Introduction (Vehicle suspension analysis using Fuzzy Logic) Generally for analysis of vehicle suspension systems various types of vehicle suspension models were taken by the researchers. The most commonly used models are 1. Quarter car model 2. Half car model 3. Full car model The details of the three types are discussed below 1.1 Quarter car model On this particular model, only ¼ of the vehicle is taken into consideration to develop a vehicle suspension low level controller. Model is a two dimensional model because only movement on z direction is taken into consideration. The general representation of a quarter car model is shown in figure 1.1. It basically consists of a single wheel which is represented in the form of a spring. However in some cases the wheel can be considered as equivalent to a parallel combination of spring and a damper. The actual shock absorber is assumed to support only one fourth of the weight of the total car body mass including passenger’s weight.
Fig 1.1 Quarter car model
The advantages of these types of models are that they are simple and easy to analyze mathematical relations involved in the model. 1.2 Half car model Unlike quarter car model where only one wheel is analyzed half car model considers two wheels, viz. one front and one rear wheel. In this type of models half of the weights of the entire car including that of passengers are considered for analysis purpose. The main advantages of this type of models are 1. Vehicle pitch motions can be simulated. 2. Front and rear dampers and spring characteristics can be modeled differently which is also different on the actual vehicle. 3. Body motions and center of gravity effect can be simulated.
Fig 1.2 Half car model Fig 1.2 shows the general representation of half car model. As shown in the figure both the front wheel and back wheel supports half of the car weight by means of separate dampers attached to them. Model is again a two dimensional model which has a movement only on Z direction. Vehicle Models
Full Car model In full car model, total weights of the car body as well as the passengers are
considered and four wheels were taken for analysis. The pitch and roll motions of the car were also taken into consideration. Model is a three dimensional model which has a movement on Z direction. On full-car model 1. Vehicle pitch and roll motions can be simulated. 2. Different front and rear suspension system geometries can be modeled (for example, vehicle has independent suspension on the front and a solid dead beam on the rear and this can be geometrically modeled on a full car model). 3. Left and right hand side body and tire motions of the vehicle can be simulated separately. 4. Un-sprung and sprung mass motions can be evaluated for both front & rear right and the left hand side suspension systems. A full-car model is based on the four identical quarter-car models, which are coupled together by solid rods with respect to pitch and roll moment of inertia. Then braking, accelerating and steering influences should be reflected, i.e. longitudinal and lateral acceleration are considered. Therefore vehicle body roll and pitch, which cause the center of gravity movements and this is an important attribute for car stability during driving through the curves. In general, based on the damper used vehicle suspension systems can be classified into three types. They are 1. Passive 2. Semi Active 3. Active suspension systems.
Each type has its own advantages and disadvantages. However semiactive and active models are the one most commonly used in practical applications. The details of the three types are given in the following sections. 1.4 Passive suspension system Passive suspension system consists of an energy dissipating element, which is the damper, and an energy-storing element, which is the spring. Since these two elements cannot add energy to the system this kind of suspension systems are called passive. Figure 1.4 shows...
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