Page 233 - Automotive Engineering Powertrain Chassis System and Vehicle Body

Types of suspension and drive CHAPTER 8.1

simple rear axle design – e.g. compound crank or
rigid axles – possible;
long wheelbase making high ride comfort possible;
short power flow because the engine, gearbox and
differential form a compact unit;
good engine cooling (radiator in front), and an elec-
tric fan can be fitted;
effective heating due to short paths;
smooth car floor pan;
exhaust system with long path (important on cars
with catalytic converters);
a large boot with a favourable crumple zone for rear
end crash.

The disadvantages are:

under full load, poorer drive-off capacity on wet
and icy roads and on inclines (Fig 8.1-36);
Fig. 8.1-55 Double wishbone front suspension on the Honda
models, Prelude and Accord, with short upper wishbones with powerful engines, increasing influence on
with widely spaced bearings, lower transverse control arms steering;
and longitudinal rods whose front mounts absorb the engine length limited by available space;
dynamic rolling stiffness of the radial tyres. The spring shock with high front axle load, high steering ratio or power
absorbers are supported via fork-shaped struts on the
transverse control arms and are fixed within the upper link steering is necessary;
mounts. This point is a good force input node. Despite the with high located, dash-panel mounted rack and
fact that the upper wheel carrier joint is located high, which pinion steering, centre take off tie rods become
gives favourable wheel kinematics, the suspension is necessary (Figs. 8.1-57 and 9.1-39) or significant
compact and the bonnet can be low to give aerodynamic kinematic toe-in change practically inevitable;
advantages. The large effective distance c between the
upper and lower wheel hub carrier joints seen in Fig. 8.1-5 geometrical difficult project definition of a favourable
results in low forces in all mounts and therefore less elastic interference force lever arm and a favourable steering
deflection and better wheel control. roll radius (scrub radius);
engine gearbox unit renders more difficult the
arrangement of the steering package;
the power plant mounting has to absorb the engine
8.1.6.2 Advantages and disadvantages moment times the total gear ratio;
of front-wheel drive it is difficult to design the power plant mounting –
booming noises, resonant frequencies in conjunction
Regardless of the engine position (see Fig. 8.1-52), front- with the suspension, tip in and let off torque effects
wheel drive has numerous advantages: etc., need to be suppressed;
there is load on the steered and driven wheels; with soft mountings, wavy road surfaces excite
good road-holding, especially on wet roads and in the power plant to natural frequency oscillation (so-
wintry conditions – the car is pulled and not called ‘front end shake’;
pushed (Fig. 8.1-35); there is bending stress on the exhaust system from
good drive-off and sufficient climbing capacity with the power plant movements during drive-off and
only few people in the vehicle; braking (with the engine);
tendency to understeer in cornering; there is a complex front axle, so inner drive shafts
insensitive to side wind; need a sliding CV joint (Fig. 8.1-53);
although the front axle is loaded due to the weight the turning and track circle is restricted due to the

of the drive unit, the steering is not necessarily limited bending angle (up to 50 ) of the drive joints;
heavier (in comparison with standard cars) during high sensitivity in the case of tyre imbalance and non-
driving; uniformity on the front wheels;
axle adjustment values are required only to higher tyre wear in front, because the highly loaded
a limited degree for steering alignment; front wheels are both steered and driven;

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