Abstract:
A system and method for monitoring the state of health of the connection between a generator and a battery includes detecting an interruption in power between the generator and the battery, incrementing a counter each time an interruption is detected, generating a trend of a number of interruptions over time based on a number of increments in the counter, monitoring a rate of increase in the number of interruptions over time and determining if the rate of increase in the number of interruptions over time is greater than a predetermined threshold.

Description:
BACKGROUND 
     1. Field of the Invention 
     This invention relates generally to monitoring the state of health of electrical connections and, more particularly, to detecting and prognosing electrical interconnection problems between an alternator and a battery. 
     2. Discussion of the Related Art 
     There is a constant effort in the automotive industry to improve the quality and reliability of vehicles by incorporating fault diagnosis and prognosis features into vehicles. Certain conditions, however, are more difficult to diagnose and predict than others, especially when the problems are intermittent. For example, the connections between a battery and an alternator are characteristically difficult to effectively monitor due to loosening connectors and/or corrosion that can cause anomalies to appear sporadically. 
     In addition, known techniques for monitoring the health of a battery or alternator are generally only capable of detecting a complete disconnection between the battery and alternator, not an intermittent or failing connection. Moreover, these techniques usually employ sophisticated signaling schemes that require additional hardware and that are difficult to implement on a vehicle due to the limited computational capacity of a vehicle&#39;s control unit. 
     Therefore, what is needed is a system and method for monitoring the state of health of the wiring between the battery and the alternator without adding additional hardware to the system. 
     SUMMARY 
     A system and method for monitoring the state of health of the connection between a generator and a battery includes detecting an interruption in power between the generator and the battery, incrementing a counter each time an interruption is detected, generating a trend of a number of interruptions over time based on a number of increments in the counter, monitoring a rate of increase in the number of interruptions over time and determining if the rate of increase in the number of interruptions over time is greater than a predetermined threshold. 
     Additional features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary connection diagram for a vehicle alternator, according to one embodiment; and 
         FIGS. 2A and 2B  are flow charts illustrating an exemplary algorithm for monitoring the health of the connections between a battery and an alternator, according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following discussion of the embodiments of the invention are directed a system and method for monitoring the health of the connections between a battery and a generator, such as an alternator. The aforementioned embodiments are merely exemplary in nature, and are in no way intended to limit the invention, its applications or uses. 
       FIG. 1  illustrates an exemplary connection diagram for a vehicle alternator  10 . The alternator  10  is connected to an automotive load  12  through a battery  14 . The automotive load  12  may include, for example, fans, lights and electronic control units (ECUs), to name a few. In one embodiment, the alternator  10  is connected to an ECU  16  through a two-pin control interface connector  18  mounted on the alternator  10 . The ECU  16  and the alternator  10  are connected by two control wires  20 ,  22  that terminate at the control interface connector  18  mounted on the alternator  10 . The first wire  20  provides a signal that sets the reference voltage V REF  for the output of the alternator  10 . The second wire  22  provides a signal to the ECU  16  that replicates the field voltage V FIELD  of the alternator  10  and is used by the ECU  16  to estimate the load  12 . In general, the field voltage V FIELD  is a pulse width modulated voltage that swings between an alternator output voltage V ALT  and ground. 
     The wiring (e.g., cable, etc.)  24  between the battery  14  and the alternator  10  is the primary connection monitored by the algorithm discussed herein. At one end  26 , the wire  24  terminates at the alternator  10  where the alternator output voltage V ALT  is measured. At the other end  28 , the wire  24  terminates on the battery  14  where the battery voltage V BATT  is measured. Although a break or disconnection may occur anywhere along wire  24 , the ends  26 ,  28  of the wire are where electrical disconnection, loosening connectors and/or contact resistance can increase due to corrosion. 
     The algorithm, discussed in detail below, is configured to monitor the health of wire  24  given two primary scenarios that describe the system behavior when an intermittent electrical connection causes an overvoltage condition on the alternator output terminal  26 . There are three measured quantities that are used to implement this algorithm, the field voltage V FIELD , the battery voltage V BATT  and the field voltage V FIELD  duty cycle. Each of these quantities is already measured by existing sensors and hardware. Thus, the implementation of the monitoring system and method disclosed herein requires no additional equipment. 
     The first scenario arises when the connection problem is severe enough to trigger an existing overvoltage protection scheme. Once triggered, the overvoltage protection causes the field voltage V FIELD  duty cycle to approach or become zero and the voltage measured at the battery V BATT  to drop from the nominal alternator output voltage V ALT , which is generally around 14 volts, to the actual battery voltage V BATT , which approximately 12.5 volts. 
     In the second scenario, the connection problem is not as severe and therefore does not trigger any overvoltage protection scheme. Instead, under these circumstances, the field voltage V FIELD  duty cycle does not approach or become zero and the peak of the field voltage V FIELD , which is the actual alternator output voltage V ALT , is different from the battery voltage V BATT . This scenario also applies to high impedance connections due to corroded contacts. 
       FIG. 2A  is a flow chart illustrating an exemplary algorithm  30  for monitoring the state of health of the connections between the battery  14  and the alternator  10 . Prior to initiating the algorithm, at step  32  certain preconditions are examined. In one embodiment, the preconditions include verifying that the vehicle&#39;s electronic control module is not unloading the engine and that there are no existing faults associated with either the reference voltage V REF  terminal or the field voltage V FIELD  terminal. If the preconditions are satisfied, algorithm  30  simultaneously detects conditions associated with each of the two scenarios discussed above. However, for ease of explanation, the methods for detecting conditions associated with each of the two scenarios will be discussed consecutively. 
     To detect the first scenario in which an overvoltage scheme is triggered, at step  34  the field voltage V FIELD  duty cycle and the battery voltage V BATT  are collected. At step  36 , algorithm  30  determines whether the field voltage V FIELD  duty cycle is less than a predetermined threshold, which is most cases, will be close to zero. If the field voltage V FIELD  duty cycle is not less than the threshold, the algorithm returns to the precondition stage at step  32 . If the field voltage V FIELD  duty cycle is less than the threshold, algorithm  30  determines at steps  38  and  40 , respectively, whether there was a significant change in the battery voltage V BATT  and how long the change lasted. Thus, at step  38  algorithm  30  determines if the battery voltage V BATT  at time=0 minus the battery voltage V BATT  at time=t 1  is greater than a first voltage threshold V THRESHOLDa . If the difference in the battery voltage V BATT  between the designated time period (i.e., t=0 to t=t 1 ) is not greater than V THRESHOLDa , the algorithm returns to the precondition stage at step  32 . If the difference in battery voltage V BATT  is greater than V THRESHOLDa , the algorithm  30  determines at step  40  if the time period for which there is a battery voltage V BATT  differential exceeds a predetermined time interval T INT . If the battery voltage V BATT  differential exceeds V THRESHOLDa  for longer than time interval T INT , then the alternator  10  has been completely disconnected from the battery  14 . Otherwise, if the battery voltage V BATT  differential has exceeded V THRESHOLDa  but not for longer than time interval T INT , the problem is intermittent and the algorithm will proceed to from the detection stage to an evaluation stage, which will be described in detail below. 
     To detect the second scenario in which the problem is not severe enough to trigger an overprotection scheme, algorithm  30  collects the field voltage V FIELD  and the battery voltage V BATT  at step  42 . At step  44 , the battery voltage V BATT  is subtracted from the field voltage V FIELD  to determine a voltage interrupt V INT . At step  46 , algorithm  30  determines if the voltage interrupt V INT  at time t is greater than a second voltage threshold V THRESHOLDb . If not, the algorithm returns to the precondition stage at step  32 . If yes, algorithm  30  determines at step  48  if the length of time the voltage interrupt V INT  is greater than voltage threshold V THRESHOLDb  exceeds a predetermined time interval T INT . If the time interval T INT  is exceeded, then the alternator  10  has been completely disconnected from the battery  14 . However, if the length of time the voltage interrupt V INT  is greater than voltage threshold V THRESHOLDb  does not exceed time interval T INT , the problem is intermittent and the algorithm will proceed to from the detection stage to an evaluation stage, which will be described in detail below. 
       FIG. 2B  is a flow chart illustrating the evaluation stage of algorithm  30 . The evaluation stage begins at step  50  where an intermittent measurement counter N is incremented by at least one negative condition at either steps  40  and  48 . In other words, if one or both of the conditions at steps  40  or  48  are not satisfied, counter N is incremented by one. 
     Next, at step  52  the number of interruptions and the rate of increase (dN/dt) for those interruptions is monitored and a trend over time is generated for the number of interruptions in accumulated in counter N. At step  54  algorithm  30  determines if the rate of increase of interruptions is greater than a predetermined threshold. If no, then the rate of intermittent interruptions is not yet considered significant enough to signal a warning and the algorithm returns to the precondition stage at step  32 . However, if the rate of intermittent events is beyond a predetermined threshold, a severe problem may be developing in the connection between the alternator  10  and the battery  14  and a warning is signaled. The signaling of a warning could be to the vehicle operator through an on-board flexible computing system such as OnStar™ or to a dealer. 
     The system described herein may be implemented on one or more suitable computing devices, which generally include applications that may be software applications tangibly embodied as a set of computer-executable instructions on a computer readable medium within the computing device. The computing device may be any one of a number of computing devices, such as a personal computer, processor, handheld computing device, etc. 
     Computing devices generally each include instructions executable by one or more devices such as those listed above. Computer-executable instructions may be compiled or interpreted from computer programs created using a variety of programming languages and/or technologies, including without limitation, and either alone or in combination, Java™, C, C++, Visual Basic, Java Script, Perl, etc. In general, a processor (e.g., a microprocessor) receives instructions, e.g., from a memory, a computer-readable medium, etc., and executes these instructions, thereby performing one or more processes, including one or more of the processes described herein. Such instructions and other data may be stored and transmitted using a variety of known computer-readable media. 
     A computer-readable media includes any medium that participates in providing data (e.g., instructions), which may be read by a computing device such as a computer. Such a medium may take many forms, including, but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, optical or magnetic disks and other persistent memory. Volatile media include dynamic random access memory (DRAM), which typically constitutes a main memory. Common forms of computer-readable media include any medium from which a computer can read. 
     It is to be understood that the above description is intended to be illustrative and not restrictive. Many alternative approaches or applications other than the examples provided would be apparent to those of skill in the art upon reading the above description. The scope of the invention should be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that further developments will occur in the arts discussed herein, and that the disclosed systems and methods will be incorporated into such further examples. In sum, it should be understood that the invention is capable of modification and variation and is limited only by the following claims. 
     The present embodiments have been particular shown and described, which are merely illustrative of the best modes. It should be understood by those skilled in the art that various alternatives to the embodiments described herein may be employed in practicing the claims without departing from the spirit and scope of the invention and that the method and system within the scope of these claims and their equivalents be covered thereby. This description should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. Moreover, the foregoing embodiments are illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application. 
     All terms used in the claims are intended to be given their broadest reasonable construction and their ordinary meaning as understood by those skilled in the art unless an explicit indication to the contrary is made herein. In particular, use of the singular articles such as “a”, “the”, “said”, etc. should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary.