A method for calculating the resistance torque between tire and road surface during stationary steering

Abstract

The present invention relates to the technical field of vehicle steering systems, and more specifically, to a method for calculating the stationary steering torque between a tire and a road surface. This method fully considers factors such as tire load, tire pressure, and the change in contact patch due to tire width, thereby solving the stationary steering torque of the tire from a mechanistic perspective, departing from purely empirical models. The present invention can adapt to tire models with varying tread widths, accurately calculating the stationary steering torque of the tire. This method can be used for steering system selection and verification of various aspects of the steering system, effectively ensuring accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle steering systems, and in particular to a method for calculating the in-situ steering resistance torque between a tire and a road surface. Background Art

[0002] In order to ensure driving safety, the various parts that make up the steering system should have sufficient strength. To verify the strength of the steering system, it is necessary to first determine the forces acting on each part. The main source of these forces is the size of the in-situ steering resistance torque between the tire and the road. The steering resistance torque between the tire and the road will also affect the selection of the power steering motor. If the in-situ steering resistance torque between the tire and the road is estimated too small, the power steering motor will be too small, the steering assist will not be enough, and the steering hand force will be heavy; if the in-situ steering resistance torque between the tire and the road is estimated too large, the power required by the motor will be too large, and the cost of the motor will be too high, resulting in the loss of price advantage in the cost of the whole vehicle and loss of product competitiveness. There is currently no set method for calculating the in-situ steering resistance torque between the tire and the road. The industry still uses the empirical calculation formula from the 1950s. For example, patent CN1 12231833B provides a method for calculating steering resistance torque, which uses the empirical formula of the last century. The error is significant. This patent uses an empirical formula from the last century that doesn't account for tire width or contact patch, only tire pressure, vertical load, and road friction coefficient. For the same vehicle, with constant vertical load and tire pressure, this empirical formula shows no change in the tire's stationary turning torque. However, replacing a 195mm tread width tire with a 245mm tread width will significantly increase the stationary turning torque, resulting in a subjective sense of heavy steering. Objective data also shows an increase in steering torque. This is contradictory to the empirical formula, as the tire's contact patch with the road has increased significantly, yet the stationary turning torque remains unchanged. Summary of the Invention

[0003] To improve the accuracy of steering system component strength verification and enhance the economic efficiency of steering assist motor selection (avoiding both excessively high motor power, which results in heavy steering effort, and excessively high motor power, which results in costly losses), a new method for estimating the in-situ steering resistance torque between the tire and the road surface is proposed. This method considers tire load, tire pressure, and the change in contact area due to tire width. The specific technical solution is as follows:

[0004] A method for calculating the in-situ steering resistance torque between a tire and a road surface comprises the following steps:

[0005] Step 1: Determine the tire crown width a (i.e., tire contact patch width a) and tire free radius r according to the tire model;

[0006] Step 2: Obtain the tire vertical stiffness kt by querying the tire stiffness curve reported by KC according to the tire pressure;

[0007] Step 3: Determine the axle load Fz of the tire according to the fully loaded design load of the front axle of the vehicle;

[0008] Step 4: Divide the axle load Fz on the tire obtained in steps 2 and 3 by the tire vertical stiffness kt to obtain the tire vertical compression Δh;

[0009] Step 5: Calculate the contact patch length b of the fully loaded and compressed tire based on the tire free radius r and the tire compression Δh obtained in step 1.

[0010] Step 6: Subdivide the tire contact patch rectangle into sufficiently small computational precision units. The contact patch width is divided into m equal parts, and the contact patch length is divided into n equal parts. The entire contact patch area is divided into m×n small squares.

[0011] Step 7: Based on step 3, the normal pressure on the entire contact area is Fz. In step 6, the contact area is divided into m×n small squares. Calculate the normal pressure on each small square as Fz / (m×n).

[0012] Step 8: According to the subdivision of step 6, the center point of each small square is the resultant point of the force on the small square. The coordinates of the resultant point are (xi, yi), and the distance from the center point 0 of the tire contact area is That is the force arm Li of the force at the resultant point of the small square;

[0013] Step 9: The friction coefficient between the ground and the tire in each small square is μ. Based on the normal pressure Fz / (m×n) applied to the small square in step 7, the friction force generated by each small square is Fi = μ*Fz / (m×n).

[0014] Step 10: Based on the friction force Fi generated on each small square in step 9 and the moment arm of each resultant force point obtained in step 8 as Li, the in-situ turning resistance torque Mi generated by each small square is the friction force Fi on the small square multiplied by the moment arm of the resultant force point Li of the small square, that is, Mi = Fi * Li;

[0015] Step 11: Integrate the resistance torque of all small grid points within the tire contact area to obtain the tire's in-situ steering resistance torque.

[0016] Furthermore, if the KC test bench conditions are not available in step 2, the vertical stiffness of the tire is estimated based on the tire pressure, and the regular curve of the tire pressure and the vertical load is estimated and determined in a 1:1 ratio.

[0017] Furthermore, the axle load Fz on the tire in step 3 is half of the fully loaded design load of the front axle.

[0018] Furthermore, the calculation accuracy unit in step 6 is 0.5-2mm. The calculation accuracy is determined according to the calculation requirements. The smaller the unit, the finer the calculation, but the slower the calculation speed. The actual choice can be determined based on the balance between calculation accuracy and calculation speed.

[0019] Furthermore, the calculation in step 11 is completed using Matlab programming language.

[0020] The present invention proposes a new theoretical calculation method that fully considers the influence of tire tread width, the vertical stiffness of the tire, etc., and solves the tire's in-situ steering resistance torque from a mechanistic perspective, breaking away from purely empirical models. The present invention can adapt to tire models with different tread widths and more accurately calculate the tire's in-situ steering resistance torque. It can be used for steering system selection and various aspects of the steering system to effectively ensure accuracy. The influence of the tire pattern can be expanded to more accurately calculate the ground contact area under the pressure of the tire. If, with the subsequent development of science and technology, there are instruments that can quickly display the positive pressure on each ground contact area, it can also be expanded to consider the inconsistent forces on each small square in the tire's ground contact footprint, and the integration concept proposed by the present invention can also be applied. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Calculation flow chart of the method of the present invention;

[0022] Figure 2 Schematic diagram of tire contact patch;

[0023] Figure 3 Tire vertical stiffness curve;

[0024] Figure 4 Schematic diagram of the tire's fully loaded compressed position;

[0025] Figure 5 The idea of ​​integration is used to subdivide the tire contact patch;

[0026] Figure 6 Coordinate diagram of the center point of the subdivided small square. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] Taking the front axle of a vehicle as an example, the maximum load of the front axle is 1400kg, the tire model is 235 / 50R20, and the tire pressure is 250kpa. The steps to accurately calculate the in-situ steering resistance torque between the tire and the road are as follows. The detailed flow chart is as follows: Figure 1As shown:

[0029] Step 1: Based on the tire model 235 / 50R20, 235 represents the tire crown width 235 in contact with the road, 50 represents the carcass aspect ratio of 50%, R20 represents a radial tire, and the rim is directly 20 inches. From the tire crown width 235, the tire contact patch width a is 235mm, as shown in the following example: Figure 2 As shown in the figure, the free radius of the tire 235 / 50R20 is 235*50%+20*25.4 / 2=371.5mm.

[0030] Step 2: Query the tire stiffness curve reported by KC according to the tire pressure to obtain the tire vertical stiffness. Automobile OEMs generally have KC test benches. Inflate the tire to the specified tire pressure, place it on the KC test bench, and query the curve of tire compression and tire load. The tire vertical stiffness is 254.3N / mm. Figure 3 This can further improve the accuracy of the results. If a KC test bench is not available, the vertical stiffness of the tire can also be estimated based on tire pressure. The relationship between tire pressure and vertical load is generally 1:1, meaning that a tire with a pressure of 250kPa has a vertical stiffness of approximately 250N / mm, and a tire with a pressure of 350kPa has a vertical stiffness of approximately 350N / mm.

[0031] Step 3: Determine the axle load Fz on a single tire based on the fully loaded design load of the vehicle's front axle. For example, if the maximum load on the fully loaded front axle is 1400kg, the weight on a single wheel is 1400 / 2=700kg, i.e., the vertical axle load on a single wheel is Fz=700*9.8=6860N.

[0032] Step 4: Divide the vertical load on the tire in steps 2 and 3 by the vertical stiffness of the tire to obtain the vertical compression of the tire Δh. The vertical axle load on the tire is 6860N, the vertical stiffness of the tire is 254.3, and the vertical compression of the tire Δh = 6860 / 254.3 = 26.98mm. Figure 4 shown.

[0033] Step 5: Based on the tire free radius r and the tire compression Δh in step 1, the contact patch length b of the fully loaded and compressed tire can be calculated. For this tire, b is 277.98 mm. Figure 2 and Figure 4 shown.

[0034] Step 6: Using the idea of ​​integration, the tire contact patch rectangle is subdivided and further subdivided into sufficiently small units. In this embodiment, taking 1mm as an example, the contact patch width is divided into m equal parts, and the contact patch length is divided into n equal parts. The entire contact patch area is divided into m x n small squares, as shown in the following example: Figure 5 A finer or acceptable coarser calculation accuracy can also be used according to the calculation requirements.

[0035] Step 7: Based on step 3, the normal pressure on the entire contact area is Fz. In step 6, the contact area is divided into m x n small squares. The normal pressure on each small square can be calculated as Fz / (m x n).

[0036] Step 8: According to the subdivision of step 6, the center point of each small square is the resultant point of the force on the small square. The coordinates of the resultant point are (xi, yi), and the distance from the center point 0 of the tire contact area is That is the force arm Li of the resultant force point of the small square, such as Figure 6 shown.

[0037] Step 9: The coefficient of friction between the ground and the tire in each small square is μ. Based on the normal pressure Fz / (m × n) on the small square in step 7, the friction force generated by each small square is Fi = μ*Fz / (m × n).

[0038] Step 10: Based on the friction force Fi generated on each small square in step 9, and the lever arm of each resultant force point obtained in step 8 is Li, then the in-situ turning resistance torque Mi generated by each small square is the friction force Fi on the small square multiplied by the lever arm Li of the resultant force point of the small square, that is, Mi = Fi*Li.

[0039] Step 11: Integrate the resistance torque of all small grid points within the tire contact area to obtain the tire's in-situ steering resistance torque. Since the length of the subdivided unit is relatively thin, only 1mm, the manual calculation amount is relatively large. Here, the program can be used for automatic calculation instead of manual calculation to improve efficiency. Here, the MATLAB program is used as an example, and other programming languages ​​can also be used.

[0040] The above describes in detail the preferred embodiments of this patent, but this patent is not limited to the above embodiments. Various changes can be made within the scope of knowledge possessed by ordinary technicians in this field without departing from the purpose of this patent.

Claims

1. A method for calculating the rotational resistance torque between a tire and a road surface, the method comprising: The steps include: Step 1: Determine the tire crown width a and tire free radius r according to the tire model; Step 2: Obtain the tire vertical stiffness kt by querying the tire stiffness curve reported by KC according to the tire pressure; Step 3: Determine the axle load Fz of the tire according to the fully loaded design load of the front axle of the vehicle; Step 4: Divide the axle load Fz on the tire obtained in steps 2 and 3 by the tire vertical stiffness kt to obtain the tire vertical compression Δh; Step 5: Calculate the contact patch length b of the fully loaded and compressed tire based on the tire free radius r and the tire compression Δh obtained in step 1. Step 6: Subdivide the tire contact patch rectangle into sufficiently small computational precision units. The contact patch width is divided into m equal parts, and the contact patch length is divided into n equal parts. The entire contact patch area is divided into m×n small squares. Step 7: Based on step 3, the normal pressure on the entire contact area is Fz. In step 6, the contact area is divided into m×n small squares. Calculate the normal pressure on each small square as Fz / (m×n). Step 8: According to the subdivision of step 6, the center point of each small square is the resultant point of the force on the small square. The coordinates of the resultant point are (xi, yi), and the distance from the center point 0 of the tire contact area is That is the force arm Li of the force at the resultant point of the small square; Step 9: The friction coefficient between the ground and the tire in each small square is μ. Based on the normal pressure Fz / (m×n) applied to the small square in step 7, the friction force generated by each small square is Fi = μ*Fz / (m×n). Step 10: Based on the friction force Fi generated on each small square in step 9 and the moment arm of each resultant force point obtained in step 8 as Li, the in-situ turning resistance torque Mi generated by each small square is the friction force Fi on the small square multiplied by the moment arm of the resultant force point Li of the small square, that is, Mi = Fi * Li; Step 11: Integrate the resistance torque of all small grid points within the tire contact area to obtain the tire's in-situ steering resistance torque.

2. A method for calculating the stationary steering resistance torque between a tire and a road surface according to claim 1, wherein: if the KC test bench conditions are not available in step 2, the tire vertical stiffness is estimated based on the tire pressure, and the regular curve of the tire pressure and vertical load is determined by estimation in a 1:1 ratio.

3. The method for calculating the stationary steering resistance torque between a tire and a road surface according to claim 1, wherein the axle load Fz applied to a single tire in step 3 is half of the fully loaded design load of the front axle.

4. The method for calculating the stationary steering resistance torque between a tire and a road surface according to claim 1, wherein: The calculation accuracy unit in step 6 is 0.5-2mm.

5. The method for calculating the rotational resistance torque between a tire and a road surface according to claim 1, wherein: The calculation in step 11 is completed using Matlab programming language.

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