Method for controlling a low-voltage storage battery housed on board a motor vehicle

Abstract

The invention relates to a method for controlling a low-voltage storage battery, in particular a 12V battery, the storage battery being housed on board a motor vehicle, the method comprising a step (20) of monitoring the storage battery and a step (30) of charging the storage battery depending on a result of the monitoring step (20), the monitoring step (20) and / or the charging step (30) being carried out while the vehicle is stationary (parking mode), the monitoring step (20) comprising a step (22) of evaluating a threshold that is variable as a function of one or more operating parameters of the storage battery, and a step (24) of triggering the charging step (30), the triggering step (24) taking into account the variable threshold.

Description

Description Title of the invention: Method for controlling a low-voltage battery installed on a motor vehicle

[0001] The invention relates to a method for controlling a low voltage accumulator, in particular a 12V battery, said accumulator being mounted on a motor vehicle.

[0002] In this field, vehicles with fully or partially electric powertrains are well-known. Such vehicles include a high-voltage (HV) electrical system equipped with a high-voltage battery that powers the vehicle's motor, offering a large energy storage capacity ranging from 5 to 100 kWh. Depending on the application, this type of vehicle also includes a low-voltage electrical system necessary for all electrical functions other than the motor, particularly in parking mode and during vehicle start-up and / or wake-up.

[0003] The low-voltage (LV) electrical network includes a low-voltage electricity source which comprises:

[0004] - a voltage converter between a high-voltage direct current and a low-voltage direct current, commonly called a DC-DC converter, which draws energy from the high-voltage battery, possibly accompanied by an alternator, for hybrid vehicles; and

[0005] - a BT accumulator, consisting of a 12-volt battery, used for storage to deliver the small amount of electrical energy needed for the non-motorization electrical functions mentioned previously.

[0006] Maintaining the charge of the BT accumulator is essential to allow at least the "wake-up" of the vehicle's electrical and electronic systems, enabling access to the vehicle as well as the activation of the DCDC converter which will then provide the electrical supply during the active phase of the vehicle, also called the mission, whether moving or not.

[0007] If the low-voltage battery is excessively discharged, it can reach a level that prevents it from properly powering basic systems, including the DC-DC converter. This will lead to a complete failure. This situation is generally referred to as a "failure to operate" and is a source of great dissatisfaction for the vehicle owner.

[0008] It is therefore necessary to maintain at all times the state of charge of the BT accumulator at a level which allows all the vehicle's services to be performed correctly and safely.

[0009] It is known that charging low-voltage batteries involves a systematic charging trigger based on a fixed, predetermined threshold. This threshold initiates charging, but it is fixed. Therefore, the charging process is not optimized.

[0010] The invention aims to overcome at least in part the previous drawbacks and proposes to this end a method for controlling a low voltage accumulator, in particular a 12V battery, said accumulator being mounted on a motor vehicle, said method comprising a monitoring step of said accumulator and a charging step of said accumulator, in particular from a high voltage device for storing electrical energy of the vehicle, according to a result of said monitoring step, said monitoring step and / or said charging step being carried out while said vehicle is stationary, said monitoring step comprising a step for evaluating a threshold, variable according to one or more operating parameters of said accumulator, and a step for triggering the charging step, said triggering step taking into account said variable threshold.

[0011] By evaluating a charging trigger threshold based on the battery's operating parameters, charging can occur at the optimal time to prevent deep discharge and avoid unnecessary recharging. This control method can be used in addition to, or as an alternative to, systematic charging triggered periodically and / or based on a predetermined, constant threshold.

[0012] Thus, the method of the invention makes it possible to monitor the possible discharge of the low voltage battery when not in operation (i.e. in parking mode) and takes into account the parameters influencing the minimum charge level of the battery below which it must not fall.

[0013] The method of the invention makes it possible to avoid excessive or untimely discharges of the BT accumulator, thus eliminating the risks of malfunction, immobilizing breakdowns and premature replacement of the BT accumulator.

[0014] According to various additional features of the invention, which may be taken together or separately and which constitute so many embodiments of the invention: - the said operating parameter(s) include a temperature of said accumulator and / or a state of said accumulator, - said variable threshold evaluation step includes a step for determining said operating parameter(s), - said variable threshold evaluation step includes a step of calculating said variable threshold from said operating parameter(s), - said threshold is an electrical voltage, representing, through a predetermined relationship, a state of charge of said accumulator, - said triggering step includes a step of comparing a voltage measured between the terminals of said accumulator, said battery voltage, and said variable threshold, - said triggering step includes a confirmation step taking into account a time during which a value in question remains below or above said variable threshold, said confirmation step delivering information to trigger the load if said time exceeds a threshold duration, - said charging stage includes an activation stage of a voltage converter enabling charging of said accumulator from the high-voltage electrical energy storage device, - said trigger information causes activation of said voltage converter, - said charging step is carried out using a charging current with a charging voltage that is a function of a target charge level of said accumulator, - said process includes a step of deactivating said voltage converter occurring once said charging step is completed, - said charging step includes a step of memorizing a context of its triggering, - said charging step includes a step of issuing an alert information, - the said operating parameter(s) include a state of said vehicle corresponding to a storage of said vehicle before driving, - said vehicle includes an electric or hybrid engine.

[0015] The invention also relates to a management system, intended to be embedded in a motor vehicle, said management system comprising hardware and / or software elements implementing the control process as described above.

[0016] The invention further relates to a motor vehicle comprising a management system as described above.

[0017] The invention also relates to a computer program product comprising program code instructions recorded on a computer-readable medium to implement the steps of the control process as described above, when said program is running on a computer.

[0018] The invention also relates to a computer-readable data storage medium on which a computer program is stored, comprising program code instructions to implement the steps of the control assistance process as described above, when said program is running on a computer.

[0019] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent in the course of the detailed explanatory description which follows, of at least one embodiment of the invention given by way of purely illustrative and non-limiting example, with reference to the accompanying schematic drawings, among which:

[0020] [Fig.1] [Fig.1] schematically illustrates a control system, intended to be embedded in a motor vehicle, for the implementation of a control method according to the invention;

[0021] [Fig.2] [Fig.2] represents a flowchart relating to an example of implementation of the control process according to the invention;

[0022] [Fig.3] [Fig.3] is a graph comprising a curve representing the relationship between the state of charge of the BT accumulator and the open-circuit voltage across the terminals of the BT accumulator;

[0023] [Fig.4] [Fig.4] is a graph including a curve representing the effect of battery aging on its state of charge;

[0024] [Fig. 5] [Fig. 5] is a graph comprising a curve representing the effect of ambient temperature on the state of charge of the battery; and

[0025] [Fig. 6] [Fig. 6] is a graph comprising a curve similar to the curve of the [Fig.3], taking into consideration aging and temperature on the state of charge of the accumulator.

[0026] Figure 1 schematically illustrates a control system 10, intended for installation in a motor vehicle with an electric or hybrid powertrain. The control system 10 is integrated, in particular, into a low-voltage (LV) electrical network 1 and a high-voltage (HV) electrical network 2. The HV network includes a high-voltage (HV) electrical energy storage device 3, specifically an HV battery or accumulator, with a large energy storage capacity that can vary between 5 and 100 kWh depending on the application. It is intended to power the vehicle's motor. The LV electrical network is intended to operate all electrical functions other than the motor (such as lighting, multimedia, vehicle access and locking, etc.). The LV electrical network includes an LV power supply, which is a secure LV power supply unit and which, in this case, comprises:

[0027] - a 4-current direct current converter from a high voltage to a low voltage, commonly called a DC-DC voltage converter, which draws in particular the energy in the high-voltage battery, possibly accompanied by a high-voltage alternator, for hybrid vehicles; and

[0028] - a BT 5 accumulator, consisting, for example, of a 12-volt battery, also called a BT lead-acid or lithium battery. The BT 5 accumulator serves as an electrical energy storage device to deliver the small amount of electrical energy required, in particular, in parking mode and / or when the vehicle is "waked up," for example, for vehicle access. Advantageously, this BT accumulator also provides backup power in the event of a failure of the converter 44.

[0029] The control system 10 is configured for control of the BT 5 accumulator. Said control system 10 is equipped for this purpose with a management system having hardware and / or software elements integrated here in a BT 5 accumulator management system 6 and / or a BT 5 accumulator charging supervisor 7.

[0030] As seen in [Fig.2], the invention relates in particular to a method of controlling the BT 5 accumulator, in particular implemented by the control system 10.

[0031] The said control process includes a step 20 of monitoring the BT 5 accumulator and a step 30 of charging the BT 5 accumulator according to a result of the monitoring step 20.

[0032] Monitoring step 20 and / or charging step 30 are executed while the vehicle is stationary, i.e., in park with the engine inactive. They are interrupted, for example, as soon as a command to activate and / or wake up the vehicle, particularly one issued by a driver or any other vehicle user, is received and / or processed by the management system.

[0033] Monitoring step 20 includes a step 22 for evaluating a threshold, which varies according to one or more operating parameters of the BT 5 accumulator, and / or a step 24 for triggering charging step 30. The triggering step 24 takes into account this variable threshold.

[0034] Thanks to the use of a variable threshold to trigger the charging of the BT 5 battery according to its operating parameters, its charging can take place at the opportune time to avoid deep discharge without multiplying unnecessary recharges.

[0035] The operating parameter(s) include, for example, a BT 5 accumulator temperature and / or a BT 5 accumulator state. An example of the BT 5 accumulator state is its aging measured in units of time.

[0036] Step 22 of the variable threshold evaluation includes, for example, a step 222 of determining the operating parameter(s).

[0037] Step 222 of determining the operating parameter(s) advantageously takes into account the technology of the BT 5 accumulator, in particular for temperature.

[0038] For example, if managing a low-voltage (LV) battery requires a LV battery management system 6, which knows, among other things, the temperature of the battery's internal cells, as is the case with lithium batteries, the method according to the invention advantageously exploits such temperature information. More precisely, corresponding to pre-established threshold values ​​(e.g., 0°C, -10°C, -20°C, -30°C), the LV battery management system 6 informs the supervisor 7, via a communication network such as CAN, of the temperature reached.

[0039] A supervisor 7 that has the ambient temperature, namely that used for a display on the vehicle's dashboard, can also be used to perform the same function.

[0040] For vehicles equipped with a BT 5 lead-acid battery, the internal temperature estimator of the BT 5 battery already present in the vehicles can be used. This involves using the "technical wake-up" protocol, which consists of waking up the supervisor 7 via the CAN network. The supervisor then proceeds to estimate the temperature of the BT 5 battery.

[0041] Step 22 of the evaluation of the variable threshold includes in particular a step 224 of calculation of the variable threshold from the operating parameter(s), for example such as those from step 222 of determination of said operating parameter(s).

[0042] The variable threshold is, for example, an electrical voltage, representing the state of charge (SOC) or charge level of the BT 5 battery. The process involves calculating the variable threshold, representing the BT 5 battery's state of charge, below which the charge must not fall, taking into account the aforementioned operating parameter(s). The variable threshold can be determined, in particular, by the relationship between the voltage across the BT 5 battery and its state of charge. This relationship, characteristic of each battery technology, is verified for a zero or low current output from the battery.

[0043] In particular, [Fig.3] illustrates the relationship between open-circuit voltage (on the ordinate) and state of charge (on the abscissa) for a given BT 5 battery.

[0044] As can be seen in this figure, if the measured open-circuit voltage is slightly below 13.5 V, this corresponds to a state of charge of approximately 50%. If, on the other hand, the measured open-circuit voltage is approximately 14.5 V, this corresponds to a state of charge of approximately 80%.

[0045] As an example, the influence of the two operating parameters mentioned above on the state of charge SOC is shown in the graphs in figures 4 to 6.

[0046] Figure 4 illustrates in particular the influence of aging on the BT 5 battery. Indeed, the wear of the BT 5 battery means that the initial performance possible at a given minimum state of charge will require increasing the state of charge value as the BT 5 battery wears down in order to maintain that performance. For example, as illustrated in Figure 4, which shows time on the x-axis and a representative performance value taking age into account, called SOC Ag, on the y-axis, if the variable threshold (or initial minimum level) is 50% with a new BT 5 battery, it can increase to 70% for an 8-year-old battery. This influence of battery performance with age is stored in the management system in the form of formulas and / or tables.

[0047] Figure 5 illustrates in particular the influence of the BT 5 battery temperature. All BT 5 battery technologies used in automobiles exhibit significantly lower performance when the temperature drops well below 0°C. To compensate for this performance reduction, the variable threshold triggering charging stage 30 will be raised when the temperature drops very low, particularly during parking phases.

[0048] Figure 5 illustrates, in particular, a state of charge (SOC) compensation factor, plotted on the y-axis as a function of temperature on the x-axis. For example, if the temperature is -30°C, the SOC compensation factor is 1.6. In other words, if the variable threshold is 50% for a positive temperature value, the new variable threshold (after accounting for temperature) is 50% x 1.6 = 80%. This temperature influence is stored in the management system as formulas and / or tables.

[0049] The process involves combining the two parameters (aging and temperature) to determine the variable threshold, as illustrated in particular in [Fig. 6]. The variable threshold is then given, for example, by the formula:

[0050] SOC Ag x Compensation SOC.

[0051] In this example, we need to calculate the variable threshold of a 2-year-old lithium battery in an environment at -17°C. The curve in [Fig. 4] shows us that the variable threshold, without considering temperature, for a 2-year-old lithium battery is 52%. The curve in [Fig. 5] shows us that the SOC compensation at -17°C is 1.2. The variable threshold, taking temperature into account, will therefore be: SOC Ag x SOC Compensation = 52% x 1.2 = 62.5%. According to the curve in [Fig. 6], 62.5% corresponds to approximately 13.5 V.

[0052] Advantageously, the result of the calculation above is limited to 98%. This gives a parking autonomy, for example, of approximately 20 hours for a 10 Ah battery and a parking consumption of 10mA.

[0053] The triggering step 24 includes a step 242 comparing a voltage measured between the terminals of the BT 5 accumulator, referred to as the battery voltage, with the variable threshold. In the illustrated example, as long as the voltage measured between the terminals of the BT 5 accumulator does not fall below 13.5 V, the state of charge (SOC) is not below the variable threshold and the charging step 30 is not triggered.

[0054] Thus, according to this embodiment of the invention, the voltage across the terminals of the BT accumulator is monitored to detect any possible crossing of the variable threshold, also expressed in the form of a voltage.

[0055] Preferably, if the voltage falls below a predetermined value, enhanced monitoring will be activated to confirm the need for recharging. For example, if the voltage remains below this threshold, particularly for a certain period of time. If the problem is confirmed, corrective action for the battery is then initiated.

[0056] In this respect, the triggering step 24 includes, in particular, a confirmation step 244 that takes into account a time during which a relevant value remains below or above the variable threshold. The confirmation step 244 provides a signal to trigger the load if the time exceeds a threshold duration. In the illustrated embodiment, the relevant value is the battery voltage, and the time is counted as long as it remains below the determined threshold, i.e., in this case, as long as it remains below 13.5 V.

[0057] Thus, when the voltage threshold is exceeded for a sufficient duration the process plans to trigger the charging step 30 of the BT accumulator 5, preferably using the HT accumulator 3 and the voltage converter 4.

[0058] The charging step 30 includes in particular a step of activation of the voltage converter 4 allowing the charging of the BT accumulator 5 from the HT accumulator 3. It is in particular the trigger information which causes an activation of the voltage converter 4.

[0059] Thus, the solution of the invention does not require any additional means to recharge the BT battery.

[0060] Step 30 of charging is carried out in particular using a charging current with a charging voltage that is a function of a target charge level of the accumulator.

[0061] To determine the target load level, the process involves, for example, adding 20% ​​to the variable threshold. In the example above, the target load state is therefore 62.5% + 20% = 82.5%.

[0062] In the case of a lithium battery, the charging voltage is set to the value corresponding to the target state of charge. Charging stops either when the charging current is below a threshold, or after a fixed delay, or based on a combination of the two previous criteria, using information provided by the battery management system.

[0063] In the case of a BT battery without a battery management system, such as a BT lead-acid battery, a fixed charging voltage is used, typically 15 volts and a fixed duration, for example two hours.

[0064] When the charging time of the low voltage battery has elapsed, the charging step 30 is interrupted and the control process advantageously returns to the monitoring step 20.

[0065] In this sense, the process here includes a step 40 of deactivation of the voltage converter 4 which occurs once the charging step 30 has been completed, namely, in the illustrated embodiment, once the target charging level has been reached.

[0066] Charging stage 30 advantageously includes a warning signal. Thus, for example, if charging stage 30 is triggered again or if it is activated too often, for example twice a week or more, a low-level warning signal can be given to the driver, notably by a message on the instrument panel, by a warning light, and / or by information transmitted by the after-sales network via a vehicle multimedia system.

[0067] Charging stage 30 advantageously includes a step for recording the context of its triggering. This step helps with troubleshooting. Through this step, an onboard network supervisor retrieves and records contextual information about the discharge: at a minimum, this includes the absolute time elapsed since the vehicle's "birth," the time spent parked since the end of the last mission, the vehicle's state (sleep, active, woken by a telematics request, etc.), and the active functions. This information is also useful for determining the cause of the unexpected discharge. This list can also include elements indicating a potential malfunction, such as a vehicle on a mission with an inactive voltage converter.

[0068] The operating parameter(s) may include a vehicle state corresponding to pre-driving vehicle storage (before initial commissioning), i.e., in particular a logistics phase corresponding to the period which extends from the end of vehicle manufacturing to delivery to the end customer. This period can last several months, during which the car remains parked. One of the goals of the specific mode associated with this logistical phase is to minimize power consumption. Furthermore, to deliver the car with a BT 5 battery in excellent condition, it is necessary to maintain the highest possible state of charge. The method of the invention therefore involves raising the activation threshold of charging step 30 to a significantly higher voltage level, for example, corresponding to a 75% state of charge at 20°C.

[0069] To perform this function, it is preferable that the HT 3 accumulator contains the electrical energy necessary to ensure all necessary recharges taking into account the maximum parking time and the discharge, however small, of the BT 5 accumulator.

[0070] As an example, the energy required to charge the HT 3 battery to perform the charge maintenance function can be calculated as follows: • a maximum parking time between manufacturing and delivery to the customer is 12 months. • The BT 5 battery, once properly charged, can provide parking power for 60 days before needing to be recharged. • The energy to be supplied to the battery during a recharge is 20% of the BT accumulator capacity + 20% of this energy to account for efficiency losses of all kinds.

[0071] In summary and describing only the steps of the process of the invention illustrated in [Fig. 2], the process includes step 20 of monitoring the BT 5 accumulator and step 30 of charging the BT 5 accumulator according to a result of the monitoring step 20.

[0072] Monitoring step 20 includes, in particular, step 22, which assesses the variable threshold. Step 22, which assesses the variable threshold, includes, among other things, step 222, which determines the operating parameter(s). Following this step 222, which determines the operating parameter(s), step 22, which assesses the variable threshold, includes, for example, step 224, which calculates the variable threshold from the operating parameter(s).

[0073] Following step 22, step 20 of the BT 5 battery monitoring includes, in particular, step 24, which triggers step 30 of the charging process. Step 24 takes into account the variable threshold.

[0074] The triggering step 24 includes, for example, step 242, which compares a voltage measured between the terminals of the BT 5 accumulator and the aforementioned variable threshold. If the voltage measured between the terminals of the BT 5 accumulator is greater than the threshold variable, the process of the invention restarts step 22 of evaluating the variable threshold.

[0075] If, on the other hand, the voltage measured across the terminals of the BT 5 accumulator is below the variable threshold, the triggering step 24 includes, following the comparison step 242, the confirmation step 244, which takes into account a period during which the value in question remains below or above the variable threshold. Thus, if the period exceeds a threshold duration, the confirmation step 244 provides a trigger signal for the charging step 30; otherwise, the process restarts step 22, which evaluates the variable threshold.

[0076] The invention further relates to a motor vehicle comprising a management system as described above.

[0077] The invention also relates to a computer program product comprising program code instructions recorded on a computer-readable medium to implement the steps of the control process as described above, when said program is running on a computer.

[0078] The invention also relates to a computer-readable data storage medium on which is stored a computer program comprising program code instructions to implement the steps of the control assistance method as described above, when said program is running on a computer.

Claims

Demands [Claim 1] A method for controlling a low-voltage accumulator (5), in particular a 12V battery, said accumulator (5) being mounted on a motor vehicle, said method comprising a monitoring step (20) for said accumulator (5) and a charging step (30) for said accumulator (5), in particular from a high-voltage electrical energy storage device (3) of the vehicle, based on a result of said monitoring step (20), said monitoring step (20) and / or said charging step (30) being carried out while said vehicle is stationary, said monitoring step (20) comprising a step (22) for evaluating a threshold, which varies according to one or more operating parameters of said accumulator (5), and a triggering step (24) for the charging step (30), said triggering step (24) taking into account said variable threshold. [Claim 2] A control method according to claim 1, wherein said operating parameter(s) include a temperature of said accumulator (5) and / or a state of said accumulator (5). [Claim 3] A control method according to claim 1, wherein said step (22) of evaluating the variable threshold includes a step (222) of determining said operating parameter(s). [Claim 4] A control method according to any one of the preceding claims, wherein said threshold is an electrical voltage, image by a predetermined relation of a state of charge of said accumulator (5). [Claim 5] A control method according to the preceding claim, wherein said triggering step (24) includes a step (242) of comparing a voltage measured between terminals of said accumulator (5), said battery voltage, and said variable threshold. [Claim 6] A control method according to any one of the preceding claims, wherein said triggering step (24) includes a confirmation step (244) taking into account a time during which a value in question remains below or above said variable threshold, said confirmation step (244) delivering a load triggering information if said time exceeds a threshold duration. [Claim 7] A control method according to any one of the preceding claims, wherein said charging step (30) comprises an activation step of a voltage converter (4) enabling a charge of said accumulator (5) from the high voltage electrical energy storage device (3). [Claim 8] A control method according to claim 7 when dependent on claim 6, wherein said trigger information causes activation of said voltage converter (4). [Claim 9] A control method according to any one of the preceding claims, wherein said loading step (30) includes a step of memorizing a context of its triggering and / or a step of emitting an alert information. [Claim 10] A control method according to any one of the preceding claims, wherein the operating parameter(s) include a state of said vehicle corresponding to a storage of said vehicle before driving. [Claim 11] Management system (10), intended to be embedded in a motor vehicle, said management system (10) comprising hardware and / or software elements implementing the control method according to any one of the preceding claims. [Claim 12] Motor vehicle comprising a management system (10) according to the preceding claim. [Claim 13] Product computer program comprising program code instructions recorded on a computer-readable medium to implement the steps of the control method according to any one of claims 1 to 10 when said program is running on a computer. [Claim 14] A computer-readable data storage medium on which is stored a computer program comprising program code instructions for implementing the steps of the control assistance method according to any one of claims 1 to 10, when said program is running on a computer.

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