Offset compensation for steering input device for trailer reversing assist

Abstract

Trailer reversing assistance system for a vehicle (14) reversing a trailer (12), comprising: a knob (30) which can be turned to positions which each output a desired curvature (ĸ2) of a reversing path (26) of the trailer (12); and a control that determines an offset from the desired curvature (ĸ2) when the knob (30) is in a neutral position, and that generates a steering command for the vehicle (14) to guide the trailer (12) with the desired curvature (ĸ2) of the reversing path (26) taking the offset into account, a torque sensor (70) coupled to the knob (30), wherein the controller determines that the knob (30) is in the center position to determine the offset when the torque sensor (70) is essentially not sensing any external torque at the knob (30) and a measure of the rotation of the knob (30) is essentially zero, wherein the measure of the rotation of the knob (30) is essentially zero when the knob (30) is stationary.

Description

FIELD OF THE INVENTION

[0001] The present disclosure relates generally to driver assistance and active safety technologies in vehicles, and more particularly to a trailer reversing assistance system configured with a steering input device. DE 10 2012 205 416 A1 discloses a trailer path curvature control for a trailer reversing aid. BACKGROUND OF THE INVENTION

[0002] Backing up a vehicle while towing a trailer can be challenging for many drivers, especially those who travel with a trailer or with different types of trailers at irregular intervals. One reason for such difficulty may be that backing up a vehicle with a trailer attached requires steering inputs that are opposite to those required when reversing without a trailer attached to the vehicle. Another reason for such difficulty may be that minor errors in steering are amplified while backing up a vehicle with a trailer attached, which can cause the trailer to quickly deviate from a desired path.Yet another reason why reversing a trailer can prove difficult is the need to control the vehicle in a manner that limits the potential for a skid condition to occur. These difficulties can also arise, and are magnified in some operations, when attempting to quickly achieve a tight turning radius or when switching between different trailers that exhibit a wide variance in their response to similar steering inputs, such as a relatively short trailer being able to respond more quickly to a steering change than a longer trailer. The above-mentioned problem is solved by a trailer reversing assistance system having the features of claim 1 and claim 5, respectively, and by a method for autonomously steering a vehicle reversing a trailer having the features of claim 10.Advantageous further training results from the subclaims. BRIEF DESCRIPTION OF THE INVENTION

[0003] According to one aspect of the present invention, a trailer backup assist system for a vehicle backing up a trailer includes a rotatable knob that can be rotated to positions that each output a desired curvature. The trailer backup assist system also includes a controller that determines an offset from the desired curvature when the knob is stationary in a center position. The controller generates a steering command for the vehicle to guide the trailer along the desired curvature, taking the offset into account.

[0004] According to another aspect of the present invention, a trailer backup assist system for a vehicle backing up a trailer includes a steering input movable between positions that each output a desired curvature for the trailer. The trailer backup assist system also includes a controller having a compensation module and a steering module. The compensation module determines an offset between zero and the desired curvature when the steering input is stationary in a center position. The steering module generates a steering command for the vehicle to guide the trailer along the desired curvature less the offset.

[0005] According to yet another aspect of the present invention, a method for autonomously steering a vehicle backing up a trailer includes providing a knob rotatable in opposite directions from a center position to multiple positions, each defining a desired curve. The method also includes a step of determining an offset of the desired curve when the knob is stationary in the center position. The method further includes a step of generating a steering command for the vehicle to guide the trailer along the desired curve, taking the offset into account.

[0006] These and other aspects, objects and features of the present invention will be understood and appreciated by those skilled in the art upon a closer examination of the following description, claims and appended drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The following applies to the drawings: Fig. 1 is a top perspective view of a vehicle attached to a trailer with one embodiment of a hitch angle sensor for operating a trailer reverse assist system; Fig. 2 is a block diagram illustrating an embodiment of the trailer backup assist system with a steering input device, a curvature control, and a trailer braking system; Fig. 3 is a schematic diagram illustrating the geometry of a vehicle and a trailer with an overlaid two-dimensional xy coordinate system identifying variables used to determine a kinematic relationship between the vehicle and the trailer for the trailer backup assist system according to one embodiment; Fig. 4 is a schematic block diagram illustrating portions of a curvature control according to an additional embodiment and other components of the trailer backup assist system according to such embodiment; Fig. 5 is a schematic block diagram of the curvature control of Fig. 4, which shows the feedback architecture and signal flow of the curvature control according to such an embodiment; Fig. 6 is a schematic diagram showing a relationship between a coupling angle and a steering angle of the vehicle as it relates to the curvature of the trailer and a breakaway angle; Fig. 7 is a plan view of a steering input device with a rotatable knob for operating the trailer backup assist system according to one embodiment; Fig. 8 is a plan view of another embodiment of a rotatable knob for selecting a desired trailer curvature and a corresponding schematic diagram illustrating a vehicle and trailer with various trailer curvatures correlating with desired curvatures that can be selected; Fig. 9 is a flowchart illustrating a method of operating a trailer backup assist system using an operating routine for autonomously steering a vehicle backing up a trailer, according to one embodiment; Fig. 10 is a flowchart illustrating a method of operating a trailer backup assist system using a steering input offset routine according to one embodiment. Fig. Figure 11 is a schematic diagram of a rotatable knob showing changes in a rotated position of the rotatable knob and the corresponding changes in the desired curvature provided by the rotated position and the resulting offset. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] For the purposes of description herein, it is to be understood that the disclosed trailer backup assist system and related methods are capable of various alternative embodiments and orientations, unless expressly stated to the contrary. It is also to be understood that the specific devices and methods illustrated in the accompanying drawings and described in the following description are simply embodiments of the inventive concepts defined in the appended claims. Although various aspects of the trailer backup assist system and related methods are described with reference to a particular illustrative embodiment, the disclosed invention is not limited to such embodiments, and additional modifications, applications, and embodiments may be practiced without departing from the disclosed invention.Therefore, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered limiting unless expressly stated to the contrary in the claims.

[0009] With reference to the Fig. 1-11: Reference numeral 10 generally designates a trailer backup assist system for controlling a reversing path of a trailer 12 attached to a vehicle 14 by allowing a driver of the vehicle 14 to specify a desired curvature 26 of the reversing path of the trailer 12. In one embodiment, the trailer backup assist system 10 automatically steers the vehicle 14 to guide the trailer 12 along the desired curvature 26 when a driver uses the accelerator and brake pedals to control the speed of reversing the vehicle 14. To monitor the position of the trailer 12 relative to the vehicle 14, the trailer backup assist system 10 may include a sensor system 16 that senses a hitch angle γ between the trailer 12 and the vehicle 14, which may be referred to as a hitch angle sensor 44.Additionally, the trailer backup assist system 10 may also include a steering input device 18, such as a rotatable knob 30, for a driver to provide the desired curvature 26 of the trailer 12. As such, the steering input device 18 may be movable between multiple positions, such as successive rotated positions of the knob 30, each providing a desired curvature 26 for the trailer 12. To provide accurate actuation of the steering input device 18, a controller 28 of the trailer backup assist system 10 may determine an offset from the desired curvature when the steering input device 18 is stationary in a center position. Once the desired curvature 26 is input, a controller may then generate a steering command for the vehicle 14 that takes the offset into account to guide the trailer 12 along the desired curvature 26.

[0010] With reference to the Fig. 1: The vehicle 14 is a pickup truck embodiment equipped with an embodiment of the trailer backup assist system 10 for controlling the reverse path of the trailer 12 mounted to the vehicle 14. In particular, the vehicle 14 is rotatably mounted to an embodiment of the trailer 12 having a box body 32 with an enclosed cargo area 34, a single axle with a right wheel assembly and a left wheel assembly, and a tongue 36 extending longitudinally forward from the enclosed cargo area 34. The illustrated trailer 12 also includes a trailer hitch connector in the form of a hitch assembly 38 connected to a vehicle hitch connector in the form of a hitch ball 40.The coupling assembly 38 engages the coupling ball 40 to provide a pivoting ball-and-socket connection 42 that accommodates the articulation of the coupling angle γ. It is understood that additional embodiments of the trailer 12 may alternatively be coupled to the vehicle 14 to provide a pivoting connection, such as by connecting it to a fifth wheel. It is also contemplated that additional embodiments of the trailer may include more than one axle and may have various shapes and sizes designed for different loads and objects, such as a boat trailer or a flatbed trailer.

[0011] Further referring to Fig. 1: The sensor system 16, in the illustrated embodiment, includes an optically based hitch angle sensor 44 for sensing the hitch angle γ between the vehicle 14 and the trailer 12. The illustrated hitch angle sensor 44 utilizes a camera 46 (e.g., an imaging video camera) that may be positioned near an upper portion of the vehicle tailgate 48 at the rear of the vehicle 14, as shown, such that the camera 46 may be at the top relative to the tongue 36 of the trailer 12. The illustrated camera 46 has an imaging field with the field of view 50 positioned and oriented to capture one or more images of the trailer 12, including an area encompassing one or more desired target placement zones for at least one target 52 to be secured.Although it is contemplated that camera 46 may capture images of trailer 12 without a target 52 to determine the hitch angle γ, in the illustrated embodiment, trailer backup assist system 10 includes a target 52 placed on trailer 12 to enable trailer backup assist system 10 to utilize information acquired via image capture and processing of target 52. For example, illustrated camera 46 may include an imaging video camera that repeatedly captures successive images of trailer 12, which may be processed to identify target 52 and its position on trailer 12 to determine the movement of target 52 and trailer 12 relative to vehicle 14 and the corresponding hitch angle γ.

[0012] With reference to the Fig. 2: The hitch angle sensor 44 provides the sensed hitch angle γ to the trailer back-up assist system 10. Likewise, the illustrated embodiment of the trailer back-up assist system 10 receives information related to the vehicle condition from additional sensors and devices. This information includes position information from a positioning device 56, which may include a global positioning system (GPS) on the vehicle 14 or a handheld device, to determine a coordinate position of the vehicle 14 and the trailer 12 based on the position of the positioning device 56 relative to the trailer 12 and / or the vehicle 14 and the sensed hitch angle γ.Other vehicle information received by the trailer backup assist system 10 may include a speed of the vehicle 14 from a speed sensor 58 and a yaw angle of the vehicle 14 from a yaw angle sensor 60.

[0013] As continued in Fig. 2, an embodiment of the trailer reversing assist system 10 is connected to a power steering system 62 of the vehicle 14 to control the steered wheels 64 ( Fig. 1) of the vehicle 14 to move the vehicle 14 in such a manner that the trailer 12 responds in accordance with the desired curvature 26 of the trailer 12. In the illustrated embodiment, the power steering system 62 is an electric power-assisted steering (EPAS) system that includes an electric steering motor 66 for turning the steered wheels 64 to a steering angle based on a steering command, wherein the steering angle may be sensed by a steering angle sensor 67 of the power steering system 62. The steering command may be provided by the trailer reverse assist system 10 for autonomous steering during a reversing maneuver and may alternatively be manually provided via a rotational position (e.g., the steering wheel angle) of a steering wheel 68 ( Fig. 1). However, in the illustrated embodiment, the steering wheel 68 of the vehicle 14 is mechanically coupled to the steered wheels 64 of the vehicle 14 such that the steering wheel 68 moves in concert with the steered wheels 64, thereby preventing manual intervention via the steering wheel 68 during autonomous steering. More specifically, a torque sensor 70 is provided on the power steering system 62 that senses torque at the steering wheel 68 that is not expected by the autonomous control of the steering wheel 68 and thus indicates manual intervention, whereby the trailer backup assist system 10 can alert the driver to discontinue manual intervention via the steering wheel 68 and / or autonomous steering.

[0014] In alternative embodiments, some vehicles include a power steering system 62 that allows a steering wheel 68 to be partially decoupled from the movement of the steered wheels 64 of such a vehicle. Accordingly, the steering wheel 68 can be rotated independently of the manner in which the vehicle's power steering system 62 controls the steered wheels 64 (e.g., autonomous steering as commanded by the trailer backup assist system 10). Therefore, in those types of vehicles where the steering wheel 68 can be selectively decoupled from the steered wheels 64 to enable their independent operation, the steering wheel 68 can be used as a steering input device 18 for the trailer backup assist system 10, as disclosed in more detail herein.

[0015] With further reference to the Fig. 2: The power steering system 62 provides information regarding a rotational position of the steered wheels 64 of the vehicle 14, including a steering angle, to the curvature control 28 of the trailer backup assist system 10. The curvature control 28 in the illustrated embodiment processes the current steering angle in addition to other conditions of the vehicle 14 and trailer 12 to guide the trailer 12 along the desired curvature 26. As also shown in Fig. 2, the vehicle's braking control system 72 may also communicate with the curvature controller 28 to provide braking information, such as wheel speed, to the trailer backup assist system 10 and to receive braking commands from the curvature controller 28.

[0016] With continued reference to Fig. 2: The trailer backup assist system 10, in the illustrated embodiment, may be in communication with one or more devices, including a vehicle warning system 76, which may provide visual, audible, and tactile warnings. For example, vehicle brake lights 78 and vehicle hazard warning lights may provide a visual warning, and a vehicle horn 79 and / or speaker 81 may provide an audible warning. Additionally, the trailer backup assist system 10 and / or the vehicle warning system 76 may be in communication with a human-machine interface (HMI) 80 for the vehicle 14. The HMI 80 may include a vehicle display 82, such as a center console-mounted navigation or entertainment display ( Fig. 1).

[0017] As continued in Fig. 2, the trailer backup assist system 10 includes a steering input device 18 connected to the curvature controller 28 to enable the transfer of information between them. It is disclosed herein that the steering input device 18 may be coupled to the curvature controller 28 in a wired or wireless manner. The steering input device 18 provides the trailer backup assist system 10 with information defining the desired reverse path of the trailer 12 for the curvature controller 28 to process and generate steering commands. More specifically, the steering input device 18 may be movable to provide selection or attitude information correlated with the desired curvature 26 of the desired reverse path of the trailer 12.The trailer steering commands provided by the steering input device 18 may also include information related to a commanded change in the travel path, such as an incremental change in the desired curvature 26, and information related to an indication that the trailer 12 should travel along a path defined by a longitudinal centerline axis of the trailer 12, such as a desired curvature value of zero, which defines a substantially straight travel path for the trailer.

[0018] As will be discussed in more detail below, according to one embodiment, the steering input device 18 may include a movable control input device to enable a driver of the vehicle 14 to command desired trailer steering actions or otherwise select and change a desired curvature. For example, the movable control input device may be a rotatable knob 30 rotatable about a rotational axis passing through a top surface or face of the knob 30. In other embodiments, the rotatable knob 30 may be rotatable about a rotational axis substantially parallel to a top surface or face of the rotatable knob 30.Furthermore, according to additional embodiments, the steering input device 18 may include alternative means for providing a desired curvature 26 or other information defining a desired reverse travel path, such as a joystick, a keypad, a series of depressible buttons or switches, a slide input device, various user interfaces on a touchscreen, an optically based system for gesture sensing, a control interface for a portable device, and other conceivable input devices as generally understood by those of ordinary skill in the art. It is contemplated that the steering input device 18 may also function as an input device for other features, such as providing inputs for other vehicle features or systems.

[0019] Further referring to the Fig. 2: The curvature controller 28 is configured with a microprocessor 84 for processing logic and routines stored in memory 86 that receives information from the steering input device 18, the hitch angle sensor 44, the power steering system 62, the vehicle brake control system 72, the trailer brake system, the powertrain control system 74, and other vehicle sensors and devices. The curvature controller 28 can generate vehicle steering information and commands as a function of all or a portion of the received information. Thereafter, the vehicle steering information and commands can be provided to the power steering system 62 to influence the steering of the vehicle 14 to achieve a commanded travel path for the trailer 12. The curvature controller 28 can include the microprocessor 84 and / or other analog and / or digital circuitry for processing one or more routines.The curvature controller 28 may also include the memory 86 for storing one or more routines, including an operating routine 132, a steering input offset routine 130, and a curvature routine 98. It will be understood that the curvature controller 28 may be an independent, dedicated controller or a shared controller integrated with other control functions, such as the sensor system 16, the power steering system 62, and other conceivable onboard or offboard vehicle control systems.

[0020] With reference to Fig. 3: We now turn to a discussion of vehicle and trailer information and parameters used to calculate a kinematic relationship between a curvature of a travel path of the trailer 12 and the steering angle of the vehicle 14 pulling the trailer 12, which may be desirable for a trailer backup assist system 10 configured according to some embodiments, including for use by a curvature routine 98 of the curvature controller 28 in one embodiment. To achieve such a kinematic relationship, certain assumptions may be made regarding parameters associated with the vehicle / trailer system. Examples of such assumptions include, but are not limited to: the trailer 12 is being reversed by the vehicle 14 at a relatively low speed, the wheels of the vehicle 14 and the trailer 12 have a negligible (e.g.,no) slippage, the tires of the vehicle 14 exhibit negligible (e.g., no) lateral compliance, the tires of the vehicle 14 and the trailer 12 exhibit negligible (e.g., no) deformation, the actuator dynamics of the vehicle 14 are negligible, and the vehicle 14 and the trailer 12 exhibit negligible (e.g., no) roll or pitch, among other conceivable factors having the potential to have an effect on the steering of the trailer 12 with the vehicle 14.

[0021] As in Fig. As shown in Figure 3, the kinematic relationship for a system defined by a vehicle 14 and a trailer 12 is based on various parameters associated with the vehicle 14 and the trailer 12. These parameters include: δ: steering angle at the steered front wheels of the vehicle; α: yaw angle of the vehicle; β: yaw angle of the trailer; γ: coupling angle (γ = β-α); W: wheelbase of the vehicle; L: length between the coupling point and the rear axle of the vehicle; D: distance between the coupling point and the axle of the trailer or the effective axle in the case of a multi-axle trailer (axle length may be an equivalent); and r2: radius of curvature for the trailer.

[0022] One embodiment of a kinematic relationship between the radius of curvature r2 of the trailer path at the center of an axle of the trailer 12, the steering angle δ of the steered wheels 64 of the vehicle 14, and the hitch angle γ can be expressed in the equation provided below. If the hitch angle γ is provided, the curvature of the trailer path κ2 can be controlled as such based on controlling the steering angle δ (where β̇ is the trailer yaw angle and η̇ is the trailer speed). κ2=1r2=β˙η˙=(W+KV2g)sinγ+LcosγtanδD((W+KV2g))cosγ−Lsinγtanδ

[0023] This relationship can be expressed to provide the steering angle δ as a function of the curvature ĸ2 of the trailer path and the coupling angle γ. δ=tan−1((W+KV2g)[κ2Dcosγ−sinγ]DLκ2sinγ+Lcosγ)=F(γ,κ2,K)

[0024] Accordingly, for a particular vehicle and trailer combination, certain parameters (e.g., D, W, and L) of the kinematic relationship are constant and assumed to be known. V is the vehicle's longitudinal velocity, and g is the acceleration due to gravity. K is a speed-dependent parameter that, when set to zero, makes the calculation of the steering angle independent of vehicle speed. For example, vehicle-specific parameters of the kinematic relationship may be predefined in an electronic control system of the vehicle 14, and trailer-specific parameters of the kinematic relationship may be entered by a driver of the vehicle 14, determined from sensed trailer behavior in response to vehicle steering commands, or otherwise determined from signals provided by the trailer 12.The curvature ĸ2 of the trailer path can be determined from the driver input via the steering input device 18. By using the equation to provide the steering angle, the curvature routine 98 can generate a corresponding steering command to control the power steering system 62 of the vehicle 14.

[0025] In an additional embodiment, the curvature routine 98 may make an assumption that a longitudinal distance L between the pivot connection and the rear axle of the vehicle 14 is zero in order to operate the trailer backup assist system 10 when connecting a gooseneck trailer or other similar trailer with a hitch ball or with a fifth wheel positioned over a rear axle of the vehicle 14. This assumption essentially requires that the pivot connection to the trailer 12 be substantially vertically aligned with the rear axle of the vehicle 14. When such an assumption is made, the curvature controller 28 may generate the steering angle command for the vehicle 14 as a function that is independent of the longitudinal distance L between the pivot connection and the rear axle of the vehicle 14.It will be understood that the mentioned gooseneck trailer generally refers to the tongue configuration being raised to be attached to the vehicle 14 at an elevated position above the rear axle, such as in a carrier of a truck, and embodiments of the gooseneck trailer may include flatbeds, enclosed beds, caravans, livestock trailers, horse trailers, low loader trailers, and other conceivable trailers having such a tongue configuration.

[0026] Yet another embodiment of the curvature control 98 of the trailer reversing assistance system 10 is shown in Fig. 4 illustrates the general architectural layout, where a measurement module 88, a hitch angle controller 90, and a curvature controller 92 are routines that may be stored in the memory 86 of the curvature controller 28. In the illustrated layout, the steering input device 18 provides the curvature controller 92 of the curvature controller 28 with a desired value for the curvature ĸ2, which can be determined from the desired reverse travel path 26 input with the steering input device 18. The curvature controller 92 calculates a desired hitch angle y(d) based on the currently desired curvature ĸ2 along with the steering angle δ provided by a measurement module 88 in this embodiment of the curvature controller 28.The measurement module 88 may be a storage device separate from or integrated with the curvature controller 28 that stores data from sensors of the trailer backup assist system 10, such as the hitch angle sensor 44, the vehicle speed sensor 58, the steering angle sensor, or alternatively, the measurement module 88 may otherwise transfer data directly from the sensors without acting as a storage device. Once the desired hitch angle γ(d) has been calculated by the curvature controller 92, the hitch angle controller 90 generates a steering angle command based on the calculated desired hitch angle γ(d), as well as a measured hitch angle γ(m), and a current speed of the vehicle 14.The steering angle command is fed to the power steering system 62 of the vehicle 14, which is then fed back to the measurement module 88 to re-evaluate the influences of other vehicle characteristics affected by the implementation of the steering angle command or other changes to the system. Accordingly, the curvature controller 92 and the hitch angle controller 90 continuously process information from the measurement module 88 to provide accurate steering angle commands that place the trailer 12 on the desired curvature ĸ2 and the desired reverse travel path 26 without significant overshoot or persistent oscillation of the travel path around the desired curvature ĸ2.

[0027] As in Fig. 5 is shown, the Fig. 4 illustrates the embodiment of the curvature routine 98 in a control system block diagram. Specifically, entering the control system is an input ĸ2 representing the desired curvature 26 of the trailer 12, which is provided to the curvature controller 92. The curvature controller 92 may be expressed as a static mapping p(κ2, δ), which in one embodiment is the following equation: p(κ2,δ)=tan−1(κ2D+Ltan(δ)κ2DLtan(δ)−W) where: κ2 represents the desired curvature of the trailer 12 or 1 / r2 as in Fig. 3 is shown; δ represents the steering angle; L represents the distance from the rear axle of the vehicle to the coupling pivot point; D represents the distance from the coupling pivot point to the axle of the trailer; and W represents the distance from the rear axle to the front axle of the vehicle.

[0028] With further reference to Fig. 5: The output coupling angle p(κ2, δ) is used as the reference signal γ ref provided to the rest of the control system, although the value of the steering angle δ used by the curvature controller 92 is fed back from the nonlinear function of the clutch angle controller 90. It is shown that the clutch angle controller 90 uses linearization of the feedback to define a feedback control law as follows: g(u,γ,v)=δ=tan−1(Wv(1+LDcos(γ))(u−vDsin(γ)))

[0029] As in Fig. 5, the feedback control law g(u, γ, v) is implemented with a proportional-integral (Pl) controller, where the integral part essentially eliminates the steady-state tracking error. More specifically, the Fig. 5 illustrated control system can be expressed as the following differential-algebraic equations: γ˙(t)=v(t)Dsin(γ(t))+(1+LDcos(γ(t)))v(t)Wδ¯ tan(δ)=δ¯=Wv(t)(1+LDcos(γ(t)))(KP(p(κ2,δ)−γ(t))−v(t)Dsin(γ(t)))

[0030] It is contemplated that the PI controller may include gain terms based on trailer length D, since shorter trailers generally have faster dynamics. Additionally, the hitch angle controller 90 may be configured to prevent the desired hitch angle γ(d) from reaching or exceeding a breakaway angle γ(j) as calculated by the controller or otherwise determined by the trailer backup assist system 10, as disclosed in more detail herein.

[0031] Now with reference to Fig. 6: In the illustrated embodiments of the disclosed subject matter, it is desirable to limit the potential for the vehicle 14 and trailer 12 to reach a breakaway angle (i.e., the vehicle / trailer system reaching a breakaway condition). A breakaway angle γ(j) refers to a hitch angle γ that cannot be overcome by the maximum steering input for a vehicle during reverse travel, such as when the steered front wheels of the vehicle 14 are moved to a maximum steered angle δ at a maximum steering angle change rate.The breakaway angle γ(j) is a function of a maximum wheel angle for the steered wheels of the vehicle 14, the wheelbase W of the vehicle 14, the distance L between the coupling point and the rear axle of the vehicle 14, and the length D between the coupling point and the axle of the trailer 12 or the effective axis of the trailer 12 if the trailer 12 has multiple axles. When the coupling angle γ for the vehicle 14 and the trailer 12 reaches or exceeds the breakaway angle γ(j), the vehicle 14 may be pulled forward to reduce the coupling angle γ. Thus, to limit the potential for a vehicle / trailer system to reach a breakaway angle, it is preferable to control the yaw angle of the trailer 12 while keeping the coupling angle γ of the vehicle / trailer system relatively small.

[0032] A representation of a kinematic model of the vehicle 14 and the trailer 12 may be used to determine a breakaway angle for the vehicle-trailer combination. With reference to Fig. 3 and Fig. 6: Accordingly, a steering angle limitation for the steered front wheels requires that the coupling angle γ cannot exceed the breakaway angle γ(j), which is also referred to as a limit coupling angle γ. Under the constraint that the coupling angle γ cannot exceed the breakaway angle γ(j), the breakaway angle γ(j) is therefore the coupling angle γ that maintains circular motion for the vehicle / trailer system when the steered wheels 64 are at a maximum steering angle δ(max). The steering angle for circular motion with the coupling angle γ is defined by the following equation. tanδmax=wsinγmaxD+Lcosγmax

[0033] Solving the above equation for the hitch angle γ allows the breakaway angle γ(j) to be determined. This solution, shown in the following equation, can be used to monitor the hitch angle γ relative to the breakaway angle when implementing the trailer reversing assistance functionality according to the disclosed subject matter. cosγ¯=−b±b2−4ac2a where: a = L 2 tan 2 δ(max) + W 2 ; b = 2 LD tan 2 δ(max); and c = D 2 tan 2 δ(max) - W 2 .

[0034] Now with reference to Fig. 7: An embodiment of the steering input device 18 is shown disposed on the center console 108 of the vehicle 14 near a shift lever 110. In this embodiment, the steering input device 18 includes a rotatable knob 30 to provide the desired reverse travel path of the trailer 12 to the curvature control 28. More specifically, the angular position of the rotatable knob 30 may correlate with a desired curvature, such that rotation of the knob 30 to a different angular position provides a different desired curvature with an incremental change based on the amount of rotation. In some embodiments, an offset may exist between the angular position controlled by the knob and the desired output curvature 26, allowing the steering input offset routine 130 to be performed, as described in more detail herein.

[0035] The rotary knob 30, as shown in the Fig. 7-8, may be biased (e.g., by a spring return) in a neutral position P(AR) between opposite ranges of rotational movement R(R), R(L). In the illustrated embodiment, a first of the opposite ranges of movement R(R) is substantially the same as a second of the opposite ranges of movement R(L), R(R). To provide a tactile indication of an amount of rotation of the rotatable knob 30, a force biasing the knob toward a neutral position P(AR) may increase (e.g., non-linearly) as a function of the amount of rotation of the rotatable knob 30 with respect to the neutral position P(AR). Additionally, the rotatable knob 30 may be configured with position-indicating detents so that the driver can clearly feel the neutral position P(AR) and so that they can feel the range ends of the opposite ranges of movement R(L), R(R) approaching (e.g.,flexible end stops).

[0036] With further reference to the Fig. 7-8: The rotatable knob 30 can generate a desired curvature value as a function of an amount of rotation of the rotatable knob 30 relative to the neutral position P(AR) and a direction of movement of the rotatable knob 30 relative to the neutral position P(AR). It is also contemplated that the amount of rotation of the rotatable knob 30 can also be used to determine the desired output curvature to the curvature controller 28. As discussed in more detail below, the neutral position P(AR) of the knob corresponds to a signal indicating that the vehicle 14 should be steered such that the trailer 12 is reversed along a substantially straight reverse travel path (driver request for trailer zero curvature) as defined by the longitudinal direction 22 of the trailer 12 when the knob is returned to the neutral position P(AR).A clockwise and counterclockwise maximum position of the knob (i.e., the limits of the opposite rotational ranges R(R), R(L)) may each correspond to a respective signal indicating a tightest radius of curvature (i.e., tightest trajectory or smallest radius of curvature) of a travel path of the trailer 12 that is possible without the corresponding vehicle steering information causing a skid condition. In this regard, the neutral position P(AR) is a position that commands zero curvature with respect to the opposite rotational ranges R(R), R(L). Accordingly, a relationship of a commanded curvature of a path of a trailer 12 (e.g., radius of a desired reverse travel path) to a corresponding amount of rotation of the knob 30 may vary across each of the opposite rotational ranges R(L), R(R) of the knob.Therefore, it is also contemplated that the ratio may be normalized based on the degree of change in the position of the knob 30 and the dimensions of a trailer assembly, so that the knob 30 may provide substantially the same desired output curvature for different trailers and may be provided by the driver. It is also contemplated that the ratio may additionally or alternatively be a function of vehicle speed, trailer geometry, vehicle geometry, coupling geometry, and / or trailer load.

[0037] To activate the trailer backup assist system 10, the driver interacts with the trailer backup assist system 10, and the trailer backup assist system 10 automatically steers when the driver reverses the vehicle 14. As explained above, the driver can command the trailer backup path using a steering input device 18, and the curvature control 28 can determine the vehicle steering angle to achieve the desired curvature 26, with the driver controlling the accelerator and brake while the trailer backup assist system 10 controls the steering.

[0038] With reference to Fig. 8: When a driver of the vehicle 14 reverses the trailer 12, the driver can turn the rotary knob 30 to provide a desired curvature 26. According to the Fig. 8, the steering input device 18 is embodied as a rotatable knob 30 to enable the driver of the vehicle 14 to command a desired reverse path of travel by specifying a desired curvature 26. In the illustrated embodiment, the rotatable knob 30 rotates about a central axis between a center position 114 corresponding to a substantially straight reverse path of travel 26 as defined by the longitudinal direction 22 of the trailer 12 and various rotated positions 116, 118, 120, 122 on opposite sides of the center position 114, commanding a desired curvature 26 corresponding to a radius of the desired reverse path of travel for the trailer 12 at the commanded rotated position.It is contemplated that the rotatable knob 30 may be configured in accordance with embodiments of the disclosed subject matter and omitted for its means of biasing to a neutral position P(AR) between opposing ranges of rotational movement. The absence of such biasing may allow a current rotational position of the rotatable knob 30 to be maintained until the rotational control input device is manually moved to a different position. It is also contemplated that the steering input device 18 may include a non-rotatable control device configured to selectively provide a desired curvature 26 and to override or supplement an existing curvature value. Examples of such a non-rotatable control input device include, but are not limited to, a plurality of depressible buttons (e.g.,turn left, turn right, and go straight), a touchscreen on which a driver traces or otherwise inputs a curve for the path commands, a knob that is movable along an axis to allow the driver to input reverse commands, or a joystick-type input, and the like.

[0039] With reference to Fig. 9: A method of operating an embodiment of the trailer backup assist system 10 is illustrated, shown as an embodiment of the operating routine 132 ( Fig. 2). In step 134, the method is initialized by activating the trailer backup assist system 10. It is contemplated that this may be accomplished in a variety of ways, such as making a selection on the display 82 of the vehicle HMI 80 when the transmission of the vehicle 14 is in a reverse mode. The next step 136 then determines the kinematic relationship between the attached trailer 12 and the vehicle 14. To determine the kinematic relationship, various parameters of the vehicle 14 and the trailer 12 must be sensed, entered by the driver, or otherwise determined for the trailer backup assist system 10 in order to generate steering commands for the power steering system 62 according to the desired curvature or reverse travel path 26 of the trailer 12. As described with reference to the Fig. 3-6, the kinematic parameters for defining the kinematic relationship include a length of the trailer 12, a wheelbase of the vehicle 14, a distance from a hitch connection to a rear axle of the vehicle 14, and a hitch angle γ between the vehicle 14 and the trailer 12, among other variables and parameters, as previously described. Accordingly, a trailer backup assist system 10 may continue to the steering input offset routine 130 at step 138. However, it is contemplated that the steering input offset routine 130 may be processed at alternative times, including when the trailer backup assist system is not operating.

[0040] As in Fig. 10, an embodiment of the steering input offset routine 130 is illustrated, which may also be referred to as a compensation module of the controller 28 ( Fig. 2). The first step of the illustrated trailer steering input offset routine 130 is a step 140 in which the amount of rotation of the knob 30 is sampled, such as a value of degrees of rotation per second. This amount of rotation may be provided directly by a signal from the steering input device 18 or otherwise determined by the controller 28 of the trailer backup assist system 10. With the amount of rotation, the steering input offset routine 130 proceeds to step 142 to determine whether the amount of rotation is zero, although it is contemplated that in additional embodiments, the determination may be made whether the amount of rotation is substantially zero, such as within a zero threshold (i.e., + / - 0.5 degrees per second).If the amount of rotation is zero or substantially zero, the rotatable knob 30 is considered stationary, and the steering input offset routine 130 may proceed to the next step. However, if the rotatable knob 30 is not stationary, the steering input offset routine 130 may be bypassed by the operation routine 132 and monitored for the amount of rotation to be zero or substantially zero to determine if an offset is present. It is also contemplated that in additional embodiments of the steering input device 18, a different amount of movement may be observed, such as a sliding movement, to determine when the steering input device 18 is stationary to determine if an offset is present.

[0041] With continued reference to the Fig. Steering Input Offset Routine 130 shown in Figure 10: Once it is determined that the knob 30 is stationary, the routine may proceed to step 144 to sample external torque on the knob 30. The external torque may be sampled by a torque sensor coupled to the knob 30, which is configured to sample torque applied to the knob 30 against the bias force required to move the knob away from its center position P(AR). If it is sampled and determined in step 146 that external torque has a magnitude greater than zero, the Steering Input Offset Routine 130 will return to step 140 to monitor the amount of rotation of the knob 30.However, if it is determined in step 146 that the magnitude of the torque applied to the knob 30 is zero or substantially zero, the steering input offset routine 130 may proceed to step 148, whereby a determination is made that the knob 30 is stationary at the center position P(AR). It is contemplated that steps 144 and 146 may be omitted, as shown by the dashed lines, such as when the knob 30 is not spring-loaded, and an alternative parameter may be monitored to determine that the knob 30 is physically at the center position P(AR). For example, the knob may be determined to be at the center position P(AR) when the output position and the corresponding desired curvature 26 are within a threshold position range (i.e., + / - 0.5 degrees) that is typically greater than the offset.Accordingly, if the knob is held at a constant angle outside the threshold position range, an offset cannot be calculated. It is also conceivable that the driver is prompted to provide confirmation that the knob is stationary and in the center position P(AR), such as via the MMS 80.

[0042] In step 150 of the Fig. 10, a determination is made that the steering input device 18 is in a state to calculate the offset, if any. Specifically, it is determined that the knob 30 is stationary and in the center position P(AR), so that the desired curvature 26 that is output should be zero. Accordingly, in step 150, an offset may be calculated by taking the magnitude of the desired output curvature 26, which may then be stored in memory 86, and then subtracting it from the magnitude of the desired output curvature 26 during continued operation of the trailer backup system 10. It is also contemplated that the offset may be immediately applied to the desired curvature 26 to recalibrate the desired curvature 26 output without needing to store the offset in memory. With the offset determined, the operating routine 132 continues to step 152.

[0043] With further reference to Fig. 9: In step 160, the hitch angle γ between the vehicle 14 and the trailer 12 is sampled, although this may occur continuously during operation of the trailer backup assist system 10. It is contemplated that in additional embodiments of the trailer backup assist system 10, the steps of determining the kinematic relationship and sampling the hitch angle γ may occur before the trailer backup assist system 10 is activated, or at any time before steering commands are generated. Accordingly, in step 162, the position and rate of change from the steering input device 18, such as the angular position and degree of rotation of the rotatable knob 30, are received to determine the desired curvature 26, taking into account the calculated offset, if any.The desired curvature and / or the position of the knob 30 captured in step 162 may be fed back to the steering input offset routine 130, as shown in dashed lines, to define a closed-loop, linear feedback system for consistently updating the offset and / or calibrating the output from the steering input device 18. The steering commands and brake application commands for the vehicle 14 that are generated may also be generated in conjunction with the processing of the curvature routine 98, as previously discussed, and which may also be used as a steering module of the controller 28 (. Fig. 2). In step 166, the steering commands and the brake application commands are executed to guide the trailer 12 on the desired curvature 26 as provided by the steering input device 18 and taking into account the calculated offset, if any.

[0044] Now with reference to Fig. 11: Further illustration is provided of the processing of the steering input offset routine 130 and the benefits of calculating and incorporating an offset from the steering input device 18 in the operation of the trailer backup assist system 10. Fig. 11 illustrates in particular four Fig. sequential movements of the rotary knob 30, which in this embodiment are provided with an arrow position indicator 178, and the corresponding output signal 176, shown in dashed lines. The rotation of the knob 30 to the left of Fig. to 170 shows that the output signal 176 is aligned with the arrow position indicator 178, which represents an offset of essentially zero. When the knob 30 is in Fig. is turned back to the center position, the output signal 176 does not follow the arrow position indicator 178 all the way back to the center position, which may be a result of a hysteresis effect in the knob 30. Accordingly, when the knob 30 remains stationary in the center position, the steering input offset routine 130 may calculate the offset and subtract or otherwise apply it to shift the desired output curvature so that the output signal 176 is again aligned with the arrow position indicator 178, as shown in Fig. is shown.

[0045] In parallel with performing the operations for receiving the trailer reverse assist requests, determining the desired curvature 26 of the trailer 12, and generating the vehicle steering commands, the trailer reverse assist system 10 may perform an operation for monitoring whether an unacceptable trailer reverse condition exists. Examples of such monitoring include, but are not limited to: evaluating a hitch angle γ to determine whether a hitch angle γ threshold is exceeded, evaluating a reverse travel speed to determine whether a reverse travel speed threshold is exceeded, evaluating the vehicle steering angle to determine whether a vehicle steering angle threshold is exceeded, evaluating other operating parameters (e.g.,Vehicle longitudinal acceleration, amount of accelerator pedal demand, and hitch angle amount) to determine whether a corresponding threshold is exceeded, and the like. The reverse travel speed may be determined based on the wheel speed information obtained from one or more wheel speed sensors 58 of the vehicle 14. If it is determined that an unacceptable trailer backing condition exists, an operation may be performed to cause the current travel path of the trailer 12 to be inhibited (e.g., stopping movement of the vehicle 14), followed by the operation performed to terminate the current trailer backing assist operation. It is disclosed herein that prior to and / or in conjunction with causing the current trailer path to be inhibited, one or more actions (e.g., operations) for providing feedback (e.g.,a warning) to the driver that such an unacceptable hitch angle condition is imminent or approaching. If such feedback results in the unacceptable hitch angle condition being resolved before a limit condition is reached, the method, in one example, may continue with providing the trailer backup assist functionality according to the operations. Otherwise, the method may continue with the operation to terminate the current trailer backup assist operation. In conjunction with performing the operation to terminate the current trailer backup assist operation, an operation to control the movement of the vehicle 14 to correct or limit a spin-out condition (e.g.,Steering the vehicle 14, slowing the vehicle 14, limiting the size and / or degree of the driver-requested trailer curvature input, limiting the size and / or degree of the steering command, and / or the like to prevent the hitch angle from being exceeded).

[0046] It is to be understood that variations and modifications of the above-mentioned structures and methods may be made without departing from the concepts of the present invention, and it is further understood that such concepts are intended to be covered by the following claims unless such claims expressly state otherwise by their language.

Claims

[1] Trailer reversing assistance system for a vehicle (14) reversing a trailer (12), comprising: a knob (30) which can be rotated into positions which each output a desired curvature (ĸ2) of a reversing path (26) of the trailer (12); and a control which determines an offset from the desired curvature (ĸ2) when the button (30) is stationary in a central position and which generates a steering command for the vehicle (14) to guide the trailer (12) with the desired curvature (ĸ2) of the reversing path (26) taking into account the offset, a torque sensor (70) coupled to the knob (30), wherein the controller determines that the knob (30) is in the center position to determine the offset when the torque sensor (70) senses substantially no external torque on the knob (30) and an amount of rotation of the knob (30) is substantially zero, wherein the amount of rotation of the knob (30) is substantially zero when the knob (30) is stationary. [2] A trailer reversing assist system according to claim 1, wherein the knob (30) is spring-loaded in the center position and rotatable in opposite first and second directions, thereby providing clockwise curvature values ​​in the first direction and counterclockwise curvature values ​​in the second direction. [3] Trailer reversing assistance system according to claim 1 or 2, wherein the knob (30) is spring-biased in the central position which is designed to provide a zero value for the desired curvature (ĸ2) in order to revert the trailer (12) along a substantially straight trajectory. [4] Trailer reversing assistance system according to one of claims 1 to 3, wherein the controller provides a steering command to the vehicle (14) taking into account the offset to reverse the trailer (12) along a substantially straight trajectory when the button (30) is in the center position. [5] Trailer reversing assistance system for a vehicle (14) reversing a trailer (12), comprising: a steering input device (18) movable between positions each providing a desired curvature (ĸ2) of a reverse travel path (26) of the trailer (12); and a control system that includes: a compensation module that determines an offset between zero and the desired curvature (ĸ2) when the steering input device (18) is stationary in a central position; and a steering module for generating a steering command for the vehicle (14) to guide the trailer (12) with the desired curvature (ĸ2) of the reversing path (26) less the offset, a sensor coupled to the steering input device (18), wherein the controller determines that the steering input device (18) is in the center position to determine the offset when the sensor senses substantially no external force on the steering input device (18) and substantially no movement, wherein a measure of movement of the steering input device (18) is substantially zero when the steering input device (18) is stationary. [6] Trailer reversing assistance system according to claim 5, wherein the steering input device (18) includes a knob (30) which is spring-loaded in the central position and is rotatable in opposite directions from there. [7] A trailer reversing assist system according to claim 6, wherein the opposite directions of rotation of the knob (30) provide clockwise curvature values ​​in a first direction and counterclockwise curvature values ​​in a second direction. [8] Trailer reversing assistance system according to one of claims 5 to 7, wherein the steering input device (18) includes a knob (30) spring-biased in the central position adapted to provide a zero value for the desired curvature (ĸ2) in order to reverse the trailer (12) along a substantially straight trajectory. [9] Trailer reversing assistance system according to one of claims 5 to 8, wherein the offset provides a steering command for the vehicle (14) to reverse the trailer (12) along a substantially straight trajectory when the steering input device (18) is in the center position. [10] A method for autonomously steering a vehicle (14) reversing a trailer (12), comprising: Providing a knob (30) rotatable from a central position in opposite directions to a plurality of positions each defining a desired curvature (ĸ2) of a reverse travel path (26) of the trailer (12); Determining an offset of the desired curvature (ĸ2) when the knob (30) is stationary in the center position; and Generating a steering command for the vehicle (14) to guide the trailer (12) with the desired curvature (ĸ2) of the reversing path (26) taking into account the offset; sensing an amount of rotation of the knob (30) such that the amount of rotation is substantially zero when the knob (30) is stationary and the offset is determined; Preloading a button (30) with a spring in the central position; and Sensing torque on the knob (30) such that it is determined that the knob (30) is in the center position when no external torque is sensed on the knob (30). [11] The method of claim 10, wherein the plurality of positions of the knob (30) provide clockwise curvature values ​​in a first rotational direction from the center position and counterclockwise curvature values ​​in a second rotational direction from the center position. [12] The method of claim 10 or 11, wherein the steering command for the vehicle (14) takes into account the offset to return the trailer (12) along a substantially straight trajectory when the button (30) is in the center position. [13] A method according to any one of claims 10 to 12, further comprising: Scanning a coupling angle (γ) between the vehicle (14) and the trailer (12), wherein the steering command is generated on the basis of the coupling angle (γ). [14] The method of claim 13, wherein the knob (30) is rotatable from the center position in opposite directions to opposite end positions, the center position defining the desired curvature (ĸ2) as zero and the opposite end positions of rotation being defined by a radius of curvature controllable for the trailer (12) without the coupling angle (γ) exceeding a breakaway threshold determined based on a length of the trailer (12) and a wheelbase of the vehicle (14).

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