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ABS is a system that stops the brakes from locking up while braking.
While making a emergency brake, most people instictivly stomp on the brake pedal for dear life and would like to push it through the firewall too if it would make the car stop faster.
This may cause the wheels to lock up, which means they will skid. A lot of tire squeel and a cloud of smoke, very spectaculair. But it won't make you stop any sooner! On the contrary! The car will skid and mostly becomes uncontrolable, because you can forget about steering while sliding on. And you will probably still hit, that what you were braking so hard for in the first place.
To solve this problem, you could try to 'pump the brakes'. That way you brake, let go to let the wheels roll again, brake, let go, etc, etc. In theory, this way the wheels don't lock up and you should stop sooner. But there is a catch. Most people just can't brake and release quick enough, certainly when they are in a panic A computer controlled system can do that a lot faster!
So in principal, a ABS system does the same thing. But with ABS, the ECU controls the pumping. This causes the brakecalipers to grab on and let go of the brakedisc multiple times every second (Some systems can cycle 15 times a second!). This results in a shorter braking distance, so you can stomp on that brakingpedal as hard as you possibly can without fearing of the brakes locking up. I'll go one further: The system works best whén you panic and stomp on the pedal all of a sudden. |
But how does it work?
Sensors near the wheels check the speed at which they are turning all the time.
By means of a toothed ring (often mounted on the outboard axle stub) generates a pulsing magnetic field that the sensor can pick up. With the help of this puls signal, the speed of the wheels can be calculated. This type of sensor is also known as a hall sensor.
The ABS ECU knows that at a certain speed, it will take a certain time and deceleration before the car comes to a controlled stop and de wheels can stop turning.
Most braking systems can let the wheels stop a lot faster than the actual car can, and thus causing the wheels to lock up!
The ABS system knows that when there is a sudden deceleration and the wheels stop to fast, there must be something wrong and it has to intervene.
The ABS ECU will make valves in each of the brakelines open and close. This couses the pulsating feel in the brakingpedal when the ABS system is active.
The speed at which the valves open and close for each independant wheel is controlled by the ABD ECU. It keeps the brakes very near the point when they start to lock up. This gives maximum braking power.
But the system is going to need pressure to operate the brakes. Normaly you provide this pressure by operating the main brake cylinder which moves the hydraulic fluid to the brakes and thus generating pressure.
But when a valve closes the brakelines, you can't build up or maintain that pressure.
To solve this problem, the system has a pump that activates when the system is active. You can often also hear the pump working when the ABS is activated.
Not only does a ABS system shorten your braking distance and stop the car sooner, but ABS also keeps the car controlable under heavy braking and let you steer around the obstacle!
The pictures above were taken from my Toyota Carina E GTi, which has a ABS system.
A ABS system was on the optionlist of the AE92 Corolla, but sadly, neither of my cars are equipped with one.
I've experienced the ABS system under various conditions: On the dry, wet and even on snow and I can tell you that it works ideal!
Even though I hate most electrical systems in cars as they tend to take away the driving experience, ABS is one of the few systems I can really recommend and would like to have on all of my cars!
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