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

Abstract

The invention relates to a method for protecting an electrical circuit (10) of an electric or hybrid vehicle comprising a screwed electrical connection (51, 52, 53, 54), a battery (20) comprising a module (21, 22) and a switch (30), the screwed electrical connection comprising a temperature sensor (41, 42, 43, 44), the method comprising the following steps: - two steps for measuring the temperature value of the screwed electrical connection; - one step for calculating a temperature time gradient value of the screwed electrical connection; - one step for opening the switch when the calculated temperature time gradient value is greater than a temperature time gradient threshold value of the screwed electrical connection. Figure 1

Description

Title of the invention: METHOD FOR PROTECTING AN ELECTRICAL CIRCUIT OF AN ELECTRIC OR HYBRID VEHICLE 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] Prior art information exists for an electrical circuit comprising a first battery module having a first voltage terminal and a second battery module having a second voltage terminal. Furthermore, the electrical circuit includes a connecting bar. A first screw-type electrical connection secures the first voltage terminal to the connecting bar. A second screw-type electrical connection secures the second voltage terminal to the connecting bar.

[0003] Prior art also shows that the vehicle generates vibrations during its use, which can cause the first screwed electrical connection to loosen. In particular, two cases of failure of the screwed electrical connection can be identified. In the first case, the connecting bar tilts relative to the screwed electrical connection. In this case, part of the connecting bar is in contact with a voltage terminal. For example, the electrical resistance value of the screwed electrical connection in this second case is approximately 0.5 mOhms. In the second case, the connecting bar and the voltage terminal are no longer in contact. As a result, the electrical circuit current flows from the connecting bar to the voltage terminal via the screwed electrical connection. Consequently, the current passes through the cross-section of the screw body.For example, the electrical resistance value of the screwed electrical connection in this first case is approximately 1 mOhm.

[0004] Due to these intermittent connections, the electrical resistance of the screw connection increases. Consequently, the failure of the first screw connection results in greater Joule heating. This heating spreads from a hot spot to the battery module, reducing battery performance. As a result, a fire can start in the first module. Furthermore, in some cases of intermittent contact failure, an electric arc is generated. In short, the aforementioned failure scenarios present a risk of fire for the battery, as well as a decrease in battery performance.

[0005] To this end, patent application EP2842797 describes a device comprising a connector, disposed on the connection bar, including a first connection part and a second connection part. Furthermore, a first detection terminal is connected to the first detection terminal in order to measure a temperature. In addition, a second detection terminal is connected to the second detection terminal in order to measure a voltage. In particular, these temperature and voltage measurements are intended for the detection of a failure of the first screwed electrical connection or the second screwed electrical connection.

[0006] The objective of the present invention is to overcome the aforementioned disadvantages and to improve driver safety while ensuring the integrity and performance of the vehicle.

[0007] To achieve this objective, the invention proposes a method for protecting an electrical circuit of an electric or hybrid vehicle comprising screwed electrical connections, a battery comprising a module and a switch, each of said screwed electrical connections comprising a temperature probe, the method comprising the following steps: - a step of measuring a first temperature value for each of the said screwed electrical connections at a first given instant; - a subsequent measurement step of a second temperature value for each of the said screwed electrical connections at a second given instant following the first given instant; - a step of calculating a time gradient value of temperature for each of the said screwed electrical links between the first temperature value measured at the first given instant and the second temperature value measured at the second given instant; - a step of opening the switch after a predetermined time in order to protect the electrical circuit when the calculated time gradient value of one of said screwed electrical links is greater than a time gradient threshold value of the screwed electrical link.

[0008] Such a method is adaptable to all electrical connections in the circuit, thereby limiting the risk of a faulty screw connection going undetected. Furthermore, wiring the electrical circuit for such measures is simple, reducing the risk of electrical arcing. In this way, the risk of fire is prevented.

[0009] Advantageously, the method comprises, between the subsequent measurement step and the calculation step: - a step of calculating an average value of the temporal temperature gradient for each of the said screwed electrical connections from the calculated temporal temperature gradient values; - a step of calculating a standard deviation value of the temporal temperature gradient for each of the said screwed electrical links from the calculated average value of the temporal temperature gradient and the calculated temporal temperature gradient values; - a step of calculating a threshold value of temporal temperature gradient, denoted S, for each of the said screwed electrical links, by the following formula, S = M + a*<7 where M is the calculated average value of temporal temperature gradient, is the calculated standard deviation value of temporal temperature gradient and a is a predetermined parameter; - a step of assigning the temperature time gradient threshold value to each of the said screwed electrical connections.

[0010] The model calculates the temperature time gradient threshold value of each of said screwed electrical connections in order to detect a faulty screwed electrical connection more quickly and more reliably.

[0011] Advantageously, the predetermined parameter is between 1 and 10.

[0012] Advantageously, the method includes a step of regulating the current intensity of the electrical circuit so as to protect the electrical circuit, the value of the current intensity of the electrical circuit being maintained below a predetermined value of electrical current intensity when the calculated time gradient value of one of said screwed electrical links is greater than the time gradient threshold value of the screwed electrical link.

[0013] This allows the driver to maintain control of the vehicle for as long as possible. The current intensity is controlled so that the driver can 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.

[0014] Advantageously, the predetermined electric current intensity value is between 0A and 500A.

[0015] The current intensity value of the electrical circuit is chosen so as to prevent the faulty screw-type electrical connection from overheating. This improves battery performance and preserves the integrity of the vehicle.

[0016] Advantageously, the temperature gradient threshold value is between 10°C / min and 100°C / min.

[0017] Such a temperature time gradient threshold value is chosen so as to avoid triggering the interruption of the electrical circuit current for a connection functional screw-on electrical connection while limiting the risk of a faulty screw-on electrical connection overheating undetected.

[0018] Advantageously, the predetermined duration is between 1s and 10min.

[0019] The predetermined duration is chosen so that the driver continues to drive even in the event of a slight failure of a screwed electrical connection, while limiting the risk of further aggravating the heating of the faulty screwed electrical connection.

[0020] The invention also relates to a computer program comprising program code instructions for executing the steps of the method for protecting an electrical circuit according to the invention, when said program is running on a computer.

[0021] The invention further relates to a vehicle comprising an electrical circuit and an electronic control unit comprising means for acquisition, processing by software instructions stored in a memory as well as control means required for the implementation of the computer program as defined above.

[0022] In practice, the electronic control unit is a battery management system, also called a BMS. Battery management systems are already commonly used in hybrid and electric vehicles. The battery management system includes a microcontroller to process the measured temperature values.

[0023] 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.l] schematically illustrates a view of an electrical circuit including a battery and a switch, according to the state of the art; - [Fig. 2] illustrates a detailed view of a screwed electrical connection of the circuit electrical, illustrated in [Fig.1], the screwed electrical connection bringing into contact a first electrical termination and a second electrical termination; - [Fig. 3] illustrates a flowchart representing the steps of a process of protection of the electrical circuit, illustrated in [Fig.1], according to an embodiment of the present invention.

[0024] Fig. 1 illustrates an electrical circuit 10 comprising a switch 30, screwed electrical connections 51, 52, 53, 54, temperature probes 41, 42, 43, 44 and a battery 20 comprising modules 21, 22. Each of said screwed electrical connections includes a temperature probe.

[0025] In what follows, n denotes the number of screwed electrical connections 51, 52, 53, 54 in the electrical circuit 10. The screwed electrical connections 51, 52, 53, 54 are denoted as follows: a first screwed electrical connection is denoted L1, a second The first screwed electrical connection is denoted L2, a third screwed electrical connection is denoted L3, an i-th screwed electrical connection is denoted Li, a k-th screwed electrical connection is denoted Lk, up to an nth screwed electrical connection is denoted Ln.

[0026] A battery management unit 20, not shown, includes a microcontroller.

[0027] Fig. 2 represents, in a detailed view, the electrical circuit 10 comprising a first electrical termination 61 and a second electrical termination 62.

[0028] Throughout the following, the elements which are included in the battery 20 of the electrical circuit 10 will be referred to as "internal" in relation to other elements referred to as "external", the "external" elements being included in the electrical circuit 10 and not in the battery 20.

[0029] In this case, the external screwed electrical connection 53, illustrated in [Fig.2], fixes the first electrical termination 61 to the second electrical termination 62. Generally, the screwed electrical connections 51, 52, 53, 54 include external screwed electrical connections 53, 54 to the battery 20.

[0030] Furthermore, the temperature probes 41, 42, 43, 44 include temperature probes 43, 44 external to the battery 20. In particular, the external temperature probe 43, illustrated in [Fig.2], is disposed on the first electrical termination 61. The external temperature probe 43 measures a temperature value of the external screwed electrical connection 53.

[0031] The arrangement of said external temperature probes to the battery 20 makes it possible to detect a faulty screwed electrical connection throughout the electrical circuit disconnection device, contributing to a more complete coverage of the risks of failure.

[0032] The external temperature probe 43 is electrically connected to the microcontroller. Thus, the microcontroller is able to digitally process the temperature value of the external screw-connected electrical link 53.

[0033] The electrical circuit 10, illustrated in [Fig. 1], comprises a battery 20 having modules 21, 22. In particular, module 21 includes a voltage terminal and a connecting bar. The screw-type electrical connections 51, 52, 53, 54 include internal screw-type electrical connections 51, 52 to the battery 20. In particular, the internal screw-type electrical connection 51 secures the connecting bar to the voltage terminal.

[0034] Furthermore, the temperature probes 41, 42, 43, 44 include internal temperature probes 41, 42 in the battery 20. In particular, the internal temperature probe 41 measures a temperature value of the internal screwed electrical connection 51.

[0035] Such an arrangement of said internal temperature probes in the battery 10 allows the existing measurement wiring on the module to be reused to transmit the temperature value, thus reducing the manufacturing costs of the electrical circuit.

[0036] Modules 21, 22 each comprise a cell controller electrically connected to the microcontroller. Internal temperature probes 41, 42 are electrically connected to the cell controllers. Thus, the microcontroller is able to process the measured temperature values ​​of the internal screw-connected electrical links 51, 52.

[0037] The electrical circuit 10 preferably puts the switch 30 and the screwed electrical connections 51, 52, 53, 54 in series. In this way, the same intensity of electric current I flows through the electrical circuit 10.

[0038] Advantageously, the switch 30 is connected to a first connection terminal of the electrical circuit 10. The electrical circuit 10 also includes a second connection terminal. Thus, the electrical circuit 10 supplies power to the electric or hybrid motor of the vehicle.

[0039] The external screw-type electrical connection 53, illustrated in [Fig. 2], comprises a screw and a nut 53E. The screw has a flat head 53T and a threaded body 53C. The threaded body 53C passes through the first electrical termination 61 and the second electrical termination 62. Thus, the electric current is able to flow between the first electrical termination 61 and the second electrical termination 62.

[0040] Advantageously, the nut is tightened so as to be flush with a surface of the first termination 61. Thus, the nut 53E exerts a uniform pressure on the surface of the first termination 61. In this way, the risks of cracking or localized damage around the tightening point are reduced.

[0041] In addition, a clamping force is used to tighten the nut 53E. Thus, the screwed electrical connection 53 generates a compressive force so that the first electrical termination 61 and the second electrical termination 62 are kept in contact.

[0042] Figure 3 illustrates a flowchart of a method for protecting the electrical circuit 10, the method comprising the steps described below according to an embodiment of the present invention. The method is applied to a screwed electrical connection, denoted Lk, chosen from among the screwed electrical connections 51, 52, 53, 54 by way of example.

[0043] In a measurement step El, a first temperature value, denoted Tk, of the screwed electrical connection, denoted Lk, is measured at a given first instant. This measurement step El is repeated for each of said screwed electrical connections 51, 52, 53, 54.

[0044] In a subsequent measurement step E2, a second temperature value, denoted Tk', of the screwed electrical connection, denoted Lk, is measured at a second given instant following the first given instant. This measurement step E2 is repeated for each of said screwed electrical connections 51, 52, 53, 54.

[0045] In a calculation step E3, a time gradient value of the temperature of the screwed electrical connection, denoted Lk, is calculated between the first temperature value measured at the first given instant and the second temperature value measured at the second given instant. This calculation step E3 is repeated for each of said screwed electrical connections 51, 52, 53, 54.

[0046] In the following, the time gradient values ​​of the temperature of the screwed electrical links 51, 52, 53, 54 are noted as follows: a first time gradient value of the temperature, associated with the first screwed electrical link L1, is noted 01, a second time gradient value of the temperature, associated with the second screwed electrical link L2, is noted 02, a third time gradient value of the temperature, associated with the third screwed electrical link L3, is noted ®3, an i-th time gradient value of the temperature, associated with the i-th screwed electrical link Li, is noted 0i, a k-th time gradient value of the temperature associated with the k-th screwed electrical link Lk, is noted 0k, up to an nth time gradient value of the temperature, associated with the nth screwed electrical link Ln, is noted 0n.

[0047] For example, in the calculation step E3, the time gradient value of temperature, denoted 0k, of the screwed electrical connection, denoted Lk, is calculated by the following formula, 0^ _ where At is a time interval value between the first instant and the second instant.

[0048] Preferably, the time interval value between the first instant and the second instant is between 500ms and 30s.

[0049] Advantageously, in a calculation step E' 1, an average value of the time gradient of temperature is calculated for the screwed electrical connection denoted Lk from the time gradient of temperature values ​​calculated for each of said screwed electrical connections 51, 52, 53, 54. This calculation step E' 1 is repeated for each of said screwed electrical connections 51, 52, 53, 54.

[0050] For example, in calculation step E' 1, the average time gradient value of temperature, denoted Mk, of the screwed electrical connection, denoted Lk, is calculated by the following formula, = ^•where n is the number of said screwed electrical connections and 0i is the calculated time gradient value of the i-th screwed electrical connection, denoted Li.

[0051] Advantageously, in a calculation step E'2, a standard deviation value of the time gradient of temperature is calculated for the screw-in electrical connection, denoted Lk, from the calculated mean value of the time gradient of temperature and the values ​​of time gradient of temperature calculated for each of the said screwed electrical links 51, 52, 53, 54. This calculation step E'2 is repeated for each of the said screwed electrical links 51, 52, 53, 54.

[0052] For example, in calculation step E'2, the standard deviation value of the temporal temperature gradient, denoted ok, of the screwed electrical connection denoted Lk, is calculated by the following formula, ok = min ( } ke [[ 1, nj )

[0053] Even more advantageously, the second calculation step E'2 is pre-recorded in the microcontroller the first time the temperature standard deviation value is calculated. This reduces the execution time of the protection process.

[0054] Advantageously, in a calculation step E'3, a temperature time gradient threshold value, denoted Sk, of the screwed electrical connection denoted Lk, is calculated by the following formula, Sk = Mk + «:W <où a est un paramètre prédéterminé. cette étape de calcul e’3 répétée pour chacune desdites liaisons électriques vissées 51, 52, 53, 54.

[0055] Preferably, the predetermined parameter a is between 1 and 10.

[0056] Advantageously, in an assignment step E'4, the gradient threshold value The time-domain temperature, denoted Sk, is assigned to the screwed electrical connection, denoted Lk. This assignment step E'4 is repeated for each of the said screwed electrical connections 51, 52, 53, 54.

[0057] Advantageously, in a regulation step E'5, the current intensity of the electrical circuit is regulated so as to protect the electrical circuit, the value of the current intensity of the electrical circuit being maintained below a predetermined value of electrical current intensity when the calculated time gradient value of one of said screwed electrical links is greater than the time gradient threshold value of the screwed electrical link.

[0058] Preferably, the predetermined electric current intensity value is between 0A and 500A.

[0059] Advantageously, in a signaling step, a signal is emitted to alert the driver of a failure when the temperature time gradient value of one of said screwed electrical links 51, 52, 53, 54 is greater than the calculated temperature threshold value of the screwed electrical link.

[0060] In an opening step E4, the switch 30 is opened after a predetermined time so as to protect the electrical circuit when the calculated time gradient value of one of said screwed electrical links 51, 52, 53, 54 is greater than the time gradient threshold value of the screwed electrical link.

[0061] Preferably, the temperature gradient threshold value is between 10°C / min and 100°C / min.

[0062] Preferably, the predetermined duration is between 1s and 10min.

Claims

Demands

1. A method for protecting an electrical circuit (10) of an electric or hybrid vehicle comprising screwed electrical connections (51, 52, 53, 54), a battery (20) comprising a module (21, 22) and a switch (30), each of said screwed electrical connections (51, 52, 53, 54) comprising a temperature probe (41, 42, 43, 44), the method comprising the following steps: - a measurement step (El) of a first temperature value for each of the said screwed electrical connections (51, 52, 53, 54) at a first given instant; - a subsequent measurement step (E2) of a second temperature value for each of the said screwed electrical connections (51, 52, 53, 54) at a second given instant following the first given instant; - a calculation step (E3) of a time gradient value of temperature for each of the said screwed electrical links (51, 52, 53, 54) between the first temperature value measured at the first given instant and the second temperature value measured at the second given instant; - an opening step (E4) of the switch (30) after a predetermined time so as to protect the electrical circuit (10) when the calculated time gradient value of one of said screwed electrical links (51, 52, 53, 54) is greater than a time gradient threshold value of the screwed electrical link.

2. A method according to claim 1, characterized in that the method comprises, between the subsequent measurement step (E2) and the calculation step (E3): - a calculation step (E' 1) of an average value of the time gradient of temperature for each of the said screwed electrical links (51, 52, 53, 54) from the calculated time gradient of temperature values; - a calculation step (E'2) of a standard deviation value of the temporal temperature gradient for each of the said screwed electrical links (51, 52, 53, 54) from the calculated average value of the temporal temperature gradient and the calculated temporal temperature gradient values; - a calculation step (E'3) of a temperature time gradient threshold value, denoted S, for each of the said screwed electrical connections (51, 52, 53, 54), by the following formula, 5 = M + a where M is the calculated average temperature time gradient value, is the calculated standard deviation temperature time gradient value and a is a predetermined parameter; - an assignment step (E'4) of the temperature time gradient threshold value to each of the said screwed electrical connections (51, 52, 53, 54).

3. Method according to claim 2, characterized in that the predetermined parameter is between 1 and 10.

4. A method according to any one of claims 1 to 3, characterized in that the method comprises a step of regulating the current intensity of the electrical circuit so as to protect the electrical circuit, the value of the current intensity of the electrical circuit being maintained below a predetermined value of electrical current intensity when the calculated time gradient value of one of said screwed electrical links (51, 52, 53, 54) is greater than the time gradient threshold value of the screwed electrical link.

5. Method according to claim 4, characterized in that the predetermined electric current intensity value is between OA and 500A.

6. A method according to any one of claims 1 to 5, characterized in that the temperature gradient threshold value is between 10°C / min and 100°C / min.

7. A method according to any one of claims 1 to 6, characterized in that the predetermined duration is between 1s and 10min.

8. Computer program comprising program code instructions for performing the steps of the method for protecting an electrical circuit (10) according to any one of claims 1 to 7, when said program is running on a computer.

9. A vehicle comprising an electrical circuit (10) and an electronic control unit, characterized in that the control unit comprises means for acquisition, processing by means of software instructions stored in memory, and means for command required for the implementation of the computer program according to claim 8.

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