A method for estimating road adhesion coefficient of four-wheel independent drive vehicle based on torque transfer

Abstract

The application discloses a four-wheel independent drive vehicle road adhesion coefficient estimation method based on torque transfer, which comprises the following steps: step one, collecting the angular velocity, longitudinal acceleration and lateral acceleration of any one wheel of the vehicle; step two, obtaining the tire longitudinal force, vertical load and slip rate of the corresponding wheel; step three, obtaining the relationship curve among the tire longitudinal force gain, vertical load, slip rate and road adhesion coefficient under different road adhesion coefficients; step four, making a MAP graph; step five, establishing a slip rate effective flag for the low slip rate range; step six, if the slip rate of the corresponding wheel is the invalid flag, then the front and rear axle torques of the vehicle are adjusted through a PID controller, so that the slip rate of the corresponding wheel meets the effective flag, and then the current tire longitudinal force gain to vertical load and slip rate are used to look up the MAP graph to identify the current road adhesion rate. The application has the characteristics of improving efficiency and accuracy.

Description

Technical Field

[0001] This invention relates to the field of tire technology, and more specifically, to a method for estimating the road adhesion coefficient of a four-wheel independent drive vehicle based on torque transfer. Background Technology

[0002] Different road surface adhesion coefficients directly affect vehicle power, braking performance, and handling stability. Existing road surface recognition methods mainly include cause-based and effect-based methods. However, both cause-based and effect-based methods have drawbacks due to the inherent characteristics of sensors. These drawbacks include high cost and complex calculations. For stable vehicle driving conditions, the slip ratio is generally low, and a simple and reliable method is needed to identify the road surface adhesion coefficient at this time. Summary of the Invention

[0003] The purpose of this invention is to design and develop a method for estimating the road surface adhesion coefficient of a four-wheel independent drive vehicle based on torque transfer. By combining tire longitudinal force, vertical load and slip ratio, the method improves computational efficiency and accuracy.

[0004] The technical solution provided by this invention is as follows:

[0005] A method for estimating the road adhesion coefficient of a four-wheel independent drive vehicle based on torque transfer includes the following steps:

[0006] Step 1: Collect the angular velocity, longitudinal acceleration, and lateral acceleration of any wheel of the vehicle;

[0007] Step 2: Obtain the longitudinal force, vertical load, and slip ratio of the corresponding wheel.

[0008] Step 3: Under different road adhesion coefficients, obtain the relationship curves between the gain of tire longitudinal force on vertical load, slip ratio and road adhesion coefficient;

[0009] Step 4: Fit the relationship curve to create a MAP plot;

[0010] Step 5: Establish effective slip ratio flags for the low slip ratio range:

[0011]

[0012] In the formula, flag is the valid flag value, and S min S is the minimum value in the low slip ratio range. max This is the maximum value within the low slip ratio range;

[0013] Step 6: If the slip ratio of the corresponding wheel satisfies flag=0, then the torque of the front and rear axles of the vehicle is adjusted by the PID controller so that the slip ratio of the corresponding wheel satisfies flag=1.

[0014] If the slip ratio of the corresponding wheel satisfies flag=1, the current road surface adhesion rate is identified by looking up the MAP map based on the gain of the longitudinal force of the tire on the vertical load and the slip ratio obtained from the current calculation.

[0015] Preferably, the longitudinal force of any one of the wheels satisfies:

[0016]

[0017] In the formula, J is the moment of inertia of the wheel. Let T be the angular velocity of the i-th wheel. i F is the resultant torque received by the i-th wheel. xi Let R be the longitudinal force of the i-th wheel, and let R be the rolling radius of the wheel. Let i = L1, R1, L2, R2. When i = L1, the wheel is the left front wheel; when i = R1, the wheel is the right front tire; when i = L2, the wheel is the left rear tire; and when i = R2, the wheel is the right rear tire.

[0018] Preferably, the vertical load on any wheel satisfies:

[0019]

[0020]

[0021]

[0022]

[0023] In the formula, F zL1 Let m be the vertical load on the left front wheel, m be the vehicle mass, g be the acceleration due to gravity, b be the distance from the rear axle to the center of mass, and L be the wheelbase. Let h be the vehicle's longitudinal acceleration and h be the height of the vehicle's center of gravity. Let F be the lateral acceleration of the vehicle, d be the track width, and F be the lateral acceleration of the vehicle. zR1 For the vertical load on the right front tire, F zL2 Let F be the vertical load on the left rear tire, 'a' be the distance from the front axle to the center of gravity, and 'F' be the distance from the front axle to the center of gravity. zR2 This represents the vertical load on the right rear tire.

[0024] Preferably, the slip ratio of any wheel satisfies:

[0025]

[0026] In the formula, S i Let be the slip ratio of the i-th wheel.

[0027] Preferably, step three specifically includes the following steps:

[0028] Step 1: Compile a table showing the tire longitudinal force, vertical load, and slip ratio of the corresponding wheels under various working conditions where the gain of tire longitudinal force on vertical load is 0.2, 0.3, ..., 1, with a road surface adhesion coefficient of 0.3.

[0029] Step 2: Compile data tables on the tire longitudinal force, vertical load, and slip ratio of the corresponding wheels under various working conditions where the gain of tire longitudinal force on vertical load is 0.2, 0.3, ..., 1 under road surface conditions with road surface coefficients of 0.4, ..., 0.9.

[0030] Step 3: Organize the obtained data tables to obtain the relationship curves between the gain of tire longitudinal force on vertical load and tire slip ratio under different road surface adhesion coefficients of 0.3, 0.4, ..., 0.9.

[0031] Preferably, step four specifically includes the following steps:

[0032] Step 1: Under the condition of road surface adhesion coefficient of 0.3, determine the range of data points selected in the curve of the relationship between the gain of the longitudinal force of the tire on the vertical load and the slip ratio of the corresponding wheel from the low slip ratio range, and perform polynomial fitting on the relationship curve.

[0033] Step 2: Under the condition of road surface adhesion coefficient of 0.4, ..., 0.9, determine the range of data points selected in the curve of the relationship between the gain of the longitudinal force of the tire on the vertical load and the slip ratio of the corresponding wheel from the low slip ratio range, and perform polynomial fitting on the relationship curve.

[0034] Step 3: Verify the fitted relationship curve and create a MAP plot.

[0035] Preferably, the low slip ratio ranges from 1% to 10%.

[0036] Preferably, the output of the PID controller satisfies:

[0037]

[0038] In the formula, ΔT represents the change in torque of the vehicle's front axle, e s K represents the error between the slip ratio and either the lower or upper limit of the slip ratio. P K is the proportional control coefficient. I K is the integral adjustment coefficient. D This is the differential adjustment coefficient.

[0039] Preferably, the error between the slip ratio and the lower limit or upper limit of the slip ratio satisfies:

[0040]

[0041] Preferably, when the PID controller outputs the change in the front axle torque of the vehicle, the rear axle torque of the vehicle undergoes the opposite change.

[0042] The beneficial effects of this invention are as follows:

[0043] This invention presents a method for estimating the road surface adhesion coefficient of a four-wheel independent drive vehicle based on torque transfer. This method addresses the problem of complex road surface adhesion coefficient identification methods under low slip ratios in existing technologies. It improves both computational efficiency and accuracy, and the required computational parameters can be obtained from the sensor configurations already present in most vehicles, thus reducing costs. Attached Figure Description

[0044] Figure 1 This is a flowchart illustrating the method for estimating the road surface adhesion coefficient of a four-wheel independent drive vehicle based on torque transfer, as described in this invention.

[0045] Figure 2 This is a schematic diagram showing the relationship between the gain of tire longitudinal force on vertical load and tire slip ratio under different road surface adhesion coefficients in the embodiments of the present invention.

[0046] Figure 3 This is a schematic diagram of a MAP in an embodiment of the present invention. Detailed Implementation

[0047] The present invention will now be described in further detail so that those skilled in the art can implement it based on the description.

[0048] like Figure 1 As shown, the present invention provides a method for estimating the road surface adhesion coefficient of a four-wheel independent drive vehicle based on torque transfer, which specifically includes the following steps:

[0049] Step 1: Collect the vehicle's motion parameters and mechanical parameters while it is in motion using sensors;

[0050] The mechanical parameters include the vehicle's mass, distance from the front axle to the center of gravity, distance from the rear axle to the center of gravity, wheelbase, center of gravity height, track width, and rolling radius.

[0051] The motion parameters are wheel angular velocity, longitudinal acceleration, and lateral acceleration.

[0052] Step 2: Based on the motion and mechanical parameters from Step 1, obtain the longitudinal force, vertical load, and slip ratio of any wheel.

[0053] According to the dynamic equilibrium equation of wheel rotation:

[0054]

[0055] In the formula, J is the moment of inertia of the wheel. Let T be the angular velocity of the i-th wheel. i F is the resultant torque received by the i-th wheel. xi Let R be the longitudinal force of the i-th wheel, and R be the rolling radius of the wheel. Let i = L1, R1, L2, R2. When i = L1, the wheel is the left front wheel; when i = R1, the wheel is the right front tire; when i = L2, the wheel is the left rear tire; and when i = R2, the wheel is the right rear tire. The above parameters are obtained from the known parameters of the vehicle and the information collected by the sensors. The longitudinal force of the left front wheel can then be calculated.

[0056] The vertical load on any wheel satisfies:

[0057]

[0058]

[0059]

[0060]

[0061] In the formula, F zL1 Let m be the vertical load on the left front wheel, m be the vehicle mass, g be the acceleration due to gravity, b be the distance from the rear axle to the center of mass, and L be the wheelbase. Let h be the vehicle's longitudinal acceleration and h be the height of the vehicle's center of gravity. Let F be the lateral acceleration of the vehicle, d be the track width, and F be the lateral acceleration of the vehicle. zR1 For the vertical load on the right front tire, F zL2 Let F be the vertical load on the left rear tire, 'a' be the distance from the front axle to the center of gravity, and 'F' be the distance from the front axle to the center of gravity. zR2 The vertical load on the right rear tire is given by the parameters above, which are known vehicle parameters and longitudinal and lateral accelerations obtained from sensors. The vertical load on the left front tire can then be calculated.

[0062] The slip ratio of any one of the wheels satisfies:

[0063]

[0064] In the formula, S i Let be the slip ratio of the i-th wheel.

[0065] Step 3: Under different road adhesion coefficients, obtain the relationship curves between the gain of tire longitudinal force on vertical load, slip ratio and road adhesion coefficient;

[0066] Step 4: Create a MAP plot by fitting the relationship curve;

[0067] Step 5: Establish effective slip ratio flags for the low slip ratio range:

[0068]

[0069] In the formula, flag is the valid flag value, and S min S is the minimum value in the low slip ratio range. max This is the maximum value within the low slip ratio range;

[0070] Step 6: Determine the validity of the slip ratio and identify the road surface adhesion coefficient.

[0071] If the slip ratio of the left front wheel satisfies flag=1, the current road surface adhesion rate is identified by looking up the map based on the gain of the longitudinal force of the tire on the vertical load and the slip ratio obtained from the current calculation.

[0072] If the slip ratio of the left front wheel satisfies flag = 0, then S i ≥S max or S i ≤S min The slip ratio S needs to be made i Only when flag=1 is the road surface adhesion coefficient identified;

[0073] When flag = 0, a PID controller is used to control the torque of the front and rear axles of the vehicle to reduce the error e. s , making the slip ratio S i To ensure flag = 1, the specific control method is as follows:

[0074]

[0075] In the formula, ΔT is the output of the PID controller, i.e., the change in torque of the vehicle's front axle, e s This is the error between the slip ratio and either the lower or upper limit of the slip ratio, i.e.:

[0076]

[0077] The change in front axle torque is obtained by using a PID controller, and the rear axle torque is also changed accordingly. This satisfies the vehicle's dynamic requirements while ensuring that flag=1 satisfies the slip ratio condition for road adhesion coefficient identification.

[0078] Example

[0079] Estimate the coefficient of friction for a four-wheel independent drive vehicle in the low slip ratio range (1%-10%):

[0080] Step 1: Collect the mechanical parameters of each tire of the vehicle while it is in motion using sensors. At the same time, obtain the vehicle's mass, distance from the front axle to the center of gravity, distance from the rear axle to the center of gravity, wheelbase, center of gravity height, track width, and rolling radius.

[0081] Step 2: Based on the mechanical parameters in Step 1, obtain the longitudinal force, vertical load, and slip ratio of the left front wheel when the vehicle is traveling on a road surface with a road adhesion coefficient of (0.3 to 0.9).

[0082] Step 3: Using the ratio of the longitudinal force on the ground to the vertical load on the left front tire as the gain, plot a curve showing the relationship between the gain increasing simultaneously with the road adhesion coefficient and the tire slip ratio at various adhesion coefficients. Specifically, this includes:

[0083] Step 1: Calculate the longitudinal force F of the left front tire of the vehicle under various working conditions where the gain (ratio) of the tire longitudinal force to the vertical load is (0.2, 0.3, ..., 1) under the road surface adhesion coefficient of 0.3. xL1 and vertical load F zL1 and slip ratio S L1 Data table;

[0084] Step 2: Calculate the longitudinal force F of the left front tire of the vehicle under various working conditions where the gain (ratio) of the tire longitudinal force to the vertical load is (0.2, 0.3, ..., 1) under road surface adhesion coefficients of 0.4, ..., 0.9. xL1 and vertical load F zL1 and slip ratio S L1 Data table;

[0085] Step 3: Organize the data tables from Steps 1 and 2 to obtain the relationship curves between the tire longitudinal force gain on vertical load and the tire slip ratio under different road adhesion coefficients (0.3, 0.4, ..., 0.9), as shown below. Figure 2 As shown;

[0086] Step 4: Determine the lower slip ratio range (1%-10%), and perform polynomial fitting on the curve showing the relationship between the tire longitudinal force gain on the vertical load and the tire slip ratio obtained from the data table compiled in Step 3. Then, create a tabble data map, specifically including:

[0087] Step 1: Under the condition of a road surface adhesion coefficient of 0.3, determine the longitudinal force F of the left front tire of the vehicle from the low slip ratio range. xL1 For vertical load F zL1 Gain and slip ratio S L1The range of data points selected in the relationship curve, and polynomial fitting performed on the curve:

[0088]

[0089] In the formula, Y3 is the dependent variable of the curve under the condition that the road surface adhesion coefficient is 0.3.

[0090] Step 2: Under the condition of road adhesion coefficients of 0.4, ..., 0.9, determine the longitudinal force F of the left front tire of the vehicle from the low slip ratio range. xL1 For vertical load F zL1 Gain and slip ratio S L1 The range of data points selected in the relationship curve, and polynomial fitting performed on the curve:

[0091]

[0092]

[0093]

[0094]

[0095] Y8 = 2.476·10 4 ·x 5 -1.86·10 4 ·x 4 +4920·x 3 -601·x 2 +34.99·x-0.02419;

[0096]

[0097] In the formula, Y4 is the dependent variable of the curve under the condition of road surface adhesion coefficient of 0.4, Y5 is the dependent variable of the curve under the condition of road surface adhesion coefficient of 0.5, Y6 is the dependent variable of the curve under the condition of road surface adhesion coefficient of 0.6, Y7 is the dependent variable of the curve under the condition of road surface adhesion coefficient of 0.7, Y8 is the dependent variable of the curve under the condition of road surface adhesion coefficient of 0.8, and Y9 is the dependent variable of the curve under the condition of road surface adhesion coefficient of 0.9.

[0098] Step 3: Organize the fitted relationship curves from Step 2 and Step 1, check the curve interference within the low slip ratio range (1%–10%), and create a tabble data map, such as... Figure 3 As shown.

[0099] Step 5: Establish effective slip ratio flags for the low slip ratio range:

[0100]

[0101] In the formula, flag is the valid flag value, and S min S is the minimum value in the low slip ratio range. max This is the maximum value within the low slip ratio range;

[0102] Step 6: Determine the validity of the slip ratio and identify the road surface adhesion coefficient.

[0103] If the slip ratio of the left front wheel satisfies flag=1, the current road surface adhesion rate is identified by looking up the map based on the gain of the longitudinal force of the tire on the vertical load and the slip ratio obtained from the current calculation.

[0104] If the slip ratio of the left front wheel satisfies flag = 0, then S i ≥S max or S i ≤S min The slip ratio S needs to be made i Only when flag=1 is the road surface adhesion coefficient identified;

[0105] When flag = 0, a PID controller is used to control the torque of the front and rear axles of the vehicle to reduce the error e. s , making the slip ratio S i To ensure flag = 1, the specific control method is as follows:

[0106]

[0107] In the formula, ΔT is the output of the PID controller, i.e., the change in torque of the vehicle's front axle, e s This is the error between the slip ratio and either the lower or upper limit of the slip ratio, i.e.:

[0108]

[0109] The change in front axle torque is obtained by using a PID controller, and the rear axle torque is also changed accordingly. This satisfies the vehicle's dynamic requirements while ensuring that flag=1 satisfies the slip ratio condition for road adhesion coefficient identification.

[0110] To achieve the control objective, this embodiment uses a trial-and-error method to tune the parameters of the PID controller, first eliminating K... I With K D The impact of the proportional control coefficient K P Start increasing from 0 until the curve begins to oscillate, and from this point K... P The value begins to decrease slightly until the curve oscillates only slightly (i.e., the oscillation amplitude decreases), after which a larger K is set. I The value is continuously decreased until the curve oscillations are eliminated, and finally K is... DStart by increasing from 0, and fine-tune K. P With K I Continue until the curve meets the performance requirements.

[0111] In this embodiment, K I The value is between 300 and 1000.

[0112] In another embodiment, the range of road adhesion coefficient can be changed, and the gain of tire longitudinal force on vertical load can be changed. The range of lower slip ratio can be changed, thereby changing the value range of each fitted curve. By changing the recognition algorithm, the road adhesion coefficient under smaller or larger slip ratio conditions can be identified.

[0113] This invention presents a method for estimating the road surface adhesion coefficient of a four-wheel independent drive vehicle based on torque transfer. This method addresses the problem of complex road surface adhesion coefficient identification methods under low slip ratios in existing technologies. It improves both computational efficiency and accuracy, and the required computational parameters can be obtained from the sensor configurations already present in most vehicles, thus reducing costs.

[0114] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A method for estimating the road adhesion coefficient of a four-wheel independent drive vehicle based on torque transfer, characterized in that, Includes the following steps: Step 1: Collect the angular velocity, longitudinal acceleration, and lateral acceleration of any wheel of the vehicle; Step 2: Obtain the longitudinal force, vertical load, and slip ratio of the corresponding wheel. The slip ratio of any one of the wheels satisfies: ； In the formula, For the first The slip ratio of each wheel; Step 3: Under different road adhesion coefficients, obtain the relationship curves between the gain of tire longitudinal force on vertical load, slip ratio and road adhesion coefficient; Step 4: Fit the relationship curve to create a MAP plot; Step 5: Establish effective slip ratio flags for the low slip ratio range: ； In the formula, For valid flag values, It is the minimum value in the low slip ratio range. This is the maximum value within the low slip ratio range; The low slip ratio range is 1% to 10%; Step 6: If the slip ratio of the corresponding wheel satisfies At that time, the PID controller adjusts the torque of the front and rear axles of the vehicle to ensure that the slip ratio of the corresponding wheels meets the requirements. ; If the slip ratio of the corresponding wheel satisfies If the current road surface adhesion rate is determined, the MAP map is retrieved by using the gain of the longitudinal force of the tire on the vertical load and the slip ratio obtained from the current calculation. The output of the PID controller satisfies: ； In the formula, This represents the change in torque on the front axle of the vehicle. This is the error between the slip ratio and either the lower or upper limit of the slip ratio. This is the proportional control coefficient. This is the integral adjustment coefficient. The differential adjustment coefficient; The error between the slip ratio and the lower limit or upper limit of the slip ratio satisfies: 。 2. The method for estimating the road surface adhesion coefficient of a four-wheel independent drive vehicle based on torque transfer as described in claim 1, characterized in that, The longitudinal force of the tire of any one of the wheels satisfies: ； In the formula, Let be the moment of inertia of the wheel. For the first The angular velocity of each wheel For the first The resultant torque received by each wheel For the first The longitudinal force of each wheel's tire. Let be the rolling radius of the wheel, and ,when At that time, the wheel was the left front wheel. At that time, the wheel was the right front tire. At that time, the wheel was the left rear tire. At that time, the wheel was the right rear tire.

3. The method for estimating the road adhesion coefficient of a four-wheel independent drive vehicle based on torque transfer as described in claim 2, characterized in that, The vertical load on any wheel satisfies: ； ； ； ； In the formula, The vertical load is for the left front wheel. For vehicle quality, It is the acceleration due to gravity. This is the distance from the rear axle of the vehicle to its center of gravity. This refers to the vehicle's wheelbase. For the longitudinal acceleration of the vehicle, For the height of the vehicle's center of gravity, For the lateral acceleration of the vehicle, The wheelbase is the distance between the wheels. This represents the vertical load on the right front tire. The vertical load is for the left rear tire. This is the distance from the front axle of the vehicle to its center of gravity. This represents the vertical load on the right rear tire.

4. The method for estimating the road adhesion coefficient of a four-wheel independent drive vehicle based on torque transfer as described in claim 3, characterized in that, Step three specifically includes the following steps: Step 1: Compile a table showing the tire longitudinal force, vertical load, and slip ratio of the corresponding wheels under various working conditions where the gain of tire longitudinal force on vertical load is 0.2, 0.3, ..., 1, with a road surface adhesion coefficient of 0.

3. Step 2: Compile data tables on the tire longitudinal force, vertical load, and slip ratio of the corresponding wheels under various working conditions where the gain of tire longitudinal force on vertical load is 0.2, 0.3, ..., 1 under road surface conditions with road surface coefficients of 0.4, ..., 0.

9. Step 3: Organize the obtained data tables to obtain the relationship curves between the gain of tire longitudinal force on vertical load and tire slip ratio under different road surface adhesion coefficients of 0.3, 0.4, ..., 0.

9.

5. The method for estimating the road adhesion coefficient of a four-wheel independent drive vehicle based on torque transfer as described in claim 4, characterized in that, Step four specifically includes the following steps: Step 1: Under the condition of road surface adhesion coefficient of 0.3, determine the range of data points selected in the curve of the relationship between the gain of the longitudinal force of the tire on the vertical load and the slip ratio of the corresponding wheel from the low slip ratio range, and perform polynomial fitting on the relationship curve. Step 2: Under the condition of road surface adhesion coefficient of 0.4, ..., 0.9, determine the range of data points selected in the curve of the relationship between the gain of the longitudinal force of the tire on the vertical load and the slip ratio of the corresponding wheel from the low slip ratio range, and perform polynomial fitting on the relationship curve. Step 3: Verify the fitted relationship curve and create a MAP plot.

6. The method for estimating the road adhesion coefficient of a four-wheel independent drive vehicle based on torque transfer as described in claim 5, characterized in that, When the PID controller outputs the change in the front axle torque of the vehicle, the rear axle torque of the vehicle changes in the opposite direction.

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