Antiblockiersystem

History

The development of ABS for applications to the car started in the years 1960 in a company called Teldix (contraction of Telefunken and Bendix , partners in this project). The performances of the electronics of the time prevent an implementation of a sufficiently reliable system for the car. The Citroen SM failed to be equipped with an ABS, but the financial problems of Automobiles Citroen and the first oil crisis are right of the project of application.

The patents and licenses of the Teldix company were repurchased by Bosch, which continued the development and leads to launching in series of the system ABS.

In October 1978, the ABS2 equips the Mercedes class S. In December 1978, it is with the tower of the BMW 7.

Principle of operation

The ABS was conceived in the beginning to help the driver to preserve the control of its vehicle, in the case of a braking under conditions of precarious adherence (rain, snow, glaze, gravel…). This one makes it possible on the one hand to keep the directivity of the vehicle so, to carry out a possible operation of avoidance, while optimizing this one, braking distance increasing considerably when the wheels are blocked and, therefore that the Pneumatique S slip on the Chaussée.

During an emergency braking, ABS controls the pressure in the brake system by adapting the maximum hydraulic pressure level for each wheel: if a wheel slows down abnormally, it slackens instantaneously the pressure of the brake system on the level of this wheel and this, as long as this one D-does not accelerate sufficiently. The system functions by impulses of unlocking (with the result that the wheels have tendency to rebloquer when the pressure goes up sufficiently in their respective brake systems), thing which one in general feels with the brake pedals which start to vibrate at the rate/rhythm variations of pressure of the brake system.

ABS preventing the wheels from blocking itself, the driver keeps the maximum capacity of deceleration, the adhesion coefficient loss to the braking of a tire which slips borders the 30 %). In the same way, the tires not slipping, they keep their directional capacity.

Of course, a good braking without ABS will be more effective than with ABS (since the principle of operation of ABS lies in the reduction in braking). Consequently, of sporting use, the driver slows down certainly better without ABS than in the presence of this system. But it is necessary well to see that, taken of surprised in situation of circulation current (a child which crosses the road behind a truck for example), the driver will carry out a braking definitely less considered and high risk to block the wheels: in this case, ABS makes it possible to have a more efficient braking with the final one.

At all events, even with an ABS, it is shown that the driver has, unfortunately, tendency not to press sufficiently extremely on the pedal of the brake (or in any case not rather quickly nor long enough) and therefore one finds from now on on much vehicle a Aide with emergency braking. This one makes it possible to have an attack with more energetic, even if it means braking to slacken the pressure if braking can be quieter (more distance than envisaged).

Therefore, to carry out a good braking, it is to better start to slow down extremely for then slackening the pressure on the brake pedals in order to adapt to the conditions, rather than the reverse (of course, a supported braking is less comfortable for the passengers). Time, that the driver realizes that braking is not supported enough (at least 1 second), was then transformed into a too large distance covered!

Finally, so in theory on dry surface, the tested driver can be more effective than ABS, in practice, with all the risks that control on road and the events certain situations not easily foreseeable, a brake comprising an ABS is very often effective and surer.

One can note that the operation of ABS is also very depend on the good quality of the system of damping of the travelling trains of the vehicle. Indeed, a defective damping does not make it possible any more to maintain the wheels of the vehicle in optimal contact with the road, causing losses of adherence which supports blockings of wheels in the event of fast deceleration.

Small truth-false

ABS makes it possible the driver to continue to direct the vehicle while strongly pressing on the freins ?

True , the wheels not blocking, the direction remains effective.

the stopping distance is shorter for a car having ABS ?

Faux , indeed braking is not more important with ABS than without, on the other hand one is thus ensured not to block the wheels (what would inevitably involve a lengthening of the braking distances). A pilot good will slow down besides certainly shorter without ABS than with, but as Mr. ToutLeMonde is not inevitably pilot its braking is ensured more with ABS than without.

On the vehicles with traction, ABS acts only on the wheels avant ?

False , the ABS installed on the majority of the vehicles functions on the four wheels.

If you feel that the brake pedals vibrate, one needs pomper ?

False , for a brake comprising ABS it is necessary to apply a pressure of braking and to keep it; there does not need more to pump with ABS (except exceptional case on ABS of more old generation on grounds very slipping for example). If one feels the pedal which vibrates, it is normal since it is the principle even of operation of the ABS which induces this.

ABS makes it possible to keep a better control of the vehicle in the event of braking brusque ?

True , indeed ABS was conceived at the same time to keep a certain control of the braking of the vehicle, but also the control of the direction of this one.

With ABS it is better to mount snow tires in hiver ?

Vrai because as the wheels do not block any more, braking with tires be can be finally less good than for a system without ABS where, the wheel blocking, it is formed a snow drift in front of the wheel what creates a slowing down shoe. It is very thus strongly advised to use tires winter for a brake with ABS (and not to forget to put 4 tires winter not to unbalance the stability of the vehicle in turns…).

See too

the Wikilivre of tribology and in particular the paragraph devoted to current research on braking.
Logical fuzzy

External bonds

Ministry for the transport of Canada

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