EMISSION CONTROL SYSTEM


  1. FUNCTION OF MAIN COMPONENTS


    1. The main components of the exhaust emission control system are as follows:

      Component Function
      TWC Oxidizes CO and HC in the exhaust gas and deoxidizes NOx at the same time, to purify them into CO2, H2O and N2.
      Heated Oxygen Sensor Detects the oxygen concentration in the exhaust emission by measuring the electromotive force which is generated in the sensor itself.
      Air Fuel Ratio Sensor Is used to determine the concentration of oxygen remaining in the exhaust gas. Has a characteristic where its output is proportional to the engine air fuel ratio. Located upstream of the catalytic converter.
      ECM Controls the volume of fuel consumed based primarily on the signal from the air fuel ratio sensor, with minor corrections based on the signal from the heated oxygen sensor. This control optimizes the exhaust emissions.

    2. The main components of the EGR system are as follows:

      Component Function
      Manifold Absolute Pressure Sensor Detects the pressure in the intake manifold and sends signals to the ECM for EGR control.
      EGR Valve Assembly Opens and closes based on signals from the ECM and controls the flow rate of the exhaust gas in the EGR bypass.
      EGR Cooler Assembly The EGR cooler cools the exhaust gas to improve EGR efficiency.
      ECM Based on the signals received from the sensors, the ECM determines the EGR volume in accordance with the engine operating conditions.

    3. The main components of the blowby gas ventilation system are as follows:

      Component Function
      PCV Valve (Ventilation Valve Sub-assembly) Opens and closes using vacuum generated in the intake manifold to control the flow rate of the blowby gas.
      Oil Separator (Ventilation Case Sub-assembly) Collects oil mist in the blowby gas, reducing the oil consumption.
      Oil Pre-separator (No. 1 Ventilation Case) Separates the engine oil from the blowby gas.

    4. The main components of the evaporative emission control system are as follows:

      Component Function
      Canister Contains activated charcoal to absorb the fuel vapor that is created in the fuel tank assembly.
      Purge VSV Opens in accordance with the signals from the ECM when the system is purging in order to send the fuel vapor that was absorbed by the canister into the intake manifold.
      ECM Controls the purge VSV in accordance with the signals from various sensor in order to achieve a purge volume that suits the driving conditions.

  2. SYSTEM CONTROL


    1. EGR Control


      1. For the EGR system, an amount of EGR gas, which is regulated in accordance with the engine operating conditions, is allowed to flow into the intake passage, reducing the peak temperature in the engine combustion chamber and achieving low fuel consumption.

      2. By sensing the engine driving conditions and actual amount of the EGR valve assembly opening, the ECM operates the EGR valve assembly and throttle control motor, to regulate the amount of exhaust gas that is recirculated.

      3. A highly efficient EGR cooler assembly is used to achieve the optimized EGR rate.

      4. EGR chambers are provided in the intake manifold so that EGR gas is equally distributed to the cylinders.

        A01VYG7E04
        Text in Illustration
        A01VYTO Intake Air B001IZ8 EGR Gas

    2. Blowby Gas Ventilation System


      1. By introducing blowby gas that has a large amount of HC into the intake manifold for combustion, the system prevents the blowby gas, which includes a large amount of HC, from being discharged into the atmosphere. The amount of airflow through the crankcase (blowby gas introduction volume) is controlled according to the engine operating conditions. This prevents the excessive consumption of engine oil, and is a factor in idle speed control.

      2. This system uses the ventilation method, which sucks the blowby gas directly from the stiffening crankcase assembly, enhancing the ventilation efficiency.

      3. An oil separator (ventilation case sub-assembly) is provided in the blowby gas passage inside the cylinder head cover sub-assembly. This separates the engine oil from the blowby gas in order to reduce oil degradation and reduce the amount of engine oil consumed.

      4. An oil pre-separator (No. 1 ventilation case) is provided in the cylinder block assembly, improving the separation of oil from the blowby gas.

      5. The Positive Crankcase Ventilation (PCV) valve (ventilation valve sub-assembly) passage returns the blowby gas into the intake manifold in accordance with the intake manifold vacuum.

      6. Under light load conditions, the intake manifold vacuum causes the blowby gas to be drawn via the PCV valve into the intake manifold.

      7. Under high load conditions, the introduction of fresh air is stopped, allowing a large amount of blowby gas to be drawn into the intake system.

        A01VZ0KE02
        Text in Illustration
        *1 Timing Chain Cover Assembly *2 Cylinder Head Cover Sub-assembly
        *3 Oil Separator (Ventilation Case Sub-assembly) *4 Cylinder Head Sub-assembly
        *5 Oil Pre-separator (No. 1 Ventilation Case) *6 Cylinder Block Sub-assembly
        *7 Stiffening Crankcase Assembly *8 Oil Pan Sub-assembly
        *9 PCV Valve (Ventilation Valve Sub-assembly) *10 Intake Manifold
        *11 Throttle Body with Motor Assembly - -
        *a from Air Cleaner Assembly *b Blowby Gas
        *c Fresh Air - -

    3. Purge Flow Control


      1. When the engine has reached a predetermined state [closed loop, engine coolant temperature above 80°C (176°F), etc.], stored fuel vapor is purged from the canister whenever the purge VSV is opened by the ECM.

      2. The ECM will change the duty ratio cycle of the purge VSV, thus controlling purge flow volume. Purge flow volume is determined by intake manifold pressure and the duty ratio cycle of the purge VSV. Atmospheric pressure is allowed into the canister to ensure that purge flow is constantly maintained whenever purge vacuum is applied to the canister.

  3. CONSTRUCTION


    1. Three-Way Catalytic Converter (TWC)


      1. TWCs are provided in the exhaust manifold sub-assembly and also in the front exhaust pipe assembly.

      2. An exhaust manifold sub-assembly with an integrated three-way catalytic converter (TWC) is used. This realizes quick warm-up of the catalytic converter, helping to reduce emissions immediately after engine start.

      3. These TWCs enable improved exhaust emissions through optimized cell density and wall thickness.

        A01VYXEE02
        Text in Illustration
        *1 Exhaust Manifold Sub-assembly *2 Front Exhaust Pipe Assembly
        *a TWC - -

    2. EGR Valve and EGR Cooler


      1. A step motor type EGR valve assembly is used to precisely control the EGR gas flow amount.

      2. The EGR cooler cools the exhaust gas to improve the EGR efficiency.

      3. Stainless steel is used for the EGR cooler assembly in consideration of reliability at high temperature.

        A01VYXZE02
        Text in Illustration
        *1 EGR Valve Assembly *2 EGR Cooler Assembly
        *a A-A Cross Section *b EGR Gas Passage
        *c Water Passage - -
        B001IZ8 EGR Gas A01VYTO Engine Coolant

    3. Canister


      1. The canister is integrated into the fuel suction tube with pump and gauge assembly.

        A01VZ24E03
        Text in Illustration
        *1 Fresh Air Port *2 EVAP Port (from Fuel Tank Assembly)
        *3 Fuel Suction Tube with Pump and Gauge Assembly *4 Purge Port (to Intake Manifold)
        *5 Canister - -

    4. Purge VSV


      1. The canister purge VSV controls purge flow volume in accordance with duty signals from the ECM. Purge flow volume is determined by the on/off intervals of the drive signal from the ECM (duty ratio).

        A01VYV1E06
        Text in Illustration
        *1 Vacuum Switching Valve *2 Filter
        *a to Purge Port *b from Canister
        *c Valve OFF (Close) *d Valve ON (Open)