Method for managing a combustion engine during a stalling phase

Abstract

The invention relates to a method for managing a combustion engine during a stalling phase, the method comprising the following steps: - during the compression phase in a cylinder, estimating the engine load by comparing the transit times of two consecutive teeth of the target; - estimating the rotational speed of the crankshaft as it passes through top dead centre at the end of the compression phase, on the basis of the engine load on the one hand and the cylinder pressure at the start of the compression phase on the other hand; and - performing an action on an ignition system to control fuel combustion in the relevant cylinder according to the estimated speed and at least one predetermined rotational speed threshold, wherein the action may involve delaying the start of a charging phase of an ignition coil, modifying the ignition angle or cutting off the ignition.

Description

Description METHOD FOR MANAGING A HEAT ENGINE IN THE STALL PHASE

[0001] The present disclosure relates to a method of managing a heat engine. Technical field

[0002] The present disclosure relates to the field of control of internal combustion engines, or heat engines. It relates more particularly to four-stroke engines, i.e. engines for which a complete combustion cycle in a cylinder is carried out over two crankshaft revolutions. In such an engine, there is a direction of rotation provided during the design of the engine which must be respected for the proper functioning of the engine. The technical problem at the origin of the present disclosure is to prevent the engine from being driven by combustion in the opposite direction (also called backward rotation) to the direction of proper operation of the engine.

[0003] On two-wheeled vehicles or similar, particularly with a kick-start system, it is important to avoid the engine being driven backwards when starting, as this causes a kickback which can be dangerous.

[0004] Once the engine is running, it is advisable to avoid driving the engine in reverse for a four-stroke engine because this reverse rotation could damage engine components such as the starter, transmission components, a belt, etc. Prior art

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

[0006] The present disclosure then aims to provide a solution making it possible to effectively prevent combustion in a thermal engine (four-stroke) from driving said engine in its opposite direction of rotation. This solution will preferably be software-based, that is to say it will not require the installation of additional physical elements or having to choose particular elements. Advantageously, this solution will be fast with little inertia, that is to say it will be as effective even at relatively high speeds. Summary

[0007] This disclosure thus improves the situation.

[0008] A method is proposed 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 rotation speed.

[0009] According to the present disclosure, said method comprises the following steps: - in 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 when passing top dead center at the end of compression as a function, on the one hand, of the engine load and, on the other hand, of the pressure in the cylinder at the start of compression, and - possible action on an ignition controlling combustion of fuel in the cylinder concerned depending on the estimate made of the speed and at least one predetermined rotation speed threshold, the action possibly being a delay in the start of charging of an ignition coil, a modification of the ignition angle or a cutting of the ignition.

[0010] This method has proven to be 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 set out in the following paragraphs may, optionally, be implemented, independently of each other or in combination with each other:

[0012] - the estimation of the engine load can be 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 an estimation of said overall load can be 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 rotational speed of the engine over a time interval and the length of said interval. In this variant, it can also be provided that the estimation of the rotational speed of the crankshaft at the passage of the top dead center at the end of compression is made iteratively.It is also possible, as an alternative or in addition, to provide that the compression resisting 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; and / or.

[0013] - the estimation of the rotation speed of the crankshaft when passing the top dead center at the end of compression is done iteratively; and / or

[0014] - three rotation speed thresholds for the estimated rotation speed at top dead center at the end of compression are defined, - - if said estimated rotation speed is lower than a first threshold but higher than a second threshold, the start of charging of the ignition coil is delayed, - - if said estimated rotation speed is lower than the second threshold but higher than a third threshold, the ignition angle is modified, and - - if the said estimated rotation speed is lower than the third threshold, the ignition is switched off.

[0015] According to another aspect, there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to implement all of the steps of a method described above.

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

[0017] According to another aspect, there is provided an electronic management system for 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 equipped with an electronic memory, configured to: - receive input data provided by the crankshaft sensor, - implement the steps of a method described above, and - provide instructions to the controlled ignition system.

[0018] Finally, this disclosure also concerns 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 analyzing the attached drawing, in 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 cylinder pressures at the start of a compression cycle. Fig. 3

[0022] [Fig. 3] shows a flowchart of a method provided by the present disclosure according to an advantageous embodiment. Fig. 4

[0023] [Fig. 4] schematically shows a vehicle in which a method according to the present disclosure can be implemented. Description of the embodiments

[0024] The following description presents a method and means enabling a four-stroke internal combustion engine rotating in one direction of rotation to avoid carrying out combustion in a cylinder which would cause the engine to rotate in the opposite direction. Indeed, a reverse rotation (other than the possible oscillations observed when the engine stops around its stop position) can be harmful to such an engine, even if the reverse rotation is of short duration.

[0025] A new approach is proposed here to detect possible involuntary stalling (not requested by the driver) and to avoid controlling a combustion which would cause the engine to run in the opposite direction to that in which it is running. This proposal concerns more particularly a spark-ignition engine in which an ignition system makes it possible to create a spark in a combustion chamber to trigger combustion of a fuel / oxidant mixture (generally gasoline / air).

[0026] As is known to those skilled in the art, a combustion engine stops running when its energy / inertia does not allow it to compress air (pure or mixed) in a combustion chamber (there are rarely two cylinders operating in phase: this concerns engines with a large number of cylinders, especially eight or more). If a piston in a cylinder does not reach its top dead center at the end of the compression phase and combustion is triggered, then the engine will be driven into rotation in the opposite direction. Such a situation must be avoided. It should be predicted well in advance in the case of a controlled combustion engine. Indeed, to trigger a spark in the combustion chamber, it is most often necessary to charge an induction coil. This therefore requires a charging time and this is not negligible. It is therefore necessary to make a relatively early decision on whether or not to control the charging of the induction coil.This charging time can be expressed in seconds (more precisely in milliseconds) or in degrees of engine rotation angle. Thus, when the engine rotation speed is high, the rotation angle concerned is relatively high. In addition, it is advisable to plan to control the ignition before passing through top dead center. Thus, in practice, a decision must be made regarding ignition in a cylinder approximately 80 to 45°CRK before passing through top dead center at the end of compression in said cylinder. It is therefore necessary to determine beforehand whether the engine risks stalling.

[0027] The original idea behind this disclosure is to: - estimate the load applied to the motor, i.e. determine a torque (resistant if the motor is in the deceleration phase and motor in the acceleration phase), - determine the resistive 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 rotation speed when passing the next top dead center at the end of compression, and - if necessary, act on an ignition system control to prevent combustion, for example.

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

[0029] The resistive torque due to air compression TQ_Comp can be estimated by assuming that the compression achieved is adiabatic. The pressure in the cylinder, and therefore the resistive action on the piston, and therefore the resistive torque exerted, can be determined from the pressure prevailing in the chamber at the start 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 illustrating the engine rotation speed as a function of the engine's angular position. In this figure, position 0 corresponds to the top dead center at the end of compression (TDC) for the cylinder considered.

[0031] On the left of Figure 1, the piston in the cylinder in question begins to rise in the cylinder. The intake valve does not close when the piston is at its bottom dead center but during the rise of the piston. Thus, during a part of its stroke, corresponding roughly to the area circled in Figure 1, the pressures on both sides of the piston are roughly balanced and the variations in the engine rotation speed depend on the overall engine / resistant 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), with 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 rotation speed corresponds to the rotation speed of a crankshaft to which the engine pistons are connected by connecting rods. This crankshaft is equipped with a circular toothed target, with similar teeth equally distributed around the periphery of the target. Often, one tooth is provided every 6° around the periphery of the target (i.e. theoretically 60 teeth) with however two missing teeth to create a singularity at the periphery of the target and thus identify each crankshaft revolution. All this is known to the person skilled in the art who knows that such a target is associated with a sensor (most often inductive) which detects each passage of a tooth in front of it and which then provides a signal making it possible, on the one hand, to know the instantaneous position of the engine and, on the other hand, its rotation speed. The sensor also makes it possible to know the time (duration) which elapses between the passage of a tooth and the next tooth.In this way, it is possible to determine the variation in rotation speed (dN) and the variation in time (dt) for two successive tooth passages. This allows the torque TQ_Ch (or at least the value TQ_Ch / J) to be determined.

[0035] Figure 2 shows the resistive torque due to compression in a cylinder. To analyze this torque, we consider that the compression before top dead center is an adiabatic compression. The pressure in the combustion chamber then depends only on the pressure at the start of the compression and the geometry of the combustion chamber. The pressure in the chamber is proportional to the pressure prevailing in it at the start of the compression during this compression.

[0036] Consequently, the resistive torque throughout the compression phase can be estimated using a table giving values ​​for each angular position of the engine, said values ​​being to be multiplied by the initial pressure at the beginning of the compression phase. Thus, in an engine for which there is no variable valve timing (or Variable Valve Timing in English, also known by the acronym VVT), that is to say for which the intake valves close at a given angular position, we have: TQ_Comp = MAP*FCT(Crk) with TQ_Comp is a compression-related couple MAP is the pressure in the combustion chamber at the moment the intake valve closes (this pressure corresponds to the pressure prevailing in the engine at the air intake and can therefore be measured by a pressure sensor), and FCT(Crk) is a function depending only on the angular position (Crk) of the motor.

[0037] Here too, the pressure exerted on the face of the piston opposite the combustion chamber must be taken into account. On this opposite face, it can be estimated as a first approximation that the pressure is approximately constant (and approximately equal to atmospheric pressure). Let TQ_Atm then be the torque linked to the pressure prevailing in the engine casing, i.e. on the side opposite the combustion chamber.

[0038] To predict the engine rotation speed when passing through the upcoming top dead center, at the end of compression, it is proposed to calculate iteratively for each tooth of the target crankshaft up to the top dead center at the end of compression which arrives taking into account the three "loads" which are exerted, that is to say the overall external load TQ_Ch, the load due to the compression in the cylinder in compression TQ_Comp and the load due to the pressure prevailing in the engine crankcase TQ_Atm. These "loads" do not have as unit a torque in Nm but a unit which takes into account the rotational inertia of the engine.

[0039] We then obtain the following global formula:

[0040] N(n)=N(n-1) - [TQ_Ch + MAP*FCT(Crk) - TQ_Atm] / N(n-1) [Formula (1)] This formula allows you to calculate the rotation 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 variation in torque due in the combustion chamber during the 180°CRK (crankshaft rotation angle) before the top dead center at the end of compression. These curves correspond to three cases for which three distinct pressures prevail in the chamber combustion at the moment of closing the intake valve. There are also curves formed by a succession of segments: these correspond to the variation of the torque due to the pressure by carrying out an iterative calculation. We note that each curve formed by a succession of segments is close to the real curve. This comparison makes it possible to validate the formula given above for calculating the engine rotation speed.

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

[0043] The flowchart in Figure 3 suggests one way to use the calculations presented above. The following description is made with reference to this Figure 3 and to Figure 1.

[0044] A step 100 makes it possible to monitor the passage of the engine to a bottom dead center located 180°CRK (i.e. half a crankshaft revolution) before a top dead center at the end of compression (TDC). From this passage through said bottom dead center, the MAP pressure of the inlet air is measured.

[0045] A step 200 determines, in particular based on the last measured engine rotation speed N, whether the engine is potentially at risk of stopping. The rotation speed N is compared to a limit value which may depend in particular on the phase in which the engine is located. For example, a limit value is provided for the engine start-up 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 motor 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 at the end 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 last readings of rotation 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 presented above. It involves calculating the estimated rotational speeds for the upcoming teeth up to the upcoming top dead center at the end 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 is to calculate N(1) and then the other values ​​N(n) corresponding to the teeth to come up to the TDC. A loop is thus carried out as long as at a 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 loop output, a value N(TDC) is obtained which corresponds to an estimated value of the rotation speed during the next passage to top dead center at the end of compression for the engine.

[0051] In Figure 1, this measurement phase (of pressure, speeds and passage times) corresponds to a range P1 which can be considered as an analysis phase of the engine behavior. This phase ends (step 600) when a decision must be made: can the next combustion occur normally or should the instructions to be sent to an 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 thus depends in particular on the time required to charge an ignition coil (range P2) and also on the range P3 corresponding 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 can be equal to the last calculated N(TDC) value, or if several N(TDC) values ​​have been calculated, the said N_PRED value can be determined from these values. This can be, for example, an average value or a minimum value. Having several predictions also makes it possible to eliminate 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 process can be planned to operate with just one limit value compared. For greater operating flexibility, two or even three separate limit values ​​can also be planned.

[0055] If only one limit is chosen, if 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 LIM1 >=N_PRED>LIM2:

[0058] In this case, it may be suggested, for example, to delay the start of coil charging. This delay can be used (once only) for a new evaluation of the rotation 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 having combustion in the combustion chamber which risks reversing the direction of rotation of the engine, it is possible to modify the ignition advance and to provide to produce a spark substantially when passing through the upcoming top dead center. Such a spark will not allow the direction of rotation of the engine to be changed.

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

[0062] This method can for example be implemented by an electronic unit on board a vehicle, for example a motor vehicle or a motorcycle, or a leisure vehicle (commonly called a quad). This electronic unit can be called a management unit or calculator and is also known by the English acronym CPU. As illustrated schematically in Figure 4, we have a vehicle V powered by an engine M, said engine being electronically managed by at least one electronic unit CPU. Industrial application

[0063] The new approach to 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 prevents 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 compared to the sensors usually used in a four-stroke engine: a simple crankshaft sensor is suitable and a simple ignition coil control.

[0065] The solution also works (especially) for engines with low inertia (single-cylinder) and / or fitted to 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. In addition, a single determination of the predicted speed may be sufficient to be effective.

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

[0069] This disclosure is not limited to the exemplary embodiment and the variants mentioned above, only as an example, but it encompasses all the variants that a person skilled in the art may envisage 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 rotation speed, characterized in that it comprises the following steps: - in the compression phase in a cylinder, estimation (300) of the engine load by comparing the passage times of two successive teeth of the target, - estimation of the rotation speed (N(TDC)) of the crankshaft when passing top dead center at the end of compression (TDC) as a function, among other things, of the engine load, itself dependent on 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 estimation 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 is calculated by decomposing said load as being the sum of a compression resisting torque (TQ_Comp) corresponding to a compression in the cylinder considered and an overall load (TQ_Ch) 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 (TQ_Ch) 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 (TQ_Ch) 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 compression resisting torque (TQ_Comp) 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 in end of compression are defined, in that if said estimated rotational 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 rotational 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 rotational speed is lower than the third threshold (LIM3), the ignition is cut.

7. Computer program comprising instructions which, when the program is executed by a computer, cause the latter to implement all the steps of a method for managing a thermal engine in the stalling phase according to one of claims 1 to 6, 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 rotation speed.

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

9. Electronic management system for 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 equipped with an electronic memory, configured to: - receive input data provided by the crankshaft sensor, - implementing the steps of a method according to one of claims 1 to 6, and - provide instructions to the controlled ignition system, - a pressure sensor, configured to measure the pressure (MAP) prevailing in the engine at the intake level.

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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