The oil metering valve unit aliases are IMV valve, EFC/MEUN valve, SCV valve, PCV valve. The housing of the fuel metering valve is usually made of pure iron by deep drawing. The name is different according to each manufacturer. But his goal is to control the oil intake and return flow of the high-pressure pump, so as to control the oil supply of the oil pump plunger to the rail, meet the set pressure of the common rail system, and form a closed-loop control of the rail pressure with the rail pressure sensor.
It is generally integrated on the high-pressure fuel pump and is directly controlled by the ECU computer. Its plug is composed of 2 wires, one is the high-end signal voltage terminal and the other is the low-end signal voltage terminal. The high end is a digital voltage of 24V, and the low end is a digital voltage of 3.5V.
The fuel metering valve is a proportional solenoid valve, usually installed at the fuel inlet position of the high-pressure fuel pump, and controlled by the PWM signal output by the ECU; the ECU controls the opening of the fuel metering valve by changing the duty cycle of the PWM signal to control The amount of fuel entering the plunger controls the common rail pressure.
Different models of common rail electronically controlled diesel engines have slightly different fuel metering valve structures, characteristics, installation positions, and electrical interface forms depending on the applied high-pressure fuel pump models and specific control strategies. They must be repaired and replaced. Pay attention to the difference, especially according to the different characteristics of the default state (in the case of power failure), the fuel metering valve is divided into two types: normally open and normally closed. In practical applications, it can be judged according to whether there is a pressure relief valve on the common rail pipe: general commercial vehicle platform engine common rail pipe has a pressure relief valve, and its fuel metering valve is normally open; passenger vehicle platform engine common rail pipe There is no pressure relief valve, and its fuel metering valve is normally closed.
For the normally open fuel metering valve, the default working state is normally open, and the flow is the largest when not energized; on the contrary, for the normally closed fuel metering valve, the default working state is normally closed, and the flow is the smallest when the power is off.
Every metering valve will have a failure situation. The following are the matters that should be paid attention to when repairing the metering valve.
1. The fuel metering valve is worn or stuck due to the failure of the fuel system oil circuit itself, such as fuel quality, fuel pump wear and other reasons. When replacing the new fuel metering valve, the entire fuel system oil circuit must be checked at the same time. Check, clean and replace fuel that meets the standards.
2. Because the huge pressure generated when the high-pressure fuel overflows may cause serious damage to the skin and eyes, and the leaked high-pressure fuel may be ignited when encountering high-temperature parts of the engine or the exhaust system, and there is a danger of fire. Therefore, when performing any operations on the high-pressure fuel system including fuel metering valves and its corresponding components, the disassembly and assembly specifications provided by the manufacturer must be followed.
3. Never disassemble or assemble the fuel metering valve when the engine is running.
4. Before checking and disassembling high-pressure fuel components, make sure that the residual fuel pressure has been completely eliminated.
5. The high-pressure fuel system can be overhauled only when the engine is cold. Pay special attention to this when you need to disassemble high-pressure oil pipelines and parts.
6. There are two types of fuel metering valves: normally open and normally closed. Pay special attention to them during maintenance.
7. In the process of disassembly, inspection, transportation and installation of the high-pressure fuel pump or fuel metering valve, care must be taken to avoid improper load and to protect the relevant fuel interface.