Anti-lock Braking System (ABS)

Anti-lock braking system

Stanley recently noticed that a red “ABS” (anti-lock braking system) light came up on the dashboard of his car. However, he has no idea what it means. The only thing he noticed about his car is that his brake pedal has been giving him all manner of responses; from being super hard and resistant to press, to going all the way to the floor… but most of the time it seemed to work fine.

 Stanley doesn’t know that his life might be in danger. Why? You ask? Well, I’ll tell you.

 Here is everything you need to know about the Anti-lock Braking System (ABS).

Why do we need the Anti-lock braking system?

When driving, there, inevitably, will be situations where you need to stop quickly, and in order to stop in those situations, you will need to slam your brakes. Consequently, slamming your brakes can cause your wheel to lock, making the car slide. This slide is the tire screech you hear before a car crashes.

Anti-lock braking system, as the name implies, prevents the wheels of a car from locking up when you press the brake hard. They are largely useful during emergency braking.

Wheel lock - anti-lock braking system
Wheel lock. Anti-lock braking system prevents this.

Driving nowadays is pretty easier than driving 20 to 30 years ago. In those times, there was a need for a variety of skills before you can consider yourself a good driver. For example, to stop a car in an emergency there were basically two techniques to learn 

  •  Cadence braking; this is also known as stutter braking that involves the pumping of the brake pedal. It is basically used to allow a car to steer (turn) and brake on a slippery surface. For instance, if a car suddenly stops in front of you and you know that no matter how hard you press the brakes you will either not stop in time to prevent a hit or your tires will lock making the vehicle to slide until it hits the car in front. Here, you need cadence braking because by pumping the brakes, the wheels will not lock and you will be able to weave around the car in front, at the same time slowing your car down. Cadence braking is especially useful in the rain and other slippery surfaces.
Cadence Braking
Notice the bounce of the vehicle, it is as a result if the pumping action on the brakes by the driver

And…

  •  Threshold braking; this one is especially used in motor racing or high-speed driving for example highway driving. It is slightly more difficult to master than cadence braking. To use threshold braking, you have to know the point where your tires will lock when you depress your brakes hard because just before that point you will have maximum braking force from your tires. So, to utilise the threshold braking, you would master the art of depressing your brakes to that point before your tires lock and holding it there, so you will be able to stop your car in the shortest distance possible. But as I said, it is quite difficult to master.

 These two techniques were considered problems by engineers and drivers because they took quite a bit of skill to use, and since a lot of people didn’t know how to use it, accidents abounded. As a result, they went out and started looking for ways to eliminate them both.

The solution; The Anti-lock Braking System.

How does the Anti-lock Braking System Work?

I don’t know if you are like me but I’ve noticed that there are three types of rear impact accident situation, that is, accident that one person hit another from the back on the road; 

  1. You hear a long screeching noise from the tires which is then followed by a loud impact. It usually involves a lot of glass breaking and bumper redesign. 
  2.  You see a car gradually lose speed but it still does not stop in time then you hear a small impact that just resembles a show or a slight push from one car to the other. It usually involves a slight dent in the bumper and cracks on the indicators or maybe just a scratch. This situation is not common because, most times, the car will stop within the short distance.
  3.  Out of nowhere, you hear a loud bang; no tire sounds before it. This one is always as a result of lack of concentration on the part of the driver and it can be very dangerous.

The first two situations help us understand the working of the anti-lock braking systems better. 

Scenario 1

The screeching noise generally comes from locked up tires in the first scenario. This happens as a result of the tires losing Grip because the translational velocity at the point is more than the resistance supplied by the contact of the tire with the ground. If you’ve ever worn shoes that lacked grip and slipped, you would know that it doesn’t matter where you want to go; if the shoe slips in a direction, your whole body will follow actively and it would even seem that you gathered more speed in that direction. The same also happens in cars.

Crash of a car without anti-lock braking system
Crash of a car without anti-lock braking system

The tires on cars without anti-lock brake systems skid when excessive braking is applied in emergency situations and these skids result in total loss of steering control and stopping power on the tyres which might lead to an accident. I’m sure we have all seen cars spinning on the road due to uneven road surfaces or some flying into the bushes;l these accidents happen because of a lack of, or bad anti-lock braking system.

Scenario 2

The second scenario is a categorical example of how anti-lock braking systems work. Cars equipped with anti-lock braking systems do not skid when the brakes are applied and this helps to retain total control on the vehicle because the vehicle is not choosing a direction of movement by itself, thereby reducing the possibility of an accident. But how does the ABS carry this out? 

Working System

To understand the working system of the anti-lock brake system we need to know the different part which play different roles in the system.

 Typically an anti-lock brake system as the major parts

  • Electronic control unit 
Electronic Control Unit
Electronic Control Unit

  •  4 wheel speed sensor
Wheel speed sensor
Wheel speed sensor on the wheel
  •  Two or more hydraulic valves in the brake hydraulics (master brake system) 

On each wheel, there is a speed sensor attached. The electronic control unit (ECU) monitors the speed of each wheel or tire using the wheel speed sensor. When the driver brakes, it monitors the speed of which wheel and when it notices that a wheel is beginning to move slower than the others which is signalling that wheel is about to lock, it immediately reduces the hydraulic pressure on the wheel, subsequently reducing the braking force on that wheel allowing to move faster, as a result, preventing the wheel lock.

 Conversely, if it detects that a wheel is moving faster than the others, it sends more hydraulic pressure to that wheel increasing the braking force on that wheel, slowing the wheel down.

So…

This braking force alternation on each wheel will result in a pumping action on the brakes, at the same time, the wheels  the maximum braking force required.

The anti-lock braking system, through this modus operandi, utilises both Cadence and Threshold Braking at a faster rate; an ABS pumps the brakes at the rate of up to 20 times per second.

The electronic control unit is programmed to ignore wheel speed below and above a set threshold. This is because a lot of times car wheels have different turning speeds especially when the vehicle is turning; the inside wheels turn slower than the outside wheels which is why vehicles use differentials.

 

 Anti-lock braking systems and modern stability control systems 

Traction control, vehicle stability control and many other systems have their foundation in anti-lock braking systems.

These systems are working in tandem to prevent the vehicle from losing grip and ensuring that the vehicle continues in the direction intended by the driver.

 How do these systems work?

Modern electronic stability control systems have at least two additional sensors joined to the ABS. The two sensors are 

  •  Steering wheel angle sensor
  •  Gyroscopic sensor- it detects the position of a body and helps to is it in an intended direction or position

The operation is quite simple. When the gyroscopic sensor detects the direction of movement of the car is not the direction of the steering wheel angle sensor it will alert the electronic control unit which will, in turn, brake the necessary individual wheels (up to three wheels and the most sophisticated cars) making sure that the vehicle goes in the direction that the driver intends due to the steering wheel input.

Cornering Brake Control

The steering wheel sensor is also a part of the Cornering Brake Control (CBC) since this will tell the anti-lock brake system that the Wheels on the inside of the cup to brake more than the wheels on the outside and it will also determine how much braking force is needed for each wheel.

Traction Control

The wheel speed sensors are also used to implement traction control systems in vehicles. When you try to accelerate and your tires lose grip and spin, the wheel sensors will alert the electronic control unit which will then slow down the wheel that is spinning just enough for the vehicle to take off quickly.

These are the reasons why it is practically impossible for a car to drift with vehicle stability control and traction control switched on, the system will fight against the intentional skid needed to perform a drift.

 

Next week…

This topic is a very wide one, so we divided it into two. In our next post, we will look at;

  • How ABS systems came into use in cars,
  • notable anti-lock braking system milestones,
  • how to test if your anti-lock braking system works fine and
  • what to do if your anti-lock braking system is faulty.

Don’t miss it!!!

Let me know what you think of anti-lock braking systems, and what you think about the write-up. If you still have not subscribed, I want to know why. Don’t forget to share.

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