Abstract:
The invention relates to a ball valve for adjusting a flow of a fluid medium. The ball valve includes a valve seat and a rounded closing element, in particular a valve ball. Furthermore, the ball valve has an inlet with a choke valve and one diffuser arranged between the choke valve and the valve seat. The diffuser includes a constriction on the side facing the valve seat.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP2008/050039 filed on Jan. 3, 2008. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is based on known ball seat valves for adjusting a flow of a fluid medium. Ball seat valves of this kind are used in many engineering fields in which it is necessary to adjust a flow of fluid media such as gases or liquids, for example in the field of hydraulic control units. 
     2. Description of the Prior Art 
     An important sample application for ball seat valves of this kind can be found in the field of automotive engineering, particularly in the field of injection technology. In numerous injection devices, ball seat valves are used for regulating hydraulic pressure and/or controlling the injection behavior of such systems. Primarily in the field of high-pressure reservoir injection systems (common rail systems), ball seat valves are used to control the lift of an injection valve closure member, which opens or closes injection openings. Examples of such devices are disclosed in DE 101 52 173 A1 and DE 196 50 865 A1. In them, a control chamber that directly or indirectly influences the lift of the injection valve closure member is connected to the ball seat valve directly via an inlet or through an additional bore. In addition to a valve ball, the ball seat valve has an actuator that presses the valve ball into a valve seat or lifts it away from the seat in order to disconnect or connect the control chamber from or to a relief chamber. 
     As is also demonstrated in DE 101 52 173 A1, for example, flow-adjusting ball seat valves known from the prior art generally have a choke valve on the side of the inlet oriented toward the control chamber. On its side oriented toward the ball seat valve, this choke valve is adjoined by one or more expansions of the inlet, which can assume various shapes. 
     In actual use, though, conventional ball seat valves known from the prior art have the disadvantage of a powerful erosion, particularly in the high-pressure reservoir injection systems functioning at pressures of several thousand bar. This erosion is in particular due to a cavitation in the choke valve, largely occurring outside the lift throttle limit. The expression “lift throttle limit” refers to the limit of the lift of the ball seat valve above which the flow no longer changes with a constant pressure upstream and downstream of the ball seat valve. As time passes, the above-described cavitation effects at the choke valve result in so-called cavitation erosion due to condensation, particularly in the seat region of the ball seat valve. As a result, a change occurs in the closing behavior of ball seat valves and this is accompanied by a change in the injection behavior of the injection device. 
     ADVANTAGES AND SUMMARY OF THE INVENTION 
     The present invention therefore proposes a ball seat valve for adjusting a flow of a fluid medium, as well as an injection device that includes a ball seat valve of this kind, both of which avoid the above-described disadvantages of the prior art. In particular, the proposed ball seat valve has a geometry, which sharply reduces cavitation erosion and with which cavitation erosion that occurs nevertheless does not damage the valve seat in a way that causes the latter to become leaky. 
     In order to optimize the ball seat valve geometry, simulation calculations were carried out that represent various parameters of the fluid medium at the ball seat valve, which parameters decisively affect cavitation erosion. In particular, these parameters are the pressure occurring in the fluid medium, the velocity of the fluid medium, the proportion of the vapor to the total volume of the fluid medium, and a mass transfer rate between the liquid phase and gaseous phase of the fluid medium. 
     In these simulation calculations, it has turned out that cavitation erosion can be sufficiently reduced if an (in particular high-pressure-side) inlet to the seat of the ball seat valve is used, which has a choke valve and a diffusor that adjoins the choke valve on the latter&#39;s end oriented toward the valve seat and has a constriction on the end oriented toward the valve seat. The term “diffusor” generally denotes the region between the choke valve and the valve seat. 
     This special form of the diffusor, with the constriction according to the invention by contrast with an (in particular step-shaped) expansion of the kind shown in DE 101 52 173 A1, yields a particular spatial curve of the above-mentioned parameters in the region of the valve seat, which avoids the occurrence of cavitation erosion. The presence of the constriction upstream of the valve seat diverts the flow of the fluid medium in such a way that it sharply reduces the risk of cavitation erosion in the region of the valve seat. 
     The bevel between the valve seat and the diffusor bore is generally referred to as the “Helget bevel”. In the known valve seat geometries, a still water region occurs in the region of this Helget bevel, i.e. a region in which the flow detaches from the bore wall. A flow detachment of this kind, however, ends up producing a flow directed toward a wall, i.e. in particular, a velocity component of the flow that is oriented toward the wall. With the geometry according to the invention, however, no detachment of the flow of the fluid medium occurs or only a sharply reduced such detachment occurs. As a result, the flow oriented toward the wail in the Helget bevel is avoided or at least sharply reduced, i.e. velocity components perpendicular to the bore wall are sharply reduced or avoided entirely. 
     The new geometry in the Helget bevel beneath the valve seat also sharply reduces the proportion of the gaseous phase of the fluid medium in the vicinity of the wall. Consequently, in the vicinity of the wall in the region of the valve seat, there is no vapor component that could condense or there is only an insignificant amount of it. Consequently, the condensation rate is infinitesimally low in this region. Through this overall occurrence of a flow parallel to the walls as well as a low proportion of vapor and low condensation rate in the vicinity of the wall, the geometry according to the invention effectively avoids cavitation erosion. 
     The ball seat valve according to the invention and the injection device according to the invention consequently have a high long-term stability. The injection devices demonstrate a steady injection behavior and low leakage rates over long periods of use. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention will be explained in greater detail in the description that follows in conjunction with the drawing, in which: 
         FIGS. 1A and 1B  show inlet geometries of conventional ball seat valves; 
         FIG. 2  shows an exemplary embodiment of a ball seat valve according to the invention, with a cylindrical diffusor; 
         FIG. 3  shows an exemplary embodiment alternative to the one in  FIG. 2 , with a conical diffusor; and 
         FIG. 4  shows a detailed depiction analogous to the one in  FIG. 1B  of the constriction in the region of the valve seat. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1A  shows a ball seat valve  110  corresponding to the prior art, which corresponds for example to the device disclosed in DE 101 52 173 A1. This example of a ball seat valve  110  is a 2/2-way directional control valve, as are those that follow. Other embodiments, however, are also conceivable. 
     The ball seat valve  110  is used, for example, in an injection device and in it, serves to connect a bore  112  that communicates with a control chamber to a relief chamber  114  or to disconnect this bore from the relief chamber. To this end, a closure member  116 , which in this case is a valve ball, is pressed into or lifted out of a conical valve seat  120  by means of an actuator  118 . In lieu of a ball-shaped closure member  116 , it is also possible to use other shapes of closure member, preferably rounded shapes, that are known to those skilled in the art. 
     The bore  112  in which a fuel pressure in the vicinity of 2000 bar can prevail, for example, communicates with the relief chamber  114  via an inlet  122  that is a component of the ball seat valve  110  and is embodied in the form of a bore in a valve body  124 . 
     On its side oriented toward the bore  112 , the inlet  122  first has a cylindrical choke valve  126  that is adjoined at its end oriented toward the valve seat  120  by a cylindrical diffusor  128 . At the transition between the choke valve  126  and diffusor  128 , a slight bevel is generally provided. The cross section of the choke valve  126  decisively influences and adjusts the flow through the ball seat valve  110  above the lift throttle limit. 
     The actuator  118  can, for example as shown in DE 196 50 865 A1, be a solenoid armature with which the position of closure element  116  is selectively adjusted by means of an electromagnet. It is, however, also possible to use other types of actuators. 
       FIG. 1B  is an enlarged, detailed depiction of the transition from the inlet  122  to the valve seat  120  when the valve is in the open position. The drawing shows that at this transition, the inlet  122 , as is likewise proposed in DE 101 52 173 A1, for example, has a conical expansion. 
     As described above, various simulation calculations were carried out in order, through simulation, to determine the above-mentioned critical parameters in the region of this transition. It turned out that in the sealing region  132  in which the closure member  116  rests against the sealing seat  120  in the closed state, which region is especially critical for the sealing behavior of the ball seat valve  110 , with the embodiment corresponding to the prior art shown in  FIGS. 1A and 1B , velocities in the range from approx. 200 to 400 m/s occurred between the relief chamber  114  and the bore  112  with pressure differences that are realistic for injection devices. In relation to the wall of the valve body  124 , these velocities were oriented at angles in the range from 30 to 45°. 
     Furthermore, this particularly critical region turned out to have a proportion of vapor to the total volume of up to 0.7 to 0.8 (the simulations were carried out predominantly for diesel fuel). In addition, the mass transfer rate from the vapor phase into the liquid phase in this sealing region  132  was comparatively high and assumed values of up to approx. 30,000 kg/(s·m 3 ) (depending on the operating point). As described above, these high velocity components perpendicular to the wall of the valve body  124 , the high condensation-prone vapor components, and the high mass transfer rate lead to cavitation erosion in the sealing region. 
     By contrast,  FIGS. 2 and 3  show embodiments of ball seat valves  110  according to the invention, which can be used, for example, in a fuel injection device  135  according to the invention, for example a common rail injector. These ball seat valves  110  likewise have an inlet (as in the prior art), whose end connected to the bore  112  has a choke valve  126 . 
     As in the exemplary embodiment according to  FIG. 1A , the end of the choke valve  126  oriented toward the valve seat  120  is adjoined by the diffusor  128 ,  FIGS. 2 and 3  show different embodiments of this diffusor  128 ; in any case, though, this diffusor has a constriction  134  at its end oriented toward the valve seat  120 . 
     In the exemplary embodiment shown in  FIG. 2 , the diffusor  128  between the choke valve  126  and the constriction  134  is embodied in the form of an essentially continuous cylindrical diffusor section  136 . In the exemplary embodiment shown in  FIG. 3 , however, the diffusor  128  between the choke valve  126  and the constriction  134  is essentially divided into three subsections: a first cylindrical diffusor section  138  that adjoins the choke valve  126 , a conical diffusor section  140  that widens out in the direction toward the valve seat  120 , and a second cylindrical diffusor section  142  that extends upward to the constriction  134 . 
     In the embodiment shown in  FIG. 3  in which the diffusor  128  is equipped with the conical diffusor section  140 , an optional parting line  144  is also provided in the valve body  124  between the conical diffusor section  140  and the second cylindrical diffusor section  142 . This parting line  144  divides two structural units of the injection device  135 , which can be attached to each other, for example, by means of an external clamping nut that is not shown in  FIG. 3 . This parting line  144  simplifies the production of the diffusor  128  considerably because in this case, the first cylindrical diffusor section  138  and the conical diffusor section  140 , for example, can be jointly produced by being drilled from above. 
     In a fashion analogous to  FIG. 1B ,  FIG. 4  shows a detailed view of the transition between the inlet  122  and the relief chamber  114  for the exemplary embodiment of the ball seat valve  110  with the constriction  134  depicted in  FIG. 2  or  3 . As is clear from  FIG. 4 , the constriction  134  is composed of three parts: the cylindrical diffusor section  136  or  142  (depending on whether one is considering the exemplary embodiment according to  FIG. 2  or  FIG. 3 ) is adjoined by a first conical constriction section  146 , followed by a cylindrical constriction section  148 , and finally a second conical constriction section  150 . 
     The first conical constriction section  146  is embodied so that in this region, the wall of the valve body  124  and the inlet axis  152  enclose an angle α between 20° and 80°, preferably between 25° and 65°. In the second conical constriction section  150 , the wall of the valve body  124  and the inlet axis  152  analogously enclose an angle β that lies in the same angular range. 
     The length of the individual constriction sections  146 ,  148 ,  150  can be selected from within a broad range. In this exemplary embodiment, the length of the cylindrical constriction section  148  is approximately 15% of the total length of the constriction  134  and the length of the first conical constriction section  146  is approximately 50% of it. Other embodiments are also possible, however, particularly deviations from the above-mentioned allocation of lengths by up to a factor of 3, for example. Furthermore, by contrast with the embodiments shown here with the abrupt transition between the cylindrical and conical constriction sections, it is also possible for rounded transitions to be provided. 
     For the total length of the constriction  134  in the direction of the inlet axis  152 , i.e. the sum of the constriction sections  146 ,  148 , and  150 , dimensions in the range of greater than 0% and less than 100% (for example between 30% and 80% or between 45% and 70%), and in particular between 0% and 50% of the maximum cross section of the diffusor have turned out to be well-suited. 
     In this exemplary embodiment, the constriction  134  has its narrowest diameter D V  in the region of the cylindrical constriction section  148 . This constriction diameter D V  is preferably in a range between 30 and 70%, particularly preferably between 40 and 60%, especially between 55 and 60% of the maximum diameter of the diffusor  128 . This maximum diameter of the diffusor  128  is labeled D D  in  FIG. 4  and in this exemplary embodiment, is the diameter of the second cylindrical diffusor section  142  (exemplary embodiment in  FIG. 3 ) or the diameter of the cylindrical diffusor section  136  (exemplary embodiment according to  FIG. 2 ). At typical pressure differences in injection devices  135 , this selection of the constriction  134  has yielded embodiments with extremely low cavitation erosion. 
     Simulation calculations for determining the above-mentioned parameters that characterize the flow and cavitation erosion were also carried out for the exemplary embodiment shown in  FIG. 4 . These simulation calculations demonstrated a significant improvement of the values in comparison to the embodiment according to the prior art shown in  FIG. 1B . 
     It has thus turned out that in the sealing region, in particular in the region in which the closure member  116  rests in the valve seat  120  when the ball seat valve  110  is closed, velocities of less than 200 m/s occur, with the flow traveling parallel to the wall of the valve body  124  in a practically continuous fashion, which once again has a decisive affect on cavitation erosion. On top of this, the volume fraction of the gaseous phase of the fluid medium (once again calculated based on diesel fuel) was significantly reduced in comparison to the results in  FIG. 1B  and yielded values of less than 0.2. In addition, the above-described mass transfer rate from the vapor phase into the liquid phase, i.e. the condensation behavior, which is a main reason that cavitation erosion occurs, was significantly reduced and was below 10,000 kg/(s·m 3 ) in the critical sealing region  132 . 
     These results demonstrate that the constriction  134  according to the invention achieves the above-described effect of reducing cavitation erosion and leads to a significant improvement in the long-term stability of the claimed ball seat valves  110 . 
     The foregoing relates to the preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.