Estimation of tire tread wear

Abstract

A method, an apparatus, and a computer program product are provided for estimating tread wear of a tire on a wheel of a vehicle. The tread wear indicates a difference between a starting tread depth and a current tread depth. The method includes obtaining a first angular velocity sensor signal indicative of an angular velocity of at least one first wheel or axle of the vehicle and a second angular velocity sensor signal indicative of an angular velocity of at least one second wheel or axle of the vehicle, respectively. The method further includes determining a tread wear difference based on the obtained angular velocity sensor signal, the tread wear difference indicating a tread wear difference between a tire at the first wheel or axle and a tire at the second wheel or axle. The method further includes estimating a first tread wear estimate for the first wheel or axle based on the determined tread wear difference and based on the estimated relationship.

Description

Technical Field

[0001] The present invention generally relates to estimating tread wear of tires on vehicle wheels. Background Art

[0002] In order to improve driving comfort and safety, the vast majority of vehicles use pneumatic rubber tires. The contact area of ​​the tire with the ground is not flat or planar, but has a tread pattern. The tread pattern is used to provide reliable grip on different surfaces and reduce the risk of harmful actions such as skidding.

[0003] The reliability of the tread function depends on the depth of the tread of the tire. During the service life of the tire, the tread wears more and more. Due to the importance of the tread for safety, there are requirements (e.g. legal requirements) to maintain it above a certain level. The tire must be replaced before the tread is completely worn out.

[0004] Therefore, there is a need for devices and methods for monitoring tread depth. Currently, many systems rely on manual or visual inspection, which is usually performed by the driver or operator of the vehicle. Such methods are prone to error because they rely on the driver to remember to check the tread regularly and rely on the subjective impression of the sometimes inexperienced operator.

[0005] Therefore, an apparatus and method that automatically provides objective information about tire tread depth may improve safety and may support maintenance planning. Summary of the invention

[0006] The invention discloses a method, an apparatus and a computer program product. In order to solve the above-mentioned type of disadvantages, the invention provides a method, an apparatus and a computer program product according to the independent claims. The dependent claims list preferred embodiments.

[0007] In a first aspect, a method for estimating tread wear of a tire on a vehicle wheel is provided. The tread wear indicates a difference between a starting tread depth and a current tread depth. The method comprises the steps of obtaining a first angular velocity sensor signal indicative of an angular velocity of at least one first wheel or a first axle of the vehicle, and obtaining a second angular velocity sensor signal indicative of an angular velocity of at least one second wheel or a second axle of the vehicle.

[0008] The method further includes the step of determining a tread wear difference value based on the obtained first angular velocity sensor signal and the second angular velocity sensor signal, the tread wear difference value indicating a difference in tread wear between a tire at a first wheel or axle and a tire at a second wheel or axle. The method further includes the step of estimating a first tread wear estimate value for the first wheel or axle based on the determined tread wear difference value and based on the estimated relationship.

[0009] In some embodiments, the determination may be based on a comparison of the first angular velocity sensor signal and the second angular velocity sensor signal, which signals are optionally corrected for slip of the drive wheel or drive shaft.

[0010] In particular, the determination may be based on a formula corresponding to:

[0011]

[0012] Wherein, d1 represents the tread depth of the first tire, d2 represents the tread depth of the second tire, ω1 represents the first angular velocity, ω2 represents the second angular velocity, R represents the default rolling radius, and K represents the proportional constant.

[0013] In some implementations, the estimated relationship may be a linear relationship.

[0014] For example, the estimation may be based on a relationship corresponding to:

[0015]

[0016] Wherein, d1 represents the tread depth of the first tire, d2 represents the tread depth of the second tire, and C represents a linear constant different from 1.

[0017] In some embodiments, the estimated relationship may be based on one or more of: expected or actual vehicle load, expected or actual vehicle type, driving type. Additionally or alternatively, the estimated relationship may be based on expected or actual vehicle acceleration.

[0018] In some embodiments, the determining and / or estimating may not require the use of a speed signal indicating an absolute speed of the vehicle. Additionally or alternatively, the determining and / or estimating may not require the use of a position signal indicating a position of the vehicle. Furthermore, the determining and / or estimating may not require determining an absolute rolling radius.

[0019] In some embodiments, the estimating may further comprise the step of estimating a second treadwear estimate for a second wheel or axle based on the determined treadwear difference and based on the estimated relationship.

[0020] In some embodiments, the at least one first wheel may be or include a wheel on a driven axle of the vehicle. Additionally or alternatively, the at least one second wheel may be or include a wheel on a non-driven axle of the vehicle.

[0021] Thus, the teachings of the present invention may be applied to a comparison of a driven drive axle (or all drive wheels) to a non-driven axle (or all non-driven wheels). Alternatively, the present invention may be applied to a comparison of one drive wheel to one non-driven wheel. In other alternatives, the above methods may be combined, for example, by comparing one drive wheel to multiple (or all) non-driven wheels.

[0022] For example, the vehicle may be a (primarily) rear wheel drive vehicle or a front wheel drive vehicle.

[0023] In some embodiments, the method may further comprise the step of outputting a tread wear alert in response to the estimating.

[0024] In some embodiments, the estimation may include statistical regression analysis (including recursive estimation such as a Kalman filter), or batch analysis (such as a least squares fit of the relationship between the measured signals).

[0025] In some embodiments, the method may further include the step of adjusting the estimated treadwear estimate based on expected tire growth.

[0026] For example, the adjustment may be based on a growth model. Examples of growth models may include: a first phase, the first phase lasting a first duration and having a first growth rate; and a second phase, the second phase lasting a second duration and having a second growth rate, wherein the second growth rate is less than the first growth rate and / or approaches zero growth.

[0027] In particular, the growth model may be based on one or more of: distance driven; age of the tire; forces exerted on the tire.

[0028] In a second aspect, a computer program product is provided, comprising program code configured to, when executed in a computing device, perform the steps of the method according to the first aspect.

[0029] In a third aspect, there is provided an apparatus for estimating tread wear of a tyre on a vehicle wheel. The apparatus comprises a processing portion configured to perform the steps of the method according to the first aspect.

[0030] In a fourth aspect, a system is provided having the apparatus according to the third aspect and at least two angular velocity sensors configured to provide angular velocity sensor signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The following detailed description refers to the accompanying drawings, in which:

[0032] Figure 1 A flow chart of a method according to an embodiment is schematically shown.

[0033] Figure 2A A top view of a vehicle according to an embodiment is shown.

[0034] Figure 2B A side view of a vehicle according to this embodiment is shown.

[0035] Figure 3 A wheel with a tire with worn tread is shown.

[0036] Figure 4 A graph showing tread depth versus distance traveled is shown.

[0037] Figure 5 A graph of experimental data showing the relationship between front axle tread wear and rear axle tread wear.

[0038] Figure 6 A diagram showing a model according to an embodiment.

[0039] Figure 7 An apparatus according to an embodiment is shown. DETAILED DESCRIPTION

[0040] Figure 1 A flow chart of a method 10 according to an embodiment is schematically shown.

[0041] Method 10 is used to estimate tread wear of tires on vehicle wheels. Tread wear indicates the difference between a starting tread depth and a current tread depth. Method 10 includes step 12 and step 14, step 12 obtains a first angular velocity sensor signal indicating an angular velocity of at least one first wheel or a first axle of the vehicle, and step 14 obtains a second angular velocity sensor signal indicating an angular velocity of at least one second wheel or a second axle of the vehicle. Non-limiting examples of angular velocity sensors include gear-type sensors, such as those used in ABS (anti-lock braking systems), which provide a quasi-continuous angular velocity data stream. Such angular velocity sensors are configured to provide an angular velocity signal (e.g., in revolutions per second).

[0042] More specifically, the at least one first wheel may be or include a wheel at a drive shaft of the vehicle, and the at least one second wheel may be or include a wheel at a non-drive shaft of the vehicle. For example, the vehicle may be a (primarily) rear-wheel drive vehicle or a (primarily) front-wheel drive vehicle.

[0043] Figure 2A A top view of a vehicle 20 according to an embodiment is shown. The vehicle 20 has a front axle 24 with a left front wheel 22 and a right front wheel 23. The vehicle 20 also has a rear axle 28 with a left rear wheel 26 and a right rear wheel 27.

[0044] The example shown is a front-wheel drive vehicle, in which the front axle 24 is the drive axle. However, the invention is also applicable to rear-wheel drive vehicles, or even to four-wheel drive vehicles with variable drive (e.g., one axle is mainly driven and the other axle is only driven briefly under acceleration or low grip conditions). In the following, a description is given of the situation in which a first wheel / axle is driven and a second wheel / axle is not driven (or at least not always driven).

[0045] In some embodiments of the present invention, the difference in tread wear between the front axle and the rear axle can be determined. In this example, the front axle (both front wheels 22 and 23) can be used to complete Figure 1 Step 12 in order to obtain the first angular velocity. The rear axle (both rear wheels 26 and 27) can be used to complete Figure 1 Step 14 in , to obtain the second angular velocity. For example, to obtain the axle angular velocity, the average or effective angular velocity can be calculated based on the corresponding wheel angular velocities of the axle. Alternatively, the axle angular velocity can be measured directly at the axle.

[0046] In other examples of the present invention, the tread wear difference between only one front wheel (e.g., the left front wheel 22) and only one rear wheel (e.g., the left rear wheel 26) may be determined. In such an example, the angular velocity signal from one front wheel (the left front wheel 22) is used as the first angular velocity ( Figure 1 In step 12), the angular velocity signal from one rear wheel (the left rear wheel 26) is used as the second angular velocity ( Figure 1 Step 14 in ). For example, Figure 2B A side view of a vehicle according to this embodiment is shown, wherein the front wheel 22 is equipped with a front wheel speed sensor 74 and the rear wheel 26 is equipped with a rear wheel speed sensor 76. Both wheel speed sensors provide their signals to a central processing unit 70 (which may be in the vehicle or elsewhere), as will be referred to below. Figure 7 As explained in further detail.

[0047] return Figure 1 , method 10 also includes step 16: determining a tread wear difference based on the obtained first angular velocity sensor signal and the second angular velocity sensor signal, the tread wear difference indicating a tread wear difference between a tire at a first wheel or a first axle and a tire at a second wheel or a second axle.

[0048] The determination 16 takes as input the first angular velocity sensor signal and the second angular velocity sensor signal and uses these signals in a calculation to determine the tread wear difference.Alternatively, the velocity signal may have been corrected for slip of the drive wheel or drive shaft.

[0049] More specifically, using the first angular velocity ω1 and the second angular velocity ω2, the determination 16 may be based on the following formula:

[0050]

[0051] Alternatively, an equivalent formula may be used. In the above formula, d1 represents the tire tread depth of the first wheel or axle, and d2 represents the tire tread depth of the second wheel or axle, so (d2-d1) is the tread wear difference. R represents the default rolling radius and K represents the proportionality constant.

[0052] As described above, at the first angular velocity and the first axle (eg Figure 2A The second angular velocity is related to the front axle 24, and the second angular velocity is related to the second axle (eg, Figure 2A In an embodiment related to the rear axle 28), the tire tread depth and tread wear difference can be calculated on an axle-based level.

[0053] In other embodiments, whether the first angular velocity is related to the first wheel (eg Figure 2B 22), whether the second angular velocity is related to the second wheel (eg, Figure 2B The tire tread depth and tread wear difference can be calculated on a wheel-based level.

[0054] return Figure 1 The method 10 further comprises a step 18 of estimating a first tread wear estimate value for the first wheel or axle based on the determined tread wear difference value and based on the estimated relationship.

[0055] In particular, the estimated relationship to be used may preferably be a linear relationship. For example, the estimate 18 may be based on the following relationship:

[0056]

[0057] Wherein, d1 represents the tread depth of the first tire, d2 represents the tread depth of the second tire, and C represents a linear constant. The inventors have recognized that the wear on the first wheel or axle (e.g., the drive wheel or drive axle) is roughly proportional to the wear on the second wheel or axle (e.g., the non-drive wheel or non-drive axle). The linear constant C is a proportional factor between the two values. In some embodiments, the linear relationship may also include an offset.

[0058] The linear constant is different from 1 because the wear on the first wheel / axle and the second wheel / axle is not the same. Instead, they present a tread wear difference. When the linear constant is 1, no tread wear difference is observed and the tread wear difference cannot be used to infer the actual first tread wear estimate / second tread wear estimate.

[0059] Estimation 18 may use statistical regression analysis (including recursive estimation such as a Kalman filter) or batch analysis (such as a least squares fit of the relationship between the measured signals) to relate the estimated relationship to the actual tread depth.

[0060] The above estimated relationships (and values ​​of linear constants) may be (pre)determined based on characteristics such as (expected or actual) vehicle load, (expected or actual) vehicle type, driving type. For example, vehicle load and / or vehicle type may affect the weight distribution between wheels / axles and thus the wear. For example, if the weight is mainly distributed on the drive shaft, the wear on the drive shaft will be more pronounced. Similarly, an active or sporty drive type will wear the drive shaft / drive wheels faster than, for example, a comfort drive type.

[0061] Additionally or alternatively, the estimated relationship may be based on (expected or actual) vehicle acceleration.Cumulative or average vehicle acceleration allows inference of how "dynamic" the driving behavior is, and whether the amount of acceleration will increase wear on a particular axle / wheel.

[0062] More generally, by monitoring and accumulating the forces (acceleration, load, etc.) on the tire, a more reliable estimate of the tread wear rate can be obtained. In the context of the present invention, such accumulated measurements can be used to continuously adjust the estimated relationship. To this end, the method according to the present invention can also take into account acceleration data provided by the vehicle's (lateral and / or longitudinal) acceleration sensors, engine drive torque data provided by the electronic control unit, pressure data provided by the (hydraulic) braking system, and / or load data provided by the vehicle's axle height sensor. One or more of these data sources can be accumulated (with corresponding linear factors) to obtain a more reliable estimate of the estimated relationship. Therefore, the estimated relationship does not need to be static, but can evolve according to the actual forces experienced by the tire.

[0063] As can be seen from the above examples, the relationship (and / or the value of the constant) used in the estimation step 18 can be predetermined over the life of the vehicle based on known or expected characteristics. In other examples, the relationship can be (pre)determined and dynamically adjusted during vehicle operation based on actual measured characteristics.

[0064] In some embodiments, the determining step 16 and / or estimating step 18 may not require the use of a speed signal indicating the absolute speed of the vehicle. Additionally or alternatively, the determining and / or estimating may not require the use of a position signal indicating the position of the vehicle. This allows the present teachings to be implemented even in vehicles with limited sensor capabilities (or areas with low GPS accuracy), or as an accuracy enhancement supplement to other methods using absolute speed. In addition, the determining and / or estimating may not require the determination of an absolute rolling radius. This allows for a reduction in the processing required for the implementation process.

[0065] In the example shown, the estimation step 18 is intended to estimate the tread of a first wheel or axle (e.g., a driven wheel or axle). Optionally, the estimation step 18 may also include estimating a second tread wear estimate for a second wheel or axle, i.e., another (e.g., non-driven) axle. The estimate may also be based on the determined tread wear difference and the estimated relationship.

[0066] Thus, the teachings of the present invention may be applied to a comparison of a driven axle (or all driven wheels) to a non-driven axle (or all non-driven wheels). Alternatively, the teachings of the present invention may be applied to a comparison of one driven wheel to one non-driven wheel. In other alternatives, the above methods may be combined, for example, by comparing one driven wheel to multiple (or all) non-driven wheels.

[0067] Back to Figure 1 , method 10 may optionally include a further step (not shown) of outputting a tread wear alert in response to the estimation. For example, such a tread wear alert may be output when the first (and / or second) tread wear estimate exceeds a predetermined threshold. Such a threshold may be expressed as an absolute value or a relative value. An example of an absolute tread wear value may be any value exceeding 2 mm, more preferably exceeding 5 mm. An example of a relative tread wear value may be any value exceeding 50%, more preferably exceeding 70%, of the starting tread depth.

[0068] Figure 3 A wheel 22 is shown with a tire having tread wear. Wheel 22 has a center 22m and a default rolling radius 22r. The tread wear of wheel 22 is shown with reference to inset portion 22z. As can be seen from inset portion 22z, the starting tread depth is indicated by reference numeral 22s, while the current tread depth is indicated by reference numeral 22c. The current tread depth 22c is closer to the center of wheel 22 than the starting tread depth 22s. The difference between the starting tread depth 22s and the current tread depth 22c is indicated by two arrows and is referred to as tread wear in this disclosure.

[0069] Figure 4 A schematic diagram showing the variation of tread depth with distance traveled is shown. For illustration purposes, Figure 4 Wear is shown for a front wheel drive vehicle as it may experience variation with distance driven. Figure 4 The evolution of the tread depth of the rear axle and the front axle is schematically shown. In this example, the front axle is the driven axle and the rear axle is the non-driven axle. Figure 4 As can be seen, the non-driven (rear) axle wears slower than the driven (front) axle. The rear axle wear increases more slowly than the front axle wear. Relative wear is defined as the difference between the front axle wear and the rear axle wear. Figure 4It has also been demonstrated that rear axle wear is proportional to front axle wear. In other words, by knowing the proportionality factor between rear axle wear and front axle wear and knowing the relative amounts of wear, the absolute front axle wear (and rear axle wear) can be inferred.

[0070] Figure 5 Graph 50 of experimental data showing the relationship between front axle tread wear and rear axle tread wear.

[0071] Figure 5 It is confirmed that all data points roughly follow a linear trend that reflects the correlation of the wear of the front axle with the wear of the rear axle. For example, by regression analysis, a proportionality constant that correlates the wear of the front axle with the wear of the rear axle can be determined. It can also be seen that the proportionality constant is different from 1. In the example shown, the front axle wears faster than the rear axle because the front axle is the (main) drive axle. The proportionality constant 1 corresponds to the dotted line (no tread wear difference). After determining the proportionality constant (different from 1), the absolute wear of the (front and / or rear) axle can be inferred based on the tread wear difference. In the example shown, the value of the proportionality constant is about 2.1, which means that the front axle wears about twice as fast as the rear axle. A typical proportionality constant (in the case of a vehicle in which the axle corresponding to the y-axis is the main drive axle) can be in the range of 1.1 to 10, more preferably between 1.5 and 2. In the case of a vehicle in which the axle corresponding to the x-axis is the main drive axle, a typical proportionality constant will correspond to the reciprocal of the above values ​​given.

[0072] In the example shown, the linear trend of the correlation of the front axle wear to the rear axle wear passes through the origin, which means that no offset needs to be considered. In other examples, the linear trend may include a (small) offset.

[0073] In other examples (not shown), the data points may lie below the dashed line, which means that the rear axle is wearing faster than the front axle. This may be the case in a (primarily) rear wheel drive vehicle.

[0074] Figure 6 Graph 60 illustrates a tire growth model that may be used to adjust tread wear estimates based on expected tire growth, according to an embodiment.

[0075] The growth model describes the change of tire expansion over time or travel distance. In the example shown, the growth model includes a first phase and a second phase, the first phase lasts for a first duration / a first distance traveled and has a first growth rate, and the second phase lasts for a second duration / a second distance traveled and has a second growth rate. Figure 6 In , the first stage is labeled "initial", and in Figure 6The second stage is marked as "continuous" in FIG. The second growth rate is less than the first growth rate. More specifically, the second growth rate approaches zero growth. The tire growth model can be predetermined or can be adjusted based on parameters such as driving distance, tire age, and forces applied to the tire. Adjustment of the tire model can be achieved by adjusting the (first and / or second) duration or adjusting the (first, second) growth rate.

[0076] Typical values ​​for the first distance may be in the range of 100km to 1000km, more preferably in the range of 500km to 1000km. Typical values ​​for the second distance may be in the range of 10000km to 50000km, more preferably in the range of 25000km to 50000km.

[0077] Typical values ​​for the first rate may be in the range of 0.1% to 1% per 100 km. Typical values ​​for the second rate may be in the range of 0.01% to 0.2% per 10 000 km.

[0078] In addition to modeling tire growth as a function of distance, it may also be modeled as a function of time or as a function of the cumulative forces (eg, acceleration, load, etc.) exerted on the tire, as described above.

[0079] Figure 7 An apparatus 70 according to an embodiment is shown. The apparatus 70 comprises a processing part 72, which is configured to execute the method according to the invention (e.g. Figure 1 The method of 10).

[0080] Figure 7 Further depicted is a first wheel speed sensor 74 , which may be assigned to a first wheel or axle. Figure 7 Also depicted is a second wheel speed sensor 76, which may be attributed to a second wheel / axle. In another aspect of the invention, the device 70, the wheel speed sensor 74 and the wheel speed sensor 76 may form a system for estimating tread wear.

Claims

1. A method for estimating tread wear of a tire on a wheel of a vehicle (10), the tread wear indicating a difference between a starting tread depth and a current tread depth, the method comprising the steps of: - obtaining a first angular velocity sensor signal, the first angular velocity sensor signal being indicative of an angular velocity of at least one first wheel or a first axle of the vehicle; - obtaining a second angular velocity sensor signal, the second angular velocity sensor signal being indicative of an angular velocity of at least one second wheel or a second axle of the vehicle; - determining a tread wear difference value based on the obtained first angular velocity sensor signal and the second angular velocity sensor signal, the tread wear difference value indicating a difference in tread wear between a tire at the first wheel or the first axle and a tire at the second wheel or the second axle; - estimating a first treadwear estimate value for said first wheel or said first axle based on the determined treadwear difference value and based on the estimated relationship.

2. The method according to claim 1, wherein: The determination is based on a comparison of the first angular velocity sensor signal and the second angular velocity sensor signal, which signals are optionally corrected for slip of the drive wheel or drive shaft.

3. The method according to claim 1 or 2, wherein: The determination is based on a formula corresponding to: Wherein, d1 represents the tread depth of the first tire, d2 represents the tread depth of the second tire, ω1 represents the first angular velocity, ω2 represents the second angular velocity, R represents the default rolling radius, and K represents the proportional constant.

4. The method according to any one of claims 1 to 3, wherein: The estimated relationship is a linear relationship.

5. The method according to any one of claims 1 to 4, wherein: The estimate is based on the relationship corresponding to: Wherein, d1 represents the tread depth of the first tire, d2 represents the tread depth of the second tire, and C represents a linear constant different from 1.

6. The method according to any one of claims 1 to 5, wherein: The estimated relationship is based on one or more of the following: - expected or actual vehicle load, expected or actual vehicle type, driving type; or - Expected or actual vehicle acceleration.

7. The method according to any one of claims 1 to 6, wherein: The determining and / or the estimating does not require using one or more of the following: - a speed signal indicative of the absolute speed of the vehicle; or - a position signal indicative of the position of said vehicle.

8. The method according to any one of claims 1 to 7, wherein: The estimating further includes estimating a second tread wear estimate for the second wheel or the second axle based on the determined tread wear difference and based on the estimated relationship.

9. The method according to any one of claims 1 to 8, wherein: - said at least one first wheel is or comprises a wheel on a drive axle of said vehicle, and - said at least one second wheel is or comprises a wheel on a non-driven axle of said vehicle.

10. The method according to any one of claims 1 to 9, wherein: The vehicle is a rear-wheel drive vehicle or a front-wheel drive vehicle.

11. The method according to any one of claims 1 to 10, wherein: The method also includes outputting a tread wear alert in response to the estimating.

12. The method according to any one of claims 1 to 11, wherein: The estimation may include statistical regression analysis including recursive estimation such as a Kalman filter or batch analysis such as least squares fitting of the relationship between the measured signals.

13. The method of any one of claims 1 to 12, further comprising adjusting the estimated tread wear estimate based on expected tire growth.

14. The method according to claim 13, wherein: The adjustment is based on a growth model, in particular the following growth model, which includes: a first stage, which lasts for a first duration and has a first growth rate; and a second stage, which lasts for a second duration and has a second growth rate, wherein the second growth rate is less than the first growth rate and / or approaches zero growth.

15. The method according to claim 14, wherein: The growth model is based on one or more of: distance driven; age of the tire; forces exerted on the tire.

16. A computer program product comprising program code configured to, when executed in a computing device, perform the steps of any one of the preceding claims.

17. An apparatus for estimating tread wear of a tyre on a wheel of a vehicle (10), the tread wear indicating a difference between a starting tread depth and a current tread depth, the apparatus comprising a processing portion configured to perform the steps of any one of claims 1 to 14.

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