Exhaust Gas Recirculation - Solenoid
of Exhaust Gas Recirculation (EGR) is to recycle a small amount of the exhaust
gas back into the induction process to reduce oxides of nitrogen (NOx). NOx is
produced when combustion temperatures are high, often associated with lean
burn engines. By recycling a small amount of exhaust gas the combustion charge
temperature is lowered and there is a reduction in NOx. The EGR solenoid will
be control by the Electronic Control Module (ECM) and will also work in
association with other devices that monitors the amount of gas that is
recycled. This set up will often be different for each manufacture and there
is normally a combination of vacuum and electrical solenoid valves.
operation will take place under very specific conditions. The ECM will control
the earth path to the solenoid valve. The information that the ECM requires
for this operation is; engine temperature, vehicle speed and engine load. With
such precise data required it will only be possible to see the activation of
the EGR solenoid valve whilst the vehicle is on the dyno.
of Exhaust Gas Recirculation (EGR) is to lower Oxides of Nitrogen (NOx) under
certain circumstances. As the internal combustion temperature rises, the
nitrogen within the Air/Fuel mixture will start to oxidise causing NOx to be
produced. This burning of the nitrogen is both unacceptable and unavoidable as
the Air/Fuel ratio is increased and a weaker mixture is ignited.
output is at a maximum when the engine has reached its normal operating
temperature and the vehicle is subjected to light throttle or light load
converter is designed to eradicate the majority of the NOx by neutralising it
when it comes into contact with the precious metal Rhodium, but by reducing
the NOx before it reaches the 'cat' ensures even lower outputs. The EGR valve
will allow a small amount of the exhaust gasses to 'bleed' back into the inlet
manifold to lower the combustion temperature and reduce the chances of the
Nitrogen burning. The EGR valve is a small mechanical device that allows the
passage of exhaust gas when it receives a vacuum supply.
is governed by a vacuum switch which in turn is activated by a signal from the
Electronic Control Module (ECM). NOx, like hydrocarbons, are measured in parts
per million and the reading recorded in a workshop environment is
significantly lower to that recorded when the vehicle is at cruise.
diagram of an typical EGR set up, with the EGR valve in the closed position.
EGR taken to
excess can affect combustion and increase hydrocarbons. It is therefore
necessary to monitor the amount of exhaust gas that enters the inlet manifold.
Different manufacturers perform this task in different ways, some general
examples of this are described below.
Honda use an
ECM with a programmed map contained within it. The map contains information on
the correct amount of EGR according to factors such as; engine speed, road
speed, temperature and load.
right conditions for EGR to take place, the ECM earths the path of the
solenoid valve and this allows a vacuum source to operate the EGR valve. The
EGR valve also includes a lift sensor, this is a similar device to a throttle
potentiometer. It will have a 5 volt supply, earth and variable signal back to
the ECM depending on the position of the EGR valve. If the amount of exhaust
gas passing through the valve exceeds the parameters within the ECM's map, the
ECM will shut the solenoid valve by removing its earth path. This making and
breaking, or 'pulsing', of the earth path allows fine adjustments to be made
ensuring the precise amount of EGR takes place.
a similar system, however, the solenoid valve, lift sensor and the EGR valve
are all one unit. Fault finding is also made harder
by the fact that EGR takes places inside the cylinder head through a passage
connecting the exhaust and inlet manifolds.
always, have some interesting names and acronyms for the components within
their EGR system. To start with the control solenoid is referred to as an
Electronic Vacuum Regulator (EVR) and their method of monitoring the amount of
EGR is by a Differential Pressure Feedback Electronic System (DPFE).
DPFE sensor measures the pressure inside of the EGR tube either side of a
This pressure difference is then converted into a voltage and sent to the ECM
for reference. Again the ECM contains a map for the correct amount of EGR and
if this differs the ECM adjusts the control of the EVR to trim the amount of
gas passing to the inlet manifold.