Abstract:
A high-pressure fuel pump with a pressure relief valve which has improved hydraulic properties and a reduced number of high-pressure sealing points.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a high-pressure fuel pump with a delivery chamber that is connected on the intake side via an intake valve to a low-pressure fuel line and is connected on the pressure side via a high-pressure connection to a high-pressure fuel line, in which a check valve and a pressure relief valve connected parallel to it are provided between the delivery chamber contained in a housing and the high-pressure connection connected in a fluid-tight manner to the housing, and the pressure relief valve is contained in a blind hole bore of the housing.  
         [0003]     2. Description of the Prior Art  
         [0004]     A high-pressure fuel pump of the type with which this invention is concerned is known from DE 103 27 411, which was published after the priority date of the present application. The advantage of this high-pressure fuel pump is that the pressure relief valve does not open during the delivery stroke and consequently, transient pressure peaks that occur during the delivery stroke of the high-pressure fuel pump do not reduce the volumetric efficiency of the high-pressure fuel pump. Only during the intake stroke when a much lower pressure prevails in the delivery chamber than in the high-pressure fuel line does the pressure relief valve open if the high-pressure fuel line contains an impermissibly high pressure, thus effectively protecting the high-pressure fuel pump and the entire high-pressure region of the fuel injection system from impermissibly high pressures.  
         [0005]     Another feature of the high-pressure fuel pump according to the invention is that the blind hole bore that contains the pressure relief valve starts from a chamber delimited by the high-pressure connection and the housing.  
       OBJECT AND SUMMARY OF THE INVENTION  
       [0006]     It is possible to integrate the pressure relief valve into the housing of the high-pressure fuel pump, without an additional high-pressure sealing point in the high-pressure region of the high-pressure fuel pump. This achieves significant cost savings and also reduces the number of high-pressure sealing points since a check valve is already provided between the high-pressure connection and the delivery chamber. In other words, according to the invention, the check valve and the pressure relief valve can be mounted in the housing before the high-pressure connection assembly is installed onto the housing and connected to it in a pressure-tight manner. The high-pressure connection can be welded to the housing or screwed into it.  
         [0007]     The high-pressure fuel pump according to the invention is consequently very simple in design and particularly well-suited to a maximally automated series production since the check valve and the pressure relief valve are mounted close to each other in the housing of the high-pressure fuel pump and as a rule, the mounting direction of the pressure relief valve and that of the check valve are aligned parallel to each other. All of these features significantly simplify production, particularly mass production, of the high-pressure fuel pump according to the invention.  
         [0008]     In addition, the high-pressure fuel pump according to the invention has a very advantageous operating behavior, which will be evident from the following explanations:  
         [0009]     The pressure relief valve according to the invention is prevented from opening in an undesirable fashion in that the pressure pulsations produced by the high-pressure pump during the delivery stroke act on the valve element from both sides, i.e. from both the inlet and outlet. As a result of this, the pressure pulsations, whose maximum can be considerably higher than the opening pressure of the pressure relief valve, do not produce a resultant hydraulic force on the valve element. This assures that the valve element does not lift up from its valve seat during the delivery stroke and consequently, the pressure relief valve does not open.  
         [0010]     The pressure relief valve according to the invention also prevents the occurrence of impermissibly high pressures in the high-pressure region of the fuel system during the intake stroke of the high-pressure pump. Precisely stated, the check valve between the delivery chamber of the high-pressure pump and the high-pressure region of the fuel system is closed during the intake stroke and a possibly increased pressure in the high-pressure region of the fuel system opens the valve element of the pressure relief valve so that a pressure decrease occurs.  
         [0011]     Another advantageous embodiment of the invention includes the provision that the pressure relief valve has a housing with a valve seat and a spring chamber, that the spring chamber contains a spring, which rests against the housing at one end and rests against the valve element at the other end, that the spring chamber is hydraulically connected to the outlet, that the valve seat is disposed in a seat sleeve, and that the seat sleeve is fastened in a blind hole bore of the housing. This exemplary embodiment is particularly simple from a production engineering standpoint since a spring, the valve element, and the seat sleeve need only be inserted into the blind hole bore that is provided anyway. The opening pressure of the pressure relief valve can be set by selecting the depth at which the seat sleeve is fastened in the blind hole bore, whether by means of welding, press-fitting, or caulking.  
         [0012]     The production of the pressure relief valve is further simplified if the valve seat is disposed in a seat sleeve and this seat sleeve is attached in a blind hole bore of the housing, for example by being press-fitted and/or welded in place.  
         [0013]     Another embodiment is characterized in that the pressure relief valve has a spring retainer and in that a spring is provided between the spring retainer and the valve seat, which rests against the spring retainer at one end and rests against the valve element at the other end, thus allowing the pressure relief valve to be integrated into the high-pressure fuel pump in different installation positions. This also simplifies the production of the pressure relief valve.  
         [0014]     Another modification of the invention includes the provision that the spring retainer is connected to the seat sleeve so that the production, testing, and calibration of the pressure relief valve can occur outside the high-pressure fuel pump. In addition, the operating behavior of the high-pressure fuel pump is improved if the opening pressure of each pressure relief valve is measured and set before installation.  
         [0015]     Alternatively, the spring retainer can also be attached to the bottom of the blind hole bore of the housing, thus reducing the number of components. The spring retainer can also be provided with a supporting arbor to prevent the spring from moving out of the way laterally.  
         [0016]     The pressure relief valve according to the invention is particularly suited for use in a one-cylinder piston pump. The delivery pulsations are particularly pronounced in a high-pressure pump of this kind, so the action of the pressure relief valve according to the invention is particularly effective in this kind of pump. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments, taken in conjunction with the drawings, in which:  
         [0018]      FIG. 1  is a schematic representation of a fuel system with a fuel pump that has a pressure relief valve attached to it;  
         [0019]      FIG. 2  is a section through a region of the high-pressure pump and a first exemplary embodiment of a pressure relief valve from  FIG. 1 ;  
         [0020]      FIG. 3  is a graph in which the marches of pressure in the delivery chamber and high-pressure region of the fuel system are plotted over time; and  
         [0021]     FIGS.  4  to  8  show other exemplary embodiments of pressure relief valves according to the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     In  FIG. 1 , a fuel system is labeled as a whole with reference numeral  10 , and includes a low-pressure region  12  and a high-pressure region  14 . The low-pressure region  12  includes a tank  16  in which fuel  18  is stored. The fuel  18  is fed from the tank  16  by a first fuel pump  20 , which is an electric fuel pump. The electric fuel pump  20  feeds into a low-pressure fuel line  22  provided with a filter  24  downstream of the electric fuel pump  20 . Upstream of the filter  24 , a first branch line  26  branches off from the low-pressure fuel line  22  and leads back to the tank  16 . The first branch line  26  contains a pressure relief device  28 .  
         [0023]     The low-pressure line  22  leads to a high-pressure pump  30 , which is driven in a manner not shown here by the camshaft of an internal combustion engine, not shown. The high-pressure pump  30  is a one-piston high-pressure pump. Upstream of the high-pressure pump  30  a pressure damper  32  and an intake valve  34  are also provided in the low-pressure fuel line  22 . Between the filter  24  and the pressure damper  32 , a second branch line  36  that contains a low-pressure regulator  38  branches off from the low-pressure fuel line  22 . The second branch line  36  also leads to the tank  16 . A leakage line  40  leads from the high-pressure pump  30  to the second branch line  36 .  
         [0024]     On the outlet side, the high-pressure pump  30  feeds into a high-pressure fuel line  42 , which leads via a check valve  44  to a fuel accumulator  46 . The fuel accumulator  46  is in turn connected to fuel injection valves  48 , which inject the fuel into a combustion chamber, not shown, of the engine. A pressure sensor  50  detects the pressure in the fuel accumulator  46 .  
         [0025]     In order to improve the operating behavior of the high-pressure region  14  of the fuel system  10 , a throttle (not shown) can be provided in the high-pressure fuel line  42  upstream of the fuel accumulator  46 . The throttle reduces pressure fluctuations and an undesirable noise generation in the high-pressure region  14 .  
         [0026]     In the exemplary embodiment according to  FIG. 1 , the pressure in the high-pressure fuel line  42  and the high-pressure accumulator  46 , i.e. in the high-pressure region  14  of the fuel system  10 , is controlled by means of a quantity control valve  52  connected to the high-pressure side. This valve connects the region of the high-pressure fuel line  42  disposed between the check valve  44  and the fuel accumulator  46  to the region of the low-pressure fuel line  22  disposed between the intake valve  34  and the pressure damper  32 . The connection is provided by a third branch line  54 . The quantity control valve  52  is triggered by a control and regulating unit not shown in  FIG. 1 , which in turn receives signals from the pressure sensor  50 . This provides a closed control loop for controlling the pressure in the high-pressure region  14  of the fuel system  10 . FIGS.  4  to  8  show a pressure relief valve provided on the intake side to control the pressure regulation in the high-pressure region.  
         [0027]     In the event of the failure of the quantity control valve  52 , a pressure relief valve  56  is integrated into the high-pressure pump  30  in order to prevent an excess pressure in the fuel accumulator  46  that could impair the functional capability of the injection valves  48 . The design and function of the pressure relief valve  56  will be explained below in conjunction with  FIG. 2  and FIGS.  4  to  8 :  
         [0028]      FIG. 2  shows a first exemplary embodiment of a pressure relief valve  56  according to the invention, which is integrated into a housing  58  of the high-pressure pump  30 . The housing  58  contains a delivery chamber  60  that is delimited on one side by a piston  62  of the high-pressure pump  30 . The piston  62  is driven to oscillate in a bore  64  of the housing  58 . The drive mechanism of the piston  62  is not shown in  FIG. 2 . A double arrow  66  in  FIG. 2  indicates the oscillating motion of the piston  62 .  
         [0029]     The sectional view of the high-pressure pump  30  depicted in  FIG. 2  does not show the quantity control valve  52  and the hydraulic connection between the low-pressure fuel line  22  and the delivery chamber  60 , with the intake valve  34  connected between them, but does clearly show the hydraulic connection between the pressure damper  32  and the low-pressure fuel line  22  by means of a connecting bore  110 , which is embodied in the form of a stepped bore.  
         [0030]     The delivery chamber  60  is hydraulically connected to the high-pressure fuel line  42  via a stepped bore  61  in the housing  58  and a high-pressure connection  63  tightly connected to the housing  58 . The high-pressure fuel line  42  is connected to the high-pressure connection  63  by means of a clamping nut  65 . The check valve  44  is press-fitted into the stepped bore  61 .  
         [0031]     The high-pressure connection  63 , the housing  58 , and the check valve  44  delimit a chamber  68 . A blind hole bore  69  is drilled into the housing  58  starting from this chamber  68 . The pressure relief valve  56  according to the invention is contained in this blind hole bore, which constitutes a section  70 a of the fourth branch line  70 . Between the delivery chamber  60  and the blind hole bore  69 , a connecting bore is provided, which constitutes a section  70 b of the fourth branch line  70 .  
         [0032]     The blind hole bore  69  can also be embodied as a stepped bore (not shown), in which case seat sleeve  102  is press-fitted into the stepped bore so that it is affixed in the axial direction against a shoulder of the stepped bore. The position of this shoulder determines the opening pressure of the pressure relief valve.  
         [0033]     In the exemplary embodiment shown in  FIG. 2 , the pressure relief valve  56  is embodied in the form of a ball valve. According to the invention, however, other forms of seat valves and even slide valves can also be used.  
         [0034]     The lower part of  FIG. 2  shows an enlargement of the pressure relief valve  56  according to the invention and the components of the pressure relief valve  56  are provided with reference numerals. For the sake of clarity, these reference numerals are not fully represented in the upper part of  FIG. 2 , which shows the pressure relief valve  56  installed in the housing  58 . The pressure relief valve  56  is essentially comprised of a spring  76  that rests against the housing  58  at one end and rests against a spring plate  94  at the other end. The spring plate in turn rests against a valve element  74 , which the spring  76  presses into a valve seat  72  of a seat sleeve  102 . The seat sleeve  102  contains a bore  104 . A number of grooves  105  are provided distributed over the circumference of the spring plate  94  so that fuel can flow through the bore  104 , past the valve element  74 , and through the grooves  105  of the spring plate  94  as soon as the pressure of the fuel (not shown) in the bore  104  is sufficient to exceed the spring force that the spring  76  exerts on the valve element  74 . It is naturally also possible to omit the grooves  105  and to provide a corresponding amount of play between the spring plate  94  and the blind hole bore  69  in the housing  58 , thus allowing the fuel to flow through the pressure relief valve  56  and back into the delivery chamber  60  (see  FIG. 2  top) as soon as the pressure in the high-pressure fuel line  42  and in the chamber  68  exceeds the maximum permissible pressure during the intake stroke of the piston  62 . The opening pressure of the pressure relief valve  56  according to the invention can be set by selecting the depth at which the seat sleeve  102  is press-fitted into blind hole bore  69 . The seat sleeve  102  is either press-fitted or welded into the blind hole bore  69  or is positioned and securely connected to the housing  58  in some other way.  
         [0035]     Because the spring chamber  78  and therefore also the back side of the valve element  74  is acted on with the pressure prevailing in the delivery chamber  60 , the valve element  74  does not lift away from the valve seat  72  during the delivery stroke of the high-pressure fuel pump  30 , even if pressure pulsations occur in the delivery chamber  60  or in the high-pressure fuel line  42 . Precisely stated, during the delivery stroke, the check valve  44  is open so that the pressure is the same in the high-pressure fuel line  42 , the fourth branch line  70 , the spring chamber  78 , and the delivery chamber  60 , and consequently, the hydraulic forces acting on the valve element  74  cancel each other out.  
         [0036]     Only during the intake stroke, namely when the pressure in the delivery chamber  60  decreases and the check valve  44  closes, does a pressure differential arise between the sections  70   a  and  70   b  of the fourth branch line  70 , which causes a resultant hydraulic force to be exerted on the valve element  74 . If this resultant hydraulic force exceeds the closing force that the spring  76  exerts on the valve element  74 , then the pressure relief valve  56  opens and an impermissibly high pressure in the high-pressure fuel line  42  is discharged into the delivery chamber  60  via the fourth branch line  70  and the pressure relief valve  56 .  
         [0037]     As can be inferred from the description of the first exemplary embodiment, the pressure relief valve  5  is embodied as simply as other pressure relief valves known from the prior art. Because of the connection according to the invention, the pressure relief valve  56  remains closed even when pressure pulsations occur during the delivery stroke of the high-pressure fuel pump  30 . As a result, the pressure reduction occurs as desired during normal operation of the engine. Only if the pressure in the high-pressure fuel line  42  exceeds the opening pressure of the pressure relief valve  56  during the intake stroke of the high-pressure pump  30  does the pressure relief valve  56  open and thus permit a pressure reduction in the high-pressure fuel line  42 .  
         [0038]     In  FIG. 3 , the marches of pressure in the delivery chamber  60  and in the high-pressure fuel line  42  downstream of the check valve  44  are plotted over the stroke of the piston  62  of the high-pressure pump  30 .  
         [0039]     A first line  80  represents the path of the piston  62  in the bore  64 . The movement from the lower dead center to the upper dead center is referred to as the delivery stroke and is indicated by the double arrow  82  in  FIG. 3 .  
         [0040]     The path of the piston from upper dead center to lower dead center is referred to as the intake stroke  84 .  
         [0041]     A second solid line  86  represents the pressure in the delivery chamber  60 . It is clear in  FIG. 3  that a so-called pressure pulsation  85  is generated during the delivery stroke. That is, a pressure peak with a maximum value of P max  is generated, which is significantly higher than an opening pressure P DBV  of the pressure relief valve  56 .  
         [0042]     A dashed third line  88  is plotted in  FIG. 3 , which represents the pressure in the high-pressure line  42  downstream of the check valve  44  and in the section  70   a  of the fourth branch line  70 . In  FIG. 3 , it is clear that the line  88 , i.e. the pressure in the high-pressure fuel line  42 , follows the pressure in the delivery chamber  60  (second line  86 ) during the delivery stroke  82 , even if the pressure exceeds the opening pressure P DBV  of the pressure relief valve  56 . Only if the pressure in the delivery chamber  60  drops sharply during the intake stroke  84  (see the second solid line  86 ) can a pressure differential arise between the pressure in the high-pressure fuel line  42  and the pressure in the delivery chamber  60 . In the operating state of the fuel system shown in  FIG. 3 , the pressure in the high-pressure fuel line  42  remains equal to the opening pressure P DBV  of the pressure relief valve  56  during the intake stroke, whereas the pressure drops sharply in the delivery chamber  60 . In other words: the pressure relief valve  56  prevents the occurrence of impermissibly high pressures during the intake stroke in that the fuel quantity delivered into the fuel accumulator  46  during the delivery stroke is discharged into the delivery chamber  60  again during the intake stroke.  
         [0043]     The second exemplary embodiment of a pressure relief valve  56  according to the invention shown in  FIG. 4  is embodied in the form of a preassembled component comprised of the seat sleeve  102  with a seat  72  and a bore  104  as well as a spring retainer  106 , a spring  76 , and a valve element  74 .  FIG. 4  shows a preassembled pressure relief valve  56  of this kind, outside the housing  58 .  
         [0044]     As is clear from  FIG. 4 , the spring retainer  106  is attached to the seat sleeve  102  by crimping and welding (see the welded seam  109 ). The spring  76  rests against the spring retainer  106  at one end and against the valve element  74  and the other end. If the seat sleeve  102  and the spring retainer  106  are attached to each other, then the opening pressure of the pressure relief valve  56  can be adjusted by compressing the spring retainer  106  slightly in the direction of its longitudinal axis. This increases the prestressing force that the spring  76  exerts on the valve element  74  and as a result, also increases the opening pressure of the pressure relief valve. Consequently, this pressure relief valve  56  according to the invention can be fully assembled and adjusted outside the high-pressure fuel pump  30 . This is advantageous in terms of production cost. It also significantly reduces the variation in the operating behavior among different exemplars of mass-produced pressure relief valves  56  according to the invention.  
         [0045]      FIG. 5  shows another exemplary embodiment of a pressure relief valve  56  according to the invention, outside the housing  58 . As in the other exemplary embodiments, the installation position of this exemplary embodiment corresponds to the installation position of the first exemplary embodiment.  
         [0046]     The spring retainer  106  is inserted into the blind hole bore  69  (not shown in  FIG. 5 , see  FIG. 2 ). Then the spring  76  and the seat sleeve  102  are mounted in the way described above. In this exemplary embodiment of a pressure relief valve  56  according to the invention, there is no direct connection between the seat sleeve  102  and spring retainer  106 . A supporting arbor  112  is provided on the spring retainer  106  to prevent the spring  76  from moving out of the way laterally.  
         [0047]      FIG. 6  shows another exemplary embodiment of a pressure relief valve  56  according to the invention. Components that are the same have been provided with the same reference numerals and that which has been said in relation to  FIGS. 2, 4 , and  5  applies correspondingly. By contrast with the first exemplary embodiment according to  FIG. 2 , for example, a dividing piston  90 , which is guided in a sealed fashion in the spring retainer  106 , is provided between the delivery chamber  60  and the valve element  74 , which piston protrudes into the spring chamber  78 , and rests against the valve element  74 . In this exemplary embodiment, the spring retainer  106  is mounted far enough away from the bottom of the blind hole bore  69  that the spring retainer  106  hydraulically divides the spring chamber  78  from the bore  70   b  (see  FIG. 2 ) and a coupling occurs exclusively via the dividing piston  90 .  
         [0048]     If a higher pressure prevails in the delivery chamber  60  than in the spring chamber  78 , then the dividing piston  90  is moved in the direction of the valve element  74  and presses it into its seat  72 . The provision of the dividing piston  90  reduces the dead volume in the delivery chamber  60  and thus improves the volumetric efficiency of the high-pressure pump  30 .  
         [0049]     In this exemplary embodiment, the spring chamber  78  is connected to an unpressurized leakage line or to the low-pressure fuel line  22  (see  FIG. 1 ). This means that during the delivery stroke of the high-pressure pump  30 , the dividing piston  90  presses against the valve element  74 , thus preventing the pressure relief valve  56  from opening during the delivery stroke  82 .  
         [0050]     The diameters of the dividing piston  90  and valve seat  72  can also be selected to achieve a hydraulic boosting of the hydraulic force that the dividing piston  90  exerts on the valve element  74  during the delivery stroke. The dividing piston  90  maximizes the volumetric efficiency of the high-pressure fuel pump  30 .  
         [0051]     The exemplary embodiment of a pressure relief valve  56  according to  FIG. 6 , like the exemplary embodiment according to  FIG. 4 , can be fully assembled and adjusted outside the high-pressure pump  30  since a sleeve  116  with at least one lateral bore  118  is provided between the seat sleeve  102  and spring retainer  106 . The sleeve  116  is welded to the spring retainer  106  and seat sleeve  102  when the prestressing of the spring  76  is sufficient to achieve a desired opening pressure of the pressure relief valve  56 . Naturally, the sleeve  116  can also be attached to the spring retainer  106  and/or the seat sleeve  102  by means other than a welding seam  109 .  
         [0052]     Then the preassembled and adjusted pressure relief valve  56  is press-fitted as a compact unit into the blind hole bore  69 .  
         [0053]     The pressure relief valve according to the invention has the following main functions:  
         [0054]     During normal operation, the system pressure of the fuel injection system when the engine is being overrun is limited if the pressure in the fuel accumulator  46  increases due to the fuel being heated by the engine heat.  
         [0055]     During emergency running operation, for example if the quantity control valve  52  jams in a position in which the high-pressure fuel pump  30  always delivers the maximum delivery quantity, the system pressure of the fuel injection system is likewise limited.  
         [0056]     In the exemplary embodiment according to  FIG. 2 , during overrunning operation when the quantity control valve is fully open (emergency running operation), the maximum amount of the fuel quantity delivered by the high-pressure fuel pump  30  can be discharged back into the delivery chamber  60 . A pressure increase due to the heating of the fuel in the fuel accumulator  46  cannot be compensated for. It is therefore preferable in this instance for the injection valves  48  to inject enough fuel into the combustion chambers (not shown) to prevent an impermissible pressure increase in the high-pressure region of the fuel system  10 .  
         [0057]     With the pressure relief valves  56  according to  FIGS. 7 and 8 , it is possible both during normal operation and during emergency running operation to discharge the entire fuel quantity and therefore achieve the pressure reduction under all circumstances, without additional intervention by the control unit of the motor control. It can be useful, however, to reduce the maximum engine speed during emergency running operation in order to have enough time for the pressure decrease in the fuel accumulator  46  during the intake phase of the high-pressure pump  30 .  
         [0058]      FIG. 7  shows a sectional view of another exemplary embodiment of a pressure relief valve  56  according to the invention. The exemplary embodiment according to  FIG. 7  has parallels to the exemplary embodiment according to  FIG. 2 , so only the modifications according to the invention will be described here; otherwise, reference is made to the description given above with regard to  FIG. 2 . In the exemplary embodiment according to  FIG. 7 , the valve seat  72  adjoins a cylindrical guide section  124  in the seat sleeve  102 , which guides the valve element  74  in the axial direction as soon as it has lifted away from the valve seat  72 .  
         [0059]     The diameter of the guide section  124  and the diameter of the valve element  74  embodied in the form of a ball are matched to each other so that an annular throttle gap  126  is formed between the valve element  74  and the guide section  124 . This exemplary embodiment of a pressure relief valve according to the invention functions as follows:  
         [0060]     During emergency running operation, if the pressure in the delivery chamber  60  decreases after the end of the delivery stroke, then the pressure relief valve  56  opens at the opening pressure established by the prestressing force of the spring  76  and the hydraulic force acting on the valve element  74 . The fuel quantity flowing from the section  70   a  of the fourth branch line into the spring chamber  78  at the beginning of the opening of the pressure relief valve  56  is throttled in the throttle gap  126  and the entire projected area of the valve element  74  is subjected to the dynamic pressure. This leads to a very rapid opening movement of the valve element  74  and an abrupt increase in the flow cross section as soon as the valve element  74  has left the guide section  124  in the direction of the spring chamber  78  because the guide section  124  widens out into the spring chamber  78 , which has a much larger diameter. Because of this rapid reaction of the pressure relief valve  56 , a large quantity of fuel can flow out of the high-pressure region  14  and back into the delivery chamber  60  in a short time. The reaction behavior of the pressure relief valve  26  can be optimized and adapted to a particular application through the dimensioning of the throttle gap  126  and the length of the guide section  124 . In the dimensioning of the throttle gap  126 , however, it should be noted that when the pressure relief valve  56  reacts due to a pressure increase caused by the heating of the fuel during normal operation, no throttling occurs in the throttle gap  120  since otherwise, the pressure in the fuel accumulator  46  would abruptly decrease in accordance with the pressure step in the pressure relief valve  56 . But since in this case, the overflow quantities are very low, the throttle gap  126  can be designed so as to achieve the function described at the beginning.  
         [0061]     In the exemplary embodiment according to  FIG. 8 , the spring plate  94  and not the valve element  74  is guided in a guide section  124  of the housing  58 . As a result, the throttle gap  126  is formed between the guide section  124  and the spring plate  94 . This makes it possible to select the area exposed to the dynamic pressure, independent of the diameter of the valve element. This permits greater latitude in optimizing the dynamic behavior of the pressure relief valve  56 . This structural measure solves the dilemma inherent in the fact that at high speeds (in the event of a malfunction due to a jammed quantity control valve  52 ), there is no longer enough time during the intake phase of the high-pressure pump  30  to completely discharge the fuel quantity supplied into the high-pressure region  14  back into the delivery chamber  60 . Particularly during overrunning operation of the engine, the intake valve  34  would then always aspirate a particular fuel quantity and therefore the pressure in the fuel accumulator  46  could increase in an impermissible manner.  
         [0062]     The exemplary embodiments according to  FIGS. 7 and 8  in particular can prevent an impermissible pressure increase from occurring in the fuel accumulator  46 , even if the quantity control valve  52  jams and/or the control unit malfunctions, since the pressure relief valves  56  permit a sufficiently large return flow of fuel from the high-pressure region  14  into the delivery chamber  60  during the intake stroke of the high-pressure pump  30 .  
         [0063]     All of the features explained in conjunction with the drawings, their description, and the claims can be essential to the invention both individually and in combination with one another.  
         [0064]     The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.