Piston Fuel Pump for an Internal Combustion Engine

Abstract

A piston fuel pump for an internal combustion engine includes a pump cylinder and a pump piston that is configured to be axially displaced in the pump cylinder. A working chamber is defined by the pump piston. A seal is provided on the pump cylinder, which seals the working chamber counter to a low pressure region. The seal is applied directly to the pump piston by an injection molding method.

Claims

1. A piston fuel pump for an internal combustion engine, comprising: a pump cylinder; a pump piston configured to be moved axially in the pump cylinder; a working chamber delimited by the pump piston; and a seal disposed on the pump piston so as to seal off the working chamber from a low-pressure region, the seal applied directly to the pump piston by an injection molding.

2. The piston fuel pump as claimed in claim 1, wherein the seal seals off an end region of the pump piston adjacent to the working chamber completely from the working chamber.

3. The piston fuel pump as claimed in claim 1, wherein an end section of the pump piston adjacent to the working chamber has a cylindrical basic shape, and the seal has a recess with a cylindrical basic structure, and wherein the end section of the pump piston adjacent to the working chamber is arranged in the cylindrical basic structure.

4. The piston fuel pump as claimed in claim 1, wherein an end section of the pump piston adjacent to the working chamber has a cylindrical basic shape, and the seal has a recess with a cylindrical basic structure that is filled by the end section of the pump piston adjacent to the working chamber.

5. The piston fuel pump as claimed in claim 1, wherein an end section of the pump piston adjacent to the working chamber and the seal are in positive engagement with one another.

6. The piston fuel pump as claimed in claim 1, wherein an end section of the pump piston adjacent to the working chamber has a first surface structure and the seal has a second surface structure, and the first surface structure and the second surface structure are one or more of complementary to one another and engage in one another.

7. The piston fuel pump as claimed in claim 6, wherein the first surface structure and the second surface structure fill each other.

8. The piston fuel pump as claimed in claim 6, wherein the first surface structure and the second surface structure have a structure depth in a range of from 0.1 mm to 2 mm, measured in a radial direction.

9. The piston fuel pump as claimed in claim 6, wherein a structure size, measured in one or more of a tangential direction and an axial direction, is in a range of from 0.4 mm to 8 mm.

10. The piston fuel pump as claimed in claim 6, wherein the first surface structure and the second surface structure have a structure depth, measured in a radial direction, and a structure size, measured in one or more of a tangential direction and an axial direction, and the structure size is a multiple of the structure depth, and wherein the multiple is a factor of two to ten.

11. The piston fuel pump as claimed in claim 6, wherein the first surface structure is a knurled structure, or wherein the first surface structure is a groove or wave structure running radially around the end section of the pump piston.

12. The piston fuel pump as claimed in claim 1, wherein the seal is held nonpositively on the end section of the pump piston adjacent to the working chamber.

13. The piston fuel pump as claimed in claim 1, wherein the seal comprises a thermoplastic material.

14. The piston fuel pump as claimed in claim 1, wherein the seal has an annular basic structure and is molded directly onto the end section of the pump piston adjacent to the working chamber by injection molding in an axial molding direction.

15. The piston fuel pump as claimed in claim 1, wherein a radially outer surface of the seal, which is situated opposite an inner surface of the pump cylinder, is configured in such a way in an axial end region of the seal that the radially outer surface rests on the pump cylinder when the pump piston is at rest relative to the pump cylinder and that a relative movement between the pump cylinder and the pump piston in an axial direction promotes liftoff of the seal from the pump piston in a radially inward direction.

16. The piston fuel pump as claimed in claim 11, wherein the knurled structure is a cross-cut knurled structure according to DIN 82 of 1973.

17. The piston fuel pump as claimed in claim 13, wherein the thermoplastic material is a fiber-reinforced thermoplastic material.

18. The piston fuel pump as claimed in claim 15, wherein the radially outer surface of the seal slopes radially inward at an angle α of 10° to 60° to the inner wall of the pump cylinder in an axial end region of the seal in order to promote liftoff of the seal from the pump piston in the radially inward direction.

Description

[0046] In the drawings:

[0047] FIG. 1 shows a schematic illustration of a fuel system of an internal combustion engine with a detail of a piston fuel pump according to the invention

[0048] FIG. 2 shows an enlarged section through the detail of the piston fuel pump shown in FIG. 1

[0049] FIGS. 3a-3f show alternative embodiments of the piston fuel pump

[0050] A sealing lip of the seal is illustrated on an enlarged scale in FIG. 4.

EMBODIMENTS

[0051] In FIG. 1, a fuel system of an internal combustion engine bears the reference sign 10 overall. It comprises a fuel tank 12, from which an electric feed pump 14 delivers the fuel into a low-pressure line 16. This leads to a high-pressure pump in the form of a piston fuel pump 18. From the latter, a high-pressure line 20 leads to a fuel rail 22. Connected to the latter is a plurality of injectors 24, which inject the fuel directly into combustion chambers (not shown) respectively associated therewith.

[0052] The piston fuel pump 18 comprises a pump housing 26, indicated only in part, in which a pump piston 28 is movably guided and supported. A reciprocating motion can be imparted to this pump piston by a cam drive (not shown), this being indicated by a double arrow 30 shown at the side. The pump piston 28 is urged by a helical spring 32 toward an end position, which is at the bottom in FIG. 1. The pump piston 28 and the pump housing 26 delimit a working chamber 34. This working chamber 34 can be connected to the low-pressure line 16 by means of an inlet valve 36. The working chamber 34 can furthermore be connected to the high-pressure line 20 by means of an outlet valve 38.

[0053] Both the inlet valve 36 and the outlet valve 38 are embodied as check valves. Although not illustrated, it is possible here to embody the inlet valve 36 as a quantity control valve. In the case of such a valve, the inlet valve 36 can be forcibly opened during a delivery stroke of the pump piston 28, thus ensuring that the fuel is not pumped into the fuel rail 22 but is pumped back into the low-pressure line 16. It is thereby possible to set the fuel quantity pumped into the fuel rail 22 by the piston fuel pump 18.

[0054] The pump piston 28 is guided in a pump cylinder 40, which is thus part of the pump housing 26. At an end facing the working chamber 34, the pump piston 28 has an end section 42, which is arranged at the top in FIG. 1. In the vicinity of this end section 42 adjacent to the working chamber, the pump piston 28 furthermore has an annular offset 44 in the form of a radially projecting encircling collar. A seal 46 comes to rest on the pump piston 28 or on the offset 44 and encloses the end section 42 of the pump piston 28 adjacent to the working chamber axially and radially. The end section 42 of the pump piston 28 adjacent to the working chamber is thereby sealed off completely from the working chamber 34, a medium in the working chamber thus does not come into contact with the end section 42 of the pump piston 28 adjacent to the working chamber and a hydraulic pressure acting in the working chamber thus no longer acts on the end section 42 of the pump piston 28 adjacent to the working chamber or acts on it only indirectly via the seal 46.

[0055] At its end remote from the working chamber 34, the pump piston 28 furthermore has an end section 52, which is at the bottom in FIG. 1. In the vicinity of this bottom end section 52, a guide sleeve 54 is arranged in a fixed manner on the pump housing 26. An O-ring seal 56 is arranged in a groove 58 between the guide sleeve 54 and the pump housing 26. The guide sleeve 54 has a cylindrical section 60, which extends coaxially with the pump piston 28 and through which the helical spring 32 is guided. Along a piston longitudinal axis 62, the helical spring 32 enters at least partially into a spring locating groove 64 of the guide sleeve 54, where it is supported axially against the guide sleeve 54.

[0056] In the interior, the guide sleeve 54 furthermore has a circular-cylindrical receiving section 66, which is formed essentially by the inner circumferential wall of the cylindrical section 60. An annular sealing element 68 is arranged in this receiving section 66 in a fixed location relative to the pump housing 26, wherein the sealing element 68 has an H-shaped cross section. A guide element 72 is furthermore likewise arranged in a fixed location relative to the pump housing 26 in a collar section 70 extending radially inward on the projecting end of the cylindrical section. Together with the seal 46, this guide element 72, which is thus spaced apart to a significant extent from the seal 46 when viewed in the axial direction of the pump piston 28, provides the guide or two-point support for the pump piston 28.

[0057] The embodiment of the seal 46 and the mounting thereof on the pump piston is of particular significance in the present case. These aspects will therefore be discussed in detail with reference to the following FIGS. 2-4.

[0058] FIG. 2 shows a section through a detail of the piston fuel pump 18, wherein the end section 42 of the pump piston 28 adjacent to the working chamber and the seal 46 are shown on an enlarged scale.

[0059] The seal 46 has a recess 74 of cylindrical configuration, which is completely filled by the end section 42 of the pump piston 28 adjacent to the working chamber, with the result that, in interaction with the sealing function existing between the seal 46 and the pump cylinder 40, the end section 42 of the pump piston 28 adjacent to the working chamber is sealed off completely from the working chamber 34. At the same time, the seal 46 covers an end 421 of the end section 42 of the pump piston 28 adjacent to the working chamber and a lateral surface 422 of the end section 42 of the pump piston 28 adjacent to the working chamber, being molded directly onto said surface, and therefore the end section 42 of the pump piston 28 adjacent to the working chamber is completely covered by the seal 46.

[0060] A sealing lip 50, which interacts sealingly with the pump cylinder 40, is provided radially outside on the seal 46.

[0061] In this example, the seal 46 consists of the fiber-reinforced thermoplastic polymer PEEK 150CA30 or PA66CF20. The seal 46 is produced by an injection molding method, in which the liquefied thermoplastic polymer is applied directly to the end section 42 of the pump piston adjacent to the working chamber in an axial molding direction along the piston longitudinal axis 62. For this purpose, use can be made, for example, of a hot-channel tool, in which the molten thermoplastic polymer is introduced at a relatively high temperature into a cavity formed between the end section 42 of the pump piston 28 adjacent to the working chamber and an injection mold. Following the cooling and solidification of the thermoplastic polymer, the pump piston 28 with the seal 46 fixed thereon can be removed from the injection mold. The seal 46 has a thickness d of one millimeter in order to ensure high strength, a low mass and simplicity of manufacture in equal measure.

[0062] In this illustrative embodiment, the end section 42 of the pump piston 28 adjacent to the working chamber and the inner contour of the recess 74 in the seal 46, said inner contour being in contact with the pump piston, have a largely smooth surface. In FIG. 3a, which shows the detail X from FIG. 2, this is shown once again on an enlarged scale.

[0063] The following illustrative embodiments differ from the previous illustrative embodiments in having modified surface structures on the end section 42 of the pump piston 28 adjacent to the working chamber and on the inner contour of the seal 46.

[0064] In FIG. 3b, the end section 42 of the pump piston 28 adjacent to the working chamber and the inner contour of the seal 46 have encircling grooves. The grooves have a depth t of 0.5 mm and a periodicity of 1 mm in the axial direction x. There can be a multiplicity of grooves, each of which runs around in a self-contained way. However, the encircling grooves can also form a single- or multi-turn thread overall. The groove structure formed on the surface of the end section 42 of the pump piston 28 adjacent to the working chamber is obviously designed to be complementary to the inner contour of the seal 46, i.e. as a negative, this being obtained easily by the injection molding process in the present case.

[0065] In another embodiment, which is particularly simple to produce, the grooves have a depth t of just 0.1 mm and a periodicity of 1 mm in the axial direction x.

[0066] In yet another embodiment, which ensures particularly good interlocking between the end section 42 of the pump piston 28 adjacent to the working chamber and the seal 46, the grooves have a depth t of 2 mm and a periodicity of 9 mm in the axial direction x. These grooves can also be designed as waves, see FIG. 3c.

[0067] Examples of end sections 42 of the pump piston 28 adjacent to the working chamber which have relatively large grooves spaced further apart from one another are shown in FIGS. 3b and 3e.

[0068] As an alternative to groove structures, it is also possible to provide knurled structures or cross-cut knurled structures on the end section 42 of the pump piston 28 adjacent to the working chamber and on the inner contour of the seal 46. An example of such an end section 42 of the pump piston 28 adjacent to the working chamber is shown in FIG. 3f.

[0069] In addition to the regular surface structures shown above, it is of course also possible to provide irregular surface structures on the end section 42 of the pump piston 28 adjacent to the working chamber and on the inner contour of the seal 46, said structures representing in particular a roughness of the pump piston 28 and of the seal 46. In one example, the Pt value of a measurement of the surface of the pump piston is 0.2 mm and the wavelength at which the maximum of a spectral decomposition of the surface roughness (Ra spectrum) occurs is 1 mm.

[0070] With reference to FIG. 4, the fine geometry of the sealing lip 50 of the seals illustrated in the preceding embodiments will now be explained.

[0071] In the present case, an axial end region 464 of the seal 46 is formed on the sealing lip 50 on the working-chamber side. Provision is made for a radially outer surface of the seal 46, which is situated opposite an inner surface of the pump cylinder 40, to slope radially inward at an angle α of 10° to 60° to the inner wall of the pump cylinder 40 in an axial end region 464 of the seal 46. This has the effect or, alternatively, it is envisaged that a relative movement between the pump cylinder 40 and the pump piston 28 in an axial direction, in particular in the direction of the working chamber 34, promotes liftoff of the seal 46 from the pump cylinder 28 in a radially inward direction. In this case, a liquid film consisting of fuel forms between the seal 46 and the pump cylinder 40 and, with slight leakage, considerably reduces the wear on the piston fuel pump 18.

[0072] For this purpose an outward-pointing encircling ridge 468 is formed integrally at or on the sealing lip 50, said ridge having, in a longitudinal direction and in cross section, approximately the shape of an isosceles triangle, of which the two opposite acute angles point in axial directions and the third, obtuse angle rests (statically) on the pump cylinder 40. It is envisaged that only this ridge comes to rest (statically) on the pump cylinder 40, while the seal 46 or the sealing lip 50 is otherwise spaced apart from the pump cylinder 40 by a gap 77. A width s of the gap 77 is 20 μm, for example. As explained above, liftoff of the ridge 468 from the pump cylinder 40 is furthermore also envisaged during relative movement.