Understanding Driving Torque and Motion Limits in Multibody Dynamics

Welcome to the Multibody Dynamics for Automotive Applications using MotionView and MotionSolve blog series! In this chapter, we explore how to apply a driving torque and limit the motion of a joint in a four-bar mechanism. Additionally, we compare kinematic and dynamic simulations to understand their differences in multibody dynamics modeling. 

Setting Up the Driving Torque in MotionView 

In multibody dynamics simulation, torque plays a crucial role in driving mechanical systems. To begin, we deactivate the existing motion from the previous exercise and remove the initial velocity condition from Joint Zero. Next, we introduce a driving torque in the system. 

Steps to Apply a Driving Torque 

• Create a New Force Entity – Right-click on the force toolbar and name the torque appropriately (e.g., "Driving Torque"). 
• Set the Force Option – Choose Action-Reaction mode. 
• Select Rotation Properties – Define the torque as a rotational force. 
• Assign Torque to a Joint – Select Body 1 as the active body and Ground as the reaction body. 
• Define Torque Magnitude – Apply 150 Newton-mm in the Y-direction. 

After configuring the torque, we save the model and run the dynamic simulation using MotionSolve software. The animation reveals that the small bar in the four-bar mechanism completes one full rotation due to the applied torque. The speed is high because of the 150 N-mm torque, illustrating the importance of carefully selecting torque values in vehicle dynamics simulation. 

Applying Motion Limits with a BYSTOP Function 

To limit the motion of the four-bar mechanism, we use the BYSTOP function. This function defines an angular displacement constraint, preventing the joint from exceeding a set range. 

Steps to Apply the BYSTOP Function 

• Create a New Force Entity – Right-click on the force toolbar and name it "BYSTOP Torque". 
• Select Force Type – Choose Action-Reaction mode. 
• Set the Reference Frame – Keep it the same as the global frame. 
• Apply Rotation Properties – Change from Linear to Expression mode. 
• Build the BYSTOP Expression – Use the Expression Builder to define the function. 
• Define Limits – Set the lower bound as -10 × π/180 and the upper bound as +10 × π/180 (converted to radians). 

When we run the simulation, we notice that the driving torque moves the mechanism until it reaches the BYSTOP torque limit. The mechanism then bounces back, demonstrating how torque constraints affect system motion in automotive simulation software. 

Conclusion 

Applying driving torque and using the BYSTOP function to limit motion is essential in multibody dynamics for automotive applications. These techniques allow MotionView for automotive engineers to simulate real-world constraints in vehicle dynamics modeling. The next step is to analyze the differences between dynamic and kinematic simulations, which we will cover in the following blog. 

Stay tuned for more insights on multibody dynamics using MotionView and MotionSolve software! 

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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