Patent Publication Number: US-2023160464-A1

Title: Integrated gearbox in electric motor systems

Description:
TECHNICAL FIELD 
     The present description relates generally to systems for integrating a gearbox into a housing of an electric motor for a vehicle. 
     BACKGROUND AND SUMMARY 
     In electric vehicles, the powertrain architecture may include a high voltage battery, an electric motor with power controller electronics, and a transmission, which may include a gearbox. Voltage from the battery may be supplied to the electric motor in order for the electric motor to generate power to drive the electric vehicle, which may then be transmitted to the drive wheels via the gearbox. 
     Multi-speed transmissions have been deployed in certain electric vehicles (EVs) due to their increased responsiveness and the gains in motor operating efficiency that the transmission affords when compared to EVs using single speed geartrains. Tradeoffs may however be made between the number of selectable gears and transmission efficiency due to losses that arise from geartrains with a comparatively high number of gears. Further, transmissions with a relatively high number of selectable gears may pose packaging constraints on other vehicle systems such as the suspension and energy storage systems. Further, previous powertrains have exhibited inefficiencies in their cooling system designs which use independent coolant loops for motor and transmission cooling. 
     U.S. Pat. No. 9,435,415 B2 to Gassmann discloses an electric drive for a motor vehicle. In one of the embodiments presented in Gassmann, the electric drive includes a switchable planetary drive with two planetary gear stages, which are coupled in parallel. The electric drive additionally includes a switching clutch with a sliding sleeve that allows the system to switch between multiple ratios by grounding two distinct ring gears in the system. 
     The inventors have recognized several drawbacks with Gassmann&#39;s transmission system as well as other previous electric drivelines. Gassmann&#39;s transmission may exhibit space inefficiencies due to the use of a multi-stage planetary gear reduction. Consequently, difficulties may arise when attempting to package the transmission into vehicle platforms with rigorous packaging demands. Using a multi-stage planetary reduction increases geartrain losses, when compared to transmissions with fewer stages. 
     The inventors have recognized the aforementioned issues and developed a gearbox assembly including an electric motor enclosed in a housing and a gearbox enclosed in the housing. The gearbox includes an idler gear coupled to an electric motor gear. In this way, a more power dense transmission is provided while reducing a packaging size. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    shows a schematic example of an electric motor in a vehicle. 
         FIG.  2    shows a schematic example of a first configuration of a gearbox and the electric motor of a vehicle integrated into a same housing. 
         FIG.  3    shows a schematic example of a second configuration of the gearbox and the electric motor of a vehicle. 
         FIG.  4    shows a schematic of the electric motor, the gearbox, and a differential arranged in a same housing. 
         FIG.  3    is shown approximately to scale. 
     
    
    
     DETAILED DESCRIPTION 
     The following description relates to systems for enclosing a gearbox within a housing of an electric motor. Such systems may be integrated in a vehicle system, shown schematically in  FIG.  1   . A gearbox including an idler gear for increased power density may be integrated within the housing of the electric motor as shown in  FIGS.  2 - 3   . A differential may also be included in the housing, as shown in  FIG.  4   . 
       FIG.  1    shows a schematic depiction of a vehicle system  6  that can derive propulsion power from an electric motor  54 . Electric motor  54  receives electrical power from a traction battery  58  to provide torque to rear vehicle wheels  55 . Electric motor  54  may also be operated as a generator to provide electrical power to charge traction battery  58 , for example, during a braking operation. It should be appreciated that while  FIG.  1    depicts an electric motor  54  mounted in a rear wheel drive configuration, other configurations are possible, such as employing electric motor  54  in a front wheel configuration, or in a configuration in which there is an electric motor mounted to both the rear vehicle wheels  55  and front vehicle wheels  56 . 
     Electric motor  54  may include a gearbox integrated therein (to be described further therein). The integrated gearbox may include a differential and a planetary gear set for transmitting power from the electric motor  54  to the rear vehicle wheels  55 . A pump system  130  may be coupled to the gearbox of the electric motor  54  to flow lubricating (transmission) oil through the electric motor  54  during operation. Additionally, electric motor  54  may include a cooling system  148 , including a coolant pump, and a heat exchanger in fluidic communication with the pump via a conduit. The cooling system  148  may be described more with reference to  FIGS.  2 - 3   . Electric motor  54  may also include at least one clutch. Controller  112  may send a signal to an actuator of the clutch to engage or disengage the clutch, so as to couple or decouple power transmission from the electric motor  54  to the rear vehicle wheels  55 . Controller  112  may also be electronically coupled to the cooling system  148 , e.g. in order to modulate operation of the cooling pump in response to the temperature of the electric motor  54 . 
     Controller  112  may form a portion of a control system  114 . Control system  114  is shown receiving information from a plurality of sensors  116  and sending control signals to a plurality of actuators  181 . As one example, sensors  116  may include sensors such as a battery level sensor, clutch activation sensor, etc. As another example, the actuators may include the clutch, pump system  130 , etc. The controller  112  may receive input data from the various sensors, process the input data, and trigger the actuators in response to the processed input data based on instruction or code programmed therein corresponding to one or more routines. 
       FIG.  2    schematically illustrates a cross-sectional view  200  of an electric motor  202  and a gearbox  203  of a vehicle system (such as vehicle system  6  of  FIG.  1   ) in a housing  204 . The electric motor  202  may be the same as the electric motor  54  of  FIG.  1   . The cross-sectional view may be taken along a y-z plane of axis system  290 , with the radial direction of the electric motor  202  parallel to z-axis of the axis system  290  and the axial direction of the electric motor  202  parallel to the y-axis of the axis system  290 . The electric motor  202  may be one of a variety of suitable electric alternating current (AC) motor configurations. For example, the electric motor  202  may be an AC motor, the types of which may include asynchronous (e.g., squirrel cage and wound rotor) and synchronous style motors. Synchronous motors such as multiphase, may be used in certain configurations. The styles of multiphase motors that may be deployed include permanent magnet, synchronous reluctance, hybrid synchronous (e.g., permanent magnet assisted synchronous reluctance), synchronous induction, and hysteresis. Continuing with the AC motor use-case, a synchronous permanent magnet motor may be utilized, in some instances, due to its relatively high conversion efficiency. 
     The electric motor  202  and the gearbox  203  may be enclosed by the housing  204 . The housing  204  may enclose the electric motor  202  and the gearbox  203  from other components within the vehicle system. The housing  204  may be an integral casing shaped to cover each of the electric motor  202  and the gearbox  203 . The housing  204  may surround an entirety of each of the electric motor  202  and the gearbox  203 . The housing  204  may further include a first side  292  corresponding to a motor output side of the electric motor  202  and a second side  294  opposite of the first portion of the housing  204 , the second side  294  proximal to the gearbox  203 . 
     The housing  204  may be manufactured via a mold, additive manufacturing, or other process. The housing  204  may be a single, continuous piece. The housing  204  may include solid materials, configured to separate the electric motor  202  and the gearbox  203  from components outside of the housing  204 . In one example, the housing  204  may include one or more of carbon fiber, aluminum, cast iron, steel, stainless steel, plastic, composites, and the like. 
     The electric motor  202  and the gearbox  203  may be integrally arranged within the same housing to reduce an amount of cooling and lubricant used, which may increase an efficiency of cooling or lubrication techniques performed by systems in the vehicle. The housing  204  may include an outer housing portion and an inner housing portion such that coolant may flow between the inner housing portion and the outer housing portion. Coolant may enter coolant channels of the housing  204  (e.g., via a coolant inlet) and may exit the housing  204  (e.g., via a coolant outlet) after flowing through the coolant channels. The housing  204 , in one example, may include a plurality of stator laminations that are positioned within the housing  204 . The electric motor  202  may further include an oil inlet that is mounted to and extends through the housing  204 . The stator laminations may have a radial opening that are designed to receive oil from the oil inlet and direct the oil into at least one oil duct. In the motor, the oil duct may axially extend through at least a portion of the stator laminations. By flowing coolant through the housing in this way, the oil may be efficiently cooled without the use of an external heat exchanger, if desired. Consequently, the cooling arrangement of the motor may exhibit greater compactness than previous motor cooling systems, in some instances. Further, by omitting a heat exchanger for the oil cooling circuit, the electric motor may be more efficiently manufactured, if wanted. 
     In one example, collector rings may be positioned at opposing axial ends of the stator laminations included in the housing  204 , whereby oil flowing through any oil ducts may be collected in cavities which may be defined radially outward of the collector ring. Oil flowing through the oil duct may be collected in the cavities radially outward from the collector rings. Further, the cavities may be interconnected and in fluidic communication (e.g., direct fluidic communication) with components included in the housing  204  (e.g., electric motor  202 , gearbox  203 , differential, shown in  FIG.  3   , and the like) that receive oil for cooling and/or lubrication. Thus, a hydraulic line may be fluidly coupled to the cavity (e.g., through the housing) so as to provide a flow path for routing oil to any lubricated components. In one example, the hydraulic line may be hydraulically coupled to the cavity formed above the collector ring and may route oil collected therein to another component. In this way, the oil may be effectively used to cool and/or lubricate other components in the electric drive unit in an efficient manner. In some examples, such as when the oil inlet is positioned at one axial end of the housing  204 , one collector ring may be positioned at an axial end of the stator laminations opposite the axial end at which the oil inlet is located. 
     The housing  204  may further include a first bearing  210 , which may be coupled to a first shaft  206 . In one example, the first shaft  206  is an electric motor output shaft. The first shaft  206  may rotate relative to the first bearing  210  and transmit power to other components of the gearbox  203 . A first gear  208  may be engaged with the first shaft  206  such that when the first shaft  206  rotates, the first gear  208  may rotate in a direction similar to a direction of rotation of the first shaft  206 . In one example, the first gear  208  is an electric motor gear. 
     The first gear  208  may mesh with an idler gear  214 , via teeth, such that when the first gear  208  rotates, the idler gear  214  may also rotate. In one example, the first gear  208  rotates in a first direction and the idler gear  214  rotates in a second direction, opposite the first direction. In one example, the first gear  208  and the idler gear  214  form a first gear stage, where the gear stage includes a driving gear (e.g., the first gear  208 ) and a driven gear (e.g., the idler gear  214 ), where the driving gear may be directly coupled to a power source (e.g., the first shaft  206  of the motor  202 ) and the driven gear may be meshed with the driving gear. A change in speed and torque may occur between the driving gear and the driven gear in a gear stage. 
     The idler gear  214  may be arranged on a second shaft  215 , which may also be referred to herein as an idler gear shaft. In one example, the second shaft  215  is a support shaft. The second shaft  215  may rotate with the idler gear or it may be stationary and allow the idler gear  214  to rotate relatively thereto. The second shaft  215  may be placed in direct contact with a second bearing  212  and a third bearing  213 . The second shaft  215  may extend in a direction parallel to the first shaft  206 . In one example, the second bearing  212  and the third bearing  213  may be arranged proximally to the first bearing  210 , wherein a portion of the housing  204  extends inwards and forms a physical barrier between the first bearing  210  and the second and third bearing  212 ,  213 . In one example, a size (e.g., a circumference) of the idler gear  214  may be larger than a size of the first gear  208 . 
     The idler gear  214  may mesh with a second gear  216  via a plurality of teeth. As the idler gear  214  rotates in the second direction, the second gear  216  may rotate in the first direction, identical to the rotation of the first gear  208 . The idler gear  214  and the second gear  216  may form a second gear stage. A size of the second gear  216  may be larger than a size of the idler gear  214 . In the example of  FIG.  2   , the second gear  216  is the largest gear of the gearbox  203 . In some examples, the sizes of one or more of the first gear  208 , the idler gear  214 , and the second gear  216  may be adjusted. In one example, the second gear  216  is an accessory gear. 
     Second gear  216  may be arranged on a third shaft  219 . The third shaft  219  may be parallel to each of the first shaft  206  and the second shaft  215 . The housing  204  may be contoured to accommodate the third shaft  219  while reducing an overall profile of the housing  204 . In one example, the housing  204  may be more narrow (e.g., extend inward) at a region where the idler gear  214  and the second gear  216  engage with one another. The housing  204  may be less narrow at the third shaft  219 . A size of the housing  204  may be tailored to a size of each of the electric motor  202  and the gearbox  203  such that the size of the housing  204  is relatively small. 
     When the second gear  216  rotates, the third shaft  219  may rotate in a direction identical to a direction of rotation of the second gear  216 . The third shaft  219  may be rotate relatively to a fourth bearing  217  and a fifth bearing  218 , where the fourth bearing  217  may be placed on a first side of the second gear  216  and the fifth bearing  218  may be placed on a second side of the second gear  216 . The second gear  216  may be further coupled to a differential which may also be included in the same housing. 
     In one example, the idler gear  214  may transfer rotation from the first shaft  206  to the third shaft  219  and may preserve a power density of the system included in the housing  204 . Although  FIG.  2    shows the idler gear  214  in the first gear stage and the second gear stage, idler gears may be optionally included in other gear stages as well in alternate embodiments of  FIG.  2   . The housing  204 , in conjunction with the first bearing  210 , the second bearing  212 , the third bearing  213 , the fourth bearing  217 , and the fifth bearing  218 , may serve to fluidly seal the electric motor  202  and the gearbox  203 . 
       FIG.  3    schematically illustrates a cross-sectional view  300  of an electric motor  302  and a gearbox  303  of a vehicle system (such as vehicle system  6  of  FIG.  1   ). The cross-sectional view  300  is illustrated showing the electric motor  302 , the gearbox  303 , and the differential  330  in an expanded view for reasons of clarity. In one example, a portion of the cross-sectional view  300  including the electric motor  302  and the gearbox  303  is taken along to the y-z plane. The portion of the cross-sectional view  300  including the gear box  303  and the differential  330  may be taken along the x-y plane, normal to the y-z plane. In this way, when arranged in a shared housing, a central axis  396  of the differential may be between the central axis  392  of the electric motor  302  and the central axis  394  of a second gear  318  of the gearbox  303  along the y-z plane. In this way, when measured along the y-z plane, a distance between the central axis  392  and the central axis  396  may be less than a distance between the central axis  392  and the central axis  394 . A schematic of the electric motor  302 , the gearbox  303  and the differential  330  arranged in a common housing  402  is shown in the embodiment  400  of  FIG.  4   . The electric motor  302  and the gearbox  303  may be integrally arranged in a same housing. The electric motor  302  may be the same as the electric motor  54  of  FIG.  1   . 
     The electric motor  302  may include a first shaft  306  (interchangeably referred to as an electric motor shaft  306 ). The first shaft  306  may include an input end  301  and an output end  304 . Along a central portion of the first shaft  306 , nozzles  321  may be positioned to spray lubricant from a journal onto windings  322  and stator  324 . The journal may extend along a majority of a length of the first shaft  306 . which may be longer in the axial direction than electric motor  302 . The first shaft  306  may rotate relatively to the first bearing  309  and the second bearing  310 . Lubricant ejected from the nozzles  321  may flow to the first bearing  309  and the second bearing  310  via lubricant channels shaped within the housing. 
     A first gear  308  may be engaged with the first shaft  306 . The engagement between the first gear  308  and the first shaft  306  may force the first gear  308  to rotate as the first shaft  306  rotates. The first gear  308  may be in a meshed engagement with an idler gear  314 . The idler gear  314  may be arranged on a support shaft  316  (interchangeably referred to as a second shaft  316 ), which may be fixed or moveable. An axis of the second shaft  316  may be parallel to the central axis  392  of the first shaft  306  and the central axis  394  of a third shaft  320 . The idler gear  314  may be in meshed engagement with the second gear  318  arranged on the third shaft  320 . 
     The second gear  318  may be in communication with a differential  330 . The differential  330  may be driven via the second gear  318 . The differential  330  may include an input differential gear  332  in meshed engagement with the second gear  318 . The input differential gear  332  may rotate along an axis normal to the central axis  394 . In one example, each of the first gear  308 , the idler gear  314 , and the second gear  318  rotate about axes parallel to one another and normal to the input differential gear  332 . 
     One or more hypoid gears  334 ,  344  may be in meshed engagement with the input differential gear  332 . In one example, one or more of the hypoid gears may be an accessory gear. The hypoid gears  334  may be configured to rotate via energy received from the input differential gear. In one example, each of the hypoid gear  334 ,  344  may rotate individual shafts  336 ,  346 , respectively. In one example, a first hypoid gear  334  rotates a first differential shaft  336  coupled to a first rotor  338 . A second hypoid gear  344  rotates a second differential shaft  346  coupled to a second rotor  348 . 
     In the example of  FIG.  3   , each of the electric motor  302 , the gearbox  303 , and the differential  330  may be arranged which in a single housing. The housing may further include lubricant passages configured to lubricate one or more of the electric motor  302 , the gearbox  303 , and the differential  330 . By integrating the electric motor  302  and the gearbox  303  in the same housing, an overall size on an electric motor system coupled to a gearbox including an idler gear may be reduced. The idler gear may provide a large ratio flexibility relative to gear systems without an idler gear. The idler gear may provide low ratios for slow rotating motors and high ratios for faster rotating motors. The idler gear may further decrease an overall size of the housing due to a larger gear being needed in the same gear stage, if the idler gear is omitted. The larger gear may be heavier than the idler gear, which may decrease a power density of the system. 
     The housing may be tailored to the shape of each of the electric motor, the gearbox, and the differential. The housing may be spaced away from surfaces of the electric motor, the gearbox, and the differential based on tolerances set by a manufacturer. The housing may contour to match indentations and protrusions of the components arranged therein so as to minimize an interior volume of the housing. In this way, a compact housing is provided with an electric motor and gearbox including an idler gear, which allows for a range of compact power dense axles. 
     In this way, by integrating a differential, a gearbox, and an electric motor into a same housing, a weight and a footprint of an electric drive unit may be reduced and an amount of coolant used may be reduced. Further, by integrating an idler gear into the gearbox, a power density of the electric drive unit may be increased. Example configurations described above may offer distinct advantages. In one example, integrating the idler gear into the gearbox may provide an increased allowable range of gear ratios, relative to a conventional gearbox arrangement, as well as a compact and power dense geometry, as the entire gearbox may be included in the same housing as other components in the electric drive unit. Additionally, coolant and lubrication may be shared between the gearbox and the electric motor, providing simplified cooling and lubrication mechanisms compared to a conventional electric drive unit. 
     The disclosure also provides support for a gearbox assembly including an electric motor enclosed in a housing, a gearbox enclosed in the housing, the gearbox having an idler gear coupled to an electric motor gear. In a first example of the system, the idler gear is directly coupled to the electric motor gear, the electric motor gear directly coupled to an electric motor output shaft. In a second example of the system, optionally including the first example, an electric motor rotational axis is parallel with an idler gear rotational axis. In a third example of the system, optionally including one or both of the first and second examples, the housing has a first portion coupled on a motor output side and a second portion opposite the first portion, the first and second portions enclosing the electric motor and gearbox. In a fourth example of the system, optionally including one or more or each of the first through third examples, the system further comprises: an accessory gear coupled directly to the idler gear. In a fifth example of the system, optionally including one or more or each of the first through fourth examples, an accessory gear rotational axis is parallel with the idler gear rotational axis. In a sixth example of the system, optionally including one or more or each of the first through fifth examples the system further comprising a differential, the differential driven by the accessory gear. 
     The disclosure also provides support for a system including a gearbox comprising an idler gear coupled to an electric motor gear of an electric motor, and a housing surrounding an entirety of each of the gearbox and the electric motor. In a first example of the system, the housing is a single piece. In a second example of the system, optionally including the first example, the idler gear is further coupled to an accessory gear, wherein the accessory gear drives a differential. In a third example of the system, optionally including one or both of the first and second examples, the differential is arranged outside the housing. In a fourth example of the system, optionally including one or more or each of the first through third examples, the housing is tailored to the gearbox and the electric motor. In a fifth example of the system, optionally including one or more or each of the first through fourth examples, lubricant from the electric motor travels to the gearbox within the housing. In a sixth example of the system, optionally including one or more or each of the first through fifth examples, the idler gear and the electric motor gear rotate along parallel axes. 
     The disclosure also provides support for a vehicle system including an electric motor and a gearbox integrally arranged within a housing, wherein an electric motor gear is coupled to an idler gear of the gearbox, and wherein the idler gear is coupled to an accessory gear. In a first example of the system, the accessory gear is arranged within the housing, and wherein the accessory gear and the electric motor gear rotate in identical directions. In a second example of the system, optionally including the first example, the accessory gear drives a differential. In a third example of the system, optionally including one or both of the first and second examples, the housing shapes a physical barrier between a first bearing and a second bearing, wherein the first bearing is arranged on an electric motor shaft and the second bearing is arranged on a support shaft. In a fourth example of the system, optionally including one or more or each of the first through third examples, the idler gear is arranged on the support shaft. In a fifth example of the system, optionally including one or more or each of the first through fourth examples, the accessory gear is larger than the idler gear, and wherein the idler gear is larger than the electric motor gear. 
     It will be appreciated that the configurations herein are exemplary in nature, and that these specific examples are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to a variety of systems that include electric motors. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
     As used herein, the terms “approximately” and “substantially” are construed to mean plus or minus five percent of the range unless otherwise specified. 
       FIGS.  2 - 4    show example configurations with relative positioning of the various components. If shown directly contacting each other, or directly coupled, then such elements may be referred to as directly contacting or directly coupled, respectively, at least in one example. Similarly, elements shown contiguous or adjacent to one another may be contiguous or adjacent to each other, respectively, at least in one example. As an example, components laying in face-sharing contact with each other may be referred to as in face-sharing contact. As another example, elements positioned apart from each other with only a space there-between and no other components may be referred to as such, in at least one example. As yet another example, elements shown above/below one another, at opposite sides to one another, or to the left/right of one another may be referred to as such, relative to one another. Further, as shown in the figures, a topmost element or point of element may be referred to as a “top” of the component and a bottommost element or point of the element may be referred to as a “bottom” of the component, in at least one example. As used herein, top/bottom, upper/lower, above/below, may be relative to a vertical axis of the figures and used to describe positioning of elements of the figures relative to one another. As such, elements shown above other elements are positioned vertically above the other elements, in one example. As yet another example, shapes of the elements depicted within the figures may be referred to as having those shapes (e.g., such as being circular, straight, planar, curved, rounded, chamfered, angled, or the like). Further, elements shown intersecting one another may be referred to as intersecting elements or intersecting one another, in at least one example. Further still, an element shown within another element or shown outside of another element may be referred as such, in one example. 
     The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.