Abstract:
A control valve for injectors of injection systems for internal combustion engines is proposed, in which the final control element is actuated by an actuator via a hydraulic booster.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE 00/03583 filed on Oct. 12, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a double-switching control valve for the injector of a fuel injection system for internal combustion engines, having a final control element actuated by an actuator, wherein the final control element and a bore of a housing form a radially defined annular chamber, which on its ends has a first recess and a second recess, and the final control element is axially displaceable by means of a tappet guided in a first guide bore and has both means for sealing off the annular chamber from the first recess and means for sealing of annular chamber from the second recess. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     The object of the invention is to furnish a double switching control valve for an injector of a fuel injection system which allows the metering of the tiniest preinjection quantities and which is constructed simply and compactly. 
     This object is attained according to the invention by a control valve for the injector of a fuel injection system for internal combustion engines, having a final control element actuated by an actuator, wherein the final control element and a bore of a housing form a radially defined annular chamber, which on its ends has a first recess and a second recess, and the final control element is axially displaceable by means of a tappet guided in a first guide bore and has both means for sealing off the annular chamber from the first recess and means for sealing off the annular chamber from the second recess, and wherein the tappet is actuated by the actuator by means of a hydraulic booster. 
     The control valve of the invention has the advantage that the hydraulic booster shortens the switching times. The control pressure of the injector builds up an initial tension counter to the actuation direction of the actuator, so that the hydraulic booster does not become operative until it has built up a suitable counterpressure and is already in motion. Because of the very short switching times, very small preinjection quantities can also be metered. In addition, the control valve of the invention is simple in construction and consequently compact. 
     Variants of the invention provide that the first recess is in communication with a fuel return, and that the second recess is in communication with a control chamber, so that the demand for driving energy for the actuator is only slight, since only during the preinjection does the actuator have to perform work counter to the hydraulic forces acting on the final control element. Furthermore, the actuator is subject only to pressure stress, which is especially advantageous when piezoelectric actuators are used. 
     In a feature of the invention, the face end, remote from the final control element, of the tappet and a piston actuated by the actuator define a fluid-filled pressure chamber of the hydraulic booster, so that the travel or force boosting is effected simply and with little loss. 
     Another variant provides that a closing spring is present, which acts on the final control element counter to the actuation direction of the actuator, so that even if pressure is absent in the control chamber, the control valve always has a defined switching position, and the sealing action in the switching position between the main injection and the preinjection is improved. 
     Further in the invention, it is provided that the closing spring is disposed in the second recess and is braced against a shoulder in the housing and against the final control element, so that the engineering effort and expense are low. In a further embodiment, the closing spring is disposed in a third recess, which adjoins the control chamber, and is braced via a thrust rod, guided in a second guide bore, against the final control element and a Seeger ring that is disposed in an annular groove in the third recess, so that the second recess and the diameter of the second sealing seat can be kept small. 
     In a further variant, it is provided that the closing spring is disposed in a third recess, which adjoins the control chamber, and is braced via a thrust rod, guided in a second guide bore, against the final control element and a control piston protruding into the control chamber, so that a closing spring with a low spring rate and a small diameter can be used. 
     In a further embodiment, the thrust rod has at least one longitudinally extending groove, longitudinal bore, or flat face extending essentially over the length of the thrust rod, so that a hydraulic communication exists between the control chamber and the second recess. Furthermore, by suitable dimensioning of the groove, longitudinal bore or flat face, the function of the outlet throttle can be integrated into the thrust rod. 
     In one version of the invention it is provided that the final control element has a collar disposed coaxially to the longitudinal axis of the tappet, and that the means for sealing off the annular chamber from the second recess and/or the means for sealing off the annular chamber from the first recess have a frustoconical sealing cone disposed coaxially to the longitudinal axis of the tappet, so that over the entire service life of the control valve, good sealing action is achieved. 
     Further in the invention, the second sealing cone is part of a sleeve disposed coaxially to the longitudinal axis of the final control element, facilitating assembly, and the sleeve is also centered by the tappet. 
     A variant provides that the end face of the sleeve toward the final control element is smooth, and that the end face of the final control element toward the sleeve is smooth, so that the sleeve is centered not by the control piston but rather by the second sealing seat, and the sealing cone of the sleeve rests in the best possible way on the sealing face in the housing. The aforementioned smooth end faces furthermore seal off the annular chamber from the control chamber. 
     In a further feature of the invention, it is provided that the end face of the sleeve toward the final control element and the end face of the final control element toward the sleeve are frustoconical, so that the sleeve is centered by the tappet. Furthermore, the aforementioned end faces seal the annular chamber off from the control chamber. 
     In a further feature of the invention, the sleeve is separably joined to the final control element, so that assembly is simplified and there is no need to split the housing. 
     Another variant provides that the final control element is embodied spherically, and that the means for sealing off the annular chamber from the second recess and/or the means for sealing off the annular chamber from the first recess are sealing lines extending over the spherical surface, so that an especially compact, simple construction is achieved. Furthermore, the first guide bore and the first and second sealing seat need not be precisely aligned, since the spherical valve member centers itself. 
     In addition, between the bore and both of the first and second recesses, sealing faces are embodied, which cooperate with the means for sealing off the annular chamber from the first recess and/or the means for sealing off the annular chamber from the second recess, so that a still further improved sealing is achieved. 
     Further in the invention, it is provided that the housing is embodied in one piece, so that the number of sealing faces is reduced. 
     In one embodiment of the invention, the control valve is operated as a 2/3-way control valve, so that the metering of the tiniest preinjection quantities is improved, and at the same time large main injection quantities become possible. 
     In a variant of the invention, the actuator is a piezoelectric actuator, so that major forces and a rapid response are assured. 
     Further in the invention, it is provided that the injection system is a common rail injection system, so that the advantages of the control valve of the invention also benefit these injection systems. 
     The object stated above is also attained by an injector for a fuel injection system for internal combustion engines, having a control chamber controlled by a control valve, wherein the control valve has a final control element actuated by an actuator, wherein the final control element and a bore of a housing form a radially defined annular chamber, which on its ends has a first recess and a second recess, and the final control element is axially displaceable by means of a tappet guided in a first guide bore and has both means for sealing off the annular chamber from the first recess and means for sealing off the annular chamber from the second recess, and wherein the tappet is actuated by the actuator by means of a hydraulic booster. 
     The control valve of the invention has the advantage of shortened switching times. The control pressure of the injector builds up an initial tension counter to the actuation direction of the actuator, so that the hydraulic booster does not become operative until it has built up a suitable counterpressure and is already in motion. Because of the very short switching times, very small preinjection quantities can also be metered. In addition, the control valve of the invention is simple in construction and consequently compact. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages and of the invention can be learned from the ensuing description, in conjunction with the drawing, in which: 
     FIG. 1 is a sectional view of an injector for a fuel injection system, with a control valve shown schematically; 
     FIG. 2 is a fragmentary sectional view of a first embodiment of a control valve of the invention; 
     FIG. 3 is a view similar to FIG. 2, showing a second embodiment of a control valve of the invention; 
     FIG. 4 is a view similar to FIGS. 2 and 3 and showing a third embodiment of a control valve of the invention and 
     FIG. 5 is a graph of the course over time of an injection. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, an injector of the invention is shown in which, via a high-pressure connection  1 , fuel is carried via an injector  5  to an injection nozzle  7  and via an inlet throttle  9  into a control chamber  11 . The control chamber  11  communicates with a fuel return  17  via an outlet conduit  12  and an outlet throttle  13 , which throttle can be opened by a control valve  15 . 
     The control chamber  11  is defined by a control piston  19 . Adjoining the piston  19  is a nozzle needle  21 , which prevents the fuel, which is under pressure, from flowing into the combustion chamber, not shown, between injections. The nozzle needle  21  has a cross-sectional change  23  from a large diameter  25  to a smaller diameter  27 . With its larger diameter  25 , the nozzle needle  21  is guided in a housing  29 . The cross-sectional change  23  defines a pressure chamber  31  of the injection nozzle  7 . 
     When the outlet throttle  13  is closed, the hydraulic force acting on an end face  33  of the valve piston  19  is greater than the hydraulic force acting on the cross-sectional change  23 , since the area of end face  33  of the the annular area of the cross-sectional change  23 . As a consequence, the nozzle needle  21  is pressed into a nozzle needle seat  35  and seals off the inlet conduit from the combustion chamber, not shown. 
     When the high-pressure pump, not shown, of the fuel injection system is not driven, which is because the engine is stopped, then a nozzle spring  39 , acting on a shoulder  37  of the nozzle needle  21 , closes the injection nozzle  7  or injector. 
     When the outlet throttle  13  or the control valve  15  is opened, the pressure in the control chamber  11  drops, and thus the hydraulic force acting on the end face  33  of the control piston  19  also drops. As soon as this hydraulic force is less than the hydraulic force acting on the cross-sectional change  23 , the nozzle needle  21  opens, so that the fuel can reach the combustion chamber through the injection ports, not shown. The indirect triggering of the nozzle needle  21  via a hydraulic force booster system is necessary since the forces required for fast opening of the nozzle needle  21  cannot be generated directly by the control valve  15 . The so-called “control quantity” required for this in addition to the fuel quantity injected into the combustion chamber reaches the fuel return  17  via the inlet throttle  9 , control chamber  11 , and control valve  15 . 
     In addition to the control quantity, leakage also occurs at the nozzle needle guide and the valve piston guide. The control and leakage quantities can amount to as much as 50 mm 3  per stroke. These quantities are returned to the fuel tank, not shown, again via the fuel return  17 . Between injections, the outlet throttle  13  is closed by the control valve. 
     FIG. 2 shows a first embodiment of a control valve of the invention. A bore  41  is provided in the housing  29 . There is a first guide bore  43  coaxial with the bore  41 . The bore  41 , on its ends, has a first recess  45  and a second recess  47 . The final control element  49  has a collar  50  and a first sealing cone  51  and a second sealing cone  53 . The bore  41  and the collar  50  form an annular chamber  54 . 
     A tappet  55  that is joined to the final control element  49  is guided in the first guide bore  43 . 
     The bore  41  has a smaller diameter than the first guide bore  43 . The transition between the tappet  55  and the collar  50  is formed by a truncated cone embodied as the first sealing cone  51 . Between the bore  41  and the first recess  45 , a first sealing seat  57  is embodied in the housing  29 ; with the first sealing cone  51 , this sealing seat can hydraulically disconnect the annular chamber  54  from the first recess  45 . The second sealing cone  53 , together with a second sealing seat  59  disposed between the bore  41  and the second recess  47  can disconnect the annular chamber  54  from the second recess  47 . 
     The second sealing cone  53  is part of a sleeve  61 . The sleeve  61  can be joined to the collar  50  via a weld seam  62  via a peg  63 . Alternatively, the sleeve  61  can be joined to the collar by screws or a groove in the peg  63  and by a Seeger ring. 
     In the embodiment shown, the end face of the collar  50  and a corresponding end face  67  of the sleeve  61  are frustoconical, so that the sleeve is centered. At the same time, sealing occurs between the sleeve  61  and the portion of the final control element  47  forming the annular chamber  54 . 
     Alternatively, especially if the sleeve  61  is screwed to the collar  50 , the sealing face can be smooth, so that the sleeve  61  is centered not by the collar  50  but by the second sealing seat  59 . This is made easier if there is play between the peg  63  and a center bore  65  of the sleeve  61 . 
     It can also be seen in FIG. 2 that the second recess communicates with the control chamber  11  via an outlet conduit  12  and an outlet throttle  13 , and that the first recess  45  communicates with the fuel return  17 . Alternatively, by suitable dimensioning, the annular chamber  54  can take over the function of the outlet throttle  13 . 
     The control valve is actuated by an actuator, not shown, that acts on the tappet  55  via a hydraulic booster  69 . The actuator is connected to a piston  71 , which exerts pressure on the fluid located in the pressure chamber  73  of the booster  69 . If the actuator is a piezoelectric actuator, then the actuator can exert major forces over a short distance. In this case, the configuration shown for the booster is appropriate, where the piston  71  has a larger diameter than the tappet  55 . If the actuator functions electromagnetically, for instance, then small forces can be transmitted over a long distance. In that case, it is recommended that the diameter of the piston  71  be selected as smaller than that of the tappet  55 . 
     A closing spring  75  disposed in the second recess  47  is braced on one side against a shoulder  77  of the housing  29  and on the other side against the sleeve  61 . By means of the closing spring  75 , it is assured that even if pressure is absent in the control chamber  11 , the final control element  49  will be moved into the first switching position a (FIG.  5 ). Furthermore, the actuator is subjected only to pressure stress, which is important especially when piezoelectric actuators are used, since such actuators function reliably only in response to pressure. 
     The control valve of the invention is used as a rule in the form of a 2/3-way control valve. In the first switching position a, the second recess  47  is hydraulically disconnected from the annular chamber  54 . In the second switching position b, the first recess  45  is hydraulically disconnected from the annular chamber  54 . 
     In both switching positions a and b, the control chamber  11  is disconnected from the fuel return  17 ; that is, the injection nozzle  7  is closed. At the transition from the first switching position a to the second switching position b, a hydraulic communication briefly exists between the control chamber  11  and the fuel return  17 ; that is, the pressure in the control chamber  11  at least partly collapses, and the injection nozzle  7  briefly opens. This brief opening is utilized for a preinjection. The preinjection quantity and duration can be fixed structurally with high replicability by means of the design of the actuator and the outlet throttle  13 , or annular chamber  54 . In the third switching position c, the final control element  49  assumes an intermediate position, in which the first and second sealing cones  51  and  53  do not rest on the first or second sealing seat  57 ,  59 . This switching position C trips the main injection. 
     In FIG. 3, a second embodiment of the invention is shown. Identical elements have been identified by the same reference numerals. Below, only the differences between the embodiments of FIGS. 2 and 3 will be addressed. 
     The final control element  49  comprises a ball  79 . Together with the first and second sealing seats  57  and  59 , this produces a first sealing line  81  and a second sealing line  83  on the ball  79 . The first sealing line  81  and second sealing line  83  can have different diameters from one another. The result is different hydraulic closing forces originating from the pressure in the control chamber  11 . If the tappet  55  and the final control element  49  are not solidly joined together, then the final control element  49  can center itself, regardless of whether the longitudinal axes of the first and second sealing cones  51  and  53  and of the first guide bore  43  coincide; as a result, the sealing action is always good, and the production cost drops. 
     The closing spring  75  is disposed in a third recess  85  that adjoins the control chamber  11 . The closing spring is braced on one side via a Seeger ring  87  and a disk  88  and on the other side via a thrust rod  91 , guided in a second guide bore  89  in the housing  29 , against the ball  79 . The Seeger ring  87  is in turn disposed in an annular groove  92  in the third recess  85 . To establish the hydraulic communication between the control chamber  11  or third recess  85 , and the second recess  47 , flat faces are present in the thrust rod  91 . Alternatively, grooves or bores, not shown, can also be provided in the thrust rod  91 . By suitable dimensioning of the flat faces, grooves or bores, these features can take over the function of the outlet throttle  13 . 
     FIG. 4 shows a further embodiment according to the invention, in which the closing spring  75  is braced on one side against the valve piston  19 . It can also be seen in FIG. 4 that the motion of the valve piston  19  in the direction of the control valve  15  is limited by a stroke stop  93  in such a way that a communication always exists between the inlet throttle  9  and the second recess  47 . 
     FIG. 5 shows the course over time of the stroke  95  of the nozzle needle  21 , as a function of the three switching positions a, b and c. In both graphs  5   a  and  5   b , the time t is plotted on the abscissa. The ordinate in graph  5   a  shows the switching positions a, b, and c of the control valve, while the ordinate in graph  5   b  shows the stroke  95  of the nozzle needle  21 . 
     Beginning at the first switching position a, the control valve  15  is moved by the actuator into the second switching position b. During the transition between the two switching positions, the nozzle needle  21  opens slightly. As a result, the preinjection quantity is injected into the combustion chamber. To increase the preinjection quantity, the control valve  15  can also briefly remain in the third switching position c during the preinjection. This variant is represented by the dashed lines. 
     The main injection effected by controlling the control valve to move from the second switching position b into the third switching position c. This switching position is maintained until such time as the requisite injection quantity has been injected. After that the main injection is terminated by moving the control valve into the first switching position a. This sequence also makes a further advantage of the control valve of the invention clear: The actuator has to perform work counter to the pressure in the control chamber  11  only at the transition from the first switching position a to the second switching position b, so that the demand for driving energy is very low. Furthermore, the dropping pressure in the control chamber during this transition leads to a low demand for performance. 
     The foregoing relates to 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.