EP1403510B1 - High pressure fuel injection system with means for pressure wave damping - Google Patents

Abstract

The fuel injection system has symmetric or asymmetric resistive attenuators (71-72, 91-92) and capacitive attenuators (73,93) to attenuate hydraulic waves, particularly waves at a frequency corresponding to the resonant frequency of the injection system. The electronic controller (20) takes account of residual pressure fluctuations at different injectors (10a-10d).

Description

The present invention relates to a method of constructing a high pressure fuel injection system. More specifically, the invention relates to the management of pressure waves in such an injection system, to control the amount of fuel introduced into each cylinder during injection.

The figure 1 drawings in the appendix present, schematically, a fuel supply device known to the engine of a vehicle.

This feed device comprises a low pressure part, the various elements of which will now be described. A tank 1 contains fuel. For example, in the case of a diesel engine, the fuel is diesel. A low-pressure low-pressure pipe 3 makes it possible to route the fuel to a pump 5. The fuel is filtered through a filter 4 placed along the low-pressure forward pipeline 3. A low-pressure return pipe 6 makes it possible to return one too much. full of fuel from pump 5 to tank 1.

The feed device comprises a high pressure part or injection system, which will now be described. This injection system has different mechanical elements. The pump 5 compresses the fuel and injects it into a high-pressure inlet pipe 7. The fuel is conveyed to a common rail 8 via the high pressure inlet pipe 7 which is connected to an inlet E of the common rail 8. The common rail 8 constitutes a high pressure fuel accumulation chamber. The fuel contained in the common rail 8 is then conveyed to different injectors 10a-10d. This is achieved by means of the injection pipes 9a-9d respectively connected to outputs Sa-Sd of the common rail 8. An electro-hydraulic valve (not shown), which equips each injector 10a-10d, is then actuated in order to injecting a quantity of fuel into the corresponding cylinder (not shown). A return line 11 makes it possible to recycle the fuel used for the operation of the valve which does not have injected, by circulating injectors 10a-10d to the pump 5.

From a hydraulic point of view and in the rest of this document, the different pipelines are taken in a broad sense. That is to say that under the generic term of pipe we join the tubular conduits, the fastening elements of these pipes to other elements of the injection system and possibly the holes drilled through these elements in the extension of tubing. For example, the injection line extends to the seat of the injection valve and is generally pierced in the injector door

The injection system also comprises a programmed computer, the motor controller 20. The opening and closing of the electro-hydraulic valves fitted to the injectors 10a-10d are controlled by the motor controller, via at least one actuator connection of the injectors 21a. Similarly, the operation of the pump 5 is controlled by the motor controller 20 via an actuating connection of the pump 21b and an actuator 22. The pressure in the common rail is measured by a sensor 24 and the signal corresponding to this measurement is routed to the motor controller 20 via the pressure acquisition connection 23a. The motor controller 20 is connected to other sensors (not shown) via at least one data acquisition connection 23b. These other sensors are, for example, a sensor measuring the acceleration required by the driver of the vehicle or a sensor indicating the instant of the engine cycle in which the engine is located. Thus, depending on the engine speed to be attained and according to the current engine parameters, the engine controller 20 determines the amount of fuel to be injected into each of the engine cylinders. Consequently, the motor controller 20 determines, on the one hand, the operating pressure that must be reached in the common rail 8 and, on the other hand, the opening and closing times of the electro-hydraulic valves of each of the injectors. 10a-10d. According to these parameters, signals are respectively emitted by the motor controller 20 on the actuating connections of the pump 23a to actuate the pump 5 and actuating the valves 23b to actuate the opening and closing of the corresponding electro-hydraulic valves.

In general, such high-pressure fuel injection systems are disturbed by hydraulic waves. These hydraulic waves can be either pressure waves or velocity waves, knowing that these two types of waves are correlated.

Pressure waves are generated by the rapid opening and closing of the electro-hydraulic valves that equip the injectors of the injection system: the opening creating a significant depression, closing a high overpressure. Pressure waves are also generated by the pulsed flow rate of the pump.

The waves generated by the operation of the injectors propagate along the injection lines against the current, that is to say upstream of the main flow. They then propagate in the common rail, then either in the inlet pipe to the pump, or in the other injection lines to the other injectors.

The waves generated by the operation of the pump propagate along the inlet pipe in the direction of flow. They then propagate in the common rail, then in the various injection lines towards the injectors.

Throughout the injection system, these different main waves undergo multiple reflections and multiple transmissions. This gives rise to secondary waves.

Finally, a large number of pressure waves, correlated to velocity waves, pass through the injection system and create, at a given point, pressure fluctuations around an operating pressure of the injection system.

In particular, at each of the electro-hydraulic valves fitted to the injectors, the fuel pressure undergoes fluctuations over time. For a given injector, the fluctuations of greater amplitude are therefore due either to the pulsed flow rate of the pump 5 or to the opening and closing of the electro-hydraulic valves of the other injectors, or to the opening and closing of the electro-hydraulic valve of the injector considered, at an earlier time of the engine cycle.

In particular, at the moment of opening of the electro-hydraulic valve of said injector in question, the fuel pressure is not precisely known.

A first consequence is that the flow is not known precisely. During the opening period of the electro-hydraulic valve, the amount of fuel injected into the cylinder is thus not controlled.

A second consequence is that when the electro-hydraulic valve is expected to open or close, it undergoes an additional mechanical force due to a change in pressure. This additional force facilitates or opposes the opening or closing operation of the electro-hydraulic valve. The opening or closing time of the valve is changed. Thus, the pressure fluctuations imply that the moment and the opening period of the valve equipping the injector vary. Once again, the amount of fuel injected into the cylinder is not controlled. Moreover, the exact moment of injection is not controlled either.

These pressure fluctuations at the injector, and their consequences on the amount of fuel injected into the engine cylinder, are particularly detrimental when it comes to a multiple injection engine. In this case, during an engine cycle, several short injections are made successively, in order, among other things, to improve the efficiency of the engine. The use of a multiple injection engine therefore requires control of the amount of fuel injected into the cylinder at each injection.

Many documents, known to those skilled in the art, describe mechanical means for mitigating pressure fluctuations:

The document US 5845621 proposes to add a dissipative element 18 ( figure 1 ) at one end of the main bore of the common rail.

The document US 6314942 proposes to add inside the common rail 20 a attenuation element 110 of the pressure waves. This element is in the form of a rod coaxial with the common rail and extending over the entire length of the latter. In addition, the section cross section of this element has several lobes able to reflect the pressure waves ( figure 1 ).

The document US 4161161 proposes the addition of a capacitive element 30 constituted by a volume in branch of the pipe 2 connecting the pump 1 to the injector 3 ( figure 1 ). In the preferred embodiment, this capacitive element is placed near the electro-hydraulic valve of the injector.

In the same way, the document FR 2783284 proposes to place a capacitive element 10 in series on each of the injectors. Each capacitive element is, moreover, in fluid communication with the others.

The document FR 2786225 gives a list of different embodiments of capacitive elements intended to be placed on the injection lines, close to the outputs of the common rail 1 ( figure 1 ).

The document JP-802 13 33 discloses an injection system according to the preamble of claim 1. According to this document, the hydraulic waves are attenuated by resistive and capacitive elements having characteristic frequencies corresponding to characteristic frequencies of the pipes of the injection system.

In general, the means implemented to attenuate the pressure waves constitute a series of local processes that are more or less effective and that are more of a know-how. No overall response is provided to the problem of pressure wave propagation across the entire injection system. In particular, the pressure waves whose frequency agrees with one of the eigenfrequencies of the injection system, lead to the establishment of standing waves through the entire injection system.

The main object of the present invention is to provide a general solution for attenuating the pressure waves and in particular the pressure waves whose frequency corresponds to the lowest eigenfrequencies.

Another object of the present invention is to control, with the aid of a programmed device, the quantity of fuel injected at each injection into the various cylinders of the engine, by evaluating the residual variations of the pressure at the level of the injectors.

The present invention relates to a method of constructing an injection system as described in the preamble of claim 1.

The resistive elements may be asymmetrical resistive elements.

The attenuation means serve to attenuate the hydraulic waves whose frequency corresponds to a first resonance frequency of said injection system which is the lowest natural frequency.

Preferably, the attenuation means also make it possible to attenuate the hydraulic waves whose frequency corresponds to a second resonant frequency of said injection system which is the natural frequency just above the lowest natural frequency.

In a first preferred embodiment, some of said resistive and capacitive elements are placed at the ends of said inlet pipe.

Preferably, the upstream end of the inlet pipe comprises a resistive element in series with a capacitive element, and the downstream end of the inlet pipe comprises a resistive element.

In a second preferred embodiment, some of said resistive and capacitive elements are placed at the ends of each of said injection lines.

Preferably, the upstream end of each of the injection pipes comprises a resistive element, and the downstream end of each of the injection pipes comprises a capacitive element.

Preferably, each of the injection pipes further comprises a resistive element placed in the second third of said injection pipes, these being oriented in the direction of the fuel flow, from upstream to downstream. .

The preferred embodiment combines both the relative layout of the inlet pipe and the injection pipe arrangement, which have been described above.

Preferably, the programmed computer calculates a corrected pressure at the injector and actuates each of said injectors according to said corrected pressure in order to inject a desired quantity of fuel Q ₂ .

The corrected pressure P ^th _inj is a function of a _rail pressure P in the common rail, a fuel temperature, a quantity of fuel Q ₁ injected by the same injector during a previous injection, the quantity of fuel. fuel Q ₂ desired during a current injection and a temporal separation s between the previous injection and the current injection.

où l'on somme sur différentes fréquences propres f_i, où g est une fonction périodique selon la séparation s et où h est une fonction d'atténuation selon la séparation temporelle s.In the preferred embodiment, the corrected pressure P ^th _inj is obtained by the following relation: $${{\mathrm{P}}^{\mathrm{th}}}_{\mathrm{inj}}\mathrm{=}{\mathrm{P}}_{\mathrm{rail}}\mathrm{+}{\mathrm{\Sigma }}_{\mathrm{i}}{\mathrm{boy\; Wut}}_{\mathrm{fi}}\left({\mathrm{Q}}_{\mathrm{1}},{\mathrm{Q}}_{\mathrm{2}},\mathrm{s},{\mathrm{P}}_{\mathrm{rail}},\mathrm{T}\right)\mathrm{x}{\mathrm{h}}_{\mathrm{fi}}\left({\mathrm{Q}}_{\mathrm{1}},{\mathrm{Q}}_{\mathrm{2}},\mathrm{s},{\mathrm{P}}_{\mathrm{rail}},\mathrm{T}\right)$$

where we sum on different natural frequencies f _i , where g is a periodic function according to the separation s and where h is an attenuation function according to the temporal separation s.

• la figure 1 est une vue générale schématique d'un dispositif d'alimentation en carburant d'un moteur diesel ;
• la figure 2 montre, superposées à un schéma du système d'injection selon l'art antérieur, une courbe de pression et une courbe de vitesse qui correspondent à une onde hydraulique stationnaire dont la fréquence est égale à la fréquence du premier mode propre de résonance du système d'injection ;
• la figure 3 montre, superposées à un schéma du système d'injection selon l'art antérieur, une courbe de pression et une courbe de vitesse qui correspondent à une onde hydraulique stationnaire dont la fréquence est égale à la fréquence du deuxième mode propre de résonance du système d'injection;
• la figure 4 est une section transversale d'un insert comportant un élément résistif asymétrique;
• La figure 4A est une vue agrandie de la zone entourée de la figure 4;
• la figure 5 est un schéma illustrant le mode de réalisation préféré du système d'injection selon l'invention; et,
• la figure 6 montre une courbe représentant en fonction du temps la pression corrigée estimé par le contrôleur moteur, une courbe représentant en fonction du temps la quantité de carburant injectée sans correction logicielle, et une courbe représentant en fonction du temps la quantité de carburant injectée avec une correction logicielle tenant compte de la pression corrigée.

The invention will be better understood, and other objects, details, features and advantages thereof will appear more clearly in the following description of a particular embodiment of the invention, given solely for illustrative purposes and not limiting, with reference to the accompanying drawings. On these drawings:

• the figure 1 is a schematic overview of a fuel supply device of a diesel engine;
• the figure 2 shows, superimposed on a diagram of the injection system according to the prior art, a pressure curve and a velocity curve which correspond to a stationary hydraulic wave whose frequency is equal to the frequency of the first eigenmode of the resonance system. injection;
• the figure 3 shows, superimposed on a diagram of the injection system according to the prior art, a pressure curve and a velocity curve which correspond to a stationary hydraulic wave whose frequency is equal to the frequency of the second eigenmode of the resonance system. 'injection;
• the figure 4 is a cross section of an insert having an asymmetrical resistive element;
• The Figure 4A is an enlarged view of the area surrounded by the figure 4 ;
• the figure 5 is a diagram illustrating the preferred embodiment of the injection system according to the invention; and,
• the figure 6 shows a curve representing as a function of time the corrected pressure estimated by the motor controller, a curve representing as a function of time the quantity of fuel injected without software correction, and a curve representing as a function of time the quantity of fuel injected with a software correction taking into account the corrected pressure.

The figure 1 drawings in the appendix schematically shows a device for supplying fuel to a heat engine. The description of this device, and in particular of the injection system, has already been made earlier in this document.

The operating pressure prevailing in the common rail 8 varies between 200 and 2000 bar during the operation of the engine and the requested power. Around this operating pressure, the pressure undergoes variations over time which can reach an amplitude of 300 bars.

The injection system as any mechanical system is characterized by a series of eigen modes each characterized by a natural frequency of resonance. The first eigenmode corresponding to the lowest resonant frequency. The second eigenmode corresponds to the eigenfrequency just above said lowest resonant frequency. Pressure waves, or velocity, whose frequency is adapted to one of these eigenfrequencies, are not attenuated during their propagation in the injection system. There is, ultimately, establishment of a standing wave.

The figure 2 illustrates the case of a standing wave whose frequency corresponds to the first natural frequency of the injection system.

The curve 2Pa represents the amplitude of the standing pressure wave along the inlet pipe 7. The amplitude of the standing pressure wave is maximum at the level of the pump 5. This point corresponds to a belly of pressure. The amplitude of the standing pressure wave gradually decreases in the direction of the main flow indicated by the arrow. Finally, the amplitude of the stationary pressure wave is canceled a first time at the input E of the common rail 8. This point corresponds to a pressure node. In the same way the curve 2Pb represents the amplitude of the standing pressure wave along the various injection lines 9a-9d. The amplitude of the stationary pressure wave is zero at the outputs Sa-Sd of the common rail 8. The amplitude increases progressively in the direction of the main flow, to reach a first maximum at the various injectors 10a. 10d.

The curves 2Va and 2Vb represent the amplitude of the stationary speed wave respectively along the inlet pipe 7 and the various injection pipes 9a-9d. This stationary speed wave is associated with the pressure wave previously described. At the level of the pump 5, the amplitude of the stationary speed wave is maximum. The amplitude of the stationary speed wave remains constant throughout the input channel 7. The amplitude of the stationary speed wave is therefore maximum at the input E of the common rail 8. From the similarly, on the curve 2Vb, the amplitude of the stationary speed wave is maximum at the different outputs Sa-Sd of the common rail 8. It is a belly of the stationary speed wave. The amplitude of the stationary speed wave gradually decreases along the injection lines 9a-9d to cancel a first time at the injectors 10a-10d. It is then a node of the stationary speed wave.

The figure 3 represents a standing wave whose frequency corresponds to the second natural frequency of the injection system.

The curves 3Pa and 3Pb represent the amplitude of the standing pressure wave along the injection system shown schematically in the abscissa. The amplitude of the standing pressure wave is maximum at the pump 5, then decreases rapidly to cancel itself a first time at a point A located in the first third of the inlet pipe 7. The amplitude passes through a maximum at a point C located in the second third of the inlet pipe 7. Finally, the amplitude decreases to cancel again at the input E of the common rail 8. On the second curve, 3Pb, l the amplitude of the stationary pressure wave is zero at the outputs Sa-Sd of the common rail 8, then increases along the injection lines 9a-9d, to reach a first maximum at a point F located at the first third of said injection lines 9a-9d. Then, in the direction of the main flow, marked by the arrow, the amplitude of the standing pressure wave gradually decreases to cancel again at a point G, located in the second third of said pipes. injection 9a-9d. Finally, the amplitude increases again and is maximum at the injectors 10a-10d.

Correlated curves 3Va and 3Vb represent the amplitude of the stationary velocity wave along the injection system. On the curve 3Va, the amplitude of the stationary speed wave begins to be maximum at the pump 5, then decreases rapidly to cancel at a point B in the middle of the inlet pipe 7. The amplitude then increases and returns by a maximum at the input E of the common rail 8. On the second curve 3Vb, the amplitude of the stationary wave velocity is maximum at the output of the common rail 8, decreases along the injection lines 9a-9b, to cancel a first time at a point F, located in the first third of said injection pipes 9a-9d. Then, the amplitude of the stationary speed wave gradually increases to pass again by a maximum at a point G located in the second third of said injection lines 9a-9d. Finally, in a last section, the amplitude of the stationary speed wave decreases to cancel again at the different injectors 10a-10d.

It should be noted that this description is made with particular boundary conditions. For example, it is clear that, on the previous curves, the electro-hydraulic valves of the various injectors 10a-10d are closed.

It should also be noted that the velocity and pressure curves are approximately sinusoidal curves.

Finally, the maximum values of the amplitudes, if they are identical on the same curve, are not identical from one curve to another.

We will now describe how to attenuate the hydraulic waves disturbing the injection system and in particular the stationary hydraulic waves.

In the context of linear modeling of the phenomenon and of a parallel with the sinusoidal electric circuits, it is possible to attenuate these standing waves by placing passive elements at particular points of the injection system. These passive elements make it possible to dissipate the energy of the hydraulic wave. As will be described below, the preferred embodiment of the present invention uses only resistive elements, placed in series, and capacitive elements, also placed in series. Other passive elements, such as inductances could be used. Alternatively, the elements used could be placed either in series or in parallel. The notion of complex impedance groups these different variants into a common concept.

A resistive element is, for example, constituted by a reduced diameter pipe section. A capacitive element is, for example, constituted by a volume of defined dimension connected by a resistive element to a point of the main pipe.

The method of constructing an injection system according to the invention comprises resistive elements placed in series at locations which correspond to bellies of the stationary speed wave and capacitive elements placed in series at locations corresponding to bellies of the standing pressure wave. By following this rule, it is possible to construct an injection system in which the low frequency hydraulic waves are almost fully attenuated.

But, in counterpart, the operating pressure drops along the injection system. It is then necessary to work the pump significantly, so that the operating pressure is high at the injectors. In addition, the fuel supply of the injector may be momentarily insufficient.

According to a first way of avoiding this problem of pressure drop along the injection system, the present invention uses asymmetrical resistive elements, also called fluidic diodes. Such a fluidic diode placed on an insert is represented on the figure 4 .

The figure 4 represents an insert 50. This insert 50 is of generally cylindrical shape around a central axis X. The insert 50 has at each of its axial ends a radial front face 51 and a rear radial face 52. The rear radial face 52 is pierced with a bore 53 of diameter D '. The edge defined by the inner surface 56 of the bore 53 and the rear radial face 52 is chamfered and produces the surface 54. Thus, the insert 50 has a U-shaped cross section X whose wall the bottom 55 is provided with an orifice 27. The orifice 27 has a downstream cylindrical portion 29 of reduced diameter d much smaller than the diameter D '. The orifice 27 has an upstream portion 28 in the form of a funnel, whose opening of larger diameter is oriented towards the upstream of the fuel flow.

The upstream portion 28 has no sharp edges on which the boundary layer of the flow could come off as shown on the Figure 4A . The upstream portion 28 makes it possible to vary the section of the flow slowly and continuously with respect to the characteristics of the flow itself. Thus, the characteristic dimensions of the upstream portion 28 of the orifice 27, such as the radius of the rounding 30, are greater than or equal to a characteristic dimension of the orifice 27, namely d.

Thus, the section of the flow gradually narrowing, the attenuation of the pressure in the direction of the flow is weak. On the other hand, the section of the flow tightening suddenly, the attenuation of the countercurrent pressure is important. Such an asymmetrical orifice has a pressure drop up to 1.5 times higher in the "downstream to upstream" direction than in the "upstream to downstream" direction.

Such inserts may be added at the level of the inlet pipe 7 or at the various injection pipes 9a-9d as a resistive element in order to attenuate the pressure waves, and in particular the stationary pressure waves, without as much hindering the main flow of fuel.

Another way of avoiding the problem of the pressure drop along the injection system consists, firstly, in not overloading the injection system with resistive elements and accepting residual pressure variations. at the level of the injector. It is in fact to find an acceptable compromise between a drop in operating pressure along the injection system and the attenuation of low frequency standing waves. In a second step, the residual pressure variations at the injector are taken into account by means of a programmed device in order to inject into the engine cylinder only the desired amount of fuel. It is this second approach which will now be described in detail in connection with the preferred embodiment of the present invention.

In order to attenuate the hydraulic waves whose frequency corresponds to the first and the second natural frequency of said injection system ( Figure 2 and Figure 3 ), without generating a fall in unacceptable operating pressure along the injection system, the injection system is equipped with a succession of symmetrical and capacitive resistive elements. This succession will now be described in relation to the figure 5 .

The main direction of fuel flow is indicated by an arrow, to give meaning to upstream and downstream.

The inlet pipe 7 is equipped at its upstream end with a capacitive element 73 in series with a resistive element 71, and at its downstream end with a resistive element 72. The injection lines 9a-9d are respectively equipped, at their upstream end, with a resistive element 91a-91d, at a point F located at the second third of their length of a resistive element 92a-92d , and at their downstream end of a capacitive element 93a-93d. Equivalently, the resistive element 72 and the resistive elements 91a-91d may be located in the common rail respectively at the input E and outputs Sa-Sd. Likewise, the capacitive elements 93a-93d may be located in the injectors themselves, as close as possible to the electro-hydraulic valves.

This particular layout is the result of many numerical simulations. These have made it possible to find the best compromise between operating pressure drop and attenuation of pressure waves. The provision of the figure 5 allows a significant attenuation of the pressure waves generated by the pump 5 and pressure waves generated by the other injectors at a given injector. There then remain only attenuated temporal variations of pressure which correspond to the actuation of the same injector at an earlier time of the engine cycle, during a previous injection.

In the context of a multi-injection engine, this prior actuation of the injector may correspond to a first injection, or pilot injection, during which the amount of fuel introduced into the cylinder is low. The current trend is to increase the number of injections per cylinder during a motor cycle. For example, five successive injections can be performed.

Let Q _{1 be} the quantity of fuel introduced into the cylinder at a previous instant, or let Q _{2 be} the quantity of fuel that it is necessary to introduce into the cylinder at the moment considered; and let s be the temporal separation between these two successive injections.

With each new injection, the engine controller evaluates the quantity of fuel Q ₂ desired depending, among other things, the time of the engine cycle where the second injection must take place and the power that the engine must provide.

Then, the engine controller calculates the duration of opening of the electro-hydraulic valve equipping the injector for introducing the amount of fuel Q ₂ taking into account, not the pressure P _rail measured by the pressure sensor 24 at the common rail 8, but by evaluating a corrected pressure P ^th _inj at the injector. The calculation of this corrected or theoretical pressure will make it possible to evaluate the residual pressure variations at the level of the injector.

The corrected pressure P ^th _inj is obtained by adding to the pressure P _rail the sum, over the set of eigenfrequencies f _i considered, of an estimate of the residual pressure variations due to a given pressure wave of eigenfrequency.

The estimation of the residual pressure variations due to a given pressure wave of eigenfrequency is obtained by multiplying a periodic function g by a damping function h. Said periodic function g depends, for example, on the quantities of fuel Q ₁ and Q ₂ , the time separation s between each of the two injections, and thermodynamic parameters such as the _rail pressure P and the fuel temperature T. The periodic function g is typically a sinusoidal function of the time separation s.

Said damping function h is, for example, a function of the quantities of fuel Q ₁ and Q ₂ , of the time separation s between each of the two injections, and of the operating pressure measured by the pressure sensor in the common rail and of the fuel temperature T.

In mathematical form this gives the following relation: $${{\mathrm{P}}^{\mathrm{th}}}_{\mathrm{inj}}\mathrm{=}{\mathrm{P}}_{\mathrm{rail}}\mathrm{+}{\mathrm{\Sigma }}_{\mathrm{i}}{\mathrm{boy\; Wut}}_{\mathrm{fi}}\left({\mathrm{Q}}_{\mathrm{1}},{\mathrm{Q}}_{\mathrm{2}},\mathrm{s},{\mathrm{P}}_{\mathrm{rail}},\mathrm{T}\right)\mathrm{x}{\mathrm{h}}_{\mathrm{fi}}\left({\mathrm{Q}}_{\mathrm{1}},{\mathrm{Q}}_{\mathrm{2}},\mathrm{s},{\mathrm{P}}_{\mathrm{rail}},\mathrm{T}\right)$$

During operation, the motor controller 20 ( figure 1 ) does not necessarily recalculate the value of the periodic function g or the damping function h according to the values taken by the different parameters of the model. The motor controller uses rather maps or an abacus, which, according to the value of the various input parameters, gives the value of the periodic function g or of the damping function h at the output.

Such mapping is obtained from a test vehicle of a vehicle range. This test vehicle undergoes various tests, and the curves corresponding to the periodic functions g and damping h are recorded. Subsequently, during the manufacture of a particular vehicle of said vehicle range, these curves are recorded in memory means forming part of the motor controller 20 to constitute said mapping.

Referring to the figure 6 , the curve 6b represents the quantity of fuel actually injected into the cylinder in the case where the injection system represented on the figure 5 is not equipped with a software system to account for residual pressure fluctuations. The engine controller then taking into account only the pressure P _rail raised at the common rail 8 by the pressure sensor 24. The measurement of the pressure P _rail raised is substantially constant depending on the separation s, the opening time the electro-hydraulic valve controlled by the engine controller to inject a quantity of fuel Q ₂ is also. But since the actual pressure at the injector fluctuates with time, the flow at the injector also fluctuates. The amount actually introduced varies directly following the pressure variations at the injector.

On the other hand, the curve 6c represents the quantity of fuel actually injected into the cylinder in the case where the injection system represented on the figure 5 is equipped with a software system to account for residual pressure fluctuations. In this case, the motor controller calculates a corrected pressure P ^th _inj at the injector. Curve 6a represents this corrected pressure. The motor controller accordingly changes the opening time of the electro-hydraulic valve to compensate for the pressure variation. If the pressure is supposed to increase at the moment of the second injection, the opening time of the valve will be lower. On the contrary, if the pressure is supposed to decrease at the moment of the injection, the duration of opening will be slightly increased. Finally, the amount of fuel actually injected into the cylinder fluctuates less and approaches the desired amount of fuel Q ₂ , which is clearly indicated by curve 6c.

The software system therefore makes it possible to compensate for residual pressure fluctuations.

Although the invention has been described in connection with a particular embodiment, it is obvious that it is not limited thereto and that it comprises all the technical equivalents of the means described and their combinations if they are within the scope of the invention.

Claims (11)

1. Process for construction of a system for injection of high pressure fuel, including a pump (5), a common rail (8) and a plurality of injectors (10a-10d), and an input pipe (7) connecting the pump to the said common rail and a plurality of injection pipes (9a-9d) respectively connecting the said common rail to each of the injectors of the said plurality of injectors, the said injection system including a programmed computer (20) able to measure a pressure in the common rail by means of a pressure sensor (24) placed in the common rail and able to separately actuate each of the said injectors and including attenuation means which are able to attenuate stationary hydraulic waves of pressure or velocity, and which are formed of resistive elements (71-72, 91-92) and/or capacitive elements (73, 93), characterised by the fact that it includes the steps consisting of:

   - determining places which correspond to a trough of one of the stationary velocity waves and placing the said resistive elements (71-72, 91-92) there, and/or

   - determining places which correspond to a trough of one of the stationary pressure waves and placing the said capacitive elements (73, 93) there,
   The said stationary velocity wave and/or the said stationary pressure wave being hydraulic waves the frequency of which corresponds to a first resonance frequency of the said injection system which is the lowest natural frequency.
2. Process as described in claim 1, characterised by the fact that certain of the said resistive elements (71-72, 91-92) are asymmetric resistive elements (50) providing attenuation of pressure in the direction of flow different from the counterflow attenuation.
3. Process as described in one of claims 1 to 2, characterised by the fact that it includes the step consisting of placing certain of the said resistive (71-72) and capacitive (73) elements at the ends of the said input pipe (7).
4. Process as described in claim 3, characterised by the fact that it includes the step consisting of placing a resistive element (71) in series with a capacitive element (73) at the upstream end of the input pipe (7), and a resistive element (72) at the downstream end of the input pipe.
5. Process as described in one of claims 1 to 2, characterised by the fact that it includes the step consisting of placing certain of the said resistive (91a-d) and capacitive (93a-d) elements at the ends of each of the said injection pipes (9a-d).
6. Process as described in claim 5, characterised by the fact that it includes the step consisting of placing a resistive element (91a-d) at the upstream end of each of the injection pipes (9a-d), and a resistive element in series with a capacitive element (93a-d) at the downstream end of each of the injection pipes.
7. Process as described in claim 6, characterised by the fact that it includes the step consisting of placing a resistive element (92a-d) [in the] second third of each of the injection pipes (9a-d) orientated in the flow direction of the fuel from upstream to downstream.
8. Process as described in claim 7, characterised by the fact that it includes the step consisting of placing certain of the said resistive (71-72) and capacitive (73) elements at the ends of the said input pipe (7), of placing a resistive element (71) in series with a capacitive element (73) at the upstream end of the input pipe (7), and placing a resistive element (72) at the downstream end of the input pipe.
9. Process as described in one of claims 1 to 8, characterised by the fact that the said programmed computer (20) calculates a corrected pressure P^th _inj (6a) at the injector and actuates each of the said injectors (10a-10d) as a function of the said corrected pressure in order to inject a quantity of fuel (6c) close to a desired quantity Q₂.
10. Process as described in claim 9, characterised by the fact that the said corrected pressure P^th _inj is a function of a pressure P_rail in the common rail (8), of a temperature T of the fuel, of a quantity of fuel Q₁ injected by the same injector at a preceding injection, of the said quantity of fuel Q₂ desired at a current injection, and of a temporal separation s between the said preceding injection and the said current injection.
11. Process as described in claim 10, characterised by the fact that the said corrected pressure P^th _inj is obtained from the following relationship: $${{\mathrm{P}}^{\mathrm{th}}}_{\mathrm{inj}}\mathrm{=}{\mathrm{P}}_{\mathrm{rail}}\mathrm{+}{\mathrm{\Sigma }}_{\mathrm{i}}{\mathrm{g}}_{\mathrm{fi}}\left({\mathrm{Q}}_{\mathrm{1}},{\mathrm{Q}}_{\mathrm{2}},\mathrm{S},{\mathrm{P}}_{\mathrm{rail}},\mathrm{T}\right)\mathrm{x}{\mathrm{h}}_{\mathrm{fi}}\left({\mathrm{Q}}_{\mathrm{1}},{\mathrm{Q}}_{\mathrm{2}},\mathrm{S},{\mathrm{P}}_{\mathrm{rail}},\mathrm{T}\right)$$

    

    
    in which summation is performed at different natural frequencies f_i, in which g is a periodic function of the separation s, and in which h is an attenuation function of the temporal separation s.

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