CN108749916B - Multi-mode steer-by-wire device and control method thereof - Google Patents

Abstract

The invention discloses a multi-mode steer-by-wire device, which belongs to the technical field of steering-by-wire of automobiles, and comprises a second planetary gear train and a first planetary gear train which are sequentially arranged on an output shaft of an automobile; the first planetary gear train and the second planetary gear train are respectively controlled by a motor, and the working modes of the planetary gear trains are controlled by a motor controller and a whole vehicle controller; the invention also discloses a control method thereof, which is characterized in that the motor and the inner gear ring electromagnetic clutch are respectively controlled to be switched into four different working modes of pure mechanical steering, electric power-assisted steering, wire control steering and automatic driving, and in addition to the pure mechanical steering, in other three modes, when one motor fails, the main shaft is locked under the action of the electromagnetic brake, and the other motor is started to serve as a power source; when two motors fail at the same time, the invention automatically enters a pure mechanical steering mode, no extra control is needed, and the steering reliability is ensured to the greatest extent.

Description

A multi-mode steering-by-wire device and its control method

Technical field

The invention belongs to automobile active steering, and in particular relates to the technical field of automobile steering by wire. Specifically, it is a multi-mode steering by wire device and a control method thereof.

Background technique

Automobile intelligence is developing rapidly, and steer-by-wire is a key link in the development process of automobile intelligence, especially one of the necessary technologies for autonomous driving. Steer-by-wire technology has gradually matured and has been applied to a small number of models. The steering-by-wire system requires redundancy and fault-tolerance functions. It not only requires software to implement diagnosis and fault-tolerant control algorithms, but also requires hardware redundancy design, resulting in complex hardware layout of the steering-by-wire system, high cost, and low hardware utilization.

At present, there have been many studies on steer-by-wire technology. Among them, the dual-motor redundant steer-by-wire system designed by Infiniti has been successfully applied in real vehicles. This system is designed with motor tachometers on the left and right ends of the rack to drive the steering gear pinions. The rack is driven to move left and right. When the clutch fails, the clutch is closed. The left steering gear pinion is connected to the mechanical steering column to achieve steering. However, the redundant structure of the system is complex. Both motors are driven by the reducer through the rack and pinion steering gear. , low transmission efficiency.

South Korea's Hyundai Motor Company proposed a steering-by-wire device and method for a dual-motor drive rack (Patent No. US201600144890A1). This system did not solve the problem of motor space installation and the steering mode of dual-motor failure. Becker et al. proposed an electro-hydraulic steering-by-wire system (Patent No. US20160068182A1). This device controls the pressure of the steering wheel cylinder through two motor pumps and drives the tie rods on both sides to move left and right. However, the response speed of the motor to establish hydraulic pressure is slow. The high-pressure oil pipeline has unreliable factors such as increased oil leakage and the presence of bubbles, and it is impossible to achieve direct mechanical connection after the steering-by-wire failure.

Yu Leiyan designed an electric vehicle steering-by-wire system and control method (patent application number 201310649410.4). The system designed a steering wheel force feedback motor and worm reducer to simulate road feel, and the steering motor and planetary gear reducer drive the steering gear. The pinion achieves steering, and a motor and a planetary gear reducer are installed near the steering gear, which requires more layout space. The transmission through the rack and pinion steering gear reduces the working efficiency of the motor and cannot achieve the steering mode in which the motor fails.

Li Shaosong et al. designed a front-wheel active steering coupling device based on a double-row planetary gear train (patent application number 201610907896.0). The device includes a power drive device installed on the housing and a mechanical transmission device installed in the housing. Manual input Part of the power is transmitted through the input shaft, and the angle-assist motor part is transmitted through the turbine worm, and the coupled angle is output by the ring gear, realizing variable transmission ratio transmission, making the steering process safer and more flexible. However, this device adopts a single motor design and has a complicated transmission path, which reduces the working efficiency of the motor and cannot realize the steering mode in which the motor fails.

A hybrid steering-by-wire system invented by Yang Lin et al. (Patent Application No. 201610989594.2). This system separates the road-sensing motor and the power-assist motor. It only uses a set of steering actuator motors to drive the double-row planetary gear reducer, and then through the worm rack It drives the tie rod to move left and right, and has real-time controllable force transmission characteristics and angular transmission characteristics between the steering wheel unit and the steering wheel. When the system fails, it returns to the mechanical steering state through the clutch, but the system has a complex structure and low transmission efficiency.

In summary, the existing steer-by-wire system has contradictions between low transmission efficiency, complex structure and difficult spatial arrangement, as well as redundant and failure working mode requirements.

Contents of the invention

In view of the defects existing in the prior art, the present invention provides a multi-mode wire-controlled steering device. The device adopts a double-row planetary gear train structure and has real-time controllable force transmission characteristics and angular transmission between the steering wheel unit and the left and right wheels. Features: By separately controlling the brake switch of the motor and the pull-in switch of the internal ring gear electromagnetic clutch, functions such as switching between pure mechanical steering mode, electric power steering mode, steer-by-wire mode, and automatic driving mode are achieved, and the system automatically recovers when it fails. to a purely mechanical steering state, fully meeting safety regulatory requirements.

The present invention is implemented as follows:

A multi-mode wire-controlled steering device, the device includes a rack, a pinion is provided on the rack; an output shaft is provided above the pinion; a second planetary gear train and a first planetary gear are connected in sequence above the output shaft system; the output shaft is also connected to a steering wheel sensor and a steering wheel unit in sequence above the first planetary gear system.

The first planetary gear train is controlled by the first motor; the second planetary gear train is controlled by the second motor; the first planetary gear train includes a first sun gear, a first planet carrier, a first planet gear, and an internal ring gear; the second planetary gear train The gear train includes a second planet gear, a second sun gear, a second planet carrier, and an internal ring gear. The internal ring gear meshes with the first planet gear and the second planet gear at the same time. The two planetary gear trains are connected and transmit rotation angle and torque; an inner ring gear electromagnetic clutch is also provided outside the inner ring gear, and the signal of the inner ring gear electromagnetic clutch is connected to the vehicle controller; the first motor (M1), the second motor ( M2) is connected to the vehicle controller (VCU) through the first motor controller (MCU1) and the second motor controller (MCU2) signals respectively.

Further, the steering tie rod, trapezoidal arm, and steering knuckle are arranged symmetrically on both sides of the rack; the left and right wheels are connected through the steering knuckles on both sides.

Further, the output shaft is rigidly connected to the first sun gear and is connected to the first planet carrier through a bearing; the output shaft is rigidly connected to the second sun gear and is connected to the second planet carrier through a bearing.

Further, the first planet carrier is connected to the first motor; the second planet carrier is connected to the second motor.

Further, the steering wheel sensor transmits steering wheel angle and torque information to the vehicle controller. Furthermore, both the first motor and the second motor are equipped with electromagnetic brakes, which can automatically lock the motor spindle under active control or passive power outage.

The invention also discloses a control method of a multi-mode wire-controlled steering device, which switches four different working modes by respectively controlling the brake switch of the first motor, the second motor and the pull-in switch of the internal ring gear electromagnetic clutch. The electromagnetic clutch of the inner ring gear works in the normally closed mode. At this time, the inner ring gear is locked and cannot rotate freely. Only under active control or passive power outage, due to the elastic force of the spring, the clutch is separated and the inner ring gear can rotate freely.

The specific four control modes are as follows:

According to the control instructions input by the driver, the VCU automatically controls the device to work in three modes: electric power assist, wired steering or automatic driving. At the same time, it automatically switches the working mode according to the fault information: 1) No fault: first planetary gear system, second planetary gear system The planetary gear train transmits the motor driving torque, drives the pinion and rack, and realizes the steering task; 2) Fault: It is judged whether it is a single motor failure or a dual motor failure, and the vehicle controller automatically switches the steering mode according to the fault information. If there is a single motor failure, the power supply to the faulty motor will be cut off, and the non-faulty motor will provide driving torque to ensure the normal operation of the steering system; if there is a dual motor failure, the power supply to all motors will be cut off, and the inner ring gear electromagnetic clutch will be separated, automatically switching to pure steering. Mechanical steering working mode.

Pure mechanical steering mode: The first motor (M1) and the second motor (M2) are both braked, the first planet carrier and the second planet carrier are locked, and the first planet wheel and the second planet wheel can only rotate and cannot Revolution; power is input from the steering wheel unit, passes through the first sun gear, the first planetary gear, the internal ring gear, the second planetary gear, the second sun gear, the output shaft, and is transmitted to the pinion and rack;

Electric power steering mode: the first motor is braked, the first planet carrier is locked, and the first planet wheel can only rotate; the electromagnetic clutch of the inner ring gear is separated, and the inner ring gear can rotate freely; there are two power sources, one of which One is input from the steering wheel unit and passes through the first sun gear, the first planet gear and the inner ring gear; the second is the input from the second motor, which passes through the second planet carrier and the second planet gear and is coupled with the power of the inner ring gear. Acts on the second sun gear, and finally passes to the pinion and rack;

Steer-by-wire mode: The electromagnetic clutch of the inner ring gear is closed and the inner ring gear is locked; at this time, the first motor acts as a road-sensing motor and provides power to the steering wheel unit through the first planet carrier, the first planet wheel, and the first sun wheel. Road sense feedback; the second motor serves as the steering motor, passing through the second planet carrier, the second planet wheel, the second sun gear, and finally to the pinion and rack to complete the steering action;

Automatic driving mode: The first motor brakes, the electromagnetic clutch of the inner ring gear is closed, and the first planet carrier and the inner ring gear are locked; at this time, the steering wheel unit does not move, and the second motor of the motor acts as a steering motor, passing the second planetary gear carrier, second planet gear, second sun gear, and finally passed to the pinion and rack to complete the steering action.

Furthermore, it diagnoses whether the system is faulty according to the three modes of electric power steering, steer-by-wire and autonomous driving;

1) There is no fault: the first planetary gear train and the second planetary gear train transmit the motor driving torque, drive the pinion, rack, steering tie rod, trapezoidal arm, and steering knuckle to realize the steering task of the vehicle wheels;

2) Fault: Determine whether it is a single motor failure or a dual motor failure.

When it is judged to be a single motor failure: cut off the power supply of the faulty motor, the electromagnetic brake of the faulty motor will automatically close, lock the planet carrier controlled by the corresponding motor, and then calculate the drive current of the non-faulty motor, and provide the driving torque through the non-faulty motor to ensure the normal steering command. transfer;

When it is determined that there is a dual motor failure: cut off the power supply of the two faulty motors at the same time, the electromagnetic brake of the faulty motor will automatically close, lock the planet carrier corresponding to the control of the two faulty motors, and separate the inner ring gear electromagnetic clutch, without additional control, to the greatest extent to ensure the reliability of steering.

The beneficial effects of the present invention and the prior art are:

The device of the invention has a compact structure and is easy to arrange: the invention adopts a double-row planetary gear train structure and makes full use of the radial space of the input shaft of the invention - the first planetary gear train and the second planetary gear train - the output shaft to reduce the size of the motor. Instead of adding a motor reduction mechanism near the pinion and rack, the traditional mechanical steering system layout can be used. Therefore, the device of the present invention has the advantage of simple spatial layout;

High transmission efficiency: This invention adopts a planetary gear mechanism and has high transmission efficiency. The motor does not need to add an additional reduction mechanism and directly transmits the drive pinion, rack, and steering pinion, which can also improve transmission efficiency;

High fault tolerance and good safety performance: This invention adopts a dual motor structure to back up each other. In addition to pure mechanical steering, in the other three modes, when one motor fails, the spindle will be locked under the action of the electromagnetic brake. At the same time, The VCU detects a motor failure and activates another motor to act as a power source to ensure the normal transmission of steering instructions; when both motors fail at the same time, the invention automatically enters a pure mechanical steering mode without additional control, ensuring steering reliability to the greatest extent sex;

Stable high-speed driving: The method of the present invention can ensure the stability of the wire-controlled steering process by controlling the precise displacement of the pinion. When the car is running at high speed, the second motor can be reversed to provide steering damping force to improve the stability of the car's steering.

Description of the drawings

Figure 1 is a schematic diagram of the principle of a multi-mode steering-by-wire device of the present invention;

Figure 2 is a flow chart of a multi-mode steering-by-wire device control method of the present invention;

Figure 3 is a power transmission path diagram of each mode in a multi-mode wire-controlled steering device of the present invention;

Among them, 1-steering wheel unit, 2-steering wheel sensor, 3-first sun gear, 4-first planet carrier, 5-first planet gear, 6-inner ring gear, 7-inner ring gear electromagnetic clutch, 8 -The second planet gear, 9-the second planet carrier, 10-the second sun gear, 11-the second motor, 12-the first motor, 13-the first motor controller, 14-the second motor controller, 15- Vehicle controller, 16-pinion, 17-rack, 18-steering tie rod, 19-trapezoid arm, 20-steering knuckle, 21-input shaft, 22-output shaft, 23-wheel.

Detailed ways

In order to make the purpose, technical solution and effect of the present invention clearer and clearer, the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be noted that the specific implementations described here are only used to explain the present invention and are not intended to limit the present invention.

The multi-mode steering-by-wire device of the present invention includes a steering wheel unit 1, a steering wheel sensor 2 connected in sequence to the steering wheel unit 1 through an output shaft 22, a first planetary gear train, a second planetary gear train, and a pinion gear. 16. The pinion 16 is connected to the rack 17, and the steering tie rod 18, the trapezoidal arm 19, and the steering knuckle 20 are arranged symmetrically on both sides of the rack 17; the left and right wheels 23 are connected through the steering knuckles 20 on both sides.

The first planetary gear train includes a first sun gear 3, a first planet carrier 4, a first planet gear 5, and an internal ring gear 6; the second planetary gear train includes a second planet gear 8, a second sun gear 10, and a second planet gear. Carrier 9, internal ring gear 6; the first planet carrier 4 is connected to the first motor 12; the second planet carrier 8 is connected to the second motor 11. The first planetary gear train and the second planetary gear train are connected in series through the internal ring gear 6. The specific connection relationship is: the first sun gear 3 connected to the input shaft 22, the first planet carrier 4, the first planet gear 5, the internal gear Circle 6, second planet gear 8, second planet carrier 9, second sun gear 10.

The input shaft 21 is rigidly connected to the first sun gear 3 and connected to the first planet carrier 4 through bearings; the output shaft 22 is rigidly connected to the second sun gear 10 and connected to the second planet carrier 8 through bearings.

The first planetary gear train and the second planetary gear train are connected by sharing an internal ring gear. Specifically, the internal ring gear 6 meshes with the first planetary gear 5 and the second planetary gear 8 at the same time, so that the first planetary gear train and the second planetary gear train The two planetary gear trains can transmit rotation angle and torque to each other. The first motor 12 and the second motor 11 are both equipped with electromagnetic brakes, which can automatically lock the motor spindle under active control or passive power outage. The internal ring gear electromagnetic clutch 7 works in the normally closed mode. At this time, the internal ring gear 6 is locked and cannot rotate freely. Only in the case of active control or passive power outage, due to the elastic force of the spring, the clutch is disengaged and the inner ring gear 6 can rotate freely.

Four different working modes are switched by respectively controlling the brake switches of the first motor 12 and the second motor 11 and the pull-in switch of the internal ring gear electromagnetic clutch 7. The internal ring gear electromagnetic clutch 7 operates in the normally closed mode. At this time, the inner ring gear 6 is locked and cannot rotate freely. Only in the case of active control or passive power outage, due to the elastic force of the spring, the clutch is disengaged and the inner ring gear 6 can rotate freely.

As shown in Figure 2, the vehicle controller 15 collects signals such as steering wheel angle, steering wheel torque, vehicle speed, yaw angular speed, pinion angle, etc. through the steering wheel sensor 2, etc., and then determines the working model, which is divided into four different types. The working model has four modes: pure mechanical steering, electric power steering, steer-by-wire and automatic driving. During normal driving, the present invention mainly works in the steering-by-wire mode. When a fault occurs in the steer-by-wire mode, such as a fault in the second motor 11, the vehicle controller 15 detects the fault signal, actively cuts off the power supply to the second motor 11, brakes it, and the main shaft of the motor is locked. Planet carrier 9 is locked. At the same time, the control strategy of the first motor 12 is changed. The motor switches from the road sense feedback working mode to the steering power assist mode, and disengages the internal ring gear electromagnetic clutch 7. The system switches from the wired steering mode to the electric power steering mode to maintain the steering function. Normal, wait until the vehicle is safe for inspection.

When receiving an automatic driving instruction from the driver, the system automatically works in the automatic driving mode. At this time, the steering wheel unit 1 is in a free state and the steering wheel input will not have any impact on the system's steering. When the motor sends a fault, VCU15 detects the fault signal and determines it as a single motor fault or a dual motor fault. If a single motor fails, the system switches to electric power assist mode; if a dual motor fails, the system switches to pure mechanical steering mode to ensure the normal steering function of the vehicle.

As shown in Figure 2~Figure 3, the detailed introduction of the four different working models is as follows:

Pure mechanical steering mode: the first motor 12 and the second motor 11 are both braked, the first planet carrier 4 and the second planet carrier 9 are locked, and the first planet wheel 5 and the second planet wheel 8 can only rotate and cannot Revolution. The power is input from the steering wheel unit 1, passes through the first sun gear 3, the first planet gear 5, the internal ring gear 6, the second planet gear 8, the second sun gear 10, the output shaft 12, and is transmitted to the pinion gear 16 and the gear wheel 16. Article 17.

Electric power steering mode: the first motor 12 brakes, the first planet carrier 4 is locked, and the first planet wheel 5 can only rotate. The electromagnetic clutch 7 of the inner ring gear is separated, and the inner ring gear 6 can rotate freely. There are two power sources, one is the driver's hand power, which is input from the steering wheel unit 1 and passes through the first sun gear 3, the first planetary gear 5 and the internal ring gear 6; the second is the second motor 11, which passes through the The power coupling between the second planet carrier 9 and the second planet gear 8 and the internal ring gear 6 acts together on the second sun gear 10 and is finally transmitted to the pinion 16 and the rack 17 . In electric power steering mode, diagnose whether the system is faulty and whether it is a single motor fault or dual motor fault, specifically:

When the second motor 11 fails, the VCU 15 detects the fault signal, actively cuts off the power supply to the second motor 11, brakes it, the main shaft of the motor is locked, and the second planet carrier 9 is locked. At the same time, the control strategy of the first motor 12 is changed to switch to the steering assist mode to maintain the normal steering function and wait for the vehicle to be inspected after safety;

When the first motor 12 and the second motor 11 fail at the same time, the VCU 15 detects the fault signal, and at the same time actively cuts off the power supply to the first motor 12 and the second motor 11 to brake them, and the motor main shaft is locked. Planet carrier 4 and second planet carrier 9 are locked, and the system switches to pure mechanical steering mode.

Steer-by-wire mode: The internal ring gear electromagnetic clutch 7 is closed and the internal ring gear 6 is locked. At this time, the first motor 12 serves as a road-sensing motor and provides road-sensing feedback to the steering wheel 1 through the first planet carrier 4, the first planet gear 5, the first sun gear 3, and the second motor 11 serves as a steering motor, through the first The second planet carrier 9, the second planet gear 8 and the second sun gear 10 are finally transmitted to the pinion gear 16 and the rack 17 to drive the steering tie rod 18, the trapezoidal arm 19 and the steering knuckle 20 to complete the steering action of the wheel 23. In the steer-by-wire mode, diagnose whether the system is faulty and whether it is a single motor fault or dual motor fault. Specifically:

When the second motor 11 fails, the VCU 15 detects the fault signal, actively cuts off the power supply to the second motor 11, brakes it, the main shaft of the motor is locked, and the second planet carrier 9 is locked. At the same time, the control strategy of the first motor 12 is changed, from the road sense feedback operating mode to the steering power assist mode, and the internal ring gear electromagnetic clutch 7 is disengaged. The system switches from the wired steering mode to the electric power steering mode to maintain the normal steering function. , wait for the vehicle to be safely inspected.

When the first motor 12 and the second motor 11 fail at the same time, the VCU detects the fault signal, and simultaneously disconnects the power supply to the first motor 12 and the second motor 11 to brake them, and the motor spindle is locked. The first planet carrier 4 and the second planet carrier 9 are locked, and the system switches to pure mechanical steering mode.

Automatic driving mode: the first motor 12 brakes, the internal ring gear electromagnetic clutch 7 is closed, and the first planet carrier 4 and the internal ring gear 6 are locked. At this time, the steering wheel 1 does not move, and the second motor 11 serves as the steering motor, passing through the second planet carrier 9, the second planet gear 8, the second sun gear 10, and finally to the pinion 16 and the rack 17 to drive the steering. The tie rod 18, the trapezoidal arm 19, and the steering knuckle 20 complete the steering action on the wheel 23. In autonomous driving mode, diagnose whether the system is faulty and whether it is a single motor fault or dual motor fault, specifically:

When the second motor 11 fails, the VCU detects the fault signal, actively cuts off the power supply to the second motor 11, brakes it, the main shaft of the motor is locked, and the second planet carrier 9 is locked. At the same time, the control strategy of the first motor 12 is changed, from the road sense feedback operating mode to the steering power assist mode, and the internal ring gear electromagnetic clutch 7 is disengaged. The system switches from the wired steering mode to the electric power steering mode to maintain the normal steering function. , wait for the vehicle to be safely inspected.

When the first motor 12 and the second motor 11 fail at the same time, the VCU 15 detects the fault signal, and simultaneously disconnects the power supply to the first motor 12 and the second motor 11 to brake them, and the motor spindle is locked. The first planet carrier 4 and the second planet carrier 9 are locked, and the system switches to pure mechanical steering mode.

It can be understood by one of ordinary skill 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 should also be understood that terms such as those defined in general dictionaries are to be understood to have meanings consistent with their meaning in the context of the prior art, and are not to be taken in an idealized or overly formal sense unless defined as herein. explain.

The above-mentioned specific embodiments further describe the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims (5)

1. A multi-mode steering-by-wire device, characterized in that the device includes a rack (17), and a pinion (16) is provided on the rack (17); An input shaft (21) and an output shaft (22) are provided above the pinion gear (16); The first planetary gear train and the second planetary gear train are sequentially inserted between the input shaft (21) and the output shaft (22); the first planetary gear train is driven by the first motor (12); the second planetary gear train is driven by The second motor (11) drives; Above the first planetary gear train, the steering wheel sensor (2) and the steering wheel unit (1) are connected in sequence through the input shaft (21); The first planetary gear train includes a first sun gear (3), a first planet carrier (4), a first planet gear (5), and an internal ring gear (6); the second planetary gear train includes a first Second planet gear (8), second sun gear (10), second planet carrier (9), internal ring gear (6); The internal ring gear (6) meshes with the first planetary gear (5) and the second planetary gear (8) at the same time; An internal ring gear electromagnetic clutch (7) is also provided outside the internal ring gear (6), and the signal of the internal ring gear electromagnetic clutch (7) is connected to the vehicle controller (15); The first motor (12) and the second motor (11) are respectively connected to the vehicle controller (15) via signals from the first motor controller (13) and the second motor controller (14); The input shaft (21) is rigidly connected to the first sun gear (3) and is connected to the first planet carrier (4) through bearings; the output shaft (22) is rigidly connected to the second sun gear (10) and is connected to the second sun gear (10). The planet carrier (9) is connected through a bearing; the first planet carrier (4) is connected to the first motor (12); the second planet carrier (9) is connected to the second motor (11); the The steering tie rod (18), trapezoidal arm (19), and steering knuckle (20) are arranged symmetrically on both sides of the rack (17); the left and right wheels (23) are connected through the steering knuckles (20) on both sides. 2. A multi-mode steering-by-wire device according to claim 1, characterized in that the steering wheel sensor (2) transmits information to the vehicle controller (15). 3. A multi-mode steering-by-wire device according to claim 1, characterized in that both the first motor (12) and the second motor (11) are equipped with electromagnetic brakes. 4. The control method of a multi-mode steering-by-wire device according to any one of claims 1 to 3, characterized in that by respectively controlling the brake switch and the brake switch of the first motor (12) and the second motor (11). The pull-in switch of the internal ring gear electromagnetic clutch (7) switches to four different control modes: pure mechanical steering, electric power steering, steer-by-wire and automatic driving, as follows: Pure mechanical steering mode: the first motor (12) and the second motor (11) are both braked, the first planet carrier (4) and the second planet carrier (9) are locked, and the first planet wheel (5) and the second planetary gear (8) can only rotate but not revolve; the power is input from the steering wheel unit (1) and passes through the first sun gear (3), the first planetary gear (5), the internal ring gear (6), the second The planet gear (8), the second sun gear (10), and the output shaft (22) are transmitted to the pinion (16) and the rack (17); Electric power steering mode: the first motor (12) brakes, the first planet carrier (4) is locked, and the first planet wheel (5) can only rotate; the inner ring gear electromagnetic clutch (7) is separated, and the inner gear The ring (6) can rotate freely; there are two power sources, one of which is input from the steering wheel unit (1) and passes through the first sun gear (3), the first planetary gear (5) and the internal ring gear (6); the other The second is the input of the second motor (11). After passing through the second planet carrier (9) and the second planet gear (8), it is coupled with the power of the inner ring gear (6), and acts together on the second sun gear (10). Finally, Transmitted to the pinion (16) and rack (17); Steering-by-wire mode: the inner ring gear electromagnetic clutch (7) is closed and the inner ring gear (6) is locked; at this time, the first motor (12) serves as a road-sensing motor and passes through the first planet carrier (4) and the first The planetary gear (5) and the first sun gear (3) provide road feel feedback for the steering wheel unit (1); the second motor (11) serves as a steering motor through the second planetary carrier (9) and the second planetary gear (8). ), the second sun gear (10), and finally passed to the pinion (16) and rack (17) to complete the steering action; Automatic driving mode: The first motor (12) brakes, the internal ring gear electromagnetic clutch (7) is closed, and the first planet carrier (4) and the internal ring gear (6) are locked; at this time, the steering wheel unit (1) The second motor (11) acts as a steering motor, passing through the second planet carrier (9), the second planet gear (8), the second sun gear (10), and finally to the pinion gear (16) and the gear wheel. Article (17), complete the steering action. 5. A control method for a multi-mode steering-by-wire device according to claim 4, characterized by diagnosing whether the system is faulty according to three modes: electric power steering, steering-by-wire and automatic driving; 1) There is no fault: the first planetary gear train and the second planetary gear train transmit the motor driving torque and drive the pinion (16) and rack (17) to achieve the steering task; 2) There is a fault: and determine whether it is a single motor fault or a double motor fault.