Page 223 - Automotive Engineering Powertrain Chassis System and Vehicle Body

Types of suspension and drive CHAPTER 8.1

A long exhaust system with good silencing and cata-
lytic converter configuration.
Good front crumple zone, together with the
‘submarining’ power plant unit, i.e. one that goes
underneath the floor panel during frontal collision.
Simple and varied front axle designs are possible irre-
spective of drive forces.
More even tyre wear thanks to function distribution
of steering/drive.
Uncomplicated gear shift mechanism.
Optimum gearbox efficiency in direct gear because
no force-transmitting bevel gear is in action.
Sufficient space for housing the steering system in
the case of a recirculating ball steering gear.
Good cooling because the engine and radiator are at
the front; a power-saving fan can be fitted.
Effective heating due to short hot-air and water paths.

The following disadvantages mean that, in recent years,
only a few saloon cars under 2 l engine displacement
have been launched internationally using this design,
and performance cars also featured the front-mounted
design:

Unstable straight-running ability (Fig. 8.1-35), which
can be fully corrected by special front suspension
geometry settings, appropriate rear axle design and
Fig. 8.1-38 Front hub carrier (steering knuckle) on the
Mercedes-Benz S class (W40, 1997) with a large effective suitable tyres.
distance c (see also Fig. 8.1.4). The upper transverse control The driven rear axle is slightly loaded when there are
arm 6 forms the casing for the ball pivot of the guiding joint, only two persons in the vehicle, leading to poor trac-
whereas the lower supporting joint 7 is pressed into the hub tion behaviour in wet and wintry road conditions –
carrier 5. The ventilated brake disc 34 (dished inwards), the linked to the risk of the rear wheels spinning, partic-
wheel hub 9, the double-hump rim 43 with asymmetrical drop ularly when tight bends are being negotiated at speed.
centre and the space for the brake caliper (not included in the This can be improved by setting the unladen axle load
picture) are clearly shown.
distribution at 50%/50% which, however, is not
always possible (Fig. 8.1-36). It can be prevented by
8.1.4.1 Advantages and disadvantages means of drive-slip control.
of the front-mounted engine, A tendency towards the torque steer effect
rear-mounted drive design (Fig. 10.1-53) and, therefore,
complex rear independent wheel suspension with
The standard design has a series of advantages on chassis subframe, differential gear case and axle
passenger cars and estate cars: drive causing
restrictions in boot size
Thereishardlyanyrestrictiononenginelength,making The need for a propshaft between the manual gear-
it particularly suitable for more powerful vehicles (in box and differential (Fig. 8.1-32) and, therefore,
other words, for engines with 8–12 cylinders). a tunnel in the floor pan is inevitable, plus an unfav-
There is low load on the engine mounting, as only the ourable interior to vehicle–length ratio.
maximum engine torque times the conversion of the
lowest gear without differential transmission has to
be absorbed. 8.1.4.2 Non-driven front axles
Insulation of engine noise is relatively easy.
Under full load, most of the vehicle mass is on the The standard design for passenger cars that have come
driven rear axle (important for estate cars and onto the market in recent years have McPherson struts on
trailers (Fig. 8.1-36). the front axle, as well as double wishbone or multi-link

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