FR3103224A1 - Method of managing the injection of an internal combustion engine - Google Patents

Abstract

Method for managing the power supply of an engine (100) in which: - when approaching a top dead center by a piston (200), instructions concerning future combustion are established, - when approaching of a top dead center (TDC), a prediction of the engine rotation speed (N_TDC) when passing the upcoming top dead center is carried out, - a first rotation speed threshold (S1) and a second threshold ( S2) of rotational speed are predetermined, - when a prediction of rotational speed at the next TDC is between the two thresholds (S1, S2), then the setpoint corresponding to the start of fuel injection is modified so that fuel injection only occurs after a possible passage of TDC, and - when a prediction of rotation speed at the next TDC is below the first threshold (S1), the next planned combustion is inhibited. Abstract figure: Figure 1

Description

Method for managing the injection of an internal combustion engine

The present invention relates to a method for managing the injection of an internal combustion engine. It relates more particularly to the management of an engine at the time of stopping the latter in order to avoid a reverse rotation of the engine with undesired combustion.

The present disclosure relates to the field of four-stroke engine management operating according to the Diesel cycle, that is to say with compression ignition, but it also relates to engines operating according to the Beau de Rochas (or Otto) cycle, i.e. spark-ignition engines.

In an engine, when it stops, it may happen that to reach its equilibrium position, the engine rotates backwards. It is then advisable to avoid at this moment that combustion comes to drive the motor 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, a reverse rotation of such a dual-mass system accelerated by undesired combustion can be very damaging for this system and is therefore to be avoided.

It is already known, to attempt to predict a reverse rotation of the engine, to predict its speed of rotation when passing the next top dead center. Depending on this predicted speed, a stoppage of the motor and a possible reverse rotation can be predicted. Provision is then made to cut off the fuel supply (injection cut-off) and/or engine ignition.

The document FR2995939A1 proposes a method for estimating the speed of an engine in a predetermined position and in certain cases for inhibiting the fuel injection and/or the ignition control.

With such a method, reverse rotation can be predicted by estimating the speed (of engine rotation) at top dead center (of a piston in a cylinder) a few degrees, for example 24° (by way of non-limiting illustration), before this top dead center. If the predicted speed is close to zero or even negative, then top dead center will potentially not be reached by the piston and there is a good chance that the motor will spin backwards. In this case, the control of the injectors and/or the spark plugs is interrupted to avoid accentuating the reverse rotation and then risking damage to the dual-mass flywheel, the secondary mass of which is still driven forwards.

The instructions concerning the combustion (amount to be injected and angular position for the injection) are most often determined before predicting the rotational speed of the engine at top dead center so as to be able to effectively prepare this combustion. By way of illustration, the setpoints concerning the combustion can for example be determined at 80° before the top dead center. In some cases, in order to optimize (minimize) pollutant emissions, the start of combustion may take place, under certain conditions, before the piston has crossed top dead center.

Thus, in certain critical situations in which a significant speed variation occurs, for example during a violent stall during which the rotational speed of the engine can drop from 1000rpm to 0 in 60°, the conditions between the moment of the calculation of the combustion instructions and the moment when they must be put into practice change a lot.

It is therefore advisable to prevent combustion from being initiated before top dead center in the event that the direction of rotation of the engine changes between the moment when combustion begins and top dead center.

The object of the present invention is therefore to provide a method for managing the supply of an internal combustion engine on approach to an improved top dead center making it possible to avoid carrying out a combustion driving the engine in reverse rotation, even in severe stall conditions.

Summary

The present disclosure improves the situation by proposing a method for managing the power supply of an internal combustion engine in which:

- at the approach of a top dead center by a piston in the compression phase, instructions concerning a combustion to come, in particular a fuel injection start instruction, are established, and a prediction of the speed of rotation of the engine when passing from top dead center to come is carried out,

- a first rotational speed threshold and a second rotational speed threshold greater than the first are predetermined,

when a rotational speed prediction at the next top dead center is between the two rotational speed thresholds, then the setpoint corresponding to the start of fuel injection is modified such that fuel injection only occurs 'after a possible passage of the top dead center, and

when a rotational speed prediction at the next top dead center is less than the first threshold, the next predicted combustion is inhibited.

It is thus proposed here in a completely original way to modify the fuel injection instructions, which is unusual in the management of internal combustion engines. This modification of the injection instructions has a very limited impact on the emission of pollutants and is all the more acceptable since the cases where the instructions have to be modified are very limited and infrequent. Above all, this modification makes it possible to mechanically protect the engine by preventing combustion in a cylinder from driving the engine in its opposite direction of rotation. The proposed method makes it possible to choose a relatively low first threshold, that is to say the speed threshold below which no more fuel is injected and where it is therefore decided to stall the engine, which increases the driving pleasure in that the engine stalls less often.

In this process for managing the power supply to a motor, it is also possible to provide that, when a rotation speed prediction at the next top dead center is above the two rotation speed thresholds, then the instructions concerning the upcoming combustion are executed. This is a case where it is deemed that there is no risk of engine stalling.

To take account of certain parameters, for example the speed of rotation of the engine, provision can be made in the method below to also have an initialization step during which it is determined at what moment the prediction of the speed of the engine when passing from top dead center to come is carried out. This initialization step can for example be carried out after each passage to top dead center of a piston at the end of compression.

According to a particular embodiment, the step of predicting the rotational speed of the engine during the passage to the next top dead center is triggered when the position of the engine is for example between 18° and 36° before said top dead center.

To guarantee that the injection is not carried out before the top dead center considered, in the case where the engine comprises a flywheel provided with teeth and an associated sensor cooperating with means for determining the direction of rotation of the flywheel to determine, on the one hand, the position of the pistons of the engine and, on the other hand, the speed of rotation of the engine, it is then advantageously provided that when a prediction of speed of rotation at the next top dead center is between the two rotational speed thresholds, then the setpoint corresponding to the start of fuel injection is modified so that fuel injection only occurs after detection of a falling edge of a tooth and a rising edge of a tooth and confirmation that the direction of rotation of the motor has not changed, one of the edges corresponding either to the position of the top dead center considered, or to the first edge after said top dead center.

To limit the calculation load of the calculation means on board the engine, the method described above is only implemented when the rotational speed of the engine is below a third threshold.

The present invention also relates to a device for managing an engine, characterized in that it comprises means for implementing each of the steps of a method for managing the supply of an engine described below. above.

The invention also relates to an internal combustion engine, characterized in that it comprises an engine management device defined in the preceding paragraph. Such an engine may for example be a diesel-type engine, that is to say a compression ignition engine and/or an engine comprising a dual-mass type flywheel.

Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the appended drawing, on which:

Fig. 1

illustrates a flowchart for the implementation of a method for managing the power supply of an internal combustion engine, and

Fig. 2

schematically shows an engine for implementing the method of Figure 1.

The drawing and the description below contain, for the most part, certain elements. They may therefore not only serve to better understand this disclosure, but also contribute to its definition, where applicable.

Reference is now made to FIG. 2. This represents very schematically an internal combustion engine 100, for example but not exclusively a so-called diesel or compression ignition engine.

In a manner known to those skilled in the art, in such an engine, at least one piston 200 moves in a cylinder back and forth between a position called top dead center (or PMH or even TDC) and a position called bottom dead center (or PMB or BDC). It rotates a crankshaft 300 which rotates 180° when piston 200 moves from top dead center to bottom dead center or vice versa. The crankshaft 300 has a toothed wheel which cooperates with a sensor 400 in order to know the position of the crankshaft and of the engine pistons. An engine cycle (intake, compression, combustion and expansion, exhaust) takes place over two revolutions of the crankshaft 300, i.e. 720°. When an angular measurement or an angular position relates to the crankshaft, it is usually specified, and in the remainder of the description, by the addition of the three letters CRK.

The sensor 400 communicates the measured data to an electronic unit 500 which most often takes the form of a microprocessor within a computer, for example an engine control unit known by the acronym ECU (Engine ControlUnit). This electronic unit 500 also communicates with an injection system 600 which makes it possible to inject fuel and to control the injection in a combustion chamber associated with the piston 200.

The purpose of the process described below is to manage the supply (injection) of fuel to the engine at very low speeds, when there is a risk that the engine will stall, i.e. stop running. . An engine stalls when the resistive torque, or load, applied to it is greater than the engine torque created by the combustions within the combustion chambers and transmitted by the pistons to the crankshaft. The engine stalls when a 200 piston fails to reach top dead center. In this case, due to the pressure in the corresponding combustion chamber, it is driven towards its bottom dead center, then inducing a rotational movement of the crankshaft in the opposite direction to its normal direction of rotation. This type of rotation will be called “reverse rotation” in the following.

When the motor stops, reverse rotation almost always occurs. When the engine is scheduled to stop, this reverse rotation is limited and the forces acting on the pistons correspond substantially to the compression carried out in the cylinder in the compression phase when there is no combustion. In addition, when there are several pistons, the forces exerted on some compensate those exerted on others, limiting the torque exerted on the crankshaft. It is advisable to avoid having a combustion in a cylinder which would drive the engine in reverse rotation. This is especially true when the engine is fitted with a dual-mass flywheel. In this case, the crankshaft toothed wheel is associated with an auxiliary mass connected to the toothed wheel by springs. The auxiliary mass is mechanically linked to the gearbox and to the drive wheels. Thus, the mechanical assembly associated with the auxiliary mass has a large inertia and a change in rotation of the auxiliary mass supposes large constraints. When the engine stalls suddenly, the auxiliary mass driven in rotation by its associated inertia exerts a strong stress on the springs connecting it to the toothed wheel which comes to a sudden stop. If, when the toothed wheel stops abruptly and the auxiliary mass is still rotating in the normal direction of rotation, the toothed wheel is driven in reverse rotation by combustion in a combustion chamber, then the stresses exerted on the springs connecting the auxiliary mass to the toothed wheel are increased accordingly, thus increasing the risk of breakage at the level of these springs.

Such a case may occur in situations which are exceptional but which may exist. Conventionally in an engine, when the engine speed is relatively low, before each passage of top dead center of a piston in the compression phase, the rotational speed of the engine at top dead center is predicted in order to be able to anticipate engine stalling: if it is predicted that the engine will stall, that is to say that the predicted speed at the next top dead center is below a given threshold, it becomes unnecessary to inject fuel and the injection is then cut off. However, in the case of very sudden stalling, it is possible that the engine rotation speed estimated for the next passage to the top dead center of a piston is quite high, that is to say greater than the aforementioned threshold. , for a fuel injection to be commanded. If then the injection is programmed to be started before the arrival at the top dead center of the piston, and that the piston begins its descent towards the bottom dead center in the opposite direction of rotation just before its arrival at the top dead center after the injection of fuel, then the latter will burn and this combustion will forcefully push the piston towards its bottom dead center accentuating the acceleration of the toothed wheel in reverse rotation. There is therefore a need here to improve the management of an engine, in particular an engine equipped with a dual-mass flywheel, to avoid such a situation.

To avoid such a case, and other cases of stalling which could lead to combustion causing the engine to rotate in reverse, the method for managing the fuel supply to the engine illustrated in figure 1 is proposed.

In known manner, as mentioned above, provision is made to make a prediction of the rotational speed of the engine, corresponding to the rotational speed of the crankshaft 300, before the piston 200 reaches its top dead center corresponding to the end of a compression phase. A method for thus predicting the rotational speed of the engine is for example explained in the document FR2995939. This last document also mentions the determination of a threshold such that if the predicted speed is lower than said threshold, the fuel injection is cut off.

A first step 10 (FIG. 1) consists in determining when the speed prediction must be performed. It must be carried out early enough to be able to act according to the result of the prediction but must not be too hasty to have a reliable prediction. During this step, a value called TRIG is thus initialized. This value is expressed in °CRK, for example 24°CRK, which means that the prediction of the speed of rotation when the piston 200 concerned will reach its top dead center is made when the crankshaft 300 is in a rotated position of 24 ° relative to the position it must have when the piston 200 is at its top dead center. This value of 24°CRK may be dependent on the rotational speed of the engine.

During a monitoring step 20 of the process, the sensor 400 measures the position (CRK) of the crankshaft and determines when this position corresponds to the position TRIG defined previously. As long as the TRIG position is not reached (result N), monitoring step 20 is repeated.

When the position of the crankshaft 300 corresponds to the predetermined position TRIG, a prediction step 30 is launched. It is appropriate here to predict what will be the speed of rotation of the engine when the piston 200 reaches the next top dead center corresponding to an end of the compression phase. It is assumed here that the piston 200 will reach this top dead center even if indeed the prediction may be that the piston will not reach this position. It is assumed for example that if N_TDC is the predicted speed, this speed will be positive if it is predicted that the piston 200 will reach the next top dead center and that it is negative otherwise.

Two rotation speed thresholds are predetermined: S1 and S2. The function of these thresholds will be described below. Their values depend on the motor structure. These thresholds can be fixed once and for all for a type of engine and for the whole life of this engine.

It is assumed by way of non-limiting and purely illustrative example that the thresholds S1 and S2 take the following values:

S1 = 200 rpm or about 21 rad/s

S2 = 400 rpm or approximately 42 rad/s.

Threshold S2 is the threshold beyond which there is no immediate risk of engine stalling. In other words, if the predicted speed N_TDC is greater than this threshold S2, it is estimated that the piston 200 will definitely cross the next top dead center.

Conversely, threshold S1 corresponds to a limit for which it is estimated that it is not possible to prevent the engine from stalling very soon.

Thus, as shown in Figure 1, if the N_TDC value is greater than S2 (result O, i.e. yes, when comparing N_TDC with S2), then no particular action is taken and only one reset action 40 of the TRIG value (depending on the engine rotational speed for example) is performed before continuing to monitor (monitoring step 20) the angular position of the crankshaft 300.

If the predicted value N_TDC is lower than the threshold S1, then an action is carried out during an inhibition step 50 so that the next planned fuel injection is cancelled. It is in fact pointless to inject fuel if an engine stop appears inevitable.

When the predicted value N_TDC is on the other hand between the thresholds S1 and S2, it is not determined whether the engine is going to stall immediately and a combustion adaptation step 60 is provided to ensure protection of the engine, in particular from its dual-mass flywheel and ensure that no combustion causes the engine to rotate in reverse.

During the adaptation step 60, it is planned to act on the instructions to be sent to the injection system 600 by modifying them if necessary. It is proposed here in an original way to modify the fuel injection setpoints at least with regard to the time of fuel injection so as to be sure that the injection of fuel into the combustion chamber associated with the piston 200 does not occurs only when the piston 200 has exceeded top dead center. Provision is thus made to modify an instruction CRK_INJ corresponding to the instant of injection so that this instruction corresponds to an angular position of the crankshaft 300 after the passage of the top dead center of the piston 200.

Indeed, it is accepted that when the top dead center is crossed by the piston in the compression phase, it is not possible to have a rotation in the opposite direction of the engine. It is therefore necessary to ensure that the top dead center has passed before injecting fuel. In a manner known to those skilled in the art, the rotational speed of the engine is determined by detecting the passage of teeth arranged at the periphery of the engine flywheel in front of a sensor which is associated, in a manner known to those skilled in the art, with means for determining the direction of rotation of the engine (i.e. the direction of rotation of the engine flywheel). To ensure that the top dead center has passed for the piston in the compression phase, it is necessary to detect the passage of a tooth after the top dead center. It must be ensured that the passage of the tooth front corresponds to the top dead center (if a tooth front is provided at the 0° position) or the first tooth front after the top dead center, for example a descending tooth front. Passage of this rising tooth front normally ensures passage to top dead center. However, it must be ensured that this detected rising edge does not correspond to the detection of the previous tooth in reverse rotation. It is therefore advisable to wait for the following - rising - edge to ensure that the motor has not started in reverse rotation.

It is possible, as a variant embodiment, to possibly vary other setpoints concerning the injection, such as for example the profile of the injection and/or the quantity of fuel injected to adapt to the new setpoint concerning the moment of the injection. 'injection.

Generally, it is not recommended to shift an injection position because the calculated injection position corresponds to an optimal position in terms of pollution and performance.

However, such performance degradation is offered here because it is exceptional and can prevent major engine damage. It is therefore proposed, for a certain speed prediction zone, between thresholds S1 and S2, to possibly shift the injection position to inject only after the piston has passed top dead center in order to protect the engine.

In this method, the calibration of the threshold S2 aims to ensure the mechanical protection of the engine and more particularly of its dual-mass flywheel. S2 is chosen such that if the rotational speed predicted at the next top dead center is greater than said threshold, then there is no risk of stalling. The choice of threshold S1 has an influence in particular on the driving pleasure in the operating phases that risk leading to engine stalling. Indeed, by lowering this threshold, the engine stalls less easily, which increases driving pleasure. The method proposed here makes it possible to slightly lower the threshold S1 compared to the threshold chosen in the prior art as the limit threshold below which the injection is inhibited.

To limit the computing resources at the level of the on-board electronics of the vehicle, provision may be made to implement the method described only if the rotational speed of the engine falls below a third threshold S3. This threshold could be for example double or triple S2 (purely illustrative and non-limiting value).

The technical process can find application in particular for internal combustion engines. It is more particularly suited to a 4-stroke engine of the diesel type with direct injection but could also be implemented on other engines (possibly 2-stroke).

This disclosure is not limited to the preferred embodiment described above, solely by way of example, and to the variants mentioned, but it encompasses all the variants that a person skilled in the art may consider in the context of the protection sought.

Claims (10)

A method of power management for an internal combustion engine (100) wherein:
-on approaching a top dead center by a piston (200) in the compression phase, setpoints concerning future combustion, in particular a setpoint for the start of fuel injection, are established, and a prediction of the speed of rotation of the engine (N_TDC) when passing from top dead center to come is carried out,
-a first rotational speed threshold (S1) and a second rotational speed threshold (S2) greater than the first are predetermined,
characterized in that
when a rotational speed prediction at the next top dead center is between the two rotational speed thresholds (S1, S2), then the setpoint corresponding to the start of fuel injection is modified such that the injection of fuel only occurs after a possible passage of top dead center, and
when a rotational speed prediction at the next top dead center is lower than the first threshold (S1), the next predicted combustion is inhibited. Method for managing the supply of a motor according to claim 1, characterized in that, when a rotational speed prediction (N_TDC) at the next top dead center is above the two thresholds (S1, S2) of rotation speed, then the instructions concerning the combustion to come are carried out. Method for managing the supply of a motor according to one of Claims 1 or 2, characterized in that it comprises an initialization step (10, 40) during which it is determined at what moment the prediction of the engine speed when passing the next top dead center is realized. Method for managing the supply of an engine according to claim 3, characterized in that the initialization step (40) is carried out after each passage to top dead center of a piston at the end of compression. Method for managing the power supply to a motor according to one of Claims 1 to 4, characterized in that the motor comprises a flywheel provided with teeth and an associated sensor cooperating with means for determining the direction of rotation the engine flywheel to determine, on the one hand, the position of the engine pistons and, on the other hand, the speed of rotation of the engine,
in that when a rotational speed prediction at the next top dead center is between the two rotational speed thresholds (S1, S2), then the setpoint corresponding to the start of fuel injection is modified such that the fuel injection occurs only after detection of a falling edge of one tooth and a rising edge of one tooth and confirmation that the direction of rotation of the engine has not changed, one of the edges corresponding either to the position of the top dead center considered, or to the first edge after said top dead center. Method for managing the supply of a motor according to one of Claims 1 to 5, characterized in that it is implemented only when the speed of rotation of the motor is lower than a third threshold. Device (500) for managing a motor, characterized in that it comprises means for implementing each of the steps of a method for managing the power supply to a motor according to one of Claims 1 at 6. Internal combustion engine (100), characterized in that it comprises an engine management device (500) according to claim 7. Internal combustion engine (100) according to claim 8, characterized in that it is a diesel type engine, that is to say a compression ignition engine. Internal combustion engine (100) according to one of Claims 8 or 9, characterized in that it comprises a flywheel of the dual-mass type.