JPH08261109A - Fuel injection pump - Google Patents

Abstract

PURPOSE: To provide a fuel injection pump in which the occurrence of a cavity in an oil supplying/discharging hole when the oil supplying/discharging hole has been closed by a plunger can be eliminated, and also the occurrence of cavitation erosion due to a high-pressure discharge oil at the time of the completion of injection can be prevented. CONSTITUTION: A jerk fuel injection pump is provided with both a circular ring-shaped groove 21 that has been provided on the inside surface of a plunger barrel 2 while keeping such a positional relationship as the upper periphery of the groove is closed by the cutout lower periphery 9 of the plunger, when the plunger 3 is lifted so that the oil supplying/discharging hole 6 bored in the plunger barrel 2 is closed by the top surface 7 of the plunger, and an oil discharging hole 22 that is communicated with the lower part of an oil supplying chamber 5 through the circular ring-shaped groove 21 and the plunger barrel 2.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a fuel injection pump for a diesel engine.

[0002]

2. Description of the Related Art FIG. 3 is a sectional view of a conventional jerk fuel injection pump. 1 is a fuel injection pump main body, 02 is a plunger barrel, 3 is a plunger, 4 is an oil supply pipe joint, 5
Is an oil supply chamber, 6 is an oil supply / drain hole, 7 is a plunger top surface, 8 is a plunger cutout, 9 is a plunger cutout lower edge, 10 is a plunger vertical groove, 11 is a plunger chamber, and 12 is a discharge valve.

The operation of the conventional example will be described with reference to FIG. The fuel is filled from the oil supply pipe joint 4 to the oil supply chamber 5, the oil supply / discharge hole 6, and the plunger chamber 11 by an oil supply device (not shown). When the plunger 3 is lifted by a cam (not shown), the fuel in the plunger chamber 11 flows back to the oil supply chamber 5 side until the oil supply / discharge hole 6 is closed.

When the oil supply / exhaust hole 6 is closed by the plunger 3, the fuel in the plunger chamber 11 is compressed to a high pressure and pushes up the discharge valve 12 to move the high pressure fuel injection pipe (not shown) to the inside of the cylinder of the engine from the fuel valve. Is injected into. When the plunger 3 further rises and the plunger notch 8 is applied to the lower edge of the oil supply / drain hole 6, the high-pressure fuel in the plunger chamber 11 communicates with the fuel chamber 5 from the plunger vertical groove 10 and is discharged to a low pressure. Finish the injection.

[0005]

FIG. 4 shows the operation of the conventional jerk type fuel injection pump, showing the pressure condition of each portion corresponding to the positions of the plunger 3 and the oil supply / drain hole 6, and explaining the problems. . FIG. 2A shows the cam lift (plunger lift), the pump outlet pressure, and the oil supply chamber pressure, and FIG.
A to d correspond to the cam lifts A to D, and show the positional relationship between the plunger 3 and the oil supply / discharge oil hole 6 and the flow of fuel in the oil supply / discharge oil hole 6.

The position A is where the plunger 3 begins to rise. In this position, the plunger top surface 7 is at the lower edge of the oil supply / drain hole 6. At the position B, the plunger top surface 7 is at a position where the oil supply / drain hole 6 is closed by about half, and the plunger chamber 1
The fuel of No. 1 flows out from the oil supply / discharge hole 6 into the oil supply chamber 5. At this time, since the area of the oil supply / exhaust hole 6 is smaller than the area of the plunger 3, the backflow speed of the fuel in the oil supply / exhaust hole 6 is considerably high, and the pressure in the oil supply chamber 5 is also increased.

At the position C, the plunger top surface 7 is where the oil supply / drain hole 6 is closed. Here, the fuel flowing back is suddenly stopped, but due to its inertia, it tries to continue the flow and a cavity is generated in the oil supply / discharge oil hole 6. Therefore, the pressure in the fuel supply chamber 5 is reduced.

When the plunger 3 further rises to the position D, the plunger notch 8 is applied to the lower edge of the oil supply / drain hole 6 and high-pressure fuel is ejected to the oil supply / drain hole 6. At this time, the cavity previously generated is crushed by this high-pressure flow, and cavitation erosion occurs on the plunger surface and the oil supply / drain hole 6.

At this time, the pressure in the oil supply chamber 5 is a high-frequency fluctuation indicating the destruction of the cavity described above. The cavitation erosion may cause seizure or sticking of the plunger 3 due to the damage, and the plunger barrel 2 may be cracked if it occurs in the oil supply / drain hole 6 of the plunger barrel 2.
It may interfere with the operation of the engine.

An object of the present invention is to eliminate cavities in the oil supply / exhaust holes when the plunger closes the oil supply / exhaust holes, prevent cavitation erosion due to high-pressure oil discharge at the end of injection, and improve durability and reliability. To provide a highly fuel-injecting pump.

[0011]

The fuel injection pump of the present invention is a jerk type fuel injection pump, in which the plunger rises to close the oil supply / drain hole formed in the plunger barrel by the plunger top surface and at the same time as the plunger notch. An annular groove 21 provided on the inner surface of the plunger barrel in such a positional relationship that the upper edge of the groove is closed by the lower edge, and the annular groove and the oil supply chamber below the oil supply / discharge hole of the plunger barrel are communicated with each other. It is characterized by having an oil drain hole 22.

[0012]

Since the new oil drain communication passage consisting of the annular groove 21 and the oil drain hole 22 is newly provided, the area of the oil drain hole is increased. As a result, the backflow velocity of fuel into the fuel supply chamber 5 due to the rise of the plunger can be reduced. As a result, when the oil supply / drain hole is closed by the plunger, the number of cavities generated in the oil supply / drain hole is reduced, and cavitation erosion due to high-pressure oil discharge is eliminated, so that safe operation can be performed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a sectional view of a fuel injection pump according to a first embodiment of the present invention, and FIG. 2 is an operation explanatory view of the fuel injection pump. In FIG. 1, 1 to 12 are the same as the conventional example. Reference numeral 21 is an annular groove provided on the inner surface of the plunger barrel 2, and when the plunger 3 rises and the top surface of the plunger 3 closes the oil supply / drain hole formed in the plunger barrel, the circular notch is formed by the plunger notch lower edge 9. Ring groove 2
1 is provided at a position where the upper edge of the 1 is closed. Reference numeral 22 is an oil drain hole that connects the annular groove 21 and the oil supply chamber 5.

Next, the operation of the above embodiment will be described with reference to FIG. FIG. 2A shows the cam lift (plunger lift), the pump outlet pressure, and the oil supply chamber pressure, respectively. Corresponding to the cam lifts A to D, the plunger 3 and the oil supply / drain hole 6 are shown.
The positional relationship with is shown by a to d.

The plunger 3 starts to rise from the position A. At this time, the plunger top surface 7 is at the lower edge of the oil supply / drain hole 6. The lower cutout edge 9 of the plunger 3 is also at the lower edge of the annular groove 21. The position of B is the plunger top surface 7 and the oil supply / drain hole 6
Is about half closed, and the plunger cutout lower edge 9
Also closes the annular groove 21 by half.

At this time, the backflow fuel from the plunger chamber 11 is supplied from the oil supply / discharge hole 6, the plunger vertical groove 10, the annular groove 21,
In addition, the outflow speed in the oil supply / drain hole 6 is not so high. At the C position, the plunger top surface closes the oil supply / drain hole 6, and the notch lower edge 9 of the plunger closes the annular groove 21. However, since the outflow speed is low, the inertial force is small and the oil supply / drain hole 6 does not have a cavity.

At the D position, when the plunger 3 moves up,
The plunger notch 8 is applied to the lower edge of the oil supply / drain hole 6, and the high-pressure fuel in the plunger chamber 11 is ejected from the oil supply / drain hole 6.
As described above, no cavity is formed in the oil supply / drain hole 6, so that cavitation erosion does not occur on the surface of the plunger or the oil supply / drain hole 6, and the pressure rises smoothly.

[0018]

By implementing the present invention, it is possible to reduce the backflow velocity of fuel in the oil supply / exhaust oil holes, and eliminate the occurrence of cavities in the oil supply / exhaust oil holes when the oil supply / exhaust oil holes are closed. be able to. Therefore, cavitation erosion can be prevented even if the high-pressure waste oil flows backward at the end of injection.
Therefore, a highly durable and highly reliable fuel injection pump can be supplied.

[Brief description of drawings]

FIG. 1 is a sectional view of a fuel injection pump according to a first embodiment of the present invention.

FIG. 2 is an explanatory view of the action of the above injection pump.

FIG. 3 is a prior art example corresponding to FIG. 1.

FIG. 4 is a diagram corresponding to FIG. 2 of a conventional example.

[Explanation of symbols]

1 ... Fuel injection pump body, 2 ... Plunger barrel, 3 ...
Plunger, 4 ... Oil supply pipe joint, 5 ... Oil supply chamber, 6 ... Oil supply / drain hole, 7 ... Plunger top surface, 8 ... Plunger notch, 9 ... Plunger notch lower edge, 10 ... Plunger vertical groove, 11 ... Plunger chamber, 12 ... discharge valve, 21 ... annular groove, 22 ... oil drain hole.

Claims (1)

[Claims] 1. In a jerk type fuel injection pump, the plunger is moved up so that the top surface of the plunger closes the oil supply / drain hole formed in the plunger barrel, and at the same time, the upper edge of the groove is closed by the lower edge of the notch of the plunger. An annular groove (21) provided on the inner surface of the plunger barrel at
And a drainage hole (22) communicating with the oil supply chamber below the oil supply and drain hole of the plunger barrel.