U.S. patent application number 09/753853 was filed with the patent office on 2001-05-24 for computer program product for estimating the service life of a battery.
Invention is credited to Galbraith, Robert Edward, Gisi, Jessica Marie, Norgaard, Steven Paul, Reetz, Dennis David, Ziebarth, Donald James.
Application Number | 20010001532 09/753853 |
Document ID | / |
Family ID | 23646602 |
Filed Date | 2001-05-24 |
United States Patent
Application |
20010001532 |
Kind Code |
A1 |
Galbraith, Robert Edward ;
et al. |
May 24, 2001 |
COMPUTER PROGRAM PRODUCT FOR ESTIMATING THE SERVICE LIFE OF A
BATTERY
Abstract
An apparatus is provided for estimating the service life of a
battery. The apparatus includes a temperature measurement circuit
that measures a temperature of an operating environment of the
battery and outputs a signal representative of the temperature of
the operating environment. A controller coupled to the temperature
measurement circuit receives the temperature signal therefrom and
estimates the service life of the battery based on the temperature
signal. Preferably, the temperature measurement circuit outputs a
signal representative of a temperature range in which the measured
operating environment temperature resides and the controller
estimates the service life of the battery based on the temperature
range signal output by the temperature measurement circuit. A
method and a computer program product also are provided for
similarly estimating the service life of a battery.
Inventors: |
Galbraith, Robert Edward;
(Rochester, MN) ; Gisi, Jessica Marie; (Rochester,
MN) ; Norgaard, Steven Paul; (Rochester, MN) ;
Reetz, Dennis David; (St. Charles, MN) ; Ziebarth,
Donald James; (Rochester, MN) |
Correspondence
Address: |
IBM Corporation
Intellectual Property Law - 972E
1000 River Street
Essex Junction
VT
05452
US
|
Family ID: |
23646602 |
Appl. No.: |
09/753853 |
Filed: |
January 3, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09753853 |
Jan 3, 2001 |
|
|
|
09415652 |
Oct 12, 1999 |
|
|
|
Current U.S.
Class: |
320/132 |
Current CPC
Class: |
G01R 31/392 20190101;
G01R 31/3648 20130101; G01R 31/378 20190101; H02J 7/0047 20130101;
H02J 7/005 20200101 |
Class at
Publication: |
320/132 |
International
Class: |
H02J 007/00 |
Claims
The invention claimed is:
1. A computer program product comprising: a medium readable by a
computer, the computer readable medium having: means for inputting
a signal representative of a temperature range in which a
temperature of an operating environment of a battery resides; and
means for estimating a service life of the battery based on the
signal.
2. The computer program product of claim 1 wherein the means for
estimating the service life of the battery comprises: means for
determining a time the battery is operated within each of a
plurality of temperature ranges; and means for estimating the
service life of the battery based on the time the battery is
operated within each of the plurality of temperature ranges.
3. The computer program product of claim 1 wherein the means for
estimating the service life of the battery comprises means for
estimating the service life of the battery based on the time the
battery is operated within each of the plurality of temperature
ranges and based on a pro-rate factor for each temperature
range.
4. The computer program product of claim 1 wherein the means for
estimating the service live of the battery comprises: a plurality
of counter means, each counter means having a count and a
temperature range associated therewith, each counter means for
counting a time the battery is operated within the temperature
range associated with the counter means; and estimation means for
estimating the service life of the battery based on the count of
each counter means.
5. The computer program product of claim 4 wherein the estimation
means comprises means for estimating the service life of the
battery based on the count of each counter means and a pro-rate
factor for each counter means that depends on the temperature range
associated with the counter means.
6. The computer program product of claim 5 wherein the plurality of
counter means comprise: a first counter means having a temperature
range of less than about 28.degree. C. associated therewith; a
second counter means having a temperature range of between about
28.degree. C. and about 32.degree. C. associated therewith; a third
counter means having a temperature range of between about
32.degree. C. and about 36.degree. C. associated therewith; and a
fourth counter means having a temperature range of greater than
about 36.degree. C. associated therewith.
7. The computer program product of claim 6 wherein: the pro-rate
factor for the first counter means is about 1.0; the pro-rate
factor for the second counter means is about 1.22; the pro-rate
factor for the third counter means is about 1.5; and the pro-rate
factor for the fourth counter means is about 1.83.
8. The computer program product of claim 1 further comprising means
for periodically estimating the service life of the battery.
9. The computer program product of claim 8 further comprising means
for estimating the service life of the battery about every 5
minutes.
10. The computer program product of claim 1 further comprising
means for generating an alarm if a maximum service life of the
battery is exceeded.
11. The computer program product of claim 1 wherein the means for
inputting a signal comprises means for inputting at least one bit
representative of the temperature range in which the operating
environment temperature of the battery resides.
12. The computer program product of claim 11 wherein the means for
inputting a signal comprises means for inputting a plurality of
bits indicative of the temperature range in which the operating
environment temperature resides.
Description
[0001] This application is a divisional of U.S. patent application
Ser. No. 09/415,652, filed Oct. 12, 1999, which is incorporated
herein in its entirety by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to battery
technology, and more particularly to a method and apparatus for
estimating the service life of a battery.
BACKGROUND OF THE INVENTION
[0003] For years single use and rechargeable nickel-cadmium (NiCd)
batteries have been employed to power portable radios, shavers,
laptop computers, non-volatile memory components, etc. NiCd
batteries exhibit good capacity (i.e., the length of useable time
between charges), reusability (i.e., the ability to be recharged)
and service life (i.e., the length of time a battery may be used
before a minimum useful battery capacity, such as 60% of the
battery's maximum or "initial" capacity, is unachievable by
re-charging). However, due to environmental concerns over the
disposal of heavy metals such as cadmium, alternative battery
technologies have been developed.
[0004] Nickel metal hydride (NiMH) batteries offer a more
environmentally friendly alternative to NiCd batteries. NiMH
batteries have better capacity than NiCd batteries, but suffer from
poor battery service life in hot operating environments (e.g.,
above 36.degree. C.). For example, for operating environments
having a temperature of about 28.degree. C. or less, the service
life of a NiMH battery is about 36 months. However, for operating
environments having a temperature of about 36.degree. C. or higher,
the service life of a NiMH battery is only about 19.5 months.
[0005] Because batteries typically are rated based on the worst
case operating environment (e.g., about 40.degree. C. for NiMH
batteries) even though actual battery operating environments rarely
approach the worst case operating environment, NiMH batteries often
are changed prematurely. The high costs associated with service
calls, service disruption and battery disposal that accompany
battery replacement necessitate longer battery service life.
SUMMARY OF THE INVENTION
[0006] To address the need for longer battery service life, a
method and an apparatus for estimating the service life of a
battery are provided. Specifically, battery service life is
estimated based on the actual temperature of the operating
environment of a battery rather than on a worst case operating
environment temperature. Preferably battery service life is
estimated periodically or is otherwise "integrated" during battery
operation to account for any changes in the operating environment
temperature of the battery during its operation and to account for
both the present and the past operating environment temperatures of
the battery. By estimating the service life of a battery based on
its actual operating environment temperature, a worst case service
life need not be assumed for the battery, and the battery need not
be replaced prematurely. Maximum service life is therefore
extracted from every battery.
[0007] In a first aspect of the invention, an apparatus is provided
for estimating the service life of a battery. The apparatus
includes a temperature measurement circuit that measures a
temperature of an operating environment of the battery and outputs
a signal representative of the temperature of the operating
environment. The apparatus further includes a controller coupled to
the temperature measurement circuit that receives the temperature
signal therefrom and estimates the service life of the battery
based on the temperature signal. Preferably, the temperature
measurement circuit outputs a signal representative of a
temperature range in which the measured operating environment
temperature resides and the controller estimates the service life
of the battery based on the temperature range signal output by the
temperature measurement circuit.
[0008] In a second aspect of the invention, a method is provided
for estimating the service life of a battery by measuring a
temperature of an operating environment of the battery and by
estimating the service life of the battery based on the measured
operating environment temperature. Preferably, measuring the
temperature of the operating environment of the battery includes
outputting a signal representative of a temperature range in which
the measured operating environment temperature resides. The service
life of the battery is estimated based on the temperature range
signal.
[0009] In a third aspect of the invention, a computer program
product is provided for estimating the service life of a battery as
described above. The inventive computer program product is carried
by a medium readable by a computer (e.g., a carrier wave signal, a
floppy disc, a hard drive, a random access memory, etc.).
[0010] Other objects, features and advantages of the present
invention will become more fully apparent from the following
detailed description of the preferred embodiments, the appended
claims and the accompanying drawings.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] The present invention is described with reference to the
accompanying drawings. In the drawings, like reference numbers
indicate identical or functionally similar elements. Additionally,
the left-most digit of a reference number identifies the drawing in
which the reference number first appears.
[0012] FIG. 1 is a schematic diagram of a novel service life
estimation circuit for estimating the service life of a battery in
accordance with the present invention; and
[0013] FIG. 2 is a flow chart of a service life estimation
algorithm for use with the service life estimation circuit of FIG.
1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] FIG. 1 is a schematic diagram of a novel circuit (e.g.,
service life estimation circuit 100) for estimating the service
life of a battery in accordance with the present invention. The
service life estimation circuit 100 comprises a temperature
measurement circuit 102 for measuring the temperature of an
operating environment of a battery and for outputting a signal
representative of the measured temperature; and a controller 104
coupled to the temperature measurement circuit 102 for receiving
the temperature signal and for estimating the service life of the
battery based thereon.
[0015] In the preferred embodiment of the present invention, the
temperature measurement circuit 102 measures an operating
environment temperature of a battery and outputs to the controller
104 a temperature range signal that indicates in which of a
plurality of temperature ranges the measured operating environment
temperature resides. Within the controller 104 a counter is
associated with each of the plurality of temperature ranges set by
the temperature measurement circuit 102. Each counter counts the
amount of time the battery is operated within the temperature range
associated with the respective counter. The battery's total
operation time thereby can be obtained by adding together the
counts of each counter.
[0016] Moreover, to determine if the battery's service life has
been exceeded, and thus whether the battery should be replaced, a
pro-rated operation time (rather than the actual operation time) of
the battery is computed (e.g., by multiplying any battery operation
time at elevated temperatures by a pro-rate factor which is greater
than one) to account for elevated temperature operation of the
battery. The pro-rated operation time of the battery is compared to
a maximum service life of the battery (e.g., the service life of
the battery if the battery is operated in a low temperature
environment such as 28.degree. C. or less for a NiMH battery). If
the pro-rated operation time exceeds the maximum service life of
the battery, an alarm is generated to indicate that the battery
should be replaced. Thus, although battery life varies depending on
the environmental temperature in which the battery operates, the
invention allows for an accurate estimate of battery life
regardless of the operating environment temperature.
[0017] With reference to FIG. 1, the temperature measurement
circuit 102 comprises a thermistor 106 (e.g., a Mitsubishi
Materials Corporation Model No. TH20-3V103F thermistor or any other
suitable thermistor) coupled to an encoder circuit 108 via a first
voltage divider circuit 110, and a second voltage divider circuit
112 coupled to the encoder circuit 108. The first voltage divider
circuit 110 comprises a first resistor 114 coupled between a power
supply rail (V.sub.cc) and a thermistor node 116, and a second
resistor 118 coupled between the thermistor node 116 and ground.
The thermistor 106 also is coupled between the thermistor node 116
and ground.
[0018] The second voltage divider circuit 112 comprises a third
resistor 120 coupled between the power supply rail (V.sub.cc) and a
first reference node 122, a fourth resistor 124 coupled between the
first reference node 122 and a second reference node 126, a fifth
resistor 128 coupled between the second reference node 126 and a
third reference node 130, and a sixth resistor 132 coupled between
the third reference node 130 and ground. As described further
below, each voltage divider circuit 110, 112 generates one or more
reference voltages based on a common voltage supply (e.g., the
power supply rail (V.sub.CC)). Accordingly, the power supply rail
(V.sub.CC) need not be tightly regulated because any voltage
fluctuations present thereon will have an equivalent affect on each
voltage divider circuit (and any reference voltage or voltages
generated thereby). It will be understood that regulated reference
voltages and conventional regulation circuitry associated therewith
(e.g., Zener diodes and the like) may be employed to generated the
various reference voltages described herein.
[0019] The encoder circuit 108 comprises a first comparator 134, a
second comparator 136 and a third comparator 138 each having a
positive input terminal coupled to the thermistor node 116. The
negative input terminals of the first comparator 134, the second
comparator 136 and the third comparator 138 are coupled to the
first reference node 122, to the second reference node 126 and to
the third reference node 130, respectively. The output of the
second comparator 136 serves as an "X" output of the encoder
circuit 108 and the outputs of the first comparator 134 and the
third comparator 138 are combined via an XOR gate 140 to serve as a
"Y" output of the encoder circuit 108. The comparators 134-138 may
comprise any conventional comparator, but preferably comprise
comparators having hysteresis (such as Maxim Corporation Model No.
MAX8214 comparators) so as to limit toggling of the X and Y outputs
of the encoder circuit 108 as described below. Note that a
decoupling capacitor 141 preferably is coupled between the power
supply rail (V.sub.cc) and ground for noise reduction purposes as
is known in the art.
[0020] In operation, the temperature measurement circuit 102
generates a two bit output signal (e.g., outputs X, Y of the
encoder circuit 108) that indicates in which of four temperature
ranges the temperature (as measured by the thermistor 106) of an
operating environment of a battery resides. Specifically, as shown
in TABLE 1 below, the thermistor 106 has a resistance (R.sub.106)
that varies with temperature from about 10 Kohms at 25.degree. C.
to about 6.258 Kohms at 36.degree. C. In response to the resistance
variations of the
1TABLE 1 T R.sub.106 V.sub.116 V.sub.122 V.sub.126 V.sub.130
(.degree. C.) (ohms) (volts) (volts) (volts) (volts) Y X 25 10K
2.075 2.007 1.910 1.808 0 1 28 8.77K 2.005 2.007 1.910 1.808 1 1 32
7.392K 1.907 2.007 1.910 1.808 1 0 36 6.258K 1.805 2.007 1.910
1.808 0 0
[0021] thermistor 106, the first voltage divider circuit 110
generates a temperature-sensitive voltage signal at the node 116
(V.sub.116) that depends on the resistance (R.sub.106) of the
thermistor 106, the resistance (R.sub.114) of the first resistor
114, the resistance (R.sub.118) of the second resistor 118 and the
power supply rail voltage (V.sub.cc) via equation (1) below: 1 V
116 = V cc R TOTAL R TOTAL + R 114 where R TOTAL = R 106 R 118 R
106 + R 118 ( 1 )
[0022] TABLE 1 lists values for the temperature-sensitive voltage
signal (V.sub.116) at operating environment temperatures of
25.degree. C., 28.degree. C., 32.degree. C. and 36.degree. C. (for
the resistance values listed in TABLE 2).
2TABLE 2 R.sub.114 R.sub.118 R.sub.120 R.sub.124 R.sub.128
R.sub.132 (ohms) (ohms) (ohms) (ohms) (ohms) (ohms) 6.04K 7.50K
60.4K 1.96K 2.05K 36.5K
[0023] The temperature-sensitive voltage signal (V.sub.116) is fed
to the negative input terminal of each of the comparators 134-138,
while the positive voltage terminal of each comparator 134-138 is
held at a reference voltage V.sub.122, V.sub.126 and V.sub.130,
respectively (the voltages of the first, second and third reference
nodes 122, 126, 130). The reference voltages V.sub.122, V.sub.126
and V.sub.130 are set by the second voltage divider circuit 112 and
are governed by equations (2)-(4) below: 2 V 122 = V cc R 124 + R
128 + R 132 R 120 + R 124 + R 128 + R 132 ( 2 ) V 126 = V cc R 128
+ R 132 R 120 + R 124 + R 128 + R 132 ( 3 ) V 130 = V cc R 132 R
120 + R 124 + R 128 + R 132 ( 4 )
[0024] where R.sub.120, R.sub.124, R.sub.128 and R.sub.132 are the
resistances, respectively, of the resistors 120-132. TABLE 1 lists
the values of the first, second and third reference voltages
V.sub.122, V.sub.126, V.sub.130 of the first, second and third
reference nodes 122, 126, 130, respectively, for the resistance
values listed in TABLE 2.
[0025] With the reference voltage of each comparator 134-138 thus
fixed, each comparator 134-138 outputs a positive voltage level
(e.g., V.sub.cc) if the temperature-sensitive voltage signal
(V.sub.116) is greater than the comparator's reference voltage, and
outputs zero volts if the temperature-sensitive voltage signal
(V.sub.116) is less than the comparator's reference voltage. For
example, with reference to TABLE 1, if the operating environment
temperature of a battery (as measured by the thermistor 106) is
25.degree. C. or less, the temperature-sensitive voltage signal
(V.sub.116) exceeds the first, the second and the third reference
voltages V.sub.122, V.sub.126 and V.sub.130. Each comparator output
is driven high (e.g., to V.sub.cc) and in response thereto, the X
output of the encoder circuit 108 is driven high by the second
comparator 136 and the Y output of the encoder circuit 108 is
driven low by the XOR gate 140.
[0026] The temperature-sensitive voltage signal (V.sub.116) remains
above all three reference voltages V.sub.122, V.sub.126 and
V.sub.130 until a temperature of about 28.degree. C. when the
temperature-sensitive voltage signal (V.sub.116) no longer exceeds
the first reference voltage V.sub.122, but remains in excess of the
second and third reference voltages V126, V.sub.130. With the first
reference voltage V.sub.122 no longer exceeded, the output of the
first comparator 134 is low while the outputs of the second and
third comparators 136, 138 remain high. In response thereto, the X
output of the encoder circuit 108 remains high (due to the high
voltage level output by the second comparator 136) while the Y
output of the encoder circuit 108 is driven high (e.g., due to the
low voltage level and the high voltage level from the first and
third comparators 134, 138, respectively, fed to the XOR gate
140).
[0027] Note that because the comparators 134-138 preferably have
hysteresis associated therewith, once the temperature-sensitive
voltage signal (V.sub.116) exceeds a reference voltage associated
with one of the comparators 134-138, and the comparator's output
voltage switches polarity in response thereto, the comparator's
output polarity will remain in its new polarity state despite small
variations in the voltage signal (V.sub.116) about the reference
voltage. In this manner, small temperature fluctuations about a
temperature that represents a temperature range "boundary" of the
temperature measurement circuit 102 (e.g., about 28.degree. C.,
32.degree. C. or 36.degree. C.) will not cause the X and Y outputs
of the encoder circuit 108 to transition. The number of X and Y
output transitions thereby is reduced, as is the likelihood that
the controller 104 will read a transitorial and potentially false
voltage level on either the X or Y output during battery service
life estimation (described below). To further reduce potential
false voltage level readings by the controller 104, the X and Y
outputs of the encoder circuit 108 switch polarity using a "grey
code" scheme wherein only one of the X and Y outputs switches
polarity when a temperature range boundary is reached. Accordingly,
even if the controller 104 erroneously reads one of the X and Y
outputs before or while it transitions, and identifies an improper
temperature range based thereon, the improperly identified
temperature range will be within one temperature range of the
proper temperature range (e.g., minimizing the error). A grey code
scheme also eliminates any potential false readings by the
controller 104 due to differing switching rates of the X and Y
outputs of the encoder circuit 108.
[0028] The temperature-sensitive voltage signal (V.sub.116) remains
above the second and third reference voltages V.sub.126, V.sub.130
until a temperature of about 32.degree. C. when the
temperature-sensitive voltage signal (V.sub.116) no longer exceeds
the second reference voltage V.sub.126, but remains in excess of
the third reference voltage V.sub.130. With the first and second
reference voltages V.sub.122, V.sub.126 no longer exceeded, the
outputs of the first and second comparators 134, 136 are low while
the output of the third comparator 138 remains high. In response
thereto, the X output of the encoder circuit 108 is driven to zero
volts by the second comparator 136 while the Y output of the
encoder circuit 108 remains high (as the voltage levels that feed
the XOR gate 140 remain unchanged).
[0029] The temperature-sensitive voltage signal (V.sub.116) remains
above the third reference voltage V.sub.130 until a temperature of
about 36.degree. C. is reached. Thereafter, with no reference
voltage exceeded, the output of each comparator 134-138 is driven
low, as are the X and Y outputs of the encoder circuit 108. Because
the temperature-sensitive voltage (V.sub.116) continues to decrease
with increasing temperature, the X and Y outputs remain low for all
temperatures in excess of 36.degree. C.
[0030] In summary, the temperature measurement circuit 102 measures
a temperature of an operating environment of a battery (via the
thermistor 106) and outputs a signal (the X and Y outputs) that
represents a temperature range in which the measured operating
temperature resides. In the preferred embodiment of FIG. 1, an
embodiment specifically adapted for use with NiMH batteries, the
four temperature ranges in which a measured temperature may reside
(and the corresponding X and Y outputs from the encoder circuit
108) are listed in TABLE 3. It will be understood that the
temperature measurement circuit 102 may be configured for use with
other batteries and/or other or more temperature ranges if
desired.
3TABLE 3 TEMPERATURE RANGE (.degree. C.) Y OUTPUT X OUTPUT <28 0
1 about 28-32 1 1 about 32-36 1 0 >36 0 0
[0031] The controller 104 receives the X and Y outputs (e.g., the
temperature range signal) from the temperature measurement circuit
102 and estimates the service life of a battery based thereon (as
described below). Preferably the controller 104 comprises a
microcontroller or microprocessor such as an IBM PowerPC.TM. 403
processor having program code stored therein that performs battery
service life estimation functions. For example, the X and Y outputs
of the temperature measurement circuit 102 may be input by an
input/output (I/O) module 142 of the controller 104 (e.g., via I/O
pins (not shown) of an I/O port 144 of the controller 104). The
temperature range information encoded by the X and Y outputs (TABLE
3) then may be used by software (e.g., program code) within a
random access or read only memory (represented generally by
reference number 146) of the controller 104 for battery service
life estimation as described below. Alternatively, hardware (e.g.,
discreet counters, logic modules, application specific integrated
circuits, etc.) or a combination of hardware and software may be
similarly employed.
[0032] The operation of the controller 104 is now described with
reference to FIG. 1 and with reference to FIG. 2 which is a flow
chart of a preferred service life estimation algorithm 200. It is
assumed that a new battery such as a NiMH battery (not shown)
having its maximum service life remaining (e.g., 36 months for an
operating temperature of about 28.degree. C. or less) is monitored
by placing the thermistor 106 proximate the battery (e.g., on, next
to or sufficiently close to the battery to monitor the operating
environment temperature of the battery).
[0033] With reference to FIG. 2, in step 201, the service life
estimation algorithm 200 begins. In step 202, a counter is
initialized (e.g., is created and is set to zero) for each
temperature range to be monitored. For the preferred embodiment of
the service life estimation circuit 100 of FIG. 1, four temperature
ranges may be monitored as shown in TABLE 3 (e.g., less than about
28.degree. C., between about 28-32.degree. C., between about
32-36.degree. C. and greater than about 36.degree. C.).
Accordingly, four counters 148, 150, 152 and 154 are initialized
for (i.e., are associated with) the temperature ranges of less than
about 28.degree. C., between about 28-32.degree. C., between about
32-36.degree. C. and greater than about 36.degree. C.,
respectively. The counters 148-154 preferably are software-based,
8-byte counters defined within the memory 146 as is known in the
art. It will be understood that the spatial boundaries and
arrangement of the counters 148-154 in FIG. 1 are arbitrary and are
shown merely for convenience.
[0034] Following initialization of the counters 148-154, in step
203 the controller 104 waits or "sleeps" for a predetermined time
period (e.g., to allow the battery to age). The preferred sleep
period for the controller 104 is about 5 minutes although any other
time period (if any) may be employed.
[0035] In step 204, the temperature range signal (e.g., the X and Y
outputs) of the temperature measurement circuit 102 is sampled to
identify in which of the four temperature ranges the current
operating environment temperature of the battery resides (e.g.,
below about 28.degree. C., between about 28-32.degree. C., between
about 32-36.degree. C. or above about 36.degree. C.). Specifically,
program code within the memory 146 (represented in FIG. 1 as
estimation and processing code 156 for convenience) directs the I/O
module 142 to input the voltage levels of the X and Y inputs.
Thereafter, in step 205, the estimation and processing code 156
interprets these voltage levels in accordance with TABLE 3 to
determine in which temperature range the current operating
environment temperature of the battery resides. The counter
associated with the temperature range also is identified.
[0036] In step 206, the estimation and processing code 156 adds the
sleep time of the controller 104 (e.g., the time between
temperature samples) to the count of the counter associated with
the temperature range identified by the X and Y outputs of the
temperature measurement circuit 102. For example, if in step 205
the estimation and processing code 156 determines that the
operating environment temperature of the battery resides within the
temperature range from about 28.degree. C. to 32.degree. C. (e.g.,
because the X and Y outputs of the temperature measurement circuit
102 have high logic levels), the estimation and processing code 156
increases the count of the second counter 150 by the sleep time of
the controller 104 (e.g., by about 5 minutes).
[0037] In step 207, the estimation and processing code 156 computes
the total operation time of the battery by adding together the
count of each counter 148-154. To compensate for the decrease in
battery service life from its maximum value (e.g., 36 months for
NiMH batteries operated at about 28.degree. C. or less) that
accompanies battery operation at elevated temperatures, a pro-rate
factor is assigned to each counter 148-154 that weights the count
of each counter 148-154 based on the temperature range associated
with the counter. Specifically, the counts of counters having high
temperature ranges associated therewith (e.g., counters 152 and
154) are weighted more heavily than the counts of counters having
low temperature ranges associated therewith (e.g., counters 148 and
150) so that when the battery is operated at temperatures above
about 28.degree. C. the computed operating time of the battery
exceeds the actual operating time of the battery. The battery
thereby is aged more quickly when operated at higher temperatures.
Preferably, the pro-rate factor for the count of the first counter
148 (.sub.148) is 1.0, the pro-rate factor for the count of the
second counter 150 (C.sub.150) is 1.22, the pro-rate factor for the
count of the third counter 152 (C.sub.152) is 1.50 and the pro-rate
factor for the count of the fourth counter 154 (C.sub.154) is 1.83.
The pro-rated operation time (T.sub.PRORATED) of the battery
therefore is governed by equation (5) below:
T.sub.PRORATED'C.sub.138+1.22C.sub.150+1.5C.sub.152+1.83C.sub.154
(5)
[0038] In this manner, if a battery is operated at a temperature of
about 28.degree. C. or less, the battery is aged at its actual rate
(so that an effective service life of 35.75 months is employed for
the battery), but if the battery is operated at a temperature of
about 36.degree. C. or higher, the battery is aged at 1.83 times
its actual rate (so that an effective service life of 19.5 months
is employed for the battery). The battery is aged at an
intermediate rate for intermediate temperature operation. Further,
by including the time the battery is operated within each
temperature range during battery service life estimation, both the
present and the past operating environment temperatures of the
battery are considered during battery life estimation. Accordingly,
an accurate estimation of battery service life is computed even if
a battery is operated at several different operating environment
temperatures during its lifetime. Note that for a binary count,
pro-rate factors of 1.25, 1.5 and 1.875 may be obtained by
appropriate shifting and addition operations as will be apparent to
one of ordinary skill in the art (e.g., to generate 1.875X for a
count of X, the count X may be added to the count X shifted to the
right by 1 bit, shifted to the right by 2 bits and shifted to the
right by 3 bits).
[0039] In step 208, the estimation and processing code 156 compares
the pro-rated operation time of the battery to the maximum service
life of the battery (e.g., the service life of the battery if
operated at 28.degree. C. or less). If the pro-rated operation time
of the battery is less than the maximum service life of the
battery, control passes to step 203, and steps 203-207 are repeated
(e.g., the controller 104 sleeps, a new temperature range signal is
sampled, the controller sleep time is added to the appropriate
counter and the pro-rated operation time is computed). This process
is repeated until the pro-rated operation time exceeds the maximum
service life of the battery, after which time control passes to
step 209.
[0040] In step 209, the estimation and processing code 156
generates a signal (e.g., an alarm signal output by the I/O module
142 of the controller 104) to indicate that the service life of the
battery has been exceeded and that the battery should be replaced.
In step 210, the service life estimation algorithm 200 ends.
[0041] The foregoing description discloses only the preferred
embodiments of the invention, modifications of the above disclosed
apparatus and method which fall within the scope of the invention
will be readily apparent to those of ordinary skill in the art. For
instance, while the present invention has been described primarily
with reference to NiMH batteries, other battery technologies may
similarly benefit from the invention. Other temperature measurement
means than the thermistor 106 such as a silicon pn-junction diode
may be employed, as may other resistance values for the resistors
114-132, other temperature ranges and other pro-rate factors.
[0042] Accordingly, while the present invention has been disclosed
in connection with the preferred embodiments thereof, it should be
understood that other embodiments may fall within the spirit and
scope of the invention, as defined by the following claims.
* * * * *