METHOD FOR MANAGING AN INTERNAL COMBUSTION ENGINE DURING STALLING PHASE

Abstract

A method for managing an internal combustion engine during the timing phase, comprising the following steps: - during the compression stroke in a cylinder, estimation of the engine load by comparing the timing of two successive teeth on the target; - estimation of the crankshaft rotational speed at top dead center at the end of the compression stroke, based on the engine load and the cylinder pressure at the beginning of the compression stroke; and - action on the ignition system to control fuel combustion in the cylinder concerned, based on the estimated speed and at least one predetermined rotational speed threshold. This action may involve delaying the start of the ignition coil's charging, modifying the ignition timing, or cutting off the ignition. (See diagram: Figure 3)

Description

Title of the invention: METHOD FOR MANAGING AN INTERNAL COMBUSTION ENGINE DURING STALLING PHASE

[0001] This disclosure relates to a method for managing a heat engine. technical field

[0002] This disclosure falls within the field of internal combustion engine control, or heat engines. It relates more specifically to four-stroke engines, that is, engines in which a complete combustion cycle in a cylinder takes place over two crankshaft revolutions. In such an engine, there is a direction of rotation defined during the engine design that must be respected for proper engine operation. The technical problem that gives rise to this disclosure is preventing the engine from being driven by combustion in the opposite direction (also called reverse rotation) to the direction of proper engine operation.

[0003] On two-wheeled or similar type vehicles, especially those with a kick-start system, care should be taken to prevent the engine from being driven backwards during starting, as this causes a kick-back which can be dangerous.

[0004] Once the engine is running, it is important to avoid reversing the engine for a four-stroke engine because this reverse rotation could damage engine components such as the starter, transmission components, a belt, etc. Previous technique

[0005] It is known to prevent reverse rotation of a four-stroke engine. These solutions most often involve specific hardware, such as an additional crankshaft position sensor or modified ignition control means to allow for late cancellation of an ignition command.

[0006] The purpose of this disclosure is to provide a solution for effectively preventing combustion in a four-stroke internal combustion engine from driving the engine in the opposite direction of rotation. This solution will preferably be software-based, meaning it will not require the implementation of additional physical components or the selection of specific components. Advantageously, this solution will be fast with low inertia, meaning it will remain effective even at relatively high engine speeds. Summary

[0007] This disclosure thus improves the situation.

[0008] A method for managing a heat engine during the stalling phase is proposed, said engine comprising at least one cylinder and a piston sliding in each cylinder, the movement of each piston driving in rotation a crankshaft equipped with a target with teeth associated with a sensor detecting the passage of the teeth to indicate the angular position of said crankshaft and its speed of rotation.

[0009] According to this disclosure, said process comprises the following steps: - during the compression phase in a cylinder, estimation of the engine load by comparing the passage times of two successive teeth of the target, - estimation of the crankshaft rotation speed at top dead center at the end of the compression stroke, based on, firstly, the engine load and, secondly, the cylinder pressure at the beginning of the compression stroke, and - possible action on an ignition controlling fuel combustion in the cylinder concerned based on the estimated speed and at least a predetermined rotation speed threshold, the action being a delay in the start of the charging of an ignition coil, a change in the ignition angle or a cut-off of the ignition.

[0010] Such a method has proven particularly effective and does not require any specific hardware components. It can be used on any type of engine (four-stroke with spark ignition).

[0011] The features described in the following paragraphs may optionally be implemented independently of each other or in combination with each other:

[0012] - the motor load estimate can be calculated by decomposing said load as being the sum of a resisting compression torque corresponding to compression in the cylinder in question and an overall load integrating internal engine loads and loads exerted on the vehicle in which the engine is mounted, and an estimation of said overall load can be made at the beginning of the compression phase, neglecting the effect of compression on engine deceleration, by determining the ratio between a change in engine speed over a time interval and the length of said interval. In this variant, it can also be assumed that the estimation of the crankshaft speed at top dead center at the end of compression is made iteratively.Alternatively or in addition, it is possible to provide that the compression resistance torque takes into account, on the one hand, the pressure in a combustion chamber associated with the cylinder concerned, assuming that the compression is adiabatic and knowing the pressure at the beginning of compression, and, on the other hand, taking into account the atmospheric pressure exerted on a side of the piston considered opposite to the combustion chamber; and / or .

[0013] - estimating the crankshaft rotation speed at top dead center The compression process is iterative; and / or

[0014] - three rotational speed thresholds for the estimated rotational speed at neutral The top of the compression curve is defined. - - if the estimated rotational speed is below a first threshold but above a second threshold, the start of the ignition coil charging is delayed, - - if the estimated rotational speed is below the second threshold but above a third threshold, the ignition angle is modified, and - - if the said estimated rotation speed is less than the third threshold, the ignition is cut off.

[0015] According to another aspect, a computer program is proposed comprising instructions which, when the program is executed by a computer, lead the latter to implement all the steps of a process described above.

[0016] According to another aspect, a non-transient, computer-readable recording medium is proposed, characterized in that a computer program defined above is recorded on said medium.

[0017] According to another aspect, an electronic management system for an internal combustion engine is proposed, comprising: - a crankshaft sensor, configured to detect the passage of teeth on a crankshaft target; - a controlled ignition system; - a computer equipped with electronic memory, configured for: - receive input data supplied by the crankshaft sensor, - to implement the steps of a process described above, and - provide instructions to the controlled ignition system.

[0018] Finally, this disclosure also relates to a vehicle (with two, three or four wheels, or even more) comprising a four-stroke internal combustion engine with: - a crankshaft equipped with a target and associated with a crankshaft sensor, - a controlled ignition system, characterized in that it comprises an electronic system as defined above. Brief description of the drawing

[0019] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analysis of the attached drawing, on which: Fig. 1

[0020] [Fig.1] shows rotational speed curves of a motor on a diagram with angular positions on the abscissa and rotational speeds on the ordinate. Fig. 2

[0021] [Fig.2] shows corresponding torque curves illustrating variations in compression torque in a cylinder for different pressures in the cylinder at the beginning of a compression cycle. Fig. 3

[0022] [Fig. 3] shows a flowchart of a process proposed by this disclosure according to an advantageous embodiment. Fig. 4

[0023] [Fig.4] schematically shows a vehicle in which a process according to the This disclosure can be implemented. Description of the implementation methods

[0024] The following description presents a method and means enabling a four-stroke internal combustion engine rotating in one direction of rotation to avoid combustion in a cylinder that would drive the engine in the opposite direction of rotation. Indeed, reverse rotation (other than any oscillations observed when the engine is stopped around its stopping position) can be damaging to such an engine, even if the reverse rotation is of short duration.

[0025] A new approach is proposed here for detecting any unintentional stalling (not requested by the driver) and preventing the ignition of a combustion that would cause the engine to run in the opposite direction to its rotation. This proposal relates more specifically to a spark-ignition engine in which an ignition system produces a spark in a combustion chamber to trigger the combustion of a fuel / oxidizer mixture (generally gasoline / air).

[0026] As is known to those skilled in the art, an internal combustion engine stops rotating when its energy / inertia prevents it from compressing air (pure or mixed) in a combustion chamber (two cylinders rarely operate in phase: this applies to engines with a large number of cylinders, particularly eight or more). If a piston in a cylinder fails to reach top dead center at the end of its compression stroke and combustion is triggered, then the engine will rotate in the opposite direction. Such a situation must be avoided. It is important to anticipate it well in advance in the case of a spark-ignition engine. Indeed, to trigger a spark in the combustion chamber, it is usually necessary to energize an induction coil. This requires a charging time, which is not negligible. Therefore, a decision must be made relatively early on whether or not to energize the induction coil.This charging time can be expressed in seconds (more precisely in milliseconds) or in degrees of the motor's rotation angle. Thus, when the motor's rotation speed is high, the relevant rotation angle is relatively high. Furthermore, it is important to... The ignition timing should be planned before the engine reaches top dead center. In practice, this means deciding when to fire a cylinder approximately 80° to 45°CRK before it reaches top dead center at the end of the compression stroke. Therefore, it's crucial to determine beforehand if the engine is likely to stall.

[0027] The original idea underlying this disclosure is: - estimate the load applied to the motor, i.e. to determine a torque (resistance if the motor is in deceleration phase and motor in acceleration phase), - determine the resisting torque exerted on the engine by the compression phase (generally, as indicated above, only one compression phase at a time), - predict, by calculation, the engine's rotational speed at the next top dead center at the end of the compression stroke, and - if necessary, act on an ignition system control to prevent, for example, combustion.

[0028] The load applied to the TQ_Ch engine can be determined, for example, by observing the variation in the engine's rotational speed outside of a compression phase. This can be done while the intake valve is still open.

[0029] The resisting torque due to air compression TQ_Comp can be estimated by assuming that the compression is adiabatic. The pressure in the cylinder, and therefore the resisting action on the piston, and thus the resisting torque exerted, can be determined from the pressure in the chamber at the beginning of compression (from the closing of the intake valve) and the angular position of the engine (compression ratio achieved).

[0030] Figure 1 illustrates, in the case of engine deceleration, several curves showing the engine's rotational speed as a function of its angular position. In this figure, position 0 corresponds to top dead center at the end of the compression stroke (TDC) for the cylinder in question.

[0031] On the left of [Fig. 1], the piston in the cylinder under consideration begins to rise. The intake valve does not close when the piston is at bottom dead center but during the piston's upward movement. Thus, during a portion of its stroke, corresponding approximately to the area circled in [Fig. 1], the pressures on both sides of the piston are substantially balanced, and the variations in engine speed depend on the overall engine / load torque acting on the vehicle. The general physical formula:

[0032] TQ_Ch = J (d(N) / dt)

[0033] then applies in which: TQ_Ch is the torque (usually in Nm), J is a moment of inertia (usually in kgm), N is the rotational speed (usually in radians per second: rad / s), d(N) / dt being the derivative of the rotational speed with respect to time, or variation of the rotational speed over time.

[0034] In an engine, the engine's rotational speed corresponds to the rotational speed of a crankshaft to which the engine's pistons are connected via connecting rods. This crankshaft is fitted with a toothed circular target, with similar teeth evenly distributed around its periphery. Often, a tooth is placed every 6° around the periphery of the target (theoretically 60 teeth), with two teeth missing to create a singularity at the periphery of the target and thus track each crankshaft revolution. All of this is known to those skilled in the art, who know that such a target is associated with a sensor (most often inductive) that detects each time a tooth passes in front of it and then provides a signal allowing, on the one hand, the instantaneous position of the engine to be determined, and on the other hand, its rotational speed. The sensor also allows us to know the time (duration) that elapses between the passage of one tooth and the next tooth.In this way, it is possible to determine, for two successive tooth passages, the variation in rotational speed (dN) and the variation in time (dt). We can thus determine the torque TQ_Ch (or at least the value TQ_Ch / J).

[0035] Figure 2 relates to the resisting torque due to compression in a cylinder. To analyze this torque, the compression before top dead center is considered adiabatic. The pressure in the combustion chamber then depends only on the pressure at the beginning of the compression and the geometry of the combustion chamber. The pressure in the chamber during this compression is proportional to the pressure present in it at the beginning of the compression.

[0036] Consequently, the resisting torque throughout the compression phase can be estimated using a table giving values ​​for each angular position of the engine, these values ​​being multiplied by the initial pressure at the beginning of the compression phase. Thus, in an engine without variable valve timing (VVT), i.e., in which the intake valves close at a given angular position, we have: TQ_Comp = MAP*FCT(Crk) with TQ_Comp is a compression-related pair MAP is the pressure in the combustion chamber at the time of the intake valve closing (this pressure corresponds to the pressure in the engine at the air intake and can therefore be measured by a pressure sensor), and FCT(Crk) is a function that depends only on the angular position (Crk) of the engine.

[0037] Here too, the pressure exerted on the face of the piston opposite to the combustion chamber. On this opposite face, we can estimate as a first approximation that the pressure is essentially constant (and approximately equal to atmospheric pressure). Let TQ_Atm then be the torque related to the pressure prevailing in the engine crankcase, that is to say on the side opposite the combustion chamber.

[0038] To predict the engine's rotational speed as it passes through the upcoming top dead center at the end of the compression stroke, it is proposed to iteratively calculate, for each tooth of the crankshaft target, the speed up to the top dead center at the end of the compression stroke, taking into account the three "loads" acting upon it: the overall external load TQ_Ch, the load due to compression in the cylinder during compression TQ_Comp, and the load due to the pressure within the engine crankcase TQ_Atm. These "loads" are not measured in Nm of torque but in units that take into account the engine's rotational inertia.

[0039] We then obtain the following overall formula:

[0040] N(n)=N(n-1) - [TQ_Ch + MAP*FCT(Crk) - TQ_Atm] / N(n-1) [Formula (1)] This formula allows us to calculate the rotational speed of the motor at each tooth passage.

[0041] Figure 2 illustrates the torque exerted when TQ_Ch=0. This figure shows three curves representing the torque variation in the combustion chamber during the 180°CRK (crankshaft rotation angle) before top dead center at the end of the compression stroke. These curves correspond to three scenarios where three distinct pressures exist in the combustion chamber at the moment the intake valve closes. There are also curves formed by a series of segments: these correspond to the torque variation due to pressure, calculated iteratively. It can be seen that each curve formed by a series of segments closely matches the actual curve. This comparison validates the formula given above for calculating the engine speed.

[0042] At each passage of a tooth, a new iterative calculation can be made using formula (1) to estimate the rotational speed N of the engine when the piston is at top dead center at the end of compression.

[0043] The logic diagram in [Fig. 3] proposes a way of using the calculations presented above. The following description is made with reference to this [Fig. 3] and to [Fig. 1].

[0044] A step 100 allows monitoring of the engine's passage through a bottom dead center located 180°CRK (i.e., half a crankshaft revolution) before a top dead center at the end of the compression stroke (TDC). From this passage through said bottom dead center, the MAP pressure of the intake air is measured.

[0045] A step 200 determines, particularly based on the last measured motor speed N, whether the motor is potentially at risk of stopping. The motor speed N is compared to a limit value which may depend, in particular, on the phase in which the motor is located. For example, a limit value is provided for the motor's starting phase and another limit value for continuous operation.

[0046] If there is no risk of stalling (option 0), the process returns to step 100 of monitoring the engine position.

[0047] If a risk is detected (option 1), a step 300 analyzes the engine position. Depending on the engine, an angular position value is monitored, for example 90°CRK before the top dead center of compression (TDC). When this value is reached (option 1), a calculation of the engine load TQ_Ch is performed, for example as explained above, using the latest readings of rotational speed N and passage time (or length of the time interval between two successive passages of teeth of the crankshaft target) T.

[0048] Once the engine load TQ_Ch is determined, an initialization step (INI) is performed. This step is the beginning of the iterative calculation described above. It involves calculating the estimated rotational speeds for the upcoming teeth up to the next top dead center of compression. The speed value is initialized (N(0)) by taking the value of the last rotational speed measured at the last tooth passage in front of the crankshaft target.

[0049] The next step consists of calculating N(l) and then the other values ​​N(n) corresponding to the teeth to come up to the TDC. A loop is thus maintained as long as, at step 500, the value of n does not yet correspond to the tooth corresponding to the TDC. The values ​​N(n+1) can be calculated from the initialized values ​​N(n) or calculated according to Formula (1) given above, for example.

[0050] At the output of the loop, a value N(TDC) is obtained which corresponds to an estimated value of the rotational speed during the next passage through top dead center at the end of compression for the engine.

[0051] In [Fig. 1], this measurement phase (of pressure, speeds, and timing) corresponds to a PI range, which can be considered an engine behavior analysis phase. This phase ends (step 600) when a decision must be made: can the next combustion occur normally, or should the instructions sent to the ignition system be modified? Step 600 is used to check when the engine passes through a DEC position (which can be variable). The DEC position depends on the engine and its ignition system. This position depends, in particular, on the time required to charge an ignition coil (range P2) and also on the P3 range, which corresponds to the possible angular values ​​for ignition control (ignition advance).

[0052] Once the DEC position has been exceeded, a decision must be made based on a rotation speed N_PRED. This speed may be equal to the last value N(TDC) is calculated, or if several N(TDC) values ​​have been calculated, the N_PRED value can be determined from these values. It could be, for example, an average value or a minimum value. Having multiple predictions also allows for the elimination of a value that stands out from the others and is therefore implausible.

[0053] The N_PRED value is then compared with at least one limit value.

[0054] The operation of the process can be predicted simply by comparing it with a limit value. For greater operational flexibility, two, or even three, distinct limit values ​​can also be provided.

[0055] If only one limit is chosen, and the N_PRED value is below this limit, it can be decided, for example, that there will be no ignition. The coil is then not charged. Otherwise, the ignition is controlled normally with the programmed ignition advance and the expected coil charging time.

[0056] A preferred variant with three limit values ​​LIM1, LIM2 and LIM3 is described below. It is assumed: LIM1 > LIM2 > LIM3

[0057] If we have LIM 1>=N_PRED>LIM2:

[0058] In this case, it may be possible, for example, to delay the start of the coil loading. This delay can be used (only once) for a new evaluation of the rotational speed at the next top dead center at the end of compression.

[0059] If we have LIM2>=N_PRED>LIM3:

[0060] In this case, to avoid combustion in the combustion chamber which could reverse the engine's direction of rotation, it is possible to modify the ignition timing and plan for a spark to occur approximately as the engine passes through the next top dead center. Such a spark will not reverse the engine's direction of rotation.

[0061] In the last scenario where LIM3>=N_PRED, then the ignition coil is not powered and no spark is produced for this top dead center passage. The engine will then probably stall, but without risk of being driven in the opposite direction.

[0062] This method can, for example, be implemented by an electronic unit installed on board a vehicle, such as a car, motorcycle, or recreational vehicle (commonly called a quad bike). This electronic unit can be called a control unit or computer and is also known by the English acronym CPU. As schematically illustrated in [Fig. 4], there is a vehicle V powered by an engine M, said engine being electronically controlled by at least one electronic CPU unit. Industrial application

[0063] The new approach for preventing an engine from rotating in the opposite direction to its normal operating direction is reliable in all vehicle operating modes and for any engine. It makes it possible to prevent an engine from rotating in the opposite direction, even for a (very) brief period.

[0064] The proposed solution is purely software-based and does not require any additional sensors beyond those usually used in a four-stroke engine: a simple crankshaft sensor and a simple ignition coil control are sufficient.

[0065] The solution also works (especially) for engines with low inertia (single-cylinder) and / or those powering light vehicles (two-wheelers, for example). The process described above is (very) responsive and works even at relatively high speeds.

[0066] With the proposed method, the engine load is estimated well before the arrival of a top dead center at the end of compression and thus allows a reliable calculation of said load.

[0067] The reliability of the process is due in particular to the fact that the parameters involved, such as the inertia of the motor and its geometry, are physical characteristics that do not vary. Furthermore, a single predicted speed determination may be sufficient to be effective.

[0068] An advantage of the method proposed here is also that the prediction can be made well before top dead center, in particular before any action on the ignition coil whose charging time can sometimes prove limiting for other solutions of the prior art.

[0069] This disclosure is not limited to the example of embodiment and the variants mentioned above, only by way of example, but encompasses all the variants that a person skilled in the art may consider within the framework of the protection sought.

Claims

Claims

1. Method for managing a thermal engine in the stall phase, said engine comprising at least one cylinder and a piston sliding in each cylinder, the movement of each piston making it possible to drive in rotation a crankshaft provided with a target with teeth associated with a sensor detecting the passage of the teeth to indicate the angular position of said crankshaft and its rotational speed, characterized in that it comprises the following steps: - in the compression phase in a cylinder, estimation (300) of the engine load (TQ_Ch) by comparison of the passage times of two successive teeth of the target, - estimation of the rotational speed (N(TDC)) of the crankshaft at the passage of the top dead center at the end of compression (TDC) as a function, on the one hand, of the engine load (TQ_Ch) and, on the other hand, of the pressure in the cylinder at the start of compression (MAP),and - possible action on an ignition (700) controlling a combustion of fuel in the cylinder concerned as a function of the estimate made of the speed (N_PRED) and at least one predetermined rotation speed threshold (LIM1, LIM2, LIM3), the action possibly being a delay in the start of the charge of an ignition coil, a modification of the ignition angle or a cutting of the ignition.,

2. Method according to claim 1, characterized in that the estimation of the engine load (TQ_Ch) is calculated by decomposing said load as being the sum of a compression resisting torque corresponding to a compression in the cylinder considered and an overall load integrating loads internal to the engine and loads exerted on a vehicle in which the engine is mounted, and in that an estimation of said overall load is carried out at the start of the compression phase, neglecting the effect of compression on a deceleration of the engine, by determining the ratio between a variation in the rotation speed of the engine over a time interval and the length of said interval.

3. Method according to claim 2, characterized in that the estimation of the overall load of the engine is carried out approximately 90°CRK before the top dead center at the end of compression.

4. Method according to one of claims 2 or 3, characterized in that the compressive resistance torque takes into account, on the one hand, the pressure in a combustion chamber associated with the cylinder concerned, assuming that the compression is adiabatic and knowing the pressure at the start of compression and, on the other hand, taking into account the atmospheric pressure exerted on one side of the piston considered opposite the combustion chamber.

5. Method according to one of claims 1 to 4, characterized in that the estimation of the rotation speed (N_PRED) of the crankshaft when passing the top dead center at the end of compression is done iteratively.

6. Method according to one of claims 1 to 5, characterized in that three rotation speed thresholds (LIM1, LIM2, LIM3) for the estimated rotation speed at top dead center at the end of compression are defined, in that if said estimated rotation speed is lower than a first threshold (LIM1) but higher than a second threshold (LIM2), the start of charging of the ignition coil is delayed, in that if said estimated rotation speed is lower than the second threshold (LIM2) but higher than a third threshold (LIM3), the ignition angle is modified, and in that if said estimated rotation speed is lower than the third threshold (LIM3), the ignition is cut off.

7. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to implement all the steps of a method according to one of claims 1

8. a o. Non-transitory, computer-readable recording medium, characterized in that a computer program according to claim 7 is recorded on said medium.

9. Electronic system for managing an internal combustion engine comprising: - a crankshaft sensor, configured to detect the passages of the teeth of a crankshaft target; - a controlled ignition system; - a computer provided with an electronic memory, configured to: - receive as input data supplied by the crankshaft sensor, - implement the steps of a method according to one of claims 1 to 6, and - provide instructions to the controlled ignition system.

10. Vehicle comprising a four-stroke internal combustion engine with : - a crankshaft equipped with a target and associated with a crankshaft sensor, - a controlled ignition system, characterized in that it comprises an electronic system according to claim 9.

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