METHOD FOR PROTECTING AN ELECTRIC OR HYBRID VEHICLE BATTERY CIRCUIT COMPRISING A SCREWED ELECTRICAL CONNECTION

Abstract

The invention aims to improve driver safety and ensure the integrity of an electric or hybrid vehicle by providing a protection method for an electrical circuit (10) comprising a switch (60) and a battery. The battery comprises a first module (21) and a second module (22) connected by a connecting bar (30) attached to the terminals of the first and second modules by, respectively, a first screwed electrical connection (51) and a second screwed electrical connection (52). The method includes steps for measuring the voltage, current, and calculating the resistance of the screwed electrical connections, enabling the identification of faulty screwed electrical connections (50). The method includes opening the switch (60) in the event of a critical failure. Temperature probes can be added to the screwed electrical connections of the circuit to provide an additional means of detection. Figure 1

Description

Title of the invention: METHOD FOR PROTECTING AN ELECTRIC OR HYBRID VEHICLE BATTERY CIRCUIT COMPRISING A SCREWED ELECTRICAL CONNECTION

[0001] The invention relates to electric vehicles, that is to say, those equipped with at least one battery for storing electrical energy intended for their propulsion. This includes vehicles with a single means of electric propulsion, as well as hybrid vehicles incorporating at least one mode of electric propulsion.

[0002] An electrical circuit comprising a battery and a switch is known from the prior art. The battery comprises modules connected in series by connecting bars. Each module has a positive terminal and a negative terminal. Busbars are connected to the terminals of the modules. Screw-type electrical connections secure the connecting bars to the busbars of the modules.

[0003] However, during vehicle operation, the tightness of the screwed electrical connections may loosen. Indeed, the vehicle generates vibrations during use, which can consequently cause the screwed electrical connections to loosen. If this occurs, the screwed electrical connection fails and overheats. The overheating then spreads to the battery module, reducing battery performance. As a result, a fire may start in the modules. Furthermore, when a faulty screwed electrical connection carries a current, a series electrical arc may be generated. The series electrical arc can generate heat, or even projections of incandescent material. In short, the integrity of the vehicle and the safety of the passengers may be compromised.

[0004] To this end, French patent application FR 3 123 990 A1 describes a method for detecting faulty screw-type electrical connections. The method includes voltage measurements that can be taken on the battery circuit. A voltage calculation then identifies whether a screw-type electrical connection is defective. If so, a circuit switch is opened. Consequently, current no longer flows in the electrical circuit. As a result, the screw-type electrical connection stops heating up, and the risk of fire is thus prevented. In this way, the preferred protection method is to open the switch as soon as a risk is detected.

[0005] However, the driver may be endangered due to the power outage. Indeed, the battery generates the electricity necessary for the vehicle's traction. A sudden loss of traction can be dangerous for the driver and other road users in certain traffic situations. For example, this is the case when the driver is overtaking another vehicle, or when the driver is merging, or if road traffic is heavy.

[0006] The objective of the present invention is to improve driver safety and to ensure vehicle integrity and performance.

[0007] To achieve this objective, the invention proposes a method for protecting an electrical circuit comprising a switch and a battery, the battery comprising: - a first module and a second module, the first module having a first terminal, the second module having a second terminal; - a first omnibus bus connected to the first terminal, and a second omnibus bus connected to the second terminal; - a connection bar; - a first screw-in electrical connection fixing the connecting bar to the first busbar, and a second screw-in electrical connection fixing the connecting bar to the second busbar, The process includes the following steps: - a step of measuring an electrical voltage recorded between the first busbar and the second omnibus bar, and an electric current intensity measured in the electrical circuit, - a step of calculating a resistance value RI of the first electrical connection screw calculated using the following formula: । _ L. _ _ / £3°ù U is the electrical voltage measured between the first bar omnibus and the second omnibus bar, I is the electric current intensity measured in the electrical circuit, R2 is a predetermined resistance value of the second screwed electrical connection and R3 is a predetermined resistance value of the connecting bar; - a step to report a failure in the first screwed electrical connection, a signal is emitted to alert the driver of the fault when R1 4 Rmin where Rmin is a predetermined resistance threshold value and RI is the value calculated resistance of the first screwed electrical connection; - a threshold calculation step (E4) for a maximum current intensity value Imax calculated using the following formula: Imax ~ PI is a predetermined maximum power value that can be dissipated by the first screwed electrical connection when RI 4 Rminoù RI is the calculated resistance value of the first screwed electrical connection; - a step of limiting the value of the current intensity of the electrical circuit in order to protect said electrical circuit, the value of the current intensity of the electrical circuit being kept lower than the value of the maximum current intensity Imax calculated when the value of the current intensity of the electrical circuit measured is lower than the value of the maximum current intensity Imax calculated; - a step of opening the switch so as to protect the electrical circuit when the value of the current intensity of the electrical circuit is greater than the calculated maximum current intensity value Imax.

[0008] This allows the driver to maintain control of the vehicle for as long as possible. The current intensity is chosen to allow the driver to continue driving even in the event of a minor failure of the screw-on electrical connection. In this way, the driver has the necessary time to perform maneuvers safely. At the same time, other road users are not surprised, as the vehicle can continue to move without necessarily losing traction in the event of a failure. Thus, the collective safety of road users is improved. Furthermore, the current intensity in the electrical circuit is limited to prevent the faulty screw-on electrical connection from overheating. This improves battery performance and preserves the integrity of the vehicle.

[0009] Furthermore, the protection method thus designed offers greater adaptability to vehicle maneuvers and battery status. The electrical circuit current is thus interrupted when significant vehicle acceleration, corresponding to an increase in the electrical circuit current, risks further overheating a faulty screw connection. Consequently, a fire is prevented without compromising the vehicle's maneuverability before reaching such electrical current levels. In this way, the driver is protected from both excessive heating of the faulty screw connection and a sudden loss of vehicle traction control.

[0010] Advantageously, the first screwed electrical connection or the second screwed electrical connection comprises a screw having a threaded body, a screw head embedded in a part of the first module, and a clamping nut.

[0011] Tightening the screwed electrical connection ensures reliable and stable electrical contact. On the one hand, such tightening ensures reliable electrical contact by maintaining constant and uniform pressure. This significantly reduces the risk of intermittent connections, which can lead to current interruptions or unexpected fluctuations in the electrical circuit. On the other hand, the assembly is designed to maintain a firm electrical contact. Such tightening is capable of resisting to vibrations and movements that could otherwise loosen the screwed electrical connections. This contributes to the reliability and durability of the screwed electrical connections. Furthermore, screwed electrical connections designed with simple components are easy to inspect and maintain.

[0012] Advantageously, the first screwed electrical connection has a temperature probe, the method further comprises the following steps: - a step of measuring a temperature value of the first electrical connection screwed by the temperature probe; - a temperature comparison step between the measured temperature value of the first screwed electrical connection and a predetermined temperature value, - a step of issuing an alert warning the driver of a failure in the first screwed electrical connection when the temperature value of the screwed electrical connection is greater than a predetermined minimum temperature value, a signal being emitted to alert the driver, - a step of opening the switch when the temperature value of the screwed electrical connection is greater than a predetermined maximum temperature value.

[0013] This provides an additional means of fault detection. Thus, the protection method is more reliable. Furthermore, it allows access to screwed electrical connections whose voltage cannot be easily measured. Consequently, temperature measurements provide more comprehensive vehicle protection. Moreover, obtaining temperature readings is straightforward and easy to implement in practice.

[0014] Advantageously, during the reporting step or during the alert issuance step, the signal is a lit indicator light.

[0015] The illuminated warning light may also flash at shorter intervals and / or have a higher brightness depending on the severity of the fault. This makes the warning easier to spot and improves driver safety.

[0016] Advantageously, during the signaling step or during the signal emission step, the signal is an audible signal.

[0017] This allows all vehicle passengers to be warned. The audible signal can be designed to emit a sound at shorter intervals and / or with a higher volume depending on the severity of the malfunction. This makes the alert easier to detect and improves the safety of vehicle users.

[0018] The invention further relates to a computer program comprising program code instructions for executing the steps of the method for protecting an electrical circuit as defined above, when said program is running on a computer.

[0019] The invention will be further detailed by describing non-limiting embodiments, and based on the accompanying figures illustrating variants of the invention, in which: - [Fig.1] schematically illustrates a view of an electrical circuit comprising a battery and a switch, the method of protecting the electrical circuit according to the present invention being applicable to such a circuit; - [Fig.2] illustrates a detailed view of a screwed electrical connection of a connection screwed electrical, illustrated in [Fig.1], which connects a busbar and a connecting bar; - [Fig. 3] illustrates a flowchart of the protection process according to the present invention.

[0020] Figure 1 illustrates an electrical circuit 10 comprising a switch 60 and a battery according to a first embodiment of the invention. The battery comprises a first module 21 and a second module 22. The first module has a first terminal. The second module 22 has a second terminal. In one embodiment, the first terminal is a positive terminal of the first module 21, while the second terminal is a negative terminal of the second module 22. In another embodiment, the first terminal is the negative terminal of the first module 21, while the second terminal is a positive terminal of the second module 22. A first busbar 41 is connected to the first terminal. A second busbar 42 is connected to the second terminal.The battery includes a connecting bar 30 and a first screwed electrical link 51 fixing the connecting bar 30 to the first omnibus bar 4L. The battery also includes a second screwed electrical link 52 fixing the connecting bar 30 to the second omnibus bar 42.

[0021] Figure 1 illustrates the electrical circuit 10 connecting the switch 60 and the battery in series. In this way, the same electric current, denoted I, flows through the electrical circuit. Furthermore, the switch 60 is connected to one terminal of the electrical circuit. Similarly, the battery is connected to another terminal of the electrical circuit. Thus, the electrical circuit has two terminals. A potential difference, denoted U, is present between the two terminals. The two terminals of the electrical circuit can be connected to the terminals of the vehicle's motor. Therefore, the electrical circuit can supply power to the vehicle's electric or hybrid motor. In one embodiment, the two terminals of the electrical circuit can also be connected to any other type of electrical load.According to one variant, the electrical voltage is recorded by measuring the electrical potential on the first busbar 41 and the electrical potential on the connecting busbar 30.

[0022]

[0023]

[0024] The diagnostic system is capable of operating at a lower current level than the current required during vehicle operation. For example, the diagnostic of a screwed electrical connection can be performed with a current of 50A in the electrical circuit. In typical use, the current is around 100A or even less. Therefore, the diagnostic system remains operational while the vehicle is in use. Figure 3 illustrates a flowchart representing the steps of the protection process. In a measurement step El, the voltage value U is recorded by measuring the electrical potential on the first busbar 41 and the electrical potential on the second busbar 42. In this way, the measured electrical voltage includes the electrical voltage of the first screw connection 51 and the electrical voltage of the second screw connection 52. Furthermore, the voltage value U is taken at a sampling frequency of approximately 1 second. In calculation step E2, the electrical resistance RI of the first screwed electrical connection 41 is calculated from the following formula: _ LL _ jjp _ j^^where R2 is a predetermined resistance value of the second screwed electrical connection 52 and R3 is a predetermined resistance value of the connecting bar 30. For example, the predetermined resistance value R2 of the second screwed electrical connection 52 is 50 qOhms, and the predetermined resistance value of the connecting bar 30 is about 0.1 mOhms.

[0025] Figure 2 illustrates in more detail the first screwed electrical connection 51. The first screwed electrical connection 51 comprises a screw 51V and a nut 51E. According to one embodiment, the screw 51V and the nut 51E can, of course, be replaced by any other fastening means. The screw 51V comprises a flat head 53T and a threaded body 53C. The threaded body 53C passes through the connecting bar 30, the first busbar 41, and a portion 21P of the first module 21. In Figure 2, the first busbar 41 is shown below the connecting bar 30. According to another embodiment, the connecting bar 30 is located below the busbar 4L.

[0026] The nut 51E is tightened so as to be flush with a surface of the connecting bar 30. Thus, the nut 51E exerts a uniform pressure on the surface of the connecting bar 30. In this way, the risks of cracking or localized damage around the point of tightening are reduced.

[0027] The screw head is recessed into part 21P of the first module 21. In this way, part 21P of the first module 21 provides a secure anchor for the screwed electrical connection 51. The material of part 21P of the first module 21 is preferably plastic. According to one embodiment, the material of part 21P of the first module 21 can be replaced by any electrically insulating material.

[0028] A clamping force is used to tighten the nut 51E. Consequently, the first screwed electrical connection 51 generates a compressive force on the connecting bar 30 and the first busbar 41. Thus, the connecting bar 30 and the first busbar 41 are kept in contact. In this way, an electric current is able to flow between the connecting bar 30 and the first busbar 41. Furthermore, since the body 51C of the screw is threaded, the risk of loosening the first screwed electrical connection 51 due to vibrations is minimized. In this case, the resistance RI of the first screwed electrical connection 51 takes a value of approximately 50 μOhms.

[0029] Vibrations are generated during vehicle operation. Due to these vibrations, nut 51E may loosen or detach from the bolt. As a result, the compressive force on connecting bar 30 and the first busbar 41 is reduced, or even eliminated. Generally, two types of failures of the first screwed electrical connection 51 can be identified.

[0030] In a first case, the connecting bar 30 and the busbar 41 are no longer in contact. Consequently, the electrical circuit current flows from the connecting bar 30 to the first busbar 41 only via the first screwed electrical connection 51. Therefore, the current is forced to flow through the cross-section of the body 51C of the screw 51V. In this first case, the electrical resistance RI of the first screwed electrical connection 51 takes a value of approximately 1 mOhm.

[0031] In a second case, the connecting bar 30 can be tilted. In this case, only a part of the connecting bar 30 is in contact with the first busbar 41. In this second case, the electrical resistance RI of the first screwed electrical connection 51 takes a value of approximately 0.5 mOhms.

[0032] Due to these intermittent connections, the electrical resistance of the screw-type electrical connection 51 increases. Thus, a failure of the screw-type electrical connection 51 results in greater Joule heating. Furthermore, in the event of intermittent connections, a series electrical arc can be created between the connecting bar 30 and the bus bar 41. In short, the aforementioned types of failures present a risk of fire for the battery, as well as a decrease in battery performance.

[0033] In a signaling step E3 of a failure in the first screwed electrical connection 51, a signal is emitted to alert the driver of the failure when Rl>Rmin where Rmin is a predetermined resistance threshold value and RI is the calculated resistance value of the first screwed electrical connection 51. For example, Rmin is 0.1 Ohms. The signal can be an audible and / or visual signal.

[0034] In a threshold calculation step E4, a maximum current intensity value Imax is calculated using the following formula:

[0035] Imax ~ °ù PI is a predetermined maximum power value dissipated by the first screwed electrical connection (51) when R > Rmin where RI is the calculated resistance value of the first screwed electrical connection (51). The predetermined maximum power PI that can be dissipated by the first screwed electrical connection 51 is the amount of energy per unit time that can pass through the first screwed electrical connection 51 without partially melting it. For example, the predetermined maximum power PI that can be dissipated by the first screwed electrical connection 51 is approximately 90 W. In a current limiting step E5, the current value of the electrical circuit is kept below the calculated maximum current value Imax when the current value of the electrical circuit is less than the calculated maximum current value Imax.

[0036] In this way, the vehicle's acceleration is low at the time the current intensity of the electrical circuit is measured. Furthermore, the vehicle's acceleration is preventively limited below a certain threshold. For example, for a resistance measurement RI of the first screwed electrical connection 51 of 1 mOhm and a predetermined maximum permissible power value PI of 90W, the maximum current intensity is 300A. Thus, the vehicle cannot accelerate sharply, which would correspond, for example, to an increase in the current intensity in the electrical circuit 10 beyond 300A, when a screwed electrical connection fails. Therefore, the heating of the faulty screwed electrical connection is not exacerbated.

[0037] According to one embodiment, the maximum current intensity is limited with a safety margin. For example, the safety margin may be 30%; using the previous example, the maximum current intensity is 210 A.

[0038] In an opening step E6, the switch 60 is opened when the value of the current intensity of the electrical circuit is greater than the calculated maximum current intensity value Imax.

[0039] In this way, the vehicle's acceleration is high at the time the current intensity in the electrical circuit is measured. Using the previous example, the vehicle's motor is powered off when the current intensity in the electrical circuit exceeds 300 A. Therefore, switch 60 only opens when the vehicle is accelerating rapidly and a screw-type electrical connection is faulty.

[0040] In a second embodiment not illustrated, the first screwed electrical connection 51 has a temperature probe, the method further comprising the following steps: - a step of measuring a temperature value of the first screwed electrical connection 51 by the temperature probe; - a temperature comparison step between the measured temperature value of the first screwed electrical connection 51 and a predetermined temperature value, - a step of issuing an alert warning the driver of a failure in the first screwed electrical connection 51 when the temperature value of the screwed electrical connection is greater than a predetermined minimum temperature value, a signal being emitted to alert the driver, - a step of opening switch 60 when the value of the temperature of the screwed electrical connection is greater than a predetermined maximum temperature value.

[0041] In this way, the risks of further heating of the faulty screwed electrical connection are reduced. Furthermore, by using temperature measurements, the protection process is more precise and reliable in its detection of faulty screwed electrical connections. Indeed, vibrations can cause variations in the electrical resistance measurements of screwed electrical connections. Temperature measurements help to limit the impact of these measurement errors on the identification of faults.

[0042] In a third embodiment not shown, a first battery module is connected to the switch. A second battery module is connected directly to a terminal of the electrical circuit. The first and second modules each comprise a first terminal and a second terminal, respectively. A first connector is connected to the switch. A first busbar is connected to the first terminal. A first screw-type electrical connection secures the first busbar and the first connector. A second connector is connected to a terminal of the electrical circuit. A second busbar is connected to the second terminal. A second screw-type electrical connection secures the second busbar and the second connector. A first temperature probe is arranged on the first screw-type electrical connection. Similarly, a second temperature probe is arranged on the second screw-type electrical connection.The temperature measurements obtained by the first and second temperature probes are subjected to the operating procedure described in the supplementary temperature monitoring steps of the second embodiment. Consequently, all screw-connected electrical connections of circuit 10 are diagnosed. As a result, the protection method is more comprehensive and reliable.

Claims

1. Demands Method for protecting an electrical circuit (10) comprising a switch (60) and a battery, the battery comprising: - a first module (21) and a second module (22), the first module (21) having a first terminal, the second module (22) having a second terminal; - a first omnibus bar (41) connected to the first terminal, and a second omnibus bar (42) connected to the second terminal; - a connection bar (30); - a first screwed electrical connection (51) fixing the connecting bar (30) to the first busbar (41), and a second screwed electrical connection (52) fixing the connecting bar (30) to the second busbar (42), the method comprising the following steps: - a measurement step (El) of an electrical voltage (U) recorded between the first busbar (41) and the second busbar (42), and of an electrical current intensity (I) measured in the electrical circuit (10), - a calculation step (E2) of a resistance value RI of the first screwed electrical connection (51) calculated by the following formula: J = y _ ^2 - / n° where U is the electrical voltage measured between the first busbar (41) and the second busbar (42), I is the electrical current intensity measured in the electrical circuit (10), R2 is a predetermined resistance value of the second screwed electrical connection (52) and R3 is a predetermined resistance value of the connecting bar (30); - a signaling step (E3) of a failure in the first screwed electrical connection (51), a signal being emitted to alert the driver of the failure when Rl> Rmin where Rmin is a predetermined resistance threshold value and RI is the calculated resistance value of the first screwed electrical connection (51); - a threshold calculation step (E4) of a maximum current intensity value Imax calculated by the following formula: Imax ~ PI is a predetermined maximum power value that can be dissipated by the first screwed electrical connection (51) when RI > Rmin where RI is the calculated resistance value of the first screwed electrical connection (51); - a limiting step (E5) of the current value of the electrical circuit so as to protect said electrical circuit (10), the current value of the electrical circuit being maintained below the calculated maximum current value Imax when the measured current value of the electrical circuit is less than the calculated maximum current value Imax; - an opening step (E6) of the switch (60) so as to protect said electrical circuit (10) when the current value of the electrical circuit is greater than the calculated maximum current value Imax.

2. Method according to claim 1, characterized in that the first screwed electrical connection (51) or the second screwed electrical connection (52) comprises a screw (51V) having a threaded body (51C), a screw head (51T) embedded in a part (21P) of the first module (21), and a clamping nut (51E).

3. A method according to claim 1 or 2, characterized in that the first screwed electrical connection (51) has a temperature probe, the method further comprising the following steps: - a step of measuring a value of the temperature of the first screwed electrical connection (51) by the temperature probe;- a temperature comparison step between the measured temperature value of the first screwed electrical connection (51) and a predetermined temperature value, - a step of issuing an alert warning the driver of a failure in the first screwed electrical connection (51) when the temperature value of the screwed electrical connection is greater than a predetermined minimum temperature value, a signal being emitted to alert the driver, - a step of opening the switch (60) when the temperature value of the screwed electrical connection is greater than a predetermined maximum temperature value.

4. A method according to any one of claims 1 to 3, characterized in that during the signaling step or during the alert issuance step, the signal is a lit indicator light.

5. A method according to any one of claims 1 to 4, characterized in that during the signaling step or during the signal emission step, the signal is an audible signal.

6. Computer program comprising program code instructions for performing the steps of the method for protecting an electrical circuit according to any one of claims 1 to 5, when said program is running on a computer.

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