EXHAUST GAS RECIRCULATION SYSTEM





When the combustion gas temperature becomes high, generation of the environment polluting NOx (nitrogen oxides) increases rapidly. Exhaust gas recirculation system is used to decrease the volume of NOx generated. Exhaust gas recirculation system re-circulates exhaust gas inside the inlet manifold. It increases specific heat of the combustion gases and reduces combustion speed to lower the combustion temperature and reduce the volume of NOx generated. Engine-ECU calculates the exhaust gas recirculation introduction volume according to engine operating conditions and controls the exhaust gas recirculation valve opening angle at optimum. Also, immediately after the ignition switch ON signal is input, it drives fully closed stepper motor and performs initialization.

EXHAUST GAS RECIRCULATION VALVE



Depending on the vehicle, the installation location of the exhaust gas recirculation valve is as follows.
Exhaust gas recirculation valve is installed in EGR valve support.
The exhaust gas recirculation valve controls exhaust gas recirculation flow volume using the stepper motor method and reduces exhaust gas (NOx) and fuel consumption. The exhaust gas recirculation valve drives the stepper motor based on the signal from engine-ECU. When stepper motor rotor turns in clockwise or anti-clockwise direction, the shaft fitted with a rotor and a screw expands and contracts and the movement of the shaft causes the valve to go up and down. Thus, exhaust gas recirculation path gap is controlled minutely. The stepper motor turns 15° per step. The stepper motor turns forward or back only up to the angle dictated by the number of pulse signals (number of steps) from the engine-ECU. In other words, increase and decrease of the exhaust gas recirculation flow volume depends on the number of signals (number of steps) from engine-ECU. Engine-ECU changes current flow to the 4 coils (A, B, C, D) in the stepper motor in sequence according to the phase pattern in the following chart in order to turn the stepper motor rotor. Open valve changes phase in order of 0 → 1 → 2 → 3 → 0. Close valve changes phase in order of 3 → 2 → 1 → 0 → 3.
Phase number
Stepper motor coil
Coil A
Coil B
Coil C
Coil D
0
ON
OFF
OFF
ON
1
ON
OFF
ON
OFF
2
OFF
ON
ON
OFF
3
OFF
ON
OFF
ON