ABS usually offers improved vehicle control and decreases stopping distances on dry and slippery surfaces; however, on loose gravel or snow-covered surfaces. ABS can significantly increase braking distance, although still improving vehicle steering control.
An anti-lock braking system or anti-skid braking system (ABS) is a car safety system that allows the wheels on a motor vehicle to maintain active contact with the road according to driver inputs while braking, preventing the wheels from locking up and avoiding uncontrolled skidding. It is an automated system that uses the principles of threshold braking and cadence braking which were experienced by skillful drivers with previous generation braking systems. It does this at a much faster rate and with much better control than many drivers could manage.
Anti-lock braking system working principle
The basic theory behind anti-lock brakes is modest. It prevents the wheels from locking up, thus avoiding uncontrolled skidding. ABS generally offers improved vehicle control and decreases stopping distances on dry and slippery surfaces. With ABS, you get better stability and control over a car while braking a skidding wheel (where the tire contact patch is sliding relative to the road) has less traction (grip of the tire on the road) than a non-skidding wheel.
For example, if your car drives over a road covered in ice, it is impossible to move forward and the wheels will keep spinning, since no traction is present. This is because the contact point of the wheel is sliding towards to the ice. ABS modifies the brake fluid pressure, independent of the amount of pressure being applied on the brakes, to bring the speed of the wheel back to the minimum slip level that is compulsory for optimal braking performance.
Anti-lock braking system diagram
Anti-lock braking system components
1) Speed sensor
This sensor monitors the speed of each wheel and regulates the necessary acceleration and deceleration of the wheels. It consists of an exciter (a ring with v-shaped teeth) and a wire coil/magnet assembly, which produces the pulses of electricity as the teeth of the exciter pass in front of it.
The valves control the air pressure to the brakes during the ABS action. There is a valve in the brake line of each brake that is controlled by the ABS. In the first position, the brake valve is open and it allows the pressure from the master cylinder to be transferred to the brakes. In the second position, the brake valve remains closed and pressure from the master cylinder to the brakes is constrained. In the third position, the valve releases some of the pressure on the brakes. The third step is repeated until the car comes to a halt. The resistance that you feel when brake suddenly at high speeds is actually the brake valves controlling the pressure that is being shifted to the brakes from the master cylinder.
3) Electronic control unit (ECU)
The ECU is an electronic control unit that receives, amplifies and filters the sensor signals for computing the wheel rotational speed and acceleration. The ECU receives a signal from the sensors in the circuit and regulates the brake pressure, according to the data that is analyzed by the unit.
4) Hydraulic control unit
The hydraulic control unit collects signals from the ECU to apply or release the brakes under the anti-lock conditions. The hydraulic control unit controls the brakes by increasing the hydraulic pressure or bypassing the pedal force to decrease the braking power.
Advantages of anti-lock braking system (ABS):
- The vehicle with ABS can be stopped at a lesser distance than a non ABS vehicle.
- Steering control is effective, i.e., the vehicle can be steered smoothly while braking. Thus minimizes the accidents.
- A driver without experience can drive ABS vehicle effectively, then an experienced driver on the non ABS vehicle.
- ABS reduces friction on wheels and road, thus increases the efficiency of tires (up to 30%).
- Anti-lock braking system (ABS) guarantees stable braking characteristics on all road surfaces, hence avoids overturning of the vehicle.
Disadvantages of anti-lock braking system (ABS):
- On concrete roads, the ABS vehicle stopping distance might be needed more.
- Initial cost for anti-lock braking system (ABS) vehicle is high.
- Maintenance issues arise as the whole braking system is controlled by engine control unit.
Need of anti-lock braking system
When brakes lockup on wet and greasy roads or during a panic stop, steering control is lost and the automobile rotates. Rear wheel ABS prevents wheel lockup so that the car resides smoothly. If the automobile has ABS control on all the wheels, and the steering also controlled. If a car has steering control, it is probable to avoid a collapse by steering around dangers if a car is not stopped in time.
When do anti-lock brakes take effect
Anti-lock brake systems have a control unit or what known as a computer box that takes sensor readings from each wheel hub via what called a tone ring. The sensor senses exact speed from the tone ring and sends that information to the computer. The anti-lock system is activated when the anti-lock computer senses a difference in speed between any of the four wheels during braking via the wheel sensors and tone rings. Once this occurs brake application pressure in the line is reduced to that particular wheel via a modulator valve. Keep in mind that anti-lock brakes does not make you stop on faster speed quickly, they merely keep the automobile strait during braking on slippery surfaces. Contrary to popular belief, Anti-lock brakes can cause longer stopping distances.
When will anti-lock brakes not prevent skidding
- On surface water.
- In foggy conditions and
- At night on unlit roads.
- On loose road surfaces.
- On dry tarmac.
ABS brakes problems
If you drive on loose surfaces, ABS can interfere with how effortlessly you can stop your car. On loose dirt, mud or snow, or any low-grip surfaces, the anti-locking function can become jumbled, and the constant releasing that the electronics engage in can in fact extend stopping distances. On loose surfaces, a locked wheel is more effective at stopping because it ‘digs in’ to help bring a car to a stop. That’s why many off-roaders feature a special off-road mode, which lessens the effectiveness of the ABS or turns it off entirely to boost low-speed grip.
What happens when the anti-lock brakes fail?
Most anti-lock brake systems are designed to switch off if any of the components fail. There are rare instances when a valve will stick open, but the brakes will usually continue to work normally. If the pedal doesn’t fade or sink, that typically means the vehicle is safe to drive. You will have to pump the brakes if you find yourself in a panic stop situation, so it’s crucial to remain vigilant if your ABS quits working.
The ABS light turned on to alert a driver to a potential problem with the anti-lock braking system (ABS). This system keeps your vehicle’s wheels from locking up in a sudden stop to avoid skidding out of control, especially on wet or icy roads.
ABS light comes on and off
Being that the ABS light keeps going on and off indicates a bad or loose connection or low brake fluid level. If it was a sensor or module the light would stay on continuously. The most common is the wiring going to the wheel sensors. As the car moves over bumps and rough road the wiring flexes and may cause disruption or break a connection. Check to make sure the connections are fitted and secure, check for continuity in the wiring when the light is on.
The light will automatically turn off when the malfunction is terminated or connection is re-established. Also check your brake lights, specially the third brake light in the middle. Check to make sure your brake fluid level is full. When light is on, detach the wire connector going to the master cylinder to see if the light goes off as the float inside the reservoir could be the problem.
ABS light came on while driving
Very few things cause as much worry as when a light on your car’s dashboard comes on while you’re driving. However, many drivers may not know exactly what some of the lights may be indicating.
- Malfunctioning ABS
Traction control and ABS often share the same control module and internal self-diagnostics system. Sometimes an issue in the ABS can trigger the traction control light to come on. If that is the case, then both the ABS and traction control lights will be on.
- Low fuel levels in ABS fluid reservoir
One reason your vehicle’s ABS light is on is because it may be sensing abnormally low levels of brake fluid. You’ll be able to notice if your brake fluid is low by the way your car brakes. The braking may seem soft or spongy. However, if the brake fluid is low, you’ll probably see more than just the ABS light come one.
- Wheel speed sensors are broken
Wheel speed sensors determine the rate at which each wheel is moving. The sensors send that information to the traction control module, which determines whether or not power needs to be shifted. Wheel speed sensors can get dirty or damaged and stop working, which keeps the traction control module from knowing when to enable the system.
- Traction control is turned off
Many new vehicles give drivers the option to turn off the traction control in their vehicles. So, if your vehicle’s traction control light is on, it may be as simple as making sure your traction control isn’t turned off.
Is it safe to drive a car with ABS light on?
Yes, your automobile is safe to drive; however, you should have to look it over if the light stays on. It’s also important to note that if both the ABS and brake system warning lights come on at the same time while you’re driving, you must stop your car or truck as quickly and safely as you can and call for a tow.
How do you reset the ABS light?
- Ignition off. Car of flat surface with steering in neutral position.
- Press the brakes firmly for 10 seconds. Don’t take the foot of the brakes till the end of this exercise.
- Turn ignition on. Keep pressing the brake for another 10 seconds.
- Start the engine. Keep pressing the brake for another 10 seconds.
- Take foot off the brakes. ABS light should turn off within 1-2 minutes.
- Sometimes the light doesn’t turn off immediately, but after driving the car a couple of minutes.