Architecture and method for steer-by-wire fault backup for direct yaw control actuators

Abstract

A method for controlling a steering system includes: receiving vehicle data and a steering request from a vehicle; determining, using the vehicle data, whether a road steering wheel actuator of the vehicle has failed; in response to determining that a road steering wheel actuator of the vehicle fails, determining a target wheel slip of the vehicle based on the steering request, and maintaining the target wheel slip of the vehicle while the vehicle is traveling; and adjusting a wheel speed of at least one wheel of the vehicle based on a feedback signal indicative of a road wheel angle while the vehicle is traveling.

Description

Technical Field

[0001] The present disclosure relates to an architecture and method for steer-by-wire fail-backup using a direct yaw control actuator. Background Art

[0002] This introduction generally presents the background of the present disclosure. To the extent that the work performed by the present inventors described in this introduction and various aspects of the specification is performed, it is not intended to be prior art at the time of filing the application, and it is never explicitly or implicitly admitted to be prior art to the present disclosure.

[0003] Steer-by-wire systems do not rely on a mechanical connection to the wheels. Instead, these system cables send electronic signals to the vehicle's gears to steer the vehicle. Many vehicles are equipped with steer-by-wire systems. Therefore, it would be useful to develop a system and method for backup in the event of a steer-by-wire system failure. Summary of the invention

[0004] The disclosed method and architecture is intended to provide a torque vectoring and / or differential braking backup system for a downgraded steering-by-wire (SbW) system that does not require changes to the suspension / steering system and remains effective even in the case of a non-steering axle. The wheel speed control-based approach is a solution that does not require physical changes to the vehicle suspension system. Because the disclosed method does not subject the vehicle to wheel instability (e.g., directly controlling wheel slip), driving under the backup system does not produce common side effects such as tire saturation and potential vehicle instability.

[0005] In one aspect of the present disclosure, a method for controlling a steer-by-wire system includes: receiving vehicle data and a steering request from a vehicle; using the vehicle data, determining whether a road steering wheel actuator of the vehicle has failed; in response to determining that the road steering wheel actuator of the vehicle has failed, determining a target wheel slip of the vehicle based on the steering request; maintaining the target wheel slip of the vehicle while the vehicle is traveling; and, based on a feedback signal, adjusting a wheel speed of at least one wheel of the vehicle, wherein the feedback signal indicates a road wheel angle while the vehicle is traveling.

[0006] The method may also include arbitrating between a target wheel slip to follow a desired path and controlling wheel instability. The steering request includes a requested steering wheel angle, and the target wheel slip calculation of the vehicle depends on the requested steering wheel angle. Using the Ackerman steering geometry of the steer-by-wire system, the target wheel slip of the vehicle is determined based on the steering request. The method may also include using model predictive control (MPC) to maintain the target wheel slip of the vehicle while the vehicle is moving. The MPC includes a linear time-varying (LTV) solver. The method may also include using a control strategy to maintain the target wheel slip of the vehicle while the vehicle is moving. The control strategy depends on the driveline configuration of the vehicle.

[0007] The present disclosure also describes a vehicle including a sensor, a steer-by-wire system, and a controller in communication with the sensor and the steer-by-wire system. The controller is programmed to perform the above method. The present disclosure also describes a tangible, non-transitory machine-readable medium including machine-readable instructions, which, when executed by a processor, causes the processor to perform the above method.

[0008] Further areas of applicability will become apparent from the detailed description provided herein.It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

[0009] The above features and advantages and other features and advantages of the disclosed systems and methods are apparent from the following detailed description, including claims and exemplary embodiments, when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present disclosure will be more fully understood from the detailed description and accompanying drawings, in which:

[0011] Figure 1 is a block diagram depicting an embodiment of a vehicle including a steer-by-wire system.

[0012] Figure 2 is a flow chart of a method for controlling a steer-by-wire system. DETAILED DESCRIPTION

[0013] Reference will now be made in detail to several examples of the present disclosure illustrated in the accompanying drawings. Whenever possible, the same or similar reference numerals are used in the drawings and the description to refer to the same or similar components or steps.

[0014] Reference Figure 1, the vehicle 10 generally includes a chassis 12, a body 14, front wheels and rear wheels 17, and may be referred to as a vehicle system. In the depicted embodiment, the vehicle 10 includes two front wheels 17a and two rear wheels 17b. The body 14 is disposed on the chassis 12 and substantially surrounds the components of the vehicle 10. The body 14 and the chassis 12 may together form a vehicle frame. Each wheel 17 is rotatably coupled to the chassis 12 near a corresponding corner of the body 14. The vehicle 10 includes a front axle 19 coupled to the front wheels 17a and a rear axle 25 coupled to the rear wheels 17b.

[0015] The vehicle 10 is an autonomous vehicle, and the control system 98 is incorporated into the vehicle 10. The system 98 may be referred to as a system or a system for controlling the steering system 24. The vehicle 10 is, for example, a vehicle that is automatically controlled to transport passengers from one location to another. The vehicle 10 is depicted as a pickup truck in the illustrated embodiment, but it should be understood that other vehicles may also be used, including trucks, sedans, sports cars, sports utility vehicles (SUVs), recreational vehicles (RVs), etc. In an embodiment, the vehicle 10 may include a so-called secondary, tertiary, tertiary or tertiary driving automation system. The tertiary system represents "high automation" and refers to the driving mode-specific performance of the autonomous driving system for all aspects of the dynamic driving task, even if the human driver does not respond appropriately to the intervention request. The tertiary system represents "full automation" and refers to the full-time execution of the autonomous driving system for all aspects of the dynamic driving task under a variety of road and environmental conditions that can be managed by a human driver. In a level 3 vehicle, the system 98 performs the entire dynamic driving task (DDT) within its designed area. In a level 2 vehicle, the system provides steering, braking / acceleration support, lane centering and adaptive cruise control. However, even when these systems are activated, the vehicle operator at the steering wheel must steer and constantly supervise the automated functions.

[0016] As shown, the vehicle 10 generally includes a propulsion system 20, a transmission system 22, a steering system 24, a braking system 26, a sensor system 28, an actuator system 30, at least one data storage device 32, at least one controller 34, and a communication system 36. The steering system 24 is a wire-controlled steering system. In various embodiments, the propulsion system 20 may include an electric motor (such as a traction motor) and / or a fuel cell propulsion system. The vehicle 10 may also include a battery (or battery pack) 21 electrically connected to the propulsion system 20. Therefore, the battery 21 is configured to store electrical energy and provide electrical energy to the propulsion system 20. In certain embodiments, the propulsion system 20 may include an internal combustion engine. The transmission system 22 is configured to transfer power from the propulsion system 20 to the wheels 17 according to a selectable speed ratio. According to various embodiments, the transmission system 22 may include a stepped automatic transmission, a continuously variable transmission, or other suitable transmission. The braking system 26 is configured to provide braking torque to the wheels 17. In various embodiments, the braking system 26 may include a friction brake, a wire control brake, a regenerative braking system (such as a motor), and / or other suitable braking systems. The steering system 24 affects the position of the wheels 17 and may include a steering wheel 33. Although depicted as including a steering wheel 33 for purposes of illustration, in some embodiments contemplated within the scope of the present disclosure, the steering system 24 may not include a steering wheel 33.

[0017] The sensor system 28 includes one or more sensors 40 (i.e., sensing devices) that sense observable conditions of the external environment and / or the internal environment of the vehicle 10. The sensors 40 communicate with the controller 34 and may include, but are not limited to, one or more steering wheel sensors 45, one or more radars, one or more light detection and ranging (lidar) sensors, one or more proximity sensors, one or more odometers, one or more ground penetrating radar (GPR) sensors, one or more steering angle sensors, global navigation satellite system (GNSS) transceivers (e.g., one or more global positioning system (GPS) transceivers), one or more tire pressure sensors, one or more cameras 41 (e.g., eye trackers), one or more gyroscopes, one or more accelerometers, one or more inclinometers, one or more speed sensors, one or more ultrasonic sensors, one or more inertial measurement units (IMUs), one or more night vision devices, thermal imaging sensors, and / or other sensors. Each sensor 40 is configured to generate a signal indicative of a sensed observable condition of the external environment and / or the internal environment of the vehicle 10. Because the sensor system 28 provides data to the controller 34, the sensor system 28 and its sensors 40 are considered to be information sources (or simply sources). The vehicle 10 and / or the system 98 do not include a light sensor capable of detecting light inside the vehicle 10 .

[0018] The actuator system 30 includes one or more actuators 42 that control one or more vehicle features, such as, but not limited to, the propulsion system 20, the transmission system 22, the steering system 24, and the braking system 26. In various embodiments, the vehicle features may also include interior and / or exterior vehicle features, such as, but not limited to, doors, trunks, and cabin features, such as air, music, lighting, etc. The actuator 43 may be part of the steering system 24 and include one or more road wheel actuators (RWA) and hand wheel actuators (HWA).

[0019] The data storage device 32 stores data for automatically controlling the vehicle 10. In various embodiments, the data storage device 32 stores a defined map of the navigable environment. In various embodiments, the defined map may be predefined and obtained by a remote system. For example, the defined map may be assembled by a remote system, transmitted to the vehicle 10 (wirelessly and / or wiredly), and stored in the data storage device 32. The data storage device 32 may be part of the controller 34, separate from the controller 34, or part of the controller 34 and part of a separate system.

[0020] The vehicle 10 may also include one or more airbags 35 in communication with the controller 34 or another controller of the vehicle 10. The airbags 35 include inflatable airbags and are configured to transition between a stowed configuration and a deployed configuration to cushion the effects of external forces applied to the vehicle 10. The sensors 40 may include airbag sensors (e.g., IMUs) configured to detect external forces and generate signals indicating the magnitude of such external forces. The controller 34 is configured to command the deployment of the airbags 35 based on signals from one or more sensors 40 (e.g., airbag sensors). Thus, the controller 34 is configured to determine when the airbags 35 have been deployed.

[0021] The controller 34 includes at least one processor 44 and a non-transitory computer readable storage device or medium 46. The processor 44 can be a custom or commercially available processor, a central processing unit (CPU), a graphics processing unit (GPU), a secondary processor of several processors associated with the controller 34, a semiconductor-based microprocessor (in the form of a microchip or chipset), a macroprocessor, a combination thereof, or generally a device for executing instructions. The computer readable storage device or medium 46 can include volatile and non-volatile storage in, for example, read-only memory (ROM), random access memory (RAM), and keep-alive memory (KAM). KAM is a persistent or non-volatile memory that can be used to store various operating variables when the processor 44 is powered off. The computer readable storage device or medium 46 can be implemented using a variety of storage devices, such as PROM (programmable read-only memory), EPROM (electrically programmable read-only memory), EEPROM (electrically erasable programmable read-only memory), flash memory, or other electrical, magnetic, optical, or combination storage devices capable of storing data (some of which represent executable instructions when the controller 34 controls the vehicle 10). The controller 34 of the vehicle 10 may be referred to as a vehicle controller and may be programmed to perform the method 100 (described in detail below). Figure 2 ).

[0022] The instructions may include one or more separate programs, each of which includes an ordered list of executable instructions for implementing logical functions. When executed by the processor 44, the instructions receive and process signals from the sensor system 28, execute logic, calculations, methods and / or algorithms for automatically controlling components of the vehicle 10, and generate control signals to the actuator system 30 to automatically control components of the vehicle 10 based on the logic, calculations, methods and / or algorithms. Although Figure 1 , embodiments of the vehicle 10 may include multiple controllers 34 that communicate via a suitable communication medium or combination of communication mediums and cooperate to process sensor signals, execute logic, calculations, methods and / or algorithms, and generate control signals to automatically control features of the vehicle 10. In various embodiments, one or more instructions of the controller 34 are embodied in the control system 98.

[0023] The vehicle 10 includes a user interface 23, which may be a touch screen in the instrument panel. The user interface 23 may include, but is not limited to, an alarm, such as one or more speakers 27 for providing audible sounds, tactile feedback in a vehicle seat or other object, one or more displays 29, one or more microphones 31, and / or other devices suitable for notifying a vehicle user of the vehicle 10. The user interface 23 is in electronic communication with a controller 34 and is configured to receive input from a vehicle occupant 11 (e.g., a vehicle driver or a vehicle passenger). For example, the user interface 23 may include a touch screen and / or buttons configured to receive input from a vehicle occupant 11. Thus, the controller 34 is configured to receive input from a user via the user interface 23. The vehicle 10 may include one or more displays 29, which are configured to display information to a vehicle occupant 11 (e.g., a vehicle operator or a passenger) and may be a head-up display (HUD).

[0024] The communication system 36 communicates with the controller 34 and is configured to wirelessly transmit information to and receive information from other remote vehicles 48, such as, but not limited to, other vehicles ("V2V" communication), infrastructure ("V2I" communication), remote systems located at a remote call center (such as General Motors' ON-STAR), and / or personal electronic devices (such as mobile phones). In the present disclosure, the term "remote vehicle" refers to a vehicle, such as an automobile, that is configured to send one or more signals to the vehicle 10 but is not physically connected to the vehicle 10. In some embodiments, the communication system 36 is a wireless communication system configured to communicate via a wireless local area network (WLAN) using the IEEE 802.11 standard or by using cellular data communications. However, additional or alternative communication methods such as dedicated short-range communication (DSRC) channels are also considered within the scope of the present disclosure. A DSRC channel refers to a one-way or two-way short-range to medium-range wireless communication channel designed specifically for automotive use, and a set of corresponding protocols and standards. Therefore, the communication system 36 may include one or more antennas and / or communication transceivers 37 for receiving and / or transmitting signals, such as collaborative sensing messages (CSM). The communication transceiver 37 may be considered a sensor 40. The communication system 36 is configured to wirelessly transmit information between the vehicle 10 and another vehicle. Additionally, the communication system 36 is configured to wirelessly transmit information between the vehicle 10 and infrastructure or other vehicles.

[0025] Figure 21 is a flow chart of a method 100 for controlling a steer-by-wire system. The purpose of the method 100 is to provide a torque vectoring and / or differential braking backup system for a steer-by-wire (SbW) system 24 that is degraded and that does not require changes to the suspension or steering system 24 and remains effective even on non-steered axles. The wheel speed control-based method 100 is a solution that does not require physical changes to the suspension system. Because the method 100 does not subject the vehicle to wheel instability (e.g., directly controlling wheel slip), driving under the backup system does not produce common side effects such as tire saturation and potential vehicle instability. The method 100 begins at box 102. Box 102 entails determining whether one or more road wheel actuators have failed or at least degraded to a certain extent. To this end, the controller 34 receives vehicle data (e.g., signals from road wheel actuators) and then uses the vehicle data to determine whether a road wheel actuator (RWA) has failed or at least degraded to a certain extent. Although the method 100 can be performed when one or more road steering wheel actuators fail, the steering wheel sensor from the hand wheel angle actuator (HWA) should be functioning properly. In the event of a complete failure of the HWA, the controller 34 reads the third steering angle sensor (SAS) and determines the RWA target. If the controller 34 determines that one or more road steering wheel actuators have failed or at least degraded to a certain extent, the method 100 proceeds to box 104.

[0026] Block 104 entails determining (e.g., calculating) a target wheel slip based on a steering request. Thus, the controller 34 receives a steering request from a vehicle driver, an advanced driver assistance system (ADAS) of the vehicle 10, and / or an autonomous vehicle feature. The steering request includes a requested steering wheel angle. In response to receiving the steering request, the controller 34 calculates a target or desired wheel slip (i.e., wheel incremental velocity). The desired yaw rate for a given requested steering wheel angle can be determined using the following equation:

[0027]

[0028] in:

[0029] ω zd is the desired yaw rate;

[0030] δ f is the requested steering wheel angle;

[0031] v x is the longitudinal speed of the vehicle 10;

[0032] a is the distance from the center of gravity of the vehicle 10 to the front axle;

[0033] b is the distance from the center of gravity of the vehicle 10 to the rear axle; and

[0034] K us is the understeer coefficient.

[0035] The target wheel slip may be calculated based on a steering request using Ackermann steering geometry of the steer-by-wire system 24. Specifically, the target wheel speed may be calculated using the following equation.

[0036]

[0037]

[0038]

[0039]

[0040]

[0041]

[0042] in:

[0043] v x is the longitudinal speed of the vehicle 10;

[0044] δ o is the outer wheel steering angle;

[0045] δ i is the inner wheel steering angle;

[0046] w r is the track size of the vehicle's rear axle;

[0047] l is the wheelbase;

[0048] δ is the steering wheel angle;

[0049] is an intermediate variable;

[0050] is an intermediate variable;

[0051] ω zd is the required wheel speed;

[0052] R is the vehicle turning speed;

[0053] b is the distance from the center of gravity of the vehicle 10 to the rear axle;

[0054] R eff is the effective radius of the tire;

[0055] is the desired wheel speed at the rear inner wheel;

[0056] is the desired wheel speed at the rear outer wheel;

[0057] is the desired wheel speed at the front inner wheel; and

[0058] is the desired wheel speed at the front outer wheel.

[0059] After frame 104, method 100 continues to frame 106. At frame 106, controller 34 implements a control strategy to maintain a target wheel slip for the vehicle while the vehicle is traveling. The control strategy depends on the driveline configuration of the vehicle. If vehicle 10 is front-wheel drive, braking torque vectoring is used to maintain a target wheel slip for the vehicle while the vehicle 10 is traveling. If vehicle 10 is rear-wheel drive, differential braking on the front axle and braking torque vectoring on the rear axle are used to maintain a target wheel slip for vehicle 10 while the vehicle is traveling. If vehicle 10 is all-wheel drive, braking torque vectoring on the front and rear axles are used to maintain a target wheel slip for vehicle 10 while the vehicle is traveling. If vehicle 10 has two rear electric motors and one front electric motor, torque vectoring on the rear axle and braking torque vectoring on the front axle are used to maintain a target wheel slip for the vehicle while the vehicle 10 is traveling.

[0060] The control strategy for maintaining a target wheel slip for the vehicle 10 as it travels can be determined using the following equations of motion:

[0061]

[0062]

[0063] in:

[0064] M is the mass of the vehicle 10;

[0065] a is the acceleration of the vehicle 10;

[0066] F xi is the longitudinal tire force at each corner of the vehicle, with index i∈{1,2,3,4};

[0067] δ i is the inner turning road angle;

[0068] F yi is the lateral tire force at each corner of the vehicle 10, with index i∈{1,2,3,4};

[0069] T w1 is the wheel torque at each corner of the vehicle 10, with index i∈{1,2,3,4};

[0070] n f is the differential ratio;

[0071] T eFr is the front axle torque;

[0072] is the rear axle torque;

[0073] I w is the wheel moment of inertia;

[0074] is the wheel acceleration;

[0075] T wi is the wheel traction torque at each corner of the vehicle 10, with index i∈{1,2,3,4};

[0076] R eff is the effective radius of the tire;

[0077] is the wheel braking torque at each corner of the vehicle 10, index i∈{1,2,3,4}; and

[0078] and They are the wheel traction torque at the right rear corner respectively.

[0079] The goal of the control strategy is to follow the desired wheel speed at each corner of the vehicle 10 while maintaining the overall desired vehicle acceleration and longitudinal velocity. Positive excess acceleration is not allowed in the control strategy. In addition, negative deviations from the reference acceleration and longitudinal velocity are penalized in the control strategy due to the limitation of the actuation capacity. Although the above control strategy can be used to maintain the target wheel slip of the vehicle 10 while the vehicle 10 is traveling, any other suitable control strategy can be used to achieve the target wheel slip.

[0080] Model predictive control (MPC) theory may alternatively be used as a control strategy to maintain a target wheel slip of the vehicle 10 as the vehicle 10 travels. In this case, the MPC includes a linear time-varying (LTV) solver for solving a constrained optimization problem at each sampling time with the following objective and cost terms:

[0081]

[0082]

[0083] x0=x(t)

[0084] u min ≤u t+k ≤u max ,k=0,…,N-1

[0085] y min ≤Cx t+k ≤y max ,k=1,…,N

[0086] in:

[0087] y t+k,t is the predicted longitudinal speed of the vehicle 10;

[0088] is the reference longitudinal speed of the vehicle 10;

[0089] u t+k,t For control actions, including front, left rear and right rear torque distribution (traction and braking);

[0090] For reference control actions, including front, left rear, and right rear torque distribution (traction and braking);

[0091] Δu t+k,t To control the changes in movement;

[0092] For reference control action changes;

[0093] J(x(t),U) is the objective function of the optimization problem;

[0094] p is the size of the prediction level;

[0095] x is the vehicle state vector;

[0096] t is the variable “time”;

[0097] U is the control action vector;

[0098] is the target vehicle state at the prediction level intrinsic time “k” starting from “t”;

[0099] W1 is the weight matrix of the state tracking item;

[0100] W2 is the weight matrix of the control action;

[0101] W3 is the weight matrix that controls the action rate;

[0102] W4 is the weight matrix satisfied by the total torque;

[0103] For the front torque distribution sequence;

[0104] torque distribution sequence for the left rear;

[0105] torque distribution sequence for the right rear;

[0106] is the driver torque request;

[0107] x t+k+1,t is the predicted vehicle state at time “t+k+1” within the prediction horizon starting from t;

[0108] A is the system state matrix;

[0109] B is the control contribution matrix;

[0110] W is the model perturbation;

[0111] is the nominal operating point of the state;

[0112] is the commanded nominal operating point;

[0113] k is a counter of the prediction level;

[0114] u min To control the lower bound of the action;

[0115] u t+k is the control action at time k within the forecast horizon starting from time t;

[0116] u max is the upper bound of the control action;

[0117] y min is the lower bound of the output variable;

[0118] is the output matrix C multiplied by the vehicle state at time k in the predicted horizon starting from time t; y max The upper bound of the output variable;

[0119] x0 is the initial state x; and

[0120] x(t) is the vehicle state variable at time t.

[0121] In the above MPC, the output can be described as follows:

[0122] y={v x a x …ω1ω2ω3ω4} T

[0123] in:

[0124] y is the output vector;

[0125] v x is the longitudinal speed of the vehicle 10;

[0126] a x is the longitudinal acceleration of the vehicle 10;

[0127] ω1 is the wheel speed of the left front wheel;

[0128] ω 22 is the wheel speed of the right front wheel;

[0129] ω3 is the wheel speed of the left rear wheel; and

[0130] ω4 is the wheel speed of the right rear wheel.

[0131] The nominal operating point of state may be calculated based on solving a nonlinear vehicle / wheel model, and the nominal operating point of command may be calculated outside of MPC by, for example, feedforward control.

[0132] The adaptive cost function can be optimized in an online manner to find a set of feasible control actions that minimize the error. The cost function can be expressed as follows:

[0133]

[0134] stGU≤W+Sx(t)

[0135] in: is the optimal solution, H>0 and C, Y, G, W, S are matrices of appropriate dimensions; and

[0136] x′(t) is the transpose of the vehicle state vector;

[0137] Γ is the weight matrix of vehicle state in the objective function;

[0138] G is the weight matrix of the control action;

[0139] W is the perturbation matrix;

[0140] S is the weight matrix of the vehicle state in the constraint function;

[0141] U is the control action vector;

[0142] C′ is the state control action penalty matrix;

[0143] H is the Hessian matrix;

[0144] is the first variable in the sequence of control actions within the prediction horizon; and

[0145] is the last variable in the control action sequence within the prediction level.

[0146] The MPC control algorithm is based on the following iteration: At time t, measure or estimate the current state x(t), and solve the quadratic programming (QP) problem to obtain the optimal sequence. If the future input changes U * (x(t)), then apply Then, the remaining best move is discarded and the process is repeated again at time t+1.

[0147] After frame 106, method 100 proceeds to frame 108. At frame 108, controller 34 adjusts the wheel speed of one or more wheels 17 of vehicle 10 based on the feedback signal. The feedback signal may originate from sensor 40 and indicate the road wheel angle when vehicle 10 is traveling. The desired wheel speed should be adjusted to ensure that the control system remains robust under uncertain factors (e.g., inaccurate effective tire radius, road conditions, etc.). Feedback from, for example, a rack position sensor or an estimate of the road wheel angle and / or rack position may be used to adjust the wheel speed target to achieve the desired steering angle. The wheel speed adjustment strategy may be any suitable feedback method. For example, a proportional control strategy may be employed as a feedback method and may be expressed as follows:

[0148]

[0149] in:

[0150] is the adjusted initial wheel speed target;

[0151] ω d is the initial wheel speed target;

[0152] K p is the proportional control gain matrix;

[0153] is the desired steering rack position; and

[0154] Δ r is the actual steering rack position.

[0155] The method 100 then proceeds to box 110. At box 110, the controller 34 arbitrates between the target wheel slip to follow the desired path and controlling wheel instability. Some of the possible wheel slips determined by the method 100 are inconsistent with the desired wheel slip requested by the vehicle motion control (wheel stability) feature. In this case, the wheel slip requested by the wheel stability feature is generally prioritized. As a result, the driver's steering request cannot be met. The fact that the driver's steering angle request is not an actionable command will be communicated to the driver through the user interface 23. However, if tire capacity is available at any axle or corner, the torque capacity at that corner can be utilized first before ignoring the driver's steering angle request.

[0156] Although exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms covered by the claims. The words used in the specification are descriptive rather than restrictive, and it should be understood that various changes can be made without departing from the spirit and scope of the present disclosure. As previously mentioned, the features of the various embodiments can be combined to form other embodiments of the system and method of the present disclosure that may not be explicitly described or shown. Although the various embodiments have been described by providing advantages for one or more desired characteristics or being preferred over other embodiments or prior art implementations, it is recognized by those of ordinary skill in the art that one or more features or characteristics can be compromised to achieve the desired overall system properties that depend on a specific application and implementation. These properties may include, but are not limited to, cost, strength, life, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, ease of production, assembly, etc. Therefore, embodiments described as inferior to other embodiments or prior art implementations for one or more characteristics are not outside the scope of the present disclosure and can be expected to be used for specific applications.

[0157] The drawings are in simplified form and not drawn to exact scale. Directional terms such as top, bottom, left, right, upward, above, above, below, below, behind, and in front may be used with respect to the drawings for convenience and clarity only. These directional terms and similar directional terms should not be construed to limit the scope of the present disclosure in any way.

[0158] Embodiments of the present disclosure are described herein. However, it should be understood that the disclosed embodiments are merely examples, and other embodiments may take various alternative forms. The drawings are not necessarily drawn to scale, and certain features may be enlarged or minimized to show the details of specific components. Therefore, the specific structural and functional details disclosed herein should not be interpreted as restrictive, but merely as a representative basis for teaching those skilled in the art to adopt the systems and methods of the present disclosure in different ways. As will be understood by those of ordinary skill in the art, the various features shown and described with reference to any of the accompanying drawings may be combined with the features shown in one or more other figures to produce embodiments that are not explicitly shown or described. The combination of the features shown provides representative embodiments of typical applications. However, for specific applications or implementations, various combinations and modifications of features consistent with the teachings of the present disclosure may be required.

[0159] Embodiments of the present disclosure may be described herein in terms of functional and / or logical block components and various processing steps. It should be understood that such block components may be implemented by multiple hardware, software, and / or firmware components configured to perform specified functions. For example, embodiments of the present disclosure may employ various integrated circuit components, such as memory elements, digital signal processing elements, logic elements, lookup tables, etc., which may perform various functions under the control of one or more microprocessors or other control devices. In addition, those skilled in the art will appreciate that embodiments of the present disclosure may be practiced in conjunction with a variety of systems, and the systems described herein are merely exemplary embodiments of the present disclosure.

[0160] For the sake of brevity, the present invention may not describe in detail the technology related to the signal processing, data fusion, signaling, control and other functional aspects of the system (and the various operating components of the system). In addition, the connecting lines shown in the various figures contained herein are intended to represent example functional relationships and / or physical connections between the various elements. It should be noted that there may be alternative or additional functional relationships or physical connections in the embodiments of the present disclosure.

[0161] This description is merely illustrative in nature and is in no way intended to limit the present disclosure, its application or use. The broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, although the present disclosure includes specific examples, the true scope of the present disclosure should not be limited thereto, as other modifications will become apparent after studying the drawings, the specification and the appended claims.

Claims

1. A control method for a steer-by-wire system, comprising: receiving vehicle data and steering requests from the vehicle; using the vehicle data, determining whether a road-steering wheel actuator of the vehicle is faulty; determining a target wheel slip for the vehicle based on the steering request in response to determining that a road-steering wheel actuator of the vehicle has failed; When the vehicle is traveling, maintaining a target wheel slip of the vehicle; as well as Based on a feedback signal, a wheel speed of at least one wheel of the vehicle is adjusted, wherein the feedback signal is indicative of a wheel angle of a road on which the vehicle is traveling. 2 . The method of claim 1 , further comprising arbitrating between the target wheel slip following a desired path and controlling wheel instability.

3. The method according to claim 2, wherein: The steering request includes a requested steering wheel angle, and a target wheel slip calculation for the vehicle is dependent upon the requested steering wheel angle.

4. The method according to claim 2, wherein: A target wheel slip for the vehicle is determined based on the steering request using Ackermann steering geometry of the steer-by-wire system. 5 . The method of claim 1 , further comprising using model predictive control (MPC) to maintain a target wheel slip of the vehicle while the vehicle is traveling. The method of claim 4 , wherein the MPC comprises a linear time-varying LTV solver. 7 . The method of claim 1 , further comprising using a control strategy to maintain a target wheel slip of the vehicle while the vehicle is traveling, wherein the control strategy is dependent on a driveline configuration of the vehicle.

8. A vehicle comprising: Multiple sensors; a steer-by-wire system including a road-steering wheel actuator; a controller in communication with the steer-by-wire system and the plurality of sensors, wherein the controller is programmed to: receiving vehicle data and steering requests from the vehicle; using the vehicle data, determining whether a steering wheel actuator of the vehicle is faulty; determining a target wheel slip for the vehicle based on the steering request in response to determining that a road-steering wheel actuator of the vehicle has failed; When the vehicle is traveling, maintaining a target wheel slip of the vehicle; as well as The wheel speed of at least one wheel of the vehicle is adjusted according to a feedback signal, wherein the feedback signal indicates a wheel angle of a road when the vehicle is traveling.

9. The vehicle of claim 8, wherein the controller is programmed to arbitrate between following the target wheel slip and controlling wheel instability.

10. The vehicle of claim 9, wherein the steering request comprises a requested steering wheel angle and a target wheel slip calculation for the vehicle is dependent upon the requested steering wheel angle.

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