Magnetic actuator for actuating fuel injectors, fuel injector

Abstract

Magnetic actuator for actuating fuel injectors, comprising a magnetic core (1), a magnetic coil (2) and an armature (3) cooperating with the magnetic coil (2), which is guided in a stroke-movable manner via an armature pin (4) fixedly connected to the armature (3), characterized in that the armature pin (4) has a central bore (5) and / or a groove (7) extending helically over an outer circumferential region (6) as a flow channel for a fluid, in particular fuel, wherein the bore (5) and / or the groove (7) extend over a predetermined guide region (8) of the armature pin (4) and beyond the guide region (8) through the armature (3).

Description

[0001] The invention relates to a magnetic actuator for actuating fuel injectors with the features of the preamble of claim 1. Furthermore, a fuel injector with such a magnetic actuator is proposed. State of the art

[0002] Magnetic actuators of the type described above are well known. They are frequently used in fuel injectors to control a movable nozzle needle, the movement of which opens or closes at least one injection port. For this purpose, the magnetic actuator typically comprises a magnetic core, a magnetic coil, and a movable armature that interacts with the magnetic coil. In direct actuation of the fuel injector via the magnetic actuator, the armature can be coupled to the nozzle needle directly or indirectly, for example, via a force amplification device in the form of a hydraulic coupler. In indirect actuation, the magnetic actuator is part of a solenoid valve, which controls the control pressure acting on the nozzle needle in the closing direction.

[0003] An example of a fuel injector directly actuated via a magnetic actuator is described in German patent application DE 10 2007 002 758 A1. The magnetic actuator comprises an annular magnetic coil inserted into a magnetic core and interacting with a movable, plate-shaped armature, which is rigidly connected to a coupler piston that passes through the armature. The coupler piston, with its combustion chamber-side end, defines a hydraulic coupler chamber, which is further defined by an end face of a nozzle needle. The coupler piston and the nozzle needle can be hydraulically coupled via the coupler chamber. When the magnetic coil of the magnetic actuator is energized, the armature and the coupler piston move towards the magnetic coil, and the pressure in the coupler chamber drops. Due to the pressure drop, the nozzle needle opens.The selected area ratio of the hydraulically actuated surfaces of the coupler piston and the nozzle needle, which define the coupler chamber, reduces the armature stroke and translates the magnetic force of the magnetic actuator. When the magnetic coil is de-energized, the armature and the coupler piston are returned to their initial position by the spring force of an armature spring, causing the pressure in the coupler chamber to rise again and closing the nozzle needle. In this fuel injector, the fuel to be injected is guided through an actuator chamber that houses the magnetic actuator and through the armature chamber. The armature chamber is connected to the actuator chamber via a connecting channel that passes through the magnetic core and to a high-pressure bore that houses the nozzle needle via another connecting channel formed in an intermediate body. The armature, which is designed as a flat armature, is thus surrounded by fuel during operation of the fuel injector.

[0004] Furthermore, magnetic actuators for directly actuated fuel injectors are known, which interact with an armature designed as a diving armature. In this case, it is advantageous with regard to the achievable magnetic force if any air gaps between the magnetic actuator and the armature are minimized. The fuel can then be guided through the armature, which for this purpose has at least one bore and / or a slot on its outer circumference. In the case of a bore, this is usually angled, which, however, shifts the armature's center of gravity away from the central axis. Flow deflections also lead to lateral forces on the armature, which in turn can cause the armature to strike a stop surface eccentrically. Slots have the disadvantage of requiring more complex manufacturing and reducing the pole area of ​​the armature, which in turn reduces the driving force.

[0005] Utility model DE 85 17 345 U1 and patent application US 2 981 483 A also disclose magnetic actuators for actuating fuel injectors.

[0006] There is therefore a need to optimize the flow guidance in a fuel injector. To achieve this, a magnetic actuator for actuating fuel injectors with the features of claim 1 and a fuel injector with the features of claim 9 are proposed here. Disclosure of the invention

[0007] The proposed magnetic actuator for actuating fuel injectors comprises a magnetic core, a magnetic coil, and an armature interacting with the magnetic coil, which is guided in a stroke-moving manner by an armature pin rigidly connected to the armature. According to the invention, the armature pin has a central bore and / or a helical groove extending over an outer circumferential region as a flow channel for a fluid, in particular fuel. The alternatively or additionally proposed measures enable a centric or nearly centric fluid guidance through the armature assembly. In this way, air gaps or guide clearances between the components of the armature assembly can be minimized, thereby achieving maximum actuating forces and optimal guidance. The bore and / or the helical groove extends at least over a predetermined guide region of the armature pin and beyond this guide region through the armature.This means that the bore and / or the groove in the anchor is continued or is continued through a bore in the anchor.

[0008] In a fluid guidance system using a central bore in the anchor pin, the fluid is guided in the center of the anchor assembly, i.e., where the material does not contribute significantly to the bending stress of the anchor pin due to transverse magnetic forces and can therefore be easily removed. The fluid can also be guided through the central bore, which preferably has a circular flow cross-section, largely without restriction or flow deflection. This reduces the load on the anchor assembly from transverse forces. At the same time, optimal guidance of the anchor assembly is achieved because, compared to guidance via segmented guide surfaces, the guidance is provided across the entire circumference of the anchor pin by means of multiple grindings. The hollow bore of the anchor pin also results in a lower moving mass, which is also advantageous with regard to the required drive forces.Furthermore, the advantage arises that an axial working air gap between the armature and the magnetic core is connected to the fluid guide, so that pressure equalization is possible during the stroke of the armature.

[0009] In a fluid guide via a helical groove extending over an outer circumference, the fluid is guided approximately centrally through the armature assembly. Compared to the previously mentioned multiple grinding methods, the helical groove provides improved guidance of the armature pin and thus of the armature assembly. This is because there is no area where the outer circumferential surface of the armature pin is interrupted along the entire guide length. Furthermore, the torque induced by the helical shape of the groove proves advantageous, as it excites a rotational movement of the armature assembly and thereby improves lubrication in the guide gap.

[0010] According to a preferred embodiment of the invention, the bore and / or the groove provides a hydraulic connection between an armature chamber and a spring chamber, which preferably serves to accommodate a return spring. The armature chamber and the spring chamber can be arranged in one or more body components of the fuel injector, wherein at least one body component has a guide bore in which the armature pin is guided. The guide clearance can be minimized because the fluid is guided via the central bore and / or the helical groove of the armature pin.

[0011] Depending on the specific design of the anchor pin, the central bore for fluid guidance can be a blind hole. In this case, at least one additional bore branching off from the central bore is provided, exiting the anchor pin on an outer circumference. This branching bore can be radial or inclined, whereby, to minimize flow deflection, the angle of an inclined bore should be as small as possible relative to the longitudinal axis of the anchor pin.

[0012] The flow deflection caused by the branching bore can also offer advantages. This deflection generates an additional closing force that can be transmitted from the armature pin to the nozzle needle, allowing for targeted control of the nozzle needle's closing behavior to terminate an injection process.

[0013] Where the term "bore" is used in this context, it shall be understood to mean any opening or recess of any shape which has been produced by drilling, milling or in any other way.

[0014] The branching bore ensures the hydraulic connection between the central bore, designed as a blind hole, and a pressure chamber, such as the spring chamber for housing the return spring. Designing the central bore as a blind hole has the advantage that the armature pin can be guided right up to the directly actuated nozzle needle of the fuel injector, thus enabling, for example, a mechanical coupling of the armature pin to the nozzle needle by striking an end face of the nozzle needle. Fluid flow continues through the solid section of the armature pin via a pressure chamber surrounding the armature pin, such as the spring chamber.

[0015] According to a particularly preferred embodiment of the invention, the anchor pin is inserted into a central through-bore of the anchor and connected to the anchor by force-fit, form-fit, and / or material-fit connection. This allows for a simple continuation of the central bore or the helical groove in the anchor. The force-fit, form-fit, and / or material-fit connection can be achieved, for example, by insertion, pressing, forming, and / or welding. If a weld is used, the weld seam, preferably by laser welding, can be applied as a fillet weld to the top or bottom of the anchor. Forming methods such as flanging and / or riveting are particularly suitable.

[0016] According to an alternative preferred embodiment, the anchor pin is attached to the anchor and connected to the anchor by force-fit, form-fit, and / or material-fit connection. The anchor pin can be butt-fitted or pushed onto a cylindrical or hollow cylindrical projection of the anchor. The connection methods already mentioned above can be used for the force-fit, form-fit, and / or material-fit connection.

[0017] Furthermore, it is proposed that the anchor be designed as a diving anchor. Compared to a flat anchor, a diving anchor allows for a greater anchor stroke. In addition, the centric or near-centric fluid flow minimizes air gaps, which has a positive effect on the achievable magnetic force.

[0018] Depending on the specific design of the anchor, it may have at least one additional flow channel. This can be a bore through the anchor, a longitudinal groove on the outer circumference, and / or a chamfer. For example, a central bore for receiving an anchor pin may be provided with a helical groove, which then interacts with the groove to form a flow channel.

[0019] Since the magnetic actuator according to the invention is preferably used in a fuel injector, a fuel injector with such a magnetic actuator is further proposed. The fuel injector can preferably be actuated directly via the magnetic actuator. This means that the armature pin acts directly or indirectly, via a force amplification device, on a nozzle needle of the fuel injector.

[0020] Preferred embodiments of the invention are described in more detail below with reference to the accompanying drawings. These show: Fig. 1 a schematic longitudinal section through a magnetic actuator according to the invention inserted into a fuel injector in a first preferred embodiment and Fig. 2 a perspective view of an armature assembly of a magnetic actuator according to the invention in an alternative preferred embodiment. Detailed description of the drawings

[0021] The one in Fig. Figure 1, a magnetic actuator according to the invention for actuating a fuel injector, comprises a magnetic core 1, which is surrounded in one end section by an annular magnetic coil 2. The magnetic coil 2 interacts with a movable armature 3, which in this case is designed as a plunger armature and has an armature pin 4 as a force transmission element. The armature 3 is also guided by the armature pin 4. For this purpose, the armature pin 4 is received in an axial bore 16 of a body component 17 of the injector. The body component 17, the magnetic coil 2, and the magnetic core 1 are axially clamped by means of a clamping nut 18 that encompasses the components.

[0022] When the magnetic coil 2 is energized, a magnetic field is generated that pulls the armature 3, including the armature pin 4, towards the magnetic core 1 to close a working air gap 19 between the armature 3 and the magnetic core 1. The stroke of the armature pin 4 causes a pressure drop in a hydraulic coupler chamber 20, which is further bounded by an end face of a movable nozzle needle 15, so that the stroke of the armature pin 4 causes the stroke of the nozzle needle 15 to follow. The size ratio of the hydraulic effective areas of the nozzle needle 15 and the armature pin 4, which bound the hydraulic coupler chamber 20, is selected such that a force amplification is achieved. The injection process begins with the opening stroke of the nozzle needle 15.

[0023] The fuel to be injected is guided through the magnetic actuator. For this purpose, the magnetic core 1 has a central bore 21 that opens into an armature chamber 9, in which the armature 3 is housed. The armature 3 is penetrated by a through bore 13, in which the armature pin 4 is housed. The armature pin 4 has a central bore 5 designed as a blind hole, which is hydraulically connected to a spring chamber 10 via radially extending bores 12. From the armature chamber 9, the fuel is thus guided through the central bore 5 and the bores 12, which exit the armature pin 4 in an outer circumferential region 6', and which is located in the spring chamber 10. The fuel is therefore guided through the center of the armature assembly, at least via a guide section 8 of the armature pin 4 within the axial bore 16 of the body component 17. This has several advantages.Firstly, the secondary air gap 22 remaining between the armature 3 and the magnetic actuator can be reduced to a minimum, which has a positive effect on the magnetic force achievable via the magnetic circuit. Secondly, the guide play between the armature pin 4 and the body component 17 in the area of ​​the axial bore 16 can be minimized, thereby improving guidance. Furthermore, the central bore 5 of the armature pin 4 eliminates the need for external flow channels, for example in the form of longitudinal grooves and / or multiple grindings, so that the entire circumference of the armature pin 4 is available for guidance. From the spring chamber 10, the fuel is then supplied to a high-pressure bore 23 in which the nozzle needle 15 is located.

[0024] Instead of the radially extending bores 12, which connect the central bore 5 of the anchor pin 4 with the spring chamber 10, one or more obliquely extending bores 12 may also be provided (see reference numerals in parentheses, where the dashed line merely indicates a possible orientation or the angle of an oblique bore). As already mentioned, "bore" refers to an opening or recess of any shape that has been produced by drilling, milling, or other means.

[0025] To terminate the injection process, the current to the solenoid coil 2 is interrupted. The spring force of a return spring 11, housed in spring chamber 10, then returns the armature 3 and the armature pin 4 to their initial position. During this process, the armature pin 4 enters the coupler chamber 20, causing the pressure in the coupler chamber 20 to rise again, which in turn closes the nozzle needle 15.

[0026] The anchor 3 and the anchor pin 4 are firmly connected. For this purpose, the anchor pin 4 is inserted into the through-hole 13 of the anchor 3 and connected by means of a weld 24 in the form of a fillet weld placed on the underside of the anchor 3.

[0027] An alternative embodiment of a magnetic actuator according to the invention is described in the Fig. 2 shown. The illustration is limited to the version compared to the embodiment of the Fig. 1 modified part, i.e., the armature assembly. Otherwise, the magnetic actuator and / or the fuel injector may be of the same design.

[0028] In contrast to the embodiment of the Fig.In this case, the anchor pin 4 does not have a central bore 5, but rather a helical groove 7 that extends over an outer circumferential area 6. Here, too, the anchor pin 4 is inserted into a through bore 13 of the anchor 3, which interacts with the groove 7 of the anchor pin 4 to form a flow channel 14. The connection between the anchor pin 4 and the anchor 3 can again be made via a weld 24.

Claims

[1] Magnetic actuator for actuating fuel injectors, comprising a magnetic core (1), a magnetic coil (2) and an armature (3) cooperating with the magnetic coil (2), which is guided in a stroke-movable manner via an armature pin (4) fixedly connected to the armature (3), characterized by , that the anchor pin (4) has a central bore (5) and / or a groove (7) extending helically over an outer circumferential area (6) as a flow channel for a fluid, in particular fuel, wherein the bore (5) and / or the groove (7) extend over a predetermined guide area (8) of the anchor pin (4) and beyond the guide area (8) through the anchor (3). [2] Magnetic actuator according to claim 1, characterized by that the bore (5) and / or the groove (7) hydraulically connects an anchor chamber (9) with a spring chamber (10), which preferably serves to accommodate a return spring (11). [3] Magnetic actuator according to any one of the preceding claims, characterized by, that the bore (5) is designed as a blind bore and at least one further bore (12) branching off from the bore (5) is provided, which exits the anchor pin (4) in an outer circumferential area (6'). [4] Magnetic actuator according to any one of the preceding claims, characterized by , that the anchor pin (4) is inserted into a central through-hole (13) of the anchor (3) and is connected to the anchor (3) by force, form and / or material connection. [5] Magnetic actuator according to any one of claims 1 to 3, characterized by , that the anchor pin (4) is attached to the anchor (3) and is connected to the anchor (3) by force, form and / or material connection. [6] Magnetic actuator according to any one of the preceding claims, characterized by , that the anchor (3) is designed as a diving anchor. [7] Magnetic actuator according to any one of the preceding claims, characterized by, that the anchor (3) has at least one further flow channel (14) which is preferably designed as a bore through the anchor (3), as a longitudinal groove on the outer circumference and / or as a polished surface. [8] Fuel injector with a magnetic actuator according to one of the preceding claims, wherein the fuel injector can preferably be actuated directly via the magnetic actuator.

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