Anti-reflection device for fuel injection valve and fuel injection valve

The present invention relates to an anti-reflection device for preventing the reflection of pressure waves inside a fuel injection valve. It further relates to a fuel injection valve with an anti-reflection device.

An injection valve for injecting fuel directly or indirectly into the combustion chamber of a vehicle is disclosed in document EP 2 333 297 Bl . One typical problem of such injection valves, in particular high-pressure valves, is the generation of pressure waves or pressure pulsations caused by an injection event.

Internal pressure pulsations cause problems in particular for multiple injection applications, because when pressure con ^¬ ditions inside the injector are not stable or not known at the time of opening of the valve, the amount of injected fuel cannot be controlled.

Reopening of the valve out of control causes tip wetting and combustion problems, which increase the emission of particles. Furthermore, growing of particles sticking on the tip of the injector affect the performance of the injector.

It is an object of the present invention, to block pressure waves, in particular pressure waves coming from the rail, from propagating inside the injector.

This object is achieved by means of an anti-reflection device and an injection valve having the features of the independent claims. Advantageous embodiments and developments are specified in the dependent claims, the following description and the drawings.

According to an aspect of the invention, an anti-reflection device for preventing the reflection of pressure waves inside a fuel injection valve is provided. The expression "for preventing the reflection of pressure waves" shall also encompass em ^¬ bodiments in which reflections of pressure waves are not completely suppressed, but in particular only largely reduced.

The anti-reflection device comprises an essentially cylindrical base body with a first base side, a second base side and an outer surface. The outer surface in particular extends from the first base side to the second base side - in particular along the cylinder axis of the base body - and may expediently connect the first and second base sides to one another. The anti-reflection device further comprises a longitudinal axis L intended to be orientated parallel to a propagation direction of a pressure wave, the longitudinal axis penetrating the first base side and the second base side. In an expedient embodiment, the longi ^¬ tudinal axis is parallel - preferably coaxial - to the cylinder axis of the base body. The anti-reflection device further comprises a flow path for fuel which is formed between the first base side and the second base side, the flow path forming a curve around the longitudinal axis L. The cylindrical base body may have the flow path formed on its outer surface in one embodiment.

By an essentially cylindrical base body it is in particular understood that it is possible to fit the cylindrical base body into a cylindrical hollow body. In other words, the base body has a cylindrical basic shape . The base body may comprise a structured periphery, e.g. structured to shape the flow path. Preferably, the envelope of the structured periphery also has a cylindrical shape . This antireflection device has the advantage, that fuel coming from the first base side and flowing through the anti-reflection device towards the second base side is forced to take a curved path around the longitudinal axis L. This helps to dissipate energy and to dampen pressure pulsations.

If a pressure waves enters through the anti-reflection device and is reflected inside the injector, the pressure wave would encounter fuel entering through the anti-reflection device on the curved flow path and having rotational energy. If the reflected pressure wave would return through the anti-reflection device, it would have to overcome this rotational energy first and turn the direction of the current to re-enter the anti-reflection device. Thus, a large amount of energy would be dissipated. As a consequence, no stationary waves are formed inside the injector and pressure waves are dampened.

According to an embodiment, the flow path has the form of a helical curve around the longitudinal axis L. To put it differently, the flow path has a center line which is a helical curve around the longitudinal axis L, i.e. in particular around the cylinder axis of the base body.

This embodiment has the advantage, that a helical curve may be formed easily on the anti-reflection device and that a helical curve would help to create a rotational flow of fuel.

According to an embodiment, the base body has a cylindrical inner section and an outer section comprising a helically curving wall formed on a circumferential surface of the inner section and being arranged coaxially with the cylindrical inner section, the flow path being formed by the circumferential surface of the inner section and two adjacent turnings of the wall. This embodiment has the advantage, that the flow path can be created easily by forming a thread on the circumferential surface of the inner section. Such a thread is easy to manufacture. According to an embodiment of the invention, the flow path has a cross-sectional area of 1 to 4 mm ² . With a cross-section of 1 to 4 mm ² it is possible to achieve a negligible overall pressure drop across the anti-reflection device. The cross-section of the flow path can be adjusted to the discharge rate of the valve itself. For many types of valves, a cross-section of 3 to 4 mm ² is suitable.

The base body may be formed of plastic material. Alternatively, it may be formed of a metal, for example stainless steel. The base body may be formed by injection molding.

According to one embodiment, a hollow cone is formed in the base body coaxially with the base body and being orientated with its base plane forming a part of the first base side.

This has the advantage that pressure waves can be reflected into the cone shape with a coefficient lower than 1 which improves the dampening of pressure waves. The hollow cone may have an angle of opening between 30° and 100°.

According to an aspect of the invention, a fuel injection valve is provided, comprising a valve body with a central longitudinal axis comprising a cavity with a fluid inlet portion and a fluid outlet portion. The fuel injection valve further comprises a valve needle axially movable in the cavity, the valve needle preventing fluid flow through the fluid outlet portion in a closing position and releasing the fluid flow through the fluid outlet portion in further positions. The injection valve further comprises an electromagnetic ac ^¬ tuator unit being designed to actuate the valve needle.

Furthermore, the injection valve comprises at least one an- tireflection device as described above being arranged inside the cavity, the first base side being directed towards the fluid inlet portion .

The fuel injection valve has the advantage, that pressure waves entering from the rail are dampened and prevented from being transmitted into the injector. Furthermore, the injector wet path can be considered decoupled from the rail, which improves the stability of pressure conditions inside the injector, thus avoiding reopening events of the valve. Additionally, the anti-reflection device can be useful to decouple the injector from noise generated by a fuel pump and the rail and other inj ectors .

The anti-reflection device may in particular be arranged upstream of an armature of the electromagnetic actuator unit.

The anti-reflection device may be arranged close to the fluid inlet portion of the injector, thereby dampening pressure waves entering from the rail as early as possible.

According to an embodiment, the anti-reflection device is press-fitted into an inlet tube of the valve body. This has the advantage, that the anti-reflection device can be mounted easily. Further advantages, advantageous embodiments and developments of the anti-reflection device and the fluid injection valve will become apparent from the exemplary embodiments which are de ^¬ scribed below in association with the schematic figures. Figure 1 shows a cross-section of an injection valve according to an embodiment of the invention,

Figure 2 shows several views of an anti-reflection device according to a first embodiment of the invention and

Figure 3 shows several views of an anti-reflection device according to a second embodiment of the invention. Figure 1 shows an injection valve 1 for the injection of fuel into an internal combustion engine. The injection valve 1 comprises a valve assembly 3 with a valve body 4 with a central longitudinal axis L. The valve body 4 comprises a cavity 9 with a fluid inlet portion 5 and a fluid outlet portion 7.

A valve needle 11 is arranged axially movable in the cavity 9. The valve needle 11 prevents a fluid flow through the fluid outlet portion 7 in a closing position. To achieve this, the needle 11 has a ball 13 welded to its lower end which interacts with a valve seat (not shown in detail) of the valve body 4.

The injection valve 1 further comprises an electromagnetic actuator unit 20 to actuate the valve needle 11. The actuator unit 20 comprises an armature 21 which may be fixed to the needle 11 or coupled to the needle 11 in some other way to cause the needle 11 to move axially in the cavity 9 in response to a magnetic field. The actuator unit 20 further comprises a coil 23 which may be energized to induce a magnetic field. The magnetic field acts on the armature 21 to cause it to travel upwards and take the needle 11 with it against the force of the calibration spring 25. Thus, the ball 13 leaves the valve seat and fuel is released through the fluid outlet portion 7. When the magnetic field ceases, the valve needle 11 is moved downwards by the force of the calibration spring 25 and the fluid outlet portion 7 is closed again. The cavity 9 has an upper part which is enclosed by the inlet tube 27. The inlet tube 27 is the part of the valve body 4 which is closest to the fuel inlet portion 5. In this part of the cavity 9, pressure pulsations coming from the rail and entering through the fluid inlet portion 5 propagate. To dissipate the energy of pressure pulsations and prevent pressure waves from being transmitted inside the injector 1, an antireflection device 29 is arranged in the cavity 9 and press-fitted into the inlet tube 27. Details of the anti-reflection device 29 are shown in figures 2 and 3.

Figure 2a) shows a side view of the anti-reflection device 29, figure 2b) shows the anti-reflection device 29 from above, figure 2c) shows a cross-section of the anti-reflection device 29 and figure 2d) shows a view of the anti-reflection device 29 from below .

The anti-reflection device 29 according to figure 2 is a first embodiment of the invention and has a cylindrical base body 31 which is arranged coaxially with the valve body 4. The base body 31 has an inner section 38 and an outer section 39. The inner section 38 has the form of a cylinder with a circumferential surface 37. The circumferential surface 37 is in particular an outer surface of the inner section 38 in this and other embodiments. The anti-reflection device 29 further comprises a first base side 33 and a second base side 35 and an outer surface 36 of the base body 31. On the outer surface 36 there is arranged a wall 45 forming a thread 43 on the circumferential surface 37. Thus, the wall 45 extends around the circumferential surface 37 in a helical curve and is arranged coaxially with the cylindrical inner section 38. Between single turns of the wall 45, a flow path 47 is formed for fuel entering the injector 1 through the fluid inlet portion 5. The flow path 47, which in this embodiment has a square cross-section, has a cross-sectional area of 3 to 4 mm ² . All fuel entering through the fluid inlet portion 5 and being intended to exit the injector 1 through fluid outlet portion 7 must pass through the flow path 47.

The anti-reflection device 29 furthermore has a hollow cone 41 arranged in the base body 31 coaxially with the base body 31. The hollow cone 41, which may have an opening angle of 30° to 100°, improves the dampening of pressure waves entering the injector 1 through the fluid inlet portion 5. To achieve this, the anti-reflection device 29 is arranged with the first base side 33 being oriented towards the fluid inlet portion 5 and the second base side 35 being oriented towards the fluid outlet portion 7. When fuel enters the anti-reflection device 29, the flow is forced on the helically curving flow path 47. Thus, a rotating flow is generated. The rotating flow decouples the cavity 9 above the anti-reflection device 29 from the cavity 9 below the anti-reflection device 29. Furthermore, the rotation of flow would have to be stopped by a pressure wave which has been reflected in the injector 1 and propagates towards the fluid inlet portion 5. Stopping of the rotation of the flow, however, would dissipate energy. Thus, the propagation and the reflection of pressure waves inside the injector 1 are minimised. Figure 3 shows several views of an anti-reflection device 29 according to a second embodiment of the invention. This em ^¬ bodiment differs from the first embodiment shown in figure 2 only in the form of the thread 43 formed on the circumferential surface 37. According to the second embodiment, the walls 45 are thicker compared to the cross section of the flow path 47, thereby reducing the length of the flow path 47.