Abstract:
A vehicle drive system comprising three motor/generators, an engine and an electrical energy storage device. The system is arranged so that two axles can be driven at the same time. Each axle can be driven using power generated by the engine or provided by the electrical energy storage device. The system can also be configured to drive one of axles using mechanical power from the engine.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/675,647, entitled “All Wheel Drive System for a Serial PHEV” and filed on Jul. 25, 2012. 
     
    
     BACKGROUND 
       [0002]    This application relates generally to hybrid or electric vehicles, and particularly to a plurality of operating modes associated with hybrid or electric vehicles. 
         [0003]    Vehicles, such as motor vehicles, utilize an energy source in order to provide power to operate the vehicle. While petroleum-based products, such as gasoline, dominate as an energy source in traditional combustion engines, alternative energy sources are available, such as methanol, ethanol, natural gas, hydrogen, electricity, solar, and/or the like. A hybrid powered vehicle, referred to as a “hybrid vehicle,” utilizes a combination of energy sources in order to power the vehicle. For example, a battery maybe utilized in combination with the traditional combustion engine to provide power to operate the vehicle. Such vehicles are desirable because they take advantage of the benefits of multiple fuel sources in order to enhance performance and range characteristics of the hybrid vehicle relative to a comparable gasoline-powered vehicle. 
         [0004]    An example of a hybrid vehicle is a vehicle that utilizes a combination of stored electric energy and an internal combustion engine as power sources to propel the vehicle. An electric vehicle is environmentally advantageous due to its low emissions characteristics and the general availability of electricity as a power source. The battery may be quite large, depending on the energy requirements of the vehicle, and will generate heat that is dissipated using various techniques. Batteries can be quiet emitting low sound. Adjustment between a supplemental energy source, like an engine, can be improved to provide desired vehicle performance characteristics. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a schematic block diagram of a vehicle drive system in accordance with various embodiments of the disclosure. 
           [0006]      FIG. 2  is a schematic cross-section view of an engine assembly in accordance with various embodiments of the disclosure. 
           [0007]      FIG. 3  is a schematic end view of two gears of a front gear box coupled to an engine assembly in accordance with various embodiments of the disclosure. 
           [0008]      FIG. 4  is a schematic cross-section view of an engine assembly in accordance with various embodiments of the disclosure. 
           [0009]      FIG. 5  is a schematic end view of two gears of a front gear box coupled to an engine assembly in accordance with various embodiments of the disclosure. 
           [0010]      FIG. 6  is a schematic block diagram of a vehicle drive system operating in a rear wheel drive mode according to an exemplary embodiment. 
           [0011]      FIG. 7  is a schematic block diagram of a vehicle drive system operating in a rear wheel drive mode according to an exemplary embodiment. 
           [0012]      FIG. 8  is a schematic block diagram of a vehicle drive system operating in all wheel drive mode according to an exemplary embodiment. 
           [0013]      FIG. 9  is a schematic block diagram of a vehicle drive system operating in a rear wheel drive according to an exemplary embodiment. 
           [0014]      FIG. 10  is a schematic block diagram of a vehicle drive system operating in a rear wheel drive according to an exemplary embodiment. 
           [0015]      FIG. 11  is a schematic block diagram of a vehicle drive system operating in all wheel drive mode according to an exemplary embodiment. 
           [0016]      FIG. 12  is a schematic block diagram of a vehicle drive system operating in all wheel drive mode according to an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Referring to  FIG. 1 , a vehicle, such as a hybrid vehicle  10 , includes a rechargeable energy storage system (RESS)  12  coupled to an engine  14 . The engine  14  may generally refer to any apparatus operable to augment power or range beyond the RESS  12 . For example, the engine  14  can be an internal combustion engine that consumes gasoline. The RESS  12  can be, for example (but not limited to) a high-voltage battery, such as a high-voltage lithium ion battery pack. Operation of the vehicle  10  can be driven by each power source and/or both. The vehicle  10  may include multiple electrical motor/generators that may be operated either as drive motors that convert electrical power to rotational mechanical energy or as generators that convert rotational mechanical energy to electrical energy. The motor/generators are at times referred to simply as motors but, as described herein, include the ability to be driven to generate electricity. The motor/generators can be electrically driven and coupled to the engine  14  and the RESS  12 . 
         [0018]    According to various embodiments, the vehicle  10  includes a first motor/generator  20  that primarily serves as a generator. The vehicle  10  further includes a second motor/generator  22  (e.g., rear wheel drive (RWD) motor) that engages a drive shaft that turns one or more rear wheels  16 . One or more intermediate devices, such as a rear gearbox  23  and a rear differential  24 , may be provided between the second motor/generator  22  and the rear wheels  16 . The vehicle  10  still further includes a third motor/generator  26  (e.g., all wheel drive (AWD) motor) that engages a drive shaft that turns one or more front wheels  18 . One or more intermediate devices, such as a front gearbox  27  and a front differential  28 , may be provided between the third motor/generator  26  and the front wheels  18 . The gearboxes  23  and  27  may be single speed gearboxes or multi-speed gearboxes. The motor/generators  20 ,  22 , and  26  and the RESS  12  may be coupled to a common DC bus  30 . In some embodiments, the first motor/generator  20  and the third motor/generator  26  may be AC devices and electric conversion devices such as inverters  32  and  34  may be coupled between the motor generators  20  and  26  and the DC bus  30 . The vehicle  10  may be operated normally as a RWD vehicle, with the front wheels  18  only powered when needed for additional power or traction. 
         [0019]    When the vehicle accelerates or increases energy consumption, speed of the drive motors (e.g., motor/generators  22  and  26 ) increase to deliver more power or energy to the rear wheels  16  and/or the front wheels  18 . The turning of the motors can be reversed to provide regenerative braking, which provides the impression of down-shifting the vehicle  10 . This also generates energy that can be stored in the RESS  12 . Accordingly, in some embodiments, the vehicle  10  can actuate regenerative braking to slow the vehicle  10  rather than causing brake pads (not shown) to slow the wheels  16  and  18  when a brake pedal of the vehicle is depressed. To slow the vehicle  10  beyond the speed caused by the regenerative braking, the brake pads can engage the wheels  16  and  18  under predetermined circumstances that are input into a controller of the vehicle (not shown). For instance, the brake pads can take over once requested braking surpasses a prefixed set point or threshold. 
         [0020]    Various embodiments provide for one or more driver-selectable powertrain operating modes for a vehicle such as a hybrid vehicle. The modes may also be automatically engaged according to predetermined criteria such as, for example, vehicle or vehicle component operating conditions. The operation of the various systems and components thereof that are described herein may be controlled via one or more processors, controllers or computers such as, for example, the vehicle controller mentioned above. In some embodiments, a first mode or “stealth” mode is a default operating mode for the vehicle  10 . In stealth mode, fuel economy can be favored over performance. To favor fuel economy, the vehicle  10  is powered by the RESS  12  (e.g., high-voltage battery) with little or no supplemental power from the engine  14 . The RESS  12  is used to operate the vehicle  10  until the RESS  12  reaches a state of charge threshold. The state of charge threshold may be predetermined and programmed into a controller of the vehicle  10  (not shown). The state of charge threshold may be targeted to maintain battery longevity and performance targets. In stealth mode, the vehicle controller is programmed to prevent operation of the engine  14  until the RESS  12  reaches its target state of charge threshold. 
         [0021]    A second mode or “sport” mode can be a selectable mode that emphasizes performance aspects of the vehicle  10  by allowing for operation of the engine  14  to provide additional power to the RESS  12  as compared to stealth mode. In an example, the driver can switch to sport mode and back to stealth via a device such as a bidirectional push/pull sport hand paddle on a steering wheel. In the sport mode, the vehicle  10  uses more than one power source (e.g., the RESS  12  and the engine  14 ) to achieve performance targets. The engine  14  may still turn off when the driver does not demand substantial power, but without significantly sacrificing response time. Sport mode can affect various systems of the vehicle  10  as well, but with the target of creating a performance-oriented driving experience. 
         [0022]    Referring now in general to  FIGS. 2-5 , the engine  14  may be combined with one or more of the motor/generators to form a relatively compact engine assembly  40 . The engine assembly  40  can provide advantages in package size and cost compared to a vehicle drive system with a separate engine/generator and AWD systems. According to various embodiments, the engine assembly  40  includes the engine  14 , the first motor/generator  20 , and the third motor/generator  26 , which are coupled together on concentric shafts that are able to rotate independently of each other. The engine assembly  40  further includes a planetary gear set  42  coupled to the output shaft of the engine  14 . A first clutch  44  is coupled between the gear set  42  and the first motor/generator  20 . A second clutch  46  is coupled between the first motor/generator  20  and the third motor/generator. A third clutch  48  is coupled between the front gearbox  27  and the front differential  28 . Through the selective engagement and disengagement of the clutches  44 ,  46 , and  48 , the engine  14 , the first motor/generator  20 , and the third motor/generator  26  may be operated independently or may coupled together to achieve a variety of vehicle drive system modes of operation. 
         [0023]    In some embodiments, the engine assembly  40  includes the engine  14  on a first end of the engine assembly  40 , the first motor/generator  20  on a second end of the second end of the engine assembly  40 , and the third motor/generator  26  between the engine  14  and the first motor/generator  20 . The planetary gear set  42  is provided between the engine  14  and the third motor/generator  26 . An engine output shaft  50  (e.g., crankshaft) is coupled to a ring gear  52  of the planetary gear set  42 . A planet carrier  54  of the planetary gear set  42  is fixed to a housing  41  of the engine assembly  40  via a shaft  55  that is concentric with the engine output shaft  50  and extends through the third motor/generator  26  and the first motor/generator  20 . A sun gear  56  of the planetary gear set  42  is coupled to a shaft  58  that is concentric with the engine output shaft  50  and the shaft  55 . The shaft  58  is a hollow shaft that surrounds a portion of the length of the shaft  55  and extends through the third motor/generator  26 . The shaft  58  can be coupled to the first motor/generator  20  with the first clutch  44 . The shaft  58  can be coupled to the third motor/generator  26  with the second clutch  46 . In particular embodiments, the third motor/generator  26  is permanently coupled to a power pickup gear  60  that engages the gearbox  27 . The gearbox  27  drives a front drive shaft  62 , which may be coupled to the front differential  28  with the third clutch  48 . 
         [0024]    In some embodiments, the engine assembly  40  includes the engine  14  on a first end of the engine assembly  40 , the first motor/generator  20  on a second end of the second end of the engine assembly  40 , and the third motor/generator  26  between the engine  14  and the first motor/generator  20 . The planetary gear set  42  is provided between the third motor/generator  26  and the first motor/generator  20 . The engine output shaft  50  (e.g., crankshaft) extends through the third motor/generator  26  and is coupled to the ring gear  52  of the planetary gear set  42 . The planet carrier  54  of the planetary gear set  42  is fixed to the housing  41  of the engine assembly  40  via a shaft  55  that is concentric with the engine output shaft  50  and extends through the first motor/generator  20 . The sun gear  56  of the planetary gear set  42  is coupled to the shaft  58  that is concentric with the engine output shaft  50  and the planet carrier shaft  55 . The shaft  58  is a hollow shaft that extends through the first motor/generator  20  and surrounds the shaft  55 . The shaft  58  can be coupled to the first motor/generator  20  with the first clutch  44 . The first motor/generator  20  can be coupled to the third motor/generator  26  with the second clutch  46 . In particular embodiments, the third motor/generator  26  is permanently coupled to a power pickup gear  60  that engages the gearbox  27 . The gearbox  27  drives the front drive shaft  62 , which may be coupled to the front differential  28  with the third clutch  48 . 
         [0025]    The planetary gear set  42  and the clutches  44 ,  46 , and  48  may be configured to enable an ideal speed ratio between the components of the engine assembly  40  and allow the engine  14 , the first motor/generator  20 , and the third motor/generator  26  to each be operated at their respective optimal efficiency regions. 
         [0026]    With reference to  FIGS. 6-12 , in various embodiments, several operational modes of the drive system for the vehicle  10  are shown. The vehicle  10  may be a rear wheel drive vehicle with the second motor/generator  22  being utilized to drive the rear wheels  16  in any of the operational modes and the modes may be differentiated by the used of the engine  14 , the first motor/generator  20 , and the third motor/generator  26 . For clarity, the drive system of the vehicle  10  is simplified and does not show the gearboxes  23  and  27 ; the differentials  24  and  28 ; the inverters  30 ,  32 , and  34 ; or the planetary gear set  42 . Any stealth mode or rear wheel drive mode described in the disclosure (e.g., the modes shown in  FIGS. 6-10 ) may operate in either to propel the vehicle forward or in reverse. 
         [0027]    Referring to  FIG. 6 , in a first mode or RWD stealth mode, the engine  14 , the first motor/generator  20 , and the third motor/generator  26  are each turned off The first clutch  44  and the second clutch  46  may be engaged or disengaged without affecting the drive system. The second motor/generator  22  draws electrical power from the DC bus  30  to drive the rear wheels  16 . The third clutch  48  is disengaged, allowing the front wheels  18  to rotate freely. 
         [0028]    Referring to  FIG. 7 , in a second mode or AWD stealth mode, each of the engine  14  and the first motor/generator  20  is turned off and the third motor/generator  26  is operated as a motor. The first clutch  44  may be engaged or disengaged without affecting the drive system. The second clutch  46  is disengaged to decouple the third motor/generator  26  from the first motor/generator  20 . The third clutch  48  is engaged to couple the third motor/generator  26  to the front wheels  18 . The third motor/generator  26  draws electrical power from the DC bus  30  to drive the front wheels  18 . The second motor/generator  22  draws electrical power from the DC bus  30  to drive the rear wheels  16 . The AWD stealth mode allows both the front wheels  18  and rear wheels  16  to be driven solely on electrical power without turning on the engine  14 . 
         [0029]    Referring to  FIG. 8 , in a third mode or AWD stealth max mode, the engine  14  is turned off and the first motor/generator  20  and the third motor/generator  26  are both operated as motors. The first clutch  44  is disengaged to decouple the engine  14  from the first motor/generator  20 . The second clutch  46  is engaged to couple the third motor/generator  26  to the first motor/generator  20 . The third clutch  48  is engaged to couple the third motor/generator  26  to the front wheels  18 . The first motor/generator  20  and the third motor/generator  26  draw electrical power from the DC bus  30  to drive the front wheels  18 . The second motor/generator  22  draws electrical power from the DC bus  30  to drive the rear wheels  16 . The AWD stealth max mode allows both the front wheels  18  and rear wheels  16  to be driven solely on electrical power without turning on the engine  14  and provides maximum torque to the front wheels  18  through the use of both the first motor/generator  20  and the third motor/generator  26  as motors. 
         [0030]    Referring to  FIG. 9 , in a fourth mode or RWD charge mode, the engine  14  is turned on, the first motor/generator  20  is operated as a generator, and the third motor/generator  26  is turned off. The first clutch  44  is engaged to couple the engine  14  to the first motor/generator  20 . The second clutch  46  is disengaged to decouple the third motor/generator  26  from the first motor/generator  20 . The third clutch  48  is disengaged, allowing the front wheels  18  to rotate freely. The first motor/generator  20  is operated as a generator and converts mechanical power from the engine  14  to recharge the RESS  12  via the DC bus  30 . The second motor/generator  22  draws electrical power from the DC bus  30  to drive the rear wheels  16 . The RWD charge mode allows the vehicle  10  to travel an extended range by using an onboard fuel source such as a gas tank to provide additional electrical power beyond the capacity of the RESS  12  (e.g., the charge stored in the RESS  12  before departure of the vehicle  10 , such as by being plugged into a source such as the electrical power grid). 
         [0031]    Referring to  FIG. 10 , in a fifth mode or RWD charge sustain/sport max mode, the engine  14  is turned on and the first motor/generator  20  and the third motor/generator  26  are operated as generators. The first clutch  44  is engaged to couple the engine  14  to the first motor/generator  20  and the second clutch  46  is engaged to couple the third motor/generator  26  to the first motor/generator  20 . The third clutch  48  is disengaged, allowing the front wheels  18  to rotate freely. The first motor/generator  20  and the third motor/generator  26  are both operated as generators and convert mechanical power from the engine  14  to recharge the RESS  12  via the DC bus  30 . The second motor/generator  22  draws electrical power from the RESS  12  to drive the rear wheels  16 . The RWD charge sustain/sport max mode allows the vehicle  10  to travel an extended range by using an onboard fuel source, such as a gas tank, to recharge the RESS  12  and provides maximum electrical power to the second motor/generator  22  through the use of both the first motor/generator  20  and the third motor/generator  26  as generators. 
         [0032]    Referring to  FIG. 11 , in a sixth mode or AWD charge sustain/sport mode, the engine  14  is turned on, the first motor/generator  20  is operated as a generator, and the third motor/generator  26  is operated as a motor. The first clutch  44  is engaged to couple the engine  14  to the first motor/generator  20  and the third clutch  48  is engaged to couple the third motor/generator  26  to the front wheels  18 . The second clutch  46  is disengaged to decouple the third motor/generator  26  from the first motor/generator  20 . The first motor/generator  20  is operated as a generator and converts mechanical power from the engine  14  to recharge the RESS  12  via the DC bus  30 . The third motor/generator  26  is operated as a motor and draws electrical power from the DC bus  30  to drive the front wheels  18 . The second motor/generator  22  draws electrical power from the DC bus  30  to drive the rear wheels  16 . The AWD charge sustain/sport mode allows the vehicle  10  to travel an extended range by using an onboard fuel source, such as a gas tank, to recharge the RESS  12  and allows both the front wheels  18  and rear wheels  16  to be driven solely on electrical power. The charge sustain/sport max modes (both RWD and AWD) can be configured to maintain the battery charge level above a predetermined (e.g., 70 percent of total capacity). 
         [0033]    Referring to  FIG. 12 , in a seventh mode or power split mode, the engine  14  is turned on, and the first motor/generator  20  and the third motor/generator  26  are both operated as generators. The first clutch  44  is engaged to couple the engine  14  to the first motor/generator  20 , the second clutch  46  is engaged to couple the third motor/generator  26  to the first motor/generator  20 , and the third clutch  48  is engaged to couple the third motor/generator  26  to the front wheels  18 . The mechanical power from the engine  14  can be split between being utilized to directly power the front wheels  18  and being utilized to operate the first motor/generator  20  and the third motor/generator  26  as generators to provide power to the DC bus  30 , which may be utilized to recharge the RESS  12  or drive the rear wheels  16  with the second motor/generator  22 . The power split mode allows the vehicle  10  to provide increased torque to the front wheels  18  or propel the vehicle  10  solely with the engine  14  (e.g., if there is a malfunction in the electrical system). 
         [0034]    The selective coupling and decoupling of the engine  14 , the first motor/generator  20 , the third motor/generator  26 , and the front wheels  18  with the clutches  44 ,  46 , and  48  allows the first motor/generator  20  and the third motor/generator  26  to be utilized in tandem (e.g., both operated as motors or as generators) or to be utilized for different purposes simultaneously. When used in tandem, the first motor/generator  20  and the third motor/generator  26  can provide maximum torque to the front wheels  18  in an AWD mode or can provide maximum electrical power to the DC bus  30 . 
         [0035]    The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.