Method and apparatus for regulating a volumetric fuel flow between a feed pump and a high-pressure pump

A method and an apparatus for regulating a volumetric fuel flow regulate a fuel flow delivered by a feed pump to a high-pressure pump of an injection system as a function of a volumetric fuel discharged from a high-pressure reservoir through a high-pressure regulating valve. The regulation is effected through the use of a pressure regulating valve or a volumetric flow regulating valve.

BACKGROUND OF THE INVENTION 
Field of the Invention 
The invention relates to a method for regulating a volumetric fuel flow 
delivered by a feed pump to a high-pressure pump connected to a 
high-pressure reservoir. The invention also relates to an apparatus for 
regulating the volumetric fuel flow delivered by a feed pump to a 
high-pressure pump. 
Regulating a volumetric fuel flow in an inflow to a high-pressure pump, 
which pumps fuel into a high-pressure reservoir of a common rail injection 
system of an internal combustion engine, requires optimized adaptation, 
since on one hand it must be assured that the high-pressure pump is 
supplied with enough fuel to suit the engine operating conditions, and on 
the other hand, the high-pressure pump should nevertheless not pump excess 
fuel into the high-pressure reservoir, since the excess fuel is returned 
to the engine tank through a high-pressure valve and thus causes warming 
of the fuel in the tank. In addition, fuel is highly compressed 
unnecessarily by the high-pressure pump as a result, which represents an 
unnecessary power loss. 
Published European Patent Application 0 299 337 A2 describes a method and 
an apparatus for regulating the volumetric fuel flow that is supplied by a 
feed pump to a high-pressure pump. A regulatable throttle that is 
triggered by a control unit is disposed between the feed pump and the 
high-pressure pump. An arithmetic unit monitors the fuel pressure in the 
high-pressure reservoir and controls the regulatable throttle in 
accordance with the fuel demand of the engine and the fuel pressure in the 
high-pressure reservoir. 
Regulating the fuel pressure in the high-pressure reservoir is relatively 
complicated. In that method both the fuel pressure and the expected 
consumption by the engine must be ascertained and an opening cross section 
of the regulatable throttle must be calculated by the arithmetic unit from 
those variables. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the invention to provide a method and an 
apparatus for regulating a volumetric fuel flow, which overcome the 
hereinafore-mentioned disadvantages of the heretofore-known methods and 
apparatuses of this general type, which are simple and which can be used 
for regulating the volumetric fuel flow of a feed pump for a high-pressure 
pump. 
With the foregoing and other objects in view there is provided, in 
accordance with the invention, a method for regulating a volumetric fuel 
flow delivered by a feed pump to a high-pressure pump connected to a 
high-pressure reservoir, which comprises draining fuel from the 
high-pressure reservoir, beyond a limit pressure, through a high-pressure 
valve; and regulating the volumetric fuel flow between the feed pump and 
the high-pressure pump as a function of a quantity of the fuel drained 
out. 
In accordance with another mode of the invention, there is provided a 
method which comprises regulating the volumetric fuel flow by varying fuel 
pressure between the feed pump and the high-pressure pump. 
In accordance with a further mode of the invention, there is provided a 
method which comprises regulating the volumetric fuel flow by varying fuel 
pressure between the feed pump and the high-pressure pump and by varying a 
cross section of a connecting line between the feed pump and the 
high-pressure pump. 
With the objects of the invention in view, there is also provided an 
apparatus for regulating a volumetric fuel flow delivered by a feed pump 
to a high-pressure pump, comprising a housing having a piston chamber 
therein and having a continuous reference conduit therein communicating 
with the piston chamber; an inflow conduit and an outflow conduit 
communicating with the piston chamber; and a movable control piston in the 
piston chamber, the control piston having a first piston part and a second 
piston part operatively connected to the first piston part; the first 
piston part operatively connected to the reference conduit and sealing off 
the reference conduit from the piston chamber; the second piston part 
having a position of repose opening a predeterminable connecting cross 
section between the inflow conduit and the outflow conduit; the first 
piston part being displaced with increasing pressure in the reference 
conduit for exerting a force upon the second piston part displacing the 
second piston part to increase the connecting cross section between the 
outflow conduit and the inflow conduit. 
In accordance with another feature of the invention, the second piston part 
has a larger diameter than the first piston part; the reference conduit 
and the inflow conduit define a first region therebetween; the first 
piston part protrudes into the reference conduit and seals off the piston 
chamber in the first region; the inflow conduit discharges into the piston 
chamber in a second region; the piston chamber has a larger diameter than 
the first piston part in the second region; the first piston part extends 
beyond the second region; the first piston part is connected directly to 
the second piston part; the second piston part is adapted to the piston 
chamber for sealing off the piston chamber with the second piston part; 
the control piston has a position of repose in which the second piston 
part partly opens the outflow conduit; and there is provided a spring 
element associated with the control piston; the control piston being 
displaceable by fuel pressure in the reference conduit counter to the 
spring element, causing the second piston part to open a larger opening 
cross section between the outflow conduit and the piston chamber. 
In accordance with a further feature of the invention, there is provided a 
first spring element resiliently supporting the first piston part; a 
second spring element interconnecting the second piston part and the first 
piston part; a third spring element resiliently supporting the second 
piston part counter to a motion in the direction of the reference conduit; 
a regulating chamber disposed between the first and second piston parts in 
the piston chamber and sealed off by the first and second piston parts; 
the inflow conduit discharging into the regulating chamber and the outlet 
conduit leading away from the regulating chamber; the first and second 
piston parts and the first, second and third spring elements causing the 
outlet conduit to be opened to a predeterminable cross section as a 
function of fuel pressure in the reference conduit; and the outflow 
conduit opening to a predeterminable further cross section. 
In accordance with an added feature of the invention, there is provided a 
supply line connecting the feed pump to the high-pressure pump, a 
connecting line connecting the inflow conduit to the connecting line, a 
high-pressure reservoir, an outlet line connected between the 
high-pressure reservoir and the reference conduit, a high-pressure valve 
in the outlet line, and a tank with which the outflow conduit and the 
reference conduit communicate. 
In accordance with an additional feature of the invention, there is 
provided a supply line connected to the feed pump and to the inflow 
conduit, a supply line connected from the outlet conduit to the 
high-pressure pump, an outlet line connected between a high-pressure 
region of an injection system and the reference conduit, a high-pressure 
valve in the outlet line, and a tank with which the outflow line and the 
reference conduit communicate. 
In accordance with yet another feature of the invention, there is provided 
a throttle through which the reference conduit communicates with the 
outflow conduit. 
With the objects of the invention in view there is additionally provided an 
apparatus for regulating a volumetric fuel flow delivered by a feed pump 
to a high-pressure pump, comprising a housing having a piston chamber 
therein; an inflow conduit and an outflow conduit offset from one another 
longitudinally of the piston chamber, the inflow and outflow conduits 
communicating with the piston chamber and each having a mouth; a movable 
control piston disposed in the piston chamber between the mouth of the 
outflow conduit and the mouth of the inflow conduit, the control piston 
having a position of repose opening a predeterminable connecting cross 
section between the outflow conduit and the inflow conduit; and a device 
acting upon the control piston with a reference force exerted toward the 
inflow conduit for increasingly closing the outflow conduit and raising 
pressure in the inflow conduit, with an increase in the reference force. 
In accordance with another feature of the invention, there is provided a 
diaphragm operatively connected to the control piston for transmitting the 
reference force to the control piston. 
In accordance with a further feature of the invention, the reference force 
is generated by charge pressure of a turbocharger of an internal 
combustion engine. 
In accordance with a concomitant feature of the invention, the housing has 
a connection, and the device includes a piston rod connected to the 
control piston and extended through a bore to the connection, for 
transmitting pressure applied at the connection to the control piston 
through the piston rod. 
A simple method and a simple apparatus are attained due to the fact that 
the volumetric fuel flow to the high-pressure pump is regulated as a 
function of the volumetric fuel flow with which excess fuel is discharged 
through a high-pressure valve from the high-pressure region of the 
injection system. The feed flow of the high-pressure pump is thus adapted 
to the demand in a simple way by self-regulation. 
Other features which are considered as characteristic for the invention are 
set forth in the appended claims. 
Although the invention is illustrated and described herein as embodied in a 
method and an apparatus for regulating a volumetric fuel flow, it is 
nevertheless not intended to be limited to the details shown, since 
various modifications and structural changes may be made therein without 
departing from the spirit of the invention and within the scope and range 
of equivalents of the claims. 
The construction and method of operation of the invention, however, 
together with additional objects and advantages thereof will be best 
understood from the following description of specific embodiments when 
read in connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the figures of the drawings in detail and first, 
particularly, to FIG. 1 thereof, there is seen a common rail injection 
system with a feed pump 1 which pumps fuel out of a tank 19 into a feed 
line 32. The feed line 32 leads through a throttle 13 of constant cross 
section to a high-pressure pump 3 and also communicates upstream of the 
throttle 13 through a connecting line 33 with an inflow conduit 7 of a 
pressure regulating valve 2. The high-pressure pump 3 is connected through 
a high-pressure line 34 to a high-pressure reservoir 5, which communicates 
through an injection line 35 with injection valves 6. The high-pressure 
line 34 communicates through a high-pressure valve 4 and an outlet line 39 
with an outlet conduit 8 of the pressure regulating valve 2, which 
represents a reference conduit. The pressure regulating valve 2 regulates 
a volumetric fuel flow that is made available to the high-pressure pump 3 
by the feed pump 1 by varying a pressure of fuel in the feed line 32 in 
the inflow to the throttle 13, as a function of the volumetric fuel flow 
that is discharged by the high-pressure valve 4. An outlet conduit 37 of 
the pressure regulating valve 2, which communicates with the outlet 
conduit 8 through an outlet aperture 12, is connected to the tank 19. 
The structure of the pressure regulating valve 2 will now be described in 
detail: The pressure regulating valve 2 has a housing 36, into which the 
inflow conduit 7 and the outlet conduit 8 are introduced. The inflow 
conduit 7 and the outlet conduit 8 are parallel to one another, and a 
piston chamber 38 which connects the inflow conduit 7 and the outlet 
conduit 8 with one another extends perpendicular to the inflow conduit 7 
and the outlet conduit 8. A movable control piston 10 is introduced into 
the piston chamber 38, extends past the inflow conduit 7 toward the outlet 
conduit 8, and is resiliently supported against the housing 36 by a 
pressure-holding spring 11, so that the pressure-holding spring 11 
counteracts any motion of the control piston 10 toward the inflow conduit 
7. A stop is advantageously provided, so that the motion of the control 
piston 10 toward the outlet conduit is limited. The control piston 10 is 
adapted to the piston chamber 38, so that the piston chamber 38 is sealed 
off between the inflow conduit 7 and the outlet conduit 8. The control 
piston 10 has a first piston part 16 and a second piston part 14 which has 
a larger diameter than the first piston part 16. The first piston part 16 
extends from the outlet conduit 8 through the inflow conduit 7 into an 
upper region of the piston chamber 38. The upper region of the piston 
chamber 38 is adapted in its diameter to the second piston part 14 in such 
a way that the second piston part 14 seals off the upper region of the 
piston chamber 38. The reference conduit 8 and the inflow conduit 7 define 
a first region therebetween and the inflow conduit 7 discharges into the 
piston chamber 38 in a second region. 
An outflow conduit 9 is provided in the region of the second piston part 14 
and extends laterally into the piston chamber 38 above the inflow conduit 
7. This outflow conduit 9 is sealed off in a position of repose of the 
control piston 10 by the second piston part 14, except for a 
predeterminable cross-section, and the pressure-holding spring 11 is 
constructed accordingly. The outflow conduit 9 communicates through a 
connecting conduit 26 with a region of the piston chamber 38 where the 
pressure-holding spring 11 is disposed. In addition, the outflow conduit 9 
is extended through a return conduit 22 and through the outlet conduit 37 
that is connected to the tank 19. The outlet conduit 8 is also extended to 
the outlet conduit 37, and the outlet aperture 12 is made in the outlet 
conduit 8 between the region where the control piston 10 protrudes into 
the outlet conduit 8 and the outlet conduit 37. 
The mode of operation of the pressure regulating valve 2 will now be 
explained: If a fuel pressure in the high-pressure reservoir 5 is below a 
predetermined desired value, then no fuel is blown out through the 
high-pressure valve 4. Consequently, the control piston 10 protrudes into 
the outlet conduit 8 in accordance with the prestressing of the 
pressure-holding spring 11 and the upper part 14 of the control piston 10 
closes the outflow conduit 9 far enough to ensure that the maximum 
possible pressure, defined by the structure of the pressure-holding spring 
11 and a first pressure surface 10a of the piston, is established in the 
feed line 32 and at the throttle 13. In this way, the excess portion of 
the volumetric fuel flow pumped by the feed pump 1 is returned to the tank 
19 through the outflow conduit 9 and the outlet conduit 37. The volumetric 
fuel flow to be pumped by the high-pressure pump 3 is supplied to it 
through the feed line 32 and the throttle 13. 
The throttle 13 is dimensioned in such a way that at the maximum possible 
pressure in the feed line 32 and at low to medium rpm of the high-pressure 
pump 3, more fuel is admitted than the high-pressure pump 3 requires. The 
throttle 13 does not become operative until a high rpm of the 
high-pressure pump 3 and/or until the pressure in the feed line 32 drops, 
as will be described below: 
If the fuel pressure in the high-pressure reservoir 5 and therefore also in 
the high-pressure line 34 is too high, then fuel is returned through the 
high-pressure valve 4, the outlet line 39, the outlet conduit 8, the 
outlet aperture 12 and the outlet conduit 37 to the tank 19. The 
consequence is that the control piston 10 is displaced counter to the 
pressure-holding spring 11 by the pressure of the fuel carried in the 
outlet conduit 8, and thus further opens the connecting cross section 
between the outflow conduit 9 and the inflow conduit 7. Thus more fuel is 
returned from the feed line 32, through the inflow conduit 7, the outflow 
conduit 9 and the outlet conduit 37 to the tank 19. This leads to a 
lowering of the fuel pressure in the feed line 32 in the inflow to the 
throttle 13 and thus to a lowering of the volumetric fuel flow that is 
made available to the high-pressure pumps 3 by the feed pump 1. Thus less 
fuel is pumped into the high-pressure reservoir 5 by the high-pressure 
pump 3, and since fuel is simultaneously drawn from the high-pressure 
reservoir 5 by the injection valve 6, the pressure in the fuel in the 
high-pressure reservoir 5 is reduced. A pressure reduction in the 
high-pressure reservoir 5 can also be effected if no fuel is withdrawn by 
the injection valves 6, since the high-pressure valve 4 can allow more 
fuel to drain off than is supplied to the high-pressure pump 3. 
The pressure conditions will now be described in further detail: The 
volumetric fuel flow blown off by the high-pressure valve 4 generates a 
pressure p.sub.ab upstream of the outlet aperture 12. This pressure acts 
upon a second pressure surface 10b of the control piston 10 that borders 
the outlet conduit 8. 
The first pressure surface 10a of the control piston 10, which is 
constructed as an annular surface on the second piston part 14 and adjoins 
the inflow conduit 7, is acted upon by a pilot pressure p.sub.vor that 
prevails in the feed line 32. The maximum fuel pressure in the feed line 
32 is predetermined by the pressure-holding spring 11 if no fuel is blown 
out through the high-pressure valve 4. In operation, the pilot pressure 
establishes itself in such a way that an equilibrium of all of the forces 
engaging the control piston 10 prevails, and an edge of the piston surface 
10a and a lower edge of the outflow conduit 9 are located at approximately 
the same height, so that the outflow conduit 9 is nearly closed. The size 
of the inflow throttle 13 and the value of the pilot pressure p.sub.vor 
define a volumetric fuel flow which is supplied to the high-pressure pump 
3, and which is equal to the sum of an outlet flow Q.sub.ab that is 
discharged by the high-pressure valve 4 and a feed flow Q.sub.w supplied 
to the injection valves 6. 
The relationship between the actual feed flow Q.sub.w, a maximum feed flow 
Q.sub.w,m which depends on the engine rpm, the inflow throttle 13 and the 
maximum pilot pressure, and the outlet flow Q.sub.ab blown off by the 
high-pressure valve 4, is determined by following relationship: 
##EQU1## 
In the equation, the character .alpha. indicates a ratio between the first 
and second pressure surfaces 10a, 10b. The character .delta. is a ratio 
between the actually selected controllable cross section of the outlet 
aperture 12 and a reference value for this cross section. In this 
reference value, and at a value of .alpha.=1, the pressure p.sub.ab in the 
outlet conduit B downstream of the high-pressure valve 4 would be equal to 
the maximum possible pilot pressure p.sub.vor,m at full blowoff, or in 
other words if Q.sub.ab =Q.sub.w,m. The pressure regulating valve 2 is 
constructed to meet the various requirements with the aid of the 
parameters .alpha. and .delta.. 
FIG. 2 shows a common rail injection system corresponding to FIG. 1, but in 
which the volumetric fuel flow delivered to the high-pressure pump 3 is 
regulated not only by the fuel pressure in the feed line 32 but also by 
the cross section of a throttle slit 18 with a combined volumetric 
flow/pressure regulating valve 40. To that end, the feed line 32 of the 
feed pump 1 is connected to the inflow conduit 7 of the volumetric 
flow/pressure regulating valve 40. The inflow conduit 7 communicates with 
a regulating chamber 21, which also communicates with the throttle slit 18 
as an outlet. The regulating chamber 21 is part of the piston chamber 38. 
A feed line 41 extends from the throttle slit 18 to the high-pressure pump 
3. 
The high-pressure line 34 communicates through the high-pressure valve 4 
and the outlet line 39 with the outlet conduit 8 of the volumetric 
flow/pressure regulating valve 40. The outlet conduit 37 of the volumetric 
flow/pressure regulating valve 40 is connected to the tank 19. 
The structure of the volumetric flow/pressure regulating valve 40 will now 
be described in further detail: The inflow conduit 7, the throttle slit 18 
and the outlet conduit 8, which communicate with the piston chamber 38, 
are formed in the housing 36 of the volumetric flow/pressure regulating 
valve 40. The pressure-holding spring 11 is disposed in the upper region 
of the piston chamber 38. A pressure piston 42 that seals off the piston 
chamber 38 is introduced into the piston chamber 38 adjacent the 
pressure-holding spring 11 and above the inflow conduit 7. The pressure 
piston 42 is resiliently supported against the housing 36 in the 
longitudinal direction of the piston chamber 38 by the pressure-holding 
spring 11. A regulating piston 43, which is resiliently coupled to the 
pressure piston 42 by a regulating spring 44, is disposed in the piston 
chamber 38, adjacent the throttle slit 18. An outlet chamber 46 is formed 
in the piston chamber 38, between the regulating piston 43 and the outlet 
conduit 8. A throttle spring 45 which is provided in the outlet chamber 
46, resiliently supports the regulating piston 43 against the housing 36 
in the longitudinal direction of the piston chamber 38. 
The regulating piston 43 seals off the piston chamber 38. The regulating 
chamber 21, with which the inflow conduit 7 and the throttle slit 18 
communicate, is formed between the pressure piston 42 and the regulating 
piston 43. The outflow conduit 9 is formed in the piston chamber 38 in the 
region of the pressure piston 42 and communicates with the outlet conduit 
37 through the return conduit 22. The outlet conduit 8 thus communicates 
with the outlet conduit 37 through the outlet aperture 12. 
The mode of operation of the volumetric flow/pressure regulating valve 40 
will now be described in further detail: If the fuel pressure in the 
high-pressure reservoir 5 and thus in the high-pressure line 34 as well is 
below a predetermined value, then no fuel is delivered through the 
high-pressure valve 4 and the outlet line 39 to the outlet conduit 8. As a 
consequence, the regulating piston 43 and the pressure piston 42 are in a 
position of repose, in which the regulating piston 43 uncovers the 
throttle slit 18 and the pressure piston 42 closes the outflow conduit 9 
far enough to ensure that a maximum pressure in the regulating chamber 21 
is established, as determined by the pressure-holding spring 11, the 
regulating spring 44, the throttle spring 45 and the surface area of the 
pressure piston 42. Thus on one hand the volumetric fuel flow pumped by 
the feed pump 1 flows through the feed line 32, the inflow conduit 7, the 
regulating chamber 21, the throttle slit 18 and the supply line 41 to the 
high-pressure pump 3. The excess fuel pumped by the feed pump 1 is also 
returned through the outflow conduit 9 and the outlet conduit 37 to the 
tank 19. 
If the fuel pressure in the high-pressure reservoir 5 and thus in the 
high-pressure line 34 is above the desired value, then fuel is carried 
through the high-pressure valve 4 and the outlet line 39 to the outlet 
conduit 8 and is delivered through the outlet chamber 46, the outlet 
aperture 12 and the outlet conduit 37 to the tank 19. As a consequence, a 
fuel pressure builds up in the outlet chamber 46 that displaces the 
regulating piston 43 upward in the direction of the pressure piston 42, so 
that on one hand the opening cross section of the throttle slit 18 is 
decreased by the regulating piston 43, and moreover a force is exerted on 
the pressure piston 42 through the regulating spring 44, so that the 
pressure piston 42 is displaced in the direction of the pressure-holding 
spring 11 and thus enlarges the open cross section between the regulating 
chamber 21 and the outflow conduit 9, and as a result a low pressure is 
established in the regulating chamber 21. Due to the reduction of the 
pressure in the regulating chamber 21 and the narrowing of the cross 
section of the throttle 18, a larger portion of the volumetric fuel flow 
that is pumped by the feed pump 1 through the feed line 32 into the 
regulating chamber 21 is returned to the tank through the outflow conduit 
9 and the outlet conduit 37, so that a smaller volumetric fuel flow is 
made available to the high-pressure pump 3 by the feed pump 1. 
The volumetric fuel flow that is made available by the feed pump 1 to the 
high-pressure pump 3 is regulated as a function of the fuel pressure in 
the outlet chamber 46. The fuel pressure in the outlet chamber 46 rises 
with the volumetric fuel flow that is discharged by the high-pressure 
valve 4. 
The pressure conditions will now be explained in further detail: The 
pressure-holding spring 11 specifies a maximum pilot pressure P.sub.v,m 
which prevails in the regulating chamber 21 and thus in the feed or supply 
line 41. The outlet flow Q.sub.ab occurring at the high-pressure valve 4 
generates a pressure p.sub.ab upstream of the outlet aperture 12, which 
pressure acts upon the throttle piston 43. With the aid of the throttle 
spring 45, the position of the throttle piston 43 is adjusted in such a 
way that the throttle piston 43 uncovers the throttle slit 18 completely 
in the absence of an outlet flow. The regulating spring 44 transmits the 
pressure p.sub.ab through the position of the throttle piston 43 to the 
pressure regulating piston 42. 
Advantageously, the springs and the pistons are dimensioned identically, so 
that errors in assembly are avoided. It is also advantageous if the 
volumetric flow/pressure regulating valve 40 forms a unit with the 
high-pressure pump 4. 
In the case of the ensuing mode of observation, it is assumed that all of 
the springs have the same spring constant and that the regulating spring 
44 is relaxed at maximum pilot pressure and in the absence of an outlet 
flow. This dictates corresponding prestressed lengths of the springs. The 
pilot pressure is then compensated for through the prestressing of the 
pressure-holding spring 11 and of the throttle spring 45. 
In this situation, the throttle slit 18 has also just now been uncovered 
completely by the regulating piston 43. 
The relationship between the feed flow Q.sub.w that is supplied to the 
injection valve 6, the maximum possible feed flow Q.sub.w,m and the outlet 
flow Q.sub.ab, wherein the maximum possible feed flow is determined by the 
engine rpm, the cross section of the throttle slit 18 and the maximum 
pilot pressure, is defined by the following equation: 
##EQU2## 
The ratio between the actual value of the throttle cross section of the 
outlet aperture 12 and a reference variable is defined by the character 
.delta.. If the maximum feed flow Q.sub.w,m =Q.sub.ab is blown off, then 
the pilot pressure p.sub.ab is equal to the maximum possible pilot 
pressure p.sub.v,m. The character .lambda. indicates the ratio between the 
actual slit length of the throttle slit 18 parallel to the direction of 
motion of the regulating piston 43 and a reference length. The reference 
length of the throttle slit 18 is such that upon blowoff of Q.sub.ab 
=Q.sub.w,m the resultant pressure is p.sub.ab =p.sub.v,m and the 
regulating piston 43 has just been thrust all the way past the throttle 
slit 18. 
The width of the throttle slit in each case is adapted by the selection of 
the parameter .lambda. in such a way that the total area of the throttle 
slit remains the same. Thus the maximum feed flow Q.sub.w,m remains the 
same as well. With the aid of the equation given, it is possible to check 
how the actual feed flow is adapting itself to a desired feed flow by way 
of various parameters .delta. and .lambda.. 
FIG. 3 shows a first variant of a pressure regulating valve 2, which has a 
housing 36 in which an inflow conduit 7 is provided that communicates with 
an outflow conduit 9. However, the opening cross section between the 
outflow conduit 9 and the inflow conduit 7 is regulated by a control 
piston 10 that is resiliently supported against the housing 36 through a 
pressure-holding spring 11 in such a way that the spring force of the 
pressure-holding spring 11 counter-acts an opening of the opening cross 
section. Moreover, the control piston 10 is connected through a piston rod 
25 to a diaphragm 24. The diaphragm 24 and one part of the housing 36 form 
a reference chamber 31 that has a connection 23. 
The mode of operation of the pressure regulating valve shown in FIG, 3 will 
now be described in further detail: The inflow conduit 7 is connected, for 
instance, to the connecting line 33 of the feed line 32 corresponding to 
FIG. 1, and the outflow conduit 9 communicates directly with a tank 19. 
The connection 23 communicates with the pressure chamber of a turbocharger 
of an internal combustion engine, for instance. The pressure generated by 
the turbocharger presses the diaphragm 24 downward, so that the control 
piston 10 is likewise pressed downward. In this way, the pressure 
prevailing in the inflow conduit 7 is regulated through the force acting 
upon the control piston 10 and the surface area of the control piston 10. 
FIG. 4 shows a further embodiment of a pressure regulating valve 2, 
corresponding to FIG. 3, but in which the diaphragm 24 is omitted, and a 
reference pressure, in particular a pressure in a high-pressure reservoir 
of the injection system, acts directly on the piston rod 25. It is also 
possible, instead of the diaphragm 24, to provide an electromagnet that 
acts upon the control piston 10 with a corresponding force.