FR2848154A1 - Motor vehicle transmission control has computer to analyze information from sensors to determine driving parameters and optimize shift operation - Google Patents

Abstract

The motor vehicle gearbox (4) shift control has sensors (20,24,26) for vehicle operating parameters and a computer (12) to analyze the parameter data. The computer analyses driver gear shift input to determine a shift movement accuracy in regard to the operating conditions and select an optimum ratio. The computer establishes a correction parameter between the actual and required transmission shift and corrects downshift movement.

Description

i

  The invention relates to a system and method for controlling a gearbox of a motor vehicle. It also relates to means of analysis implemented in the system.

  Such systems have already been disclosed in French patent application FR 2 795 796. These known systems include: - means for acquiring information relating to the conditions of movement of the vehicle; means of acquiring information relating to the operating conditions of the vehicle engine; - means of acquiring information relating to the driving of the vehicle by the driver; a clutch / disengage pedal allowing the driver of the vehicle to adjust the clutch / disengage level of the clutch mechanism; - means for detecting the depression of this clutch / disengage pedal by the driver; and - means for analyzing the acquired information able, in response to the detection of the depressing of the clutch / disengaging pedal, to: - establish, using different analysis criteria, vectors 20 d information representative of the driver's desire to change the gearbox, each analysis criterion providing an information vector comprising at least one decision variable defining desired gear change information and one variable degree of confidence in this decision; - determine a new gearbox report to be engaged from the established information vectors; and issue corresponding control orders to the gearbox to initiate this report.

  These known systems automatically determine, in response to the depressing of the clutch / disengaging pedal, the gear ratio to be engaged. The analysis criteria used are established for typical travel conditions. These typical travel conditions correspond to the most frequent situation, that is to say a movement of the vehicle without excessive load and on a horizontal road. Thus, this automatic determination does not take into account, for example, the inclination of the road with respect to the horizontal. Consequently, if the road is inclined with respect to the horizontal, and in particular in the case of a climb, the ratio 5 determined automatically may not be optimal and lead to operation of the motor vehicle under engine speed.

  The invention aims to remedy this drawback.

  The subject of the invention is therefore a system as described above, characterized in that the analysis means are able to: - establish a parameter for correcting analysis criteria, the value of which is a function of a difference between the actual movement conditions of the motor vehicle and at predetermined reference conditions; and correcting at least one information vector supplied by an analysis criterion as a function of the value of the correction parameter so as to provide a corresponding information vector capable of facilitating the determination by the analysis means of a downward gear to be engaged when the actual movement conditions of the vehicle are more difficult than the predetermined reference conditions.

  The system described above corrects at least one information vector 20 from the value of a correction parameter, the value of which is itself a function of a difference between the actual driving conditions of the motor vehicle and the conditions of predetermined reference.

  If the predetermined reference conditions of movement of the vehicle used by the analysis means to establish the information vectors correspond to a horizontal road, then an inclination of the road relative to the horizontal results in a correction parameter whose value is not zero.

  Thus, the information vectors used to automatically determine the gear ratio to be engaged also take into account the slope of the road on which the motor vehicle is traveling, which allows the analysis means to determine a new gearbox ratio appropriate to the inclination of the road.

  According to other characteristics of the system according to the invention - the analysis means are capable of establishing the value of the correction parameter by determining the difference between the actual conditions of movement of the vehicle measured by the acquisition means and the theoretical travel conditions on flat ground calculated from information relating to the operation of the vehicle engine; the analysis means are able to establish the value of the correction parameter by determining the difference between the actual acceleration of the vehicle and the theoretical acceleration of the vehicle on flat ground; - it includes: - a button allowing the driver of the motor vehicle to indicate that he wishes to change the gearbox ratio; - means for detecting the button being pressed by the driver; and the analysis means are suitable for determining a new gearbox ratio to be engaged in response to the detection of the button being pressed by the driver; the analysis means are capable of establishing information vectors corresponding to the following analysis criteria: - a safety analysis criterion from which a first information vector is established which is a function of the actuation by the driver d a vehicle braking device; a criterion for analyzing the speed of the motor vehicle from which a second vector of information is established as a function of the speed of the motor vehicle and of the current ratio; and an acceleration analysis criterion from which a third information vector is established as a function of the acceleration of the vehicle and of the current ratio; the analysis means are capable of establishing information vectors solely on the basis of criteria for analyzing safety, speed and acceleration; the degree of confidence of the second information vector represents the usefulness of the choice of a downward ratio as a function of the speed of the vehicle, and this degree of confidence is established at least using a nonlinear function of the speed of the vehicle exhibiting at least: a plateau of constant maximum value for a speed of the vehicle between a substantially zero speed and a minimum speed threshold; - a decreasing linear function of the vehicle speed 5 for a vehicle speed between said minimum speed threshold and a maximum speed threshold; and a plateau of constant minimum value for a speed of the vehicle greater than said maximum speed threshold; the values of said minimum and maximum speed thresholds are a function of the current ratio; - The values of said minimum and maximum speed thresholds are a function of the speed at which the last gear change was made; the analysis means are capable of correcting the non-linear function of the speed of the vehicle as a function of the value of the correction parameter, so as to facilitate the determination of a downward gear to be engaged when the real displacement conditions of the vehicle are more difficult than the predetermined reference conditions.

  the degree of confidence of the third information vector represents the usefulness of the choice of a descending ratio as a function of the acceleration of the vehicle, and this degree of confidence is established at least with the aid of a function not linear acceleration of the vehicle having at least: - a plateau of constant maximum value for an acceleration of the vehicle comprised between a substantially zero acceleration and a minimum acceleration threshold; - a decreasing linear function of the acceleration of the vehicle for an acceleration of the vehicle between said minimum acceleration threshold and a maximum acceleration threshold; and a plateau of constant minimum value for an acceleration of the vehicle greater than said maximum acceleration threshold; the values of said minimum and maximum acceleration thresholds are a function of the current ratio; the analysis means are capable of correcting the non-linear function of the acceleration of the vehicle as a function of the value of the correction parameter, so as to facilitate the determination of a downward ratio to be engaged when the real displacement conditions of the vehicle are more difficult than the predetermined reference conditions.

  the analysis means are capable of implementing the theory of possibilities for determining the new gearbox ratio to be engaged from the established information vectors.

  The invention also relates to a method for controlling a gearbox of a motor vehicle, in which: - acquisition means acquire information relating to the operation of the motor of the motor vehicle, to the conditions of movement of the motor vehicle and / or the conditions under which the driver drives the vehicle; and - means for analyzing the information acquired: - establish, using different analysis criteria, 15 information vectors representative of the driver's desire to change the gearbox ratio, each analysis criterion providing an information vector comprising at least one decision variable defining information on the desired gear change and a confidence degree variable relating to this decision, - determine a new gearbox report to be engaged from established information vectors; and - issue corresponding control orders to the gearbox to initiate this report; characterized in that the analysis means: - establish a parameter for correcting analysis criteria, the value of which is a function of a difference between the actual conditions of movement of the motor vehicle and at predetermined reference conditions; and correcting at least one information vector supplied by an analysis criterion as a function of the value of the correction parameter so as to provide a corresponding information vector capable of facilitating the determination, by the analysis means, a descending gear to be engaged when the actual movement conditions of the vehicle are more difficult than the predetermined reference conditions.

  According to other characteristics of the method according to the invention - the analysis means establish the value of the correction parameter by determining the difference between the actual movement conditions of the vehicle measured by the acquisition means and the conditions of 5 theoretical displacement on flat ground calculated from information relating to the operation of the vehicle engine; the analysis means establish the value of the correction parameter by determining the difference between the actual acceleration of the vehicle and the theoretical acceleration of the vehicle on flat ground; the analysis means determine a new gearbox report to be engaged only in response to the detection of the button being pressed by the driver; the analysis means establish information vectors corresponding to the following analysis criteria: a safety analysis criterion on the basis of which a first information vector is established as a function of the actuation by the driver of a vehicle braking device; a criterion for analyzing the speed of the motor vehicle from which a second vector of information is established as a function of the speed of the motor vehicle and of the current ratio; and an acceleration analysis criterion from which a third information vector is established as a function of the acceleration of the vehicle and of the current ratio; the analysis means establish information vectors 25 solely on the basis of the criteria for analyzing safety, speed and acceleration. The subject of the invention is also electronic means of analysis capable of being implemented in a system according to the invention, these means of analysis being able, from the information acquired in said system, to: establish, using different analysis criteria, information vectors representative of the driver's desire to change the gearbox ratio, each analysis criterion providing an information vector comprising at least one variable decision defining a desired gear change information and a confidence level variable relating to this decision; - determine a new gearbox report to be engaged from the established information vectors; and - issue corresponding control orders to the gearbox of said system to initiate this report; characterized in that the analysis means are able to: - establish a parameter for correcting analysis criteria, the value of which is a function of a difference between the actual conditions of movement of the motor vehicle and at predetermined reference conditions ; and correcting at least one information vector provided by an analysis criterion as a function of the value of the correction parameter so as to provide a corresponding information vector capable of facilitating the determination by the analysis means of a Descending gear to be engaged when the actual movement conditions of the vehicle are more difficult than the predetermined reference conditions.

  The invention will be better understood on reading the description which follows, given solely by way of example and made with reference to the drawings 20 in which: - Figure 1 is a schematic view of the architecture of a system for controlling a mechanical gearbox according to the invention; - Figure 2 is a flow diagram of a method for controlling a mechanical gearbox according to the invention; - Figures 3a and 3b are graphs each illustrating an analysis criterion used in the method of Figure 2; and - Figure 4 is a graph illustrating a variant of the analysis criterion of Figure 3a.

  FIG. 1 represents a motor vehicle 2 equipped with a mechanical gearbox 4 and a manual clutch / disengage mechanism 6 associated with this gearbox. This vehicle 2 is also equipped with a gearbox control system 4 designated by the general reference 10.

  The gearbox 4 is here a gearbox with five ratios respectively numbered in the ascending order of the gear ratios from 1 to 5. The ratio 1 corresponds to the smallest gear ratio while the ratio 5 corresponds to the largest gear of speed.

  This system 10 comprises means for acquiring information connected to an input of an electronic computer 12 suitable for controlling, as a function of the information acquired, means 14 for actuating the gearbox 4 to engage a gear ratio ascending or descending speed. To this end, the computer 12 is a programmable computer produced conventionally and capable of executing instructions recorded in a memory 16. These instructions are arranged so that the computer executes the method described with reference to FIG. 2. In the embodiment described here, this memory 16 also forms means 15 for storing information for the different coefficients and parameters necessary for the execution of the method of FIG. 2.

  In addition, a module 18 for calculating the acceleration of the vehicle 2 from information on the speed of the latter is implemented in the computer 12.

  The information acquisition means here comprise: - means 20 for acquiring information on the conditions of movement of the motor vehicle including, in particular, a sensor 22 for acquiring the speed of the vehicle 2; means 24 for acquiring information on the operating conditions of the vehicle engine; and means 26 for acquiring information relating to the behavior of the driver.

  More specifically, the means 24 for acquiring information relating to the operating conditions of the engine here comprise a sensor 30 30 of the torque developed by the drive shaft of the driving wheels of the vehicle, and a sensor 32 of the angular speed of that same tree.

  The means 26 for acquiring information relating to the behavior of the driver comprise a detector 34 for depressing a clutch / disengage pedal 36 capable of actuating the clutch mechanism 6. This pedal 36 therefore forms here, in more than a conventional mechanical actuation means of the clutch mechanism 6, a clutch / disengage button allowing the driver of the motor vehicle 5 to indicate when he depresses this pedal that he wishes to change the gear ratio speeds.

  The means 26 also comprise a detector 38 of the position of a brake pedal 40 and a lever 41 for controlling the movement of the vehicle 2.

  The detector 38 is capable of indicating to the computer 12 that the driver wishes to slow down the vehicle 2.

  The control lever 41 can be moved under the driver's control between three positions, respectively a front position, a neutral position and a rear position. These front, neutral, rear positions 15 correspond to the driver's wishes respectively to initiate an upshift gear ratio, to shift to neutral, or to engage a reverse gear transmission ratio. Thus, this lever 41 allows the driver to start, stop the vehicle or even move the vehicle in reverse. However, only the pedal 36 allows the driver 20 to indicate that he wishes to change the gearbox ratio when the vehicle is traveling in forward gear.

  The brake pedal 40 is capable of actuating a device 42 for braking the motor vehicle 2.

  Finally, the system 10 also includes means 44 for acquiring the current or currently engaged ratio of the gearbox 4. The means 44 are connected to the gearbox 4 and to the computer 12.

  The operation of the system 10 will now be described with reference to FIG. 2.

  After the vehicle 2 has been started, all of the elements of the system 10 are supplied and activated. From this moment, and permanently, the computer 12, in step 60, acquires all of the information noted and delivered by the various acquisition means of the system 10. In particular, the information relating to the speed of the vehicle 2 is transmitted to the module 18 of the computer 12 so that the latter permanently establishes the real acceleration of the motor vehicle.

  Then, in step 62, the computer 12 regularly establishes from the information acquired in step 60 the value of a correction parameter representative of the vehicle load. To this end, the computer 12 carries out a first operation 64 of calculating the theoretical acceleration AcCTH of the vehicle 2 on a horizontal road from information relating to the operation of the engine. For example, the computer 12 establishes the acceleration ACcTH using the following formulas: AcCTH = (PMotor PRresistance) / (Mveh * Vitveh) PMotor = CMotor * a) PResistor motor = VitVeh * (FRulsion + FAerodynamics) FAerodynamics = 0.5 * p * Scx * Vitveh2 o: - Pmotor is the power developed by the motor; - Presence is the power developed by the forces opposing the movement of the vehicle 2; - Mveh is the mass of vehicle 2; - Vitveh is the actual vehicle speed measured by the sensor 22; - Cmoteur is the torque of the drive wheel drive shaft whose value is measured by the sensor 30; - comotor is the angular speed of the drive wheel drive shaft measured by the sensor 32; - Rolling is the rolling force opposing the movement of the vehicle and caused by the interactions between the vehicle tires and the road, this force is determined in a conventional manner; Faerodynamics is the force exerted by air on the vehicle and opposing its movement; - p is a constant representing the density of the air; and - Scx is a constant representing the area of the section of the vehicle 2 perpendicular to the direction of movement of this vehicle. he

  After establishing the theoretical acceleration ACCTH, the computer 12 establishes during operation 66 the difference between this theoretical acceleration AcCTH and the actual acceleration delivered by the module 18.

  The difference between these two accelerations corresponds here to the value of the correction parameter.

  When the vehicle is moving forward, each time the driver of the vehicle 2 depresses the pedal 36, this information is detected by the detector 34 and then transmitted to the computer 12. The computer 12 is thus informed that the driver wishes to make a change 10 gearbox report. Consequently, and for example only in response to the detection of the depressing of the pedal 36 by the detector 34, the computer immediately proceeds to a step 70 of automatic control of the gearbox 4. During this step 70, the computer establishes, during sub-steps 72 to 74 of information vectors from predefined analysis criteria then 15 during a sub-step 76, it determines from these information vectors the new gearbox ratio of speeds to be engaged and finally, it delivers, in sub-step 78, the corresponding control orders of the gearbox 4 to the actuation means 14.

  Here, in order to simplify the steering process, the automatic steering of the gearbox 4 is carried out solely on the basis of a speed analysis criterion, an acceleration analysis criterion and d 'a security analysis criterion.

  During each of these sub-steps 72 to 74, the computer establishes an information vector composed, for example only, of a variable 25 representing the decision to be made, that is to say here, for example, initiating a downlink report, and a variable representative of a degree of confidence in this decision.

  In step 72, the computer 12 establishes a first vector of information using the speed analysis criterion represented in the graph of FIG. 3A. In this graph, the actual speed of vehicle 2 is shown on the abscissa while the ordinate represents the degree of confidence relative to the decision. In the particular case of the speed analysis criterion, this degree of confidence indicates the usefulness of the choice of a descending gear as a function of the actual speed of the vehicle.

  To simplify the graph in FIG. 3A, only the degree of confidence variable corresponding to the current ratio has been represented.

  The curve represented on this graph first presents a constant value equal to 0.9 for all the speeds whose measured value is between 0 and a minimum speed threshold VitMin. Beyond the VitMin threshold, the curve decreases linearly as a function of the actual speed of the vehicle from the value of 0.9 to a value of 0.1 for a value of 10 of the actual speed equal to a threshold of VitMax maximum speed. Beyond that, the degree of confidence variable has a constant value equal to 0.1.

  With the aid of this graph, if the actual measured speed is between 0 and the VitMin threshold, the computer 12 delivers as value of information the value -1 as a decision variable associated with the value 0.9 as 15 as confidence level variable.

  In the opposite case, that is to say if the measured speed is greater than the VitMax threshold, the computer delivers as information vector the same decision variable equal to -1 but this time associated with a degree variable of confidence equal to 0.1. In the intermediate situation, that is to say if the measured speed is between the VitMin threshold and the VitMax threshold, the computer delivers as information vector always the same decision variable equal to -1, but this time -this associated with a degree of confidence variable having an intermediate value between 0.9 and 0.1 established using the linearly decreasing part of the curve of FIG. 3A.

  The value of the VlitMin and VitMax thresholds depends on the current ratio.

  The table below illustrates the possible values of these thresholds respectively for speed ratios 2, 3 and 4.

  VitMin 1 report VitMax 2 8 25 3 35 45

I

  I 75 These VitMin and VitMax thresholds are constant for a given speed ratio and are established for the most frequent travel conditions, that is to say here, for an unloaded vehicle traveling on a horizontal road.

  For the gear ratios equal to 1 and to 5, the degree of confidence variable is constant and respectively equal to O and to 1 indicating thereby that when the current gear and the first gear, the depressing of the clutch pedal / declutching is certainly representative of a desire on the part of the driver to engage the higher gear ratio. On the contrary, if the current ratio is currently the fifth, that is to say the highest, the depressing of the pedal 36 by the driver certainly indicates that the latter wishes to downshift and therefore shift down.

  Shifts to neutral and reverse are only controlled from lever 41.

  During sub-step 72, the computer establishes the value of the degree of confidence variable using the following formula: YO = (VitVeh VitMin) / (VitMin - VitMax) + 1.0 + a * DiffAccel o: - YO is the value of the degree of confidence variable; - DiffAccel is the value of the correction parameter established during step 62; and - a is a constant coefficient suitable for modulating the importance of the correction. It is here chosen for example equal to 1.

  During sub-step 73, the computer 12 establishes a second information vector using the acceleration analysis criterion represented in the graph of FIG. 3B. This graph represents the acceleration on the abscissa and the confidence degree variable Yl on the ordinate.

  Here, the variable Y1 represents the utility of a choice of a descending ratio as a function of the actual acceleration of the vehicle 2 and the decision variable associated with this variable of degree of confidence is always equal to - 1.

  The value of the variable YI is constant and equal to 0.9 as long as the acceleration measured is less than an AccelMin threshold. This value then decreases linearly from the value 0.9 to the value 0.1 depending on the acceleration measured when it is between the AccelMin threshold and 5 an AccelMax threshold, then is constant for the values of l measured acceleration above the AccelMax threshold. The value of the AccelMin and AccelMax thresholds depends on the current ratio indicated by the acquisition means 44. As an example, the values of these thresholds for the second, third

  and fourth reports are given by the following table: AccelMin report AccelMax 2 -0.8 1.2 3 -0.8 1.2 4 -0.8 1.2 For a given report, the AccelMin and AccelMax thresholds are constant and are established for the most frequent travel conditions, c that is, here, for an unloaded vehicle traveling on a horizontal road.

  For the ratios 1 and 5, the values of the variable YI are constant and respectively equal to 0 and to 1 indicating by this that when the first gear is engaged, a depressing of the pedal 36 is significant of a will of the driver to engage a higher gear, while in the opposite situation, that is to say when the current gear is equal to the greatest gear ratio of the gearbox, the same depressing of the pedal 36 is significant d 'a willingness of the driver to initiate a lower gear. During sub-step 73, the computer 12 establishes the value of the confidence degree variable YI, for example using the following relation: Y1 = (AccelCal AccelMin) / (AccelMin - AccelMax) +1.0 + / 3 * DiffAccel o: - AccelCal is the value of the real acceleration of the vehicle established by the module 18, B is a constant coefficient suitable for modifying the importance of the correction parameter, it is for example chosen equal to 0.8 .

  During sub-step 74, the computer establishes a third vector of information on the basis of the security analysis criterion. This criterion is a function both of the detection by the means 38 of the depressing of the brake pedal and of the current ratio. It is for example established in the same way as described in patent FR-2 795 796 and will therefore not be described in more detail here.

  Then, in sub-step 76, the computer determines a new gearbox ratio to be engaged from these three information vectors 10. This sub-step is identical to that described in patent application FR-2 795 796. We will content ourselves here with specifying that this sub-step 76 comprises an operation 82, called merging, during which the computer establishes a ratio of gearbox to engage using for this the theory known as "possibility theory".

  Then, the computer delivers, in step 78, orders corresponding to the gearbox ratio to be engaged to the actuating means 14.

  In response, the actuating means 14 then engage the corresponding gearbox ratio.

  When the vehicle 2 climbs a climb or when the vehicle tows a load such as a caravan, the actual acceleration of the vehicle established by the module 18 is less than the theoretical acceleration.

  Under these conditions, the value of the correction parameter corresponding to the difference between the value of the theoretical acceleration and the value of the actual acceleration is positive. The values of the variables YO and Yl 25 representing the utility of a descending choice established using the criteria of speed and acceleration analysis are each increased by a positive quantity proportional to the value of the correction parameter. Thus, the probability that a descending gear is selected at the end of sub-step 76 increases compared to a situation in which the vehicle is traveling on a flat road. Thus, the choice of a descending gear is favored during an ascent which leads to automatically limiting the situations in which the engine of the vehicle is operating under engine speed.

  FIG. 4 represents a graph of a variant of the analysis criterion represented in FIG. 3A. In this variant, the VitMin and VitMax thresholds are determined according to the VitPass speed at which the previous gearbox change was made. For example, the VitMin threshold value is chosen equal to the VitPass speed +10 km / h when the last gear engaged is an ascending gear while the VitMax threshold retains a pre-recorded value, which corresponds to the curve 100 from the top of the graphic. Such a strategy for choosing the values of the VitMin and VitMax thresholds here leads to favoring a downward gear if after having engaged an upward gear, the driver of the vehicle does not accelerate.

  Otherwise, that is to say if the last gear engaged is a down gear, the value of the pre-recorded VitMin threshold is unchanged and the value of the VitMax threshold is chosen equal to the VitPass speed -10 km / h. This situation corresponds to the curve 102 at the bottom in the graph of FIG. 4. The curve 102 leads to favoring the determination of an ascending gear if after having engaged a descending gear, the driver of the vehicle does not decelerate. The system has been described here in the particular case where the value of the torque developed by the drive wheel drive shaft is measured by a torque sensor 30. As a variant, this same information is calculated from the data of a fuel injection computer.

  In the system described here, it is the clutch / disengage pedal 36 which acts as a button for activating a gear change.

  As a variant, the vehicle is additionally equipped with a clutch / declutch pedal 25 with a button for activating a gear change independent of the clutch / declutch pedal.

Claims (21)

  1. A control system for a gearbox (4) of a motor vehicle (6), this system comprising: - means (20, 24, 26) for acquiring information relating to the operation of the engine of the motor vehicle, the conditions of movement of the motor vehicle and / or the conditions of driving of the vehicle by the driver; and - means of analysis (12) of the acquired information suitable for: - establishing, using different analysis criteria, vectors 10 of information representative of the driver's desire to change the gear ratio gearbox, each analysis criterion providing an information vector comprising at least one decision variable defining information on the desired gear change and a confidence degree variable relating to this decision; - determine a new gearbox report to be engaged from the established information vectors; and - issue corresponding control orders to the gearbox (4) to initiate this report; characterized in that the analysis means (12) are capable of: - establishing a parameter for correcting analysis criteria, the value of which is a function of a difference between the actual conditions of movement of the motor vehicle and under conditions of predetermined reference; and correcting at least one information vector supplied by an analysis criterion as a function of the value of the correction parameter so as to provide a corresponding information vector capable of facilitating the determination by the analysis means of a downward gear to be engaged when the actual movement conditions of the vehicle are more difficult than the predetermined reference conditions.   2. System according to claim 1, characterized in that the analysis means (12) are able to establish the value of the correction parameter by determining the difference between the real conditions of movement of the vehicle measured by the means of acquisition (20, 24, 26) and the theoretical travel conditions on flat ground calculated from information relating to the operation of the vehicle engine.   3. System according to claim 1 or 2, characterized in that the analysis means (12) are capable of establishing the value of the correction parameter 5 by determining the difference between the actual acceleration of the vehicle and the theoretical acceleration of the vehicle on level ground.   4. System according to any one of the preceding claims, characterized in that it comprises: - a button (36) allowing the driver of the motor vehicle 10 to indicate that he wishes to change the gearbox ratio (4 ); - Means (34) for detecting the depression of the button (36) by the driver; and in that the analysis means (12) are suitable for determining a new gearbox ratio to be engaged in response to the detection of the button being pressed (36) by the driver.   5. System according to any one of the preceding claims, characterized in that the analysis means (12) are capable of establishing information vectors corresponding to the following analysis criteria: a security analysis criterion from which is established a first information vector based on the actuation by the driver of a vehicle braking device (42); a criterion for analyzing the speed of the motor vehicle from which a second vector of information is established as a function of the speed of the motor vehicle and of the current ratio; and an acceleration analysis criterion from which a third information vector is established which is a function of the acceleration of the vehicle and of the current ratio.   6. The system as claimed in claim 5, characterized in that the analysis means (12) are capable of establishing information vectors only on the basis of criteria for analysis of safety, speed and acceleration . 7. System according to claim 5 or 6, characterized in that the degree of confidence of the second information vector represents the usefulness of the choice of a downward ratio as a function of the speed of the vehicle, and in that this degree of confidence is established at least with the aid of a non-linear function of the speed of the vehicle having at least: a plateau of constant maximum value for a speed of the vehicle between a speed which is substantially zero and a minimum speed threshold; - a decreasing linear function of the vehicle speed for a vehicle speed between said minimum speed threshold and a maximum speed threshold; and a plateau of constant minimum value for a speed of the vehicle greater than said maximum speed threshold.   8. System according to claim 7, characterized in that the values of said minimum and maximum speed thresholds are a function of the current ratio.   9. System according to claim 7 or 8, characterized in that the values of said minimum and maximum speed thresholds are a function of the speed at which the last gear change was made.   10. System according to any one of claims 7 to 9, characterized in that the analysis means (12) are capable of correcting the non-linear function of the speed of the vehicle as a function of the value of the correction parameter, so as to facilitate the determination of a downward gear to be engaged when the real conditions of movement of the vehicle are more difficult than the predetermined reference conditions.   11. System according to claim 5 or 6, characterized in that the degree of confidence of the third information vector represents the usefulness of the choice of a descending ratio as a function of the acceleration of the vehicle, and in that degree of confidence is established at least with the aid of a non-linear function of the acceleration of the vehicle having at least: a plateau of constant maximum value for an acceleration of the vehicle comprised between a substantially zero acceleration and a threshold d 'minimum acceleration; - a decreasing linear function of the acceleration of the vehicle for an acceleration of the vehicle between said minimum acceleration threshold and a maximum acceleration threshold; and a plateau of constant minimum value for an acceleration of the vehicle greater than said maximum acceleration threshold.   12. System according to claim 11, characterized in that the values of said minimum and maximum acceleration thresholds are a function of the current ratio.   13. System according to claim 11 or 12, characterized in that the analysis means (12) are capable of correcting the non-linear function of the acceleration of the vehicle as a function of the value of the correction parameter, so as to facilitate the determination of a downward gear to be engaged when the real conditions of movement of the vehicle are more difficult than the predetermined reference conditions.   14. System according to any one of the preceding claims, characterized in that the analysis means (12) are capable of implementing the theory of possibilities for determining the new gearbox ratio to be engaged from the vectors d 'established information.   15. Method for controlling a gearbox (4) of a motor vehicle, in which: - acquisition means (20, 24, 26) acquire (at 60) information relating to the operation of the engine of the motor vehicle, the conditions of movement of the motor vehicle and / or the conditions of driving of the vehicle by the driver; and - means of analysis (12) of the information acquired: - establish (at 72, 73, 74), using different analysis criteria, information vectors representative of the driver's desire to proceed a gearbox change, each analysis criterion providing an information vector comprising at least one decision variable defining a desired gear change information and a confidence degree variable relating to this decision, determine ( in 76) a new gearbox report to be engaged from the established information vectors; and - issue (at 78) corresponding control orders to the gearbox to initiate this report; characterized in that the analysis means (12): - establish (at 62) a parameter for correcting analysis criteria 5, the value of which is a function of a difference between the actual conditions of movement of the motor vehicle and at predetermined reference conditions; and - correct (at 72, 73, 74) at least one information vector provided by an analysis criterion as a function of the value of the correction parameter so as to provide a corresponding information vector capable of facilitating the determination , by the analysis means (12), of a descending ratio when the real conditions of movement of the vehicle are more difficult than the predetermined reference conditions.   16. Method according to claim 15, characterized in that the analysis means (12) establish (at 62) the value of the correction parameter by determining the difference between the actual conditions of movement of the vehicle measured by the means of acquisition (20, 24, 26) and the theoretical travel conditions in flat terrain calculated from information relating to the operation of the vehicle engine.   17. Method according to claim 15 or 16, characterized in that the analysis means (12) establish (at 66) the value of the correction parameter by determining the difference between the actual acceleration of the vehicle and the theoretical acceleration of the vehicle on level ground.   18. Method according to any one of claims 15 to 17, characterized in that the analysis means (12) determine a new gearbox ratio to be engaged only in response to the detection of the depression of a button (36) by the driver.   19. Method according to any one of claims 15 to 18, characterized in that the analysis means (12) establish (at 72, 73, 74) information vectors corresponding to the following analysis criteria: a safety analysis criterion from which a first information vector is established as a function of the actuation by the driver of a vehicle braking device (42); a criterion for analyzing the speed of the motor vehicle from which a second vector of information is established as a function of the speed of the motor vehicle and of the current ratio; and a criterion for analyzing the acceleration from which a third information vector is established as a function of the acceleration of the vehicle and of the current ratio.   20. The method as claimed in claim 19, characterized in that the analysis means (12) establish (at 72, 73, 74) information vectors solely on the basis of criteria for analyzing security, speed and of 10 acceleration.   21. Electronic analysis means (12) able to be implemented in a system according to any one of claims 1 to 14, these analysis means (12) being clean, from the information acquired in said system , to: - establish, using different analysis criteria, information vectors representative of the driver's desire to change the gearbox ratio, each analysis criterion providing a vector of information comprising at least one decision variable defining desired gear change information and a confidence degree variable relating to this decision; - determine a new gearbox report to be engaged from the established information vectors; and - issue corresponding control orders to the gearbox of said system to initiate this report; characterized in that the analysis means (12) are capable of: - establishing a parameter for correcting analysis criteria, the value of which is a function of a difference between the actual conditions of movement of the motor vehicle and under conditions of predetermined reference; and correcting at least one information vector supplied by an analysis criterion as a function of the value of the correction parameter so as to provide a corresponding information vector capable of facilitating the determination by the analysis means (12 ) a descending gear to be engaged when the actual conditions of movement of the vehicle are more difficult than the predetermined reference conditions.