Abstract
A method and test stand for determining tire properties of a vehicle tire which is rotatably positioned on a rim via a wheel bearing. The interior of vehicle tire is pressurized by a fluid and the vehicle tire is applied with a wheel load. The vehicle tire is accelerated to a final speed in accordance with a pre-determinable speed ramp. The vehicle tire, in accordance with a tire speed, undergoes an oscillation excitation and reacts to the oscillation excitation with an oscillation. The method includes continuously capturing an effective tire force of the vehicle tire in the wheel bearing, due to the oscillation, and creating a data set which shows the tire force over the tire speed and tire frequency, by applying a timing signal of the speed ramp to a Fourier transformation.
Claims
1-20. (canceled)
21. A method for determination of tire properties in which a vehicle tire (1) is rotatably mounted on a rim (2) via a wheel bearing, an interior of the vehicle tire (1) is pressurized by a fluid, the vehicle tire (1) is subjected to a wheel load, the vehicle tire (1) being accelerated to a final speed in accordance with a pre-determinable speed ramp, and the vehicle tire (1), in accordance with a tire speed, undergoes oscillation excitation and reacts to the oscillation excitation with an oscillation, and the method comprising: continually capturing an effective tire force of the vehicle tire (1) in the wheel bearing, due to the oscillation, generating a data set, by applying a timing signal of the speed ramp to a Fourier transformation, which shows the tire force over the tire speed and tire frequency,.
22. The method according to claim 21, wherein the Fourier transformation is a fast Fourier transformation.
23. The method according to claim 21, wherein the data set for each value pair of tire speed and tire frequency comprises a tire force value.
24. The method according to claim 21, further comprising that classification of the tire properties takes place where the tire force is compared with a reference force in a predetermined and established window and over a tire frequency spectrum as well as a tire speed spectrum.
25. The method according to claim 24, further comprising that the window is predetermined for an intended use of the vehicle tire.
26. The method according to claim 21, further comprising assigning an order of a resonance of the tire frequency occurring in the data set to a cause of the resonance.
27. The method according to claim 26, further comprising assigning a resonance of a first order to an eccentricity and/or an imbalance.
28. The method according to claim 26, further comprising assigning a resonance of a second order to an ovality.
29. The method according to claim 26, further comprising assigning a resonance of an n-order to a construction defect or a design defect of a n-order.
30. The method according to claim 26, further comprising assigning a resonance of non-integer orders to a non-linear effect.
31. The method according to claim 26, further comprising tire forces assigned to an oscillation of an order are represented as a generated curve over the tire speed to determine an oscillation power by determining an area under the curve.
32. The method according to claim 31, further comprising carrying out classification of the tire properties by comparing the generated curve with a reference curve.
33. The method according to claim 31, further comprising approximating curves of the individual orders via a quadratic equation.
34. The method according to claim 31, further comprising assigning an unevenness in material distribution to a quadratic part of the equation.
35. The method according to claim 31, further comprising assigning a speed proportional mechanism to a linear part of the equation.
36. The method according to claim 31, further comprising assigning a construction defect or a stiffness defect to a constant part of the equation.
37. The method according to claim 21, further comprising generating an effective tire force (22) by forming a quadratic average value of the captured tire force of one order.
38. The method according to claim 37, further comprising classifying the tire properties when the effective tire force (22) is compared with an effective reference force.
39. A test stand for determination of tire properties, the test stand comprising a rim, a wheel bearing, means for applying pressure in a vehicle tire, means for applying the vehicle tire with a wheel load, means for accelerating the vehicle tire (1), means for capturing a tire speed, means for capturing of a tire power and/or a tire oscillation, the vehicle tire (1) is rotatably mounted on the rim via the wheel bearing, an interior of the vehicle tire (1) is pressurized with a fluid by the means for applying pressure in the vehicle tire (1), the vehicle tire (1) is applied with a wheel load by the means to apply the vehicle tire (1) with a wheel load, the vehicle tire (1) is accelerated by the means for accelerating of the vehicle tire (1), in accordance with a predetermined speed ramp to the final speed so that the vehicle tire, in accordance with the tire speed, experiences oscillation excitation and reacts to the oscillation excitation with an oscillation, and where the tire speed is captured by the means to capture the tire speed, a tire force which is present at the wheel bearing, due to the oscillation, is continuously captured by means of the capturing of the tire force and/or the tire or oscillation, and the test stand further comprises electronic calculation devices, the electronic calculation devices are designed to generate a data set describing the tire force over the tire speed and over the tire frequency by subjecting a timing signal of the speed ramp to a Fourier transformation.
40. The test stand according to claim 39, wherein the test stand is designed to execute the method for the determination of tire properties, whereby the vehicle tire (1) is rotatably mounted on the rim (2) via the wheel bearing, the interior of the vehicle tire (1) is pressurized by means of the fluid, the vehicle tire (1) is subjected to a wheel load, the vehicle tire (1) is accelerated to a final speed in accordance with a pre-determinable speed ramp, and the vehicle tire (1), in accordance with a tire speed, undergoes oscillation excitation and reacts to the oscillation excitation with an oscillation, the method comprising: continually capturing an effective tire force of the vehicle tire (1) in the wheel bearing due to the oscillation, generating a data set, by applying a timing signal of the speed ramp to a Fourier transformation, which shows the tire force over the tire speed and tire frequency.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] In the following, the invention is exemplary explained based on the presented embodiments in the drawings.
[0046] It shows:
[0047] FIGS. 1a-1f schematically an overview about the six different oscillation degrees of freedom of a vehicle tire,
[0048] FIG. 2 exemplary and schematically a created data set in accordance with the invention,
[0049] FIG. 3 exemplary and schematically tire forces which are assigned to oscillations of different order,
[0050] FIG. 4 exemplary and schematically an additional created data set in accordance with the invention, and
[0051] FIG. 5 exemplary and schematically the data set in FIG. 4, whereby an effective tire force was created.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0052] Same objects, functional units, and comparable components are marked, concerning all drawings, with the same reference characters. These objects, functional units and comparable components are designed identically with regard to their technical features, unless the description explicitly or implicitly states otherwise.
[0053] FIGS. 1a-1f schematically show an overview of the six different oscillation degrees of freedom of a vehicle tire 1 which is mounted on the rim 2. Along each of the presented oscillation degrees of freedom, also self-oscillations exist. These self-oscillations comprise beside the respective fundamental oscillation, which is generally called also an oscillation of the first order, or for instance as oscillation of second order or as oscillation of third order etc. A direction of the oscillations is in each case illustrated by an arrow at the vehicle tire 1. FIG. 1a shows of the first oscillation degree of freedom which allows and oscillation along the rotational direction of a running surface of the vehicle tire 1. Such an oscillation usually occurs often during the operation of the vehicle tire 1 in conjunction with tire slippage. A second degree of freedom is shown in FIG. 1b. Hereby, the vehicle tire 1 oscillates along a radial axis, forward and backward whereby opposite sides of the vehicle tire 1 oscillate in phase. FIG. 1c shows an additional possible oscillation degree of freedom whereby the vehicle tire 1, in accordance with the oscillation degrees of freedom shown in FIG. 1c, oscillates lateral to its drive direction, meaning along its rotational axis. All sides of the vehicle tire 1 oscillate here in phase. FIG. 1d shows again in an additional oscillation degree of freedom where the vehicle tire 1 is tilted, due to the oscillation with respect to its rotational axis. Again an additional oscillation degree of freedom can be seen in FIG. 1e, in accordance with the vehicle tire 1 oscillates similar to the oscillation in FIG. 1b, however, the oscillation in FIG. 1e takes place along two radial axis of the vehicle tire 1 with an offset of 90°. The oscillation along each of the radial axis is out of phase. Finally, FIG. 1f shows again in an additional oscillation degree of freedom of the vehicle tire 1 where the vehicle tire 1 also oscillates laterally along its rotational axis. However, the center of the vehicle tire 1 and outer areas of the vehicle tire 1 are oscillating out of phase.
[0054] FIG. 2 shows, by way of example and schematically, a data set generated according to the invention, which describes the tire force as a function of the tire speed and of the tire frequency. The data set was created where initially a vehicle tire 1 was rotatably mounted via a wheel bearing on a rim 2, by means of a fluid, exemplary by means of air, impinged in its interior with pressure and whereby the vehicle tire 1 was also accelerated from a standstill in accordance with a pre-determinable speed ramp to an end speed. While driving through the speed ramp, the vehicle tire 1 was subjected to a constant wheel load according to the example. As a result, the vehicle tire 1 was excited to oscillate at a tire frequency in accordance with a tire speed, which in turn led to a tire force acting on the wheel bearing, which was continuously recorded. A time signal of the speed ramp, for example a change in the detected tire force over time while driving through the speed ramp, was then subjected to a fast Fourier transformation. The tire speed as in FIG. 2 is hereby presented on the Y-axis and the tire frequency on the X-axis. The tire force can be recognized based on a color or hatching, respectively. As can be seen in FIG. 2, lines 3-16 are formed in the representation of the tire force as a function of the tire speed and as a function of the tire frequency, at which the tire force is greater than in the surrounding areas. These lines 3-16 show resonances of different orders. Where an excitation frequency meets a resonance of the vehicle tire 1 or a resonance of the fluid which is used for pressurization in the vehicle tire 1, a clear increase of the recorded tire force occurs. In accordance with the example, the lines 11-16 in the right section of the data set, meaning in the resonances at approximately 200 Hz, are hereby resonances which can be traced back to a pressure oscillation of the fluid in the vehicle tire 1. Because the amplitudes as well as the frequency positions of these resonances are characterized by the type rims used, and where for instance a test rim was used for the creation of the data set, these resonances are not suitable to classify the vehicle tire 1 for use on a conventional vehicle rim. As can further be seen, all presented lines in FIG. 2 run through the origin and are linear in reference to the tire speed and therefore to the rotational speed of the vehicle tire 1. Each specific position of the resonant frequencies of the vehicle tire 1 is characterized by the dimensions of the vehicle tire 1, as well as its mass, stiffness, its pressurization by the fluid and a wheel load. Each line 3-16 represents an oscillation of different order. The line 3 shows the oscillation of the first order, line 4 the oscillation of the second order, the line 5 the oscillation of the third order, line 6 the oscillation of the fourth order, etc. until line 16 which represents the oscillation of the 14.sup.th order. It can also be seen in FIG. 2 that the tire force in lines 6 and 7 clearly increases in the ranges 6′ and 7′. In accordance with this example, the ranges 6′ and 7′ are each at a frequency of 75 Hz, because the vehicle tire 1 has here a strong resonance and the oscillation shows accordingly a large amplitude. For the evaluation whether the vehicle tire 1 is suitable for the intended use, exemplary as a vehicle tire 1 for a sports car, a classification of the tire properties takes place by comparing the captured tire force with a reference force in a pre-determinable established window and over a tire frequency spectrum as well as a tire speed spectrum. Since a sports car is usually expected also for the movement at high speeds, the window is established over a tire speed spectrum from zero to 300 km/h in over a tire speed spectrum in accordance with a tire frequency spectrum from zero to 200 Hz. Since the vehicle tire is expected to roll evenly, a reference force of 35 N is predetermined within this window. However, since the captured tire forces in the range 6′ and 7′ are positioned above 35 N, the tire properties are here classified in this example as not suitable for a sports car.
[0055] FIG. 3 schematically shows by way of example the tire forces which are assigned to oscillations of different orders, as curves 17, 18, 19 over the tire speed. Exemplarily presented are the oscillation of the first order 17, second order 18, and third order 19. By means of the determination of an area under the curves 17, 18, 19, an oscillation power of the oscillation is determined for the respective order. Each of the determined oscillation powers is now compared with each reference power and its respective order, to classify the tire properties. As in the example, the comparison indicates that the oscillation power which is assigned to the second order 18 is larger than the reference power which is assigned to the second order, so that the vehicle tire 1 is classified as not suitable for the intended use. The oscillation power assigned to the first order 17 and the third order 19 are below each of the respectively assigned reference power but an exceeding of the reference power assigned to the second order 18 is sufficient to classify the vehicle tire 1 as not suitable.
[0056] In accordance with an additional embodiment, also presented in FIG. 3, the curves 17, 18, and 19 are each approximated via a quadratic equation of the form ax.sup.2+bx+c=0. The quadratic part “ax.sup.2” of the equation is hereby assign to the imbalance, the linear part “bx” of the equation is assigned to a speed proportional mechanism, and the constant part “c” of the equation to a design defect or a stiffness defect. Thereafter, the coefficients a, b, and c of the quadratic equation are for each curve 17, 18, and 19 compared with reference coefficients. If the coefficients a, b, and c are each smaller than the respective reference coefficients, the vehicle tire 1 is classified as suitable for the intended use. Otherwise, the vehicle tire 1 is classified as not suitable for the intended use.
[0057] FIG. 4 shows, by way of example and schematically, a further data set generated according to the invention, which describes the tire force as a function of the tire speed and as a function of the tire frequency. The data set in FIG. 4 corresponds mainly with the data set in FIG. 2 but shows who the lines 20 and 21 in the areas 20′ in 21′ resonance oscillations of a non-integer order. In accordance with the example, the resonance oscillation in the areas 20′ and 21′ are each located at 175 Hz. Through a division with the frequency of each assigned resonance frequency of the first order and an identical tire speed, it produces the respective order of a resonance in the areas 20′ and 21′. The frequency of the first order which is assigned to the resonant frequency in the area 20′ can be taken from line 3 and a tire speed of 170 km/h, meaning in the area 3′. In accordance with the example, that frequency is 21.4 Hz which results for the resonant frequency in the area 20′ in the non-integer order of 8.17. The order of the resonant frequency in the area 21′ can analogically be determined. In accordance with the example, the frequency amounts to 14.3.Hz in the area 3″ which results in a resonance frequency in the area 21′ of a non-integer order 12.23. The appearance of the non-integer resonance frequencies in the area 20′ and 21′ are assigned with a material inconsistency of the vehicle tire 1. Thus, the data set as shown in FIG. 4 indicates the presence of a material inconsistency of the vehicle tire 1 and the vehicle tire 1 can be classified accordingly.
[0058] FIG. 5 shows exemplarily and schematically the data set of FIG. 4, whereby an effective tire force 22 was created through the formation of a quadratic average value of the captured tire force of one order. The formation of a quadratic average value is hereby executed in accordance with the example based on the so-called “Root-Mean-Square” method. The effective tire force is then presented as a function of the speed, whereby the speed-dependent maxima 23 and 24 of the effective tire force can be seen. The maxima 23 and 24 corresponds hereby with the frequencies in the areas 20′ and 21′ of the lines 20 and 21. Through the comparison with a reference curve, a classification of the tire properties can now take place, whereby the tire properties in accordance with the example are classified as suitable for the intended use, if the effective tire force 22 is lower for all speeds than the effective tire force. Otherwise, the tire properties are classified as not suitable for the intended use.
REFERENCE CHARACTERS
[0059] 1 Vehicle Tire
[0060] 2 Rim
[0061] 3-16 Lines, excitation frequency
[0062] 3′, 3″ Frequency Range
[0063] 6′, 7′, 8′ Area, in which the resonance frequency is located
[0064] 17 Oscillation of the first order
[0065] 18 Oscillation of the second order
[0066] 19 Oscillation of the third order
[0067] 20 Line, excitation frequency, resonance frequency
[0068] 20′ Area, in which the resonance frequency is located
[0069] 21 Line, excitation frequency, resonance frequency
[0070] 21′ Area, in which the resonance frequency is located
[0071] 22 Effective Tire Force
[0072] 23, 24 Maxima of the effective tire force
