Patent Publication Number: US-2015069151-A1

Title: Fluid Injection Valve

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to EP Patent Application No. 13183481 filed Sep. 9, 2013. The contents of which are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to a fluid injection valve. 
     BACKGROUND 
     Injection valves are in widespread use, in particular for internal combustion engines, 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 differing needs for various types of 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 may accommodate an actuator for actuating a needle of the injection valve, which may, for example, be an electromagnetic actuator or piezoelectric actuator. 
     SUMMARY 
     One embodiment provides a fluid injection valve, comprising a fluid inlet tube with a recess, a valve body having a central longitudinal axis and a cavity with a fluid outlet portion, a valve needle received in the recess of the fluid inlet tube and in the cavity of the valve body, the valve needle being axially displaceable with respect to the fluid inlet tube and the valve body between a closing position that prevents a fluid flow through the fluid outlet portion and other positions that allow the fluid flow through the fluid outlet portion, and a spring element arranged in the recess and arranged to interact with the valve needle to bias the valve needle in an axial direction towards the closing position, wherein a spring stiffness of the spring element depends on a pressure of fluid in the recess. 
     In a further embodiment, the valve needle comprises a spring rest, and the spring element is arranged between the valve body and the spring rest of the valve needle. 
     In a further embodiment, the spring element comprises an elastically deformable material, and the spring stiffness of the spring element depends on a pressure of fluid in the recess as a function of the elastically deformable material interacting with the fluid. 
     In a further embodiment, the spring element comprises a coil spring with a defined number of spring turns, and the elastically deformable material is arranged along at least part of an axial extension of the coil spring between the respective spring turns. 
     In a further embodiment, the spring element comprises an elastic ring-shaped tube. 
     In a further embodiment, the tube is hollow and has an interior that is sealed with respect to the recess. 
     In a further embodiment, the interior is filled with a gas or another fluid. 
     In a further embodiment, the valve is configured to open in a flow direction of the fluid at the fluid outlet portion and the spring element biases the valve needle in a longitudinal direction opposite to said flow direction. 
     Other embodiments provides an internal combustion engine, comprising a plurality of the fluid injection valves disclosed above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example embodiments of the fluid injection valve are explained below with reference to the figures, in which: 
         FIG. 1  shows a fluid injection valve with a valve assembly according to a first exemplary embodiment in a longitudinal section view, 
         FIG. 2   a  shows a force diagrams explaining the forces acting on a spring element of the fluid injection valve according to  FIG. 1 , 
         FIG. 2   b  shows a schematic longitudinal section view of the spring element of the fluid injection valve according to  FIG. 1 , 
         FIG. 3  shows a fluid injection valve with a valve assembly according to a second exemplary embodiment in a longitudinal section view, 
         FIG. 4   a  shows the spring element of the fluid injection valve according to  FIG. 3  in a longitudinal section view, 
         FIG. 4   b  shows a schematic longitudinal section view of the spring element of the fluid injection valve according to  FIG. 3 , 
         FIG. 5   a  shows the load distributions of a valve needle in a conventional fluid injection valve, and 
         FIG. 5   b  shows the load distribution of a fluid injection valve according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention to specify an injection valve which can be manufactured in a simple way and which facilitates a reliable and precise functioning. 
     A fluid injection valve is specified. It comprises a fluid inlet tube with a recess and a valve body including a central longitudinal axis. The valve body comprises a cavity with a fluid outlet portion. The recess in particular has a fluid inlet portion at an axial end opposite to the fluid outlet portion of the cavity. The fluid inlet tube and the valve body are preferably positionally fixed with respect to each other. The recess and the cavity are hydraulically connected. Expediently, the fluid injection valve may be configured such that fluid can flow from the fluid inlet portion of the recess through the recess into the cavity and further to the fluid outlet portion of the cavity. The fluid injection valve is in particular configured for dispensing fluid from the fluid outlet portion. Furthermore, the injection valve comprises a valve needle. 
     The valve needle is received in the recess of the fluid inlet tube and in the cavity of the valve body. Preferably, a first axial end of the valve needle is arranged in the recess of the fluid inlet tube and the valve needle extends from said end into the cavity of the valve body, and in particular through the fluid outlet portion to a second axial end of the valve needle. The second axial end in particular projects longitudinally beyond the cavity, preferably it projects longitudinally beyond the valve body. 
     In this case, the fluid injection valve is in particular an outward opening valve. In other words, the fluid injection valve is in particular configured to open in a flow direction of the fluid at the fluid outlet portion. 
     The valve needle is axially displaceable with respect to the fluid inlet tube and the valve body for preventing a fluid flow through the fluid outlet portion in a closing position and releases the fluid flow through the fluid outlet portion in other positions. In case of an outward opening valve, the valve needle is in particular axially moved away from the closing position in the above mentioned flow direction at the fluid outlet portion for opening the valve. 
     The injection valve comprises a spring element. The spring element is arranged in the recess and operable to mechanically interact with the valve needle for biasing the valve needle towards the closing position. In particular, the spring element is operable to act on the valve needle to move the valve needle in axial direction in its closing position and/or to keep the valve needle in its closing position. In case of an outward opening valve, the spring element is in particular operable to bias the valve needle in a longitudinal direction opposite to the above mentioned flow direction. 
     The spring element is configured such that a spring stiffness of the spring element depends on a pressure of fluid in the recess. Expediently, the spring element may be configured such that its spring stiffness increases with increasing fluid pressure and decreases with decreasing fluid pressure. 
     More specifically, the fluid injection valve may be configured to be supplied with pressurized fluid through the fluid inlet portion—for example from a fuel rail to which the fluid injection valve may be connected—so that the recess is filled with the pressurized fluid during operation of the fluid injection valve. The spring element may be configured to interact with the pressurized fluid in the recess in such fashion that its spring stiffness varies with the pressure of the pressurized fluid in the recess. 
     For example, the spring element may comprise an elastically deformable material for interacting with the pressurized fluid. In particular, the spring element may be configured in such fashion that the fluid interacts with the elastically deformable material to vary the shape and/or the elastic modulus of the latter in dependence of the pressure. 
     By means of the fluid injection valve according to the present disclosure, it is possible to control a needle load regardless of the fuel pressure to always guarantee the closing function and a tip sealing function. The spring stiffness being fuel pressure dependent allows a more reliable closing of the injector and helps avoiding uncontrolled valve needle opening if the fuel pressure increases. Thus, the fluid injection valve has a particularly low risk of unintended opening at high fluid pressures. 
     The subject fluid injection valve also makes it possible to operate the injection valve without additional or with a smaller amount of energy at fluid pressures which are lower than the maximum fluid pressure for which the fluid injection valve is specified. In conventional injection valves, a constant spring force of a spring element would have to be specified at the maximum fluid pressure to be sufficient to counter the hydraulic force tending to move the valve needle away from the closing position. When the hydraulic force is lower at low fluid pressures, the actuator unit would have to additionally supply the force difference to open the valve against the constant spring force in such a conventional injection valve. 
     As a result of this, actuator unit dimensions can be kept small in the fluid injection valve according to the present disclosure and, therefore, a minimum controllable fuel quantity can be reduced since the actuator becomes faster. The fact that the actuator unit becomes faster also facilitates performing multiple injections with minimized dwell time between consecutive injections, therefore supporting stratified combustion charge. Overall injection valve dimensions can be limited. Hydraulically balancing elements, like e. g. bellows or a dry actuator are made redundant. 
     In an advantageous embodiment, the valve needle comprises a spring rest and the spring element is arranged between the valve body and the spring rest of the valve needle. This allows a reliable and exact arrangement of the spring element. 
     In a further advantageous embodiment, the spring element comprises a coil spring with a given number of spring turns, wherein, along at least part of the axial extension of the coil spring between the respective spring turns, the elastically deformable material is arranged. By means of this, a desired dependency of the spring stiffness on the fuel pressure—in particular an increasing stiffness with increasing fuel pressure—can easily be achieved. 
     In a further advantageous embodiment, the spring element comprises an elastic ring-shaped tube. This allows an easy and cost-effective assembly of the injection valve. 
     The tube is in particular hollow and has an interior which is sealed with respect to the recess. The interior may be filled with a gas, such as air, or with a further fluid. The gas or the further fluid in the interior of the tube preferably has a pressure which is different—in particular lower—than the pressure of the pressurized fluid in the recess. 
       FIG. 1  shows an injection valve  10  which is suitable for dosing fluids, i.e. a fluid injection valve, and which comprises a valve assembly  14  and an inlet tube  12  and an actuator unit (not shown here). The injection valve  10  of this embodiment or any other embodiment according to the present disclosure may in particular be suitable for dosing fuel to an internal combustion engine. 
     The valve assembly  14  comprises a valve body  20  with a central longitudinal axis L. A cavity  24  is arranged in the valve body  20 . A valve needle  22 , which is movable in the axial direction, is arranged in the cavity  24 . 
     The fluid inlet tube  12  has a fluid inlet portion at one axial end and is fixed to the valve body  20  at its opposite axial end. The cavity  24  is hydraulically coupled to the recess  44  of the fluid inlet tube  12  and a fuel connector (not shown here). The fuel connector is designed to be connected to a high pressure fuel chamber of an internal combustion engine, in which the fuel is stored under high pressure. The high pressure chamber may, for example, be a fuel rail. 
     The injection valve  10  is of an outward opening type. 
     On one of the free ends of the cavity  24 , a fluid outlet portion  28  is formed, which is closed or opened depending on the axial position of the valve needle  22 . Outside the closing position of the valve needle  22 , there is a gap between the valve body  20  and the valve needle  22  at an axial end of the injection valve  10  facing away from of the fluid inlet tube  12 . The gap forms a valve nozzle. 
     Furthermore, the valve needle  22  has a lower needle portion  42 . The lower needle portion  42  has a groove  46 . The groove  46  has a basically annular shape. The groove  46  allows a fluid flow to the fluid outlet portion  28 . 
     At an axial end of the lower needle portion  42  which faces away from the fluid inlet tube  12 , the valve needle  22  has a tip portion  50 . Preferably, the tip portion  50  may, for example be conical, frusto-conical or semispherical. The tip portion  50  cooperates with the valve body  20  to prevent or enable the fluid flow through the fluid outlet portion  28 . 
     The fluid is led from fluid inlet portion of the fluid inlet tube  12  through the recess  44  and further through the cavity  24  to the lower needle portion  42  to be led on through the groove  46  to the fluid outlet portion  28  near the tip portion  50  of the valve needle  22 . The valve needle  22  prevents a fluid flow through the fluid outlet portion  28  in the valve body  20  in a closing position of the valve needle  22 . 
     The valve needle is axially displaceable away from the closing position in direction of the fluid flow and the fluid outlet portion  28 , i.e. downwards in  FIG. 1 . The tip portion  50  which projects longitudinally beyond the valve body  20  is moved further away from the valve body  20  in downstream direction when the needle is displaced out of the closing position. 
     The valve assembly  14  is provided with an actuator unit (not shown here), which preferably is an electro-magnetic actuator. The actuator unit  16  may, however, also comprise another type of actuator which is known to a person skilled in the art for this purpose. Such other type of actuator may be, for example, a piezoelectric actuator. 
     The electro-magnetic actuator unit comprises a coil (not shown here), which is preferably arranged inside a housing (not shown here). Furthermore, the electro-magnetic actuator unit comprises an armature (not shown here). The armature is, for instance, mechanically coupled with the valve needle  22  and is axially movable along the central longitudinal axis L. The coil is arranged such as to interact with the armature. The coil is designed and arranged such as to move the armature into the direction of the fluid outlet portion  28 . 
     The armature cooperates with the valve needle  22  such that at least part of the lift generated by the coil with respect to the armature  3  is transferred to the valve needle  22 , thereby moving the valve needle  22  in its opening position. 
     A spring element  30  is arranged in the recess  44  provided in the fluid inlet tube  12 . For instance, the valve needle  22  comprises a spring rest  34  and the spring element  30  is arranged between the valve body  20  and the spring rest  34  of the valve needle  22 . For instance, the valve body  20  comprises a brace element for the spring element  30 . The brace element may be formed integrally with the valve body  20 . The valve body  20  and the spring rest  34  of the valve needle  22  support the spring element  30 . The spring element  30  is arranged to act on the valve needle  22  such as to move the valve needle  22  in the axial direction into its closing position and to retain the valve needle  22  in its closing position against the hydraulic force of the fluid. The spring element  30  is configured such that a spring stiffness of the spring element  30  depends on a fluid pressure in the recess  44 . 
     The spring element  30  may force the valve needle  22  in longitudinal upstream direction. When the actuator unit  16 , in particular the coil, is de-energized, the spring  30  is operable to force the valve needle  22  to move in the upstream axial direction into its closing position. k 
     In the embodiment shown in  FIG. 1 , the spring element  30  comprises an elastic ring-shaped tube  56 . Preferably, the ring-shaped tube  56  is a hollow tube. The interior of the tube is in particular sealed from the recess  44 , i.e. hydraulically separated from the recess  44 . It may, for example, be filled with a gas such as air or a further fluid which may be the same fluid as the fluid dispensed from the fluid injection valve  10  or another sort of fluid. 
       FIG. 2   a  shows an example of a force diagram explaining the change in spring stiffness depending on the fuel pressure of the fluid in the recess  44 . 
     The fuel pressure p F  of the pressurized fluid in the recess  44  acts on the surface A of the ring-shaped tube  56  and generates a force F on the surface A. The force F effects a strain force U along a circumference of the ring-shaped tube  56 . The strain force U can be split in its vector components. One of these components is a longitudinal axial force V. 
     A resulting spring stiffness can be calculated by means of the following equations: 
         A=r*θ   eq. 1
 
         Ao=r *sin θ  eq. 2
 
         Ao =( A /θ)*sin θ
 
         F =( p   F   −P 0)/ A    eq. 3
 
         U *cos α= F/ 2   eq. 4
 
         V=U *sin α  eq. 5
 
         V =( F/ 2)*tan α
 
         V=[[Ao *( p   F   −P 0)]*tan α]/2
 
         K 0= L/ 6   eq. 6
 
         K =( L+V )/δ  eq. 7
 
     wherein p F  is the fuel pressure and P0 is the pressure of the gas or further fluid inside the ring-shaped tube  56 , so that p F −P0 represents the effective fuel pressure. Ao is the effective surface. K0 is the basic spring stiffness, representing the compression of the ring-shaped tube  56  by a distance δ when a load L is applied under the condition that p F  equals P0. K* is the resulting spring stiffness when p F  does not equal P0. 
     The longitudinal axial force V is the force component which supports the needle closing function. Consequently, an increase in fluid pressure p F  results in an increased longitudinal axial force V. 
     As can be seen from eq. 7, the resulting spring stiffness K* increases depending on the longitudinal axial force V. 
       FIG. 2   b  shows an example of the forces resulting from the effective fuel pressure p F −P0 on the ring-shaped tube  56 . The forces are roughly indicated by arrows in  FIG. 2   b.    
       FIG. 3  shows an injection valve  10  with another embodiment of the spring element  30 . The spring element  30  comprises a coil spring with a given number of spring turns  52 , wherein, along at least part of the axial extension of the coil spring between the respective spring turns  52 , an elastically deformable material  54  is arranged. In  FIG. 3 , the elastically deformable material  54  is, for instance, arranged along the whole axial extension of the coil spring between the respective spring turns  52 . The spring turns  52  are preferably completely embedded in the elastically deformable material  54 , for example except from the upper and lower end surfaces which face upstream and downstream, respectively, in longitudinal direction. Spring turns  52  may be exposed at the upper and lower end surfaces. This may allow a particularly precise positioning of the spring element  30 . 
       FIG. 4   a  shows a perspective view of the coil spring with the elastically deformable material  54  being partially cut away for better representation.  FIG. 4   b  shows a cross-sectional view of the coil spring with the elastically deformable material  54 . 
     The spring element  30  may expediently be dimensioned such that it is compressed when the distance d H  between the spring seat  34  of the valve needle  22  and the spring seat of the valve body  20  is maximal, i.e. when the valve needle  22  is in the closing position in the present embodiment. 
     The elastically deformable material  54  may comprise rubber or consist of rubber. Alternatively or additionally, the elastically deformable material  54  may comprise a plastic. As the fuel pressure increases, the elastically deformable material  54  arranged between the spring turns  52  becomes stiffer. Also, by means of this arrangement, it can be achieved that the spring stiffness increases as the fuel pressure increases, which has the effect that the needle is retained in its closing position by a greater force when the fuel pressure increases. The arrows indicate the direction of the fuel pressure. 
       FIGS. 5   a  and  5   b  show the load distributions of the valve needle  22  of a conventional valve ( FIG. 5   a ) and of the fluid injection valves according to the above embodiments ( FIG. 5   b ). The forces F N  in Newton (N) acting on the valve needle  22  are shown as function of the fuel pressure p F  in bar in these figures. Forces F N  with positive sign tend to force the valve needle  22  away from the closing position. Forces F N  with negative sign bias the valve needle towards the closing position. The absolute force and pressure values are only to be understood as being exemplary and may be varied according to the requirements of the fluid injection valve. 
     The dotted line represents a hydraulic load H on the valve needle  22  generated by the pressurized fluid in the recess  44  and in the cavity  24 . The dashed line represents the spring load S of a spring element  30  biasing the valve needle  22  towards the closing position. The solid line represents a total needle load T of the valve needle  22  resulting from adding the hydraulic load H and the spring load S. 
     In  FIG. 5   a  the spring element  30  of the conventional injection valve has a constant spring stiffness. 
     When the solid line, which represents the total needle load T, crosses the x-axis representing the fuel pressure p F , the injector valve opens without coil activation (see the position marked by the arrow pointing downward in  FIG. 5   a ). This is an uncontrollable operating condition. 
     In  FIG. 5   b  the spring element  30  of the fluid injection valves  10  according to the above embodiments comprises a variable spring stiffness. The spring stiffness increases with increasing fluid pressure p F . The increase in spring stiffness is configured such that it compensates or overcompensates the increase of the hydraulic load H with the fluid pressure p F . In this case, the solid line, which represents the total needle load T, at no point crosses the x-axis. The injector valve does not open without coil activation. When the spring stiffness increase compensates the hydraulic load increase, the spring load S of the spring element  30  and the hydraulic load H have the same gradient. The total needle load T is independent of the fuel pressure p F  in this case. In case that the gradients are different, i.e. in the case of an overcompensation of the hydraulic load increase, the pressure range of the fluid injection valve&#39;s operating pressure may be further increased.