Patent Publication Number: US-2004045537-A1

Title: High-pressure fuel pump for a fuel system of direct injection internal combustion engine, fuel system and internal combustion engine

Description:
PRIOR ART  
       [0001] The invention first relates to a high-pressure fuel pump for a fuel system of a direct-injection internal combustion engine, having a housing, having a low-pressure inlet and having a high-pressure outlet which is connectable to a fuel collection line.  
       [0002] One such high-pressure fuel pump is known on the market. It comprises a conventional radial piston pump that is driven directly by the engine via a mechanical connection. The known radial piston pump, via a fuel line, pumps into a fuel collection line, which is also known generally as a “rail”. The fuel is stored in this rail at very high- pressure (several hundred bar). From the rail, individual branch lines branch off, leading to the individual injection valves at the combustion chambers of the engine.  
       [0003] The object of the present invention is to refine a high-pressure fuel pump of the type defined at the outset in such a way that it is as small and compact in structure as possible and can be produced inexpensively.  
       [0004] In a high-pressure fuel pump of the type defined at the outset, this object is attained in that the fuel collection line is integrated into the housing of the high-pressure fuel pump.  
       ADVANTAGES OF THE INVENTION  
       [0005] By integrating the fuel collection line with the housing of the high-pressure fuel pump, the course taken by the fuel from the high-pressure outlet to the fuel collection line is extremely short. This in turn reduces the flow losses between the high-pressure fuel pump and the fuel collection line, so that for the same pressure in the fuel collection line, the moving parts of the high-pressure fuel pump can be made smaller. Moreover, it is no longer necessary to provide a special high-pressure fuel line between the high-pressure fuel pump and the fuel collection line. This reduces the costs.  
       [0006] Advantageous refinements of the invention are defined by dependent claims.  
       [0007] In a first refinement, it is stated that the high-pressure fuel pump includes a pump part that is rotatable about a rotationally fixed shaft, and the fuel collection line is disposed at least in some regions in the rotationally fixed shaft, in particular coaxially to the rotationally fixed shaft. This high-pressure fuel pump is especially compact in structure, since in it, the space required anyway for the shaft is used to accommodate at least part of the fuel collection line.  
       [0008] This can be achieved especially easily then if the high-pressure fuel pump includes a radial piston pump. The courses between the high-pressure outlet and the fuel collection line can then be kept especially short if the radial piston pump is a radially inward-pumping radial piston pump. In this case, the fuel collection line can be connected directly to the high-pressure outlet of the radial piston pump.  
       [0009] The radial piston pump can furthermore include a pump chamber, in which a rotor is disposed that is supported rotatably on a shaft disposed eccentrically to the longitudinal axis of the pump chamber; that the pump chamber can be defined radially by a rotatable ring; and that at least one piston can be provided, which is disposed radially displaceably in the rotor and rests with one radial end on the rotatable ring. A radial piston pump of this kind with a rotatable ring operates mechanically with especially little loss and can therefore, for generating a certain pressure in the fuel collection line, be relatively small in size.  
       [0010] This advantage becomes still greater if the rotatable ring is supported by an encompassing roller bearing.  
       [0011] The refinement of the high-pressure fuel pump of the invention which includes a prefeed pump and a main feed pump disposed fluidically downstream of the prefeed pump, which main feed pump pumps into the high-pressure outlet is especially preferred. With this kind of two-stage high-pressure fuel pump, it is possible with a compact structure to achieve an especially high pressure level at the high-pressure outlet.  
       [0012] It is especially preferred if the prefeed pump includes a vane cell pump, and the main feed pump includes a radial piston pump. A vane cell pump has very good efficiency at low to medium pressures, which conversely the radial piston pump is especially well suited for compression from medium to high pressures.  
       [0013] It is also proposed that the annular chamber of the radial piston pump, formed between the rotor and the radially outer wall of the pump chamber, communicates fluidically with the outlet side of the prefeed pump via a first throttle and a with an outlet via a second throttle. By suitable adaptation of the throttles, the pressure in the annular chamber is less than the pressure in the inlet to the radial piston pump. This reinforces the aspiration motion of the pistons during the intake stroke.  
       [0014] It is also especially preferred that the prefeed pump and the main feed pump are driven by a common shaft. Such a high-pressure fuel pump is also especially compact in structure.  
       [0015] It is also proposed that the housing is in multiple parts. This facilitates both the production of individual parts and the production of the bores present in the housing, through which bores the fuel is meant to flow.  
       [0016] The refinement in which the fuel collection line is provided in a housing part, whose outer contour, in one region, forms the stationary shaft can also be used. Such a part is relatively simple to produce and inexpensively unites two functions in one part.  
       [0017] The housing part in which the fuel collection line is provided can in turn be in multiple parts. In this case, the recess that forms the fuel collection line can be made more easily and can also have a complex geometry, which optimally utilizes the available space in the housing part.  
       [0018] The refinement in which a pressure limiting valve is disposed at the fuel collection line is also preferred. Moreover, the fuel line, which leads away from the pressure limiting valve, can be extended over a short course to the low-pressure inlet, for instance. This can be achieved by suitable bores in the housing. Expensive additional operations to produce a fluid communication thus become unnecessary.  
       [0019] A pressure sensor can also be disposed at the fuel collection line. This makes it possible to monitor the actual pressure prevailing in the fuel collection line, so that any malfunction of the high-pressure fuel pump can be detected immediately and suitable steps can be initiated.  
       [0020] The present invention also relates to a fuel system having a fuel tank, having at least one injection valve that injects the fuel directly into the combustion chamber of an internal combustion engine, having at least one high-pressure fuel pump, and having a fuel collection line to which the injection valve is connected.  
       [0021] In such a fuel system, in order to lower the production costs, it is proposed that the high-pressure fuel pump be embodied as defined above. In that case, the number of separate parts can be reduced, as can the expense required to produce the individual fuel connections.  
       [0022] Finally, the invention relates to an internal combustion engine, having at least one combustion chamber into which the fuel is injected directly.  
       [0023] To reduce the production costs for an internal combustion engine of this kind, it is proposed that the engine have a fuel system of the type defined above. Since because of the reduced number of separate parts and the reduced number of fluid connections to be produced this fuel system can be produced more easily, the total cost of the engine is reduced as a result. 
     
    
    
     DRAWING  
     [0024] Below, exemplary embodiments of the invention are described in detail in conjunction with the accompanying drawing. Shown in the drawing are:  
     [0025]FIG. 1, a longitudinal section through a first exemplary embodiment of a high-pressure fuel pump with a multi-part housing;  
     [0026]FIG. 2, a fragmentary section taken along the line II-II in FIG. 1;  
     [0027]FIG. 3, a longitudinal section, similar to FIG. 1, through a secod exemplary embodiment of a high-pressure fuel pump;  
     [0028]FIG. 4, a longitudinal section, similar to FIG. 1, of a third exemplary embodiment of a high-pressure fuel pump; and  
     [0029]FIG. 5, a basic illustration of an internal combustion engine having a fuel system using the high-pressure fuel pump of FIG. 1. 
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS  
     [0030] In FIG. 1, a high-pressure fuel pump is identified overall by reference numeral  10 . It includes a housing  12  that is constructed in multiple parts. The housing  12  includes one part  14 , disposed essentially on the left in FIG. 1, and one part  16 , disposed essentially on the right in FIG. 1. The high-pressure fuel pump  10  includes a low- pressure inlet  18 , which is connected to a fuel line not shown in FIG. 1. The high-pressure fuel pump  10  further includes a high-pressure outlet  20 , to which a fuel collection line  22  (also called a “rail”) is connected directly. The fuel collection line  22  is integrated with the part  16 , shown on the right in FIG. 1, of the housing  12  of the high-pressure fuel pump  10 .  
     [0031] A step-shaped recess  24  is made in the left-hand part  14  of the housing  12 . A shaft  28  is supported via a bearing  30  and sealing rings  32  in the region of the step-like recess  24  that has the smallest diameter (reference numeral  26 ). A vane cell pump  34  is driven by the shaft  28 . The vane cell pump  34  is of conventional design. It is not described in detail here. The vane cell pump  34  acts as a prefeed pump, which pumps from the crescent-shaped low-pressure inlet  18  into an also crescent-shaped prefeed pump outlet  36 .  
     [0032] A slaving disk  38  is secured to the right-hand end of the shaft  28 , in terms of FIG. 1, and onto it, two drivers  40  extending in the axial direction are formed. An annular sealing element  42  is provided between the slaving disk  38  and the vane cell pump  34 . The drivers  40  engage corresponding recesses  44  in a rotor  46 , and the rotor is part of a radial piston pump  48  acting as a main feed pump (see FIG. 3).  
     [0033] The rotor  46  is an annular part, into the wall of which radially extending through bores  50  are made. The through bores  50  are distributed over the circumference of the rotor  46 . Feed pistons  52  are guided radially displaceably in these bores. The length of the feed pistons  52  is approximately equivalent to the radial wall thickness of the rotor  46 .  
     [0034] The rotor  46  is mounted on a peglike protrusion  54  that is formed by the outer contour of the right-hand part  16  of the housing  12 . The protrusion  54  thus forms a shaft on which the rotor  46  is rotatably retained. The longitudinal axis of the shaft  54  is aligned with the longitudinal axis of the shaft  28 . Both axes are identified by reference numeral  56 .  
     [0035] A ring  58  is disposed radially on the outside around the rotor  46 . The inside diameter of the ring  58  is greater than the outside diameter of the rotor  46 . The longitudinal axis (not shown) of the ring  58  is parallel to but radially offset from the longitudinal axis  56  of the shaft  54 . The rotor  46  is thus disposed eccentrically relative to the ring  58 . The ring  58  is supported rotatably via a needle bearing  60  relative to an outer ring  62 . The outer ring  62  is in turn fitted in a manner fixed against relative rotation into a region  64  of the step-like recess  24  in the left-hand part  14 .  
     [0036] From the prefeed pump outlet  36 , a flow conduit  66  leads to a metering unit  68 . The flow conduit  66  is contained entirely in the left-hand part  14 . From the metering unit  68 , a flow conduit  70  in the part  16  of the housing  12  leads to a crescent-shaped main feed pump inlet  72 . The metering unit is essentially a magnet valve that controls the inflow of fuel to the main feed pump  48 .  
     [0037] The high-pressure outlet  20  is also embodied in crescent form. The fuel collection line  22  has one portion  74  of smaller diameter, which is connected directly to the high-pressure outlet  20 . It also has one portion  76  of greater diameter. Toward the outside, the fuel collection line  22  is closed with a stopper piece  78 , which is screwed into the portion  76  of the fuel collection line  22 .  
     [0038] In the stopper piece  78 , there is a central stepped bore  80 , into whose portion of larger diameter (not identified by a reference numeral) a pressure limiting valve  82  is screwed. From the portion  76  of the fuel collection line, a plurality of branch lines  84  also branch off; they open into threaded connections  86  for valve connections, not shown in the drawing. A pressure sensor  88  is also secured to the right-hand part  16  of the housing  12 ; in a manner not visible in the drawing, it communicates fluidically with the fuel collection line  22 .  
     [0039] Between the rotor  46  and the ring  58 , an annular chamber  90  is formed. Via a flow throttle  92  in the sealing element  42 , this annular chamber communicates fluidically with the prefeed pump outlet  36 . Via a further flow throttle, not visible, the annular chamber  90  communicates with an outlet that is at normal atmospheric pressure.  
     [0040] The high-pressure fuel pump  10  functions as follows: From the low-pressure inlet  18 , the fuel is precompressed to a certain level via the vane cell pump  34 . This pressure level prevails at the prefeed pump outlet  36 . The precompressed fuel is pumped via the flow conduit  66 , the metering unit  68 , and the flow conduit  70  to the main feed pump inlet  72 . Since because of the flow throttle  92  and the other flow throttle, not visible, the pressure in the annular chamber  90  between the rotor  46  and the ring  58  is less than the pressure at the main feed pump inlet  72 , the feed pistons  52 , upon a rotation of the rotor  46 , initially move radially outward. This motion is reinforced by centrifugal force.  
     [0041] Thus the corresponding feed chamber  94  located in the through bores  50  is filled with fuel. By means of the shaft  28 , the rotor  46  is rotated onward, so that the fuel-filled feed chamber  94  is disconnected from the crescent-shaped main feed pump inlet  72 . In the course of the motion, the feed chamber  94  is made to communicate instead with the high-pressure outlet  20 . Because of the eccentricity between the rotor  46  and the ring  58 , the feed piston  52  is simultaneously pressed radially inward, so that the fuel located in the feed chamber  94  is pumped into the fuel collection line  22  via the high-pressure outlet  20 .  
     [0042] In the fuel collection line  22 , the fuel is stored at high pressure. From the fuel collection line  22 , the fuel can be output again via the branch lines  84  and the threaded connections  86 . The pressure in the fuel collection line  22  is limited to a maximum value by the pressure limiting valve  82 . The monitoring of the pressure in the fuel collection line  22  is done by the pressure sensor  88 .  
     [0043] The exemplary embodiment shown in FIG. 3 will now be described. In it, only those parts that differ from the first exemplary embodiment are identified by reference numerals. All the other parts are essentially identical.  
     [0044] The primary difference between the exemplary embodiment shown in FIG. 3 and the exemplary embodiment of a high-pressure fuel pump  10  shown in FIGS. 1 and 2 is that the housing  12  of the high-pressure fuel pump  10  shown in FIG. 3 is not in only two parts but instead is in three parts. The corresponding parts are identified by reference numerals  14   a,    14   b,  and  16 .  
     [0045] In the exemplary embodiment of a high-pressure fuel pump  10  shown in FIG. 4, the same comment about the reference numerals as for FIG. 3 applies. In contrast to the exemplary embodiment shown in FIG. 3, in the exemplary embodiment of FIG. 4 the housing  12  is not merely in three parts but instead is in four parts. These parts are identified by reference numerals  14   a,    14   b,    16   a  and  16   b.  In addition, the fuel collection line  22  is designed in a way that is optimized volumetrically.  
     [0046] In FIG. 5, an internal combustion engine is schematically shown. It is identified by reference numeral  96 . It includes a fuel system  98 . The fuel system in turn contains a fuel tank  100 , from which the fuel is pumped, via an electric fuel pump  102 , to the high-pressure fuel pump  10 . This high-pressure fuel pump is embodied as in FIG. 1. A total of four injection valves  104  are connected to the high-pressure fuel pump  10  and inject the fuel directly into a combustion chamber  106 .