Repair Manual MAN-00
190
THAR
CRDe
BS-IV
MAY
2012
/Rev 1
The repair methods given by the manufacturer in this document are based on the technical specifications, current at the time of release. The methods may be modified as a result of changes introduced by the
manufacturer in the production of the various component units and accessories from which the vehicles are manufactured. The reproduction, translation, transmission, in part of or whole of the present
document, are prohibited without the prior written consent of Mahindra & Mahindra Ltd. The use of this document by any person other than the trained personnel, at the Authorized Service Centre of
Mahindra & Mahindra Ltd., will amount to unauthorized use and shall be liable for penalty/prosecution© 2012 Mahindra & Mahindra Ltd.
Description
The THAR CRDe engine meets the BS IV emission norms. To control the NOx an Exhaust gas
recirculation is used. Overall, two systems are used.
•
Working Principle of the Exhaust Gas Recirculation
During acceleration and in higher loads the engine generates high combustion temperatures. The high
combustion temperatures increase the NOx generation. The higher percentage of NOx generated in
the combustion chamber come out through the tail pipe spreads in the atmosphere.
To reduce the amount of NOx coming through the tail pipe the EGR system adds exhaust gases into
the fresh air that is going into the combustion chamber. Since the exhaust, gas is already burnt hence
when mixed with fresh air acts an inert gas. Thus when the exhaust gas mixed with fresh air enters the
combustion chamber. The role it does is that it reduces the amount of oxygen available for
combustion. The net effect is that it reduces the peak combustion temperatures. This results in lower
amount of NOx being generated.
To control the amount/percentage of exhaust gases to be circulated back to the combustion chamber
an ECU is used. The ECU monitors the coolant temperature, attitude, engine speed, and accelerator
pedal position. Based on the above parameters the ECU operates a switch that
in turn controls the
amount of
vacuum going to the EGR valve. The amount of vacuum applied controls the lift of the EGR
valve through vacuum modulator.
The inputs of the engine speed (from the Engine RPM Sensor); Throttle position (accelerator pedal
sensor) is fed in one map. Another map uses the throttle position and correlate in terms of the
acceleration. The third map uses the water temperature. The inputs from the 3 maps are added
together to give an input to the EGR pressure modulator.
At the same time it has a set point that if the water temperature is less than 25
°
C or more than
95
°
C. Then the EGR will not be operated.
Temperature
Sensor
RPM sensor
Load Sensor
Air flow
Intake Air
E
C
U
Vacuum
Modulator
Engine
Exhaust Air
EGR
Vacuum
pump
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