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 revs. One of the main components of the diesel engine fuel system is the pump. Its design includes a plunger pair of injection pumps. What is this part and what is it for? We will talk about this in our today's article.
Characteristic
The high pressure fuel pump is based on a special pump section. It includes a plunger (piston) and a cylinder shaped like a small sleeve. This pair of parts is made from high strength steels because it works under high pressure.
The injection pump plunger pair performs the function of creating fuel pressure necessary for its further atomization in the combustion chamber. Note that this mechanism ishigh precision. The main characteristic of the injection pump plunger pair (including Zexel) is the exact dosage of fuel and the regulation of its pressure.
Device
This knot consists of two grooves:
- Spiral.
- Longitudinal.
The pair itself includes 4 sleeves and 5 plungers. In the first there are 2 channels - bypass and supply. Both are connected to each other with a combustion chamber. Above the plunger pair is a fitting with a landing cone.
Due to the high precision of the processing of the inner cylinder, the plunger pair of the injection pump can operate under pressure up to 200 MPa. The characteristics of such pumps are several times higher than those of conventional piston injection pumps.
Fuel dosage is due to plunger strokes. So, the amount of the 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 interface between the inner and outer surfaces of the cylinder should not exceed 3 microns.
The plunger pair of injection pump has a rail in the housing. It drives the gear sector. Thanks to this, the bushing (cylinder) itself is controlled. The rail is moved by the crankshaft rotation regulator. In this way, the dosage of the cyclic feed is achieved without changing the stroke of the plunger.
Working principle
The algorithm of the mechanism is based on the reciprocating movements of the two main parts. This is a cylindrical piston and a bushing. During reciprocating movementsfuel is drawn into the pump. 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 dose the fuel and supply it to the cylinders. In addition to the exact volume, this fuel should only enter the cylinders at a certain moment. In order for the mechanism to work without failures, high technical requirements are placed on this pair of mechanisms.
Thus, during the operation of the injection pump, the high-pressure channels between the plunger and the fuel line are blocked. This achieves a reduction in fuel pressure, which is necessary for fast and accurate closing of the nozzle nozzles. This operation of the mechanisms prevents the appearance of drops of fuel. 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 cyclic. It occurs until the moment when the plunger does not start its working stroke again.
User Requirements
The Bosch injection pump plunger pair is a mechanism that requires special attention during operation. In particular, this concerns the quality of the fuel used. When operating a plunger pair, it is worth excluding 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 workingthe surface of the plunger and sleeve, the lubricating film loses its integrity. As a result, the friction force of the pair of elements increases. This leads to heating and subsequent deformation of the parts.
As for the dust particles, they can cause the plunger mechanism to wedge. After all, the working clearance between the cylinder and the piston is 0.0018 mm. It is worthwhile to diagnose parts in time to prevent their premature failure. We also note that the plunger pair of high pressure fuel pump 4d56 changes in a complex way. This is due to the high precision of manufacturing parts.
Fault details
A common defect is plunger sticking 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 traces of corrosion on the working surface leads to loss of tightness. Such a malfunction is eliminated by reassembling the mechanism. How do they do it? The sleeve and plunger are ground to a roughness of 0.1 µm. Permissible taper should not exceed 0.4 µm, and ovality - 0.2 µm. Next, the injection pump plunger pair is divided into size groups with an interval of 4 microns. Parts are selected according to the corresponding bushings. After grinding, the mechanism is washed in gasoline and assembled 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 intake window. In this case, the wear of the working surface of the sleeve is measured. Determine the taper and ovality of the hole. If the parameter is notcorresponds to the norm, the element must be replaced. Metal chipping or chipping are defects that cannot be repaired.
How do malfunctions of the injection pump plunger pair manifest themselves? This can be determined by a decrease in engine power and increased fuel consumption. There is also an unstable idling of the engine.
Conclusion
So, we found out what a plunger pair is. This is an integral part of diesel fuel pumps, which operates under high pressure and doses fuel with high accuracy. The main requirements for operation are high-quality fuel. The operation of the plunger is detrimental to water and dirt, which accelerates corrosion processes and leads to scoring.
