Page 255 - Automotive Engineering Powertrain Chassis System and Vehicle Body

9.1
Chapter 9.1

Steering

Jornsen Reimpell, Helmut Stoll and Jurgen Betzler

This chapter gives only the essential aspects of the subject, from desired direction). These factors would include for
‘Steering’. example, the roll inclination of the body, the feeling of
The steering system is type-approved on all new pas- being held steady in the seat (transverse acceleration) and
senger cars and vans coming on to the market; it is the self-centring torque the driver will feel through the
governed by the following EC directives. steering wheel. The most important information the driver
70/311/EWG 91/662/EWG receives comes via the steering moment or torque which
74/297/EWG 92/62/EWG provides him with feedback on the forces acting on the
wheels.
Figs. 9.1-1, 8.1-45, 8.1-56 and 8.1-70 show the complete It is therefore the job of the steering system to convert
steering system of a front-wheel-drive passenger vehicle the steering wheel angle into as clear a relationship as
with left-hand steering.
possible to the steering angle of the wheels and to convey
feedback about the vehicle’s state of movement back to
9.1.1 Steering system the steering wheel. This passes on the actuating moment
applied by the driver, via the steering column to the
9.1.1.1 Requirements steering gear 1 (Fig. 9.1-3) which converts it into pulling
forces on one side and pushing forces on the other, these
On passenger cars, the driver must select the steering being transferred to the steering arms 3 via the tie rods 2.
wheel angle to keep deviation from the desired course These are fixed on both sides to the steering knuckles and
low. However, there is no definite functional relation- cause a turning movement until the required steering
ship between the turning angle of the steering wheel angle has been reached. Rotation is around the steering
made by the driver and the change in driving direction, axis EG, also called kingpin inclination, pivot or steering
because the correlation of the following is not linear rotation axis (Fig. 8.1-3).
(Fig. 9.1-2):
9.1.1.2 Steering system on independent
turns of the steering wheel; wheel suspensions
alteration of steer angle at the front wheels;
development of lateral tyre forces;
If the steering gear is of a type employing a rotational
alteration of driving direction. movement, i.e. the axes ofthe meshing parts (screw shaft 4

and nut 5, Fig. 9.1-15) are at an angle of 90 to one another,
This results from elastic compliance in the components of on independent wheel suspensions, the insides of the tie
the chassis. To move a vehicle, the driver must continually rods are connected on one side to the pitman arm 4 of the
adjust the relationship between turning the steering wheel gear and the other to the idler arm 5 (Fig. 9.1-3). As shown
and the alteration in the direction of travel. To do so, the in Figs. 9.1-12 and 9.1-36–9.1-38, parts 4 and 5 are
driver will monitor a wealth of information, going far connected by theintermediate rod 6. Inthe caseofsteering
beyond the visual perceptive faculty (visible deviation gears, which operate using a shift movement (rack and
Automotive Chassis: Engineering Principles; ISBN: 9780750650540
Copyright Ó 2001 Elsevier Ltd; All rights of reproduction, in any form, reserved.