Page 261 - Automotive Engineering Powertrain Chassis System and Vehicle Body
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Steering      CHAPTER 9.1








































           Fig. 9.1-11 Top view of the rack and pinion steering of the front-wheel-drive Opel (Vauxhall) Astra (up to 1997) and Vectra
           (up to 1996); the steering arms on the McPherson strut point backwards and the steering gear is located relatively high. For this reason the
           tie rods have to be jointed in the middle and (in order not to come into contact with the gear housing when the wheels are turned) have to
           be bent. The guide-bearing in the groove of the housing prevents the steering rack from twisting. On the inside, both tie rods have the
           eye-type joint; the distance a to the steering rack centre, which causes a bending moment, and a torque (when the wheels bump and
           rebound) is also shown. The two bolts 6 gripping into the steering rack are secured.
           Once the screws 3 and 4 have been loosened, toe-in to the left and right can be set by turning the connecting part 5. The steering gear
           has two fixing points on the dashpanel, which are a long way apart and which absorb lateral force moments with minimal flexing. As also
           shown in Fig. 9.1-10, the pinion is carried by a ball and a needle bearing (positions 20 and 23) and is also pressed onto the
           steering rack by a helical spring. The illustration shows the possible path s of the rack guide. Figs. 9.1-46–9.1-48 show the reason for the
           length of the tie rods on McPherson struts and strut dampers.


           the steering gear has to be located fairly high up. This is  will be heavy, whereas if they are too loose, there is a risk
           because the steering tie rods must thus be very long in  of rattling noises when the vehicle is in motion.
           order to prevent unwanted steering movements during  As the steering forces are introduced at a relatively
           wheel travel (Fig. 9.1-46).                        large distance from the bearing points of the steering axle
             In such cases, the inner joints are fixed in the centre of  (suspension strut support bearings at the top, ball-and-
           the vehicle to the steering rack itself, or to an isolator that  socket joint on the transverse link at the bottom), elastic
           is connected to it. The designer must ensure that the  (flexural) deformations occur on the suspension strut and
           steering rack cannot twist when subject to the moments  shock-absorber strut. As a result, steering precision and
           that arise. When the wheels rebound and compress, the  response characteristics worsen.
           tie rods are moved to be at an angle, something which
           also happens when the wheels are steered. The effective
           distance a between the eye-type joints of the tie rods and  9.1.3 Recirculating ball steering
           the steering rack centre line, shown in Fig. 9.1-11, gives
           a lever, via which the steering could be twisted. Two  9.1.3.1 Advantages and disadvantages
           guide pieces which slide in a groove in the casing stop this
           from happening. However, the need to match the fit for  Steering gears with a rotating movement are difficult to
           the bearing of the steering rack and the guide groove can  house in front-wheel-drive passenger cars and, in a stan-
           lead to other problems. If they are too tight, the steering  dard design vehicle with independent wheel suspension,


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