FR2817589A1 - Fuel injection control method for motor vehicle internal combustion engine starting involves steadily increasing the amount of gaseous fuel injected during the starting phase - Google Patents

Abstract

The fuel injection control method for motor vehicle internal combustion engine starting has a quantity (Q) of gas fuel injected during a combustion cycle in the starting phase determined by an injection quantity control algorithm. The quantity injected increases steadily during the starting phase from a predetermined minimum quantity.

Description

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Injection method for an internal combustion engine using a gaseous fuel
The present invention relates to a method for adjusting the quantity of gaseous fuel injected for internal combustion engines operating on gaseous fuel, in particular during the start-up phase, as well as a system and a computer program for carrying out the method. .

 Such an engine converts chemical energy into mechanical energy. Fuel is stored in a vehicle tank, and oxygen is present in atmospheric air in the environment.

 The ratio of the amount of fuel to the amount of air is called the richness of the mixture. A richness for which the proportion of fuel relative to the proportion of air is greater or lower than the stoichiometric richness of the combustion reactants in the chemical sense is called, respectively, over-richness or under-richness.

 The richness influences the efficiency of the engine, or more precisely, the degree of efficiency of the conversion of the energy contained in the fuel into motive force. The richness also influences the composition of the gas mixture expelled from the engine, in particular the proportion of gas generated during combustion which are likely to harm the environment.

 Fuel has traditionally been supplied in liquid form.

In indirect injection engines, the fuel is vaporized in the carburetor, then mixed with air and leads to the combustion chambers of the engine. In direct injection engines, the fuel is aspirated by a high pressure metering pump and is injected through a nozzle into combustion chambers, where the fuel arrives in the form of small droplets.

 Recently, gas fueled engines have been developed. Compared to liquid fuel engines, gaseous fuel engines are more

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 effective. In addition, they have the advantage of producing environmentally friendly combustion gases.

 Natural gas can be used as a gaseous fuel. Natural gas is, from its various sources, a gaseous compound whose main contents may vary. This variation in the composition induces, among other things, a variation in the quantity of mass energy (PCI). This makes it difficult to develop engines operating on gaseous fuel, in particular wealth management. In addition, to comply with pollution control standards, and to take into account that the behavior of engines operating on gaseous fuel differs from the behavior of engines operating on liquid fuel, the operation of an engine operating on gaseous fuel must be fully controlled.

 Generally, engines running on liquid fuel tolerate a certain degree of excess. The liquid fuel injected into the combustion chambers tends to be stored partly on the walls, especially at low temperatures, during a starting phase of the engine, in a cold state, where vaporization is difficult. As soon as the temperature in the chamber increases, the part of the fuel which is stored on the walls begins to be released and contributes to the quantity of fuel present in the combustion chambers and available for combustion. The quantity of fuel present in the combustion chambers and available for combustion is therefore variable, even if the quantity injected is constant over time.

 The mixture of fuel and air present in the combustion chambers has an increasing richness with the destocking (and time). Thus, the correct flammability conditions characterized by the richness of the mixture as a function of the temperature, will be encountered during the start-up phase despite the dispersions of the engine and of the fuel composition. Liquid fuel metering systems take into account the effect of fuel storage and destocking.

 The indirect gas fuel injection systems come from the injection systems used for liquid fuel.

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 In gas fueled engines, there is no fuel storage on the walls of the combustion chambers.

In addition, the richness must be set at a lower level than in engines running on liquid fuel.

 Methods for adjusting the amount of liquid fuel indirectly injected into engines operating on liquid fuel are ill-suited for use in engines operating on gaseous fuel. For example, taking into account valid for engines running on liquid fuel, the evolution of the proportion of the quantity of fuel resulting from the destocking of the walls, especially during the start-up phase, when the engine has not yet reached its running temperature, can, in engines operating on gaseous fuel, lead to a situation where the quantity of gaseous fuel injected is too low or too high and where, in extreme situations, the conditions of flammability are not met .

 According to one aspect, the invention aims to provide a method of injecting gaseous fuel during the engine start-up phase which avoids the disadvantages of applying the methods of injecting fluid fuel for engines operating on gaseous fuel. According to another aspect, the invention aims to provide a process for injecting gaseous fuel during the start-up phase which is capable of managing the variations in fuels resulting from the variable composition of natural gas and the dispersions of the operation and of the state of the engines and its drifts, and which, moreover, avoids the overbought. According to yet another aspect, the method provides for memorizing the enrichment necessary to start the engine, on the one hand for the purpose of ensuring enrichment for a normal operating phase after the engine starts allowing a correct transition and d on the other hand to anticipate in part the enrichment necessary for the next departures, while taking into account variations in the composition of natural gas.

 Generally, the process for injecting gaseous fuel into an internal combustion engine having as phases

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 operation, a start-up phase and a normal operation phase after the start-up phase, in which a quantity of gaseous fuel is injected during an engine combustion cycle in the engine start-up phase determined by a control algorithm. quantity injected (Qi), so that during the start-up phase the quantity injected (Qi) is monotonous increasing in time from a predetermined minimum quantity (Qmin).

 The quantity injected (Qi) increases to a final value corresponding to the instant of the actual start of the engine (Qdem) or to a predetermined ceiling (Qmax).

 Advantageously, the effective departure of the motor is detected according to the speed of rotation.

 The algorithm for controlling the quantity injected during the start-up phase is able to cooperate with a second control algorithm operating during the normal function phase after the start-up phase. The second algorithm could include a self-adaptive learning mode or a non-learning mode.

 Preferably, if the composition of the gaseous fuel has changed since the last start, said minimum quantity takes a basic value. More preferably, said base value is determined as a function of the engine temperature.

 Preferably, if the composition of the gaseous fuel has not changed since the last start and if the second control algorithm is not in the learning mode, said minimum quantity is determined as a function of the final value corresponding to l 'instant of the last effective start, by subtracting a correction as a function of the engine temperature. More precise, this correction is made by subtracting from the final value of the quantity injected corresponding to the instant of the last effective start of the engine, a corrective value determined as a function of the temperature of the engine.

 The engine temperature is advantageously measured according to the temperature of the engine coolant.

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 Preferably, if the composition of the gaseous fuel has not changed since the last effective start of the engine and if the second control algorithm is in the learning mode, said minimum quantity is determined as a function of the final value corresponding to l 'instant of the last effective start, taking into account a correction determined during the normal operating phases prior to the current start phase.

 Advantageously, after filling a tank, it is considered that the composition of the gaseous fuel has changed.

 Preferably, the increase in the quantity injected (Qi) during the start-up phase follows a function of the form Qi = Qmin (l + DEMGAZ) / a which depends on a parameter DEMGAZ increasing monotonically over time between a minimum value (DEMGAZmin) and a maximum value (DEMGAZmax).

 The increase in the DEMGAZ variable can be determined by an increment (INCREGAZ) and a time interval (DURGAZ).

Preferably, the increment and / or the time interval are determined as a function of the temperature of the motor. Preferably, the increase in the DEMGAZ variable is linear over time.

 The invention also relates to a system for injecting gaseous fuel into an internal combustion engine comprising a metering means for dosing an amount of gaseous fuel injected during a combustion cycle of the engine, a means for detecting an effective departure of the engine, a means for detecting changes in the fuel composition, means for measuring the operation of the engine and a means capable of executing an algorithm for controlling the quantity injected, characterized in that, during an engine start-up phase , the system increases the quantity injected monotonically increasing over time from a predetermined minimum quantity (Qmin).

 Furthermore, the invention relates to a computer program comprising program code means for implementing the steps of the process for injecting gaseous fuel into an internal combustion engine mentioned above.

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 Other advantages and characteristics of the invention will appear on examining the detailed description of modes of implementation and embodiment of the invention, in no way limiting, and the appended drawings in which: - Figure 1 schematically illustrates a curve representing the increase over time of the quantity injected, - Figure 2 illustrates the increase in the quantity injected incrementally, and - Figure 3 is a flowchart of steps for implementing an algorithm of management of the quantity of fuel injected into the engine.

 As illustrated in FIG. 1, a phase of starting the engine begins at a time t1, when the engine is started by the starter, and ends at a time t2, when the engine performs its effective starting and a transition to a phase normal operation. Before the moment tl, the quantity injected Qi is zero. When the engine is launched, the quantity injected Qi begins, from a minimum quantity Qmin, to increase monotonically over time. The increase in the quantity injected continues up to a value Qdem corresponding to the actual starting t2 of the engine. Then, the engine continues to run in a normal operating phase.

 The instant of actual start of the engine can be recognized by an effective start detection means, for example a sensor which measures the number of revolutions, a sensor which measures the torque of the motor and / or a sensor which measures the quantity of air drawn in during a combustion cycle, said sensor being linked to an evaluation circuit capable of recognizing sudden changes in the quantity measured by the sensor.

 For safety, if the engine does not start, for whatever reason, the increase in the quantity injected is limited by a predetermined maximum value Qmax.

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During the start-up phase, a multiplicative term is applied to increase the quantity injected Qi from the value Qmin according to the following equation:
Qi = Qi (DEMGAZ) = Qmin * (l + DEMGAZ) / a (1)
The quantity injected Qi is managed monotonically by a variable DEMGAZ. A variable a makes it possible to preserve the homogeneity of the calculation of Qi by reducing or proportionally increasing the quantity injected Qi.

As illustrated in FIG. 2, to increase the quantity injected Qi from the value Qmin until reaching the value Qdem corresponding to the time of the actual start of the engine or reaching the maximum safety value Qmax, the variable DEMGAZ performs an increase from a minimum value DEMGAZmin corresponding to the minimum quantity Qmin until reaching a value MEMOGAZ corresponding to the actual starting of the engine or a maximum value DEMGAZmax corresponding to the safety value Qmax, respectively. The DEMGAZmax value will be managed according to the engine temperature. So,
Qmin = Qi (DEMGAZmin),
Qdem = Qi (MEMOGAZ), and (2)
Qmax = Qi (DEMGAZmax)
The Qdem value and / or the MEMOGAZ value is preferably memorized. This memorization makes it possible to correct the quantity of fuel injected after the start-up phase, in the normal operating phase, to satisfy the need of the engine.

It can also be used to anticipate the additional quantity at the start of the next start phase to shorten the next start phase, if the fuel composition has not changed since the last engine start.

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 The progressive increase of the DEMGAZ variable over time takes place as a sequence of steps characterized by an INCREGAZ increment and a DURGAZ time interval. To better adapt the increase to variable conditions in the engine environment and / or to the engine temperature, the increment (INCREGAZ) and the time interval (DURGAZ) are able to be calibrated as a function of the temperature of the engine. It is helpful to use the temperature of an engine coolant as an indicator of the engine temperature.

To optimize the management of the quantity of fuel injected into the engine during the normal operating phase, that is to say the phase after the starting phase, taking into account the dispersions of the engines and variations in the composition of the gaseous fuel, a second algorithm for controlling the quantity injected Q is provided, operating during the normal operating phase, comprising a learning mode which adapts to the behavior of the engine and to the composition of the fuel. Such algorithms operating during the normal operating phase are well known to those skilled in the art. One embodiment of such an algorithm provides that the quantity injected is the addition of a sum of additive terms and of a product of multiplicative terms which takes the following form:
Q = (sum of additive terms) + ...

... (multiplicative terms) * (l + ADGAIN) / P * (l + ADGAZ) / y (3)
The sum of the additive terms represents the quantity injected during idling phases and can be adapted to provide only the minimum engine requirement during the idling phases. The sum of the additive terms is a function of an ADZERO parameter. The ADZERO parameter can be made to depend on the engine temperature, the composition of the gaseous fuel and / or other variable parameters.

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 The product of the multiplicative terms represents the additional injected quantity supplied to the engine outside the idling phases, in particular when the engine supplies energy to move and / or accelerate the vehicle. An ADGAIN parameter is known in usual self-adaptation algorithms to compensate for dispersions and drifts of engine components. An ADGAZ parameter comes from the MEMOGAZ variable to ensure the operation of the engine outside the start-up phase and is involved in the formula for calculating the quantity Q injected according to equation 3 outside the start-up phase with the same formulation as the ADGAIN parameter. .

 In equation 1 which describes the management of the quantity injected Qi during the start-up phase, the multiplicative term (1 + DEMGAZ) / a takes the same form as the multiplicative adaptation terms in equation 3 for calculating the quantity injected during the normal operating phase. This facilitates the harmonization between the formulation for the quantity of fuel injected during the starting phase Qi and the quantity injected after the actual starting of the engine in the normal operating phase Q. The management of the variable DEMGAZ will be particular according to the cases described below.

 We now refer to Figure 3. It is assumed that previously where parameter ADGAIN was assigned the value G or parameter ADZERO was assigned the value Z and ADGAZ has a constant value.

 Firstly, a distinction is made between the case where the composition of the fuel has changed, for example after filling, and the case where the composition of the fuel is known.

To see a filling, we can interpret data received from the sensors of the fuel mass variation on board the vehicle, in particular in a fuel tank. A filling of the tank is noted in the event that a relative mass difference between the mass currently measured and a stored mass is greater than a certain threshold, such a threshold being programmable.

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 Since the fuel in the tank is in the gaseous state, a change in mass can preferably be measured as a change in the pressure in the tank. When determining the difference between the current pressure and the stored pressure, it is necessary to take into account a possible change in the temperature of the gaseous fuel, which requires measuring this temperature.

 A distinction is also made between cases where the second algorithm for controlling the quantity injected during the normal operating phase of the engine operates in a self-adaptive learning mode to the dispersions of the engine and its drifts and to the variations in the composition of the fuel, and the case where the second algorithm operates in a mode without self-adaptive learning.

If a change in fuel composition has been detected, for example if filling has taken place since the last start-up phase, the variables are initialized. The variable DEMGAZmin takes a predetermined basic value which ensures that the minimum quantity Qmin at the start of the start-up phase is less than the upper combustion limits to avoid an over-state for any composition of the fuel and which state of the engine and its drifts. The variable DEMGAZ can be predetermined for the extreme situation where the fuel is very rich and the engine not very demanding. Even under these constraints, it is possible to take into account the motor temperature in the initialization of the variable DEMGAZmin. Then, the initializations according to the step INITIALIZATION 1 are the following:
DEMGAZmin = f (temperature)
DEMGAZmax = f (temperature)
INCREGAZ = f (temperature)
DURGAZ = f (temperature)
In the case where the learning-free mode is effective during the normal operating phase, but if the algorithm has not yet had the material time to correctly adapt the ADZERO and ADGAIN parameters since the last detection of change in fuel composition, we do a variable initialization and

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parameters referenced INITIALIZATION 2. The variable DEMGAZmin will take as value the value of the parameter ADGAZ in order to always ensure that the minimum quantity Qmin at the start of the start-up phase is less than the upper combustion limits to avoid an over-state. The ADGAZ parameter will not be changed. The assignments according to the INITIALIZATION step 2 are as follows:
DEMGAZmin = ADGAZ
DEMGAZmax = f (temperature)
ADGAZ-ADGAZ
INCREGAZ = f (temperature)
DURGAZ = f (temperature)
In case the no learning mode is effective during the normal operating phase, and if the parameters ADZERO and ADGAIN already had the new values ADZERO (n + l) and ADGAIN (n + l) since the last detection of change in composition of the fuel, an initialization of the variables and parameters referenced INITIALIZATION 3. In particular, the variable DEMGAZmin is assigned a value which takes into account the adaptation of these parameters to the state of the engine and its drifts and the composition of the fuel. The ADGAZ parameter will not be changed:
DEMGAZmin = ADGAZ + (ADGAIN (n + l) -ADGAIN (n))
DEMGAZmax = f (temperature)
ADGAZ = ADGAZ
INCREGAZ = f (temperature)
DURGAZ = f (temperature)
The management of the ADGAZ parameter during the normal engine operating phase after the starting phase will be specific depending on the cases described below.

 In case the mode without learning is effective during the normal operating phase, or in the case where the learning mode is effective during the normal operating phase, but if the algorithm has not yet had time to correctly adapt the ADZERO and ADGAIN parameters since the last

Claims (14)

ADGAZ = MEMOGAZ-CORGAZ and corrected by a CORGAZ term depending on the engine temperature. The values of the ADZERO and ADGAIN parameters remain frozen on their previous values ADZERO (n) and ADGAIN (n). detection of fuel composition change, the ADGAZ parameter comes from the MEMOGAZ variable according to:  If the learning mode is effective during the normal operating phase, and if the ADZERO and ADGAIN parameters already had the new values ADZERO (n + 1) and ADGAIN ') since the last detection of fuel composition change, then ADGAZ remains frozen at its previous value.  The algorithm for managing, during the start-up phase, the quantity injected of a gaseous fuel into an engine operating on gaseous fuel described above avoids over-abundance and makes it possible to meet the conditions of flammability whatever the composition of the gaseous fuel and whatever the operation and / or the particular state of the engine. The algorithm ensures that the engine starts regardless of the gaseous fuel used and, by analyzing the operation of the engine in the start-up phase, makes it possible to anticipate the actual and optimal needs of the engine in the normal operation phase after the current start-up phase and the next start-up sequence. <Desc / Clms Page number 13> 1. A method of injecting gaseous fuel into an internal combustion engine having, as operating phases, a start-up phase and a normal operating phase subsequent to the start-up phase, in which a quantity of gaseous fuel is injected during a cycle of combustion of the engine in the starting phase of the engine determined by an algorithm for controlling the quantity injected (Qi), so that during the starting phase the quantity injected (Qi) is monotonically increasing in time from a predetermined minimum quantity (Qmin).

 2. Method according to claim l, characterized in that the quantity injected (Qi) increases to a final value corresponding to the instant of the effective start of the engine (Qdem) or to a predetermined ceiling (Qmax).  3. Method according to claim 1 or 2, characterized in that the effective departure of the motor is detected according to the speed of rotation.  4. Method according to any one of claims 1 to 3, characterized in that the algorithm for controlling the quantity injected during the start-up phase is capable of cooperating with a second control algorithm operating during the normal posterior operating phase during the start-up phase.  5. Method according to any one of claims 1 to 4, characterized in that if the composition of the gaseous fuel has changed since the last start, said minimum quantity takes a basic value.  6. Method according to claim 5, characterized in that said basic value is determined as a function of the engine temperature.  7. Method according to claim 4, characterized in that, if the composition of the gaseous fuel has not changed since the last start and if the second control algorithm is not in the learning mode, said minimum quantity is determined as a function of the final value corresponding to the instant of the last effective start, by subtracting a correction as a function of the engine temperature. <Desc / Clms Page number 14>  8. Method according to claim 4, characterized in that, if the composition of the gaseous fuel has not changed since the last start and if the second control algorithm is in the learning mode, said minimum quantity is determined as a function of the final value corresponding to the instant of the last effective start, taking into account a correction determined during the normal operating phases prior to the current start phase.  9. Method according to any one of claims 5 to 8, characterized in that after filling a tank, it is considered that the composition of the gaseous fuel has changed.  10. Method according to any one of claims 1 to 9, characterized in that the increase in the quantity injected (Qi) during the start-up phase follows a function of the form Qi = Qmin (1 + DEMGAZ) / a which depends on a monotonically increasing DEMGAZ parameter in time between a minimum value (DEMGAZmin) and a maximum value (DEMGAZmax).  11. Method according to claim 10, characterized in that the increase in the variable DEMGAZ is determined by an increment (INCREGAZ) and a time interval (DURGAZ).  12. Method according to claim II, characterized in that the increment and / or the time interval are determined as a function of the temperature.  13. Method according to any one of claims 10 to 12, characterized in that the increase in the variable DEMGAZ is linear over time.  14. System for injecting gaseous fuel into an internal combustion engine comprising a metering means for dosing an amount of gaseous fuel injected during an engine combustion cycle, a means for detecting an effective start of the engine, a means for detecting changes in the composition of the fuel, means for measuring the operation of the engine and a means capable of executing an algorithm for controlling the quantity injected, characterized in that, during a starting phase of the engine, the system makes increase the amount injected so <Desc / Clms Page number 15>  monotonic increasing over time from a predetermined minimum quantity (Qmin).