AEB frequently fails. Is the active safety system really safe?

Recently, the official appraisal result of the serious traffic accident at Wenjie M7 in Yuncheng, Shanxi has not yet been given, but online public opinion has pointed the finger at the AEB failure. Because it concerns life safety, it has become the focus of heated discussion in online public opinion.

Complaints about AEB failures are increasing year by year

AEB, or Autonomous Emergency Braking, is a preventive active safety technology that consists of a driving environment information collection unit (sensor), an electronic control unit (central processor), and an execution unit (actuator). In principle, it is a closed-loop process of perception-computation-execution. When a vehicle encounters an emergency in a non-adaptive cruise state or the distance between it and the vehicle in front and pedestrians is less than the safe distance, the AEB system will actively brake to reduce the occurrence of rear-end collisions and other collisions.

In recent years, with the gradual popularization of intelligent assisted driving technology, AEB has become a standard feature of more and more models, and major domestic automakers are also making every effort to develop and promote this function. According to the latest data from the China Passenger Car Association, the AEB function installation rate of passenger cars will reach 51.1% in 2023, an increase of 3.1 percentage points from 2022. However, in actual application, AEB has become a double-edged sword. Once a failure occurs, it will put the driver and passengers in the car in danger.

According to data from the Auto Quality Network, from 2019 to April 2024, there were nearly 600 complaints about AEB failures, covering many car brands, of which new power brands accounted for a large proportion, such as Tesla, Xiaopeng, Leapmotor, Ideal and Wenjie. From the change of complaint data, it shows an increasing trend year by year, especially in 2023, the number of complaints showed a leapfrog growth, with a year-on-year increase of nearly 2 times. From January to April this year, the number of complaints about AEB failures was 57, which was basically the same as the same period in 2023.

Specifically, the proportion of AEB failures in domestic brands is relatively high, exceeding 60% of the total. In terms of the time period of the problem, complaints about failures within one month of purchase account for the highest proportion, and the total proportion of failures within 12 months of purchase is close to 70% of the total. It can be seen that the probability of AEB failure is relatively high in the quasi-new and new car stages. In addition, from the proportion of complaints by energy type, it can be seen that AEB failures are more concentrated in gasoline models, and the proportion of pure electric and plug-in hybrid models is also relatively high, especially pure electric models, which account for more than 1/5 of the total complaints.

Success or failure is all due to the original sin of AEB

The original purpose of the AEB function was to help drivers reduce the incidence of traffic accidents and was considered a line of defense for active safety. Unfortunately, this line of defense not only fails to work in all situations, but has even become the initiator of traffic accidents. Why does AEB frequently "go on strike"? Combining complaints from the Auto Quality Network and traffic accidents caused by AEB failures in recent years, there are no more than the following reasons.

1. AEB function failure

When it comes to functional failure, there are two types of situations. One is complete failure, which means that the AEB function is not triggered. According to feedback from Mr. Li from Zhengzhou, Henan, he reported to Chezhi.com that the imported European brand SUV he purchased had a rear-end collision with the vehicle in front during normal driving. During this process, the vehicle did not perform emergency avoidance or active braking as officially advertised, resulting in injuries to people. The estimated economic loss is more than 200,000 yuan. The reason why AEB completely fails is mainly due to hardware or software failures in the AEB system. For example, the sensor fails to identify obstacles in front, the software algorithm has bugs, etc., which causes the AEB function to fail to be triggered normally.

The other refers to the "lag" in the triggering of the AEB function. In this case, the AEB function is not not triggered, but the triggering time node is delayed compared to the normal state, resulting in insufficient execution time of the braking system, and the vehicle cannot slow down or stop in time. The causes of this type of problem are mainly related to sensor performance, algorithm computing power and braking system capabilities. This is actually very easy to understand. For example, vehicles equipped with higher-definition cameras and lidars can not only collect more obstacle details and improve recognition accuracy, but also have longer ranging capabilities and detect obstacles earlier. In addition, algorithm optimization and computing power improvement also play a vital role in decision-making accuracy and response speed. Often shortening the decision-making time by a few milliseconds can avoid a collision accident.

2. AEB function is triggered incorrectly

The so-called false triggering of the AEB function means that when the vehicle is driving, there is no risk of collision in front, but the AEB function is triggered, which has a great impact on the comfort and safety of the vehicle. Especially in terms of safety, many rear-end collisions are caused by sudden braking of the vehicle in front. Compared with the failure of the AEB function, the probability of false triggering is much higher. This can be seen from the complaint data of the Auto Quality Network. Complaints related to false triggering of AEB account for about 47.4% of the total. According to feedback from Mr. Zou from Shaoguan, Guangdong, he bought a new energy SUV of a certain independent brand. In less than a month of use, the AEB active braking was falsely triggered 4 times, which brought great fright to the passengers in the car. Fortunately, no traffic accidents were caused.

Mr. Cai from Shanghai was not so lucky. He bought a new energy vehicle of a foreign new power brand. During normal driving on the provincial road, the vehicle braked suddenly for no reason when the road conditions were good, causing the vehicle behind to have no time to avoid it and causing a rear-end collision. There are many reasons for the false triggering of the AEB function, such as sensor recognition errors, system algorithms and special environments.

3. Driver cognitive factors

In fact, in traffic accidents related to AEB, in addition to the problems of AEB itself, a certain proportion of the reasons are related to the driver's cognition. In real life, some drivers rely too much on the AEB function promoted by car companies, believing that it can "stop in time" before a collision occurs, but the actual situation is contrary to their wishes. The first to bear the brunt are some sudden traffic conditions, such as the "ghost head" that is common in traffic accidents. At this stage, the AEB function is also difficult to fully play its role. Previously, the media had conducted relevant tests on many popular models, and the results showed that most models could not avoid collisions.

There are also some drivers who have only a vague understanding of the AEB function and think that AEB can be triggered when any collision risk occurs, but the reality is not the case. The AEB function has a working range and can only be triggered normally within the calibrated vehicle speed range, and the calibration of the triggering vehicle speed range by each car company is also different. For example, in the recent traffic accident of Wenjie M7 in Yuncheng, Shanxi, the vehicle was traveling at 115km/h when it collided, while the working range of AEB in the Bosch solution used was 4-85km/h. At this stage, although some car companies have calibrated very high speed limits, they are often not achieved in actual applications. Previously, Ling Shiquan, CEO of Radar Auto, said on his personal social media that "the highest braking speed range for AEB to avoid collision in the industry is 50km/h-60km/h".

In addition, the driver's misunderstanding of the AEB function of his own vehicle is also one of the factors that lead to traffic accidents. These drivers believe that since it is "automatic emergency braking", as long as this function is turned on, the vehicle can stop when encountering a collision risk. But the actual situation is that the AEB functions of different brands and models are not exactly the same. Some models can stop autonomously after the AEB function is triggered, while others require driver intervention to stop. Taking Ideal L8 Max as an example, its automatic emergency braking will release the brakes after a maximum speed drop of 70km/h. This means that if the automatic emergency braking is triggered at a speed of 80km/h, the vehicle will not perform the braking action when the speed drops to 10km/h. At this time, the driver must take over in time and continue the braking operation to stop the vehicle.

Of course, some car companies simplify the AEB function and avoid the important issues in their publicity, which will also make some drivers "take it for granted" about the AEB function, thinking that since the vehicle has the AEB function, it must be available for the entire vehicle. This is like going to a store to buy shoes. You must buy a pair, and the store cannot sell you only one. However, it is precisely because of such misunderstandings that some unnecessary traffic accidents will occur. For example, in November last year, the QX5 Smart Driving Edition "rode" on the BYD Dolphin while reversing. Yu Chengdong responded by saying, "The vehicle's rear emergency braking does not recognize stationary vehicles." But the actual situation is that the QX5 Smart Driving Edition does not have an AEB program set for the rear of the vehicle. To put it bluntly, the vehicle's AEB function is only half given to you.