VALVE OF A FUEL INJECTOR

Description

[0001] The present invention relates to a valve for a fuel injector. Fuel injectors, also called injection nozzles, are an essential component of every internal combustion engine, as they introduce the required amount of combusting fuel into the combustion chamber. For clean combustion, it is crucial to maintain the rapid opening and closing of the injector throughout its entire service life in order to continuously deliver a precise amount of fuel.

[0002] Those skilled in the art know that a valve is provided to transition the injector from a closed to an open state. This valve separates a high-pressure fuel region from a low-pressure region. When the regions are connected by the valve moving to its open position, this leads to fuel injection by the injector via a hydraulic-mechanical chain of action.

[0003] According to the prior art, a solenoid valve is typically used for this purpose. In a closed state, a magnetizable part, the armature, which is guided in a guide, is subjected to a preload force by means of a spring element. This preload force presses the armature in the axial direction away from the magnet towards a seat plate which has an opening. By pressing the armature onto the seat plate, the armature closes the opening, thus closing a connection extending through the opening between the high-pressure region and the low-pressure region of the fuel. This is typically achieved by a sealing plate of the armature facing the seat plate closing the opening in the seat plate, so that the high-pressure region is separated from a low-pressure region. The high-pressure region corresponds to the system pressure with which the fuel is injected into the combustion chamber.The area with lower pressure corresponds to the tank pressure or the ambient pressure.

[0004] In the open state, the connection between the high-pressure and low-pressure areas is released via the opening in the seat plate by an axial movement of the armature toward the magnet, allowing fuel to flow from the high-pressure area to the low-pressure area. Through the hydraulic-mechanical chain of action briefly mentioned above, at least one fuel inlet from the injector into the combustion chamber is opened, allowing fuel to enter the combustion chamber.

[0005] When lifting the armature from the closed to the open position, it is common practice in the state of the art for the armature to strike a stop surface of the magnet and bounce off the stop surface, causing significant wear on the armature. This bouncing is also disadvantageous because it severely impairs the armature's switching times.

[0006] US2014 / 0367595 A1 shows a valve for controlling a fuel-gas mixture, which has several damping elements formed asymmetrically and spaced radially from the central axis of an armature.

[0007] EP 1 970 557 A2 discloses a valve for fuel injectors in which a valve element is fixedly connected to an armature, the valve being in an open state when the armature or valve element is in an intermediate position in which the armature is neither completely repelled nor completely attracted by an electromagnet.

[0008] WO 2017 / 158788 discloses a solenoid valve in which a metal armature is provided with a thick, rubber-elastic body to reduce the impact noise.

[0009] Accordingly, the aim of the present invention is to minimize armature bounce when the armature strikes the magnet, so that the associated disadvantages can be mitigated or overcome.

[0010] This is achieved by means of a valve of a fuel injector having all the features of claim 1. Advantageous embodiments of this valve can be found in the dependent claims.

[0011] According to the invention, the valve of a fuel injector for selectively separating a high-pressure region from a low-pressure region of a fuel comprises an opening in a seat plate, an armature configured to close the opening of the seat plate, a spring element biasing the armature toward a position closing the opening, and an electromagnet for lifting the armature from the position closing the opening into a position releasing the opening. The valve according to the invention is characterized in that it further comprises an elastically compressible damping element for limiting an armature stroke when the armature is lifted from the seat plate into the releasing position.

[0012] This elastically compressible damping element therefore dampens the movement of the armature when the magnet is activated and the armature is subsequently pulled away from the opening, so that the bouncing between the magnet and the armature is prevented or reduced.

[0013] It is advantageous if the damping element is a soft, elastic damping element. As will be shown later in the description of the figures, a soft, elastic design of the damping element is particularly well suited to suppressing the oscillating vibration of the armature, which occurs when the damping element impacts while the magnetic attraction force is continuously directed away from the opening.

[0014] According to an optional modification of the present invention, the stiffness of the damping element is smaller than the stiffness of the anchor.

[0015] Furthermore, according to the invention, it can be provided that the damping element is a damping pin with a substantially cylindrical shape, which preferably has a cross-sectional reduction between its two end faces. One of the two end faces is designed to serve as a stop surface for the armature. With the other of the two end faces, it can be provided that the pin is arranged in a recess in the magnet. The cross-sectional reduction can be a groove surrounding the outer circumference of the pin, which preferably runs completely around the outer circumference. For improved durability, it can be provided that the circumferential groove has an arc shape when viewed in cross-section, which is rounded at the groove transitions.

[0016] According to the invention, the damping element has a spherical section on its contact surface with the armature in order to minimize a contact surface with the armature.

[0017] On the one hand, this creates a small contact area with the armature, which is desirable in order to keep the remanence force of the magnet as low as possible.

[0018] The advantage of this is that the magnetic flux across the contact surface is as low as possible. Furthermore, the spherical contact surface ensures that the contact area between the damping element and the armature is always the same, even if the damping element is misaligned due to tolerances.

[0019] Furthermore, it can be provided that the poles of the electromagnet and the end face of the damping element contacting the armature lie in a common plane when the damping element is in a relaxed state. In other words, the end sections of the poles facing the armature and the end face of the damping element contacting the armature are arranged in a common plane when the armature is in its relaxed state and is not attracted by the magnet.

[0020] According to a further development of the invention, the damping element is designed separately from a housing of a fuel injector. Thus, it can be provided that the damping element is mounted and held in position by a press fit. The press fit can be implemented, for example, by providing a recess in the magnet into which the damping element is received.

[0021] Furthermore, the invention can provide for the preload force of the spring element to be adjustable, preferably via adjusting discs for changing the position of the spring element relative to the damping element and / or the armature. This allows the spring preload force to be precisely adjusted, even in the event of an undesired deviation of the spring force from the expected spring force value.

[0022] According to a further development of the invention, the end face of the damping element facing away from the armature is designed as a flat seat. The flat seat can be arranged in the magnet.

[0023] According to an optional modification of the present invention, the armature has a raised surface on its surface facing the damping element, with which the armature strikes the damping element. Therefore, in the attracted state, i.e., when the magnet is active and the armature is in the release position, a gap can be provided between the pole cores of the magnet and a non-raised end face of the armature. This prevents contact between the armature and the magnet.

[0024] Furthermore, the anchor can be designed in several parts, so that it comprises an anchor part and a seat part or consists of these parts.

[0025] According to a further preferred embodiment of the invention, the spring element is a spiral spring, which preferably extends spirally around the damping element or winds spirally around the damping element. The damping element is thus partially or completely accommodated in the space defined by the spiral shape of the spring element.

[0026] Furthermore, the invention provides that the armature only comes into contact with the damping element during the transition from the position closing the opening to the position releasing it. Naturally, while still sealed, the armature contacts the seat plate with a sealing surface and also the spring element, which exerts a spring force toward the opening. However, there is no direct contact between the magnet or a stop surface formed by the magnet.

[0027] Furthermore, it can be provided that the structure of the valve is rotationally symmetrical or rotationally symmetrical to a rotation axis, which is preferably identical to a rotation axis of the damping element.

[0028] The invention also relates to a fuel injector with a valve according to one of the variants listed above, in particular a diesel fuel injector.

[0029] With the help of the invention described above, it is possible to reduce armature bounce when the armature strikes the magnet, thereby achieving more stable injection quantity control. Furthermore, the reduced armature bounce allows for a smaller armature stroke, so that the armature has less momentum when it hits the damping element, which can further mitigate the problem of armature bounce. These positive effects ultimately lead to a smaller dispersion of the injection quantity between the various injectors, as well as between different injection processes of an injector. Finally, the present invention makes it possible to accelerate the switch-off times of the solenoid valve due to the lower remanence force between the armature and the contact on the damping element.This is because, due to a reduced contact area between the damping element and the armature, a smaller magnetic flux passes through the damping element than would be the case with a larger contact area, as is typically found in the prior art.

[0030] Further features, details, and advantages of the invention will become apparent from the following description of the figures. These show: Fig. 1: a half sectional view through the valve according to the invention, Fig. 2: a force diagram during the transition of the armature between its two positions, and Fig. 3: a representation of the armature stroke as a function of different elasticities of the damping element.

[0031] Figur 1 shows a half sectional view of the valve 1 according to the invention. The seat plate 3, which separates the high-pressure area (on the underside) from a low-pressure area (on the top), has an opening 2 that can connect a high-pressure area and a low-pressure area of ​​fuel. This opening 2 is closed by an armature 4, which seals the opening 2 with its sealing surface 15 in its closed state. The armature 4 can be lifted from this position when the magnet 6 is activated and thus pulls the armature 4 away from the opening 2. When the magnet 6 is deactivated, a spiral spring 5 ensures that the armature 4 is pressed with its sealing surface 15 against the opening 2. The magnet 6 has a coil 61 and a coil casing 62, so that a magnetic force can be generated by a current flowing through the coil 61.In the space defined by the coil spring 5, a damping element 7 is arranged, which in the illustration shown corresponds to a damping pin. This damping pin 7 has a first end face 8 facing the armature 4. In this case, the end face 8 is rounded or corresponds to a section of a sphere, so that when the armature 4 impacts the damping element 7, only the smallest possible contact area is created between the armature 4 and the damping element 7. It can also be seen that the damping element 7 has a recess 14 in its circumference, which ensures lower rigidity and thus a certain elasticity of the damping element 7. This recess 14 can be rounded, as can be seen from the reference numeral 12. The damping element 7 can be held in the magnet 6 by a press fit.Furthermore, an adjusting disc 11 can be provided to adjust the preload force of the spring element 5, with which the spring can be moved in its position in the axial direction.

[0032] The armature 4 can have a raised portion 13 with which the armature 4 strikes the contact surface 8 of the damping element 7.

[0033] An armature guide 16 is provided to guide the armature during a transition from its sealing position to the position that releases the opening 2. A spacer ring 17 shields the armature 4 from the housing 10 of a fuel injector. Reference numeral 9 designates the magnetic poles of the magnet 6.

[0034] The axis of symmetry 13 shows that the valve 1 is constructed with mirror symmetry and / or rotational symmetry.

[0035] In a closed state, a magnetizable part guided in the armature guide 16, here the armature 4, is subjected to a force defined by the adjusting disc 11, the preload force, by means of the spring element 5, which closes the armature 4 in the axial direction away from the magnet 6 toward a sealing part of the seat plate 3. As mentioned, the seat plate 3 separates a high-pressure area from a low-pressure area of ​​the fuel.

[0036] In an open state, the connection between the high pressure area and the low pressure area is released via the opening 2 in the seat plate 3 by an axial movement of the armature 4 in the direction of the magnet 6, so that fuel is discharged from the Fig. 1 high pressure area located below into the low pressure area, which is in the Fig. 1 arranged above the seat plate 3. Via a hydraulic-mechanical chain of action, at least one fuel inlet is released from the injector into the combustion chamber and fuel is supplied to the combustion chamber.

[0037] To open the solenoid valve 1, i.e., the transition from a closed to an open state, a voltage source generates a current that flows through the windings of coil 61. The windings of coil 61 are surrounded by a coil sheath 62, which in turn is surrounded radially inward and outward by a ferromagnetic core 6, which serves to amplify the magnetic field induced by the current in coil 61.

[0038] Due to the magnetic field, a force acts between the magnetic pole 9 of the magnet 6 and the armature 4. With a sufficiently strong current signal and a sufficiently long control duration, the attractive magnetic force between the magnetic pole 9 and the armature 4 exceeds the opposing preload force of the spring 5. As a result, the armature is then attracted towards the magnet 6 in the axial direction, so that the opening 2 in the seat plate 3 is released.

[0039] The armature 4 is continuously accelerated by the attractive magnetic force, which increases with decreasing distance, until the armature 4 comes into contact with the damping element 7. The armature 4 then strikes a contact surface 8 of the damping element 7, which is formed by a pin projecting from it.

[0040] The damping pin 7 acts like a very hard spring, but has comparatively low stiffness compared to the armature 4. The stiffness of the damping pin or damping element can be less than 70%, preferably less than 50%, and most preferably less than 30% of the stiffness of the armature 4. The damping pin 7 completely decelerates the armature 4, whereby the damping pin 7 is elastically compressed. Apart from the contact between the armature 4 and pin 7, there is no further mechanical contact between the armature 4 and the magnet 6.

[0041] After a maximum compression of the pin 7, the restoring force of the spring 5 and the pin 7 causes the pin 7 to expand in the direction of the opening 2 of the seat plate 3. In an oscillating process, the pin 7 is deformed to a degree at which the sum of the forces acting on the armature 4 (the attractive magnetic force and the repulsive restoring force by spring 5 and pin deformation) cancel each other out in the force equilibrium.

[0042] When the voltage source is switched off, the electric current and the magnetic field are reduced again. The magnetic force attracting the armature 4 rapidly decreases and can no longer overcome the restoring force of the spring. The armature is then pushed back into the closed position by the spring 5, so that the opening 2 in the seat plate 3 is closed by the armature 4 and the high-pressure chamber (below the seat plate 3) is again separated from the low-pressure chamber (above the seat plate 3). This means that, via the hydraulic-mechanical chain of action, one or more fuel inlets from the injector into the combustion chamber are closed again, and no more fuel is fed into the combustion chamber.

[0043] How Fig. 2 shows, the realization of the stop of the armature 4 on the damping element 7, which is designed to be relatively soft and elastic, leads to a very advantageous behavior of the armature 4. If the armature 4 hits the damping element 7, it only oscillates with a very low oscillation amplitude for a manageable period of time.

[0044] Fig. 3 shows this vibration behavior of the armature based on the armature stroke h in comparison with different elasticities of the damping element 7. A solid line shows a hard elasticity, whereas the dashed line shows a soft elasticity of the damping element 7. It can be seen that the vibration amplitude of the soft elastic version Δh we is smaller than that of the hard elastic version Δh he . This is because the deformation of the damping element 7 upon impact of the armature leads to the distance between magnet 6 and armature 4 initially being further reduced to a distance that is smaller than the distance that would occur in a static equilibrium of forces.This results in the magnetic force F Mag attracting the armature 4 between the armature 4 and the magnet 6 increasing disproportionately compared to a linearly increasing restoring force F Rück , caused by the spring and damping element 7. The disproportionate increase in force significantly dampens the spring-back effect of the damping element 7, so that the bouncing of the armature when the magnet strikes is reduced.

[0045] This is shown graphically in Fig. 2, where the solid line represents the magnitude of the magnetic force F Mag and the dashed line represents the magnitude of the restoring force F Rück. If, for example, in a design with a hard-elastic damping element, the armature 4 is only attracted up to the distance x A1 due to the magnetic force, the resulting magnetic force F A1 is significantly lower than the magnetic force F A2 that is achieved when the armature 4 is attracted up to the position x A2, which results in a soft-elastic damping element design.

[0046] However, since the design with a soft-elastic damping element exerts a stronger overall force on armature 4 than would be the case with the hard-elastic design, the oscillating behavior of armature 4, which continues until a static force equilibrium is reached, is significantly reduced. This allows for more stable control of the injection quantity, resulting in an overall improvement in the fuel injector.

Claims

1. Valve (1) of a fuel injector for a selective separation of a high pressure region from a low pressure region of a fuel comprising: an opening (2) in a seat plate (3); an armature (4) that is configured to close the opening (2) of the seat plate (3); a spring element (5) that preloads the armature (4) in the direction of a position closing the opening (2); and an electromagnet (6) for raising the armature (4) from the position closing the opening (2) into a position releasing the opening (2), an elastically compressible damping element (7) to bound an armature stroke on the raising of the armature (4) from the seat plate (3) into the releasing position, characterized in that the damping element (7) has a spherical section (8) at its contact surface to the armature (4) to minimize a contact surface with the armature (4), and the armature (4), except for the contact to the damping element (7), does not have any further mechanical contact with the electromagnet (6) or an abutment surface formed by the electromagnet on the transition from the position closing the opening (2) into the position releasing the opening (2), in which the armature (4) is completely braked by the damping element (7).

2. Valve (1) in accordance with claim 1, wherein the damping element (7) is a soft-elastic damping element (7).

3. Valve (1) in accordance with one of the preceding claims, wherein the stiffness of the damping element (7) is smaller than the stiffness of the armature (4).

4. Valve (1) in accordance with one of the preceding claims, wherein the damping element (7) is a damping pin having a substantially cylindrical shape that preferably has a cross-sectional reduction (12) between its two end surfaces.

5. Valve (1) in accordance with one of the preceding claims, wherein the poles (9) of the electromagnet (6) and an end side of the damping element (7) contacting the armature (4) are disposed in a common plane in a relaxed state of the damping element (7).

6. Valve (1) in accordance with one of the preceding claims, wherein the damping element (7) is separate from a housing (10) of a fuel injector.

7. Valve (1) in accordance with one of the preceding claims, wherein the preload force of the spring element (5) can be set, preferably via setting plates (11) to change the position of the spring element (5) with respect to the damping element (7) and / or the armature (4).

8. Valve (1) in accordance with one of the preceding claims, wherein the end side of the damping element (7) remote from the armature (4) is designed as a flat seat.

9. Valve (1) in accordance with one of the preceding claims, wherein the armature (4) has an elevated portion (13) in its surface facing the damping element (7) at which the armature (4) impacts the damping element (7).

10. Valve (1) in accordance with one of the preceding claims, wherein the armature (4) is designed in multiple parts and comprises an armature part and a seat part or consists of these parts.

11. Valve (1) in accordance with one of the preceding claims, wherein the spring element (5) is a spiral spring that extends in a spiral manner around the damping element (7).

12. Valve (1) in accordance with one of the preceding claims, wherein the design of the valve (1) is rotationally symmetrical to an axis of rotation (13) that is identical to an axis of rotation of the damping element (7).

13. Fuel injector having a valve (1) in accordance with one of the preceding claims, in particular a diesel fuel injector.