Patent Publication Number: US-2010126474-A1

Title: High-pressure fuel pump for a fuel injection system of an internal combustion engine

Description:
PRIOR ART 
     The invention relates to a high-pressure fuel pump for a fuel injection system of an internal combustion engine, as defined by the preamble to claim  1 . 
     One such high-pressure fuel pump is known in the form of a radial piston pump from German Patent Disclosure DE 103 22 604 A1. It is relatively compact in size, since the drive of the pump piston is effected not via a drive shaft built into the pump but by a camshaft of an internal combustion engine, for instance. The radial piston pump can be inserted at least partially into the housing of an internal combustion engine, so that a camshaft of the engine can drive the piston of the radial piston pump via roller or cup tappets. 
     The known radial piston pump has an electromagnetic quantity control valve, which directly actuates an inlet valve that is disposed upstream of the reception chamber of the radial piston pump. 
     In addition, European Patent Disclosure EP 0 299 337 A2 and German Patent Disclosure DE 197 29 791 A1 are mentioned for their general relevance. 
     Based on the radial piston pump described at the outset, the object of the present invention is to create an especially compact high-pressure pump with good efficiency. 
     This object is attained by a radial piston pump having the characteristics of claim  1 . 
     Advantageous features are recited in the dependent claims. 
     ADVANTAGES OF THE INVENTION 
     By integrating a throttle restriction with or onto the housing of the preferably single-stroke radial piston pump, a compact unit can be created. By dispensing with a drive shaft of its own, a small pump housing can be employed. This avoids energy losses that can otherwise occur if a pump has its own drive shaft that in turn has to be driven via driving means, such as toothed belts. 
     By means of the throttle restriction, the reception chamber of the radial piston pump can be supplied with exactly the fuel quantity needed in the high-pressure region of the injection system. As a result, hydraulic energy losses are minimized. 
     Characteristics recited in dependent claims  14  through  19  lead to an especially compact construction, with which bores provided in the pump housing can be disposed optimally. Transverse bores and the use of closure elements can then be avoided or at least minimized. 
    
    
     
       DRAWINGS 
       Especially preferred exemplary embodiments of the present invention are described in further detail below in conjunction with the drawings. In the drawings: 
         FIG. 1  is a schematic view of an internal combustion engine with a fuel injection system and a single-stroke radial piston pump, in a first exemplary embodiment; 
         FIG. 2  is a perspective view of the radial piston pump of  FIG. 1 ; 
         FIGS. 3 through 7  are sectional views of the radial piston pump of  FIG. 1 ; 
         FIG. 8  is a schematic illustration of an internal combustion engine with a fuel injection system having a radial piston pump in a second embodiment and a further radial piston pump; 
         FIGS. 9 through 11  are sectional views of the radial piston pump of  FIG. 8 ; 
         FIG. 12  is a perspective view of the further pump in  FIG. 8 ; 
         FIG. 13  is a first sectional view through the further pump of  FIG. 12 ; and 
         FIG. 14  is a second sectional view of the further pump of  FIG. 12 . 
     
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     In  FIG. 1 , an internal combustion engine is identified by reference numeral  10 . It is supplied with fuel via a fuel injection system identified overall by reference numeral  12 . The fuel flows from a fuel collection container  14  (“tank”) to a prefeed pump  16 , which delivers the fuel to a single-stroke radial piston pump  18 . The pump  18  is driven directly by a camshaft of the engine  10 . The pump  18  has a fuel metering unit  20 , which is triggered via a control line  22  by a control unit  24 . 
     The fuel metering unit  20  has a throttle restriction, hereinafter called an intake throttle valve, which is described below in conjunction with  FIGS. 4 and 6 . When an intake throttle valve is used, a certain leak fuel quantity occurs. It is carried back to the tank  14  from the radial piston pump  18  via a line  26 . 
     The radial piston pump  18  pumps fuel, subjected to high pressure, into a high-pressure line  28 . This line discharges into a high-pressure reservoir  30 . The pressure in the high-pressure reservoir  30  can be detected via a pressure sensor  32 , and corresponding data can be forwarded to the control unit  24  with the aid of a data line  34 . 
     The fuel, at high pressure, can be carried out of the high-pressure reservoir  30  to injection devices  36 , which inject the fuel into respective combustion chambers of the engine  10 . In  FIG. 1 , as an example, only two of a higher number of injection devices are shown. 
     For triggering the fuel metering unit  20 , further data can be taken into account, such as the rpm of the engine  10  that can be detected by an rpm sensor  38  and forwarded to the control unit  24  via a data line  40 . Via a temperature sensor  42  and a data line  44 , the temperature, for instance of the engine coolant, can also be taken into account. 
     In  FIG. 2 , the radial piston pump  18  shown schematically in  FIG. 1  is shown in perspective. The pump  18  has a pump housing  46 , whose outer surface is approximately in the form of a hexagon (see  FIG. 6 ). A housing cap  48  is disposed on the pump housing  46 . The pump housing  46  can be secured to the engine  10  shown in  FIG. 1  via a flange  50 . Protruding from the pump housing  46  is a pump piston  52 , which is surrounded by a piston spring  54 . The pump piston  52  and the piston spring  54  can be inserted into the housing of the engine  10 , where the pump piston  52  can be driven via roller or cup tappets by the camshaft of the engine  10 . 
     Various connections for fuel lines are disposed on the outside of the pump housing  46 . The middle connection in  FIG. 2  is formed by a low-pressure connection stub  56 , which is supplied from the prefeed pump  16  shown in  FIG. 1  and leads to a low-pressure region of the radial piston pump  18 . The connection shown on the left in  FIG. 2  is formed by a high-pressure connection stub  58 , which is associated with a high-pressure region of radial piston pump  18  and supplies the high-pressure line  28  ( FIG. 1 ). The connection shown on the right in  FIG. 2  is formed by a stub  60  that discharges into the line  26 , through which the leak fuel quantity from the radial piston pump  18  can be delivered to the tank  14 . 
     The fuel metering unit  20  is disposed on the pump housing  46 , at a right angle to the longitudinal axis of the radial piston pump  18 . This unit is provided with an electrical terminal  62 , which can be made to communicate with the control line  22  ( FIG. 1 ). 
       FIG. 3  shows a section through the radial piston pump  18 , in a plane that extends through the low-pressure connection stub  56  (see  FIG. 2 ). In the interior of the pump housing  46 , a work chamber  64  is provided, to which fuel can be delivered in order to subject it to pressure as well by means of the pump piston  52 . The pump piston  52  is displaceably supported in a cylinder element  66 , which is solidly connected to the pump housing  46 . The pump piston  52  and the cylinder element  66  are sealed off from one another via a sealing element  68  that is disposed in a seal holder  70 . 
     The pump piston  52 , on its end remote from the work chamber  64 , has a spring plate  72  that is solidly connected to the pump piston  52 . Between the spring plate  72  and the seal holder  70  is the piston spring  54 , which is braced between these elements and presses the pump piston  52  in a direction facing away from the work chamber  64 . As a result, the pump piston  52  and downstream roller or cup tappets can be kept in contact with the camshaft of the engine  10 , this camshaft forming the external drive of the radial piston pump  18 . 
     The fuel delivered to low-pressure connection stub  56  can be delivered through a bore  74  to a filter  76  and finally to a pressure damper chamber  78  that is defined by the pump lid  48 . A pressure damper  80  is provided in the pressure damper chamber  78  in order to damp pressure fluctuations and to assure a high output by the high-pressure pump, even at high rpm of the engine  10  and even when there is an increased number of drive cams. 
     In the pump housing  46 , a further bore  82  is provided, which is disposed between the seal holder  70  and the low-pressure connection stub  56 . The bore  82  makes it possible for a leak fuel quantity to be carried away that comes from the work chamber  64  and passes between the pump piston  62  and cylinder element  66  and past the sealing element  68  to reach the seal holder  70 . 
       FIG. 4  shows the radial piston pump  18  in a sectional plane that extends through the high-pressure connection stub  58  and the fuel metering unit  20 . 
     This unit includes an electromagnet  84 , a connection piece  86 , and an intake throttle valve  88 , which is disposed inside the pump housing  46 . 
     Between the intake throttle valve  88  and the work chamber  64  is an inlet valve  90 . Downstream of the work chamber  64 , there is an outlet valve  92 , which leads to the high-pressure connection stub  58 . A bypass valve  94  is also provided between the pressure damper chamber  78  and the high-pressure connection stub  58 . 
     The electromagnet  84  has a magnet coil  96  as well as a magnet armature  98 , displaceable in the coil, with a magnet needle  100 . The magnet needle  100  extends through the connection piece  86 , and this connection piece is welded in leakproof fashion to the pump housing  46  via a welded connection  102 . 
     The intake throttle valve  88  has a slide element  104 , which is guided displaceably inside a cylinder element  106 . The intake throttle valve  88  further includes a bracing element  108 , which is press-fitted into the cylinder element  106 , and a spring  110 , which is braced on one end on a shoulder of the slide element  104  and on the other on the bracing element  108 . 
     The fuel that reaches the pressure damper chamber  78  via the low-pressure connection stub  56  shown in  FIG. 3  can reach a first annular chamber  114 , surrounding the cylinder element  106 , via a bore  112  in the pump housing  46 . Depending on the position of the slide element  104  inside the cylinder element  106 , the fuel can then reach a second annular chamber  118 , via control openings  116  embodied in the cylinder element  106 . This second annular chamber is sealed off from the first annular chamber  114  with the aid of a sealing element  120 . The components described thus far of the intake throttle valve  88  are shown enlarged in  FIG. 5 . The construction of the inlet valve  90 , outlet valve  92 , and bypass valve  94  will now be described in conjunction with  FIG. 5 . 
     The inlet valve  90  has a counterpart plate  122 , solidly joined to the pump housing  46 , as well as a valve plate  124 , which is urged by a valve spring  126  in the direction of the counterpart plate  122 . The valve spring  126  is braced, on the side facing away from the valve plate, on a valve sleeve  128 . The inlet valve  94  communicates hydraulically with the above-described second annular chamber  118  via a bore  130 . 
     The outlet valve  92  likewise has a counterpart plate  132 , which is connected to the pump housing  46 , and also has a valve plate  134 , a valve spring  136 , and a valve sleeve  138 . The outlet valve  92  communicates with the work chamber  64  via a bore  140 . On the side toward the high-pressure connection stub  58 , the outlet valve  92  protrudes into a bore  142 , branching off from which is a further bore  144  in which the bypass valve  94  is disposed. This valve comprises a valve seat  146 , solidly connected to the pump housing  46 , as well as a valve body  148 , a valve spring  150 , and a valve  152 . 
     For metering the fuel that reaches the work chamber  64  from the pressure damper chamber  78 , the electromagnet  84  can be triggered appropriately. The electromagnet  84  and the intake throttle valve  88  can be designed such that in the currentless state of the electromagnet  84 , the intake throttle valve is completely open or completely closed. In  FIGS. 4 and 5 , the electromagnet  84  is shown in the currentless state; the slide element  104  of the intake throttle valve  88  closes the control openings  116 , so that no fuel from the pressure damper chamber  78  can reach the work chamber  64 . When current is supplied to the electromagnet  84 , the magnet armature  98  and magnet needle  100  can exert a pressure force on the slide element  104 , causing this element to be displaced counter to the action of the spring  110  and correspondingly opening the control openings  116 . As a result of the opening of the control openings  116 , fuel can flow out of the first annular chamber  114  into the second annular chamber  118  and from there through the inlet valve  90  to reach the work chamber  64 . The pressure force of the spring  110  can be adjusted upon assembly of the intake throttle valve  88  by press-fitting the bracing element  108  into a suitable position inside the cylinder element  106  in accordance with the desired initial stress of the spring  110 . 
     If the electromagnet  84  is supplied more weakly with current or is no longer supplied with current, then the spring  110  presses the slide element  104  back into the position shown in  FIG. 4 . 
     The inlet valve  90  opens when the pump piston  52  moves out of the work chamber  64 . The pressure built up upstream of the inlet valve  90  by the prefeed pump  16  suffices to move the valve plate  124  away from the counterpart plate  122 , counter to the action of the valve spring  126 , so that fuel from the bore  130  can reach the work chamber  64 . 
     The inlet valve  90  closes automatically at the end of the intake phase. As a result of the upward motion of the pump piston  52 , the fuel contained in the work chamber  64  can be subjected to high pressure and delivered via the bore  140 , with opening of the outlet valve  92 , to the high-pressure connection stub  58 . To enable assuring emergency operation of the injection system  12  even if the intake throttle valve  88  is defective or is at least temporarily out of operation, the bypass valve  94  is provided. Trouble can occur, for instance when an intake throttle valve  88  has been closed without current, if the supply of current to the electromagnet  84  is interrupted or incorrect. In order nevertheless to be able to assure that the high-pressure connection stub  58  is supplied with fuel, the bypass valve  94  can open, at the pressure that is generated by the prefeed pump  16 . Thus fuel from the pressure damper chamber  78  can be delivered to the bore  144 , the bore  142 , and the high-pressure connection stub  58 . The opening pressure of the bypass valve  94  should be less than the sum of the opening pressures of the inlet valve  90  and outlet valve  92 . As a result, it can be attained when the engine  10  is put into operation, the bypass valve  94  briefly opens, as long as the radial piston pump  18  has not yet built up high pressure. The brief opening of the bypass valve  94  assures that this valve remains functional and will not become contaminated with dirt particles over the course of time. During the normal operation of the radial piston pump  18 , high pressure prevails in the high-pressure region of the radial piston pump  18  and thus also in the bore  144 , and thus the valve body  148  is pressed into the valve seat  146 , and the bypass valve  94  remains closed. 
     In  FIG. 6 , the radial piston pump  18  is shown in a sectional plane that extends perpendicular to the sectional plane selected in  FIG. 4 . 
     Between the second annular chamber  118 , downstream of the intake throttle valve  88 , and the stub  60  that communicates with the return  26 , a zero-feed throttle restriction  154  is disposed. Between the slide element  104  and the cylinder element  106  of the intake throttle valve  88 , leakage occurs during operation of the fuel injection system  12 . If the fuel quantity required by the engine  10  is less than the leak fuel quantity of the intake throttle valve  88 , then this quantity can be carried away through the zero-feed throttle restriction  154  into the line  26  to the tank  14 . 
     The design of the zero-feed throttle restriction  154  depends primarily on the pressure difference at this throttle restriction. In normal operation, the least pressure upstream of the zero-feed throttle restriction  154  is the sum of the vapor pressure of the fuel and the opening pressure of the inlet valve  90 . Downstream of the zero-feed throttle restriction  154 , atmospheric pressure prevails as a rule, or in other words approximately 1 bar. To make it possible for a fuel quantity to be diverted, the pressure upstream of the zero-feed throttle restriction  154  must be greater than downstream of it. For that reason, the opening pressure of the inlet valve  90  should not be less than 1 bar. The fuel quantity that flows out, at the given pressure difference, via the zero-feed throttle restriction  154  must be greater than the leak fuel quantity of the intake throttle valve  88 , so that the case of zero feeding can also be covered. The inside diameter of the zero-feed throttle restriction  154  should be at least 0.3 mm, to prevent the zero-feed throttle restriction  154  from becoming blocked by dirt particles. It is understood that the zero-feed throttle restriction  154  may also be integrated with the stub  60 . 
       FIG. 7  shows the radial piston pump  18  in a sectional plane that extends through the high-pressure connection stub  58  and perpendicular to the sectional plane of  FIG. 4 . The work chamber  64  communicates with the high-pressure connection stub  58  via the outlet valve  92 . This high-pressure region can be made to communicate with the work chamber  64  again with the aid of a pressure limiting valve  156 , in order to protect the fuel injection system  12  from pressures that exceed the allowable maximum pressure. The pressure limiting valve  156  is disposed in a bore  158  that discharges on the outlet side of the outlet valve  92  in the bore  142 . The pressure limiting valve  156  has a valve seat  160 , a valve body  162 , a valve spring  164 , and a spring receptacle  166 . The valve spring  164  is braced on one end on the spring receptacle  166  and on the other on the end of the bore  158 . The bore  158  communicates with the work chamber  64  via a transverse bore  168 . The transverse bore  168  is sealed off from the outside of the radial piston pump  18  with the aid of a closure body  170 . 
     If the pressure applied in the bore  142  exceeds an allowable maximum pressure, then the valve body  162  can be moved out of the valve seat  160 , counter to the pressure force of the valve spring  164 , so that fuel can be carried back into the work chamber  64  through the transverse bore  168 . The initial tension of the valve spring  164  should thus be selected such that the opening pressure of the pressure limiting valve  156  amounts to the highest possible maximum pressure in the bore  142 . 
     A second exemplary embodiment will now be described, in conjunction with  FIGS. 8-14 . 
     In  FIG. 8 , a fuel injection system  212  is shown schematically. The components that match those of the fuel injection system  12  of  FIG. 1  are identified by the same reference numerals. In this respect, the description of the first exemplary embodiment is applicable to its full extent. In a distinction from the fuel injection system  12 , the fuel injection system  212  has a radial piston pump  218  that requires no return (comparable to the line  26  in  FIG. 1 ). The radial piston pump  218  has a fuel metering unit  220  that is modified compared to the first exemplary embodiment and is described below in conjunction with  FIGS. 9-11 . In addition to the radial piston pump  218 , a further pump  222  is provided. The radial piston pump  218  and the further pump  222  are each driven by a camshaft of an internal combustion engine  210 . The further pump  222  is supplied from the radial piston pump  218  with the aid of a line  224 . Via a high-pressure line  226 , the further pump  222  can deliver fuel, subjected to high pressure, to the high-pressure line  28 , from which the fuel reaches the high-pressure reservoir  30 . To attain good overall efficiency, the line  224  should be as short as possible, and in particular shorter than 30 cm. By the use of a further pump  222 , the maximum deliverable fuel quantity of the fuel injection system  212  can be increased compared to the fuel injection system  12 . If a further increase is desired, then additional pump elements can be connected to the radial piston pump  218 . 
       FIG. 9  shows the radial piston pump  218  in a sectional plane that extends through the fuel metering unit  220 . 
     The radial piston pump  218  and the fuel metering unit  220  include a pump housing  46 , with a work chamber  64  that is preceded upstream by an inlet valve  90  and followed downstream by an outlet valve  92 . An electromagnet  284  that is triggerable via an electrical terminal  62  is provided on the pump housing  46 . The electromagnet  284  has a magnet coil  296 , a magnet armature  294 , and a magnet needle  300 . The electromagnet  284  is connected to the pump housing  46  via a connection piece  286  via a welded connection  302 . 
     The electromagnet  284  opens an intake throttle valve  288 , which is modified compared to the intake throttle valve  88  described in conjunction with the first exemplary embodiment. This modified intake throttle valve will be described hereinafter in conjunction with  FIG. 10 . The installation situation of the intake throttle valve  288  is comparable to that of the intake throttle valve  88 . Thus the fuel delivered to the pressure damper chamber  78  can flow via the bore  112  into a first annular chamber  114 , via the intake throttle valve  288  into a second annular chamber  118 , and from there into a bore  130  to reach the inlet valve  90  and finally the work chamber  64 . The first annular chamber is sealed off from the second annular chamber with the aid of a sealing element  120 . 
     The intake throttle valve  288  and its mode of operation will now be described in conjunction with  FIG. 10 , in which the detail marked X in  FIG. 9  is shown. The intake throttle valve  288  can be coupled to a pressure limiting valve  400 . The intake throttle valve  288  has a cylinder element  306 , which is solidly connected to the connection piece  286  and in which a slide element  304  is displaceably supported. The slide element  304  is pressed in the direction of the pressure limiting valve  400  with the aid of a spring  310 . Depending on the position of the slide element  304 , control openings  316  embodied in the cylinder element  306  are opened or closed. 
     The pressure limiting valve  400  discharges, on the side remote from the intake throttle valve  288 , in a bore  402  that is communication with the bore  144  for the bypass valve  94 . The bore  402  communicates, on the side opposite the bypass valve  94 , with a bore  404  that discharges in the bore  142  on the outlet side of the outlet valve  92 . The bore  142  is located adjacent to the high-pressure connection stub  58 . 
     The pressure limiting valve  400  has a pressure piece  406 , which is solidly connected to the pump housing  46 . The pressure piece  406  is also solidly connected to the cylinder element  306  of the intake throttle valve  288 . A valve seat  408  is press-fitted into the pressure piece  406 , and a valve body  410  of a coupling element  412  is associated with this valve seat. The coupling element  412  is braced via a valve spring  414  on the cylinder element  306 , so that the valve body  410  is pressed into the valve seat  408 . The coupling element  412  has slaving elements  416 , which can cooperate with the slide element  304  of the intake throttle valve  288 . This will be described in further detail hereinafter. 
     The slide element  304  is connected, on the side opposite the pressure limiting valve  400 , to the magnet needle  300  of the electromagnet  284  via a connecting element  418 . 
     The magnet valve  284  shown in  FIG. 9  is open in its currentless state, so that fuel from the first annular chamber  114  can reach the second annular chamber  118  via the control openings  116 . The spring  310  urges the slide element  304  in the direction of the pressure limiting valve  400 . 
     When current is supplied to the electromagnet  284 , the magnet needle  300  is pulled out of the pump housing  46 . This motion is transmitted via the connecting element  418  to the slide element  304 , so that the slide element  304  gradually closes the control openings  316 . As current continues to be supplied to the electromagnet  284 , the slide element  304  engages the slaving elements  416  of the coupling element  412 , so that the coupling element  412  and the valve body  410  disposed on it are subjected to an opening force counter to the action of the valve spring  414 . If the opening force is high enough, the pressure limiting valve  400  is opened and establishes a communication among the bores  142 ,  404  and  402  and the first annular chamber  114 , so that fuel subjected to high pressure can be carried from the high-pressure side of the radial piston pump  218  back to the low-pressure side. The fuel thus diverted can be received in the pressure damper chamber  78 . 
     Diverting the fuel that is at high pressure is advantageous so as to make it possible to reduce an undesirably high pressure in the high-pressure region of the radial piston pump  218 . Such situations occur in the overrunning mode, for instance, or upon shutoff of the engine  210 . 
     For the manufacture of the bores  144  and  404 , it is advantageous if they are aligned with one another, so that bores can be made in one machining operation. If both bores  144  and  404  have the same diameter, then both bores can be made simultaneously with a continuously identical diameter with the same drill. 
       FIG. 11  shows the radial piston pump  218  in a sectional plane that is perpendicular to the plane chosen in  FIG. 9 . The pump housing  46  with the high-pressure connection stub  58  and the low-pressure connection stub  56  can all be seen. A connection stub  420  for the further pump  222  schematically shown in  FIG. 8  is also provided. The connection stub  420  leads to the line marked  224  in  FIG. 8 . 
     The fuel delivered to the radial piston pump  218  can flow via the first annular chamber  114  and via the intake throttle valve  288  to reach the second annular chamber  118 . From there, it can be carried to the connection stub  420  via a bore  422 . 
       FIG. 12  shows the further pump  222  in a perspective view. The pump  222  has a pump housing  424 , which can be secured to the engine  210  via a flange  426 . The pump  222  has a pump piston  428  and a piston spring  430 , which can both be introduced into the housing of the engine  210  so that the pump piston  428  can be driven by a camshaft of the engine  210 . 
     A low-pressure connection stub  432  is provided on the pump housing  424  and is supplied with fuel by the radial piston pump  218  via the line  224 . On the high-pressure side of the pump  222 , a high-pressure connection stub  434  is provided, which leads to the high-pressure line  226 . 
     The pump  222  is shown in  FIG. 13 , in a sectional plane through the pump housing  424  and the pump piston  428 . 
     The pump piston  428  defines a work chamber  436  and is supported displaceably in a cylinder element  438 . The cylinder element  438  is solidly connected to the pump housing  424 . The sealing of the cylinder element  438  and the pump piston  428  is effected via a sealing element  440  that is received in a seal holder  442 . A leak fuel quantity emerging via the sealing element  440  can be delivered via a bore  446  to a bore  448  in the low-pressure region of the pump  222 . 
     An inlet valve  450  is disposed upstream of the work chamber  436 , and a bore  452  that leads to an outlet valve  454  is disposed downstream of the work chamber. On the outlet side of the outlet valve  454 , a bore  456  is provided, which leads to the high-pressure connection stub  434 . 
     Fuel delivered through the low-pressure connection stub  432  flows via the bore  448  to reach the inlet valve  450 , which opens when the piston  428  moves out of the work chamber  436 . The motion of the pump piston  428  out of the work chamber is effected with the aid of the piston spring  430 , which presses the pump piston  428  against a drive cam of the engine  210 . If the pump piston  428  is moved into the work chamber  436  by the camshaft of the engine  210 , then the fuel subjected to pressure flows via the bore  452  to reach the outlet valve  454 . This valve opens, and the fuel subjected to pressure reaches the high-pressure connection stub  434  and from there the high-pressure line  226  (see  FIG. 8 ). 
     In  FIG. 14 , the pump  222  is shown in a sectional plane perpendicular to the plane chosen in  FIG. 13 . To protect the fuel injection system  212  against an overload, a pressure limiting valve  458  is provided, by which the bore  456 , adjacent to the high-pressure connection stub  434 , can be made to communicate with the work chamber  436 . The pressure limiting valve  458  is disposed in a bore  460  and has a valve seat  462 , a valve body  464 , and a valve spring  466  that is braced on a spring holder  468  and on the end of the bore  460 . The bore  460  communicates with the work chamber  436  via a transverse bore  470 . The transverse bore  470  is closed off from the outside by a closure body  472 . If the fuel located in the bore  456  exceeds an allowable maximum pressure, the pressure limiting valve  458  is opened, so that the fuel can flow through the bore  460  and the transverse bore  470  back into the work chamber  436 .