Building a Four-Bar Mechanism in MotionView for Multibody Dynamics Simulation

Welcome to the Multibody Dynamics for Automotive Applications using MotionView and MotionSolve blog series! In this chapter, we will complete the four-bar mechanism model, integrate it with the automotive trunk lid assembly, and prepare it for vehicle dynamics simulation. This is a crucial step in multibody dynamics analysis, as it forms the foundation for automotive simulation tools used in mechanical system simulation.

Completing the Four-Bar Mechanism in MotionView

In the previous chapter, we developed the basic structure of the four-bar mechanism. Now, we will finalize the model by creating three additional points:

• Point G (X: 830, Y: 580, Z: 1080)
• Point H (X: 790, Y: 580, Z: 1088)
• Point I (X: 825, Y: 580, Z: 1109)

Once these points are created, they need to be assigned to cylindrical bodies to represent mechanical links. Each cylinder is fixed to Body 1, and their connectivity must be defined between the respective points. The cylinder radius is set to 2mm, ensuring accurate geometric representation in the multibody dynamics simulation.

Adjusting Center of Mass

After setting up the geometry, we shift the center of mass of Body 1 from Point 4 to Point G. This adjustment is necessary for accurate vehicle system modeling and ensures correct dynamic behavior in the multibody dynamics software.

• Defining Motion for the Mechanism
• Deactivating Existing Forces and Torques

Before applying new motion constraints, we deactivate:

• By Stop Torque
• Driving Torque

Assigning Motion Using a 2D Spline Curve

Instead of using a simple linear function, we import a CSV file containing a 2D spline curve that defines the motion profile. This is essential in multibody simulation software, as real-world mechanisms rarely operate under idealized conditions.

• Import the motion curve via the Curve Import Tool.
• Associate the curve with the motion function applied to the four-bar mechanism.
• Validate the motion curve using the "Show Curve" preview option.

Renaming Components for Clarity

For better visualization and understanding, we rename the parts:

• Follower Link → Body Follower
• Coupler Link → Body Coupler
• Input Link → Body Input

Setting Up Output Requests for Displacement Analysis

MotionView for automotive engineers allows us to request displacement outputs for further analysis. We define two types of outputs:

• Displacement Output Between Two Bodies
• Measures the movement of the input body relative to the ground.
• Expression-Based Displacement Calculation
• Utilizes the DX function to compute relative displacement between two reference points.

Saving and Running the Model

Once the setup is complete, we save the model and run the simulation. The MotionSolve solver processes the motion constraints, and we analyze the results in HyperView.

Conclusion

This chapter successfully completes the four-bar mechanism model, a critical step in multibody dynamics for automotive applications. The motion profile and outputs are now defined, preparing us for importing CAD components and simulating a real-world trunk lid mechanism in the next chapter. Stay tuned as we explore collision detection and advanced analysis techniques in MotionSolve for automotive engineers.

This blog is part of our ongoing Multibody Dynamics blog series. If you missed the previous posts, check them out here.

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