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Title:
METHOD AND APPARATUS FOR SWAY CONTROL OF TRACTOR-TRAILERS USING AN ACTIVE HITCH
Document Type and Number:
WIPO Patent Application WO/2019/033210
Kind Code:
A1
Abstract:
An active hitch for controlling sway between a tractor-trailer including an attachment mechanism and a controller. The controller receives signals associated with driving characteristics or driving conditions and then determines if the active hitch needs to be moved in order to control sway. If needed, the active hitch is urged to move such that the angle between the tractor and trailer can be changed in order to control sway.

Inventors:
KHAJEPOUR AMIR (CA)
SYKORA CONNOR (CA)
Application Number:
PCT/CA2018/050987
Publication Date:
February 21, 2019
Filing Date:
August 15, 2018
Export Citation:
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Assignee:
KHAJEPOUR AMIR (CA)
International Classes:
B60D1/30; B60D1/58; B60W40/10
Foreign References:
US20040021291A12004-02-05
Attorney, Agent or Firm:
WONG, Jeffrey et al. (CA)
Download PDF:
Claims:
What is Claimed is:

1 . An apparatus for tractor-trailer sway control comprising:

an active hitch component enabling a trailer to be connected to a tractor; and a controller for receiving driving characteristic measurements and for determining instructions to be transmitted to the active hitch component to control sway.

2. The apparatus of Claim 1 wherein the active hitch component comprises:

an attachment mechanism.

3. The apparatus of Claim 2 wherein the attachment mechanism comprises:

a hitch component; and

an actuator component for moving the hitch component with respect to the tractor and trailer.

4. The apparatus of Claim 3 wherein the actuator component further comprises: a linkage arm portion whereby the hitch component is mounted to the linkage arm portion;

wherein motion of the linkage arm portion is controlled by the actuator

component.

5. The apparatus of Claim 2 wherein the active hitch component further comprises: a frame portion for mounting the active hitch component to the tractor or the trailer.

6. The apparatus of Claim 1 further comprising a power source.

7. The apparatus of Claim 6 wherein the power source is a battery, a set of power cables connecting to a tractor battery or a hydraulic power pack power pack.

8. The apparatus of Claim 3 wherein the hitch component is a hitch ball component or a hitch pin component.

9. The apparatus of Claim 1 further comprising:

a set of sensors for sensing and transmitting driving characteristic measurements to the controller.

10. The apparatus of Claim 1 wherein the controller receives driving characteristic measurements from the tractor or the trailer.

1 1 . The apparatus of Claim 1 wherein the controller transmits signals to the active hitch component to move the active hitch component.

12. The apparatus of Claim 1 wherein the driving characteristic measurements is an angle between the tractor and the trailer.

13. A method of controlling sway in a tractor-trailer comprising:

receiving driving measurements associated with operation of the tractor-trailer; processing the driving measurements to determine active hitch instructions;

and

transmitting the active hitch instructions to an active hitch;

wherein the active hitch instructions cause the trailer to move with respect to the tractor to control sway.

14. The method of Claim 13 wherein the driving measurements comprise at least one of an error signal, tractor yaw rate, tractor steering angle, tractor speed, engine steering information or braking information.

15. The method of Claim 13 wherein the active hitch instructions comprise:

signals to actuate an actuator component of the active hitch to move a hitch component of the active hitch to change an angle between the tractor and the trailer.

16. The method of Claim 13 wherein processing the driving measurements comprises:

determining a desired angle between the tractor and trailer;

calculating amount of hitch component movement needed to achieve the desired angle; and

translating the amount of hitch component movement as active hitch instructions.

Description:
METHOD AND APPARATUS FOR SWAY CONTROL OF TRACTOR-TRAILERS

USING AN ACTIVE HITCH

Cross-reference to related applications

This application claims the benefit of priority of U.S. Provisional Patent

Applications No. 62/546, 129 filed August 16, 2017 which is hereby incorporated by reference.

Field of the Disclosure

The disclosure is generally directed at automobiles and, more specifically, at a method and apparatus for sway control of tractor-trailers using an active hitch.

Background of the Disclosure

Articulated vehicles refer to any vehicle configurations with pivoting joints, allowing the vehicle to carry a larger payload, while still maintaining the ability to navigate sharp turns. Articulated vehicles typically include a tractor, which contains the prime mover for the system, and one or more trailers, which contain the extra cargo space hitched to the tractor. These vehicles have widespread use in commercial and passenger vehicle applications, however, the articulation of the trailer hitch, or joint, introduces new modes of instability. This added instability, coupled with the ubiquity of articulated vehicles in the transportation industry, demands that these systems be studied to determine general trends in stability and to apply appropriate active safety measures.

The handling and yaw stability characteristics of vehicles (or tractor) are drastically changed when towing a trailer, which can lead to unsafe oscillations in the trailer yaw, known as trailer sway.

Trailer sway is characterized by transient oscillations in the trailer articulation angle, which transmit forces to the tractor and the driver, thereby decreasing handling. If these oscillations persist or become divergent, the tires will saturate their lateral handing ability, usually leading to an accident. Trailer sway may occur even when the tractor is in an understeer configuration, whereas single mass vehicles are inherently stable when they are understeer.

Current vehicle anti-sway solutions either revolve around passive systems that introduce friction into the trailer joint, or use trailer brakes to apply even or differential braking force to the system.

Therefore, there is provided a novel method and apparatus for sway control of tractor-trailers using an active hitch.

Summary of the Disclosure

The disclosure is directed at a method and apparatus for sway control of tractor- trailers using an active hitch. In one embodiment, the system of the disclosure includes and active hitch that is controlled based on information provided to the active hitch via sensors.

In one embodiment, the disclosure is directed at a system including an

articulating hitch ball position to reduce sway behavior in tractor-trailer configurations. One advantage of an articulating hitch ball design is that it is not dependent on the trailer being towed, providing stability improvements to the wide variety of trailers that a vehicle may tow over its life cycle.

Changes in the lateral position of the hitch relative to the tractor create dynamic changes to the heading angle of the trailer relative to the tractor, which act as

compensating steering inputs into the system.

In one aspect of the disclosure, there is provided an apparatus for tractor-trailer sway control an active hitch component enabling a trailer to be connected to a tractor; and a controller for receiving driving characteristic measurements and for determining instructions to be transmitted to the active hitch component to control sway.

In another aspect, the active hitch component includes an attachment

mechanism. In another aspect, the attachment mechanism includes a hitch component; and an actuator component for moving the hitch component with respect to the tractor and trailer. In a further aspect, the actuator component includes a linkage arm portion whereby the hitch component is mounted to the linkage arm portion; wherein motion of the linkage arm portion is controlled by the actuator component. In yet another aspect, the active hitch component further includes a frame portion for mounting the active hitch component to the tractor or the trailer.

In another aspect, the system further includes a power source. In another aspect, the power source is a battery, a set of power cables connecting to a tractor battery or a hydraulic power pack power pack. In yet another aspect, the hitch component is a hitch ball component or a hitch pin component. In a further aspect, the system further includes a set of sensors for sensing and transmitting driving

characteristic measurements to the controller. In yet a further aspect, the controller receives driving characteristic measurements from the tractor or the trailer. In an aspect, the controller transmits signals to the active hitch component to move the active hitch component. In an aspect, the driving characteristic measurements is an angle between the tractor and the trailer.

In another aspect of the disclosure, there is provided a method of controlling sway in a tractor-trailer including receiving driving measurements associated with operation of the tractor-trailer; processing the driving measurements to determine active hitch instructions; and transmitting the active hitch instructions to an active hitch;

wherein the active hitch instructions cause the trailer to move with respect to the tractor to control sway.

In another aspect, the driving measurements include at least one of an error signal, tractor yaw rate, tractor steering angle, tractor speed, engine steering

information or braking information. In another aspect, the active hitch instructions include signals to actuate an actuator component of the active hitch to move a hitch component of the active hitch to change an angle between the tractor and the trailer. In a further aspect, processing the driving measurements includes determining a desired angle between the tractor and trailer; calculating amount of hitch component movement needed to achieve the desired angle; and translating the amount of hitch component movement as active hitch instructions.

Description of the Drawings

Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached Figures. Figure 1 is a schematic diagram of a system for sway control of tractor-trailers using an active hitch;

Figure 2a is a schematic diagram of apparatus for sway control of tractor-trailers using an active hitch;

Figure 2b is a schematic diagram of another apparatus for sway control of tractor-trailers using an active hitch;

Figure 3 is a flowchart outlining a method of sway control of a tractor-trailer using an active hitch;

Figure 4a is a schematic diagram of an active hitch;

Figure 4b is a top planar view of a hitch joint;

Figure 4c is an isometric view of the hitch joint of Figure 4b;

Figure 4d is a schematic diagram of an in-line configuration for a hitch joint;

Figure 4e is a schematic diagram of a planar linkage configuration for a hitch joint;

Figure 4f is a section view of components of the trailer hitch;

Figure 4g is a schematic view of welded sections of the linkage arm (left) and mounting bracket (right) of the hitch joint;

Figure 4h is a diagram of a Class III hitch component;

Figure 4i is a schematic diagram of another embodiment of an active hitch;

Figure 5 is a table showing advantages of actuator configurations for an active hitch;

Figure 6 is schematic kinematics diagram

Figure 7 are graphs showing kinematic characteristics;

Figure 8 is a photograph showing an active hitch mounted on a vehicle hitch; Figure 9 is a schematic diagram of one embodiment of sensor placement for an active hitch; and

Figure 10 is a schematic diagram of an actuation power loop.

Detailed Description

The disclosure is directed at a method and apparatus for sway control of tractor- trailers using an active hitch. The apparatus is preferably useable on a variety of tractor-trailer configurations. As such, the control design preferably functions with limited sensing, and is robust to changes in tractor-trailer lateral dynamics. For some embodiments, such as a standalone system, the active hitch may not receive all measurements taken by the tractor (such as by the on-board computer), so the embodiment includes a sensing mechanism. The active hitch system should preferably be able to adequately control any trailer configuration, where the stability of those configurations is also dependent on the overall vehicle speed.

Turning to Figure 1 , a schematic diagram of a system for sway control of a tractor-trailer is shown. The system 10 includes an active hitch 12 that is used to connect a tractor 14 to a trailer 16 and to provide sway control to the tractor-trailer combination, when necessary. In one embodiment, the trailer 16 may be seen as being mounted to a rear of the tractor 14 via the active hitch 12. The system 10 further includes a central processing unit (CPU) 18 that is "connected" to the active hitch 12 to provide instructions or signals to the hitch 12 based on measurements received by the CPU 18. As such, the CPU 18 may not be physically connected to the hitch 12 but is communicatively connected to the hitch 12.

The system 10 may further include a set of sensors 20 that are located throughout the tractor 14 and/or trailer 16 for sensing driving characteristics while the vehicle is in motion. The sensors 20 transmit measurements based on the sensed driving characteristics to the CPU 18 which then processes the measured signals to determine and transmit instructions or signals to the active hitch 12. Along with the signals transmitted by the sensors or instead of the signals transmitted by the sensors, the CPU 18 may receive signals or driving characteristics from the onboard computer of the tractor and/or trailer. In some embodiments, there may not be any sensors as the CPU receives measurements (or driving characteristics) directly from either the onboard computers of the tractor or trailer, or both. As will be described below, the instructions/signals transmitted by the CPU 18 cause the active hitch to adjust in response to driving conditions being experienced by the tractor-trailer. For instance, the sensed driving characteristics may reflect that the trailer is swaying and therefore, the active hitch may react and move laterally. Turning to Figure 2a, a schematic diagram of a control architecture for the system is shown. Figure 2a provides one embodiment of the type of signals that may be transmitted to the CPU 18 via the sensors 20 or the onboard computers or both. The CPU 18 may be seen as an active hitch controller or Hitch ECU.

The signals transmitted by the active hitch controller 18 to the active hitch 12 are based on a feedback control model such as will be discussed below. In Figure 2, the solid lines correspond to measured signals and the dotted lines correspond to physical movement or forces. This schematic represents a non-exhaustive number of possible configurations for the controller.

In operation, as the tractor and trailer is in motion, signals are transmitted to the CPU 18. Signals that are transmitted from a tractor CAN BUS 22 may include, but are not limited to, a longitudinal speed of the tractor, a brake position of the tractor and values from an inertial measurement unit (IMU). In one embodiment, these signals are generated via the measurements or sensing of tractor dynamics. Signals that are transmitted from the active hitch 12 (such as via the set of sensors 20) may include, but are not limited to, a hitch position, a trailer position, a hitch angle or a power pack monitoring signal. Signals that are transmitted by the trailer may include, but are not limited to, one or more trailer IMU values.

Based on the received signals, the CPU 18 processes the signals to determine commands to be transmitted to the active hitch 12 (such as in the form of a motion command) and/or to the trailer components 24 (such as in the form of a brake command). A flowchart outlining a method of using an active hitch for sway control is shown in Figure 3.

As further shown in Figure 2a, between the trailer 16 and the active hitch 12, a trailer angle may be monitored and between the tractor 14, trailer 16 and hitch 12, a hitch displacement may be measured or monitored.

As will be understood, Figure 2a provides one embodiment of signals that may be used by the CPU to control the active hitch. Other embodiments of signals are contemplated. For example, communication with trailer auxiliary components 24 or with the tractor CAN bus 22 may not be necessary to control the hitch, so they can be excluded in simpler configurations of the active hitch controller 18. In an alternative embodiment, use of signals from the tractor 14 and/or trailer 16 may provide extra safety systems and supplementary measurements for the system.

In a preferred embodiment, the measurements received by the controller 18 include the articulation angle between the tractor and trailer and the tractor and/or trailer yaw rate. In one embodiment, these measurements can be made using the set of embedded sensors 20.

In yet another embodiment, assuming no further knowledge of the system, the controller can articulate the hitch based on an error signal. Since sway behavior is characterized by oscillations between the tractor and trailer, the oscillatory component of the articulation angel between the tractor and trailer may be chosen as an error signal. The hitch controller activates the hitch motion to eliminate or reduce this oscillatory articulation angle. This embodiment can be improved further by including the tractor yaw rate and/or steering angle for better detection of trailer sway.

In yet another embodiment, the controller can articulate the hitch based on the tractor steering angle, speed, and yaw rate. The hitch controller uses the tractor steering angle and speed to find the expected tractor yaw rate. This expected yaw rate is compared with the measured tractor yaw rate and the difference is used to

manipulate the hitch motion.

The use of the error signals sets the basis for non-model-based controllers such as a PD feedback controller, fuzzy inference or neural networks for the active hitch system. More complicated model-based controllers such as model predictive controllers were may also be used for manipulating the hitch to control the trailer sway. This control model is based on measurement of additional system states.

For dynamic modeling, to model the multibody dynamics of the tractor-trailer combination, a lateral handling model may be contemplated. The active hitch is concerned primarily with yaw dynamics, so a state space realisation was developed based on a bicycle handling model. The bicycle model is used widely in vehicle dynamics modeling, and is used to simply describe the response of a vehicle to steering inputs. The bicycle model assumes a single track (one tire per axle) and ignores the effect of weight transfer in the tires during lateral maneuvers. Since the model is derived into a linearized state space representation, it can make use of heuristics and methods from classical control theory.

Based on experimental simulations (as outlined below), an embodiment of an active hitch was designed. Along with a design of the active hitch, the hitch may include auxiliary components to actuate the hitch. Extra systems that were used in the test setup (custom test trailer, test tractor, HIL implementation) are discussed below.

Turning to Figure 2b, a schematic diagram of the tractor and trailer with an active hitch for controlling trailer sway is shown. The hitch 12 is connected to the tractor 14 (which in the current diagram is seen as the carbody) and to the trailer 16. The tires 50 of the tractor and tires 52 of the trailer are connected to the 14 and 16 via appropriate joints 60 and 62. Joint 62 is for the steering of the tractor. In this model, the driver 64 follows the road in 66 by controlling the engine 58, the brakes 54, and by steering 55. The ABS module 56 is also included to protect against the wheel(s) from locking in harsh braking. In this simulation model, non-model and model based controllers for the active hitch can be tested and evaluated.

Turning to Figure 3, a flowchart outlining a method of sway control of a tractor- trailer using an active hitch is shown. Initially, driving characteristics, or driving characteristic measurements/estimations, are received by the active hitch controller 70. These measurements may be received either directly from the on-board computer of the tractor, from the on-board computer of the trailer or a set of sensors located within the active hitch system, or any combination. Other measurements may also be received by the active hitch controller to assist in sway control. The driving characteristics, or driving characteristic measurements/estimations are dependent on the active hitch controller type and include, but is not limited to, the driver steering angle, vehicle speed, hitch angle, tractor yaw rate, trailer yaw rate, and brake pressure.

The driving characteristic measurements are then processed by the active hitch controller 72. Depending on the measurements received, these measurements are then processed, such as via a set of predetermined algorithms, to determine if it is necessary to transmit instructions to the active hitch 74. For instance, the controller may determine that the tractor-trailer is experiencing sway (based on the processing of the measurements) and therefore determines that there is a need to adjust the active hitch to control the sway. If necessary, the instructions are then transmitted to the active hitch 76. For example, if the tractor-trailer is experiencing sway, the controller may transmit instructions to change the position of the hitch whereby the angle between the tractor and trailer is changed. In order to change the position of the active hitch, an actuator component of the active hitch is controlled to move the hitch component of the active hitch. Control of a hitch component via actuators or an actuator component will be understood.

In another embodiment, the controller may determine a desired angle or desired angle within a preferred angle range) between the tractor and trailer and then based on the current angle (from the received measurements), calculate the amount that the hitch component has to move in order to achieve a desired angle between the tractor and trailer and then translate the amount of hitch component movement as active hitch instructions. The instructions are then transmitted to the active hitch to move the hitch component accordingly (such as by the actuator component).

Turning to Figure 4a, a schematic diagram of the active hitch is shown. The active hitch may include a frame portion 84 that is attached to a rear of the tractor, or vehicle. In other embodiments, such as schematically shown in Figure 4i, the frame portion may be mounted to the front of the trailer. In some vehicles or trailers, a hitch component may be a standard component and therefore, the active hitch may not need a frame portion. The active hitch further includes an attachment mechanism 12, such as a hitch ball or hitch pin portion, that allows a tractor/trailer to be mounted therefor. As will be understood, the hitch ball portion includes an apparatus for connecting to the frame portion such as via a square bar receiver. The active hitch further includes a power source 80 that is used to power the components of the active hitch and the controller (or processor) 82.

Figure 4h shows an example of a frame portion which can be seen as a medium- duty hitch attachment. In a preferred embodiment, the power source, such as in the form of a battery, power cables from the tractor or a hydraulic power pack, is preferably mounted to the frame portion.

Figures 4b and 4c are a top planar view and a isometric view of another embodiment of the attachment mechanism of Figure 4a. As can be seen in Figures 4b and 4c, the attachment mechanism further includes a hitch ball. In a preferred embodiment, the hitch ball should be able to laterally move, preferably, a predetermined amount, such as 10cm, in either direction although other lateral distances are contemplated. Movement of the hitch ball (to change the angle between the tractor and trailer, provides a counterbalance to the sway being experienced in order to control the sway. The lateral movement of the hitch will also improve the steerability of the tractor/trailer in reverse and back up driving as the hitch lateral movement can change the angle between the tractor and trailer.

In experimentation, by reducing or limiting lateral movement of the hitch ball to 10cm, significant sway reductions were observed without requiring unreasonable actuation speed or an excessively bulky attachment mechanism. In one embodiment, the power source preferably drives the hitch ball laterally at 25cm/s, while the frame portion preferably simultaneously supports a lateral load of 3000N and a vertical load of 1500N.

Movement and/or control of the hitch ball is enabled by an actuator that allows the hitch ball to move the required distance. The control of the actuator In one embodiment of the attachment mechanism, the actuator is a linear actuator although other types of actuators are contemplated. A linear actuator, either actuated electrically or hydraulically, allows precise movement that can support the reaction forces of the trailer that is mounted on or attached to the hitch ball. Both electrical or hydraulic linear actuators have some type of mechanical locking which reduces or prevents the trailer forces from driving the active hitch. Electric actuators use worm gears that cannot be driven by the meshing spur gear, and hydraulic actuators, or power loops, generally feature components that can only be driven one way or in one direction. These features allow the hitch ball to remain stationary when not powered.

Although different linear actuators can be used, in the preferred embodiment, an in-line or a planar linkage actuator is preferred. Schematics of the two configurations are shown in Figures 4d (in-line) and 4e (planar linkage).

Turning to Figure 4i, another embodiment of an active hitch is shown. In this embodiment, the frame portion is mounted to the trailer such that the active hitch can then be mounted to the trailer via the frame portion. The in-line configuration of the tractor 14, hitch 12 and trailer 16 creates pure lateral motion (as shown by the arrow) of the hitch ball 12, by restricting or reducing motion on a linear guideway. The actuator can be placed to one side, or be incorporated into the guideway, such as in CNC machine rails. The planar linkage configuration relies on the rotation of a pivoting linkage (as shown by the arrow), and therefore produces a component of longitudinal motion. The advantages of each actuator are listed in the table of Figure 5.

In a more preferred embodiment, the planar linkage actuator is used in the active hitch although it is understood the in-line configuration may also be used.

For the planar linkage embodiment, the kinematics of the hitch linkage were designed to reduce or minimize the overall size of the attachment mechanism (subject to the system requirements), and to create a nearly linear relationship between actuator movement and hitch lateral movement.

In order to determine a design for the planar linkage embodiment, software was created to simulate the motion profile of different configurations. Inputs for the simulation included the desired lateral hitch ball travel, the locations of the rigid supports, the length of the control arm (distance from the hitch ball from the main pivot point), and the location where the actuator connects to the control arm. Inverse kinematic calculations were also calculated to determine a required range of motion for the actuator, to determine the rate of change of the actuator with respect to the hitch ball, and to determine the force on the actuator for a given lateral force on the hitch ball (hereafter referred to as the force multiplier). Forward kinematic calculations were performed to confirm the results of the inverse kinematics calculations. Figure 6 is a schematic diagram of a kinematics diagram showing the parameters that were used to perform the kinematics calculations.

The trigonometric equations that define the linkage kinematics reveal that the rate of change of the actuator length ball with respect to the hitch ball movement is the inverse of the force multiplier at a given hitch position. The actuator length l ac forms a triangle with l B and l L . The opposite angle θ α is used with the cosine law to find l ac .

d0 ac άθ Η

θ αε = 90° + Θ Β - (Θ Η + 0 ,

dy H dy H lac = l + 1 L 2 - 2l B l L cos(0 ac ) Eq. 3 dlac d6 ac dl ac 1

dy H dy H d0 ac l H ^ l - y* Jl + ll - 2l B l L cos(0 ac ) And using statics to get the force multiplier— at a given hitch positon, first take the sum of moments about the central pivot to find the force acting perpendicular to line

Again using cosine law, the angle δ between the perpendicular line to l L and the axis of the actuator is calculated, and this angle can be used to project the force perpendicular to l L onto the actuator axis:

The second term can be expanded and re-simplified by using the definition of Z, from equation 3:

The above is the inverse (or negative inverse) of equation Eq. 4, so by creating a nearly linear relationship between actuator movement and hitch movement, the actuator will also have a nearly constant force multiplier for different hitch positions. In order to reduce or minimize the overall size, and also to create a regular force multiplier, the following heuristic rules were used to determine a preferred layout of the mechanism:

• For compactness, increase or maximise the ratio between actuator motion range and actuator total length.

• To ensure small variations in the actuator axis angle, restrict endpoints of

actuator motion to have the same actuator angle.

• Define a ratio of total lateral hitch travel to total actuator motion and chose the value that best balances resultant trade-offs (higher ratio puts more force into actuator but is slower).

These heuristics were implemented in a CAD model of the linkage with various actuators and sizes, which defined the kinematics from Figure 6. One embodiment of the hitch configuration (based on the simulations) combines packaging constraints with the kinematic performance requirements, and is shown in Figure 7. The figure shows the linkage dimensions, the mapping of actuator movement to lateral hitch ball movement, and how the force multiplier changes at different actuator positions

(equivalent to the rate of change of the mapping curve).

The motion profile is nearly linear; there is a variation of <1% between the peak rate of change and the average value of 2.53. The rate of change is also nearly symmetric about the midpoint of the hitch motion, so the performance will be even in both directions, despite the asymmetry of the actuator placement.

Since the hitch ball will travel around a circular path, it will experience a change in longitudinal position of 3.29cm. Further reduction of this unwanted motion would result in a longer linkage, which results in greater moments transferred to the mechanism and to the hitch mounts. The axis of the actuator deviates in direction by <3° throughout the motion, allowing it to be packed more tightly with the rest of the assembly. When the hitch ball position is centered, the direction of the actuator axis is perpendicular to the line l L , which means that the axial force in the actuator will not transfer excessive off -axis forces into the linkage and the mounting bracket. In one embodiment, since the hitch linkage and supporting components are relatively small compared to most vehicles, weight savings are not of primary concern when designing the structural components.

The linkage design includes three primary mechanical parts: the linkage arm, the actuator, and the support bracket which attaches to the vehicle hitch via a mating square tube. A rendering of the structural components are shown in Figures 4b and 4c.

In a preferred embodiment, the actuator may be a 1500psi rated hydraulic cylinder and the linkage is supported by a set of fasteners, such as SAE grade 8 fasteners. The fasteners are sized such that they have a safety factor of approximately double the safety factor of the main components. To facilitate motion of the linkage, the actuator is attached to the linkage arm via a rod end, which is preferably rated for l OOOOIbs of static loading. The main pivot is comprised of a shoulder bolt that interfaces with two flanged oil-impregnated bushings, which are pressed into the linkage arm. The flanges reduce friction along the pivot and the clamping surfaces, as shown in Figure 4f.

The bushings are preferably rated for a combined dynamic loading of 3000lbs while rotating at 60rpm, which is adequate for expected kinematic requirements.

In a preferred embodiment, the structural components are made from mild steel plate, and are cut into sections via known methods such as a laser cutter. The configuration for the linkage arm is based on an I-beam, which is ideal for various loading types, with a possible exception of twisting loads.

Where possible, the linkage arm and the bracket use perpendicular connections to best make use of the two-dimensional nature of the cut parts. The linkage may also include self-aligning tabs to reduce jigging to maintain dimensions. The tabs are placed in regions that experience lower relative stress so the material discontinuities are less likely to develop cracks or micro-yielding. A schematic diagram of individual sections of the structures are shown in Figure 4g.

In addition to the alignment tabs, bolts and spacers may be used to help maintain concentric holes. Figure 8 is a photo of a linkage (or hitch mechanism) attached to a vehicle, such as a tractor.

In controlling the active hitch, as discussed above, non-model and model based controllers can be used. In one embodiment, the hitch angle is measured and the controller tries to manipulate the hitch lateral motion to eliminate any oscillatory component between the tractor and trailer (sway motion). In another embodiment, the hitch angle and the yaw of the tractor are measured to control the trailer sway. In other embodiments, more measurements/information such as vehicle speed, steering angle, trailer yaw rate may be used.

In a preferred embodiment, the sensors have a range of measurement of approximately 100°, and can easily be fitted with custom mounting to attach to various chassis linkages. They are also spring-loaded to decrease mechanical play during articulation. Since the sensor have a limited range of motion, they are meant to be configured into four bar linkages, where the sensor rotation acts as the follower, and the suspension component acts as the crank.

One embodiment of how the sensors may be configured is shown in Figure 9. The inboard sensor is bolted to the inside of the structural bracket while the outboard sensor is clamped onto the end of the hitch arm, where the bolts index on the curvature of the hitch arm, preventing sliding. The outboard sensor plates also have slots and indexed holes, so that the plates can accommodate mounting to different hitch couplers.

Figure 9 further shows how the active hitch might attach to the hitch coupler on a trailer. Since the outboard sensor link must be attached to the same spot on the coupler each time the trailer is attached, this particular method of measurement may not be viable for commercial use, however, other methods of sensing the hitch angle between the tractor and trailer such as ultrasonic sensing, laser distance measurement and customized hitch balls may be used. Ultrasonic or laser distance sensors can be mounted on the tractor or trailer to measure directly the angle between the tractor and trailer.

With respect to the power source for the active hitch, in a preferred embodiment, the active hitch system is powered by a hydraulic power loop. The power source may also be an electric solution rather than a hydraulic one. A simplified layout of the components required to drive the hitch is shown in Figure 10. It serves to enumerate the main components of the system, and does not reflect specific routing of hydraulic lines (tank, pressure) or driving electronics. In one embodiment, the power loop uses a high- performance car battery as the primary power source. The battery drives the pump motor and the stepper motor, which in turn drive the hydraulic loop. The battery charge is maintained through power from the high voltage pack of the test vehicle.

In one embodiment of the hitch, the highest system flow rate of 5.3GPM comes from the performance limit of the flow valve. The OSPM 32 PB valve diverts flow through the cylinder ports, allowing reciprocal motion of the hitch. The valve is powered by a NEMA 42 stepper motor. This particular motor was selected out of convenience rather than peak performance, since the supporting electronics and hardware for this type of motor were already installed in the test vehicle during manufacturing. Since the valve delivers 32cc/rev, the benchmark hitch speed requires the stepper motor to rotate 382RPM peak. This rotation rate is typically achievable by stepper motors of this size, further discussion of motor performance is provided in the testing chapter.

The pump is a standard configuration of a 1 .6cc/rev gear pump, driven by electric motor. Pressure in the system is regulated by a gap-action controller, which attempts to keep the pressure in the range of 1300-1500psi, the rated pressure for the cylinder. This motor/pump combination can nominally supply 1 .1 GPM at 1500 psi. This is equivalent to moving the hitch ball only 16cm/s, while supporting the required 3000N lateral force. This shortcoming in performance is addressed by including and accumulator on the pressure line. The 0.25 gallon capacity accumulator can be charged by the pump, and can deliver stored fluid at up to 100GPM, which is far in excess of the 5.3GPM limit of the valve. Combining the pump and the accumulator, the system is able to produce the full speed hitch movement at a 20% duty cycle, and can maintain the full speed movement for 3.5s. Simulation results have shown that the active hitch can remove transient oscillation in approximately 3s, where the full speed movement is only required for the first oscillation period of the transient response.

The hydraulic components are routed using a combination of flexible hose and aluminum piping. Both types of selected tubing are rated to 3000psi, which is well above the expected high or maximum pressure in the system. Tubes were sized based on the SAE ARP994, a standard dealing with best-practice for hydraulic components. The primary concern for correctly sizing tubing is preventing cavitation and excessive head loss.

The extended Bernoulli equation that includes head loss (where / and K represent friction/loss factors of particular fittings or tubing material) shows that higher flow velocity will result in a higher pressure drop. If the pressure is low, such as at the inlet of the pump, vapor cavities can form, which damage the components when they collapse. The head loss is also a function of velocity squared, so larger tubes will prevent excessive head loss for a given volumetric flow rate. Based on these principles, ARP994 recommends high or maximum fluid velocities of 15-20ft/s in pressure lines, 10-15ft/s in tank lines, and 5ft/s in suction lines. Combining these recommendations with a high or maximum achievable flow of 5.3GPM, the tubes in this hydraulic system have a 3/8in inner diameter, with a larger 1 /2in hose for the suction line at the pump inlet.

In one embodiment of controller implementation and tuning,

The controller design was implemented through a Simulink build of the test vehicle, and was loaded onto the memory of the AutoBox. The I/O on the AutoBox are routed into the Simulink model through proprietary routing blocks. The Simulink build was made as simple as possible, to reduce the time required to rebuild the model when implementing changes. The active hitch module contains three sub-controllers: the main active hitch feedback controller, the low-level stepper motor controller, and the trailer brake controller.

The trailer brake controller may be used as a safety precaution where differential braking may be applied to the trailer if the trailer angle reaches a threshold value. It will also apply differential trailer braking if the driver depresses the brake pedal past a certain threshold. The brakes act through a relay block, so the brakes do not release until the trailer has settled.

Standard filtering techniques are used to extract a cleaner signal from the trailer sensors. A 200Hz refresh rate is chosen because it is twice the rate of a standard production vehicle, so it has additional information for research purposes, but is still suited for commercial sensors and controllers. Low-pass filters may be used to block the EM noise produced by powertrain motors. For numerical differentiation, signal noise is significantly increased, so more time steps need to be used on filtering of signal derivatives. Differentiation was implemented using an FIR filter that calculates the slope of the line running through a set of points by least squares regression. Least squares creates a better fit to the data than simply taking an average. Tthe slope of the line in a least squares regression can be formulated in the form of an FIR filter. Since the dependent variable (time) is increasing evenly, significant algebraic simplifications can take place, which removes the nonlinear terms from the least squares formulation and leaves a weighted sum of the time steps, where the weights are given by:

12/ - 6(N - 1)

R- 5 1

Pl N(N 2 - 1)

And where N is the chosen number of time steps used in the filter. The weights are negative symmetric, which means that the earlier time steps will be weighed negatively.

Attempts to drive the hitch at high speeds initially resulted in stalling of the motor. The stepper motor controller had to be tuned in software and in hardware to ensure that the hitch could move the required load at a reasonable speed. The stepper motor has 200 permanent magnet poles, but the motor driver allows for microstepping, where the drive sends interfering signals that make the motor behave as though it has more poles. This is useful for smoothing the motion of the hitch, specifically in reaction to

measurement noise on the kinematics sensors. There is a compromise to be made, since the use of microstepping introduces some hysteresis which results in a small loss in motor torque. Additionally, the high mircostepping signal require high frequency signalling from the ECU, and will cause a stall if the AutoBox cannot consistently produce the frequency content. A microstep setting of 6400 pulses/rev was found to be the best balance of noise reduction, speed, and torque handling.

The stepper motor is driven by its own feedback controller, which acts on the difference between the actual hitch position and the position requested by the main controller. Since the requested position is constantly changing, a certain tracking error will develop, where the hitch will lag behind its required position. As discussed above, the active hitch controller is unstable for delays of greater than 0.25s. Simply increasing the gain on the low-level stepper controller will cause excessive noise and controller resonances, so some compensating techniques are required to reduce or minimize the tracking error.

Feedforward control can be used to compensate for disturbances in a system, or to reduce or eliminate tracking error. In this case, it anticipates future hitch value requests by taking the derivative of the hitch request and applying a gain.

The feedforward compensator uses the linear regression filter to calculate the rate of change of the hitch request. Since numerical differentiation is noisy even when filtered, the feedforward gain must be set modestly. The selection of 0.3 for the feedforward gain resulted in a 50% reduction in peak tracking error over sinusoidal hitch requests, which is also reflected in the full scale test results.

As predicted in simulation, the addition of derivative action on the main controller was not effective, since the noise content of the differentiated signal is larger than the expected range of the signal. More extreme filtering on the signal simply results in non- trivial delays in measurement, which are more detrimental than neglecting the derivative action.

One advantage of the disclosure is that the apparatus may also assist in improving steerability of a trailer when it is being backed up.

Although the present disclosure has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present disclosure.

In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments. However, it will be apparent to one skilled in the art that these specific details may not be required. In other instances, well-known structures may be shown in block diagram form in order not to obscure the understanding. For example, specific details are not provided as to whether elements of the embodiments described herein are implemented as a software routine, hardware circuit, firmware, or a combination thereof. Embodiments of the disclosure or components thereof can be provided as or represented as a computer program product stored in a machine-readable medium (also referred to as a computer-readable medium, a processor-readable medium, or a computer usable medium having a computer-readable program code embodied therein). The machine-readable medium can be any suitable tangible, non-transitory medium, including magnetic, optical, or electrical storage medium including a diskette, compact disk read only memory (CD-ROM), memory device (volatile or non-volatile), or similar storage mechanism. The machine-readable medium can contain various sets of instructions, code sequences, configuration information, or other data, which, when executed, cause a processor or controller to perform steps in a method according to an embodiment of the disclosure. Those of ordinary skill in the art will appreciate that other instructions and operations necessary to implement the described implementations can also be stored on the machine-readable medium. The instructions stored on the machine-readable medium can be executed by a processor, controller or other suitable processing device, and can interface with circuitry to perform the described tasks.