EP3445961B1 - Method for optimising a heat engine restart time by controlling the pressure in an injection rail - Google Patents

Description

The invention relates to a method for optimizing a restart time of a heat engine by controlling the pressure in a rail for injecting fuel into the engine when the engine is stopped. The heat engine, advantageously a gasoline engine, is part of the powertrain of a motor vehicle, the vehicle being able to be a hybrid vehicle comprising for its propulsion in addition to the heat engine a motor other than heat, for example an electric motor.

On a conventional petrol engine, the thermal engine stopping phase is always carried out from an idling speed, this can result from a stress due to a turbocharger when this is present. If a heat engine has to be stopped while it is at a speed higher than the idle speed, it must go through an idle phase before it can be stopped.

In known manner, a heat engine comprises one or more cylinders, an injector being associated with the cylinder (s) for supplying fuel to the cylinder or cylinders. The fuel passing through an engine fuel supply system comprising a fuel tank and a high pressure pump is sent to each injector by a pressurized injection rail up to 200 bar for a petrol fuel engine. . The pressure in the injection rail during the stopping phase of the engine is that of the idling speed, located around 50 bars.

During a shutdown phase, two cases must be taken into consideration. In the first case, there is a significant difference between the temperature of the engine and the temperature of the fuel in the injection rail. The pressure in the injection rail will then gradually increase after the engine stop phase.

Indeed, the engine hotter than the rail will heat the injection rail while gradually cooling during the shutdown time of the engine. Once the temperature and the pressure in the injection rail have stabilized, the pressure in the injection rail will gradually drop depending on the natural leaks from the high pressure pump and the decrease in temperature of the injection rail following substantially that of the engine. This configuration is called heat stroke.

In the second case, the temperatures of the heat engine and of the fuel, in particular in the injection rail, are identical or close to one another. There is therefore no possibility of the injection rail heating up by the heat engine and the pressure in the injection rail increasing at the start of the heat engine shutdown period. The pressure in the injection rail drops progressively as a function of natural leaks from the high-pressure pump and the temperature of the heat engine, but faster than in the first case and without having gone through a maximum. This configuration therefore does not present a heat stroke.

When restarting the engine, performance in restart time must be observed. One of the predominant levers for obtaining this time performance is obtaining the minimum injection pressure to inject. This can for example be between 35 and 55 bars.

Between stopping the engine and restarting the next engine, the optimal solution is therefore to manage to stay in the injection rail for as long as possible above the minimum restart injection pressure to inject fuel into the combustion engine, so that fuel can be injected very quickly during the next start.

This phase, where the engine is stopped, can last up to 1.5 hours in the context of a hybrid vehicle. It is likely that after such a stop, the pressure in the injection rail can drop below the minimum restart injection pressure. Specific cases will now be detailed with regard to the figures 1 to 4 .

The Figures 1 and 2 illustrate a respective configuration according to the first case detailed above with a large temperature difference ΔT + between the temperatures of the injection rail and of the heat engine, this respectively for a hot engine MotC and a cold engine MotF. The Figures 1 and 2 illustrate optimal configurations because they make it possible to take advantage of the hotstroke phenomenon to maximize the stop time spent with a pressure in the rail above the minimum pressure in the rail to inject during a restart.

The figures 3 and 4 illustrate a respective configuration according to the second case detailed above with a small temperature difference ΔT- between the temperatures of the injection rail and the heat engine, this respectively for a hot engine MotC and a cold engine MotF.

For the figures 1 to 4 , the engine speed Rm is symbolized by the curve with dots. The engine speed Rm is just before the engine stops at the engine idling speed Rr and is canceled quickly after the engine stops. The curve with squares symbolizes the pressure in the injection rail or Prail measured in bars, the speed and pressure curves being a function of time t. The figures 1 and 3 show the case of a relatively hot MotC heat engine while the figures 2 and 4 show the case of a relatively cold MotF heat engine.

To the Figures 1 and 2 , the pressure in the injection rail starting from an initial injection rail pressure at standstill around 50 bars passes in 18 minutes by a maximum of 220 bars before decreasing in time for, at the figure 1 , respectively reach a pressure of 35 bars in 92 minutes, a total time of 110 minutes or, at the figure 2 , respectively reach a pressure of 55 bars in 27 minutes, i.e. a total time of 45 minutes at the figure 2 .

To the figures 3 and 4 , the pressure in the injection rail cannot go through a maximum due to the small temperature difference ΔT- between the temperatures of the injection rail and the heat engine. Starting from an initial injection rail pressure at standstill around 50 bars, the pressure in the injection rail decreases in 7 minutes to reach a pressure of 35 bars then becomes zero in 18 minutes at the figure 3 , the engine being a hot MotC engine in this figure.

To the figure 4 which is like at the figure 2 the most unfavorable configuration with a cold MotF engine, starting from an initial injection rail pressure at standstill around 50 bars, the pressure in the injection rail becomes zero in 8 minutes. As a result, in the cases of figures 3 and 4 , that the time spent above the minimum rail pressure to inject is very low, at most 7 minutes, which is linked to the fact that the stop is done at idle speed Rr, with a pressure value associated weak rail of about 50 bars.

For hybrid vehicles, the heat engine shutdown phases can last up to 1 hour 30 minutes, with restart time performance which is degraded by the fact that each restart requires the injection system to increase in pressure in order to obtain the minimum injection pressure to inject fuel into the engine.

The document FR-A-2 994 714 describes a process for managing the preparation for (re) starting a petrol petrol engine for a hybrid vehicle with sending a request for preparation of the heat engine to a preparation manager driving at least one device for preparing the heat engine to reduce the overall (re) start time of the heat engine. The manager receives several parameters representative of the operation of the engine and determines a recommended waiting time before training and a necessary training time of the thermal engine for its (re) start.

This document does not, however, anticipate a drop in pressure in the injection rail with this pressure becoming lower than the minimum injection pressure and preventing restarting of the heat engine. It therefore does not provide any preventive solution against a restart made impossible under these pressure conditions, but only palliative solutions implemented to promote the restart.

We still know the document EP2336531A1 corresponding to the preamble of claim 1.

Consequently, the problem underlying the invention is to anticipate when the heat engine stops the pressure drop in the injection rail associated with the heat engine so that the pressure in the injection rail is , for the duration of the shutdown, as long as possible maintained above a minimum injection pressure to ensure a restart of the engine.

To achieve this objective, there is provided according to the invention a method for optimizing a restart time of a thermal engine of a motor vehicle, the thermal engine being associated with a rail for injecting pressurized fuel, the pressure in the injection rail which must be above a threshold that can be calibrated as the minimum injection authorization pressure during restart of the heat engine following a stop time of the heat engine during which the pressure in the injection rail decreases from a so-called initial pressure setpoint at the start of the combustion engine shutdown, and a forced increase in the pressure in the prevailing injection rail is effected when the engine stops until '' to obtain the initial pressure setpoint, controlling the initial pressure setpoint maximizing an interval of the stopping time during which the pressure in the injection rail is above the minimum auto pressure injection during restart
characterized in that the initial pressure setpoint is determined on the basis of an estimate of a future increase in the pressure in the injection rail experienced during the phase when the engine is stopped, from the difference between temperatures of the injection rail and of the heat engine, this estimate of the increase in pressure in the injection rail comprising a predetermined conversion of the difference between the temperatures of the injection rail and of the heat engine into an increase in pressure in the injection rail and the addition of a correction corresponding to a pressure difference between a target of maximum pressure in the injection rail and a maximum pressure recorded in the injection rail for the difference between the temperatures of the injection rail and of the heat engine.

The function of controlling the pressure in the injection rail when the engine of a powertrain is stopped makes it possible to optimally manage the pressure in the rail as a function of the difference between the temperature of the fuel in the rail which can be taken as the temperature of the rail and the temperature of the heat engine which can be taken as the temperature of the coolant. This allows the pressure in the injection rail to remain as long as possible, during a prolonged shutdown of the internal combustion engine, above the minimum injection authorization pressure during restart.

The solution proposed by the present invention makes it possible to avoid having a high pressure pump in the fuel supply system of the heat engine more efficient than that commonly used, which provides a very strong economic advantage. Indeed, the disadvantage of the commonly used pump was that it could not quickly increase the pressure during a restart. This is no longer necessary by application of the method according to the present invention, the pressure in the injection rail being maintained for as long as possible during a stop of the vehicle at a pressure level allowing the restart of the heat engine. The benefits in restart time are therefore improved.

Advantageously, this increase in pressure being a function of the difference between the temperatures of the injection rail and of the heat engine, the forced increase in pressure is greater the smaller the difference between the temperatures of the injection rail and of the heat engine. . In fact, when the difference between the temperatures of the injection rail and of the heat engine is large, the pressure in the injection rail can rise due to the heating of the rail by the warmer engine with high thermal inertia which begins to cool. This is not the case for a small difference between the temperatures of the injection rail and the heat engine. In this case, the pressure in the injection rail can only go down as well as the temperature of the injection rail during such a stop.

Advantageously, this pressure difference is obtained by learning during the stopping of the heat engine.

Advantageously, learning begins at a request to stop the heat engine, for a defined learning time.

Advantageously, the learning time can be calibrated as a function of the difference in temperatures of the injection rail and of the heat engine).

Advantageously, as soon as the learning time has elapsed, if the maximum rail pressure value recorded is greater than the value contained in a pressure learning variable then the old value of the learning variable is replaced by the new value learned.

Advantageously, updating the learning of the pressure difference for a given temperature difference is authorized when the learning number reaches a learning threshold.

Advantageously, when the pressure in the injection rail is limited in use to a maximum pressure in operation of the injection rail, the initial pressure setpoint of the injection rail is less than or equal to the maximum pressure in operation of the rail d 'injection.

Advantageously, the temperature of the injection rail is the temperature of the fuel leaving a high pressure pump located upstream of the injection rail in a fuel supply system to the heat engine and the temperature of the heat engine is the temperature of a cooling fluid circulating in a cooling system of the heat engine.

The invention relates to a motor vehicle comprising a powertrain comprising a heat engine with at least one cylinder, an injector being associated with the cylinder for supplying fuel to said at least one cylinder, the fuel being sent to the injector by a rail. injection system under pressure in operation, characterized in that when the engine stops, an initial pressure setpoint in the injection rail is determined as a function of a difference between temperatures of the injection rail and of the engine, and that a forced increase in the pressure in the prevailing injection rail is carried out when the engine is stopped until the initial pressure setpoint is obtained, the initial pressure setpoint being controlled by a computer on board the motor vehicle for implementing a method according to any of the variants described above.

Such a computer which may be an engine control computer is already present on board the vehicle. It suffices simply to add a software part specifically dedicated to controlling the pressure in the rail when the vehicle is stopped, which is an inexpensive solution and does not require additional mechanical means. This software part can be integrated without difficulty into the strategy for controlling the pressure in the injection rail during the operation of the thermal engine already present in the engine control.

Advantageously, the vehicle is a hybrid vehicle comprising the powertrain and an engine other than a combustion engine for propelling the vehicle, the combustion engine of the powertrain being frequently stopped and restarted, the vehicle being propelled by the engine other than combustion engine. '' a stop of the engine.

• les figures 1 et 2 illustrent de courbes de pression dans un rail d'injection de carburant pour moteur thermique et de régime moteur lors d'un arrêt du moteur, le moteur étant relativement chaud à la figure 1 et froid à la figure 2, une forte différence de température existant entre le rail d'injection et le moteur, la pression n'étant pas pilotée conformément à un procédé selon la présente invention à ces figures,
• les figures 3 et 4 illustrent de courbes de pression dans un rail d'injection de carburant pour moteur thermique et de régime moteur lors d'un arrêt du moteur, le moteur étant relativement chaud à la figure 3 et froid à la figure 4, une faible différence de température existant entre le rail d'injection et le moteur, la pression n'étant pas pilotée conformément à un procédé selon la présente invention à ces figures,
• la figure 5 illustre deux courbes respectivement de pression dans un rail d'injection de carburant pour moteur thermique et de régime moteur lors d'un arrêt du moteur, la pression étant pilotée conformément à un procédé selon la présente invention, l'échelle de temps étant montrée agrandie par rapport aux figures 1 à 4 en ne montrant que la durée de temps suivant immédiatement une demande d'arrêt du moteur,
• la figure 6 est un logigramme montrant les diverses étapes d'un procédé d'optimisation d'un temps de redémarrage d'un moteur thermique de véhicule automobile par pilotage de la pression dans le rail d'injection pendant l'arrêt du moteur selon un mode de réalisation de la présente invention,
• les figures 7 et 8 illustrent de courbes de pression dans un rail d'injection de carburant pour moteur thermique et de régime moteur lors d'un arrêt du moteur, le moteur étant relativement chaud à la figure 7 et froid à la figure 8, une faible différence de température existant entre le rail d'injection et le moteur, la pression dans le rail d'injection étant pilotée conformément à un procédé selon la présente invention à ces figures.

Other characteristics, aims and advantages of the present invention will appear on reading the detailed description which follows and with regard to the appended drawings given by way of nonlimiting examples and in which:

• the Figures 1 and 2 illustrate pressure curves in a fuel injection rail for a combustion engine and engine speed when the engine is stopped, the engine being relatively hot at figure 1 and cold to the figure 2 , a large difference in temperature existing between the injection rail and the engine, the pressure not being controlled in accordance with a process according to the present invention in these figures,
• the figures 3 and 4 illustrate pressure curves in a fuel injection rail for a combustion engine and engine speed when the engine is stopped, the engine being relatively hot at figure 3 and cold to the figure 4 , a small temperature difference existing between the injection rail and the engine, the pressure not being controlled in accordance with a method according to the present invention in these figures,
• the figure 5 illustrates two curves respectively of pressure in a fuel injection rail for a thermal engine and of engine speed during an engine stop, the pressure being controlled according to a method according to the present invention, the time scale being shown enlarged relative to figures 1 to 4 showing only the time immediately following a request to stop the engine,
• the figure 6 is a flow diagram showing the various steps of a method for optimizing a restart time of a thermal engine of a motor vehicle by controlling the pressure in the injection rail during engine shutdown according to an embodiment of the present invention,
• the Figures 7 and 8 illustrate pressure curves in a fuel injection rail for a combustion engine and engine speed when the engine is stopped, the engine being relatively hot at figure 7 and cold to the figure 8 , a small temperature difference between the injection rail and the engine, the pressure in the injection rail being controlled according to a method according to the present invention in these figures.

It should be borne in mind that the figures are given by way of examples and are not limitative of the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily at the scale of practical applications.

In what follows, reference is made to all the figures taken in combination. When reference is made to one or more specific figures, these figures are to be taken in combination with the other figures for the recognition of the designated numerical references.

The figures 1 to 4 have already been described in the introductory part of this application.

Referring to Figures 5 to 8 , the present invention relates to a method for optimizing a restart time of a heat engine of a motor vehicle, the heat engine being associated with a rail for injecting fuel under pressure. In this process, it is sought to allow the restart of the heat engine in a very short time, the pressure of the injector rail not having to drop too low, which shortens the restart time.

In fact, the injection rail is to be maintained for the longest possible stop time at least at a minimum restart injection pressure to restart the engine. This minimum injection pressure is predetermined and known for each type of engine and corresponds to the pressure in the injection rail necessary to ensure a fuel supply to the heat engine sufficient for its restart.

During the duration of the stopping of the engine, the pressure in the injection rail can however pass at the beginning of this stopping by a maximum of pressure as shown in the Figures 1 and 2 when the temperature difference ΔT + between the rail injection and the engine is high. In this case, the engine heats the injection rail and increases the pressure in the injection rail directly after stopping due to its thermal inertia while starting to decrease in temperature. Then the rail and motor temperatures decrease simultaneously.

According to the invention, the initial pressure setpoint Cons Prail ini is controlled as a function of a difference ΔT between temperatures of the Trail injection rail and of the heat engine Tmot. Control of the Cons Prail ini initial pressure setpoint maximizes an interval of the stop time during which the pressure in the injection rail is above the minimum restart injection pressure.

With particular reference to Figures 7 and 8 which show the most unfavorable cases of pressure reduction with a temperature difference ΔT- between the injection rail and the relatively small heat engine and which are to be compared with figures 3 and 4 which show cases according to the state of the art, there is an increase in pressure in the injection rail starting in the vicinity of the engine stopping instant.

This can be done a little before the engine stops, just a little after or just when the engine stops, the first solution being shown to Figures 7 and 8 . The pressure rise in the injection rail thus obtained is much faster than the pressure rise by thermal inertia of the engine previously called heat stroke, while this heat stroke may not be present for a temperature difference ΔT- between the injection rail and the relatively weak heat engine.

With particular reference to Figures 5 and 6 , after a request to stop the DAmot thermal engine, the engine speed symbolized by the curve with dots and which was at idle speed Rr decreases rapidly while there is a forced increase in the pressure of the Prail rail symbolized by the curve with squares. The pressure in the Prail injection rail can then go from 50 bars to 200 bars relatively quickly, the latter pressure being taken as the initial pressure setpoint at the start of the engine shutdown. The duration scale shown in figure 5 is enlarged compared to the duration scales previously shown in figures 1 to 4 .

With particular reference to Figures 5 to 8 , the initial pressure of the injection rail must rise to the target pressure Prail M of the injection rail, the target pressure Prail M being less than or equal to the maximum operating pressure of the injection rail. As an idea, without being limiting, the maximum operating pressure of the injection rail can be around 200 to 250 bars for a petrol engine.

It is therefore possible to effect a forced increase in the pressure in the prevailing injection rail when the engine is stopped until the initial pressure set point Cons Prail ini is obtained. This pressure increase is a function of the temperatures of the Trail injection rail and of the Tmot thermal engine, the forced increase in pressure being greater the smaller the difference ΔT between the temperatures of the Trail injection rail and of the Tmot thermal engine.

Indeed, when the difference ΔT between the temperatures of the Trail injection rail and of the Tmot heat engine is small, if no forced increase in pressure is exerted on the injection rail, the pressure as well as the temperature in the injection rail can only descend more or less gradually during a prolonged shutdown of the engine.

Several possibilities of forced increase of the pressure in the injection rail can be implemented as an alternative or in addition. For example, when the engine is stopped, it is possible to exert an overpressure on the fuel supplying the injection rail. This can be done by a high pressure pump located upstream of the injection rail in the engine fuel supply system.

As an alternative or in addition, this can be done by additional heating of the injection rail increasing its temperature and consequently its pressure. The latter solution has a thermal inertia which will not cause a very rapid increase in pressure and is not preferred taken as an alternative alone to a pressure increase.

The figure 6 illustrates a flow diagram showing the successive stages of the method for optimizing a restart time of a thermal engine of a motor vehicle according to the invention.

During the request to stop the heat engine, an estimator 7 of pressure in the injection rail in the heat engine stop phase determines an increase in the pressure ΔPrail ini in the injection rail suffered during the phase where the engine is stopped. This determination is carried out with, on the one hand, the temperature of the Trail injection rail and, on the other hand, the temperature of the heat engine Tmot, a difference ΔT between these two temperatures Trail and Tmot being established.

The temperature of the Trail injection rail can be measured or estimated. This temperature of the Trail injection rail can be the temperature of the fuel leaving a high pressure pump located directly upstream of the injection rail in a fuel supply system to the engine. The temperature of the Tmot heat engine can be measured or estimated. This temperature of the heat engine Tmot can be the temperature of a cooling fluid circulating in a cooling system of the heat engine.

The difference ΔT between these two temperatures Trail and Tmot is transmitted to a pre-established map 1 which can be associated with a correction map 2. At least map 1 makes it possible to convert the difference ΔT between temperatures of the Trail injection rail and of the heat engine Tmot in a pressure difference ΔPrail ini in the injection rail at the start of the engine shutdown. Correction mapping 2, if used, makes it possible to optimize the estimation of the pressure difference ΔPrail ini in the injection rail thanks to a learning system.

Depending on the level of increase of the rail pressure in the stopped heat engine phase predicted by the estimator 7, therefore to come, the pressure in the injection rail of the injection system is controlled, via a mapping 3, to an initial Cons Prail ini pressure setpoint to maximize the time spent above the minimum injection pressure to inject fuel during a new start.

This pressure setpoint may be the maximum target pressure value Prail M in the case where the increase in the rail pressure predicted in the stopped heat engine phase is zero, the maximum operating value possibly being from 220 to 250 bars or more. This is advantageous in the case where the difference ΔT between temperatures of the Trail injection rail and of the Tmot heat engine is small, that is to say in the case where the pressure in the rail will not increase at the start of stopping the heat engine by possible heating of the injection rail by the heat engine.

In the case where the increase in the predicted rail pressure in the stopped heat engine phase is not zero, this pressure setpoint is less than the maximum target pressure value Prail M to take into account the increase in the predicted rail pressure and thus do not exceed this maximum operating pressure of the injection rail.

The application of the initial pressure reference Cons Prail ini and the implementation of the method according to the invention can be carried out following a request to stop the DAmot thermal engine. The method according to the invention can be implemented by a computer, advantageously an engine control of the heat engine already in charge of the voucher. operation of the fuel injection system in normal operation of the engine.

Usually, when the engine is running, a pressure setpoint for the injection rail is established, referred to here as the pressure setpoint when off. Cons Prail HA of the injection rail so as to be differentiated from the pressure setpoint when stopped. of the heat engine as proposed by the method according to the invention. On the basis of this Cons Prail HA non-stop pressure setpoint, it is known to control the pressure of the injection rail during the operation of the heat engine by a pressure setpoint in the Cons Prail injection rail.

In the context of the present invention, when the thermal engine is stopped, the initial pressure setpoint Cons Prail ini is used to control the pressure of the injection rail during the stopping of the thermal engine. A switch, advantageously virtual, in the computer can be provided to selectively, on the one hand, suspend the pressure setpoint when Cons Consil HA stops while the engine is stopped by replacing it with the initial pressure setpoint Cons Prail ini and , on the other hand, suspend the application of the method according to the present invention and the application of the initial pressure setpoint Cons Prail ini during the operation of the heat engine from the start or restart of the heat engine.

In a preferred embodiment of the present invention, a learning system 9 may be provided. Following a learning authorization, the operation of the learning system 9, as may be envisaged in the context of the present invention, is described below:

A learning block 4 is defined. In this learning block 4, it is defined x pressure variables A1 to Ax, x being the dimension of the mapping 1, the variables A1 to Ax each being associated with a difference of temperature ΔT1 to ΔTx. A block 6 for updating the correction cartography 2 is defined. In this block 6, x pressure correction variables B1 to Bx are defined. A counter block 5 is defined. In this counter block 5, there are defined x variables C1 to Cx for counting the learning number.

The variables B1 to Bx correspond to the x points of the correction map 2 for each temperature difference ΔT. We define n the index, between 1 and x, corresponding to the temperature difference ΔT observed at the start of learning. The maximum pressure target Prail M in the injection rail during the stopped phase of the heat engine is introduced at the input of learning block 4. It is used to calculate the pressure correction at the output of this learning block 4. This output is equal to the pressure difference between the value taken by An and this target of maximum pressure Prail M. This target of maximum pressure in the rail Prail M can be calibrated and can be different depending on the type of internal combustion engine.

The learning is carried out following a request to stop the DAmot thermal engine and for a learning time that can be calibrated, in particular as a function of the difference ΔT of the temperatures of the Trail injection rail and of the Tmot thermal engine. At the input of learning unit 4, there is the maximum pressure target Prail M and the measured pressure Prail mes of the injection rail from the stopping of the heat engine during the learning time.

In parallel, as soon as the learning time has elapsed, the counter Cn between C1 and Cx and belonging to the block referenced 5 is incremented. If the value of this counter Cn is greater than the calibratable learning threshold then the variable Bn is updated such that Bn = An - Prail M, this update AMaj being done in block 6. A zero setting of R counter Cn and the variable An are then carried out.

A learning phase can start at the request to stop the heat engine and ends when the learning time defined for a temperature difference ΔT between the temperatures of the injection rail and the heat engine has elapsed, the difference of temperature ΔT being read at the time of the stop request. Throughout the learning phase, the measured rail pressure Prail mes is observed and the maximum of this pressure is noted.

In the preferred mode of carrying out the learning, as soon as the learning time has elapsed, if the maximum rail pressure value noted is greater than the value contained in the pressure learning variable An then the old value of An is replaced by the new learned value.

The reference 5 symbolizes the counter of the number of learning per mapping point, the mapping points being the variables C1 to Cx of the counter. At the output of the learning number counter, an update authorization is carried out on a learning threshold AMaj, this learning threshold can be calibrated. The update is referenced 6 and relates to the variables of correction vectors B1 to Bx. A counter R is then reset to zero.

The learning time can be different depending on the temperature difference ΔT. The learning time and the learning threshold must be large enough for the correction made by the pressure estimator 7 in the injection rail to be robust, but they must also allow a significant learning frequency.

In the event that a restart takes place during learning, i.e. the learning time has not been reached, learning stops, counter 5 is not incremented and the variable An is not updated.

Referring also to the figure 6 for the reference Cons Prail ini, the Figures 7 and 8 are to be compared to figures 3 and 4 to observe the gains obtained by implementing the method according to the present invention. Maintaining the pressure at the Cons Prail ini setpoint in the injection rail at the start of the engine shutdown for a hot MotC engine is illustrated in figure 7 and reaches 92 minutes, a gain of 92 - 7 = 85 minutes compared to the figure 3 symbolizing a duration obtained under the same conditions according to a process of the state of the art.

Maintaining the pressure at the Cons Prail ini setpoint in the injection rail at the start of the thermal engine stop for a MotF cold engine is illustrated in figure 8 and reached 27 minutes, a gain of 27 - 0 = 27 minutes compared to the figure 4 symbolizing a duration obtained under the same conditions according to a process of the state of the art.

The invention also relates to a motor vehicle comprising a powertrain comprising a heat engine, the heat engine advantageously but not limited to a gasoline engine. In known manner, the heat engine comprises at least one cylinder, an injector being associated with the cylinder for supplying fuel to said at least one cylinder, the fuel being sent to the injector by an injection rail pressurized during operation. .

When the engine stops, an initial Cons Prail ini pressure setpoint in the injection rail is controlled as a function of a difference ΔT between temperatures of the Trail injection rail and of the heat engine Tmot, the pressure setpoint initial Cons Prail ini being controlled by a computer on board the motor vehicle for the implementation of such a method for optimizing a restart time.

The computer comprises means for receiving the temperatures of the Trail injection rail and of the Tmot heat engine, means for establishing a difference ΔT in temperature and means for calculating the initial pressure setpoint Cons Prail ini to be applied to the pressure in the injection rail at the start of the engine shutdown. The computer can also include a learning system as previously described.

A preferred application of the invention, but not limiting, is for a hybrid vehicle comprising the previously described powertrain and an engine other than a combustion engine for propelling the vehicle, advantageously an electric motor. The engine of the powertrain of such a hybrid vehicle is frequently stopped and restarted, the vehicle being propelled by the engine other than the engine when the engine is stopped.

Such hybrid vehicles develop more and more over the years due to environmental constraints and the resolution of the problem of an optimized restart with a reduced restart time is crucial for their development.

The invention is in no way limited to the embodiments described and illustrated which have been given only by way of examples.

Claims (11)

1. A method for optimising a motor vehicle heat engine restart time, the heat engine being associated with a pressurised fuel injection rail, the pressure in the injection rail necessarily being above a threshold that can be calibrated as minimum authorisation pressure of the injection during the restart of the heat engine following a stoppage period of the heat engine during which the pressure in the injection rail reduces from a pressure setpoint designated as initial (Cons Prail ini) at the beginning of the stoppage of the heat engine, and a forced increase is carried out of the pressure prevailing in the injection rail at the stoppage of the engine until the initial pressure setpoint (Cons Prail ini) is obtained, the control of the initial pressure setpoint (Cons Prail ini) maximising an interval of the stoppage period during which the pressure in the injection rail is above the minimum authorisation pressure of the injection during the restart,
   characterized in that the initial pressure setpoint (Cons Prail ini) is determined as a function of an estimation of a future increase of the pressure (ΔPrail ini) in the injection rail which is undergone during the phase in which the engine is stopped, from the difference (ΔT) between temperatures of the injection rail (Trail) and of the heat engine (Tmot), this estimation of the increase of the pressure (ΔPrail ini) in the injection rail including a predetermined conversion of the difference (ΔT) between the temperatures of the injection rail (Trail) and of the heat engine (Tmot) into a pressure increase (ΔPrail ini) in the injection rail and the addition of a correction corresponding to a pressure difference (Bn) between a maximum pressure target (Prail M) in the injection rail and a maximum detected pressure (An) in the injection rail for the difference (ΔT) between the temperatures of the injection rail (Trail) and of the heat engine (Tmot).
2. The method according to Claim 1 in which, this pressure increase being a function of the difference (ΔT) between the temperatures of the injection rail (Trail) and of the heat engine (Tmot), the forced pressure increase is greater, the smaller the difference (ΔT) is between the temperatures of the injection rail (Trail) and of the heat engine (Tmot).
3. The method according to Claim 1 or 2, characterized in that this pressure difference (Bn) is obtained by a learning phase during the stoppage of the heat engine.
4. The method according to Claim 3, in which the learning starts at a stoppage request (DAmot) of the heat engine, for a defined learning period.
5. The method according to Claim 4, in which the learning period is able to be calibrated as a function of the difference (ΔT) of the temperatures of the injection rail (Tail) and of the heat engine (Tmot).
6. The method according to Claim 4 or Claim 5 in which, once the learning period has elapsed, if the maximum detected rail pressure value is greater than the value contained in a learning variable of the pressure, then the former value of the learning variable is replaced by the new learnt value.
7. The method according to any one of Claims 3 to 6, characterized in that the updating of the learning of the pressure difference (Bn) for a given temperature difference (ΔT) is authorised when the learning number reaches a learning threshold (AMaj).
8. The method according to any one of the preceding claims in which, when the pressure in the injection rail is limited in use to a maximum functioning pressure (Prail M) of the injection rail, the initial pressure setpoint (Cons Prail ini) of the injection rail is less than or equal to the maximum functioning pressure (Prail M) of the injection rail.
9. The method according to any one of the preceding claims, in which the temperature of the injection rail (Trail) is the temperature of the fuel at the outlet of a high pressure pump situated upstream of the injection rail in a fuel supply system to the heat engine, and the temperature of the heat engine (Tmot) is the temperature of a cooling fluid circulating in a cooling system of the heat engine.
10. A motor vehicle comprising a powertrain including a heat engine with at least one cylinder, an injector being associated with the cylinder for the supply with fuel of said at least one cylinder, the fuel being delivered to the injector by an injection rail which is pressurised in operation, characterized in that at the stoppage of the heat engine, an initial pressure setpoint (Cons Prail ini) in the injection rail is determined as a function of a difference (ΔT) between temperatures of the injection rail (Trail) and of the heat engine (Tmot), and a forced increase is carried out of the pressure in the injection rail prevailing at the stoppage of the eng until the initial pressure setpoint (Cons Prail ini) is obtained, the initial pressure setpoint (Cons Prail ini) being controlled by an onboard computer in the motor vehicle for an implementing of a method according to any one of the preceding claims.
11. The vehicle according to Claim 10, which is a hybrid vehicle including the powertrain and a motor other than a heat engine for a propulsion of the vehicle, the heat engine of the powertrain being frequently stopped and restarted, the propulsion of the vehicle being carried out by the motor other than a heat engine during a stoppage of the heat engine.

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