DESCRIPTION AND OPERATION
Page 55
Exhaust Aftertreatment System (EATS)
Equipment installed to remove the maximum
amount of noxious emissions from the exhaust
gases after they leave the combustion chamber
before they reach the atmosphere. This includes
exhaust gas recirculation (EGR), the variable
geometry turbocharger (VGT), the discharge
recirculation valve (DRV), the aftertreatment fuel
injector (AFI) and the diesel particulate filter
(DPF).
Exhaust Gas Recirculation (EGR)
A system whereby a pre-determined amount of
exhaust gas is returned to the combustion
chambers. Adding a small percentage of exhaust
gas to the fuel/air mixture lowers the combustion
temperature reducing the formation of nitrogen
oxides (NOx).
Hydrocarbons (HC)
Chemical compounds composed only of carbon
and hydrogen. Gasoline, diesel fuel and motor oil
are all examples of a very large group of
hydrocarbons. The largest source of
hydrocarbons is petroleum.
Idler Gear
A gear running between a driving and a driven
gear to make the driven gear rotate in the same
direction as the driving gear.
Idler Tensioner
A belt tensioning device designed to maintain
optimum tension under varying engine speeds
and load.
Intake Air Temperature and Humidity Sensor
Mounted in the air intake between the air cleaner
and the turbocharger compressor housing,
detects outside air temperature and humidity and
relays these values to the EECU.
Oxides of Nitrogen (NOx)
High temperatures and pressures of combustion
produce oxides of nitrogen (NOx). When
combustion temperature exceeds 1372°C
(2,500°F), oxygen and nitrogen combine in large
quantities to form NOx. By themselves, NOx
emissions are no great hazard; however, when
mixed with the right amount of HC in the air, NOx
will combine in the presence of sunlight to form
smog.
Passive Regeneration
Cleaning a particulate filter by spontaneous
burning of soot that collects on it. The exhaust
temperature remains continuously high enough to
incinerate the soot.
Poly-V Belt
A multi-ribbed belt design incorporated into the
accessory drive belt and pulley arrangement at
the front of the engine.
Regeneration
Cleaning a diesel particulate filter so as to renew
its capacity to function efficiently.
Roller Follower
A type of lifter with an axle-mounted roller that
rides on (or follows) a camshaft lobe. The rolling
motion of this design provides increased load
capacity with less friction than the flat-faced lifter
design. Roller followers provide the rocker arm
lifting action for the electronic unit injector, intake
and exhaust valves and exhaust brake.
Soot
Carbonaceous particulate matter, black in color,
found in diesel exhaust. Soot particles are
extremely fine. Captured by the diesel particulate
filter, their chemical characteristics are changed
by the heat to which they are exposed, turning the
soot into ash.
Variable Geometry Turbocharger (VGT)
Turbocharger turbine housing has moving
components to control flow of exhaust gas and
build back-pressure in the exhaust system for
EGR flow. Referred to as Variable Turbine
Geometry (VTG) turbocharger on past model
engines. The VGT also serves as an exhaust
brake.
VGT Wheel Speed
A sensor mounted in the turbocharger bearing
housing that detects turbine and compressor
wheel speed and relays this data to the EECU.
Vehicle Electronic Control Unit (VECU)
A microprocessor-based controller, sometimes
referred to as a module, mounted in the cab,
inside the dash panel. With the MACK V-MAC IV
system, the VECU controls engine speed, cruise
control, accessory relay controls, idle shutdown
and trip recorder functions.
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