CN111186490B - Steering wheel corner estimation method and system based on Ackerman steering theorem - Google Patents
Steering wheel corner estimation method and system based on Ackerman steering theorem Download PDFInfo
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- CN111186490B CN111186490B CN202010070304.0A CN202010070304A CN111186490B CN 111186490 B CN111186490 B CN 111186490B CN 202010070304 A CN202010070304 A CN 202010070304A CN 111186490 B CN111186490 B CN 111186490B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D15/00—Steering not otherwise provided for
- B62D15/02—Steering position indicators ; Steering position determination; Steering aids
- B62D15/021—Determination of steering angle
- B62D15/024—Other means for determination of steering angle without directly measuring it, e.g. deriving from wheel speeds on different sides of the car
Abstract
The invention provides a steering wheel corner estimation method and system based on Ackerman steering theorem, which can identify the vehicle working condition through the existing sensor signals of vehicle speed, wheel speed, steering torque of a steering wheel and the like under the straight-ahead working condition and the steering working condition, can output the estimated steering wheel corner through the preset vehicle running working condition state parameters to achieve the ASIL D grade, does not need to increase the physical cost of the vehicle, and does not need to occupy the internal space of the vehicle. For users who only need to meet the minimum requirement of ASIL B, only a steering wheel rotation angle estimation module needs to be omitted, so that compared with a scheme of realizing ASIL D grade by using an angle sensor redundancy design, the cost is reduced.
Description
Technical Field
The invention relates to the field of vehicle steering control, in particular to a steering wheel corner estimation method and system based on Ackerman steering theorem.
Background
With the development of socio-economic, motor vehicles are increasingly used, especially four-wheeled or more than four-wheeled motor vehicles. Motor vehicles typically control the direction in which the vehicle is heading by controlling the steering of the front wheels via a steering wheel. Moreover, the steering performance of the motor vehicle directly affects the maneuverability, flexibility and driving stability of the whole vehicle, especially for large motor vehicles.
Vehicles, especially vehicles with four wheels and above, have different pointing circle centers of the paths of the inner and outer steering wheels when turning, and form Ackermann steering geometry (Ackermann steering geometry). According to the Ackermann steering geometry designed vehicle, when the vehicle turns along a curve, the steering angle of the inner side wheel is larger than that of the outer side wheel by about 2-4 degrees by utilizing the equal crank of the four connecting rods, so that the circle centers of the paths of the four wheels approximately intersect with the instantaneous steering center on the extension line of the rear shaft, and the vehicle can smoothly turn.
Also, in the present vehicles, a "steering wheel angle sensor" has been widely used in an automotive dynamic stability control system (ESP) and an electric power steering system (EPS), by which a steering wheel angle position and a change rate are calculated in real time while a motor vehicle is turning, thereby providing a data basis for control units of the EPS and ESP.
The steering wheel angle sensor is a component of the vehicle stability control system and is used to measure the angle of rotation and the number of turns made. The steering wheel angle sensor is mainly installed in a steering column below a steering wheel, is generally connected with a control unit through a CAN bus, and CAN be divided into an analog steering wheel angle sensor and a digital steering wheel angle sensor.
At present, the "steering wheel angle sensor" for calculating the absolute position angle of the steering wheel usually adopts a mechanical structure of a gear set with three gears in terms of physical structure, as shown in fig. 1, a large gear ring is adopted as a driving gear 5, the inside of the driving gear 5 is fixedly connected with a pipe column, and the outside is engaged with two small driven gears, namely a first driven gear 2 and a second driven gear 3. The driving gear 5 rotates along with the steering wheel column, the two pinions have a fixed difference in tooth number, are fixed on the vehicle body together with the sensor shell, and rotate along with the rotation of the steering wheel and the driving of the driving gear 5. The two small gears respectively collect the rotating angles along with the steering wheel, and meanwhile, different turns differ by a specific angle due to the difference of fixed teeth, so that the absolute rotating angle of the steering wheel can be obtained through calculation.
In driving, the stability and accuracy of the steering wheel angle sensor are directly related to driving safety. According to the requirement of the road vehicle function Safety standard ISO 26262, the ASIL (automatic Safety Integrity Level) grade of the steering wheel angle sensor is the lowest grade to reach the ASIL B grade under the condition of manual driving. The ASIL standard has four grades, A, B, C, D, wherein, grade a is the lowest grade and grade D is the highest grade. In an automatic driving scenario, the steering wheel angle needs to reach ASIL D to meet functional safety standards.
If the safety level is to reach the ASIL D standard, higher requirements are put forward on the mechanism and the precision of the gear set of the three gears, and particularly, a redundant design needs to be added for angle detection of the driven gear so as to ensure the reliability and the precision of the angle detection of the driven gear. Therefore, the steering wheel angle sensor reaching ASIL D by adopting the existing technical scheme will compress the originally limited inner space of the automobile, bring new difficulties to designers, and increase the cost, and the complexity of the structure will also affect the working stability.
Disclosure of Invention
The invention aims to provide a steering wheel angle estimation method and system based on Ackerman steering theorem, so that the performance and the safety level of a steering wheel angle sensor are maximized under the condition that the volume of the steering wheel angle sensor is not increased, namely, extra internal space of an automobile is not occupied.
In order to achieve the purpose, the invention adopts the following technical scheme:
a first aspect of the present application provides a steering wheel angle estimation method based on ackermann steering theorem, including:
setting a steering moment threshold value, a stable running speed lower limit threshold value, a straight-going steering wheel rotating speed upper limit threshold value, a yaw velocity threshold value, a front-rear shaft speed difference threshold value and a stable steering wheel torque threshold value;
the vehicle is in a running state;
reading the steering torque of a steering wheel from a steering wheel torque sensor, judging whether the steering torque of the steering wheel is lower than a steering torque threshold value, if so, starting a straight-driving working condition judging step, otherwise, starting a steering working condition judging step;
the straight-driving working condition judging step comprises the following steps: reading the vehicle speed from a vehicle speed sensor, if the vehicle speed is higher than a stable running speed lower limit threshold value and the rotating speed of a steering wheel is lower than a straight-going steering wheel rotating speed upper limit threshold value, accumulating a straight-going confidence factor, and if not, returning to an initial state; if the straight-driving confidence factor is accumulated to meet the requirement, judging the straight-driving working condition and calculating the steering wheel angle, otherwise returning to the initial state and waiting for the working condition judgment of the next cycle;
the steering condition judging step comprises the following steps: calculating a yaw velocity, if the yaw velocity is lower than a yaw velocity threshold value, the speed difference of the front shaft and the rear shaft is lower than a speed difference threshold value of the front shaft and the rear shaft, and the steering moment of the steering wheel is lower than a torque threshold value of a steering wheel with stable steering, judging that the vehicle is in a stable steering working condition at the moment, and calculating the steering angle of the steering wheel; otherwise, judging that the vehicle is in an unstable steering working condition at the moment, returning to an initial state, and waiting for the working condition judgment of the next cycle;
after the steering wheel angle is calculated, calculating the difference value between the calculated steering wheel angle and the actual steering wheel angle value measured by the steering wheel angle sensor to obtain the steering wheel angle error, if the steering wheel angle error meets the requirement, accumulating angle confidence factors, otherwise, judging that the vehicle is in an unstable state, stopping the calculation of the wheel speed difference and the angle confidence factors, returning to the initial state, and waiting for the working condition judgment of the next cycle; if the angle confidence factor is accumulated to meet the requirement, marking the steering wheel angle zero position under the straight-driving working condition, outputting the calculated steering wheel angle, and directly outputting the calculated steering wheel angle under the stable steering working condition.
Preferably, the vehicle is in a driving state, comprising the steps of:
setting a lowest vehicle speed threshold value and a wheel speed difference threshold value;
carrying out a first judgment step: reading the vehicle speed of a vehicle speed sensor, comparing the vehicle speed with a vehicle speed minimum threshold value, judging that the vehicle is in a running state if the vehicle speed is higher than the vehicle speed minimum threshold value, and executing a second judgment step; otherwise, judging that the vehicle is in an unstable state and returning to the initial state;
performing a second judgment step: reading wheel speed data of the four wheel speed sensors, calculating an average wheel speed, and if the difference value between each wheel speed and the average wheel speed is lower than a wheel speed difference value threshold value, judging that the vehicle is in a stable running state; otherwise, returning to the initial state.
Preferably, the step of calculating the yaw rate includes:
acquiring the speed of a left rear wheel and the speed of a right rear wheel from a wheel speed sensor;
calculating a wheel speed difference according to the left rear wheel speed and the right rear wheel speed;
calculating a yaw angular velocity according to the wheel speed difference and a preset constant;
and performing filtering processing on the calculated yaw rate.
More preferably, the predetermined constant is 10.1 deg/m.
More preferably, the filtering process employs a first order low pass filter.
Preferably, the step of calculating the steering wheel angle according to the formula includes:
acquiring the speed of a left rear wheel and the speed of a right rear wheel from a wheel speed sensor;
calculating a wheel speed difference according to the left rear wheel speed and the right rear wheel speed, wherein the wheel speed difference is the left rear wheel speed-the right rear wheel speed; and substituting the formula to calculate the steering wheel angle estimation value:
the steering wheel angle estimation value is wheel speed difference × estimation value constant/((left rear wheel speed + right rear wheel speed)/2);
calculating an absolute value of the calculated steering wheel angle estimation value to obtain an absolute value of the steering wheel angle estimation value;
performing two-dimensional linear difference calculation by using the absolute value of the steering wheel angle estimation value, and checking a data table to obtain a steering ratio corresponding to the absolute value of the steering wheel angle estimation value;
and calculating the steering wheel angle according to the product of the steering wheel angle estimated value and the steering ratio.
More preferably, the data table is a two-dimensional table, the X-axis coordinate of the two-dimensional table is an absolute value of steering wheel angle estimation value preset at equal intervals, and the Y-axis coordinate is a steering ratio; the X-axis coordinate and the Y-axis coordinate are in one-to-one correspondence and satisfy a linear increasing relationship.
More preferably, the step of two-dimensional linear interpolation calculation includes:
the absolute value of the steering wheel angle estimate is a variable x, a first point (x0, y0) and a second point (x1, y1) are found in the data table, the size of x0 and x1 is closest to the size of x, and x0< x 1;
and calculating the corresponding Y-axis coordinate Y of the variable x in the data table as follows: y0- (y1-y0) (x-x0)/(x 1-x 0),
wherein x0 represents the absolute value of the steering wheel angle estimation value preset at the first point, y0 represents the steering ratio value of the first point, x1 represents the absolute value of the steering wheel angle estimation value preset at the second point, y1 represents the steering ratio value of the second point, and y represents the steering ratio value corresponding to the absolute value of the steering wheel angle estimation value.
Preferably, the step of calculating the straight-going confidence factor accumulation includes:
a motor position sensor samples to obtain a motor position angle value;
the vehicle speed sensor samples to obtain the vehicle speed;
calculating a difference value between the motor position angle value at the current moment and an absolute zero calibration value of a steering wheel to obtain a first deviation value;
calculating a straight-moving confidence factor accumulation, wherein the straight-moving confidence factor accumulation is (a motor position angle value + a first deviation value) multiplied by a vehicle speed multiplied by a first accumulated gain value; wherein the first cumulative gain value is a predetermined constant.
Preferably, the step of calculating the angular confidence factor accumulation comprises:
a steering wheel angle sensor samples to obtain an actual steering wheel angle value (or called steering wheel absolute position angle);
the vehicle speed sensor samples to obtain the vehicle speed;
calculating a difference value between the calculated steering wheel angle and a preset target value to obtain a second deviation value;
calculating an angle confidence factor accumulation, wherein the angle confidence factor accumulation is (steering wheel corner actual value + second deviation value) multiplied by vehicle speed multiplied by a second accumulated gain value; wherein the second cumulative gain value is a predetermined constant.
A second aspect of the present application provides a steering wheel angle estimation system, including:
the sensor signal reading module is used for reading data collected by sensors, wherein the sensors comprise a vehicle speed sensor, a wheel speed sensor, a steering wheel corner sensor and a steering wheel torque sensor;
the vehicle running condition judging module comprises a straight running condition judging module and a steering condition judging module, wherein,
the straight-driving working condition judging module is used for judging whether the vehicle speed acquired by the vehicle speed sensor is higher than a stable driving speed lower limit threshold value and whether the rotating speed of the steering wheel is lower than a straight-driving steering wheel rotating speed upper limit threshold value when the steering torque of the steering wheel acquired by the steering wheel torque sensor is lower than a steering torque threshold value, if yes, accumulating a straight-driving confidence factor, and if the straight-driving confidence factor is accumulated to meet the requirement, judging that the vehicle is driven to be in a straight-driving working condition;
the steering condition judging module is used for judging whether the yaw velocity is lower than a yaw velocity threshold value or not, whether the speed difference between the front shaft and the rear shaft is lower than a front-rear shaft speed difference threshold value or not and whether the steering moment of the steering wheel is lower than a stable steering wheel torque threshold value or not when the steering moment of the steering wheel acquired by the steering wheel torque sensor is higher than or equal to a steering moment threshold value, and judging that the vehicle runs to a stable steering condition if the yaw velocity is lower than the yaw velocity threshold value and the front-rear shaft speed difference threshold value and the steering moment of the steering wheel is lower than the stable steering wheel torque threshold value; otherwise, judging that the vehicle is in an unstable steering working condition;
-a steering wheel angle estimation module for estimating a steering wheel angle value according to a formula;
the steering wheel angle error calculation module is used for calculating the difference value between the estimated steering wheel angle value and the actual steering wheel angle value measured by the steering wheel angle sensor to obtain a steering wheel angle error;
the angle confidence factor accumulation module is configured to accumulate the angle confidence factor when the steering wheel angle error calculated by the steering wheel angle error calculation module meets the requirement;
the steering wheel angle output module is configured to output the estimated steering wheel angle value when the angle confidence factor accumulated by the angle confidence factor accumulation module satisfies the requirement.
Preferably, the sensor signal reading module communicates with the vehicle running condition judging module through a CAN communication bus to send corresponding sensing data.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
the invention provides a novel steering wheel corner estimation method and system based on Ackerman steering theorem, which can identify the vehicle working condition through the existing sensor signals of vehicle speed, wheel speed, steering torque of a steering wheel and the like under the straight-ahead working condition and the steering working condition, can output the estimated steering wheel corner through the preset vehicle running working condition state parameters to achieve the ASIL D grade, does not need to increase the physical cost of the vehicle, and does not need to occupy the internal space of the vehicle. For users who only need to reach the minimum requirement of ASIL B, only a steering wheel rotation angle estimation module in the system needs to be omitted, so that compared with a scheme of realizing ASIL D grade by using an angle sensor redundancy design, the cost is reduced.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application. In the drawings:
fig. 1 is a schematic structural view of a steering wheel angle sensor currently used;
fig. 2 is a plan view of a structure of a steering wheel angle sensor currently used;
fig. 3 is an operational view of the steering wheel angle sensor of the present invention;
FIG. 4 is a schematic diagram of a steering wheel angle estimation system of the present invention;
fig. 5 is a flowchart of a steering wheel angle estimation method of the present invention.
Illustration of the drawings:
1. a magnetic core; 2. a first driven wheel; 3. a second driven wheel; 4. a sensor; 5. a driving gear; 6. a circuit board; 7. a CPU control unit; 8. a steering column; 10. a front wheel; 91. a sensor signal reading module; 92. a vehicle running condition judgment module; 9201. a straight-driving working condition judgment module; 9202. a steering condition judgment module; 93. a steering wheel steering estimation module; 94. a steering wheel angle error calculation module; 95. an angle confidence factor accumulation module; 96. and a steering wheel angle output module.
Detailed Description
The invention provides a steering wheel angle estimation method and system based on Ackerman steering theorem, and in order to make the purpose, technical scheme and effect of the invention clearer and clearer, the invention is further described in detail by referring to the attached drawings and taking examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the above-described drawings are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order, it being understood that the data so used may be interchanged under appropriate circumstances. Furthermore, the terms "comprises," "comprising," and any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
Specifically, as shown in the structural plan view of the steering wheel angle sensor shown in fig. 2, because a tooth is arranged between the first driven wheel 2 and the second driven wheel 3, when the driving gear 5 is driven to rotate, the rotating speeds of the two driven wheels are different, the rotating speeds of the two driven wheels can be detected respectively through the magnetic cores at the centers of the driven wheels, and then the real-time vehicle running condition can be calculated according to the rotating difference value between the first driven wheel 2 and the second driven wheel 3 and the steering wheel angle estimation method disclosed by the invention.
The application identifies the working condition of the vehicle through the signals of the existing sensors such as the vehicle speed, the wheel speed and the steering torque of the steering wheel, and the estimated steering wheel angle can be output through the preset running working condition state parameters of the vehicle.
As shown in fig. 3, when the vehicle is running, it is first determined whether the vehicle is in a normal running state, specifically, two determination steps are included:
a first judgment step: reading the vehicle speed of a vehicle speed sensor, comparing the vehicle speed with a vehicle speed minimum threshold value, judging that the vehicle is in a running state if the vehicle speed is higher than the vehicle speed minimum threshold value, and executing a second judgment step; otherwise, judging that the vehicle is in an unstable state, for example, the vehicle is about to stop or just started, and returning to the initial state;
a second judgment step: reading wheel speed data of the four wheel speed sensors, calculating an average wheel speed, and if the difference value between each wheel speed and the average wheel speed is lower than a wheel speed difference value threshold value, judging that the vehicle is in a stable running state, so that the next detection and judgment work can be carried out; otherwise, returning to the initial state.
Fig. 4 is a schematic structural diagram of a steering wheel angle estimation system according to the present application. As shown in fig. 4, a steering wheel angle estimation system includes a sensor signal reading module 91, a vehicle driving condition determination module 92, a steering wheel angle estimation module 93, a steering wheel angle error calculation module 94, an angle confidence factor accumulation module 95, and a steering wheel angle output module 96.
The sensor signal reading module 91 is used for reading data collected by a sensor, wherein the sensor comprises a vehicle speed sensor, a wheel speed sensor, a steering wheel corner sensor and a steering wheel torque sensor; in this application, the sensor signal reading module 91 may communicate with the vehicle driving condition determining module 92 through a CAN communication bus, thereby transmitting corresponding sensing data.
The vehicle driving condition judging module 92 comprises a straight driving condition judging module 9201 and a steering condition judging module 9202, wherein the straight driving condition judging module 9201 is used for judging whether the vehicle speed acquired by a vehicle speed sensor is higher than a stable driving speed lower limit threshold value or not and whether the rotating speed of a steering wheel is lower than a straight driving steering wheel rotating speed upper limit threshold value or not when the steering torque of the steering wheel acquired by a steering wheel torque sensor is lower than a steering torque threshold value, if so, accumulating a straight driving confidence factor, and if so, judging that the vehicle is driven to be in a straight driving condition; a steering condition judgment module 9202, configured to, when the steering torque of the steering wheel, acquired by the steering wheel torque sensor, is higher than or equal to a steering torque threshold, judge whether a yaw rate is lower than the yaw rate threshold, and whether a front-rear shaft speed difference is lower than a front-rear shaft speed difference threshold, and meanwhile, whether the steering torque of the steering wheel is lower than a stable steering wheel torque threshold, and if both are satisfied, judge that the vehicle is in a stable steering condition; otherwise, judging that the vehicle is in an unstable steering working condition.
And a steering wheel angle estimation module 93, configured to estimate a steering wheel angle value according to a formula.
And a steering wheel angle error calculation module 94, configured to perform difference calculation between the estimated steering wheel angle value and an actual steering wheel angle value measured by the steering wheel angle sensor, so as to obtain a steering wheel angle error.
And an angle confidence factor accumulation module 95, configured to accumulate the angle confidence factor when the steering wheel rotation angle error calculated by the steering wheel rotation angle error calculation module 94 meets the requirement.
And a steering wheel angle output module 96 for outputting the estimated steering wheel angle value when the angle confidence factor accumulated by the angle confidence factor accumulation module 95 satisfies the requirement.
The method guarantees that the specified conditions are met by judging conditions of straight running conditions, judging conditions of steering conditions and judging methods of unstable states, and using two state parameters of straight running confidence factors and angle confidence factors. Specifically, fig. 5 is a flowchart of the steering wheel angle estimation method of the present application.
As shown in fig. 5, the steering wheel angle estimation method includes:
step S1: reading the vehicle speed of a vehicle speed sensor, comparing the vehicle speed with a vehicle speed minimum threshold value, judging that the vehicle is in a running state if the vehicle speed is higher than the vehicle speed minimum threshold value, and executing step S2; otherwise, the vehicle is judged to be in an unstable state, for example, to be stopped or just started, and then the initial state is returned.
Step S2: wheel speed data of four wheel speed sensors are read, an average wheel speed is calculated, and a difference value between each wheel speed and the average wheel speed is calculated.
Step S3: judging whether the difference value between each wheel speed and the average wheel speed is lower than a wheel speed difference value threshold value, if so, judging that the vehicle is in a stable driving state (working conditions such as no slip), and executing step S4; otherwise, stopping calculation and returning to the initial state.
Step S4: reading the steering torque of a steering wheel from a steering wheel torque sensor, judging whether the steering torque of the steering wheel is lower than a steering torque threshold value, if so, executing a step S501, and starting a straight-driving working condition judging step; otherwise, executing step S601 and starting the steering condition judging step.
Step S501: judging whether the vehicle speed acquired by the vehicle speed sensor is higher than a stable running speed lower limit threshold value or not, and if so, executing a step S502; otherwise, stopping calculation and returning to the initial state.
Step S502: judging whether the rotating speed of the steering wheel is lower than the upper limit threshold of the rotating speed of the straight-going steering wheel, if so, executing a step S503; otherwise, stopping calculation and returning to the initial state.
Step S503: straight-ahead confidence factor accumulation is performed.
Specifically, the calculation step of the straight-going confidence factor accumulation comprises the following steps:
1) a motor position sensor samples to obtain a motor position angle value;
2) the vehicle speed sensor samples to obtain the vehicle speed;
3) calculating a difference value between the motor position angle value at the current moment and an absolute zero calibration value of a steering wheel to obtain a first deviation value;
4) the straight-forward confidence factor accumulation is calculated according to the following formula:
the straight-moving confidence factor is accumulated as (motor position angle value + first deviation value) multiplied by vehicle speed multiplied by first accumulated gain value; wherein the first cumulative gain value is a predetermined constant.
Step S504: judging whether the straight-moving confidence factor accumulation meets the requirement, and if so, executing a step S505; otherwise, stopping calculation and returning to the initial state.
Step S505: and satisfying the straight-driving working condition detection window and judging that the vehicle runs in a straight-driving working condition.
Step S506: the steering wheel angle is estimated according to the formula.
Specifically, the step of calculating the steering wheel angle includes:
1) acquiring the speed of a left rear wheel and the speed of a right rear wheel from a wheel speed sensor;
2) calculating a wheel speed difference Diff according to the left rear wheel speed and the right rear wheel speed, wherein the wheel speed difference Diff is equal to the left rear wheel speed-the right rear wheel speed;
3) and substituting the formula to calculate the steering wheel angle estimation value:
the wheel rotation angle estimated value is wheel speed difference Diff × estimated value constant C/((left rear wheel speed + right rear wheel speed)/2), and the estimated value constant C may be temporarily set to 100 deg;
4) calculating an absolute value of the calculated steering wheel angle estimation value to obtain an absolute value of the steering wheel angle estimation value, namely the absolute value of the steering wheel angle estimation value is | the steering wheel angle estimation value |;
5) performing two-dimensional linear difference calculation by using the absolute value of the steering wheel angle estimation value, and checking a data table to obtain a steering ratio corresponding to the absolute value of the steering wheel angle estimation value;
the data table is a two-dimensional table, the X-axis coordinate of the two-dimensional table is the absolute value of steering wheel corner estimation value preset at equal intervals, and the Y-axis coordinate is the steering ratio; the X-axis coordinate and the Y-axis coordinate are in one-to-one correspondence and satisfy a linear increasing relationship.
The step of two-dimensional linear interpolation calculation includes:
the absolute value of the steering wheel angle estimate is a variable x, a first point (x0, y0) and a second point (x1, y1) are found in the data table, the size of x0 and x1 is closest to the size of x, and x0< x 1;
and calculating the corresponding Y-axis coordinate Y of the variable x in the data table as follows: y0- (y1-y0) (x-x0)/(x 1-x 0),
wherein x0 represents the absolute value of the steering wheel angle estimation value preset at the first point, y0 represents the steering ratio value of the first point, x1 represents the absolute value of the steering wheel angle estimation value preset at the second point, y1 represents the steering ratio value of the second point, and y represents the steering ratio value corresponding to the absolute value of the steering wheel angle estimation value.
6) And calculating the steering wheel angle according to the product of the steering wheel angle estimation value and the steering ratio, namely, the steering wheel angle is equal to the steering wheel angle estimation value multiplied by the steering ratio.
Step S507: calculating the difference value between the estimated steering wheel angle and the actual steering wheel angle value measured by the steering wheel angle sensor to obtain a steering wheel angle error, judging whether the steering wheel angle error meets the requirement, and if so, executing a step S508; otherwise, it is determined that the vehicle is traveling in an unstable state, and step S606 is executed.
Step S508: angle confidence factor accumulation is performed.
Specifically, the calculation step of the angle confidence factor accumulation comprises the following steps:
1) a steering wheel angle sensor samples to obtain an actual steering wheel angle value (or called steering wheel absolute position angle);
2) the vehicle speed sensor samples to obtain the vehicle speed;
3) calculating a difference value between the calculated steering wheel angle and a preset target value to obtain a second deviation value;
3) calculating an angle confidence factor accumulation, wherein the angle confidence factor accumulation is (steering wheel corner actual value + second deviation value) multiplied by vehicle speed multiplied by a second accumulated gain value; wherein the second cumulative gain value is a predetermined constant.
Step S509: judging whether the angle confidence factor accumulation meets the requirement, if so, executing the step S510; otherwise, returning to the initial state, and waiting for the working condition judgment of the next cycle and the calculation of the steering wheel angle.
Step S510: and marking the zero position of the steering wheel rotation angle.
Step S511: the estimated steering wheel angle is output and the estimation method ends.
Step S601: a yaw angle calculation constant is set, for example, to 10.1 deg/m.
Step S602: and inputting the left rear wheel speed, the right rear wheel speed and a yaw angle calculation constant, calculating the yaw angular speed and performing filtering processing.
Specifically, the yaw rate is calculated according to the formula:
the yaw rate (left rear wheel speed — right rear wheel speed) × yaw angle calculation constant;
wherein the calculation constant of the yaw angle is 10.1 deg/m; the filtering process uses a first order low pass filter.
Step S603: judging whether the yaw rate is lower than a yaw rate threshold value, and if so, executing a step S604; otherwise, it indicates that the vehicle is in an unstable state at this time, and step S606 is executed.
Step S604: judging whether the speed difference of the front axle and the rear axle is lower than a speed difference threshold value of the front axle and the rear axle, if so, executing a step S605; otherwise, it indicates that the vehicle is in an unstable state at this time, and step S606 is executed.
Step S605: judging whether the steering torque of the steering wheel is lower than a stable steering wheel torque threshold value or not, if so, indicating that the vehicle is stably steered (no working conditions such as slipping) at the moment, and executing a step S607; otherwise, it indicates that the vehicle is in an unstable state at this time, and step S606 is executed.
Step S606: and stopping the calculation of the wheel speed difference and the angle confidence factor of the wheel, and returning to the initial state.
Step S607: the steering wheel angle is estimated according to the formula.
Specifically, the step of calculating the steering wheel angle is the same as step 506.
Step S608: estimating a steering wheel angle, calculating a difference value between the estimated steering wheel angle and an actual steering wheel angle value measured by a steering wheel angle sensor to obtain a steering wheel angle error, judging whether the steering wheel angle error meets the requirement, and if so, executing a step S609; otherwise, it is determined that the vehicle is in an unstable state, and step S606 is executed.
Step S609: angle confidence factor accumulation is performed.
Specifically, the calculation step of the angle confidence factor accumulation comprises the following steps:
1) a steering wheel angle sensor samples to obtain an actual steering wheel angle value (or called steering wheel absolute position angle);
2) the vehicle speed sensor samples to obtain the vehicle speed;
3) calculating a difference value between the calculated steering wheel angle and a preset target value to obtain a second deviation value;
4) calculating an angle confidence factor accumulation (the actual steering wheel angle value + the second deviation value x the vehicle speed x the second accumulated gain value); wherein the second cumulative gain value is a predetermined constant.
Step S610: judging whether the angle confidence factor accumulation meets the requirement, if so, executing a step S511; otherwise, returning to the initial state, and waiting for the working condition judgment of the next cycle and the calculation of the steering wheel angle.
The embodiments of the present invention have been described in detail, but the embodiments are merely examples, and the present invention is not limited to the embodiments described above. Any equivalent modifications and substitutions to those skilled in the art are also within the scope of the present invention. Accordingly, equivalent changes and modifications made without departing from the spirit and scope of the present invention should be covered by the present invention.
Claims (8)
1. A steering wheel angle estimation method based on Ackerman steering theorem is characterized by comprising the following steps:
setting a steering moment threshold value, a stable running speed lower limit threshold value, a straight-going steering wheel rotating speed upper limit threshold value, a yaw velocity threshold value, a front-rear shaft speed difference threshold value and a stable steering wheel torque threshold value;
the vehicle is in a running state;
reading the steering torque of a steering wheel from a steering wheel torque sensor, judging whether the steering torque of the steering wheel is lower than a steering torque threshold value, if so, starting a straight-driving working condition judging step, otherwise, starting a steering working condition judging step;
the straight-driving working condition judging step comprises the following steps: reading the vehicle speed from a vehicle speed sensor, if the vehicle speed is higher than a stable running speed lower limit threshold value and the rotating speed of a steering wheel is lower than a straight-going steering wheel rotating speed upper limit threshold value, accumulating a straight-going confidence factor, and if not, returning to an initial state; if the straight-driving confidence factor is accumulated to meet the requirement, judging the straight-driving working condition and calculating the steering wheel angle, otherwise returning to the initial state and waiting for the working condition judgment of the next cycle;
the steering condition judging step comprises the following steps: calculating a yaw velocity, if the yaw velocity is lower than a yaw velocity threshold value, the speed difference of the front shaft and the rear shaft is lower than a speed difference threshold value of the front shaft and the rear shaft, and the steering moment of the steering wheel is lower than a torque threshold value of a steering wheel with stable steering, judging that the vehicle is in a stable steering working condition at the moment, and calculating the steering angle of the steering wheel; otherwise, judging that the vehicle is in an unstable steering working condition at the moment, returning to an initial state, and waiting for the working condition judgment of the next cycle;
after the steering wheel angle is calculated, calculating the difference value between the calculated steering wheel angle and the actual steering wheel angle value measured by the steering wheel angle sensor to obtain the steering wheel angle error, if the steering wheel angle error meets the requirement, accumulating angle confidence factors, otherwise, judging that the vehicle is in an unstable state, stopping the calculation of the wheel speed difference and the angle confidence factors, returning to the initial state, and waiting for the working condition judgment of the next cycle; if the angle confidence factor is accumulated to meet the requirement, marking the steering wheel corner zero position under the straight-driving working condition, outputting the calculated steering wheel corner, and directly outputting the calculated steering wheel corner under the stable steering working condition;
wherein, the straight-moving confidence factor accumulation = (motor position angle value + first deviation value) × vehicle speed × first accumulated gain value; in the formula, a motor position angle value is obtained by sampling of a motor position sensor, a first deviation value refers to a difference value between the motor position angle value at the current moment and an absolute zero calibration value of a steering wheel, a vehicle speed is obtained by sampling of a vehicle speed sensor, and a first accumulated gain value is a preset constant;
wherein the angle confidence factor is accumulated = (actual steering wheel angle + second deviation value) × vehicle speed × second accumulated gain value; in the formula, the actual value of the steering wheel angle is sampled by a steering wheel angle sensor, the second deviation value is the difference value between the calculated steering wheel angle and a preset target value, the vehicle speed is sampled by a vehicle speed sensor, and the second cumulative gain value is a preset constant.
2. The method for estimating a steering wheel angle according to claim 1, wherein the vehicle is in a driving state, and the method comprises the steps of:
setting a lowest vehicle speed threshold value and a wheel speed difference threshold value;
carrying out a first judgment step: reading the vehicle speed of a vehicle speed sensor, comparing the vehicle speed with a vehicle speed minimum threshold value, judging that the vehicle is in a running state if the vehicle speed is higher than the vehicle speed minimum threshold value, and executing a second judgment step; otherwise, judging that the vehicle is in an unstable state and returning to the initial state;
performing a second judgment step: reading wheel speed data of the four wheel speed sensors, calculating an average wheel speed, and if the difference value between each wheel speed and the average wheel speed is lower than a wheel speed difference value threshold value, judging that the vehicle is in a stable running state; otherwise, returning to the initial state.
3. The method of claim 1, wherein the step of calculating the yaw rate comprises:
acquiring the speed of a left rear wheel and the speed of a right rear wheel from a wheel speed sensor;
calculating a wheel speed difference according to the left rear wheel speed and the right rear wheel speed;
calculating a yaw angular velocity according to the wheel speed difference and a preset constant;
and performing filtering processing on the calculated yaw rate.
4. The method of claim 1, wherein the step of calculating the steering wheel angle comprises:
acquiring the speed of a left rear wheel and the speed of a right rear wheel from a wheel speed sensor;
calculating a wheel speed difference according to the left rear wheel speed and the right rear wheel speed, wherein the wheel speed difference = the left rear wheel speed-the right rear wheel speed;
and substituting the formula to calculate the steering wheel angle estimation value:
steering wheel angle estimate = wheel speed difference × estimate constant/((left rear wheel speed + right rear wheel speed)/2);
calculating an absolute value of the calculated steering wheel angle estimation value to obtain an absolute value of the steering wheel angle estimation value;
performing two-dimensional linear difference calculation by using the absolute value of the steering wheel angle estimation value, and checking a data table to obtain a steering ratio corresponding to the absolute value of the steering wheel angle estimation value;
and calculating the steering wheel angle according to the product of the steering wheel angle estimated value and the steering ratio.
5. The steering wheel angle estimation method based on ackermann steering theorem according to claim 4, wherein: the data table is a two-dimensional table, the X-axis coordinate of the two-dimensional table is the absolute value of steering wheel corner estimation value preset at equal intervals, and the Y-axis coordinate is the steering ratio; the X-axis coordinate and the Y-axis coordinate are in one-to-one correspondence and satisfy a linear increasing relationship.
6. The method of claim 4, wherein the step of calculating the two-dimensional linear interpolation comprises:
the absolute value of the steering wheel angle estimate is a variable x, a first point (x0, y0) and a second point (x1, y1) are found in the data table, the size of x0 and x1 is closest to the size of x, and x0< x 1;
and calculating the corresponding Y-axis coordinate Y of the variable x in the data table as follows: y = y0+ (y1-y0) (x-x0)/(x 1-x 0),
wherein x0 represents the absolute value of the steering wheel angle estimation value preset at the first point, y0 represents the steering ratio value of the first point, x1 represents the absolute value of the steering wheel angle estimation value preset at the second point, y1 represents the steering ratio value of the second point, and y represents the steering ratio value corresponding to the absolute value of the steering wheel angle estimation value.
7. A steering wheel angle estimation system, comprising:
the sensor signal reading module is used for reading data collected by a sensor, and the sensor comprises a vehicle speed sensor, a wheel speed sensor, a steering wheel corner sensor and a steering wheel torque sensor;
the vehicle running condition judging module comprises a straight running condition judging module and a steering condition judging module, wherein,
the straight-driving working condition judging module is used for judging whether the vehicle speed acquired by the vehicle speed sensor is higher than a stable driving speed lower limit threshold value and whether the rotating speed of the steering wheel is lower than a straight-driving steering wheel rotating speed upper limit threshold value when the steering torque of the steering wheel acquired by the steering wheel torque sensor is lower than a steering torque threshold value, if yes, accumulating a straight-driving confidence factor, and if the straight-driving confidence factor is accumulated to meet the requirement, judging that the vehicle is driven to be in a straight-driving working condition; wherein, the straight-moving confidence factor accumulation = (motor position angle value + first deviation value) × vehicle speed × first accumulated gain value; in the formula, a motor position angle value is obtained by sampling of a motor position sensor, a first deviation value refers to a difference value between the motor position angle value at the current moment and an absolute zero calibration value of a steering wheel, a vehicle speed is obtained by sampling of a vehicle speed sensor, and a first accumulated gain value is a preset constant;
the steering condition judging module is used for judging whether the yaw velocity is lower than a yaw velocity threshold value or not, whether the speed difference between the front shaft and the rear shaft is lower than a front-rear shaft speed difference threshold value or not and whether the steering moment of the steering wheel is lower than a stable steering wheel torque threshold value or not when the steering moment of the steering wheel acquired by the steering wheel torque sensor is higher than or equal to a steering moment threshold value, and judging that the vehicle runs to a stable steering condition if the yaw velocity is lower than the yaw velocity threshold value and the front-rear shaft speed difference threshold value and the steering moment of the steering wheel is lower than the stable steering wheel torque threshold value; otherwise, judging that the vehicle is in an unstable steering working condition;
the steering wheel corner estimation module is used for calculating wheel speed difference according to the left rear wheel speed and the right rear wheel speed, substituting the wheel speed difference into a formula to estimate a steering wheel corner value, wherein the formula is as follows: steering wheel angle estimate = wheel speed difference × estimate constant/((left rear wheel speed + right rear wheel speed)/2);
the steering wheel corner error calculation module is used for calculating the difference value between the estimated steering wheel corner value and the actual steering wheel corner value measured by the steering wheel corner sensor to obtain the steering wheel corner error;
the angle confidence factor accumulation module is used for accumulating the angle confidence factors when the steering wheel angle error calculated by the steering wheel angle error calculation module meets the requirement; the angle confidence factor accumulation = (steering wheel corner actual value + second deviation value) × (vehicle speed × second accumulated gain value), in the formula, the steering wheel corner actual value is obtained by sampling of a steering wheel corner sensor, the second deviation value is a difference value between a calculated steering wheel corner and a preset target value, the vehicle speed is obtained by sampling of a vehicle speed sensor, and the second accumulated gain value is a preset constant;
and the steering wheel angle output module is used for outputting the estimated steering wheel angle value when the angle confidence factors accumulated by the angle confidence factor accumulation module meet the requirement.
8. A steering wheel angle estimating system according to claim 7, wherein: and the sensor signal reading module is communicated with the vehicle running condition judging module through a CAN communication bus.
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| CN112278071A (en) * | 2020-10-13 | 2021-01-29 | 广州汽车集团股份有限公司 | Steering wheel angle calibration device and method |
| CN112455540B (en) * | 2020-11-30 | 2022-05-03 | 东风商用车有限公司 | Steering zero position identification method and system based on vehicle posture |
| CN112896307A (en) * | 2020-12-30 | 2021-06-04 | 杭州湘滨电子科技有限公司 | Control method suitable for steering wheel angle of EPS (electric Power steering) of vehicle |
| CN113064193B (en) * | 2021-03-25 | 2022-12-16 | 上海智能新能源汽车科创功能平台有限公司 | Combined positioning system based on vehicle road cloud cooperation |
| CN115303280B (en) * | 2022-08-04 | 2023-08-15 | 清智汽车科技(苏州)有限公司 | Redundant low-delay vehicle driving road identification method and device |
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