MONITORING THE LOCKED STATE OF A DIFFERENTIAL COUPLED TO AN ELECTRIC DRIVE MACHINE OF A LAND VEHICLE

Abstract

A monitoring method is implemented in a land vehicle comprising a first half-axle equipped with a first wheel, a second half-axle equipped with a second wheel and a coupling device that can be placed in connected and disconnected states, and an electric drive unit coupled to a differential that can be placed in locked and unlocked states and coupled to the half-axles. This method includes a step (10-70) in which, when a locking state of the differential is requested, the state of the coupling device is determined, and if this determined state is the disconnected state, the coupling device is placed in the connected state. Then, the electric drive unit is instructed to provide a variable motor torque, and, in the presence of variation(s) in the motor torque received by at least one of the first and second wheels, the differential is allowed to be placed in the locked state. Figure 3

Description

Title of the invention: MONITORING THE PLACEMENT IN THE BLOCKED STATE OF A DIFFERENTIAL COUPLED TO AN ELECTRIC DRIVE MACHINE OF A LAND VEHICLE Technical field of the invention

[0001] The invention relates to land vehicles comprising an electric motor coupled to two half-wheel sets via a differential with locked and non-locked states, and more specifically to the monitoring within such vehicles of the placement of the differential in the locked state. State of the art

[0002] Certain land vehicles, possibly of the automobile type, comprise a transmission chain comprising, for example in a rear part, a first half-train provided with a first wheel, a second half-train provided with a second wheel and a coupling device, and an electric motor coupled to a differential which can be placed in locked and unlocked states and coupled to the first and second half-trains.

[0003] Here, the term "electric motor machine" means an electric machine arranged at least so as to provide engine torque to the first and second half-axles, to which it is coupled via the associated differential, to move its vehicle when it is supplied with electrical energy.

[0004] In the aforementioned vehicles, the coupling device can be selectively placed either in a connected state in which the second wheel is connected (or coupled) to the second half-train (and therefore driven at the same time as the latter), or in a disconnected state in which the second wheel is disconnected (or decoupled) from the second half-train (and therefore cannot be driven at the same time as the latter). This advantageously makes it possible to decouple the electric drive machine from the first and second half-trains.

[0005] Quite frequently, the differential can be selectively placed in an unlocked state, allowing different rotational speeds of the first and second wheels, or in a locked state, imposing identical rotational speeds of the first and second wheels. In this case, if the differential lock occurs while the coupling device is placed in its disconnected state, the torque and speed of the electric motor are entirely directed towards the first wheel which is the only one connected to its first half-train, and therefore the vehicle risks performing a spin, which can be dangerous for the safety of the vehicle and its passengers, but also for the safety of objects and people located in the vicinity of this vehicle.

[0006] Currently, it is the driver of the vehicle who must ensure that the coupling device is placed in its connected state before placing the differential in its blocked state, which is difficult to achieve, in particular because the information signaling the state in which the coupling device is placed is not 100% reliable. It may indeed happen that this information signals the connected state while in reality the coupling device is placed in its disconnected state.

[0007] The invention therefore aims in particular to improve the situation. Presentation of the invention

[0008] For this purpose, it proposes in particular a monitoring method intended to be implemented in a land vehicle comprising:

[0009] - a first half-train provided with a first wheel,

[0010] - a second half-train provided with a second wheel and a coupling device capable of being placed in connected and disconnected states in which the second wheel is respectively connected and disconnected, and

[0011] - an electric motor coupled to a differential which can be placed in blocked and unblocked states and coupled to the first and second half-trains.

[0012] This monitoring method is characterized by the fact that it comprises a step in which, when a placement of the differential in the blocked state is requested, the state in which the coupling device is placed is determined and if this determined state is the disconnected state, the coupling device is placed in the connected state, then the electric motor is ordered to provide a variable engine torque and, in the presence of at least one variation in engine torque received by at least one of the first and second wheels, this placement of the differential in the blocked state is authorized.

[0013] Thanks to the invention, it is now known with certainty whether the first and second half-trains are actually coupled to the electric motor before placing the differential in its locked state, which reinforces the safety of the vehicle and its passengers, but also the safety of objects and people located in the environment of the vehicle.

[0014] The monitoring method according to the invention may include other characteristics which may be taken separately or in combination, and in particular:

[0015] - in its step, it can be ordered that the electric motor provides a engine torque varying according to a predefined variation law;

[0016] - in the presence of the first option, in its step, the predefined variation law can consist of a monotonic increase followed by a monotonic decrease. alternatively, the predefined variation law may consist of a monotonic decrease followed by a monotonic increase;

[0017] - also in the presence of the first option, in its step, when the couple motor has a known initial value when the electric motor is ordered to provide the variable motor torque, the predefined variation law can be applied to this known initial value;

[0018] - in its step, it is possible to prohibit the placement of the differential in the blocked state when a current vehicle speed is greater than a chosen threshold;

[0019] - in the presence of the last option, in its step, the chosen threshold can be understood between 20 km / h and 40 km / h.

[0020] The invention also provides a computer program product comprising a set of instructions which, when executed by processing means, is capable of implementing a monitoring method of the type presented above, in a land vehicle comprising a first half-train provided with a first wheel, a second half-train provided with a second wheel and a coupling device which can be placed in connected and disconnected states in which the second wheel is respectively connected and disconnected, and an electric motor coupled to a differential which can be placed in locked and unlocked states and coupled to the first and second half-trains, to monitor the placement of the differential in the locked state.

[0021] The invention also proposes a monitoring device intended to equip a land vehicle comprising:

[0022] - a first half-train provided with a first wheel,

[0023] - a second half-train provided with a second wheel and a coupling device capable of being placed in connected and disconnected states in which the second wheel is respectively connected and disconnected, and

[0024] - an electric motor coupled to a differential which can be placed in blocked and unblocked states and coupled to the first and second half-trains.

[0025] This monitoring device is characterized by the fact that it comprises at least one processor and at least one memory arranged to carry out the operations consisting, when a placement of the differential in the blocked state is requested, in determining the state in which the coupling device is placed and if this determined state is the disconnected state in triggering a placement of the coupling device in the connected state, then in requiring that the electric motor provides a variable engine torque and, in the presence of at least one variation in engine torque received by at least one of the first and second wheels, in authorizing the placement of the differential in the blocked state.

[0026] The invention also proposes a land vehicle, possibly of the automobile type, and comprising, on the one hand, a first half-train provided with a first wheel, a second half-train provided with a second wheel and a coupling device capable of be placed in connected and disconnected states in which the second wheel is respectively connected and disconnected, and an electric prime mover coupled to a differential which can be placed in locked and unlocked states and coupled to the first and second half-trains, and, on the other hand, a monitoring device of the type presented above. Brief description of the figures

[0027] Other characteristics and advantages of the invention will appear on examining the detailed description below, and the appended drawings, in which:

[0028] [Fig-1] schematically and functionally illustrates an example of the embodiment of a land vehicle comprising a transmission chain including in particular a monitoring device according to the invention and an electric motor controlled by a machine computer and coupled to a differential, itself coupled to half-wheel sets, one of which comprises a coupling device,

[0029] [Fig.2] schematically and functionally illustrates an exemplary embodiment of a machine calculator comprising an exemplary embodiment of a monitoring device according to the invention, and

[0030] [Fig.3] schematically illustrates an example of an algorithm implementing a monitoring method according to the invention. Detailed description of the invention

[0031] The invention aims in particular to propose a monitoring method, and an associated monitoring device DS, intended to enable monitoring of the placement in the blocked state of the differential DR which is coupled to a first wheel set T1, provided with a first coupling device DC1, and to a first electric motor MM1 of a land vehicle V.

[0032] In the following, it is considered, by way of non-limiting example, that the land vehicle V is of the automobile type. It is for example a car, as illustrated in [Fig.l]. But the invention is not limited to this type of land vehicle. It in fact relates to any type of land vehicle comprising a transmission chain comprising a differential coupled to a wheel set, provided with a coupling device, and to an electric drive machine. Thus, it relates to utility vehicles, camper vans, minibuses, coaches, trucks, road machinery, construction machinery, and agricultural machinery, for example.

[0033] Furthermore, it is considered in the following, by way of non-limiting example, that the land vehicle V comprises a hybrid (thermal and electric) powertrain (or GMP) transmission chain. But the GMP could be of the all-electric type (and in this case the drive is provided exclusively by at least one electric motor (here MM1)).

[0034] [Fig.l] schematically shows a (land) vehicle V comprising a transmission chain including in particular a monitoring device DS according to the invention, a service battery BS, a rechargeable battery BR, a converter CV, and a first electric motor MM1, controlled by a machine computer CM and coupled to a differential DR, having blocked and non-blocked states and itself coupled to first DTI and second DT2 half-wheel sets, one of which (here DT2) comprises a first coupling device DC1.

[0035] It will be noted that in the example illustrated non-limitingly in [Fig.l] the transmission chain also comprises a second thermal motor MM2 and a possible third electric motor MM3, and a supervision computer CS. But the powertrain (or GMP) of the transmission chain could comprise only the first electric motor MM1, or the first MM1 and third MM3 electric motors, or even the first electric motor MM1 and the second thermal motor MM2.

[0036] It is recalled that the term “drive machine” here means a machine arranged at least so as to provide torque to move the vehicle V when it is supplied with drive energy.

[0037] The operation of the transmission chain (and therefore of the GMP) is supervised by a CS supervision computer.

[0038] The service battery BS is responsible for supplying electrical energy to the on-board network of the vehicle V, in addition to that supplied by the CV converter powered by the rechargeable battery BR via a main electrical circuit, and sometimes instead of this CV converter. For example, this service battery BS may be arranged in the form of a very low voltage type battery (typically 12 V, 24 V or 48 V). It is rechargeable at least by the CV converter. It is considered in the following, by way of non-limiting example, that the service battery BS is of the 12 V Lithium-ion type.

[0039] The on-board network is an electrical power supply network to which electrical (or electronic) equipment (or components) that consume electrical energy are coupled.

[0040] The main electrical circuit (or "high voltage" or "power") is connected, on the one hand, to the rechargeable battery BR via an interface device, and, on the other hand, to electronic equipment, such as for example the CV converter and the first MM1 and third MM3 (electric) motor machines. It also allows the rechargeable battery BR to be recharged by an external power source and temporarily coupled to a charging connector of the vehicle V.

[0041] The first electric motor MM1 (here an electric motor) is coupled to the rechargeable battery BR via the main electrical circuit, in order to be supplied with electrical energy, as well as possibly supplying this rechargeable BR battery with electrical energy during a regenerative braking phase.

[0042] Furthermore, this first electric motor MM1 is coupled to the differential DR via a first transmission shaft ATI. This differential DR is coupled to a first train T1 (of wheels) subdivided into a first half-train DTI provided with a first wheel RR1 and a second half-train DT2 provided with a second wheel RR2 and the first coupling device DC1. In addition, the differential DR can be selectively placed in an unlocked state, allowing different rotational speeds of the first RR1 and second RR2 wheels, or in a locked state, imposing identical rotational speeds of the first RR1 and second RR2 wheels.

[0043] The first coupling device DC1 can be selectively placed in a connected state in which the second wheel RR2 is connected to the sub-part of the second half-train DT2 which can be driven by the differential DR, or in a disconnected state in which the second wheel RR2 is disconnected from this same sub-part of the second half-train DT2.

[0044] For example, the first coupling device DC1 may be a dog clutch device. But this is not mandatory.

[0045] The first train T1 is here located in the rear part PRV of the vehicle V. But in a variant this first train T1 could be the one which is here referenced T2 and which is located in the front part PVV of the vehicle V.

[0046] The operation of the first electric motor MM1 is controlled by a machine computer CM, and supervised by the supervision computer CS.

[0047] It will be noted that in the example illustrated non-limitingly in [Fig.l] the transmission chain also comprises a first gearbox BV1 interposed between the output of the first electric motor MM1 and the first transmission shaft ATI. But this is not an obligation.

[0048] The second driving machine MM2 is thermal and is responsible, when supplied with fuel, for producing a driving torque and supplying the latter to a driving shaft AM which is connected to a second coupling device DC2. The latter (DC2) is capable of coupling the second driving machine MM2 to a primary shaft AP of a second gearbox BV2 to supply it with the driving torque produced by the second driving machine MM2.

[0049] The output shaft of the second gearbox BV2 is coupled to a second transmission shaft AT2 which is itself coupled to the second wheel set T2, preferably via a differential DV.

[0050] For example, the second coupling device DC2 may be a hydraulic circuit clutch. But it could be of another type.

[0051] Also for example, the second gearbox BV2 can be automated. So, for example, it can be dual clutch (or DCT (“Dual Clutch Transmission”)). But this is not obligatory.

[0052] It will be noted that in the example illustrated non-limitingly in [Fig.l] the crankshaft of the second prime mover MM2 is also coupled to a belt, itself coupled to an alternator-starter AD which is supplied with electrical energy by the service battery BS (and which can also recharge the latter (BS)). Thus, the alternator-starter AD can supply torque to the belt, which can supply this torque to the crankshaft.

[0053] The third driving machine MM3 is electric and is responsible, when supplied with electrical energy by the rechargeable battery BR, for producing a motor torque.

[0054] Furthermore, this third driving machine MM3 is capable of being coupled, downstream of the second coupling device DC2, by a third coupling device DC3, to the second gearbox BV2 to provide it with the engine torque that it produces.

[0055] The operation of the third electric motor MM3 is controlled by a machine computer (not shown), and supervised by the supervision computer CS.

[0056] The third coupling device DC3 can be placed in coupled and decoupled states, depending on a state instruction generated by the GMP supervision computer CS.

[0057] Furthermore, this third coupling device DC3 may, for example, comprise a cascade of pinions connecting the third driving machine MM3 to the input of the second gearbox BV2 (downstream of the second coupling device DC2).

[0058] The CV converter is also responsible, here, during the driving phases of the vehicle V for converting part of the electric current stored in the rechargeable battery BR to supply converted electric current to the on-board network and the service battery BS (to recharge it).

[0059] The rechargeable battery BR here powers the first MM1 and third MM3 electric motors, it constitutes a main (or traction) battery. It may, for example, comprise electrical energy storage cells, possibly electrochemical (for example of the lithium-ion (or Li-ion) or Ni-Mh or Ni-Cd type). Also for example, the rechargeable battery BR may be of the low voltage type (typically 450 V for illustration purposes). But it could be of the medium voltage or high voltage type.

[0060] It will also be noted that the vehicle V has a (current) speed vev which is estimated, preferably periodically. For example, this period may be between 10 milliseconds and 100 milliseconds. As an illustrative example, the period may be equal to 50 milliseconds.

[0061] For example, this (current) speed vev can be estimated by a possible trajectory control device equipping the vehicle V and which can be of the ESP / ABS type (ESP: “Electronic Stability Program”), ABS: “Anti-Blocking System”)), from information provided by a sensor associated here with one of the drive wheels. For example, this sensor can be coupled to a wheel hub and can constitute an angular encoder determining a number of teeth passing in front of it per second, and the computer of the trajectory control device can determine the distance traveled as a function of the number of teeth indicated by the sensor and the wheel development, then estimate the speed vev by integrating this distance traveled over time.

[0062] But the speed estimates (or measurements) vev could have an origin other than the trajectory control device calculator.

[0063] As mentioned above, the invention proposes in particular a monitoring method intended to enable monitoring of the placement in the blocked state of the differential DR of the land vehicle V.

[0064] This (monitoring) method can be implemented at least partially by the monitoring device DS (illustrated at least partially in FIGS. 1 and 2) which comprises for this purpose at least one processor PR1, for example a digital signal processor (or DSP ("Digital Signal Processor")), and at least one memory MD. This monitoring device DS can therefore be implemented in the form of a combination of electrical or electronic circuits or components (or "hardware") and software modules (or "software"). For example, it can be a microcontroller.

[0065] The memory MD is RAM in order to store instructions for the implementation by the processor PR1 of at least part of the monitoring method. The processor PR1 may comprise integrated (or printed) circuits, or several integrated (or printed) circuits connected by wired or wireless connections. An integrated (or printed) circuit is understood to mean any type of device capable of carrying out at least one electrical or electronic operation.

[0066] In the example illustrated non-limitingly in Figures 1 and 2, the monitoring device DS is part of the machine computer CM. But this is not obligatory. Indeed, the monitoring device DS could comprise its own dedicated computer, which is then coupled to the machine computer CM, or could be part of another computer of the vehicle V, such as for example the supervision computer CS.

[0067] As illustrated non-limitingly in [Fig. 3], the (monitoring) method, according to the invention, comprises a step 10-70 which is implemented each time the vehicle V has its GMP in operation and its first electric motor MM1 must provide or provides an engine torque cm.

[0068] Step 10-70 of the method comprises a sub-step 20 in which, when a When the DR differential is placed in the blocked state, the state in which the first coupling device DC1 is placed (i.e. connected or disconnected) is determined (e.g. the DS monitoring device).

[0069] It will be noted that the request for placement in the blocked state can come from the driver of the vehicle V or from a computer of the latter (V), such as for example the supervision computer CS.

[0070] Step 10-70 of the method also comprises a sub-step 30 in which, when the state determined in sub-step 20 is the disconnected state, the (for example the monitoring device DS triggers the placement of the) first coupling device DC1 is placed in the connected state. It will be noted that, when the state determined in sub-step 20 is the connected state, a sub-step 40 described below is directly carried out.

[0071] Step 10-70 of the method also comprises sub-step 40 in which, when the state determined in sub-step 20 is the connected state (or when the first coupling device DC1 has just been placed in the connected state in sub-step 30), the first electric motor MM1 is ordered to provide a variable motor torque cmv.

[0072] For example, the monitoring device DS can generate a request requiring the first electric motor MM1 to supply the variable motor torque cmv to the machine computer CM, and, upon receipt of this request, the machine computer CM controls the first electric motor MM1 so that it supplies this variable motor torque cmv.

[0073] Step 10-70 of the method also comprises a sub-step 60 in which, in the presence of at least one variation in engine torque cm received by at least one of the first RR1 and second RR2 wheels, one (for example the monitoring device DS) authorizes the placement of the differential DR in the blocked state.

[0074] It will be understood in fact that if the first coupling device DC1 is actually in its connected state, at least one of the first RR1 and second RR2 wheels must receive a portion of the variable engine torque cmv since this means that the first train T1 is coupled to the first electric motor MM1. Consequently, the variations of this portion of the variable engine torque cmv must be observable at the level of at least one of the first RR1 and second RR2 wheels.

[0075] It will therefore also be understood that, if the first coupling device DC1 is actually in its disconnected state (due to an absence of variation in engine torque received at at least one of the first RR1 and second RR2 wheels), one (for example the monitoring device DS) prohibits the placing of the differential DR in the blocked state in a sub-step 70 of step 10-70, as illustrated non-limitingly in [Fig.3].

[0076] The invention therefore makes it possible to automatically determine, with certainty, whether the first train T1 is actually coupled to the first electric motor MM1 before placing the differential DR in its locked state. There is therefore no longer any risk of the differential DR locking even though the second wheel RR2 cannot be rotated by this differential DR, which reinforces the safety of the vehicle V and its passengers, but also the safety of objects and people located in the environment of the vehicle V.

[0077] Preferably, the maximum variation amplitude of the variable engine torque cmv is small so as not to significantly disrupt the operation of the transmission chain and not to consume too much electrical energy stored in the rechargeable battery BR. For example, this maximum variation amplitude can be between 3 Nm and 10 Nm. As an illustrative example, the maximum variation amplitude can be equal to 5 Nm. But other values ​​of maximum variation amplitude can be used. For example, the value of the maximum variation amplitude can be chosen during the development phase of the vehicle V.

[0078] It will be noted that the engine torque received at a first RR1 or second RR2 wheel can be estimated from measurements made by at least one sensor coupled to this first RR1 or second RR2 wheel.

[0079] Also for example, and as illustrated non-limitingly in [Fig.3], step 10-70 may comprise a sub-step 50 in which one (for example the monitoring device DS) may analyze information representative of the engine torque cm received by at least one of the first RR1 and second RR2 wheels while the first electric motor MM1 provides the variable engine torque cmv. In this case, in the absence of variation in the analyzed received engine torque cm, sub-step 70 is carried out, while in the presence of at least one variation in the analyzed received engine torque cm, sub-step 60 is carried out.

[0080] Also for example, in sub-step 40 of step 10-70, it may be ordered (for example the monitoring device DS may require) that the first electric motor MM1 provides a motor torque cmv which varies according to a predefined variation law. This option makes it possible to anticipate the type of variation which must be observed at the level of at least one of the first RR1 and second RR2 wheels. But it could also be envisaged that the variation does not follow a predefined law. Thus, the variation could be purely punctual (small increase or reduction of a single value).

[0081] Also for example, in sub-step 40 of step 10-70, when using a predefined variation law, the latter may consist of a monotonic increase followed by a monotonic decrease. One could also use a predefined variation law consisting of a monotonic decrease followed by an increase monotonic. Preferably, the value of the motor torque at the end of the predefined variation law is the same as that which is in effect at the beginning of the latter. This makes it possible to operate the first electric motor MM1 in the same way just before and just after the application of the predefined variation law. Of course, other types of predefined variation law can be used, including sinusoidal or square-wave variation, for example.

[0082] Also for example, in sub-step 40 of step 10-70, when a predefined variation law is used and the motor torque cm has an initial value vi which is known when the first electric motor MM1 is ordered to supply the variable motor torque cmv, the predefined variation law can be applied (for example the monitoring device DS can trigger the application of) to the known initial value vi.

[0083] It will be understood that if the initial value vi is zero and therefore the first electric motor MM1 does not yet provide any motor torque, the predefined variation law starts from the zero value. On the other hand, if the initial value vi is non-zero and therefore the first electric motor MM1 already provides a motor torque cm of a known value, the predefined variation law starts from this known value. This makes it possible to avoid significantly disrupting the operation of the GMP.

[0084] It will also be noted that in step 10-70 it is possible to prohibit (for example the monitoring device DS can trigger a prohibition of) placing the differential DR in the blocked state when the current speed vev of the vehicle V is greater than a threshold if chosen. It is indeed preferable that a blocking of the differential DR is not carried out beyond a certain current speed vev, to avoid damaging at least one element of the transmission chain (for example the first coupling device DC1 and / or the differential DR).

[0085] In this case, and as illustrated non-limitingly in [Fig.3], step 10-70 may comprise a sub-step 10 in which one (for example the monitoring device DS) may begin by comparing the current speed vev with the threshold si.

[0086] If the result of the comparison indicates that the current speed vev is less than or equal to the threshold si, sub-step 20 is carried out.

[0087] On the other hand, if the result of this comparison indicates that the current speed vev is greater than the threshold si, sub-step 10 will be carried out again when the next current speed vev is available. It will be noted that one (for example the monitoring device DS) can also request a reduction in the speed of the vehicle V so that it becomes less than or equal to the threshold si, for example from the supervision computer CS.

[0088] For example, in substep 10 of step 10-70 the threshold si can be understood between 20 km / h and 40 km / h. As an illustrative example, the threshold si can be equal to 30 km / h. But other threshold si values ​​can be used. For example, the threshold si value can be chosen during the vehicle development phase V.

[0089] It will also be noted, as illustrated non-limitingly in [Fig. 2], that the machine computer CM (or the computer of the monitoring device DS) can also comprise a mass memory MEM, in particular for storing each current state of the first coupling device DC1, each piece of information representative of the engine torque cm received by at least one of the first RR1 and second RR2 wheels while the first electric motor machine MM1 provides the variable engine torque cmv, and each possible current speed vev, as well as any intermediate data involved in all its calculations and processing.Furthermore, this machine calculator CM (or the calculator of the monitoring device DS) may also comprise an input interface IE for receiving at least each request for placement in the blocked state, each information representative of the engine torque cm received by at least one of the first RR1 and second RR2 wheels while the first electric motor MM1 provides the variable engine torque cmv, and each possible current speed vev, to use them in calculations or processing, possibly after having formatted and / or demodulated and / or amplified them, in a manner known per se, by means of a digital signal processor PR2. In addition, this machine calculator CM (or the calculator of the monitoring device DS) may also comprise an output interface IS, in particular for delivering a message (or order) authorizing or prohibiting placement in the blocked state, and a possible request to reduce the speed of the vehicle V..

[0090] It will also be noted that the invention also proposes a computer program product (or computer program) comprising a set of instructions which, when executed by processing means of the electronic circuit (or hardware) type, such as for example the processor PR1, is capable of implementing the monitoring method described above to monitor in the land vehicle V the placement of the differential DR in the blocked state.

Claims

Claims

1. Monitoring method for a land vehicle (V) comprising i) a first half-train (DTI) provided with a first wheel (RR1), ii) a second half-train (DT2) provided with a second wheel (RR2) and a coupling device (DC1) capable of being placed in connected and disconnected states in which said second wheel (RR2) is respectively connected and disconnected, and iii) an electric motor (MM1) coupled to a differential (DR) capable of being placed in locked and unlocked states and coupled to said first (DTI) and second (DT2) half-trains, characterized in that it comprises a step (10-70) in which, when a placement of said differential (DR) in the locked state is requested, the state in which said coupling device (DC1) is placed is determined and if this determined state is said disconnected state, said coupling device (DC1) is placed in the connected state,then said electric motor (MM1) is ordered to provide a variable engine torque and, in the presence of at least one variation in engine torque received by at least one of said first (RR1) and second (RR2) wheels, said placement of the differential (DR) in the blocked state is authorized.,

2. Method according to claim 1, characterized in that in said step (10-70) it is ordered that said electric motor (MM1) provides a motor torque varying according to a predefined variation law.

3. Method according to claim 2, characterized in that in said step (10-70) said predefined variation law consists of a monotonic increase followed by a monotonic decrease.

4. Method according to claim 2, characterized in that in said step (10-70) said predefined variation law consists of a monotonic decrease followed by a monotonic increase.

5. Method according to one of claims 2 to 4, characterized in that in said step (10-70), when said engine torque has a known initial value when said electric motor (MM1) is ordered to provide said variable engine torque, said predefined variation law is applied to said known initial value.

6. Method according to one of claims 1 to 5, characterized in that in said step (10-70) said placement of the differential (DR) in the blocked state is prohibited when a current speed of said vehicle (V) is greater than a chosen threshold.

7. Method according to claim 6, characterized in that in said step (10-70) said chosen threshold is between 20 km / h and 40 km / h.

8. A computer program product comprising a set of instructions which, when executed by processing means, is suitable for implementing the monitoring method according to one of claims 1 to 7, in a land vehicle (V) comprising i) a first half-train (DTI) provided with a first wheel (RR1), ii) a second half-train (DT2) provided with a second wheel (RR2) and a coupling device (DC1) capable of being placed in connected and disconnected states in which said second wheel (RR2) is respectively connected and disconnected, and iii) an electric motor (MM1) coupled to a differential (DR) capable of being placed in locked and unlocked states and coupled to said first (DTI) and second (DT2) half-trains, for monitoring the placement of said differential (DR) in the locked state.

9. Monitoring device (DS) for a land vehicle (V) comprising i) a first half-train (DTI) provided with a first wheel (RR1), ii) a second half-train (DT2) provided with a second wheel (RR2) and a coupling device (DC1) capable of being placed in connected and disconnected states in which said second wheel (RR2) is respectively connected and disconnected, and iii) an electric motor (MM1) coupled to a differential (DR) capable of being placed in locked and unlocked states and coupled to said first (DTI) and second (DT2) half-trains, characterized in that it comprises at least one processor (PR1) and at least one memory (MD) arranged to carry out the operations consisting, when a placement of said differential (DR) in the locked state is requested,to determine the state in which said coupling device (DC1) is placed and if this determined state is said disconnected state to trigger a placement of said coupling device (DC1) in the connected state, then to require that said electric motor (MM1) provides a variable engine torque and, in the presence of at least one variation in engine torque received by at least one of said first (RR1) and second (RR2) wheels, to authorize said placement of the differential (DR) in the blocked state.,

10. Land vehicle (V) comprising i) a first half-train (DTI) provided with a first wheel (RR1), ii) a second half-train (DT2) provided with a second wheel (RR2) and a coupling device (DC1) capable of being placed in connected and disconnected states in which said second wheel (RR2) is respectively connected and disconnected, and iii) a electric motor (MM1) coupled to a differential (DR) which can be placed in locked and unlocked states and coupled to said first (DTI) and second (DT2) half-trains, characterized in that it further comprises a monitoring device (DS) according to claim 9.

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