Advantageous further developments and improvements to the injection nozzle
given in Claim I are possible by means of the measures listed in the further claims.
In accordance with a preferred embodiment of the invention, the injection holes of the various injection hole rows, located one above the other, each open into a connecting passage to the pressure space. The injec- tion holes are designed as radial passages, preferably radial drillings, whose passage or drilling axes are inclined by an acute, so-called angle of elevation relative to the nozzle needle axis. The angles of elevation of all the injection holes within an injection hole row, i.e. half the jet cone angle, are preferably the same. In order to ensure optimum fuel combustion at certain load points of the internal combustion engine, it is additionally possible to have a different configuration of the angles of elevation of the injec- tion holes in the injection hole rows located one above the other.
In accordance with alternative embodiments of the invention, the spring closing appliance can consist of a single spring with a linear or progressive spring 4 characteristic or of two or more springs arranged one behind the other in the stroke direction of the nozzle needle. It is - in principle - possible to use as springs any spring elements, such as helical springs, plate springs, annular springs, etc and all possible combinations of these spring elements.
When a single spring with a progressive or linear spring characteristic is used, the distance between the injection hole rows located one above the other is matched to the spring characteristic. Large distances then facilitate the design of the springs.
When a plurality of individual springs are used, the stable stroke positions of the nozzle needle between the injection hole rows located one above the is other are defined by stops which are arranged within the stroke of the nozzle needle and which can only be overcome by the nozzle needle after a relatively large increase in fuel pressure occurs in the pressure space.
In accordance with a preferred embodiment of the invention, with the provision of two rows of injection holes located one above the other and two compression springs connected in series or individually, the stop fixing the stable stroke position of the nozzle needle with the control edge located between the injection hole rows is formed by a stop element displaceably seated on the nozzle needle, the compression springs being supported on the stop element at one end and on the nozzle body or the nozzle needle at the other. A mating stop, which comes into contact with the stop element after a preliminary stroke and subsequently short-circuits, i.e. makes ineffective, one of the compression springs within the stroke of the nozzle needle, is permanently connected to the nozzle needle. In the case of individual connection of the two compression springs, the stop element located between the two compression springs is supported on one side in the nozzle space so that it cannot be displaced in the direction of the closing stroke of the nozzle needle. In the case of series connection of the two springs, the stop element is freely movable and can move in both the closing and opening stroke directions of the nozzle needle. The individual connection has the advantage that the springs, and thus the opening pressures for the individual injection hole rows, can be set independently of one another, whereas the series connection with two springs has the advantage that the two springs can be set to the desired opening pressure simultaneously by means of one setting washer.
In accordance with an advantageous embodiment of the invention. the spring closing appliance in accommodated in a spring chamber which is arranged in a nozzle holder coaxially with the nozzle needle axis and which is connected to a fuel supply via a coaxial fuel supply passage, on the one hand, and to the pressure space via a central hole located in the nozzle body and accommodating the nozzle needle, on the other. In addition to the advantages of freedom from leakage, and therefore the disappearance of scale and return conduits, this design configuration of the injection nozzle also has the substantial advantage that in the case of a sufficiently large wall thickness, the spring chamberaccommodating the spring closing appliance can be designed to be relatively large. A large space f or accommodating the spring closing appliance can theref ore be made available without increasing the design size of the injection nozzle. The spring volume of the single-part or multi-part spring closing appliance can therefore be made larger so that the matching and setting possibilities at the spring closing appliance f or achieving the stable stroke positions and the unstable transition regions within the nozzle needle stroke can be substantially improved and refined.
The injection nozzle can, of course, also be designed to be "subject to leakage oil". In this case, the coaxial spring chamber is connected to a leakage oil return conduit and the coaxial pressure space is connected to the f uel supply via a supply hole sur rounding the spring chamber.
6 Drawing The invention is explained in more detail in the following description using embodiment examples repre5 sented in the drawing. In this:
Fig. 1 show longitudinal sections through a multijet and 2 fuel injection nozzle in accordance with a first and a second embodiment example respectively, Fig. 3 shows a magnified perspective representation of the lower region of the injection nozzle in Fig. 1 or 2, partially sectioned, shows a diagram of the stroke of the nozzle needle as a function of the fuel pressure in the nozzle space in order to explain the mode of operation of the injection nozzle, show, as excerpts. longitudinal sections through the injection nozzle in Fig. 2 in accordance with third and fourth embodiment examples respectively, shows a representation of the spring characteristic of the spring closing appliance in the injection nozzle shown in Fig. 5 or 6, shows, as excerpt. a longitudinal section through an injection nozzle in accordance with a fifth embodiment example, shows a representation of the spring characteristic of the spring closing appliance in the injection nozzle of Fig. 8.
Fig. 4 Fig. 5 and 6 Fig. 7 Fig. 8 Fig. 9 7 Description of the embodiment examples The multijet fuel injection nozzle for injecting fuel into the combustion space of an internal combustion engine, as represented in longitudinal section in Fig. 1, consists essentially of a nozzle holder 10, a nozzle body 11 with a nozzle collar 111 and a central axial through hole 112, together with a nozzle needle 12 guided so that it can be displaced axially in the central hole 112 in the nozzle body 11. The nozzle holder 10 is placed on the nozzle collar 111 of the nozzle body 11 and the two are connected together in a liquid-tight manner by a union or clamping nut 13. The nozzle holder 10 and the nozzle body 11 together enclose a spring chamber 14 which is coaxial with the nozzle needle 12 and into which opens a fuel supply passage 15 which extends coaxially with the nozzle needle 12 in the nozzle holder 10. The spring chamber 14 is supplied with fuel under pressure from a fuel injection pump via the supply passage 15.
At its combust ion- space end, the nozzle needle 12 has a sealing cone 16 which is pressed by spring f orce against the end, in tIA-Ae shape of a truncated cone, of the nozzle body 11 whose inner edge bounding the central hole 112 f orms a control edge 17. The spring force is applied by a spring closing appliance 18 which is arranged in the spring chamber 14 and which acts on the nozzle needle 12 in the closing direction against the fuel pressure. A cylindrical section 121 is formed on the end of the nozzle needle 12, by means of which the latter is displaceably guided in the lower end of the central hole 112. A needle head 122, which is located outside the nozzle body 11 and carries the sealing cone 16 (already mentioned) for sealing the injection nozzle, adjoins this cylindrical section 121.
An annular space 19, which is in connection with the spring chamber 14, remains above the cylindrical section 121 between the nozzle needle 12 and the inner wall of the central hole 112 so that the annular space 19 forming the nozzle pressure space is likewise filled 8 with f uel and the fuel pressure loads the cylindrical section 121 of the nozzle needle 12 in the opening direction. Supply holes 20, which end in the manner of blind holes in the needle head 122 and which are set in a slightly oblique manner, are introduced into the cylindrical section 121 of the nozzle needle 12, starting f rom the annular space 19. Two radial drillings 21, 22 which are introduced from the outside into the cylindrical section 121 and which form the injection holes 23, 22 visible on the periphery of the cylindrical section 121 of the nozzle needle 12, open into each of the supply holes 20. The injection holes 23, 24 are arranged one above the other and at a distance from one another in the stroke direction of the nozzle needle 12 so that two injection hole rows are provided in the outer surface of the cylindrical section 121. The radial drillings 21, 22 are inclined relative to the axis of the nozzle needle 12 and enclose with this axis the so-called angle of elevation. This angle of 20 elevation of the radial drillings 21, 22 or the axes of the injection holes 23, 24 determines the direction of injection of the fuel sprayed in jets by means of the injection holes 23, 24. Twice the angle of elevation of the injection holes 23 or 24 is referred to as the 25 jet cone angle whose precise optimization has a substantial influence on the results of the combustion of the fuel in the combustion space of the internal combustion engine. The spring closing appliance 18, which is accommo30 dated in the spring chamber 14 and loads the nozzle needle 12 in the closing direction against the fuel pressure, is of substantial importance for the satisfactory functioning of the injection nozzle. This spring closing appliance 18 is configured in such a way 35 that the nozzle needle 12 takes up a stable stroke position each time the full hole cross-section of the injection holes 23 or of the injection holes 23 and 24 is completely freed by the control edge 17 of the nozzle body 11, on the one hand, and that the 9 transition of the nozzle needle 12 from one stable stroke position to the other takes place substantially abruptly,. on the other. Reference is made to Fig. 4 to illustrate the configuration of the spring closing appliance 18. This represents the stroke diagram of the nozzle needle 12 and, specifically, the nozzle needle stroke h as a function of the fuel pressure acting on the nozzle needle 12. One injection hole pair 23, 24 from the injection hole rows located one above the other and one section of the control edge 17 formed on the nozzle body 11 are represented for illustration in each case.
As may be seen from Fig. 4, the injection nozzle is initially closed. It is only when the fuel pressure in the pressure space 19 has substantially increased and, specifically, to a value which is slightly below the desired nozzle opening pressure (PDOE1) that the nozzle begins to open, only a slight increase in pressure then causing the nozzle needle 12 to execute a needle stroke hl (preliminary stroke). After this needle stroke hl has been executed, the nozzle needle 12 again reaches a stable stroke position from which it can only be moved by a further relatively large increase in pressure. In this stable stroke position, of the nozzle needle 12, represented in the centre of Fig. 4, the injection holes 23 of the first injection hole row are completely free and the injection holes 24 of the injection hole row located above them are still completely covered. The control edge 17 in located approximately centrally between the two injection hole rows. The fuel is sprayed via the freed injection holes 23 at the predetermined jet cone angle fixed by the injection hole axes. After this preliminary stroke hl of the nozzle needle 12, the fuel pressure in the pressure space 19 must first rise sufficiently far for it to reach the second opening pressure PDOE2. The nozzle needle 12 now executes a further needle stroke abruptly and moves, in total, by the stroke h2 (total stroke). In this position, it again reaches a stable stroke position in which it has been displaced suf ficiently far for the control edge 17 on the nozzle body 11 to be located beyond the uppermost injection hole row and completely free the hole cross-sections of all the injection holes 24 also. Fuel is now sprayed via the injection holes 23 and the injection holes 24 into the combustion space of the internal combustion engine. The jet cone angle of the fuel jets is exclusively determined by the hole axes of the injection holes 23 and 24 and is not inf luenced by the control edge 17. Def lection of the jet cone angle due to the control edge 17 takes place exclusively during the transitions of the nozzle needle 12 from one stable stroke position to the subsequent one. These,, however, are brought about by small increases in pressure due to the design of the spring closing appliance 18 and are therefore traversed very quickly by the nozzle needle 12 so that the temporary disadvantageous influence on the jet cone angle by the control edge 17 can be neglected as far as the combustion result in the combustion space of the internal combustion engine is concerned.
The spring closing appliance 18 can be configured in various manners in order to achieve this control behaviour. In Fig. 1, the spring closing appliance 18 is effected by a single helical compression spring 25 with a progressive or linear spring characteristic. The helical compression spring 25 surrounds the nozzle needle 12 coaxially and is supported on the nozzle body 11 or, stated more precisely, on the end of its nozzle collar 111, on the one hand, and on a spring plate 26 permanently connected to the nozzle needle 12,, on the other. The correct setting of the spring characteristic of the helical compression spring 25 is facilitated if relatively large distances are provided between the injection hole rows in the nozzle needle 12 so that the nozzle needle 12 must execute relatively large strokes.
In Fig. 2, the spring closing appliance 18 is effected by means of two compression springs, which are is 11 arranged one behind the other in the stroke direction of the nozzle needle 12 and which are supported on the nozzle body 11, on the one hand, and on the nozzle needle 12, on the other. one spring is configured as a helical compression spring 25 and the other spring as a plate spring 28. The two springs are connected in series. The construction and mode of operation of this spring closing appliance 18 is similar to the spring closing appliance 18 represented in Fig. 5 and 6 and is explained there in detail.
The spring closing appliance 18 represented to an enlarged scale in Fig. 5 and which can be likewise employed in the injection nozzles of Fig. 1 and 2, con sists of two helical compression springs 31, 32 in so called series connection. They are arranged one behind the other in the stroke direction of the nozzle needle 12. The two helical compression springs 31, 32 coaxi ally surround the nozzle needle 12 and are supported at their ends on opposite sides of a stop disc 33 dis placeably seated on the nozzle needle 12. The upper helical compression spring 31 is supported on the nozzle needle 12 by means of a setting washer 34 and a retention ring 35 and the lower helical compression spring 32 is supported on the end of the nozzle collar 111 on the nozzle body 11 via an intermediate ring 36 and a stop ring 37. Two mating stops 38, 39 are formed on the nozzle needle 12 and these are effected by two radial collars whose diameter is larger than that of the needle. The mating stop 38 interacts with the stop disc 33 and the mating stop 39 interacts with the stop ring 37, the mating stop 38 coming into contact with the stop disc 33 after a needle stroke hl (preliminary stroke) of the nozzle needle 12 and the mating stop 39 coming into contact with the stop ring 37 after a needle stroke h2 (total stroke) of the nozzle needle 12.
In the case of the series connection of the two helical compression springs 31, 32, as represented in is 6 12 Fig. 5, the resultant spring constant given by:
cl C2 C-total m cl + C2 (c-value) is where cl is the c-value of the helical compression spring 31 and c2 is the c-value of the helical compression spring 32. The resultant c-value is therefore always smaller than the smallest individual c-value of the two helical compression springs 31, 32, which permits a "gentle" preliminary stroke step to be effected in which the increase in pressure over the stroke is only small. When the first opening pressure PDOE1 is reached, only a small increase in pressure is needed to bring the nozzle needle 12 into contact with the stop disc 33 and to hold it there in a quasi-stable position. This behaviour is represented in the left-hand illustration and the central illustration in the diagram of Fig. 4. In the stable stroke position of the nozzle needle 12 (central illustration in Fig. 4), the control edge 17 completely frees the injection holes 23. The two helical compression springs 31, 32 are simultaneously preloaded to the desired opening pressure PDOE1 by means of the setting washer 34.
If the mating stop 38 has come into contact with the stop ring 33, the helical compression spring 31 is "short-circuited", i.e. ineffective. It no longer has any influence on the further course of the stroke. Only the second helical compression spring 32 is still effective. Because the spring constant (C2-value) of the helical compression spring 32 is substantially larger than the c-value of the total arrangement, the increase in force is now also larger. The fuel pressure in the pressure space 19 must therefore markedly increase in order to move the nozzle needle 12 out of the quasi-stable preliminary stroke position and on to the end stop. The end stop is reached when the mating 13 stop 39 on the nozzle needle 12 meets the stop ring 37. On reaching the end stop, the nozzle needle 12 takes up a position with respect to the control edge 17 on the nozzle body 11 such as is represented on the right of the diagram in Fig. 4. Both injection hole rows, i.e. all the injection holes 23 and all the injection holes 24, have been completely opened.
The spring characteristic of the -spring closing appliance 18 described is represented in Fig. 7. As may be seen from this, the second opening pressure PDOE2 depends on the spring constants cl and c2 selected and on the first opening pressure PDOE1 selected.
The spring closing appliance 18 in Fig. 6 is modified to the extent that the mating stop 38 on the nozzle needle 12 is omitted and its function is undertaken by the setting washer 34 and that the stop ring 33 is replaced by a sleeve 40, which is displaceably seated an the nozzle needle 12; one of its ends comes into contact with the setting washer 34 after the preliminary stroke hl of the nozzle needle 12. Near its other end, the sleeve 40 has a flange 41 on which are supported the two helical compression springs 31 and 32. The upper helical compression spring 31 is sup- ported on the flange 41 via a setting washer 42. The spring characteristic of the spring closing appliance 18 constructed in this way is identical to the spring characteristic reproduced in Fig. 7. Otherwise, the mode of operation is like that of the spring closing appliance 18 in Fig. 5.
A spring closing appliance 18 is sketched in Fig. 8 which is again composed of two helical compression springs 51, 52 which are arranged one behind the other in the stroke direction of the nozzle needle 12. In contrast to the spring closing appliance 18 in Fig. 5 and 6, however, the two helical compression springs 51,, 52 are individually connected so that the spring preload of each helical compression spring 51, 52 can be set independently of the other. A stop sleeve seated 14 53 and a mating stop sleeve 54 are displaceably on the nozzle needle 12. Each of the two sleeves 53, 54 has a radial flange 531 or 541. The helical compression spring 51 is supported on the radial flange 531 of the stop sleeve 53 via a setting washer 55 and is supported on the radial flange 541 of the mating stop sleeve 54 via an intermediate disc 56.
By this means, the radial flange 541 is pressed onto the nozzle needle 12 via a setting washer 57 and a retention ring 50 and the mating stop sleeve 54 is therefore fixed on the nozzle needle 12. The second helical compression spring 52 is supported on the oppo site side of the radial flange 531 of the stop sleeve 53 and, via an intermediate ring 58 and a stop ring 59, on the end of the nozzle collar 111 on the nozzle body 11. A mating stop 60 is in turn f ormed at a stroke distance h2 before the stop ring 59 on the nozzle needle 12 and this mating stop 60 comes into contact with the stop ring 59 after the total stroke h2 of the nozzle needle 12 and therefore limits the maximum stroke of the nozzle needle 12. The stop sleeve 53 is spatially fixed by the helical compression spring 52 in the spring chamber 14 to the extent that it cannot be displaced in the closing direction of the nozzle needle 12. For this purpose, an annular shoulder 61 is formed on the nozzle holder 10 in the spring chamber 14 and the stop sleeve 53 is in contact on one side with the annular shoulder 61 via the setting washer 55.
The spring characteristic of the spring closing appliance 18 described is represented in Fig. 9. The first opening pressure PDOEl is specified by means of the setting washer 57 and the second opening pressure PDOE2 is set by the setting washer 55. The preliminary stroke hl of the nozzle needle 12 is determined by the two sleeves 53, 54 and the total stroke h2 Of the noz zle needle 12 is determined by the thickness of the stop ring 59. As can be seen from the characteristic in Fig. 9, the second opening pressure PDOE2 is speci fied by the spring preload on the helical compression is spring 52. The f irst opening pressure PDOEl is exclusively determined by the preload on the f irst helical compression spring 51, which assumes that the spring force of the helical compression spring 51 is smaller than the preload on the helical compression spring 52 over the whole of the stroke range hl.
The invention is not limited to the embodiment examples described above. As an example, more than two injection hole rows located one above the other can be provided in the nozzle needle. The spring closing appliance has then to be set in such a way that the nozzle needle can respectively reach a stable stroke position whenever the control edge in located between two injection hole rows. The spring closing appliance can here be constructed from more than two individual springs.
In the spring closing appliances represented in Fig. 5, 6 and 8, other spring elements can also be used instead of helical compression springs. As an example, one helical compression spring can be replaced by a plate spring, as is represented in Fig. 2, without the mode of operation of the spring closing appliance being changed.
The injection nozzles represented in Fig. 1 and 2 are "leak-free", i.e. the fuel flows to the pressure space 19 via the spring chamber 14. For this purpose, the spring chamber 14 is connected to the fuel supply via the coaxial fuel supply passage 15. The injection nozzles described can also, however, be designed to be "subject to leakage oil". In this case, the fuel supply passage connected to the fuel supply leads to the pressure space while bypassing the spring chamber and the spring chamber is connected to a fuel return conduit - as is described in DE 43 10 154 Al. The spring chamber is substantially sealed relative to the pressure space so that only small fuel quantities.(so-called leakage oil) pass from the pressure space into the spring chamber and are led from there back to the injection pump via the return conduit.
16 Claims 1. Multijet fuel injection nozzle, for internal combustion engines, having a noz zle needle (12) guided so that it can be longitudinally displaced in a nozzle body (11), which nozzle needle (12) in provided with a row, which extends over the periphery of the nozzle needle, of injection holes (23, 24) for spraying fuel which are arranged at a distance from one another and are in connection with a fuel-filled pressure space is (19), having a spring closing appliance (18) which holds the nozzle needle (12) in a closed position against the fuel pressure acting on the nozzle needle (12) in the opening direction, and having a control edge (17) formed on the nozzle body (12), which control edge (17) frees a hole cross-section which increases with increasing pressure with a displacement of the nozzle needle (12) from its closed position after an increase in pressure in the pressure space (19), characterized in that at least one further injection hole row arranged at an axial distance from the other injection hole row in the stroke direction of the nozzle needle (12) is provided in the nozzle needle (12) and in that the spring closing appliance (18) is configured in such a way that the nozzle needle (12) takes up a stable stroke position in each case whenever the full hole cross-section of the injection holes (23, 24) of an injection hole row is freed by the control edge (17), on the one hand, and the transition of the nozzle needle (12) from one stable stroke position to the other stable stroke position takes place substantially abruptly, on the other.