ELECTRIC MACHINE WITH A COOLING ASSEMBLY

Systems and methods for electric machine cooling. The electric machine, in one example, includes a rotor that includes an outer circumferential surface with one or more spiral grooves, a stator that circumferentially surrounds the rotor and includes end windings, and an air passage radially extending from the stator to an air gap between the stator and the rotor. The electric machine further includes a cooling assembly configured to spray a coolant towards the end windings.

TECHNICAL FIELD

The present disclosure relates to an electric machine that drives airflow through the air gap and includes a cooling assembly.

BACKGROUND AND SUMMARY

In electric motors, such as electric motors in electric vehicle (EV) applications, cooling systems has been used in an attempt to achieve greater motor efficiency. For instance, oil may be directed onto stator end windings to increase motor efficiency. After the oil spray hits the end windings it is collected into a sump. However, some of the oil spray may enter the air gap between the rotor and the stator. Oil in the air gap increases drag losses of the motor, thereby driving down efficiency.

US 2013/0221772 A1 to Miyamoto et al. discloses a cooling structure for an electric motor. The cooling structure includes a rotor shaft with an internal passage that radially distributes coolant to passages in the rotor core. The coolant that is directed through the rotor core may make its way into the air gap between the rotor and stator, thereby increasing the motor's drag losses and driving down motor efficiency. Further, Miyamoto's cooling structure may not deliver a targeted amount of coolant to the end windings, thereby constraining the motor's efficiency. Miyamoto's motor applicability may be constrained to platforms that do not demand a relatively high efficiency.

To overcome at least some of the abovementioned issues the inventors developed an electric machine. The electric machine includes, in one example, a rotor that includes an outer circumferential surface with one or more spiral grooves. The electric machine further includes a stator that circumferentially surrounds the rotor and includes end windings. The electric machine even further includes an air passage which radially extends from the stator to an air gap between the stator and the rotor. Still further, the electric machine includes a cooling assembly configured to spray a coolant (e.g., oil) towards the end windings. In one example, the one or more spiral grooves may be formed in a stack of rotor laminations. The spiral grooves passively generate airflow through the air gap during machine operation, thereby reducing the chance of coolant entering the gap and increasing drag losses. Consequently, the machine's efficiency may be increased in comparison to previous motor that do not constrain the amount of cooling oil entering the air gap.

In one example, the electric machine may further include a breather positioned at an inlet of the air passage. In this way, a target airflow rate in the air gap is achieved, further reducing the amount of coolant entering the air gap.

DETAILED DESCRIPTION

An electric machine, is described herein, that includes a cooling assembly that cools stator end windings and is designed to drive airflow axially outward through the air gap to reduce the amount of coolant (e.g., oil) that enters the air gap. The cooling and airflow features work in conjunction to increase motor efficiency by cooling end windings while reducing the chance of the coolant used for end winding cooling entering the air gap. To achieve this air gap airflow pattern, the rotor includes spiral grooves in an outer circumferential surface as well as an air passage that radially extends through the stator. To elaborate, the spiral grooves may be formed in the outer circumferential surface of a stack of rotor laminations. The electric machine further includes a cooling assembly that sprays coolant (e.g., oil) towards the stator end windings, to remove heat from the windings and increase motor efficiency. In this way, the efficiency gains made via stator ending winding cooling may not be significantly diminished from the losses caused by the coolant entering the air gap. The electric machine may further include a breather at the inlet of the air passage. The breather allows a desired amount of airflow to be generated through the air gap.

FIGS.1A-1Bshow a first example of an electric machine with a cooling assembly and spiral grooves that facilitate an increase in machine efficiency.FIGS.2A-2Bshows a second example of an electric machine with an alternate cooling assembly configuration.FIGS.3A-3Cshow examples of spiral grooves that may be included in a rotor and are designed to drive airflow through the air gap.FIG.3Dshows an example of a rotor lamination stack.

FIG.1Ashows an illustration of an electric machine100. The electric machine100may be designed as an electric motor (e.g., motor-generator) and may be included in a system102which may take a variety forms. For instance, the electric machine100may be incorporated into an electric drive of an electric vehicle (EV). In the EV example, the EV may be an all-electric vehicle (e.g., a battery electric vehicle (BEV)), in one example, or a hybrid electric vehicle (HEV), in another example. For instance, the electric machine may be mechanically coupled to a transmission (e.g., gearbox) that is coupled to drive wheels using one or more differentials for example. Further, in the EV example, the electric machine may be a traction motor that delivers mechanical power to drive wheels. In the HEV example, the electric machine may be included in an electric axle and an internal combustion engine may provide motive power to another drive axle. However, the motor may be used in other suitable systems (e.g., stationary systems), in other examples, such as in industrial machines, agricultural systems, mining systems, and the like.

The electric machine100includes a rotor104that electromagnetically interacts with a stator106to drive rotation of a rotor shaft108that is included in the rotor. The stator106at least partially surrounds the rotor104. As such, the electric machine100may be a radial flux style motor.

The electric machine100in the illustrated example includes a housing110. The housing110may form an enclosure (e.g., a sealed enclosure)111that contains stator end windings, cooling assembly components, and the like, which are expanded upon herein. The housing may include an electrical interface. The electrical interface may be a multi-phase electrical interface with multiple electrical connectors. The electrical interface may be three-phase interface in one example or a six or nine phase interface, in other examples. More generally, the electric machine100may be a multi-phase alternating current (AC) machine. However, in other examples, the electric machine100may be a direct current (DC) machine.

As illustrated inFIG.1, the electric machine100may be electrically coupled to an inverter116. The inverter116is designed to covert direct current (DC) power to alternating current (AC) power and vice versa. As such, the electric machine100may be an AC electric machine, as indicated above. However, in other examples, the electric machine100may be a DC electric machine (as previously indicated), and the inverter116may therefore be omitted from the system102. The inverter116may receive electric energy from one or more energy storage device(s)118(e.g., traction batteries, capacitors, combinations thereof, and the like). Arrows120signify the electric energy transfer between the electric machine100, the inverter116, and the energy storage device(s)118that may occur during different modes of system operation.

The rotor104may include a core122with a stack of laminations. An example, of a lamination stack350in a rotor352is depicted inFIG.3D. In the stack, laminations, that may be formed of steel, may be sequentially arranged and coupled (e.g., bonded and/or welded) to one another. Further, the rotor lamination stack may include teeth.

Continuing withFIG.1A, the stator106may include a core124through which windings extend. These windings protrude from the stator core on either axial end to form end windings126. The end windings may be positioned on opposing axial sides128and130of the electric machine. Further, the stator core124may include a stack of laminations which may include teeth and gaps at an inner periphery. The stator core124and end windings126are schematically illustrated. However, it will be understood that they have greater structural complexity.

The end windings126generate heat during machine use. As such, cooling of the end windings to increase motor efficiency may be desired. A cooling assembly146is provided to remove heat from the end windings126.

The cooling assembly146in the illustrated example, includes a coolant pump148and a filter151that includes a pick-up152in a sump154. The sump154is positioned in an internal enclosure of the electric machine100and is contoured to collect coolant156that is sprayed at the end windings126. The coolant used in the cooling assembly146may specifically be oil (e.g., natural and/or synthetic oil), in one example. However, other suitable types of coolant have been contemplated. The coolant pump148is shown incorporated into the housing110of the electric machine. However, the coolant pump may be spaced away from the electric machine and therefore positioned external to the electric machine's housing, in alternate examples.

To direct coolant towards the end windings, the cooling assembly146may include coolant conduits157and nozzles158. Additional or alternative coolant routing techniques may be used in other examples. For instance, spray rings, expanded upon herein with regard toFIGS.2A and2Bmay be used to direct coolant at the end windings126for cooling.

The conduits157may at least partially extend through the housing110and/or other suitable portions of the machine. Further, the nozzles158may be positioned on opposing axial sides of the stator106. To elaborate, the nozzles may spray coolant160inwards toward the end windings in one example. Additional or alternative nozzles may spray coolant in an outward radial direction to cool the end windings. For instance, additionally or alternatively, channels (e.g., nozzles) in spray rings which are coupled to the stator core may be used to spray coolant onto the end windings.

To generate airflow in the air gap134the rotor104(e.g., rotor core122) includes spiral grooves132,133on an outer circumferential surface162. To elaborate, a first axial side164of the rotor104may include the first spiral groove132that drives airflow axially towards the first axial side128of the machine and a second axial side of the rotor may include another spiral groove that is differently shaped from the first spiral groove and drives airflow axially towards the second axial side166of the machine. However, in other examples, the rotor104may include a sole spiral groove that runs from one axial end of the rotor to the opposing end. Incorporating the spiral grooves in the rotor allow an air gap airflow pattern to be generated which decreases the chance of coolant (e.g., oil) ingress in to the air gap. Consequently, significant drops in machine efficiency caused by drag losses may be avoided. Further, the spiral grooves132,133allow the airflow to be passively generated during machine operation, thereby increasing machine longevity when compared to systems that may include components which are actively controlled to drive airflow through the air gap.

The spiral grooves132and133are depicted via dashed lines as an abstracted visual representation of the grooves. However, it will be appreciated that the grooves inFIG.1Aare not illustrated to scale. The specific geometry of the spiral grooves that may be used in the electric machines described herein is expanded upon with regard toFIGS.3A and3B.

The spiral groove132may have a profile that generates airflow through the air gap134towards the axial side128of the electric machine100during machine operation. Conversely, the spiral groove133may have a profile that generate airflow through the air gap134towards the axial side130of the electric machine100during machine operation. In this way, the airflow in the gap has a pattern that reduces the ingress of coolant into the gap and expels any coolant that may have entered the gap.

The electric machine100further includes an air passage136that radially extends through the stator106(e.g., the stator core124) and opens into the air gap134. To elaborate, the air passage136extends from an outer diameter137of the stator106to the air gap134. To air passage136may therefore include an inlet138and an outlet139. At the inlet138, a breather140may be positioned. The breather140allows a desired amount of airflow to be achieved through the air passage136and the air gap134. The breather140may include an air filter142which is designed to capture oil droplets and reduce the amount of oil in the air entering the air passage136. The outlet139of the air passage136may be adjacent to a center line144of the rotor core122to allow the air to be symmetrically directed outward towards opposing axial ends of the machine100.

The breather140may be constructed out of a polymer (e.g., plastic) and/or aluminum. Further, in one example, the breather may be constructed as a plate at or near the axial mid-point of the stator lamination stack. As such, the breather plate may be axially positioned between stator laminations. In such an example, the plate may have a breather channel between the air gap and the stator's outer diameter. The machine may further include a breather vent141in the housing110. The breather vent may extend radially through the housing, in one example.

Additional air passages may be directed through the stator to allows a greater amount of air to be directed through the air gap, in operating environments where higher airflow is desired.

Arrows150denote the general direction of airflow through the air passage136and the air gap134. As shown, air travels from the vent141into the breather140and through the breather140into the inlet138of the air passage136. Then air travels radially inward towards the rotational axis199of the machine through the air passage136and then into the air gap134by way of the outlet139of the air passage136. In the illustrated example, the air then moves axially outward in opposing directions towards the opposing axial sides128,130of the of the machine100. In this way, an airflow pattern that reduces the likelihood of coolant (e.g., oil) ingress into the air gap and expels coolant that may have entered the air gap.

The system102may additionally include a control sub-system180with a controller182. The controller182includes a processor184and memory186. The memory186may hold instructions stored therein that when executed by the processor184cause the controller182to perform the various methods, control techniques, and the like, described herein. The processor184may include a microprocessor unit and/or other types of circuits. The memory186may include known data storage mediums such as random access memory, read-only memory, keep alive memory, combinations thereof, and the like.

The controller182may receive various signals from sensors188positioned in different locations in the system102. The sensors188may include an electric machine speed sensor, energy storage device temperature sensor(s), an energy storage device state of charge sensor(s), an inverter power sensor, and the like. The controller182may also send control signals to various actuators190coupled at different locations in the system102. For instance, the controller may send signals to the inverter116to adjust the rotational speed of the electric machine100. In another example, the controller182may send a command signal to the electric machine100and/or the inverter116and in response motor speed may be adjusted. The other controllable components in the system102may function in a similar manner with regard to command signals and actuator adjustment.

The system102may additionally include one or more input device(s)192(e.g., an accelerator pedal, a brake pedal, a console instrument panel, a touch interface, a touch panel, a keyboard, combinations thereof, and the like). The input device(s)192, responsive to user input, may generate a motor speed adjustment request.

An axis system is provided inFIG.1A, as well asFIGS.1B-2B, for reference. The z-axis may be a vertical axis (e.g., parallel to a gravitational axis), the x-axis may be a lateral axis (e.g., horizontal axis), and/or the y-axis may be a longitudinal axis, in one example. However, the axes may have other orientations, in other examples. Rotational axes199of the electric machine100is further provided for reference inFIG.1Aas well asFIG.2B. Cutting planes for the cross-sectional views shown inFIGS.1A-1Bas well as2A-2B extend through the rotational axes199.

FIG.1Bshows a detailed view of the air passage136and the air gap134. The stator106is again shown along with the rotor104and the spiral grooves132,133therein. The spiral grooves132,133are formed (e.g., cut into) the circumferential surface162. A flow pattern of the air traveling through the air passage136and the air gap134is again denoted via arrows150. The arrows150denote the general direction of airflow. However, it will be understood that the airflow pattern has greater complexity, in practice. As shown inFIG.1B, air is directed inward through the air passage towards the machine's rotational axis and then axially outwards away from the center170of the machine towards axially opposing ends of the machine. The spiral grooves132,133may have a mirrored geometry to generate the axially outward airflow. In this way, the likelihood of coolant entering the air gap is significantly reduced and any coolant that has found its way into the gap is expelled therefrom. Consequently, machine drag losses are reduced.

FIG.2Ashows another example, of an electric machine200. The electric machine200shown inFIG.2Aincludes some components that are similar to the electric machine100shown inFIG.1A. For instance, the electric machine200includes a stator202with end windings204and an air passage206, a rotor208with spiral grooves210and212and a shaft213, and a housing214. Repeated description of the structure and functionality of these components is omitted for brevity.

A cooling assembly216in the machine depicted inFIG.2Ahas an alternate configuration to the cooling assembly146depicted inFIG.1A. To elaborate, the cooling assembly216includes a sump218with coolant220and a filter222with a pick-up224. However, a pump226in the cooling assembly216is positioned external to the housing in the illustrated example. The pump may be alternatively incorporated into the electric machine. For instance, the pump may be coupled to the housing214at an external or internal location. Further, the pump226directs coolant through coolant passages227. A portion of the coolant passages227traverse the stator202and are in fluidic communication with spray rings228. The spray rings228are positioned on opposing axial sides230and232of a stator core234. To elaborate, the spray rings228may be coupled (e.g., adhesively bonded, welded, press-fit, combinations thereof, and the like) to surfaces236of the stator202. The spray rings228include channels238. The channels238are in fluidic communication with a portion of the coolant passages227. Specifically, outlets239of some of the channels238open into the channels238of the spray rings228. The channels238may be profiled to generate a coolant spray241that is directed toward the end windings204. Further, the spray rings228may have annular shapes that allow the end windings204to pass therethrough. The spray rings228may be coupled to opposing axial side surfaces (e.g., axial end faces) of the stator core234.

A detailed view of one of the spray rings228, the stator202, and associated components is depicted inFIG.2B. The channel238of the spray ring228is further shown inFIG.2B. The channel238extends axially through the ring and directing the coolant radially inwards toward the end windings204in the form of the coolant spray241. The other spray rings in the electric machine200, shown inFIG.2Amay be constructed in a similar manner. In this way, coolant may be effectively directed towards the end windings.

FIGS.3A and3Bdepict examples of spiral grooves300and302, respectively. These spiral grooves300,302may be positioned on opposing axial sides of a rotor304in which they are formed. In this way, air flow may be generated in a direction that is axially outward towards the axial ends of the rotor lamination stack. Consequently, the chance of coolant entering the air gap is reduced.

The pitch306of the spiral groove300is illustrated inFIG.3A. Likewise, the pitch308of the spiral groove302is illustrated inFIG.3B. Each of the pitches306and308may be less than or equal to 1.0 centimeters (cm). In this way, a targeted amount of airflow through the air gap may be generated that strategically reduces the amount of coolant that enters the air gap. However, in other examples, the pitches306and308may not be equivalent.

The pitches306and/or308of the spiral grooves300and302, respectively may remain constant along the axial length of the rotor304. However, in other examples, the pitches may be progressively increase or decrease in an axially outward direction away from the longitudinal center of the machine to enable the flow dynamics of the airflow through the gap to be tuned, if desired.

FIG.3Cshows another example of a spiral groove370of a rotor372with a core373. The spiral groove370is an example of any of the previously described spiral grooves. The spiral groove370has a depth374that extends radially inward into the rotor core. To elaborate, the groove may be cut (e.g., milled) or otherwise formed in the rotor core's outer circumferential surface. The depth374may be less than or equal to 0.1 millimeters (mm) to enable a desired amount of airflow to be generated in the air gap without unduly impacting the electromagnetic characteristics of the rotor.

FIGS.1A-3Dprovide for a method used to rotate a rotor in an electric machine and spray a coolant towards stator end windings, in one example. In this example, the electric machine includes a rotor with an outer circumferential surface that has multiple spiral groove. The electric machine further includes an air passage which radially extends from the stator to an air gap between the stator and the rotor.

The technical effect of the motor cooling system operating methods described herein is to increase machine efficiency by reducing drag losses caused by coolant (e.g., oil) in the machine's air gap.

The invention will be further described in the following paragraphs. In one aspect, an electric machine is provided that comprises a rotor that includes an outer circumferential surface with one or more spiral grooves; a stator that circumferentially surrounds the rotor and includes end windings; an air passage radially extending from the stator to an air gap between the stator and the rotor; and a cooling assembly configured to spray a coolant towards the end windings.

In another aspect, a method for operation of an electric machine is provided that comprises rotating a rotor in the electric machine; and spraying a coolant towards end windings of a stator; wherein the electric machine includes: a rotor that includes an outer circumferential surface with one or more spiral grooves; the stator that circumferentially surrounds the rotor and includes end windings; and an air passage radially extending from the stator to an air gap between the stator and the rotor.

In yet another aspect, an electric motor-generator is provided that comprises a rotor that includes an outer circumferential surface with plurality of laminations that are formed in a stack; wherein an outer surface of the stack of laminations includes one or more spiral grooves configured to generate airflow through a gap between the rotor and a stator; wherein a stator that circumferentially surrounds the rotor and includes end windings; an air passage radially extending through the stator to the air gap; and a cooling assembly that is configured to spray a coolant towards the end windings.

In any of the aspects or combinations of the aspects, the one or more spiral grooves may be formed in a stack of rotor laminations.

In any of the aspects or combinations of the aspects, the electric machine may further comprise a breather positioned at an inlet of the air passage.

In any of the aspects or combinations of the aspects, the inlet of the air passage may be positioned adjacent to an outer surface of the stator.

In any of the aspects or combinations of the aspects, the breather may include a filter.

In any of the aspects or combinations of the aspects, the one or more spiral grooves may have a depth of less than 0.1 millimeters (mm).

In any of the aspects or combinations of the aspects, the one or more spiral grooves may have a pitch that is less than or equal to 1.0 centimeters (cm).

In any of the aspects or combinations of the aspects, the cooling assembly may include a plurality of nozzles that spray the coolant toward the end windings.

In any of the aspects or combinations of the aspects, the cooling assembly may include a plurality of spray rings that are coupled to a stator core and directs the coolant towards the end windings.

In any of the aspects or combinations of the aspects, the coolant may be oil.

In any of the aspects or combinations of the aspects, the electric machine may be a traction motor in an electric drive of a vehicle.

In any of the aspects or combinations of the aspects, the cooling assembly may include a sump configured to collect the coolant.

In any of the aspects or combinations of the aspects, the electric machine may further comprise a pump configured to receive coolant from the sump, wherein the pump may be incorporated within the electric machine.

In any of the aspects or combinations of the aspects, the electric machine may include a breather positioned at an inlet of the air passage.

In any of the aspects or combinations of the aspects, the electric motor-generator may further comprise a breather positioned at an inlet of the air passage and including a filter.

In any of the aspects or combinations of the aspects, the spiral grooves may have a depth of less than 0.1 millimeters (mm) and a pitch that is less than or equal to 1.0 centimeters (cm).

In any of the aspects or combinations of the aspects, the traction motor-generator may be a multi-phase motor generator and wherein the stator is configured to electrically couple to an inverter.

In any of the aspects or combinations of the aspects, the cooling assembly may include a plurality of spray rings that are coupled to a stator core and directs the coolant towards the end windings.

In another representation, a motor cooling system is provided that comprises a rotor core that is formed of a stack of laminations with spiral depressions extending around a peripheral surface of the stack of laminations and configured to drive airflow through an air gap between the rotor core and the stator, where a radial air passage extends through the stator and opens into the air gap between a first axial end of the stack of laminations and a second axial end of the stack of laminations.

Note that the example control and estimation routines included herein can be used with various motor configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other system hardware in combination with the electronic controller. As such, the described actions, operations, and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the vehicle and/or driveline control system. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. One or more of the method steps described herein may be omitted if desired.

While various embodiments have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant arts that the disclosed subject matter may be embodied in other specific forms without departing from the spirit of the subject matter. The embodiments described above are therefore to be considered in all respects as illustrative, not restrictive. As such, the configurations and routines disclosed herein are exemplary in nature, and that these specific examples are not to be considered in a limiting sense, because numerous variations are possible. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.