CN111666636A - Unmanned vehicle dynamics limit characteristic envelope online observation method - Google Patents
Unmanned vehicle dynamics limit characteristic envelope online observation method Download PDFInfo
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Abstract
The invention discloses an unmanned vehicle dynamics limit characteristic envelope line online observation method. Firstly, an ideal G-G diagram of the unmanned vehicle is obtained in a virtual simulation mode, and the kinetic limit which can be reached by the unmanned vehicle is clearly and clearly shown in the form of the G-G diagram. The adjustment coefficient is obtained through online observation of the tire ground adhesion coefficient and relevant post-processing calculation, and the ideal G-G diagram is further corrected online, so that the G-G diagram of the unmanned vehicle under the actual working condition is accurately represented, and finally, the dynamics limit characteristic envelope curve of the unmanned vehicle is accurately observed online. The method is suitable for unmanned vehicles with various configurations, can effectively describe the dynamics limit characteristics of the unmanned vehicles, provides a foundation for dynamics control of the unmanned vehicles under the limit working condition, improves the track tracking capability and the maneuvering capability of the unmanned vehicles, and meets the use requirements of the unmanned vehicles under the civil complex scene or the military scene.
Description
Technical Field
The invention belongs to the technical field of unmanned vehicles and automatic driving vehicles, and particularly relates to an on-line observation method for an envelope curve of dynamics limit characteristics of an unmanned vehicle.
Background
The automatic driving vehicle is an important development direction of the future automobile industry and is one of important fields of artificial intelligence technology landing. The unmanned vehicle is a vehicle with autonomous behavior capability and completely omitting a human driving mechanism, and has the characteristics of intellectualization, wire control, robotization and multiple functions. The unmanned vehicle aims to replace human beings to execute operation tasks, including but not limited to civil or military tasks such as striking, fighting, patrol, reconnaissance, logistics, transportation, ferrying, distribution, cleaning and the like, has a very wide application prospect in the civil or military field, is an important component part of future intelligent transportation and smart city construction, and is an important support for development of new-generation army equipment in China. Therefore, the research of the unmanned vehicle theory and technology has important strategic significance on national economic development and national defense safety construction in China.
Disclosure of Invention
In view of this, the invention aims to provide an online observation method for an envelope curve of a dynamic limit characteristic of an unmanned vehicle, which can accurately describe the dynamic limit characteristic of the vehicle and provide a basis for high-performance dynamic control of the unmanned vehicle.
An unmanned vehicle dynamics limiting characteristic envelope line online observation method comprises the following steps:
in the formula: i is 1,2 is front and rear axle respectively, j is 1,2 is left and right side respectively, Fxi,j(k) For sampling the left front wheel k timesThe longitudinal force of the tire, the right front tire, the left rear tire and the right rear tire, k is the number of sampling times, RtIs the wheel radius, omegai,j(k-1) is the rotation speed of each wheel at k-1 sampling, ItIs the inertia of the wheel.
in the formula: m is the total vehicle mass, ax(k-1),ay(k-1) longitudinal and transverse accelerations obtained by k-1 times of sampling respectively, h is the height of the center of mass of the unmanned vehicle, and lr、lfDistances from the vehicle's centroid position to the rear and front axles, respectively, L, B wheelbase and wheelbase, respectively, KΦf,KΦrRoll stiffness, h, of the front and rear suspension, respectivelyrf,hrrThe roll centers of the front and rear suspensions, respectively;
and 3, observing the tire ground adhesion coefficient of each wheel by the following formula:
the average tyre ground adhesion coefficient is ∑i,j＝1,2μi,j(k-1)/4.
Determining the maximum value mu of the tyre ground mean adhesion coefficient of all the sampling moments obtained at the present timemaxFinally according to λ ═ μmax/μ0An adjustment parameter lambda is calculated. Wherein, mu0The maximum adhesion coefficient of the test runway is adopted for testing the mechanical properties of the tire when an ideal G-G graph is obtained.
And finally, correcting the ideal G-G diagram by using the adjusting parameter lambda to obtain a corrected G-G diagram boundary:
in the formula: λ aymax、λaxmaxTAnd λ axmaxBThe maximum lateral acceleration, the maximum longitudinal acceleration and the maximum longitudinal deceleration of the unmanned vehicle are respectively.
And 4, the corrected G-G diagram is the result of the observed unmanned vehicle dynamics limit characteristic envelope curve.
The invention has the following beneficial effects:
the invention provides an unmanned vehicle dynamics limit characteristic envelope line online observation method, which comprises the steps of firstly obtaining an ideal G-G diagram of an unmanned vehicle in a virtual simulation mode, and clearly representing dynamics limits which can be reached by the unmanned vehicle by using the form of the G-G diagram. The adjustment coefficient is obtained by online observation of the tire ground adhesion coefficient, and then the ideal G-G diagram is corrected online, so that the G-G diagram of the unmanned vehicle under the actual working condition is accurately represented, and finally the dynamics limit characteristic envelope curve of the unmanned vehicle is accurately observed online. The method is suitable for unmanned vehicles with various configurations, can effectively describe the dynamics limit characteristics of the unmanned vehicles, provides a foundation for dynamics control of the unmanned vehicles under the limit working condition, improves the track tracking capability and the maneuvering capability of the unmanned vehicles, and meets the use requirements of the unmanned vehicles under the civil complex scene or the military scene.
Drawings
FIG. 1 is a schematic diagram of G-G;
FIG. 2 is a flow chart of an observation algorithm of the present invention.
Detailed Description
The invention is described in detail below by way of example with reference to the accompanying drawings.
In some specific use scenes, especially military scenes, the dynamic performance of the unmanned vehicle needs to be fully exerted, so that the unmanned vehicle can work under the driving limit condition, and the unmanned vehicle can pass through a given path as soon as possible and complete a given task. The method has the advantages that the effective dynamic control of the unmanned vehicle under the limit working condition needs to accurately describe the limit dynamic characteristics of the unmanned vehicle by using a G-G diagram. The G-G diagram is an important means of describing the acceleration capability of a vehicle, which is plotted from the lateral acceleration and the longitudinal acceleration of the vehicle in a coordinate system, the boundaries of which describe the extreme dynamics of the vehicle. Therefore, the method realizes the on-line observation of the G-G diagram of the unmanned vehicle by utilizing the multi-dimensional state parameter sensor of the unmanned vehicle, and is a key technology for realizing the dynamics control of the unmanned vehicle under the limit working condition.
The invention provides an unmanned vehicle dynamics limit characteristic envelope line online observation method which can be used for online observation of limit dynamics characteristics of unmanned vehicles with various configurations. The envelope line used by the unmanned vehicle dynamics limit characteristic envelope line online observation method provided by the invention is a G-G diagram, and dynamics limit characteristic description is carried out on the unmanned vehicle by utilizing the G-G diagram. The method comprises the steps of firstly obtaining an ideal G-G diagram of the unmanned vehicle in a virtual prototype simulation mode, and adjusting the boundary of the ideal G-G diagram obtained by virtual simulation into the boundary of an actual G-G diagram through online observation of the ground adhesion coefficient of the tire in the use of actual engineering, so that the ideal G-G diagram is corrected, and the aim of accurately describing the dynamic limit characteristics of the vehicle is fulfilled.
FIG. 1 shows a schematic representation of G-G. The G-G diagram is an important means for describing the limit speed characteristic of the vehicle. The G-G plot is plotted with lateral and longitudinal acceleration, with the origin in the middle. The boundary of the G-G graph represents the limit acceleration of the vehicle, the boundary of the first quadrant and the second quadrant represents the limit acceleration (the lateral acceleration and the longitudinal acceleration are combined together) when the unmanned vehicle enters the curve for acceleration, the boundary of the third quadrant and the fourth quadrant represents the limit acceleration (the lateral acceleration and the longitudinal deceleration are combined together) when the unmanned vehicle enters the curve for braking, the physical meaning of the intersection point of the G-G graph and the X-axis positive half shaft and the X-axis negative half shaft is the maximum lateral acceleration of the vehicle, the physical meaning of the intersection point of the G-G graph and the Y-axis positive half shaft is the maximum acceleration of the vehicle, and the physical meaning of the intersection point of the G-G graph and the Y-axis negative half shaft is the maximum deceleration of the vehicle. The circles in fig. 1 represent the tire friction circle limits and the two horizontal lines represent the maximum traction and braking force limits. The G-G diagram boundary has larger clearance with the area formed by two transverse lines and circles, which is caused by the dynamics such as vertical load transfer of the tire. Therefore, the G-G diagram provides accurate observation of the vehicle limit, and is beneficial to the accurate control of the unmanned vehicle control system so as to realize the limit driving of the unmanned vehicle.
The invention firstly obtains an ideal G-G diagram of the unmanned vehicle in an off-line way in a virtual simulation mode. The virtual prototype simulation employed a 7-degree-of-freedom nonlinear dynamical model including body longitudinal, lateral and yaw movements and 4 wheel rotations. The tire dynamics characteristics are obtained through experiments and are modeled by a magic formula, wherein the magic formula is shown as the following formula:
F＝Dsin{C arctan[BX-E(BX-arctan(BX))]} (1)
in the formula: f is the longitudinal force or the lateral force of the tire, B is the rigidity coefficient, C is the shape factor, D is the peak factor, E is the curvature coefficient, and X is the longitudinal slip rate or the transverse slip angle.
The invention obtains an ideal G-G diagram by using a phase plane method, sets vehicle state variables such as a vehicle speed u, a transverse speed v, a yaw rate r and the like as different initial values aiming at different running conditions on the basis of the 7-degree-of-freedom nonlinear vehicle dynamics model, enables a vehicle dynamics system to realize free oscillation and stable recovery under an initial value state, records motion parameters of all vehicle state variables and draws a phase diagram. The longitudinal acceleration and the lateral acceleration of the vehicle dynamic system are recorded in a coordinate system, and the stable region of the vehicle dynamic system is an ideal G-G map of the vehicle.
The boundaries of the ideal G-G diagram can be represented by two semi-ellipses:
in the formula: a isx、ayLongitudinal and transverse accelerations, respectively, aymaxAt maximum ideal lateral acceleration, axmaxT、axmaxBMaximum ideal acceleration and maximum ideal deceleration, respectively.
The G-G diagram boundary in equation (2) is based on a non-linear vehicle model that includes an ideal tire mechanics model that is constructed based on test data obtained from a test apparatus with good adhesion conditions. However, the actual road conditions are more complicated and varied, and the tire ground adhesion coefficient is drastically changed, so that the boundary of the ideal G-G map must be corrected according to the actual tire ground adhesion coefficient to obtain the actual G-G map boundary, thereby improving the accuracy of the G-G map.
In the process of correcting the ideal G-G diagram, there are two assumptions: first, it is assumed that the change value of the maximum acceleration capability of the unmanned vehicle is proportional to the change value of the maximum tire ground adhesion coefficient. Defining a regulation parameter lambda as mumax/μ0In which μ0For the maximum coefficient of adhesion of the test runway, μmaxThe method is the maximum value of the mean value of the actual ground adhesion coefficients of the four wheels at each sampling moment in the control process. Second, the ground adhesion coefficient is assumed to be constant throughout a given path.
For unmanned vehicles, in order to improve the maneuverability, stability, maneuverability and controllability of the unmanned vehicles, the unmanned vehicles mostly adopt independent driving and independent steering technologies of each wheel, so that parameters such as wheel rotation speed, steering angle, motor current and the like in the driving process of each wheel can be acquired in real time, and therefore, the real-time ground adhesion coefficient meets the condition of online observation. According to the acquired parameters and the intrinsic parameters of the motor and the wheels, the longitudinal force of each wheel is calculated by using a driving wheel dynamic equation, and the noise caused by the difference of the rotating speeds of the wheels is eliminated by using a low-pass filter.
The wheel longitudinal force can be obtained by observing the dynamic equation of the driving wheel:
in the formula: i-1, 2 for front and rear axle, respectively, j-1, 2 for left and right side, respectively, Fxi,j(k) The longitudinal force of the left front tire, the right front tire, the left rear tire and the right rear tire is sampled for k times, k is the serial number of the sampling times, RtIs the wheel radius, omegai,j(k-1) is the rotation speed of each wheel at k-1 sampling, ItIs the inertia of the wheel. By collecting the motor current, the torque constant and the gear ratio, the acting torque T on each wheel can be calculatedi,j(k-1)。
The method comprises the following steps of acquiring longitudinal and transverse accelerations of the unmanned vehicle by using an inertial navigation sensor loaded on the unmanned vehicle, calculating the vertical load of each wheel according to parameters such as the height of the mass center, the wheelbase, the roll stiffness of a suspension, the roll center and the like of the vehicle, and observing the vertical loads of four wheels through the following formula:
in the formula: m is the total vehicle mass, ax(k-1)、ay(k-1) longitudinal and transverse accelerations obtained by k-1 times of sampling respectively, h is the height of the center of mass of the unmanned vehicle, and lr、lfDistances from the vehicle's centroid position to the rear and front axles, respectively, L, B wheelbase and wheelbase, respectively, KΦf、KΦrRoll stiffness, h, of the front and rear suspension, respectivelyrf、hrrRespectively, the roll centers of the front and rear suspensions.
The tire ground adhesion coefficient of each wheel can be observed by the following formula:
the average tyre ground adhesion coefficient is ∑i,j＝1,2μi,j(k-1)/4.
After obtaining the observed value of the tire ground average adhesion coefficient, determining the maximum value mu of the tire ground average adhesion coefficient at all the sampling moments obtained currentlymaxFinally according to λ ═ μmax/μ0An adjustment parameter lambda is calculated. According to the assumption made, the maximum transverse acceleration, the maximum longitudinal acceleration and the maximum longitudinal deceleration of the unmanned vehicle can be represented by lambda aymax,λaxmaxTAnd λ axmaxBTo describe. According to the above result, the ideal G-G diagram obtained by simulation can be corrected, and the corrected G-G diagram boundary can be described as:
in summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (1)
1. An unmanned vehicle dynamics limiting characteristic envelope line online observation method is characterized by comprising the following steps:
step 1, the longitudinal force of each driving wheel can be obtained by observing the dynamic equation of the driving wheel:
in the formula: i is 1,2 is front and rear axle respectively, j is 1,2 is left and right side respectively, Fxi,j(k) The longitudinal force of the left front tire, the right front tire, the left rear tire and the right rear tire is sampled for k times, k is the serial number of the sampling times, RtRepresenting the wheel radius, ωi,j(k-1) is the rotation speed of each wheel at k-1 sampling, ItIs the inertia of the wheel;
step 2, the vertical loads of the four wheels are obtained by observing according to the following formula:
in the formula: m is the total vehicle mass, ax(k-1)、ay(k-1) longitudinal and transverse accelerations obtained by k-1 times of sampling respectively, h is the height of the center of mass of the unmanned vehicle, and lr、lfRepresenting the distance of the vehicle's centroid position to the rear and front axles, respectively, L, B wheelbase and wheelbase, respectively, KΦf、KΦrRoll stiffness, h, of the front and rear suspension, respectivelyrf、hrrThe roll centers of the front and rear suspensions, respectively;
and 3, observing the tire ground adhesion coefficient of each wheel by the following formula:
the average tyre ground adhesion coefficient is ∑i,j＝1,2μi,j(k-1)/4 calculation;
determining the maximum value mu of the tyre ground mean adhesion coefficient of all the sampling moments obtained at the present timemaxFinally according to λ ═ μmax/μ0Calculating a regulation parameter lambda [ mu ], [ mu ]0The maximum adhesion coefficient of a test runway is adopted for testing the mechanical properties of the tire when an ideal G-G diagram is obtained;
and finally, correcting the ideal G-G diagram by using the adjusting parameter lambda to obtain a corrected G-G diagram boundary:
in the formula: λ aymax、λaxmaxTAnd λ axmaxBThe maximum transverse acceleration, the maximum longitudinal acceleration and the maximum longitudinal deceleration of the unmanned vehicle are respectively;
and 4, the corrected G-G diagram is the observed result of the envelope curve of the unmanned vehicle dynamics limit characteristic.
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| CN112257267A (en) * | 2020-10-23 | 2021-01-22 | 华人运通(江苏)技术有限公司 | Method and system for manufacturing vehicle tire envelope |
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