System and method for downhill tracking operation control for speed control

Abstract

A cruise control method includes determining that a host vehicle is traveling downhill and determining an axle torque command to maintain a predetermined separation distance from the host vehicle to a leader vehicle while the host vehicle is traveling downhill. The method further includes determining that a brake of the host vehicle is applied to provide the previously determined axle torque command and comparing the axle torque command to a brake termination threshold to determine whether the axle torque command is greater than the brake termination threshold. The method further includes comparing the following separation distance between the host vehicle and the leader vehicle to a follow-exit threshold to determine whether the following separation distance between the host vehicle and the leader vehicle is greater than the follow-exit threshold.The method also includes commanding the release of the brake of the host vehicle to terminate braking.

Description

INTRODUCTION

[0001] The present disclosure relates to adaptive cruise control. Specifically, the present disclosure describes a system and method for downhill tracking operation control using cruise control.

[0002] This introduction sets forth the general content of the disclosure. Both the work of the presently named inventors, to the extent described in this introduction, and those aspects of the description that do not otherwise qualify as prior art at the time of filing are not expressly or implicitly admitted as prior art against this disclosure. When a host vehicle travels downhill, it is difficult to maintain a following distance between the host vehicle and a lead vehicle due to the use of two actuators (i.e., the propulsion and braking systems) and the gravitational forces due to the roadway gradient. Since two actuators are involved during the downhill movement of the host vehicle, two actuation control instructions are necessary to maintain the following distance between the host vehicle and the lead vehicle.When this following distance is maintained, gravitational forces cause the host vehicle 10 to accelerate toward the lead vehicle. If the roadway is sufficiently steep and sufficiently long, braking may be necessary to maintain the following distance between the host vehicle and the lead vehicle. Once the desired following distance is reached, the braking command is terminated, and the host vehicle accelerates again toward the lead vehicle. However, this braking and propulsion cycle causes, among other things, driver discomfort and oscillating control of the following distance. It is therefore desirable to develop a method and system for maintaining the following distance from the host vehicle 10 to the lead vehicle such that the oscillatory nature of the braking and propulsion cycles is avoided. SUMMARY

[0003] The present disclosure describes a cruise control method. The cruise control method also includes determining that a host vehicle is traveling downhill and determining the command of an axle torque to maintain a predetermined following distance from the host vehicle to a lead vehicle while the host vehicle is traveling downhill along a roadway. The lead vehicle is located immediately ahead of the host vehicle. The axle torque command is a function of a roadway gradient of the roadway. The roadway has a roadway surface. The roadway gradient is the angle of the roadway surface to a virtual horizontal line.The method further includes determining that a brake of the host vehicle is being applied to provide the previously determined axle torque command, and comparing the axle torque command to a braking cessation threshold to determine whether the axle torque command is greater than the braking cessation threshold. In response to determining that the axle torque command is greater than the braking cessation threshold, the method further includes comparing the following distance between the host vehicle and the leader vehicle to a follow-exit threshold to determine whether the following distance between the host vehicle and the leader vehicle is greater than the follow-exit threshold.The method also includes, in response to determining that the predetermined following distance between the host vehicle and the leader vehicle is greater than the threshold for exiting the following operation, commanding the release of the brake of the host vehicle to cease braking. Further embodiments of this aspect include corresponding computer systems, devices, and computer programs recorded in 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 maintaining a predetermined distance between a host vehicle and a leader vehicle when the host vehicle is traveling downhill and by resorting to cruise control, thereby minimizing the risk of the host vehicle coming into contact with the leader vehicle when traveling downhill.

[0004] According to some aspects of the present disclosure, the cruise control method may include determining a maximum axle torque command. The maximum torque command is a function of road grade. Further, in response to determining that the axle torque command is not greater than the brake cessation threshold, the method includes limiting the axle torque command to the maximum axle torque command. The speed delta is the difference between the speed of the lead vehicle and the speed of the host vehicle. The cruise control method may include comparing the speed delta to a lead speed threshold to determine whether the speed delta is greater than the lead speed threshold.The cruise control method may further comprise, in response to determining that the speed delta is greater than the lead speed threshold, determining that the deceleration stop threshold is equal to a difference between an initial deceleration stop threshold and a deceleration offset value. The cruise control method may comprise, in response to determining that the speed delta is greater than the lead speed threshold, determining that the follow mode exit threshold is equal to a difference between an initial follow mode exit threshold and a follow mode offset value.The cruise control method may include, in response to determining that the speed delta is not greater than the lead speed threshold, determining that the stop braking threshold is equal to an initial stop braking threshold. The cruise control method may include, in response to determining that the speed delta is not greater than the lead speed threshold, determining that the exit follow mode threshold is equal to an initial exit follow mode threshold. The axle torque command is a function of the predetermined following distance from the host vehicle to the lead vehicle. The vehicle is attached to a trailer. The axle torque command is determined using an equation: AxCommand=K1*HDerr+K2*ΔHDerr−mg*sin(θ) where: m is the mass of the vehicle plus the mass of the trailer; K1 is a first calibration factor; K2 is a second calibration factor; g is the gravitational constant; V is the speed of the host vehicle; HT is the tracking operating time selected by the driver; HD is the specified following distance (V*HT) from the host vehicle to the lead vehicle; L is the measured distance from the host vehicle to the lead vehicle; HD err the tracking operation error is HD - L; θ is the angle from the road surface to the virtual horizontal line; and ΔHD err is a first derivative of the tracking error with respect to time.

[0005] The present disclosure further describes a vehicle including sensors, a propulsion system, a braking system, and a controller. The controller is in communication with the sensors, the braking system, and the propulsion system and is programmed to perform the method described above.

[0006] The present disclosure also describes a tangible non-transitory machine-readable medium containing machine-readable instructions that, when executed by a processor, cause the processor to perform the method described above.

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

[0008] The above-described features and advantages and other features and advantages of the presently disclosed system and method will be apparent from the detailed description, including the claims and exemplary embodiments, when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present disclosure will be more fully understood from the detailed description and the accompanying drawings, in which: Fig. 1 is a schematic diagram of a host vehicle including a cruise control system; Fig. 2 is a schematic representation of a host vehicle attached to a trailer, the host vehicle traveling downhill and spaced from the lead vehicle, and the lead vehicle also traveling downhill; Fig. 3 is a flowchart of a speed control method for maintaining a following distance between a host vehicle and a lead vehicle while the host vehicle is traveling downhill; and Fig. 4 is a flowchart of a method for determining a threshold for stopping braking and a threshold for exiting tracking operation used in the method of Fig. 3 can be used. DETAILED DESCRIPTION

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

[0011] With reference to Fig. 1, a host vehicle 10 generally includes a body 12 and a plurality of wheels 14 coupled to the body 12. The host vehicle 10 may be an autonomous vehicle. In the illustrated embodiment, the host vehicle 10 is depicted as a sedan, however, it should be appreciated that other vehicles, including trucks, coupes, sport utility vehicles (SUVs), recreational vehicles (RVs), etc., may also be used.

[0012] The host vehicle 10 further includes one or more sensors 24 coupled to the body 12. The sensors 24 detect observable conditions of the external environment and / or the internal environment of the host vehicle 10.As non-limiting examples, the sensors 24 may include one or more cameras, one or more light detection and ranging sensors (LIDAR sensors), one or more radars, one or more Global Positioning System (GPS) transceivers, one or more tilt sensors, one or more inertial measurement units (IMUs), one or more accelerometers, one or more vehicle speed sensors, one or more wheel speed sensors, one or more yaw rate sensors, one or more gyroscopes, one or more proximity sensors, one or more cameras, one or more ultrasonic sensors, one or more thermal imaging sensors, and / or other sensors 24. Each sensor 24 is configured to generate a signal representative of the sensed observable conditions (e.g., sensor data) of the external environment and / or the internal environment of the host vehicle 10.

[0013] The host vehicle 10 includes a vehicle controller 34 in communication with the sensors 24. The vehicle controller 34 includes at least one vehicle processor 44 and a non-transitory computer-readable vehicle storage device or a non-transitory computer-readable vehicle storage medium 46. The vehicle processor 44 may be a custom-manufactured or off-the-shelf processor, a central processing unit (CPU), a graphics processing unit (GPU), an auxiliary processor among multiple processors associated with the vehicle controller 34, a semiconductor-based microprocessor (in the form of a microchip or a chipset), a macroprocessor, a combination thereof, or generally a device for executing instructions. The computer-readable vehicle storage device or the computer-readable vehicle storage medium 46 may, for example,Volatile and non-volatile memory can be included in read-only memory (ROM), random access memory (RAM), and maintainable memory (KAM). KAM is persistent or non-volatile memory that can be used to store various operating variables while the vehicle processor 44 is powered off. The vehicle computer-readable storage device or medium 46 can be implemented using a number of storage devices such as PROMs (programmable read-only memories), EPROMs (electrical PROMs), EEPROMs (electrically erasable PROMs), flash memory, or other electrical, magnetic, optical, or combination storage devices that can store data, some of which represents executable instructions used by the vehicle controller 34 in controlling the host vehicle 10. The vehicle controller 34 of the host vehicle 10 can be programmed to implement the method 100 (. Fig. 3) and procedure 200 ( Fig. 4) as described in detail below.

[0014] The instructions may include one or more separate programs, each comprising an ordered list of executable instructions for implementing logical functions. When executed by the vehicle processor 44, the instructions receive and process signals from sensors, perform logic, calculations, methods, and / or algorithms to automatically control the components of the host vehicle 10, and generate control signals to automatically control the components of the host vehicle 10 based on the logic, calculations, methods, and / or algorithms. Although in Fig. 1, embodiments of the host vehicle 10 may include multiple vehicle controllers 34 that communicate via a suitable communication medium or combination of communication media and that cooperate to process the sensor signals, perform logic, calculations, methods, and / or algorithms, and generate control signals to automatically control features of the host vehicle 10. The vehicle controller 34 is part of a system 21 for downhill tracking operation control using full-range adaptive cruise control.

[0015] The host vehicle 10 includes a propulsion system 26 for propelling the host vehicle 10. The propulsion system 26 is coupled to one or more wheels 14 and may include an internal combustion engine 28 and / or an electric motor 30. The propulsion system 26 is in communication with the vehicle controller 34. Accordingly, the vehicle controller 34 may receive information from the propulsion system 26. Furthermore, the vehicle controller 34 may send instructions to the propulsion system 26.

[0016] Additionally, the host vehicle 10 includes a braking system 32 for decelerating the host vehicle 10. The braking system 32 is coupled to one or more wheels 14 and includes one or more brakes 36. The braking system 32 is in communication with the vehicle controller 34. Accordingly, the vehicle controller 34 can receive information from the braking system 32. Furthermore, the vehicle controller 34 can send instructions to the braking system 32.

[0017] If the host vehicle 10, as in Fig. 2, it is desirable to maintain a predetermined following distance 38 (e.g., three meters) from the lead vehicle 40. The lead vehicle 40 is directly and immediately in front of the host vehicle 10, and thus, no other vehicle is between the host vehicle 10 and the lead vehicle 40. A trailer 42 may be attached to the host vehicle 10 while the host vehicle 10 is traveling downhill. In this case, the host vehicle 10 is traveling along a roadway 48 having a road surface 50. The roadway gradient of the roadway 48 is defined as the angle θ from the road surface 58 to a virtual horizontal line 52.

[0018] Fig. 3 shows a method 100 for maintaining the predetermined following distance 38 between the host vehicle 10 and the lead vehicle 40 while the host vehicle 10 is traveling downhill. The method 100 begins at block 102. At block 102, the vehicle controller 34 determines whether the host vehicle 10 is traveling downhill. To do so, the vehicle controller 34 may receive road grade data from the sensors 24 (e.g., one or more tilt sensors) and / or GPS data from the GPS transceivers. The vehicle controller 34 then uses the road grade data to determine that the host vehicle 10 is traveling downhill. The road grade data may include the road grade (i.e., the angle θ from the road surface 58 to a virtual horizontal line 52) of the roadway 48.Additionally, the vehicle controller 34 determines the axle torque command to maintain the predetermined following distance 38 from the host vehicle 10 to the lead vehicle 40 while the host vehicle 10 travels downhill along the roadway 48. As explained, the lead vehicle 40 is immediately in front of the host vehicle 10. The axle torque command is a function of a roadway gradient of the roadway 48. As explained above, the roadway gradient is defined as the angle θ from the road surface 58 to a virtual horizontal line 52. The axle torque command may be a braking command. During a braking command, the vehicle controller 34 commands the braking system 32 to apply the brakes 36 to decelerate the host vehicle 10. The vehicle controller 34 may use the following equation to determine the axle torque command: . AxCommand=K1*HDerr+K2*ΔHDerr−mg*sin(θ) where: m is the mass of the host vehicle 10 plus the mass of the trailer 42; K1 is a first calibration factor; K2 is a second calibration factor; g is the gravitational constant; V is the speed of the host vehicle; HT is the tracking operating time selected by the driver; HD is the specified following distance (V*HT) 38 from the host vehicle to the lead vehicle; L is the measured distance from the host vehicle to the lead vehicle; HD err the tracking operation error is HD - L; θ is the angle from the road surface 50 to the virtual horizontal line 52; and ΔHD err is a first derivative of the tracking operation error 38 with respect to time.

[0019] The method 100 then proceeds to block 104. In block 104, the vehicle controller 34 determines whether to apply one or more brakes 36 of the host vehicle's braking system 32 to provide the previously determined axle torque command to maintain the predetermined following distance 38 from the host vehicle 10 to the lead vehicle 40.

[0020] If one or more brakes 36 are not applied, the method 100 continues to block 104. In block 104, the vehicle controller 34 sets the brake application flag to false. The method 100 then continues to block 106. In block 106, the method 100 restarts. If the one or more brakes 36 are applied, the method 100 continues to block 108.

[0021] In block 108, the vehicle controller 34 determines the maximum axle torque command. The maximum axle torque command is the maximum allowable braking command relative to acceleration and is a function of the road gradient. The maximum axle torque command can be determined using a lookup table. This lookup table can be developed through testing of the host vehicle 10 and includes the road gradient and acceleration as inputs and the maximum axle torque command as the output. Alternatively, the vehicle controller 34 can use the following equation to determine the maximum axle torque command: AxCommandMax=max(0,g*sin(θ)) where: AxCommandMax is the maximum axle torque command; g is the gravitational constant; and θ is the angle from the road surface 50 to the virtual horizontal line 52, and where θ is defined as a positive value when driving downhill and as a negative value when driving uphill and g*sin(θ) is a positive value.

[0022] The method 100 then proceeds to block 110. In block 110, the vehicle controller 34 determines a threshold for stopping braking, which is Fig. 4. The method 100 then continues with block 112. In block 112, the vehicle controller 34 determines the threshold for exiting the tracking mode, which is Fig. 4. Method 100 then proceeds to block 114.

[0023] In block 114, the controller 34 compares the maximum axle torque command to the stop braking threshold to determine if the axle torque command is greater than the stop braking threshold. If the axle torque command is greater than the stop braking threshold, the method 100 proceeds to block 116. In block 116, the vehicle controller 34 compares the current following distance from the host vehicle 10 to the leader vehicle 40 to a follow-exit threshold to determine if the current following distance from the host vehicle 10 to the leader vehicle 40 is greater than the follow-exit threshold. If the current following distance from the host vehicle 10 to the leader vehicle 40 is greater than the follow-exit threshold, the method 100 proceeds to block 104.In block 104, the vehicle controller 34 commands the braking system 32 (and thus one or more brakes 36) of the host vehicle 10 to release brakes to terminate braking. If the current following distance from the host vehicle 10 to the lead vehicle 40 is not greater than the threshold to exit tracking mode, the method 100 proceeds to block 118. In block 118, the vehicle controller 34 limits the axle torque command to the maximum axle torque command. Therefore, braking is not terminated in block 118 but is limited to the maximum axle torque command. After block 118, the method 100 proceeds to block 106.

[0024] Fig. 4 shows a flowchart of a method 200 for determining a threshold for stopping braking and a threshold for exiting tracking operation, which are used in the method 100 of Fig.3 may be used. The method 200 begins in block 202. The method 200 then proceeds to block 204. In block 104, the vehicle controller 34 determines an initial braking termination threshold. The initial braking termination threshold is determined using a lookup table developed through testing of the host vehicle 10. The input to the lookup table is the roadway grade of the roadway 48. Therefore, the initial braking termination threshold is a function of the roadway grade. The method 200 then proceeds to block 206.

[0025] In block 206, the vehicle controller 34 determines a deceleration offset value. As explained below, the deceleration offset value is used when the speed of the lead vehicle 40 is greater than the speed of the host vehicle and the lead vehicle 40 is therefore moving away from the host vehicle 10. The deceleration offset value is determined using a lookup table developed through testing of the host vehicle 10. The input to this lookup table is the roadway grade of the roadway 48. Therefore, the deceleration offset value is a function of the roadway grade. Method 300 then proceeds to block 208.

[0026] In block 208, the vehicle controller 34 determines an initial threshold for exiting tracking mode. The initial threshold for exiting tracking mode is determined using a lookup table developed through testing of the host vehicle 10. The input to the lookup table is the roadway grade of roadway 48. Therefore, the initial threshold for exiting tracking mode is a function of the roadway grade. Method 200 then proceeds to block 210.

[0027] In block 210, the vehicle controller 34 determines a tracking offset value. The tracking offset value is determined using a lookup table developed through testing of the host vehicle 10. The input to this lookup table is the roadway gradient of roadway 48. Therefore, the tracking offset value is a function of the roadway gradient. Method 300 then proceeds to block 212.

[0028] In block 212, the vehicle controller 34 determines a speed delta. The speed delta is the difference between the speed of the lead vehicle 40 and the speed of the host vehicle 10. The vehicle controller 34 then compares the speed delta to a lead speed threshold to determine if the speed delta is greater than the lead speed threshold. If the speed delta is greater than the lead speed threshold, the method 200 proceeds to block 214. If the speed delta is not greater than the lead speed threshold, the method 200 proceeds to block 218.

[0029] At block 214, in response to determining that the speed delta is greater than the guidance speed threshold, the vehicle controller 34 sets the braking termination threshold equal to a difference between the initial braking termination threshold and the deceleration offset value. Method 200 then proceeds to block 216.

[0030] At block 216, in response to determining that the speed delta is greater than the guidance speed threshold, the vehicle controller 34 sets the tracking exit threshold equal to a difference between an initial tracking exit threshold and a tracking offset value. Method 200 then proceeds to block 222. At block 222, method 200 ends.

[0031] In block 218, the vehicle controller 34 sets the braking termination threshold equal to the braking termination initial threshold. The method 200 then proceeds to block 220. In block 220, the vehicle controller 34 sets the tracking exit initial threshold equal to the tracking exit initial threshold. The method 200 then proceeds to block 222. The method 200 ends in block 22w.

[0032] While exemplary embodiments are described above, these embodiments are not intended to describe all possible forms encompassed by the claims. The words used in the application text are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments may be combined to form further embodiments of the presently disclosed system and method, which need not be expressly described or illustrated.While various embodiments may have been described as providing advantages or being preferred over other prior art embodiments or implementations with respect to one or more desired characteristics, those skilled in the art will recognize that one or more features or characteristics may be compromised to achieve desired overall system characteristics depending on the specific application and implementation. These features may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, usability, weight, manufacturability, ease of assembly, etc.Therefore, embodiments that are described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for certain applications.

[0033] The drawings are presented in simplified form and are not exactly to scale. For convenience and clarity only, directional terms such as top, bottom, left, right, upward, over, above, below, beneath, back, and front may be used with reference to the drawings. These and similar directional terms should not be construed as limiting the scope of the disclosure in any way.

[0034] Embodiments of the present disclosure are described herein. However, it should be understood that the disclosed embodiments are merely examples, and further embodiments may take various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the presently disclosed system and method.As will be understood by those skilled in the art, various features illustrated and described with reference to any of the figures may be combined with features illustrated in one or more other figures to produce embodiments not explicitly illustrated or described. The combinations of illustrated features provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desirable for particular applications or implementations.

[0035] Here, embodiments of the present disclosure may be described in terms of functional and / or logical block components and various processing steps. It should be appreciated that such block components may be implemented by multiple hardware, software, and / or firmware components configured to perform the specified functions. For example, an embodiment of the present disclosure may employ various integrated circuit components, e.g., memory elements, digital signal processing elements, logic elements, lookup tables, or the like, capable of performing a variety of functions under the control of one or more microprocessors or other control devices.In addition, those skilled in the art will understand that embodiments of the present disclosure may be practiced in connection with multiple systems and that the systems described herein are merely exemplary embodiments of the present disclosure.

[0036] For brevity, techniques related to signal processing, data fusion, signaling, control, and other functional aspects of the systems (and the individual operational components of the systems) need not be described in detail here. Furthermore, the interconnections shown in the various figures included herein are intended to represent examples of functional relationships and / or physical couplings between the various elements. It should be noted that alternative or additional functional relationships or physical connections may be present in an embodiment of the present disclosure.

[0037] This description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure may be implemented in various forms. Therefore, while this disclosure contains specific examples, the true scope of the disclosure should not be so limited, since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. legend

[0038] In the drawings, N stands for No and Y stands for Yes.

Claims

[1] Cruise control procedure which includes: Determining that a host vehicle is traveling downhill; Determining an axle torque command to maintain a predetermined following distance from the host vehicle to a lead vehicle while the host vehicle is traveling downhill along a roadway, the lead vehicle being immediately in front of the host vehicle, the axle torque command being a function of a roadway gradient, the roadway having a roadway surface, and the roadway gradient being an angle from the roadway surface to a virtual horizontal line; Determining that a brake of the host vehicle is applied to provide the previously determined axle torque command; Comparing the axle torque command to a braking termination threshold to determine whether the axle torque command is greater than the braking termination threshold; Comparing, in response to determining that the axle torque command is greater than the braking stop threshold, a current following distance between the host vehicle and the lead vehicle with a follow-exit threshold to determine whether the current following distance between the host vehicle and the lead vehicle is greater than the follow-exit threshold; and Commanding the release of the brake of the host vehicle in response to determining that the predetermined following distance between the host vehicle and the lead vehicle is greater than the exit follow threshold to terminate braking. [2] A speed control method according to claim 1, further comprising: Determining a maximum axle torque command, wherein the maximum axle torque command is a function of the road gradient; and In response to determining that the axle torque command is not greater than the brake cessation threshold, limiting the axle torque command to the maximum axle torque command. [3] A speed control method according to claim 2, further comprising: Determining a speed of the host vehicle; Determining a speed of the lead vehicle; and Determining a speed delta, where the speed delta is a difference between the speed of the lead vehicle and the speed of the host vehicle. [4] A speed control method according to claim 3, further comprising: Comparing the speed delta to a leading speed threshold to determine if the speed delta is greater than the leading speed threshold. [5] A speed control method according to claim 4, further comprising: In response to determining that the speed delta is greater than the master speed threshold, setting the braking cessation threshold to a difference between an initial braking cessation threshold and a deceleration offset value. [6] A speed control method according to claim 5, further comprising: Setting the tracking exit threshold, in response to determining that the speed delta is greater than the lead speed threshold, to a difference between an initial tracking exit threshold and a tracking offset value. [7] A speed control method according to claim 4, further comprising: In response to determining that the speed delta is not greater than the guide speed threshold, determining that the braking cessation threshold is equal to an initial braking cessation threshold. [8] A speed control method according to claim 7, further comprising: In response to determining that the speed delta is not greater than the initial tracking exit threshold, determining that the tracking exit threshold is equal to an initial tracking exit threshold. [9] The cruise control method of claim 1, wherein the axle torque command is a function of the predetermined following distance from the host vehicle to the lead vehicle. [10] The cruise control method of claim 1, wherein the host vehicle is attached to a trailer and the axle torque command is determined using an equation: AxCommand=K1*HDerr+K2*ΔHDerr−mg*sin(θ) where: m is the mass of the vehicle plus the mass of the trailer; K1 is a first calibration factor; K2 is a second calibration factor; g is the gravitational constant; V is a speed of the host vehicle; HT is a tracking operating time selected by the driver; HD is a predetermined following distance (V*HT) from the host vehicle to the lead vehicle; L is a measured distance from the host vehicle to the lead vehicle; HD err a tracking operation error HD - L is; θ is an angle from the road surface to the virtual horizontal line; and ΔHDerr is a first derivative of the tracking error with respect to time.

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