Method for detecting a mechanical stop state of a three-cylinder four-stroke combustion engine

Abstract

The invention relates to a method for detecting a mechanical stop of a three-cylinder combustion engine, the method being implemented by a computing unit configured to detect a rising or falling edge of a voltage signal from a crankshaft magnetic sensor, the method comprising: a step of triggering a timeout TStopEstim, and a step of estimating a mechanical stop when the timeout TStopEstim has elapsed. The method further comprises, prior to the triggering step, upon each detection of a rising edge of the voltage signal: a step of determining a direction of rotation of the motor; when the determined direction of rotation corresponds to a reverse direction of rotation, a step of detecting a dip in the speed of rotation; a step of calculating a value Tp on the basis of a current measured value of the speed of rotation of the engine and a predetermined law for the temporal change in the decrease in the speed of rotation of the engine, the predetermined law for the temporal change in the decrease in the speed of rotation being an affine law with a predetermined slope; a step of triggering the timeout TStopEstim, wherein the value of the timeout TStopEstim is equal to the value Tp; and a step of estimating a mechanical stop when the timeout TStopEstim has elapsed.

Description

Method for detecting a mechanical shutdown state of a three-cylinder four-stroke thermal engine Description Field of invention The present invention relates to a method for detecting a mechanical shutdown state of a three-cylinder four-stroke thermal engine. Prior art Starting an internal combustion engine is conventionally facilitated by a starter, which comprises a shaft fitted with a pinion to initiate rotation of the engine by gearing with a pinion carried by it. In the event of a possibly brief engine stop, it is necessary to determine a complete stop state in order to restart the engine. Indeed, if the engine is not completely stopped when the starter is operated, the engagement of the gears can damage the engine and the starter. The combustion cycle of an internal combustion engine comprises several phases whose occurrence is staggered in time for each cylinder, the synchronized control of the valves of the thermal engine being carried out by the camshaft. In order for the combustion cycle to proceed normally, it is necessary to have a reliable angular reference on the basis of which each phase of each cylinder is determined. The camshaft is rotated by the crankshaft. The crankshaft is a mechanical device that, through a connecting rod, transforms the rectilinear movement of a piston into a continuous rotational movement, and vice versa, thus ensuring the transmission of the combustion energy of the fuel in the cylinders into mechanical energy. Thus, knowing the angular position of the crankshaft makes it possible to know a reliable angular reference on the basis of which each phase of each cylinder is determined. Such a reference is available via a toothed wheel, also called a target, which rotates with the crankshaft. The wheel is associated with a dedicated sensor, called a crankshaft sensor, whose ultimate role is to determine the angular position and rotation speed of the toothed wheel. The sensor is equipped with a sensitive element. In one example, the wheel is metallic and the sensitive element is capable of detecting metal, such as a Hall effect sensor. The profile of the wheel typically includes a target which is provided with markers, also called teeth, distributed around its periphery. The function of the crankshaft sensor is to transform the measured magnetic field into an electrical signal. According to the state of the art, some sensors are connected to the control unit by three wires (ground, power supply and signal) and have the capacity to determine the direction of rotation of a crankshaft target.The passage of a tooth of the gear associated with the crankshaft generates an electrical pulse on the signal wire. The predetermined duration is representative of the direction of rotation (typically 45 ps for a forward direction of rotation, and 90 ps for a reverse direction of rotation). The crankshaft sensor is typically mounted near the flywheel which serves as a rotating target or supports such a target. The rotating target has a signature, also called a long tooth or gap, formed by a singularity in the (otherwise regular) profile usually corresponding to two missing marks, and which allows a reference to be set for the crankshaft position. Such a signature generates a signal different from the other marks, which makes it possible to determine when the rotating target has completed a complete rotation. A commonly used rotating target consists of 60 marks distributed around the periphery of the rotating target, and two consecutive marks removed to create the signature. Such a target is called a 60-2 rotating target. Another known rotating target is the 36-2 rotating target (34 marks plus two missing marks). The rotation of the rotating target causes periodic changes in the magnetic flux due to the passage of the markers, which are transformed by the sensor into voltage variations that can then be sent to the engine management computer. The voltage variations include rising and falling edges forming a periodic signal synchronized with the passage of the markers in front of the sensor. From the voltage data produced by the crankshaft sensor, the person skilled in the art knows how to calculate the rotational speed and the angular position of the crankshaft to obtain the basic data necessary for determining the injection point and adjusting the ignition advance point. To determine an engine stop state, it is known to exploit the data acquired by the crankshaft rotation sensor. The engine stop is detected at the end of a time delay, for example 300 ms, started from the last detected tooth. If a new tooth is detected before the time delay expires, it is interrupted and the engine is considered to be moving. This process involves systematically waiting for the end of the time delay, i.e. 300 ms, to detect an engine stop, and therefore to authorize the restart of the engine. However, it is desirable to be able to restart the engine as quickly as possible, for example in vehicles equipped with an automatic stop and restart device for the engine of a vehicle of the "stop and start" type or similar, for example in so-called change of mind circumstances (for example, when arriving at a red light which turns green at the time of stopping). Furthermore, the toothed targets mounted on engine crankshafts have a spacing of at least 6° between two consecutive teeth. Therefore, if there remains a movement of the engine which is contained within this angular amplitude of 6°, this movement will not be detected. Thus, this detection method only allows one to conclude with certainty that the engine has stopped after a very long time. Document FR3076861 is known, which proposes a method for detecting the physical shutdown of a four-stroke internal combustion engine comprising at least four cylinders. The above method does not work for three-cylinder four-stroke engines. This is because the method is based on analyzing engine oscillations during shutdown. These oscillations are characteristic of four-stroke combustion engines with four or more cylinders (a compression phase in one cylinder is always counterbalanced by a combustion phase in another cylinder). The invention aims to overcome the drawbacks of the prior art described above. In particular, one aim of the invention is to enable the detection of a mechanical shutdown state of a three-cylinder four-stroke thermal engine within a time of less than 300 ms. Another aim of the invention is to enable the engine to be stopped with certainty. Statement of the invention To this end, according to a first aspect of the invention, a method for detecting a mechanical stoppage of a three-cylinder thermal engine is proposed, implemented by a computing unit, configured to detect a rising edge, respectively falling edge, of a voltage signal from a magnetic crankshaft angular position sensor, the voltage signal having rising and falling edges corresponding to detections of rising and falling edges of a series of teeth of a toothed wheel mounted integral with the axis of rotation of the crankshaft, the method comprising: • a step for triggering a TstopEstim time delay, and • a step of estimating a mechanical stop when the TstopEstim time delay is over. The timer trigger step TstopEstim consists of triggering a clock that counts down from an initial time value t=Tinit. A timer TstopEstim is finished when it reaches the value t=0. If necessary, a new triggering step of the timer TstopEstim is implemented before a previously triggered timer reaches t=0, which postpones an estimation time of a mechanical stop. This is the case, for example, in the event of a new detection of a rising or falling edge before the timer has ended. The method further comprises, prior to the step of triggering the time delay, upon each detection of a rising or falling edge of the voltage signal: • / a / a step of determining a direction of rotation of the motor, then when the determined direction of rotation corresponds to a reverse direction of rotation, • / b / a step of detecting an inflection in the rotation speed, then • / c / a step of calculating a value Tp from a current value of a measurement of the rotation speed of the motor and a predetermined law of temporal evolution of the decrease in the rotation speed of the motor, the predetermined law of temporal evolution of the decrease in the rotation speed being an affine law of predetermined slope, then • / d / the step of triggering the timer TstopEstim, the value of the timer TstopEstim being equal to the value Tp, then • / e / the step of estimating a mechanical stop when the TstopEstim time delay is over. Advantageously, the method may further comprise: • an initialization step prior to the step of determining a direction of rotation of the motor / a / , the initialization step comprising the assignment of a zero value to a variable xA, and • the step of determining a direction of rotation of the motor / a / further comprising the assignment of a unit value to the variable xA when the direction of rotation of the motor determined during the step of determining a direction of rotation of the motor / a / corresponds to a reverse direction of rotation, and • subsequently to the step of determining a direction of rotation of the motor / a / and if the determined direction of rotation of the motor corresponds to a forward direction of rotation, for each detection of a rising or falling edge, • a step of comparing the variable xA and the unit value, then if the variable xA is equal to the unit value, • the step of triggering the time delay TstopEstim, the value of the time delay TstopEstim being equal to a predetermined time delay value called margin time delay Tmargin- The method may comprise, subsequently to the step of determining a direction of rotation of the motor / a / if the determined direction of rotation of the motor corresponds to a forward direction of rotation, or subsequently to the comparison step Er when it exists and the variable xA is not equal to the unit value, for each detection of a rising edge, respectively falling edge, a step Es comprising the assignment to the time delay TstopEstim of a predetermined time delay value called safety time delay T sa fe, then the timer trigger step TstopEstim- According to another aspect of the invention, a module is proposed for detecting a mechanical stoppage of a three-cylinder thermal engine, the module implementing a calculation unit configured to detect a rising edge, respectively falling edge, of a voltage signal from a magnetic crankshaft angular position sensor, the voltage signal having rising and falling edges corresponding to detections of rising and falling edges of a series of teeth of a toothed wheel mounted integral with the axis of rotation of the crankshaft and, for each of the detected edges: • trigger a TstopEstim timer, and • estimate a mechanical stop when the TstopEstim time delay is over, The computing unit is further configured to, prior to the timer triggering step: • determine a direction of rotation of the motor, then when the determined direction of rotation corresponds to a reverse direction of rotation, • detect an inflection in the engine rotation speed if the determined direction of rotation of the engine corresponds to a reverse direction of rotation, then • calculate a value Tp from a current value of a measurement of the rotation speed of the motor and a predetermined law of temporal evolution of the decrease in the rotation speed of the motor, the predetermined law of temporal evolution of the decrease in the rotation speed being an affine law of predetermined slope, then • trigger the TS timer t0P Estim, the value of the time delay TstopEstim being equal to the value Tp, then estimate the mechanical stop when the time delay TS t0P Estimation is complete. Brief description of the figures Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which one will refer to the appended drawings in which: • [Fig. 1] illustrates a characteristic graph of the evolution of the rotation speed of a three-cylinder four-stroke thermal engine before it stops, • [Fig. 2] illustrates an embodiment of a method according to the invention, • [Fig. 3] illustrates an embodiment of a module according to the invention and its physical environment. Detailed description of the invention The embodiments described below being in no way limiting, it will be possible in particular to consider variants of the invention comprising only a selection of the characteristics described, subsequently isolated from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. This selection comprises at least one characteristic, preferably functional without structural details, or with only a part of the structural details if this part alone is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. Figure 1 represents a characteristic graph of the evolution of the rotation speed of a three-cylinder four-stroke thermal engine (on the ordinate) as a function of time (on the abscissa) when the engine is stopped. The curve typically represents 4 parts: • a first part of reduction of the rotational speed of the engine due to friction and the transfer of rotational energy towards the increase of the gas pressure in the cylinder in the compression stage, the engine continuing to rotate in a forward direction of rotation, • a second part A of the start of reversal of the direction of rotation of the engine, initiated by a transition instant T corresponding to the piston reaching the maximum relative high position, the speed of movement of the piston increasing due to the expansion of the gas, • a third part B following part A, during which we observe an inflection in the rotation speed of the engine, the piston being accelerated by the expansion of the previously compressed gas, • a fourth part C following part B, during which we observe a reduction in the speed of the engine due to the reduction in pressure and an increase in friction until it stops at time Ts. There is now described, with reference to Figure 2, an embodiment of a method P for detecting a mechanical stoppage of a three-cylinder thermal engine implemented by a calculation unit Uc, at the same time as a module M implementing a calculation unit Uc. The method and module according to the invention take advantage of the existence of a magnetic device S for the angular position of the crankshaft A. The magnetic device S generates a voltage signal representative of the passage of a tooth comprising, for each detected tooth, a rising edge and a falling edge. It is thus possible to determine the rotation speed by analyzing the signal generated by the magnetic device. The magnetic device S is, for example, a bidirectional sensor of the CPDD type, for Crankshaft Position and Direction Determination, capable of generating signals of different widths depending on the direction of rotation of the crankshaft. It is thus possible to determine the direction of rotation by analyzing the signal generated by the magnetic device. For example, with the sensor in question, the falling electrical edge and the rising electrical edge are spaced apart by a duration of 45 ps when the toothed wheel moves in one direction of rotation, and by a duration of 90 ps when the toothed wheel moves in the other direction of rotation. The magnetic sensor S is typically associated with a magnetic target C mounted integral with the rotation of the crankshaft A. The computing unit Uc is configured to detect a rising edge, respectively a falling edge, of the voltage signal of the magnetic crankshaft angular position sensor, the voltage signal having rising and falling edges corresponding to detections of rising and falling edges of a series of teeth of a toothed wheel mounted integrally with the rotation axis of the crankshaft. The P process includes: • a step Ed for triggering a TS timer t0P Estimate, and • a step Ee for estimating a mechanical stop when the time delay TstopEstim is over. According to the invention, the method further comprises, prior to the step of triggering the time delay, upon each detection of a rising or falling edge of the voltage signal: • / a / a step Ea of determining a direction of rotation of the motor, then when the determined direction of rotation corresponds to a reverse direction of rotation, • / b / a step Eb of detection of an inflection of the rotation speed, then • / c / a step Em of calculating a value Tp from a current value of a measurement of the rotation speed of the motor and a predetermined law of temporal evolution of the decrease in absolute value of the rotation speed of the motor, then • / d / the triggering step Ed of the time delay TstopEstim, the value of the time delay TstopEstim being equal to the value Tp, then • / e / the step of estimating a mechanical stop when the TstopEstim time delay is over. Step Ea of determining a direction of rotation of the motor / a / According to one possibility, the step Ea of determining the direction of rotation of the engine can implement a variable available at the level of an ECU unit for controlling the engine or a software component monitoring the signal from the crankshaft sensor, in English driver. Said variable can have a value depending on the direction of rotation of the engine. The detection of a direction of rotation back then consists of receiving a state change event of this variable, or monitoring the state change of this variable. According to another possibility, the step Ea of determining a direction of rotation of the motor can for example implement an acquisition of the signal generated by the device s, when the latter makes it possible to determine the direction of rotation. In this case, the step Ea of determining a direction of rotation of the motor is carried out by processing the acquired signal. When the determined direction of rotation of the motor corresponds to a reverse direction of rotation, the method continues with step Eb of detecting an inflection in the rotation speed of the motor / b / . Stage Eb

[0039] According to one possibility, the step Eb of detecting an inflection in the rotation speed of the engine can for example be initiated by a change of state of a variable associated with the detection of an inflection in the rotation speed. This variable can for example be available at the level of the engine control ECU. According to one possibility, the step Eb of detecting an inflection in the rotation speed of the engine can for example be initiated by a change of state of a variable associated with the detection of an inflection in the rotation speed. This variable can for example be available at the level of the engine control ECU. According to another possibility, the step Eb of detecting an inflection in the rotation speed of the motor may include an acquisition of the rotation speed of the motor. The engine rotation speed may for example be known to the engine control unit, and acquiring the engine rotation speed then involves receiving the engine rotation speed from the control unit. Alternatively, the acquisition of the rotation speed of the motor can for example implement the processing of an acquired voltage signal generated by the device S. When step Eb of detecting an inflection in the rotation speed of the motor / b / includes the acquisition of the rotation speed, step Eb also includes a determination of the passage through a maximum of the rotation speed. The determination of the passage through a maximum of the rotation speed is for example detected when the absolute value of the gradient of the evolution of the rotation speed is lower than a predetermined threshold. Noting Tsys n and Tsys n + 1 the absolute times of detection of passage of two consecutive teeth in front of the crankshaft sensor, and T n the time difference between these two instants Tsys n and Tsys n + i and Sn the rotation speed obtained by the formula Sn=Toothlength / T n , where Toothlenght is the angular distance between two teeth (or two consecutive fronts of the same nature) (for example 6° for a 60-2 target or 10° for a 36-2 target), the gradient Grd n of the evolution of the speed can be written: Grd n = (Sn-S n -i) / T n . The determination of the passage through a maximum of the rotation speed is for example detected when the absolute value of Grd nis less than a predetermined Thresholdcrd value, with for example ThresholdGrd=50 rpm / s (for English revolutions per minute per second). When an inflection in the engine rotation speed is detected, the process continues with step Em of calculating a value Tp. Step Em of calculating a Tp value Knowing the time law and the current value of the rotation speed allows the time delay to be updated by assigning it the value of the time remaining before the motor stops. For example, if the current speed at time t is v(t), and knowing the graph allows a time ts to be determined accordingly, from which the speed will be zero. The process can then continue with the triggering of the time delay with the predetermined value ts. The predetermined time-dependent law of rotational speed decay can be approximated by an affine law of predetermined slope. In other words, the time-dependent law of decay can be approximated linearly by a predetermined decay slope, denoted slope. For example, slope = 750 rpm / s. The process can then continue with the triggering of the timer with the value Tp = Sn / slope. Preferably, the value of the time delay Tp can be increased by a margin time delay Tmargin, for example Tmargin = 50mS. Alternatively, the method may include acquiring a current temperature. The current temperature may be measured, for example, by means of a temperature sensor. Alternatively, the module may receive the current temperature information from the engine control unit (ECU). This is usually the oil or cooling water temperature, which are closest to the sensor value and the crankshaft target. The value of the decay slope may be modified depending on the measured temperature. Step Ee of detecting a mechanical stop when the time delay is over When the timer ends, the process detects a mechanical stop when the timer is over. Optional step Er According to a first variant, described only for its differences, the method P may comprise an initialization step Ei prior to the step Ea of determining a direction of rotation of the motor / a / , which comprises the assignment of a zero value to a variable xA. Step Ea of determining a direction of rotation of the motor / a / includes the assignment of a unit value to the variable xA when the direction of rotation of the motor determined during step Ea of determining a direction of rotation of the motor / a / corresponds to a reverse direction of rotation. Subsequent to step Ea of determining a direction of rotation of the motor / a / and if the determined direction of rotation of the motor corresponds to a forward direction of rotation, for each detection of a rising edge, respectively a falling edge, the method continues with a step Er of comparing the variable xA and the unit value, then if the variable xA is equal to the unit value, by the step Ee of triggering the time delay TstopEstim, the value of which is equal to the margin time delay T marg in. When the variable xA is not equal to the unit value, the process continues with step Es if it exists. Optional Step Es According to a second variant, possibly combinable with the first variant, the method comprises an optional step Es which begins when the direction of rotation of the motor determined by step Ea is a forward direction of rotation, or subsequently to step Er when it exists and the variable xA is not equal to the unit value, for each detection of a rising edge, respectively a falling edge, preferably when the rotation speed of the motor decreases. Step Es involves assigning a predetermined time delay value called safety time delay T to the time delay TstopEstim. sa fe. The safety time delay value T sa fe is for example 300 ms. Step Es continues with the triggering step Ed of the time delay whose value is equal to the predetermined time delay value. More generally Prior to implementing the initialization step, the computing unit may undergo a decay slope calibration step. According to one embodiment, the calibration step is carried out prior to the implementation of the method according to the invention, for example on a test vehicle representative of another vehicle equipped with the module M according to the invention. According to a variant, the calibration step can be implemented on a vehicle whose engine is new, for example after the engine has been replaced. The module M according to the invention can be implemented in the form of an electronic module comprising a memory in which is stored a computer program product comprising instructions intended to be executed by the calculation unit UC or by the engine control unit ECU which then replaces the calculation unit UC. Finally, the method according to the invention and the corresponding module can be implemented with sensors other than magnetic ones, provided that the sensor is sensitive to the passage of target reference elements. Of course, the invention is not limited to the examples just described and many adjustments can be made to these examples without departing from the scope of the invention. In addition, the various features, forms, variants and embodiments of the invention can be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive.

Claims

Claims 1) Method (P) for detecting a mechanical stop of a three-cylinder thermal engine implemented by a calculation unit (Uc) configured to detect a rising edge, respectively falling edge, of a voltage signal of a magnetic crankshaft angular position sensor, the voltage signal having rising and falling edges corresponding to detections of rising and falling edges of a series of teeth of a toothed wheel mounted integrally with the axis of rotation of the crankshaft, the method comprising: a step (Ed) of triggering a time delay TstopEstim, and a step (Ee) of estimating a mechanical stop when the time delay TstopEstim is finished, characterized in that it further comprises, prior to the step of triggering the time delay, upon each detection of a rising edge, respectively falling edge, of the voltage signal: / a / a step (Ea) of determining a direction of rotation of the motor, then when the determined direction of rotation corresponds to a reverse direction of rotation, / b / a step (Eb) of detecting an inflection in the rotation speed, then / c / a step (Em) of calculating a value T p from a current value of a measurement of the rotation speed of the motor and a predetermined law of temporal evolution of the decrease in the rotation speed of the motor, the predetermined law of temporal evolution of the decrease in the rotation speed being an affine law of predetermined slope, then / d / the trigger step (Ed) of the timer TstopEstim, the value of the timer TstopEstim being equal to the value T p , Then / e / the step (Ee) of estimating a mechanical stop when the time delay TstopEstim is over. 2) Method according to claim 1, further comprising: a step (Ei) of initialization prior to the step (Ea) of determining a direction of rotation of the motor / a / , the initialization step comprising the assignment of a zero value to a variable xA, and the step (Ea) of determining a direction of rotation of the motor / a / further comprising the assignment of a unit value to the variable xA when the direction of rotation of the motor determined during the step (Ea) of determining a direction of rotation of the motor / a / corresponds to a reverse direction of rotation, and subsequently to the step (Ea) of determining a direction of rotation of the motor / a / and if the direction of rotation of the motor determined corresponds to a forward direction of rotation, for each detection of a rising edge, respectively falling edge, a step (Er) of comparing the variable xA and the unit value, then if the variable xA is equal to the unit value, the step (Ed) of triggering the time delay TstopEstim, the value of the time delay TstopEstim being equal to a predetermined time delay value called margin time delay Tmargin- 3) Method according to claim 1, further comprising, subsequently to step (Ea) of determining a direction of rotation of the motor / a / if the direction of rotation of the determined motor corresponds to a forward direction of rotation, or subsequently to step (Er) when dependent on claim 2 and the variable xA is not equal to the unit value, for each detection of a rising edge, respectively a falling edge, a step Es comprising the assignment to the time delay TstopEstim of a predetermined time delay value called safety time delay T sa fe, then step (Ed) triggering of the time delay TstopEstim- 4) Module (M) for detecting a mechanical stop of a three-cylinder thermal engine, the module implementing a calculation unit (Uc), configured to detect a rising edge, respectively falling edge of a voltage signal of a magnetic crankshaft angular position sensor, the voltage signal having rising and falling edges corresponding to detections of rising and falling edges of a series of teeth of a toothed wheel mounted integrally with the axis of rotation of the crankshaft and, for each rising edge, respectively falling edge, detected: trigger a time delay TstopEstim, and estimate a mechanical stop when the time delay TstopEstim is finished, characterized in that it is further configured to, prior to the step of triggering the time delay: determine a direction of rotation of the engine, then when the determined direction of rotation corresponds to a reverse direction of rotation,detecting an inflection in the rotation speed of the motor if the determined direction of rotation of the motor corresponds to a reverse direction of rotation, then calculating a value Tp from a current value of a measurement of the rotation speed of the motor and a predetermined law of temporal evolution of the decrease in the rotation speed of the motor, the predetermined law of temporal evolution of the decrease in the rotation speed being an affine law of predetermined slope, then triggering the time delay TS, tO pEstim, the value of the time delay TstopEstim being equal to the value Tp, then estimate the mechanical stop when the time delay TS t0P Estimation is complete.

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