National VI Postprocessing System Decryption

1. Aftertreatment system: configuration route

【 DOC 】: Heating exhaust gas to assist in active regeneration of DPF; Manufacturing NO2 to assist in passive regeneration of DPF and improve SCR efficiency
[DPF]: Wall flow particle trap
SCR+ASC: Catalytic reducer+ammonia trap
Bosch DNOx2.2 system: urea pump, urea pipe, urea nozzle HCI system: during regeneration, fuel is injected before DOC to increase exhaust temperature, MU (supply unit) and IU (injection unit)
【 Sensor 】: Exhaust temperature sensor * 4
Nitrogen oxide sensor * 2
PM sensor * 1
Differential pressure sensor * 1
Urea tank liquid level temperature quality sensor assembly * 1
SCR heating system: cooling water valve, heating urea pipe
【1】 DOC+CDPF+SCR+ASC
【2】 Copper based molecular sieve efficient SCR (Cu Zeolite)
【3】 DPF regeneration: A control strategy combining passive regeneration and active regeneration (HCI) to meet the safe and reliable regeneration requirements of different engineering applications

2. Introduction to MIL Lamp
According to the requirements of GB17691-2018, there is a Mil light on the instrument panel to indicate emission related faults.
The difference between National VI MIL lamp and National V lamp: The display status of National VI MIL lamp is more complex, but it is no longer directly related to emission limits.
The OBD system is used to monitor and control emission control systems. Based on the different impact of each fault on emissions, all emission related faults can be divided into four categories: Class A, Class B1, Class B2, and Class C. The OBD system responds with four different MIL lamp activation modes based on different fault types.
3. Sensors
National VI post-processing system, including the following individual sensors: (Sensors integrated in each subsystem are introduced in the subsystem)
DOC front temperature sensor (new)
DPF front temperature sensor (new)
SCR front temperature sensor (National V)
SCR rear temperature sensor (new)
DPF differential pressure sensor (new)
SCR front nitrogen oxygen sensor (new)
SCR post ammonia oxygen sensor (National V)
PM sensor (new)
Urea mass liquid level temperature sensor assembly (new)
PM sensor principle
The PM sensor is used to monitor the efficiency of DPF, and the measurement principle is to utilize the conductivity of particulate matter to the finger current.

Introduction to Differential Pressure Sensors
The pressure difference sensor is used to monitor the pressure difference between the two ends of the DPF. When there is too much carbon accumulation in the DPF, the high pressure difference fault will be activated. When the high pressure difference fault in the DPF is activated, the active regeneration of the DPF is disabled.

Sensor related faults can be classified into the following categories:
1. Circuit fault: simple open circuit, short circuit, etc
2. CAN fault: PM, NOx, urea quality/liquid level/temperature sensor hardware adopts CAN communication
3. Rationality failure: Refers to sensor failure or system issues that result in unreasonable measurement values. 4. Sensor self diagnosis failure: such as PM sensor self diagnosis temperature too high
among
1. Circuit faults have a high probability of occurrence and can be easily identified through wiring harness drawings.
2. CAN faults have a low probability of occurrence, and it is generally necessary to investigate factors such as CAN wires, resistors, and CAN interference.
3. Sensor self-diagnostic faults have a low probability of occurrence, usually due to sensor damage.
4. Reasonability failure, when the sensor drifts, or the sensor is installed incorrectly, or there is a system issue that causes the measured value to be unreasonable, will cause a rationality failure to be reported.
Among them, categories 1, 2, and 3 are basically the same as those in country 5, with a focus on troubleshooting circuit and sensor faults. There are fewer rationality type faults in country 5, but in country 6, almost all sensors and actuators need to be diagnosed. If a rationality type fault occurs, it is necessary to troubleshoot misinstallation, system faults, sensor drift, CAN interference, etc.