Abstract:
The invention is based on a hydraulic control device ( 60 ), in particular for an injector ( 16 ) of a fuel injection system ( 10 ) in motor vehicles. Known control devices have a piezoelectric actuator, which controls a multi-position valve ( 75 ), embodied as an outward-opening valve with a valve member ( 74 ) guided in a valve bore ( 76 ). 
     According to the invention, it is proposed that a booster ( 62 ) that reverses the deflection motion of the actuator ( 52 ) be disposed between the actuator ( 52 ) and the valve member ( 74 ), and that the multi-position valve ( 75 ) be embodied as an inward-opening 3/2-way valve. The valve member ( 74 ) of this valve, in operative connection with a valve seat ( 98 ) and a control edge ( 96 ), alternatingly opens or closes pressure fluid connections between pressure fluid conduits ( 86, 88, 92 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 U.S.C. 371 application of PCT/DE 00/03590, filed on Oct. 12, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is based on a hydraulic control device for an injector of a fuel injection system in motor vehicles. 
     2. Description of the Prior Art 
     One hydraulic control device known from German Patent Disclosure DE 196 24 001 A1 comprises a piezoelectric actuator and a multi-position valve, controlled by the actuator, with a valve member guided displaceably in a valve bore. The multiposition valve is embodied as a conventional seat valve and controls a pressure fluid connection between a pressure fluid conduit, which carries fuel under high pressure, and a return line. In the non-triggered state of the actuator, the valve member is lifted from the valve seat and thus opens the aforementioned pressure fluid connection. As a result, the pressure level in an injection nozzle, also coupled to the pressure fluid conduit that carries high pressure, drops. Once the pressure drops below a mechanically specified opening pressure, a pressure-controlled closing element of the injection nozzle uncovers injection openings. Through these injection openings, fuel reaches a combustion chamber of an internal combustion engine. With the closure of the valve seat by an electrical triggering of the actuator, the injection event is terminated. 
     The pressure drop at the valve seat is in the same direction as the stroke motion of the valve member, so that the multi-position valve forms an outward opening or so-called A-valve. Outward-opening valves have fluid disadvantages, since the closing motion takes place counter to high pressure, and hence the actuator must be embodied as suitably powerful and voluminous. Furthermore, outward-opening valves are more expensive to produce. 
     SUMMARY OF THE INVENTION 
     The hydraulic control device of the invention has the advantage of being embodied as an inward-opening I-valve. In inward-opening valves, the pressure drop at the valve seat is oriented counter to the direction of motion of the valve member. As a result, upon opening of the multi-position valve, the stroke motion of the valve member is reinforced by an additional hydraulic force, so that actuators with lesser actuating forces suffice to control the valve. Such actuators are correspondingly smaller in size and more compact and require less electrical power. The load on the actuators thus drops, so that they function more robustly and reliably. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One exemplary embodiment of the invention is described in detail herein below, with reference to the drawings, in which: 
     FIG. 1 shows a fuel injection system with an outward-opening valve of the kind already known from the prior art, and 
     FIG. 2 shows the detail X of FIG. 1, on an enlarged scale, with an I-valve opening inward according to the invention, upstream of which is a hydraulic booster, and in which a force reversal takes place in the booster. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1, in a schematically simplified illustration, shows a fuel injection system  10 . This system comprises a driven pressure generator  12  and a pressure reservoir  14  coupled to it. The latter communicates with an injector  16 . An electronic control unit  18  is also present, which with the aid of a pressure sensor  20  and a pressure regulating valve  22  keeps the pressure in the pressure reservoir  14  constant. A plurality of injectors  16  can be connected to the pressure reservoir  14 , but in FIG. 1 for the sake of example only one of these injectors  16  is shown. 
     This injector  16  has a housing  24 , in whose interior  26  a needle  28  is disposed. With its tip, this needle controls injection openings  30 , which discharges into the combustion chamber of an internal combustion engine, not shown. The needle  28  is acted upon mechanically by a closing spring  32 , which is braced on the wall of the interior  26  and on a plate  34  embodied on the inner end of the needle  28 . Also acting on the plate  34  is a tappet  36 , disposed coaxially to the closing spring  32 . This tappet is guided in a cylindrical bore  38  of the housing  24 . The cylindrical bore  38  communicates hydraulically, via a tie line  40 , with a throttle  42  disposed in it, with the interior  26 , so that the tappet  36  can be relieved hydraulically. 
     A pressure fluid conduit  44  arriving from the pressure reservoir  14  supplies the interior  26  and the cylindrical bore  38  with fuel which is at high pressure. The pressure of this fuel, via the tappet  36 , puts a load on the needle  28 . Together with the force of the closing spring, the resultant force on the needle  28  suffices to keep it in the closing position, shown. 
     In addition, a tie line  46  discharging into a valve bore  48  branches off from the cylindrical bore  38 . A valve member  50  acted upon by a piezoelectric actuator  52  is guided in the valve bore  48 . The valve member, in the triggered state of the actuator  52 , closes a valve seat  54 , embodied at the point of discharge of the tie line  46  into the valve bore  48 , and thus interrupts a pressure fluid communication with a return line  56 , which likewise branches off from the valve bore  48 . Thus high pressure prevails in the interior  26  of the injector  16 . 
     With the withdrawal of the electrical triggering of the actuator  52 , the valve member  50  lifts from the valve seat  54  and opens the aforementioned pressure fluid connection. The high pressure in the injector thereupon builds up, and the hydraulic pressure force acting on the tappet  36  is eliminated. The mechanical pressure force exerted by the closing spring  32  does not by itself suffice to keep the needle  28  in its closing position. The needle  28  therefore opens and uncovers the injection openings  30 . 
     Upon re-triggering of the actuator  52 , the valve seat  54  is closed again by the valve member  50 , as a result of which high pressure builds up again in the interior  26  of the injector  16 . The accordingly hydraulically loaded needle  28  closes the injection openings  30  again and terminates the injection event. 
     When the valve seat  54  is open, the pressure drop is accordingly in the same direction as the stroke motion of the valve member  50 . Hence this valve member  50  forms an outward-opening valve. An injection event is initiated by withdrawal of the triggering of the actuator  52  and is terminated by the triggering of the actuator. The actuator  52  must close the valve member  50  counter to high pressure and must be embodied correspondingly powerfully. Along with the load on the actuator  52 , its structural volume is thus also increased. 
     To avoid these disadvantages, in FIG. 2 a control device  60  is proposed which is embodied as an inward-opening valve. This control device  60 , in which the actuator is represented only symbolically by a force arrow F, has a hydraulic booster  62 . This hydraulic booster comprises a cup-shaped first piston  64  and a second piston  66 , guided in its interior, of lesser pressure area. With their end faces, the pistons  64 ,  66  define a pressure-fluid-filled booster chamber  68 , which is located outside a hollow chamber  70  that is enclosed by the two pistons  64  and  66  and is ventilated to the outside. A closing spring  72  is accommodated in this hollow chamber  70  and is braced on the two pistons  64  and  66 . 
     The piston  66  is either connected to the valve member  74  of a multi-position valve  75  or embodied in one piece with such a valve member; the valve member  74  is guided displaceably in a valve bore  76 . This valve member  74  has a control head  78 , toward the booster  62 , which with increasing distance from the piston  66  changes over into a constriction  80  and then into a guide portion  82 . The guide portion  82  is provided with a flat face  84  on its outer circumference. The constriction  80  comprises a waist  81 , toward the control head  78 , and a cylindrical bore  83 , located adjacent the guide portion  82 , that has a smaller outer diameter than the valve bore  76 . 
     A pressure fluid conduit  86 , leading to an injection nozzle, not shown, branches off from the valve bore  76  in the region of the constriction  80 , while a fuel supply conduit  88  discharges into the valve bore  76  in the region of the control head  78 . An annular conduit  90  is also provided, in the form of a groovelike enlargement of the valve bore  76  in the region of the guide portion  82 . This conduit is connectable via the flat face  84  to a return line  92 , which branches off from a pressure chamber  94  embodied at the end of the valve bore  76 . 
     A control edge  96  of the valve member  74 , embodied at the transition from the constriction  80  to the guide portion  82 , controls a first control cross section  97  located between the pressure fluid conduit  86  and the return line  92 . This first control cross section  97  is open in its basic position, as shown in FIG.  2 . The injection nozzle, not visible in FIG. 2, is thus pressure-relieved. 
     The valve bore  76  is reduced in its outer diameter at the transition from the control head  78  to the constriction  80 . The resultant change in diameter is embodied as a chamfer, which functions as a valve seat  98 . This valve seat forms a second control cross section  99 , which is controllable by the control head  78  of the valve member  74  and which is closed in the basic position shown. 
     With the withdrawal of the triggering of the actuator  52 , the valve member  74  coupled to the piston  66  is imparted a stroke motion that is oriented counter to the deflection motion of the actuator  52 . The valve member  74  accordingly opens the first control cross section  99  and simultaneously, with its control edge  96 , closes the first control cross section  97 . The resultant pressure fluid connection between the fuel supply conduit  88  and the pressure fluid conduit  86  causes the injection nozzle to come under high pressure and assume its closing position. Accordingly, in the manner typical of an inward-opening valve, the flow of pressure fluid at the opened valve seat  98  is oriented counter to the stroke motion of the valve member  74 . 
     In the multi-position valve  75  described, the hydraulically operative faces of the valve seat  98  and of the guide portion  82  are designed as being equal in size. Thus in the basic position shown, a pressure equilibrium prevails at t he valve member  74 . Accordingly, the actuator must overcome only the contrary force of the closing spring  72  in order to put the valve member  74  in its closing position, and the actuator can accordingly be designed in compact form. If the valve member  74  is in the switching position, the hydraulic forces acting on the valve member  74  are essentially balanced by the contrary force of the closing spring  72 . Unlike an outward-opening valve (FIG.  1 ), an injection event takes place by triggering of the actuator  52 , and is terminated again by withdrawal of this triggering. 
     It is understood that changes or additions to the exemplary embodiment described are possible with out departing from the fundamental concept of the invention.