Isuzu 4HK-1, Manual, Page: 20 / 50

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Exhaust gas Recirculation (EGR) System
Exhaust Gas Recirculation system is abbreviated to EGR system. It recirculates part of
exhaust gas into intake manifold to mix an inert gas with intake air. This leads to lower
the combustion temperature to limit emissions of nitrogen oxide (NOx).
It controls amount of EGR by opening/closing the EGR valve installed between exhaust
manifold and intake manifold. It determines amount of EGR, based on the engine
speed and load rate on engine (fuel injection amount), and operates the EGR valve to
control the amount of EGR.
The cooling system (EGR cooler) equipped on the EGR gas passage allows to cool
down high temperature EGR gas and mix it with new air to lower the combustion
temperature further, resulting in limiting NOx effectively (Cooled EGR).
On the 4HK1 and 6HK1-TC model engines, the EGR system has the check valve to
stop backward flow of EGR gas and flows it in one direction only.
The engine control module (ECM) operates the EGR motor according to engine speed,
engine load, etc. to control amount of EGR valve lift. The amount of valve lift is
detected by EGR position sensor. The dark color area in the figure shows that the valve
lift amount is large, and the darkest color area shows that the valve lift amount is almost
100%.