Abstract:
The invention provides a switching valve having a valve element which is movable in a housing, an actuating apparatus acting on the valve element in a first direction and a spring apparatus charging the valve element in a second direction. According to the invention, the first and second directions are in opposition and the spring apparatus has a progressive spring characteristic.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2010/064331 filed on Sep. 28, 2010. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a switching valve. 
     2. Description of the Prior Art 
     Switching valves, especially fast-switching solenoids, are known on the market. They are used in the automotive field, for instance, in injection systems, automatic transmissions, or anti-lock brake systems. Often, they have short ON and OFF times and hence are switched on and off especially frequently. Such switching valves are often actuated by an electromagnet, and a magnet armature executes an axial motion that is limited by a seat of repose and a stroke stop. Often, upon actuation the armature is supplied with current, and after the current is switched off, the armature is moved back to its original position by a spring. It is also known for to damp such a switching valve by means of a device that is adapted to the structural type of the switching valve. 
     The following published references are also mentioned: German patent disclosures DE 10 2007 034 038 A1, DE 10 2007 028 960 A1, DE 10 2005 022 661 A1, DE 10 2004 061 798 A1, DE 2004 016 554 A1, DE 103 27 411 A1, and DE 198 34 121 A1, and European patent disclosures EP 1 701 031 A1, EP 1 471 248 A1, and EP 1 296 061 A2. 
     Advantages and Summary of the Invention 
     The switching valve of the invention has the advantage that the impact speed of a valve element, or of an armature coupled to it, against a stop is reduced without substantially lengthening the switching times of the switching valve. Because of the lesser impact speed, there is less wear on the switching valve. Pressure pulsations in the medium to be delivered are likewise lessened. In addition, the excitation of mechanical vibration and the attendant noise emission are reduced. 
     The invention is based on the concept of designing the spring device such that for an increasing spring travel, it requires not a linear but a progressive spring constant. By means of this kind of progressive spring characteristic (characteristic spring curve), the valve element can be effectively braked in its motion, in particular before reaching a terminal position. The spring action ensues comparatively early, but softly, and it becomes markedly stronger only toward the end of the motion of the valve element. This means that over a wide range of motion, the valve element is acted upon only weakly by the spring device, so that initially, a fast acceleration of the valve element is made possible. For example, beyond half of a stroke of the valve element, as a consequence of the progressively increasing spring force, there is no further acceleration of the valve element. Temporarily—depending on the properties of the actuating device and of the spring—an approximately uniform motion may result. Comparatively shortly before the terminal position is reached, the valve element is braked markedly more strongly, and by no later than the terminal position it will have been braked to a standstill. Compared with a spring force that increases only linearly, the impact speed is reduced more sharply. In the process, the switching times of the switching valve are not lengthened substantially. A further advantage of the invention is that—in contrast to an arrangement having only one spring portion with a high spring constant—the spring prestressing force is less vulnerable to tolerances, and thus the spring prestressing is easier to adjust. 
     The switching valve functions better if the spring device includes a series circuit of at least two spring portions, and the maximum spring travel of a spring portion is less than the maximum stroke of the valve element. By means of such an arrangement of at least two spring portions, the prerequisite of dimensioning the spring device in manifold ways is met. As a function of the series circuit of the spring portions and their optionally different stiffness, the stroke of the valve element is distributed among the individual spring portions; that is, the maximum spring travel of each spring portion is less than the total spring travel. 
     To that end it is provided that at least two spring portions are coupled via an adapter piece, and the adapter piece strikes a portion of the housing before the maximum stroke of the valve element is reached, so that the softer spring portion is subsequently bridged. The result is an action of the spring device as follows: In a first phase of the motion of the valve element, the adapter piece has not yet struck the portion of the housing, and thus the force acts on all the spring portions that are connected in series. All the spring portions are upset with the same force. Accordingly, the resultant total spring constant is relatively low, so that the spring device initially acts with only a comparatively slight force on the valve element that is to be moved. In the further course of the motion of the valve element, the adapter piece strikes the portion of the housing. As a result, at least one spring portion is bridged, since after that it cannot be upset any more strongly. In the further course of the motion of the valve element, accordingly only the remaining spring portion or spring portions are upset further. On account of the series circuit of the spring portions, the resultant spring constant becomes greater; that is, upon each identical change of travel, the associated change of force is greater. In this way, the motion of the valve element is now braked with comparatively great force and thus more strongly. 
     With this basic arrangement of the spring device, many embodiments are possible. For instance, a plurality of spring portions can be connected in series, with one adapter piece disposed between each two spring portions. Preferably—if there is a plurality of adapter pieces—the adapter pieces strike the respective portions of the housing successively in the course of the motion of the valve element. Hence the resultant characteristic spring curve can be dimensioned in manifold ways. For example, it can be favorable for a first phase of the armature motion, in which no adapter piece has yet struck its stop, to be designed as comparatively long within the maximum armature stroke available, so that the braking action ensues comparatively late, but in turn strongly. A characteristic spring curve that is progressive overall is even achieved if the individual spring portions have the same spring constant. The spring portions can for instance be implemented in the form of separate springs, which at their end portions are each firmly coupled via a respective adapter piece. Alternatively, they form one cohesive spring, onto which one or more adapter pieces are placed at specified intervals. As a result, only one spring in all is needed, which reduces production costs and enhances the reliability of the spring device. 
     A switching valve is also proposed whose spring portions have different spring constants. Regardless of their number, embodiment and disposition, the individual spring portions can have a characteristic spring curve that is intrinsically constant, or progressive. The latter option is structurally possible with helical springs, for example. Overall, the switching valve of the invention further increases the progression of the characteristic spring curve. Accordingly, the effect when the valve element is braked before reaching the terminal position is even greater. 
     The spring device of the switching valve of the invention can be used more flexibly if at least one spring portion includes a helical spring, plate spring, annular washer, and/or wave washer. As a result, the spring device can be embodied in numerous further variants, so that it can be adapted even better to the demands that arise in terms of force, characteristic curve, spring stroke, space required, durability, or production costs. 
     A further embodiment of the invention provides that the at least two spring portions include helical springs with different diameters, and that the adapter piece has a cup-shaped structural form, such that two spring portions each are connected functionally in series, but in spatial terms are disposed coaxially one inside the other. In this way, an especially compact structural form of the spring device can be produced, so that the switching valve as a whole can be small. 
     One embodiment of the invention provides that the switching valve is an electromagnetic switching valve. The invention can thus advantageously be employed for an especially frequently occurring structural type of switching valves. 
     A further embodiment of the switching valve provides that it is a switching valve in an injection system, an automatic transmission, or an anti-lock brake system of a motor vehicle. Such applications demand especially precise operation of the switching valve. This is reinforced by the spring device of the invention, which comprises mechanical components that can be manufactured with precision. The overall result is correspondingly precise operation of the switching valve. The invention is especially well suited to use in a quantity control valve of a high-pressure fuel pump in a common-rail system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Below, exemplary embodiments of the invention are described in conjunction with the drawings. In the drawings: 
         FIG. 1  is a functional block circuit diagram of a spring device of a switching valve; 
         FIG. 2  shows a characteristic spring curve that fits  FIG. 1 ; and 
         FIG. 3  shows an embodiment of a switching valve in a sectional view. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In all the drawing figures, the same reference numerals are used for elements and sizes that are functionally equivalent, even in different embodiments. 
       FIG. 1 , in a simplified schematic diagram, shows a region of a switching valve  10  having an electromagnetic actuating device  9  and a spring device  11 . The switching valve  10  may for instance be an electromagnetic quantity control valve, with which a fuel quantity that is delivered to a high-pressure pump in a common-rail fuel system is controlled. 
     Various portions are shown of a housing  12  that is not shown in further detail. In the left-hand part of  FIG. 1 , an armature  14  is shown, which is coupled with a valve element not shown in  FIG. 1  and which in the outset position shown rests on a seat of repose  16 . Further elements of the aforementioned actuating device, such as a coil or a pole core, are not shown in  FIG. 1 . The seat of repose  16  either is an element of the housing  12  or is connected to it. On the right in the drawing, a portion  13  of the housing  12  is shown on which a first spring portion  18  of the spring device  11  is supported. The first spring portion  18  is adjoined toward the left in the drawing by a second spring portion  20 , which on its left end portion rests on the armature  14 . The two spring portions  18  and  20  are accordingly braced between the armature  14  and the housing portion  13 . An adapter piece  22  is disposed between the first spring portion  18  and the second spring portion  20 . A stroke stop  24  that is part of the housing  12  limits the motion of the armature  14  to the right in the drawing. The attainable stroke stop is marked  26 . A stop  28 , also part of the housing, limits the motion of the adapter piece  22 , and the attainable stroke distance of the adapter piece  22  is marked  30 . In the region shown, the switching valve  10  is constructed essentially rotationally symmetrically. 
     In  FIG. 1 , an outset position of the switching valve  10  when current is not being supplied is shown. The armature  14  rests on its seat of repose  16 , while the adapter piece  22  is not resting on its stop  28 . The motion of the armature  14 , of the two spring portions  18  and  20 , and of the adapter piece  22  is effected in the axial direction, or in other words in the drawing in  FIG. 1  in the horizontal direction. An arrow  32  illustrates this. 
     When current is supplied to the switching valve or an exciter coil, the armature  14  is moved as indicated by the arrow  32 . In the process, the spring portions  18  and  20  are subjected to pressure, or in other words are upset. In the present instance, the second spring portion  20  has a higher spring constant than the first spring portion  18 . Accordingly, upon the motion of the armature  14 , the first spring portion  18  is compressed more than the second spring portion  20 . That is, the second spring portion  20  is comparatively stiff. In the course of the motion of the armature  14 , the adapter piece  22  strikes the stop  28 . As a result, the first spring portion  18  is bridged; it cannot be compressed further and to this extent is without any effect. It follows that after this, the spring action of the spring device is determined only by the second, stiffer spring portion  20 . Because of the higher spring constant of the second spring portion  20 , the behavior of the spring device is “abruptly” progressive. The effect of the second, stiffer spring portion  20  extends predominately to a range of motion of the armature  14  near the stroke stop  24 . In this final phase of the armature motion, the armature  14  is therefore braked especially strongly. The motion of the armature  14  ends at the stroke stop  24 , at which any residual kinetic energy is reduced to nothing. 
     It can be seen that the maximum stroke distance  30  of the adapter piece  22  must be selected such that the adapter piece rests on the stop  28  before the armature  14  comes into contact with the stroke stop  24 . Overall, the effect of the spring device is such that the armature, in its first phase of motion, beginning at the seat of repose  16 , is initially braked only little. This means that the armature motion can happen comparatively fast, and the switching valve  10  also switches at high speed. Only shortly before the stroke stop  24  is reached does a comparatively strong braking action by the spring device ensue. This greatly reduces the impact speed of the armature on the stroke stop  24 . 
     If the current supply is interrupted, then the magnetic force acting in the direction of the arrow  32  disappears. As a consequence, the armature  14  is moved back onto the seat of repose  16  by the spring device  11 , counter to the direction of the arrow  32 . No additional devices for moving the armature  14  back onto the seat of repose  16 —such as a second exciter coil—are shown in  FIG. 1 . 
     A further embodiment, not shown, of the switching valve is constructed as in  FIG. 1 , but instead of two spring portions, it has three, and instead of only one adapter piece, it has two. The spring portion located close to the housing portion has a low spring constant; the spring portion located close to the armature has a high spring constant; and a middle spring portion, located between the other two spring portions, has a medium spring constant. Fitting this situation, a distance that defines the stroke of the second adapter piece is, in terms of its size, between the distance that determines the armature stroke and the distance that determines the stroke of the first adapter piece. 
     Another embodiment of the switching valve, which is not shown, has one spring portion with a plate spring and one spring portion with an annular washer. Still another embodiment of the switching valve, also not shown, has one spring portion with a dc and one spring portion with a wave washer. 
       FIG. 2  shows a resultant characteristic spring curve for an arrangement that is similar to  FIG. 1  and comprises two spring portions. A coordinate system is shown, on the abscissa of which a spring travel  34  is plotted that determines the motion of the armature  14  and on the ordinate of which a spring force  36  is plotted. A characteristic spring curve  38  illustrates the relationship. A spring travel  34  of zero is equivalent to an outset state, when current is not being supplied, as in  FIG. 1 . 
     Beginning at a spring travel of zero in the left-hand region of  FIG. 2  and with a spring force  40 , the spring force increases as the spring travel increases. At a spring travel  42 , a spring force  44  is attained. This is precisely the spring travel at which the adapter piece  22  comes into contact with the stop  28 . Beyond that stroke, the first spring portion  18  is bridged; that is, it is not compressed further. In the further course of the motion of the armature  14  in the direction of the stroke stop  24 , only the second spring portion  20  is now acted upon. In accordance with a higher spring constant of the second spring portion  20 , the characteristic spring curve  38  rises more steeply beyond the spring travel  42 ; that is, the overall characteristic curve is progressive. Finally, at a spring travel  46 , the armature  14  strikes its stroke stop  24 , whereupon a maximum spring force  48  is reached. The spring travel  46  corresponds to the distance  26  in  FIG. 1 . 
     It can be seen how, by means of a series circuit of two spring portions  18  and  20 , the resultant characteristic spring curve  38  becomes highly progressive, with an abrupt change in the steepness of the characteristic spring curve  38 . A progression in the characteristic spring curve  38  automatically ensues whenever the spring constants of the first spring portion  18  and of the second spring portion  20  are equal. This also happens if—unlike what is shown in FIG.  1 —the two spring portions  18  and  20  form a single spring, and the adapter piece  22  is permanently inserted only into the helical part of the spring. 
     If the spring constant for the first spring portion is R 1  and the spring constant for the second spring portion is R 2 , the result is the relationship expressed by the following equation:
 
 R   total =1/(1 /R 1+1 /R 2)
 
     The resultant total spring constant R total  is accordingly less than R 1  and less than R 2  and thus is comparatively soft, as long as both spring portions are functioning. 
     In  FIG. 2 , this equation applies to a spring travel  34  between zero and the spring travel  42 . Between the spring travel  42  and the spring travel  46 , conversely, the spring constant R 1  of the first spring portion  18  is no longer operative; only the spring constant R 2  applies. In general, in the series circuit of a plurality of spring portions according to the invention, it is true that in the course of the spring travel, the stiffness of the resultant spring can only increase, but not decrease. 
       FIG. 3  shows an embodiment of a switching valve  10  as an electromagnetic switching valve  49  for switching a fluid. The fluid-carrying regions are not shown in the view shown in  FIG. 3 . The elements shown in  FIG. 3  are essentially embodied rotationally symmetrically about an axis  50 . The axis  50  extends vertically in terms of the drawing in  FIG. 3 . 
     In the housing  12 , there is an axially displaceable valve element  52 , with a valve plate  54  disposed fixedly on it. Here, the armature  14  is also coupled fixedly to the valve element  52 . The first spring portion  18  is disposed between the cup-shaped adapter piece  22  and the stop  28 . The second spring portion  20  is disposed between the cup-shaped adapter piece  22  and the plate  54 . Thus the two spring portions  18  and  20  are coupled and connected functionally in series via the adapter piece  22 . In this instance, the two spring portions  18  and  20  are embodied as helical springs with different diameters. 
     The status of the switching valve  10  of  FIG. 3  is equivalent to the outset state, when current is not being supplied, of  FIG. 1 , and the valve plate  54  rests on the seat of repose  16 . 
     When current is supplied to the switching valve  10 , the armature  14  and the valve element  52  connected fixedly to the armature  14  move upward in terms of the drawing, in the direction of an arrow  56 . In the process, the cup-shaped adapter piece  22  fastened between the spring portions  18  and  20  is moved as well, and after traversing the distance  30  it strikes the stop  28 . For the remainder of the stroke of the armature  14 , therefore only the spring portion  20  is acted upon and, with its high spring constant, brakes the valve element  52  especially strongly in the final phase of the motion. The motion ends with the impact of the valve plate  54  against the stroke stop  24 . 
     It can be seen that the distance  30  that predetermines the maximum stroke of the adapter piece  22  is shorter than the distance  26  that determines stroke of the valve plate  54  or of the armature  14 . Compared to the dimensions of the switching valve  10 , both distances  26  and  30  are short. The two spring portions  18  and  20  are disposed coaxially on the inside and outside of the adapter piece  22 , respectively. The cup shape that defines the adapter piece  22  makes a particular contribution to the fact that the spring device  11  and thus the entire switching valve  10  are constructed in a space-saving way. The switching valve in  FIG. 3  is suitable for use in motor vehicles, in an injection system, an automatic transmission, or an anti-lock brake system. 
     If the supply of current is interrupted, the switching valve resumes the outset position shown in  FIG. 3 . To the extent that this applies, this process is equivalent to that in the description of  FIG. 1 . 
     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.