Method for monitoring an alternator-starter for a heat engine of a motor vehicle

Abstract

The invention relates to a method for monitoring an alternator-starter (21) of a motor vehicle power train (2) by means of a control unit (28), said power train (2) comprising a heat engine (22). Cleverly, the monitoring method comprises: a step of calculating the torque of the alternator-starter (21) based on a determination of an output torque of the heat engine (22) and an estimation of a theoretical torque of a crankshaft (26) of the heat engine (22); a step of defining an operating mode of the alternator-starter (21), determined as a function of a sign of the torque of the alternator-starter (21) previously calculated; and a step of comparing the measured operating mode of the alternator-starter (21) with a state setpoint of the alternator-starter (21) in order to determine a possible malfunction of the alternator-starter (21).

Description

[0001] DESCRIPTION

[0002] TITLE OF THE INVENTION: METHOD FOR MONITORING AN ALTERNATOR-STARTER FOR A HEAT ENGINE OF A MOTOR VEHICLE

[0003] [1] The present invention claims priority from French application No. 2304526 filed on 05.05.2023, the content of which (text, drawings and claims) is incorporated herein by reference.

[0004] [2] The technical context of the present invention is that of monitoring the proper functioning of an alternator-starter of a powertrain for a motor vehicle, and more particularly for those of the hybrid or microhybrid type, that is to say equipped with a thermal engine associated with such an alternator-starter. More particularly, the invention relates to a method of monitoring an alternator-starter for a thermal engine of a motor vehicle.

[0005] [3] In the state of the art, hybrid motor vehicles equipped with an alternator-starter do not have specific and precise monitoring of the correct operation of the alternator-starter. On the contrary, such monitoring is carried out visually by maintenance teams during servicing of these motor vehicles.

[0006] [4] Furthermore, on known thermal motor vehicles equipped with an alternator-starter, it is customary to monitor the state of charge level of a low-voltage electric battery associated with the alternator-starter, once said electric battery is fully charged. During this monitoring, if the state of charge of the supposedly charged low-voltage electric battery is below a threshold value, for example 10.5 V in the case of a 12 V electric battery, a light indicator warns the driver of the motor vehicle that the low-voltage electric battery is malfunctioning and that a service of the motor vehicle is then necessary.

[0007] [5] A known disadvantage is that this indicator light does not indicate to the technician in charge of the revision the exact source of the fault. On the contrary, the indicator only shows that the low-voltage electric battery is no longer fully recharging. Also, during this revision, the technician will then check the correct operation of the low-voltage electric battery, that of the alternator-starter or the alternator-starter drive belt, or even the electrical power cables connecting the low-voltage electric battery to the alternator-starter and to the on-board network.

[0008] [6] This imprecision in failure detection leads to increased complexity at the time of vehicle overhaul, and an increase in the cost and time spent to verify all failure hypotheses.

[0009] [7] Thus, in the currently known methods for monitoring the general proper functioning of a motor vehicle, it is known to check the proper functioning of the alternator-starter consecutively to monitoring a good state of charge of the low-voltage electric battery. However, the current provisions do not allow the proper functioning of the alternator-starter to be checked precisely during regular use of the motor vehicle. Therefore, a failure of the alternator-starter itself will not be detected directly. On the contrary, it is rather the inability to start the thermal engine associated with the alternator-starter which could - among other hypotheses - put the technician on the trail of a malfunction of the alternator-starter.

[0010] [8] Thus, in known diagnostic systems and protocols, only failures such as a failure to fully recharge the low-voltage electric battery or failure to start the thermal engine allow for a check of the correct operation of the alternator-starter. There is therefore a need for more detailed monitoring of the correct operation of the alternator-starter during use.

[0011] [9] Finally, the advent of new ecological standards for motor vehicles leads to the imposition of ever more efficient and comprehensive fault diagnostics in order to reduce any excess energy consumption of the motor vehicle.

[0012]

[0010] The object of the present invention is to propose a new method for monitoring the alternator-starter in order to respond at least to a large extent to the preceding problems and to also lead to other advantages.

[0011] Another object of the invention is to propose more precise monitoring of the correct operation of such an alternator-starter in order to better detect failures.

[0013]

[0012] Another aim of the invention is to reduce the pollution of a motor vehicle equipped with such an alternator-starter.

[0014]

[0013] Another aim of the invention is to facilitate the servicing of a motor vehicle equipped with such an alternator-starter and to simplify repairs.

[0015]

[0014] According to a first aspect of the invention, at least one of the aforementioned objectives is achieved with a method for monitoring an alternator-starter for a thermal engine of a powertrain of a motor vehicle, the monitoring method being implemented by a control unit and comprising the following steps:

[0016]

[0015] - a step of estimating a theoretical torque of a crankshaft of the heat engine from state variables of the heat engine;

[0017]

[0016] - a step of determining an output torque of the heat engine;

[0018]

[0017] - a step of calculating a torque of the alternator-starter from the output torque of the thermal engine and the theoretical torque of the crankshaft;

[0019]

[0018] - a step of defining a measured operating mode of the alternator-starter as a function of a sign of the calculated alternator-starter torque;

[0020]

[0019] - a step of comparing the measured operating mode of the alternator-starter with a state setpoint of said alternator-starter.

[0021]

[0020] In the context of the present invention, the control unit implementing the monitoring method according to the first aspect of the invention comprises calculation and / or storage means. By way of non-limiting example, the control unit is a supervisor / calculator of the powertrain of the motor vehicle. The control unit advantageously comprises at least one microprocessor and / or at least one microcontroller and / or at least one memory - temporary or permanent - as used in the computer field. The control unit takes the form of an electronic card and / or an integrated circuit.

[0021] During the step of defining the operating mode of the alternator-starter, if a value of the torque of the alternator-starter is positive, then the alternator-starter operates in a starter type operating mode.On the other hand, if a value of the alternator-starter torque is negative, then the alternator-starter operates in an alternator type operating mode.

[0022]

[0022] Thus, the control unit responsible for monitoring the operating mode of the alternator-starter is now capable of determining whether the behavior of said alternator-starter complies with its control instructions, i.e. whether there is a correspondence between the measured operating mode of the alternator-starter and the status instruction which was used to configure said alternator-starter. If there is such a correspondence, then the alternator-starter is configured in a correct operating mode. On the other hand, if the status instruction differs from the measured operating mode for the alternator-starter, then said alternator-starter is not configured in the correct operating mode and it is now possible to warn the user of the motor vehicle.

[0023]

[0023] Indeed, when a computer of the powertrain equipped with the alternator-starter and responsible for monitoring the operating mode of said alternator-starter, receives the instruction according to which the alternator-starter must be configured in an alternator type operating mode, then, after a first latency period of the order of a few hundred milliseconds, the control unit checks whether the torque of the alternator-starter is indeed of the resistive type and that the alternator-starter is indeed operating in an alternator type operating mode in which it takes torque from the crankshaft of the thermal engine in order to transform it into electric current for recharging the low-voltage electric battery.

[0024]

[0024] Conversely, when the computer receives the instruction that the alternator-starter must be configured in a starter-type operating mode, then, after a second latency period of the order of a few hundred milliseconds, the control unit checks whether the torque of the alternator-starter is indeed of the motor type and that the alternator-starter is indeed operating in a starter-type operating mode in which it supplies mechanical torque to the output shaft and / or to the crankshaft of the heat engine in order to start the heat engine or to provide additional power to said heat engine.

[0025]

[0025] Thus, the monitoring method according to the first aspect of the invention makes it possible to propose more precise monitoring of the proper functioning of such an alternator-starter in order to better detect failures. Consequently, the monitoring method according to the invention makes it possible to avoid operating the motor vehicle for too long while the alternator-starter is faulty, thus leading to a reduction in the pollution emitted by said motor vehicle. Furthermore, the monitoring method according to the invention makes it possible to optimize and facilitate the servicing of a motor vehicle equipped with such an alternator-starter and to simplify repairs.

[0026]

[0026] The monitoring method according to the first aspect of the invention advantageously comprises at least one of the improvements below, the technical characteristics forming these improvements being able to be taken alone or in combination:

[0027]

[0027] - the state variables comprise (i) an atmospheric pressure value taken in an inlet duct of an air intake of the heat engine, and / or (ii) an air temperature value taken in an inlet throat of the air intake of the heat engine, and / or (iii) a manifold temperature value taken in a manifold of the air intake of the heat engine, and / or (iv) a flow rate value of the air entering through the air intake into the heat engine, and / or (v) a real speed value of a crankshaft of the heat engine. Preferably, the state variables from which the output torque of the heat engine is calculated consist exactly of all the aforementioned values, taken together;

[0028]

[0028] - the air flow rate entering through the air intake is measured by an air intake flow meter. The incoming air flow rate value is either read directly by the flow meter and transmitted directly to the control unit, or is available on an on-board network to which the control unit is connected;

[0029]

[0029] - the crankshaft speed is measured by a speed sensor of the thermal engine. The crankshaft speed value is either read directly by the speed sensor and transmitted directly to the control unit, or available on an on-board network to which the control unit is connected;

[0030] - atmospheric pressure is measured by a pressure sensor placed in or near the air intake inlet duct. The atmospheric pressure value is either read directly by the pressure sensor and transmitted directly to the control unit, or is available on an on-board network to which the control unit is connected;

[0030]

[0031] - the manifold temperature is measured by a first temperature sensor placed in or near the air intake manifold. The manifold temperature value is either read directly by the pressure sensor and transmitted directly to the control unit, or is available on an on-board network to which the control unit is connected;

[0031]

[0032] - the air temperature is measured by a second temperature sensor placed in or near the inlet neck of the air intake. The air temperature value is either read directly by the pressure sensor and transmitted directly to the control unit, or is available on an on-board network to which the control unit is connected;

[0032]

[0033] - the torque estimation step includes a step of comparing the values ​​of the state variables with a predetermined map of the heat engine, so as to find in said map an estimator of the theoretical torque of the crankshaft - directly or by approximation from one or two map states close to the values ​​of state variables. The step of comparison with the map thus makes it possible to estimate the engine torque at the crankshaft as a function of the values ​​of the different state variables measured during operation of the heat engine. The map is defined during a preliminary phase of development of the heat engine, said heat engine then being tested and monitored in multiple configurations and for numerous operating points which are all recorded in the map.The mapping is stored in the memory of the control unit implementing the monitoring method in accordance with the first aspect of the invention;

[0033]

[0034] - according to a first variant embodiment, the step of determining the output torque of the heat engine comprises a step of measuring the output torque at an output shaft of the heat engine or at a flywheel associated with the heat engine;

[0034]

[0035] - alternatively, according to a second embodiment, the step of determining the output torque of the heat engine comprises a step of calculating said output torque from the product of an angular acceleration and an inertia of a shaft line at the output of the heat engine. For this purpose, a sensor of a rotation speed on the output shaft makes it possible to determine a rotation speed of the heat engine. Such a rotation speed is for example determined by measuring an angular rotation of the output shaft during a predetermined time interval. By measuring such an angular speed over several successive time intervals, it is then possible to determine the angular acceleration by difference of the two determined angular speeds, divided by the overall duration of measurement of the two angular speeds;

[0035]

[0036] - additionally, the inertia of the shaft line at the output of the thermal engine is determined in particular from predetermined inertia values ​​of a clutch and a gearbox of the powertrain. For this purpose, the control unit takes into account for this determination pre-recorded inertia values ​​of different elements of a traction chain associated with the powertrain, and including in particular the clutch and the gearbox. These values ​​are advantageously recorded in a memory area of ​​the control unit or in the computer of the powertrain.By way of non-limiting examples, the inertia values ​​of the drive train and taken into account during the step of determining the output torque of the heat engine comprise (i) an inertia seen by the heat engine when the clutch is configured in its open state, and / or an inertia seen by the heat engine when the clutch is configured in its closed state, the gearbox being engaged in one of the gear ratios, such inertia being calculated for each gear ratio of the gearbox, including reverse gear;

[0036]

[0037] - the step of calculating the torque of the alternator-starter includes a step of calculating the difference between the output torque of the heat engine and the theoretical torque of the crankshaft. The torque of the alternator-starter is a driving torque or a resistive torque. By driving torque, we understand that the alternator-starter generates a positive torque on the output shaft of the heat engine, relative to the torque generated by said heat engine itself. Conversely, by resistive torque, we understand that the alternator-starter generates a negative torque on the output shaft of the heat engine, relative to the torque generated by said heat engine itself;

[0037]

[0038] - if the status setpoint differs from the measured operating mode for the alternator-starter, then the monitoring method comprises a step of warning of such a malfunction. The warning step comprises, for example, the establishment of an incident report stored in the memory of the control unit of the powertrain of the motor vehicle, and / or the configuration of a warning signal - for example a light indicator - on a dashboard of the motor vehicle.

[0038]

[0039] According to a second aspect of the invention, there is provided a powertrain for a motor vehicle, the powertrain comprising:

[0039]

[0040] - a heat engine;

[0040]

[0041] - an alternator-starter associated with the thermal engine;

[0041]

[0042] - a control unit configured to implement the alternator-starter monitoring method according to the first aspect of the invention or according to any of its improvements.

[0042]

[0043] According to a third aspect of the invention, there is provided a motor vehicle comprising a powertrain according to the second aspect of the invention.

[0043]

[0044] Advantageously, the motor vehicle is of the thermal motor vehicle type or a microhybrid motor vehicle.

[0044]

[0045] Various embodiments of the invention are provided, incorporating, in all their possible combinations, the various optional features set out herein.

[0045]

[0046] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several examples of embodiment given for informational and non-limiting purposes with reference to the attached schematic drawings on the other hand, in which:

[0046]

[0047] [Fig.1] illustrates a schematic view of a powertrain according to the second aspect of the invention;

[0047]

[0048] [Fig.2] illustrates a block diagram of a powertrain monitoring process shown in FIGURE 1.

[0048]

[0049] Of course, the features, variants and different embodiments of the invention may be combined with each other, in various combinations, provided that they are not incompatible or mutually exclusive. In particular, variants of the invention may be imagined comprising only a selection of features described below in isolation from the other features described, if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0049]

[0050] In particular, all the variants and embodiments described can be combined with each other if there is no technical obstacle to this combination.

[0050]

[0051] In the figures, elements common to several figures retain the same reference.

[0051]

[0052] With reference to FIGURE 1, the invention addresses a powertrain 2 controlled by a control unit 28 configured to implement the monitoring method 1 which will be described later with reference to FIGURE 2. In the context of the present invention, the control unit 28 can be included in a computer 23 or a supervisor 24 of the powertrain 2, or the control unit 28 can form an independent unit.

[0052]

[0053] Generally, the control unit 28 comprises calculation and storage means. For this purpose, the control unit 28 comprises, for example, at least one microprocessor and / or at least one microcontroller and / or at least one memory.

[0053]

[0054] Such a powertrain 2 comprises a heat engine 22 configured to generate engine torque on an output shaft (not shown), said heat engine 22 being coupled to said output shaft via a crankshaft 26 and a flywheel 27. The heat engine 22 is further coupled to an alternator-starter 21 via a distribution 224 and an accessory drive belt which makes it possible to mechanically couple said alternator to the output shaft coupled to the heat engine 22.

[0054]

[0055] The powertrain 2 further comprises a speed sensor 25 configured to measure a rotational speed of the output shaft cut off to the heat engine 22. The speed sensor 25 is located near the crankshaft 26 or the flywheel 27 of the powertrain 2.

[0055]

[0056] Thus, when the alternator-starter 21 is configured in its starter operating mode, it generates an engine torque on the output shaft, in addition to that generated by the heat engine 22 itself or as priming of said heat engine 22. Conversely, when the alternator-starter 21 is configured in its alternator operating mode, it generates a resistive torque on the output shaft, in opposition to that generated by the heat engine 22, so as to generate electrical energy transmitted to the on-board network of a motor vehicle equipped with such a powertrain 2 and, where appropriate, to a low-voltage electric battery of said motor vehicle in order to recharge it.

[0056]

[0057] In such a powertrain 2, the computer 23 controls the alternator-starter 21. Optionally, the alternator-starter 21 can also be controlled by the supervisor 24. In addition, the computer 23 also controls an injection of fuel into a combustion chamber of the heat engine 22, as well as an air flow supplying said combustion chamber via openings of an air intake butterfly. Finally, the computer 23 and / or the supervisor 24 are electrically connected to the speed sensor 25 in order to recover the measured values ​​of the rotational speed of the output shaft.

[0057]

[0058] With reference to FIGURE 2, the invention aims to establish fine monitoring of the alternator-starter 21 in order, on the one hand, to determine the operating mode in which the alternator-starter 21 is configured at each instant and, on the other hand, to verify that this operating mode in which it is configured is indeed in line with the operation of the heat engine 22. The objective here is to verify the correct operation of the alternator-starter 21 and to be able to detect, if necessary, a malfunction of said alternator-starter 21 with respect to its expected operating mode with regard to the operation of the heat engine 22 and several powertrain state variables 2.

[0058]

[0059] For this purpose, the invention addresses a method 1 for monitoring the alternator-starter 21 associated with the thermal engine 22 of a powertrain 2 for a motor vehicle. Such a monitoring method 1 is implemented by the control unit 28 of the powertrain 2 and comprises the following steps:

[0059]

[0060] - a step 11 of estimating a theoretical torque of the crankshaft 26 of the heat engine 22 from state variables of the heat engine 22. Advantageously, the torque estimation step 11 comprises a comparison of the values ​​of the state variables with a predetermined map 111 of the heat engine 22, so as to find in said map 111 an estimator of the theoretical torque of the crankshaft 26. The comparison with the map 111 thus makes it possible to estimate the engine torque at the crankshaft 26 as a function of the values ​​of the different state variables measured during operation of the heat engine 22;

[0060]

[0061] - a step 12 of determining an output torque of the heat engine 22.

[0061] The determination of the output torque supplied by the heat engine 22 on the output shaft can be carried out by measuring 121 the output torque at the output shaft or at the flywheel 27, or the step of determining 12 the output torque supplied by the heat engine 22 on the output shaft can be carried out by calculating 122 from the product of an angular acceleration - determined from the speed sensor 25 and an inertia of a shaft line at the output of the heat engine 22;

[0062]

[0062] - a step 13 of calculating a torque of the alternator-starter 21 from the output torque of the heat engine 22 and the theoretical torque of the crankshaft 26. For this purpose, the step 13 of calculating the torque of the alternator-starter 21 comprises a calculation of the difference 131 between the output torque of the heat engine 22 determined during the determination step 12 and the theoretical torque of the crankshaft 26 estimated during the estimation step 11;

[0063] - a step 14 of defining a measured operating mode of the alternator-starter 21 as a function of a sign of the calculated torque of the alternator-starter 21. Thus, if the calculated torque of the alternator-starter 21 is positive, then the measured operating mode of said alternator-starter 21 corresponds to a starter-type operating mode, said alternator-starter 21 generating a positive torque on the output shaft of the heat engine 22, relative to the torque generated by said heat engine 22 itself. Conversely, if the calculated torque of the alternator-starter 21 is negative, then the measured operating mode of said alternator-starter 21 corresponds to an alternator-type operating mode, said alternator-starter 21 generating a negative torque on the output shaft of the heat engine 22, relative to the torque generated by said heat engine 22 itself;

[0063]

[0064] - a comparison step 15 of the measured operating mode of the alternator-starter 21 with a state setpoint of said alternator-starter 21. Thus, if the status instruction - transmitted by the computer 23 or the supervisor 24 to the alternator-starter 21 - differs from the operating mode measured for the alternator-starter 21, then it is deduced that the alternator-starter 21 is not in phase with the instruction which had been transmitted to it, thus revealing a malfunction of said alternator-starter 21 and / or of the powertrain 2. Conversely, if the status instruction - transmitted by the computer 23 or the supervisor 24 to the alternator-starter 21 - corresponds to the operating mode measured for the alternator-starter 21, then it is deduced that the alternator-starter 21 is in phase with the instruction which had been transmitted to it, and that said alternator-starter 21 is operating correctly.

[0064]

[0065] Consequently, in the event of a malfunction, the monitoring method 1 comprises a step of warning of such a malfunction. The warning step 16 comprises, for example, the establishment of an incident report stored in the memory of the control unit 28 of the powertrain 2 of the motor vehicle, and / or the configuration of a warning signal - for example a light indicator - on a dashboard of the motor vehicle.

[0065]

[0066] Advantageously, the state variables taken into account during estimation step 11 include:

[0067] - an atmospheric pressure value taken in an inlet duct of an air intake of the heat engine 22. The atmospheric pressure is measured by a pressure sensor placed in or near the inlet duct of the air intake. The atmospheric pressure value is either read directly by the pressure sensor and transmitted directly to the control unit 28, or available on an on-board network to which the control unit 28 is connected; and / or

[0066]

[0068] - an air temperature value taken from an inlet neck of the air intake of the heat engine 22. The air temperature is measured by a second temperature sensor placed in or near the inlet neck of the air intake. The air temperature value is either read directly by the pressure sensor and transmitted directly to the control unit 28, or available on an on-board network to which the control unit 28 is connected; and / or

[0067]

[0069] - a manifold temperature value taken from a manifold of the air intake of the heat engine 22. The manifold temperature is measured by a first temperature sensor placed in or near the manifold of the air intake. The manifold temperature value is either read directly by the pressure sensor and transmitted directly to the control unit 28, or available on an on-board network to which the control unit 28 is connected; and / or

[0068]

[0070] - a flow rate value of the air entering through the air intake into the heat engine 22. The flow rate of air entering through the air intake is measured by an air intake flow meter. The incoming air flow rate value is either read directly by the flow meter and transmitted directly to the control unit 28, or available on an on-board network to which the control unit 28 is connected; and / or

[0069]

[0071] - an actual speed value of a crankshaft 26 of the heat engine 22. The crankshaft speed 26 is measured by a speed sensor 25 of the heat engine 22. The crankshaft speed value 26 is either read directly by the speed sensor 25 and transmitted directly to the control unit 28, or available on an on-board network to which the control unit 28 is connected.

[0070]

[0072] In summary, the invention relates to a method 1 for monitoring by a control unit 28 an alternator-starter 21 of a powertrain 2 of a motor vehicle, said powertrain 2 comprising a heat engine 22. The monitoring method 1 cleverly comprises a step 13 of calculating a torque of the alternator-starter 21 from the determination of an output torque of the heat engine 22 and the estimation of a theoretical torque of a crankshaft 26 of said heat engine 22, a step 14 of defining an operating mode of the alternator-starter 21, determined as a function of a sign of the torque of the alternator-starter 21 calculated previously, and a step 15 of comparing the measured operating mode of the alternator-starter 21 with a state setpoint of said alternator-starter 21 in order to determine a possible malfunction of said alternator-starter 21.

[0073] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention. In particular, the different characteristics, forms, variants and embodiments of the invention can be associated with each other in various combinations insofar as they are not incompatible or mutually exclusive. In particular, all the variants and embodiments described above can be combined with each other.

Claims

Claims

1. Method for monitoring (1) an alternator-starter (21) for a thermal engine (22) of a powertrain (2) of a motor vehicle, the monitoring method (1) being implemented by a control unit (28) and comprising the following steps: - a step of estimating (11) a theoretical torque of a crankshaft (26) of the heat engine (22) from state variables of the heat engine (22); - a step of determining (12) an output torque of the heat engine (22); - a step of calculating (13) a torque of the alternator-starter (21) from the output torque of the thermal engine (22) and the theoretical torque of the crankshaft (26); - a step of defining (14) a measured operating mode of the alternator-starter (21) as a function of a sign of the torque of the alternator-starter (21) calculated; - a comparison step (15) of the measured operating mode of the alternator-starter (21) with a state setpoint of said alternator-starter (21).

2. Monitoring method (1) according to the preceding claim, in which the state variables comprise: - an atmospheric pressure value taken in an inlet duct of an air intake of the heat engine (22); - an air temperature value taken in an inlet neck of the air intake of the heat engine (22); - a collector temperature value taken in a collector of the air intake of the heat engine (22); - a flow rate value of the air entering through the air intake into the heat engine (22); - an actual speed value of a crankshaft (26) of the heat engine (22).

3. Monitoring method (1) according to any one of the preceding claims, in which the torque estimation step (11) comprises a step of comparing (15) the values of the state variables with a predetermined mapping (111) of the heat engine (22), so as to find in said mapping (111) an estimator of the theoretical torque of the crankshaft (26) - directly or by approximation from one or two mapping states (111) close to the values of state variables.

4. Monitoring method (1) according to any one of the preceding claims, in which the step of determining (12) the output torque of the engine comprises a step of calculating (13) said output torque from the product of an angular acceleration and an inertia of a shaft line at the output of the heat engine (22).

5. Monitoring method (1) according to the preceding claim, in which the inertia of the shaft line at the output of the thermal engine (22) is determined in particular from predetermined inertia values of a clutch and a gearbox of the powertrain (2).

6. Monitoring method (1) according to any one of the preceding claims, in which the step of calculating (13) the torque of the alternator-starter (21) comprises a step of calculating (13) the difference between the output torque of the heat engine (22) and the theoretical torque of the crankshaft (26).

7. Monitoring method (1) according to any one of the preceding claims, in which, if the state setpoint differs from the operating mode measured for the alternator-starter (21), then the monitoring method (1) comprises a step of warning of such a malfunction.

8. Powertrain (2) for a motor vehicle, the powertrain (2) comprising: - a heat engine (22); - an alternator-starter (21) associated with the thermal engine (22); - a control unit configured to implement the monitoring method (1) of the alternator-starter (21) according to any one of the preceding claims.

9. Motor vehicle comprising a powertrain (2) according to the preceding claim, i

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