Method for measuring the actual tire size of a vehicle's tire

Abstract

The invention relates to a method for measuring the actual tire size of a tire of a vehicle. In the method, which allows particularly accurate determination of the tire size, the actual tire size of the vehicle is ascertained during driving of the vehicle by means of GPS signals.

Description

Technical Field

[0001] The invention relates to a method for measuring the actual tire size of a tire of a vehicle. Background Art

[0002] It is known that different tires are used in winter than in summer. The tires can differ in vehicle size. Therefore, the vehicle speed shown on the dashboard of the vehicle, which is calculated based on the standard tire size, is not always correct. Summary of the invention

[0003] The invention is based on the object of proposing a method for determining the actual tire size of a tire of a vehicle.

[0004] According to the invention, the object is achieved in that the actual tire size of the vehicle is ascertained with the aid of GPS signals while the vehicle is traveling by dividing the sum of the distance traveled by the vehicle and the accuracy of the GPS signal by the number of revolutions of the wheel. This has the advantage that a high-quality measuring system is not required to ascertain the actual tire size, since GPS systems are now included in all vehicles. The proposed solution is therefore based solely on the use of software, thereby reducing the costs for determining the tire size.

[0005] Advantageously, the tire size stored in the vehicle is automatically corrected using the actual tire size. By means of this correction, the correct tire size is provided to a large number of vehicle assistance systems or safety systems present in the vehicle, thereby enabling reliable control of the vehicle.

[0006] In one embodiment, the stored tire size is replaced by the actual tire size when the difference between the stored and actual tire size exceeds a predefined limit value. The selection of the limit value ensures that the two tire sizes differ significantly.

[0007] In one variant, the current speed of the vehicle is determined using the actual tire size. The speed is determined based on the engine speed, the tire radius and other parameters. By replacing the preset tire size with the actually determined tire size, the vehicle speed is always correctly determined and thus correctly provided to the assistance and safety systems and also correctly displayed to the driver in the instrument cluster.

[0008] In one variant, the GPS signal is checked for a predetermined accuracy before the actual tire size is determined. The more accurate the GPS signal, the more accurately the tire size can be determined.

[0009] In a further refinement, the actual tire size is ascertained as a function of the accuracy of the speed sensor.

[0010] Advantageously, the actual tire size is determined as a function of the load difference on the tire. This is particularly relevant since the actual tire deformation change is a function of the load change and the initial deformation. Thus, deformations of the tire due to different loadings of the vehicle can also be taken into account when determining the tire size, thereby improving the accuracy of the tire size when determining it.

[0011] In another specific embodiment, the actual tire size is determined in conjunction with a trajectory evaluation when the vehicle changes lanes. The distance covered by the vehicle is taken into account by means of the trajectory evaluation in order to improve the GPS assessment of the tire size.

[0012] In one embodiment, an estimation error is taken into account in the trajectory estimation. The estimation error must be as small as possible so that it can function reliably when determining the tire size. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention allows for numerous embodiments, one of which will be further explained with reference to the figures shown in the accompanying drawings.

[0014] The accompanying drawings show:

[0015] Figure 1 An exemplary embodiment of a vehicle for carrying out the method according to the invention is shown.

[0016] Figure 2 An embodiment of the method according to the invention is shown,

[0017] Figure 3 A schematic diagram for determining a lane change is shown.

[0018] Figure 4 shows a schematic diagram for determining the deformation of a vehicle tire,

[0019] Figure 5 One embodiment showing the correlation of error to tire size. DETAILED DESCRIPTION

[0020] exist Figure 1 1 shows an exemplary embodiment of a vehicle for carrying out the method according to the invention. The vehicle 1 comprises a control unit 2, which is coupled to a GPS receiver 3. Furthermore, the control unit 2 is coupled to a rotational speed sensor 4 for determining the wheel rotational speed. A wheel size determination unit 5 is provided in the control device 2, which is coupled to a vehicle speed determination unit 6. Furthermore, the two units 5 and 6 are connected to a storage unit 7.

[0021] Combination Figure 2An exemplary embodiment of the method according to the invention will be described. In block 100, the quality of the GPS signal received by the GPS receiver 2 is estimated and the traffic conditions are estimated. In block 110, a check is performed to determine whether all conditions correspond to the predefined conditions. If this is not the case, the process returns to block 100. If all conditions are present satisfactorily, the real-time program implemented in the tire size determination unit 5 is started in block 120. As a result, the actual tire size R of the vehicle 1 is calculated in block 130. cal Then, the actual tire size R is formed. cal and the preset tire size R stored in the storage unit 7 current The numerical value of the difference between the tire size R and the tire size R is compared with a preset threshold value β in box 140. If the numerical difference is greater than the threshold value β, the process proceeds to box 150, where the actual tire size R is calculated. cal Replace the currently stored tire size R current The vehicle speed determination unit 6 now uses the new actually determined tire size R cal To obtain the vehicle speed. Subsequently, the real-time program ends. When the value of the tire size difference determined in box 140 is less than the threshold value, the program ends in box 160 as well.

[0022] In addition, the method for determining the actual tire size R is described in detail. cal In general, there are several sources of influence on the calculation of the tire size. Some of them, such as temperature and air humidity, are very small and can be ignored. Other influences, such as the accuracy of the speed sensor, GPS accuracy, load differences and estimation errors when changing lanes, are taken into account in the calculation. Tire size R cal It is calculated as follows:

[0023]

[0024] The equation 1 is simplified to equation 2.

[0025]

[0026] The speed N is linearized with the aid of the approximation equation 3.

[0027]

[0028] It turns out that:

[0029]

[0030]

[0031] In the equations described, it applies that:

[0032] S is the distance travelled by the vehicle

[0033] ε GpS GPS signal accuracy status

[0034] ε CL Error estimation for lane change

[0035] ε N Speed ​​sensor accuracy

[0036] n Number of lane changes

[0037] N revolutions

[0038] ΔR FL Load-Dependent Error Estimation

[0039] In equation 5, the parameter ε N , ε CL and ε GPS is less than 1, so the product of two of the parameters is very small and can be ignored in further consideration.

[0040]

[0041]

[0042]

[0043] If we substitute equation 7 into equation 6, for tire size R cal The following is obtained:

[0044]

[0045] In order to obtain high accuracy, an accurate rotation speed sensor should be selected. The accuracy should not exceed 0.5%. The influence of the GPS signal is related to the distance traveled and the quality of the GPS signal. Generally, the standard GPS system (SPS) has an accuracy of 22.5m. The improved GPS signal precise positioning service (PPS) provides an accuracy of 9m. In addition, the accuracy can be improved to 0.02m with the help of an additional differential measurement system. In normal use when the signal quality is 11.7m, the influence of GPS inaccuracy can be reduced to 0.5% after a driving distance of 2340m.

[0046] exist Figure 3 The schematic diagram for lane change of a vehicle is shown in FIG. Assuming that the frequency of lane change K(S) is below a limit value, for example t / km, then it is possible to use

[0047] n=K(S)*s (9)

[0048] Describe the error type as

[0049]

[0050] Among them, the applicable ones are:

[0051] S W Distance in the direction of travel during the lane change,

[0052] S L The distance perpendicular to the direction of travel,

[0053] S RW Actual path used for lane change

[0054] S RWR Simplified path for lane changes

[0055] V sclar Estimation factor for the true estimated path relative to the actual path

[0056] εCLM Speed ​​sensor accuracy

[0057] The error εCL describes the actual distance of the drive relative to the measured distance:

[0058]

[0059] On the other hand, the actual driving section S RW Approximately S RWR :

[0060]

[0061] If we substitute equation 12 into equation 11, we get:

[0062]

[0063] In one embodiment, at a distance S perpendicular to the lane, L is 3.5 m and the distance S in the direction of travel during the lane change W is 50m and the frequency of lane change K(S) is 1 / km, the scaling factor V sclar =1.1 and the accuracy εCLM of the speed sensor is 1%, the influence of the estimation error is reduced to 0.75%.

[0064] Furthermore, the load difference has a great influence on the determination of the tire size, since the actual tire deformation changes due to the load change. Figure 4 The schematic diagram for the magnitude of deformation of the tire is shown in FIG.

[0065] The relationship between the deformation and load of the tire is approximately shown by Equation 14.

[0066]

[0067] The equation 14 is described as equivalent in equation 15.

[0068]

[0069]

[0070] in

[0071] F L is the load on the vehicle tires,

[0072] F Lo is the initial load on the vehicle,

[0073] p o is the initial pressure,

[0074] b is the width of the tire,

[0075] x is the deformation of the tire,

[0076] x o is the initial deformation,

[0077] r is the radius of the undeformed tire,

[0078] ΔF L is the load difference, and

[0079] α is the coefficient of load difference.

[0080] Since the deformation of the tire x must be less than the radius r of the tire, the solution is found in Equation 16, where from the current load S L To initial load F Lo , the radius r changes in

[0081]

[0082] The load variation is described in Equation 18.

[0083] ΔF L =F L -F L0 =αF L0 -F L0 =(α-1)F L0 (18)

[0084] α is here a factor which is compared with the initial load.

[0085] If equations 16 and 18 are applied to equation 17, we obtain:

[0086]

[0087] Equation 19 is simplified as follows:

[0088]

[0089] The actual radius of the tire is described as follows:

[0090] R real =r-x0 (21)

[0091] If equation 21 is input into equation 20, the normalized equation 22 is obtained.

[0092]

[0093] This means that the actual tire deformation change is related to the load change and the initial deformation. Assuming that the empty vehicle with one passenger weighs 1 t and the current vehicle has a weight of 1.2 t, since 4 people take up space in the vehicle, the coefficient of the load difference is α=1.2. The initial deformation of the tire is 2%, so the relative change in the expected deformation change is 0.8. This error can be suppressed with the help of an accurate weight sensor.

[0094] When transforming Equation 8, the overall relative measurement error of the described system can be shown as follows:

[0095]

[0096] After a tire is replaced, the tire size increases or decreases by approximately 1 inch. Therefore, the measurement system requires an accuracy of 1 / 2 inch, which is derived from Equation 24.

[0097]

[0098] For example,

[0099]

[0100] Figure 5 The correlation of tire size and required distal accuracy is shown. If the tire size is 17 inches, an accuracy of 2.4% is assumed, assuming a total relative systematic error of 2.37 as expected in the last part of this specification.

[0101] Description of Reference Numerals

[0102] 1 vehicle 2 control unit 3 GPS receiver 4 rotation speed sensor 5 tire size determination unit 6 vehicle speed determination unit 7 storage unit.

Claims

1. A method for determining the actual tire size of a tire of a vehicle, It is characterized in that During driving of the vehicle, an actual tire size of the vehicle is determined with the aid of a GPS signal by dividing a sum of a distance traveled by the vehicle and an accuracy of the GPS signal by the number of revolutions of the wheels; and the actual tire size is determined in relation to a trajectory evaluation when the vehicle changes lanes, wherein the actual tire size is determined taking into account an error estimate of the lane change of the vehicle and the number of lane changes.

2. The method according to claim 1, It is characterized in that The tire size stored in the vehicle is corrected using the actual tire size.

3. The method according to claim 2, It is characterized in that If the value of the difference between the stored and actual tire dimensions exceeds a predefined threshold value, the stored tire dimensions are replaced by the actual tire dimensions.

4. The method according to claim 3, It is characterized in that The current driving speed of the vehicle is determined using the actual tire dimensions.

5. The method according to claim 1, It is characterized in that Before determining the actual tire size, the GPS signal is checked for a preset accuracy.

6. The method according to claim 1, It is characterized in that The actual tire size is determined as a function of the accuracy of the speed sensor.

7. The method according to claim 1, It is characterized in that The actual tire dimension is ascertained as a function of the load difference on the tire.

8. The method according to any one of claims 1 to 7, It is characterized in that Consider the estimation error during trajectory estimation.

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