ELECTRIC MACHINE SLOT LINER WITH ENHANCED VARNISH CONTROL

An electric machine includes a stator core having an outer circumferential surface, an inner circumferential surface, and longitudinal slots recessed into the inner circumferential surface. Each of the slots has first and second radial walls, an outboard circumferential wall extending between the radial walls, an entrance portion having opposing first and second angled walls extending divergently away from the inner circumferential surface, a first shoulder connecting the first radial wall to the first angled wall, and a second shoulder connecting the second radial wall to the second angled wall. Windings are disposed in the slots. Slot liners are also disposed in the slots such that the windings are disposed in an interior of the slot liners. At least one of the slot liners has first and second flaps angled towards each other from opposing sidewalls of the slot liner, wherein the first and second flaps cooperate to define an inner varnish dam, and the first flap, the second flap, and the corresponding one of the slots cooperate to define an outer varnish dam.

TECHNICAL FIELD

The present disclosure relates to electric machines and more specifically to electric machines that include slots liners having varnish-control features.

BACKGROUND

Vehicles such as fully electric vehicles and hybrid-electric vehicles contain a traction-battery assembly to act as an energy source for the vehicle. The traction battery may include components and systems to assist in managing vehicle performance and operations. The traction battery may also include high-voltage components, and an air or liquid thermal-management system to control the temperature of the battery. The traction battery is electrically connected to an electric machine that provides torque to driven wheels. Electric machines typically include a stator and a rotor that cooperate to convert electrical energy into mechanical motion or vice versa.

SUMMARY

According to one embodiment, an electric machine includes a stator core having an outer circumferential surface, an inner circumferential surface, and longitudinal slots recessed into the inner circumferential surface. Each of the slots has first and second radial walls, an outboard circumferential wall extending between the radial walls, an entrance portion having opposing first and second angled walls extending divergently away from the inner circumferential surface, a first shoulder connecting the first radial wall to the first angled wall, and a second shoulder connecting the second radial wall to the second angled wall. Windings are disposed in the slots. Slot liners are also disposed in the slots such that the windings are disposed in an interior of the slot liners. At least one of the slot liners has first and second flaps angled towards each other from opposing sidewalls of the slot liner, wherein the first and second flaps cooperate to define an inner varnish dam, and the first flap, the second flap, and the corresponding one of the slots cooperate to define an outer varnish dam.

According to one embodiment, an electric machine includes a stator core having an outer circumferential surface, an inner circumferential surface, and longitudinal slots recessed into the inner circumferential surface. Each of the slots has first and second radial walls, an outboard circumferential wall extending between the radial walls, an entrance portion having opposing first and second angled walls extending divergently away from the inner circumferential surface, a first shoulder connecting the first radial wall to the first angled wall, and a second shoulder connecting the second radial wall to the second angled wall. Slot liners are disposed in the slots. At least one of the slot liners includes a pair of opposing sidewalls spaced apart in a circumferential direction of the core, an outer end wall extending between sidewalls and cooperating with the sidewalls to define an interior, a first flap extending from one of the sidewalls at an angle towards the inner circumferential surface and terminating at an edge that engages with the second angled wall, and a second flap extending from the other of the sidewalls at an angle towards the inner circumferential surface and terminating at an edge that engages with a surface of the first flap to close the interior. Windings disposed in the interior of the slot liners.

According to another embodiment, an electric machine includes a stator core having an outer circumferential surface, an inner circumferential surface, and longitudinal slots recessed into the inner circumferential surface, each of the slots including first and second radial walls, an outboard circumferential wall extending between the radial walls, and an entrance portion. Windings are disposed in the slots. Slot liners are disposed in the slots such that the windings are disposed in an interior of the slot liners. At least one of the slot liners has a pair of opposing sidewalls, a first flap extending from one of the sidewalls at an angle towards the inner circumferential surface and terminating at an edge that engages with a side of the slot, and a second flap extending from the other of the sidewalls at an angle towards the inner circumferential surface and terminating at an edge that engages with a surface of the first flap to close the interior.

DETAILED DESCRIPTION

Referring toFIG.1, an electric machine20may be used in a vehicle such as a fully electric vehicle or a hybrid-electric vehicle. The electric machine20may be referred to as an electric motor, a traction motor, a generator, or the like. The electric machine20may be a permanent magnet machine, an induction machine, or the like. In the illustrated embodiment, the electric machine20is a three-phase alternating current (AC) machine. The electric machine20is capable of acting as both a motor to propel the vehicle and as a generator such as during regenerative braking.

The electric machine20may be powered by a traction battery of the vehicle. The traction battery may provide a high-voltage direct current (DC) output from one or more battery-cell arrays, sometimes referred to as battery-cell stacks, within the traction battery. The battery-cell arrays may include one or more battery cells that convert stored chemical energy to electrical energy. The cells may include a housing, a positive electrode (cathode), and a negative electrode (anode). An electrolyte allows ions to move between the anode and cathode during discharge, and then return during recharge. Terminals allow current to flow out of the cells for use by the vehicle.

The traction battery may be electrically connected to one or more power electronics modules. The power electronics modules may be electrically connected to the electric machines20and may provide the ability to bi-directionally transfer electrical energy between the traction battery and the electric machine20. For example, a typical traction battery may provide a DC voltage while the electric machine20may require a three-phase (AC) voltage. The power electronics module may include an inverter that converts the DC voltage to a three-phase AC voltage as required by the electric machine20. In a regenerative mode, the power electronics module may convert the three-phase AC voltage from the electric machine20acting as a generator to the DC voltage required by the traction battery.

Directional terms used herein are made with reference to the views and orientations shown in the exemplary figures. A central axis is shown in one or more of the figures and described below. Terms such as “outer” and “inner” are relative to the central axis. For example, an “outer” surface means that the surfaces faces away from the central axis, or is outboard of another “inner” surface. Terms such as “radial,” “diameter,” “circumference,” etc. also are relative to the central axis. The terms “front,” “rear,” “upper” and “lower” designate directions in the drawings to which reference is made. The terms, connected, attached, etc., refer to directly or indirectly connected, attached, etc., unless otherwise indicated explicitly or by context.

Referring toFIGS.1and2, the electric machine20includes a housing21that encloses the stator22and the rotor24. The stator22is fixed to the housing21and includes a cylindrical core32having an inner circumferential surface or inner diameter (ID) that defines a hole30, an outer circumferential surface or outer diameter (OD)29, and windings40. The core32may be formed from a plurality of stacked laminations. The rotor24is supported for rotation within the hole30about a central axis27. The rotor24may include windings or permanent magnets that interact with windings of the stator22to generate rotation of the rotor24when the electric machine20is energized. The rotor24may be supported on a driveshaft26that extends through the housing21and is concentric with the central axis27. The driveshaft26is configured to couple with a drivetrain of the vehicle.

The stator core32defines slots34circumferentially arranged around the core32and extending outward from the inner diameter28. The slots34may be equally spaced around the circumference and extend axially from a first end36of the core32to a second end38. In the illustrated embodiment, the core32defines forty-eight slots and has eight poles, but the core32may include more or fewer slots and/or poles in other embodiments. For example, the core32may define seventy-two slots and have twelve poles.

Slots liners35are received in the slots34with each slot having one liner35therein. The liners35provide electrical insulation between the stator core32and the windings40. As will be described in more detail below, the liners35also include features for controlling the flow of varnish.

The windings40may be hairpin (as shown), distributed, or concentrated. In the example embodiment, the windings40comprise a plurality of interconnected hairpins42. Hairpin windings are an emerging technology that enhance efficiency for electric machines used in vehicles and other applications. The hairpin windings40enhance efficiency by providing a greater amount of stator conductors to reduce resistance of the winding40without encroaching into space reserved for the electrical steel and the magnetic flux path. The hairpins are generally U-shaped with each bent to include a pair of legs joined by a crown. The hairpins42are installed in the stator core32by inserting the legs through corresponding ones of the slots34. All of the hairpins may be installed from the same end of the stator core32, e.g., end36, so that all of the crowns are located on one end of the stator, e.g., end36, and the ends of the legs are located on the other end, e.g., end38. Once installed, the legs of the hairpins42are bent to form twists that connect with the twists of other hairpins. The ends of corresponding twists are joined by a connection such as a weld. The hairpins are typically made of bar conductors having a rectangular cross-section, but the hairpins may have a circular or other cross-sectional shape.

The windings40may include three phases. Each phase includes one or more paths. For example, each phase may include two parallel paths. The paths are formed by a plurality of interconnected pins42, that once connected, form a continuous circuit. Each of the paths includes a first end that starts a terminal and a second end that ends at a neutral connection, e.g., a neutral bar

Referring toFIGS.2and3, each of the slots34may contain the legs43of six hairpins42disposed within an interior48of the liner35, for example. Each of the slots34may include first and second radial walls,50,52, an outboard circumferential wall54extending between the radial walls, an entrance portion56. The entrance portion56opens into the air gap (space between stator and rotor) at the inner diameter28. The entrance portion56may have opposing first and second angled walls60,62extending divergently away from the inner circumferential surface (ID)28, a first shoulder64connecting the first radial wall50to the first angled wall60, and a second shoulder66connecting the second radial wall52to the second angled wall62. The angled walls terminate at the ID28with a gap or opening68defined therebetween. The above-described walls, shoulders, etc. may extend continuously along the entire length of the stator core32.

The slot liner35may include a pair of opposing sidewalls80,82are spaced apart in the circumferential direction of the core32. An outer end wall84extends between the sidewalls80,82and cooperates with the sidewalls to define the interior48. A first flap86extends from the sidewall80at an angle towards the inner circumferential surface28and terminates at an edge90that engages with the second angled wall62. A second flap88extends from the sidewall82at an angle towards the inner circumferential surface28and terminates at an edge92that engages with a surface94of the first flap86to close the interior48. The above-described walls and flaps may be internally formed portions of the liner35. The liner35may have a constant cross-sectional shape along its entire length with the above-described walls and flaps extending longitudinally between opposing ends of the liner35.

The stator is varnished following complete assembly to increase structural rigidity, enhance thermal conduction, and provide electrical insulation. The varnish may be applied by a drip-the machine that has drip nozzles. The nozzles may be placed near the end windings and apply varnish at the conductor/liner interface and the liner/slot interface to achieve the desired in-slot varnish fill. In order to enhance retention of the varnish within the slot liner interior48, and within the gap between the slot and the liner, and prevent the flow varnish into the air gap, varnish dams are provided.

For example, the flaps86and88cooperate with each other and the stator core to define varnish dams configured to inhibit the flow of varnish. In the example ofFIG.3, the first and second flaps86,88cooperate to define an inner varnish dam100, and the first flap, the second flap, and the slot cooperate to define an outer varnish dam102. The inner varnish dam100traps varnish within the interior48of the slot liner35, whereas the outer varnish dam102traps varnish within the slot34and mitigates the flow varnish into the air gap. The shoulders64,66also engage with liner35and/or flaps86,88to inhibit the flow of varnish from the void space between the slot34and the liner35towards the air gap.

The first flap86defines a first angle with the sidewall80, and the second flap defines a second angle with the sidewall82. The second angle may be greater than the first angle so that the first flap86engages with the stator core32and the second flap88engages with the first flap86. However, in other embodiments, this may be flipped. The first flap86may also be wider than the second flap88.

The embodiment ofFIG.3is but one example of a slot liner cooperating with a slot to define varnish dams.FIGS.4and5described alternative embodiments for the slot liner. In these figures, common components will maintain their reference numerals and may not be discussed again for brevity,

FIG.4illustrates another liner110having a first flap112and the second flap114. The first flap extends from the sidewall116as a tip118that engages with the angled wall62of the slot34. SimilarFIG.4, the second flap114extends from the sidewall120of the liner and has a tip122that engages with a surface of the first flap112. The angle of the flaps in this embodiment are increased to increase the size of the inner dam124. The first flap112is still wider than the second flap, but the angle of the second flap114relative to the wall120is greater than the angle between the flap112and the wall116to provide the larger inner dam124. The size of the outer dam126is reduced compared toFIG.3.

FIG.5illustrates another liner130having even larger inner dam132. In this embodiment, the first flap134extends from the sidewall135and the first angle forming a first segment136and then extends circumferentially to form a second segment138. The second segment138the entrance or opening68of the slot34. The first segment136may contact the slot34at the shoulder64and near the entrance68. The second segment138includes an end portion that engages with the angle sidewall62. A second flap140extends from the sidewall142and an angle similar to that of embodiment ofFIG.4. An edge144of the flap140engages with the second segment138, e.g., surface146, to close the interior150of the slot liner130.

The above-described varnish dams inhibit the flow varnish to unwanted areas while retaining the varnish within desired areas. This results in more uniform varnish cover within the slots and slot liners while reducing or eliminating varnish flow within the air gap between the stator and the rotor.