Why does automatic emergency braking not work in all speeds?

  • Context: Automotive 
  • Thread starter Thread starter techniker
  • Start date Start date
  • Tags Tags
    Automatic Braking Work
Click For Summary

Discussion Overview

The discussion centers around the functionality of automatic emergency braking (AEB) systems in vehicles, particularly why these systems may not operate effectively at higher speeds. Participants explore various factors influencing AEB performance, including sensor limitations, manufacturer variations, and the differences between AEB and adaptive cruise control (ACC).

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants note that AEB systems may only function at or below 50 mph in certain high-end vehicles, suggesting this could be due to sensor limitations or manufacturer liability concerns.
  • Others argue that different manufacturers produce AEB systems, which may lead to variations in performance and capabilities.
  • A few participants highlight the distinction between AEB and ACC, questioning why AEB cannot operate at high speeds if both systems utilize similar sensors.
  • There are mentions of the detection ranges of AEB and ACC, with some participants providing theoretical values for radar systems used in these technologies.
  • Some contributions discuss the potential use of cameras versus radar in AEB systems and the implications of this choice on performance, especially at higher speeds.
  • Concerns are raised about the risks of AEB systems reacting to roadside objects at high speeds, which could lead to unintended braking.
  • One participant describes a vehicle's ultrasonic 'park assist' system that functions similarly to AEB, indicating the variety of technologies available for collision mitigation.

Areas of Agreement / Disagreement

Participants express differing views on the reasons behind AEB's speed limitations, the effectiveness of various sensor technologies, and the operational differences between AEB and ACC. There is no consensus on these issues, and the discussion remains unresolved.

Contextual Notes

Some claims about the performance of AEB systems depend on specific vehicle models and manufacturers, which may not be universally applicable. The discussion also touches on the technical specifications of radar systems and their programming, which may influence AEB functionality.

techniker
Messages
39
Reaction score
2
Adaptive/active/radar cruise control (Update: It is not adaptive cruise control. It is automatic emergency braking) works only at or below 50 miles (per hour) in some high end cars like range rover, and even below that in other cars.
Does anyone know why?Thanks a lot
 
Last edited:
Engineering news on Phys.org
First, there are a few companies that produce ACC for the automobile industry, so they may not all be the same.
If you mean 50mph (not 50 miles), it could be that the car is aware of the speed limit and keeps to that limit.
 
.Scott said:
First, there are a few companies that produce ACC for the automobile industry, so they may not all be the same.
If you mean 50mph (not 50 miles), it could be that the car is aware of the speed limit and keeps to that limit.
Yes, 50 mph.
I have to find the source where I got the info from, and till then please forget about my question.
Thanks
 
The thread is wrong. It is not adaptive cruise. It is automatic emergency braking. Watch the video at 1:18.
 
techniker said:
I have to find the source where I got the info from, and till then please forget about my question.
Thanks
The one you mentioned from the Range Rover was likely built by Delphi Automotive.
DSC00551.jpg

Other makers are: Autoliv, Continental, Magna International, Valeo, Hyundai Mobis, VBOX Automotive, Mando, Robert Bosch, ZF-TRW, TRW Automotive, WABCO and Denso.
And then, the radar model can be adapted for a particular auto maker. So there is no reason to believe that they will perform in the same way.
The best source for what the unit does would be the Car's Owner's Manual.
 

Attachments

  • DSC00551.jpg
    DSC00551.jpg
    31.2 KB · Views: 1,223
.Scott said:
The one you mentioned from the Range Rover was likely built by Delphi Automotive.
View attachment 213291
Other makers are: Autoliv, Continental, Magna International, Valeo, Hyundai Mobis, VBOX Automotive, Mando, Robert Bosch, ZF-TRW, TRW Automotive, WABCO and Denso.
And then, the radar model can be adapted for a particular auto maker. So there is no reason to believe that they will perform in the same way.
The best source for what the unit does would be the Car's Owner's Manual.
Thanks for the info.
 
techniker said:
works only at or below 50 miles (per hour) in some high end cars like range rover, and even below that in other cars.
It may be a limitation of the sensors, or some liability issue that the car manufacturers are worried about...

http://www.howsafeisyourcar.com.au/aeb/
What is AEB?
Auto Emergency Braking (AEB) is a feature that alerts a driver to an imminent crash and helps them use the maximum braking capacity of the car. AEB will independently brake if the situation becomes critical and no human response is made. AEB comes in three categories:

  • Low speed system – works on city streets to detect other vehicles in front of your car to prevent crashes and non-life threatening injuries such as whiplash
  • Higher speed system – scans up to 200 metres ahead using long range radar at higher speeds
  • Pedestrian system – detects pedestrian movement in relation to the path of the vehicle to determine the risk of collision
Front collision warning systems vary between manufacturers – and even models. Some vehicles feature two or more AEB systems.
 
berkeman said:
It may be a limitation of the sensors, or some liability issue that the car manufacturers are worried about...

http://www.howsafeisyourcar.com.au/aeb/

If adaptive cruise control works at very high speeds, why can't automatic emergency braking do it? Don't they use the same sensor/radar?
 
techniker said:
If adaptive cruise control works at very high speeds, why can't automatic emergency braking do it? Don't they use the same sensor/radar?
What's adaptive cruise control? I'm guessing it uses sensors to help follow another car? That only has to work for a few 10s of meters, not for 100s of meters...
 
  • #10
berkeman said:
What's adaptive cruise control? I'm guessing it uses sensors to help follow another car? That only has to work for a few 10s of meters, not for 100s of meters...

Does not acc let you select a certain distance between you and a potential, not yet existing, car, and then whenever your car detects another car at that distance away, it will slow down. I don't know.
Check the video at 1:17
 
  • #11
What is your reply to my comment about the different distances involved between the two systems?
 
  • #12
berkeman said:
What is your reply to my comment about the different distances involved between the two systems?

Yes sorry I didn't reply.
For ACC, I don't know about actual systems automakers use, but I got a theoretical value:
The 77-GHz Autocruise radar system made by TRW has a forward-looking range of up to 492 feet (150 meters)
 
Last edited:
  • #14
techniker said:
Since acc works at very high speeds, and can detect cars far enough for it to slow down and keep the distance you chose, and not just barely avoid the car in front, then it must have a high detection range.
I'm not sure why you say that. When the cars are linked with ACC, I don't think the following distance is all that far...
 
  • #15
techniker said:
If adaptive cruise control works at very high speeds, why can't automatic emergency braking do it? Don't they use the same sensor/radar?
Yes, they use the very same sensor.
For the Autoliv 77GHz Gen 1.2, the range is 160 meters.

The range of the radar is actually a function of the software loaded onto the radar. The MMIC (the component that actually works at 77GHz) can be programmed to transmit different radar signals. There are trade offs between range resolution, range limit, Doppler resolution, azimuth resolution, etc.

But once a trade-off is made, it applies to all applications running on that sensor (ACC, Braking, Lane assist, BSM, PSIS, etc.).

Older units use 24GHz.
 
  • #16
techniker said:
The thread is wrong. It is not adaptive cruise. It is automatic emergency braking. Watch the video at 1:18.
This is a camera system, not a radar system.
Part of the problem at higher speeds is that it may be reacting to something on the side of the road.
The worse thing it could do is apply the brakes just as you need to turn to keep in your lane.
 
  • #17
berkeman said:
I'm not sure why you say that. When the cars are linked with ACC, I don't think the following distance is all that far...

Do you have to link with an existing car?
 
  • #18
.Scott said:
This is a camera system, not a radar system.
Part of the problem at higher speeds is that it may be reacting to something on the side of the road.
The worse thing it could do is apply the brakes just as you need to turn to keep in your lane.

A camera? Yes you are right, I just realized this. Why would they use a camera?
I will look into whether other makers use radars.
 
  • #19
techniker said:
A camera? Yes you are right, I just realized this.
I will look into whether other makers use radars.
Most of the time radar it used because it supports many features, can be hidden behind the fascia, and is a bit more resilient to dirt and weather conditions.
 
  • Like
Likes   Reactions: techniker
  • #20
berkeman said:
I'm not sure why you say that. When the cars are linked with ACC, I don't think the following distance is all that far...
techniker said:
Do you have to link with an existing car?
The "link" he's talking about is just one vehicle tracking the one in front of it.
Currently, consumer vehicles do not share navigation data with each other.
 
  • Like
Likes   Reactions: berkeman
  • #21
Our car has an ultrasonic 'park assist' system that doubles as a 'mishap mitigator'. Translated, if the 4+4 sensors spot something, they'll squawk and red-flag their neat display. If 'urgent', the system will auto-apply the anti-skid brakes, harder and faster than a human.

It is meant to mitigate 'fender benders', brake for jay-walkers etc. It WILL slam-on for a wind-swayed kerb-side bush or low-flying trash-bag. Fortunately, the traffic was sparse enough that we weren't rear-ended...

An unexpected facility is its 'gap keeping' alert. This warns that, given your speed, you're getting too close to the vehicle in front. It will also warn that you're being tail-gated. When a 'rear quarter' sounds off, you know the vehicle that just changed lanes really did come too close for comfort...
 

Similar threads

Automotive Determining the Brake Caliper Force for a Car
  • · Replies 6 ·
Replies
6
Views
8K
A practical way to vaporize fuel for high MPG?
  • · Replies 39 ·
2
Replies
39
Views
4K
How does a viscoelastic brake mechanism work for satellite deployment systems?
  • · Replies 9 ·
Replies
9
Views
3K
Why Does Angular Speed Not Increase Indefinitely in Rotating Systems?
  • · Replies 4 ·
Replies
4
Views
5K
How much work does the brake system have to do to stop the car at each speed?
  • · Replies 5 ·
Replies
5
Views
5K
Automotive Gas Turbines in Cars: Efficiency, Power & More
  • · Replies 13 ·
Replies
13
Views
6K
Can Carnie Stop in Time to Avoid the Roadblock?
  • · Replies 4 ·
Replies
4
Views
2K
High School What Determines the Speed of Light Limit?
  • · Replies 30 ·
2
Replies
30
Views
8K
Why such a large engine/generator in a Chevy Volt?
  • · Replies 21 ·
Replies
21
Views
10K
An overlooked point in fuel-efficient car driving speed
  • · Replies 6 ·
Replies
6
Views
6K