How Do Autonomous Brake Systems Work?

Over the past decade, cars have gotten a lot safer, meaning you can worry less about accidents while driving. This is thanks to new active and passive safety features, especially in modern cars, which have significantly reduced accident rates. One standout feature is the Autonomous Emergency Braking (AEB) System, which we’ll delve into in this article to give you a better understanding of how it works.

What Does Autonomous Emergency Braking Do?

a self-driving system data playback showing a car detecting a bicycle

Autonomous braking, also known as automatic emergency braking (AEB), is a significant breakthrough in automotive safety technology. This system allows vehicles to engage the brakes automatically when a potential collision is detected, often faster than a human driver can react.

Essentially, AEB makes your car a smarter and safer driver. Remember when engineers came up with the Anti-lock Braking System (ABS)? It was a game-changer, preventing skidding and saving countless lives and vehicle damages by allowing you to brake hard without locking up. ABS eventually became mandatory in all new cars, and now it’s joined by other life-saving tech like ESP (Electronic Stability Program).

But ABS still relied on you, the sometimes forgetful driver, to hit the brake pedal for it to kick in. Now, with AEB, that’s changed. AEB takes matters into its own hands. It notices when you’re not braking quickly enough and does it for you, effectively preventing rear-end collisions at speeds of up to 60 km/h in some cars.

How Does It Work?

Autonomous braking systems use a combination of sensors, cameras, radar, and sometimes LiDAR (Light Detection and Ranging) to monitor the vehicle’s surroundings. These sensors are constantly scanning the environment for obstacles, be it vehicles, pedestrians, or other objects. When a potential collision is detected, the system first alerts the driver with visual, audible, or haptic warnings. If the driver fails to respond appropriately, the AEB system automatically takes over and applies the brakes.

Here’s a detailed explanation of the process:

  • Detection: The first step is the detection of a potential collision. Using a combination of sensors, the car continuously monitors the area around it. These sensors are designed to detect objects in the vehicle’s path, such as other vehicles, pedestrians, or obstacles.
  • Data analysis: The data collected by the sensors are relayed to the vehicle’s computer system. Here, sophisticated algorithms analyze the data to determine the likelihood of a collision. This analysis considers factors like the relative speed and distance of the object, the vehicle’s speed, and the trajectory of both.
  • Warning: If the system calculates a high risk of collision, it initially warns the driver. This warning can be visual (flashing lights on the dashboard), auditory (alarm sounds), or haptic (vibrations in the steering wheel or seat).
  • Brake preparation: In some systems, upon detecting a potential collision, the system pre-loads the brakes, bringing the pads closer to the rotors. This reduces the time taken to apply full braking force when needed.
  • Autonomous braking: If the driver fails to respond to the warning or if the system deems the situation critical, it autonomously applies the brakes. The intensity of braking can vary from partial to full braking power, depending on the situation.
  • Post-collision management: Some advanced AEB systems also help in post-collision management by keeping the brakes engaged after a collision to prevent secondary impacts.

Basic Components of AEB Systems

An autonomous braking system is a complex integration of various components that work together to detect and respond to potential collisions:

  • Sensors: These are the ‘eyes’ of the AEB system. There are several types of sensors used in AEB systems, including:
  • Radar sensors: These use radio waves to detect objects and their speed relative to the vehicle.
  • Cameras: Often mounted near the rearview mirror, cameras add a visual layer to object detection, capable of recognizing shapes like vehicles and pedestrians.
  • Ultrasonic sensors: Typically used for low-speed functions like parking assistance, these sensors can also play a role in close-range detection for AEB.
  • Control unit: This is the ‘brain’ of the AEB system. It processes the data received from the sensors to identify potential hazards. Advanced algorithms analyze the speed, trajectory, and other variables of both the vehicle and detected objects to determine the likelihood of a collision.
  • Actuators: These components physically engage the vehicle’s braking system. Once the control unit decides that emergency braking is necessary, it sends a signal to the actuators to apply the brakes. The level of force applied can vary depending on the system’s assessment of the situation.
  • User interface: Most AEB systems include a user interface that provides feedback and warnings to the driver. This can involve visual alerts on the dashboard, auditory alarms, or haptic feedback like steering wheel or seat vibration.

Why is Autonomous Braking Important?

The primary importance of autonomous braking lies in its ability to reduce the number and severity of accidents. According to various studies, AEB has been shown to significantly lower the risk of rear-end collisions, which are among the most common types of road accidents. By reducing the frequency and impact of crashes, AEB not only saves lives but also reduces the economic costs associated with accidents, such as medical expenses, vehicle repairs, and insurance claims.

Furthermore, autonomous braking is a stepping stone towards fully autonomous vehicles. As cars become more capable of sensing and responding to their environment without human input, the dream of self-driving cars becomes increasingly realistic and safer.

Pros of Autonomous Braking

Autonomous emergency brakes (AEB) offer lots of advantages, such as: 

  • Significant reduction in collision rates: One of the most compelling advantages of AEB is its proven ability to reduce the frequency of collisions, especially rear-end crashes. By automatically applying brakes in critical situations, AEB helps avoid accidents or reduce their severity.
  • Enhanced pedestrian safety: Modern AEB systems are increasingly capable of detecting pedestrians and cyclists, thereby reducing the likelihood of accidents involving these vulnerable road users.
  • Support in diverse driving conditions: AEB systems can be particularly beneficial in challenging driving conditions like low visibility, heavy traffic, or when the driver is momentarily distracted, offering an additional layer of safety.
  • Increased car resale value: Vehicles equipped with advanced safety features like AEB tend to maintain their value better over time, as they are more desirable in the used car market.
  • Insurance premium discounts: Many insurance companies offer lower premiums for vehicles equipped with AEB, recognizing the reduced risk of accidents.
  • Stress reduction for the driver: Knowing that your vehicle has an extra safety feature can reduce driver stress and fatigue, especially during long drives or heavy traffic.
  • Compliance with safety regulations: In some regions, having AEB systems is becoming a regulatory requirement for new vehicles, helping manufacturers comply with these evolving standards.

Cons of Autonomous Braking

Below are the common disadvantages of AEB: 

  • Potential over-reliance by drivers: There’s a concern that drivers might become overly reliant on AEB, leading to reduced attention and vigilance while driving.
  • System limitations: AEB systems, while advanced, could be better. They have limitations, particularly in extreme weather conditions like heavy rain, snow, or fog, where sensor visibility can be compromised.
  • False alarms and unintended braking: Some AEB systems may trigger false alarms or apply brakes unexpectedly in non-hazardous situations, which can be startling and potentially dangerous, especially at high speeds. At the least, it can be annoying to the driver.
  • High cost of repair and maintenance: Vehicles with AEB systems can be more expensive to repair and maintain. The sensors and cameras used in these systems are sophisticated and costly to replace if damaged.
  • Increased vehicle cost: Incorporating AEB systems can increase the initial cost of a vehicle, making it less affordable for some buyers.
  • Compatibility issues with older vehicles: There can be compatibility issues when driving among a mix of vehicles with and without AEB systems on the road. For example, an AEB-equipped vehicle might react differently in traffic compared to older vehicles, potentially causing confusion or unexpected situations.
  • Complex system calibration: AEB systems require precise calibration to function correctly. Incorrect calibration, whether due to improper service or modifications to the vehicle (like changing tire size), can affect the system’s performance.
  • Battery drain in electric and hybrid vehicles: In electric and hybrid vehicles, the additional power required for the continuous operation of sensors and cameras can lead to increased battery drain, potentially reducing the vehicle’s range.

Types of Autonomous Braking Systems

Autonomous brakes can be of different types, depending on the make and model of the cars. 

1. Forward AEB

This system represents a more basic form of AEB. It primarily functions by warning the driver when a frontal collision risk is detected. If the system senses that the vehicle is getting too close to an object ahead, it alerts the driver through visual, auditory, or haptic signals.

If the driver doesn’t react sufficiently, the system engages brake support, which pre-charges the brakes and increases the sensitivity of the brake assist. This ensures that when the driver does hit the brakes, the response is quicker and more forceful.

2. Rear AEB

While most AEB systems focus on forward movement, rear or reverse automatic emergency braking is designed to prevent collisions when the vehicle is backing up. This system is handy in detecting objects or pedestrians that might be in the blind spot behind the car, which is especially handy in parking lots and driveways.

3. Dynamic brake support (DBS)

Dynamic Brake Support steps in when the driver initiates braking but not forcefully enough to avoid a collision. In such scenarios, the system supplements the driver’s braking effort. DBS is designed to close the gap between the driver’s reaction and the vehicle’s potential to avoid a crash. It’s beneficial in situations where the driver is aware of the hazard but underestimates the required braking force.

4. Crash imminent braking (CIB)

Crash Imminent Braking is an advanced AEB system that autonomously applies the brakes when it determines that a collision is unavoidable, even if the driver has not taken any action. This system is designed to either prevent the crash entirely or significantly reduce the impact speed and, consequently, the severity of the collision. CIB systems often use a combination of radar, cameras, and other sensors to accurately detect imminent collisions.

5. Low-speed AEB

Also known as city AEB, this variant is specifically designed to function at lower speeds, typically in urban or congested traffic environments. It’s particularly effective in preventing or mitigating fender-benders and other common city-driving collisions. These systems are adept at recognizing slower-moving or stationary objects and are a boon in stop-and-go traffic conditions.

6. AEB with pedestrian detection

An increasingly common feature in modern AEB systems is pedestrian detection. This system uses advanced sensors and algorithms to identify pedestrians in the vehicle’s path. If a potential collision with a pedestrian is detected and the driver does not respond in time, the system automatically applies the brakes. This feature is essential in urban areas and has become a key focus in the development of safer vehicle technologies.

7. Intersection collision avoidance

Emerging technologies in AEB systems include intersection collision avoidance. This system aims to prevent collisions in intersections by detecting cross-traffic threats. Using advanced sensors, the system can identify potential hazards from the side, such as another vehicle running a red light, and automatically apply the brakes to avoid a side-impact collision.

Autonomous Braking vs. Anti-Lock Brakes

While both AEB and ABS are integral to vehicle safety, they serve different purposes. ABS prevents the wheels from locking up during hard braking, ensuring the driver maintains steering control. In contrast, AEB automatically applies the brakes to prevent or mitigate a collision. ABS is a reactive system that comes into play during a braking event, whereas AEB is proactive, seeking to prevent a collision before it occurs.

Here are the ways these systems differ from one another:

1. Purpose

AEB is designed to prevent collisions or reduce their severity by autonomously applying the brakes when a potential collision is detected.

On the other hand, the primary goal of ABS is to prevent the vehicle’s wheels from locking up during heavy braking, thereby maintaining traction and allowing the driver to retain steering control.

2. Functionality

AEB uses sensors, cameras, and radar to monitor the vehicle’s surroundings, detect potential collision threats, and automatically apply the brakes if the driver fails to respond in time.

Meanwhile, ABS constantly monitors wheel speed. When it detects a wheel about to lock up, it modulates the brake pressure to that wheel, preventing skidding and allowing the driver to maintain steering control.

3. Interaction with the driver

AEB is a proactive system that can take control away from the driver in critical situations. It primarily acts without the driver’s initiation, though it usually provides warnings before taking action. The system’s intervention is based on its assessment of potential collisions, independent of the driver’s actions.

Conversely, ABS is a reactive system that operates only when the driver applies the brakes. It does not initiate braking but modulates it once the driver has already taken action. The system’s function is to assist the driver in maintaining control during emergency braking rather than taking control away from the driver.

4. Operational conditions

AEB is operational mainly when the vehicle is at risk of a collision, typically at higher speeds or in situations where obstacles suddenly appear. Its effectiveness can vary based on the system’s ability to detect obstacles, which can be influenced by factors like weather conditions, sensor obstructions, or the type of obstacle.

Meanwhile, ABS only takes effect during hard braking, regardless of the presence of a collision threat. It functions effectively in various conditions, including slippery or uneven surfaces, helping maintain control during emergency braking in diverse environments.

5. Technological complexity

AEB is a more technologically complex system involving advanced sensors, data processing units, and algorithms to assess the driving environment and make split-second decisions.

While ABS is a sophisticated system, it is less complex compared to AEB. It relies on wheel speed sensors and a control unit to modulate brake pressure. It has been standard in vehicles for several decades and is well-established in the automotive industry.

6. Impact on vehicle dynamics

AEB impacts vehicle dynamics by autonomously initiating braking, potentially leading to a sudden decrease in speed or an unexpected stop. Meanwhile, ABS affects vehicle dynamics by preventing wheel lock-up, thus maintaining traction and control during braking. Its primary impact is on enhancing the driver’s ability to steer and control the vehicle under heavy braking conditions.

7. Integration in vehicle safety systems

AEB is often integrated with other advanced driver-assistance systems (ADAS) like adaptive cruise control, lane-keeping assist, and pedestrian detection systems.

Meanwhile, ABS is a fundamental component. It is often integrated with electronic stability control (ESC) and traction control systems.