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Friday, December 06, 2013

About ABS & EBD Brake Systems

We all know that pushing down on the brake pedal slows a car to a stop. But how does this happen? How does your car transmit the force from your leg to its wheels? How does it multiply the force so that it is enough to stop something as big as a car?

When you depress your brake pedal, your car transmits the force from your foot to its brakes through a fluid. Since the actual brakes require a much greater force than you could apply with your leg, your car must also multiply the force of your foot. It does this in two ways


When you apply your brakes, you want your car to slow down, but you also want to be sure that you don't lose control of the vehicle. For this reason, many modern cars are fitted with anti-lock braking systems (ABS) which allow the driver to stop the car in the shortest distance possible without skidding or spinning out of control. They also allow the driver to continue to steer the vehicle while the brakes are applied.

So, cars fitted with ABS are inherently safer. But is ABS achieving its potential? RACV was concerned about overseas research which suggested that it wasn't, so we commissioned Monash University Accident Research Centre (MUARC) to examine the Australian experience. MUARC analysed the crash records for a number of models that came equipped both with ABS and without it, and compared their actual crash involvement.

The results were mixed, and rather disturbing. For multi-vehicle crashes, ABS-equipped vehicles were less likely to be involved (by about 18%) compared with the same model without ABS. However, for single-vehicle run-off-road crashes, e.g. leaving the road on a bend, ABS vehicles were over-involved by about 35% compared with the equivalent model without ABS. This increased involvement of ABS-equipped vehicles in run-off-road crashes is particularly concerning.

Why should this be so? Why should an inherently safer vehicle be over-involved in certain types of crash? The answer probably lies in the way in which ABS is used - or misused - by the driver.

ABS feels different, particularly under heavy braking; the car may seem to shudder or vibrate. This is explained by the way ABS works. It monitors the speed of each individual wheel, and when the control unit detects the onset of brake lock-up, it momentarily reduces brake hydraulic pressure to that wheel. This adjustment can be made many times in the space of a second, which the driver will feel as a pulsing sensation through the brake pedal.

Perhaps some drivers, not having experienced this, may respond by taking their foot off the brake. In fact, the correct response is to maintain braking pressure. In other words, push as hard as possible when a quick stop is necessary - " Stomp and steer!" ABS will do the rest.

Of course, you need to know if your car is fitted with ABS, so check the owner's manual. And read the instructions in the manual, as most will provide driving hints about how best to use the brakes.

Just as importantly, drivers must not become overconfident in the mistaken belief that their ABS brakes will get them out of any trouble. In fact, stopping distances and travelling speeds may not be any different between ABS and non-ABS equipped vehicles. Indeed, on some surfaces such as loose gravel, an ABS-equipped car may have a longer braking distance.

There are other braking and stability technologies starting to come on the market (see above), and the MUARC research indicated many of these have the potential to provide substantial benefits. Currently, these are seen mostly on the more expensive luxury models, but they will likely filter down to more popular models soon. RACV will continue to monitor the potential of these technologies.

RACV is confident about the potential for ABS to prevent crashes, and encourages motorists to choose ABS-equipped vehicles. But drivers should consider the warnings and tips discussed here to make the most of the technology.


The sensors on the wheels might get contaminated by metallic dust. When this condition occurs the sensors become less efficient in picking up problems. In modern ABS systems, two more sensors are added to help:

► wheel angle sensor
► gyroscopic sensor

The idea behind this is that when the gyroscopic sensor detects that the car’s direction is not the same as what the wheel sensor reports, the ABS software will cut in to brake the necessary wheel in order to help the car go the direction the driver intends.



EBD (Electronic Brake Force Distribution) is a technology that enables the braking force of a vehicle to be increased or applied automatically, depending on road conditions, speed of the vehicle, weight of vehicle, etc. 

In a regular braking system, when the brake pedal is applied, the brake fluid travels from the master cylinder to the brake cylinders. When the fluid goes inside the brake cylinder, the pressure of the fluid being applied forces the two pistons to push out resulting in the brake shoes or pads being pushed out. This push or pressure is in direct proportion to the push by the pistons, which causes the shoes or pads to rub against the drum or caliper. This reaction creates friction and decreases the turning of the wheels. 

What EBD does is it electronically monitors, through sensors, the conditions of the road, the feel of pressure on the brake pedal, and vehicle weight, to determine when to apply pressure to the wheel cylinders. The sensors are designed to monitor the movements of the wheels and determine based on weight, which wheels may need the maximum force applied, as per the condition met. Supposedly, this is to provide better and more precise braking under every condition imaginable. 

Since the front end has the most weight on a vehicle, the EBD system recognizes this and electronically controls the back brakes so when the driver applies the brakes, the back brakes do not lock up causing a skid.

 EBD is a good system for drivers because it can increase the vehicle’s ability to stop under any conditions. But this is only effective if the brains of the computer works, along with the sensors that make up the system. If one of those sensors should fail, and you run into a bad situation, you could end up in a precarious predicament. 


By : Automotive News & Super Modified Sports Cars

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