FR2708313A1 - Fuel injection pump for an engine. - Google Patents

Abstract

a) Fuel injection pump for heat engine. b) pump characterized in that the spring chamber (67) of the pressure check valve (53) receiving the valve spring (73) is connected from the discharge line (55) by a blind hole drilling (76) axial, opening into the large front surface of the spring side of the stepped piston (59) and a radial bore (77) intersecting the axial blind hole, in the large diameter part of the following stepped piston (59) the position of the stepped piston (59), either with a throttle bore (81) or with an inlet opening (83) of the housing (56) of the pressure check valve (53). c) The invention relates to a fuel injection pump for a heat engine.

Description

Fuel injection pump for a thermal engine

  The invention relates to a fuel injection pump for a combustion engine, in particular a distributor injection pump comprising an injection control system having an injection-control piston sliding in a cylinder, with the help of means provided for this purpose in the cylinder, by a front face, a working chamber exposed to the

  control pressure, controlled according to the

  rotational speed, and by the other end face, a return chamber containing a spring 9 urging the injection adjusting piston with a force of

  recall, a transfer pump driven in synchro-

  with the fuel injection pump, whose transfer pressure is controlled as control pressure by a pressure control valve having

  a mobile wall against a restoring force,

  by the control pressure, this separating wall

  a pressure chamber of a return chamber

  the return spring, this chamber being permanently connected to the pressure chamber by a throttling bore, the moving movement of the movable partition in the pressure control valve controlling an outlet pipe connecting the pressure chamber to a discharge chamber and the return chamber discharges via a valve

  pressure retaining device whose closure member

  in the form of a stepped piston receives on its small diameter front face the transfer pressure of the transfer pump and which controls against

  the force of a valve spring, from a pressure

  determined pressure of the transfer pump, by its

  opening phase, the opening of a

  charge of the return valve of the control valve

  pressure gauge and whose annular piston shoulder formed between the large diameter portion and the

  small diameter part of the step piston is required

  cited by the transfer pressure of the transfer pump from a certain stroke of the piston to

  step to be maintained by the latter in a posi-

  opened in one of the discharge pipes against

the force of the valve spring.

  In the case of a fuel injection pump,

  As disclosed in DE-OS 31 48 215, the transfer pump driven in synchronism with the rotational speed of the engine supplies fuel to the suction chamber of a fuel injection pump.

  dispenser pump form; car feeding

  burant is controlled from the transfer pump to the suction chamber using the pressure control valve which controls the opening of the

  return line arranged in the transmission line

  fert. For a low and low temperature rotational speed of the supplied heat engine, the pressure control valve is hydraulically locked in a position that closes the return line, so that all transferred fuel arrives in the suction chamber of the engine. dispensing pump and that the increase in pressure is done quickly. This rise in pressure in the suction chamber has repercussions on the injection control system connected to

  that room and which in turn

  quickly from the beginning of the injection by the pump of in-

  jection of fuel in the direction of advance. Thus, for the cold start of the engine, there is

  enough time to prepare the fuel

  jected into the combustion chamber to ensure a

optimal combustion.

  Hydraulic blocking of the control valve

  pressure during cold start is

  ordered in the case of the fuel injection pump

  known pressure relief valve which closes the discharge line of the spring chamber of the pressure control valve as a function of

  temperature or pressure, so that the pis-

  your solicited by the supply pressure of the pressure control valve will have executed only one stroke opening the return pipe, the pressure of

  transfer being transmitted by the choke hole

  piston, delayed to the spring chamber. The pressure control valve shows the stepped piston leading into a stepped bore, the small front end of which limits the work volume into which the discharge line of the

  spring chamber of the pressure control valve

  if we. Thus the stepped piston is displaced by the supply pressure increasing against the force of the

  return spring on its large front end and

  after a determined adjustment stroke a

  retainer by its small frontal side in the suction line of the discharge pump, so that the pressure can relax in the

  spring chamber of the pressure control valve

  and the pressure control valve may

  only require the flow of fuel from the con-

  supply line in the return line, only

  depending on the force of the return spring of the valve spring and thus can control the pressure in the suction chamber of the injection pump

fuel.

  When starting a heat engine,

  already hot, an adjuster depending on the temperature

  temperature, connected to the cooling circuit of the

  thermistor, keeps the stepped piston in its position releasing the return line avoiding an increase in pressure and thus a maladjustment, in advance of the start of the injection of the pump

fuel injection.

  To avoid closing the pressure-retaining valve when the rotational speed falls while the heat engine is running, the step piston controls with its shoulder created by the diameter reduction, the opening of a retaining line connected to transfer conduct and who

  transmits the transfer pressure further to a small

  the front surface on the annular front surface of the stepped piston; the force of the pressure of the transfer pressure is exerted by this increased active pressure surface, whereas even at low speeds of rotation of the heat engine, it is sufficient

  keeping the stepped piston against the force of

  return stroke in a position opening the return line to the suction side of the transfer pump. The known fuel injection pump, however, has the disadvantage that to avoid the adjustment in advance of the start of the injection

  when the engine is started when it is hot, the engine

  The temperature-dependent adjustment process results in greater manufacturing and further increases the volume of the cold acceleration system. In addition, the

  known system does not allow to regulate

  The increase in pressure starts when the cold engine is started and adapted to each engine. Advantages of the invention: For this purpose, the invention relates to a fuel injection pump corresponding to the type defined above, characterized in that the spring chamber

  of the pressure-retaining valve receiving the

  valve fate is connected from the conduct of

  discharge through an axial blind hole,

  singing in the large frontal area on the

  out of the stepped piston and a radial bore intersecting the axial blind hole, in the large diameter portion of the stepped piston in the stepped position,

  with a throttling hole, either with an opening

  inlet valve of the pressure-retaining valve housing whose diameter is greater than that of the throttle bore which is itself connected by a connecting pipe, permanently with the return chamber of the pressure control valve and in that a pressure line transmitting the transfer pressure of the transfer pump to the small end face of the step piston and connected by another

  blind, axial drilling from the small frontside

  Piston-stepped and a radial bore that cuts

  this blind hole, for a position of displacement dé-

  of the stepped piston, with an annul-

  re of the pressure relief valve, which chamber is delimited by an annular shoulder of the housing

  formed by the recess of the housing bore

  the step piston and the annular piston shoulder formed by a recess on the stepped piston. The fuel injection pump according to the invention offers the advantage that a hydraulically timed return movement for the piston of the pressure-retaining valve, after stopping the engine, makes it possible to give up the a temperature-dependent control member, which presents

  a considerable advantage in terms of manufacturing cost

  cation of the fuel injection pump. The volume between the shoulder of the piston and the annular shoulder of the bore of the housing, during the sudden drop in the pressure in the system resulting from the stopping of the engine first controls the stopping of the piston stepped in a position opening the non-throttled connection between the return chamber of the pressure control valve and a discharge line, in contrast to the known injection pump, so that when the engine is started again temperature still warm, the cold start acceleration function and thus the adjustment of the advance of the injection start remain cut and that the pressure control in the suction chamber of the fuel injection pump does not only through the pressure control valve. During a prolonged shutdown of the engine, the pressure of the chamber volume

  annular, imprisoned, decreases progressively

  of the leak between the peripheral surface of the piston

  stepped in the direction of the small frontier

  and / or the annular groove of the piston and the di-

  reshaping of the annular chamber and the play of the step piston and the bore of the housing make it possible to adapt the shape of the discharge curve and thus the return movement created by the valve spring for the step piston as a function of the curve of

  cooling temperature of the engine.

  In each case, the discharge curve of the annular chamber is such that when the heat engine

  is cold, the stepped piston is in a positive

  closing the non-throttled connection between the pressure control valve return chamber and the

discharge pipe.

  It is advantageous that the stepped piston,

  during the operation of the engine, do not

  not stand in his position closing the foreign

  of the pressure control valve, because in the event of a pressure drop of the heat engine which continues to run at a minimum value, the stepped piston

  and pushed as far as possible into its position forming the

  However, the non-throttled connection between the return chamber of the pressure control valve and the discharge line remains open. In this situation, the stepped piston remains hydraulically locked as a result of which

  no leak can come out of the ring volume during

  the existing operating pressure.

  Another advantage results from the realization

  an annular piston groove at the level of the

  the radial drilling outlet

  large diameter stepped piston, which allows

  strangulation piercing and opening

  entering the housing of the pressure-retaining valve, with a high degree of control by the stepped piston, sufficiently distant from each other, the end of the annular groove of the piston

  not facing the small diameter of the piston to

  din forms a control edge which cooperates with the non-throttled inlet opening of the connecting pipe towards the pressure control valve so that during the return stroke of the stepped piston, the exchange takes place only when overlap with the unobstructed entry opening, when drilling

  of the small diameter portion of the piston to

  din enters the small diameter part again

  of the guide bore and is closed by this wall.

  The advantageous arrangement of a foreign organ

  between the pressure control valve return chamber and the connection with the discharge pipe in the position of the stepped piston closing the non-throttled discharge opening (cold start) allows, thanks to the sizing of the pressure section strangely to adjust the curve of the climb into

  until the accelerator function is switched off.

  cold start, in a flexible manner and

  optimally adapt it to the internal combustion engine

  pectif. The soft adjustment is further complemented by the adjustable spring force of the valve spring in

  the pressure-retaining valve which fixes by the de-

  unscarred load of the booster chamber of the

  pressure control valve, the moment of opening

  ture and thus the end of the start advance setting

  injection; this spring force is always

  days from the outside by the depth of penetration

shutter screw.

  Another advantage in terms of manufacturing

  This results from the realization of the two-part stepped piston, each piston diameter corresponding to a single piston and these two pistons are held in position.

  axial support, when mounted by the valve spring.

  The present invention will be described hereinafter in more detail with the aid of the accompanying drawings showing in simplified manner an injection pump.

fuel.

  Thus: FIG. 1 is a schematic view of a pump

  fuel injection system with a

the beginning of the injection.

  FIG. 2 shows the pressure curve in the pressure chamber of the pressure control valve.

  the suction chamber of the injection pump

  fuel for different operating positions

  of the step piston of the pressure relief valve.

  Description of the exemplary embodiment

  The fuel injection pump represents

  schematically in FIG. 1 forms part of a dispensing type fuel injection pump.

  1 comprising an injection adjusting device

  3 having an injection control piston 7

  Smoothing in a cylinder 5. One of the end faces of the cylinder is subjected to the action of a return spring 9 which bears in a fixed manner against a front face of the cylinder 5 and is housed in a return chamber 11 ; this chamber is delimited by the front face and the wall of the cylinder 5 and by the face of the injection adjusting piston 7 on the spring side; this chamber is permanently connected by a return line 19 to the fuel tank

  21, which releases it into pressure when one does not

  does not try to modify the adjustment characteristic of the injection according to the operating parameters

  by the introduction of an additional control pressure

  in the return chamber 11. The front face

  the injection adjusting piston 7 opposite to the

  reminder spell 9 delimits a working chamber of

  injection setting 13 in the cylinder 5. This chamber

  bre is connected by a constriction piercing

  in the adjusting piston 7 to a suction chamber

  17 inside the fuel injection pump.

butrice 1.

  The suction chamber 17 is supplied with fuel by the fuel injection pump 1 via a pressure line 25 from a transfer pump 23 driven in synchronism with the distributor injection pump 1 The transfer pump 23 takes the fuel into the tank 21 by means of the suction line 27. A bypass line 29 connects the pressure line 25 to the

  suction line 27 equipped with a control valve

  pressing 31 which controls this conduct. This-

  the pressure control valve 31 has an adjustable control piston-shaped partition 33

  sliding in a cylindrical sleeve

  35 and delimiting by its frontal face a cham-

  pressing pressure 37 in which leads the pipe

  29. By its other end face, the piston

  control tone 33 defines a return chamber 39 housing a return spring 41 fixed between the closed end face of the cylindrical sleeve 35 and the front face of the control piston 33. In addition, the cylindrical wall of the pressure chamber 37 comprises a control end piercing 43 whose edge is located

  side of the pressure chamber forms a cutting edge

  45; this bore is closed during movement of the piston and connects the pressure chamber 37 to the suction line 27 of the transfer pump 23 through an outlet line 47 which is part of the bypass line 29. The return chamber 39 is connected by a throttling bore 49, permanently with the pressure chamber 37. In addition, a pipe

  link 41 connects the return chamber 39 to its de-

  pressure load; this connecting pipe may itself be connected with the interposition of a pressure-retaining valve 53 to a discharge pipe

  connected to the suction line 27.

  The pressure relief valve 53 includes

  For this purpose, in a housing 56, a bore 57 in the form of a stepped bore accommodates, in axial sliding, a stepped piston 59 whose small end surface delimits a working chamber 61 in the portion 63 of FIG.

  small diameter of the bore 57.

  65 connected to the pressure line 25 opens into this working chamber 61. The front face of the

  stepped piston 59 not turned towards the working chamber

  61 defines a spring chamber 67 in the

  tie 69 of large diameter of the bore 57; a driving

  discharge 55 connects this chamber to the suction pipe 27 and between the large front face of the

  stepped piston 59 and a closure screw 71 which

  the large-diameter portion 69 of the bore 57 has a valve spring 73. The biasing force exerted by the valve spring 73 is governed by the screw-in depth of the sealing screw 71, since the face frontal of this screw penetrating into the bore 57 of the housing serves as a bearing surface for the valve spring 73. To better guide the valve spring 73, it is also possible to machine cavities in the face

  front of the plug screw and step piston.

  When the pressure-retaining valve 53 in position

  When the pressure is at rest, that is, when there is no pressure in the working chamber 61, the valve spring 73 holds the step piston 59 resting by its piston ring shoulder 73. formed by the reduction of the diameter, against the internal shoulder of the housing formed by the recess of the bore

57 made in the housing.

  The stepped piston 59 has in its end face of the spring an axial blind hole 76 which extends into the large diameter portion of the stepped piston 59 and which is cut by a radial bore.

  the openings of this pierce open into the

  peripheral face of the stepped piston 59 through

  An annular groove 79 of the piston 79. This annular groove 79 of the piston cooperates with a bore

  throttling 81 and an inlet opening 83 of di-

  larger meter, made in the wall of the housing 56; this opening 83 communicates through a part of the connecting pipe 51 with the return chamber 39 of the

  pressure control piston 31 to discharge this

  the latter in pressure according to the position of the piston to

  din 59 by a throttled or non-throttled connection to the spring chamber 67 and thus to the pipe of

pressure relief 55.

  Another axial blind hole 85 takes its original

  in the small front surface of the piston to

  din 59, delimiting the working chamber 61; this blind hole enters the small diameter portion of the stepped piston 59 to be also cut by a

  radial drilling 87. For a certain position of the piston

  stepped tone, the piercing 87 passes during its

  adjusting the annular shoulder 75 of the housing, so that the pressurized fuel exits the chamber 61 in the annular space formed between the annular shoulder 75 of the housing and the annular shoulder 74 of the piston (this does not appear not in the

  position shown for stepped piston). The sur-

  The face of the annular shoulder 75 of the piston then constitutes an additional active surface on which the pressure of the fluid of the working chamber 61 acts. The radial bore 87 in the small part

  diameter of the stepped piston 59 is remote from the

  located on the spring side of the annular groove 79 of the piston which forms a control edge 91 for

  that this edge of command does not pass on the shoulder-

  75 of the housing during the movement of the stepped piston generated by the pressure prevailing in

  the working chamber 69 only when the cutting edge

  Mande 91 has already commanded the clearance of the inlet opening 83, itself provided on the side facing the closure screw 71 next to the throttling hole 81, so that the step piston 59 covers, in its position Figure 1 shows that the throttle bore through the annular groove 79

  when the system is not under pressure and the

  sition of the annular shoulder 74 of the piston is in

  bearing against the annular shoulder 75 of the housing.

  The description of the operation of the pump

  fuel injection according to the invention will be made

  using Figure 1; the pressure curve p res-

  pective in the system and particularly in the

  suction chamber 17 of the injection pump dis-

  1 being shown in Figure 2 as a function of

  rotation speed n of the motor.

  In the output position that is to say when the heat engine is cut and the system is without pressure, the springs 9, 41, 73 maintain the pistons 7, 33, 59 in the rest position and the bypass pipe 29 of the pressure line 25 is

then closed.

  At the start of the heat engine, the feed pump 23 creates a fuel pressure transmitted by the pressure line 25 to the suction chamber 17 of the distributor injection pump 1, the branch line 29 into the pressure chamber 37 of the pressure control valve 31 and by the bypass line 65 in the chamber of

  working 61 of the pressure retaining valve 53.

  This pressure in the working chamber 61 of the pressure control valve 53 is not sufficient at the beginning to move the stepped piston 59 against the

  the force of the valve spring 73 so that the annular groove

  nular 79 comes on the inlet opening 83. The return chamber 39 of the control valve of

  pressure 31 is thus connected to the control line

  charge 55 than by the throttling hole 81 of sec-

  smaller than that of the throttle hole 49 of the control piston 33; the fuel that comes

  of the pressure chamber 37 by the throttle member

  49 can not escape sufficiently quickly and the control piston 33 locks hydraulically in its position closing the control end hole 43. Since the end of the fuel transfer can not be controlled by the pressure control valve 31, substantially all the quantity supplied first arrives in the suction chamber 17 of the dispensing injection pump 1 in which is established

  quickly an effective pressure transmitted by the person

  9 to the working chamber 13 of the injection adjusting device 3 and drives in known manner, by axial movement of the piston of

  injection setting 7, a setting of the start of the injection

  in the sense of advance. This rapid rise in pressure corresponds in the diagram of Figure 2 (ordinate: pressure p, abscissa: rotation speed n) to the range between 0 and A of the curve in solid lines; the slope of the climb in

  pressure in this range is governed by the

  choke hole drilling 81.

  From a certain speed of rotation

  of the engine, the pressure acting on the small

  the front face of the stepped piston 59 is sufficient to overcome the force developed by the valve spring 73 of the pressure retaining valve 53;

  the step piston 59 is lifted and during its movement

  ment, it passes its annular groove 79 over the

  entrance opening 83; the pressure prevailing in the return chamber 39 of the pressure control valve 31 can thus drop in a non-throttled manner

  in the discharge line 55. This fall in

  reminder chamber 39 implies that the pres-

  sion prevailing in the pressure chamber 37 then undergoes to move the control piston 33 against the force of the return spring 41 and thus release the control end hole 43 by the control edge

of the control piston 33.

  Like only a part of the fuel

* supplied can not escape by the derivation

  29 of the pressure control valve 31 and pass into the return line 47, this results in a decrease in the sudden rise in pressure in the suction chamber 17 and the corresponding forward movement of the injection adjustment system 3. If the speed of rotation continues to

  up, we again have a growing pressure curve

  with the speed of rotation and which is regulated according to the speed of rotation by the pressure control valve 31 because of the clearance more or

  less important of the end of drilling 43.

  The step piston 59 of the check valve

  The pressure relief valve 53 passes after the inlet opening opening control 83 by the annular piston 79 if the fuel pressure continues to increase and the radial bore 87 passes over the annular shoulder 75 of the housing. The fuel pressure of the chamber of

  61 can then be reflected in the

  formed between the annular shoulder 75 of the housing and the annular shoulder 74 of the piston for acting

  in a complementary manner on the step piston 59.

  This additional active surface of the stepped piston 59, even for a pressure that decreases first,

  keeps the piston in its position controlling the

  The biasing of the inlet opening 83. The preloading of the valve spring 73 makes it possible to regulate both the release control pressure of the inlet opening 83 and the filling pressure of the annular volume, ie ie "hooking" of the stepped piston 59e in its position. When the system pressure drops below a determined value to a minimum pressure, for example when the engine is idling, and the stepped piston 59 is further moved by the valve spring 73 into a position for which the radial bore 87 emerges from the annular volume, the stepped piston 59

  is maintained in this position by the volume of

  burant imprisoned in the annular volume; in this-

  position, the annular groove 79 of the piston

  the entrance opening 83, so that the

  setting the advance of the start of the injection which

  initially blit as described above when starting the engine remains cut off in a guaranteed way

  during operation of the engine.

  After shutting down the engine at a high speed of rotation and controlling the opening of the

  radial drilling 87 and after the pressure drop cons-

  in the system, the valve spring 73 de-

  place the stepped piston 59 first towards the chamber

  working piece 61 until the radial bore 87 is closed by the wall of the housing bore 57.

  step piston 59 remains first in this position.

  for which the annular groove 79 of the piston again covers the inlet opening 83, since another displacement by the volume trapped in the annular volume is prevented, volume which flows by a leak between the stepped piston 59 and the 57 bore of the housing and the flow in time of this leakage

  and if the delayed return movement of the piston to

  din 59 can be influenced by the interplay between

  these; at the latest when the engine is cooled down, the rest position for the piston is reached

  step 59 that is to say, its coming in support against the

annularly 75 of the housing.

  To start the still warm heat engine again, the volume that is still in the

  annular chamber prevents the piston from being in a

  in which the non-throttled discharge of the return chamber 39 of the control valve of the

  pressure 31 is closed, so that the piston of com-

  33 of the pressure control valve 31 regulates

  immediately offsets the pressure profile and avoids a particular advance in the start of the injection for the cold start, due to a rapid rise in

pressure in the system.

  When the cold engine is started, the stepped piston 59 again occupies its rest position and the operations proceed as it has already done.

has been described above.

  It is thus possible to order an access

  leration by starting cold without additional temperature-dependent regulator, and

  for which one avoids with certainty a setting of the

  the beginning of the injection when starting the

  hot heat meter. The pressure relief valve

  can be mounted either in the pump housing

or outside the case.

Claims (3)

  1) Fuel injection pump for mo-   heat pump, in particular a distributed injection pump   trice with an adjustment system for the in-   jection (3) having an injection adjusting piston (7) sliding in a cylinder (5), by the means provided for this purpose in the cylinder (5), by a front face, a working chamber ( 13) exposed to   control pressure, controlled according to the   rotation speed, and by the other end face, a   return chamber (11) containing a spring (9)   citing the injection adjusting piston (7) with a restoring force, a driven transfer pump (23)   in synchronism with the fuel injection pump   rant, whose transfer pressure is controlled com-   control pressure by a pressure control valve (31) having a wall (33) movable against a restoring force (41), biased by the control pressure, this wall separating a pressure chamber (37) from a return chamber (39) receiving the spring   (41), this chamber being permanently connected   the pressure chamber (37) by a throttle bore (49), the movement of movement of the movable partition (33) in the pressure control valve (31) controlling an outlet pipe (47) connecting the pressure chamber (37) at a discharge chamber (21) and the return chamber (39) unloads   through a pressure relief valve   sion (53), the shutter member in the form of a stepped piston (59) receiving on its small-diameter end face the transfer pressure of the transfer pump (23) and which controls against force of a valve spring (73), from a determined pressure of the transfer pump (23), by its opening movement, the opening of a discharge pipe (51, 55) of the recall room (39) from   the pressure control valve (31) and whose   substantially annular piston (74) formed between the   large diameter portion and the small diameter portion of the stepped piston (59) is biased by the transfer pressure of the transfer pump (23) from a certain stroke of the stepped piston (59) to be held by the latter in an open position in one of the discharge lines (51, 55) against the force of the valve spring (73), characterized in that the spring chamber (67) of the pressure-retaining valve (53) receiving the   valve spring (73) is connected from the   discharge pipe (55) via an axial blind hole bore (76) opening into the large frontal area   on the spring side, the step piston (59) and one   radial drilling (77) intersecting the axial blind hole, in the   large diameter portion of the step piston (59)   the position of the stepped piston (59), either with a throttle bore (81) or with an inlet opening (83) of the housing (56) of the pressure-retaining valve (53) having a diameter is larger than that of the throttle bore (81) which is itself connected by a connecting pipe (51), permanently   with the return chamber (39) of the control valve   pressing means (31) and that a pressure line (65) transmitting the transfer pressure of the transfer pump (23) to the small end face   the step piston (59) is connected by another   blind geometry (85), axial from the small frontside   stepped piston (59) and a radial bore (87)   who cuts this blind hole, for a position of displacement   determined step of the step piston, with an annular chamber of the pressure-retaining valve (53), which chamber is delimited by an annular shoulder (75) of the housing closed by the recess of the housing bore (57) housing the step piston (59) and by   the annular piston shoulder (74) formed by a die   crooked on the stepped piston (59).   2) fuel injection pump according to claim 1, characterized in that the distance between an end (91) located on the side of the spring,   the outlet orifice of the radial bore (77) and the   the end of the radial bore (87) connected to the pressure line (65) is formed in the piston portion   step of small diameter so that the drilling   dial (87) connected to the pressure line (65) does not   beyond the annular housing shoulder (75) during the opening movement of the step piston (59) only when the spring-side end (91) of the radial bore outlet ( 77) has already passed on the edge of the entrance opening (83) no   turned towards the spring chamber (67).   30) Fuel injection pump according to   claim 1 or 2, characterized in that the opening   outlet of the radial bore (77) connected to the con-   discharge pipe (55) opens into the pis-   stepped large diameter, in an annular groove   piston ring (79) formed in the peripheral surface of the step piston (59).   ) Fuel injection pump according to   claim 3, characterized in that in its posi-   at rest, when the system is without pressure, the step piston (59) is held by the valve spring (73) with its annular piston shoulder (74) bearing against the annular housing shoulder (75), the annular groove (79) of the overlying piston   in this rest position only the drilling of   tranglement (81) of the wall (56) of the housing of the   pressure relief valve (53).   Fuel injection pump according to claim 1, characterized in that the stepped piston (59) is in two parts and the large diameter portion and the small diameter portion of the stepped piston are constituted by a single piston maintained in   axial support by the valve spring (73).   6 ") Fuel injection pump according to claim 1, characterized in that the housing bore (57) of the pressure-retaining valve (53) is closed with respect to the outside at its end. (69) large diameter by a screw plug (71)   whose front face penetrates into the housing bore   (57) is supported by the valve spring (73) and the depth of penetration of the sealing screw (71) into the housing bore (57) regulates the force of   prestressing of the valve spring (73).