Control method and device
阅读说明：本技术 一种控制方法和装置 (Control method and device ) 是由 约瑟夫.艾哈迈德.古奈姆 孙玉 牛小锋 张英富 徐波 王彬彬 陈建宏 于 2020-05-18 设计创作，主要内容包括：本发明提供了一种控制方法及装置,应用于具有电动助力转向系统的车辆,电动助力转向系统包括第一控制子系统和第二控制子系统,方法包括：获取车辆的前转向角、转向扭矩、横摆率和车速；根据前转向角、转向扭矩、横摆率和车速,确定与第一控制子系统关联的车辆横摆率；基于车辆横摆率,确定与第二控制子系统关联的期望偏差值；基于期望偏差值确定控制参数,以使车辆按照控制参数调整转向扭矩进行行驶。本发明可以控制车辆按照控制参数调整转向扭矩,增强车辆的总体车辆操纵特性,避免采用较大的制动操作以大幅度的降低车辆的速度,避免出现导致轮胎寿命减短的情况。(The invention provides a control method and a control device, which are applied to a vehicle with an electric power steering system, wherein the electric power steering system comprises a first control subsystem and a second control subsystem, and the method comprises the following steps: acquiring a front steering angle, a steering torque, a yaw rate and a vehicle speed of a vehicle; determining a vehicle yaw rate associated with the first control subsystem based on the front steering angle, steering torque, yaw rate, and vehicle speed; determining a desired deviation value associated with the second control subsystem based on the vehicle yaw rate; and determining a control parameter based on the expected deviation value, so that the vehicle can run by adjusting the steering torque according to the control parameter. The invention can control the vehicle to adjust the steering torque according to the control parameters, enhance the overall vehicle operating characteristics of the vehicle, avoid adopting larger braking operation to greatly reduce the speed of the vehicle and avoid the condition of shortening the service life of the tire.)
1. A control method, applied to a vehicle having an electric power steering system including a first control subsystem and a second control subsystem, the method comprising:
acquiring a front steering angle, a steering torque, a yaw rate and a vehicle speed of the vehicle;
determining a vehicle yaw rate associated with the first control subsystem based on the front steering angle, the steering torque, the yaw rate, and the vehicle speed;
determining a desired deviation value associated with the second control subsystem based on the vehicle yaw rate;
and determining a control parameter based on the expected deviation value so that the vehicle can run by adjusting the steering torque according to the control parameter.
2. The method of claim 1, wherein determining a control parameter based on the desired deviation value to cause the vehicle to travel with the steering torque adjusted by the control parameter comprises:
and when the expected deviation value is within a first preset range, determining a steering angle feedforward control parameter so that the vehicle can adjust the steering torque to run according to the steering angle feedforward control parameter.
3. The method of claim 1, wherein determining a control parameter based on the desired deviation value to cause the vehicle to travel with the steering torque adjusted by the control parameter comprises:
and when the expected deviation value is within a second preset range, determining a steering angle feedback control parameter so that the vehicle can adjust the steering torque to run according to the steering angle feedback control parameter.
4. The method of claim 2, wherein determining a steering angle feed-forward control parameter when the desired deviation value is within a first predetermined range to cause the vehicle to travel with the steering torque adjusted by the steering angle feed-forward control parameter comprises:
when the expected deviation value is within the first preset range, acquiring a proportional gain of a proportional gain function;
and determining the steering angle feedforward control parameter according to the product of the proportional gain and the steering torque, so that the vehicle can adjust the steering torque to run according to the steering angle feedforward control parameter.
5. The method of claim 3, wherein determining a steering angle feedback control parameter when the desired deviation value is within a second predetermined range to cause the vehicle to travel with the steering torque adjusted according to the steering angle feedback control parameter comprises:
when the expected deviation value is within a second preset range, acquiring a proportional differential gain of a proportional differential function;
and determining a steering angle feedback control parameter based on the proportional differential gain so that the vehicle can drive by adjusting the steering torque according to the steering angle feedback control parameter.
6. A control apparatus for a vehicle having an electric power steering system including a first control subsystem and a second control subsystem, the apparatus comprising:
the acquisition module is used for acquiring a front steering angle, a steering torque, a yaw rate and a vehicle speed of the vehicle;
a first determination module to determine a vehicle yaw rate associated with the first control subsystem based on the front steering angle, the steering torque, the yaw rate, and the vehicle speed;
a second determination module to determine a desired deviation value associated with the second control subsystem based on the vehicle yaw rate;
and the third determining module is used for determining a control parameter based on the expected deviation value so that the vehicle can adjust the steering torque to run according to the control parameter.
7. The apparatus of claim 6, wherein the third determining module comprises:
and the first determining submodule is used for determining a steering angle feedforward control parameter when the expected deviation value is within a first preset range, so that the vehicle can adjust the steering torque to run according to the steering angle feedforward control parameter.
8. The apparatus of claim 6, wherein the third determination submodule comprises:
and the second determining submodule is used for determining a steering angle feedback control parameter when the expected deviation value is within a second preset range, so that the vehicle can adjust the steering torque to run according to the steering angle feedback control parameter.
9. The apparatus of claim 7, wherein the first determination submodule comprises:
the first obtaining unit is used for obtaining the proportional gain of a proportional gain function when the expected deviation value is within the first preset range;
a first determination unit for determining the steering angle feedforward control parameter based on a product of the proportional gain and the steering torque.
10. The apparatus of claim 8, wherein the second determination submodule comprises:
the second obtaining unit is used for obtaining the proportional differential gain of the proportional differential function when the expected deviation value is in a second preset range;
and the second determining unit is used for determining a steering angle feedback control parameter based on the proportional differential gain so as to enable the vehicle to adjust the steering torque to run according to the steering angle feedback control parameter.
Technical Field
The invention relates to the technical field of vehicle control, in particular to a control method and a control device.
Background
With the gradual development of the technical field of vehicle control, the performance of an active control subsystem in a vehicle is continuously improved, and the comfort and safety of a driver can be enhanced by the active control subsystem.
Currently, the active control subsystem mainly includes an Electronic Stability Control (ESC) system. ESC systems typically sense wheel slip based on relevant parameter inputs from wheel speed sensors, steering angle sensors, vehicle speed sensors, and yaw rate sensors, which are used by the ESC system to reduce engine torque and apply vehicle brakes to help maintain the vehicle in a predetermined path for the purpose of assisting the vehicle driver in driving on wet or rough road surfaces (e.g., ice, snow, or debris).
However, in severe road conditions, such as excessively wet or rough road surfaces, the ESC system may employ greater braking operations to substantially reduce the speed of the vehicle, resulting in reduced tire life.
Disclosure of Invention
Accordingly, the present invention is directed to a control method and apparatus for solving the problem that the conventional ESC system may employ a large braking operation to greatly reduce the speed of the vehicle, resulting in a shortened tire life.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
in a first aspect, an embodiment of the present invention provides a control method applied to a vehicle having an electric power steering system, where the electric power steering system includes a first control subsystem and a second control subsystem, and the method includes:
acquiring a front steering angle, a steering torque, a yaw rate and a vehicle speed of the vehicle;
determining a vehicle yaw rate associated with the first control subsystem based on the front steering angle, the steering torque, the yaw rate, and the vehicle speed;
determining a desired deviation value associated with the second control subsystem based on the vehicle yaw rate;
and determining a control parameter based on the expected deviation value so that the vehicle can run by adjusting the steering torque according to the control parameter.
Optionally, the determining a control parameter based on the desired deviation value to enable the vehicle to run by adjusting the steering torque according to the control parameter includes:
and when the expected deviation value is within a first preset range, determining a steering angle feedforward control parameter so that the vehicle can adjust the steering torque to run according to the steering angle feedforward control parameter.
Optionally, the determining a control parameter based on the desired deviation value to enable the vehicle to run by adjusting the steering torque according to the control parameter includes:
and when the expected deviation value is within a second preset range, determining a steering angle feedback control parameter so that the vehicle can adjust the steering torque to run according to the steering angle feedback control parameter.
Optionally, when the expected deviation value is within a first preset range, determining a steering angle feedforward control parameter so that the vehicle drives by adjusting the steering torque according to the steering angle feedforward control parameter includes:
when the expected deviation value is within the first preset range, acquiring a proportional gain of a proportional gain function;
and determining the steering angle feedforward control parameter according to the product of the proportional gain and the steering torque.
Optionally, when the expected deviation value is within a second preset range, determining a steering angle feedback control parameter so that the vehicle drives by adjusting the steering torque according to the steering angle feedback control parameter includes:
when the expected deviation value is within a second preset range, acquiring a proportional differential gain of a proportional differential function;
and determining a steering angle feedback control parameter based on the proportional differential gain so that the vehicle can drive by adjusting the steering torque according to the steering angle feedback control parameter.
In a second aspect, an embodiment of the present invention provides a control apparatus for a vehicle having an electric power steering system including a first control subsystem and a second control subsystem, the apparatus including:
the acquisition module is used for acquiring a front steering angle, a steering torque, a yaw rate and a vehicle speed of the vehicle;
a first determination module to determine a vehicle yaw rate associated with the first control subsystem based on the front steering angle, the steering torque, the yaw rate, and the vehicle speed;
a second determination module to determine a desired deviation value associated with the second control subsystem based on the vehicle yaw rate;
and the third determining module is used for determining a control parameter based on the expected deviation value so that the vehicle can adjust the steering torque to run according to the control parameter.
Optionally, the third determining module includes:
and the first determining submodule is used for determining a steering angle feedforward control parameter when the expected deviation value is within a first preset range, so that the vehicle can adjust the steering torque to run according to the steering angle feedforward control parameter.
Optionally, the third determining sub-module includes:
and the second determining submodule is used for determining a steering angle feedback control parameter when the expected deviation value is within a second preset range, so that the vehicle can adjust the steering torque to run according to the steering angle feedback control parameter.
Optionally, the first determining sub-module includes:
the first obtaining unit is used for obtaining the proportional gain of a proportional gain function when the expected deviation value is within the first preset range;
a first determination unit for determining the steering angle feedforward control parameter based on a product of the proportional gain and the steering torque.
Optionally, the second determining sub-module includes:
the second obtaining unit is used for obtaining the proportional differential gain of the proportional differential function when the expected deviation value is in a second preset range;
and the second determining unit is used for determining a steering angle feedback control parameter based on the proportional differential gain so as to enable the vehicle to adjust the steering torque to run according to the steering angle feedback control parameter.
Compared with the prior art, the embodiment of the invention has the following advantages:
according to the control method provided by the embodiment of the invention, the vehicle with the electric power steering system acquires the front steering angle, the steering torque, the yaw rate and the vehicle speed of the vehicle, determines the vehicle yaw rate associated with the first control subsystem according to the front steering angle, the steering torque, the yaw rate and the vehicle speed, determines the expected deviation value associated with the second control subsystem based on the vehicle yaw rate, and determines the control parameter based on the expected deviation value, so that the vehicle adjusts the steering torque according to the control parameter to run on a severe road surface, such as a road surface which is too wet or rough, the electric power steering system can control the vehicle to adjust the steering torque according to the control parameter, the overall vehicle handling characteristic of the vehicle is enhanced, the situation that the vehicle speed is greatly reduced by adopting a large braking operation is avoided, and the situation that the service life of tires is shortened is avoided.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
fig. 1 is a flowchart illustrating steps of a control method according to an embodiment of the present invention;
FIG. 2 is a flow chart illustrating steps of a control method according to a second embodiment of the present invention;
FIG. 3 is a schematic diagram of a vehicle having an electric power steering system according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of an electric power steering system provided by an embodiment of the present invention;
FIG. 5 is a diagram illustrating a method for calculating an estimated behavior index according to an embodiment of the invention;
FIG. 6 illustrates an exemplary trace of natural frequency and damping ratio using nominal values of vehicle parameters provided by an embodiment of the present invention;
FIG. 7 illustrates a graphical representation of exemplary values using nominal vehicle parameters as a function of vehicle speed provided by an embodiment of the present invention;
FIG. 8 is a schematic diagram illustrating the steps for calculating a feedforward control signal according to an embodiment of the present invention;
FIG. 9 is a schematic diagram illustrating the steps for calculating a feedback control signal according to an embodiment of the present invention;
FIG. 10 is a schematic diagram illustrating a method for determining a target steering assist torque for an EPS provided by an embodiment of the present invention;
fig. 11 shows a schematic structural diagram of a control device according to a third embodiment of the present invention.
Detailed Description
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
An Electric Power Steering (EPS) system is an intelligent actuator that superimposes electronic control of assist torque to provide to a vehicle steering system. The main purpose of the EPS system is to provide comfort to the driver by increasing torque. However, recent developments have shown that EPS systems can also be used to enhance the stability of the vehicle.
The EPS system performs a steering torque superposition work by being mounted on a steering column, a rack, or a pinion and incorporating an electric motor. The main function of the EPS system is to provide electric power steering assistance, so that a driver can easily steer the steering wheel, and the driving comfort is improved. The steering assist provided by the EPS system is that the amount of assist torque, which is calculated from the characteristic curve, is proportional to the driver's steering torque input. Further, the EPS system may be designed such that the motor provides different steering torques under various driving conditions to improve steering feel, vehicle stability, or maneuverability. The following describes some of the functions of the EPS system in widespread use.
Transferring variable steering torque as a function of vehicle speed is one of the primary assist functions of an EPS system. To reduce the amount of steering assist provided when increasing vehicle speed, the basic EPS system acceleration curve is expanded to accommodate vehicle speed and used as an additional input to the steering torque look-up table. This will increase the damping of the vehicle and help the driver to maintain smooth control of the vehicle in the event of a high speed maneuver.
Vehicle networking communication protocols provide an opportunity for data exchange between the EPS system and other existing vehicle dynamics systems. Thus, not only the parameters of speed, steering angle and steering torque, but also other existing vehicle dynamics sensors (e.g., yaw rate sensors) may be used to determine the desired amount of assist torque for a particular operating condition. During understeer periods of the vehicle, known EPS systems provide additional steering torque based on the difference between the desired yaw angle defined by the driver steering input and the actual yaw angle of the vehicle, thereby subjecting the front wheels of the vehicle to additional torque, which may saturate the amount of torque experienced by the front wheels, resulting in a reduction in the overall performance of the vehicle.
The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
Referring to fig. 1, a flowchart illustrating steps of a control method according to an embodiment of the present invention is provided, where the control method may be applied to a vehicle having an electric power steering system including a first control subsystem and a second control subsystem.
As shown in fig. 1, the control method may specifically include the following steps:
step 101: a front steering angle, a steering torque, a yaw rate, and a vehicle speed of the vehicle are obtained.
In the present invention, an electric power steering system may include: a front steering angle sensor operable to measure a front steering angle of the vehicle; a steering torque sensor operable to measure a steering torque of the driver; a yaw rate sensor operable to measure a yaw rate of the vehicle; further comprising: a speed sensor operable to measure a vehicle speed, and a controller including instructions that, when executed by the processor, cause the processor to determine a first control subsystem providing feed forward control and a second control subsystem providing feedback control to control an angle of the front wheels and a vehicle steering torque by changing the angle of the front wheels.
Step 102 is performed after acquiring the front steering angle, steering torque, yaw rate, and vehicle speed of the vehicle.
Step 102: a vehicle yaw rate associated with the first control subsystem is determined based on the front steering angle, steering torque, yaw rate, and vehicle speed.
In the present invention, the controller determines a vehicle yaw rate associated with the first control subsystem based on the front steering angle, steering torque, yaw rate, and vehicle speed.
After determining the vehicle yaw rate associated with the first control subsystem based on the front steering angle, steering torque, yaw rate, and vehicle speed, step 103 is performed.
Step 103: based on the vehicle yaw rate, a desired deviation value associated with the second control subsystem is determined.
In the present invention, the controller determines a desired deviation value for the yaw rate associated with the second control subsystem based on the vehicle yaw rate.
After determining the desired deviation value associated with the second control subsystem based on the vehicle yaw rate, step 104 is performed.
Step 104: and determining a control parameter based on the expected deviation value, so that the vehicle can run by adjusting the steering torque according to the control parameter.
Alternatively, when the expected deviation value is within a first preset range, the steering angle feedforward control parameter is determined, so that the vehicle drives by adjusting the steering torque according to the steering angle feedforward control parameter.
Specifically, when the expected deviation value is within a first preset range, the proportional gain of the proportional gain function is obtained; and determining a steering angle feedforward control parameter according to the product of the proportional gain and the steering torque, so that the vehicle can drive by adjusting the steering torque according to the steering angle feedforward control parameter.
Optionally, when the expected deviation value is within a second preset range, determining a steering angle feedback control parameter so that the vehicle can run by adjusting the steering torque according to the steering angle feedback control parameter.
Specifically, when the expected deviation value is within a second preset range, acquiring a proportional differential gain of a proportional differential function; and determining a steering angle feedback control parameter based on the proportional differential gain so that the vehicle can run by adjusting the steering torque according to the steering angle feedback control parameter. Wherein the proportional term is determined by multiplying a proportional gain by a yaw rate error signal, which may be derived from the yaw rate, and the derivative term is determined by multiplying a derivative gain by a yaw acceleration error signal, which may be derived from the vehicle speed.
According to the control method provided by the embodiment of the invention, the vehicle with the electric power steering system acquires the front steering angle, the steering torque, the yaw rate and the vehicle speed of the vehicle, determines the vehicle yaw rate associated with the first control subsystem according to the front steering angle, the steering torque, the yaw rate and the vehicle speed, determines the expected deviation value associated with the second control subsystem based on the vehicle yaw rate, and determines the control parameter based on the expected deviation value, so that the vehicle adjusts the steering torque according to the control parameter to run on a severe road surface, such as a road surface which is too wet or rough, the electric power steering system can control the vehicle to adjust the steering torque according to the control parameter, the overall vehicle handling characteristic of the vehicle is enhanced, the situation that the vehicle speed is greatly reduced by adopting a large braking operation is avoided, and the situation that the service life of tires is shortened is avoided.
Referring to fig. 2, a flowchart illustrating steps of a control method according to a second embodiment of the present invention is provided, where the control method can be applied to a vehicle having an electric power steering system including a first control subsystem and a second control subsystem.
As shown in fig. 2, the control method may specifically include the following steps:
step 201: a front steering angle, a steering torque, a yaw rate, and a vehicle speed of the vehicle are obtained.
In the present invention, an electric power steering system may include: a front steering angle sensor operable to measure a front steering angle of the vehicle; a steering torque sensor operable to measure a steering torque of the driver; a yaw rate sensor operable to measure a yaw rate of the vehicle; further comprising: a speed sensor operable to measure a vehicle speed, and a controller including instructions that, when executed by the processor, cause the processor to determine a first control subsystem providing feed forward control and a second control subsystem providing feedback control to control an angle of the front wheels and a vehicle steering torque by changing the angle of the front wheels.
The electric power-assisted system has a feedforward control function and a feedback control function, and is used for controlling the angle of the front wheels to correct the steering torque of the vehicle so as to recover the stability of the vehicle. Based on the vehicle stability condition, the increased steering focus will be the same as or opposite to the driver input torque.
The Electric Power Steering (EPS) system of the present invention can provide additional feed forward control to the EPS system based on the steering torque input by the driver and adjust the feedback/feed forward control based on the degree of understeer/oversteer of the vehicle.
Fig. 3 shows a schematic diagram of a vehicle with an electric power steering system according to an embodiment of the present invention, and as shown in fig. 3, the vehicle 10 includes an Electric Power Steering (EPS)
Referring to fig. 3, the vehicle 10 also includes a steering wheel 12, the steering wheel 12 being rotatable in response to a steering torque input by the driver, the steering wheel 12 being connectable to a steering column 14, the steering column 14 being connectable to a steering mechanism 16. The steering mechanism 16 is a rack and pinion assembly, and may be other steering assemblies, which are not particularly limited in the embodiments of the present invention. The steering assembly 26 and steering mechanism 16 may ultimately orient the front wheels 25 relative to the road surface 27 by moving the tie rods 18 over a set of front axles.
The torque sensor 23 and the steering wheel angle sensor 21 may be fixedly arranged relative to the steering column 14. The torque sensor 23 measures a torque sensor signal (arrow 123) and transmits the torque sensor signal to the controller 50. Similarly, the steering wheel angle sensor 21 measures a steering wheel angle signal (arrow 121) and transmits the steering wheel angle signal to the controller 50. The controller 50 processes the torque sensor signal, the steering wheel angle signal, and other vehicle operating data (arrow 11), such as vehicle speed, yaw rate, and mass, to determine the amount of steering torque required by the
As shown in fig. 3, the controller 50 may transmit the motor control signals (arrow 13) to the
Step 202 is performed after acquiring the front steering angle, steering torque, yaw rate, and vehicle speed of the vehicle.
Step 202: a vehicle yaw rate associated with the first control subsystem is determined based on the front steering angle, steering torque, yaw rate, and vehicle speed.
In the present invention, the controller determines a vehicle yaw rate associated with the first control subsystem based on the front steering angle, steering torque, yaw rate, and vehicle speed.
In an embodiment of the present invention, the sensor module 54 disposed within the controller 50 may be used to execute the signals required by the
Fig. 4 shows a schematic diagram of an electric power steering system provided by an embodiment of the present invention, and as shown in fig. 4, the EPS system 110 includes an actuator 114 and a
The
After determining the vehicle yaw rate associated with the first control subsystem based on the front steering angle, steering torque, yaw rate, and vehicle speed, step 203 is performed.
Step 203: based on the vehicle yaw rate, a desired deviation value associated with the second control subsystem is determined.
In the present invention, the controller determines a desired deviation value for the yaw rate associated with the second control subsystem based on the vehicle yaw rate.
After determining the desired deviation value associated with the second control subsystem based on the vehicle yaw rate, step 204 is performed.
Step 204: and when the expected deviation value is in a first preset range, determining a steering angle feedforward control parameter so that the vehicle can run by adjusting the steering torque according to the steering angle feedforward control parameter.
Referring to FIG. 4, the yaw rate command processing module 118 may also receive a vehicle speed signal and a driver steering angle and generate a yaw rate command signal. The feed forward
The feed-forward control signal Δ FF and the feedback control signal Δ FB are added together to provide the steering request signal Δ c. The control interface module 130 converts the steering request signal Δ c into a torque overlay control request signal. The torque overlay control request signal, driver steering Torque (TD) and torque assist request (TA) calculated from the characteristic curves are applied to the summer 134 to provide the electric steering torque command signal. The electric steering torque command signal is applied to the
Specifically, when the expected deviation value is within a first preset range, indicating that the vehicle is under steering, and acquiring the proportional gain of a proportional gain function; and determining a steering angle feedforward control parameter according to the product of the proportional gain and the steering torque, so that the vehicle can drive by adjusting the steering torque according to the steering angle feedforward control parameter.
The present invention uses two degree of freedom models to determine vehicle understeer behavior and vehicle yaw correction moments for EPS system stability improvement.
During operation of the vehicle 10, the vehicle not only undergoes yaw motion, but also simultaneously undergoes lateral motion. Yaw plane dynamics determine the performance of vehicle yaw motion characterized by vehicle yaw speed and lateral motion characterized by lateral speed.
The following terms will be used in the expressions and formulas below:
a is the distance (meters, m) from the center of gravity of the vehicle 10 to the front axle;
b is the distance (meters, m) from the center of gravity of the vehicle 10 to the rear axle;
l is the wheelbase (meter, m) of the vehicle 10, (L ═ a + b);
cf is the cornering stiffness (N/rad ) of the two tires of the front axle;
cr is the cornering stiffness (N/rad ) of the two tires of the rear axle;
cf0 is the nominal cornering stiffness (N/rad ) of the two tires of the front axle;
cr0 is the nominal cornering stiffness (N/rad ) of the two tires on the rear axle;
IZ is the moment of inertia (kgm) of the vehicle 10 about the yaw axis2)；
M is the total vehicle mass (kg);
vy is the lateral velocity of the center of gravity of the vehicle (m/sec, m/s);
vyd is the lateral velocity (m/sec, m/s) required by the center of gravity of the vehicle;
vx is the longitudinal speed of the vehicle's center of gravity (m/sec, m/s);
is the steering angle (rad) input by the driver;
ng is the steering gear ratio;
f is the steering angle (rad) of the front wheels/Ng;
ay is the lateral acceleration (m/sec/m/sec) of the vehicle 102)；
Ku is an understeer behavior index (radians/gram, rad/g) for the vehicle 10;
Vehicle yaw plane dynamics can be described by a second order equation of state as:
wherein the content of the first and second substances,
Fyf＝Cfαf(3)；
Fyr＝Crαr(4)；
the forward slip angle and the aft slip angle follow the following relationship:
under steady state conditions, the following general steering equations can be derived from the yaw plane model described in equations (1), (2), (3), (4), (5), and (6):
equation (7) is valid over a linear range of tire performance under steady state conditions when the lateral force generated by the tire is proportional to the tire slip angle. Under nonlinear tire behavior or transient state conditions, the general steering equation becomes inaccurate, and the understeer-oversteer behavior index cannot be determined using this mathematical expression. Therefore, there is a need to determine an understeer behavior indicator.
Fig. 5 shows a schematic diagram of calculating an estimated behavior index provided by an embodiment of the present invention, and table 1 is provided as a key, where, corresponding to a process for calculating an estimated turn, the blocks of numerical labels and corresponding functions are described below, corresponding to a process for calculating an estimated turn behavior index (116).
TABLE 1
This variable α is called a weighting factor, which must be able to continuously track the transient and steady-state behavior of the vehicle, since the objective is to estimate the understeer behavior indicators for the steady and transient behavior of the vehicle.
However, when the vehicle is in transient mode, α ═ 1 is not appropriate for transient conditions, because in this case p (k) converges to zero rapidly, and the estimator is turned off2(k) Will increase, P (k) will increase rapidlySo that the system can be adapted quickly and, after adaptation,2(k) decreases and should return to approximately 1.
Referring to FIG. 4, the desired yaw rate command processing module 118 is determined by the desired vehicle response to the driver's steering inputs. The desired vehicle response is based on the structure of the system input-output transfer functions derived from the vehicle yaw plane dynamics equations (1), (2), (3), (4), (5), and (6), as follows:
wherein the content of the first and second substances,
equation (13) can be reproduced from the system natural frequency and damping ratio as follows:
wherein the content of the first and second substances,
equation (16) is the steady state gain for the desired yaw rate command, which is listed in a look-up table based on steering angle (degrees) and vehicle speed (km/hour, km/h). An example of this look-up table is shown in table two below:
watch two
vxδ
0
2.35
4.7
7.05
9.41
11.76
14.11
16.47
18.81
21.16
23.52
25.87
28.22
20
0
1.84
1.87
1.9
1.91
1.9
1.92
1.94
1.94
1.93
1.93
1.92
1.9
30
0
2.62
2.69
2.73
2.74
2.73
2.75
2.75
2.7
2.57
2.32
2.11
1.94
40
0
3.3
3.39
3.41
3.39
3.26
3
2.6
2.27
2.02
1.82
1.65
1.5
50
0
3.85
3.9
3.81
3.49
2.94
2.45
2.1
1.84
1.63
1.47
1.34
1.23
60
0
4.28
4.2
3.77
3.07
2.46
2.05
1.76
1.54
1.37
1.23
1.12
1.03
70
0
4.54
4.22
3.44
2.64
2.11
1.76
1.51
1.32
1.17
1.06
0.96
0.88
80
0
4.68
4.05
3.07
2.31
1.85
1.54
1.32
1.16
1.03
0.93
0.84
0.77
90
0
4.7
3.78
2.74
2.06
1.65
1.37
1.18
1.03
0.91
0.82
0.75
0.69
100
0
4.62
3.5
2.47
1.85
1.48
1.23
1.06
0.93
0.82
0.74
0.67
0.62
110
0
4.52
3.24
2.24
1.68
1.34
1.12
0.96
0.84
0.75
0.67
0.61
0.56
120
0
4.35
2.99
2.05
1.54
1.23
1.03
0.88
0.77
0.68
0.62
0.56
0.51
130
0
4.18
2.78
1.89
1.42
1.13
0.95
0.81
0.71
0.63
0.57
0.52
0.47
140
0
4.01
2.59
1.75
1.32
1.05
0.88
0.75
0.66
0.58
0.53
0.48
0.44
150
0
3.82
2.42
1.63
1.23
0.98
0.82
0.7
0.61
0.54
0.49
0.45
0.41
160
0
3.65
2.27
1.53
1.15
0.92
0.76
0.66
0.57
0.51
0.46
0.42
0.38
Wherein the damping ratio and natural frequency of the desired vehicle performance can be expressed in terms of system parameters as:
FIG. 6 illustrates an exemplary trace of natural frequency ω n (arrow 440) and damping ratio ζ (arrow 450) as a function of vehicle speed (arrow 410) using nominal values of vehicle parameters provided by embodiments of the present invention.
For yaw rateThe variable may be expressed as:
FIG. 7 illustrates a graphical plot of typical values (arrow 460) for vehicle speed using nominal vehicle parameters (arrow 480) provided by an embodiment of the present invention, and FIG. 6 may also modify FIG. 7 during vehicle control calibration to reflect the desired design of desired vehicle handling characteristics.
According to equation (15), the desired yaw rate command is determined as:
as described above, the vehicle corrective yaw moment control of the electric power steering system proposed in the present invention is only to improve the steering dynamics of the vehicle. The structure for correcting the yaw moment of the vehicle consists of feedforward compensation and yaw rate feedback compensation relative to the front steering angle, and is shown as the following formula:
the feed forward compensation is described as:
FF(s)＝GFFP(s) (21)；
wherein GFFP is the proportional gain of the feedforward control;
the feedback compensation is described as:
wherein GFBP and GFBD are proportional, and the differential gain of feedback control.
The feed-forward and feedback control of the present invention will now be described in detail, with reference to FIG. 4, with the feed-forward
FIG. 8 is a schematic diagram showing the steps of calculating a feedforward control signal according to an embodiment of the present invention, where Table three is provided as a key, where the blocks of the numerical labels and the corresponding functions corresponding to the process for calculating feedforward control are as follows.
Watch III
The feedforward gain GFFP is listed in the form of an understeer behavior index (deg/g) and vehicle speed (km/h) in a look-up table, an example of which is shown in Table four below:
it should be noted that in severe oversteer situations, i.e. when the understeer behaviour indicator Ku has a large negative value, the feed forward control will generate a steering torque that is opposite to the driver input torque. When the feedforward gain is greater than 1, as will be shown in the look-up table example described in table four, in this case the feedforward signal will be greater than the driver input shown in equation (24), and the result will be opposite to the initial input.
When the vehicle experiences a large degree of oversteer, the driver needs to steer back to stabilize the vehicle, in which case the feed forward control will produce a torque superposition that will prompt the driver to steer back.
Step 205: and when the expected deviation value is within a second preset range, determining a steering angle feedback control parameter so that the vehicle can drive by adjusting the steering torque according to the steering angle feedback control parameter.
Specifically, when the expected deviation value is within a second preset range, indicating that the vehicle oversteers, and acquiring a proportional differential gain of a proportional differential function; and determining a steering angle feedback control parameter based on the proportional differential gain so that the vehicle can run by adjusting the steering torque according to the steering angle feedback control parameter. Wherein the proportional term is determined by multiplying a proportional gain by a yaw rate error signal, which may be derived from the yaw rate, and the derivative term is determined by multiplying a derivative gain by a yaw acceleration error signal, which may be derived from the vehicle speed.
Referring to FIG. 4, the yaw rate command processing module 118 may also receive a vehicle speed signal and a driver steering angle and generate a yaw rate command signal. The feed forward
The feed-forward control signal Δ FF and the feedback control signal Δ FB are added together to provide the steering request signal Δ c. The control interface module 130 converts the steering request signal Δ c into a torque overlay control request signal. The torque overlay control request signal, driver steering Torque (TD) and torque assist request (TA) calculated from the characteristic curves are applied to the summer 134 to provide the electric steering torque command signal. The electric steering torque command signal is applied to the
Fig. 9 shows a schematic diagram of a step of calculating the feedback control signal Δ FB provided by an embodiment of the present invention, where a table five is provided as a key, wherein corresponding to a process for calculating the feedback control, wherein the numbered blocks and corresponding functions are as follows.
Watch five
The dead zone Db (rad/sec) is listed in a look-up table according to the steering wheel angle (deg) and vehicle speed (km/h). An example of this look-up table is shown in table six below:
watch six
Careful study of the feedback control shows that the sign of the control signal is opposite to that of the control signal when the vehicle is under-steered. Similar to the feed forward, the reason for this is to reduce the steering input of the front wheels during a severe understeer operation, thereby laughing the understeer of the vehicle and enhancing the stability of the vehicle.
The feed-forward control signal Δ FF and the feedback control signal Δ FB are added together to provide the steering request signal Δ c as follows:
Δc＝ΔFF+ΔFB(26)；
a steering command and a feedback control of the feedforward are input as angle requests, but a controller of the EPS requires a steering torque. To determine the dynamics of the steering model, an approximate estimate can be made by an autoregressive moving average discrete model by:
the parameters { a1, a2, a3, b1, b2} are unknown, are the input steering angle (known), T is EPS torque assist (known), and recursive least squares are used to estimate the model parameters.
Equation (27) may be updated as:
wherein
θT(k)＝[-b1-b2a1a2a3](28)。
Least squares are used to estimate the model parameters as follows:
the parameters in equation (29) are estimated in experiments performed at different vehicle speeds to determine the steering angle versus torque relationship described in equation (27), and these parameters can be programmed next.
The control interface module 130 uses these and programmed parameters to establish a relationship between steering angle Δ c control and torque overlay control TOC. An example of such a relationship at 120kph vehicle speed is as follows:
fig. 10 is a diagram showing a method for determining a target steering assist torque for an EPS, which is experimentally obtained by an EPS system, according to an embodiment of the present invention. The
TA＝f(vx，Td) (31)。
the following table illustrates example values for target torque assistance:
watch seven
The torque overlay control request signal (TOC), driver steering Torque (TD) and torque assist request (TA) listed in the
The EPS torque superposition control system has the characteristic of integrating chassis steering and braking control, and can help a driver to control a vehicle under the most severe driving condition. This integration assists the driver in controlling the vehicle by electronically comparing the operation the driver wishes to perform with the actual corresponding manner of the vehicle. If the vehicle fails to respond to the driver's maneuver or runs into the risk of spin or coast runaway, appropriate steering and braking controls are automatically initiated to stabilize and assist the driver in controlling the vehicle.
The EPS control and electronic stability control system of the invention are integrated together, which can give the driver higher probability of being able to control the vehicle in the form of severe road conditions such as ice, snow, gravel or wet road surface, and when making emergency lane change or evasion.
The control method provided by the embodiment of the invention comprises the steps that a vehicle with an electric power steering system obtains a front steering angle, a steering torque, a yaw rate and a vehicle speed of the vehicle, the vehicle yaw rate associated with a first control subsystem is determined according to the front steering angle, the steering torque, the yaw rate and the vehicle speed, an expected deviation value associated with a second control subsystem is determined based on the vehicle yaw rate, when the expected deviation value is in a first preset range, a steering angle feedforward control parameter is determined, so that the vehicle can adjust the steering torque to run according to the steering angle feedforward control parameter, when the expected deviation value is in a second preset range, a steering angle feedback control parameter is determined, so that the vehicle can adjust the steering torque to run according to the steering angle feedback control parameter, so that on the road surface with serious conditions, such as the road surface which is too wet or too rough, the electric power steering system can control the vehicle to adjust the steering torque according to the control parameter, the overall vehicle handling characteristics of the vehicle are enhanced, the situation that the speed of the vehicle is greatly reduced by adopting larger braking operation is avoided, and the service life of the tire is shortened is avoided.
Referring to fig. 11, a schematic structural diagram of a control device according to a third embodiment of the present invention is shown, where the control device is applied to a vehicle having an electric power steering system, and the electric power steering system includes a first control subsystem and a second control subsystem.
As shown in fig. 11, the control device 800 may specifically include:
an obtaining
a
a
a third determining
Optionally, the third determining module includes:
and the first determining submodule is used for determining the steering angle feedforward control parameter when the expected deviation value is in a first preset range, so that the vehicle can drive by adjusting the steering torque according to the steering angle feedforward control parameter.
Optionally, the third determining sub-module includes:
and the second determining submodule is used for determining the steering angle feedback control parameter when the expected deviation value is in a second preset range, so that the vehicle can adjust the steering torque to run according to the steering angle feedback control parameter.
Optionally, the first determining sub-module includes:
the first obtaining unit is used for obtaining the proportional gain of the proportional gain function when the expected deviation value is in a first preset range;
and the first determining unit is used for determining the steering angle feedforward control parameter according to the product of the proportional gain and the steering torque.
Optionally, the second determining sub-module includes:
the second obtaining unit is used for obtaining the proportional differential gain of the proportional differential function when the expected deviation value is in a second preset range;
and a second determination unit for determining a steering angle feedback control parameter based on the proportional differential gain to cause the vehicle to travel by adjusting the steering torque in accordance with the steering angle feedback control parameter.
The specific implementation of the control device in the embodiment of the present invention has been described in detail at the method side, and therefore, the detailed description thereof is omitted here.
According to the control method provided by the embodiment of the invention, a vehicle with an electric power steering system can obtain a front steering angle, a steering torque, a yaw rate and a vehicle speed of the vehicle through an obtaining module, then a first determining module determines the vehicle yaw rate associated with a first control subsystem according to the front steering angle, the steering torque, the yaw rate and the vehicle speed, a second determining module determines an expected deviation value associated with a second control subsystem according to the vehicle yaw rate, and finally a third determining module determines a control parameter according to the expected deviation value, so that the vehicle can adjust the steering torque to run according to the control parameter, so that on the road with serious conditions, such as too wet or too rough road, the electric power steering system can control the vehicle to adjust the steering torque according to the control parameter, the overall vehicle control characteristic of the vehicle is enhanced, and the situation that a larger braking operation is adopted to greatly reduce the vehicle speed is avoided, the condition that the service life of the tire is shortened is avoided.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
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