Research and Analysis of the Sealing and Lubrication of the Injector Pump Plunger

Plunger coupling is one of the most important and precise components in the fuel injection pump assembly. Its clearance has a great influence on the fuel supply and injection pressure of the fuel injection pump. With stricter emission regulations, in-line fuel injection pumps are designed to improve the spray atomization parameters such as fuel spray cone angle, penetration, and mist size, so that fuel and air can be better mixed in the combustion chamber, and the combustion can be more complete. Improving injection pressure is a major measure. With the increase of the injection pressure, the sealing and lubrication problems of the plunger parts are even more prominent.

The hydraulic friction pair requires three functions, namely sealing, lubrication and hydraulic action. The slipping mating surface of the coupling should form a proper oil film so that the oil film acts as a lubricant. If the oil film is too thin or unformable, the friction pair will wear out or burn out. If the oil film is too thick, it will also affect the sealing effect, resulting in a large amount of fuel leakage, reducing the compression efficiency, and even unable to establish the oil quantity and performance requirements of the fuel injection pump. pressure. Therefore, the formation of oil film and its changes are crucial for the lubrication and sealing of the plunger coupler.

1 Oil film theory 11 Coupling friction analysis According to the general theory of friction, the frictional power loss (A) and the relative sliding speed (U), the positive pressure (F), and the friction coefficient (/integral ratio) between sliding surfaces are shown in the following formula. : Among them, with different oil film and lubrication state formed between friction pairs, f is not the same: pure liquid lubrication (complete oil film)/=0 001~001 boundary lubrication (part of oil film)/=005~03 dry friction (no Oil film) 0 3 can be seen in the formation of the oil film between the friction pair. 2U 1 into the pure liquid lubrication or boundary film lubrication, f will be greatly reduced.

12 The analysis of the interstitial flow shows that the Reynolds number of fuel flow in the gap between the plungers is generally small, which belongs to the laminar flow category. There are two reasons for the movement of fuel in the gap: one is the flow due to the pressure difference, which is called differential pressure flow or Poiseuilfe flow; the other is that the fuel flow in the gap is caused by the relative movement of the walls that make up the gap. Cut flow or Couette flow. The superposition of the two is called the Couete Poiseuille flow.

The Hagen Poiseuille theory of laminar flow considers the flow rate change graph to be linear when fluid enters the annular gap. The velocity of the fluid on the side of the plunger sleeve is equal to the plunger sleeve movement speed, and on the plunger surface it is consistent with the plunger movement speed. The flow field in the mating gap is determined by two aspects: First, the shear flow velocity field is trapezoidal due to the difference in the relative movement speed of the parts; Second, due to the high pressure fuel in the plunger chamber, the fuel in the gap A gradient of a certain pressure is formed along the axial direction, and this pressure difference is particularly effective for the intermediate layer fuel except for the boundary layer, forming an axial differential pressure flow field. The two kinds of flow field synthesis eventually form parabolic velocity field distributions as shown. Based on this, it can be deduced that the leakage rate through the gap is calculated as follows: difference; L is the length of the leak; u is the plunger movement speed; Rb is the plunger center hole radius; Rp is the plunger radius.

13 Thermal Wedge Effect and Extrusion Effect Even if an oil film exists between the coupling parts, due to the relatively high-speed sliding of the friction surface, the conversion of the mechanical work consumed by this sliding friction force into heat will increase the temperature of the oil film. The increase in oil temperature produces three effects: a. The viscosity of the oil is reduced, the lubricity is reduced, the leakage is increased, and the oil temperature is too high and the oil is cracked and deteriorated; b. The other part of the heat energy will make the metal wall of the friction pair. Produce local temperature rise; c oil film thermal expansion due to temperature rise, so that it produces an additional pressure field, the pressure of the pressure of the composition of the site has the ability to support a certain external load, called the thermal wedge effect of the oil film.

The heat energy generated by the gap pressure differential flow will first warm up the liquid flow before it is conducted to the wall surface, so it can be regarded as an adiabatic process approximately. Thona derives the relationship between pure pressure differential current and temperature rise on the assumption that: at is the temperature difference between the outlet and the inlet; Ap is the pressure difference; p is the fuel density; it is the specific heat of the fuel.

F. Buckbrook's research suggests that the frictional heat generated by the liquid shear flow causes the liquid to rise in temperature, and the temperature rise causes the oil to expand and create an additional pressure field, thus constituting a hot wedge flow. Therefore, the shear flow in the case of this thermal effect is actually a combination of shear flow and thermal wedge flow. The temperature rise expression is: the viscosity and density of the fuel under conditions of pressure and pressure; hL is the gap between the Sealing length.

In actual work, differential pressure flow and shear flow act at the same time, and the temperature rise of oil is not a simple superposition of the two. When the differential pressure flow is orthogonal to the shear flow, the temperature rise is: When the differential pressure flow is in the same direction or in the opposite direction to the shear flow, the temperature rise is: /12W) The shear flow qc = bhu/2) The width (perimeter) c is equal volume heat.

The temperature rise caused by the combined action of shear flow and differential pressure flow forms an additional pressure field, which constitutes a new bearing capacity and can balance part of the applied load. The bearing capacity can be expressed by the following formula: The thickness of the oil film is closely related. The thinner the oil film, the higher the temperature rise and the corresponding carrying capacity.

The initial thickness of the oil film formed between the friction pairs is squeezed and thinned under the action of the external load. At the same time, a pressure field is formed between the friction pairs. The resultant force of the pressure field can balance the external load force. The effect of balancing the external load force produced by the squeeze film is called the squeeze effect of the oil film. The relationship between the oil film bearing capacity and the change of the film thickness produced by the piston extruding the oil film in the gap can be expressed by the following formula: d£/dt£ is the eccentricity of the plunger after transverse pressure and ££eA (e is eccentric Distance) is determined by the plunger fitting clearance and the oil film thickness.

From the above formula, it can be seen that the squeeze bearing capacity of the oil film increases with the increase of the eccentricity ratio, that is, the thickness of the oil film, and is related to the viscosity of the oil and the radius of the plunger. The thinner the thickness of the oil film, the greater the carrying capacity of the film, which is very favorable for us to use the oil film extrusion effect.

14 Minimum Oil Film Thickness The above discussed temperature rise under pure liquid rubbing conditions does not apply to boundary friction. The boundary film is extremely thin, and there are always rough peaks or fine particles in the fuel oil on the surface of the coupling part. Under the action of the load, the actual contact area of ​​the convex peak part is much smaller than the apparent contact area, and thus the contact of the convex peak part The stress is much higher than the average contact stress of the surface area. In this local area, the boundary film is peeled off, resulting in direct contact between the two metal surfaces. As the plunger slides at a high speed, the heat generated by the friction will cause a very high temperature rise at the contact peak, causing sticking and subsequent avulsion by the applied sliding torque. The process of sticking, avulsion, re-adhesion and re-avulsion is the process of adhesive wear of the frictional web. If the pressure and speed are further increased, the contact area and temperature rise of the peaks will also increase, resulting in a large area of ​​adhesion or gluing, so that the applied torque is not sufficient to abrade the contact parts again. The couple can no longer work.

From this analysis, there are mainly three factors that lead to the occurrence of “killing” of the coupling parts, namely the surface roughness of the parts, the fuel cleanliness and the coupling clearance. Dawson and Higginson conducted extensive numerical calculations on the isotherm contact isometric flow under various loads, speeds, and materials. Based on this, a practical minimum oil film thickness formula was proposed, and the pressure on the assembly was affected by the assembly. The stress and the fuel pressure during the movement cause the plunger and the plunger sleeve to deform due to the fluctuation characteristics during high-speed movement of the plunger. The total fluctuation amplitude may be greater than their gap value, thus destroying the oil film between them, causing boundary friction, and then producing a sticking phenomenon. He believes that the plunger's minimum process clearance (△ r) value should be greater than the possible deformation of the plunger sleeve and the plunger, and can ensure that the coupling has a good seal: when the amount of radial deformation; r. Plunger sleeve undulation deformation.

The above formula shows that the plunger sleeve assembly torque should be reasonable, the force should be uniform, in order to reduce the radial deformation; vibration intensity and the coupling size, material, assembly conditions and fuel pressure, plunger cavity pressure increases Rate stability and avoidance of abnormal camshaft vibration can effectively reduce the amplitude of the fluctuating coupling.

2 Gap fluid flow theory Due to the random vibration of the camshaft, the non-uniform lateral hydraulic pressure of the oil inlet and outlet holes, and the cyclic pressure increase and pressure release in the high pressure chamber, the annular gap between the plunger and the plunger sleeve is stored in the memory. In an unstable drain flow and lubrication flow (see), therefore, the laminar flow theory differs greatly from the measured ones, due to: a. The wall around the plunger is flexible, even when the plunger is stuck. With the increase of pressure, the crevice volume also has a large change; b. Pressure asymmetry causes the radial movement of the plunger, which causes the surface of the gap to move. The pressure in the gap during pressure boosting and pressure relief is significantly asymmetric, resulting in correspondingly sized radial pressure.

This unsteady flow creates an asymmetric gap pressure distribution, causing the radial movement of the plunger to cause the plunger to decenter and even skew. This increases the amount of fuel leakage and at the same time there is a risk that the gap pressure on one side will be too large and the plunger will seize.

Changes in pressure in the high pressure chamber over time and inhomogeneous movement of the plunger will produce unstable gap flow. At this time, the physical properties of the liquid (density and viscosity) change with the change of the local gap pressure, and the boundary of the gap is also due to the plunger sleeve wall. The expansion, the radial movement of the plunger, and the periodicity of the slot length change over time. The average circumferential velocity um of the fuel along the gap width in the gap flow and the mean axial velocity Vm are: Substituting the two into the continuous equation, and assuming that the flow is quasi-steady flow, the “corrected Reynolds lubrication equation” can be obtained.

In the case of plunger eccentricity, the gap width is represented by the average gap width h: the plunger eccentric position sees the dimensionless dimensioning of the parameters such as gap width and coordinates, y=y/Lh=hA., then the relative eccentricity represents To: Integrate the Reynolds lubrication equation along the entire loop gap, and obtain the basic differential equation used to calculate the force-axis distribution of the mean pressure on the circumferential surface: The p in the equation used to calculate the PKh sum is replaced with >, and the plunger is taken into account. When the boundary conditions at the entrance of the joint of the coupler plane are -H, =e and the boundary condition at the exit of the gap is equal to 0 = y, the equation can be obtained when the crack pressure distribution is solved from equation (1): Fuel density (P, Both the dynamic viscosity and the gap width (h) are calculated from the above two equations and the integral constant K1 can be calculated. Then the mass leakage rate from the drain slot can be calculated by the following equation: Yes: a is the fuel injection system at nominal speed 1 150rmin The result of the simulation of the gap 3 5n. It can be seen that the effect of the plunger leakage amount on the circulation supply is 23mm3. With the decrease of the oil supply amount, the injection pressure is reduced. It is shown that the maximum pressure difference between the two considered in the plunger chamber is 0.7 bar, which indicates that the leakage curve of the coupling part is in line with the pressure curve, and the pressure in the plunger chamber is larger, and the pressure difference between the coupling gaps is ~ The larger the leak, the greater the amount of leakage; b The speed of the plunger is related to the cam speed and the cam profile. Leakage rate increases as the plunger movement speed increases, but the maximum leakage does not occur at the maximum plunger movement speed. When the effective plunger stroke is completed (approximately 35° or so), the drain hole is opened. The pressure in the plunger chamber rapidly decreases, and the plunger speed continues to rise; 10 is divided into the plunger leakage amount when the clearance value is 35Mm, 5n, 6n. From the figure, it can be seen that the clearance value has a great influence on the leakage amount, and when the plunger coupler wears, the clearance increases, which will greatly reduce the circulating oil supply, especially when the diesel engine starts at low speed. Obviously insufficient. Therefore, it is more appropriate for the maximum clearance of the plunger fitting to be controlled within 3.5Mm; at 7°, the pressure in the plunger chamber reaches a maximum of 9966bar and the deformation of the plunger sleeve also reaches a maximum value of 11Mm at the same time. Change in clearance to the gap e The viscosity of the fuel decreases significantly with increasing temperature and increases with increasing pressure. Tests have shown that the fuel temperature in the pump chamber of the P-type pump is up to 110°2 at room temperature and 100°C. Next, the effect of fuel characteristics on the leakage characteristics of the plunger. It can be seen that as the viscosity decreases, the amount of fuel leakage increases significantly.

Plunge chamber pressure and plunger leakage rate el Liuteng 2 fuel characteristics on the leakage characteristics 4 Conclusion Through the above research and analysis, you can get the following conclusions: a When the oil film formed by the coupling gap reaches pure liquid lubrication or When the boundary film is lubricated, the friction coefficient is greatly reduced; b. The movement of the plunger increases the temperature of the fuel, thereby reducing the viscosity of the lubricant and increasing the risk of the “sticking” of the coupling, but at the same time generating a thermal wedge effect. The additional pressure field allows the oil film to have the ability to support a certain external load; the thermal wedge effect of the oil film is closely related to the thickness of the oil film, and the thinner the oil film, the higher the temperature rise and the corresponding carrying capacity; c The extrusion of the oil film The bearing capacity increases as the thickness of the oil film decreases, and is related to the viscosity of the oil and the radius of the plunger. The thinner the thickness of oil film, the greater the carrying capacity of the film, which is very favorable for us to use the oil film extrusion effect; d The oblique movement of the plunger increases the amount of fuel leakage, and at the same time makes the gap pressure on one side too large. There is a danger of the plunger slamming. The initial thickness of the oil film is squeezed and thinned, and a pressure field is formed between the friction pairs to allow the oil film to have the ability to balance the external load force. e When determining the minimum clearance of the coupling parts, not only the formation of the oil film but also the plunger coupling must be considered. Good sealing performance, but also consider the elastic deformation of the coupling parts during assembly and use; f the leakage of the clearance between the plunger and the plunger has a non-negligible influence on the injection pressure, the circulating oil supply, and the lubrication. Leakage is related to factors such as fuel viscosity, cavity pressure, plunger movement speed, plunger diameter, gap length, relative eccentricity, etc. From the perspective of fuel leakage, this article studies the maximum matching clearance of the plunger of an injection pump. The control of 3.g controls the head clearance of the plunger parts, the mateability of the coupling parts along the axis line of the plunger and the clearance range of the coupling parts of the skirt to reduce and control the lateral movement of the plunger and avoid the column. It is the most direct and effective method for jamming and leaking of plug-in parts. This puts very high requirements on the wear process of plunger parts, the control of fit clearance, the geometrical accuracy of the parts, and the control of the texture and roughness indicators of the work surface.

Cast Iron Radiators

Cast Iron Radiators,Iron Radiator,Cast Radiators,Antique Radiator

Hebei Chunfeng International Trade Co., Ltd , https://www.cfironcastings.com