An EGR valve controls the rate, at which exhaust gases are being re-circulated. The valve consists of a valve body with two dampers. The dampers are controlled by an electronic control unit (ECU). Controlling the two dampers makes it possible to quickly and accurately adjust EGR rate within the entire range of engine operating conditions.
ECU - Electronic Control Unit
An electronic control unit contains an algorithm for exact positioning of the valve corresponding to any and all speed and load combinations.
Other system components are: an EGR cooler, an exhaust back-pressure sensor and a secondary filter. The purpose of an EGR cooler is to decrease emissions of nitrogen oxides, carbon monoxide, hydrocarbons and particulate matter through cooling of EGR gas. Cooling has to be chosen carefully for optimum reduction of nitrogen oxide emissions. After treatment provides particulate free exhaust gases. An exhaust back-pressure sensor is used for the purpose of system monitoring. The secondary filter prevents an engine from being contaminated with PM in a case of a failure of PM filter or EGR recirculation pipes.