Recently, more and more people began to use diesel cars. And there are reasons for that. So, this is a high compression ratio, low fuel consumption, good traction at low speeds. One of the main components of the fuel system of a diesel engine is a pump. Its design includes a plunger pair of injection pump. What is this part and why is it needed? We’ll talk about this in our article today.
Characteristic
The high pressure fuel pump is based on a special pump section. It includes a plunger (piston) and a cylinder in the form of a small sleeve. This pair of parts is made of high strength steels because it operates under high pressure.
The plunger pair of the high-pressure fuel pump performs the function of creating the fuel pressure necessary for its further atomization in the combustion chamber. Note that this mechanism is highly accurate. The main characteristic possessed by the injection pump plunger pair (including Zexel) is the exact dosage of the fuel and the regulation of its pressure.
Device
This node consists of two grooves:
The pair itself includes 4 sleeves and 5 plungers. In the first are 2 channels - bypass and lead. Both are interconnected with a combustion chamber. Above the plunger pair is a fitting with a landing cone.
Due to the high accuracy of processing the inner cylinder, the injection pump plunger pair can operate under pressure up to 200 MPa. The characteristics of such pumps are many times higher than those of conventional piston injection pumps.
Fuel is dosed due to plunger strokes. So, the amount of mixture can vary up or down depending on the mode of operation of the motor. The requirements for the assembly of these elements are quite high - the conjugation between the inner and outer surfaces of the cylinder should not exceed 3 microns.
The plunger pair of the injection pump has a rail in the housing. It sets in motion a gear sector. Due to this, the sleeve itself (cylinder) is controlled. The rail is moved by the crankshaft rotation regulator. This achieves the dosage of cyclic feed without changing the stroke of the plunger.
Principle of operation
The algorithm of the mechanism is based on the reciprocating movements of the two main parts. This is a piston of cylindrical shape and a sleeve. During reciprocating movements, fuel is sucked into the pump. The injection occurs through special holes on the sleeve. Note that the main task of the operation of such a mechanism as a plunger is to meter the fuel and supply it to the cylinders. In addition to the exact volume, this fuel should enter the cylinders only at a certain point. In order for the mechanism to work without failures, high technical requirements are imposed on this pair of mechanisms.
Thus, during the operation of the high pressure fuel pump, the high pressure channels overlap between the plunger and the fuel line. This achieves a reduction in fuel pressure, which is necessary for quick and accurate closure of
atomizer nozzles. This operation of the mechanisms prevents the appearance of fuel droplets. When the injection stroke occurs, the discharge valve cone rises. Further, high-pressure fuel is supplied to the atomizer passing through the valve holder and fuel lines. When the drain channel is opened, the pressure in the chamber decreases. A spring on the discharge valve presses the plunger body against the seat. This process is cyclical. It occurs until the moment when the plunger does not restart its working stroke.
Operating requirements
Bosch injection pump plunger pair is a mechanism that requires special attention during operation. In particular, this relates to the quality of the fuel used. When working with a plunger pair, it is necessary to exclude the presence of water and dust particles in the fuel. Why are such high demands placed on this mechanism? Everything is very simple. When water enters the working surface of the plunger and sleeve, the lubricating film loses its integrity. As a result, the friction force of a pair of elements increases. This leads to heating and subsequent deformation of the parts.
As for the dust particles, they can cause a wedge of the plunger pair mechanism. After all, the working clearance between the cylinder and the piston is 0.0018 millimeters. It is time to diagnose parts in time to prevent their premature failure. We also note that the plunger pair of the injection pump 4d56 varies comprehensively. This is due to the high accuracy of manufacturing parts.
Fault Details
A common defect is a stuck plunger in the cylinder. How to diagnose the mechanism? To do this, check the stroke of the plunger in different positions when installing the pair at an angle of 45 degrees. The presence of corrosion on the working surface leads to a loss of tightness. Such a malfunction is eliminated by re-assembly of the mechanism. How do they do it? The bushing and plunger are rubbed to a roughness of 0.1 μm. Permissible taper should not exceed 0.4 microns, and ovality - 0.2 microns. Next, the plunger pair of high pressure fuel pump is divided into size groups with an interval of 4 μm. Details are selected according to the corresponding bushings. After lapping, the mechanism is washed in gasoline and collected back.
The next defect is chipping or chipping at the holes. May be accompanied by scratches, scuffs and an increase in the diameter of the inlet window. In this case, the wear of the working surface of the sleeve is measured. The conicity and ovality of the hole are determined. If the parameter is not correct, the element must be replaced. Metal spalling or chipping are defects that cannot be repaired.
How are the malfunctions of the plunger pair of the injection pump? This can be determined by reducing engine power and increased fuel consumption. Unstable engine idling is also observed.
Conclusion
So, we found out what a plunger pair is. This is an integral part of diesel engine fuel pumps, which operates under high pressure and dispenses fuel with high accuracy. The main requirements for operation are high-quality fuel. Water and dirt are detrimental to the operation of the plunger, which accelerates corrosion processes and leads to scoring.