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The steering system converts the rotation of the steering wheel into a swivelling movement of the road wheels in such a way that the steeringwheel rim turns a long way to move the road wheels a short way. The system allows a driver to use only light forces to steer a heavy car. The rim of a 15 in. The steering effort passes to the wheels through a system of pivoted joints. These are designed to allow the wheels to move up and down with the suspension without changing the steering angle.
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 low-current series circuit triggers the high-current 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 front-end 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 The module also contains an igniter, a canister of flammable gas, and sodium azide pellets 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 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 10 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