Integrating the Steering System in Multibody Dynamics Simulation

Welcome to the Multibody Dynamics for Automotive Applications using MotionView and MotionSolve blog series. In this chapter, we take another step forward in vehicle system modeling by integrating a steering system into our simple car model. Steering is a critical part of multibody dynamics for automotive applications, as it dictates vehicle maneuverability and stability. We will also explore how to define couplers, which synchronize steering motion with wheel movement. 

Importing and Understanding the Steering System 

To begin, we import a partially completed steering system into the existing multibody simulation software environment. The steering system includes: 

• A steering wheel body. 
• Three graphical components—steering wheel, steering shaft, and an indicator. 
• A revolute joint between the vehicle body and the steering wheel. 
• Steering motion to control the system. 

Additionally, the steering system contains attachments such as: 

• Steering wheel center attachment. 
• Vehicle body attachment. 
• Steering shaft attachment. 
• Left and right cylindrical joint attachments. 

These attachments will be used to couple the steering motion with the front wheels, ensuring synchronized movement. 

Defining Couplers in MotionView 

Couplers in MotionView software define a ratio of displacement between joints, allowing the front wheels to turn in proportion to the steering wheel movement. 

Steps to Add Couplers in MotionView 

• Right-click on the steering system > Add Coupler. 
• Define the first coupler: Steering to Left Wheel. 
• Define the second coupler: Left Wheel to Right Wheel. 
• Select the number of joints to constrain (2 or 3). 
• Assign the first joint to the steering wheel joint and the second to the left cylindrical joint (for steering to left wheel). 
• For the second coupler, connect the left cylindrical joint to the right cylindrical joint. 
• Change the motion type to "Rotational" and set an initial ratio of -1 (we will fine-tue it later). 

At this stage, the steering system is linked to the front wheels, but the motion needs to be adjusted to achieve a realistic turning effect. 

Fine-Tuning the Steering Motion 

• Deactivate the original steering motion from the front suspension. 
• Modify the steer motion in the properties tab by changing the type from "Linear" to "Expression" and entering: 30×S2×π×time30 \times S2 \times \pi \times \text{time}30×S2×π×time This expression helps define steering wheel rotation in radians per second. 
• Run the initial simulation and observe the wheel rotation. 

Initially, the wheels turn too aggressively, indicating that the coupler ratio needs fine-tuning. By adjusting the steering ratio to 20:1, the simulation produces a more realistic steering response. 

Conclusion 

The steering system plays a crucial role in multibody dynamics simulation by enabling realistic vehicle maneuvering. By defining couplers and adjusting motion expressions, we ensure that the wheels respond appropriately to steering input. This step is essential in automotive multibody simulation for accurately modeling vehicle behavior. 

In the next chapter, we will introduce road modeling and contact simulation, allowing our vehicle to move realistically along a surface. Stay tuned! 

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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