Page 203 - Automotive Engineering Powertrain Chassis System and Vehicle Body

8.1
Chapter 8.1

Types of suspension and drive

Jornsen Reimpell, Helmut Stoll and Jurgen Betzler

This chapter deals with the principles relating to drives For the purpose of ensuring the optimum handling
and suspensions. characteristics of the vehicle in a steady state as well as
in a transient state, the wheels must be in a defined
position with respect to the road surface for the pur-
8.1.1 General characteristics pose of generating the necessary lateral forces. The
of wheel suspensions build-up and size of the lateral wheel forces are de-
termined by specific toe-in and camber changes of the
The suspension of modern vehicles need to satisfy wheels depending on the jounce and movement of the
a number of requirements whose aims partly conflict body as a result of the axle kinematics (roll steer) and
because of different operating conditions (loaded/ operative forces (compliance steer). This makes it
unloaded, acceleration/braking, level/uneven road, straight possible for specific operating conditions such as load
running/cornering). and traction to be taken into consideration. By estab-
The forces and moments that operate in the wheel lishing the relevant geometry and kinematics of the
contact area must be directed into the body. The kingpin axle, it is also possible to prevent the undesirable diving
offset and disturbing force lever arm in the case of the or lifting of the body during braking or accelerating and
longitudinal forces, the castor offset in the case of the to ensure that the vehicle does not exhibit any ten-
lateral forces, and the radial load moment arm in the case dency to oversteer and displays predictable transition
of the vertical forces are important elements whose ef- behaviour for the driver.
fects interact as a result of, for example, the angle of the Other requirements are:
steering axis. independent movement of each of the wheels on
Sufficient vertical spring travel, possibly combined
with the horizontal movement of the wheel away from an an axle (not guaranteed in the case of rigid axles);
uneven area of the road (kinematic wheel) is required for small, unsprung masses of the suspension in order to
reasons of ride comfort. The recession suspension should keep wheel load fluctuation as low as possible
also be compliant for the purpose of reducing the rolling (important for driving safety);
stiffness of the tyres and short-stroke movements in the introduction of wheel forces into the body
a longitudinal direction resulting from the road surface in a manner favourable to the flow of forces;
(longitudinal compliance, Fig. 8.1-1), but without the necessary room and expenditure for construction
affecting the development of lateral wheel forces and purposes, bearing in mind the necessary tolerances
hence steering precision, for which the most rigid wheel with regard to geometry and stability;
suspension is required. This requirement is undermined ease of use;
as a result of the necessary flexibility that results from behaviour with regard to the passive safety of passen-
disturbing wheel movements generated by longitudinal gers and other road users;
forces arising from driving and braking operations. costs.

Automotive Chassis: Engineering Principles; ISBN: 9780750650540
Copyright Ó 2001 Elsevier Ltd. All rights of reproduction, in any form, reserved.