BATTERY PROTECTION FOR ELECTRIC OR HYBRID MOTOR VEHICLES WITH PYROTECHNICAL CUT-OFF

Abstract

A protection system for a power supply battery of an electric traction machine of an electric or hybrid motor vehicle, comprising a pyrotechnic cut-off device (10) for the current delivered by the battery (2), and a control means for triggering the pyrotechnic cut-off device (10) when the delivered current exceeds a threshold intensity, this control means having a variable time delay before the triggering of the pyrotechnic cut-off (10), which has a decreasing time delay duration as the delivered current increases. Figure 1

Description

Title of the invention: PROTECTION OF THE BATTERY OF AN ELECTRIC OR HYBRID MOTOR VEHICLE WITH PYROTECHNIC CUT-OFF

[0001] The present invention relates to a system for protecting a battery of an electric or hybrid motor vehicle, comprising a pyrotechnic current cut-off device, as well as a motor vehicle equipped with such a protection system.

[0002] A type of power supply circuit for an electric traction machine of an electric or hybrid motor vehicle, presented in particular by document DE-Al-102013017409, comprises a high-voltage battery delivering a current to several particular circuits arranged in parallel, each comprising a safety device installed in series in order to interrupt its current in the event of a failure resulting in excessively high current which is dangerous. The high voltage is generally between 400 and 800V.

[0003] A pyrotechnic cut-off device, called a "pyroswitch" in English, installed inside the battery, comprises a detonator actuated by an electric control current delivered by the battery management system, called a "battery management system" in English, "BMS" for short, to cut a connection strip directly at the output of the electrochemical elements delivering the electrical power. The pyrotechnic cut-off device has a very high reactivity allowing it to intervene in a few milliseconds to completely open the internal circuit of the high-voltage battery in the event of a significant risk.

[0004] The particular high-voltage electrical circuits include the power supply circuit of the traction machine, and generally circuits for other functions such as a system for heating the heat exchange fluid of the electric machine and its power system, or a system for recharging the low-voltage battery of the on-board network, passing through a DC-DC current transformer delivering a direct current of 12V.

[0005] For this type of vehicle it is known to have on each particular electrical circuit a suitable protection allowing it to be opened when an excessive current passes so as to isolate only this circuit which is faulty, and to maintain the power supply to the other circuits arranged upstream or in parallel in order to keep them in service. The protection may include fuses or controlled relays.

[0006] In certain cases, it is possible to maintain use of the vehicle with the circuits in good condition. remaining condition, which is desirable to maintain the movement of the vehicle if safety is assured, with the best possible level of performance and comfort.

[0007] The high-voltage electrical circuit of the vehicle can be divided at various times into several branches of particular parallel circuits, each receiving a part of the current intensity, with each time a reduced current flow section adapted to its consumption. In this case it is known to have on each departure of a new branch a protection comprising a reduced caliber to protect this branch.

[0008] In the event of an excessively high intensity in a specific branch, the smaller gauge of its own protection normally allows it to open before the protections located upstream which are designed to receive a higher intensity.

[0009] This arrangement of protections achieves selectivity of cuts, with a maintenance of the current supply to the branches arranged in parallel or upstream which remain in service. In addition, the repair of the vehicle is limited with the repair of the faulty branch to the replacement only of the small caliber protection which is specific to it, which limits the costs.

[0010] However, in some cases, failures of the cut-off devices can be observed. In particular, controlled relays can open with a delay due to the operation of the control software, or to failures of other functions, for example in an accident. The relay contacts can also remain stuck after wear of the coating which has undergone a certain number of maneuvers.

[0011] The pyrotechnic cut-off device, arranged upstream of all the branches of the circuit, triggered by detection of a threshold of intensity of the current delivered by the battery which is carried out by the management system of this battery, presents with its high reactivity an ultimate protection which will isolate the faulty branch like all the others. In particular, it is possible to establish an intensity threshold of 1000 to 1500A, exceeding any maximum normal consumption, which signals a serious failure requiring the imperative opening of the electrical circuit.

[0012] However, the pyrotechnic cut-off controlled solely by the measurement of the current intensity in the battery exceeding the threshold, which is very reactive, can be triggered before the slower protection devices installed downstream have had time to react, while the vehicle's electrical system was not immediately in danger.

[0013] Repairing the pyrotechnic cut-off device installed inside the battery leads to problems of removing, opening and repairing this battery which take time, require qualified personnel, are complex to carry out and require the exchange of elements with a high price. This results in a long vehicle downtime and a significant repair cost.

[0014] The present invention aims in particular to avoid these problems of the prior art.

[0015] To this end, it proposes a system for protecting a power supply battery of an electric traction machine of an electric or hybrid motor vehicle, comprising a pyrotechnic cut-off device for the current delivered by the battery, and a control means triggering the pyrotechnic cut-off device for a delivered current exceeding an intensity threshold, this system being remarkable in that the control means comprises a variable time delay before triggering the pyrotechnic cut-off, which has a reduction in the time delay duration as a function of an increase in the delivered current.

[0016] An advantage of this protection system is that to avoid triggering the pyrotechnic device too quickly and perhaps unnecessarily, it provides a minimum delay thanks to the time delay in order to allow the downstream protections time to operate, while managing the safety of the delay thanks to this time delay depending on the intensity of the measured current which can be longer if the current overshoot is low and shorter if the overshoot is significant with high risks.

[0017] The protection system according to the invention may further comprise one or more of the following characteristics, which may be combined with each other.

[0018] Advantageously, from the current threshold the control means comprises a time delay exhibiting a regular decrease to reach the minimum achievable tripping delay, with a value always lower than a curve of actual protection requirement.

[0019] In particular, the current intensity threshold can be between 1000 and 1500A.

[0020] Advantageously, the control means comprises a device for instantaneous measurement of the current delivered which takes this measurement into account at the precise moment of deciding to trigger the pyrotechnic cut-off.

[0021] Advantageously, the control means comprises at the input of the measurement of the intensity of the delivered current an optocoupler delivering a level of intensity of this delivered current with a low voltage of 5V.

[0022] Advantageously, the control means comprises an analog circuit which manages the time delay duration.

[0023] In this case, advantageously the analog circuit comprises a first operational amplifier creating an increasing timing signal with a speed depending on the increase in the intensity of the current delivered, which is applied to a second amplifier carrying out an end of timing detection by measuring a threshold of this increasing signal calibrated by resistors.

[0024] Furthermore, advantageously the analog circuit comprises a third operational amplifier receiving the measurement of the intensity of the delivered current, which detects whether this delivered current is still greater than the intensity threshold when the end of the time delay arrives.

[0025] In this case, advantageously the end of time delay signal delivered by the second amplifier and the current detection signal still higher than the threshold delivered by the third amplifier, are delivered to an addition function which gives the final signal for activating the pyrotechnic cut-off.

[0026] The invention also relates to an electric or hybrid motor vehicle equipped with an electric traction machine and a battery supplying this machine, remarkable in that it comprises a battery protection system comprising any one of the preceding characteristics, comprising the pyrotechnic cut-off device which is integrated in the battery.

[0027] The invention will be better understood and other characteristics and advantages will appear more clearly on reading the description below given by way of example, with reference to the appended drawings in which:

[0028] [Fig.l] shows an electrical circuit of a motor vehicle comprising electric traction, equipped with a protection system according to the invention;

[0029] [Fig.2] is a diagram showing the triggering time delay as a function of different current intensities, and

[0030] [Fig.3] is a block diagram of an analog circuit for controlling the device of pyrotechnic cut-off.

[0031] [Fig.l] shows a battery 2 for supplying an electric traction machine of a motor vehicle, comprising electrochemical cells 4 connected together in series which deliver, via a positive terminal 20 and a negative terminal 22, a current to several particular circuits arranged in parallel 8.

[0032] The positive pole of the electrochemical cells 4 successively comprises in series a controlled pyrotechnic cut-off device 10, a controlled main relay 12 arranged in parallel with a precharge circuit 14 comprising a resistor and a precharge relay in series, a resistor with a measurement of the potential difference at its terminals forming a current sensor 16, then a main fuse 18 before arriving at the positive terminal 20. The negative pole of the electrochemical cells 4 is connected by a manual contactor 26 to the negative terminal of the battery 22.

[0033] A battery management system BMS 6 receives information from the electrochemical cells 30, the current sensor 16 and external vehicle control systems 32, to issue commands to the pyrotechnic cut-off device 10, the main relay 12 and the precharge circuit relay 14.

[0034] In particular when starting the vehicle from cold, the precharge circuit relay 14 is activated and the main relay 12 is opened so as to ensure for a short time a limitation of the current in the particular circuits 8 to protect them.

[0035] The particular circuits 8 each supply via a secondary input fuse 24 an electrical function 26 comprising the electrical machine, a heating of the fluid thermal regulation of the engine or a charger of the on-board network battery. Each secondary fuse 24 is adjusted according to the maximum consumption of its particular circuit 8, so as to quickly detect any abnormal intensity on this circuit to protect it.

[0036] The main fuse 18, supplying all the particular circuits 8 arranged downstream, is calibrated according to the sum of the intensities that they can consume at the same time. Alternatively, the battery 2 may comprise only a pyrotechnic cut-off device 10, without the main fuse 18, which fulfills the same function as this fuse.

[0037] In the event of a failure of a particular circuit 8 resulting in a short circuit and an abnormal increase in the intensity of its current, its own secondary fuse 24 having a smaller rating than that of the main fuse 18 opens first, which makes it possible to isolate this particular circuit while allowing the use of the other circuits which remain powered.

[0038] However, the current sensor 16 can measure a very short intensity peak before the secondary fuse 24 or the main fuse 18 opens, which is sufficient to send a safety alert transmitted to the battery management system BMS 6, designed to be very reactive, which can, depending on the conditions, control the pyrotechnic cut-off device 10. This results in actuation of the pyrotechnic cut-off device 10 even though the secondary fuse 24 of the particular circuit concerned 8 has not had time to open, and the electrical system was not immediately in danger.

[0039] The pyrotechnic cut-off device 10 integrated in the battery 2 is an expensive element which requires the removal and opening of this battery to change it, which results in significant repair costs for the vehicle.

[0040] To avoid this, the battery management system 6 includes a control of the pyrotechnic cut-off device 10 comprising a time delay before triggering this cut-off which depends on the intensity of the current measured by the current sensor 16. In the event of measurement of an intensity exceeding a safety threshold, a time delay is activated in order to allow time for the secondary fuse concerned 24 to open, which is increasingly shorter depending on the extent of this excess to ensure safety.

[0041] The time delay is designed to allow a transient current peak within this time period which remains short enough not to damage the battery 2, while waiting for the faulty particular circuit 8 to open. In the event of the current peak continuing beyond the time delay, the pyrotechnic cut-off 10 is activated, which ensures safety.

[0042] [Fig.2] is a diagram showing, as a function of the intensity of the current I in amperes, presented on the horizontal axis, of the time delays T before the opening of different security systems.

[0043] For the cut-off devices according to the prior art, the pyrotechnic cut-off curve according to the prior art 40, with a vertical line calibrated for a threshold current II of 1000A, shows above this threshold a systematic triggering of the pyrotechnic cut-off 10 which is accomplished with a very short minimum reaction time T1.

[0044] Four secondary fuse curves 24 successively comprise for the first 42, the second 44, the third 46 and the fourth curve 48 increasingly high intensity levels corresponding to the necessary protection of their particular circuits 8. In all cases the cut-off curve according to the prior art 40 shows from the current threshold II of 1000A a curve passing below those of the secondary fuses 42, 44, 46, 48, which gives above this threshold the systematic actuation of this pyrotechnic cut-off before that of the fuse concerned.

[0045] Curve 50 presents a real minimum need for protection, comprising from the threshold of 1000A a time delay T which decreases as a function of the increase in intensity I.

[0046] The cut-off time delay curve according to the invention 52 presents the time delay before the triggering of the protection system, comprising for the threshold current I1 of 1000A a time delay T2 slightly lower than the actual protection requirement curve 50, which then decreases according to the increase in this intensity, to reach at a maximum intensity Imax the greatest triggering speed corresponding to the minimum reaction time T1 of the pyrotechnic cut-off 10. In all cases the time delay curve according to the invention 52 remains below the actual requirement curve 50 to ensure safety.

[0047] It is noted that for the first three secondary fuse curves 42, 44, 46 their cut-off reaction time T as a function of the intensity of the current I falls below the time delay curve according to the invention 52, which gives them time to open before triggering the pyrotechnic cut-off 10 which is not activated.

[0048] From the current threshold II the fourth secondary fuse curve 48 passes above the time delay curve according to the invention 52, which in this case only triggers the pyrotechnic cut-off 10 before this fuse opens. It is noted that the pyrotechnic cut-off 10 is not activated in the majority of cases.

[0049] [Fig. 3] shows a diagram of an analog circuit for controlling the pyrotechnic cut-off device 10, comprising as input information on the intensity of the current 60 delivered by the battery 2, given by the current sensor 16, which is transmitted to an optocoupler 62 transforming the high voltage of this information input into a low voltage signal limited to 5 V.

[0050] The signal delivered by the optocoupler 62 is applied via a first resistor 64 to a first operational amplifier 66, comprising between its input and its output a second resistor 68 arranged in parallel with a capacitor 80 in order to produce an integrator by the progressive charging of this capacitor. The integrator creates a variable timing signal dependent on the voltage of the input signal representing the current intensity 60.

[0051] The signal delivered by the first amplifier 66 is applied to a negative input of a second operational amplifier 82, the other positive input being connected to ground by a third resistor 84. The positive input is also connected by a fourth resistor 86 to the output of the second operational amplifier 82.

[0052] The second amplifier 82 uses the increasing signal from the first amplifier 66 to detect the end of the time delay when this signal is high enough according to a level calibrated by the third resistor 84 and the fourth resistor 86, which gives a low OFF signal when the delay has not expired and a high ON signal when it has expired.

[0053] The signal delivered by the optocoupler 62 is also applied in parallel to a third operational amplifier 88, comprising, as for the second amplifier 82, two resistors 90, 92, which detects whether the battery current 60 is still greater than the intensity threshold when the end of the time delay arrives.

[0054] The second amplifier 82 and the third amplifier 88 both deliver their signal to an AND addition function 94, which adds up the two representing both the time delay ended and the battery current 60 still exceeding the threshold, to give the final signal 96 for activating the pyrotechnic cut-off 10. The addition function 94 makes it possible to avoid activating the pyrotechnic cut-off 10 in the case where at the end of the time delay, at the precise moment of the decision, another system for protecting the electrical circuit causing the current to drop would have already operated.

[0055] The analog circuit of the protection system allows for very responsive control, which is not subject to slowdowns or software operating risks.

[0056] The protection system according to the invention thus ensures optimization of the operation of the pyrotechnic cut-off device 10, by reducing its triggering occurrence without increasing the risks due to an electrical fault in the vehicle. The detection threshold can in particular be between 1000 and 1500A, which largely covers the needs of electric or hybrid vehicles.

Claims

Claims

1. System for protecting a power supply battery of an electric traction machine of an electric or hybrid motor vehicle, comprising a pyrotechnic cut-off device (10) for the current delivered by the battery (2), and a control means triggering the pyrotechnic cut-off device (10) for a delivered current exceeding an intensity threshold (II), characterized in that the control means comprises a variable time delay before triggering the pyrotechnic cut-off (10), which has a reduction in the time delay duration as a function of an increase in the delivered current.

2. Protection system according to claim 1, characterized in that from the current threshold (II) the control means comprises a time delay exhibiting a regular decrease to reach the minimum achievable tripping delay (Tl), with a value always lower than a curve of actual protection requirement (50).

3. Protection system according to claim 1 or 2, characterized in that the current intensity threshold (II) is between 1000 and 1500A.

4. Protection system according to any one of the preceding claims, characterized in that the control means comprises a device for instantaneous measurement of the current delivered above the intensity threshold (II) which takes this measurement into account at the precise moment of deciding to trigger the pyrotechnic cut-off (10).

5. Protection system according to any one of the preceding claims, characterized in that the control means comprises at the input of the measurement of the intensity of the delivered current (60) an optocoupler (62) delivering a level of intensity of this delivered current (60) with a low voltage of 5V.

6. Protection system according to any one of the preceding claims, characterized in that the control means comprises an analog circuit which manages the time delay duration.

7. Protection system according to claim 6, characterized in that the analog circuit comprises a first operational amplifier (66) creating an increasing time delay signal with a speed depending on the increase in the intensity of the delivered current (60), which is applied to a second amplifier (82) carrying out an end of time delay detection by measuring a threshold of this increasing signal calibrated by resistors (84, 86).

8. Protection system according to claim 7, characterized in that the analog circuit comprises a third operational amplifier (88) receiving the measurement of the intensity of the delivered current (60), which detects whether this delivered current is still greater than the intensity threshold (II) when the end of the time delay arrives.

9. Protection system according to claim 8, characterized in that the end of time delay signal delivered by the second amplifier (82) and the current detection signal still higher than the threshold delivered by the third amplifier (88), are delivered to an addition function (94) which gives the final signal (96) for activating the pyrotechnic cut-off (10).

10. Electric or hybrid motor vehicle equipped with an electric traction machine and a battery (2) for supplying this machine, characterized in that it comprises a system for protecting the battery (2) according to any one of the preceding claims, comprising the pyrotechnic cut-off device (10) which is integrated in the battery (2).

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