Car Care

How braking technology prevents a fraction too much friction


There’s lots of physics involved in a moving car… weight, mass, speed, friction, energy and some other techie stuff. Geometry is there as well with pitch, roll and yaw… and you thought you’d never need maths again.

All of those forces and actions are applied to just four smartphone-sized patches of rubber between you and the road. As the driver, you have the most control over just one of them with your right foot.

Too much speed, braking at the wrong time, sharp turns or slippery road conditions are just some of the reasons that can cause those small patches of rubber to not cope.

Then came the engineers who invented anti-lock braking systems (ABS), which does exactly what its name suggests by preventing the wheels from locking when you brake and allowing you to steer the vehicle while safely bringing it to a stop.

Electronic Brakeforce Distribution (EBD) goes a little further than ABS with a collection of sensors that detect what impact all the various forces have on the car and then control the level of braking on each wheel independently. Typically, the front end of a vehicle will carry the most weight so the EBD applies less pressure to the rear brakes, preventing them from locking and causing the car to skid.

EBD in conjunction with ABS

Under heavy braking without ABS and EBD, the wheels will typically lock and the friction created between the road surface and the tyre will slow the car to a stop. This usually isn’t a problem on a straight dry road, but add in a bit of rain or a slippery surface like gravel, ice or snow, and the stopping distance has to increase.

If the wheels were to lock up on a corner, the angle that the front wheels are turned becomes irrelevant as the car’s mass opts for a straight line which could mean crossing the white line into oncoming traffic, finding a ditch or meeting a tree.

When you bring ABS into the picture, the situation improves significantly by preventing the wheels from locking and bringing the vehicle to a stop in a more controlled way.

Control of the car relies on its wheels continuing to turn and this is where EBD helps. Under heavy braking, sensors monitor wheel speed and release pressure on individual wheels. Modern systems have individual brake lines to each wheel and can compensate for friction changes on different road surfaces. Less brake pressure is needed to lock a wheel on icy or gravel roads, compared to tar sealed surfaces.

EBD in conjunction with electronic stability control (ESC)

EBD can also work with ESC to manipulate the speed of acceleration when cornering.

In most cases, taking a corner at speed will lead to understeering - when the nose doesn’t swing around as much as you expect, or oversteering - when the car turns quicker than intended potentially forcing the back end to slide out. To avoid this scenario, ESC employs something called a yaw rate sensor to detect both the angle of the steering wheel and the direction that the vehicle is turning.

If the yaw sensor detects oversteer or understeer from different angles between the steering wheel and the tyres, ESC will activate one of the front or rear brakes to rotate the car back on to its intended course.

ABS braking helps prevent wheels from locking and EBD applies the appropriate brake force to allow ESC to work effectively and easily. Combined with safe driving, these safety assist technologies are helping to prevent crashes.

Manufacturers continue to add to the suite of safety assist and crash prevention technology. While this technology is reliable, it is only as good as the sensors that enable it to work, so if you see a warning light illuminate on your dashboard, make sure you get your car inspected as soon as possible.

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