The opening of the pressure limiting valve is divided into two situations: active opening and

passive opening.

Active opening

When receiving fault information from some related components, the engine electronic control unit (ECU) will execute a protection strategy and instruct the pressure limiting valve to open (even if the rail pressure is not too high), thereby avoiding serious engine failure. Which component fault information will trigger the ECU to execute a protection strategy?

1. Rail pressure sensor signal

When the rail pressure sensor sends a rail pressure over-limit signal to the ECU, whether it is too high or too low, it will cause the ECU to execute a protection strategy and open the pressure limiting valve. There are many reasons for the track pressure sensor to report a fault message. The essence is abnormal oil inlet pressure or oil return pressure, such as insufficient oil supply in the low-pressure oil line, wear of the high-pressure pump, poor sealing of the pressure-limiting valve, and excessive oil return volume from the injector. Oil line is clogged, etc.

2. Fuel metering valve failure signal

In order to improve efficiency, the high-pressure pump of the common rail system is equipped with a metering unit for fuel quantity control, namely a fuel metering valve. It controls the oil pressure in the high-pressure rail by regulating the amount of oil entering the high-pressure pump. The ECU controls the metering unit by changing the duty cycle inside the metering unit through pulse signals. When the metering valve fails, it means that the ECU cannot complete accurate control of the rail pressure. Therefore, once it receives fault information related to the metering valve, such as short circuit, open circuit fault, or abnormal temperature fault, the ECU will implement a protection strategy to limit the The pressure valve will also open.

3. Sensor power supply module 3 fault signal

The sensor power supply module 3 provides 5V power supply for multiple sensors, including rail pressure sensors. When the sensor power supply module 3 fails, it means that all the sensors it is responsible for may work abnormally. Therefore, once the ECU receives fault information related to the sensor power supply module 3, it will execute the protection strategy and the pressure limiting valve will therefore open.

4. ECU related faults

As the commander-in-chief of the common rail system, the consequences of ECU failure can be imagined. Therefore, when the system detects ECU-related fault information, it will also implement a protection strategy.

Passive opening

Common reasons for passive opening include: fuel metering valve or relief valve failure, high-pressure pump failure, rail pressure sensor damage resulting in rail pressure out of control, oil return pipe blockage, etc.