EMISSION CONTROL SYSTEM DETAILS


  1. SYSTEM CONTROL


    1. EGR Control System


      1. This system is designed to reduce and control NOx formation due to a slight reduction of peak temperature in the engine combustion chamber, which is accomplished by introducing a small amount of inert gas into intake manifold.

      2. By sensing the engine driving conditions and actual amount of EGR valve opening, the engine ECU electrically operates the E-VRV (for EGR valve control) and VSV (for EGR valve close), which controls the magnitude of vacuum introduced into diaphragm of EGR valve and throttle valve opening angle by throttle control motor, and the amount of recirculating exhaust gas is regulated. EGR valve opening amount is controlled by modulated negative pressure.

      3. The VSV (for EGR valve close) is activated when the EGR control is stopped, in order to introduce the atmospheric pressure to the EGR valve diaphragm and improve EGR valve closure response to maintain drivability.

      4. The EGR function is stopped under the conditions given below to ensure drivability and to reduce diesel smoke.


        • While engine is cold.

        • The vehicle is under high load condition.

        • During deceleration (the EGR operation at idle).

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  2. CONSTRUCTION


    1. EGR Valve


      1. An EGR valve is provided in the midstream of the intake air passage. By cooling the EGR valve in this manner, a greater volume of exhaust gas can be processed.

      2. A vacuum port for a VSV (for EGR valve close) to cut off EGR is used to improve valve closure response.

      3. An EGR valve position sensor has been provided in the EGR valve in order to directly measure the actual amount of the valve opening. This measurement is then input into the engine ECU in order to improve the precision of EGR control.

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        Text in Illustration
        *1 EGR Valve Position Sensor - -
        *a Vacuum Port *b from Air Cleaner
        *c to Intake Manifold - -
        A01KAGS EGR Gas A01KAIP Intake Air

    2. EGR Cooler


      1. A water-cooled type EGR cooler is used. That lowers the exhaust gas temperature to recirculate the great amount of exhaust gas, realizing the reduction of NOx.

      2. The EGR cooler is comprised of the six-layered heat exchanger tube, which contains the inner fins inside.

      3. The inner fins have a wavy shape to enhance cooling efficiency and prevent them from becoming clogged with carbon deposits. The water flows around the heat exchanger tubes to cool down the exhaust gas.

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        Text in Illustration
        *1 Heat Exchanger Tube *2 Inner Fin (Wavy Shaped)
        *a from Cylinder Head *b to EGR Valve
        *c A-A Cross Section - -
        A01KAGS Water A01KAIP Exhaust Gas