car anti-skid system

30-01-2015, 13:38Print
The anti-skid system (ABS) is a technical system of more safe driving and less wear in the treads of the wheels. In the German StVZO one says "anti-lock braking system" (ABV). It is used mainly in automobiles, but also in railways and airplane chassis.

ABS counteracts with the braking against possible blocking of the wheels by decrease of the brake pressure. Through this it allows with the braking of automobiles and airplanes a better Lenkbarkeit and directional stability. Moreover, the system about the regulation of the wheel slip can shorten the braking distance on wet street. On dry street and loose subsoil – for example, grit or snow – the braking distance can be extended against it. With railways Gleitschutz called system the education of the flats which lead to a typical blow noise during the journey should prevent.

The maximum brake deceleration is reached as a function of roadway state and tyre with about 8-25% of slip. 20% of brake slip mean that in the same period in which the vehicle puts back a way from 1 metre the wheels unroll only 0.8 metres. After the achievement of the braking power maximum – to that slip value with which the highest delay is achieved – the slip grows with sinking braking power further, until the wheel blocks, finally (= 100% of brake slip). In the blocked state it is braked only about sliding friction. The ABS steers the braking power in every wheel in such a way that the slip remains during the brake process any time very near with the optimum value. With strong braking the slip oscillates around this point of the maximum braking power.

Moreover, with planing of the tyre no transference of side forces is possible. Because the vehicle above the whole support surface of the tyres slides, a steering lock stop causes no direction change. In addition, so-called brake plates can develop in the wheel while blocking from selective wear. Both is avoided by ABS.

Construction and impact

4-canal ABS in the 1995th Fiat Punto.
Number plates are four individually to the wheels to controlled brake pipes and the electronic control on the right under the lid described with "ABS".
The first ABS arrangements were 3-canal systems, i.e. the brake pressure for both back wheels could be steered only together. Meanwhile are used in passenger cars admitted anew excluding 4-canal ABS which steers all wheels individually.

An ABS arrangement is an enlargement of the present standardised dual-circuit brake system. Two four wheel cylinders are operated together of one of both main brake cylinders. With a 4-canal ABS the pressure can be diminished regardless of this basic version in each of four wheel cylinders individually.

In every wheel is an induction transducer or with the newer vehicles a Hall-effect pulse generator as well as a hole disk or serrated washer by which the rev is measured. The brake pressure in a wheel is diminished if his rev sinks during the braking in comparison to those of the other wheels disproportionately. In the hydraulic part of the ABS of usual construction two magnet valves are right in the pressure pipe leading to every wheel. First the first valve closes the management. If the rev further sinks, brake fluid is let out with the second valve closed in the rest state at the side and the brake pressure sinks. The playful liquid is promoted with an at the same time starting electric pump in the space and on the pressure level between main brake cylinder and the first magnet valve back. Otherwise the liquid would be absent there, and the brake pedal would be further stepped if the first magnet valve opens after rev rise again, the brake pedal would not have soon completely pedaled and braking any more possibly. Many such working cycles take place successively and fast (about 10 per second, with motorcycles 15 per second). The pressure rise as a result of the perceived in the pedal with the foot as a vibration. By automatic, quick stuttering of the brakes the vehicle jerks and rattles clearly. According to elementary concept of the hydraulic separation in two circles two pumps exist (often, however, with only one electric motor powered).

With moderate braking in the normal traction mode and with breakdown of the ABS the braking system works like a normal 2-of a circle arrangement. The brake pressure of the master cylinder works about the open pipes undiminished on the wheel cylinders. Both valves (eight per 4-bicycle vehicle) are closed in the rest state with spring tension openly (the first valve) or (the second valve) are held. The normal braking functions in this manner also with stream breakdown.

The extensive signal processing occurs in a central prozessing unit. Below a general minimum speed (about 6 km/h) the ABS is switched off. With the turning on of the ignition and with the turning on of the ABS after excess of the minimum speed selftests occur. Recognised mistakes are enrolled in an electronic accumulator to make easier the error analysis with defects.

With Lkws with compressed air brake systems the ABS works after the same principle. Because an air compressor works constantly, the return pumps are cancelled for the playful air. The additional valves are directly with the wheel cylinders, because atmospheric pressure changes from a central point about long pipes would come too late with the wheels. However, hydraulic pressure changes have substantially shorter terms.

Additional functions
Brake circuit scheme

Newer versions of the ABS also take over the brake circuit scheme (electronic brake circuit scheme – EBV) between front axle and rear axle (4-canal systems) and substitute with it earlier for usual mechanical regulators (brake distribution unit) which are inserted partially still with truck. Several advantages arise from it:

Optimum exploitation of the Kraftschlussbeiwertes in both axes – incl. the diagonal bicycle loads which cannot be shown with mechanical regulators optimally.
Already with light brakings the rear axle is cobraked and a known problem is removed: With the mechanical brake circuit scheme it could seem that the brake disks were cleaned in the rear axle too seldom by the braking and thus corrosion reduced the braking action in the surface or dirt.
Furthermore the emergency wheel recognition also belongs to newer systems. Emergency wheels have a smaller Abrollumfang and turn faster, so that the ABS can correctly process the feedback of his rev sensor in case of a full braking.

In the meantime, ABS is complemented increasingly with ESC (Electronic Stability Program).

Avarice moment assuagement

\mu-Split
If the vehicle is on a roadway with different Reibwerten between the right and left side (for example, snow or wet foliage in the roadway edge), one moment would appear with a sudden full braking without ABS around the avarice axis aside with the higher static friction (avarice moment) because the vehicle side on the useful subsoil is stronger braked than the side on the smooth subsoil. By the vehicle tuning of the ABS the manufacturers provide for the fact that the brake pressure of the wheel on useful subsoil rises not so quickly strongly as it would be physically possible. The driver thereby receives additional response time to react by countersteering. The time which needs the ABS to come on useful subsoil to the full braking efficiency is depending on the manufacturer's philosophy. It is usually shorter with sporty vehicles than with saloons. By the slowed down construction of the braking power the braking distance is also extended. Nevertheless, this is accepted in view of the advantages concerning the vehicle control.

In the meantime, there are also the systems which substitute for the avarice moment assuagement with an automatic intervention in the steering. With active countersteering by means of a heterodyne steering (active steering) the lengthening of the braking distance is cancelled by the avarice moment assuagement.

Offroad ABS
Offroad ABS is an additional function offered above all in cross-country vehicle which lifts the present system-conditioned braking distance lengthening on loose subsoil extensively. The braking action of the wedge which forms with the braking before the wheel is used by interval-like blocking of one or several wheels. On other road surfaces the system functions like a customary ABS. The additional function was introduced in 2006 in VW Touareg under the name ABSplus and today is available also with other manufacturers. The changed brake regulation can be activated with some manufacturers also by hand.

History
The first application of an anti-wheel-lock braking system was tested in the aviation, so that the airplane remained after the landing with the braking from high speed in the track. Already in 1920 the French car pioneer and airplane pioneer Gabriel Voisin used a hydraulically functioning system. In the 1950s various traffic airplanes were equipped with the Maxaret-Anti-Skid of the British company Dunlop.

In 1928 the German Karl Wessel received a patent for a load sensing valve for cars, indeed, he did not come out about the paper stage. In 1936 there was of Bosch a patent for a device for preventing of the festival braking of the wheels of an automobile. The devices existed of about 1000 analogous components and were still very unwieldy and slow. The amount of the components on about 140 pieces could be reduced by the digital technology. With it ABS was ready to go into mass production.

In 1969 the first generation of an ABS (electronically controlled anti-lock braking system) on the International Motor Show was presented by the American enterprise ITT Automotive (till 1967 Alfred Teves).

In 1970 Citroen stood shortly before the market launch of the Teldix ABS (Teldix for tele-spark - Bendix) which failed, finally, on account of financial problems of the car manufacturer as well as the first oil crisis. In 1975 Bosch took over the patents and licences from Teldix.

Passenger cars
The first passenger car with mechanical ABS was Jensen FF with Dunlop Maxaret ABS from 1966. In 1969 Ford equipped Lincoln Continental Mark III with an ABS system only working on the back wheels called sura track Brake system; also Ford Thunderbird. From 1971 to 1973 the Chrysler group offered his luxury model Imperial against surcharge with a sura to Brake the called electronic anti-skid system of Bendix in which enclosed front wheels and back wheels. In 1978 Bosch put on the market his electronic ABS; at the same time the concept ABS was protected by Bosch juridically. Other manufacturers call its systems partially ABV (anti-lock braking system). First ABS was available for the S-Class W 116 of Mercedes-Benz, then for the BMW 7er of the class E23. In 1985 the Ford Scorpio was the first passenger car which disposed serially of ABS. From 1987 were available in Volkswagen also the VW GOLF II, Passat III and the transporter T3 against high surcharges with the system (Golf: 1800 DM, Passat: 2200 DM, transporters: 3720 DM, prices in 1989). In the end of 2003 about 90 percent of the admitted new vehicles in Germany had ABS. On account of a selfobligation of the European automobile industry (ACEA) all vehicles are equipped since the 1st of July, 2004 with less than 2.5 t of gross weight rating serially with ABS. The Japanese automobile associations have delivered same-being obligations.

Trucks
Mercedes-Benz offers the ABS for air brakes since 1981, develops together with the company WABCO. Since 1987 all coaches and since 1991 are also equipped all truck with ABS. Since January, 1991 may be admitted truck with more than 3.5 t of gross weight rating and penalty with more than eight seats only with ABS.

Motorcycles

The first ABS for motorcycles was introduced in 1985 by Lucas Girling. The first standard manufacturer was the company FTE automotive with headquarter in boars / Lower Franconia (at that time one more section of the company FAG Kugelfischer). His ABS was introduced in 1988 first to the BMW K models as an option and at that time cost 1980 DM of surcharge. Today Bosch, Nissin, Continental-Teves and Brembo also deliver ABS. The Federal Ministry of traffic, construction and urban development recommends to prescribe ABS legally. The representatives of the German delegation demand same in a working group of the economic commission for Europe. The scientific base of the demand is a study of the government institution of street being. The way of the plan meets with criticism now and again.

Meanwhile there increases the offer of motorcycles and motor scooters which are equipped optionally or serially with ABS. The latest studies of ADAC go out in projections from 160 not killed motorcyclists per year and up to 6900 motorcycle accidents with injuries could have been prevented in 2009 if the drivers ABS had had aboard. Criticises the too low spreading of ABS with motorcycles. With motorcycles less than 250 cm ³ ABS is spread even only at less than 1 percent of the models. With the heavier machines there is the security system at a good 25 percent of the two-wheeled vehicles in Europe.

Till present the motorcycle ABS is laid out (state in 2010) to maintain the driving stability with full brakings straight ahead. Newer systems are valid than restrictedly suitably for bend, systems fully suited for bend are still in the development. The systems are different according to manufacturer. The pressure modulation is carried out either about electronically regulated magnet valves (e.g., BMW, Ducati, Kawasaki, KTM, Suzuki, Yamaha), Plunger system (BMW old, Honda) or magnet system (Honda). Also the control frequency lies according to system development far apart. The first systems (ABS I) lay with maximum 7 control processes seconds, the newest systems can show 15 control processes. Below 4 km/h (BMW, Honda etc.) or 10 km/h (Honda SH 300) the system is switched off control-partly.

Studies confirm the purchase interest in ABS, availability and economic Vertretbarkeit provided. The surcharge amounts to 600 to 1050 euros. There raised maintenance costs come specifically for model differently compared with conventional brake assemblies. Besides, some systems can be waited only in an authorised workshop with special devices properly.

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