Abstract:
A battery assembly for use in an aircraft. The battery assembly may include a battery and a circuit configured to monitor the battery in situ. The circuit may include at least one sensor positioned to sense at least one property of the battery and a processor in communication with the sensor. The battery assembly may also include a battery housing, wherein the battery and the circuit are positioned within the battery housing. A method for evaluating a battery in an electric device. The method may include collecting operational information from the battery. The operational information may be collected without removing the battery from the electric device. The method may also include comparing the operational information to a degradation routine describing a property of the battery and calculating a capacity of the battery.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 10/991,798 filed on Nov. 18, 2004, now U.S. Pat. No. 7,791,347 which is incorporated herein by reference in its entirety and also claims priority under 35 U.S.C. §119(e) to U.S. Patent Application Ser. No. 60/523,171 filed on Nov. 18, 2003, which is also incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Batteries today are used in a variety of applications by a variety of electric devices. For example, most aircraft require batteries to power both starter motors and auxiliary devices such as lights, avionics, etc. Traditional automobiles also require batteries for similar purposes. Even some modern automobiles, such as, for example, gas-electric hybrid and fuel cell automobiles rely on batteries to provide electric power for locomotion. These and other electric devices may use various kinds of batteries including, for example, lead acid batteries, nickel cadmium batteries, etc. 
     What is lacking in the art, however, is the capability to determine the capacity and remaining charge of a battery without removing the battery from its electric device. Accordingly, there is a need for a battery assembly including a circuit or smart chip for monitoring the battery. Also, there is a need for methods of monitoring the capacity and remaining charge of a battery as well as methods for predicting premature battery failure. 
     SUMMARY OF THE INVENTION 
     One embodiment of the present invention relates to a battery assembly for use in an aircraft. The battery assembly may include a battery and a circuit configured to monitor the battery in situ. The circuit may include at least one sensor positioned to sense at least one property of the battery and a processor in communication with the sensor. The battery assembly may also include a battery housing, wherein the battery and the circuit are positioned within the battery housing. 
     Another embodiment of the present invention relates to a method for evaluating a battery in an electric device. The method may include collecting operational information from the battery. The operational information may be collected without removing the battery from the electric device. The method may also include comparing the operational information to a degradation routine describing a property of the battery and calculating a capacity of the battery. 
     Another embodiment of the present invention relates to a method for evaluating a battery. The method may include finding an indicator of the battery&#39;s age and deriving a first value of a first discharge function factor from a discharge function describing the battery. The deriving may be based on the indicator. The method may also include calculating a capacity of the battery, wherein the calculating is based on the first value. 
     Another embodiment of the present invention relates to a method for evaluating a battery. The method may include sensing a voltage of the battery and monitoring fluctuations in the rate of change of the voltage. The method may also include comparing the fluctuations to at least one voltage decay profile for the battery and determining a remaining charge of the battery based on the comparing. 
     Unless otherwise indicated, all numbers expressing quantities of electrical values, time, temperatures and so forth used in the present specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. 
     The reader will appreciate the foregoing details and advantages of the present invention, as well as others, upon consideration of the following detailed description of embodiments of the invention. The reader also may comprehend such additional details and advantages of the present invention upon making and/or using embodiments within the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1A  is a front view of a battery assembly according to various embodiments; 
         FIG. 1B  is a top view of a portion of a battery assembly according to various embodiments; 
         FIG. 2  is a block diagram of a system for monitoring a battery according to various embodiments; 
         FIG. 3  is a flow chart of a method for monitoring a battery according to various embodiments; 
         FIG. 4  is a chart of discharge functions of a battery according to various embodiments; 
         FIG. 5  is a flow chart of a method for monitoring a battery according to various embodiments; 
         FIG. 6  is a flow chart of a method for monitoring a battery according to various embodiments; and 
         FIG. 7  is a flow chart of a method for monitoring a battery according to various embodiments. 
     
    
    
     DESCRIPTION 
     It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, other elements. Those of ordinary skill in the art will recognize, however, that these and other elements may be desirable. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. 
     In various embodiments, the present apparatus, assemblies, devices methods and systems may be used in an aviation setting to comply with Federal Aviation Administration (FAA) requirements. For example, aspects of the present invention may be used to comply with FAA&#39;s requirement that the capacity of aircraft batteries be checked at periodic intervals. It is also envisioned that the present apparatus, methods and systems may be used in any other setting in which a battery is desirable. 
       FIG. 1A  shows a battery assembly  100  according to various embodiments of the present invention. The battery assembly  100  may include a case  104 , a cover  102  and a lid  110 . A battery and monitoring circuit (not shown) may be housed within the assembly  100 . Terminal pins  106  may facilitate an electrical connection between the battery assembly  100  and a load to be powered by the battery. Also, data port  108  may provide an electrical connection to the battery monitoring circuit. 
     The battery assembly  100  may be adapted for use in various electric devices in a variety of applications. For example, the battery assembly  100  may be used in aviation applications as a starter battery or an auxiliary battery. When the battery assembly  100  is used in aviation applications, terminal pins  106  may be connected to an aircraft using quick-disconnect connectors, for example those made by REBLING and/or CANNON. In other various embodiments, the battery assembly  100  may be used in automotive applications as either a starter battery or an auxiliary battery. It is envisioned that the battery assembly  100 , as well other embodiments of the apparatus and methods of the present invention, can be adapted to any application requiring the use of a battery, and may incorporate any kind of battery including, for example, a lead acid battery, a nickel cadmium battery, an alkaline battery, etc. 
       FIG. 1B  shows an interior view of the cover  102  of the battery assembly  100  according to various embodiments. Terminal pins  106  are shown in the lower central area of the cover  102 . An inset  130  in the cover  102  may house a battery monitoring circuit  120 . The battery monitoring circuit  120  may include a processor  124  and memory  126 . Data port  108  may be electrically connected to the battery monitoring circuit  120  and may protrude through the cover  102  of the battery assembly through aperture  128 . 
     The battery monitoring circuit  120  may be electrically connected to one or more sensors  122 ,  132 , and  134 . The sensors  122 ,  132  and  134  may sense properties of the battery. Sensors  132  may sense a voltage across the terminal pins  106 . Sensor  122  may sense a current delivered through the terminal pins  106 . In various embodiments, sensor  122  may be a Hall effect sensor and may be placed parallel to the axis of the terminal pins  106 . Sensor  134  may sense the temperature of the battery. The sensor  134  may be mounted on the battery monitoring circuit  120  as shown or in other various embodiments may be mounted at other locations within the battery assembly  100 . 
     In various embodiments the portion of the cover  102  including the circuit  120 , sensors  122 ,  132 ,  134  and other components may be potted with a filling material to prevent damage due to heat or other elements. The filling material may be any suitable material known in the art, for example, epoxy. 
       FIG. 2  shows a block diagram of a system  200  for monitoring a battery  204  according to various embodiments. The system  200  may include a battery monitoring circuit  202  or smart chip. The battery monitoring circuit  202  may include a processor  206  and memory  208 . The battery monitoring circuit  202  may also include various sensors including, for example, a current sensor  210 , a voltage sensor  212  and a temperature sensor  214 . The circuit  202  may also include a data port  216 . The data port  216  may allow the circuit  202  to communicate with various external processing devices  218 ,  220 ,  222 . Communication between the data port  216  and the external processing devices  218 ,  220 ,  222  may be configured according to any acceptable wired or wireless protocol including, for example, a serial communication protocol, such as the USB protocol, a parallel communication protocol, a wireless communication protocol such as the BLUETOOTH protocol, etc. The external processing devices may include, for example, a personal digital assistant  218 , a personal computer  220 , a laptop computer  222 , or other functionally suitable devices. 
     In various embodiments, the system  200  may collect and analyze operational data or information from the battery  204 , e.g., current, voltage, temperature, etc. For example, operational data may be collected from sensors  210 ,  212 ,  214  and stored at memory  208 . The processor  206  may perform analysis of the operational data. In various embodiments, the circuit  202  may monitor the life stage of the battery, e.g., the number of starts and/or cycles as discussed below. 
     Additional data storage and analysis may be performed by external processing devices  218 ,  220 ,  222 . In various embodiments, circuit  202 , including processor  206  and memory  208 , may gather and store operational data that may be uploaded to one or more external processing devices  218 ,  220 ,  222  for analysis. Also, in various embodiments, operational information may be gathered, stored and analyzed in situ, without removing the battery  204  from its electric device. 
     Analysis of the operational data, by processor  206  or one or more external processing devices  218 ,  220 ,  222 , may yield information about the state of the battery  204  including, for example, the number of starts that the battery  204  has performed, the number of charge/discharge cycles that the battery  204  has gone through, the capacity of the battery  204 , whether the battery  204  is near failure, and other like information. 
     In various embodiments, the circuit  202  may also be in communication with an instrument panel  224  of the electric device. For example, if the electric device is an aircraft or automobile, the instrument panel  224  may be in a cockpit or driver seating area. The circuit  202  may provide the instrument panel  224  with, for example, any of the capacity, charge and premature failure data described herein. 
     In various embodiments, the system  200  may provide information regarding the capacity of a battery. A battery&#39;s capacity, expressed in Amp-hours (Ah), for example, may be a measure of the current that the battery is capable of delivering and the discharge time over which the battery is capable of delivering it. The discharge time may be the time over which the battery is capable of delivering a current before the battery voltage drops below a predetermined level. For example, a battery cell providing 2 volts may be considered discharged when its voltage drops below 1.67 volts while under load. Referring back to capacity, a battery with a capacity of 3 Ah may deliver 1 Amp over a discharge time of three hours, 3 Amps over a discharge time of one hour, etc. In various embodiments, the capacity of a battery may be expressed as the hours of discharge at a given current, or the current that the battery can support over a given discharge time. 
     In various embodiments, the capacity of a battery may be modeled according to a degradation routine such as a discharge function. A discharge function may mathematically express the various chemical and electrical factors affecting the battery&#39;s capacity. Batteries with different chemical and electrical configurations may have different discharge functions. For example, the capacity of some lead acid batteries may be expressed by the Peukert equation as follows:
 
I n t=K  (1)
 
where I is the current delivered by the battery; t is the time over which the current may be delivered during discharge; and n and K are constants over similar ranges of discharge conditions. The factors n and K may be referred to as discharge function factors and may be dependent on the battery&#39;s age as described below.
 
     A battery&#39;s age may be expressed in a variety of forms, for example, the number of charge and recharge cycles that the battery has gone through in its lifetime. The age of a battery may also be expressed as a number of starts. Each start may refer to one instance where the battery has delivered a very high load, such as, for example, starting an internal combustion engine. In various embodiments, an equivalency may be developed to express a given number of starts that degrade the battery similar to an equivalent number of cycles. In various embodiments, the circuit  202  of the system  200  may sense the number of starts that battery provides and derive the battery&#39;s age as an equivalent number of cycles. 
       FIG. 3  shows a flowchart of a process flow  300  for developing a model of a battery&#39;s discharge function considering the battery&#39;s age according to various embodiments. At step  302 , the battery may be discharged at a first current value when the battery is at a first stage of its life. A first discharge time representing the time required to discharge the battery at the first current value may be recorded at step  304 . At step  306 , the battery may be recharged. The battery may be discharged again at step  308 , though at a second current value. A second discharge time representing the time required to discharge the battery at the second current value may be recorded at step  310 . In various embodiments, the discharging of steps  302  and  308  may be carried out in consecutive cycles of the battery to insure that the measurements at steps  304  and  310 , as nearly as possible, are taken at the same point of the battery&#39;s life. 
     At step  312 , discharge equation factors may be calculated for the first stage of the battery&#39;s life. For example, if the discharge function of the battery is described by the Peukert equation, shown above in Equation 1, then the values for K and n may be found by inserting the first current and the first discharge time into one instance of Equation 1, inserting the second current and the second discharge time into a second instance of Equation 1 and then solving for K and n using the set of two independent equations. 
     The process flow  300  may show the steps necessary to model a battery, such as, for example, a lead acid battery, described by the Peukert equation, or another function having two factors depending on battery age. It will be appreciated that certain steps may be omitted and/or added to the process flow  300  when different batteries having different discharge functions are modeled depending, for example, on the number of discharge function factors. 
     At step  314 , the steps  302 - 312  may be repeated at various stages of the battery&#39;s life. This may yield data representing the discharge function of the battery, and values for the factors of the discharge function, at different stages in the battery&#39;s life. At step  316  distributions of discharge function factors may be found as a function of the battery&#39;s age. In various embodiments, the distributions may take the form of look-up tables showing the values of the discharge function factors corresponding to battery age, for example, a given number of battery cycles. In various other embodiments, the distributions may be expressions of the discharge function factors as a function of battery age. The expressions may be derived by any suitable method including, for example, linear regression, partial least squares, etc. 
       FIG. 4  shows a chart  400  of an example of the discharge function of a valve regulated lead acid battery at different stages of its life according to various embodiments. The chart  400  is a log-log chart as is known in the art. The discharge functions show discharge rate (axis  404 ) as a function of discharge time (axis  402 ). The curves  406 ,  408 ,  410 ,  412  show the discharge function of the battery at various stages of its life. For example, curve  406  shows the discharge function of the battery at zero cycles, curve  408  at 100 cycles, etc. Chart  400  may demonstrate the change in a battery&#39;s discharge function over its life. 
       FIG. 5  shows a flowchart of a process flow  500  for finding a battery&#39;s capacity according to various embodiments. At step  502 , an indicator of the battery&#39;s age may be found. The indicator may be, for example, a number of cycles, a number of starts, etc. At step  504 , discharge function factors for the battery may be derived based on the indicator of the battery&#39;s age. For example, the discharge function factors may be derived with the use of a look-up table showing values for discharge function factors at different battery ages. In various embodiments, the discharge function factors may be derived using a mathematical expression describing the factors as a function of battery age. 
     If, for example, the battery is a lead-acid battery whose discharge function may be described by Equation 1 above, then the discharge function factors may be K and n as described above. It can be appreciated that other kinds of batteries described by other discharge functions may require the derivation of different discharge function factors. 
     At step  506 , the capacity of the battery may be calculated, for example, using the discharge function describing the battery and the discharge function factors found at step  504 . For example, if the battery is a lead-acid battery whose discharge function is described by Equation 1 above, then the discharge function factors K and n may be used. The capacity of the battery may, in various embodiments, be expressed in Amp-hours, as the discharge time at a particular current level, or as the one-hour rate. 
     In certain situations, it may be desirable to find a second reading of a battery&#39;s remaining charge in addition to or instead of a reading derived from battery&#39;s capacity. For example, a battery may fail prematurely before the time predicted by its capacity if, for example, it has a defect or has been subjected to an abnormal load. Monitoring a battery&#39;s voltage decay under load over time may provide a second reading of the battery&#39;s remaining charge according to various embodiments. The battery&#39;s voltage decay under load may be compared to various degradation routines in the form of voltage decay profiles. In various embodiments, the system  200  may monitor a battery&#39;s voltage decay under load exclusively. 
       FIG. 6  shows &amp; flowchart of a process flow  600  for developing a voltage decay profile of a battery according to various embodiments. At step  602 , battery voltage fluctuations may be monitored during a first failure of the battery. In various embodiments, fluctuations in the rate of change of battery voltage may be particularly monitored. The first failure of the battery may be, for example, a premature failure due to a defect in the battery, the result of the battery reaching the end of its charge, etc. At step  604 , a voltage decay profile of the first failure may be derived. It can be appreciated that the steps  602  and  604  may be repeated to derive voltage decay profiles for a variety of different battery failures, for example, caused by a variety of different factors. 
       FIG. 7  shows a flowchart of a process flow  700  for determining the remaining charge of a battery according to various embodiments. At step  702 , fluctuations in battery voltage may be monitored. The fluctuations may be compared to one or more voltage decay profiles at step  704 . Based on the comparison, it may be determined whether the battery is near a failure at step  706 . 
     One skilled in the art will appreciate that the capacity and/or remaining charge of a battery may be affected by the battery&#39;s temperature. For example, if the experimental data describing discharge function factors in terms of the battery&#39;s age, e.g., as shown in  FIG. 3 , or the derivation of voltage decay profiles as shown in  FIG. 6  were taken at a first temperature, then they may not accurately describe a battery operating at a second temperature. Accordingly, the circuit  202  and/or the external processing devices  218 ,  220 ,  222  may correct the capacity or the voltage decay profiles for effects due to temperature. 
     The benefits of the present apparatus, methods and systems are readily apparent to those skilled in the art. The various embodiments described herein may provide representations of the capacity, the remaining charge, or the likelihood of failure of a battery. Various portions and components of various embodiments of the present invention, for example processes to be executed by circuit  202  or external processing devices  218 ,  220 ,  222  may be implemented in computer software code using any suitable language, for example, Visual Basic, C, C++, or assembly language using, for example, standard or object-oriented techniques. 
     While several embodiments of the invention have been described, it should be apparent, however, that various modifications, alterations and adaptations to those embodiments may occur to persons skilled in the art with the attainment of some or all of the advantages of the present invention. It is therefore intended to cover all such modifications, alterations and adaptations without departing from the scope and spirit of the present invention as defined by the appended claims.