Abstract:
A fuel filter for a fuel supply system of an internal combustion engine may include a filter housing, which may have an untreated-side inlet, a treated-side outlet, and an untreated-side return line. The fuel filter may also include a filter element arranged in the filter housing, and a closure element, which in an operationally ready state of the fuel filter may close off the return line. The fuel filter may include an untreated space and a treated space, and may separate in the filter housing the untreated space communicating with an inlet and the return line from the treated space communicating with the outlet. The fuel filter may further include a pressure sensor configured to measure a pressure build-up in the treated space, wherein the fuel filter may be configured to enable the pressure build-up to reach a predetermined threshold at which the engine may be started.

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
       [0001]    This application is a continuation of and thus claims priority to U.S. patent application Ser. No. 12/304,831, filed Dec. 15, 2008, which is a National Stage application which claims the benefit of International Application No. PCT/EP2007/0555469 filed Jun. 4, 2007, which claims priority based on German Patent Application No. DE 10 2006 028 148.9, filed Jun. 16, 2006, all of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a fuel filter for a fuel supply system of an internal combustion engine, in particular in a motor vehicle. 
       BACKGROUND 
       [0003]    Internal combustion engines have a fuel supply system for their supply with liquid fuel. Such a fuel supply system comprises typically a fuel tank, a fuel pump, a fuel filter, and an injection system. To reduce the risk of damage of the injection system or the internal combustion engine, respectively, it is required to clean the fuel supplied to the internal combustion engine from contamination carried along with the fuel. Hence, the fuel filter is a component which is relevant for the functional reliability of the internal combustion engine. Such a fuel filter has typically a filter housing which comprises an untreated-side inlet and a treated-side outlet. Furthermore, a filter element is provided, which is arranged in the filter housing and which separates in the filter housing an untreated space communicating with the inlet from a treated space communicating with the outlet. The filter element is a wear part which is replaced in certain maintenance intervals. When replacing the filter element, there is a risk that it is not properly installed in the filter housing. Moreover, there is a risk that the fuel filter is operated, accidentally or knowingly, without filter element. With missing or improper installed filter element, there is the risk that contamination can get unhindered to the injection system or to the internal combustion engine, respectively. 
       SUMMARY 
       [0004]    The present invention is concerned with the problem to propose an improved embodiment for a fuel filter, for which in particular the risk is reduced that unfiltered fuel can get to the internal combustion engine. 
         [0005]    This problem is solved in the invention by means of the subject matters of the independent claims. Advantageous embodiments are subject matter of the dependent claims. 
         [0006]    The invention is based on the general idea to in addition provide the fuel filter with an untreated-side return line, which, in the operationally ready state, is closed by means of a closure element. In an inoperable state of the fuel filter, thus, for example, with missing closure element and/or missing filter element, the return line is open, so that fuel supplied through the inlet into the filter housing preferably flows off through the return line and, for example, flows back into the fuel tank. In this case, no, or not enough, fuel is supplied. Subsequently, the internal combustion engine cannot be started. The risk of damage of the injection system, or the internal combustion engine, respectively, can thereby be reduced. To ensure that with missing filter element, the fuel entering the filter housing exits through the return line and not through the outlet, the flow resistance through the return line to the tank, for example, can be rated considerably lower than the flow resistance from the outlet to the internal combustion engine. With inserted filter element and with missing or improper attached closure element, the return line to the untreated space is open, while the outlet towards the treated space is open and is separated by the filter element from the untreated space. By means of the filter element, an increased flow resistance is forced to occur towards the outlet. Accordingly, also in this constellation, the fuel discharges through the return line from the filter housing. In this constellation, the filter element subsequently prevents the supply of contamination to the internal combustion engine, whereby the same cannot be started at the same time, since it is not supplied, or only insufficiently, with fuel through the outlet. 
         [0007]    In a preferred embodiment, the closure element is formed or arranged at the filter element such that the closure element, with a filter element properly inserted into the filter housing, closes off the return line. By means of this integrated construction, it is ensured that the return line is closed off only with inserted, and correctly inserted, filter element. In other words, the proper installation state of the filter element, or the operationally ready state of the fuel filter, respectively, is only given when the filter element is inserted into the filter housing such that the closure element closes off the return line. The reliability or the handling of the fuel filter is thereby improved. 
         [0008]    In another embodiment, a positioning device can be provided, which comprises at least one positioning element on the filter element side, and one positioning element on the filter housing side, which interact during inserting of the filter element into the housing for finding of an orientation, which is aligned with the insertion direction of the closure element shaped as a pin, between the pin and a return line opening, which is open towards the untreated space, of the return line. By means of this design, during mounting of the fuel filter, the finding of the relative position between filter element and filter housing is made easier. The risk of a faulty installation is thereby reduced. 
         [0009]    In another advantageous embodiment, a guiding device can be provided, which comprises at least one guiding element on the filter element side, and at least one guiding element on the filter housing side, which interact during insertion of the filter element into the filter housing according to the key-lock principle, such that they allow the interacting between the positioning elements of the positioning device only with matching guiding elements. By means of this construction, the risk is reduced that a wrong filter element, thus a filter element, which is not specifically adapted to the fuel filter, can be inserted into the filter housing. In the ideal case, an internal combustion engine, the fuel supply system of which is equipped with the fuel filter according to the invention, can be started only when the associated and correct filter element is properly inserted into filter housing. 
         [0010]    Further important features are apparent from the sub-claims, from the drawings, and from the associated description of the figures by means of the drawings. 
         [0011]    It is to be understood the aforementioned and the following features still to be illustrated are not only usable in the respective mentioned combination, but also in other combinations or on its own, without departing from the scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Preferred exemplary embodiments of the invention are illustrated in the drawings, and are explained in the following description in more detail, wherein identical reference numbers refer to identical, or similar, or functionally identical components. 
           [0013]      FIG. 1  shows schematically a perspective and partial cross section of a fuel filter, 
           [0014]      FIG. 2  shows schematically a partial cross section and a greatly simplified side view in the region of a return line during installation of a filter element, 
           [0015]      FIG. 3  shows schematically a perspective view on a cover of the filter housing in a simplified illustration, 
           [0016]      FIG. 4  shows a top view on the cover according to  FIG. 3  corresponding to an arrow IV in  FIG. 3 , 
           [0017]      FIG. 5  shows a view as in  FIG. 4 , but for a different embodiment, 
           [0018]      FIG. 6  shows schematically a detail section along the section lines VI in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    According to  FIG. 1 , a fuel filter  1 , which is suitable for filtering a liquid fuel, such as, e.g., gasoline or diesel, comprises a filter housing  2  and a filter element  3 . The filter housing  2  comprises an untreated-side inlet  4 , a treated-side outlet  5 , and an untreated-side return line  6 . The filter housing  2  is assembled from a cup-shaped cover  7  and a cup-shaped bottom  8 , which can be screwed together by means of a threaded connection  9 . Inlet  4 , outlet  5  and return line  6  are formed here at the cover  7 . The filter housing  2  is preferably provided for a hanging mounting position so that for maintenance of the fuel filter  1 , the bottom  8  can be screwed off downwards, while the upper cover  7  remains stationary. Alternatively, a standing mounting position can also be provided, whereby then the cover  7  comprising the connections  4 ,  5 , and  6  is arranged at the bottom, remains stationary, and functionally forms rather a “housing bottom”, while in this mounting situation the bottom  8  is arranged at the top, and functionally rather forms a “housing cover”. The axial dimension can vary here. In particular, in the standing arrangement, the cover  7 , thus the functional housing bottom, can accommodate the bigger portion of the filter element  3 , while in the shown hanging arrangement, the bottom  8  accommodates the bigger portion of the filter element  3 . 
         [0020]    The fuel filter  1  is provided for mounting into a fuel supply system of an internal combustion engine, which is preferably arranged in a motor vehicle. For this, the inlet  4  can be connected to an inlet line  10 , symbolized by an arrow, of the fuel supply system, the outlet  5  to an outlet line  11 , symbolized by an arrow, of the fuel supply system, and the return line  6  to a return pipe  12 , symbolized by an arrow, of the fuel supply system. The inlet line  10  includes, for example, a fuel pump, and comes from a fuel tank. The outlet line  11  runs, for example, to a fuel injection system. The return pipe  12  runs preferably back to the fuel tank. 
         [0021]    The filter element  3  is arranged in the mounted state of the fuel filter  1  in the filter housing  2  such that it separates within the filter housing  2  an untreated space  13  from a treated space  14 . In the shown exemplary embodiment, the filter element  3 , without restriction of the generality, is shaped as ring filter element, which, with respect to a longitudinal center axis  15  of the ring filter element  3 , is arranged coaxial to a longitudinal center axis  16  of the filter housing  2 . Furthermore, the ring filter element  3  includes at least one axial end disk  17 , wherein in  FIG. 1  only one end disk is visible. The respective end disk  17  borders axially a filter material  18  which allows a radial flow-through. 
         [0022]    The inlet  4  communicates via an inlet opening, not shown here, with the untreated space  13 , and the outlet  5  communicates via an outlet opening, not shown, with the treated space  14 . Furthermore, the return line  6  communicates with the untreated space  13  as well. For this, the return line  6  includes, for example, a return line opening  19 , which is open towards the untreated space  13 . 
         [0023]    For the fuel filter  1 , in addition, a closure element  20  is provided which serves for closing off the return line  6  in the operationally ready state of the fuel filter  1 . Here, the closure element  20  closes off, for example, the return line opening  19 . In the operationally ready state of the fuel filter  1 , hence with closed return line  6 , the fuel pump supplies, during the operation of the fuel supply system, fuel through the inlet  4  into the untreated space  13 . From the untreated space  13 , the fuel gets through the filter material  18  radially to the treated space  14 . From the treated space  14 , the fuel discharges again through the outlet  5  from the filter housing  2 . With missing closure element  20 , or when the return line  6  is not closed off by the closure element  20 , respectively, the fuel from the untreated space  13  can exit directly through the return line  6  out of the filter housing  2 . The flow resistance through the filter material  18  to the treated side  14  hereby provides that within the treated space, thus at the outlet  5 , the required fuel pressure for starting the internal combustion engine cannot be built up since the fuel from the untreated space  13  can discharge substantially unrestricted through the return line  6 . 
         [0024]    In the preferred embodiment shown here, the fuel filter  1  can in addition be equipped with a pressure sensor  21 , by means of which the treated fuel pressure can be measured. The pressure sensor  21  is attached, for example, at the cover  7 . For example, when starting the internal combustion engine, an engine control device can monitor the pressure build-up in the treated space, and generates the respective start signals for starting the internal combustion engine only at a sufficient pressure build-up. With a closed return line  6 , the here required pressure in the treated space cannot build up, so that the necessary start signals are not generated. Besides, with an open return line  6 , the pressure build-up in the treaded space can turn out so low that the required fuel supply for starting the internal combustion engine is not possible, so that the internal combustion engine cannot be started due to the insufficient or missing fuel supply. This construction is based on the idea that the unclosed return line is evaluated as an indication that the closure element  20  is not, or not properly, inserted into the return line opening  19 , and/or that the filter element  3  is not, or not properly, inserted into the filter housing  2 . The unclosed return line  6  can also indicate that a wrong filter element was inserted into the filter housing  2 . In the mentioned states, the fuel filter  1  is not operationally ready. The internal combustion engine should then not be started to avoid damage of the internal combustion engine, or the injection system, respectively, by unfiltered fuel. By means of the proposed fuel filter  1 , this goal is achieved comparatively easily and effectively. 
         [0025]    In the preferred embodiment shown here, the closure element  20  is formed at the filter element  3 , or is arranged thereon, respectively. Thus, the return line  6  is automatically closed off when the filter element  3  is inserted properly into the filter housing  2 . A missing filter element  3 , a wrongly inserted filter element, and the use of a wrong filter element  3  result in each case in an unclosed return line  6 , whereby the starting of the internal combustion engine can be prevented. 
         [0026]    In the example, the closure element  20  is arranged at the end disk  17  facing towards the cover  7 . The closure element  20  is shaped here as pin  22 , which projects axially from the end disk  17 , thus parallel to the longitudinal center axis  15  of the ring filter element  3 . The pin  22  interacts with the return line opening  19  for closing off the return line  6 . In particular, the pin  22  can be plugged in axially into the return line opening  19 . The pin  22  can be equipped with a radial seal  23 , in particular with an O-ring. The return line opening  19  can be equipped with a fitting or a tube section, which are not described here in more detail. In the plugged-in state, the radial seal  23  causes a sufficient sealing of the return line opening  19 . 
         [0027]    In the embodiment shown here, the fuel filter  1  is additionally equipped with a vent throttle  24 , through which the return line  6  also communicates with the untreated space  13 . The vent throttle  24  is characterized by a flow-through resistance, which is substantially higher than the flow-through resistance of the filter element  3  and the outlet  5  with closed-off return line  6 . With closed-off return line  6 , the vent throttle  24  allows a ventilation of the filter housing  2  during starting of the internal combustion engine. In the subsequent normal operation, it allows a comparatively small return flow through the return line  6 , which, however, due to the comparatively strong throttle effect of the vent throttle  24 , does not hinder the required pressure build up in the treated space  14 . In particular, the flow-through resistance of the vent throttle  24  is even higher than the flow-through resistance of the filter element  3  alone. 
         [0028]    For a standing arrangement, a different, in particular higher, positioning of the vent throttle is thinkable. In the standing position, the return line  6 , which is then arranged at the bottom, can serve as idle, which, at removal of the bottom  8  located at the top, or at pulling out of the filter element  3 , opens up automatically. 
         [0029]    According to  FIG. 2 , the fuel filter  1  can be equipped with a positioning device  25 . The positioning device  25  comprises on the filter element side at least one position element, which is formed here by a slide face  26  at the free end of the pin  22 , and, on the filter housing side, at least one positioning element, which is formed here by a ramp  27 . The positioning elements  26 ,  27  are shaped such that they interact during placing of the filter element  3  into the filter housing  2  for finding of an orientation, which is aligned with the insertion direction of the pin  22 , between the pin  22  and the return line opening  19 . 
         [0030]    In the preferred embodiments shown here, as a positioning element on the filter housing side, the said ramp  27  is provided, which projects axially into the untreated space  13 . The ramp  27  begins at  29  at the return line opening  19  and ends at  30  at the return line opening  19  as well. Between its beginning  29  and its end  30 , the ramp  27  extends circular or helical, respectively, concentric to the longitudinal center axis  16  of the filter housing. From its beginning  29  to its end  30 , the ramp  27  declines towards the return line opening  19 . The said slide face  26  is formed at the pin  22  as a position element on the filter element side, in fact on a side of the pin  22  remote from the end disk  17 . Here, the pin  22  is arranged eccentrically with respect to the longitudinal center axis  15  of the filter element  3 , wherein the eccentricity of the pin  22  is selected approximately equal to the radius of the ramp  27 . Accordingly, the pin  22  can rest with its slide face  26  axially against the ramp  27  during insertion of the filter element  3 , coaxial to the longitudinal center axis  16  of the filter housing  2 . During turning of the filter element  3  around its longitudinal center axis  15  corresponding to an arrow  31 , the pin  22  slides with its slide face  26  along the ramp  27 . Hereby, the orientation of the pin  22  is forced to occur towards the return line opening  19 . A corresponding sliding movement is symbolized in  FIG. 2  by an arrow  32 . The orientation of the ramp slope is preferably selected such that the turning direction during tightening of the bottom  8  is forced to generate the desired turning direction  31  for the filter element  3  arranged therein, whereby the filter element  3  during attaching of the bottom  8  automatically slides along the ramp  27 . Upon obtaining the aligned orientation between pin  22  and the return line opening  19 , the beginning  29  of the ramp  27  restricts a further turning of the filter element  3 . With further tightening of the bottom  8 , the filter element  3  is forced to be inserted corresponding to the insertion direction  28  with its pin  22  into the return line opening  19 . 
         [0031]    According to  FIGS. 3 to 6 , the fuel filter  1  can additionally be equipped with a guiding device  33 . This guiding device  33  can comprise on the filter element side at least one guiding element, which, for example, can be formed by a guiding section  34  formed at the pin  22 , as well as on the filter housing side at least one guiding element, which, for example, can be formed by one or more guiding walls  35 . The guiding elements  34 ,  35  are shaped such that they interact during insertion of the filter element  3  into the filter housing  2  according to the “keylock principle”. This means that the guiding elements  34 ,  35  allow interacting between the positioning elements  26 ,  27 , thus between the ramp  27  and the slide face  26 , only when the matching guiding elements  34 ,  35  interact with each other. In the case that the guiding elements  34 ,  35  interacting with each other during insertion of the filter element  3  into the filter housing  2  do not match, the interacting of the positioning elements  26 ,  27  for finding the aligned orientation between the pin  22  and the return line opening  19 , is considerably hindered or made impossible by the guiding device  33 . 
         [0032]    In the shown embodiment, the guiding elements on the filter housing side are formed by guiding walls  35  which extend radially inside and/or radially outside along at least one extension section  36  of the ramp  27 , thereby projecting beyond the ramp  27  in axial direction. In each of the examples of  FIGS. 3 and 4 , respectively, only one extension section  36  is provided, which is positioned in the region of the end  30  of the ramp  27 . Here, in the extension section  36 , two parallel guiding walls  35  are provided, one of which borders the ramp  27  radially inside and the other one radially outside. In the embodiment shown in  FIG. 5 , a total of three extension sections  36  are provided, in each of which two parallel extending guiding walls  35  are provided, which border the ramp  27  radially inside and outside. The guiding element on the filter element side of the embodiments shown here is formed by the guiding section  34 , which projects axially on the side of the pin  22 , which is facing away or is remote from the end disk  17 . The said guiding section  34  comprises the slide face  26  of the pin  22 . Furthermore, the guiding section  34  is adjusted with respect to its positioning at the pin  22  and with respect to its dimensioning to the guiding walls  35  such that the guiding section  34 , during installation of the fuel filter  1 , extends radially alongside the respective guiding wall  35  or between the two parallel guiding walls  35 , respectively, thereby resting with the slide face  26  axially against the ramp  27  and keeping the pin  22  axially spaced apart from the respective guiding wall  35 . This relationship is particularly apparent in  FIG. 6 . There, the guiding section  34  contacts the ramp  27  running between the guiding walls  35  with the slide face  26 , and ensures an axial clearance between the walls  35  and an outer side  37 , facing away from or remote from the end disk  17 , of the pin  22 , and from which the guiding section  34  projects. The said outer side  37  can be plane and can merge via a chamfer  38  into the rest of the pin  22 . 
         [0033]    The above mentioned key-lock principle now causes that the pin  22  with its slide face  26  can slide along the entire ramp  27  only until the aligned orientation to the return line opening  19  when the guiding section  34  is present, when the guiding section  34  is sufficiently narrow in radial direction to fit through the opposing guiding walls  35 , and when the guiding section  35  is sufficiently long in axial direction to adjust the required axial clearance between pin  22  and the guiding walls  35 . With missing or wrong guiding section  34 , the pin  22  would rest against the face ends of the walls  35  when sliding along the ramp  27  in circumferential direction, whereby the turnability of the filter element  3  is blocked. Then, the filter element  3  cannot be readily installed properly. 
         [0034]    In the  FIGS. 3 to 6 , in addition an outlet fitting  39  is illustrated, which is provided at the cover  7  and onto which the filter element can be slipped.  FIG. 6  shows a special embodiment in which the pin  22  is attached through a web  40  to the end disk  17 . Said web  40  is flexible in radial direction and allows a tolerance compensation between the radial position of the guiding section  34  and the radial position of the guiding walls  35 . As is apparent from  FIG. 1 , the pin  22  also can be attached comparatively rigid to the end disk  17 .