Abstract:
A hybrid vehicle powertrain includes an internal combustion engine, first and second electric machines, traction wheels, and an output shaft having meshing gears configured to establish a final drive ratio between the output shaft and the traction wheels. The powertrain additionally includes a first mechanical linkage and a second mechanical linkage. The first mechanical linkage is configured to selectively transmit engine torque to the fraction wheels and selectively transmit electric machine torque to the traction wheels. The second mechanical linkage is configured to selectively transmit engine torque to the traction wheels. When transmitting engine torque to the wheels, the second mechanical linkage defines a fixed overdrive speed relationship between the engine and the fraction wheels.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to powertrains for hybrid electric vehicles. 
       BACKGROUND 
       [0002]    One class of hybrid electric vehicle powertrains, commonly referred to as a powersplit powertrain, has two sources of power. The first source includes an internal combustion engine, and the second source includes a combination of an electric motor, a generator and a battery. The engine and the generator, together with a planetary gear set, a countershaft and a motor, establish a mechanical torque flow path and an electromechanical torque flow path to vehicle traction wheels. The battery is an energy-storing device for the generator and the motor. Engine power is divided into two power flow paths at any generator speed and vehicle speed. Engine speed is controlled by the generator, which implies that the engine speed can be decoupled from the vehicle speed within the allowed speed range of the generator. This mode of operation is called “positive power split”, when the generator is generating electrical power using mechanical power input from the engine. 
         [0003]    Because of the mechanical properties of the planetary gear set, the generator can distribute power to the planetary gear set to drive the vehicle. This mode of operation is called “negative power split”. The combination of a generator, a motor and a planetary gear set thus can be considered to have electrical continuously variable (e-CVT) transmission characteristics. 
         [0004]    A generator brake can be activated so that engine output power is transmitted with a fixed gear ratio to the torque output side of the powertrain through a mechanical path only. The first power source can only effect forward propulsion of the vehicle since there is no reverse gear. The engine requires either generator control or application of a generator brake to transmit output power for forward drive. 
         [0005]    When the second power source is active, the electric motor draws power from the battery and drives the vehicle independently of the engine for both forward drive and reverse drive. 
         [0006]    The motor may also generate power and charge the battery if the engine produces power exceeding driver demand, or in a regenerative mode capturing vehicle kinetic energy. In addition, the generator can draw power from the battery and drive against a one way clutch on the engine power output shaft to propel the vehicle in a forward direction. This mode of operation is called “generator drive mode”. A vehicle system controller coordinates the two power sources so that they work together seamlessly to meet a driver&#39;s torque demand without exceeding powertrain system limits. The vehicle system controller allows continuous regulation of engine speed for any given vehicle speed and power request. The mechanical power flow path provides efficient power delivery through the planetary gear set to the driveshaft. 
       SUMMARY 
       [0007]    A hybrid vehicle according to the present disclosure includes an internal combustion engine, first and second electric machines, traction wheels, and an output shaft coupled to the traction wheels by meshing gears. The meshing gears are configured to establish a final drive ratio between the output shaft and the traction wheels. The vehicle additionally includes a first gearing arrangement and a second gearing arrangement. The first gearing arrangement, which may include a planetary gear set, is configured to selectively transmit engine torque to the traction wheels and selectively transmit electric machine torque to the traction wheels. The second gearing arrangement, which includes a clutch and which may define an overdrive gear set, is configured to selectively transmit engine torque to the output shaft. When transmitting engine torque to the wheels, the second mechanical linkage defines an overdrive speed and torque relationship between the engine and the output shaft. The vehicle additionally includes a controller. The controller is configured to engage the clutch in response to a first operating condition, maintain the clutch in an engaged position in response to the clutch being engaged and a second operating condition, and disengage the clutch in response to the clutch being engaged and a third operating condition. 
         [0008]    The clutch may be, in various embodiments, a dog clutch or a one-way clutch. 
         [0009]    The first operating condition may be one of the following: a generally constant driver power demand during a first acceleration event, a decrease in driver power demand and subsequent generally constant driver power demand after a second acceleration event, or a decrease in driver power demand and activation of regenerative braking after a third acceleration event while the engine is on. The second operating condition may include a change in vehicle charging mode. The third operating condition may correspond to one of the following: a decrease in driver power demand that exceeds a first associated threshold, an actuation of a brake pedal that exceeds a second associated threshold, an increase in driver power demand that exceeds a third associated threshold, a generally constant driver power demand and a decrease in vehicle speed that exceeds a fourth associated threshold, or an engine shutdown request. 
         [0010]    A method of controlling a hybrid vehicle includes controlling the vehicle in a continuously variable mode and selectively engaging an overdrive mechanical linkage. The vehicle has a powersplit powertrain, providing an electrical power transmission path to vehicle wheels and a first mechanical power transmission path to the vehicle wheels. The vehicle additionally includes an overdrive mechanical linkage that is selectively engageable to transmit engine torque to the vehicle wheels in a fixed speed relationship. The overdrive mechanical linkage may be engaged in response to a first operating condition 
         [0011]    In one embodiment, the powersplit powertrain includes a generator and the overdrive mechanical linkage includes an electromagnetic one-way clutch selectively coupled to the engine. In such an embodiment, engaging the overdrive mechanical linkage includes overrunning the clutch by rotating the generator in a disengagement direction, electronically activating the one-way clutch while overrunning, engaging the activated clutch by rotating the generator in an engagement direction opposite the disengagement direction until the clutch is engaged to prevent further rotation in the engagement direction, transferring engine torque carried by the generator to the activated clutch, and turning off the generator after the engine torque is transferred. In such embodiments, disengaging the overdrive mechanical linkage includes turning on the generator while the clutch is activated and engaged, rotating the generator to overrun and disengage the clutch, and deactivating the clutch while overrunning. 
         [0012]    In another embodiment, the powersplit powertrain includes a generator and the overdrive mechanical linkage includes a dog clutch selectively coupled to the engine. In such an embodiment, engaging the overdrive mechanical linkage includes controlling the generator according to a target speed range to synchronize the clutch, engaging the clutch, transferring engine torque carried by the generator to the engaged clutch, and turning off the generator after the engine torque is transferred. In such embodiments, disengaging the overdrive mechanical linkage includes turning on the generator while the clutch is engaged, transferring torque to the generator from the clutch, and disengaging the clutch. 
         [0013]    Some embodiments further include maintaining the overdrive linkage in response to a second operating condition. Further embodiments may include disengaging the overdrive mechanical linkage to de-establish the overdrive speed relationship in response to a third operating condition. 
         [0014]    A hybrid vehicle according to the present disclosure includes an internal combustion engine, an electric machine, traction wheels, a first mechanical linkage, and a second mechanical linkage. The first mechanical linkage, which includes a planetary gearset, is configured to selectively transmit engine torque to the traction wheels and selectively transmit electric machine torque to the traction wheels. The second mechanical linkage is configured to selectively transmit engine torque to the traction wheels. The second mechanical linkage defines a fixed speed relationship between the engine and the traction wheels when transmitting torque. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  illustrates a hybrid vehicle having a powersplit powertrain; 
           [0016]      FIG. 2  illustrates torque and speed transmission through a powersplit powertrain; 
           [0017]      FIG. 3  illustrates a hybrid vehicle having a powertrain according to the present disclosure; 
           [0018]      FIG. 4  illustrates a method of controlling a powertrain according to the present disclosure in flowchart form; 
           [0019]      FIG. 5  is a schematic view of an electromagnetic one-way clutch; 
           [0020]      FIG. 6  is a detail view of an electromagnetic one-way clutch; 
           [0021]      FIGS. 7 a  and 7 b    illustrate methods of engaging a one-way clutch and a dog clutch, respectively, according to the present disclosure in flowchart form; and 
           [0022]      FIGS. 8 a  and 8 b    illustrate methods of disengaging a one-way clutch and a dog clutch, respectively, according to the present disclosure in flowchart form. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may 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. 
         [0024]    Referring now to  FIG. 1 , a hybrid electric vehicle having a powersplit powertrain is illustrated. The powertrain includes two power sources that are connected to the driveline: (1) an engine  16  and an electric machine  50  (which may be referred to as a generator) connected together via a planetary gear arrangement  20 ; and (2) an electric drive system including a battery  12 , an electric machine  46  (which may be referred to as a motor) and generator  50 . Battery  12  is an energy storage system for motor  46  and generator  50 . 
         [0025]    A vehicle system controller (VSC)  10  is configured to send control signals to and receive sensory feedback information from one or more of battery  12 , engine  16 , motor  46 , and generator  50  in order for power to be provided to vehicle traction wheels  40  for propelling the vehicle. Controller  10  controls the power source proportioning between battery  12  and engine  16  for providing power to propel the vehicle and thereby controls the state of charge (SOC) of battery  12 . 
         [0026]    Transmission  14  includes planetary arrangement  20 , which includes a ring gear  22 , a sun gear  24 , and a carrier assembly  26 . Ring gear  22  distributes torque to step ratio gears comprising meshing gear elements  28 ,  30 ,  32 ,  34 , and  36 . A torque output shaft  38  of transmission  14  is driveably connected to wheels  40  through a differential-and-axle mechanism  42 . Gears  30 ,  32 , and  34  are mounted on a counter shaft  31  with gear  32  engaging a motor-driven gear  44 . Motor  46  drives gear  44 . Gear  44  acts as a torque input for counter shaft  31 . Engine  16  distributes torque through input shaft  18  to transmission  14 . Battery  12  delivers electric power to motor  46  through power flow path  48 . Generator  50  is connected electrically to battery  12  and to motor  46 , as shown at  52 . 
         [0027]    While battery  12  is acting as a sole power source with engine  16  off, input shaft  18  and carrier assembly  26  are braked by an overrunning coupling (i.e., one-way clutch (OWC))  53 . A mechanical brake  55  anchors the rotor of generator  50  and sun gear  24  when engine  16  is on and the powertrain is in a parallel drive mode, sun gear  24  acting as a reaction element. 
         [0028]    Controller  10  receives a signal PRND (park, reverse, neutral, drive) from a transmission range selector  63 , which is distributed to transmission control module (TCM)  67 , together with a desired wheel torque, a desired engine speed, and a generator brake command, as shown at  71 . A battery switch  73  is closed after vehicle “key-on” startup. Controller  10  issues a desired engine torque request to engine  16 , as shown at  69 , which is dependent on accelerator pedal position sensor (APPS) output  65 . A brake pedal position sensor (BPPS) distributes a wheel brake signal to controller  10 , as shown at  61 . A brake system control module (not shown) may issue to controller  10  a regenerative braking command based on information from the BPPS. TCM  67  issues a generator brake control signal to generator brake  55 . TCM  67  also distributes a generator control signal to generator  50 . 
         [0029]    Referring now to  FIG. 2 , a block diagram of power flow paths between the various components of the powertrain of  FIG. 1  is shown. Fuel is delivered to engine  16  under the control of the driver using an engine throttle. Engine  16  delivers engine power (τ e ω e , where τ e  is engine torque and ω e  is engine speed) to planetary arrangement  20 . Planetary  20  delivers power (τ r ω r , where T r  is the ring gear torque and W r  is the ring gear speed) to counter shaft  31 . Output shaft  38  outputs power (P out =τ s ω s , where τ s  and ω s  are the torque and speed of output shaft  38 , respectively) to wheels  40 . Generator  50  can deliver power to or be driven by planetary  20 . Similarly, power distribution between motor  46  and counter shaft  31  can be distributed in either direction. Driving power from battery  12  or charging power to battery  12  is represented by the bi-directional arrow  48 . 
         [0030]    The engine output power (τ e ω e ) can be split into a mechanical power flow path (τ r ω r ) and an electrical power flow path (τ g ω g  to τ m ω m , where τ g  is the generator torque, ω g  is the generator speed, τ m  is the motor torque, and ω m  is the motor speed). In this so-called positive split mode of operation, engine  16  delivers power to planetary  20  which delivers power (τ r ω r ) to counter shaft  31  which in turn drives wheels  40 . A portion of the planetary gearing power (τ g ω g ) is distributed to generator  50 , which delivers charging power to battery  12 . Battery  12  drives motor  46 , which distributes power (τ m ω m ) to counter shaft  31 . 
         [0031]    If generator brake  55  is activated, a parallel operating mode is established. In the parallel operating configuration, engine  16  is on and generator  50  is braked. Battery  12  powers motor  46 , which powers counter shaft  31  simultaneously with delivery of power from engine  16  to planetary  20  to counter shaft  31 . During operation with the second power source (described as including battery  12 , motor  46 , and generator  50 ), motor  46  draws power from battery  12  and provides propulsion independently from engine  16  to the drivetrain. 
         [0032]    As described, the HEV has two power sources for delivering driving power to wheels  40 . The first power source includes engine  16  and the second power source includes battery  12 . Engine  16  and battery  12  can provide traction power either simultaneously or independently. Controller  10  controls the electric energy and fuel energy proportioning to meet the propulsion requirements and thereby controls engine  16  and battery  12  accordingly. 
         [0033]    As may be observed, the planetary gearing arrangement  20  imposes speed and torque relationships among the engine  16 , generator  50 , and the vehicle traction wheels  40 . As discussed above, the generator  50  may be controlled to transfer power from the engine  16  to vehicle traction wheels  40  using the planetary gearing arrangement  20  as a CVT. However, at some operating conditions, the losses incurred by operating the generator  50  exceed the energy benefit of the CVT. 
         [0034]    As an example, when the vehicle is in “steady state” operation, such as cruising at a generally constant speed, the generator  50  incurs operational losses, which may exceed one kW, while the gear ratio between the engine  16  and traction wheels  40  remains generally unchanged. Here, steady state operation refers to a constant vehicle speed, constant driver power request, and generally consistent quantity of engine power used to charge the vehicle. This generally occurs when the driver power demand is roughly the same as the “road load”, or the sum of forces acting on the vehicle (e.g. rolling resistance, aerodynamic drag, etc.). 
         [0035]    Referring now to  FIG. 3 , a powertrain according to the present disclosure is illustrated. The powertrain includes two power sources that are connected to the driveline: (1) an engine  16 ′ and a generator  50 ′ connected together via a planetary gear arrangement  20 ; and (2) an electric drive system including a battery  12 ′, an electric motor  46 ′, and generator  50 ′. The planetary gearing arrangement  20 ′, in conjunction with meshing gear elements  28 ′,  30 ′,  32 ′,  34 ′, and  36 ′, define a first mechanical linkage between the engine  16 ′, generator  50 ′, and traction wheels  40 ′. Meshing gear elements  30 ′,  32 ′, and  34 ′ rotate about a common output shaft  79 , and meshing gear elements  34 ′ and  36 ′ define a final drive ratio between the output shaft  79  and traction wheels  40 ′. 
         [0036]    In addition, the powertrain includes a parallel overdrive shaft  80  fixedly coupled to gear element  30 ′ for joint rotation with the output shaft  79 . The overdrive shaft  80  is coupled to gear element  82 , which is in meshing rotation with gear element  84 . A clutch  86  is operable to selectively couple gear element  84  to the engine  16 ′. In a preferred embodiment, the clutch  86  is a dog clutch or an electronically controlled hydraulic rocker one-way clutch. Meshing gearing elements  84  and  82  have a fixed gear ratio configured to define an overdrive speed and torque relationship between the engine  16 ′ and the output shaft  79  when the clutch  86  is engaged. A controller  88  is configured to selectively command the clutch  86  to engage or disengage in response to various operating conditions, as will be discussed below with respect to  FIG. 4 . Other gearing arrangements that impose an overdrive speed relationship between the engine  16 ′ and output shaft  79  may, of course, be used. 
         [0037]    Referring now to  FIG. 4 , a method of controlling operation of the powertrain is illustrated in flowchart form. The hybrid vehicle powertrain is operated according to a nominal logic with the clutch disengaged, as illustrated at block  90 . A determination is then made of whether a first operating condition is satisfied, as illustrated at operation  92 . The first operating condition generally corresponds to a change from non-steady state operation to steady state operation, or to a decrease in magnitude of a difference between a driver power demand and the road load. The first operating condition may be one of the operating conditions of list A, illustrated at block  94 . The first operating condition may be a generally constant driver power demand through a first steady acceleration event. The first operating condition may also be a second acceleration event followed by a decrease in power demand to be generally equal to road load. The first acceleration event may also be a third acceleration event followed by a decrease in driver power demand and activation of regenerative braking It should be noted that with respect to the acceleration events, “first”, “second”, and “third” are used for the sake of clarity, and not to indicate any sequence or requirement of co-incidence. If the first operating condition is not satisfied, control returns to block  90 . If the first operating condition is satisfied, the clutch is engaged and the powertrain is controlled in overdrive mode, as illustrated at block  96 . 
         [0038]    A determination is then made of whether a second operating condition is satisfied, as illustrated at operation  98 . The second operating condition generally corresponds to continuing in steady state operation, or to a generally constant difference between driver power demand and road load. The second operating condition may be one of the operating conditions of list B, illustrated at block  100 . The second operating condition may include a small deviation in vehicle speed or driver power demand. In some embodiments, a speed deviation threshold or power demand deviation threshold may be provided. In such embodiments, speed or power demand deviations that do not exceed the respective thresholds may satisfy the second operating condition. The second operating condition may also be a generally constant driver power demand with a change in vehicle charging mode. In some speed and torque ranges charging is more efficient using a motor, and in other ranges charging is more efficient using a generator. A switch from motor charging to generator charging or from generator charging to motor charging, in conjunction with a generally constant driver power demand, would thus satisfy the second operating condition. Similarly, a change from a “not charging” mode to a charging mode, in conjunction with a generally constant driver power demand, would thus satisfy the second operating condition. If a determination is made that the second operating condition is satisfied, then the clutch is maintained in the engaged position, as illustrated at block  102 . Control then returns to operation  98 . The powertrain is thus controlled in overdrive mode while steady state operation continues. 
         [0039]    If a determination is made that the second operating condition is not satisfied, then a determination is made of whether a third operating condition is satisfied, as illustrated at block  104 . The third operating condition generally corresponds to a change from steady state operation to non-steady state operation, or to an increase in magnitude of the difference between driver power demand and road load. The third operating condition may be one of the operating conditions of list C, illustrated at block  106 . The third operating condition may be a large decrease in power demand or a large increase in power demand. In some embodiments, a power demand deviation threshold is provided, and the third operating condition is satisfied if a driver power demand deviation exceeds the threshold. This may include a first threshold for decreases in power demand and a second threshold for increases in power demand. The third operating condition may also be a heavy application of vehicle brakes. In some embodiments, a braking threshold is provided, and the third operating condition is satisfied if a driver brake application exceeds the threshold. The third operating condition may also be a large decrease in vehicle speed. In some embodiments, a speed deviation threshold is provided, and the third condition is satisfied if a decrease in vehicle speed exceeds the threshold. The third operating condition may be an engine shutdown request. If a battery state of charge is sufficient to support electric operation and an engine shutdown request is issued, the third condition is satisfied. If a determination is made that the third operating condition is not satisfied, control proceeds to block  102 . If the third operating condition is satisfied, the clutch is disengaged, as illustrated at block  108 . Control then returns to block  90 . 
         [0040]    Referring now to  FIGS. 5 and 6 , an electromagnetic one-way clutch  110  as may be used in conjunction with the present disclosure is illustrated schematically. The one-way clutch  110  includes a rocker plate  112  having pockets  114 , each pocket  114  containing a corresponding rocker  116  which is pivotally hinged within the respective pockets  114 . The clutch  110  also includes a cam plate  118 , which has a plurality of notches  120  that define teeth. When the rockers  116  are pivoted relative to the pockets  114 , the teeth may catch inwardly extending portions of the rockers  116 . The rockers  116  are biased by a spring  121  to remain within the pockets without protruding. In this configuration, there is no engagement between the rockers  116  and the notches  120 , and thus no torque is transferred between the rocker plate  112  and cam plate  118 .  FIG. 5  illustrates the clutch  110  in this disengaged position. 
         [0041]    The cam plate  118  contains a coil [not illustrated] that may be selectively electrified to produce a magnetic force and engage the clutch  110 . In response to the magnetic force, the rockers  116  pivot outward from the pockets  114 , against the bias force of the spring  121 , such that a portion of the rockers  116  protrudes beyond a radially inward face of the rocker plate  112 . The protruding portion of the rockers  116  may engage with the notches  120  and transfer torque between the rocker plate  112  and cam plate  118  in one direction of rotation.  FIG. 6  illustrates the clutch  110  in this engaged position. 
         [0042]    Referring now to  FIGS. 7 a  and 7 b   , methods of engaging a clutch are illustrated as may be used in conjunction with the present disclosure.  FIG. 7 a    illustrates a method of engaging a one-way clutch. The generator is controlled to overrun the clutch, as illustrated at block  122 . This may be performed by rotating the rocker plate in a disengagement direction. The clutch is then activated, as illustrated at block  124 . As discussed above with respect to  FIG. 6 , this may include electrifying a coil to produce a magnetic field, in response to which rockers pivot and engage with notches in a cam plate. The clutch is then engaged, as illustrated at block  126 . This is performed by rotating the rocker plate a short distance in an engagement direction to engage rockers with teeth in the cam plate. Torque carried by the generator is then transferred to the clutch, as illustrated at block  128 . 
         [0043]      FIG. 7 b    illustrates a method of engaging a dog clutch. A generator speed is controlled to a target speed to synchronize with the clutch, as illustrated at block  130 . The clutch is then engaged, as illustrated at block  132 . Torque carried by the generator is then transferred to the clutch, as illustrated at block  134 . 
         [0044]    Referring now to  FIGS. 8 a  and 8 b   , methods of disengaging a clutch are illustrated as may be used in conjunction with the present disclosure.  FIG. 8 a    illustrates a method of disengaging a one-way clutch. Torque carried by the clutch is transferred to the generator, as illustrated at block  136 . The generator is controlled to overrun the clutch, as illustrated at block  138 . This may be performed by rotating the generator in the disengagement direction. The clutch is then deactivated, as illustrated at block  140 . Generator control is then returned to nominal operation, as illustrated at block  142 . 
         [0045]      FIG. 8 b    illustrates a method of disengaging a dog clutch. Torque carried by the clutch is transferred to the generator, as illustrated at block  144 . The clutch is then disengaged, as illustrated at block  146 . Generator control is then returned to nominal operation, as illustrated at block  148 . 
         [0046]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, 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 invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.