Patent Publication Number: US-6340015-B1

Title: Fuel injection valve with integrated spark plug

Description:
FIELD OF THE INVENTION 
     The present invention concerns a fuel injection valve having an integrated sparkplug. 
     BACKGROUND INFORMATION 
     A fuel injection valve having an integrated sparkplug for direct injection of fuel into the combustion chamber of an internal combustion engine and for igniting the fuel injected into the combustion chamber is discussed in from German Published Patent Application No. 196 38 025. With this fuel injection valve having an integrated sparkplug, a valve closing body that opens on the outside works together with a valve body to form a seal seat. The valve closing body is designed in one piece with a valve needle extending into the interior of the sleeve-shaped valve body. The valve needle is guided through the valve closing body on one end and through a guide ring provided at the inlet on the other end. The valve body can receive an electrical high voltage over a high-voltage cable and it has an ignition electrode on its spray end. The valve body is surrounded radially by a ceramic insulating body which is in turn surrounded by a metal housing body having another ignition electrode. The valve needle and the valve closing body, which is designed in one piece with the valve needle, are actuated in the opening direction by an armature working together with a solenoid. The armature acts by way of a tappet on an insulating spacer which is in contact with the guide ring of the valve needle. 
     One disadvantage of this design of a fuel injection valve having an integrated sparkplug is that the valve needle does not have a high-voltage insulating element. Therefore, the insulation is provided by the aforementioned spacer, which is connected to the valve needle only in a non-positive manner but not in a positive manner. Therefore, this design is suitable only for externally opening fuel injection valves. Since only an opening force can be transmitted via the spacer to the valve closing body but no closing force can be transmitted via the valve needle to the valve closing body, a valve closing spring must be integrated into the valve body to produce the closing force. It is believed that this leads to a relatively complicated design and thus to relatively high manufacturing and assembly costs. 
     Another fuel injection valve having an integrated sparkplug is discussed in European Published Patent Application No. 0 661 446. Again with this fuel injection valve having an integrated sparkplug, no insulating element is provided in the valve needle. Instead, the high voltage is supplied via the valve needle, which is insulated radially on the outside by complicated insulating bodies extending in the feed direction. With this unfavorable design, a total of four insulating bodies are necessary, leading to high manufacturing and assembly costs. 
     SUMMARY OF THE INVENTION 
     The fuel injection valve having an integrated sparkplug an exemplary embodiment of the present invention has the advantage that an insulating section which provides insulation in the axial direction is integrated into the valve needle, separating the two metal guide sections from one another. The magnetic needle is guided through the metal guide sections which may be made of hardened steel, for example, and therefore permit precision manufacturing and their surfaces have a low coefficient of friction. A first guide section is arranged on the spray end and may be designed in one piece with the valve closing body. The second metal guide section is arranged on the inlet end with regard to the insulating section arranged between the guide sections and is guided in the insulating body. The guide sections having the insulating section are also connected in a positive manner as well as in a non-positive manner, so that force can be transmitted via the valve needle in the opening direction as well as the closing direction. Therefore, it is not necessary to integrate a restoring spring inside the valve body. This yields a simple design which can be produced at a low manufacturing and assembly cost. The insulating body can be manufactured as an injection molded ceramic part at a low manufacturing cost. Since the insulating section is responsible only for the insulation and not for guidance of the valve needle, it is believed that no particularly high demands are made of the manufacturing accuracy and abrasion resistance of the insulating section. 
     The fuel injection valve an exemplary embodiment of the present invention having an integrated sparkplug has the advantage that the valve needle designed as a one-piece ceramic part with the valve closing body can be designed to be especially short, because no metal parts are used and the total length of the valve needle functions as an insulating path. Shortening the valve needle yields a definite reduction in weight, which in turn leads to relatively short switching times. 
     It is advantageous to design the insulating section of the valve needle as a ceramic sleeve body, because an especially low weight, and thus a short switching time, is obtained because of the material saved when the insulating section is designed as a sleeve body. The connection between the guide sections and the insulating section is preferably by way of connecting pins which engage in corresponding recesses. The connection can be accomplished by friction flow, gluing or even in part by shrink fit. 
     If the valve needle and the valve closing body are designed as a one-piece ceramic part, the valve closing body is preferably spherical or partially spherical in shape to prevent material from splintering out in the seat area. 
     The insulating body preferably has a recess at the side through which a high-voltage cable is guided to the valve body and is electrically connected to it. It is advantageous to fill the recess with a casting compound which provides electrical insulation, because this yields especially good protection of the welded or soldered junction of the high-voltage cable with the valve body. It may be especially advantageous for an electric burn-off resistor or an insulating film with high-voltage strength to be cast in the casting compound to improve insulation of the solder joint or weld. 
     One embodiment of the present invention is illustrated in simplified form in the drawing and explained in greater detail in the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The FIGURE shows a cross-section of a fuel injection valve having an integrated sparkplug according to an exemplary embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     The FIGURE shows a fuel injection valve having an integrated sparkplug for direct injection of fuel into a combustion chamber of an internal combustion engine with compression of a mixture and spark ignition and for igniting the fuel injected into the combustion chamber according to an exemplary embodiment of the present invention. 
     The fuel injection valve having an integrated sparkplug and labeled with reference number  1  in general has a first housing body  2 , which can be screwed into a receiving bore of a cylinder head (not shown) by a thread  3 , and also has a second housing body  4  and a third housing body  5 . The metal housing formed by housing bodies  2 ,  4 ,  5  surrounds an insulating body  6  which in turn surrounds radially on the outside a valve body  7  and at least partially a swirl insert  14  and a valve needle  9  extending in the interior of swirl insert  14  beyond inlet end  8  of valve body  7 . Valve needle  9  is connected at the spray end to conical valve closing body  10  which together with an inside conical face on spray end  11  of valve body  7  forms a seal seat. In the embodiment illustrated here, valve needle  9  and valve closing body  10  are designed in one piece. When valve closing body  10  is lifted up from the valve seating face of valve body  7 , valve closing body  10  releases an outlet opening  12  formed in valve body  7 , so that a conical spray jet indicated by line  13  is sprayed out. For a better peripheral distribution of fuel, at least one swirl groove  14   a  is provided in swirl insert  14  in the embodiment illustrated here. 
     First ignition electrodes  15  are provided on first housing body  2  and work together with second ignition electrodes  16  provided on valve body  7  to generate an ignition spark. In the embodiment shown here, ignition electrodes  15 ,  16  are designed as partially parallel finger electrodes. A first ignition electrode  15  and a second ignition electrode  16  are arranged opposite one another in alternation at a predetermined electrode spacing. First ignition electrodes  15  carry ground potential, while second electrodes  16  can receive a high voltage. The lengths of ignition electrodes  15  and  16  are to be adapted to the beam angle and form of fuel jet  13 . Ignition electrodes  15 ,  16  may be immersed in fuel jet  13  or fuel jet  13  may pass by ignition electrodes  15 ,  16  at a slight distance, without ignition electrodes  15 ,  16  being wetted by the fuel. Immersion of ignition electrodes  15 ,  16  in gaps between individual jets produced by one or more outlet openings  12  is also conceivable. 
     Valve body  7  is preferably designed in two parts, a first body part  7   a and a second body part  7   b  that are welded together at weld  17  to accommodate swirl insert  14 . 
     According to an exemplary embodiment of the present invention, valve needle  9  is divided into a first metal guide section  9   a  on the spray end, a second metal guide section  9   b  on the inlet end and a ceramic insulating section  9   c  which is sleeve-shaped in this embodiment. First guide section  9   a  is guided in swirl insert  14  mounted concentrically to valve body  7 . A second guidance of valve needle  9  is accomplished by second guide section  9   b  in insulating body  6 . To do so, lateral surface  19  of second guide section  9   b  works together with a bore  20  in insulating body  6 . Guide sections  9   a  and  9   b  which provide guidance are designed as metal parts and can be produced with the manufacturing accuracy required for the guidance. Because of the low surface roughness of the metal parts, there is only a low coefficient of friction on the guides. Insulating section  9   c , however, may be produced as an injection molded ceramic part. Since insulating section  9   c  does not provide guidance for valve needle  9 , low demands are made regarding the dimensional accuracy and surface roughness. Therefore, no reworking of the injection molded ceramic part is necessary. 
     According to an exemplary embodiment of the present invention, guide sections  9   a  and  9   b  are joined to insulating section  9   c  by both positive and non-positive methods. In the embodiment illustrated here, guide sections  9   a  and  9   b  each have a pin  21  and  22 , respectively, inserted into a recess in insulating section  9   c  designed as a bore  23 . Preferably a connection is established between pins  21  and  22  and guide sections  9   a  and  9   b  by frictional engagement, gluing or to some extent even by shrink fitting. For a shrink-fit connection, it is advantageous if guide section  9   b  has a recess into which a pin of insulating section  9   c  can be inserted, in another exemplary embodiment shown here. Metal guide section  9   b  may then be heated before shrinkage, and the pin of insulating section  9   c  can be inserted into the recess when this guide section has been heated. When guide section  9   b  cools, it contracts, yielding a tight connection to insulating section  9   c.    
     Insulating section  9   c  is preferably designed in the form of a sleeve. Weight is saved due to the material saved in comparison with a solid body, thus resulting in shorter switching times of fuel injection valve  1 . 
     According to an another exemplary embodiment not shown here, it is also possible to design valve needle  9  and valve closing body  10  as a one-piece ceramic part. Valve needle  9  may then be designed shorter in comparison with the exemplary embodiment shown in the figure because valve needle  9  has insulating properties over its entire length. This yields weight savings for valve needle  9 , leading to shorter switching times. If valve needle  9  and valve closing body  10  are designed as a one-piece ceramic part, it is advantageous if valve closing body  10  is spherical or partially spherical to prevent material from splintering out at the seal seat. 
     Silicon nitride or zirconium oxide is suitable for achieving an especially low weight for insulating section  9   c  and for valve needle  9  with valve closing body  10 , which are designed as a one-piece ceramic part according to the alternative embodiment. 
     Second guide section  9   b  is connected to an armature  24  which works together with a solenoid  25  for electromagnetic operation of valve closing body  10 . A cable  26  is used to supply electric current to solenoid  25 . A field spool  27  accommodates solenoid  25 . A sleeve-shaped core  28  passes at least partially through solenoid  25  and is a distance away from armature  24  due to a gap (not shown in the Figure) in the closed position of the fuel injection valve. The magnetic flux circuit is closed by ferromagnetic parts  29  and  30 . Fuel flows through a fuel inlet connection  31 , which can be connected by a thread  32  to a fuel distributor (not shown), and into the fuel injection valve  1  having an integrated sparkplug. Fuel flows first through a fuel filter  33  and then into a longitudinal bore  34  in core  28 . An adjusting sleeve  36 , which has a hollow bore  35  and can be screwed into longitudinal bore  34  of core  28 , is provided in longitudinal bore  34 . Adjusting sleeve  36  is used to adjust the initial tension of a restoring spring  37  which acts on armature  24  in the closing direction. A locking sleeve  38  secures the adjustment of adjusting sleeve  36 . 
     Fuel flows further through a longitudinal bore  39  into second guide section  9   b  of valve needle  9  and enters a hollow space  41  of insulating body  6  at an axial recess  40 . Fuel flows from there into a longitudinal bore  42  of valve body  7  through which valve needle  9  also extends, and ultimately the fuel reaches swirl groove  14   a  of swirl insert  14  described above. 
     As described above, first ignition electrodes  15  connected to housing body  2  carry ground potential while second ignition electrodes  16  connected to valve body  7  carry a high voltage to generate ignition sparks. A high-voltage cable  50  which is inserted into insulating body  6  through a pocket-like recess  51  at the side supplies the high voltage. Bare end  52  of high-voltage cable  50  is soldered or welded to a contact clip  54  at a solder junction or weld  53 . Contact clip  54  clamps valve body  7  and establishes a secure electrical contact between bare end  52  of high-voltage cable  50  and valve body  7 . For better accessibility of solder junction or weld  53 , insulating body  6  has a radial bore  55  through which a soldering or welding tool can be guided to the solder junction or weld  53 . After establishing the soldered or welded connection, pocket-like recess  51  is filled with a casting compound  56  which provides electrical insulation. A burn-off resistor  57  integrated into high-voltage cable  50  may also be cast in casting compound  56 . For improved insulation of solder junction or weld  53 , a film  58  having high-voltage strength may be inserted into pocket-like recess  51  of insulating body  6  and also cast with casting compound  56 . Silicone, for example, is suitable for use as casting compound  56 . 
     Insulating body  6  and valve body  7  may be screwed together by a thread  60 . Furthermore, insulating body  6  may be screwed to housing body  2  with another thread  61 . Thread  60  and  61  are preferably secured with a suitable adhesive, although in the exemplary embodiment of the present invention, the adhesive does not come into direct contact with the fuel. Insulating body  6  may be manufactured inexpensively as an injection molded ceramic part. Valve body  7  and insulating body  6  may be screwed and glued to an assembly mandrel to compensate for alignment errors in the guidance of valve needle  9 . 
     The spatially close arrangement of burn-off resistor  57  to ignition electrodes  15 ,  16  reduces the burn-off of ignition electrodes  15 ,  16  and allows a solid metal jacketing of fuel injection valve  1  having an integrated sparkplug by metal housing bodies  2 ,  4  and  5 , despite an increased electric capacitance between ignition electrodes  15 ,  16 .