DE102018206312A1 - Sealing device for a high-pressure fuel pump with a piston - Google Patents

Abstract

The invention relates to a method for producing a sealing device (74) for a high-pressure fuel pump (28) with a piston (30) at whose end section facing a drive the sealing device is radially enclosing the piston (30), 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). It is envisaged that the sealing portion (78) is produced by machining at a temperature below room temperature.

Description

State of the art

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

• 1 eine vereinfachte schematische Darstellung eines Kraftstoffsystems für eine Brennkraftmaschine;
• 2 einen Längsschnitt durch eine Kraftstoff-Hochdruckpumpe des Kraftstoffsystems von 1;
• 3 einen Ausschnitt von 2 in einer vergrößerten Darstellung;
• 4 eine axiale Schnittansicht einer Dichteinrichtung für einen Kolben der Kraftstoff-Hochdruckpumpe;
• 5 ein Flussdiagramm für ein Verfahren zum Herstellen der Dichteinrichtung.

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

• 1 a simplified schematic representation of a fuel system for an internal combustion engine;
• 2 a longitudinal section through a fuel high-pressure pump of the fuel system of 1 ;
• 3 a section of 2 in an enlarged view;
• 4 an axial sectional view of a sealing device for a piston of the high-pressure fuel pump;
• 5 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.

1 shows a fuel system 10 for a further not shown internal combustion engine in a simplified schematic representation. From a fuel tank 12 will fuel through a suction line 14 , by means of a pre-feed pump 16 , via a low pressure line 18 , via an inlet 20 one of an electromagnetic actuator 22 actuatable quantity control valve 24 a pump room 26 a fuel high-pressure pump 28 is supplied. For example, the quantity control valve 24 a forcibly opening inlet valve of the high-pressure fuel pump 28 be.

The present is the high-pressure fuel pump 28 designed as a piston pump, wherein a piston 30 by means of a cam disc 32 ("Drive") can be moved vertically in the drawing. Hydraulically between the pumping room 26 and an outlet 36 the fuel high-pressure pump 28 is one in the 1 as spring-loaded check valve drawn outlet valve 40 arranged, which to the outlet 36 can open. The outlet 36 is to a high pressure line 44 and via this to a high-pressure accumulator 46 ("Common rail") connected. Furthermore, there is hydraulic between the outlet 36 and the pump room 26 a likewise drawn as a spring-loaded check valve pressure relief valve 42 arranged, which can open to the pumping chamber 26 out.

In operation of the fuel system 10 promotes the pre-feed pump 16 Fuel from the fuel tank 12 in the low pressure line 18 , The quantity control valve 24 can be closed and opened depending on a particular need for fuel. This becomes the high-pressure accumulator 46 subsidized fuel quantity influenced. The electromagnetic actuator 22 is controlled by a control and / or regulating device 48 driven.

2 shows the fuel high-pressure pump 28 from 1 in an axial sectional view. The fuel high pressure pump 28 includes a housing 50 , which by means of a flange 52 on an engine block 53 the internal combustion engine can be screwed. The housing 50 also has several hydraulic channels 54 . 55 . 56 and 58 on. I'm in the 2 Upper area includes the high-pressure fuel pump 28 a lid 60 and a pressure damper 62 , The fuel high pressure pump 28 is at least partially rotationally symmetric to a longitudinal axis 64 executed.

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

Furthermore, the fuel high pressure pump includes 28 : The pump room 26 , the piston 30 and a liner 66 , The along the longitudinal axis 64 sliding 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 he is in the bushing 66 is guided, and a second section (in the drawing below) with a relatively small diameter.

A lower area of 2 is characterized by a frame III and in the 3 shown enlarged. In particular, the shows 3 an approximately cup-shaped seal carrier 68 , as well as a radially outside around a portion of the seal carrier 68 arranged and designed as a helical spring piston spring 70 , which forms an end portion on the seal carrier 68 is supported, which is why this is also referred to as "spring recording". At an in the drawing lower and the drive-facing end portion of the piston 30 is a spring plate 72 pressed on which an end portion of the piston spring 70 is included.

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

Present is the sealing device 74 in the 2 up through one inside the seal carrier 68 arranged and also in approximately hat-shaped holding section 76 axially supported. In the drawing, a space area above the sealing means characterize 74 a "fuel side" and a space below the sealing device 74 an "oil side".

Furthermore, the sealing device 74 in the 2 down through a radially inwardly curved peripheral edge portion of the seal carrier 68 axially supported. It is understood that the sealing device 74 within a through the holding section 76 and the said edge portion may optionally have a small axial clearance.

The sealing device 74 is along the longitudinal axis 64 radially outward on the piston 30 arranged. Here is the sealing device 74 designed to be substantially rotationally symmetrical, wherein in the drawing, upper and lower portions of the sealing device 74 in this example, they are axially symmetrical with respect to each other. Nevertheless, asymmetrical designs are possible and even advantageous if necessary. The sealing device 74 includes in this example a machined post-processed injection molded part 77 , This preferably comprises or is made of an elastic material, preferably a perfluoroalkoxy material ("PFA"), and is produced by means of an injection molding process. Furthermore, it can be seen that the machined post-injection molded part 77 the sealing device 74 at spaced apart axial end portions radially inwardly only one circumferential sealing portion 78 having. By means of the sealing sections 78 there is a "dynamic" seal against the relative to the sealing device 74 axially movable piston 30 ,

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

4 shows the sealing device 74 in a further enlarged sectional view. This is the sealing device 74 however, as an unassembled item before, that is, it is not present in the present case by the piston 30 or the seal carrier 68 deformed. The sealing device 74 is at least substantially rotationally symmetrical to the longitudinal axis 64 executed. Furthermore, the sealing device 74 in this example, mirror-symmetrical to a (horizontal in the drawing and to the longitudinal axis 64 right-angled) transverse plane 89 executed.

Furthermore, the machined post-processed injection molded part 77 the sealing device 74 at spaced axial end portions radially outwardly each have a circumferential sealing bead 82 , By means of the sealing beads 82 can the sealing device 74 against a radially inner portion of the seal carrier 68 "static" seal. This is the sealing device 74 non-positively in the seal carrier 68 arranged. In a radially middle section of the machined after-injection molded part 77 the sealing device 74 are at mutually remote axial end portions of the sealing device 74 radially encircling and so far annular springs 84 received, which are each made of a spring plate and in the sectional plane of the 4 are formed in approximately U-shaped. The feathers 84 are in the 4 each up or down open. By the springs 84 On the one hand, the two sealing sections 78 against the piston 30 and on the other hand the sealing beads 82 acted upon the seal carrier 68.

Radially inward around the longitudinal axis 64 has the sealing device 74 a rotationally symmetric centric recess 86 in the manner of a through hole. The recess 86 includes two (outer) first axial sections 86a , followed by two (each "middle") second axial sections 86b and then two (each inner) third axial sections 86c , Axially centered between the third axial sections 86c is a single fourth axial section 86d arranged. The first, second and third axial sections 86a . 86b and 86c , as well as the fourth axial section 86d each have associated radially inner first, second, third and fourth wall sections 88a . 88b . 88c and 88d on.

One through the first, second and third wall sections 88a . 88b and 88c formed radially inner contour of the recess 86 is each cone-shaped. The first axial sections open 86a each axially outward. The second and third axial sections 86b and 86c open in each case axially inward, ie to the transverse plane 89 out. The axially inner fourth wall section 88d is however parallel to the longitudinal axis 64 , so cylindrical.

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

The sealing device shown 74 points per sealing section 78 only a sealing lip. Alternatively, but not shown here, can also have more than one sealing lip per sealing section 78 be provided, for example, as it is from the WO2008061581 A1 or from the WO2016 / 083587 A1 already known in principle.

5 shows a flowchart for a method for producing the sealing device 74 the fuel high-pressure pump 28 according to the 2 to 5 , In a starting block 100 begins the procedure shown.

In a following block 102 An injection molding of the sealing device takes place 74 to a starting form. In a following block 104 an axial centric hole is drilled in the initial shape. In a following block 106 a subsequent machining takes place of a radially inner contour of the injected or drilled initial shape, whereby a first and a second radially inwardly encircling sealing portion 78 be prepared, wherein the first and the second sealing portion 78 in each case at mutually remote axial end portions of the sealing device 74 are arranged. In this example, the sealing device exists 74 made of PTFE with a carbon fiber content of 5% by weight. The cutting takes place at -10 ° C.

In another example, the sealing device 74 made of PFA with a carbon fiber content of 15% by weight. In this example, the cutting takes place at -5 ° C.

In a following endblock 108 ends in the 5 presented procedure.

In a preferred alternative embodiment of the method for producing the sealing device 74 includes those in the block 102 produced starting form already the axial centric bore, which in this case is not generated by a separate drilling operation. Therefore, the drilling process is in the block 104 so dispensable, what in the 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 is as indicated in the preceding examples.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102014225319 A1 [0001]
• WO 2008061581 A1 [0029]
• WO 2016/083587 A1 [0029]

Claims (10)

Method for producing a sealing device (74) for a high-pressure fuel pump (28) with a piston (30), at whose end section facing the drive, the sealing device can be provided radially enclosing the piston (30), so that the piston (30) along its longitudinal axis (64) is displaceable relative to the sealing device (74), wherein the sealing means (74) at least one radially inner circumferential sealing portion (78), characterized in that the sealing portion (78) is produced by machining at a temperature below room temperature , Method according to Claim 1 , characterized in that the contour of the sealing device (74) wholly or only in the region of the sealing portion (78) is produced by machining at a temperature below room temperature. 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) consists of a plastic or of a fiber-plastic composite material. 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 - 20 wt% ceramic, glass and / or carbon fibers. Method according to one of Claims 3 or 4 , characterized in that the machining is carried out 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 part of the fiber-plastic composite material. Method according to 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. Method according to one of the preceding claims, characterized in that initially a blank is produced by means of injection molding, from which the sealing device (74) emerges from the blank by means of machining. Method for producing a high-pressure fuel pump (28) with a piston (30), at whose end portion facing a drive, a sealing device according to one of Claims 1 - 6 is made, the piston (30) is provided radially umschließend so that the piston (30) along its longitudinal axis (64) relative to the sealing device (74) is displaceable, wherein the sealing means (74) at least one radially inner circumferential sealing portion (78) having. 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) at least one radially inner circumferential sealing portion (78), characterized in that the sealing portion (78) has a closed structure and / or a small roughness. High-pressure fuel pump (28) with a piston (30), at whose end facing a drive end 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).

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