The
cab is an enclosed space where the driver is seated. A
sleeper is a compartment attached to the cab where the driver can rest while not driving, sometimes seen in
semi-trailer trucks.
There are several possible cab configurations:
Cab over engine (COE) or flat nose; where the driver is seated above the front axle and theengine. This design is almost ubiquitous in Europe, where overall truck lengths are strictly regulated, but also widely used in the rest of the world as well. They were common in theUnited States, but lost prominence when permitted length was extended in the early 1980s. To access the engine, the whole cab tilts forward, earning this design the name of tilt-cab. This type of cab is especially suited to the delivery conditions in Europe where many roads follow the layout of much more ancient path, and trackways which require the additional turning capability of the cab over engine type. The COE design was invented by Viktor Schreckengost.[11]- Conventional cabs are the most common in North America, and are known in the UK asAmerican cabs. The driver is seated behind the engine, as in most passenger cars or pickup trucks. Conventionals are further divided into large car and aerodynamic designs. A "large car" or "long nose" is a conventional truck with a long (6 to 8 foot (1.8 to 2.4 m) or more) hood. With their very square shapes, these trucks experience a lot of wind resistance and typically consume more fuel. They also provide somewhat poorer visibility than their aerodynamic or COE counterparts. By contrast, Aerodynamic cabs are very streamlined, with a sloped hood and other features to lower drag.
- Cab beside engine designs also exist, but are rather rare and are mainly used inside shipping yards, or other specialist uses such as aircraft baggage loading.
Cummins ISB 6.7L medium duty truck diesel engine
[edit]Drivetrain
A truck rear suspension and drive axles overview
Eaton Roadranger 18 speed "crash box" with automated gearshift
Small trucks use the same type of
transmissions as almost all
cars, having either an automatic transmission or a manual transmission with
synchromesh (synchronizers). Bigger trucks often use manual transmissions without synchronisers, saving bulk and weight, although synchromesh transmissions are used in larger trucks as well. Transmissions without synchronizers, known as "crash boxes", require
double-clutching for each shift, (which can lead to repetitive motion injuries), or a technique known colloquially as "floating", a method of changing gears which doesn't use the clutch, except for starts and stops, due to the physical effort of double clutching, especially with non power assisted clutches, faster shifts, and less clutch wear.
Double-clutching allows the driver to control the engine and transmission revolutions to synchronize, so that a smooth shift can be made, e.g., when upshifting, the accelerator pedal is released and the clutch pedal is depressed while the gear lever is moved into neutral, the clutch pedal is then released and quickly pushed down again while the gear lever is moved to the next higher gear. Finally, the clutch pedal is released and the accelerator pedal pushed down to obtain required engine speed. Although this is a relatively fast movement, perhaps a second or so while transmission is in neutral, it allows the engine speed to drop and synchronize engine and transmission revolutions relative to the road speed. Downshifting is performed in a similar fashion, except the engine speed is now required to increase (while transmission is in neutral) just the right amount in order to achieve the synchronization for a smooth, non-collision gear change. Skip changing is also widely used; in principle operation is the same as double-clutching, but it requires neutral be held slightly longer than a single gear change.
Common North American setups include 9, 10, 13, 15, and 18 speeds.
Automatic and
semi-automatic transmissions for heavy trucks are becoming more and more common, due to advances both in transmission and engine power. In Europe 8, 10, 12 and 16 gears are common on larger trucks with manual transmission, while automatic or semi-automatic transmissions would have anything from 5 to 12 gears. Almost all heavy truck transmissions are of the "range and split" (double H shift pattern) type, where range change and so-called half gears or splits are air operated and always preselected before the main gear selection.
A truck rear frame (chassis) section view
A truck
frame consists of two parallel boxed (tubular) or C-shaped rails, or beams, held together by crossmembers. These frames are referred to as
ladder frames due to their resemblance to a ladder if tipped on end. The rails consist of a tall vertical section (two if boxed) and two shorter horizontal flanges. The height of the vertical section provides opposition to vertical flex when weight is applied to the top of the frame (beam resistance). Though typically flat the whole length on heavy duty trucks, the rails may sometimes be tapered or arched for clearance around the engine or over the
axles. The holes in rails are used either for mounting vehicle components and running wires and hoses, or measuring and adjusting the orientation of the rails at the factory or repair shop.
Though they may be welded,
crossmembers are most often attached to frame rails by
bolts or
rivets. Crossmembers may be boxed or stamped into a c-shape, but are most commonly boxed on modern vehicles, particularly heavy trucks.
The frame is almost always made of
steel, but can be made (whole or in part) of
aluminium for a lighter weight. A
tow bar may be found attached at one or both ends, but heavy trucks almost always make use of a
fifth wheel hitch.
-2004.jpg)
.jpg)
