Abstract:
The invention relates to a valve for controlling fluids, having an actuator unit for actuating a valve member which has a first piston and a second piston, separated from it by a hydraulic chamber, and which actuates a valve closing member that divides a low-pressure region at system pressure from a high-pressure region. For leakage compensation, a filling device connectable to the high-pressure region is provided with a hollow chamber, in which a throttle body is disposed such that a line leading to the high-pressure region discharges into the hollow chamber on one end of the throttle body, and on the other end a system pressure line leading to the hydraulic booster branches off. The system pressure is built up as a function of the prevailing pressure in the high-pressure region, by means of geometrically defining the throttle body, a gap surrounding it, and the dimensions of the piston along which the system pressure is reduced.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE 01/01055 filed on Mar. 20, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is directed to valves for controlling fluids in systems such as fuel injection systems for internal, combustion engines. 
     2. Description of the Prior Art 
     One such valve is described in European Patent Disclosure EP 0 477 400 A1, for instance, in which the deflection of a piezoelectric actuator is transmitted via a hydraulic chamber that functions as a hydraulic booster or tolerance compensation element and encloses a common compensation volume between two pistons defining this chamber, one of which is embodied with a smaller diameter and connected to a triggering valve closing member, and the other of which is embodied with a larger diameter and is connected to the piezoelectric actuator. Thus the actuating piston executes a stroke that is lengthened by the boosting ratio of the piston diameter, when the larger piston is moved a certain distance by the piezoelectric actuator. 
     This known valve is intended to separate a low-pressure region from a high-pressure region and can for instance be used in fuel injectors, in particular common rail injectors, or pumps of motor vehicles, where such valves are also known in various versions in the industry. 
     If such a valve is to be functional, the hydraulic system requires a system pressure in the low-pressure region, especially in the hydraulic coupler, but this system pressure drops as a function of leakage unless adequate replenishment with hydraulic fluid takes place. As a rule, a filling device is therefore provided, with which pressure medium from the high-pressure region can be resupplied to the system pressure region. 
     For common rail injectors, solutions to this problem are known in the industry, in which the system pressure, which is expediently generated in the valve itself and should also be as constant as possible upon system starting, is assured by delivering hydraulic fluid from the high-pressure region of the fuel to be controlled to the low-pressure region, where system pressure prevails, with the aid of leakage gaps, represented for example by leakage or filling pins. Typically, the system pressure is adjusted by a valve and can for instance also be kept constant by plurality of common rail valves. 
     A system pressure in the hydraulic chamber that is essentially constant and is at least largely independent of the prevailing high pressure in the high-pressure region presents the problem, however, that at high pressure values, great actuator force is required to open the valve closing member counter to the high-pressure direction, which this dictates a correspondingly large, cost-intensive dimensioning of the actuator unit. Furthermore, at high pressure in the high-pressure region, the positive displacement of hydraulic volume out of the hydraulic chamber via the gaps surrounding the adjacent pistons is reinforced accordingly, meaning that under some circumstances, the refilling time for building up and maintaining the counterpressure on the low-pressure region is prolonged, so that for lack of complete refilling, in the event of a re-actuation of the valve soon thereafter, a shorter valve stroke will be executed, which can adversely affect the opening behavior of the entire valve. 
     SUMMARY OF THE INVENTION 
     The valve of the invention for controlling fluids has the advantage that the system pressure is variable in a structurally simple way as a function of the pressure prevailing in the high-pressure region. Because of the high-pressure-dependent refilling, at a high pressure level in the high-pressure region an increase in the system pressure in the hydraulic chamber is possible, as a result of which the actuating piston is reinforced for opening the valve closing member counter to the existing high pressure. Advantageously, a reduced trigger voltage of the actuator unit is thus required, compared to a valve with a constant system pressure, and the valve of the invention can therefore be equipped with a smaller, less expensive actuator unit. The valve of the invention also makes a defined filling of the low-pressure region, especially the hydraulic chamber, possible. When the pressure in the high-pressure region is increasing, with the variable system pressure the refilling time can be shortened. 
     Structurally, the embodiment according to the invention is distinguished by its simplicity, which makes it possible to define the variable system pressure in the hydraulic chamber by means of easily adjustable geometric variables such as the diameters and lengths of the throttle body and of the piston, along which the system pressure is reduced toward the low-pressure region. Along with the low costs for production and assembly, above all the resistance of the system pressure supply to particles or dirt in the hydraulic fluid is advantageous; this can be ascribed to designing the refilling device with a quasi-secondary flow. The secure furnishing of the requisite system pressure over the entire engine performance graph is thereby assured. 
     In an especially advantageous version, it can be provided that the at least one throttle body is axially adjustably disposed in the hollow chamber and is preferably movable such that it at least partly intersects the branching point of the system pressure line when the system pressure drops. Thus the length of the gap around the throttle body through which a flow is required is shortened, resulting in a higher flow rate and an increase in the system pressure. 
     The valve according to the invention is especially well suited to triggering fuel injection valves, but in principle it can also be realized in all hydraulically boosted systems with a piezoelectric actuator or with a magnetic final control element, such as in pumps. 
     Further advantages and advantageous features of the subject of the invention can be learned from the description, drawing and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Two exemplary embodiments of the valve of the invention for controlling fluids are shown in the drawing and will be explained in further detail in the ensuing description. Shown are 
     FIG. 1, a schematic, fragmentary view of a first exemplary embodiment of the invention for a fuel injection valve for internal combustion engines, in longitudinal section; and 
     FIG. 2, a schematic, fragmentary view of a further exemplary embodiment of the invention in longitudinal section, in which a throttle body of a filling device is supported axially displaceably. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The exemplary embodiment shown in FIG. 1 illustrates a realization of a valve according to the invention in a fuel injection valve  1  for internal combustion engines of motor vehicles. This fuel injection valve  1  here is embodied as a common rail injector for injecting preferably Diesel fuel; the fuel injection is controlled via the pressure level in a valve control chamber  2  that communicates with a high-pressure supply. 
     Via force ratios in the fuel injection valve  1 , an injection onset, injection duration and injection quantity are set. To that end, a valve member  3  is triggered via an actuator unit embodied as a piezoelectric actuator  4 , which is disposed on the side of the valve member  3  remote from the valve control chamber  2  and is constructed of multiple layers in a manner known per se. On its side toward the valve member  3 , the piezoelectric actuator  4  has an actuator head  5 , and on its side remote from the valve member  3 , it has an actuator foot  6 , which is braced against a wall of a valve body  7 . Resting on the actuator head  5  via a support  8  is a first piston  9  of the valve member  3 , which can also be called a control piston. The valve member  3  includes, besides this first piston  9 , a second piston  11 , likewise disposed displaceably in a longitudinal bore of the valve body  7 , that actuates a valve closing member  12  and is therefore also called an actuating piston. 
     The two pistons  9  and  11  define a hydraulic chamber, which serves as a hydraulic coupler and transmits the deflection of the piezoelectric actuator  4 . Since the diameter A 1  of the second piston  11  is less than the diameter A 0  of the first piston  9 , the second piston  11  executes a stroke that is lengthened by the boosting ratio of the piston diameter when the larger first piston  9  is moved a certain distance by the piezoelectric actuator  4 . 
     Along with its function as a hydraulic coupler, the hydraulic chamber  13  also serves to compensate for tolerances resulting from temperature gradients in the component or different coefficients of temperature expansion of the materials used as well as possible settling effects, so that these factors continue to have no effect on the position of the valve closing member  12  to be triggered. 
     On the end toward the valve control chamber  2  of the valve member  3 , the ball-like valve closing member  12  cooperates with valve seats  14 ,  15  embodied on the valve body  7  and in the process separates a low-pressure region  16  at the system pressure p_sys from a high-pressure region  17  at a high pressure or rail pressure p_R. The valve seats  14 ,  15  are embodied in a valve chamber  18  formed by the valve body  7 , from which a leakage outlet conduit  19  leads away on the side of the valve seat  14  toward the piezoelectric actuator  4 . On the high-pressure side, the valve chamber  18  can be made to communicate with the valve control chamber  2  of the high-pressure region  17 , via the second valve seat  15  and an outlet throttle  20 . In this valve control chamber  2 , not shown in detail, a movable valve control piston can be disposed in a manner known per se, by whose axial motions in the valve control chamber  2 , which in the usual way communicates with an injection line that in turn communicates with a high-pressure reservoir (common rail) that is common to a plurality of fuel injection valves and that supplies an injection nozzle with fuel, the injection behavior of the fuel injection valve  1  is controlled. 
     The end of the housing bore toward the piezoelectric actuator and having the valve member  3  is adjoined by a further valve pressure chamber  21 , which is defined by the valve body  7 , the first piston  9 , and a sealing element  22  that is connected to both the first piston  9  and the valve body  7 . A leakage line  23  leads out of this valve pressure chamber  21 . In the version shown, the sealing element  22  is embodied as a bellowslike diaphragm and prevents the actuator  4  from coming into contact with the fuel contained in the low-pressure region  16 . 
     To compensate for leakage losses on the low-pressure region  16  upon an actuation of the fuel injection valve  1 , a filling device  24  is provided. It has a conduit-like hollow chamber  25 , in which a pinlike throttle body  26  is disposed, with a gap  27  surrounding it. Discharging into a region of the hollow chamber  25  on one end of the throttle body  26  is a line  33 , originating at the high-pressure region  17 , and a system pressure line  28  that leads to the hydraulic chamber  13  branches off from a region of the hollow chamber  25  on the opposite end of the throttle body  26 . The system pressure line  28 , in the preferred embodiment shown, discharges into a gap  29  which surrounds the first piston  9  and by way of which the system pressure is reduced toward the valve pressure chamber  21  and thus toward the low-pressure region  16 . 
     It is understood that in a version that deviates from this it may also be provided that the system pressure line  28  discharges into a gap  30  surrounding the second piston  11 , as indicated in FIG. 1 with the line  28 ′ drawn in dashed lines, or that the system pressure line discharges directly into the hydraulic chamber  13 . The indirect filling of the hydraulic chamber  13 , however, serves to improve the pressure holding capacity in the hydraulic chamber during the triggering. 
     The arrangement shown in FIG. 1 thus represents an in-line connection of two separate pistons, namely the throttle body  26  and the first piston  9 , by way of which the high pressure p_R is reduced toward the low-pressure region  16 . The high pressure p_R is reduced to the system pressure p_sys across the gap  27  of the throttle body  26 , which is disposed essentially axially immovably in the hollow chamber  25 . The pressure divider ratio is adjusted by means of the ratio of the lengths and diameters of the throttle body  26  and the downstream piston  9 . Adjusting the system pressure p_sys by means of the separate pistonlike components makes it possible to make the length of the throttle body very slight, since the second half of the pressure divider is formed by the piston  9 . The short lengths or greater diameters make a higher quality of the components possible, while simultaneously reducing costs for production and above all for the adjustment or assembly. 
     The system pressure p_sys, which is reached after an injection after a certain refilling time, and the ratio of the diameters and leakage gap lengths at the throttle body  26  and the piston  9  are dependent on a plurality of parameters, among which are the seat diameter A 2  of the first valve seat  14  and the ratio of the diameter A 0  of the first piston  9  to the diameter A 1  of the second piston  11 . In the embodiment shown, in which upon relief of the high-pressure region  17  the valve closing member  12  is kept in the closing position against the first valve seat  14  by a spring force F_F of a spring  31  that is disposed between the valve closing member  12  and the second valve seat  15 , the spring force F_F is still another parameter for the geometric definition of the throttle body  26  and of the first piston  9 . 
     The system pressure p_sys is adjusted such that it is always less than a maximum allowable system pressure, which in turn is equivalent to a pressure level at which an automatic valve opening ensues without actuation of the actuator unit  4 . 
     In FIG. 2, a variant embodiment of the exemplary embodiment shown in FIG. 1 is shown, in which for the sake of simplicity, functionally identical components are identified by the same reference numerals used in FIG.  1 . 
     Compared to the version of FIG. 1, in which the throttle body  26  is disposed essentially axially immovably in the hollow chamber  25  of the filling device  24 , here the throttle body  26  is disposed axially displaceably in the hollow chamber  25  by means of a spring device  32 . In the hollow chamber  25 , the throttle body  26  is displaced against a stop  33  on the high-pressure side by the spring force of the spring device  32  upon relief of the high-pressure region  17 . When high pressure p_R is applied, the throttle body  26  is displaced counter to the spring force of the spring device  32  and to the system pressure. The spring force and the dimensioning of the throttle body  26  are designed such that the throttle body  26 , with its end toward the system pressure that forms a control edge  34 , at least partly intersects the branching point of the system pressure line  28  if the system pressure p_sys drops impermissibly. The spring device  32  thus makes an automatic correction of the system pressure p_sys possible, as a function of the leakage via the pistons  9  and  11  resulting from temperature and positional factors. Specifically, as soon as the system pressure p_sys drops, the overlap of the control edge  34  and the branching point of the system pressure line  28  shortens the effective sealing length or leakage gap length along the throttle body  26 , and the leaks are compensated for. In this way, the system pressure p_sys can be kept constant in the hydraulic chamber. 
     Along with the function of the spring device  32  of forming a self-regulating system with the throttle body  26  that can react to pressure changes, that is, pressure losses in the system pressure region, the axial mobility of the throttle body  26  advantageously also assures that the gap  27  is automatically cleaned and does not become plugged with dirt particles contained in the fuel. 
     In both embodiments shown, the line  33  of the filling device  24  that branches off from the high-pressure region  17  communicates with the valve chamber  18 , in which the valve closing member  12  is movable between the valve seats  14  and  15 , and which can also be integrated with a high-pressure line. 
     In a departure from this, it is understood that it can also be provided that the line  33  leading away from the high-pressure region  17  can communicate with a high-pressure inlet from a high-pressure pump to the valve control chamber  2  or with other regions in the high-pressure region  17 , such as the valve control chamber or the outlet throttle  20 . 
     The fuel injection valve  1  of FIG. 1 or FIG. 2 functions as follows. 
     When there is no current to the piezoelectric actuator  4 , that is, in the closed state of the fuel injection valve  1 , the valve closing member  12  is pressed against the upper valve seat  14  assigned to it by the high pressure or rail pressure p_R and the spring  31 . 
     Upon slow actuation, for instance because of temperature-caused changes in length of the piezoelectric actuator  4  or other valve components, the first piston  9  upon an increase in temperature forces its way into the hydraulic chamber  13  and is retracted from it again upon a temperature drop, without this having any overall effects on the closing and opening position of the valve closing member  12  and of the fuel injection valve  1 . 
     To open the valve and thus for injection through the fuel injection valve  1 , the piezoelectric actuator  4  is acted upon by voltage, so that it suddenly expands axially. In the process, the piezoelectric actuator  4  is braced against the valve body  7  and builds up an opening pressure in the hydraulic chamber  13 . When the valve  1  is in equilibrium because of the system pressure p_sys in the hydraulic chamber  13 , the second piston  11  of the valve closing member  12  moves out of its upper valve seat  14  into a middle position between the two valve seats  14 ,  15 . At a high rail pressure p_R, a greater force is necessary to attain the equilibrium pressure on the side of the piezoelectric actuator. This greater force is brought to bear by the filling device  24 , in that at a high rail pressure p_R, the pressure p_sys in the hydraulic chamber  13  is increased accordingly as well. In this way, the piezoelectric force on the valve closing member  12  is increased, for the same voltage on the piezoelectric actuator  4 ; the increase in pressure is due to the system pressure p_sys and the diameter Al of the second piston  11 . This pressure increase is equivalent to a substantially higher voltage that would have to be applied to the piezoelectric actuator, and thus the force reserve gained can be utilized for instance to make the piezoelectric actuator smaller. 
     As soon as the valve closing member  12  has reached its lower valve seat  15  counter to the rail pressure p_R, the voltage to the piezoelectric actuator  4  is disrupted, whereupon the valve closing member  12  returns to its middle position, and another fuel injection takes place. At the same time, refilling of the hydraulic chamber  13  to the system pressure p_sys takes place via the filling device  23 . 
     The embodiments described each pertain to a so-called double-seat valve, but it is understood that the invention can also be applied to single-switching valves with only a single valve seat. 
     The foregoing relates to preferred exemplary embodiment 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.