Drive-by-wire steering control and calibration method for off-highway wide-body mining dump trucks

Abstract

This invention discloses a steer-by-wire control and calibration method for off-highway wide-body mining dump trucks, belonging to the field of steer-by-wire technology for mining dump trucks. Existing systems mostly use electro-hydraulic servo valves, which are sensitive to hydraulic oil cleanliness and lack end-to-end hardware redundancy. The high dust and strong vibration environments of mining areas easily lead to steering performance degradation and sensor failure. This solution provides a system including a main controller, a first drive controller, a second drive controller, a first drive device, a second drive device, a hydraulic steering assist mechanism, a hydraulic actuator, a linear displacement detection device disposed on the hydraulic actuator, and a steering mechanism. The output ends of the first and second drive devices are mechanically connected to the input ends of the hydraulic steering assist mechanism, and the output end of the hydraulic steering assist mechanism is hydraulically connected to the hydraulic actuator. The first drive controller is electrically connected to the first drive device, and the second drive controller is electrically connected to the second drive device.

Description

Technical Field

[0001] This invention belongs to the field of steer-by-wire technology for mining dump trucks. More specifically, this invention relates to a steer-by-wire control and calibration method for off-highway wide-body mining dump trucks. Background Technology

[0002] As off-highway wide-body mining dump trucks gradually adopt autonomous driving technology in mining scenarios, they require steer-by-wire systems to meet remote or automatic steering control needs. Currently, steer-by-wire systems for mining dump trucks have the following problems in three aspects: hardware architecture, control methods, and calibration procedures.

[0003] In terms of hardware architecture, existing steer-by-wire systems generally employ electro-hydraulic servo valves or electro-hydraulic proportional valves as actuators in an electro-hydraulic combined control scheme. Electro-hydraulic servo valves require high hydraulic oil cleanliness, but the high dust concentration and severe equipment vibration in mining environments cause hydraulic oil cleanliness to decline rapidly during use. This decline in cleanliness affects the valve core movement accuracy and response characteristics of the electro-hydraulic servo valve, leading to a degradation in steering function and performance. Furthermore, some solutions use angle sensors to directly measure wheel or steering knuckle angles, but the angle sensors on mining dump trucks are subjected to significant impact loads and continuous vibrations, resulting in a high failure rate for the sensors and their connecting components, and difficulty in guaranteeing signal stability. Regarding redundancy design, existing solutions mostly adopt a primary / backup switching architecture, i.e., setting up a primary steering channel and a backup steering channel, switching to the backup channel when the primary channel fails. This architecture experiences a brief interruption in steering response during the transition from primary channel failure to backup channel takeover, and end-to-end hardware redundancy from the controller to the actuator is not yet widely implemented.

[0004] Regarding control methods, the control strategy under the master-slave switching architecture has the following shortcomings. When a non-serious fault occurs in the master channel, the system usually directly triggers switching or exits the drive-by-wire mode, lacking control means to continue drive-by-wire operation under reduced power conditions. Each drive controller independently reports the status information of the drive unit it controls, but there is a lack of a mechanism to couple the status information of the two independent drive units to generate a unified quantitative overall status level, resulting in unclear redundancy decision-making basis for the upper-level controller. In addition, when the mining dump truck switches between unmanned driving mode and manual driving mode, a reliable and remotely triggered mode switching control logic is required; when two drive units act on the same steering mechanism simultaneously, inconsistent responses caused by manufacturing tolerances or wear differences will lead to angle following errors, affecting steering control accuracy; when the system maintains operation in a reduced power state, if the boundary conditions and fault status of the current steering capability cannot be reported to the unmanned driving system in a timely manner, it will affect the safe adjustment of the driving strategy by the unmanned driving system.

[0005] Regarding calibration procedures, existing zero-point calibration methods are mainly divided into mechanical fine-tuning and dynamic driving calibration. Mechanical fine-tuning requires a fine-tuning mechanism between the steering knuckle and the axle, using mechanical adjustments to change the relative position of the angle sensor to complete calibration. This process is cumbersome and time-consuming, unsuitable for the practical need for rapid calibration when vehicles are off the production line in mining areas. Dynamic driving calibration relies on positioning information and motion data collected during vehicle operation for zero-point calculation. However, in scenarios such as deep mine pits where there are no satellite positioning signals or the signals are blocked, this method struggles to guarantee calibration accuracy. Furthermore, it requires the vehicle to reach a certain straight-line speed and travel a certain distance before the calibration conditions are triggered, meaning calibration cannot be completed immediately after the vehicle is off the production line or parts are replaced. In addition, after long-term operation in mining areas, the hinge clearance of the steering mechanism gradually increases due to wear, and parts deform, causing zero-point drift and requiring recalibration. Existing recalibration methods often require the vehicle to be stopped and operated according to specific procedures, affecting the continuity of production in mining areas. In a scheme where a single hydraulic actuator is equipped with a single linear displacement detection device, there is a lack of means to perform zero-position verification and sensor fault diagnosis by comparing displacement signals from both sides. Summary of the Invention

[0006] To achieve these objectives and other advantages of the present invention, according to one aspect of the present invention, a steer-by-wire system for a non-highway wide-body mining dump truck is provided, comprising a main controller, a first drive controller, a second drive controller, a first drive device, a second drive device, a hydraulic steering assist mechanism, a hydraulic actuator, a linear displacement detection device disposed on the hydraulic actuator, and a steering mechanism. The output end of the first drive device is mechanically connected to the input end of the hydraulic power steering mechanism, the output end of the second drive device is mechanically connected to the input end of the hydraulic power steering mechanism, the output end of the hydraulic power steering mechanism is hydraulically connected to the hydraulic actuator, and the output end of the hydraulic actuator is mechanically connected to the steering mechanism. The first drive controller is electrically connected to the first drive device, and the second drive controller is electrically connected to the second drive device; The linear displacement detection device is used to collect the linear displacement signal of the hydraulic actuator; The main controller is communicatively connected to the first drive controller, the second drive controller, and the linear displacement detection device.

[0007] This invention also provides a control method for a steer-by-wire system based on an off-highway wide-body mining dump truck, comprising the following steps: The main controller receives the linear displacement signal collected by the linear displacement detection device and calculates the current wheel steering angle based on the linear displacement signal; The main controller receives a target steering angle request sent by an external system, and sends motion control signals to the first drive controller and the second drive controller respectively according to the target steering angle request; The first drive controller controls the first drive device to operate according to the received motion control signal and reports the status information of the first drive device to the main controller. The second drive controller controls the second drive device to operate according to the received motion control signal and reports the status information of the second drive device to the main controller. When the status information of the first drive device and the status information of the second drive device both meet the preset serious fault exit conditions, the main controller controls the exit of the steer-by-wire mode; when at least one of the status information of the first drive device and the status information of the second drive device does not meet the preset serious fault exit conditions, the main controller maintains the steer-by-wire mode.

[0008] Preferably, the status information of the first drive device is divided into three levels—warning fault, general fault, and serious fault—by the first drive controller according to the severity of the fault of the first drive device, and the status information of the second drive device is divided into three levels—warning fault, general fault, and serious fault—by the second drive controller according to the severity of the fault of the second drive device. When the status information of the first drive device is a general fault and the status information of the second drive device is a general fault, the main controller maintains the steer-by-wire mode and operates with a preset power reduction limit.

[0009] Preferably, the first drive controller combines the fault level of the first drive device with the fault level of the second drive device to generate an overall fault level, and reports the overall fault level to the main controller. The overall fault level is divided into 0 to 5 levels, where level 0 corresponds to normal, level 1 corresponds to warning, levels 2 and 3 correspond to a power reduction state that can maintain the steer-by-wire mode, and levels 4 and 5 correspond to a shutdown state that cannot maintain the steer-by-wire mode. When the overall fault level is level 4 or 5, the main controller determines that the preset serious fault exit condition is met and controls the exit from the steer-by-wire mode; when the overall fault level is level 3 or below, the main controller maintains the steer-by-wire mode.

[0010] Preferably, the main controller receives a steer-by-wire mode request sent by an external system via the CAN bus. When the steer-by-wire mode request is received, the main controller switches the steering mode from manual driving mode to steer-by-wire mode.

[0011] Preferably, the main controller performs a closed-loop comparison between the calculated current wheel steering angle and the target steering angle request. When the deviation between the current wheel steering angle and the target steering angle request exceeds a preset threshold range, the main controller adjusts the motion control signals sent to the first drive controller and the second drive controller until the deviation falls within the preset threshold range.

[0012] Preferably, when the main controller maintains the steer-by-wire mode, the main controller simultaneously reports the current status information on the ability to maintain the steer-by-wire mode and fault alarm information to the external system.

[0013] This invention also provides a calibration method for a steer-by-wire system based on a wide-body off-highway mining dump truck, comprising the following steps: The main controller acquires pre-stored vehicle chassis structure parameters, including the angle between the steering knuckle arm and the transverse axis at zero turning angle, the length of the hydraulic actuator at zero turning angle, the distance from the intersection of the steering knuckle arm and the front axle to the intersection of the hydraulic actuator and the transverse axis, the distance from the connection point of the hydraulic actuator and the front axle to the centerline of the front axle, the distance from the equivalent intersection of the steering knuckle arm and the front axle to the intersection of the hydraulic actuator and the transverse axis, and the distance from the connection point of the steering knuckle arm and the hydraulic actuator to the intersection of the steering knuckle arm and the wheel. The main controller calculates the theoretical zero-position steering angle based on the vehicle chassis structure parameters and uses the theoretical zero-position steering angle as the initial zero-position calibration value. The main controller acquires the first limit displacement value collected by the linear displacement detection device when the steering mechanism moves to the left limit position, and the second limit displacement value collected by the linear displacement detection device when the steering mechanism moves to the right limit position; The main controller calculates the correction zero-position angle corresponding to the midpoint of the extreme position based on the first limit displacement value and the second limit displacement value, and uses the correction zero-position angle to correct the initial zero-position calibration value to obtain updated zero-position calibration data.

[0014] Preferably, the hydraulic actuator includes a left hydraulic actuator and a right hydraulic actuator, and the linear displacement detection device includes a first linear displacement detection device disposed on the left hydraulic actuator and a second linear displacement detection device disposed on the right hydraulic actuator; the main controller receives a first linear displacement signal collected by the first linear displacement detection device and a second linear displacement signal collected by the second linear displacement detection device, and performs zero-position verification and angle diagnosis by comparing the first linear displacement signal and the second linear displacement signal.

[0015] Preferably, during vehicle operation in the mining area, the main controller receives path angle information sent by the unmanned driving path planning system, and corrects the zero-position calibration data based on the deviation between the path angle information and the linear displacement signal collected by the linear displacement detection device.

[0016] The present invention offers at least the following advantages: The steer-by-wire control and calibration method for off-highway wide-body mining dump trucks described herein employs dual drive units mechanically connected to the hydraulic power steering mechanism, each controlled by its own independent drive controller. Simultaneously, a linear displacement detection device is installed on the hydraulic actuator to collect linear displacement signals. This eliminates the reliance on electro-hydraulic servo valves as steer-by-wire actuators, thus eliminating the direct impact of hydraulic oil cleanliness on steer-by-wire functionality and reducing the risk of steering performance degradation due to hydraulic oil contamination in high-dust mining environments. The linear displacement detection device, located inside or outside the hydraulic actuator, reduces the impact load and vibration amplitude compared to angle sensors directly mounted on the wheels or steering knuckles, improving signal stability. The independent configuration of the dual drive controllers and dual drive units achieves end-to-end hardware redundancy from controller to actuator, preventing system-wide failure due to a single point of failure.

[0017] The main controller makes a comprehensive redundancy judgment based on the independent status information of the two drive devices. When the status of at least one drive device does not reach the preset serious fault exit condition, the steer-by-wire mode is maintained, which avoids the switching delay and brief response interruption under the main-standby switching architecture and improves the continuity of the steering control process.

[0018] The status information of the drive unit is divided into three levels: warning fault, general fault and serious fault. When both drive units are in general fault, the system continues to operate with a preset power reduction limit. This allows the steering system to continue to provide steer-by-wire function when a non-serious fault occurs, without having to immediately disengage or switch modes, thus reducing unnecessary mode exits caused by non-serious faults.

[0019] The two drive controllers combine the fault levels of their respective drive devices to generate an overall fault level, which is then divided into levels 0 to 5. Levels 2 and 3 correspond to the power reduction state that can maintain the steer-by-wire mode, while levels 4 and 5 correspond to the shutdown state that cannot maintain the steer-by-wire mode. This provides the main controller with a unified quantitative state basis after coupling processing, thereby improving the clarity and systematic nature of the redundancy exit decision.

[0020] The main controller receives steer-by-wire mode requests from external systems via the CAN bus. Upon receiving the request, it switches the steering mode from manual driving mode to steer-by-wire mode, providing a standardized mode switching control logic that can be remotely triggered for the autonomous driving system.

[0021] The main controller performs a closed-loop comparison between the calculated current wheel steering angle and the target steering angle request. When the deviation exceeds the preset threshold range, it adjusts the motion control signal so that the angle following error caused by the inconsistent response when the two drive devices drive the same hydraulic power steering mechanism at the same time can be dynamically adjusted and compensated.

[0022] When the main controller maintains the steer-by-wire mode, it simultaneously reports the current status information and fault warning information of the steer-by-wire mode to the external system, so that the autonomous driving system can know the boundary conditions of the current steering capability and provide a basis for adjusting the driving strategy.

[0023] By obtaining the vehicle chassis structural parameters to calculate the theoretical zero-position steering angle as the initial zero-position calibration value, and then obtaining the limit displacement value collected by the linear displacement detection device when the steering mechanism moves to the left and right limit positions to calculate and correct the zero-position angle, the repeated adjustment operation of the mechanical fine-tuning mechanism is eliminated, and the calibration efficiency when the vehicle is off the production line is improved. At the same time, this calibration process does not rely on satellite positioning signals or vehicle driving data, and can be completed in scenarios without positioning signals, such as deep pits in mines.

[0024] The hydraulic actuators are configured as a left-side hydraulic actuator and a right-side hydraulic actuator, and a first linear displacement detection device and a second linear displacement detection device are respectively configured. By comparing the linear displacement signals collected from both sides, zero-position verification and angle diagnosis are performed, so that single-side sensor failure or zero-position drift can be identified through the difference between the two-side signals.

[0025] During operation in the mining area, the system receives path angle information from the unmanned driving path planning system. Based on the deviation between the path angle information and the linear displacement signal collected by the linear displacement detection device, the zero-position calibration data is corrected. This allows zero-position drift caused by wear of parts and increased hinge gaps to be dynamically corrected during operation without the need for the vehicle to stop for recalibration.

[0026] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0027] Figure 1 This is a frame diagram of the steer-by-wire system for the off-highway wide-body mining dump truck described in this invention.

[0028] Figure 2 This is a flowchart of the control method for the steer-by-wire system of a non-highway wide-body mining dump truck according to the present invention.

[0029] Figure 3This is a flowchart of the calibration method for the steer-by-wire system of a non-highway wide-body mining dump truck according to the present invention.

[0030] Figure 4 This is a framework diagram of the system in Comparative Example 1.

[0031] Figure 5 This is a framework diagram of the system in Comparative Example 2. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can implement it based on the description.

[0033] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0034] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation plan are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0035] The present invention provides a steer-by-wire system for a non-highway wide-body mining dump truck, comprising a main controller, a first drive controller, a second drive controller, a first drive device, a second drive device, a hydraulic steering assist mechanism, a hydraulic actuator, a linear displacement detection device disposed on the hydraulic actuator, and a steering mechanism; The output end of the first drive device is mechanically connected to the input end of the hydraulic power steering mechanism, the output end of the second drive device is mechanically connected to the input end of the hydraulic power steering mechanism, the output end of the hydraulic power steering mechanism is hydraulically connected to the hydraulic actuator, and the output end of the hydraulic actuator is mechanically connected to the steering mechanism. The first drive controller is electrically connected to the first drive device, and the second drive controller is electrically connected to the second drive device; The linear displacement detection device is used to collect the linear displacement signal of the hydraulic actuator; The main controller is communicatively connected to the first drive controller, the second drive controller, and the linear displacement detection device.

[0036] In this technical solution, the steer-by-wire system of the off-highway wide-body mining dump truck consists of a vehicle control unit (VCU), a first electronic control unit (ECU1), a second electronic control unit (ECU2), a first steering motor, a second steering motor, a hydraulic power steering system, a three-position four-way solenoid directional valve, a double-acting hydraulic cylinder, a magnetostrictive displacement sensor, and a steering trapezoidal mechanism. The VCU and ECU1 are connected via a first CAN bus, and the VCU and ECU2 are connected via a second CAN bus, with the CAN communication rate set to 500kbps. The output shaft of the first steering motor is connected to the input end of the hydraulic power steering system via a first flexible coupling, and the output shaft of the second steering motor is connected to the input end of the same hydraulic power steering system via a second flexible coupling. The two motors can drive the power steering system independently or jointly. The outlet of the hydraulic power steering system is connected to the inlet of the three-position four-way solenoid directional valve via a hydraulic pipeline. The two working ports of the directional valve are respectively connected to the rod chamber and rodless chamber of the hydraulic cylinder via pipelines. The directional control valve integrates a relief valve, whose opening pressure is set to 20 MPa to limit the maximum working oil pressure. ECU1 is electrically connected to the first steering motor via a three-phase cable and a resolver signal line, and ECU2 is electrically connected to the second steering motor in the same way. The waveguide of the magnetostrictive displacement sensor is mounted on the inner wall of the hydraulic cylinder, the position magnetic ring is fixed to the piston, and the sensor's signal cable is connected to the analog acquisition port of the VCU. The piston rod end of the hydraulic cylinder is connected to one end of the steering knuckle arm via a ball joint, and the other end of the steering knuckle arm is mounted on the front axle via the steering kingpin. The VCU exchanges data with ECU1, ECU2, and the displacement sensor via a CAN bus. The embedded processor inside the VCU runs angle calculation and redundancy judgment programs.

[0037] The system operates as follows: as the hydraulic cylinder piston rod extends and retracts under hydraulic pressure, the magnetic ring of the displacement sensor moves synchronously with the piston. The sensor converts the magnetic ring position into an analog voltage signal ranging from 0.5V to 4.5V, corresponding to the real-time linear displacement of the hydraulic cylinder. The VCU acquires this displacement signal at 10-millisecond intervals and reads the vehicle chassis geometric parameters pre-stored in memory, including six parameters such as the angle between the steering knuckle arm and the axle transverse axis at zero steering angle, the cylinder mounting length, and the distance from the steering knuckle arm hinge point to the cylinder fixing point. Based on the cosine theorem and the steering trapezoidal geometry, the VCU calculates the current wheel steering angle in real time from the cylinder displacement. The external autonomous driving system sends a target steering angle request to the VCU via the CAN bus, with this request message updated every 20 milliseconds. The VCU converts the target angle into the position increments that the two steering motors should reach and generates a first motion control signal and a second motion control signal, respectively, which are then sent to ECU1 and ECU2 via the CAN bus. ECU1 controls the first steering motor to rotate according to a signal, and ECU2 controls the second steering motor to rotate according to a signal. The two motors drive the hydraulic power steering unit together or independently, causing the hydraulic cylinder to extend and retract, thereby actuating the steering knuckle arm to turn the wheels. During this process, ECU1 and ECU2 each collect the three-phase current, rotor position, and speed of their respective motors in real time, calculate the actual output torque, and report the torque, speed, and number of revolutions relative to the mechanical zero position as status information to the VCU via the CAN bus every 20 milliseconds.

[0038] The system's independent configuration of dual motors and dual ECUs completely eliminates the need for electro-hydraulic servo valves. Hydraulic oil serves only as the transmission medium; a decrease in oil cleanliness only affects hydraulic efficiency and does not cause valve core jamming or control failure. The linear displacement sensor is encapsulated inside the cylinder, receiving double buffering from the cylinder body and hydraulic fluid, significantly reducing the impact of mining truck travel shocks on the measuring element. Its signal stability is superior to angle sensors directly mounted on the steering knuckle. The parallel architecture of dual ECUs and dual motors creates full hardware redundancy from controller to actuator. A single-path failure will not cause the system to immediately exit drive-by-wire mode, providing the autonomous driving system with decision-making and takeover time.

[0039] This invention also provides a control method for a steer-by-wire system based on an off-highway wide-body mining dump truck, comprising the following steps: The main controller receives the linear displacement signal collected by the linear displacement detection device and calculates the current wheel steering angle based on the linear displacement signal; The main controller receives a target steering angle request sent by an external system, and sends motion control signals to the first drive controller and the second drive controller respectively according to the target steering angle request; The first drive controller controls the first drive device to operate according to the received motion control signal and reports the status information of the first drive device to the main controller. The second drive controller controls the second drive device to operate according to the received motion control signal and reports the status information of the second drive device to the main controller. When the status information of the first drive device and the status information of the second drive device both meet the preset serious fault exit conditions, the main controller controls the exit of the steer-by-wire mode; when at least one of the status information of the first drive device and the status information of the second drive device does not meet the preset serious fault exit conditions, the main controller maintains the steer-by-wire mode.

[0040] In this technical solution, the specific implementation process of the control method in the above system is as follows. Within each 10-millisecond control cycle, the VCU first reads the current linear displacement value of the hydraulic cylinder sent by the displacement sensor via the CAN bus, and calculates the current wheel angle by combining it with the stored geometric parameters. Then, the VCU checks whether there is a target steering angle request from the autonomous driving system in the CAN receive buffer. If such a request exists, it calculates the difference between the request and the current wheel angle, and generates a target speed command through the position loop proportional-integral regulator based on the difference. This command is then written as a motion control signal into the CAN messages sent to ECU1 and ECU2 respectively. After receiving the motion control signal, ECU1 controls the first steering motor to run at the target speed through its internal current loop and speed loop, and ensures that the motor outputs sufficient torque to overcome steering resistance; ECU2 controls the second steering motor in the same way. Both motors jointly apply torque to the input shaft of the hydraulic power steering unit, which, after hydraulic amplification, pushes the hydraulic cylinder piston rod to move. Every 20 milliseconds, ECU1 and ECU2 respectively transmit their respective motor status information back to the VCU, including actual torque, current speed, and the cumulative number of revolutions of the rotor relative to the power-on zero position.

[0041] During operation, the VCU continuously monitors the first status information reported by ECU1 and the second status information reported by ECU2. When the VCU detects that both status information meet the preset critical fault exit conditions—that is, both motors experience winding short circuits, open circuits, rotor stalling, or controller power stage damage, resulting in a failure to output torque—the VCU immediately disables the steer-by-wire mode and switches to manual driving mode, while illuminating the steering fault warning light in the driver's cab. Conversely, if at least one motor in the first or second status information does not exhibit the aforementioned critical fault (e.g., only one motor experiences a critical fault while the other can still output torque normally), the VCU maintains the steer-by-wire mode, and the normal motor continues to drive the hydraulic power steering to complete steering. Simultaneously, the VCU reports the current degraded operation status and available torque limit to the autonomous driving system via the CAN bus. This redundant exit logic ensures that even if one motor or ECU completely fails, the steering system can still maintain controlled steering capability, avoiding sudden steering changes or brief loss of control due to switching transients in the primary / backup switchover scheme.

[0042] In another technical solution, the status information of the first drive device is divided into three levels—warning fault, general fault, and serious fault—by the first drive controller according to the severity of the fault of the first drive device, and the status information of the second drive device is divided into three levels—warning fault, general fault, and serious fault—by the second drive controller according to the severity of the fault of the second drive device. When the status information of the first drive device is a general fault and the status information of the second drive device is a general fault, the main controller maintains the steer-by-wire mode and operates with a preset power reduction limit.

[0043] In this technical solution, ECU1 and ECU2 each run a fault diagnosis program, classifying the fault status of the driven motor into three levels. Level 1 is a warning fault, including situations such as motor winding temperature exceeding 120℃ but not reaching the 150℃ protection threshold, and CAN communication experiencing self-recovering frame drops. Level 2 is a general fault, including situations where the insulation resistance of a motor phase winding drops to between 10 kΩ and 100 kΩ, and the DC bus voltage drops to 70% to 85% of the rated value due to power fluctuations, allowing for short-term continued operation. Level 3 is a serious fault, including situations where motor phase-to-phase short circuits, winding open circuits, rotor mechanical seizure, and drive bridge arm power device breakdown prevent safe operation. When ECU1 diagnoses a general fault in the first motor and ECU2 diagnoses a general fault in the second motor, ECU1 and ECU2 report this level information to the VCU. The VCU determines that both drive units are in an intermediate state where reduced power operation is permissible, and therefore modifies the maximum permissible torque parameter in the motion control signals sent to both ECUs to 50% of the rated torque, but does not exit the drive-by-wire mode. At this point, the steering system can still provide steering assistance under light loads. If the vehicle is currently in a low-speed, unloaded state, it can continue to complete the unmanned transportation task. If the failure of any motor subsequently escalates from a general fault to a serious fault, the VCU will immediately perform a redundancy exit judgment after receiving the updated status from the corresponding ECU.

[0044] In another technical solution, the first drive controller combines the fault level of the first drive device with the fault level of the second drive device to generate an overall fault level, and reports the overall fault level to the main controller. The overall fault level is divided into 0 to 5 levels, where level 0 corresponds to normal, level 1 corresponds to warning, levels 2 and 3 correspond to the power reduction state that can maintain the steer-by-wire mode, and levels 4 and 5 correspond to the shutdown state that cannot maintain the steer-by-wire mode. When the overall fault level is level 4 or 5, the main controller determines that the preset serious fault exit condition is met and controls the exit from the steer-by-wire mode; when the overall fault level is level 3 or below, the main controller maintains the steer-by-wire mode.

[0045] In this technical solution, the specific implementation of the overall fault level combination method is as follows: After each fault diagnosis, ECU1 encodes its own fault level into a 2-bit binary value, where "00" represents no fault or warning, "01" represents a general fault, and "10" represents a serious fault; ECU2 also generates its own fault level code. ECU1 reads the fault code of ECU2 through the CAN bus and combines it with its own code according to a preset truth table to generate an overall fault level of 0 to 5. The truth table rules are as follows: when both motors have no faults or only a warning fault exists, the overall level is 0; when any motor has a general fault but no serious fault, if the number of faulty motors is 1, the overall level is 2 or 3; if both motors have general faults, it is defined as level 2; when only one motor has a serious fault, the overall level is 4; when both motors have serious faults, the overall level is 5. ECU1 puts the calculated overall fault level into a CAN message and sends it to VCU. When the VCU determines the overall level to be 4 or 5, it unconditionally exits the steer-by-wire mode; when the overall level is 0 to 3, it maintains the steer-by-wire mode and adjusts the output range of available torque according to the level value, with levels 2 and 3 corresponding to reduced power operation. This centralized combination method means that the redundancy exit decision no longer relies on the VCU comparing scattered fault signals one by one, but is based on a clear coupling level criterion, reducing the probability of misjudgment.

[0046] In another technical solution, the main controller receives a steer-by-wire mode request sent by an external system via a CAN bus. When the steer-by-wire mode request is received, the main controller switches the steering mode from manual driving mode to steer-by-wire mode.

[0047] In this technical solution, the VCU's CAN communication module is configured to listen for mode control messages from the autonomous driving system. These messages contain an 8-bit mode request field. When this field changes from 0x00 to 0x01, it indicates a request to switch from manual driving mode to steer-by-wire mode. Upon receiving this request, the VCU first confirms that the hydraulic power steering is in a neutral, stationary state using a displacement sensor. Then, it checks the motor status reported by ECU1 and ECU2 to confirm that at least one motor is free of serious faults. After confirmation, the VCU sends a disengagement command to the electromagnetic clutch at the steering wheel, disengaging the mechanical transmission chain between the steering wheel and the hydraulic power steering input. Simultaneously, it sets the steering control authority flag within the VCU to steer-by-wire enabled. At this point, the steering wheel is in a free-rotating state, and steering is fully executed by ECU1 and ECU2 according to the VCU's commands. The entire switching process, from receiving the request to completing the control handover, is controlled within 300 milliseconds. When the mode request field changes from 0x01 to 0x00, the VCU executes the reverse process: first, it reduces the motor output so that the speed difference between the two sides of the electromagnetic clutch at the steering wheel is less than the preset value, and then it engages the clutch to return steering control to the human.

[0048] In another technical solution, the main controller performs a closed-loop comparison between the calculated current wheel steering angle and the target steering angle request. When the deviation between the current wheel steering angle and the target steering angle request exceeds a preset threshold range, the main controller adjusts the motion control signals sent to the first drive controller and the second drive controller until the deviation falls within the preset threshold range.

[0049] In this technical solution, within each 10-millisecond control cycle, the VCU uses the calculated current wheel steering angle as the feedback value and the most recently updated and filtered target steering angle request as the setpoint, calculating the difference between the two. If the absolute value of the difference is greater than 0.5 degrees, the position loop proportional-integral regulator is activated. The proportional coefficient and integral time constant are divided into high-adhesion mode and low-adhesion mode according to the different road surface adhesion characteristics of the vehicle. High-adhesion parameters are selected on dry and hard road surfaces, and low-adhesion parameters are selected on soft and muddy road surfaces to avoid overshoot oscillation. The regulator calculates the speed compensation value, adds it to the target speed of the original motion control signal, and corrects the commands sent to ECU1 and ECU2, causing the two motors to accelerate or decelerate to reduce the angle deviation. When the absolute value of the difference decreases back to within 0.5 degrees, the regulator enters the integral holding state and stops over-adjustment. This closed-loop mechanism compensates for the synchronization error caused by inconsistent cogging force of the two motors or the difference in leakage between the left and right chambers of the hydraulic cylinder, so that the actual steering angle accurately follows the target value.

[0050] To verify the actual effect of the aforementioned closed-loop control algorithm, a hardware-in-the-loop simulation bench was built based on this system for comparative testing. The test conditions were set to simulate a complex fault condition in a mining area: the left drive channel (first drive unit) was set with a 5% torque response delay, and the maximum available torque was reduced to 80% of the rated value. Simultaneously, the hydraulic actuator (cylinder) simulated internal leakage, introducing a periodic displacement deviation of 2mm at the piston position; the right drive channel (second drive unit) maintained normal operating parameters. The target steering angle request was set to a sinusoidal signal with an amplitude of 15° and a period of 4 seconds.

[0051] Under the same fault injection conditions described above, steering angle following data were recorded when the closed-loop control algorithm was off and on, respectively. The sampling period was 10 milliseconds, and five complete sine cycles were recorded continuously. The root mean square value of the angle following error and the maximum transient deviation were calculated. The results are shown in Table 1 below: Table 1 Test metrics Closed-loop regulation off (open-loop mode) Closed-loop regulation activated (in this solution) Root mean square value of angle following error (°) 1.08 0.24 Maximum transient angular deviation (°) 2.51 0.68 Adjustment time (seconds) for the deviation to recover to within the 0.5° threshold. Continuous deviation ≤0.35 Experimental data shows that under simulated combined fault conditions, the system exhibits a significant and persistent angle deviation without closed-loop adjustment, with a maximum transient deviation of 2.51°, failing to meet the steering accuracy requirements of unmanned driving in mining areas. After activating the closed-loop adjustment algorithm of this scheme, the root mean square value of the angle following error decreased from 1.08° to 0.24°, a reduction of approximately 78%; the maximum transient deviation decreased from 2.51° to 0.68°, and the deviation could be adjusted to the preset threshold range of 0.5° within 0.35 seconds. These results verify that the position loop proportional-integral regulator can effectively compensate for the angle following error under adverse conditions such as inconsistent characteristics of the dual drive channels and internal leakage in the hydraulic system, ensuring that the steering system can still meet the accuracy requirements of the target steering angle request even under reduced power operation.

[0052] In another technical solution, when the main controller maintains the steer-by-wire mode, the main controller simultaneously reports the current status information of maintaining the steer-by-wire mode and fault alarm information to the external system.

[0053] In the above technical solution, when the VCU maintains the steer-by-wire mode but detects a non-serious fault in at least one drive unit, the VCU will construct a dedicated status reporting CAN message. This message is sent every 100 milliseconds and includes information such as the steer-by-wire mode validity flag, the current percentage of the maximum available steering torque, the overall fault level, and the fault source side (left motor or right motor). After receiving this message, the autonomous driving control system assesses whether the vehicle has the ability to complete the predetermined route steering based on the percentage of available torque. If the available torque is lower than the minimum value required for the preset route, the planning system will reduce the driving speed or switch to an emergency stopping path. The fault warning information in the message is also used for fault recording and maintenance reminders by the on-board diagnostic tool. When the overall fault level reaches level 3 or above, the VCU will also illuminate a yellow warning light on the dashboard to remind staff to perform maintenance after the vehicle is parked.

[0054] This invention also provides a calibration method for a steer-by-wire system based on a wide-body off-highway mining dump truck, comprising the following steps: The main controller acquires pre-stored vehicle chassis structure parameters, including the angle between the steering knuckle arm and the transverse axis at zero turning angle, the length of the hydraulic actuator at zero turning angle, the distance from the intersection of the steering knuckle arm and the front axle to the intersection of the hydraulic actuator and the transverse axis, the distance from the connection point of the hydraulic actuator and the front axle to the centerline of the front axle, the distance from the equivalent intersection of the steering knuckle arm and the front axle to the intersection of the hydraulic actuator and the transverse axis, and the distance from the connection point of the steering knuckle arm and the hydraulic actuator to the intersection of the steering knuckle arm and the wheel. The main controller calculates the theoretical zero-position steering angle based on the vehicle chassis structure parameters and uses the theoretical zero-position steering angle as the initial zero-position calibration value. The main controller acquires the first limit displacement value collected by the linear displacement detection device when the steering mechanism moves to the left limit position, and the second limit displacement value collected by the linear displacement detection device when the steering mechanism moves to the right limit position; The main controller calculates the correction zero-position angle corresponding to the midpoint of the extreme position based on the first limit displacement value and the second limit displacement value, and uses the correction zero-position angle to correct the initial zero-position calibration value to obtain updated zero-position calibration data.

[0055] In this technical solution, when the vehicle rolls off the production line for the first time, the operator uses diagnostic tools to write the vehicle chassis structure parameters into the VCU's EEPROM. These parameters are directly obtained from the vehicle design drawings, including the angle β between the steering knuckle arm and the transverse axis at zero steering angle, the hydraulic cylinder length W at zero steering angle, the distance a from the intersection of the steering knuckle arm and the front axle to the intersection of the hydraulic cylinder and the transverse axis, the distance b from the connection point of the hydraulic cylinder and the front axle to the centerline of the front axle, and the distance r from the connection point of the steering knuckle arm and the cylinder to the intersection of the steering knuckle arm and the wheel.

[0056] The geometric calibration method used in this scheme has the following mathematical model establishment process. For clarity, taking a single-sided steering mechanism as an example, the key hinge point of the steering trapezoidal mechanism is simplified to a planar triangle.

[0057] Take the front axle axis as the lateral reference axis. The steering knuckle arm rotates around the steering kingpin, and the intersection of the kingpin and the front axle is denoted as point O. One end of the hydraulic actuator (cylinder) is hinged to a fixed support on the front axle transverse axis, and the hinge point is denoted as point A; the other end is hinged to the steering knuckle arm, and the hinge point is denoted as point B.

[0058] In the simplified geometric model, the three sides of triangle OAB correspond to: side OA is the distance from point O to point A, the value of which has been determined in the design stage and is denoted as a′; side OB is the distance from point O to point B, which is the effective length of the steering knuckle arm and is denoted as r; side AB is the distance from point A to point B, which is equal to the total length of the hydraulic actuator, obtained by adding the fixed initial length W to the real-time displacement ΔW measured by the linear displacement detection device, i.e., (W+ΔW).

[0059] In triangle OAB, the angle between sides OA and OB is the total deflection angle of the steering knuckle arm in its current state. This total deflection angle consists of two parts: the initial angle β between the steering knuckle arm and the lateral axis (i.e., side OA) when the wheel is at the zero-turn position, and the current steering angle α of the wheel. Therefore, the angle is (α+β).

[0060] Applying the Law of Cosines for any triangle to the sides and included angle of triangle OAB establishes a mathematical relationship between the three side lengths and the included angle (α+β). The standard mathematical form of the Law of Cosines is: For any triangle, the square of any side length is equal to the sum of the squares of the other two sides minus twice the product of the cosine of those two sides and the included angle. Substituting the corresponding quantities in this scheme, we get (W+ΔW). 2 As the square of the side opposite the included angle, we have: (W+ΔW) 2 = a′ 2 + r 2 -2a′·r·cos(α+β); The above equation is the core equation representing the geometric relationship between the steering angle and the cylinder displacement in this scheme. Based on this, the current wheel steering angle α can be solved through algebraic transformations, yielding the angle calculation formula: α=arccos[(a′ 2 + r 2 -(W+ΔW) 2 ) / (2a′·r)]-β; The above derivation strictly follows the cosine theorem and the actual geometric constraints of the vehicle chassis, and the dimensions are unified to the unit of length, providing a clear mathematical basis for subsequent initial zero-position calculation, limit position correction and online dynamic correction.

[0061] During VCU power-on initialization, the geometric calibration subroutine is called. First, the distance a′ from the intersection of the equivalent steering knuckle arm and the front axle to the intersection of the hydraulic cylinder and the transverse axis is calculated. The formula is: a′=(a 2 +b 2 ) 1 / 2 ; Then, based on the law of cosines, the geometric relationship between the cylinder length and the steering angle is established. The real-time length of the cylinder is W + ΔW, where ΔW is the displacement value collected in real time by the cylinder displacement sensor. The basic equation is: (W+ΔW) 2 = a′ 2 + r 2 -2a′·r·cos(α+β); Based on this, the VCU derives the formula for calculating the current wheel steering angle α: α=arccos[(a′ 2 + r 2 -(W+ΔW) 2 ) / (2a′·r)]-β; When ΔW=0, the α value obtained by substituting it into the above formula is the theoretical zero-position turning angle. The VCU stores this value as the initial zero-position calibration value in the running memory.

[0062] Subsequently, on a level surface, test personnel remotely controlled the steering system to turn the wheels to the left to their mechanical limit position. The VCU recorded the first limit displacement value ΔW1 collected by the displacement sensor at this point. Then, the wheels were turned to the right to their mechanical limit position, and the second limit displacement value ΔW2 was recorded. The VCU calculated the arithmetic mean ΔW1 and ΔW2, ΔW2 = ΔW1. m =(ΔW1+ΔW2) / 2, let ΔW m Substituting into the angle calculation formula above, the zero-point correction angle corresponding to the midpoint of the extreme position is obtained. This zero-point correction angle is then used to overwrite the original initial calibration value, completing the offline zero-point calibration. The entire process requires no manual measurement of the wheel deflection angle, nor the use of external positioning equipment such as GPS or total stations. A specific numerical example illustrates the above calibration calculation process. Taking a certain type of 60-ton off-highway wide-body mining dump truck as an example, the design parameters of its front axle steering mechanism are as follows: At zero steering angle, the angle between the steering knuckle arm and the transverse axis is β = 8.5°. Initial length of the hydraulic actuator at zero rotation angle: W = 820 mm; Distance from the intersection of the steering knuckle arm and the front axle to the intersection of the hydraulic actuator and the transverse shaft: a = 480 mm; Distance from the hydraulic actuator connection point to the front axle centerline: b = 185 mm; Distance from the connection point between the steering knuckle arm and the hydraulic actuator to the intersection point between the steering knuckle arm and the wheel (equivalent steering knuckle arm length): r = 310 mm; Step 1: Calculate the equivalent distance a′ Substituting the parameters a=480 mm and b=185 mm into the formula a′=(a 2 +b 2 ) 1 / 2 : a′=(480 2 +185 2 ) 1 / 2 ; a′=(230400+34225) 1 / 2 ; a′=(264625) 1 / 2 ; a′≈514.42 mm; Step 2: Calculate the theoretical zero-position steering angle (initial zero-position calibration value) When ΔW=0, the total length of the hydraulic actuator is W=820 mm. Substituting W=820 mm, a′=514.42 mm, r=310 mm, and β=8.5° into the angle calculation formula: α0=arccos[(a′ 2 + r 2 -W 2) / (2a′·r)]-β; First, calculate the numerator and denominator of the cosine function: a′ 2 =514.42 2 ≈264625 mm 2 ; r 2 =310 2 =96100 mm 2 ; W 2 =820 2 =672400 mm 2 ; Mole = 264625 + 96100 - 672400 = -311675 mm 2 ; Denominator=2×514.42×310=318940.4 mm 2 ; The cosine value is approximately -311675 / 318940.4 ≈ -0.97722. arccos(-0.97722)≈167.75°; α0=167.75°-8.5°=159.25°; This value indicates that when the cylinder is at its initial length W, the current angle between the steering knuckle arm and the transverse axis is 167.75°. After subtracting the initial angle of 8.5°, the actual wheel deflection angle is 159.25°. This value may deviate from the theoretical midpoint of the steering mechanism, so it is only stored as the initial zero-position calibration value.

[0063] Step 3: Collect displacement values ​​at the left and right extreme positions On a flat surface, the steering system is remotely controlled to turn the wheels to the left to their mechanical limit position, and the displacement sensor collects the first limit displacement value: ΔW1 = +105.8 mm (cylinder extension); Then, the wheel is turned to the right to its mechanical limit position, and the second limit displacement value is collected: ΔW2 = -96.3 mm (cylinder retraction); Step 4: Calculate the zero-position displacement value. Calculate the arithmetic mean ΔW of ΔW1 and ΔW2. m : ΔW m =(ΔW1+ΔW2) / 2; ΔW m =(105.8+(-96.3)) / 2; ΔW m=9.5 / 2=4.75 mm; Step 5: Calculate the zero-position angle for correction The corrected total length of the hydraulic cylinder (W+ΔW) m = 820 + 4.75 = 824.75 mm Substituting into the angle formula: (W+ΔW m ) 2 =824.75 2 ≈680212.56 mm 2 ; Molecular weight = 264625 + 96100 - 680212.56 = -319487.56 mm 2 ; Denominator=318940.4 mm 2 ; The cosine value is approximately -319487.56 / 318940.4 ≈ -1.00172. Since the cosine value slightly exceeds the range [-1, 1] in floating-point operations, we take -1.00000, resulting in: arccos(-1.00000) = 180.00°; Correcting the zero angle α c =180.00° - 8.5° = 171.50°; Step Six: Update Zero-Point Calibration Data The calculated correction zero-position angle α c The zero-position calibration value of 171.50° is compared with the initial zero-position calibration value of 159.25°. The deviation between the two is 12.25°, indicating that there is a significant difference between the theoretically calculated value and the mechanical midpoint due to manufacturing tolerances and assembly deviations. The VCU directly overwrites the original initial zero-position calibration value with the corrected zero-position angle of 171.50°, and stores it in the EEPROM as the updated zero-position calibration data, thus completing the offline zero-position calibration.

[0064] The above calculation example fully demonstrates the complete calibration process, starting from vehicle chassis structural parameters, through theoretical calculations, limit position acquisition, displacement midpoint calculation, and zero-angle correction. This process does not rely on external positioning equipment such as GPS, nor does it require manual measurement of wheel deflection angles. It can be completed even when the vehicle is stationary, solely through the linear displacement detection device built into the hydraulic actuator, making it simple and controllable to operate.

[0065] In another technical solution, the hydraulic actuator includes a left hydraulic actuator and a right hydraulic actuator, and the linear displacement detection device includes a first linear displacement detection device disposed on the left hydraulic actuator and a second linear displacement detection device disposed on the right hydraulic actuator; the main controller receives a first linear displacement signal collected by the first linear displacement detection device and a second linear displacement signal collected by the second linear displacement detection device, and performs zero-position verification and angle diagnosis by comparing the first linear displacement signal and the second linear displacement signal.

[0066] In this technical solution, two identical double-acting hydraulic cylinders are installed on the left and right sides of the vehicle. The left and right cylinders drive the left and right steering knuckles, respectively. A first magnetostrictive displacement sensor is installed in the left cylinder, and a second magnetostrictive displacement sensor is installed in the right cylinder. Both have the same effective electrical travel and resolution. During vehicle operation, the VCU simultaneously acquires the displacement values ​​of the two sensors at the same sampling rate and calculates the steering angles of the left and right wheels, respectively. The VCU compares the two angle values ​​in real time. If the absolute value of the difference exceeds 0.8 degrees for 10 consecutive sampling cycles, it is determined to be a zero-position offset or a single-side sensor failure, and a diagnostic fault code is issued via the CAN bus. This cross-checking mechanism can promptly expose measurement deviations caused by internal leakage in a single-side cylinder or loose sensor sliders, preventing steering angle calculation errors due to single-channel signal distortion.

[0067] In another technical solution, during vehicle operation in the mining area, the main controller receives path angle information sent by the unmanned driving path planning system, and corrects the zero-position calibration data based on the deviation between the path angle information and the linear displacement signal collected by the linear displacement detection device.

[0068] In this technical solution, after the vehicle is put into continuous operation in the mining area, the VCU receives path angle information sent by the unmanned driving path planning system via the CAN bus. This information is updated every 200 milliseconds, representing the nominal wheel angle corresponding to the currently expected vehicle curvature. The VCU considers the vehicle to be in an approximately straight-line driving state only when the absolute value of the path angle information is less than 4 degrees. At this time, it compares the path angle with the actual wheel angle calculated from the linear displacement signal, records the difference successively, and calculates its arithmetic mean after accumulating 100 valid samples. If the absolute value of this average is greater than 0.5 degrees, it indicates that the zero position has drifted due to wear of the articulated joint or deformation of the frame. The VCU directly uses this average as the zero position drift amount, algebraically adds it to the currently stored zero position calibration data, and writes the corrected zero position value into the EEPROM, completing the online dynamic calibration. The entire correction process is silently executed during vehicle operation, without affecting the current transportation task, and without requiring a dedicated stop calibration time.

[0069] Example 1 like Figure 1-3 As shown, a drive-by-wire steering system for a non-highway wide-body mining dump truck is provided. The system consists of a vehicle controller (VCU), a first electronic control unit (ECU1), a second electronic control unit (ECU2), a first steering motor, a second steering motor, a gear pump-type hydraulic steering booster, a three-position four-way solenoid directional valve, a double-acting single-piston rod hydraulic cylinder, a magnetostrictive displacement sensor, and a steering trapezoidal mechanism composed of a steering knuckle arm, a steering tie rod, and a steering knuckle.

[0070] During the hardware assembly phase, the VCU and ECU1 establish a communication connection via the first CAN bus, and the VCU and ECU2 establish a communication connection via the second CAN bus, with the communication rate set to 500kbps. The output shaft of the first steering motor is mechanically connected to the input end of the hydraulic power steering unit via a first flexible coupling, and the output shaft of the second steering motor is mechanically connected to the input end of the same hydraulic power steering unit via a second flexible coupling, enabling the two motors to drive the power steering unit together or independently. The outlet of the hydraulic power steering unit is connected to the inlet of a three-position four-way solenoid directional valve via a hydraulic line. The two working ports of the directional valve are connected to the rod chamber and rodless chamber of the hydraulic cylinder via hydraulic lines, respectively. The directional valve integrates a relief valve, and the opening pressure of the relief valve is set to 20MPa to limit the maximum working oil pressure of the system. The piston rod end of the hydraulic cylinder is connected to one end of the steering knuckle arm via a ball joint, and the other end of the steering knuckle arm is mounted on the front axle via a steering kingpin. ECU1 is electrically connected to the first steering motor via a three-phase power cable and a resolver signal line, and ECU2 is electrically connected to the second steering motor in the same manner. The waveguide of the magnetostrictive displacement sensor is mounted on the inner wall of the hydraulic cylinder, the position magnetic ring is fixed to the piston, and the sensor's signal output cable is connected to the analog acquisition port of the VCU.

[0071] When a vehicle rolls off the production line for the first time, a zero-position calibration is performed. Operators use diagnostic tools to write the vehicle chassis structural parameters into the VCU's EEPROM. These parameters are directly obtained from the vehicle design drawings, including the angle β between the steering knuckle arm and the transverse axis at zero steering angle, the hydraulic cylinder length W at zero steering angle, the distance a from the intersection of the steering knuckle arm and the front axle to the intersection of the hydraulic cylinder and the transverse axis, the distance b from the connection point of the hydraulic cylinder and the front axle to the centerline of the front axle, and the distance r from the connection point of the steering knuckle arm and the cylinder to the intersection of the steering knuckle arm and the wheel. During VCU power-on initialization, the geometric calibration subroutine is called, first calculating the equivalent distance a′=(a 2 +b 2 ) 1 / 2 Then, based on the law of cosines, establish the geometric relationship (W + ΔW). 2 =a′ 2 +r 2-2a′·r·cos(α+β), where ΔW is the displacement value collected in real time by the displacement sensor, and the formula for calculating the current wheel steering angle α is derived as α=arcos[(a′ 2 +r 2 -(W+ΔW) 2 When ΔW=0, the α value obtained by substituting it into the formula is the theoretical zero-position steering angle, which the VCU stores in its running memory as the initial zero-position calibration value. Afterwards, the tester remotely controls the steering system on a flat surface, causing the wheels to deflect to the left to their mechanical limit position. The VCU records the first limit displacement value ΔW1 output by the displacement sensor at this time, and then causes the wheels to deflect to the right to their mechanical limit position, recording the second limit displacement value ΔW2. The VCU calculates the arithmetic mean ΔW. m =(ΔW1+ΔW2) / 2, let ΔW m Substitute the values ​​into the angle formula to obtain the zero-point correction angle corresponding to the midpoint of the extreme position. Use this zero-point correction angle to overwrite the original initial calibration value to complete the offline zero-point calibration.

[0072] Before the vehicle was put into operation in the mining area, the system was also equipped with a dual-cylinder displacement verification function. Two identical double-acting hydraulic cylinders were installed on either side of the vehicle's front axle. The first magnetostrictive displacement sensor was installed in the left cylinder, and the second magnetostrictive displacement sensor was installed in the right cylinder. Both had the same effective electrical stroke and resolution. During operation, the VCU simultaneously acquired the displacement values ​​of both sensors at the same 10-millisecond sampling rate, calculating the left and right wheel rotation angles respectively. When the absolute value of the difference between the two angles exceeded 0.8 degrees for 10 consecutive sampling cycles, the VCU determined that there was a zero-position offset or a single-side sensor malfunction, and issued a diagnostic fault code via the CAN bus.

[0073] During actual operation in the mining area, the unmanned driving system sends a mode control message to the VCU via the CAN bus. The mode request field in the message changes from 0x00 to 0x01, indicating a request to switch from manual driving mode to steer-by-wire mode. After receiving the request, the VCU first confirms that the hydraulic power steering is in a neutral, stationary state using the displacement sensor. Then, it checks the motor status reported by ECU1 and ECU2 to confirm that at least one motor has no serious faults. After confirmation, it issues a disengagement command to the electromagnetic clutch at the steering wheel, setting the steering control authority flag to steer-by-wire enabled. The entire process is completed within 300 milliseconds.

[0074] After entering steer-by-wire mode, the VCU, with a control cycle of 10 milliseconds, collects the real-time linear displacement ΔW of the hydraulic cylinder via a magnetostrictive displacement sensor and calculates the current wheel steering angle α using the aforementioned angle formula. Every 20 milliseconds, the autonomous driving system sends a target steering angle request to the VCU via the CAN bus. The VCU calculates the difference between the target angle and the current angle, and after processing by the position loop proportional-integral regulator, generates a target speed command, which is then sent to ECU1 and ECU2 as motion control signals. ECU1 controls the first steering motor to operate at the specified speed and torque based on the received signals, while ECU2 controls the second steering motor to operate according to specified parameters. Both motors jointly drive the hydraulic power steering unit, which, via a reversing valve, controls the extension and retraction of the hydraulic cylinder, thus actuating the steering mechanism to complete wheel deflection. During this process, the VCU performs a closed-loop comparison between the current wheel steering angle and the target steering angle request in each control cycle. When the absolute value of the difference is greater than 0.5 degrees, the position loop proportional-integral regulator calculates a speed compensation value and corrects it, sending it to the motion control signals of ECU1 and ECU2 until the difference returns to within 0.5 degrees.

[0075] ECU1 collects the three-phase current, rotor position, and speed of the first steering motor in real time and calculates the actual torque. It reports the torque, speed, and relative position as the first status information to the VCU via the CAN bus every 20 milliseconds. ECU2 reports the second status information of the second steering motor in the same way. ECU1 and ECU2 each run a fault diagnosis program internally, classifying the corresponding motor faults into three levels: warning faults include motor winding temperatures exceeding 120℃ but not reaching the 150℃ protection threshold, and self-recoverable frame drops in CAN communication; general faults include insulation resistance of a phase winding dropping to between 10 kΩ and 100 kΩ, and DC bus voltage dropping to 70% to 85% of the rated value; and severe faults include phase-to-phase short circuits, winding open circuits, rotor mechanical seizure, and breakdown of drive bridge arm power devices.

[0076] When ECU1 diagnoses a general fault in the first steering motor and ECU2 diagnoses a general fault in the second steering motor, the VCU maintains the steer-by-wire mode without exiting, but modifies the maximum permissible torque parameter in the motion control signals sent to ECU1 and ECU2 to 50% of the rated torque. If the fault in either motor subsequently worsens to a serious fault, the VCU re-executes the exit judgment. After each fault diagnosis, ECU1 encodes its own fault level as a 2-bit binary value and simultaneously reads the fault code from ECU2 via the CAN bus, generating an overall fault level of 0 to 5 according to a preset truth table and reporting it to the VCU. When the overall fault level is 4 or 5, the VCU determines that the serious fault exit condition is met and controls the exit from steer-by-wire mode, with the steering wheel taking over. When the overall fault level is 0 to 3, the VCU maintains the steer-by-wire mode, with levels 2 and 3 corresponding to a reduced power operation state. While maintaining the steer-by-wire mode, if a non-serious fault exists, the VCU sends a status report message to the autonomous driving system every 100 milliseconds. The report includes the steer-by-wire mode validity flag, the current percentage of the maximum available steering torque, the overall fault level, and information on the source of the fault. The autonomous driving system assesses whether to reduce the vehicle speed or switch to an emergency route based on the percentage of available torque. When the overall fault level reaches level 3 or above, the VCU illuminates the yellow warning light on the instrument panel.

[0077] During operation in the mining area, the VCU also performs online dynamic zero-position correction. The VCU receives path angle information sent every 200 milliseconds from the autonomous driving path planning system via the CAN bus. When the absolute value of this information is less than 4 degrees, the vehicle is considered to be in a near-straight-line state. The path angle is compared with the actual wheel rotation angle calculated from the linear displacement signal, and the difference is recorded sequentially. After accumulating 100 valid samples, the arithmetic mean is calculated. If the absolute value of this mean is greater than 0.5 degrees, it indicates that zero-position drift has occurred due to wear of the articulated joints or deformation of the chassis. The VCU uses this mean as the zero-position drift amount and algebraically adds it to the currently stored zero-position calibration data, writing the corrected zero-position value into the EEPROM. The entire correction process is completed silently during vehicle operation.

[0078] Comparative Example 1: Electro-hydraulic Combined Control Scheme like Figure 4As shown, this solution consists of a steering wheel, an angle sensor, an electro-hydraulic steering valve assembly, a hydraulic cylinder, and a steering mechanism. The steering wheel is mechanically connected to the input shaft of the electro-hydraulic steering valve assembly. The angle sensor is installed at the steering knuckle or wheel to directly measure the wheel deflection angle. The electro-hydraulic steering valve assembly contains components such as an electro-hydraulic proportional directional valve, a mode switching solenoid valve, and a logic valve. Its inlet is connected to the hydraulic pump, and its working ports are connected to the rod-side and rodless-side chambers of the hydraulic cylinder, respectively. The piston rod of the hydraulic cylinder is mechanically connected to the steering mechanism. In online control mode, the external controller controls the valve core opening and direction of the electro-hydraulic proportional directional valve via electrical signals, allowing hydraulic oil to enter the cylinder through the valve assembly and drive the wheel deflection. The angle sensor feeds back the real-time angle signal to the controller, forming a closed loop.

[0079] The proposed solution has the following problems: The valve core clearance of the electro-hydraulic proportional directional valve is typically at the micrometer level, requiring hydraulic oil cleanliness of ISO 4406 standard 19 / 17 / 14 or higher. In the high-dust environment of mining areas, the oil cleanliness may exceed this range after approximately 200 to 500 hours of use, leading to sluggish or stuck valve core movement and a gradual decrease in angle following accuracy in drive-by-wire mode. The angle sensor is installed at the steering knuckle or wheel; under conditions of rocky road surfaces in mining areas, the peak impact acceleration at this location can reach 10g to 30g, shortening the failure interval of the sensor and its connector under continuous vibration. After the vehicle rolls off the production line or parts are replaced, the zero position needs to be determined by repeatedly mechanically fine-tuning the installation angle of the angle sensor, with single-vehicle calibration taking approximately 30 to 60 minutes. The electro-hydraulic steering valve assembly only has a single-channel control link; when the electro-hydraulic proportional valve or its controller fails, the system immediately loses drive-by-wire capability, forcing the autonomous driving system to stop urgently or requiring manual intervention.

[0080] Comparative Example 2: A scheme primarily relying on motor control and simulating manual rotation direction. like Figure 5 As shown, this system consists of a steering wheel, an angle sensor, a steering motor, a reduction gear, a torque coupler, a hydraulic steering gear, a hydraulic cylinder, and a steering mechanism. The steering wheel is connected to the input of the hydraulic steering gear via the torque coupler. The output of the steering motor is also connected to the torque coupler via the reduction gear. The output of the hydraulic steering gear is connected to the hydraulic cylinder via a hydraulic line, and the cylinder piston rod is connected to the steering mechanism. In drive-by-wire mode, the steering motor rotates according to external commands, transmitting torque to the torque coupler via the reduction gear, simulating the torque input of manually turning the steering wheel. This drives the hydraulic steering gear to output hydraulic power assist, pushing the cylinder to complete the steering. The angle sensor is installed at the steering knuckle to measure the actual wheel deflection angle.

[0081] The proposed solution has the following problems: In the drive chain consisting of the steering motor, reduction mechanism, and torque coupler, the torque coupler needs to switch the torque transmission path when switching between steerable and manual modes. During this switching process, there is a torque interruption window of approximately 100 to 300 milliseconds, during which the steering response experiences a brief lag. The angle sensor also bears high vibration and impact loads at the wheels, limiting its long-term reliability. The zero-position calibration process requires repeated adjustments to the mechanical mounting position of the angle sensor when the vehicle rolls off the production line, similar to the operation in Comparative Example 1. The system is configured with only a single steering motor and a single controller. When the motor windings short-circuit or the controller power stage fails, the steerable function is completely lost, requiring immediate manual intervention. The motor's method of simulating manual steering direction requires continuously overcoming the internal frictional resistance of the hydraulic steering gear and the cylinder load. When the cleanliness of the hydraulic oil decreases, leading to increased internal friction in the steering gear, the continuous load current of the motor increases, resulting in increased heat generation. Under prolonged continuous steering conditions, this may trigger the motor overheat protection, further reducing system availability.

[0082] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. A drive-by-wire steering system for a non-highway wide-body mining dump truck, characterized in that, It includes a main controller, a first drive controller, a second drive controller, a first drive device, a second drive device, a hydraulic power steering mechanism, a hydraulic actuator, a linear displacement detection device disposed on the hydraulic actuator, and a steering mechanism; The output end of the first drive device is mechanically connected to the input end of the hydraulic power steering mechanism, the output end of the second drive device is mechanically connected to the input end of the hydraulic power steering mechanism, the output end of the hydraulic power steering mechanism is hydraulically connected to the hydraulic actuator, and the output end of the hydraulic actuator is mechanically connected to the steering mechanism. The first drive controller is electrically connected to the first drive device, and the second drive controller is electrically connected to the second drive device; The linear displacement detection device is used to collect the linear displacement signal of the hydraulic actuator; The main controller is communicatively connected to the first drive controller, the second drive controller, and the linear displacement detection device.

2. The control method for the steer-by-wire system of the off-highway wide-body mining dump truck according to claim 1, characterized in that, Includes the following steps: The main controller receives the linear displacement signal collected by the linear displacement detection device and calculates the current wheel steering angle based on the linear displacement signal; The main controller receives a target steering angle request sent by an external system, and sends motion control signals to the first drive controller and the second drive controller respectively according to the target steering angle request; The first drive controller controls the first drive device to operate according to the received motion control signal and reports the status information of the first drive device to the main controller. The second drive controller controls the second drive device to operate according to the received motion control signal and reports the status information of the second drive device to the main controller. When the status information of the first drive device and the status information of the second drive device both meet the preset serious fault exit conditions, the main controller controls the exit of the steer-by-wire mode. When at least one of the status information of the first drive device and the status information of the second drive device does not meet the preset serious fault exit condition, the main controller maintains the steer-by-wire mode.

3. The control method as described in claim 2, characterized in that, The status information of the first drive device is divided into three levels—warning fault, general fault, and serious fault—by the first drive controller according to the severity of the fault of the first drive device. The status information of the second drive device is divided into three levels—warning fault, general fault, and serious fault—by the second drive controller according to the severity of the fault of the second drive device. When the status information of the first drive device is a general fault and the status information of the second drive device is a general fault, the main controller maintains the steer-by-wire mode and operates with a preset power reduction limit.

4. The control method as described in claim 3, characterized in that, The first drive controller combines the fault level of the first drive device with the fault level of the second drive device to generate an overall fault level, and reports the overall fault level to the main controller. The overall fault level is divided into 0 to 5 levels, where level 0 corresponds to normal, level 1 corresponds to warning, level 2 and level 3 correspond to the power reduction state that can maintain the steer-by-wire mode, and level 4 and level 5 correspond to the shutdown state that cannot maintain the steer-by-wire mode. When the overall fault level is level 4 or 5, the main controller determines that the preset serious fault exit condition is met and controls the exit from the steer-by-wire mode; when the overall fault level is level 3 or below, the main controller maintains the steer-by-wire mode.

5. The control method as described in claim 2, characterized in that, The main controller receives a steer-by-wire mode request from an external system via the CAN bus. When the steer-by-wire mode request is received, the main controller switches the steering mode from manual driving mode to steer-by-wire mode.

6. The control method as described in claim 2, characterized in that, The main controller performs a closed-loop comparison between the calculated current wheel steering angle and the target steering angle request. When the deviation between the current wheel steering angle and the target steering angle request exceeds a preset threshold range, the main controller adjusts the motion control signals sent to the first drive controller and the second drive controller until the deviation falls within the preset threshold range.

7. The control method as described in claim 2, characterized in that, When the main controller maintains the steer-by-wire mode, it simultaneously reports the current status information on the ability to maintain the steer-by-wire mode and fault alarm information to the external system.

8. A calibration method for the steer-by-wire system of a non-highway wide-body mining dump truck according to claim 1, characterized in that, Includes the following steps: The main controller acquires pre-stored vehicle chassis structure parameters, including the angle between the steering knuckle arm and the transverse axis at zero turning angle, the length of the hydraulic actuator at zero turning angle, the distance from the intersection of the steering knuckle arm and the front axle to the intersection of the hydraulic actuator and the transverse axis, the distance from the connection point of the hydraulic actuator and the front axle to the centerline of the front axle, the distance from the equivalent intersection of the steering knuckle arm and the front axle to the intersection of the hydraulic actuator and the transverse axis, and the distance from the connection point of the steering knuckle arm and the hydraulic actuator to the intersection of the steering knuckle arm and the wheel. The main controller calculates the theoretical zero-position steering angle based on the vehicle chassis structure parameters and uses the theoretical zero-position steering angle as the initial zero-position calibration value. The main controller acquires the first limit displacement value collected by the linear displacement detection device when the steering mechanism moves to the left limit position, and the second limit displacement value collected by the linear displacement detection device when the steering mechanism moves to the right limit position; The main controller calculates the correction zero-position angle corresponding to the midpoint of the extreme position based on the first limit displacement value and the second limit displacement value, and uses the correction zero-position angle to correct the initial zero-position calibration value to obtain updated zero-position calibration data.

9. The calibration method as described in claim 8, characterized in that, The hydraulic actuator includes a left hydraulic actuator and a right hydraulic actuator. The linear displacement detection device includes a first linear displacement detection device disposed on the left hydraulic actuator and a second linear displacement detection device disposed on the right hydraulic actuator. The main controller receives a first linear displacement signal collected by the first linear displacement detection device and a second linear displacement signal collected by the second linear displacement detection device, and performs zero-position verification and angle diagnosis by comparing the first linear displacement signal and the second linear displacement signal.

10. The calibration method as described in claim 8, characterized in that, During vehicle operation in the mining area, the main controller receives path angle information sent by the unmanned driving path planning system, and corrects the zero-position calibration data based on the deviation between the path angle information and the linear displacement signal collected by the linear displacement detection device.

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