EP1517766B1 - Method for the hydro-erosive rounding of an edge of a part and use thereof - Google Patents

Description

The invention relates to a method for the hydro-erosive rounding of an edge of a component, in particular an edge in a channel of a high-pressure-resistant component, in which a fluid mixed with abrasive bodies is conducted along the edge to be rounded. The invention also relates to a use of the aforementioned method.

It is well known that in high pressure resistant components, such as injectors for diesel fuel, arranged in the region of a nozzle needle seat of the injector injection holes for the fuel are eroded into the housing of the injection nozzle. After the eroding of the injection holes of the diesel injection nozzle, these, in particular their inlet edges, are rounded off in a hydro-erosive manner in order to counteract the occurrence of local stress peaks favoring component fatigue. In hydro-erosive rounding is a liquid grinding process in which an offset with abrasive particles liquid, preferably an oil, the injection holes flows through under pressure, so that the inlet edges of the injection holes are rounded. On the one hand, this grinding process fulfills the task of adjusting the flow coefficient of the injection holes and thus of optimizing the efficiency of the injection nozzle. For this purpose, a desired target flow coefficient is set, whereby the flow tolerance is also reduced. On the other hand, the aging process occurring during engine operation of the injection nozzle is anticipated, so that it only occurs slightly during operation. In recent years, it has been shown that injectors, the one have high efficiency, achieve particularly good emission and performance values. An increase in efficiency can be achieved by a higher degree of rounding.

The disadvantage here, however, that only comparatively low Verrundungsgrade can be achieved with the standard oil used as grinding liquid, since at an increase in the delivery pressure of the grinding liquid as a function of the flow and pressure conditions in the region of the edge to be rounded leaching are observed, the Out of roundness of the injection holes and thus lead to a reduction in efficiency.

The risk of leaching can be circumvented for example by an extrusion honing process for rounding. Here, a grinding paste is pressed through the spray holes. With this grinding process very high degrees of rounding can be achieved without leaching.

The disadvantage here is that the flow of the grinding paste during the grinding process can not be determined, so that the adjustment of the flow accuracy of the injection holes suffers. In addition, the injectors must be cleaned consuming by this method, so that no residue of the grinding paste in the nozzle and their injection holes remains. Corresponding residues can lead to clogging of the spray holes or hinder sealing of the nozzle by the nozzle needle.

Another known variant for avoiding leaching is to greatly reduce the grinding pressure of the erosive fluid by lowering the flow velocity. This increases the grinding times explosively and the quality achieved leaves many wishes unfulfilled. It is also possible to round off in a further variant with back pressure hydro-erosive. The washouts are then less but the equipment required for the rounding device is greater. Nevertheless, even with this variant, the grinding times are very long and therefore not suitable for a series process.

In addition, it is well known that high pressure resistant fuel injectors due to production, in the area where the guide bore for the nozzle needle and at an acute angle to the guide bore and merging into the guide bore fuel inlet bore, creates a circumferential edge. In the mouth region, the guide bore is frequently widened to create a high-pressure chamber. The web-like region of the edge, which is enclosed between guide bore and fuel inlet bore, is also referred to as a spool. The edge or the spall is known to be a place where local stress peaks occur under load, which can lead to failure of the injectors. To make the injectors more resistant to high pressure, the edge has to be rounded with the spade. For this purpose, various methods are generally known in the prior art. In injection nozzles, which are used up to an operating pressure of about 1600 bar, edges and spades are rounded by means of electrochemical material removal (ECM). This electrochemical material removal is also used to expand the guide bore for creating the high pressure chamber. A high-pressure resistance of more than 1600 bar can not be achieved with the electro-chemical removal of material, since this method creates a pore-like rough surface which leads to local stress peaks. A Another variant for increasing the high pressure resistance is to produce so-called oblique shoulder nozzles. Here, a voltage is introduced into the injection nozzle during assembly, which is opposite to the compressive stress during operation of the injection nozzle, so that overall the high pressure resistance of the injection nozzle can be increased. In combination with the above-described electrochemical material removal, the high pressure resistance of the injection nozzle can be increased up to about 1800 bar. Injection nozzles with compressive strengths of more than 1800 bar are rounded up at the spool by means of a paste mixed with abrasive particles. For this purpose, the paste is pressed through the fuel inlet bore through the body of the injection nozzle and out of the guide bore. This process is also known under Extrudehone. Here, however, there is the problem that the injector must be cleaned consuming to remove the remaining after rounding in the injector grinding paste. There is also the risk that residues of the paste remain in the injection nozzle and clog the injection holes arranged at the end of the guide bore for the nozzle needle or the nozzle needle loses its sealing function due to the remaining paste.

Furthermore, a method and a device for rounding edges in mechanically, thermally or otherwise highly stressed components is known from the German patent application DE 199 53 131 A1. A particular area of application is the rounding of edges at intersections of channels in high pressure accumulators of fuel injection systems. In such highly stressed components occur in the range of edges of all kinds voltage spikes, which can lead to a component failure, in particular to a rupture of the component. To design the component high-pressure resistant, its edges are rounded. The rounding takes place via the flow around the edge to be rounded with an erosive liquid, which is conveyed by a feed pump through the component. In the area of the edge, to increase the erosive effect of the liquid, its flow velocity is increased via a cross-sectional taper. By adjusting the delivery pressure, the flow velocity of the liquid and thus also the material removal in the region of the edge can be influenced. The delivery pressures are approximately in the range of 50 bar to 140 bar. In addition, it is generally stated without further details that the flow direction of the liquid and the longitudinal axis of the edge to be rounded preferably enclose an angle of 90 °. For a rounding of the edge-like transition of a nozzle needle seat and a subsequent antechamber to the injection holes of an injection nozzle is described there to introduce a conical body in the region of the nozzle needle seat of the blind hole injection nozzle so that in the region of the edge an annular gap is formed. This annular gap serves to achieve the desired increase in the flow velocity in the region of the edge to be rounded.

Furthermore, a method is described in WO 87/05552, in which a mixed with abrasive bodies plastic medium for the rounding of edges by a component, for example by an injection nozzle for fuel, is pressed.

The present invention has for its object to provide a method for hydro-erosive rounding of an edge of a component, in particular an edge in a channel of a high pressure-resistant component, and a use for this purpose, with which an optimization of the rounding result is achieved.

This object is achieved by a method for hydro-erosive rounding of an edge of a component with the features of claim 1. A use for this method is given in claim 4. In the dependent claims 2 and 3 and 5 to 7 advantageous embodiments of the method or use are given.

According to the invention, in a method for the hydro-erosive rounding of an edge of a component, in particular an edge in a channel of a high-pressure-resistant component, in which a liquid mixed with abrasive bodies is passed along the edge to be rounded, is achieved by using as liquid a highly viscous liquid a viscosity in the range of 10 to 100 mm ² / s is used, worked up to a predetermined distance from a desired target value of the hydraulic flow and then ground in a second stage with a target fluid to the target value.

Advantageously, the hydro-erosively rounded components with the method according to the invention, in particular injection nozzles for fuels, achieve a high-pressure resistance of over 1800 bar. Also, the oil can be dissolved in other oils, such as diesel or diesel-like oils, so that after the rounding process, the component is easy to clean. Elaborate cleaning processes compared to the Extrudehone process can be omitted. It is sufficient after the rounding process to rinse the component with oil to remove any remaining abrasive particles. The disposal is simplified (no hazardous waste) and the high viscosity ensures a homogeneous and stable distribution of the abrasive particles. These requirements are made by met a lot of organic oils. Also, the grinding times are significantly reduced, so that cycle times are available that allow use of the rounding process in series production. The grinding times can be selectively kept low and the roughness to be achieved can be selectively varied via the delivery pressure, the Schleifkörperkonzentration- and size, the viscosity of the grinding oil and the flow velocity of the grinding oil.

In a preferred embodiment of the invention, it is provided that, to control and control the progress of the rounding process at a preset and largely constant volume flow of the liquid, the pressure in the liquid is measured and the rounding process is terminated when a preselected pressure in the liquid is reached. Thus, a use of this method in series production is possible and desired Verrundungsgrade can be targeted achieved. In particular, this type of control is suitable for the rounding of spray holes of an injection nozzle for fuels. Also, therefore, an easier adaptation of this method to the geometric and fluidic conditions of other components is possible.

Advantageously, the rounding method according to the invention can be used for components of a fuel injection system in order to increase the high-pressure resistance to more than 1800 bar. As a component of the fuel injection system to be rounded, in particular an edge, in particular a spade, comes into consideration in the area of intersection of a fuel inlet bore with a guide bore of an injection nozzle or an edge in the region of the injection hole of an injection nozzle.

It is also possible to drive the grinding method according to the invention at largely freely selectable grinding pressures, so that different nozzle types can be rounded on the spool with a liquid. For example, components whose edges are to be rounded only slightly, with low grinding pressures and nozzles that are to be highly rounded, can be machined with high grinding pressures.

Figur 1

eine Schnittansicht einer hochdruckfesten Einspritzdüse für Kraftstoffe,

Figur 2

eine Ausschnittsvergrößerung von Figur 2 aus dem Bereich der Kraftstoffzulaufbohrung der Einspritzdüse und

Figur 3

ein Diagramm, das für verschiedene Schleiföle den Durchflussbeiwert der Spritzlöcher über dem Verrundungsgrad zeigt.

Hereinafter, the present invention will be described with reference to an embodiment shown in a drawing. Show it:

FIG. 1

a sectional view of a high-pressure fuel injector,

FIG. 2

an enlarged detail of Figure 2 from the range of fuel inlet bore of the injection nozzle and

FIG. 3

a diagram showing the flow coefficient of the injection holes over the rounding degree for different grinding oils.

The method according to the invention for the hydro-erosive rounding of edges in high-pressure-resistant components is carried out using a high-viscosity liquid mixed with abrasive bodies. As highly viscous liquids grinding oils are used with a viscosity in the range of 10 to 100 mm ² / s, preferably of about 50 mm ² / s. For example, a mineral oil can be used. The supply of the liquid to the edges via a feed pump, not shown, with a delivery pressure of about 10 to 500 bar, preferably 100 bar works. By adjusting the delivery pressure and the flow rate of the liquid, the rounding speed and the degree of rounding can be influenced.

The rounding method according to the invention will be described in more detail below in a use for an injection nozzle 1 for diesel fuel. FIG. 1 shows a sectional view of a high-pressure-resistant injection nozzle 1 for diesel fuel. The overall elongated injection nozzle 1 has centrally a guide bore 2 for the nozzle needle 3, which extends in each case with its longitudinal extent parallel to the longitudinal axis of the injection nozzle 1. The nozzle needle 3 is slidably guided in the guide bore 2 in the longitudinal direction thereof in order to close and release the spray holes 4 arranged in the region of a nozzle needle seat at the front end of the injection nozzle 1. In the guide bore 2 opens at an acute angle, a fuel inlet bore 5, which is directed with its longitudinal extent substantially to the front end of the injection nozzle 1. In the region in which the fuel inlet bore 5 opens into the guide bore 2, the guide bore 2 is expanded to a high-pressure chamber 6.

This mouth region of the injection nozzle 1 is shown in detail in FIG. 3, which shows an enlarged detail of FIG. 2 from the region of the fuel feed bore 5 of the injection nozzle 1. It can be seen that the fuel inlet bore 5, the guide bore 2 and the high pressure chamber 6 intersect each other, so that a circumferential edge 7 is formed in the course of production. The web-like region of the peripheral edge 7, which faces the guide bore 2, is also called Spickel 8. To increase the high-pressure strength of Einspitzdüse 1 this edge 7 is rounded with the Spickel 8 by means of a highly viscous and staggered with grinding wheels 9 liquid 10. For this purpose, the liquid 10 is introduced under high pressure into the fuel inlet bore 5, flows through the fuel inlet bore 5, is deflected in the region of the peripheral edge 7 and the spit 8 and leaves the guide bore 2 at the end facing away from the spray holes 4. This above-described flow path of the liquid 10 is shown in the figure 2 by the arrow S. In the region of the deflection of the liquid 10, the edge 7 or the spike 8 is rounded by abrasive particles 9 contained in the liquid 10, which impinge on the edge 7 or the spike 8.

It goes without saying that other high-pressure-resistant components with related geometries similar to the previously described spade 9 can also be rounded with the method according to the invention. Also, this new method can be combined with other means to make components high pressure resistant, such as angular shoulder nozzles.

FIG. 3 shows a diagram showing the flow coefficient HD of the injection holes 4 (see FIG. 2) over the rounding degree HE for a standard grinding oil A and two highly viscous grinding oils B and C with increasing viscosity in the range from 2 to 100 mm ² / s , As grinding oils B and C, for example, mineral oils or synthetic oils come into question. The degree of rounding HE is directly related to the rounding time. It can be illustrated with reference to FIG. 3 that the hydro-erosive grinding process is subdivided into different phases I to IV. First, in a first phase I, the leading edge of the injection hole 4 of the injection nozzle 1 is rounded. In a second phase II will be the roughness peaks in the spray holes 4 smoothed, then it comes in a third phase III to a controlled increase in diameter. In the last and fourth phase IV, the spray holes 4 are washed out uncontrollably. This forms flow channels that lead to a deviation of the spray holes 4 from the roundness. These individual aforementioned phases have a strong effect on the flow coefficient HD of the nozzle 1 with the spray holes 4, which is proportional to the efficiency of the nozzle 1. In the first two phases, the efficiency increases, then it stagnates in the third phase to drop again in the fourth phase. This also shows that by using different grinding oils A, B and C, the maximum efficiency can be influenced. In particular, it is found that with the highly viscous grinding oils B and C higher degrees of rounding HE and thus also better flow coefficients F of the injection nozzle 1 are achieved. The higher degrees of rounding HE are also accompanied by an improved high-pressure resistance of the injection nozzle 1.

FIG. 3 also shows that with the highly viscous grinding oils B and C according to the invention, there is a lower risk of leaching during the grinding process into the region of phase IV. In addition, the rounding times can be significantly reduced due to the optimized grinding effect, so that cycle times are achieved, allowing an application of this rounding process in a series production.

Also, in the context of the rounding of spray holes 4, the hydraulic flow of grinding fluid is measured during the grinding process, allowing for control and targeted control of the rounding process is possible. For this purpose, two methods of measurement come into question. First, for a given constant volumetric flow rate of the grinding fluid, the pressure occurring during the grinding process can be measured.

Second, the volume flow can be measured at a constant pressure. Here, the grinding process is then stopped when a desired volume flow. Analogous to the first method, the desired hydraulic flow with a corresponding degree of rounding or flow coefficient is established.
The former method is preferred because the measurement of pressure provides more reliable results.

To achieve the target value of the hydraulic flow, the method steps are carried out according to claim 1.

In connection with the selection of the grinding oil as well as the control and targeted control of the rounding process by measuring the hydraulic flow of the grinding fluid during the grinding process, it should be taken into account that the grinding oil is in a 1-phase based on the pressure conditions and the flow geometry in the component to be rounded Flow or 2-phase flow can flow. For example, in one application case, a standard grinding oil in the form of a 2-phase flow can flow during the grinding process, whereas under the same boundary conditions, a highly viscous grinding oil according to the invention is not cavitated and present as a 1-phase flow. As is known, the flow behavior of a 1-phase over a 2-phase flow strongly different. This has a decisive effect on the resulting flow coefficient HD.

In the above case, no continuous correlation can be found between the standard grinding oil and the high-viscosity grinding oil. If both oils cavitate or both do not cavitate, there is a clear correlation. With this knowledge, the ideal grinding oil can now be selected. It is important that as high a viscosity as possible oil is used to minimize leaching and fast grinding times can be realized.

The target fluid corresponds to a test oil that is used to check the hydraulic flow and that is mixed with abrasive particles.

Other applications may be in addition to the rounding of all possible spray holes and the rounding of chokes in the injector body. Of course, this method can also be used for high-pressure resistant components in gasoline engines.

Claims (7)

1. Method for hydro-erosive rounding of an edge of a part, in particular of an edge in a duct of a high-pressure-resistant part, comprising the steps:

   - direction of a high-viscosity liquid (10) to which abrasive elements have been added, said liquid (10) having a viscosity in the range between 10 mm²/s and 100 mm²/s, along the edge to be rounded up to a defined distance from a desired target value of the hydraulic flow, and subsequently

   - direction of a target liquid, which is different from the liquid (10) and to which abrasive elements have been added, along the edge to be rounded up to the desired target value.
2. Method according to claim 1, the liquid (10) having a viscosity of approximately 50 mm²/s.
3. Method according to one of claims 1 or 2, whereby in order to check on and control the progress of the rounding process in the case of a pre-set and as constant as possible volume flow of the liquid (10) the pressure occurring in the liquid (10) is measured and the rounding procedure is terminated when a preselected pressure is reached in the liquid (10).
4. Use of the method according to one of claims 1 to 3 for parts of a fuel injection system.
5. Use of the method according to claim 4, the part of the fuel injection system to be rounded being an edge (7), in particular a wedge (8), in the area of intersection between a fuel feed bore (5) and a guide bore (2) of an injection nozzle (1).
6. Use of the method according to claim 4, the part of the fuel injection system to be rounded being an edge (7) in the area of the injection hole (4) of an injection nozzle (1).
7. Method according to one of claims 1 to 6, the liquid (10) having a pressure of over 40 to 300 bar.

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