U.S. patent application number 09/852075 was filed with the patent office on 2002-12-12 for strategy to use an on-board navigation system for electric and hybrid electric vehicle energy management.
Invention is credited to Patil, Prabhakar B., Pilutti, Thomas E., Stuntz, Ross M., Woestman, Joanne T..
Application Number | 20020188387 09/852075 |
Document ID | / |
Family ID | 25312441 |
Filed Date | 2002-12-12 |
United States Patent
Application |
20020188387 |
Kind Code |
A1 |
Woestman, Joanne T. ; et
al. |
December 12, 2002 |
STRATEGY TO USE AN ON-BOARD NAVIGATION SYSTEM FOR ELECTRIC AND
HYBRID ELECTRIC VEHICLE ENERGY MANAGEMENT
Abstract
The present invention integrates an on-board navigation system
to provide energy management for an electric vehicle (EV) and a
hybrid electric vehicle (HEV). The HEV control strategy of the
present invention accommodates the goals of fuel economy while
always meeting driver demand for power and maintaining the
functionality of the traction motor battery system using battery
parameter controllers. In the preferred embodiment of the present
strategy, a vehicle system controller tightly integrates the
navigation system information with energy management while en route
to a known destination. Present vehicle location is continuously
monitored, expectations of driver demand are determined, and
vehicle accommodations are made. The system can be configured to
includes as part of its present vehicle location data on road
patterns, geography with date and time, altitude changes, speed
limits, driving patterns of a vehicle driver, and weather. The
vehicle accommodations can be configured to use discrete control
laws, fuzzy logic, or neural networks.
Inventors: |
Woestman, Joanne T.;
(Dearborn, MI) ; Patil, Prabhakar B.; (Southfield,
MI) ; Stuntz, Ross M.; (Birmingham, MI) ;
Pilutti, Thomas E.; (Ann Arbor, MI) |
Correspondence
Address: |
JOHN M. NABER
313 SOUTH WASHINGTON SQUARE
LANSING
MI
48933
US
|
Family ID: |
25312441 |
Appl. No.: |
09/852075 |
Filed: |
May 9, 2001 |
Current U.S.
Class: |
701/22 ;
180/65.235; 180/65.27; 180/65.29 |
Current CPC
Class: |
B60W 2556/50 20200201;
B60W 10/26 20130101; B60K 6/365 20130101; Y02T 10/84 20130101; B60L
58/22 20190201; B60W 10/08 20130101; B60W 20/12 20160101; Y02E
60/00 20130101; Y02T 90/16 20130101; B60K 6/00 20130101; B60L
15/2045 20130101; B60W 20/00 20130101; Y02T 10/72 20130101; Y02T
10/64 20130101; B60K 31/0058 20130101; B60L 58/12 20190201; B60K
6/40 20130101; Y02T 90/14 20130101; B60L 55/00 20190201; B60L
2240/62 20130101; Y02T 10/62 20130101; B60K 1/02 20130101; B60L
50/16 20190201; B60W 50/0097 20130101; Y02T 10/70 20130101; Y04S
10/126 20130101; B60W 2510/244 20130101; Y02T 10/40 20130101; Y02T
90/12 20130101; B60L 50/61 20190201; B60K 6/445 20130101; B60W
2555/40 20200201; B60L 2260/56 20130101; Y02T 10/7072 20130101;
B60L 53/63 20190201; B60L 53/14 20190201 |
Class at
Publication: |
701/22 ;
180/65.3 |
International
Class: |
B60L 011/00 |
Claims
We claim:
1. A system to manage energy in a vehicle with an electric traction
motor comprising: a powertrain comprising at least one motor and an
engine; a battery connected to the motor; a vehicle system
controller (VSC) connected to the vehicle powertrain; a device
connected to the VSC to continuously locate a present vehicle
location and infer expectations of driver demand; and the VSC
further comprising a strategy to continuously accommodate fuel
economy, driver demand for power and functionality of the
battery.
2. The system of claim 1 wherein present vehicle location further
comprises data on road patterns.
3. The system of claim 1 wherein present vehicle location further
comprises data on geography with date and time.
4. The system of claim 1 wherein present vehicle location further
comprises data on altitude changes.
5. The system of claim 1 wherein present vehicle location further
comprises data on speed limits.
6. The system of claim 1 wherein present vehicle location further
comprises data on driving patterns of a vehicle driver.
7. The system of claim 1 wherein present vehicle location further
comprises data on weather.
8. The system of claim 1 wherein the strategy uses discrete control
laws.
9. The system of claim 1 wherein the strategy uses fuzzy logic.
10. The system of claim 1 wherein the strategy uses neural
networks.
11. The system of claim 1 wherein expectations of driver demand are
inferred by a driver communicating an intended drive route.
12. The system of claim 1 wherein expectations of driver demand are
inferred by a search of maps for the locale of the vehicle.
13. The system of claim 1 wherein the strategy accommodates
functionality of the battery with battery parameter
controllers.
14. The system of claim 13 wherein the battery parameter
controllers control battery state of charge.
15. The system of claim 13 wherein the battery parameter
controllers control battery charge rate.
16. The system of claim 13 wherein the battery parameter
controllers control battery discharge rate.
17. The system of claim 13 wherein the battery parameter
controllers control battery temperature.
18. The system of claim 13 wherein battery parameter controllers
remove all loads from the battery
19. A method of managing energy in a vehicle comprised of a
powertrain comprising a motor, an engine, and a battery connected
to the motor, comprising the steps of; locating continuously a
present vehicle location; inferring expectations of driver demand
based on present vehicle location; and accommodating continuously
fuel economy, driver demand for power and functionality of the
battery.
20. The method of claim 19 wherein the step of locating
continuously the present vehicle location comprises data on road
patterns.
21. The method of claim 19 wherein the step of locating
continuously the present vehicle location comprises data on
geography with date and time.
22. The method of claim 19 wherein the step of locating
continuously the present vehicle location comprises data on
altitude changes.
23. The method of claim 19 wherein the step of locating
continuously the present vehicle location comprises data on speed
limits.
24. The method of claim 19 wherein the step of locating
continuously the present vehicle location comprises data on driving
patterns of a vehicle driver.
25. The method of claim 19 wherein the step of locating
continuously the present vehicle location comprises data on
weather.
26. The method of claim 19 wherein accommodating continuously fuel
economy, driver demand for power and functionality of the battery
uses discrete control laws.
27. The method of claim 19 wherein accommodating continuously fuel
economy, driver demand for power and functionality of the battery
uses fuzzy logic.
28. The method of claim 19 wherein accommodating continuously fuel
economy, driver demand for power and functionality of the battery
uses neural networks.
29. The method of claim 19 wherein inferring expectations of driver
demand comprises the step of a driver communicating an intended
drive route.
30. The method of claim 19 wherein inferring expectations of driver
demand comprises the step of a searching of maps for the locale of
the vehicle.
31. The method of claim 19 wherein accommodating continuously the
functionality of the battery comprises the step of controlling
battery parameters.
32. The method of claim 31 wherein the step of controlling battery
parameters comprises controlling battery state of charge.
33. The method of claim 31 wherein the step of controlling battery
parameters comprises controlling battery charge rate.
34. The method of claim 31 wherein the step of controlling battery
parameters comprises controlling battery discharge rate.
35. The method of claim 31 wherein the step of controlling battery
parameters comprises controlling battery temperature.
36. The method of claim 31 wherein the step of controlling battery
parameters comprises removing all loads from the battery.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to electric vehicles
(EVs) and hybrid electric vehicles (HEVs), and specifically to
using an on-board navigation system for energy management.
[0003] 2. Discussion of the Prior Art
[0004] The need to reduce fossil fuel consumption and emissions in
automobiles and other vehicles predominately powered by internal
combustion engines (ICEs) is well known. Vehicles powered by
electric motors attempt to address these needs. Another alternative
solution is to combine a smaller ICE with electric motors into one
vehicle. Such vehicles combine the advantages of an ICE vehicle and
an electric vehicle and are typically called hybrid electric
vehicles (HEVs). See generally, U.S. Pat. No. 5,343,970 to
Severinsky.
[0005] The HEV is described in a variety of configurations. Many
HEV patents disclose systems where an operator is required to
select between electric and internal combustion operation. In other
configurations, the electric motor drives one set of wheels and the
ICE drives a different set.
[0006] Other, more useful, configurations have developed. For
example, a series hybrid electric vehicle (SHEV) configuration is a
vehicle with an engine (most typically an ICE) connected to an
electric motor called a generator. The generator, in turn, provides
electricity to a battery and another motor, called a traction
motor. In the SHEV, the traction motor is the sole source of wheel
torque. There is no mechanical connection between the engine and
the drive wheels. A parallel hybrid electrical vehicle (PHEV)
configuration has an engine (most typically an ICE) and an electric
motor that work together in varying degrees to provide the
necessary wheel torque to drive the vehicle. Additionally, in the
PHEV configuration, the motor can be used as a generator to charge
the battery from the power produced by the ICE.
[0007] A parallel/series hybrid electric vehicle (PSHEV) has
characteristics of both PHEV and SHEV configurations and is
sometimes referred to as a "powersplit" configuration. In one of
several types of PSHEV configurations, the ICE is mechanically
coupled to two electric motors in a planetary gear-set transaxle. A
first electric motor, the generator, is connected to a sun gear.
The ICE is connected to a carrier. A second electric motor, a
traction motor, is connected to a ring (output) gear via additional
gearing in a transaxle. Engine torque can power the generator to
charge the battery. The generator can also contribute to the
necessary wheel (output shaft) torque if the system has a one-way
clutch. The traction motor is used to contribute wheel torque and
to recover braking energy to charge the battery. In this
configuration, the generator can selectively provide a reaction
torque that may be used to control engine speed. In fact, the
engine, generator motor and traction motor can provide a continuous
variable transmission (CVT) effect. Further, the PSHEV presents an
opportunity to better control engine idle speed over conventional
vehicles by using the generator to control engine speed.
[0008] The desirability of electric motor powered vehicles (EVs)
and combining an ICE with electric motors (HEVs) is clear. Fuel
consumption and emissions can be reduced with no appreciable loss
of vehicle performance or drive-ability. The HEV allows the use of
smaller engines, regenerative braking, electric boost, and even
operating the vehicle with the engine shutdown. Nevertheless, new
ways must be developed to optimize EVs and HEVs potential
benefits.
[0009] One way to optimize electric powered vehicles is efficient
energy management. A successful energy management strategy must
balance fuel economy, maintain critical vehicle function capacity,
(i.e., assuring sufficient stored electrical energy) , while always
meeting driver demand for power. For example, the control system
needs to maintain the battery state-of-charge (SOC) at a level to
meet performance requirements while allowing it to accept any
upcoming regenerative braking energy. Without knowledge of the
possible upcoming power requirements or regenerative braking
events, the control system has to conservatively predict and
compromise battery SOC.
[0010] A possible solution to assist a vehicle system controller
(VSC) to predict and adapt to upcoming vehicle power requirements
and regenerative braking is the use of a navigational system that
uses a global positioning system (GPS) and a digital map database.
While this idea is known in the prior art, such systems do not
utilize the full potential of navigation system derived information
for energy management and efficiency.
[0011] U.S. Pat. No. 5,892,346 to Moroto et al. generates an
electric power schedule for an EV or an HEV based on a starting
point and a destination. A navigation system acts as an arbitrator
for feasible routes based on distance traveled en route to the
destination compared to the distance capacity of the vehicle. This
invention uses the navigation system as a pre-trip planning tool
that would, for example, reject the longest proposed routes. See
also, U.S. Pat. Nos. 5,832,396 and 5,778,326 to Moroto et al.
Similarly, U.S. Pat. No. 5,927,415 to Ibaraki et al., allows the
use of a navigation system in advance as a pre-trip planning tool
for an HEV to assure power demands are met.
[0012] U.S. Pat. No. 6,202,024 to Yokoyama et al. discloses the use
of a navigational system on a continuous basis to provide a "best
drive route." The invention is not concerned with energy
management, nor is it concerned with electric vehicles. For
example, it can use a bi-directional navigation system to develop,
among other things, a database of road conditions in any given area
based on receipt of the same road condition data from a plurality
of vehicles in the same area. If several vehicles are reporting use
of anti-lock braking systems or air bag deployment, the "best drive
route" would be diverted from that area.
[0013] A vehicle control system for an EV or HEV that can tightly
integrate a navigational system, such as a GPS with a map database,
for continuous vehicle energy management is needed.
SUMMARY OF THE INVENTION
[0014] Accordingly, the present invention integrates an on-board
navigation system to provide energy management for an electric
vehicle (EV) and a hybrid electric vehicle (HEV).
[0015] The present invention provides a system and method to manage
energy in a vehicle with an electric traction motor comprising, a
powertrain with at least one motor and an engine, a battery
connected to the motor, a vehicle system controller (VSC) connected
to the vehicle powertrain, a device connected to the VSC to
continuously locate a present vehicle location and infer
expectations of driver demand, and a strategy to continuously
accommodate fuel economy, driver demand for power and function of
the battery.
[0016] The system can be configured to include as part of its
present vehicle location data on road patterns, geography with date
and time, altitude changes, speed limits, identification of
intersections with traffic control features such as stop signs and
traffic lights, driving patterns of a vehicle driver, and
weather.
[0017] The strategy can be configured to use discrete control laws,
fuzzy logic, or neural networks.
[0018] Driver demand or expectation can be based on a driver
communicating an intended drive route, or through the use of a
search of maps for the locale of the vehicle.
[0019] Other objects of the present invention will become more
apparent to persons having ordinary skill in the art to which the
present invention pertains from the following description taken in
conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE FIGURES
[0020] The foregoing objects, advantages, and features, as well as
other objects and advantages, will become apparent with reference
to the description and figures below, in which like numerals
represent like elements and in which:
[0021] FIG. 1 illustrates a general hybrid electric vehicle (HEV)
configuration.
[0022] FIG. 2 illustrates the overall vehicle system control energy
management strategy of the present invention with integrated
navigation system.
[0023] FIG. 3 illustrates the logic flow of the energy management
control strategy of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] The present invention relates to electric vehicles (EVs) and
hybrid electric vehicles (HEVs). The proposed strategy can be
applied to both EVs and HEVs, but for purposes of illustration
only, the preferred embodiment is configured for an HEV.
[0025] The HEV control strategy of the present invention balances
the goals of fuel economy while always meeting driver demand for
power and maintaining the functionality of the traction motor
battery system. An integrated navigation system (such as a GPS or
other device to detect the present location of a vehicle with
respect to a map database) can help achieve this goal by providing
information about what driver demand to expect. In one embodiment,
this information can be provided by the driver communicating an
intended drive route to the system or in an alternate embodiment by
a predicted path search of maps for the locale of the vehicle.
While the strategies are likely to be similar for the two
implementations, it may be possible to enact a more aggressive
strategy in the case where the route is known.
[0026] To better understand the present invention, FIG. 1
illustrates a parallel/series hybrid electric vehicle (powersplit)
configuration that has an internal combustion engine and at least
one motor. In this basic HEV example, a planetary gear set 20
mechanically couples a carrier gear 22 to an engine 24 via a one
way clutch 26. The planetary gear set 20 also mechanically couples
a sun gear 28 to a generator motor 30 and a ring (output) gear 32.
The generator motor 30 also mechanically links to a generator brake
34 and is electrically linked to a battery 36. A traction motor 38
is mechanically coupled to the ring gear 32 of the planetary gear
set 20 via a second gear set 40 and is electrically linked to the
battery 36. The ring gear 32 of the planetary gear set 20 and the
traction motor 38 are mechanically coupled to drive wheels 42 via
an output shaft 44.
[0027] The planetary gear set 20, splits the engine 24 output
energy into a series path from the engine 24 to the generator motor
30 and a parallel path from the engine 24 to the drive wheels 42.
Engine 24 speed can be controlled by varying the split to the
series path while maintaining the mechanical connection through the
parallel path. The traction motor 38 augments the engine 24 power
to the drive wheels 42 on the parallel path through the second gear
set 40. The traction motor 38 also provides the opportunity to use
energy directly from the series path, essentially running off power
created by the generator motor 30. This reduces losses associated
with converting energy into and out of chemical energy in the
battery 36 and allows all engine 24 energy, minus conversion
losses, to reach the drive wheels 42.
[0028] A vehicle system controller (VSC) 46 controls many
components in this HEV configuration by connecting to each
component's controller. An engine control unit (ECU) 48 connects to
the engine 24 via a hardwire interface. All vehicle controllers can
be physically combined in any combination or can stand as separate
units. They are described as separate units here because they each
have distinct functionality. The VSC 46 communicates with the ECU
48, as well as a battery control unit (BCU) 50 and a transaxle
management unit (TMU) 52 through a communication network such as a
controller area network (CAN) 54. The BCU 50 connects to the
battery 36 via a hardwire interface. The TMU 52 controls the
generator motor 30 and traction motor 38 via a hardwire
interface.
[0029] One way to regulate the use of the battery 36 is to control
it to a target state-of charge (SOC). The traction motor 38 can be
used more intensely to deliver power to the vehicle powertrain when
the SOC is above the target and is more aggressively charged either
directly from the engine 24 or indirectly from regenerative braking
whenever the SOC is below the target.
[0030] There are at least two distinct operational strategies that
can be applied in HEVs. In either case, the driver demand for power
from the system varies with time and the VSC 46 needs a strategy to
determine how to deliver this power. In a "load-leveling" strategy,
the engine 24 power is held relatively constant and the traction
motor 38 power is varied to ensure that the sum of the powers
equals driver demanded power. This allows the engine 24 to operate
at an efficient operating point leading to high fuel economy. In
addition, it provides responsive driving feel since the electric
drive system can respond quite quickly. In a "load-following"
strategy, engine 24 power changes more quickly to nearly follow the
driver demanded power and the traction motor 38 is used only when
the engine 24 is off or when the engine 24 power can not be changed
fast enough to meet driver demand. This reduces the battery 36
power throughput thereby reducing wear. This extends battery 36
while still providing responsive driving feel.
[0031] The VSC 46 can include battery 36 conditioning strategies to
maintain battery 36 functionality while extending useful life. Some
possible battery 36 conditioning strategies used by various battery
parameter controllers (not shown) include the following: charging
the battery to a high state of charge to balance the charge across
multiple cells; discharging or charging the battery to a very low
or very high state of charge to calibrate the state of charge
estimation routine; changing the charging/discharging pattern of
the battery by, for example, moving the target SOC, to erase any
memory effects; removing all loads from the battery to allow
re-zeroing of the battery system current sensor; or cooling the
battery with a cooling system (not shown) such as a radiator or
air-conditioner.
[0032] In general, the present invention is the combination of the
VSC 46 with information from a navigational system such as a global
positioning system (GPS) with a digital map database. A GPS/Map
integrated VSC 46 can adapt to local geography, possibly including
(but not limited to) grade, terrain, traffic and road pattern which
can add far more precision to this balance.
[0033] To balance the goals of achieving high fuel economy and
delivering required performance, the strategy of the present
invention may use the traction motor 38 whenever it is more
efficient or whenever the engine 24 cannot meet driver demand
alone. At the same time the strategy needs to manage the battery 36
state of charge (SOC) so that SOC never goes too low to meet any
upcoming performance requirement while never getting too high to
accept any upcoming regenerative braking energy. If
navigation-based information is integrated into the VSC 46 strategy
decisions, less conservative strategy decisions are possible while
still ensuring upcoming demands can be met.
[0034] By way of general examples of meeting performance demands,
if the VSC 46 knows, from incoming navigation system position data,
there are no significant changes in grade in the vicinity of the
vehicle, it can use more of the battery 36 SOC range to meet its
efficiency goals with confidence that it will meet all its near
term grade performance goals. Conversely, if the navigation system
derived data indicates mountainous terrain in the direction of the
vehicle, the VSC 46 can protect for likely upcoming grade
performance needs with strategy modifications. Also, if the
navigation system indicates the vehicle is likely to be entering a
highway, it can choose to turn on the engine 24 to prepare for an
expected demand for a sudden increase in acceleration as the
vehicle merges into the highway. And finally, if the VSC 46
integrated with navigation system derived information indicates
frequent intersections with traffic lights, or heavy traffic in the
vicinity, the strategy can assume that a slow, stop and go driving
pattern is likely in the near future and can alter its operating
strategy accordingly.
[0035] The second general goal of the strategy of the present
invention is maintenance of the battery 36 state of charge (SOC).
Generally, the VSC 46 maintains battery 36 SOC from current
operating conditions, such as accelerator position and other
associated vehicle loads such as the air conditioner. These
monitored conditions reflect the current and past operating regime,
and are used to predict the future energy needs. When past
conditions match the future conditions, energy management based on
past data can be accomplished acceptably. However, when the future
conditions vary significantly from the past, energy management
assumptions based on past data can lead to compromised vehicle
performance.
[0036] For example, a route guidance system such as the global
positioning system with an integrated map navigation system
integrated within the VSC 46 can reduce compromised battery 36 SOC
conditions by adding knowledge of upcoming vehicle elevation
gradients. In urban driving, the amount of starts and stops through
intersections could be anticipated. Additionally, with real-time
traffic information, traffic density can also be considered in
energy management.
[0037] In the preferred embodiment of the present strategy, the VSC
46 tightly integrates the navigation system information with energy
management while en route to a known destination (i.e., not as
merely a pre-trip prior art planing tool). The approach takes the
next logical step, and uses road network information from the map
database to influence charge/recharge strategies. One approach is
to take the navigation route and plan charge/recharge cycles based
on elevation gradient, or other factors that can be extracted from
the map database that would be of use to the energy management
controller. In this way, the energy management controller can
schedule appropriate power level cycling.
[0038] An alternative embodiment provides a route preview of a
specified distance or time, which would enable the energy
management controller to effect accessory load decisions based on,
for example, downhill (or uphill) grade expected ahead as well as
traffic conditions. Real-time use of navigation system derived
information will allow more efficient use of energy for accessory
loads and regenerative braking while driving.
[0039] GPS/Map data make the comprehensive energy management
approach of the present invention possible. The following table
shows some examples of the information available from a GPS
navigation system and the driver demand expectations that the VSC
46 could infer from it.
1 Navigation System Inferred Expectations of Information Driver
Demand Altitude change Grade expectations Road pattern (interstate
Speed expectations highway, rural, city) or speed limit Road
pattern (interstate, Braking expectations highway, rural, city) or
stop light/sign locations Driver driving patterns Braking and speed
expectations Intersection density and Braking and speed traffic
control information expectations Weather Speed expectations
Geography and time/date Temperature expectations
[0040] FIG. 2 illustrates the overall VSC 46 energy management
strategy of the present invention with integrated navigation
system. A GPS and map navigation system 56 can be used by the VSC
46 to manage the battery 36 and regenerative braking systems 62 so
that vehicle fuel economy and range are increased.
[0041] The GPS and map navigation system 56 has as inputs desired
departure, arrival times and locations. It can also receive traffic
updates, road conditions and terrain information. The GPS and map
navigation system 56 can estimate the number of vehicle
starts/stops, and accelerations/decelerations from these input
data. That data with the estimated vehicle speed from a vehicle
speed sensor (not shown) can input to an energy management
controller 58. The energy management controller 58 is a functional
part of the VSC 46 ,but is shown separate in the figure to aid in
understanding the invention.
[0042] The energy management controller 58 can determine any output
parameters to adjust the output of the regenerative braking process
to best match the upcoming driving cycle to a regenerative brake
system controller 60, which interacts with the regenerative braking
system (RBS) 62. The energy management controller 58 can also
output to the VSC 46 and BCU 50 the ideal SOC target range.
[0043] For example purposes only, an anticipated route with high
speeds and long ascents and descents would need an aggressive
regenerative strategy, and as much headroom in the battery 36 to
store energy as possible. Alternately, a route at a nearly constant
speed over flat terrain would require a SOC as high as possible to
facilitate passing assist boost with little opportunity to
regenerate energy.
[0044] Chassis dynamometer tests over urban cycles (Federal Urban
Driving Schedule) and high-speed (Highway Driving Schedule) cycles
have confirmed the benefits of energy management to match the
driving cycle. In less interactive battery systems (and thus more
conservative), controllers try to match a fixed SOC target band
(e.g., between 40 percent and 70 percent) to be sure the battery
always has some room to collect regenerated energy while never too
low to start the vehicle.
[0045] The present invention allows multiple SOC target ranges. For
example, the hilly high-speed cycle might be best matched with a 40
percent to 60 percent target window. Whereas the high speed, flat
terrain cycle might be best matched by a 60% to 80% target
window.
[0046] The present invention can be implemented utilizing classic,
discrete control laws, fuzzy logic, or neural networks. Fuzzy logic
control is an approach that incorporates a rule-based strategy in
the control hierarchy. Neural network control uses a network of
cells that are trained with prior examples to model future outputs
based on learned training data.
[0047] FIG. 3 illustrates the logic flow of the energy management
control strategy of the present invention using classic discrete
logic controls. The energy management controller 58 within the VSC
46 can take actions based on the inferred expectations of driver
demand outlined in the table above to ensure that the system can
optimize its fuel economy, protect its traction battery
functionality and meet the driver demand. To better understand the
logic decisions illustrated in FIG. 3, the following assumptions
within the strategy are provided as follows:
[0048] If a steep uphill grade is expected, the VSC can control the
battery SOC to a high value so that when the driver power demand
increases to cause the vehicle to climb the hill, there exists
sufficient battery power to provide electric assist and to allow
the engine to remain on its optimal efficiency curve.
[0049] If a steep downhill grade is expected, the strategy can
control battery SOC to a low value so that when the driver demand
for negative (braking) power occurs to cause the vehicle to descend
the grade in a controlled manner, the strategy is able to maximize
the amount of regenerative braking energy that it is able to
capture.
[0050] If extended city road patterns are expected, the strategy
can expect a significant amount of stop and go driving that would
cause significant battery power throughput and it can choose to
operate in a more load following manner to protect the
functionality of the battery.
[0051] Similarly, if extended hilly road patterns are expected with
frequent uphill and downhill grades that would cause significant
battery power throughput, the strategy can choose to operate in a
more load following manner to protect the functionality of the
battery.
[0052] If extended light load conditions are expected, as inferred
by moderately high speed on flat highway surfaces, the control
strategy can choose to enact some battery conditioning strategies
during this time, confident that the demand on the electric
strategy is unlikely to change during the strategy enactment.
[0053] Similarly, if extended light load conditions are expected,
as inferred by moderately high speed on flat highway surfaces, the
control strategy can choose to operate in a load leveling strategy,
providing quick response without severe wear on the traction
battery.
[0054] If extended high temperature is expected (particularly if it
knows that the vehicle is likely to be turned off in the near
future, as inferred, for example by the imminent completion of the
specified trip), the strategy may choose to operate at a lower
target SOC to reduce self-discharging when the vehicle is turned
off and left sitting.
[0055] Similarly, if extended low temperature is expected, SOC
(particularly if it knows that the vehicle is likely to be turned
off in the near future, as inferred, for example by the imminent
completion of the specified trip), the strategy may choose to
operate at a higher target SOC to ensure that sufficient energy
will be available to restart the vehicle after the vehicle is
turned off and left sitting (this is particularly important if the
traction battery also serves as the source of engine starting
power).
[0056] If entrance to a highway is expected, the strategy may
choose to prepare for an increase in driver demanded power either
by turning the IC engine on if it is not already or by charging up
the battery if the engine is already on.
[0057] Turning back to logic flow diagram in FIG. 3, at Step 70,
the strategy receives drive route information input from the
navigation system (generated from either the driver or local maps).
The strategy commands an analysis of the drive route to determine
system expectations at Step 72 and assumes a load following
strategy with average SOC target and no battery conditioning at
Step 74.
[0058] Next, at Step 76, the strategy determines if significant
grade variations or frequent stop and go events are expected. If
yes, the strategy accommodates this expectation at Step 78 by, for
example, moving toward a load following to protect the battery,
then returning to Step 70. If no, the strategy determines if
significant downhill grades or decelerations from high speed are
expected at Step 80. If yes, the strategy changes to accommodate
this expectation by, for example, discharging the battery at Step
82, then returning to Step 70. If no, the strategy determines if
significant uphill grades or accelerations onto a highway are
expected at Step 84. If yes, the strategy changes to accommodate
this expectation by, for example, charging the battery at Step 86,
then returning to step 70. If no, the strategy next determines
whether extended light loads are expected at Step 88. If yes, the
strategy must make an additional determination of whether battery
conditioning is required at Step 90. If yes, the strategy enacts
battery-conditioning strategies at Step 92, then returns to Step
70. If battery conditioning is not required at Step 90, the
strategy changes to accommodate this expectation by, for example,
moving toward load leveling for improved fuel economy at Step 94,
then returning to step 70.
[0059] If extended light loads are not expected at Step 88, the
strategy determines at Step 96 whether high ambient temperatures
are expected. If yes, the strategy further determines at Step 98
whether the vehicle is likely to be turned off soon. If yes at Step
98, the strategy changes to accommodate this expectation by, for
example, decreasing battery SOC at Step 100, then returning to Step
70. If Step 96 or Step 98 are no, the strategy at Step 102
determines whether low ambient temperatures are expected. If yes at
Step 102, again the strategy changes to accommodate this
expectation at Step 106, then returning to Step 70. If the
determination at Step 102 is no, the strategy next makes a
determination of whether an increase in vehicle speed is
anticipated such as whether entrance to a highway is expected at
Step 104. If yes, the strategy can turn on the engine and charge
the battery at Step 108, then return to Step 70. Otherwise, the
strategy simply returns to Step 70.
[0060] The above-described embodiment(s) of the invention is/are
provided purely for purposes of example. Many other variations,
modifications, and applications of the invention may be made.
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