EP1364114B1 - Fluid dosing device with a throttle point - Google Patents

Description

The present invention relates to a Fluiddosiervorrichtung for a pressurized fluid having a chamber located in a housing, which is supplied through a fluid supply line, the pressurized fluid, and with a valve needle guided through the chamber, the first end portion is acted upon outside the chamber with a stroke and whose second end portion forms a valve seat connected to the chamber with a valve seat provided on the housing.

Various sealing or feedthrough elements for fluid metering devices are known in the prior art. For the application of the metering of pressurized fuel with a pressure of up to, for example, 300 bar and a working temperature of -40 ° C to + 150 ° C, special requirements are placed on a product suitable for series production. In particular, high requirements in terms of embrittlement, wear and reliability must be met. The creep resistance of previously used O-ring seals does not meet the above requirements. Instead of O-rings, membrane seals such as e.g. Metal beads or the like be used. When using such membranes as a lead-through element of a valve needle by a pressurized chamber, however, the requirements can not be met with respect to a high axial compliance at the same time sufficient compressive strength.

The valve needle can continue to take place similar to diesel injectors by a clearance of the needle in a cylindrical housing bore. The disadvantage here is the unavoidable leakage along the needle feedthrough. By the larger hydraulic losses also reduce the overall efficiency of the engine.

A fluid device according to the preamble of claim 1 is known from EP1046809 A2.

Object of the present invention is to provide in a generic Fluiddosiervorrichtung particular dense implementation of the valve needle, which achieves a required creep rupture strength.

According to the invention this is achieved in a Fluiddosiervorrichtung according to the preamble of claim 1, characterized in that circumferentially provided between the valve needle and the chamber inner wall at least one throttle point in the chamber section between the lead-through element and the mouth of the fluid supply line into the chamber. Measurements have shown that for use in high-pressure injection valves, for example vehicle technology, metal bellows designed as lead-through elements can easily withstand static pressure loads of up to approx. 200 bar. By increasing the wall thickness and a much higher compressive strength can be achieved. Further studies on moving metal bellows seals also showed that a high-pressure-loaded metal bellows undergoes no degradation when carrying out an axial movement of up to 50 μm with a frequency of 50 Hz typical for the injection valves. The use of a metal bellows thus hermetic sealing of the fuel chamber is achieved with sufficient pressure resistance.

However, it was surprisingly found that the metal bellows fail when used in a high-pressure injection valve at a static pressure load of 200 bar already after about 10 min. This is due to the fact that when opening and closing the injector or injector pressure waves in the fuel chamber of the injector are triggered, in response to the opening and closing time of the injector with an amplitude of up to ± 50% of the set fuel pressure and a frequency from about 500 Hz - 10 kHz, typically in the range of about 500 - 800 Hz, to swing the set basic pressure. The occurrence of such pressure oscillations leads to failure of the metal bellows seal when pressure waves are triggered. The throttle points provided according to the invention protect the metal bellows against the destructive effect of these pressure oscillations.

In summary, the invention thus a sufficient tightness of the fuel chamber is realized by the metal bellows, the bellows seal is protected from the pressure waves occurring during operation and thereby a motor vehicle technically typical creep rupture strength of at least 10 ⁹ load cycles (about 2000 operating hours) is reached.

Advantageously, the metal bellows has a wall thickness of 25 to 500 μm. These low wall thicknesses have proven to be completely sufficient at high pressures of for example 300 bar. Experiments have shown that a formation of the metal bellows in the form of - visible in longitudinal section - juxtaposed semicircular segments provides particular advantages. These semicircular segments can each be supplemented by intervening straight sections.

According to a preferred embodiment it is provided that the elastic feedthrough element is fastened to a mounting sleeve, in particular by a welded connection. This is particularly favorable in terms of production since, in particular, a metal bellows can be attached directly to the valve needle only with comparatively great effort. With the mounting sleeve is also an element ready, can be realized by a simple way a precisely dimensioned throttle in the fuel chamber.

In order to be able to provide a suitable throttle point in the fuel chamber, an upper guide sleeve is an alternative or in addition to the suitably dimensioned mounting sleeve designed such that a tight and long as possible clearance fit is realized by this valve needle guide. Since the upper valve needle guide is provided anyway at the fuel injector, additional components can be omitted.

If both throttling points - "mounting sleeve" and "upper valve needle guide" - realized simultaneously in the Fluiddosiervorrichtung, the respective throttle gaps can be made larger and / or shorter in the axial direction, without negatively affecting the protective effect of the throttle bodies for the metal bellows. In addition, misalignments that could lead to a jamming of the valve needle can be avoided. However, this also applies if the throttle point formed by the mounting sleeves is dispensed with, wherein the throttle point formed by the upper guide sleeve is to be interpreted accordingly.

In order to prevent or greatly restrict the propagation of the pressure waves in the fuel chamber in the direction of the metal bellows, the free cross section between the valve needle and the chamber inner wall is changed abruptly in the region of the throttle point. This results in the desired reflection of the pressure waves at the chamber inner wall section extending transversely to the propagation direction of the pressure waves.

The gap width of the throttle point is selected as a function of the position of the throttle point in the fuel chamber and the length of the throttle gap, taking into account the static and dynamic pressure conditions. There have been some microns as a typical value for the gap width of the throttle point in the fuel chamber of a high pressure fuel injector.

Fig. 1a

in einem Längsschnitt das erste Ausführungsbeispiel der Fluiddosiervorrichtung,

Fig. 1b

zwei Querschnittdarstellungen entlang der Linien A-A und B-B in Fig. 1a,

Fig. 2

in einem Längsschnitt das zweite Ausführungsbeispiel,

Fig. 3a

in einem Längsschnitt das dritte Ausführungsbeispiel der Fluiddosiervorrichtung, sowie

Fig. 3b

zwei Querschnittdarstellungen entlang der Linien A-A und B-B in Fig. 3a.

Four exemplary embodiments of the fluid metering device according to the invention are described below with reference to schematic representations. Show it:

Fig. 1a

in a longitudinal section, the first embodiment of the fluid metering device,

Fig. 1b

two cross-sectional views along the lines AA and BB in Fig. 1a,

Fig. 2

in a longitudinal section the second embodiment,

Fig. 3a

in a longitudinal section, the third embodiment of the Fluiddosiervorrichtung, as well

Fig. 3b

two cross-sectional views along the lines AA and BB in Fig. 3a.

In an injector 1 shown schematically in Fig. 1a, b according to a first embodiment, the per se well-known actuator unit is not shown for reasons of simplification. The fuel injection valve 1 has a housing 3 with a central bore in which a valve body 5 is mounted. In a valve body bore 7 of the valve body, a valve needle 9 is guided axially displaceable. For this purpose, in the valve body bore 7 at the lower and upper end portion of the valve body 5, a lower and front and an upper or rear guide sleeve 11, 13 are attached, forming the corresponding valve needle guides. The constrictions realized thereby are designed so that they do not hinder or restrict a liquid flow when opening and closing the valve 1. For this purpose, the valve needle 9 is provided both at the level of the lower and the upper guide sleeve 11, 13 and the two valve needle guides with a circumferentially protruding, rounded square section according to Fig. 1a, b (section AA and section BB). In this case, the valve needle 9 with the rounded edge regions 14 with a clearance of less than 2 microns in the two guide sleeves 11, 13 fitted. The free gap between the four side surfaces of the square of the valve needle 9 and the cylindrical inner wall of the guide sleeves 11, 13 is designed to be significantly larger in order to avoid any throttling effect.

In the base state, a valve plate 15 formed on the front end portion of the valve needle 15 closes a valve seat 16 in the valve body. The valve body has a valve body fuel supply line 17 which, viewed in the axial extent, lies between the lower and upper guide sleeves 11, 13 with a junction 19 the valve body bore 7 opens. Accordingly, a housing fuel supply line 21 is provided in the valve housing 3. At the upper end portion of the valve needle 9, a spring plate 23 is attached to this. In this presses a nozzle spring 25, which is supported on the housing side and thereby biases the valve needle 9 in the closing direction. Above the upper guide sleeve 13, an outer mounting sleeve 27 is fixed in the central bore of the valve housing 3. The outer mounting sleeve 27 has at the lower end a sleeve collar 44 which rests on an annular bearing surface 45 on the housing 3. The sleeve collar has an outer surface 46, which is arranged an inner wall 47 of the housing 3. Between the outer surface 46 and the inner wall 47, a sealing element 48 is inserted in the form of a sealing ring. The sleeve collar 44 is sealed with an annular circumferential weld 49 tightly welded to the inner wall 47. This forms through an opening in a sleeve bottom 29 a needle feedthrough, which is sealed as described below. In a limited extending in the axial direction portion of the outer mounting sleeve 27 whose inner wall forms a bottleneck described in more detail below with the outer wall of an inner mounting sleeve 31, which in turn is attached to the valve needle 9. To the outer and inner mounting sleeve 27, 31 is welded a cylindrical metal bellows 33, through which the valve needle 9 is guided to the outside. The metal bellows 33 serves to hermetically seal the fuel chamber 35 with respect to a pressureless, air-filled gap 36. Preferably, the metal bellows 33 in the region of the opening on Sleeve bottom 29 and mounted on a surface of the inner mounting sleeve 31, which faces the sleeve bottom 29.

The use of the metal bellows 33 in the needle feedthrough allows a complete, permanent and reliable sealing of the high-pressure region in the chamber 35 of the injection valve 1 with respect to the gap 36 with the drive region, not shown. The metal bellows 33, despite a small wall thickness of, for example, 50 to 500 μm, withstand very high pressures due to its high radial rigidity, without being irreversibly deformed. The metal bellows 33 may be further configured to provide high mechanical compliance, i. a small spring constant in the direction of movement of the valve needle or axial direction is achieved. This ensures that the deflection of the valve needle 9 is not affected, and that caused by temperature-induced changes in length of the needle feedthrough into the valve needle forces are kept as small as possible. Furthermore, the fuel leakage can be prevented by the use of the metal bellows 33 in the needle feedthrough with high reliability.

The metal bellows-sealed needle feedthrough in the outer mounting sleeve 27 can also be designed so that the forces acting on the valve needle 9 pressure-related forces compensate each other. As a result, the valve needle 9 is kept completely free of pressure. For this purpose, the hydraulically effective diameter of the metal bellows is selected so that it corresponds exactly to the diameter of the valve seat 16 (not shown). As a result, it is achieved that the pressure force exerted by the pressurized fuel on the valve needle 9 with the valve disk 15 and the pressure-induced force introduced into the valve needle by the metal bellows 33 compensate one another. Thus, no resulting pressure force component acts on the valve needle 9. This ensures that the injection valve 1 shows a nearly independent of the fuel pressure switching behavior, since the opening and closing forces solely by the actuator element, for example, biased in a tube spring piezoelectric actuators, and the force of the biased nozzle spring 25 are determined. Due to its metallic material, the metal bellows 33 furthermore have a wide operating temperature range with constant functionality. Thermal changes in length of the metal bellows 33 themselves lead due to the small axial spring constant of the metal bellows only negligible force changes to the valve needle 9 in the axial direction. The metal bellows can also partially or completely replace the nozzle spring 25 due to its mechanical spring action in the axial direction.

The outer mounting sleeve 27 is shown in FIG. 1a now designed so that it forms a close and long as possible clearance together with the inner mounting sleeve 31. The game is only a few microns. Due to the throttling effect of this long cylindrical fit, rapid pressure changes in the fuel chamber 35 are kept away from the metal bellows 33, while static pressures can act unimpeded on the bellows wall. In addition, the pressure waves in the region of the jump in cross section of the first throttle body 37 are reflected at the chamber wall section or the sleeve end face extending transversely to the axial direction so that only a pressure wave with a greatly reduced pressure amplitude continues into the annular gap formed by the first throttle restriction 37.

In a fuel injection valve 1 according to the second embodiment, in contrast to the valve 1 according to the first embodiment, only a modification in the first throttle body 37 made in that the free inner diameter of the sleeve collar 44 of the outer mounting sleeve 27 at the same throttle gap dimensions in favor of Outer diameter of the inner mounting sleeve 31 is reduced. As in the valve according to the first embodiment, the throttle gap between inner and outer Mounting sleeve 27, 31 chosen so small and long that a sufficient throttling effect is realized. The triggered during the opening and closing of the valve 1 in the fuel chamber 35 pressure waves can not or only slightly act on the metal bellows 33 due to the small distance between the inner and outer mounting sleeve 27, 31.

A fuel injection valve 1 according to the third embodiment shown in Fig. 3a, b, instead of the first throttle point according to the first two embodiments, alternatively, a second throttle point 39 in the region of the upper valve needle guide and the upper guide sleeve 13. Since the fuel supply line 17 opens below the upper valve needle guide 13 into the space between the valve needle 9 and the valve body 5 or the fuel chamber 35, the fuel to be injected therein does not have to pass the upper valve needle guide 13. Therefore, the upper valve needle guide itself can be formed as a tight, long cylindrical clearance of the valve needle 9 in the upper guide sleeve 13, as shown in section BB in Fig. 3b. In this case, the valve needle 9, in contrast to the lower valve needle guide (section AA) is not formed as a square, but cylindrical (section BB). At this second throttle point 39, the pressure waves triggered during opening and closing operations are reflected and a dynamic volume exchange in the direction of the metal bellows 33 is strongly throttled. By integrating the throttle body 39 in the valve needle guide and multiple adjustments can be avoided. The throttling action of the upper valve needle guide 13 separates the fuel chamber 35 into two sub-volumes, namely first and second chamber sub-volumes 41, 43. Although large-amplitude dynamic pressure changes can be generated in the lower first sub-volume 41 of the fuel chamber 35 by opening and closing the injector these strongly weakened by the dynamic sealing effect of the second throttle body 39 in the upper second sub-volume 43 of the fuel chamber 35 act, in which the metal bellows needle feedthrough located. Thus, the metal bellows 33 is protected against dynamic pressure changes.

According to the fourth embodiment of a fuel injection valve (not shown), the throttling points 37, 39 shown in FIGS. 1, 2 and 3 are realized together in one valve. The first throttle body 37 is formed by the inner and outer mounting sleeves 27, 31 and the second throttle body 39 is formed by the upper guide sleeve 13 and the upper valve needle guide, respectively.

In the described embodiments, a bellows in the form of a metal bellows has been described as an elastic feedthrough element. However, the invention is not limited to this type of elastic feedthrough element but can also be applied to other types of elastic feedthrough elements such as e.g. a membrane or a resilient plastic or rubber sleeve are used. The membrane is preferably made of metal. The membrane and the sleeve are glued or welded according to the described metal bellows with the inner and outer mounting sleeve 27, 31.

In general, the pressure in the second chamber sub-volume 43 can be adjusted by the choice of the diameter of the clearance fit of the valve needle 9 compared to the hydraulically effective diameter of the metal bellows 33. By adjusting the diameter of the clearance larger (or smaller) than the hydraulically effective diameter of the metal bellows 33 is achieved that the pressure in the second chamber sub-volume 43 when opening the injector decreases (or increases). It is particularly advantageous if the diameter of the clearance fits the hydraulically effective diameter of the metal bellows 33, because in this way the pressure in the second chamber sub-volume 43 remains substantially constant when the injection valve is opened; the metal bellows 33 is then exposed in all operating conditions only a constant pressure load.

Claims (9)

1. Fluid dosing device for a pressurised fluid with a chamber (35) located in a housing (3), to which the pressurised liquid is guided through a liquid supply line (17, 21), and with a valve needle (9) guided through the chamber (35), the first end section of which it is possible to lift outside the chamber and the second end section thereof forming, in conjunction with a valve seat (16) disposed on the housing (3), a valve which is connected to the chamber (35), with a flexible leadthrough element (33) being provided for the first end section of the valve needle (9) when seen from the chamber (35) in an outward direction, which seals the chamber in said region in a tight manner,
   characterised in that
   at least one throttle point (37, 39) is provided circumferentially between the valve needle (9) and the inner wall of the chamber in the section of the chamber between the leadthrough element (33) and the mouth (19) of the liquid supply line (17) into the chamber (35), a gap representing the throttle point (37, 39) being a few µm wide.
2. Fluid dosing device according to Claim 1,
   characterised in that bellows, in particular metal bellows (33), are provided as the leadthrough element.
3. Fluid dosing device according to Claim 2,
   characterised in that the metal bellows (33) have a wall strength of 25 to 500 µm.
4. Fluid dosing device according to Claim 1 to 3,
   characterised in that the leadthrough element (33) is attached to an assembly sleeve (31), in particular by means of a welded connection.
5. Fluid dosing device according to Claim 4,
   characterised in that the throttle point (37) is created in the chamber (35) by the assembly sleeve (31).
6. Fluid dosing device according to one of the preceding claims,
   characterised in that an upper valve needle guide (13) is provided and that the throttle point (39) is created in the chamber (35) by the upper valve needle guide.
7. Fluid dosing device according to one of the preceding claims,
   characterised in that the free cross-section between the valve needle (9) and the inner wall of the chamber is changed abruptly in the region of the throttle point (37, 39).
8. Fluid dosing device according to one of the preceding claims,
   characterised in that fuel is used as the liquid and the fuel pressure is in the range of between 1 and 500 bar.
9. Fluid dosing device according to one of the preceding claims,
   characterised in that
   the diameter of a clearance fit of the valve needle (9) corresponds to a hydraulically effective diameter of the metal bellows (33).

Images