A vehicle steering system and control method that combines energy saving, high efficiency and redundant safety functions

Abstract

The present invention discloses a vehicle steering system and control method that take into account energy saving, high efficiency and redundant safety functions, relating to the technical field of automobile steering systems, including a steering wheel, a steering shaft, a steering tie rod, a VCU, a first reversible motor and a second reversible motor, wherein the upper end of the steering shaft is connected to the steering wheel, the two ends of the steering tie rod are connected to trapezoidal arms, the end of the trapezoidal arm away from the steering tie rod is connected to a steering knuckle, the steering knuckle is connected to a wheel via a bearing, and both wheels are equipped with a hub motor for receiving a control signal from the VCU. In the present invention, the steering system realizes automatic switching between different steering modes through the coordinated action of multiple electric motors and electromagnetic clutches to cope with different situations of electronic device failure and steering torque requirements, ensures that the steering system has redundant safety functions, improves the stability and safety of the vehicle, and realizes energy recovery and efficient steering assistance during the steering process.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile steering systems, and in particular to a vehicle steering system and a control method that combines energy saving, high efficiency and redundant safety functions. Background Art

[0002] Traditional automobile steering systems mainly rely on hydraulic power assistance or purely mechanical structures to achieve steering operations. Most of the energy consumed by such systems during the steering process is dissipated in the form of heat energy and cannot be effectively recovered and reused. With the development of electric vehicles and hybrid vehicles, improving energy utilization efficiency has become an important research direction.

[0003] Existing steering systems usually do not have energy recovery capabilities, resulting in the energy consumed during the steering operation not being effectively utilized, which not only wastes energy but also reduces the overall energy transmission efficiency of the vehicle. In addition, traditional steering systems lack effective redundant safety measures when electronic components fail. When the steering motor fails, the steering assist will be greatly reduced or even completely lost. The driver needs to exert greater force to complete the steering operation, especially in high-speed driving or emergency situations. This situation may cause the vehicle to lose control and increase the risk of traffic accidents. Therefore, a vehicle steering system and control method that takes into account energy saving, high efficiency and redundant safety functions are proposed. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems in the prior art and to propose a vehicle steering system and control method that take into account energy saving, high efficiency and redundant safety functions.

[0005] A vehicle steering system and control method that combines energy saving, high efficiency, and redundant safety functions, including a steering wheel, a steering shaft, a steering tie rod, a VCU, a first reversible motor, and a second reversible motor;

[0006] The upper end of the steering shaft is connected to the steering wheel, the two ends of the steering tie rod are connected to trapezoidal arms, the end of the trapezoidal arm away from the steering tie rod is connected to the steering knuckle, the steering knuckle is connected to the wheel through a bearing, both wheels are equipped with a hub motor for receiving the control signal of the VCU, one of the wheels is equipped with a front wheel angle sensor for obtaining the front wheel angle signal and transmitting it to the VCU, the input end of the steering tie rod is connected to the steering rack, the lower end of the steering shaft is coaxially connected to the steering gear, and the steering gear is meshed with the steering rack;

[0007] A first reduction mechanism and a second reduction mechanism are installed on the steering shaft, the output end of the first reduction mechanism is connected to the steering shaft, the input end of the first reduction mechanism is connected to the rotor of the first reversible motor, the output end of the second reduction mechanism is connected to the steering shaft, the input end of the second reduction mechanism is connected to the rotor of the second reversible motor, a first electromagnetic clutch is connected between the first reduction mechanism and the first reversible motor, and the first electromagnetic clutch is directly controlled by the VCU to open or close, a second electromagnetic clutch is connected between the second reduction mechanism and the second reversible motor, and the second electromagnetic clutch is directly controlled by the VCU to open or close.

[0008] Preferably, the first reversible motor is connected to a first reversible motor controller for receiving VCU control signals and directly controlling the first reversible motor, and the second reversible motor is connected to a second reversible motor controller for receiving VCU control signals and directly controlling the second reversible motor. The first reversible motor and the second reversible motor switch between electric mode and power generation mode according to the control signal provided by the VCU. In the power generation mode, when the driver turns the steering wheel, the first reduction mechanism and the second reduction mechanism respectively drive the rotors of the first reversible motor and the second reversible motor to rotate, and the permanent magnets on the rotors cut the stator windings to generate current; in the electric mode, the stator is energized through the control system to generate a rotating magnetic field, which drives the rotor to rotate, providing additional steering assistance for the steering wheel.

[0009] Preferably, the first reversible motor controller and the second reversible motor controller are both connected to a power converter, the power converter is connected to a power supply, and the power converter has the functions of converting DC power into AC power and reverse rectification, adjusting the output voltage, and providing overcurrent and overtemperature protection.

[0010] Preferably, an angle torque sensor is installed at the upper end of the steering shaft and below the steering wheel. The angle torque sensor is used to obtain an angle signal and a torque signal, and transmit the angle signal and the torque signal to the VCU.

[0011] A vehicle steering system control method that takes into account energy saving, high efficiency and redundant safety functions is based on the above-mentioned steering system and includes the following steps:

[0012] S1, system self-test, the VCU reads the self-test signals of the first reversible motor, the second reversible motor, and the hub motor;

[0013] S2. Judging the steering torque based on the self-test results, and selecting the corresponding steering mode for switching;

[0014] The steering torque is judged in step S2, including the steering torque being Tr, and the steering torque Tr being compared with the maximum differential torque Ta that can be provided by the hub motor and the maximum steering torque Tb that can be provided by the first reversible motor;

[0015] The steering modes in step S2 include a full energy-saving steering mode, a partial energy-saving steering mode, a multi-motor efficient coordinated steering mode, a three-level redundant safety steering mode, a safety energy-saving steering mode one, a safety energy-saving steering mode two, a safety energy-saving steering mode three, a safety energy-saving steering mode four, a first-level redundant safety non-energy-saving steering mode, a first-level performance-guaranteed non-energy-saving steering mode, a performance-guaranteed energy-saving steering mode one, a performance-guaranteed energy-saving steering mode two, a balanced energy-saving steering mode and a performance energy-saving steering mode.

[0016] Preferably, the steering mode switching method in step S2 is as follows:

[0017] (1) If there is no motor fault signal, the steering torque Tr demand is determined. If Tr is less than or equal to Ta, the full energy-saving steering mode is executed; if Tr is greater than Ta but less than Ta+Tb, the partial energy-saving steering mode is executed; if Tr is greater than Ta+Tb, the multi-motor efficient coordinated steering mode is executed;

[0018] (2) If the second reversible motor, the first reversible motor, or the hub motor fails, the three-level redundant safety steering mode will be executed;

[0019] (3) If the second reversible motor and the first reversible motor fail, but the hub motor does not fail, the secondary redundant safety steering mode is executed. In this mode, the steering torque Tr requirement is determined. If Tr is less than or equal to Ta, the safety and energy-saving steering mode 1 is executed. If Tr is greater than Ta, the safety and energy-saving steering mode 2 is executed.

[0020] (4) If the second reversible motor fails, but the first reversible motor and the hub motor do not fail, the first level redundant safety steering mode is executed, and the steering torque Tr requirement is judged in this mode. If Tr is less than or equal to Ta, the safety energy-saving steering mode 3 is executed; if Tr is greater than Ta, the safety energy-saving steering mode 4 is executed;

[0021] (5) If the second reversible motor or the hub motor fails, but the first reversible motor does not fail, the first-level redundant safety non-energy-saving steering mode will be executed;

[0022] (6) If the first reversible motor and the hub motor fail, but the second reversible motor does not fail, the first-level performance-guaranteed non-energy-saving steering mode will be executed;

[0023] (7) If the first reversible motor fails, and the second reversible motor and the hub motor do not fail, the second-level guaranteed performance steering mode is executed. In this mode, the steering torque Tr requirement is determined. If Tr is less than or equal to Ta, the guaranteed performance energy-saving steering mode 1 is executed. If Tr is greater than Ta, the guaranteed performance energy-saving steering mode 2 is executed.

[0024] (8) If the hub motor fails and the first reversible motor and the second reversible motor do not fail, the balanced performance steering mode is executed, and the steering torque Tr requirement is judged in this mode. If Tr is less than or equal to Tb, the balanced energy-saving steering mode is executed. If Tr is greater than Tb, the performance energy-saving steering mode is executed.

[0025] Compared with the existing technology, the advantages of the present invention are:

[0026] The steering system in the present invention realizes automatic switching between different steering modes through the coordinated action of multiple electric motors and electromagnetic clutches to cope with different situations of electronic device failure and steering torque requirements, ensures that the steering system has redundant safety functions, improves the stability and safety of the vehicle, and realizes energy recovery and efficient steering assistance during the steering process. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic structural diagram of the steering system of the present invention.

[0028] Figure 2 It is a flow chart of the steering system control method in the present invention.

[0029] In the figure: 1 steering wheel, 2 rotation angle torque sensor, 3 first reduction mechanism, 4 steering shaft, 5 second reduction mechanism, 6 front wheel rotation angle sensor, 7 wheel, 8 steering knuckle, 9 trapezoidal arm, 10 steering tie rod, 11 steering gear, 12 steering rack, 13 second electromagnetic clutch, 14 second reversible motor, 15 second reversible motor controller, 16 wheel hub motor, 17 power supply, 18 power converter, 19 first reversible motor controller, 20 VCU, 21 first reversible motor, 22 first electromagnetic clutch. DETAILED DESCRIPTION

[0030] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0031] Reference Figure 1-2 As shown, a vehicle steering system that takes into account energy saving, high efficiency and redundant safety functions includes: a steering wheel 1, a steering shaft 4, a steering tie rod 10, a VCU 20, a first reversible motor 21 and a second reversible motor 14;

[0032] The upper end of the steering shaft 4 is connected to the steering wheel 1, and the two ends of the steering tie rod 10 are connected to the trapezoidal arm 9. The end of the trapezoidal arm 9 away from the steering tie rod 10 is connected to the steering knuckle 8. The steering knuckle 8 is connected to the wheel 7 through a bearing. Both wheels 7 are equipped with a hub motor 16 for receiving the control signal of the VCU 20. One of the wheels 7 is equipped with a front wheel angle sensor 6 for obtaining the front wheel angle signal and transmitting it to the VCU 20. The input end of the steering tie rod 10 is connected to the steering rack 12. The lower end of the steering shaft 4 is coaxially connected to the steering gear 11, and the steering gear 11 is meshed with the steering rack 12.

[0033] The steering shaft 4 is equipped with a first reduction mechanism 3 and a second reduction mechanism 5. The output end of the first reduction mechanism 3 is connected to the steering shaft 4, and the input end of the first reduction mechanism 3 is connected to the rotor of the first reversible motor 21. The output end of the second reduction mechanism 5 is connected to the steering shaft 4, and the input end of the second reduction mechanism 5 is connected to the rotor of the second reversible motor 14. A first electromagnetic clutch 22 is connected between the first reduction mechanism 3 and the first reversible motor 21, and the first electromagnetic clutch 22 is directly controlled by VCU20 to be opened or closed. A second electromagnetic clutch 13 is connected between the second reduction mechanism 5 and the second reversible motor 14, and the second electromagnetic clutch 13 is directly controlled by VCU20 to be opened or closed.

[0034] In this embodiment, the first reversible motor 21 is connected to a first reversible motor controller 19 for receiving a control signal from VCU20 and directly controlling the first reversible motor 21; the second reversible motor 14 is connected to a second reversible motor controller 15 for receiving a control signal from VCU20 and directly controlling the second reversible motor 14; the first reversible motor 21 and the second reversible motor 14 switch between an electric mode and a power generation mode according to a control signal provided by VCU20; in the power generation mode, when the driver turns the steering wheel 1, the first reduction mechanism 3 and the second reduction mechanism 5 respectively drive the rotors of the first reversible motor 21 and the second reversible motor 14 to rotate, and the permanent magnets on the rotors cut the stator windings to generate current; in the electric mode, the stator is energized through the control system to generate a rotating magnetic field, which drives the rotor to rotate, providing additional steering assistance for the steering wheel 1.

[0035] In this embodiment, the first reversible motor controller 19 and the second reversible motor controller 15 are both connected to a power converter 18, and the power converter 18 is connected to a power supply 17. The power converter 18 has the functions of converting direct current into alternating current and reverse rectification, adjusting the output voltage, and providing over-current and over-temperature protection.

[0036] In this embodiment, a rotation angle torque sensor 2 is installed at the upper end of the steering shaft 4 and below the steering wheel 1. The rotation angle torque sensor 2 is used to obtain a rotation angle signal and a torque signal, and transmit the rotation angle signal and the torque signal to the VCU 20.

[0037] A vehicle steering system control method that takes into account energy saving, high efficiency and redundant safety functions is based on the above-mentioned steering system and is characterized by comprising the following steps:

[0038] S1, system self-test, the VCU 20 reads the self-test signals of the first reversible motor 21, the second reversible motor 14, and the hub motor 16;

[0039] S2. Judging the steering torque based on the self-test results, and selecting the corresponding steering mode for switching;

[0040] The steering torque is judged in step S2, including the steering torque being Tr, and the steering torque Tr being compared with the maximum differential torque Ta that can be provided by the hub motor 16 and the maximum steering torque Tb that can be provided by the first reversible motor 21;

[0041] The steering modes in step S2 include a full energy-saving steering mode, a partial energy-saving steering mode, a multi-motor efficient coordinated steering mode, a three-level redundant safety steering mode, a safety energy-saving steering mode one, a safety energy-saving steering mode two, a safety energy-saving steering mode three, a safety energy-saving steering mode four, a first-level redundant safety non-energy-saving steering mode, a first-level performance-guaranteed non-energy-saving steering mode, a performance-guaranteed energy-saving steering mode one, a performance-guaranteed energy-saving steering mode two, a balanced energy-saving steering mode and a performance energy-saving steering mode.

[0042] In this embodiment, the steering mode switching method in step S2 is as follows:

[0043] (1) If there is no motor fault signal, the steering torque Tr demand is determined. If Tr is less than or equal to Ta, the full energy-saving steering mode is executed; if Tr is greater than Ta but less than Ta+Tb, the partial energy-saving steering mode is executed; if Tr is greater than Ta+Tb, the multi-motor efficient coordinated steering mode is executed;

[0044] (2) If the second reversible motor 14, the first reversible motor 21, or the hub motor 16 fails, the three-level redundant safety steering mode is executed;

[0045] (3) If the second reversible motor 14 and the first reversible motor 21 fail, but the hub motor 16 does not fail, the secondary redundant safety steering mode is executed. In this mode, the steering torque Tr requirement is determined. If Tr is less than or equal to Ta, the safety and energy-saving steering mode 1 is executed. If Tr is greater than Ta, the safety and energy-saving steering mode 2 is executed.

[0046] (4) If the second reversible motor 14 fails, and the first reversible motor 21 and the hub motor 16 do not fail, the first level redundant safety steering mode is executed, and the steering torque Tr requirement is determined in this mode. If Tr is less than or equal to Ta, the safety energy-saving steering mode 3 is executed. If Tr is greater than Ta, the safety energy-saving steering mode 4 is executed.

[0047] (5) If the second reversible motor 14 and the hub motor 16 fail, but the first reversible motor 21 does not fail, the first level redundant safety non-energy-saving steering mode is executed;

[0048] (6) If the first reversible motor 21 and the hub motor 16 fail, and the second reversible motor 14 does not fail, the first-level performance-guaranteed non-energy-saving steering mode is executed;

[0049] (7) If the first reversible motor 21 fails, and the second reversible motor 14 and the hub motor 16 do not fail, the second guaranteed performance steering mode is executed. In this mode, the steering torque Tr requirement is determined. If Tr is less than or equal to Ta, the guaranteed performance energy-saving steering mode 1 is executed. If Tr is greater than Ta, the guaranteed performance energy-saving steering mode 2 is executed.

[0050] (8) If the hub motor 16 fails, and the first reversible motor 21 and the second reversible motor 14 do not fail, the balanced performance steering mode is executed, and the steering torque Tr requirement is determined in this mode. If Tr is less than or equal to Tb, the balanced energy-saving steering mode is executed. If Tr is greater than Tb, the performance energy-saving steering mode is executed.

[0051] A steering system mode switching rule that takes into account energy saving, high efficiency and redundant safety functions is shown in Table 1, where motor state 0 represents no fault and motor state 1 represents a fault.

[0052] Table 1: A steering system mode switching rule that takes into account energy saving, high efficiency and redundant safety functions

[0053]

[0054] The following are detailed descriptions of the various steering modes:

[0055] All energy-saving steering mode: In this mode, VCU20 controls the first electromagnetic clutch 22 to close and the second electromagnetic clutch 13 to close. At this time, Tr is less than or equal to Ta. The first reversible motor 21 and the second reversible motor 14 execute the power generation mode to reduce energy consumption and improve the overall efficiency of the system. At this time, the steering torque is provided by the hub motor 16.

[0056] Partial energy-saving steering mode: In this mode, VCU20 controls the first electromagnetic clutch 22 to close and the second electromagnetic clutch 13 to close. At this time, Tr is greater than Ta and less than or equal to Ta+Tb. The first reversible motor 21 executes the power generation mode and the second reversible motor 14 executes the electric mode. The steering torque is provided by the hub motor 16 and the second reversible motor 14.

[0057] Multi-motor efficient coordinated steering mode: In this mode, VCU20 controls the first electromagnetic clutch 22 to close and the second electromagnetic clutch 13 to close. At this time, Tr is greater than Ta+Tb, and the first reversible motor 21 and the second reversible motor 14 both execute the electric mode to provide sufficient steering torque to meet normal steering requirements. At this time, the steering torque is provided by the hub motor 16, the first reversible motor 21, and the second reversible motor 14.

[0058] Level 3 redundant safety steering mode: In this mode, VCU20 controls the first electromagnetic clutch 22 to disconnect and the second electromagnetic clutch 13 to disconnect. At this time, since all motors fail, in order to ensure the normal steering function, VCU20 controls the first reversible motor 21 and the second reversible motor 14 to stop working. At this time, the steering torque is directly provided by the driver.

[0059] Safe and energy-saving steering mode 1: In this mode, VCU20 controls the first electromagnetic clutch 22 to close and the second electromagnetic clutch 13 to close. At this time, Tr is less than or equal to Ta. The first reversible motor 21 and the second reversible motor 14 execute the power generation mode to reduce energy consumption and improve the overall efficiency of the system. At this time, the steering torque is provided by the hub motor 16.

[0060] Safety and energy-saving steering mode 2: In this mode, VCU20 controls the first electromagnetic clutch 22 to disconnect and the second electromagnetic clutch 13 to disconnect. At this time, Tr is greater than Ta. To ensure the normal steering function, VCU20 controls the first reversible motor 21 and the second reversible motor 14 to stop working. At this time, the steering torque is provided by the hub motor 16.

[0061] Safe and energy-saving steering mode five: In this mode, VCU20 controls the first electromagnetic clutch 22 to close and the second electromagnetic clutch 13 to close. At this time, Tr is less than or equal to Ta. At this time, the first reversible motor 21 and the second reversible motor 14 execute the power generation mode to reduce energy consumption and improve the overall efficiency of the system. At this time, the steering torque is provided by the hub motor 16.

[0062] Safety and energy-saving steering mode six: In this mode, VCU20 controls the first electromagnetic clutch 22 to close and the second electromagnetic clutch 13 to disconnect. At this time, Tr is greater than Ta. At this time, VCU20 controls the first reversible motor 21 to execute the electric mode, and the second reversible motor 14 stops working. At this time, the steering torque is provided by the hub motor 16 and the first reversible motor 21.

[0063] Level 1 redundant safety non-energy-saving steering mode: In this mode, VCU20 controls the first electromagnetic clutch 22 to close and the second electromagnetic clutch 13 to disconnect. At this time, VCU20 controls the first reversible motor 21 to execute the electric mode, and the second reversible motor 14 stops working. At this time, the steering torque is provided by the first reversible motor 21.

[0064] Level 1 performance-guaranteed non-energy-saving steering mode: In this mode, VCU20 controls the first electromagnetic clutch 22 to disconnect and the second electromagnetic clutch 13 to close. At this time, VCU20 controls the first reversible motor 21 to stop working, and the second reversible motor 14 to execute the electric mode. At this time, the steering torque is provided by the second reversible motor 14.

[0065] Performance-guaranteed energy-saving steering mode 1: In this mode, VCU20 controls the first electromagnetic clutch 22 to close and the second electromagnetic clutch 13 to close. At this time, Tr is less than or equal to Ta. To ensure performance, VCU20 controls the first reversible motor 21 to execute the power generation mode and the second reversible motor 14 to execute the electric mode. At this time, the steering torque is provided by the hub motor 16 and the second reversible motor 14.

[0066] Performance-guaranteed energy-saving steering mode 2: In this mode, VCU20 controls the first electromagnetic clutch 22 to disconnect and the second electromagnetic clutch 13 to close. At this time, Tr is greater than Ta, VCU20 controls the first reversible motor 21 to stop working, and the second reversible motor 14 executes the electric mode. At this time, the steering torque is provided by the hub motor 16 and the second reversible motor 14.

[0067] Balanced energy-saving steering mode: In this mode, VCU20 controls the first electromagnetic clutch 22 to close and the second electromagnetic clutch 13 to close. At this time, Tr is less than or equal to Tb. VCU20 controls the first reversible motor 21 to execute the power generation mode and the second reversible motor 14 to execute the electric mode. At this time, the steering torque is provided by the second reversible motor 14.

[0068] Performance energy-saving steering mode: In this mode, VCU20 controls the first electromagnetic clutch 22 to close and the second electromagnetic clutch 13 to close. At this time, Tr is greater than Tb. In order to improve performance, VCU20 controls the first reversible motor 21 to execute the electric mode and the second reversible motor 14 to execute the electric mode. At this time, the steering torque is provided by the first reversible motor 21 and the second reversible motor 14.

[0069] In summary, the steering system of the present invention realizes automatic switching between different steering modes through the coordinated action of multiple electric motors and electromagnetic clutches to cope with different situations of electronic device failure and steering torque requirements, and realizes energy recovery and efficient steering assistance during the steering process, while ensuring that the steering system has redundant safety functions.

[0070] It is understood from common technical knowledge that the present invention may be implemented by other embodiments that do not depart from its spirit or essential features. Therefore, the embodiments disclosed above are, in all respects, merely illustrative and not exclusive. All modifications within the scope of the present invention or equivalent to the scope of the present invention are intended to be encompassed by the present invention.

Claims

1. A vehicle steering system that combines energy saving, high efficiency, and redundant safety features, characterized by: It includes a steering wheel (1), a steering shaft (4), a steering tie rod (10), a VCU (20), a first reversible motor (21), and a second reversible motor (14); The upper end of the steering shaft (4) is connected to the steering wheel (1), the two ends of the steering tie rod (10) are connected to the trapezoidal arms (9), the end of the trapezoidal arms (9) away from the steering tie rod (10) is connected to the steering knuckle (8), the steering knuckle (8) is connected to the wheel (7) through a bearing, and the two wheels (7) are both equipped with a hub motor (16) for receiving the control signal of the VCU (20), one of the wheels (7) is equipped with a front wheel angle sensor (6) for obtaining the front wheel angle signal and transmitting it to the VCU (20), the input end of the steering tie rod (10) is connected to the steering rack (12), the lower end of the steering shaft (4) is coaxially connected to the steering gear (11), and the steering gear (11) is meshed with the steering rack (12); A first reduction mechanism (3) and a second reduction mechanism (5) are installed on the steering shaft (4), the output end of the first reduction mechanism (3) is connected to the steering shaft (4), the input end of the first reduction mechanism (3) is connected to the rotor of the first reversible motor (21), the output end of the second reduction mechanism (5) is connected to the steering shaft (4), the input end of the second reduction mechanism (5) is connected to the rotor of the second reversible motor (14), a first electromagnetic clutch (22) is connected between the first reduction mechanism (3) and the first reversible motor (21), the first electromagnetic clutch (22) is directly controlled to be opened or closed by the VCU (20), a second electromagnetic clutch (13) is connected between the second reduction mechanism (5) and the second reversible motor (14), the second electromagnetic clutch (13) is directly controlled to be opened or closed by the VCU (20); The vehicle steering system uses a control method comprising the following steps: S1, system self-test, the VCU (20) reads the self-test signals of the first reversible motor (21), the second reversible motor (14), and the hub motor (16); S2. Judging the steering torque based on the self-test results, and selecting the corresponding steering mode for switching; The judgment of the steering torque in step S2 includes the steering torque being Tr, and comparing the steering torque Tr with the maximum differential torque Ta that can be provided by the hub motor (16) and the maximum steering torque Tb that can be provided by the first reversible motor (21); The steering modes in step S2 include a full energy-saving steering mode, a partial energy-saving steering mode, a multi-motor efficient coordinated steering mode, a three-level redundant safety steering mode, a safety energy-saving steering mode 1, a safety energy-saving steering mode 2, a safety energy-saving steering mode 3, a safety energy-saving steering mode 4, a first-level redundant safety non-energy-saving steering mode, a first-level performance-guaranteed non-energy-saving steering mode, a performance-guaranteed energy-saving steering mode 1, a performance-guaranteed energy-saving steering mode 2, a balanced energy-saving steering mode, and a performance energy-saving steering mode; The steps of the steering mode switching method in step S2 are as follows: (1) If there is no motor fault signal, the steering torque Tr demand is determined. If Tr is less than or equal to Ta, the full energy-saving steering mode is executed; if Tr is greater than Ta but less than Ta+Tb, the partial energy-saving steering mode is executed; if Tr is greater than Ta+Tb, the multi-motor efficient coordinated steering mode is executed; (2) If the second reversible motor (14), the first reversible motor (21), or the hub motor (16) fails, the three-level redundant safety steering mode is executed; (3) If the second reversible motor (14) and the first reversible motor (21) fail, and the hub motor (16) does not fail, the secondary redundant safety steering mode is executed, and the steering torque Tr requirement is judged in this mode. If Tr is less than or equal to Ta, the safety energy-saving steering mode 1 is executed; if Tr is greater than Ta, the safety energy-saving steering mode 2 is executed; (4) If the second reversible motor (14) fails, and the first reversible motor (21) and the hub motor (16) do not fail, the first level redundant safety steering mode is executed, and the steering torque Tr requirement is judged in this mode. If Tr is less than or equal to Ta, the safety energy-saving steering mode 3 is executed. If Tr is greater than Ta, the safety energy-saving steering mode 4 is executed.

2. The vehicle steering system according to claim 1, characterized in that: The first reversible motor (21) is connected to a first reversible motor controller (19) for receiving a control signal from a VCU (20) and directly controlling the first reversible motor (21). The second reversible motor (14) is connected to a second reversible motor controller (15) for receiving a control signal from a VCU (20) and directly controlling the second reversible motor (14). The first reversible motor (21) and the second reversible motor (14) switch between an electric mode and a power generation mode according to a control signal provided by the VCU (20). In the power generation mode, when the driver turns the steering wheel (1), the first reduction mechanism (3) and the second reduction mechanism (5) respectively drive the rotors of the first reversible motor (21) and the second reversible motor (14) to rotate, and the permanent magnets on the rotors cut the stator windings to generate current. In the electric mode, the stator is energized through the control system to generate a rotating magnetic field, which drives the rotor to rotate, providing additional steering assistance for the steering wheel (1).

3. The vehicle steering system according to claim 2, characterized in that: The first reversible motor controller (19) and the second reversible motor controller (15) are both connected to a power converter (18), and the power converter (18) is connected to a power supply (17). The power converter (18) has the functions of converting direct current into alternating current and reverse rectification, regulating output voltage, and providing overcurrent and overtemperature protection.

4. The vehicle steering system according to claim 1, characterized in that: A rotation angle torque sensor (2) is installed at the upper end of the steering shaft (4) and below the steering wheel (1). The rotation angle torque sensor (2) is used to obtain a rotation angle signal and a torque signal, and transmit the rotation angle signal and the torque signal to the VCU (20).

5. The vehicle steering system according to claim 1, characterized in that: The steering mode switching method in step S2 further includes: (5) If the second reversible motor (14) and the hub motor (16) fail, and the first reversible motor (21) does not fail, the first level redundant safety non-energy-saving steering mode is executed; (6) If the first reversible motor (21) and the hub motor (16) fail, and the second reversible motor (14) does not fail, the first-level performance-guaranteed non-energy-saving steering mode is executed; (7) If the first reversible motor (21) fails, and the second reversible motor (14) and the hub motor (16) do not fail, the secondary performance-guaranteed steering mode is executed, and the steering torque Tr requirement is determined in this mode. If Tr is less than or equal to Ta, the performance-guaranteed energy-saving steering mode 1 is executed; if Tr is greater than Ta, the performance-guaranteed energy-saving steering mode 2 is executed; (8) If the hub motor (16) fails, and the first reversible motor (21) and the second reversible motor (14) do not fail, the balanced performance steering mode is executed, and the steering torque Tr requirement is determined in this mode. If Tr is less than or equal to Tb, the balanced energy-saving steering mode is executed. If Tr is greater than Tb, the performance energy-saving steering mode is executed.

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