Technical field

The present invention generally relates to estimating tread wear of tires on wheels of a vehicle.

Background of the invention

For purposes of increased driving comfort and safety, the vast majority of vehicles use pneumatic rubber tires. The tires' contact area with the grounds is not flat or planar, but features a tread pattern. The tread pattern serves to provide reliable grip on varying surfaces, and reduce the risk of unwanted behavior such as aquaplaning.

The reliability of the tread pattern’s function depends on the depth of a tire tread pattern. During the lifetime of the tire, tread is increasingly worn down. In light of the tread pattern’s importance for safety, there are requirements (e.g., mandated by law) for it to be kept above a certain level. Tires must be replaced before the tread pattern is fully worn off.

Thus, there is a need for apparatus and method for monitoring tread depth. Currently, many systems rely on a manual or visual inspection which is often left to the vehicle's driver or operator. Such approaches are error-prone as they rely on the driver remembering to check the tread regularly and as they rely on subjective impressions by the sometimes inexperienced operator.

Thus, apparatus and methods automatically providing objective information about the tires' tread depth may increase safety and may support planning of maintenance.

Summary of the invention

Methods, apparatuses and computer program products are disclosed. To address the shortcomings of the type mentioned above, the present invention provides for methods, apparatuses and computer program products according to the independent claims. The dependent claims set out preferred embodiments.

In a first aspect, a method for estimating tread wear of tires on wheels of a vehicle is provided. The tread wear is indicative of the difference between a starting tread depth and a current tread depth. The method comprises a step 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 a step of 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.

The method further comprises a step of determining, based on the obtained first and second angular velocity sensor signals, a tread wear difference value, which is indicative of the difference in tread wear between the tires at the first and second wheels or axles. It further comprises a step of estimating, based on the determined tread wear difference value and based on a estimation relationship, a first tread wear estimate for the first wheel or axle.

In some embodiments, the determining may be based on a comparison of the first and second angular velocity sensor signals, optionally corrected for slip at driven wheels or axles.

In particular, the determining may be based on a formula corresponding to: di) wherein denotes a first tire tread depth, d ₂ denotes a second tire tread depth, denotes a first angular velocity, m ₂ denotes a second angular velocity, R denotes a default rolling radius, and K denotes a proportionality constant.

In some embodiments, the estimation relationship may be a linear relationship.

For instance, the estimating may be based on a relationship corresponding to: wherein denotes a first tire tread depth, d ₂ denotes a second tire tread depth, and C denotes a linearity constant, which is different from 1. In some embodiments, the estimation relationship may be based on one or more of the following: expected or actual vehicle load, expected or actual vehicle type, drive type. Additionally, or alternatively, it may be based on expected or actual vehicle acceleration.

In some embodiments, the determining and/or the estimating may not require using a velocity signal indicative of an absolute speed of the vehicle. Additionally, or alternatively, the determining and/or the estimating may not require using a location signal indicative of a location of the vehicle. Furthermore, the determining and/or the estimating may not require determining an absolute rolling radius.

In some embodiments, the estimating may further comprise a step of estimating, based on the determined tread wear difference value and based on a estimation relationship, a second tread wear estimate for the second wheel or axle.

In some embodiments, the at least one first wheel may be or comprise wheels at a driven axle of the vehicle. Additionally, or alternatively, the at least one second wheel may be or comprise wheels at a non-driven axle of the vehicle.

Hence, the teaching of the present disclosure may be applied to a comparison of a driven axle (or all driven wheels) driven with a non-driven axle (or all non-driven wheels). Alternatively, it may be applied to a comparison of one driven wheel with one non-driven wheel. In other alternatives, the afore-mentioned approaches may be combined, e.g., by comparing one driven wheel to multiple (or all) non-driven wheels.

For instance, the vehicle may be a (predominantly) rear- wheel driven vehicle or a front- wheel driven vehicle.

In some embodiments, the method may further comprise a step of outputting a tread wear alarm in response to the estimating. In some embodiments, the estimating may comprise a statistical regression analysis, including a recursive estimation such as a Kalman filter, or a batch analysis such as a least-squares-fit of a relationship between the measured signals.

In some embodiments, the method may further comprise a step of adjusting the estimated tread wear estimate based on an expected tire growth.

For instance, the adjusting may be based on a growth model. An example of a growth model may have a first phase of a first duration with a first growth rate and a second phase of a second duration with a second growth rate, wherein the second growth rate is smaller than the first growth rate and/or converging to zero growth.

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

In a second aspect, a computer program product is provided, which includes program code configured to, when executed in a computing device, to carry out the steps of a method according to the first aspect.

In a third aspect, an apparatus for estimating tread wear of tires on wheels of a vehicle is provided. The apparatus comprises a processing part configured to carry out the steps of a method according to the first aspect.

In a fourth aspect, a system is provided, with an apparatus according to the third aspect and with at least two angular velocity sensors configured to supply angular velocity sensor signals.

Short description of the drawings

The following detailed description refers to the appended drawings, wherein: Fig. 1 schematically illustrates a flowchart of a method according to an embodiment.

Fig. 2A illustrates a top view of a vehicle according to embodiment.

Fig. 2B illustrates a side view of the vehicle according to the embodiment.

Fig. 3 illustrates a wheel with a tire with tread wear.

Fig. 4 illustrates a graph of tread depth as a function of distance driven.

Fig. 5 shows a graph with experimental data of the relationship between tread wear on a front axle versus tread wear on rear axle.

Fig. 6 shows a graph of a model according to embodiments.

Fig. 7 shows an apparatus according to an embodiment.

Detailed description of embodiments

Fig. 1 schematically illustrates a flowchart of a method 10 according to an embodiment.

The method 10 is for estimating tread wear of tires on wheels of a vehicle. The tread wear is indicative of the difference between a starting tread depth and a current tread depth. Method 10 comprises a step 12 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 a step 14 of 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. Non-limiting examples of the angular velocity sensors include the toothed wheel -type sensors used, for instance, in ABS (anti-lock braking system) and which provide a quasi-continuous stream of angular velocity data. Such angular velocity sensors are configured to provide angular velocity signals (e.g. in units of revolutions per second). More specifically, the at least one first wheel may be or comprise wheels at a driven axle of the vehicle, whereas the at least one second wheel may be or comprise wheels at a non-driven axle of the vehicle. For instance, the vehicle may be a (predominantly) rear- wheel driven vehicle or a (predominantly) front-wheel driven vehicle.

Fig. 2A illustrates a top view of a vehicle 20 according to embodiment. Vehicle 20 has a front axle 24 with a front left wheel 22 and a front right wheel 23. The vehicle 20 further has a rear axle 28 with a left rear wheel 26 and a right rear wheel 27.

The example shown is a front-wheel driven vehicle, wherein the front axle 24 is the driven axle. However, the present disclosure is also applicable to rear-wheel driven vehicles or even to four-wheel-drive vehicles with variable drive (e.g., where one axle is driven predominantly and the other axle is driven only momentarily, e.g., during acceleration or low-grip situations). In the following, a description is given where the first wheel/axle is driven, whereas the second wheel/axle is not (or at least not always) driven.

In some embodiments of the present disclosure, a tread wear difference between the front axle and the rear axle may be determined. In such examples, the front axle (both front wheels 22 and 23) may be used to obtain a first angular velocity step 12 in Fig. 1. The rear axle both rear wheels 26 and 27 may be used to obtain the second angular velocity step 14 in Fig. 1. For instance, to obtain an axle angular velocity, a mean or effective angular velocity may be computed based on the corresponding wheel angular velocities of that axle. Alternatively, an axle angular velocity may be measured at the axle directly.

In other examples of the present disclosure, a tread wear difference between only one front wheel (for instance front left wheel 22) and only one rear wheel (for instance rear left wheel 26) may be determined. In such examples, the angular velocity signal from the one front wheel (left front wheel 22) is used as the first angular velocity (step 12 in Fig. 1) and the angular velocity signal from the one rear wheel (left rear wheel 26) is used as the second angular velocity (step 20 step 14 in Fig. 1). For instance, Fig. 2B illustrates a side view of the vehicle according to the embodiment, wherein front wheel 22 is equipped with a front wheel speed sensor 74 and 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 car or elsewhere), as will be explained in further detail with reference to Fig. 7 further below.

Returning to Fig. 1, method 10 further comprises a step 16 of determining, based on the obtained first and second angular velocity sensor signals, a tread wear difference value, which is indicative of the difference in tread wear between the tires at the first and second wheels or axles.

The determining 16 takes as an input the first and second angular velocity sensor signals, and uses them in a computation to determine a tread wear difference value. Optionally, the velocity signals may have been corrected for slip at driven wheels or axles.

More specifically, using a first angular velocity oq and a second angular velocity m ₂ , the determining 16 may be based on the formula: di)

Alternatively, an equivalent formula may be used. In the formula above, denotes the tire tread depth of the first wheel or axle, whereas and d ₂ denotes the tire tread depth of the second wheel or axle, such that (d ₂ — d- is a tread wear difference value. R denotes a default rolling radius, and K denotes a proportionality constant.

As explained above, in embodiments where the first angular velocity relates to a first axle (for instance front axle 24 of Fig. 2A) and the second angular velocity relates to a second axle (for instance rear axle 28 of Fig. 2A), the tire tread depths and the tread wear difference value may be computed on an axle-wise level.

In other embodiments whether first regular velocity relates to a first wheel (for instance front wheel 22 of Fig. 2B) the second angular velocity relates to a second wheel (for instance rear wheel 26 of Fig. 2B), the tire trip depths and the tread were difference value may be computed on a wheel-wise level. Returning to Fig. 1, method 10 further comprises a step 18 of estimating, based on the determined tread wear difference value and based on a estimation relationship, a first tread wear estimate for the first wheel or axle.

In particular, the estimation relationship to be used may preferably be a linear relationship.

For instance, the estimating 18 can be based on the relationship: cZ-i C ⁼ wherein denotes a first tire tread depth, d ₂ denotes a second tire tread depth, and C denotes a linearity constant. The inventors have recognized that the wear on the first wheel or axle (e.g., on driven wheels or axles) is approximately proportional to the wear on the second wheel or axle (e.g., on non-driven wheels or axles). The linearity constant C is the proportionality factor between both values. In some embodiments, the linear relationship may further include an offset.

The linearity constant is different from 1, as the wear on the first wheel/axle and the second wheel/axle is not identical. Instead, they present a tread wear difference. With a linearity constant of 1, no tread wear difference would be observed and a tread wear difference could not be used to deduce the actual first/second tread wear estimate.

The estimating 18 may use statistical regression analysis (including a recursive estimation such as a Kalman filter), or a batch analysis (such as a least-squares-fit of a relationship between the measured signals) in order to link the estimation relationship and the actual tread depth.

The estimation relationship mentioned above (and the value of the linearity constant) may be (pre)determined based on characteristics such as (expected or actual) vehicle load, (expected or actual) vehicle type, drive type. For instance, vehicle load and/or vehicle type may influence the weight distribution between the wheels/axles and thus have an effect on the wear. For instance, if the weight is distributed predominantly towards the driven axle, then the wear will be more pronounced on the driven axle. Similarly, an active or sportive drive type will incur a faster wear on the driven axle/wheels than for instance a comfortable drive type.

Additionally, or alternatively, the estimation relationship may be based on (expected or actual) vehicle acceleration. Cumulating or averaging the vehicle acceleration allows to infer how “dynamic” the driving behavior is and whether the amount of acceleration increases the wear on a particular axle/wheel.

More generally, by monitoring and cumulating the forces (acceleration, load, etc.) on the tires, a more reliable estimate of the tread wear rate can be obtained. In the context of the present disclosure, such cumulated measurments may be used to continuously adapt the estimation relationship. To this end, the method according to the present disclosure may further take into account acceleration data provided by (lateral and/or longitudinal) acceleration sensors of the vehicle, engine drive torque data provided by the electronic control unit, pressure data provided by the (hydraulic) brake system, and/or load data provided by axle height sensors of the vehicle. One or more of these data sources may be cumulated (with corresponding linearity factors) to obtain a more reliable estimate of the estimation relationship. As such, the estimation relationship does not need to be static, but may evolve depending on the actual forces experienced by the tires.

As can be seen from the above examples, the relationship (and/or the value of the constant) used in the estimating step 18 may be predetermined in the sense of being predefined for the entire lifetime of the vehicle based on the known or expected characteristics. In other examples, it may be (pre)determined and dynamically adjusted based on the actually measured characteristics during the operation of the vehicle.

In some embodiments, the determining step 16 and/or the estimating step 18 may not require using a velocity signal indicative of an absolute speed of the vehicle. Additionally, or alternatively, the determining and/or the estimating may not require using a location signal indicative of a location of the vehicle. This allows for the teaching to be implemented even in vehicles with limited sensor capability (or in areas with low GPS accuracy) or serve as an accuracy-increasing complement to other methods that make use of absolute speed. Furthermore, the determining and/or the estimating may not require determining an absolute rolling radius. This allows to reduce the processing needed for the implementation.

In the example shown, the estimating step 18 is directed towards estimating the tread of the first wheel or axle (e.g., the driven wheel or axle). Optionally, it may further comprise estimating a second tread wear estimate for the second wheel or axle, i.e., the other (e.g., nondriven) axle. This estimating may also be based on the determined tread wear difference value and on the estimation relationship.

Hence, the teaching of the present disclosure may be applied to a comparison of a driven axle (or all driven wheels) with a non-driven axle (or all non-driven wheels). Alternatively, it may be applied to a comparison of one driven wheel with one non-driven wheel. In other alternatives, the afore-mentioned approaches may be combined, e.g., by comparing one driven wheel to multiple (or all) non-driven wheels.

Returning to the description of Fig. 1, method 10 may optionally comprise a further step (not illustrated) of outputting a tread wear alarm in response to the estimating. Such tread wear alarm may be outputted for instance when the first (and/or second) tread wear estimate exceeds a predetermined threshold. Such threshold may be expressed in absolute or relative values. 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

Fig- 3 illustrates wheel 22 with a tire with tread wear. The wheel 22 features a center 22m and a default rolling radius 22r. The tread wear of the wheel 22 is illustrated in reference to the inset portion 22z. As can be seen from inset 22z, a starting tread depth is illustrated with reference numeral 22s whereas the current tread depth is illustrated with reference numeral 22c. The current tread depth 22c is located closer to the center of the wheel 22 than the starting tread depth 22s. The difference between the starting tread depth 22s and the current tread depth 22c is designated by two arrows and is referred to as tread wear throughout the present disclosure. Fig- 4 illustrates a schematic graph of tread depth as a function of distance driven. For illustration purposes, Fig. 4 shows wear for a front- wheel -driven vehicle as it can be experienced as a function of distance driven. It schematically shows the evolution of tread depth for a rear axle and for a front axle. In this example, the front axle is the driven axle and the rear axle is the non-driven axle. As can be seen from Fig. 4, the non-driven (rear) axles wears more slowly than the driven (front) axle. The rear axle wear increases more slowly than the front axle wear. The relative wear is defined as the difference between the front wear and the rear wear. Fig. 4 also confirms that the rear wear is proportional to the front wear. In other words, by knowing the proportionality factor between the rear and front wear and by knowing the amount of relative wear, one can deduce the absolute front wear (and rear wear).

Fig- 5 shows a graph 50 with experimental data of the relationship between tread wear on a front axle versus tread wear on rear axle.

Fig. 5 confirms that all data points follow approximately a linear trend which relates the front axle wear to the rear axle wear. By virtue of, for instance, a regression analysis, the proportionality constant linking the front axle wear and the rear axle wear can be determined. It can also be seen that the proportionality constant is different from 1. In the example shown the front axle wears more rapidly than the rear axle, since it is the (predominantly) driven axle. A proportionality constant of 1 would correspond to the dashed line (no tread wear difference). Having determined the proportionality constant (being different from 1), one can deduce the absolute (front and/or rear) axle wear based on the tread wear difference. In the example shown, the proportionality constant has a value of approximately 2.1, which means that the front axle wears approximately twice as fast as the rear axle. Typical proportionality constants (in the case of a vehicle where the axle corresponding to the y axis is the predominantly driven axle) may be comprised in the range from 1.1 to 10, more preferably between 1.5 and 2 . In the case of a vehicle where the axle corresponding to the x axis is the predominantly driven axle, the typical proportionality constants would correspond to the inverse of the values given above. In the example shown the linear trend relating the front axle wear and rear axle wear passes through the origin, which means that no offset needs to be accounted for. In other examples, the linear trend may include a (small) offset.

In other examples (not shown), the data points may lie below the dashed line, which would mean that the rear axle wear faster than the front axle. This may be the case in (predominantly) rear- wheel -driven vehicles.

Fig- 6 shows a graph 60 of a tire growth model, which may be used for adjusting the tread wear estimate based on an expected tire growth, according to embodiments.

The growth model describes the tire expansion as a function of time or of distance driven. In the example shown, it has a first phase of a first duration/di stance with a first growth rate and a second phase of a second duration/di stance with a second growth rate. The first phase is labelled “initial” in Fig. 6, whereas the second phase is labelled “continuous” in Fig. 6. The second growth rate is smaller than the first growth rate. More specifically, it is converging to zero growth. The tire growth model may be predetermined or it may be adjusted based on parameters such as driven distance; tire age; forces exerted on the tires. The adjusting of the tire model may occur by virtue of adjusting the (first and/or second) durations or adjusting the (first and/or second) growth rates.

Typical values for the first distance may be comprised in the range of 100 to 1.000 km, more preferably of 500 to 1.000 km. Typical values for the second distance may be comprised in the range of 10.000 to 50.000 km, more preferably of 25.000 to 50.000 km.

Typical values for the first rate may be comprised in the range of 0.1 to 1 % per 100 km . Typical values for the second rate may be comprised in the range of 0.01 to 0.2 % per 10.000 km.

Instead of modeling the tire growth as a function of distance, it may also be modelled as a function of time or as a function of the cumulated forces exerted on the tires (e.g., acceleration, load, etc.), as described above. Fig- 7 shows an apparatus 70 according to an embodiment. Apparatus 70 includes a processing part 72, which is configured to perform the steps of a method according to the present disclosure, for instance the method 10 of Fig. 1.

Fig. 7 further depicts a first wheel speed sensor 74, which may be attributed to a first wheel or axle. It further depicts a second wheel speed sensor 76 which may be attributed to a second wheel/axle. In another aspect of the present disclosure the apparatus 70, the wheel speed sensor 74 and the wheel speed sensor 76 may form a system for estimating tread wear.