CN115726956A

CN115726956A - Piston pump, in particular high-pressure fuel pump for an internal combustion engine

Info

Publication number: CN115726956A
Application number: CN202211061649.5A
Authority: CN
Inventors: W·比泽; D·海因青格; D·纳克; K·格哈德; M·格克; R·博恩; S·芙洛
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2021-08-31
Filing date: 2022-08-31
Publication date: 2023-03-03
Also published as: DE102021209531A1

Abstract

The invention relates to a piston pump (10), in particular a high-pressure fuel pump for an internal combustion engine, comprising a pump housing (12), a pump piston (14), and an annular seal (26) which is arranged partially between the pump housing (12) and the pump piston (14) and which bears axially against a mating surface (46) of the pump housing (12) at least in the region of an end surface (44). According to the invention, the end face (44) of the seal (26) and/or the counter-face (46) of the pump housing (12) are at least partially spherically curved.

Description

Piston pump, in particular high-pressure fuel pump for an internal combustion engine

Technical Field

The invention relates to a piston pump, in particular a high-pressure fuel pump for an internal combustion engine.

Background

DE 10 2017 212 A1 discloses a piston pump which can be used, for example, in an internal combustion engine with direct gasoline injection. Such piston pumps have a seal between the pump housing and the pump piston. As a seal, a sealing ring is used which is static with respect to the pump housing and which is produced from a plastic material. The sealing ring is arranged between the pump housing and the pump piston in such a way that it is acted upon by the pressure acting from the delivery chamber at least in regions radially inwardly against the pump piston and axially against a counter surface of the pump housing. The sealing ring is thus "activated" approximately by the pressure acting from the delivery chamber.

Disclosure of Invention

The invention proposes a piston pump, in particular a high-pressure fuel pump for an internal combustion engine, having a pump housing, a pump piston and an annular seal which is arranged partially between the pump housing and the pump piston and which bears axially against a mating face of the pump housing at least in the region of an end face, wherein the end face of the seal and/or the mating face of the pump housing is at least partially spherically curved.

The problem on which the invention is based is solved by a piston pump according to the invention. Advantageous embodiments are given below.

According to the invention, it has been recognized that, in the piston pumps known to date, the tolerance-induced tilting of the pump piston relative to the housing-side piston guide can lead to a sickle-shaped gap in the contact region between the end face of the seal and the counter-face of the pump housing, through which gap a leakage flow forms which prevents a rapid build-up of pressure and thus a "activation" of the seal and thus a deterioration of the delivery efficiency of the piston pump. By the measure according to the invention, the formation of the sickle-shaped gap is prevented or at least reduced even in such an inclined position. Instead, as small a circumferential and approximately parallel annular gap as possible, if present, is ensured. In this way, a good function of the piston pump is ensured, namely a rapid build-up of pressure, a low leakage rate and a good delivery efficiency, and the hitherto customary manufacturing tolerances of the piston guide can be widened here, since the tilting is compensated by the invention. Thereby enabling a new manufacturing technique that can be cost effective. Nor is it necessary to carry out elaborate post-treatment (milling) of the contact surfaces. All this is possible without having to change the basic design of the piston pump up to now.

In particular, this is achieved by a piston pump, in particular a high-pressure fuel pump for internal combustion engines. Such high-pressure fuel pumps are used both in diesel engines and in gasoline engines. The high-pressure fuel pump generally compresses the fuel to a very high pressure and delivers it into a fuel collecting line ("rail"), from where it is injected directly into the associated combustion chamber of the internal combustion engine by means of injectors. The piston pump according to the invention comprises a pump housing and a pump piston. The pump piston is guided in the pump housing by a piston guide. This can be configured, for example, as guide rings spaced axially apart from one another, which are held in recesses in the pump housing.

A radial gap exists between the pump piston and the pump housing, which is sealed by an annular seal. I.e. the seal is arranged locally between the pump housing and the pump piston. In operation, the radially inner surface of the seal bears at least partially against the radially outer surface of the pump piston. During operation, the seal bears axially against a counter surface of the pump housing at least in the region of one end face. The mating surface of the pump housing can be realized, for example, by an annular end face of a retaining ring which is received in a recess of the pump housing, for example pressed into the recess and/or welded to the pump housing.

According to the invention, it is provided that the end face of the seal and/or the mating face of the pump housing are at least partially spherically curved. The center point of the spherical curvature is preferably located approximately on the longitudinal axis of the pump piston or the seal. In this way, a "ball joint" is realized which allows the end face of the seal to be tilted relative to the housing without thereby forming a significant gap between the end face and the counter-face.

In one embodiment, it is provided that both the end face of the seal and the mating face of the pump housing are at least partially of a curved configuration, and that the end face and the mating face are at least substantially of a complementary configuration relative to one another. In this way, one face becomes the "ball" of the ball joint and the other face becomes the "socket" of the ball joint, in which the ball is received. This is responsible for preventing gap formation as much as possible when the seal is tilted.

In one embodiment, it is provided that the front face of the seal is of convex design, while the mating face on the housing side is of concave design. This configuration has manufacturing advantages. In principle, however, the opposite configuration is also conceivable.

In one embodiment, it is provided for this purpose that the radius of curvature of the spherically curved configuration of the end face of the seal is greater than the radius of curvature of the spherically curved configuration of the mating face of the pump housing. It is thereby ensured that the initial contact between the end face and the counter face takes place at least primarily (at the start of the pressure build-up) in the radially outer region.

In one embodiment, it is provided that the radius of curvature of the spherically curved configuration corresponds at least approximately to the guide length of the pump piston in the pump housing (for example the distance between two guide rings). The design dimensions cover the maximum inclination very well without the configuration of the end faces and/or counter faces becoming too complex.

In one embodiment, it is provided that the seal is at least substantially made of a plastic material. However, such plastic seals compensate better for the small tilting between the pump piston and the piston guide due to the relative softness of the material. However, in reality, a tilting of up to approximately 1.5 ° may occur, which can no longer be compensated by the flexibility of the seal, even if the clearance fit between the seal and the pump piston is small. The measures according to the invention result in particular advantages here.

In one embodiment, it is provided that the seal is at least substantially made of metal, in particular steel. Unlike the seals made of plastic material just described, seals made substantially of metal cannot or hardly compensate for small inclinations between the pump piston and the piston guide by deformation of the seal due to the relative rigidity of the material itself. Without the measures according to the invention, the above-described sickle-shaped gap is already formed between the end face and the counter-face even at a minimum inclination. The measures according to the invention make it possible to produce the seal from metal, which also has a significant advantage with regard to wear.

In one embodiment, it is provided that the end face of the seal is present on a radially outwardly extending circumferential collar of the seal, which collar is thinner in the radially outer region than in the radially inner region. This achieves that, when the pressure in the delivery chamber of the piston pump is relatively low or the pressure difference over the seal is relatively low, the end face in the radially outer region of the flange is also pressed against the counter surface and thereby closes the gap between the end face and the counter surface.

In one embodiment, it is provided that the end face and the mating face are finished, in particular ground, at least in regions. By means of this finishing, it is possible to achieve that a "hydraulic bond" occurs between the two mating surfaces, thereby improving the seal again.

In one embodiment, the end face and the counter face have a Pt value of at most about 1 μm. Such Pt values are an optimum compromise between processing effort and sealing efficiency.

Drawings

The invention is elucidated below with reference to the drawings. Shown in the drawings are:

FIG. 1: a partial longitudinal section of a piston pump with a ring seal and a pump piston;

FIG. 2: FIG. 1 is an enlarged schematic view of the ring seal and pump piston; and

FIG. 3: similar to the view of the ring seal and pump piston of figure 2.

Detailed Description

A piston pump in the form of a high-pressure fuel pump is generally indicated by reference numeral 10 in fig. 1. The piston pump 10 belongs to a fuel system of an internal combustion engine, not further shown. Piston pumps typically deliver fuel to a fuel rail to which a plurality of injectors are connected, which inject the fuel into combustion chambers of an internal combustion engine.

The piston pump 10 comprises an inlet valve, not shown, and an outlet valve, also not shown, and a pump housing 12. In which a pump piston 14 is reciprocatingly received. The pump piston 14 is set in motion by a drive, not shown. The drive may be, for example, a camshaft or an eccentric shaft of an internal combustion engine.

The pump piston 14 is currently configured, for example, as a stepped piston, which has a section 16 of smaller diameter and a section 18 of larger diameter. The section 18 of the pump piston 14 with the larger diameter delimits, together with the pump housing 12, a delivery chamber 20 which is only symbolically shown and arranged above in fig. 1. The pump housing 12 may be formed as a rotationally symmetrical part as a whole. Pump piston 14 is received in a receiving opening 22 present there in pump housing 12, which is designed as a stepped bore 24 having sections 24', 24 "and 24"', shown here, each having a different diameter.

An annular seal 26 is arranged between the section 18 of the pump piston 14 and the inner circumferential wall of the bore 24 in the region of the section 24 ". This ring seal seals directly between the pump piston 14 and the pump housing 12 and thus seals the delivery chamber 20 ("high-pressure region") located above the ring seal 26 in fig. 1 from the region disposed below the ring seal 26 in fig. 1 ("low-pressure region"). The detailed configuration and function of the annular seal 26 will be discussed in greater detail below.

An annular guide element 28, which is separate from the annular seal 26, is arranged in the section 24' of the bore between the section 18 of the pump piston 14 and the inner circumferential wall of the bore 24. The guide element 28 is functionally located between the annular seal 26 and the delivery chamber 20. Which serves to guide the pump piston 14. A pretensioning element, not shown, for example a spring, can be arranged between the guide element 28 and the annular seal 26. The prestressing element loads the annular seal 26 in fig. 2 downward against an annular retaining element 30, which retaining element 30 is functionally part of the pump housing 12 and is arranged in the bore 24 or in a section 24' ″ of the receiving opening 22. The annular seal 26 bears against the retaining element 30 in such a way that a static sealing point is formed there, which seals the seal 26 with respect to the retaining element 30 and thus with respect to the pump housing 12. This will be discussed in more detail below.

Retaining element 30 may be pressed into pump housing 12, or the retaining element may be wedged in hole 24 or welded to pump housing 12. The piston pump 10 has a further guide element 32, which is also annular and is arranged in a carrier 34. The guide elements 32 also serve to guide the pump piston 14 relative to the pump housing 12. The distance between the two

guide elements

28 and 32 forms the guide length F of the pump piston 14.

The detailed configuration of the annular seal 26 and the retaining element 30 will now be explained with reference to fig. 2 and 3: the annular seal 26, viewed from the top downwards in fig. 2 and 3, firstly comprises a sleeve-shaped and cylindrical and relatively long section with a constant wall thickness D1. Joined thereto is a relatively short section 38 having a wall thickness D2 which is smaller than the wall thickness D1. This is achieved by a constriction 40 on the radial outside of the seal 26. Adjoining the short portion 38 is an abutment portion shaped in the form of a flange 42 and directed radially outward. The flange has an annularly circumferential end face 44 on its axially outer side which is located in the lower position in the drawing and is directed toward the holding element 30. Opposite the end face 44, the retaining element 30 has an annularly encircling counter surface 46 which points toward the end face 44. As can be seen from the drawing, the flange 42 has a smaller thickness D3 in the radially outer region than in the radially inner region (thickness D4).

As can be seen in particular from fig. 2 and 3, in the present exemplary embodiment both the end face 44 and the counter face 46 are of spherically curved design. The end face 44 is formed convexly, while the mating face 46 is formed concavely, so that they are at least substantially complementary to one another, similar to a ball joint. Here, the end face 44 forms a "ball" and the mating face 46 forms a "socket". It can also be seen from fig. 2 and 3 that the radius of curvature R1 of the spherically curved configuration of the end face 44 of the seal 26 is greater than the radius of curvature R2 of the spherically curved configuration of the mating face 46 of the retaining element 30 of the pump housing 12. In the rest position shown in fig. 2 and 3 (largely pressureless delivery chamber 20), the gap 50 between the end face 44 and the counter face 46 is therefore smaller in the radially outer region than in the radially outer region.

The center of curvature of both the end face 44 and the counter-face 46 is located approximately on the longitudinal axis 48 of the pump piston 14 or the seal 26 (fig. 1). However, the difference between the two radii R1 and R2 is relatively small. In general, both radii R1 and R2 approximately correspond to the aforementioned guide length F of the pump piston 14 in the pump housing 12.

In the exemplary embodiment shown at present, the annular seal 26 is at least substantially manufactured from a plastic material. It is conceivable here for a thin, sleeve-shaped reinforcement (not shown) to be present in the region of the cylindrical section 36. In one embodiment, which is not shown, the annular seal 26 is at least substantially made of metal, in particular steel.

In an embodiment not shown, both the end face 44 and the counter-face 46 may be finished, e.g. ground, preferably with a Pt value of at most about 1 μm.

The operation and function of the seal 26 is set forth below: when the delivery chamber 20 is pressureless, the same pressure, i.e. the ambient pressure, is present at all points on the outside of the seal 26, and a uniform gap 56 of substantially constant thickness is present between the circumferential surface 52, which is internal to the annular seal 26 and straight in this operating condition, and the outer circumferential surface 54 of the pump piston 14. The end face 44 bears against the counter face 46 in the radially outer region of the flange 42 or a small gap 50 exists between the end face 44 and the counter face 46, as is shown in fig. 2 and 3.

If the piston pump 10 is put into operation, the fluid in the delivery chamber 20 is compressed to a very high pressure during the delivery stroke. This pressure acts substantially unreduced on the gap between the pump piston 14 and the pump housing 12 above the guide element 28 in fig. 1 and acts beyond the guide element 28 as far as the annular seal 26 in a manner not visible in the drawing. In this way, the pressure prevailing essentially in the delivery chamber 20 acts on the end face 58 of the seal 26, which is located above in fig. 2 and 3, on the radial outer circumferential surface 60 of the cylindrical section 36 and of the short section 38, and on the end face 62 of the flange 42, which faces the delivery chamber 20, and on the radial outer circumferential surface 64 of the flange 42.

This pressure is also present in the upper region of the inner circumferential surface 52 of the seal 26 in fig. 2 and 3. However, in the gap 56, a pressure gradient exists from top to bottom or from a high pressure region to a low pressure region due to viscous or frictional flow through the gap 54 in fig. 2 and 3. In the region of the short section 38, the pressure acting on the inner circumferential surface 52 of the seal 26 is therefore significantly lower than the pressure acting there on the outer circumferential surface 60. As a result, the sealing element 26 is pressed radially inward, in particular in the region of the constriction 40, the gap 56 is reduced and sealing is thereby achieved.

Along the radial extension of the flange 42, a pressure gradient Δ p also exists in the gap 50. This pressure gradient, in combination with the variable thickness D3 or D4 of the flange 42 and the different radii of curvature R1 and R2, causes the end face 44 to first come into contact with the counter-face 46 in the radially outer region and thereby to effect a seal. If, as described above, the end face 44 and the mating face 46 are finished, for example ground, a so-called "hydraulic bond" is produced between the end face 44 and the mating face 46, whereby the tightness is further improved.

As can be readily seen from the illustrations in fig. 1 to 3, if tilting of the pump piston 14 occurs, for example, as a result of a guide gap between the two

guide elements

28 and 32 on the one hand and the pump piston 14 on the other hand, the seal 26 can tilt together with the pump piston 14, wherein the end face 44 can move approximately parallel to the counter face 46 as a result of the spherical curvature without the size of the gap 50 between the end face 44 and the counter face 46 being thereby significantly changed. The sealing of the seal 26 in the axial direction relative to the retaining element 30 or the pump housing 12 is therefore largely unaffected by this tilting of the pump piston 14.

Claims

1. A piston pump (10), in particular a high-pressure fuel pump for an internal combustion engine, having a pump housing (12), a pump piston (14) and an annular seal (26) which is arranged partially between the pump housing (12) and the pump piston (14) and which bears axially at least in the region of an end face (44) against a counter-face (46) of the pump housing (12), characterized in that the end face (44) of the seal (26) and/or the counter-face (46) of the pump housing (12) are at least partially spherically curved.

2. Piston pump (10) according to claim 1, characterized in that both the end face (44) of the seal (26) and the counter face (46) of the pump housing (12) are at least partially of geodesic curved configuration, and the end face (44) and the counter face (46) are at least substantially complementarily configured relative to one another.

3. Piston pump (10) according to at least one of the preceding claims, characterized in that the end face (44) is configured convexly and the counter face (46) is configured concavely.

4. A piston pump (10) according to claim 3, characterized in that the radius (R1) of the spherical curvature of the end face (44) of the seal (26) is greater than the radius (R2) of the spherical curvature of the counter face (46) of the pump housing (12).

5. Piston pump (10) according to at least one of the preceding claims, characterized in that the radius (R1, R2) of the spherical curvature corresponds at least approximately to the guide length (F) of the pump piston (14) in the pump housing (12).

6. Piston pump (10) according to at least one of the preceding claims, characterized in that the seal (26) is at least substantially manufactured from a plastic material.

7. Piston pump (10) according to at least one of claims 1 to 5, characterized in that the seal (26) is at least substantially manufactured from metal, in particular from steel.

8. Piston pump (10) according to at least one of the preceding claims, characterized in that the end face (44) of the seal (26) is present on a radially outwardly extending circumferential flange (42) of the seal (26), which flange is thinner in a radially outer region than in a radially inner region.

9. Piston pump (10) according to at least one of the preceding claims, characterized in that the end face (44) and the counter face (46) are finished, in particular ground, at least in regions.

10. Piston pump (10) according to claim 9, characterized in that the end face (44) and the counter face (46) have a Pt value of at most about 1 μm.