Thoughts on the safety and reliability of electric vehicles

Huigen Yu, chief engineer of Beijing New Energy Automobile Co., Ltd., delivered a speech entitled “Analysis of Electric Vehicle Fault Tree”. The following is a report of the speech report:

Distinguished guests, ladies and gentlemen, good morning, I am Huigen Yu from Beiqi New Energy. I am very grateful to the organizing committee for giving me this opportunity. From the second half of last year to the present, everyone has seen the development speed of new energy vehicles. Very fast, at such a good time, for us, I want to say that we should pay more attention to what? What are you thinking about? What I want to talk about today should be more about security and reliability. The topic I am talking about today is the analysis of the fault tree of electric vehicles.

In the analysis of electric vehicle fault tree, today I mainly talk about the fault analysis of electric vehicle fire and explosion, as well as the analysis of high-voltage fault tree and the analysis of low-voltage fault tree, three parts.

The analysis of the electric vehicle fire fault tree is generally divided into two reasons: internal cause and external cause. The internal cause is high pressure, and the other is low pressure and low pressure. The difference between traditional vehicles is not very large, but for high pressure, the difference is very large. For external reasons, everyone knows that electric cars are more complicated like big cities. There is an integrated garage. If the car below is on, what should I do with the car above? So it includes direct fire, the other is baking, mainly considering several analyses, one is high altitude drop, it will achieve the effect of collision. The other is the frontal touch, the rear-end collision, and the side impact, which will cause the battery to deform, so it is squeezed for the battery, but it is a collision for the car. Dragging the bottom, this is also related to the extrusion. For example, in the process of Tesla's fast running, the whole battery box is cut open, which is different from the extrusion. The last one is water immersion, full immersion. We have not found that the battery will catch fire, and the half immersion has fire. This is the current situation, so from the fault tree analysis of the electric car fire, we are divided into internal and external reasons.

Next, for the high-voltage fault tree, it is also divided. In this case, in general, every high-voltage component has high-voltage analysis, including component failure, and a lithium-ion battery system. One is the drive motor, the other is the inverter, one is DC/DC, one is BOX fault, one is PTC, there is air conditioner A/C for summer, there is car charger, and there is fast charge. For these reasons, once under high pressure, such as short circuit, under the premise of failure, there is a risk of fire. For these high-voltage components, there are many wiring harnesses connected, short-circuiting, etc., which may cause failure.

This has a greater relationship with us. Lithium-ion battery systems, battery packs can fail, battery packs are overheated, cooling system faults, overheat protection faults, and thermal management design flaws. The battery pack overheated and the fault will be seen later. There are heat dissipation for the cooling system failure, and the heat dissipation port and the heat dissipation port are blocked. For overheating, there are temperature sensors, as well as hardware and software failures, etc., as well as failures caused by temperature sensors.

The battery pack is hot, this is the next one. If the battery pack is hot, there is too much power, too heavy, and the battery pack is damaged, including the terminal, including strength, etc., of course, including defective products, defective products, or There are ways to control it, so it is put to the end.

The following is the failure of the single battery in the battery pack. The first one is electrolyte leakage, the other is internal short circuit, one is repeated over discharge, and the other is thermal management design defect. Electrolyte leakage Everyone knows that we first had a fire incident in China, and later analyzed that it is electrolyte leakage, but in fact, from the current point of view, because of three conditions of fire, one is temperature, one is combustible, and the other is oxygen. Therefore, if there is electrolyte leakage inside the entire battery system and local overheating, it does have a fire risk. Short circuit, I think everyone here is more professional than me. Here we also roughly divided the head. For repeated over-discharge, the electric car is a full life cycle, so if it is repeatedly released, it will lead to the possibility of fire. We have already done experiments, and indeed there is a risk.

This mainly talks about BMS failures, one is BMS overheating, its own overheating, another BMS thermal management design, BMS overheating also includes current, including connection point contact, and connection point solution. For the current overheating, I will explain it later.

This is a fault in the relay. What happens if the relay fails? One is that the relay is hot. When the relay is hot, it may cause failure. For reasons such as the size of the current carrying, the coil of the coil, the contamination of the contacts, so for the entire battery system, sometimes we It is also said that it needs to maintain a certain degree of cleanliness.

This is a pre-charge resistor. This is relatively simple. If the design is reasonable, this problem should not be particularly large, but the head may need to consider several aspects. One is whether the coil will be burnt, including the bearing capacity, such as the size of allowable current.

This page is mainly not wiring faults, mainly including two aspects, one is overheating and the other is electric spark. If it is overheated, it will generate heat for the internal high-voltage wiring, including, for example, the design of the current that can be carried, and the current is too large. One of the electric sparks is insulation, one is the damage of the conductor fixing parts, and the foreign matter is mixed in.

The following is for the working conditions of the whole vehicle, such as the requirement of ten years and twenty kilometers, the possibility of this effect under the vibration and bumpy conditions of the whole vehicle.

This is mainly about the failure of battery thermal management, one is the heating of the board, and the other is the defect of the thermal management design. The board is hot; the design capacity is insufficient, and so on.

This page mainly talks about the current is too large, one is the discharge current is too large, and the other is the high voltage circuit short circuit. Excessive discharge current is mainly caused by current limit control and VCU current limit control failure. For the short circuit of the high voltage circuit, the main thing is the foreign matter.

Drive motor failure, we know that the power inside the electric car is completely from the drive motor, so the battery is mainly supplied by the drive motor to drive, so the drive motor includes the drive motor overheating, poor overheat protection, and thermal management design defects. The overheating of the drive motor mainly includes the heating and cooling of the drive motor, because the inside of the motor usually has a cable system or an air cooling system. Poor overheat protection, like the drive motor overheat protection control failure, because in general, the heating temperature rises, I generally reduce the power, if I reduce the power is not enough, this temperature will always rise, so it is very important for this strategy The temperature sensor, if something goes wrong, means that all my monitoring fails.

This is a drive motor fault, and an analysis of the fault tree for the drive motor heating, including mechanical, including current, including short circuit. Mechanical failures include lubrication, tank deformation, and impellers throughout the life cycle. Then the current is too large, mainly due to faults in inverter control. Then the high-voltage circuit is short-circuited, and it can be seen that it is insulated, fixed, and foreign matter. So for this piece, for the motor, the whole should be waterproof and dustproof.

This is the drive motor inverter, which is equivalent to the inverter that sends my DC power to the motor. It is called an inverter. It should be similar to the motor. One is overheating, one is overheat protection, and the other is the design of overheating. This is the inverter heating, one is the current is too large, one is the short circuit, the related fault tree is decomposed down, one is the control problem, one is insulation, one is fixed, one is foreign matter mixed.

This is DC/DC. For the whole car, because I have high voltage, I have low voltage. Now, lead-acid batteries are powered by generators directly. Now I don’t have a generator, so I pass the high voltage through DC. /DC ensures that the power supply is normal, and this will also cause corresponding faults, including the frequency converter, including overheating, including design.

This also involves the heating of DC/DC, one is that the current is too large, and the other is a high voltage short circuit. Because the whole new energy car will do integration, called the high voltage box, the relay will be generally put, I will integrate the insurance into this, and there may be malfunctions in this.

This is for relay faults, involving relay heating, one is thermal design, include missing, including carrying current, including contact pollution faults.

This is a fast charge relay fault, generally similar to the previous relay, including the coil, including the current that can be carried, including contact contamination.

This is the internal wiring, and the entire high-voltage box should also be wired inside, which is similar to the previous one, and will not be said anymore. This is for the current is too large, divided into the following aspects, one is the transformer current is too large, one is DC / DC inverter current is too large, one is the charging bolt current is too large, and carrying the charger, A / C Short circuits in PTC and high voltage circuits may cause excessive current.

This is PTC heating, PTC heating, in fact, now generally includes two aspects, now there is a PTC heating of the whole vehicle, another PTC heating is placed inside the battery bag, to the entire power battery system, for heating under low temperature conditions. For this PTC heating, one is the PTC heating overheating, and the overheat protection is not good.

This is a fault of the PTC heater itself, including excessive current and high voltage short circuit. If the current is too large, the heater adjusts the current control fault and the PTC electric heater fails. Short circuits in high voltage circuits include insulation, conductors, and foreign objects. Insulation is mainly related to the quality of the selected parts. The fixing is mainly related to the installation process.

For poor heat dissipation, one is the heater liquid and the other is the heater cycle. If the heater indicates that the liquid is insufficient, the heating may be abnormal. If the circulation is abnormal, and the place is blocked, it may cause an abnormality. Including the pump out of the literature, it will also cause thermal failure.

This is an air conditioner. For air conditioning failures, it also includes A/C compressor overheating, then poor protection, and design flaws. A/C, for example, compressor heat, heat dissipation, inadequate design, and compressor overheat protection control failure, temperature sensor failure, some sensors are improperly fixed. There will be deviations in temperature measurement.

This is the A/C compressor heating, one is a mechanical fault, one is the current, and the other is the high voltage short circuit fault. This is basically similar to a traditional car.

This is a car charger that includes overheating of the car charger, including protection, including design flaws. This is for the car charger to heat up, one is the current is too large. One is the high voltage short circuit. Short-circuit is still the three aspects, insulation, fixing and foreign objects.

This is a fast charge fault, which is equivalent to a ground charger. In fact, there is only one interface on the car. The charger is ground. Therefore, one of the main considerations is to fast charge and another protection. Because the wires are connected if overheated. If the ground charger is not well protected, it will also affect my car.

This is a fast charge, including too much current, and short circuit.

This is the last point. The low-voltage fault is basically similar to our original conventional car, but in general, it is not deployed here, including fuses, including relays, as well as vehicle controllers, including steering, including braking, including doors and windows. , including rearview mirror bends, including lighting, speakers, and more. The 12V power supply is more like a fault caused by an aging short circuit.

This is what I want to say about the electric car so far, for example, the general fault tree of the unsafe, combed a bit, there are a lot of similar content, including failures, including overheating. From the current point of view, more attention is paid to electric vehicles. One is that the connection is not reliable, and the other is the internal short circuit of the battery. If the two pieces are done well, including collisions like water immersion, we all can be in control. My report is over, thank you!

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