EP1990532A1 - Fuel injector for a combustion engine with common rail injection system - Google Patents

Abstract

The injector has a fluid path, which leads from a high pressure connection to a sealing seat (33). The fluid path runs away over a closing piston (58), which is coupled with a valve element (28). The fluid path includes a flow choke (68) over the closing piston. An area, which lies between the closing piston and the high pressure connection, of the fluid path includes a relief valve (70), which opens out into the fluid path. The closing piston is in the ring shape, and is arranged coaxially to the valve element.

Description

State of the art

The invention relates to a fuel injector for an internal combustion engine with common-rail injection system according to the preamble of claim 1.

From the market are known internal combustion engines with a common rail to which a plurality of fuel injectors are connected, which inject the fuel directly into them associated combustion chambers. The known fuel injectors have a stroke-controlled valve element which cooperates with a housing-side sealing seat and, when lifted from this sealing seat, allows fuel to escape from fuel outlet channels into the combustion chamber. A prevailing in a hydraulic control chamber control pressure acts on the valve element in its closed position. The control pressure can be lowered for opening the valve element. The advantage of such stroke-controlled fuel injectors is that the injection pressure can be adapted to the load and speed of the internal combustion engine.

To improve the emission values, a high injection pressure is advantageous. In order nevertheless to keep the leakage amount low, a valve element is used, which is completely surrounded by high fuel pressure, ie without a so-called "low-pressure stage" manages. To improve the closing behavior and the stability of such a fuel injector, especially in the metering small injection quantities is not pre-published in the DE 10 2006 036 447.3 a slight restriction of the fuel in the fluid path from the high pressure port proposed to the sealing seat, whereby an additional hydraulic closing force is generated. In addition, there is shown to increase the pressure surface acting in the closing direction by using an additional annular closing piston.

Disclosure of the invention

Object of the present invention is to provide a fuel injector, which has a good closing and opening behavior at high injection pressure and low leakage.

This object is achieved with the features of claim 1. Advantageous developments of the invention are specified in subclaims. In addition, essential features of the invention are also to be found in the following description and the figures, wherein the features alone or in different combinations may be essential to the invention, without any explicit reference being made thereto.

By using a closing piston, which is coupled to the valve element, the pressure surface acting in the closing direction is selectively increased, whereby the closing behavior is also in a valve element which has no low-pressure stage and is completely surrounded by high pressure fuel by increasing the closing force is improved. In the same direction, the inventively provided flow restrictor, which also generates an additional hydraulic closing force by means of the flowing fuel.

The present invention provided relief valve limits the pressure difference, which adjusts over the flow restrictor away, to a maximum value. In that regard, the relief valve may also be referred to as a pressure relief valve. As a result, an excessive force acting in the closing direction during opening of the valve element can be avoided. In accordance with the invention, it has been recognized that fuel must be displaced from the space lying between the high-pressure connection and the closing piston by the closing piston and the flow restrictor when the valve element is opened, which results in a pressure difference at the flow restrictor which acts counter to the opening movement. Through the relief valve, the pressure in this between high pressure port and Closing piston lying area limited to a maximum value, whereby a too high closing force is avoided when opening the valve element. As a result, the operating behavior of the fuel injector is stabilized. In addition, the pressure loss required to produce a sufficiently large closing force is reduced, which in turn improves the efficiency of the fuel injector of the present invention. A simple realization possibility is that the relief valve is arranged fluidically parallel to the flow restrictor.

A first refinement of the fuel injector according to the invention is characterized in that the relief valve opens to the fluid path lying between the closing piston and the sealing seat. This improves the efficiency of the fuel injector since the fuel flowing out of the fluid path between the closing piston and the high-pressure port is used for the injection.

A compact and easy to manufacture construction of the fuel injector according to the invention provides that the closing piston is annular and coaxial with the valve element.

In this case, the relief valve may be arranged in the closing piston. The injector housing can thus remain unchanged, so that the relief valve provided according to the invention does not affect the production costs of the injector housing.

The closing piston can also be integrally formed with the injector or on this. This eliminates the handling of an additional separate part in the assembly of the fuel injector, which simplifies the production.

But it is also particularly advantageous if the closing piston forms a valve element of the relief valve. The closing piston is therefore also a pressure limiting or relief piston, so that an additional component for limiting the pressure in the lying between the high-pressure port and closing piston area of the fluid path or to limit the pressure difference between this area and the area between closing piston and sealing seat area not is required.

In a further development, it is proposed that the closing piston is acted upon by a spring, which is supported on the valve element, against a sealing section on the valve element. Thus, the closing force acting on the closing piston is transmitted via the spring to the valve element. As a result, the closing force can be kept almost constant, so that pressure vibrations affect only slightly on the closing force. This leads to an improvement of the injection tolerances, the amount of fuel is thus injected with higher precision.

Also to reduce manufacturing costs contributes, if the flow restrictor is arranged in the closing piston. An additional processing of the injector to realize the flow restrictor is then not required.

The flow restrictor can also be realized in a particularly simple manner by realizing a gap between the closing piston and an adjacent section. This may be an annular gap or a longitudinal groove, through which the gap is implemented locally.

Advantageously, the closing piston in the injector housing is guided in a fluid-tight manner. The sealing seat associated with the closing piston thus lies on the valve element, so that no additional closing force is exerted on the valve element by the closing piston, at least in the idle state.

In a further development, it is proposed that a radial clearance is present between closing piston and valve element. This avoids a complicated manufacture of the double guide of the valve element.

Brief description of the drawings

Figur 1

einen teilweisen und schematischen Schnitt durch eine erste Ausführungsform eines Kraftstoffinjektors;

Figur 2

eine Darstellung ähnlich Figur 1 einer zweiten Ausführungsform; und

Figur 3

eine Darstellung ähnlich Figur 1 einer dritten Ausführungsform.

Hereinafter, embodiments of the present invention will be explained in more detail with reference to the accompanying drawings. In the drawing show:

FIG. 1

a partial and schematic section through a first embodiment of a fuel injector;

FIG. 2

a representation similar FIG. 1 a second embodiment; and

FIG. 3

a representation similar FIG. 1 a third embodiment.

Embodiments of the invention

A fuel injector carries in FIG. 1 Overall, it is the reference numeral 10. It is used in an internal combustion engine (not shown) with common rail injection system for direct injection of the fuel in a fuel injector directly associated combustion chamber.

The fuel injector 10 comprises a multi-part injector housing 12, which, in FIG. 1 from top to bottom, a control valve piece 14, an end plate 16, an elongate injector body 18 and a nozzle body 20 includes. At the in FIG. 1 lower end of the nozzle body 20, a plurality of fuel outlet channels 22 are provided, through which the fuel is injected during operation of the fuel injector 10 in the associated combustion chamber.

In the injector body 18 there is a through bore 24 and in the nozzle body 20 there is a stepped bore 26 adjoining it. In this an elongate valve element 28 is accommodated, which comprises a control rod 30 and, adjacent to the fuel outlet channels 22, a nozzle needle 32. This in FIG. 1 lower end of the nozzle needle 32 cooperates with a housing-side sealing seat 33. The lower end of the control rod 30 is guided over guide portions 34 in the nozzle body 20. Between the guide portions 34 flattened areas 36 are present. In FIG. 1 Immediately below the guide portions 34 and the flattened regions 36, a conical and in the opening direction acting pressure surface 37 is present on the nozzle needle 32. On the in FIG. 1 upper end of the control rod 30, a sealing sleeve 38 is placed. This is supported by its upper edge on the end plate 16.

Between the valve element 28 and the injector 12, an annular space 40 is formed. This is connected to a high pressure port 42, which in turn is connected to a common rail 44. An in FIG. 1 This limits together with the sealing sleeve 38 and the end plate 16, a hydraulic control chamber 48 via an inlet throttle 50, this communicates with the annulus 40. Via an outlet throttle 52 communicates the hydraulic control chamber 48 with an electromagnetic Switching valve 54, which connects the hydraulic control chamber 48 with a low pressure port 56 in the open position. In one embodiment, not shown, instead of the electromagnetic switching valve 54 and a piezoelectric valve may be used.

In order to avoid tensioning of the valve element 28 between the sealing sleeve 38 and the guide sections 34, regions with reduced bending stiffness may be provided on the valve element 28 (in FIG FIG. 1 not shown). Alternatively, the valve member may comprise a control rod and a nozzle needle which are coupled together or otherwise mechanically interconnected via a hydraulic coupler without substantially transmitting bending moments from one member to the other. It is further understood that in an embodiment not shown, the valve element may be in one piece, and / or that the valve element may be significantly shorter than in the FIG. 1 illustrated embodiment.

The fuel injector 10 has an annular closing piston 58 which is coaxial with the valve element 28 and is guided with its radially outer circumferential surface (without reference number) in the stepped bore 26 in the nozzle body 20 in a fluid-tight manner. Between the radially inner circumferential surface (without reference numeral) of the closing piston 58 and the control rod 30 of the valve element 28, a gap 60 is present, which ensures a radial clearance between closing piston 58 and valve element 28. On the control rod 30 is, in FIG. 1 below the closing piston 58, a support ring 62 rigidly attached. This extends radially outward slightly further than the gap 60, so that the closing piston 58 can be supported on it. For this purpose, the closing piston 58 is acted upon by a transmission sleeve 64, which is also pushed with radial play on the control rod 30 and disposed between closing piston 58 and sealing sleeve 38. Between transmission sleeve 64 and sealing sleeve 38 is a Compression spring 66 braced. Through this, on the one hand, the sealing sleeve 38 is acted upon against the end plate 16 and on the other hand, the closing piston 58 against the support ring 62.

In the closing piston 58, a flow restrictor 68 is arranged, which is designed as a throttle bore and a located between the high-pressure port 42 and closing piston 58 portion 40a of the annular space 40 with a lying between the closing piston 58 and sealing seat 33 portion 40b of the annular space 40 connects. In an alternative, not shown embodiment, the flow restrictor 68 is simply formed by an annular gap between closing piston 58 and injector 12 or a groove in the radially outer surface of the closing piston 58.

Furthermore, a relief valve 70 formed by a spring-loaded check valve is integrated in the closing piston 58, which opens toward the region 40b of the annular space 40 between closing piston 58 and sealing seat 33 and in this open state connects the region 40a and 40b of the annular space 40 with one another. As a valve element, the relief valve 70 comprises a valve ball 72, which is acted upon by a valve spring 74 against a formed on the closing piston 58 sealing portion 76. It can be seen that the fuel injector 10 comprises a fluid path which from the high-pressure port 42 via the region 40a of the annular space 40, by means of the flow restrictor 68 and optionally also by means of the (open) relief valve 70 via the closing piston 58 to the region 40b of the annular space 40, ie leads over the flattened areas 36 to the sealing seat 33. The relief valve 70 is thus arranged fluidly parallel to the flow restrictor 68.

The fuel injector 10 operates as follows: In the idle state, with the switching valve 54 closed, the high fuel pressure prevailing at the high-pressure port 42 prevails in the entire annular space 40. This is also transmitted via the inlet throttle 50 into the hydraulic control chamber 48. The corresponding force resultant on the hydraulic control surface 46 acts on the valve element 28 in the closing direction of the valve element 28 against the sealing seat 33. The fluid path described above thus ends at the sealing seat 33, fuel can not escape through the fuel outlet channels 22. The relief valve 70 is closed.

If fuel is to be injected, the electromagnetic switching valve 54 is opened, whereby fuel flows from the hydraulic control chamber 48 via the outlet throttle 52 to the low pressure port 56. As a result, the pressure in the hydraulic control chamber 48 drops and, correspondingly, the force-resultant force acting on the hydraulic control surface 46 and acting in the closing direction decreases. If the forces acting in the closing direction on the valve element 28 sink below the force acting on the pressure surface 37 in the opening direction, the valve element 28 moves upwards. The high fuel pressure in the region 40b now also acts on the lower conical tip 72 of the nozzle needle 32, as a result of which additional forces in the opening direction act on the valve element 28.

With the opening movement of the valve member 28 shifts due to the entrainment by the support ring 62 and the closing piston 58 upwards, whereby the volume of the portion 40a of the annular space 40 is reduced. The pressure difference between the regions 40a and 40b which is established when flowing through the flow throttle 38 across the closing piston 58 is thereby reinforced, which produces an additional hydraulic force acting on the closing piston 58 in the closing direction, which also acts on the valve element 28 via the support ring 62 , This could, without any countermeasures, slow down the opening movement of the valve element 28 and, as a result, cause stability problems. These will be at the in FIG. 1 However, fuel injector 10 shown by the function of the relief valve 70 avoided: namely, this is a maximum possible pressure difference between the areas 40a and 40b of the annular space 40 is set. When the pressure difference between these two spaces 40a and 40b exceeds the opening pressure difference of the relief valve 70, it opens, relieving the pressure in the space 40a into the space 40b.

If the fuel injection is to be terminated, the electromagnetic switching valve 54 is closed, whereby the outflow of fuel from the hydraulic control chamber 48 to the low pressure port 56 is terminated. Fuel flows into the hydraulic control chamber 48 via the inlet throttle 50, so that the pressure there again rises approximately to that level which prevails in the annular space 40a or at the high-pressure port 42. Due to the flow restrictor 68, the pressure in the region 40b of the annular space 40 is slightly lower than in the region 40a and thus also somewhat lower than in the hydraulic control chamber 48 Surface equality between on the one hand the hydraulic control surface 46 and the other hand, the pressure surface 37 and the conical tip 72 now outweigh the forces acting in the closing direction on the valve element 28 - also because the closing piston 58 additionally acts in the closing direction force - so that they again in the direction moved to the sealing seat 33. If the nozzle needle 32 approaches the sealing seat 33, the pressure at the conical tip 72 drops due to throttling effects, as a result of which the forces acting in the opening direction on the valve element 28 decrease again and the closing process is accelerated. If the nozzle needle 32 again at the sealing seat 33, no fuel can escape from the fuel outlet channels 22, and it ends the fuel flow from the area 40a in the area 40b. It now turns back to a state in which there is approximately the same hydraulic pressure in the entire annular space 40 and in the hydraulic control chamber 48.

An alternative embodiment of a fuel injector 10 is shown in FIG FIG. 2 shown. Here, as in the following, such elements and regions which have equivalent functions to elements and regions which have already been explained in connection with a preceding figure bear the same reference numerals.

The in FIG. 2 shown fuel injector 10 differs from that of FIG. 1 in that the closing piston 58 is not arranged in the region of the nozzle body 20, but in the area of the injector body 18, in the vicinity of the sealing sleeve 38. A transmission sleeve is therefore not necessary. In addition, the closing piston 58 is integrally formed with the control rod 30, so there is no gap between the control rod 30 and the closing piston 58.

Another alternative embodiment shows FIG. 3 In this, the valve element 72 of the relief valve 70 is formed by the closing piston 58 itself. The sealing portion 76, with which the closing piston 58 cooperates, is realized by a collar on the control rod 30. Against this, the closing piston 58 is acted upon by a spring 74, which is supported on a support ring 62.

If the pressure difference between the regions 40a and 40b of the annular space 40 exceeds a desired value, in particular during the opening process of the valve element 28, the closing piston 58 lifts off from the annular collar 76, whereby fuel in addition to the flow throttle 68th from area 40a into area 40b, which limits the pressure in annulus 40a. At the same time, the hydraulic force acting on the closing piston 58 and acting in the closing direction of the valve element 28 is transmitted via the spring 74 and the support ring 62 to the control rod 30 and the nozzle needle 32.

The in the embodiments in the FIGS. 1 and 2 comparatively rigid coupling between the closing piston 58 and the valve element 28 takes place at the in FIG. 3 The spring 74 acts thereby dampening, so that pressure fluctuations, in particular in the area 40a of the annular space 40, only have a reduced effect on the valve element 28. As a result, the precision of the metering of the injected fuel quantity is improved. Here, too, it is understood that in an embodiment not shown, the arrangement consisting of annular collar 76, closing piston 58 or valve element 72 and valve spring 74 can also be disposed further up in the injector body 18. It is also conceivable in all the embodiments described above, the flow restrictor 68 through the opening gap between the valve element 72 of the relief valve 70 and the associated sealing portion 76 to realize.

Claims (11)

Fuel injector (10) for an internal combustion engine with common-rail injection system, comprising an injector housing (12), a stroke-controlled valve element (28) which cooperates on the one hand with a housing-side sealing seat (33) and on the other hand limits a hydraulic control chamber (48), and a fluid path (40) leading from a high - pressure port (42) to the sealing seat (33), characterized in that the fluid path (40) extends across a closing piston (58) coupled to the valve element (28) Fluid path (40) over the closing piston (58) across a flow restrictor (68), and that between closing piston (58) and high-pressure port (42) lying region (40a) of the fluid path (40) comprises a relief valve (70). Fuel injector (10) according to claim 1, characterized in that the relief valve (70) opens to the between the closing piston (58) and sealing seat (33) lying fluid path (40b) out. Fuel injector (10) according to one of claims 1 or 2, characterized in that the closing piston (58) is annular and coaxial with the valve element (28). Fuel injector (10) according to one of the preceding claims, characterized in that the relief valve (70) in the closing piston (58) is arranged. Fuel injector (10) according to any one of the preceding claims, characterized in that the closing piston (58) with the valve element (28) is in one piece. Fuel injector (10) according to one of claims 1 or 2, characterized in that the closing piston (58) forms a valve element (72) of the relief valve (70). Fuel injector (10) according to claim 6, characterized in that the closing piston by a spring (74), which is supported on the valve element (28), against a sealing portion (76) on the valve element (28) is acted upon. Fuel injector (10) according to one of the preceding claims, characterized in that the flow throttle (68) in the closing piston (58) is arranged. Fuel injector according to one of the preceding claims, characterized in that the flow restrictor comprises a gap between closing piston and an adjacent portion. Fuel injector (10) according to one of the preceding claims, characterized in that the closing piston (58) is guided in the injector housing (12). Fuel injector (10) according to claim 10, characterized in that between the closing piston (58) and valve element (28) a radial clearance (60) is present.

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