Method and system for controlling a vehicle in the presence of hydroplaning

Abstract

A control method and system (99) for a vehicle (1) moving on a road surface, wherein the system comprises: a detection module (2) for detecting in real time the corresponding hydroplaning intensity (HI) of each tire (3) of the vehicle (1); an actuating device (9) connected to each wheel (7) of the vehicle (1); and a command and control unit (8) programmed and configured to execute a control method, the control method comprising: - comparing each corresponding hydroplaning intensity (HI) with a first threshold value; - when a start condition occurs so that the corresponding hydroplaning intensity (HI) of at least one tire (3) reaches the first threshold value, then: - calculating in real time a reference value (YRr) of a parameter representing the lateral movement of the vehicle (1) based on the longitudinal speed (Vxc) and the steering angle (STA) of the vehicle; - calculating in real time a correction torque (Mz) based on the reference value (YRr) and the current value (YRc) of the parameter detected in real time; - applying in real time a corresponding torque (Tr) to each wheel (7), the corresponding torque being calculated in real time based on the correction torque (Mz) and the hydroplaning intensity (HI) of the corresponding tire (3).

Description

Technical Field

[0001] The present invention relates to a method and system for controlling a vehicle moving on a road surface in the presence of hydroplaning. The present invention also relates to a vehicle comprising the control system. Background Art

[0002] The tire typically has a generally toroidal structure about its axis of rotation during operation and presents an equatorial plane orthogonal to the axis of rotation, which is typically a (substantially) geometrically symmetrical plane (e.g. ignoring any minor asymmetries such as tread pattern and / or text on the side and / or internal structure).

[0003] “Crown portion” means the portion of the tire situated at the tread band.

[0004] The terms "radial" and "axial" are used with reference to a direction perpendicular to the tire's axis of rotation and a direction parallel to the tire's axis of rotation, respectively.

[0005] The term "tangential" is used with reference to a direction of rotation generally according to the rolling direction of the tire, which is perpendicular to both the radial and axial directions.

[0006] "Footprint" means that portion of the outer surface of the tread band which, during rolling of a mounted tyre subjected to a load (e.g. due to being mounted under a vehicle), is always in contact with a rolling surface. The footprint generally has a substantially zero curvature (or a substantially infinite radius of curvature), or in any case it substantially assumes the form of a rolling surface. "Footprint portion" means that portion of the crown portion which corresponds to the footprint.

[0007] The term "longitudinal" is used to refer to a direction that is tangential to the trajectory of the vehicle at any given moment (preferably having a direction that coincides with the forward direction of travel of the vehicle).

[0008] The term "transverse" (or equivalently "lateral") is used to refer to a direction substantially orthogonal to the longitudinal direction and substantially parallel to the road surface.

[0009] In the present context, hydroplaning is understood to mean a condition in which a tire rolling on a road surface has a reduced or even completely lost grip on the road surface due to the presence of a layer of water between the tire and the road.

[0010] Aquaplaning generally occurs when water cannot be adequately drained and driven from the channels and / or grooves of the tread in the footprint area, causing water to accumulate between the tire and the road surface, thereby being able to lift the tire off the road surface (more or less) in the footprint area.

[0011] This lifting leads in particular to a reduction in the footprint area and thus to the aforementioned reduction in the grip of the tire on the road surface, with the result that this part of the tire itself suffers from a loss of directionality and traction.

[0012] In the following, "hydroplaning intensity" or "hydroplaning condition intensity" will generally refer to an estimate of the residual grip of the tire on the road surface. This estimate may range from a level corresponding to a substantially maximum grip condition in the case of the tire rolling on a substantially dry surface or on a surface with a thin layer of water (which does not substantially change the footprint of the tire itself on the ground) to one or more levels corresponding to one or more conditions of partial hydroplaning (i.e., partial loss of tire grip due to the presence of a layer of water (but there is still a partial residual footprint area between the tire and the road surface)) and one or more levels corresponding to a complete hydroplaning condition (i.e., complete or substantially complete loss of tire grip with the road surface (i.e., the footprint area of ​​the tire on the ground completely or substantially completely disappears).

[0013] The phenomenon of hydroplaning can be extremely dangerous because, in this condition, the driver may substantially lose control of the vehicle and no longer be able to follow the road, avoid obstacles, etc.

[0014] Document US2018 / 0178769 A1 describes a method and a device for assisting driving in hydroplaning situations.

[0015] Document EP 2 832 617 A1 describes a control device for a vehicle that adjusts the rotational phase of each wheel based on a correlation between the rotational phase of the wheel and the hydroplaning characteristics when the vehicle is in a hydroplaning state. Summary of the invention

[0016] In the context of methods for controlling a vehicle, the Applicant has found that there is currently no system on the market that is able to activate control of a vehicle in a hydroplaning situation. The Applicant has also found that the methods and devices proposed in the above documents present several problems.

[0017] For example, the method for triggering a driver assistance routine of US2018 / 0178769 A1 is based on the detection of a possible hydroplaning state of the vehicle based on signals from the front wheel speed sensors (e.g., ABS encoders): If these sensors indicate severe slip (positive or negative, depending on the type of traction of the vehicle), i.e., if the slip of at least one of the front wheels exceeds a given range, a hydroplaning state is identified. In this case, the activation of the driver assistance routine is activated by acting on the rear wheels (braking), assuming that the rear wheels are not in a hydroplaning state.

[0018] The Applicant has found that the method of US2018 / 0178769 A1 described above works only in a state where at least one front wheel is fully hydroplaning by intervening when the front tires have fully lifted and are sliding relative to the road surface (and have therefore substantially lost grip).

[0019] However, the Applicant has observed that, under real driving conditions, the tyre may also experience a partial hydroplaning state, i.e. a state in which, due to the layer of water, the tyre is partially lifted, resulting in a reduction in the footprint area and reduced grip, while still at least partially maintaining grip on the road surface (i.e. having a sufficiently low slip value).

[0020] Therefore, in a persistent partial hydroplaning condition, the method of US 2018 / 0178769 A1 will never intervene.

[0021] Similarly, activating the assist routine only when a full hydroplaning condition occurs may mean that, under certain conditions, the routine is activated only at the end of a transient period of time when the tire is in a partial hydroplaning condition.

[0022] Therefore, both of the above scenarios may result in a potentially dangerous situation for the driver and passengers because the driver's control of the vehicle may have been affected and / or limited, particularly in the event of a sudden maneuver (e.g., a sudden change of direction) long before the assistance routine of US2018 / 0178769 A1 is activated and the routine is unable to compensate for this.

[0023] The Applicant has also observed that determining a hydroplaning condition based on the slip of the front wheels may run the risk of being indistinguishable from other conditions where the vehicle is travelling on a slippery surface (e.g. ice) where the tires of all wheels are slipping abnormally or in any case at least one of the rear wheels is also slipping abnormally. In such a case, activating a driving assistance routine such as that described in US 2018 / 0178769A1 may entail a risk, since the rear wheels may lock, leading to a loss of control of the vehicle.

[0024] Furthermore, the applicant points out that the assistance routine of US2018 / 0178769 A1 runs the risk of overestimating the maximum grip that can be generated by the rear wheels.

[0025] With regard to EP 2 832 617 A1, the Applicant considers that the routine described therein, besides being extremely complex to carry out in practice, may also run the risk of overestimating the real grip of the tyres.

[0026] The Applicant has therefore solved the problem of achieving control of a vehicle moving in a hydroplaning state that is practical, robust in the face of various situations in which hydroplaning occurs, and capable of achieving a high degree of driving safety.

[0027] According to the applicant, the above-mentioned problem is solved by a control method and system for a vehicle, which is activated in case the movement of the vehicle does not comply with safety conditions (for example, the attitude of the vehicle does not comply with the driver's intention and / or the speed / acceleration of the vehicle is too high), wherein the intensity of the hydroplaning state of each tire is determined in real time, and if the hydroplaning intensity of at least one tire is greater than or equal to a given threshold, a torque (for example, a braking torque and / or a driving torque) is applied to the vehicle wheels, wherein the torque is calculated based on the correction moment and / or the correction longitudinal force of the attitude and the corresponding hydroplaning intensity.

[0028] According to one aspect, the invention relates to a method for controlling a vehicle moving on a road surface.

[0029] The method includes:

[0030] - for each tire of the vehicle rolling on the road surface, determining in real time the corresponding hydroplaning intensity;

[0031] - comparing each corresponding hydroplaning intensity with a first threshold in real time;

[0032] - when the activation condition occurs so that the corresponding hydroplaning intensity of at least one tire reaches the first threshold, one or more of the following operations are performed:

[0033] Preferably, provision is made for the current value of the longitudinal speed of the vehicle to be acquired in real time.

[0034] Preferably, provision is made for the steering angle of the vehicle to be acquired in real time.

[0035] Preferably, provision is made that a reference value for a parameter representative of the lateral movement of the vehicle is calculated in real time as a function of the current value of the longitudinal speed and the steering angle.

[0036] Preferably, it is provided that the current value of the parameter is detected in real time;

[0037] Preferably, it is provided that the correction torque is calculated in real time according to the reference value and the current value of the parameter;

[0038] Preferably, provision is made that a corresponding torque calculated in real time according to the correction moment and the hydroplaning intensity of the corresponding tire is applied to each wheel of the vehicle in real time.

[0039] Preferably, provision is made for the reference value of the parameter representative of the longitudinal movement of the vehicle to be calculated in real time.

[0040] Preferably, provision is made for the current value of the parameter representing the longitudinal movement to be acquired in real time.

[0041] Preferably, provision is made that the corrective longitudinal force is calculated in real time as a function of the reference value and the current value of the parameter representative of the longitudinal movement.

[0042] Preferably, provision is made that a corresponding torque calculated from the corrected longitudinal force and the hydroplaning intensity of the corresponding tire is applied in real time to each wheel of the vehicle.

[0043] According to another aspect, the present invention is directed to a control system for a vehicle moving on a road.

[0044] The system includes:

[0045] - a detection module, for detecting in real time the corresponding hydroplaning intensity of each tire of the vehicle rolling on the road surface;

[0046] - an actuating device operatively connected to each wheel of the vehicle;

[0047] - A command and control unit operatively connected to said detection module and to said actuation means.

[0048] Preferably, the command and control unit is programmed and configured to:

[0049] - comparing each respective hydroplaning intensity with a first threshold value;

[0050] When the activation condition occurs such that the corresponding hydroplaning intensity of at least one tire reaches the first threshold, one or more of the following operations are performed:

[0051] - receiving as input in real time a first signal representing a current value of the longitudinal speed of the vehicle;

[0052] - receiving a second signal as input in real time, the second signal representing a steering angle of the vehicle;

[0053] - calculating in real time a reference value of a parameter representative of the lateral movement of the vehicle based on the first signal and the second signal;

[0054] - receiving a third signal as input in real time, said third signal representing the current value of said parameter;

[0055] - calculating the correction torque in real time according to the reference value and the current value of the parameter;

[0056] - commanding the actuating device to apply a corresponding torque to each wheel in real time, the corresponding torque being calculated based on the correction moment and the hydroplaning intensity of the corresponding tire.

[0057] Preferably, the command and control unit is programmed and configured to:

[0058] - comparing each respective hydroplaning intensity with a first threshold value;

[0059] When the activation condition occurs such that the corresponding hydroplaning intensity of at least one tire reaches the first threshold, one or more of the following operations are performed:

[0060] - setting a reference value of a parameter representative of the longitudinal movement of said vehicle;

[0061] - receiving as input in real time a (fourth) signal, said signal representing the current value of said parameter of longitudinal movement;

[0062] - calculating in real time a corrective longitudinal force from said reference value and said current value of said parameter representative of the longitudinal movement;

[0063] - commanding the actuating device to apply to each of the wheels in real time a corresponding torque calculated according to the corrected longitudinal force and the hydroplaning intensity of the corresponding tire.

[0064] According to a further aspect, the invention relates to a vehicle comprising a control system according to the invention.

[0065] The expression "steering angle" refers to a value representing the angle formed between the direction presented by the vehicle's steered wheels (usually the front wheels) and the longitudinal extension direction of the vehicle, such as the rotation angle (clockwise and / or counterclockwise) of the vehicle's steered wheels relative to the neutral position of the steered wheels (i.e., the position in which the vehicle is moving straight forward), or a parameter set by the vehicle's electronic equipment in an autonomous driving system, or the angle itself formed between the direction presented by the vehicle's steered wheels (usually the front wheels) and the longitudinal extension direction of the vehicle.

[0066] According to the Applicant, the determination of the hydroplaning intensity of each tire allows the rolling state of all tires to be monitored continuously and in real time.

[0067] In this way, not only a possible hydroplaning condition can be detected quickly, but also the respective strength of each tire, thus enabling a wide range of real driving situations to be identified.

[0068] The fact that the method then carries out a correction routine under the condition that the hydroplaning intensity of at least one tire reaches a first threshold value gives the correction a higher activation sensitivity and is therefore also able to operate for partial hydroplaning conditions, which can also occur for a single tire out of four typical rolling tires.

[0069] Finally, the torque applied to each wheel is not only a function of the calculated corrective moment and / or the calculated corrective longitudinal force, but also a function of the hydroplaning strength of the tire itself, which allows to adjust the control actions, whatever their purpose, taking into account the real situation of tire grip and thus limiting the risk of wheel locking.

[0070] In particular, the application of each respective torque (ie, the implementation of a specific control action) may be directed to:

[0071] - changing the trajectory of the vehicle according to the driver's intention, in which case each corresponding torque is calculated according to the correction torque (which in turn is calculated according to the steering angle); or

[0072] - decelerating the vehicle, each corresponding torque being calculated as a function of a corrective longitudinal force calculated as a function of a reference value and a current value of a parameter representative of the longitudinal movement; or

[0073] - Both changing the trajectory of the vehicle according to the driver's intention and decelerating the vehicle, since each respective torque can be calculated from both the correction moment and the correction longitudinal force.

[0074] The present invention may have one or more of the following preferred features.

[0075] Preferably, the command and control unit is programmed and configured to perform one or more of the following operations preferably provided for the method.

[0076] Preferably, the method comprises: for each tire, detecting in real time (at least) a corresponding quantity representative of the movement of the tire, more preferably of the crown portion of the tire. Preferably, the (at least one) corresponding quantity comprises (at least) one of the following quantities related to (the crown portion of) a single tire: displacement, velocity, acceleration (e.g. radial and / or axial and / or tangential acceleration), and deformation.

[0077] Preferably, the real-time determination of the respective hydroplaning intensity is performed based on the respective quantity (e.g. by processing a respective signal of the variation of the respective quantity over time and / or the rotation angle of the tire). In this way, the hydroplaning intensity is robustly determined based on information related to the interaction of a single tire with the rolling surface.

[0078] Preferably, the corresponding quantity is detected at the inner surface of the tire at the crown portion. In this way, the quantity directly represents the movement of the crown portion of the tire (ie the portion in contact with the rolling surface).

[0079] Preferably, said detection module comprises a respective monitoring device associated with each tyre, each monitoring device being fixed at said crown portion of the respective tyre, more preferably fixed on the inner surface at said crown portion. Preferably, said monitoring device is suitable for detecting said at least one respective quantity relating to the respective tyre.

[0080] Preferably, the actuating device comprises a braking system and / or a motor (eg an electric motor). In this way, a braking torque and / or a driving torque can be applied to the wheels.

[0081] Preferably, said parameter representative of lateral motion comprises or consists of (at least) one of the following quantities: yaw rate, lateral acceleration, slip angle (also called drift angle). For the purposes of the present invention, the Applicant has considered these quantities to be particularly effective in representing aspects of lateral motion of a vehicle.

[0082] In particular, the applicant considers that yaw rate is a very efficient and simple quantity to handle in real-time processing.

[0083] Preferably, calculating the correction torque in real time comprises: performing in real time a difference between the reference value and the current value of the parameter representing the lateral motion of the vehicle; and calculating the correction torque based on the difference. In this way, the correction torque represents a torque to be applied to the vehicle (e.g., by braking and / or accelerating at least one wheel) to ensure that the current value of the parameter representing the lateral motion of the vehicle is equal to a (target) reference value, the reference value being calculated based on the current value of the longitudinal speed and the steering angle.

[0084] Preferably, the (maximum value of) the corresponding torque decreases as the hydroplaning intensity of the corresponding tire increases (and vice versa). In this way, the corrective action can be distributed to the wheel in real time according to the current grip of the corresponding tire.

[0085] Preferably, under the condition that the corresponding hydroplaning intensity of the corresponding tire is greater than or equal to a second threshold value (preferably greater than the first threshold value), the corresponding torque is zero. In other words, when the hydroplaning intensity reaches / exceeds the second threshold value, the maximum value of the corresponding torque is zero. In this way, the risk of locking at the corresponding wheel is eliminated, thereby improving safety.

[0086] Preferably, said parameter representing the longitudinal motion comprises or consists of (at least) one of the following quantities: longitudinal acceleration, longitudinal velocity. For the purposes of the present invention, the applicant has determined that these quantities are particularly effective in representing the longitudinal motion of the vehicle. For example, it may be advantageous to use the longitudinal acceleration in order to safely decelerate the vehicle, thereby avoiding sudden movements that could result in a loss of control of the vehicle.

[0087] Preferably, said corrective longitudinal force is calculated as a function of the difference between said current value and said reference value of said parameter representative of longitudinal movement.

[0088] Preferably, the corresponding torque is calculated based on the longitudinal correction force and based on the correction moment. In this way, the above two correction actions are combined to improve safety.

[0089] Preferably, the method comprises (typically when the parameter representative of longitudinal motion does not include or consist of the longitudinal speed) setting a reference value for the longitudinal speed of the vehicle. The reference value for the longitudinal speed represents a desired safe speed at which the vehicle is to be driven.

[0090] Preferably, the method comprises (typically when the parameter representative of the longitudinal movement does not include or consist of the longitudinal velocity), acquiring in real time a current value of the longitudinal velocity of the vehicle when the activation condition occurs. Preferably, the method comprises comparing in real time the current value of the longitudinal velocity with the reference value of the longitudinal velocity. Preferably, the method comprises cancelling the corrective longitudinal force on the condition that the current value of the longitudinal velocity reaches the reference value of the longitudinal velocity. In this way, the vehicle is decelerated only when necessary.

[0091] Preferably, each respective torque applied to a wheel is also calculated as a function of the respective hydroplaning intensities of the tires associated with the other wheels of the vehicle, more preferably by distributing the respective torques so as to minimize one or more (more preferably all) of the respective torques (relative to respective maximum values). Preferably, provision is made to maximize a parameter representing as a whole the difference between each respective torque (in modulus) and the respective maximum value (in modulus) calculated in real time as a function of the respective hydroplaning intensities of the respective tires. In other words, among the possible sets of torques capable of correcting the lateral and / or longitudinal motion of the vehicle as a function of the calculated correction moment and / or correction longitudinal force, preferably those sets of torques are selected which include torque values ​​as far away as possible from the respective maximum applicable value. In this way, the torque applied to each wheel is kept away from the respective maximum value, thereby further reducing the risk of wheel locking and improving safety. In fact, as described above, the maximum torque value applicable to each wheel varies with the detected hydroplaning intensity, which may decrease sharply in the event of a sudden change in the asphalt conditions, leading to a transient dangerous situation in which the current value of the torque may be very close to the respective maximum value, or even greater than the respective maximum value, and the risk of complete wheel locking (and therefore loss of control) is high.

[0092] Preferably, when the activation condition occurs, the method comprises interrupting the transmission of driving force from a motor of the vehicle to drive wheels of the vehicle in order to reduce the speed of the vehicle and further increase safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] Figure 1 A vehicle according to the invention is schematically shown;

[0094] Figure 2 Schematically shows Figure 1 Details of the vehicle;

[0095] Figure 3 A logic block diagram showing the steps of an embodiment of a control method according to the present invention.

[0096] Figure 4 , 5 and 6 show in detail Figure 3 The corresponding logic blocks of the logic block diagram;

[0097] Figure 7a , 7b , 7c, 8a, 8b, 8c, 9a, 9b, 9c and 10 show some results of simulations according to the method of the present invention. DETAILED DESCRIPTION

[0098] Characteristics and advantages of the invention will further become clear from the following detailed description of some embodiments given by way of non-limiting example of the invention, with reference to the accompanying drawings.

[0099] Figure 1 A vehicle 1 according to the invention is schematically shown. The vehicle 1 may be a vehicle with an endothermic motor and / or an electric motor, with two or more driven wheels.

[0100] Exemplarily, the vehicle 1 comprises four wheels 7, each of which is provided with a corresponding tire 3 (also shown) for rolling on a road surface (not shown). Figure 2 The wheels 7 are exemplarily identified as a right front wheel FR, a left front wheel FL, a right rear wheel RR, and a left rear wheel RL.

[0101] The vehicle 1 includes a control system 99 for the vehicle moving on a road.

[0102] The system 99 comprises a detection module 2 for detecting in real time the corresponding hydroplaning intensity of each tire 3 of the vehicle 1 rolling on the road surface.

[0103] Exemplarily, the detection module 2 comprises a monitoring device 4 ( Figure 1 and Figure 2). For example, the monitoring device 4 may be of the type described in one of the following documents under the name of the same applicant: WO 2018 / 065846 A1, WO 2019 / 123118 A1, WO 2020 / 026281 A1, WO 2020 / 026282 A1. Preferably, the monitoring device 4 may include at least one accelerometer capable of detecting the acceleration of the tire in the radial direction, and / or the axial direction, and / or the tangential direction.

[0104] Exemplarily, each monitoring device 4 is fixed to the inner surface 5 of the tire at the crown portion 6 of the corresponding tire 3 ( Figure 2 ). In particular, the monitoring device 4 may be fixed to the lining of the tire 3, typically by gluing (e.g. by a structural adhesive or by a pressure-sensitive adhesive). Preferably, the monitoring device 4 may be fixed substantially at the equatorial plane 100 of the tire 3. Additional monitoring devices (not shown) may be arranged at more lateral positions on the inner surface of the tire 3 and / or may be arranged at different angular positions along the inner circumference of the tire 3.

[0105] The system 99 also comprises an actuating device 9 operatively connected to each wheel 7 of the vehicle 1 (only in Figure 1 Schematically shown in FIG.

[0106] By way of example, the actuating device 9 comprises a brake system of the vehicle 1 .

[0107] In an embodiment not shown, the actuating 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 driven wheels).

[0108] The control system 99 also comprises a command and control unit 8 operatively connected to the detection module 2 and the actuation device 9 (only in Figure 1 Schematically shown in FIG.

[0109] Exemplarily, the command and control unit 8 is operatively connected to the four monitoring devices 4 of the detection module 2 by radio signals.

[0110] In use, the control system 99 allows the method for controlling a vehicle moving on a road surface according to the invention to be carried out, typically with the aid of one or more hardware devices programmed by one or more software modules resident and / or loaded in appropriate memories.

[0111] Now refer to Figure 3-6 An embodiment of the control method according to the present invention is described.

[0112] Exemplarily, the command and control unit 8 is programmed and configured to execute the control method provided and in Figure 3 The following operations are symbolically shown in four sequential routines (where SL and SA are executed in parallel, as described below). The routines are exemplified as follows:

[0113] - signal processing routine SP (signal processing);

[0114] - The vehicle's speed limit routine SL (Speed ​​Limit);

[0115] - Routine SA (Stability Adjustment) for adjusting the stability of the vehicle;

[0116] - Calculation routine TC (Torque Calculation) of the corresponding torque to be applied to the wheels of the vehicle.

[0117] Routine SP

[0118] Firstly, the method comprises: for each tire 3 of the vehicle 1 rolling on the road surface, determining in real time a corresponding hydroplaning intensity HI.

[0119] Exemplarily, the method comprises, for each tyre 3 , detecting in real time a respective quantity Q representative of the movement of the crown portion 6 of the tyre 3 .

[0120] By way of example, a respective quantity Q is detected by a respective monitoring device 4 at an inner surface 5 of the tyre 3 at a crown portion 6 .

[0121] Exemplarily, the real-time determination of the corresponding hydroplaning intensity HI is performed based on the detected corresponding quantity Q.

[0122] Exemplarily, the corresponding quantity Q is the radial acceleration to which the crown portion 6 is subjected during the rolling of the tire 3 on the road surface. In more detail, the control method exemplarily comprises: starting from the detection of an acceleration signal (e.g. representative of the aforementioned radial acceleration), determining the hydroplaning intensity HI for each tire 3. More particularly, the hydroplaning intensity can be determined by analyzing the derivative of the radial acceleration signal, in particular its relative maximum value, as described, for example, in WO 2019 / 123501A1 in the name of the same applicant.

[0123] In another example, the hydroplaning intensity can be determined by frequency analysis of the portion of the acceleration signal corresponding to the tread and / or an area adjacent to the tread area (or more generally, a signal related to the deformation experienced by the tire), as described in WO 2010 / 046871 A1, also in the name of the same applicant.

[0124] Preferably, the hydroplaning intensity HI of each tire (which may be determined as a continuous value) may be discretized into discrete levels, called "hydroplaning levels". For example, it is conceivable that the number of hydroplaning levels is greater than or equal to three and less than or equal to ten, for example equal to eight (i.e. 0-7). In the latter case, the hydroplaning intensity HI of each tire 3 determined as described above may present values ​​between zero (absence of hydroplaning) and seven (full hydroplaning). Intermediate levels represent different partial hydroplaning states, wherein gradually increasing levels correspond to a reduction in the level of grip between the tire and the road surface.

[0125] The method then exemplarily comprises, for the command and control unit 8, comparing each respective hydroplaning intensity HI with a first threshold which exemplarily coincides with the selected hydroplaning level (eg level two) taking into account the discretization presented by the hydroplaning intensity.

[0126] When the activation condition occurs such that the respective hydroplaning intensity of at least one tire 3 reaches a first threshold value (ie HI≧2), it is provided by way of example that routines SL, SA and TC (described in detail below) are continued.

[0127] Routine SL

[0128] Figure 4 The speed limiting routine SL is shown schematically.

[0129] To execute routine SL, the method comprises, for example, acquiring in real time a current value Vxc of the longitudinal speed of vehicle 1 . To this end, command and control unit 8 is exemplarily programmed and configured to receive in real time a first signal representative of the current value Vxc of the longitudinal speed of vehicle 1 .

[0130] Exemplarily, the current value Vxc of the longitudinal velocity of the vehicle 1 can be obtained by ( Figure 1 At least one detection sensor 10 (for example, an ABS encoder) for detecting the rotation speed of at least one wheel 7 (only schematically shown in FIG. 1 ) and / or at least one monitoring device in the monitoring device 4 and / or another method (for example, GPS detection) is used to obtain. Exemplarily, Figure 1 The right rear wheel RR of the middle combined vehicle shows the detection sensor 10. Equivalently, the detection sensor 10 may be combined with any other wheel, or each wheel may include a corresponding rotation speed detection sensor.

[0131] Exemplarily, the method comprises setting a reference value Axr (negative) of the longitudinal acceleration of the vehicle. The reference value Axr may be set as a function of the detected current value Vxc of the longitudinal speed and / or the detected maximum hydroplaning intensity.

[0132] For example, it can also be provided that the current value Axc of the longitudinal acceleration is acquired in real time. To this end, the control system 99 exemplarily includes an acceleration sensor 11 ( Figure 1 ), said acceleration sensor being connected to the command and control unit 8 and preferably mounted on the vehicle 1. For example, the acceleration sensor 11 may be of the 3DOF IMU type.

[0133] Preferably, provision is made for the correction longitudinal force Fx to be calculated in real time from a reference value Axr and a current value Axc of the longitudinal acceleration. In particular, the correction longitudinal force Fx is calculated from the difference between the current value Axc and the reference value Axr of the longitudinal acceleration.

[0134] Exemplarily, the method further includes: setting a reference value Vxr of the longitudinal speed of the vehicle; comparing the current value Vxc of the longitudinal speed with the reference value Vxr in real time; and canceling the correction longitudinal force Fx under the condition that the current value Vxc of the longitudinal speed reaches the reference value Vxr.

[0135] In combination with the use of the current value Axc and the reference value Axr of the longitudinal acceleration, or as an alternative to the use of the current value Axc and the reference value Axr of the longitudinal acceleration, it can be provided that: a reference value Vxr of the longitudinal speed is set (for example, as a function of the corresponding current value Vxc); and a corrective longitudinal force Fx is calculated in real time based on the current value Vxc and the reference value Vxr of the longitudinal speed.

[0136] Exemplarily, the method further includes interrupting the transmission of driving force from a motor (not shown) of the vehicle to the vehicle drive wheels. To this end, routine SL also outputs an ECR (Engine Cut Request) command to a control unit (not shown) of the vehicle.

[0137] Exemplarily, the method also includes ignoring acceleration requests from an accelerator of the vehicle (eg, a pedal and / or software for cruise control and / or autonomous driving, not shown).

[0138] Routine SA

[0139] Figure 5 A stability control routine for vehicle SA is schematically shown, which is exemplarily executed in parallel with routine SL.

[0140] To execute routine SA, the method exemplarily comprises acquiring in real time a current value Vxc of the longitudinal speed of the vehicle 1 (eg as described above).

[0141] Exemplarily, the method further comprises acquiring in real time the steering angle STA of the vehicle 1. To this end, the command and control unit 8 is exemplarily programmed and configured to receive as input in real time a second signal representing the steering angle STA of the vehicle 1.

[0142] Exemplarily, the method thus comprises calculating in real time, as a function of the current value Vxc of the longitudinal speed and the steering angle STA, a reference value YRr of a parameter representative of the lateral movement of the vehicle 1. To this end, the command and control unit is exemplarily programmed and configured to calculate in real time, as a function of the first signal and the second signal, a reference value YRr of a parameter representative of the lateral movement of the vehicle.

[0143] Exemplarily, the method comprises calculating the reference value YRr on the basis of a mathematical model VM (vehicle model) of the vehicle 1 , which model VM has previously been loaded into the command and control unit 8 .

[0144] In practice, the reference value YRr corresponds to the expected (or ideal) behavior of the vehicle as a function of the current value of the longitudinal speed Vxc and of the steering angle STA.

[0145] Exemplarily, the method further comprises detecting in real time a current value YRc of a parameter representative of the lateral movement of the vehicle.

[0146] By way of example, the parameter representative of the lateral movement is formed by the yaw rate of the vehicle.

[0147] Exemplarily, the command and control unit 8 is programmed and configured to receive in real time as input a third signal representing the current value YRc of the yaw angular velocity. To this end, the control system 99 exemplarily includes a detection sensor 12 ( Figure 1 ). The sensor 12 is exemplarily connected to the command and control unit 8 and arranged on the vehicle and may be, for example, of the 3DOF IMU type (preferably, it may be identical to the sensor 11 ).

[0148] In one embodiment (not shown), the parameter representative of lateral motion may include lateral acceleration and / or slip angle of the vehicle (eg, in addition to or as an alternative to yaw rate).

[0149] Exemplarily, the method thus comprises calculating in real time the correction torque Mz ( Figure 5 box MzC).

[0150] Exemplarily, calculating the correction torque Mz in real time includes: performing a difference between a reference value YRc and a current value YRc of a parameter representing the lateral movement of the vehicle in real time; and calculating the correction torque Mz according to the aforementioned difference.

[0151] Routine TC

[0152] Figure 6 A routine TC for calculating the corresponding torque to be applied to the wheels 7 is schematically shown.

[0153] Exemplarily, the method includes calculating a corresponding torque Tr (real torque) to be applied to each wheel 3 of the vehicle based on the correction moment Mz, the correction longitudinal force Fx and the hydroplaning intensity HI of each tire 3 of the vehicle.

[0154] By way of example, provision is made for each wheel to calculate the respective first torque T1 solely as a function of the correction torque Mz.

[0155] The set of respective first torques T1 ideally represents a set of torques that, once applied to the respective wheels, generate a resultant torque on the vehicle 1 (due to the air pressure-road surface interaction) equal to the correction torque Mz.

[0156] For example, in order to obtain a given correction torque Mz causing the vehicle to turn left relative to the direction of travel, routine TC exemplarily calculates:

[0157] - in the case of a braking torque, a respective first torque to be applied to at least one of the left wheels, said respective first torque being greater than the first torque to be applied to the right wheel, or

[0158] - In the case of a driving torque, a respective first torque to be applied to at least one of the right wheels, said respective first torque being greater than the first torque to be applied to the left wheel.

[0159] For example, the calculations of routine TC may result in the corresponding first braking torque T1 of the left rear wheel RL being non-zero, while the corresponding first torques T1 of the remaining wheels are zero.

[0160] By way of example, it is also provided that for each wheel the respective second torque T2 is calculated solely as a function of the correction longitudinal force Fx.

[0161] The set of respective second torques T2 ideally represents a set of torques which, once applied to the respective wheels, generate on the vehicle 1 a resultant force equal to the corrective longitudinal force Fx (due to the tire-road interaction).

[0162] For example, the calculations of routine TC may result in a respective second torque T2 for each wheel of the vehicle being non-zero, wherein the respective second torques T2 are preferably equal to one another for wheels belonging to the same axle (for braking the vehicle without inducing instability).

[0163] Thus, by way of example, provision is made to calculate a respective theoretical torque Tt for each wheel, each respective theoretical torque Tt being given by the algebraic sum of a respective first torque T1 and a respective second torque T2 .

[0164] Therefore, the corresponding theoretical torque Tt represents the total torque that is ideally applied to the corresponding wheel.

[0165] However, the applicant has noticed that in a hydroplaning state, the grip between the tire and the road surface is lower than in a non-hydroplaning state. Therefore, the corresponding theoretical torque Tt when applied to the corresponding wheel may be too large and cause the wheel to lock, thereby creating a strong unstable state for the vehicle (and therefore very dangerous).

[0166] To solve this problem, the control method of the present invention also inserts the dependency on the hydroplaning intensity HI of each tire into the calculation of each corresponding torque Tr.

[0167] Exemplarily, it is therefore provided that each torque Tr to be applied to each corresponding wheel is calculated according to the corresponding theoretical torque Tt and the hydroplaning intensity HI of all tires. In particular, the following criterion can be applied:

[0168] - the calculated maximum value of the corresponding torque Tr decreases as the hydroplaning intensity of the corresponding tire increases (and vice versa);

[0169] - under the condition that the corresponding hydroplaning intensity HI of the corresponding tire 3 is greater than or equal to a second threshold value greater than the first threshold value, the calculated corresponding torque Tr for one wheel is zero (the second threshold value is exemplarily set based on the aforementioned hydroplaning level, for example, if HI ≥ 5, then Tr = 0);

[0170] - Each respective torque Tr is calculated by redistributing the respective torque Tr so as to distribute each torque Tr to the respective wheels thereby reducing the torque close to its maximum value.

[0171] In other words, each theoretical torque Tt is converted (eg using appropriate mathematical methods, such as error minimization) into a respective torque Tr according to a combination of the above criteria and as a function of the respective hydroplaning intensity HI of the tyre.

[0172] Exemplarily, the method finally comprises applying the calculated corresponding torque Tr to each wheel of the vehicle. To this end, the command and control unit 8 is exemplarily programmed and configured to command the actuation device 9 to apply the calculated corresponding torque Tr to each wheel 7 of the vehicle.

[0173] simulation

[0174] Now refer to Figure 7a-10 The graphs depict results obtained from simulations of the control method according to the present invention.

[0175] Figure 7a-9c The graph has on the abscissa the time axis t (expressed in seconds) and on the ordinate the corresponding dimensions / parameters related to the control method, as described below.

[0176] The exemplary simulated situation is that of a rear-wheel drive vehicle including the above-described control system 99, which must move at a constant longitudinal speed Vxc ( Figure 7a Solid line) faces a curve, where the current longitudinal acceleration value Axc is essentially zero ( Figure 7b solid line), and the steering angle STA increases from 0° to 25° ( Figure 7c ) and then kept constant at 25° so as to face the bend.

[0177] In the simulation, the road surface has an area with a water layer at the right part of the road (outside the curve).

[0178] At time t1, which is exemplarily about 4 seconds, the vehicle encounters the aforementioned wet road area and the hydroplaning intensity HI of the right front wheel FR rises sharply to level five (expressed as a hydroplaning level from zero to seven), as shown in FIG. Figure 8b (solid line). Therefore, the aforementioned start-up conditions exist.

[0179] On the other hand, it can be noted that since the wet area is located on the right side of the road, the hydroplaning intensity HI of the left front wheel FL and the left rear wheel RL remains zero ( Figure 8b and Figure 9b dotted line).

[0180] It can also be noted that since the right front wheel FR entering the water layer will move the water and thus clear the way for the right rear wheel, the hydroplaning intensity of the right rear wheel RR also remains zero ( Figure 9b solid line).

[0181] Once the enabling conditions occur, the method executes the operations of routines SL, SA, and TC described above.

[0182] For routine SL, the reference value Axr for the longitudinal acceleration is set to -2 m / s 2 ( Figure 7b dotted line), and obtain the current value of the vehicle's longitudinal acceleration Axc ( Figure 7b The reference value Axr is a dotted line (more precisely, in this example, it is continuously acquired). The correction longitudinal force Fx (not shown) is then calculated in real time based on the difference values ​​Axr and Axc. It can be observed that the current value Axc of the longitudinal acceleration stabilizes almost immediately at the reference value Axr, so that the calculated force Fx will remain substantially zero, probably after the initial peak. This happens because the deceleration caused by the corresponding torque calculated based on the unique correction moment Mz (described below) together with any interruption in the transmission of the motor drive force is sufficient to keep the current value Axc of the longitudinal acceleration controllable.

[0183] For routine SA, the current value of the yaw angular velocity YRc ( Figure 8aSolid line), and calculates the reference value YRr of the yaw rate in real time according to the current value Vxc of the longitudinal velocity and the steering angle STA ( Figure 8a dotted line).

[0184] It can be noted that before the start condition, ie for the time before t1, when the vehicle responds to the driver's command, the current value YRc of the yaw rate coincides with the reference value YRr.

[0185] When entering a wet area of ​​the road, there will be a deviation between the two values, and the system will continue to calculate the correction torque Mz in real time ( Figure 9a In this example, the correction torque Mz is used, for example, to generate a counterclockwise rotation of the vehicle so that it rotates according to the set steering angle STA ( Figure 7c ) and the current value of the longitudinal velocity Vxc moves.

[0186] Then, as described above, the corresponding torque Tr is calculated in real time based on the correction moment Mz, the correction longitudinal force Fx and the corresponding hydroplaning intensity HI of all tires. Figure 8c (front wheel) and Fig.9c The time trend of the calculated corresponding torque Tr expressed as the pressure (bar) applied by the vehicle's braking system at the brake caliper of each wheel is shown in (rear wheels).

[0187] About the front wheel ( Figure 8c ), it can be observed that routine TC initially distributes the corresponding torque Tr only to the left front wheel FL (dashed line), while the corresponding torque of the right front wheel remains zero until about 10 seconds. This happens because initially the hydroplaning intensity of the right front wheel FR is equal to five, which is too high, so the corresponding torque cannot be distributed to this right front wheel without the risk of the wheel locking itself (in other words, the maximum value of the corresponding torque is zero).

[0188] For the rear wheel ( Fig.9c ), routine TC initially distributes the corresponding torque Tr only to the left rear wheel RL (dashed line). The combined effect of the corresponding torque Tr of the left wheel allows the vehicle to turn left according to the driver's intention.

[0189] from Figure 8b As can be seen from the graph of , the hydroplaning intensity HI of the tire of the right front wheel FR decreases over time. This is because at the same time the longitudinal speed Vxc of the vehicle is also decreasing due to the respective braking torques Tr applied to the left wheels FL and RL.

[0190] Since the hydroplaning intensity HI of the right front wheel FR is determined in real time, the time t2 (about 10 seconds) when the hydroplaning intensity falls below the second threshold value (while remaining above the first threshold value) can be detected.

[0191] In this way, Figure 8cAs shown in (solid line), the routine TC for calculating each corresponding torque Tr in real time according to the hydroplaning intensity HI of all tires continues to distribute the corresponding torque Tr to the right front wheel FR as well (because according to the corresponding hydroplaning intensity value, the tire of the right front wheel can now withstand the corresponding torque Tr without causing wheel locking).

[0192] like Figure 7a-9c As shown in the curve diagram, the entire system enters a stable state due to the real-time operation, at which time the vehicle has decelerated and the hydroplaning intensity of the right front wheel FR is restored to below the first threshold (HI<2, ie HI=1).

[0193] When this occurs, the system returns control to the driver (eg, reestablishes drive torque transfer from the motor to the drive wheels and reestablishes the possibility of acceleration).

[0194] Final Reference Fig.10 , which compares (on the Cartesian plane XY) the corresponding trajectory followed by a vehicle in the above example on which the control system according to the invention acts (HESC—solid line) and the trajectory of the same vehicle under the same driving conditions described above without using this control system (SESC—dashed line).

[0195] Thanks to the control system and method according to the invention, a vehicle HESC is able to follow a trajectory responsive to the driver's intention (and therefore complete the curve even in the event of a sudden hydroplaning on the right side of the vehicle), whereas a vehicle SESC is unable to maintain the desired turning radius and / or achieves a much larger turning radius than the vehicle intended (thereby presenting a risk of collision and / or loss of control).

Claims

1. A method for controlling a vehicle (1) moving on a road surface, the method comprising: - for each tire (3) of the vehicle (1) rolling on the road surface, determining in real time a corresponding hydroplaning intensity (HI); - comparing each respective hydroplaning intensity (HI) with a first threshold in real time; - When a starting condition occurs such that the corresponding hydroplaning intensity (HI) of at least one tire (3) reaches the first threshold, then: - obtaining in real time the current value (Vxc) of the longitudinal velocity of the vehicle (1); - obtaining the steering angle (STA) of the vehicle (1) in real time; - calculating in real time, from said current value of said longitudinal speed (Vxc) and said steering angle (STA), a reference value (YRr) of a parameter representative of the lateral movement of said vehicle (1); - Real-time detection of the current value of said parameter (YRc); - calculating in real time the correction torque (Mz) according to said reference value (YRr) of said parameter and said current value (YRc) of said parameter; - applying a corresponding torque (Tr) to each wheel (7) of the vehicle (1) in real time, the corresponding torque being calculated in real time based on the correction moment (Mz) and the hydroplaning intensity (HI) of the corresponding tire (3).

2. The method according to claim 1, wherein: The method comprises: for each tire (3), detecting in real time at least one corresponding quantity (Q) representative of the movement of the tire (3), and wherein the at least one corresponding quantity (Q) comprises at least one of the following quantities related to the single tire (3): displacement, velocity, acceleration and deformation.

3. The method according to claim 2, wherein: The at least one corresponding quantity (Q) represents a movement of a crown portion (6) of the tire (3), and wherein the corresponding quantity (Q) is detected at an inner surface (5) of the tire (3) at the crown portion (6).

4. The method according to any one of claims 2 and 3, wherein: A real-time determination of the respective hydroplaning intensity (HI) is performed as a function of the respective quantity (Q).

5. The method according to any one of claims 1 to 3, wherein: The parameter representative of the lateral movement comprises at least one of the following quantities: yaw rate, lateral acceleration, slip angle.

6. The method according to claim 5, wherein: The parameter representative of the lateral movement is constituted by the yaw rate.

7. The method according to any one of claims 1 to 3, wherein: Calculating the correction torque (Mz) in real time includes: performing a difference between the reference value (YRr) of the parameter representing the lateral movement of the vehicle and the current value (YRc) of the parameter in real time; and calculating the correction torque (Mz) based on the difference.

8. The method according to any one of claims 1 to 3, wherein: The corresponding torque (Tr) decreases as the hydroplaning intensity (HI) of the corresponding tire (3) increases.

9. The method according to any one of claims 1 to 3, wherein: The maximum value of the corresponding torque (Tr) decreases as the hydroplaning intensity (HI) of the corresponding tire (3) increases.

10. The method according to any one of claims 1 to 3, wherein: Under the condition that the corresponding hydroplaning intensity (HI) of the corresponding tire (3) is greater than or equal to a second threshold, the corresponding torque (Tr) is zero, and the second threshold is greater than the first threshold.

11. The method according to any one of claims 1 to 3, wherein: The method comprises: when the start condition occurs, setting a reference value (Axr, Vxr) of a parameter representing the longitudinal movement of the vehicle (1); acquiring a current value (Axc, Vxc) of the parameter representing the longitudinal movement in real time; and calculating a corrective longitudinal force (Fx) in real time based on the reference value (Axr, Vxr) of the parameter representing the longitudinal movement and the current value (Axc, Vxc) of the parameter representing the longitudinal movement, wherein the corresponding torque (Tr) is also calculated based on the corrective longitudinal force (Fx).

12. The method according to claim 11, wherein: The parameter representative of the longitudinal movement comprises at least one of the following quantities: longitudinal acceleration, longitudinal velocity.

13. The method according to any one of claims 1 to 3, wherein: Each respective torque (Tr) applied to a wheel (7) of the vehicle is also calculated as a function of the respective hydroplaning intensity (HI) of the tires associated with the remaining wheels (7) of the vehicle.

14. A control system (99) for a vehicle (1) moving on a road, the control system comprising: - a detection module (2), the detection module being used to detect in real time the corresponding hydroplaning intensity (HI) of each tire (3) of the vehicle (1) rolling on the road surface; - an actuating device (9) operatively connected to each wheel (7) of the vehicle (1); - a command and control unit (8) operatively connected to the detection module (2) and the actuation device (9) and programmed and configured to: - comparing each respective hydroplaning intensity (HI) with a first threshold value; - When a starting condition occurs such that the corresponding hydroplaning intensity (HI) of at least one tire (3) reaches the first threshold, then: - receiving in real time as input a first signal representing the current value (Vxc) of the longitudinal velocity of the vehicle (1); - receiving in real time as input a second signal, the second signal representing a steering angle (STA) of the vehicle (1); - calculating in real time, based on said first and second signals, a reference value (YRr) of a parameter representative of the lateral movement of said vehicle (1); - receiving as input in real time a third signal, said third signal representing the current value of said parameter (YRc); - calculating in real time the correction torque (Mz) according to said reference value (YRr) of said parameter and said current value (YRc) of said parameter; - commanding the actuating device (9) to apply a corresponding torque (Tr) to each wheel (7) in real time, the corresponding torque being calculated in real time based on the correction moment (Mz) and the hydroplaning intensity (HI) of the corresponding tire (3).

15. The control system (99) of claim 14, wherein: The detection module (2) comprises a respective monitoring device (4) associated with each tire (3), each monitoring device (4) being fixed at a crown portion (6) of the respective tire (3), wherein the monitoring device (4) is suitable for detecting at least one respective quantity (Q) relating to the respective tire, the at least one respective quantity (Q) representing the movement of the crown portion (6) of the tire (3), and wherein the at least one respective quantity (Q) comprises at least one of the following quantities relating to the single tire (3): displacement, velocity, acceleration and deformation.

16. The control system (99) of claim 15, wherein: The command and control unit (8) is programmed and configured to execute a method for controlling a vehicle moving on a road surface according to any one of claims 2 to 13, and wherein the actuating device (9) comprises a brake system and / or an engine system.

17. A vehicle (1) comprising a control system (99) according to any one of claims 14 to 16.

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