Fuel injection pump for internal combustion engines

A fuel injection pump of the distributor pump type having a pump piston driven for simultaneous reciprocation and rotation, the supply quantity of which that is effective for injection is controlled by the opening of a relief conduit of the pump work chamber in that with the aid of a mechanical regulator an annular slide is moved into variable stroke positions on the pump piston. Additionally, for an electronic regulation of the total injection quantity, a pre-stroke (hv) is provided, which is determined by a first valve and which, under the control of a second, electrically controlled valve connected to the output side of the first valve, is added to the basic supply stroke in a variably effective manner in terms of injection. Thus the fuel injection quantity can be regulated within the context of the fuel injection quantity difference resulting from the pre-stroke.

BACKGROUND OF THE INVENTION 
The invention is based on a fuel injection pump for internal combustion 
engines. A fuel injection pump of this kind, known from German 
Offenlegungsschrift No. 26 44 698, has a first and a second relief 
conduit, both of which extend in the pump piston and at the pump piston 
circumference discharge inside the suction chamber of the fuel injection 
pump. The mouths of the relief conduits are disposed offset in terms of 
the stroke, or in other words are opened in a staggered manner by a 
control edge of the annular slide in the course of the pump piston stroke. 
Only the first relief conduit communicates directly with the pump work 
chamber. During an initial portion of the stroke, that is, the pre-stroke 
hv, of the pump piston, the second relief conduit communicates with the 
pump work chamber via the first pump piston valve, which is embodied by an 
annular groove in the pump cylinder wall and a second outlet opening of 
the first relief conduit. On its other end, the second relief conduit 
communicates with the suction chamber, in all the operating ranges except 
during engine starting. During starting, the outlet of the second relief 
conduit is closed by the annular slide, which thus forms the second valve, 
when it is put into the starting position. For starting the internal 
combustion engine driven with the fuel injection pump, the apparatus 
furnishes a structurally dictated constant fuel injection quantity over 
the course of the prestroke hv. 
OBJECT AND SUMMARY OF THE INVENTION 
The fuel injection pump according to the invention has an advantage over 
the prior art that a supplemental fuel injection quantity, which is 
electrically controlled, can be superimposed for regulating purposes upon 
a variable basic fuel injection quantity which is regulated by a known 
mechanical fuel injection quantity regulator. Thus, the fuel injection 
quantity effectively supplied by the fuel injection pump can be adapted to 
the special characteristic curves of the engine involved, both with 
respect to the full-load injection quantity and to the breakaway 
characteristic when the maximum idling rpm of the engine is attained. In 
an adaptation to special operating conditions, the fuel quantity can also 
be adapted as a function of external pressure or charge pressure, or of 
temperature, and in particular to the requirements in cold starting and 
the warmup phase. For particularly sensitive quantity control, the fuel 
quantity can also be controlled as a function of a bucking correction 
signal and/or a quiet-idling correction signal. Apparatuses for forming 
such signals are known. 
This invention has an advantage that at little expense, exact regulation of 
the fuel injection quantity can be attained in a Diesel injection pump, 
with all the advantages of electric regulation, and on the other hand in 
the event the electric regulation fails, safe emergency operation of the 
engine is possible with only a slight decrease in power. In particular, 
the mechanical regulation protects the engine from damage if electronic 
regulation fails. The adjustment of the injection onset toward "early" 
that results from adding the initial additional fuel injection quantity 
can be corrected by adjusting the injection onset in a known manner, by 
measuring the additional fuel quantity. 
In an advantageous feature of the invention, a principle according to the 
invention is applied to a fuel injection pump that operates with control 
of the end of supply. In another feature, it is also possible to use 
electrically controlled valves that are not pressure-balanced or are not 
safe under high pressure for controlling the effective injection during 
the pre-stroke length of the pump piston. In a further development of this 
feature, intake grooves are advantageously used for effecting 
communication of the valve element, embodied by the annular groove, of the 
first valve with the pump work chamber. 
In another feature of the invention, the idle volume in the high-pressure 
circuit is reduced to a minimum. Another feature of the invention offers a 
substantial advantage that an additionally imposed fuel injection quantity 
as well as the basic fuel injection quantity that is controllable by the 
mechanical regulator can be detected exactly, enabling exact regulation of 
the actual injection quantity. To this end, the parameters recited herein 
can be taken into account. In particular, features set forth provide an 
advantage that a shift of the fuel injection onset toward "early" 
resulting from an additional fuel injection quantity can be corrected 
again by an injection onset regulating device known per se. For cold 
starting, a shift of the instant of injection toward "early" is desirable 
in any case, and now results automatically because of the increase in fuel 
quantity attained via the pre-stroke. This is also advantageous, because 
the injection adjustment range in which the actual injection adjuster 
functions can be kept narrow. 
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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A bushing 2 is disposed in a housing 1 of a fuel injection pump shown in 
FIG. 1. In an inner bore, of this bushing 2, a pump cylinder 3 is formed, 
a pump piston 4 executes a simultaneously reciprocating and rotation 
motion in the pump cylinder driven by a cam drive 5. On one face end, the 
pump piston encloses a pump work chamber 6 and the other end protrudes 
partway out of the pump cylinder into a pump suction chamber 7, which is 
enclosed in the housing 1. 
As long as the pump piston is executing its intake stroke or assumes its 
bottom dead center position, the pump work chamber 6 is supplied with 
fuel, via longitudinal grooves, serving as intake grooves 8, disposed in 
the jacket face of the pump piston and via a suction line 9 which 
originates at the pump suction chamber 7, passes radially through the 
bushing 2 and extends within the housing 1. For shutting off the fuel 
supply to the pump work chamber, a magnetic shutoff valve 10 is disposed 
in the suction line 9; when this valve 10 is excited, it closes the 
suction line 9. The pump suction chamber is supplied with fuel from a fuel 
tank 12 via a feed pump 11. By means of a pressure control valve 13, the 
pressure is typically controlled in accordance with rpm in the pump 
suction chamber in a known manner, so as to enable making an rpm-dependent 
injection adjustment, for example hydraulically, via this pressure 
controlled as a function of rpm. The injection adjuster engages the cam 
drive 5 in a known manner, not shown in detail here. With increasing rpm, 
the stroke onset of the pump piston is adjusted to "early" in a known 
manner. 
In the pump piston, a longitudinal conduit 14, which is embodied as a blind 
bore and serves as a relief conduit, leads away from the pump work chamber 
6. Branching off from the conduit 14 is a transverse bore 15, which leads 
to a first outlet opening 16 on the circumference of the pump piston 4, in 
a region in which the pump piston protrudes into the suction chamber 7. 
The outlet openings 16 are preferably diametrically opposite one another, 
which leads to a balanced hydraulic load on the pump piston. Disposed on 
the pump piston in this region is a quantity adjusting device in the form 
of an annular slide 18, which is displaceable tightly on the pump piston 
and with its upper face end forms a control edge 19, by means of which the 
outlet openings 16 are controlled. 
Also branching off from the relief conduit 14 between the work chamber and 
the transverse bore 15 is a radial bore 20, which leads to a distributor 
opening 21 in the form of a longitudinal groove on the circumference of 
the pump piston. In the operating region of this distributor opening, 
pressure lines 22 branch off from the pump cylinder 3 in a radial plane, 
which are equally distributed on the circumference of the pump cylinder in 
accordance with the number of cylinders of the associated engine that are 
to be supplied with fuel. The pressure lines lead via one injection nozzle 
23 each to the cylinders of the engine that are to be supplied. As soon as 
the suction line 9 is closed by the jacket face of the pump piston, at the 
onset of the supply stroke of the pump piston following a corresponding 
rotation of the pump piston, the fuel located in the pump work chamber 6 
is pumped to these injection nozzles via the relief conduit 14, the radial 
bore 20 and the distributor groove 21. This pumping is interrupted 
whenever the outlet openings 16, in the course of the pump piston stroke, 
are opened by the annular slide 18 and come into communication with the 
suction chamber 7. From that point on, the remaining fuel positively 
displaced by the pump piston is pumped only into the suction chamber. The 
higher the level at which the annular slide 18 is adjusted toward the pump 
work chamber, the greater the quantity of fuel pumped by the pump piston. 
A fuel injection quantity regulator 25 provided for the adjustment of the 
annular slide 18 has a tensioning lever 25, which is pivotable about a 
shaft 27, has one arm, and is coupled at its lever arm end to a governor 
spring assembly 28. This assembly comprises an idling spring 29 disposed 
between the head of a coupling element 30 and the tensioning lever; the 
coupling element is passed through an opening in the tensioning lever, and 
at its other end, remote from the head, it is connected to a main governor 
spring 31. The main governor spring 31, in turn, is suspended at one end 
from a pivot arm 33, which is adjustable with the aid of an adjusting 
lever 35, via a shaft 34 which passes through the pump housing. The 
adjusting lever is arbitrarily actuatable between an adjustable full-load 
stop 36 and an adjustable idling stop 37 by a person operating it and in 
accordance with the example given is actuated in accordance with the 
torque desired. Instead of the simple helical spring shown here as the 
main governor spring, it is naturally also possible to use other governor 
spring assemblies that are of the multistage and/or pre-stressed type. 
A starting lever 39 is also pivotable about the shaft 27; it is two-armed, 
and with one arm, via a ball head 40, engages a groove 41 in the annular 
slide 18 and serves to adjust this annular slide. The other arm of the 
starting lever has a leaf spring 49, which as the starting spring is 
braced against the tensioning lever 26 by being spread open against it. 
Acting upon this particular lever arm of the starting lever 39 is also the 
final control element 42 of an rpm transducer in the form of a flyweight 
control assembly 43 of a known type, which is driven synchronously with 
the drive shaft 44, which also drives the cam drive 5, of the fuel 
injection pump, via a gear train 45. With increasing rpm, the final 
control element 42, along with the starting lever 39 and the annular slide 
18, is accordingly displaced counter to the force of the starting spring 
49, until the starting spring comes to rest on the tensioning lever. In 
this process, the annular slide is adjusted away from a highest position, 
nearest the pump work chamber and corresponding to a starting quantity 
setting, toward the pump piston drive side, thus reducing the increased 
starting quantity. Once the starting lever comes to rest on the tensioning 
lever, both levers become pivotable counter to the force of the idling 
spring 29, until the main governor spring 31 comes into action, adjacent 
the idling range. For adjustment, the shaft 27 is supported on an 
adjusting lever 26, which is pivotable about a shaft 47 attached to the 
housing and is kept in contact with an adjustable stop 50 by a spring 48. 
To the extent described thus far, the fuel injection pump is equivalent to 
a standard, known version. In a further version, an annular groove 52 is 
now provided in the jacket face of the pump piston 4, in the vicinity of 
the intake grooves 8; this annular groove 52 cooperates with a connecting 
conduit 53 leading away from the pump cylinder 3. These two elements, the 
annular groove and the outlet opening 54 of the connecting conduit 53 on 
the pump cylinder 3, form a first valve, by way of which, at a 
corresponding stroke position of the pump piston, communication is 
established between the pump work chamber 6 and the connecting conduit 53. 
Instead of this arrangement, the annular groove can also be provided in 
the pump cylinder wall, if the first valve is embodied as a pairing of an 
annular groove with an outlet opening, or as a pairing of an annular 
groove with an annular groove. The connecting conduit 53 leads on to a 
second valve 56, in the form of a magnetic valve of known type. The 
connection conduit 53 is monitored there by the closing element 57 of the 
magnetic valve and is closed upon excitation of the magnet. Acting in the 
opening direction is a spring 58 on the valve closing member, which member 
in the open position, when the electromagnet is not excited, connects the 
connecting conduit 53 with the suction chamber 7, or some other relief 
chamber, via a line 59. The annular groove 52 communicates via the intake 
grooves 8 with the pump work chamber 6 and is disposed such that it does 
not come into direct communication with the inlet opening of the intake 
line 9. The communication with the outlet opening 54 of the connecting 
conduit 53 remains in force over a stroke distance of the fixedly 
predetermined length h.sub.vmax, beginning at the pump piston supply 
onset. Only from this stroke on, when the second valve 56 is opened, can 
fuel be put under high pressure in the pump work chamber and attain 
injection. In addition to this pumped quantity, a remaining pre-stroke 
h.sub.ve, which is a portion of the entire pre-stroke h.sub.vmax, also 
becomes effective in terms of injection, subsequent to the execution of a 
partial pre-supply stroke h.sub.va that is not effective in terms of 
injection; this event depends upon when the second valve 56 closes after 
the stroke onset, during the pre-stroke distance h.sub.vmax. The closing 
point of the second valve accordingly determines the magnitude of an 
additional fuel injection quantity, which is added to the injection 
quantity that is controlled following the closure of the first valve 54, 
53 by the mechanical regulator 25. 
These relationships are shown in FIG. 2, in the performance graph diagram 
in which fuel quantities are plotted over rpm. The solid lines indicate 
the injection quantities that, depending on the control outcome of the 
mechanical governor 25, result when the second valve 56 is continuously 
open. These are the full-load characteristic curve VL.sub.G, the 
partial-load characteristic curves TL.sub.G, the idling characteristic 
curve LL.sub.G and the breakaway characteristic curve A.sub.G. The 
dot-dash lines VL.sub.max and A.sub.max indicate the situation in which 
the second valve 56 is continuously closed. Between these two extreme 
values, an arbitrary characteristic curve course can be achieved, by 
variable control of the second valve 56 and by appropriate triggering of 
the second magnetic valve by means of a control unit 66. The result then 
is characteristic curves that approximate the actual needs of the engine 
as closely as possible. These are, for example, the full-load 
characteristic curve VL.sub.a, the idling characteristic curve LL.sub.a, 
or the partial-load characteristic curve TL.sub.a. The breakaway curve 
A.sub.a, too, can be adapted to the corresponding needs. 
The appropriate correction can be performed by means of the control unit 
66, for example via a performance graph as a function of the rpm and the 
load. The control device 66 also controls the magnetic shutoff valve 10 in 
a known manner. In particular, however, the desired fuel injection 
quantity can also be regulated, by measuring the additional fuel quantity 
attaining injection during the pre-stroke. This is done, first, by 
detecting the position of the valve closing member 57 of the second valve 
56, with the aid of a closing-point and/or opening-point transducer 67 of 
a known type. A second annular groove 61 that communicates continuously 
with the pump work chamber can also be provided on the pump piston. 
Cooperating with this second annular groove 61 is a contact opening 62 in 
the wall of the pump cylinder 3. The contact opening communicates via a 
line 63 with a pressure sensor 64, the output signals of which are 
supplied to the control unit 66. The second annular groove 61 comes into 
communication with the contact opening 62 at the stroke onset. 
The above-described control principles, which are also the basis for 
feedback signals to the control unit, are illustrated in FIG. 3. There the 
pump piston elevation curve, or the cam course, is plotted over the 
rotational angle .alpha.. The diagram includes a supply onset line F.sub.B 
parallel to the abscissa and spaced apart from it by the pre-stroke 
h.sub.vmax ; a line FE.sub.VL, parallel to F.sub.B and spaced apart from 
it by the useful stroke h.sub.N, which characterizes the end of fuel 
supply at full load; and a line St, parallel to the others and spaced 
apart from FE.sub.VL by the starting quantity stroke, which represents the 
pump piston supply stroke that is effective for injection in the case of 
starting. 
From FIG. 3, it is apparent that with an increasing length of the 
pre-stroke h.sub.ve that is effective for injection, the injection onset 
is shifted toward "early". This is advantageous when increasing the 
starting quantity for a cold start, because an earlier injection onset is 
regularly needed in connection with the cold start. In an engine that has 
warmed up to operating temperature, this shift toward "early" can also be 
corrected and compensated for by causing appropriate correction of the 
injection onset to be performed by the injection onset adjusting device 
associated with the cam drive 5. To this end, the injection adjusting 
device is advantageously, and in a known manner, electrically controlled 
by a correction signal of the control unit 66. To detect the extent of the 
shift toward "early" effected by the increase in the quantity, the fuel 
injection pump is advantageously provided with a closing- and/or 
opening-point transducer 67. With it, the proportion of the portion 
h.sub.ve of the total prestroke hv.sub.max that is effective in terms of 
injection is detected. The additional fuel quantity imposed, and the shift 
to early, are thus detected at the same time as well. The result is a 
feedback of the aforementioned quantity correction, such that regulation 
is attainable. Naturally the additional first fuel injection quantity can 
also be measured in some other known manner, such as with the aid of a 
needle stroke transducer in the injection valve 23. The disposition of the 
pressure sensor 64 provides another possible way of detecting the portion 
of the pre-stroke that is effective in injection. As long as the second 
valve 56 is still open, a pressure that corresponds to a transfer pressure 
reaches the pressure sensor, after the second annular groove 61 has come 
into coincidence with the contact opening 62. This pressure is the 
pressure that is established in the pump work chamber 6 as long as this 
chamber is relieved via the connecting conduit 63. Accordingly, the 
pressure sensor emits a first signal. Because of throttling, this pressure 
is higher than the suction chamber pressure 7 but lower than the injection 
pressure. If the second valve 56 now closes, high pressure corresponding 
to the injection pressure is then produced in the pump work chamber, and 
this pressure is then detected by the pressure sensor as well, which emits 
a second signal. From the interval between the first signal, corresponding 
to the transfer pressure, and the second signal, the idling stroke 
h.sub.va can be detected, and by relating it with the structurally 
dictated maximum pre-stroke h.sub.vmax, the additional fuel quantity that 
is effective for injection can be detected via the pre-stroke h.sub.ve 
that is effective for injection. 
In the above exemplary embodiment, the second valve 56 is mounted as a 
closing element on the face-end side of the bushing 2 and closes the pump 
work chamber 6. A magnet valve disposed centrally in this way is 
particularly advantageous in a distributor injection pump, in which the 
individual pressure lines 22 leading away from the housing to the 
injection valves 23 are distributed around the magnetic valve 56. With 
this arrangement, the second magnetic valve is also disposed downstream of 
the first valve, that is, the valve embodied by the first annular groove 
52 and the outlet opening 54. This is necessary because the valve provided 
here is not pressure-balanced, and must not be exposed continuously to 
high pressure. The result is a somewhat larger idle volume during the 
initial phase of fuel supply. In a departure from this, the second valve 
56' in the exemplary embodiment shown in FIG. 4 is disposed upstream of 
the first valve. Here an annular groove 52' in the pump piston 4' is 
provided that does not communicate directly with the pump work chamber 6. 
Communicating with the annular groove 52', at least over the entire 
pre-stroke hv.sub.max, is the connecting conduit 153a. This conduit 
effectively discharges into the pump work chamber 6, and directly before 
where it discharges into the pump work chamber it has a magnetic valve 
56', corresponding to the magnetic valve 56 of FIG. 1. However, this valve 
must be high-pressure-proof, because in emergency operation, that is, in 
the event the regulation fails, the valve is opened and is continuously 
exposed to the high pressure during the supply phase of the pump piston. 
As in the exemplary embodiment of FIG. 1, the first valve is again 
embodied by a pairing of an annular groove and an outlet opening; the 
annular groove 52' controls the outlet opening 54' of the portion 153b of 
the connecting conduit that leads from the pump cylinder 3 to the relief 
side, or to the suction line 9. The annular groove 52' is put in 
communication with this portion 153b at the stroke onset and is separated 
from it after hv.sub.max. Otherwise, the fuel injection pump of FIG. 4 is 
identical in embodiment to that of FIG. 1. Functionally as well, it can be 
described as set forth above for the first exemplary embodiment. As in 
that case, the fuel injection pump is controlled by a control unit 66. 
With the embodiments described above, a fuel injection pump having an 
electronic regulating device is particularly attained, at lesser cost 
while maintaining safety, because emergency operation is possible with a 
basic fuel injection quantity, with the aid of the mechanical regulator. 
The electronic regulator has all the advantages that are attainable only 
in a fuel injection pump that is electronically regulatable. The 
mechanical regulator may also be embodied in some other known manner, for 
instance as a hydraulic regulator. 
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.