Patent Publication Number: US-2022219785-A1

Title: Drive unit for electric vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Patent Application No. 63/135,466, filed Jan. 8, 2021, and U.S. Provisional Patent Application No. 63/135,474, filed Jan. 8, 2021, which are incorporated by reference in their entirety herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to electric vehicles and, in particular embodiments, to powertrain components of electric vehicles. 
     BACKGROUND 
     Electric powertrains of electric vehicles, including electric powersport vehicles (e.g., all-terrain vehicles (ATVs), personal watercraft (PWC), and snowmobiles), typically include a battery system, one or more electrical motors, each with a corresponding electronic power inverter (sometimes referred to as a motor controller), and various auxiliary systems (e.g., cooling systems). Efficiencies in size, weight, and energy consumption of system components improve vehicle performance (e.g., responsiveness, range, and reliability) and cost, particularly for electric powersport vehicles where space and weight are at a premium. 
     SUMMARY 
     Some embodiments of the present disclosure relate to drive units with efficiencies and power densities that are suitable for use in electric powersport vehicles. Such drive units may provide, inter alia, high efficiencies at maximum power and/or compact configurations of a rotor, stator and/or power inverter. 
     One example provides a drive unit for an electric vehicle comprising a drive unit housing defining a form factor having a volume of less than 27,000 cm 3 , an electric motor comprising a rotor, a stator and a rotor shaft, and an electric inverter in electrical communication with the electric motor. Both the electric motor and the electric inverter may be housed within the drive unit housing and the drive unit may provide a continuous power density of greater than 5 kW/kg. The electric vehicle may be an off-road powersport vehicle. 
     In some examples, the electric motor comprises a hub between the rotor shaft and a rotor laminate. The hub may comprise a less dense material than the rotor laminate. Optionally, the rotor comprises an inner diameter of greater than 90 mm and an outer diameter of less than 170 mm. 
     In some examples, a combination of the drive unit housing, electric motor and electric inverter have a combined weight of less than 30 kg. 
     In some examples, flux weakening of the drive unit occurs at a motor shaft speed of greater than 75% of a rated speed. 
     In some examples, the maximum power is provided at greater than 80% of a rated speed. 
     In some examples, the drive unit provides a torque density of greater than 7.5 Nm/kg. 
     In some examples, the rotor comprises magnets positioned in a V-shape. The magnets may define 8 poles and the stator may comprise 48 slots. Optionally, each magnet comprises a volume greater than 7000 mm 3 . The stator may comprise symmetric windings with four parallel coils, with three turns per coil. Alternatively or additionally, the rotor defines a rotor skew between at least two rotor slices. For example, the rotor may define a rotor skew between 3 slices with a 2-4 degree shift between slices. In some examples, the magnets may define 10 poles and the stator may comprise 66 slots. 
     In some examples, the drive unit housing defines a first compartment for the electric motor and a second compartment for the electric inverter, the first and second compartments being separated by a shared wall. The first compartment and second compartment may be positioned adjacent each other along a longitudinal axis of the form factor. Cooling passages may be present in the shared wall separating the electric motor and the electric inverter. 
     One example provides a snowmobile comprising an electric motor comprising a rotor and a stator, an electric inverter in electrical communication with the electric motor, and a drive unit housing in which both the electric motor and electric inverter are disposed. A combination of the electric motor, electric inverter and drive unit housing may weigh less than 30 kg and the drive unit provides a power density of greater than 5 kW/kg. 
     One example provides a power inverter of an electric drive unit, the power inverter comprising: a housing comprising a compartment at least partially formed by a first wall and an opposing second wall; a plurality of electrical switches to convert direct current (DC) power into alternating current (AC) power, the plurality of electrical switches coupled to the first wall within the compartment; a power controller to control the plurality of electrical switches, the power controller coupled to the plurality of electrical switches; and a motor controller to control the power controller, the motor controller disposed between the power controller and the second wall. 
     In some examples, the power controller is disposed between the plurality of electrical switches and the motor controller. 
     In some examples, the motor controller is secured to the second wall. Optionally, a plate is disposed between the power controller and the motor controller, the plate being coupled to the second wall to secure the motor controller to the second wall. The plate may be coupled to the second wall via fasteners. For example, the fasteners may comprise bolts, the second wall may comprise through-holes to receive the bolts, and the plate may comprise threaded openings to couple to the bolts. The plate may be electrically grounded to electrically shield the motor controller. 
     In some examples, the first wall, the plurality of switches, the power controller, the motor controller and the second wall are arranged in a stack along a longitudinal axis of the housing. A capacitor may be disposed in the compartment. The capacitor may have a first length along the longitudinal axis of the housing, the stack may have a second length along the longitudinal axis of the housing, and the second length may be less than or substantially equal to the first length. 
     In some examples, the power controller comprises a first circuit board and the motor controller comprises a second circuit board. 
     In some examples, the first wall comprises a fluid chamber to cool the plurality of electrical switches. 
     In some examples, the second wall is a removeable cover of the housing. 
     In some examples, the plurality of electric switches convert the DC power into three-phase AC power. 
     In some examples, the power inverter comprises an electrical connector to connect to the motor controller to carry control signals to the motor controller. The electric drive unit may be implemented in an electric vehicle and the electrical connector may carry throttle signals to the motor controller. 
     In some examples, a cable is connected between the power controller and the motor controller to provide communication between the power controller and the motor controller. 
     In some examples, the first wall is a shared wall separating the compartment from an electric motor of the drive unit. 
     One example provides a power inverter of an electric drive unit, the power inverter comprising: a housing comprising a compartment at least partially formed by a first wall and an opposing second wall, the compartment having a first portion, a second portion and a third portion, the second portion being adjacent to the first portion and to the third portion; at least one capacitor connected between positive and negative leads of a direct current (DC) power supply, the at least one capacitor disposed within the first portion of the compartment; a plurality of electrical switches disposed within the second portion of the compartment, the plurality of electrical switches connected to the positive and negative leads of the DC power supply to convert DC power to AC power; and a plurality of terminals connected to the plurality of electrical switches to transfer the AC power to an electric motor of the electric drive unit, the plurality of terminals disposed within the third portion of the housing. 
     In some examples, the second portion is disposed between the first portion and the second portion. Optionally, the first portion, the second portion and the third portion of the compartment are arranged along a transverse axis of the housing. 
     In some examples, the power inverter comprises a current sensor to measure electric current in one of the plurality of terminals, the current sensor disposed in the third portion of the housing and coupled to the first wall. 
     One example provides a method of assembly for a power inverter of an electric drive unit, the method comprising: coupling a plurality of electrical switches to a first wall of a housing of the power inverter, the plurality of electrical switches to convert direct current (DC) power into alternating current (AC) power; coupling a power controller to the plurality of electrical switches opposite the first wall, the power controller to control the plurality of electrical switches; positioning a motor controller between the power controller and a second wall of the housing, the motor controller to control the power controller; and securing the motor controller to the second wall of the housing. 
     Additional and/or alternative features and aspects of examples of the present technology will become apparent from the following description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an electric vehicle, in particular, an electric power sport vehicle, including a drive unit in accordance with one example of the present disclosure. 
         FIG. 2  is a block and schematic diagram illustrating an electric vehicle including a drive unit in accordance with the present disclosure. 
         FIGS. 3A-3C  are perspective views illustrating a drive unit, according to one example of the present disclosure. 
         FIG. 4  is an exploded view illustrating portions of a drive unit, according to one example of the present disclosure. 
         FIG. 5  is a perspective view illustrating portions of an inverter housing of a drive unit, according to one example of the present disclosure. 
         FIG. 6  is a cross-sectional view of a drive unit housing, according to one example of the present disclosure. 
         FIG. 7  is a cross-sectional view of a drive unit, according to one example of the present disclosure. 
         FIG. 8  is a perspective view illustrating portions of a shared wall of a drive unit housing, according to one example of the present disclosure. 
         FIG. 9  is a schematic diagram illustrating a cross-sectional view of a hollow portion of a motor shaft, according to one example of the present disclosure. 
         FIGS. 10A-10B  are perspective views illustrating portions of a network of fluid circulation pathways for circulating a thermal transfer fluid through a drive unit, according to one example of the present disclosure. 
         FIG. 11  is a flow diagram illustrating a method, according to one example of the present disclosure. 
         FIG. 12A  is a front plan view of a rotor of a drive unit, according to one example of the present disclosure; 
         FIG. 12B  is a front plan view of a rotor of a drive unit, according to another example of the present disclosure. 
         FIG. 13A  is a front plan view of a rotor and stator of a drive unit, according to one example of the present disclosure. 
         FIG. 13B  is a front plan view of a rotor and stator of a drive unit, according to another example of the present disclosure. 
         FIG. 14  is a graph illustrating a torque vs speed curve for a drive unit, according to one example of the present disclosure. 
         FIG. 15  is a plan view of an inverter of a drive unit with the end cover removed, according to one example of the present disclosure. 
         FIG. 16  is a perspective view of an inverter of a drive unit with the end cover removed, according to one example of the present disclosure. 
         FIG. 17  is a cross-sectional view of an inverter of a drive unit, taken along a transverse axis of the drive unit, according to one example of the present disclosure. 
         FIG. 18  is a plan view of an inverter of a drive unit, according to another example of the present disclosure. 
         FIG. 19  is a plan view of capacitors, a power controller, a power switching network and terminals in an inverter of a drive unit, according to one example of the present disclosure. 
         FIG. 20  is a perspective view of capacitors, a power controller, a power switching network and terminals in an inverter of a drive unit, according to one example of the present disclosure. 
         FIG. 21  is a flow diagram illustrating a method for assembling of an inverter of a drive unit, accord to one example of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific examples in which the disclosure may be practiced. It is to be understood that other examples may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense. It is to be understood that features of the various examples described herein may be combined, in part or whole, with each other, unless specifically noted otherwise. 
     Electric powertrains for electric vehicles, including electric powersport vehicles (e.g., motorcycles, all-terrain vehicles (ATVs), personal watercraft (PWC), (e.g., side-by-side) utility task vehicles (UTVs) and snowmobiles), typically include a battery system, one or more electrical motors, each with a corresponding electronic power inverter (sometimes referred to as a motor controller), and various auxiliary systems (e.g., cooling systems). Efficiencies in size, weight, and energy consumption of system components improve vehicle performance (e.g., responsiveness, range, and reliability) and cost, particularly for electric powersport vehicles where space and weight are at a premium. 
     The conflicting requirements of being small and light, while also being robust, powerful and efficient have made designing and producing electric drive units for off-road powersport vehicles challenging. As used herein, the term “drive unit” refers to electric motors and associated motor controllers (i.e. power inverters) suitable for transmitting motive power. While particular examples of electric motors and associated motor controllers are described below, the term “drive unit” should not be limited to the examples provided and may encompass other designs and configurations for electric motors. 
     Off-road powersport vehicles differ from on-road automotive vehicles (e.g. cars, trucks and motorcycles) both in terms of the way they are driven and the performance expectations of their riders. Electric drive units for on-road automotive vehicles are designed to operate well below their maximum power capability during typical driving conditions (such as during city driving and/or highway driving). In contrast, according to one aspect of the present disclosure, off-road powersport vehicles are designed to operate fairly continuously at, or near, their maximum power capability. These powersport vehicles may provide an improved rider experience by enabling extended operation at high speeds and/or high torque values. For example, high torque may be useful in some off-road environments where a powersport vehicle might be prone to getting stuck (e.g., in deep snow). A challenge associated with continuously operating an electric drive unit of a powersport vehicle near its maximum power capability is mitigating the buildup of heat in the drive unit (e.g., preventing the overheating of a motor), which may reduce power and may also damage the drive unit. In some embodiments, electric drive units are designed and configured to address these challenges by providing a high efficiency at a maximum power capability. Increasing motor efficiency may, inter alia, reduce the amount of potentially harmful waste heat being generated at high motor speeds (i.e. rpm) and/or high torque values. Because electric drive units for on-road automotive vehicles are rarely operated at their maximum power capability, high efficiency at maximum power is typically not a concern for the electric drive units of on-road automotive vehicles. 
     In addition to providing high power at high motor efficiencies, electric drive units for powersport vehicles are designed to be relatively small to permit accommodation within the limited space available within the powersport vehicle. Electric drive units for powersport vehicles are also designed to be relatively light weight to maintain battery range-efficiency for the vehicle. The heavier the drive unit, the more energy (i.e., battery capacity) is required to achieve a desirable range. 
     To accommodate the requirements of the electric powersport vehicles according to the present disclosure (e.g., electric snowmobiles), some embodiments provide a drive unit that provides a continuous power density of greater than 5 kW/kg from the combination of a motor and inverter contained within a drive unit housing having a volume of less than 27,000 cm 3 . A compactly designed form factor for the motor and inverter, combined with a stator and rotor construction that balances motor losses with light weight power generation, provide a drive unit with performance characteristics suitable for an electric powersport vehicle. Specifically, the drive unit may provide a maximum efficiency at maximum power of greater than 96%, and in some embodiments greater than 97%. Further detail regarding such a drive unit is provided elsewhere herein. One aspect of the present disclosure provides a snowmobile having a drive unit comprising an electric motor, an electric inverter and a drive unit housing that together weigh less than 30 kg (and in some examples less than 26 kg) and provide a power density greater than 5 kW/kg. 
       FIG. 1  generally illustrates an electric vehicle  10  including an electric drive unit  30 , in accordance with examples of the present disclosure. Although illustrated as a snowmobile for example purposes, electric vehicle  10  could be other types of electric vehicles, including other types of powersport vehicles such as personal watercraft (PWC) and side-by-side vehicles. Electric vehicle  10  includes a seat  11 , which is shown as a straddle-seat, to accommodate an operator of electric vehicle  10 . Electric vehicle  10  employs an electric powertrain  12  including a battery system  14 , an electric motor  16 , and an electronic power inverter  18  for controlling electric motor  16 . Powertrain  12  is configured to propel the electric vehicle by driving one or more wheels (e.g., in the case of a motorcycle, ATV or UTV), by driving an endless track (e.g., in the case of a snowmobile) or by driving a propeller or impeller (e.g., in the case of a PWC). 
     In some examples, electric motor  16  may be a permanent magnet synchronous motor. Electric motor  16  may have a power output of between 120 and 180 horsepower. Alternatively, electric motor  16  may have a maximum output power of greater than 180 horsepower. In some examples, battery system  14  may include a rechargeable multi-cell lithium ion or other type of battery that provides a source of direct current (DC) power. Battery system  14  may include multiple battery units each including multiple battery cells. The battery cells may be pouch cells, cylindrical cells and/or prismatic cells, for example. The battery units may be housed within a battery enclosure for protection from impacts, water and/or debris. In some examples, battery system  14  may be configured to output electric power at a voltage of between 300-400 volts, or up to 800 volts, for example. 
     According to one example of the present disclosure, as will be described in greater detail herein, drive unit  30  includes a housing having a first compartment  22  and a second compartment  24  separated from one another by a shared wall  26 . In one example, as illustrated, inverter  18  is disposed in first compartment  22  and motor  16  is disposed in second compartment  24 . Together, housing  20  with motor  16  and inverter  18  disposed therein form drive unit  30  for electric vehicle  10 . 
     As will be described in greater detail below, by disposing motor  16  and inverter  18  together within housing  20 , drive unit  30  provides a volumetrically efficient form factor (e.g., a generally longitudinal form factor, such as a cylindrical form factor, for instance) which consumes less space within electric vehicle  10 . Additionally, drive unit  30  provides shortened electrical conductor lengths between output terminal of inverter  18  and input terminals of motor  16  which reduces electrical inductance and line losses (relative to separately housed motor-inverter combinations). Accordingly, drive unit  30 , in accordance with the present disclosure, provides efficiencies in both space and performance relative to conventional, separately housed motor-inverter combinations. 
       FIG. 2  is a block and schematic diagram generally illustrating one example of electric vehicle  10 , where, in addition to including electric powertrain  12  employing drive unit  30 , electric vehicle  10  further includes a thermal management system  32 . In one example, thermal management system  32  manages the temperatures (e.g., cooling) of electric powertrain  12  components, including battery system  14 , motor  16 , and inverter  18 . Thermal management system  32  may be a closed-loop cooling system and/or an open-loop cooling system. The thermal management system  32  may utilize a liquid-to-liquid cooling system (e.g., in the case of a PWC), a snow-to-liquid cooling system (e.g., in the case of a snowmobile), an air-to-liquid cooling system (e.g., using a radiator), or a combination thereof. In accordance with examples of the present disclosure, as will be described in greater detail below, housing  20  of drive unit  30  includes a network of fluid circulation pathways  34  through which the thermal transfer fluid is circulated, as indicated arrows  36 , to manage the temperatures of motor  16  and inverter  18 . 
       FIGS. 3A-3C  illustrate perspective views of drive unit  30 , according to examples of the present disclosure.  FIG. 4  is an exploded view illustrating portions of drive unit  30 , according to one example. In some examples, housing  20  includes a first housing section  40  forming a first compartment  22  for housing inverter  18 , and a second housing section  42  forming a second compartment  24  for housing electric motor  16 . First and second housing sections  40  and  42  may each include at least some walls or other structural components of housing  20 . While first and second housing sections  40  and  42  form first and second compartments  22  and  24 , respectively, first and second housing sections  40  and  42  might not fully enclose first and second compartments  22  and  24 . 
     In one example, a perimeter of housing  20  is confined within a generally longitudinal form factor  44  (graphically represented by dashed lines in  FIG. 3A ), where first and second housing sections  40  and  42 , respectively forming first and second compartments  22  and  24 , are disposed longitudinally relative to one another within the form factor. In one example, as illustrated, form factor  44  is generally cylindrical in shape with first and second housing sections  40  and  42  being disposed longitudinally relative to one another along a longitudinal axis  48  of generally cylindrical form factor  44 . Shared wall  26  is generally circular in shape. In one example, longitudinal axis  48  of form factor  44  generally coincides with a longitudinal axis of a shaft  46  (i.e., a rotor shaft) of motor  16  (which extends from second housing section  42 ). In examples, as described below, first and second housing sections  40  and  42  are separable from one another. 
     In one example, first housing section  40  includes shared wall  26 , which provides a base for first housing section  40  and which is disposed transversely to longitudinal axis  48  of form factor  44 . Shared wall  26  may be integrally formed with first housing section  40 . In one example, shared wall  26  is substantially circular in shape, but any suitable shape may be employed. First housing section  40  further includes a perimeter sidewall casing  50 . In one example, as illustrated, perimeter sidewall casing  50  is ring- or band-shaped to form a generally tubular or circumferentially extending perimeter sidewall. In one example, the ring- or band-shaped perimeter sidewall casing  50  may be formed of a partial or continuous curved wall section, or may be formed from multiple straight wall sections extending from shared wall  26  that together form the ring- or band-shaped sidewall casing  50 . In one example, perimeter sidewall casing  50  extends orthogonally from shared wall  26  and longitudinally relative to form factor  44 , where shared wall  26  and circumferentially extending sidewall  50  together are generally can- or cup-shaped to form first compartment  22  for housing inverter  18 . An end cover  52  is separably or removably coupled to sidewall casing  50  to enclose first compartment  22 . 
     In one example, second housing section  42  includes a perimeter sidewall casing  54  separably coupled to shared wall  26 , such as via a number of fasteners  55  (e.g., screws or bolts) arranged about perimeter sidewall casing  50  of first housing section  40 . In one example, perimeter sidewall casing  54  is ring- or tube-shaped to form a generally tubular or circumferentially extending perimeter sidewall. In one example, perimeter sidewall casing  54  extends orthogonally from shared wall  26  and longitudinally relative to form factor  44  with shared wall  26  serving as a base for second housing section  42 , and with shared wall  26  and perimeter sidewall casing  54  together being drum-shaped to form second compartment  24  for housing motor  16 . An end cover  56  is separably coupled to an end of perimeter sidewall casing  54  opposite shared wall  26  to enclose second compartment  24 . Alternatively, end cover  56  may be integrally formed with sidewall casing  54  of the second housing section  42 , such that the shared wall  26  acts as an endplate for enclosing the second compartment  24 . 
     While shared wall  26  is described as being part of first housing section  40 , in other examples, shared wall  26  may be part of second housing section  42 . In other examples, shared wall  26  may be separable from both first and second housing sections  40  and  42 . 
     In one example, end cover  52  includes positive and negative DC connection terminals  60  and  62  extending there through for electrical connection of capacitors of inverter  18  (see  120  in  FIG. 7 ) to battery system  14  (see  FIGS. 1 and 2 ). In one example, end cover  52  includes an electrical connector  64  for low voltage and control signal connection to control circuitry of inverter  18  (see  124  in  FIG. 7 ). 
     In one example, as will be described in greater detail below, first housing section  40  respectively includes inlet and outlet fluid ports  66  and  68  (see  FIG. 3B-3C ) for connecting fluid pathways of thermal management system  32  to fluid pathways within housing  20  of drive unit  30  for cooling of motor  16  and inverter  18 . Inlet  66  may receive a fluid from thermal management system  32 , and outlet  68  may discharge the fluid back into thermal management system  32 . It is noted that in other examples, inlet and outlet fluid ports  66  and  68  may be reversed, and that in other examples, more than one inlet and/or outlet port may be employed. In one example, as illustrated, sidewall casing  50  includes recesses  70  and  72  in which inlet and outlet fluid ports  66  and  68  are respectively disposed so that inlet and outlet fluid ports  66  and  68  are disposed within the confines of form factor  44 . 
     In one example, as illustrated by  FIG. 3A , a number of channels  73  extend circumferentially about sidewall casing  54  of second housing section  42 . When a casing sleeve  75  is disposed about the circumference of sidewall casing  54 , channels  73  become fluid pathways  74  (see  FIG. 6 ) extending about the circumference of second housing section  42 , where such fluid pathways  74  are part of the network of fluid pathways  34  through which fluid  36  is circulated by thermal management system  32  (see  FIG. 2 ) to cool motor  16 . In some examples, fluid pathways  74  may form a continuous spiral around sidewall casing  54 . In other examples, fluid pathways  74  may be separate pathways disposed in parallel with one another. In other examples, fluid pathways  74  may be a continuous pathway employing a switchback configuration. Any number of suitable implementations may be employed. 
     Reference is now made to  FIG. 4 , which illustrates end cover  52  being removed from sidewall casing  50  of first housing section  40 , and showing first and second housing compartments  22  and  24 . Motor  16  includes a rotor  76  and a stator  78  which are disposed within second compartment  24  of second housing section  42 . As will be described in greater detail below (see  FIG. 9 ), an end  80  of shaft  46  facing shared wall  26  is hollow to enable circulation of thermal transfer fluid there through to cool motor  16 . A set of electrical input leads  84  extend from stator  78  for connection to inverter  18  within compartment  22  of first housing section  40 . 
     In one example, first compartment  22  of first housing section  40  includes a first compartment portion  90  for housing capacitors of inverter  18 , and a second compartment portion  92  for housing electronic control and switching components (e.g., insulated-gate bipolar transistors (IGBTs)) of inverter  18  (see  122  and  124  in  FIG. 7 ). In one example, a set of one or more openings  94  extend through shared wall  26  to enable electrical connection between input leads  84  of stator  78  and output terminals of inverter  18 . First compartment  22  may further include a third compartment portion  93 . As shown, second compartment portion  92  may be adjacent to both first compartment portion  90  and third compartment portion  93 . In one example, second compartment portion  92  may be disposed between first compartment portion  90  and third compartment portion  93  along a radial or transverse axis of housing  20 . In one example, input leads  84  from stator  78  extend through openings  94  into third compartment portion  93  for connection to output terminals of inverter  18 . In other examples, output terminals of inverter  18  may extend through openings  94  into second housing section  42  for connection to input leads  84  of stator  78 . 
     In one example, second compartment portion  92  and third compartment portion  93  may be considered a single compartment portion. In this way, first compartment  22  may only include two compartment portions. 
       FIG. 5  is a perspective view illustrating first housing section  40  with end cover  52  removed. In one example, input power leads  84  of stator  78  extend through the set of openings  94  in shared wall  26  and terminate at a set of terminals  96  (illustrated as terminals  96   a ,  96   b , and  96   c ) in third compartment portion  93 . Sensor wiring  98  extends from motor  16  through shared wall  26  to inverter control electronics. For example, sensor wiring may connect to a resolver  98  in motor  16  to provide information regarding the position of rotor  76 . By aligning the set of openings  94  through shared wall  26  (see also  FIG. 8 ) with input leads  84  of stator  78  and with terminals  96 , the lengths of conductor pathways between inverter  18  and stator  78  are reduced which, in-turn, reduces electrical inductances and power loss, thereby improving the electrical efficiency of drive unit  30 . 
     As discussed in further detail elsewhere herein, housing  20  includes a network of fluid pathways  34  (also referred to as a fluid network) extending therethrough for cooling of motor  16  and inverter  18 . In one example, in addition to inlet and outlet ports  66  and  68 , fluid network  34  includes a fluid chamber  100  in shared wall  26  having a fluid inlet  102  and a fluid outlet  104  connecting fluid chamber  100  with other portions of the fluid network  34 . It is noted that a cover over fluid chamber  100  is not shown in  FIG. 5 . In one example, a switching module including a network of power switches (e.g., IGBTs) is mounted to shared wall  26  over fluid chamber  100  so as to be cooled by fluid circulated there through. 
       FIG. 6  is a cross-sectional view of housing  20 , according to one example, where sidewall casing  50  of first housing section  40  contiguously and integrally extends from shared wall  26 , and which together with end cover  52  forms first compartment  22 . First compartment  22  includes first compartment portion  90  for housing capacitors of inverter  18 , second compartment portion  92  for housing control and switching electronics of inverter  18 , and third compartment portion  93  for housing terminals  96 . In one example, shared wall  26  includes a bearing pocket  110  facing second compartment  24 , where bearing pocket  110  is to receive end  80  of shaft  46  of electric motor  16  and through which thermal transfer fluid circulates, as described below. In one example, fluid circulated through fluid chamber  100  acts to cool bearing pocket  110  and/or end  80  of shaft  46 . 
     Sidewall casing  54  and end cover  56  of second housing section  42  together with shared wall  26  form second compartment  24 . End cover  56  includes a bearing pocket  112  to receive an opposing end of shaft  46  of motor  16  and an aperture  114  from which shaft  46  extends. Gaskets  116  and  118  respectively form seals between shared wall  26  and sidewall casing  54  to seal second compartment  24 , and between end cover  52  and sidewall casing  50  to seal first compartment  22 . 
       FIG. 7  is a cross-sectional view of drive unit  30 , according to one example. DC capacitors  120  of inverter  18  are disposed in first compartment portion  90 , power switching network  122  and control electronics  124  of inverter  18  are disposed in second compartment portion  92 , and terminals  96  are disposed in third compartment portion  93 . Input power leads  84  from stator  78  of motor  16  extend through shared wall  26  and terminate at terminals  96  in third compartment portion  93 . Motor  16  is disposed within second compartment  24  with hollow end  80  of shaft  46  disposed within bearing pocket  110  of shared wall  26 . Further detail regarding DC capacitors  120 , power switching network  122  and control electronics  124  is provided elsewhere herein. 
       FIG. 8  is a perspective view illustrating portions of first housing section  40  facing second (motor) compartment  24  including shared wall  26  and sidewall casing  50 , according to one example. In one example, as illustrated, sidewall casing  50  contiguously extends from shared wall  26  such that shared wall  26  and sidewall casing  50  form a single base component for first housing section  40 . A plurality of ribs, such as rib  130 , extend from an inner surface of sidewall casing  50  to support a central hub  132  including bearing pocket  110  for supporting hollow end  80  of shaft  46  of motor  16 . Also illustrated is the set of openings  94  through shared wall  26 , illustrated as openings  94   a - 94   c  arrayed along an arc to align with input leads  84  of stator  78  (see  FIG. 4 ). While three openings  94   a - 94   c  are shown in the Figures, this is exemplary only. In one example, shared wall  26  may include a single opening  94  for input leads  84  and terminals  96 , or any other suitable number of openings  94 . 
     In one example, end wall  26  includes a portion of the network of fluid pathways  34  through which a thermal transfer fluid is circulated to cool components of motor  16  and inverter  18 . The network  34  of fluid pathways, which will be described in greater detail below (see  FIG. 10 ) includes inlet and outlet ports  66  and  68 , as well as fluid chamber  100  having inlet and outlet  102  and  104  (see  FIG. 5 ). In one example, network  34  further includes a tube  134  which extends within hub  132  and, as will be described below (see  FIG. 9 ), extends into hollow end  80  of shaft  46  to form inlet and outlet fluid pathways within shaft  46  to enable circulation of thermal transfer fluid therein to cool motor  16 . 
       FIG. 9  is a schematic diagram generally illustrating the circulation of thermal transfer fluid within hollow end  80  of shaft  46 . As illustrated, tube  134  extends into hollow end  80  of shaft  46  from bearing pocket  110  (disposed within hub  132 ) to form an inlet fluid pathway  136  within tube  134 , and an outlet fluid pathway  138  between the outer wall of tube  134  and inner wall of shaft  46 . In this way, tube  134  and hollow end  80  of shaft  46  form fluid pathways in shaft  46 . In one example, inlet and outlet fluid pathways  136  and  138  are respectively in fluid communication with fluid pathways  140  and  142  of the network of fluid pathways  34  (see  FIG. 10  below). 
       FIGS. 10A and 10B  are perspective views illustrating portions of network  34  of fluid pathways, according to one example, for circulating thermal transfer fluid through housing  20  to cool components of motor  16  and inverter  18 .  FIGS. 10A and 10B  illustrate network  34  as respectively viewed from second (motor) compartment  24  and first (inverter) compartment  22 . 
     In one example, as illustrated, thermal transfer fluid is received via inlet port  66  and travels through pathways  140  to inlet fluid pathway  136  within tube  134  inside shaft  46  (see  FIG. 9 ). Fluid then travels through outlet fluid pathway  138  and exits shaft  46  via fluid pathway  142 , which is concentrically disposed about end  80  of shaft  46 . Fluid then travels through a fluid pathway  144 , which forms a fan-like, semicircular path along or within shared wall  26  proximate to first compartment portion  90  of first compartment  22  to cool DC capacitors  120  of inverter  18  (see  FIG. 7 ). 
     Fluid then enters chamber  100  via inlet opening  102 , where fluid within chamber  100  cools the power switching network  122  and control electronics  124  of inverter  18  disposed within second compartment portion  92  of first compartment  22  (see  FIG. 7 ). Fluid then exits chamber  100  via outlet opening  104  and travels through a fluid pathway  146  to fluid pathways  74  circumferentially disposed about sidewall casing  54  of second housing section  42  to cool motor  16  (see, for example,  FIGS. 3A and 7 ). Fluid then exits fluid pathways  74  to outlet port  68 . 
     In one example, the fluid pathways of network  34  of fluid pathways forms a continuous fluid pathway through housing  20  such that the components of drive unit  30  are cooled in series (e.g., shaft  46 , capacitors  120 , power switching network  122 , and motor stator  78 ). In one example, the fluid pathways of shared wall  26  are disposed in series with the fluid pathways of perimeter sidewall  54  of second housing section  42  between inlet and outlet ports  66  and  68 . In one example, the fluid pathways of shared wall  26  and perimeter sidewall  54  of second housing section  42  are disposed in series with fluid pathways within hollow end  80  of shaft  46  of electric motor  16 . 
     By employing a single continuous cooling loop, the cooling system is simplified (relative to systems employing parallel pathways), such that the network of fluid pathways  34  of the present disclosure provides high efficiency and requires fewer parts relative to known systems. Additionally, disposing the network of fluid pathways  34  within the confines of housing  20  (i.e., within form factor  44 ), including disposing inlet and outlet ports  66  and  68  on end cover  52  of first housing section  40  maintains the perimeter of drive unit  30  within the generally longitudinally extending form factor  44  (see  FIG. 3A ). As described above, such form factor is volumetrically efficient and provides improved ease of installation within electric vehicles (particularly electric powersport vehicles). 
     It is noted that the network of fluid pathways  34  specifically described herein is for illustrative purposes, and represents only one example implementation of fluid network  34 . In the example shown, the fluid pathways  34  travel from an inlet port  66 , to the shaft  46 , to the channels within the shared wall  26 , to the circumferentially disposed pathways  74  in the sidewall casing  54 , and finally to the outlet port  68 . In other examples, the configuration of the fluid pathways of fluid network  34  and the order in which components are cooled may be different from that illustrated herein. In another example, the fluid pathways  34  may travel from an inlet port  66 , to the channels within the shared wall  26 , to the shaft  46 , to the circumferentially disposed pathways  74  in the sidewall casing  54 , such that the inverter  18  components are cooled prior to the motor components. For example, fluid network  34  may be implemented such that thermal transfer fluid is first directed to cool DC capacitors  120  of inverter  18 , as such capacitors may have a narrow thermal tolerance. Any number of configurations are possible. Further, one or more pathways in the network of fluid pathways may be omitted in some examples. For example, a network of fluid pathways may omit fluid pathways in shaft  46 . The fluid pathways may travel from an inlet port  66 , to the channels within the shared wall  26 , to the circumferentially disposed pathways  74  in the sidewall casing  54 , and finally to the outlet port  68 . 
     Housing  20  may be made, in whole or in part, from metals, metal alloys, composites and/or plastics. Similarly, the channels/pathways of fluid network  34  may be made, in whole or in part, from metals, metal alloys, composites and/or plastics. It is further noted that the components of housing  20 , including the channels/pathways of fluid network  34  may be manufactured according to any know technique, including machining, casting, and 3D-printing, for example. 
     In one example as shown in  FIG. 6 , the form factor  44  of the housing  20  of the drive unit  30  that is suitable for a powersport vehicle  10  may have a length “l” of 10 cm to 30 cm and a diameter “d” of 20 cm to 30 cm, or width and depth “w”, in the case of a square or rectangular cross-section, of 20 cm to 30 cm each. Accordingly, the volume of the form factor of the housing  20  may be in the order of 4,000 cm 3  to 27,000 cm 3 . In some examples, the volume of the form factor of the housing  20  may be in the order of 10,000 cm 3  to 20,000 cm 3 . In some examples, the volume of the form factor of the housing  20  may be in the order of 18,000 cm 3 . In one example, the thickness of the shared wall  26  may be between 3 mm and 8 mm, which provides a sufficient thickness to accommodate channel  144  and chamber  100 . It should be understood that the form factor  44  and shared wall  26  thickness may have any suitable dimensions, and that these dimensions may vary depending on the application and power requirements of the drive unit  30 . 
     In one example, the motor  16 , the inverter  18  and the housing  20  of the drive unit  30  may have a combined weight of less than 30 kg (and in some cases less than 26 kg) when there is no fluid circulating within the network of fluid pathways. In another example, the motor  16 , the inverter  18  and the housing  20  of the drive unit  30  may have a combined weight of less than 25 kg. In some examples, the motor  16 , the inverter  18  and the housing  20  of the drive unit  30  may have a combined weight of between 23 kg and 30 kg, and in some examples, between 24 kg and 26 kg. 
       FIG. 11  is a flow diagram illustrating a method  200  for cooling components of a drive unit, according to one example of the present disclosure. The method  200  may be performed by a drive unit housing such as housing  20 , for example. Block  202  includes receiving a fluid via an inlet port of the housing. For example, block  202  may include inlet  66  receiving a fluid. Block  204  includes circulating the fluid. In some examples, the fluid is circulated through fluid pathways formed in the housing to cool an electrical inverter and/or an electrical motor. For example, block  204  may include circulating the fluid through fluid pathways formed in a shared wall (e.g., shared wall  26 ) of the housing to cool the electrical inverter. The shared wall may separate a first compartment of the housing in which the electrical inverter is disposed and a second compartment of the housing in which the electric motor is disposed. Alternatively or additionally, block  204  may include circulating the fluid through fluid pathways formed in a perimeter sidewall of the housing (e.g., perimeter sidewall casing  54 ) to cool the electric motor. Alternatively or additionally, block  204  may include circulating the fluid through fluid pathways formed in a rotor shaft (e.g., shaft  46 ) of the electric motor to cool the electric motor. Block  206  includes discharging the fluid via an outlet port of the housing, such as outlet port  68 , for example. 
       FIG. 12A  is a front plan view of a rotor  76   a , and  FIG. 12B  is a front plan view of a rotor  76   b , according to examples of the present disclosure.  FIGS. 12A and 12B  provide two different examples of rotors  76   a ,  76   b  suitable for use with drive unit  30 . Like components will be described using like reference numbers for both rotors  76   a ,  76   b . Rotors  76   a ,  76   b  each comprise a rotor shaft  308 , a hub  310  and a rotor laminate  312  located radially outward from the hub  310 , such that the hub is positioned between the rotor shaft  308  and the rotor laminate  312 . The hub  310  may comprise a material that is less dense than the rotor laminate  312 . In one example, the hub  310  may be made of aluminum. In one example, the hub  310  may comprise an inner hub  314  surrounding the rotor shaft  308 , an outer hub  316  in communication with the rotor laminate  312  and spokes  318  extending between the inner hub  314  and the outer hub  316 , creating void regions  320  of no material between circumferentially adjacent spokes  318 . The less dense material of the hub  310  and the void regions  320  of no material, create weight efficiencies which improve power density for the drive unit  30 . 
     The rotor laminate  312  may comprise a steel material, such as silicon steel, or nickel-iron steel, among other possibilities. An inner diameter id r  of the rotor laminate  312  may be greater than 90 mm. In some examples, the inner diameter id r  may be between 90-120 mm. In some examples, the inner diameter id r  may be between 105-115 mm. 
     An outer diameter od r  of the rotor laminate  312  may be less than 170 mm. In some examples, the outer diameter od r  of the rotor laminate  312  may be between 150-165 mm. In some examples, the outer diameter od r  of the rotor laminate  312  may be between 155-160 mm. 
     An axial length of the rotor may be in the order of 45-65 mm, and in some examples in the order of 50-60 mm. 
     Embedded within the rotor laminate  312  are magnets  322 . In one example, pairs of the magnets  322  are positioned in a V-shape. The V-shape of magnets  322  provides increased flux and thus increased power to the drive unit  30  compared to magnets positioned in a straight arrangement and spanning the same circumference of the rotor laminate  312 . More specifically, the V-shape magnets provide a greater magnet surface area than a straight magnet occupying the same rotor surface (i.e. two sides of a triangle as opposed to one straight side). The V-shape topology also provides higher dq inductances which provide more torque and wider speed range than a rotor with a straight magnet occupying the same rotor surface. 
     With reference to  FIG. 12A , the magnets  322  of rotor  76   a  comprise 10 poles. With reference to  FIG. 12B , the magnets  322  of rotor  76   b  comprise 8 poles. The magnets  322  of rotor  76   b  are larger than the magnets of rotor  76   a . The magnets  322  of rotor  76   b  may comprise a volume of greater than 7000 mm 3 , and in some examples greater than 7500 mm3. In one example, the magnets  322  of rotor  76   b  have a volume between 7300 mm 3  and 7600 mm 3 . In contrast, the magnets  322  of rotor  76   a  may have a volume between 6400 mm 3 -6700 mm 3 . The use of larger magnets with a reduced number of poles may reduce the core losses in comparison to a rotor having smaller magnets and a larger number of poles. 
       FIG. 13A  is a front plan view of rotor  76   a  and a stator  78   a , and  FIG. 13B  is a front plan view of rotor  76   b  and a stator  78   b , according to examples of the present disclosure. With reference to  FIG. 13A , rotor  76   a  is shown together with a corresponding stator  78   a . Stator  78   a  comprises sixty six (66) slots  330  with a double layer asymmetric winding pattern having one turn per coil. With reference to  FIG. 13B , rotor  76   b  is shown together with a corresponding stator  78   b . Stator  78   b  comprises forty eight (48) slots  330  with a single layer symmetric winding pattern having four parallel paths (coils) with three turns per coil, which is more practical for automated mass-manufacturing. Furthermore, a winding pattern having three turns per coil provides an increased inductance compared to a winding pattern having less turns per coil. The increased inductance provides a smoother current supply making the drive unit easier to control while limiting the power via a voltage limit. 
     The stators  78   a  and  78   b  may have an inner diameter id s  greater than 150 mm. In some examples, the inner diameter id s  may be between 150-170 mm. In some examples, the inner diameter id s  may be between 155-160 mm. 
     An outer diameter od s  of the stator  78   a ,  78   b  may be less than 250 mm. In some examples, the outer diameter od s  may be between 230 mm-250 mm. In some examples, the outer diameter od s  of the stator  78   a ,  78   b  may be between 230-240 mm. 
     An air gap between the outer diameter od r  of the rotor  76   a ,  76   b  and the inner diameter id s  of the stator  78   a ,  78   b  may be approximately 0.5 mm-1 mm. 
     Although not shown in the Figures, in one example, either rotor  76   a  or rotor  76   b  may provide a rotor skew where the rotor is divided into slices along its axial length, with each slice being shifted in relation to the other slices. In one example, rotor  76   a ,  76   b  may be divided into three slices with each slice shifted (e.g. rotated) by approximately 2-4 degrees in relation to an adjacent slice. In some embodiments, the rotor  76   a ,  76   b  may be divided into more or less slices, with each slice shifted by between 1.5 and 4 degrees in relation to an adjacent slide. Providing a rotor skew may reduce cogging torques which may reduce the instant forces required to start rotating the rotor. In the case of powersport vehicles such as snowmobiles where a rider may be required to push the vehicle out of a snowbank or snowdrift, having reduced cogging torques may facilitate pushing the vehicle from a stopped state and may reduce the level of vibration and acoustic noise of the powertrain. 
     Shown in  FIG. 14  is a normalized maximum torque to rated speed graph for the motors of  FIGS. 13A and 13B . In one example, the arrangement of windings and magnets for motors  16  having stator and rotor  76   a ,  78   a  and stator and rotor  76   b ,  78   b  provide relatively consistent (e.g. flat) torque for speeds up to 75% to 88% of a rated speed. In some examples, flux weaking, where the voltage in the windings becomes equal to the DC voltage in the battery, starts to occur after approximately 88% of a rated speed. Designing the motor  16  to have flux weakening occur after approximately 88% of a rated speed allows for high power with minimal losses. In one example, the arrangement of windings and magnets for the motors  16  having stator and rotor  76   a ,  78   a  and stator and rotor  76   b ,  78   b  provide a max power at speeds of greater than 75% of a rated speed, and in other examples at speeds of greater than 80%, and in yet other examples ( FIG. 14 ) at speeds of greater than 88% of a rated speed. If flux weakening were designed to occur at lower motor speeds, the max torque provided to the motor could be higher, but this would sacrifice the maximum power capable of being provided by the motor, which would be less desirable for powersport vehicles. In one example, motor  16  may have a rated speed of between 7000 rpm and 12000 rpm and a peak speed of between 8000 rpm-15000 rpm. 
     In one example, the arrangement of windings and magnets for motors  16  having stator and rotor  76   a ,  78   a  and stator and rotor  76   b ,  78   b  provide a torque density of between 7.0 and 8.0 Nm/kg, and in some examples between 7.2 and 7.8 Nm/kg. 
     The design and packaging of motor  16 , including stator and rotor  76   a ,  78   a  or stator and rotor  76   b ,  78   b , helps provide a compact form factor and high-power densities for drive unit  30 . The design and packaging of inverter  18  may also contribute to a compact form factor and high-power densities for drive unit  30 . 
       FIG. 15  is a plan view of inverter  18  of drive unit  30  with end cover  52  removed, according to one example of the present disclosure.  FIG. 15  illustrates the arrangement of capacitors  120 , power switching network  122 , control electronics  124  and terminals  96  along a transverse axis  49  (or radial axis) of drive unit  30 . Capacitors  120 , power switching network  122 , control electronics  124  and terminals  96  are disposed within first compartment  22  of housing  20 , which is formed between shared wall  26  and opposing end cover  52 . 
     First compartment portion  90  of first compartment  22  may house a DC bus or DC link of inverter  18 . Capacitors  120  are disposed within first compartment portion  90 . Also disposed within first compartment portion  90  may be high and low DC voltage leads (see  190 ,  192  in  FIG. 19 ). The high and low DC voltage leads may be connected to battery system  14  via DC connection terminals  60 ,  62 . In the illustrated example, capacitors  120  include a bank of four capacitors  120   a ,  120   b ,  120   c ,  120   d . Each of capacitors  120  are connected between the high and low DC voltage leads of inverter  18 . Capacitors  120  may reduce the voltage variations between the high and low DC voltage leads. Capacitors  120  may also or instead provide a low-impedance path for ripple currents generated by power switching network  122 . 
     Second compartment portion  92  of first compartment  22  includes power switching network  122  and control electronics  124  to convert DC power from battery system  14  to alternating current (AC) power to drive motor  16 . In some examples, motor  16  is a three-phase motor and power switching network  122  converts the DC power into three-phase AC power. Power switching network  122  is connected to the high and low DC voltage leads in first compartment portion  90  to receive the DC power. The configuration and arrangement of power switching network  122  and control electronics  124  in second compartment portion  92  is discussed in further detail elsewhere herein. 
     Third compartment portion  93  of first compartment  22  includes terminals  96  connected to outputs of the power switching network  122  to transfer the AC power to motor  16 . For example, terminals  96  may be connected to input leads  84  of stator  78  within third compartment portion  93 . When motor  16  is a three-phase motor, each of terminals  96   a ,  96   b ,  96   c  may transfer a different phase of AC power from power switching network  122  to motor  16 . 
     Third compartment portion  93  may further include current sensors  154  to measure the current in one or more terminals  96  and input leads  84 . In the illustrated example, current sensor  154   a  measures the current flowing through terminal  96   a  (and the associated input lead  84 ) and current sensor  154   b  measures the current flowing through terminal  96   c  (and the associated input lead  84 ). In some examples, current sensors  154  are Hall effect sensors; however, other types of sensors may also or instead be implemented. Current sensors  154  may have a ring-link structure and be positioned around the periphery of the terminals  96  and/or input leads  84  to measure magnetic fields using the Hall effect. Current in the terminals  96  and/or input leads  84  may then be calculated based on the magnitude of the magnetic field. In some examples, current sensors  154  are coupled to the shared wall  26  using fasteners and/or adhesives. Additionally, current sensors  154  may be disposed within respective cavities or recesses formed in shared wall  26 . In this way, current sensors  154  may be integrated into shared wall  26  to improve space-efficiency in third compartment portion  93 . 
     Second compartment portion  92  may be adjacent to both first compartment portion  90  and third compartment portion  93  in inverter  18 , which may reduce the length of connections between different components in first, second and third compartment portions  90 ,  92 ,  93 . For example, as shown in  FIG. 15 , the arrangement of first, second and third compartment portions  90 ,  92 ,  93  along transverse axis  49  (i.e., with second compartment portion  92  being disposed between first compartment portion  90  and third compartment portion  93 ) enables components of inverter  18  to be arranged linearly or in series. Capacitors  120  are adjacent to power switching network  122 , and power switching network  122  is adjacent to terminals  96 . In this way, the length of electrical connections between capacitors  120 , power switching network  122  and terminals  96  may be reduced, which may in turn reduce the inductance in inverter  18 . Reducing inductance may improve the performance of inverter  18 , such as by reducing voltage spikes that may be harmful to inverter  18 , drive unit  30  and/or battery system  14 , for example. Further, reducing inductance in inverter  18  may allow the capacitance and corresponding size of capacitors  120  to be reduced, which may enable a smaller form factor for inverter  18 . 
     It should be noted that other ways of arranging second compartment portion  92  adjacent to both first compartment portion  90  and third compartment portion  93  are also contemplated. For example, first, second and third compartment portions  90 ,  92 ,  93  may each occupy a respective sector of first compartment  22  (i.e., a respective space enclosed between an arc on the periphery of first compartment  22  and two radii at either end of that arc). 
       FIG. 16  is a perspective view of inverter  18  of drive unit  30  with end cover  52  removed, according to one example of the present disclosure.  FIG. 17  is a cross-sectional view of inverter  18  of drive unit  30 , taken along a transverse axis of drive unit  30 , according to one example of the present disclosure.  FIGS. 16 and 17  illustrate a stacked arrangement of power switching network  122  and control electronics  124  along longitudinal axis  48  of drive unit  30 .  FIG. 17  also illustrates the delineation of first, second and third compartment portions  90 ,  92 ,  93  using dashed lines that are parallel to longitudinal axis  48 . In this way, first, second and third compartment portions  90 ,  92 ,  93  might not overlap along the longitudinal direction of drive unit  30 . 
     In some examples, power switching network  122  includes multiple electric switches to convert DC power from battery system  14  into AC power for motor  16 . A non-limiting example of electrical switches are IGBT switches. The electrical switches may be housed inside of an enclosure or module to protect the electrical switches. In the illustrated example, power switching network  122  is coupled to shared wall  26  within first compartment portion  92  of first compartment  22 . In some examples, power switching network  122  may be rigidly coupled to shared wall  26  using fasteners, snap-fit couplings and/or adhesives, for example. One wall of power switching network  122  may enclose and seal fluid chamber  100  in shared wall  26 , which circulates fluid to cool the electrical switches. 
     Control electronics  124  include a motor controller  150  and a power controller  160 . In the illustrated example, motor controller  150  and power controller  160  are separate components that are stacked or otherwise arranged along longitudinal axis  48 . As discussed in further detail elsewhere herein, this configuration of motor controller  150  and power controller  160  may enable control electronics  124  to have a smaller overall footprint and occupy less space in first compartment  22 , potentially providing a more compact form factor for drive unit  30 . 
     The power controller  160  is electrically connected to power switching network  122  to control the electrical switches therein. For example, power controller  160  may include power electronics that control the state of the electrical switches (e.g., whether an electrical switch is open or closed) and control the timing of state changes (e.g., when an electrical switch changes from open to closed, and vice versa). In this way, power controller  160  may control, inter alia, the phase and frequency of the AC power generated by power switching network  122 . 
     Power controller  160  may include a computer including one or more data processors and non-transitory machine-readable memory storing instructions for execution by the one or more data processors. Power controller  160  may also or instead include an application specific integrated circuit (ASIC) and/or a field programmable gate array (FPGA). In some examples, power controller  160  includes a circuit board, such as a printed circuit board, having electronics mounted thereon. 
     As illustrated, power controller  160  is coupled to power switching network  122  opposite shared wall  26 . In some examples, power controller  160  may be rigidly coupled to power switching network  122  using fasteners, snap-fit couplings and/or adhesives, for example. In some examples, power switching network  122  includes connection pins extending parallel to longitudinal axis  48  that are received by through-holes in a circuit board of power controller  160 . Solder may be used to electrically connect power controller  160  to the pins. 
     In some examples, motor controller  150  is or includes a motor control unit or a motor control module. Motor controller  150  is electrically connected to power controller  160  to control power controller  160 . In some examples, motor controller  150  is connected to electrical connector  64  to receive control signals from other components of electric vehicle  10 . Non-limiting examples of such control signals include a throttle (e.g. accelerator) signal from a throttle of electric vehicle  10 , a performance mode signal indicating the performance mode set for the electric vehicle  10  (e.g., eco, performance or sport mode), and sensor data for drive unit  30  and/or other components of electric vehicle  10  (e.g., the temperature of battery pack  14 ). Based on one or more control signals, motor controller  150  may execute logic to determine a set of parameters for drive unit  30  (e.g., speed, torque and/or power of drive unit  30 ). These parameters may be communicated to power controller  160 , which may control power switching network  122  to output AC power that is consistent with the parameters. Electrical connection and communication between motor controller  150  and power controller  160  may be provided by a cable (not shown) connected between motor controller  150  and power controller  160 . A non-limiting example of such a cable is a flexible ribbon cable. Motor controller  150  and power controller  160  include respective connectors  152 ,  162  to connect to the cable. 
     Motor controller  150  may include a computer including one or more data processors and non-transitory machine-readable memory storing instructions for execution by the one or more data processors. Motor controller  150  may also or instead include an ASIC and/or a FPGA. In some examples, power controller  150  includes a circuit board, such as a printed circuit board, having control electronics mounted thereon. 
     In the illustrated example, motor controller  150  is disposed between power controller  160  and end cover  52  within second compartment portion  92 . Power controller  160  is also disposed between motor controller  150  and power switching network  122 . Motor controller  150  and power controller  160  may have similar dimensions (e.g., a similar length and/or width). In some examples, motor controller  150  may be rigidly coupled to power controller  160  using mounting posts and/or fasteners. However, in other examples, motor controller  150  and power controller  160  might not be rigidly coupled together (e.g., there might not be a direct mechanical connection between motor controller  150  and power controller  160 ). Motor controller  150  may instead be secured to, and supported by, end cover  52 . Securing motor controller  150  to end cover  52  may enable control electronics  124  to be assembled more reliably as compared to when motor controller  150  is rigidly coupled to power controller  160 . For example, in the case that motor controller  150  is coupled to power controller  160 , variations in the dimensions of control electronics  124  (e.g., in the thickness along longitudinal axis  48 ) may result in there being too little room or too much room for electronical connector  64  between motor controller  160  and end cover  52 . This might produce a mechanical strain on a circuit board of motor controller  150  if, for example, the circuit board deformed to compensate for the variations in dimensions. Further, coupling motor controller  150  to power controller  160  may involve the use of a support structure (e.g., mounting posts) that might not be needed to secure motor controller  150  to end cover  52 . In this way, securing motor controller  150  to end cover  52  may reduce the number of components needed to assemble control electronics  124 . 
     In the illustrated example, a plate  170  is disposed between power controller  160  and motor controller  150  to secure motor controller to end cover  52 . Plate  170  may be a generally flat and rigid component made from metal, for example. The dimensions (e.g., length and width) of plate  170  may be similar to the dimensions of motor controller  150  and/or power controller  160 . Plate  170  may be coupled to end cover  52  to secure motor controller  150  to the end cover  52 . In the illustrated example, plate  170  is coupled to end cover  52  using fasteners  172 . Fasteners  172  may be bolts that are received by through-holes  174  in end cover  52  and coupled to threaded openings in plate  170  (see fastener  172  and through-hole  174  in  FIG. 17 ). However, other types of fasteners may also or instead be employed to couple plate  170  to end wall  52 . Motor controller  150  may also define through-holes to receive fasteners  172 . In some examples, plate  170 , motor controller  150 , end cover  52  and/or other components of inverter  18  may have alignment features to help aid the alignment of through-holes  174  with corresponding threaded openings in plate  170 . 
     Motor controller  150  may be pressed or pinned between plate  170  and end cover  52  to secure motor controller  150  to end cover  52 . Plate  170  and/or end cover  52  may also provide electrical shielding for motor controller  150 . For example, housing  20  including end cover  52  may be electrically grounded. Plate  170  may be made of a conductive material (e.g., metal) and that is also grounded via conductive fasteners  172 . 
       FIG. 18  is a plan view of inverter  18  of drive unit  30  showing end cover  52 , according one example of the present disclosure.  FIG. 18  shows four through-holes  174  for receiving fasteners  172 . Fasteners  172  may be inserted into through-holes  174  and screwed into plate  170  while end cover  52  is coupled to housing  20 . 
     In some examples, shared wall  26 , power switching network  122 , power controller  160 , plate  170 , motor controller  150  and end cover  52  are arranged in a stack along longitudinal axis  48  of drive unit  30 . The stack has a length  182  along longitudinal axis  48  within first compartment  22 . Length  182  does not include the length of electrical connector  64 . In some examples, length  182  may be less than, or substantially equal to, a length  180  of capacitors  120  along longitudinal axis  48 . In some examples, length  180  and/or length  182  is less than 100 mm. In some examples, length  180  and/or length  182  is greater than 20 mm. In some examples, length  180  and/or length  182  is between 80 mm and 40 mm. In some examples, length  180  is between 55 and 60 mm and length  182  is between 70 and 75 mm. 
     Capacitors  120  may be a relatively large component of inverter  18 , and might therefore provide a lower limit for the length of first compartment  22  along longitudinal axis  48 . For example, the distance between shared wall  26  and end cover  52  may be based on length  180  of capacitors  120 . Designing length  182  to be less than, or substantially similar to, length  180  may more efficiently utilize the interior space of first compartment  22 . A length of terminals  96  may also or instead be designed to be to be less than, or substantially equal to, length  180 . In some examples, capacitors  120  may define a length envelope within first compartment  22  in a direction extending along longitudinal axis  48 , where both the terminals  96  and the stack formed by power switching network  122  and control electronics  124  are positioned within first compartment  22  within the length envelope. 
       FIG. 19  is a plan view of capacitors  120 , power controller  160 , power switching network  122  and terminals  96  in inverter  18  of drive unit  30 , according to one example of the present disclosure.  FIG. 20  is a perspective view of capacitors  120 , power controller  160 , power switching network  122  and terminals  96  in inverter  18  of drive unit  30 , according to one example of the present disclosure.  FIGS. 19 and 20  illustrate high and low DC voltage leads  190 ,  192  that are connected to battery system  14  via DC connection terminals  60 ,  62 . As discussed elsewhere herein, capacitors  120  are coupled between DC voltage leads  190 ,  192  to provide a low impedance path for high frequency voltage ripples produced by power switching network  122 . 
     Six connections  194  are formed between DC voltage leads  190 ,  192  and power switching network  122 . Connections  194   a ,  194   b  form a first pair of connections to DC voltage leads  190 ,  192 , connections  194   c ,  194   d  form a second pair of connections to DC voltage leads  190 ,  192 , and connections  194   e ,  194   f  form a third pair of connections to DC voltage leads  190 ,  192 . Each pair of connections  194  between power switching network  122  and DC voltage leads  190 ,  192  may be used to convert DC power to AC power having a different phase. For example, the three pairs of connections  194  may each be used to generate AC power for a respective one of terminals  96 . Power switching network  122  is electrically connected to terminals  96  via connections  198 . Specifically, terminal  96   a  is connected to power switching network  122  via connection  198   a , terminal  96   b  is connected to power switching network  122  via connection  198   b , and terminal  96   c  is connected to power switching network  122  via connection  198   c . In some examples, connections  194 ,  198  may include conductive tabs extending from power switching network  122  that are connected to DC voltage leads  190 ,  192  and/or to terminals  96  using bolts. 
     As discussed elsewhere herein, the arrangement of capacitors  120 , power switching network  122  and terminals  96  may reduce inductance in inverter  18 . By positioning capacitors  120  directly adjacent to power switching network  122 , a distance  196  between capacitors  120  and power switching network  122  may be reduced. This may reduce the length and inductance of connections  194 . Distance  196  may be a straight-line distance or an electrical path length between capacitors  120  and power switching network  122 . As shown, distance  196  may be defined between an edge of capacitors  120  and an edge of an enclosure of power switching network  122 . In other examples, distance  196  may be defined between an edge of capacitors  120  and a point of attachment (e.g., the position of a bolt or other fastener) in connections  194 . In some examples, distance  196  is less than 50 mm. In some examples, distance  196  is less than 20 mm. In some examples, distance  196  is less than 10 mm. In some examples, distance  196  is approximately 15 mm. 
     Similarly, by positioning power switching network  122  directly adjacent to terminals  96 , a distance between power switching network  122  and terminals  96  may be reduced. This may help reduce the length and the inductance of connections  198 . Distance  198  may be a straight-line distance or an electrical path length between power switching network  122  to terminals  96 . In some examples, the length of connections  198  is less than 50 mm. In some examples, the length of connections  198  is less than 20 mm. In some examples, the length of connections  198  is less than 10 mm. In some examples, the length of connections  198  is approximately 15 mm. 
       FIG. 21  is a flow diagram illustrating a method  400  for assembling an inverter of a drive unit, according to one example of the present disclosure. In some examples, method  400  may be implemented to assemble control electronics  124  of inverter  18 . Block  402  includes coupling a plurality of electrical switches to a first wall of a housing of the inverter. For example, block  402  may include coupling power switching network  122  to shared wall  26  using fasteners and/or an adhesive. Block  404  includes coupling a power controller to the plurality of electrical switches opposite the first wall. For example, block  404  may include coupling power controller  160  to power switching network  122  opposite shared wall  26 . Block  406  includes positioning a motor controller between the power controller and a second wall of the housing. For example, block  406  may include positioning motor controller  150  on top of power controller  160 , optionally with plate  170  disposed between motor controller  150  and power controller  160 . End cover  52  may then be installed over motor controller  150 . Block  408  includes securing the motor controller to the second wall of the housing. For example, block  408  may include securing motor controller  150  to end cover  52 . As discussed elsewhere herein, plate  170  may be used to secure motor controller  150  to end cover  52 . Once end cover  52  is installed, fasteners  172  may be inserted into through-holes  174  in end cover  52  and coupled to plate  170 . Initial alignment between through-holes  174  and corresponding threaded openings in plate  170  may be achieved by manually manipulating electrical connector  64  on motor controller  150  to achieve the alignment. Alternatively or additionally, alignment features on end cover  52 , plate  170 , motor controller  150 , power controller  160  and/or other components of inverter  18  may be used to help achieve the alignment. Tightening fasteners  72  may force motor controller  150  against end cover  52  to secure and retain motor controller  150 . 
     As mentioned above, drive unit  30  provides a power density greater than 5 kW/kg. In one example, the drive unit  30  provides a power density of greater than 5.5 kW/kg. In another example, the drive unit  30  provides a power density of greater than 5.75 kW/kg and in yet another example, the drive unit  30  provides a power density of greater than 6 kW/kg. 
     As mentioned above, the compact packaging of the motor  16 , inverter  18  and housing  20 , together with a stator  78   a ,  78   b  and rotor  76   a ,  76   b  construction that balances motor losses with light weight power generation, provide a drive unit  30  with performance characteristics suitable for electric powersport vehicles. Specifically, the stator  78   a ,  78   b  and rotor  76   a ,  76   b  designs shown in  FIGS. 13A, 13B  may provide a drive unit  30  with a maximum efficiency of greater than 97%, and in some examples of greater than 98%. In addition, the stator  78   a ,  78   b  and rotor  76   a ,  76   b  designs shown in  FIGS. 13A, 13B  provide a drive unit  30  with a maximum efficiency at maximum power of greater than 96%, and more particularly of greater than 97%. These high efficiency levels make the drive unit  30  suitable for use in powersport vehicles that are operated fairly continuously at, or near, their maximum power. Having a high maximum efficiency prevents harmful heat generation from causing damage to the drive unit  30 . 
     Although specific examples have been illustrated and described herein, a variety of alternate and/or equivalent implementations may be substituted for the specific examples shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific examples discussed herein. 
     Example embodiments of the present disclosure will now be provided. 
     Example embodiment 1: A drive unit for an electric vehicle comprising: 
     a housing having a first compartment and a second compartment separated from one another by a shared wall; an electrical inverter disposed within the first compartment and having a set of electrical output terminals; an electric motor disposed within the second compartment and having electrical input terminals electrically coupled to the output terminals via one or more openings extending through the shared wall. 
     Example embodiment 2: The drive unit of example embodiment 1, the input terminals of the electric motor comprising electrical leads extending through the one or more openings into the first compartment. 
     Example embodiment 3: The drive unit of example embodiment 1, a perimeter of the housing being confined within a generally longitudinal form factor, the first and second compartments being disposed axially to one another along an axis of the longitudinal form factor. 
     Example embodiment 4: The drive unit of example embodiment 3, the longitudinal form factor being generally cylindrical in shape. 
     Example embodiment 5: The drive unit of example embodiment 1, the inverter including a set of solid-state switches providing electrical power to the electrical output terminals, the switches and output terminals disposed within the first compartment such that the set of output terminals axially aligns with the electrical input terminals of the electric motor to minimize conductor lengths between the electric motor and the set of solid-state switches. 
     Example embodiment 6: The drive unit of example embodiment 5, the electrical output terminals arrayed along an arc to axially align with the electrical input terminals. 
     Example embodiment 7: The drive unit of example embodiment 5, the inverter including a set of capacitors to receive DC power from a battery source, the capacitors laterally offset in a radial direction of the cylindrical form factor from the set of solid state switches. 
     Example embodiment 8: A drive unit housing for an electric vehicle comprising: a first housing section defining a first compartment to house an electrical inverter; and a second housing section defining a second compartment to house an electric motor, the first and second housing sections separably coupled to one another with the first and second compartments separated by a shared wall. 
     Example embodiment 9: The drive unit housing of example embodiment 8, the first housing section including the shared wall. 
     Example embodiment 10: The drive unit housing of example embodiment 8, wherein perimeters of the first and second housing sections are confined within a generally longitudinal form factor with the first and second housing sections being disposed axially to one another along an axis of the longitudinal form factor. 
     Example embodiment 11: The drive unit housing of example embodiment 10, the axis of the longitudinal form factor aligned with an axis of a rotor shaft of the electric motor when disposed within the second compartment. 
     Example embodiment 12: The drive unit housing of example embodiment 8, the first housing section including: a tubular perimeter casing defining a circumference of the first compartment and having first and second open ends; the shared wall coupled to and closing the first open end; and a cover plate separably coupled to the tubular perimeter casing to cover the second open end. 
     Example embodiment 13: The drive unit housing of example embodiment 12, the shared wall and the tubular perimeter casing comprising a contiguous piece. 
     Example embodiment 14: The drive unit housing of example embodiment 12, the cover plate including electrical terminals for connection to the inverter unit from a battery system. 
     Example embodiment 15: The drive unit housing of example embodiment 8, the second housing section including: a tubular perimeter casing defining a circumference of the second compartment and having first and second open ends; and a cover plate coupled to and closing the first end. 
     Example embodiment 16: The drive unit housing of example embodiment 15, the shared wall closing the second end when the tubular perimeter casing is coupled thereto. 
     Example embodiment 17: The drive unit housing of example embodiment 8, the shared wall including a bearing pocket on a side facing the second compartment to receive an end of a rotor shaft of the electric motor. 
     Example embodiment 18: The drive unit housing of example embodiment 8, the first compartment including a first compartment portion to house capacitors of the inverter and a second compartment portion to house power switching and control electronics of the inverter. 
     Example embodiment 19: The drive unit housing of example embodiment 8, the shared wall including one or more openings extending there through to provide electrical connection of the electric motor to the electrical inverter. 
     Example embodiment 20: The drive unit housing of example embodiment 19, wherein electrical power leads from a stator of the electric motor pass through the one or more openings from the second compartment to the first compartment. 
     Example embodiment 21: A drive unit housing for an electric vehicle comprising: a first housing section having perimeter sidewalls forming a first compartment to house an electrical inverter; and a second housing section having perimeter sidewalls forming a second compartment to house an electric motor, the first compartment separated from the second compartment by a shared wall, the shared wall including fluid pathways to circulate fluid to cool the electrical inverter and the perimeter sidewalls of the second housing section including fluid pathways to circulate fluid to cool the electric motor. 
     Example embodiment 22: The housing of example embodiment 21, the fluid pathways of the shared wall disposed in series with the fluid pathways of the perimeter sidewalls of the second housing section between a fluid inlet port and a fluid outlet port. 
     Example embodiment 23: The housing of example embodiment 22, the fluid pathways of the shared wall and perimeter sidewalls disposed in series with fluid pathways within a hollow rotor shaft of the electric motor disposed within the second housing section. 
     Example embodiment 24: The housing of example embodiment 21, a perimeter of the housing being confined within a generally longitudinal form factor, the first and second compartments being disposed axially to one another along an axis of the longitudinal form factor. 
     Example embodiment 25: The drive unit of example embodiment 24, the longitudinal form factor being generally cylindrical in shape. 
     Example embodiment 26: The drive unit of example embodiment 21, the first housing section including the shared wall. 
     Example embodiment 27: The drive unit of example embodiment 21, the first housing section separable from the second housing section. 
     Example embodiment 28: A drive unit for an electric vehicle comprising: a housing including: a first housing section having perimeter sidewalls forming a first compartment; and a second housing section having a perimeter sidewalls forming a second compartment, the first and second compartments separated from one another by a shared wall; an electrical inverter disposed within the first compartment, the electrical inverter including inverter components mounted to the shared wall; and an electric motor disposed within the second compartment, the shared wall including fluid pathways to circulate fluid to cool the electrical inverter and the perimeter sidewalls of the second housing section including fluid pathways to circulate fluid to cool the electric motor. 
     Example embodiment 29: The drive unit of example embodiment 28, the electric motor including a hollow rotor shaft having an inlet fluid pathway and an outlet fluid pathway to circulate fluid through the shaft to cool the electric motor, an end of the rotor shaft disposed within a bearing pocket on the shared wall, the inlet and outlet fluid pathways in fluidic communication with fluid pathways of the shared sidewall via the end of the rotor shaft. 
     Example embodiment 30: The drive unit of example embodiment 29, the fluid pathways of the shared wall, the inlet and output fluid pathways of the rotor shaft, and the fluid pathways of the perimeter sidewalls of the second housing section form a continuous fluid pathway between a fluid inlet port and a fluid outlet port. 
     Example embodiment 31: The drive unit of example embodiment 30, the electrical inverter including a set of capacitors mounted to the shared wall, the fluid pathways arranged so as to first pass the capacitors downstream of the fluid inlet port. 
     Example embodiment 32: The drive unit of example embodiment 27, the perimeter sidewalls of the second housing section including a cylindrical housing extending about a perimeter of a stator section of the electric motor, the fluid pathways extending about a circumference of the cylindrical housing. 
     Example embodiment 33: The drive unit of example embodiment 32, the fluid pathways extending in a spiral fashion about the circumference of the cylindrical housing. 
     Example embodiment 34: The drive unit of example embodiment 28, a perimeter of the housing being confined within a generally longitudinal form factor, the first and second compartments being disposed axially to one another along an axis of the longitudinal form factor. 
     Example embodiment 35: The drive unit of example embodiment 34, the longitudinal form factor being generally cylindrical in shape. 
     Example embodiment 36: A drive unit housing for an electric vehicle comprising: a first housing section having perimeter sidewalls forming a first compartment to house an electrical inverter; and a second housing section having perimeter sidewalls forming a second compartment to house an electric motor, the first compartment separated from the second compartment by a shared wall, the first and second housing sections having perimeters confined within a generally longitudinal form factor and being disposed axially to one another along an axis of the longitudinal form factor; and a continuous fluid pathway extending through the first and second housing sections between an inlet and an outlet port to circulate fluid to cool the electrical inverter and the electric motor. 
     Example embodiment 37: The drive unit housing of example embodiment 36, the continuous fluid pathway including a portion disposed in the shared sidewall. 
     Example embodiment 38: The drive unit housing of example embodiment 36, the continuous fluid pathway in series with a fluid pathway within a hollow rotor shaft of the electric motor. 
     Example embodiment 39: The drive unit housing of example embodiment 38, the continuous fluid pathway in fluid communication with the fluid pathway within the hollow rotor shaft via a portion of the fluid pathway disposed within the shared wall. 
     Example embodiment 40: The drive unit of example embodiment 36, the continuous fluid pathway including a spiral pathway disposed about a perimeter of the second housing section to cool the electric motor.