Abstract:
Known fuel injectors have a valve housing in which an actuator and an hydraulic coupler are arranged, an electrical plug being provided on the valve housing for contact with a voltage source. The cables running from the plug to the actuator must be guided around the coupler to the actuator. It is disadvantageous that the compensating movements put heavy mechanical stress on the cables, so that a cable fracture as a result of material fatigue occurs after a predefined service life of the fuel injector, or that the solder or welding points of the cables tear. This leads to malfunctioning of the fuel injector. In the present fuel injector, the service life is increased by the provision of connections without cables. The earth pole of the actuator is electrically connected to the ground terminal of the plug in a cable-less manner, and the positive pole of the actuator is electrically connected to the positive terminal in a cable-less manner.

Description:
BACKGROUND INFORMATION  
       [0001]     A fuel injector having a valve housing in which a piezoelectric armature and an hydraulic coupler are arranged has already been proposed in German Patent Application No. 103 60 449, the piezoelectric actuator having a positive pole and an earth pole, an electrical plug with a positive terminal and a ground terminal being provided on the valve housing for the contacting with a voltage source. Via a cable in each case, the positive pole of the piezoelectric actuator is connected to the positive terminal of the plug, and the earth pole of the piezoelectric actuator is connected to the ground terminal of the plug. Since the hydraulic coupler between the valve housing and the actuator is arranged in a section of the fuel injector that faces the plug, the cables originating from the plug must be guided around the coupler to reach the actuator. Due to the fact that the hydraulic coupler executes thermally caused compensating movements, the cables cannot be taut, but must be non-tensioned by providing additional length. The cables are not allowed to be in contact with adjacent components, since the many compensating movements may otherwise cause them to fray over time. It is disadvantageous that the compensating movements put heavy mechanical stress on the cables, so that a cable fracture as a result of material fatigue will occur after a predefined service life of the fuel injector, or the solder or welding points of the cables will tear. This leads to malfunctioning of the fuel injector.  
       SUMMARY OF THE INVENTION  
       [0002]     The fuel injector according to the present invention has the advantage that an improvement is achieved in a simple manner to the effect that the service life of the fuel injector is increased in that the earth pole of the actuator is electrically connected to the ground terminal of the plug, and the positive pole of the actuator is connected to the positive terminal in a cable-less manner. This prevents malfunctioning of the fuel injector due to a cable fracture. Since two cables are omitted, space is saved, so that the fuel injector is able to have a smaller design.  
         [0003]     It is particularly advantageous if the earth pole of the actuator is electrically connected to the ground terminal of the plug via the valve housing and/or an actuator housing, since this utilizes an already existing electrically conductive connection in the fuel injector. Furthermore, the ground contacting of the actuator reduces electromagnetic interference radiation of the actuator.  
         [0004]     In addition, it is advantageous if the positive pole of the actuator is electrically connected to the positive terminal by way of the hydraulic coupler, since in this way the current supply to the actuator is implemented via an existing electrically conductive connection.  
         [0005]     According to an advantageous further development, the actuator is prestressed for compression in an actuator sleeve between an actuator top and an actuator base, and the earth pole of the actuator is electrically contacted to the actuator top, the actuator top being electrically connected to the actuator base via the actuator sleeve. The actuator base is electrically connected to the valve housing and/or the actuator housing via a valve needle, a shoulder of the valve needle and a restoring spring cooperating with the valve needle.  
         [0006]     Furthermore, it is advantageous if the positive terminal of the plug is electrically connected to a head part of the hydraulic coupler, and the positive pole of the actuator is electrically connected to a foot part of the hydraulic coupler, the head part and the foot part of the hydraulic coupler in turn being interconnected in an electrically conducting manner via an elastic sealing element. This allows the current to be supplied by way of the hydraulic coupler.  
         [0007]     It is advantageous if a first electrical insulation is provided between the hydraulic coupler and the actuator, and a second electrical insulation is provided between the hydraulic coupler and the valve housing since this prevents a short circuit. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0008]     The FIGURE shows an exemplary embodiment of a fuel injector according to the present invention in a schematic representation.  
     
    
     DETAILED DESCRIPTION  
       [0009]     The fuel injector is used in the so-called direct injection, for instance, and injects fuel such as gasoline or diesel into a combustion chamber of an internal combustion engine.  
         [0010]     The fuel injector has a valve housing  1  with an input port  2  for the fuel. The valve housing includes a housing component  1 . 1  in the shape of a cup, for instance, and a housing lid  1 . 2  sealing cup-shaped housing component  1 . 1 . Input port  2  is provided in housing lid  1 . 2 , for example.  
         [0011]     A schematically illustrated actuator  3  such as a piezoelectric or magneto-restrictive actuator is arranged in valve housing  1  for the axial adjustment of a valve needle  4 .  
         [0012]     Valve needle  4  is provided in valve housing  1  so as to be axially displaceable, and has, for instance, a needle shaft  7  facing actuator  3 , and a valve-closure member  8  facing away from actuator  3 . Actuator  3  transmits its movement to needle shaft  7  of valve needle  4 , which causes valve-closure member  8  cooperating with a valve seat  9  to open or close the fuel injector. The fuel injector is a so-called outwardly opening valve, for instance, valve needle  4  executing a lift in the direction of a combustion chamber  10 . When the fuel injector is closed, the entire circumference of valve-closure member  8  rests sealingly against valve seat  9  with line and surface contact, forming a sealing seat  11 .  
         [0013]     Piezoelectric actuator  3  is made up of a multitude of piezo-ceramic layers, which expand in the axial direction when an electrical voltage is applied. In the process, the so-called inverse piezoelectric effect is utilized in which electrical energy is converted into mechanical energy. The expansion of the piezo-ceramic layers caused by the application of the electrical voltage is transmitted to valve needle  4 , valve needle  4  executing a lift of 40 to 50 micrometer, for instance. After the valve has been opened, actuator  3  shortens in response to the electrical voltage being switched off, and restoring spring  14  moves valve needle  4  back again in the direction of valve seat  9 , closing the fuel injector.  
         [0014]     To protect piezoelectric actuator  3  from tensile and bending stresses, it is arranged in an actuator sleeve  12  between an actuator top (head)  16  and an actuator base  17 , actuator sleeve  12  being designed as so-called tube spring and made from a metal such as steel.  
         [0015]     Actuator top  16  is arranged on a front-side end of actuator sleeve  12  facing away from valve needle  4  and integrally and/or frictionally connected to actuator sleeve  12 , for instance by welding. Actuator base  17  is disposed at a front-side end, facing valve needle  4 , of actuator sleeve  12  and likewise integrally and/or frictionally connected to actuator sleeve  12 , for instance by welding.  
         [0016]     Actuator sleeve  12  prestresses actuator  3  for compression between actuator top  16  and actuator base  17 .  
         [0017]     Needle shaft  7  of valve needle  4  has a shoulder  18  against which restoring spring  14  rests by one end so as to press needle shaft  7  of valve needle  4  against actuator base  17  of actuator sleeve  12  and to press valve-closure member  8  in the direction of valve seat  9 .  
         [0018]     Since actuator  3  and the other components of the fuel injector such as valve housing  1  expand to different degrees in response to temperature changes because of different thermal expansion coefficients, an hydraulic coupler  15  is provided, which compensates for the differences in the various linear expansions in order to ensure that the fuel injector with valve needle  4  will always implement the same lift regardless of the individual temperature of the fuel injector. No lift losses at which the lift of actuator  3  is not fully transmitted to valve needle  4  must occur, so that the lift of valve needle  4  is smaller than the lift of actuator  3 .  
         [0019]     Hydraulic coupler  15  is arranged between housing lid  1 . 2  and actuator top  16  of actuator sleeve  12 , for instance.  
         [0020]     Hydraulic coupler  15  includes a cup-shaped cylinder  21 , for example, and a piston  22  which is axially displaceable in cup-shaped cylinder  21 . A so-called coupler gap  23  is present between cup-shaped cylinder  21  and piston  22 . Starting from cup-shaped cylinder  21 , an elastic sealing element  24 , which is configured as convoluted bellows and made of metal, extends up to piston  22 . Elastic sealing element  24  encloses a coupler volume  25 , which is connected to coupler gap  23  via the fluid by way of a throttle element  28 . Coupler volume  25  and coupler gap  23  are filled with a fluid such as fuel or a second medium such as silicon oil, for instance. The pressure in the fluid of coupler volume  25  is increased with the aid of a spring element  26 , for example, in that spring element  26  exerts a pressure force on elastic sealing element  24  from the outside, or is provided within elastic sealing element  24 , for instance in piston  22 , and exerts a pressure force on the fluid of coupler volume  25 . For instance, piston  22  has a cavity which is connected to coupler gap  23  via throttle element  28 , and which is connected to the circumference of piston  22  via a flow opening.  
         [0021]     In displacement processes acting rapidly on hydraulic coupler  15 , for instance the expansion of actuator  3  in response to an electrical voltage supply, hydraulic coupler  15  reacts as extremely rigid component since barely any fluid is able to flow out of coupler gap  23  through throttle element  28  into coupler volume  25  within the short period of time. Since coupler gap  23  thus remains constant in this situation, the lift of actuator  3  is transmitted to valve needle  4  in its entirety.  
         [0022]     In displacement processes that act slowly on hydraulic coupler  15 , such as the expansion in response to temperature changes, coupler gap  23  becomes smaller or larger since the fluid has enough time to flow out of or into coupler gap  23  via throttle element  28 .  
         [0023]     Cylinder  21  of hydraulic coupler  15  faces actuator  3 , for instance, and piston  22  of hydraulic coupler  15  faces housing lid  1 . 1 , or vice versa. The part of hydraulic coupler  15  facing housing lid  1 . 1  forms a head part  29 , and the part facing actuator  3  forms a foot part  30  of hydraulic coupler  15 .  
         [0024]     Hydraulic coupler  15 , actuator  3  with actuator sleeve  12 , and valve needle  4  are arranged concentrically with respect to a valve axis  27 , for instance.  
         [0025]     Actuator sleeve  12  and hydraulic coupler  15  are, for instance, centered and fixed relative to one another, for example with the aid of an extrusion coat  36 , which begins at actuator top  16  and extends to foot part  30  of hydraulic coupler  15 .  
         [0026]     To encapsulate actuator  3  and hydraulic coupler  15  with respect to fuel, an actuator housing  31  which hermetically surrounds actuator  3  and hydraulic coupler  15  and seals them from the fuel, is provided in valve housing  1 . Actuator housing  31  has a cylindrical design, for example, and divides the interior space of valve housing  1  into a pressure chamber  32  loaded with fuel and connected to input port  2  via the fluid, and an actuator chamber having actuator  3  and hydraulic coupler  15 . Actuator housing  31  is arranged in valve housing  1  in a concentric manner, for example, and rests against valve housing  1  at the front-side ends. For example, on the front side facing housing lid  1 . 2 , actuator housing  31  is connected to housing lid  1 . 2  in an integral and/or non-positive manner, for instance by soldering. Starting from actuator base  17 , needle shaft  7  of valve needle  4  extends in actuator chamber  33  in the direction facing away from actuator  3  and projects through actuator housing  31  into pressure chamber  32  through an opening  34 ; opening  34  is sealed by an elastic seal  35 , so that no fuel is able to travel from pressure chamber  32  into actuator chamber  33 . Seal  35  is designed as elastic convoluted bellows, for instance, which is made of metal, for example, and extends in an annular manner from needle shaft  7  to actuator housing  31 .  
         [0027]     Restoring spring  14  rests against shoulder  18  of valve needle  4  via its one end, and against actuator housing  31  by its other end.  
         [0028]     Actuator  3  has a positive pole  38  and an earth pole  39 , which is the electrical negative pole. Provided on valve housing  1 , for instance on housing lid  1 . 2 , is a two-pole electrical plug  40 , for example, which has a positive terminal  41  and a ground terminal  42  for the contacting with an external voltage source  43 . Depending on the setting of a high-power switch  44 , either a high voltage of voltage source  43  or no voltage is applied at plug  40 . High-power switch  44  is connected to a positive pole of voltage source  43 . Voltage source  43  is a transformer, for example, which, for instance, raises a 12V on-board voltage of a vehicle to a high voltage.  
         [0029]     According to the present invention, earth pole ( 39 ) of actuator ( 3 ) is electrically connected to ground terminal ( 42 ) of plug ( 40 ) in a cable-less manner, and positive pole ( 38 ) of actuator ( 3 ) is electrically connected to positive terminal ( 41 ) of plug  40  in a cable-less manner. Because of the cable-free connection, cable breaks, which would lead to malfunctioning of the fuel injector, are prevented.  
         [0030]     According to an advantageous embodiment, earth pole  39  of actuator  3  is electrically connected to ground terminal  42  of plug  40  via actuator housing  31  and/or valve housing  1 . This reduces the electromagnetic interference radiation of actuator  3 .  
         [0031]     Positive pole  38  of actuator  3  is electrically contacted by positive terminal  41  via hydraulic coupler  15 , for instance. According to this circuit arrangement, the current is fed from plug  40  to actuator  3  via hydraulic coupler  15 .  
         [0032]     For example, earth pole  39  of actuator  3  is in electrical contact with actuator top  16 , actuator top  16  being connected to actuator base  17  by way of actuator sleeve  12 . Actuator base  17  in turn is electrically connected to actuator housing  31  via needle shaft  7  of valve needle  4 , shoulder  18  of valve needle  4  and restoring spring  14  resting against shoulder  18 .  
         [0033]     Positive terminal  41  of plug  40  is electrically connected to head part  29  of hydraulic coupler  15 , for instance, and positive pole  38  of actuator  3  to a foot part  30  of hydraulic coupler  15 .  
         [0034]     Head part  29  and foot part  30  of hydraulic coupler  15  are connected to one another in an electrically conducting manner by way of elastic sealing element  24 .  
         [0035]     Provided between hydraulic coupler  15  and actuator  3  is a first electrical insulation  46 , and provided between hydraulic coupler  15  and valve housing  1  is a second electrical insulation  47  so as to prevent a short circuit between positive pole  38  and earth pole  39  of actuator  3  or between positive terminal  41  and ground terminal  42  of plug  40 . Insulations  46 ,  47  are in the shape of disks, for example, and made of ceramic or some other electrically insulating material.  
         [0036]     Positive pole  38  of actuator  3  extends, for instance, through a through hole  50  in actuator top  16  and projects through first electrical insulation  46  through a first opening  48  so as to provide contacting with foot part  30  of hydraulic coupler  15 . Positive terminal  41  of plug  40  runs through a connecting duct  51  in housing lid  1 . 2  and projects through second electrical insulation  47 , for instance through a second opening  49 , so as to provide contacting with head part  29  of hydraulic coupler  15 .  
         [0037]     Second insulation  47  may also be embodied as piezo-ceramic for analyzing the power profile of actuator  3  and utilizing it to regulate the injection.  
         [0038]     In valve housing  1 , the fuel is guided from input port  2  into pressure chamber  32  to valve-closure member  8  upstream from sealing seat  11 . When the fuel injector is opened, valve-closure member  8  lifts off from sealing seat  11 , thereby opening a connection to combustion chamber  10  of the internal combustion engine, so that fuel is flowing into combustion chamber  10  by way of an annular discharge gap  52  formed between valve-closure member  8  and valve seat  9 . The greater the lift of valve needle  4  in the opening direction, the larger discharge gap  52  becomes and the more fuel will be injected into combustion chamber  10  per time unit.