ARCHITECTURE AND METHOD FOR FAILURE PROTECTION OF A STEER-BY-WIRE STEERING SYSTEM USING DIRECT YAW CONTROL ACTUATORS

Abstract

A method for controlling a steer-by-wire steering system comprises receiving vehicle data and a steering request from a vehicle, determining, using the vehicle data, whether a steering track actuator of the vehicle has failed, determining, based on the steering request in response to the determination that the steering track actuator of the vehicle has failed, a target wheel slip value of the vehicle, maintaining the target wheel slip value of the vehicle while the vehicle is in motion, and adjusting, based on a feedback signal, a wheel speed of at least one wheel of the vehicle, wherein the feedback signal specifies a track wheel angle while the vehicle is in motion.

Description

INTRODUCTION

[0001] The present disclosure relates to an architecture and method for steer-by-wire steering failover using direct yaw control actuators.

[0002] This introduction sets out the content of the disclosure in general. The work of the presently named inventors, to the extent described in this introduction, as well as those aspects of the description which do not otherwise qualify as prior art at the time of filing, are neither expressly nor implicitly admitted as prior art against this disclosure.

[0003] Steer-by-wire steering systems do not rely on mechanical connections to the vehicle's wheels. Instead, these systems use cables that send electronic signals to the vehicle's transmission to steer the vehicle. Many vehicles contain steer-by-wire steering systems. It therefore makes sense to develop a system and procedure for fail-safe operation of a system-by-wire system. SUMMARY

[0004] The method and architecture disclosed herein aim to provide a torque distribution backup system and / or a differential braking backup system for steer-by-wire (SbW) degradation that does not require any modification of the suspension / steering system and remains effective even on non-steerable axles. The wheel speed control-based method is a solution that does not require any physical changes to the vehicle's suspension system. Since the method disclosed herein does not subject the vehicle to wheel instabilities (e.g., wheel slip is directly controlled), driving under a backup system also does not cause common side effects such as tire saturation and potential vehicle instability.

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

[0006] The method may further comprise mediating between the wheel slip target to follow a desired path and controlling wheel instability. The steering request comprises a requested steering wheel angle, wherein the vehicle's wheel slip target is calculated as a function of the requested steering wheel angle. The vehicle's wheel slip target is determined based on the steering request using an Ackermann steering geometry of the steer-by-wire steering system. The method may further comprise using model predictive control (MPC) to maintain the vehicle's wheel slip target while the vehicle is in motion. The MPC includes a linear time-varying (LTV) resolver. The method may further comprise using a control strategy to maintain the vehicle's wheel slip target while the vehicle is in motion. The control strategy depends on the driveline configuration of the vehicle.

[0007] The present disclosure further describes a vehicle including sensors, an electromechanical steering system, and a controller in communication with the sensors and the electromechanical steering system. The controller is programmed to perform the method described above. The present disclosure further describes a tangible, non-transitory, machine-readable medium containing machine-readable instructions that, when executed by a processor, cause the processor to perform the method described above.

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

[0009] The above-described features and advantages and other features and advantages of the presently disclosed system and method will be apparent from the detailed description, including the 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 the accompanying drawings, in which: Fig. 1 is a block diagram illustrating an embodiment of a vehicle with a steer-by-wire steering system; and Fig. 2 a flowchart of a method for controlling the steer-by-wire steering system. DETAILED DESCRIPTION

[0011] Reference will now be made in detail to some examples of the disclosure illustrated in the accompanying drawings. Where possible, the same or similar reference numerals are used throughout the drawings and the description to refer to the same or similar sections or steps.

[0012] With reference to Fig. 1, a vehicle 10 generally includes a chassis 12, a body 14, and front and rear wheels 17, and may be referred to as a vehicle system. In the illustrated 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 encloses components of the vehicle 10. The body 14 and the chassis 12 may together form a frame. The wheels 17 are each rotationally coupled to the chassis 12 near a respective 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.

[0013] The vehicle 10 is an autonomous vehicle, and a control system 98 is incorporated into the vehicle 10. The system 98 may be referred to as the system or the system for controlling the steering system 24. The vehicle 10 is, for example, a vehicle that is automatically controlled to guide passengers from one location to another. The vehicle 10 is shown as a pickup truck in the illustrated embodiment, but it should be appreciated that other vehicles, including trucks, sedans, coupes, sport utility vehicles (SUVs), recreational vehicles (RVs), etc., may also be used. In one embodiment, the vehicle 10 may include a so-called level two, level three, level four, or level five driving automation system.A level four system indicates "high automation," which refers to the drive-mode-specific performance by an automated driving system of aspects of the dynamic driving task, even when a human driver does not appropriately respond to a request to intervene. A level five system indicates "full automation," which refers to the full-time performance by an automated driving system of aspects of the dynamic driving task under multiple road and environmental conditions that can be managed by a human driver. In Level 3 vehicles, the system 98 performs the entire dynamic driving task (DDT) within the range in which it is designed to do so. In Level 2 vehicles, systems provide steering, braking / acceleration assistance, lane centering, and adaptive cruise control.However, even when these systems are activated, the vehicle operator must be behind the wheel and constantly monitor the automated features.

[0014] 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 an electromechanical steering system. The propulsion system 20, in various embodiments, may include an electric work machine such as a traction motor and / or a fuel cell propulsion system. The vehicle 10 may further include a battery (or battery pack) 21 electrically connected to the propulsion system 20. Accordingly, the battery 21 is configured to store electrical energy and to supply 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 vehicle wheels 17 according to selectable speed ratios. According to various embodiments, the transmission system 22 may include a stepped-ratio automatic transmission, a continuously variable transmission, or other suitable transmission. The braking system 26 is configured to impart braking torque to the vehicle wheels 17. In various embodiments, the braking system 26 may include friction brakes, electromechanical braking, a regenerative braking system such as an electric machine, and / or other suitable braking systems. The steering system 24 influences the position of the vehicle wheels 17 and may include a steering wheel 33. While illustrated as including a steering wheel 33 for illustrative purposes, in some embodiments contemplated within the scope of the present disclosure, the steering system 24 may not include a steering wheel 33.

[0015] The sensor system 28 includes one or more sensors 40 (i.e., sensing devices) that sense observable conditions of the exterior environment and / or the interior environment of the vehicle 10. The sensors 40 are in communication with the controller 34 and may include one or more steering wheel sensors 45, one or more radars, one or more light detection and ranging sensors (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, one or more 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 tracking devices, 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 the sensed observable conditions 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 sources of information (or simply sources). The vehicle 10 and / or the system 98 do not include any light sensors capable of detecting light within the vehicle 10.

[0016] 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 further include interior and / or exterior vehicle features, such as, but not limited to, doors, a trunk, and cabin features such as air, music, lighting, etc. The actuators 43 may be part of the steering system 24 and include one or more roadway wheel actuators (RWAs) and a handwheel actuator (HWA).

[0017] The data storage device 32 stores data for use in automatically controlling the vehicle 10. In various embodiments, the data storage device 32 stores defined maps of the navigable environment.

[0018] According to various embodiments, the defined maps may be predefined by and obtained from a remote system. For example, the defined maps may be compiled by the remote system and communicated to the vehicle 10 (wirelessly and / or in a wired manner) 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.

[0019] The vehicle 10 may further include one or more airbags 35 in communication with the controller 34 or another controller of the vehicle 10. The airbag 35 includes an inflatable bladder and is configured to transition between a stowed configuration and a deployed configuration to cushion the effects of an external force applied to the vehicle 10. The sensors 40 may include an airbag sensor, such as an IMU, configured to detect an external force and generate a signal indicative of the magnitude of such an external force. The controller 34 is configured to command the airbag 35 to deploy based on the signal from one or more sensors 40, such as the airbag sensor. Accordingly, the controller 34 is configured to determine when the airbag 35 has deployed.

[0020] The controller 34 includes at least one processor 44 and a non-transitory computer-readable storage device or storage medium 46. The processor 44 may be a custom-built or off-the-shelf processor, a central processing unit (CPU), a graphics processing unit (GPU), an auxiliary processor among multiple 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 storage medium 46 may include, for example, volatile and non-volatile memory in read-only memory (ROM), random access memory (RAM), and retained memory (RAM).KAM is persistent or non-volatile memory that can be used to store various operating variables while the processor 44 is powered off. The computer-readable storage device or medium 46 can be implemented using a number of storage devices such as PROMs (programmable read-only memories), EPROMs (electrical PROMs), EEPROMs (electrically erasable PROMs), flash memory, or other electrical, magnetic, optical, or combination storage devices that can store data, some of which represents executable instructions used by the controller 34 in controlling the vehicle 10. The controller 34 of the vehicle 10 may be referred to as a vehicle controller and may be programmed to implement a method 100 (. Fig. 2), which is described in detail below.

[0021] The instructions may include one or more separate programs, each comprising an ordered list of executable instructions for implementing logical functions. The instructions, when executed by the processor 44, receive and process signals from the sensor system 28, perform logic, calculations, methods, and / or algorithms to automatically control the components of the vehicle 10, and generate control signals to the actuator system 30 to automatically control the components of the vehicle 10 based on the logic, calculations, methods, and / or algorithms. Although in Fig. 1, embodiments of the vehicle 10 may include multiple controllers 34 that communicate via a suitable communication medium or combination of communication media and that cooperate to process the sensor signals, perform logic, calculations, methods, and / or algorithms, and generate control signals to automatically control features of the vehicle 10. In various embodiments, one or more commands of the controller 34 are embodied in the control system 98.

[0022] The vehicle 10 includes a user interface 23, which may be a touchscreen 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 an audible sound, haptic feedback in a vehicle seat or other object, one or more display devices 29, one or more microphones 31, and / or other devices suitable for providing notification to the vehicle user of the vehicle 10. The user interface 23 is in electronic communication with the controller 34 and is configured to receive inputs from a vehicle occupant 11 (e.g., a vehicle driver or a vehicle passenger). For example, the user interface 23 may include a touchscreen and / or buttons configured to receive inputs from a vehicle occupant 11.Accordingly, the controller 34 is configured to receive inputs from the user via the user interface 23. The vehicle 10 may include one or more display devices 29 configured to display information about the vehicle occupant 11 (e.g., the vehicle operator or the passenger) and may be a head-up display (HUD).

[0023] The communication system 36 is in communication with the controller 34 and is configured to wirelessly communicate information to and from other remote vehicles 48, such as, but not limited to, other vehicles ("V2V" communication), infrastructure ("V2I" communication), remote systems at a remote call center (e.g., ON-STAR from GENERAL MOTORS), and / or personal electronic devices such as a cellular phone. In the present disclosure, the term "remote vehicle" means a vehicle, such as a passenger car, that is configured to send one or more signals to the vehicle 10 while not physically connected to the vehicle 10. In certain embodiments, the communication system 36 is a wireless communication system configured to communicate via a wireless local area network (WLAN) using IEEE 802.11 standards or using cellular data communication.However, additional or alternative communication methods, such as a dedicated short-range communication (DSRC) channel, are also considered within the scope of the present disclosure. DSRC channels refer to unidirectional or bidirectional short- to medium-range wireless communication channels specifically designed for use in motor vehicles and a corresponding set of protocols and standards. Accordingly, the communication system 36 may include one or more antennas and / or communication transceivers 37 for receiving and / or transmitting signals such as cooperative sensing messages (CSMs). The communication transceivers 37 may be considered sensors 40. The communication system 36 is configured to wirelessly communicate information between the vehicle 10 and another vehicle.Furthermore, the communication system 36 is configured to wirelessly communicate information between the vehicle 10 and infrastructure or other vehicles.

[0024] Fig.2 shows a flowchart of a method 100 for controlling a steer-by-wire steering system. The method 100 aims to provide a torque distribution backup system and / or a differential braking backup system for the degradation of the steer-by-wire (SbW) system 24 that does not require any modification of the suspension / steering system 24 and remains effective even on non-steerable axles. The wheel speed control-based method 100 is a solution that does not require any physical changes to the suspension system. Because the method 100 does not subject the vehicle to wheel instabilities (e.g., wheel slip is directly controlled), driving under a backup system also does not cause common side effects such as tire saturation and potential vehicle instability. The method 100 begins in block 102.Block 102 includes determining whether one or more steering road wheel actuators have failed or have at least degraded to a certain degree. To do so, the controller 34 receives vehicle data, such as signals from the steering road wheel actuators, and then uses the vehicle data to determine whether the road wheel actuators (RWA) have failed or have at least degraded to a certain degree. Although the method 100 may be performed if one or more steering road wheel actuators have failed, the steering wheel sensors of the handwheel actuators (HWAs) should be functioning properly. In the event of a complete HWA failure, the controller 34 reads a tertiary steering angle sensor (SAS) and determines the RWA setpoint.If the controller 34 determines that one or more steering road wheel actuators have failed or have degraded to at least some degree, the method 100 proceeds to block 104.

[0025] Block 104 includes determining (e.g., calculating) the wheel slip target value based on a steering request. Thus, the controller 34 receives a steering request from the vehicle driver, the advanced driver assistance system (ADAS) of the vehicle 10, and / or the autonomous vehicle feature. The steering request includes a requested steering wheel angle. In response to receiving the steering request, the controller 34 calculates the wheel slip target value or the desired wheel slip (i.e., the delta wheel speed). The desired yaw rate for a given requested steering wheel angle can be determined using the following equation: ωzd=vx×δf(a+b)+Kusvx2 where: ω zd is the desired yaw rate; δ f the requested steering wheel angle; v x is the longitudinal speed of the vehicle 10; a is the distance from the centre of gravity to the front axle of the vehicle 10; b is the distance from the center of gravity to the rear axle of the vehicle 10; and K us is the undertax coefficient.

[0026] The wheel slip command can be calculated based on the steering demand using an Ackermann steering geometry of the steer-by-wire steering system 24. Specifically, the following equations can be used to calculate the wheel speed command. cot(δo)−cot(δi)=wrl,cot(δ)=(cot(δo)=cot(δi))2, R=Vxωzd=12b2+(I*cot(δ))2, Rof=I / sin(δo),Rif=I / sin(δi), ωidr=ωzd×(R×cos(δ)−wr2)Reff, ωodr=ωzd×(R×cos(δ)+wr2)Reff, ωidf=ωzd×(Rif)Reff, ωodf=ωzd×(Rof)Reff, where: v xis the longitudinal speed of the vehicle 10; δ o is the steering angle of the outer wheel; δ i the steering angle of the inner wheel; w r the track width of the vehicle on the rear axle; I is the wheelbase; δ is the steering wheel angle; Rof is an intermediate variable; Reef is an intermediate variable; ω zd the desired wheel speed; R is the vehicle rotation speed; b is the distance from the centre of gravity to the rear axle of the vehicle 10; R eff is the effective radius of the tire; ωidr the desired wheel speed at the rear inner wheel; ωodr the desired wheel speed at the rear outer wheel; ωidf the desired wheel speed at the front inner wheel; and ωodf the desired wheel speed on the front outer wheel.

[0027] After block 104, the method 100 proceeds to block 106. In block 106, the controller 34 implements a control strategy to maintain the vehicle's wheel slip target while the vehicle is in motion. The control strategy depends on the vehicle's driveline configuration. If the vehicle 10 has front-wheel drive, brake torque distribution is used to maintain the vehicle's wheel slip target while the vehicle 10 is in motion. If the vehicle 10 has rear-wheel drive, the differential brakes on the front axle and brake torque distribution on the rear axle are used to maintain the vehicle's 10 wheel slip target while the vehicle is in motion. If the vehicle 10 has all-wheel drive, brake torque distribution on the front axle and rear axles is used to maintain the vehicle's 10 wheel slip target while the vehicle is in motion.If the vehicle 10 has two rear electric motors and one front electric motor, the torque distribution on the rear axle and the braking torque distribution on the front axle are used to maintain the vehicle's wheel slip target while the vehicle 10 is in motion.

[0028] The control strategy to maintain the wheel slip setpoint of the vehicle 10 while the vehicle 10 is in motion can be determined using the following equations of motion: Max=∑i=14(Fxi cos δi−Fyi sin δi) Tw1=nf2(TeFr)−Tbr1Tw2=nf2(TeFr)−Tbr2Tw3=(TeRerl)−Tbr3Tw4=(TeRerr)−Tbr4}→Iwω˙1=Twi−ReffFxi,i=1,2,3,4 where: M is the mass of the vehicle 10; a is the acceleration of the vehicle 10; F xi is the longitudinal tire force at each corner of the vehicle, and the index i ∈ {1, 2, 3, 4}; δ i is the inner steering angle; F yiis the transverse tire force at each corner of the vehicle 10, index i ∈ {1, 2, 3, 4}; T w1 the wheel torque at each corner of the vehicle 10 is index i ∈ {1, 2, 3, 4}; n f is the gear ratio of the differential; T eFr is the front axle torque; T br1 is the rear axle torque; I w is the wheel moment of inertia; ω̇ l is the wheel acceleration; T wi the wheel drive torque at each corner of the vehicle 10 is index i ∈ {1, 2, 3, 4}; R eff is the effective radius of the tire; T bri the wheel drive torque at each corner of the vehicle 10 is index i ∈ {1, 2, 3, 4}; and T eRerl and T eRerr the wheel drive torques at the rear right corners are.

[0029] The task of the control strategy is to follow the desired wheel speeds at each corner of the vehicle 10 while maintaining the overall intended vehicle acceleration and longitudinal speed. Positive additional acceleration is not provided for in the control strategy. Furthermore, the control strategy penalizes a negative deviation from a reference acceleration and longitudinal speed, but due to the limitation of the actuation capabilities. While the control strategy described above can be used to maintain the wheel slip target of the vehicle 10 while the vehicle 10 is in motion, any other suitable control strategy can be used to achieve the wheel slip target.

[0030] Model predictive control theory (MPC) can alternatively be used as a control strategy to maintain the wheel slip target of the vehicle 10 while the vehicle 10 is in motion. In this case, the MPC includes a linear time-varying (LTV) solver to solve a constrained optimization problem at each sample time with the following task and cost terms: J(x(t),U)=∑k=1p‖yt+k,t−yt+k,tRef‖W12︸Motion error term+∑k=0p−1‖ut+k,t−ut+k,tRef‖W22︸Control action error+‖Δut+k,t −Δut+k,tRef‖W32︸Control action variation error+‖Tft+k,t+Trlt+k,t+Trrt+k,t−Tdrivert+k,tRef‖W42︸Total torque error stxt+k+1,t=A(xt+k,t−x¯t)+B(ut+k,t−u¯t)+W,k=0,…,p−1 x0=x(t) umin≤ut+k≤umax,k=0,…,N−1 ymin≤Cxt+k≤ymax,k=1,…,N where: y t+k,t is the predicted longitudinal speed of the vehicle 10; yt+k,tRef is the reference longitudinal speed of the vehicle 10; u t+k,t the control actions, which include the front, rear left and rear right torque distributions (for both propulsion and braking); ut+k,tRef the reference control actions, which include the front, rear left and rear right torque distributions (for both propulsion and braking), are; Δu t+k,t is a control action variation; Δut+k,tRef is a reference control action variation; J(x(t), U) is the objective function of the optimization problem; p is the size of the forecast horizon; x is the vehicle state vector; t is the variable “time”; U is the control action vector; yt+k,tRef the desired vehicle state at time ‘k’ is within the prediction horizon started from ‘t’; W1 is the weight matrix for the state tracking term; W2 is the weighting matrix for the control actions; W3 is the weighting matrix for the control action rates; W4 is the weighting matrix for the total torque saturation; T ft+k,t is a front torque distribution sequence; T rlt+k,t is a left rear torque distribution sequence; T rrt+k,t is a right rear torque distribution sequence; Tdriver+k,tRef a driver torque request; x t+k+1,t is the predicted vehicle state at time ‘t+k+1’ within the prediction horizon started from ‘t’; A is the system state matrix; B is the control contribution matrix; W is the model perturbation; x t is the nominal operating point for the condition; u tis the nominal operating point for the instruction; k is the numerator for the forecast horizon; u min is the lower bound of the control actions; u c+u the control action at time ‘k’ is within the prediction horizon from time ‘t’; u max is the upper bound of the control actions; y min is the lower bound of the output variable; Cx t+k the output matrix C multiplied by the vehicle states at time ‘k’ within the prediction horizon starting at time ‘t’; y max is the upper bound of the output variable; x0 is the initial state “x”; and x(t) is a vehicle state variable at time “t”.

[0031] In the MPC described above, the output can be described as follows: y={vxaxω1ω2ω3ω4}T where: y v x is the longitudinal speed of the vehicle 10; a x is the longitudinal acceleration of the vehicle 10; ω1 is the wheel speed of the front left wheel; ω2 is the wheel speed of the front right wheel; ω3 is the wheel speed of the rear left wheel; and ω4 is the wheel speed of the rear right wheel.

[0032] The nominal operating point for the state can be calculated based on solving the nonlinear vehicle / wheel model and the nominal operating point for the instruction can be calculated outside the MPC, e.g., by an on-board controller.

[0033] The adaptive cost function can be optimized online to find a feasible set of control actions to minimize the error. The cost function can be expressed as follows: U*(x(t))≜arg minU12U'HU+x'(t)C'U+12x'(t)YΓx(t) st GU≤W+Sx(t) where: U*(x(t))=[u'0*(x(t))…u'N−1*(x(t))]' is the optimal solution, H > 0 and C, Y, G, W, S are matrices with suitable dimensions; and x'(t) is the transpose of the vehicle state vector; Γ is the weighting matrix for vehicle states in the objective function; G is the weight matrix for control actions; W is the perturbation matrix; S is the weighting matrix for vehicle states in the constraint function; U is the control action vector; C' is the state control action penalty matrix; H is the Hessian matrix; u'0*(x(t)) is the first variable of the control action sequence within the prediction horizon; and u'N−1*(x(t)) is the last variable of the control action sequence within the forecast horizon.

[0034] The MPC control algorithm is based on the following iterations: Measure or estimate the current state x(t) at time t, solve the quadratic programming (QP) problem to arrive at the optimal sequence. If the future input shifts by U*(x(t)), u(t)=u0*(x(t)) Then discard the remaining optimal shifts and repeat the process for time t+1.

[0035] After block 106, the method 100 proceeds to block 108. In block 108, the controller 34 adjusts a wheel speed of one or more wheels 17 of the vehicle 10 based on a feedback signal. The feedback signal may be from the sensors 40 and is indicative of a road wheel angle while the vehicle 10 is in motion. The desired wheel speeds should be adjusted to ensure that the control system remains robust under uncertainties, such as an inaccurate effective tire radius or inaccurate road surface conditions. Feedback from, for example, the handlebar position sensor or an estimate of the road wheel angle and / or handlebar position may be used to adjust the wheel speed setpoints to achieve the desired steering angle. The wheel speed adjustment strategy may be any suitable feedback method.For example, a proportional control strategy can be used as a feedback method and can be expressed as follows:. ωd*=ωd+Kp(Δrd−Δr) where: ωd* the set original wheel speed target value; ω d is the original wheel speed setpoint; K p is the proportional control gain matrix; Δrd the desired handlebar position; and Δ r the actual handlebar position.

[0036] Method 100 then proceeds to block 110. In block 110, controller 34 communicates the wheel slip setpoint to follow a desired lane and control wheel instability. Some possible wheel slips determined by method 100 are inconsistent with the desired wheel slip requested by the vehicle motion control feature (the wheel stability feature). In such a case, priority is generally given to the wheel slip requested by the wheel stability feature. As a result, the driver's steering request may not be honored. In the event that the driver steering angle request is not an executable command, communication with the driver occurs via user interface 23.However, if tire capacity is available for any axle or corner, the torque capacity in that corner can be used first before ignoring the driver steering angle request.

[0037] While exemplary embodiments are described above, these embodiments are not intended to describe all possible forms encompassed by the claims. The words used in the application text are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments may be combined to form further embodiments of the presently disclosed system and method, which need not be expressly described or illustrated.While various embodiments may have been described as providing advantages or being preferred over other prior art embodiments or implementations with respect to one or more desired characteristics, those skilled in the art will recognize that one or more features or characteristics may be compromised to achieve desired overall system characteristics depending on the specific application and implementation. These features may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, usability, weight, manufacturability, ease of assembly, etc.Therefore, embodiments that are described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for certain applications.

[0038] The drawings are presented in simplified form and are not exactly to scale. For convenience and clarity only, directional terms such as top, bottom, left, right, upward, over, above, below, beneath, back, and front may be used with reference to the drawings. These and similar directional terms should not be construed as limiting the scope of the disclosure in any way.

[0039] Embodiments of the present disclosure are described herein. However, it should be understood that the disclosed embodiments are merely examples, and further embodiments may take various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the presently disclosed system and method.As will be understood by those skilled in the art, various features illustrated and described with reference to any of the figures may be combined with features illustrated in one or more other figures to produce embodiments not explicitly illustrated or described. The combinations of illustrated features provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desirable for particular applications or implementations.

[0040] Here, embodiments of the present disclosure may be described in terms of functional and / or logical block components and various processing steps. It should be appreciated that such block components may be implemented by multiple hardware, software, and / or firmware components configured to perform the specified functions. For example, an embodiment of the present disclosure may employ various integrated circuit components, e.g., memory elements, digital signal processing elements, logic elements, lookup tables, or the like, capable of performing a variety of functions under the control of one or more microprocessors or other control devices.In addition, those skilled in the art will understand that embodiments of the present disclosure may be practiced in connection with multiple systems and that the systems described herein are merely exemplary embodiments of the present disclosure.

[0041] For brevity, techniques related to signal processing, data fusion, signaling, control, and other functional aspects of the systems (and the individual operational components of the systems) need not be described in detail here. Furthermore, the interconnections shown in the various figures included herein are intended to represent examples of functional relationships and / or physical couplings between the various elements. It should be noted that alternative or additional functional relationships or physical connections may be present in an embodiment of the present disclosure.

[0042] This description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure may be implemented in various forms. Therefore, while this disclosure contains specific examples, the true scope of the disclosure should not be so limited, since other modifications will become apparent upon a study of the drawings, the specification, and the following claims.

Claims

[1] A method for controlling a steer-by-wire steering system, comprising: Receiving vehicle data and a steering request from a vehicle; Determining, using the vehicle data, whether a steering road wheel actuator of the vehicle has failed; Determining, based on the steering request in response to determining that the steering road wheel actuator has failed, a wheel slip target of the vehicle; Maintaining the vehicle’s wheel slip target while the vehicle is moving; and Adjusting a wheel speed of at least one wheel of the vehicle based on a feedback signal, the feedback signal indicative of a road wheel angle while the vehicle is in motion. [2] The method of claim 1, further comprising mediating between the wheel slip setpoint to follow a desired path and controlling wheel instability. [3] The method of claim 2, wherein the steering request includes a requested steering wheel angle and the wheel slip target value of the vehicle is calculated as a function of the requested steering wheel angle. [4] The method of claim 2, wherein the wheel slip target of the vehicle is determined based on the steering request using an Ackermann steering geometry of the steer-by-wire steering system. [5] The method of claim 1, further comprising using a model predictive control (MPC) to maintain the vehicle's wheel slip target while the vehicle is in motion. [6] The method of claim 4, wherein the MPC comprises a linear time-varying (LTV) resolver. [7] The method of claim 1, further comprising using a control strategy to maintain the wheel slip target of the vehicle while the vehicle is in motion, the control strategy depending on a driveline configuration of the vehicle. [8] Vehicle that includes: multiple sensors; a steer-by-wire steering system including a steering road wheel actuator; a controller in communication with the steer-by-wire steering system and the plurality of sensors, the controller programmed to: Receiving vehicle data and a steering request from a vehicle; Determining, using the vehicle data, whether a steering road wheel actuator of the vehicle has failed; Determining, based on the steering request in response to determining that the steering road wheel actuator has failed, a wheel slip target of the vehicle; Maintaining the vehicle’s wheel slip target while the vehicle is moving; and Adjusting based on a feedback signal a wheel speed of at least one wheel of the vehicle, the feedback signal indicative of a road wheel angle while the vehicle is in motion. [9] The vehicle of claim 8, wherein the controller is programmed to mediate between the wheel slip setpoint to follow a desired path and controlling wheel instability. [10] A vehicle according to claim 9, wherein the steering request includes a requested steering wheel angle and the wheel slip target value of the vehicle is calculated as a function of the requested steering wheel angle.

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