U.S. patent application number 13/803000 was filed with the patent office on 2014-09-18 for extended-range electric vehicle with supercapacitor range extender.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS LLC. The applicant listed for this patent is GM GLOBAL TECHNOLOGY OPERATIONS LLC. Invention is credited to Ravikanth G V, Aurobbindo Lingegowda, Kumpatla V Naidu, Viswa Madan Pulavarthi, Awadesh Tiwari.
Application Number | 20140277870 13/803000 |
Document ID | / |
Family ID | 51358659 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140277870 |
Kind Code |
A1 |
G V; Ravikanth ; et
al. |
September 18, 2014 |
EXTENDED-RANGE ELECTRIC VEHICLE WITH SUPERCAPACITOR RANGE
EXTENDER
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.
Inventors: |
G V; Ravikanth; (Bangalore,
IN) ; Naidu; Kumpatla V; (Bangalore, IN) ;
Tiwari; Awadesh; (Bangalore, IN) ; Lingegowda;
Aurobbindo; (Bangalore, IN) ; Pulavarthi; Viswa
Madan; (Bangalore, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GM GLOBAL TECHNOLOGY OPERATIONS LLC |
Detroit |
MI |
US |
|
|
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS
LLC
Detroit
MI
|
Family ID: |
51358659 |
Appl. No.: |
13/803000 |
Filed: |
March 14, 2013 |
Current U.S.
Class: |
701/22 ;
180/65.245; 903/946 |
Current CPC
Class: |
B60K 6/28 20130101; B60Y
2400/114 20130101; B60K 6/387 20130101; B60K 6/42 20130101; B60W
20/00 20130101; Y10S 903/946 20130101; B60W 10/02 20130101 |
Class at
Publication: |
701/22 ;
180/65.245; 903/946 |
International
Class: |
B60W 20/00 20060101
B60W020/00 |
Claims
1. A vehicle comprising: an internal combustion engine having a
driveshaft; an electric traction motor having an output shaft; a
final drive assembly; a rechargeable battery pack; a supercapacitor
module that is electrically connected to the battery pack; first
and second clutches having, at all times, opposite apply states,
wherein the first clutch connects the driveshaft to the traction
motor when applied to thereby establish a neutral-charging mode,
and wherein the second clutch connects the output shaft to the
final drive assembly when applied to thereby establish a drive
mode; and a controller in communication with the first and second
clutches, wherein the controller includes a processor and tangible,
non-transitory memory on which is recorded instructions for
controlling the state of the clutches, and wherein: the processor
is configured to execute the instructions in response to a set of
input signals to thereby select between the drive mode and the
neutral-charging mode; the drive mode uses energy from the
supercapacitor module and the battery pack to power the traction
motor; and the neutral-charging mode uses output torque from the
engine to charge the supercapacitor module and the battery
pack.
2. The vehicle of claim 1, wherein the vehicle is characterized by
an absence of any planetary gear sets.
3. The vehicle of claim 2, wherein the first and second clutches
are pneumatically-actuated.
4. The vehicle of claim 1, wherein the engine has a displacement of
less than 300 cubic centimeters.
5. The vehicle of claim 1, further comprising an air conditioning
compressor that is driven via the driveshaft, wherein the engine is
configured to power the air conditioning compressor.
6. The vehicle of claim 5, further comprising a third clutch that
disconnects the driveshaft from the air compressor when the third
clutch is released.
7. The vehicle of claim 1, wherein the battery pack is a lead acid
battery pack.
8. The vehicle of claim 7, wherein the battery pack includes six
8-volt or eight 6-volt lead acid battery cells.
9. The vehicle of claim 1, wherein the battery pack is rated for at
least 48VDC and the supercapacitor module is configured to store at
least 125% of the charge of the battery pack.
10. A powertrain for a vehicle having an engine, comprising: an
electric traction motor having an output shaft; a rechargeable
battery pack; a supercapacitor module that is electrically
connected to the battery pack; and first and second clutches
having, at all times, opposite apply states, wherein the first
clutch, when applied, connects the traction motor to the engine to
thereby establish a neutral-charging mode, and wherein the second
clutch, when applied, connects the output shaft to a drive axle to
establish a drive mode; wherein the drive mode uses energy from the
supercapacitor module and the battery pack to power the traction
motor and the neutral-charging mode uses output torque from the
engine to charge the supercapacitor module and the battery
pack.
11. The powertrain of claim 10, further comprising a controller in
communication with the first and second clutches, wherein the
controller includes a processor and tangible, non-transitory memory
on which is recorded instructions for controlling the state of the
clutches, and wherein the processor is configured to execute the
instructions in response to a set of input signals to thereby
select between the drive mode and the neutral-charging mode.
12. The powertrain of claim 10, wherein the powertrain is
characterized by an absence of any planetary gear sets.
13. The powertrain of claim 12, wherein the first and second
clutches are pneumatically-actuated.
14. The powertrain of claim 10, wherein the battery pack is a lead
acid battery pack having at least six lead acid battery cells.
15. The powertrain of claim 10, wherein the battery pack is rated
for at least 48 VDC and the supercapacitor module is configured to
store at least 125% of the charge of the battery pack.
16. A vehicle comprising: an internal combustion engine having a
driveshaft and a displacement of less than 300 cubic centimeters;
an electric traction motor having an output shaft; a final drive
assembly; a rechargeable lead acid battery pack; a supercapacitor
module that is electrically connected to the battery pack; first
and second pneumatic clutches having, at all times, opposite apply
states, wherein the first clutch connects the driveshaft to the
traction motor when applied to thereby establish a neutral-charging
mode, and wherein the second clutch connects the output shaft to
the final drive assembly when applied to thereby establish a drive
mode; an air conditioning compressor that is driven via the
driveshaft in each of the drive and neutral-charging modes; a
pneumatic actuator configured to apply the first and second
clutches; and a controller in communication with the first and
second pneumatic clutches, wherein the controller includes a
processor and tangible, non-transitory memory on which is recorded
instructions for controlling the state of the clutches, and
wherein: the processor is configured to execute the instructions in
response to a set of input signals to thereby select between the
drive mode and the neutral-charging mode; the drive mode uses
energy from the supercapacitor module and the battery pack to power
the traction motor via a drivepath that is characterized by an
absence of planetary gear sets; and the neutral-charging mode uses
output torque from the engine to charge the supercapacitor module
and the battery pack.
17. The vehicle of claim 16, further comprising a third clutch that
disconnects the driveshaft from the air compressor when the third
clutch is released.
18. The vehicle of claim 16, wherein the battery pack is rated for
at least 48 VDC and the supercapacitor module is configured to
store at least 125% of the charge of the battery pack.
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.sub.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=.omega..tau.. In this equation, .omega. is the rotational
speed of the engine 12 in radians/second and .tau. 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.sub.3, S.sub.2, and S.sub.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.sub.1, N.sub.2, and N.sub.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.
* * * * *