CN115773233A

CN115773233A - Piston pump and method for producing a piston seal for a piston pump

Info

Publication number: CN115773233A
Application number: CN202211087562.5A
Authority: CN
Inventors: W·比泽; D·纳克; F·波尔; K·格哈德; R·维尔姆斯; S·芙洛
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2021-09-07
Filing date: 2022-09-07
Publication date: 2023-03-10
Also published as: DE102021209832A1

Abstract

The invention relates to a piston pump comprising a pump housing, a pump piston (14), a delivery chamber delimited by the pump housing and the pump piston, and an annular piston seal (26), wherein the piston seal (26) has a higher radial stiffness in a first axial region (36) facing the delivery chamber than in a second axial region (38) facing away from the delivery chamber. The invention proposes that the piston seal (26) is produced from metal, in particular steel, and that the second axial region (38) comprises an axial section (45) extending in the circumferential direction, the material thickness of which is less than the material thickness in the two axial regions (36, 42) adjacent to the section (45), wherein the section (45) with the lower material thickness is produced at least essentially without cutting.

Description

Piston pump and method for producing a piston seal for a piston pump

Technical Field

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

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 places 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, a delivery chamber which is delimited at least by the pump housing and the pump piston, and an annular piston seal which is arranged locally between the pump housing and the pump piston in such a way that it is loaded at least locally against the pump piston by a pressure acting from the delivery chamber, wherein the piston seal has a higher radial stiffness in a first axial region facing the delivery chamber than in a second axial region facing away from the delivery chamber, wherein the piston seal is made of metal, in particular steel, and the second axial region comprises an axial section extending in the circumferential direction, the material thickness of which is less than the material thickness in two axial regions adjacent to the section, wherein the section with the smaller material thickness is produced at least essentially without cutting.

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

The piston pump according to the invention has an increased service life and reliability without adversely affecting the efficiency, i.e. the volumetric efficiency of the piston pump. This is achieved by the relatively low frictional power between the annular piston seal and the pump piston, since the length of contact between the annular piston seal and the pump piston is limited or reduced by the stiffness change caused by the design. In operation, the annular piston seal heats up only slightly as a result of the reduced frictional power, as a result of which the rigidity of the annular piston seal also changes only slightly and the service life of the piston seal increases. By reducing the stiffness in the region in which the piston seal is loaded radially inward by the pressure acting from the delivery chamber, a faster contact is achieved there, i.e. a faster "activation" of the piston seal is achieved. This means that relatively large radial tolerances which are not available or can only be used poorly in terms of functional technology up to now are absolutely possible. By the measure according to the invention, a significant improvement in the volumetric efficiency of the piston pump is thus achieved over all manufacturing tolerances.

The invention allows the piston seal to be produced from metal, in particular steel. The service life of the piston seal is thereby significantly improved, and the piston seal can also be used with fuel and at temperatures at which problems arise in the interaction with piston seals made of plastic. According to the invention, a limited reduction in the material thickness can be achieved in a structurally limited manner, at least substantially without machining the sleeve, and the sleeve does not require any further machining, so that considerable costs are saved and individual parts can be installed over the entire production cycle of the sleeve.

This is achieved in particular by a piston pump, in particular a high-pressure fuel pump for an internal combustion engine. Such an internal combustion engine can be used, for example, in a motor vehicle. The high-pressure fuel pump may belong to a fuel system which compresses the fuel to a high pressure and injects it directly into the combustion chamber of the internal combustion engine. The piston pump comprises a pump housing, which may be, for example, a generally cylindrical part, and a pump piston, which is received in a receiving opening present there in the pump housing and which may, for example, be designed as a stepped piston and may be set in a reciprocating motion by a drive. A delivery chamber, into which fluid is drawn in on the suction stroke and which is compressed to a high pressure and discharged through an outlet valve, is delimited by the pump housing and the pump piston.

The annular piston seal is arranged between the receiving opening of the pump housing and the pump piston in such a way that it is loaded at least partially radially inwardly against the pump piston by the pressure acting from the delivery chamber during the delivery stroke. The desired maximum sealing effect of the piston seal is thus only brought about by the high pressure acting on the piston seal from the radially outer to the radially inner side. The annular piston seal has a higher radial stiffness in a first axial region facing the delivery chamber than in a second axial region facing away from the delivery chamber. The axial extent of the first axial region having the higher radial stiffness can be greater than the axial extent of the second axial region.

If the high pressure from the delivery chamber acts on the annular piston seal from the radial outside, the longer first axial region is therefore less strongly pressed radially inwards than the shorter second axial region. The contact length or the friction length which is particularly effective for hydraulic piston seals is therefore substantially limited to the second axial region. However, in the first axial region, a pressure drop and thus a certain sealing behavior already occurs in the radial gap between the inside of the piston seal and the outside of the pump piston.

According to the invention, the piston seal is made of metal, in particular steel. For example, steel variants made of austenitic steels which are particularly suitable in the present case can be considered. The aforementioned second axial region comprises an axial section extending in the circumferential direction with a material thickness that is smaller than the material thickness in two axial regions adjacent to the section. The term "axial" section means that the section extends a distance in the axial direction of the piston seal.

This axial section extending in the circumferential direction may form the entire second axial region or also only have a smaller axial extent than the second axial region. The axial section extending in the circumferential direction may extend completely over the entire circumference in the circumferential direction, like a continuous groove, or only over a partial region or partial regions of the circumference. The axial section with the smaller material thickness is already produced at least substantially non-cutting by a corresponding shaping process, which can be identified, for example, in the sectional image on the basis of the crystal structure and/or on the basis of surface properties. Honing is not necessary.

In one embodiment of the piston pump according to the invention, it is provided that the section with the smaller material thickness is produced by a deep drawing process, in particular a drawing process, or by rolling. The invention relates to inexpensive, highly accurate and rapidly executable modifications and forming processes.

In a further development of the piston pump according to the invention, it is provided that the transition from the greater material thickness to the lesser material thickness extends at least substantially continuously. Stress peaks in the material can thereby be prevented, thereby increasing the service life.

In one embodiment of the piston pump according to the invention, it is provided that the axial extent of the first axial region is greater than the axial extent of the second axial region. In this way, a certain pressure drop is already produced in the first axial region, as a result of which the volumetric efficiency of the piston pump is improved again.

The invention also comprises a method for manufacturing a piston seal for a piston pump of the type described above, comprising the steps of:

a. manufacturing a cylindrical semi-finished piece from metal;

b. the axial section extending in the circumferential direction is produced without cutting, the material thickness of which is less than in the two axial regions adjacent to this section.

The same advantages and detailed explanations apply here as already explained above for the piston pump.

In one embodiment of the piston pump according to the invention, it is provided that in step b the section with the smaller material thickness is produced by a deep-drawing process, in particular a drawing process. An inexpensive and rapidly performable forming process can be involved here.

In one embodiment of the piston pump according to the invention, it is provided that in step b the semifinished part is clamped in two axial regions adjacent to the axial sections and then stretched in the axial direction. This can be achieved simply in the usual deep-drawing tools.

In a further development of the piston pump according to the invention, it is provided that after step b the following steps are included:

c. the inner diameter is enlarged to the desired inner diameter, in particular by introducing a calibration mandrel.

In this way, the inner circumferential surface of the annular piston seal is brought precisely to the desired diameter dimension, i.e., the "calibration" dimension. Furthermore, it is possible to achieve a renewed displacement of the material in such a way that a small material thickness of the axial section extending in the circumferential direction is only brought about by the constriction onto the radial outer side of the annular piston seal, and the annular seal rests with its straight, radially inner circumferential surface on the pump piston as best as possible, i.e. with the smallest possible distance.

d. the radially inner surface and/or the radially outer surface of the piston seal is at least partially subjected to a coler stirling process.

This again reduces wear on the piston seal surfaces. In such a coler stirling process, the surface is hardened by a carbon diffusion process and is therefore particularly wear resistant.

Drawings

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

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

FIG. 2: the annular piston seal and the pump piston of fig. 1 are enlarged in a first operating state.

FIG. 3: similar to the schematic diagram of fig. 2, in a second operating state;

FIGS. 4a-4e: FIGS. 1-3 are schematic views of the piston seal during its manufacture; and

FIG. 5: a graph of the pressure drop in the gap between the piston seal and the pump piston and the gap size over the length of the piston seal for the piston seal according to the invention and the piston seal from the prior art.

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 smaller-diameter section 16 and a larger-diameter section 18. 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. The pump piston 14 is received in a receiving opening 22 present there in the pump housing 12, which is designed as a stepped bore 24 having sections 24', 24 "and 24"', respectively, shown here with different diameters.

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, which pretensioning element loads the annular seal 26 downward in fig. 2 against an annular retaining element 30, which 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 piston seal 26 against the retaining element 30.

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 detailed configuration of the annular seal 26 will now be explained with reference to fig. 2-3: the annular seal 26, viewed from the top downwards in fig. 2, firstly comprises a sleeve-shaped and cylindrical and relatively long first axial region 36 with a constant wall thickness D1. Adjoining this first axial region is a relatively short second axial region 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 second axial region 38 is a third axial region 42 which comprises an abutment section 44 shaped in the form of an annular flange and directed radially outward. Thus, the piston seal 26 shown here by way of example has a generally approximately L-shaped cross section. The axial region of the constriction 40 forms in this respect an axial section 45 which extends over the entire circumference in the circumferential direction and has a material thickness which is less than the material thickness in the two

axial regions

38 and 42 adjacent to the section 45.

As can be seen from fig. 1 and fig. 2 to 3, the transition from the larger material thickness D1 to the smaller material thickness D2 is continuous, i.e. without "sharp" steps. The same applies from the material thickness D2 of the section 45 to the third axial region 42 with the abutting section 44. The piston seal 26 is currently produced from metal, i.e. steel, in particular austenitic steel.

The operation and function of the piston seal 26 will now be explained with particular reference to fig. 2 and 3, wherein for the sake of clarity not all reference numerals are drawn in fig. 3. In fig. 2, an initial situation is shown which exists when the piston pump 10 is not operating. The same pressure, i.e. the ambient pressure, is present at all points on the outside of the piston seal 26, and a uniform gap 50 of substantially constant thickness is present between the inner, in this operating condition straight circumferential surface 46 of the annular piston seal 26 and the outer circumferential surface 48 of the pump piston 14.

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 undiminished 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 piston seal 26 in a manner not visible in the drawing. In this way, the pressure prevailing in the delivery chamber 20 acts on the upper end face 52 of the piston seal 26 in fig. 3, on the radial outer circumferential faces 54 of the first section 36 and the second section 38, and on the end face 56 facing the delivery chamber 20 and the radial outer circumferential face 58 of the abutment section 44, which is illustrated in fig. 3 by corresponding arrows, all of which have the same length and one of which is designated, for example, by P20.

This pressure P20 is also present in the upper region of the inner circumferential surface 46 of the piston seal 26 in fig. 3. However, in the gap 50, 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 50 in fig. 3. In the axial section 45 of the piston seal 26, the pressure acting on the inner circumferential surface 46 of the piston seal 26 is therefore significantly lower than the pressure acting there on the radial outer circumferential surface 54. Furthermore, since the stiffness in the axial section 45 of the piston seal 26 is significantly lower than in the adjacent first axial region 36 due to the smaller material thickness D2, the piston seal 26 is pressed radially inward in the region of the axial section 45 against the pump piston 14, which is illustrated by the shaded region 60 in fig. 3. At the point at which the piston seal 26 is pressed radially inward, it bears against the pump piston 14 via a contact length region 62 extending in the axial direction. A particularly strong sealing effect is thus produced in the contact length region 62 and, as a result, correspondingly large pressure differences are produced, as is shown by the schematic diagram Δ P in fig. 3.

As can be seen from fig. 3, the first axial region 36 has a higher radial stiffness due to the greater material thickness D1 than the second axial region 38 or the axial section 45 with the smaller material thickness, the first axial region 36 having a greater axial extent of about 2.5 times greater than the second axial region 38.

The production of the constriction 40 or the axial section 45 will now be explained in more detail with reference to fig. 4. The first step of the production method is shown directly above in fig. 4 a. In this first step, a pot-shaped semifinished part 70 is produced from the sheet metal strip 64 by a deep-drawing process by means of a cylindrical punch 66 and a surrounding outer die 68.

In a second step (fig. 4 b), the semifinished part 70 is placed in a surrounding outer die 72 which tapers towards the semifinished part 70 and is surrounded above the outer die 72 by an annular outer piston 74. The outer piston 74 bears in a press-fit manner against the outer surface of a peripheral wall (no reference numeral) of the semifinished part 70, which is indicated in fig. 4b by the radially inwardly pointing arrow, and the cylindrical punch 66 bears internally also in a press-fit manner against the inner surface of the peripheral wall of the semifinished part 70, however only above the axial position of the surrounding outer die 72.

In a third step (fig. 4 c), the punch 66 and the outer piston 74 are moved in the direction of the arrow 76, whereby the circumferential wall of the semi-finished part 70 is stretched in the region of the radially inner edge of the outer die 72 and the material thickness is thereby reduced there. In this way, the constricted portions are formed not only on the outer surface but also on the inner surface of the peripheral wall of the work in process 70.

In a fourth step (fig. 4 d), the semifinished part 70 thus produced is placed in a further outer mold 78. Then, the calibration mandrel 80 is introduced into the work in process piece 70, whereby the inner diameter of the work in process piece 70 is enlarged to a desired inner diameter. The constriction is completely displaced onto the outside of the circumferential wall of the semifinished part 70 by appropriate dimensioning of the calibrating mandrel 78.

In a fifth step (fig. 4 e), the bottom of the semifinished part 70 is separated, for example by stamping by means of a stamping piston 82. In this way, a piston seal 26 is obtained which is already largely finished. A kolstericerning process (kolstericerung) is also now performed on the piston seal, where the surface is hardened by a carbon diffusion process. Thereafter, the inner diameter of the piston seal 26 needs to be recalibrated again if necessary.

In fig. 5, the abscissa indicates the length L of the piston seal 26, wherein the left end of the abscissa corresponds to the upper end of the piston seal 26 in fig. 1-3. The ordinate represents the pressure drop Δ p in the gap 50 and the width of the gap 50, wherein the curve W1 represents the width of the gap 50 in the case of the piston seal 26 of fig. 1-3, while the other curves represent the width of the gap 50 in the case of various embodiments in the prior art. It can be seen that the contact length area 62 is relatively small.

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), a delivery chamber (20) which is delimited at least by the pump housing (12) and the pump piston (14), and an annular piston seal (26) which is arranged locally between the pump housing (12) and the pump piston (14) in such a way that it is loaded at least locally against the pump piston (14) by a pressure acting from the delivery chamber (20), wherein the piston seal (26) has a higher radial stiffness in a first axial region (36) facing the delivery chamber (20) than in a second axial region (38) facing away from the delivery chamber (20), characterized in that the piston seal (26) is manufactured from metal, in particular steel, and the second axial region (38) comprises an axial section (45) extending in the circumferential direction, the material thickness of which is smaller than the material thickness in the two axial regions (36, 42) adjacent to the section (45), wherein the material thickness of the section (45) is at least substantially smaller.

2. Piston pump (10) according to claim 1, characterized in that the section (45) with the smaller material thickness is produced by a deep drawing process, in particular a drawing process, or by rolling.

3. Piston pump (10) according to at least one of claims 1 to 2, characterized in that the transition from the greater material thickness (D1) to the lesser material thickness (D2) extends at least substantially continuously.

4. Piston pump according to at least one of claims 1 to 3, characterized in that the axial extension of the first axial region (36) is greater than the axial extension of the second axial region (38).

5. Method for manufacturing a piston seal for a piston pump according to any of the preceding claims, characterized in that the method comprises the steps of:

a. -producing a cylindrical semifinished part (70) from metal;

b. an axial section (45) extending in the circumferential direction is produced without cutting, the material thickness of said section being less than the material thickness in two axial regions (36, 42) adjacent to said section (45).

6. Method according to claim 5, characterized in that in step b the section (45) with the smaller material thickness is also produced at least by a deep drawing process, in particular a drawing process.

7. Method according to claim 6, characterized in that in step b the semi-finished piece (70) is clamped in two axial regions (36, 42) adjacent to the section (45) with the smaller material thickness and then stretched in the axial direction.

8. Method according to at least one of the claims 5-7, characterized in that the method comprises after step b the steps of:

c. the inner diameter is enlarged to the desired inner diameter, in particular by introducing a calibration mandrel (80).

9. Method according to at least one of the claims 5-8, characterized in that the method comprises after step b the steps of:

d. a kerr stirling treatment is applied at least partially to a radially inner surface and/or a radially outer surface of the piston seal.