FR2921975A1 - Fuel e.g. ethanol, injecting method for e.g. supercharged indirect injection and controlled ignition combustion engine, of motor vehicle, involves separating injection period from another period by period during which fuel is not injected - Google Patents

Abstract

The method involves realizing a splitted fuel injection phase comprising several fuel injection periods in injection mode during each cycle of engine, where the injection phase has a place in which an inlet valve is open. Each injection period is temporarily separated from another period by a period during which a fuel such as less volatile fuel e.g. ethanol, is not injected. The injection mode is implemented as long as a delay triggered by the starting of engine is not expired and the engine does not attain threshold temperature. An independent claim is also included for a fuel injection system comprising hardware and software units.

Description

The present invention relates to a fuel injection method in a heat engine and more particularly to a fuel injection method in an intake manifold of a spark ignition engine.

The formation of the mixture in the starting phase and more particularly in the cold start phase of spark ignition and indirect injection engines is a crucial problem to be dealt with. Indeed, the fuel injected on the cold walls of the intake ducts by indirect injection vaporizes very little. The formation of a homogeneous air-fuel mixture (necessary for good combustion) is then very difficult to obtain. Combustion thus generates high emissions of pollutants (in particular unburned hydrocarbons) during these phases of cold operation.

For engines that operate on a very low volatile fuel such as ethanol, this vaporization is even more difficult and also causes start-up difficulties.

To improve the preparation of an air-fuel mixture as homogeneous as possible, during this cold operation, various solutions exist.

Some offer to heat the fuel before injection, others to heat the walls on which the fuel is injected, or to use an air-assisted injection to reduce the size of fuel drops in the intake ducts.

These solutions have the particular disadvantage of conditioning the state of the fuel before the passage of the intake valve or valves. MS \ RENO36EN.dpt In the case of a closed intake valve (IVC) injection, the fuel is deposited on the walls of the intake duct and on the inlet valve tulip and forms a film of fuel which quickly takes the temperature of the cold walls. The solutions mentioned above therefore largely lose their effectiveness.

In the case of an injection in open intake valves (IVO), a larger part of the fuel enters directly into the combustion chamber, which allows a priori to take better advantage of these solutions.

However, in the starting phase at a engine speed of approximately 300tr / min or cold-accelerated idle at an engine speed of about 1200rpm, the injection duration is low compared to the duration of admission of the gases into the engine. engine cylinder. Typically, the injection time is about 10% of the admission time of the gases in the cylinder. Figure 1 shows the intake valve lift depending on the position of the crankshaft and an example of fuel injection time for a 300 rpm engine speed in the starting phase. The injection time is then of the order of 10 ms (about 20 ° crankshaft). Figure 2 shows the intake valve lift as a function of the crankshaft position and the fuel injection time for an engine speed of 1200 rpm in accelerated idle phase. The injection time is then of the order of 4 ms (a little less than 30 ° crankshaft).

These low injection times imply a high heterogeneity of the air-fuel mixture during the intake phase, a heterogeneity that remains largely until the end of compression and which generates an increase in unburned hydrocarbon emissions in the best case. or even a very difficult start because of a wealth of random mixture in the vicinity of the spark plug. MS \ RENO36EN.dpt The solutions mentioned above do not improve this situation of heterogeneous mixing.

WO 00/50763 proposes a heated nose nozzle to reduce unburned hydrocarbon emissions during the cold start phase. An Open Valve (IVO) and Closed Valve (IVC) injection strategy is used to optimize emissions. However, this strategy has the disadvantages described above.

It is also proposed in document JP 2003 247443 the use, in cold operation, by indirect injection, of a variable lift system of intake valves to generate high flow rates in the combustion chamber. The fuel injection is performed in phase with this low valve lift. These high flow rates ensure a better spray in the combustion chamber and, consequently, reduce polluting emissions.

It is further proposed in GB 2 281 101 a vaporized fuel injection device. It incorporates an injector that delivers fuel into a cavity equipped with a heating element. This cavity is fed by a source of air under pressure or at atmospheric pressure. This device allows a good vaporization of the fuel leaving the cavity and, consequently, a reduction of polluting emissions.

The object of the invention is to provide a fuel injection method obviating the disadvantages identified above and to improve the fuel injection methods known from the prior art. In particular, the invention proposes a method for injecting MS \ RENO36FR.dpt with simple fuel which makes it possible to substantially improve the homogeneity of the air-fuel mixture, in particular in engine start-up phases where strategies are used. injection of the open-valve type. In addition, the invention proposes an injection system implementing such an injection method.

The method according to the invention makes it possible to inject a fuel into an intake manifold of a heat engine. It is characterized in that it comprises a first injection mode in which, during each cycle of the engine, a fractional fuel injection phase comprising a plurality of fuel injection periods and such that each period of fuel injection is carried out. fuel injection is temporally separated from another injection period by a period during which there is no fuel injection.

Each fractional fuel injection phase may comprise between 2 and 10 fuel injection periods. The split fuel injection phase can take place while an intake valve is open. The first injection mode can be implemented as long as a delay triggered by the engine start is not over and / or until the engine has reached a threshold temperature. Following the first mode of injection, it is possible to implement a second mode of injection characterized by a non-fractionated injection phase during each cycle of the engine, this injection phase starting while the valve or valves admission are closed. The fuel injection system according to the invention comprises hardware and software means for implementing the method defined above.

The heat engine according to the invention comprises a fuel injection system defined above. The motor vehicle according to the invention comprises a fuel injection system defined above or a heat engine defined previously.

The accompanying drawings show, by way of example, two embodiments of a fuel injection method according to the invention and an embodiment of an injection system implementing such a method.

FIG. 1 is a graph showing intake valve lift versus crankshaft position and a fuel injection phase for 300 rpm engine speed in the start-up phase, the injection taking place according to FIG. a method known from the prior art.

FIG. 2 is a graph showing the intake valve lift versus crankshaft position and a fuel injection phase for an engine speed of 1200 rpm in the accelerated idle phase, the injection taking place according to a method known from the prior art.

Fig. 3 is a graph showing intake valve lift as a function of crankshaft position and a fuel injection phase, the injection taking place according to a first embodiment of the invention. FIG. 4 is a graph showing the intake valve lift as a function of the crankshaft position and a fuel injection phase, the injection taking place according to a second embodiment of the invention. invention.

FIG. 5 is a graph showing the time evolution of the engine speed in a transient start-up phase.

Figure 6 is a diagram of an embodiment of an injection system according to the invention.

The injection system 1 shown in FIG. 6 mainly comprises injectors 3 (an injector per cylinder) and a computer 2. It makes it possible to inject a fuel into a heat engine, particularly into the intake ducts of an engine. internal combustion, indirect injection and spark ignition. The engine is for example used to drive a motor vehicle.

The computer 2 allows the control of the injectors. In particular, it makes it possible to control the instants of start of fuel injection and end of fuel injection. It includes for this purpose control outputs connected to each of the injectors. It further comprises a set of inputs connected to different sensors. For example, an engine temperature sensor 6 and / or an engine speed sensor and / or a crankshaft position sensor and / or an engine start detection sensor 7.

The computer comprises a first software means 4 and a second software means 5 for controlling the operation of the injection system. The first software means 4 allows the implementation of a first injection mode MS \ RENO36FR.dpt and the second software means 5 allows the implementation of a second injection mode. These software means include for example computer programs.

The principle of the operating method according to the invention is to split, in a first injection mode, the fuel injection into the engine. Thus, for each cylinder of the engine and for each cycle of the engine, during a fractional injection phase, the quantity of fuel is injected into an inlet duct of the cylinder several times. As a result, a split injection phase comprises a plurality of time-spaced injection periods, each injection period permitting a portion of the amount of fuel required for the desired combustion to be sent. Thanks to such a principle, the seeding of the air by the fuel is more homogeneous at the end of admission. The homogenization is much faster in the compression phase until the ignition of the mixture. Thus, the preparation of the mixture in the combustion chamber during cold engine operation is improved during the starting phase. Such an injection strategy is implemented during injection in open valves (IVO).

The homogeneity of the seeding of the air by the fuel is of course the better the number of injection periods per injection phase is important. However, the engine control and the control of the injectors is even more difficult to manage that the number of injection periods per injection phase is important.

Preferably, each injection phase comprises a number of injection periods worth any integer value between two and ten. The choice of one of these values is based on a compromise involving various parameters such as the MS \ RENO36FR.dpt

The nature of the fuel used (in particular its volatility), the internal aerodynamics of the intake ducts and the combustion chambers, (a more turbulent flow favors the homogenization of the air-fuel mixture), the minimum duration of injection which can be performed by the injectors and the ability of the computer to handle a large number of injection periods.

In a first embodiment of an injection method according to the invention, an injection phase comprising two injection periods is used in a first injection mode. Such a principle is shown in FIG. 3, in which the features Tif and Ti2 represent the two injection periods.

In a second embodiment of an injection method according to the invention, an injection phase comprising five injection periods is used in the first injection mode. Such a principle is represented in FIG. 4, in which the lines Tif, Ti2, Ti3, Ti4 and Ti5 represent the five injection periods represented in FIG.

The different injection periods may have substantially identical durations as in the first embodiment of the method. The different injection periods may have substantially different durations as in the second embodiment of the method shown in FIG. 4.

Similarly, the spacings or time periods separating each injection period from the subsequent injection period may be different. MS \ RENO36EN.dpt A fuel injection process is described below in more detail following engine start. This description is made with reference to FIG.

In a first start-up phase while the engine is driven by the starter, a first injection mode is used in which the injection phases comprise several injection periods while the intake valves are open (the walls of the engines). intake ducts and valve tulips being cold). In the case of operation of the engine with a fuel currently marketed today, this first injection mode reduces the quantities injected during the start-up phase by better fuel vaporization and better homogeneity of the air-fuel mixture. . As a result, polluting emissions, in particular unburned hydrocarbon emissions, are reduced.

Moreover, this first mode of injection makes it possible to reduce the starting time in very cold weather thanks to a better preparation of the air-fuel mixture.

In the case of operation of the engine with a less volatile fuel such as ethanol, the first mode of injection must allow to overcome or significantly reduce the use of solutions such as fuel heating, to make possible cold start of the engine.

In a second phase, after the start-up phase (that is to say when the motor is no longer driven by the starter), the first injection mode in which the injection phases comprise several injection periods while the intake valves are open (the walls of the intake ducts and the MS \ RENO36FR.dpt valve tulips being cold). This use of the first injection mode makes it possible, whatever the type of fuel used, to reduce the polluting emissions and in particular the emissions of unburned hydrocarbons.

These first and second phases are represented by the double arrow IVO + split inj. in Figure 5.

In a third phase, once the valve tulips have reached a sufficient temperature (so that the fuel injected vaporizes sufficiently in contact with the tulips of the intake valves), a second injection mode is used in which the injector is injected. only once the fuel and start this injection while the intake valve (s) are still closed IVC. Indeed, the temperature of the valve tulips can then be used to produce a sufficient vaporization and a homogeneous air-fuel mixture. The fuel sent in the form of micro-drops on the valve tulips is, because of the temperature thereof, partially converted into gas which is then easily mixed with the combustion air. The air-fuel mixture is then more homogeneous than that obtained with the first injection mode. This third phase is represented by the double arrow IVC in FIG.

For example, it is possible to use the second injection mode as soon as the temperature of the valves is higher than a threshold temperature, for example between 50 ° C. and 100 ° C. To avoid having to determine the temperature of the valve tulips, it is assumed that this temperature is reached after a first period of 5 to 10 seconds (typically 6 seconds) after the start of rotation of the engine during a start at cold. Thus, the start of rotation of the motor, detected by the sensor 7, is used by the computer 2 to trigger a timer whose value is the first previously mentioned duration MS \ RENO36FR.dpt. As soon as this time delay expires, the injection process switches from the first injection mode to the second injection mode.

When the engine is warm, when starting, the duration of this delay can be reduced or reduced to zero if the engine is hot enough. To do this, the temperature sensor 6 is used.

To optimize the efficiency of the second injection mode, the jet of fuel from the injector must be properly targeted to the intake valve (s), without impacting upstream the intake duct.

The principle of the invention is applicable to internal combustion engines with indirect injection controlled ignition, whether of natural suction type or supercharged type.

Thanks to the invention, the cold starts are improved when using fuels of the ethanol or FlexFuel type, pollutant emissions, especially unburned hydrocarbon emissions are reduced in the cold operating phase. wherein the catalyst is not yet primed.

The principle of the invention is simple and more effective than prior art solutions which involve additional means of heating or spraying. MS \ RENO36FR.dpt

Claims (8)

claims : 1 method for injecting fuel into an intake manifold of a heat engine, characterized in that it comprises a first injection mode in which, during each engine cycle, an injection phase is carried out; fractionated fuel comprising several fuel injection periods and such that each fuel injection period is temporally separated from another injection period by a period during which there is no fuel injection. 2. Fuel injection method according to claim 1, characterized in that each fractional fuel injection phase comprises between 2 and 10 periods of fuel injection. Fuel injection method according to claim 1 or 2, characterized in that the fractional injection phase of fuel takes place while an intake valve is open. 20 4. fuel injection method according to one of the preceding claims, characterized in that the first injection mode is implemented as a delay triggered by the engine start is not expired and / or so the engine has not reached a threshold temperature. 25 5. fuel injection method according to the preceding claim, characterized in that, following the first injection mode, it implements a second injection mode characterized by a non-fractionated injection phase during each cycle of the engine, this injection phase starting while the intake valve or valves are closed. MS \ RENO36FR.dpt15 6. Fuel injection system (1) comprising material means (2, 3, 6, 7) and software (4, 5) for implementing the method according to one of the preceding claims. A heat engine comprising a fuel injection system according to claim 6. 8. Motor vehicle comprising a fuel injection system according to claim 6 or a heat engine according to claim 7. MS \ RENO36FR.dpt