Active rear wheel steering system

Abstract

The invention discloses an active rear wheel steering system, which comprises a signal acquisition module used for receiving a vehicle motion parameter signal required by active rear wheel steering control in real time from a whole vehicle communication system; the control logic module is electrically connected with the signal acquisition module, a vehicle speed boundary 1 and a vehicle speed boundary 2 are preset in the control logic module, and the control logic module performs logic judgment based on the vehicle motion parameter signal and executes rear wheel steering control; wherein the rear wheel steering control comprises rear wheel and front wheel different-direction steering control, rear wheel and front wheel same-direction steering control, over-steering compensation and under-steering compensation. According to the method, the low-speed control convenience can be improved, the out-of-control risk of a low-attached road surface can be reduced, dynamic self-adaptive adjustment can be achieved, and the high-speed driving stability can be improved.

Description

Technical Field

[0001] This invention relates to the automotive field, and in particular to an active rear-wheel steering system. Background Technology

[0002] The automotive industry is developing rapidly, with an increasing variety of large vehicles. However, these models typically have a large turning radius, making them difficult to maneuver on narrow roads and reducing ease of handling, thus increasing driving difficulty. Vehicle handling stability is also a crucial factor. On low-friction surfaces, vehicles are prone to skidding and other risks, increasing the risk of accidents and injuries. Rear-wheel steering systems can alleviate these problems. Rear-wheel steering allows the front and rear wheels to move in opposite directions, reducing the vehicle's turning radius and improving handling convenience. The rear wheels moving in the same direction as the front wheels improve overall handling stability, reducing the risk of skidding and skidding, making it easier for the driver to recover, and contributing to overall vehicle handling stability.

[0003] Rear-wheel steering (RWS) is a system where a motor drives a pulley via a belt, which in turn drives a lead screw in a linear reciprocating motion, thus rotating the rear wheels. RWS systems have two modes: opposite-direction steering and same-direction steering. When the rear wheel angles are opposite to the front wheel angles, the turning radius is reduced, improving handling. When the rear wheel angles are in the same direction as the front wheels, the risk of skidding is reduced, making it easier for the driver to recover and improving overall stability. Traditional RWS systems only change the direction of rear wheel rotation with vehicle speed. However, on low-friction surfaces, before reaching the turning speed limit, the opposite-direction operation of the front and rear wheels, while reducing the turning radius, also increases the risk of loss of control.

[0004] The following technical problems exist in existing rear-wheel steering systems and need to be solved;

[0005] 1. Traditional RWS systems have a single steering mode, switching between opposite and same-direction modes only based on vehicle speed. They cannot adjust in real time according to the vehicle's dynamic state (such as yaw rate and yaw acceleration). On low-friction surfaces and when the vehicle speed for changing direction is not reached, opposite-direction steering will increase the risk of loss of control of the entire vehicle.

[0006] 2. Traditional RWS systems lack targeted compensation mechanisms for oversteer ("fishtailing") and understeer (deviation from the trajectory), making it difficult to cope with vehicle instability issues in different driving scenarios and unable to further improve the overall vehicle handling stability and safety. Summary of the Invention

[0007] The summary of this invention introduces a series of simplified concepts, all of which are simplifications of existing technologies in the field, and will be further explained in detail in the detailed description section. This summary is not intended to limit the key features and essential technical features of the claimed technical solution, nor is it intended to determine the scope of protection of the claimed technical solution.

[0008] The technical problem to be solved by the present invention is to provide an active rear wheel steering system that receives vehicle motion parameter signals in real time and controls the rear wheel steering through logical judgment, thereby solving the technical problems existing in the prior art.

[0009] To solve the above-mentioned technical problems, the present invention provides an active rear-wheel steering system, comprising:

[0010] The signal acquisition module is used to receive vehicle motion parameter signals required for active rear wheel steering control in real time from the vehicle communication system.

[0011] The control logic module is electrically connected to the signal acquisition module. It has preset vehicle speed boundary 1 and vehicle speed boundary 2. It performs logical judgment based on the vehicle motion parameter signal and executes rear wheel steering control.

[0012] The rear-wheel steering control includes: rear-wheel and front-wheel opposite steering control, rear-wheel and front-wheel same-direction steering control, oversteering compensation, and understeering compensation.

[0013] Preferably, the active rear-wheel steering system is further improved in that the vehicle motion parameter signals required for active rear-wheel steering control include: vehicle speed signal, steering wheel angle signal, steering wheel speed signal, and yaw rate signal.

[0014] Preferably, the active rear-wheel steering system is further improved in that the control logic module controls the target displacement of the rear wheels through the steering execution module to drive the rear wheels to steer.

[0015] For example, the steering actuation module includes a motor, a pulley, and a lead screw. The motor drives the lead screw to perform linear reciprocating motion through the pulley, thereby driving the rear wheel to rotate.

[0016] Preferably, the active rear-wheel steering system is further improved to meet the following condition A, thereby activating the rear-wheel and front-wheel opposite steering control;

[0017] Condition A: Vehicle speed ≤ vehicle speed boundary 1.

[0018] Preferably, the active rear-wheel steering system is further improved to meet the following condition B, thereby activating rear-wheel and front-wheel opposite steering control, oversteering compensation, or understeering compensation;

[0019] The activation priority is: oversteering compensation > understeering compensation > rear wheel and front wheel opposite steering control.

[0020] Condition B: Vehicle speed boundary 1 < vehicle speed ≤ vehicle speed boundary 2.

[0021] Preferably, the active rear-wheel steering system is further improved to activate oversteering compensation when the following condition C or condition D is met;

[0022] Condition C: Vehicle speed boundary 1 < vehicle speed ≤ vehicle speed boundary 2; and, vehicle yaw rate ≤ - yaw rate boundary for oversteering; and, yaw acceleration ≤ - yaw acceleration boundary for oversteering.

[0023] Condition D: Vehicle speed boundary 1 < vehicle speed ≤ vehicle speed boundary 2; and, vehicle yaw rate ≥ yaw rate boundary for oversteering.

[0024] Furthermore, the yaw acceleration is greater than or equal to the yaw acceleration boundary of the oversteering opening.

[0025] Preferably, the active rear-wheel steering system is further improved by activating oversteering compensation with a pre-exit state, which allows for oversteering compensation to be performed again.

[0026] If the following condition E is met, pre-exit is activated; if the following condition F is met in the pre-exit activated state, steering overcompensation is re-entered.

[0027] Condition E: The yaw rate of the whole vehicle is greater than or equal to the yaw rate boundary of the oversteer compensation pre-exit;

[0028] Furthermore, the yaw rate of the entire vehicle is less than or equal to the yaw rate boundary for the pre-exit of oversteer compensation;

[0029] Furthermore, the steering wheel angular velocity is less than or equal to the steering wheel angular velocity boundary for oversteer compensation pre-exit.

[0030] Furthermore, the steering wheel angular velocity is ≥ - the steering wheel angular velocity boundary for oversteering compensation pre-exit;

[0031] Condition F: Yaw acceleration ≥ Yaw acceleration boundary at oversteering opening;

[0032] Alternatively, the yaw acceleration ≤ - the yaw acceleration boundary of oversteering.

[0033] Preferably, the active rear-wheel steering system is further improved to activate understeer compensation when the following condition G or condition H is met;

[0034] Condition G: |Steering wheel angle| ≥ Steering wheel angle boundary when understeering compensation is activated;

[0035] Furthermore, vehicle speed boundary 1 < vehicle speed ≤ vehicle speed boundary 2;

[0036] Furthermore, the yaw rate is greater than 0 and the yaw rate is less than the theoretical yaw rate;

[0037] Furthermore, the yaw rate difference is greater than or equal to the yaw rate difference boundary when understeering compensation is activated;

[0038] Condition H: |Steering wheel angle| ≥ Steering wheel angle boundary when understeering compensation is activated;

[0039] Furthermore, vehicle speed boundary 1 < vehicle speed ≤ vehicle speed boundary 2;

[0040] Furthermore, (yaw rate < 0 and yaw rate > - theoretical yaw rate];

[0041] Furthermore, the yaw rate difference is greater than or equal to the yaw rate difference boundary when understeering compensation is activated.

[0042] Preferably, the active rear-wheel steering system is further improved to disengage understeering compensation when any one of the following conditions I, J, K, L and M is met;

[0043] Condition I: Vehicle speed ≤ vehicle speed boundary 1;

[0044] Condition J: Vehicle speed boundary 2 ≤ vehicle speed;

[0045] Condition K: |Steering wheel angle signal| ≤ Steering wheel angle boundary when understeering compensation is activated;

[0046] Condition L: Yaw velocity > 0 and yaw velocity > theoretical yaw velocity;

[0047] Condition M: Yaw velocity < 0 and yaw velocity < - theoretical yaw velocity.

[0048] Preferably, the active rear-wheel steering system is further improved to meet the following condition N: it exits understeer compensation or oversteer compensation and enters rear-wheel steering control in the same direction as the front wheels.

[0049] Vehicle speed boundary 2 < vehicle speed.

[0050] The working principle of this invention is explained below;

[0051] The active rear-wheel steering system provided by this invention achieves its function through three steps: "signal acquisition → logic judgment → steering execution," with its core being dynamic mode adjustment based on multiple signals.

[0052] The signal acquisition module acquires four key signals in real time: vehicle speed, steering wheel angle, steering wheel speed, and yaw rate, providing a data foundation for logical judgment.

[0053] The control logic module determines the initial opposite-direction mode (low speed) or same-direction mode (high speed) based on the relationship between the vehicle speed and the two vehicle speed boundaries (Active_RWS_VehSpdBound1, Active_RWS_VehSpdBound2).

[0054] In the medium speed range (Active_RWS_VehSpdBound1<VehSpd≤Active_RWS_VehSpdBound2), based on signals such as yaw rate, yaw acceleration, and steering wheel angle, it is determined whether to activate oversteer compensation (to deal with "fishtailing") or understeer compensation (to deal with trajectory deviation), and rules for pre-exit, reactivation, and mode switching are set.

[0055] The target displacement of the rear wheels is calculated using the corresponding formulas according to different modes (initial opposite direction, same direction, oversteering compensation, understeering compensation).

[0056] The motor of the steering execution module drives the lead screw to perform linear reciprocating motion through the pulley, converting the target displacement of the rear wheel into the actual steering angle of the rear wheel, realizing opposite or same-direction steering, and completing the mode adjustment.

[0057] This invention can achieve at least the following technical effects;

[0058] 1. This invention improves the ease of low-speed operation;

[0059] Although traditional RWS systems also have low-speed reverse steering functions, this invention uses formula (1) to accurately calculate the target displacement of the rear wheel, ensuring that the reverse steering angle matches the steering wheel operation, avoiding oversteering or understeering, and further optimizing the ease of operation.

[0060] At low speeds (VehSpd≤Active_RWS_VehSpdBound1), the rear wheels steer in the opposite direction to the front wheels, significantly reducing the vehicle's turning radius and making it easier to pass through narrow roads or make U-turns.

[0061] 2. This invention can reduce the risk of loss of control on low-adhesion road surfaces;

[0062] Traditional systems rely on a single parameter, vehicle speed. Steering in the opposite direction at medium speeds and low-friction surfaces can amplify vehicle instability. This invention adds a compensation mode in the medium speed range: when oversteering occurs, the rear wheels move in the same direction as the front wheels to balance the sideslip angles of the front and rear wheels, optimize the distribution of lateral forces, and suppress "fishtailing". When understeering occurs, the rear wheels move in the opposite direction to the front wheels to compensate for the insufficient actual steering angle, correct the trajectory, and reduce the risk of loss of control from a dynamic adjustment perspective.

[0063] This invention solves the problems of traditional RWS systems, which only allow for directional steering in the middle and are prone to loss of control on low-friction surfaces, reducing the risk of "fishtailing" and trajectory deviation, and improving driving safety.

[0064] 3. This invention can achieve dynamic adaptive adjustment;

[0065] This invention uses multi-signal acquisition (vehicle speed, steering wheel angle, yaw rate, etc.) and multi-layer logic judgment (basic mode, compensation mode, pre-exit / reactivation) to perceive vehicle dynamics in real time, rather than relying on a fixed vehicle speed threshold, to achieve closed-loop control of "perception-judgment-adjustment" and adapt to different road conditions and driving operations.

[0066] This invention can actively switch modes according to the vehicle's real-time driving status (such as yaw rate and steering wheel operation) without requiring additional operation from the driver, and is suitable for complex driving scenarios (such as low-friction surfaces and emergency steering).

[0067] 4. This invention can improve high-speed driving stability;

[0068] When driving at high speed, the vehicle has a large inertia. Steering in the same direction can increase the lateral stability of the whole vehicle. This invention calculates the target displacement of the rear wheel through formula (7) to ensure that the steering angle in the same direction matches the vehicle dynamics, enhances the handling stability when driving at high speed, and avoids the problem of lag in the high-speed mode response of traditional systems.

[0069] At high speeds (VehSpd > Active_RWS_VehSpdBound2), the rear wheels steer in the same direction as the front wheels, reducing the risk of vehicle skidding and "fishtailing" and making it easier for the driver to "rescue" the vehicle in an emergency. Attached Figure Description

[0070] The accompanying drawings are intended to illustrate the general characteristics of the methods, structures, and / or materials used in specific exemplary embodiments of the invention, supplementing the description in the specification. However, the drawings are schematic diagrams not drawn to scale and may not accurately reflect the precise structural or performance characteristics of any of the given embodiments. The drawings should not be construed as limiting or restricting the range of numerical values ​​or properties covered by exemplary embodiments of the invention. The invention will now be described in further detail with reference to the accompanying drawings and specific embodiments:

[0071] Figure 1 This is a schematic diagram of the logical framework of the present invention.

[0072] Figure 2 This is a schematic diagram of the understeering compensation data of the present invention.

[0073] Figure 3 This is a schematic diagram of the overcompensation data for steering in this invention. Detailed Implementation

[0074] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can fully understand other advantages and technical effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through different specific embodiments, and various details in this specification can also be applied based on different viewpoints, with various modifications or changes made without departing from the overall design concept of the invention. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. The following exemplary embodiments of the present invention can be implemented in many different forms and should not be construed as being limited to the specific embodiments set forth herein. It should be understood that these embodiments are provided to make the disclosure of the present invention thorough and complete, and to fully convey the technical solutions of these exemplary embodiments to those skilled in the art. It should be understood that when an element is referred to as "connected" or "combined" to another element, the element can be directly connected or combined to the other element, or there may be intermediate elements. The difference is that when an element is referred to as "directly connected" or "directly combined" to another element, there are no intermediate elements. Throughout the drawings, the same reference numerals always denote the same elements. Example

[0075] This invention provides an active rear-wheel steering system, comprising:

[0076] The signal acquisition module is used to receive vehicle motion parameter signals required for active rear wheel steering control in real time from the vehicle communication system (e.g., CAN bus).

[0077] For example, the vehicle motion parameter signals required for active rear wheel steering control include: the vehicle speed signal VehSpd, the steering wheel angle signal StrWheelAng, the steering wheel speed signal StrWheelAngSpd, and the yaw rate signal DynYawRate. These parameters are necessary for realizing the main design concept of this invention. Under the overall design concept of this invention, other vehicle parameters can also be converted into the above-mentioned necessary parameters through mathematical calculations, or vehicle motion-related parameters can be added to improve control accuracy.

[0078] The control logic module is electrically connected to the signal acquisition module. It has preset vehicle speed boundary 1 Active_RWS_VehSpdBound1 and vehicle speed boundary 2 Active_RWS_VehSpdBound2. It performs logical judgment based on the vehicle motion parameter signal and executes rear wheel steering control.

[0079] The rear-wheel steering control includes: rear-wheel and front-wheel opposite steering control, rear-wheel and front-wheel same-direction steering control, oversteering compensation, and understeering compensation.

[0080] When the vehicle speed is less than the speed boundary 1, i.e., VehSpd≤Active_RWS_VehSpdBound1, the rear wheel steering system is in the opposite mode, i.e. the rear wheel steering angle moves in the opposite direction to the front wheel steering angle. This is called the initial state of rear wheel steering. The target displacement of the lead screw in the RWS system is calculated as follows.

[0081] RWS_TarDisplacement=StrWheelAng×Normal_Factor×Sign(OppositeDir) formula 1;

[0082] RWS_TarDisplacement is the target displacement of the rear wheel, StrWheelAng is the steering wheel angle, OppositeDir is the direction of the target displacement of the rear wheel, which is -1 or 1 and is related to the rear steering mechanism layout. OppositeDir is used to ensure that the rear wheels are in the opposite direction to the front wheels, and Normal_Factor is the speed coefficient.

[0083] When Active_RWS_VehSpdBound1 < VehSpd ≤ Active_RWS_VehSpdBound2, the RWS system, in addition to the normal mode of front and rear wheel counter-steering, can also achieve understeer and oversteer compensation. The active rear wheel steering state ControlState differs in different modes. The activation priority is: Oversteer compensation (OverStrCompState) ControlState = 3 > Understeer compensation (UnderStrCompState) ControlState = 2 > Rear wheel and front wheel counter-steering control (NormalState) ControlState = 0.

[0084] Insufficient rear wheel grip can cause oversteer, leading to a "fishtailing" phenomenon. When the rear wheels move in the same direction as the front wheels, it balances the front and rear wheel sideslip angles, optimizes lateral force distribution, reduces or improves the "fishtailing" phenomenon, and enhances overall vehicle stability. In the RWS system, when the system is in oversteer compensation mode, the rear wheels move in the same direction as the front wheels.

[0085] Activate oversteering compensation, ControlState = 3, where the yaw rate AccDynYawRate is calculated as follows, Formula 2:

[0086] AccDynYawRate=[DynYawRate(t)–DynYawRate(t-DelayN)] / DelayN*SWCTimes Formula 2;

[0087] DelayN is the delay length, SWCTimes is the software execution cycle in milliseconds, and AccDynYawRate is the yaw rate.

[0088] Active_RWS_VehSpdBound1<VehSpd≤Active_RWS_VehSpdBound2; and, DynYawRate≤-Active_RWS_OverYawRateBound; and, AccDynYawRat≤-SteeringOver-Active_RWS_OverAccYawRateBound;

[0089] Active_RWS_VehSpdBound1<VehSpd≤Active_RWS_VehSpdBound2; and, DynYawRate≥Active_RWS_OverYawRateBound&&

[0090] AccDynYawRat≥Active_RWS_OverAccYawRateBound.

[0091] Active_RWS_VehSpdBound1 is the vehicle speed boundary 1, Active_RWS_VehSpdBound2 is the vehicle speed boundary 2, DynYawRate is the overall vehicle yaw rate, Active_RWS_OverYawRateBound is the yaw rate boundary for oversteering, AccDynYawRate is the yaw acceleration, and Active_RWS_OverAccYawRateBound is the yaw acceleration boundary for oversteering.

[0092] Furthermore, during the transition to the overcompensation activation state, it can also enter the pre-exit state OverStrCompStateExitPre. The logic for entering the pre-exit state is as follows, and the following conditions are denoted as Conditions2:

[0093] DynYawRate≥-Active_RWS_OverYawRatePreExitBound1&&

[0094] DynYawRate≤Active_RWS_OverYawRatePreExitBound1&&

[0095] StrWheelAngSpd≤Active_RWS_OverStrWheelAngSpdBound&&

[0096] StrWheelAngSpd≥-Active_RWS_OverStrWheelAngSpdBound.

[0097] Active_RWS_OverYawRatePreExitBound1 is the yaw rate boundary for pre-exit of oversteer compensation, StrWheelAngSpd is the steering wheel angular velocity, and Active_RWS_OverStrWheelAngSpdBound is the steering wheel angular velocity boundary for pre-exit of oversteer compensation. In this state, ControlState=3. If the duration of the pre-exit state exceeds Active_RWS_OverPreExitLastTime, the system enters the opposite direction mode, ControlState=0, and exits oversteer compensation.

[0098] When ControlState=3, the calculation logic for the target displacement RWS_TarDisplacement of the RWS system is as follows;

[0099] RWS_TarDisplacement=StrWheelAng×Normal_Factor×Sign(SameDir)+

[0100] DynYawRate×Over_Factor×Sign(StrWheelAng) formula 3;

[0101] RWS_TarDisplacement is the target displacement of the rear wheels, StrWheelAng is the steering wheel angle, Normal_Factor is the speed coefficient, DynYawRate is the yaw rate, Over_Factor is the speed coefficient, SameDir is the direction, which is -1 or 1 and is related to the rear steering mechanism layout. SameDir is used to ensure that the rear wheels are in the same direction as the front wheels.

[0102] Furthermore, the oversteer pre-exit state can also re-enter the oversteer compensation state, with the following judgment logic, and the following conditions are denoted as Conditions3:

[0103] AccDynYawRate≥Active_RWS_OverAccYawRateAgainBound||

[0104] AccDynYawRate≤-Active_RWS_OverAccYawRateAgainBound

[0105] Active_RWS_OverYawRateBound is the yaw rate boundary for oversteering, and AccDynYawRate is the yaw acceleration.

[0106] Insufficient front wheel grip can easily lead to understeer. When understeer occurs, the actual steering angle is less than the steering wheel input angle, causing the vehicle to deviate from its intended trajectory and increasing the risk of collision. Understeer can be mitigated by reversing the steering wheel input angle when the actual yaw rate is lower than the theoretical value.

[0107] Activate oversteering compensation and calculate the theoretical yaw rate in real time. The theoretical yaw rate RWS_ActualDynYawRate is obtained from empirical formula 4:

[0108] RWS_ActualDynYawRate=(VehSpd×tan(StrWheelAng×π / 180×i) / LFormula 4;

[0109] Where RWS_ActualDynYawRate is the theoretical yaw rate, VehSpd is the vehicle speed, StrWheelAng is the steering wheel angle, and L is the vehicle wheelbase;

[0110] Calculate the difference in yaw rate:

[0111] RWS_DiffDynYawRate=|RWS_ActualDynYawRate-DynYawRate| Formula 5;

[0112] Where RWS_DiffDynYawRate is the difference in yaw rate, RWS_ActualDynYawRate is the theoretical yaw rate, and DynYawRate is the actual yaw rate;

[0113] The following conditions are denoted as Conditions4:

[0114] |StrWheelAng|≥Active_RWS_UnderAllowStrWheelAngBound&&

[0115] Active_RWS_VehSpdBound1<VehSpd≤Active_RWS_VehSpdBound2&&

[0116] [(DynYawRate>0&&DynYawRate <RWS_ActualDynYawRate)&&

[0117] RWS_DiffDynYawRate≥Active_RWS_UnderDiffYawRateBound; ||

[0118] |StrWheelAng|≥Active_RWS_UnderAllowStrWheelAngBound&&

[0119] Active_RWS_VehSpdBound<VehSpd≤Active_RWS_VehSpdBound2&&

[0120] (DynYawRate<0&&DynYawRate>-RWS_ActualDynYawRate]&&

[0121] RWS_DiffDynYawRate≥Active_RWS_UnderDiffYawRateBound.

[0122] StrWheelAng is the steering wheel angle, Active_RWS_UnderAllowStrWheelAngBound is the steering wheel angle boundary for enabling understeer compensation, Active_RWS_VehSpdBound1 is vehicle speed boundary 1, Active_RWS_VehSpdBound2 is vehicle speed boundary 2, RWS_ActualDynYawRate is the theoretical yaw rate, RWS_DiffDynYawRate is the yaw rate difference, and Active_RWS_UnderDiffYawRateBound is the yaw rate difference boundary for enabling understeer compensation. When the above conditions are met and the duration exceeds Active_RWS_UnderPreActiveLastTime, understeer compensation is initiated, and ControlState = 2.

[0123] When ControlState = 2, the calculation logic for the target displacement RWS_TarDisplacement of the RWS system is as follows, see Formula 6:

[0124] RWS_TarDisplacement=StrWheelAng×Normal_Factor×Sign(OppositeDir)+(RWS_ActualDynYawRate-DynYawRate)×Under_Factor×Sign(OppositeDir) Formula 6;

[0125] RWS_TarDisplacement is the target displacement of the rear wheels, StrWheelAng is the steering wheel angle, Normal_Factor is the speed coefficient, DynYawRate is the yaw rate, Over_Factor is the speed coefficient, OppositeDir is the direction (-1 or 1), which is related to the rear steering mechanism layout. OppositeDir is used to ensure that the rear wheels are in the opposite direction to the front wheels, and Under_Factor is the speed coefficient.

[0126] The understeering compensation will be discontinued when any of the following conditions are met, denoted as Conditions5:

[0127] VehSpd≤Active_RWS_VehSpdBound1||

[0128] Active_RWS_VehSpdBound2≤VehSpd||

[0129] |StrWheelAng|≤Active_RWS_UnderAllowStrWheelAngBound||

[0130] DynYawRate>0&&DynYawRate>RWS_ActualDynYawRate||

[0131] DynYawRate<0&&DynYawRate<-RWS_ActualDynYawRate

[0132] Active_RWS_VehSpdBound1 is the vehicle speed boundary 1, Active_RWS_VehSpdBound2 is the vehicle speed boundary 2, StrWheelAng is the steering wheel angle, Active_RWS_UnderAllowStrWheelAngBound is the steering wheel angle boundary for understeer compensation exit, and RWS_ActualDynYawRate is the yaw rate boundary for understeer compensation exit.

[0133] When the following conditions occur, the system will transition from understeering compensation to oversteering compensation. The specific judgment logic is the same as that for oversteering. The understeering compensation state can be directly updated to the oversteering compensation state.

[0134] When the following conditions occur, the front and rear wheels disengage from understeer or oversteer logic and enter the same-direction working mode for the entire process, called SameDirState. In this mode, ControlState = 4. The specific judgment logic is as follows, and the following conditions are denoted as Conditions6:

[0135] Active_RWS_VehSpdBound2<VehSpd

[0136] When ControlState = 4, the calculation logic for the target displacement RWS_TarDisplacement of the RWS system is as follows, see Formula 7:

[0137] RWS_TarDisplacement=StrWheelAng×Normal_Factor×Sign(SameDir) Formula 7;

[0138] In the above, Active_RWS_VehSpdBound2 is the vehicle speed boundary 2, VehSpd is the vehicle speed, StrWheelAng is the steering wheel angle, Normal_Factor is the coefficient with respect to vehicle speed, SameDir is the direction, which is -1 or 1, and is related to the rear steering mechanism layout. SameDir is used to ensure that the rear wheels are in the same direction as the front wheels.

[0139] Table 1 Variable Definitions;

[0140]

[0141]

[0142] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It will also be understood that, unless expressly defined herein, terms such as those defined in a general dictionary shall be interpreted as having the meaning consistent with their meaning in the relevant field context, and not as having an idealized or overly formal meaning.

[0143] The present invention has been described in detail above through specific embodiments and examples, but these are not intended to limit the invention. Many modifications and improvements can be made by those skilled in the art without departing from the principles of the invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. An active rear-wheel steering system, characterized in that, include: The signal acquisition module is used to receive vehicle motion parameter signals required for active rear wheel steering control in real time from the vehicle communication system. The control logic module is connected to the signal acquisition module. It has preset vehicle speed boundary 1 and vehicle speed boundary 2. It performs logical judgment based on the vehicle motion parameter signal and executes rear wheel steering control. The rear-wheel steering control includes: rear-wheel and front-wheel opposite steering control, rear-wheel and front-wheel same-direction steering control, oversteering compensation, and understeering compensation.

2. The active rear-wheel steering system as described in claim 1, characterized in that, The vehicle motion parameter signals required for active rear-wheel steering control include: vehicle speed signal, steering wheel angle signal, steering wheel speed signal, and yaw rate signal.

3. The active rear-wheel steering system as described in claim 1, characterized in that: The control logic module controls the target displacement of the rear wheels through the steering execution module to drive the rear wheels to steer.

4. The active rear-wheel steering system as described in claim 1, characterized in that: The rear-wheel and front-wheel counter-steering control is activated when the following condition A is met; Condition A: Vehicle speed ≤ vehicle speed boundary 1.

5. The active rear-wheel steering system as described in claim 1, characterized in that: If the following condition B is met, the rear wheel and front wheel opposite steering control, oversteering compensation, or understeering compensation will be activated. The activation priority is: oversteering compensation > understeering compensation > rear wheel and front wheel opposite steering control. Condition B: Vehicle speed boundary 1 < vehicle speed ≤ vehicle speed boundary 2.

6. The active rear-wheel steering system as described in claim 1, characterized in that: Condition C: Vehicle speed boundary 1 < vehicle speed ≤ vehicle speed boundary 2; and, vehicle yaw rate ≤ - yaw rate boundary for oversteering; and, yaw acceleration ≤ - yaw acceleration boundary for oversteering. Condition D: Vehicle speed boundary 1 < vehicle speed ≤ vehicle speed boundary 2; and, vehicle yaw rate ≥ yaw rate boundary for oversteering. Furthermore, the yaw acceleration is greater than or equal to the yaw acceleration boundary of the oversteering opening.

7. The active rear-wheel steering system as described in claim 1, characterized in that: If the following condition E is met, pre-exit is activated; if the following condition F is met in the pre-exit activated state, steering overcompensation is re-entered. Condition E: The yaw rate of the whole vehicle is greater than or equal to the yaw rate boundary of the oversteer compensation pre-exit; Furthermore, the yaw rate of the entire vehicle is less than or equal to the yaw rate boundary for the pre-exit of oversteer compensation; Furthermore, the steering wheel angular velocity is less than or equal to the steering wheel angular velocity boundary for oversteer compensation pre-exit. Furthermore, the steering wheel angular velocity is ≥ - the steering wheel angular velocity boundary for oversteering compensation pre-exit; Condition F: Yaw acceleration ≥ Yaw acceleration boundary at oversteering opening; Alternatively, the yaw acceleration ≤ - the yaw acceleration boundary of oversteering.

8. The active rear-wheel steering system as described in claim 1, characterized in that: Understeering compensation is activated when either condition G or condition H is met. Condition G: |Steering wheel angle| ≥ Steering wheel angle boundary when understeering compensation is activated; Furthermore, vehicle speed boundary 1 < vehicle speed ≤ vehicle speed boundary 2; Furthermore, the yaw rate is greater than 0 and the yaw rate is less than the theoretical yaw rate; Furthermore, the yaw rate difference is greater than or equal to the yaw rate difference boundary when understeering compensation is activated; Condition H: |Steering wheel angle| ≥ Steering wheel angle boundary when understeering compensation is activated; Furthermore, vehicle speed boundary 1 < vehicle speed ≤ vehicle speed boundary 2; Furthermore, (yaw rate < 0 and yaw rate > - theoretical yaw rate]; Furthermore, the yaw rate difference is greater than or equal to the yaw rate difference boundary when understeering compensation is activated.

9. The active rear-wheel steering system as described in claim 1, characterized in that: If any one of the following conditions I, J, K, L, and M is met, exit the under-compensation for turning; Condition I: Vehicle speed ≤ vehicle speed boundary 1; Condition J: Vehicle speed boundary 2 ≤ vehicle speed; Condition K: |Steering wheel angle signal| ≤ Steering wheel angle boundary when understeering compensation is activated; Condition L: Yaw velocity > 0 and yaw velocity > theoretical yaw velocity; Condition M: Yaw velocity < 0 and yaw velocity < - theoretical yaw velocity.

10. The active rear-wheel steering system as described in claim 1, characterized in that: When the following condition N is met, the understeer compensation or oversteer compensation is discontinued, and the rear wheel steering control is engaged in the same direction as the front wheel steering. Vehicle speed boundary 2 < vehicle speed.

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