SYSTEM AND METHOD FOR ADJUSTING THE STEERING RATIO IN TRAILER OPERATION USING A STEER-BY-WIRE SYSTEM

Abstract

A vehicle uses a method for towing a trailer. A speedometer measures the vehicle's current speed. A trailer hitch length sensor receives the trailer's current length. A steering angle sensor measures the steering wheel angle of the vehicle's steering wheel. A processor determines the speed difference between the vehicle's current speed and a rated speed, determines the length difference between the current trailer length and a rated trailer length, calculates a dynamic steering ratio based on the length difference and the speed difference, determines a road wheel angle for the vehicle from the steering wheel angle and the dynamic steering ratio, and controls a road wheel actuator to achieve this road wheel angle for steering the vehicle.

Description

[0001] The present disclosure relates to towing a trailer behind a vehicle and in particular to a system and a method for dynamically adjusting a steering ratio of a steer-by-wire system of the vehicle in order to provide the same trailer coupling angle over different trailer lengths and towing speeds at the same steering angle.

[0002] Steering while towing a trailer can be a challenging maneuver, especially if the driver tows trailers of varying lengths as part of their daily routine. When turning, the trailer hitch angle between the vehicle and the trailer can vary based on the dynamic parameters of the trailer's movement, which are influenced by factors such as trailer length and vehicle speed. The driver must adjust their driving style to accommodate these changes in dynamic parameters. This requires a high level of skill. Therefore, it is desirable to establish a system and procedure to reduce or eliminate differences in trailer behavior when changes in these dynamic parameters occur. SUMMARY

[0003] According to an exemplary embodiment, a method for towing a trailer behind a vehicle is disclosed. The vehicle's current speed is measured. The trailer's current length is measured. A speed difference between the vehicle's current speed and a rated vehicle speed is determined. A length difference between the current trailer length and a rated trailer length is determined. A dynamic steering ratio is calculated based on the length difference and the speed difference. The vehicle's steering wheel angle is measured. A road wheel angle is determined for the vehicle from the steering wheel angle and the dynamic steering ratio. A road wheel actuator is controlled to maintain the road wheel angle for steering the vehicle.

[0004] In addition to one or more of the features described here, the method also includes calculating the dynamic steering ratio based on a vehicle wheelbase and a trailer distance between a trailer coupling point and a rear axle of the trailer.

[0005] In addition to one or more of the features described herein, the procedure further includes determining whether the trailer is coupled to the vehicle and performing either the calculation of the road wheel angle using the dynamic steering ratio if the trailer is coupled, or the calculation of the road wheel angle using a static steering ratio if the trailer is not coupled.

[0006] In addition to one or more of the features described herein, the procedure further includes steering the vehicle using the static steering ratio when the vehicle is not moving in reverse and / or the vehicle's speed is outside a selected speed range and / or the vehicle is swaying outside a selected stability range.

[0007] In addition to one or more of the features described herein, the method also includes determining an equation of motion for a trailer coupling angle based on the nominal trailer length and the nominal speed.

[0008] In addition to one or more of the features described herein, the method further includes the use of the dynamic steering ratio to obtain a selected trailer hitch angle for a selected steering wheel angle for a first trailer of a first length and to obtain the selected trailer hitch angle for the selected steering wheel angle for a second trailer of a second length.

[0009] In addition to one or more of the features described herein, the method further includes the use of the dynamic steering ratio to obtain a selected trailer hitch angle for a selected steering wheel angle when the vehicle is traveling at a first speed, and to obtain the selected trailer hitch angle for the selected steering wheel angle when the vehicle is traveling at a second speed.

[0010] According to another exemplary embodiment, a system for towing a trailer behind a vehicle is disclosed. The processor is configured to obtain the current speed of the vehicle, the current length of the trailer, determine the speed difference between the current speed of the vehicle and a rated speed of the vehicle, determine the length difference between the current trailer length and a rated trailer length, calculate a dynamic steering ratio based on the length difference and the speed difference, obtain the steering wheel angle of the vehicle, determine a road wheel angle for the vehicle from the steering wheel angle and the dynamic steering ratio, and control a road wheel actuator to obtain the road wheel angle for steering the vehicle.

[0011] In addition to one or more of the features described here, the processor is further configured to calculate the dynamic steering ratio based on a vehicle wheelbase and a trailer distance between a trailer coupling point and a rear axle of the trailer.

[0012] In addition to one or more of the features described herein, the processor is further configured to determine whether the trailer is coupled to the vehicle and to either calculate the road wheel angle using the dynamic steering ratio if the trailer is coupled, or to calculate the road wheel angle using a static steering ratio if the trailer is not coupled.

[0013] In addition to one or more of the features described here, the processor is further configured to steer the vehicle using the static steering ratio when the vehicle is not moving in reverse and / or the vehicle's speed is outside a selected speed range and / or the vehicle is swaying outside a selected stability range.

[0014] In addition to one or more of the features described here, the processor is further configured to determine an equation of motion for a trailer hitch angle based on the nominal trailer length and the nominal speed.

[0015] In addition to one or more of the features described here, the processor is further configured to use the dynamic steering ratio to obtain a selected trailer hitch angle for a selected steering wheel angle for a first trailer of a first length, and to obtain the selected trailer hitch angle for the selected steering wheel angle for a second trailer of a second length.

[0016] In addition to one or more of the features described here, the processor is further configured to use the dynamic steering ratio to obtain a selected trailer hitch angle for a selected steering wheel angle when the vehicle is traveling at a first speed, and to obtain the selected trailer hitch angle for the selected steering wheel angle when the vehicle is traveling at a second speed.

[0017] According to a further exemplary embodiment, a vehicle for towing a trailer is disclosed. The vehicle includes a speedometer for measuring the vehicle's current speed, a trailer hitch length sensor for obtaining the current trailer length, a steering angle sensor for measuring the steering wheel angle of the vehicle's steering wheel, and a processor.The processor is configured to determine a speed difference between the vehicle's current speed and a rated vehicle speed, a length difference between the current trailer length and a rated trailer length, calculate a dynamic steering ratio based on the length difference and the speed difference, determine a road wheel angle for the vehicle from the steering wheel angle and the dynamic steering ratio, and control a road wheel actuator to obtain the road wheel angle for steering the vehicle.

[0018] In addition to one or more of the features described here, the processor is further configured to calculate the dynamic steering ratio based on a vehicle wheelbase and a trailer distance between a trailer coupling point and a rear axle of the trailer.

[0019] In addition to one or more of the features described herein, the processor is further configured to determine whether the trailer is coupled to the vehicle and to either calculate the road wheel angle using the dynamic steering ratio if the trailer is coupled, or to calculate the road wheel angle using a static steering ratio if the trailer is not coupled.

[0020] In addition to one or more of the features described here, the processor is further configured to steer the vehicle using the static steering ratio when the vehicle is not moving in reverse and / or the vehicle's speed is outside a selected speed range and / or the vehicle is swaying outside a selected stability range.

[0021] In addition to one or more of the features described here, the processor is further configured to determine an equation of motion for a trailer hitch angle based on the nominal trailer length and the nominal speed.

[0022] In addition to one or more of the features described herein, the processor is further configured to use the dynamic steering ratio to obtain a selected trailer hitch angle for a selected steering wheel angle for a first trailer of a first length and to obtain the selected trailer hitch angle for the selected steering wheel angle for a second trailer of a second length, and / or to use the dynamic steering ratio to obtain a selected trailer hitch angle for a selected steering wheel angle when the vehicle is traveling at a first speed, and to obtain the selected trailer hitch angle for the selected steering wheel angle when the vehicle is traveling at a second speed.

[0023] The above features and advantages and other features and advantages of the disclosure are easily evident from the following detailed description when considered in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further features, advantages and details appear in the following detailed description only as examples, the detailed description referring to the drawings; they show: Fig. 1 a side view of a vehicle towing a trailer, according to an exemplary embodiment; Fig. 2 a schematic top view of the vehicle and the trailer according to Fig. 1; Fig. 3 an architecture of a software system for steering a vehicle using different steering ratios; Fig. 4 a release flowchart for a procedure that is executed in the controller to determine whether a dynamic steering ratio should be calculated and used in the steer-by-wire module; Fig. 5 a graphical representation of different angles over time for a vehicle towing a trailer using a constant steering ratio; and Fig. 6 A graphical representation of different angles over time for a vehicle towing a trailer using an adjustable steering ratio. DETAILED DESCRIPTION

[0025] The following description is merely exemplary and is not intended to limit the present disclosure, its application, or use. It should be recognized that throughout the drawings, corresponding reference numerals denote identical or equivalent parts and features. As the term "module" is used herein, it refers to a processing circuit arrangement that may include an application-specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or grouped), memory executing one or more software or firmware programs, a combinational logic circuit, and / or other suitable components providing the described functionality.

[0026] According to an exemplary embodiment, Fig. Figure 1 shows a side view 100 of a vehicle 102 towing a trailer 104. The vehicle 102 has a trailer hitch 106 (or coupling device) extending from a rear bumper of the vehicle along a longitudinal axis of the vehicle. The trailer hitch 106 generally has a ball or post 108. The trailer 104 has a drawbar 110 at its front end, which is hooked onto the post 108, thus coupling the trailer to the vehicle 102. The drawbar 110 is coupled to the trailer hitch 106 to allow rotational flexibility between the trailer 104 and the vehicle 102.

[0027] Various sensors on the vehicle 102 acquire measurements suitable for operating the vehicle to tow a trailer. These sensors include a steering angle sensor 112, a trailer hitch connection sensor 114, and a trailer hitch length sensor 116. The steering angle sensor 112 measures the steering wheel angle. The trailer hitch connection sensor 114 is located on the trailer hitch 106 and detects whether the trailer is attached to the vehicle. The trailer hitch length sensor 116 is located on the rear bumper of the vehicle and detects the distance between the rear bumper of the vehicle 102 and the front end of the trailer 104. The trailer hitch length sensor 116 can be an ultrasonic sensor.According to one embodiment, the trailer hitch length sensor 116 sends an acoustic or electromagnetic signal, receives a reflection of the signal, measures the time of flight of the signal and calculates the trailer hitch distance based on the time of flight.

[0028] The data from the sensors are provided to a steer-by-wire system 118. The steer-by-wire system 118 includes a controller 120 for performing steer-by-wire operation using the methods disclosed herein. The controller 120 may include a processing circuit arrangement that may contain an application-specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or grouped), memory that executes one or more software or firmware programs, a combinational logic circuit, and / or other suitable components that provide the described functionality.The controller 120 may contain a non-transient, computer-readable medium that stores instructions which, when processed by one or more processors of the controller 120, implement a method for determining a dynamic steering ratio between the steering wheel angle and the road wheel angle and for steering the vehicle using the steering ratio according to one or more embodiments described in detail herein.

[0029] A steering ratio is a relationship between the steering wheel angle at the steering wheel and the road wheel angle applied at the wheels. The steering ratio can be a constant value or can be configurable by software, as discussed here. According to various embodiments, the steer-by-wire system 118 calculates a road wheel angle (RWA) corresponding to the steering wheel angle (SWA) using either a static steering ratio or a dynamic steering ratio, sending a steering command to a road wheel actuator 122, which generates the road wheel angle at the vehicle's wheels.

[0030] Fig. Figure 2 shows a schematic top view 200 of the vehicle 102 and the trailer 104. Fig. 1. The top view 200 shows various parameters relevant to towing the trailer 104. The vehicle 102 shows a front axle 202 connecting the front tires and a rear axle 204 connecting the rear tires. Parameter c is the length of the vehicle's wheelbase (i.e., the longitudinal distance between the front axle 202 and the rear axle 204). Parameter e is a trailer coupling distance (i.e., the longitudinal distance from the rear axle 204 to a trailer coupling point 206 where the post 108 is connected to the drawbar 110). Parameter L is the length of the trailer 104 (i.e., the longitudinal distance from a rear axle 208 of the trailer 108 to the trailer coupling point 206).

[0031] During a turn, the vehicle 102 and the trailer 104 can form a non-zero angle with each other, as shown by the trailer coupling angle θ between the drawbar 110 and the trailer coupling 106 at the coupling point 206. The trailer coupling angle θ is measured between the longitudinal axis of the vehicle 102 and the longitudinal axis of the trailer 104. Arrow 210 indicates the forward longitudinal speed v of the vehicle 102.

[0032] Fig. 3 is an architecture 300 of a software system for steering a vehicle using different steering ratios. The architecture 300 includes the vehicle sensors 302, the steer-by-wire system 118, and the road wheel actuator 122. The vehicle sensors 302 provide various data. The data includes a steering wheel angle 304 (from the steering angle sensor 112), a trailer hitch bit 306 of the trailer (from the trailer hitch connection sensor 114), which indicates whether a trailer is attached to the vehicle, and a trailer hitch length 308 (from the trailer hitch length sensor 116).

[0033] The steer-by-wire system 118 includes a steer-by-wire module 310 and a monitoring control module 312, which run on a processor of the controller 120. The monitoring control module 312 performs calculations to control an operation at the steer-by-wire module 310 to tow the trailer 104 using either a static steering ratio between the steering angle and the road wheel angle or a dynamic steering ratio between the steering angle and the road wheel angle.

[0034] Box 314 calculates a trailer coupling angle θ based on the steering wheel angle 304 and the trailer coupling length 308. The trailer coupling angle θ is provided to a release module in box 320 and to a steering ratio calculator in box 322.

[0035] In box 316, a detection algorithm, based on the trailer coupling bit 306 of the trailer, determines whether a trailer is detected as attached to the vehicle. If no trailer is detected, the process continues to box 318. In box 318, a static steering ratio K is selected. The static steering ratio K can be a standard steering ratio defined by the manufacturer. The standard steering ratio K is provided to the steer-by-wire module 310. The steer-by-wire module 310 sends a road wheel angle command to the road wheel actuator 122 to generate the road wheel angle using the steering wheel angle 304 and the static steering ratio K.

[0036] If a trailer is detected back at box 316, the procedure continues to box 320. Release tests are performed in box 320 (as in Fig. (as shown in Figure 4) to determine whether the conditions are suitable for setting the steering ratio. If the release tests are passed, the procedure continues to Box 322. Otherwise, the procedure continues to Box 318 to allow the steer-by-wire module 310 to operate using the static steering ratio.

[0037] Box 322 calculates a dynamic steering ratio K based on various towing parameters. The dynamic steering ratio K is a steering ratio set to provide a consistent steering wheel angle for a given trailer configuration, such as any trailer length and / or towing speed. Box 324 provides the dynamic steering ratio K to the steer-by-wire module 310. The steer-by-wire module 310 generates a road wheel angle command using the steering wheel angle 304 and the dynamic steering ratio K. The steer-by-wire module 310 then provides the road wheel angle command to the road wheel actuator 122, based on the steering angle and the dynamic steering ratio.

[0038] Fig. Figure 4 shows a release flowchart 400 for a procedure executed in the controller (box 318) to determine whether a dynamic steering ratio should be calculated and used in the steer-by-wire system 118. The procedure begins in box 402. In box 404, the trailer connection is checked to determine whether a trailer 104 is coupled. The trailer connection can be confirmed by detecting a signal from a trailer brake and / or detecting a signal indicating a trailer connection status. If no trailer is coupled, the procedure continues to box 412. In box 412, the procedure ends to execute steering in the steer-by-wire module 310 using the constant steering ratio K. If a trailer is coupled, the procedure continues to box 406, returning to box 404.

[0039] In box 406, the vehicle's driving gears are checked to determine if the vehicle is in reverse. Reverse gear can be determined by a signal indicating the transmission status or by determining that the vehicle speed is less than a suitable forward speed threshold. If the vehicle is in reverse, the procedure continues to box 412. Otherwise (i.e., the vehicle is moving forward), the procedure continues to box 408.

[0040] Box 408 measures the vehicle speed. If the vehicle is outside a selected speed range, the procedure continues to box 412. The selected speed range may be a calibrated range. Otherwise (i.e., the vehicle is within the selected speed range), the procedure continues to box 410.

[0041] Box 410 measures trailer sway. Sway is a rapid lateral oscillation of the trailer that occurs under certain conditions or at certain speeds. If the trailer sway is outside a selected stability range, the procedure continues to Box 412. The stability range can be a calibrated range. Otherwise (i.e., the sway is within the selected stability range), the procedure continues to Box 412. In Box 412, the procedure continues to calculate a dynamic steering ratio for use by the steer-by-wire module 310.

[0042] The dynamic steering ratio K is determined using various parameters, such as the trailer coupling angle, trailer length, vehicle speed, vehicle wheelbase, trailer distance, steering wheel angle, and steering ratio. An equation of motion for the trailer coupling angle for a vehicle traveling at a given speed and a trailer of a selected length is shown in Eq. (1): θ˙=vLsinθ−vctanKδh(1+eLcosKδh) where v is the speed of the vehicle, L is the length of the trailer, c is the length of the wheelbase of the vehicle, e is the trailer coupling length measured from the rear axle to the trailer coupling point, K is the steering ratio, and δ h The steering wheel angle (or handwheel angle) is shown. A linearized form of Eq. (1) for small angles is shown in Eq. (2): θ˙=vLθ−(vc+vecL)Kδh Eq. (2) can be used for a standard trailer with a nominal trailer length L n to be solved, which is equipped with a standard speed or nominal speed v n is towed. If the nominal values ​​are substituted into Eq. (2), the equation of motion is as shown in Eq. (3): θ˙=vnLnθ−(vnc+vnecLn)Kδh

[0043] The nominal solution to the equation of motion can be used as a starting point for trailers of different lengths being towed at different speeds. The current speed v of the vehicle can be written as shown in Eq. (4): v¯=vn+Δv where Δv is the speed difference between the current speed and the rated speed v n Similarly, an actual pendant length L of the pendant (i.e., the actual pendant length) can be written as shown in Eq. (5): L¯=Ln+ΔL where ΔL is the difference in length between the current trailer length and the nominal trailer length L n is.

[0044] From Eq. (2) an equation of motion for the current trailer length L and the current velocity v can be written, as shown in Eq. (6), θ˙=(vn+Δv)(Ln+ΔL)θ−((vn+Δv)c+(vn+Δv)ec(Ln+ΔL))Kδh

[0045] A dynamic steering ratio K can be defined with respect to the static steering ratio K, as shown in Eq. (7). K¯=(ΔvΔL−(Δvc+ΔvecΔL)θδ)K

[0046] Using the dynamic steering ratio from Eq. (7), the equation of motion from Eq. (3) can be rewritten as shown in Eq. (8): θ˙=vnLnθ−(vnc+vnecLn)K¯δh

[0047] Eq. (8) can then be used by the steer-by-wire module 310 to steer the vehicle.

[0048] Fig. Figure 5 shows a graph of 500 different angles over time for a vehicle towing a trailer using a constant steering ratio. Time is shown in seconds (s) along the abscissa, while angle is shown in degrees (°) along the ordinate. A first curve, 502, represents one-tenth of a steering wheel angle (SWA / 10), while a second curve, 504, shows a steering wheel angle corresponding to the road wheel angle. The handwheel angle is rotated from zero degrees to 250 degrees in approximately 0.2 seconds. Because the steering ratio is constant (after approximately 0.2 seconds), the road wheel angle maintains a constant relationship to the handwheel angle over the time frame shown.

[0049] A third curve, 506, represents a trailer hitch angle for a vehicle towing a trailer 3 meters long. With a steering wheel angle of 250 degrees, the trailer hitch angle stabilizes at approximately -18 degrees. A fourth curve, 508, represents a trailer hitch angle for a vehicle towing a trailer 5 meters long. With a steering wheel angle of 250 degrees, the trailer hitch angle stabilizes at approximately -15 degrees. A fifth curve, 510, represents a trailer hitch angle for a vehicle towing a trailer 7 meters long. With a steering wheel angle of 250 degrees, the trailer hitch angle stabilizes at approximately -12 degrees.

[0050] Fig.Figure 6 shows a graph of 600 different angles over time for a vehicle towing a trailer using an adjustable steering ratio. Time is shown along the abscissa in seconds (s), while the angle is shown along the ordinate in degrees (degrees). A first curve, 602, represents one-tenth of a steering wheel angle (SWA / 10). A second curve, 604, shows a road wheel angle corresponding to the handwheel angle for a trailer 3 meters long. A third curve, 606, shows a road wheel angle corresponding to the handwheel angle for a trailer 5 meters long. A fourth curve, 608, shows a road wheel angle corresponding to the handwheel angle for a trailer 7 meters long.Because the steering ratio is adjusted based on the trailer length, the road wheel angle is different for each of the second curve 604 (L = 3 m), the third curve 606 (L = 5 m), and the fourth curve 608 (L = 7 m). The speed is assumed to be constant for this test to better illustrate the results when the trailer length changes. However, the same result is expected at different speeds.

[0051] A fifth curve 610 represents a trailer hitch angle for a trailer length of L = 3 m. A sixth curve 612 represents a trailer hitch angle for a trailer length of L = 5 m. A seventh curve 614 represents a trailer hitch angle for a trailer length of L = 7 m. Due to the use of the dynamic steering ratio, the trailer hitch angles for each of the lengths (L = 3 m, L = 5 m, L = 7 m) converge over time to the same value (e.g., approximately -15 degrees). As a result, it can be seen that the fifth curve 610, the sixth curve 612, and the seventh curve 614 converge over time to overlap each other.

[0052] Consequently, the steering angle required by the driver during a turn is the same regardless of the trailer length or vehicle speed. With a first trailer of a certain length, the driver can turn the steering wheel by a selected angle and achieve a selected trailer hitch angle between the vehicle and the trailer. With a second trailer of a different length, the driver can turn the steering wheel by the same selected angle and achieve the same selected trailer hitch angle. Similarly, if the vehicle is traveling at a certain speed, the driver can turn the steering wheel by a selected angle and achieve a selected trailer hitch angle. If the vehicle is traveling at a different speed, the driver can turn the steering wheel by the same selected angle and achieve the same selected trailer hitch angle.

[0053] The terms "one" and "an" do not denote a quantity limitation, but rather indicate the presence of at least one of the designated element. The term "or" means "and / or" unless the context clearly indicates otherwise. References throughout the application text to "an aspect" mean that a particular element (e.g., a feature, structure, step, or property) described in connection with that aspect is contained in at least one aspect described therein and may or may not be present in other aspects. Furthermore, it should be understood that the described elements in the various aspects can be combined in any suitable way.

[0054] When an element, such as a layer, film, area, or substrate, is described as being "on" another element, it may be located directly on top of that element, or there may be intervening elements. Conversely, when an element is described as being "directly on" another element, there are no intervening elements.

[0055] Unless otherwise specified herein, all testing standards are the most recent standard in force since the date of filing of this application or, if priority is claimed, the date of filing of the earliest priority application in which the testing standard appears.

[0056] Unless otherwise defined, the technical and scientific terms used herein have the same meanings as generally understood by a person skilled in the field to which this disclosure relates.

[0057] While the above disclosure has described exemplary embodiments, those skilled in the art recognize that various modifications can be made and elements can be replaced by their equivalents without altering its scope of protection. Furthermore, many modifications can be made to adapt a particular situation or material to the teachings of the disclosure without altering its essential scope of protection. Therefore, it is intended that the present disclosure is not limited to the specific embodiments disclosed, but includes all embodiments that fall within its scope of protection.

Claims

[1] Method for towing a trailer behind a vehicle, comprising: Measuring the current speed of the vehicle; Measuring the current length of the trailer; Determining the speed difference between the current speed of the vehicle and a rated speed of the vehicle; Determining the length difference between the current trailer length and a nominal trailer length; Calculating a dynamic steering ratio based on the length difference and the speed difference; Measuring the steering wheel angle of the vehicle; Determining a road wheel angle for the vehicle from the steering wheel angle and the dynamic steering ratio; and Controlling a road wheel actuator to obtain the road wheel angle in order to steer the vehicle. [2] The method of claim 1, further comprising determining whether the trailer is coupled to the vehicle and performing either (i) calculating the road wheel angle using the dynamic steering ratio when the trailer is coupled; or (ii) calculating the road wheel angle using a static steering ratio when the trailer is not coupled. [3] Method according to claim 2, further comprising steering the vehicle using the static steering ratio when: (i) the vehicle is not moving in reverse and / or (ii) the vehicle's speed is outside a selected speed range and / or (iii) the vehicle is swaying outside a selected stability range. [4] Method according to claim 1, further comprising determining an equation of motion for a trailer coupling angle based on the nominal trailer length and the nominal speed. [5] Method according to claim 1, further comprising using the dynamic steering ratio to obtain a selected trailer coupling angle for a selected steering wheel angle for a first trailer of a first length and to obtain the selected trailer coupling angle for the selected steering wheel angle for a second trailer of a second length. [6] System for towing a trailer behind a vehicle, comprising: a processor that is configured: to obtain the current speed of the vehicle; to obtain a current trailer length; to determine a speed difference between the current speed of the vehicle and a rated speed of the vehicle; to determine the difference in length between the current trailer length and a nominal trailer length; to calculate a dynamic steering ratio based on the difference in length and the difference in speed; to obtain a steering wheel angle of the vehicle; to determine a road wheel angle for the vehicle from the steering wheel angle and the dynamic steering ratio; and to control a road wheel actuator in order to obtain the road wheel angle in order to steer the vehicle. [7] System according to claim 6, wherein the processor is further configured to determine whether the trailer is coupled to the vehicle, and: either (i) perform the calculation of the road wheel angle using the dynamic steering ratio when the trailer is coupled; or (ii) perform the calculation of the road wheel angle using a static steering ratio when the trailer is not coupled. [8] System according to claim 7, wherein the processor is further configured to steer the vehicle using the static steering ratio when: (i) the vehicle is not moving in reverse and / or (ii) the vehicle speed is outside a selected speed range and / or (iii) the vehicle is swaying outside a selected stability range. [9] System according to claim 6, wherein the processor is further configured to determine an equation of motion for a trailer coupling angle based on the nominal trailer length and the nominal speed. [10] System according to claim 6, wherein the processor is further configured to use the dynamic steering ratio to obtain a selected trailer hitch angle for a selected steering wheel angle for a first trailer of a first length and to obtain the selected trailer hitch angle for the selected steering wheel angle for a second trailer of a second length.

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