Abstract:
A fuel injector for a fuel injection system of an internal combustion engine is described. The fuel injector, has a fuel inlet connection piece for supplying fuel, a piezoelectric or magnetostrictive actuator, which is sealed off from the fuel by a seal, and a valve closing body actuatable by the actuator via a valve valve closing body working together with a valve seat surface to form a seal seat. The seal includes an inlet-side gasket, which is arranged between the fuel inlet connection piece and the actuator, and an actuator jacket that is elastically deformable in a longitudinal direction and is connected to the inlet-side gasket.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a fuel injector. 
     BACKGROUND INFORMATION 
     German Patent No. 195 34 445 describes a fuel injector. The fuel injector described in this document has a valve body in which a valve needle is coaxially guided. The valve body has a connection piece through which fuel is supplied to the fuel injector. The valve needle is provided with a central borehole. On the injection side the valve needle forms a seal seat with the valve body. The fuel is supplied to the seal seat via the central borehole of the valve needle. On the outside the valve needle is sealed with respect to the surrounding valve body. A piezoelectric actuator acts upon the valve needle via a pressure shoulder. The pressure shoulder is permanently connected to the valve needle and is tightly guided on the valve body on the inlet side. This protects the actuator against the effect of the fuel pressure. The conventional fuel injector has the following disadvantages: 
     Because the valve needle is permanently connected to the pressure shoulder, the valve needle on the injection side and the pressure shoulder on the inlet side are sealingly and movably guided in the valve body, therefore manufacturing is relatively complicated and the valve needle of the fuel injector is subject to bending and stresses and the relative positions of the two sliding surfaces are subject to modification. 
     Because the pressure shoulder, i.e., the valve needle is movably guided with respect to the valve body, the sealing surface is wetted with fuel and, due to the high fuel pressure, the fuel may flow toward the actuator. Thus the actuator is only protected against the effect of the fuel pressure but not against the effect of the fuel. Due to the seal between the pressure shoulder, i.e., the valve needle and valve body, friction losses occur when the fuel injector is actuated. This negatively affects the shapability of the fuel jet further, the switching times of the injector are increased, the actuator power is less efficiently utilized, and fuel injector wear is increased. In particular, the seal at the sealing surfaces between the pressure shoulder, i.e., the valve needle and the valve body deteriorates during operation. 
     Since the central borehole in the valve needle is a part of a fuel line extending from the fuel inlet connection piece to the seal seat, the manufacture of the valve needle is complicated and the fuel injector is subject to dirt deposits, in particular on its seal seat-side end. 
     SUMMARY 
     The fuel injector according to the present invention has the advantage over conventional fuel injectors of a simple, more cost-effective, low-wear, friction-free and considerably more compact design. Furthermore, the seal is independent of the design of the valve needle and can therefore be integrated into a plurality of fuel injectors. 
     In addition, the actuator sealed with respect to the fuel in this manner can be integrated using the seal, without major structural changes, both into an inward-opening and an outward-opening fuel injector. In addition, the actuator is protected by the seal both against the effect of the fuel and the effect of the fuel pressure. 
     The actuator jackets advantageously have an undulated or pleated design. This allows a large actuator stroke in the actuator housing in a compact construction. The actuator is advantageously prestressed by the actuator jacket. Additional components such as, for example, compression springs are not needed. A heat-conducting material, for example a heat-conducting paste, is advantageously provided between the actuator jacket and the actuator. This allows the energy generated by the actuation of the actuator and dissipated in the actuator to be conducted away from the actuator on the heat-conducting material and to the actuator housing. The heat load on the actuator is thus reduced and the service life of the fuel injector is extended. 
     The seal advantageously has a tubular sleeve that traverses the cutout of the actuator and is at least partially surrounded by the actuator. Thus, the inside of the tubular sleeve is sealed with respect to the actuator and therefore can be traversed by fuel. 
     The seal advantageously has a seal seat-side gasket that is connected to the actuator jacket and/or to the sleeve. Thus, the actuator can act upon the devices of the fuel injector and/or be supported by them via the seal seat-side gasket. In addition, the seal seat-side gasket can be designed like the inlet-side gasket which facilitates the manufacture of the seal. 
     The gaskets advantageously have a pot-shaped design whereby devices of the fuel injector can be accommodated within the gaskets. In addition, the gaskets can thereby be more easily guided in a guide. 
     Each gasket advantageously has a cutout that is traversed by the sleeve. The sleeve is bent back on at least one gasket and widened, and is connected to the gasket at its end facing away from the respective other gasket, allowing a large actuator stroke in the actuator housing. 
     At least one of the gaskets advantageously has a pot-shaped design and an end zone of the gasket projects over the bent-back zone of the sleeve, protecting the bent-back zone of the sleeve. 
     The inlet-side gasket advantageously has at least one supply channel through which at least one electrical lead is run to the actuator, allowing the electrical lead to enter the seal in a simple manner. 
     The supply channel is advantageously sealed with respect to the fuel, thus integrating the seal of the electrical lead with respect to the fuel into the gasket, making an additional seal is unnecessary and resulting in a more compact design. 
     The sleeve is advantageously part of a fuel line extending from the fuel inlet connection piece to the seal seat. This simplifies the fuel line in particular for an end-mounted fuel connection piece. In addition, no additional fuel line is needed, resulting in fewer components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a partial axial through section of a first embodiment of a fuel injector that has an inward-opening design according to the present invention. 
     FIG. 2 shows a partial axial through section of a second embodiment of a fuel injector that has an outward-opening design according to the present invention. 
     FIG. 3 shows an axial through section of an actuator that has a seal according to the present invention. 
     FIG. 4 shows an axial through section of a gasket according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows in a partial axial section a fuel injector  1  according to the present invention. Fuel injector  1  is used for direct injection of fuel, for example gasoline, into a combustion chamber of a compressed mixture, externally ignited internal combustion engine as a “direct gasoline injector.” Fuel injector  1  according to the present invention is also suitable for other applications. 
     Fuel injector  1  is designed as an inward-opening fuel injector  1 . Fuel injector  1  has a valve housing  3  and a fuel inlet connection piece  4 , representing the fuel inlet, which together form the housing of fuel injector  1 . A valve closing body  6 , which in the embodiment illustrated is designed in one piece with a valve needle and which can be actuated by valve needle  5 , is located in valve housing  3 . Valve closing body  6  has a truncated cone shaped tapering in the direction of injection. Valve closing body  6  works together with a valve seat surface  8  formed on a valve seat body  7  to form a seal seat. Valve needle  5  is guided in its axial movement by valve needle guides  9 ,  10 , which are attached to valve housing  3 . In order to allow fuel to flow through, valve needle guides  9 ,  10  have slot-shaped cutouts  11 ,  12 . 
     An actuator  13 , which has a piezoelectric or magnetostrictive design, is used to actuate fuel injector  1 . Actuator  13  is actuated by an electrical control signal, supplied to actuator  13  by an electrical lead, which is not shown in this embodiment for the sake of simplicity. When actuator  13  is actuated, it expands and acts upon baseplate  15 , to which valve needle  5  is attached, via an inlet-side gasket  14 . Actuator  13  is supported by valve housing  3  via a seal seat-side gasket  16 . Thus valve needle  5  is moved in the axial direction onto fuel inlet connection piece  4 , whereby valve closing body  6  is lifted from valve seat surface  8  of valve seat body  7 , exposing the seal seat. Due to the gap formed between valve closing body  6  and valve seat body  7 , fuel exits from a fuel chamber  17  of fuel injector  1  into the combustion chamber of the internal combustion engine. Valve needle  5  is reset in this embodiment via a compression spring  18 , supported on one side by baseplate  15  and on the other side by fuel inlet connection piece  4 . 
     Valve housing  3 , fuel inlet connection piece  4 , baseplate  15 , inlet-side gasket  14  and seal seat-side gasket  16  are attached to one another via welds  19   a  through  19   f.  However, they can also be attached in some other fashion. 
     An actuator jacket  20  and a sleeve  21  are attached to inlet-side gasket  14  and seal seat-side gasket  16 . Actuator jacket  20  is permanently connected to inlet-side gasket  14  by a peripheral weld  22  and to seal seat-side gasket  16  by a peripheral weld  23 . The joint may, however, also be of a different kind, including a detachable joint. Inlet-side gasket  14  and seal seat-side gasket  16  have internal cutouts  24 ,  25 , traversed by sleeve  21 . Sleeve  21  is widened and bent back on inlet-side gasket  14  in a bent-back zone  39 , and is connected to one end face  37  of inlet-side gasket  14  at a peripheral weld  26  and to seal seat-side gasket  16  at a peripheral weld  27 . Inlet-side gasket  14  has an end zone  38  at which inlet-side gasket  14  is connected to baseplate  15 . Edge zone  38  of inlet-side gasket  14  projects over a bent-back zone  39  of sleeve  21 . Sleeve  21  widened and bent back on inlet-side gasket  14  can be moved in the direction of fuel inlet connection piece  4  due to the pot-shaped design of inlet-side gasket  14  as actuator  13  expands, the seal of actuator  13  remaining with respect to the fuel due to seals  14 ,  16 ,  20 ,  21 . For the same reason, actuator jacket  20  has an undulated or pleated design. Actuator  13  can be prestressed by actuator jacket  20  so that compression spring  18  is no longer necessary. 
     Fuel is supplied into a fuel chamber  17  by fuel inlet connection piece  4 , through boreholes  28   a,    28   b  in baseplate  15 , and through an internal longitudinal opening  31  in sleeve  21 , through which valve needle  5  also extends. Fuel can also be conducted, as an alternative, through internal space  29  of valve housing  3 , in which case appropriate through openings are provided in seal seat-side gasket  16 . 
     A heat-conducting material, for example a heat-conducting paste, can be introduced in a gap  30  between actuator jacket  20  and actuator  13 , whereby the heat of actuator  13  is conducted to valve housing  3  via heat-conducting paste in gap  30  and via seal seat-side gasket  16 . In a similar manner, the space between actuator  13  and sleeve  21  can also be filled with a heat-conducting paste in order to transmit heat to the fuel. 
     FIG. 2 shows in a partial axial section of a second embodiment of fuel injector  1  according to the present invention. Elements described previously are provided with the same reference symbols, making repetition of the description unnecessary. 
     The second embodiment of fuel injector  1  is an outward-opening fuel injector  1 . Pot-shaped, inlet-side gasket  14  is supported by fuel inlet connection piece  4 , so that when actuator  13  is actuated, the latter expands in the direction of the seal seat and acts upon valve needle  5  via seal seat-side gasket  16  and baseplate  15 , whereby truncated cone-shaped valve closing body  6 , widening in the direction of injection and designed in one piece with valve needle  5 , is lifted from valve seat surface  8  of valve seat body  7  exposing the seal seat. Valve closing body  6  is pressed against valve seat surface  8  of valve seat body  7  via compression spring  18  supported on one side by valve housing  3  and on the other side by baseplate  15 . As described with reference to the embodiment illustrated in FIG. 1, the function of compression spring  18  can be assumed fully or in part by actuator jacket  20 . 
     The electrical leads can be run to actuator  13  via supply channels  32  and  33  in fuel inlet connection piece  4 , i.e., in gasket  14 . Supply channels  32 ,  33  may also be used for de-aerating seal  14 ,  16 ,  20 ,  21  or to remove leakage fluid from seal  14 ,  16 ,  20 ,  21 . Fuel flows toward the seal seat via longitudinal opening  31  and boreholes  28   a,    28   b  in baseplate  15 . As in the embodiment illustrated in FIG. 1, a heat-conducting material, for example a heat-conducting paste, can be introduced in gap  30  between actuator jacket  20  and actuator  13  and/or between sleeve  21  and actuator  13 . 
     FIG. 3 shows in the sectional view a further embodiment of seal  14 ,  16 ,  20  of actuator  13 . Actuator jacket  20  is welded to inlet-side gasket  14  and seal seat-side gasket  16  via peripheral welds  22  and  23 , respectively. Actuator  13  is located between the two pot-shaped gaskets  14 ,  16 . A supply channel  33  for accommodating an electrical lead leading to actuator  13  is provided in inlet-side gasket  14 . Supply channel  33  may, however, also be provided in seal seat-side gasket  16 . In this embodiment sleeve  21  is not used; therefore actuator  13  is designed without internal longitudinal opening  31 . Fuel is therefore supplied outside actuator jacket  20 . 
     FIG. 4 shows, in a sectional view, a further embodiment of inlet-side gasket  14 . In this embodiment, supply channel  33  is designed with a bend, with supply channel  33  opening at peripheral surface  35  of inlet-side gasket  14 . Inlet-side gasket  14  can be attached to the internal wall of valve housing  3  via peripheral surface  35 , for example by welding. Thus the electrical lead can be run via a terminal provided in valve housing  3  from the side of fuel injector  1  through supply channel  33  to actuator  13 . The opening of supply channel  33  at peripheral surface  35  must be sealed with respect to the fuel in order to prevent fuel from entering. A weld running around the opening between peripheral surface  35  and valve housing  3  is particularly well-suited for this purpose. Actuator jacket  20  may be attached to lower peripheral surface  36  of inlet-side gasket  14 , which has a smaller diameter than upper peripheral surface  35 . The above-described design of inlet-side gasket  14  is also suitable for seal seat-side gasket  16  without restrictions. 
     In order to make supply of fuel possible in the embodiment illustrated in FIG. 4, gasket  14  has a fuel channel  40 . As an alternative, gasket  14  can be provided with a cutout  24  as shown in FIG.  1 . 
     The present invention is not restricted to the embodiments described. In particular, a different design of actuator jacket  20 , sleeve  21 , bent-back zone  39  of sleeve  21 , and the two gaskets  14 ,  16  is possible. Furthermore, the action of actuator  13  on valve needle  5  in FIGS. 1 and 2 is illustrated in a simplified manner and should not limit the present invention in this respect. In particular, the present invention is characterized by the possibility of using seal  14 ,  16 ,  20 ,  21  in a plurality of fuel injectors  1 .