Method for evaluating a vehicle tire, and tire evaluation system

Abstract

The invention relates to a method for evaluating a vehicle tire (4), comprising the following steps: - rotatably receiving the vehicle tire (4) and bringing the vehicle toward a test surface (PO), the test surface (PO) being located in a closed evaluation space (2); - setting evaluation conditions, wherein an actual ozone concentration (O3ist) in the closed evaluation space (2) of greater than 0 pphm and at most 15 pphm is set as one of the evaluation conditions; - driving the test surface (PO) by means of a first drive unit (A3) and / or driving the vehicle tire (4) by means of a second drive unit (A4) such that the vehicle tire (4) rolls on the test surface (PO); - stopping the movement of the test surface (PO) and the rotation of the vehicle tire (4) after the vehicle tire (4) has rolled on the test surface (PO) for a predefined evaluation duration under the set evaluation conditions (B), and defining a crack susceptibility evaluation factor for evaluating the vehicle tire (4), the crack susceptibility evaluation factor characterizing the extent to which cracks have formed in grooves of the vehicle tire (4) within the evaluation duration (dt).

Description

[0001] Description

[0002] Procedure for evaluating a vehicle tire and tire evaluation system

[0003] The invention relates to a method for evaluating a vehicle tire and a tire evaluation system for carrying out the method.

[0004] Ozone generally causes cracks in rubber products – especially those based on diatomaceous earth rubber – when used outdoors (in the field). This particularly affects vehicle tires, where ozone exposure can lead to groove base cracking in passenger car tires. This means the groove base of the circumferential and lateral grooves that form the tire's tread pattern can tear open or crack. Such cracks most commonly occur in summer tires, as ozone levels are typically higher during summer use. Winter tires, on the other hand, are less frequently affected because there is generally significantly less ozone in the air during winter.

[0005] To optimize the crack resistance or crack formation in the groove base of the respective grooves in the profile of the vehicle tire, the prior art involves testing the fatigue resistance or crack growth under static or dynamic load and under increased ozone concentration in the laboratory on representative rubber samples that have the same or a comparable material mixture as the later vehicle tire, taking into account specified standards, under the influence of ozone.

[0006] Alternatively, cracking can occur at ozone concentrations typically measured in pg / m³ 3The ozone concentration, which is specified in ppm (parts per million) or pph (parts per hundred million), can also be tested directly on the vehicle tire, which rolls on a test drum or flat track, both located in an ozone chamber. The high ozone concentration is used to deliberately accelerate the aging of the vehicle tire or rubber compound (time acceleration). This is described, for example, in JP 2021 063 733 A for a test on a flat track at 50–250 pph and in JP 4369836 B2 for a test on a test drum at 20–40 pph, where the weathering or aging of the sidewall over time is examined. Further test machines for vehicle tires are described in JP 5956385 B2 and CN116952746A. To adjust such ozone concentrations under test conditions in the laboratory, an ozone adjustment system according to EP 1650500 B1 can be used, for example.

[0007] The crack resistance or crack susceptibility of the respective tread compound is investigated in the state of the art under static or dynamic stress in the laboratory or in the respective test machine using accelerated time (controlled aging) at a corresponding ozone concentration between 20 and 250 ppmh. However, these test conditions do not allow for the correct characterization of crack resistance directly in the grooves of the tread of, for example, winter tires, all-season tires, or even summer tires. Thus, laboratory tests under these conditions yield assessments for the respective tire that are not consistent with field performance or operation in the field, because ozone concentrations differ in the field compared to the laboratory or the test machine, and the relationship between mechanical stress and ozone exposure also differs in the field.Therefore, such laboratory tests for winter tires or all-season tires must be verified through customer feedback, market observation, long-term field tests or long-distance vehicle tests, since laboratory tests alone cannot differentiate between good and poor winter performance.

[0008] The following invention is therefore based on the objective of providing a method and a tire evaluation system with which a reliable evaluation of a tire can be ensured in a simple manner. These objectives are achieved by a method and a tire evaluation system according to the independent claims. The dependent claims specify preferred embodiments.

[0009] According to the invention, a method for evaluating a vehicle tire is provided in which grooves, in particular circumferential grooves and / or transverse grooves, which may also be designed as shoulder grooves, are introduced into a tread, comprising at least the following steps:

[0010] Providing at least one vehicle tire to be evaluated with an inflation pressure, wherein the provided vehicle tire to be evaluated is intended for operation under natural ozone levels, for example as a summer tire, winter tire or all-season tire; rotatably picking up the at least one provided vehicle tire from a picking device, for example on a shaft, at a test position of a tire evaluation system, so that the picked-up vehicle tire can be set into rotation, and bringing the rotatably picked-up vehicle tire close to a test surface, for example a test drum (outer drum or inner drum) which has a preferably cylindrical outer surface radially outside or a preferably cylindrical inner surface radially inside as a test surface, or a test belt designed as a flat track with a band-shaped flat surface as a test surface, such thatthat the respective vehicle tire is pressed against the respective test surface (surface of the test drum or flat surface of the test belt) with a radially external or radially internal pressure load, or from above / below, wherein the test surface is located in a closed evaluation chamber of the tire evaluation system, wherein the evaluation chamber is preferably closed or enclosed externally by walls in order to establish and maintain a controlled environment within the evaluation chamber; targeted setting of evaluation conditions, wherein one of the evaluation conditions is an actual ozone concentration in the closed evaluation chamber of greater than Opphm but a maximum of 15 ppm, preferably a maximum of 10 ppm, for example by specifying a target ozone concentration that is greater than Opphm but less than or equal to 15 ppm, preferably less than or equal to 10 ppm;

[0011] Driving the respective test surface with a first drive unit to set the test surface in motion at a test speed (test drum at a drum circumferential speed or test belt at a belt speed), and / or (independently thereof) driving the vehicle tire with a second drive unit that differs from the first drive unit and the test surface to set the vehicle tire in rotation about a tire axis at a tire circumferential speed, so that the vehicle tire rolls on the test surface;

[0012] Stopping the movement of the test surface and the rotation of the respective vehicle tire after the vehicle tire has rolled on the test surface for a predetermined evaluation period under the set evaluation conditions, i.e., in a controlled environment, and determining a crack susceptibility rating factor to evaluate the respective vehicle tire with regard to its crack susceptibility or crack resistance, wherein the crack susceptibility rating factor characterizes the extent to which cracks have formed or are present in the grooves, in particular in a groove root of the respective grooves (the circumferential grooves and / or the transverse grooves) of the respective vehicle tire within the evaluation period, i.e., a specific crack susceptibility rating factor is assigned to the respective vehicle tire.

[0013] Advantageously, the unusually low ozone concentration, greater than 15 ppm but no more than 15 ppm, and particularly no more than 10 ppm, brings the relationship between tire damage from mechanical stress and the influence of ozone, especially for winter or all-season tires, into a range close to field conditions. The ozone concentration, or actual ozone concentration, is the proportion of ozone in the air, typically expressed in pg / m³. 3 , i.e., as weight per volume, or in ppm (“parts per million”) or pphm (“parts per hundred million”), i.e., as a volume fraction of ozone per 10 6 (ppm) or 10 8 (pphm) volume fraction of air or as the number of ozone molecules per million (ppm) or hundred million (pphm) air molecules per volume. In this case, therefore, an ozone volume fraction of greater than 0 and a maximum of 15, preferably a maximum of 10, per 10 8(pphm) Volume fractions of air or a volume fraction of ozone greater than 0 and a maximum of 0.15, preferably a maximum of 0.10, per 10 6 (ppm) Volume fraction of air present. At an air pressure of 1013 hPa and a temperature of 20 °C, 15 ppm or 0.15 ppm corresponds to a value of approximately 300 pg / m³ according to standard conversion. 3 and 10 ppmh or 0.10 ppm, a value of approximately 200 pg / m³ 3 Further values ​​can be derived accordingly.

[0014] The disadvantage of previous methods—that at high actual ozone concentrations, excessive cracking occurs in order to achieve the fastest possible aging / acceleration, which does not correspond to actual field behavior and makes it impossible to reliably differentiate between tire damage caused by ozone and damage caused by mechanical stress—can therefore be avoided. Consequently, the assessment according to the invention no longer needs to be verified through customer feedback, market observation, long-term field tests, or long-distance vehicle tests, making the method significantly more economical. Furthermore, the assessment method can be carried out with less regulatory effort, since the ozone concentrations are within the field-like or natural range.

[0015] In contrast to the prior art, this method deliberately sets a low actual ozone concentration to approximate real-world operating conditions, whereas the prior art deliberately sets a higher actual ozone concentration to accelerate tire aging. However, this accelerated aging caused by elevated ozone levels is neither desired nor intended in the present assessment procedure, in order to enable a more precise differentiation between the various damaging influences.

[0016] At the same time, the evaluation according to the invention is more reproducible than driving tests, since the relevant evaluation conditions can be directly controlled or specifically adjusted. An initial evaluation can be performed without any or with only minimal mechanical stress on the vehicle tire in order to assess the influence of ozone on a specific rubber compound of the vehicle tire in isolation. Due to the low ozone content, a more pronounced difference in crack formation can be observed between different rubber compounds than in the prior art, thus allowing for a more precise assessment of actual field behavior. Subsequently, specific mechanical stresses, such as driven or braked driving, as well as a certain degree of steering or camber, can be added to more precisely assess their influence under near-field conditions and to include them in the evaluation.In this way, for example, even stiffer profiles of summer tires can be reliably evaluated in the laboratory using such an evaluation method.

[0017] According to a preferred embodiment, the actual ozone concentration in the enclosed evaluation chamber is set to a value between 2 ppmh and 15 ppmh, preferably between 4 ppmh and 12 ppmh, particularly between 8 ppmh and 11 ppmh, and preferably less than 10 ppmh. Thus, particularly low values ​​for the actual ozone concentration are set under test conditions, which at least closely approximate real-world field conditions (between 1 and 6 ppmh over the course of a year) and which have not previously been achieved in evaluation procedures on a test surface (test drum or test belt), especially since known methods deliberately set a high actual ozone concentration to accelerate the aging of the vehicle tires. An excessively low actual ozone concentration is therefore generally undesirable in the prior art.Preferably, it is further provided that, as an additional evaluation condition, an evaluation temperature in the evaluation chamber and / or the contact load and / or the inflation pressure of the vehicle tire and / or an angular position of the tire axis relative to the test surface in each of the three spatial directions can be specifically set individually or in combination. The angular position of the tire axis relative to the test surface is specified, for example, by the position of the tire axis relative to the drum axis of the test drum or by the position of the tire axis relative to a transverse axis running perpendicular to the drive direction of the test belt. Accordingly, further parameters, which are also normally present in the field, can be set to enable a more targeted evaluation.

[0018] In particular, the contact pressure and angular position can be used to precisely control the mechanical load on the vehicle tire. For example, if the tire axle is twisted or tilted relative to the test surface, a lateral mechanical load is also induced in the tire, leading to a correspondingly altered crack formation, as lateral forces also act on the groove base, just as they do during normal operation. In this way, crack formation in the circumferential grooves can be depicted more accurately, since during straight-line driving, only very low mechanical loads typically act on the groove base.The relationship between damage to the rubber material caused by mechanical stress and by the ozone content can therefore be specifically altered, whereby a lower ozone content allows for better differentiation even at low mechanical stresses.

[0019] Preferably, the angular position of the tire axis relative to the test surface is adjusted such that the tire axis and the drum axis in the case of a test drum, or the transverse axis in the case of a test belt, are aligned parallel to each other, which corresponds to straight-ahead driving; or that the tire axis and the drum axis in the case of a test drum, or the transverse axis in the case of a test belt, are twisted relative to each other and therefore not aligned parallel to each other, with the tire axis being tangential to the test surface of the test drum or test belt in order to simulate a steering driving situation; or that the tire axis and the drum axis in the case of a test drum, or the transverse axis in the case of a test belt, are tilted relative to each other and therefore not aligned parallel to each other, with the tire axis not being tangential to the test surface of the test drum or test belt in order to simulate a driving situation with camber.It is therefore possible to deliberately induce mechanical loads that are also caused by a fall or steering / tracking during normal operation.

[0020] Preferably, the test surface and the vehicle tire are driven independently of each other such that the test speed (the drum circumferential speed of the test drum or the belt speed of the test belt) corresponds to the tire circumferential speed within a tolerance to simulate a free-rolling driving situation; or the test speed, taking the tolerance into account, is lower than the tire circumferential speed to simulate a driving situation; or the test speed, taking the tolerance into account, is higher than the tire circumferential speed to simulate a braking situation. The tolerance is determined depending on the adjustable resolution of the test speed and the tire circumferential speed, which is within the scope of the skilled person's knowledge.Accordingly, a free-rolling driving situation is achieved by minimizing the adjustable difference between the test speed and the tire's circumferential speed. The other driving situations are then achieved by increasing this difference, depending on the desired propulsion or braking effect.

[0021] Such a setting also induces a mechanical load in the treads, which, for example in the case of transverse grooves, leads to targeted cracking on the groove base adjacent to the trailing flanks or the leading flanks, which can better reflect the behavior in the field and can thus be taken into account in the evaluation.

[0022] Preferably, the determination of the crack susceptibility rating factor is carried out using reference crack patterns and / or reference tires, wherein each reference crack pattern and reference tire is assigned a crack susceptibility rating factor, preferably a different one for each, and wherein a test crack pattern of the vehicle tire to be evaluated, which has been rolled on the test surface within the evaluation period, is compared with the reference crack patterns and / or the reference tires, and if there is a match, the crack susceptibility rating factor of the matching reference crack pattern and / or the matching reference tire is adopted for the vehicle tire to be evaluated. Thus, a comparison is made with known references for which a crack susceptibility rating factor has already been reliably assigned.This can be done, for example, using six classes, which are also used in other common evaluation methods. If a match with a specific reference and thus with a specific class is found, the respective crack susceptibility rating factor or class of the reference is adopted, enabling a reliable evaluation. Preferably, the crack susceptibility rating factor is further determined based on the set evaluation conditions and / or the tire circumferential speed and test speed. Therefore, as already mentioned, the evaluation can take into account, for example, the angle setting, the contact pressure, or the speeds and their differences, in order to include the influence of mechanical stress in addition to the ozone content.

[0023] Preferably, the evaluation period is at least 48 hours, preferably at least 96 hours. With such evaluation periods, the vehicle tire can cover large distances of between 6,000 km and 7,000 km, within which, under the given evaluation conditions, cracks can normally already form in the grooves. This enables a rapid evaluation, which further improves the cost-effectiveness of the process.

[0024] Preferably, the vehicle tire is further aged in an aging process before being rolled on the test surface, for example by exposing the tire to be tested, unloaded, to temperatures between, for example, 60° and 90°C for an aging period of at least seven days. In this simple way, additional time acceleration can be achieved even without ozone exposure, thus enabling a reliable evaluation of older vehicle tires as well.

[0025] According to the invention, a tire evaluation system is also provided, in particular for carrying out the method according to the invention, comprising at least: an enclosed evaluation chamber or one completely enclosed by walls; a test surface arranged in the enclosed evaluation chamber, for example a test drum, preferably with a cylindrical (outer or inner) surface, or a test belt with a flat surface (flat-track), wherein the test surface interacts with a first drive unit configured to set the test surface in motion at a test speed (circumferential speed of the test drum or belt speed of the test belt); at least one receiving device for rotatably receiving a vehicle tire, for example on a shaft, wherein the respective receiving device is arranged at a test position associated with it in the enclosed evaluation chamber.wherein the respective holding device can be adjusted by an actuator in such a way as to allow a vehicle tire rotatably mounted on the holding device to be pressed against the test surface (cylindrical outer or inner surface of the test drum or flat surface of the test belt) with a pressure load from the radial outside or radial inside or from above / below; a second drive unit configured to act on the vehicle tire rotatably mounted on the holding device in order to set the vehicle tire into rotation about a tire axis at a tire circumferential speed, wherein the first drive unit differs from the second drive unit so that the test surface and the vehicle tire can be driven or set in motion independently of each other; an ozone adjustment system for the targeted adjustment of an actual ozone concentration in the enclosed evaluation space,wherein the ozone adjustment system comprises at least one ozone generator for increasing the actual ozone concentration in the enclosed evaluation chamber, at least one ozone destroyer for reducing the actual ozone concentration in the enclosed evaluation chamber, at least one ozone sensor for measuring the actual ozone concentration in the enclosed evaluation chamber, and an ozone control unit, which is connected to the other components via signal transmission, for controlling the ozone adjustment system, wherein the ozone control unit is configured to control the ozone adjustment system such that an actual ozone concentration of greater than Opphm but not more than 15 ppm, preferably not more than 10 ppm, prevails in the enclosed evaluation chamber for a defined evaluation period, for example by specifying a target ozone concentration, which is greater than Opphm but less than or equal to 15 ppm, preferably less than or equal to 10 ppm, to the ozone control unit.

[0026] With this tire evaluation system, it is advantageously possible to set up or maintain a controlled environment with a very low ozone actual concentration in an enclosed evaluation room and to carry out the evaluation of a vehicle tire on a test surface in this controlled environment, in particular according to the method according to the invention with the above advantages.

[0027] Preferably, the at least one ozone generator and / or at least one ozone destroyer is / are arranged in the enclosed evaluation chamber or is / are connected to the enclosed evaluation chamber via pipes. This allows for a flexible arrangement of the individual components to create a controlled atmosphere in the evaluation chamber.

[0028] Preferably, the at least one ozone sensor is arranged adjacent to one of the test positions in the enclosed evaluation chamber. This allows the actual ozone concentration to be recorded directly near the test position(s), enabling a better assessment and evaluation of the ozone's influence on the vehicle tire.

[0029] Preferably, the actuator is further configured to rotate and / or tilt the mounting device so that an angular position of the tire axis of a rotatably mounted vehicle tire relative to the test surface can be set in order to simulate a steering driving situation and / or a driving situation with camber. In this way, targeted and controlled lateral mechanical loads can be induced in the vehicle tire under evaluation to simulate damage caused by mechanical loads in addition to the influence of ozone damage.

[0030] Preferably, the first drive unit and the second drive unit can be controlled independently of each other such that the test speed corresponds to the tire circumferential speed within a tolerance to simulate a free-rolling driving situation; or the test speed, taking the tolerance into account, is lower than the tire circumferential speed to simulate a driving situation; or the test speed, taking the tolerance into account, is higher than the tire circumferential speed to simulate a braking situation. In this way, targeted and controlled circumferential mechanical loads can be induced in the vehicle tires under evaluation in order to simulate damage caused by mechanical loads in addition to the influence of ozone damage.

[0031] The drawings show:

[0032] Fig. 1 shows a tire evaluation system for carrying out a procedure to evaluate a vehicle tire;

[0033] Fig. 2 shows a flowchart of the procedure for evaluating a vehicle tire; and Figs. 3A, 3B, 3C show exemplary test crack patterns for a groove of a vehicle tire to be evaluated according to Fig. 2.

[0034] Figure 1 schematically shows a tire evaluation system 1 (test machine) which has an evaluation chamber 2 containing a test drum 3. The evaluation chamber 2 can, for example, be an enclosed chamber containing the test drum 3 or an enclosed hall in which, among other things, the test drum 3 is located. Accordingly, the evaluation chamber 2 has walls that enclose it. The test drum 3, shown here as the outer drum, can be set into controlled rotation by a first drive unit A3, so that the test drum 3 rotates about a drum axis 3a at a drum circumferential speed v3. At a number N of test positions Pi (i=1, 2,...,N), here N=4, vehicle tires 4 to be evaluated can each be rotatably held by a mounting device 5, which, for example, has a shaft 5a.The receiving device 5 defines a tire axle 4a around which the vehicle tire 4 can rotate driven by a second drive unit A4 at a tire circumferential speed v4.

[0035] To test or evaluate the respective vehicle tire 4, it is approached radially from the outside of a cylindrical outer surface 3b of the test drum 3 such that a surface 4b of the respective vehicle tire 4 contacts the outer surface 3b of the test drum 3. The first drive unit A3 and / or the second drive unit A4 can then be controlled to set the vehicle tire 4 into rotation while it is in contact with the test drum 3. By appropriately adjusting the rotation speeds v3, v4, different driving situations (free-rolling, braking, accelerating) can be simulated.

[0036] According to a further embodiment, the test drum 3 can be designed as an inner drum instead of an outer drum, as shown in detail in Fig. 1A, in which case the tire 4 is approached radially from the inside to an inner surface 3c of the test drum 3. The test drum 3 is then driven analogously to the outer drum via a corresponding first drive unit A3, by which a corresponding drum circumferential speed v3 can be set.

[0037] According to another embodiment, instead of a test drum 3, a test belt 30 with a band-shaped flat surface 30a (flat-track) can also be provided, as shown in detail in Fig. 1B. The test belt 30 runs endlessly on rollers 31. One of the rollers 31 is driven by the first drive unit A3 to drive the test belt 30 at a specific belt speed v30. The tire 4 is then brought close to the flat surface 30a of the test belt 30 from above.

[0038] In the described embodiments, the outer surface 3b of the test drum 3 (as the outer drum), the inner surface 3c of the test drum 3 (as the inner drum), and the flat surface 30a of the test belt 30 each form test surfaces PO in concave, convex, or flat shapes, respectively, on which the tire 4 can roll, depending on the embodiment. The respective test surface PO can be driven by the first drive unit A3 to set it in motion at a test speed vP.

[0039] The receiving device 5 or the tire axle 4a can also be adjusted in a controlled manner by a corresponding actuator 6 in such a way that the contact loads L (contact force) of the vehicle tire 4 on the respective test surface PO, i.e. the outer or inner surface 3b, 3c of the respective test drum 3 (outer drum or inner drum) or on the flat surface 30a of the test belt 30, can be changed or specifically adjusted.Furthermore, the angular position W of the tire axle 4a relative to the respective test surface PO can be adjusted in such a way that the angular position of the vehicle tire 4 relative to the respective test surface PO can be changed in each of the three spatial directions (individually or in combination) in order to simulate, for example, different camber angles, different tracks of the steered wheels of the vehicle or a cornering maneuver, so that the vehicle tire 4 can be subjected to different evaluation conditions B in a controlled manner on the test surface PO.

[0040] As a further such evaluation condition B, an ozone actual concentration 03lst in evaluation chamber 2 of the tire evaluation system 1 can be set via an ozone adjustment system 0. For this purpose, an ozone control unit 10 is located in or immediately adjacent to evaluation chamber 2, which is connected by signal transmission to at least one ozone generator 11, at least one ozone destroyer 12, and at least one ozone sensor 13. The ozone actual concentration 03lst in evaluation chamber 2 can be selectively increased via the ozone generator 11, selectively decreased via the ozone destroyer 12, and measured via the ozone sensor 13. To prevent external influences, evaluation chamber 2 is enclosed by appropriate walls.

[0041] The ozone generator 11 produces ozone, which is introduced into the enclosed evaluation chamber 2 in a targeted and controlled manner, for example, via a fan, in order to increase the ozone concentration O3lst in the evaluation chamber 2 in a targeted and uniform manner. The ozone generator 11 can be located inside or outside the evaluation chamber 2, with the generated ozone being introduced into the evaluation chamber 2 via a channel 2a and an inlet 2b in a correspondingly uniform manner. The tire evaluation system 1 can also have several such ozone generators 11 to achieve a uniform distribution of ozone throughout the entire evaluation chamber 2.

[0042] The ozone destroyer 12 utilizes known effects to destroy ozone absorbed or drawn in from assessment area 2. The ozone destroyer 12 can be located inside or outside assessment area 2, in which case the ozone present in assessment area 2 is either diverted or extracted accordingly. This reduces the ozone concentration O3lst in assessment area 2. The tire assessment system 1 can also incorporate several such ozone destroyers 12 to achieve a uniform reduction of ozone across the entire assessment area 2.

[0043] The ozone control unit 10 can compare the measured actual ozone concentration 03lst with a predefined target ozone concentration 03Soll and then control the ozone generator(s) 11 or the ozone destroyer(s) 12 so that the actual ozone concentration 03lst changes towards the target ozone concentration 03Soll. Depending on the application, this can be done in a control loop or by a controller. In this way, a controlled environment with a defined actual ozone concentration 03lst can be created in the enclosed evaluation room 2 via the ozone adjustment system 0.

[0044] As further evaluation conditions B, for example an evaluation temperature T in the evaluation room 2 and / or a filling pressure p4 of the vehicle tire 4 can be specifically set in order to create controlled conditions for an evaluation.

[0045] This is particularly important in a process in which the vehicle tire 4 is evaluated using this tire evaluation system 1. Such an evaluation includes an assessment of the crack resistance or crack susceptibility of grooves 4c, especially circumferential grooves 4c1 and / or transverse grooves 4c2, which may also be designed as shoulder grooves and which are incorporated into the rubber material of a tread 4d that radially closes off the vehicle tire 4, as shown by way of example in Figures 3A, 3B, and 3C. For this purpose, a crack susceptibility rating factor F is determined in the process, which indicates the extent to which cracks R form in the grooves 4c, especially in a groove root 4e of the respective grooves 4c, during the operation of the vehicle tire 4. Such cracks R are fractures or fissures that can form due to the presence of ozone in combination with mechanical stress on the rubber material during the operation of the vehicle tire 4.

[0046] Depending on the rubber compound, such cracks R form more or less quickly depending on the environmental and / or operating conditions of the respective vehicle tire 4. Since this susceptibility to cracking is relevant for the approval of a vehicle tire 4, the environmental and / or operating conditions under which a specific vehicle tire 4 is operated are simulated by appropriately adjusting the aforementioned evaluation conditions B in the tire evaluation system 1, and the vehicle tire 4 in question is operated under these simulated evaluation conditions B.

[0047] The characterization of crack susceptibility via the crack susceptibility rating factor F is to be carried out in such a way that the mechanical stress and the ozone exposure on the vehicle tire 4 are brought into a corresponding balance, so that the evaluation can still differentiate between crack formation due to mechanical stress and due to ozone exposure. Acceleration or aging of the vehicle tire 4 due to ozone exposure is therefore kept to a minimum or minimized by deliberately setting a correspondingly low actual ozone concentration 03lst in the evaluation space 2. For this purpose, actual ozone concentrations 03lst are preferably set in the evaluation space 2 that are between 2 ppmh and 15 ppmh, preferably between 4 ppmh and 12 ppmh, particularly between 8 ppmh and 11 ppmh, and preferably less than or equal to 10 ppmh.

[0048] The process flow of the method according to the invention, which is illustrated by way of example in a flowchart in Fig. 2, is as follows: In an initial step STO, at least one vehicle tire 4 to be tested or evaluated is provided, having a tread 4d and grooves 4c incorporated therein, in particular circumferential grooves 4c1 and / or transverse grooves 4c2. The inflation pressure p4 of the vehicle tire 4 is set to a predetermined value, for example 2.5 bar, and this inflation pressure p4 is kept approximately constant during the process.

[0049] In a first step ST1, the at least one vehicle tire 4 to be evaluated is rotatably suspended on one of the test positions Pi on the respective mounting device 5, for example on the shaft 5a, so that it can be rotated accordingly and brought closer to the test surface PO (cylindrical outer or inner surface 3b, 3c of the test drum 3 or to the flat surface 30a of the belt 30) by means of a corresponding adjustment by the actuator 6 in order to touch the respective test surface PO.

[0050] In a second step ST2, the evaluation conditions B are set according to a specification. In particular, the actual ozone concentration O3lst in the evaluation chamber 2 is adjusted via the ozone adjustment system O to a value between 2 ppmh and 15 ppmh, preferably between 4 ppmh and 12 ppmh, and more specifically between 8 ppmh and 11 ppmh, preferably less than or equal to 10 ppmh. This is done via the ozone control unit 10, which is given the corresponding value as the target ozone concentration O3Soll, so that it can subsequently continuously regulate or control deviations of the actual ozone concentration O3lst from the specified target ozone concentration O3Soll and minimize them. As a further evaluation condition B, an evaluation temperature T of, for example, between 5° and 40°, preferably between 20° and 30°, is set in the evaluation chamber 2 via appropriate temperature control elements.This evaluation temperature T is subsequently kept approximately constant. Additionally, depending on the specifications for the evaluation process, an angular position W of the tire axle 4a relative to the test surface PO can be set in one or a combination of the three spatial directions to simulate, for example, different camber angles and / or different tracking of the steered wheels of the vehicle and / or cornering. Furthermore, a specific contact load L of, for example, approximately 800 kg is set via the actuator 6 as evaluation condition B, with which the respective vehicle tire 4 is pressed against the test surface PO. These evaluation conditions B (L, W) can optionally be changed during the course of the process, depending on the specifications for the evaluation in the following steps, for example, to simulate a specific driving profile.

[0051] The approach of the vehicle tire 4 to the test surface PO via the actuator 6 in the first step ST1 and the setting of the respective evaluation conditions B in the second step ST2 can also be carried out in reverse order or at least partially simultaneously.

[0052] Once the respective evaluation conditions B (L, W, 03lst, T, p4) are set and the vehicle tire 4 is approaching the test surface PO, the vehicle tire 4 to be evaluated is set into rotation in a third step ST3 via the second drive unit A4 at a defined tire circumferential speed v4. Furthermore, a specific test speed vP of the test surface PO, i.e., a specific drum circumferential speed v3 or a specific belt speed v30, can be set via the first drive unit A3. A free-rolling driving situation FF can be simulated, i.e., vP,v3;v30=v4, or a braking driving situation FB, i.e., vP,v3;v30>v4, or a driving driving situation FA, i.e., vP,v3;v30 <v4. Die jeweilige Fahrsituation ist dabei ebenfalls eine Bewertungs-Bedingung B, die bei der nachfolgenden Bewertung Berücksichtigung findet.In a first embodiment of the procedure, the vehicle tire 4 is operated for a defined evaluation period dt of at least 48h, for example 96h, at a constant tire circumferential speed v4, rolling freely (vP,v3;v30=v4), with a contact load L of approx. 800kg, a constant inflation pressure p4 of approx. 2.5bar, no camber and no toe of the steered wheels of the vehicle.

[0053] Once the specified evaluation period dt (here 96h) has elapsed, the tested vehicle tire 4 is stopped, and in a fourth step ST4, the evaluation takes place, specifically the determination of the crack susceptibility rating factor F, which is assigned to the respective tested vehicle tire 4. For this purpose, the extent to which cracks R have formed in the grooves 4c in the tread 4d of the vehicle tire 4 being evaluated, particularly at the groove base 4e, is visually determined using reference tires 4Ref or reference crack patterns BRef. The number of cracks R, as well as their length and width R, can be included in the evaluation, as is the case in common evaluation methods.

[0054] The crack susceptibility rating factor F typically has six classes or levels, from class 1 (no damage) to class 6 (significant damage). Depending on the occurrence of cracks R, specific crack susceptibility rating factors F are assigned to each reference tire 4Ref or reference crack pattern BRef; that is, at least six such reference tires 4Ref or reference crack patterns BRef are available. By comparing the test crack pattern B4 of the vehicle tire 4 to be evaluated, which has been rolled on the respective test surface PO for the evaluation duration dt, with the reference tires 4Ref or the reference crack patterns BRef, the reference tire 4Ref or the reference crack pattern BRef that most closely matches the test crack pattern B4 can be selected to determine the classification. Figures 3A, 3B, and 3C show different views of a groove 4c as examples.Exemplary test crack patterns B4 are shown after the evaluation period dt has elapsed. For the vehicle tire 4 in Fig. 3A, a crack susceptibility rating factor F of class 1 (no damage) is determined by comparison with the reference tires 4Ref or the reference crack patterns BRef, in Fig. 3B a crack susceptibility rating factor F of class 3 (medium damage) and in Fig. 3C a crack susceptibility rating factor F of 6 (pronounced damage).

[0055] To determine the crack susceptibility rating factor F, several test crack patterns B4 of the vehicle tire 4 to be tested are preferably used and each of these is compared with the reference tires 4Ref or the reference crack patterns BRef in order to obtain an average rating and to compensate for deviations.

[0056] To perform the evaluation for a vehicle tire 4 even more accurately using this method, a further variant may additionally provide that during the evaluation period dt in the third step ST3 a braking driving situation FB (vP,v3;v30>v4) or a driving situation FA (vP,v3;v30) is implemented at least temporarily or permanently. <v4) durch eine entsprechende Ansteuerung der ersten Antriebseinheit A3 bzw. der Einstellung der Prüf-Geschwindigkeit vP, d.h. der Trommel-Umfangsgeschwindigkeit v3 oder der Band-Geschwindigkeit v30, und der zweiten Antriebseinheit A4 bzw. der Reifen-Umfangsgeschwindigkeit v4, eingestellt wird.

[0057] In addition to the low ozone exposure, this induces a mechanical stress in the rubber material, which does not occur during a free-rolling driving situation FF and which, during a braking driving situation FB, leads to an additional mechanical stress on the groove base 4e adjacent to a trailing flank 4e1 of the respective groove 4c, particularly in the transverse groove 4c2 or a groove 4c with a laterally extending portion. Similarly, a driving driving situation FA leads to an additional mechanical stress on the groove base 4e in the area of ​​a leading flank 4e2 of the respective groove 4c, particularly in the transverse groove 4c2 or a groove 4c with a laterally extending portion.In this way, the mechanical stress in the circumferential direction of the vehicle tire 4, which frequently occurs during normal operation, can also be simulated, whereby a targeted differentiation between the respective damage effects occurring is also possible due to the low ozone exposure.

[0058] To perform the evaluation of a vehicle tire 4 using this method even more precisely or specifically, a further embodiment may additionally provide that, during the evaluation period dt in the third step ST3, a steering driving situation FL and / or a driving situation with camber FS is set, at least temporarily or permanently, by adjusting the actuator 6 accordingly. In a steering driving situation FL, the angular position W of the tire axis 4a relative to the test surface PO is adjusted such that the tire axis 4a is no longer parallel to the drum axis 3a of the test drum 3 or parallel to a transverse axis Q30 running perpendicular to the drive direction R30 of the test belt 30, but remains tangential to the test surface PO or at an angle of 90° to a perpendicular S on the test surface PO.In a driving situation with camber FS, the tire axis 4a is adjusted relative to the respective test surface PO in such a way that the tire axis 4a is tilted relative to the drum axis 3a of the test drum 3 or relative to the transverse axis Q30 of the test belt 30, so that the tire axis 4a is no longer tangential to the respective test surface PO or is at an angle of non-90° to the perpendicular S on the respective test surface PO.

[0059] A steering driving situation FL can also be combined with a driving situation with camber FS, whereby the tire axle 4a is then rotated and tilted accordingly relative to the respective test surface PO. A braking driving situation FB or a driving situation FA can also be combined in this way to more accurately represent driving behavior in the field. The selected driving situation can then be taken into account during the evaluation. For example, when considering a circumferential groove 4c1, which generally runs circumferentially, without setting a driving situation with camber FS and / or a steering driving situation FL, there are usually no or only very minor mechanical loads on the groove base 4e, so that grooves R form primarily due to ozone exposure, and the influence of mechanical loads is rather small.Accordingly, a different crack pattern results in the groove bottom 4e, and therefore also a potentially inaccurate classification via the crack susceptibility assessment factor F. However, when the corresponding driving situation FS, FL is set, mechanical loads will also occur at the groove bottom 4e in the area of ​​flanks with at least a partial circumferential component, which promote the formation of cracks R during the assessment duration dt.

[0060] In summary, in addition to the low ozone exposure, a targeted additional mechanical stress can be induced in the rubber material to more accurately simulate its behavior in the field. A further improvement in the evaluation can be achieved by subjecting the vehicle tire 4 to controlled aging in an aging process STA before the third step ST3, thus enabling an evaluation even for older vehicle tires 4. This can be accomplished, for example, by exposing the vehicle tire 4 to be tested to temperatures between, for example, 60° and 90°C for an aging period tA of at least seven days. Additionally, an inflation pressure p4 of, for example, greater than 3 bar can be set. Reference numeral list

[0061] 1 tire rating system

[0062] 2 Assessment area

[0063] 2a Channel

[0064] 2b Entrance

[0065] 3 test drum

[0066] 3a Drum axle

[0067] 3b Outer shell surface

[0068] 3c Inner coat surface

[0069] 4 vehicle tires

[0070] 4a Tire axle

[0071] 4b Surface of the vehicle tire 4

[0072] 4c Grooves in the vehicle tire 4

[0073] 4c1 circumferential groove

[0074] 4c2 transverse groove

[0075] 4d Tread of the vehicle tire 4

[0076] 4e Groove base

[0077] 4e1 trailing flank

[0078] 4e2 leading flank

[0079] 4Ref Reference Tires

[0080] 5 Recording device

[0081] 5a wave

[0082] 6 Actuator

[0083] 10 Ozone control unit

[0084] 11 Ozone generator

[0085] 12 Ozone Destroyers

[0086] 13 Ozone sensor

[0087] 30 test tape

[0088] 30a flat surface of the test belt 30

[0089] 31 rollers A3 first drive unit

[0090] A4 second drive unit

[0091] B. Evaluation Conditions

[0092] BRef Reference Crack Image

[0093] B4 Test crack pattern dt Assessment duration

[0094] F Crack susceptibility rating factor

[0095] FA driving situation

[0096] FB braking driving situation

[0097] FF free-rolling driving situation

[0098] FL steering driving situation

[0099] FS driving situation with fall

[0100] L pressure load

[0101] N number

[0102] 0 Ozone adjustment system

[0103] 03lst Ozone Actual Concentration

[0104] O3 Target Ozone Target Concentration

[0105] Pi i. Test position p4 filling pressure

[0106] PO test surface

[0107] Q30 Transverse axis of the test belt 30

[0108] R Riss

[0109] R30 Drive direction of the test belt 30

[0110] S Perpendicular to the lateral surface 3b

[0111] STA aging process

[0112] T Evaluation temperature tA Aging period v3 Drum circumferential speed v4 Tire circumferential speed v30 Belt speed vP Test speed

[0113] W angle position

[0114] STO, ST1, ST2, ST3, ST4 Steps of the procedure

Claims

Patent claims 1. Method for evaluating a vehicle tire (4) in which grooves (4c) are incorporated in a tread (4d), comprising at least the following steps: Providing at least one vehicle tire (4) to be evaluated with an inflation pressure (p4) (STO); rotatably picking up the at least one provided vehicle tire (4) from a picking device (5) at a test position (Pi) of a tire evaluation system (1), and bringing the rotatably picked-up vehicle tire (4) close to a test surface (PO) such that the respective vehicle tire (4) is pressed against the test surface (PO) with a pressure load (L) (ST1), wherein the test surface (PO) is located in a closed evaluation chamber (2) of the tire evaluation system (1); Setting evaluation conditions (B) (ST2), wherein one of the evaluation conditions (B) is an ozone actual concentration (03lst) in the enclosed evaluation space (2) of greater than 0.0 ... Driving the test surface (PO) with a first drive unit (A3) to move the test surface (PO) at a test speed (vP), and / or driving the vehicle tire (4) with a second drive unit (A4) to rotate the vehicle tire (4) about a tire axis (4a) at a tire circumferential speed (v4) (ST3), so that the vehicle tire (4) rolls on the test surface (PO); Stopping the movement of the test surface (PO) and the rotation of the respective vehicle tire (4) after the vehicle tire (4) has rolled on the test surface (PO) for a predetermined evaluation duration (dt) under the set evaluation conditions (B), and defining a crack susceptibility evaluation factor (F) to evaluate the respective vehicle tire (4), wherein the crack susceptibility evaluation factor (F) characterizes the extent to which cracks develop within the evaluation duration (dt). (R) have formed in the grooves (4c) of the respective vehicle tire (4).

2. Method according to claim 1, characterized in that the ozone actual concentration (03lst) in the enclosed evaluation space (2) is adjusted to a value of between 2pphm and 15pphm, preferably between 4pphm and 12pphm, in particular between 8pphm and 11pphm, preferably to less than 10pphm.

3. Method according to claim 1 or 2, characterized in that as a further evaluation condition (B) an evaluation temperature (T) in the evaluation space (2) and / or the contact load (L) and / or the inflation pressure (p4) of the vehicle tire (4) and / or an angular position (W) of the tire axle (4a) relative to the test surface (PO) is set.

4. Method according to claim 3, characterized in that the test surface (PO) is an outer shell surface (3b) or an inner shell surface (3c) of a test drum (3) rotatable about a drum axis (3a) with a drum circumferential speed (v3) or a flat surface (30a) of a test belt (30) movable with a belt speed (v30) in a drive direction (R30).

5. Method according to claim 4, characterized in that the angular position (W) of the tire axle (4a) relative to the test surface (PO) is adjusted such that the tire axle (4a) and the drum axle (3a) of the test drum (3), in the case of an outer shell surface (3b) or an inner shell surface (3c) as the test surface (PO), or that the tire axle (4a) and a transverse axis (Q30) of the test belt (30), in the case of a flat surface (30a) as the test surface (PO), are aligned parallel to each other; or that the tire axis (4a) and the drum axis (3a) of the test drum (3), in the case of an outer shell surface (3b) or an inner shell surface (3c) as the test surface (PO), or that the tire axis (4a) and the transverse axis (Q30) of the test belt (30), in the case of a flat surface (30a) as the test surface (PO), are twisted relative to each other and therefore not aligned parallel to each other, and that the tire axis (3a) is tangential to the respective test surface (PO) in order to simulate a steering driving situation (FK);or that the tire axis (4a) and the drum axis (3a) of the test drum (3), in the case of an outer shell surface (3b) or an inner shell surface (3c) as the test surface (PO), or that the tire axis (4a) and a transverse axis (Q30) of the test belt (30), in the case of a flat surface (30a) as the test surface (PO), are tilted relative to each other and therefore not parallel to each other, and the tire axis (3a) is not tangential to the test surface (PO) in order to simulate a driving situation with camber (FS).

6. Method according to one of the preceding claims, characterized in that the test surface (PO) and the vehicle tire (4) are driven independently of each other such that the test speed (vP) corresponds within a tolerance of the tire circumferential speed (v4) to simulate a free-rolling driving situation (FF); or the test speed (vP) is less than the tire rotation speed (v4) taking into account the tolerance to simulate a driving situation (FA); or the test speed (vP) is greater than the tire circumferential speed (v4) taking into account the tolerance to simulate a braking driving situation (FB).

7. Method according to one of the preceding claims, characterized in that the determination of the crack susceptibility rating factor (F) is carried out on the basis of reference crack patterns (BRef) and / or on the basis of reference tires (4Ref), wherein a crack susceptibility rating factor (F) is assigned to each of the reference crack patterns (BRef) and the reference tires (4Ref), and wherein a test crack pattern (B4) of the vehicle tire (4) to be evaluated, which has been rolled on the test surface (PO) within the evaluation period (dt), is compared with the reference crack patterns (BRef) and / or the reference tires (4Ref) and, in the event of a match, the crack susceptibility rating factor (F) of the matching reference crack pattern (BRef) and / or the matching reference tire (4Ref) is adopted for the vehicle tire (4) to be evaluated.

8. Method according to one of the preceding claims, characterized in that the determination of the crack susceptibility rating factor (F) is carried out depending on the occurrence of cracks (R) in circumferential grooves (4c1 ) and / or in transverse grooves (4c2) of the vehicle tire (4) to be evaluated, in particular in a groove base (4e) of the circumferential grooves (4c1 ) and / or transverse grooves (4c2).

9. Method according to one of the preceding claims, characterized in that the determination of the crack susceptibility rating factor (F) is carried out depending on the set rating conditions (B) and / or depending on the setting of the tire circumferential speed (v4) and the test speed (vP).

10. Method according to one of the preceding claims, characterized in that The evaluation period (dt) should be at least 48 hours, preferably at least 96 hours.

11. Method according to one of the preceding claims, characterized in that the vehicle tire (4) is aged in an aging process (STA) before the vehicle tire (4) is rolled on the test surface (PO), for example by exposing the vehicle tire (4) to be tested to temperatures of, for example, between 60° and 90° for an aging period (tA) of, for example, at least seven days.

12. Tire evaluation system (1), in particular for carrying out a method according to one of the preceding claims, comprising at least: an enclosed evaluation chamber (2); a test surface (PO) arranged in the enclosed evaluation chamber (2), wherein the test surface (PO) interacts with a first drive unit (A3) configured to move the test surface (PO) at a test speed (vP); at least one receiving device (5) for rotatably receiving a vehicle tire (4), wherein the receiving device (5) is arranged at a test position (Pi) in the enclosed evaluation chamber (2), wherein the receiving device (5) can be adjusted by an actuator (6) in the direction of the test surface (PO) such that a vehicle tire (4) rotatably received on the receiving device (5) can be pressed against the test surface (PO) with a pressure load (L);a second drive unit (A4) configured to act on the vehicle tire (4) rotatably mounted on the receiving device (5) in order to rotate the vehicle tire (4) about a tire axis (4a) at a tire circumferential speed (v4); an ozone adjustment system (O) for setting an ozone actual concentration (O3lst) in the enclosed evaluation chamber (2), wherein the ozone; The adjustment system (0) comprises at least one ozone generator (11) for increasing the actual ozone concentration (03lst) in the enclosed evaluation chamber (2), at least one ozone destroyer (12) for reducing the actual ozone concentration (03lst) in the enclosed evaluation chamber (2), at least one ozone sensor (13) for measuring the actual ozone concentration (03lst) in the enclosed evaluation chamber (2), and an ozone control unit (10) for controlling the ozone adjustment system (O), characterized in that the ozone control unit (10) is configured to control the ozone adjustment system (O) in such a way that an actual ozone concentration (03lst) of greater than 0.010 ppm and a maximum of 15 ppm, preferably a maximum of 10 ppm, prevails in the enclosed evaluation chamber (2) for a defined evaluation period (dt).

13. Tire evaluation system (1) according to claim 12, characterized in that the at least one ozone generator (11) and / or at least one ozone destroyer (12) is arranged in the enclosed evaluation space (2) or is connected to the enclosed evaluation space (2) via a channel (2a), and / or wherein the at least one ozone sensor (13) is arranged adjacent to one of the test positions (Pi) in the enclosed evaluation space (2).

14. Tire evaluation system (1) according to one of claims 12 to 13, characterized in that the actuator (6) is configured to rotate and / or tilt the receiving device (5) so that an angular position (W) of the tire axis (4a) of a rotatably received vehicle tire (4) relative to the test surface (PO) can be set in order to set a steering driving situation (FL) and / or a driving situation with camber (FS).

15. Tire evaluation system (1) according to one of claims 12 to 14, characterized in that the first drive unit (A3) and the second drive unit (A4) can be controlled independently of each other such that - the test speed (vP) is within a tolerance of the tires- circumferential speed (v4) corresponds to simulate a free-rolling driving situation (FF); or the test speed (vP) is less than the tire circumferential speed (v4) taking into account the tolerance, to simulate a driving situation (FA); or the test speed (vP) is greater than the tire circumferential speed (v4) taking into account the tolerance, to simulate a braking situation (FB).

Images