FR3080890A1 - METHOD FOR MANAGING THE INJECTION AND IGNITION OF AN INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

The subject of the present invention is a method for managing the supply and ignition of an internal combustion engine with the following steps: a first threshold (S1) of speed of rotation and a second threshold (S2) of speed of rotation higher than the first are predetermined, • when approaching a top dead center, a prediction of the speed of rotation of the engine during the passage of the upward dead center is made, and • when a phase of fuel injection and ignition, a prediction of rotational speed at the next top dead center is between the two thresholds (S1, S2) of rotational speed, then the power is off but the ignition is maintained for the next engine time while if the rotational speed prediction is lower than the two thresholds (S1, S2) rotational speed, then the power and ignition are cut off.

Description

The present invention relates to a method for managing the injection and ignition of an internal combustion engine. It relates more particularly to the management of an engine when it is stopped to avoid reverse rotation of the engine with unburned fuel or with unwanted combustion.

It is therefore a question here of managing a four-stroke engine operating according to the Beau de Rochas (or Otto) cycle, that is to say engines commonly called petrol engines. More particularly, the present invention relates to an indirect injection engine but not exclusively.

In an engine, when it stops, it may happen that to reach its equilibrium position, the engine turns backwards. It is then advisable to avoid at this time that combustion comes to drive the engine in this direction of rotation. This is to be avoided more particularly when the engine is fitted with a dual mass flywheel (better known as Dual Mass Flywheel or the acronym DMF in English). Indeed, backward rotation of such a dual mass system accelerated by unwanted combustion can be very damaging for this system and is therefore to be avoided.

It is already known, in an attempt to predict a rear rotation of the engine, to predict its speed of rotation when passing from the next top dead center. Depending on this speed, engine shutdown and possible reverse rotation can be predicted. It is then planned to cut the fuel supply (injection cut off) and the engine ignition.

The present invention aims to improve the existing methods of the prior art. It starts from an original observation which was made by the Inventors. It has in fact been noted that the management of the stopping of an engine, called a petrol engine, according to the techniques known from the prior art leads to an emission of unburned hydrocarbons in the exhaust in the case where this engine stopping is not wanted by the driver but by unintentional stalling for example.

The present invention therefore more particularly aims to provide a method for managing an engine limiting the emission of unburned fuel (petrol) in the exhaust, in particular when the engine is stopped / restarted.

To this end, the present invention provides a method for managing the power supply and the ignition of an internal combustion engine in which, when approaching a top dead center, a prediction of the engine rotation speed. when passing from top dead center to come is performed.

According to the invention, a first speed threshold and a second speed threshold greater than the first are predetermined, and when after a fuel injection and ignition phase, a prediction of speed at the next top dead center is located between the first two and the second speed thresholds, then the power is cut but the ignition is maintained for the next engine time while if the speed prediction is lower than the first two and second speed thresholds, then the power and ignition are cut.

It is thus provided in this process to come and burn fuel while keeping the ignition active without, however, injecting fuel again into the engine when an engine stop is in sight. Except in very specific cases, all the fuel injected is then burned, which of course limits the emission of unburnt hydrocarbons during a next start.

In such a method of managing the power and ignition of an engine, it can also be provided that, when after a fuel injection and ignition phase, a prediction of rotation speed at the next point dead high is located above the two first and second speed thresholds, so power and ignition are maintained for the next time. This concerns in particular the configuration in which the engine rotation speed is certainly low but the engine does not seem to be stopping imminently (more than two passages at least by a top dead center provided).

To complete this process for managing the power and ignition of an engine, it is proposed to define, for example, four states of the engine:

• first state: injection and ignition are maintained, • second state: injection is cut and ignition is maintained, • third state: injection and ignition are cut, and • fourth state: l injection is maintained and the ignition is switched off.

A complete decoupling of the injection function from the ignition function is carried out here. In this configuration, the following management of power (injection) and engine ignition is proposed:

• when the engine is in the second state it goes into the third state when the speed prediction at the next top dead center is less than a third speed threshold and in the fourth state otherwise; and / or • when the engine is in the third state it goes into the fourth state when the speed prediction at the next top dead center is greater than a fourth speed threshold and remains in the third state otherwise; and / or • when the engine is in the fourth state:

- it goes into the first state when the speed prediction at the next top dead center is greater than a fifth speed threshold,

it goes into the second state when the speed prediction at the next top dead center is between the fifth speed threshold and a sixth speed threshold lower than the fifth threshold, and

- it goes into the third state otherwise.

The present invention also provides a device for managing an engine, characterized in that it includes means for implementing each of the steps of a method for managing the power supply and the ignition of a motor as described above.

The present invention is now illustrated by a nonlimiting embodiment using the attached drawing in which:

FIG. 1 illustrates a "conventional" stopping of a combustion engine, and

- Figure 2 is a flowchart illustrating an embodiment of a method of managing power and ignition of an engine.

Figure 1 is a schematic diagram illustrating the time on the x-axis and a speed of rotation on the y-axis. The curve drawn on this diagram shows the actual speed of rotation of an engine when it stops.

On the diagram, three lines are drawn. These are the equation lines:

y = S1, for example y = 200 rpm y = S2, for example y = 400 rpm, and y = S3, for example y = 600 rpm.

Of course, the numerical values given are given purely by way of illustration and are in no way limiting. Those skilled in the art note that these values are rounded values in order to simplify the description which follows.

Here we observe an engine that stops and we want to prevent, or limit as much as possible, the reverse rotation of the engine with unburned fuel or with unwanted combustion. The rotation is said to be reverse with respect to the usual direction of rotation of the motor.

On the left of the diagram, we notice that the motor rotation speed decreases while remaining however higher than the value S3. Before reaching each top dead center, a prediction of the engine speed at this next top dead center is calculated. Various methods can be used to make this prediction. The document FR2995939 proposes for example such a prediction method.

An arrow 2 shows diagrammatically in FIG. 1 the first fuel injection carried out while the engine rotation speed has dropped below the speed threshold S3. It is assumed in the present embodiment that the engine is an engine operating according to the Beau de Rochas (or Otto) cycle, more commonly called gasoline engine, and that it includes a fuel supply system - gasoline - by injection. indirect.

An arrow 4 shows diagrammatically in FIG. 1 the instant at which a prediction of rotational speed is made after the injection of petrol but before reaching the next top dead center. A star 6 symbolizes the prediction made and is plotted on the time line called TDC1 corresponding to the transition to the next top dead center.

In the example illustrated, the prediction of rotation speed (which is assumed to be good and which is accomplished) is between 200 and 400 rpm, that is to say between the values S1 and S2.

The prediction made here then suggests that the engine will still go through another top dead center but will stop afterwards. The strategy adopted here is then to carry out an ignition (flash 8) to come and burn the fuel - gasoline - which has been injected but not to inject any more fuel thereafter.

Note that the combustion produced after ignition (lightning 8) contributes to slightly increasing the engine speed. Before arriving at the next top dead center, a new prediction of the speed of rotation (arrow 10) is carried out to estimate the speed of rotation of the motor at top dead center according to TDC2. This prediction is symbolized by a second star 12. This prediction confirms the previous one in that it is again between the threshold values S1 and S2. This therefore confirms that the engine is going to stop. It is therefore planned to cut and fuel injection and ignition. As illustrated, the engine speed then decreases to 0 rpm and the engine stops.

Below the x-axis, it indicates the operating state of the engine. In this example, the motor goes through three states:

• first state = IGN + INJ: the engine is operating normally, the INJ injection and IGN ignition are commanded at each shift to top dead center;

• second state = IGN + NOJNJ: the engine will stop but not immediately, the injection is cut (NOJNJ) but the IGN ignition works;

• third state = NOJGN + NOJNJ: the engine will stop imminently, the injection and ignition are cut (NOJGN and NOJNJ).

However, even if most of the engine stops occur as shown in Figure 1, there are other cases to consider. Figure 2 tries to identify all the cases. It is proposed to define four states, including the three states above. A fourth state: NOJGN + INJ is defined when it is decided not to start the ignition but to inject fuel. This state aims to achieve an imminent restart of the engine with ignition planned during the next combustion cycle.

In Figure 2 are shown the four states previously announced and the conditions for switching from one state to another are indicated. In this figure, the values S1, S2 and S3 correspond to those of Figure 1 if it is the same engine. As indicated, these values are purely illustrative. They do not correspond to a real example if only because of their roundness.

The first assumption is that the engine is running. Its engine speed is then higher than the third threshold S3 (600 rpm). Before each passage of a piston at its top dead center, the speed of rotation of the engine during the passage of this piston at its top dead center is estimated by an engine control and management system and the value of this estimate is called N_Tdc_Estim in Figure 2 and in this description. This estimated value is then compared with the three threshold values S1, S2 and S3.

At the start with the engine running, its speed is greater than the S3 threshold and to operate it, it needs fuel and the ignition function to burn the injected fuel. The state of the engine is therefore the first state (IGN + IN J). In addition, as long as the engine is running "normal", each time the value of the estimate N_Tdc_Estim remains above the threshold S3. As indicated by a loop at the IGN + INJ state, this state is maintained when N_Tdc_Estim is greater than the S3 threshold but also when it is between the S2 threshold and the S3 threshold. We can indicate that this state is the state in which we are in an intentional starting phase of the engine.

It seems easier for the understanding of the description to use numerical values rather than names for the thresholds. It is important to note that there are at least two thresholds (three here but possibly more) which are to be defined for each engine. Still for the sake of clarity and / or simplification, we consider that:

• the threshold S1 corresponds to a speed of 200 revolutions per minute (rpm or rpm), • the threshold S2 corresponds to a speed of 400 revolutions per minute and • the threshold S3 corresponds to a speed of 600 revolutions per minute.

We now assume that the engine is entering the stop phase. At some point or other, the value of the N_Tdc_Estim estimate will fall below 600 rpm. As long as this value remains above 400 rpm, it is estimated that the engine can remain in its first state and the ignition and injection continue to operate normally.

If the value of N_Tdc_Estim is now between 200 and 400 rpm, then we choose not to inject fuel but to let the ignition work to burn the fuel that has already been injected. Here we are in the case described with reference to Figure 1 where it is estimated that the engine will not only pass the next top dead center but also the next.

If now the value of N_Tdc_Estim immediately becomes less than or equal to 200 rpm, the injection and ignition are cut off. The engine will stop quickly and nothing is done to stop it.

After having analyzed the various situations that can occur when the engine is in the first state, a similar analysis is made for the second state (IGN + NOJNJ).

First, if the engine speed increases again, this restart is supported by fuel injection. However, there is no need to operate the ignition since in this state there was no fuel injection. The engine then goes into the fourth state (NOJGN + IN J) if the engine speed is greater than 400 rpm. Finally, if the rotation speed decreases or at least remains less than or equal to 400 rpm, then the engine goes into the third state (NOJGN + NOJNJ) without fuel injection or ignition.

Once in this third state, it can be decided that either the engine actually starts and then petrol is injected again, or the engine speed remains low and the engine is kept in its third state. We can consider here that the engine will restart if N_Tdc_Estim becomes greater than 600 rpm. In this case, the engine goes into the fourth state (NOJGN + IN J) since there is no need to operate the ignition, no fuel having been injected just before. This can correspond to the case of a car driven downhill for example or that you push to start it.

Finally, when the engine is in the fourth state, if the rotation speed prediction is low, i.e. less than 200 rpm, then the engine goes into the third state (NOJGN + NOJNJ) and its stop is imminent.

If the predicted rotational speed is "average", that is to say between 200 and 600 rpm, then the gasoline which has just been injected is burned but no fuel is injected again: the engine then goes into its second state (IGN + NOJNJ). It is estimated here that the combustion which will be carried out by the ignition will not be sufficient to restart the engine.

On the other hand, if the engine starts again, that is to say if the speed of rotation predicted at the next top dead center returns above the first threshold of 600 rpm, then the engine returns to its first nominal operating state .

FIG. 2 provides only three distinct rotational speed thresholds S1, S2, S3, corresponding to the thresholds shown in FIG. 1. However, other thresholds can be envisaged. So for example when the engine is in its second state, it can be predicted that it will go into the third state when the estimate of rotation speed is less than a fourth threshold (for example 450 rpm with the values taken above ) and in the fourth state otherwise. Likewise, another threshold can be defined when the engine is in the third state and two other thresholds (fifth and sixth) can be chosen in the fourth state to determine the changes (or not changes) of state.

The process proposed here thus makes it possible to manage the stopping of an engine by limiting the emission of unburnt hydrocarbons during the next start. It is original here to manage ignition and injection independently of each other.

This process can be implemented without a specific sensor. Therefore, it does not require specific means and can be implemented without adding additional material cost.

Of course, the present invention is not limited to the embodiments described above and to the alternative embodiments proposed. It also relates to the 15 variant embodiments within the reach of those skilled in the art.

Claims (7)

1. Method for managing the power supply and the ignition of an internal combustion engine in which, when approaching a top dead center (TDC1, TDC2), a prediction of the engine rotation speed during coming from top dead center to come 5 is carried out, characterized in that a first threshold (S1) of rotational speed and a second threshold (S2) of rotational speed greater than the first are predetermined, and in that, when after a fuel injection phase and ignition, a prediction of rotation speed at the next top dead center (TDC1, TDC2) is between the first and second thresholds (S1, S2) of rotation speed, then the power supply is cut 10 but the ignition is maintained for the next engine time while if the prediction of rotation speed is lower than the first and second thresholds (S1, S2) of rotation speed, then the supply and the ignition are cut. 2. Method for managing the power supply and the ignition of an engine according to claim 1, characterized in that, when after a fuel injection phase 15 and ignition, a prediction of rotation speed at the next top dead center (TDC1, TDC2) is located above the two first and second thresholds (S1, S2) of rotation speed, then the power supply and the ignition are maintained for the next time. 3. Method for managing the power supply and the ignition of an engine according to one of claims 1 or 2, characterized in that four states of the engine are defined: • first state: injection and ignition are maintained, • second state: injection is cut and ignition is maintained, • third state: injection and ignition are cut, and • fourth state: l injection is maintained and the ignition is switched off. 25 4. A method of managing the power supply and the ignition of an engine according to claim 3, characterized in that when the engine is in the second state it goes into the third state when the speed prediction at the next dead center high is less than or equal to a third threshold (S3) of rotation speed and in the fourth state otherwise. 5. Method for managing the power supply and the ignition of an engine according to one of claims 3 or 4, characterized in that when the engine is in the third state it goes into the fourth state when the prediction speed at the next top dead center is greater than a fourth speed threshold and remains in the third state otherwise. 6. Method for managing the power supply and the ignition of an engine according to one of claims 3 to 5, characterized in that when the engine is in the fourth state: • it goes into the first state when the speed prediction at the next point 5 top dead is greater than a fifth speed threshold, • it goes into the second state when the speed prediction at the next top dead center is between the fifth speed threshold and a sixth lower speed threshold at the fifth threshold, and • it goes into the third state otherwise. 10 7. An engine management device, characterized in that it comprises means for the implementation of each of the steps of a process for managing the power supply and the ignition of an engine according to the one of claims 1 to 6.