Electronically Controlled Common Rail System of Diesel Generator

The electronically controlled high-voltage common rail technology is an electronically controlled technology commonly used by the diesel generator industry to meet the national three emission standards. The main difference between the EFI diesel generator and the traditional diesel generator is its the fuel supply system is different. The former uses an electronically controlled fuel system, while the latter uses a mechanical fuel system. At present, the electronically controlled fuel system can be divided into the following three types:

1. Electronically controlled in-line pump fuel system;

2. Electric control distribution pump fuel system;

3. Electronically controlled high pressure common rail fuel system.

At present, the electronically controlled common rail system of diesel generator sets is mainly composed of high pressure fuel pump, high pressure fuel rail, high pressure fuel pipe, high pressure fuel pipe connection, electronically controlled fuel injector, low pressure fuel pipe, diesel filter and fuel tank.

1. Electronically controlled high pressure oil pump

(1) High pressure oil pump of Denso common rail system

The high-pressure oil pump has two high-pressure plunger pumps, the oil pump at the flywheel end and the oil pump at the front end. Driven by two cams (3 flanges on each cam), the fuel required by the six-cylinder is supplied to the high-pressure rail on time.

(2) Hand oil pump

The hand oil pump is used to discharge the air in the oil circuit in the fuel injection system. The oil transfer pump is located on the left side of the high-pressure oil pump and is integrated with the high-pressure oil pump to provide fuel with a certain pressure of the high-pressure oil pump. The two yellow valve bodies located on the upper part of the oil pump are pressure control valves (PCV), which control the oil supply amount and oil supply time of the two pumps respectively. Each of the two solenoid valves corresponds to a wiring harness plug, the valve (PCV1) near the flywheel and the valve (PCV2) near the front. Its function is to adjust the fuel pressure in the common rail pipe by adjusting the amount of fuel that the oil pump presses into the common rail pipe.

(3) Camshaft position sensor (G sensor)

The camshaft position sensor is used to judge the arrival time of the compression top dead center of the first cylinder of the diesel generator as a reference signal for fuel injection. A camshaft position sensor and two corresponding signal discs are integrated in the high-pressure oil pump. The plug of the camshaft position sensor is located in the middle of the front of the oil pump.

When the plunger goes down, the pressure control valve opens, and the low-pressure fuel flows into the plunger cavity through the control valve.

When the plunger goes up, because the control valve is not energized yet, it is in the open state, and the low-pressure fuel flows back to the low-pressure chamber through the control valve.

When the timing of fuel supply is reached, the control valve is energized to close it, the return oil circuit is cut off, the fuel in the plunger cavity is compressed, and the fuel enters the high-pressure fuel rail through the fuel outlet valve. Use the difference in the closing time of the control valve to control the amount of oil entering the high-pressure rail, so as to achieve the purpose of controlling the pressure of the high-pressure rail.

After the cam has passed the maximum lift, the plunger enters the descending stroke, the pressure in the plunger cavity is reduced, the oil outlet valve is closed, and the oil supply is stopped. At this time, the control valve stops the power supply, and is in the open state. next cycle.

2. High pressure common rail pipe assembly

The high-pressure common rail pipe supplies the high-pressure fuel provided by the fuel supply pump to the fuel injectors of each cylinder after being stabilized and filtered, and acts as a pressure accumulator. Its volume should reduce the oil supply pressure fluctuation of the high-pressure oil pump and the pressure oscillation caused by the injection process of each injector, so that the pressure fluctuation in the high-pressure fuel rail is controlled below 5MPa.

(1) The function of the rail pressure limiting valve is that when the common rail pressure exceeds the maximum pressure that the common rail pipe can withstand, the rail pressure limiting valve will automatically open to reduce the common rail pressure to about 30MPa.

(2) There are six flow limiting valves (same as the number of cylinders) on the upper part of the common rail pipe, which are respectively connected to the high-pressure oil pipes of the six cylinders. When the high-pressure fuel pipe of a certain cylinder leaks or the fuel injector fails and the fuel injection address exceeds the limit, the flow limiting valve will act to cut off the fuel supply of the cylinder. There are 1~2 oil inlets on the outside of the common rail, which are respectively connected with the oil outlet of the high pressure oil of the high pressure oil pump. The rail pressure sensor is located on the right side of the common rail with a harness connector.

3. Common rail system control system

The electronically controlled common rail system can be divided into three parts: sensors, computers and actuators.

The computer is the core part of the electronically controlled common rail fuel system. According to the information of each sensor, the computer calculates and completes various processing, finds the best injection time and the most suitable fuel injection quantity, and calculates when and for how long to open the fuel injector. Solenoid valve, or the command to close the solenoid valve, etc., so as to precisely control the working process of the diesel generator. The core of the electronic control system is ECU - electronic control unit. An ECU is a microcomputer. The input of the ECU is various sensors and switches installed on the generator set and diesel generator; the output of the ECU is the electronic information sent to each actuator.

4. Common rail system fuel supply system

The main components of the fuel supply system are the fuel supply pump, the common rail and the fuel injector. The basic working principle of the fuel supply system is that the fuel supply pump pressurizes the fuel to high pressure and feeds it into the common rail; the common rail is actually a fuel distribution pipe. The fuel stored in the common rail is injected into the diesel generator cylinder through the injector at the appropriate time. The fuel injector in the electronically controlled common rail system is a fuel injection valve controlled by a solenoid valve, and the opening and closing of the solenoid valve is controlled by a computer.