CN114261288B - Yaw torque control method for electric four-wheel drive vehicle - Google Patents
Yaw torque control method for electric four-wheel drive vehicle Download PDFInfo
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Abstract
The invention discloses a yaw torque control method for an electric four-wheel drive vehicle, which is used for monitoring the change of the yaw speed of the vehicle in real time, and when the occurrence of understeer or oversteer of the vehicle is detected, vector torque is reversely loaded, the motion gesture of the vehicle is corrected, and the vehicle is restored to a stable running and path tracking state. The beneficial effects of the invention are mainly as follows: estimating an instability index value according to the instability type of the wheels of the vehicle, limiting the driving torque, and outputting the calculated required torque of the front axle and the rear axle or the left wheel and the right wheel to a torque coordination function module so as to rapidly and accurately realize the yaw rate control; the driving torque vector of the VCU and the ESP braking torque vector function are combined, so that the stability control characteristic of the electric four-wheel drive vehicle can be exerted to the greatest extent.
Description
Technical Field
The invention relates to the field of vehicle power control, in particular to a yaw torque control method of an electric four-wheel drive vehicle.
Background
Four-wheel independent driving electric automobile based on in-wheel motor, four wheel torque is independent controllable, can improve the dynamic performance of vehicle through torque control distribution, has increased control degree of freedom. In addition, the motor can drive and brake, and compared with the traditional internal combustion engine and hydraulic braking system, the motor has higher torque response speed and control precision, and is beneficial to improving the performance of a power control system. Therefore, four-wheel independent drive electric vehicles have obvious advantages in power control, and have become a research hot spot in recent years.
Chinese patent CN111891125 discloses a lane departure active correction method based on torque control, which calculates a compensation torque by feedforward torque, feedback torque and steering wheel torque, and inputs the compensation torque to a steering system to complete the torque correction control. The feedforward torque and the feedback torque are complex in calculation mode, and torque control is performed without considering actual vehicle driving conditions. The types of vehicle wheel instability can generally be categorized into the following categories depending on the actual vehicle driving conditions.
First, unexpected yaw motion during straight travel due to abnormal yaw motion of the vehicle caused by wheel slip; this phenomenon is common when the left and right wheels travel on a road surface with a separation adhesion coefficient, the vehicle accelerates on a straight road, and the wheels slip due to the driving force exceeding the road-tire adhesion limit and accompanying cornering motions, at which time the vehicle may yaw while slipping.
Second, understeer yaw motion, which is common in curved or changing road travel, is caused by severe understeer due to insufficient steering wheel angle, with the front wheels slipping outward and deviating from the desired travel path.
Oversteer yaw motion, which is a phenomenon commonly found in curved or lane-changing travel, is caused by oversteer of the rear wheels, which occurs to slip outward, deviating from the desired travel path, due to the driving force exceeding the tire-road lateral adhesion limit.
Torque drive control is also currently implemented according to road conditions, as disclosed in chinese patent CN 108248455. There is currently no method for yaw torque control based on the type of vehicle wheel instability.
Disclosure of Invention
The invention aims to solve the technical problems and provides a yaw torque control method of an electric four-wheel drive vehicle.
The aim of the invention is achieved by the following technical scheme:
a yaw torque control method of an electric four-wheel drive vehicle comprises the following steps,
S1, judging whether a calculation result of the target yaw rate and the actual yaw rate is effective;
S2, when the target yaw rate and the actual yaw rate are both effective, checking the road surface state, estimating the tire-road surface lateral adhesive force limit value, judging the type of the instability of the vehicle wheels in real time, and judging the instability degree of the vehicle in real time by combining the wheel-road surface lateral adhesive force limit value to generate an instability index;
S3, calculating a feedforward control required torque and a feedback control required torque required by vehicle yaw rate control by using a feedforward control algorithm and a feedback control algorithm;
And S4, the calculated feedforward control required torque is fed back to control the required torque, a torque distribution mode and a distribution proportion are defined according to the structural form of the electric four-wheel drive system, and the required torque of each of the front axle, the rear axle or the left wheel and the right wheel is output to a torque coordination functional module to control the yaw rate.
Preferably, the specific process of step S1 is that,
S11, performing fault diagnosis on a vehicle speed and steering wheel corner signal required by calculating the target yaw rate, if the input signal is valid, judging that the calculation result of the target yaw rate is valid, otherwise, invalidating the calculation result;
s12, performing fault diagnosis on the yaw rate sensor signal, and if the yaw rate sensor signal is valid, enabling an actual yaw rate result to be valid, otherwise disabling the yaw rate result.
Preferably, in the result of step S1, only the feedforward control algorithm is used to improve the vehicle instability condition when only the target yaw rate calculation result is valid.
Preferably, in the step S2, the "checking the road surface state and estimating the tire-road surface lateral adhesion limit" includes the following steps:
s21, judging the road surface state through modes such as vehicle slip rate calculation or image recognition, and dividing the road surface state into three typical attached road surfaces of high, medium and low by adopting a clustering algorithm;
s22, estimating the lateral adhesive force limit value of the tire and the pavement in the current and future specific time periods by using a vehicle dynamics formula according to the motion state and the driving intention of the vehicle.
Preferably, in the step S2, the "determining the type of the instability of the vehicle wheel in real time and determining the degree of the instability of the vehicle in real time by combining the limit value of the lateral adhesion of the wheel to the road surface" includes the following steps:
S23, judging the yaw state of wheels of the vehicle according to the actual motion track of the vehicle, wherein the yaw state comprises an unexpected yaw state, an understeer yaw state and an oversteer yaw state;
S24, if the vehicle has a steering instability trend, the vehicle instability degree is judged in real time by combining with the lateral adhesion limit value of the wheel-road surface, an instability index is generated, and the driving torque is limited according to the estimated instability index value, wherein the instability index is defined as follows: 0 represents no instability (no); 1 represents slightly unstable (low); 2 represents relatively unstable (medium); 3 represents severe instability (high); 4 represents a very unstable (dangerous) condition.
Preferably, the step S3 of performing the yaw rate control by using a feedforward and feedback control algorithm specifically includes:
the feedforward control of the yaw rate adopts a hierarchical PID control algorithm,
Controller input: a target yaw rate;
a first stage controller: adopting a PD control algorithm, setting a control dead zone and an upper limit value and a lower limit value according to the vehicle speed, and preventing the controller from overshooting;
a second level controller: a decremental integrator control algorithm is adopted for eliminating static errors;
Controller output: feedforward control demand torque;
The calculation formula is as follows:
= ̇d+ d̈d− (−1)̇d(1)
Wherein: ̇ d is the target yaw rate;
̈ d is a differential value of the target yaw rate;
The control coefficient is P items;
Is the I control coefficient;
d is a D term control coefficient;
the torque demand for feed-forward control;
The yaw rate feedback control adopts a PID control algorithm,
Controller input: deviation of the target from the actual yaw rate;
core control algorithm: a PID control algorithm is adopted, and a control dead zone and an upper limit value and a lower limit value are set according to the speed of a vehicle through the PID control algorithm, so that the overshoot of a controller is prevented; meanwhile, setting a D item control selection output switch according to the deviation value through the PID control algorithm, and closing the D item control when the deviation is smaller to prevent the controller from vibrating;
controller output: feedback control of the demanded torque;
The calculation formula is as follows:
= ̇+ d̈+ (−1)̇(2)
wherein: ̇ is yaw rate deviation;
̈ is a differential value of the yaw-rate deviation;
the control coefficient is P items;
Is the I control coefficient;
D is a D term control coefficient;
The torque is demanded for feedback control.
Preferably, in the step S4, the "defining the torque distribution mode and the distribution proportion according to the structural form of the electric four-wheel drive system" specifically includes the following steps,
S41, determining the structural form of the four-wheel drive system;
s42, defining a torque distribution mode and a torque distribution proportion, and implementing front and rear axle torque distribution for the vehicle type of the front and rear axle single drive motor; for the vehicle types of a front axle single motor and a rear axle double motor, front and rear axle torque distribution and rear axle left and right wheel torque vector distribution are implemented; for a four-wheel motor driven vehicle model, four-wheel torque vector distribution is implemented.
Preferably, in the step S4, the "output the required torque of each of the front and rear axles or the left and right wheels to the torque coordination function module to perform yaw rate control" is performed by performing yaw rate control according to the yaw state of the wheels of the vehicle,
When the vehicle is in an unexpected yaw state, firstly judging that the wheels are in a yaw state rather than a slip state, and activating an oversteer control mode;
when in the understeer yaw state, an understeer control mode is adopted,
A1, analyzing the current road surface state, switching a driving mode into a four-wheel driving mode, reducing the driving force of the inner wheels, increasing the driving force of the outer wheels, and forming more yaw moment steering inwards;
a2, if the driving force reaches the tire-road surface lateral adhesion limit value, reducing the total driving force by applying a limiting torque;
a3, if the road adhesion coefficient is very low, applying braking force through motor reversal, and then carrying out yaw moment calculation again to finally restore the running track of the vehicle to an expected state;
When in the oversteer yaw state, an oversteer control mode is adopted,
B1, analyzing the current road surface state, switching the driving mode into a four-wheel driving mode, increasing the driving force of the inner wheels, reducing the driving force of the outer wheels, and forming more yaw moment for steering outwards;
b2, if the driving force reaches the tire-road surface lateral adhesion limit value, reducing the total driving force by applying a limiting torque;
And B3, if the road adhesion coefficient is very low, applying braking force through motor reversal, then carrying out yaw moment calculation again, and finally recovering the running track of the vehicle to an expected state.
Preferably, the limiting torque is inversely proportional to the instability index.
The beneficial effects of the invention are mainly as follows: and estimating an instability index value according to the instability type of the vehicle wheel, limiting the driving torque, and outputting the calculated required torque of the front axle and the rear axle or the left wheel and the right wheel to a torque coordination functional module to rapidly and accurately realize the yaw rate control. The driving torque vector of the VCU and the ESP braking torque vector function are combined, so that the stability control characteristic of the electric four-wheel drive vehicle can be exerted to the greatest extent.
Drawings
Fig. 1: is a control flow diagram of a preferred embodiment of the present invention.
Fig. 2: torque calculation and distribution schematic diagrams are provided for the preferred embodiment of the present invention.
Fig. 3: a schematic diagram of the relation between the vehicle motion instability index and the torque limit thereof according to the preferred embodiment of the invention.
Detailed Description
The objects, advantages and features of the present invention are illustrated and explained by the following non-limiting description of preferred embodiments. These embodiments are only typical examples of the technical scheme of the invention, and all technical schemes formed by adopting equivalent substitution or equivalent transformation fall within the scope of the invention.
The invention discloses a yaw torque control method of an electric four-wheel drive vehicle, which has the core concept of monitoring the change of the yaw speed of the vehicle in real time in the running process of the vehicle, and when an electric four-wheel drive system controller detects that the vehicle is under-steered or over-steered, the electric four-wheel drive system controller reversely loads vector torque to correct the motion gesture of the vehicle so as to restore the vehicle to a stable running and path tracking state.
As shown in fig. 1 and 2, the preferred embodiment of the present invention includes the steps of,
S1, judging whether a calculation result of the target yaw rate and the actual yaw rate is effective; the specific process is as follows:
S11, performing fault diagnosis on a vehicle speed and steering wheel corner signal required by calculating the target yaw rate, if the input signal is valid, judging that the calculation result of the target yaw rate is valid, otherwise, invalidating the calculation result;
s12, performing fault diagnosis on the yaw rate sensor signal, and if the yaw rate sensor signal is valid, enabling an actual yaw rate result to be valid, otherwise disabling the yaw rate result.
S2, when only the target yaw rate calculation result is effective, the vehicle instability condition is improved only by using a feedforward control algorithm.
When the target yaw rate and the actual yaw rate are both effective, checking the road surface state, estimating the lateral adhesion limit value of the tire-road surface, judging the type of the instability of the vehicle wheels in real time, and judging the instability degree of the vehicle in real time by combining the lateral adhesion limit value of the wheels-road surface to generate an instability index.
The specific process of the step S2 is as follows:
s21, judging the road surface state through modes such as vehicle slip rate calculation or image recognition, and dividing the road surface state into three typical attached road surfaces of high, medium and low by adopting a clustering algorithm;
S22, estimating the lateral adhesive force limit value of the tire and the pavement in the current and future specific time periods by using a vehicle dynamics formula according to the motion state and the driving intention of the vehicle;
S23, judging the yaw state of wheels of the vehicle according to the actual motion track of the vehicle, wherein the yaw state comprises an unexpected yaw state, an understeer yaw state and an oversteer yaw state;
S24, if the vehicle has a steering instability trend, the vehicle instability degree is judged in real time by combining with the lateral adhesion limit value of the wheel-road surface, an instability index is generated, and the driving torque is limited according to the estimated instability index value, wherein the instability index is defined as follows: 0 represents no instability (no); 1 represents slightly unstable (low); 2 represents relatively unstable (medium); 3 represents severe instability (high); 4 represents a very unstable (dangerous) condition.
S3, calculating a feedforward control required torque and a feedback control required torque required by vehicle yaw rate control by using a feedforward control algorithm and a feedback control algorithm.
The "control of yaw rate using feedforward and feedback control algorithms" specifically includes:
the feedforward control of the yaw rate adopts a hierarchical PID control algorithm,
Controller input: a target yaw rate;
a first stage controller: adopting a PD control algorithm, setting a control dead zone and an upper limit value and a lower limit value according to the vehicle speed, and preventing the controller from overshooting;
a second level controller: a decremental integrator control algorithm is adopted for eliminating static errors;
Controller output: feedforward control demand torque;
The calculation formula is as follows:
= ̇d+ d̈d− (−1)̇d(1)
Wherein: ̇ d is the target yaw rate;
̈ d is a differential value of the target yaw rate;
The control coefficient is P items;
Is the I control coefficient;
d is a D term control coefficient;
torque is required for feed-forward control.
The yaw rate feedback control adopts a PID control algorithm,
Controller input: deviation of the target from the actual yaw rate;
Core control algorithm: adopting a PID control algorithm, setting a control dead zone and an upper limit value and a lower limit value according to the vehicle speed, and preventing the controller from overshooting; meanwhile, setting a D item control selection output switch according to the deviation value, and closing the D item control when the deviation is smaller to prevent the controller from vibrating;
controller output: feedback control of the demanded torque;
The calculation formula is as follows:
= ̇+ d̈+ (−1)̇(2)
wherein: ̇ is yaw rate deviation;
̈ is a differential value of the yaw-rate deviation;
the control coefficient is P items;
Is the I control coefficient;
D is a D term control coefficient;
The torque is demanded for feedback control.
And S4, the calculated feedforward control required torque is fed back to control the required torque, a torque distribution mode and a distribution proportion are defined according to the structural form of the electric four-wheel drive system, and the required torque of each of the front axle, the rear axle or the left wheel and the right wheel is output to a torque coordination functional module to control the yaw rate.
The specific process of the step S4 is as follows,
S41, determining the structural form of the four-wheel drive system;
s42, defining a torque distribution mode and a torque distribution proportion, and implementing front and rear axle torque distribution for the vehicle type of the front and rear axle single drive motor; for the vehicle types of a front axle single motor and a rear axle double motor, front and rear axle torque distribution and rear axle left and right wheel torque vector distribution are implemented; for a four-wheel motor driven vehicle model, four-wheel torque vector distribution is implemented.
When the vehicle is in an unexpected yaw state, firstly judging that the wheels are in a yaw state rather than a slip state, and activating an oversteer control mode;
when in the understeer yaw state, an understeer control mode is adopted,
A1, analyzing the current road surface state, switching a driving mode into a four-wheel driving mode, reducing the driving force of the inner wheels, increasing the driving force of the outer wheels, and forming more yaw moment steering inwards;
a2, if the driving force reaches the tire-road surface lateral adhesion limit value, reducing the total driving force by applying a limiting torque;
a3, if the road adhesion coefficient is very low, applying braking force through motor reversal, and then carrying out yaw moment calculation again to finally restore the running track of the vehicle to an expected state;
When in the oversteer yaw state, an oversteer control mode is adopted,
B1, analyzing the current road surface state, switching the driving mode into a four-wheel driving mode, increasing the driving force of the inner wheels, reducing the driving force of the outer wheels, and forming more yaw moment for steering outwards;
b2, if the driving force reaches the tire-road surface lateral adhesion limit value, reducing the total driving force by applying a limiting torque;
And B3, if the road adhesion coefficient is very low, applying braking force through motor reversal, then carrying out yaw moment calculation again, and finally recovering the running track of the vehicle to an expected state.
As shown in fig. 3, in the step a2\b2, the applied limiting torque is inversely proportional to the instability index. The electric four-wheel drive system also typically reduces the total torque of the rear axle as vehicle speed increases to increase controllability at high speed instability.
The beneficial effects of the invention are mainly as follows: and estimating an instability index value according to the instability type of the vehicle wheel, limiting the driving torque, and outputting the calculated required torque of the front axle and the rear axle or the left wheel and the right wheel to a torque coordination functional module to rapidly and accurately realize the yaw rate control. The driving torque vector of the VCU and the ESP braking torque vector function are combined, so that the stability control characteristic of the electric four-wheel drive vehicle can be exerted to the greatest extent.
The invention has various embodiments, and all technical schemes formed by equivalent transformation or equivalent transformation fall within the protection scope of the invention.
Claims (7)
1. The yaw torque control method for the electric four-wheel drive vehicle is characterized by comprising the following steps of: comprises the following steps of the method,
S1, judging whether a calculation result of the target yaw rate and the actual yaw rate is effective;
S2, when the target yaw rate and the actual yaw rate are both effective, checking the road surface state, estimating the tire-road surface lateral adhesive force limit value, judging the type of the instability of the vehicle wheels in real time, and judging the instability degree of the vehicle in real time by combining the wheel-road surface lateral adhesive force limit value to generate an instability index;
S3, calculating a feedforward control required torque Tff and a feedback control required torque Tfb required by vehicle yaw rate control by using a feedforward control algorithm and a feedback control algorithm;
s4, defining a torque distribution mode and a distribution proportion according to the structural form of the electric four-wheel drive system by using the calculated feedforward control required torque Tff and feedback control required torque Tfb, and outputting the required torques of the front axle, the rear axle or the left wheel and the right wheel to a torque coordination functional module for controlling the yaw angular speed;
the specific process of the step S1 is that,
S11, performing fault diagnosis on a vehicle speed and steering wheel corner signal required by calculating the target yaw rate, if the input signal is valid, judging that the calculation result of the target yaw rate is valid, otherwise, invalidating the calculation result;
s12, performing fault diagnosis on a yaw rate sensor signal, and if the yaw rate sensor signal is valid, enabling an actual yaw rate result to be valid, otherwise, disabling the yaw rate result;
the specific process of the step S3 is as follows:
the feedforward control algorithm adopts a hierarchical PID control algorithm,
Controller input: a target yaw rate;
A first stage controller: adopting a PD control algorithm, setting a control dead zone and an upper limit value and a lower limit value according to the vehicle speed, and preventing the controller from overshooting;
A second level controller: a decremental integrator control algorithm is adopted for eliminating static errors;
controller output: feed forward control demand torque Tff;
The calculation formula is as follows:
wherein: Is the target yaw rate;
A differential value of the target yaw rate;
kp is the P term control coefficient;
ki is the I term control factor;
kd is a D control coefficient;
tff is the feedforward control demand torque;
1/s mathematically represents an integral; 1/(s-ki) represents the mathematical expression of the integral term with step adjustment;
the feedback control algorithm adopts a PID control algorithm,
Controller input: deviation of the target from the actual yaw rate;
core control algorithm: adopting a PID control algorithm, setting a control dead zone and an upper limit value and a lower limit value according to the vehicle speed, and preventing the controller from overshooting; meanwhile, setting a D item control selection output switch according to the deviation value, and closing the D item control when the deviation is smaller to prevent the controller from vibrating;
controller output: feedback control demand torque Tfb;
The calculation formula is as follows:
wherein: is yaw rate deviation;
is a differential value of yaw rate deviation;
kp is the P term control coefficient;
ki is the I term control factor;
kd is a D control coefficient;
Tfb is the feedback control demand torque.
2. The method according to claim 1, characterized in that: and when only the target yaw rate calculation result is valid in the result of the step S1, the vehicle instability condition is improved by only using a feedforward control algorithm.
3. The method according to claim 1, characterized in that: in the step S2, the specific process of "checking the road surface state and estimating the tire-road surface lateral adhesion limit" is as follows:
S21, judging the road surface state through vehicle slip rate calculation or image recognition, and dividing the road surface state into three typical attached road surfaces of high, medium and low by adopting a clustering algorithm;
s22, estimating the lateral adhesive force limit value of the tire and the pavement in the current and future specific time periods by using a vehicle dynamics formula according to the motion state and the driving intention of the vehicle.
4. A method according to claim 1 or 3, characterized in that: in the step S2, the "real-time determination of the type of instability of the vehicle wheel" and the real-time determination of the degree of instability of the vehicle by combining the limit value of lateral adhesion of the wheel to the road surface "are performed to generate an instability index, and the specific process is as follows:
S23, judging the yaw state of wheels of the vehicle according to the actual motion track of the vehicle, wherein the yaw state comprises an unexpected yaw state, an understeer yaw state and an oversteer yaw state;
and S24, if the vehicle has a steering instability trend, the vehicle instability degree is judged in real time by combining the lateral adhesion limit value of the wheels and the road surface, an instability index is generated, and the driving torque is limited according to the estimated instability index value.
5. The method according to claim 1, characterized in that: in the step S4, the torque distribution mode and the distribution proportion are defined according to the structural form of the electric four-wheel drive system, and the specific process is that,
S41, determining the structural form of the four-wheel drive system;
s42, defining a torque distribution mode and a torque distribution proportion, and implementing front and rear axle torque distribution for the vehicle type of the front and rear axle single drive motor; for the vehicle types of a front axle single motor and a rear axle double motor, front and rear axle torque distribution and rear axle left and right wheel torque vector distribution are implemented; for a four-wheel motor driven vehicle model, four-wheel torque vector distribution is implemented.
6. The method according to claim 5, wherein: in the step S4, the "output the required torque of each of the front and rear axles or the left and right wheels to the torque coordination function module to perform yaw rate control" specifically includes performing yaw rate control according to the yaw state of the wheels of the vehicle,
When the vehicle is in an unexpected yaw state, firstly judging that the wheels are in a yaw state rather than a slip state, and activating an oversteer control mode;
when in the understeer yaw state, an understeer control mode is adopted,
A1, analyzing the current road surface state, switching a driving mode into a four-wheel driving mode, reducing the driving force of the inner wheels, increasing the driving force of the outer wheels, and forming more yaw moment steering inwards;
a2, if the driving force reaches the tire-road surface lateral adhesion limit value, reducing the total driving force by applying a limiting torque;
a3, if the road adhesion coefficient is very low, applying braking force through motor reversal, and then carrying out yaw moment calculation again to finally restore the running track of the vehicle to an expected state;
When in the oversteer yaw state, an oversteer control mode is adopted,
B1, analyzing the current road surface state, switching the driving mode into a four-wheel driving mode, increasing the driving force of the inner wheels, reducing the driving force of the outer wheels, and forming more yaw moment for steering outwards;
b2, if the driving force reaches the tire-road surface lateral adhesion limit value, reducing the total driving force by applying a limiting torque;
And B3, if the road adhesion coefficient is very low, applying braking force through motor reversal, then carrying out yaw moment calculation again, and finally recovering the running track of the vehicle to an expected state.
7. The method according to claim 6, wherein: the limit torque is inversely proportional to the instability index.
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| CN108437978A (en) * | 2018-05-14 | 2018-08-24 | 武汉理工大学 | Four wheel hub electricity drive vehicle running surface automatic identification and stability integrated control method |
| CN113085578A (en) * | 2021-04-26 | 2021-07-09 | 浙江吉利控股集团有限公司 | Four-wheel-drive automobile yaw control method and device based on fuzzy PID |
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