Suspension System Comparison and plotting functions

Study of different Suspension System and plotting functions

Aim:

To use Simulink to plot a function and to understand the basics of Suspension system comparison.

Theory:

Traditionally automotive suspension system designs have been compromise between the three
conflicting criteria’s namely the road handling, load carrying capacity and passenger comfort. The suspension system must support the vehicle, provide directional control using handling manoeuvres and provide effective isolation of passengers and load disturbance.

In this project we are studying the effect of following three different suspension systems.

1.Shock Absorber block which includes linear stiffness and damping

2.Nonlinear Translational Spring and a Nonlinear Translational Damper specified by symmetric polynomials

3.Variable Translational Spring and Variable Translational Damper

We achieve adaptive suspension system by using a closed loop control by which spring constant is varied during the simulation and damping coefficient are adjusted to ensure critical damping is achieved.

Velocity Modelling

The velocity modelling for input of suspension system is provided using sine wave block and pulse generators.

sine model 1-->0.1*Sin(3t)

pulse generator 1-->Amplitude=1;period=120 sec; pulse width percentage=100/6; delay=0

sine model 2-->0.1*Sin(15t)

pulse generator 2-->Amplitude=1;period=120 sec; pulse width percentage=100/6; delay=120*2/6 s

sine model 3-->0.1*Sin(75t)

pulse generator 3-->Amplitude=1;period=120 sec; pulse width percentage=100/6; delay=120*4/6 s

Final velocity=product of (sine model 1,pulse generator 1)+product of (sine model 2,pulse generator 2)+product of (sine model 3,pulse generator 3)

The pulse generators are used to cut the sine wave to get a suddenly vaying velocity at required times.

The velocity output will be as shown below.

The above velocity model is passed through a Simulink P-S converter which converts input signal to a Physical signal.

Shock Absorber(linear stiffness and damping)

A shock absorber or damper is a mechanical or hydraulic device designed to absorb and damp shock impulses. It does this by converting the kinetic energy of the shock into another form of energy (typically heat) which is then dissipated. Most shock absorbers are a form of dashpot (a damper which resists motion via viscous friction).

In linear stiffness and damping the force varies linearly with respect to displacement or velocity.

Above figure shows a linear and non linear spring.

Non linear shock absorber

The variation of stiffnesss will be non linear.

The deformation happens till spring displacement becomes very low. Due to this large vibrations will be caused.

Variable shock absorber

The pitch of the spring varies as shown.

Result Simulink:

Above graph shows variation of sprung mass displacement with respect to velocity distribution in the wheel. The variation is too much forvariable shock absorber and least for linear shock absorber.

As seen above in graph for variable shock absorber the spring is initially prestressed due to ehich deflection is negative. When stiffness is decreassed in 40 to 80 sec the initial pre stress decreses and the dispacement reaches to zero position. The displacement is inversely proportional to stiffness of spring.

The above graph shows noise level variation in terms of power (dbm/Hz) of different shock absorber.

Conclusion:

The study has helped in understanding different shock absorber in real life applications. We come to the conclusion from graph that a linear shock absorber is the best one for damping the variation when vehicle runs on an uneven surface.

Function plotting

The function block was created in two ways. One using Matlab script function and other using plain function block

Results: