FR2964715A1 - METHOD FOR STORING AMOUNT REPORTS FOR AUTOMATIC GEARBOX OF A MOTOR VEHICLE - Google Patents

Abstract

According to this method, the vehicle comprising a clutch for transmitting a torque (CM) of a motor shaft to a primary shaft and the gearbox comprising two couplers each for transmitting a torque from the primary shaft to a secondary shaft: a) the two couplers are placed in their sliding state, b) the clutch is placed in its sliding state, c) the torque (CCI) transmitted by said initial coupler is reduced and the torque (CCF) transmitted by the final coupler, d) when the torque transmitted by the initial coupler reaches a zero value, it imposes on the final coupler and the clutch two torque setpoints causing a decrease in the speed of rotation of the primary shaft to a target value, then, when it is reached, e) the final coupler is placed in its locked state, then f) the torque of the motor shaft is controlled to synchronize the motor shaft and the primary shaft, and then the clutch in its state Locked. According to this method, in step d), the torque setpoint imposed on the clutch causes the reduction of the torque transmitted by the clutch from a reference value (Cref) to a target value (C target) of lower torque.

Description

TECHNICAL FIELD TO WHICH THE INVENTION RELATES The present invention relates to a method for shifting gear ratios for an automatic transmission of a motor vehicle, said vehicle comprising a clutch for transmitting a torque of a motor shaft driven by the motor of the motor vehicle. vehicle to a primary shaft and said gearbox having at least two couplers each for transmitting a torque from the primary shaft to a secondary shaft, the clutch and each coupler being adapted to transmit either the entire torque when are placed in a locked state, either an adjustable part of the torque when placed in a sliding state, or no torque when placed in an open state, comprising the following steps: a) a first one of said couplers, called initial coupler, being initially in its locked state, while the second coupler, called the final coupler, is in its open state, the two couplers are placed in their sliding state, b) the clutch is placed in its sliding state, c) the torque transmitted by said initial coupler is reduced and the torque transmitted by the final coupler is increased, d) when the torque transmitted by the initial coupler reaches a zero value, the final coupler and the clutch are imposed two torque setpoints, adapted to cause a decrease in the speed of rotation of the primary shaft to a value speed target, then, when this target value is reached, e) we put the final coupler in its locked state, then f) we drive the torque of the motor shaft to synchronize the motor shaft and the primary shaft and then place the clutch in its locked state. BACKGROUND OF THE INVENTION Document FR1050957 (not published on the filing date) is particularly known from such a method in which in step c) the final coupler is imposed with a first increasing and linear torque set point having a first constant growth rate. . In step d), in a first phase, the final coupler is then imposed with a second set of linear increasing torque of growth rate equal to said first growth rate, the torque transmitted by the clutch being kept constant. During this step d), the torque transmitted by the final coupler becomes greater than the torque transmitted by the clutch, which causes a decrease in the speed of rotation of the primary shaft. The step according to which the speed of rotation of the primary shaft is decreased to reach a target value of speed is called in the following stage of synchronization of the primary shaft.

According to the method described in this document, when the synchronization of the primary shaft is initiated, that is to say when a difference in speed of rotation greater than a threshold value is detected between the primary shafts and motor motor, in a second phase, the final coupler is imposed with a synchronization instruction of the primary shaft.

This synchronization setpoint of the primary shaft is initially equal to the estimated real value of the torque transmitted by the final coupler at the moment when the rotation speed difference becomes greater than said threshold and then increases linearly according to a second growth rate lower than said first rate of growth.

This method has defects related to a slow response dynamics of the final coupler to the setpoint imposed on it. Thus, even though the synchronization setpoint of the primary shaft is applied to the final coupler and imposes a torque increase slower than in the first phase of step d) described in this document, the torque transmitted by the final coupler continues to grow according to the first high growth rate of this first phase. The difference between the couples transmitted by the final coupler and the clutch therefore increases faster than expected according to the instructions imposed. The angular acceleration of the primary shaft being proportional to this torque deviation transmitted by the final coupler and the clutch, the synchronization is performed faster than expected according to the imposed instruction. The difference between the actual and the target torque is also greater than expected at the end of the reduction in the speed of rotation of the primary shaft, which causes a shock to the wheel at the end of synchronization of the primary shaft, when the final coupler is locked and the wheel torque suddenly returns to the value before the start of synchronization. This shock to the wheel is perceived unpleasantly by the driver. OBJECT OF THE INVENTION The object of the present invention is to improve the comfort of the driver during the shift gearbox. For this purpose, according to the invention, there is provided a method for shifting gears according to which, in step d), the torque setpoint imposed on the clutch performs a step d1) of reducing the torque transmitted by the clutch. from a reference value to a torque target value less than this reference value. The angular acceleration of the primary shaft is proportional to the difference between the torque transmitted by the clutch and the torque transmitted by the final coupler. Indeed, the following relation is present during the synchronization of the primary shaft: Cemb - Cfin = Jp.ap where - Cemb is the torque transmitted by the clutch, - Cfin is the torque transmitted by the final coupler, - Jp is the inertia constant of the primary shaft, - ap is the angular acceleration of the primary shaft. While in the state of the art, the reduction in the speed of rotation of the primary shaft, achieved by a negative angular acceleration, is obtained by imposing on the final coupler an increasing torque setpoint greater than a torque setpoint of 1. constant clutch, according to the invention, it imposes a torque setpoint to the decreasing clutch, so that the torque transmitted by the clutch becomes lower than the torque transmitted by the final coupler. The method according to the invention makes it possible to eliminate the shocks felt by the driver at the end of decreasing the speed of rotation of the primary shaft and thus to improve the comfort of the driver. According to other advantageous and non-limiting characteristics of the method according to the invention, the torque setpoint imposed on the clutch performs after step d1 a step d2) of increasing the torque transmitted by the clutch up to said reference value; step d1) is performed at the moment when the torque transmitted by the initial coupler reaches a zero value; during step d2), the difference between said reference value and the torque setpoint imposed on the clutch can be chosen equal to the product of the inertia constant of the primary shaft and a desired decay for the speed of rotation of the primary shaft; during step d2), the torque setpoint imposed on the clutch is determined as a function of the difference between the speed of rotation of the primary shaft and said target value of speed; during step d2), the torque setpoint imposed on the clutch imposes an increase in torque, and therefore a return to the reference value of this couple, which is faster and faster as the the difference between the speed of rotation of the primary shaft and said target speed value decreases; in step d), said torque setpoint imposed on the final coupler is a constant torque setpoint; in step d), said torque setpoint imposed on the final coupler is an increasing torque setpoint; in step c), the final coupler is imposed with a first increasing torque setpoint having a first constant growth rate, and in step d), the final coupler is imposed with a second increasing torque setpoint having a second growth less than said first growth rate; in step d), if the difference between the speed of rotation of the primary shaft and said target value of speed is not zero after a predetermined time after the moment when the torque transmitted by the coupler initial reaches a zero value, the torque setpoint imposed on the clutch performs again the step d1) of decreasing the torque transmitted by the clutch, then the step d2) of increasing the torque transmitted by the clutch.

The invention also relates to a motor vehicle comprising: - a clutch for transmitting a torque from a motor shaft driven by the vehicle engine to a primary shaft, - a gearbox comprising at least two couplers each making it possible to transmit a torque from the primary shaft to a secondary shaft, the clutch and each coupler being adapted to transmit either the entire torque when placed in a locked state or an adjustable portion of the torque when placed in a state slip, or no torque when placed in an open state, each coupler being associated with a gearbox having a torque reduction coefficient associated with a ratio of said gearbox, and a computer programmed to drive a change of gearbox. transmission ratios according to the method described above. DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT The following description, with reference to the appended drawings, given by way of non-limiting example, will make it clear what the invention consists of and how it can be achieved. In the accompanying drawings: - Figure 1 is a schematic representation of the transmission means of a motor torque to the wheels of a motor vehicle; FIG. 2A shows the evolution of the R-speed of the motor (RM curve) and of the primary shaft (RP curve) as a function of time; FIG. 2B shows the evolution of the operating state E of the clutch (EE curve), of the initial coupler (ECI curve) and of the final coupler (ECF curve) as a function of time; FIG. 2C shows the evolution of the torque C transmitted by the clutch (curve CE), by the initial coupler (curve CCI), by the final coupler (curve CCF) and by the motor (curve CM) as a function of time . FIG. 3A shows the evolution of the R speed of the primary shaft (curve RP) as a function of time and FIG. 3B shows the corresponding evolution of the torque transmitted by the clutch CE as a function of time; - Figures 4A and 4B are enlarged partial views of Figures 2A and 2C between instants t1 and t4 aligned vis-à-vis Figure 4C which shows the evolution of the torque transmitted to the vehicle wheels as a function of time. Device Diagrammatically in Figure 1 an internal combustion engine 1 of a motor vehicle comprising a motor block 12 which projects one end of a crankshaft 2 called in the following "motor shaft 2". This drive shaft 2 is rotated about its axis by the engine block 12. Transmission means 15 ensure the transmission of the torque of the drive shaft 2 to 11 motor wheels of the motor vehicle.

There is shown the case of a vehicle having two drive wheels 11 integral in rotation with two lateral transmission shafts 13. In practice, these two 11 drive wheels are the front wheels of the vehicle. The torque transmission means comprise a clutch 4 whose input shaft is integral in rotation with the drive shaft 2, an automatic gearbox 16 including the input shaft 3, hereinafter referred to as "shaft 3 "primary, is integral in rotation with the output shaft of the clutch 4, and a differential 10 whose input shaft is integral in rotation with the output shaft 9 of the gearbox 16, called in the following "secondary shaft" and whose output shafts 13 are integral in rotation with the two lateral transmission shafts 13. The clutch 4 is a temporary coupling device between the drive shaft 2 and the primary shaft 3. It comprises at least two disks adapted to come into contact with each other to gradually transmit the torque from the drive shaft 2 to the primary shaft 3. The automatic gearbox 16 comprises at least two couplers 5, 6. These couplers 5, 6 are here conical couplers compor each of them two complementary parts adapted to come into contact with each other to gradually transmit torque from the primary shaft 3 to the secondary shaft 9. In practice, the gearbox has as many couplers as reports . Each coupler 5, 6 is associated with a gearbox 7, 8 which has a coefficient of reduction of the characteristic torque of the ratio of the gearbox corresponding to this coupler. The clutch 4 and each of the couplers 5, 6 of the gearbox 16 can be placed in three different operating states, including a locked state, denoted V in FIG. 2B, an open state, noted O in FIG. 2B, and a slip state, noted G in Figure 2B. When the clutch 4 or one of the couplers 5, 6 is locked, it transmits integrally the torque of its input shaft to its output shaft.

Thus, when the clutch 4 and the coupler 5, 6 chosen by the automatic gearbox 16 are locked, the torque supplied by the engine 1 is integrally transmitted to the wheels 11 of the vehicle. When the clutch 4 or one of the couplers is open, no torque is transmitted by this clutch 4 or this coupler 5, 6.

Thus, when the clutch 4 or all the couplers 5, 6 are open, the torque transmission is interrupted so that the vehicle is freewheeling. When the clutch 4 or one of the couplers 5, 6 is in the sliding phase, the disks of the clutch 4 or the complementary parts of each coupler 5, 6 slide against each other. In this state, it is possible to precisely modulate the transmitted torque by controlling the pressurizing force of the two disks of the clutch or the two complementary parts of each coupler against each other. To control the various components of the motor vehicle 1 and in particular the clutch 4 and the gearbox 16, there is provided a computer (not shown). The computer is adapted to receive input signals from different sensors. These input signals make it possible to determine parameters relating to the operation of the vehicle, such as, for example, the speed of the vehicle V, or the speeds of rotation, hereinafter referred to as "speeds", and the angular accelerations of the driving shaft 2. primary shaft 3, secondary shaft 9 and lateral shafts 13.

The computer includes in memory vehicle parameters, such as its mass for example, and maps obtained from calibrations giving the target value of the engine shafts 2 and 3 of the vehicle based on the speed of the vehicle and the gear ratio. the gearbox used, that is to say according to the coupler 5, 6 chosen.

Thanks to the parameters measured by the sensors and to the stored parameters, the computer 100 is adapted to generate, for each operating condition of the vehicle, output signals transmitted to the various components of the vehicle to drive them. Process FIGS. 2A, 2B and 2C show in parallel the evolutions: of the R speed of the motor shaft, hereinafter "motor speed" (RM curve) and of the primary shaft, hereinafter "primary speed" ( curve RP), - the operating state E of the clutch (curve EE), an initial coupler (curve ECI) and a final coupler (curve ECF) and - the torque C transmitted by the clutch (CE curve), by the initial coupler (CCI curve), by the final coupler (CCF curve) and by the motor (CM curve) as a function of time. The coupler of the gearbox, which transmits the torque before the shifting, is called the initial coupler and the coupler of the gearbox that transmits the torque after the shifting is called the final coupler. The method described here relates to a change of upward ratios. For example, the gearbox 8 associated with the coupler 6 has a torque reduction coefficient lower than the gear reduction coefficient of the gearbox 7 associated with the coupler 5. The initial coupler is then in this example the coupler 5 of the gearbox and the gearbox. The final coupler is the coupler 6. The time t1 corresponds to the moment when the transmission gear shift 16 is triggered. Before this instant t1, as shown in FIG. 2B, the initial coupler 5 and the clutch 4 are locked and the final coupler 6 is open. As a result, as shown in FIG. 2C, the torque CCF transmitted by the final coupler 6 is zero before t1, while the initial coupler 5 and the clutch 4 transmit a pair CCI whose value Cref is the reference value corresponding to the torque demanded by the driver considering inertial losses and friction.

In the shifting example described in detail below, it is assumed that this Cref value is constant during the shifting. At the time t1 of the beginning of the gear change, the vehicle computer places, in a step a), the initial couplers 5 and final 6 in their slip state (Figure 2B).

Here the vehicle computer also places, in a step b) simultaneously in step a), the clutch 4 in its sliding state (Figure 2B). Alternatively, this step b) can be performed later, as explained below. In this state, the initial coupler 5 and the clutch 4 continue between the time t1 and the time t2 to transmit the same pair CCI, EC as when they were locked (Figure 2C). Between times t2 and t3, the computer controls, according to a step c) of the method, the transfer of the torque between the initial couplers 5 and final 6. For this, the computer imposes on the final coupler 6 a first set of increasing torque. This first torque setting is here linear, that is to say that it has a first constant growth rate in the example shown in the figures. However, it is possible to envisage other types of first torque setpoint, for example a linear torque setpoint in a first phase and then increasing more slowly so that its growth rate is canceled when the torque transfer is completed. The rate of change of the function of time associated with the setpoint under consideration is called growth rate, when this rate of variation is positive. It corresponds here to the slope of the line representative of this instruction.

The first growth rate is predetermined. The driver computer preferably for the transfer of torque a passage under torque: it controls a decrease in the torque CCI transmitted by the initial coupler 5 and an increase in the torque CCF transmitted by the final coupler 6, so that the sum of the couples transmitted by the two initial and final couplers remains constant during this step c). The sum of the two couples transmitted by the initial couplers 5 and final 6 thus remains equal to the reference value Cref.

The torque CR applied to the wheels of the vehicle being equal to the sum of the torques transmitted by each coupler weighted by the reduction coefficient of the associated reducer, and the reduction coefficient of the reducer associated with the final coupler being lower than that of the reducer associated with the initial coupler , the CR torque applied to the vehicle wheels then decreases steadily during step c). This reduction in the torque CR applied to the wheels is shown in FIG. 4C between the times t2 and t3. The torque transmitted by all of the two initial couplers 5 and final 6 thus remaining constant and the reduction of the torque CR applied to the wheels during the torque transfer being regular and continuous, this makes it possible to avoid any unpleasant feeling for the driver, for example. example any shock sensation. As represented in FIG. 2A, during the steps a), b) and c) previously described, that is to say between the times t1 and t3, the engine speed RM and the primary regime RP follow the same evolution according to the time determined by a target regime Cl. This target speed C1 is predetermined according to the ratio of the gearbox 16 and the speed of the vehicle. The target regime C1 shown in Figs. 2A, 3A and 4A corresponds to the target engine speed for the ratio of the initial coupler 5 and for an increasing vehicle speed. The torque transfer step c) ends at time t3 when the torque CC1 transmitted by the initial coupler 5 becomes zero, which indicates that the initial coupler 5 is open. The final coupler 6 then transmits a torque CCF equal to the reference value Cref and is still in its sliding state (FIGS. 2B and 2C). It is therefore also possible to define the time t3 as that at which the torque CCF transmitted by the final coupler 6 becomes equal to the reference value Cref. In a step d) occurring between the time t3 and a time t4, the computer imposes on the final coupler 6 and the clutch 4 torque setpoints adapted to cause a decrease in the primary regime, so as to converge the value of the primary regime RP to a new target regime C2 corresponding to the ratio associated with the final coupler 6 (FIG. 2A). This target regime C2 is shown in FIGS. 2A, 3A and 4A for an increasing vehicle speed and corresponds to the target rotational speed values of the primary shaft 3 for the final report. This step corresponds to the synchronization of the primary shaft 3. According to the relation Cemb-Cfin = CE-CCF = Jp.ap, in which Jp represents the inertia constant of the primary shaft 3, which is valid during the synchronization of the primary shaft 3, the angular acceleration ap of the primary shaft 3 is negative when the torque difference transmitted between the clutch 4 and the final coupler 6 is negative.

The computer therefore controls the reduction of the primary speed RP by imposing on the final coupler 6 a second torque setpoint and imposing on the clutch 4 a third torque set point that the torque CE transmitted by the clutch 4 is less than the transmitted torque. by the final coupler 6 during this step d).

Remarkably, according to the invention, the third torque setpoint imposed by the computer on the clutch 4 performs a fading of the torque transmitted by the clutch 4. More specifically, the third torque setpoint imposed on the clutch 4 realizes a step d1) of decreasing the torque transmitted by the clutch 4 from said reference value Cref to a target value C target of torque less than this reference value Cref (FIGS. 2C, 3B and 4B). The dimming of the torque CE transmitted by the clutch 4 then comprises a step d2) of slower increase of the torque CE transmitted by the clutch to its initial value before the shading, that is to say Cref .

The difference between the reference value of the pair Cref and the value C target of the beginning of the shading is calibrated. Step d1) is performed at time t3 when the torque CC1 transmitted by the initial coupler 5 reaches a zero value. The clutch 4 must be placed in its sliding state before this time t3. It can be placed in this slip state at any time between times t1 and t3. The fact of placing the clutch 4 in its slip state before the time t3 is advantageous because it ensures an immediate response of the clutch 4 to the third setpoint imposed on it from the time t3. According to a first embodiment of the method according to the invention, during step d2) of increasing the torque, the difference between said torque reference value Cref and the third torque setpoint is equal to the product of the constant d inertia of the primary tree and a desired rate of decay for the primary diet. The rate of change associated with the function representing the regime as a function of time, when this rate of variation is negative, is called the decay rate. In other words, the third torque set point imposing the increase of the torque CE during step d2) can be determined by the computer according to the desired slope for the curve RP (FIGS. 2A, 3A and 4A) between t3 and t4. It is possible, for example, to choose a desired duration for the decrease of the primary regime, equal to the difference t4 - t3. Knowing the primary regime difference RP between the target regimes C1 and C2 which are in the computer's memory, the latter determines the third setpoint as a function of the ratio between the target speed difference and the desired duration. According to a second embodiment of the method according to the invention, during step d2), the third torque setpoint is determined by the computer as a function of the difference between the primary regime RP and the target regime C2 at each instant . This second embodiment is shown schematically in FIGS. 3A and 3B.

More precisely, said third set point imposes an increase in the torque CE transmitted by the clutch 4 faster and faster as the difference between the primary regime RP and said target regime C2 decreases. The computer then uses, in order to determine the third torque setpoint, a predetermined map as a function of the differences between the primary regime RP and said target regime C2 and in memory of the computer. Whatever the third torque setpoint imposed on the clutch 4, said second torque setpoint imposed on the final coupler 6 is such that the torque CCF transmitted by the final coupler 6 remains greater than the torque CE transmitted by the clutch 4. torque difference transmitted between the clutch 4 and the final coupler 6 is then negative and the primary regime decreases. The second torque setpoint is, for example, an increasing torque setpoint between times t3 and t4, as shown in FIGS. 2C and 4B. More precisely, the first torque setpoint imposed on the final coupler 6 during the linearly increasing torque transfer according to said first growth rate, the second torque setpoint is an increasing torque setpoint having a growth rate lower than said first growth rate. In particular, this second torque setpoint is linear and has a second constant growth rate and less than said first growth rate. It can also be envisaged that this second torque setpoint is not linear but always has a growth rate lower than said first growth rate. It may be for example a second set of torque increasing more slowly. With this second set of increasing torque, a negative torque difference is maintained between the clutch 4 and the final coupler 6 even when the torque CE transmitted by the clutch 4 becomes very close to the reference value Cref, so as to allow the completion of synchronization of the primary shaft. In a variant, said second torque setpoint is a constant torque setpoint equal to the reference value Cref. At time t4, the primary regime RP reaches the target regime C2. The primary shaft 3 is then synchronized to the target speed corresponding to the ratio associated with the final coupler 6. As represented in FIG. 4, the torque CR applied to the wheels of the vehicle decreases steadily between t3 and t4, during this synchronization step of FIG. primary shaft, continuously with the reduction of the CR wheel torque initiated during the transfer of torque between t2 and t3. No jerk is thus felt by the driver during synchronization of the primary shaft.

The final coupler 6 is then locked (FIG. 2B) in a step e) and transmits from this instant t4 the entirety of the reference torque Cref requested by the driver. If the computer does not detect that the difference between the primary speed and the new target speed C2 becomes zero after a predetermined time after the moment when the torque CCI transmitted by the initial coupler reaches a zero value in step c ), the computer is programmed to impose again the step d1) of decreasing the torque CE transmitted by the clutch 4 and the step d2) of increasing the torque CE transmitted by this clutch 4. Once the synchronization of the primary shaft 3 on the new target speed C2, the computer controls the synchronization of the motor shaft 2 on the primary shaft 3. For this, the clutch 4 in its sliding state is used to achieve a reduction of the engine torque CM authorizing the decrease of the engine speed RM towards the target mode C2. The smearing of the motor torque CM causing the synchronization of the motor shaft 2 is carried out between the times t4 and t5 (FIGS. 2A to 2C). A sudden decrease in the motor torque CM from the reference value Cref to a lower torque value is followed by a slower increase in the engine torque to its initial value equal to the reference value Cref. When the computer detects that the engine speed RM is equal to the new value of the target speed C2 at time t5, it places the clutch 4 in its locked state and the shift of the gearbox 16 is completed. The smearing of the engine torque CM is thus achieved by the sliding of the clutch 4 and not the final coupler 6, it avoids the creation of vibrations propagated in the transmission means 15 and causing unpleasant sensations and noises for the occupants of the vehicle.

In addition, the final coupler is thus not damaged by prolonged sliding: the clutch is more resistant to the energy dissipation caused by this sliding. The gearshift method proposed therefore allows gear shifting to provide improved driver comfort, avoiding noise and shock sensations. The present invention is not limited to the embodiments described and shown, but the skilled person will be able to make any variant consistent with his mind.

Claims (11)

REVENDICATIONS1. A gearshift method for an automatic transmission (16) of a motor vehicle, said vehicle having a clutch (4) for transmitting a torque (CM) of a motor shaft (2) driven by the motor (1 ) of the vehicle to a primary shaft (3) and said gearbox (16) having at least two couplers (5, 6) each for transmitting a torque from the primary shaft (3) to a secondary shaft (9), the clutch (4) and each coupler (5, 6) being adapted to transmit either the entire torque when they are placed in a locked state or an adjustable part of the torque when they are placed in a sliding state , or no torque when placed in an open state, said method comprising the following steps: a) a first (5) of said couplers, called initial coupler (5), being initially in its locked state, while the second coupler (6), called final coupler (6), is in its open state, the two couplers (5, 6) are placed in their sliding state, b) the clutch (4) is placed in its sliding state, c) the torque (CCI) transmitted by the coupler is reduced; initial (5) and increases the torque (CCF) transmitted by the final coupler (6), d) when the torque (CCI) transmitted by the initial coupler (5) reaches a zero value, the final coupler (6) is imposed and at the clutch (4) two torque setpoints, adapted to cause a decrease in the rotational speed (RP) of the primary shaft (3) to a target value (C2) of speed, and then when this target value (C2) is reached, e) the final coupler (6) is placed in its locked state, then f) the torque of the motor shaft is controlled to synchronize the motor shaft (2) and the primary shaft ( 3) then the clutch (4) is placed in its locked state, characterized in that, in step d), the torque setpoint imposed on the clutch (4) performs a step d1) of reducing the clutch u torque transmitted by the clutch (4) from a reference value (Cref) to a target value (target) of torque less than this reference value (Cref). 2. Method according to claim 1, wherein step dl) is performed at the moment when the torque (CCI) transmitted by the initial coupler (5) reaches a zero value. 3. Method according to one of claims 1 and 2, wherein in step d), the torque setpoint imposed on the clutch (4) performs after step dl) a step d2) of increasing the torque ( CE) transmitted by the clutch (4) to said reference value (Cref). 4. Process. according to claim 3, wherein, in step d2), the difference between said reference value (Cref) and the torque setpoint imposed on the clutch (4) is equal to the product of the inertia constant (Jp) of the primary shaft (3) and a desired decay rate for the rotational speed of the primary shaft (3). 5. Method according to claim 3, wherein, in step d2), the torque setpoint imposed on the clutch (4) is determined as a function of the difference between the speed of rotation of the primary shaft ( 3) and said target value (C2) of speed. 6. The method of claim 5, wherein, in step d2), the torque setpoint imposed on the clutch (4) imposes a torque increase faster and faster as the gap between the rotational speed of the primary shaft (3) and said target value (C2) of speed decreases. 7. Method according to one of the preceding claims, wherein in step d), said torque setpoint imposed on the final coupler (6) is a constant torque setpoint. 8. Method according to one of the preceding claims, wherein in step d), said torque setpoint imposed on the final coupler (6) is an increasing torque setpoint. 9. The method according to claim 8, wherein, in step c), imposing on the final coupler (6) a first increasing torque setpoint having a first constant growth rate and in step d), imposing the final coupler (6) a second increasing torque setpoint having a second growth rate lower than said first growth rate. The method according to claim 3, wherein in step d), if the difference between the speed of rotation of the primary shaft (3) and said target value (C2) speed is not zero at after a predetermined time after the moment when the torque (CCI) transmitted by the initial coupler (5) reaches a zero value, the torque setpoint imposed on the clutch (4) again performs the step d1) of decreasing torque (CE) transmitted by the clutch (4), then step d2) increasing the torque (CE) transmitted by the clutch (4). 11. Motor vehicle comprising: - a clutch (4) for transmitting a torque (CM) of a motor shaft (2) driven by the engine (1) of the vehicle to a primary shaft (3), - a gearbox (16) comprising at least two couplers (5, 6) each for transmitting a torque from the primary shaft (3) to a secondary shaft (9), the clutch (4) and each coupler (5, 6) being adapted to transmit either the entire torque when placed in a locked state, or an adjustable portion of the torque when placed in a slip state, or no torque when placed in an open state, each coupler (5, 6) being associated with a gearbox (7, 8) having a torque reduction coefficient associated with a ratio of said gearbox, characterized in that it comprises a computer programmed to control a change of gear ratios. the gearbox (16) according to the method of one of the endications 1 to 10.