CN111231956B - Acceleration constraint control algorithm of vehicle constant-speed cruise system - Google Patents

Acceleration constraint control algorithm of vehicle constant-speed cruise system Download PDF

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CN111231956B
CN111231956B CN202010119081.2A CN202010119081A CN111231956B CN 111231956 B CN111231956 B CN 111231956B CN 202010119081 A CN202010119081 A CN 202010119081A CN 111231956 B CN111231956 B CN 111231956B
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acceleration
vehicle
speed
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control algorithm
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何友国
刘鑫
袁朝春
蔡英凤
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Jiangsu University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units, or advanced driver assistance systems for ensuring comfort, stability and safety or drive control systems for propelling or retarding the vehicle
    • B60W30/14—Adaptive cruise control
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W40/00—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models
    • B60W40/10—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models related to vehicle motion
    • B60W40/107—Longitudinal acceleration

Abstract

The invention discloses an acceleration restraint control algorithm of a vehicle constant-speed cruising system, which restrains the acceleration of a vehicle in the constant-speed cruising process from the aspects of vehicle fuel consumption and passenger riding comfort. The invention introduces the asymmetric obstacle Lyapunov function into the design of the constant-speed cruise speed-acceleration controller, the controller solves the problem of overlarge acceleration during the constant-speed cruise speed switching by controlling the wheel torque, the proposed algorithm can ensure that the acceleration always works in a comfort level area, and the fuel consumption of the automobile is better improved under the condition of not violating the constraint condition. In the process, the brake torque and the wheel rotating speed are not shaken, so that the comfort of the vehicle is further improved.

Description

Acceleration constraint control algorithm of vehicle constant-speed cruise system
Technical Field
The invention relates to intelligent automobile auxiliary driving, and the control algorithm is used for restraining the acceleration of a vehicle cruising at a constant speed in a speed switching process from the aspects of vehicle fuel consumption and passenger riding comfort.
Background
The constant-speed cruise system is one of self-adaptive cruise control strategies of the automobile, and is characterized in that the main automobile takes the speed set by the ACC system as the target speed, and runs quickly after reaching the set speed, so that the longitudinal movement of the automobile is automatically controlled, and the labor intensity of a driver is reduced. If no vehicle is in front of the main vehicle or the main vehicle is far away from a target vehicle in front and the speed is high, the control mode selection module activates the cruise mode control module, and the ACC system automatically adjusts an accelerator pedal and the like according to the vehicle speed set by a driver and the speed of the main vehicle acquired by a wheel speed sensor, so that the main vehicle reaches the set vehicle speed and cruises to run. With the continuous development and improvement of the modern control theory, a plurality of ACC system control algorithms, such as PID control, fuzzy control, model predictive control and the like, have been proposed in the existing literature. However, when the longitudinal speed of the vehicle is controlled to change, the control algorithm of the ACC system in the existing literature calculates the expected acceleration mainly according to the driving safety of the vehicle, so that the value of the acceleration is increased, and the comfort of the vehicle during cruising is neglected. In addition, during acceleration, because the engine is in a transient working condition, when the engine is accelerated rapidly, in order to enable the engine to work smoothly, more oil needs to be sprayed, and over-lean mixed steam is avoided, so that the acceleration has great influence on the fuel consumption. The document 'BackStepping method research and simulation of vehicle adaptive cruise control' applies a BackStepping design method, designs an adaptive cruise nonlinear controller, but does not restrict the acceleration of the vehicle when the longitudinal speed changes.
Disclosure of Invention
Aiming at the problems, the invention provides an acceleration constraint control algorithm of a vehicle constant-speed cruise system based on a vehicle longitudinal acceleration model in order to realize the constraint of the vehicle on the acceleration under the constant-speed cruise, and the good comfort and the fuel economy of the vehicle can be realized in the cruise speed switching process. The invention establishes a speed-acceleration model based on a simplified vehicle tire model and a vehicle longitudinal dynamics model, and reflects the change rule of speed, wheel rotating speed and acceleration in the speed switching process. The invention adopts the asymmetric obstacle Lyapunov function to solve the problem of acceleration restriction of the vehicle in the acceleration or deceleration process, the designed algorithm can ensure that the acceleration is always in a range area with better comfort level, and in the process, the braking torque and the wheel rotating speed do not shake, thereby further improving the comfort level of the vehicle.
The technical scheme of the invention is as follows: an acceleration constraint control algorithm of a vehicle constant-speed cruise system is composed of a constant-speed cruise system modeling and an acceleration constraint control algorithm. The constant-speed cruise system modeling is responsible for establishing a vehicle longitudinal speed-acceleration model on the basis of a tire dynamic model and a vehicle longitudinal dynamic model, and reflecting the change conditions of speed and acceleration. The acceleration constraint control algorithm is responsible for designing a barrier Lyapunov function and a constraint controller to constrain the acceleration.
The constant-speed cruise system is modeled as follows:
suppose that: the vehicle runs on a straight and dry road surface, and the researched vehicle is a front-drive vehicle.
The vehicle longitudinal dynamics model is established as follows:
ma＝Fxf-Faero-fmg (1)
wherein m is the mass of the automobile, FxfIs the driving force that the vehicle is subjected to,Faerois the air resistance of the vehicle, f is the rolling resistance coefficient, and g is the gravity acceleration.
The slip ratio is defined as follows:
Figure BDA0002392408200000021
wherein v isxFor the longitudinal speed of the vehicle, r is the effective radius of the wheel, ωfIs the wheel roll angular velocity. From the assumption, the slip ratio λiGenerally between (-0.1 to 0.1), in which case FxfAnd λiThe following relationship is satisfied,
Fxf＝k·λi (3)
wherein k is a proportionality coefficient. Air resistance F to the vehicleaeroCan be represented by formula
Faero≈cdvx 2 (4)
Wherein, cdFor the coefficient of air resistance, the wheel tyre is rigid without any deformation, given neglecting the wheel lateral forces, considering a simplified tyre dynamics, with
Figure BDA0002392408200000022
Wherein J is the moment of inertia of the tire, TaFor the driving torque applied to the front wheel, r is the radius of the tyre, omegafIs the wheel angular velocity.
The vehicle dynamics equation is as follows:
Figure BDA0002392408200000031
the time t of the formula (1) is differentiated to obtain
Figure BDA0002392408200000032
The system acceleration model can be obtained by the joint formulas (2) to (6)
Figure BDA0002392408200000033
Defining system state variables: x is the number of1＝vx，x2A, a represents acceleration, and the controller inputs: u-TaAnd outputting by the system: y is x1The velocity-acceleration state equation is a system model expression as follows:
Figure BDA0002392408200000034
in the formula (I), the compound is shown in the specification,
Figure BDA0002392408200000035
the speed-acceleration constraint control algorithm of the invention is as follows:
defining the minimum value of the expected acceleration of the acceleration as YlThe maximum value of the desired acceleration is YhThe upper limit of the acceleration constraint is kchThe lower limit of the acceleration constraint is kclThe constraint boundary of the acceleration tracking error of the vehicle is
Figure BDA0002392408200000036
The first step is as follows: design Lyapunov function to ensure state variable x1Closed loop stability with target speed tracked.
Defining velocity tracking error as z1＝v(t)-v*，v*Virtual error z for the desired target velocity2＝x2-α1，α1Selecting Lyapunov function for virtual controller
Figure BDA0002392408200000037
Figure BDA0002392408200000038
Designing a virtual controller α1In order to realize the purpose,
α1＝-k1z1 (14)
substituting (14) into (13) can be obtained
Figure BDA0002392408200000041
From the formula, z2→ 0, there are
Figure BDA0002392408200000042
k1To control the gain, a normal number. According to the Lyapunov stable theorem, the closed-loop system is gradually stable.
The second step is that: the barrier Lyapunov function is designed such that the variable x2The closed loop stabilizes without violating the constraints.
Figure BDA0002392408200000043
Wherein the content of the first and second substances,
Figure BDA0002392408200000044
Figure BDA0002392408200000045
V＝V1(z1)+V2(z2) (18)
Figure BDA0002392408200000046
the design controller is
Figure BDA0002392408200000047
Substituting equation (20) into equation (19) results in
Figure BDA0002392408200000048
According to the Lyapunov stable theorem, the closed-loop system is gradually stable. Obtained in the first step when t → ∞, z1→ 0, and the tracking error is always within the constraint range, ensuring that the acceleration is always in the region that satisfies the comfort of the vehicle.
The invention has the beneficial effects that:
in order to ensure that the vehicle meets comfort and lower fuel consumption in constant-speed cruise speed switching, the invention establishes a vehicle longitudinal speed-acceleration model based on a simplified tire model and a vehicle longitudinal dynamics model, can accurately describe the change rule of the speed, the acceleration and the wheel rotating speed of a vehicle constant-speed cruise system, and simultaneously fundamentally avoids the problem of overlarge acceleration of the vehicle during each acceleration or braking.
Drawings
FIG. 1 is a vehicle longitudinal dynamics model.
FIG. 2 is a simplified vehicle tire model.
Fig. 3 is a block diagram of the control process of the present invention.
Parameters in the figure are as follows: m is the mass of the automobile, FxfIs the driving force applied to the vehicle, FaeroIs the air resistance of the vehicle, f is the rolling resistance coefficient, g is the gravity acceleration, vxFor the longitudinal speed of the vehicle, r is the effective radius of the wheel, ωfFor wheel rolling angular velocity, TaFor driving torque applied to the front wheels, yd(t) is the desired speed and λ is the slip ratio.
Detailed Description
The invention will be further explained with reference to the drawings.
The concept and the specific working process of the invention will be described more clearly and completely with reference to the attached drawings and examples. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive efforts based on the embodiments of the present invention, and all embodiments are within the scope of the present invention.
As shown in fig. 1-3, an acceleration constraint control algorithm for a vehicle cruise control system is composed of a vehicle model, a speed-acceleration model and an acceleration constraint controller.
Firstly, establishing a speed-acceleration model according to the vehicle model; secondly, calculating an acceleration tracking error constraint limit; and finally, designing a self-adaptive speed-acceleration constraint controller.
Defining the minimum value of the expected acceleration of the acceleration as YlThe maximum value of the desired acceleration is YhThe upper limit of the acceleration constraint is kchThe lower limit of the acceleration constraint is kclThe constraint boundary of the acceleration tracking error of the vehicle is
Figure BDA0002392408200000051
The specific implementation steps are as follows:
(1) establishing a velocity-acceleration model
Establishing a speed acceleration model of a constant-speed cruise system according to a vehicle longitudinal dynamic model and a simplified tire model
Figure BDA0002392408200000061
In the formula (I), the compound is shown in the specification,
Figure BDA0002392408200000062
wherein the vehicle parameters are as follows:
m is the mass of the automobile, FxfIs the driving force applied to the vehicle, FaeroIs the air resistance of the vehicle, f is the rolling resistance coefficient, g is the gravity acceleration, vxFor the longitudinal speed of the vehicle, r is the effective radius of the wheel, ωfFor the wheel rolling angular velocity, k is the proportionality coefficient, cdIs the coefficient of air resistance, J is the moment of inertia of the tire, TaThe acceleration tracking error constraint upper bound is k for the drive torque applied to the front wheelb1The lower bound of the acceleration tracking error is ka1。
(2) Computing acceleration tracking error constraint limits
Figure BDA0002392408200000063
Wherein the minimum value of the expected acceleration of the acceleration is YlThe maximum value of the desired acceleration is YhThe upper limit of the acceleration constraint is kchThe lower limit of the acceleration constraint is kcl。
(3) Design acceleration restraint controller
Defining velocity tracking error as z1＝v(t)-v*Virtual error z2＝x2-α1，α1In order to be a virtual control function,
Figure BDA0002392408200000064
wherein v is*At the desired speed.
Designing an acceleration constraint controller as follows:
Figure BDA0002392408200000071
wherein the virtual control function is:
α1＝-k1z1
controller gain parameter k1＞0,k2＞0
The above-listed series of detailed descriptions are merely specific illustrations of possible embodiments of the present invention, and they are not intended to limit the scope of the present invention, and all equivalent means or modifications that do not depart from the technical spirit of the present invention are intended to be included within the scope of the present invention.

Claims (2)

1. An acceleration constraint control algorithm of a vehicle constant-speed cruise system is characterized by comprising a constant-speed cruise system modeling and an acceleration constraint control algorithm; the constant-speed cruise system modeling is responsible for establishing a vehicle longitudinal speed-acceleration model on the basis of a tire dynamic model and a vehicle longitudinal dynamic model so as to obtain the change of speed and acceleration; the acceleration constraint control algorithm is responsible for designing a barrier Lyapunov function and a constraint controller and constraining the acceleration;
the constant-speed cruise system modeling method comprises the following steps:
the vehicle longitudinal dynamics model is established as follows:
ma＝Fxf-Faero-fmg (1)
wherein m is the mass of the automobile, FxfIs the driving force applied to the vehicle, FaeroIs the air resistance borne by the vehicle, f is the rolling resistance coefficient, and g is the gravity acceleration;
the modeling method of the constant-speed cruise system further comprises the following steps:
establishing a slip expression:
Figure FDA0002987188190000011
wherein v isxFor the longitudinal speed of the vehicle, r is the effective radius of the wheel, ωfIs the wheel roll angular velocity; slip ratio lambdaiGenerally between (-0.1 to 0.1), in which case FxfAnd λiThe following relationship is satisfied,
Fxf＝k·λi (3)
wherein k is a proportionality coefficient;
the modeling method of the constant-speed cruise system further comprises the following steps:
the air resistance of the automobileFaeroRepresented by the formula
Faero≈cdvx 2 (4)
Wherein, cdFor the coefficient of air resistance, the wheel tyre is rigid without any deformation, given neglecting the wheel lateral forces, considering a simplified tyre dynamics, with
Figure FDA0002987188190000021
Wherein J is the moment of inertia of the tire, TaFor the driving torque applied to the front wheel, r is the radius of the tyre, omegafIs the wheel angular velocity;
the modeling method of the constant-speed cruise system further comprises the following steps:
the vehicle dynamics equation is established as follows
Figure FDA0002987188190000022
And differentiating the time t of the formula (1) to obtain
Figure FDA0002987188190000023
The joint equations (2) - (6) obtain the system acceleration model:
Figure FDA0002987188190000024
the design method of the acceleration constraint control algorithm comprises the following steps:
defining the minimum value of the expected acceleration of the acceleration as YlThe maximum value of the desired acceleration is YhThe upper limit of the acceleration constraint is kchThe lower limit of the acceleration constraint is kclThe constraint boundary of the acceleration tracking error of the vehicle is
Figure FDA0002987188190000025
The design method of the acceleration constraint control algorithm further comprises the following steps:
design Lyapunov function to ensure state variable x1Closed loop stability in the case of tracking to a target speed; the method comprises the following specific steps:
defining velocity tracking error as z1＝v(t)-v*Virtual error z2＝x2-α1，α1Selecting Lyapunov function for virtual controller
Figure FDA0002987188190000026
Figure FDA0002987188190000027
Designing a virtual controller α1In order to realize the purpose,
α1＝-k1z1 (14)
substituting (14) into (13) can be obtained
Figure FDA0002987188190000031
From the formula, z2→ 0, there are
Figure FDA0002987188190000032
k1To control gain, normal; according to the Lyapunov stability theorem, the closed-loop system is gradually stabilized;
the design method of the acceleration constraint control algorithm further comprises the following steps:
the barrier Lyapunov function is designed such that the variable x2Closed loop stability without violating constraints;
Figure FDA0002987188190000033
Figure FDA0002987188190000034
V＝Vl(Zl)+V2(Z2) (18)
Figure FDA0002987188190000035
Figure FDA0002987188190000036
the design controller is
Figure FDA0002987188190000037
Substituting equation (20) into equation (19) results in
Figure FDA0002987188190000038
According to the Lyapunov stable theorem, the closed-loop system is gradually stable.
2. The vehicle cruise control system acceleration constraint control algorithm according to claim 1, characterized in that the cruise control system modeling method further comprises:
defining system state variables: x is the number of1＝vx，x2A, the controller inputs: u-TaAnd outputting by the system: y is x1The expression for the velocity-acceleration equation of state is as follows:
Figure FDA0002987188190000041
in the formula (I), the compound is shown in the specification,
Figure FDA0002987188190000042
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