WO2019206491A1

WO2019206491A1 - Sealing device for a high pressure fuel pump having a piston

Info

Publication number: WO2019206491A1
Application number: PCT/EP2019/053934
Authority: WO
Inventors: Patrick Hallas; Anja KEETMAN
Original assignee: Robert Bosch Gmbh
Priority date: 2018-04-24
Filing date: 2019-02-18
Publication date: 2019-10-31
Also published as: DE102018206312A1

Abstract

The invention relates to a method for producing a sealing device (74) for a high-pressure fuel pump (28) having a piston (30), said piston having an end section facing a drive, on which the sealing device can be provided radially surrounding the piston (30), such that the piston (30) can be shifted along its longitudinal axis (64) relative to the sealing device (74), wherein the sealing device (74) has at least one radially inner circumferential sealing section (78). According to the invention, the sealing section (78) is produced via machining at a temperature below the ambient temperature.

Description

description

title

Sealing device for a high-pressure fuel pump with a piston

State of the art

For example, from DE102014225319 A1 are sealing devices for high-pressure fuel pumps with a piston, at its end facing a drive the sealing means the piston radially enclosing providable so that the piston along its longitudinal axis relative to the sealing device is displaceable, wherein the sealing means at least one radially inside circumferential sealing portion has known.

The density devices are made wholly or partly by machining, according to the prior art, this is done at room temperature.

Disclosure of the invention

The invention is based on the recognition that a machining at room temperature, ie at 20 ° C, is not optimal in terms of the properties of the product produced.

It was recognized that at lower temperatures (<20 ° C) machining can be carried out with greater dimensional accuracy. The manufactured

Sealing devices have, in particular, a more closed surface, a smaller roughness depth and have lower dimensional variations among one another.

Consequently, the sealing devices produced in this way are less prone to wear and tear, especially during the initial installation of the seal. The reason for the better dimensional accuracy of the sealing devices produced is to be considered that the hardness of the sealing device below the

Room temperature is greater, so that it comes to a lesser extent by the machining to elastic and / or plastic deformation of the sealing device.

A sealing device according to the invention and the high-pressure fuel pump according to the invention have improved tightness.

Preferably, the machining does not take place below the

Glass transition temperature of the material of the sealing device. This takes into account the observation that in this temperature range, the material of the sealing device is brittle, whereby the result of machining again deteriorates.

Other developments of the invention are the subject of the dependent claims and the description.

Hereinafter, exemplary embodiments of the invention will be explained with reference to the drawings. In the drawing show:

Figure 1 is a simplified schematic representation of a fuel system for an internal combustion engine;

2 shows a longitudinal section through a fuel high-pressure pump of

Fuel system of Figure 1;

3 shows a detail of Figure 2 in an enlarged view;

FIG. 4 shows an axial sectional view of a sealing device for a piston of the high-pressure fuel pump;

FIG. 5 shows a flow chart for a method for producing the

Sealing device. The same reference numerals are used for functionally equivalent elements and sizes in all figures, even in different embodiments.

FIG. 1 shows a fuel system 10 for a further not shown

Internal combustion engine in a simplified schematic representation. Fuel is supplied from a fuel tank 12 via a suction line 14, by means of a prefeed pump 16, via a low-pressure line 18, via an inlet 20 of a quantity control valve 24 which can be actuated by an electromagnetic actuating device 22 to a delivery chamber 26 of a high-pressure fuel pump 28. For example, the quantity control valve 24 may be a forcibly opening inlet valve of the high-pressure fuel pump 28.

In the present case, the high-pressure fuel pump 28 is designed as a piston pump, wherein a piston 30 can be moved vertically by means of a cam disk 32 ("drive") in the drawing. Hydraulically between the delivery chamber 26 and an outlet 36 of the high-pressure fuel pump 28, a drawn in the figure 1 as a spring-loaded check valve outlet valve 40 is arranged, which can open to the outlet 36 out. The outlet 36 is at a

High-pressure line 44 and connected via this to a high-pressure accumulator 46 ("common rail"). Furthermore, a likewise drawn as a spring-loaded check valve pressure relief valve 42 is arranged hydraulically between the outlet 36 and the delivery chamber 26, which can open to the delivery chamber 26 through.

During operation of the fuel system 10, the prefeed pump 16 delivers fuel from the fuel tank 12 into the low pressure line 18. The quantity control valve 24 may be closed and opened in response to a respective demand for fuel. As a result, the amount of fuel delivered to the high-pressure accumulator 46 is influenced. The electromagnetic actuator 22 is controlled by a control and / or regulating device 48.

FIG. 2 shows the high-pressure fuel pump 28 of FIG. 1 in an axial sectional representation. The high-pressure fuel pump 28 comprises a housing 50, which by means of a flange 52 on an engine block 53 of the

Internal combustion engine is screwed. The housing 50 also has several hydraulic channels 54, 55, 56 and 58 on. In the upper area in FIG. 2, the high-pressure fuel pump 28 comprises a cover 60 and a cover

Pressure damper 62. The high-pressure fuel pump 28 is at least partially rotationally symmetrical to a longitudinal axis 64 executed.

In a left-hand area in the drawing, the high-pressure fuel pump 28 has the outlet 36 for connection to the high-pressure line 44. Hydraulically connected to the outlet 36, the outlet valve 40 (in a left-hand portion in the drawing) and the pressure-limiting valve 42 (in a middle portion) are disposed in the housing 50. In a middle right section of the housing 50 in the drawing, the quantity control valve 24 is arranged.

Furthermore, the high-pressure fuel pump 28 includes: the delivery chamber 26, the piston 30 and a bushing 66. The along the longitudinal axis 64th

slidable piston 30 is designed as a so-called "stepped piston" and has essentially two sections. A first section (in the drawing above) with a comparatively large diameter, by means of which it is guided in the bushing 66, and a second section (in the drawing below) with a comparatively small diameter.

A lower region of FIG. 2 is identified by a frame III and shown enlarged in FIG. In particular, Figure 3 shows a roughly cup-shaped seal carrier 68, as well as a radially outwardly disposed about a portion of the seal carrier 68 and designed as a helical spring piston spring 70 which extends with an end portion on the

Seal carrier 68 is supported, which is why this is also referred to as "spring recording". At one in the drawing lower and the drive

facing end portion of the piston 30, a spring plate 72 is pressed, to which an end portion of the piston spring 70 is received.

Radially inside the seal carrier 68, a piston seal (also referred to as a "low-pressure seal"), referred to as a sealing device 74, which radially surrounds the lower second section (which faces the drive) of the piston 30 and which exists between the housing 50 and the seal carrier 68 Fluid space ("step room") seals to the outside to the engine block 53 out. The piston 30 is displaceable along the longitudinal axis 64 relative to the sealing device 74. To a rough approximation, the sealing device 74 has an overall annular structure.

In the present case, the sealing device 74 in FIG. 2 is supported axially upwardly by a holding section 76 which is arranged inside the seal carrier 68 and which likewise has an approximately hat-shaped design. In the drawing

characterize a space area above the sealing device 74 a

"Fuel side" and a space below the sealing device 74, an "oil side".

Furthermore, the sealing device 74 in FIG. 2 is supported axially downward by a peripheral edge portion of the seal carrier 68 bent radially inwards. It is understood that the sealing device 74 may optionally have a slight axial play within a region defined by the holding section 76 and the said edge section.

The sealing device 74 is arranged along the longitudinal axis 64 radially outward on the piston 30. In this case, the sealing device 74 is designed substantially rotationally symmetrical, wherein in the drawing, upper and lower portions of the sealing device 74 in this example are mutually axially mirror-symmetrical. Nevertheless, asymmetrical designs are possible and even advantageous if necessary. The sealing device 74 comprises in this example a machined post-processed injection molded part 77. This preferably comprises an elastic material, preferably a perfluoroalkoxy material ("PFA"), or is made of this, and is by means of a

Injection molding produced. Furthermore, it can be seen that the machined after-injection molded part 77 of the sealing device 74 at radially spaced apart from each other radially inwardly each having only one circumferential sealing portion 78. By means of the sealing portions 78, a "dynamic" seal against the relative to the sealing device 74 axially movable piston 30 takes place.

Preferably, an axial distance 80 of the sealing portions 78 corresponds to at least one stroke of the piston 30. Thus, the sealing portions 78, the fuel (in the drawing above the sealing device 74) and the oil (in the drawing below the sealing device 74) particularly good "strip" and thus prevent mixing of the fuel with the oil or at least minimize.

Figure 4 shows the sealing device 74 in a further enlarged

Sectional view. However, the sealing device 74 is present as an unassembled item, that is, it is not deformed in the present case by the piston 30 or the seal carrier 68. The sealing device 74 is at least in

Essentially rotationally symmetrical to the longitudinal axis 64 executed. Furthermore, in this example, the sealing device 74 is mirror-symmetrical to a transverse plane 89 (horizontal in the drawing and perpendicular to the longitudinal axis 64).

Furthermore, the machined after-injection molded part 77 of the

Sealing means 74 at radially opposite axial end portions remote from each other a circumferential sealing bead 82. By means of the sealing beads 82, the sealing means 74 against a radially inner portion of the seal carrier 68 "static" seal. For this purpose, the sealing device 74 is arranged non-positively in the seal carrier 68. In a radially central portion of the machined post-processed injection molded part 77 of the sealing device 74 radially encircling and so far annular springs 84 are added to mutually remote axial end portions of the sealing device 74, each consisting of a

Federblech are made and formed in the sectional plane of Figure 4 in approximately U-shaped. The springs 84 are open in the figure 4 each up or down. By the springs 84 on the one hand the two sealing portions 78 against the piston 30 and on the other hand, the sealing beads 82 acted upon against the seal carrier 68.

Radially inwardly about the longitudinal axis 64, the sealing device 74 has a rotationally symmetrical centric recess 86 in the manner of a

Through hole on. The recess 86 comprises two (outer) first axial portions 86a, then two (each "middle") second axial portions 86b and then two (each inner) third axial portions 86c. Axially centered between the third axial portions 86c is a single fourth axial portion 86d. The first, second and third axial portions 86a, 86b and 86c, and the fourth axial portion 86d each have respective radially inner first, second, third and fourth

Wall sections 88a, 88b, 88c and 88d.

A radially inner contour of the recess 86 formed by the first, second and third wall sections 88a, 88b and 88c is in each case conical. In this case, the first axial portions 86a each open axially outward. The second and third axial sections 86b and 86c respectively open axially inwards, ie towards the transverse plane 89. However, the axially inner fourth wall portion 88d is parallel to the longitudinal axis 64, that is cylindrical.

The cone-shaped first wall sections 88a each have, with respect to a plane perpendicular to the longitudinal axis 64, an angle a of from approximately 30 degrees to approximately 60 degrees. The cone-shaped second wall sections 88b each have an angle β with respect to the longitudinal axis 64. In this case, the angle β is preferably (but not necessarily) approximately half the size of the angle a. The cone-shaped third wall sections 88c each have an angle g (not shown in the drawing) with respect to the longitudinal axis 64, wherein the angle g is preferably smaller than the angle β.

The sealing device 74 shown has only one sealing lip per sealing section 78. Alternatively, but not shown here, more than one sealing lip per sealing section 78 may also be provided, for example as is already known in principle from WO 02/008061581 A1 or from WO2016 / 083587 A1.

FIG. 5 shows a flow chart for a method for producing the

Sealing means 74 of the high-pressure fuel pump 28 according to the figures 2 to 5. In a start block 100, the procedure shown begins.

In a following block 102, the sealing device 74 is injection-molded into an initial shape. In a following block 104, an axially central bore is drilled in the initial shape. In a following block 106, a subsequent machining of a radially inner contour of the injected or drilled initial shape, whereby a first and a second radially inner circumferential sealing portion 78 are made, wherein the first and the second sealing portion 78 respectively at mutually remote axial End portions of the sealing device 74 are arranged. In this example, the sealing means 74 is made of PTFE with a proportion of

Carbon fibers, which is 5% by weight. The cutting takes place at -10 ° C. In another example, the sealing device 74 is made of PFA with a

Proportion of carbon fibers, which is 15% by weight. In this example, the cutting takes place at -5 ° C.

In a following end block 108, the procedure illustrated in FIG. 5 ends.

In a preferred alternative embodiment of the method for

Manufacture of the sealing device 74 comprises that produced in block 102

Initial form already the axial centric bore, which is not generated in this case by a separate drilling operation. Therefore, the drilling process in the block 104 is thus dispensable, which in the figure 5 by a dashed line

(outside around the block 104 around) is indicated.

The material of the sealing device 74 and the temperature at which the machining takes place are as indicated in the preceding examples.

Claims

claims

1. A method for producing a sealing device (74) for a high-pressure fuel pump (28) with a piston (30), at the end portion facing a drive, the sealing means the piston (30) radially enclosing providable, so that the piston (30) along its longitudinal axis (64) relative to the sealing device (74) is displaceable, wherein the sealing means (74) has at least one radially inwardly encircling sealing portion (78), characterized in that the

Sealing section (78) is produced by machining at a temperature below room temperature.

2. The method according to claim 1, characterized in that the contour of the sealing device (74) entirely or only in the region of

3. The method according to claim 1 or 2, characterized in that the

Contour of the sealing device (74) entirely or only in the region of the sealing portion (78) made of a plastic or a fiber-plastic composite material.

4. The method according to claim 3, characterized in that the plastic is one of the following materials: PTFE, PFA, PEEK and that the fiber-plastic composite material additionally contains 0.1 to 20 wt% ceramic, glass and / or carbon fibers ,

5. The method according to any one of claims 3 or 4, characterized in that the machining takes place at a temperature which is between the room temperature and the glass transition temperature of the plastic or the fiber-plastic composite material or the plastic portion of the fiber-plastic composite material.

6. The method according to any one of claims 3 to 5, characterized in that the machining is carried out at a temperature between -40 ° C and 10 ° C, in particular between -25 ° C and 0 ° C.

7. The method according to any one of the preceding claims, characterized

characterized in that first a blank is produced by means of injection molding, from which the sealing device (74) emerges from the blank by means of machining.

8. A method for producing a high-pressure fuel pump (28) having a piston (30), at the end portion facing a drive, a sealing device, which is made according to one of claims 1 - 6, the piston (30) is provided radially enclosing, so the piston (30) along its longitudinal axis (64) relative to the sealing device (74) is displaceable, wherein the sealing means (74) has at least one radially inwardly encircling sealing portion (78).

9. sealing device (74) for a high-pressure fuel pump (28) with a piston (30), at whose end facing a drive the sealing means the piston (30) radially enclosing providable, so that the piston (30) along its longitudinal axis (64 ) is displaceable relative to the sealing device (74), wherein the sealing device (74) has at least one radially inwardly encircling sealing portion (78), characterized in that the sealing portion (78) has a closed structure and / or a small roughness.

10. High-pressure fuel pump (28) with a piston (30), at whose end portion facing a drive a sealing device according to claim 9, the piston (30) is provided radially enclosing, so that the piston (30) along its longitudinal axis (64) relative to the sealing device (74) is displaceable, wherein the sealing means (74) has at least one radially inwardly encircling sealing portion (78).