chap89 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 89, the reader should be able to: • Prepare for ASE Suspension and Steering (A4) • • • certification test content area “A” (Steering System Diagnosis and Repair) Discuss steering columns and intermediate shafts Explain how a recirculating ball-nut and worm gear steering gear system works Describe how a rack-and-pinion steering gear works 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: collapsible column • flexible coupling • gear lash inflator module • kickback • lock plate • overcenter adjustment pinion torque • pitman arm • pitman shaft • preload rack and pinion • rack support sector gear • sector shaft • steering shaft • stub shaft telescoping steering column • tilt steering column universal joint • variable ratio • worm gear 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 When the driver turns the steering wheel in a circle, or in a rotary motion, the steering linkage moves side to side, or in a lateral motion, to steer the 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 STEERING WHEELS The steering wheel, which consists of a rigid rim and a number of spokes connecting the rim to a center hub, attaches to the top of the steering shaft at its center Most steering wheel hubs have internal splines that fit over  external splines on the steering shaft. A bolt or nut at the center of the hub secures the wheel to the shaft.  The steering wheel may also contain controls for the cruise  control and audio controls, as well as the driver’s airbag 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 Horn Operation The horn circuit is in a series circuit in which  current has one path that it can follow when the circuit is complete A normally open switch in an electrical circuit is inside the horn  button. When the driver pushes the horn button, the contacts on the  switch close, allowing electrical current through the circuit to  operate the horn A relay circuit is a more common method of wiring the horn. In a  relay, closing a switch in a low­current series circuit triggers the  high­current circuit that powers the horn See Figure 89–1.  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 Figure 89–1 The horn button is a normally open (NO) switch When the button is depressed, the switch closes, which allows electrical current to flow from the battery to sound the horn Most horn circuits use a relay to conduct the horn current 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 Airbags  An airbag is made of nylon cloth covered with neoprene,  folded and stored in the center of the steering wheel. In a front­end  collision, the airbag inflates to provide a cushion between the  driver and the steering wheel and dashboard.  Figure 89–2 The airbag inflates at the same time the driver moves toward the steering wheel during a front-end collision and supplements the protection of the safety belt The part of the steering  wheel where the airbag  is stored is called the  inflator module.  Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman The module also contains  an igniter, a canister of  flammable gas, and  sodium azide pellets.  ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The sodium azide pellets burn quickly, and rapidly release nitrogen  gas, which fills the airbag. As it inflates, the airbag tears open the  module cover and spreads out across the steering wheel,  windshield, and dashboard.  The entire process, from sensor reaction to full airbag deployment,  takes 30 to 65 milliseconds. Within one second of inflating, the bag  deflates partially. Once deployed, an airbag cannot be reused Electrical current is provided to the airbag through the spiral cable,  which is also known as a coil. The spiral cable is a tightly coiled  metal strip that connects to the airbag module with two wire leads  and allows steering wheel rotation while maintaining electrical  continuity See Figure 89–3 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 CAUTION: Whenever working on the steering column, consult service  information for the recommended airbag disabling procedure The module fits in front of the nut that secures the steering wheel to  the steering shaft. Bolts at the back of the steering wheel fasten the  airbag module to the steering wheel Figure 89–3 The airbag module attaches to the steering wheel and is removed as an assembly to service the steering wheel and column Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 10 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The steering gear input shaft is splined to the steering shaft U­joint.  At the end of the steering gear input shaft, which extends into the  rack housing, is the pinion gear.  Two ball bearings reduce friction between the shaft and the  steering gear housing. The upper bearing is a press­fit on the input  shaft, and the lower bearing installs inside the housing at the  bottom of the pinion gear.  A cover, which fits around the shaft and threads into the housing,  seats on top of the upper ball bearing to preload it and close the top  of the steering gear housing An oil seal between the cover and the input shaft keeps lubricant  from leaking out of the housing. A lock nut holds the top cover in  position. See Figure 89–30.  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 89–30 A typical manual rack-and-pinion steering gear used in a small front-wheel-drive vehicle Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 53 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The teeth of the pinion gear mesh with the teeth of the rack. The  teeth are at one end of the rack and the pinion is offset at one side  of the housing The rack is encased in the long, tubular steering gear housing with  a mounting flange on the pinion end. Rubber bushings fit into the  mounting flange bolt holes to absorb vibration and isolate the  assembly from the frame A spring­loaded rack support and related hardware install through  a hole at the back of the steering gear housing to position the rack The face of the rack support curves to match the back of the rack,  which rests on it and slides back and forth across it.  See Figure 89–31 54 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 89–31 The spring-loaded rack support positions the rack to keep it from rubbing against the housing and establishes the pinion torque A spring behind the rack  support cushions it from  vibration and shocks.  The rack support  provides a sliding surface  to reduce friction at the  pinion end of the rack The rack rides in a  bushing pressed into the  steering gear housing at  the opposite end to  reduce friction 55 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 To adjust the rack­and­pinion  gear preload, follow these steps: Figure 89–32 To adjust the rack-and-pinion gear preload, loosen the retaining nut and tighten the adjuster nut until it bottoms Then loosen 60 degrees (one “flat” of the six-sided retainer) Tighten retaining nut Loosen adjuster plug lock nut Turn adjuster plug  clockwise until the  adjuster plug bottoms in the gear assembly Turn the adjuster plug  back 50 to 70 degrees  (approximately one flat) 56 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 Most rack­and­pinion units use a small metal tube running along  the outside of the housing to connect the two boots and transfer air  from one to the other.  Figure 89–33 A small air tube is used to transfer air between the boots as they extend and compress during turns If there were no means for air displacement between the boots,  they might collapse as they expanded or explode as they  Continued compressed 57 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 Internal threads on each end of the rack allow attachment of the  externally threaded tie rods A rubber boot at each side of the steering gear housing covers the  end of the rack and the inner tie rod end to prevent dirt, water,  and other contaminants from entering the assembly Band clamps fasten the ends of the boots to the housing and tie rods. The tie rods move back and forth with the rack and  connect it to the wheels through the steering linkage The housing bolts to either a flange on the firewall or to the  subframe or engine cradle See Figure 89–34.  58 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 89–34 This manual rack-and-pinion steering gear mounts to the bulkhead (firewall), whereas others mount to the engine cradle or frame of the vehicle The mounting points have rubber cushions  to isolate the steering gear from shock and  vibration, called kickback, inevitable with  a rack­and­pinion steering gear Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 59 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 RACK AND PINION ADJUSTMENTS Figure 89–35 Pinion torque is a turning torque force measured in inch-pounds or Newton -meters Tightening the rack support against the rack increases the pinion torque Some rack­and­pinion steering  gears can be adjusted. Pinion  torque is a measure turning force  is needed at the input shaft for the  pinion to overcome the rack  resistance and move it.  The measurement gives an  indication of how closely  meshed the pinion teeth and the rack teeth are.  Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 60 Continued ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Like gear mesh preload in a standard steering gear, pinion torque  indicates steering system responsiveness. The adjustment method is  to thread the rack support cover farther into the steering gear  housing to reduce gear lash, or thread it out to increase gear lash Manufacturers specify an acceptable range of pinion torque in inch­ pounds or Newton­meters Because the middle teeth on the rack wear before the teeth at either  end, pinion torque should be checked across the whole stroke of the  rack Reducing gear lash to a very close tolerance in the middle may  cause binding as the pinion travels toward the end of the rack 61 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 Pinion bearing preload in a rack­ and­pinion steering gear is the  same as worm bearing preload in a standard steering gear.  Figure 89–36 Pinion bearing preload is a measurement of the turning force required to overcome the resistance of the pinion shaft bearings It is a measure of force required  to turn the steering gear input  shaft against the force, or  preload, the bearings apply to the pinion gear and shaft.  Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 62 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 To provide adjustable pinion bearing preload, there may be a  threaded adjustment mechanism or selectively sized shims that  install behind a shim cover To set pinion bearing preload, the rack may need to be removed or  loosened to prevent false readings caused by the resistance of the  gears Pinion bearing preload, when adjustable, must be set before  pinion torque is measured and adjusted Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 63 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY Most horn circuits use a relay. The horn button or contact on  the steering wheel completes the control circuit of the relay,  which then completes the power circuit to the horn(s) The driver’s side airbag uses a clockspring spiral cable in the  steering column electronically connecting the airbag inflator  module The steering column, which connects the steering wheel to the  steering gear, includes the steering shaft universal joint and  flexible coupling 64 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.) Conventional steering gears consist of an input gear and output  gear, also called the sector gear Steering gear ratio is the number of degrees the steering wheel  is rotated compared to the number of degrees the front wheels  are rotated. Most steering gears provide a ratio of between 14:1  and 22:1 A recirculating­ball­type steering gear is the most commonly  used conventional steering gear A rack­and­pinion steering gear ties the two tie rods together in  a straight line Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman 65 ©©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 66 ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ... is off The ignition lock cylinder, which is under the lock plate, moves a  bellcrank that in turn operates a spring and lever assembly linked to the ignition switch actuating rod Automotive Technology: ... 89–18 Steering gear ratio is the ratio between the number of degrees the steering wheel is rotated to the number of degrees the front wheel turns 32 Continued Automotive Technology: Principles,... The steering wheel, which consists? ?of? ?a rigid rim and a number of? ?spokes connecting the rim to a center hub, attaches to the top? ?of? ?the steering shaft? ?at? ?its center Most steering wheel hubs have internal splines that fit over