A motivation to look on Vehicle dynamics

As the name suggest, we study about vehicles and its motion. When we talk about vehicle no of things come to our mind first thing that come to mind is the part of the vehicle. What constitutes the vehicle? The components that are going to be used in Vehicle dynamics study are divided into three main categories- Power (Engine, Gear box, axle), Chassis (Number of subsystems like suspension , Steering, Tires Wheel), Body. All these sub system are going to work in coordination to move the vehicle from one place to another.

Vehicle main purpose is to carry people. It has to do what he wants to do in effective and very prompt way. When they do, they have 3 important points that should be kept in mind-

1. Safety
2. Comfortably
3. Economically

When we say safety we are not looking at the situation like crash, we are looking to safety in dynamics point of view. Safety means vehicle has to listen to driver.  We mean when a vehicle turns how safe we are. When we break how it behaves and so on.

Comfort- We look how our comfort, as we travel in vehicle is affected. What are the sub systems that are going to affect comfort? How does road profile interact with the vehicle and affect your comfort. And more importantly what defines comfort.

Economy is not of vehicle dynamics consideration. Vehicle dynamics study does not include engine but tires are important aspects and how it affects economy.

Driver Interaction with the vehicle which means when we give steering to vehicle, He may accelerate the vehicle and may break the vehicle and so on. He interacts with the vehicle by means of things which is around him. Because of this interaction there is response of the vehicle as it responds as acceleration or deceleration.

We study Vehicle dynamics by using mathematical models, which means vehicle is represented by set of mathematical differential equation. Vehicle will reduced into system with input and output. This mathematical model will have input from the driver and it will give a set of output,  like in control system.

When we talk about dynamics we have to talk about newton equation which will create our basics. That being basic the language of defining vehicle is going to be different. It will be in terms of mass of the vehicle, Moment of Inertia of the vehicle. We will talk about stiffness of spring which form part of suspension system. We will talk about damping. We will talk about compliance’s.

Mathematical model looks the vehicle at very different prospective in terms of different quantities. All the dynamics we have done throughout carrier will be used here.

We have ISO standard to understand vehicle behavior.  For example we want to take over the vehicle in actual scenario on a highway what we do, we do double lane change or single lane change. To understand how my vehicle is going to behave, there is test in ISO called DLC or SLC for this.

Take an example of Pulse test. A steering input of 40 degree and change it back to zero in a second is an example of pulse test. We may not be using it in our day to day life but it brings out the dynamics of our vehicle. J-Hook test an example, these test brings out the extremities condition of vehicle.

So what is done is there are test which are done by either input to steering or through brake or acceleration these are input to Mathematical model. The output we are going to look on is the comfort level and safety. Let’s take the condition of braking so I said I want safety during breaking what does that mean? How does this output look like, if we want to look at the safety we are going to see stopping distance, acceleration, velocity.

These are some of the important aspects which we come through via vehicle dynamics. So before making of any vehicle concepts of vehicle dynamics should be clear.

Books to be followed are-

• Gillespie The fundamental of vehicle dynamics
• Reya and Tailor – Vehicle Dynamics Theory and Explanation
• Hans Pacejka Tyre and Vehicle dynamics
• Bernd hiebing chassis handbook

Do share your knowledge with us on vehicle dynamics. mail us on rohit@bajatutor.org , bajatutor@gmail.com