FR2834000A1 - Dosing fuel for direct injection internal combustion engine, involves controlling all injectors according to difference between mean injected fuel and stored desired quantity for operating point - Google Patents

Abstract

The method involves determining the actual fuel quantity injected into the combustion chambers at each operating point, forming the mean injected quantity, forming the difference between the mean and a stored desired quantity for the relevant operating point and controlling all injectors to achieve an injected quantity in all chambers corresponding to the desired mean

Description

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 The invention relates to a method for metering the quantity of a fuel, in particular for a direct injection internal combustion engine comprising a plurality of combustion chambers, at least one fuel supply installation which comprises at least one injector for each chamber. of combustion, and a control installation.

 Internal combustion engines with direct injection and spark ignition can operate either with a stratified mixture or with a homogeneous mixture. The operation of an internal combustion engine with a stratified mixture allows a reduced consumption of fuel, in particular because of the reduction of the losses during the changes of load and the reduction of the losses of heat by the walls. In operation with a stratified mixture, the fuel is injected during the compression phase with, preferably, an air fuel mixture 1 made with a significant excess of air, that is to say with X In this case, the fuel is present in the combustion chamber in laminated form, and the fuel / air mixture can be ignited reliably because of the excess air. In the case of operation with a homogeneous mixture, the fuel is injected during the suction phase, so that at the firing point a homogeneous mixed cloud is present in the combustion chamber.

 The goal of recent direct injection (Otto) engines with direct injection is to reduce fuel consumption and exhaust gas production. The benefits are achieved by special control of the injection valves or injectors during the injection process, which optimizes the flow of the combustion process. This command allows an optimization of the characteristics of the injected jet. For the control of injectors with adjustable stroke opening, it is advisable to use

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 piezo-actuators, which can transform almost without delay an electrical signal into a mechanical movement. This movement can be accurately controlled both in size and duration by applying a high voltage to the piezo-actuator.

 Flow variations may occur in piezo-controlled injectors, as a result of manufacturing tolerances, and this may lead to injection behavior of piezo-actuator fuel injection devices that differ from the predicted 'after the injection parameters. As a result, particularly in the case of direct injection and spark ignition combustion engines, the fuel consumption is increased.

 DE 19903555 C2 discloses a device for adjusting a voltage supply at several different voltage levels, the selection of which enables the valve opening to be switched between several different positions, which makes it possible to have the necessary plurality opening positions for the valves, without incurring additional costs in the order.

 The device described above does not allow an identical adjustment of the individual cylinders, while an adjustment of the amount of fuel supplied by the injectors of the engine, to a nominal value, is necessary. To ensure this, the present invention provides a method for an internal combustion engine with direct injection, which allows identical adjustment of the individual cylinders to different operating conditions of the engine.

 This objective is achieved by means of a method for metering the quantity of a fuel, in particular for a direct injection internal combustion engine comprising a plurality of combustion chambers,

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 at least one fuel supply installation which comprises at least one injector for each combustion chamber, and a control installation.

 According to a first embodiment of the method according to the invention, typically: at an operating point of the internal combustion engine, a determination is made of the amount of fuel which is injected into each combustion chamber, to obtain the quantity of fuel actually injected, - the quantities of fuel actually injected into the individual combustion chambers are used to calculate an average value, - a value of the difference between the calculated average value and the quantity of reference fuel stored in the control system for the operating point in question is calculated, - then, thanks to the control system, all the injectors are adjusted so that in each combustion chamber, the quantity of fuel injected corresponds to the calculated average value. , and - then, the amount of fuel injected into each chamber The amount of fuel injected into each combustion chamber corresponds to the amount of fuel of the setpoint.

 Preferably, the adjustment of the amount of fuel injected into each combustion chamber on the average value is done during operation with a homogeneous mixture or with a stratified mixture.

 According to another advantageous preferred arrangement, the modification of the quantity of fuel injected into each combustion chamber is modified by the value of the difference so that the

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 amount of fuel injected coincides with the amount of fuel setpoint, in operation with a homogeneous mixture.

 In the process of the invention, it is provided that, for the determination of the amount of fuel, in particular in the case of an internal combustion engine with direct injection and controlled ignition, the quantity of fuel injected is modified to a set value. As a general rule, an internal combustion engine operates, depending on the load, with a homogeneous mixture and / or a stratified mixture. The amount of fuel injected into a combustion chamber is metered or adjusted by the injector by changing the duration of the injection and / or the stroke of the injector. At the point of operation considered, the amount of fuel injected into each cylinder of the internal combustion engine is determined. This is the amount of fuel actually injected. Then, the quantity of fuel actually injected is compared with the amount of fuel of the setpoint for the operating point in question, kept in the control installation, the quantity of fuel actually injected being the average of the quantities of fuel actually injected into each cylinder. According to the invention, the control system acts on the injectors so that the quantities of fuel injected correspond to the average value calculated from the quantities of fuel actually injected.

 Known methods are used to adjust the injectors of the individual cylinders which involve a change in the stroke of the injector and / or the duration of the injection so as to standardize the amount of fuel injected, the amount of fuel injected in each cylinder being increased or decreased until the average value is reached. The correction on the average value can be done in operation with a homogeneous mixture or with a stratified mixture.

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 In a subsequent operation, the injectors are adjusted in such a way that the quantity of fuel injected into each cylinder corresponds to the quantity of reference fuel. The adjustment on the reference fuel quantity consists of calculating the value of the difference between the determined average value and a target fuel quantity corresponding to the operating point considered and kept in the control installation. After the adjustment step to the average value, the quantity of fuel injected into each combustion chamber is modified by the value of the difference, so that the quantity of fuel injected into each combustion chamber corresponds to the amount of fuel of the fuel. setpoint.

 According to the invention, the adjustment of the amount of fuel injected into the various cylinders on the target fuel quantity is carried out during operation with a homogeneous mixture. The quantity injected is modified by modifying the stroke of the injector and / or the duration of the injection during operation with a homogeneous mixture until the adjustment error of the lambda value takes a zero value. .

 According to a second embodiment of the method according to the invention, typically: at an operating point of the internal combustion engine, a determination is made of the amount of fuel that is injected into each combustion chamber, to obtain the quantity of fuel actually injected, - the quantities of fuel actually injected into the individual combustion chambers are used to calculate a first average value,

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 - a value of the difference between the first average value and the target fuel quantity stored in the control system for the operating point in question is calculated, - then, thanks to the control system, all injectors are set so that the quantity of fuel injected into each combustion chamber is modified by the value of the difference so that a second average value obtained from the quantities of fuel injected corresponds to the quantity of fuel of setpoint and - then all the injectors are controlled so that the quantity of fuel injected into each combustion chamber corresponds to the amount of reference fuel.

 In addition, preferably, the control of each injector, to change the amount of fuel injected by the value of the difference, is during operation of the internal combustion engine with a homogeneous mixture.

 Also, according to another advantageous preferred arrangement, the adjustment of the amount of fuel injected into each combustion chamber on the target fuel quantity is done during operation of the internal combustion engine with a homogeneous mixture and 1 or a mixture laminate.

 According to the second embodiment of the invention, at an operating point and for each cylinder of the internal combustion engine, the quantity of injected fuel, constituting the quantity of fuel actually injected, is determined. The quantities of fuel actually injected into the individual combustion chambers are used to calculate a first average value. Then, the value of the difference between the first average value and the target fuel quantity corresponding to the operating point considered and kept in the installation of

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 command. Then, the quantity of fuel injected into each cylinder is modified by the value of the difference, until a second average value of the fuel quantity determined from the quantities of fuel injected, corresponds to the fuel quantity of the fuel. setpoint. In other words, the quantities of fuel injected are modified until an average value is obtained from the quantities of fuel injected which corresponds to the second average value. This adjustment is made during operation with a homogeneous mixture.

 According to the invention, in a final operation, each injector of each cylinder is adjusted by means of the control system so that the quantity of fuel injected corresponds to the amount of fuel of setpoint. This adjustment of the amount of fuel injected into the individual cylinders can be done during operation with a homogeneous mixture and / or with a stratified mixture.

 Also, advantageously and preferably, the following provisions are adopted alone or continuously: the determination of the quantity of fuel injected into each combustion chamber is based on a measurement of the rotational torque and / or a measure of the lambda value for each room.

 the injection of the fuel into each combustion chamber is carried out by means of a piezoelectric injector, the modification in the quantity of fuel injected into each combustion chamber is done by means of a modification of the duration of injection and / or stroke of the injector; and the modification of the duration of the injection and / or the opening of the injector of the internal combustion engine is made from a field of characteristics, kept in the control installation.

 According to the invention, the amount of fuel introduced into each cylinder operating with a homogeneous mixture is determined

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 from the measurement of the torque and / or the measurement of the lambda values of the individual cylinders, whereas the determination of the amount of fuel introduced during operation with a stratified mixture is based on the measurement of the torque of rotation.

 It is preferable that the injection of the fuel into the combustion chamber is done by means of a piezoelectric injector. The variation of the duration of the injection and / or the stroke of the injector is done at each operating point of the internal combustion engine by using a field of characteristics, kept in the control installation. When a piezo-injector is used, the correction values of the voltage for the piezo-actuator are determined by the method according to the invention and by using the field of the injection characteristics, stored in the control system. which makes it possible to regulate the quantities of injected fuel actually necessary.

 The method of the invention makes it possible to reduce the effect of manufacturing tolerances, in particular at the level of the injector of the fuel injection installation. This is important especially in the case of internal combustion engines with direct injection and spark ignition, in which, to obtain a better use of the fuel, it is necessary to ensure a regular and adapted fuel supply. A modification of the opening of the stroke of the injector and / or the duration of injection allows a uniform injection in the different injectors and automatic adaptation to the operating conditions.

 The quantities of fuel injected by the individual injectors during operation with a homogeneous mixture and / or with a stratified mixture are modified until the target fuel quantity is reached by all the injectors. Of this

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 in this way, the fuel supply is adjusted to the nominal value for each injector of the internal combustion engine.

 The method of the present invention allows an adjustment of the fuel supply for each injector, by a balancing of the cylinders, from the measurement of the torque at the crankshaft and / or by the measurement of the lambda values of the individual cylinders. by means of a lambda probe, in the exhaust gas circuit. When only the measurement of the lambda value of the individual cylinders is used, the quantity of fuel injected is determined by measuring the lambda value () of each cylinder and the air mass. Another possibility is to ensure that the fuel quantity can be determined by a fuel measurement system or from values such as the opening time and the pressure of the fuel injector.

 In the case of a measurement of the rotational torque, the rotational torque of the crankshaft produced by the cylinders is measured, whereby the irregularities in the injection of the individual injectors are determined, whereas in the case of the measurement of the lambda value of the individual cylinders, the correction of the amount of fuel injected is made from the air ratio of the individual cylinders of the internal combustion engine. It is possible to accurately determine the amount of fuel injected into the individual cylinders from the proportion of combustion air. Since the air ratio of the individual cylinders is not always equal because of manufacturing tolerances at the injection nozzles, deviations occur in the air ratio of the individual cylinders. An adjustment of the lambda value eliminates such deviations and it is effected by the injection into all the cylinders of more or less fuel so that we have overall the desired air / fuel ratio in the exhaust gas and that the adjustment error is zero.

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 However, since the control error does not depend on the target fuel quantity, this means that the injected fuel quantities calculated from a characteristic field do not correspond to the target fuel quantities. By determining the lambda value (X) of the individual cylinders, it is possible to determine the errors of adjustment of the injected quantity of the fuel. This can be achieved, for example, by a high temporal resolution of the signal produced by a measurement sensor of the lambda value. The sequence of ignitions of the internal combustion engine is such that it is possible to measure in the exhaust gases with a measurement probe of the lambda value, the adjustment error for each cylinder with respect to the proportion of air deposit.

 Preferred embodiments of the invention are illustrated by the drawings and will be described hereinafter. In these drawings: FIG. 1 is a graph with the characteristic curves of the individual injectors illustrating the adjustment error with respect to the desired characteristic curve, and FIG. 2 is a graph with the characteristic curves (superimposed) of the individual injectors after the correction of the quantity of fuel injected by the injectors.

 An internal combustion engine (not shown) with four cylinders operates, preferably and in a known manner, with a four-stroke cycle, during which the fuel is injected directly into a combustion chamber. For fuel injection, piezo injectors are used. The injection point and the quantity injected are modified according to the load. It is also conceivable that the total amount of fuel injected, is injected into the combustion chamber in several partial doses.

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 The characteristic curves of FIG. 1 show the difference between the characteristic curves of the individual injectors and the setpoint curve. The characteristic curves illustrate the injection behavior of each injector and show how the effective quantity of the fuel differs from the set value, conserved in a control of the engine.

 The injectors used are controlled by a piezo-actuator and a voltage source provides the voltage necessary for adjusting the opening of the injector. A control system provides the necessary information to the voltage source and the piezo-actuator provides adjustment of the opening of the stroke of the injector. Because of manufacturing tolerances, fuel flows in the injector are obtained which differ from the set value for the opening in question. In fig. 1, for example in the case of the injector 4, a flow rate corresponding to 60% of the maximum flow rate is observed for a setting at 50% of the maximum flow rate.

 According to the invention and as shown in FIG. 1, is determined at an operating point and for each cylinder of the internal combustion engine, the amount of fuel injected, which represents the amount of fuel actually injected. This value is compared in the control system with the setpoint of the fuel quantity at the point of operation considered, which allows to know the injection behavior of each injector.

 The quantities of fuel actually injected by each injector are used to calculate their average. At this moment, the control unit acts on the injectors so that the quantity of fuel injected corresponds to the average value obtained from the quantities of fuel actually injected. The injectors have at this time the behavior illustrated in FIG. 2, in this case the curves of the injectors 1 to 4 are superimposed.

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 According to the invention, the adjustment of the quantity of fuel supplied by each injector is ensured by a balancing of the cylinders from the measurement of the rotational torque on the crankshaft and / or by the measurement of the lambda value for each cylinder, by a probe (Â) in the exhaust gas circuit. The adjustment of the injector stroke and / or the injection duration during operation with a homogeneous mixture, is modified for each injector until the adjustment error of the lambda value reaches a value nothing. The field of injection characteristics stored in a control unit allows, in accordance with the method of the invention, to produce and use correction values for the necessary adjustment of the quantities of fuel actually injected.

 In a subsequent operation, a final correction is made for all four injectors by the value of the difference between the average value and the set value, so that we obtain the injection, by all the injectors, the amount of fuel corresponding to the amount of fuel. This gives the injection of the desired amount of fuel to ensure proper operation of all injectors. This ensures an equalization of the amount of fuel injected by each of the four injectors, at the nominal value.

 In another variant, the control installation can produce a modification of the injection duration while keeping the opening for the injected fuel unchanged in order to reach the desired flow rate. For this, the voltage to be applied to the piezo-actuator is determined by the control unit from voltage curves stored in a characteristic field, and is then applied to the piezo-actuator for the appropriate duration.

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 In the internal combustion engine, small deviations occur in the amount of air admitted, because of the way in which the cylinders are mounted, with respect to the air intake duct, but this is then corrected, during operation with a stratified mixture, by the setting of the injectors ensured by a modification of the opening / the stroke of the injector and / or the duration of the injection.

Claims (10)

 1. A method for metering the amount of a fuel for a direct injection internal combustion engine comprising a plurality of combustion chambers, at least one fuel supply installation which comprises at least one injector for each combustion chamber, and a control installation, in which - at an operating point of the internal combustion engine, a determination is made of the quantity of fuel that is injected into each combustion chamber, to obtain the quantity of fuel actually injected, - the quantities of fuel actually injected into the individual combustion chambers are used to calculate an average value; - a value of the difference between the calculated average value and the target fuel quantity retained in the control installation for the operating point in question is calculated, - then, thanks to the command installation, all the injectors are adjusted so that in each combustion chamber, the quantity of fuel injected corresponds to the calculated average value, and then the quantity of fuel injected into each combustion chamber is modified by the value of the difference so that the amount of fuel injected into each combustion chamber corresponds to the amount of fuel setpoint. 2. Method according to claim 1, characterized in that the adjustment of the amount of fuel injected into each combustion chamber on the average value is done during operation with a homogeneous mixture or with a stratified mixture. 3. Method according to claim 1 or claim 2, characterized in that the modification of the quantity of injected fuel <Desc / Clms Page number 15>  in each combustion chamber is modified by the value of the difference so that the amount of fuel injected coincides with the target fuel quantity, in operation with a homogeneous mixture. 4. A method for metering the amount of fuel for a direct injection internal combustion engine comprising a plurality of combustion chambers, at least one fuel supply installation which comprises at least one injector for each combustion chamber and a fuel injection plant. control, in which - at an operating point of the internal combustion engine, a determination is made of the amount of fuel that is injected into each combustion chamber, to obtain the amount of fuel actually injected, - the quantities of fuel actually injected in the individual combustion chambers are used to calculate a first average value, - a value of the difference between the first average value and the target fuel quantity retained in the control facility for the operating point in question is calculated; then, thanks to the command facility, all the The injectors are adjusted so that the quantity of fuel injected into each combustion chamber is modified by the value of the difference so that a second average value obtained from the quantities of fuel injected corresponds to the amount of fuel of the fuel. setpoint and - then, all the injectors are controlled so that the amount of fuel injected into each combustion chamber corresponds to the amount of fuel setpoint. 5. Method according to claim 4, characterized in that the control of each injector, to change the amount of fuel <Desc / Clms Page number 16>  injected by the value of the difference, is done during operation of the internal combustion engine with a homogeneous mixture. 6. A method according to claim 4 or claim 5, characterized in that the adjustment of the amount of fuel injected into each combustion chamber on the target fuel quantity is done during operation of the internal combustion engine with a homogeneous mixture and / or a stratified mixture. 7. Method according to one of claims 1 to 6, characterized in that the determination of the amount of fuel injected into each combustion chamber is based on a measurement of the rotational torque and / or a measurement of the lambda value for each combustion chamber. 8. Method according to one of claims 1 to 7, characterized in that the fuel injection in each combustion chamber is done by means of a piezoelectric injector. 9. Method according to one of claims 1 to 8, characterized in that the change in the amount of fuel injected into each combustion chamber is made through a change in the injection time and / or stroke of the fuel. 'injector. 10. Method according to claim 9, characterized in that the modification of the duration of the injection and / or the stroke of the injector of the internal combustion engine is made from a field of characteristics, preserved in the control installation.