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Emissions Control (H6DO) - Mechanism & Function: Overview Subaru Outback BP

Theory & Operation 2 illustrations

System Overview

There are three emission control systems which are as follows

  1. Crankcase emission control system
  2. Exhaust emission control system Catalytic converter Air/fuel (A/F) control system Ignition control system
  3. Evaporative emission control system On-board refueling vapor recovery (ORVR) system
ItemViMain componentsFunction
Crankcase emission control systemPositive crankcase ventilation (PCV) valveDraws blow-by gas into intake manifold from crankcase and burns it together with air-fuel mixture. Amount of blow-by gas to be drawn in is controlled by intake manifold pressure.
Exhaust emission control systemCatalytic converterFrontCatalytic converterOxidizes HC and CO contained in exhaust gases as well as reducing NOx.
Rear
Air/fuel (A/F) control systemEngine control module (ECM)Receives input signals from various sensors, compares signals with stored data, and emits a signal for optimal control of air-fuel mixture ratio.
Front oxygen (A/F) sensorDetects density of oxygen contained exhaust gases.
Rear oxygen sensorDetects density of oxygen contained in exhaust gases.
Throttle position sensorDetects throttle opening.
Manifold absolute pressure sensorDetects absolute pressure of intake manifold.
Intake air temperature sensorDetects intake air temperature of air cleaner case.
Ignition control systemECMReceives various signals, compares signals with basic data stored in memory, and emits a signal for optimal control of ignition timing.
Crankshaft position sensorDetects engine speed (revolution).
Camshaft position sensorDetects reference signal for combustion cylinder discrimination.
Engine coolant temperature sensorDetects coolant temperature.
Knock sensorDetects engine knocking.
Evaporative emission control systemCanisterAbsorbs evaporative gas which occurs in fuel tank when engine stops, and releases it to combustion chambers for a complete burn when engine is started. This prevents HC from being discharged into atmosphere.
Purge control solenoid valveReceives a signal from ECM and controls purge of evaporative gas absorbed by canister.
Pressure control solenoid valveReceives a signal from ECM and controls evaporative gas pressure in fuel tank.
ORVR systemVent valveOpens a valve during refueling to let fuel vapor in the fuel tank flow to the canister. The system also closes the port to the canister when the fuel tank is full of fuel.
Drain valveCloses the evaporation line by receiving a signal from ECM to check the evaporation gas leak.

MAIN COMPONENTS SPECIFICATION

Scheme 17

Scheme 17: Schematic Diagrams

Scheme 18

Scheme 18