CV Joint Performance and Durability in MotionSolve

John_Dagg_0

Introduction

In the world of automotive engineering, the performance and reliability of drivetrains relies on the design and performance of constant velocity (CV) joints. These critical components facilitate smooth torque transfer while accommodating varying angles between connected shafts, making their implementation essential for steering and suspension systems. Analysis and validation of CV joints, whether Rzeppa or universal, is crucial for understanding durability and performance.

One effective approach to this analysis is the use of simulation, particularly through the implementation of a half car vehicle model. This method allows engineers to study the dynamic behavior of CV joints under realistic operating conditions while minimizing complexity. By modeling half of the vehicle, it captures the essential dynamics without the computational overhead of a full vehicle model. This focused approach enables detailed examination of how suspension dynamics, road inputs, and driving conditions affect the performance of CV joints.

Altair’s MotionSolve provides engineers with a powerful tool for analyzing vehicle models. A vehicle assembly tool creates half- or full-car models in a few clicks, ready to be populated with vehicle parameters. Detailed CV joint models can be integrated with the vehicle models for a comprehensive analysis of the joints. Drive torque, steering inputs, and suspension travel can be adjusted to predict or validate performance across a wide range of vehicle conditions.

Building the Model

1. Go to File>Extensions and enable the Vehicle Tools extension.
2. Navigate to the vehicle tools tab.
3. Select Assembly in the Vehicle Tools toolbar.
4. Select the following options in the assembly wizard:
   
   Page 1: Front End of Vehicle
   Page 2: No Driveline
   Page 3: Vehicle Body – Body Fixed to Ground
   Front Subframe – None
   Front Suspension – Front SLA susp (1 pc LCA)
   Steering Linkages – Rackpin Steering
   Powertrain – None
   Tires – Tires
   Page 4: Steering Column – None Steering Boost – None
   Page 5: Front Shocks – None
   Front Spring – Front Coil Spring
   Front Stabilizer Bars – None
   Page 6: Front Jounce Bumpers – None
   Front Rebound Bumpers – None
   Page 7: Finish
   
5. Update the tire and road property files for the tire entity.
   1. Tire: fiala_195_55_R16.tir
   2. Road: DrumRoad_for_cv_joint.rdf
6. Import the CV joint model definition in the attached zip file. File > Import > MDL Definition
   
7. Update the CV Joint System attachments.
   
8. Create a road actuator body with the Ground CM Marker Point as the origin of the body’s CM Coordinate System.
9. Set the Road Reference Marker’s body to the new road actuator body.
10. Create a translational joint between the ground body and road actuator body at the Ground CM Marker Point.
11. Create a motion on the translation joint to control the displacement on the suspension.
12. Run an analysis.

Software Requirements

MotionView (2024 or newer)

MotionSolve (2024 or newer)

Model Files

CV_Joint_Half_Car.zip

MotionSolve_Auto_CVJoint_SolutionOverview.pdf

Running the Model

1. Open CV_Joint.mdl in MotionView.
   1. Run an analysis.
   2. Review results.
2. Open the .plt file in HyperGraph to review key performance indicators.
3. Open the .h3d file in HyperView to review the animation and CV joint forces.

Results

The overall motion of the vehicle and CV joint is shown in Figure 1. Vector plots can be used to show the suspension forces in Figure 2 and the contact forces for the CV joint in Figure 3.

Figure 1: CV Joint Motion during Suspension Travel

Figure 2: Suspension Forces

Figure 3: CV Joint Contact Forces

Fatigue life of CV joints is a critical design consideration. Multibody dynamics can be used to predict the loads on a CV joint under a wide range of operating conditions. Engineers can extract loads from the MBD model, like those shown in Figure 4 and Figure 5, and apply the loads to an FEA model to predict the cyclic stresses during operation.

Figure 4: CV Joint Ball Bearing – Inner Race Contact Forces

Figure 5: CV Joint Ball Bearing – Outer Race Contact Forces

In addition to informing accurate loading conditions for fatigue, the contact forces can be processed to find the vibrational frequency of the CV joint. Then engineers can tune the natural frequency of the system to prevent resonance in the CV joint or surrounding components.

HyperGraph also allows other performance metric to be measured and plotted in a few clicks. This includes data such as tire contact forces and slip angles.

Figure 6: CV Input & Output Shaft Velocities

Figure 7: Tire Vertical Force

Figure 8: Tire Longitudinal Force

Figure 9: Tire Longitudinal Slip

Conclusion

Simulation provides engineers with a timely, cost-effective method of validating the performance of CV joints before production. Combining the CV joint model with a half- or full-car vehicle model allows engineers to simulate a wide range of realistic vehicle conditions. This can help engineers optimize the design to minimize vibrations, maximize fatigue life, and ensure efficient power delivery. Drive torques, steering inputs, and suspension travel can be tuned to predict joint forces which can be used as inputs to stress or fatigue analysis. Ultimately, this comprehensive approach not only enhances the design process but also ensures that CV joints meet performance, durability, and safety standards before they reach production, reducing both development time and costs.

Authors

John Dagg, Systems Engineering Intern

Christopher Fadanelli, Solution Engineer – Systems Integration

Ananth Kamath Kota, Global Technical Manager - Systems Integration