Method for controlling a low-voltage battery installed on a motor vehicle

Abstract

The invention relates to a method for controlling a low-voltage accumulator, in particular a 12V battery, said accumulator being installed in a motor vehicle, said method comprising a step (20) for monitoring said accumulator and a step (30) for charging said accumulator based on a result of said monitoring step (20), said monitoring step (20) and / or said charging step (30) being performed while said vehicle is stationary (parking mode), said monitoring step (20) comprising a step (22) for evaluating a threshold, variable according to one or more operating parameters of said accumulator, and a step (24) for triggering the charging step (30), said triggering step (24) taking into account said variable threshold. Figure 2

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 motors are known. Such vehicles include a high-voltage (HV) network equipped with a high-voltage battery used to power the vehicle's motor, with 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 network 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 electrical network, referred to as LV, comprises a low-voltage electricity source which includes:

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

[0005] - a BT accumulator, consisting of a 12-volt battery, serving as storage in order to to deliver the small amount of electrical energy required 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 will no longer allow the basic systems, particularly the DC-DC converter, to function properly. 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 enables all the services of the vehicle to be provided correctly and safely.

[0009] It is known in this sense to charge BT batteries with a charging trigger operated systematically taking into account a constant trigger threshold, fixed in advance. This threshold triggers a charge, but it is fixed. The charge is therefore not triggered in an optimized manner.

[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 opportune time to avoid deep discharge without unnecessary recharging. This control method can be implemented in addition to, or as an alternative to, any charging that is systematically triggered on a periodic basis and / or based on a constant, predetermined threshold.

[0012] Thus, the method of the invention makes it possible to monitor the possible discharge of the low voltage accumulator when not in operation (i.e. in parking mode) and takes into account the parameters influencing the minimum charge level of the accumulator 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 data storage medium, readable by a computer, on which a computer program 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 that 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 to be carried in a motor vehicle, for the implementation of a control method conforming to the invention;

[0021] [Fig.2] [Fig.2] represents a flowchart relating to an example of an embodiment 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 comprising a curve representing the effect of aging of the accumulator 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 accumulator; and

[0025] [Fig.6] [Fig.6] is a graph comprising a curve similar to the curve in [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 to be installed 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, in particular 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 functions, etc.). The LV electrical network includes an LV power supply, which is a secure LV power supply unit and which here comprises:

[0027] - a DC converter 4 from a high voltage to a low voltage voltage, commonly called a DCDC 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, called Also, a BT lead-acid or lithium battery. The BT 5 battery serves as an electrical energy storage device to deliver the small amount of electrical power needed, particularly in parking mode and / or when the vehicle is "waked up," for example, when accessing the vehicle. Advantageously, this BT battery 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 provided 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] Said control method 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 parking mode with the engine in an inactive state. They are interrupted, for example, as soon as an activation and / or wake-up command for the vehicle, particularly one issued by a driver or any other vehicle user, is received and / or processed by said management system.

[0033] The 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 the charging step 30. The triggering step 24 takes into account said variable threshold.

[0034] Thanks to the use of a variable threshold to trigger the charging of the BT 5 accumulator 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 temperature of the BT 5 accumulator and / or a state of the BT 5 accumulator. An example of the state of the BT 5 accumulator is its aging measured in units of time.

[0036] Step 22 of the evaluation of the variable threshold 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 battery requires a low-voltage 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 a temperature. More precisely, corresponding to pre-established threshold values ​​(e.g., 0°C, -10°C, -20°C, -30°C), the low-voltage battery management system 6 informs the supervisor 7, via a communication network, such as a CAN network, of the temperature reached.

[0039] A supervisor 7 which 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. The protocol called "technical wake-up" is then used, which consists of waking up, via the CAN network, the supervisor 7, which will then proceed to estimate the temperature of the BT 5 battery.

[0041] Step 22 of evaluating the variable threshold includes in particular a step 224 of calculating the variable threshold from the operating parameter(s), for example such as those from step 222 of determining 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. Thus, the method provides for calculating the variable threshold, representing the state of charge of the BT 5 battery, below which the current must not fall, notably by taking into account the aforementioned operating parameter(s). The variable threshold can be determined, in particular, by the relationship between the voltage across the terminals of the BT 5 battery and its state of charge. This relationship, characteristic of each battery technology, is verified for a zero or low current exiting the battery.

[0043] In particular, [Fig. 3] illustrates the relationship between the open-circuit voltage (on the ordinate) with the state of charge (on the x-axis) 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] By way of example, the influence of the two operating parameters mentioned above on the state of charge SOC is shown in the graphs of 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, in order to maintain this performance, increasing the state of charge value as the BT 5 battery wears. For example, and 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 rise 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 temperature of the BT 5 accumulator. All accumulator technologies used in automobiles have significantly lower performance when the temperature drops well below 0 °C. To compensate for this decrease in performance, 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 compensation factor, "SOC Compensation," on the ordinate axis, as a function of temperature on the abscissa 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% in the case of a positive temperature value, the new variable threshold (after taking temperature into account) is 50% x 1.6 = 80%. This influence of temperature is stored in the management system in the form of formulas and / or tables.

[0049] The process notably 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 SOC compensation.

[0051] In this embodiment, the variable threshold for a 2-year-old lithium battery is calculated in an environment at -17°C. The curve in [Fig. 4] shows that the variable threshold, without taking temperature into account, for a 2-year-old lithium battery is 52%. The curve in [Fig. 5] shows 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 above calculation 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 10 mA.

[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 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 by calculation 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 sense, 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., here, as long as it remains below 13.5 V.

[0057] Thus, when the voltage threshold is exceeded for a sufficient duration, the process provides for triggering 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] In this way, the solution of the invention does not require any additional means to recharge the BT battery.

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

[0061] To determine the target load level, or target load, the method provides, for example, for adding 20% ​​to the variable threshold. In the example above, the target load state is thus 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 is stopped either when the charging current is below a threshold, or after a fixed delay, or based on a combination of the two preceding criteria, using information provided by the battery management system 6.

[0063] In the case of a BT accumulator 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 information emission stage. 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 information can be given to the driver, in particular by a message on the instrument panel, by a warning light, and / or by information transmitted by the after-sales network via a multimedia system in the vehicle.

[0067] Charging step 30 advantageously includes a step for recording the context of its triggering. This step helps, in particular, to facilitate diagnosis. Through this step, an onboard network supervisor retrieves and records contextual information about the discharge: at a minimum, it can record the absolute time elapsed since the vehicle's "birth," the time spent parked since the end of the last mission, the vehicle's state (asleep, active, awakened by a telematics request, etc.), and the active functions, which is also useful for determining the cause of the unexpected discharge. This list can include elements indicating a potential malfunction, such as a vehicle on a mission with a voltage converter 4 inactive, for example.

[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 the necessary recharges taking into account the maximum duration of parking and the discharge, even small, of the BT 5 accumulator.

[0070] By way of example, a calculation of the energy required to charge the HT 3 accumulator to ensure the charge maintenance function can be carried out 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 for evaluating the variable threshold. Step 22 for evaluating the variable threshold includes, in particular, step 222 for determining the operating parameter(s). Following this step 222 for determining the operating parameter(s), step 22 for evaluating the variable threshold includes, for example, step 224 for calculating the variable threshold from the operating parameter(s).

[0073] Following step 22, step 20 of monitoring the BT 5 accumulator includes, in particular, step 24, which triggers the charging step 30. The triggering 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 said 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 between 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 time during which the value in question remains below or above the variable threshold. Thus, if the time exceeds a threshold duration, the confirmation step 244 provides a triggering signal for the charging step 30; otherwise, the process restarts the variable threshold evaluation step 22.

[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

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.

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).

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).

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).

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.

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.

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).

8. A control method according to claim 7 when dependent on claim 6, wherein said trigger information causes activation of said voltage converter (4).

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.

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.

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.

12. Motor vehicle comprising a management system (10) according to the preceding 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.

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.

Images