Towing Trailer Stability Study using MotionSolve

John_Dagg_0
John_Dagg_0
Altair Employee
edited July 12 in Altair Exchange

Overview

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PREFACE

Driving a vehicle while hauling a trailer can be challenging, more so if the trailer is susceptible to instability. In the design and loading of a trailer it is crucial to be aware of the trailer’s center of gravity. A center of gravity behind the trailer’s axle can cause small disturbances to lead to complete trailer instability, a danger to the driver and others on the road.

INTRODUCTION

Physical vehicle testing can be performed to test the impact of trailer loading configurations, an expensive, time-consuming, and potentially dangerous task. Alternatively, multibody dynamics (MBD) simulation can be used to predict trailer behavior. This approach can be performed earlier in the design process to improve trailer design prior to manufacturing allowing for all trailer designs to be tested and compared. Potential software choices include Altair MotionSolve, MSC Adams, and Ansys Motion.

For this example, we will use Altair MotionSolve, an intuitive MBD software with extensive vehicle tools, to create a vehicle model with a trailer. We will test two weight distributions and examine the results in HyperView, a powerful post-processing tool used to review the animation results. The model uses a driver controller to emulate realistic driver behavior, and a MF-swift tire model which uses a Magic Formula steady state model, making it suitable for vehicle handling analysis. Finally, a flexible hitch towbar is utilized to account for the compliance of the structure and allows the prediction of towbar stresses.

Pre-Requisite

SOFTWARE REQUIREMENTS

Altair MotionView (2024 or newer)

Altair MotionSolve (2024 or newer)

MODEL FILES

Trailer_Model.zip (See attachments)

Usage/Installation Instructions

MODEL SETUP

This setup guide serves to demonstrate the overall steps required to build the model but is not a comprehensive tutorial.

  1. Open a new session in MotionView.
  2. Create a vehicle using the assembly wizard in vehicle tools.
    1. Front macpherson suspension with a stabilizer bar.
    2. Rear trailing arm suspension with a stabilizer bar.
    3. Electric powertrain and floor mounted battery pack.
    4. Independent FWD.
    5. Disk brakes with ABS.
  3. Define tire property files for the front and rear tires.
  4. Import trailer geometry and align it with the vehicle.
  5. Create bodies for each of the trailer graphics.
  6. Add AutoTires to the trailer.
  7. Connect the trailer components with joints.
  8. Connect the trailer to the vehicle with joints.
  9. Add a lateral disturbance force to the trailer which occurs at 5 seconds.
  10. Replace the trailer hitch with a flexible body prepared in HyperMesh.
  11. Create a road course event which ends after 15 seconds with an initial velocity of 50 mph.
  12. Import road graphics.

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MBD Model in MotionView after Setup

SIMULATION STEPS

  1. Open Trailer_Stable_Model.mdl or Trailer_Unstable_Model.mdl in MotionView.
  2. Run a simulation after selecting an output directory.
  3. Open the resulting .h3d in HyperView to review the animation.
  4. Graph key performance indicators in HyperGraph from the .plt in the results directory.

Post-Requisite

RESULTS

The simulation was performed for two possible weight distributions. One scenario has a center of gravity between the hitch and trailer axle. This results in stable trailer behavior as the oscillations decay over time. A second scenario depicts a center of gravity past the trailer axle. The disturbance causes the system to become unstable, and the oscillations increase in amplitude over time.

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Results for Two Trailer Weight Distributions

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Trailer Angle for Stable and Unstable Loading

An unstable vehicle experiences greater lateral forces on the tires and requires the driver carefully steer to remain on the road. Oversteer or understeer could worsen the situation causing the vehicle to exit the road.

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Tire Force for Stable and Unstable Weight Distributions

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Lateral Tire Forces

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Required Driver Steer Angle

A flexible trailer hitch allows contours of displacement and stress to be reviewed in HyperView. The results can indicate any stress hotspots for design changes or fatigue analysis depending on model intent.

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Von Mises Stresses on the Trailer Hitch after the Disturbance Force

CONCLUSION

Altair MotionSolve is a powerful MBD tool which can be used to analyze a wide range of mechanisms with extensive vehicle tools. We used MotionSolve to accurately predict the difference in performance for trailers with two distinct weight distributions. One configuration revealed the trailer would become unstable after a disturbance. Conversely, the second configuration would allow the trailer to remain stable despite disturbances, which can be attributed to the center of gravity location. In addition to vehicle motion, we plotted stresses in the trailer hitch and reviewed the difference in lateral tire forces. As a simple example, it demonstrates key advantages to using MBD software to analyze a system. More complex vehicle models and trailers can be modeled using a similar process to identify flaws and improve the design.

AUTHORS

John Dagg, Systems Engineering Intern

Spyridon Mallios, Technical Specialist - Model Based Systems

Christopher Fadanelli, Solution Engineer – Systems Integration

 

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