CN106773714A - A kind of wheel-hub motor driven vehicle control method based on self-regulation particle model - Google Patents

Abstract

The application is related to a kind of wheel-hub motor driven vehicle control method based on self-regulation particle model, the self-regulation particle model is set up according to dynamics of vehicle principle, suitable for the linear processes region of vehicle, rational state of motion of vehicle reference value under the limit of adhesion of road surface can be especially provided, to ensure the control stability and driving safety of vehicle.The foundation of the self-regulation particle reference model is comprised the steps of：First, according to dynamics of vehicle neutral steer characteristic, the Changing Pattern of vehicle desired reference side acceleration is obtained with two degrees of freedom linear reference model analyzing；2nd, vehicle has longitudinal acceleration and side acceleration demand simultaneously when, set up in G G acceleration friction circles from the one-to-one mapping function MAP relations with reference to resultant acceleration to preferable resultant acceleration；3rd, by the conversion between vehicle movement trajectory coordinates system and vehicle centroid coordinate system, vehicle desired reference state of motion value is obtained.Control stability and active safety of the vehicle under limit of adhesion are ensure that, and ensures controllability of the driver to vehicle.

Description

Wheel hub motor driven vehicle control method based on self-adjusting particle model

Technical Field

The present application relates to a control method for an in-wheel motor driven vehicle, and more particularly to a method for providing reasonable vehicle motion state values at road adhesion limits based on a self-adjusting particle model.

Background

The in-wheel motor driven vehicle is one of research hotspots in the field of electric vehicles at present, and when the in-wheel motor driven vehicle runs at an adhesion limit, a reference model is usually required to provide a reasonable vehicle reference motion state value, so that the performance advantage of the in-wheel motor driven vehicle can be really exerted. At present, a two-degree-of-freedom linear model is generally adopted as a reference model to generate a vehicle control system reference state value. However, the two-degree-of-freedom linear model has the following three limitations: (a) the two-degree-of-freedom model is linear and can only represent the basic characteristic of the vehicle in a linear region with the lateral acceleration less than 0.4g, and cannot truly reflect the dynamic characteristic of the vehicle in a nonlinear region (large lateral acceleration); (b) near road-tire adhesion limits, the two-degree-of-freedom model will provide unreasonable vehicle dynamics state values; (c) when the vehicle demand generalized force exceeds the road adhesion limit, the vehicle target state value is saturated in a certain mode, and the driver input signal is analyzed by adopting a nonlinear reference model; otherwise, the mutual coupling relationship between the driver input signal and the target trajectory of the vehicle will become very weak at the saturation point, in other words, the driver will lose the controllability of the vehicle's driving trajectory.

Therefore, it is necessary to establish a reference model suitable for linear and nonlinear regions to ensure the handling stability and active safety of the vehicle under the adhesion limit and to ensure the controllability of the vehicle by the driver.

Disclosure of Invention

In view of the above technical problems in the art, the present invention provides a self-adjusting particle model of an in-wheel motor driven vehicle. The model applies the tire friction circle to the full vehicle level, modeling the vehicle in motion as a particle (particle). The construction of the model specifically comprises the following steps:

when the vehicle runs on a curve at a constant speed, according to a driver input signal, analyzing through a two-degree-of-freedom linear reference model of the vehicle to obtain a vehicle reference lateral acceleration; and according to the vehicle dynamic neutral steering characteristic, establishing a change rule of the ideal lateral acceleration along with the reference lateral acceleration, namely, the product of the vehicle reference lateral acceleration and the ideal lateral acceleration is the square of the product of the vehicle road adhesion coefficient and the gravity acceleration, so that reasonable motion state values of the vehicle in linear and nonlinear areas, particularly under the adhesion limit can be obtained.

When the vehicle runs on a non-uniform speed curve, the requirements of longitudinal acceleration and lateral acceleration are met, and in a vehicle friction circle, a self-adjusting particle mapping relation between reference resultant acceleration and ideal resultant acceleration is constructed to obtain an ideal resultant acceleration vector;

and thirdly, converting the ideal resultant acceleration vector of the vehicle from a vehicle motion track coordinate system to a vehicle mass center coordinate system to obtain an ideal reference motion state value of the vehicle.

The step ① of obtaining the desired lateral acceleration of the vehicle through self-tuning particle model analysis includes analyzing the reference lateral acceleration when the vehicle has only the lateral acceleration requirement inputted by the driverWhen the vehicle is in a neutral position, an ideal resultant acceleration of lateral acceleration and braking acceleration is applied to the vehicle, and the ideal resultant acceleration and the direction of the resultant speed of the center of mass of the vehicle form an obtuse angle; according to reference lateral accelerationAnd ideal lateral accelerationThe product of (a) is equal to the square of the product of the vehicle road adhesion coefficient mu and the gravity acceleration g, and the ideal lateral acceleration of the vehicle is obtained:

the step ② of obtaining the desired vehicle acceleration includes obtaining a reference lateral acceleration of the vehicle in the self-adjusting particle mapping relationshipReference longitudinal accelerationAnd ideal lateral accelerationIdeal longitudinal accelerationWhen the following relationship exists:

phi is a bias angle and is an included angle between a ray on a reference resultant acceleration mapping vehicle friction circle and an abscissa; the ideal resultant acceleration is determined by the following equation:

when reference lateral acceleration of the vehicleReference longitudinal accelerationAnd ideal lateral accelerationAnd ideal longitudinal accelerationWhen the following relationship exists:

the ideal resultant acceleration is determined by the following equation:

the implementation of the third step adopts the following formula:

wherein β is the vehicle centroid slip angle,is the longitudinal acceleration of the vehicle in the coordinate system of the center of mass,is the lateral acceleration of the vehicle in the centroid coordinate system.

When the vehicle centroid deflection angle β is 0, the vehicle reference dynamic state value can be expressed by the following formula:

wherein v is_xIs the vehicle initial longitudinal speed;is the ideal longitudinal speed, r, of the vehicle in its coordinate system of the center of mass^refIs the vehicle yaw rate.

The method provided by the invention is suitable for linear and nonlinear areas of the vehicle, can provide reasonable vehicle motion state reference values under the road adhesion limit, and can ensure the operation stability and the driving safety of the vehicle.

Drawings

FIG. 1 is a schematic diagram of a self-adjusting particle model in a friction circle of a vehicle

FIG. 2 is a mapping of the driver's resolved reference resultant acceleration to the MPR ideal reference resultant acceleration in the first quadrant of the G-G plot

FIG. 3 is an MPR map-normalized G-G plot of driver-resolved reference combined acceleration to ideal reference combined acceleration

FIG. 4 is a schematic diagram of the transformation of the ideal acceleration of the vehicle between the vehicle motion coordinate system and the vehicle mass center coordinate system

Detailed Description

The present invention is directed to the entire vehicle, and therefore each acceleration in the present invention refers to the acceleration of the vehicle.

It is known to use tires as a research object, the grip of the tire has a limit during the turning of the vehicle, although the total grip is limited, there is no limit on how to distribute, and the tire can be simultaneously distributed to acceleration and turning, or deceleration and turning, so the tire grip amount and distribution are described by friction circles. Since the invention takes the whole vehicle as a research object, the concept of the tire friction circle is utilized to put forward the vehicle friction circle to describe the overall gripping capacity and distribution of the vehicle.

In the invention, in the self-adjusting particle model, the included angle between a ray and the abscissa on the point mapping vehicle friction circle with reference to the resultant acceleration is called as an offset angle, and the letter phi represents. Under the condition that the vehicle is in an acceleration turning condition (with both longitudinal acceleration requirement and lateral acceleration requirement), if lateral dynamics is prioritized, the optimal choice is that phi is 0; if the longitudinal dynamics have priority, then φ > 0 is taken. Generally, the offset angle φ is considered a design parameter and is adjusted according to various criteria, such as driving style and human factors.

In the self-adjusting particle model of the present invention, the function relationship between the reference resultant acceleration and the ideal resultant acceleration is also referred to as a mapping from the reference resultant acceleration to a friction circle of the vehicle, which is called a self-adjusting particle mapping or MPR mapping.

The present invention will be described in further detail with reference to the accompanying drawings. As shown in fig. 1, a represents a reference resultant acceleration obtained by a two-degree-of-freedom linear model analysis, and a' represents an ideal resultant acceleration obtained by a self-adjusting particle model analysis.

When the vehicle runs on a curve with a constant speed, according to a signal input by a driver, ideal lateral acceleration is obtained through self-adjusting particle model analysis, as shown in A' in figure 1. The method specifically comprises the following steps: when the vehicle only has the lateral acceleration requirement and the reference lateral acceleration is obtained by analysisWhen the vehicle is in a neutral position, a resultant acceleration vector of lateral acceleration and braking acceleration is applied to the vehicle, and the resultant acceleration vector and the combined speed direction of the mass center of the vehicle form an obtuse angle; according to reference lateral acceleration(OB) and ideal lateral accelerationThe product of (OC) is equal to the square relation of the product of the road adhesion coefficient mu and the gravity acceleration g of the vehicle, and the ideal lateral acceleration is obtained

Resolving reference lateral accelerationAnd ideal lateral accelerationThe right-angle triangle projection theorem is satisfied:can obtain the product

When the vehicle runs on a non-uniform speed curve, in order to establish the mapping from the analytic reference combined acceleration to the vehicle friction circle, the invention analyzes the change rule of the ideal lateral acceleration of the vehicle along with the reference combined acceleration under the action of the accelerated turning working condition and different offset angles. As shown in FIG. 2, the square points in the graph represent the reference resultant acceleration obtained by the two-degree-of-freedom linear model analysis, and the circular point table represents the ideal resultant acceleration obtained according to the self-adjusting particle model. In the figure, in the friction circle diagram of the vehicle, the first quadrant is divided into four parts: the parts of the first, second, third and fourth are areas outside the friction circle of the vehicle.

As shown in fig. 2, the region C is representative, and the region C is a point C for a brief explanation, and C represents a reference resultant acceleration obtained by the two-degree-of-freedom linear model analysis.

C′₀C′₁C₂C₂C₃The ideal resultant acceleration is obtained by utilizing self-adjusting particle model analysis.

With point C as a starting point, one of the mapping options is to reduce the vertical demand to zero, i.e. to select the horizontal mapping C → C₀Then using the MPR mapping under pure lateral acceleration requirement, C, as shown in FIG. 1₀→C′₀. Obviously, the reference resultant acceleration is close to a_yThe mapping is also continuous with the axis. Other more general mapping options include an offset angle φ, i.e., reducing both longitudinal and lateral acceleration requirements, such as: c → C₁→C′₁。

On the premise that phi is less than pi/2, the reference resultant acceleration a^DIClose to a_yThe mapping is continuous with the axis the offset angle phi of regions ② and ④ should be bounded to avoid signs of reversal of the lateral acceleration sign.

In fig. 2, the specific mapping is as follows:

(a) in region ①, the driver reference resultant accelerationAnd ideal resultant accelerationThe relationship between can be expressed as:

A_iis the ideal resultant acceleration at different bias angles, e.g. A₀、A₁、A₂The effective range of the bias angle phi is more than or equal to 0 and less than pi/2.

(b) In region ②, the driver reference resultant acceleration B and the ideal resultant acceleration B_iThe same relationship is true in region ①, except that the effective range of the bias angle phi is different, i.e., the bias angle phi is different

(c) In region ③, if 0 ═ φ, the MPR mapping point at the corresponding pure lateral acceleration requirement is C₀The reference acceleration is then mapped to point C 'on the vehicle friction circle following MPR theory under pure lateral acceleration demand as shown in FIG. 1'₀；

If it is notThe corresponding MPR mapping point is C₁The reference resultant acceleration is then mapped to point C 'on the vehicle friction circle following MPR theory under pure lateral acceleration demand as shown in FIG. 3'₁；

If it is notThe corresponding MPR mapping point is C2;

from the above, see ifThe corresponding acceleration point is C₀、C₁Or C₂Driver reference resultant accelerationAnd ideal resultant accelerationThe relationship between can be expressed as:

the reference acceleration is then mapped to point C 'on the vehicle friction circle following the MPR theory under pure lateral acceleration demand'₀、C′₁、C₂As shown in fig. 2.

Otherwise, ifThe corresponding MPR acceleration point is C₃Or C₄And region ①.

(d) The mapping in the region (c) is substantially the same as the mapping in the region (c), except for the working region of the offset angle phi.

The influence rule of different offset angles on the ideal longitudinal acceleration and the ideal lateral acceleration of the vehicle under the condition of accelerating and turning of the vehicle is analyzed, and the influence rule is also suitable for the deceleration and braking conditions of the vehicle. When the vehicle is turning with deceleration at the road adhesion limit, in the second quadrant of the vehicle friction map, phi > 0 (steering and braking combined,) Rather, deceleration is emphasized. The resulting map is displayed in the normalized vehicle friction circle, as shown in FIG. 3.

The MPR mapping shown in fig. 3, the top and bottom half-plane mapping is symmetric, while the left and right plane mapping is asymmetric (braking/accelerating); the square points in the graph represent the reference resultant acceleration obtained by analyzing the two-degree-of-freedom linear model, and the circular table obtains the ideal resultant acceleration according to the self-adjusting particle model. When the driver resolves the acceleration demandIn the region of points D or G, the ideal resultant acceleration can be expressed as:

when the driver-resolved input acceleration request is in the region of point E (or F), the desired resultant acceleration of the output regulated by MPR may be defined as:

the reference resultant acceleration vector obtained from the self-adjusting particle model is in a vehicle track coordinate system (x, y), the x axis is the motion direction of the vehicle centroid, and the y axis is perpendicular to the x axis; and the vehicle state values are generally expressed on a vehicle centroid coordinate system (X, Y), as shown in fig. 4, wherein the included angle between the X-axis and the X-axis is the vehicle centroid slip angle β. The conversion of the ideal reference resultant acceleration between the vehicle track coordinate system and the vehicle mass center coordinate system is realized by the following formula:

wherein,is the longitudinal acceleration of the vehicle in the coordinate system of the center of mass,is the lateral acceleration of the vehicle in the centroid coordinate system.

When the reference value of the vehicle centroid slip angle is set to zero, the vehicle reference dynamic state value can be expressed by the following formula:

wherein v is_xIs the vehicle initial longitudinal speed;is the ideal longitudinal speed, r, of the vehicle in its coordinate system of the center of mass^refIs the vehicle yaw rate.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (5)

1. A control method of a wheel hub motor driven vehicle based on a self-adjusting particle model is characterized in that:

the resultant acceleration is referred and is obtained by analyzing a two-degree-of-freedom linear model of the vehicle;

the relation between the vehicle friction circle, the overall vehicle gripping capacity and the distribution;

the self-adjusting particle mapping relation is a function relation of ideal resultant acceleration obtained by referring to the mapping from the resultant acceleration to a vehicle friction circle;

the method specifically comprises the following steps:

when the vehicle turns at a constant speed, analyzing ideal lateral acceleration through a self-adjusting particle reference model according to a signal input by a driver;

when the vehicle does not turn at a constant speed, obtaining ideal resultant acceleration in the vehicle friction circle according to the self-adjusting particle mapping relation;

and thirdly, converting the ideal resultant acceleration from a vehicle motion track coordinate system to a vehicle mass center coordinate system to obtain an ideal reference motion state value of the vehicle.

2. The method of claim 1, wherein step ① comprises analyzing the reference lateral acceleration when the vehicle has only a driver-entered lateral acceleration requirementTime, reference lateral accelerationAnd ideal lateral accelerationThe product of the two is equal to the square of the product of the vehicle road adhesion coefficient mu and the gravity acceleration g, and the ideal lateral acceleration of the vehicle is obtained:

$a_y^{ref}=\frac{{\left(\mathrm{\μ}g\right)}^2}{a_y^{DI}}---\left(1\right).$

3. the method of claim 1, wherein:

the offset angle is an included angle between a ray mapped on the vehicle friction circle by the reference combined acceleration and the abscissa;

the step ② of obtaining the desired resultant acceleration includes obtaining a reference lateral acceleration of the vehicle in the self-adjusting particle mapping relationshipReference longitudinal accelerationAnd ideal lateral accelerationIdeal longitudinal accelerationWhen the following relationship exists:

$\left\{\begin{array}{c}{\left(a_x^{ref}\right)}^2+{\left(a_y^{ref}\right)}^2={\left(\mathrm{\μ}g\right)}^2\\ tan\mathrm{\φ}=\frac{a_y^{DI}-a_y^{ref}}{a_x^{DI}-a_x^{ref}}\end{array}\right.---\left(2\right)$

wherein phi is an offset angle; the ideal resultant acceleration is determined by the following equation:

$\begin{array}{c}{a}_y^{ref}=a_y^{DI}\\ a_x^{ref}=sign\left(a_x^{DI}\right)\·\sqrt{{\left(\mathrm{\μ}g\right)}^2-{\left(a_y^{ref}\right)}^2}\end{array}---\left(3\right);$

when reference lateral acceleration of the vehicleReference longitudinal accelerationAnd ideal lateral accelerationAnd ideal longitudinal accelerationWhen the following relationship exists:

$\left\{\begin{array}{c}{a}_x^{{\mathrm{ref}}^{\′}}=0\\ a_y^{{\mathrm{ref}}^{\′}}=a_y^{DI}-\tan \mathrm{\φ}\·a_x^{DI}\end{array}\right.---\left(4\right)$

the ideal resultant acceleration is determined by the following equation:

$\left\{\begin{array}{c}{a}_y^{ref}=\frac{{\left(\mathrm{\μ}g\right)}^2}{a_y^{DI}}\\ a_x^{ref}=-\sqrt{{\left(\mathrm{\μ}g\right)}^2-{\left(a_y^{ref}\right)}^2}\end{array}\right.---\left(5\right).$

4. the method of claim 1, wherein: the implementation of the step III adopts the following formula:

$\left[\begin{array}{c}{a}_X^{ref}\\ a_Y^{ref}\end{array}\right]=\left[\begin{array}{cc}cos\mathrm{\β}& -sin\mathrm{\β}\\ sin\mathrm{\β}& \cos \mathrm{\β}\end{array}\right]\left[\begin{array}{c}{a}_x^{ref}\\ a_y^{ref}\end{array}\right]---\left(6\right)$

wherein β is the vehicle centroid slip angle,is the longitudinal acceleration of the vehicle in the coordinate system of the center of mass,is the lateral acceleration of the vehicle in the centroid coordinate system.

5. The method of claim 4, wherein: when the vehicle centroid deflection angle β is 0, the vehicle reference dynamic state value can be expressed by the following formula:

$\left\{\begin{array}{c}{v}_x^{ref}=v_x+\∫a_x^{ref}dt\\ r^{ref}=\frac{a_y^{ref}}{v_x^{ref}}\end{array}\right.---\left(7\right)$

wherein v is_xIs the vehicle initial longitudinal speed;is the ideal longitudinal speed, r, of the vehicle in its coordinate system of the center of mass^refIs the vehicle yaw rate.