EP0219591B1 - Method of manufacturing an injection nozzle housing - Google Patents

Abstract

To improve the strength properties of the seat face (4) of a nozzle body (1), which seat face cooperates with the tip of a nozzle needle (2) and contains the mouths of fuel injection holes (5), it is proposed to effect a plastic deformation of the nozzle body (1) beyond the yield point adjacent to the seat face (4) for the nozzle needle in such a manner tha the plastic deformation is effected only in part of the wall thickness of the nozzle body adjacent to the seat face (4) for the nozzle needle. To effect that plastic deformation, a mandrel consisting particularly of the nozzle needle (2) is used as a tool. Adjacent to the seat face (4) for the nozzle needle that mandrel has preferably a multiconical or crowned shape. The apparatus for carrying out the process comprises an abutment (10) for the nozzle body (1) and a hydraulic press (11), by which a nozzle needle (2) can be forced against the associated seat face (4) (FIG. 4 ).

Description

The invention relates to a method for producing an injection nozzle body for injection nozzles for internal combustion engines, in particular for high-speed diesel engines, with spray holes emanating from the seat surface of a nozzle needle.

Injection nozzles, the duration of which is controlled as a function of nozzle needles moved in the axial direction, are part of the prior art. In these known constructions, a distinction is made between designs in which the spray holes originate from a blind hole below the valve seat and a design in which the spray holes originate from the area of the valve seat itself. It is known that drips are observed in designs in which the spray holes originate from the blind bores. The dripping fuel can no longer be burned due to a lack of sufficient atomization, which reduces the fuel economy and the emission behavior, in particular the emission of unburned hydrocarbons, deteriorates.

In order to counteract such dripping, it has already been proposed to arrange the spray holes in the seat area of the nozzle needle. The arrangement of spray holes in the seat itself poses a number of hard-to-solve strength problems, and such spray holes arranged in the seat have always led to a great risk of breakage in tests in the past. For this reason, seat-drilled nozzles are still not used in series production in high-speed diesel engines.

The stress on the material of the nozzle needle body in the region of the nozzle needle seat, which can subsequently lead to the nozzle needle body breaking, is composed of a series of individual stresses, which are listed below, for example. A pulsating hydrostatic pressure with an average supply pressure of approximately 200 bar in particular causes high circumferential tensions, whereby this pulsating hydrostatic pressure naturally also results in high dynamic pressure peaks. In order to ensure that the spray holes are closed securely after the specified injection time, the nozzle needle has to hit the nozzle needle seat at a relatively high speed, as a result of which longitudinal stresses are introduced into the nozzle needle body. These longitudinal stresses overlap with the high circumferential stresses caused by the hydrostatic pressure. The spray holes themselves have a pronounced notch effect, so that in the event of a break, the root of the break usually originates from the spray holes themselves. In addition, a cavitation can often be observed on the inlet side of the spray holes due to the fuel, which leads to intercrystalline notches and thereby further reinforces the notch effect per se by the arrangement of the spray holes. In use, the outside of injection nozzle bodies for internal combustion engines is subjected to temperatures in the order of magnitude of 350 ° C., a relatively clear temperature gradient developing over the wall thickness of the nozzle needle body, which decreases steeply towards the inside. In addition, hot gas corrosion occurs inside the nozzle body through the penetration of combustion gases through the spray holes. Overall, the interaction of a pulsating three-axis tensile stress condition with notch and corrosion effects is particularly disadvantageous.

A number of pressure and temperature treatments for pipes have become known which improve the strength properties of the walls of pipes. In particular, DE-A-1 583 992 has already disclosed a method for strengthening thick-walled pipes, in which, among other things, a ball is driven through a tube, which has a larger outer diameter than the nominal inner diameter of the tube. Furthermore, it is already known to convert the pressure and stress zones within a pipe into a defined basic state by means of appropriate combined temperature and pressure treatment over the pipe thickness, in which a tensile stress is observed outside and a compressive stress is observed inside.

In order to prevent hot gas corrosion in the interior of the nozzle body, the valve must close before the pressure in the combustion chamber, that is to say outside the nozzle body, is greater than the pressure in the interior of the nozzle body. On the one hand, the valve must start to close as early as possible and on the other hand, it must close as quickly as possible.

The closing begins as soon as the hydraulic force on the valve needle has dropped below the force of the closing spring. Since the contact area for the hydraulic pressure when the needle is open is larger than when the needle is closed - the ratio of these areas is expressed by the closing ratio - the closing pressure is always less than the opening pressure. In order to start closing as early as possible, the seat diameter must be as small as possible, but the surface pressure on the valve seat increases.

Fast closing of the needle requires a hard closing spring, which increases the needle impact on the valve seat.

According to the state of the art, early closing and quick closing were not feasible for reasons of strength.

The invention now aims to provide a method for the production of injection hole bodies drilled in the seat hole, in which the strength is increased to such an extent that the valve needle can still be closed suddenly even at high injection pressure and has a favorable seating relationship. To achieve this object, the method according to the invention is essentially characterized in that residual compressive stresses of between 50 and 300 N / mrn2 are applied to the seat surface of the nozzle needle, which go to 0 at a depth of 30 to 70% of the wall thickness of the injection nozzle body, starting from the seat surface .

For the production of nozzle bodies, which all Stresses, i.e. also the stress caused by corrosive gases, the method according to the invention is preferably carried out in such a way that the nozzle body in the region of the nozzle needle seat surface is deformed over the distance limit by means of a mandrel acting on the sealing surface of the nozzle body, the plastic deformation only over extends part of the wall thickness of the nozzle body in the region of the nozzle needle seat. Due to the fact that the nozzle body is deformed beyond the yield point in the area of the nozzle needle seat surface, residual residual stresses, namely compressive stresses, remain on the inside of the nozzle body in the area of the seat surface, since the plastically deformed regions are put under pressure by the elastically deformed zones located further out. As a result, these residual residual stresses mean that stress peaks can be safely absorbed, while the residual stresses in the area of the spray holes significantly reduce the notch effects. This local consolidation also makes it possible to reduce the needle diameter because the surface pressure can be increased by the valve needle. This leads to a more favorable seating ratio and, within certain limits, to a lower mass of the nozzle needle, which in turn enables faster closing. In order to ensure such plastic deformation, which should only extend over part of the wall thickness of the nozzle body in the region of the nozzle needle seat, forces between 3000 N and 7000 N, preferably, can be used with nozzles of the size used for high-speed diesel engines 5000 N, are applied so that they increase from 0 to the nominal value in 0.5 to 3 seconds, preferably 1 second. The nozzle body usually consists of high-temperature, tough, high-temperature corrosion-resistant special steel with high strength and can be case-hardened or nitrided before treatment.

The deformation, which is to be restricted essentially to the region of the nozzle needle seat, can be carried out in a simple manner by means of a dome with a shape that is matched to the seat surface. In addition to a conical shape, the configuration with a spherical or stepped conical shape is particularly preferred, in which the extent of the plastic deformation can also be geometrically concentrated on preferred areas of the seat surface. In this way, the zones of greatest prestress can be shifted into the area of the mouth of the spray holes, for which purpose the method is preferably carried out in such a way that a spherical shape of the dome is formed such that the dome touches the seat surface prior to the deformation along a circle takes place, which is adjacent to the spray holes. With such a procedure, the greatest residual compressive stress can be shifted into the area of the spray holes (itself), the crowning of the work surfaces of the dome being greatest at the point that, when the tool is in contact, touches the seat along a circle in which the upper edges meet of the spray holes. In this way it is achieved that the greatest pressure preload occurs at the point of the highest circumferential stress peak and somewhat above - at the point at which the needle stroke, which is strengthened by the desired favorable seating ratio, has the greatest effect. By choosing the crown, the optimal position of the maximum pressure preload can be set precisely.

The spherical contour can be approximated by a polygon, in which case a stepped conical formation of the mandrel arises. Such a stepped conical design offers a significant simplification and cheaper manufacture of the mandrel, whereby due to the small angle differences between individual truncated cone shells there is no adverse influence on the stress pattern.

In the context of the method according to the invention, the deformation itself can be carried out in a particularly simple manner by means of the nozzle needle. This nozzle needle can have a conical, offset conical or spherical seat surface, no special tool being required and the precise guidance of the needle in the upper part of the nozzle body being ensured. There is no need for a separate tool guide and a simple hydraulic press can be used. With such a procedure, the exact fit of the valve needle can also be achieved with less manufacturing accuracy of the needle itself. Due to the intimate contact between the needle and the seat, the sealing surfaces, that is the part of the seat above the spray hole mouth, are embossed so that they seal particularly well later in operation. The sealing gap can therefore be shorter, which again benefits the seating position.

The method according to the invention can be carried out in a simple manner in such a way that the compressive residual stresses are introduced through a mandrel with an outside diameter adapted to the inside width of the nozzle body and a conical, offset conical or crowned pressing surface at the end to be inserted into the nozzle body supported by an abutment, wherein an axial drive, in particular a hydraulic cylinder-piston unit or a spindle drive is specified for the free end of the mandrel. The guide seat of a nozzle needle in the upper part of the nozzle body means that separate guidance of the tool can be dispensed with, the nozzle needle itself naturally being particularly suitable as a tool in a particularly simple manner.

The invention is explained in more detail below with reference to exemplary embodiments shown in the drawing. 1 shows an axial section through a nozzle body with an inserted nozzle needle according to the prior art; 2 and 3 special needle or tool shapes in the area of the needle seat; 4 shows a schematic illustration of a device for carrying out the method according to the invention, partly in section; 5 shows a graphical representation of the stress state in the area of the seat after the action of a deformation force with a conical tool, and FIG. 6 shows a graphical representation of the stress state in the region of the Seat after a deformation force with a crowned tool.

1 shows a nozzle body 1, in which a nozzle needle 2 is displaceably guided in the axial direction. The nozzle needle 2 has a frustoconical end region 3, which cooperates with a seat 4 in the interior of the nozzle body 1. Starting from this seat 4, spray holes 5 are shown. The spray holes 5 are opened and closed by axial movement of the nozzle needle 2. 1, they are located on a relatively small diameter. The seat 4 ends in a blind hole 6.

2 shows the spherical shape of a tool or a nozzle needle 2, in which the design is such that when the force is applied it first touches the seat surface of the nozzle body along a circle 7, which is in the region 8 of the upper edges of the spray hole openings runs. When such a tool or a nozzle needle shaped in this way is acted upon in the direction of arrow 9, pressing forces are exerted in the area of the needle seat 4, the action being to take place such that the forces in the direction of arrow 9 for plastic deformation at least in area 8 of the needle seat 4 are sufficient. The plastic deformation should not extend over the entire cross-sectional area or wall thickness of the nozzle needle body 1 in the region of the seat surface. Instead of the needle shape or tool shape according to FIG. 2, a stepped conical shape can also be selected, as suggested in FIG. 3. The design here is such that the nozzle needle 2 initially has a conical lateral surface with a first angle a for the conicity in the area of the needle seat. Subsequently, in the axial direction, starting from the tip, a second offset jacket surface is arranged at an angle β and subsequently a third offset jacket surface at an angle y. The design here is such that the angle a is chosen to be smaller than the angle β and the angle β to be smaller than the angle y, as a result of which an approximation of the crowning can be achieved by means of a polygonal train.

A simple device for carrying out the method according to the invention is illustrated in FIG. The nozzle body 1 is supported against an abutment 10 and a hydraulic press 11 is provided, by means of which a force in the direction of the arrow 9 can be exerted on a tool or a nozzle needle 2. The tool 2 is guided in the clear width of the nozzle body, which can be assumed in particular if the tool is formed by the nozzle needle 2 itself. The forces introduced are effective in the area of the seat surface 4, the forces having a particular effect on the lower edge or the upper edge of the taper when the tool or the nozzle needle is conical. In the case of a more or less crowned configuration, the point of attack can be shifted to certain cross-sectional planes in the vertical direction in order to achieve the desired effect.

The schematic representation in FIG. 5 shows how the introduction of pressure into a tool 2 takes effect, or which residual residual stresses remain after the pressure has been reduced. For this purpose, the seat 4 is shown enlarged in FIG. 5. The individual lines define areas with the same residual residual stresses in the circumferential direction. The stresses are defined in descending order from 3 to 8 as compressive stresses, with 9 a neutral zone is defined, whereas the areas 10 already characterize tensile stresses. A qualitative picture of this type results after the application of a force in the direction of arrow 9 as residual stress after the relief. Stress patterns, as shown in FIG. 5, can be calculated in advance using the finite element method, whereby for the sake of order it is again stated that the simplified representation in FIG. 5 only illustrates the residual stresses in the circumferential direction after the action of a conical tool.

FIG. 6 shows a representation of the peripheral stresses analogous to FIG. 5 after the action of a tool with a spherical contour.

For the sake of simplicity, only circumferential tensions were mentioned. Naturally, tensions in other spatial directions or comparative tensions can also be calculated and graphically represented in a similar way.

Claims (8)

1. Process for the manufacture of an injector body (1) of an injector for internal combustion engines, in particular for high-speed diesel engines, with spray holes (5) issuing from the seating face (4) of a jet needle (2), characterised in that pressure residual stresses between 50 and 300 N/mm² are introduced on the seating face (4) of the jet needle (2), which fall towards 0 at a depht of 30 to 70% of the wall thickness of the injection jet body (1), starting from the seating face (4).

2. Process according to claim 1, characterised in that the injector body (1) in the region of the jet needle seating face (4) is deformed beyond the yield point by means of an arbor, whereby the plastic deformation only extends over part of the wall thickness of the jet body (1) in the region of the jet needle seating face (4).

3. Process according to claim 2, characterised in that the deformation is brought about by means of an arbor with a cambered shape.

4. Process according to claims 2 or 3, characterised in that the cambered shape of the arbor is formed in such a way that the contact of the arbor with the seating face (4) before the deformation takes place is along a circle (7), which is adjecent to the spray holes (5), and which in particular touches or crosses them.

5. Process acording to claim 2, 3 or 4, characterised in that the deformation is implemented by the jet needle (2) itself.

6. Process according to claim 5, characterised in that forces between 3000 N and 7000 N, and preferably about 6000 N, are introduced on the arbor or the needle (2).

7. Process according to one of claims 1 to 6, characterised in that the rate of introduction of the force is selected so that the full force is exerted between 0.5 and 3s, and preferably about 1 s, after the beginning of the introduction of the force on to the seating face (4).

8. Process according to one of claims 1 to 7, characterised in that the pressure residual stresses are introduced by an arbor with an outer diameter appropriate to the inside diameter of the injector body (1) and with a conical, stepped conical or cambered pressure surface on the end that is to be introduced into the injector body (1) which is supported by an abutment, whereby the axial force is applied to the free end of the arbor by a drive (11), and particularly by a hydraulic cylinder-piston unit or a spindle drive.

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