JPH06299931A - Fuel injection pump for internal combustion engine - Google Patents

Abstract

(57) [Abstract] [Purpose] To avoid piston sticking in the head area. A fuel injection pump for an internal combustion engine comprises a pump piston axially guided in a cylinder hole of a cylinder bush, the pump piston limiting a pump working chamber by an end surface and an annular groove in a peripheral surface of the head. It is divided into a part and a shaft part. In order to avoid piston sticking in the area of the head part, the diameter of the head part of the pump piston is made smaller than the diameter of the shaft part and only with a slight play against the wall of the cylinder hole in the cylinder bore. Is guided by an elliptical cross-sectional shape or by the spherical shape of the head part in axial section and by means of this line the head part can be reliably guided axially and has a control edge. The play between the head part and the wall of the cylinder bore is enlarged in the dangerous range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection pump for an internal combustion engine of the type described in the superordinate concept of claim 1.

[0002]

2. Description of the Prior Art West German Patent Application Publication No. 362413
In the case of a fuel injection pump of the above-mentioned type known from U.S. Pat. No. 4, the pump piston driven by the cam drive is axially guided in the cylinder bore of the cylinder bush and in this cylinder bore, in the cylinder bush. The end face of the pump piston that rushes into the chamber limits the pump working chamber connected to the combustion chamber of the internal combustion engine to be replenished.

The pump piston is divided into a shaft part and a head part by means of an annular groove, in which case the peripheral surface of the head part is provided with a control notch with an inclined edge, which control notch is provided. It is constantly connected to the pump working chamber via a flute and cooperates with a radial control hole provided in the wall of the cylinder bore for controlling the discharge rate.

In this case, in a fuel injection pump of an internal combustion engine which discharges at an extremely high working pressure, in the range of the head portion, in this case, especially at the control edge of the control notch, frequently, the head portion of the pump piston and the cylinder hole are frequently replaced. So-called piston sticking occurs due to direct metallic contact with the walls, in which case the lubricating film (usually diesel fuel) maintained between the two parts is also caused by the high lateral force acting on the piston. Or it is pushed away based on the geometrical molding accuracy of the head part.

In order to avoid the above-mentioned wear process, which frequently results in tightening of the piston in the cylinder bushing and mechanical destruction of the components, in known fuel injection pumps the head part is coated with a titanium nitride layer. ing. However, the disadvantage of such a coating is that it is uneconomical because the material is expensive and the fabrication is relatively cumbersome.

[0006]

The object of the present invention is to avoid the above-mentioned drawbacks.

[0007]

The above problem has been solved by the fuel injection pump according to the present invention as set forth in the characterizing part of the first claim.

[0008]

The advantages of the fuel injection pump of the present invention are that the desired expansion of the play between the peripheral surface of the head portion of the pump piston and the wall of the cylinder bore allows the pump piston and the cylinder bush to be separated from each other. This is to ensure that metallic contact between them is avoided.

In this case, it is particularly advantageous to maintain the slight play required for guiding the head part in the cylinder bush in a safe range outside the control notch which does not cause piston sticking due to wear. can do. This is because, in this range, a molded body having a sharp edge cannot be provided in the peripheral surface of the pump piston.

Therefore, the play between the head part and the wall of the cylinder bushing in the dangerous area of the control cutout is prevented without disturbing the axial guidance of the head part by means of the line guide defined by a small play in the safe range. Can be expanded.

In this case, it is particularly advantageous if the intended line of minimum play is realized by the elliptical shape of the head part in cross section or by the spherical or barrel shape of the head part in cross section. This is because in this case existing manufacturing equipment can be used.

Another possibility of increasing the play is to uniformly reduce the cross section of the entire head portion of the pump piston, which is particularly simple to carry out. In this case, the piston is guided in the cylinder bore via the peripheral surface of the shaft portion of the pump piston.

Therefore, in a fuel injection pump operating at high pump pressures, the play between the head portion of the pump piston and the cylinder wall is enlarged to a dangerous extent without the need for tedious and uneconomical coating of the pump piston. As a result, it is possible to reliably avoid piston sticking that hinders the injection amount control function.

Advantageous configurations of the invention are described in the other claims.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings, only the main constituent members of a fuel injection pump according to the present invention are shown.

As is apparent from FIG. 1, the pump piston 1 is axially guided in a cylinder bore 3 of a cylinder bush 5 inserted in a pump casing (not shown), in which case fuel injection is performed. The pump can be configured as a single cylinder injection pump as well as a row injection pump.

The pump piston 1 is reciprocally driven in the axial direction against the restoring force by a cam drive (also not shown) in a known manner and has a pump working chamber 9 at the end face 7 which projects into the cylinder bushing 5. I have a limit. This pump working chamber is connected via a fuel conduit 11 to the injection point of the combustion chamber of the internal combustion engine to be replenished.

The pump piston 1 comprises an annular groove 1 which divides the pump piston into a shaft portion 15 and a head portion 17.
Have three.

A control notch 19 as an inclined groove or a control notch 19 as an enlarged portion of the annular groove 13 having a diagonally extending limiting edge is provided in the peripheral surface of the head portion 17 of the pump piston 1. The control notch and the annular groove 13 are always connected to the pump working chamber 9 via the longitudinal groove 21 and the inclined limiting edge of the control notch on the pump working chamber side forms the control edge 23.

This control edge 23 cooperates with a radial control hole 25 provided in the wall of the cylinder bushing 5 for controlling the fuel discharge rate.

In this case, in FIG. 1, the diameter of the head portion 17 of the pump piston 1 is smaller than that of the shaft portion 15 by a small amount, preferably 0.01% to 0.03% of the diameter of the shaft portion 15. Head part 1
A larger play is formed for the cylinder bore 3 over the entire circumference of the shaft 7 than in the shaft part 15.

In the second embodiment shown in FIG. 2, the head portion 17 of the pump piston has an elliptical cross-sectional shape, the minor axis of the ellipse lying in the region of the longitudinal groove 21 and The smaller elliptical diameter D2 is smaller than the larger elliptical diameter D1 corresponding to the diameter of the shaft portion 15 of the pump piston 1 by approximately 0.001 mm to 0.003 mm, and the ellipse major axis is relative to the axis extending through the longitudinal groove 21. Are arranged vertically.

The head part of the pump piston is thereby guided in the cylinder bore with a slight play against the wall of the cylinder bore 3 via an axial line which is kept away from the dangerous area of the control cutout 19. Since the pump piston 1 can be reliably guided, the control notch 1
The play between the wall of the cylinder bore 3 and the head part 17 can be increased in a dangerous range of 9.

The third embodiment shown in FIG. 3 differs from the second embodiment described above in the construction of the head portion 37 of the piston piston, and therefore FIG. 3 shows only the pump piston. There is.

In this case, the contour of the peripheral surface of the head portion 37 is formed into a barrel shape or a spherical shape, and in this case, the diameter D2 of the head portion is at the upper and lower limiting edges 31,
Since the head portion 37 is smaller than the diameter D1 located exactly in the middle between the limiting edges corresponding to the diameter of the shaft portion 15 of the pump piston 1 by approximately 0.001 mm to 0.003 mm, the head portion 37 has a diameter of D1. Whereas it is guided axially in the cylinder bushing 3 with little play via the radial lines only in the cross-section range,
The other peripheral areas of the head part 37 have a large play against the wall of the cylinder bore.

[Brief description of drawings]

FIG. 1 is a partial view of a first embodiment of a fuel injection pump according to the present invention having a pump piston in which the diameter of the head portion is uniformly reduced compared to the diameter of the shaft portion.

FIG. 2 is a radial cross-sectional view of a second embodiment of the head portion of a pump piston having an elliptical cross-sectional shape.

FIG. 3 shows a third embodiment of the head part of a pump piston having a barrel-shaped or spherical contour.

[Explanation of reference numerals] 1 pump piston 3 cylinder hole 5 cylinder bush 7 end face 9 pump working chamber 11 fuel conduit 13 annular groove 15 shaft portion 17,37 head portion 19 control notch 21 vertical groove 23 control edge 25 control hole 31 control edge

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Stanislau Boatzack Austria, Salzburg Harfau-Hoffmanstal-Strasse 62

Claims (10)

[Claims] 1. A fuel injection pump for an internal combustion engine, comprising:
The pump piston (1), which is axially guided in the cylinder hole (3) of the cylinder bush (5) and is reciprocally driven by a cam drive, has a pump working chamber (9) in the cylinder bush (5) due to the end face. And a control notch on the circumference that is constantly connected to the pump working chamber (9),
Inclined groove (1) with an advantageously inclined control edge (23)
9), the control notch cooperating with a control hole (25) in the wall of the cylinder bush (5), and the pump piston further comprising an annular groove () in the pump piston (1). 13) a head part (17, 37) of the pump piston (1), of the type divided into a head part (17, 37) and a shaft part (15)
Is provided between the peripheral surface of the head portion (17, 37) and the wall of the cylinder hole (3), and the play is provided along one or two lines of the peripheral surface of the head portion (17, 37). 17,3
Fuel injection pump for internal combustion engines, characterized in that it has a certain minimum value which is smaller than the play between the peripheral surface of the other range of 7) and the wall of the cylinder bore. 2. A peripheral surface line forming a control edge (23) in which the peripheral surface line of the head portion having a minimum play between the head portion (17, 37) and the wall of the cylinder bore (3) forms the control edge (23). The fuel injection pump according to claim 1, wherein the fuel injection pump is located outside the vehicle. 3. The fuel injection pump according to claim 2, wherein the head portion (17) is formed in an elliptical shape when viewed in a radial sectional plane. 4. The ellipse has an ellipse minor axis (D2) and an ellipse major axis (D1), the ellipse minor axis (D2) extending through a circumferential area having a longitudinal groove (21). The fuel injection pump according to claim 3. 5. The diameter of the ellipse minor axis range is 0.0 greater than the diameter of the ellipse major axis range located perpendicular to the ellipse minor axis range.
The fuel injection pump according to claim 3 or 4, which is smaller by 01 mm to 0.003 mm. 6. A head portion (3) of a pump piston (1).
The fuel injection pump according to claim 2, wherein the peripheral contour of (7) is formed in a spherical shape when viewed in a sectional plane in the axial direction. 7. In the region of the upper and lower limiting edges (31), the diameter of the head part (37) is 0.001 mm to 0.00 respectively from the cross section located between the limiting edges (31).
7. The fuel injection pump according to claim 6, which is smaller by 3 mm. 8. The fuel injection pump according to claim 7, wherein the maximum diameter cross section of the head portion (37) is located midway between the upper and lower limiting edges (31). 9. A fuel injection pump for an internal combustion engine, comprising:
The pump piston (1), which is axially guided in the cylinder hole (3) of the cylinder bush (5) and is reciprocally driven by a cam drive device, has a cylinder bush (5) with an end surface.
A sloping groove (19) with a control notch, which limits the pump working chamber (9) therein and is constantly connected to the pump working chamber (9) on the peripheral surface, preferably with a sloping control edge (23) And the control notch cooperates with a control hole (25) in the wall of the cylinder bush (5), and the pump piston has an annular groove (13) provided in the pump piston (1). Depending on the head part (17, 37) and the shaft part (1
5), the diameter of the pump piston (1) in the range of the head part (17) is invariable than the diameter of the pump piston (1) in the range of the shaft part (15). A fuel injection pump for an internal combustion engine, characterized in that it is formed small in size. 10. The fuel injection pump according to claim 9, wherein the diameter difference between the head portion (17) and the shaft portion (15) is 0.01% to 0.03%.