METHOD, CONTROL DEVICE AND SYSTEM FOR DETERMINING THE TREAD DEPTH OF A TIRE

Description

[0001] The invention relates to a method for determining the tread depth of a tire mounted on a rim of a vehicle, in which its current dynamic rolling radius is continuously determined during usage phases by determining a current rotational speed of the tire from data determined by a first sensor and a current speed of the vehicle from data determined by a second sensor, and on the basis of the determined current rotational speed of the tire and the current speed of the vehicle, the current dynamic rolling radius is determined, wherein at the beginning of a first usage phase a starting value of the dynamic rolling radius is recorded and a current tread depth of the tire is determined from deviations of the current dynamic rolling radius from the starting value.The invention further relates to a control unit and a system for a vehicle for determining the tread depth of a tire mounted on the vehicle.

[0002] In the field of determining the actual tread depth of a tire mounted on a vehicle, the so-called rolling radius-based approach is a very promising method for estimating the current tread depth of a tire without requiring manual measurement. The basic principle of this method is that the dynamic rolling radius of the tire, and thus its number of revolutions per distance traveled, changes when the tread depth decreases due to tire wear. In this case, the dynamic rolling radius decreases for a given tire pressure and load, while the number of tire revolutions per distance traveled, and therefore its speed, increases. For an example, see DE 10 2012 217 901 B3.

[0003] Using a vehicle-mounted GPS receiver, the vehicle speed and, for example, the current rotational speed of the tire are determined using wheel speed sensors. The dynamic rolling radius is calculated from these values. By comparing a starting value of the dynamic rolling radius at the beginning of the first usage phase with the currently determined dynamic rolling radius, the current tread depth of the tire can be calculated from its decrease over time. Mathematical methods are used to try to keep the determined values ​​stable and to eliminate any inevitable disturbances and fluctuations in the data from the first and second sensors.

[0004] However, the problem arises that if a tire is not used for an extended period, i.e., during a period of disuse, the last calculated value of the dynamic rolling radius is stored and then used to calculate or determine the current tread depth when the tire is used again. This is particularly problematic for tires that remain mounted on the rims as complete wheel sets and, for example, as a set of summer or winter tires, only have a usage period of several months followed by a period of disuse of several months. This is because the tire's physical dimensions change due to unavoidable creep or aging effects of the rubber material or other tire components.In particular, if a tire is stored as a complete wheel under pressure at the intended tire pressure during a period of non-use, such a tire tends to increase in diameter, which also changes the dynamic rolling radius and can distort the determination of the current tread depth in a subsequent period of use of the tire.

[0005] The object of the invention is therefore to provide a method, a control unit and a system for determining the tread depth of a tire profile, which takes into account the non-use or storage of the tire when determining the tread depth.

[0006] To solve the problem posed, a method according to the features of claim 1 is proposed according to the invention.

[0007] Advantageous embodiments and further developments of the method according to the invention are the subject of the dependent claims.

[0008] A control unit for solving the stated problem is the subject of claim 9 and a system is the subject of claim 10.

[0009] According to the invention, it is provided that an additional current movement status of the tire is determined from data acquired by a third sensor, by determining a usage phase as the movement status when data acquired above a predetermined limit value is present, and a non-use phase as the movement status when data acquired below a predetermined limit value is present over a predetermined period of time, and when the movement status changes from a non-use phase to a subsequent usage phase, a new starting value of the dynamic rolling radius is recorded, which is then compared with the subsequently determined current dynamic rolling radii to continuously determine the current tread depth, replacing the previous starting value.

[0010] In other words, when a period of non-use is detected lasting a predetermined time, a movement status is generated. Upon resumption of use, this status first establishes a new starting value for the dynamic rolling radius. This value is then replaced with the starting value established during the previous period of use and compared to the current dynamic rolling radii and the resulting current tread depth. In this way, dimensional changes of the tire during periods of non-use are automatically taken into account, as they are incorporated into the newly determined starting value.

[0011] Here and in the following, the dynamic rolling radius is understood to be the rolling radius that a rigid wheel has in order to have the same rolling circumference at a given speed as the actual tire at that speed. The rolling circumference is the distance that a wheel travels without slippage in one revolution.

[0012] To determine the tire's movement status, an acceleration sensor is used as a third sensor according to one proposal of the invention. This sensor provides data on the tire's radial or tangential acceleration or the corresponding change in acceleration. A magnetic sensor can also be used as a third sensor.

[0013] The threshold value of the acceleration determined by the third sensor, which triggers the generation of a non-use phase as a movement status if present for a predetermined period, is an acceleration value that is atypically low for tire use on the vehicle or is equal to zero.

[0014] The predetermined time period after which the non-use phase is generated as a movement status when the limit value is consistently undershot can be freely chosen by a specialist, as long as it is suitable for indicating, for example, the change from summer to winter tires and the associated non-use phase by storing the other set of tires. For example, the time period can be set to at least 14 days, at least 30 days, or similar.

[0015] The first sensor for determining the current rotational speed of the tire can, for example, be a speed sensor installed on the vehicle, such as those used by common driver assistance systems like ABS or ESP. This allows the rotational speed of the tire to be determined simply and reliably.

[0016] Determining the current rotational speed of the tire typically involves determining the current angular velocity of the tire.

[0017] According to one aspect of the invention, a third sensor for determining the current movement status is a tire pressure monitoring system (TPMS) sensor associated with the tire. Such sensors are typically capable of measuring tire pressure and temperature and are also typically equipped with an accelerometer to determine whether the tire or complete wheel is in use and whether a signal should be sent to a corresponding vehicle receiver. Such signal transmission usually only occurs when the vehicle is in use to limit energy consumption, although the sensors also measure pressure, temperature, and acceleration when the vehicle is stationary, but do not transmit this data to the vehicle receiver.Typically, a TPMS sensor switches to a parked state when it detects a constant and low radial acceleration of less than 3g for a minimum duration, for example, 15 minutes. Then, pressure, temperature, and acceleration are measured only periodically, for example, every 16 seconds, an average value is calculated, and this average is stored. If, over several measurements within the predetermined period, the sensor determines that these values ​​are characteristic of extended storage, for example, due to seasonal storage, a non-use phase can be generated as a movement status. This status is then transmitted to the vehicle's receiver as soon as the TPMS sensor detects renewed use of the vehicle.a new current radial acceleration is determined, indicating a change from the non-use phase to a subsequent renewed use phase and causing a corresponding change in the movement status of the tire.

[0018] According to a proposal of the invention, when a non-use phase of the tire is detected, a corresponding signal value can be set or generated, which can subsequently be sent to the vehicle-side receiving device and indicates the change from a non-use phase to a use phase.

[0019] For example, once the TPMS sensor detects a new driving cycle or usage phase—that is, a radial acceleration higher than the predefined limit—it can periodically transmit the information generated during storage, particularly the average pressure, temperature, acceleration, and signal value, to the vehicle's receiver during the first few minutes after the new driving cycle begins, for example, for 10 minutes. The transmission of the signal value triggers the recording of a new starting value for the dynamic roll radius, which replaces the previous starting value and is compared with subsequently determined current dynamic roll radii to continuously determine the current tread depth.Thus, after the resumption of use, a new learning cycle is initiated to determine the new tire geometry and adjust the parameters used to calculate the current tread depth. The generated signal value is then deleted. Alternatively, instead of setting a signal value, a new starting value could be recorded and used immediately in place of the previous one by measuring the duration of the non-use phase and exceeding a predetermined time period of, for example, 14 or 30 days.

[0020] In this way, dimensional changes that occur during the tire's non-use phase over the predetermined period are automatically taken into account in the subsequent determination of the current tread depth during the use phase.

[0021] It is understood that the re-recording of a start value and the replacement of the previously used start value with this newly recorded start value can be repeated as often as desired within the framework of the inventive method following a longer storage period, which has resulted in the generation of the movement status as a non-use phase.

[0022] In a further embodiment of the invention, the TPMS sensor can manage a counter for extended storage periods, which is incrementally increased after each extended storage period. This information can cover cases of infrequent tire use, where the tire in question might be mounted on different vehicles over time, with alternating periods of use and non-use, and thus potentially experience several extended periods of non-use without the ability to transmit the information to each vehicle.

[0023] Without such a counter for longer periods of non-use, a first vehicle would be informed about a period of non-use, while a second vehicle subsequently equipped with this tire would not be able to detect such a "previous" period of non-use.

[0024] By incorporating a counter, the vehicle in question can decide to trigger the recording of a new starting value by comparing the current value of the counter for the non-use phases reported by the TPMS sensor with the last value known to the vehicle in question.

[0025] According to one aspect of the invention, the dynamic rolling radius is determined using data on the current speed of a vehicle, which is acquired by a second sensor selected from the group comprising a satellite-based sensor, i.e., a GPS sensor, a radar sensor, a lidar sensor, an ultrasonic sensor, and an optical camera, all of which enable a precise determination of the actual vehicle speed over the ground. Any other sensor that provides the speed independently of the wheel rotation is also suitable as a second sensor within the meaning of the invention.

[0026] According to a further proposal of the invention, correction factors can also be taken into account to increase the accuracy of determining the current tread depth, taking into account, for example, the tire dimensions, tire pressure, tire type, temperature, tire load and / or tire age.

[0027] Furthermore, according to another proposal, the horizontal or vertical orientation of the tire during storage can also be determined when assessing a non-use phase, particularly via the accelerometer included in the measurement, since this storage orientation influences the change in the tire's geometric properties during non-use. For example, it is known that when a tire is stored vertically under load, flat spots can form on the tire's circumference, resulting in a reduction of the rolling circumference. This can then be taken into account within the scope of the invention by means of appropriate correction factors.

[0028] The current tire tread depth, determined as described above, can be transmitted to the vehicle's electronics to calculate service requirements and / or displayed in the vehicle to inform the user when the minimum tread depth has been reached and the tires need replacing. Furthermore, the measured tread depth can be provided to the vehicle's dynamic control systems to influence their parameters. The measured tread depth can also be transmitted to a remote control station as part of a telemetry application to monitor the tread depth and tire condition from a distance, which is advantageous for fleet management, car-sharing providers, and similar applications.

[0029] The invention also relates to a control unit for a vehicle for determining the tread depth of a tire mounted on the vehicle. The control unit has at least one receiver for receiving the current rotational speed of the tire and the current speed of the vehicle.Furthermore, it has a determination device for determining a dynamic rolling radius of the tire based on the determined current rotational speed of the tire and the current speed of the vehicle compared to a definable starting value, wherein the receiving device is designed to receive a movement status encompassing usage and non-use phases, and the determination device can be controlled by the receiving device when the movement status changes from a non-use phase to a usage phase in such a way that a new starting value of the dynamic rolling radius can be defined and used instead of the previous starting value to determine the tread depth.

[0030] The control unit can be designed as a standalone control unit for the vehicle or be part of another control unit, for example a control unit for the TPMS sensors of a tire pressure monitoring system, an anti-lock braking system and / or a vehicle dynamics control system.

[0031] The invention further relates to a system for a vehicle for determining the tread depth of a tire mounted on a rim of the vehicle. The system comprises a control unit according to the aforementioned embodiment, wherein the movement status can be generated by a sensor of a tire pressure monitoring system associated with the tire.

[0032] One embodiment of the invention is explained in more detail below with reference to the accompanying figures.

[0033] Figure 1 shows a schematic side view of a tire attached or mounted on a vehicle not shown here.

[0034] Figure 2shows a diagram in which the course of the dynamic rolling radius of a tire is recorded over its service life.

[0035] In the schematic representation according to Figure 1A tire 2 is shown, mounted on a rim 1 and attached together with the rim as a complete wheel to a motor vehicle (not shown). The tire 2 rolls along the surface U with its outer circumference. The original radius r0 of the tire 2 is shown with dashed lines, and the radius at the end of its service life is marked re and shown with solid lines. The difference between the original radius r0 and the radius re at the end of its service life represents the usable tread depth tp of the tire 2. The currently existing tread depth tp is thus a measure of whether the tire 2 can still be used, as it is still within its intended service life, or whether it has been reduced to the minimum tread depth by reaching the radius re at the end of its service life, thus necessitating replacement of the tire 2.

[0036] In order to determine the tread depth tp of the tire 2 during use on the vehicle without taking a manual measurement, the current rotational speed ω of the tire 2 is determined in a manner known per se, e.g. according to WO 2014053322 A1, by means of a first vehicle-side sensor not shown here, for example by means of corresponding speed sensors of an ABS or ESP system.

[0037] Furthermore, a second vehicle-side sensor, for example a GPS sensor 21 of the vehicle's built-in navigation system, determines the actual speed V of the vehicle, including the tires 2 mounted on it, in a horizontal direction above the ground U. From these determined data for the current rotational speed ω of the tire 2 and the current speed V of the vehicle, the current dynamic rolling radius R d is determined according to the equation R d = V / ω.

[0038] At the beginning of the service life of tire 2, a starting value S 1 of the dynamic rolling radius R d is recorded, as shown in the graphical representation according to Figure 2 as can be seen at time T 0.

[0039] Subsequently, the current rotational speeds ω of the tire 2 and the corresponding current speeds V of the vehicle are continuously determined, or at fixed time intervals, from the data acquired by the first and second sensors 21. The corresponding dynamic rolling radius R d is then determined and compared with the initial value S 1. Since the radius of the tire 2 decreases from the original radius r 0 towards the radius re due to wear, the dynamic current rolling radius R d also decreases accordingly. This is directly proportional to the current tread depth tp, which can therefore be determined from the observed deviation of the current dynamic rolling radius R d from the initial value S 1.

[0040] In the Figure 2 It can be seen that, for example, with a summer tire, the dynamic rolling radius Rd and, consequently, the resulting current tread depth tp decrease due to wear along a downward-sloping line K1 during the first usage phase A1. At the end of the first usage phase A1, this tire 2 is replaced with, for example, a winter tire and stored in a corresponding non-use phase N for the duration of the winter tire's use; that is, the radial acceleration B of tire 2 continuously has the value "0".

[0041] In order to determine the standstill of tire 2 even when stored without being mounted on the vehicle, a sensor 20 of a tire pressure monitoring system (TPMS sensor) installed on the rim 1 of tire 2 is used, which, in addition to the tire pressure and tire temperature, also determines the radial acceleration B acting on tire 2 by means of a corresponding acceleration sensor, from which a movement status of tire 2 can be derived, which is determined either as usage phase A 1 , A 2 or as non-use phase N.

[0042] A radial acceleration B determined by sensor 20 above a predefined limit value leads to the movement status being determined as usage phase A 1 , A 2.

[0043] However, as soon as the determined radial acceleration B remains below a predetermined limit value for a predetermined period of time, for example 30 days, the movement status is determined as a non-use phase N and the sensor 20 generates a signal value which is stored in the sensor 20 alongside the periodically stored values ​​for tire pressure and temperature.

[0044] As soon as another wheel change is due at the end of the non-use phase N and the currently stored tires 2 are put back into use, as shown in the illustration according to Figure 2During the usage phase A 2, the sensor 20 of the tire pressure monitoring system sends its measured values ​​stored during the non-use phase N, as well as the generated signal value, to a vehicle-side receiving device, whereby the signal value transmitted along with the tire pressure and temperature values ​​causes a new starting value S 2 to be determined when the dynamic rolling radius R d is determined again, which is used as the basis for further measurement analysis instead of the previous starting value S 1.

[0045] Following the typical behavior of a stored tire 2 under inflation pressure, this tire has undergone an increase in its radius during non-use phase N due to the mechanical properties inherent in the tire material, so that a continuation of the comparison of the deviations of the current dynamic rolling radius R d from the starting value S 1 along the imaginary line K 1 ' continued from the line K 1 would lead to a distortion of the measurement result, since this radial increase of the tire 2 would be disregarded.

[0046] By setting the new starting value S 2 at the beginning of the next usage phase A 2 following the non-use phase N, the result from the representation according to Figure 2The radial increase visible as a vertical offset is taken into account, and the subsequently determined current dynamic rolling radii R d are compared along line K 2 with the new starting value S 2 in order to accurately depict the exact decrease in tread depth tp despite the increased radius of tire 2 during the non-use phase N. This compensates for the previously unavoidable distortion of the measurement result when considering the dynamic rolling radius R d of a tire 2 that has been unused for an extended period, for example, in storage.

[0047] Typically, the tread depth tp is continuously measured while the vehicle is in operation. This can involve determining both an absolute value of the tread depth tp and a relative change in the tread depth tp compared to a previously measured value.

[0048] The tread depth tp is preferably determined for all tires 2 of the vehicle, i.e. the determination of the respective current rotational speed, the current dynamic rolling radius and any correction values ​​is carried out separately for each tire 2 and is related to the current speed of the vehicle determined jointly for all tires 2.

[0049] A key advantage of the aforementioned method, as well as the control unit and the system for a vehicle, is that the quality of the determined tread depth estimation of tire 2 is significantly improved using the so-called rolling radius-based approach. Geometric changes to tire 2 that occur gradually during tire storage are taken into account in the determination. This is particularly important in markets with a high number of users who seasonally change the tires 2 on their vehicles. Reference symbol list:

[0050] 1: Rim 2: Tire 20: Third sensor 21: Second sensor A1: First usage phase N: Non-use phase A2: Second usage phase B: Radial acceleration V: Current speed K1: First line K1': Imaginary continuation K2: Second line ω: Current rotational speed Rd: Dynamic rolling radius r0: Original radius re: Radius at the end of the usage period S1: First starting value S2: New starting value T0: Time of the start of the usage period tp: Tread depth U: Surface

Claims

1. Method for determining the profile depth (tp) of a profile of a tyre (2) fitted on a wheel rim (1) on a vehicle, in which method the current dynamic rolling radius (Rd) of the tyre (2) is continually determined in phases of use (A1, A2) thereof, in that a current rotational speed (ω) of the tyre (2) is determined from data determined by a first sensor and a current speed (V) of the vehicle is determined from data determined by a second sensor (21) and the current dynamic rolling radius (Rd) is determined on the basis of the determined current rotational speed (ω) and the current speed (V) of the vehicle, characterized in that a starting value (S1) of the dynamic rolling radius (Rd) is recorded at the beginning of a first phase of use (A1) and a current profile depth (tp) of the tyre (2) is determined from deviations of the current dynamic rolling radius (Rd) from the starting value, wherein a current movement status of the tyre (2) is determined from data determined by a third sensor (20), in that when there are data determined above a specified limit value a phase of use (A1, A2) is determined as the movement status and when there are data determined below a specified limit value over a predetermined time period a phase of non-use (N) is determined as the movement status, and when there is a change in the movement status from a phase of non-use (N) to a subsequent phase of use (A2) the recording of a new starting value (S2) of the dynamic rolling radius (Rd) is instigated and, instead of the previous starting value, is compared with the subsequently determined current dynamic rolling radii (Rd) for the continued determination of the current profile depth (tp).

2. Method according to Claim 1, characterized in that the third sensor (20) determines the radial acceleration (B) of the tyre (2) or the tangential acceleration of the tyre (2) or changes in the acceleration of the tyre (2).

3. Method according to Claim 1 or 2, characterized in that the third sensor (20) takes the form of a sensor of a tyre pressure monitoring system (TPMS) that is assigned to the tyre (2).

4. Method according to one of Claims 1 to 3, characterized in that a signal value is generated in the determination of a phase of non-use (N).

5. Method according to Claim 4, characterized in that a counter of which the value is incrementally increased each time a signal value is generated is provided for the signal value.

6. Method according to one of Claims 1 to 5, characterized in that the first sensor is designed as a rotational-speed sensor.

7. Method according to one of Claims 1 to 6, characterized in that the second sensor (21) is selected from the group comprising a satellite-assisted sensor, a radar sensor, a lidar sensor, an ultrasound sensor and an optical camera.

8. Method according to one of Claims 1 to 7, characterized in that correction factors, comprising the tyre size, the tyre pressure, the tyre type, the temperature, the tyre load and / or the tyre age, are taken into account in the determination of the current profile depth (tp).

9. Method according to one of Claims 1 to 8, characterized in that determination of a phase of non-use (N) of the tyre (2) also causes the horizontal or vertical orientation of the tyre (2) to be determined and to be used for forming a correction factor which is taken into account in the determination of the current profile depth (tp).

10. Control device for a vehicle for determining the profile depth (tp) of a profile of a tyre (2) fitted on a wheel rim (1) on a vehicle, comprising at least one receiving device for receiving a current rotational speed (ω) of the tyre and a current speed (V) of the vehicle, characterized in that the control device has a determining device for determining a dynamic rolling radius (Rd) of the tyre (2) on the basis of the current rotational speed (ω) of the tyre (2) and the current speed (V) of the vehicle in comparison with a starting value (S1) that can be fixed for determining the profile depth (tp), the receiving device being designed for receiving a movement status comprising phases of use and phases of non-use and, when there is a change in the movement status from a phase of non-use to a subsequent phase of use, the determining device being activatable by the receiving device in such a way that a new starting value (S2) of the dynamic rolling radius (Rd) can be fixed and can be used instead of the starting value (S1) for determining the profile depth (tp).

11. System for a vehicle for determining the profile depth (tp) of a profile of a tyre (2) fitted on a wheel rim (1) on a vehicle, having a control device according to Claim 10, it being possible for the movement status to be generated by a sensor of a tyre pressure monitoring system assigned to the tyre (2).