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| Illustration 1 | g06087628 |
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Diesel Exhaust Fluid (DEF) dosing control cabinet components Valves are shown in a static state (1) DEF line to injector at Clean Emissions Module (CEM) (2) Air line to injector at CEM (3) Compressed air source (customer supplied) (4) DEF Filter Screen (5) DEF source (customer supplied) (6) DEF pressure sensor (7) Air assist pressure sensor (8) Air pressure regulator (9) Air assist valve (10) DEF buffer tank return valve (11) DEF buffer tank fill valve (12) DEF pump (13) DEF level sensor (14) DEF buffer tank | |
The Diesel Exhaust Fluid (DEF) buffer tank is located within the dosing cabinet. DEF is supplied to the DEF buffer tank from the remote DEF tank that is supplied by the customer.
The DEF buffer tank contains a DEF level sensor and temperature sensor. This sensor sits in the DEF buffer tank and reads the level of the DEF within the buffer tank and the DEF temperature.
When the DEF tank level sensor reads below a certain threshold, the DEF tank refill valve will open and allow the DEF buffer tank to refill. Once the level passes above a threshold, the DEF tank refill valve will close.
The DEF pump is located in the dosing cabinet. The DEF pump is powered by a 120 VAC power source.
The Electronic Control Module (ECM) controls the DEF pump by sending a Pulse Width Modulated (PWM) signal to the pump.
The DEF pump is a fixed displacement pump. The higher the duty cycle of the PWM signal, the more DEF is dosed into the exhaust stream.
The air manifold is where all the air connections to the dosing cabinet are made.
The air manifold contains internal passages for the air and contains the air assist valve and the air pressure regulator.
The DEF manifold is where all the DEF connections to the dosing cabinet are made.
The DEF manifold contains internal passages for the DEF and contains the solenoids required for operation of the DEF manifold portion of the dosing system.
The DEF lines are connected to the dosing cabinet.
The DEF supply line is routed from the remote customer tank to the DEF inlet on the dosing cabinet.
The DEF injector supply line is routed from the outlet of the dosing cabinet to the DEF injector on the Clean Emissions Module (CEM).
Both of these lines are supplied by the customer.
Protect Mode Against Cold (defreeze)
The system will enter protect mode against cold for either of the following:
- DEF manifold temperature drops below
−5° C (23° F) - DEF tank temperature drops below
−10° C (14° F)
Temperature sensors are monitored to indicate if there is a freeze potential for the DEF. Heaters are utilized to prevent the freezing of DEF.
While in this mode the DEF buffer tank automatic filling is disabled.
Upon completion of the protect mode against cold, the process will continue on to preparing dosing readiness.
The Selective Catalyst Reduction (SCR) dosing system checks the operations of the air assist valve, DEF control valves, and DEF dosing pump.
The system will annunciate a fault code for any unexpected voltage, current, or pressure values.
The system will continue to cycle the valves until all indications determine the system is ready to dose DEF.
Step 1 Preparing Dosing Readiness
The air assist valve is energized causing the valve to open. The resulting air pressure is measured at the DEF pressure sensor. The DEF buffer tank return valve is energized causing the DEF buffer tank return valve to close.
This action is taken to check for the following conditions:
- Blockage in the DEF or Air lines
- Stuck Open DEF buffer tank return valves
- All air lines and DEF lines are present and properly connected
- Leak in DEF or Air lines
- Plugged DEF injector
Step 2 Preparing Dosing Readiness
The DEF buffer tank return valve is de-energized causing the valve to open. The expected result is a drop in pressure at the DEF pressure sensor.
If a pressure drop does not occur, the DEF buffer tank return valve may be stuck. A code will be set and the system will return to the dormant state.
Step 3 Protect Against Heat/Priming
The air assist valve is de-energized causing the valve to close. This action reduces the back pressure on the DEF dosing pump.
The DEF dosing pump is commanded on by the SCR system ECM and circulates DEF back into the DEF buffer tank. This action primes the DEF dosing pump.
Step 4 Protect Against Heat/Priming
The DEF buffer tank return valve is energized causing the valve to close. This results in the pump priming DEF to the injector.
The air assist valve is energized causing the valve to open. Once DEF pressure indicates a complete system prime, the SCR dosing system will move on to normal dosing operation.
Note: While in "Preparing Dosing Readiness", "Protect Against Heat/Priming" mode and "Protect Against Cold" mode the DEF buffer tank automatic filling is disabled. If the system fails to build sufficient pressure in Step 4, the system will return to Step 3 multiple times in an attempt to build pressure. If the system still cannot build pressure, an event code will be set and the system will return to the dormant state.
If the exhaust temperature has reached
While in this mode the DEF buffer tank automatic filling is enabled. The tank will fill if the level sensor indicates that a fill is necessary to maintain a sufficient DEF level.
While in this mode the DEF buffer tank automatic filling is disabled.
When any dosing component that is required to maintain proper NOx reduction fails, a code will be set. If the condition goes away, the dosing process will resume. The dosing system will automatically purge from the injector to the DEF buffer tank as long as 24V is still provided to the dosing control cabinet.
This will happen if a code is set during normal dosing, exhaust temperatures drop below a threshold, or engine speed drops below a certain threshold set in software.
Note: Permanent Purge (SHUTOFF): If there is an issue detected within the dosing pump, pump power relay, or emergency breaker switch the system will enter permanent purge. The air valve will be open and return valve will be open, causing the DEF to return to the DEF tank. Once the condition causing this state is healed, the DC breaker will have to be power cycled to reset the system.