Abstract:
There is described a method of diagnosing a motor vehicle battery, wherein, at each start-up of the vehicle engine, a number of parameters, related to the pattern of an electric quantity supplied by the battery during a transient start-up state of the engine, are recorded; and the recorded parameters are then memorized to create a database which is used to determine the charge status of the battery.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method of diagnosing a motor vehicle battery.  
           [0003]    2. Description of the Related Art  
           [0004]    As is known, like any other component, batteries supplying the electrical power required for normal operation of a vehicle, such as a car, are subject, with use, to deterioration and malfunctioning. A faulty battery may be incapable of starting the engine or adequately powering all the connected user devices, which therefore operate poorly. Very often, a vehicle equipped with a battery in poor condition cannot be run at all, and, since the user is normally unable to predict malfunctioning of the battery, no servicing is carried out until a fault actually occurs.  
           [0005]    By way of a solution to the problem, diagnosis methods have been devised to determine the charge status of the battery and signal any anomalous operating conditions, so that appropriate servicing may be carried out in time. More specifically, the diagnosis methods devised so far are based on measuring the internal resistance of the battery, which, as is known, is related to various factors, including ageing and the charge of the battery. That is, internal resistance is measured in predetermined battery conditions, is compared with a nominal reference value, and, if a significant difference is detected, an alarm signal is generated.  
           [0006]    Known methods, however, have several drawbacks. For the necessary measurements to be made, the battery and/or control unit supervising operation of the engine must be equipped with sensors. More specifically, to measure the internal resistance of the battery, both a voltage and a current sensor are required, whereas one sensor would be more preferable. Using two sensors not only increases cost but also increases the risk of malfunctioning and reduces reliability.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    It is an object of the present invention to provide a diagnosis method designed to eliminate the aforementioned drawbacks, and which, in particular, can be implemented using simpler equipment.  
           [0008]    According to the present invention, there is provided a method of diagnosing a battery of a motor vehicle, characterized by comprising the steps of:  
           [0009]    determining, at each start-up of the engine of said vehicle, a number of parameters related to the pattern of an electric quantity supplied by said battery during a transient start-up state of said engine;  
           [0010]    storing said parameters to create at least one database; and  
           [0011]    determining a charge status of said battery using said database.  
           [0012]    According to a further aspect of the invention, the electric quantity is the voltage supplied by the battery.  
           [0013]    Since the method according to the invention provides for determining the charge status of the battery on the basis of a single electric quantity, namely the battery voltage, the equipment by which to implement the method calls for only a voltage sensor, and no current sensors, which is clearly an advantage not only in terms of cost but also in terms of reliability by reducing the risk of operating defects. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    A non-limiting embodiment of the invention will be described by way of example with reference to the accompanying drawings, in which:  
         [0015]    [0015]FIG. 1 shows a simplified block diagram of equipment implementing the diagnosis method according to the present invention;  
         [0016]    [0016]FIG. 2 shows a graph of a quantity relating to the FIG. 1 equipment;  
         [0017]    [0017]FIG. 3 shows a flow chart of the diagnosis method according to the present invention;  
         [0018]    [0018]FIG. 4 shows a graph of quantities relating to the diagnosis method according to the present invention;  
         [0019]    [0019]FIG. 5 shows a more detailed block diagram of part of the FIG. 1 equipment;  
         [0020]    [0020]FIGS. 6 and 7 show ranges of quantities relating to the diagnosis method according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    [0021]FIG. 1 shows schematically a vehicle engine  1  (vehicle not shown) connected to terminals  2   a  of a battery  2  supplying a battery voltage V B . For the sake of simplicity, the electrically powered devices of the vehicle are not shown in detail in FIG. 1, but are all considered included in engine  1 . A control unit  3 , comprising a voltage sensor  5 , a processing unit  6 , and a memory  7 , is connected to both engine  1  and battery  2 . More specifically, voltage sensor  5  has inputs connected to terminals  2   a  of battery  2  to receive battery voltage V B , and an output connected to processing unit  6 . In other words, sensor  5  measures the instantaneous battery voltage V B  value, and supplies it to processing unit  6 .  
         [0022]    Processing unit  6  has inputs  6   a  receiving a number of operating parameters, such as cylinder intake air temperature T A  and cooling water temperature T W , and an output connected to engine  1  to supply a number of control signals S C , and is two-way connected to memory  7  to read and write data as required.  
         [0023]    [0023]FIG. 2 shows the pattern of battery voltage V B  in a transient startup state of engine  1 . Just before start-up, battery voltage V B  has a stable initial value V I , on account of battery  2  supplying substantially no current. When engine  1  is started up, the user devices connected to battery  2  simultaneously draw high start-up currents, so that the battery is temporarily unable to maintain the initial value V I  of voltage V B , which falls more or less instantaneously to a minimum value V MIN . More specifically, at this stage, there is a voltage drop of V D =V I −V MIN . The battery voltage V B  value then rises, exceeds initial value V I , and settles to oscillate about a steady-state value V R  normally higher than initial value V I . More specifically, battery voltage V B  passes from minimum value V MIN  to initial value V I  within a rise time  T     R   .  
         [0024]    According to observations made by the inventors, initial value V I , voltage drop V D , and rise time  T     R    are operating parameters related to the charge status of battery  2 . That is, for each of the above operating parameters, normal-charge and prealarm-charge ranges can be identified. When the charge status of the battery is normal, variations in the three parameters remain within respective normal-charge ranges between one vehicle mission and the next; whereas, conversely, at least one of them drifts outside the normal-charge or even the prealarm-charge range.  
         [0025]    Moreover, initial value V I , minimum value V MIN , and rise time  T     R    are strongly affected by the operating conditions of engine  1 , in particular air temperature T A  and water temperature T W , so that different operating conditions of engine  1  and battery  2 , defined by respective sets of air temperature T A  and water temperature T W  values, can be identified. More specifically, each operating condition corresponds to a respective predetermined region Z 1 , Z 2 , . . . , Z M  in a T A T W  diagram, as shown by way of example in FIG. 4.  
         [0026]    With reference to FIG. 3, when engine  1  is started up, control unit  3  is initialized by setting a status register ST relative to the charge status of battery  2  to an initializing value, e.g. a normal-charge value NORM (block  100 ).  
         [0027]    The initial battery voltage value V I  just before start-up of engine  1  is then acquired (block  105 ), and is preferably calculated as the average of a predetermined number of battery voltage V B  readings made by voltage sensor  5  before engine  1  is started up.  
         [0028]    When the engine is started up, minimum value V MIN  and rise time  T     R    are acquired successively (block  110 ), voltage drop V D =V I −V MIN  is calculated (block  115 ), and processing unit  6  acquires air temperature T A  and water temperature T W  (block  120 ).  
         [0029]    Initial value V I , voltage drop V D , and rise time  T     R    are then memorized in memory  7  (block  125 ). More specifically, memory  7  contains a number of tables  10 . 1 ,  10 . 2 , . . . ,  10 .M (FIG. 5), each associated with a respective operating condition of engine  1 , i.e. with a respective region Z 1 , Z 2 , . . . , Z M  in the T A T W  diagram; and each operating condition, as stated, is defined by a respective set of air temperature T A  and water temperature T W  values. At the first start-up, i.e. when battery  2  is new and used for the first time, tables  10 . 1 ,  10 . 2 , . . . ,  10 .M are empty, and one of them is incremented at each subsequent start-up. At this stage, one of tables  10 . 1 ,  10 . 2 , . . . ,  10 .M corresponding to the present operating condition of engine  1 , i.e. to the measured air temperature T A  and water temperature T W  values, is selected, and initial value V I , voltage drop V D , and rise time  T     R    of battery voltage V B  are entered into the selected table  10 . 1 ,  10 . 2 , . . . ,  10 .M.  
         [0030]    Initial value V I , voltage drop V D , and rise time T R  are then processed and compared with the content of the selected table  10 . 1 ,  10 . 2 , . . . ,  10 .M (block  130 ). More specifically, a first, second, and third variation index IV 1 , IV 2 , IV 3 , relative to initial value V I , voltage drop V D , and rise time  T     R    respectively, are calculated on the basis of the difference between each of the three operating parameters measured at start-up of engine  1 —here indicated by a time index K—and the corresponding operating parameter last measured at start-up under the same operating conditions (here indicated by a time index K−1). In other words, the operating parameter values to be subtracted to calculate variation indexes IV 1 , IV 2 , IV 3  are the latest memorized in the selected table  10 . 1 ,  10 . 2 , . . . ,  10 .M, so that:  
           IV   1 ( K )= V   I ( K )− V   I ( K− 1)  
           IV   2 ( K )= V   MIN ( K )− V   MIN ( K− 1)  
           IV   3 ( K )= T     R   ( K )− T     R   ( K− 1)  
         [0031]    The initial value V I , voltage drop V D , and rise time  T     R    recorded at start-up of engine  1  are therefore correlated with historic data memorized previously under the same operating conditions. A check is then made to determine whether variation indexes IV 1 , IV 2 , IV 3  exceed, in absolute value, respective first-level warning thresholds SW I-1 , SW I-2 , SW I-3 , which are preferably calibratable (block  135 ). That is, a respective normal variation range INTV 1 , INTV 2 , INTV 3 , ranging between limits symmetrical with respect to zero (FIG. 6), is determined for each variation index IV 1 , IV 2 , IV 3 . Alternatively, asymmetrical normal variation ranges may also be determined.  
         [0032]    If at least one of first, second, and third variation indexes IV 1 , IV 2 , IV 3  exceeds the respective first-level warning threshold SW I-1 , SW I-2 , SW I-3 , i.e. is outside the respective normal variation range INTV 1 , INTV 2 , INTV 3  (YES output of block  135 ), a further test is performed (block  140 ) to determine whether a respective first-level alarm threshold SA I-1 , SA I-2 , SA I-3  is also exceeded (again in absolute value). First-level alarm thresholds SA I-1 , SA I-2 , SA I-3  are also calibratable and higher than respective first-level warning thresholds SW I-1 , SW I-2 , SW I-3 . In other words, warning variation ranges INTVW 1 , INTVW 2 , INTVW 3 , symmetrical with respect to zero and comprising respective normal variation ranges INTV 1 , INTV 2 , INTV 3 , are defined. In this case, too, the warning variation ranges may also be asymmetrical.  
         [0033]    If at least one of variation indexes IV 1 , IV 2 , IV 3  exceeds the respective first-level warning threshold SW I-1 , SW I-2 , SW I-3 , i.e. is also outside the respective warning variation range INTVW 1 , INTVW 2 , INTVW 3  (YES output of block  140 ), the status register ST is set to a first alarm value W 1  (block  145 ) indicating a serious malfunction calling for immediate attention. That is, at least one of initial value V I , voltage drop V D , and rise time  T     R    has shown a sharp variation with respect to previously recorded values, thus indicating malfunctioning of battery  2 . Conversely, if none of variation indexes IV 1 , IV 2 , IV 3  exceeds the respective first-level alarm threshold SA I-1 , SA I-2 , SA I-3  (i.e. if variation indexes IV 1 , IV 2 , IV 3  are all within respective warning variation ranges INTVW 1 , INTVW 2 , INTVW 3 , but at least one is outside respective normal variation range INTV 1 , INTV 2 , INTV 3 —NO output of block  140 ), the status register ST is set to a second alarm value W 2  (block  150 ) indicating battery  2  has suddenly shown signs of deterioration, though still with a certain margin of safety. In both the cases described, however, an anomalous charge status of battery  2  is indicated.  
         [0034]    If variation indexes IV 1 , IV 2 , IV 3  are all below respective first-level warning thresholds SW I-1 , SW I-2 , SW I-3 , i.e. are within respective normal variation ranges INTV 1 , INTV 2 , INTV 3  (NO output of block  135 ), respective drift indexes ID 1 , ID 2 , ID 3  of interval N, where N is a whole number, e.g.  10 , are calculated (block  155 ) for initial value V I , voltage drop V D , and rise time  T     R   . In this case, from the currently recorded initial value V I , voltage drop V D , and rise time  T     R   , are subtracted the corresponding values memorized at a distance of N locations in the selected table  10 . 1 ,  10 . 2 , . . . ,  10 .M, i.e. the corresponding operating parameters recorded N start-ups before the last, in the same operating conditions (i.e. with the same air temperature T A  and water temperature T W  values). That is:  
           ID   1 ( K )= V   I ( K )− V   I ( K−N )  
           ID   2 ( K )= V   D ( K )− V   D ( K−N )  
           ID   3 ( K )= T     R   ( K )− T     R   ( K−N )  
         [0035]    In this case, too, since all the values involved are taken from the same selected table  10 . 1 ,  10 . 2 , . . . ,  10 .N, the processed values are acquired under the same operating conditions of engine  1  and battery  2 .  
         [0036]    Processing unit  6  then determines (block  160 ) whether at least one of drift indexes ID 1 , ID 2 , ID 3  exceeds a respective calibratable second-level warning threshold SW II-1 , SW II-2 , SW II-3 , so as to determine, for each drift index ID 1 , ID 2 , ID 3 , a normal drift range INTD 1 , INTD 2 , INTD 3  ranging between limits symmetrical with respect to zero.  
         [0037]    If drift indexes ID 1 , ID 2 , ID 3  are all below respective second-level warning thresholds SW II-1 , SW II-2 , SW II-3 , i.e. are within respective normal drift ranges INTD 1 , INTD 2 , INTD 3  (NO output of block  160 ), the status register ST is set to the normal operation value NORM to indicate normal operation of battery  2  (block  165 ). Conversely (YES output of block  160 ), a further test is performed to determine whether at least one of drift indexes ID 1 , ID 2 , ID 3  also exceeds a respective calibratable second-level alarm threshold SA II-1 , SA II-2 , SA II-3 , i.e. is outside a respective warning drift range INTDW 1 , INTDW 2 , INTDW 3  (block  170 ). In this case, too, warning drift ranges INTDW 1 , INTDW 2 , INTDW 3  range between limits symmetrical with respect to zero, but may also be asymmetrical.  
         [0038]    If the above condition is confirmed (YES output of block  170 ), the status register ST is set to a third alarm value W 3  indicating serious ageing of battery  2  (block  175 ). In fact, even though none of the operating parameters has undergone significant variations over the last N start-ups of engine  1 , more gradual deterioration of battery  2  may give rise to variations always of the same sign, so that, over a prolonged period of time, drift of one or more of the operating parameters indicates operation of battery  2  is gradually worsening. If the test condition of block  170  is not confirmed (NO output of block  170 ), the status register ST is set to a fourth alarm value W 4  (block  180 ) indicating initial deterioration: the charge status of battery  2  is not perfect, but there is still a certain margin of safety. In both cases, however, an anomalous charge status of battery  2  is indicated.  
         [0039]    The procedure is then terminated (block  185 ).  
         [0040]    Clearly, changes may be made to the method as described herein without, however, departing from the scope of the present invention.