阅读说明：本技术 用于确定车辆中轮胎-道路摩擦的方法和系统 (Method and system for determining tire-road friction in a vehicle ) 是由 M·约纳松 N·奥尔松 S·姆皮里西蒂 S·罗伊乔杜里 赵敏茗 于 2019-06-12 设计创作，主要内容包括：一种用于基于车队的轮胎-道路摩擦特性来估算车辆的轮胎特性的方法。该方法包括：在多个指定位置处确定(100)属于车队的多个车辆的轮胎-道路摩擦；确定(102)车队在每个指定位置处的基准轮胎-道路摩擦；在车辆(200)中,确定(104)在作为指定位置之一的第一位置(202)处的当前轮胎-道路摩擦；确定(106)当前轮胎-道路摩擦与用于第一位置的车队的基准轮胎-道路摩擦之间的差异；基于所确定的差异估算(108)车辆的轮胎特性。还提供了一种被配置为执行所述方法的系统。(A method for estimating tire characteristics of a vehicle based on tire-road friction characteristics of a fleet of vehicles. The method comprises the following steps: determining (100) tire-road friction of a plurality of vehicles belonging to a fleet of vehicles at a plurality of specified locations; determining (102) a reference tire-road friction for the fleet at each of the designated locations; in a vehicle (200), determining (104) a current tire-road friction at a first location (202) as one of the designated locations; determining (106) a difference between a current tire-road friction and a reference tire-road friction for the fleet of vehicles at the first location; estimating (108) a tire characteristic of the vehicle based on the determined difference. A system configured to perform the method is also provided.)

1. A method of estimating tire performance of a vehicle based on tire-road friction performance of a fleet of vehicles, the method comprising:

determining tire-road friction of a plurality of vehicles belonging to a fleet of vehicles at a plurality of specified locations;

determining a reference tire-road friction for the fleet of vehicles at each of the plurality of designated locations as a weighted average of the friction values determined at the respective designated locations;

determining, in the vehicle, a current tire-road friction at a first location that is one of the plurality of designated locations;

determining a difference between the current tire-road friction and a fleet reference tire-road friction at the first location; and

estimating a tire characteristic of the vehicle based on the determined difference.

2. The method of claim 1, further comprising: providing an indication to a driver to control a tire if the current tire-road friction is more than a predetermined amount below the reference friction.

3. The method of claim 2, further comprising determining: at least a predetermined number of friction determinations are that the current tire-road friction is less than the reference friction by more than a predetermined amount within a predetermined period of time before providing an indication to the driver to control the tire.

4. The method of claim 1, further comprising: providing tire-road friction information to a vehicle control system to modify vehicle behavior based on the current tire-road friction if the current tire-road friction is less than the reference friction by more than a predetermined amount.

5. The method of claim 1, wherein determining tire-road friction of a vehicle further comprises determining a confidence value for the determined tire-road friction, and wherein the weight for determining the reference friction is based on each determined confidence value for tire-road friction.

6. The method of claim 5, wherein the confidence value is based on a quality of an input signal provided to a friction estimator function in a vehicle.

7. The method of claim 5, wherein determining the confidence value comprises evaluating whether temperature and/or weather conditions are considered in determining the tire-road friction.

8. The method of claim 1, wherein a specified location covers a predetermined area, and wherein the road conditions are assumed to be the same within the predetermined area.

9. The method of claim 8, further comprising: modifying the area of the designated location if the average tire-road friction determined for a portion of the area of the designated location differs from the average tire-road friction for the entire area of the designated location by more than a predetermined amount.

10. The method of claim 1, further comprising defining the designated locations by clustering tire-road friction values based on geographic location and friction values to derive regions, such that each designated location is defined by an area exhibiting the same tire-road friction.

11. The method of claim 1, further comprising updating the reference tire-road friction by discarding earlier tire-road friction determinations obtained prior to a predetermined point in time to account for changing road conditions.

12. The method of claim 1, wherein determining a reference tire-road friction comprises excluding tire-road friction determined to be below a predetermined threshold.

13. The method of claim 1, wherein determining tire-road friction of a vehicle at a location comprises determining tire-road friction of each of four tires of the vehicle individually.

14. A system for determining tire characteristics of a vehicle based on tire-road friction characteristics of a fleet of vehicles, the system comprising:

a remote server in communication with each of a plurality of vehicles forming a fleet of vehicles, each vehicle including a tire-road friction determination control unit configured to determine a current tire-road friction when the vehicle is at one of a plurality of designated locations, the remote server configured to receive the determined tire-road friction from the plurality of vehicles and determine a reference tire-road friction for the fleet at each designated location as a weighted average of the friction values determined at the respective designated location; and

a vehicle configured to determine a difference between a current tire-road friction and a reference tire-road friction for the fleet at a first location; and estimating tire performance of the vehicle based on the difference.

15. The system of claim 14, wherein the remote server is further configured to define the designated locations by clustering tire-road friction values based on geographic location and friction values to derive regions, such that each designated location is defined by an area exhibiting the same tire-road friction.

Technical Field

The present invention relates to a method and system for determining tire-road friction of a vehicle. Furthermore, the invention relates to a method for determining the friction properties of a vehicle tyre.

Background

With the development of automotive technology, the active safety of today's automobiles is becoming more and more advanced. For example, most new vehicles are equipped with active safety devices in the form of the well-known ABS braking system, which enable the vehicle driver to perform a more controllable braking action.

In the driving situation of a vehicle, the friction between the road and the tires is very important, since it determines the amount of force that can be transmitted from the vehicle to the ground. Friction is therefore an important parameter of active safety systems when decisions must be taken, for example relating to vehicle braking and steering. This is relevant for both manually driven vehicles and automated vehicles.

In addition, for semi-automatic or fully automatic vehicles, there are additional systems that rely on accurate and reliable friction estimates for proper operation. Such a system may include, for example, a curve processing system.

However, in tire-road friction measurements, the resulting tire-road friction is clearly a result of the tire and road characteristics, and the low friction may be a result of a reduced friction due to a low coefficient of friction of the road or worn tires.

Accordingly, there is a need for further improved methods and systems for determining tire-road friction in a vehicle.

Disclosure of Invention

In view of the above-mentioned and other drawbacks of the prior art, it is an object of the present invention to provide a method for determining tire characteristics in a vehicle using tire-road friction measurements.

According to a first aspect of the present invention, a method for estimating vehicle tire characteristics based on tire-road friction characteristics of a fleet of vehicles is provided. The method comprises the following steps: determining tire-road friction for a plurality of vehicles at a plurality of designated locations; determining a reference tire-road friction for the fleet of vehicles at each of the plurality of designated locations as a weighted average of the friction values determined at the respective designated locations; determining, in the vehicle, a current tire-road friction at a first location that is one of the plurality of designated locations; determining a difference between the current tire-road friction and a fleet reference tire-road friction at the first location; and estimating a tire characteristic of the vehicle based on the determined difference.

It may be assumed that the fleet includes vehicles that are sufficiently similar such that the vehicle tire-road friction determinations within the fleet are similar. The fleet management system may also know the tire type of each vehicle in the fleet and determine a reference friction for a particular tire type to make a comparison between the current tire-road friction and the reference friction for the same tire type.

In a typical tire-road friction determination in a vehicle, the observable friction is estimated and reported, meaning it is the combined friction of the tire and the road surface at the specific location of the friction measurement. Other cars in the fleet may then use the determined friction. In general, one potential assumption is that observable friction is considered to be that of the road. This assumption is based on the assumption that: the properties of the road vary much more than the tires, for example assuming that all cars have the same tires. Therefore, it is a general problem that the friction estimation value does not distinguish between the road and the tire. Thus, a car with an abnormal tire will report an incorrect friction to the fleet management system, e.g., a car with a bad tire will typically report a low friction, which may result in an incorrect low friction warning to other cars in the fleet. A high frequency of false alarms may reduce the trustworthiness of the system, thereby increasing the risk of accidents. Furthermore, when a single car estimates low friction, it is not known whether the tires are bad or the road is slippery. Therefore, when the friction is low, the driver cannot be warned that the tire is bad. If the tires of the vehicle are worn out, the driver needs to be informed that the tires should be replaced, otherwise the risk of accidents is increased.

The invention is therefore based on the recognition that: by comparing the current tire-road friction with the fleet's reference friction, an individual tire friction estimation independent of road characteristics can be achieved, thereby providing an estimate of vehicle tire mass.

The difference between the current tire-road friction and the reference friction can be considered as a direct estimate of the tire mass, where a current tire-road friction below the reference friction indicates that the tire is worse than the average tire in the fleet.

The reference tire-road friction at the specified location is determined as a weighted average of the plurality of determined tire-road friction at the specified location. Thus, the reference friction value can be selectively made more reliable, since the selected friction value, time or position can be given a lower or higher weight.

According to an embodiment of the invention, the method may further comprise: if the current tire-road friction is more than a predetermined amount below the reference friction, an indication is provided to the driver to control the tires. The indication may be provided as a visual or audible indication, or as a combination thereof. The indication may also vary based on the magnitude of the difference, where the intensity of the alarm may increase proportionally with increasing difference.

According to an embodiment of the invention, the method may further comprise determining: at least a predetermined number of friction determinations within a predetermined time period before providing an indication to the driver to control the tires are that the current tire-road friction is below the reference friction by more than a predetermined amount. Thus, a single measurement is not sufficient in order to determine that the tyre needs to be controlled. The bias measurements indicative of low tire friction may be due to several different reasons, such as based on unpredictable road characteristics such as a patch of ice, rain, wet leaves, or any other situation that rapidly affects road conditions. Thereby, a more reliable estimation of the tire performance is achieved.

According to one embodiment of the invention, the method may further comprise providing information of the tire-road friction to a vehicle control system to modify the vehicle behavior in dependence of the current tire-road friction, if the current tire-road friction is below the reference friction by more than a predetermined amount. Thus, the vehicle control system may be alerted to the reduced friction even if the difference does not exceed the predetermined amount. This allows the vehicle control system to modify the behavior of the vehicle based on suspected wear of the tires. This may have the following effect, for example: the vehicle speed through a curved road is reduced compared to the case where the tires exhibit normal friction.

According to one embodiment of the invention, determining the tire-road friction of the vehicle further comprises determining a confidence value for the determined tire-road friction, and wherein the weight for determining the reference friction is based on the confidence value for each determined tire-road friction. The confidence value should be considered as a degree of certainty that the determined friction value corresponds to the true friction value. Thus, a high confidence value indicates that the friction value can be relied upon to accurately reflect true friction, while a low confidence value means that the determined friction may deviate from the actual friction.

According to one embodiment of the invention, the confidence value may be based on the quality of the input signal provided to a friction estimator function (friction estimator function) in the vehicle. The friction estimation in a vehicle is most often performed in the control unit of the vehicle based on signals received from on-board sensors. The sensor signal represents one or more physical parameters required to determine tire-road friction, and the quality of the signal may vary. For example, it may be the case that sensor signals from certain sensor types are less reliable under certain conditions, resulting in a lower confidence in the measured friction values under such conditions. Other factors that may affect the confidence value may be the noise characteristics of the signal and/or the quality of the analog-to-digital conversion of the signal, since it may be assumed that the control unit determining the friction is a digital circuit.

According to one embodiment of the invention, determining the confidence value comprises evaluating whether temperature and/or weather conditions are considered in determining the tire-road friction. If it is known that the vehicle performing the tire-road friction determination takes into account temperature and/or weather conditions, it may be assumed that the friction value is more reliable, and thus has a higher confidence than if the environmental conditions were not taken into account. Additional factors that may affect the confidence of the friction measurements may include: which method is used to determine friction if the vehicle is braking or accelerating during the friction measurement, and if so the amount of vehicle braking/acceleration. In general, the determination of tire-road friction is more reliable when performed using methods that require vehicle braking or acceleration, thereby increasing confidence in the friction value.

According to one embodiment of the invention, the specified location covers a predetermined area, and wherein the road conditions are assumed to be the same within the predetermined area. Thus, it may be assumed that one reference tire-road friction value is valid for the entire area, and the entire area may be considered as one location when determining the reference tire-road friction.

According to an embodiment of the invention, the method may further comprise: the area of the specified location is modified if the average tire-road friction determined for a portion of the area differs from the average tire-road friction for the entire area by more than a predetermined amount. Thus, local changes in road conditions can be addressed by modifying the area defining the specified location, possibly by creating a new specified location defined by a sub-area of the original area. However, the difference must exceed a certain threshold to avoid that the area becomes unreasonably small. The observed difference may also be required to persist for a period of time and/or for an amount of reported current tire-road friction before modifying the original area.

According to one embodiment of the invention, the method may further comprise defining the designated locations by clustering tire-road friction values based on geographic location and friction values to derive regions, such that each designated location is defined by an area exhibiting the same tire-road friction. Thereby, a plurality of designated positions in the region of interest can be automatically generated by the clustering method. The clustering may be performed during an initial training phase or may be performed continuously when the method is used in a fleet of vehicles.

According to one embodiment of the present invention, the method may further comprise updating the reference tire-road friction by discarding an earlier tire-road friction determination obtained before the predetermined point in time, thereby taking into account the changing road condition. Thus, the updated reference friction is maintained based on the recent road conditions when earlier values are discarded. It is also possible to weigh the determination of tire-road friction by a weight that decreases as the friction measurement progresses, thereby gradually reducing the effect of earlier friction values in determining the reference friction. This may cope with changes in road conditions, for example due to changes in weather.

According to one embodiment of the invention, determining the reference tire-road friction may include excluding determined tire-road friction below a predetermined threshold. Thus, the impact from low friction tires is reduced, since the purpose of the reference value is to provide a measure of tire-road friction for a tire that is "normal" without excessive wear or damage. Transient and temporary variations in road conditions can also be excluded from the reference value for a given location by excluding determined tire-road friction values below a predetermined threshold.

According to one embodiment of the invention, determining the tire-road friction of a vehicle at a location comprises determining the tire-road friction of each of the four tires of the vehicle individually. Thus, for example, it is possible to estimate whether one of the tires is excessively worn and wears faster than the other tires. However, it is equally possible to make tire-road friction estimates for only two tires of a vehicle (preferably for the tire that wears the fastest).

According to a second aspect of the present invention, a system for determining vehicle tire characteristics based on tire-road friction characteristics of a fleet of vehicles is provided. The system includes a remote server in communication with each of a plurality of vehicles forming a fleet, each vehicle including a tire-road friction determination control unit configured to determine a current tire-road friction when the vehicle is at one of a plurality of designated locations, the remote server configured to receive the determined tire-road friction from the plurality of vehicles and determine a reference tire-road friction for the fleet at each designated location; and a vehicle configured to determine a difference between a current tire-road friction and a reference tire-road friction for the fleet of vehicles at the first location; and estimating the tire performance of the vehicle based on the difference.

The effects and features of the second aspect of the invention are largely analogous to those described above in connection with the first aspect of the invention.

Other features and advantages of the invention will become apparent when studying the appended claims and the following description. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

Drawings

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing exemplary embodiments of the invention, wherein:

FIG. 1 is a flow chart summarizing the general steps of a method according to one embodiment of the invention;

FIG. 2 schematically illustrates a method according to one embodiment of the invention; and is

Fig. 3 schematically shows a system according to an embodiment of the invention.

Detailed Description

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which presently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout.

Fig. 1 is a flow chart summarizing the general steps of a method according to one embodiment of the invention, and the method will be further described with reference to fig. 2, fig. 2 schematically showing parts of a system according to one embodiment of the invention.

The described method is applicable to a fleet of vehicles, where all vehicles of the fleet are of a similar type with similar tires. The method may be used, for example, by a vehicle manufacturer, a carrier, or any other entity where the characteristics of vehicles in a fleet may be assumed to be well known.

In a first step, tire-road friction of a plurality of vehicles belonging to a fleet of vehicles is determined 100 at a plurality of designated locations. This may be performed during training in which a selected vehicle having known tire characteristics is driven through a range of locations of interest. It is also possible to perform the steps during normal operation of the vehicle. To determine a reliable reference friction, a minimum number of vehicles that determine a certain amount of friction value over a period of time may be required to be confident within the reference friction.

It should also be noted that the location here refers to an area where it can be assumed that the road friction is the same for the entire area. Thus, if different characteristics of two adjacent roads cause different friction, the adjacent roads may belong to different locations. However, the method is equally applicable to embodiments in which the specified location relates to a particular road feature (e.g. a road intersection, a bridge, etc.).

The determined tire-road friction is provided from the vehicle to a central server 204, which central server 204 may be a distributed cloud server or a central server, where the reference tire-road friction of the fleet at each specified location is determined 102. Thus, the reference tire-road friction will statistically reflect the "true" friction, i.e. the weighted tire attributes of the fleet are used as the reference.

Next, in the vehicle 200, the current tire-road friction is determined 104 at a first location 202, which first location 202 is any one of the locations. The vehicle 200 may request the reference friction value for the specified location 202 from the remote server 204, or the vehicle may have received the reference friction value, for example, upon approaching or entering the specified location.

Once the current tire-road friction is determined, a difference between the current tire-road friction and a reference tire-road friction for the fleet of vehicles at the first location is determined 106. Finally, tire characteristics of the vehicle are estimated 108 based on the differences. If the current friction value determined by the vehicle is above the reference friction value by more than a predetermined threshold, it is assumed that the tire is in a better condition than the average tire of the fleet and no further action is taken. However, if the current friction value is below the reference friction value by more than a predetermined threshold, the driver may be warned that the tire needs to be inspected. Thus, the estimated tire characteristics may include an indication of whether the tire is above or below an average tire in the fleet. The estimated tire characteristics may also more specifically provide a measure of the amount of tire wear. More accurate determination of tire performance requires knowledge of such tire characteristics as wear versus tire-road friction deviation from baseline friction. Such information may be gathered from a fleet of vehicles during use of the method to facilitate more specific estimation of tire characteristics.

In one embodiment of the method, the friction of two or more tires is determined independently, in which case the driver may be alerted as to which particular tire needs to be controlled. The determined current friction, which is significantly lower than the reference friction, may also trigger other actions in the vehicle, such as controlling the vehicle to reduce the curve speed in response to reduced tire grip.

In addition, the remote server is also provided with the current vehicle-to-road friction value along with the time required to obtain the friction value and the vehicle geographical coordinates, so that the reference friction value can be updated with the latest friction value. The friction difference may also be reported to the remote server 204, or the friction difference may be determined in the remote server based on the friction reported from the vehicle. Thus, the remote server is also able to monitor the tire characteristics of the vehicle.

Reference friction mu for a given position within a limited period of time_refCan be determined as

Where n is the number of observations, i.e., the number of tire-road friction values determined for a given location, and w_iIs the friction value mu_iTo the corresponding weight of. The weight may in turn be determined as a function w ═ f (confidence) of the confidence of each determined tire-road friction value, wherein the function f should be monotonically increasing, i.e. a higher confidence should always result in a higher weight, and the weight should not be negative. The confidence value is a quality measure of the friction estimate from the friction estimator. Confidence may be expressed in a number between 0 and 1, where 0 represents no confidence and 1 represents full confidence. Confidence may therefore be considered as the likelihood that the friction estimate is equal to the ground truth. For example, may be based on a user identifying the vehicleThe sensor signal of the friction in the vehicle determines the confidence value. If the quality of the sensor signal is low or the sensor providing the signal to the friction estimator in the vehicle has a low confidence, a low confidence in the estimated friction is usually caused. As an example, currently available physics-based models typically rely on several in-vehicle sensor signals as inputs to tire-road friction estimates. Since it is possible to measure the quality of the signal in the vehicle, for example in terms of signal-to-noise ratio (SNR), a signal with a low SNR is more likely to result in a low confidence in the determined friction value.

Another example of a factor that determines or affects the confidence value is whether a physical model is used to describe friction. Such a model may be configured to handle different instances, some of which are more uncertain than others. An uncertain instance is a situation when the effectiveness of the model is low, thus resulting in a lower confidence value when the estimated friction is uncertain. For example, the physical properties of a tire are more easily modeled as low slip, i.e., high friction, meaning that there is a higher uncertainty when there is high slip. High slip typically occurs when the vehicle exhibits high acceleration, while low friction further increases slip, presenting an indeterminate situation. Therefore, if it is known that the vehicle is running in a high slip state, a high uncertainty can be expected, and therefore the confidence should be set low. Other situations where confidence may be low include extreme ambient temperatures, because tire characteristics are very temperature dependent, and temperature dependence is difficult to model and therefore is often ignored. A third example that may be difficult to deal with is excessive variation in tire pressure.

Fig. 3 is a system 300 for determining tire characteristics of a vehicle based on tire-road friction characteristics of a fleet of vehicles in accordance with one embodiment of the present invention. The system includes a remote server 204 in communication with each of a plurality of vehicles forming a fleet. Each vehicle includes a tire-road friction determination control unit 302 configured to determine a current tire-road friction when the vehicle is in one of a plurality of designated locations. The remote server includes a friction estimator 304, the friction estimator 304 configured to receive the determined tire-road friction from the plurality of vehicles and determine a reference tire-road friction for the fleet of vehicles at each designated location.

The system further comprises a vehicle 200, the vehicle 200 comprising a friction determination control unit 302, the friction determination control unit 302 being configured to determine a difference between a current tire-road friction and a reference tire-road friction for the fleet of vehicles at the first location; and estimating the tire performance of the vehicle based on the difference. The control unit may include a microprocessor, microcontroller, programmable digital signal processor, or other programmable device. The control unit may also or alternatively comprise an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device or a digital signal processor. Where the control unit comprises a programmable device such as the microprocessor, microcontroller or programmable digital signal processor described above, the processor may also comprise computer executable code which controls the operation of the programmable device.

The friction determination control unit 302 further comprises a low pass filter 306 which suppresses rapid changes in the determined friction. The vehicle also includes a "check tires" warning system and a "low friction" warning system 310 coupled to an HMI (human machine interface) of the vehicle 200 to provide a warning to the driver. In addition, the vehicle 200 includes a vehicle controller 312 that takes as input a friction estimate for potentially adjusting the behavior of various vehicle systems based on the determined friction.

It should be noted that the described method is equally applicable to autonomous and fully or semi-autonomous vehicles, where a correct estimation of the tyre characteristics is important to be able to control the vehicle in a safe manner.

Although the present invention has been described with reference to specific exemplary embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Moreover, it should be noted that portions of the method and system may be omitted, interchanged, or arranged in various ways that still perform the functions of the present invention.

In addition, variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.