chap81 pps Automotive technology at University of Cambridge

start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 81, the reader should be able to: • • • Prepare for ASE Brakes (A5) certification test content area “F” (Antilock Brake System Diagnosis and Repair) Explain the reason for ABS Describe the purpose and function of the ABS components, such as wheel speed sensors, electrohydraulic unit, and electronic controller Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 81, the reader should be able to: • • Discuss how the ABS components control wheel slippage Explain how the ABS components control acceleration traction control Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: accumulator • active sensor • air gap • antilock braking systems (ABS) channel • control module Electronic Stability Control (ESC) • flash codes integral ABS • isolation solenoid • nonintegral ABS pressure decay stage • pressure dump stage • pressure holding stage • pressure increase stage • pressure reduction stage • pressure release stage Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: Rear Antilock Braking System (RABS) • Rear Wheel AntiLock (RWAL) • release solenoid select low principle • solenoid valves tire slip • tone ring • traction • traction control wheel speed sensors (WSS) Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ABS CHARACTERISTICS Antilock braking systems (ABS) help prevent the wheels from  locking during sudden braking, especially on slippery surfaces.  They eliminate lockup and minimize the danger of skidding,  allowing the vehicle to stop in a straight line.  ABS can optimize braking when road conditions are less than  ideal, as when making a sudden panic stop or when braking on a  wet or slick road ABS does this by monitoring the relative speed of the wheels to  one another. It uses this information to modulate brake pressure as  needed to control slippage and maintain traction when the brakes  are applied Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ABS and Tire Traction  Preventing brake lockup is important  because of the adverse effect a locked wheel has on tire traction Figure 81–1 Maximum braking traction occurs when tire slip is between 10% and 20% A rotating tire has 0% slip and a locked-up wheel has 100% slip The brakes slow rotation of the wheels;  friction between tire and road stops the  vehicle and allows it to be steered.  If tire traction is reduced, stopping  distances increase, and directional stability of the vehicle suffers A free­rolling wheel has nearly zero tire slip, while a locked wheel has 100% tire slip See Figure 81–1 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Tire Slip and Braking Distance On dry or wet pavement,  maximum braking traction occurs when tire slip is held between  approximately 15% and 30%.  On snow­ or ice­covered pavement, the optimum slip range is 20%  to 50%. In each case, if tire slip increases beyond these levels, the  amount of traction decreases.  Figure 81–2 Traction is determined by pavement conditions and tire slip Shortest stopping distances are obtained when the brakes are applied with just enough  force to keep the tire slip in the range where traction is  greatest Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Tire Slip and Vehicle Stability  A tire’s contact patch with the  road can provide only a certain amount of traction. When a  vehicle is stopped in a straight line, nearly all available traction  can be used to provide braking force. If a vehicle has to stop and  turn at the same time, the available traction must be divided to  provide both cornering (lateral) and braking force No tire can provide full cornering and full braking power at the  same time. When a brake is locked and the tire has 100% slip, all  of available traction is used for braking; none is left for steering A skidding tire follows the path of least resistance. If the rear  brakes lock, the back end of the vehicle will swing around toward  the front. If the front brakes lock, steering control will be lost and  the vehicle will slide forward in a straight line Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ABS and Base Brakes  An antilock braking system is an “add­on”  to the existing base brake system, and only comes into play when  traction conditions are marginal or during stops when the tires lose  traction and slip excessively. The rest of the time ABS has no  effect on normal driving, handling, or braking A vehicle with ABS brakes uses the same brake linings, calipers,  wheel cylinders, and other system components as a vehicle without  ABS brakes. The only exception being the master cylinder All ABS are also designed to be as “fail­safe” as possible. Should a  failure occur that affects the operation of the ABS, the system will  deactivate itself and the vehicle will revert to normal braking ABS failure will not prevent the vehicle from stopping Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Traction Active Lamp  On most applications, a “TRAC CNTL”  indicator light or “TRACTION CONTROL ACTIVE” message  flashes when the system is engaging traction control This helps alert the driver that the wheels are losing traction. In  most applications, the message does not mean there is anything  wrong with the system—unless the ABS warning lamp also comes  on, or the traction control light remains on continuously Traction Deactivation Switch  Vehicles with traction control have  a dash­mounted switch that allows the driver to deactivate the  system when desired An indicator light shows when the system is on or off, and may  also signal the driver when the traction control system is actively  engaged during acceleration Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ELECTRONIC CONTROLLER OPERATION The electronic controller is the computer in the system that  controls all parts of ABS operation, including the following: A Self­Test  The controller runs a self­test of all its  components every time the ignition is turned on The Wheel Hydraulic Controls  The controller looks at rate  of wheel deceleration and compares it with normal stopping  rates using an internal computer program that is based on  vehicle weight, tire size, and so on. If a wheel is slowing too  fast, the controller activates hydraulic pressure controls NOTE: Since an antilock braking system is a safety­related system, if it malfunctions, people can be injured. This is one reason why the system does a complete “system check” every time the ignition is cycled Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Is Chirp Normal With ABS? Some owners of vehicles complain that their ABS is not working correctly because their tires chirp and occasionally experience tire lockup during hard braking, especially at low speed These conditions are perfectly normal because, for maximum braking, between 12% and 20% of slip means that the tire will slip or skid slightly during an ABS stop It is also normal for vehicles with ABS to have the tires lock and skid slightly when the speed is below mph (8 km/h) This occurs because the wheel speed sensors cannot generate usable speed signals for the electronic controller This low-speed wheel lockup seldom creates a problem Before attempting to troubleshoot or diagnose an ABS problem, be sure that the problem is not just normal operation of the system NOTE: When the brakes are applied during these corrections, a thumping  sound and vibration may be sensed Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Stop On a Dime? Vehicles that are equipped with ABS help the driver avoid skidding and losing total control during braking This is especially true for road surfaces that are slippery However, vehicles equipped with ABS must still have traction between the tire and the road to stop This author had an experience with ABS on a snow-covered road I applied the brakes while approaching a stop sign and the brake pedal started to pulsate, the electrohydraulic unit started to run, and the vehicle continued straight through the intersection! Luckily, no other vehicles were around The vehicle did not stop for a long distance through the intersection, but it did stop straight— avoiding skidding Because of ice under the snow, the vehicle did not have traction between the tires and the road A common ABS complaint is that it didn’t stop the vehicle, while it did stop the skidding or traveling out of control, though short stops are not always possible The tech should explain the purpose and function of ABS before attempting to repair a problem that may be normal on the vehicle being inspected The primary purpose of ABS is vehicle control—not short stopping distance! Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ELECTRONIC STABILITY CONTROL Electronic Stability Control (ESC) uses the steering wheel position  sensor and G­force and/or yaw sensor to determine if a vehicle is not  under control The ESC system, also called Electronic Stability Program (ESP), applies  individual wheel brakes to control the vehicle. The following occurs if  the vehicle is oversteering or understeering: Oversteering  The rear of the vehicle breaks loose resulting in  the vehicle spinning out of control. This condition is also called  loose. If detected during a left turn, the ESC system would apply  right front brake to bring the vehicle under control Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Understeering  In this condition, the front of the vehicle continues  straight ahead when turning, a condition that is also called plowing  or tight. If detected during a right turn, the ESC would apply the  right rear wheel brake to bring the vehicle back under control.  Figure 81–25 The electronic stability control (ESC) system applies individual wheel brakes to keep the vehicle under control of the driver Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 STABILITY CONTROL SYSTEMS BY MFG The purpose of the vehicle stability enhancement system along  with the antilock brake system (ABS) is to provide vehicle stability  enhancement during oversteer or understeer conditions. Stability  control systems are offered under the following names: Acura: Vehicle Stability Assist (VSA) Audi: Electronic Stabilization Program (ESP) BMW: Dyanmic Stability Control (DSC), including Dynamic  Traction Control Chrysler: Electric Stability Program (ESP) Dodge: Electronic Stability Program (ESP) Ferrari: Controllo Stabilita (CST) Ford: AdvanceTrac and Interactive Vehicle Dynamics (IVD) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 General Motors: StabiliTrak (Except Corvette––Active  Handling) Hyundai: Electronic Stability Program (ESP) Honda: Electronic Stability Control (ESC), Vehicle Stability  Assist (VSA), and Electronic Stability Program (ESP) Infiniti: Vehicle Dynamic Control (VDC) Jaguar: Dynamic Stability Control (DSC) Jeep: Electronic Stability Program (ESP) Kia: Electronic Stability Program (ESP) Land Rover: Dynamic Stability Control (DSC) Lexus: Vehicle Dynamics Integrated Management (VDIM)  with Vehicle Stability Control (VSC) and Traction Control  (TRAC)  systems Lincoln: Advance Trak Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Maserati: Maserati Stability Program (MSP) Mazda: Dynamic Stability Control Mercedes: Electronic Stability Program (ESP) Mercury: Advance Trak Mini Cooper: Dynamic Stability Control Mitsubishi: Active Skid and Traction Control MULTIMODE Nissan: Vehicle Dynamic Control (VDC) Porsche: Porche Stability Management (PSM) Rover: Dynamic Stability Control (DSC) Saab: Electronic Stability Program (ESP) Saturn: Stabili Trak Subaru: Vehicle Dynamics Control Systems (VDCS) Suzuki: Electronic Stability Program (ESP) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Toyota: Vehicle Dynamics Integrated Management (VDIM)  with Vehicle Stability Control (VSC) Volvo: Dynamic Stability and Traction Control (DSTC) VW: Electronic Stability Program (ESP) See the complete list on Page 1000 & 1001  of your textbook.  Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Wheel Speed Sensor Step-By-Step Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Wheel Speed Sensor Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY ABS diagnosis starts with checking the status of both the red  brake warning lamp and the amber ABS warning lamp The second step in diagnosis of an ABS problem is to perform  a thorough visual inspection The third step in diagnosis of an ABS problem is to test­drive  the vehicle and verify the fault Always consult the factory service information for the specific  vehicle being serviced for the proper procedure to use to  retrieve and clear diagnostic trouble codes (DTCs) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) A breakout box is used with a digital multimeter to diagnose  electrical ABS components Hydraulic service on most integral ABS units requires that the  brake pedal be depressed as many as 40 times with the  ignition key “off” to depressurize the hydraulic system Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458