chap85 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 85, the reader should be able to: • Prepare for ASE Suspension and Steering (A4) • • certification test content area “B” (Suspension System Diagnosis and Repair) List various types of suspensions and their component parts Explain how coil, leaf, and torsion bar springs work 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 85, the reader should be able to: • • Describe how suspension components function to allow wheel movement up and down and provide for turning Describe how shock absorbers control spring forces 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: air spring • anti-dive • anti-squat ball joints • bulkhead • bump stop center bolt • coil springs • composite leaf spring • control arms • cradle full frame • gVW • hooke’s law independent suspension • insulators kingpin • ladder frame • lateral links leaf springs • load-carrying ball joint 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: mono leaf • non-load-carrying ball joint perimeter frame • platforms • rebound clips shackles • shock absorbers • space frame • spring pocket • spring rate • springs • sprung weight • stabilizer bars • steering knuckles • stress riser • strut rod • struts • stubtype frame torsion bar unit-body • unsprung weight wheel rate 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 Street-driven cars and trucks use a suspension system to keep the tires on the road and to provide acceptable riding comfort A vehicle with a solid suspension, or no suspension, would bounce off the ground when the tires hit a bump If the tires are off the ground, even for a fraction of a second, loss of control is possible 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 FRAME CONSTRUCTION Frame construction consists of channel­shaped steel beams  welded and/or fastened together. The frame supports all the  “running gear”, including the engine, transmission, rear axle  assembly (if rear­wheel drive), and all suspension components Referred to as full frame, it is so complete that most vehicles can  usually be driven without the body. Most trucks and larger rear­ wheel­drive cars use a full frame Ladder Frame  A common name for a type of perimeter frame  where the transverse (lateral) connecting members are straight  across is ladder frame. When viewed with the body removed, the  frame resembles a ladder. Most pickup trucks are constructed with  a ladder­type frame. See Figures 85–1 and 85–2 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 85–1 A typical truck frame is an excellent example of a ladder-type frame The two side = members are connected by a crossmember 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 Perimeter Frame A perimeter frame consists  of welded or riveted frame  members around the entire  perimeter of the body.  Figure 85–2 Rubber cushions used in body or frame construction isolate noise and vibration from traveling to the passenger compartment This means frame members  provide support underneath  the sides as well as for the  suspension and suspension  components 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 Stub­Type Frames A stub­type frame is a partial  frame often used on unit­body  vehicles to support power train  and suspension components.  (a) It is also called a cradle on  many front­wheel­drive  vehicles.  Figure 85–3 (a) Separate body and frame construction; (b) unitized construction: the small frame members are for support of the engine and suspension components Many vehicles attach the suspension components directly to the reinforced sections of the body and not require the rear frame section (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 Air pressure is used to inflate the bag, which raises the installed  height of the shock. As the shock increases in height, the rear of  the vehicle is raised. Typical maximum air pressure in air shocks  ranges from 90 to 150 PSI (620 to 1,030 kPa) As the air pressure increases in the air­inflatable reservoir of the  shock, the stiffness of the suspension increases. This additional  stiffness is due to the shock taking weight from the spring, and  therefore the air in the air shock becomes an air spring.  It is important that the load capacity of the vehicle not be  exceeded or serious damage can occur to the vehicle’s  springs, axles, bearings, and shock support mounts 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 Air Springs  Some electronically controlled suspension systems  use air springs. A basic air spring consists of a rubber air  chamber, generally closed at the bottom by a piston fitted into a  control arm, or by a strut shock absorber Electronically controlled suspension systems that use air springs as the only springs are available on some Hummer, and many Ford, Mercury and Lincoln vehicles See Figures 85–52   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 85–52 (a) The front suspension of a Lincoln with an air-spring suspension (b) Always check in the time for the cutoff switch for a refile equipped with an air suspension before hoisting or touring the vehicle 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 85–53 Some air springs are auxiliary units to the coil spring and are used to control ride height while the coil spring is the weight-bearing unit Some air springs are in effect auxiliary  springs inside a coil­spring strut.  In these designs, the coil spring  supports the weight of the vehicle,  while the air spring raises or lowers  the body to adjust ride height  according to load 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 Coil­Over Shocks  A coil­over shock absorber uses an external  coil spring to boost the performance of the basic shock absorber.  The spring usually extends from the upper  shock mount to a seat on the lower portion  of the cylinder.  The spring rate added to the hydraulic  resistance makes the shock stiffer Figure 85–54 A coil-over shock is a standard hydraulic shock absorber with a coil spring wrapped around it to increase stiffness and/or take some of the carrying weight off of the springs 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 STRUTS A strut is a sturdy shock absorber that is also a structural  component of the suspension A strut is a suspension link as well as a shock absorber. The casing  of a strut must be strong and rigid to function as a suspension link The shock absorber assembles inside the casing of a strut, and may be either a removable cartridge or an integral part of the strut 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 85–55 A strut is a structural part of the suspension and includes the spring and shock absorber in one assembly MacPherson Struts The MacPherson strut, named after Earle S. MacPherson, who  developed the suspension design in the late 1940s and patented it in 1953, is the most commonly used type.  A MacPherson strut includes the  suspension spring—a coil spring that surrounds the strut casing— so that it transfers weight of the body to the wheel.  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 A MacPherson strut typically incorporates an upper and a lower  spring seat, a shock absorber mount and dust cap, a dust cover for  the piston rod, and a bump stop. The upper mount secures the  upper spring seat to the strut tower.  A rubber bushing at the top of the strut absorbs vibrations. A  bearing on a front­wheel strut allows it to rotate on the vertical  steering axis without rubbing against the strut tower when the  steering knuckle turns The lower spring seat is attached to the strut casing 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 Modified Struts  Unlike a MacPherson unit, a modified strut does  not include a spring as part of the assembly and is used in the front  on some vehicles and on the rear of others. Most modified strut rear  suspensions use coil springs mounted on the lower control arm Figure 85–56 A modified strut used on the rear suspension; it is part of the structural part of the assembly 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 BUMP STOPS All suspension systems have a limit of travel. If the vehicle hits a  large bump in the road, the wheels are forced upward toward the  vehicle with tremendous force. This force is absorbed by the  springs of the suspension system If the bump is large enough, the suspension is compressed to its  mechanical limit. Instead of allowing the metal components of the suspension to hit the frame or body of the vehicle, a rubber or foam bumper is used to absorb and isolate the suspension from the frame or body See Figure 85–57 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 These bumpers are called bump stops, suspension bumpers, strike­ out bumpers, or jounce bumpers.  Figure 85–57 Suspension bumpers are used on all suspension systems to prevent metal-to- metal contact between the suspension and the frame or body of the vehicle when the suspension “bottoms out” over large bumps or dips in the road Bumpers are made from rubber  or microcellular urethane, a  high­strength material with good  resistance to wear and tear as  well as good chemical resistance  to most fluids.  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 Damaged suspension­limiting bump stops can be caused by: Sagging springs that result in lower­than­normal ride  (trim) height Worn or defective shock absorbers Most suspensions also use a rubber or foam stop to limit the  downward travel of the suspension during rebound.  The rebound stop also prevents metal­to­metal contact of the  suspension on the frame when the vehicle is on a body­ contact­type hoist and the wheels are allowed to hang or droop  down.  Some stops are built into the shock absorber or strut 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 lighter the wheel/tire combination, the lower the unsprung  weight and the better the ride and handling of the vehicle All springs—including the coil, leaf, and torsion bar types— share Hooke’s Law, which states that the force exerted by the  spring is directly proportional to the amount the spring is  deflected All springs are similar to torsion bars. As the torsion bar  becomes longer or smaller in diameter, it becomes easier to  twist. If a coil spring is cut, the remaining spring is shorter, yet  stiffer 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.) Ball joints attach to control arms and allow the front wheels to  move up and down, as well as turn Suspension designs include a straight or solid­axle, two­ control arm­type called an SLA or a MacPherson strut All shock absorbers dampen the motion of the suspension to  control ride and handling 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