EP1701814A2

EP1701814A2 - Method of producing channels in a fuel injection device, electrode adapted for said method and device thus obtained

Info

Publication number: EP1701814A2
Application number: EP05717369A
Authority: EP
Inventors: Bernard Bourdon
Original assignee: Lajous Industries
Current assignee: Lajous Industries
Priority date: 2004-01-09
Filing date: 2005-01-06
Publication date: 2006-09-20
Also published as: FR2864916A1; WO2005072899A3; WO2005072899A2; WO2005072899A8

Abstract

The invention relates to a method of producing a channel in a fuel injection device. The inventive method comprises the following steps consisting in: producing a channel (32) or (32') in the body (30) of the device, which opens into a cavity (33) by means of an opening; placing an electrode (34) in the cavity, said electrode being equipped with a stripped zone (34A) or (34A'), opposite the aforementioned opening; and applying a potential difference between the body and the opening in the presence of an electrolyte flowing in the cavity, such as to deburr the periphery of the opening by means of electro-chemical spark machining. In this way, several openings can be deburred simultaneously with the formation of an optional counterbore on at least one part of the periphery of said openings.

Description

Method for producing channels in a fuel injection device, electrode adapted to its application and device thus obtained

The invention relates to the production of channels in a fuel injection device, and more particularly to the deburring of the mouth of a channel in a cavity. As is known, the injection of fuel into an engine takes place under increasing pressure. Thus, in the field of diesel engines, pressures of the order of 1,500 bars are currently used, and pressures of up to 20,000 bars can be envisaged. Such pressures are in particular sought to improve engine performance, including from the point of view of environmental impact. In fact, there is a tendency to seek higher pressures for diesel engines (the injection device is then commonly called "rail", often made of steel or the like) than for petrol engines (the injection device is then commonly called "ramp", commonly made of aluminum or the like). An injection device is in practice a body comprising channels opening into a cavity, and the pressures used require that there is good deburring at the mouth of the channels in the cavity, to avoid any detachment of particles during service, such as machining chips. Various procedures have been set up for this purpose, including a so-called chemical deburring procedure, the principle of which is presented in FIG. 1. In this figure are shown a body 1 comprising a channel 2 opening into a larger channel 3. The channel 2 is in practice made at by means of a drill, and a deburring is useful for rounding, or chamfering, the edge at the mouth of this channel 2 in the channel 3. To do this, an electrode 4 is engaged in the channel which has just been made until presenting its stripped end 4A at the mouth to be deburred. This electrode is brought to a negative potential while the body 1 is a positive potential while the channels 2 and 3 are filled with an electrolyte maintained in recirculation so as to ensure good evacuation of the chemical deburring debris. This solution gives very good results and is widely used with satisfaction. However, it has drawbacks and limits. Thus, taking into account that the distance between the end of the negative electrode (cathode) and the edge to be deburred must be precisely controlled, it is necessary to have an electrode geometry for each diameter possible drilling. It must also be possible to precisely control the depth to which the end of this electrode is engaged. Furthermore and above all, this procedure is only valid above a threshold of channel diameter, since it is necessary to be able to handle with precision an electrode of smaller diameter than that of the channel being finished. However, the tendency to increase the injection pressures is accompanied by a tendency to reduce the diameters of the injection channels (the smaller the diameter, the greater the pressure). As an indication, it is now sought to produce channels with a diameter substantially less than 4 mm. This is why there is currently the need to have a chemical deburring procedure which lends itself to a wide range of diameters, while being simple and easy to implement, even with very small diameters, taking advantage of as much know-how developed with current procedures as possible. The invention proposes for this purpose a method of producing a channel in a fuel injection device according to which a channel is created in the body of this device opening out through a mouth into a cavity, an electrode is placed in the cavity, this electrode being provided with a stripped zone facing this mouth, and a difference of potential between this body and this electrode, in the presence of an electrolyte circulating in the cavity so as to deburr by electro-erosion the periphery of this mouth. It should be noted that, the skilled person used to want to locate the negative electrode in the channel which had just been drilled, taking advantage of the fact that it is in principle easier to position a rod (the electrode) in a small channel only in a large cavity, and that it is not necessary to take into consideration the geometry of the channel into which the small channel opens. Of course, it is necessary, according to the method according to the invention, to use a new electrode geometry, with stripped zones arranged in precise places of the periphery (they are advantageously lateral projections). However, it appeared that placing the chemical deburring electrode, no longer in the small channel, but in the cavity into which this channel opens, could be done reliably, while guaranteeing good positioning of a stripped portion of this electrode opposite the mouth of this small channel. Thus, according to a first embodiment of the invention, the stripped portion of the electrode used has substantially the same dimensions as a stripped end according to conventional procedures, therefore with in particular a diameter substantially smaller than that of the canal whose mouth is to be deburred. Indeed, to ensure the deburring of the edge defining the mouth of the small channel in the cavity so as to simply round the transition between the surfaces of this channel and of this cavity, it is important that the stripped portion of the negative electrode either at similar distances from the internal surfaces of the small channel and the cavity connected by this edge. However, according to a very particularly advantageous characteristic of the invention, the stripped portion of the electrode has dimensions at least equal to those of the section of the channel which opens out. It has indeed appeared, contrary to what the skilled person would have thought, that the possible formation of a counterbore around the mouth of the channel in the cavity does not imply significant degradation of the resistance to pressure, or to corrosion, of the body in which this cavity and this channel are formed. Of course, the resistance to the pressure of the body implies that the connection between the counterbore and the surrounding surface of the cavity is also correctly rounded, but experience has confirmed that this was indeed so, when used, in the cavity, an electrode having a projection of dimensions at least of the order of those of the mouth to be deburred. There was in fact a tendency to consider that it was necessary to minimize all the disturbances on the surface of the cavity likely to lead to degrading the mechanical strength or the corrosion resistance of the body, but it appeared that the counterbores to which can lead the use of a bare area at least equal in size to that of the mouth of a canal was of no significant impact. Of course, it is desirable to keep the depth of such counterbore at a low level, for example at a fraction of a millimeter, typically on the order of a tenth of a millimeter. More generally, the depth of this counterbore can be between around a hundredth of a millimeter and a few millimeters. An important consequence is that it is therefore possible to choose for the stripped portions of various geometries, making it possible for example to minimize the manufacturing constraints of these new electrodes. Furthermore, it becomes possible, if desired, to use the same electrode geometry for several channel diameters. According to another advantageous characteristic of the invention, the same electrode is used to, simultaneously, deburr several mouths of channels in the same cavity, which leads to a significant reduction in cost. This single electrode can thus include a longitudinal row of bare areas. It can also include a ring of such stripped areas for deburring at once the mouths of an annular plurality of channels arranged around the longitudinal axis of the electrode. However, the single electrode can also have an annular rib, taking advantage of the fact that the geometry of the bare area can be defined fairly freely, independently of the precise geometry of the channels; thus there can be continuity between the bare areas intended to cooperate with each mouth. The cavity can be a channel of constant section, and open at its ends. It can also be a dead end pocket, the access to which may have a smaller section than that of the pocket at the location of the mouths to be deburred. It is then possible to use a laterally extendable electrode capable of bringing the stripped areas of the mouths to be deburred transversely to the axis. Thus, according to advantageous characteristics of the invention, possibly combined: - this bare area has dimensions smaller than those of the mouth, - this bare area has dimensions at least equal to those of the mouth, electro-erosion of the periphery of this mouth leading to the appearance of counterbore on at least part of this periphery, - the dimensions of this bare area are generally between once and twice that of the mouth deburring, - EDM is conducted to a maximum depth of counterbore which can reach several millimeters, for example of the order of a tenth of a millimeter, - the depth of the counterbore is equal to or greater than of hundredth of a millimeter, - the electrode is provided with several stripped zones and the electro-chemical deburring of several mouths of channels opening into the cavity is carried out simultaneously - deburring of several mouths offset longitudinally in the cavity, - Simultaneously deburring several mouths offset radially around a longitudinal axis of the cavity, - To simultaneously deburr several mouths offset radially, an annular rib is formed on the electrode forming all of the bare areas. The invention further provides, for implementing the method, an electrode comprising at least one bare area projecting transversely. According to preferred characteristics of this electrode, possibly combined: - it comprises a plurality of stripped projections offset longitudinally along the axis of this electrode, - it comprises a plurality of stripped projections angularly offset around the longitudinal axis of this electrode , - the plurality of projections forms a continuous annular rib, - the angularly offset projections are radially movable. The invention further provides an injection device, the body of which comprises a cavity into which opens at least one channel, characterized in that the mouth of this channel in the cavity is surrounded, on at least part of its periphery, by a counterbore bordered by rounded areas of connection to the surrounding surfaces. According to other preferred characteristics, possibly combined: - in this cavity open several longitudinally offset channels whose mouth is surrounded by a counterbore, - in this cavity open several angularly offset channels whose mouth is surrounded by a counterbore, - l the mouth has, with the counterbore, dimensions between once and three times the dimensions of the channel, - the counterbore has a depth of at most a few millimeters, for example of the order of a tenth of a millimeter, - the counterbore has a depth equal to or greater than about a hundredth of a millimeter, - the cavity is a channel of constant section, - the cavity is a dead end pocket. Objects, characteristics and advantages of the invention appear from the following description, given by way of nonlimiting illustrative example, with reference to the appended drawings in which: FIG. 1 is a schematic representation of a conventional deburring process chemical, Figure 2 is a schematic representation of a chemical deburring process according to the invention, - Figure 3 is a schematic representation of another chemical deburring process according to the invention, Figure 4 is a view enlarged view of the mouth of a canal in a cavity, deburred according to the method of FIG. 3, FIG. 5 is a schematic representation of another method according to the invention for the simultaneous deburring of several mouths, FIG. 6 is a variant, and Figure 7 is another variant. FIG. 2 represents an embodiment of the method of the invention, according to which, in a body 10 in which a cavity 13 and a channel 12 have been previously produced, a negative electrode 14 is placed, no longer in this channel 12, but in the cavity 13, in principle of larger size than the channel. This electrode has a bare area 14A, preferably made up of a projection. This projection, as shown, is a lower height than the stripped end 4A of Figure 1, but a barely larger width. Indeed, this projection has dimensions smaller than those of the mouth to be deburred. This electrode and the body are put at appropriate potentials for an appropriate time, while a given electrolyte circulates under appropriate conditions (all these operating conditions are within the reach of the skilled person, in the light of his know-how developed with the classic procedure). By way of example, these operating conditions are as follows: potential difference: - duration of deburring: nature of the electrolyte: As in the case of FIG. 1, one obtains at the periphery of the mouth of the canal , a rounding of radius R typically of the order of a tenth of a millimeter. The body 10 may, depending on the applications, be made of a light alloy, for example of aluminum alloy in the case of an injection device for a gasoline engine, or of steel in particular, in the case of a injection for diesel engine. The realization of the cavity and the channel are made by any suitable known means and will not be detailed here. FIG. 3 represents a variant of the method described with reference to FIG. 2, in the sense that an electrode 24 is used, the projection 24A of which is at least equal in size to that of the mouthpiece to be deburred (the elements of this figure 3 which are similar to those of FIG. 2 are designated by reference signs which are deduced therefrom by adding the number 10. It may be noted that, unlike channel 12 which is of constant cross section, channel 22 includes a large diameter section 22A and a smaller diameter section 22B, typically having the same diameter as the channel 12. For example, the diameter of the section 22A is 4 mm, while that of the section is 1 mm ( The implementation of operating conditions analogous to those used for FIG. 3 leads, to the connection between the surface of the channel and that of the cavity, to a recess 26 which is shown on a larger scale on the figure 4. More specifically, it is observed that there is, at the lower end of the channel 22B, a rounded 26A, in principle similar to that to that of FIG. 2 (here it has a radius of curvature of 0.2 mm). This rounding is connected to a flat or to any rounded shape, designated by the term counterbore, 26B which surrounds the mouth bordered by the round 26A. This counterbore is connected to the internal surface of the cavity 23 by a second rounded 26C, for example of curvature substantially equal to that of the rounded 26A. This counterbore can have a depth ranging from about a hundredth of a millimeter to a few millimeters. The detail of Figure 4 is taken parallel to the axis of the cavity; it is clear that, depending on the shape chosen for the projection 24A of the electrode, this shape is more or less modified in other cutting planes of the body 20 passing through the axis of the channel 22. It may be noted that the counterbore 26B is shallow, in particular with respect to the diameter of the channel, and that it is not bordered by any sharp edge. This is why it can be understood that tests have led to the conclusion that these counterbores have no effect on the pressure or corrosion resistance of the injection body 20. FIGS. 1 to 3 correspond to case where the cavity is a channel of constant section, in which the channels are offset longitudinally. It is easy to understand that, unlike the case of FIG. 1, the configurations of FIGS. 2 and 3 allow simultaneous deburring of the mouths of several longitudinal offsets: it suffices to have several stripped projections on the electrode, according to the same geometrical arrangement. than the mouths to be deburred. This is shown schematically in dotted lines in the left part of FIG. 3 Similarly, if several mouthpieces are arranged in the body, at the same longitudinal level (in other words, if there are several mouthpieces simply offset angularly by one screw vis-à-vis the others) it suffices to have stripped projections on the electrode, according to the same annular arrangement as the mouthpieces. This is shown in Figure 5, in a configuration where the cavity 33 is a dead end pocket, the access, in the lower part is of smaller section than the central part of this cavity. Elements analogous to those of FIG. 3 are designated by reference signs which are deduced from those of FIG. 3 by adding the number 10. The cavity 33, being of short length, the various channels are arranged radially with respect to the longitudinal axis of this cavity (vertical in this figure 5); one thus distinguishes, in this figure, two channels arranged diametrically opposite, respectively designated by 32 and 32 '. The production of such an injection device body, with a dead end cavity and radially arranged channels is known per se from document WO-99/60263 or its equivalent US-6196192 and will not be detailed here. According to the invention, an electrode 34 is engaged in the cavity, provided with bare areas 34A and 34A ', until these bare areas are positioned, here constituted by projections, as precisely as possible opposite the mouths of the channels (it can therefore there are some in front and behind the plane of the figure). A negative potential is applied to the electrode 34 while the body

30 is set to a positive potential while circulating in the cavity, all around the electrode 34, a suitable known electrolyte: simultaneously deburring of all the mouths of the channels opposite which have projections 34A or 34A '... Figure 6 shows an alternative embodiment of the electrode all the other elements of the body being identical. This electrode, denoted 44, comprises, opposite the mouths of the channels, no longer an annular plurality of individual stripped projections, but a continuous stripped rib 44A. In this way, it is no longer necessary to seek to position this electrode with great angular precision. However, it appeared that the deburring phenomenon obtained is quite similar to that obtained with the electrode 34 of FIG. 5. FIG. 7 represents an alternative embodiment of the electrode, all the other elements of the body being identical . This electrode 54 is transversely deformable, in the sense that the projections 54A and 54A 'are radially movable, here against a spring of reminder 55. More precisely, each projection is disposed at the end of a link and, by action on the end 56 common to these links, for example by means of a slide movable along the body 57 of this electrode, we can force the projection of the projections. An electrode thus makes it possible to arrange the projections at any suitable distance from the mouths to be deburred, independently of the passage section of the access opening to the cavity. As before, the simultaneous deburring of the mouths of the various channels is carried out, by adopting the appropriate operating conditions. The above has been presented in connection with the production of injection channels within a fuel injection device, but this generalizes to any other channel in an injection device, and even to the realization at any device comprising a channel, the mouth of which in a cavity must be carefully deburred. It will be appreciated that the dimensions of the stripped projections are preferably between once and twice (advantageously between once and one and a half times) that of the mouthpieces to be deburred, and that the mouthpiece, after deburring, has a dimension worth, with the counterbore, between one and a half and three times the dimension before deburring (in FIG. 4, the ratio is barely greater than 2).

Claims

CLAIMS 1. Method for producing a channel in a fuel injection device according to which a channel (12, 22, 32, 32 ') opens out in the body (10, 20, 30) of this device by an opening in a cavity (13, 23, 33), there is an electrode (14, 24, 34, 44, 54 in the cavity, this electrode being provided with a stripped zone (14A, 24A, 34A, 34A ') , 44A, 54A, 54A '), opposite this mouth, and a potential difference is applied between this body and this electrode, in the presence of an electrolyte circulating in the cavity so as to deburr by electro-chemical erosion the periphery of this mouth.

2. Method according to claim 1, characterized in that this bare area has dimensions smaller than those of the mouth.

3. Method according to claim 1, characterized in that this bare area has dimensions at least equal to those of the mouth, the electro-erosion of the periphery of this mouth leading to the appearance of a counterbore (26 ) on at least part of this periphery.

4. Method according to claim 3, characterized in that the dimensions of this bare area are generally between once and twice that of the mouth to be deburred.

5. Method according to claim 3 or claim 4, characterized in that the spark erosion is carried out to a depth of counterbore between about a hundredth of a millimeter and a few millimeters.

6. Method according to claim 5, characterized in that the depth of the counterbore is of the order of a hundredth of a millimeter.

7. Method according to any one of claims 1 to 6, characterized in that, the electrode is provided with several stripped zones (24A, 34A, 34A ', 44A, 54A, 54A') and deburring is carried out simultaneously. electrochemical of several mouths of channels opening into the cavity.

8. Method according to claim 7, characterized in that one carries out (24A) simultaneously the deburring of several mouths offset longitudinally in the cavity.

9. Method according to claim 7 or claim 8, characterized in that simultaneously deburring (34A, 34A ', 44A, 54A, 54A') of several mouths offset radially around a longitudinal axis of the cavity .

10. The method of claim 9, characterized in that to simultaneously deburr several radially offset mouths is formed on the electrode an annular rib (44A) forming all of the bare areas.

11. Electrode (14, 24, 34, 44, 54) suitable for implementing the method according to any one of claims 1 to 10, comprising at least one bare area projecting transversely (14A, 24A, 34A, 34A ', 44A, 54A, 54A').

12. An electrode according to claim 11, characterized in that it comprises a plurality of stripped projections (24A) offset longitudinally along the axis of this electrode.

13. An electrode according to claim 11 or claim 12, characterized in that it comprises a plurality of stripped projections (34A, 34A ', 44A, 54A, 54A') offset angularly around the longitudinal axis of this electrode.

14. An electrode according to claim 13, characterized in that the plurality of projections forms a continuous annular rib (44A).

15. An electrode according to claim 13, characterized in that the angularly offset projections (54A, 54A ') are radially movable.

16. Injection device comprising, in a body (20, 30), a cavity (23, 33) into which opens at least one channel, this channel being surrounded, on at least part of its periphery, by a countersink ( 26) bordered by rounded contours.

17. Device according to claim 16, characterized in that in this cavity open several channels (22) offset longitudinally whose mouth is surrounded by a countersink.

18. Device according to claim 16 or claim 17, characterized in that in this cavity open several channels (32, 32 ') angularly offset whose mouth is surrounded by a countersink (26).

19. Device according to any one of claims 16 to 18, characterized in that the mouth has, with the counterbore, dimensions between once and three times the dimensions of the channel.

20. Device according to any one of claims 16 to 19, characterized in that the counterbore has a depth of between about a hundredth of a millimeter and a few millimeters.

21. Device according to claim 20, characterized in that the counterbore has a depth of the order of a hundredth of a millimeter.

22. Device according to any one of claims 16 to 21, characterized in that the cavity (23) is a channel of constant section.

23. Device according to any one of claims 16 to 21, characterized in that the cavity (33) is a dead end pocket.