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A rod, called a tie rod, connects to each end of the rack.The pinion gear is attached to the steering shaft. When you turn the steering wheel, the gear spins, moving the rack. The tie rod at each end of the rack connects to the steeringarm on the spindle. In fig.15 we can see the rack-and-pinion steering.16
Fig. 15 the rack-and-pinion steeringThe rack-and-pinion gearset does two things:It converts the rotational motion of the steering wheel into the linear motion needed to turn the wheels.It provides a gear reduction, making it easier to turn the wheels.On most cars, it takes three to four complete revolutions of the steering wheel to make the wheels turn from lock to lock (from far left to far right).The steering ratio is the ratio of how far you turn the steering wheel to how far the wheels turn. For instance, if one complete revolution (360 degrees) of the steering wheel results in the wheels of the car turning 20 degrees, then the steering ratio is 360 divided by 20, or 18:1. A higher ratio means that you have to turn the steering wheel more to get the wheels to turn a given distance. However, less effort is required because of the higher gear ratio.Generally, lighter, sportier cars have lower steering ratios than larger cars and trucks. The lower ratio gives the steering a quicker response -- you don't have to turn the steering wheel as much to get the wheels to turn a given distance -- which is a desirabletrait in sports cars. These smaller cars are light enough that even with the lower ratio, the effort required to turn the steering wheel is not excessive.Some cars have variable-ratio steering, which uses a rack-and-pinion gearset that has adifferent tooth pitch (number of teeth per inch) in the center than it has on the outside. This makes the car respond quickly when starting a turn (the rack is near the center), and also reduces effort near the wheel's turning limits17
Power Rack-and-pinionWhen the rack-and-pinion is in a power-steering system, the rack has a slightly differentdesign. In fig. 16 we can see a power rack-and-pinion diagram.Fig.16 diagram of the power-rack-and-pinionPart of the rack contains a cylinder with a piston in the middle. The piston is connected to the rack. There are two fluid ports, one on either side of the piston. Supplying higher-pressure fluid to one side of the piston forces the piston to move, which in turn moves the rack, providing the power assist.We'll check out the components that provide the high-pressure fluid, as well as decide which side of the rack to supply it to.Recirculating-ball SteeringRecirculating-ball steering is usedonmany trucks and SUVs today. Thelinkage that turns the wheels isslightly different than on a rack-and-pinion system.The recirculating-ball steering gearcontains a worm gear. You canimage the gear in two parts. Thefirst part is a block of metal with athreaded hole in it. This block hasgear teeth cut into the outside of it,which engage a gear that moves thepitman arm. In fig.17 we see a recirculating-ball steering diagram.