FR2717227A1 - Method of fuel injection for motor vehicle IC engine with controlled ignition and direct injection - Google Patents

Abstract

The fuel injection method is for an internal combustion engine of the type having electronic injection (5) with a cylinder fed with pressurised fuel and which is driven by an electronic control unit (7) which controls the fuel injection time. For an injector (5) and a given engine cycle, the total duration of the injection time determined by the control unit (7), from the operating conditions of the engine, is spread into first and second distinct injection periods (T1,T2) essentially spread over the suction and compression cycle of the engine.

Description

FUEL INJECTION PROCESS FOR
DIRECT INJECTION INTERNAL COMBUSTION ENGINE AND
IGNITION CONTROL
The present invention relates to a fuel injection method for a multicylinder internal combustion engine with direct injection and spark ignition intended in particular for equipping a motor vehicle. The invention relates more particularly to a fuel injection method suitable for an internal combustion engine by which the fuel injection is carried out in several distinct periods per engine cycle.

 We know in particular from French patent applications n02,650,629 and n02,650,630 filed by the Applicant examples of internal combustion engines, direct injection and spark ignition. Direct injection takes place inside the cylinders downstream of the combustion air intake valve (s).

 Direct injection has the particular advantage of being able to overcome the butterfly for controlling the air flow in the intake manifold, which is essential for indirect injection.

The engine torque is then directly regulated by the amount of gasoline injected directly into each cylinder, resulting in a significant reduction in pumping losses, which therefore significantly improves the efficiency of the engine.

 Direct injection also allows stratification of the charge admitted into the cylinders. The injection which takes place late in the cycle, during the compression phase makes it possible to create a rich zone around the candle in order to start the combustion which will then propagate in a leaner mixture. This heterogeneity of the fuel mixture present in the combustion chambers makes it possible to perfectly control the combustion, in particular for the very small amounts of fuel injected, which leads to reducing fuel consumption and lowering the emissions of polluting gases from the engine during engine operations. the latter at low loads or partial loads.

 However, current direct injection has drawbacks as the load increases and therefore the quantity of fuel to be injected increases. The Applicant has been able to show that the favorable effect of the stratification of the injected fuel decreases with the load and even turns out to be detrimental to the good progress of the combustion at high load.

 As the load increases, it appears preferable, to produce the maximum power, to make the best use of the admitted air, and for this to make the mixture homogeneous and therefore to introduce the fuel as far upstream possible in the cycle to promote the preparation of the mixture. However, to be able to operate as long as possible in a lean mixture in order to reduce the emission of pollutants, it remains important to keep a fuel-rich zone in the vicinity of the spark plug during the spark.

 The aim of the process which is the subject of the present invention is therefore to improve the injection of fuel into the cylinders by operating a distribution of the injection of fuel during the engine cycle which makes it possible to take into account different needs in preparing the fuel mixture. according to the engine operating points.

 The fuel injection method according to the invention relates more particularly to a multicylinder internal combustion engine with spark ignition and direct injection of the type comprising an electro-injector per cylinder supplied with fuel under pressure and controlled by an electronic control system which controls the duration of injection.

 According to the invention the injection process is characterized in that for a given injector and for a given engine cycle, the total injection time determined by the electronic control system from the engine operating conditions is divided into a first and a second separate injection periods distributed essentially during the suction and compression phases of the engine cycle.

 According to another characteristic of the injection method which is the subject of the invention, the first injection period is defined by its initial instant and by its duration.

 According to another characteristic of the injection method which is the subject of the invention, the initial instant of the first injection period coincides with the instant of closing of the exhaust valve.

 According to another characteristic of the injection method which is the subject of the invention, the duration of the first injection period increases with the load and the engine speed.

 According to another characteristic of the injection method which is the subject of the invention, the second injection period is defined by its final instant and by its duration.

 According to another characteristic of the injection process which is the subject of the invention, the final instant of the second injection period coincides with the triggering of the ignition spark.

 According to another characteristic of the injection method which is the subject of the invention, the second injection period decreases with the load and the engine speed.

The aims, aspects and advantages of the present invention will be better understood from the description given below of an embodiment of the invention applied to a four-stroke and four-cylinder engine, this embodiment being given by way of nonlimiting example, with reference to the appended drawing, in which
FIG. 1 is a diagram of an internal combustion engine with direct injection fitted with an engine control system for implementing the method according to the invention;
FIG. 2 is a circular injection diagram characteristic of the method according to the invention.

 In accordance with FIG. 1, the engine referenced 1, of the four-stroke internal combustion type, with four in-line cylinders, with spark ignition and with direct injection, is therefore equipped with an electronic injection control system, also called engine control system 7. The electronic injection control system 7 therefore relates to the implementation of the injection process in accordance with the present invention.

 The electronic injection control system 7 conventionally comprises a computer comprising a CPU, a random access memory (RAN), a read only memory (ROM), A / D converters (analog-digital), and various input interfaces and of outputs.

 This injection control system 7 receives a certain number of input signals providing the value of the main parameters characterizing the operation of the engine: speed, load, manifold pressure, water temperature, accelerator pedal position or even the battery voltage, and information on the position of the pistons in the cylinders originating in particular from a position sensor 9 cooperating with a toothed target 3 secured to the flywheel carried by the crankshaft.

 The electronic injection control system then proceeds, on the basis of this different information and according to actuation strategies or methods implemented in the CPU, to control the flow rate of the electro-injectors 5 while controlling for each of them the injection start phase or the injection end phase and the opening time, thus determining a precise flow of fuel for each injector 5 which is supplied with fuel under a substantially constant pressure.

 The actuation mode of the injectors 5 is specified in accordance with the injection pattern presented in FIG. 2.

 The proposed injection pattern consists, for an injector and for an engine cycle, in dividing the total injection time T which is determined by the electronic engine control system from the engine operating conditions, into two periods of separate injections T1, T2, (which may possibly be zero) distributed over the intake and compression phases of the engine cycle.

 The first period T1 is essentially characterized by its instant or start phase and its duration which depends on the engine operating point. The start and duration of the period T1 are preferably determined by the engine control system 7 in the form of the angle of rotation of the crankshaft. The initial instant of the period T1 is in fact chosen at the start of the suction phase to allow the homogenization of the fuel injected with the fresh air admitted. Preferably, one can choose to start the first injection period when the exhaust valve closes (marked RFE in Figure 2). This moment of closing the exhaust valve can change before or after Top Dead Center (TDC) depending on the type of engine.

The duration of the first period T1 is therefore adjusted according to the operating point of the engine. The values are for example stored in a predetermined map as a function of the load and the engine rotation speed. The duration of the T1 period increases directly with the load and the regime. In general, the first T1 period ends before the end of the aspiration phase at
Bottom dead center (PMB).

 The second period T2 is it, essentially characterized by its instant or end phase and its duration which depends on the engine operating point. The end of the period T2 is in fact chosen at the end of the compression phase to allow the formation of a fuel-rich zone in the vicinity of the spark plug. Preferably, it is possible to choose to have the second injection period T2 terminate at the time of the ignition spark (marked OE in FIG. 2). This instant of triggering of the ignition spark can evolve more or less before Top Dead Center (TDC) depending on the engine operating conditions.

 The duration of the second period T2 is therefore adjusted according to the operating point of the engine. The values are for example stored in a predetermined map as a function of the load and the engine rotation speed. The duration of the T2 period decreases directly with the load and the regime.

 The injection periods are therefore operated, under the partial load operating conditions in two distinct periods T1 and T2 during the suction and compression phases of the engine cycle defined by the rotation of 1800 crankshaft angle from the Point Death High admission.

The first injection makes it possible to obtain a homogeneous lean mixture while the second injection generates a fuel-rich zone around the spark plug at the time of ignition. This combination makes it possible to perfectly control the combustion and propagation of the flame and thus to ensure very low emissions of nitrogen oxides NOx.

 The load and the richness can be, in an alternative embodiment, also regulated by controlling the flow of fresh air admitted into the combustion chambers by means of a throttle valve arranged in the intake duct upstream of the combustion chambers. combustion.

 The method according to the invention is extremely simple to implement since it requires no additional device than the high pressure injectors 5 opening directly into the combustion chambers and their electronic control system 7.

 Of course, the invention is in no way limited to the embodiment described and illustrated, which has been given only by way of example.

 On the contrary, the invention includes all the technical equivalents of the means described and their combinations if these are carried out according to the spirit.

Claims (1)

 (13 Fuel injection method for a multicylinder internal combustion engine with spark ignition and direct injection, of the type comprising an electro-injector (5) per cylinder supplied with pressurized fuel and controlled by an electronic control system (7 ) which controls the injection time, characterized in that for an injector (5) and for a given engine cycle, the total injection time determined by the electronic control system (7) from the engine operating conditions is divided into first and second separate injection periods (T1, T2) distributed essentially during the suction and compression phases of the engine cycle. [23 Fuel injection method according to claim 1, characterized in that said first injection period (T1) is defined by its initial instant and by its duration.  (3] Fuel injection method according to claim 2, characterized in that the initial instant of said first injection period (T1) coincides with the instant of closing of the exhaust valve (RFE).  [4] Fuel injection method according to any one of claims 2 to 3, characterized in that the duration of said first injection period (T1) increases with the load and the engine speed.  [5] Fuel injection method according to any one of claims 1 to 4, characterized in that said second injection period (T2) is defined by its final instant and by its duration.  (6] Fuel injection method according to claim 5, characterized in that the final instant of said second injection period (T2) coincides with the triggering of the ignition spark (OE). [7] Fuel injection method according to any one of claims 5 to 6, characterized in that the duration of said second injection period (T2) decreases with the load and the engine speed.