Automates at NUV

Vehicle dynamics #8

Multi body Systems (MBS) consist of a finite number of rigid or flexible bodies. The bodies and particles are interconnected with each other and with the environment by springs, dampers and actuators as well as by bearings, joints and servomechanisms, all of them without mass.

Finite element systems (FES) consist of simple, non rigid elements like rods, beams, plates etc. with a finite number as degrees of freedom.

Continuous systems (COS) consist of non-rigidb odies with distributed mass and stiffness parameters.

The analysis of the different models is strongly depending on the kind and the time behavior of the acting forces.The following kinds of forces are distinguished:

1. External forces and internal forces,
2. Applied forces and constraint forces,
3. Surface forces and volume forces.

Vehicle dynamics #7

Now after Approaches of modeling, the physical model is needed on which mathematical analysis can be done.The first step is the choice of a "Physical Model" which is determined by the engineering task. Vehicles consist mainly of the mechanical components which can be modeled by

• Multi Body Systems (MBS),
• Finite Element Systems (FES),
• Continuous Systems (COS).

The range of application of these structural different modeling approaches
depends on the geometry and the stiffness of the components to be modeled.(SEE PIC).

However, the boundaries of these ranges of application are open, and the engineer has some freedom for his choice. The corresponding mathematical models have also different structures.

An important feature is the number of degrees of freedom characterizing the linear independent possibilities of motion of the physical model mathematically described by a corresponding number of time-varying generalized coordinates.

-AJ

Vehicle dynamics #6

On principle, there are two procedures known for modeling...
• the empirical approach, and
• the axiomatic approach.

The empirical approach is based on measurements with prototypes of components or vehicles, respectively, which are processed by identification methods resulting in a mathematical model.(FOR DETAIL REFER BOOKS).

The axiomatic approach results directly in a mathematical model by application of fundamental, already mathematically described physical principles. This model emphasizes the structure of the system as well as relations between the system parameters.(FOR DETAIL REFER BOOKS).

The mathematical description of complex dynamical systems requires in general a combination of both approaches. Whenever possible, the less expensive axiomatic approach will be applied. The missing parameter values have to be found by experiments, and the final results should be validated empirically. The modeling is considered to be satisfactory if theoretical
predictions coincide with the experimental findings.

In the following the axiomatic approach to modeling will be presented in detail for all the vehicle systems under consideration. To cover as many different designs as possible, firstly the components are treated separately by realistic models. Then, the components are assembled systematically resulting in the mathematical model of the global system easy to assess and efficient to be analyzed computationally.

-AJ

Vehicle dynamics #5

The basis of a theoretical analysis of vehicle systems is an appropriate mathematical model adapted to the given engineering task. The quality of results achievable on a system’s dynamical behavior depends on the underlying model.

Therefore, the mathematical model has to be as detailed as possible to represent accurately and completely all the essential properties of the vehicle system. On the other hand, the model has to be as simple as possible to allow efficient and fast simulations of the vehicle motions essential for manufacturers competing on a global market.

These conflicting requirements show that modeling is a difficult engineering task, in particular, for complex systems like today’s vehicles.For the modeling it is advisable to decompose the total system in subsystems,e.g. the components with interfaces for forces and motions clearly defined. Then, the subsystems may be modeled separately and composed by modular assembly to the mathematical model of the overall system. The modular concept allows different modeling approaches for the individual subsystems, it offers the required flexibility for design variations and it is essential for the lucidity of large complex systems.

-AJ

Vehicle dynamics #4

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.

-AJ

Vehicle Dynamics #3

After the basic understanding, Vehicle dynamics can be represented by mathematical models, which means the 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 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(MOI) 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 will be used.

-AJ

Vehicle dynamics #2

1.Safety- When we say safety we are not looking at the situation like crash, we are looking to safety in dynamics point of view. 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.

2.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.

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

Driver Interaction with 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.

-AJ

Vehicle dynamics #1

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 are-

1. Safety
2. Comfortably
3. Economically

-AJ