WO2023104620A1

WO2023104620A1 - Piston pump, in particular a high-pressure fuel pump for an internal combustion engine

Info

Publication number: WO2023104620A1
Application number: PCT/EP2022/084006
Authority: WO
Inventors: Jurij Giesler; Frank Nitsche; Siamend Flo; Andreas Jesse; Guido Bredenfeld; Stephan Wehr; Ekrem CAKIR
Original assignee: Robert Bosch Gmbh
Priority date: 2021-12-08
Filing date: 2022-12-01
Publication date: 2023-06-15
Also published as: DE102021213933A1

Abstract

A piston pump (10) comprises a pump piston (20), a delivery chamber (28), a seal (32) arranged in a ring shape around the pump piston (20) and interacting at least intermittently with the latter, and an annular portion (34) which is arranged in a ring shape around the pump piston (20) and, seen in the axial direction, is arranged between seal (32) and delivery chamber (28). It is proposed that the annular portion (34) is directly adjacent to the seal (32) and that, in the region of the mutually adjacent ends of annular portion (34) and seal (32), there is at least one flow passage (46) having overall a substantially radial extent.

Description

title

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

State of the art

The invention relates to a piston pump, in particular a high-pressure fuel pump for an internal combustion engine, according to the preamble of claim 1.

DE 102017212 498 A1 discloses a piston pump that can be used, for example, in internal combustion engines with direct gasoline injection. Such piston pumps have a seal between the pump housing and the pump piston. A sealing ring, which is stationary relative to the pump housing and is made of a plastic material, is used as the seal. 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 pumping chamber, at least in some areas, radially inwards against the pump piston and axially against a mating surface assigned to the pump housing. It is thus quasi "activated" by the pressure acting from the pumping chamber. In addition, it is acted upon axially by a spring device against the mating surface associated with the pump housing.

Disclosure of Invention

The problem on which the present invention is based is solved by a piston pump having the features of claim 1 . Advantageous developments are specified in the dependent claims. In the case of the piston pump according to the invention, it is made possible for the seal to center itself hydraulically “automatically”, namely largely unhindered, relative to the pump piston. This reduces or evens out the load on the seal and improves the lubrication and cooling of the seal. Overall, this leads to an increase in the service life of the seal and thus also of the piston pump. Due to the omission of the previously existing spring, which acts on the seal in the axial direction, assembly is also simplified and costs are reduced. In addition, less installation space is required, thereby reducing the dead volume. This increases the volumetric efficiency of the piston pump.

Specifically, this is achieved by a piston pump, in particular a high-pressure fuel pump for an internal combustion engine. Such a high-pressure fuel pump is used both in diesel and in gasoline internal combustion engines. It usually compresses the fuel to a very high pressure and feeds it into a fuel collection line ("rail"), from where the fuel is injected directly into associated combustion chambers of the internal combustion engine by means of injectors., The piston pump according to the invention comprises a pump piston which is a receiving opening of a pump housing is received. The pump housing, together with the pump piston and possibly other components, delimits a pumping chamber in which the fuel can be compressed.

A seal which at least temporarily interacts with the pump piston is arranged in the form of a ring around the pump piston. This is typically ring-shaped or sleeve-shaped. It seals a radial gap between the pump piston and the pump housing, "radial" being understood here and below as a direction that is at least approximately orthogonal to the longitudinal axis of the above-mentioned receiving opening in the pump housing or orthogonal to the longitudinal axis of the pump piston. The seal is therefore arranged in regions between the pump housing and the pump piston and essentially coaxially with the pump piston.

During normal operation of the piston pump, a radial inner surface of the seal lies at least in regions on a radial outer surface of the pump piston. During normal operation of the piston pump, at least one area of an end face of the seal rests axially against a mating surface that is assigned to the pump housing and is arranged on the side of the seal that faces away from the pumping chamber. This counter surface can be created, for example, by an annular end face of a retaining ring, which is accommodated in a recess in the pump housing, for example pressed into it and/or welded to the pump housing.

The abutment of the radial inner surface of the seal on the pump piston and the axial front surface of the seal on the counter surface is caused in the piston pump according to the invention as well as in corresponding seals from the prior art during normal operation of the piston pump, in particular by a comparatively high hydraulic pressure acting from the pumping chamber acts on a radial outer surface of the seal and on a surface of the seal acting away from the delivery chamber in the axial direction. The desired maximum sealing effect of the seal thus only occurs after the piston pump has started operating. The seal is thus "activated" by the start of operation of the piston pump.

The piston pump according to the invention also includes an annular section which is arranged in a ring shape around the pump piston and seen in the axial direction between the seal and the pumping chamber. According to the invention it is provided that the ring-shaped section is directly adjacent to the seal. A spring, which in conventional piston pumps acts on the seal against the counter surface, is therefore no longer present in the piston pump according to the invention. The seal is thus "free" insofar as its radial movement is not restricted by a spring contacting it. The seal is thus held in the axial direction between the mating surface and the annular section with little axial play. This enables the advantage mentioned at the outset that the seal centers itself hydraulically.

In order to nevertheless ensure that the seal, as mentioned above, can be activated, in the area of the mutually adjacent ends of the ring-shaped section and seal, for example between the ring-shaped Section and the seal, at least one substantially radially extending flow passage present. Even if the seal is (still) in contact with the ring-shaped section at the start of operation of the piston pump, the pressure build-up radially outside of the seal is thus ensured. The flow cross section of the flow passage should be dimensioned in such a way that there is almost no throttling. In any event, the pressure drop across the flow passage should be significantly less than the pressure drop across the initial gap between the seal and mating surface.

In a further development it is provided that at least one flow passage is present in or on the seal, for example in or on an edge facing the annular section. Since the seal is usually made of plastic, this is easy to produce.

In a further development it is provided that at least one flow passage is present in or on the ring-shaped section, for example in or on an edge facing the seal. Thus, the design of the seal can remain unchanged. This reduces the manufacturing costs.

In a further development it is provided that the ring-shaped section is a guide section for the pump piston. In this case, the ring-shaped section can preferably be provided as a guide element which is separate from the pump housing and which is inserted into the receiving opening in the pump housing and fixed in this. For example, the ring-shaped section can be pressed into the receiving opening. Such a guide section ensures—at least also—the radial centering of the pump piston. A corresponding guide gap is present between the guide section and the pump piston, through which a high pressure is transmitted from the delivery chamber in the direction of the seal during operation of the piston pump.

In a further development it is provided that in the region of the mutually adjacent ends of the ring-shaped section and the seal there is a plurality of flow passages which extend essentially radially and which extend essentially axially between them Spacers are formed, the total extent of the flow passages seen in the circumferential direction being greater than the total extent of the spacers seen in the circumferential direction. It is hereby created a quasi "crown-like" edge. As mentioned above, the spacers may be integral with both the gasket and the annular portion. The flow passages are preferably distributed evenly over the circumference. The measure specified here ensures the lowest possible throttling.

In a further development it is provided that the spacers have a round, preferably circular, cross-section when viewed in the axial direction. Thus, the spacers can be designed in the form of axially extending nub-like projections. This keeps stresses in the material low.

In a further development, it is provided that the spacers have a rectangular cross-section when viewed in the axial direction. This is very easy to produce.

In a further development, it is provided that during operation of the piston pump, the seal is supported in the axial direction on a counter surface with an end facing away from the pumping chamber, and that the hydraulic gap between the seal and the counter surface is designed in such a way that when the piston pump starts to operate, the seal is laminar in the gap Flow conditions prevail, in particular that the gap has a width in the range of 5-300 pm. This can be achieved, for example, by appropriately dimensioning the distance between the mating surface and the annular section. The measure provided causes a noticeable drop in pressure in the gap at the start of operation of the piston pump.

This allows the pressure radially outside of the seal to be significantly higher than radially inward of the gap, which, in conjunction with a corresponding pressure surface on the seal, can result in a resultant force that presses the seal against the mating surface. As a result, the gap between the seal and the mating surface is reduced or closed, as a result of which the pressure increases significantly again radially outside of the seal and the seal, as explained above, is forced radially inward against the pump piston and is thus "activated".

In a further development it is provided that the seal is made of a plastic material. Such a seal is particularly easy to produce.

Embodiments of the invention are explained below with reference to the drawings. Show in the drawing:

FIG. 1 shows a longitudinal section through a piston pump;

FIG. 2 shows an enlarged schematic longitudinal section through a region of the piston pump from FIG. 1 with a pump piston, a seal, an annular section in the form of a guide element and a retaining element;

Figure 3 is a perspective view of the seal of Figure 2;

FIG. 4 shows a schematic longitudinal section through the right-hand area of FIG. 2 to explain leakage paths;

FIG. 5 shows a simplified hydraulic circuit diagram of the arrangement of FIG. 4;

Figure 6 is a perspective view similar to Figure 3 of an alternative embodiment of a seal; and

Figure 7 is a perspective view similar to Figure 3 of yet another alternative embodiment of a seal.

In the following, functionally equivalent elements and areas in different embodiments and/or figures bear the same reference symbols. A piston pump in the form of a high-pressure fuel pump bears the reference numeral 10 overall in FIG. It usually conveys the fuel to a fuel rail to which a number of injectors are connected, which injects the fuel in the combustion chambers of the internal combustion engine.

The piston pump 10 comprises a controllable inlet valve 12 and an outlet valve 14 designed as a check valve, as well as a pump housing 16. A receiving opening 18 for a pump piston 20 is present in this housing. The pump piston 20 can be moved in the receiving opening 18 parallel to a longitudinal axis 22 of the receiving opening 18 . A drive, not shown in the drawing, is used for this purpose. This can be, for example, a camshaft or an eccentric shaft of the internal combustion engine.

In the present case, the pump piston 20 is designed, for example, as a stepped piston with a section 24 with a smaller diameter and a section 26 with a larger diameter, although this is by no means mandatory. The section 26 of the pump piston 20 with the larger diameter, together with the pump housing 16, delimits a pumping chamber 28. This is fluidically connected to the inlet valve 12 and the outlet valve 14 via channels that are not designated further. The pump housing 16 can be designed as an overall rotationally symmetrical part. The pump piston 20 is received in the pump housing 16 in the receiving opening 18, which is designed as a stepped blind hole with sections that each have different diameters.

A sleeve-shaped seal 32 made of a plastic material is arranged between the section 26 of the pump piston 20 and an inner peripheral wall 30 of the receiving opening 18 . This seals, as will be explained in more detail below, directly between the pump piston 20 and the pump housing 16, and thus seals the pumping chamber 28 ("high-pressure area") located above the annular seal 32 in FIG. 1 compared to that in FIG 1 below the annular seal 32 arranged area (“low pressure area”). Between the section 26 of the pump piston 20 and the inner peripheral wall 30 of the receiving opening 18 there is a sleeve-shaped guide element 34 which is separate from the sleeve-shaped seal 32 and is arranged above the seal 32, which to this extent forms an annular section. It is used for the radial guidance of the pump piston 20. In FIG. 1, below the seal 32, there is also a sleeve-shaped holding element 36, which is arranged in the lower region of the receiving opening 18 in FIG. During normal operation of piston pump 10, sleeve-shaped seal 32 rests against a mating surface (without reference number in Figure 1) of retaining element 36 that faces seal 32 in such a way that a static sealing point is formed there, which seals seal 32 from retaining element 36.

The retaining element 36 can be pressed into the pump housing 12 or it can be caulked in the receiving opening 18 or welded to the pump housing 16 . The piston pump 10 has a further guide element 38, which is also a sleeve-shaped part and is arranged in a carrier (no reference number) which protrudes downwards from the pump housing 16 in FIG. The guide element 38 also serves to guide the pump piston 20 relative to the pump housing 16.

As can be seen in particular from FIGS. 2 and 3, the seal 32 has a first section 39 which extends in the axial direction and which is therefore overall sleeve-shaped or cylindrical. From the bottom edge of the seal 32 in the figures, that is to say the edge facing the holding element 36, a circumferential second section 40 extends radially outwards in the manner of a circumferential annular collar. In normal operation of the piston pump 10, a lower end face 42 of the seal 32 or of the radially extending section 40 in Figure 2 contacts a mating face 44 of the holding element 36 which faces upwards in Figure 1.

As can be seen from FIGS. 2 and 3, in the region of the mutually adjacent ends of annular section 34 and seal 32 there are a plurality of flow passages 46 which at least also extend radially overall (ie allow a radial flow). In the present case, these are present on an upper edge 48 of the seal 32 in the figures. The Flow passages 46 are formed between each adjacent spacer 50 as viewed in the circumferential direction. It can be seen in particular from FIG. 3 that the total extent of the flow passages 46 seen in the circumferential direction is considerably greater than the total extent of the spacers 50 seen in the circumferential direction. In the present exemplary embodiment, the spacers 50 have a rectangular cross section when viewed in the axial direction. They are formed integrally with the seal 32 in the manner of axially extending projections or nubs.

In the embodiment shown in FIGS. 1-3, three spacers 50 are provided, distributed uniformly over the circumference. It goes without saying that more spacers can also be provided in non-illustrated embodiments.

The hydraulic conditions that prevail at the beginning of the operation of the piston pump 10 are shown in FIGS. R1 denotes the leakage path through the gap between the pump piston 20 and the receiving opening 18 of the pump housing 16 above the annular portion 34. R2 denotes the leakage path between the seal 32 and the pump piston 20. R3 denotes the leakage path through the flow passages 46 through. R4 denotes the leakage path between the radial outside of the annular collar 40 and the receiving opening 18. R5 denotes the leakage path through the initially existing gap between the lower end face 42 of the annular collar 40 of the seal 32 and the counter surface 44 of the retaining element 36. R6 denotes the leakage path between the Holding element 36 and the pump piston 20.

P1 denotes the pressure that is present above the gap between the pump piston 20 and the receiving opening 18, with P1 essentially corresponding to the pressure in the pumping chamber 28 (pressure in the high-pressure area). PO designates the pressure that is present below the gap between the pump piston 20 and the holding element 36, with PO essentially corresponding to the pressure in the low-pressure area. P1 is > PO. This is achieved by appropriate dimensioning of R5, taking into account all tolerances and boundary conditions. The gaps are to be dimensioned in such a way that there are sufficient cross sections on the leakage paths R1, R3, R4 and R6 that there is almost no throttling. The gap at the throttling point R5 should be designed in such a way that laminar flow conditions prevail in it for narrow gaps. As can be seen from FIG. 5, ultimately only two relevant throttle points remain, namely the leakage paths R2 and R5.

The seal 32 is accommodated with a small, defined axial play between the annular section 34 and the holding element 36 . At the beginning of the operation of the piston pump 10 there is therefore a small gap between the counter surface 44 and the front surface 42 (leakage path R5). Typically this gap is in the range of 5-300 pm. There is also a small gap between the seal 32 and the pump piston 20 (leakage path R2). All other gaps or leakage paths are comparatively large. If the piston pump 10 is now started, the high pressure from the delivery chamber 28 is transmitted via the leakage path R1 and through the flow passages 46 (leakage path R3) into the space 52 between the seal 32 and the receiving opening 18 of the pump housing 16 .

Due to the relevant throttling in the leakage paths R2 and R5, a comparatively high pressure builds up in this space 52 (higher than P0), which causes a resultant force on an annular surface 54 of the annular collar 40 facing away from the retaining element 36 that is directed axially toward the retaining element 36. As a result, the end face 42 of the annular collar 40 is pressed against the mating face 44, as a result of which the leakage path R5 is closed. This leads to a further increase in pressure in the space 52, through which the cylindrical section 39 of the seal 32 is pressed radially inwards against the outer lateral surface of the pump piston 20. The seal 32 thus rests against the pump piston 20 and seals there.

In the alternative embodiment shown in Figure 6, the seal 32 is similar to that shown in Figure 3. However, the spacers 50 are round, namely circular, in cross-section. Figure 7 shows the guide element or the annular section 34 of a further embodiment of a piston pump 10. In this embodiment, the spacers 50 are not on the seal 32, but on a lower one in the figure and to the seal 32 pointing edge of the guide element 34, specifically in the form of spacers 50 having rectangular cross sections.

In a further embodiment that is not shown, the flow passage is provided as a channel, for example in the form of a radial or inclined radial bore, in the seal and/or the annular section.

Claims

Expectations

1. Piston pump (10), in particular a high-pressure fuel pump for an internal combustion engine, with a pump piston (20), a pumping chamber (28), a seal (32) arranged annularly around the pump piston (20) and interacting with it at least temporarily, and an annular section (34) which is arranged annularly around the pump piston (20) and seen in the axial direction between the seal (32) and the pumping chamber (28), characterized in that the annular section (34) to the seal (32) is immediately adjacent, and that in the region of the mutually adjacent ends of the annular section (34) and the seal (32) there is at least one flow passage (46) which extends essentially radially overall.

2. Piston pump (10) according to claim 1, characterized in that at least one flow passage (46) is present in or on the seal (32).

3. Piston pump (10) according to at least one of the preceding claims, characterized in that at least one flow passage (46) is present in or on the annular section (34).

4. Piston pump (10) according to at least one of the preceding claims, characterized in that the annular section is a guide section (34) for the pump piston (20).

5. Piston pump (10) according to at least one of the preceding claims, characterized in that in the region of the mutually adjacent ends of the annular section (34) and seal (32) there is a plurality of essentially radially extending flow passages (46). between spacers (50) are formed, the total extent of the flow passages (46) in the circumferential direction seen is greater than the total extent of the spacers (50) seen in the circumferential direction. Piston pump (10) according to Claim 5, characterized in that at least one spacer (50) has a round, preferably circular, cross section when viewed in the axial direction. Piston pump (10) according to Claim 5 or 6, characterized in that at least one spacer (50) has a rectangular cross section when viewed in the axial direction. Piston pump (10) according to at least one of the preceding claims, characterized in that when the piston pump (10) is in operation, the seal (32) is supported in the axial direction with an end remote from the pumping chamber (28) on a counter-surface (44), and that at the start of operation, the hydraulic gap between the seal (32) and counter-surface (44) is designed in such a way that laminar flow conditions prevail, in particular that the gap has a width in the range of 5-300 μm. Piston pump (10) according to at least one of the preceding claims, characterized in that the seal (32) is made of a plastic material.