Calculation method for in-situ steering resistance torque between tire and road surface

Abstract

The invention relates to the technical field of vehicle steering systems, in particular to a method for calculating in-situ steering resistance torque between a tire and a road surface. The tire load, the tire pressure and the ground contact area change caused by the tire width are fully considered, the tire in-situ steering resistance moment is solved from the mechanism, and a pure empirical model is separated. The method can adapt to tire models with different tread widths, the in-situ steering resistance moment of the tire is accurately calculated, the method can be used for model selection of a steering system and checking of the steering system in all aspects, and the precision is effectively guaranteed.

Description

Technical Field

[0001] The 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 to be too small, the power motor will be too small, the steering gear will not provide enough power, and the steering hand will be heavy; if the in-situ steering resistance torque between the tire and the road is estimated to be too large, the power required for the motor will be too large, and the cost of the motor will be too high, resulting in the loss of price advantage and product competitiveness of the vehicle cost. 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 large. This patent uses the empirical formula of the last century, which does not take into account the tire width and the tire contact area, but only the tire pressure, vertical load and road friction coefficient. For the same vehicle, if the vertical load and tire pressure remain unchanged, the tire's in-situ steering resistance torque will not change according to this empirical formula. In fact, if the 195 tread width tire is replaced with a 245 tread width tire, the in-situ steering resistance torque will increase significantly, and the steering can be clearly felt to be heavy subjectively. Objective data also shows that the steering torque has increased. Because the contact area between the tire and the road has increased significantly, the in-situ steering resistance torque has not changed according to the empirical formula, which is contrary to the principle. Summary of the invention

[0003] In order to improve the accuracy of the strength verification of steering system components and improve the economy of the selection of steering gear power motor (to avoid the selection of motor power that is too small, resulting in heavy steering force for the whole vehicle, and to avoid the selection of motor power that is too large, resulting in cost waste), a new method for estimating the in-situ steering resistance torque between tires and roads is proposed, which takes into account tire load, tire pressure, and the change in contact area caused by 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, determining the tire crown width a (i.e., tire contact patch width a) and the tire free radius r according to the tire model;

[0006] Step 2, query the tire stiffness curve reported by KC according to the tire pressure to obtain the tire vertical stiffness kt;

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

[0008] Step 4, dividing 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, according to the tire free radius r and the tire compression amount Δh in step 1, calculate the contact patch length b of the tire after full load compression;

[0010] Step 6, subdividing the tire contact patch rectangle into sufficiently small calculation accuracy units, the contact patch width is divided into m equal parts, the contact patch length is divided into n equal parts, and the entire contact patch area is divided into m×n small squares;

[0011] Step 7, according to step 3, the normal pressure on the entire contact area is Fz, and the contact area in step 6 is divided into m×n small squares. The normal pressure on each small square is 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 It 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 of each small square is μ. According to the positive 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);

[0014] Step 10, according to the friction force Fi generated on each small square in step 9, the force arm of each resultant 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 force arm Li of the resultant point 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 in-situ steering resistance torque:

[0016] Furthermore, if the KC test bench conditions are not met 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 better, but the calculation speed will be slower. The actual selection can be determined according to the balance between calculation accuracy and calculation speed.

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

[0020] The present invention proposes a new theoretical calculation method, which fully considers the influence of tire tread width, tire vertical stiffness, etc., solves the tire's in-situ steering resistance torque from a mechanism point of view, and deviates from the purely empirical model. 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 steering system verification to effectively ensure accuracy. The influence of tire pattern can be expanded to more accurately calculate the ground contact area of ​​the tire pressure. With the subsequent development of science and technology, there will be instruments that can quickly display the positive pressure on each ground contact area. It can also be expanded to consider the inconsistent force on each small square in the tire ground contact mark, 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 area;

[0023] Figure 3 Tire vertical stiffness curve;

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

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

[0026] Figure 6 Coordinate map of the center points of the subdivided small squares. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0028] Take 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: According to the tire model 235 / 50R20, 235 represents the tire crown width 235 where the tire contacts the road surface, 50 represents the tire body aspect ratio of 50%, R20 represents a radial tire, and the rim is 20 inches. From the tire crown width 235, the tire contact surface width a is 235mm, such as Figure 2 As shown in the figure, the free radius of the tire can be obtained from 235 / 50R20 as 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, query the curve of tire compression and tire load, and obtain the tire vertical stiffness of 254.3N / mm. Figure 3 As shown, this can further make the results more accurate. If the KC test bench is not available, the vertical stiffness of the tire can also be estimated based on the tire pressure. The regular curve of tire pressure and vertical load is generally 1:1, that is, the vertical stiffness of the tire with a tire pressure of 250kpa is about 250N / mm, and the vertical stiffness of the tire with a tire pressure of 350kpa is about 350N / mm.

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

[0032] Step 4: The vertical compression of the tire Δh is obtained by dividing the vertical load on the tire in steps 2 and 3 by the vertical stiffness of the tire. 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, such as 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, 1 mm is taken as an example. The contact patch width is divided into m parts, and the contact patch length is divided into n parts. The entire contact patch area is divided into m x n small squares, such as Figure 5 As shown in the figure, a finer or more acceptable coarse calculation accuracy can also be used according to the calculation requirements.

[0035] Step 7: According to step 3, the normal pressure on the entire contact area is Fz. In step 6, the contact area is divided into mXn small squares, and the normal pressure on each small square can be calculated as Fz / (mXn).

[0036] Step 8: According to the subdivision of step 6, the center point of each small square is the resultant force point of the small square, the coordinates of the resultant force 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 small square resultant point, such as Figure 6 shown.

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

[0038] Step 10: Based on the friction force Fi generated on each small square in step 9, the lever arm of each resultant force point obtained in step 8 is 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 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 implementation of this patent, but this patent is not limited to the above implementation. Various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of this patent.

Claims

1. A method for calculating the in-situ steering resistance torque between a tire and a road surface, the characteristics of which are: The steps include: Step 1, determining the tire crown width a and the tire free radius r according to the tire model; Step 2, query the tire stiffness curve reported by KC according to the tire pressure to obtain the tire vertical stiffness kt; Step 3, determining the axle load Fz of the tire according to the fully loaded design load of the front axle of the vehicle; Step 4, dividing 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, according to the tire free radius r and the tire compression amount Δh in step 1, calculate the contact patch length b of the tire after full load compression; Step 6, subdividing the tire contact patch rectangle into sufficiently small calculation precision units, the contact patch width is divided into m equal parts, the contact patch length is divided into n equal parts, and the entire contact patch area is divided into m×n small squares; Step 7, according to step 3, the normal pressure on the entire contact area is Fz, and the contact area in step 6 is divided into m×n small squares. The normal pressure on each small square is 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 It 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 of each small square is μ. According to the positive 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); Step 10, according to the friction force Fi generated on each small square in step 9, the force arm of each resultant 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 force arm Li of the resultant point 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 in-situ steering resistance torque:

2. A method for calculating the in-situ steering resistance torque between a tire and a road surface according to claim 1, wherein if the KC test bench conditions are not met 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 determined by a 1:1 estimation.

3. The method for calculating the in-situ steering resistance torque between a tire and a road surface according to claim 1 is characterized in that: the axle load Fz of the tire single wheel in step 3 is half of the full-load design load of the front axle.

4. The method for calculating the in-situ 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 in-situ steering 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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