Driver feedback for steering-by-wire systems

Abstract

Driver feedback for a steer-by-wire system is provided. A steer-by-wire system is configured to provide driver feedback to enable a vehicle driver to perceive when a vehicle may approach or operate at its adhesion limit. The driver feedback may be determined based on a corrected responsive rack force derived as a function of the observed responsive rack force, the reference responsive rack force, the target responsive rack force, and / or the minimum saturation value.

Description

[0001] introduction Technical Field

[0002] The present disclosure relates to providing driver feedback for a vehicle having a steer-by-wire system, such as to enable the driver to sense when the vehicle may be approaching or operating at its adhesion limit. Background Art

[0003] The adhesion limit may correspond to the maximum amount of traction or grip that the suspension and steering system can provide before the vehicle begins to lose traction and / or begins to slip. The adhesion limit may vary widely depending on the different suspension and steering kinematics of a particular vehicle, and whether the vehicle includes wheels or other features for guiding movement. For example, in the case of a wheeled vehicle, it may be beneficial to provide driver feedback so that the driver can sense when the wheels may be approaching or operating at their adhesion limit, which the driver can then take into account when deciding how to continue operating the vehicle. Some vehicles may be equipped with a steer-by-wire system, whereby steering may be provided via operation of actuators, motors and / or other components without a direct physical link between the driver and the wheels. In a steer-by-wire vehicle, the lack of a force-transmitting mechanical connection between the driver and the wheels may limit the driver's ability to sense when the vehicle may be approaching or operating at its adhesion limit. Summary of the Invention

[0004] One aspect of the present disclosure relates to providing driver feedback. Driver feedback can be operable to assist the driver in sensing when the vehicle, or more specifically, when one or more wheels of the vehicle may be approaching or operating at the limit of adhesion. Driver feedback can be provided via an actuator or other electromechanical device of a steer-by-wire system to provide driver feedback without relying on a physical link to transmit mechanical force directly from the wheels to the driver.

[0005] One aspect of the present disclosure relates to a method for providing driver feedback for a vehicle having a steer-by-wire system. The method may include: determining an observed response rack force based on response rack force measurements taken using a response rack force observer for the steer-by-wire system, optionally wherein the observed response rack force represents a force exerted by one or more wheels of the vehicle resisting a steering force provided to the wheels by the steer-by-wire system; estimating a reference response rack force based on a reference model of the steer-by-wire system, optionally wherein the reference model represents current suspension and steering kinematics of the steer-by-wire system and the reference response rack force represents a reference force resisting the steering force modeled for the wheels using the reference model; estimating a target response rack force based on a target model of the steer-by-wire system, optionally wherein the target model represents target suspension and steering kinematics of the steer-by-wire system and the target response rack force represents a target force resisting the steering force modeled for the wheels using the target model; determining a corrected response rack force as a function of the observed response rack force, the reference response rack force, and the target response rack force; and determining a driver feedback torque based on the corrected response rack force.

[0006] The method may include determining a corrected response rack force based on a rack equation, optionally wherein the rack equation is defined as:

[0007] CRF=max((RRF-TRF)+ORF),MSV)

[0008] where CRF equals the corrected response rack force, RRF equals the reference response rack force, TRF equals the target response rack force, ORF equals the observed response rack force, and MSV equals the minimum saturation value of the steer-by-wire system.

[0009] The method may include providing a driver feedback torque to a steering wheel actuator configured to apply a responsive steering force to a steering wheel of a steer-by-wire system in proportion to the driver feedback torque.

[0010] The method may include determining a plurality of steer-by-wire variables representing influences on the operation of the steer-by-wire system, estimating a reference response rack force based on processing the steer-by-wire variables with a reference model, and estimating the reference response rack force based on processing the steer-by-wire variables with the reference model.

[0011] The method may include a reference model estimating a reference response rack force based on a defined reference curve relative to one or more of the steer-by-wire variables, and a target model estimating a target response rack force based on a defined target curve relative to one or more of the steer-by-wire variables.

[0012] The method may include defining a normal handling range, a non-linear handling range, a near-limit handling range, and an adhesion limit of the steer-by-wire system with respect to one or more of the steer-by-wire variables.

[0013] The method may include the target curve having a smoother gradient than the reference curve in the near-limit treatment range.

[0014] The method may include the target curve having a slope that decreases at a constant rate in the near-limit treatment range.

[0015] The method may include the target curve having a similar gradient to the reference curve over the normal treatment range.

[0016] The method may include defining the reference profile and the target profile relative to a lateral acceleration of the vehicle and / or a steering wheel angle of a steering wheel, the lateral acceleration and / or the steering wheel angle being included as part of the steer-by-wire variables.

[0017] The method may include determining a minimum saturation value as a function of a vehicle speed determined for the vehicle, the vehicle speed being included as part of the steer-by-wire variable.

[0018] One aspect of the present disclosure relates to a system for providing driver feedback in a vehicle having a steer-by-wire system. The system may include an observer configured to measure an observed response rack force of the steer-by-wire system, optionally wherein the observed response rack force represents a response force exerted by one or more wheels of the vehicle opposing a steering force applied to the wheels by the steer-by-wire system. The system may include a monitoring system configured to determine a plurality of steer-by-wire variables representing operational influences on the steer-by-wire system. The system may include a reference model defined relative to current suspension and steering kinematics of the steer-by-wire system, optionally wherein the reference model is configured to estimate a reference response rack force for the steer-by-wire system based on modeling one or more of the steer-by-wire variables. The system may include a target model defined relative to target suspension and steering kinematics of the steer-by-wire system, optionally wherein the target model is configured to estimate a target response rack force for the steer-by-wire system based on modeling one or more of the steer-by-wire variables. The system may include a response rack force controller configured to determine a corrected response rack force as a function of an observed response rack force, a reference response rack force, and a target response rack force. The system may include a steering wheel controller configured to determine a driver feedback torque based on the corrected response rack force.

[0019] The system may include an operating mode controller configured to determine when the steer-by-wire system is operating in a non-near-limit handling range and a near-limit handling range, optionally wherein the near-limit handling range is a first predefined operating range that occurs before a wheel adhesion limit is reached, and the non-near-limit handling range is a second predefined operating range that occurs before the near-limit handling range is reached.

[0020] The system may include a response rack force controller configured to determine a corrected response rack force according to a near-limit rack equation when the steer-by-wire system operates in a near-limit handling range, optionally wherein the near-limit rack equation is defined as:

[0021] CRF=(RRF-TRF)+ORF)

[0022] Where CRF equals the corrected response rack force, RRF equals the reference response rack force, TRF equals the target response rack force, and ORF equals the observed response rack force.

[0023] The system may include a responsive rack force controller configured to increase the corrected responsive rack force to a minimum saturation value when the corrected responsive rack force is less than an adhesion threshold value defined relative to the adhesion limit.

[0024] The system may include a steering wheel actuator configured to apply a responsive steering force to a steering wheel of the steer-by-wire system in proportion to the driver feedback torque.

[0025] The system may include a reference configured for estimating a reference response rack force based on a defined reference curve relative to one or more of the steer-by-wire variables; and a target model configured for estimating a target response rack force based on a defined target curve relative to one or more of the steer-by-wire variables, optionally wherein the target curve differs in shape from the reference curve within a near-limit handling range.

[0026] The system may include a target curve configured with a smoother gradient than the reference curve in a near-limit treatment range and with a similar gradient to the reference curve in a non-near-limit treatment range.

[0027] One aspect of the present disclosure relates to a vehicle having: a plurality of wheels operable to facilitate movement of the vehicle; a powertrain operable to rotate one or more of the wheels in response to mechanical power generated using an internal combustion engine and / or an electric motor; and a steer-by-wire system configured to steer one or more of the wheels. The steer-by-wire system can be configured to determine an observed response rack force based on a response rack force measurement taken using a response rack force observer of the steer-by-wire system, estimate a reference response rack force based on a reference model of the steer-by-wire system, estimate a target response rack force based on a target model of the steer-by-wire system, determine a corrected response rack force based on a rack equation, and determine a driver feedback torque based on the corrected response rack force. The corrected response rack force can be based on a rack equation, which is defined as:

[0028] CRF=max((RRF-TRF)+ORF),MSV)

[0029] where CRF equals the corrected response rack force, RRF equals the reference response rack force, TRF equals the target response rack force, ORF equals the observed response rack force, and MSV equals the minimum saturation value of the steer-by-wire system.

[0030] The vehicle may include: a reference model configured to estimate a reference response rack force based on a reference curve defined relative to current suspension and steering kinematics of the steer-by-wire system and one or more steer-by-wire manipulated variables; and a target model configured to estimate a target response rack force based on a target curve defined relative to target suspension and steering kinematics of the steer-by-wire system and one or more steer-by-wire manipulated variables, optionally wherein the target curve has a smoother gradient than the reference curve within a near-limit handling range of the steer-by-wire system, and the near-limit handling range corresponds to a predefined operating range that occurs before a wheel adhesion limit is reached.

[0031] The present invention also includes the following solutions:

[0032] Solution 1. A method for providing driver feedback to a vehicle having a steer-by-wire system, comprising:

[0033] determining an observed response rack force based on a response rack force measurement taken by a response rack force observer of the steer-by-wire system, the observed response rack force representing a force exerted by one or more wheels of the vehicle opposing a steering force provided to the wheels by the steer-by-wire system;

[0034] estimating a reference response rack force based on a reference model of the steer-by-wire system, the reference model characterizing current suspension and steering kinematics of the steer-by-wire system, the reference response rack force representing a reference force resisting a steering force modeled for a wheel using the reference model;

[0035] estimating a target response rack force based on a target model of the steer-by-wire system, the target model representing target suspension and steering kinematics of the steer-by-wire system, the target response rack force representing a target force resisting a steering force modeled for a wheel using the target model;

[0036] determining a corrected response rack force as a function of the observed response rack force, the reference response rack force, and the target response rack force; and

[0037] A driver feedback torque is determined based on the corrected response rack force.

[0038] Solution 2. The method according to solution 1, further comprising:

[0039] The corrected response rack force is determined from the rack equation, which is defined as:

[0040] CRF=max((RRF-TRF)+ORF),MSV)

[0041] where CRF equals the corrected response rack force, RRF equals the reference response rack force, TRF equals the target response rack force, ORF equals the observed response rack force, and MSV equals the minimum saturation value of the steer-by-wire system.

[0042] Option 3. The method according to Option 2, further comprising:

[0043] A driver feedback torque is provided to a steering wheel actuator configured to apply a responsive steering force to a steering wheel of a steer-by-wire system in proportion to the driver feedback torque.

[0044] Option 4. The method according to Option 3, further comprising:

[0045] determining a plurality of steer-by-wire variables representing effects on the operation of the steer-by-wire system;

[0046] estimating a reference response rack force based on processing the steer-by-wire variables using the reference model; and

[0047] A reference response rack force is estimated based on processing the steer-by-wire variables using a reference model.

[0048] Solution 5. The method according to solution 4, further comprising:

[0049] The reference model estimates a reference response rack force based on a reference curve defined relative to one or more of the steer-by-wire variables; and

[0050] The target model estimates a target response rack force based on a defined target curve relative to one or more of the steer-by-wire variables.

[0051] Solution 6. The method according to solution 5, further comprising:

[0052] A normal handling range, a nonlinear handling range, a near-limit handling range, and an adhesion limit of the steer-by-wire system are defined with respect to one or more of the steer-by-wire variables.

[0053] Option 7. The method according to Option 6, further comprising:

[0054] The target curve has a smoother gradient than the reference curve in the near-limit treatment range.

[0055] Option 8. The method according to Option 6, further comprising:

[0056] The target curve has a slope that decreases at a constant rate in the near-limit treatment range.

[0057] Option 9. The method according to Option 7, further comprising:

[0058] The target curve has a similar gradient to the reference curve over the normal treatment range.

[0059] Solution 10. The method according to solution 9, further comprising:

[0060] The reference profile and the target profile are defined relative to a lateral acceleration of the vehicle and / or a steering wheel angle of the steering wheel, which are included as part of the steer-by-wire variables.

[0061] Solution 11. The method according to solution 10, further comprising:

[0062] A minimum saturation value is determined as a function of a vehicle speed determined for the vehicle, the vehicle speed being included as part of the steer-by-wire variable.

[0063] Solution 12. A system for providing driver feedback in a vehicle having a steer-by-wire system, comprising:

[0064] an observer configured to measure an observed response rack force of the steer-by-wire system, the observed response rack force representing a response force exerted by one or more wheels of the vehicle resisting a steering force provided to the wheels using the steer-by-wire system;

[0065] a monitoring system configured to determine a plurality of steer-by-wire variables indicative of an effect on the operation of the steer-by-wire system;

[0066] a reference model defined relative to current suspension and steering kinematics of the steer-by-wire system, the reference model configured to estimate a reference response rack force of the steer-by-wire system based on modeling one or more of the steer-by-wire variables;

[0067] a target model defined relative to target suspension and steering kinematics for the steer-by-wire system, the target model configured to estimate a target response rack force for the steer-by-wire system based on modeling one or more of the steer-by-wire variables;

[0068] a response rack force controller configured to determine a corrected response rack force as a function of the observed response rack force, the reference response rack force, and the target response rack force; and

[0069] A steering wheel controller is configured to determine a driver feedback torque based on the corrected response rack force.

[0070] Solution 13. The system according to solution 12, further comprising:

[0071] An operating mode controller is configured to determine when the steer-by-wire system is operating in a non-near-limit handling range and a near-limit handling range, wherein the near-limit handling range is a first predefined operating range that occurs before the wheel adhesion limit is reached, and the non-near-limit handling range is a second predefined operating range that occurs before the near-limit handling range is reached.

[0072] Option 14. The system of Option 13, wherein:

[0073] The response rack force controller is configured to determine a corrected response rack force according to a near-limit rack equation when the steer-by-wire system operates in a near-limit handling range, the near-limit rack equation being defined as:

[0074] CRF=(RRF-TRF)+ORF)

[0075] Where CRF equals the corrected response rack force, RRF equals the reference response rack force, TRF equals the target response rack force, and ORF equals the observed response rack force.

[0076] Option 15. The system of Option 14, wherein:

[0077] The response rack force controller is configured to increase the corrected response rack force to a minimum saturation value when the corrected response rack force is less than an adhesion threshold value defined relative to the adhesion limit.

[0078] Solution 16. The system according to solution 15, further comprising:

[0079] A steering wheel actuator is configured to apply a responsive steering force to a steering wheel of a steer-by-wire system in proportion to a driver feedback torque.

[0080] Option 17. The system of Option 16, wherein:

[0081] The reference model is configured to estimate a reference response rack force based on a defined reference curve relative to one or more of the steer-by-wire variables;

[0082] The target model is configured to estimate a target response rack force based on a target curve defined relative to one or more of the steer-by-wire variables, the target curve differing in shape from a reference curve within a near-limit handling range.

[0083] Option 18. The system of Option 17, wherein:

[0084] The target curve is configured with a smoother gradient than the reference curve in the near-limit treatment range, and is configured with a similar gradient to the reference curve in the non-near-limit treatment range.

[0085] Solution 19. A vehicle comprising:

[0086] a plurality of wheels operable to facilitate movement of the vehicle;

[0087] a powertrain operable to rotate one or more of the wheels in response to mechanical power generated using the internal combustion engine and / or the electric motor;

[0088] A steer-by-wire system configured to steer one or more of the wheels, the steer-by-wire system configured to:

[0089] determining an observed response rack force based on a response rack force measurement obtained using a response rack force observer of the steer-by-wire system;

[0090] Estimating the reference response rack force based on a reference model of the steer-by-wire system;

[0091] Estimate the target response rack force based on the target model of the steer-by-wire system;

[0092] The corrected response rack force is determined from the rack equation, which is defined as:

[0093] CRF=max((RRF-TRF)+ORF),MSV)

[0094] where CRF equals the corrected response rack force, RRF equals the reference response rack force, TRF equals the target response rack force, ORF equals the observed response rack force, and MSV equals the minimum saturation value of the steer-by-wire system; and

[0095] A driver feedback torque is determined based on the corrected response rack force.

[0096] Option 20. The vehicle of Option 19, wherein:

[0097] a reference model configured to estimate a reference response rack force based on a reference curve defined relative to current suspension and steering kinematics of the steer-by-wire system and one or more steer-by-wire manipulated variables; and

[0098] The target model is configured to estimate a target response rack force based on a target curve defined relative to target suspension and steering kinematics of the steer-by-wire system and one or more steer-by-wire manipulated variables, the target curve having a smoother gradient than a reference curve within a near-limit handling range of the steer-by-wire system, the near-limit handling range corresponding to a predefined operating range occurring before a wheel adhesion limit is reached.

[0099] These features and advantages of the present teachings and other features and advantages may be readily apparent from the following detailed description of the modes for carrying out the present teachings when considered in conjunction with the accompanying drawings. It should be understood that although the following figures and embodiments may be described separately, their individual features may be combined into additional embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0100] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate implementations of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0101] Figure 1 A feedback system for providing driver feedback according to one aspect of the present disclosure is illustrated.

[0102] Figure 2 A schematic diagram of a steer-by-wire system providing driver feedback according to one aspect of the present disclosure is illustrated.

[0103] Figure 3 A flow chart illustrating a method of providing driver feedback according to one aspect of the present disclosure is shown.

[0104] Figure 4 A graph illustrating response rack force according to one aspect of the present disclosure is shown. DETAILED DESCRIPTION

[0105] As required, detailed embodiments of the present disclosure may be disclosed herein; however, it is understood that the disclosed embodiments may be merely illustrative of the disclosure, which may be embodied in various and alternative forms. The figures may not necessarily be to scale; some features may be exaggerated or minimized to illustrate details of particular components. Therefore, the specific structural and functional details disclosed herein may not be construed as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present disclosure.

[0106] Figure 1 A feedback system 10 for providing driver feedback according to one aspect of the present disclosure is illustrated. Feedback system 10 can be configured to provide driver feedback to a driver or other passenger of a vehicle 12, such as to assist the driver in sensing when the vehicle 12 may be approaching or operating at the limits of adhesion. For illustrative purposes, vehicle 12 is shown as an automobile, as this disclosure fully contemplates that feedback system 10 can be similarly beneficial in other types of vehicles, equipment, etc. Vehicle 12 may include an electric traction motor 14 operable to convert electrical power into mechanical power for work purposes, such as for mechanically powering a powertrain 16 to propel vehicle 12. Because powertrain 16 optionally includes an internal combustion engine (ICE) 18 for generating mechanical power, vehicle 12 is illustrated as a hybrid vehicle. Vehicle 12 may alternatively omit electric motor 14 and / or ICE 18. Powertrain 16 may include components that facilitate the transmission of mechanical rotational force from traction motor 14 and / or ICE 18 to one or more of wheels 20, 22, 24, and 26. The vehicle 12 may include a steering and suspension system 28 having a steer-by-wire system 29 for providing steering, which is shown for exemplary purposes as corresponding to steering the front wheels 20, 24. However, the present disclosure fully contemplates that the steer-by-wire system 29 may be operable to alternately steer the rear wheels 22, 26 and / or provide four-wheel or all-wheel steering. The vehicle 12 may include a rechargeable energy storage system (RESS) 30 to store and supply power to the traction motor 14 and / or other components, systems, etc. 32 on the vehicle 12, such as via a first bus 34 (e.g., a main bus or HV bus) and a second bus 36 (e.g., an auxiliary bus or LV bus).

[0107] The vehicle 12 may include a vehicle controller 38 to facilitate monitoring, controlling, measuring, and otherwise directing operations, performance, and the like on the vehicle 12, which may include performing measurements, taking readings, or otherwise collecting data to facilitate operations. The vehicle controller 38 may include additional controllers, wherein operations associated therewith are optionally performed according to one or more processors executing corresponding non-transitory instructions stored on one or more computer-readable storage media. The controller 38 may be configured to interact with other systems, controllers, and features included on and / or outside the vehicle 12 to facilitate operations, processes, and other activities associated with providing driver feedback in the manner described herein. Although primarily described with respect to providing driver feedback to the driver, the present disclosure fully contemplates that the feedback system 10 and / or associated feedback controller 42 may be operable in conjunction with an advanced driver assistance system (ADAS), an autonomous driving system, or other system associated with the vehicle 12. Driver feedback may be operable in conjunction with such a system to facilitate associated actions without necessarily requiring corresponding communication to the driver and / or associated feedback interaction with the driver.

[0108] Figure 2A schematic diagram of a suspension system 28 providing driver feedback according to one aspect of the present disclosure is illustrated. The suspension system 28, or more specifically the steer-by-wire system 29 therein, can be shown to include a steering actuator 50 and a wheel actuator 52 that cooperate with a steer-by-wire controller 58 to facilitate steering the vehicle 12. The steering wheel actuator 52 is configured to electromechanically actuate, rotate, or otherwise engage with a hand wheel or other steering implement accessible to the driver. The wheel actuator 52 can be configured to electromechanically actuate, rotate, or otherwise engage with the suspension system 28 associated with rotating one or more of the wheels 20, 24. Operation of the steer-by-wire system 29 may include: the steering actuator 50 generating a steering signal 60 to reflect the driver applying a steering force to the hand wheel for the purpose of steering the vehicle 12; the steer-by-wire controller 58 being responsible for generating a wheel signal 62 for directing the wheel actuator 52 to steer the wheels 20, 24 accordingly via a component 63 of the suspension system 28; the wheel actuator 52 providing a rack force signal 64 to the steer-by-wire controller 58 to indicate that the responsive rack force experienced at the suspension system 28 as a result of the movement of the vehicle 12 tends to counteract the wheels 20, 24 or turn the wheels 20, 24 back toward the center or resist rotation of the wheel actuator 52; the steer-by-wire controller 58 responsively providing a driver feedback signal 66 to the steering actuator 50 based on the responsive rack force; and the steering actuator 50 converting the driver feedback signal 66 into a driver torque or other force 68 sufficient to be used to actuate the hand wheel accordingly to provide driver feedback. The driver feedback can correspond to a resistance or response force generated by the steering actuator 50 against the steering force applied by the driver to the hand wheel, that is, the driver feedback 68 can be used to provide a slight reaction force to the force applied by the driver so that the driver can feel or otherwise tactilely sense the response rack force.

[0109] The ability to provide driver feedback 68 via tactile control of the hand wheel helps allow the driver to sense the operation of the wheels 20, 24 without having to rely on a direct physical link between the driver and the wheels 20, 24. In other words, the driver feedback 68 contemplated herein can be used to compensate for the lack of a force-transmitting mechanical connection between the driver and the wheels 20, 24, thereby enabling the driver to physically assess the wheels 20, 24 when there is no physical link to the wheels 20, 24. The ability of the present disclosure to implement driver feedback 68 can help, for example, allow the driver to assess whether the vehicle 12, or more particularly the steering wheels 20, 24, may be approaching an adhesion limit. The adhesion limit may correspond to the maximum amount of traction or grip that the suspension system 28 can provide before the wheels 20, 24 begin to lose traction and / or begin to slip. The adhesion limit can vary widely depending on the different suspension and steering kinematics of a particular vehicle 12, how fast the vehicle 12 is traveling, the tread or type of tires, the road surface, etc.; however, regardless of these variables and / or the capabilities of the suspension system 28, the driver feedback 68 can be beneficial in allowing the driver to consider whether the vehicle 12 is approaching the adhesion limit and how to operate the vehicle 12 accordingly.

[0110] Figure 3 A flowchart 80 illustrating a method for providing driver feedback 68 according to one aspect of the present disclosure is shown. The method is described with respect to a steer-by-wire system 29, whereby steering of the wheels 20, 24 can be performed based on signals carried by wires or other communication media that are not physically linked or capable of transmitting forces. Although described with respect to a four-wheeled vehicle 12 having front wheel steering, the present disclosure fully contemplates that the method can be advantageously used to facilitate driver feedback 68 for other types of vehicles, including autonomous vehicles that may employ similar types of steering systems. The method can be embodied and / or assisted by the operation of a steer-by-wire controller 58 and / or other controllers or systems on and / or external to the vehicle 12, which in turn can operate based on one or more processors executing a corresponding plurality of non-transitory instructions stored on one or more associated computer-readable storage media. The method is described with respect to the use of a response rack force, as those skilled in the art understand that the force acting on the wheels 20, 24 resisting the steering provided thereto is a suitable indicator. This is done for non-limiting purposes of this disclosure, and it is fully contemplated that this approach is similarly beneficial when implemented based on other constraints besides responsive rack force.

[0111] Block 82 relates to a monitoring system, included as part of the steer-by-wire controller 58 or as a standalone system, that determines a plurality of steer-by-wire variables. The steer-by-wire variables can be used to represent operational influences on the steer-by-wire system 29 and / or vehicle 12, such as, but not necessarily limited to, the steering wheel angle of the hand wheel while the vehicle 12 is traveling, the speed of the vehicle 12, the road friction of the road surface on which the vehicle 12 may be riding, the lateral acceleration of the vehicle 12, and / or other variables or factors that can be measured, sensed, calculated, estimated, etc. Block 84 relates to an observer, included as part of the steer-by-wire controller 58 or as a standalone system, that measures an observed response rack force 86 of the steer-by-wire system 29. The observed response rack force 86 can be measured using a sensor attached to a tie rod or another component of the suspension system 28 connected to the wheels 20, 24, such that the measurement quantifies the response force applied to the suspension system 28 as a result of the wheels acting against the vehicle 12's steering in response to its movement until the adhesion limit is exceeded. The observed response rack force 86 may represent the actual or real-world force or power applied by one or more wheels 20 , 24 to resist the rotational force provided by the wheel actuator 52 , i.e., the counter-response provided by the wheel 20 , 24 to resist the wheel actuator 52 .

[0112] Block 88 involves the steer-by-wire controller 58 being programmed with or otherwise generating a reference model for the steering kinematics of the current suspension and suspension system 28. The reference model can be a bicycle model or other suitable model defined with respect to the components, handling capabilities, and / or other aspects of the suspension system 28 actually or currently included on the vehicle 12 to model its performance. The reference model can be configured to estimate a reference response rack force 90 for the steer-by-wire system 29 based on modeling one or more of the steer-by-wire variables. The reference response rack force 90 can represent a reference force modeled for the wheels 20, 24 to reflect the force generated by the wheels 20, 24 that resists the turning force applied to the handwheel by the driver and / or the force applied by the wheel actuator 52 to rotate the wheels 20, 24. The reference response rack force 90 may be equivalent to the observed response rack force 86, with one difference being that the reference response rack force 90 is estimated using a reference model, and the observed response rack force 86 is an actual force measured using sensors included on the vehicle 12. The reference model may be constructed as a theoretical framework or mathematical model based on assumptions, principles, and data about the suspension system 28, such that the reference model may be used to predict how the suspension system 28 may respond under various scenarios that can be input to the model reference model as a function of one or more of the steer-by-wire variables.

[0113] Block 92 involves the steer-by-wire controller 58 being programmed with or otherwise generating a target model relative to target or desired suspension and steering kinematics. The target model can be defined relative to components, operational capabilities, and / or other aspects of the desired or target steering and / or suspension system 28 that are not actually or currently included on the vehicle 12. In contrast to a reference model, the target model can be used to model an ideal or desired steering and suspension system 28 that differs from the steering and suspension system actually included on the vehicle 12. The target model can be generated based on desired performance characteristics and used as a comparison tool with the reference model. However, like the reference model, the target model can be similarly configured to estimate a target response rack force 94 for the steer-by-wire system 29 based on modeling one or more of the steer-by-wire variables. The target response rack force 94 can represent a target force modeled for the wheels 20, 24 to reflect the force generated by the wheels 20, 24 in opposition to the steering force applied to the handwheel by the driver and / or the force applied to the wheels 20, 24 by the wheel actuators 52. The target response rack force 94 can be equivalent to the observed response rack force 86, with one difference being that the target response rack force 94 is estimated using a target model, and the observed response rack force 86 is an actual force measured using wheel sensors included on the vehicle 12. The target model can be constructed as a theoretical framework or mathematical model based on assumptions, principles, and data about an idealized or desired steering and suspension system 28, such that the target model can be used to predict how the idealized or desired steering and suspension system 28 might respond to various scenarios. The target model can differ from the reference model in that it models the hypothetical response of another configuration of the suspension system 28 that is not currently on the vehicle 12, which may be different from the suspension system 28 included on the vehicle 12. This type of comparative modeling can be beneficial in evaluating actual or current performance estimated using the reference model relative to target performance estimated using the target model.

[0114] Figure 4A graph 100 of response rack forces according to one aspect of the present disclosure is illustrated. Graph 100 may include a vertical axis 102 representing force (e.g., in Newtons (N)) and a horizontal axis 104 representing one or more steer-by-wire variables (e.g., lateral acceleration), which may be expressed in units of gravity (g). Graph 100 may include an observation curve 106 reflecting observed response rack forces 86 measured using an observer. Observation curve 106 may correspond to the observer actually measuring the response rack forces while vehicle 12 is being driven, optionally with the observer recording steer-by-wire variables consistent therewith. The graph may additionally include a reference curve 108 and a target curve 110 to illustrate and compare reference and target response rack forces 94, respectively, generated using respective reference and target models relative to observation curve 106. Reference and target curves 108, 110 may be derived from processing respective reference and target models of the steer-by-wire variables recorded when generating observation curve 106. Assuming the reference model is an accurate representation of the suspension system 28, the observed curve 106 can be expected to align closely with the reference curve 108. The target curve 110 is shown as slightly different from the observed curve 106 and the reference curve 108 because the target model generates a target or desired response rack force that may be desired for the vehicle 12, even though the suspension system 28 on the current vehicle 12 may not achieve the same result on its own.

[0115] The graph 100 can be defined or divided according to a normal handling range 112, which can include a nonlinear handling range 114, a near-limit handling range 116, and an adhesion limit 118. The adhesion limit 118 can vary from vehicle to vehicle and is illustrated for exemplary purposes as corresponding to approximately 0.95 g. The adhesion limit 118 can correspond to the point at which the wheels 20, 24 lose traction or begin to slip, which, as illustrated, can correspond to the observed responsive rack force 86 dropping to zero due to the accompanying wheel slip preventing or effectively limiting the force provided or generated by the wheels 20, 24 resisting the wheel actuator 52. The near-limit handling range 116 can correspond to a predefined or selectable operating range that occurs before the adhesion limit is reached and is illustrated as starting at the point at which the responsive rack force begins to decrease due to the wheels 20, 24 initially beginning to lose traction or partially slip. The nonlinear handling range 114 can correspond to a predefined or selectable operating range that occurs before the near-limit operating range within the normal handling range 112. Ranges 112, 114, 116, 118 are presented for non-limiting purposes to highlight different handling ranges that can be used to define events associated with conditions during which wheel slip may be unlikely to occur - i.e., during the normal and / or nonlinear operating handling ranges - where wheel slip may occur while providing at least some real response rack force - i.e., during the near-limit handling ranges - and where wheel slip may cause the steering and suspension system 28 to generate zero actual response rack force.

[0116] The target curve 110 can be graphically created based on the corresponding configuration of the target model such that the target curve 110 differs from the observed curve 106 and the reference curve 108, particularly as the vehicle 12 approaches the near-limit handling range 116. This difference can reflect how the vehicle 12 would experience the response rack force if the suspension system 28 were able to induce the corresponding response rack force. For example, after reaching a peak response rack force at the beginning of the near-limit range 116, the target curve 110 can match the reference curve 108 and can decay at a lower lateral acceleration than the reference curve 108, such as 5% to 20%, at a slope per lateral acceleration in the range of 5% to 50% of the reference curve 108, or decay in another manner. For example, the target curve 110 can have a smoother gradient than the reference curve 108 within the near-limit handling range 116, match or track the amount or rate of change of the reference curve 108 but by a smaller amount, and / or at a steady or fixed rate. The ability to adjust the target curve 110, or more specifically, the target model, relative to the desired response rack force performance can be beneficial in comparing the performance of the actual suspension system 28 to a desired standard, particularly with respect to identifying how the desired suspension system 28 may operate within a near-limit handling range. One aspect of the present disclosure contemplates configuring the target model to represent a desired feel or other sensory feedback to the driver, which can be based on comparing the observed response rack force 86 and the reference response rack force 90 to the target response rack force 94, such that the difference therebetween can form the basis of the driver feedback 68.

[0117] return Figure 3Block 122 involves an offset process, whereby the steer-by-wire controller 58 can determine an offset or difference 124 between the target response rack force 94 and the reference response rack force 90. The response rack force offset 124 can be determined by subtracting the target response rack force 94 from the reference response rack force 90, or otherwise determining the difference therebetween. The response rack force offset 124 can be used to quantify the deviation of the suspension system 28 from the hypothetical suspension system 28 used for the target model, which can correspond to a value representing the separation between the target curve 110 and the reference curve 108 for a given set of steer-by-wire variables present during modeling. Block 126 involves a correction process for determining a corrected response rack force 128. The corrected response rack force 128 can be determined by adding the response rack force offset 124 to the observed response rack force 86, which can correspond to the corrected response rack force 128 being greater or less than the observed response rack force 86 depending on whether the response rack force offset 124 is greater than or less than the observed response rack force 86. The generation of a corrected response rack force 128 based on the response rack force offset 124 can be derived from the difference between the reference model and the target model in this manner. Estimating the response rack force offset 124 independently of the observed response rack force 86 can enable the present disclosure to determine the corrected response rack force 128 without having to base its calculation on the observed response rack force 86. In other words, the reference model and the target model can operate as a function of steer-by-wire variables rather than requiring input of the observed response rack force 86, which in turn can permit a more efficient calculation of the response rack force offset 124 and / or without having to account for the relatively rapid and nearly constant changes in the observed response rack force 86 that often occur while driving.

[0118] Block 132 relates to a saturation process whereby the steer-by-wire controller 58 may determine a minimum saturation value. The minimum saturation value may be used to set a minimum value for the corrected response rack force 128. In the event that the corrected response rack force 128 is below a minimum threshold, the minimum saturation value may be used to increase the corrected response rack force. The steer-by-wire controller 58 may include a saturation model for determining the minimum saturation value, which may be based on one or more of the steer-by-wire variables. One aspect of the present disclosure contemplates a saturation model based on vehicle speed, lateral acceleration, and / or road friction, such that the minimum saturation value may increase or decrease in magnitude depending on vehicle 12 operation, e.g., the saturation value may be smaller when the vehicle 12 is traveling slower and the saturation value may be larger when the vehicle 12 is traveling faster. Figure 4 A saturation curve 134 is shown that may represent a minimum saturation value. Thus, when the minimum saturation value is included, the corrected response rack force may be determined according to the rack equation, which is defined as:

[0119] CRF=max((RRF-TRF)+ORF),MSV)

[0120] Wherein, CRF equals the corrected response rack force, RRF equals the reference response rack force 90, TRF equals the target response rack force 94, ORF equals the observed response rack force 86, and MSV equals the minimum saturation value of the steer-by-wire system 29. Alternatively, when the minimum saturation value is optionally omitted, the corrected response rack force may be determined according to a near-limiting rack equation, which is defined as:

[0121] CRF=(RRF-TRF)+ORF)

[0122] Where CRF equals the corrected response rack force, RRF equals the reference response rack force 90 , TRF equals the target response rack force 94 , and ORF equals the observed response rack force 86 .

[0123] return Figure 2 , a corrected response rack force 128 can be provided from the steer-by-wire controller 58 to the steering actuator 50 within signal 66. The steering actuator 50 can, in turn, generate a response torque or force 68 on the handwheel. This response action can be generated to provide driver feedback 68, optionally with driver feedback 68 more closely aligned with the target curve 110, so that the driver can better feel and sense when the vehicle 12 is approaching the adhesion limit and when the vehicle 12 is approaching the adhesion limit. The driver feedback 68 can be provided with a smoother and / or more consistent gradient as shown, so that the driver feedback 68—i.e., the response action on the handwheel—slowly or steadily decreases as the vehicle 12 moves through the near-limit range. This can be more beneficial than feedback derived from the reference response rack force 90 and / or observed response rack force 94, as those forces would result in feedback with more abrupt changes, which in turn limits the feel and timing at which the driver can sense that the adhesion limit is approaching.

[0124] Although various embodiments have been described, this description is intended to be illustrative, not restrictive, and it will be apparent to those skilled in the art that many more embodiments and implementations are possible within the scope of the embodiments. Unless otherwise specified, any feature of any embodiment may be used in combination with or substituted for any other feature or element in any other embodiment. Therefore, the embodiments are not to be limited except in light of the appended claims and their equivalents. Furthermore, various modifications and variations may be made within the scope of the appended claims. While several modes for practicing many aspects of the present teachings have been described in detail, those skilled in the art to which these teachings relate will recognize various alternative aspects for practicing the present teachings within the scope of the appended claims. It is intended that all matter contained in the foregoing description or shown in the accompanying drawings be construed as illustrations and examples of the entire range of alternative embodiments, which will be recognized by those skilled in the art as implied by, structurally and / or functionally equivalent to, or otherwise apparent from the included content, and are not limited to those embodiments explicitly depicted and / or described.

Claims

1. A method for providing driver feedback to a vehicle having a steer-by-wire system, comprising: determining an observed response rack force based on a response rack force measurement taken by a response rack force observer of the steer-by-wire system, the observed response rack force representing a force exerted by one or more wheels of the vehicle opposing a steering force provided to the wheels by the steer-by-wire system; estimating a reference response rack force based on a reference model of the steer-by-wire system, the reference model characterizing current suspension and steering kinematics of the steer-by-wire system, the reference response rack force representing a reference force resisting a steering force modeled for a wheel using the reference model; estimating a target response rack force based on a target model of the steer-by-wire system, the target model representing target suspension and steering kinematics of the steer-by-wire system, the target response rack force representing a target force resisting a steering force modeled for a wheel using the target model; determining a corrected response rack force as a function of the observed response rack force, the reference response rack force, and the target response rack force; and A driver feedback torque is determined based on the corrected response rack force.

2. The method according to claim 1, further comprising: The corrected response rack force is determined from the rack equation, which is defined as: CRF=max((RRF-TRF)+ORF),MSV) where CRF equals the corrected response rack force, RRF equals the reference response rack force, TRF equals the target response rack force, ORF equals the observed response rack force, and MSV equals the minimum saturation value of the steer-by-wire system.

3. The method according to claim 2, further comprising: A driver feedback torque is provided to a steering wheel actuator configured to apply a responsive steering force to a steering wheel of a steer-by-wire system in proportion to the driver feedback torque.

4. The method according to claim 3, further comprising: determining a plurality of steer-by-wire variables representing effects on the operation of the steer-by-wire system; estimating a reference response rack force based on processing steer-by-wire variables using a reference model; and A reference response rack force is estimated based on processing the steer-by-wire variables using a reference model.

5. The method according to claim 4, further comprising: The reference model estimates a reference response rack force based on a reference curve defined relative to one or more of the steer-by-wire variables; and The target model estimates a target response rack force based on a defined target curve relative to one or more of the steer-by-wire variables.

6. The method according to claim 5, further comprising: A normal handling range, a nonlinear handling range, a near-limit handling range, and an adhesion limit of the steer-by-wire system are defined with respect to one or more of the steer-by-wire variables.

7. The method according to claim 6, further comprising: The target curve has a smoother gradient than the reference curve in the near-limit treatment range.

8. The method according to claim 6, further comprising: The target curve has a slope that decreases at a constant rate in the near-limit treatment range.

9. The method according to claim 7, further comprising: The target curve has a similar gradient to the reference curve over the normal treatment range.

10. The method according to claim 9, further comprising: The reference profile and the target profile are defined relative to a lateral acceleration of the vehicle and / or a steering wheel angle of the steering wheel, which are included as part of the steer-by-wire variables.

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