Abstract:
A high-pressure pump having a plurality of individual feed pumps is described, the feed pumps being designed as modular pump units and being able to be lined up next to one another via their housings, which are provided with fluid-connecting channels. At least one line module being provided which can be coupled at least on one side to a housing of a modular pump unit and in which the fluid-connecting channels of the respectively adjacent housings form intake and discharge channels which, on the one hand, lead on further and/or, on the other hand, lead outward.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a high-pressure pump for a common-rail injection system for internal combustion engines.  
           [0003]    2. Discussion of the Background  
           [0004]    Common-rail injection systems are used in internal combustion engines, in which, in order to optimize the combustion power, the fuel is to be present in the combustion chambers of the individual cylinders in a finely atomized form. For this purpose, the fuel is compressed in a high-pressure pump and is distributed to the injectors of the individual cylinders via a rail. Finally, the process of injecting the fuel into the combustion chambers is triggered via an electric signal, the fuel, which is under high pressure, being finely distributed at high speed in the combustion chambers of the engine via the injection nozzles of the injectors.  
           [0005]    A high-pressure pump of the type specified at the beginning which is suitable for common-rail injection systems for diesel engines is disclosed in EP-A-0 881 380. High-pressure pumps of this type which, as a rule, have a plurality of piston/cylinder feed elements make it possible to achieve high feed pressures with the required operational reliability, these main pumps having to be adapted in their design in a specific manner to the particular intended use, i.e. having to be constructed especially in each case.  
           [0006]    Also known are high-performance diesel engines which are provided with a classical injection system, each cylinder in this system being assigned a pump feed element. A plurality of injection pumps is therefore generally necessary for high-performance diesel engines with a high number of cylinders. For example, in the case of a V-16 cylinder engine, two in-line injection pumps each having eight pump feed elements one behind another are arranged between the two cylinder banks. If an engine of this type is to be provided with a common-rail diesel injection system, a high-pressure pump which is specially adapted in terms of power and in terms of overall size and to the given spatial conditions is required for this.  
           [0007]    U.S. Pat. No. 4,184,817 discloses a multicylinder high-pressure plunger pump, the plunger being sealed by means of two spaced apart lip seals. The seal on the feed-space side is lubricated by means of diesel oil and is intended at the same time to ensure that diesel oil does not pass into a space placed between these two lip seals and on the eccentric-drive side. An annular chamber which is connected via channels to a diesel induction chamber is furthermore connected upstream of this lip seal. The lower, second lip seal, i.e. the one placed on the eccentric-drive side, is used for sealing off the plunger against the lubricating oil present in the eccentric drive. Labyrinth-like elements are provided between the two lip seals and trap small, remaining overflow amounts of diesel and lubricating oil in the space which is placed between the two lip seals and is connected via a bore to the surroundings.  
         SUMMARY OF THE INVENTION  
         [0008]    The object of the present invention is, especially, to provide a high-pressure pump which ensures high feed pressures, which can be realized in a particularly economic manner, and high operational reliability and can be adapted individually and without any problems to the requirements present in the individual case and also satisfies the exacting requirements placed on the service life.  
           [0009]    This object is achieved essentially by a high-pressure pump having the features according to patent claim  1 .  
           [0010]    The modular manner of constructing the pump units and the combination options with specially designed line modules enable high-pressure pumps to be realized without any problems and in a space-saving manner, it being possible for said pumps to be adapted in the best possible manner to the requirements present in each case as a function of the particular combination of modules. Using this combination of modules and by appropriate design of the channels, optimum guides can also be achieved for the low-pressure supply and the high-pressure removal of fuel, in particular diesel oil, for the removal of leakages and for lubricating-oil supplies and oil return lines.  
           [0011]    Each modular pump unit preferably in each case comprises at least two plungers which lie diametrically opposite each other and are actuated by the same eccentric section, together with an associated feed space and common housing, the feed space and plunger bore preferably being formed in a high-pressure part which can be screwed to the housing.  
           [0012]    The line module or the plurality of line modules which may be present can be largely freely arranged within the overall construction of the particular high-pressure pump, with the result that, for example in the individual case, the connecting points can be positioned in an optimum position.  
           [0013]    According to one preferred embodiment, line modules can simultaneously be configured with a bearing for the drive shaft, specifically either if a line module of this type is arranged between pump modules or if a line module of this type forms the end of a high-pressure pump constructed from individual modules.  
           [0014]    According to the invention, a high-pressure pump, which is of modular construction particularly in the described manner, can be provided with a plurality of plungers which are moved to and fro via a common drive shaft provided with eccentric sections, are guided in each case in the plunger bore leading into a feed space and are actuated by an eccentric section counter to the action of a restoring spring in particular via a cup tappet guided in a bore in the housing, in which case, firstly, an eccentric space through which the drive shaft passes and, secondly, at least one annular lubricating channel which surrounds the respective plunger or cup tappet and is formed in the housing are connected to a lubricating-oil pressure supply, and an annular space which is connected to a lubricating-oil return flow is provided in the region of that section of the plunger or cup tappet which is on the feed-space side, and in which case, furthermore, an annular collecting space for overflow lubricating oil and overflow diesel oil is formed on the feed-space side in the wall of the plunger bore and is connected via channels to a diesel-oil tank, in particular.  
           [0015]    A refinement of a high-pressure pump in such a way results, firstly, in a desired increase in the service life and, secondly, in the fact that virtually no diesel oil passes into that space of the eccentric drive which is filled with lubricating oil, and, conversely, that also virtually no lubricating oil mixes with the diesel oil, which mixture would sooner or later pass via the injection nozzles into the combustion chambers of the engine and would have a negative effect on the exhaust-gas emission of the engine.  
           [0016]    The separation of diesel oil and lubricating oil is obtained in a simple manner and not prone to faults.  
           [0017]    A further aspect which is essential for the invention and can be used in general in high-pressure pumps of this type resides in the fact that, instead of rolling rings which are conventionally provided between an eccentric drive and the plunger or cup tappet thereof which is to be actuated, use is made of sliding shoes of two-part design. This configuration of rolling elements in the form of two-part sliding shoes results especially in making installation easier and also permits installation of rolling elements of this type even if this is no longer possible using conventional rolling rings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    Further particularly advantageous refinements of the invention and features which are significant to the invention are specified in the dependent claims and will also be explained in the following description of exemplary embodiments with reference to the drawings, in which:  
         [0019]    [0019]FIG. 1 shows a schematic illustration of a pump unit with a common rail, the pump unit being illustrated in accordance with a section along the line I-I of FIG. 2,  
         [0020]    [0020]FIG. 2 shows an axial longitudinal section through a high-pressure pump which is of modular construction according to the invention,  
         [0021]    [0021]FIG. 3 shows an illustration of part of a high-pressure pump according to the invention with a centrally arranged line module (partially illustrated) and assigned diesel-oil tank and lubricating-oil tank,  
         [0022]    [0022]FIG. 4 shows a schematic sectional illustration of a pump unit corresponding to a section along the line V-V of FIG. 2 in order to explain the profile of the low-pressure diesel intake line,  
         [0023]    [0023]FIG. 5 shows an embodiment of a high-pressure pump according to the invention that is extended in comparison to the high-pressure pump shown in FIG. 2,  
         [0024]    [0024]FIG. 6 shows an illustration of a refinement of a high-pressure pump according to the invention that is reduced in comparison to the embodiment according to FIG. 2, and  
         [0025]    [0025]FIG. 7 shows a schematic illustration of a pump unit with rolling elements which are designed in the form of sliding shoes. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    [0026]FIG. 1 shows, in the form of a schematic illustration, a pump unit  2  (illustrated in section) of a high-pressure pump which is constructed from pump units of this type and from line modules  1  which have yet to be explained in detail, for a common-rail injection system for internal combustion engines. The storage volume  6 ′ of a common rail  6  that is fed via a high-pressure output line  26  is respectively connected in a known manner via high-pressure connecting lines  4  to injectors  5 .  
         [0027]    The pump unit  2 , which is shown in cross section, comprises two plunger units which are arranged diametrically opposite each other and are in each case formed by a plunger  14  which is guided in a reciprocating manner in a bore  37  and is assigned a cup tappet  36  which is guided in the housing  22 . The plunger  14  with its cup tappet  36  is prestressed against an eccentric drive  10 ,  11  via a restoring spring  50 . The plunger bore  37  leads into a feed space  18  which is connected via a pressure-controlled inlet valve  25  to a low-pressure supply line  24  and via a pressure-controlled outlet valve  27  to the high-pressure output line  26 . The low-pressure supply line  24  is connected to a diesel-oil tank  33  having ventilating means  57 , specifically via an intake line  23  which leads to a low-pressure pre-feed pump  21 . A flow-regulating element  3  is arranged in the low-pressure supply line  24  for diesel oil.  
         [0028]    The plunger bore  37 , the feed space  18  and the accommodating regions for the valves  25  and  27  are formed in a high-pressure part  7  which is screwed to the housing  22 .  
         [0029]    The plunger  14  or the cup tappet  36  is driven via a drive shaft  9 , the center of rotation of which is indicated by  63 . The eccentric section acting on the cup tappet  36  bears the reference number  10 . A rolling ring  11  is situated in a conventional manner between the eccentric section  10  and cup tappet  36 , the sliding bearing  12  or a ball bearing being provided between the rolling ring  11  and eccentric element  10 . The eccentric center is referred to by the letter E and the maximum eccentricity is indicated by H/2.  
         [0030]    In the region separating the high-pressure part  7  and the housing  22 , an annular space  34 ′ (which has yet to be explained in detail) is widened in such a manner that it ensures the passage of the high-pressure bore  26  in such a manner that should an overflow occur at the separating point of the high-pressure bore, the overflow quantity which arises can entirely escape into the space  34 ′.  
         [0031]    The central-symmetrical design of the pump unit  2  which has already been discussed is clarified by FIG. 1 and it thus suffices to describe the upper part of this pump unit, since the same applies to the lower part of the pump unit. The measures undertaken for lubrication and for separating lubricating oil and diesel oil will be explained in detail with reference to the following figures.  
         [0032]    The axial sectional illustration according to FIG. 2 shows a high-pressure pump which is constructed in a modular manner in accordance with the invention and has modular pump units  2  and a line module  1 , which is arranged centrally in this case. All in all, there is therefore an arrangement of eight plungers which are combined to form a pump, and this arrangement is advantageous especially because it permits the construction of a narrow, tall pump similar to a classical in-line injection pump. This enables a pump according to the invention to be accommodated without any problem in a structural space which is already present, for example between the cylinder banks of a V-engine.  
         [0033]    The lubrications which are effective in the individual pump units and the means of guiding the lubricating oil, diesel oil and leakages are explained with reference to the pump unit  2  (which is illustrated at the left end in FIG. 2) by way of representation for all of the pump units.  
         [0034]    An annular space  45  arranged above the cup tappet  36  is connected via a forced-oil line  31 , which extends through the entire construction of the high-pressure pump, to a lubricating-oil tank  40  (illustrated in FIG. 3), the lubricating oil being supplied at the required pressure via a feed pump  19 . This feed pump  19  is used to supply the bearings of the drive shaft  9  (eccentric shaft) in the same manner with lubricating oil, specifically via the axial lubricating-oil channel  30  and the radial bores  46 . Overflow oil from the bearings of the drive shaft  9  passes into the eccentric space  58 .  
         [0035]    The feed pump  19  can be the lubricating-oil pump of the engine. In this case, the lubricating-oil tank  40  is at the same time the engine lubricating-oil tank.  
         [0036]    In the region of movement of the open end of the cup tappet  36 , a further annular space  41 ′ is provided which leads via an axially parallel channel  41  to a channel section  41 ″, which runs perpendicularly outward thereto in the line module  1 . Instead of the channel  41 , openings could also be manufactured in the lower region of the cup tappet  36 . In this case, overflow oil from the upper side of the cup tappet  36  would pass from the space  41 ′ through the inner empty space of the cup tappet  36  via the openings into the eccentric space  58 .  
         [0037]    An annular collecting and mixing space  35  is formed on the inner wall of the plunger bore  37  in the high-pressure part  7  and is connected via a channel  60  to an annular space  34 ′ which is connected via a channel  34 , formed in the housing  22 , to the channel  34 ″ which is perpendicular thereto, is formed in the line module  1  and is guided outward. An O-ring seal seals off the annular space  41 ′ from the annular space  34 ′.  
         [0038]    The effect achieved by this refinement is that, firstly, the cup tappet  36  is reliably and satisfactorily lubricated and, secondly, it is ensured that no lubricating oil can pass into the annular space  34 ′ and consequently into the feed space  18 .  
         [0039]    In addition to the two channel sections  34 ″ and  41 ″, channels for the low-pressure supply line  24  (FIG. 1) for diesel oil and for a high-pressure output line  26 ″ are also formed in the line module  1 . The channel  24 ″ which is assigned to the low-pressure supply line cannot be seen in the illustration according FIG. 2, but is illustrated by dashed lines in FIG. 1.  
         [0040]    The lubricating-oil flow which is guided via the channels  31  and conducted to the annular space  45  passes during operation into the annular space  41 ′ and from there via the channels  41  and  41 ″ back to the oil tank  40 , which may also be the oil sump of an engine provided with the high-pressure pump.  
         [0041]    Both lubricating-oil leakages, via the extremely small gap between plunger  14  and plunger bore  37 , and diesel-oil leakages can pass into the annular space  35 , so that there is a corresponding leakage mixture in this annular space  35 , said mixture being removed from the high-pressure pump via the channel  60 , the space  34 ′ and the channels  34  and  34 ″. This mixture of overflow diesel oil and overflow lubricating oil can be conducted back into the diesel tank  33  shown in FIG. 3. The percentage amount of overflow lubricating oil in the overflow diesel oil can be kept very small, preferably smaller than 1% and, in certain places, even only 2%. The amount of overflow lubricating oil passing into the diesel tank  33  is further diluted therein and then passes into the feed space  18 , into the injection system and is finally injected into the engine combustion chamber. The exhaust-gas quality is not negatively affected by this small amount of oil in the injected fuel. The overflow lubricating-oil amount is a priori small because the gap between the plunger  14  and plunger bore  37  is extremely small. Furthermore, the viscosity of the diesel oil is substantially lower than that of lubricating oil and, in addition, the pressure in the feed space  18  during the feed stroke is up to 1000 times higher than the lubricating-oil pressure. Both facts in themselves already bring about a dominance of the overflow diesel oil over the overflow lubricating oil. A further favorable refinement in order to keep the overflow lubricating-oil amount very small will be described in greater detail in conjunction with FIG. 3.  
         [0042]    In the same manner as the high-pressure parts  7  are sealed off with respect to the housing  22  by high-pressure sealing elements  8 , corresponding high-pressure sealing elements  8 ′ are also provided between the particular housing  22  and the adjoining line module  1 . Further sealing elements (for example O-rings) are used as low-pressure seals for the bores  31 ,  34  and  41 . In this manner, a leakproof, cohesive line system is provided by the bores, such as  24 ,  26 ,  31 ,  34  and  41 , provided in the housing  22 , said system being connected to the corresponding lines or channels  24 ″,  26 ″,  34 ″,  41 ″ in the line modules  1 , it being possible for the line modules  1  to be designed in such a manner that they have pure lead-through channels and/or also channels leading outward. Furthermore, the central bearing  59  of the drive shaft  9  is formed in the line module  1 , this bearing being dimensioned in such a manner and being of such a size that the drive shaft  9  together with the eccentric sections  10  can be pushed through it for installation purposes.  
         [0043]    At one end of the high-pressure pump, the end piece  15 , in which pressurized supply channels  30 ,  31  for the lubricating oil are provided, is fitted in a sealing manner onto the outer end wall  13  of the housing.  
         [0044]    The illustration according to FIG. 3 shows, in conjunction with the high-pressure pump which has already been explained with reference to FIG. 2, the associated diesel-oil tank  33  with feed pump  21  and associated front pipe and the lubricating-oil tank  40  which is ventilated in a corresponding manner together with the feed pump  19  and forced-oil line  30 . The forced-oil supply with the bearings of the drive shaft  9  via bores  46  is also indicated in FIG. 3.  
         [0045]    It is particularly advantageous to arrange a pressure-maintaining valve  32  in the overflow line  34 ′, which guides the mixed leakage of diesel oil and smaller amount of lubricating oil and is connected to the annular collecting and mixing space  35 . This pressure-maintaining valve  32 , which is loaded, for example, by a compression spring, enables a somewhat increased pressure to be built up upstream of this valve and therefore also in the annular collecting and mixing space  35 . Owing to this increase in pressure in the space  35 , the direction of flow of the leakage can be affected in such a manner that virtually no lubricating oil at all can pass into the mixing space  35 , this being an essential requirement in conjunction with the high-pressure pumps formed in accordance with the invention.  
         [0046]    However, in this case, depending on the amount of increase in pressure, a very small amount of diesel oil can pass from the annular collecting space  35  into the oil return-flow annular space  41 ′ and therefore into the lubricating-oil tank  40 . However, this amount of diesel oil is so small that the lubricating oil is thereby only insignificantly diluted, i.e. is virtually not diluted. In this case, the mixing of the very small amount of diesel oil with the lubricating oil is not a problem both with respect to the oiliness and also in terms of combustion.  
         [0047]    Furthermore, the mixing of the diesel oil and lubricating oil in the annular collecting and mixing space  35  can be affected by the length “L” of the extremely small gap between the plunger  14  and plunger bore  37 . It is particularly favorable if “L” is greater than 2×E=H, i.e. greater than the stroke of the eccentric  10  and therefore of the plunger  14 . During a plunger stroke, particles are moved in the extremely small gap at most by the distance H. Together with the increase in pressure in the annular space  35 , mixing can be effectively avoided.  
         [0048]    Two measures of increase in pressure and length “L” may also be taken independently of each other.  
         [0049]    In one variant (not illustrated) the pressure-maintaining valve  32  can be controlled (for example electrically or electronically) in order to be able to adapt the increase in pressure in the annular space  35  to the operating state of the pump and/or of the engine, in order to obtain a minimal mixing.  
         [0050]    The sectional illustration according to FIG. 4 shows the position of the channels running axially parallel according to FIGS. 2 and 3 and, in particular, shows the bore  24 ″ which cannot be seen in FIG. 2 and which constitutes the low-pressure supply line for diesel oil.  
         [0051]    [0051]FIG. 5 shows a refinement of a modularly constructed high-pressure pump according to the invention that is expanded in comparison to the embodiment according to FIG. 2. In this case, three modular pump units  2  are combined with two line modules  1 , so that in total twelve cylinder/plunger units are in use. In this refinement, it can be seen that line modules  2  can be formed both with exclusively continuous channels and also with channels which are continuous and branch outward. Both line modules  1  can be used at the same time for the mounting of the drive shaft  9 .  
         [0052]    [0052]FIG. 6 shows a high-pressure pump which is reduced in comparison to the embodiment according to FIG. 2 and in which a total of just four plungers are used, said plungers being provided with high-pressure parts  7  in a housing  22  in the manner already explained.  
         [0053]    The line module  1  used here is used, in turn, for mounting the shaft, but has, on the one hand, channel sections which lead outward and, on the other hand, continuous channels  31  for the forced-oil supply of the pump. The housing  22  remains identical to that according to FIGS. 1 and 2. Since the line module  1  takes on at the same time the function of an outer end wall of the housing, it is, by contrast, slightly modified, since not all of the channel sections can be permeable.  
         [0054]    [0054]FIG. 7 shows a sectional illustration of a pump similar to FIG. 1, but instead of a rolling ring  11  a two-part sliding shoe  47 ,  47 ′ is used. The two sliding-shoe parts  47 ,  47 ′ are held together by means of screws  48 . A sliding bearing or a ball bearing can be provided between the eccentric section  10  and this two-part sliding shoe  47 ,  47 ′. Since the eccentric space  58  is filled with lubricant, no annoying friction occurs between the flat sides  64  of the sliding shoe  47 ,  47 ′ and the cup tappet  36  or a plunger  14  which is optionally directly actuated.  
         [0055]    A substantial advantage of the sliding-shoe arrangement resides in the fact that the sliding shoes can be fitted without any problem even if the rolling rings  11  used according to the figures explained above between the line modules  1  can no longer be pushed through the bearings  59  which are provided.  
         [0056]    If appropriate, a combination of rolling rings and sliding shoes may also be used, but preferably all of the rolling rings are replaced by sliding shoes  47 ,  47 ′.  
         [0057]    The present application claims priority to Swiss Patent Application 2002 1702/02 filed on Oct. 14, 2002, which is incorporated herein by reference in its entirety.