When making a sudden stop, it is possible that one or more of your vehicle’s wheels could lock up, leaving you with little control of your vehicle. Today, ABS technology automates the brake pumping process so you can concentrate on steering the vehicle to safety during an emergency situation. By preventing your car’s wheels from locking, an anti-lock braking system ensures that you are able to steer during a hard braking event.
In an anti-lock braking system, your car’s wheel speed is monitored and if a wheel lock is detected, a sensor sends a message to a controller that releases and applies the brake up to 20 times per second, preventing a lock up and helping you maintain control of your vehicle.
In many of today’s newer cars and trucks, anti-lock brakes work in conjunction with other safety systems like traction control and electronic stability control to deliver a safer driving experience. So, what exactly are anti-lock braking systems, and how do they work? Keep reading to learn all about these systems.
What Is an Anti-Lock Braking System?
An anti-lock braking system (ABS) is a safety anti-skid braking system used on aircraft and on land vehicles, such as cars, motorcycles, trucks, and buses. ABS operates by preventing the wheels from locking up during braking, thereby maintaining tractive contact with the road surface and allowing the driver to maintain more control over the vehicle.
ABS is an automated system that uses the principles of threshold braking and cadence braking, techniques that were once practiced by skillful drivers before ABS was widespread. ABS operates at a much faster rate and more effectively than most drivers could manage.
Related: What is Brake?
Although ABS generally offers improved vehicle control and decreases stopping distances on dry and some slippery surfaces, on loose gravel or snow-covered surfaces ABS may significantly increase braking distance, while still improving steering control.
Since ABS was introduced in production vehicles, such systems have become increasingly sophisticated and effective. Modern versions may not only prevent wheel lock under braking but may also alter the front-to-rear brake bias.
This latter function, depending on its specific capabilities and implementation, is known variously as electronic brakeforce distribution, traction control system, emergency brake assist, or electronic stability control (ESC).
When Was ABS Invented?
Anti-lock brakes were first tested on railway cars and aircraft in the 1950s. Around this time, the braking system was also implemented on motorcycle prototypes to help prevent skidding and loss of traction.
By the 1960s, the system was used on the world’s first four-wheel drive Formula One car. From here, Daimler and Mercedes-Benz began working on a system that could be applied to cars. After much trial and error, Mercedes-Benz revealed the technology at a Daimler test track in 1978.
From then on, anti-lock braking systems were implemented in more and more cars. Today, it’s a standard in almost all cars and it’s safe to say ABS has greatly improved the safety of the roads we drive on.
How does the Anti-Lock Braking System work?
ABS works by releasing and then reapplying or ‘pumping’ the brakes to a motorcycle wheel or car wheels in heavy braking situations. Sensors on each wheel are used to detect ‘locking’ or when a wheel stops moving and starts to skid.
Although not all ABS systems are the same, with some only preventing wheels on the rear axle from locking up. When a lock-up is detected, ABS pumps the brakes, 100’s of times a second. This stops the wheel or wheels from skidding and helps keep the driver in control of the vehicle.
So essentially, ABS works in three stages:
- Brake pedal is pushed: Four-wheel anti-lock brakes help you steer as you brake during an emergency.
- Wheel sensors detect skidding or ‘locking’: Wheel sensors detect when your car’s tires begin locking up. Then, they rapidly apply and release (pulse) the brakes to automatically keep your tires from skidding.
- ABS pumps the brakes: When you feel or hear the ABS vibrating, continue to firmly press and hold the brake then steer to safety.
Parts Of Anti-Lock Brake System
There are five major components of ABS: ABS speed sensor, valves, a pump, brake fluid, and a controller.
1. ABS speed Sensor
The ABS sensor normally consists of a toothed ring and a magnet enclosed within a coil. The contact between the ring and the magnet induces an electric field due to which a sign is generated. This sign is then transformed into a digital signal and sent to the ABS controller. The controller then determines the speed of each wheel individually. ABS sensor is a key component in controlling the drift of the car under any conditions.
Valves play a major role in the ABS system it controls the pressure and limits it to a certain amount. When the brake pedal is pushed harder, the valves limit the pressure on the brakes. When a valve is jammed it stops functioning; open, close, or change position.
An inoperable valve will prevent the system from changing or controlling the pressure supplied to the brakes. The valve has three positions open, block, and release.
- In the open position, it allows the pressure to flow through the brake.
- In the block position, it blocks the extra pressure and maintains a limited pressure on the brakes.
- In the release position, it releases the pressure held on the brakes
The pump in the ABS is used to restore the pressure to the hydraulic brakes after the valves have released it. The controller will change the pump’s status in order to produce the desired amount of pressure and reduce sliding.
4. Brake fluid
In the hydraulic brake fluid system, brake fluid is the main applicator of the brakes. It is used to transfer force from the hydraulic lines to the braking mechanism near the wheels. As brakes produce a lot of heat, the brake fluid has a high boiling point for effective operations. It also prevents corrosion of the materials in contact.
A controller is a unit in the ABS which receives the information from the individual wheel ABS speed sensor. When an individual wheel loses traction, a signal is sent to the controller. The controller will then limit the brake force and activate the ABS modulator.
How Effective Are Anti-Lock Brakes?
Drivers are benefitting from the effectiveness of ABS according to an 11-year study in the U.S, conducted by the National Highway Traffic Safety Administration (NHTSA):
- ABS reduces the overall crash-involvement rate by 6% for passenger cars and 8% for LTVs (light trucks, including pickup trucks and SUVs)
- Fatal collisions with pedestrians, bicyclists or animals decrease with ABS: by 13% for cars and 14% for LTVs
- Culpable fatal involvements with other vehicles on wet, snowy or icy roads were reduced by 12% for passenger cars
Additionally, according to the Insurance Institute for Highway Safety (IIHS), the rate of fatal crashes is 31% lower for motorcycles equipped with ABS than for the same models without them.
One thing to note is that while anti-lock braking systems have proven to be very effective on normal road conditions, they can be less effective in certain conditions, such as if there is ice, snow and gravel on the road. These elements can bring additional challenges and make it harder for the vehicle to stop, even with ABS.
When driving during extreme weather, it’s important not to assume ABS will work exactly the way it would in normal conditions. Always exercise caution by driving slowly, allowing more room for the vehicle to stop, and by paying close attention to how your car is reacting to the road.
What is the difference between ABS and conventional automobile brakes?
Conventional brakes allow wheels to be locked by the driver and produce a loss of rolling traction. ABS engages when a wheel speed sensor detects impending wheel lock-up, allowing the vehicle to be steered while helping maintain vehicle stability.
Conventional brakes consist of a basic hydraulic system that sends fluid to each wheel when the brake pedal is applied. This system utilizes a combination of mechanical components to increase the force on the drums or rotors when you press the brake pedal to activate the brakes, bringing the vehicle to a stop.
In the event of a sudden stop requiring fast, hard, continued pressure on the brake pedal, conventional brakes can allow the wheels to lock up, causing loss of traction and contact with the road.
Related: What is Disc Brake?
Anti-Lock Brake Systems
ABS systems consist of a hydraulic system similar to the conventional system but also have wheel speed sensors, hydraulic actuator, pressure release valves, and the ABS control module or computer.
ABS systems come in three and four-channel systems. Three-channel systems control the braking pressure on both front wheels independently and control the rear wheels together as one. Four-channel systems are often found on most modern-day vehicles and control all four wheels independently, providing a better level of control.
Advantages of ABS Brakes
So, in a nutshell, what are the benefits:
- ABS helps you to stop sooner when you panic brake in many driving conditions
- Even when stopping distances are increased, ABS allows you to maintain steering control of your vehicle
- Many insurance companies offer premium discounts when your vehicle(s) are fitted with ABS
- The resale value on a vehicle is higher with ABS included
- You have the peace of mind that your car is equipped with an advanced safety system that, at a minimum, allows you to steer effectively even when hard braking
Disadvantages of ABS Brakes
- Inconsistent stopping distances on various surfaces under variable conditions.
- Under generally poor road conditions, ABS braking increases stopping distance.
- Experienced drivers can often brake better manually than with ABS brakes.
- More expensive to repair and maintain.
- Increases the cost of the vehicle.
- Involves the use of an extra sensor and a controller which increases the complexity.
- On concrete roads, the ABS vehicle stopping distance might be needed more.