CN103612634B - The evaluation method of distributing In-wheel motor driving electronlmobil coefficient of road adhesion - Google Patents

Abstract

The invention discloses a method for estimating the road surface adhesion coefficient of an electric vehicle driven by a distributed hub motor, belonging to the technical field of electric vehicles. Collect the current wheel speed, vehicle speed and driving torque of the electric vehicle in real time through the wheel speed sensor, vehicle speed sensor and motor controller; calculate the slip rate, vertical load and driving force; calculate the slope of the corresponding point on the u-in curve at the current moment, when When the slope is less than m, it is determined that the road surface adhesion coefficient at this moment is the road surface peak adhesion coefficient, otherwise continue to calculate the slope at the next moment; or if the slope is not less than m within 1s, take the maximum road surface adhesion coefficient calculated within 1s as the relative The peak adhesion coefficient of the road surface; by comparing the peak adhesion coefficient of the road surface obtained by the four tires, it can be judged whether the current road surface is a homogeneous road surface, a split road surface, a butt joint road surface or a single-wheel independent road surface. The invention has good robustness, can better identify various road surfaces, and is suitable for real-time estimation of road surface adhesion coefficients of various road surfaces during vehicle running.

Description

Estimation method for road adhesion coefficient of electric vehicles driven by decentralized in-wheel motors

technical field

The invention relates to a method for estimating the road surface adhesion coefficient of an electric vehicle driven by a decentralized hub motor during driving, in particular to a method for real-time measuring the longitudinal adhesion characteristics of tires and the road surface on an actual road surface, belonging to the technical field of electric vehicles.

Background technique

Distributed in-wheel motor-driven electric vehicles install the in-wheel motors in or near the four wheels of the electric vehicle. It has the characteristics of fast response, short transmission chain, efficient transmission, and compact structure. It makes full use of the precise observation and fast controllability of the motor. It is an important development direction of electric vehicles.

The change characteristics of the adhesion coefficient of electric vehicle tires on different road surfaces is an important technical index for evaluating the performance of vehicle tires, and it has an important impact on vehicle performance. The change characteristics of the adhesion coefficient between the tire and different road surfaces is also an important original parameter for the simulation calculation of vehicle dynamics and braking performance.

At present, a lot of work has been done in the field of pavement adhesion coefficient identification at home and abroad, mainly including the following methods.

1) The road surface adhesion coefficient estimation method based on the slope of the road surface adhesion coefficient and wheel slip rate curve. This method is simple and easy to implement, but it can only be used when the vehicle is at a low slip rate. In the case of a high slip rate, the linear relationship between the slip rate and the adhesion coefficient does not satisfy.

2) Estimation method of road adhesion coefficient based on tire model. This method can obtain the slip characteristics of the wheel through the tire model, and directly estimate the road surface adhesion coefficient, with high accuracy. However, its accuracy depends too much on the tire model used. It takes too long to calculate the slip rate by using a complex tire model, and the simplified tire model will affect the accuracy of the adhesion coefficient.

There are many other methods that are based on these two as prototypes and have their own advantages and disadvantages.

Contents of the invention

Aiming at the inaccurate estimation of the existing road surface adhesion coefficient, the purpose of the present invention is to provide a method for estimating the road surface adhesion coefficient of an electric vehicle driven by a decentralized in-wheel motor, which is used to accurately estimate the road surface condition and make driving safer.

To achieve the above object, the present invention takes the following technical solutions:

A method for estimating the road surface adhesion coefficient of an electric vehicle driven by a decentralized in-wheel motor, the method steps are:

1) Establish an estimation system for the road surface adhesion coefficient of electric vehicles, including: a driving torque sensor set on the motor controller, a wheel speed sensor set at the wheel, a vehicle speed sensor, a wheel slip rate calculation module, and road surface adhesion coefficient estimation module, simplified tire model module. The road surface adhesion coefficient estimation module has an algorithm for estimating the road surface adhesion coefficient based on the road surface adhesion coefficient and the wheel slip rate curve.

2) In the case of ignoring the tire rolling resistance, the tire driving force is observed in real time according to formula (1).

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; *</span>\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, R—the rolling radius of the wheel, Jω—the moment of inertia of the wheel, —Wheel angular acceleration, F _z —wheel vertical load, T _Z —driving torque.

where T _z is the driving torque, which is known. Assuming that the wheel angular velocity sensor collects the adjacent moments k-1 and k, and the interval time is T, the wheel speed signals ω(k) and ω(k-1) collected in real time, so the wheel center acceleration can be calculated by formula (2) .

$\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Then formula (3) is obtained to calculate the tire driving force:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; *</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

The vertical load of the distributed in-wheel motor driven electric vehicle is calculated as follows, where the vertical loads of the front, rear, left and right wheels are equal,

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; mg</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; mah</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; mg</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; mah</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

In the formula, _Lr —the vertical distance from the center of mass of the vehicle to the axle of the rear wheels, _Lf —the vertical distance from the center of mass of the vehicle to the axle of the front wheels, L—the vertical distance between the axles of the front and rear wheels, h—the height from the center of mass of the vehicle to the ground.

Among them, a is the acceleration of the electric vehicle. It is assumed that the vehicle speed sensor collects the adjacent moments k-1 and k, the interval time is T, and the wheel speed signals V(k) and V(k-1) are collected in real time, so ( 6) Formula to calculate the vehicle acceleration.

$\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ,</span>$

The current road surface adhesion coefficient is calculated by formula (6):

μ(k)=F _i (k)/F _zi (6)

The calculation of the slip rate at the current moment can be calculated by formula (7):

$\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

In the formula, λ—slip ratio, ω—wheel angular velocity, R—wheel rolling radius, v _w —vehicle speed.

3) Calculate the slope of the current road surface adhesion coefficient and slip rate curve by formula (8):

$\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; d\&mu;</span>}}{\mathrm{<span\; class="notranslate">\; d\&lambda;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

Comparison: |p|<m, (9)

Among them, m is the set value;

i) When |p|<m, it can be judged that the current road surface adhesion coefficient is the peak road surface adhesion coefficient, and the flag bit flag=0 is set; if the absolute value of the slope p |p|>m, continue to calculate the next moment The slope p, until |p|<m;

ii) If the slope p still does not reach |p|<m within 1s, take the maximum road surface adhesion coefficient calculated within 1s as the relative road surface peak adhesion coefficient, and set a flag flag=1;

4) Calculate the road surface peak adhesion coefficient and flag position of the four tires respectively, and denote them as u1, u2, u3, u4, flag1, flag2, flag3, flag4; among them, u1, flag1 represent the road surface peak adhesion coefficient of the left front wheel and Flag position; u2, flag2 represent the road surface peak adhesion coefficient and flag position of the right front wheel; u3, flag3 represent the road surface peak adhesion coefficient and flag position of the left rear wheel; u4, flag4 represent the road surface peak adhesion coefficient and flag position of the right rear wheel ;

Compare the road surface peak adhesion coefficients u1, u2, u3, u4 of the four tires with the flags flag1, flag2, flag3, flag4; to further judge whether the current road surface is a homogeneous road surface, a split road surface, a butt joint road surface or a single-wheel independent road surface;

If the flags of the four tires are the same, and the difference between the peak adhesion coefficients of the road surface is within n, where n is the set value, it is determined that the current road surface is a homogeneous road surface, and its road surface adhesion coefficient U=(u1+u2+u3+u4) /4;

If the marks of the first two tires and the last two tires are the same, and the difference between the road surface peak coefficients is within n, and n is the set value, it is determined that the current road surface is a butt joint road surface, and its road surface adhesion coefficient U1=(u1+ u2)/2, U2=(u3+u4)/2;

If the marks of the two tires on the left and the two tires on the right are the same, and the difference between the road surface adhesion coefficients is within n, and n is the set value, then it is determined that the current road surface is a split road surface, and its road surface adhesion coefficient U1=(u1 +u3)/2, U2=(u2+u4)/2;

If the above conditions are not met, it is determined that the current road surface is a single-wheel independent road surface, and the road surface adhesion coefficient is calculated according to the situation.

Due to the adoption of the above technical scheme, the present invention has the following advantages: first, the present invention collects the current wheel speed, vehicle speed and driving torque of the electric vehicle in real time through the wheel speed sensor, the vehicle speed sensor and the motor controller, and then calculates the current values of the four tires respectively. slip ratio, vertical load, and drive force. Use these three values to calculate the slope of the corresponding point on the μ-λ curve at the current moment. When the slope is close to zero, it is determined that the road surface adhesion coefficient at this moment is the road surface peak adhesion coefficient, otherwise continue to calculate the slope at the next moment; or if 1s If the inner slope is not close to zero, then take the maximum road surface adhesion coefficient calculated within 1s as the relative road surface peak adhesion coefficient. By comparing the road surface adhesion coefficients calculated by the four tires, it is judged whether the current road surface is a homogeneous road surface, a split road surface, a butt joint road surface or a single-wheel independent road surface. The invention has good robustness, can better identify various road surfaces, and is suitable for real-time estimation of road surface adhesion coefficients of various road surfaces during vehicle running.

Description of drawings

Fig. 1 is a schematic diagram of the system relationship of the present invention.

Fig. 2 is a flow chart of the method of the present invention.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is a schematic diagram of the system relationship of the present invention. The system shown in Figure 1 includes a vehicle drive torque sensor, wheel speed sensor, and vehicle speed observer. Road adhesion coefficient estimation module, including tire force estimation module, wheel slip rate calculation module and simplified tire model.

Based on the above system, the real-time estimation method of the road surface adhesion coefficient during vehicle running in the present invention includes the following steps, as shown in Fig. 2 (Fig. 2 is the method flow chart of the present invention).

A method for estimating the road surface adhesion coefficient of an electric vehicle driven by a decentralized in-wheel motor, the method steps are:

1) In the case of ignoring the tire rolling resistance, the tire driving force is observed in real time according to formula (1).

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; *</span>\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, R—the rolling radius of the wheel, Jω—the moment of inertia of the wheel, —Wheel angular acceleration, F _z —wheel vertical load, T _Z —driving torque.

where T _z is the driving torque, which is known. Assuming that the wheel angular velocity sensor collects the adjacent moments k-1 and k, and the interval time is T, the wheel speed signals ω(k) and ω(k-1) collected in real time, so the wheel center acceleration can be calculated by formula (2) .

$\stackrel{<span\; class="notranslate">\; \&CenterDot;</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Then formula (3) is obtained to calculate the tire driving force:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; *</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

The vertical load of the electric vehicle driven by the distributed in-wheel motor is calculated as follows, where the vertical loads of the front, rear, left and right wheels are equal,

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; mg</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; mah</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; mg</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; mah</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

In the formula, _Lr —the vertical distance from the center of mass of the vehicle to the axle of the rear wheels, _Lf —the vertical distance from the center of mass of the vehicle to the axle of the front wheels, L—the vertical distance between the axles of the front and rear wheels, h—the height from the center of mass of the vehicle to the ground.

Among them, a is the acceleration of the electric vehicle. It is assumed that the vehicle speed sensor collects the adjacent moments k-1 and k, the interval time is T, and the wheel speed signals v(k) and v(k-1) are collected in real time, so ( 6) Formula to calculate the vehicle acceleration.

$\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ,</span>$

The current utilization road surface adhesion coefficient can be calculated by formula (6):

μ(k)=F _i (k)/F _zi , (6)

The calculation of the slip rate at the current moment can be calculated by formula (7):

$\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

In the formula, λ—slip ratio, ω—wheel angular velocity, R—wheel rolling radius, v _w —vehicle speed.

2) Calculate the slope of the current road surface adhesion coefficient and slip rate curve by formula (8):

$\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; d\&mu;</span>}}{\mathrm{<span\; class="notranslate">\; d\&lambda;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

Comparison: |p|<m, (9),

Wherein, here m is 0.1; n is 0.05.

i) When |p|<0.1, it can be judged that the current road surface adhesion coefficient is the peak road surface adhesion coefficient, and the flag bit flag=0 is set; if the absolute value of the slope p|p|>0.1, continue to calculate the next moment The slope p, until |p|<0.1;

ii) If the slope p still does not reach |p|<0.1 within 1s, take the maximum road surface adhesion coefficient calculated within 1s as the relative road surface peak adhesion coefficient, and set a flag flag=1;

3) Calculate the road surface peak adhesion coefficient and flag position of the four tires respectively, and record them as u1, u2, u3, u4, flag1, flag2, flag3, flag4; among them, u1, flag1 represent the road surface peak adhesion coefficient and Flag position; u2, flag2 represent the road surface peak adhesion coefficient and flag position of the right front wheel; u3, flag3 represent the road surface peak adhesion coefficient and flag position of the left rear wheel; u4, flag4 represent the road surface peak adhesion coefficient and flag position of the right rear wheel ;

Compare the road surface peak adhesion coefficients u1, u2, u3, u4 of the four tires with the flags flag1, flag2, flag3, flag4; to further judge whether the current road surface is a homogeneous road surface, a split road surface, a butt joint road surface or a single-wheel independent road surface;

If the flags of the four tires are the same, and the difference between the peak adhesion coefficients of the road surface is within n, where n is the set value, it is determined that the current road surface is a homogeneous road surface, and its road surface adhesion coefficient U=(u1+u2+u3+u4) /4;

If the marks of the first two tires and the last two tires are the same, and the difference between the road surface peak coefficients is within n, and n is the set value, it is determined that the current road surface is a butt joint road surface, and its road surface adhesion coefficient U1=(u1+ u2)/2, U2=(u3+u4)/2;

If the marks of the two tires on the left and the two tires on the right are the same, and the difference between the road surface adhesion coefficients is within n, and n is the set value, then it is determined that the current road surface is a split road surface, and its road surface adhesion coefficient U1=(u1 +u3)/2, U2=(u2+u4)/2;

If the above conditions are not met, it is determined that the current road surface is a single-wheel independent road surface, and the road surface adhesion coefficient is calculated according to the situation.

Due to the adoption of the above technical scheme, the present invention has the following advantages: first, the present invention collects the current wheel speed, vehicle speed and driving torque of the electric vehicle in real time through the wheel speed sensor, the vehicle speed sensor and the motor controller, and then calculates the current values of the four tires respectively. slip ratio, vertical load, and drive force. Calculate the slope of the corresponding point on the μ-λ curve at the current moment through these three values. When the slope is close to zero, it is determined that the road surface adhesion coefficient at this moment is the road surface peak adhesion coefficient. By comparing the road surface adhesion coefficients calculated by the four tires, it is judged whether the current road surface is a homogeneous road surface, a split road surface, a butt joint road surface or a single-wheel independent road surface. The invention has good robustness, can better identify various road surfaces, and is suitable for real-time estimation of road surface adhesion coefficients of various road surfaces during vehicle running.

Claims (3)

1. The method for estimating road surface adhesion coefficient of distributed hub motor driven electric vehicles is characterized in that the method contains steps: 1) Neglecting the tire rolling resistance, the tire driving force is observed in real time according to formula (1); The formula (1) is: $f_i=(T_z-J_{\mathrm{\&omega;}}*\stackrel{\&Center\; Dot;}{\mathrm{\&omega;}})/R,---\left(1\right)$ In the formula, R—the rolling radius of the wheel, J _ω —the moment of inertia of the wheel, — wheel angular acceleration, F _z — wheel vertical load, T _Z — driving torque; Among them, T _z is the driving torque, which is known; assuming that the wheel angular velocity sensor collects the adjacent moments k-1 and k, and the interval time is T, the real-time collected wheel speed signals ω(k) and ω(k- 1), then the wheel center acceleration is calculated by equation (2): $\stackrel{<span\; class="notranslate">\; \&Center\; Dot;</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$ Calculate the tire driving force according to formula (3): ${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; *</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$ The vertical load of the distributed in-wheel motor driven electric vehicle is calculated as follows, where the vertical loads of the front, rear, left and right wheels are equal, namely: ${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; mg</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; mah</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$ ${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; mg</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; mah</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$ In the formula, _Lr —the vertical distance from the center of mass of the vehicle to the axle of the rear wheels, _Lf —the vertical distance from the center of mass of the vehicle to the axle of the front wheels, L—the vertical distance between the axles of the front and rear wheels, h—the height from the center of mass of the vehicle to the ground; Among them, a is the acceleration of the electric vehicle. It is assumed that the vehicle speed sensor collects the adjacent moments k-1 and k, and the interval time is T. The wheel speed signals v(k) and v(k-1) collected in real time are obtained by the following Formula to calculate vehicle acceleration: $\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ,</span>$ The current road surface adhesion coefficient is calculated by formula (6): μ(k)=F _i (k)/F _zi (6) The calculation of the slip rate at the current moment can be calculated by formula (7): $\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; max</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; *</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$ In the formula, λ—slip rate, ω—wheel angular velocity, R—wheel rolling radius, v _w —vehicle speed; 2) Calculate the slope p of the current road surface adhesion coefficient and slip rate curve by formula (8): $\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; d\&mu;</span>}}{\mathrm{<span\; class="notranslate">\; d\&lambda;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$ Comparison: |p|<m, (9) Among them, m is the set value; When |p|<m, it can be judged that the current road surface adhesion coefficient is the peak road surface adhesion coefficient, and the flag bit flag=0 is set; if |p|>m, continue to calculate the slope p at the next moment until |p |<m; If the slope p still does not reach |p|<m within 1s, take the maximum road surface adhesion coefficient calculated within 1s as the relative road surface adhesion coefficient, and set a flag flag=1; 3) Calculate the road surface peak adhesion coefficient and flag position of the four tires respectively, which are denoted as u1, u2, u3, u4, flag1, flag2, flag3, flag4; among them, u1, flag1 represent the road surface peak adhesion coefficient of the left front wheel and Flag position; u2, flag2 represent the road surface peak adhesion coefficient and flag position of the right front wheel; u3, flag3 represent the road surface peak adhesion coefficient and flag position of the left rear wheel; u4, flag4 represent the road surface peak adhesion coefficient and flag position of the right rear wheel ; Compare the road surface peak adhesion coefficients u1, u2, u3, u4 of the four tires and the flags flag1, flag2, flag3, flag4; to further judge whether the current road surface is a homogeneous road surface, a split road surface, a butt joint road surface or a single-wheel independent road surface; If the flags of the four tires are the same, and the difference between the peak adhesion coefficients of the road surface is within n, where n is the set value, it is determined that the current road surface is a homogeneous road surface, and its road surface adhesion coefficient U=(u1+u2+u3+u4) /4; If the marks of the first two tires and the last two tires are the same, and the difference between the road surface peak coefficients is within n, and n is the set value, then it is determined that the current road surface is a butt joint road surface, and its road surface adhesion coefficient U1=(u1+ u2)/2, U2=(u3+u4)/2; If the marks of the two tires on the left and the two tires on the right are the same, and the difference between the road surface adhesion coefficients is within n, and n is the set value, then it is determined that the current road surface is a split road surface, and its road surface adhesion coefficient U1=(u1 +u3)/2, U2=(u2+u4)/2; If the above conditions are not met, it is determined that the current road surface is a single-wheel independent road surface, and the road surface adhesion coefficient is calculated according to the situation. 2. The method for estimating the road surface adhesion coefficient of a distributed in-wheel motor driven electric vehicle according to claim 1, wherein said m is 0.1. 3. The method for estimating the road surface adhesion coefficient of a distributed in-wheel motor driven electric vehicle according to claim 1, wherein said n is 0.05.