EP2212176A1

EP2212176A1 - System for generating an estimation of the ground speed of a vehicle from measures of the rotation speed of at least one wheel

Info

Publication number: EP2212176A1
Application number: EP08848402A
Authority: EP
Inventors: Jean-Louis Linda; Daniel Walser
Original assignee: Michelin Recherche et Technique SA Switzerland; Michelin Recherche et Technique SA France; Societe de Technologie Michelin SAS
Current assignee: Compagnie Generale des Etablissements Michelin SCA; Michelin Recherche et Technique SA France
Priority date: 2007-11-09
Filing date: 2008-11-10
Publication date: 2010-08-04
Also published as: CN101855117A; FR2923437B1; KR20100096078A; WO2009060092A1; US8370013B2; FR2923437A1; CN101855117B; US20100324766A1

Abstract

The invention relates to a system for generating an estimation of the global speed of a vehicle relative to the ground, that comprises developing a measure of the instantaneous adhesion coefficient (μr) of at least one wheel (1) of an electric traction vehicle in which an electric rotary machine (2) is coupled to said wheel for individually driving the same upon traction or braking. The system includes an indicator of the torque applied at each moment to said wheel on the basis of the measure of the current (Ic) in the electric machine, an indicator of the instantaneous dynamic load on said wheel, and a stage for calculating the instantaneous adhesion coefficient of said wheel (1) relative to the ground, from the torque indicator and the dynamic load indicator in order to determine the ratio between the tangential force applied on the ground by the wheel under the action of said torque and the normal force applied on the ground by the wheel under the action of the dynamic load. One or more tests of the adhesion coefficient value thus calculated are carried out in order to determine the capability of a measure of the circumferential speed of a corresponding wheel to provide a sufficient estimation of the vehicle movement speed at the location of said wheel.

Description

System for producing an estimate of the ground speed of a vehicle from measurements of the rotational speed of at least one wheel

FIELD OF THE INVENTION

The present invention relates to land vehicles, including road. It aims in particular the techniques of controlling the behavior of such vehicles and the determination of their speed relative to the ground for this purpose, in order to adjust the parameters which determine this behavior and to improve the conditions and the safety of the running. It is particularly well suited to the case where the movement of the vehicle on the ground is controlled by one or more specific electrical machines coupled to a drive wheel to apply a driving torque or braking as needed.

STATE OF THE ART

[0002] The proposals for electric vehicles have developed a great deal in recent years. For example, US Pat. No. 5,418,437, which describes a four-wheeled hybrid series vehicle, each wheel being driven by an electric machine of its own, a controller for controlling the motors integrated in the wheel and ensuring managing the supply of energy to the motors from an alternator or a battery. When the supply of energy is interrupted, the movement of the wheel under the action of the inertia of the vehicle can in turn drive the electric machine and allow it to operate as a generator to an electric load by applying a couple of so-called regenerative braking at this wheel.

This patent remains silent on the management of electric braking obtained, but there are in the state of the art examples of such a management to complete the mechanical friction control by conventional friction. For example, the published UK patent application GB 2344799 discloses a vehicle capable of generating several levels of regenerative braking power from electric traction motors, so as to provide a function simulating compression braking. or engine braking normally available with internal combustion engines, in addition to the traditional mechanical braking function. In general, it has already been proposed to use the faculty offered by an electric machine on board a vehicle to drive flexibly and accurately the torque applied to a wheel of a vehicle that is team. Such a possibility has for example been used with anti-lock wheel systems. US Patent 6,709,075 discloses a vehicle equipped with a power train with an electric motor. A braking function resulting from the operation of this engine as a generator may be superimposed on the friction braking torque applied to each wheel as a function of its behavior as determined from an ABS (anti-lock brake control) system fitted to the engine. vehicle. Arrangements are made to prevent regenerative braking from interfering with the proper functioning of the ABS system for the regulation of friction braking.

This ability to accurately control the torque applied to a wheel is, more generally, well suited to stability control systems, by the modulation of the braking torque alone or also with that of the engine torque. The PCT patent application published under the reference WO0 1/76902 describes a vehicle propulsion and braking system in which each wheel that can be driven by an internal combustion engine is also coupled to an electric machine capable of selectively applying a complementary engine torque or braking torque according to the controls of a vehicle operating stability control system in response to a yaw sensor.

[0006] Finally, the patent application in the United Kingdom under reference GB 2 383 567 also describes a system in which an electric machine is provided to provide a torque to certain wheels of a vehicle equipped with an internal combustion engine. The level of this extra torque is modulated according to the data provided by a yaw sensor.

Thus, it is well known to use the engine or braking torque provided by an electric machine to adjust the forces applied to the wheels of a vehicle by an internal combustion engine. It is also known to use the torque produced by such a machine to adapt the friction braking forces applied to the wheels of an electric traction vehicle.

In the two previous examples a yaw sensor is used on board the vehicle to determine the level of torque to apply or add to some wheels of the vehicle to achieve the desired effects on the behavior. Other parameters can be measured and used for this purpose. The European patent application EP 0 881 114 discloses a control system for a four-wheeled vehicle, each coupled to an independent electric motor, capable of applying a driving or braking torque on each of the steering wheels or not. A braking system conventional discs is further provided and a steering angle sensor makes it possible to know at any moment the orientation of the steering wheels. Each wheel motor is equipped with a wheel speed sensor. An indication of the speed of the vehicle relative to the ground is obtained by the control unit of the system by combining the information from the signals of the wheel sensors. It is stated (without more details) that this indication can be specified using information from onboard accelerometers and a satellite navigation system. The system control unit continuously monitors the level of torque applied to each wheel, the speed and steering angle of that wheel, and the estimate of the ground speed of the vehicle. It also calculates the yaw rate and from all this information determines the instantaneous slip of each wheel. The control unit controls the traction and braking torques based on the slip values determined for each wheel and to optimize braking, acceleration and steering in response to driver commands.

In practice, the indication of the ground speed of the vehicle is an essential data for a control as proposed in this document. No direct measurement in the vehicle alone allows access not only easy but above all economic and reliable to this fundamental data to characterize the behavior of the vehicle. It must therefore be determined by calculations from other measures easier to obtain live. It is known that the instantaneous speed of each wheel is an essentially variable factor, which is affected from the outside by the soil conditions, both as regards the regularity of its profile and its surface state, and from the inside, by the controls whose wheel is the object and which affect both its direction and the couples that are applied to it, and by the dynamic reactions of the vehicle itself that are transmitted to it via the suspension of the vehicle.

Thus the simple combination of the measurement signals produced by the individual wheel sensors is insufficient to provide a valid determination of the speed of the vehicle relative to the ground, itself sufficiently precise, dynamic and reliable for a real-time appreciation. the behavior of the vehicle and its wheels. In addition, to be practically acceptable, a solution must be able to be implemented easily and at low cost on the vehicle.

Various solutions have already been put forward to try to improve the resolution of this problem. For example, the publication document of the French patent application FR 2,871,889 describes a system that makes a diagnosis of the quality of each instantaneous measurement of the longitudinal speed of a wheel, based on the speed of rotation provided by a sensor. attached to this wheel, and calculates a longitudinal speed of the vehicle from an average of the longitudinal wheel speeds obtained, weighted by quality indices from the previous diagnosis. This diagnosis also includes verification that the longitudinal velocity of each wheel considered is within a range of values ensuring that the method of calculation covered by the patent is applicable (speed not less than 15 kph and not greater than 250 kph). This diagnosis also includes a verification that the derivative of the rotational speed of each wheel considered is within a certain range indicating that the wheel is neither locked nor in a state of slippage, to reject the non indications. compliant. So the method does not apply outside of these different ranges. The calculation is no longer valid outside these limits to provide a measure of the slip itself. In the case of a complete absence of indication according to a given time, the system provides a vehicle speed value extrapolated values determined at previous times. Regardless of any discussion regarding the applicability of the proposed method to all situations, the proposed extrapolation technique is unsuitable for monitoring the behavior of the vehicle by the system continuously, or during transition phases that may last several seconds, for example. opposition to the case of discontinuous operation, for example in an anti-lock wheel control, where the system normally permits a resumption of adhesion involving a new valid measurement of the speed, after a fraction of a second following the detection of a fault.

Another proposal to overcome the above difficulties is set forth in the publication document of the French patent application FR 2 894 033, in which the longitudinal speed of the vehicle is calculated by combining estimates of the longitudinal speed of certain selected wheels, obtained from sensors for measuring the rotational speed of these wheels.

The calculation mode is adapted to each driving mode of the vehicle. The longitudinal speed of each wheel is corrected according to the possible position of the wheel in a turn, then the state of the wheel (locking or slipping) is tested according to the value of the torque applied to this wheel. A test is then performed on the consistency between the value of the acceleration obtained from the longitudinal speed obtained above and the longitudinal acceleration measurement provided by an accelerometer on board the vehicle. If the consistency is verified, the calculated longitudinal velocity is retained. In the opposite case it is a value obtained by integrating the measurement of the accelerometer which is adopted.

In practice, the measurement of the accelerometer is tainted with the error due to the component of the earth acceleration following the possible slope of the ground on which the vehicle moves. It follows that, on the one hand, validity tests on longitudinal velocity measurements proposed for the wheels does not appear accurate enough to provide reliable indications of the vehicle speed and that, on the other hand, the proposed method for testing the consistency of accelerations and, in case of lack of consistency, to determine the speed is tainted Incompatible with continuous operation for periods which may be prolonged for several seconds, for example in the case of prolonged emergency braking (or pronounced acceleration).

The determination of the overall speed of a vehicle relative to the ground remains a substantial stake for the development of vehicle behavior control systems. This is particularly the case, as explained above, for vehicles that have one or more wheels each coupled to an independent electric machine. In addition, this issue is particularly important in the case of an electric vehicle which not only the traction but also the braking are integrally and directly derived from the electrical energy. The applicant recently proposed for example in the patent application No. WO 2007/107576 such a vehicle equipped with reliable means to ensure in all circumstances the ability to have a regenerative electric braking torque on each relevant wheel sufficient to ensure the vehicle safety, without the addition of mechanical braking. It is expedient to be able to make such a vehicle benefit from the possibilities of dynamic and precise control of the traction and braking torques offered by the electric machines for controlling the behavior of such a vehicle.

SUMMARY OF THE INVENTION

Thus, the present invention aims to provide a solution that helps to determine at any time a sufficiently accurate, dynamic and reliable estimate of the speed of a vehicle relative to the ground, including in phases of driving where the measurement of the usual vehicle monitoring parameters such as the speed of rotation of its wheels does not provide a reliable estimate of this speed at any time. It is particularly well suited to controlling the behavior of a vehicle, some wheels of which are each coupled for traction and / or braking to at least one electric machine specific to this wheel.

For this purpose a system according to the invention for determining an instantaneous speed estimate with respect to the ground of a vehicle from measurements derived from at least one motion sensor of a vehicle wheel comprises : a circumferential speed indicator of at least one wheel of the vehicle from the measurements of a sensor of the movement of this wheel, a test stage for validating the indication of the circumferential speed at the output of said indicator if it makes it possible to to deduce a sufficiently accurate and reliable representation of the speed of advance of the vehicle according to at least one predetermined criterion, and a module adapted to combine the circumferential speed wheel indications validated by the test stage to provide an estimate the speed of advance of the vehicle relative to the ground.

The system according to the invention is characterized in that it comprises a device for calculating the instantaneous coefficient of adhesion of said wheel from the data available on board the vehicle and in that said test stage is clean. testing the value of the coefficient of adhesion obtained for each wheel concerned, as a function of a relationship which makes it possible to determine whether the corresponding difference, or slip, between the circumferential speed of the wheel and the forward speed of the vehicle relative to the ground at this moment is sufficiently small so that said circumferential wheel speed can be retained by said module as a datum for estimating the speed of advance of the vehicle relative to the ground.

According to a preferred application the system can be readily applied to a vehicle, each wheel used in the adhesion measurement is coupled to an individual rotary electric machine, adapted to apply a traction torque and / or electrical braking, and in which the device for calculating the coefficient of adhesion of each of these wheels is operative in response to a measurement of the instantaneous torque applied to this wheel by the respective electric machine and to an information function of the load of this wheel at the instant.

In the study of movements that involve adhesion phenomena between a movable body and a fixed body, it is customary to use, for each condition of contact between these two bodies, a representative diagram of the relationship. between, on the one hand, the coefficient of adhesion, expressed in percentage, which characterizes the capacity of bodies to withstand the efforts that tend to slide them relative to each other and, on the other hand, the sliding rate, also in percent, which characterizes the shift between the speeds of these two bodies under the effect of the friction forces that hold them to one another.

Vehicle control systems which implement a rolling coefficient of adhesion measurement are known per se. US Pat. No. 5,419,624, for example, discloses an apparatus for determining a critical drive torque of a wheel by incrementally increasing its speed. rotation while testing the corresponding rotational speed of said wheel to determine at regular intervals optimal performance conditions and exploit them on board the vehicle. However, the provisions advocated in this document are not intended to provide criteria for testing the possibility of using a velocity measurement derived from a wheel sensor to determine a reliable estimate of the speed of a vehicle in view. in particular control of the behavior of the latter.

In a system according to the invention, the test stage may be able to verify that the value of the coefficient of adhesion is less than a predetermined threshold indicating that the value of the corresponding slip of the wheel is less than 5%. . Preferably, a threshold of 3% or even preferably 2% is chosen so that the corresponding circumferential wheel speed is retained by the speed estimation module.

According to another form of implementation, the test stage is suitable for determining whether the value of the coefficient of adhesion is lower than a predetermined threshold in a range between 30% and 70%, above which coefficient la corresponding wheel speed is not retained by the speed estimation module. Advantageously, this value of the predetermined threshold of adhesion coefficient implemented by the test stage may be around 50%.

Other criteria related to adhesion phenomena may be implemented in addition to the above indications. It can thus be advantageous in particular in cases where the first indications of circumferential speed do not seem reliable or stable to check whether the coefficient of adhesion of the wheel at said instant is equal to or less than a predetermined threshold sufficiently low to indicate that the wheel recovered a suitable adhesion regardless of the state of the tread of said wheel. For example, if the coefficient of adhesion is less than 15%, it is an indication that the adhesion is present even with a very slippery soil such as ice.

Another indication of adhesion, or corroboration of adhesion recovery, can be obtained with a vehicle equipped with a rate detection system or slip coefficient of a wheel derived from the measurement of deviations observed between the circumferential speed of the wheel and the vehicle speed (brought back to the location of this wheel to take into account the possible position of the wheel in a bend). Information that the slip rate is less than 2% or even 3% for example provides confirmation that the wheel concerned has retained or recovered its adhesion with the ground, regardless of the surface state of the latter, and that the measurement of speed The result of the wheel sensor is sufficiently precise to be considered as representative of the vehicle speed.

BRIEF DESCRIPTION OF THE FIGURES

Other objects and advantages of the invention will become clear in the following description of preferred but nonlimiting exemplary embodiments, illustrated by the following figures in which:

Figure 1a schematically shows a control system of the drive and braking of a four-wheel drive electric vehicle, producing electrical energy on board; Figure Ib is a more detailed diagram of a portion of Figure la; Figure 2 is a diagram illustrating the variation of the coefficient of adhesion of a wheel according to the sliding of the wheel relative to the ground; FIG. 3 is a block diagram illustrating the operation of a sliding measurement module and current control as a function of this measurement according to one aspect of the invention; Figures 4a and 4b are flow charts of the operation of another module of the system of the invention; FIGS. 5a and 5b illustrate the explanations concerning the determination of the slope angle of the ground from the data measured by the vehicle: FIG. 6 very schematically illustrates a signal processing stage for the correction of the measurements of slope and of acceleration. FIGS. 7a, 7b and 7c are diagrams of the signals produced in the signal processing stage of FIG. 6.

Figure 8 specifies the definition of the points of application of the forces acting on the vehicle.

DESCRIPTION OF ONE OR MORE EXAMPLES OF REALIZATION

[0026] In Figure la shows a diagram of a vehicle with four wheels 1A _V _G> _V D ^ A ^ Arg ^and

^ ArD- wheels are denoted iavg F ^or the left front ^wheel, IA _V ^our DP ^has the front right ^wheel, iarg F ^or the left rear ^wheel and casualty for the right rear wheel. Each wheel is equipped with an electric machine that is mechanically coupled to it. We see the electric machines 2A _V G _> ^ A _V D '- ^ ArG ^and ^ ArD- In the following, we will not take again the indices specifically designating the position of the wheel 1 or the electric machine 2 in the vehicle when that does not add anything to the clarity of the presentation. Electric traction machines 2 are self-controlled synchronous type three-phase machines. They are each equipped with a resolver-type angular position sensor 11 (FIG 3) integrated at the rear of the machine and are each controlled by a respective electronic wheel control module 23 to which they are connected by power lines. of power 21.

The electronic wheel control modules 23 are designed to drive the electrical machines in torque from the measurement of the currents in the machine and the measurement of the sensor 11 of angular position. Each wheel control electronic module 23 makes it possible to impose selectively on the wheel in question a driving torque determined in amplitude and in sign. As a result, the electrical machines can be used as motor and generator. Each electronic module calculates by a numerical treatment the rotational speed Ωr of the rotor of the machine as well as its angular acceleration Ω'r. Knowing the reference development of the wheel, and more precisely of its tire, defined as the linear distance traveled by the vehicle for a wheel revolution in the absence of any torque and longitudinal force, and knowing the reduction of the gear of connection between the axis of the rotor and the wheel, each electronic module 23 converts the angular speed and acceleration, respectively Ωr and Ω'r, in linear speed and acceleration, respectively, V _r and γ _r , brought back to the vehicle. It should be noted, however, that certain principles of the invention could be implemented with an independent wheel speed measurement, for example, for wheels not equipped with motors, use a speed sensor of the Hall effect sensor type for ABS system ( Anti Blocking System) or working on any other principle.

For the record, in this example each of the rear wheels IARG ^and IA _Γ D ^{is further} equipped with a mechanical brake device 71 of the wheel stopped and only stopped, controlled by an electric actuator 7 driven by a brake control unit. In the application described herein of the invention, none of the wheels of the vehicle comprises a mechanical service brake. Whatever the amplitude of the brake control signal, that is to say, even for the most intense braking, the braking is ensured only by driving the electric machines in generator. The means are provided to ensure the consumption of all the power produced even in a particularly powerful braking. These means may comprise a storage capacity, circuits for using the energy produced in real time and means for dissipating the power in excess of the two previous modes of consumption. Each wheel has one or more dedicated electrical machines to be able to generate a braking force selectively on each wheel, which one could not do with a common electric machine with several wheels, for example the wheels of an axle, because there would be in this case a mechanical transmission and a differential between the wheels. Electrical machines are sized appropriately to impose the highest possible braking force on each wheel.

In order to make it possible to absorb a high electrical power, cooled dissipation electrical resistors have been installed efficiently, for example by circulating water, the known electric accumulators not being able to absorb the electrical power produced by an emergency braking or not being able to absorb all the electrical energy produced by a long-term braking, except to install a capacity such that the weight of the vehicle would be really prohibitive. Thus, the electrical system shown here, a more detailed description can be found for example in the published patent application WO 2007/107576 A1, in the name of one of the applicants, is an autonomous electrical system isolated from the environment, without exchange of electrical energy with the outside of the vehicle, thus also applicable to motor vehicles, application of electric braking systems much more difficult than in the case of vehicles connected to an electrical network such as trains or urban trams.

For example, one can choose to have several electrical machines whose couples add up. In this case, an electronic wheel module can drive several electrical machines in parallel installed in the same wheel. Regarding the installation of several electrical machines in a wheel, see for example the patent application WO 2003/065546 and the patent application FR 2776966.

In the example here chosen and illustrated there is described an application to a vehicle ensuring the production of electrical energy on board. FIG. 4 shows a fuel cell 4 delivering an electric current on a central electrical line 40. Of course, any other means of supplying electrical energy may be used, for example batteries. We also see an electrical energy storage device constituted in this example by a bank of super capacitors 5, connected to the central electrical line 40 by an electronic recovery module 50. We see an electrical dissipation resistor 6, preferably dipped in a coolant discharging heat to an exchanger (not shown), constituting an energy absorbing device adapted to absorb the electrical energy produced by all the electrical machines during braking. The dissipation resistor 6 is connected to the central electrical line 40 by an electronic dissipation module 60. A central computing and control unit 3 manages various functions, including the electric traction system of the vehicle. The central unit 3 communicates with all the electronic wheel control modules 23 as well as with the electronic recovery module 50 via the electrical lines 3OA (CAN bus ®). The central unit 3 also communicates with a plurality of commands detailed in FIG. 1b, namely in particular an acceleration control 33 via an electric line 3OE, with a braking command 32 (service brake) via an electric line 30F, and with a control 31 selecting the forward or reverse via a 30C power line. The central unit 3 also communicates, via a 30G electrical line, with a sensor or measuring system 35 linked to the steering control 41 of the vehicle and making it possible to determine the turning radius Ray. Finally, for the management of the dynamic behavior of the vehicle in this example, the central unit 3 communicates, via an electric line 30D, with an acceleration sensor 34 γx along the longitudinal axis X of the vehicle, via an electric line 30H, with a sensor or measurement system 36 of the acceleration γ y along a transverse axis Y of the vehicle, via a line 301, with a sensor 37 of angular velocity of yaw Ω_ _z around a vertical axis Z of the vehicle, and finally , via a line 30J, with a sensor 38 of angular velocity _Ω _ _y about the transverse axis Y. The information from these sensors, allow the calculation by the central unit 3, among other results, dynamic loads on the wheels, as resulting from the load offsets between the front and rear wheels as well as between the right and left wheels of the vehicle as a function of the longitudinal (along the X axis) and the transverse (Y axis) accelerations. transverse to when the vehicle is running).

The central unit 3 manages the longitudinal movement of the vehicle, for this purpose it controls all the electronic wheel control modules 23. It comprises on the one hand a mode of traction operation activated by a signal control whose amplitude is representative of the total desired traction force for the vehicle, said control signal coming from the acceleration control 33, and secondly a mode of braking operation activated by a control signal of which the amplitude is representative of the total braking force desired for the vehicle, said control signal coming from the brake control 32. In each of these operating modes, regardless of the amplitude of the respective control signal, the central unit 3 controls all the electronic wheel control modules 23 so that the sum of the longitudinal forces coming from the rotating electrical machines on the assembly the wheels 1 is a function of said amplitude of the control signal. This is the case, in particular for the braking operation mode. In other words, there is no mechanical service brake; the electric braking system described here is the service brake of the vehicle. Furthermore, the central unit 3 is programmed to control the application of a specific target torque on each wheel according to the dynamic load of each wheel so as to work each tire according to a determined behavior program. Thus, in the example described here, the program adjusts the torque on each wheel (and therefore the tangential force respectively applied to the ground by each wheel) according to an external strategy fixed a priori. As a result, as will be seen further, each electronic wheel control module receives from the central unit a torque setpoint from which it determines a corresponding reference value I _cc for the control current of the corresponding electrical machine.

Returning to Figure la, as indicated above, the actuator 7 of the mechanical parking brake device 39 is controlled via the power line 3OK only by this parking brake control 39, and absolutely not by the control of braking 32 of the service brake, a safety device being provided to prevent the implementation of this brake outside the parking situation. Finally, the electronic recovery module 50 communicates with the electronic dissipation module 60 via an electrical line 30B.

We now discuss the aspects concerning the implementation of the invention itself. FIG. 2 represents three curves of variation of the coefficient of adhesion (μ) of a wheel 2 of a vehicle, which can be typically equipped with a tire, as a function of the sliding (λ) measured in contact with the running ground, a 101 in the case of a dry ground, another 102 in the case of a wet ground, so more slippery, and the third 103 in the case of an ice so very slippery soil. We can distinguish in the plane of these curves a first hatched area Zl bounded on the right by a line joining the maxima of the adhesion coefficients of these curves. In this zone Z1, the operation of the wheel is stable, ie the more the slip increases and the coefficient of adhesion also increases. This makes it possible to transmit to the ground the tangential forces resulting from the engine or braking torque applied to the wheel. In a second zone Z2 corresponding to the higher slip values the operation becomes unstable. As can be seen for the curve 101, when the slip exceeds a certain threshold, here about 15%, the coefficient of adhesion decreases. The tangential force passed to the ground therefore decreases and the excess of non-transmitted torque further slows down the speed of rotation of the wheel, which again causes an increase in sliding and so on; it is the phenomenon of loss of adhesion that leads quickly (usually a few tenths of a second) to the momentary cancellation of the speed of rotation of the wheel by braking before its spinning in spin in the opposite direction of the movement of the vehicle, or at its setting accelerated skating in the direction of movement of the vehicle.

The maximum value of the coefficient (μ) depends on the tire, the nature of the conditions (dry, wet, etc.) of the running ground. In the case of a passenger vehicle equipped with tires of good quality in adhesion, the optimal value of the coefficient of adhesion corresponds to a slip being around 5% to 15% Knowing that the coefficient of adhesion (here considered) is defined by the ratio of the tangential force to the ground by the load perpendicular to the surface of the latter in the contact area of the ground wheel, the values mentioned therefore allow a maximum deceleration of 1.15g, (g here being the acceleration of gravity) on dry ground, 0.75g on wet ground and 0.18g on ice, to the extent that one could manage to maintain the point of operation of the wheel on the ground at this time. optimum. One of the aims pursued by the present invention is to approach as much as possible of this operation by a suitable control of the torques applied at each moment to at least some of the wheels of the vehicle and, in particular, to the wheels having a drive and 'electric machine braking.

FIG. 3 very schematically shows the elements of a device for controlling the traction or braking torque applied to each wheel by the corresponding electric machine 2 as a function of the sliding measurements made on this wheel in accordance with FIG. 'invention. This mode of representation is convenient for a good understanding of the explanations that follow. Naturally, the invention can be implemented using conventional hardware and software devices used in the management and control of road vehicles. The electronic wheel module 23 has the primary role of driving in torque the engine or engines associated with it (s). Since the torque-current characteristic of 3-phase synchronous autopilot machines 2 is well known, controlling the current in these machines is therefore equivalent to driving these machines in torque. In the wheel drive module 23, this basic function is shown schematically by the module 23A which controls the current on the power line 21 from a current setpoint Ic and an angular position measurement αr of the rotor of the machine 2, delivered by the resolver 11. A calculation module 23F converts the torque setpoint Cc delivered by the central unit 3 to the current setpoint Icc necessary to generate this torque. The angular position information αr of the rotor of the machine 2 delivered by the resolver 11 is also exploited by a module 23B to calculate the angular velocity, Ωr, as well as the angular acceleration, Ω'r, of said rotor. Knowing the reference development of the wheel, and more precisely of its tire, defined as the linear distance traveled by the vehicle for a wheel revolution in the absence of any torque and longitudinal force, and knowing the reducing the linkage gear between the rotor axis and the wheel, the module 23C converts the angular velocity, Ωr, as well as the angular acceleration, Ω'r, of the rotor respectively into a circumferential linear velocity indication, V _r , wheel (brought back to the vehicle as discussed below) and an indication of circumferential linear acceleration wheel, γ _r . These indications of circumferential wheel speed and acceleration, respectively V _r and γ _r , are transmitted to the central unit 3 on the CAN communication bus 3OA.

In addition to the torque setpoint Cc, the control module 23 receives from the central unit 3, via the communication bus CAN 3OA, an acceptable maximum slip value (λ-c) and an indication of the speed on the ground (V _v ) of the vehicle itself, to which we will return later.

With a periodicity of 1 ms to 2 ms, the wheel control module 23 performs a calculation of the slip λ at the instant considered according to the formula (V ₁ -V _v ) / V _v , schematized by a block 23D which receives the numerical indications V _v , of the central unit 3, and V _r , issuing from the module 23C. During an acceleration phase of the wheel, the wheel speed is greater than the vehicle speed and the sliding, according to the formula defined above, is positive whereas during a braking the wheel speed V _r is lower than the vehicle speed V _v and the slip is negative. To simplify the discussion, λ is subsequently considered as the absolute value of the slip, as well as the maximum slip setpoint λc and the current setpoint Icc will always be considered as positive. The calculated sliding indication is used (as shown schematically by a comparison module 16) to provide a signal indicative of the difference ελ between the calculated slip and the target slip (λc) delivered by the central unit 3. In the when the difference ελ between the calculated slip λ and the set slip λc indicates an overshoot of this maximum set point by the instantaneous slip, this information is used by a regulator 23E, which can be for example a conventional PID regulator (Proportional Integral Derivative), to generate, a current setpoint Iλc. A global current setpoint Ic is then calculated (adder block 17) by summation: (i) of the initial current setpoint Icc, generated from the torque setpoint (block 23F), and (ii) of the current setpoint Iλc issued from the regulator 23E. It is this global instruction Ic which is applied to the module 23A controlling the current of the electric machine 2, which also receives the indication of the angular position of the rotor of the electric machine delivered by the resolver 11. For example, as long as the slip λ remains below the setpoint λc, during an acceleration phase, nothing happens. If the wheel begins to spin, in which case λ becomes greater than λc, the difference with The setpoint slip becomes negative. The corresponding current indication Iλc at the output of the module 23E also negative decreases the indication of the initial target current Icc in the summing block 17 so as to reduce the torque applied to the wheel and maintain the sliding at maximum at λc.)

The information processed by the central unit 3 (torque setpoint Cc, vehicle speed V _v , and slip setpoint λc are delivered to the wheel module 23 at a relatively slow rate of 10 to 20 ms, relatively slow but well adapted On the other hand, the information derived from the modules belonging to each wheel (23B, 23C, etc.) and the processing carried out by the modules 16, 17, 23D and 23E are carried out at a relatively fast rate, corresponding to at a period of 1 to 2 milliseconds, well adapted to the wheel dynamics, finally knowing that each electronic wheel control module 23 makes it possible to impose selectively on the wheel in question a driving torque determined in amplitude and in sign, it is possible to thus a fast and efficient system allowing a permanent control of the sliding in the direction braking (anti-inversion of rotation) and in the direction motor (anti-skating) and that on each wheel com driven in full traction and braking by the single electric machine. In this way, a real automatic control of the adhesion of the wheel with its tire is realized.

According to another aspect of the invention, the system is arranged to determine a value generally representative of the ground speed of the vehicle using the instantaneous measurements obtained on board and possibly correct this value to obtain the ground speed of the vehicle at the location of each wheel so that the calculation of the corresponding slip remains as accurate as possible in all circumstances and especially in bends.

Some aspects of this technique rely on the determination of the coefficient of adhesion of a given wheel at a given moment that must be exposed beforehand. When the wheel is subjected only to the torque provided by the electrical machine or machines to which it is coupled, (either because it does not involve an internal combustion engine drive or mechanical braking, typically by friction - in accordance with the teachings of the patent application filed by the applicant recalled in the preamble - or because it is temporarily in this condition at the moment considered), this torque on the wheel is in direct correspondence with the current passing through the said electrical machines 2. Knowing the reference radius of the wheel 1 we can deduce at each moment the tangential force exerted on the ground by the wheel. Moreover, knowing the wheelbase E of the vehicle (see Figure 8), the total mass of the vehicle M, its distribution kM and (lk) M between the rear axle and the front axle and the height Hg of the center of gravity , knowing finally measuring the linear accelerations γ _x and γ _y provided by the sensors or measuring systems 34 and 36 (FIG Ib), the central unit 3 is able to calculate at each moment the load, or normal force F _AV and F _AR , on the front and rear axles. Knowing the track V of the vehicle the central unit 3 is also able to determine the load distribution between the wheels of each of the front and rear trains.

The magnitudes of mass and position of the center of gravity can be measured when the vehicle is powered up by a suitable sensor system or any other equivalent. In the example described here we have more simply opted for nominal values corresponding to the vehicle model considered with two passengers on board. As indicated above, the central unit then calculates the instantaneous adhesion coefficient μ _r of the wheel as the ratio between the tangential force and the normal force exerted on the ground by the wheel at the instant in question.

Returning now to the determination of the vehicle speed, it is based on a calculation of the average of the circumferential speed values of the wheels V _r derived from the measurements of the sensors 11 and previously validated according to criteria which are now described, for retain only those values that are considered reliable for this calculation. Thus, as long as at least one of the wheel speed values is valid, based on these criteria, it serves to determine the reference vehicle speed at the given instant according to the formula:

V _v = Sum V _r valid / Nb valid wheels (g)

If no circumferential wheel speed is valid at the given moment, the vehicle speed is then calculated by the central unit, from the last valid vehicle speed obtained, by integration of an indication of the acceleration of vehicle movement estimated as will be seen below.

The measure V _r is considered valid if the following conditions are met:

[0048] (a) The system does not detect a fault in the digital information exchange circulating on the CAN bus 30A. The electronic components specifically responsible for managing the communication on the CAN bus, and integrated respectively in the central unit 3 and in each of the electronic wheel modules 23, verify the proper functioning of the communication system as well as the integrity of the digital information which circulate there. said components generate, if necessary, CAN fault information usable by the central unit 3 and / or the electronic wheel modules 23. Moreover, the central unit 3 regularly sends information (setpoints; V _v ; see Figure 3) electronic wheel modules 23 with a rate of between 10 and 20 ms (here 16 ms). If this rate is not respected, the electronic module detects a CAN fault (central unit missing due to a fault, a cut in the CAN connection, etc.) and ignores the data coming from the CAN bus. In symmetry, the modules 23 respond to the central unit (V ₁ , current, faults, ...) with the same rate of 16 ms. If the central unit finds that the rate is not respected for one of the electronic modules 23, it declares the module concerned as absent and ignores its data (in particular V _r ).

[0049] (b) The electronic control module 23 associated with the wheel in question does not detect a fault of the resolver 11.

[0050] (c) Said wheel has not lost its grip on the ground. In this regard, it is considered that there is loss of adhesion mainly when the circumferential wheel acceleration γ -r is abnormal, that is to say, too high for the physics of the vehicle. For example, it is considered that a value exceeding 0.7 g in the engine direction and 1.2 g in the braking direction indicates a loss of adhesion of the wheel. Note that these values of the acceleration here are derived from the information provided by the resolver 11 to the wheel drive module 23 and the CPU. When a loss of adhesion has been detected on one of the wheels, the return to a normal adhesion, and therefore to a valid speed measurement for said wheel, intervenes only if the slip measurement of the wheel considered takes a value sufficiently the error is acceptable for the measurement of the vehicle speed (3%), or when μr is sufficiently low to guarantee wheel adhesion whatever the state of the ground (15%). % in view of a very slippery ground condition corresponding to the curve 103 of Figure 2).

(D) The coefficient of adhesion (μr) calculated at the instant in question is less than a limit value (μ Hm) beyond which sliding, as a result of the curves μ (λ) of Figure 2 is considered too high to continue to consider the circumferential speed of the wheel as a first acceptable approximation of the vehicle speed at the location of said wheel. If one considers for example a value of (μ-lim) as represented around 50%, one can note that the sliding values corresponding to the values of μr lower than this limit are small (curves 101 and 102). They lead to an error in the determination of the average speed which does not exceed 1.5 to 3%, which is considered acceptable. The observation of the curves of FIG. 2 shows that said curves are not very dependent on the state of the soil, for μr values lower than μ-lim (around 50%), when the maximum adhesion of the ground μ _m a _x exceeds μ-lim (case of μ _max i and μ _maX2 for curves 101 and 102). Therefore, knowing the characteristic μ (λ) of the tire used, in particular for μ less than 50%, it would be possible to determine the slip λ corresponding to the μr of work at the instant considered and to weight accordingly the measurement of wheel speed V _r

The indication of the coefficient of adhesion determined as it has been explained may be tainted with an error, for example corresponding to the variations of the actual vehicle load with respect to a nominal load taken into account for the calculation of the 'normal effort on the wheel. However, it can be seen from the observation of curves 101 and 102 that a large error in the coefficient of adhesion around 50% has little influence on the corresponding value of the slip. It has been determined in practice that for the purpose of applying the validity criterion described herein (ie the validity of the approximation of using the circumferential speed of a wheel instead of the vehicle speed measured at the (c) that these inaccuracies did not appreciably affect the quality of the decision made from the value of the coefficient of adhesion.

Considering now the case of a soil with a particularly low coefficient of adhesion (curve 103), the indicated value of (μ-lim) exceeds the maximum coefficient of adhesion μ _m a _x of the soil. The wheel concerned tends to accelerate very quickly abnormally but the loss of adhesion is then detected by the criterion (c) discussed above. On the other hand, it can be seen that if the coefficient of adhesion μ is less than 15%, the wheel is in a state of adhesion with the ground whatever the state thereof (curves 101, 102 or 103). This value provides a test criterion for maintaining or regaining adhesion of the wheel. (See step 113 of Figure 4)

The system thus determines a value of the vehicle speed which does not strictly represent the speed of a predetermined fixed point of the vehicle (for example the center of gravity of the vehicle) and which will be described here as "global" . To calculate the slip of a given wheel, the system must further ensure that this value is sufficiently close to the moment considered of the ground speed of the vehicle at the location of the wheel considered in the path of the vehicle.

This is normally the case if the vehicle is traveling in a straight line. In this case, the overall speed V _v transmitted by the central unit to the module 23 makes it possible to directly obtain the adequate representation of the slip from the wheel speed indication V _r . This is not the case, however, when the vehicle is cornering. In this case the overall speed of the vehicle and its speed at the level of the wheel differ by a correction coefficient which is both a function of the turning radius and the position (inside or outside) of the wheel in the turn. The central unit 3 is programmed to determine this correction coefficient according to the indication of the turning radius Ray transmitted on the line 3OG coming from the measuring system 35 linked to the steering control 41 and a factor which holds account of the position (inside or outside) of the wheel in the turn.

The correction coefficients are established according to an empirical relationship for each type of vehicle considered in this example on the basis of real measurements made on the vehicle considered. The value of the correction coefficient appropriate to each wheel in the instantaneous situation of the vehicle (direction and radius of the turn) is used by the central unit 3 to calculate a corresponding correction value of the circumferential speed:

Δ V _r A _r int, Δ V _r ^ r ^ext> Δ V Δ ^and _r ^mt Av Av V _r ^ext> ⁼ f (Ray),

(where Ray represents the turning circle here), for the front wheels (AvX rear (Ar), inside (int) and outside (ext.) at the turn.

The value V _v is transmitted to the control module 23 corresponding to each wheel and combined with the circumferential speed of the corrected wheel (V ₁ + AV _r ) to determine the value of the slip at the corresponding instant with a precision sufficient. It should be noted here that, for the sake of clarity, the process of transmitting and generating the corrected speed values is not shown in FIG. On the other hand, the principle of this correction is well taken into account in the flowchart of Figure 4b below.

The tests of the applicant have shown that it was possible to determine for each wheel a correction coefficient which gives corrected measures consistent to 1.5% for all the wheels concerned.

At this stage, FIGS. 4a and 4b give a simplified flowchart of the procedure for determining the vehicle speed, for a four-wheeled vehicle electrically driven in pairs, like that of FIG. 1. The flowchart of FIG. 4b illustrates the processing of the circumferential speed signal V _{Γ AVD} of the right front wheel I _AVD of the vehicle at a given instant

(step 101) and starts with a calculation (step 102) of the value of this speed V _{rc AVD} compensated for the eventual turns by a factor f (Ray, avd) which takes into account both the turning circle of the vehicle and the the position of the wheel I _AVD relative to the direction of the turn. The system proceeds then to examine its validity as a first approximation of the vehicle speed at the location of this wheel. For this purpose, the absence of fault of the CAN network (step 103) and the information of the corresponding resolver 11 (step 105) are successively checked, then, if so, the value of the angular acceleration of said wheel ( step 109) with respect to an upper limit for entry into slippage and a lower limit corresponding to a deceleration that can lead to a reversal of the direction of rotation of the wheel. If this acceleration value is outside the range defined by these limits an adhesion failure indicator is activated (step 111). In the opposite case, the process tests (step 113) if the last calculated sliding value is less than 3% or if the value of the adhesion coefficient μ is less than 15%, which results in the wheel finding a new value. condition of adhesion to the ground at the end of a loss of adhesion, even in the case of the curve 103 (ice, Figure 3). If so, this results in the activation of an adhesion indicator (step 115). If not, the process checks the status of the indicators 111 and 115 (step 117) and if an adhesion indication has been detected verifies whether the value of the adhesion coefficient μ determined for the wheel at that moment is less than the limit. upper μi _im (step 107). If the result of one of the tests 103, 105, 117 or 107 is negative, the process goes directly to the end of the processing (terminal 121) for the wheel 1 _AVD at the instant considered and passes to the next wheel (as explained below with reference to the flowchart of FIG. 4a If the test at the end of step 107 is positive, a counter of the number of wheels selected at the end of the processing of the wheel signals V _r in the sequence The speed of the last selected wheel is added to the sum Σ V _r of the wheel speeds already selected (step 119).

The processing that has just been reviewed is in a step 301 of a process for determining the overall vehicle speed (terminal 300) which starts with an initialization (step 301) of the selected wheel counter and of the summation register of the selected wheel speeds, already mentioned. As indicated also, the signals of the wheels A1 are successively processed in the processing steps 303 to 309. At the end of this phase, the state of the selected wheel counter is checked (step 311). If this number is not zero, the system calculates the average V _v of the selected wheel speeds (step 313) and displays it as the overall vehicle speed for the moment considered (terminal 315) at the end of the process. If step 311 detects that no wheel has been selected, the output of triggers a sub-process (step 317) as will be explained hereinafter.

Thus, when no circumferential wheel speed measurement taken from the wheel sensors or resolvers 11 can be used to estimate the ground speed of the vehicle at a given instant. Given, as for example in the case of a braking supported, the central unit 3 calculates the vehicle speed by digital integration of the longitudinal acceleration of motion γ _x _ _mvt from the overall speed determined for the previous moment. The vehicle velocity at each instant i is then provided by the formula: V _v (i) = V _v (i-1) + γ _x-mvt .Δt, (f) where VV (ι) is the estimated vehicle speed at 1 instant t _λ ; VV (, i) is the estimated vehicle speed at time t ₍ l_i ₎ ; γ _x _ _mvt is the vehicle acceleration and Δt is the time interval between two successive calculations (ie 16 ms as indicated for this example).

Of course, it is important to have a reliable measurement of the vehicle movement acceleration γ _x _ _mvt . Conventionally, the accelerometer 34 used in the present example is sensitive to the acceleration γ _x _ _mes resulting from the forces applied to the vehicle in the direction and direction of sound of the longitudinal displacement. It is assumed to simplify the explanations that the axis of the accelerometer 34 is oriented parallel to the ground when the vehicle is stopped and initially neglected the pitch oscillations of the vehicle body. If the ground is horizontal, the measurement γ _{x mes} of the accelerometer 34 actually corresponds to the acceleration of movement γ _x _ _mvt of the vehicle. On the other hand, when the running ground 280 is inclined, forming an angle δ with the horizontal (FIG. 5a), the acceleration of movement of the vehicle 285 along its axis of displacement XX is the result of the acceleration γ _{x mes} measured along this axis XX and the component of the acceleration of the gravity g along said axis of movement of the vehicle XX (see Figure 5a and 5b). The value of this component represents a deviation of g.sinδ between the value of the acceleration measurement γ _{x mes} and the real value of the acceleration γ _x _ _mvt of movement of the vehicle. For example, an uncompensated 5% slope induces an error of 5% on the acceleration measurement if one brakes to Ig (but 10% if one brakes only to 0.5g) and on the speed a error of 7 km / h after 4 s. It is therefore necessary to correct the value γ _x _ _mvt to have an acceptable vehicle speed measurement for the regulation of the slip according to the relation:

Yx-mvt = Yx my "g.SUlδy (a)

The correction is performed by the central unit 3 which consequently requires reliable information on the value of the angle δ.

We can have a first access to the angle δ using the measurements from the wheel sensors 11. The central unit 3 calculates a first approximation γ _{x wheel} s of the acceleration of movement of the vehicle from the circumferential acceleration values of each wheel γ _r transmitted to it by the wheel modules 23. The relation (a) above makes it possible to deduce an estimate of the angle δ according to the formula :

δ _y -acc = Arcsin [(γ _{x mes} - γ _{x rθ} ues) / g] (b)

This calculation is the subject of a first digital signal processing stage (F1) illustrated by the block 201 of FIG.

In practice, the signal corresponding to this estimate is very noisy. It is visible in FIG. 7a which represents (FIG. 200) a diagram of the curve of variation 200 as a function of time of the angle δ_ _ree i of 0 to 1 (arbitrary values) during a change of slope of the ground and the corresponding variation of the estimate 221 (relation (b)) at the output of the stage F1. An additional step to improve the quality of the measurement consists in performing a low-pass digital filtering (stage F2 - block 203) of the Numerical values from Fl. In FIG. 7a, the variation curve 223 of the signal δ _y _i _at t at the output of F2 is shown, which is behind the variation of the angle but offers good accuracy over the long term.

[0065] For an improved indication of the angle δ which exhibits both a sufficient accuracy and dynamic, the central processing unit 3 combines the result with another angle approximation δ_ _dyn end of the sensor 38 measures the angular velocity of the vehicle Ω _y about the YY axis parallel to the ground and perpendicular to the axis XX of movement of the vehicle. This signal is integrated in time (stage F3, block 205 Fig. 6) to provide an estimate of the variation of the angle δ (δ _y _ _Ωy; ) at the output of F2 represented in 225 on the diagram of the figure 7b. This signal is well representative of the angle variation sought on the short term but subject to drift over the long term. It is the subject of a high-pass digital filtering (stage F4 - block 207 - figure 6) with the same time constant as the low-pass filtering performed by the stage F2 to provide the numerical indication of which we see the representation 227 in Figure 7b. The outputs of the stages F2 and F4 (FIG. 6) are summed in a stage 209 to provide the compensated indication 210 sought for the angle δ, (see curve 210 of the diagram of FIG. 7c).

The place of the operations which have just been detailed here in the whole process of determining the overall speed of the vehicle according to the invention is represented by step 317 of the flowchart of FIG. 4a. Knowing the angle δ with the desired precision, the system calculates the acceleration of movement as explained with relation (a) and then the overall vehicle speed is calculated according to the relation (f). The The overall vehicle speed thus calculated for the moment considered is displayed in step 315, in the absence of a valid determination that would result directly from the wheel signals.

In fact, the slope angle δ is the sum of two components, namely the slope δi of the actual taxiway and the angle δ ₂ between the axis of movement of the vehicle XX and the ground in FIG. function of the pitch oscillations of the vehicle around a YY axis. In practice, the calculation and the tests show that the variation of this angle has a small impact on the precision of the corrections which one seeks to carry out, knowing that in all rigor the correction could be carried out by the calculation according to the preceding principles if the circumstances require it.

In an exemplary embodiment based on the principles which have just been described in detail, with a four-wheel drive vehicle controlled only by electrical machines, that is to say in particular without mechanical braking movement , we obtained average braking decelerations of 80 km / h at zero km / h of the order of 1 to 1.05g on dry ground. In this embodiment, a single set slip value for all wheels set at 15% was adopted. However, the implementation of the invention does not exclude the adoption of more sophisticated control schemes in which the sliding setpoint is varied in a self-adaptive manner, for example by observing the adhesion or any other relevant factor which has led to to activate the slip regulator at the instant considered, to approach as close as possible to the optimum deceleration of the wheel which allows to maintain the grip and the good behavior of the vehicle in the particular conditions of driving of the moment.

Of course there are in practice other methods to access certain data necessary to properly exploit the measurements made. Thus for example the use of an inclinometer on board the vehicle could provide additional measures to make reliable the instantaneous determination of the angle δ.

Thus we also know vehicle speed determination techniques based on a very short interruption of the torque applied to one or more wheels to obtain a value of the vehicle speed directly from the corresponding wheel sensor. . It can be reduced periodically for a few fractions of a second the torque on a wheel train

(Front ^or rear F ^or example) briefly to restore the adhesion of a sliding wheel ground and obtain one or more measurements of the velocity V _r which are recognized as valid for a readjusted estimate of overall speed from which by For example, integration of the acceleration of motion can be continued in the absence of valid signals from the wheel sensors. It should be emphasized how the application of the invention is suitable for a system such as that which has been retained above as an example. Such a vehicle is equipped with four driving wheels which are each coupled to a respective rotary electric machine designed and arranged so that traction and braking are entirely ensured from the torques exerted by this machine on the corresponding wheel, without any mechanical braking. This system allows precise knowledge at any time of the direction and intensity of these couples and therefore their precise control according to the slip values calculated to optimize the adhesion of each wheel independently and in all circumstances.

The invention may also find applications to vehicles comprising only one or two wheels (for example at the front) coupled to a rotary electric machine and one or two non-driving wheels. In this case the drive wheels can benefit from pure electric braking or in addition to a mechanical braking, the brake control pedal then actuating a sensor in the first part of its travel, via the central unit, a purely braking electric on both front wheels. In the course of its course the brake pedal acts on a conventional hydraulic circuit to generate additional mechanical braking on all four wheels.

The principle of determining the vehicle speed can be adapted to a speed measurement only on two wheels equipped with engines (for example at the front). One can also consider in this case, as mentioned above, to equip the rear wheels of the vehicle with only speed sensors to also participate in the generation of the vehicle speed indication relative to the ground. As a result, the slip regulator can work quite well on the front wheels in the engine direction (prevention of slippage). It can also operate in the braking direction to avoid the cancellation and reversal of the rotation of the wheels in the first part of the stroke of the brake pedal where the braking is purely electric.

Of course, the invention is not limited to the examples described and shown and various modifications can be made without departing from its scope as defined by the appended claims.

Claims

A system for determining an estimate of the instantaneous speed of a vehicle relative to the ground from measurements from at least one vehicle wheel motion sensor, comprising: an indicator (23B) of the circumferential speed of at least one wheel of the vehicle from the measurements of the motion sensor of this wheel, a test stage (107) for validating the indication of the circumferential speed at the output of said indicator if it makes it possible to deriving a sufficiently accurate and reliable representation of the speed of advance of the vehicle according to at least one predetermined criterion, and a module (119, 313) adapted to combine the circumferential speed wheel indications validated by the test stage for providing an estimate of the speed of travel of the vehicle relative to the ground, characterized in that it comprises a device (3) for calculating the instantaneous coefficient of adhesion of said wheel from given are available on board the vehicle and in that said test stage (107) is adapted to test the value of the coefficient of adhesion obtained for each wheel concerned, as a function of a relationship which makes it possible to determine whether the corresponding difference, or slip, between the circumferential speed of the wheel and the vehicle forward speed with respect to the ground at this moment is sufficiently small so that this circumferential wheel speed can be retained by said module as a datum for the determination of an estimate the speed of advance of the vehicle relative to the ground.

2. System for determining a speed estimation according to claim 1, in a vehicle in which each wheel used in the adhesion measurement is coupled to an individual rotary electric machine (2) suitable for applying to it a traction torque. and / or electrical braking, characterized in that the device for calculating the coefficient of adhesion of each of these wheels is operative in response to a measurement of the instantaneous torque applied to this wheel by the respective electric machine and to information according to the load of this wheel at the moment.

System for determining a speed estimation according to Claim 1 or 2, characterized in that the test stage is suitable for checking that the value of the coefficient of adhesion (U ₁ ) is less than a predetermined threshold indicating that the value of the corresponding slip of the wheel is less than 5% and preferably less than 2%, so that the corresponding circumferential wheel speed is retained by the module estimation of the speed.

System for determining a speed estimation according to Claim 1 or 2, characterized in that the test stage is capable of determining whether the value of the coefficient of adhesion (μ _r ) is below a predetermined threshold. in a range between 30% and 70%, above which coefficient the corresponding wheel speed is not retained by the speed estimation module.

5. System for determining a speed estimate according to claim 4, characterized in that the value of the predetermined threshold of adhesion coefficient implemented by the test stage (107) is around 50%. .

A system for determining a speed estimate according to claim 1 or 2, characterized in that said test stage (113) is adapted to determine that the coefficient of adhesion of the wheel at said instant is equal to or less than one predetermined threshold sufficiently low to indicate that said wheel has retained or recovered a suitable adhesion, irrespective of the state of the tread of said wheel, to admit the corresponding wheel speed value as a possible input for the estimation module vehicle speed.

System for determining a speed estimate according to Claim 6, characterized in that the predetermined threshold level for the coefficient of adhesion is

15%.

8. System for determining a speed estimation according to one of claims 1 to 7, characterized in that it also comprises a wheel slip test stage (113) calculated from the indication of circumferential speed of said wheel, this stage being able to verify if the value of this slip is less than a predetermined threshold sufficiently low to indicate that said wheel has retained or recovered a suitable adhesion, whatever the state of the running ground of said wheel.

9. System for determining a speed estimate according to one of claims 1 to

8, characterized in that it also comprises a test stage (109) able to determine whether the acceleration of the wheel at said instant is within a range of predetermined values indicating that said wheel is or is not in a state of adhesion to the moment considered.

10. System for determining a speed estimation according to one of claims 1 to

9, characterized in that it further comprises means (102) for correcting the circumferential speed indication of each wheel as a function of its position relative to the trajectory of the vehicle in a turn before applying this indication to the module for estimating the overall speed of advance of the vehicle relative to the ground at this time.