Abstract:
A valve for controlling fluids, having a piezoelectric actuator unit for actuating a valve member is proposed, which has at least one adjusting piston and at least one actuating piston that is guided in a valve body and actuates a valve closing body, which valve closing body cooperates with at least one valve seat embodied on the valve body and in the closing direction disconnects a control bore from an outlet chamber, from which a return conduit branches off, wherein between the adjusting piston and the actuating piston, a hydraulic chamber is disposed, which transmits a motion of the adjusting piston to the actuating piston. To keep the size of the actuator unit small, the actuating piston, at least when the valve closing body is closed, is supported essentially in a hydraulically force-balanced fashion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE02/1293 filed on Apr. 9, 2002. 
    
    
     FIELD OF THE INVENTION 
     The invention directed to an improved valve for controlling fluids and more particularly to a valve used in conjunction with a fuel injector for injecting fuel into the combustion chamber of an internal combustion engine. 
     DESCRIPTION OF THE PRIOR ART 
     A valve of the type with which this invention is concerned is known in the industry and is used for instance in conjunction with an injection valve, in particular an injection valve of a common rail injection system for Diesel internal combustion engines. An injection valve of this kind has a valve control piston, which forms a structural unit with a nozzle needle and is surrounded at least partly by a chamber which communicates via a fuel supply line with a high-pressure connection and contains fuel. The nozzle needle cooperates with a correspondingly embodied valve seat, so that depending on the position of the valve control piston, the fuel injection into the combustion chamber of the engine can be controlled via an opening in the injection valve leading to the combustion chamber. The position of the valve control piston and thus of the nozzle needle is fixed by means of the valve for controlling fluids described at the outset, which is In operative communication with the valve control piston via a so-called valve control chamber. 
     The valve control chamber is in operative communication via an inlet throttle with the fuel supply line and via a so-called outlet throttle with the valve mentioned at the outset, or so-called valve control module, and adjoins the free end, that is, the end remote from the nozzle needle, of the valve control piston. This design makes a purposeful pressure buildup and pressure reduction, tripped by the valve control module and described below, possible in the valve control chamber. 
     In the closing direction of the valve control module, which is embodied like a valve, the high pressure exerted via the inlet throttle, or in the case of a common rail injection system the so-called rail pressure, prevails in the valve control chamber. Under these pressure conditions, the valve control piston and thus the nozzle needle as well are in the closing direction. If the piezoelectric actuator unit, for instance, of the valve control module is then actuated, the valve closing body of the valve control module opens. As a result, the fuel located in the valve control chamber can flow out into a return conduit via a control bore and an outlet chamber that are associated with the valve control module; the pressure in the valve control chamber accordingly drops. As a result, the structural unit comprising the valve control piston and the nozzle needle is displaced in the direction of the valve control chamber, so that the opening leading to the combustion chamber is uncovered and fuel is injected into the combustion chamber. As soon as the valve closing body of the valve control module is returned to the closing direction again, the so-called rail pressure builds up again in the valve control chamber via the inlet throttle, and the valve control piston is thus moved back into the closing direction. As a result, the injection valve is tightly closed off from the combustion chamber, and no fuel reaches the combustion chamber. 
     BACKGROUND OF THE INVENTION 
     In the known injection valve of the type defined at the outset and described above, which is embodied for instance as a single-seat valve, there is the disadvantage that a high opening force is required to actuate the nozzle needle. Moreover, the refilling of the hydraulic chamber, which is always necessary because of leakage, proves complicated and expensive. 
     SUMMARY OF THE INVENTION 
     The valve of the invention in which the actuating piston, at least when the valve closing body is closed, is supported essentially in a hydraulically force-balanced fashion, has the advantage over the prior art that only considerably lesser forces are required to open the valve closing body. This is because—unlik in the valves of the prior art—the actuating piston need not be opened counter to the fluid pressure acting on the valve closing body, or in the case of a common rail injection system counter to the so-called rail pressure, which can be as high as 1.6 kbar. 
     It is hence possible to use piezoelectric actuators of a smaller size, which in turn leads to a reduction in the cost of the switching valve. Alternatively or in addition, the actuator, in particular a piezoelectric actuator, in the valve of the invention can also be triggered with a lower voltage, which in turn leads to a reduction in the energy required, compared to the valves of the prior art. 
     In an advantageous embodiment of the valve of the invention, the valve closing body is preferably a constituent part of the actuating piston. Advantageously, the actuating piston has an axial bore that branches off from the control chamber and extends through the actuating piston. This axial bore leads for instance from the control chamber, disposed upstream of the valve seat, to a chamber disposed on the opposite side of the actuating piston, so that in this chamber, at least when the valve closing body is closed, the pressure prevailing in the control chamber also prevails. 
     Advantageously, the axial bore is embodied as a stepped bore, and the region of increased diameter is embodied on the end of the actuating piston remote from the control chamber, and a guide pin is disposed in this region. This guide pin then defines the chamber which is located on the end remote from the control chamber of the actuating piston and in which the pressure prevailing in the control bore prevails. 
     To enable pressing the guide pin in a defined way against a wall of the valve body, this guide pin advantageously has a blind bore, which is located essentially in the axis of the axial bore of the actuating piston. 
     The actuating piston is embodied for instance as a stepped cylinder. The shoulder face of this stepped cylinder can then form the face of the actuating piston that is exposed to the pressure, exerted by the adjusting piston on the actuating piston by means of the hydraulic chamber. 
     The shoulder face can be oriented in such a way that the actuating piston moves in the direction away from the control bore when the actuator unit is actuated. 
     The actuating piston can be prestressed in the closing direction by means of a compression spring disposed in a spring chamber. The spring chamber can be in communication with the return conduit, so that the pressure prevailing in the return conduit is present in the spring chamber as well. 
     To assure, even when there is a different radial play of the adjusting piston and of the actuating piston, that the same pressure always prevails in the hydraulic chamber as in the spring chamber, the spring chamber can communicate via a pressure equalization conduit with an annular chamber, which is formed by an annular groove embodied on the circumference of the adjusting piston. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the valve of the invention are described more fully herein below, in conjunction with the drawings, in which: 
         FIG. 1 , a region relevant to the invention of an injection valve with a valve control unit of the invention, in longitudinal section; and 
         FIG. 2 , an alternative embodiment of an injection valve embodied according to the invention, in longitudinal section. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The exemplary embodiment shown in the drawings has a fuel injection valve  1 , which is intended for installation in an internal combustion engine, not shown, of a motor vehicle and is embodied here as a common rail injector for injecting preferably Diesel fuel. To that end, as its essential structural units, the fuel injection valve  1  includes a nozzle module  2  and a valve control module  3 . 
     The nozzle module  2  includes a nozzle body  4 , in which a so-called valve control piston  5  is disposed, which is in operative communication with, or forms a structural unit with, a nozzle needle, not shown here, which controls an opening of the injection valve  1  leading to a combustion chamber of the engine. 
     Also disposed in the nozzle module  2  is a spring plate  6 , in which the free end of the valve control piston  5  is guided and which together with the latter defines a valve control chamber  7 . The spring plate  6  is braced via a spring  8  on a support  9  that is connected to the valve control piston  5 . 
     A radially outward-oriented, so-called inlet throttle  10  is embodied in the spring plate  6 , or in its wall surrounding the receptacle for the valve control piston  5 , and this throttle leads from the valve control chamber  7  to a high-pressure chamber  11 , which is embodied between the outer contour of the spring plate  6  and the nozzle body  4  surrounding it and which communicates with a high-pressure reservoir, not shown here, or so-called common rail via a fuel supply line  12 . In the axial direction, the valve control chamber  7  is in communication, via a so-called outlet throttle  13 , with a control chamber  14  that is associated with the valve control module  3 . 
     The position of the valve control piston  5  and thus of the nozzle needle is controlled via the pressure level in the valve control chamber  7 . This level is adjusted in turn by means of the valve control module  3 . 
     The valve control module  3  includes a control module body  15 , in which a stepped actuating piston  16  is guided in a stepped bore  17 . Via a hydraulic chamber  18 , the actuating piston  16  is in operative communication with an adjusting piston  19 . The adjusting piston  19  can be disposed at any arbitrary place inside or outside the control module body  15 . It is actuated by means of an actuator unit  20 , here embodied as a piezoelectric actuator. 
     Via the compensation volume of the hydraulic chamber  18 , tolerances resulting from temperature gradients or different coefficients of temperature expansion of the materials used and possible settling effects can be compensated for, without a resultant change In the position of the actuating piston  16  to be triggered. The hydraulic chamber  18  here comprises a cylindrical chamber  21 , associated with the adjusting piston  19  and defining the free face end thereof, and also comprises a conduit  22  and an annular chamber  23 , surrounding the region of reduced diameter of the stepped actuating piston  16 . 
     On the end toward the control chamber  14 , the actuating piston  16  in the present exemplary embodiment is embodied as a valve closing body, which cooperates with a valve seat  24  and which in the closing direction disconnects the control chamber  14  from a so-called outlet chamber  25 , from which a fuel return conduit  26  branches off, leading to a fuel tank, not shown here. 
     A conduit  27  oriented axially and embodied for instance as a bore is disposed in the actuating piston  16 ; it leads from the control chamber  14  to the end, remote from the control chamber, of the actuating piston  16  and widens in bore or region  36  of increased diameter. 
     A guide pin  28  is disposed in the region  36  of increased diameter and has a blind bore  29  on the side toward the control chamber  14 . 
     The diameter d 1  of the guide pin  28  and thus also the diameter of the bore region  36  is essentially equivalent to the diameter d 2  of the valve seat  24 , or in other words to the sealing diameter of the region, embodied as a valve closing body, of the actuating piston  16 . The guide pin  28  is embodied such that it is guided with minimal play and a maximum guide length L in the bore region  36 . 
     On the face end of the actuating piston  16  remote from the nozzle module  2 , the nozzle module is engaged by a compression spring  30 , which is disposed on a spring chamber  31  and surrounds the guide pin  28  and is braced on a wall of the control body  151 . The spring chamber  31  communicates with the fuel return conduit  26  via a transverse conduit  32 . Downstream of the discharge point of the transverse conduit  32 , a pressure limiting valve  33  is disposed in the fuel return conduit  26 . 
     The injection valve described above functions as follows: 
     In the closed state of the fuel injection valve  1 , that is, when no voltage is applied to the piezoelectric actuator  20 , the region, embodied as a valve closing body, of the actuating piston  16  is located on the valve seat  24  assigned to it. In this state, via the inlet throttle  10  in the valve control chamber  7  and thus via the outlet throttle  13  in the control chamber  14 , the pressure prevailing in the high-pressure chamber  11  prevails, that is, in the present case the rail pressure. Via the bore  27 , this pressure is transmitted onward into the chamber of the bore region  36  located between the guide pin  28  and the actuating piston  16 . 
     The surface area of the free face end of the actuating piston  16  which is acted upon by the rail pressure and surrounds the orifice of the bore  27  corresponds to the surface area of the face, oriented parallel to it, of the actuating piston  16  that surrounds the orifice of the bore  27  into the bore region  36 . Thus the same hydraulic force acts on the actuating piston  16  on its opposite sides, so that the actuating piston is supported in a hydraulically force-balanced fashion. The closing direction of the actuating piston  16  is assured by means of the compression spring  30 , which exerts the requisite pressure on the actuating piston. 
     If the injection valve  1  is to be opened, or in other words if the injection nozzle, closed by means of the nozzle needle not shown here, is to be opened, a voltage is applied to the piezoelectric actuator  20 , whereupon the piezoelectric actuator expands abruptly in the axial direction, that is, in the direction of the adjusting piston  19 . The adjusting piston  19  is as a result displaced in the direction remote from the actuator  20 . This in turn, via the hydraulic chamber  18 , trips a displacement of the actuating piston  16 , specifically in such a way that the pressure, imparted by the adjusting piston  19  via the hydraulic chamber  18 , is exerted on the shoulder face  34  of the stepped actuating piston  16  and displaces it, counted to the pressure exerted by the compression spring  30 , in the direction remote from the control chamber  14 , thus establishing a communication between the control chamber  14  and the outlet chamber  25 . As a result, fuel located in the control chamber  14  flows into the outlet chamber  25  and from there into the fuel return conduit  26 . Via the outlet throttle  13 , the valve control chamber  7  is relieve as a result, so that the pressure in it diminishes, and the valve control piston  5  is displaced in the direction of the valve control module  3 . As a result, the opening leading to the combustion chamber of the engine is uncovered, so that fuel under high pressure that is located in the high-pressure chamber  11  is injected into the combustion chamber. 
     The fuel carried away via the fuel return conduit  26  flows back into the fuel tank once the pressure in the return conduit  26  exceeds a certain value, such as  30  bar. This means that this pressure is exerted into the spring chamber  31  and from there, via a leakage gap  38  surrounding the region of increased diameter of the actuating piston  16 , into the annular chamber  23 , the conduit  22 , and the cylindrical chamber  21 , so that filling of the hydraulic chamber  18  that may be necessary can take place at any time. 
     As already noted above, the guide pin  28  is guided with minimal play and a maximal guide length L in the bore  36  of the actuating piston  16 . The ratio between the diameter d 1  of the bore  36  and the sealing diameter d 2  determines the hydraulic force that is exerted on the actuating piston  16 . In the present case, this ratio is approximately equal to 1, so that the actuating piston  16  is supported in a hydraulically force-balanced manner. As a result, only a slight force, which can be exerted by means of the actuator  20 , is needed to displace the actuating piston  16  by means of the adjusting piston  19 . 
     If the voltage applied to the piezoelectric actuator  20  is interrupted, then the adjusting piston  19  is moved back again, and as a result the pressure prevailing in the hydraulic chamber  18  is reduced, and the actuating piston  16  is moved by the spring  30  in the direction of the nozzle module  2 , until it comes to rest in the valve seat  24 . As a result, the so-called rail pressure builds up again in the valve control chamber  7 , so that the valve control  5  and thus the nozzle needle are move back into the closing direction. 
     The exemplary embodiment of  FIG. 2 , in which for reasons of simplicity the same reference numerals as in  FIG. 1  are selected for functionally identical components, differs from that of  FIG. 1  in that the spring chamber  31  communicates, via a pressure equalization conduit  41 , with an annular chamber that is formed by an annular groove  40  of the adjusting piston  19 . 
     By means of the pressure equalization conduit  41 , it is assured that the same constant pressure as in the spring chamber  31  always prevails in the hydraulic chamber  21  as well. As a result, pressure differences that might occur because of the radial play of the actuating piston  16  in the stepped bore  17  and the radial play of the adjusting piston  19  in its guide bore are compensated for, so that constant loads on the piezoelectric actuator  20  always prevail, and variations in the injection quantities injected by means of the injection valve  1  are largely precluded. 
     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.