EP2102476B1 - Fuel supply system for an internal combustion engine and related control method - Google Patents

Description

The invention relates to the field of gasoline or diesel engines, with n cylinders, equipped with an injection system (also called fuel supply system), and in particular the injection systems involving at least one actuator (or regulator) the flow and / or the pressure of the fuel. More specifically, the invention relates to petrol direct injection systems or high pressure diesel, commonly called "common rail" ("Common Rail" injection systems).

Conventionally, if there is a difference between the desired feed rail pressure and the actual measured pressure, the actuator is controlled to adjust the fuel flow through the pump (as part of a flow actuator) so that the measured pressure reaches the desired pressure.

To do this, the actuators are generally controlled using Pulse Width Modulated (PWM) type control signals.

A control signal may be a control current proportional to the electromotive force allowing the actuator to move.

However, the reaction time of the actuator with respect to the control can be particularly long because, for example, microblocking of internal parts due to the misalignment of the internal parts of the actuator, or to the wear of the guide of these pieces.

We know, by the document n ° DE 4,020,654 a method for improving the properties, in particular dynamic properties, of this regulation of the flow (or pressure) of the fuel by modifying the control signal of the actuator. However, this method requires, on the one hand, modifying the calculation unit of the control signal and, on the other hand, adding a device measuring the arrangement of the actuator member to be adjusted, which is particularly expensive and cumbersome.

Another example of the prior art is given by the document EP 1 298 307 . The invention aims to provide a solution to this problem.

An object of the invention is therefore to provide a fuel supply system, the or integrated actuators within the pump are particularly responsive to the control signal for regulating the flow (or pressure) of the fuel.

For this purpose, a first aspect of the invention relates to a fuel supply system for an internal combustion engine, comprising a pump system disposed between an injection rail and a fuel tank, with at least one actuator whose opening is controlled by a pulse modulation type signal, so as to make successive adjustments of the opening of said actuator with a control variable according to a cycle ratio setpoint.

This cycle report setpoint reflects the duration during which the control signal of the opening of the actuator is applied.

The power system also includes an electronic control unit.

According to a general characteristic of this first aspect of the invention, said electronic control unit further comprises auxiliary means capable of increasing the amplitude of the oscillations of said control variable around an average value, if the value of said Cycle report setpoint is included in a given critical area.

In other words, if the cycle ratio setpoint reaches values that are too large or too small, the amplitude of the oscillation of the control quantity of the actuator is increased. Thus, the actuator is no longer maintained in a fixed position, but is continuously moving around an average position, which greatly reduces the reaction time of the actuator.

Indeed, the inventors have observed that the reaction time was particularly long when the control variable was weakly oscillating. This case corresponds to particularly high or particularly low values of opening duty cycle values.

More precisely, as mentioned above, the necessary variation (oscillations) of the electromotive force around its mean value to guarantee the displacement of the actuator is directly proportional to the variations of the control current which is the current flowing through the coil. of the actuator.

avec :

• Fem : la force électro-motrice,
• k : un coefficient de proportionnalité,
• I_PWM : le courant traversant la bobine de l'actuateur.

Indeed, the relation between the electromotive force and the current passing through the coil of the actuator is written: $$\mathrm{fem}={\mathrm{kI}}_{\mathrm{PWM}}$$

with:

• Fem: the electro-motor force,
• k: a coefficient of proportionality,
• I _PWM : the current flowing through the coil of the actuator.

In order for the actuator to move, the oscillations of the electromotive force must be greater than the different friction forces (dry friction or Stribeck effect).

To do this, the current in the coil must have sufficiently large amplitude variations (or oscillations). If this is not the case the electro-motor force fails to "fight" against friction and response time of the actuator increases. This situation is illustrated on the Figures 9 and 10 . In these figures, it can be seen that for a 50% cycle ratio setpoint (curves referenced RCO501 and RCO502), the amplitude of the control current (curves referenced I _PWM 501 and I _PWM 502), which is proportional to the force corresponding electro-motor, is sufficient to cause a continuous displacement of the actuator around an average position. The opposing forces (friction forces) are thus permanently overcome and if the setpoint of the actuator changes, it will quickly reach the value corresponding to the new setpoint.

On the other hand, if the cycle ratio setpoint is higher (90% on the figure 9 , curve referenced RCO90) or lower (10% on the figure 10 , curve referenced RCO10) at a certain threshold the amplitudes of the control currents (respectively referenced I _PWM 90, and I _PWM 10) are no longer sufficient. The actuator is therefore at a standstill because the variations of the electromotive force (corresponding to the control current) around the average value are no longer sufficient to overcome the friction forces.

In this situation, if the actuator displacement instruction changes, it will first have to overcome the friction forces before reaching this new setpoint. The response time of the actuator is therefore considerably increased.

The invention thus makes it possible to prevent this situation from occurring, by causing under certain conditions the increase of the amplitude of the oscillations of the control signal of the actuator, and consequently the increase of the oscillation of the electro force. -motoring.

According to a preferred embodiment, said auxiliary means are capable of increasing the amplitude of the oscillations of said control quantity by decreasing the frequency of the control signal.

In this case, the system may further comprise first storage means capable of storing the value of a lower limit of the frequency of the control signal, determined according to the characteristics of the fuel supply system of the engine.

The system may also comprise second storage means capable of storing the value of an upper limit of the frequency of the control signal, lower than the natural frequency of said actuator.

According to one embodiment, wherein said pump system comprises an auxiliary pump called "low pressure" coupled between the actuator and said fuel tank. Said auxiliary means can then be further adapted to adjust the frequency of the control signal of the actuator so that it is out of the vicinity of an integer value of the discharge frequency of said low pressure auxiliary pump.

When said pump system comprises an auxiliary pump called "high pressure" coupled between the actuator and the injection rail, said auxiliary means may also be able to adjust the frequency of the control signal of the actuator so that it or out of the vicinity of an integer value of the suction frequency of said high pressure auxiliary pump.

Moreover, said auxiliary means may also be able to adjust the frequency of the control signal of the actuator so that it is different from the natural frequency of the actuator relative to its environment (mechanical, hydraulic).

In the case where the pump is coupled to said fuel tank via a return loop comprising a mechanical pressure limiter. Said auxiliary means may then be able to adjust the frequency of the control signal of the actuator so that it is different from the natural frequency of said mechanical pressure limiter relative to its environment (mechanical, hydraulic).

According to another embodiment, the system may also comprise at least one fuel temperature sensor, said auxiliary means then being able to oscillate said quantity also if the value of the fuel temperature is lower than a predetermined critical value.

For example, at least one of the actuators of the pump is a flow and / or pressure actuator.

According to a second aspect of the invention, there is provided a method of controlling a fuel supply system for an internal combustion engine comprising a pump system disposed between an injection rail and a fuel tank, said method comprising controlling the opening of at least one actuator of the pump system, by means of a pulse modulation type control variable, so as to perform successive adjustments of the opening of said actuator by function of a cycle report setpoint.

According to a general characteristic of this second aspect of the invention, the amplitude of the oscillations around an average value of said control quantity is increased, if the value of said cycle ratio setpoint is included in a given critical zone.

• la figure 1 illustre schématiquement un moteur Diesel à combustion interne ;
• la figure 2 illustre schématiquement le piston de l'actuateur du système d'alimentation en carburant associé au moteur représenté sur la figure 1 ;
• la figure 3 illustre l'évolution du courant de commande du piston selon le rapport cyclique d'ouverture ;
• la figure 4a illustre un exemple de courbe caractéristique simplifiée d'un actuateur de débit pour un régime de pompe donné ;
• la figure 4b illustre un exemple de courbe caractéristique inverse simplifiée d'un actuateur de débit pour un régime de pompe donné ;
• la figure 5 illustre l'élaboration de la commande du piston de l'actuateur selon l'invention ;
• la figure 6 illustre plus précisément le système de pompe inséré au sein du système d'alimentation en carburant du moteur Diesel ;
• la figure 7 illustre plus en détail les éléments haute pression de la pompe représentée sur la figure 6 ;
• la figure 8 illustre un mode de mise en oeuvre du procédé selon l'invention ; et
• les figures 9 et 10 illustrent les variations du courant de commande de l'actuateur selon l'art antérieur.

Other advantages and characteristics of the invention will appear on examining the detailed description of an embodiment and a non-limiting embodiment, and the appended drawings, in which:

• the figure 1 schematically illustrates an internal combustion diesel engine;
• the figure 2 schematically illustrates the piston of the actuator of the fuel supply system associated with the engine shown on the figure 1 ;
• the figure 3 illustrates the evolution of the control current of the piston according to the opening duty cycle;
• the figure 4a illustrates an example of a simplified characteristic curve of a flow actuator for a given pump speed;
• the figure 4b illustrates an example of a simplified inverse characteristic curve of a flow actuator for a given pump speed;
• the figure 5 illustrates the development of the control of the piston of the actuator according to the invention;
• the figure 6 illustrates more precisely the pump system inserted into the fuel system of the diesel engine;
• the figure 7 illustrates in more detail the high pressure elements of the pump shown on the figure 6 ;
• the figure 8 illustrates an embodiment of the method according to the invention; and
• the Figures 9 and 10 illustrate the variations of the control current of the actuator according to the prior art.

On the figure 1 is very schematically represented an internal combustion diesel engine referenced 1a, supplied with fuel via a feed system 1b (of course, the invention can also be applied to the gasoline engine). In this example, the engine includes four cylinders. The fuel supply system 1b of this engine comprises four injectors referenced 2, each connected by a high pressure hose 3 to the accumulator 4 called "the rail".

The fuel supply system 1b also comprises a pump 5, which draws fuel from the tank 6 of the vehicle via a low pressure circuit 7. The function of the pump 5 is to compress the fuel taken from the tank 6 of the vehicle and push it back into the rail 4.

As will be seen in more detail below, the pump 5 is composed of a low pressure part (transfer pump) and a high pressure part (high pressure pump). Note that the pump 5 is also connected to the tank 6 via a return circuit 8. This return circuit 8 serves to regulate the leakage rate of the high pressure part, as well as the lubrication and cooling rate.

A flow actuator 9 (or flow valve) is integrated with the low pressure side pump 5. This flow actuator 9 makes it possible to adjust the amount of fuel that will be sent to the rail 4, to which the pump 5 is connected via a connection 10.

In addition, the feed system 1b can also be equipped at the output of the pump 5 on the side of the connection 10, or directly on the rail 4, a pressure actuator also called discharge actuator. For simplification purposes, this pressure actuator is not shown.

Finally, the engine 1a and its feed system 1b are controlled by an electronic control unit or computer 11. This computer 11 comprises conventional components, such as microprocessors, EEPROM type hard memories and RAM type buffers.

Moreover, it receives input information via a connection 13. This information comes from different sensors placed on the engine 1a and its ancillary systems, such as the injection system, the air supply system, etc. .

The computer 11 then processes the input data 12 to define or calculate control levels 14 outputted from the computer 11 via a connection 15. The control levels 14 are sent to the various actuators that participate in the control of the ancillary systems and therefore of the motor. More particularly, these control levels are transmitted via a connection 16 to the injectors 2, and a connection 17 to the actuator 9.

More specifically, the information 12 transmitted to the computer 11, such as, for example, the engine coolant temperature, the engine speed, the engine oil temperature, the air temperature in the engine, the pressure turbocharger air, the position of the accelerator pedal, etc., are processed via functions or mappings stored in an EEPROM type memory, for example.

These maps make it possible to define the value of the desired PCONS pressure in the rail 4. The control levels 14 are then calculated as a function of this pressure value PCONS.

Conventionally, the value of the PCONS pressure setpoint is compared with the value of the effectively measured pressure PMES in the rail 4. This value PMES is delivered via a connection 18 to the computer 11, in parallel with the information 12.

According to the pressure difference ΔP identified (with ΔP = PCONS-PMES), the controller 11 using for example a software corrector of the PID (Proportional Integral Derivative) type, adjusts the control signal of the flow actuator 9 so that the measured pressure PMES reaches the pressure set PCONS. If the difference ΔP is positive, the controller 11 acts to increase the flow (in the case of a flow actuator). Conversely, if ΔP is negative, the controller acts to decrease the flow.

Generally, actuator control signals are Pulse Width Modulated (PWM) type. The control signal is characterized by its nominal voltage U _PWM and its frequency F _PWM . The percentage of the opening duty cycle (OCR) is between 0 and 100%. This translates the duration during which the voltage U _PWM is applied over the period T _PWM (T _PWM is equal to 1 / F _PWM ). The intensity of the average current I _PWM created by the control signal of the PWM type is then proportional to the percentage of the opening duty cycle RCO.

In a simplified manner, as already mentioned above, it can be said that the average current I _PWM created by the control signal generates an electromagnetic force Fem as represented on FIG. figure 2 .

This electromagnetic force Fem is proportional to the percentage of the opening duty ratio RCO, which allows the displacement of an internal piston 20 (or needle) of the flow actuator 9. The position of the piston 20 determines the passage section ( and therefore the flow rate) of the fuel entering the pump via inlets 21 and 22.

The fuel leaves through an opening referenced 23.

A friction force Ff opposes the electromagnetic force Fem. This friction force Ff results in example of a misalignment of parts or wear of the guidance of parts.

As shown on the upper part of the figure 3 , the percentage of the RCO opening duty cycle applied to the amplitude modulation control signal of the actuator makes it possible to establish a more or less significant average current I _PWM .

The upper part of the figure 3 corresponds to an opening duty cycle of 30% and the lower part to an opening duty cycle of 90%.

At this average current I _PWM corresponds to the average electromagnetic force Fem, which makes it possible to control the displacement and the position of the piston of the actuator, thus fixing the desired passage section for the flow of the fuel (more or less significant flow).

For example, a simplified characteristic curve of a flow actuator is shown in FIG. figure 4a . This characteristic corresponds to a given pump speed, knowing that the pump is rotated by the motor with a drive ratio R. Thus, the higher the flow demand (in liters / minute), the higher the duty cycle. RCO opening (for a fixed PWM amplitude modulation frequency) to be applied will be important.

There are so-called inverse characteristics, such as the one represented on the figure 4b , where unlike the one shown on the figure 4a the lower the flow demand, the greater the duty cycle RCO to apply.

So, as illustrated on the figure 3 when the RCO is low (in this example 30%), the average current I _PWM corresponding to the U _PWM voltage for a given RCO, oscillates around an average position.

As explained above, in the general case, if the opening duty cycle RCO is particularly high or particularly low, the average current stabilizes and the flow actuator will have a rather fixed position. This considerably increases the reaction time of the actuator during a change of operating point of the engine (by action of the driver on the accelerator pedal, for example) because of the difficulty in overcoming the friction force Ff.

Therefore, when the opening duty cycle RCO reaches a high value (in this example 90%) or low (in this example 10%), the invention makes it possible to make the oscillating current with a sufficient amplitude of oscillation.

A particularly advantageous solution for a PWM type signal is to increase the _PWM period _PWM control signal (as illustrated on the lower part of the figure 3 for RCO = 90%), which consequently makes the average current I _PWM oscillating again.

The electromagnetic force Fem generated is then also oscillating. Thus, the position of the piston of the actuator is no longer maintained at a fixed position, but is set in motion around an average position. The generation of these micromovements of the piston of the actuator by variation or adaptation of the frequency of the PWM type control signal in the flow zone or zones deemed critical (corresponding to a high or low opening ratio RCO), allows to greatly reduce the reaction time because of the increased facility to overcome the frictional force Ff.

The invention makes it possible to reduce the setpoint overruns of the pressure within the rail 4.

One embodiment of the actuator control method, implemented within the control unit 11, is represented on the figure 5 .

First, the control unit 11 stores a first mapping 30, called open loop mapping, for determining the positioning of the flow actuator according to a DC fuel flow setpoint and the engine speed. of the vehicle Nm respectively delivered at the input of the map 30 via connections 31 and 32. The mapping 30 makes it possible to develop a nominal current setpoint CCN for the control of the flow actuator.

Furthermore, another mapping 33 is able to develop the pressure set point of the rail PCONS as a function of the fuel flow setpoint DC delivered via a connection 34, and the engine speed Nm delivered via a connection 35 as well as the parameters 12 delivered. via the connection 13.

The instruction PCONS is delivered to a comparator 36 which also receives via the connection 18 the pressure PMES measured at the level of the rail 4.

The difference .DELTA.P between the two pressure values PCONS and PMES is delivered, via a connection 36a, to a corrector 37 (for example a corrector of the PID type) which generates a corrective current setpoint ICOR.

This instruction ICOR is delivered to an adder 38 via a connection 39. This adder 38 also receives on another input via a connection 40 the rated nominal current CCN.

The output of the adder 38 is connected via a connection 41 to auxiliary means 42 whose role is to determine the frequency F _PWM of the control signal of the actuator and the percentage of the opening duty cycle. RCO, applied to this actuator.

For this purpose, the auxiliary means 42 also receives the engine speed Nm via a connection 43, the fuel temperature TC via a connection 44, and the value of the fuel flow DC via a connection 45. The role of these variables TC and DC are explained in more detail below.

Auxiliary means 42 derives from all these variables the frequency-modulated control signal F _PWM , and the opening duty cycle RCO. This control signal is transmitted to the actuator 9 via the connection 15.

However, when the frequency of the control signal F _PWM is changed, in particular for a high or low percentage of BCR, the choice of the frequency must take into account the specific characteristics of the components of the system, to avoid creating a pressure instability in the rail 4.

Indeed, contrary to what was described in document no. DE 1 033 04665 , the inventors have observed that the presence of oscillations at the level of the pressure of the rail 4 is not explained solely because of the impact of the frequency of the flow of the fuel leaving the rail, but also because of the impact the frequency of the flow entering the rail, which directly influences the actuator 9, by the frequency F _PWM of its control signal.

To understand this phenomenon, we refer to the figure 6 which more precisely illustrates the pump system 5.

The latter comprises a booster pump 50 or a low-pressure pump and a high-pressure pump 51. The flow actuator 9 is disposed between these two pumps 50 and 51, to which it is respectively connected via connections 52 and 53.

Optionally, a pressure actuator (not shown for simplification purposes) could be installed at the outlet of the high-pressure pump on the connection 10.

The pressure between the flow actuator 9 and the high pressure pump 51 is called P2. The pressure between the booster pump 50 and the flow actuator 9 is called P1.

A mechanical pressure limiter referenced 54 is connected between the connection 8 and the node common to the booster pump 50 and the flow actuator 9.

The limiter 54 is connected to this common node via a connection 55. Note Q1 the flow delivered by the booster pump, Q2 the flow through the pressure limiter 54, Q3 the flow through the flow actuator 9 and Q4 the flow rate admitted by the high pressure pump 51.

For a given pump regime, the volume admitted by each element of the pump system 5 is directly determined by the flow rate Q4 admitted by the high-pressure pump 51 (considered throughout the duration of admission). This flow Q4 is also directly related to the effective supply pressure P2, both from a static and dynamic point of view (mean value and oscillation frequency). Different interactions exist between the pressure P2 and the flow Q4. In order to identify them, we refer to the figure 7 which illustrates in more detail the high-pressure pump 51.

The high-pressure pump 51 receives as input the setpoint DPS corresponding to the displacement of the piston of the flow actuator 9. This DPS instruction has a direct impact on the flow Q3 passing through the flow actuator 9 and thus on the effective supply pressure P2. An intake valve 60 is connected to a pumping element 61 via a connection 62.

The output of the pumping element 61 is connected to another intake valve 63 via a connection 64.

The other intake valve 63 is connected to the rail 4 via the connection 10.

Different interactions exist between the effective supply pressure P2 and the admitted flow rate Q4 by the high-pressure pumping element 51.

When the oscillation frequency of the feed pressure P2 and the pumping frequency (given by the multiplication between the number of elements contained in the high-pressure pump system 51 and the speed of this same high-pressure pump system, pressure 51) are equal (or when they are integer values of each other), the flow rates, and therefore the volume admitted at each stroke of the pump system 5, are stable or repeatable. The average value of the rail pressure (at the level of the elementary pressure discharge cycle) is thus stable. The volume admitted to each shot, then depends on the phasing between the variations of the pressure and the pumping cycle. Indeed, the openings / closures of the valves occur at different times in the oscillation cycle of the effective supply pressure P2.

When the oscillation frequency of the supply pressure P2 and the pumping frequency are very close (or when they are almost integer values of each other), the flow rate, and therefore the volume admitted to each shot Q4, has a low frequency variation. The value of this low harmonic frequency is directly related to the ratio between the two frequencies: we find this low frequency variation in the value of the pressure of the rail 4.

When the oscillation frequency of the supply pressure P2 and the pumping frequency are not integer values of each other, the values taken by the admitted flow rate Q4 at each stroke are fairly dispersed. However, the average value is stable over a much lower cycle number than in the previous case.

In view of the foregoing, it appears that the oscillation frequency of the pressure P2 is particularly related to the oscillation frequency of the flow Q4, itself directly related to the number of elements that comprises the high-pressure pump 51 and at the speed of the pump system 5.

In addition, the oscillation frequencies of the pressure P2 are related to the oscillation frequency of the flow rate Q3 and the flowrate Q1.

The frequency of oscillation of the flow rate Q3 depends, of course, on the oscillations of the pressure difference across the flow actuator (P2-P1), but also on the oscillations at the passage section of the flow actuator, which are in turn directly related to the frequency of the pulse modulation type control signal.

Finally, the frequency of the oscillations of the flow Q1 is directly related to the number of elements of the low-pressure pump 50 and the speed of the pump system.

• aux harmoniques des oscillations liées au refoulement effectué par la pompe basse-pression 50 (liées au nombre d'éléments de refoulement que comporte la pompe basse pression et au régime du système de pompe 5) ;
• aux harmoniques des oscillations du pompage effectué par la pompe haute-pression 51 (liées au nombre d'éléments que comporte la pompe haute pression et du régime de pompage) ;
• à la fréquence F_PWM du signal de commande de type à modulation d'impulsion de l'actuateur 9.

Therefore, it follows from the aforementioned observations of the inventors, that the oscillations of the pressure of the rail 4 are due inter alia:

• the harmonics of the oscillations related to the discharge carried out by the low-pressure pump 50 (related to the number of discharge elements that comprises the low-pressure pump and the speed of the pump system 5);
• to the harmonics of the oscillations of the pumping performed by the high-pressure pump 51 (related to the number of elements that comprises the high-pressure pump and the pumping rate);
• at the frequency F _PWM of the pulse modulation type control signal of the actuator 9.

Greater stability is achieved when all these frequencies are integer values of each other.

Nevertheless, the value of the flow rate Q4 admitted by the high-pressure pump 51 also depends on the timing of the oscillations, that is to say the angular relationship existing between the periods of discharge between at least two outputs of the high-pressure pump. 51.

• la fréquence F_PWM n'est pas trop élevée, c'est-à-dire inférieure à la fréquence propre de l'actuateur de débit, pour garantir le mouvement de ce dernier,
• la fréquence F_PWM ne doit pas être trop lente (la limite inférieure étant déterminée d'après des caractéristiques du système d'alimentation en carburant du moteur), pour qu'il n'y ait pas de répercussion au niveau de la pression du rail ;
• la fréquence F_PWM ne se situe pas au voisinage d'une valeur entière de la fréquence d'aspiration de la pompe haute-pression (en tenant compte du régime de la pompe) ;
• la fréquence F_PWM ne doit pas se trouver au voisinage d'une valeur entière de la fréquence de refoulement de la pompe basse pression (en tenant compte du régime de la pompe).

The choice of the frequency F _PWM of the pulse modulation type control signal according to the speed of the pump system 5 must therefore fulfill the following conditions:

• the frequency F _PWM is not too high, that is to say lower than the natural frequency of the flow actuator, to guarantee the movement of the latter,
• the F _PWM frequency shall not be too slow (the lower limit being determined by the characteristics of the engine fuel system), so that there is no impact on the rail pressure ;
• the frequency F _PWM is not in the vicinity of an integer value of the suction frequency of the high-pressure pump (taking into account the speed of the pump);
• the F _PWM frequency must not be in the vicinity of an integral value of the discharge frequency of the low-pressure pump (taking into account the pump speed).

• de ne pas être égale aux fréquences propres de l'actuateur de débit (ni au voisinage), de façon à maîtriser l'amplitude des oscillations de débit ;
• de ne pas être égale aux fréquences propres du limitateur de pression 54 (ni au voisinage), de façon à maîtriser l'amplitude des oscillations de la pression en amont de l'actuateur de débit 9.

In addition, for reasons of stability of the components and therefore the behavior of the pump system 5, it is added that the frequency F of the _PWM pulse modulated control signal based on the pump speed must also ensure:

• not to be equal to the natural frequencies of the flow actuator (or in the vicinity), so as to control the amplitude of the flow oscillations;
• not to be equal to the natural frequencies of the pressure limiter 54 (or in the vicinity), so as to control the amplitude of the oscillations of the pressure upstream of the flow actuator 9.

The invention makes it possible to determine a frequency F _PWM of the pulse modulation type control signal, achieving the best compromise on all of these criteria. One mode of implementation is detailed below.

On the other hand, the inventors have observed that it is highly advantageous to also take into account the fuel temperature conditions for varying the frequency F of the _PWM of the actuator control signal, in particular in areas deemed critical flow rate, when the opening cycle ratio RCO is particularly high or particularly low.

Indeed, it is when the temperature of the fuel is particularly low that the reaction time of the actuator is the longest and therefore the most harmful. Thus, in order to minimize the wear that is generated by the generation of micromovements of the actuator pistons, the invention makes it possible to modify the frequency of the control signal when the fuel temperature is particularly low.

For this purpose, the fuel temperature information TC is supplied to the auxiliary means 42 (see FIG. figure 1 ) by means of a sensor placed either at the inlet of the pump 5 or at the return circuit 8 between the vehicle tank 6 and the pump 5 (for the sake of simplification, these sensors are not shown).

In order to implement what has been stated above, two maps F1 and F2 are stored in the computer 11. Each map is associated with a function that makes it possible to determine the frequency of the control signal F _PWM to be applied in engine speed function Nm.

The function associated with the mapping F1 gives the predetermined frequencies F _PWM (such as F _PWM = F1 (Nm)), taking into account the specific characteristics of the components of the injection system in order to limit pressure oscillations in the rail, according to the different conditions set out above.

• la consigne du débit carburant DC est au-dessus d'un seuil critique calibrable DCcr2 (par exemple 90%) correspondant à des zones de fort débit dans le cas d'actuateurs à caractéristique « normale » (correspondant à des zones de faible débit dans le cas d'actuateurs à caractéristique dite « inverse »),
• la consigne du débit carburant DC est au-dessous d'un seuil critique calibrable DCcr1 (par exemple 10%) correspondant à des zones de faible débit dans le cas d'actuateurs à caractéristique « normale » (correspondant à des zones de fort débit dans le cas d'actuateurs à caractéristique dite « inverse »), et
• lorsque la température du carburant TC est inférieure à un seuil critique calibrable TCcr (dans le cas où le système d'alimentation en carburant du moteur comprend des capteurs de température du carburant.

The function associated with the mapping F2 gives the predetermined frequencies F _PWM (such as F _PWM = F2 (Nm)) lower than those provided by the function associated with the mapping F1 and used when:

• the setpoint of the fuel flow rate DC is above a calibratable critical threshold DCcr2 (for example 90%) corresponding to zones of high flow rate in the case of actuators with "normal" characteristic (corresponding to zones of low flow in the case of actuators with "inverse" characteristic),
• the setpoint of the fuel flow rate DC is below a calibratable critical threshold DCcr1 (for example 10%) corresponding low-flow zones in the case of actuators with "normal" characteristics (corresponding to zones of high flow in the case of actuators with "inverse" characteristics), and
• when the fuel temperature TC is below a calibratable critical threshold TCcr (in the case where the fuel supply system of the engine comprises fuel temperature sensors.

The lower frequencies obtained from the mapping F2 will then allow the generation of micromovements of the piston of the actuator around a mean position. These micromovements play in favor of a strong reduction of overshoots of the rail pressure setpoint in the areas considered critical. To do this, the organization chart of the figure 8 can be implemented within the auxiliary means 42.

At vehicle start 100, the flow of the DC fuel is compared with the critical values DCcr1 and DCcr2 and the fuel temperature TC is compared with the critical fuel temperature TCcr, step 101.

If the fuel flow rate is greater than the associated critical value DCcr2 or lower than the associated critical value DCcr1, and if the fuel temperature is lower than the associated critical value and the fuel temperature is lower than the associated critical value, the frequency F of the _PWM of the actuator control signal is developed from the mapping F2, step 102.

Otherwise, the frequency F _PWM is developed from the mapping F1, step 103.

Once the elaboration of the frequency F _{PWM is} carried out, if the engine is stopped, step 104, the process is terminated, step 105, otherwise, the steps 101 to 104 are repeated.

Of course, the invention is not limited to the embodiments and embodiments presented above.

For example, the control of the actuator by varying the frequency F _PWM of the control signal also applies to the pressure actuators that can be integrated into the fuel supply system. In this case, the mimic diagram of the regulation loop represented on the figure 5 is adapted to the case of a pressure actuator: for example, the maps 30 and 33 are no longer dependent on the engine speed Nm and the fuel flow setpoint DC.

Claims (12)

1. Fuel supply system for an internal combustion engine comprising a pump system (5) arranged between an injection rail (4) and a fuel tank (6), with at least one actuator (9) of which the opening is caused by a control quantity (I_PWM) determined by a cycle ratio setpoint (RCO) of a control signal (U_PWM) of the pulse modulation type emitted by an electronic control unit (11) so as to carry out successive adjustments of the opening of the said actuator, characterized in that the said electronic control unit comprises auxiliary means (42) capable of increasing the amplitude of oscillations of the said control quantity (I_PWM) about a mean value if the value of the said cycle ratio setpoint (RCO) is within a predefined value range.
2. System according to Claim 1, in which the said auxiliary means are configured to increase the amplitude of the oscillations of the said control quantity (I_PWM) by reducing the frequency (F_PWM) of the control signal (U_PWM) while maintaining the same cycle ratio setpoint (RCO) therefor.
3. System according to Claims 1 and 2, in which the said auxiliary means are configured to increase the amplitude of the oscillations of the said control quantity (I_PWM) if the cycle ratio setpoint is below a first predefined threshold.
4. System according to one of Claims 1 to 3, in which the said auxiliary means are configured to increase the amplitude of the oscillations of the said control quantity (I_PWM) if the cycle ratio setpoint is above a second predefined threshold.
5. System according to one of Claims 1 to 4, additionally comprising at least one fuel temperature sensor, and in which the said auxiliary means are additionally configured to increase the amplitude of the oscillations of the said control quantity (I_PWM) if the fuel temperature value is below a predetermined critical value.
6. System according to one of Claims 1 to 5, in which the auxiliary means comprise two maps (F1, F2) each connecting the rotational frequencies of the engine, and signal frequency values (F_PWM), the signal frequency values (F_PWM) of one of the maps being systematically lower than the signal frequency values of the other map.
7. System according to one of Claims 1 to 6, where the said pump system comprises an auxiliary pump (50), termed low-pressure pump, coupled between the actuator (9) and the said fuel tank (6), the said auxiliary means (42) being additionally able to adjust the frequency of the control signal of the actuator such that it is outside the vicinity of an integer value of the delivery frequency of the said low-pressure auxiliary pump.
8. System according to one of Claims 1 to 7, where the said pump system comprises an auxiliary pump (51), termed high-pressure pump, coupled between the actuator (9) and the injection rail (4), the said auxiliary means (42) being additionally able to adjust the frequency of the control signal of the actuator (9) such that it is outside the vicinity of an integer value of the suction frequency of the said high-pressure auxiliary pump.
9. System according to one of Claims 1 to 8, in which the said auxiliary means (42) are additionally able to adjust the frequency of the control signal of the actuator such that it is different from the natural frequency of the actuator (9) with respect to its environment.
10. System according to one of Claims 1 to 9, where the pump is coupled to the said fuel tank via a return loop comprising a mechanical pressure limiter (54), and in which the said auxiliary means (42) are additionally able to adjust the frequency of the control signal of the actuator such that it is different from the natural frequency of the said mechanical pressure limiter (54) with respect to its environment.
11. System according to one of Claims 2 to 9, in which at least one of the actuators of the pump is a flow or pressure actuator.
12. Method for controlling a fuel supply system for an internal combustion engine comprising a pump system arranged between an injection rail and a fuel tank, in which a control quantity (I_PWM) determined by a cycle rati setpoint (RCO) of a control signal (U_PWM) of the pulse modulation type is used to carry out successive adjustments of the opening of an actuator of the pump system, characterized in that the amplitude of the oscillations of the said control quantity (I_PWM) is increased about a mean value if the value of the said cycle ratio setpoint (RCO) is within a predefined value range.

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