Note: Descriptions are shown in the official language in which they were submitted.
~ WO9C/18178
PCT~S95/15941
PERFORMANCE MO~llOR POR ELECTRIC VE~ICLE
This invention generally relates to systems and
methods for monitoring the transitory ~m~nAc for electric
S current from the traction batteries of an electrically-powered
vehicle. More specifically, this invention relates to systems
and methods for monitoring the transitory demAn~ for current
from the ~ehicle's batteries so as to provide its operator with
an indication as to how those transitory d~m~n~ for current
relate to the m~; m~tl~ amount of current available from the
batteries for immediate use, thereby apprising the vehicle
operator of any potential current-based restriction on vehicle
performance. This invention further relates to systems and
methods for modifying current usage in an electric vehicle
l~ based on transitory usage of a~ailable battery current.
In an effort to improve air quality, battery-powered
"electric" ~ehicles are becoming increasingly common in today's
automotive mar~etplace. These electric vehicles typically
include traction batteries for supplying electric current to
one or more traction motors which, in turn, provide motive
power to the vehicle. Accordingly, the vehicle~s ability to
perform a manoeuvre at any given time at the direction of the
vehicle operator directly depends upon the condition of the
traction batteries at that time. The condition of each
battery, in turn, ~aries upon such transitory factors as its
temperature and its state of charge, as well as other long-term
factors as battery aging, polarization effects, etc. Variation
in these parameters wiIl substantively affect the manner in
which each battery can supply current to the vehiclels traction
motors and, hence, the m~n~er in which the vehicle will respond
to commands from its operator. Stated another way, in certain
situations or under certain load conditions, the vehicle's
WO96118178
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traction batteries may be unable to meet the transitory current
~em~n~ of the vehicle which, in turn, will limit the vehicle~s
temporal capability to perform.
Significantly, the vehicle operator may not realize
the qualitative and quantitative limitation on vehicle
perfor~ imposed by the condition of the traction batteries.
Indeed, these limitations will likely conflict with the
operator's own expectations of vehicle perfonmance, given that
he will likely have become accustomed to the ~mler in which
vehicles powered by internal combustion engines operate.
Specifically, the output of an internal combustion engine and,
hence, the responsiveness of a vehicle powered by such an
engine, is not noticeably dependent upon the temporal quality
of the hydrocarbon-based fuel stored within the vehicle's fuel
lS tank, e.g., the temperature or age of the fuel. Rather, the
engine's output is singularly dep~n~Pnt upon the presence of
such fuel within the fuel tank. So long as fuel is present,
the engine will provide full power upon ~em~n~. Indeed, absent
an nearly-empty fuel tank, the operator of a vehicle powered by
an internal combustion engine will not typically check the
vehicle~s fuel gauge ;mme~;~tely prior to executing, say, a
passing manoeuvre, since it will have no bearing on the
vehicle~s performance capabilities.
Given the likely expectations of the vehicle
operator, there may come a time when he will attempt a
manoeuvre that cannot be performed given the amount of current
immediateiy available from the traction batteries, thereby
placing the operator, his vehicle and others at great risk of
injury. What is needed, then, is a performance monitor for an
electric vehicle which can COm~m ~ cate to the vehicle operator,
preferably in a familiar fashion, an indication of his present
use of available battery "power" so that the operator may then
form a reasonable expectation as to the vehicle~s further
capability to perform at that instant.
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5S115941
Another limitation on the temporal performance
capabilities of the typical electric vehicle derives from the
correlative use of the traction batteries for supplying current
to noncritical electrical components within the ~ehicle, such
S as the climate control system's blower fan motor, AC compressor
or resistance heater. As a result, the traction batteries are
forced to perfonm "double duty," even in the face of a d~m~
for increased moti~e perfonmance from the vehicle operator
The increased load from these noncritical components may
dangerously limit the amount of current available as for an
emergency manoeu~re, again, placing the operator, his vehicle
and others at risk. What is also needed, then, is a vehicle
performance monitor for an electric ~ehicle that can shed these
noncritical loads on the traction batteries should their
current requirements reduce reserve battery current below an
acceptable minimum level, given the transitory amount of
current then being supplied to the traction motors.
An object of the invention is to provide a system and
method for displaying to the operator of an electric vehicle an
indication of vehicle performance reserve available at any
given time.
Another object of the invention is to provide a
system and method for displaying to the operator of an electric
vehicle an indication of his present use of available battery
current so that the operator ~ay then form a reasonable
expectation as to the vehicle's further capability to perform.
A further object of the invention is to provide a
means and method for controlling power usage in an electric
vehicle whose traction batteries supply current to both a
traction motor and noncritical electrical components, wherein
noncritical loads are shed as the ratio of current being drawn
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from the batteries to the ~ m amount of current ;mme~iately
available therefrom exceeds a first m~x; ~m threshold le~el.
Yet another object of the invention is to provide a
means and method ~or controlling current usage in an electric
- 5 ~ehicle, wherein the supply of current from the ~ehicle~s
traction batteries to noncritical components is interrupted and
the supply of current to the traction motor is limited as the
ratio of current being drawn from the batteries to the ~im
amount of current immediately available therefrom exceeds a
second m~x;mllm threshold level.
Under the present invention, in a vehicle having at
least one traction battery supplying current to a traction
motor and a noncritical electrical component, a system for
monitoring the transitory usage of the battery's m~x; m~m-
a~ailable current includes a means for detecting the currentbeing drawn from the battery; and a means connected to the
battery for determining the m~ m amount of current available
from the battery for immediate use. In a preferred em~odiment,
the means for deter~ining the maximum amount of current
immediately available from the battery includes a means for
sensing the condition of the battery through measurement and/or
tracking of such battery parameters as temperature, state-of-
charge, age, charging history, etc.
The system of the present invention further includes
a means responsive to the drawn-current signal and the m~xim1lm-
available-current signal for generating a signal representative
of the ratio of the drawn-current signal to the maximum-
available-current signal. This ratiometric signal thus
provides information as to the relative transitory usage of the
battery~s maximum-available current.
The system also includes a display, such as an analog
meter, responsive to the usage signal for displaying the usage
signal to the operator of the vehicle. The vehicle operator
: W096/18178 ; ~ ~S/l5g41
may thus make an infonmed judgment as to the propriety of, for
example, a passing m~nsPl~vre~ given his transitory usage of the
battery's m~;ml~m-available current. In a preferred
embo~;m~nt, the analog meter is calibrated from zero-percent to
S one-hundred percent usage of m~Y;m~m-available current, thereby
providing the vehicle operator with a familiar display that is
somewhat analogous to a tachometer in a gasoline-powered
vehicle.
In accordance with another feature of the present
invention, the system preferably i~cludes a load-che~;ng means
responsive to the usage signal for interrupting the supply of
current from the battery to noncritical electrical components
when the usage signal exceeds a first ~;ml~m threshold level.
The system preferably also includes a current limiter, likewise
lS responsive to the usage signal, for limiting the supply of
current from the traction battery to the traction motor when
the usage signal exceeds a second maximum threshold level, with
the second ~x~mllm threshold level being greater than the first
maximum threshold level at which the shedding of noncritical
loads occurs.
FIG. l is a diagram of a preferred system for
monitoring the transitory usage of current from an electric
vehicle's traction battery in accordance with the invention;
and
- FIG. 2 is a partial view in elevation of a dashboard
for an electric vehicle which includes an analog meter to
display to the vehicle operator its transitory usage of the
battery's available current.
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A preferred system 10 for monitoring the transitory
usage by an electric ~ehicle of its traction battery~s
av~ hle current is illustrated in FIG. 1. Specifically, an
electric vehicle (not shown) typically includes at least one,
but more typically many, traction batteries 12 for supplying
electric current to one or more traction motors 14. The
traction motors 14 in turn provide motive power for the
~ehicle. And, as in the typical electric ~ehicle, the traction
batteries 12 also supply electric current to one or more
noncritical electrical components 16 within the vehicle. A
noncritical component 16 is a cs~rQ~nt to which current may be
interrupted upon experiencing a shortage of available battery
current, without compromising the safety of the vehicle or its
passengers. An example of a noncritical component 16 is the
blower fan motor used in a vehicle's climate control system.
As seen in FIG. 1, a pair of signal generators 18
and 20 are connected to the traction batteries 12. The first
signal generator 18 generates a signal representative of the
current then being drawn from the batteries 12, both by the
traction motors 14 and by the noncritical components 16. The
second signal generator 20, itself responsive to one or more
battery parameters, generates a signal representative of the
maximum current immediately available from the batteries 12.
The specific battery parameters used ~y the second
signal generator 20 in generating the ~;t~;mtlm-available-current
signal will be recognized by those of ordinary skill as
including, without limitation, such parameters as temperature
state-of-charge, age, charging history, etc. The second signal
generator 20 will preferably also be responsive to such other
factors as the variations between the par~meters of individual
cells in a multi-cell battery pack, including the presence of
a bad cell in the battery pack. The specific manner in which
the second signal generator 20 itself generates the ~ximt~m-
WO9al8178 ~ ~ a~ l5g41
. _
available-current signal from such battery parameters is
likewise known to those of ordinary skill.
A third signal generator 22 receives as input the
drawn-current signal generated by the first signal generator 18
S and the m~;mllm-a~ailable-current signal generated by the
second sig~al generator 20, respecti~ely. The third signal
generator 22 then generates a signal representati~e of the
ratio of drawn current to the m~xi~lm-available current. This
ratiometric signal, or usage signal, generated by the third
signal generator 22 thus represents, in real time, the
vehicle's relative usage of the batteries' ~x;m~l~-available
current at any gi~en time.
The usage signal is then provided to a suitable
display, such as an analog meter indicated at 24 in FIG 1 and
lS further shown as part of a vehicle dashboard 26 in FIG. 2.
With this information, the vehicle operator may make an
informed judgment as to the propriety of, for example, a
passing manoeu~re, given the displayed usage of the traction
batteries' maximum-available current.
And, as seen in FIG. 2, the usage meter 24 is
preferably calibrated f-rom zero-percent to one-hundred percent
usage of the traction batteries's ~im~lm-available current,
thereby providing the vehicle operator with a familiar display
that is somewhat analogous to a tachometer in a gasoline-
powered ~ehicle. Indeed, as further illustrated in FIG. 2, the
u~age meter 24 may include a colloquially-descriptive but
otherwise technically inaccurate caption, "~ POWER USED."
And, in a m~nn~r further analogous to the markings on
a tachometer, "redline" markings are preferably provided
beginning at perhaps eighty to ninety percent relative usage to
indicate to the operator the likely absence of available "power
margin" at such usage levels. Such redline markings are
likewise shown in FIG. 2 as an arcuate band on the usage
WO9~18178 ~ ~ ~ P~ g~l594
meter 24 extending from eighty-five percent to one-hundred
percent "power" usage.
Referring again to FIG. 1, in accordance with another
feature of the present invention, the traction batteries 12 are
connected to the noncritical components 16 through a load-shed
means, such as a load-shed relay 28. The load-shed relay 28 is
responsi~e to the control signal so as to interrupt the flow of
current from the batteries 12 to the noncritical component 16
when the control signal exceeds a first m~;mllm threshold
level. In this m~nn~r, the operation of noncritical components
16 is interrupted to effectively provide a current reserve for
other components whose continued operation is essential to
maintaining the safety of the vehicle and its passengers.
Unfortunately, even after the she~ g of noncritical
load, it is still possible that the m~;mllm amount of current
available from the traction batteries 12 for ;~me~;ate use is
less than the current requirements of the traction motors 14
standing alone. Indeed, such a situation may arise
notwithst~n~ing a relatively-high battery state-of-charge due,
for example, to extreme temperatures or, even, a bad cell
within a given battery pack. Accordingly, in the system 10
shown in FIG. 1, the traction batteries 12 are connected to the
traction motors 14 through a current limiter 30.
The current limiter 30 is itself responsive to the
usage signal to limit the flow of current from the traction
batteries 12 to the traction motors 14 when the usage signal
exceeds a second mA~im~m threshold level. And, since current
to the traction motors 14 should ~e limited only a~ter
noncritical loads have already been shed, the second maximum
threshold level triggering such current limiting is necessarily
greater than the first m~;mllm threshold level triggering
interruption of the supply of current to the noncritical
components 16. In this m~nn~r, the present system lo acts to
prevent deleterious deep discharge of the traction batteries 12
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6t8178 P~ 9~lS941
when m~;m~ available current is insufficient to accommodate
even the current requirem~nts of the traction motors 14 alone.
In accordance with yet another feature of the present
invention, the system 10 as seen in FIG. 1 further includes a
fourth signal generator 32. The fourth signal generator 32
generates a signal e~aluative of the temporal capacity of the
traction batteries 12, as mlght be approximated using battery
state-of-charge. The system 10 further includes an indicator
light 34 responsive to the battery-capacity signal for
1~ displaying battery-capacity information directly to the vehicle
operator. The indicator light 34 may be incorporated into the
vehicle dashboard 26 proximate to the usage signal's analog
display 24, as illustrated in FIG. 2. In this way, the
indicator light 34 can serve to draw the attention of the
vehicle operator to the usage meter 24 in the event a reduced
battery capacity further restricts the capability of the
vehicle to perform. A second analog display 36 on the vehicle
dashboard, also responsive to the battery-capacity signal,
provides a "fuel gauge" for use by the vehicle operator.
The load-shed relay 28, described above as being
responsive to the usage signal, is preferably further
responsive to the battery-capacity signal generated by the
fourth signal generator 32. Specifically, the load-shed
relay 28 will preferably operate to shed noncritical loads when
the battery-capaCity signal falls below a first minimum
threshold level.
Similarly, the current limiter 30 described above as
being responsive to the usage signal is likewise also
responsive to the battery-capacity signal generated by the
fourth signal generator 32. The current limiter 30 will thus
operate to limit the current being supplied to the vehicle's
traction motors 14 when the battery-capacity signal falls below
falls below a second mi~ m threshold level. For reasons
similar to those discussed hereinabove with respect to the
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first and second m~ m threshold levels, the second minin~
threshold level is quantitatively less than the f irst m; ~i m~m~
threshold level, so that the current supplied to the traction
motors 14 is limited only af ter noncritical loads have been
S shed.
