Report on ABS


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Report on ABS

  1. 1. 2011Anti-LockBrAking SyStem“An Advance Braking Technology”Reported By:Kou s h i k PaulRoll No.- 60 rdMech. Engg. [3 Year]Bengal College Of Engineering &Technology
  2. 2. ANTI-LOCK BRAKING SYSTEM 2011 ACKNOLEDGEMENTAt first I would like to honor my respected SirDebajyoti Ray for his advice andencouragement to making this seminar. I wouldalso thank him for always being available forguidance and help.Finally,I would like to thank my Parents fortheirlove. I would also like to acknowledge withappreciation of their support in my studies. 1
  3. 3. ANTI-LOCK BRAKING SYSTEM 2011 Ta b l e o f C o n t e n t s TOPICS Page No1. INTRODUCTION 32. HISTORY 43. HOW IT IS WORKS 5 1
  4. 4. ANTI-LOCK BRAKING SYSTEM 2011 4. COMPONETS 8 5. USE OF ABS 10 6. TYPE OF ABS 11 7. EFFECTIVENESS 13 8. ABS QUESTIONS??? 16 1. INTROUCTION A brake is one of the most important parts of any type ofvehicle.Brake is used to retard or stop a vehicle. Here Kinetic energy 1
  5. 5. ANTI-LOCK BRAKING SYSTEM 2011transferred into Heat energy. The kinetic energy increases with the squareof the velocity. So, K.E.=1/2mv² .An anti-lock braking system (ABS, fromGerman: Antiblockiersystem) is a safety system that allows the wheels ona motor vehicle to continue interacting tractively with the road surface asdirected by driver steering inputs while braking, preventing the wheelsfrom locking up (that is, ceasing rotation) and therefore avoiding skidding. Stopping a car in a hurry on a slippery road can be very challenging.Anti-lock braking systems (ABS) take a lot of the challenge out of thissometimes nerve-wracking event. In fact, on slippery surfaces, evenprofessional drivers cant stop as quickly without ABS as an average drivercan with ABS. An ABS generally offers improved vehicle control and decreasesstopping distances on dry and slippery surfaces for many drivers;however, on loose surfaces like gravel or snow-covered pavement, anABS can significantly increase braking distance, although still improvingvehicle control. Since initial widespread use in production cars, anti-lock brakingsystems have evolved considerably. Recent versions not only preventwheel lock under braking, but also electronically control the front-to-rearbrake bias. This function, depending on its specific capabilities andimplementation, is known as Electronic BrakeforceDistribution (EBD), Traction Control System (TCS), emergency brakeassist, or Electronic Stability Control (ESC). 2. HISTORY 1
  6. 6. ANTI-LOCK BRAKING SYSTEM 2011Early Systems: The ABS was first developed for aircraft use in 1929 bythe French automobile and aircraft pioneer, Gabriel Voisin, as thresholdbraking on airplanes is nearly impossible. An early system was DunlopsMaxaret system, which was introduced in the 1950s and is still in use onsome aircraft models.These systems use a flywheel and valve attached toa hydraulic line that feeds the brake cylinders. The flywheel is attached toa drum that runs at the same speed as the wheel. In normal braking, thedrum and flywheel should spin at the same speed. However, if a wheelwere to slow down, then the drum would do the same, leaving the flywheelspinning at a faster rate. This causes the valve to open, allowing a smallamount of brake fluid to bypass the master cylinder into a local reservoir,lowering the pressure on the cylinder and releasing the brakes. The use ofthe drum and flywheel meant the valve only opened when the wheel wasturning. In testing, a 30% improvement in braking performance was noted,because the pilots immediately applied full brakes instead of slowlyincreasing pressure in order to find the skid point. An additional benefitwas the elimination of burned or burst tires. In 1958, a Royal Enfield Super Meteor motorcycle was used bythe Road Research Laboratory to test the Maxaret anti-lock brake.[4] The experiments demonstrated that anti-lock brakes can be of greatvalue to motorcycles, for which skidding is involved in a high proportionof accidents. Stopping distances were reduced in most of the testscompared with locked wheel braking, particularly on slippery surfaces,in which the improvement could be as much as 30 percent. Enfieldstechnical director at the time, Tony Wilson-Jones, saw little future in thesystem, however, and it was not put into production by the company. A fully mechanical system saw limited automobile use in the 1960sin the Ferguson P99 racing car, the Jensen FF, and the experimental allwheel drive Ford Zodiac, but saw no further use; the system provedexpensive and unreliable in automobile use.Modern Systems: 1
  7. 7. ANTI-LOCK BRAKING SYSTEM 2011 Chrysler, together with the Bendix Corporation, introduced acomputerized, three-channel, four-sensor all-wheel ABS called "SureBrake" for its 1971 Imperial. It was available for several years thereafter,functioned as intended, and proved reliable. In 1971, GeneralMotors introduced the "Trackmaster" rear-wheel only ABS as an option ontheir Rear-wheel drive Cadillac models. In the same year, Nissan offeredan EAL (Electro Anti-lock System) as an option on the Nissan President,which became Japans first electronic ABS. ABS brakes on a BMW motorcycle In 1988, BMW introduced the first motorcycle with an electronic-hydraulic ABS: the BMW K100. Honda followed suit in 1992 with thelaunch of its first motorcycle ABS on the ST1100 Pan European. In2007, Suzuki launched its GSF1200SA (Bandit) with an ABS. In 2005,Harley-Davidson began offering ABS as an option for police bikes. In2008, ABS became a factory-installed option on all Harley-DavidsonTouring motorcycles and standard equipment on select models. 1
  8. 8. ANTI-LOCK BRAKING SYSTEM 2011 3. HOW IT IS WORKS The anti-lock brake controller is also known as the CAB (Controller Anti-lock Brake). A typical ABS includes a central electronic control unit (ECU),four wheel speed sensors, and at least two hydraulic valves within thebrake hydraulics. The ECU constantly monitors the rotational speed ofeach wheel; if it detects a wheel rotating significantly slower than theothers, a condition indicative of impending wheel lock, it actuates thevalves to reduce hydraulic pressure to the brake at the affected wheel,thus reducing the braking force on that wheel; the wheel then turns faster.Conversely, if the ECU detects a wheel turning significantly faster than theothers, brake hydraulic pressure to the wheel is increased so the brakingforce is reapplied, slowing down the wheel. This process is repeatedcontinuously and can be detected by the driver via brake pedal pulsation.Some anti-lock system can apply or release braking pressure 16 times persecond. The ECU is programmed to disregard differences in wheel rotativespeed below a critical threshold, because when the car is turning, the twowheels towards the centre of the curve turn slower than the outer two. Forthis same reason, a differential is used in virtually all roadgoing vehicles. If a fault develops in any part of the ABS, a warning light will usuallybe illuminated on the vehicle instrument panel, and the ABS will bedisabled until the fault is rectified. 1
  9. 9. ANTI-LOCK BRAKING SYSTEM 2011 The modern ABS applies individual brake pressure to all four wheelsthrough a control system of hub-mounted sensors and a dedicated micro-controller. ABS is offered or comes standard on most road vehiclesproduced today and is the foundation for ESC systems, which are rapidlyincreasing in popularity due to the vast reduction in price of vehicleelectronics over the years. Modern electronic stability control (ESC or ESP) systems are anevolution of the ABS concept. Here, a minimum of two additional sensorsare added to help the system work: these are a steering wheel anglesensor, and a gyroscopic sensor. The theory of operation is simple: whenthe gyroscopic sensor detects that the direction taken by the car does notcoincide with what the steering wheel sensor reports, the ESC softwarewill brake the necessary individual wheel(s) (up to three with the mostsophisticated systems), so that the vehicle goes the way the driverintends. The steering wheel sensor also helps in the operationof Cornering Brake Control (CBC), since this will tell the ABS that wheelson the inside of the curve should brake more than wheels on the outside,and by how much. The ABS equipment may also be used to implement a tractioncontrol system(TCS) on acceleration of the vehicle. If, when accelerating,the tire loses traction, the ABS controller can detect the situation and takesuitable action so that traction is regained. More sophisticated versions ofthis can also control throttle levels and brakes simultaneously. 1
  10. 10. ANTI-LOCK BRAKING SYSTEM 2011 4. COMPONENTSThere are four main components to an ABS: speed sensors, valves, apump, and a controller.1) Speed Sensor : These sensors use a magnet and a coil of wire to generate a signal.The rotation of the wheel or differential induces a magnetic field aroundthe sensor. The fluctuations of this magnetic field generate a voltage intothe sensor. A schematic of this system is shown in figure below. The ABScontroller interprets this signal. Since the voltage inducted on the sensor is a result of the rotatingwheel, this sensor can become inaccurate at slow speeds. The slowerrotation of the wheel can cause inaccurate fluctuations in the magneticfield and thus cause inaccurate readings to the controller.2)Valves : The valves within an ABS serve three distinct functions. The firstfunction of the valves is to open and allow the hydraulic fluid from thebrake pedal or the pump to reach the braking system. The second functionof the valves is to maintain the current pressure provided to the brakingsystem. This is accomplished by closing the valve to resist furtherpressure from the brake pedal. The third function of these valves is toreduce the amount of hydraulic pressure at the braking system. This isaccomplished by opening the valves to allow the hydraulic fluid to bereleased from the braking system. A picture of a standard ABS valve andpumping system is show in figure below. 1
  11. 11. ANTI-LOCK BRAKING SYSTEM 2011 The majority of problems with the valve system occur due to cloggedvalves. When a valve is clogged it is unable to open, close, or changeposition An inoperable valve will prevent the system from modulating thevalves and controlling pressure supplied to the brakes.3) Pumps : The pump in the ABS is used to restore the pressure to the hydraulicbrakes after valves have released it. A signal from the controller willrelease the valve at the detection of wheel slip. After a valve releasethe pressure supplied from the user, the pump is used to restore a desiredamount of pressure to the braking system. The controller will modulate thepumps status in order to provide the desire amount of pressure andreduce slipping. A picture of the pumping systemis shown in figure above. Similar to the valves, the major limitation or mode of failure is due toblockage within the pump. A blockage within the pump will prevent thepump from supplying the correct pressure to the pumping system.4) Controller : The controller is an ECU type unit in the car which receives informationfrom each individual wheel speed sensor, in turn if a wheel loses tractionthe signal is sent to the controller, the controller will then limit thebrakeforce (EBD) and activate the ABS modulator which actuates thebraking valves on and off. 1
  12. 12. ANTI-LOCK BRAKING SYSTEM 2011 5. USE OF ABS There are many different variations and control algorithms for use inan ABS. One of the simpler systems works as follows: 1. The controller monitors the speed sensors at all times. It islooking for decelerations in the wheel that are out of the ordinary. Rightbefore a wheel locks up, it will experience a rapid deceleration. If leftunchecked, the wheel would stop much more quickly than any car could. Itmight take a car five seconds to stop from 60 mph (96.6 km/h) under idealconditions, but a wheel that locks up could stop spinning in less than asecond. 2. The ABS controller knows that such a rapid deceleration isimpossible, so it reduces the pressure to that brake until it sees anacceleration, then it increases the pressure until it sees the decelerationagain. It can do this very quickly, before the tire can actually significantlychange speed. The result is that the tire slows down at the same rate asthe car, with the brakes keeping the tires very near the point at which theywill start to lock up. This gives the system maximum braking power. 3. When the ABS system is in operation the driver will feel a pulsingin the brake pedal; this comes from the rapid opening and closing of thevalves. This pulsing also tells the driver that the ABS has been triggered. 1
  13. 13. ANTI-LOCK BRAKING SYSTEM 2011Some ABS systems can cycle up to 16 times per second. 6. TYPES OF ABS Anti-lock braking systems use different schemes depending on thetype of brakes in use. We will refer to them by the number of channels --that is, how many valves that are individually controlled -- and the numberof speed sensors. There are mainly three types of ABS. 1) Four-channel, Four-sensor ABS This is the best scheme. There is a speed sensor on all four wheelsand a separate valve for all four wheels. With this setup, the controller 1
  14. 14. ANTI-LOCK BRAKING SYSTEM 2011monitors each wheel individually to make sure it is achieving maximumbraking force. 2) Three-channel, Three-sensor ABS This scheme, commonly found on pickup trucks with four-wheel ABS,has a speed sensor and a valve for each of the front wheels, with onevalve and one sensor for both rear wheels. The speed sensor for the rearwheels is located in the rear axle. This system provides individual control of the front wheels, so theycan both achieve maximum braking force. The rear wheels, however, aremonitored together; they both have to start to lock up before the ABS willactivate on the rear. With this system, it is possible that one of the rearwheels will lock during a stop, reducing brake effectiveness. 3) One-channel, One-sensor ABS This system is commonly found on pickup trucks with rear-wheelABS. It has one valve, which controls both rear wheels, and one speedsensor, located in the rear axle. This system operates the same as the rear end of a three-channelsystem. The rear wheels are monitored together and they both have to 1
  15. 15. ANTI-LOCK BRAKING SYSTEM 2011start to lock up before the ABS kicks in. In this system it is also possiblethat one of the rear wheels will lock, reducing brake effectiveness. This system is easy to identify. Usually there will be one brake linegoing through a T-fitting to both rear wheels. You can locate the speedsensor by looking for an electrical connection near the differential on therear-axle housing. 7. EFFECTIVENESSA 2003 Australian study by Monash University Accident Research Centrefound that ABS: • Reduced the risk of multiple vehicle crashes by 18 %. • Reduced the risk of run-off-road crashes by 35%.. 1
  16. 16. ANTI-LOCK BRAKING SYSTEM 2011 On high-traction surfaces such as bitumen, or concrete, many (thoughnot all) ABS-equipped cars are able to attain braking distances better (i.e.shorter) than those that would be easily possible without the benefit ofABS. In real world conditions even an alert, skilled driver without ABSwould find it difficult, even through the use of techniques like thresholdbraking, to match or improve on the performance of a typical driver with amodern ABS-equipped vehicle. ABS reduces chances of crashing, and/orthe severity of impact. The recommended technique for non-expert driversin an ABS-equipped car, in a typical full-braking emergency, is to press thebrake pedal as firmly as possible and, where appropriate, to steer aroundobstructions. In such situations, ABS will significantly reduce the chancesof a skid and subsequent loss of control. In gravel, sand and deep snow, ABS tends to increase brakingdistances. On these surfaces, locked wheels dig in and stop the vehiclemore quickly. ABS prevents this from occurring. Some ABS calibrationsreduce this problem by slowing the cycling time, thus letting the wheelsrepeatedly briefly lock and unlock. Some vehicle manufacturers provide an"off-road" button to turn ABS function off. The primary benefit of ABS onsuch surfaces is to increase the ability of the driver to maintain control ofthe car rather than go into a skid, though loss of control remains morelikely on soft surfaces like gravel or slippery surfaces like snow or ice. Ona very slippery surface such as sheet ice or gravel, it is possible to lockmultiple wheels at once, and this can defeat ABS (which relies oncomparing all four wheels, and detecting individual wheels skidding).Availability of ABS relieves most drivers from learning threshold braking. 1
  17. 17. ANTI-LOCK BRAKING SYSTEM 2011 A June 1999 National Highway Traffic Safety Administration (NHTSA)study found that ABS increased stopping distances on loose gravel by anaverage of 22 % according to the NHTSA, "ABS works with your regular braking system by automatically pumpingthem. In vehicles not equipped with ABS, the driver has to manually pumpthe brakes to prevent wheel lockup. In vehicles equipped with ABS, yourfoot should remain firmly planted on the brake pedal, while ABS pumpsthe brakes for you so you can concentrate on steering to safety." When activated, some earlier ABS systems caused the brake pedal topulse noticeably. As most drivers rarely or never brake hard enough tocause brake lock-up, and a significant number rarely bother to read thecars manual, this may not be discovered until an emergency. Whendrivers do encounter an emergency that causes them to brake hard, andthus encounter this pulsing for the first time, many are believed to reducepedal pressure, and thus lengthen braking distances, contributing to ahigher level of accidents than the superior emergency stopping capabilitiesof ABS would otherwise promise. Some manufacturers have thereforeimplemented a brake assist system that determines that the driver isattempting a "panic stop" (by detecting that the brake pedal wasdepressed very fast, unlike a normal stop where the pedal pressure wouldusually be gradually increased, Some systems additionally monitor therate at the accelerator was released) and the system automaticallyincreases braking force where not enough pressure is applied. Hard orpanic braking on bumpy surfaces, because of the bumps causing thespeed of the wheel(s) to become erratic may also trigger the ABS.Nevertheless, ABS significantly improves safety and control for drivers inmost on-road situations. 1
  18. 18. ANTI-LOCK BRAKING SYSTEM 2011 Anti-lock brakes are the subject of some experiments centredarround risk compensation theory, which asserts that drivers adapt to thesafety benefit of ABS by driving more aggressively. In a Munich study, halfa fleet of taxicabs was equipped with anti-lock brakes, while the other halfhad conventional brake systems. The crash rate was substantially thesame for both types of cab, and Wilde concludes this was due to drivers ofABS-equipped cabs taking more risks, assuming that ABS would take careof them, while the non-ABS drivers drove more carefully since ABS wouldnot be there to help in case of a dangerous situation. A similar study wascarried out in Oslo, with similar results. 8. ABS QUESTIONS??? • Should I pump the brake pedal when stopping in slippery conditions? 1
  19. 19. ANTI-LOCK BRAKING SYSTEM 2011 You absolutely should not pump the brake pedal in a car with ABS.Pumping the brakes is a technique that is sometimes used in slipperyconditions to allow the wheels to unlock so that the vehicle stayssomewhat straight during a stop. In a car with ABS the wheels shouldnever lock in the first place, so pumping the brakes will just make you takelonger to stop. In an emergency stop in a car with ABS, you should apply the brakepedal firmly and hold it while the ABS does all the work. You will feel apulsing in the pedal that may be quite violent, but this is normal so dont letoff the brake. • Do anti-lock brakes really work? Anti-lock brakes really do help you stop better. They prevent wheelsfrom locking up and provide the shortest stopping distance on slipperysurfaces. But do they really prevent accidents? This is the true measure ofthe effectiveness of ABS systems. The Insurance Institute for Highway Safety (IIHS) has conductedseveral studies trying to determine if cars equipped with ABS are involvedin more or fewer fatal accidents. It turns out that in a 1996 study, vehiclesequipped with ABS were overall no less likely to be involved in fatalaccidents than vehicles without. The study actually stated that althoughcars with ABS were less likely to be involved in accidents fatal to theoccupants of other cars, they are more likely to be involved in accidentsfatal to the occupants of the ABS car, especially single-vehicle accidents. There is much speculation about the reason for this. Some people thinkthat drivers of ABS-equipped cars use the ABS incorrectly, either by 1
  20. 20. ANTI-LOCK BRAKING SYSTEM 2011pumping the brakes or by releasing the brakes when they feel the systempulsing. Some people think that since ABS allows you to steer during apanic stop, more people run off the road and crash. Some more recent information may indicate that the accident rate forABS cars is improving, but there is still no evidence to show that ABSimproves overall safety. THE END 1