Piston pump

Abstract

A piston pump, in particular a high-pressure fuel pump for an internal combustion engine, includes a pump housing, a pump piston, and a delivery chamber that is delimited at least by the pump housing and the pump piston. The piston pump further includes a seal configured to seal the delivery chamber and a separate guide element configured to guide the pump piston. The seal and the guide element are arranged between the pump piston and the pump housing. The seal is formed as a plastic ring with a substantially sleeve-shaped base portion.

Claims

1. A piston pump, comprising: a pump housing; a pump piston; a conveying space delimited at least by the pump housing and the pump piston; a seal configured to seal off the conveying space; and a separate guide element configured to guide the pump piston, wherein the seal and the guide element are arranged between the pump piston and the pump housing, and wherein the seal is configured as a plastic ring and comprises: a substantially sleeve-shaped base portion extending axially along the pump piston the sleeve-shaped base portion including a cylindrical outer surface and an inner surface that sealingly contacts the pump piston; and a first flange projecting radially outwardly from the cylindrical outer surface a first axial end region of the base portion, the seal terminating at an outer radial end of the first flange.

2. The piston pump as claimed in claim 1, further comprising a fastening ring arranged between the pump housing and the pump piston and configured to retain the seal between the pump housing and the pump piston.

3. The piston pump as claimed in claim 2, further comprising a spring element, which biases the seal against the fastening ring, arranged between the pump piston and the pump housing.

4. The piston pump as claimed in claim 1, further comprising a further guide element arranged in a seal carrier of the piston pump.

5. The piston pump as claimed in claim 1, wherein the seal has an overall L-shaped cross-section, with the base portion defining a first leg of the L-shaped cross-section and the first flange defining a second leg of the L-shaped cross-section.

6. The piston pump as claimed in claim 1, wherein the seal further comprises, at a second axial end region of the base portion, a second flange projecting radially outwardly from the base portion such that the seal has an overall U- or C-shaped cross-section with the base portion forming a central leg of the U- or C-shaped cross-section.

7. The piston pump as claimed in claim 6, wherein a radially outer edge of one or both of the first flange and the second flange has play to a circumferential wall of a recess of the pump housing in which the pump piston is received.

8. The piston pump as claimed in claim 1, wherein the seal further comprises a circumferential collar projecting axially from an axial end face of the seal.

9. The piston pump as claimed in claim 2, wherein the guide element and the fastening ring are combined so as to define a single component.

10. The piston pump as claimed in claim 1, further comprising an O-ring arranged between a radially outer lateral surface of the base portion and the pump housing.

11. The piston pump as claimed in claim 1, wherein the piston pump is configured as a high-pressure fuel pump for an internal combustion engine.

12. The piston pump as claimed in claim 10, further comprising a supporting ring arranged between the radially outer lateral surface of the base portion and the pump housing and configured to support the O-ring.

13. The piston pump as claimed in claim 1, wherein the outer radial end of the first flange is spaced apart from an inner circumferential wall of the pump housing such that the outer radial end of the first flange has a radial play.

14. A piston pump, comprising: a pump housing; a pump piston; a conveying space delimited at least by the pump housing and the pump piston; a seal configured to seal off the conveying space; and a separate guide element configured to guide the pump piston, wherein the seal and the guide element are arranged between the pump piston and the pump housing, wherein the seal is configured as a plastic ring with a substantially sleeve-shaped base portion having a cylindrical outer surface and an inner surface that sealingly contacts the pump piston, wherein the seal further comprises a first flange projecting radially outwardly from the cylindrical outer surface, and wherein the seal is configured as a pressure-activated seal in which, at an initial pressure, the base portion is spaced apart from the pump piston and, as pressure is built up in the conveying space, the pressure acts on the cylindrical outer surface of the base portion to urge the base portion into contact with the pump piston.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure is explained in greater detail below on the basis of the figures, wherein identical or functionally identical elements are, where applicable, only provided with reference numbers once. In the figures:

(2) FIG. 1 shows a schematic representation of a fuel system with a high-pressure fuel pump in the form of a piston pump;

(3) FIG. 2 shows a partial longitudinal section through the piston pump from FIG. 1;

(4) FIG. 3 shows an enlarged view of a pump piston, a seal, a guide element and a fastening ring of the piston pump from FIG. 1;

(5) FIG. 4 shows the seal from FIG. 3 in an enlarged sectional view;

(6) FIG. 5 shows a partial longitudinal section through an alternative configuration of the piston pump from FIG. 1;

(7) FIG. 6 shows a partial longitudinal section through an alternative configuration of the piston pump from FIG. 1 with seal in a 1.sup.st orientation;

(8) FIG. 7 shows the piston pump from FIG. 6 with seal in a 2.sup.nd orientation;

(9) FIG. 8 shows the piston pump from FIG. 6 with a spring element;

(10) FIG. 9 shows the seal from FIG. 3 in an enlarged sectional view with O-ring and supporting ring;

(11) FIG. 10 shows the seal from FIG. 6 in an enlarged sectional view with O-ring and supporting ring; and

(12) FIG. 11 shows an alternative configuration of a seal for the piston pump from FIG. 2.

DETAILED DESCRIPTION

(13) A fuel system of an internal combustion engine bears in general in FIG. 1 reference number 10. It comprises a fuel container 12 from which an electric pre-feed pump 14 conveys the fuel to a high-pressure fuel pump formed as a piston pump 16. This conveys the fuel further to a high-pressure fuel rail 18 to which several fuel injectors 20 are connected which inject the fuel into combustion chambers, not represented, of the internal combustion engine.

(14) Piston pump 16 comprises an inlet valve 22, an outlet valve 24 and a pump housing 26. A pump piston 28 is received therein so as to be able to move to and fro. Pump piston 28 is brought into movement by a drive 30, wherein drive 30 is only represented schematically in FIG. 1. Drive 30 can be, for example, a camshaft or an eccentric shaft. Inlet valve 22 is formed as a quantity control valve by which the quantity of fuel conveyed by piston pump 16 can be adjusted.

(15) The structure of piston pump 16 is further apparent from FIG. 2, wherein only the key components are mentioned below. Pump piston 28 is formed as a stepped piston with a lower tappet portion 32 in FIG. 2, a guide portion 34 which adjoins it and an upper end portion, not represented in greater detail. Guide portion 34 has a larger diameter than tappet portion 32 and the end portion.

(16) The end portion and guide portion 34 of pump piston 28 delimit together with pump housing 26 a conveying chamber 38, not represented in greater detail. Pump housing 26 can be formed as an overall rotationally symmetrical part. Pump piston 28 is received in pump housing 26 in a recess 40 present there which is formed as a stepped bore 42. Bore 42 has several steps (three steps 42′, 42″, 42′″; see FIGS. 2 and 3).

(17) A seal 44 is arranged between guide portion 34 of pump piston 28 and an inner circumferential wall of bore 42 (step 42″). It seals directly between pump piston 28 and pump housing 26 and thus seals off the conveying chamber (high-pressure region) located above seal 44 from the region. (low-pressure region) arranged below seal 44 in FIG. 2, in which latter region, among other things, tappet portion 32 of pump piston 28 is located. Seal 44 is formed as a plastic ring. Seal 44 has a substantially sleeve-shaped base portion 45 which has a cylindrical outer surface.

(18) A guide element 46 separate from seal 44 is arranged between guide portion 34 of pump piston 28 and the inner circumferential wall of bore 42 (step 42′). Guide element can be axially adjacent to seal 44 and is arranged above seal 44 in FIG. 2 (facing the conveying chamber) Guide element 46 is formed to be annular (guide ring) and can be fastened to step 42′. Piston pump 16 has a further guide element 48 which is arranged in a seal carrier 50 of piston pump 16 (see FIG. 2). Guide element 46 and further guide element 48 serve to guide pump piston 28. Further guide element 48 is formed to be annular (guide ring) and can be fastened to seal carrier 50.

(19) Piston pump 16 has, between guide portion 34 of pump piston 28 and the inner circumferential wall of bore 42 (step 42′″), a fastening ring 52 for seal 44. Seal 44 lies on fastening ring 52. A static sealing point 53 is formed by the lying contact surfaces of seal 44 and fastening ring 52 (see FIG. 3). Seal 44, guide element 46, further guide element 48 and fastening ring 52 form a seal assembly.

(20) Seal 44 has at its first axial end 54 radially outwardly projecting web 56 (see FIG. 4) which projects from base portion 45. Web 56 is formed as an annular shoulder which radially protrudes over outer lateral surface 58 of seal 44. Web 56 runs fully around seal 44 (lateral surface 58).

(21) Seal 44 has at its second axial end 60 a further radially outwardly projecting web 62 which projects from base portion 45. Further web 62 is also formed as an annular shoulder which radially protrudes over outer lateral surface 58 of seal 44. Further web 62 runs fully around seal 44 (lateral surface 58). Seal 44 has a U-shaped cross-section.

(22) Web 56 and further web 62 have radial play 64 at their radially outer edge to the circumferential wall of recess 40 which receives pump piston 28 (step 42″) (see FIG. 3). As a result of this, seal 44 can be oriented in the radial direction to pump piston 28. Pressure 65 prevailing in the conveying chamber also travels via this gap (play 64) to outer lateral surface 58 so that seal wall 66 undergoes a deformation 69 radially inward (see FIG. 4) as a result of the force acting there (arrow 68). A dynamic sealing point is thus formed between pump piston 28, in particular between guide portion 34, and seal 44 (radially internal ring edge 70).

(23) The pressure prevailing in the conveying chamber also ensures that a force F (arrow 72) acts on first face side of seal 44 (see FIG. 4 on the right). Seal 44 optionally has a circumferential collar 76 at the face side at first axial end 54, on which web 56 is arranged. It is thus ensured that force F (axial force; arrow 72) optimally runs through seal 44 and is introduced exactly into static sealing point 53. Circumferential collar 76 is formed on radially internal ring edge 70 of seal 44 on second face side 78.

(24) According to one alternative configuration, first guide element 46 and fastening ring 52 can be formed in a combined manner to form one component 80 (see FIG. 5). Component 80 takes on the function of guiding and fastening. Component 80 and seal 44 axially overlap one another (axial direction of pump piston 28). An overlapping portion 82 of combined component 80 is thus arranged radially between pump piston 28 (guide portion 34) and pump housing 26 (circumferential wall of bore 42). Guidance can be carried out at a lower portion 84 in FIG. 5. Fastening of component 80 in bore 42 can be carried out in lower portion 84 or in overlapping portion 82, for example, by means of a projection 86 which projects radially outward.

(25) FIG. 6 shows an alternative configuration of piston pump 16 from FIG. 3, wherein seal 44 only has first web proceeding from base portion 45 and circumferential collar 76. Further web 62 is omitted. Seal 44 thus has an L-shaped cross-section. Web 56 faces fastening ring 52. This brings about a deformation 88 of seal 44 in lower region 90 in FIG. 6 in the case of pressure acting on seal 44 (conveying phase) as a result of force F (arrow 68).

(26) FIG. 7 shows further alternative configuration of piston pump 16 from FIG. 3 which corresponds to the configuration of piston pump 16 from FIG. 6, wherein seal 44 is oriented such that web 56 faces (first) guide element 46. This brings about a deformation 88 of seal 44 in lower region 92 in FIG. 7 (facing fastening ring 52) in the case of pressure acting on seal 44 (conveying phase) as a result of force F (arrow 68).

(27) FIG. 8 shows a further alternative configuration of piston pump 16 from FIG. 3 which corresponds largely to the configuration of piston pump 16 from FIG. 6 and additionally has a spring element 47. A spring element 47 which pushes seal 44 against fastening ring 52 can thus be arranged between pump piston 28 and pump housing 26. Spring element 47 can, in the axial direction of pump piston 28, be arranged between guide element 46 and seal 44. Spring element 47 can be formed as a pressure spring in the form of spring disk or helical spring. Spring element 47 bears at one end axially, in particular against guide element 46, and at the other end pushes seal 44 against fastening ring 52.

(28) An O-ring 94 can be arranged between radially outer lateral surface 58 of seal 44 and pump housing 26 (see FIGS. 9 and 10). This serves to reinforce static sealing point 53 and improves the sealing action. A supporting ring 96 for O-ring 94 can furthermore be arranged between radially outer lateral surface 58 of seal 44 and pump housing 26. Supporting ring 96 serves to protect O-ring 94, for example, to avoid an extrusion of O-ring 94. FIG. 9 illustrates the configuration with O-ring 94 and supporting ring 96 at seal 44 with a U-shaped profile in accordance with FIGS. 3 and 4. FIG. 10 illustrates this configuration in the case of a seal 44 with only one web 56 (L-shaped profile) according to FIGS. 6, 7 and 8.

(29) FIG. 11 shows an alternative embodiment, with a simple structure, of a seal 44 which only has base portion 45 and is overall formed to be sleeve-shaped. Seal 44 has a uniform seal wall 66 in the case of which inner lateral surface 70 and outer lateral surface 58 are parallel to one another. Seal 44 thus has an I-shaped cross-section. If a force F (arrow 68) acts on seal 44, parallel displacement 102 thus arises. This may be advantageous if a larger sealing surface is required. Such a configuration of the seal with a rectangular profile in cross-section is comparatively simple in the production process.