Method of diagnosing a motor vehicle battery based on parameters related to an electric quantity supplied by the battery

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.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of diagnosing a motor vehicle battery.

2. Description of the Related Art

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.

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.

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

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.

According to the present invention, there is provided a method of diagnosing a battery of a motor vehicle, characterized by comprising the steps of: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;storing said parameters to create at least one database; anddetermining a charge status of said battery using said database.

According to a further aspect of the invention, the electric quantity is the voltage supplied by the battery.

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.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows schematically a vehicle engine1(vehicle not shown) connected to terminals2aof a battery2supplying a battery voltage VB. For the sake of simplicity, the electrically powered devices of the vehicle are not shown in detail inFIG. 1, but are all considered included in engine1. A control unit3, comprising a voltage sensor5, a processing unit6, and a memory7, is connected to both engine1and battery2. More specifically, voltage sensor5has inputs connected to terminals2aof battery2to receive battery voltage VB, and an output connected to processing unit6. In other words, sensor5measures the instantaneous battery voltage VBvalue, and supplies it to processing unit6.

Processing unit6has inputs6areceiving a number of operating parameters, such as cylinder intake air temperature TAand cooling water temperature TW, and an output connected to engine1to supply a number of control signals SC, and is two-way connected to memory7to read and write data as required.

FIG. 2shows the pattern of battery voltage VBin a transient startup state of engine1. Just before start-up, battery voltage VBhas a stable initial value VI, on account of battery2supplying substantially no current. When engine1is started up, the user devices connected to battery2simultaneously draw high start-up currents, so that the battery is temporarily unable to maintain the initial value VIof voltage VB, which falls more or less instantaneously to a minimum value VMIN. More specifically, at this stage, there is a voltage drop of VD=VI−VMIN. The battery voltage VBvalue then rises, exceeds initial value VI, and settles to oscillate about a steady-state value VRnormally higher than initial value VI. More specifically, battery voltage VBpasses from minimum value VMINto initial value VIwithin a rise timeTR.

According to observations made by the inventors, initial value VI, voltage drop VD, and rise timeTRare operating parameters related to the charge status of battery2. 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.

Moreover, initial value VI, minimum value VMIN, and rise timeTRare strongly affected by the operating conditions of engine1, in particular air temperature TAand water temperature TW, so that different operating conditions of engine1and battery2, defined by respective sets of air temperature TAand water temperature TWvalues, can be identified. More specifically, each operating condition corresponds to a respective predetermined region Z1, Z2, . . . , ZMin a TATWdiagram, as shown by way of example inFIG. 4.

With reference toFIG. 3, when engine1is started up, control unit3is initialized by setting a status register ST relative to the charge status of battery2to an initializing value, e.g. a normal-charge value NORM (block100).

The initial battery voltage value VIjust before start-up of engine1is then acquired (block105), and is preferably calculated as the average of a predetermined number of battery voltage VBreadings made by voltage sensor5before engine1is started up.

When the engine is started up, minimum value VMINand rise timeTRare acquired successively (block110), voltage drop VD=VI−VMINis calculated (block115), and processing unit6acquires air temperature TAand water temperature TW(block120).

Initial value VI, voltage drop VD, and rise timeTRare then memorized in memory7(block125). More specifically, memory7contains a number of tables10.1,10.2, . . . ,10.M (FIG. 5), each associated with a respective operating condition of engine1, i.e. with a respective region Z1, Z2, . . . , ZMin the TATWdiagram; and each operating condition, as stated, is defined by a respective set of air temperature TAand water temperature TWvalues. At the first start-up, i.e. when battery2is new and used for the first time, tables10.1,10.2, . . . ,10.M are empty, and one of them is incremented at each subsequent start-up. At this stage, one of tables10.1,10.2, . . . ,10.M corresponding to the present operating condition of engine1, i.e. to the measured air temperature TAand water temperature TWvalues, is selected, and initial value VI, voltage drop VD, and rise timeTRof battery voltage VBare entered into the selected table10.1,10.2, . . . ,10.M.

Initial value VI, voltage drop VD, and rise timeTRare then processed and compared with the content of the selected table10.1,10.2, . . . ,10.M (block130). More specifically, a first, second, and third variation index IV1, IV2, IV3, relative to initial value VI, voltage drop VD, and rise timeTRrespectively, are calculated on the basis of the difference between each of the three operating parameters measured at start-up of engine1—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 IV1, IV2, IV3are the latest memorized in the selected table10.1,10.2, . . . ,10.M, so that:
IV1(K)=VI(K)−VI(K−1)
IV2(K)=VMIN(K)−VMIN(K−1)
IV3(K)=TR(K)−TR(K−1)

The initial value VI, voltage drop VD, and rise timeTRrecorded at start-up of engine1are therefore correlated with historic data memorized previously under the same operating conditions. A check is then made to determine whether variation indexes IV1, IV2, IV3exceed, in absolute value, respective first-level warning thresholds SWI-1, SWI-2, SWI-3, which are preferably calibratable (block135). That is, a respective normal variation range INTV1, INTV2, INTV3, ranging between limits symmetrical with respect to zero (FIG. 6), is determined for each variation index IV1, IV2, IV3. Alternatively, asymmetrical normal variation ranges may also be determined.

If at least one of first, second, and third variation indexes IV1, IV2, IV3exceeds the respective first-level warning threshold SWI-1, SWI-2, SWI-3, i.e. is outside the respective normal variation range INTV1, INTV2, INTV3(YES output of block135), a further test is performed (block140) to determine whether a respective first-level alarm threshold SAI-1, SAI-2, SAI-3is also exceeded (again in absolute value). First-level alarm thresholds SAI-1, SAI-2, SAI-3are also calibratable and higher than respective first-level warning thresholds SWI-1, SWI-2, SWI-3. In other words, warning variation ranges INTVW1, INTVW2, INTVW3, symmetrical with respect to zero and comprising respective normal variation ranges INTV1, INTV2, INTV3, are defined. In this case, too, the warning variation ranges may also be asymmetrical.

If at least one of variation indexes IV1, IV2, IV3exceeds the respective first-level warning threshold SWI-1, SWI-2, SWI-3, i.e. is also outside the respective warning variation range INTVW1, INTVW2, INTVW3(YES output of block140), the status register ST is set to a first alarm value W1(block145) indicating a serious malfunction calling for immediate attention. That is, at least one of initial value VI, voltage drop VD, and rise timeTRhas shown a sharp variation with respect to previously recorded values, thus indicating malfunctioning of battery2. Conversely, if none of variation indexes IV1, IV2, IV3exceeds the respective first-level alarm threshold SAI-1, SAI-2, SAI-3(i.e. if variation indexes IV1, IV2, IV3are all within respective warning variation ranges INTVW1, INTVW2, INTVW3, but at least one is outside respective normal variation range INTV1, INTV2, INTV3—NO output of block140), the status register ST is set to a second alarm value W2(block150) indicating battery2has suddenly shown signs of deterioration, though still with a certain margin of safety. In both the cases described, however, an anomalous charge status of battery2is indicated.

If variation indexes IV1, IV2, IV3are all below respective first-level warning thresholds SWI-1, SWI-2, SWI-3, i.e. are within respective normal variation ranges INTV1, INTV2, INTV3(NO output of block135), respective drift indexes ID1, ID2, ID3of interval N, where N is a whole number, e.g.10, are calculated (block155) for initial value VI, voltage drop VD, and rise timeTR. In this case, from the currently recorded initial value VI, voltage drop VD, and rise timeTR, are subtracted the corresponding values memorized at a distance of N locations in the selected table10.1,10.2, . . . ,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 TAand water temperature TWvalues). That is:
ID1(K)=VI(K)−VI(K−N)
ID2(K)=VD(K)−VD(K−N)
ID3(K)=TR(K)−TR(K−N)

In this case, too, since all the values involved are taken from the same selected table10.1,10.2, . . . ,10.N, the processed values are acquired under the same operating conditions of engine1and battery2.

Processing unit6then determines (block160) whether at least one of drift indexes ID1, ID2, ID3exceeds a respective calibratable second-level warning threshold SWII-1, SWII-2, SWII-3, so as to determine, for each drift index ID1, ID2, ID3, a normal drift range INTD1, INTD2, INTD3ranging between limits symmetrical with respect to zero.

If drift indexes ID1, ID2, ID3are all below respective second-level warning thresholds SWII-1, SWII-2, SWII-3, i.e. are within respective normal drift ranges INTD1, INTD2, INTD3(NO output of block160), the status register ST is set to the normal operation value NORM to indicate normal operation of battery2(block165). Conversely (YES output of block160), a further test is performed to determine whether at least one of drift indexes ID1, ID2, ID3also exceeds a respective calibratable second-level alarm threshold SAII-1, SAII-2, SAII-3, i.e. is outside a respective warning drift range INTDW1, INTDW2, INTDW3(block170). In this case, too, warning drift ranges INTDW1, INTDW2, INTDW3range between limits symmetrical with respect to zero, but may also be asymmetrical.

If the above condition is confirmed (YES output of block170), the status register ST is set to a third alarm value W3indicating serious ageing of battery2(block175). In fact, even though none of the operating parameters has undergone significant variations over the last N start-ups of engine1, more gradual deterioration of battery2may 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 battery2is gradually worsening. If the test condition of block170is not confirmed (NO output of block170), the status register ST is set to a fourth alarm value W4(block180) indicating initial deterioration: the charge status of battery2is not perfect, but there is still a certain margin of safety. In both cases, however, an anomalous charge status of battery2is indicated.

The procedure is then terminated (block185).

Clearly, changes may be made to the method as described herein without, however, departing from the scope of the present invention.