EP2329122B1 - Method for starting an internal combustion engine - Google Patents

Description

The invention relates to a method for starting an internal combustion engine for a motor vehicle. In general, the invention aims to reduce pollutant emissions at the source, gasoline engines especially during cold starts.

The quality of the fuel used for the vehicles is very variable, in particular according to the geographical area where the vehicle circulates. A particularly variable physical property of fuel is its ability to vaporize. This capacity is well known in the Anglo-Saxon literature under the acronym PVR for Steam Pressure Raid. This acronym will be used in the following description of the invention. For fuels that vaporize well, we talk about HPVR (High PVR) fuel and for fuels that vaporize badly, we talk about fuel BPVR (Low PVR).

To be able to start correctly, a gasoline engine needs to have a mixture of air and gasoline close to a stoichiometric mixture. This assumes that the amount of fuel in gaseous form is well controlled. However, according to the PVR of the fuel, the amount of fuel in gaseous form participating in the cold start combustion and in the engine actuation varies enormously for the same quantity of fuel injected.

In order to guarantee a sufficient quantity of fuel in gaseous form to achieve good combustions at engine start-up and start-up, the calibrations are performed with a fuel representative of a BPVR type fuel. Then, checks are made to ensure that when using HPVR fuel, the injected amounts are not too large and do not risk to prevent combustion by excess gasoline vapor. The mixture would not be flammable.

The setting is unique regardless of the fuel. As a result, when using an HPVR fuel, the amount of fuel in vapor form is in excess when starting and operating the engine. This excess does not participate in combustion and is found in the exhaust of the engine in the form of unburned hydrocarbons (HC). This has a direct impact on the polluting emissions of the engine. When the vehicle is equipped with a catalyst, it is not cold-initiated and unburned hydrocarbons escape into the atmosphere.

When starting very cold, when the ambient temperature is below -15 ° C, the excess fuel in vapor form also creates black exhaust fumes.

An attempt has been made to solve this problem by adjusting the amount of fuel injected into a cylinder of the engine during start-up phases depending on the fuel capacity to vaporize. The direct measurement of this capacity being difficult to achieve in the vehicle, the fuel capacity to vaporize was estimated based on a rise in engine speed after the first combustion. Indeed, starting with a fuel that vaporizes poorly will cause a rise in slow speed. This rise can be calibrated according to different types of fuels having different capacities to vaporize.

Another method is to measure the time required for the starter to start the engine. This duration can be calibrated according to different types of fuels.

In general, these two methods compare an evolution of the engine speed during a cold start phase compared to a reference engine speed evolution. This improves the adaptation of the amount of fuel injected into the engine during a start-up operation.

The vehicle includes a fuel tank. The filling operations of the tank are carried out with the engine stopped and when starting after filling, the last estimate of the fuel capacity to vaporize is not representative of the fuel actually present in the tank after filling. We can then be in an extreme situation where for example, the last estimate gives an HPVR fuel, the tank was almost empty and a full tank of fuel was made with a fuel BPVR. The fuel present in the tank after filling is very close to a BPVR fuel and we may not start the engine, especially in cold weather using the latest estimate.

The invention aims to overcome this problem by proposing to ignore the latest estimate of the fuel capacity to vaporize when filling the tank.

The document US5542394 discloses a method of starting an internal combustion engine using fuel stored in a tank, having an estimate of an ability to vaporize fuel, and an adjustment of the amount of fuel to be injected into a cylinder of the engine, when starting the engine according to the estimated capacity to vaporize the fuel. When starting after a fuel boost, the estimated value is replaced by the ability to vaporize the estimated fuel before refueling until the calculation of the fuel property is complete.

For this purpose, the subject of the invention is a method for starting an internal combustion engine according to claim 1, in particular for a vehicle, and more particularly for a motor vehicle, the engine using fuel stored in a tank. This method includes an estimate of the amount of fuel present in the tank, an estimate of a fuel vaporization capacity (PVR), and an adjustment of the amount of fuel to be injected into a cylinder of the engine, when the fuel is started. engine according to the estimated capacity to vaporize the fuel and is characterized by the replacement of the estimated value of the ability to vaporize the fuel by a given value for any start immediately following a fuel refill in the tank.

By add-on, normally means a more or less complete filling of the tank. Optionally, a supplement of a very small volume compared to the amount of fuel present in the tank may not be taken into account to reset the value of the fuel capacity to vaporize.

This reset will be done after a certain period of time during which the value will be used the ability to vaporise the estimated fuel before refueling. Thus, it is taken into account that the engine is initially powered by fuel present in the ducts between the tank and the engine, so a fuel corresponding to the previous full.

This delay can be for example defined as a given period of time or from a count of the number of top dead centers or any other value that can be associated with the rotation of the crankshaft of the engine.

The ability to vaporize fuel can vary between two extreme values and advantageously the value given is an average of the two extreme values. These two extreme values may for example be chosen by reference to more or less volatile fuels marketed in a traffic region of the vehicle, or by reference to a range of fuel quality recommended for the engine.

The value given may be a function of an engine temperature. In such a case, a map may be used to assign a given value taking into account this temperature.

If after replacing the estimated value of the ability to vaporize the fuel by the given value, the next start fails, the estimated value can be replaced by a representative value of a low-capacity fuel to vaporize.

The value given is for example fixed during the construction of the vehicle.

Advantageously, as long as the fuel situated between the tank and the engine has not been entirely consumed by the engine, the ability to vaporise the estimated fuel before filling is used for a subsequent start up to filling the tank.

In other words, the estimated value is replaced by the value given after fuel injection into the engine of a given quantity of fuel and the quantity given advantageously corresponds to a quantity of fuel included in the pipes of the vehicle and making it possible to bring the fuel from the tank to the engine cylinder or cylinders.

• la figure 1 illustre sous forme de bloc diagramme un exemple de procédé selon l'invention ;
• la figure 2 représente plus en détail et sous forme d'algorithme, une partie du procédé illustré à l'aide de la figure 1.

The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, a description illustrated by the attached drawing in which:

• the figure 1 illustrates in block diagram form an exemplary method according to the invention;
• the figure 2 represents in more detail and in the form of an algorithm, part of the process illustrated using the figure 1 .

In the block diagram of the figure 1 two reference gradients are defined. These gradients represent the evolution of the engine speed during its cold start. The gradient 10 is given for a fuel having a low vaporization capacity or BPVR fuel and the gradient 11 is given for a fuel having a high capacity to vaporize or HPVR fuel. Each gradient 10 and 11 is expressed in the form of a table whose inputs are a motor temperature and a number of turns made by the engine since the first combustion, for example expressed by counting the passage from one of the engine cylinders to its engine. top dead center, noted "Nb PMH" in the figure. The temperature of the engine is for example that of a cooling fluid of the engine, denoted "water" at the input of the gradients 10 and 11.

The data from each gradient, given 12 for the gradient 10 and given 13 for the gradient 11 form two inputs of a function 14 for defining a gradient 15 of the fuel present in the reservoir according to an estimate 16 of the capacity to vaporize the fuel, estimate made during a previous engine start. The estimate 16 forms a third input of the function 14. The gradient 15 makes it possible to define by means of a function 17 a mass of fuel 18 to be injected into the engine to cause the next explosion in the engine

Moreover, the function 17 makes it possible to ignore the gradient 15 in the case where a tank of the vehicle, tank containing the fuel, has been filled. In this case, information item 19 denoted "Reset" becomes active and function 17 replaces the gradient 15 by a given value 20 which is no longer a function of the estimate 16. The given value 20 can be fixed at the time of construction of the vehicle.

The value given is for example equal to an average of the two data 12 and 13. More specifically, the two data 12 and 13 are added by means of a first operator 21 whose result is divided by two by means of a second operator 22. Thus, in the event of detection of a filling of the fuel tank, the information 19 is activated and the function 17 no longer determines the mass of fuel 18 from the gradient 15 but from the average of the data 12 and 13, in other words, from data representative of a fuel having an average vaporization capacity between an HPVR and BPVR fuel.

The figure 2 shows in more detail and in the form of an algorithm, the activation of the information 19 denoted "Reset" as well as a backup strategy in the event that a start of the engine fails after replacement of the gradient 15 by the given value 20.

At the beginning of the algorithm, the information 19 is inactive. From this state of the information 19, denoted "Reset = 0" to the frame 30, a possible filling of the tank is monitored. As long as a filling is not detected, the information 19 is kept in the idle state. This condition is represented by a test 31 which loops back on the frame 30 as long as the detection of filling is not done. The vehicle is usually equipped with a sensor measuring the fuel level in the tank. This probe can be used to detect the filling of the tank.

The detection occurs for example when an instantaneous variation of the level of the reservoir exceeds a predefined positive threshold. After the detection of the filling information 19 is activated in the frame 32 to replace the gradient 15 by the data 20 by means of the function 17. The activation of the information 19 is noted "Reset = 1" to the frame 32. When the next engine start, shown in frame 33, the determination of the mass of fuel to be injected now uses the data 20 to replace the gradient 15. At start 33, it is possible to estimate a new value of capacity to vaporize fuel present in the tank after filling thereof and return to the inactive state of the information 19 to the frame 30.

The activation of the information 19 is delayed until the fuel situated between the reservoir and the engine has been entirely consumed by the engine. Indeed, the fuel present in the pipes and the fuel pump located between the reservoir and the engine does not mix with the fuel added during filling and the last estimate 16 of the ability to vaporize the fuel still remains valid for the fuel located between the tank and the engine.

This offset between the detection of filling of the reservoir and the activation of the information 19 carried out in the frame 32 is for example made by summing all the fuel volumes injected into the engine after detecting the filling. This summation is represented in frame 34. When the result of this summation reaches a calibrated volume, the activation operation of the information 19 is authorized. The calibrated volume can be defined during the construction of the vehicle and corresponds to the fuel not yet consumed by the engine and not being mixed with fuel added to the tank during the filling operation. A test comparing the result of the summation to the calibrated volume is shown in box 35.

A backup strategy can be provided in the event that a starting of the engine fails after use of the data item 20 for determining the mass of fuel to be injected during this start-up. This backup strategy starts with a monitoring of the success of the start 33. This monitoring can be carried out by a test 36 verifying whether one or more explosions have occurred in a cylinder of the engine in a predefined time starting at the initialization of the start 33.

The predefined duration can be expressed in number of PMH. If the start 33 has been successful, it returns to the inactive state of the information 19 to the frame 30. If on the contrary, the startup failed, the frame 37 is again modified the value of PVR to be taken into account by the function 17 to determine a mass of fuel 18 to be injected. For example, the data 12 representative of a BPVR fuel is applied, which makes it possible to increase the richness of the air-fuel mixture and thus to reduce the risk of absence of starting. After the application of this new value of PVR, it is again a start 38 before returning to the inactive state of the information 19 to the frame 30. During startup 38, it is estimated a new value of ability to vaporize fuel present in the tank after filling thereof. This new estimate will be taken into account by function 17 through function 14.

For example, from an HPVR fuel initially present in the tank, the tank is filled with BPVR fuel. In this case, the start following the tank fill detection and use of the fuel located between the tank and the engine will use an average value of PVR to determine the mass of fuel to be injected and in case of failure, a low value of PVR. . This strategy makes it possible to limit the emission of pollutants and to gradually lower the value of PVR taken into account.

It is possible to perform the start test 36 and change the value of PVR 37 during start 33, if it continues without explosion beyond a predefined time which can be expressed in number of PMH . Thus, the vehicle user can see only one start operation grouping the operations carried out at frames 33, 36, 37 and 38.

Claims (9)

1. A method for starting an internal combustion engine using fuel stored in a tank, comprising an estimation of the quantity of fuel present in the tank, an estimation of a capacity of the fuel to vaporize (PVR), and an adaptation of the quantity of fuel to be injected into a cylinder of the engine, during the starting of the engine, as a function of the estimated capacity of the fuel (16) to vaporize, characterized by the replacement of the estimated value of the capacity of the fuel to vaporize (15) by a given value (20) during a starting following a topping up of fuel in the tank detected following the estimation of the quantity of fuel present in the tank, said given value being used after a certain time period, and in that during this time period the estimated capacity of the fuel to vaporize is used before the topping up with fuel.
2. The method according to Claim 1, characterized in that this time period corresponds to the period of consumption of the fuel present in the ducts between the tank and the engine.
3. The method according to Claim 1, characterized in that this time period corresponds to a certain number of rotations of the crankshaft of the engine.
4. The method according to Claim 1, characterized in that the capacity of the fuel to vaporize can vary between two extreme values (BPVR, HPVR) and in that the given value (20) is an average of the two extreme values (BPVR, HPVR).
5. The method according to one of the preceding claims, characterized in that the given value (20) is a function of a temperature (Teau) of the engine.
6. The method according to one of the preceding claims, characterized in that if, after having replaced the estimated value of the capacity of the fuel to vaporize (15) by the given value (20), the following start-up (33) fails, the estimated value is replaced (37) by a value representative of a fuel with low capacity to vaporize (BPVR).
7. The method according to one of the preceding claims, characterized in that the given value (20) is fixed.
8. The method according to any one of the preceding claims, characterized in that it is only implemented if the topping up with fuel has exceeded a specified volume.
9. An application of the method according to any one of the preceding claims to the starting of a motor vehicle.

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