A steer-by-wire system with variable-ratio device and control method thereof
Patent Information
- Application Number
- CN202611228277.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-13
- Publication Date
- 2026-09-15
Smart Images
Figure CN122747992A_ABST
Abstract
Description
Technical Field
[0001] This invention pertains to the field of automotive steer-by-wire technology, and in particular to a steer-by-wire system and its control method that features variable transmission ratio adjustment and fault redundancy. Background Technology
[0002] With the rapid development of intelligent driving technology, steer-by-wire (SBW) systems have become the core development direction of automotive steering technology because they eliminate the mechanical hard connection between the steering wheel and the steering wheels, and have advantages such as flexible layout, adjustable steering characteristics, and compatibility with advanced autonomous driving.
[0003] Existing steer-by-wire systems typically have separate road feel simulation motors and steering actuation motors, with each system handling human-machine interaction and steering drive functions respectively. Furthermore, most systems use a fixed road feel feedback transmission ratio, making it difficult to dynamically adjust road feel feedback characteristics based on operating conditions. In single-motor failure scenarios, the road feel motor cannot amplify torque through transmission ratio adjustment to provide steering assistance, resulting in limited adaptability and fault redundancy. Some steer-by-wire systems with variable transmission ratio functionality do not couple the variable transmission ratio mechanism with the road feel simulation motor, failing to achieve coordinated adjustment of road feel characteristics and steering assist capability. Moreover, transmission interruption is prone to occur when the variable transmission ratio adjustment mechanism fails, lacking a reliable fault tolerance mechanism and failing to guarantee continuous steering function output in fault conditions.
[0004] In terms of system reliability, the redundancy design of conventional steer-by-wire systems is mostly concentrated on a single component, lacking a complete redundancy strategy covering the entire link of motor, sensors, and communication. When the core motor or transmission component fails, steering function is prone to failure, posing a significant driving safety hazard. Therefore, it is necessary to develop a steer-by-wire system with a reasonable variable transmission ratio, strong adjustment tolerance, and comprehensive redundancy protection to meet the steering needs and functional safety requirements under multiple operating conditions. Summary of the Invention
[0005] The purpose of this invention is to provide a steer-by-wire system with a variable transmission ratio device and its control method. This invention enables dynamic adjustment of the transmission ratio on the road feel feedback side, improving road feel adaptability and fault redundancy torque amplification capability. Furthermore, relying on a self-locking adjustable drive source and a multi-layer redundancy strategy, it effectively ensures steering function under fault conditions, making it suitable for steer-by-wire systems in intelligent driving vehicles.
[0006] The technical solution of the present invention: a steer-by-wire system with a variable transmission ratio device, comprising a steering input component, a steering output component, and a steering actuation motor, wherein the steering actuation motor is drivenly connected to the steering output component; further comprising a road feel simulation motor and a variable transmission ratio device drivenly connected between the road feel simulation motor and the steering input component;
[0007] A switchable mechanical transmission link is formed between the steering input component and the steering output component;
[0008] The steering actuator motor is used to output the main steering power and directly drive the steering output component to complete the steering action;
[0009] The road feel simulation motor is used to provide road feel torque feedback to the driver;
[0010] The variable transmission ratio device has an adjustment end for actively adjusting its transmission ratio, and the adjustment end is connected to an adjustment drive source with reverse self-locking characteristics.
[0011] The aforementioned steer-by-wire system with a variable transmission ratio device is a planetary gear type planetary wheel train mechanism.
[0012] The aforementioned steer-by-wire system with a variable transmission ratio device includes a planetary gear train mechanism comprising an input component, an output component, and an adjustment component.
[0013] The input component is driven to the output shaft of the road feel simulation motor, the output component is driven to the steering input component, and the adjustment component constitutes the adjustment end of the variable transmission ratio device and is driven to the adjustment drive source.
[0014] The aforementioned steer-by-wire system with a variable transmission ratio device includes a transmission ratio regulating motor and a worm gear transmission mechanism. The output shaft of the transmission ratio regulating motor is connected to the worm gear of the worm gear transmission mechanism, and the worm wheel of the worm gear transmission mechanism is connected to the regulating end of the variable transmission ratio device. The reverse self-locking characteristic is achieved by the worm gear transmission mechanism.
[0015] The aforementioned steer-by-wire system with a variable gear ratio device further includes a controller and an electromagnetic clutch. The controller is configured to control the adjustment drive source to adjust the gear ratio of the variable gear ratio device according to vehicle operating condition signals, including vehicle speed, steering wheel angle, and wheel angle. When the adjustment drive source fails, due to the reverse self-locking characteristic of the adjustment drive source, the planetary gear train of the variable gear ratio device is locked as a fixed-axis gear train, and the gear ratio is fixed to a constant value. The controller is also configured to control the on / off state of the electromagnetic clutch. The electromagnetic clutch is located between the mechanical transmission link of the steering input component and the steering output component, and is configured to connect the mechanical transmission link of the steering input component and the steering output component in the engaged state.
[0016] The controller adopts a bidirectional interactive closed-loop independent redundant control architecture, including a main electronic control unit, a first electronic control unit, and a second electronic control unit. Under normal operation, the first and second electronic control units continuously transmit operating status signals and execution feedback signals back to the main electronic control unit. When the feedback signal of any control unit is lost, the main electronic control unit activates the redundancy logic, simultaneously sends control commands to the two electronic control units, and synchronously receives execution feedback. The main electronic control unit cross-compares and arbitrates the two feedback signals. If the two feedbacks are consistent, the command execution is confirmed. If the feedbacks are inconsistent, a single point of failure or communication error is determined. After the arbitration identifies the fault channel, the main electronic control unit performs fault isolation, cuts off the control of the faulty electronic control unit, blocks its erroneous output, and switches the system to the preset mechanical assistance mode.
[0017] In the aforementioned steer-by-wire system with a variable gear ratio device, the controller is further configured to perform mode switching control:
[0018] In the first mode, namely the intelligent driving drive-by-wire mode, the electromagnetic clutch is disengaged, the road feel simulation motor is controlled to work in the road feel simulation mode and outputs road feel feedback torque to the steering input component after the speed is adjusted by the variable transmission ratio device, and the steering execution motor is controlled to output the main steering power to directly drive the steering output component to complete the steering action.
[0019] In the second mode, namely the mechanical power-assisted mode, the electromagnetic clutch is engaged, and the road feel simulation motor and / or the steering actuator motor are controlled to work in the power-assisted mode, and the steering power-assisted torque is output in coordination.
[0020] The triggering conditions for switching from intelligent driving drive-by-wire mode to mechanical power-assisted mode include driver active takeover and failure of driving conditions:
[0021] When the vehicle receives active operation commands from the driver, such as turning the steering wheel, pressing the accelerator pedal, pressing the brake pedal, or moving the gear shift lever, or when the steering wheel torque sensor detects continuous torque input, the system recognizes that the driver intends to take over and executes a mode switch.
[0022] When the vehicle does not meet the conditions for intelligent driving operation, including lane line recognition failure, GPS signal loss, or construction sections in the driving route, the system automatically triggers mode switching.
[0023] In the aforementioned steer-by-wire system with a variable gear ratio device, the controller is further configured to perform single-motor fault redundancy control:
[0024] When a fault is detected in the steering actuator motor, in intelligent driving drive-by-wire mode, the mechanical transmission link is engaged and connected. The road feel simulation motor takes into account both road feel simulation and steering power output. The output torque is amplified by increasing the transmission ratio of the variable transmission ratio device, and a steering performance degradation warning is output at the same time. In mechanical power assist mode, the road feel simulation motor is controlled to output steering assist at full power.
[0025] When a fault is detected in the road feel simulation motor, in the intelligent driving drive-by-wire mode, the steering actuator motor is controlled to maintain the main steering power output. At the same time, the road feel status is calculated by algorithm based on vehicle operating parameters, and a road feel failure warning signal is output. In the mechanical power assist mode, the road feel is transmitted in reverse through the complete mechanical transmission link formed by the engagement of the electromagnetic clutch.
[0026] In the aforementioned steer-by-wire system with a variable gear ratio device, the controller is further configured to perform dual-motor fault degradation control:
[0027] When both the road feel simulation motor and the steering actuator motor are detected to be malfunctioning, the electromagnetic clutch is engaged to form a mechanical transmission link connecting the steering input component and the steering output component. The driver's steering operation is transmitted to the steering output component, thus achieving mechanical steering backup.
[0028] In the event of a dual-motor failure, the controller enters a degraded operation mode, maintains the engagement of the electromagnetic clutch, and outputs a fault warning signal to alert the driver that the vehicle is in an emergency steering state.
[0029] The control method for the aforementioned steer-by-wire system with a variable gear ratio device includes the following steps:
[0030] Acquire vehicle operating condition signals, including vehicle speed signal, steering wheel angle signal, and wheel angle signal;
[0031] Based on the vehicle operating condition signal, an adjustment command is output to the adjustment drive source at the adjustment end of the variable transmission ratio device to actively adjust the transmission ratio of the variable transmission ratio device;
[0032] The worm gear transmission mechanism of the regulating drive source has a reverse self-locking characteristic; when the regulating drive source is detected to be faulty, the reverse self-locking characteristic locks the planetary gear train of the variable transmission ratio device into a fixed-axis gear train, and the transmission ratio is maintained at a fixed value.
[0033] The aforementioned control method further includes mode switching and fault redundancy control steps: determining the current driving mode; if it is an intelligent driving drive-by-wire mode, then controlling the electromagnetic clutch to disengage, controlling the road feel simulation motor to operate in road feel simulation mode, outputting road feel torque to the steering input component via a variable transmission ratio device, and simultaneously controlling the steering actuator motor to output main steering power; if it is a mechanical power assist mode, then controlling the electromagnetic clutch to engage, controlling the road feel simulation motor and / or the steering actuator motor to collaboratively output steering assist torque; when a fault is detected in the road feel simulation motor or the steering actuator motor, a degraded control strategy of single motor redundancy switching or dual motor mechanical backup is executed accordingly.
[0034] The trigger determination steps for switching from intelligent driving drive-by-wire mode to mechanical power-assisted mode are as follows:
[0035] Recognize the driver's active operation commands, including steering wheel rotation, accelerator pedal, brake pedal, shift lever action, or detect the continuous torque input of the steering wheel torque sensor. When the torque value exceeds the preset threshold and remains for a set duration, it is determined that the driver has the intention to take over and triggers mode switching.
[0036] Alternatively, it can identify the vehicle's intelligent driving operating conditions and automatically trigger mode switching when scenarios such as lane line recognition failure, GPS signal loss, or road construction sections along the driving route do not meet the driving conditions.
[0037] It also includes a two-way interactive closed-loop independent redundant control step: Under normal operating conditions, the first electronic control unit and the second electronic control unit continuously transmit operating status signals and execution feedback signals back to the main electronic control unit; when the feedback signal of any control unit is lost, the main electronic control unit activates the redundancy logic, and simultaneously issues control commands to the two electronic control units and receives execution feedback synchronously; the main electronic control unit cross-compares and arbitrates the two feedback signals, and if the two feedbacks are consistent, the command execution is confirmed; if the feedbacks are inconsistent, a single point of failure or communication error is determined; after the arbitration identifies the fault channel, fault isolation is immediately performed, the control of the faulty electronic control unit is cut off, its erroneous output is blocked, and the system is switched to the preset mechanical assistance mode.
[0038] Compared with the prior art, the present invention has the following beneficial effects:
[0039] 1. The steer-by-wire system of this invention places a variable transmission ratio device between the road feel simulation motor and the steering input component, which can dynamically adjust the torque and speed characteristics of the road feel feedback to adapt to the road feel feedback requirements at different vehicle speeds. Simultaneously, relying on an adjustable drive source with reverse self-locking characteristics, the transmission ratio can be automatically locked when the adjustable drive source fails, ensuring continuous operation of the road feel transmission link and possessing inherent fault tolerance. The control method of this invention can adjust the transmission ratio in real time according to operating condition signals such as vehicle speed and steering angle. At low speeds, the transmission ratio can be adjusted to optimize the ease of road feel, while at high speeds, the transmission ratio can be adjusted to ensure road feel stability. In redundant scenarios where the steering actuator motor fails, the output torque of the road feel simulation motor can be amplified by increasing the transmission ratio of the variable transmission ratio device, allowing the road feel simulation motor to also handle steering power output, effectively expanding the redundancy capability under single motor failure, and balancing operating condition adaptability and operational reliability.
[0040] 2. This invention enables the switching between intelligent driving steer-by-wire mode and mechanical power assist mode via an electromagnetic clutch. Combined with the functional reuse of the road feel simulation motor and the steering execution motor, it can match different driving needs under normal operating conditions. In the event of a single motor failure, redundant operation is achieved through motor function switching. In the event of a dual motor failure, mechanical steering backup is activated, thus constructing a complete hierarchical redundancy protection system and effectively improving the functional safety level of the steer-by-wire system. Attached Figure Description
[0041] Figure 1 This is an overall structural diagram of the steer-by-wire system with a variable transmission ratio device according to the present invention;
[0042] Figure 2 This is a schematic diagram of the structural principle of the variable transmission ratio device of the present invention;
[0043] Figure 3 This is a schematic diagram of the hierarchical architecture of the control system of the present invention.
[0044] The labels in the attached diagram are as follows: 1. Steering wheel; 2. Steering column; 3. Electromagnetic coil; 4. Armature; 5. Steering tie rod; 6. Steering actuator motor; 7. Road feel simulation motor; 8. Variable transmission ratio device; 9. First electronic control unit; 10. Second electronic control unit; 11. Main electronic control unit; 12. Transmission ratio adjustment motor; 13. Planetary carrier housing worm gear external gear; 14. Output planetary gear; 15. Input planetary gear; 16. Input sun gear; 17. Output spindle; 18. Combined planetary carrier; 19. Input spindle; 20. Connecting rod. Detailed Implementation
[0045] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.
[0046] Example 1: As Figure 1As shown, this embodiment provides a steer-by-wire system with a variable transmission ratio device, including a steering column 2, a steering tie rod 5, a steering actuator motor 6, a steering output component, and a variable transmission ratio device 8. The steering input component is the steering column 2, and the steering output component includes the steering tie rod 5 and a ball screw transmission pair. The steering column 2 is in transmission cooperation with the steering tie rod 5 through the ball screw transmission pair.
[0047] The steering column 2 is fixedly equipped with a steering wheel 1 at its input end, and a torque sensor is installed on the steering column 2 to collect the steering torque signal applied by the driver in real time.
[0048] The electromagnetic clutch is located between the output end of the steering column 2 and the input end of the ball screw drive pair, configured to connect the steering column 2 and the ball screw drive pair in the engaged state. The ball nut of the ball screw drive pair is hinged to the end of the steering tie rod, and the ball screw drive pair converts rotational motion into axial linear motion of the steering tie rod 5. The electromagnetic clutch includes an electromagnetic coil 3 and an armature 4. The electromagnetic coil 3 is fixed to the stationary housing of the clutch, and the armature 4 is coaxially fixed to the input shaft of the ball screw drive pair. The engagement and disengagement of the armature 4 are controlled by the on / off state of the electromagnetic coil 3, thereby controlling the on / off state of the mechanical transmission link between the steering column 2 and the ball screw drive pair. In the engaged state, the rotational torque of the steering column 2 is transmitted to the ball screw drive pair via the electromagnetic clutch.
[0049] The road feel simulation motor 7 is used to provide road feel torque feedback to the driver. The variable transmission ratio device 8 is connected between the road feel simulation motor 7 and the steering column 2. Specifically, the output shaft of the road feel simulation motor 7 is connected to the input end of the variable transmission ratio device 8, and the output end of the variable transmission ratio device 8 is connected to the steering column 2. The torque output by the road feel simulation motor 7 is transmitted to the steering column 2 after being adjusted by the variable transmission ratio device 8, so as to provide road feel feedback to the driver.
[0050] The steering actuator motor 6 is connected to the steering output component for outputting main steering power and directly driving the steering tie rod 5 to complete the steering action.
[0051] The variable transmission ratio device 8 has an adjustment end for actively adjusting its transmission ratio, and the adjustment end is connected to an adjustment drive source with reverse self-locking characteristics. For example... Figure 2 As shown, the variable transmission ratio device 8 is a planetary gear type rotary gear system mechanism, including an input component, an output component, and an adjustment component.
[0052] Specifically, the planetary gear type rotary wheel system mechanism includes an input sun gear 16, an input planetary gear 15, an output planetary gear 14, a combined planetary carrier 18, an input main shaft 19, an output main shaft 17, and a connecting rod 20; wherein the input main shaft 19 serves as an input component and is driven to the output shaft of the road feel simulation motor 7, the output main shaft 17 serves as an output component and is driven to the steering column 2, and the combined planetary carrier 18 serves as an adjustment component, constituting the adjustment end of the variable transmission ratio device 8.
[0053] The adjustment drive source includes a transmission ratio adjusting motor 12 and a worm gear transmission mechanism. The output shaft of the transmission ratio adjusting motor 12 is connected to the worm gear of the worm gear transmission mechanism. The worm gear of the worm gear transmission mechanism is connected to the adjusting end (combined planetary carrier 18) of the variable transmission ratio device 8. The reverse self-locking characteristic is realized by the worm gear transmission mechanism. In this embodiment, the output end of the transmission ratio adjusting motor 12 is a worm, which meshes with the external teeth 13 of the worm gear on the planetary carrier housing to form a worm gear transmission. The worm gear transmission ratio is fixed at 40. When the transmission ratio adjusting motor 12 rotates, it can drive the combined planetary carrier 18 to rotate. By changing the speed of the combined planetary carrier 18, the transmission ratio between the input spindle 19 and the output spindle 17 is adjusted, thereby realizing the dynamic increase and decrease adjustment of the road feel output torque.
[0054] The worm gear transmission mechanism has a reverse self-locking characteristic. When the transmission ratio adjustment motor 12 malfunctions and stops or reverses, the worm gear automatically locks, the planetary carrier 18 remains fixed, and the planetary gear train is converted from a planetary gear train to a fixed-axis gear train. The input spindle 19 and the output spindle 17 continue to transmit power at a fixed transmission ratio to ensure that the road feel transmission link is not interrupted. That is, when the adjustment drive source fails, due to the reverse self-locking characteristic of the adjustment drive source, the planetary gear train of the variable transmission ratio device 8 is locked as a fixed-axis gear train, and the transmission ratio is fixed to a constant value.
[0055] like Figure 2 As shown, the transmission ratio calculation principle of the variable transmission ratio device 8 is as follows:
[0056] Let the speed of the transmission ratio regulating motor 12 be... The worm gear transmission ratio is , Then the rotational speed of the combined planetary carrier 18 is:
[0057] ;
[0058] In this embodiment, the worm gear transmission ratio ;
[0059] Planetary gear trains satisfy the basic speed equation:
[0060] ;
[0061] in, The rotational speed of the sun gear. The rotational speed of the gear ring is... For the planetary carrier rotation speed, This is the ratio of the number of teeth on the sun gear to the number of teeth on the ring gear.
[0062] Since the input spindle 19 transmits power to the sun gear at the input end, let the rotational speed of the input spindle 19 be... The input sun gear speed is also... For the entire planetary gear train, the transmission ratio is calculated using a conversion mechanism method. Ultimately, the speed of the planetary carrier is adjusted by regulating the speed of the transmission ratio regulating motor 12, thereby adjusting the transmission ratio of the variable transmission ratio device 8, which in turn changes the output shaft speed, achieving dynamic adjustment of the road feel output torque and realizing the effect of speed reduction and torque increase. When the transmission ratio regulating motor 12 malfunctions and stops, and the road feel reaction force attempts to drive the regulating end (combined planetary carrier) in the reverse direction, relying on the reverse self-locking characteristic of the worm gear, the worm gear cannot drive the worm to rotate, and the combined planetary carrier is locked and fixed. At this time, the planetary gear train is converted into a fixed-axis gear train, with the input shaft and output shaft transmitting power at a fixed transmission ratio, allowing for continuous output of steering power. The transmission ratio is calculated based on the conversion of the fixed-axis gear train, i.e., the intermediate shaft of the planetary gear is fixed. The calculation results are shown in Table 1.
[0063] Table 1. Changes in Angular Velocity
[0064] ;
[0065] ;
[0066] because Connected to the rack, and the rack rotates at high speed. Depending on the transmission ratio of motor 12, the number of teeth on the sun gear and the planet gears is fixed, so it can be obtained that... ,
[0067] ;
[0068] According to the transformation mechanism method, when adding a post-transformation mechanism to the planetary gear system... This is transformed into a fixed-axis gear train. In a fixed-axis gear train, the rotational speeds of the sun gear, planet gears, and planet carrier satisfy the following relationship:
[0069] ;
[0070] in, , It is the rotational speed of the sun gear relative to the planet carrier. The rotational speed of the sun gear can be obtained by calculating the rotational speed of the planetary gears relative to the planet carrier.
[0071] ;
[0072] in, It is the number of teeth on the sun gear. It is the number of teeth on the planetary gear at the right end. planetary carrier rotation speed
[0073] After merging the formulas, the output shaft speed is
[0074] ;
[0075] The frame speed is adjusted by regulating the speed of the transmission ratio regulating motor 12, and the transmission ratio of the variable transmission ratio device 8 is adjusted to change the speed of the output shaft, thereby achieving dynamic adjustment of the output torque and realizing the effect of speed reduction and torque increase. When the transmission ratio regulating motor 12 fails and reverses, the frame and the transmission ratio regulating motor 12 are locked due to the self-locking effect of the worm gear. At this time, the planetary gear train is converted into a fixed-axis gear train, and the input shaft speed is synchronized with the output shaft. It can still operate normally as long as the road feel simulation motor 7 does not fail.
[0076] The entire gear train adopts a straddle support structure. The input spindle 19 and the output spindle 17 are respectively connected to external power components through couplings. Both shaft ends are supported on the housing by bearings, forming a stable span support structure.
[0077] The steering tie rod 5 works in conjunction with the ball screw transmission pair. The ball screw converts the rotational motion into the axial linear motion of the steering tie rod 5, thereby driving the wheel to deflect. The ball screw structure has high transmission efficiency, small backlash, high control precision, and strong load-bearing capacity, making it suitable for the precise position control requirements of steer-by-wire.
[0078] like Figure 3 As shown, the system's controller adopts a hierarchical control architecture, divided into a decision layer, a control layer, and an execution layer from top to bottom. The decision layer is the vehicle's main electronic control unit 11, responsible for determining the driving mode and issuing commands. The control layer consists of the first electronic control unit 9 and the second electronic control unit 10, responsible for the closed-loop control of each motor. The execution layer comprises each motor, clutch, and sensor. The first electronic control unit 9 is electrically connected to the steering actuator motor 6 and the transmission ratio adjustment motor 12, respectively, and is responsible for controlling the main steering power and transmission ratio adjustment. The second electronic control unit 10 is electrically connected to the road feel simulation motor 7 and the torque sensor, respectively, and is responsible for road feel simulation and power assist torque distribution. The first electronic control unit 9 and the second electronic control unit 10 exchange data through the Controller Area Network (CAN) bus and jointly receive commands from the vehicle's upper-level main controller.
[0079] The system employs a bidirectional interactive closed-loop independent redundant control mechanism: Under normal operating conditions, the first electronic control unit 9 and the second electronic control unit 10 continuously transmit their own operating status signals and execution feedback signals back to the main electronic control unit 11. When the feedback signal from any control unit is lost, the main electronic control unit 11 activates redundancy logic, simultaneously issuing control commands to the first electronic control unit 9 and the second electronic control unit 10, and synchronously receiving execution feedback from both control units. The main electronic control unit 11 cross-compares and arbitrates the two feedback signals: if the two feedback results are consistent, the command is confirmed to be executed normally; if the two feedback results are inconsistent, it is determined that there is a single point of failure or communication error in the system. Once the arbitration identifies the fault channel, the main electronic control unit 11 immediately performs fault isolation operation, cutting off the control of the faulty electronic control unit, blocking its erroneous output, and switching the system to the preset mechanical power steering mode to ensure stable operation of the steering function.
[0080] The controller is configured to adjust the transmission ratio of the drive source and the variable transmission ratio device 8 according to the vehicle operating condition signal. The vehicle operating condition signal includes vehicle speed signal, steering wheel angle signal and wheel angle signal.
[0081] Both the steering input side and the steering execution side are equipped with dual redundant sensor groups, including paired torque sensors, steering wheel 1 angle sensors, rack displacement sensors, and wheel angle sensors. The two sets of sensors synchronously collect data and transmit it to the first electronic control unit 9 and the second electronic control unit 10 respectively, achieving data redundancy backup. Each electronic control unit communicates with each motor controller and sensor using a dual CAN bus communication architecture. The two buses synchronously transmit the same data, and automatic seamless switching occurs in the event of a single bus failure, ensuring communication reliability.
[0082] Based on the aforementioned steer-by-wire system with a variable transmission ratio device, the control method includes: acquiring vehicle operating condition signals, including vehicle speed signals, steering wheel angle signals, and wheel angle signals; outputting adjustment commands to the adjustment drive source of the variable transmission ratio device according to the vehicle operating condition signals, and actively adjusting the transmission ratio of the variable transmission ratio device; wherein, the worm gear transmission mechanism of the adjustment drive source has a reverse self-locking characteristic; when the adjustment drive source is detected to fail, the planetary gear train of the variable transmission ratio device is locked into a fixed-axis gear train by means of the reverse self-locking characteristic, and the transmission ratio is maintained at a fixed value.
[0083] Based on the above control methods, the controller can also output clutch control signals according to driving commands and vehicle operating status, and switch between intelligent driving drive-by-wire mode and mechanical power assist mode by switching the mechanical transmission link on and off through the electromagnetic clutch; it can also monitor the operating status of each module in real time, and when a motor, sensor or communication failure is detected, it triggers the corresponding redundancy strategy control system to degrade operation to maintain basic steering function.
[0084] The specific mode switching control logic is as follows: In intelligent driving drive-by-wire mode, the electromagnetic clutch is disengaged, the road feel simulation motor 7 operates in road feel simulation mode, and after speed adjustment by the variable transmission ratio device 8, it outputs road feel feedback torque to the steering column 2, and controls the steering actuator motor 6 to output main steering power, directly driving the steering tie rod 5 to complete the steering action. The road feel simulation motor 7 adopts a dual closed-loop control strategy of position outer loop and torque inner loop. The second electronic control unit 10 combines signals such as vehicle speed, steering angle, and lateral acceleration to calculate the target road feel torque based on the road feel model, and performs torque compensation in combination with the real-time transmission ratio of the variable transmission ratio device 8. The motor current is adjusted through a PID control algorithm to achieve accurate torque tracking and ensure the authenticity and linearity of the road feel feedback. The steering actuator motor 6 adopts a dual closed-loop control strategy of position and torque. The outer loop is the position loop, which calculates the target rack displacement based on the steering angle command and the vehicle dynamics model; the inner loop is the torque loop, which adjusts the motor output torque through the current loop to ensure that the rack position accurately tracks the target value, while suppressing road disturbances. The transmission ratio regulating motor 12 adopts a transmission ratio closed-loop control strategy. The initial transmission ratio is determined according to the steering mode, and the target transmission ratio is calculated through multi-objective optimization by combining the target steering angle and vehicle stability. The error between the target transmission ratio and the current transmission ratio is input into the PID controller, and the output control quantity is used to adjust the speed of the transmission ratio regulating motor 12, thereby realizing the dynamic adjustment of the transmission ratio.
[0085] In mechanical power steering mode, the electromagnetic clutch is engaged, controlling the road feel simulation motor 7 and / or the steering actuator motor 6 to operate in power steering mode, collaboratively outputting steering assist torque. The controller collects the driver input torque from the steering column 2, and combines it with vehicle speed, steering wheel 1 angle, and torque change rate to calculate the target transmission ratio and assist torque distribution value through fuzzy inference; it controls the road feel simulation motor 7 to output pre-steering assist through the variable transmission ratio device 8, while simultaneously controlling the steering actuator motor 6 to output the main assist torque in the opposite direction to the steering resistance, and adjusting the transmission ratio adjustment motor 12 to rotate forward to increase the transmission ratio of the variable transmission ratio device 8, thereby improving steering ease.
[0086] The trigger logic for switching from intelligent driving drive-by-wire mode to mechanical power-assisted mode falls into two categories:
[0087] One type is triggered by driver active takeover: when the vehicle receives active operation commands from the driver, such as turning the steering wheel, pressing the accelerator pedal, pressing the brake pedal, or moving the gear shift lever, or when the steering wheel torque sensor detects continuous torque input (the torque value exceeds the preset threshold and remains for a set duration), the system recognizes that the driver has the intention to take over, automatically executes mode switching, engages the electromagnetic clutch, and enters the mechanical power assist mode;
[0088] Another type is triggered by failure of driving conditions: when the vehicle senses a scenario that does not meet the operating conditions of intelligent driving, including lane line recognition failure, GPS signal loss, construction sections in the driving path, etc., the system automatically triggers mode switching, disconnects intelligent driving drive-by-wire control, switches to mechanical power assist mode and issues a prompt to the driver.
[0089] The specific fault redundancy control logic is as follows:
[0090] (1) Single motor fault redundancy control
[0091] When a fault is detected in the steering actuator motor 6, the intelligent driving drive-by-wire mode immediately engages the electromagnetic clutch, connecting the mechanical transmission link between the steering column 2 and the steering tie rod 5. The road feel simulation motor 7, which handles both road feel simulation and steering power output, increases the transmission ratio of the variable transmission ratio device 8 by controlling the transmission ratio adjustment motor 12, amplifying the output torque of the road feel simulation motor 7. Power is transmitted to the steering tie rod 5 via the steering column 2, electromagnetic clutch, and ball screw drive pair. The system alerts the driver via the instrument panel and voice prompts indicating a decrease in steering performance. In mechanical power assist mode, the road feel simulation motor 7 is controlled to output full steering assistance, reminding the driver to drive cautiously.
[0092] When a fault is detected in the road feel simulation motor 7, the steering actuator motor 6 is controlled in the intelligent driving drive-by-wire mode to maintain the main steering power output. At the same time, the road feel status is calculated by algorithm based on vehicle operating parameters such as vehicle speed and steering angle, and a road feel failure warning signal is output to prompt the driver to switch to mechanical power assist mode. In mechanical power assist mode, the road reaction force is directly transmitted to the steering wheel 1 in the reverse direction by relying on the complete mechanical transmission link formed by the engagement of the electromagnetic clutch, providing mechanical road feel.
[0093] When the transmission ratio adjustment motor 12 malfunctions and stops, the road feel reaction force on the steering column side cannot drive the worm gear to rotate in the reverse direction. Relying on the reverse self-locking characteristic of the worm gear, the planetary carrier 18 is locked and fixed, and the planetary gear train is converted from a planetary gear train to a fixed-axis gear train. The input spindle 19 and the output spindle 17 continue to transmit power with a fixed transmission ratio. The road feel simulation motor 7 and the steering actuation motor 6 continue to work in their original mode, only losing the ability to dynamically adjust the transmission ratio, and the basic steering function remains unaffected.
[0094] (2) Dual-motor fault degradation control
[0095] When both the road feel simulation motor 7 and the steering actuator motor 6 are detected to be malfunctioning simultaneously, the electromagnetic clutch is engaged, creating a mechanical transmission link between the steering input and output components. The driver's steering input is transmitted to the steering tie rod via the steering column 2, the electromagnetic clutch, and the ball screw drive pair, achieving a pure mechanical steering backup. In the event of a dual-motor malfunction, the controller enters a degraded operation mode, maintaining the engagement of the electromagnetic clutch and outputting a fault warning signal to alert the driver that the vehicle is in an emergency steering state.
[0096] When both the steering actuator motor 6 and the transmission ratio adjustment motor 12 fail, the road feel simulation motor provides steering assistance, transmitting torque through a variable transmission ratio device with a fixed transmission ratio to maintain the power steering function; only when the road feel simulation motor also fails, it switches to pure mechanical steering backup, and issues an emergency alarm in intelligent driving drive-by-wire mode to prompt the driver to stop as soon as possible; when both the road feel simulation motor 7 and the transmission ratio adjustment motor 12 fail, the steering actuator motor 6 independently drives the steering, prompting the driver that the steering feel is abnormal.
[0097] (3) Sensor and communication redundancy control
[0098] The system uses dual redundant sensors to collect data synchronously. When a single sensor fails, the system automatically switches to the data from the other normal sensor and verifies and corrects the data using the vehicle dynamics model. If both sensors fail simultaneously, the system estimates the steering status using related parameters such as motor speed and steering column angle, and prompts the driver to drive cautiously.
[0099] Data is transmitted synchronously via dual CAN buses. If one bus is disconnected or short-circuited, the system automatically switches to the other bus. If both buses fail simultaneously, each motor controller switches to emergency mode and independently controls the system based on local sensor data and preset default parameters to maintain basic steering function while prompting the driver to stop and inspect the vehicle as soon as possible.
[0100] After a fault occurs, the control module records the fault time, location and type, provides graded alerts to the driver through the instrument panel and audible and visual signals, and supports reading the fault log during maintenance.
[0101] In summary, this invention enables dynamic adjustment of the transmission ratio on the road feel feedback side, improving the adaptability to road feel conditions and the ability to amplify fault-based redundant torque. At the same time, relying on a self-locking adjustable drive source and a multi-layer redundancy strategy, it effectively ensures the steering function under fault conditions, making it suitable for steer-by-wire systems in intelligent driving vehicles.
Claims
1. A steer-by-wire system with a variable transmission ratio device, comprising a steering input component, a steering output component, and a steering actuator motor (6), wherein the steering actuator motor (6) is drive-connected to the steering output component; characterized in that: It also includes a road feel simulation motor (7) and a variable transmission ratio device (8) that is connected between the road feel simulation motor (7) and the steering input component. A switchable mechanical transmission link is formed between the steering input component and the steering output component; The steering actuator motor (6) is used to output the main steering power and directly drive the steering output component to complete the steering action; The road feel simulation motor (7) is used to provide road feel torque feedback to the driver; The variable transmission ratio device (8) has an adjustment end for actively adjusting its transmission ratio, and the adjustment end is connected to an adjustment drive source with reverse self-locking characteristics.
2. The steer-by-wire system with a variable transmission ratio device according to claim 1, characterized in that: The variable transmission ratio device (8) is a planetary gear type planetary gear train mechanism.
3. The steer-by-wire system according to claim 2, characterized in that: The planetary gear type planetary gear train mechanism includes an input component, an output component, and an adjustment component; The input component is driven to the output shaft of the road feel simulation motor (7), the output component is driven to the steering input component, and the adjustment component constitutes the adjustment end of the variable transmission ratio device (8) and is driven to the adjustment drive source.
4. The steer-by-wire system according to claim 1, characterized in that: The adjustment drive source includes a transmission ratio adjustment motor (12) and a worm gear transmission mechanism. The output shaft of the transmission ratio adjustment motor (12) is connected to the worm gear transmission mechanism. The worm wheel (13) of the worm gear transmission mechanism is connected to the adjustment end (18) of the variable transmission ratio device (8). The reverse self-locking characteristic is realized by the worm gear transmission mechanism.
5. The steer-by-wire system according to claim 2, characterized in that: It also includes a controller and an electromagnetic clutch. The controller is configured to control the adjustment drive source to adjust the transmission ratio of the variable transmission ratio device (8) according to the vehicle operating condition signal, which includes vehicle speed signal, steering wheel angle signal and wheel angle signal. When the adjustment drive source fails, due to the reverse self-locking characteristic of the adjustment drive source, the planetary gear train of the variable transmission ratio device (8) is locked as a fixed-axis gear train, and the transmission ratio is fixed to a fixed value. The controller is also configured to control the on / off state of the electromagnetic clutch. The electromagnetic clutch is located between the mechanical transmission link of the steering input component and the steering output component, and is configured to connect the mechanical transmission link of the steering input component and the steering output component in the engaged state. The controller adopts a bidirectional interactive closed-loop independent redundant control architecture, including a main electronic control unit (11), a first electronic control unit (9), and a second electronic control unit (10). Under normal operation, the first electronic control unit (9) and the second electronic control unit (10) continuously transmit operating status signals and execution feedback signals back to the main electronic control unit (11). When the transmission signal of any control unit is lost, the main electronic control unit (11) enables redundancy logic, sends control commands to the two electronic control units, and receives execution feedback synchronously. The main electronic control unit (11) cross-compares and arbitrates the two feedback signals. If the two feedback signals are consistent, the command execution is confirmed. If the feedback signals are inconsistent, a single point of failure or communication error is determined. After the arbitration identifies the faulty channel, the main electronic control unit (11) performs fault isolation, cuts off the control of the faulty electronic control unit, shields its erroneous output, and switches the system to the preset mechanical assistance mode.
6. The steer-by-wire system according to claim 5, characterized in that: The controller is also configured to perform mode switching control: In the first mode, i.e. intelligent driving drive-by-wire mode, the electromagnetic clutch is disengaged, the road feel simulation motor (7) is controlled to work in the road feel simulation mode and outputs the road feel feedback torque to the steering input component after being adjusted by the variable transmission ratio device (8), and the steering execution motor (6) is controlled to output the main steering power to directly drive the steering output component to complete the steering action; In the second mode, namely the mechanical power-assisted mode, the electromagnetic clutch is engaged, and the road feel simulation motor (7) and / or the steering actuator motor (6) are controlled to work in the power-assisted mode, and the steering power-assisted torque is output in coordination. The triggering conditions for switching from intelligent driving drive-by-wire mode to mechanical power-assisted mode include driver active takeover and failure of driving conditions: When the vehicle receives active operation commands from the driver, such as turning the steering wheel (1), pressing the accelerator, pressing the brake, or moving the shift lever, or when the steering wheel torque sensor detects continuous torque input, the system recognizes that the driver has the intention to take over and executes the mode switch. When the vehicle does not meet the conditions for intelligent driving operation, including lane line recognition failure, GPS signal loss, or construction sections in the driving route, the system automatically triggers mode switching.
7. The steer-by-wire system according to claim 6, characterized in that: The controller is also configured to perform single-motor fault redundancy control: When a fault is detected in the steering actuator motor (6), the mechanical transmission link is engaged in the intelligent driving drive-by-wire mode to connect the mechanical transmission link. The road feel simulation motor (7) takes into account both road feel simulation and steering power output. The output torque is amplified by increasing the transmission ratio of the variable transmission ratio device (8), and a steering performance reduction warning is output at the same time. In mechanical power steering mode, the road feel simulation motor (7) is controlled to output full power steering assistance; When a fault is detected in the road feel simulation motor (7), the steering actuator motor (6) is controlled in the intelligent driving drive-by-wire mode to maintain the main steering power output. At the same time, the road feel status is calculated by algorithm based on the vehicle operating parameters, and a road feel failure warning signal is output. In the mechanical power assist mode, the road feel is transmitted in reverse by relying on the complete mechanical transmission link formed by the engagement of the electromagnetic clutch.
8. The steer-by-wire system according to claim 7, characterized in that: The controller is also configured to perform dual-motor fault degradation control: When the road feel simulation motor (7) and the steering execution motor (6) are both detected to be malfunctioning, the electromagnetic clutch is controlled to engage, so that the steering input component and the steering output component form a connected mechanical transmission link, and the driver's steering operation is transmitted to the steering output component to realize mechanical steering backup. In the event of a dual-motor failure, the controller enters a degraded operation mode, maintains the engagement of the electromagnetic clutch, and outputs a fault warning signal to alert the driver that the vehicle is in an emergency steering state.
9. A control method for a steer-by-wire system with a variable transmission ratio device, characterized in that, Includes the following steps: Acquire vehicle operating condition signals, including vehicle speed signal, steering wheel angle signal, and wheel angle signal; According to the vehicle operating condition signal, the adjustment command is output to the adjustment drive source of the variable transmission ratio device (8) to actively adjust the transmission ratio of the variable transmission ratio device (8); The regulating drive source has a reverse self-locking characteristic; when the regulating drive source fails, the reverse self-locking characteristic locks the planetary gear train of the variable transmission ratio device (8) into a fixed-axis gear train, and the transmission ratio is maintained at a fixed value.
10. The control method according to claim 9, characterized in that: It also includes mode switching and fault redundancy control steps: determine the current driving mode. If it is the intelligent driving drive-by-wire mode, control the electromagnetic clutch to disengage, control the road feel simulation motor (7) to work in the road feel simulation mode, and output the road feel torque to the steering input component through the transmission ratio device (8). At the same time, control the steering execution motor (6) to output the main steering power. If it is the mechanical power assist mode, control the electromagnetic clutch to engage, and control the road feel simulation motor (7) and / or the steering execution motor (6) to output the steering assist torque in coordination. When a fault is detected in the road feel simulation motor (7) or the steering execution motor (6), a degraded control strategy of single motor redundancy switching or dual motor mechanical backup is executed accordingly. The trigger determination steps for switching from intelligent driving drive-by-wire mode to mechanical power-assisted mode are as follows: Recognize the driver's active operation commands, including steering wheel (1) rotation, accelerator pedal, brake pedal, shift lever action, or detect the continuous torque input of the steering wheel torque sensor. When the torque value exceeds the preset threshold and remains for a set time, it is determined that the driver has the intention to take over and triggers mode switching. Alternatively, it can identify the vehicle's intelligent driving operating conditions and automatically trigger mode switching when scenarios such as lane line recognition failure, GPS signal loss, or road construction sections along the driving route do not meet the driving conditions. It also includes a two-way interactive closed-loop independent redundant control step: Under normal operating conditions, the first electronic control unit (9) and the second electronic control unit (10) continuously transmit operating status signals and execution feedback signals back to the main electronic control unit (11); when the transmission signal of any control unit is lost, the main electronic control unit (11) enables the redundancy logic, and simultaneously sends control commands to the two electronic control units and receives execution feedback synchronously; the main electronic control unit (11) cross-compares and arbitrates the two feedback signals. If the two feedback signals are consistent, the command execution is confirmed. If the feedback signals are inconsistent, it is determined that there is a single point of failure or communication error. After identifying the faulty channel, the arbitration immediately isolates the fault, cuts off the control of the faulty electronic control unit, blocks its erroneous output, and switches the system to the preset mechanical power assist mode.