METHOD AND SYSTEM FOR FRICTION-CONSCIOUS COLLISION AVOIDANCE

Abstract

A method for controlling a vehicle includes detecting that an object is located along a path of the vehicle and within a predetermined distance from the vehicle; in response to the detection of the object located along the path of the vehicle and within the predetermined distance from the vehicle, determining a coefficient of friction between a road and a tire of the vehicle in real time; and in response to determining the coefficient of friction between the road and the tire of the vehicle, commanding the vehicle to perform a steering action.

Description

INTRODUCTION

[0001] The present disclosure relates to a method and system for controlling a vehicle. More specifically, the present disclosure relates to a method and system for friction-aware collision avoidance.

[0002] This introduction generally presents the context of the disclosure. Works by the presently named inventors, to the extent described in this introduction, as well as aspects of the description that may not otherwise be considered prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against this disclosure.

[0003] The movement of a vehicle can be influenced by the friction between the road and the vehicle tires. Therefore, it is useful to know the coefficient of friction between the road surface and the vehicle tires. Furthermore, it is desirable to consider the friction between the road and the vehicle tires when controlling vehicle movement. SUMMARY

[0004] The present disclosure describes a method for friction-aware collision avoidance. In one aspect of the present disclosure, the method includes detecting that an object is located along a path of the vehicle and within a predetermined distance from the vehicle, determining a coefficient of friction between a road and a tire of the vehicle in real time in response to detecting the object being located along the path of the vehicle and within the predetermined distance from the vehicle, and in response to determining the coefficient of friction between the road and the tire of the vehicle, commanding the vehicle to perform a control action. Other embodiments of this aspect include corresponding computer systems, devices, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.The method described in this paragraph improves vehicle technology by using the coefficient of friction between the road and the vehicles' tires to avoid collisions with objects.

[0005] Implementations may include one or more of the following features. The method may include applying a braking load to a wheel of the vehicle, monitoring a movement of the vehicle (e.g., longitudinal deceleration, wheel speed, and / or GNSS speed) at the same time the braking load is applied to the vehicle wheel, and determining the coefficient of friction between the road and the vehicle tire in real time based on the movement of the vehicle during the braking load. The control action may be continuously applying the braking load to the vehicle wheel in response to determining that the coefficient of friction between the road and the vehicle tire is less than the predetermined friction threshold. Alternatively or additionally, the control action may be to steer the vehicle to avoid the object located along the vehicle's path.in response to determining that the coefficient of friction between the road and the tire of the vehicle is equal to or greater than the predetermined friction threshold. The steering path has a radius of curvature. The method may include determining a radius of curvature of the steering path. The radius of curvature of the steering path may be based on the coefficient of friction between the tire and the road. The method may include determining a time to impact with the object located along the path of the vehicle and within the predetermined distance from the vehicle; determining a last time to determine friction; determining a last time to steer the vehicle to avoid the object located along the path of the vehicle; determining a sum of the last time to determine friction and the last time to steer the vehicle to avoid the object located along the path of the vehicle.and comparing the time to collision with the object located along the path of the vehicle with the sum of the last time to determine friction and the last time to steer the vehicle to avoid the object located along the path of the vehicle to determine whether the time to collision with the object located along the path of the vehicle is greater than the sum of the last time to determine friction and the last time to steer the vehicle to avoid the object located along the path of the vehicle. The method may include determining the last time to brake to avoid the object located along the path of the vehicle in response to determining that the time to collision with the object located along the path of the vehicle is greater than the sum of the last time to collision with the object,that is along the path of the vehicle is less than the sum of the last time to determine friction and the last time to steer the vehicle to avoid the object that is along the path of the vehicle. The method may include determining a sum of the last time to brake to avoid the object that is along the path of the vehicle and the time to determine friction in response to determining that the time to impact the object that is along the path of the vehicle is greater than the sum of the last time to determine friction and the last time to steer the vehicle to avoid the object that is along the path of the vehicle. Further, the method may include comparing the time to impact the object that is along the path of the vehicle with the sum of the last time to brake to avoid the object,located along the path of the vehicle and the time to determine friction, for determining whether the time to collision is less than the sum of the last time to brake to avoid the object located along the path of the vehicle and the time to determine friction in response to determining that the time to collision with the object located along the path of the vehicle is greater than the sum of the last time to determine friction and the last time to steer the vehicle to avoid the object located along the path of the vehicle. The coefficient of friction between the road and the tire of the vehicle can be determined exclusively in response to: (a) detecting the object located along the path of the vehicle and within the predetermined distance from the vehicle; and (b) determiningthat the time to collision is less than the sum of the last time to brake to avoid the object located along the path of the vehicle and the time to determine the friction. The method may include determining an updated last time to steer to avoid the object located along the path of the vehicle based on the coefficient of friction between the road and the tire of the vehicle in response to determining that the coefficient of friction between the road and the tire of the vehicle is equal to or greater than the predetermined friction threshold, and comparing the time to collision with the object located along the path of the vehicle with the updated last time to steer to avoid the object located along the path of the vehicle to determinewhether the time to collision with the object along the vehicle's path is greater than the updated last time to steer to avoid the object located along the vehicle's path. The vehicle may be commanded to perform the control action solely in response to determining that the time to collision with the object along the vehicle's path is greater than the updated last time to steer to avoid the object located along the vehicle's path. The control action may be to steer the vehicle to avoid the object located along the vehicle's path in response to determining that the coefficient of friction between the road and the vehicle's tire is equal to or greater than the predetermined friction threshold. The control action may include commanding a display of the vehicle to display a warning,such as "brake" and / or "do not steer"). For example, the display 29 may issue a warning to the driver (e.g., "continue braking" and / or "do not steer"). Insufficient road friction may be used as a condition to prevent prompts or "nudges" that suggest an evasive maneuver to the driver (e.g., alarms, vibrations, on-screen messages, HUD warnings, etc.). Insufficient road friction may serve as a condition to prevent evasive steering assistance that activates after the driver begins to steer. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium.

[0006] The present disclosure also describes a system comprising sensors and a controller in communication with the sensors. The controller is programmed to perform the method described above. The present disclosure also describes a tangible, non-transferable, machine-readable medium comprising machine-readable instructions that, when executed by a processor, cause the processor to perform the method described above.

[0007] 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 provided for purposes of illustration only and are not intended to limit the scope of the disclosure.

[0008] The foregoing features and advantages, as well as other features and advantages of the presently disclosed system and method, are readily apparent from the detailed description, including the claims and exemplary embodiments, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present disclosure will be more fully understood from the detailed description and the accompanying drawings, in which: Fig. 1 is a block diagram of a vehicle. Fig. 2 is a flowchart of a method for friction-aware collision avoidance. Fig. Figure 3 is a schematic diagram of the vehicle approaching an object. DETAILED DESCRIPTION

[0010] Reference will now be made in detail to several examples of the disclosure, which are illustrated in the accompanying drawings. Wherever possible, the same or similar reference numerals are used throughout the drawings and the description to refer to the same or similar parts or steps.

[0011] With reference to Fig. 1, a vehicle 10 is configured to be driven on a road 39 and generally includes a chassis 12, a body 14, wheels 15, front and rear tires 17, and may be referred to as a vehicle system. In the illustrated embodiment, the vehicle 10 includes two front tires 17a and two rear tires 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 together may form a frame. The wheels 15 are each rotatably coupled to the chassis 12 near a corner of the body 14. Each tire 17 is coupled to one of the wheels 15. The vehicle 10 has a front axle 19 coupled to the front tires 17a and a rear axle 25 coupled to the rear tires 17b.

[0012] The vehicle 10 may be an autonomous vehicle, and a control system 98 is installed in the vehicle 10. The vehicle 10 is, for example, a vehicle that is automatically controlled to transport passengers from one location to another. The vehicle 10 is a pickup truck in the illustrated embodiment, but other vehicles such as 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 automation system. A level four system indicates a "high degree of automation" and refers to the drive mode-specific execution of aspects of the dynamic driving task by an automated driving system, even if a human driver does not appropriately respond to a request for intervention.A Level 5 system indicates "full automation," which refers to an automated driving system fully performing all aspects of the dynamic driving task under a range of road and environmental conditions that can be handled by a human driver. In Level 3 vehicles, the system performs the entire dynamic driving task (DDT) within the range for which it was designed. In Level 2 vehicles, the systems assist with steering, braking / acceleration, lane centering, and adaptive cruise control. However, even when these systems are activated, the driver must be behind the wheel and constantly monitor the automated features.

[0013] As illustrated, 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 may be a steer-by-wire system or an electronic power steering system. The propulsion system 20, in various embodiments, may include an electric 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 provide electrical energy to the propulsion system 20. In certain embodiments, the propulsion system 20 may include an internal combustion engine.The transmission system 22 is configured to transfer power from the drive system 20 to the wheels 17 according to selectable gear 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 apply braking torque to the vehicle tires 17. The braking system 26 may, in various embodiments, include friction brakes, wire-based brakes, 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 tires 17 and may include a steering wheel 33. Although shown as including a steering wheel 33 for illustrative purposes, the steering system 24 may not include a steering wheel 33 in some embodiments contemplated within the scope of the present disclosure.

[0014] The sensor system 28 includes one or more sensors 40 (i.e., measuring devices) that sense observable conditions of the external environment and / or the internal environment of the vehicle 10. The sensors 40 are in communication with the controller 34 and may include, but are not limited to, one or more steering wheel sensors 45, one or more radars, one or more lidar (light detection and ranging) sensors, one or more proximity sensors, one or more odometers, one or more ground penetrating radar (GPR) sensors, one or more steering angle sensors, global navigation satellite system (GNSS) transceivers (e.g., one or more (GPS) transceivers), one or more tire pressure sensors, one or more cameras 41 (e.g.,Eye trackers), one or more gyroscopes, one or more accelerometers, one or more inclinometers, one or more speed sensors, one or more ultrasonic sensors, one or more inertial measurement units (IMUs), one or more night vision devices, thermal imaging sensors, and / or other sensors. Each sensor 40 is configured to generate a signal indicative of 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.

[0015] The actuator system 30 includes one or more actuator devices 42 that control one or more vehicle functions, such as, but not limited to, the drive system 20, the transmission system 22, the steering system 24, and the braking system 26. The steering system 24 may include front and possibly rear-wheel steering. The rear-wheel steering may be controlled by a separate controller. In various embodiments, the vehicle features may further include interior and / or exterior features of the vehicle, such as doors, a trunk, and interior features such as air, music, and lighting, etc. The actuators 42 may be part of the steering system 24 and may include one or more road wheel actuators (RWAs) and a hand wheel actuator (HWA).

[0016] The data storage device 32 stores data used in automatically controlling the vehicle 10. In various embodiments, the data storage device 32 stores defined maps of the navigable environment. In various embodiments, the defined maps may be predefined 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 wired), 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.

[0017] 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 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 that 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.

[0018] The controller 34 includes at least one processor 44 and a non-transitory computer-readable storage device or media 46. The processor 44 may be any custom 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 media 46 may include volatile and non-volatile memory, such as read-only memory (ROM), random access memory (RAM), and keep-alive memory (KAM). 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 media may be implemented using a number of storage devices, such as PROMs (programmable read-only memories), EPROMs (erasable PROMs), EEPROMs (electrically erasable PROMs), flash memory, or other electrical, magnetic, optical, or combination storage devices capable of storing data, some of which may be 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.

[0019] The instructions may comprise one or more separate programs, each of which comprises an ordered list of executable instructions for implementing logical functions. The instructions, when executed by processor 44, receive and process signals from sensor system 28, perform logic, calculations, methods, and / or algorithms to automatically control the components of vehicle 10, and generate control signals for actuator system 30 to automatically control one or more components of vehicle 10 based on the logic, calculations, methods, and / or algorithms. Although a single control unit 34 in Fig. 1, embodiments of the vehicle 10 may include a plurality of controllers 34 that communicate and cooperate via a suitable communication medium or combination of communication media 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 instructions of the controller 34 are embodied in the control system 98.

[0020] 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 alert, such as one or more speakers 27 for emitting an audible tone, haptic feedback on a vehicle seat or other object, one or more displays 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). The user interface 23 may, for example, include a touchscreen and / or buttons configured to receive inputs from a vehicle occupant 11.Accordingly, the controller 34 is configured to receive user inputs via the user interface 23. The vehicle 10 may include one or more displays 29 configured to display information to the vehicle occupant 11 (e.g., the vehicle driver or passenger), and may be a head-up display (HUD).

[0021] 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 devices such as a cellular phone. In the present disclosure, the term “remote vehicle” refers to a vehicle, such as a car, that is configured to transmit one or more signals to the vehicle 10 without being 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 via cellular data communication.However, additional or alternative communication methods, such as Dedicated Short Range Communication (DSRC), are also contemplated within the scope of the present disclosure. DSRC channels refer to one-way or two-way short- to medium-range wireless communication channels specifically designed for use in vehicles, as well as 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 the infrastructure or other vehicles.

[0022] With reference to Fig. 1 and Fig. 3, the system 98 is configured to avoid collisions with an object 200 along a path 202 by taking into account the friction between the tires 18 and the road 39. When a collision with an object 200 is imminent, it can be avoided by automatic emergency braking or an automatic evasive maneuver. At high speeds, avoiding a collision by steering gives the driver or the automated system more time to react, but this maneuver can cause other problems when road surface friction is low. The system 98 estimates surface friction when a collision is imminent and uses this estimate to take the appropriate action to avoid a collision, given the road conditions.Surface friction can be estimated by a short braking pulse when a collision is imminent, just before the decision between braking and steering must be made. The vehicle's longitudinal behavior is used to estimate friction. If friction is low, the braking pulse is maintained, and system 98 proceeds to automatic emergency braking. If friction is sufficient, automatic evasive steering can be activated, and system 98 can use the estimated friction as a control parameter.

[0023] With reference to Fig. 2 and Fig.3, a method 100 is configured for friction-aware collision avoidance with another object 200 along a path 202 of the vehicle 10. As non-limiting examples, the object 200 may be another vehicle, a stationary building, a pedestrian, etc. The method 100 begins in block 102. In block 102, the controller 34 receives sensor data from the sensors 40 (e.g., the camera 41). The sensor data may indicate, among other things, the location and movement of objects in the vicinity of the vehicle 10. In block 102, the vehicle controller 34 detects an object 200 that is located in the path 202 of the vehicle 10 and that is within a predetermined distance from the vehicle 10 using the sensor data.Alternatively or additionally, the vehicle 10 may use V2V or V2I communication to detect the object 200 located along the path 202 of the vehicle 10 and within a predetermined distance from the vehicle 10. The method 100 then proceeds to block 104.

[0024] In block 104, the vehicle control unit 34 determines the time to impact (TTI) with the object 200 using, among other things, the vehicle speed and the distance from the vehicle 10 to the object 200. The vehicle speed of the vehicle 10 and the distance from the vehicle 10 to the object 200 may be detected by the sensors 40. The vehicle control unit 34 also determines the last time to steer (LTTS). The LTTS is the shortest possible time before a collision in which the vehicle 10 could steer and avoid a collision with the object 200. The control unit 34 may also determine the time to determine friction (TTDF), which may be a predetermined value. The TTDF is the time required to determine the coefficient of friction between the road 39 and the tires 17. As a non-limiting example, the TTDF can be between 300 and 500 microseconds.In block 104, the controller 34 then determines the sum of LTTS plus TTDF. The controller 34 then compares the TTI to the sum of LTTS and TTDF. If the TTI is equal to or less than the sum of LTTS and TTDF, the method 100 proceeds to block 106. In block 106, the controller 34 commands the vehicle 10 to perform an immediate autonomous emergency braking application. In other words, in block 106, the controller 34 commands the braking system 26 to decelerate the vehicle 10 immediately. If the TTI is greater than the sum of LTTS and TTDF, the method 100 proceeds to block 108.

[0025] In block 108, controller 34 determines whether the last time to brake (LTTB) to avoid object 200 located along the path of vehicle 10 is sufficient. LTTB is the shortest possible time before a collision in which vehicle 10 could brake and avoid a collision with object 200. LTTB may be determined using, among other things, sensor data from sensors 40. LTTB may be determined using, for example, the vehicle speed of vehicle 10, the distance from vehicle 10 to object 200, and / or the speed of object 200. Controller 34 then determines the sum of LTTB and TTDF. Controller 34 then compares TTI to the sum of LTTB and TTDF. If TTI is less than the sum of LTTB and TTDF, method 100 proceeds to block 110. If the TTI is equal to or greater than the sum of LTTB and TTDF, the method 100 returns to block 102.In block 110, the vehicle controller 34 commands the braking system 26 to apply a braking load to the wheels 15 to determine the coefficient of friction between the road 39 and the tires 17. Thus, the initiation of the braking pulse in block 110 depends on the estimated TTI. The braking pulse may only be initiated in a time window that is less than the LTTB plus buffer (i.e., TTDF) and greater than the LTTS. Specifically, in block 110, the vehicle controller 34 may command the braking system 26 to apply a braking pulse (e.g., friction or regeneration) to one or more wheels 15 for a predetermined period of time (e.g., 300 to 500 microseconds) for the purpose of road friction estimation. The braking pulse may serve as a warning to the driver that a potential collision is imminent. This braking may be accompanied by other warnings to the driver.For example, at this point, controller 34 may command user interface 23 to provide a visual and / or audible notification indicating that a collision is imminent. For example, display 29 may provide a warning to the driver (e.g., "continue braking" and / or "do not steer"). Insufficient road friction may be used as a condition to inhibit prompts or "nudges" that suggest an evasive maneuver to the driver (e.g., alarms, vibrations, on-screen messages, HUD warnings, etc.). Insufficient road friction may serve as a condition to prevent evasive steering assistance that activates after the driver begins to steer. In this case, system 98 may continue to apply the brakes and use automatic steering commands to stabilize vehicle 10 rather than avoid object 200.

[0026] In one embodiment, evasive steering only intervenes once the driver begins to steer, assisting the driver in avoiding a collision. In this embodiment, the friction estimate can be used as a condition to inhibit prompts suggesting an evasive maneuver to the driver. For example, if the estimated friction coefficient is less than a predetermined threshold, controller 34 can command vehicle 10 to inhibit evasive steering assistance, which begins after the driver begins to steer.

[0027] To determine the coefficient of friction between the road 39 and the tires 17, the controller 34 monitors a longitudinal response (e.g., longitudinal deceleration) of the vehicle 10 using the sensor data from the sensors 40 at the same time that the braking load is applied to the wheels 15 of the vehicle 10. Using this longitudinal response (e.g., longitudinal deceleration), the controller 34 determines (i.e., estimates) in real time the coefficient of friction between the road 39 and the tires 17. The method 100 then proceeds to block 112. This friction estimate is used to make a decision regarding the optimal collision avoidance control action (e.g., braking and / or steering). The control action may be a fully autonomous action or an assistive action of the vehicle 10. After executing block 110, the method 100 proceeds to block 112.

[0028] In block 112, the controller 34 compares the coefficient of friction between the road 39 and the tires 17 of the vehicle 10 to a predetermined friction threshold. If the coefficient of friction between the road 39 and the tires 17 of the vehicle 10 is less than the predetermined friction threshold, the method 100 proceeds to block 114. In block 113, the controller 34 commands the braking system 26 to further decelerate the wheels 15 to avoid or mitigate a collision with the object 200. In other words, if the friction of the road is insufficient for an evasive maneuver, the controller 34 commands the braking system 26 to further decelerate the wheels 15 to avoid or mitigate a collision with the object 200. The magnitude of braking may be different from that used to detect the friction coefficient. The term "braking load" includes the braking load and / or a regenerative braking torque.If the coefficient of friction between the road 39 and the tires 17 of the vehicle 10 is equal to or greater than the predetermined friction threshold, the method 100 proceeds to block 116.

[0029] In block 116, the controller 34 determines an updated last time to steer (ULLTS) based on the friction coefficient between the road 39 and the tire 17 of the vehicle 10 to avoid the object 200 located along the path 202 of the vehicle 10. In other words, the controller 34 recalculates the LTTS. The method 100 then proceeds to block 118.

[0030] In block 118, controller 34 compares the TTI to the ULLTS. If the TTI is equal to or less than the ULLTS, method 100 proceeds to block 120.

[0031] If the TTI is greater than the ULTTS, the method 100 returns to block 112.

[0032] In block 120, controller 34 commands steering system 24 to initiate an automatic steering maneuver to avoid object 200 along path 202. A classification of road friction (e.g., medium versus high or wet versus dry asphalt) may be used to change the timing or form of the evasive maneuver. If road friction is lower, the evasive maneuver may be initiated earlier to accommodate a path with a lower curvature. Thus, in block 120, controller 34 may determine a steering path and the radius of curvature of the steering path. The radius of curvature of the steering path may be based on the coefficient of friction between tire 17 and road 39. A continuous estimation of road friction may be used in path planning or control.For example, the estimated friction or the maximum lateral and longitudinal accelerations derived from it can be used as constraints in path planning to shape the desired trajectory according to the tire limits. Furthermore, the estimated friction coefficient can be used as a model parameter in model predictive control or another model / parameter-based control methodology and / or as a variable for calculating the gains for each feedback control unit. The maximum lateral acceleration resulting from the estimated friction coefficient can also be used as a constraint in the control.

[0033] Although exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification 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 other embodiments of the presently disclosed system and method that may not be explicitly described or illustrated.Although various embodiments may have been described as providing advantages or being preferred over other prior art embodiments or designs with respect to one or more desired characteristics, those of ordinary skill in the art will recognize that one or more features or properties may be compromised to achieve desired overall system attributes depending on the specific application and design. These attributes may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, usability, weight, manufacturability, ease of assembly, etc.As such, embodiments that are described as less desirable than other embodiments or prior art embodiments with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for certain applications.

[0034] The drawings are presented in simplified form and are not to scale. For convenience and clarity, and for these reasons only, directional terms such as top, bottom, left, right, upward, above, above, below, below, back, and front may be used with reference to the drawings. These and similar directional terms should not be construed to limit the scope of the disclosure in any way.

[0035] Embodiments of the present disclosure are described herein. However, it should be understood that the disclosed embodiments are merely examples, and other embodiments may take various and alternative forms. The figures are not necessarily to scale; some features may be larger or smaller to show details of particular components. Therefore, the specific structural and functional details disclosed herein are not to be considered limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the presently disclosed system and method.As one of ordinary skill in the art will understand, various features illustrated and described with reference to one of the figures may be combined with features illustrated in one or more of the other figures to produce embodiments not explicitly illustrated or described. The illustrated feature combinations provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desired for particular applications or implementations.

[0036] Embodiments of the present disclosure may be described herein in terms of functional and / or logical block components and various processing steps. It should be understood that such block components may be implemented by a number of hardware, software, and / or firmware components configured to perform the specified functions. For example, an embodiment of the present disclosure may utilize various integrated circuit components, e.g., memory elements, digital signal processing elements, logic elements, lookup tables, or the like, capable of performing a plurality of functions under the control of one or more microprocessors or other control devices.Furthermore, those skilled in the art will recognize that embodiments of the present disclosure may be used in connection with a number of systems and that the systems described herein are merely embodiments of the present disclosure.

[0037] For the sake of brevity, a detailed description of techniques for signal processing, data fusion, signaling, control, and other functional aspects of the systems (and the individual operating components of the systems) is omitted. Furthermore, the connecting lines depicted in the various figures included herein are intended to represent exemplary functional relationships and / or physical connections 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.

[0038] This description is merely illustrative and is not intended to limit the disclosure, its application, or uses in any way. The broad teachings of the disclosure may be embodied in a variety of forms. Therefore, while this disclosure includes specific examples, the true scope of the disclosure should not be limited thereto, since other modifications will become apparent upon study of the drawings, the patent specification, and the following claims. legend

[0039] In the drawings, N stands for No and Y stands for Yes.

Claims

[1] A method for controlling a vehicle, comprising: Detecting that an object is located along a path of the vehicle and within a predetermined distance from the vehicle; in response to detecting the object located along the path of the vehicle and within the predetermined distance from the vehicle, determining a coefficient of friction between a road and a tire of the vehicle in real time; and in response to determining the coefficient of friction between the road and the vehicle's tire, command the vehicle to perform a control action. [2] The method of claim 1, wherein determining a coefficient of friction between a road and a tire of the vehicle in real time comprises: Applying a braking load to a wheel of the vehicle; Monitoring a movement of the vehicle at the same time as the braking load is applied to the wheel of the vehicle; and Determine the coefficient of friction between the road and the vehicle's tire based on the vehicle's movement during braking in real time. [3] The method of claim 2, further comprising: Comparing the coefficient of friction between the road and the tire of the vehicle with a predetermined friction threshold to determine whether the comparison of the coefficient of friction between the road and the tire of the vehicle is less than the predetermined friction threshold; and wherein the control action is the continuous application of the braking load to the wheel of the vehicle in response to determining that the coefficient of friction between the road and the tire of the vehicle is less than the predetermined friction threshold. [4] The method of claim 2, further comprising: Comparing the coefficient of friction between the road and the tire of the vehicle with a predetermined friction threshold to determine whether the coefficient of friction between the road and the tire of the vehicle is equal to or greater than the predetermined friction threshold; and wherein the control action is to steer the vehicle to avoid the object located along the path of the vehicle in response to determining that the coefficient of friction between the road and the tire of the vehicle is equal to or greater than the predetermined friction threshold. [5] The method of claim 4, further comprising: Determining a steering path to avoid the object located along the path of the vehicle in response to determining that the coefficient of friction between the road and the tire of the vehicle is equal to or greater than the predetermined friction threshold, wherein the steering path has a radius of curvature; and wherein determining the steering path to avoid the object located along the path of the vehicle comprises determining a radius of curvature of the steering path; and where the radius of curvature of the steering path is based on the coefficient of friction between the tire and the road. [6] The method of claim 2, further comprising: Determining a time to collision with the object located along the path of the vehicle and within the predetermined distance from the vehicle; Determining a time to determine friction; Determining a last time to steer the vehicle to avoid the object located along the path of the vehicle; Determining a sum of the time to determine the friction and the last time to steer the vehicle to avoid the object located along the path of the vehicle; and Comparing the time to collision with the object located along the path of the vehicle with the sum of the last time to determine friction and the last time to steer the vehicle to avoid the object located along the path of the vehicle to determine if the time to collision with the object located along the path of the vehicle is less than the sum of the last time to determine friction and the last time to steer the vehicle to avoid the object located along the path of the vehicle. [7] The method of claim 6, further comprising: in response to determining that the time to impact the object along the path of the vehicle is greater than the sum of the time to determine friction and the last time to steer the vehicle to avoid the object along the path of the vehicle, determining the last time to brake to avoid the object along the path of the vehicle; in response to determining that the time to impact the object along the path of the vehicle is less than the sum of the time to determine friction and the last time to steer the vehicle to avoid the object along the path of the vehicle, determining a sum of the last time to brake to avoid the object along the path of the vehicle and the time to determine friction; and in response to determining that the time to collision with the object located along the path of the vehicle is less than the sum of the last time to determine friction and the last time to steer the vehicle to avoid the object located along the path of the vehicle, comparing the time to collision with the object located along the path of the vehicle to the sum of the last time to brake to avoid the object located along the path of the vehicle and the time to determine friction, determining if the time to collision is less than the sum of the last time to brake to avoid the object located along the path of the vehicle and the time to determine friction. [8] The method of claim 7, wherein the coefficient of friction between the road and the tire of the vehicle is determined solely in response to: (a) detecting the object located along the path of the vehicle and within the predetermined distance from the vehicle; and (b) determining that the time to collision is less than the sum of the last time to brake or less than the last time to steer to avoid the object located along the path of the vehicle and the time to determine the friction. [9] The method of claim 8, further comprising: Comparing the coefficient of friction between the road and the tire of the vehicle with a predetermined friction threshold to determine whether the coefficient of friction between the road and the tire of the vehicle is equal to or greater than the predetermined friction threshold; and wherein the control action is to steer the vehicle to avoid the object located along the path of the vehicle in response to determining that the coefficient of friction between the road and the tire of the vehicle is equal to or greater than the predetermined friction threshold; in response to determining that the coefficient of friction between the road and the tire of the vehicle is equal to or greater than the predetermined friction threshold, determining an updated last time to steer to avoid the object located along the path of the vehicle based on the coefficient of friction between the road and the tire of the vehicle; and Comparing the time to collision with the object along the path of the vehicle with the updated last time to steer to avoid the object located along the path of the vehicle to determine if the time to collision with the object along the path of the vehicle is greater than the updated last time to steer to avoid the object located along the path of the vehicle. [10] The method of claim 9, wherein insufficient road friction is used as a condition to prevent evasive steering assistance from commencing after a vehicle operator begins to steer.

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