Abstract:
A hybrid electric vehicle axle includes two separate pinion gears meshing with a single beveled ring gear. One pinion gear conveys power from the internal combustion powertrain while the other pinion conveys power from an electric motor. Power from the electric motor is conditioned by a two-speed gearbox between the electric motor and the second pinion gear. The gearbox may utilize layshaft gearing or planetary gearing such as a Ravgneaux gear set.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application Ser. No. 62/130,322 filed Mar. 9, 2015, the disclosure of which is hereby incorporated in its entirety by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to the field of hybrid electric vehicles. More particularly, this disclosure is related to a hybrid electric vehicle having a two-speed gearbox and two pinion gears meshing with a single ring gear. 
       BACKGROUND 
       [0003]    Traditionally, the majority of general purpose road vehicles are powered by liquid fuels such as gasoline or diesel fuel. When the vehicle needs power, an internal combustion engine converts the chemical energy in the fuel into mechanical energy and a powertrain delivers that mechanical energy to vehicle wheels. The vehicles are used over a wide range of vehicle speeds, including both forward and reverse movement. Some types of internal combustion engines, however, are capable of operating efficiently only within a narrow range of speeds. Consequently, the powertrain typically includes a variable speed ratio transmission. Also, a differential assembly may connect the transmission output shaft to the vehicle wheels, providing an additional fixed speed ratio and permitting the left and right wheel to rotate at slightly different speeds as the vehicle turns. 
         [0004]    In an effort to reduce the consumption of liquid fuel, some vehicles, called hybrid electric vehicles, utilize electrical energy storage such as a battery. The energy storage capability provides flexibility to perform the conversion of chemical energy when the conversion can be done most efficiently as opposed to always performing the conversion at the moment the power is demanded. Some hybrid electric vehicles, called plug-in hybrid electric vehicles, are also adapted to receive power directly in electrical form. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a schematic diagram of a first hybrid electric vehicle axle; 
           [0006]      FIG. 2  is a schematic diagram of a second hybrid electric vehicle axle; and 
           [0007]      FIG. 3  is a schematic diagram of a third hybrid electric vehicle axle. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments may take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
         [0009]    A gearing arrangement is a collection of rotating elements and shift elements configured to impose specified speed relationships among the rotating elements. A component is called a rotating element if it rotates with respect to the transmission housing in at least some operating conditions. Some speed relationships, called fixed speed relationships, are imposed regardless of the state of any clutches. Other speed relationships, called selective speed relationships, are imposed only when particular clutches are fully engaged. 
         [0010]    A group of elements are fixedly coupled to one another if they are constrained to rotate at the same speed and about the same axis in all operating conditions. Elements may be fixedly coupled by spline connections, welding, press fitting, machining from a common solid, or other means. Slight variations in rotational displacement between fixedly coupled elements can occur such as displacement due to spline lash or shaft compliance. In contrast, two elements are selectively coupled by a shift element when the shift element constrains them to rotate at the same speed about the same axis whenever the clutch is fully engaged and they are free to rotate at distinct speeds in at least some other operating condition. Two rotating elements are coupled if they are either fixedly coupled or selectively coupled. Shift elements include actively controlled devices such as hydraulically or electrically actuated clutches and passive devices such as one way clutches. A shift element may couple rotating elements using friction or may create a positive engagement such as interlocking teeth. A shift element that holds a rotating element against rotation by selectively coupling the rotating element to the housing may be called a brake. 
         [0011]      FIG. 1  schematically illustrates a two-speed hybrid electric axle utilizing layshaft gearing. Power from an internal combustion engine is delivered, preferably via a multiple speed transmission, to stub shaft  10 . Stub shaft  10  is supported for rotation with respect to a housing (not shown) by bearing  12  and  14 . Bearings  12  and  14  may be, for example, tapered roller bearings, needle bearings, ball bearings, or bushings. First pinion  16 , fixedly coupled to stub shaft  10 , meshes with ring gear  18 , which is supported for rotation with respect to the housing about an axis perpendicular to the axis of rotation of stub shaft  10 . Pinion  16  and ring gear  18  are bevel gears and the gear teeth may be spiral gear teeth. The axis of stub shaft  10  may be offset below the axis of ring gear  18  in which case a hypoid gear profile is used. Ring gear  18  drives left and right axle shafts  20 ,  22  via a differential (not shown) that permits slight speed differences such as when the vehicle turns a corner. 
         [0012]    Power from electric motor  24  is delivered to second pinion  26  via gearbox  28 . Pinion  26  meshes with the same gear teeth on ring gear  18  as first pinion  16 , but at a different circumferential position. The circumferential location of pinion  26  is based on the physical location of electric motor  24  and gearbox  28  relative to axle shafts  20  and  22 , which may vary depending on available packaging space in the vehicle. For a rear wheel drive vehicle, pinion  16  may be in front of the rear axle shafts whereas pinion  26  is behind the rear axle shafts. Pinion gear  26  may be offset above the axis of ring gear  18 . If the offsets of pinions  16  and  26  are of equal magnitude, then identical gear profiles may be used which reduces manufacturing cost. 
         [0013]    Motor  24  includes a stator  30  fixed to the housing and a rotor  32  fixed to a rotor shaft  34  that is supported for rotation by bearings. The motor may be a direct current (DC) motor or an alternating current (AC) motor such as a synchronous permanent magnet motor or an induction motor. The term motor, as used here, includes reversible electric machines that are capable of both converting electrical power into mechanical power and converting mechanical power into electrical power. In the AC motor illustrated in  FIG. 1 , the torque exerted on shaft  30  by rotor  32  is related to electrical currents flowing through windings of stator  30 . During motoring operation, inverter  36  draws direct current electrical power from a battery  38  and supplies three phases of alternating current to windings of stator  30 . Controller  40  sends signals to inverter  36  directing inverter  36  to regulate the voltage, frequency, and phase in each winding such that a desired torque is exerted by rotor  34 . During generating operation, controller  40  directs inverter  36  to control the voltage, frequency, and phase such that the torque exerted is opposite the direction of rotation. Electrical power produced is converted to direct current and stored in battery  38 . 
         [0014]    Gearbox  28  includes a layshaft  42  fixedly coupled to second pinion  26  and to gears  44  and  46 . Layshaft  42  is substantially parallel to motor shaft  34 . Motor shaft  34  may be physically above layshaft  42  as shown in  FIG. 1  or it may be offset below, to the left or right side of the vehicle, or diagonally, as dictated by available packaging space. Gears  48  and  50  are journalled on motor shaft  34  and mesh with gear  44  and  46  respectively. Coupler  52  alternately selectively couples gears  48  and  50  to motor shaft  34 . In other words, coupler  52  selectively couples either gear, one at a time, to the shaft. When coupler  52  is moved to the right, it selectively couples gear  50  to motor shaft  34  to establish a low range power flow path from the rotor shaft  34  to ring gear  18  via gear  50 , gear  46 , shaft  42 , and pinion  26 . When coupler  52  is moved to the left, it selectively couples gear  48  to motor shaft  34  to establish a high range power flow path from the rotor shaft  34  to ring gear  18  via gear  48 , gear  44 , shaft  42 , and pinion  26 . When coupler  52  is in the intermediate position shown in  FIG. 1 , no power flow path is established. Gear ratios of approximately 3.0:1 for low range and approximately 1.4:1 for high range are recommended. In an alternative embodiment, gears  48  and  50  may be fixedly coupled to shaft  34  and a coupler may selectively couple gears  44  and  46  to shaft  42 . Coupler  52  may be a synchronizer of the type generally used in manual transmissions which includes blocker rings that synchronize the speeds of the gear and the shaft before positively engaging. Alternatively, coupler  52  may be a simple dog clutch and synchronization may be performed by active speed control of motor  24 . 
         [0015]    The position of coupler  52  is controlled via an actuation mechanism that includes an actuator  54 , a rail  56 , and a fork  58 . In response to control signals from controller  40 , actuator  54  causes fork  58  to move axially along rail  56 . Various types of linear actuators may be utilized. For example, rail  56  may have threads that engages threads in fork  58  and actuator  54  may be a motor that rotates rail  56 . Fork  58  engages coupler  52  in a manner that constrains them to have the same axial position but permits coupler  52  to rotate with shaft  34 . 
         [0016]      FIG. 2  schematically illustrates a two-speed hybrid electric axle utilizing planetary gearing. Elements that are common to both the layshaft embodiment of  FIG. 1  and the planetary embodiment of  FIG. 2  are labeled with the same reference number. In the planetary embodiment, the rotor is fixedly coupled to a shaft  60  that is co-axial with second pinion gear  26 . Gearbox  62  includes a Ravigneaux planetary gear set. First sun gear  64  is fixedly coupled to shaft  60 . Ring gear  66  is fixedly coupled to second pinion gear  26 . Carrier  68  and second sun gear  70  are both supported for rotation about the axis of shaft  60  and second pinion  26 . A set of long planet gears  72  are supported for rotation with respect to carrier  68 . Each long planet gear  72  meshes with both second sun gear  70  and ring gear  66 . A set of short planet gears  74  are also supported for rotation with respect to carrier  68 . Each short planet gear first sun gear  64  and with one of the long planet gears  72 . The Ravigneaux gear set creates a fixed linear speed relationship. Specifically, sun gears  64  and  70  always have the most extreme speeds and the speeds of carrier  68  and ring gear  66  have intermediate speeds. The speeds of carrier  68  and ring gear  66  are a weighted average of the speeds of sun gear  64  and sun gear  70  with fixed weighting factors determined by the relative number of gear teeth. 
         [0017]    Braking element  76  moves axially with fork  58  but does not rotate. When braking element  76  is moved to the left, it engages carrier  68  to hold carrier  68  against rotation. This establishes a low range power flow path between shaft  60  and ring gear  18 . When braking element  76  is moved to the right, it engages second sun gear  70  to hold second sun gear against rotation and establish a high range power flow path. Other arrangements of planetary gearing impose a fixed linear speed relationship among four rotating elements. If the weighting factors are similar to those of the Ravigneaux gear set of  FIG. 2 , then such a gear set may be substituted for the Ravigneaux gear set of  FIG. 2  to achieve comparable results. Four example, two simple planetary gear sets with each carrier fixedly coupled to the opposite ring gear imposes such as relationship with the two sun gears again having the most extreme speeds. As another example, two simple planetary gear sets with the two sun gears fixedly coupled to one another and one carrier fixedly coupled to the opposite ring gear impose a suitable fixed linear speed relationship with the linked sun gear and the unlinked ring gear having the most extreme speeds. To reduce manufacturing cost, especially when the production volume is low, it is advantageous to use planetary gearing that has been developed for other purposes, such as for use in the transmission used to transmit power from the internal combustion engine to stub shaft  10 . 
         [0018]      FIG. 3  shows an embodiment in which the motor and gearbox have been rotated  90  degrees such they rotate about axes parallel to the ring gear axis. Ring gear  18  includes helical gear teeth  80  in addition to the hypoid gear teeth that mesh with first pinion  16 . Pinion  82 , which has helical gear teeth, meshes with the helical gear teeth of ring gear  18  and is fixedly coupled to Ravigneaux ring gear  66 . 
         [0019]    In use, controller  40  directs actuator  54  whether to engage low range, high range, or neutral and directs inverter  36  whether to provide positive or negative motor torque. Controller  40  may be integrated with or in communication with a vehicle systems controller such that it has access to various information about vehicle condition, the condition of other vehicle systems, and about driver intent. For example, controller  40  receives information about vehicle speed, engine torque, brake torque, accelerator pedal position, and brake pedal position. Controller  40  also maintains information about the state of charge of battery  38 . 
         [0020]    When the vehicle is at low speed, controller  40  directs actuator  54  to engage low range. Selection of low range multiplies the motor torque such that more torque is delivered at ring gear  18  than when in high range for a given motor torque. When the vehicle is at high speed, controller  40  directs actuator  54  to engage high range. Selection of high range reduces the speed of rotor  32  relative to vehicle speed. The threshold speed at which a transition, or shift, occurs may be based on factors such as accelerator pedal position. Also, a shift may be delayed when the motor is being used to provide or withdraw power. To perform a shift, controller first directs inverter  36  to set the motor torque to zero. Then, it directs actuator  54  to disengage the currently selected range. Then, it directs inverter  36  to control the speed of the motor to close to the speed in the destination range. Once the speed is acceptably close to the target speed, controller  40  directs actuator  54  to engage the destination range. The acceptable speed tolerance may depend upon whether coupler  52  or braking element  76  includes a blocker ring to aid in synchronization. 
         [0021]    When the accelerator pedal position indicates a driver demand for acceleration, controller  40  may direct inverter  36  to provide torque to boost performance. This action may be coordinated with the engine controller and transmission controller such that the total torque at ring gear  18  complies with a driver demand. During boost, electrical power is withdrawn from battery  38 , reducing the state of charge. 
         [0022]    When the brake pedal indicates a driver demand for deceleration, controller  40  may direct inverter  36  to provide torque in the opposite direction of rotation. This regenerative braking torque tends to recharge battery  38 . Some regenerative braking torque may also be commanded when the driver has not depressed either the accelerator pedal or the brake pedal. The regenerative braking torque may be coordinated with a brake controller such that the total negative wheel torque is properly related to brake pedal pressure or movement. Coordination may also be required to ensure that the relative portion of the brake torque on front wheels and rear wheels is acceptable. Finally, regenerative braking may be coordinated with an anti-lock braking system. 
         [0023]    If the state of charge of the battery becomes too low, controller  40  may direct inverter to induce a torque opposite the direction of rotation for the purpose of recharging the battery. This action may be coordinated with an engine controller such that the engine produces additional torque and the total torque delivered to vehicle wheels satisfies the driver demand. 
         [0024]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments may be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.