chap92 pps Automotive technology at University of Cambridge

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chap92 pps  Automotive technology at University of Cambridge

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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 92, the reader should be able to: • Prepare for ASE Suspension and Steering (A4) • • certification test content area “D” (Wheel Alignment Diagnosis, Adjustment, and Repair) Discuss which vehicle handling problems can and cannot be corrected by an alignment Define camber, toe, caster, SAI, included angle, scrub radius, turning radius, setback, and thrust 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 OBJECTIVES: After studying Chapter 92, the reader should be able to: • Explain how camber, caster, and toe affect the handling and tire wear of the vehicle 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: BJI • camber • camber roll • caster dog tracking • drift four-wheel alignment • included angle • KPI • lead MSI • pull • returnability • road crown SAI • scrub radius • setback • shimmy • steering dampener • steering offset thrust line • toe • toot • tramp wander 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 A wheel alignment is the adjustment of the suspension and steering to ensure proper vehicle handling with minimum tire wear When a vehicle is new, the alignment angles are set at the factory After many miles and/or months of driving, the alignment angles can change slightly By adjusting the suspension and steering components, proper alignment angles can be restored An alignment includes checking and adjusting, if necessary, both front and rear wheels 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 ALIGNMENT-RELATED PROBLEMS Most alignment diagnosis is symptom­based diagnosis. The  problem with the alignment is determined from symptoms such as  excessive tire wear or a pull to one side of the road.  Pull  Defined as a definite tug on the steering wheel or pull   toward the left or the right while driving straight on a level road.  Figure 92–1 A pull is usually defined as a tug on the steering wheel toward one side or the other Bent, damaged,   worn suspension  and/or steering  components or  tire problems can cause this 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 Road Crown Effects  Most roads are constructed with a slight  angle to permit water to drain from the road surface. On a two­lane  road, the center of the road is often higher than the berms, resulting  in a road crown.  Figure 92–2 The crown of the road refers to the angle or slope of the roadway needed to drain water off the pavement (Courtesy of Hunter Engineering Company) 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 Lead or Drift  A lead or drift is a mild pull that does not cause a  force on the steering wheel the driver must counteract. A lead or  drift is observed by momentarily removing your hands from the  steering wheel while driving on a straight, level road. If the vehicle  moves toward one side or the other, this is lead or drift On a four­lane expressway (freeway), the crown is often between  the two sets of lanes. Because of this slight angle to the road,  some vehicles may lead or drift away from the road crown CAUTION: When test­driving a vehicle for a lead or a drift, make sure  that the road is free of traffic and that your hands remain close to the  steering wheel. Your hands should be away from the steering wheel for  just a second or two—long enough to check for a lead or drift condition 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 Wander  A condition where constant steering wheel corrections  are necessary to maintain a straight­ahead direction on a straight,  level road is called wander.  Worn suspension and/or steering components are the likely cause  of this condition. Incorrect or unequal alignment angles such as  caster and toe, as well as defective tire(s), can cause this condition Figure 92–3 Wander is an unstable condition requiring constant driver corrections Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Continued ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Stiff Steering or Slow Return to Center  Hard­to­steer problems  are commonly caused by leaks, either low tire pressure (due to the  leak of air) and/or lack of proper power steering (due to the leak  of power steering fluid). Other causes include excessive positive  caster on the front wheels or binding steering linkage Tramp or Shimmy Vibration Tramp  Vertical­type (up­and­ down) vibration usually caused by out­of­balance or defective  tires or wheels. Shimmy is a back­and­forth vibration that can be  caused by an out­of­balance tire or defective wheel or by an  alignment problem NOTE: Wheel alignment will not correct a tramp­type vibration 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 TURNING RADIUS (TOE-OUT ON TURNS) When a vehicle turns a corner, the inside wheel has to turn at a  sharper angle than the outside wheel because the inside wheel has  a shorter distance to travel.  Turning radius, a nonadjustable  angle, is called toe­out on turns,  TOT or TOOT.  It is determined by angle of the  steering knuckle arms, and  Figure 92–44 To provide handling, the inside should be measured to check wheel has to turn at a greater turning radius than the outside wheel if the steering arms are bent or damaged.   Tire squeal noise during normal Symptoms of out­of­spec  cornering, even at low speeds turning angle include: Scuffed tire wear 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 The proper angle of the steering arms is where imaginary lines drawn  from the steering arms should intersect exactly at the center of the rear  axle. This angle is called the Ackerman Effect (named for its promoter,  English publisher, Rudolph Ackerman, ca. 1898) Figure 92–45 The proper toe-out on turns is achieved by angling the steering arms 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 SETBACK Setback is the angle formed by a line drawn perpendicular (at 90  degrees) to the front axles.  (a) Figure 92–46 (a) Positive setback (b) Negative setback (Courtesy of Hunter Engineering Company) (b) 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 Positive setback means the right front wheel is set back farther  than the left; negative setback means the left front wheel is set  back farther than the right Setback can be measured with a four­wheel alignment machine or  can be determined by measuring the wheel base on both sides of  the vehicle Setback is a nonadjustable measurement, even though it may be corrected.  NOTE: The wheel base of any vehicle is the distance between the center of the front wheel and the center of the rear wheel on the same side. The wheel base should be within 1/8 in. (3 mm) side­to­side 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 The causes of setback include the following: Cradle placement not correct on a front­wheel­drive vehicle.  This can be caused by incorrectly installing the cradle after a  transmission, clutch, or engine replacement or service. See  Figure 92–47 An accident that affected the frame or cradle of the vehicle  and was unnoticed or not repaired Figure 92–47 Cradle placement affects setback 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 THRUST ANGLE If both rear wheels have zero toe, then the thrust angle is the same  as the geometric centerline of the vehicle. The total of the rear toe  setting determines the thrust line, or the direction the rear wheels  are pointed Thrust angle is the angle of the rear wheels as determined by the total rear toe.  On vehicles with an independent rear suspension, if both wheels  do not have equal toe, the vehicle will pull in the direction of the  side with the most toe­in See Figure 92­48 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 Figure 92–48 (a) Zero thrust angle (b) Thrust line to the right (c) Thrust line to the left (Courtesy of Hunter Engineering Company) (a) (b) (c) 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 TRACKING The rear wheels should track directly behind the front wheels. If  the vehicle has been involved in an accident, it is possible that  the frame or rear axle mounting could cause dog tracking To check the frame for possible damage, two diagonal  measurements of the frame and/or body are required. The  diagonal measurements from known points at the front and the  rear should be within 1/8 in. (3 mm) of each other See Figure 92–49 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 Figure 92–49 (a) Proper tracking (b) Front wheels steering toward thrust line (a) (b) 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 FOUR WHEEL ALIGNMENT Four­wheel alignment refers to the checking and/or adjustment  of all four wheels. Four­wheel alignment is important for proper  handling and tire wear, to check the camber and the toe of the  rear wheels of front­wheel­drive vehicles Some rear­wheel­drive vehicles equipped with independent rear  suspension can be adjusted for camber and toe. Rear­wheel  caster cannot be measured or adjusted because to measure caster,  the wheels must be turned from straight ahead 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 Since rear wheels are securely attached, a caster sweep (turning  the wheels to take a caster reading) is not possible. While rear  camber can cause tire wear problems, by far the greatest tire wear  occurs due to toe settings Unequal toe in the rear can cause the vehicle to pull or lead. The  rear camber and toe are always adjusted first before adjusting the  front caster, camber, and toe. This procedure ensures that the  thrust line and centerline of the vehicle are the same 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 The need for a wheel alignment results from wear or damage  to suspension and steering components Low or unequal tire pressures can often cause symptoms such  as wander, pull, and excessive tire wear Camber is both a pulling angle (if not equal side­to­side) as  well as a tire wearing angle (if not set to specifications) Incorrect camber can cause tire wear and pulling if camber is  not within 1/2 degree from one side to the other 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.) Toe is the most important alignment angle because toe is  usually the first requiring correction. When incorrect, toe  causes severe tire wear Incorrect toe causes excessive tire wear and creates instability  if not within specifications Caster is the basic stability angle, yet it does not cause tire  wear (directly) if not correct or equal side­to­side SAI and included angle (SAI and camber added together) are  important diagnostic tools 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.) If the toe­out on turns (TOOT) reading is not within  specifications, a bent steering spindle (steering knuckle) is the  most likely cause 10 A four­wheel alignment includes aligning all four wheels of  the vehicle; a thrust line alignment sets the front toe equal to  the thrust line (total rear toe) of the rear wheels 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 ... Feather-edge wear pattern caused by excessive toe-in or toe-out Figure 92–29 Excessive toe-in and the type of wear that can occur to the outside of the left front tire Continued Automotive Technology: ... degree? ?of? ?the SAI? ?of? ?the other  side? ?of? ?the vehicle Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc... Figure 92–17 As the spindle rotates, it lifts the weight of the vehicle due to the angle of the steering axis (Courtesy of Hunter Engineering Company) Continued Automotive Technology: Principles, Diagnosis,

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Mục lục

  • PowerPoint Presentation

  • OBJECTIVES:

  • Slide 3

  • KEY TERMS:

  • Slide 5

  • ALIGNMENT-RELATED PROBLEMS

  • Figure 92–2 The crown of the road refers to the angle or slope of the roadway needed to drain water off the pavement. (Courtesy of Hunter Engineering Company)

  • Slide 8

  • Figure 92–3 Wander is an unstable condition requiring constant driver corrections.

  • Slide 10

  • CAMBER AND CASTER

  • Figure 92–4 Positive camber. The solid vertical line represents true vertical; the dotted line the angle of the tire.

  • Slide 13

  • Figure 92–7 Excessive positive camber and how the front tires would wear due to the excessive camber.

  • Figure 92–8 Excessive negative camber and how the front tires would wear due to the excessive camber.

  • Figure 92–9 Positive camber tilts the tire and forms a cone shape that causes the wheel to roll away or pull outward toward the point of the cone.

  • Figure 92–10 Negative camber creates a pulling force toward the center of the vehicle.

  • Slide 18

  • Figure 92–12 Positive camber applies the vehicle weight toward the larger inner wheel bearing. This is desirable because the larger inner bearing is designed to carry more vehicle weight than the outer bearing.

  • Slide 20

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