CN108909828B - Drive-by-wire steering and braking system and control method thereof - Google Patents

Drive-by-wire steering and braking system and control method thereof Download PDF

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Publication number
CN108909828B
CN108909828B CN201810537315.8A CN201810537315A CN108909828B CN 108909828 B CN108909828 B CN 108909828B CN 201810537315 A CN201810537315 A CN 201810537315A CN 108909828 B CN108909828 B CN 108909828B
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wheel
steering
brake
cylinder
front wheel
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CN108909828A (en
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王衍圣
王春燕
赵万忠
鲁广超
钱兴国
吴刚
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Nanjing University of Aeronautics and Astronautics
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Nanjing University of Aeronautics and Astronautics
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D5/00—Power-assisted or power-driven steering
    • B62D5/04—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear
    • B62D5/0457—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear characterised by control features of the drive means as such
    • B62D5/046—Controlling the motor
    • B62D5/0463—Controlling the motor calculating assisting torque from the motor based on driver input
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D5/00—Power-assisted or power-driven steering
    • B62D5/04—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear
    • B62D5/0457—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear characterised by control features of the drive means as such
    • B62D5/0475—Controlling other elements
    • B62D5/0478—Clutches
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D5/00—Power-assisted or power-driven steering
    • B62D5/04—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear
    • B62D5/0457—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear characterised by control features of the drive means as such
    • B62D5/0481—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear characterised by control features of the drive means as such monitoring the steering system, e.g. failures
    • B62D5/0487—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear characterised by control features of the drive means as such monitoring the steering system, e.g. failures detecting motor faults
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D6/00—Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits
    • B62D6/001—Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits the torque NOT being among the input parameters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/72—Electric energy management in electromobility

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Steering Control In Accordance With Driving Conditions (AREA)
  • Regulating Braking Force (AREA)

Abstract

The invention discloses a steer-by-wire and braking system and a control method thereof. The control method is characterized in that the data of a steering wheel angle sensor, a front wheel rotation angle sensor, a vehicle speed sensor, a wheel speed sensor, a yaw angle speed sensor and a brake pedal sensor are collected in the running process to measure the working state of the vehicle, the control modes are changed through the information to control the steering motor and the four-wheel brake cylinder of the vehicle under different working conditions, the light and flexible steering running of the vehicle under the normal working state and the low-speed steering running are ensured, the stability and the reliability of the vehicle under the high-speed steering running are also provided, and the control method of the vehicle under the emergency state is also provided, so that the vehicle-by-wire control vehicle plays the advantage of vehicle integrated control.

Description

Drive-by-wire steering and braking system and control method thereof
Technical Field
The invention relates to the technical field of steering systems and braking systems, in particular to a steer-by-wire and braking system and a control method thereof.
Background
In recent years, with the continuous development of electronic and control technologies, chassis electronic control systems such as an anti-lock braking system, a traction control system, an electronic stability control system and an active suspension system have been widely used in automobiles, and the application of these electronic control systems has greatly improved the steering stability, active safety and driving comfort of automobiles.
However, at present, whether steering or braking is still in a mechanically coupled stage, the mechanical coupling of the steering system results in a strong nonlinear time-varying behavior of the steering characteristics of the vehicle as a function of vehicle speed, steering wheel angle, and road surface adhesion conditions. In order to control the vehicle to travel along the path desired by the driver, the driver must adjust his own characteristics at all times, which increases the mental and physical burden of the driver, and in particular, it is often difficult for non-professional drivers to adapt. When encountering complex working conditions (such as split road surfaces, lateral wind, low adhesion road surfaces and the like), a driver can hardly control the automobile, and traffic accidents can easily happen. Therefore, researchers in various countries are continuously researching new steering technologies in order to solve the above problems, and steering-by-wire systems have been developed. The brake-by-wire system changes the traditional hydraulic or pneumatic brake actuating element into an electric driving element, has the characteristics of good controllability and high response speed, and has good development prospect.
At present, a method which has strong universality and is simple and easy to realize is lacking for the integrated control of the drive-by-wire system.
Disclosure of Invention
The invention aims to solve the technical problem related to the background technology and provides a steer-by-wire and braking system and a control method thereof.
The invention adopts the following technical scheme for solving the technical problems:
a steer-by-wire and brake system comprising a steer-by-wire system, a brake-by-wire system and an electronic control unit:
the drive-by-wire steering system comprises a steering wheel, a steering wheel angle sensor, an upper steering column, a lower steering column, a road sensing motor, a first speed reducing mechanism, an electromagnetic clutch, a steering motor, a second speed reducing mechanism, a front shaft, a front wheel steering angle sensor, a vehicle speed sensor, a wheel speed sensor and a yaw rate sensor;
the upper end of the upper steering column is fixedly connected with the steering wheel, the lower end of the upper steering column is connected with the upper end of the lower steering column through the electromagnetic clutch, and the electromagnetic clutch is in a disconnection state;
the steering wheel angle sensor is arranged on the upper steering column and is used for obtaining the steering wheel angle and transmitting the steering wheel angle to the electronic control unit;
the output shaft of the road sensing motor is connected with the upper steering column through the first speed reducing mechanism and is used for transmitting road sensing feedback to a steering wheel through the upper steering column;
the lower end of the lower steering column is connected with the front shaft through the gear rack steering gear;
the two ends of the front axle are respectively connected with a left front wheel and a right front wheel of the automobile;
the output shaft of the steering motor is connected with the lower steering column through the second speed reducing mechanism and is used for transmitting steering torque to the lower steering column so as to drive two front wheels of the automobile to steer through a rack-and-pinion steering gear;
the front wheel rotation angle sensor and the wheel speed sensor are arranged on one front wheel of the automobile, are respectively used for obtaining the front wheel rotation angle and the front wheel speed of the automobile, and are transmitted to the electronic control unit;
the vehicle speed sensor and the yaw rate sensor are arranged on the vehicle and are respectively used for obtaining the vehicle speed and the yaw rate of the vehicle and transmitting the vehicle speed and the yaw rate to the electronic control unit;
the brake-by-wire system comprises a brake pedal sensor, a left front wheel brake cylinder, a right front wheel brake cylinder, a left rear wheel brake cylinder and a right rear wheel brake cylinder;
the brake pedal sensor is arranged at the tail end of an automobile brake pedal and is used for collecting pedal signals generated when a driver brakes and transmitting the pedal signals to the electronic control unit;
the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder are respectively used for controlling the left front wheel, the right front wheel, the left rear wheel and the right rear wheel to brake;
the electronic control unit is respectively and electrically connected with the steering wheel angle sensor, the front wheel angle sensor, the vehicle speed sensor, the wheel speed sensor, the yaw angle sensor, the brake pedal sensor, the road sensing motor, the steering motor, the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder, and is used for controlling the road sensing motor, the steering motor, the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder and the left rear wheel brake wheel cylinder according to the data measured by the steering wheel angle sensor, the front wheel angle sensor, the vehicle speed sensor, the wheel speed sensor, the yaw angle sensor and the brake pedal sensor.
The invention also discloses a control method based on the steer-by-wire and braking system, which comprises the following steps:
step 1), steering wheel angle speed omega measured by a steering wheel angle sensor r Steering wheel angle theta r The method comprises the steps of carrying out a first treatment on the surface of the Brake pedal opening delta measured by brake pedal sensor r Rate of change alpha of brake pedal r The method comprises the steps of carrying out a first treatment on the surface of the Front wheel rotation angle eta measured by front wheel rotation angle sensor and wheel speed sensor respectively r And front wheel speed; vehicle speed sensor, yaw rate sensor and slip rate sensor for respectively measuring vehicle speed V of current vehicle r And yaw rate beta r ；
Step 2), the electronic control unit controls the steering wheel rotation angle speed omega r And a preset steering wheel angular velocity threshold ω m Comparing θ r And a preset steering wheel angle threshold value theta m Comparing the vehicle speed V r And a preset vehicle speed threshold V m Comparing the opening delta of the brake pedal r And a brake pedal opening threshold delta m Comparing the brake pedal change rate alpha r And a brake pedal rate of change threshold alpha m Comparison:
step 2.1) when θ r Greater than theta m And V is r Greater than V m When or when theta r Less than theta m 、ω r Greater than omega m And V r Greater than V m When the steering characteristic parameter is A; otherwise, the steering characteristic parameter is set as B;
step 2.2), when delta r Greater than delta m 、α r Greater than alpha m And V r Greater than V m When the braking characteristic parameter is A; otherwise, making the braking characteristic parameter be B;
and 3) when the steering characteristic parameter is B and the braking characteristic parameter is B, the system works in an on-line control normal working mode:
step 3.1), the electronic control unit is controlled according to theta r Controlling the steering motor to work so that the front wheel rotation angle of the automobile is iθ r, wherein ：
Figure BDA0001678107070000031
C af is the cornering stiffness of the front tire; c (C) ar Is the cornering stiffness of the rear wheel tyre; a is the axle distance from the mass center to the front axle; b is the axle distance from the mass center to the rear axle; l=a+b; m is the mass of the automobile;
step 3.2), the electronic control unit is controlled according to delta r And a preset brake coefficient K controls the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder to respectively generate Kdelta r Braking force;
step 4), when the steering characteristic parameter is A and the braking characteristic parameter is B, the steer-by-wire emergency steering mode is as follows:
step 4.1), the electronic control unit is based on beta r And ideal yaw rate beta w Calculating the required additional rotation angle q of the front wheel θ The calculation formula is as follows:
Figure BDA0001678107070000032
wherein ,
Figure BDA0001678107070000033
step 4.2), the electronic sub-control unit is controlled according to theta r Controlling the steering motor to work so that the front wheel rotation angle of the automobile is iθ r +q θ ；
Step 4.3), the electronic control unit is controlled according to delta r And a preset first brake coefficient K controls the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder to respectively generate Kdelta r Braking force;
step 5), when the steering characteristic parameter is B and the braking characteristic parameter is A, the system works in an emergency braking mode:
step 5.1), the electronic control unit is controlled according to theta r Controlling the steering motor to work so that the front wheel rotation angle of the automobile is iθ r ；
Step 5.2), the electronic control unit is used for controlling the front wheel according to the front wheel rotation angle eta r And the front wheel speed calculates the slip rate of the automobile;
step 5.3), the electronic control unit is controlled according to delta r And a preset brake coefficient K controls the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder to respectively generate Kdelta r Braking force;
and 5.4), adjusting braking forces of the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder according to the automobile slip rate:
step 5.4.1), when the slip ratio is less than 15%, simultaneously increasing the braking force of the left front wheel braking wheel cylinder, the right front wheel braking wheel cylinder, the left rear wheel braking wheel cylinder and the right rear wheel braking wheel cylinder according to the preset braking force step length until the slip ratio is equal to 15%;
step 5.4.2), when the slip ratio is larger than 15%, simultaneously reducing the braking force of the left front wheel braking wheel cylinder, the right front wheel braking wheel cylinder, the left rear wheel braking wheel cylinder and the right rear wheel braking wheel cylinder according to the preset braking force step length until the slip ratio is equal to 15%;
step 6), when the steering characteristic parameter is A and the braking characteristic parameter is A, the steering-by-wire emergency collision avoidance mode is as follows:
step 6.1), the electronic control unit is based on beta r And ideal yaw rate beta w Calculating the required additional rotation angle q of the front wheel θ The calculation formula is as follows:
Figure BDA0001678107070000041
step 6.2), the electronic control unit is used for controlling the front wheel according to the front wheel rotation angle eta r And the front wheel speed calculates the slip rate of the automobile;
step 6.3), the electronic control unit controls the electronic control unit according to the steering angle eta of the front wheels in the vehicle curve r Yaw rate beta r And velocity V r Solving a current stability index Q:
Figure BDA0001678107070000042
the current stability index Q is used for representing understeer, neutral steering and oversteer, wherein the neutral steering is performed when Q=0, the understeer is performed when Q > 0, and the oversteer is performed when Q < 0;
step 6.4), the electronic control unit is controlled according to delta r And a preset brake coefficient K controls the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder to respectively generate Kdelta r Braking force;
step 6.5), the braking forces of the left front wheel braking wheel cylinder, the right front wheel braking wheel cylinder, the left rear wheel braking wheel cylinder and the right rear wheel braking wheel cylinder are adjusted according to the current stability index Q:
step 6.5.1), when left turn and oversteer, the electronic control unit applies additional K to the front right brake cylinder 1 Delta braking force to make the braking force of the right front brake wheel cylinder K delta + K 1δ, wherein ,K1 Is a preset second braking coefficient;
6.5.2) when the left wheel is turned left and the steering is insufficient, the electronic control unit applies additional K to the left rear brake wheel cylinder 2 Delta braking force to make the braking force of left rear brake wheel cylinder K delta + K 2δ, wherein ,K2 Is a preset second braking coefficient;
step 6.5.3), when the vehicle turns right and turns too much, the electronic control unit applies additional K to the front left brake wheel cylinder 1 Delta braking force to make the braking force of the front left brake wheel cylinder K delta + K 1 δ；
Step 6.5.4), when the right turn is insufficient and the steering is right-turn, the electronic control unit applies additional K to the right rear brake wheel cylinder 2 Delta braking force to make the braking force of the right rear brake wheel cylinder K delta + K 2 δ。
Compared with the prior art, the technical scheme provided by the invention has the following technical effects:
1. the invention provides a mode conversion and control method, which can solve the problem of joint control in a steering-by-wire and braking system;
2. different steering and braking working modes can be switched according to different automobile driving working conditions and driver operations, and a vehicle body control method under emergency working conditions is provided.
Drawings
FIG. 1 is a schematic diagram of the structure of the present invention;
fig. 2 is a schematic diagram of a steering control flow according to the present invention.
In the figure, a 1-steering wheel, a 2-steering wheel angle sensor, a 3-road sensing motor and a first speed reducing mechanism, a 4-electronic control unit, a 5-electromagnetic clutch, a 6-steering motor and a second speed reducing mechanism, a 7-gear rack sensor, an 8-left front brake wheel cylinder and a 9-brake pedal sensor.
Detailed Description
The technical scheme of the invention is further described in detail below with reference to the accompanying drawings:
this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the components are exaggerated for clarity.
As shown in fig. 1, the present invention discloses a steer-by-wire and brake system, comprising a steer-by-wire system, a brake-by-wire system and an electronic control unit:
the drive-by-wire steering system comprises a steering wheel, a steering wheel angle sensor, an upper steering column, a lower steering column, a road sensing motor, a first speed reducing mechanism, an electromagnetic clutch, a steering motor, a second speed reducing mechanism, a front shaft, a front wheel steering angle sensor, a vehicle speed sensor, a wheel speed sensor and a yaw rate sensor;
the upper end of the upper steering column is fixedly connected with the steering wheel, the lower end of the upper steering column is connected with the upper end of the lower steering column through the electromagnetic clutch, and the electromagnetic clutch is in a disconnection state;
the steering wheel angle sensor is arranged on the upper steering column and is used for obtaining the steering wheel angle and transmitting the steering wheel angle to the electronic control unit;
the output shaft of the road sensing motor is connected with the upper steering column through the first speed reducing mechanism and is used for transmitting road sensing feedback to a steering wheel through the upper steering column;
the lower end of the lower steering column is connected with the front shaft through the gear rack steering gear;
the two ends of the front axle are respectively connected with a left front wheel and a right front wheel of the automobile;
the output shaft of the steering motor is connected with the lower steering column through the second speed reducing mechanism and is used for transmitting steering torque to the lower steering column so as to drive two front wheels of the automobile to steer through a rack-and-pinion steering gear;
the front wheel rotation angle sensor and the wheel speed sensor are arranged on one front wheel of the automobile, are respectively used for obtaining the front wheel rotation angle and the front wheel speed of the automobile, and are transmitted to the electronic control unit;
the vehicle speed sensor and the yaw rate sensor are arranged on the vehicle and are respectively used for obtaining the vehicle speed and the yaw rate of the vehicle and transmitting the vehicle speed and the yaw rate to the electronic control unit;
the brake-by-wire system comprises a brake pedal sensor, a left front wheel brake cylinder, a right front wheel brake cylinder, a left rear wheel brake cylinder and a right rear wheel brake cylinder;
the brake pedal sensor is arranged at the tail end of an automobile brake pedal and is used for collecting pedal signals generated when a driver brakes and transmitting the pedal signals to the electronic control unit;
the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder are respectively used for controlling the left front wheel, the right front wheel, the left rear wheel and the right rear wheel to brake;
the electronic control unit is respectively and electrically connected with the steering wheel angle sensor, the front wheel angle sensor, the vehicle speed sensor, the wheel speed sensor, the yaw angle sensor, the brake pedal sensor, the road sensing motor, the steering motor, the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder, and is used for controlling the road sensing motor, the steering motor, the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder and the left rear wheel brake wheel cylinder according to the data measured by the steering wheel angle sensor, the front wheel angle sensor, the vehicle speed sensor, the wheel speed sensor, the yaw angle sensor and the brake pedal sensor.
As shown in fig. 2, the invention also discloses a control method based on the steer-by-wire and braking system, which comprises the following steps:
step 1), steering wheel angle speed omega measured by a steering wheel angle sensor r Steering wheel angle theta r The method comprises the steps of carrying out a first treatment on the surface of the Brake pedal opening delta measured by brake pedal sensor r Rate of change alpha of brake pedal r The method comprises the steps of carrying out a first treatment on the surface of the Front wheel rotation angle eta measured by front wheel rotation angle sensor and wheel speed sensor respectively r And front wheel speed; vehicle speed sensor, yaw rate sensor and slip rate sensor for respectively measuring vehicle speed V of current vehicle r And yaw rate beta r ；
Step 2), the electronic control unit controls the steering wheel rotation angle speed omega r And a preset steering wheel angular velocity threshold ω m Comparing θ r And a preset steering wheel angle threshold value theta m Comparing the vehicle speed V r And a preset vehicle speed threshold V m Comparing the opening delta of the brake pedal r And a brake pedal opening threshold delta m Comparing the brake pedal change rate alpha r And a brake pedal rate of change threshold alpha m Comparison:
step 2.1) when θ r Greater than theta m And V is r Greater than V m When or when theta r Less than theta m 、ω r Greater than omega m And V r Greater than V m When the steering characteristic parameter is A; otherwise, the steering characteristic parameter is set as B;
step 2.2), when delta r Greater than delta m 、α r Greater than alpha m And V r Greater than V m When the braking characteristic parameter is A; otherwise, making the braking characteristic parameter be B;
and 3) when the steering characteristic parameter is B and the braking characteristic parameter is B, the system works in an on-line control normal working mode:
step 3.1), the electronic control unit is controlled according to theta r Controlling the steering motor to work so that the front wheel rotation angle of the automobile is iθ r, wherein ：
Figure BDA0001678107070000071
C af is the cornering stiffness of the front tire; c (C) ar Is the cornering stiffness of the rear wheel tyre; a is the axle distance from the mass center to the front axle; b is the axle distance from the mass center to the rear axle; l=a+b; m is the mass of the automobile;
step 3.2), the electronic control unit is controlled according to delta r And a preset brake coefficient K controls the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder to respectively generate Kdelta r Braking force;
step 4), when the steering characteristic parameter is A and the braking characteristic parameter is B, the steer-by-wire emergency steering mode is as follows:
step 4.1), the electronic control unit is based on beta r And ideal yaw rate beta w Calculating the required additional rotation angle q of the front wheel θ The calculation formula is as follows:
Figure BDA0001678107070000072
wherein ,
Figure BDA0001678107070000073
step 4.2), the electronic sub-control unit is controlled according to theta r Controlling the steering motor to work so that the front wheel rotation angle of the automobile is iθ r +q θ ；
Step 4.3), the electronic control unit is controlled according to delta r And a preset first brake coefficient K controls the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder to respectively generate Kdelta r Braking force;
step 5), when the steering characteristic parameter is B and the braking characteristic parameter is A, the system works in an emergency braking mode:
step 5.1), the electronic control unit is controlled according to theta r Controlling the steering motor to work so that the front wheel rotation angle of the automobile is iθ r ；
Step 52) the electronic control unit is used for controlling the front wheel according to the front wheel rotation angle eta r And the front wheel speed calculates the slip rate of the automobile;
step 5.3), the electronic control unit is controlled according to delta r And a preset brake coefficient K controls the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder to respectively generate Kdelta r Braking force;
and 5.4), adjusting braking forces of the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder according to the automobile slip rate:
step 5.4.1), when the slip ratio is less than 15%, simultaneously increasing the braking force of the left front wheel braking wheel cylinder, the right front wheel braking wheel cylinder, the left rear wheel braking wheel cylinder and the right rear wheel braking wheel cylinder according to the preset braking force step length until the slip ratio is equal to 15%;
step 5.4.2), when the slip ratio is larger than 15%, simultaneously reducing the braking force of the left front wheel braking wheel cylinder, the right front wheel braking wheel cylinder, the left rear wheel braking wheel cylinder and the right rear wheel braking wheel cylinder according to the preset braking force step length until the slip ratio is equal to 15%;
step 6), when the steering characteristic parameter is A and the braking characteristic parameter is A, the steering-by-wire emergency collision avoidance mode is as follows:
step 6.1), the electronic control unit is based on beta r And ideal yaw rate beta w Calculating the required additional rotation angle q of the front wheel θ The calculation formula is as follows:
Figure BDA0001678107070000081
step 6.2), the electronic control unit is used for controlling the front wheel according to the front wheel rotation angle eta r And the front wheel speed calculates the slip rate of the automobile;
step 6.3), the electronic control unit controls the electronic control unit according to the steering angle eta of the front wheels in the vehicle curve r Yaw rate beta r And velocity V r Solving a current stability index Q:
Figure BDA0001678107070000082
the current stability index Q is used for representing understeer, neutral steering and oversteer, wherein the neutral steering is performed when Q=0, the understeer is performed when Q > 0, and the oversteer is performed when Q < 0;
step 6.4), the electronic control unit is controlled according to delta r And a preset brake coefficient K controls the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder to respectively generate Kdelta r Braking force;
step 6.5), the braking forces of the left front wheel braking wheel cylinder, the right front wheel braking wheel cylinder, the left rear wheel braking wheel cylinder and the right rear wheel braking wheel cylinder are adjusted according to the current stability index Q:
step 6.5.1), when left turn and oversteer, the electronic control unit applies additional K to the front right brake cylinder 1 Delta braking force to make the braking force of the right front brake wheel cylinder K delta + K 1δ, wherein ,K1 Is a preset second braking coefficient;
6.5.2) when the left wheel is turned left and the steering is insufficient, the electronic control unit applies additional K to the left rear brake wheel cylinder 2 Delta braking force to make the braking force of left rear brake wheel cylinder K delta + K 2δ, wherein ,K2 Is a preset second braking coefficient;
step 6.5.3), when the vehicle turns right and turns too much, the electronic control unit applies additional K to the front left brake wheel cylinder 1 Delta braking force to make the braking force of the front left brake wheel cylinder K delta + K 1 δ；
Step 6.5.4), when the right turn is insufficient and the steering is right-turn, the electronic control unit applies additional K to the right rear brake wheel cylinder 2 Delta braking force to make the braking force of the right rear brake wheel cylinder K delta + K 2 δ。
It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
While the foregoing is directed to embodiments of the present invention, other and further details of the invention may be had by the present invention, it should be understood that the foregoing description is merely illustrative of the present invention and that no limitations are intended to the scope of the invention, except insofar as modifications, equivalents, improvements or modifications are within the spirit and principles of the invention.

Claims (1)

1. A control method of a steer-by-wire and brake system comprising a steer-by-wire system, a brake-by-wire system and an electronic control unit:
the drive-by-wire steering system comprises a steering wheel, a steering wheel angle sensor, an upper steering column, a lower steering column, a road sensing motor, a first speed reducing mechanism, an electromagnetic clutch, a steering motor, a second speed reducing mechanism, a rack-and-pinion steering gear, a front axle, a front wheel steering angle sensor, a vehicle speed sensor, a wheel speed sensor and a yaw rate sensor;
the upper end of the upper steering column is fixedly connected with the steering wheel, the lower end of the upper steering column is connected with the upper end of the lower steering column through the electromagnetic clutch, and the electromagnetic clutch is in a disconnection state;
the steering wheel angle sensor is arranged on the upper steering column and is used for obtaining the steering wheel angle and transmitting the steering wheel angle to the electronic control unit;
the output shaft of the road sensing motor is connected with the upper steering column through the first speed reducing mechanism and is used for transmitting road sensing feedback to a steering wheel through the upper steering column;
the lower end of the lower steering column is connected with the front shaft through the gear rack steering gear;
the two ends of the front axle are respectively connected with a left front wheel and a right front wheel of the automobile;
the output shaft of the steering motor is connected with the lower steering column through the second speed reducing mechanism and is used for transmitting steering torque to the lower steering column so as to drive two front wheels of the automobile to steer through a rack-and-pinion steering gear;
the front wheel rotation angle sensor and the wheel speed sensor are arranged on one front wheel of the automobile, are respectively used for obtaining the front wheel rotation angle and the front wheel speed of the automobile, and are transmitted to the electronic control unit;
the vehicle speed sensor and the yaw rate sensor are arranged on the vehicle and are respectively used for obtaining the vehicle speed and the yaw rate of the vehicle and transmitting the vehicle speed and the yaw rate to the electronic control unit;
the brake-by-wire system comprises a brake pedal sensor, a left front wheel brake cylinder, a right front wheel brake cylinder, a left rear wheel brake cylinder and a right rear wheel brake cylinder;
the brake pedal sensor is arranged at the tail end of an automobile brake pedal and is used for collecting pedal signals generated when a driver brakes and transmitting the pedal signals to the electronic control unit;
the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder are respectively used for controlling the left front wheel, the right front wheel, the left rear wheel and the right rear wheel to brake;
the electronic control unit is respectively and electrically connected with the steering wheel angle sensor, the front wheel angle sensor, the vehicle speed sensor, the wheel speed sensor, the yaw angle sensor, the brake pedal sensor, the road sensing motor, the steering motor, the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder, and is used for controlling the road sensing motor, the steering motor, the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder according to the data measured by the steering wheel angle sensor, the front wheel angle sensor, the vehicle speed sensor, the wheel speed sensor, the yaw angle sensor and the brake pedal sensor;
the control method of the steer-by-wire and braking system is characterized by comprising the following steps of:
step 1), steering wheel angle speed omega measured by a steering wheel angle sensor r Steering wheel angle theta r The method comprises the steps of carrying out a first treatment on the surface of the Brake pedal opening delta measured by brake pedal sensor r Rate of change alpha of brake pedal r The method comprises the steps of carrying out a first treatment on the surface of the Front wheel rotation angle eta measured by front wheel rotation angle sensor and wheel speed sensor respectively r And front wheel speed; vehicle speed sensor, yaw rate sensor and slip rate sensor for respectively measuring vehicle speed V of current vehicle r And yaw rate beta r ；
Step 2), the electronic control unit controls the steering wheel rotation angle speed omega r And a preset steering wheel angular velocity threshold ω m Comparing θ r And a preset steering wheel angle threshold value theta m Comparing the vehicle speed V r And a preset vehicle speed threshold V m Comparing the opening delta of the brake pedal r And a brake pedal opening threshold delta m Comparing the brake pedal change rate alpha r And a brake pedal rate of change threshold alpha m Comparison:
step 2.1) when θ r Greater than theta m And V is r Greater than V m When or when theta r Less than theta m 、ω r Greater than omega m And V r Greater than V m When the steering characteristic parameter is A; otherwise, the steering characteristic parameter is set as B;
step 2.2), when delta r Greater than delta m 、α r Greater than alpha m And V r Greater than V m When the braking characteristic parameter is A; otherwise, making the braking characteristic parameter be B;
and 3) when the steering characteristic parameter is B and the braking characteristic parameter is B, the system works in an on-line control normal working mode:
step 3.1), the electronic control unit is controlled according to theta r Controlling the steering motor to work so that the front wheel rotation angle of the automobile is iθ r, wherein ：
Figure QLYQS_1
C af is the cornering stiffness of the front tire; c (C) ar Is the cornering stiffness of the rear wheel tyre; a is the axle distance from the mass center to the front axle; b is the axle distance from the mass center to the rear axle; l=a+b; m is the mass of the automobile;
step 3.2), the electronic control unit is controlled according to delta r And a preset braking coefficient K controls the left front wheel braking wheel cylinder and the right front wheel braking wheel cylinderThe wheel brake cylinder, the left rear wheel brake cylinder and the right rear wheel brake cylinder respectively generate Kdelta r Braking force;
step 4), when the steering characteristic parameter is A and the braking characteristic parameter is B, the steer-by-wire emergency steering mode is as follows:
step 4.1), the electronic control unit is based on beta r And ideal yaw rate beta w Calculating the required additional rotation angle q of the front wheel θ The calculation formula is as follows:
Figure QLYQS_2
wherein ,
Figure QLYQS_3
step 4.2), the electronic control unit is controlled according to theta r Controlling the steering motor to work so that the front wheel rotation angle of the automobile is iθ r +q θ ；
Step 4.3), the electronic control unit is controlled according to delta r And a preset brake coefficient K controls the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder to respectively generate Kdelta r Braking force;
step 5), when the steering characteristic parameter is B and the braking characteristic parameter is A, the system works in an emergency braking mode:
step 5.1), the electronic control unit is controlled according to theta r Controlling the steering motor to work so that the front wheel rotation angle of the automobile is iθ r ；
Step 5.2), the electronic control unit is used for controlling the front wheel according to the front wheel rotation angle eta r And the front wheel speed calculates the slip rate of the automobile;
step 5.3), the electronic control unit is controlled according to delta r And a preset brake coefficient K controls the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder to respectively generate Kdelta r Braking force;
and 5.4), adjusting braking forces of the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder according to the automobile slip rate:
step 5.4.1), when the slip ratio is less than 15%, simultaneously increasing the braking force of the left front wheel braking wheel cylinder, the right front wheel braking wheel cylinder, the left rear wheel braking wheel cylinder and the right rear wheel braking wheel cylinder according to the preset braking force step length until the slip ratio is equal to 15%;
step 5.4.2), when the slip ratio is larger than 15%, simultaneously reducing the braking force of the left front wheel braking wheel cylinder, the right front wheel braking wheel cylinder, the left rear wheel braking wheel cylinder and the right rear wheel braking wheel cylinder according to the preset braking force step length until the slip ratio is equal to 15%;
step 6), when the steering characteristic parameter is A and the braking characteristic parameter is A, the steering-by-wire emergency collision avoidance mode is as follows:
step 6.1), the electronic control unit is based on beta r And ideal yaw rate beta w Calculating the required additional rotation angle q of the front wheel θ The calculation formula is as follows:
Figure QLYQS_4
step 6.2), the electronic control unit is used for controlling the front wheel according to the front wheel rotation angle eta r And the front wheel speed calculates the slip rate of the automobile;
step 6.3), the electronic control unit controls the electronic control unit according to the steering angle eta of the front wheels during the turning of the vehicle r Yaw rate beta r And the vehicle speed V r Solving a current stability index Q:
Figure QLYQS_5
the current stability index Q is used for representing understeer, neutral steering and oversteer, wherein the neutral steering is performed when Q=0, the understeer is performed when Q > 0, and the oversteer is performed when Q < 0;
step 6.4), the electronic control unit is controlled according to delta r And a preset brake coefficient K controls the left front wheel brake wheel cylinder, the right front wheel brake wheel cylinder, the left rear wheel brake wheel cylinder and the right rear wheel brake wheel cylinder to respectively generate Kdelta r Braking force；
Step 6.5), the braking forces of the left front wheel braking wheel cylinder, the right front wheel braking wheel cylinder, the left rear wheel braking wheel cylinder and the right rear wheel braking wheel cylinder are adjusted according to the current stability index Q:
step 6.5.1), when left turn and oversteer, the electronic control unit applies additional K to the brake cylinder of the right front wheel 1 δ r Braking force, the braking force of the brake wheel cylinder of the right front wheel is K delta r +K 1 δ r, wherein ,K1 Is a preset first braking coefficient;
6.5.2) when the left wheel is turned left and the steering is insufficient, the electronic control unit applies additional K to the left rear wheel brake cylinder 2 δ r Braking force, the braking force of the left rear wheel brake cylinder is K delta r +K 2 δ r, wherein ,K2 Is a preset second braking coefficient;
step 6.5.3), when the vehicle turns right and turns too much, the electronic control unit applies additional K to the left front wheel brake cylinder 1 δ r Braking force, the braking force of the left front wheel braking wheel cylinder is K delta r +K 1 δ r ；
Step 6.5.4), when the right turn is insufficient and the steering is right-turn, the electronic control unit applies additional K to the brake wheel cylinder of the right rear wheel 2 δ r Braking force, the braking force of the brake wheel cylinder of the right rear wheel is K delta r +K 2 δ r 。
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