Control method for the injection of fuel for an internal combustion engine with indirect injection and spark ignition

The present invention relates to a fuel injection control method for an internal combustion engine with indirect injection and spark ignition.

It is aimed particularly at petrol engines including a multipoint indirect injection device.

A device for indirect injection of gasoline is shown in Figure 1 and comprises, for each cylinder of the engine, an injector 1 associated with the intake duct 3 of the cylinder 2 and of which the injection end issues into the conduit 3 upstream of the corresponding intake valve 4. the orientation of the injector 1 to the inside of the intake duct 3 that much of the injected fuel strikes the inner walls of the intake duct 3 and the outer surface of the intake valve 4 before entering the combustion chamber in the open position of this valve.

Indirect injection, part of the injected gasoline projected on the walls of the intake duct 3 as shown in A is deposited on these walls in the form of a fuel liquid film, as shown schematically in B.

Early failure of the fuel injection, the liquid film present on the intake duct evaporating as shown in C, it enters the combustion chamber and does not burn. It then creates a peak unburned hydrocarbons HC leaving the engine and upstream of the catalyst as shown in Figure 2 which shows a peak P of HC in the fuel cut C. This peak unburnt hydrocarbon HC is treated with the catalyst when the latter is started (warm), but it creates an exothermic temperature rise of the catalytic bread. Such temperature rise produces a more rapid aging of the catalyst. Moreover, when the catalyst starts to get old, the peak of unburned hydrocarbons (HC) present in engine output is not processed completely by this catalyst and fuel injection cut then has an impact on emissions polluting.

To reduce the peak of unburned hydrocarbons in the fuel injection cut, it is necessary to decrease the amount of gas present on the walls of the intake pipe before this break.

For this, two possibilities exist:<ul><li>optimize the injector by choosing an angle of inclination thereof with respect to the intake duct as shown in Figure 1, or by using an improved spray nozzle;</li><li>optimize engine control by an electronic computer according to one of the fuel injection control strategy before the interruption of this injection.</li></ul>

The invention falls within this second option whereby an injection control strategy has been identified, as will be seen later, to reduce the amount of fuel present on the walls of the intake pipe before the cutoff injection and ignition.

This strategy was developed based on the following findings.

Testing of hydrocarbon concentration measuring unburned using a fast analyzer concentration of SIFT-type (Flame Ionization Detector) at the output of the exhaust valves were used to quantify the mass of liquid film present before the fuel cut.

It appears that the phasing of the fuel injection has a significant impact on the mass of liquid or fluid film before the fuel cut as shown in FIGS 3 and 4, where 3 represents the evolution of mass fluid film for different injection rates according to the angle of rotation of the engine crankshaft and Figure 4 shows the lifting of SE exhaust and intake valves SA on the basis of the rotation angle of said crankshaft . Indeed, when the injection takes place with the inlet valve SA opened, the fluid film mass is significantly higher and this trend is explained by the fact that the evaporation time of the fluid film before the closure of the intake valve is lower.

It thus appears of Figures 3 and 4, it is advantageous, in order to have a small amount of unburned hydrocarbons in early failure of injection, controlling the injection during the exhaust phase before that the inlet valve opens. This setting is used today on petrol engines with indirect injection and as shown in Figure 2, the peak of unburned hydrocarbons in this case is important.

The present invention aims to propose a new strategy to further optimize the fuel injection cut to reduce the amount of unburned hydrocarbons in the beginning of the fuel cut.

To this end, according to the invention, the fuel injection control method for an internal combustion engine with indirect injection and controlled ignition including at least one cylinder, an injector associated with the cylinder of the intake duct and controlled during that cycle operating the motor so as to inject fuel, such as gasoline, in the intake conduit upstream of the open inlet valve of the cylinder before entering the combustion chamber of the cylinder, is characterized in that it consists of driving the injector by shifting the fuel injection phasing in the intake beyond the closing timing of the intake valve driven before switching off the injection and simultaneously decrease the time fuel injection during these phases extended injection until the cutoff of the injection, in order to decrease the amount of fluid fuel film present on the walls of the intake duct.

The gap period of the injection phasing until the cutoff of the injector can be configured in number of engine operating cycles.

The invention also provides an internal combustion engine with indirect injection and controlled ignition including multiple cylinders, inlet ducts, each associated with a cylinder to which the intake ports communicate via an inlet valve cylinder, each of the injectors associated with an intake duct and driven during the engine operating cycle so as to inject fuel, such as petrol, into the inlet ducts upstream of the inlet valves, and which is characterized in that each of the injectors is controlled according to the method as defined above.

The invention will be better understood and other objects, features, details and advantages thereof will appear more clearly in the explanatory description which will follow with reference to the accompanying schematic drawings given solely as an example illustrating a mode embodiment of the invention and in which:<ul><li>Figure 1 is a longitudinal sectional view of an intake duct comprising a fuel injector of an indirect injection device for engine with indirect injection and spark ignition;</li><li>Figure 2 is a graph showing the unburnt hydrocarbon peaks expressed in particles per million (ppm) during the fuel injection cut on a standard test cycle extract; </li><li>3 shows the evolution of the mass of the fluid film present on the wall of an intake duct according to the angle of rotation of the engine crankshaft;</li><li>4 shows the lifts of the exhaust and intake valves depending on the crankshaft rotation angle;</li><li>5 shows the variation in injection phasing according to the invention as a function of engine operating time proportional to the number of cycles of the engine;</li><li>Figure 6 is a representative GAPHE enrichment the engine as a function of time of operation thereof during the variation of injection phasing of Figure 5;</li><li>Figure 7 is a graph representing the injection time in microseconds as a function of engine operating time following the injector control strategy according to the invention; and</li><li>Figure 8 shows the evolution of the injection phasing as a function of engine operating time and in accordance with the injection strategy before injection cut-off of Figure 7.</li></ul>

The strategy of the invention for reducing the amount of unburned hydrocarbons HC at the start of disconnection of the invention is achieved by two simultaneous actions comprising influencing the injection phasing and an action on the injection time.

As shown in Figures 5 to 8, the strategy concerning action on the injection phasing relative to the crankshaft angular position, consists in performing an injection phasing tilting through an injection valve phasing open intake as shown in PAO an intake valve injection phasing closed as shown PAF before the interruption of the injection. In other words, the injector 1 is controlled for shifting the fuel injection phasing in the intake 3 beyond the closing timing of the intake valve 4 before switching off the injection channel. Such tilting created an engine E enrichment as shown in Figure 6, when keeping the same fuel injection time. To compensate for the engine enrichment due to the variation or change in the injection phasing, the second strategy of action is to reduce simultaneously the first action, the injection time as shown in Figure 7 prior to cleavage of the C 'injection. Thus, Figures 7 and 8 taken together show that the injector 1 is controlled by the electronic computer engine control during an injection time of 4000 microseconds when phasing injection PAO intake valve 4 open and, when phasing injection PAF valve closed inlet, the injection time at the time of this phase shift is lowered as shown in Ab before the injection cut C occurring at intake valve closed. The decline of the injection time during this extended phasing injection has the effect of decreasing the amount of gas fluid film present on the walls of the intake duct 3 that the amount of projected gasoline on the walls depends flow injected by the injector 1. the period or duration of time between time t1 of the injection phase and the time t2 of injection cut-off is paramétrale number of engine cycles.

The injector control strategy according to the invention reduces not only the unburned HC emissions of hydrocarbons, but also the exotherm of the catalyst generally found in the prior art and, therefore, slow down the aging this one.

The inventive control strategy requires no modification of the engine and / or its components, but only a change in the engine control of the electronic computer software. Thus, this strategy operates at low cost.