Electric drive unit having cover assembly with integrated cooling channels

An electric drive unit for powering a load, e.g., road wheels of a motor vehicle, includes a housing having a floor section separating the housing into upper and lower chambers. The floor section defines an elongated drain opening, drain holes, and an oil supply port in fluid communication with an oil pump. A rotary electric machine is enclosed within the lower chamber, and has electrical leads positioned directly below the drain opening. A cover assembly is fastened to the housing within the upper chamber, and has a coolant channel assembly integrally connected to a cover plate. The coolant channel assembly includes electrical terminals that project through the drain opening and are fastened at a first distal end of the electrical terminals to the electrical leads. The cover assembly defines a primary coolant channel in fluid communication with the oil supply port, and directs oil to the electrical terminals.

INTRODUCTION

Electric motors, generators, and combined motor/generator units are broadly referred to as rotary electric machines, and are used to produce torque for use in a wide variety of systems. For instance, the individual phase windings of a polyphase/alternating current (AC) traction motor for a powertrain may be energized via a power inverter module, which in turn is electrically connected to a multi-cell battery pack or other direct current (DC) power supply. Heat is generated during sustained operation of the AC motor, including the phase leads, stator windings, electrical terminals or connectors, and other electrically-conductive machine structure. As a result, thermal management systems are typically used to regulate temperature of a rotary electric machine.

High-voltage polyphase electric machines are commonly used in powertrain drive units. For instance, a motor vehicle having an electric drivetrain uses one or more traction motors as prime movers. The rotary electric machine in a vehicular powertrain application may be used as part of a drive unit disposed within a housing and coupled to a set of road wheels, possibly via a final drive unit. Motor torque from the energized electric machine is directed to the road wheels to propel the vehicle. In a regenerating mode, torque from the electric machine may be used to generate electricity. The generated electricity is then directed to the individual battery cells to recharge the battery pack, and/or used to power onboard electrical accessories.

Unlike a hybrid electric vehicle in which an internal combustion engine is used as a prime mover, a battery electric vehicle lacks the engine, and thus lacks an engine-driven oil pump for circulating oil to the electric machine. As a result, oil distribution for the purpose of cooling the electric machine may be suboptimal, particularly at low rotational speeds of the electric machine. For instance, a rotor of the rotary electric machine may rotate within an oil pool and/or a spray tube may be used to help distribute oil onto exposed surfaces of the electric machine at low rotational speeds.

SUMMARY

An electric drive unit is disclosed herein. The electric drive unit includes a multi-chamber housing, e.g., a cast metal drive unit case, with the housing defining upper and lower chambers separated from each other by a floor section. The electric drive unit also includes a rotary electric machine disposed within the lower chamber. The electric machine is cooled via oil that is deposited onto the electric machine through the floor section and a cover assembly. The cover assembly, which includes electrical terminals configured to connect to the electric machine, is configured to direct oil onto the electrical terminals for the purpose of cooling the electrical terminals.

Regarding the upper and lower chambers of the housing, the terms “upper” and “lower” have their customary relative meaning, i.e., the upper chamber is positioned above the lower chamber. In the disclosed configuration, gravitational forces cause oil that is present in the upper chamber to flow in a directed manner onto targeted surfaces of the electric machine within the lower chamber. The cover assembly is specifically configured to direct oil to the electrical terminals as noted above, with the drain holes of the floor section also directing some of the oil onto other exposed surfaces of the electric machine.

The upper chamber of the housing receives oil through an oil supply port, e.g., a circular orifice or opening defined by the housing. The oil supply port may be in fluid communication with an oil pump. For instance, the electric drive unit may be optionally used as part of a powertrain having a final drive unit, with a mechanical oil pump driven by a gear element of the final drive unit, e.g., a ring gear. In such an embodiment, for instance when the electric drive unit used as part of a battery electric vehicle powertrain, the oil pump circulates oil to the oil supply port. However, absent use of the cover assembly described herein, the distribution of oil to the electrical terminals of the cover assembly may be less than optimal, e.g., by possibly requiring the use of additional hardware such as spray tubes, electric oil pumps, or other associated hardware.

According to an exemplary embodiment, the cover assembly may include a cover plate and a coolant channel assembly that are integrally connected together, e.g., welded or heat-staked to form an integral unit. The coolant channel assembly, which has first and second ends, secures the electrical terminals of the cover assembly at the first end. The second end of the coolant channel assembly defines a fluid inlet in proximity to the oil supply port, with the fluid inlet being configured to admit oil from the oil supply port.

An elongated primary coolant channel is defined by the integrally-connected cover plate and coolant channel assembly. The primary coolant channel directs oil along the length of the coolant channel assembly and toward the electrical terminals. The oil passes from the primary coolant channel into direct wetted contact with the electrical terminals, e.g., via shorter secondary channels each terminating at a respective one of the electrical terminals. The oil flows around a perimeter surface of the electrical terminals before passing through a narrow gap defined between each of the electrical terminals and the surrounding structure of the coolant channel assembly. Upon passing through the gap, the oil flows evenly downward via gravity along an exposed outer surface of the electrical terminals, and in this manner cools the electrical terminals.

A particular embodiment of the electric drive unit includes a housing having a floor section separating the housing into an upper chamber and a lower chamber, with the floor section defining an elongated drain opening, a plurality of drain holes, and an oil supply port in fluid communication with an oil pump. The drive unit, which powers a load, further includes a rotary electric machine enclosed within the lower chamber, and having electrical leads positioned directly below the elongated drain opening.

Additionally, the drive unit in this embodiment includes a cover assembly fastened to the housing within the upper chamber, and having a coolant channel assembly integrally connected to a cover plate. The coolant channel assembly includes electrical terminals that project through the elongated drain opening, and that are fastened at a first distal end of the electrical terminals to the electrical leads of the electric machine. The cover assembly, which defines a primary coolant channel in fluid communication with the oil supply port, is configured to direct oil admitted through the oil supply port to the electrical terminals to thereby cool the electrical terminals.

The rotary electric machine may be embodied as a polyphase electric machine having three or more phase leads as the electrical leads. The load may be a set of road wheels of a motor vehicle.

The coolant channel assembly may be separated from the electrical terminals by an annular gap, with the cover assembly defining secondary coolant channels that collectively direct the oil from the primary coolant channel into the annular gap. The annular gap in some embodiments has a width of less than 0.5 millimeters.

Each of the electrical terminals includes an annular shoulder having a radially-outermost surface. The annular gap in such an embodiment extends between the radially-outermost surface and the coolant channel assembly.

A respective second distal end of each the electrical terminals may project through the cover plate and be connected to a power inverter connector block.

A cover assembly is also disclosed for the electric drive unit, with the cover assembly in an exemplary embodiment having a cover plate fastened to the housing within the upper chamber, and a coolant channel assembly integrally connected to the cover plate. The cover assembly includes electrical terminals configured, when the cover assembly is in an installed position with respect to the housing, to project through the elongated drain opening, and to be fastened to the electrical leads of the rotary electric machine at a first distal end of the electrical terminals. The cover assembly also defines an elongated primary coolant channel that, in the installed position, is in fluid communication with the oil supply port, such that the cover assembly is configured to direct oil admitted through the oil supply port to the electrical terminals and thereby cool the electrical terminals.

A motor vehicle is also disclosed herein. In a possible embodiment, the motor vehicle includes a high-voltage direct current (DC) battery pack, a power inverter module (PIM) connected to the high-voltage battery pack via a DC bus, an electric drive unit, and a set of road wheels. The electric drive unit includes the housing noted above, as well as a polyphase alternating current (AC) rotary electric machine connected to the PIM via a power inverter connector block, and connected to the road wheels. The rotary electric machine is enclosed within the lower chamber and has multiple phase leads positioned directly below the elongated drain opening. A cover assembly has a cover plate fastened to the housing within the upper chamber, and a coolant channel assembly integrally connected to the cover plate. The coolant channel assembly includes electrical terminals that project through the elongated drain opening and are fastened at a first distal end of the electrical terminals to the multiple phase leads of the rotary electric machine. The coolant channel assembly and the cover plate together define an elongated primary coolant channel in fluid communication with the oil supply port, such that the cover assembly is configured to direct oil admitted through the oil supply port to the electrical terminals to thereby cool the electrical terminals.

The present disclosure is susceptible to various modifications and alternative forms, and some representative embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the inventive aspects of this disclosure are not limited to the particular forms disclosed. Rather, the disclosure is to cover all modifications, equivalents, combinations, sub-combinations, and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims.

DETAILED DESCRIPTION

Referring to the drawings, wherein like reference numbers refer to like components throughout the several views, an electric drive unit10is shown inFIG. 1having a housing12that forms a protective drive unit case. The electric drive unit10may be used in a host of beneficial applications, including but not limited to use as part of powertrain of a motor vehicle80described below with particular reference toFIG. 8. The housing12may be cast or otherwise formed to define separate upper and lower chambers14and16, respectively, with an outer flange15defining periphery bolt holes17. The electric drive unit10also includes an oil-cooled rotary electric machine20, depicted inFIG. 1as a polyphase/alternating current (AC) machine, which is disposed within the lower chamber16of the housing12.

An outer cover (not shown) of the housing12shown inFIG. 1may be bolted to the outer flange15via the periphery bolt holes17to thereby enclose the upper chamber14. Within the upper chamber14, a cover assembly22is attached to the housing12via fasteners13arranged around the periphery of the cover assembly22. Once the cover assembly22is in the illustrated installed position, the cover assembly22forms an integral cooling manifold configured as described below with reference toFIGS. 4-7.

The electric machine20ofFIG. 1may be energized via a high-voltage battery pack83(seeFIG. 8), e.g., a multi-cell battery pack having a relatively high voltage capability. As used herein, “high-voltage” may encompass voltage levels in excess of typical 12-15V auxiliary levels. In some embodiments, the electric machine20may be used as part of a powertrain assembly of the motor vehicle80ofFIG. 8, e.g., a battery electric vehicle characterized by an absence of an internal combustion engine. In such an embodiment, DC voltage levels may approach or exceed 400V, for instance, and therefore sustained operation of the electric machine20may result in the generation of substantial amounts of heat. The electric machine20is therefore oil-cooled during its operation, with construction of the cover assembly22facilitating such the cooling function.

When the electric machine20ofFIG. 1is electrically energized by a power inverter module (PIM)84, which as shown inFIG. 8is connected to the above-noted battery pack83, a rotor of the electric machine20(not shown inFIG. 1, but shown schematically at20R inFIG. 8) disposed radially within a stator24of the electric machine20will rotate radially within the stator24within a pool of oil (not shown). Such rotation will tend to disperse some of the oil away from the rotor20R onto surrounding structure of the electric machine20. To enhance the cooling function, the cover assembly22is configured to deposit oil onto the electric machine20from above, and in particular to direct oil onto electrical terminals34of the of cover assembly22and electrical leads28of the electrical machine20connected thereto, with an exposed portion of the electrical terminals34depicted inFIG. 1as protruding through the cover plate22.

Referring toFIG. 2, the electric machine20in an exemplary polyphase embodiment includes a stator yoke25that is securely fastened within the lower chamber16of the housing12shown inFIG. 1. The cover assembly22is positioned within the upper cavity14of the housing12(FIG. 1) directly above the electric machine20. The cover assembly22is secured to the housing12, e.g., using bolts13(FIG. 1) inserted through mating bolt holes32defined adjacent to perimeter edge36of the cover assembly22. The cover assembly22is oriented within the upper chamber14ofFIG. 1such that a respective first distal end E1of each electrical terminal34is exposed within the upper chamber14. An opposing second distal end E2of the electrical terminals34is positioned adjacent to a respective one of the electrical leads28of the electric machine20as shown.

The electrical terminals34are then ultimately fastened to the electrical leads28, e.g., ring-shaped lugs as shown, as indicated by arrows AA. The connection between the electrical terminals34and the electrical leads28may be achieved using suitable copper or other electrically-conductive fasteners (not shown). Within the upper chamber14ofFIG. 1, a power inverter connector block40having flat connector lugs42and44may be used to electrically connect the power inverter connector block40to the PIM84ofFIG. 8. That is, the connector lugs42may be fastened to the electrical terminals34at the first distal end E1, as indicated by arrows BB, and to the above-noted PIM84, represented by “[84]” inFIG. 2, via the connector lugs44as indicated by arrows CC.

High-speed pulse-width modulation or other switching control of semiconductor switches residing within the PIM84ofFIG. 8is used to control powerflow to or from the electric machine20during motoring or generating operating modes, respectively. The power switching control process can rapidly heat the electric machine20. Therefore, it is advantageous to cool the electrical terminals34and the connected electrical leads28with oil during operation of the electric machine20. To this end, the cover assembly22as described herein is configured as an integral cooling manifold to facilitate delivery of oil to the electrical terminals34and the electrical leads28, as will now be described with reference toFIGS. 3-8.

Referring briefly toFIG. 3, the upper cavity14of the housing12depicted inFIG. 1is shown with the cover assembly22removed for illustrative clarity. An inner flange150of the housing12provides a flat surface against which the cover assembly22seals when the cover assembly22is in the installed position ofFIG. 1, possibly with the assistance of a sealing gasket. The inner flange150defines perimeter mounting holes170spaced around a periphery of the inner flange150, with each of the mounting holes170receiving a respective fastener13(seeFIG. 1) when the cover assembly22is attached to the inner flange150.

The housing12ofFIG. 1also includes a floor section12F that separates the housing12into the upper and lower chambers14and16. That is, the floor section12F forms a physical boundary between the upper and lower chambers14and16, such that structure located above or below the floor section12F is in the upper or lower chambers14or16, respectively. The floor section12F defines a plurality of drain holes21which allow oil to flow via gravity from the upper cavity14into the lower cavity16(FIG. 1). Thus, the floor section12F may be angled, contoured, or otherwise configured to direct oil present in the upper chamber14toward and into the drain holes21. Oil passing through the drain holes21is deposited onto targeted areas of the electric motor20located within the lower chamber16.

The inner flange150further defines an elongated drain opening29located directly above the electric machine20. The elongated drain opening29is at least co-extensive with the electrical leads28, which along with a portion of the electric machine20are visible through the drain opening29from the perspective ofFIG. 3. The area of the drain opening29, e.g., an elongated racetrack-shaped, elliptical, or oval-shaped opening, is large enough to admit the electrical connectors34(FIG. 5) when the cover assembly22ofFIGS. 2 and 3is attached to the inner flange150.

As noted above, the housing12ofFIG. 1defines a fluid passage that opens to an oil supply port19. The oil supply port19admits oil into the cover assembly22ofFIG. 2, with the admitted oil ultimately being directed through the cover assembly22and into the elongated drain opening29, where the oil is gravity-fed onto and around the electrical terminals34shown inFIG. 2. Construction of the cover assembly22for the purpose of distributing oil in such a manner will now be described with reference toFIGS. 4-7.

FIG. 4depicts a bottom/inside view of the cover assembly22, i.e., the side of the cover assembly22facing the floor section12F ofFIG. 3when the cover assembly22is in the installed position. The cover assembly22includes a cover plate51constructed of molded plastic, aluminum, or another suitable lightweight material, with the perimeter bolt holes32distributed around the periphery of the cover plate51. A fluid seal53may be contained within a periphery channel defined by the cover plate51to help seal the cover plate51against the inner flange150shown inFIG. 3. A coolant channel assembly52, described below with reference toFIG. 5, may be welded or heat-staked to the cover plate51to form an integrated unit or assembly as shown.

The coolant channel assembly52, in the depicted plan view, has a generally oar-shaped or paddle-shaped perimeter, i.e., a first end54having a larger surface area than an opposing second end55. The above-noted second distal end E2of each respective one of the electrical terminals34projects through the first end54of the coolant channel assembly52, through the elongated drain opening29ofFIG. 3, and toward the electric machine20. The second end55of the coolant channel assembly52defines a fluid inlet57, e.g., a circular opening as shown, which itself may be circumscribed by an O-ring58for additional fluid sealing integrity. Oil flowing from the oil supply port19ofFIG. 3and into coolant channel assembly52via the fluid inlet57ultimately passes along the length of the coolant channel assembly52to reach the first end54, where the admitted oil flows around and past the electrical terminals34to cool the electrical terminals34and the electrical leads28.

Referring toFIG. 5, the electrical terminals34located at the first end54of the coolant channel assembly52are orientated as shown, i.e., with the first distal ends E1orientated upward through the cover plate51ofFIG. 4and the opposing second distal ends E2oriented downward toward the electric machine20, as best shown inFIG. 2. To facilitate attachment of the electrical terminals34ofFIG. 5to the PIM84shown inFIG. 8and to the electric machine20ofFIGS. 1 and 2, the electrical terminals34may define respective upper and lower fastener openings36and37.

The coolant channel assembly52has opposing upper and lower surfaces60and61, respectively, with the upper surface60located immediately adjacent to the cover plate51shown inFIG. 4. The coolant channel assembly52defines the elongated primary channel62. The primary channel62is in fluid communication with the fluid inlet57located at the second end55of the coolant channel assembly52, as well as with the electrical terminals34located at the first end54. Oil entering the fluid inlet57flows along the main channel62in the direction of arrow FF, i.e., toward the electrical terminals34. The primary channel62may terminate in a plurality of secondary channels64, e.g., three secondary channels64in the non-limiting example three-phase embodiment of the electrical machine20. Each of the secondary channels64may be a short length of channel directing oil from the primary channel62to a respective one of the electrical terminals34.

FIG. 6depicts a portion of the cover assembly22as a cross-sectional view of a representative one of the electrical terminals34in an installed position. Fasteners such as threaded bolts or machine screws constructed of copper or another suitable electrically-conductive material, omitted for clarity, are inserted into the upper and lower fastener openings36and37, respectively, to make the requisite electrical connections between the PIM84ofFIG. 8and the electric machine20shown inFIG. 1. A fastener inserted into the upper opening36secures a corresponding one of the connector lugs42ofFIG. 2to the electrical terminal34, while a fastener inserted into the lower fastener opening37secures the electrical terminal34to a corresponding one of the electrical leads28(likewise shown inFIG. 2). In this manner, a conductive path is established between the PIM84, the power inverter connector block40ofFIG. 2, the electrical terminal34, and a given electrical lead28of the electric machine20.

Once the cover plate51is securely connected to the coolant channel assembly52, the cover plate51encloses the primary channel62. Oil flows in the main channel62, i.e., into the page from the perspective ofFIG. 6as indicated by the “X”, and toward a body35of the electrical terminal34. A sealing gasket45may be positioned between the cover plate51and the housing12ofFIGS. 1 and 3to create a positive fluid seal along interfacing surfaces. Likewise, an O-ring72(also seeFIG. 7) may circumscribe the electrical terminal34proximate the upper fastener opening36to create a positive fluid seal between the electrical terminal34and the cover plate51above the level of the main channel62. In an exemplary embodiment, the body35of the electrical connector34is an elongated cylinder terminating in a flatted surface or land39, with the lower fastener opening37formed through the land39. Use of the land39, which is flat, may facilitate connection to the electrical leads ofFIG. 2which are similarly flat, thereby enabling good conductive surface-to-surface contact.

Once the electrical terminal34is in the installed position depicted inFIG. 6, an inner wall68of the coolant channel assembly52is situated a short distance away from the body35of the electrical terminal34. While the size of such a gap may vary with the application, the width of the gap should be minimal, e.g., about 0.20-0.30 millimeters (mm) in an exemplary embodiment, or less than 0.50 mm in another embodiment. Oil is thus permitted to flow along the coolant channel62in the direction of arrow FF and around the circumference of the body35. The oil then passes through the narrow gap between the inner wall68and the body35, whereupon gravity ensures that the oil passes downward in the direction of arrow GG along the length of the electrical terminal34to thereby cool the electrical connector34. The directions of arrows FF and GG inFIG. 6thus trace the general oil flow direction through the cover assembly22according to the present teachings. The electrical terminal34may be formed with upper and lower radial shoulders73and74, respectively, in order to optimize oil distribution on the electrical terminal34.

Referring toFIG. 7, the electrical terminals34may be constructed in a manner that facilitates even distribution of oil received from the main channel62ofFIG. 6. Under low-speed operation of the electric machine20or the motor vehicle80ofFIG. 8, oil flowing in the primary channel62may not flow evenly along the circumference of the body35. To address this potential problem, the upper and lower radial shoulders73and74may be formed as ring-shaped collars having an optional hex-head profile to facilitate installation, with the shoulders73and74separated from each other by an axial distance YY. An undersurface173of the upper radial shoulder73is immediately adjacent to the coolant channel assembly52as best shown inFIG. 5.

The lower shoulder74forms a shelf76, which is horizontally-aligned when the electrical terminal34is in the illustrated vertical/installed orientation. A radially-outermost surface174of the lower shoulder74and the inner surface68of the coolant channel assembly52(FIG. 6) together define the above-noted narrow gap through which oil flows along the body35of the electrical terminal34. Thus, viscosity of the oil supplied under low pressures, e.g., at low speeds of the electric machine20and/or the motor vehicle80ofFIG. 8, will tend to cause the oil to adhere to and flow along the shelf76around the circumference of the body35. The shelf76therefore acts as a reservoir by allowing a small amount of oil to pool under low-speed operation of the electric machine20when oil pressure levels are expected to be very low. Oil collected on the shelf76will eventually overflow, with gravity causing the overflowing oil to trickle evenly along the length of the body35and around the circumference of the body35, thereby optimizing cooling of the electrical terminal34and connected electrical leads28.

FIG. 8schematically depicts the above-noted example motor vehicle80. The motor vehicle20uses the electric drive unit10ofFIG. 1to generate and deliver motor torque (arrow TM) to a coupled set of road wheels82. The high-voltage battery pack (BHV)83is electrically-connected to the PIM84via a high-voltage DC bus (VDC). The PIM84in turn is connected to the rotary electric machine20, which is situated in the lower chamber (CL)16of the housing12, via a high-voltage AC bus (VAC), possibly using the power inverter connector block40(also seeFIG. 2).

An oil sump85contains a supply of oil86, i.e., suitable coolant for use with the electric machine20, that is circulated to the upper chamber (CU)14of the housing12via an oil pump (P)87. In a possible embodiment, the motor vehicle80may include a final drive (FD)88connected to the rotor20R of the electric machine20via a rotor shaft120, with the final drive88embodied as one or more planetary gear sets. A ring gear or another suitable gear element of the final drive88may be connected to the oil pump87such that when the motor vehicle85is moving, the driven oil pump87circulates the oil86through the cover assembly22ofFIG. 1, as indicated by arrow FF, to cool the electrical terminals34ofFIG. 6in the manner set forth above. Pumps driven by other rotating members of the electric drive unit10ofFIG. 1and/or connected thereto, or individually driven, may be used in other embodiments to circulate oil to the upper chamber14.

Other beneficial applications may be envisioned for the schematically-depicted electric drive unit10, including other vehicle applications such as rail vehicles, aircraft, or watercraft, as well as in mobile robots or platforms. Stationary applications may also be envisioned, including powerplants, mining or manufacturing hoists, etc., and therefore the embodiment ofFIG. 8is representative of the present teachings and non-limiting.

As will be appreciated by those of ordinary skill in the art in view of this disclosure, the cover assembly22described above with reference toFIGS. 1-8, with its integrated coolant channel assembly52, may be used to direct oil to targeted locations, such as the electrical terminals34shown inFIG. 1. Such electrical terminals34may be integral with the structure of the cover assembly22described above, with internal fluid passages defined by the coolant channel assembly52and the cover plate51replacing typical spray tubes or other structure. These and other benefits will be readily appreciated by one of ordinary skill in the art in view of this disclosure.

While the best modes for carrying out the disclosure have been described in detail, those familiar with the art to which this disclosure relates will recognize various alternative designs and embodiments for practicing the disclosure within the scope of the appended claims. Furthermore, the embodiments shown in the drawings or the characteristics of various embodiments mentioned in the present description are not necessarily to be understood as embodiments independent of each other. Rather, it is possible that each of the characteristics described in one of the examples of an embodiment can be combined with one or a plurality of other desired characteristics from other embodiments, resulting in other embodiments not described in words or by reference to the drawings. Accordingly, such other embodiments fall within the framework of the scope of the appended claims.