Working Principle Of Diesel Engine Electronic Control Pump (Electronic Fuel Injection Pump / Electronic Speed Control Pump)

 

Today, let's talk about the working principle of diesel engine electronic control pumps (electronic fuel injection pumps/electronic governor pumps):

 

First, distinguish between the two types of 'electronic control pumps':

 

1. Position-type electronically controlled inline pump/distributor VE pump (National II upgraded version, the most common old electronic control pump): The piston pump body structure for pumping oil is exactly the same as a mechanical pump, but the mechanical governor is removed and replaced with an ECU-controlled actuator. The ECU simply adjusts the fuel quantity by electronically moving the pump rack.

 

2. Time-type electronic control pump (electronically controlled unit pump/electronically controlled distributor pump/pump nozzle, mainstream National III): Retains the plunger cam for pumping oil, but uses a solenoid valve to directly control the timing of high-pressure oil leakage. The ECU directly determines 'when to inject fuel and for how long,' providing higher precision.

 

In general: The mechanical pump body is responsible for generating high-pressure oil; the electronic control system is responsible for precisely controlling fuel quantity and injection timing.

 

Ⅱ. The complete set of three core systems (general architecture)

 

1. Sensor Collection Layer (real-time condition reporting to ECU)
- Speed sensor: measures real-time speed of flywheel/gear ring;
- Throttle pedal position sensor: driver's throttle demand;
- Water temperature, intake pressure/temperature, oil pressure, and rack position feedback sensors;
- Camshaft phase sensor: sets reference for injection timing.

 

2. ECU Control Core (the brain)
Built-in calibration MAP (optimal parameters for vast operating conditions), receives all sensor signals, calculates in real-time: 1) how much fuel to inject currently; 2) how many degrees to advance injection; outputs electric signals to drive actuators.

 

3. Actuators (replacing mechanical governors with electronic control)
Divided into position-type actuators and solenoid valve time-control types.

 

Ⅲ. First type: Position-type electronic fuel injection pump (old inline/VE electronic pump, closest to mechanical pump)

1. Pump body oil flow process (identical to mechanical plunger pumps)

Cam drives plunger down to draw fuel → up stroke seals to build pressure → delivery valve opens to pump oil → diagonal slot returns oil to relieve pressure, basic pump oil circulation unchanged;

 

the only difference: the plunger rack is pulled by an electronic actuator instead of a flyweight spring.

 

2. Electronic closed-loop speed control process

1. Sampling: speed sensor measures actual engine speed, throttle pedal reports driver demand;

2. ECU comparison calculation: compares actual speed/load with target value via PID, calculates how far the rack needs to move;

3. Execution: ECU outputs current to drive linear solenoid/stepper motor, moving the pump rack;

- Rack moves right → plunger diagonal slot delays return → supply stroke lengthens → injection amount increases;

- Rack moves left → return early → reduces fuel supply;

- Cut-off position: rack moves to zero fuel position, engine stops;

4. Position closed-loop feedback: rack has displacement sensor, sends actual position to ECU for real-time correction, eliminating deviation.

 

3. Advantages over mechanical governor

Mechanical flyweight relies on centrifugal force, slow response, unstable idle, large speed drop under heavy load; electronic control responds in milliseconds, minimal speed fluctuation, multi-stage speed curves (idle/acceleration/heavy load/altitude compensation) can be preset.

 

4. Second type: Time-control electronic fuel injection pump (electronically controlled unit pump/VE pump, main type for China III standard)

Core innovation: no longer controls oil volume by plunger rotation, solenoid directly opens/closes spill path to control fuel supply duration.

 

1. Intake stroke: plunger moves down, diesel enters plunger chamber;

2. Pump dwell: plunger pushed up by cam, at this time spill solenoid remains energized to close spill port, plunger chamber sealed;

3. High-pressure injection: plunger continues up, pressure rises, opens injector to spray fuel;

4. Stop injection (key): ECU sets injection duration, solenoid de-energized to open spill path, high-pressure diesel in plunger chamber returns to low-pressure chamber, pressure drops sharply, injection immediately stops;

- Longer solenoid closed time → longer injection duration, more fuel;

- Solenoid closed shorter → less fuel;

5. Plunger moves down to reset, ready for next cycle.

 

Timing Control Extra Capability: The ECU adjusts the closing time of the solenoid valve based on engine speed, water temperature, and load, freely changing the fuel injection advance angle: increasing the advance angle when the engine is cold, and delaying/advancing it at high speed to optimize combustion, which is something a purely mechanical pump cannot achieve.

 

5. Complete Oil Circuit Flow:

Fuel tank → fuel pump → diesel filter → low-pressure chamber of the injection pump → plunger fuel intake → solenoid valve closes to cut off oil based on ECU command → plunger moves up to build high pressure → high-pressure oil pipe → injector atomizes fuel into the cylinder; the ECU opens the pressure relief valve as needed → pressure drops and injection stops.

 

 

6. Ultra-brief final summary

The plunger itself still relies on the cam to pressurize diesel (same principle as a mechanical pump); the only change is replacing the old flyweight spring mechanical governor with the ECU reading the entire vehicle's operating conditions, using an electric actuator/solenoid to precisely control the 'start of fuel injection and injection duration,' achieving fully intelligent closed-loop control of fuel amount and injection timing.