Patent Publication Number: US-7909270-B2

Title: Valve assembly for an injection valve and injection valve

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to EP Application No. 07023476 filed Dec. 4, 2007, the contents of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The invention relates to a valve assembly for an injection valve and an injection valve. 
     BACKGROUND 
     Injection valves are in widespread use, in particular for an internal combustion engine where they may be arranged in order to dose the fluid into an intake manifold of the internal combustion engine or directly into the combustion chamber of a cylinder of the internal combustion engine. 
     Injection valves are manufactured in various forms in order to satisfy the various needs for the various combustion engines. Therefore, for example, their length, their diameter, and all the various elements of the injection valve being responsible for the way the fluid is dosed may vary in a wide range. In addition to that, injection valves can accommodate an actuator for actuating a needle of the injection valve, which may, for example, be an electromagnetic actuator or a piezoelectric actuator. 
     In order to enhance the combustion process in view of degradation of unwanted emissions, the respective injection valve may be suited to dose fluids under high pressures. The pressures may be in case of a gasoline engine, for example, in the range of up to 200 bar. 
     SUMMARY 
     According to various embodiments, a valve assembly can be created for an injection valve and an injection valve can be created which is simple to be manufactured and which facilitates a reliable and precise function. 
     According to an embodiment, a valve assembly of an injection valve, may comprise a valve body including a central longitudinal axis, the valve body comprising a cavity forming an inner surface of the valve body, the cavity having a fluid inlet portion, and a fluid outlet portion, a valve needle axially movable in the cavity, the valve needle preventing a fluid flow through the fluid outlet portion in a closing position and releasing the fluid flow through the fluid outlet portion in further positions, wherein at least one of the valve needle and the inner surface of the valve body having a surface layer comprising a tungsten carbide layer and a carbon layer. 
     According to a further embodiment, the valve body may comprise a needle seat, the valve needle may comprise a seat part with a sealing portion, the sealing portion resting on the needle seat in the closing position, with the sealing portion of at least one of the valve needle and the needle seat comprising the surface layer. According to a further embodiment, at least one of the surface layer of the sealing portion and the surface layer of the needle seat may have a thickness of up to 3 μm. According to a further embodiment, the valve needle may comprise a front surface area facing away from the fluid outlet portion and being enabled to be in contact with a corresponding inner surface of the valve body, with at least one of the front surface area and the corresponding inner surface comprising the surface layer. According to a further embodiment, at least one of the surface layer of the front surface area and the surface layer of the corresponding inner surface may have a thickness of 0.5 μm up to 1.5 μm. According to a further embodiment, the valve body may comprise a guide element guiding the valve needle in axial direction, the valve needle comprising a slide area being in a sliding contact with the guide element, with at least one of the slide area of the valve needle and the guide element comprising the surface layer. According to a further embodiment, at least one of the surface layer of the slide area and the surface layer of the guide element may have a thickness of 0.5 μm to 2 μm. According to a further embodiment, the surface layer may comprise a plurality of tungsten carbide layers and carbon layers. According to a further embodiment, the surface layer may comprise a chromium layer. 
     According to another embodiment, an injection valve with a housing and an actuator unit may have such a valve assembly of an injection valve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are explained in the following with the aid of schematic drawings. These are as follows: 
         FIG. 1 , an injection valve in a longitudinal section view, 
         FIG. 2 , an enlarged and detailed view of a first embodiment of a valve assembly of the injection valve in a longitudinal section view, 
         FIG. 3 , an enlarged and detailed view of a second embodiment of the valve assembly of the injection valve in a longitudinal section view, and 
         FIG. 4 , a surface layer of the valve assembly of the injection valve in a sectional view. 
     
    
    
     Elements of the same design and function that appear in different illustrations are identified by the same reference characters. 
     DETAILED DESCRIPTION 
     According to various embodiments, a valve assembly of an injection valve may comprise a valve body including a central longitudinal axis, the valve body comprising a cavity forming an inner surface of the valve body, the cavity having a fluid inlet portion, and a fluid outlet portion, a valve needle axially movable in the cavity, the valve needle preventing a 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 valve needle and/or the inner surface of the valve body having a surface layer comprising a tungsten carbide layer and a carbon layer. 
     The surface layer can be arranged on parts of the valve needle and/or the inner surface of the valve body or on the whole valve needle and/or the whole inner surface of the valve body. 
     This has the advantage that good wearing characteristics of the valve needle and/or the valve body are possible in areas where the valve needle impacts on the valve body. The seat part of the valve needle may be better adapted to prevent a fluid flow through the fluid outlet portion in a closing position of the valve needle as deformations and surface roughness of the sealing portion of the seat body can be prevented. This can result in a good dynamic performance of the injection valve by the reduction of transient effects. Furthermore, a low sliding coefficient in sliding areas between the valve needle and the valve body is possible. Additionally, no further layers, in particular no further metal layers, are necessary. Consequently, a high life-time of the valve assembly is possible. 
     In an embodiment, the valve body comprises a needle seat, the valve needle comprises a seat part with a sealing portion, the sealing portion rests on the needle seat in the closing position, and the sealing portion of the valve needle and/or the needle seat comprises the surface layer. This has the advantage that good wearing characteristics of the valve needle and/or the valve body in impact sections of the valve needle on the valve body can be obtained. 
     In a further embodiment, the surface layer of the sealing portion and/or the surface layer of the needle seat have a thickness of up to 3 μm. This has the advantage that the thickness of the surface layer is sufficient to obtain good conditions against wearing in the seat area. 
     In a further embodiment, the valve needle comprises a front surface area which is facing away from the fluid outlet portion and which is enabled to be in contact with a corresponding inner surface of the valve body, with the front surface area and/or the corresponding inner surface comprising the surface layer. This has the advantage that good wearing characteristics of the valve needle and/or the valve body in impact sections of the valve needle on the valve body are possible. 
     In a further embodiment, the surface layer of the front surface area and/or the surface layer of the corresponding inner surface have a thickness of 0.5 μm up to 1.5 μm. This has the advantage that the thickness of the surface layer is sufficient to obtain good conditions against wearing. 
     In a further embodiment, the valve body comprises a guide element guiding the valve needle in axial direction, the valve needle comprises a slide area being in a sliding contact with the guide element, and the slide area of the valve needle and/or the guide element comprises the surface layer. This makes it possible to obtain a low sliding coefficient between the valve needle and the valve body. 
     In a further embodiment, the surface layer of the slide area and/or the surface layer of the guide element have a thickness of 0.5 μm to 2 μm. By this, it is possible to obtain a low sliding coefficient between the valve needle and the valve body with only small changes of the geometrical conditions of the valve needle and/or the guide element. 
     In a further embodiment, the surface layer comprises a plurality of tungsten carbide layers and carbon layers. A plurality of thin layers of tungsten carbide and carbon makes it possible to obtain very good wearing and sliding conditions in different areas of the valve needle and/or the valve body. 
     In a further embodiment, the surface layer comprises a chromium layer. The chromium layer can form an adhesive layer of the surface layer for mechanically coupling the surface layer to the valve needle. 
     An injection valve  82  ( FIG. 1 ) that is in particular suitable for dosing fuel to an internal combustion engine comprises a valve assembly  80  and a housing  6 . 
     The valve assembly  80  comprises a valve body  4  with a central longitudinal axis L and a cavity  8  which takes in a valve needle  10 . The valve body  4  comprises an inlet tube  2 . 
     The valve needle  10  comprises an armature  12 . The cavity  8  of the valve body  4  forms an inner surface  18 . 
     In the inlet tube  2  and in the armature  12 , a recess  16  is provided. A spring  14  is arranged in the recess  16  of the inlet tube  2  and the armature  12 . Preferably, it rests on a spring seat being formed by an anti-bounce disk  20 . By this, the spring  14  is mechanically coupled to the needle  10 . An adjusting tube  22  is provided in the recess  16  of the inlet tube  2 . The adjusting tube  22  forms a further seat for the spring  14  and may be axially moved during the manufacturing process of the fluid injection valve in order to preload the spring  14  in a desired way. 
     In a closing position of the valve needle  10 , it sealingly rests on a needle seat  46  of a seat body  26 , by this preventing a fluid flow through at least one injection nozzle  24 . The injection nozzle  24  may be, for example, an injection hole. However, it may also be of some other type suitable for dosing fluid. The seat body  26  may be made in one part with the valve body  4  or be a separate part. 
     Furthermore, a lower guide element  28  is provided for guiding the needle  10  and a swirl disk  30  for giving the fluid a radial velocity component. 
     In addition to that, the valve body  4  comprises an upper guide element  29  for guiding the valve needle  10 , in particular the armature  12  of the valve needle  10 . 
     The injection valve  82  is provided with an actuator unit  40  that comprises preferably an electromagnetic actuator with a coil  36  which is preferably over-molded. A valve body shell  38 , the armature  12  and the inlet tube  2  are forming an electromagnetic circuit. The actuator unit  40  may, however, also comprise another type of actuator, which is known to persons skilled in the art for that purpose. Such an actuator may be, for example, a piezoelectric actuator. 
     The valve assembly  80  has a fluid inlet portion  42  which is provided in the valve body  4 . The fluid inlet portion  42  communicates with a fluid outlet portion  44  which is part of the cavity  8  near the seat body  26 . 
     The valve needle  10  has a seat part  50  being adjacent to the seat body  26 . 
     In the embodiment shown in  FIG. 2 , the seat part  50  has a sealing portion  52 . In the closing position of the valve assembly  80  the sealing portion  52  rests on the needle seat  46 . The sealing portion  52  of the valve needle  10  has a surface layer  48 . The surface layer  48  of the sealing portion  52  has a thickness of 0.8 μm to 3.0 μm. 
     As can be seen in  FIG. 4 , the surface layer  48  is built up as a stack of layers comprising tungsten carbide layers  70  and carbon layers  72 . Preferably, the tungsten carbide layers and the carbon layers  72  are alternating as shown in  FIG. 4 . Preferably, each of the tungsten carbide layers  70  and the carbon layers  72  has a thickness of a few atoms. Additionally, the surface layer  48  has a chromium layer  74  which forms an adhesive layer of the surface layer  48  to mechanically coupling the surface layer  48  to the valve needle  10 . In a preferred embodiment, the chromium layer  74  and the adjacent tungsten carbide layer  70  are forming a common intermediate layer which enables a good adhesion between the valve needle  10  and the further layers  70 ,  72  of the surface layer  48 . 
     Furthermore, the armature  12  of the valve needle  10  has a front surface area  58  which faces away from the fluid outlet portion  44 . The front surface area  58  is facing the corresponding inner surface  18  of the inlet tube  2 . The front surface area  58  has a surface layer  48  with the tungsten carbide layers  70  and the carbon layers  72 . The surface layer  48  of the front surface area  58  has a thickness of 0.5 μm up to 1.5 μm. 
     Furthermore, the valve needle  10  has a slide area  54  near the seat part  50  and the armature  12  of the valve needle  10  has a slide area  56 . The slide area  54  near the seat part  50  is in a sliding contact with the lower guide element  28 , the slide area  56  of the armature  12  is in a sliding contact with the upper guide element  29 . The slide areas  54 ,  56  of the valve needle  10  have a surface layer  48  each, with the tungsten layers  70  and the carbon layers  72 . The surface layer  48  of the slide area  54  being in sliding contact with the lower guide element  28  has a thickness of 0.8 μm to 2.0 μm. The surface layer  48  of the slide area  56  of the armature  12  has a thickness of 0.5 μm to 2.0 μm. 
     In the embodiment of the valve assembly  80  shown in  FIG. 3 , the lower guide element  28  has a slide area  60  with the surface layer  48 . The upper guide element  29  has a slide area  62  with the surface layer  48 . A further of the surface layers  48  is arranged on the needle seat  46  of the seat body  26 . The surface layer  48  of the needle seat  46  has a thickness of 0.8 um to 3.0 μm. The surface layer  48  of the inner surface  18  facing the front surface area  58  has a thickness of 0.4 μm to 1.5 μm. The surface layer on the lower guide element  28  has a thickness of 0.8 μm to 2.0 μm. The surface layer  48  on the upper guide element  29  has a thickness of 0.5 μm to 2.0 μm. 
     In the following, the function of the injection valve is described in detail: 
     The fluid is led from the inlet tube  2  to the hollow valve needle  10  and then through an orifice  76  in the valve needle  10  to the fluid inlet portion  42  and the fluid outlet portion  44 . 
     The spring  14  forces the valve needle  10  via the anti-bounce disk  20  towards the actuator unit  40 . In the case when the actuator unit  40  is de-energized the spring  14  can force the valve needle  10  to move in axial direction in its closing position. It is depending on the force balance between the force on the valve needle  10  caused by the actuator unit  40  and the force on the valve needle  10  caused by the spring  14  whether the valve needle  10  is in its closing position or not. 
     In the closing position of the valve needle  10  the seat part  50  of the valve needle  10  sealingly rests on the needle seat  46  of the seat body  26  and consequently a fluid flow through the fluid outlet portion  44  and the injection nozzle  24  is prevented. 
     In the case that the actuator unit  40  gets energized, the actuator unit  40  may exert a force on the valve needle  10 . The valve needle  10  is able to move in axial direction out of the closing position. Outside of the closing position of the valve needle  10 , there is a gap between the seat body  26  and the valve needle  10  which enables a fluid flow through the injection nozzle  24 . 
     The movement of the valve needle  10  results in an impact of the valve needle  10  on the valve body  4 . In particular, the seat part  50  of the valve needle  10  forms an impact section relative to the needle seat  46  of the seat body  26 . By coating the sealing portion  52  of the valve needle  10  and/or the needle seat  46  of the seat body  26 , good wearing characteristics of the seat part  50  of the valve needle  10  and/or the seat body  26  can be obtained. Furthermore, the friction coefficient between the valve needle  10  and the seat body  26  is very low. By this, leakage failures of the valve assembly  80  can be kept low and a high lifetime of the valve assembly  80  is possible. 
     Covering the front surface area  58  of the valve needle  10  with the surface layer  48  allows keeping the wearing effect on the inner surface  18  facing the front surface area  58  very small. 
     The coating of the slide areas  54 ,  56  of the valve needle  10  with the surface layer  48  enables a low sliding coefficient between the valve needle  10  and the guide elements  28 ,  29  of the valve body  4 . By this, the wearing effect of the lower guide element  28  and the upper guide element  29  can be kept small. 
     In general, it is preferred that the thickness of the surface layer  48  on the seat part  50  of the valve needle  10  is the highest compared with the further surface layers  48  on the valve needle  10 . This is due to the very high load in the case of the impact of the valve needle  10  on the seat body  26 . The thickness of the surface layer  48  on the front surface area  58  of the valve needle  10  is low compared with the further surface layers  48 . Preferably, the thickness of the surface layers  48  of the slide areas  54 ,  56  of the valve  10  is higher than the thickness of the surface layer  48  of the front surface area  58  of the valve needle  10  and is lower than the thickness of the surface layer  48  of the seat part  50  of the valve needle  10 . 
     Corresponding to this, preferably the thickness of the surface layer  48  on the seat body  26  is the highest compared with the further surface layers  48  on the inner surface  18  of the valve body  4 . The thickness of the surface layer  48  on the inner surface  18  facing the front surface area  58  is low compared with the further surface layers  48  on the inner surface  18 . The thickness of the surface layers  48  on the guide elements  28 ,  29  is higher than the thickness of the inner surface  18  facing the front surface area  58  and is lower than the thickness of the surface layer  48  of the seat body  26 . 
     The selection of an appropriate thickness of the different surface layers  48  enables to obtain a good result for the wearing conditions of the valve needle and/or the valve body  4  and the sliding conditions between the valve needle  10  and the valve body  4  in connection with only small changes of the geometry of the valve needle  10  or the valve body  4 .