Liquid fuel injecting device for internal combustion engine

A device for injecting high pressure atomized fuel liquid into the combustion chamber of an internal combustion engine such as a diesel engine. The device includes a mechanism for delivering high pressure liquid fuel (16) such as a pump. The mechanism communicates via a cyclic communication device with an injection chamber (26) of variable volume having a movable element (27) returned by a resilient returning element (28) towards a stop (33), and communicates permanently with the nozzle cavity (10). The amount of liquid fuel is delivered to the injection chamber during the cyclic closing phase of a nozzle obturator (14).

FIELD OF THE INVENTION 
The present invention relates to a liquid-fuel injection device for an 
internal combustion engine. 
BACKGROUND OF THE INVENTION 
Conventionally, liquid fuel is injected into an internal combustion engine, 
for example a compression-ignition engine, using a means that establishes 
fuel pressure, which is in the form of an injection pump capable 
cyclically of placing fuel under high pressure in a variable-volume 
chamber formed in a pump cylinder and delimited by a plunger actuated by a 
camshaft that is kinematically connected to the main shaft or crankshaft 
of the engine. 
The compressed fuel is injected through an injection nozzle which 
communicates, via a number of injection holes with the working or 
combustion chamber of the engine, this nozzle including a chamber which 
communicates with the cylinder of the injection pump, generally through 
one-way passage means such as a non-return valve. The communication 
between this chamber and the working or combustion chamber is interrupted 
by a sliding needle resting, by virtue of the action of elastic return 
means, on a conical seat formed in the said nozzle upstream of the said 
injection holes. 
This needle includes a cylindrical body sliding in a bore formed in the 
nozzle and of a diameter that exceeds that of the conical bearing surface 
of the needle on its seat, so that when the pressure of the fuel exceeds a 
certain value, known as the rated pressure of the injector, it lifts off 
its seat to allow injection to take place. When the plunger of the 
injection pump has travelled beyond a certain position, beyond which the 
pump cylinder will find itself in communication with low-pressure 
fuel-supply means, the pressure in the nozzle drops and the injection 
needle is returned onto its seat, to close the nozzle again, under the 
action of the aforementioned elastic return means. 
In spite of its great simplicity, this conventional device presents serious 
drawbacks. Firstly, the injection pressure depends on the engine speed and 
varies with it. Next, because of the necessarily limited force of the 
return spring, the end of injection occurs at a low pressure which no 
longer allows the fuel to be finely atomized, this generating unburnt 
hydrocarbons and particles of soot. 
Some of these drawbacks may be avoided using an injection device of the 
type proposed in Patent FR-A-1,351,593. In such a device, fuel from the 
pressure-establishing means, such as a pump or an accumulator, is sent to 
an injection chamber delimited by a plunger moving against a powerful 
spring, so as to fill the chamber with pressurized fuel during the 
non-injection phase. This chamber opens directly into the injector cavity 
in which the shut-off means, such as a needle whose lift can be controlled 
either by an independent hydraulic circuit or by a circuit using fuel, 
move. When the needle is made to open and therefore injection is made to 
take place, the needle moves, over a long travel, until it comes into 
abutment against the plunger of the injection chamber, this plunger, as it 
advances delivering fuel from the injection chamber to the injection 
nozzle, causing the needle to close again. 
Such a device does, however, have drawbacks which make it unsuitable for 
use with very high injection pressures which are used in modern engines 
and which would result in a heightened risk of fuel leaks and in a loss of 
power because of some of the fuel spilling out of the injector volume into 
the supply circuit, not to mention the problem of over-specifying the 
return spring. 
DOS 1,944,862 has also already described an injection device comprising an 
injection chamber in which a differential plunger moves and which is in 
direct communication with the injector, control means allowing the 
injection chamber to be filled, during the non-injection phase, against 
the action of the pressure of a fuel accumulator kept charged by a 
high-pressure pump. This device does, however, present appreciable 
drawbacks. In particular, the injection pressure is only a fraction of the 
pressure supplied by the pump and the end-of-injection-travel of the 
plunger is marked by a pressure drop that is difficult to obtain 
precisely, particularly in the case of very high pressures. 
In order to overcome the drawbacks of these various solutions, modern 
developments have concentrated on accumulation-type injection systems, 
also known as "common rail" systems. 
In such systems, an accumulator is constantly filled with fuel at high 
pressure by virtue of means that generate high pressure in the fuel, and 
permanently communicates with the chamber of the injection nozzle upstream 
of the seat against which, by virtue of control means, the bearing surface 
of the injection needle presses. A distributor allows the said chamber to 
be made to communicate with another chamber delimited by the upper face of 
the needle, so that the needle is pressed against its seat under the 
effect of the pressure prevailing in the accumulator. When injection is to 
be initiated, the distributor is switched to make the said chamber 
delimited by the upper face of the needle communicate with low-pressure 
feed means so as to make the pressure exerted on the upper face of the 
needle drop so that the needle can lift. 
To end the injection, the distributor is switched again into the other 
position, so as to re-establish the accumulator pressure over the upper 
face of the needle, so that the control means return the needle onto its 
seat without it being necessary for the injection pressure to be dropped. 
Injection therefore takes place entirely at the high pressure of the 
accumulator, thus avoiding drips at the end of injection. 
Furthermore, the injection pressure is independent of the engine speed. 
Such devices, which are advantageous from the points of view of combustion 
quality and control of unburnt hydrocarbons, do, however, present other 
drawbacks. Specifically, if the needle does not close properly or if the 
needle seat is damaged, the fuel present at high pressure in the 
accumulator will spill out into the combustion chamber, with a risk of the 
engine becoming overheated and destroyed. 
Furthermore, as the permanent pressure of the common rail is sealed in by 
numerous plungers sliding in bores, a significant level of leakage creates 
mechanical losses, heating of the fuel and disturbs metering accuracy. 
BRIEF SUMMARY OF THE INVENTION 
The invention proposes to overcome these drawbacks and to provide an 
injection device that allows fuel to be injected at high pressure 
throughout practically the entire duration of injection, independently of 
engine speed. 
Another object of the invention is to produce such a device which, in an 
extremely simple way, allows an accurate and determined dose of fuel to be 
delivered in a very short period of time and at a very high pressure. 
Another object of the invention is to produce such a device in which 
injection can be performed at very high pressure throughout the injection 
phase. 
Yet another object of the invention is to produce such a device in which 
injection can be performed very quickly using relatively slow means of 
establishing a high pressure. 
Yet another object of the invention is to produce such a device with a 
reduced number of conventional components and, in particular, to use just 
one pumping and metering element to supply a number of injectors, thus 
guaranteeing a good balance between the deliveries injected into the 
various cylinders. 
Another object of the invention is to produce such a device in which the 
rate of injection can be varied, in a simple way, during injection, 
particularly to provide a start of injection at a low rate then to 
continue injection at a higher rate, using the technique sometimes known 
as rate shaping. 
Another object of the invention is to obtain the advantages of the common 
rail system with a low level of leakage. 
Another object of the invention is to reduce the energy consumption of the 
injection device. 
Another object of the invention is to obtain these advantages without using 
electronic means which are ill suited to certain environments. 
The subject of the invention is a device for the discontinuous and cyclic 
injection of atomized liquid fuel at high pressure into a combustion 
chamber of an internal combustion engine with variable-volume working 
chamber, which includes, 
an injection nozzle comprising: 
a nozzle cavity which communicates with a combustion chamber via at least 
one injection orifice, 
shut-off means allowing the communication between the said nozzle cavity 
and the said combustion chamber to be interrupted and re-established 
cyclically, 
and means of delivering liquid fuel under high pressure, these means being 
capable cyclically of delivering a metered amount of liquid fuel at high 
pressure, 
the said delivery means communicating, via cyclic-communication means, with 
a variable-volume injection chamber delimited by one wall of a moving 
element returned by elastic return means towards a fixed stop establishing 
the minimum value of the said variable volume of the said injection 
chamber, and which permanently communicates with the said nozzle cavity, 
the said injection chamber being intended temporarily to receive the said 
metered amount of liquid fuel, 
the said metered amount of liquid fuel being delivered cyclically by the 
said delivery means into the said injection chamber during the phase of 
cyclic closure of the said means of shutting off the injection nozzle, 
characterized in that the said elastic return means include a volume of 
fluid under pressure acting on the said moving element. 
As a preference, the said moving element, the wall of which delimits the 
aforementioned injection chamber, is formed by a plunger sliding in a 
cylinder in order to delimit the said chamber. Because the pressures on 
each side of the plunger can be practically balanced, the risk of leakage 
at the plunger can be practically eliminated. 
As a particular preference, the pressurized fluid contained in the volume 
and exerting its return effect may be fuel kept under pressure in an 
accumulator. 
As a preference, the moving plunger or element may be designed to seal 
against any leaks between the injection chamber and the said volume of 
liquid fuel under pressure, when it is pressed against its stop. 
The fluid under pressure may act on the said moving element via a 
multiplication means, particularly a differential plunger. 
The injection nozzle may advantageously be a nozzle of the conventional 
type, containing three cavities, namely a first chamber or sac 
communicating by injection orifices with the combustion chamber, a second 
chamber communicating with the first chamber and having a seat, the said 
chamber being delimited by the lower part of a sliding needle, the end of 
which has a bearing surface capable of pressing against the said seat to 
interrupt this communication, and a third, cylindrical, chamber in which a 
part of the needle that forms a plunger slides, so as to form above the 
needle a third chamber which is associated with control means. 
The shut-off means formed, for example, by such a needle may be controlled, 
for opening them, by electromagnetic means in a way known per se. 
These shut-off means may be sensitive to the pressure of the liquid fuel in 
the nozzle cavity, for example the aforementioned second chamber, so that 
when a high pressure is established in this cavity, the needle lifts 
against its return means as far as an against-the-stop position. This 
solution is preferred in the present invention and may be obtained simply 
by a direct and permanent communication between the said nozzle cavity and 
the said injection chamber. 
The said shut-off means may, for closing them, be sensitive to the action 
of a return spring. 
They may also, for closing them, be sensitive to the action of a fluid 
under pressure, particularly liquid fuel. 
However, as a preference, the said shut-off means may be sensitive, for 
closing them, to the direct action of the aforementioned moving element of 
the injection chamber, so that the moving element, when it returns to its 
against-the-stop position, moves the shut-off means towards a sealing 
position. 
This solution is particularly advantageous, because it makes it possible to 
ensure that the injection of atomized liquid fuel into the combustion 
chamber takes place at a high pressure, including in the very last moments 
of injection. 
The stop for the moving element may then consist of the said shut-off 
means, such as the needle, when they reach their closed position. It is, 
however, just as possible to envisage a fixed positive stop, for example 
formed by a shoulder or seat of the injection chamber, and against which 
the moving element comes to rest after having closed the aforementioned 
shut-off means, such as a needle, then having travelled a very short 
additional distance by virtue of an elastic contact between the moving 
element and the said shut-off means, for example by simple elastic 
compression of the shut-off needle when the latter is of an elongate 
shape. 
The means of delivering liquid fuel at high pressure may be entirely 
conventional and in particular may comprise a simple conventional 
reciprocating injection pump, the plunger of which is in permanent contact 
with the cam of a camshaft. Advantageously, this pump may be a metering 
pump, for example comprising, as is known in the field of injection pumps, 
a helical discharge ramp and pump plunger angular-position adjustment. 
It is possible to use centralized means of establishing pressure for 
several injection devices associated with each plunger and the pump may 
then be a conventional distributor pump. 
In an advantageous embodiment, the said means of cyclic communication which 
are arranged between the said means of delivering liquid fuel at high 
pressure and the said variable-volume injection chamber comprise a one-way 
communication means. 
Furthermore, they may, in particular, include a valve arranged upstream of 
the said one-way means and arranged in such a way as to place the said 
means of establishing high pressure in communication with a low-pressure 
discharge, therefore causing the said one-way means to close so that the 
said metered amount of fuel can be determined by the time taken for the 
said valve to close. 
The said valve may simply be a two-way valve. 
When the aforementioned nozzle shut-off means are sensitive, for closing 
them, to the pressure in a cavity containing liquid fuel, a valve, 
preferably the aforementioned valve arranged upstream of the said one-way 
means may be provided, for placing the said cavity in communication with a 
discharge in order to allow the said shut-off means to open. 
In this case, the same valve controls the connection-to-discharge of the 
said means of establishing high pressure and of the said cavity containing 
the liquid fuel acting, for the closure operation, on the said shut-off 
means so that when the said valve is closed, the said delivery means 
deliver the liquid fuel under high pressure to the said injection chamber 
through the said one-way communication means, whereas opening the said 
valve brings about the end of the said delivery and, as the same time, 
allows the said shut-off means to open and fuel to be injected into the 
combustion chamber. 
It is also possible to establish an offset between the instant of the end 
of metering and the instant of the start of injection, by leaving the 
plunger of the pump to deliver the fuel under pressure until it reaches it 
uppermost point, the pressure then being sustained by virtue of a flat cam 
profile. In this case, the valve closure instant determines how much 
volume will be injected, because the dose of fuel received by the 
injection chamber is determined by the working stroke of the pump between 
the instant of closure and the arrival at the uppermost point. 
Contrastingly, subsequent opening of the valve determines the 
start-of-injection moment. 
In another embodiment, it is possible, for opening the shut-off means, to 
use the pressure drop that is due to the downstroke of the pump plunger 
after it has reached its uppermost point. The energy of the expansion of 
the volume of fuel compressed between the pump plunger and the shut-off 
means, such as the needle, may then advantageously be recovered on the 
means that drives the pump plunger. 
In this case, the function of the two-way valve may be fulfilled by a pump 
conventional rotary distributor and an electrically controlled valve 
becomes unnecessary. 
Remarkably, the invention lends itself to the injection of liquid fuel into 
a multi-cylinder engine comprising injection nozzles specific to each 
cylinder. The pump or means of delivering liquid fuel at high pressure is 
then connected separately to each nozzle by identical specific pipes, and 
means are arranged for sending the fuel to the various nozzles in turn. 
These means may simply consist of a single conventional distributor type 
pump and it is remarkable that this pump may advantageously be connected 
to a low-pressure discharge by a single two-way valve, simple control of 
which allows all of the operations of the injection cycle to be 
determined, unless the purely hydromechanical solution defined hereinabove 
is adopted. 
Where this is the case, the aforementioned elastic means of returning the 
moving elements preferably consist of a single centralized means, for 
example a single accumulator containing liquid fuel placed at high 
pressure and acting on the said moving elements, the moving elements 
preferably being arranged in the respective nozzles in coaxial alignment 
with the means of shutting off the said nozzles. 
The aforementioned one-way communication means are then advantageously 
individually arranged at each nozzle in such a way as to reduce the 
compressed and uninjected amount of fuel. 
In order to vary the rate of delivery of fuel injected during the injection 
phase, for example by establishing a low injection rate at the start of 
injection and a high rate for the rest of injection, the device may 
advantageously comprise means allowing the fuel from the injection chamber 
to be sent to the nozzle cavity at a limited flow rate so that at the 
start of injection the rate of injection is equal to a determined rate 
from the injection chamber, reduced by a rate that corresponds to the 
increase in volume in the nozzle cavity brought about, by example, by the 
lifting of the injector shut-off means. 
To this end it is possible, for example, to envisage arranging in the 
direct communication between the injection chamber and the injector 
cavity, a restriction or nozzle with a calibrated orifice allowing the 
flow rate sent to the injector cavity to be limited, the shut-off means 
such as the needle then being associated with means allowing the needle 
lift to be controlled during a determined period of time. This means may 
itself be a restriction slowing the rate of discharge of the fluid that 
controls the shut-off means. 
This means may possibly be arranged like a variable cross section 
restrictor so that the needle lift follows a determined time-based profile 
.

DETAILED DESCRIPTION OF THE INVENTION 
Reference is first of all made to FIGS. 1 to 4. 
The injection device described is associated with a cylinder 1 of a diesel 
engine, in which there slides a piston 2 and delimiting, above it, a 
combustion and working chamber 3 closed off by a cylinder head 4. Placed, 
preferably centrally and coaxial with the chamber in which the engine 
piston 2 slides there is an injector 6 which may be produced in an 
entirely conventional way. This injector includes a nozzle 7, the lower 
end of which opens into the working chamber 3 and which includes an 
internal cavity forming a succession of three chambers, namely a first 
chamber or sac 8 of small volume, in permanent communication with the 
working chamber 3 via injection holes 9, a second chamber 10 located above 
a conical seat 11 and a third, cylindrical, chamber 12 at the end, which 
forms a stop, of which there rests a spring 13 which pushes towards the 
bearing surface 11 a conventional shut-off needle 14 sliding in the 
cylindrical chamber 12 and the narrowed front end of which has a bearing 
surface 15 which presses in leaktight fashion against the seat 11. 
The device further includes a pump 16 of a conventional type allowing a 
high fuel pressure to be established. This pump consists of a pump 
cylinder 17 in which there may slide a delivery plunger 18 returned to its 
lowermost point by a spring 19 against the cam 20 of a camshaft 21 
kinematically tied to the crankshaft (not depicted) of the engine. The 
compression chamber 17 communicates via a pipe 22 in which there is a 
simple two-position valve 23, with the low-pressure fuel-supply source 24. 
Furthermore, the compression chamber 17 communicates directly with the 
aforementioned third chamber 12 via a pipe 25 which opens into a pipe 30. 
The device according to the invention also includes an injection chamber or 
cavity 26 in which a moving element 27, consisting of a plunger, slides 
against a powerful return means 28 which may be a spring but which is 
preferably a volume of pressurized fluid, for example an accumulator 
filled with liquid fuel under pressure, preferably designed to act upon 
the plunger 27 with a force that is substantially constant throughout the 
working stroke of the plunger. The injection chamber 26 constantly 
communicates with the aforementioned second chamber 10 via a pipe 29. 
Finally, the communication between the chamber 26 and the compression 
chamber 17 is provided by the pipe in which a one-way valve 32 is fitted. 
In the position of rest, the plunger or moving element 27 rests against a 
front stop 33 of the chamber 26, so that the volume of the chamber 26 is 
minimal. 
Advantageously, the stop 33 provides a sealing seat so that when the 
plunger 27 is in this position, no leaks from the accumulator 28 towards 
the chamber 10 are possible. 
Operation is as follows. 
In the sweeping position depicted in FIG. 1, the injection needle 14 is 
pressed against its seat 11 by the return spring 13. The moving element or 
plunger 27 is pressed against its stop 33 by the powerful spring 28. The 
pump plunger 18 begins its downstroke under the action of the cam 20. The 
two-position valve 23 is in the open position which means that the pump 
chamber 17 and the third cavity 12 are at the low fuel pressure. 
In the second chamber 10 the pressure level is low enough for the needle to 
be pressed against its seat by the spring 13. The displacement of the pump 
plunger 18 has little effect on the pressures. 
The rest of the process is depicted in FIG. 2: at a given moment t in the 
engine cycle, the two-way valve 23 is rapidly closed. The injection 
plunger 18, continuing its stroke, immediately raises the fuel pressure in 
the chamber 17 and therefore in the chamber 12. At the same time, the 
liquid is driven towards the injection chamber 26 and the plunger 27 is 
pushed back against the action of its powerful spring while the same 
pressure establishes itself in the second chamber 10. The high pressure of 
the liquid fuel in the chamber 17, the chamber 26, the second chamber 10 
and the third chamber 12 is determined by the force of the spring 28 whose 
return force is preferably almost constant. Thus, the liquid fuel is 
subjected to the high pressure which will be the injection pressure, for 
example 1600 bar. 
For as long as the two-position valve 23 is closed and the injection pump 
plunger 18 continues its delivery stroke, the injection plunger 27 
retreats, compressing its elastic means 28 at constant force and storing 
up in the chamber 26 fuel that has come from the chamber 17. 
At the moment t+.DELTA.t, that is to say at the instant when the desired 
dose of fuel has been introduced, at the high injection pressure, into the 
chamber 26 and when injection proper is to commence, the two-position 
valve 23 is quickly re-opened as depicted in FIG. 3. 
The chamber 17 and the third chamber 12 immediately find themselves at the 
low pressure, notwithstanding a possible continued downstroke of the pump 
plunger 18. The one-way valve 32 immediately closes and the chamber 26 
becomes isolated from the pumping chamber 17. 
As the third chamber 12 is at a low pressure, the high pressure prevailing 
in the chamber 10 will lift the injection needle 14 which will in turn 
compress its return spring 13, until it comes to rest on its upper stop, 
establishing a communication, via the first chamber 8 and the injection 
orifices 9, with the working chamber of the engine. In consequence, the 
liquid fuel at the high injection pressure is injected and atomized into 
the working chamber. 
This high-pressure injection continues throughout the duration of the 
displacement of the plunger 26 under the action of its return means 28 
until the plunger comes against its stop 33, which means that a volume of 
fuel that corresponds to all and only all of the dose previously delivered 
into the chamber 26, is ejected through the orifices 9. 
At the end of injection, depicted in FIG. 4, the moving element 27 comes 
into abutment against the seat 33 and the pressure in the second chamber 
10 drops sharply until it becomes insufficient by comparison with the 
elastic return force of the spring 13 on the needle 14, which is then 
sharply returned onto its seat. 
The metering and the start of injection can be adjusted independently of 
one another simply by controlling a simple two-position valve 23. 
The end-of-metering moment and the start of injection can also be offset, 
for example by using a cam which has a flat high profile part for stopping 
fuel from being sent to the metering chamber 26 while at the same time 
maintaining the pressure in the third chamber 12, it being possible for 
the moment of injection to be chosen at will on the flat part of the cam 
by opening the valve 23. In this case, the fuel is discharged from the 
pump 16 starting from the moment that the valve 23 closes and throughout 
the remaining displacement of the pump plunger 18 towards its uppermost 
point. 
Finally, it is also possible, without opening the valve 23, to wait for a 
drop in pressure in the chamber 12 brought about by the plunger 18 
returning to its lower-most point. 
The injection phases are also completely independent of the position of the 
cam 20. 
The pump 16 can therefore be crude and of low delivery rate because it has 
most of the engine cycle available in which to deliver fuel to the 
injection chamber. 
In the examples just described, the pump 16 is not directly designed to 
deliver an adjustable dose of fuel, this dose being quantified by the 
stroke of the plunger 18 travelled in the time At taken for the valve to 
close. 
It will, however, be appreciated that use may also be made of engine fuel 
injection pumps of the conventional type equipped with a reversed-helix 
ramp and a device for rotation about the axis of the pump plunger so that 
a discharge orifice formed in the cylindrical wall of the pump can be 
closed and opened. The pump plunger then acts as the two-position valve 
23. 
Reference is now made to FIGS. 5 to 8, in which the components which have 
the same functions as in the earlier description have the same reference 
numerals. 
This embodiment is intended for multi-stage injection, for example with 
pre-injection, for limiting leaks and mechanical losses, and reduces the 
influence of the compressibility of the liquid fuel on the operation of 
the device to a minimum. 
In this embodiment, the pipe 30 is omitted and the pipe 25 from the pump 16 
opens, via a one-way valve 32, directly into a chamber 34 which 
simultaneously constitutes the second chamber of the injector 12 and the 
injection chamber replacing the chamber 26. The needle has an extension 
48, the diameter of which exceeds that of the seat of the needle 14 and 
which can slide through a hollow moving plunger 50 forming the moving 
element of the injection chamber 34 and which may itself slide in a 
cylinder forming a chamber 35 into which a high-pressure-liquid-fuel 
accumulator 28 opens. The extension 48 has, in the chamber 35, a collar 49 
the diameter of which is markedly smaller than that of the chamber 35 and 
against which the thrust of a needle-return spring 13 can act. The upper 
end of the extension 48, beyond the collar, slides in a cylinder which 
determines the third chamber 12 of the needle, to form a plunger, the 
diameter of which is somewhere between the diameter of the seat of the 
needle and the diameter of the extension 48. 
The volume of the chamber 35, and therefore the accumulator 28, communicate 
with the third chamber 12 via a pipe 51 which starts off radially and then 
becomes axial made in the extension 48 and which opens, via an end 
restriction, into the chamber 12. Incidentally, this chamber is connected 
to the low-pressure fuel source 24 by a valve 52 situated close to the 
chamber 12 and a pipe 53. 
In the filling position depicted in FIG. 5, the first and second valves 23, 
52 are closed and the pump 16 delivers fuel at high pressure through the 
pipe 25 into the chamber 34 so that the plunger 50 moves in the direction 
of the arrow and delivers the fuel that lies in the chamber 35 to the 
accumulator 28. All of the forces exerted by the fuel and by the spring 13 
on the needle 14 keep this needle pressed against its seat 11. After the 
pump reaches its uppermost point, the valve 32 closes and the cam recovers 
the energy of compression of the volume of fuel contained in the chamber 
17 and the pipe 25. The pressure in the various cavities of the injector 6 
is then determined by the pressure in the accumulator 28. Opening the 
first valve 23 causes the pressure in the pump to drop. The valve 52 can 
then be opened as can be seen in FIG. 6. This results in an immediate drop 
in pressure in the third chamber 12 which means that the needle 14 is 
pushed into the open position. The chamber 34 is then in communication 
with the first chamber 8 and the fuel from the chamber 34 is ejected and 
atomized under the pressure of the plunger 50 that is subjected to the 
pressure prevailing in the accumulator 28. The restriction in the pipe 51 
prevents the accumulator from emptying. 
The valve 52 can then be closed quickly again as shown in FIG. 7 so that 
this first injection phase, which constitutes a pre-injection, finishes, 
the needle 14 being pushed back towards its seat on account of the 
increase in pressure in the chamber 12 and the action of the spring 13. It 
is thus possible, by opening and closing the valve 52 several times in 
succession, to bring about multi-stage injection. The end of injection is 
obtained, as shown in FIG. 8, when the entire injectable dose contained in 
the chamber 34 has been ejected and when the plunger 50 has come into 
sealed contact with its seat 33, so that the pressure in the chamber 34, 
reduced to its minimum volume, drops and the needle closes again quickly 
under the effect of the spring 13 and the pressure exerted on the 
differential area between the extension 48 and the chamber 12. The valve 
52 is then closed again. 
It will be understood that needle control is extremely quick and precise, 
especially since the valve 52 can be placed in close proximity to the 
third chamber 12. Furthermore, no transfer between an injection chamber 
and the second chamber of the injector is required, and this means that 
the dose injected is insensitive to the compressibility of the fuel. 
Finally, leaks are limited to the sweeping of the chamber 12 through its 
restriction during the short duration of the injection. 
Reference is now made to FIGS. 9 to 12 which depict embodiments in which 
the needle is closed positively by the moving element of the injection 
chamber. 
FIG. 9 shows an injector 6 similar to the one in FIG. 1 and the third 
chamber 12 of which has no return spring. The needle 14 is continued 
upwards in the form of a long extension 37 sliding in the body of the 
injector and emerging in an injection chamber 26 that is connected to the 
pipe 25 via the valve 32 and the pipe 30. The plunger 27, which delimits 
the injection chamber 26, is acted upon by its return means, namely the 
accumulator 28 and by a spring 54, used only when stationary. 
When the pump 16 delivers fuel to the injection chamber 26, the chamber 12 
is under pressure and the needle 14 is pressed against its seat 11. During 
this time, the plunger 27 rises and the volume of the chamber 35 
increases, the plunger 27 moving away from the end of the shank 37 of the 
needle. 
Operation is similar to the operation of the device of FIG. 1. When the 
valve 23 opens, the pressure in the third chamber 12 drops and the needle 
immediately lifts until it comes against the end of the chamber 12. The 
plunger 27 starts to move down from its raised position and the fuel is 
ejected via the pipe 29 and the chamber 10. Towards the end of the 
downstroke of the plunger 27 urged by the pressure prevailing in the 
accumulator 28, the plunger 27 comes against the end of the shank 37 and 
returns the needle downwards into the closed position. Once the needle 14 
is pressed against its seat 11, the shank 37 forms a stop for the plunger 
27. The spring 54 is simply intended to make sure that the needle 14 is 
closed and the plunger kept in the position that corresponds to a minimum 
volume of the chamber 26 when, for example, with the engine stopped, the 
pressure in the accumulator 28 has not yet built up. 
Reference is now made to FIG. 10 which shows a device similar to the device 
of FIG. 9, but in which the needle 14 has a second sealing surface 62 
which interacts with a seat made in the chamber 12 and avoids leaks likely 
to come from the accumulator 28 through the clearance between the needle 
14 and the nozzle body 7. 
The device of FIG. 11 is similar to the one in FIG. 9 except that the 
plunger 27 rests against a seat 33 in the injection chamber 26 after 
having compressed the needle 14. In this case, a spring 13 with a short 
travel is depicted in the chamber 12 for pressing the needle 14 onto its 
seat 11 even when, with the accumulator 28 not under pressure, the plunger 
27 is not acted upon. In this embodiment, the length and diameter of the 
shank 37 are chosen such that the needle 14 is pressed against its seat 11 
by the plunger 27 shortly before this plunger has reached its position 
against the stop 33, the rest of the downstroke of the needle being 
allowed by the deformation of the shank 37 under compressive stress. 
The embodiment of FIG. 12 is similar to that of FIG. 5, the difference 
being that the needle 14 is closed, as in FIG. 9, by the impact of the 
injection plunger 50 against the stop 56 offered by the needle. 
Reference is now made to FIG. 13. 
In this embodiment, which is very well suited to high fuel-injection 
quantities, the nozzle, the injection chamber and its moving element, and 
the pump that generates the high pressure are coaxially aligned along the 
axis of the nozzle 7. 
The plunger 18 of the pump slides in a cylindrical chamber 17 defined 
inside the moving element 65 with a differential plunger returned in the 
injection direction by the elastic return means which consists of the 
pressurized fluid 35, for example air, in communication with an 
accumulator 36. The communication between the inlet of low-pressure fluid 
through the two-way valve 23 and the pump chamber 17 is via a radial 
passage made in the moving element 34 and communicating with the valve 23 
via a longitudinal port formed in the surface of the moving element 65. 
The injection chamber 26 is arranged under the moving plunger 65, and its 
end-of-travel stop 33 can be seen. The pipe 31 allowing the pump 16 and 
the chamber 26 to communicate, is an axial pipe which runs in an extension 
43 which extends, in the direction of the nozzle, beyond the active 
plunger surface of the part 65 which delimits the chamber 26 and which, at 
its free end, has a radial slot 44. A one-way valve 32 sliding in a sealed 
fashion on the said extension 43 and normally pressed against the face of 
the nozzle 7 by a spring such as, for example, a Belleville washer. When 
this valve lifts, the duct 31 places the pump 16 into communication with 
the chamber 26. Finally, it can be seen that the needle 14, which is 
depicted in the figure in its position of maximum lift, has its upper end 
opposite a volume 12 situated under the end of the extension 43 containing 
the duct 31, which volume is also delimited by the valve 32 when this 
valve is in its closed position. 
During the sweeping phase, the cam 20 is in a position which allows the 
pump plunger 18 to rise and draw in fuel from the low-pressure source 24 
through the valve 23 which is in the communication position so that the 
pump chamber 17 fills. 
After a certain time, with the cam 20 having rotated, the plunger 18 will 
begin its downstroke. At a moment t during this downstroke, the two-way 
valve 23 is closed. The fuel present in the pump will then be pressurized 
so that the valve 32 lifts against its return means and so that fuel 
pressurized in the pump is transferred into the chamber 26, so that the 
moving part 65 rises and the volume of the chamber 26 increases, while the 
high pressure is established in the chamber 10, just as in the volume 12 
that lies above the needle 14, through which the fuel flows to reach the 
chamber 26. The needle 14 therefore remains firmly pressed against its 
seat. 
At the moment t+.DELTA.t the valve 23 is opened. In consequence, the 
pressure drops immediately in the pump 16 and in the volume into which the 
duct 31 opens and which communicates with the third chamber 12. At this 
instant, the needle 14 lifts because of the pressure in the second chamber 
10, until it comes up against its stop as in the injection position 
depicted in FIG. 6 in which the volume of the chamber 12 has become 
minimum. The elastic return means 35, 36 push the moving element 65 back 
downwards, discharging the fuel from the injection chamber 26 towards the 
second chamber 10 whence it is expelled via the injection orifices 9 and 
atomized. 
Towards the end of its downstroke, the plunger 65 comes into contact, via 
the lower end of its end piece 43, with the needle 14 which is in its 
lifted position depicted in the figure. As the moving part 65 continues 
its downstroke, it therefore drives the needle 14 downwards until this 
needle is pressed against its seat, this allowing the needle to close 
sharply while the pressure in the chamber 10 is still at its high value, 
which means that an excellent quality end-of-injection is obtained. Once 
the needle 14 has come up against its stop, the moving part 65 descends 
slightly further downwards, by virtue of the elastic compression of its 
extension 43 containing the duct 31 and then stops definitively as it 
comes into contact with the stop 33. 
It will be understood that in this embodiment, which is highly advantageous 
when compressed air is available, no springs are needed for returning the 
needle 14, because the needle is pressed against its seat by the elastic 
tension in the extension 43 of the part 65 which is itself pressed firmly 
against its seat 33 by the pressure of the means 35, 36. 
Incidentally, the device depicted is particularly compact and the paths 
followed by the fuel leaving the pump 16 are particularly short, which 
minimizes the influence that the compressibility of the fuel has on the 
accuracy of the dose injected and also makes it possible, in the case of 
an engine that has several cylinders, to envisage injection devices that 
are practically identical and therefore deliver practically identical 
doses to each cylinder, including speed and load conditions where only 
very small doses are injected. 
Reference is now made to FIG. 14. 
This figure depicts two of the four injectors 6 of a device according to 
the invention intended for a four-cylinder engine. These injectors 6 are, 
for example, identical to the injector in FIG. 1. The plunger 27 of each 
injector delimits, via its other wall, a return chamber 38. All the return 
chambers 38 are connected directly to a single accumulator for liquid fuel 
at high pressure 39. 
Incidentally, the device includes a common distributor pump 40 operated by 
a driven shaft. 
The pump 40 is of a type that is conventional in injection devices for 
multi-cylinder engines and therefore need not be described. It includes a 
rotor 41 with four radial plungers 42 sliding in the pump cylinders 57 in 
which they move as the rotor rotates, under the effect of a stationary cam 
58, the known profile of which is determined by the number of cylinders 
and therefore of injectors 6. The lower part of the rotor forms a 
distributor 59 capable of sending liquid fuel under pressure to the 
various injectors 6 in turn via pipes 60 which replace the pipes 25 in 
FIG. 1 and lead to the pipe 30 of the various injectors. Incidentally, the 
pump chamber 57 permanently communicates with a central pipe 61 connected 
to a low-pressure source of fuel 24 via a two-position valve 23 and, in 
parallel, a pipe 63 with a one-way valve 64. 
This pump 40 can also be used to sustain the high pressure in the 
accumulator 39, by employing an assembly that communicates with the pipe 
61 and comprises a one-way means 46 and a pressure-regulating valve 47 
that is conventional in such accumulators and is connected to the 
accumulator by a pipe 45. 
It will be noted that these centralized means of sustaining the pressure in 
the accumulator 39 will draw a minimum equivalent and balanced amount of 
fuel from the injection to each cylinder. 
In operation, the pump 40 rotates with the engine. Controlling the valve 23 
allows a metered amount of fuel to be sent in turn to each of the 
injectors 6, which fuel travels along the pipe 60 and through the one-way 
valve 32 to the injection chamber 26 of the injector. Each injector 
operates in the same way as in the device depicted in FIGS. 1 to 4. 
It will therefore be understood that it is possible, using one simple 
two-way valve, to control the injection to each of the cylinders in an 
extremely precise way, and to do so using just one distributor-type 
metering pump 40 and just one elastic return means 39. Furthermore, 
injection takes place with characteristics which are constant from one 
cylinder to the next because the injection chambers 26 are in close 
proximity to the second cavities 10 and the pipes 60 can easily be 
designed to have identical internal volumes. 
Of course, the metering means and needle-control means described 
hereinabove can just as easily be applied to this case of a centralized 
device for several cylinders. 
In particular, it is possible to envisage replacing the valve 23 with the 
rotary distributor and using the pump plunger returns to open the 
injectors. The injection advance will then be set by the angular position 
of the cams 58 in the pump 40, in a way known per se. 
Reference is made to FIG. 3. To provide a timebased rate profile during 
injection with an initial injection part at low rate followed by injection 
at high rate, a nozzle or restriction member 68 which limits the flow rate 
passing through this communication to the maximum value of flow rate 
desired for injection has been installed in the pipe 29. 
A second nozzle 66 is placed in the pipe 30 for controlling the lever of 
the shut-off needle 14. 
At the start of injection, the rapid increase in fuel pressure from the 
injection chamber is communicated to the nozzle cavity 10 and lifts the 
needle 14. This lifting is not, however, instantaneous, because the nozzle 
66 slows down the discharge of fuel from the chamber 12 situated above the 
needle, which means that the needle takes a certain amount of time to 
reach the fully open against-the-stop position. Because of the nozzle 68, 
the delivery finally injected throughout the needle lifting period, which 
causes an increase in volume in the cavity 10, is equal to the regulated 
delivery passing through the communication 29 decreased by the delivery 
needed to increase the volume of the cavity 10. Once the needle has 
reached the against-the-stop position, this last delivery is cancelled and 
the entire nominal delivery passing through the communication 29 is 
discharged through the injection nozzle 9. 
The nozzle that slows down the needle lift can also be produced in the form 
of a variable cross section nozzle 67, the cross section being altered as 
the needle 14 lifts, this making it possible to obtain any desired rate 
shape at the start of injection. 
Of course, the nozzles 68 and/or 66, 67 may be functionally replaced by a 
suitable sizing (diameter and length and therefore pressure drop) of the 
lines 29 and 30.