Abstract:
A vehicle includes an engine, fraction motor, final drive assembly, battery pack, and a supercapacitor module electrically connected to the battery pack. The vehicle also has first and second clutches and a controller. The clutches have opposite apply states. The first clutch connects an engine driveshaft to the motor to establish a neutral-charging mode. The second clutch connects an output shaft of the motor to the final drive assembly to establish a drive mode. The controller selects between the drive and neutral-charging modes in response to input signals. The drive mode uses energy from the supercapacitor module and battery pack to power the traction motor. The neutral-charging mode uses output torque from the engine to charge the supercapacitor module and battery pack. The clutches may be pnemauically-actuated, and the vehicle may be characterized by an absence of planetary gear sets.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to an extended range electric vehicle having a supercapacitor range extender. 
       BACKGROUND 
       [0002]    An extended-range electric vehicle powertrain provides one or more electric-vehicle (EV) modes. In an EV mode, a high-voltage electric traction motor is powered via a rechargeable battery pack. Output torque from the electric traction motor is typically delivered to a transmission having one or more planetary gear sets. Braking energy may be recovered during a regenerative braking event to recharge the battery pack. When a state of charge of the battery pack is depleted, the EV range of the vehicle may be extended by selective operation of a small internal combustion engine, with engine torque used to generate additional electricity as needed. 
       SUMMARY 
       [0003]    An extended-range electric vehicle is disclosed herein. The vehicle includes a powertrain having reduced cost relative to conventional designs. The powertrain makes selective use of a stored electrical charge from a semiconductor module, and may be further characterized by an absence of any planetary gear sets. The vehicle includes an internal combustion engine, an electric traction motor, a rechargeable battery pack, and a final drive assembly. The final drive assembly is powered via output torque from the electric traction motor. The vehicle also includes first and second rotating clutches and a controller in communication with the various powertrain elements. 
         [0004]    In a particular embodiment, the battery pack may include multiple lead acid battery cells, e.g., eight 6-volt or six 8-volt lead acid battery cells in an example 48 VDC embodiment. Lead acid batteries are typically less efficient at recovering regenerative braking energy relative to lithium ion and nickel metal hydride batteries. Similarly, lead acid batteries may not provide the required power as effectively or efficiently as these other common battery types, particularly during periods of peak vehicle acceleration. As with most battery types, frequent charging and discharging may serve to reduce the useful operating life of the battery pack. 
         [0005]    To address these and other design challenges, the present approach electrically connects a supercapacitor module with the battery pack and uses the stored charge of the semiconductor module to help preserve the state of charge (SOC) of the battery pack. Use of the supercapacitor module in the powertrain disclosed herein may help to extend the useful operating life of the battery pack, for instance by reducing the frequency of battery charge/discharge events. An air conditioning compressor or other substantially constant electrical load is absorbed by the engine, thereby allowing the engine to operate at or near its optimum Brake-Specific Fuel Consumption (BSFC) point, as that term is defined herein and well known in the art. 
         [0006]    In operation, the controller selectively applies a designated clutch to establish one of two powertrain operating modes: a drive mode and a neutral-charging mode. In drive mode, the first clutch is applied and the second clutch is released. The electric traction motor drives the output member while the engine supplies the necessary power for running the load, e.g., the air conditioning compressor noted above. The electric traction motor draws any required power first from the supercapacitor module and then from the battery pack, thereby moderating the rate of discharge of the battery pack relative to conventional power flow control approaches. 
         [0007]    In the neutral-charging mode, the clutch apply states of the drive mode are simply reversed. That is, the first clutch is released and the second clutch is applied. The battery pack and the supercapacitor module may be recharged as needed in this mode. In all embodiments, the first and second clutches are not applied or released at the same time. In other words, the apply states of the first and second clutches are mutually exclusive. 
         [0008]    In another embodiment, the vehicle includes an engine having a displacement of less than 300 cubic centimeters, an electric traction motor, a final drive assembly, a rechargeable lead acid battery pack, and a supercapacitor module that is electrically connected to the battery pack. The vehicle also includes first and second pneumatically-actuated clutches, an air conditioning compressor, and a controller. The clutches have, at all times, opposite apply states. As noted above, the first clutch connects the driveshaft of the engine to the electric traction motor when applied to thereby establish the neutral-charging mode, while application of the second clutch connects the motor output shaft to the final drive assembly to establish the drive mode. The air conditioning compressor is driven via the driveshaft in the drive mode. The controller automatically selects between the drive and neutral-charging modes. 
         [0009]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic illustration of an extended-range electric vehicle having a range-extending supercapacitor module as described herein. 
           [0011]      FIG. 2  is a table describing two powertrain operating modes of the vehicle shown in  FIG. 1 . 
           [0012]      FIG. 3A  is a schematic lever diagram describing a first of the two operating modes of  FIG. 2 , i.e., a drive mode, which may be pneumatically applied. 
           [0013]      FIG. 3B  is a schematic lever diagram describing a second of the two operating modes shown in  FIG. 2 , i.e., a neutral-charging mode. 
           [0014]      FIG. 4A  includes example time plots of the states of charge (SOC) of a battery pack using the present approach and a nominal approach, with time plotted on the x-axis and SOC plotted on the y-axis. 
           [0015]      FIG. 4B  is a time plot of changing vehicle speed, with time plotted on the x-axis and velocity plotted on the y-axis. 
           [0016]      FIG. 4C  is a time plot of the level of energy stored in a supercapacitor module of the vehicle shown in  FIG. 1 , with time plotted on the x-axis and the level of energy plotted on the y-axis. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Referring to the drawings, wherein like reference numbers refer to similar components in the various Figures, an extended-range electric vehicle  10  is shown in schematically in  FIG. 1 . The vehicle  10  includes a controller  30  having a processor  32  and sufficient tangible, non-transitory memory  34 . Computer-executable code embodying a method  100 , which is recorded in the memory  34 , is selectively executed via the processor  32  to command a shift between two different powertrain operating modes. 
         [0018]    As explained below with reference to  FIG. 2 , the two powertrain operating modes of the vehicle  10  are a drive mode and a neutral-charging mode. Example designs for achieving the drive and neutral-charging modes are shown in  FIGS. 3A and 3B , respectively, each of which shows an optional pneumatically-actuated embodiment.  FIGS. 4A-C  collectively illustrate control values used in the execution of the present method  100 , with  FIG. 4A  depicting the effect of the method  100  on the state of charge (SOC) of a battery pack  20  given a changing vehicle speed, as shown in  FIG. 4B , and a changing percentage of remaining percentage of a maximum charge of a supercapacitor module  22  as shown in  FIG. 4C . 
         [0019]    The vehicle  10  of  FIG. 1  may include a small internal combustion engine  12 , an electric traction motor  14 , and a final drive assembly  16 , the latter of which provides a desired output gear ratio. As used herein, the term “small” when applied to the engine  12  describes a displacement of less than about 300 cubic centimeters (cc), with a range of 200-250 cc provided in an example embodiment. An output member  19  of the final drive assembly  16  is connected to a set of drive wheels  18  via one or more drive axles  21 . Therefore, output torque (arrow T O ) from the final drive assembly  16  is ultimately delivered to the drive wheels  18  to propel the vehicle  10 . 
         [0020]    A driveshaft  13  of the engine  12  is respectively connected to/disconnected from the electric traction motor  14  via application/release of a first clutch C1. Likewise, an output shaft  15  of the electric traction motor  14  is selectively connected to/disconnected from the final drive assembly  16  via a second clutch C2. As described below, the states of clutches C1 and C2 are at all times mutually exclusive. That is, when clutch C1 is applied, C2 is released and vice versa. Application of the respective first and second clutches C1 and C2 may be via any suitable actuator, including via pneumatically-actuated or hydraulically-actuated pistons. An example of the former, which provides a relatively low-cost approach to clutch actuation, is described below with reference to  FIGS. 3A and 3B . In all embodiments, the first and second clutches C1 and C2 may be rotating clutches having interspaced friction plates or any other conventional torque transfer mechanism. 
         [0021]    The electric traction motor  14  of  FIG. 1  draws electrical energy from the battery pack  20 . In a particular embodiment, the battery pack  20  is configured as a multi-cell lead acid battery pack, e.g., six 8-volt cells or eight 6-volt cells in possible non-limiting 48VDC examples. The battery pack  20  is electrically connected to the supercapacitor module  22 . The term “super” as used herein refers generally to the higher levels of capacitance relative to typical capacitors, as is well known in the art. For instance, in an example configuration the supercapacitor module  22  may have a capacitance level sufficient for storing 125% to 140% or more of the voltage of the battery pack  20 . Other combinations of capacitance and battery voltage may be used without departing from the intended inventive scope. 
         [0022]    The supercapacitor module  22  shown schematically in  FIG. 1  may use one or more double-layer capacitors (DLCs) to help store sufficient standby energy. Such DLCs may use a series of electrodes and a suitable electrolyte, e.g., an organic electrolyte, although other capacitor designs may be employed in the alternative. A supercapacitor such as those used to construct the supercapacitor module  22  can be charged very rapidly relative to the conventional battery cells. The rapid-charging characteristics thus allow selective use of the supercapacitor module  22  of the present approach in the overall operation of the simplified powertrain shown in  FIG. 1 . 
         [0023]    Additionally, torque from the engine  12  may be supplied via the driveshaft  13  to an air conditioning compressor  25  or other comparable electrical load, which is cycled on and off as needed via the controller  30  to cool a passenger compartment (not shown) of the vehicle  10  of  FIG. 1 . The air conditioning compressor  25  acts as a substantially constant electrical load on the engine  12 , for instance a load of 1.5 kW in some designs. Therefore, the engine  12  should be sized to account for the constant load of the air conditioning compressor  25  as well as all other constant and intermittent electrical loads. An optional compressor clutch C3 as shown in phantom may be used to disconnect the air conditioning compressor  25  from the engine  12  and thus minimize spin losses when the air conditioning compressor  25  is not otherwise needed, e.g., when the air conditioning compressor  25  is sufficiently charged. 
         [0024]    The controller  30  shown schematically in  FIG. 1  may be embodied as a digital computer or multiple such computers each having the processor  32  and sufficient amounts of the memory  34 , e.g., read only memory (ROM), random access memory (RAM), optical memory, additional magnetic memory, flash memory, and/or electrically-erasable programmable read only memory (EEPROM). Other associated hardware components of the controller  30  may include a high-speed digital clock, analog-to-digital (A/D) and digital-to-analog (D/A) circuitry, and any required input/output circuitry and devices (I/O), as well as appropriate signal conditioning and buffer circuitry. Any computer-executable code required for operation of the vehicle  10 , including instructions embodying the method  100 , can be recorded in memory  34  and automatically executed by the processor  32  to thereby establish a required or requested powertrain operating mode. 
         [0025]    The controller  30 , which is in communication with the engine  12 , the electric traction motor  14 , the respective first and second clutches C1 and C2, and the optional air conditioning compressor clutch C3, via a controller area network (CAN) and/or other wired/wireless network connection, receives input signals (arrow  11 ) from the various systems. In response to the received input signals (arrow  11 ), the controller  30  generates output signals (arrow  17 ), some of which cause the clutches C1-C3 to either apply or release, with the commanded clutch state depending on the required powertrain operating mode. Two possible operating modes will now be described with reference to  FIG. 2 . 
         [0026]    A table  40  is shown in  FIG. 2  that describes the two basic operating modes of the vehicle  10  shown in  FIG. 1 , i.e., the drive mode (D) and the neutral-charging (N-C) mode. In drive mode, the first clutch C1 is released (O) and the second clutch C2 is engaged (X). The electric traction motor  14  draws (−) power from the battery pack  20  and/or the supercapacitor module  22  as needed, with discharge priority given to the supercapacitor module  22  as set forth below. 
         [0027]    In drive mode, the engine  12  of  FIG. 1  supplies any required output energy for powering the air conditioning compressor  25 . This helps to ensure that the engine  12  operates at or near its optimum Brake-Specific Fuel Consumption (BSFC) point, with the engine  12  in this mode effectively decoupled from the driveline. As is well understood in the art, the BSFC point provides a measure of engine fuel efficiency, and may be calculated by dividing the fuel consumption rate (r) in grams/second by the power (P) in watts, with P=ωτ. In this equation, ω is the rotational speed of the engine  12  in radians/second and τ is engine torque in Newton meters. 
         [0028]    In neutral-charging mode (NC), the apply states of the respective first and second clutches C1 and C2 are simply reversed. That is, the first clutch C1 is applied (X) and the second clutch C2 is released (O). In this operating mode, the engine  12  may power the electric traction motor  14  as a generator. In turn, the electric traction motor  14  may charge (+) the battery pack  20  and/or the supercapacitor module  22 . The neutral-charging mode set forth herein may be particularly beneficial when operating the vehicle  10  of  FIG. 1  in a high-density area such as a city or other high-traffic environment in which the vehicle  10  is expected to spend a fair amount of time idling. This otherwise wasted time is used advantageously via the present control approach to recharge the battery pack  20  and/or the supercapacitor module  22 . Use of the supercapacitor module  22  also allows the battery pack  20  to be downsized without sacrificing responsiveness to instantaneous electric power demands. 
         [0029]    Referring to  FIGS. 3A and 3B , schematic lever diagrams are shown for the two powertrain operating modes of  FIG. 2 , with  FIGS. 3A and 3B  both showing an example low-cost pneumatically-actuated design. Diagram  50  of  FIG. 3A  corresponds to the neutral-charging mode noted immediately above, wherein the first clutch C1 is applied and the second clutch C2 is released. First, second, and third linkages  52 ,  54 , and  59 , respectively, are connected to each other via hinges  57 , which allows linkages  52 ,  54 , and  59  to rotate with respect to each other as needed. As will be evident to one having ordinary skill in the art viewing  FIGS. 3A and 3B , such a design may provide substantial cost, weight, and component count advantages relative to conventional hydraulic designs. 
         [0030]    A control solenoid  75  may be de-energized (−) via the controller  30  of  FIG. 1  to draw an arm  71  in the direction of arrow  80 . Inlet air pressure (arrow I), assisted by a return spring  74 , moves a plunger  72  within a cylinder  70  in the same direction to unblock an air passage  65 . Air pressure is fed into a pneumatic valve  60  through the air passage  65 , thus moving a piston  62  in the direction of arrow  80 . A return spring  78  is thus compressed within the pneumatic valve. Air in the housing  70  can escape to atmosphere as indicated by arrow A. 
         [0031]    The piston  62  may be connected to a rod  64  and the first linkage  52  as shown such that movement of the piston  62  in the direction of arrow  80  pulls the first linkage  52  in the same direction. Movement of the first linkage  52  in turn pulls open the second clutch C2, and thus establishes the released (O) state of second clutch C2 needed for the neutral-charging state. The same movement rotates the second linkage  54 , thus forcing the third linkage  59  in the direction of arrow  77 . The third linkage  59  compresses the first clutch C1 into an applied (X) state. A spring  61  connected between the second linkage  54  and a stationary member  42  is thus compressed, thereby storing return energy for use in entering the drive mode. 
         [0032]      FIG. 3B  shows the drive mode via diagram  150 . In this mode, the second clutch C2 is applied and the first clutch C1 is released. The control solenoid  75  is energized (+) and inlet air pressure (arrow I of  FIG. 3A ) is discontinued. The plunger  62  moves in the direction of arrow  77 , compresses the spring  74 , and is thus properly positioned for entering a subsequent neutral-charging mode. The return spring  78  within the pneumatic valve  60  pushes the piston  62  and rod  64  in the direction of arrow  77 . This moves the first linkage  52  in the same direction, which causes the second linkage  54  to rotate counterclockwise with respect to the perspective of  FIG. 3B , assisted via stored energy in the spring  61 . 
         [0033]    The movement of the first and second linkages  52  and  54  pulls the third linkage  59  in the direction of arrow  80 , and thus releases (O) the first clutch C1. The same movement pushes the first linkage  52  in the direction of arrow  77  to apply (X) the second clutch C2. The spring  61  may stretch in this motion to store potential return energy for entering the neutral-charging mode shown in  FIG. 3A . 
         [0034]    As will be appreciated by those having ordinary skill in the art, the vehicle  10  shown in  FIG. 1  with its simplified clutching architecture may provide distinct advantages relative to prior art extended-range electric vehicle powertrains. The battery pack  20  may be downsized for a given EV range, which may effectively address space constraints in certain emerging markets. Also, the vehicle  10  may use a single electric traction motor  14  to drive the vehicle  10  in drive mode, and to charge the battery pack  20  and/or the supercapacitor module  22  in the neutral-charging mode. Certain limitations in performance of lead acid battery may be overcome via selective use of the supercapacitor module  22 , which can also extend the life of the battery pack  20 . Moreover, as the engine  12  does not directly drives the output, and therefore the engine  12  can be operated at its best BSFC point with reduced emissions. 
         [0035]    The supercapacitor module  22  may also improve the regenerative energy captured during the drive cycle. This particular advantage is illustrated in  FIGS. 4A-C . In each of these Figures, time (t) is plotted on the horizontal axis.  FIG. 4A  illustrates, via trace  82 , the manner in which the SOC of the battery pack  20  of  FIG. 1  may decrease using the present control approach. Three nominal SOC levels are shown, from highest SOC to lowest, as S 3 , S 2 , and S 1 . For comparative purposes, trace  182  shows a typical trajectory for a decreasing SOC of a nominal battery pack controlled using existing methods. While traces  82  and  182  both decrease over time, note that the rate of decrease using the present method  100  may be substantially reduced relative the rate of decrease of trace  182 . 
         [0036]      FIG. 4B  shows changing velocity of the vehicle  10  shown in  FIG. 1  as trace  84  over the same time period, with relative velocities of N 1 , N 2 , and N 3 . The pattern of trace  84  is typical of driving in heavy traffic or in other stop-and-go driving routes, e.g., on urban surface streets having a substantial number of intersections and/or traffic lights.  FIG. 4C  illustrates, via trace  86 , the level of energy as a percentage (%) stored in the supercapacitor module  22  of  FIG. 1 . When trace  84  of  FIG. 4B  shows that the vehicle  10  has stopped, trace  86  of  FIG. 4C  shows that, in the same interval of time, the supercapacitor module  22  is actively charging. Trace  82  of  FIG. 4A  generally flattens out in the same interval, which indicates that the rate of decrease in SOC has slowed. As a result, the neutral-charging mode disclosed herein helps to slow the rate of decrease in SOC of the battery pack  20 , thereby extending the effective EV range of the vehicle  10  of  FIG. 1 . 
         [0037]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.