SE544696C2

SE544696C2 - Method and control arrangement for determining momentary tire wear rate of a wheel of a vehicle

Info

Publication number: SE544696C2
Application number: SE2050171A
Authority: SE
Inventors: Linus Flodin
Original assignee: Scania Cv Ab
Priority date: 2020-02-17
Filing date: 2020-02-17
Publication date: 2022-10-18
Also published as: DE102021101595A1; SE2050171A1

Abstract

A method and control arrangement (4) for determining momentary tire wear rate of a wheel (2) of a vehicle (1). The method comprises calculating (S5), for a plurality of points in time, longitudinal wheel slip values ( Kx(tx))) for a wheel slip between a surface of the wheel (2) and a corresponding road surface (10); and determining (S6) a momentary tire wear rate indicator ( TW ) based on a set of the calculated longitudinal wheel slip values ( Kx(tx))) corresponding to different points in time ( tx ) during a time period (At), wherein the momentary tire wear rate indicator (TW) is correlated with momentary tire wear rate established during the time period (At).

Description

Method and control arrangement for determining momentary tire wear rate of a wheel of a vehicle Technical Field The present disclosure relates to vehicles, and in particular to methods for determining momentary wear rate of a wheel of a vehicle.

Background Heavy vehicles such as trucks may comprise a tractor, and also one or more trailers. One or two driven axles are used for propelling the vehicle. The driven axle(s) may carry a relatively small portion of the weight of the vehicle. Consequently, the normal force on the driven axle(s) available for generating force for propelling and braking the vehicle is relatively low compared to the inertia of the vehicle which may result in high wheel slip. Trucks are also often equipped with auxiliary brakes in addition to the service brakes. Auxiliary brakes are often part of the drivetrain and thus only act on the driven wheels on the vehicle. lt is desired to use the auxiliary brakes as much as possible to spare the service brakes. lt is also desired to utilize the auxiliary brake(s) of vehicles with brake energy regeneration as much as possible, in order to recover energy. However, auxiliary brakes will only act on the driven wheels which may cause a high wheel slip and thereby wear to the tire.

Longitudinal wheel slip is a relative movement between the wheel surface and the road surface the wheel is rolling on. Longitudinal wheel slip is often denoted as a percentage difference between a longitudinal peripheral speed of the tire and a longitudinal speed of the vehicle itself. When exerting the wheel for a high longitudinal force relative to the normal force from the ground, there is a risk of causing high longitudinal wheel slip, which over time may lead to high tire wear due to increased tire temperature (caused by internal friction in the rubber) and abrasion between tire and road surface. This is especially a problem when driving with an unfavorable ratio between drive axle load and train inertia (meaning that the drive axle load is low in relation to the train inertia) and/or when driving with tires with relatively low slip stiffness (“soft tires”).

Summary Thus, trucks are often heavy and may carry heavy weight. However, the driven wheels often only carry a small part of this weight. When the trucks are operated with high longitudinal forces exerted on the driven wheels for propelling or braking the vehicle, the driven wheels may exhibit high wheel slip levels. High longitudinal wheel slip over time may lead to high tire wear. However, the longitudinal slip may have different wear effects on the tire depending on e.g. for how long time the wheel has been exposed to the slip, and tire characteristics. lt is an object of the disclosure to determine how sensitive the tire is to wear at a certain point in time when exposed to longitudinal wheel slip. lt is a further object of the disclosure to detect when the wear becomes high, based on how sensitive the tire is to wear.

These objects and others are at least partly achieved by the arrangement and the method according to the independent claims, and by the embodiments according to the dependent claims.

According to a first aspect, the disclosure relates to method, intended to be performed by a control arranqement, which method is for determining momentary tire wear rate of a wheel of a vehicle. The method comprises calculating, for a plurality of points in time, longitudinal wheel slip values for a wheel slip between a surface of the wheel and a corresponding road surface. The method further comprises determining a momentary tire wear rate indicator based on a set of the calculated longitudinal wheel slip values corresponding to different points in time during a time period, wherein the momentary tire wear rate indicator is correlated with momentary tire wear rate established during the time period and where the momentary tire wear rate describes how sensitive the tire is to wear at a certain moment in time.With the method, an indicator of momentary tire wear rate of a tire can be determined and analyzed. The momentary tire wear rate describes how sensitive the tire is to wear at a certain moment in time. Circumstances causing undesirable momentary high tire wear rates may then be mitigated or adapted to avoid excessive tire wear. Thus, the knowledge of an undesirable momentary high tire wear rate can be used to operate the vehicle in such a way that the driven wheels are not subjected to momentary high wear for long time periods. This can be achieved by indications to the driver, or automatically by limiting an admissible braking force or torque on the driven wheels, depending on the determined momentary tire wear rate. Momentary tire wear rate could alternatively be referred to as momentaneous or instantaneous tire wear rate.

Ithe method further comprises performing an action upon that the momentary tire wear rate indicator meets one or more predetermined criteria. Thus, an action might be taken in response to the development of the momentary tire wear rate indicator to avoid high levels.

According to some embodiments, the one or more predetermined criteria comprises a tire wear rate threshold that the momentary tire wear rate indicator should exceed. Thus, if the momentary tire wear rate indicator becomes too high, an action to mitigate the wear may be taken. The action is taken e.g. to generally reduce the use of auxiliary brakes, or to adapt the speed and/or distance to a preceding vehicle in case using look-ahead functionality (brake-related function), to reduce the need of using auxiliary brakes.

According to some embodiments, the action comprises indicating to the driver that the wheel has a high momentary tire wear rate. Thereby, the driver may take an action to mitigate high wear.

According to some embodiments, the action comprises controlling a brake-related vehicle function. According to some embodiments, the controlling comprises reducing the use of the brake-related vehicle function. According to someembodiments, the brake-related vehicle function comprises one or more auxiliary wheel braking functions. As auxiliary brakes are acting on driven wheels, and service brakes are acting on all wheels, the braking force is distributed on more wheels when using service brakes which leads to a reduced slip. Thus, by reducing the use of auxiliary brakes when the momentary tire wear rate is high, and instead use service brakes, the tire wear may be reduced.

According to some embodiments, the determining comprises time filtering the set of calculated longitudinal wheel slip values using a sliding window algorithm. Thus, the momentary tire wear rate indicator can then be determined in a time window that, for example, has a predetermined length but is continuously updated in time. The momentary tire wear rate indicator will then be continuously or repeatedly updated.

According to some embodiments, the determining comprises determining the momentary tire wear rate indicator using a tire wear rate model comprising a function of previous longitudinal wheel slip values over time, wherein the tire wear rate model takes the set of calculated longitudinal wheel slip values as input, and outputs the momentary tire wear rate indicator. Thus, the behavior of the tire when it is exposed to wheel slip can be determined in terms of momentary tire wear rate. Thereby, the method takes into account previous or historical exertion to high slip levels.

According to some embodiments, the function is a function of previous longitudinal wheel slip values and slip stiffness over time. Thus, characteristics for different types of tires are taken into account when determining the momentary tire wear rate indicator.

According to some embodiments, the tire wear rate model outputs the momentary tire wear rate indicator as one or more momentary tire wear rate values, where each momentary tire wear rate value represents accumulated longitudinal wheelslip values up to and including a longitudinal wheel slip value at a selected point in time. Hence, the model captures the effect of the longitudinal slip over time.

According to some embodiments, the function comprises a weight for each longitudinal wheel slip value. Hence, the model is adapted based on tire characteristics, and thus more precise.

According to some embodiments, the tire wear rate model is modelling temperature of the tire over time, and outputs the tire rate wear indicator as one or more momentary tire wear rate values where each momentary tire wear rate value represents a temperature of the tire at a selected point in time. Hence, the model describes how the temperature of the tire develops for a certain slip level.

According to some embodiments, the tire wear rate model is also based on one or more forces acting on the tire. The method comprising obtaining one or more tire forces acting on the wheel during the time period, and using the obtained one or more tire forces as input to the tire wear rate model. Hence, the model takes tire forces into account that may affect the determination of the momentary tire wear rate indicator.

According to some embodiments, the tire wear rate model is also based on ambient temperature. The method comprises obtaining ambient temperate indicating the ambient temperature during the time period, and using the obtained ambient temperature as input to the tire wear rate model. Hence, the model takes ambient temperature that may affect the determination of the momentary tire wear rate indicator into account.

According to some embodiments, the method comprises obtaining wheel speed properties indicative of wheel speed of a wheel, obtaining vehicle speed properties indicative of corresponding speed of the vehicle, and wherein the calculating comprises calculating the Iongitudinal wheel slip values based on thewheel speed properties and the corresponding vehicle speed properties. Thus, values for calculating the Iongitudinal wheel s|ip values are obtained.

According to some embodiments, the obtaining of wheel speed properties comprises obtaining wheel speed properties indicative of a predicted wheel speed of the wheel along a route on a road ahead; the obtaining of vehicle speed properties comprises obtaining vehicle speed properties indicative of corresponding vehicle speed on a route on a road ahead; and wherein the calculating comprises calculating future Iongitudinal wheel s|ip values based on the wheel speed properties and the corresponding vehicle speed properties. Thus, values for calculating the future longitudinal wheel s|ip values are obtained.

According to a second aspect, the disclosure relates to a control arrangement for determining momentary tire wear rate of a wheel of a vehicle, wherein the control arrangement is configured to execute the method according to any one of the preceding claims.

According to a third aspect, the disclosure relates to a vehicle comprises a control arrangement according to the second aspect, and a wheel speed sensor configured to sense a speed indicative of the speed of a drive wheel.

According to a fourth aspect, the disclosure relates to a computer program comprising instructions, which, when the program is executed by a control arrangement, cause the control arrangement to carry out the method according to the first aspect.

According to a fifth aspect, the disclosure relates to a computer-readable medium having stored thereon the computer program according to the fourth aspect.

Brief description of the drawinds Fig. 1 illustrates a vehicle according to an example embodiment.Fig. 2 illustrates forces acting on a driven wheel and resulting speeds during operation of the vehicle.

Fig. 3 illustrates a ﬂow chart of a method for determining momentary tire wear rate indicator of a wheel of a vehicle according to some embodiments.

Fig. 4 is a graph of slip for different types of tires.

Fig. 5 is a graph of slip stiffness for different types of tires.

Fig. 6 is a graph of tire temperature for different types of tires.

Fig. 7 illustrates a vehicle approaching a downhill.

Fig. 8 illustrates a control arrangement for determining momentary tire wear rate indicator of a wheel of a vehicle according to some embodiments.

Detailed description ln the following disclosure a method and control arrangement for determining a momentary tire wear rate indicator for a wheel of a vehicle are described. The method is especially relevant for heavy vehicles. Thus, the vehicle is for example a heavy vehicle, such as a truck, that typically comprises a tractor and optionally one or more trailers. The driven wheels of the vehicle may be exposed to high wear, and the present method aims to detect such situations by estimating the momentaneous rate of the tire wear. As previously described, the momentary tire wear rate describes how sensitive the tire is to wear at a certain moment in time. Thus, different tires may be differently sensitive to wear, and thus have different momentary tire wear rates during similar operating conditions. A high momentary tire wear rate should be avoided, but may be acceptable for a short while, until the accumulated wear of the tire is considered too large. On the other hand, a lower momentary tire wear rate may be acceptable for a longer time, as it takes longer time for the accumulated wear to reach a high value. ln the following a vehicle, where the herein disclosed method and control arrangement may be implemented, will be described. The vehicle will be explained with reference to the illustrated vehicle in Fig. 1, and thereafter forces acting on a driven wheel and resulting speeds during operation of the vehicle will be explained with reference to Fig.

The vehicle 1 in Fig. 1 is a heavy vehicle, also referred to as a heavy commercial vehicle, being operated along a road surface 10. The vehicle 1 has one driven axle (not shown) arranged for transferring power from an engine (not shown) to two driven wheels; the foremost located wheels of the vehicle. Thus, the driven axle is connected to and driven by the drivetrain of the vehicle. Only one of the two driven wheels 2 is illustrated in the figure. The vehicle 1 also has one rear tag axle that is used to support the weight of the vehicle 1. This rear axle is connected to two wheels 3. The rear axle is not connected to the drivetrain. The wheels 2, 3 have tire surfaces 11 that contact the road surface 10. lt should be understood that this vehicle 1 is only one example, and the proposed solution may of course also be used in a vehicle 1 comprising more than two axles, more driven axles and wheels, and/or which comprises axles with differentials etc. A wheel is herein defined to comprise a rim and a tire. A tire is the rubber part of the wheel that grips the road.

The vehicle 1 comprises a control arrangement 4 configured to implement the proposed technique. The control arrangement 4 will be more explained in the following, but may be implemented as an Electronic Control Unit, ECU. The vehicle 1 also comprises sensors 5 such as a vehicle speed sensor configured to sense the speed of the vehicle, a weight sensor configured to sense the weight of the vehicle 1 or at least the load of the vehicle 1. The weight of the vehicle 1 without load is normally a parameter that is known and saved in a memory in the vehicle 1. Thus, as the total weight of the vehicle 1 is known, the weight on each wheel 2, 3 of the vehicle 1 may be determined and thus also the resulting normal force acting on each wheel 2, An ECU is basically a digital computer that controls one or more electrical systems (or electrical sub systems) of the vehicle 1 based on e.g. information read from sensors and meters placed at various parts and in different components of the vehicle 1. ECU is a generic term that is used in automotive electronics for any embedded system that controls one or more functions of the electrical systemor sub systems in a transport vehicle. A vehicle typically comprises a plurality of ECUs that communicate over a Controller Area Network, CAN. The CAN is a network that is used to handle communication between the various control arrangements in the vehicle 1. Alternatively, the vehicle 1 may use an ethernet based protocol for communication. ln Fig. 2, depicting one of the drive wheels 2 of the vehicle 1 in Fig. 1, a load force m and a corresponding normal force FN acts on the wheel 2. The driven axle makes the wheel rotate with an angular velocity w. The effective radius of the wheel 2 is denoted r. The wheel center speed and its direction are illustrated as a vector u. Thus, u represents the velocity of the vehicle 1 in relation to the road surface 10. The free-rolling speed of the wheel 2 is the speed at which the wheel (and tire) would spin if no brake or drive force are applied to it. The wheel 2 is exerted to a longitudinal force Fx and thereby spins at a speed different from its “free-rotting speed”. The iongitudinai force Fx is acting on the tire surface “if reiative to the road surface 10. The iongitudinai force Fx creates friction and deformation of the rubber of the tire. The longitudinal force Fx may be known in beforehand or estimated from forces exerted by drivetrain and service brakes (measured with one or more force sensors 5c, Fig. 8). The difference in speeds is described as longitudinal wheel slip, orjust “slip ratio”. i-ience, a iongitudinai wheei siip K of the tire can be defined as the difference between the tire tangential speed (w - r) and the speed of the axle (u) relative to the road surface 10. The longitudinal wheel slip K, or siip ratio, may be determined as: K :_ ruta-u, (1) u which gives a value of the wheel K slip in a range between 55. A siip ratio in percent is obtained by muitipiying the vaiue with 100. When the iongitudinai siip is zero there is no siip. When the slip is non-zero there is thus a siip. The iongitudinai siip may be considered high when it is ciose to +1 or -1 . A wheel siip means iost traction on the road. A positive iongitudinal wheel siip means that the wheei 2 is spinning, typicaiiy caused by appiying too much throttie. A negative lO iongitudinal wheel stip means that wheel 2 is skidding, typically caused by applying too much braking force. ln the following, a method for determining momentary tire wear rate indicators of a wheel of a vehicle, typically a drive wheel of a vehicle, using longitudinal wheel slip, will be explained. The vehicle is for example the vehicle illustrated in Fig. 1. The method will be explained with reference to the flow chart in Fig. 3, the diagrams in Figs. 4-6 and the illustration in Fig. 7. The method may be implemented as a computer program comprising instructions, which, when the program is executed by a control arrangement, cause the control arrangement to carry out the method. The control arrangement may be a control arrangement 4 in a vehicle 1 as illustrated in Fig. 1. Alternatively, the control arrangement 4 may be a control arrangement that is remote from the vehicle 1, typically an off-board computer. The method may be executed using real-time sensed values from the vehicle 1, or using values that are obtained from a vehicle model that models the behavior of the vehicle when driving along a road. lt is then possible to predict the momentary tire wear rate along an upcoming or simulated route. The method is explained in relation to one wheel, but it should be understood that the method may be applied to all driven wheels of a vehicle in parallel.

The method makes use of longitudinal wheel slip values K(tx). These values may be known in beforehand in the vehicle 1, or calculated from measured or estimated values of the wheel speed and vehicle speed. ln order to determine momentary tire wear rate indicators in advance, the future route needs to be known. The method may then include obtaining S0 information of the road ahead, where the information includes route information. The route information may include geographical data and altitude data of the route ahead. Upcoming braking forces may be predicted using the weight of the vehicle and the altitude of the route, and a vehicle model. The vehicle model models how much force the wheel is exposed to, to keep a certain speed given a certain road inclination, etc., as known in the art. With the assumption that the vehicle shall ll have a certain speed along the route, or not go over a certain speed, or other assumption, it is possible to calculate that the wheel will be exposed to a certain sequence of Iongitudinal forces and thereby a sequence of s|ip levels during a certain time. The vehicle speed may thus be set in advance, and the predicted wheel speed determined from the calculated Iongitudinal forces etc. Thus, in some embodiments, the method comprises obtaining S1 wheel speed properties indicative of a predicted wheel speed of the wheel 2 along the route on a road ahead. Further, the method comprises obtaining S2 vehicle speed properties indicative of corresponding vehicle speed on the route on a road ahead. ln case the method is performed while driving, the wheel speed and the vehicle speed may already be available in the vehicle on a communication network in the vehicle 1 such as CAN. Thus, the method may include obtaining S1 wheel speed properties indicative of wheel speed of the wheel 2, and obtaining S2 vehicle speed properties indicative of corresponding speed of the vehicle 1. Alternatively, they may be determined. The wheel center speed u of the vehicle 1 corresponds to the speed of the vehicle 1, and may be measured using another speed sensor, estimated using the position of the vehicle using the Global Positioning System (GPS), or estimated using radar measurements etc. The wheel center speed u represents the tangential free rolling speed of the wheel 2. Hence, the sensed wheel speed together with knowledge or estimations of the Iongitudinal forces exerted on the driven wheel (from drivetrain and service brakes), the free rolling wheel speed can be estimated, and thus the wheel center speed. The method may then comprise obtaining S3 one or more tire forces F(t) acting on the wheel ln some embodiments, the method may make use of the temperature of the ambient, i.e., the environment. The method may then comprise obtaining S4 ambient temperate indicating the ambient temperature during a time period. The ambient temperature is for example measured using a temperature sensor in the vehicleThe longitudinal wheel slip values K(tx) are for example calculated using the equation (1), using the obtained properties. The effective radius r of the vehicle 1 is a known parameter in the vehicle 1 and the angular velocity w may be measured using a wheel speed sensor. ln other words, the method comprises calculating S5 for a plurality of points in time, longitudinal wheel slip values K(tx) for a wheel slip between a surface of the wheel 2 and a corresponding road surface 10. The wheel 2 is here a driven wheel of the vehicle.

From the step S5, a plurality of time dependent longitudinal slip values K(tx) are obtained. The step S5 may be continuously performed during operation of the vehicle 1, or simulated or predicted for a future road ahead and then calculating future longitudinal wheel slip values. The method further comprises determining S6 a momentary tire wear rate indicator TW based on a set of the calculated longitudinal wheel slip values K(tx) corresponding to different points in time tx during a time period At. The determining is typically based on a model that describes how wear properties of a tire is affected by longitudinal wheel slip. The set may be a part of, or all of, the calculated longitudinal wheel slip values K(tx) calculated during the time period At. lt may for example be every second value, every third value, etc., and may be adapted based on the computational load. However, the set should represent the time period At. Every calculated longitudinal wheel slip value K(tx) corresponds to a unique point in time during the time period At. The momentary tire wear rate indicator TW is correlated with momentary tire wear rate established during the time period A. The momentary tire wear rate indicator indicates how fast the tire is worn out during the time period. The momentary tire wear rate indicator TW may include one or more momentary tire wear rate values established during the time period At, or be a function of the momentary tire wear rate during the time period At. The momentary tire wear rate indicator TW may be a maximum or average value of the momentary tire wear rate values determined during the time period At. During the time period At, a plurality of momentary tire wear rate values may be established. Data may be collected from a plurality of such time periods At. Thetime period At may have the same length as the time period for driving a route of the vehicle 1, thus, from a start of operation until the vehicle 1 stops operating, or a predicted time for driving a predicted route ahead. Alternatively, the time period A1: may have predetermined length and be repeated continuously along the route.

Momentary (or instantaneous) tire wear rate is an estimate of how fast the tire is being worn out at a given time point, a particular instance, or for a short time period. A high rate means that the tire is worn out fast, a low rate means that the tire is worn out at a slower pace. The momentary or instantaneous tire wear rate is thus an estimate of the rate of the tire wear at a given instance. lt describes how sensitive the tire is to wear at a certain point in time. The momentary tire wear rate indicates the resistance or sensibility of the tire to wear at a certain time point. lt also describes how durable the tire is to wear at a certain time point. Fig. 5 illustrates slip stiffness for a plurality of different tires A, B, C: a soft tire A, a middle-soft tire B and a hard tire C. The soft tire A has a flatter inclination than the tires B and C, and thus a higher slip for the same longitudinal force. This means a higher heat development because of inner friction of the tire A, which means a higher wear for the same longitudinal force than tire B and C. At lower normal force FN, the inclination becomes flatter. At high normal force (heavy vehicle), it is needed to stay higher up on the curve to generate the same braking power FZ, which gives a higher heat development and thus higher wear. Generally, heavy vehicles have a relatively low normal force FN on driven wheels, and thus often problem with high heat development in their driven wheels.

As explained, the longitudinal slip values may be continuously, continually or regularly calculated while driving based on measured values or based on a vehicle model. Fig. 4 is a graph of longitudinal wheel slip K(tx) for different types oftires A, B, C over time tx. For a soft tire as illustrated by A, the slip is typically higher than for a hard tire C or a semi-hard tire B. The determining S6 is typically also repeatedly performed, for example at each time instant tx. ln some embodiments, the determining S6 comprises time filtering the set of calculatedIongitudinal wheel slip values K(tx) using a sliding window algorithm. Then, Iongitudinal wheel slip values within the sliding window are used for determining the momentary tire wear rate indicator. The time period At will then have the same length as the length of the sliding window. The sliding window may have a length of for example 1-10 minutes, more specified between for example 2-5 minutes. lt will then capture the calculated Iongitudinal wheel slip values K(tx) from the last 1-10 (or 2-5) minutes of travelling, or alternatively for the upcoming 1-10 (or 2-5) minutes of travelling if predicting using e.g. look-ahead functionality. The time filtering is then continuously performed during actual or predicted travelling along the road. Thus, the Iongitudinal wheel slip values are continuously calculated, and the sliding window algorithm selects which values that should be used for determining the momentary tire wear rate indicator.

The momentary tire wear rate indicator TW may be determined using a tire wear rate model. The tire wear rate model models how sensitive the tire is to wear at a certain point in time when exposed to Iongitudinal wheel slip. The tire wear rate models how internal friction develops in the tire when exerted to Iongitudinal slip. ln some embodiments, the determining S6 comprises determining the momentary tire wear rate indicator using a tire wear rate model comprising a function TW(tx) = f(Kx(t1: tx)) of previous Iongitudinal wheel slip values K(tx) over time tx. The tire wear rate model takes the set of calculated Iongitudinal wheel slip values K(tx) as input, and outputs the momentary tire wear rate indicator TW. lf the time period for example comprises ten time points, then x will be incremented from zero to 10 by one. ln some embodiments, the momentary tire wear rate indicator TW is calculated as the accumulated sum of previous Iongitudinal wheel slip values K(tx) during the time period. So, if the time period comprises three time points, the function TW(tx) = f(Kx(t1: tx)) will give TW(1:1) = Kx(t1), TW(1:2) = TW(1:1) + Kx(t2) and TW(1:3) = TW(t2) + Kx(t3). The momentary tire wear rate indicator TW may then include all these values. When using a sliding window algorithm, the time point 1:1 is typically the first time point in the window. lf the time period is the whole length of the route, then 1:1 may be the starting point of the route. tx will go from “1” to the end time point of the time period. Turning to Fig. 4 and using the tire wear rate model, the momentary tire wear rate indicator TW is calculated as the accumulated sum of previous longitudinal wheel slip values K(tx) during the time period. Thus, if the time period At comprises the time points 1:1, 1:2 and 1:3, the momentary tire wear rate indicator TW here in this example comprises three values: for 1:1 the value is K(t1), for 1:2 it is K(1:1) + K(t2), and for 1:3 it is K(t1) + K(t2) + K(t3). However, the indicator may be only a subset of the values, for example the maximum value of the values. Thus, in some embodiments, the tire wear rate model outputs the momentary tire wear rate indicator TW as one or more momentary tire wear rate values TW(tx) where each momentary tire wear rate value TW(tx) represents accumulated longitudinal wheel slip values up to and including a longitudinal wheel slip value TW(tx) at a selected point in time tx. The selected point in time is in the illustrated example then any of the time points 1:1, 1:2 and 1: As explained, there are different kinds of tires characterized as soft or hard or something in-between. lt is possible to take such characteristics into account by means of slip stiffness, S, in determining the momentary tire wear rate indicator. Slip stiffness is defined as the ratio between the normalized longitudinal force Fx (thus divided with the normal force FN) and wheel slip K(tx). As previously described, Fig. 5 is a graph of slip stiffness Sfor different types of tires A, B, C. Thus, in some embodiments, the function is a function TW(1;x) = f(Kx(1:1: tx), S) of previous longitudinal wheel slip values K(tx) and slip stiffness S over time tx. ln more detail, based on the slip stiffness S, a weight W(Kx(tx),S) for each longitudinal slip value may be determined. Thus, in some embodiments, the function comprises a weight W(Kx(tx),S) for each longitudinal wheel slip value K(tx). The weight may be positive or negative and may increase for an increased value of K(tx). The arrows in the figure illustrate how the weight may increase for an increased longitudinal slip. Alternatively, the weight may be independent from the longitudinal wheel slip and/or the slip stiffness, and for example be constant. Generally, the weight is intended to mirror when it is desired to increase ordecrease the tire wear indicator. The weight should be positive when the wear of the tire increases, and negative when the wear decreases. The weight should be greater the faster the wear increases (meaning that the momentary tire wear rate indicator becomes greater, typically more than a predetermined threshold). This means that the weight typically is negative when the wheel is free ro||ing, but positive when the momentary tire wear rate indicator is greater than the predetermined threshold (then, there is heat development in the tire). When the tire rate indicator increases from a previous tire rate indicator value, the When the vehicle is driven in steady-state (typically constant speed driving, e.g. high-way driving), the weight should be close to zero, or zero. For example, if the time period At comprises the time points 1:1, 1:2 and 1:3, the momentary tire wear rate value for 1:1 is TW(1:1) = TW(1:0) + K(t1) - W(Kx(t1), S), for 1:2 the momentary tire wear rate value is TW(1:2) = TW(1:1) + K(t2) - W(Kx(t2), S) and for 1:3 the momentary tire wear rate value is TW(1:3) = TW(1:2) + K(t3) - W(Kx(t3), S). The momentary tire wear rate indicator TW may be determined for example as all the values, the maximum value or an average value of the values, etc. As a summary, for each time point tx there is a certain longitudinal slip value Kxüïx). The slip stiffness S, has previously been estimated and may be considered constant during the time period At in question for the accumulation. The weight W is a function of slip stiffness S and longitudinal slip Kxüïx). For each time point tx, a momentary tire wear rate TW(tx) is accumulated, during the time period, that correlates or gives an indication of the rate of tire wear. Thus, for each time point tx, a new momentary tire wear rate TW(1:x) is accumulated and thus determined. lt has been established through experiments and simulations that this accumulated value has a strong correlation to how fast the tire is worn out at the present time point. Thus, using the present slip, high tire wear can be recognized using a tire wear model by accumulating a weighted longitudinal slip level over time.

The above-mentioned model describes a relation between longitudinal slip and momentary tire wear rate, that is correlated with how internal friction develops in the tire when exerted to longitudinal slip. ln the following another model will bedescribed, where the actual temperature of the tire is modelled. ln these embodiments, the tire wear rate model is a temperature model. This tire wear rate model is modelling temperature of the tire over time, and outputs the tire rate wear indicator TW as one or more momentary tire wear rate values TW(tx) where each momentary tire wear rate value TW(tx) represents a temperature of the tire at a selected point in time tx. Fig. 6 is a graph of tire temperature for different types of tires A, B, C. ln this embodiment, the tire wear rate model outputs an estimated temperature of the tire for each time point. Also in this embodiment, the function is a function TW(tx) = f(Kx(t1: tx), S) of previous longitudinal wheel slip values K(tx) and slip stiffness S over time tx. For each time point tx, the model estimates a tire temperature T. The temperature is correlated with the momentary tire wear rate. Typically, the momentary tire wear rate indicator TW comprises the latest estimated temperature during the time period At. ln more detail, the longitudinal wheel slip Kx(tx) and the slip stiffness S are used to model how the tire is heated up and cooled (typically the tire is heated when exposed to high slip levels and is cooled if exposed to low or no force or if the vehicle is standing still). The tire wear rate model may also include parameters with coefficients determining how fast the tire is heated up and how fast it is cooled down. These coefficients may be used to determine weights W(Kx(tx)) to be used in the calculations. For example, if the weight is positive, the momentary tire wear rate value TW(tx) will increase (the tire is heated up), and if the weight is negative, the momentary tire wear rate value TW(1;x) will decrease (the tire is cooled). ln some embodiments, the tire wear rate model is also based on one or more forces acting on the tire. The method then comprises obtaining S3 one or more tire forces F(t) acting on the wheel 2 during the time period and using the obtained one or more tire forces F(t) as input to the tire wear rate model. The tire forces are for example the longitudinal force Fx and the normal force FN (see Fig. 2). The model may also use ambient temperature and/or speed of the vehicle. Thus, in some embodiments, the tire wear rate model is also based on ambient temperature, and wherein the method comprising obtaining S3 ambient temperate indicating the ambient temperature during the time period, and using the obtained ambienttemperature as input to the tire wear rate model. The ambient temperature is for example measured using a temperature sensor in the vehicle. Hence, in summary, the tire wear rate model may estimate the tire temperature as a function of longitudinal wheel slip, slip stiffness, one or more forces acing on the driven wheel 2 and ambient temperature, over time.

The momentary tire wear rate indicator may be used for a plurality of purposes. For example, the method may comprise determining a trend of the tire wear rate from the momentary tire wear rate indicator or indicators. Thereby, is can be recognized e.g. when high momentary tire wear rate occurs. ln some embodiment, the method comprises performing S7 an action upon that the momentary tire wear rate indicator TW meets one or more predetermined criteria. For example, the one or more predetermined criteria may comprise a tire wear rate threshold that the momentary tire wear rate indicator TW should exceed. When the threshold is exceeded, one or more actions are performed. The tire wear rate threshold is typically predetermined. The tire wear rate threshold may for example be related to a maximum allowed accumulated tire wear rate that should not be exceed. When the threshold is exceeded, one or more actions are performed. The aim of the action is typically to make the momentary tire wear rate indicator TW to go below the threshold. The value or values of the momentary tire wear rate indicator may thus be compared to the threshold as soon as they are established, and as soon as a value goes above the threshold, one or more actions may be performed. ln one embodiment, the method comprises determining the maximum of the momentary tire wear rate values determined during the time window and determining if this value exceeds the tire wear rate threshold. lf exceeding the threshold, the method includes performing an action.

The action may comprise indicating S7a to the driver that the wheel 2 has a high momentary tire wear rate. The indication is for example a voice indication, a graphical indication, or a tactile indication (via a suitable interface such as a loudspeaker, dashboard, mobile device or similar). ln response, the driver may reduce use of auxiliary wheel braking functions, depending on the drivingsituation. By the actions performed by the driver, the momentary tire wear rate shall be reduced (as the Iongitudinal force on driven wheels will decrease and thus also the longitudinal wheel slip). This may also be indicated to the driver if successful, that is, that the wear is reduced. Alternatively, or in combination with the indicating, the action comprises controlling S7b a brake-related vehicle function. For example, the controlling S7b comprises reducing the use of the brake-related vehicle function. The brake related functions may for example include adaptive speed control and constant speed control. The brake-related vehicle function typically comprises one or more auxiliary wheel braking functions. The auxiliary wheel braking functions comprises for example retarder and exhaust brake. Thus, when using adaptive speed control and constant speed control, the retarder or exhaust brake is typically used, or a brake blending of the retarder and the exhaust brake (and the conventional braking system including the service brakes). The controlling S7b may be automatically performed by the vehicle 1. Thus, when controlling S7b the vehicle 1 to use the auxiliary brakes less, the conventional braking system is used more.

Fig. 7 is illustrating a vehicle 1 at a time point t0 just before a downhill start. ln order to avoid excessive wear, the method may be executed before the downhill starts, and a control strategy for the vehicle 1 may be determined in advance, based on the result of the method, that mitigates or prevents momentary tire wear rate indicators over the threshold. The control strategy may include speed, braking force, throttle commands etc. along the upcoming route. The time period At should preferably capture events such as a downhill or an uphill, e.g. the downhill 13 in Fig. 7. The time period is here from t1 to t4, and x = 1: 4. Between each time point there is one minute, and the time period At is thus three minutes. lf using a sliding window, the length of the sliding window should be at least three minutes, to capture the downhill, such that it is possible to adapt the control of the vehicle 1 before the downhill. However, this is merely an example to illustrate the principle, and typically there are many more time points than the four time points illustrated, for example one every second. ln some embodiments, the time period At (and sliding window) has such length such that it captures the vehicle 1 before the downhill 13 (or uphill), in order to adapt the behavior of the vehicle 1 before the downhill (or uphill) starts.

Upcoming slip levels may be predicted from estimated slip stiffness of the wheel and upcoming braking forces the wheel will be exerted to along the route. A predicted momentary tire wear rate indicator may be determined in beforehand and compared with different alternative scenarios, for example such that the vehicle speed is decreased before the downhill. The vehicle may then increase its speed in the downhill without braking it, or with a reduced need to brake it. The determining of predicted momentary tire wear rate may be incorporated with other driver assistance functionality where the vehicle behavior depends on predictions of the road ahead, such as cruise control with active prediction. Avoiding high tire wear could be a factor that is taken into account when planning braking or propelling the vehicle 1 ahead. Alternatively, the longitudinal wheel slip values are calculated using real sensed values, and the control of the vehicle 1 is configured “on the fly", to avoid more tire wear.

The disclosure also relates to a control arrangement for determining momentary tire wear rate indicators of a wheel 2 of a vehicle 1. Fig. 8 illustrates such a control arrangement 4. The control arrangement 4 may be arranged in a vehicle 1, or in an off-board remote computer. The control arrangement 4 is configured to execute the method according to any one of the embodiments as explained herein. The control arrangement 4, or more specifically a processor 6 of the control arrangement 4, is configured to cause the control arrangement 4 to perform all aspects of the method described herein. This is typically done by running computer program code stored in a memory 6 in the processor 5 of the control arrangement 4. The computer program may also be stored on a computer- readable medium. ln some embodiments, the control arrangement 4 is a “unit” in a functional sense. Hence, in some embodiments the control arrangement 4 is a control arrangement comprising several physical control arrangements that operate in corporation. The control arrangement 4 comprises hardware and software. The hardware comprises various electronic components on PrintedCircuit Board, PCB. The most important of those components is typically one or more processors e.g. a microprocessor, along with memory e.g. EPROM or a Flash memory chip. ln this example, the control arrangement 4 comprising the processor 6, the memory 7 and a communication interface 8. The processor 6 may include one or processing units. The memory 7 may include one or more memory units. The communication interface 8 is for example configured to communicate with other devices e.g. with other subsystems of the vehicle 1 or with devices outside the vehicle 1. lf the control arrangement 4 is arranged remote from the vehicle 1, the communication interface 8 may be configured to communicate with devices in the vehicle 1. The software (also called firmware) is typically lower-level software code that runs in the microprocessor. The control arrangement 4 is for example configured to receive and/or collect data from one or more sensors 5 in the vehicle 1, for example one or more wheel speed sensors 5a, a vehicle speed sensor 5b and/or one or more force sensor 5c. The wheel speed sensor 5a is configured to sense a speed indicative of the speed of a drive wheel 2. The vehicle 1 may comprise one such sensor for each drive wheel of the vehicle 1. The control arrangement 4 may also be configured to communicate data e.g. control data to a vehicle function 12 of the vehicle 1. The control arrangement 4 may also be configured to communicate an indication to the driver via an interface such as an indication device 9. The indication device 9 is for example a loudspeaker, a dashboard, a mobile device or similar.

The present disclosure is not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the disclosure, which is defined by the appending claims.

Claims

1. CLAIMS A method, to be performed bv a control arranqement, for determining momentary tire wear rate of a wheel (2) of a vehicle (1), the method comprising: - calculating (S5), for a plurality of points in time, Iongitudinal wheel slip values (Kx(1:x))) for a wheel slip between a surface of the wheel (2) and a corresponding road surface (10); - determining (S6) a momentary tire wear rate indicator (TW) based on a set of the calculated longitudinal wheel slip values (Kx(tx))) corresponding to different points in time (tx) during a time period (At), wherein the momentary tire wear rate indicator (TW) is correlated with momentary tire wear rate established during the time period (At), where the momentary tire wear rate describes how sensitive the tire is to wear at a certain moment in time; and: - performing (S7) an action upon that the momentary tire wear rate indicator (TW) meets one or more predetermined criteria. The method according to claim 1, wherein the one or more predetermined criteria comprises a tire wear rate threshold that the momentary tire wear rate indicator (TW) should exceed. The method according to claim 2, wherein the action comprises indicating (S7a) to the driver that the wheel (2) has a high momentary tire wear rate. The method according to any one of the claims 2 to 3, wherein the action comprises controlling (S7b) a brake-related vehicle function. The method according to claim 4, wherein the controlling (S7b) comprises reducing the use of the brake-related vehicle function. The method according to claim 4 or 5, wherein the brake-related vehicle function comprises one or more auxiliary wheel braking functions._ The method according to any one of the preceding claims, wherein the determining (S6) comprises time filtering the set of calculated longitudinal wheel slip values (Kx(tx)) using a sliding window algorithm. The method according to any one of the preceding claims, wherein the determining (S6) comprises: - determining the momentary tire wear rate indicator using a tire wear rate model comprising a function (TW(1:x) = f(Kx(t1: tx)) of previous longitudinal wheel slip values (Kx(tx))) over time (t(x)), wherein the tire wear rate model takes the set of calculated longitudinal wheel slip values (Kx(1;x)) as input, and outputs the momentary tire wear rate indicator. The method according to claim 8, wherein the function is a function ((TW(tx) = f(Kx(t1: tx),S)) of previous longitudinal wheel slip values (Kx(tx)) and slip stiffness (S) over time (tx). 10.The method according to claim 8 or 9, wherein the tire wear rate model outputs the momentary tire wear rate indicator (TW) as one or more momentary tire wear rate values (TW(tx)) where each momentary tire wear rate value (TW(1:x)) represents accumulated longitudinal wheel slip values up to and including a longitudinal wheel slip value (Kx(tx)) at a selected point in time (tx). 11.The method according to claim 9-10, wherein the function comprises a weight (W(Kx(tx))) for each longitudinal wheel slip value (Kx(tx)). 12.The method according to claim 9, wherein the tire wear rate model is modelling temperature ofthe tire over time, and outputs the momentary tire rate wear indicator (TW) as one or more momentary tire wear rate values (TW (tx)) where each momentary tire wear rate value (TW(1:x)) represents a temperature of the tire at a selected point in time (t(x)).13.The method according to claim 12, wherein the tire wear rate model is also based on one or more forces acting on the tire, and wherein the method comprising: - obtaining (S4) one or more tire forces (F(tx)) acting on the wheel (2) during the time period, and using the obtained one or more tire forces (F(tx)) as input to the tire wear rate model. 14.The method according to claim 11 or 12, wherein the tire wear rate model is also based on ambient temperature, and wherein the method comprising: - obtaining (S3) ambient temperate indicating the ambient temperature during the time period, and using the obtained ambient temperature as input to the tire wear rate model. 15.The method according to any one of the preceding claims, comprising - obtaining (S1) wheel speed properties indicative of wheel speed of the wheel (2): - obtaining (S2) vehicle speed properties indicative of corresponding speed of the vehicle (1 ); and wherein the calculating (S5) comprises calculating the longitudinal wheel slip values based on the wheel speed properties and the corresponding vehicle speed properties. 16.The method according to claim 15, wherein the obtaining (S1) of wheel speed properties comprises obtaining wheel speed properties indicative of a predicted wheel speed of the wheel (2) along a route on a road ahead; and wherein the obtaining (S2) of vehicle speed properties comprises obtaining vehicle speed properties indicative of corresponding vehicle speed on a route on a road ahead; and wherein the calculating (S5) comprises calculating future longitudinal wheel slip values based on the wheel speed properties and the corresponding vehicle speed properties. 17. A control arrangement (4) for determining momentary tire wear rate of a wheel (2) of a vehicle (1), wherein the control arrangement (4) is configured to execute the method according to any one of the preceding claims. 18. A vehicle (1) comprising - a control arrangement (4) according to claim 17, and - a wheel speed sensor (5a) configured to sense a speed indicative of the speed of a drive wheel (2). 19.A computer program comprising instructions, which, when the program is executed by a control arrangement (4), cause the control arrangement (4) to carry out the method according to any one of the claims 1 to 20.A computer-readable medium having stored thereon the computer program of claim 19.