Electric drive unit with a heat exchanger that is formed by disks having a disk spring portion and which are received into a bore in a rotor shaft of an electric motor

An electric drive unit that includes an electric motor having a rotor with a rotor shaft and a heat exchanger that is received in the rotor shaft. The heat exchanger has a plurality of heat exchanger plates, each of which having a hub, a rim member, and disc spring portion that interconnects the hub and the rib member. Each disk spring portion defines a plurality of coolant apertures. The heat exchanger plates are press-fit to the rotor shaft such that each disc spring portion is deflected from a pre-installation state, and each rim member is engaged to an interior surface of the rotor shaft while being spaced apart from adjacent rim members along a rotational axis of the rotor. A first coolant passage is disposed through the hubs of the plates. The coolant apertures in the heat exchanger plates cooperate to form a plurality of second coolant passages.

FIELD

The present disclosure relates to an electric drive unit with a heat exchanger that is formed by disks having a disk spring portion and which are received into a bore in a rotor shaft of an electric motor.

BACKGROUND

There is increasing interest on the part of vehicle manufacturers to incorporate an electric motor into the vehicle for purposes of providing propulsive power. To minimize the cost and size of the electric motor, it is frequently necessary to cool components of the electric motor with a flow of liquid coolant, such as the rotor of the electric motor. One known method for cooling the rotor of an electric motor utilizes a heat exchanger inside a hollow shaft of the rotor. The flow of liquid coolant is input to the heat exchanger at a first end of the rotor to a first passage, which is formed along the rotational axis of the rotor. At least part of the flow of liquid coolant that exits the first passage at a second, opposite end of the rotor is returned to the first end of the rotor through a plurality of second passages that are disposed concentrically about the first passage.

While such configurations are suited for their intended purpose, we have noted that the known configuration can be relatively costly and/or difficult to manufacture. In this regard, the exterior surface of the heat exchanger must contact the interior surface of the hollow shaft throughout the entire length of the heat exchanger to maximize potential heat transfer between the hollow shaft and the heat exchanger. Consequently, the known designs have the practical effect of requiring close tolerances between the exterior surface of the heat exchanger and the interior surface of the hollow shaft. Configuration in this manner can be relatively costly and/or relatively difficult to manufacture.

SUMMARY

In one form, the present disclosure provides an electric drive unit that includes an electric motor having a rotor with a rotor shaft and a heat exchanger that is received in the rotor shaft. The heat exchanger has a plurality of heat exchanger plates. Each of the heat exchanger plates having a hub, a rim member, and disc spring portion that interconnects the hub and the rib member. Each disk spring portion defines a plurality of coolant apertures. The heat exchanger plates are press-fit to the rotor shaft such that each disc spring portion is deflected from a pre-installation state, and each rim member being engaged to an interior surface of the rotor shaft. A first coolant passage is disposed through the hubs of the plates. The coolant apertures cooperate to form a plurality of second coolant passages that are disposed concentrically about the first coolant passage. The rim members of the heat exchanger plates are spaced apart from one another along a rotational axis of the rotor.

In another form, the present disclosure provides a method for assembling an electric motor. The method includes: providing a hollow rotor shaft; providing a stack of heat exchanger plates, each of the heat exchanger plates having a hub, a rim member, and disc spring portion that interconnects the hub and the rib member, each disk spring portion defining a plurality of coolant apertures; and press-fitting the stack of heat exchanger plates into the hollow rotor shaft such that the rim member of each of the heat exchanger plates is engaged to an interior surface of the rotor shaft, wherein a first coolant passage is disposed through the hubs of the plates, and wherein the coolant apertures cooperate to form a plurality of second coolant passages that are disposed concentrically about the first coolant passage.

DETAILED DESCRIPTION

With reference toFIG.1of the drawings, an exemplary electric drive module constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral10. Except as detailed herein, the electric drive module10can be configured in a manner that is similar to that of the electric drive module disclosed in International Patent Application Publication No. WO2020/219955. In brief, the electric drive module10includes a housing assembly12, an electric motor14, a transmission18, a differential assembly20, a pair of output shafts22aand22band a coolant pump24.

The housing assembly12can house the motor14, the transmission and the differential assembly20.

With reference toFIGS.1and2, the electric motor14can be any type of electric motor and can have a stator32and a rotor34that is received in the stator32for rotation about a rotational axis36. The stator32can include a plurality of field windings. The rotor34can have a rotor body38, which can be formed of a plurality of rotor laminations40, a set of windings42, which can be mounted to the rotor body38, a rotor shaft44and a heat exchanger46. The rotor shaft44can be a hollow and/or can define a heat exchanger bore48into which the heat exchanger46is received.

The transmission18can include a planetary reduction52, a shaft54and a transmission output gear56. The planetary reduction can have a sun gear, which can be unitarily and integrally formed with the rotor shaft44to keep pitch line velocity as low as possible, a ring gear, which can be grounded to or non-rotatably coupled to the housing assembly12, a planet carrier and a plurality of planet gears that can be journally supported by the planet carrier and which can be meshingly engaged with both the sun gear and the ring gear. The sun gear, the ring gear and the planet gears can be helical gears. The shaft54can be mounted to a set of bearings60that support the shaft for rotation about the rotational axis36relative to the housing assembly12. The transmission output gear56can be coupled to (e.g., unitarily and integrally formed with) the shaft54for rotation therewith about the rotational axis36.

The differential assembly20can include a final drive or differential input gear70and a differential. The differential input gear70can be rotatable about an output axis80and can be meshingly engaged to the transmission output gear56. In the example provided, the transmission output gear56and the differential input gear70are helical gears. The differential can be any type of differential mechanism that can provide rotary power to the output shafts22aand22bwhile permitting (at least in one mode of operation) speed differentiation between the output shafts22aand22b.In the example provided, the differential includes a differential case, which is coupled to the differential input gear70for rotation therewith, and a differential gearset having a plurality of differential pinions, which are coupled to the differential case and rotatable (relative to the differential case) about one or more pinion axes that are perpendicular to the second rotational axis80, and a pair of side gears that are meshingly engaged with the differential pinions and rotatable about the second rotational axis80. Each of the output shafts22aand22bcan be coupled to an associated one of the side gears for rotation therewith. In the example provided, the output shaft22bis formed as two distinct components: a stub shaft90and a half shaft92. The stub shaft90is drivingly coupled to an associated one of the side gears and extends between an associated gear and the half shaft92and is supported by a bearing94in the housing assembly12for rotation about the second rotational axis80. Each of the output shaft22aand the half shaft92has a constant velocity joint100with a splined male stem. The splined male stem of the constant velocity joint on the output shaft22ais received into and non-rotatably coupled to an associated one of the side gears. The splined male stem of the constant velocity joint on the half-shaft92is received into and non-rotatably coupled to the stub shaft90.

The pump24can be mounted to the housing assembly12and can circulate an appropriate fluid, such as automatic transmission fluid, about the electric drive module10to lubricate and/or cool various components. In the example provided, fluid discharged from the pump24is fed through a feed pipe120into the heat exchanger46in the rotor shaft44. The heat exchanger46receives the flow (inflow) of dielectric fluid along its rotational axis36, and then turns the flow at the opposite end of the rotor34so that the flow of dielectric fluid flows concentrically about the inflow toward the end of the rotor34that received the inflow of the dielectric fluid.

With reference toFIGS.2and3, the heat exchanger46comprises a plurality of heat exchanger plates150and can optionally include an input member152, a re-direction member154, and a plug member156. The heat exchanger46defines a first coolant passage160, which has a longitudinal axis that is coincident with the rotational axis36of the rotor shaft44, and a plurality of second coolant passages162that are disposed concentrically about the first coolant passage160.

With reference toFIGS.4through6, each of the heat exchanger plates150can have a hub170, a rim member172, and disc spring portion174. The hub170can be shaped in a desired manner, such as with a frusto-conical shape that can be defined by a first cone angle176. The rim member172defines the outer circumference of the heat exchanger plate150. The disc spring portion174interconnects the hub170and the rim member172and defines a plurality of coolant apertures180. In the example provided, each of the coolant apertures180has an oval or tear drop shape, but it will be appreciated that the coolant apertures180could be sized, shaped and positioned in any desired manner. The disc spring portion174is configured in a manner that is similar to a Belleville spring washer and as such, can be contoured in a desired manner to provide a desired spring rate. In the particular example provided, the disc spring portion174has a frusto-conical shape that is defined by a second cone angle182that is larger in magnitude than the first cone angle176. Optionally, all or a portion of one or both of the axial surfaces of the heat exchanger plate150can be formed to provide additional surface area. In the example provided, the disc spring portion174is formed with concentric ribs186that provide the opposite axial surfaces of the disc spring portion174with an undulating or wavy surface that provides approximately twelve percent more surface area than a configuration in which the disc spring portion174is formed with a “flat” or “smooth” (i.e., without with concentric ribs186that are shown).

With reference toFIGS.3and4, the heat exchanger plates150can be stacked against one another to create a stack190of heat exchanger plates150. In the example provided, the hubs170of the heat exchanger plates150abut one another, while the rim members172of the heat exchanger plates150are spaced apart from one another. Optionally, the hubs170can be bonded to one another, for example via a sealant and/or adhesive that is disposed between each pair of abutting hubs170, or via a weld (e.g., resistance weld) or braze. As shown, the hubs170of the heat exchanger plates150cooperate to form the first coolant passage160, while the coolant apertures180in the disc spring portions174form the plurality of second coolant passages162. Notably, the coolant apertures180can be oriented in any desired manner. Preferably, the coolant apertures180of adjacent heat exchanger plates150are rotated out of alignment with one another so that fluid coolant passing through one heat exchanger plate150must rotate about the rotational axis36before passing through one of the coolant apertures180in an adjacent heat exchanger plate150. The stack190of heat exchanger plates150is inserted (e.g., press-fit) into the rotor shaft44such that the rim members172engage an inner circumferential surface200of the hollow rotor shaft44, preferably with the rim members172being oriented perpendicular to the rotational axis36of hollow rotor shaft44to thereby maximize conductive heat transfer between the hollow rotor shaft44and the heat exchanger plates150. Due to its flexibility, the disc spring portion174can flex during installation of the stack190of heat exchanger plates150to ensure engagement of each of the rim members172to the inner circumferential surface200of the hollow rotor shaft44despite the presence of variation in the diameter of the heat exchanger bore48in the rotor shaft44. Despite the flexibility of the disc spring portion174, the rim members172of the heat exchanger46plates are spaced apart from one another along the rotational axis36of the rotor shaft44when the stack190of heat exchanger plates150is received into the rotor shaft44. Optionally, the heat exchanger plates150could be formed of a material having a different coefficient of linear thermal expansion than the material from which the rotor shaft44is formed. For example, the heat exchanger plates150could be formed of aluminum, while the rotor shaft44can be formed of steel. Configuration in this manner permits the heat exchanger plates150to grow in size due to increases in temperature (e.g., from ambient air temperature to a temperature associated with continuous and stable operation of the electric drive module10(FIG.1) at the ambient air temperature), which could be advantageous for the manufacture of the electric drive module10(FIG.1). In this regard, tolerances on the outside diameter the heat exchanger plates150, the inside diameter of the heat exchanger bore48, and the cylindricity of the heat exchanger bore48can be increased due to the ability of individual heat exchanger plates150to grow into contact with the inner circumferential surface200of the rotor shaft44as the temperature of the electric drive unit10(FIG.1) increases from ambient air temperature during continuous, stable operation of the electric drive unit10(FIG.1). Moreover, ability of the heat exchanger plates150to individually grow and move in response to heating from ambient air temperature to the operational temperature of the electric drive unit10(FIG.1) permits a design in which none, or only a few of, or all of the rim members172lightly engage the inner circumferential surface200of the rotor shaft44at a first predetermined temperature, such as −20 degrees Celsius, while the rim members172of all of the heat exchanger plates150engage the inner circumferential surface200of the rotor shaft44at a second predetermined temperature, such as 90 degree Celsius. The stack190of heat exchanger plates150could be cooled to the first predetermined temperature (while the rotor shaft44was maintained at room temperature) for the installation of the heat exchanger46to the rotor shaft44. The second predetermined temperature could be a temperature that is below a target operating temperature at which coolant is actively circulated through the heat exchanger46to cool the rotor34(FIG.1) during stable and continuous operation of the electric motor14(FIG.1). The ability of the heat exchanger plates150to thermally expand at a rate that is greater than a rate at which the rotor shaft44expands can be employed to ensure contact between the outer circumferential surface of each of the rim members172of the heat exchanger plates44(e.g., for robust heat transfer across the interface between the rotor shaft44and the rim members172) regardless of moderate variation in the diameter and/or the cylindricity of the heat exchanger bore48in the rotor shaft44.

The input member152is configured to transport coolant fluid from the feed pipe120(FIG.1) to the first coolant passage160and as such, can be configured in any desired manner. In the example provided, the input member152is configured in a manner that is similar to one of the heat exchanger plates150(i.e., with a hub170a,a rim member172aand a disc spring portion174a). However, the input member152is formed from a relatively thicker material and includes a nozzle210that extends from the hub170ain a direction away from the stack190of heat exchanger plates150. If desired, a centering element212can be mounted to the nozzle210of the input member152and can engage the inner circumferential surface200of the rotor shaft44. In the example provided, the centering element212includes a plurality of inner lobes, which engage the nozzle210, and a plurality of outer lobes that are disposed between adjacent inner lobes and which engage the inner circumferential surface200of the rotor shaft44. The relatively thicker material of the input member152permits the rim member172ato engage the inner circumferential surface200of the rotor shaft44to such an extent that the input member152can be employed to maintain the position of the stack190of heat exchanger plates150along the rotational axis36at a desired location despite the fact that the disc spring portions174of the heat exchanger plates150are deflected from their pre-installation state when the heat exchanger46is assembled to the hollow rotor shaft44. In the example shown, the hub170of one of the heat exchanger plates150abuts the hub170aof the input member152. Accordingly, it will be appreciated that that hub170aof the input member152and the hub170of the adjacent heat exchanger plate150could be sealed and/or bonded to one another.

The re-direction member154can be an annular, frusto-conically shaped structure having an annular inner mount220, which confronts the hub170of the heat exchanger plate150that faces the re-direction member154, and an outer mount222that is press-fit into engagement with the inner circumferential surface200of the hollow rotor shaft44. Alternatively, the outer mount222can be configured to slip-fit into the heat exchanger bore48in the rotor shaft44. A plurality of re-direction apertures224are formed about the circumference of the re-direction member154between the inner and outer mounts220and222.

The plug member156can be employed to close an open end of the hollow rotor shaft44into which the input member152, the stack190of heat exchanger plates150, and the re-direction member154are received. In the example provided, the plug member156includes a plug portion230, an end stop232, and a shaft mount234. The plug portion230is sized in diameter to engage the inner circumferential surface200of the rotor shaft44in a press-fit manner as well as to sealingly engage the inner circumferential surface200. The plug portion230is sized in axial length so that it positions and/or maintains the position of the re-direction member154, and thereby the positions of the stack190of heat exchanger plates150and the input member152, at desired locations along the axial length of the hollow rotor shaft44. Alternatively, a resilient element (not shown), such as a wave spring, can be disposed between the plug portion230and the re-direction member154. Configuration in this manner may help to maintain a desired axial load on the stack190of heat exchanger plates150, which could help guard against the axial separation of the heat exchanger plates150from one another to inhibit leakage in the hub-to-hub interfaces between the heat exchanger plates150. The shaft mount234can extend from the end stop232in a direction away from the plug portion230and can define a bearing surface236that is configured to receive a bearing (not shown) thereon that supports the rotor34(FIG.1) for rotation relative to the housing assembly12(FIG.1).

Fluid coolant exiting the first coolant passage160flows though the annular inner mount220of the re-direction member154and can be turned via a contoured recess240in an end of the plug member156to flow radially outward and back toward the re-direction member154where the flow passes through the re-direction apertures224and into the second coolant passages162.

While the heat exchanger46has been depicted as having a stack190of heat exchanger plates150whose annular hubs170cooperate to form a first coolant passage160, it will be appreciated that the heat exchanger46could be formed somewhat differently. With reference toFIG.7, the heat exchanger46′ is generally similar to the heat exchanger ofFIG.3, except that a tube250is inserted through the hubs170and the tube defines the first coolant passage160. In the example provided, the tube250is press-fit to the hubs170, but it will be appreciated that the tube250could be welded (e.g., resistance welded) or brazed to the heat exchanger plates150.

While the re-direction member154has been described as having an outer mount222that is press-fit into engagement with the inner circumferential surface200of the hollow rotor shaft44, it will be appreciated that the outer mount222may be configured somewhat differently. For example, the outer mount222may be configured to be received into the contoured recess240and engaged to the plug member156.

InFIG.8, a portion of another rotor and heat exchanger that has been constructed in accordance with the teachings of the present disclosure is illustrated. The heat exchanger46″ is generally similar to the heat exchanger46′ ofFIG.7, except that the tube250″ extends to a point that is relatively closer to the plug member156than the example ofFIG.7. In the particular example provided, the tube250″ extends past the point where the outer mount222and the plug portion230abut or contact one another and into the recess240. An axial end300of the tube250″ can be disposed proximate an axial end face302on the plug portion230so that fluid flowing through the tube250″ impinges or strikes the axial end face302. Configuration in this manner can improve heat transfer from the plug member156to the fluid that is circulated through the heat exchanger46″, especially in situations where air is entrained into the fluid that is circulated through the heat exchanger46″. In this regard, the placement of the axial end300of the tube250″ in the recess240and/or proximate the axial end face302on the plug portion230, can reduce or eliminate a risk that air would collect in or proximate the plug member156, which may potentially reduce heat transfer from the plug member156to the fluid that is circulated through the heat exchanger46″.

InFIG.9, a portion of yet another rotor and heat exchanger that has been constructed in accordance with the teachings of the present disclosure is illustrated. The heat exchanger46″ can be configured in a manner that is similar to the heat exchanger46ofFIG.3or the heat exchanger46′ ofFIG.7. With additional reference toFIGS.10and11, the plug member156″′ is configured with a central supply aperture400, which is formed concentrically about the rotational axis36of the rotor, and a plurality of return apertures402that are disposed circumferentially about the central supply aperture400. The central supply aperture400extends through the plug portion230″′ and the portion of the shaft mount234′ on which the bearing surface236is formed. Each of the return apertures402can be formed at an angle to the rotational axis36and can intersect the central supply aperture400proximate a distal or blind end410of the central supply aperture400. In the example provided, each of the return apertures402has a longitudinal axis416, and the longitudinal axes416of the return apertures402are disposed in a cone. An axial end face420of the plug portion230″′ can be positioned relative to the re-direction member154of the heat exchanger46″′ in a desired manner. In the example shown, the axial end face420of the plug portion230′ includes a frustoconically shaped portion through which the return apertures402extend. The exterior surface of the frustoconically shaped portion is perpendicular to the longitudinal axes of the return apertures402. Optionally, the exterior surface of the frustoconically shaped portion could be configured to match the frusto-conical angle of the re-direction member154.

In operation, fluid discharged through the first coolant passage160can be directed into the central supply aperture400and thereafter into the return apertures402to re-direct the flow of fluid toward the re-direction apertures224that are formed in the re-direction member154. Accordingly, heat from a bearing (FIG.1) that is mounted on the bearing surface236and which supports the rotor for rotation about the rotational axis36can be conducted through the plug member156″′ (i.e., the shaft mount234′) and rejected to the cooling fluid that is circulated through the rotor and plug member156″′. It may be desirable in some situations that the return apertures402intersect the central supply aperture400at a location that lies past or is proximate the end of the portion of the plug member156″′ on which the bearing is mounted. Centrifugal force on the fluid passing out of the central supply aperture400creates a kind of pumping action that forces the fluid into the return apertures402at the earliest opportunity. Accordingly, placement of the point at which the return apertures402intersect the central supply aperture400past the bearing (or proximate the end of the bearing that faces away from the rotor) can provide a configuration that rejects heat from the bearing in a quicker and/or more efficient manner.

In situations where the first coolant passage160is partly or fully formed by a tube250″′, it will be appreciated that the tube250″ could optionally be sized in its diameter and length to fit inside the central supply aperture400for a desired distance as is shown inFIG.12. Configuration in this manner helps to segregate the flow of fluid into and out of the plug member156″′. In the particular example shown, the tube250″′ is necked down in diameter after it exits or extends beyond the re-direction member154. Additionally or alternatively, the axial end face420of the plug portion230″′ could be abutted directly against the outer mount222of the re-direction member154as is shown inFIG.9A. Also optionally, the return apertures402could be aligned to the re-direction apertures224in the re-direction member154.

While the embodiments ofFIGS.9and12have been illustrated with a plug member156″′ that is integrally and unitarily formed, it will be appreciated that the plug member156″′ could be made as several discrete components that are assembled and fixedly coupled to one another. Additionally or alternatively, the re-direction member154could be combined with the plug member156″. In the example ofFIG.13, the annular inner mount220″′ of the re-direction member154″′ can be fixedly coupled to the plug portion230″′ and the re-direction apertures402in the plug member156″′ could also be the re-direction apertures224. In the example shown, the tube250is not necked-down but rather is received in a desired manner (e.g., slip fit, press-fit) to an enlarged or counter-bored portion500of the central supply aperture400″′. It will be appreciated that the central supply aperture400″ could be formed to a uniform diameter (i.e., so that the central supply aperture400″′ is not stepped).