Abstract:
A battery health or prognosis system may employ a ferrite disc embedded in a printed wiring board (PWB) to perform both a battery current sensing role and a temperature sensing role. The ferrite disc may be surrounded with a coil that may be comprised of surface conductors and electrically conductive vias of the PWB. Excursions of coil current may be produced to generate observable hysterisis loops in the ferrite disc. The generated hysterisis loops may be compared to a temperature-dependent family of hysterisis loops for the magnetic material from which the ferrite disc is constructed. A processor mounted on the PWB may collect and process outputs from a Hall-effect sensor to develop both temperature and battery current information to produce a prognosis for the battery.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention is generally in the field of assessment of condition of batteries and, more particularly, systems for sensing current to and from a battery over a period of time and for sensing temperature at which the current occurs. 
         [0002]    In some applications of batteries, such as automotive and aircraft power systems, a battery may provide continuous power at a low rate for some control systems. The same battery may also provide power at a high current rate for limited times for tasks such as engine starting. The battery may be in place within a vehicle for an extended time, during which time the vehicle may be exposed to varying environmental temperature. Recharging batteries may occur at low, so-called trickle rates and also at high current rates. 
         [0003]    A battery may have only a limited useful lifetime. Its useful lifetime may be limited by factors such as times and rates of discharge, times and rates of re-charge and amounts of time that a battery may be exposed to various temperatures. In particular, exposing a battery to low temperature may have the effect of shortening its useful lifetime. 
         [0004]    In many battery applications, battery health systems or prognosis systems may be employed to predict or determine if a battery may be capable of performing its high current tasks, such as engine starting, when needed. These prognosis systems may continuously collect data relating to rates of current discharge and/or re-charge and time periods over which these current rates occurred. Additionally, a typical battery prognostic system may continually collect data relating to times that a battery is exposed to any particular temperature. Such data may then be processed to provide a prediction of future useful life of the battery. 
         [0005]    In the past, battery prognosis systems were employed only in specialized vehicles such as high-risk military vehicles. As automotive and aircraft electrical system designs have evolved, battery prognosis systems are often used on more conventional vehicles such as civilian automobiles. In this regard, battery prognosis systems are being employed in ever increasing volumes. Consequently, manufacturing cost for such systems becomes an increasingly important consideration. 
         [0006]    Prior-art vehicular-battery prognosis systems may employ a current sensor and a separate temperature sensor. Use of two different sensors contributes to high cost and complexity of such prognosis systems. There are known techniques for measuring current and temperature with a single sensor (e.g. US Patent Application Publication 2005/0077890, R. Rannow et al). These known techniques, while combining two sensing functions in a single device, are nevertheless complex and expensive. As a result, these single sensor current/temperature measurement systems have not been employed in prior-art vehicular battery prognosis systems. 
         [0007]    Additionally, prior-art battery prognosis systems have employed sensors which are separate from processors and controls. In a typical prior-art system, a printed wiring board (PWB) may support processing and control functions while sensors are provided as devices separate from the PWB. 
         [0008]    As can be seen, there is a need to provide a battery prognosis system that may be produced at a low cost. Additionally there is a need to provide a system in which current sensing and temperature sensing may be combined in a single low cost device. Still further there is a need to provide such a system in which a sensor is integrated into a PWB on which processing and control is performed. 
       SUMMARY OF THE INVENTION 
       [0009]    In one aspect of the present invention, apparatus for determining battery prognosis comprises a ferrite disc having an axial opening through which a current carrying conductor of the battery passes, a Hall-effect sensor interposed within the ferrite disc, a coil surrounding the disc, a unit for varying current in the coil to produce observable variations in temperature dependent magnetic properties of the disc, and a processor for continually analyzing signals from the Hall-effect sensor to determine current in the conductor and to determine temperature as a function of variations in magnetic properties of the disc. 
         [0010]    In another aspect of the present invention, a battery condition detector comprises a PWB through which a conductor of the battery current passes, a ferrite disc surrounding the conductor of the battery, a coil surrounding the ferrite disc, a coil-current unit for varying current in the coil, a sensor producing an output that varies as function of the varying current in the coil and a processor comprising stored reference data relating to temperature dependent magnetic properties of the ferrite disc. The ferrite disc, the coil, the coil-current unit, the sensor and the processor are attached to the PWB. The processor receives varying output from the sensor responsive to the varying current in the coil; and compares the varying output from the sensor with the stored reference data to determine a temperature of the ferrite disc. 
         [0011]    In still another aspect of the present invention, a method for producing a prognosis for a battery comprises the steps of passing current from the battery though an opening in a ferrite disc, sensing magnetic reaction to the current from the battery, varying current in a coil surrounding the ferrite disc, sensing temperature-dependent magnetic reaction to the varying coil current, comparing the sensed magnetic reaction to coil current with processor-stored magnetic property data for the ferrite disc to determine temperature of the ferrite disc, and processing the determined temperature with the sensed magnetic reaction to battery current to produce a prognosis of the battery. 
         [0012]    These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a block diagram of a battery prognosis system in accordance with the present invention; 
           [0014]      FIG. 2  is a schematic plan view of the battery prognosis system of  FIG. 1  in accordance with the present invention; 
           [0015]      FIG. 3  is a sectional view of the battery prognosis system of  FIG. 2  taken along the section line  3 - 3  in accordance with the present invention; 
           [0016]      FIG. 4  is a graph portraying a relationship between initial permeability and temperature for a magnetic material in accordance with the present invention; 
           [0017]      FIG. 5  is a graph portraying a family of hysterisis loops for a magnetic material in accordance with the present invention; and 
           [0018]      FIG. 6  is a flow chart of a method for providing a battery prognosis in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
         [0020]    Broadly, the present invention may be useful in determining a state of health of an aircraft or automotive battery. More particularly, the present invention may provide a low-cost battery prognosis system. The present invention may be particularly useful in vehicles such as aircraft or automotive vehicles which produce a continuous drain on a battery even when the vehicle is not in an operating mode. 
         [0021]    In contrast to prior-art battery prognosis systems, which employ a first sensor for current and a second separate sensor for temperature, the present invention may provide a single low cost sensor for current and temperature. The present invention may employ a single sensing unit embedded in a printed wiring board to simultaneously determine current to and from the battery as well as a temperature at which such current occurs. Additionally, the present invention may provide a prognosis system in which processor, control and sensing functions may be incorporated on a single PWB, whereas prior-art prognosis systems are typically not integrated onto a single PWB. 
         [0022]    Referring now to  FIG. 1 , there is shown, in block diagram form, a battery condition detector or prognosis system  10  for a battery  12 . The system  10  may comprise a magnetic detector  14  and a processor  16 . The processor  16  may comprise an information storage unit  16 - 1  and a coil current unit  16 - 2 . A look-up table  16 - 3  may be incorporated into the processor  16 . The system  10 , in an illustrative embodiment, may be constructed on a printed wiring board (PWB)  20 . In operation, the system  10  may employ the magnetic detector  14  to continually sense data relating to current in a conductor  12 - 1  of the battery  12 . Additionally, the magnetic detector  14  may be employed to sense temperature data relating to a temperature of an environment in which the battery  12  may be located. Sensed temperature and current data may be collectively processed in the processor  16  to provide a continuous prognosis of the battery  12 . 
         [0023]    Referring now to  FIGS. 2 and 3 , detailed view of the magnetic detector  14  may be seen. The magnetic detector  14  may comprise a ferrite disc  22  which, in an illustrative embodiment, may be embedded within multiple layers  20 - 1 ,  20 - 2  and  20 - 3  of the PWB  20 . A Hall-effect sensor  24  may be positioned within a slot  22 - 1  formed in the ferrite disc  22 . The PWB  20  may be positioned so that the conductor  12 - 1  of the battery  12  may pass through an axial opening  22 - 2  in the ferrite disc  22 . 
         [0024]    A coil  30  may surround the ferrite disc  22 . The coil  30  may comprise surface conductors  30 - 1  which may be printed on the PWB  20 . Electrical Interconnections between the surface conductors  30 - 1  may be provided with electrically conductive vias  30 - 2  formed in the PWB  20 . The coil  30  may be connected to the coil current unit  16 - 2 . For purposes of simplicity, the coil  30  of  FIGS. 2 and 3  is shown with only a few turns around the ferrite disc  22 . It may be readily understood that the coil  30  may comprise any number of turns within the scope of the present invention. 
         [0025]    As current passes through the conductor  12 - 1 , magnetic field strength in the ferrite disc  22  may vary as a function of magnitude and direction of the current. Current magnitude and direction may be sensed by the Hall-effect sensor  24 . Data relating to current magnitude and direction may be transmitted to the storage unit  16 - 1  of the processor  16 . 
         [0026]    Additionally, magnetic flux density in the ferrite disc  22  may vary as a function of temperature to which the ferrite disc  22  may be exposed. A functional relationship between magnetic flux density and temperature may be determined for any particular magnetic material by observing a relationship between initial permeability and temperature for the material (See  FIG. 4 ). In the case of the present invention, magnetic material may be ferrite with a non-linear relationship between initial permeability and temperature. 
         [0027]    Referring now to  FIG. 5 , a graph  50  may portray various hysterisis loops for a non-linear ferrite material. A first loop  50 - 1  may portray how magnetic flux density in gauss (B) may vary with respect to magnetic field strength in oersted (H) at a temperature of 25° C. A second loop  50 - 2  may portray how B may vary with H at a temperature of 100° C. For any particular ferrite material that may be employed for the ferrite disc  22 , a family of such hysterisis loops may be determined and recorded in the processor  16  (e.g. in the look-up table  16 - 3 ). 
         [0028]    Referring now to  FIGS. 2 ,  3  and  5  it may be understood how current and temperature may be measured with the ferrite disc  22  and the Hall-effect sensor  24 . The coil current unit  16 - 2  may produce a bias current in the coil  30  so that the ferrite disc  22  does not become saturated from an overly large current in the conductor  12 - 1 . The magnitude and direction of the bias current may be determined as function of the magnitude and direction of current passing through the conductor  12 - 1 . 
         [0029]    In addition to providing a base bias current, the coil current unit  16 - 2  may produce brief current excursions. For example, if the coil current unit  16 - 2  were producing a base bias current at 1 ampere, the unit  16  may produce periodic current excursions of about plus and minus 0.1 amperes around the 1 ampere base bias current. Referring now particularly to  FIG. 5 , it may be seen that a current excursion may produce corresponding magnetic field strength changes and a resultant magnetic flux excursion in the ferrite disc  22 . Magnetic field strength H and magnetic flux density B may change in a predictable manner as a function of temperature (see for example graph lines  50 - 1  for a temperature of 25° C.). In other words, the current excursion produced by the coil current unit  16 - 2  may produce an observable hysterisis loop. 
         [0030]    The Hall-effect sensor  24  may vary its output responsively to the hysterisis loop and the processor  16  may translate the varied output into temperature data (e.g., by comparing sensed output of the Hall-effect sensor  24  with the look-up table  16 - 3  in the processor  16 ). 
         [0031]    The present invention may be performed with inexpensive and readily available ferrite materials. Inexpensive ferrite materials typically have a high degree of non-linearity between permeability and temperature. This non-linearity may make inexpensive ferrites undesirable for many applications. But the converse is true in the case of the present invention in that non-linearity is a desirable feature of the ferrite disc  22 . Low-cost ferrites may be employed and the prognosis system  10  may be produced at a low cost. 
         [0032]    Additionally, incorporation of the ferrite disc  22  into the PWB  20  may contribute to lowering of cost of the prognosis system  10  as compared to prior-art systems which may not be integrated on a single PWB. As described above, the processor  16 , and the magnetic detector  14  may be incorporated into a single one of the PWB&#39;s  20 . 
         [0033]    In one embodiment of the present invention, a method  600  is provided for determining a prognosis of a battery. Referring now to  FIG. 6 , it may be seen that in a step  602 , battery current may be passed through a ferrite disc (e.g., current from the battery  12  may pass through the conductor  12 - 1  which may be positioned in the axial opening  22 - 1  of the ferrite disc  22 ). In a step  604 , a resultant magnetic reaction to the current of step  602  may be sensed (e.g., the Hall-effect sensor  24  may respond to variations in magnetic field of the ferrite disc  22 ). In a step  606 , a bias current may be produced to preclude saturation of the ferrite disc (e.g., the coil current unit  16 - 2  may produce a base bias current in the coil  30  to prevent saturation of the ferrite disc  22 ). In a step  608 , current sensed in step  604  may be recorded (e.g., the current data from the Hall-effect sensor  24  may be recorded in the processor  16 ). 
         [0034]    In a step  610 , a current excursion may be produced in the bias current produced in step  606  (e.g., the coil current unit  16 - 2  may vary the bias current to a value slightly higher and then slightly lower than a base bias current). In a step  612 , a magnetic reaction to the bias current excursion of step  610  may be sensed (e.g., with the Hall-effect sensor  24 ). In a step  614 , A hysterisis loop produced by the bias current excursion of step  610  may be compared to magnetic data of the ferrite (e.g., the processor  16  may compare a resultant hysterisis loop such as  50 - 1  with the look-up table  16 - 3  that may contain stored hysterisis loops for the ferrite material from which the ferrite disc  22  is composed). In a step  616 , the comparison result of step  614  may be translated into temperature data (e.g., in the processor  16 . 
         [0035]    In a step  618  the temperature determined in the step  616 , may be recorded (e.g., in the processor  16 ). In a step  620  a battery prognosis may be produced, in a conventional manner, with data provided in steps  608  and  618  (e.g., in the processor  16 ). 
         [0036]    It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.