A Guide to Help FEA Engineers Get Started With Vehicle Dynamics - Part 1

When going for a test drive, customers often ensure that the vehicle drives well and feels good to drive. While those are basic requirements to fulfill from a customers' standpoint, engineers consider a lot more factors when dealing with vehicle dynamics, including:

• Is the vehicle fun and easy to drive?
• How are the dynamic steering response and feel?
• How is the drivability in terms of features? Is there smooth gear shift behavior, dynamic acceleration/deceleration, and smooth switch between drive modes?
• Is the vehicle durable and ensures no safety issues due to mechanical part failure?
• How is the mechatronic system experience in terms of sophisticated, smooth, and safe interaction between mechanics and controllers?

This post goes over the fundamentals of vehicle dynamics and suspension design, along with the latest trends in the field. It will allow you to gain practical knowledge of how the vehicle moves and how the suspension and steering behaves.

 

What Is Vehicle Dynamics?

 

 

Vehicle dynamics refers to the study of tires modeling, ride, mathematical modeling of suspensions, and handling of a vehicle. 

Simply put, vehicle dynamics studies the characteristic behavior of a vehicle in specific response to a change in its external environment. This change could be in multiple forms, including a wheel deflection due to a road input, longitudinal or lateral acceleration, or a roll due to steering input. 

The study of vehicle dynamics primarily revolves around two functions:

• Understanding the behavior of the vehicle under a certain driver input (relation between the tire and ground)
• Studying and verifying if the vehicle response is safe and comfortable to the passengers sitting inside

Vehicle dynamics engineers typically use CAE (Computer-Aided Engineering) for the development of a vehicle with MBS (Multibody Systems) and FEA (Finite Element Analysis). The concurrent use of these technologies is usually a standard in the automotive industry.

 

Main Factors affecting Vehicle Dynamics

 

There are multiple aspects of a vehicle's design which affect the dynamics. Some of these include distribution of mass, aerodynamics, suspension and steering, drivetrain & braking, and tires. Let's understand these in more detail here:

 

1. Distribution of Mass

Vehicle dynamics is highly considerate of mass, mass distribution, and the stiffness of the vehicle and its components. There are various attributes of vehicle dynamics, which are purely due to mass and its distribution. Among these are:

• Center of mass
• Roll movement
• Sprung mass
• Unsprung mass
• Moment of inertia
• Weight distribution

 

2. Geometry and Kinematics of Moving Components and Tires

Among the aspects of vehicle dynamics which are purely due to geometry and kinematics of moving components and tires are:

• Instantaneous centers – motion and roll center height
• Contact patch deflection (track change)
• Pitch geometry

 

3. Most Contributing Subsystems: Suspension, Steering Frame, Aerodynamics

 

 

A detailed and clear understanding of vehicle dynamics is required for predicting the behavior of any vehicle under different conditions. Responses of different components and intuitive feedback to the driver governs safety and handling in general. 

To help achieve this objective, the most contributing subsystems in vehicle dynamics include:

• The suspension component (spring and damper)
• The vehicle body (spring-mass)
• Tires (unsprung mass)

The suspension of a vehicle should provide the optimum kinematics of the wheels and should have minimum unsprung mass. This is why almost all race cars are equipped with a double suspension system in connection with their optimal kinematic properties.

 

4. Aerodynamics

Following are some attributes or aspects of vehicle dynamics which are purely geometric and aerodynamic in nature:

• Automotive
• Automobile drag coefficient
• Downforce
• Automotive aerodynamics

 

Current Trends in Vehicle Dynamics

There are two main trends witnessed in automotive applications. One is vehicle design itself. The second trend involves the use of modeling and simulation to complement and support the process of vehicle development and design.

 

Vehicle Design

Vehicle design is a complicated area and requires knowledge from various areas, including mechanical design, control systems, and electronics development. 

Such systems typically involve time and cost to develop. Because of this, a general vehicle system simulation is a cost-efficient and safe way to test automotive applications.

There are multiple other aspects of vehicle design:

 

1. Suspension Kinematics

Suspension kinematics can have several different purposes, from improving comfort to increasing traction in rough terrain. Irrespective of its purpose, suspension always works by the same principle that a spring suspends the rider while a damper absorbs energy coming from impacts on the rear wheel.

 

2. Suspension Ride and Roll

Vehicle suspension designers are continuously trying to achieve a compromise between handling and control performance requirements and the conflicting dynamic ride. 

Vehicle suspensions are, therefore, designed with soft springs coupled with auxiliary roll stiffness mechanisms to achieve a compromise between ride, handling, and control performance and efficiently manage space requirements of the vehicle.

 

3. Steering Kinematics

The steering kinematics mechanism is used in vehicles for changing the directions of the wheel axles with reference to the chassis to move the vehicle in the desired path.

 

4. Frame Design

One of the important stages during the vehicle designing process is the proper development of the chassis and frame of the vehicle, especially for special heavy vehicles. 

Among the most interesting methods for chassis and frame design is the SSS (Simple Structural Surfaces) method, which is a simple analytical approach for initial analyses of a preliminary design concept.

 

5. Tire Modeling

The recent years have seen various studies attracting attention on vehicle dynamics modeling, especially on tire modeling. As the tire is the only and most important part that connects the vehicle with the road, tire modeling plays a critical role in the overall vehicle dynamic modeling. 

The modeling and properties of tires under different conditions have been studied by experts and are divided into three main types:

• Empirical and semi-empirical
• Analytical
• Finite element analysis (FEA)

 

Vehicle Dynamics Simulations

Simulation software used for validation and testing is a well-established process in the field of engineering. However, recent advances in software, coupled with increased pressure from competition and regulatory requirements, are further driving simulation earlier into the design and concept stages of new product development.

Simulation during the design phase of vehicle development gives engineers the required ability to adapt and react to problems and issues much earlier. This gives them the advantage of reduced costs and development times, more reliable validation, and better-performing vehicles.

Among the main areas in the simulation are:

• Static simulation
• Quasi-static simulation
• Transient simulation
• HIL simulation

Static and quasi-static simulation both refer to models where there is no dependency on time. Quasi-static simulation typically is for a mechanism that is moving so slowly, that it is practically static.

In the case of transient analysis, it requires the material to have a density so that acceleration loads on the mass of the vehicles can be calculated.

HIL or hardware in the loop system consists of a computer simulation of the vehicle and the vehicle surroundings. In this, an active steering system with a real-time controller and sensor hardware is generally integrated into the control loop. Steering interventions by both the driver and an active actuator are then fed into the simulation and enable assessments of vehicle stability and safety performance.

 

Conclusion

As the automotive industry is going through a rapid growth phase, vehicles have become more complex and sophisticated. Vehicle development today involves an integration of both electrical and mechanical systems. As such, FEA engineers need to understand the underlying concepts of vehicle dynamics for better job prospects.

If you wish to learn more about the fundamentals of vehicle dynamics and the latest trends in the field, do consider enrolling in Skill-Lync's Vehicle Dynamics course today.