An Anti-lock Braking System (ABS) (translated from German, Anti-Blockier System) is a safety system on motor vehicles which prevents the wheels from locking while braking. The German language (de ''Deutsch'') is a West Germanic language and one of the world's major languages. A motor Vehicle is a Machine which incorporates a motor (sometimes known as an Engine) and which is used for Transportation A wheel is a circular device that is capable of rotating on its axis facilitating movement or transportation whilst supporting a load ( Mass) or performing labour in machines A brake is a device for slowing or stopping the motion of a Machine or Vehicle, or alternatively a device to restrain it from starting to move again A non-locking braking system allows the driver to maintain steering control under heavy braking, by preventing a skid, and allowing the wheel to continue to forward roll and create lateral control, as directed by driver steering inputs. Disadvantages of the system include increased braking distances under some limited circumstances (ice, snow, gravel, "soft" surfaces), and the creation of a "false sense of security" among drivers who do not understand the operation, and limitations of ABS.

Since it came into widespread use in production cars (with "version 2" in 1978), ABS has made considerable progress. Recent versions not only handle the ABS function itself (i. e. preventing wheel locking under braking), but also traction control (TCS or ASR), brake assist (BA, EBA or HBA), and electronic stability control (ESP, ESC or DSC), amongst others. A traction control system ( TCS) also known as Anti-Slip Regulation ( ASR) on current production Vehicles are typically (but not necessarily Brake Assist (BA or BAS) is a generic term for an Automobile braking technology that increases braking pressure in an emergency situation Electronic stability control ( ESC) is a computerized technology that improves the safety of a vehicle's handling by detecting and preventing skids Not only that, but the Bosch 8. Robert Bosch GmbH is a German diversified technology-based corporation which was started in 1886 by Robert Bosch in Stuttgart Germany. 0 version now weighs less than 1. 5 kilograms, compared with the 6. 3 kg version 2. 0 in 1978.

History

Anti-lock braking systems were first developed for aircraft in 1929, by the French automobile and aircraft pioneer, Gabriel Voisin, as threshold braking an airplane is nearly impossible. Year 1929 ( MCMXXIX) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar. This article is about the country For a topic outline on this subject see List of basic France topics. Gabriel Voisin ( February 5, 1880 &ndash December 25, 1973) was a French aviation pioneer Threshold braking or limit braking is a Driving technique most commonly used in motor racing but also practised in road vehicles to slow a vehicle at the optimum An early system was Dunlop's Maxaret system, introduced in the 1950s and still in use on some aircraft models. Dunlop Rubber was a British company which manufactured tyres and other rubber products for most of the 20th century The 1950s Decade refers to the years of 1950 to 1959 inclusive

A fully mechanical system saw limited automobile use in the 1960s in the Ferguson P99 racing car, the Jensen FF and the experimental all wheel drive Ford Zodiac, but saw no further use; the system proved expensive and, in automobile use, somewhat unreliable. The 1960s decade refers to the years from the beginning of 1960 to the end of 1969 Given its success in other forms of motor racing notably rallying it is perhaps surprising that Four-wheel drive (4WD has only been tried a handful of times in Formula The Jensen FF was a Four-wheel drive (4WD Grand Tourer (GT car produced by the British manufacturer Jensen Motors between 1966 and Four-wheel drive, 4WD, or 4x4 ("four by four" is a four-wheeled Vehicle with a drivetrain that allows all four Wheels to For other Ford related cars called Zephyr see Mercury Zephyr, Lincoln-Zephyr, and Lincoln Zephyr The Ford Zephyr is a However, a limited form of anti-lock braking, utilizing a valve which could adjust front to rear brake force distribution when a wheel locked, was fitted to the 1964 Austin 1800. Development It was developed at BMC as the large-car follow-up to the successful Mini and Austin 1100 under the ADO17 codename

ABS brakes on a BMW motorcycle

Chrysler, together with the Bendix Corporation, introduced a crude, limited production ABS system on the 1971 Imperial. Chrysler LLC is an American Automobile manufacturer that has been producing Automobiles since 1925 The Bendix Corporation was an American manufacturing and engineering company which during various times in its 60 year existence made brake systems aeronautical hydraulics for Chrysler branded models before 1955 and after 1983 see Chrysler Imperial Imperial was the Chrysler Corporation 's prestige Called "Sure Brake", it was available for several years, and had a satisfactory performance and reliability record. Ford also introduced anti lock brakes on the Lincoln Continental Mark III and the Ford LTD station wagon, called "Sure Trak". Ford Motor Company is an American Multinational corporation and the world's fourth largest automaker based on Worldwide vehicle sales, following See Lincoln Mark for a complete overview of the Lincoln Mark Series The German firms Bosch and Mercedes-Benz had been co-developing anti-lock braking technology since the 1930s, and introduced the first completely electronic 4-wheel multi-channel ABS system in trucks and the Mercedes-Benz S-Class in 1978. Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. Robert Bosch GmbH is a German diversified technology-based corporation which was started in 1886 by Robert Bosch in Stuttgart Germany. Mercedes-Benz is a German manufacturer of luxury Automobiles Buses coaches and Trucks It is currently a division of the The 1930s were described as an abrupt shift to more radical and conservative lifestyles as countries were struggling to find a solution to the Great Depression. This article is about the semi-truck For the North American use of the word see Pickup truck. Mercedes-Benz is a German manufacturer of luxury Automobiles Buses coaches and Trucks It is currently a division of the The Mercedes-Benz S-Class is a series of the largest Sedans produced by Mercedes-Benz, a division of Daimler AG. ABS Systems based on this more modern Mercedes design were later introduced on other cars and motorcycles. MotorCycle is the title of a 1993 album by Rock band Daniel Amos, released on BAI Records. General Motors introduced the "Trackmaster" ABS on their Cadillac models in 1971 as an option that was operational on the rear wheels for RWD models. General Motors Corporation ( GM) ( is a multinational automobile manufacturer founded in 1908 and headquartered in the United States. Cadillac is a Brand of Luxury vehicles owned by General Motors. ^[1][2]

Operation

The anti-lock brake controller is also known as the CAB (Controller Anti-lock Brake).

A typical ABS is composed of a central electronic control unit (ECU), four wheel speed sensors (one for each wheel), and two or more hydraulic valves within the vehicle brake circuit. In automotive electronics an electronic control unit (ECU also called a Control unit, or Control module, is an Embedded system that controls one or more Wheel Speed sensors or vehicle speed sensors (VSS are sender devices used for reading the speed of the vehicle's Wheel rotation. A vehicle brake is used to slow down a vehicle by converting its Kinetic energy into heat The hydraulic brake is an arrangement of braking mechanism which uses Brake fluid, typically containing Ethylene glycol, to transfer pressure from the controlling The ECU constantly monitors the rotational speed of each wheel. Rotational speed (sometimes called speed of revolution) indicates for example how fast a motor is running When it senses that any number of wheels are rotating considerably slower than the others (a condition that is likely to bring it to lock - see note below), it actuates the valves to decrease the pressure on the specific braking circuit for the individual wheel, effectively reducing the braking force on that wheel. The wheel(s) then turn faster; when they turn too fast, the force is reapplied. This process is repeated continuously, and this causes the characteristic pulsing feel through the brake pedal. A typical anti-lock system can apply and release braking pressure up to 20 times a second.

Note: The ECU needs to determine when some of the wheels turn considerably slower than any of the others because when the car is turning the two wheels towards the center of the curve inherently move slightly slower than the other two – which is the reason why a differential is used in virtually all commercial cars. This article deals with the concept of a differential in mechanical engineering.

The sensors can become contaminated with metallic dust, or other contaminants, and fail to correctly detect wheel slip; this is not always picked up by the internal ABS controller diagnostic. In this occurrence, the ABS warning light will usually be illuminated on the instrument panel, and the ABS will be disabled until the fault is rectified.

Additional developments

One step beyond ABS are modern Electronic Stability Control (ESC or ESP) systems. Electronic stability control ( ESC) is a computerized technology that improves the safety of a vehicle's handling by detecting and preventing skids Here, two more additional sensors are added to help the system work: these are a steering wheel angle sensor, and a gyroscopic sensor. A steering wheel (also called a driving wheel or hand wheel) is a type of steering Control in Vehicles and vessels ( Ships and Boats A gyroscope is a device for measuring or maintaining orientation, based on the principles of Angular momentum. The theory of operation is simple: when the gyroscopic sensor detects that the direction taken by the car doesn't coincide with what the steering wheel sensor reports, the ESC software will brake the necessary individual wheel(s) (up to three with the most sophisticated systems), so that the vehicle goes the way the driver intends. The steering wheel sensor also helps in the operation of Cornering Brake Control (CBC), since this will tell the ABS that wheels on the inside of the curve should brake more than wheels on the outside, and by how much. Cornering Brake Control or CBC is an Automotive safety system developed by BMW.

Traction control

Main article: Traction control system

The ABS equipment may also be used to implement traction control system (TCS, ASR) on acceleration of the vehicle. A traction control system ( TCS) also known as Anti-Slip Regulation ( ASR) on current production Vehicles are typically (but not necessarily A traction control system ( TCS) also known as Anti-Slip Regulation ( ASR) on current production Vehicles are typically (but not necessarily If, when accelerating, the tire loses traction, the ABS controller can detect the situation and take suitable action so that traction is regained. Manufacturers often offer this as a separately priced option even though the infrastructure is largely shared with ABS. More sophisticated versions of this can also control throttle levels and brakes simultaneously.

Mercedes-Benz was the first to offer this electronic traction control system in 1985.

Effectiveness

A 2003 Australian study^[3] by Monash University Accident Research Centre found that ABS:

• Reduced the risk of multiple vehicle crashes by 18 percent,
• Reduced the risk of run-off-road crashes by 35 percent. For a topic outline on this subject see List of basic Australia topics.

On high-traction surfaces such as bitumen, or concrete, many (though not all) ABS-equipped cars are able to attain braking distances better (i. Bitumen is a mixture of organic Liquids that are highly Viscous, black sticky entirely soluble in Carbon disulfide, and composed primarily Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag e. shorter) than those that would be easily possible without the benefit of ABS. Even an alert, skilled driver without ABS would find it difficult, even through the use of techniques like threshold braking, to match or improve on the performance of a typical driver with an ABS-equipped vehicle, in real world conditions. Threshold braking or limit braking is a Driving technique most commonly used in motor racing but also practised in road vehicles to slow a vehicle at the optimum ABS reduces chances of crashing, and/or the severity of impact. The recommended technique for non-expert drivers in an ABS-equipped car, in a typical full-braking emergency, is to press the brake pedal as firmly as possible and, where appropriate, to steer around obstructions. In such situations, ABS will significantly reduce the chances of a skid and subsequent loss of control.

In gravel, sand and deep snow, ABS tends to increase braking distances. On these surfaces, locked wheels dig in and stop the vehicle more quickly. ABS prevents this from occurring. Some ABS calibrations reduce this problem by slowing the cycling time, thus letting the wheels repeatedly briefly lock and unlock. The primary benefit of ABS on such surfaces is to increase the ability of the driver to maintain control of the car rather than go into a skid — though loss of control remains more likely on soft surfaces like gravel or slippery surfaces like snow or ice. On a very slippery surface such as sheet ice or gravel, it is possible to lock multiple wheels at once, and this can defeat ABS (which relies on comparing all four wheels, and detecting individual wheels skidding). Availability of ABS relieves most drivers from learning threshold braking.

A June 1999 National Highway Traffic Safety Administration (NHTSA) study found that ABS increased stopping distances on loose gravel by an average of 22 percent. The National Highway Traffic Safety Administration ( NHTSA, often pronounced "nit-suh" is an agency of the Executive Branch of the U ^[4]

According to the NHTSA,

"ABS works with your regular braking system by automatically pumping them. In vehicles not equipped with ABS, the driver has to manually pump the brakes to prevent wheel lockup. In vehicles equipped with ABS, your foot should remain firmly planted on the brake pedal, while ABS pumps the brakes for you so you can concentrate on steering to safety. "

When activated, some earlier ABS systems caused the brake pedal to pulse noticeably. As most drivers rarely or never brake hard enough to cause brake lock-up, and a significant number rarely bother to read the car's manual, this may not be discovered until an emergency. When drivers do encounter an emergency that causes them to brake hard, and thus encounter this pulsing for the first time, many are believed to reduce pedal pressure, and thus lengthen braking distances, contributing to a higher level of accidents than the superior emergency stopping capabilities of ABS would otherwise promise. Some manufacturers have therefore implemented a brake assist system that determines that the driver is attempting a "panic stop" and the system automatically increases braking force where not enough pressure is applied. Brake Assist (BA or BAS) is a generic term for an Automobile braking technology that increases braking pressure in an emergency situation Nevertheless, ABS significantly improves safety and control for drivers in most on-road situations.

Risk compensation

ABS brakes are the subject of some widely cited experiments in support of risk compensation theory, which support the view that drivers adapt to the safety benefit of ABS by driving more aggressively. In Ethology, risk compensation is an effect whereby individual people may tend to adjust their Behaviour in response to perceived changes in risk

The two major examples are from Munich and Oslo. In both cases taxi drivers in mixed fleets were found to exhibit greater risk-taking behaviour when driving cars equipped with ABS, with the result that collision rates between ABS and non ABS cars were not significantly different.

Design and selection of components

Given the required reliability, it is illustrative to see the choices made in the design of the ABS system. Proper functioning of the ABS system is considered of the utmost importance, for safeguarding both the passengers within, and people outside of the car. The system is therefore built with some redundancy, and is designed to monitor its own working and report failures. The entire ABS system is considered to be a hard real-time system, while the sub-system that controls the self diagnosis is considered soft real-time. In Computer science, real-time computing (RTC is the study of hardware and software systems that are subject to a "real-time constraint"—i As stated above, the general working of the ABS system consists of an electronic unit, also known as ECU (electronic control unit), which collects data from the sensors and drives the hydraulic control unit (HCU), mainly consisting of the valves that regulate the braking pressure for the wheels.

The communication between the ECU and the sensors must happen quickly and at real time. A possible solution is the use of the CAN bus system, which has been, and is still in use in many ABS systems today (in fact, this CAN standard was developed by Robert Bosch GmbH, for connecting electronic control units). Robert Bosch GmbH is a German diversified technology-based corporation which was started in 1886 by Robert Bosch in Stuttgart Germany. This allows for an easy combination of multiple signals into one signal, which can be sent to the ECU. The communication with the valves of the HCU is usually not done this way. The ECU and the HCU are generally very close together. The valves, usually solenoid valves, are controlled directly by the ECU. A solenoid valve is an Electromechanical Valve for use with Liquid or Gas controlled by running or stopping an Electric current To drive the valves based on signals from the ECU, some circuitry and amplifiers are needed (which would also have been the case if the CAN-bus was used).

The sensors measure the position of the tyres, and are generally placed on the wheel-axis. The sensor should be robust and maintenance free, not to endanger its proper working, for example an inductive sensor. An inductive sensor is an electronic Proximity sensor, which detects metallic objects without touching them These position measurements are then processed by the ECU to calculate the differential wheel rotation.

The hydraulic control unit is generally integrated with the ECU (or the other way around), and consists of a number of valves that control the pressure in the braking circuits. All these valves are placed closely together, and packed in a solid aluminium alloy block. This makes for a very simple layout, and is thus very robust.

The central control unit generally consists of two microcontrollers, both active simultaneously, to add some redundancy to the system. A microcontroller (also MCU or µC is a functional Computer system-on-a- chip. These two microcontrollers interact, and check each other's proper working. These microcontrollers are also chosen to be power-efficient, to avoid heating of the controller which would reduce durability.

The software which runs in the ECU has a number of functions. Most notably, the algorithms that drive the HCU as a function of the inputs, or control the brakes depending on the recorded wheel spin. This is the obvious main task of the entire ABS-system. Apart from this, the software also needs to process the incoming information, e. g. the signals from the sensors. There is also some software that constantly tests each component of the ABS system for its proper working. Some software for interfacing with an external source to run a complete diagnosis is also added.

As mentioned before the ABS system is considered hard real-time. The control algorithms, and the signal processing software, certainly fall in this category, and get a higher priority than the diagnosis and the testing software. The requirement for the system to be hard real-time can therefore be reduced to stating that the software should be hard real-time. The required calculations to drive the HCU have to be done in time. Choosing a microcontroller that can operate fast enough is therefore the key, preferably with a large margin. The system is then limited by the dynamic ability of the valves and the communication, the latter being noticeably faster. The control system is thus comfortably fast enough, and is limited by the valves.

References

See also

• Car safety
• Electronic brakeforce distribution
• Risk compensation

External links

• Official Chrysler announcement of the first true 4-wheel ABS
• Effect of ABS on crash and fatality risk
• Anti-lock Brakes (ABS) Video