Patent Document

PRIOR ART 
       [0001]    The invention relates to a high-pressure fuel pump for an internal combustion engine as generically defined by the preamble to claim  1 . 
         [0002]    High-pressure fuel pumps with direct injection typically have a low-pressure region and a high-pressure region. An electric prefeed pump feeds the fuel from a tank into the low-pressure region, from which the fuel is fed via the high-pressure fuel pump into a fuel collection line (called “common rail”) that communicates with the high-pressure region. The pressure in the common rail is typically regulated by a pressure regulating and/or quantity control valve, and the valves are controlled by a control and/or regulating device, among other ways via an evaluation of signals of a pressure sensor. The pressure regulating valve can also function mechanically. 
         [0003]    From European Patent Disclosures EP 0 299 337 A2, EP 0 837 986 B1, EP 0 974 008 B1, and German Patent Disclosure DE 196 12 413 A1, devices for regulating the fuel pressure are already known. 
         [0004]    From German Patent Disclosure DE 103 27 411 A1, a pressure limiting valve is known for a high-pressure fuel pump that has a pressure limiting valve. 
       DISCLOSURE OF THE INVENTION 
       [0005]    The object of the invention is to create and further refine a high-pressure fuel pump for an internal combustion engine of the type defined at the outset, which functions reliably and is compact in construction. Moreover, the high-pressure fuel pump should be economical. 
         [0006]    This object is attained by a high-pressure fuel pump for an internal combustion engine having the characteristics of claim  1 . Characteristics important to the invention are also found in the ensuing description and in the drawings; the characteristics may be important for the invention both on their own and in various combinations, without this being referred to in each case explicitly. Advantageous refinements are found in the dependent claims. 
         [0007]    Because of the design of the high-pressure fuel pump, on the one hand space in the engine region of a motor vehicle is saved, and on the other, by skilled integration of the pressure regulating device with the high-pressure fuel pump, the known external dimensions of the high-pressure fuel pump can be kept unchanged. No additional hydraulic lines are needed. This advantageously leads to a very compact construction of the high-pressure fuel pump. Because controlling the fuel quantity is dispensed with, the high-pressure fuel pump also needs no quantity control valve with an associated end stage and an electrical trigger line. The pressure sensor required for electronic control can also be dispensed with. This makes the invention especially economical and also economizes on engine performance. Since the unneeded quantity of fuel is diverted into the low-pressure region, a pressure limiting function is ensured as well. 
         [0008]    The present invention is based on the idea that when a less pressure-sensitive fuel system is used in an internal combustion engine, such as a constant-pressure system, complicated electronic quantity control of fuel can be dispensed with. On this condition, the pressure regulation in the high-pressure region is then done via a mechanical pressure regulating device, which is integrated with the high-pressure pump. The pressure regulating device is disposed hydraulically between the low-pressure region and the high-pressure region. Once a previously adjustable opening pressure of the pressure regulating device is reached, the unneeded quantity of fuel is returned from the high-pressure region to the low-pressure region. As a result, in engine operation, an at least substantially constant pressure is established on the high-pressure side. 
         [0009]    In a first refinement, it is proposed that the mechanical pressure regulating device includes a mechanical pressure regulating valve, in particular a mechanical check valve, for instance subjected to a spring. Mechanical pressure regulating valves are relatively simple in construction, reliable, and thus economical. This is true particularly for check valves. Such a valve is moreover extremely small and therefore can be integrated without problems into the high-pressure fuel pump. 
         [0010]    It is especially advantageous if a mechanical throttle restriction is disposed upstream of a valve element of the pressure regulating device, so that adverse effects on the regulating performance in the common rail, especially of single-cylinder fuel pumps are used, from unwanted pressure pulsations of the high-pressure pump are reduced. Wear to the pressure regulating valve is thus reduced as well. The throttle restriction can be embodied as a separate throttle element or other cross-sectional constriction in an inflow conduit on the high-pressure side, a valve body, or a receiving opening in the pump housing. 
         [0011]    It is also proposed that the pressure regulating valve is disposed off-center in the pump housing of the high-pressure fuel pump, in a bore, and that optionally a connecting bore from the pressure regulating valve to the high-pressure region is also disposed off-center. The middle, central region in the pump housing is reserved in a known fashion for the actual pumping functions of the high-pressure fuel pump. In the off-center region, however, there is enough room to integrate the pressure regulating function. This makes the high-pressure fuel pump into a very effectively usable, compact device. Moreover, this makes machining of the pump housing easier. 
         [0012]    It is also proposed that a limit pressure in the high-pressure region is fixed by means of a valve spring and/or a sealing diameter between the valve element and the valve seat of the pressure regulating device. This means that in the design of the pressure regulating device, and optionally upon assembly of the high-pressure fuel pump, the limit pressure can be set precisely. Accordingly, no calibration of the completed high-pressure fuel pump, or even a high-pressure fuel pump already built into a motor vehicle, is needed. 
         [0013]    In addition, it is proposed that the pressure regulating device has a cartridgelike valve housing. Thus the pressure regulating device can be manufactured and adjusted as a separate component unit and then fitted into the pump housing and kept between the sleeve and the pump housing, for instance by way of a press fit. Adjusting the function of the pressure regulating valve is simpler, since among other factors, when the opening pressure is hydraulically set, there is no need also to clean the pump housing for further assembly steps. Moreover, if an incorrect setting occurs, it does not mean the rejection of the pump housing as well. 
         [0014]    It is also advantageous if the inlet valve is disposed coaxially to the pump piston of the high-pressure fuel pump. This makes it possible to achieve a high delivery rate of fuel from the low-pressure region, which can be even further increased if, between a pressure damper of the high-pressure fuel pump and the inlet valve, the diameter of the corresponding connecting bore is relatively large compared to the opening of the inlet valve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Below, in conjunction with the drawings, exemplary embodiments of the invention are described as examples. Shown are: 
           [0016]      FIG. 1 , a schematic illustration of a fuel system with a high-pressure fuel pump; 
           [0017]      FIG. 2 , a perspective view of the high-pressure fuel pump of  FIG. 1 ; 
           [0018]      FIG. 3 , a fragmentary longitudinal section through the high-pressure fuel pump of  FIG. 1 , with an inlet region shown in section; 
           [0019]      FIG. 4 , a longitudinal section through the high-pressure fuel pump of  FIG. 1 , with an outlet region shown in section; 
           [0020]      FIG. 5 , a longitudinal section through the high-pressure fuel pump of  FIG. 1 , with a pressure regulating valve shown in section (sectional plane V-V in  FIG. 6 ); 
           [0021]      FIG. 6 , a cross section through the high-pressure fuel pump of  FIG. 1 ; and 
           [0022]      FIG. 7 , an illustration similar to  FIG. 5  of a variant of the high-pressure fuel pump of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    The construction and general function of the high-pressure fuel pump of the invention will be described in its main aspects in conjunction with  FIG. 1 .  FIG. 1  is a schematic illustration of a fuel system  8  for an internal combustion engine (not shown) having a high-pressure fuel pump  10 . The fuel system, as will also be discussed hereinafter, is subdivided in a low-pressure region  12 , shown on the left in  FIG. 1 , and a high-pressure region  14 , shown on the right. A prefeed pump  16  disposed in the low-pressure region  12  pumps fuel from a fuel tank  18  via a low-pressure line  20  at a prefeed pressure to an inlet stub  22  of the high-pressure fuel pump  10 . In the high-pressure fuel pump  10 , a filter  24  and a pressure damper  26  are disposed in the low-pressure region  12 . The pressure damper  26  damps pulsations on the low-pressure side that occur in the high-pressure fuel pump  10  and ensures a high delivery rate even at high rotary and cam speeds. 
         [0024]    Via an inlet valve  28 , the fuel is aspirated into a work chamber  30  of the high-pressure fuel pump  10 . The volume of the work chamber  30  depends on the position of a pump piston  32  and a pump cylinder  34 . During a downward motion of the pump piston  32 , the work chamber  30  is increased in size, and as a result fuel is aspirated. During the upward motion of the pump piston  32 , the fuel is highly compressed and is fed via an outlet valve  36  and an outlet stub  38 , belonging to the high-pressure region  14 , onward via a high-pressure line  40  into a rail  42 . Injection valves  44  are connected to the rail  42  and inject the fuel directly into the combustion chambers  46  of the engine. 
         [0025]    The pump piston  32  is driven via a cam  48 , which is driven by the engine—for instance via a camshaft or crankshaft (not shown). The cam  48  can also be part of the camshaft or crankshaft. Sealing off the pump piston  32  from the cam  48  is effected via a sealing element  50 . Piston leakage that occurs in the gap between the pump piston  32  and the pump cylinder  34  is returned to the low-pressure region  12  via a return line  52 . 
         [0026]    Since in normal operation the feed quantity of the pump piston  32  is greater than the injected fuel quantity, an unneeded quantity of fuel on the high-pressure side  14  is returned to the low-pressure region  12  again via a purely mechanically functioning pressure regulating valve  54 . The pressure in the common rail  42  thus substantially corresponds to the opening pressure of the pressure regulating valve  54 . 
         [0027]    In the high-pressure region  14  as well, pulsations occur, especially if single-cylinder pumps are used. These pulsations can adversely affect the pressure regulating function in the rail  42 . For decoupling, a throttle restriction  56  is disposed hydraulically upstream of the pressure regulating valve  54 , and as a result, the pulsations upstream of the pressure regulating valve  54  and wear of that valve are reduced. 
         [0028]    The following drawings show the construction of the high-pressure fuel pump  10  in perspective or sectional views in greater detail. It should be pointed out that for reasons of simplicity and clarity, not all components are identified by reference numerals in all the figures. 
         [0029]      FIG. 2  shows the high-pressure fuel pump  10  in a perspective view. The inlet stub  22  (low-pressure region  12 ) and the outlet stub  38  (high-pressure region  14 ) are disposed on a pump housing  58 . A filter  64  is integrated with the inlet stub  22 . The high-pressure fuel pump  10  further includes an inwardly-indented cap  66  and a flange plate  68  for securing the high-pressure fuel pump  10 , for instance to a cylinder head of the engine. Both parts  66  and  68  are solidly connected to the pump housing  58 . The pump piston  32  protrudes downward out of the pump housing  58 . A piston spring  70  is braced on one end on a spring plate  72  solidly connected to the pump piston  32 , and is braced on the other end (not visible) on the pump housing  58 . The force of the piston spring  70  is accordingly introduced into the pump piston  32  via the spring plate  72 . It is thus ensured that in operation, the pump piston  32  always follows the contour of the cam. 
         [0030]    As can be seen from  FIG. 3 , the inlet stub  22  with the filter  64  communicates, via a bore  74  that is eccentric to a longitudinal axis  73  of the pump housing  58 , with a receiving chamber (not identified by reference numeral) for the pressure damper  26 , the receiving chamber being located below the cap  66 . The receiving chamber in turn can be made to communicate with the pump work chamber  30 , via two bore segments  78  and  80 , which are coaxial with the pump housing  58 , and via the inlet valve  28 . The pump piston  32  is displaceably supported in a cylinder bush  82 . During an intake phase of the pump piston  32 , the fuel reaches the pump work chamber  30  via the bores  78  and  80  and the inlet valve  28 . 
         [0031]    As seen from  FIG. 4 , the pump work chamber  30  and the outlet valve  36  communicate hydraulically with one another via a bore  88  in the pump housing  58 . From  FIGS. 5 and 6 , it can be seen that the pressure regulating valve  54  in the pump housing  58  is disposed eccentrically in a bore  90  and parallel to the longitudinal axis  73 . Accordingly, the sectional plane in  FIG. 4  is not central; instead, it is spaced apart from the longitudinal axis  73 . On the high-pressure side, the pressure regulating valve  54  communicates with the outlet valve  36  via a bore  92  that is also spaced apart from the longitudinal axis  73 . On the outlet side, the pressure regulating valve  54  communicates via the bore  90  with the receiving chamber for the pressure damper  26 . The pressure regulating valve  54  includes a valve seat (not identified by reference numeral) on a valve seat body  94  having an inflow bore  95 , and also includes a ball valve body  96 , a spring guide  98 , a valve spring  100 , and a spring holder  102 . 
         [0032]    The valve seat body  94  is solidly anchored in the bore  90 , for instance via a press fit. Via the spring guide  98 , the valve spring  100  presses the valve body  96  into the valve seat. In  FIG. 5 , the valve body is ball-shaped. Depending on the spring force and the sealing diameter between the valve body  96  and the valve seat  94 , a defined opening pressure results. In the upper part of  FIG. 5 , the valve spring  100  is braced on the spring holder  102 . The spring holder  102  is in turn solidly anchored in the bore  90  (for instance via a press fit). Upon the assembly of the pressure regulating valve  54 , the opening pressure is set by way of the press-fit travel distance of the spring holder  102 . 
         [0033]    The high-pressure fuel pump  10  functions as follows: Upon a downward motion of the pump piston  32  (“intake stroke”), fuel is aspirated into the work chamber  30  via the inlet valve  28 . Upon an upward motion (“delivery stroke”), the fuel in the work chamber  30  is compressed and is fed via the outlet valve  36  into the high-pressure line  40 . If the pressure in the high-pressure region  14  exceeds the limit pressure of the pressure regulating valve  54 , the latter opens because the valve body  96  lifts from the valve seat, so that fuel can flow away into the receiving chamber of the pressure damper  26  and thus into the low-pressure region  12 . If the pressure in the high-pressure region  14  drops below the limit pressure of the pressure regulating valve  54 , the latter closes again. In this way, the pressure in the high-pressure region  14  is kept essentially constant, namely at the limit pressure or opening pressure of the pressure regulating valve  54 . 
         [0034]      FIG. 7  shows a variant of the high-pressure fuel pump  10 . In it, those elements and regions that have equivalent functions to elements and regions that have already been described are identified by the same reference numerals and will not be explained again. 
         [0035]    In the alternative variant shown, the pressure regulating valve  54  is embodied in a cartridge version. The assembly of the pressure regulating valve  54  and the setting of the opening pressure can be done here outside the pump housing  58 . The valve seat body  94  is fitted into a sleeve  104  and retained, for instance via a press fit. After the valve body  96 , spring guide  98 , and valve spring  100  are put together, the spring holder  102  is fitted into the sleeve  104  as well. Once again, the spring force and thus the opening pressure are set by the position of the spring holder  102 . The spring holder  102  can, as shown in  FIG. 7 , be screwed into the sleeve  104 . As an alternative to the screw-in version, a press fit is also possible. Once the pressure regulating valve  54  has been installed and set, it is fitted as a component unit into the pump housing  58  and retained, for instance via a press fit, between the sleeve  104  and the pump housing  58 . 
         [0036]    In the variant of the high-pressure fuel pump  10  shown in  FIG. 7 , a throttle restriction  56  is also positioned in the bore  92 . It is also conceivable to dispose the throttle restriction  56  in the bore  90 . As an alternative to the throttle restriction  56 , the inflow bore  95  can also have a reduced cross section in some regions in the valve seat body  94 , as a result of which once again a throttling function is achieved.

Technology Category: f