Fuel injector

Abstract

Fuel injector (10), in particular a common-rail injector for compression-ignition internal combustion engines, with an injector housing (12) in which a movable nozzle needle (20) is arranged for opening and closing at least one injection orifice (22), wherein the movement of the nozzle needle (20) can be controlled by influencing the pressure in a control chamber (32) by means of a control valve (42), wherein the control valve (42) has an armature bolt (60) cooperating with a magnetic armature (44), wherein the armature bolt (60) is subjected to the hydraulic pressure prevailing in the control chamber (32) at a first end face (62), wherein a second end face (64) of the armature bolt (60) is arranged in operative connection with a pressure sensor (66), and wherein the magnetic armature (44) is moved by means of an armature spring (70) towards a position closing the control chamber (32). is subjected to force, characterized bythat the armature spring (70) is supported at least indirectly in the axial direction on the armature bolt (60) on the side facing away from the magnetic armature (44), so that a spring force of the armature spring (70) can be transmitted to the pressure sensor (66) in addition to the hydraulic pressure prevailing in the control chamber (32).

Description

State of the art

[0001] The invention relates to a fuel injector, in particular a common-rail injector for self-igniting internal combustion engines, having the features of the preamble of claim 1.

[0002] A fuel injector with the features of the preamble of claim 1 is known from DE 10 2010 000 827 A1 of the applicant. The known fuel injector has a pressure sensor arranged in a low-pressure area of ​​its injector housing, which is subjected to force by an end face of an armature bolt. The hydraulic pressure prevailing in a control chamber acts on the end face of the armature bolt facing away from the pressure sensor. The armature bolt is arranged in a through-bore of a magnetic armature, which in turn serves as a component of a control valve to control the outflow of pressure medium from the control chamber depending on its axial position. By influencing the pressure in the control chamber, the opening or closing of at least one injection port in the injector housing by a nozzle needle can be controlled.The pressure sensor provides information about the pressure in the control chamber and thus, at least indirectly, about the current position of the nozzle needle. While the position of the magnetic armature can also be inferred, at least indirectly, from the pressure in the control chamber, a direct measurement of the armature stroke is not possible due to the arrangement of the armature bolt, the magnetic armature, and the pressure sensor described in the aforementioned document. In the known fuel injector, this is primarily because an armature spring, which serves to close the magnetic armature in its position preventing the outflow of fuel or pressure medium from the control chamber, is supported on the side facing away from the magnetic armature by a housing-mounted element outside the pressure sensor. One could attempt, for example, by increasing the surface area of ​​the pressure sensor, to also bring the end face of the armature spring facing the pressure sensor into operative contact with the pressure sensor.To arrange such a design, however, requires not only a specially designed pressure sensor, which, in particular, must have an enlarged contact area to ensure that the force exerted by the magnetic armature on the armature spring can be detected by the pressure sensor. The effort and space required for such a pressure sensor are, however, relatively high.

[0003] Furthermore, fuel injectors with pressure sensors are known from DE 10 2009 002 895 A1, US 2010 / 0 096 480 A1 and US 2012 / 0 031 376 A1, wherein the pressure sensors are arranged in different areas of the respective fuel injectors. Disclosure of the invention

[0004] The fuel injector according to the invention, in particular a common-rail injector for self-igniting internal combustion engines with the features of claim 1, has the advantage that the force acting on the armature spring from the magnetic armature, from which the instantaneous stroke of the magnetic armature can be deduced, can be transmitted to the pressure sensor in a particularly simple and safe manner.

[0005] The invention proposes that the armature spring be supported, at least indirectly in the axial direction, on the side facing away from the magnetic armature, so that a spring force of the armature spring can be transmitted to the pressure sensor via the armature bolt in addition to the hydraulic pressure prevailing in the control chamber. In other words, this means that the hydraulic pressure prevailing in the control chamber and the spring force acting as a function of the position of the magnetic armature are transmitted together to the pressure sensor via the armature bolt. This allows, for example, even with a pressure sensor that only enables optimal force transmission or force detection in the area of ​​the armature bolt's cross-section, a measurement of the spring force of the armature spring, which is dependent on the position of the magnetic armature, to be achieved.

[0006] Advantageous further developments of the fuel injector according to the invention are listed in the dependent claims.

[0007] The coupling between the armature bolt and the armature spring is preferably achieved by the end face of the armature spring facing away from the magnetic armature bearing at least indirectly against the armature bolt. This enables a particularly simple method of force transmission from the armature spring via the armature bolt to the pressure sensor.

[0008] In a first embodiment of the force transmission from the anchor spring to the anchor bolt, the anchor spring is axially supported by an element separate from the anchor bolt, with the separate element being connected to the anchor bolt. This has the particular advantage that an existing anchor bolt can be modified in its geometry in a particularly simple manner to form the support according to the invention. Furthermore, this minimizes the material required for manufacturing an anchor bolt suitable for this support.

[0009] Further developing the previously made proposal, it is envisaged that a positive-locking connection is formed between the separate element and the anchor bolt. For example, the separate element could be designed as a standard element in the form of a ring washer, snap ring, or similar.

[0010] In particular, it may also be provided that the anchor bolt has a groove or a shoulder running radially around its longitudinal axis, against which the element rests and thus is axially supported on the anchor bolt.

[0011] As an alternative to a separate element connected to the anchor bolt by means of a positive-locking connection, the separate element can also be connected to the anchor bolt by means of a material-bonded connection, in particular by means of a laser weld. Such a design has the particular advantage that, for example, the axial position of the separate element relative to the longitudinal axis of the anchor bolt can be varied very easily and / or that the manufacture of the anchor bolt is simplified insofar as, for example, no radially circumferential groove or shoulder needs to be provided.

[0012] In yet another alternative embodiment, it is also possible to dispense with a separate element connected to the anchor bolt. In this case, the anchor spring is axially supported directly against a stop surface of the anchor bolt that rotates radially around a longitudinal axis of the anchor bolt.

[0013] In particular with regard to the design of the fuel injector in the area of ​​the pressure sensor and a magnetic core, it may also be advantageous for space-saving reasons, for example for the arrangement of a clamping element for the magnetic core or similar, if a gap is formed between the pressure sensor and the end face of the armature spring facing the pressure sensor.

[0014] Pressure sensors using piezoelectric elements are particularly suitable, as they provide voltage signals with sufficient accuracy when pressure is applied and can be designed to be particularly compact in terms of their size.

[0015] In order to detect only forces generated by the anchor bolt or anchor spring using the pressure sensor, it is also advantageous if the pressure sensor is axially supported on a housing-fixed element on the side facing away from the anchor spring and the anchor bolt, so that the pressure sensor is only arranged in operative connection with the anchor bolt.

[0016] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawing.

[0017] This figure shows a partial axial section in the area of ​​a fuel injector.

[0018] The fuel injector 10 shown in part in the figure is designed as a so-called common-rail injector for self-igniting internal combustion engines and serves to inject fuel into the combustion chamber of the internal combustion engine, which is not shown.

[0019] The fuel injector 10 has a multi-part injector housing 12 with a high-pressure chamber 14, which can be supplied with fuel under high pressure or system pressure (the pressure of which is particularly greater than 1800 bar) via an inlet channel 16. Within the high-pressure chamber 14, a valve needle in the form of a nozzle needle 20 is arranged to move along a longitudinal axis 18. The nozzle needle 20 serves to open or close at least one injection orifice 22 formed in the injector housing 12.

[0020] A closing spring 24 holds the nozzle needle 20 in its lowered position, which closes the at least one injection port 22. The closing spring 24 is supported on the end face of a valve piece 26 opposite the at least one injection port 22. The valve piece 26 defines the high-pressure chamber 14 and has a receptacle 28 arranged concentrically to the longitudinal axis 18, which is approximately blind-hole shaped. The end region 30 of the nozzle needle 20, opposite the at least one injection port 22, extends axially into the receptacle 28 and defines a control chamber 32 within the receptacle 28. The control chamber 32 is filled, for example, with high-pressure fuel from the high-pressure chamber 14 by means of an inlet channel 34 which has an inlet restrictor.

[0021] On the side opposite the nozzle needle 20, a drain bore 36, formed in the valve piece 26 and running concentrically to the longitudinal axis 18, extends from the base of the receptacle 28 and has an integrated drain restrictor. This drain bore opens into a low-pressure area 38 of the injector housing 12. The low-pressure area 38 is in turn connected via a fuel drain 40, for example, to a fuel tank or similar.

[0022] The outflow of pressure medium or fuel from the control chamber 32 into the low-pressure area 38 is controlled by a pressure-balanced control valve 42. The control valve 42 comprises a magnetic armature 44, which is arranged to move freely along the longitudinal axis 18. The magnetic armature 44, which in this embodiment is disc- or hat-shaped, interacts with an electromagnet 46, which has a magnetic core 48 and a magnetic coil 50 arranged in a recess radially circumferential to the longitudinal axis 18. When the magnetic coil 50 is energized, the magnetic armature 44 is pulled in the direction of the magnetic core 48 or the magnetic coil 50 in a manner known per se. In the lowered position of the magnetic armature 44 shown in the figure, a radially circumferential sealing edge 52 of the magnetic armature 44 together with an opening area 54 on the valve piece 26 forms a sealing seat 56, which allows a flow of pressure medium orFuel from the control room 32 is prevented.

[0023] The magnetic armature 44 has a through-bore 58 formed concentrically to the longitudinal axis 18, which is penetrated by a pin-shaped armature bolt 60. The hydraulic pressure prevailing in the control chamber 32 acts on the end face 62 of the armature bolt 60 facing the control chamber 32. The magnetic armature 44 is guided radially in the valve piece 26.

[0024] On the side facing away from the control chamber 32, the armature bolt 62 projects a portion of its length out of the magnetic armature 44 and, with its end face 64 facing away from the control chamber 32, acts at least indirectly on a pressure sensor 66. The pressure sensor 66 is designed, in particular, using at least one piezoelectric element 68, which generates a voltage signal depending on the mechanical pressure of the armature bolt 60 acting on the piezoelectric element 68. From this signal, the hydraulic pressure in the control chamber 32, and thus the position of the nozzle needle 20, can be inferred, at least indirectly. The pressure sensor 66 is supported on the side facing away from the armature bolt 60 by a stationary housing element 80.

[0025] The outer circumference of the anchor bolt 60, whose longitudinal axis is aligned with the longitudinal axis 18, is furthermore radially surrounded by an anchor spring 70, which exerts force on the magnetic armature 44 in its closed position, in which the outflow of pressure medium or fuel from the control chamber 32 into the low-pressure area 38 is prevented. For this purpose, the anchor spring 70 is supported axially at a first end face 71 against the magnetic armature 44, and at a second end face 72 against a separate element 74 connected to the anchor bolt 70, the element 74 acting as a stop element for the anchor spring 70.

[0026] For example, the anchor bolt 60 has an annular groove 76 extending radially around the longitudinal axis 18, wherein the separate element 74 is designed, for example, as an annular washer or a snap ring, which engages positively in the annular groove 76 to form a positive connection 78 between the element 74 and the anchor bolt 60. Because the spring force acting on the anchor spring 70, which depends on the axial position of the magnetic armature 44, acts on the anchor bolt 60 via the element 74, the spring force caused by the anchor spring 70 also acts directly on the pressure sensor 66.

[0027] Furthermore, it can be seen that a distance a is formed between the element 74 or the end face 72 of the anchor spring 70 and the pressure sensor 66.

[0028] The fuel injector 10 described so far can be modified or adapted in a variety of ways without deviating from the inventive concept. For example, it is conceivable to dispense with a separate element 74 as an axial stop for the anchor spring 70 and instead design the anchor bolt 60 with a radially circumferential shoulder or step or similar feature against which the anchor spring 70 rests axially with its end face 72.

Claims

[1] Fuel injector (10), in particular a common-rail injector for compression-ignition internal combustion engines, with an injector housing (12) in which a movable nozzle needle (20) is arranged for opening and closing at least one injection orifice (22), wherein the movement of the nozzle needle (20) can be controlled by influencing the pressure in a control chamber (32) by means of a control valve (42), wherein the control valve (42) has an armature bolt (60) interacting with a magnetic armature (44), wherein the armature bolt (60) is subjected to the hydraulic pressure prevailing in the control chamber (32) at a first end face (62), wherein a second end face (64) of the armature bolt (60) is arranged in operative connection with a pressure sensor (66), and wherein the magnetic armature (44) is moved by means of an armature spring (70) towards a position closing the control chamber (32). is subjected to force, characterized by, that the armature spring (70) is supported at least indirectly in the axial direction on the armature bolt (60) on the side facing away from the magnetic armature (44), so that a spring force of the armature spring (70) can be transmitted to the pressure sensor (66) in addition to the hydraulic pressure prevailing in the control chamber (32). [2] Fuel injector according to claim 1, characterized by , that the anchor spring (70) is supported at least indirectly on the anchor bolt (60) with an end face (72) facing the pressure sensor (66). [3] Fuel injector according to claim 1 or 2, characterized by , that the anchor spring (70) is axially supported on an element (74) separate from the anchor bolt (60), which is connected to the anchor bolt (60). [4] Fuel injector according to claim 3, characterized by , that a positive locking connection (78) is formed between the separate element (74) and the anchor bolt (60). [5] Fuel injector according to claim 3 or 4, characterized bythat the anchor bolt (60) has a radially circumferential groove (76) or a radially circumferential shoulder against which the separate element (74) rests. [6] Fuel injector according to claim 3, characterized by , that the separate element (74) is connected to the anchor bolt (60) by means of a material-bonded connection, in particular by means of a laser weld. [7] Fuel injector according to claim 1 or 2, characterized by , that the anchor spring (70) is axially supported directly on a radially circumferential stop surface formed monolithically on the anchor bolt (60). [8] Fuel injector according to any one of claims 1 to 7, characterized by , that a distance (a) is formed between the pressure sensor (66) and the end face (72) of the anchor spring (70) facing the pressure sensor (66). [9] Fuel injector according to any one of claims 1 to 8, characterized by that the pressure sensor (66) has at least one piezoelectric element (68). [10] Fuel injector according to any one of claims 1 to 9, characterized by , that the pressure sensor (66) is axially supported on a housing-fixed element (80) on the side facing away from the anchor spring (70) and the anchor bolt (60).

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