Detailed explanation of Tesla braking system
Latest update time：2021-04-25
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In recent days, perhaps the hottest topic in the car circle is Tesla's "brake failure." Rumors about Tesla's "unexpected acceleration" and "brake failure" caused by rights protection at the Shanghai Auto Show have filled almost every conversation I have. There are car-related WeChat groups, but everyone agrees. So far, even though Tesla has released some data before the accident, everyone is still arguing.
So, as China’s earliest Model 3 owner, professional racing driver, and driving trainer, I will sort out how the Model 3’s braking system works and how to avoid possible “brake failure” accidents. I hope it can help. All doubts are cleared.
In addition, I also found the only
authoritative report
in the world on Tesla's "unintended acceleration" and "brake failure"
, which is an investigation report from the US Department of Transportation's Highway and Transportation Safety Administration (NHTSA). The investigation was initiated on January 13, 2020 and closed on January 8, 2021. It lasted for one year and covered four models of Model S/X/3/Y produced by Tesla between 2012 and 2020. A total of 246 accidents were investigated, and the investigation report totaled 22 pages, which was used as the basis for whether to initiate penalties or recall orders against car companies.
#tesla#
# Model 3 #
#Composition of brake system#
The braking system of Tesla Model 3 consists of 5 parts, namely
-
Brake calipers and brake discs
-
Brake lines and brake oil pipes
-
ABS and body stability control system
-
Electronic brake booster pump
-
Brake pedal
The first is the brake caliper and brake disc. This set of things can be regarded as the core of the braking system, and it is also where the braking force is actually generated. The quality of the hardware directly determines the quality of the braking effect. So what Tesla uses What hardware? The answer is Brembo, the world's top brand from Italy. This brake manufacturer has a history of more than 60 years. It began to provide braking equipment for Ferrari's F1 racing car in 1975, and now Porsche, Ferrari, Tesla Other car companies have all their models equipped with Brembo braking systems as standard.
If we make another horizontal comparison, among the imported luxury brands in the RMB 200,000-300,000 range, almost no one equips their vehicles with such good hardware, namely Brembo’s opposed four-piston calipers. Taking BMW as an example, it usually costs RMB 400,000. Only the above M Performance models have such configurations. Models in the 200,000-300,000 range, such as the BMW 320, Mercedes-Benz c200, and Audi A4, are only equipped with single-piston clamp calipers, so in terms of hardware alone, the special Silla is very good.
The rest is the brake line. In the final analysis, this thing is just a hydraulic connection. To put it bluntly, this is a physical connection and has nothing to do with electronic systems such as software. As long as this oil pipe does not rupture,
Tesla will not have brake failure.
.
The third is the ABS and body stability control system, which consists of three parts, namely the ABS module, ESC sensor, and wheel speed sensor. The products used are the products of the German company Bosch. This company has a history of more than a hundred years. From the space station to the home juicer, Bosch's shadow can be said to be the promoter of human technological progress. Most importantly, in automobiles It is a well-deserved leader in the field of ABS and stability control (TC). I dare not say that Bosch’s products are perfect, but at present, it is indeed the strongest in the world. Most car companies use Bosch ABS and TC systems. .
The fourth is the protagonist of this controversy, the Electromechanical Brake Booster. This is also a product of the German Bosch company. It is a new product mainly developed for hybrid and electric vehicles. The principle is to detect the movement of the brake pedal via an integrated travel sensor and send this information to the control unit. The control unit determines the control signals from the electric motor, while the three-stage gear unit converts the electric motor's torque into the necessary boost power and then into hydraulic pressure in the master brake cylinder. It is very similar to the vacuum booster pump of a traditional gasoline vehicle, so it has a very real and natural pedal feel, and the driver can intuitively feel the changes in the braking system.
The advantage of this approach is that the braking pressure is greatly improved compared to the traditional booster pump. According to the data provided by Tesla this time, the maximum pressure of the master cylinder reaches 140.7bar. You must know that the vacuum booster of a traditional oil vehicle is only More than 40 bar, which is three times the difference and a huge technological improvement. In theory, it will make the vehicle safer. Therefore, some media went to consult Bosch and asked them under what circumstances the system would fail. Bosch's reply was that the possibility of failure was considered at the beginning of the design, so multiple redundancies were designed. , which can guarantee nearly 100% reliability. Then someone said that it was a software bug that caused the brakes to fail. It seemed to be reasonable and had something to do with the logic of kinetic energy recovery. In fact, this theory was first proposed by Dr. Ronald Belt in two papers. During the U.S. government's investigation of Tesla's defects (
mentioned below)
, the complainant also submitted this paper to the government. However, after actual investigation, the investigative agency completely rejected Dr. Belt's paper because it was
based on inaccuracies . Correct accident data, incorrect
reconstruction of accident dynamics and incorrect assumptions about vehicle design factors.
Original text: Both papers are based upon incorrect event data, incorrect reconstructions of event dynamics, and false assumptions regarding vehicle design factors.
#USDOT#
# Highways and Transportation Safety Administration #
# Tesla Vehicle Defect Investigation Report #
(Reply "
Investigation Report
" in the background and download it directly)
File number: DP 20-001
Cause: Vehicle defect complaint
Investigation time: 2020/01/13 - 2021/01/08
Investigator: Ajit Alkondon
Reviewer: Jeff Quandt
Approved by: Stephen Ridella
Topic: Unexpected acceleration and brake failure
Manufacturer: Tesla Motors
Products: 2012-2020 Model S,
Model X
,
Model 3 and Model Y
Number of people: 662109
Description of the problem: This Bureau received a complaint stating that Tesla vehicles have defects that may cause unexpected acceleration, resulting in collisions and injuries.
Number of cases investigated: 246
Conclusion: Complaint dismissed
Content summary: On December 19, 2019, this Bureau received a complaint from Mr. Brian Sparks, requesting this Bureau to recall all Model 3, S, and X vehicles produced from 2012 to the present due to Sudden Unexpected Acceleration (SUA). Complainants provided 232 unique complaints, including 203 crashes. On January 13, 2020, the Department’s Office of Vehicle Defect Investigation (ODI) initiated this defect investigation (File No. DP20-001) to evaluate the complainant’s request. ODI's investigation included a review of information provided by the complainant, as well as 14 additional complaints related to SUA collisions. The investigation will include black box data (EDR), Tesla log data and video data.
After reviewing all data, ODI found no evidence to support a defective SUA or brake failure in the vehicle. In every accident reviewed by ODI, there was evidence that
the accident was caused by incorrect use of the pedals
. No evidence of malfunction was found in the accelerator pedal, motor control system and braking system, including the possibility of misuse of the pedals due to unreasonable design. During the investigation, the complainant’s theory that the accident was caused by malfunctions in electronic systems such as software and bugs was an inaccurate assumption.
If the Bureau's investigation reveals that a motor vehicle has a defect in design, manufacturing, or performance that poses a potential risk to safety, the Bureau has the authority to issue an order requiring the automaker to recall the defective vehicle.
Because the evidence obtained in the Bureau's investigation does not indicate that the vehicles are defective, it is unlikely to grant the complainant's request to recall Tesla vehicles. After a full review of the evidence provided by the complainant and the potential safety risks,
the complaint was dismissed.
Related documents are available at www.nhtsa.gov, including further explanation of the reasons for denying the appeal.
#tesla#
# Model 3 #
# Personal analysis about brake failure #
Since the Henan car owner did not provide a video of the accident, he dare not draw any conclusions. However, the Hainan accident that caused a stir some time ago and the accident of a Changsha car friend of mine have complete videos. I can explain it to you here. The most important thing is that you can learn from this accident and avoid similar accidents in the future.
In both accidents, car owners reported that the brakes failed and the brake pedal suddenly became very hard, making it impossible to press the brakes. But in fact, this is because the ABS system has intervened, which is completely normal. The driver only needs to continue to press the brake pedal firmly until the vehicle comes to a complete stop. Never release the brake because the pedal becomes hard. So, under what circumstances will the ABS system intervene? That is,
when
the braking force is greater than the tire grip
, it means that the braking force is very sufficient. If the tire grip is insufficient due to slippery ground, sand, ice and snow, etc., ABS will immediately intervene to help brake. However, it should be noted that ABS itself has limitations and cannot escape the laws of physics, so ABS cannot significantly reduce braking distance. The main purpose of ABS is to allow you to control the direction of the vehicle when braking on low-adhesion surfaces.
Hainan accident
We can see from the video that there was water and sand on the ground at that time, which was a typical low-adhesion ground. If you apply the brakes hard on this ground, there is a great possibility of triggering the ABS (the brake pedal becomes harder). Secondly, the test driver used the method of stepping on the vehicle for the first time, and the vehicle stopped steadily. But the second time, the car owner and his friend asked the test driver to use a three-leg braking method to reproduce the situation, that is, two feet to brake and one foot to step down, so a collision occurred. For vehicles equipped with an ABS system,
this is a
completely wrong
braking method. If we look at page 52 of the Tesla Model 3 manual, it clearly says,
"
Do not release the brake pedal immediately after pressing it. This way It will interrupt the operation of the ABS and increase the braking distance."
In addition, this regulation is not specific to one Tesla model. All models equipped with ABS should follow this procedure. If we look at the questions in Subject 1 of the driver's license test, we will also find similar questions. Therefore, when ABS has intervened,
continuing to press the brake pedal
is the only correct way to brake, and you must not brake.
Changsha accident
In this accident, the car owner reported that the Tesla's
brakes failed, automatically accelerated
, and several fault codes appeared after the collision, causing him to crash the car on the day he gave birth to his wife. He was very angry and asked Tesla for an explanation. At that time, he also asked Tesla for an explanation. He asked a big V to repost it for him.
But if we calm down and analyze carefully, you will find that this is an obvious man-made accident. First of all, we can see from the video that the environment the vehicle was driving on at that time was
a moist epoxy floor-like ground.
This kind of ground material is usually used in high-end underground garages. The advantage is that it is seamless and dust-free, but the disadvantage is that once it encounters water, the braking distance of the car on it will be increased by about three times, which means that even if you drive very slowly, , and it’s difficult to guarantee that the car will stop where you expect it to.
I remember the car owner was very angry and said in the group, "The place where the car crashed is the maternity hospital. Since my wife became pregnant, I have to go there almost every week. I am familiar with it. I am a driver with 10 years of experience." Old driver, I’m not a bad person, but this time the brakes failed and the car accelerated, which scared my wife!”
To be honest, I sympathize and understand him very much. Who wouldn’t be angry when his wife crashed into a car on the day she gave birth? But if we want to restore the essence of the matter, we should not understand the problem with emotions. At that time, I asked him a question. I said because you are very familiar with this road, do you brake at the same point every time? His answer confirmed my guess. Yes, he did not notice the situation on the ground and braked at the same position as usual. Then combined with the theory that the braking distance is tripled as I mentioned earlier, the accident here becomes A high probability event.
From the surveillance video, we can see that the vehicle wants to pass between two pillars. When it reaches position 1, the vehicle has started to turn, but has not yet started braking (the brake lights are off).
When the vehicle reaches position 2, the brake lights come on, but under these ground conditions, even if the vehicle speed is less than 20 yards as described by the owner, it is difficult to stop the vehicle safely, and triggers one of the most common vehicle out-of-control situations. Phenomenon -
head pushing (understeer).
In this accident, the driver made a total of 4 mistakes:
1. Misjudged the grip of the ground and used the same driving method as on dry ground;
2. The braking point is too late. Even if the vehicle is fully braked and the vehicle's ABS
system intervenes, it cannot stop completely before colliding with the obstacle;
3. Turning first and braking later is a completely wrong driving behavior. Whether it is a street or a track, braking in a straight line to slow down and then turning is the fastest and safest way to pass the curve;
4. When the ground grip is insufficient or the speed is too fast, braking + steering at the same time will most likely cause the vehicle to lose control. The front wheels of the vehicle have limited grip and must be used either for steering or braking. Once the limited grip is used by both If the opponent fights with all his strength, the limit of grip will be exceeded, causing the vehicle to lose control. In addition, the engine of a gasoline truck is located at the front of the vehicle, which is very heavy and will be more likely to cause a head-on accident than an electric vehicle with a mid-mounted layout.
To sum up, in fact, these two accidents are completely avoidable and have nothing to do with Tesla vehicles. Learning correct driving knowledge and improving your driving skills are the best ways to ensure that you and your family travel safely.
# SAFE DRIVING ADVICE #
To be honest, among the students I have taught, more than half of them did not know how to brake during the first test, that is, they were unable to stop the car within the prescribed distance. Therefore, for a car like Tesla with an acceleration level of 5 seconds or higher, it is even more important to learn the correct driving method. The following are some tips I give to all vehicle drivers, not just for Tesla models. I hope everyone can keep them in mind, which will be of great help to your safe travel in the future.
1. Using the correct sitting posture is the prerequisite to ensure the shortest braking distance. Many people drive very far back, just like sitting on a sofa, with their legs stretched straight and stretched. However, in an emergency, you can only rely on the strength of your ankles. To apply the brakes, you cannot use the power of your thighs. This power gap varies from person to person, which is about 2-3 times, and the feedback difference in braking distance is 10-15 meters. Therefore, be sure to
make sure that your legs are still bent after fully depressing the brake pedal.
This is the correct way to maximize the force exerted by the body and is also the prerequisite for obtaining the shortest braking distance;
2. Before cornering,
brake in a straight line to slow down, then turn into the corner
;
3. The only correct holding positions for the steering wheel are
3 o'clock and 9 o'clock
;
4. When encountering wet, sandy, rainy and snowy surfaces, be sure to brake in advance and leave a braking distance that is more than twice
that of dry asphalt roads
;
5. Under original factory conditions, when driving intensely, pay attention to the phenomenon of brake
heat exhaustion
. Continuous and vigorous braking will cause the brake pads and brake oil to heat up rapidly. Once the design temperature is exceeded, the braking effect will be significantly reduced;
6. The tire pressure can be appropriately lowered. The 3.0 tire pressure shipped by Tesla is very high. The advantage is low rolling resistance and long battery life. However, the disadvantage is that the tire contact area is reduced.
It is recommended to reduce it to 2.6 when not running long distances
to increase comfort. At the same time, it can also reduce the braking distance. (Choose to learn new pressure in maintenance, otherwise an alarm will be issued)
Conclusion
I hope China's General Administration of Quality Supervision, Inspection and Quarantine can issue an authoritative investigation report like the U.S. Department of Transportation. If vehicles are defective, penalties and recall orders should be issued. Otherwise, car companies should be cleared and
professional technical reports can be used to investigate. Only by getting rid of trouble and prejudice can we get closer and closer to reason and truth.
Attached is the full text of the U.S. Department of Transportation's Tesla defect investigation report.
You can download the PDF document
by replying to "
Investigation Report
" in the background.
Extraction code: 6158
Submission cooperation: 18918250345 (WeChat)
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