Method and system for adjusting an Anti-SKID control system of a vehicle

Abstract

Method and system (99) for adjusting an anti-skid control system (100) of a vehicle (1 ) moving on a surface (R), the system comprising an actuation device (9) operatively connected to wheels (W) of the vehicle (1 ) and a processing unit (8) programmed to perform the following steps of the method: - in response to a request (RS) of speed variation of the vehicle (1 ), applying over time a respective torque (Tr) to one or more wheels (W); - for a tyre (T1 ) mounted on a respective wheel (W1 ) having a respective current value (Ac) of the first parameter less than or equal to a predetermined target value (Atg), performing a routine of estimation of an operational value (Aop) of the first parameter for which a maximum friction (lie) is obtained between the tyre (T1 ) and the surface comprising: i) estimating a respective current value (Uc) of a second parameter (U) representative of a friction between the tyre (T1 ) and the surface (R); ii) estimating the operational value (Aop) of the first parameter as a function of the respective current value (Ac) of the first parameter and of the respective current value (Uc) of the second parameter; - on condition that the respective torque (Tr) is still applied, adjusting the anti-skid control system (100) by updating the predetermined target value (Atg) of the first parameter with a new target value (AtgN) of the first parameter as a function of the operational value (Aop) of the first parameter.

Description

[0001] DESCRIPTION

[0002] Title: METHOD AND SYSTEM FOR ADJUSTING AN ANTI-SKID CONTROL SYSTEM OF A VEHICLE

[0003] Technical field of the invention

[0004] The present invention relates to a method and a system for adjusting an anti-skid control system of a vehicle. The present invention further relates to a vehicle comprising the adjustment system.

[0005] Prior art

[0006] A tyre typically has a substantially toroidal structure around an axis of rotation thereof during operation, and presents an equatorial plane orthogonal to the axis of rotation, said equatorial plane being typically a plane of (substantial) geometric symmetry (e.g. neglecting any minor asymmetries, such as the tread pattern and / or the writings on the sidewalls and / or the internal structure).

[0007] "Crown portion" is intended as a portion of the tyre located at the tread band.

[0008] The terms "radial" and "axial" are used with reference to a perpendicular direction and to a direction parallel to the axis of rotation of the tyre, respectively.

[0009] The term "tangential" is used with reference to a direction generally turned according to the rolling direction of the tyre, perpendicular to both the radial direction and the axial direction.

[0010] The term "longitudinal" is used to indicate a direction (preferably with sense concordant with a forward direction of travel of the vehicle) that is tangent instant by instant to a trajectory of the vehicle.

[0011] The term "transverse" (or equivalently "lateral") is used to indicate a direction substantially orthogonal to the longitudinal direction and substantially parallel to the road surface.

[0012] The term "free rolling" is used to indicate a condition of substantial stationary rolling of the tyre, in the substantial absence of longitudinal and / or transverse forces applied to the tyre.

[0013] "Substantially orthogonal" relatively to geometric elements (such as straight lines, planes, surfaces, etc.) means that these elements (or elements parallel thereto and mutually incident) form an angle within the range of 90°+ / -15°, preferably within the range 90°+ / -10°.

[0014] "Substantially parallel" relatively to the aforesaid geometric elements means that these elements (or elements parallel thereto and mutually incident) form an angle within the range 0°+ / -15°, preferably within the range 0°+ / -10°.

[0015] Summary of the invention

[0016] In the context of anti-skid control systems of a vehicle, for example an ABS system and / or a traction control system, of which nowadays almost all vehicles are provided, the Applicant has made the following considerations.

[0017] Firstly, an anti-skid control system of a vehicle is typically configured to operate as a function of at least one predetermined target value of a first parameter representative of a slip of a tyre mounted on a wheel of the vehicle with respect to the surface on which the vehicle travels. In more detail, an anti-skid control system, upon the occurrence of certain critical conditions (typically overly high slip of the tyres on the surface), is typically configured so that a respective current value of the first parameter of one or more of the tyres of the vehicle is brought around such a predetermined target value of the first parameter.

[0018] The predetermined target value of the first parameter is typically a value of the first parameter for which a value of a second parameter representative of a friction between tyre and surface is maximum. Therefore, the anti-skid control system of a vehicle operates so as to maximise the coefficient of friction between tyres and surface. For example, an ABS system attempts to do the above by modulating the torque applied to the tyres over time (as known).

[0019] Graphically, for example, in a slip-friction plane, a generic curve (called characteristic curve) that represents the friction that can be developed by the tyre on the road surface as the relative slip varies typically shows an increasing trend up to an absolute maximum (the -maximum- friction available) as the slip of the tyre on the road surface increases (for example in the case of partial or total blocking of the tyre rotation), and then settling asymptotically on values lower than such a maximum value for even higher slip.

[0020] Different interaction situations between tyre and surface determine different curves, all sharing the fact of having a respective absolute maximum (generally different between one curve and the other).

[0021] Therefore, the predetermined target value of the first parameter typically represents the abscissa of the aforesaid absolute maximum of a given curve.

[0022] However, the Applicant has realised that the predetermined target value is precisely predetermined, i.e., determined a priori starting from a predetermined characteristic curve of a tyre that is assumed to be representative of any tyre-surface interaction situation. This predetermined characteristic curve, in turn, typically derives from an average of different characteristic curves each representative of a respective interaction situation, for example as a function of the type of tyre, the pressure, the temperature, the respective conditions of increasing wear, the various conditions of the rolling surface (e.g. dry, wet, icy, snowy, slippery, etc.), etc., but also from the conditions of movement of the tyre on the surface.

[0023] It therefore follows that necessarily this predetermined target value, as well as the respective predetermined characteristic curve, as averaged values, never precisely represent the real interaction situation to which the tyres of the vehicle are subject with respect to the given surface on which they are rolling.

[0024] On the other hand, in a very specific example, today some ABS systems, during the braking control phase of the vehicle, can use a methodology that is based on the use of high slip of the tyre on the surface for determining the actual coefficient of friction available between tyres and surface upon braking. However, in addition to representing a particular case which is not always applicable, this methodology is performed in the presence of high slip of the tyres, i.e., in conditions of potential danger and when the ABS has already come into operation.

[0025] The Applicant has therefore addressed the problem of improving the possible response of an anti-skid control system of a vehicle, adapting it as much as possible to the actual interaction situation between the vehicle tyres and the surface, in a preventive manner and keeping the vehicle in safe conditions.

[0026] According to the Applicant, the aforesaid problem is solved by means of a method, and a system, for adjusting an anti-skid control system of a vehicle in which at least one predetermined target value of the first parameter, as a function of which the anti-skid control system is configured to operate, is updated with a new target value of the first parameter estimated as a function of an operational value of the first parameter for which the maximum friction actually available between tyre and surface is obtained upon a request for speed variation of the vehicle.

[0027] According to an aspect, the invention relates to a method for adjusting an anti-skid control system of a vehicle moving on a surface. Preferably, said anti-skid control system is configured to operate as a function of at least one predetermined target value of a first parameter representative of a slip of a tyre mounted on a wheel of said vehicle with respect to said surface.

[0028] The method preferably comprises, in response to a speed variation request of said vehicle, applying a torque to one or more wheels of said vehicle.

[0029] The method preferably comprises, for at least one tyre mounted on a respective wheel of said one or more wheels having a respective current value of said first parameter less than or equal to said predetermined target value of said first parameter, performing a routine of estimation of an operational value of said first parameter for which a maximum friction is obtained between said tyre mounted on said respective wheel and said surface when said respective torque is applied.

[0030] Preferably, said routine of estimation comprises the steps of: i) estimating (at least) a respective current value of a second parameter representative of a friction between said tyre mounted on said respective wheel and said surface; ii) estimating said operational value of the first parameter as a function of said respective current value of the first parameter and of said respective current value of the second parameter.

[0031] The method preferably comprises, on the condition that said respective torque is still applied, adjusting said anti-skid control system by updating said predetermined target value of said first parameter with a new target value of said first parameter estimated as a function of said operational value of said first parameter.

[0032] According to another aspect, the invention relates to a system for adjusting an antiskid control system of a vehicle moving on a surface.

[0033] The system preferably comprises an actuation device operatively connected to wheels of said vehicle.

[0034] The system preferably comprises a processing unit operatively connected to said actuation device and in dialogue with said anti-skid control system of said vehicle. Preferably said processing unit is programmed for, in response to a request signal of speed variation of said vehicle, controlling said actuation device to apply a torque to one or more wheels of said vehicle.

[0035] Preferably said processing unit is programmed, for at least one tyre mounted on a respective wheel of said one or more wheels having a respective current value of said first parameter less than or equal to said predetermined target value of said first parameter, for performing a routine of estimation of an operational value of said first parameter for which a maximum friction is obtained between said tyre mounted on said respective wheel and said surface when said respective torque is applied.

[0036] Preferably, said routine of estimation comprises the steps of: i) estimating (at least) a respective current value of a second parameter representative of a friction between said tyre mounted on said respective wheel and said surface; ii) estimating said operational value of said first parameter as a function of said respective current value of the first parameter and of said respective current value of the second parameter.

[0037] Preferably said processing unit is programmed for, on the condition that said respective torque is still applied, adjusting said anti-skid control system by updating said predetermined target value of said first parameter with a new target value of said first parameter estimated as a function of said operational value of said first parameter.

[0038] According to a further aspect, the invention relates to a vehicle equipped with tyres mounted on wheels and comprising an anti-skid control system, where the vehicle comprises the adjustment system according to the present invention.

[0039] According to the Applicant, the execution of the routine of estimation of the operational value of the first parameter when the torque is applied in response to the request for speed variation allows to advantageously exploit a request for speed variation (e.g. acceleration and / or braking) that comes from the driver himself / herself for reasons related to the driving situation (e.g. obstacle to be avoided, lane change, etc.). Thereby, on the one hand the vehicle responds to the driver's commands (without introducing torques to the wheels at times not requested by the driver), and on the other hand it is possible to make the tyre work on the surface to be able to subsequently estimate the respective current values of the first and second parameter.

[0040] Performing the estimation for at least one tyre of the wheels of the vehicle having the respective current value of the first parameter less than or equal to the predetermined target value of the first parameter allows to select the tyre for which a condition of substantial stability remains, benefiting the precision of the estimation routine. Without wishing to be limited to any theory, the Applicant considers that beyond the target value the tyre could be in an unstable equilibrium condition whereby the respective current value of the first parameter could rapidly grow to very high values (and require, for example, the intervention of the anti-skid control system as a function of the predetermined target value to guarantee the safety of passengers based on the values available).

[0041] Consistently, the estimation of the operational value of the first parameter for which the maximum friction between tyre and surface is obtained as a function of the current values of the first and second parameter (for example by means of characteristic slipfriction curves of the tyre) allows to obtain the desired estimation of a value closely correlated to the actual interaction situation between the vehicle tyres and surface at the time of the speed variation request, while keeping the tyre far from the aforesaid high slip conditions. Thereby, appropriate values are obtained for the specific condition and the safety of the passengers is preserved.

[0042] Finally, the adjustment of the anti-skid control system by updating the predetermined target value of the first parameter with a new target value, as a function of the operational value of the first parameter, allows to update one of the main parameters as a function of which an anti-skid control system typically operates in a manner dependent on the actual tyre-surface interaction situation. The adjustment of the antiskid control system on the condition that the respective torque is still applied allows to perform the adjustment only if necessary so as to be able to possibly use the updated parameters in the same speed variation request from which the estimate is generated, without affecting future speed variation requests.

[0043] The present invention may have one or more of the following preferred features.

[0044] Preferably said processing unit is programmed and configured to perform one or more of the following operations preferably envisaged for the method.

[0045] Preferably said method comprises estimating at least said respective current value of said first parameter. More preferably the method comprises estimating a plurality of respective current values of the first parameter and a further plurality of respective current values of the second parameter during said applying over time said respective torque. Thereby, the precision of the operational value estimate is increased.

[0046] Preferably said method comprises adjusting said anti-skid control system again by updating said new target value of said first parameter with said predetermined target value of said first parameter once said applying over time said respective torque has ended. Thereby, the initial predetermined configuration of the anti-skid control system is restored, benefiting safety for future needs. In fact, although the operational value of the first parameter is particularly suitable to be used for the adjustment simultaneously with the request for speed variation in progress, once the consequent application of torque to the wheels has ended, the Applicant has realised that it is appropriate to restore the anti-skid control system to the predetermined initial configuration.

[0047] In an embodiment, said method can comprise maintaining said new target value of said first parameter until a subsequent speed variation request.

[0048] In an embodiment, said method comprises adjusting said anti-skid control system again by updating said new target value of said first parameter with said predetermined target value of said first parameter after a predetermined time interval starting from said adjusting said anti-skid control system. Thereby, in the event of subsequent speed variation requests subsequent to the requested date and included in the predetermined time interval, the anti-skid control system is already appropriately adjusted.

[0049] Preferably said method comprising continuously estimating, for each wheel of said one or more wheels, a respective value of a reference parameter representative of a variation over time of said torque applied to the respective wheel in response to said request of speed variation. Preferably said method comprises comparing, in continuous, each respective value of said reference parameter with a predetermined limit value of the reference parameter.

[0050] Preferably said method comprises performing said routine of estimation of said operational value of the first parameter on the condition that a respective value of said reference parameter of said respective wheel of said one or more wheels is less than said predetermined limit value of the reference parameter. Thereby, the precision and / or accuracy with which the operational value is estimated is further improved. In fact, without wishing to be limited to any theory, the Applicant has realised that with a limited torque rate, the introduction of disturbances in the detected signals from which the estimates of the current values of the first and / or second parameter are performed is also limited.

[0051] Preferably said reference parameter representative of the torque rate comprises, or consists of, a rate of said torque (e.g. derivative over time of the torque). Thereby, It is obtainable in a simple and direct manner.

[0052] In an embodiment, said reference parameter representative of the torque rate comprises, or consists of, a longitudinal acceleration rate of said vehicle.

[0053] Preferably an absolute value of said predetermined limit value of the reference parameter is, or corresponds to, a value greater than or equal to 0.1 G / s, and / or less than or equal to 0.9 G / s, more preferably less than or equal to 0.7 G / s, even more preferably less than or equal to 0.5 G / s (for example equal to 0.3 G / s). The capital letter G is intended as the value of the acceleration of gravity. The positive or negative sign of the predetermined limit value depends on the specific application, in the event of braking or traction torque. Such values have proven to be advantageous for the purposes described above.

[0054] Preferably said anti-skid control system is configured to also operate as a function of a predetermined threshold value of said first parameter, preferably said predetermined threshold value being greater than said predetermined target value. For example, the predetermined threshold value corresponds to a very high value of the first parameter, and therefore representative of a very high slip of the tyre with respect to the surface. Preferably said anti-skid control system is configured to activate an anti-skid control of a tyre for a respective current value of the first parameter greater than the predetermined threshold value of the first parameter. That is, the anti-skid control system is activated if a slip of a tyre is detected that exceeds the slip threshold value, and the anti-skid control system aims to bring the current slip of the tyre back to around the target value.

[0055] Preferably adjusting said anti-skid control system further comprises updating said predetermined target value of said first parameter with a new threshold value of said first parameter estimated as a function of said operational value of said first parameter. Thereby, the adjustment is further precise and adapted to the actual tyre-surface interaction condition.

[0056] Preferably adjusting said anti-skid control system again further comprises updating said new threshold value of said first parameter with said predetermined threshold value of said first parameter once said applying over time said respective torque has ended. Thereby, the threshold value also returns to the preset value, to the overall advantage of safety once the contingent speed variation request has ended.

[0057] In an embodiment, it may be envisaged to update the new threshold value of the first parameter with the predetermined target value of the first parameter after a respective time interval starting from said adjusting said anti-skid control system.

[0058] Preferably the expression "updating a first value with a second value", for example referring to the aforesaid predetermined target and threshold values and respective new values (and vice versa) of the first parameter, is intended to replace the first value with the second value. Preferably applying over time said torque is performed on each wheel of said vehicle.

[0059] Preferably each torque applied to said wheels is a braking torque.

[0060] Preferably said anti-skid control system is an ABS system of said vehicle. In fact, the Applicant considers it particularly advantageous to adjust the ABS system in the event of braking, to the maximum benefit of passenger safety.

[0061] Optionally, each torque applied to said wheels is a traction torque. Preferably said antiskid control system is a traction control system. In certain circumstances, it may in fact be advantageous to perform the adjustment on the traction control system and in the event of accelerations of the vehicle.

[0062] Preferably said first parameter comprises, or coincides with, a longitudinal slip of said tyre with respect to said surface. The use of longitudinal slip is particularly advantageous for the estimation of the operational value of the first parameter.

[0063] Preferably said respective current value of said first parameter is estimated as a function of a tangential speed of said respective wheel and of a value of a magnitude representative of a theoretical tangential speed of said respective wheel of said vehicle in a free rolling condition. Thereby, the estimate of the current value of the first parameter is further precise.

[0064] Preferably said respective current value of the first parameter is estimated as a function of a ratio between said tangential speed of the respective wheel and said theoretical tangential speed. Preferably said theoretical tangential speed of the respective wheel is used to estimate an overall speed of the vehicle. For example, the theoretical tangential speed can be obtained from GPS systems of the vehicle, or from an acceleration signal (e.g. longitudinal) of the vehicle, or still from a rotation speed of a further wheel of the vehicle, distinct from the respective wheel, and left in free rolling (i.e. without any torque applied). This third case may for example occur when the torque applied to the wheels is a driving torque and the vehicle has only two driving wheels (front or rear).

[0065] Preferably said actuation device belongs to a braking system of said vehicle and / or to a motor system of the vehicle (e.g. endothermic motor, electric motor, possibly dedicated to each wheel, etc.).

[0066] Preferably said second parameter comprises, or coincides with, a friction coefficient between said tyre and said surface. The use of the current value of the friction coefficient is particularly advantageous for the estimation of the operational value of the first parameter.

[0067] Preferably said respective current value of said second parameter is estimated as a function of forces acting on said tyre mounted on said respective wheel, more preferably as a function of a first resultant of forces acting on said tyre, mounted on said respective wheel, substantially parallel to said road surface and a second resultant of forces acting on said tyre, mounted on said respective wheel, substantially perpendicular to said road surface, even more preferably as a function of a ratio between said first resultant and said second resultant. Thereby, the estimate is simple. Preferably said method comprises estimating said first and second resultant of ferees acting on said tyre.

[0068] Preferably said first resultant is directed longitudinally. Thereby, the first and the second parameter are appropriately related to each other.

[0069] Preferably said second resultant is estimated using a mathematical model of distribution of a mass of said vehicle on the wheels of the vehicle. Thereby, the precision of the estimate is improved.

[0070] In an embodiment said first parameter comprises, or coincides with, a drift angle of said tyre. In such an embodiment, said first resultant is preferably directed transversely. Thereby the first and second parameter are appropriately related to each other.

[0071] In an embodiment said first resultant is estimated as a function of a longitudinal or transverse acceleration of said tyre (respectively depending on the direction along which said first resultant is directed). Thereby, the estimate is immediate.

[0072] In an embodiment, said first resultant is estimated as a function of (at least) said respective torque applied to said respective wheel. Such an estimation mode can be useful when there is no (longitudinal) acceleration and / or when the (longitudinal) acceleration signal can be disturbed.

[0073] Preferably estimating said operational value of said first parameter is performed using a model (for example that shown in Figure 5) of said tyre mounted on said respective wheel comprising a physical relationship between said first parameter and said second parameter. For example, it is envisaged to use a map of the longitudinal features of the tyre. The Applicant has found the use of such models advantageous for the purposes of the present invention, as they allow to estimate the operational value of the first parameter starting from the respective current values of the first and the second parameter in an accurate manner.

[0074] Preferably said new target value of said first parameter coincides with said operational value of said first parameter. Thereby, the adjustment is aimed at exploiting all the friction available at the time of the speed variation request.

[0075] In an embodiment said new target value of said first parameter is calculated as a fraction of said operational value of said first parameter. For example, the new target value of the first parameter can be equal to 90% of the operational value of the first parameter. Thereby, the adjustment is conservative.

[0076] In an embodiment, said method comprises estimating said new target value of said first parameter (and possibly also said new threshold value of said first parameter) as a function of a model of said tyre mounted on said respective wheel comprising a physical relationship between said first parameter and said second parameter. For example, it is preferably envisaged to obtain the new target value of the first parameter starting from the operational value of the first estimated parameter and from a respective characteristic curve for which the operational value of the first parameter represents the abscissa of the absolute maximum of the curve (which represents the maximum -coefficient of- friction available). Thereby, the estimate of the new values is quick and precise.

[0077] Preferably, said adjustment system comprises a respective monitoring device for each tyre mounted on each wheel of said vehicle. Preferably each monitoring device is fixed at a crown portion of the respective tyre.

[0078] Preferably, each monitoring device is suitable for detecting (possibly also indirectly) at least one tangential speed of the respective tyre. Thereby, the quality of the data related to the speeds of the first and second wheel is improved, benefiting the estimation of the operational value of the first parameter.

[0079] Preferably said processing unit is operatively connected to each monitoring device. Thereby, the signals measured by the sensors can be provided directly to the processing unit.

[0080] In an embodiment, said vehicle is a self-driving vehicle.

[0081] Brief description of the figures

[0082] Figure 1 schematically shows a vehicle according to the present invention;

[0083] Figure 2 schematically shows a detail of the vehicle of Figure 1 in which a monitoring device mounted on a tyre is visible; Figure 3 shows a conceptual diagram of an embodiment of an adjustment method according to the present invention;

[0084] Figure 4 shows in detail a logical block of the diagram of Figure 3,

[0085] Figure 5 shows a slip-friction graph with five examples of characteristic curves related to five different conditions of a tyre on a rolling surface, schematically illustrating the operation of a part of the adjustment method according to the present invention;

[0086] Figure 6 shows a slip-friction graph containing two distinct characteristic curves of a tyre.

[0087] Detailed description of preferred embodiments of the invention

[0088] The features and advantages of the present invention will be further clarified from the following detailed description of some embodiments, presented by way of non-limiting example of the present invention, with reference to the attached figures.

[0089] Figure 1 schematically shows a vehicle 1 according to the present invention. The vehicle 1 may be a vehicle with an endothermic and / or electric motor, with two or more driving wheels. Exemplarily, the vehicle 1 is a self-driving vehicle.

[0090] Exemplarily the vehicle 1 comprises four wheels W, each provided with a respective tyre T (partially shown also in Figure 2) rolling on a road surface (not shown). The wheels are exemplarily identified as front right FR, front left FL, rear right RR and rear left RL.

[0091] Exemplarily, the vehicle 1 comprises an anti-skid control system 100, shown only schematically in Figure 1. For example, the anti-skid control system may comprise an ABS system of the vehicle and / or a traction control system of the vehicle. The detailed operation of an anti-skid control system can depend on multiple parameters. Systems of this type are generally known and will therefore not be described in detail below. The vehicle 1 comprises an adjustment system 99 of the anti-skid control system 100. The system 99 exemplarily comprises a monitoring device 4 for each tyre T (Figures 1 and 2) of the vehicle. For example, the monitoring device 4 may be of the type described in one of the following documents on behalf of the same Applicant: WO 2018 / 065846 A1 , WO 2019 / 123118 A1 , WO 2020 / 026281 A1 , WO 2020 / 026282 A1 . Exemplarily, each monitoring device 4 is capable of detecting a tangential speed of the respective tyre. Preferably, the monitoring device 4 may also comprise at least one accelerometer capable of detecting an acceleration in a radial, and / or axial, and / or tangential direction of the tyre. Exemplarily each monitoring device 4 is fixed on an inner surface 5 of the tyre, at a crown portion 6 of the respective tyre T (Figure 2). In particular, the monitoring device 4 can be fixed to a liner of the tyre T, typically by gluing (for example by means of a structural adhesive or by means of a pressure-sensitive adhesive). Preferably, the monitoring device 4 can be substantially fixed at an equatorial plane 150 of the tyre T. Further detection devices (not shown) can be arranged in a more lateral position on the inner surface of the tyre T, and / or in different angular positions along the inner circumference of the tyre T.

[0092] The system 99 comprises an actuation device 9 (shown only schematically in Figure 1 ) operatively connected to each wheel W of the vehicle 1 .

[0093] Exemplarily the actuation device 9 comprises a braking system of the vehicle 1. Exemplarily, the anti-skid control system is connected to the actuation device 9 to control a torque applied to the wheels (as for example known for an ABS system).

[0094] In an embodiment, not shown, the actuation device 9 may comprise (in addition to or as an alternative to the braking system) a motor system (e.g. an electric motor for each wheel, typically in the case of an electric vehicle, or a motor force distribution system of an endothermic motor, in the case of a vehicle with four driving wheels). In such an embodiment, the anti-skid control system further comprises a traction control system. The system 99 exemplarily comprises a processing unit 8 (shown only schematically) operatively connected to the actuation device 9 and in dialogue with the anti-skid control system 100. Exemplarily, the processing unit 8 is installed on board the vehicle. For example, the processing unit 8 can be a calculation unit physically distinct from, in mutual data communication with, a command and control unit (not shown) of the vehicle, or they can be a same calculation unit suitably programmed to carry out the functions of both the command and control unit and the processing unit.

[0095] Exemplarily the processing unit 8 is also operatively connected to the four monitoring devices 4, for example by means of a radio signal.

[0096] In use, the adjustment system 99 allows to perform a method for adjusting the antiskid control system 100, typically by means of one or more hardware devices programmed by means of one or more software modules residing and / or loaded on appropriate memories.

[0097] An embodiment of the adjustment method according to the present invention will now be exemplarily described with particular reference to Figures 3 and 4. Exemplarily, the anti-skid control system 100 is configured to operate as a function of a predetermined target value Atg and a predetermined threshold value Ats of a first parameter A representative of a slip of a tyre mounted on a wheel of the vehicle with respect to the rolling surface of the tyre.

[0098] Very briefly, in the case, for example, of an ABS system, the latter, when a current value of the first parameter of a tyre of the vehicle greater than the predetermined threshold value Ats is detected, it is typically configured to control a torque applied to the wheels so as to bring the current value of the first parameter of the tyre back around the predetermined target value Atg of the first parameter.

[0099] In general, the operation of an ABS system is typically dependent on a plurality of parameters, often different depending on the type of ABS system. Among these, however, at least the predetermined target value (but typically also the predetermined threshold value) represents a parameter common to all ABS systems. From a qualitative point of view, the predetermined target value and the predetermined threshold value represent the abscissa of two points of a characteristic curve of a tyre of the vehicle in a friction-slip plane as a function of which the ABS system is typically configured.

[0100] Figure 6 shows, purely indicatively, an example of a characteristic curve CO of the tyre in the slip-friction plane according as a function of which the ABS system can be exemplarily configured. Exemplarily, such a generic curve CO represents a predetermined tyre-surface interaction situation. Typically such a curve CO can be for example a curve resulting from the average of various curves in such a plane, each curve representing a respective tyre-surface interaction situation, for example depending on the type and / or condition of the tyre (e.g. pressure, temperature, wear, etc.), condition of the surface, etc.

[0101] Exemplarily, the curve CO has a maximum whose abscissa corresponds to the predetermined target value Atg. The predetermined threshold value Ats instead corresponds exemplarily to the abscissa of a point more to the right on the curve CO with respect to the maximum, that is, it represents a high slip condition.

[0102] The predetermined target value Atg and the predetermined threshold value Ats are for example stored in a control unit of the vehicle in dialogue with the processing unit 8. Exemplarily, the method comprises receiving a request RS of speed variation of the vehicle 1 . The request RS exemplarily acts as a start / trigger signal for carrying out the steps of the method, exemplarily by the processing unit 8, as conceptually shown in Figures 3 and 4 and aimed at adjusting the anti-skid control system 100 by updating the predetermined target value Atg, and the predetermined threshold value Ats, of the first parameter with respective new values, as will now be described in detail. In the following, without however losing generality, the request RS will be referred to as a brake request coming from the driver of the vehicle.

[0103] Exemplarily, the steps entrusted to the processing unit 8 comprise control instructions of the actuation device 9 to perform certain actions on all the wheels W of the vehicle 1 , and a series of computational estimates, graphically summarised in the routine CE ("Condition Estimation"), shown in more detail in Figure 4 (and described below).

[0104] Exemplarily, the method comprises, in response to the request RS, applying over time a respective torque Tr to all the wheels W of the vehicle. Advantageously, the application of each respective torque Tr occurs by means of command of the actuation device 9.

[0105] Exemplarily, the method therefore comprises, for at least one tyre T1 mounted on a respective wheel W1 having a respective current value Ac of said first parameter less than or equal to the predetermined target value Atg of the first parameter, performing a routine of estimation CE of an operational value Aop of the first parameter for which a maximum friction lie is obtained between the tyre T1 mounted on the respective wheel W1 and the surface R when the respective torque Tr is applied.

[0106] Exemplarily, the method further comprises continuously estimating, for each wheel W, a respective value Tr’ of a reference parameter representative of a variation over time of the torque applied to the respective wheel in response to the speed variation request, and continuously comparing each respective value Tr’ of the reference parameter with a predetermined limit value Tr'lim of the reference parameter.

[0107] Exemplarily, the reference parameter coincides with such a variation over time of the applied torque (i.e. the drift before the respective applied torque with respect to time). Alternatively, the reference parameter may be, or comprise, a longitudinal acceleration rate of the vehicle. Such a longitudinal acceleration rate can be pre-loaded in a memory of the processing unit once calibrated as a function of a given torque, or acquired in real time from a signal returned by an acceleration sensor 11 (Figure 1 ), connected to the processing unit 8 and preferably installed on board the vehicle 1 . For example the acceleration sensor 11 may be of the 3DOF IMU type.

[0108] Exemplarily, the method therefore comprises performing the routine of estimation CE of the operational value Aop of the first parameter on condition that a respective value Tr’ of the reference parameter of the respective wheel W1 is less than the predetermined limit value Tr'lim of the reference parameter.

[0109] Therefore, the routine of estimation CE is exemplarily performed with reference to at least one tyre T1 of the vehicle whose current value Ac of the first parameter is less than or equal to the predetermined target value Atg and such that the respective wheel has a respective value Tr’ of the reference parameter less than the limit value Tr'lim. Exemplarily, the tyre T1 meets such requirements.

[0110] In the case of several tires of the vehicle which simultaneously meet the requirements described above, the routine of estimation is performed for each tyre independently of the others. In such a case, it can for example be envisaged to estimate the new target and threshold values of the first parameter as a function of an average of the estimated operational values for each tyre as described below.

[0111] The routine of estimation of the operational value Aop of the first parameter will now be exemplarily described with particular reference only to the tyre T 1 of the vehicle and to Figure 4.

[0112] Routine CE

[0113] The routine CE exemplarily comprises estimating, by the sub-routine R1 , at least one respective current value Ac of the first parameter with reference to the tyre T1. Exemplarily, the current value of the first parameter can be estimated regardless of the activation of the routine CE, i.e. before such activation so as to evaluate the requirements of the tyre.

[0114] Exemplarily the first parameter coincides with the longitudinal slip of the tyre T1 with respect to the surface R.

[0115] In detail, the method exemplarily comprises estimating the respective current value Ac of the first parameter as a function of a tangential speed Vx1 of the respective wheel W1 and of a value of a magnitude representative of a theoretical tangential speed Vxt of the same respective wheel W1 in a free rolling condition.

[0116] For example, the tangential speed Vx1 can be estimated as a function of the respective angular speed of the wheel (acquired for example by the monitoring device 4 of the respective tyre) and of the respective radius. As instead regards the value of the magnitude representative of the theoretical tangential speed Vxt, since, in the present embodiment of the adjustment method, each wheel of the vehicle subject to braking torque, i.e. none of the wheels is in free rolling, such a value of the magnitude representative of the theoretical tangential speed can be estimated starting from the longitudinal speed of the vehicle, for example obtainable by means of a GPS signal.

[0117] Exemplarily, the respective current value of the first parameter can be estimated by the following formula Ac =(Vx1 -Vxt) / Vx1 .

[0118] Exemplarily, the method further comprises estimating at least a respective current value Uc of a second parameter U representative of a friction between the tyre T1 mounted on the respective wheel W1 and the surface R. Exemplarily, the second parameter U coincides with the coefficient of friction between the tyre and the surface. Exemplarily the respective current value Uc of the second parameter is estimated in the sub-routine R2 as a function of a ratio between a first resultant Fx of forces acting on the tyre longitudinally to the surface R and a second resultant Fz of forces acting on the tyre perpendicular to the surface R.

[0119] Exemplarily, the method therefore comprises in turn estimating the first resultant Fx and the second resultant Fz.

[0120] To this end, the routine CE exemplarily comprises the sub-routine LF ("longitudinal force") for the estimation of the first resultant Fx. Exemplarily the sub-routine LF envisages the estimation of the first resultant Fx as a function of a mass M of the vehicle and of a longitudinal acceleration Ax of the vehicle.

[0121] In an embodiment (not shown), the first resultant Fx can be estimated as a function of the torque Tr applied to the respective wheel W1 and / or as a function of a braking pressure (in the case of braking torque Tr) actuated by the braking system on the respective wheel W1 .

[0122] For the estimation of the second resultant Fz, the sub-routine VL ("Vertical Load") is exemplarily envisaged, which exemplarily envisages the use of a mathematical distribution model of the mass (also called load transfer) of the vehicle on the respective wheels. The model may for example comprise a dependence of the second resultant Fz on the total mass of the vehicle, on the distance between the centre of gravity of the vehicle and the axles of the vehicle, on the longitudinal acceleration (to also take into account effects of redistribution of the mass with respect to the axles as a consequence of the respective torque Tr applied to the wheels W). In a further embodiment (not shown) the second resultant Fz can be estimated by means of the monitoring device 4 if the tyre 3 is equipped therewith.

[0123] The method therefore comprises estimating the operational value Aop of the first parameter (sub-routine R3) as a function of the respective current value Ac of the first parameter and of the respective current value Uc of the second parameter.

[0124] The estimation of the operational value Aop can for example be performed with known algorithms as a function of the respective current values of the first and second parameter, as for example described in WO2014199328A1 in the name of the same Applicant.

[0125] Exemplarily, the estimation of the operational value Aop of the first parameter is performed using a model of the tyre T1 mounted on the respective wheel comprising a physical relationship between the first parameter A and the second parameter U, for example using a map of the longitudinal features of the tyre, in particular a slip-friction map containing multiple characteristic curves of the tyre, such as that shown, for purely illustrative purposes, in Figure 5. Such multiple curves can respectively correspond to different operating conditions of the tyre (e.g. temperature, pressure) and / or the tyre model (e.g. summer, winter, all season).

[0126] With reference to the aforesaid Figure 5, the points indicated with "X" each represent respective values of a given current torque (Ac, Uc) of the first and the second estimated parameter. In more detail, the method exemplarily comprises estimating a plurality of respective current values of the first parameter and a further plurality of respective current values of the second parameter sufficient for performing the estimate of the operational value Aop. As can be seen in the figure, as the slip increases, when such estimated current values are arranged in a zone of the map where the curves begin to broaden and / or distance themselves (see the circled part in Figure 5), it is possible to approximate / estimate the operational value Aop, without further increasing the slip. Such an estimation can be carried out, for example, by reading the abscissa of the absolute maximum point of the characteristic curve which best approximates the respective current values of the first and second estimated parameter. It is thereby possible to estimate the operational value Aop while remaining far from high slip values and, in general, from the operational value itself.

[0127] Merely by way of example, in the case of Figure 5, the curve closest to the graphed estimated values is (fictitiously) the fourth curve evaluated from the bottom. Such a curve, indicatively referred to as C1 , is also shown in Figure 6 to allow a visual comparison with the aforesaid predetermined curve CO, in order to describe the adjustment of the anti-skid control system 100. The point named "0" on the curve C1 in Figure 6 corresponds to the maximum point of the curve C1 whose abscissa represents the operational value Aop of the first parameter for which the maximum friction lie between tyre and surface is obtained. Exemplarily, the maximum friction lie obtainable corresponds to the maximum friction coefficient lie (since the axis of the ordinate is exemplarily expressed in units of measurement of the second parameter U).

[0128] Adjustment of the anti-skid control system

[0129] Once the operational value Aop is estimated, the method exemplarily comprises adjusting the anti-skid control system 100 by updating the predetermined target value Atg of the first parameter with a new target value AtgN of the first parameter estimated as a function of the aforesaid operational value Aop of the first parameter (sub-routine R4 of Figure 4).

[0130] Referring again to Figure 6, it is observed that in the hypothetical case exemplarily described, the maximum (coefficient of) friction lie actually available in the pneumatic surface interaction situation represented by the curve C1 is less than the maximum (coefficient of) friction expected (i.e. the ordinate of the maximum of the predetermined curve CO). That is, in the absence of adjustment, the anti-skid control system 100, configured based on the predetermined curve CO, would overestimate the actual maximum (coefficient of) friction available between the tyre and the surface, with potential negative repercussions for safety.

[0131] The method instead exemplarily comprises updating the predetermined target value of the first parameter with a new target value AtgN of the first parameter.

[0132] Exemplarily, such a new target value AtgN of the first parameter corresponds to the operational value Aop, i.e. it corresponds to the abscissa of the maximum point from the curve C1 . That is, estimating the operational value Aop implies exemplarily knowing the curve C1 and therefore being able to obtain the abscissa of the respective maximum point. In fact, it is at this maximum of the curve C1 that the first parameter assumes the value precisely for which the friction between tyre and surface is maximum.

[0133] In an embodiment (not shown), for example in a conservative adjustment perspective, the new target value AtgN of the first parameter can be a fraction of the operational value Aop of the first parameter (e.g. 90% of the operational value Aop).

[0134] The anti-skid control system 100, once adjusted, therefore operates (in the event of activation) to bring the current value of the first parameter of one or more of the tyres around the new target value AtgN of the first parameter (and not the predetermined target value Atg), maximising the friction between tyres and surface in the actual tyresurface interaction situation (exemplarily approximated by the curve C1 ).

[0135] Exemplarily, adjusting the anti-skid control system 100 further comprises also updating the predetermined target value Ats of the first parameter with a new threshold value AtsN of the first parameter, also estimated as a function of the operational value Aop of the first parameter.

[0136] For example, the new threshold value AtsN of the first parameter can be calculated as 150% of the operational value Aop, or as 200% of the operational value Aop.

[0137] From the comparison between the curves C1 and CO, the advantage of also updating the predetermined threshold value Ats of the first parameter with the new, significantly lower, threshold value AtsN is once again evident. In fact, with the new threshold value AtsN, the anti-skid control system intervenes earlier with respect to the predetermined configuration.

[0138] Exemplarily, adjusting the anti-skid control system is performed on the condition that the respective torque is still applied (at least to the respective wheel). That is, the adjustment is performed as long as there is still torque applied to the wheels in response to the given variation request, so that the adjustment can effectively be applied on the contingent speed variation request.

[0139] Exemplarily, the method further comprises adjusting the anti-skid control system 100 again by updating the new target value AtgN of the first parameter with the predetermined target value Atg of the first parameter once the application over time of the respective torque Tr has ended. Exemplarily, the same also applies for the new threshold value AtsN of the first parameter. That is, when it is detected that there the respective torque is no longer applied to the wheels, i.e. the request for speed variation by the driver has ended, it is exemplarily envisaged to reset the anti-skid control system again to the predetermined target Atg and threshold values Ats (curve CO), i.e. the respective initial values.

[0140] Exemplarily, it is envisaged to repeat the adjustment method for each speed variation request received from the driver, both during acceleration and braking, adjusting for example a traction control system and an ABS system of the vehicle, respectively.

Claims

CLAIMS1. Method for adjusting an anti-skid control system (100) of a vehicle (1 ) moving on a surface (R), said anti-skid control system (100) being configured to operate as a function of at least a predetermined target value (Atg) of a first parameter (A) representative of a slip of a tyre mounted on a wheel of said vehicle with respect to said surface, said method comprising:- in response to a request (RS) of speed variation of said vehicle (1 ), applying over time a respective torque (Tr) to one or more wheels (W) of said vehicle (1 );- for a tyre (T1 ) mounted on a respective wheel (W1 ) of said one or more wheels (W) having a respective current value (Ac) of said first parameter less than or equal to said predetermined target value (Atg) of said first parameter, performing a routine of estimation of an operational value (Aop) of said first parameter for which a maximum friction (lie) is obtained between said tyre (T 1 ) mounted on said respective wheel (W1 ) and said surface (R) when said respective torque (Tr) is applied, said routine of estimation comprising the steps of:(i) estimating a respective current value (Uc) of a second parameter (U) representative of a friction between said tyre (T 1 ) mounted on said respective wheel (W1 ) and said surface (R);(ii) estimating said operational value (Aop) of said first parameter as a function of said respective current value (Ac) of said first parameter and of said respective current value (Uc) of said second parameter;- on condition that said respective torque (Tr) is still applied, adjusting said anti-skid control system (100) by updating said predetermined target value (Atg) of said first parameter with a new target value (Atg N) of said first parameter estimated as a function of said operational value (Aop) of said first parameter.

2. Method according to claim 1 , comprising readjusting said anti-skid control system (100) by updating said new target value (AtgN) of said first parameter with said predetermined target value (Atg) of said first parameter once said applying over time said respective torque (Tr) has ended.

3. Method according to any one of the previous claims, comprising estimating in continuous, for each wheel of said one or more wheels (W), a respective value (Tr1) of a reference parameter representative of a variation over time of said torque (Tr) applied to said wheel (W) in response to said request (RS) of speed variation, comparing in continuous each respective value (Tr1) of said reference parameter with a predeterminedlimit value (Tr'lim) of the reference parameter, and performing said routine of estimation of said operational value (Aop) of said first parameter on condition that said respective value (Tr1) of said reference parameter of said respective wheel (W1 ) of said one or more wheels (W) is less than said predetermined limit value (Tr'lim) of the reference parameter.

4. Method according to any one of the previous claims, wherein said anti-skid control system (100) is configured to operate also as a function of a predetermined threshold value (Ats) of said first parameter, said predetermined threshold value (Ats) of the first parameter being greater than said predetermined target value (Atg) of the first parameter, and wherein adjusting said anti-skid control system (100) further comprises updating said predetermined threshold value (Ats) of said first parameter with a new threshold value (AtsN) of said first parameter estimated as a function of said operational value (Aop) of said first parameter.

5. Method according to claim 4, wherein readjusting said anti-skid control system (100) further comprises updating said new threshold value (AtsN) of said first parameter with said predetermined threshold value (Ats) of said first parameter once said applying over time said respective torque (Tr) has ended.

6. Method according to any one of the previous claims, wherein applying over time said respective torque (Tr) is performed on each wheel (W) of said vehicle, and wherein each torque applied to said wheels (W) is a braking torque.

7. Method according to any one of the previous claims, wherein said first parameter (A) coincides with a longitudinal slip of said tyre with respect to said surface (R), and wherein said respective current value (Ac) of said first parameter is estimated as a function of a tangential speed (Vx1 ) of said respective wheel (W1 ) and of a value of a quantity representative of a theoretical tangential speed (Vxt) of said respective wheel (W1 ) of said vehicle (1 ) in a free rolling condition.

8. Method according to any one of the previous claims, wherein said second parameter (U) coincides with a friction coefficient between said tyre and said surface (R), and wherein said respective current value (Uc) of said second parameter is estimated as a function of a ratio between a first resultant (Fx) of forces acting on said tyre (T 1 ) mounted on said respective wheel (W1 ) substantially parallelly to said surface (R) and a second resultant (Fz) of ferees acting on said tyre (T1 ) mounted on said respective wheel (W1 ) substantially perpendicularly to said surface (R).

9. Method according to any one of the previous claims, wherein estimating said operational value (Aop) of said first parameter is performed as a function of apredetermined model of said tyre (T1 ) mounted on said respective wheel (W1 ) comprising a physical relationship between said first parameter (A) and said second parameter (U).

10. Method according to any one of the previous claims, wherein said new target value (AtgN) of the first parameter coincides with said operational value (Aop) of the first parameter.11 . System for adjusting (99) an anti-skid control system (100) of a vehicle (1 ) moving on a surface (R), said anti-skid control system (100) being configured to operate as a function of at least a predetermined target value (Atg) of a first parameter (A) representative of a slip of a tyre mounted on a wheel of said vehicle with respect to said surface, said system for adjusting (99) comprising:- an actuation device (9) operatively connected to wheels (W) of said vehicle (1 );- a processing unit (8) operatively connected to said actuation device (9) and in dialogue with said anti-skid control system (100) of said vehicle (1 ), wherein said processing unit (8) is programmed for:- in response to a request signal of speed variation of said vehicle, controlling said actuation device (9) for applying over time a respective torque (Tr) to one or more wheels (W) of said vehicle;- for a tyre (T 1 ) mounted on a respective wheel (W1 ) of said one or more wheels having a respective current value (Ac) of said first parameter less than or equal to said predetermined target value (Atg) of said first parameter, performing a routine of estimation of an operational value (Aop) of said first parameter for which a maximum friction (lie) is obtained between said tyre (T 1 ) mounted on said respective wheel (W1 ) and said surface (R) when said respective torque (Tr) is applied, said routine of estimation comprising the steps of:(i) estimating a respective current value (Uc) of a second parameter (U) representative of a friction between said tyre (T1 ) mounted on said respective wheel (W1 ) and said surface (R);(ii) estimating said operational value (Aop) of said first parameter as a function of said respective current value (Ac) of said first parameter and of said respective current value (Uc) of said second parameter;- on condition that said respective torque (Tr) is still applied, adjusting said anti-skid control system (100) by updating said predetermined target value (Atg) of said first parameter with a new target value (AtgN) of said first parameter estimated as a function of said operational value (Aop) of said first parameter.

12. System (99) according to claim 11 , wherein said processing unit (8) is programmed for performing method for adjusting according to one or more of claims from 2 to 10.

13. System (99) according to claim 11 or 12, comprising a respective monitoring device(4) for each tyre (T) mounted on each wheel (W) of said vehicle, each monitoring device (4) being fixed at a crown portion (6) of the respective tyre, wherein said processing unit(8) is in communication with each monitoring device (4), and wherein each monitoring device (4) is suitable for detecting at least a tangential speed of the respective tyre (T).

14. Vehicle (1 ) equipped with tyres (T) mounted on wheels (W) and comprising an antiskid control system (100), wherein said vehicle comprises the system for adjusting (99) according to any one of claims from 11 to 13.

15. Vehicle (1 ) according to claim 14, wherein said vehicle (1 ) is a self-driving vehicle.

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