Method for adjusting the charge level of a 12V secondary battery in an electric or hybrid vehicle

Abstract

The invention proposes a method for adjusting the charge level of a secondary battery of an electric or hybrid vehicle powered by a main battery, comprising the following steps: a) a step for detecting the end of the mission of the electric or hybrid vehicle; b) a step for detecting the charge level of the secondary battery; c) a step for stopping the charging of the secondary battery if the charge level in step b) is above a low threshold; d) a step for charging the secondary battery from the main battery if the charge level in step b) is below said low threshold; e) a further step for detecting the charge level of the secondary battery; f) a step for stopping the charging of the secondary battery if the charge level in step e) has reached a high threshold; g) a step for stopping the charging of the secondary battery if the time elapsed since step d) has reached a predetermined duration.Figure for the abbreviation: Figure 2.

Description

Title of the invention: Method for adjusting the charge level of a 12V secondary battery in an electric or hybrid vehicle. Technical field of the invention

[0001] The invention relates to a method of adjusting the charge level of a secondary battery of an electric or hybrid vehicle powered by a main battery.

[0002] Indeed, electric vehicles such as motor vehicles include a main battery, known as the traction battery, and a secondary battery, known as the service battery. The traction battery is the high-voltage battery that powers the vehicle's electric motor, while the service battery is the low-voltage battery, generally 12 to 14 volts, intended to power other functions, such as various on-board equipment of the vehicle.

[0003] The invention also relates to an electric or hybrid vehicle using said method of adjusting the charge level of the secondary battery. Technical background

[0004] The motor of an electric or hybrid vehicle is powered directly by a traction battery, via an inverter in general, through a high-voltage electrical network.

[0005] A low voltage electrical network, called the 14V on-board network of the electric vehicle, is based on a direct current converter which draws energy from the main high voltage battery, which transforms it into low voltage 14V energy, and which powers the electrical components of the car, and in particular a secondary low voltage 12V battery.

[0006] This 14V DC converter is the main source of electrical power for the car and the secondary battery is only used to provide a supplement if needed and especially to provide electricity when the vehicle is in the parking phase.

[0007] In parking phase, the secondary battery allows all the 12V equipment of the car to be powered through the low voltage network.

[0008] For example, these 12V equipment may be the following: the anti-lock braking system (ABS), the electronic vehicle stability control (ESP) system, electric seats, the dashboard, the computers, the vehicle lights / headlights, the sensors, the parking brake system, the car opening system with the key, the safety system to turn the wheels in case of failure of the main battery, the ventilation, the power steering, etc.

[0009] This low voltage network is important, and makes it possible to avoid passing high voltage throughout the vehicle.

[0010] During driving, drivers who mainly make short trips will not be able to maintain a sufficient charge level of their secondary battery, and the latter will therefore degrade more rapidly than average.

[0011] This is particularly the case for lead-acid batteries, whose internal chemistry is damaged when the charge is not complete.

[0012] Lithium batteries are less sensitive, but it is still recommended to fully charge them to optimize their lifespan.

[0013] During the parking phase, i.e., when the vehicle's mission is complete, the vehicle has a standby current consumption of a few milliamperes. If it remains stationary for a very long time, this consumption accumulates and the auxiliary battery discharges.

[0014] For example, over a month, a secondary battery discharges approximately 20%.

[0015] This can be problematic, because the secondary battery can no longer perform its safety function in the event of failure of the main battery while driving, in particular to turn the wheels and allow the driver to take shelter on the side of the road. Summary of the invention

[0016] The objective of the present invention is to overcome the various disadvantages mentioned above by means of a secondary battery, called a service battery, which is always charged, so that it does not degrade or degrades very little over time, regardless of the driver's driving mode.

[0017] This goal is achieved through a method for adjusting the charge level of a secondary battery of an electric or hybrid vehicle powered by a main battery, comprising the following steps:

[0018] a) a step for detecting the end of the mission of the electric or hybrid vehicle;

[0019] b) a step for detecting the charge level of the secondary battery;

[0020] c) a step to stop charging the secondary battery if the charge level in step b) is above a low threshold;

[0021] d) a secondary battery charging step powered from the main battery if the charge level of step b) is below said low threshold;

[0022] e) a new step for detecting the charge level of the secondary battery;

[0023] f) a step to stop charging the secondary battery if the charge level of step e) has reached a high threshold;

[0024] g) a step to stop charging the secondary battery if the time elapsed since step d) has reached a predetermined duration.

[0025] With this end-of-mission charging strategy, the main battery (energy producer) is kept on as long as the secondary battery is not sufficiently recharged, even if the vehicle's mission is over, i.e. even when the vehicle is no longer in the driving phase.

[0026] The main idea of ​​this invention is to implement a strategy for recharging the secondary battery at the end of a mission, in order to maintain the secondary battery at the correct charge level to enable it to perform its functions under optimal conditions. In particular, from the start of the next mission, the battery will be at the required charge level to ensure supply to the grid even in the event of a sudden loss of the primary power source, in this case the main battery.

[0027] Thanks to this strategy, the driver's driving style will no longer have an impact on the degradation of the secondary battery.

[0028] According to the different embodiments of the invention, which may be considered together or separately: - End-of-mission detection corresponds to a specific action performed by the driver of the electric or hybrid vehicle when stopped, such as pressing an OFF button, putting a lever in the Parking position, or getting up from their seat. - said lower threshold is between 80% and 90% of load. - said lower threshold is equal to 85%. - said upper threshold is between 90% and 100% of load. - said upper threshold is equal to 95%. - said predetermined duration is between 15 minutes and 60 minutes. - said predetermined duration is equal to 30 minutes.

[0029] The invention also relates to an electric or hybrid vehicle comprising: - a main battery used to power the vehicle's traction motor; - a secondary battery powered by the main battery via a converter; - a central unit receiving input information from various sensors, performing calculations, and sending output information to the converter;

[0030] said central unit implementing a method for adjusting a charge level of the secondary battery according to one of the preceding claims.

[0031] The central unit calculates the charge level and controls the converter to stop charging the secondary battery if necessary. Brief description of the figures

[0032] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the accompanying drawings in which:

[0033] Fig. 1 is a schematic view of the electrical network within an electric or hybrid vehicle;

[0034] The [Fig.2] is a diagram presenting the method of adjusting the charge level of a secondary battery of an electric or hybrid vehicle according to the invention;

[0035] The [Fig.3] is a graph representing the state of charge of the secondary battery as a function of time, according to the prior art;

[0036] Fig. 4 is a graph representing the state of charge of the secondary battery as a function of time, according to the invention, and with comparison to the prior art. Detailed description of the invention

[0037] Fig. 1 schematically represents the electrical network within an electric or hybrid vehicle.

[0038] This electrical network is divided into two parts, namely a high voltage network, and a low voltage network.

[0039] The high voltage network is illustrated in the lower left part of [Fig.1].

[0040] This high-voltage network includes a main battery 1, called a traction battery, which is used to power an electric motor 3. An inverter 6 is placed between the main battery 1 and the motor 3, intended to protect the motor 3 against any electrical risk.

[0041] In this high voltage network, a branch from a thermal engine 3 is also represented in the case of a hybrid vehicle.

[0042] A charger 8 is also arranged on the high voltage network and allows the main battery 1 to be recharged.

[0043] The high voltage delivered either by the main battery 1, or by the charger 8, or by the thermal engine 3, arrives in a DC / DC converter 4 which converts this high voltage into low voltage.

[0044] In general, high voltage is around 400 V, while low voltage is around 14 V.

[0045] The low voltage network at the output of converter 4 is located on the right side of [Fig.1].

[0046] This low-voltage network powers all the vehicle's low-voltage equipment, generally 12V. In [Fig. 1], only three pieces of equipment 7 are shown for clarity. Of course, the vehicle includes many other low-voltage powered components.

[0047] For example, equipment 7a corresponds to an anti-lock braking system (ABS), with the voltage Va across the terminals of this equipment 7a.

[0048] Equipment 7b corresponds to the seat adjustment device, with the voltage Vb across the terminals of this equipment 7b.

[0049] Equipment 7c corresponds to the dashboard, with the voltage Vc across the terminals of this equipment 7c.

[0050] As mentioned in the first part of the description, other equipment 7 are connected to this low voltage network.

[0051] For example, these 12V equipment may be the following: the electronic vehicle stability control (ESP) device, the control units 5, the vehicle lights / headlights, the sensors, the parking brake device, the car opening system with the key, the safety system to turn the wheels in case of failure of the main battery 1, the ventilation, the power steering, etc.

[0052] This low voltage network also supplies a secondary battery 2, known as the service battery, operating at 12 V.

[0053] The voltage Vref across the terminals of this secondary battery 2 corresponds to the reference voltage of the on-board network.

[0054] A computer 5, corresponding to a central unit, is connected to both the converter 4 and the secondary battery 2. It receives as input the measurement of the reference voltage Vref from the secondary battery 2, and gives as output a voltage setpoint to the converter 4. This makes it possible to compensate for the voltage line losses that exist between the secondary battery 2 and the converter 4.

[0055] Preferably, current sensors 9 are arranged in series with the main battery 1 and the secondary battery 2 in order to measure the current passing through the batteries.

[0056] When the vehicle is stationary, in a parked car, the user can recharge it by connecting the vehicle's charger 8 to a charging station. The main battery 1 is thus recharged by the charger 8. The secondary battery 2, however, does not recharge when the vehicle is stationary, in a parked car. The secondary battery 2 is recharged only during driving.

[0057] When the driver performs short driving phases, also called short-duration missions, the secondary battery 2 does not have enough time to recharge sufficiently. This is because the vehicle remains stationary for extended periods, i.e., while parked. Thus, with each short-duration mission interspersed with long periods of inactivity, the secondary battery 2 gradually discharges.

[0058] The secondary battery 2 is considered to be fully charged when its state of charge or remaining electrical energy is between 90% and 100%.

[0059] Estimating the state of charge of a battery can be done using an OCV (Open Circuit Voltage) method or a coulometric method. The reference voltage Vref across the terminals of the secondary battery 2 is measured and sent to the control unit 5, which can then estimate the battery's state of charge, also taking into account certain other parameters (temperature, battery type, etc.). This estimation is performed when the vehicle is parked, with very low electrical consumption, and after a sufficient rest period (typically several hours) to stabilize the voltage of the secondary battery 2 so that it accurately reflects its state of charge.

[0060] During driving, the state of charge of the secondary battery 2 varies.

[0061] The SOC (initials of the English expression "State of Charge") represents the state of Actual charge of secondary battery 2 relative to its total capacity. The SOC varies from 0% to 100%, is initialized by the OCV if available, and varies according to the integral of the current passing through secondary battery 2, therefore using the current sensor 9 of secondary battery 2, or a specific SOC current sensor.

[0062] Alternatively, a VT (Voltage Time) gauge detects the battery voltage and indicates the amount of electrical energy remaining available for life on board. This gauge ranges from 0% to 100%, is initialized by the OCV if available, and varies according to the time spent at a given voltage level. This gauge therefore does not require a current sensor. (It is not shown in [Fig. 1])

[0063] To prevent the secondary battery 2 from gradually discharging during short driving missions, a method for adjusting the charge level of the secondary battery 2 is applied by the computer 5 at the end of each mission of the electric or hybrid vehicle.

[0064] This method is illustrated in [Fig.2] and comprises the following steps:

[0065] a) a step for detecting the end of the mission of the electric or hybrid vehicle; as long as this step is not detected, it means that the electric or hybrid vehicle is in the driving phase, and that the adjustment of the battery charge level cannot start.

[0066] b) once the end of the mission has been detected, there is a step of detecting the charge level of the secondary battery 2; the computer 5 then looks at the charge level estimate, in this case the SOC or the VT gauge.

[0067] c) If the charge level of secondary battery 2 is above a low threshold, then this means that secondary battery 2 is sufficiently charged and it is not necessary to initiate the end-of-mission charging strategy. Computer 5 does not recharge secondary battery 2.

[0068] d) if the charge level of the secondary battery 2 is below the low threshold, then this means that the secondary battery 2 is not sufficiently charged and that it is It is necessary to launch the end-of-mission charging strategy. Secondary battery 2 then remains powered by primary battery 1.

[0069] e) in real time, the calculator 5 calculates the evolution of the charge level of the secondary battery 2.

[0070] f) if the charge level of the secondary battery 2 has reached a high threshold, then the computer 5 commands the cessation of the charging of the secondary battery 2. As long as this high threshold is not reached, the secondary battery 2 continues to be charged.

[0071] g) for safety, if the time elapsed since the start of the charging of the secondary battery 2 once the end of the mission has been detected has reached a predetermined duration, then the computer 5 commands the stopping of the charging of the secondary battery 2.

[0072] In summary, the operation is as follows. Once the end of the vehicle's mission is detected, the computer activates the battery charging strategy if the battery is not sufficiently charged. From that moment, it keeps the vehicle awake and the electrical generator active, and it completes the charge until it reaches the threshold of the charge level indicated on the SOC or the VT gauge. This operation is time-limited for safety reasons.

[0073] The computer 5 controls the converter 4 to stop the charging of the secondary battery 2, either when the charge level reaches the high threshold, or when the maximum charging time is exceeded.

[0074] By applying this method, the secondary battery 2 can be automatically recharged at the beginning of the stopping phases, invisibly to the vehicle driver. Thanks to these recharges, the secondary battery 2 maintains a maximum charge level, thus preventing gradual deterioration of the battery and ensuring safety functions regardless of the driver's driving style. The secondary battery 2 is therefore always operational.

[0075] In practical terms, end-of-mission detection corresponds to a specific action performed by the driver of the electric or hybrid vehicle while stationary, such as pressing an OFF button, putting a lever in the PARK position, or getting out of their seat. Other actions can be considered and fall within the scope of the present invention. These actions depend on each type of electric or hybrid vehicle.

[0076] The lower threshold is between 80% and 90% charge. Below this lower threshold, it is estimated that the secondary battery 2 is not sufficiently charged and that there is a risk of progressive discharge, and therefore ultimately a risk of failing to perform safety functions.

[0077] Preferably, said lower threshold is equal to 85%.

[0078] The upper threshold is between 90% and 100% charge. When the secondary battery 2 has reached the upper threshold, it is considered that the battery is sufficiently charged. for the next phase of driving, and that it can therefore ensure all safety functions.

[0079] Preferably, said upper threshold is equal to 95%.

[0080] The predetermined duration is between 15 minutes and 60 minutes. Indeed, it is important to limit the charging of the secondary battery 2 over time, for example if there is a fault on the secondary battery 2 and it is unable to charge, as this could lead to the discharge of the main battery 1, which is undesirable.

[0081] Preferably, said predetermined duration is equal to 30 minutes. This duration is preferable because it is known that batteries are normally sufficiently charged after 30 minutes of charging.

[0082] Fig. 3 illustrates the evolution of the state of charge of the secondary battery 2 when there is no method of adjusting the charge level of the secondary battery 2.

[0083] This figure illustrates the different driving and parking phases. This corresponds to drivers carrying out short-duration missions.

[0084] The battery charge level is initially at 80%. After the first driving stage (Driving 1), the secondary battery 2 recharged slightly, and its charge level rose to approximately 82%. This was followed by a parking stage (Parking 1), which reduced the charge level of the secondary battery 2 to 77%. The second driving stage (Driving 2) allowed the secondary battery 2 to recharge slightly, but not enough to reach 80%. This was followed by a parking stage (Parking 2), which reduced the charge level to 75%. The third driving stage (Driving 3) allowed the secondary battery 2 to recharge slightly, but again, not enough to reach 80%. This was followed by a parking stage (Parking 3), which reduced the charge level to 70%.

[0085] And so on. It is therefore understood that the charge level continues to decrease from one parking phase to the next, because the driving phases are not long enough to recharge the secondary battery 2 in the meantime.

[0086] Figure 4 illustrates the evolution of the state of charge of the secondary battery 2 when the charge level adjustment method is applied, according to the invention.

[0087] In this example, the load level to be reached, called the target SOC, and corresponding to the upper threshold, is located at 95%.

[0088] Just like [Fig.3], this [Fig.4] shows the different driving and parking phases, carried out by drivers performing repeated short-term missions.

[0089] The solid line curve represents the load level according to the prior art, according to [Fig.3].

[0090] The dashed line represents the charge level according to the invention.

[0091] The battery charge level is initially at 80%. After the first taxiing stage (Trip 1), the secondary battery 2 has recharged slightly, and its charge level has risen to approximately 85%. This is followed by an end-of-mission stage where the end-of-mission charging strategy is activated so that the battery charge level reaches 95%. Once this charge level is reached, the system enters a traditional parking phase (Parking 1) where the secondary battery 2 gradually discharges, in this case to 83%. The second taxiing stage (Trip 2) allows the secondary battery 2 to recharge slightly, this time reaching 87%. As the upper threshold has not yet been reached, it is necessary to activate the end-of-mission charging strategy again, until the battery reaches 95%.Then follows another traditional parking phase (Parking 2) where the secondary battery 2 gradually discharges, here until it reaches 85%. The third taxiing stage (Trip 3) allows the secondary battery 2 to recharge slightly, this time reaching 90%. As the upper threshold is not reached, it is therefore necessary to activate the end-of-mission charging strategy until the secondary battery reaches 95%, before switching to a parking phase (Parking 3).

[0092] With the activation of the end-of-mission charging strategy, it is therefore possible to maintain a charge level of the secondary battery which reaches or at least approaches the recommended high threshold, despite short driving phases.

[0093] This end-of-mission charging strategy has the advantage of not depending on the secondary battery technology, i.e. it can be applied to lead or lithium batteries for example.

[0094] Moreover, this strategy can be applied regardless of the technical definition of the vehicle (presence or absence of a current sensor), and does not require the addition of new components.

[0095] The configurations shown in the cited figures are only possible examples, by no means limiting, of the invention which on the contrary encompasses variants of forms and designs within the reach of a person skilled in the art.

Claims

Demands

1. A method for adjusting the charge level of a secondary battery 2 of an electric or hybrid vehicle powered by a primary battery 1, comprising the following steps: a) a step for detecting the end of the mission of the electric or hybrid vehicle; b) a step for detecting the charge level of the secondary battery 2; if the charge level in step b) is above a low threshold, c) a step for stopping the charging of the secondary battery 2; if the charge level in step b) is below said low threshold, d) a step for charging the secondary battery 2 from the primary battery 1; e) a further step for detecting the charge level of the secondary battery 2; f) a step for stopping the charging of the secondary battery 2 if the charge level in step e) has reached a high threshold; g) a step for stopping the charging of the secondary battery 2 if the time elapsed since step d) has reached a predetermined duration.

2. Method according to claim 1, characterized in that the end-of-mission detection corresponds to a specific action performed by the driver of the electric or hybrid vehicle when stopped, such as pressing an OFF button, or putting a lever in the Parking position, or getting up from his seat.

3. Method according to any one of the preceding claims, characterized in that said lower threshold is between 80% and 90% of load.

4. Method according to any one of the preceding claims, characterized in that said lower threshold is equal to 85%.

5. Method according to any one of the preceding claims, characterized in that said upper threshold is between 90% and 100% of load.

6. Method according to any one of the preceding claims, characterized in that said upper threshold is equal to 95%.

7. Method according to any one of the preceding claims, characterized in that said predetermined duration is between 15 minutes and 60 minutes.

8. Method according to any one of the preceding claims, characterized in that said predetermined duration is equal to 30 minutes.

9. Electric or hybrid vehicle comprising: - a main battery 1 for powering the vehicle's traction motor 3; - a secondary battery 2 powered by the main battery 1 via a converter 4; - a central unit 5 receiving input information from various sensors, performing calculations, and sending output information to the converter 4; said central unit 5 implementing a method for adjusting a charge level of the secondary battery 2 according to any one of the preceding claims.

10. Vehicle according to the preceding claim, characterized in that the central unit 5 calculates the charge level and controls the converter 4 to stop the charging of the secondary battery 2 if necessary.

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