Abstract:
A high-pressure fuel accumulator for a fuel injection system of an internal combustion engine, in particular for a common-rail fuel injection system, has an elongated base body having an accumulator space for high-pressure fuel extending in the longitudinal direction of the base body, communicating with multiple connecting bores. A relief space connected to a low-pressure connection is provided in the base body, with a drain channel from the accumulator space opening into it. A pressure regulating valve is installed in the base body for opening and closing the drain channel.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a high-pressure fuel accumulator for a fuel injection system of an internal combustion engine, in particular for a common-rail system. 
     BACKGROUND INFORMATION 
     In a common-rail injection system, a high-pressure pump conveys the fuel to be injected from a tank into a central high-pressure fuel accumulator, which is known as a common rail. High-pressure lines lead from the high-pressure fuel accumulator to the individual injectors associated with the cylinders of the internal combustion engine. The injectors are controlled individually by the engine electronic system as a function of the operating parameters of the internal combustion engine to inject fuel into the combustion chamber of the internal combustion engine. The base body of the high-pressure fuel accumulator is made of a forged blank, for example, with the interior of the base body being introduced as a longitudinal bore into the base body. The base body manufactured in this way is then provided with connecting bores which open into the longitudinal bore. Such a high-pressure fuel accumulator is known from German Published Patent Application No. 196 40 480 A1 (corresponding to U.S. Pat. No. 6,223,726), for example. To adjust the pressure in the high-pressure fuel accumulator as a function of the load state of the engine, a pressure regulating valve is used in the related art; this valve has its own housing part and is connected either to the high-pressure pump or is screwed onto an end connection of the high-pressure fuel accumulator by using screwable fastening means. 
     One disadvantage of the known high-pressure fuel accumulators is that because of the high pressure in the accumulator space, the sealing sites in the connection area of high-pressure fuel accumulators and pressure regulating valves may need to be manufactured with high precision, and multiple sealing elements may be necessary for the seal. In addition, problems occur at the valve seat of the pressure regulating valve, because the valve seat is under high thermal stress due to the high-pressure fuel flowing out of the high-pressure fuel accumulator, which has a negative effect on the pressure regulation of the accumulator space. When the pressure regulating valve is screwed onto the base body of the high-pressure fuel accumulator, mechanical stresses occur in the base body and may lead to cracking and fracturing of the material in the area of intersections of connecting bores and the accumulator space in operation of the fuel injection system. 
     SUMMARY OF THE INVENTION 
     The high-pressure fuel accumulator according to an exemplary embodiment of the present invention avoids the disadvantages known in the related art. Due to the fact that a pressure regulating valve installed in the base body of the high-pressure fuel accumulator is provided, a separate housing part for the pressure regulating valve may be eliminated, thus reducing manufacturing costs for the entire system. Due to the installation of a pressure regulating valve in the base body of the high-pressure fuel accumulator, the complex seals on the pressure regulating valve used in the related art may be unnecessary. Since no screw connections are used in installing the pressure regulating valve in the base body of the high-pressure fuel accumulator, this may reduce material stresses in the transition area between the connecting bores and the accumulator space of the high-pressure fuel accumulator. Therefore, the pressure regulating valve may also be arranged in spatial proximity to the connecting bores, thereby reducing the installation space in the longitudinal direction of the base body. Due to the installation of the pressure regulating valve in the base body of the high-pressure fuel accumulator, thermal stabilization of the valve seat may also be achieved to advantage, because heat may be released from the valve seat to the metal base body. 
     The pressure regulating valve may be designed as a solenoid valve whose electromagnet is installed in a recess on the end face of the base body and sealed with a cover part. 
     In another exemplary embodiment, the base body may have a connection for supplying overflow fuel, this connection being connected to the relief space provided in the base body through an inlet line. The valve seat situated in the relief space may be cooled to advantage by supplying overflow fuel, which is at a lower temperature than the fuel in the accumulator space. The overflow fuel washed in through the inlet line flows out through the low-pressure connection together with the fuel flowing out of the accumulator space through the drain channel. 
     Another exemplary embodiment, in which the relief space, the drain channel from the accumulator space, and a section of a drain line connecting the relief space to the low-pressure connection are designed in a valve part which is inserted into a longitudinal bore in the base body to form the accumulator space and seals this longitudinal bore at one end, may be advantageous. Manufacture of the valve seat and the drain channel, which may contain a throttle, may be easier and less expensive to implement in the valve part. The base body may be provided with a longitudinal bore passing through at least one side. After manufacturing the valve part, it may then be inserted through the open end of the longitudinal bore into the latter and may be connected to the inside of the longitudinal bore with a seal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cross section through an end portion of a high-pressure fuel accumulator according to an exemplary embodiment of the present invention, which end portion is equipped with a pressure regulating valve. 
     FIG. 2 shows a cross section through another exemplary embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a cross section through a high-pressure fuel accumulator having an elongated tubular base body  1  made of metal in which an accumulator space  2  is provided. In the exemplary embodiment illustrated here, accumulator space  2  is formed by a blind hole  14  having central axis  10 , its internal cross section being a circular area. However, the cross section of accumulator space  2  of base body  1  may also be other than circular, e.g., elliptical. Accumulator space  2  is connected to the outlet of a high-pressure pump by a high-pressure line, for example. The high-pressure connection for this may be provided on the end of accumulator space  2 . On its outer jacket  7 , base body  1  is provided with multiple connection fittings  4 , one connecting bore  3  leading from each into accumulator space  2 . Connection fittings  4  are provided with an external thread and are used for connecting high-pressure lines which lead to the injectors of the common-rail system. During operation, fuel from accumulator space  2  of the high-pressure fuel accumulator is distributed among the injectors of the common-rail system through connecting bores  3 . 
     As FIG. 1 also shows, a drain channel  18  having a throttle  19  branches off from accumulator space  2  coaxially with central axis  10  of blind hole  14  at one end  12  of blind hole  14  forming accumulator space  2 , opening centrally into a valve seat  24 . Valve seat  24  is situated in a relief space  20  which is connected by a drain line  15 , designed as a bore, to a low-pressure connection  5  in base body  1 . Valve seat  24 , drain channel  18  and relief space  20  are provided in base body  1  in this exemplary embodiment. An overflow connection  6  is connected to relief space  20  through an inlet line  16  in the form of a bore. Inlet line  16  and drain line  15  branch off radially to central axis  10  of accumulator space  2  and drain channel  18 . Relief space  20  is connected to a pot-shaped recess  25  on end face  9  of base body  1  by a bore  11  running coaxially with central axis  10 . Holding-down bolt  34  mounted slidably displaceably in bore  11  acts with its end inserted into relief space  20  on a valve element  21  designed in the form of a ball. An electromagnet having a coil  32 , a magnet core  31  and armature plate  33  is inserted into recess  25  in base body  1 . Recess  25  is sealed with a cover part  8 . A peripheral collar  13  on the end of base body  1  forms a flange around cover part  8 . A sealing ring  38  seals the transition area between the inside wall of recess  25  and the outside edge of cover part  8 . Connections  35  of coil  32  project from end face  9  of base body  1  through sealed recesses in cover part  8 . As FIG. 1 also shows, holding-down bolt  34  also projects from armature plate  33  to relief space  20 . 
     Armature plate  33  and holding-down bolt  34  connected to it are constantly acted upon by a valve spring  36  supported on cover part  8 , so that when the electromagnet is turned off, holding-down bolt  34  presses valve element  21  into valve seat  24 , and drain channel  18  is closed. If the pressure in accumulator space  2  is to be reduced, the electromagnet is acted upon by a voltage, so that armature plate  33  with holding-down bolt  34  is moved to the right in FIG. 1 against the tension of valve spring  36 , and drain channel  18  is opened. Fuel flowing out of drain channel  18  through throttle  19  enters relief space  20  and goes from there through drain line  15  to low-pressure connection  5  of the high-pressure fuel accumulator. When the electromagnet is turned off, control valve element  21  is pressed into valve seat  24  by the tension of valve spring  36 , and drain channel  18  is closed again. 
     As shown in FIG. 1, overflow fuel which is at a lower temperature than the fuel in accumulator space  2  may be washed through connection  6  into relief space  20  for cooling purposes and for thermal stabilization of valve seat  24 . As also shown in FIG. 1, distance “a” of the valve seat from the next connecting bore  3  may be kept very small because, due to installation of the pressure regulating valve in base body  1 , as shown here, stresses may be advantageously prevented from being transferred to the intersection in the transitional area between connecting bores  3  and accumulator space  2 . 
     In an alternative exemplary embodiment, instead of the electromagnet, a piezoelectric actuator or some other suitable actuator device may also be used to operate the valve element. 
     FIG. 2 illustrates another exemplary embodiment in which longitudinal bore  14  is designed as a through-hole running toward recess  25  on end face  9  of base body  1 . Optionally, however, a blind hole may also be introduced into base body  1  from end face  9  of base body  1  shown in FIG.  2 . In addition, recess  25  may have the same inside radius as bore  14 , which may simplify machining. As shown in FIG. 2, a valve part  40  is inserted into longitudinal bore  14  from end face  9  of base body  1  and seals the end of the longitudinal bore. The valve part is cylindrical with a central bore  11  connecting an end face  22  of the valve part to a relief space  20  in the interior of valve part  40 . Relief space  20  is connected to second end face  12  of valve part  40  facing accumulator space  2  via a drain channel  18  which is coaxial with bore  11  and has throttle  19 . Radially to the axis of bore  11  and therefore also radially to the axis of longitudinal bore  14 , connecting bores  15   a ,  16   a , which are aligned with bores  15 ,  16  in base body  1 , branch off from the valve part. Valve part  40  having valve seat  24 , drain channel  18  and throttle  19  outside of base body  1  may be made to advantage of a material having high temperature stability, preferably a metal, and then inserted into base body  1 . Outer jacket  41  of the valve part may be connected tightly to the inside wall of longitudinal bore  14  by welding, soldering, press-fitting or other suitable techniques, for example. 
     As shown in FIG.  1  and FIG. 2, a centering pin  37  may additionally be provided in accordance with the present invention, e.g., a bent-over end of valve spring  36 , which is passed through a recess in armature plate  33  and engages in a bore  28  at the base of recess  25  or in a bore on end face  22  of valve part  40 . Centering pin  37  is used as anti-rotation protection for armature plate  33 .