Types of Trucks
- a truck in which all axles are attached
to a single frame.
- this kind of a truck consists of two
or more separate frames connected by suitable couplings.
- this is designed primarily for drawing
truck trailers and is constructed to carry part of the weight and load of a
- a semitrailer is a truck trailer equipped
with one or more axles, so constructed that the end of a substantial part of
its own weight and that of its load rests upon a truck tractor.
- it is equiupped with one or more axles and
is so constructed that all of its own weight and that of its load rest upon
its own wheels.
- it is a device used to connect a truck
tractor to a semitrailer. It also permits articulation between the units. It
generally comprises of a lower half, consisting of a trunnion (pivot
assembly) plate and latching mechanism. This latching mechanism is mounted
on the truck tractor for connection with a kingpin that is again mounted on
semitrailer can be converted to a full trailer by
- A trailer-converted dolly
- An auxillary axle assembly equipped
with the lower half of a fifth wheel
- A drawbar
- Other special parts
- in heavy trucks, they can comprise of two or more
axles, one out of which may be powered. They are usually so spaced that the
distance between axle centers is not more than one and one- half times the
overall diameter of the wheel and tire. In case of the axles being separated
by a larger distance, the assembly is called a spread tandem.
Vehicular Weight (GVW)
- this is one of the methods by which trucks
- these have GVW ratings of up to 14,000
pounds (6.35 metric tonnes). 92% of all trucks sold belong to this category.
- their GVW ratings vary from 14,000 to
33,000 pounds and usually have straight designs. 4% of trucks belong to this
- these have GVW ratings of more than
33,000 pounds (15 metric tons) and are cross-country tractor-trailer
combinations and off-road construction or mining trucks. The remaining 4% of
all trucks come in this category.
- it is made of two channel sections of alloy steel
with a standardized width. Semitrailers and tank trailers in certain cases
now employ the integral or unitized type of construction.
- individual front suspension was introduced
in 1960. Its most common form is a drop-forged, one section front axle
attached to the frame through leaf springs and shock absorbers.
- trucks with a single powered axle generally have
their axle attached to the frame by leaf springs. The axle is always fully
floating and the weight is carried by the axle housing. This ensures that
the load continues to be supported by the axle housing even if a driving
axle breaks. An axle might be of a single reduction type, meaning that it
has one-gear reduction, or double reduction.
In the case of a two-speed axle, the gear change is built into the axle.
This makes it possible to have two speeds for each transmission speed.
The tandem-drive axle has two powered axles. There is a possibility of
there being two drive shafts, one to each axle. A system of levers is
inbuilt between the two axles to equalize the load.
Other types of powered axle include the Hotchkiss type, in which all the
driving and braking thrust is taken by the leaf springs and the torque-arm
type, in which all the thrusts are taken by the rods. Maintenance is
considerably reduced in this kind of an axle.
- the Ackermann system is employed in the
steering of trucks. It provides for a kingpin for each front wheel, the
maximum cramp angle for which is around 35 degrees. The minimum turning
radius depends on the wheelbase.
Engines and fuels
The diesel engine has gained popularity after the IInd World War for trucks
that a reused for long distances. Other designs have also been made but have
not been commercially successful. In 1952 an engine using liquid-propane gas
was introduced. The diesel engine has the disadvantage of high initial cost
while the propane-burning engine gived a much lower output for a given
Till World War I, large trucks were run on hard rubber tyres. In the 1930s,
cotton took the place of synthetics in the carcass and steel wire.
Fibreglass plies were substituted later. The first few years have seen the
use of a single wide tire to carry the same load as a dual wheel. Recapped
tyres extend the life of the carcass by about three times and are therefore
used by many trucking firms. Tubeless tires became available in large truck
sizes since 1955.
Trucks have been using automatic transmissions since the 1950s. It is
imperative for some diesels to operate the engine within a relatively narrow
speed range. These types of trucks need a large number of forward speeds.
One recent diesel-powered unit has 16, obtained two by combining
transmissions, each with four forward speeds.
It was in 1918 that the first brakes were introduced. In 1925, four-wheel
brakes were introduced on trucks, the internally expanding type was
introduced by 1930 and the vacuum booster, or hydraulic brake in the late
An electric brake
system employs a floating armature that
contract a rotating disk on the wheel current is applied and through a cam
arrangement applies the shoes to the drums.
Some vehicles use air-over-hydraulic brake
Air is the most widely used of all these methods of application. The
engine-driven compressor supplies air at a nominal pressure, regulated by an
air governor. Air pressure is indicated by a pressure gauge and a
low-pressure warning device, either audible or visual. Air is stored in the
reservoirs and supplied to the brake valves; a foot valve supplies air to
all brake chambers on the vehicle, including those being Towed.
Another brake valve is hand-controlled
and applies the
brakes on the Towed vehicle only. Both the foot pedal and hand valve supply
air to the same service line, which extends back to the Towed vehicles. The
second, or emergency, line carries full air pressure when the vehicle is in
operation. If this line is broken, the emergency brakes are applied on all
Towed vehicles from air reservoirs located on the Towed vehicles. After
reaching the brake chamber from the brake valves, the air acts on a
diaphragm connected to a push rod, which in turn actuates a cam that moves
the shoes against the brake drum. The cam was replaced by a wedge in the
Safety has been the buzzword in the last few years. Much attention has been
paid to the problem of brake failure arising due to loss of air pressure. If
a failure in the service line occurs, the emergency system mentioned earlier
can be utilized. Alternately, it can be remedied by the use of the tractor
protection valve and control valve. The driver can therefore apply all
brakes on the Towed vehicles.
A parking brake
is another safety device that can be as
an emergency system in case of loss of air. Known as a DD3 Actuator, the
driver has the option of using the axle on which the DD3 actuators are
mounted as a parking system or as an emergency braking system by operating a
push-pull button. A mechanical lock holds the brake on once this system is
actuated, even if all air pressure is lost.
The spring brake
is another emergency system. As long as
normal air pressure is available, the spring brake actuator is inactive and
the normal brake chambers apply the brakes. When air has been lost, springs
are used to apply the brakes. The emergency system can be put to action if
the driver wants to by means of a push-pull valve.
Air-cooled disc-type brakes
were introduced in the 1990s on
heavy-duty trucks. These units were combined with electronically controlled
antilock air brake systems in order to reduce the possibility of