SCR Control Component Description
SCR Control Component DescriptionDiesel Exhaust Fluid (DEF) Injector
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(1) DEF inlet
(2) Engine coolant inlet
(3) Engine coolant outlet
The Diesel Exhaust Fluid (DEF) injector is installed on the inlet of the SCR catalyst. The DEF injector injects the DEF that is pressurized by the DEF supply module into the exhaust pipe in accordance with the signals from the DEF control module. Also, it circulates the engine coolant inside the DEF injector for the purpose of cooling the injector.
Diesel Exhaust Fluid (DEF) Supply Pump
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(1) Pressure compensation element
(2) Engine coolant inlet
(3) DEF suction connector (with sub filter)
(4) Engine coolant outlet
(5) DEF backflow connector (with sub filter)
(6) DEF pressure connector
(7) Main filter (internal)
The DEF supply pump is installed near the DEF tank in the left side frame. After the engine has been started, the diaphragm pump is activated to pressurize the DEF up to 130 psi (900 kPa) when the operating conditions of the DEF supply pump are met. After that, the DEF control module makes a calculation based on the value from the DEF pressure sensor inside the DEF supply pump, and maintains the DEF pressure at approximately 130 psi (900 kPa). When the engine is stopped, the DEF control module operates the DEF supply pump after switching the reverting valve to return the DEF inside the DEF injector, DEF piping and DEF supply pump back into the DEF tank for preventing the DEF supply pump, etc. from being damaged due to DEF freezing.
Also, the DEF supply pump has the DEF supply pump temperature sensor built inside, and when it is cold, circulates the engine coolant into the DEF supply pump to provide the heater control which prevents freezing by defrosting the DEF or keeping it warm.
Diesel Exhaust Fluid (DEF) Level Sensor
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(1) DEF level sensor
(2) DEF tank temperature sensor
The Diesel Exhaust Fluid (DEF) level sensor is installed inside the DEF tank, and consists of the DEF tank temperature sensor and DEF level sensor. Each sensor sends the information related to the DEF inside the DEF tank to the DEF control module.
DEF Tank Temperature Sensor
The DEF tank temperature sensor measures the temperature of DEF using the resistance value changed by the thermistor according to changes in temperature. The resistance value decreases when the DEF temperature is high and increases when the DEF temperature is low. The DEF control module performs the DEF defrosting control and thermal control based on the signal from the DEF tank temperature sensor.
DEF Level Sensor
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(1) Pipe
(2) Float
The DEF level sensor consists of a float and pipe. In the float, a magnet is installed, and in the pipe, there is a board where lead switches having a different resistance are populated. The fluid level is detected by reading the resistance value at the time when the lead switches mounted on the board are turned ON by the magnetic force provided through the up and down movements of the float in synchrony with the surface level of the DEF. The DEF control module determines whether the DEF remaining level warning or the engine restart prohibition warning should be given, based on the signal from the DEF level sensor.
Diesel Exhaust Fluid (DEF) Tank
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(1) Tank body
(2) Vent hose
(3) DEF level sensor
(4) Filler cap
(5) DEF tank level gauge
(6) Drain plug
The DEF tank is installed on the frame at the left side of vehicle, and is made of special resin which provides lightweight and robustness. The DEF level sensor is installed inside the DEF tank. The fill port of DEF is designed with a smaller diameter than the fuel feed nozzle to prevent fuel from being fed mistakenly. There is a transparent level gauge installed on the outside of DEF tank to check the fluid level.
Diesel Exhaust Fluid (DEF) Heater Valve
The DEF heater valve is installed on the left side of the DEF supply pump. The coolant control valve is controlled to open and close based on the signals from the DEF control module, and circulates the DEF inside the DEF tank and the engine coolant inside the DEF supply pump to defrost the DEF or keep it warm. However, the engine coolant that is cooling the DEF injector diverges right in front of the DEF heater valve, so it does not go through the DEF heater valve.
Exhaust Gas Temperature (EGT) Sensor 3
The exhaust gas temperature (EGT) sensor 3 is a resistance temperature detector which is installed on the inlet of the SCR catalyst, and measures the temperature of exhaust gas before the SCR catalyst and transmits it to the DEF control module. The DEF control module determines whether the startup control or DPF cooperative control is required, based on the signal from the EGT sensor 3.
NOx Sensor
The NOx sensors are installed in two positions, front and rear of the SCR catalyst. The NOx sensor 1 is installed in the SCR catalyst upstream, and detects the NOx concentration exiting from the engine. The NOx sensor 2 is installed in the SCR catalyst downstream, and detects the NOx concentration after NOx conversion by the catalyst. The DEF control module monitors the NOx conversion efficiency using these 2 NOx sensors. Also, signals from the NOx sensors are transmitted to the DEF control module through the CAN circuit. The DEF control module calculates the required DEF injection amount based on the signals from the NOx sensors.