Knowledge of Fuel Injection Pumps

The structure of fuel injection pumps

Regardless of the fuel injection pump types, it is mainly composed of four parts: the oil pump mechanism, the oil supply adjustment mechanism, the driving mechanism, and the fuel injection pump body. Among them, the oil pump mechanism includes plunger couplings, oil outlet valve couplings, etc.; the oil supply adjustment mechanism refers to the rack type oil volume adjustment mechanism or the fork type oil volume adjustment mechanism; the driving mechanism includes camshafts, tappet components, etc. ; while the fuel injection pump body is the installation base of the above three, and it is required to have sufficient strength, rigidity and tightness, and it is easy to disassemble, adjust and maintain.

The working principle of fuel injection pumps

Oil suction process

The plunger is driven by the cam of the camshafts, when the convex part of the cam leaves the plunger, the plunger moves down under the action of the plunger spring, the volume of the oil chamber increases and the pressure decreases. When the radial oil inlet hole of the pump is exposed, the fuel in the low pressure oil chamber flows into the pump chamber along the oil inlet hole.

Oil pump process

When the protruding part of the cam pushes up the plunger, the volume in the pump chamber decreases, the pressure increases, and the fuel flows back to the low-pressure oil chamber along the radial oil hole on the plunger sleeve; when the plunger up until the radial oil hole on the plunger sleeve is completely blocked, the pressure on the pump chamber increases rapidly; when this pressure overcomes the pre-tightening force of the oil outlet valve spring, the oil outlet valve moves upward; when the decompression ring leaves the valve seat, the high-pressure diesel will be pumped into the high-pressure oil pipe and sprayed into the cylinder through the fuel injector.

Oil return process

 As the plunger continues to move up, when the inclined groove on the plunger communicates with the radial oil hole on the plunger sleeve, the fuel in the pump chamber will pass through the axial oil passage on the plunger. The oil passage and the oil hole on the plunger sleeve flow back to the low-pressure oil chamber, and the pump oil stops.

The function of the fuel injection pump

a. Increase oil pressure (constant pressure): increase the oil injection pressure to 10MPa~20MPa.

b. Control fuel injection time (timing): fuel injection and stop fuel injection at specified time.

c. Control the fuel injection quantity (quantitative): change the fuel injection quantity to adjust the speed and power of the diesel engineaccording to the working condition of the diesel engine.

The requirement of the fuel injection pump

a. Fuel is supplied according to the working order of the diesel engine, and the fuel supply to each cylinder is even.

b. The fuel supply advance angle of each cylinder should be the same.

c. The oil supply duration of each cylinder should be equal.

d. The establishment of oil pressure and the stop of oil supply must be rapid in case of any dripping.