air inlet 232, and passing through cover airflow space 38P, is warmed in cover airflow space 38P before being drawn, in combination with other, comparatively unwarmed cooling air received into machine 20P through central air inlet 32P, into dual purpose frame air inlet/cover air outlet 42P, which is a direct axial opening that limits the flow of air into frame airflow space 46P to the axial direction immediately upstream of the fan, causing the incoming airflow to impinge upon fan face 112P. The combined airflow drawn into frame air inlet/cover air outlet 42P, having already been partially warmed, undesirably raises the bulk temperature of the combined airflow in frame airflow space 46P relative to that drawn into cover air inlets 32P, 232, consequently reducing the ability of cooling air passing through frame airflow space 46P to convectively absorb heat from backface portion interior surface 162P and stator windings 60P. In machine 20, however, the first and second portions of cooling air absorb heat individually, whereby the ability of neither portion to absorb heat is adversely affected by the increased temperature of the other.
Furthermore, in addition to the above shortcomings of machine 20P, the inclusion of side air inlet 232 in cover 30P may permit warmed air exhausted through frame air outlets 44P to be recirculated back into cover airflow space 38P into the side air inlet 232, which increases the temperature of the cooling air received therein. Single, centrally located cover air inlet 32 of machine 20 mitigates that possibility, especially if the cover air inlet is ducted as described above.
Referring to
Referring to
Midlines 240 define the surface of an imaginary right circular cone whose apex coincides with convergence point 244. Each planar mounting surface 184 is tangential to the surface of the imaginary right circular cone and has a midline dimension LM (
Vertex angle θ may be in the range between 20° and 70°, i.e., 20°≦θ≦70°. In certain embodiments, vertex angle θ is in the range between 45° and 70°, i.e., 45°≦θ≦70°. In certain other embodiments, vertex angle θ is in the range between 50° and 60°, i.e., 50°≦θ≦60°. The projection of a mounting surface midline dimension LM rearwardly in a direction parallel to central axis 66 from an imaginary plane perpendicular to the central axis and, for example, intersecting the juncture between frame end member cylindrical and frustoconical portions 168, 170, decreases as vertex angle θ decreases. This is described in equation (1), wherein R1 is the radial distance from axis 66 to inner rim 164, and R2 is the radial distance from axis 66 to mounting surface edge 246:
The area of each mounting surface 184 is generally proportional to dimension LM. As shown, mounting surfaces 184 are generally rectangular. Thus, while substantially maintaining their respective widths, perpendicular to midline 240, substantially constant as midline dimension LM of mounting surfaces 184 increases, the area of mounting surface 184 also increases. Those of ordinary skill in the art will recognize that dimension LM of each mounting surface 184 may be increased along midline 240, thereby increasing its respective surface area, by decreasing vertex angle θ while holding R1 and R2 constant.
As an example, with the difference between R1 and R2 fixed, and radial frame air inlet gap distances D1 and D1P substantially equal, for a vertex angle θ equal to 55°, the midline dimension LM, of mounting surface 184 is increased by about twenty-two percent (22%) relative to LM of orthogonal module mounting surface 184P of prior alternator 20P shown in
In machine 20 at least some edges of mounting surfaces 184 may be substantially flush with frame end member exterior surface 160 at locations between heat sink portions 182. Alternatively, as shown, heat sink portions 182 include peripheral side surfaces 250 which project from frame end member exterior surface 160 at those locations. Referring to
Electronic modules 186 are positioned to minimally interfere with cooling airflow entering from cover inlet 32, and their bottom, heat-conducting surfaces are preferably located entirely within the bounds of mounting surfaces 184. In some embodiments of machine 20, a portion of at least one of electronic modules 186 can overhang scalloped, radially inner surface portion 252 of heat sink portion 182 as shown in
Moreover, the shape or slope of the interior surface 162 may be configured to maximize convective heat transfer between the frustoconical portion 170 and cooling air passing over interior surface 162, substantially independently of the shape or slope of exterior surface 160, particularly of its mounting surfaces 180 and 184, which may be configured to maximize conductive heat transfer from regulator master 90 and electronic modules 186 to frame end member 26.
The thicknesses of frame end member 26 need not be uniform along midlines 240; the angular dispositions of frame end member exterior and interior surfaces 160, 162 on frustoconical portion 170 may differ somewhat relative to the imaginary right circular cone. For example, interior surface 162 may be substantially disposed on a similar imaginary cone whose vertex angle β (shown in
In machine 20P, cooling air is received into frame airflow space 46P along an airflow path that is limited to being axially directed. The axial momentum of the cover air flow may cause a portion of the cooling air to directly impinge upon fan face 112P of the fan, which increases turbulence and induces eddy currents within frame airflow space 46P, as depicted by the curved, arrow-headed dot-dashed lines of
Generally, for a given radial gap distance D1, restrictions to airflow within central airflow space 40 will be reduced, and fan efficiency thus increased, by decreasing vertex angle β. Additionally, frame end member interior surface 162 is contoured proximate radially inner rim 164 to smoothly transition the flow of cooling air within frame airflow space 46, from a generally axial direction to directions having radial components, as the airflow approaches fan 104. Referring to
Transitional wall portion(s) 256 slants away or diverges from bearing support 70 in axially inward and radially outward directions. Referring to
The air exchange efficiency of fan 104 is improved in alternator 20, vis-à-vis alternator 20P, first by providing frustoconical portion 170 having a substantially conical interior surface 162, and also by selecting frame air entry angles φ that smooth the transition from axial to radial airflow within frame airflow space 46. In prior alternator 20P, as typical of prior machines, frame airflow space 46P is defined by frame end member interior surface 162P that is oriented substantially orthogonally relative to central axis 66, and has sharp-cornered transitional edge 256P at radially inner rim 164P, as shown in
In machine 20, the cooling air drawn through central airflow passage 40 passes along large axial gap D3 (
The combination of large-radii bend 260 and large axial gap D3 between rim 164 and shoulder 78 tends to minimize undesirable airflow eddy currents or turbulence experienced in prior machine 20P and, in turn, preserves the momentum of airflow received into central airflow space 40 as the airflow continues its passage through frame airflow space 46. Relative to machine 20P, the increased conservation of airflow momentum may increase the airflow velocity of the exhaust air towards and through the frame air outlets 44, minimizes eddy currents or turbulence within frame airflow space 46, and facilitates a strong suction force on cover air outlets 36 to draw warmed air from cover airflow space 38.
Accordingly, frame frustoconical portion 170 advantageously increases the available surface area to which electronic modules 186 may be mounted, and beneficially configures central airflow passage 40 such that the airflow path through frame airflow space 46 is not limited substantially to being only directly axial and directly radial, which would undesirably interrupt the momentum of cooling air flowing therethrough.
Referring to
Mounting surfaces 184 position the axially outermost edges 264 of their respective electronic modules 186 in proximity to portions of cover interior surface 130 associated with cover top wall 98, presenting cover gaps 266 through which cooling airflow is restricted within cover airflow space 38. Apart from other modifications such as to cover 30, modules 186 or their edges 264, and/or the positioning of modules 186 relative to frame frustoconical portion 170, providing a suitable cover gap 266 is also a consideration in selection of an appropriate vertex angle θ.
While exemplary embodiments incorporating the principles of the present invention have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
The present disclosure is related to the following filed patent applications: U.S. patent application Ser. No. 13/801,811, entitled HIGH EFFICIENCY B+ CONNECTION, filed Mar. 13, 2013 (Attorney Docket No. 22888-0073); U.S. patent application Ser. No. 13/801,908, entitled PHASE LEAD INSULATOR, filed Mar. 13, 2013 (Attorney Docket No. 22888-0074); and U.S. patent application Ser. No. ______, entitled ENHANCED ELECTRONICS COOLING FOR ELECTRIC MACHINES, filed ______ (Attorney Docket No. 22888-0076). The entire disclosures of all the above-listed patent applications are incorporated herein by reference.