What are the changes in the power system of light-duty trucks according to the National VI standard?

1、 Engine body: comprehensive upgrade of combustion, intake, and electronic control
a. High precision common rail fuel system
Increased fuel injection pressure, more fuel injection times (pre injection, main injection, post injection), better fuel atomization, and more complete combustion; Some models have added HC injection (seventh injector) to the exhaust pipe, which is specifically used for DPF regeneration and warming up, but this structure is basically not available in National V vehicles.
b. Air intake system upgrade
Add/optimize EGR exhaust gas recirculation valve, intake throttle valve, air flow meter, introduce some exhaust gas to reduce combustion temperature in the cylinder, and reduce NOx original emissions; The turbocharger has been recalibrated, with a focus on * * low-speed high torque * *, providing better power response for low-speed starting and climbing.
c. Optimization of cylinder structure
Redesign the combustion chamber, piston, and cooling system, popularize the four valve structure, and fine tune the compression ratio; The engine body and cylinder head are reinforced to withstand higher explosive pressures.
d. Significant upgrade of ECU electronic control system
ECM computer has stronger computing power, integrated control of engine and post-processing, and real-time linkage; The OBD onboard diagnostic system is more stringent, monitoring emissions throughout the entire process. Once emissions exceed the standard, it directly triggers torque and speed limits, and the monitoring intensity of National V OBD is much lower.
2、 Post processing system (the biggest modification of China VI Power)
National V diesel light trucks generally only have DOC+DPF (some National V vehicles do not have DPF);
National VI standard: DOC+DPF+SCR+ASC ammonia escape catalyst * * complete series after treatment assembly, which is part of the power exhaust system:
-DOC: oxidation catalyst, oxidizes CO and HC;
-DPF particulate trap: captures carbon particulate matter and requires driving/on-site regeneration;
-SCR urea injection system: Inject urea to reduce nitrogen oxides NO ₓ;
-ASC: Ammonia escape catalyst, eliminating excess ammonia gas;
-A large number of new sensors have been added, including nitrogen and oxygen sensors, differential pressure sensors, multiple temperature sensors, PM particulate matter sensors, and urea quality sensors, to monitor exhaust gas status in real-time.
3、 Changes in power output characteristics
a. Calibration bias towards low-speed torque
The same displacement National VI model has greater low-speed torque, stronger starting and climbing sensation under heavy loads; But to protect post-processing, the ECU will limit high-speed rough detonation.
b. Increased exhaust back pressure
The entire post-processing pipeline is longer, with more carriers and increased exhaust resistance. Continuous and uniform long-distance travel has minimal impact; Frequent start stop short distance driving in urban areas may slightly increase fuel consumption.
c. Protection strategy (limited torque/speed)
The unique protection logic of National VI includes: insufficient urea, DPF blockage, sensor failure, and excessive emissions. The ECU directly limits the engine power output to prevent damage to post-treatment. National V has almost no such strong power locking mechanism.
4、 Transmission and vehicle matching
The transmission and rear axle speed ratios will be recalibrated to match the low-speed and high torque characteristics of the engine; Many car models optimize the shifting range to reduce engine high load operation and lower the burden of post-processing.