How Do Anti-lock Brake Systems Work?

Ensuring safety on the road is the result of various systems on a modern car working together. Properly-inflated tyres, working headlights and taillights, and a clear and unobstructed windshield are just some of the things that can ensure a much safer ride. However, there is one very important element that can spell the difference between safety and disaster: your car’s brake system. While ordinary brake systems will help you stop your vehicle when needed, there are certain road conditions where you would not want your tyres to lock up, lest you risk skidding. This is the function of Anti-lock Braking Systems or ABS as most people prefer to call it. But just how do anti-lock brake systems work?

Why Your Car Has ABS

Before the advent of computerized modules on automobiles, there was a much greater incidence of skidding and spinning out of control in slippery road conditions. The theory behind it is quite simple. If you have a skidding wheel, you lose traction of the road surface. The greater the loss of traction, the greater is the loss of control of your vehicle. As such, the ABS allow you to reestablish traction with the road surface by preventing the wheels from skidding, allowing you to slow down and control your vehicle at the same time.

A classic example will be driving on icy road. Because ice is naturally slippery, your tyres will not really be able to get a grip on the road surface. It will spin endlessly but you’re not going anywhere. This occurs because the contact patch of your tyres is actually sliding in relation to the slippery ice surface. The same is true when driving on wet roads at high speeds. A thin film of water is pushed under the tyres, separating it from the road surface. This occurs because water pressure in front of the tyres is greater than the actual capacity of the tyres to disperse or channel it away. Some of this water is channeled downwards and under the tyres, lifting the tyres in the process called hydroplaning. Because of the loss of contact with the road surface, there is a tendency for the tyres to skid.

So how does ABS fit into all of this? Well, as the term implies, ABS prevents the complete locking of your wheels by modifying the pressure of your brake fluid regardless of the pressure applied on the brake pedals. This adjusts the rotational speed of your wheels to effect a reduction in wheel slips.

So How Do Anti-lock Brake Systems Work?

To understand how ABS works, it is important to look first at the components that make up the system.

• Speed sensor – tracks the rotational speed of the car’s wheels and determines whether it is accelerating or decelerating.
• Valves – regulate the air pressure applied on the brakes when the ABS is engaged. Some ABS systems come with 3-position valves. First, brake valves open to allow for pressure to be delivered to the brakes. Second, brake valves close to contain brake pressure. Third, brake valves release some of the brake pressure. It is the third position of the valves that is repeated several times until the car comes to a complete stop.
• Pump – puts the brake pressure released by the valves back into the master cylinder.
• Electronic control unit – receives, intensifies, and filters the signals coming from the speed sensor to calculate the acceleration and rotational speed of the wheels.
• Hydraulic control unit – increases hydraulic pressure or reduces braking power by bypassing the brake pedal force depending on the signals received from the ECU.

Looking at the ABS in action, the speed sensors continuously provide data to the electronic control unit. What the ECU is looking for are unusual decelerations such as when applying brakes suddenly. Even before your car’s wheels lock up, rapid deceleration will occur. If this is unchecked, the wheels will stop a lot faster than the ideal stopping distance of the car.

What the ECU does is that it sends signals to the HCU to reduce or even release the brake pressure sent through the valves. This increases the rotational speed of the wheels and minimizes wheel slippage. This allows the ECU to sense acceleration so it sends another set of signals to the HCU to increase brake pressure until the ECU senses deceleration again. It is this continuous release and reapplication of the brake pressure depending on the acceleration and deceleration of the wheels that epitomizes the ingenuity of the Anti-lock Brake System. What it essentially does is that it makes sure your tyres will slow down at almost the same rate as your car without causing your car’s brakes to lock up.

The Anti-lock Brake System is an essential component of any modern car as it can significantly improve safety on the road. Without it, you are simply courting accidents by increasing the risk of skidding and loss of vehicle control.