How ABS Works: ABS Dynamics. Part 2
Almost any ABS consists of a control unit, modulator which changes the pressure in hydraulic mainline, wheel side speed sensors mounted on the inner parts of a wheel hub.
The progressive humankind realized the harm of blocked wheels only in the 70s of the previous century. The pioneer company was Mercedes which in collaboration with Bosch developed a system that was installed on Mercedes S-class in 1979. The basic principle of the system was shaped then and later on it was only modernized.
The modern electronics (ABS, anti-slide system, ESP) considers not only the frequency of wheel rotation in order to keep the transversal and longitudinal dynamics of a car. The angles of the rotation of the steering wheel, body roll degree, acceleration are also under control. The pressure in braking system is generated according to the all received data plus sometimes even the track of the engine is changed.
The major purpose of ABS is to control the speed of the rotation of the wheel by changing the pressure in the braking system mainlines. In order to control side speed one has to know its value and how it is changed with time. Each wheel is equipped with a sensor which gives out electronic impulses with the frequency proportional to the rotation speed. This information goes to the control unit of ABS.
If during braking the side speed of a wheel is approaching 0 the electronic brain will immediately decide to “unbrake” it. The pressure will decrease until the wheel gains enough rotation. Then ABS will again increase the pressure in the mainline and brake the wheel. The cycle will repeat until the car stops or the driver will release the brakes to the position when there is no need for ABS.
The existing systems have quite a precise setting and enable maximal effectiveness of braking.
Some might say: it doesn’t require much wisdom. One can brake in a broken manner without the help of ABS. It is partially correct. Such a method can be used in car not equipped with ABS. When wheels block you brake, when they are “released” you get an opportunity to correct the trajectory of your motion. Of course, the braking distance increase.
But unfortunately, not a single (even the most experienced and talented one) can enable portioned braking with the frequency ABS can. The system can block-unblock wheel 15 times per second. Moreover, if such a braking is carried out by a driver it affects all the braking mechanisms, while ABS controls each wheel separately.
The majority of the modern ABS systems work with EBD (Electronic Brake Distribution) – a system that distributes braking force and meters the intensiveness of braking for each wheel.
How ABS Works: ABS Dynamics. Part 1
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