Analysis of Passive Quarter Model Suspension System; enhanced adaptation to Semi-Active control

Analysis of Passive Quarter Model Suspension System; enhanced adaptation to Semi-Active control

By: Matthew FenechTutor: Ing.Claire Seguna

Good morning, I shall deliver my work I have carried out for this year, the title goes by Analysis of bla bla1

Vehicle SuspensionsAims of a Suspension SystemVehicle Isolation from road disturbancesLink between the road and the vehicleSupporting the vehicles static weight

When we define suspension system we expect to have an elastic element, usually a spring, a damping media and an applied mass.

We often take suspension systems for granted, but nowadays it is a major concern for manufacturers to offer the best quality to the customerThe aims of a suspension system areTo isolate the vehicle from road disturbances, reducing the vertical accelerations when a road irregularity is encountered by the moving vehicle. This is what defines comfort, To attach the road surface to the vehicle, this link is achieved by the suspension components, springs, dampers wishbones, stabilizer bars and steering components but pertaining ground contact with the tyre

And to support the vehicles static weight. Because otherwise would be senseless to have a suspension system

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Types of Suspension SystemsPassiveActiveSemi-ActiveEHERMRF

In the automotive sector, there are three types of suspension systems technologies.The passive, being a suspension system having fixed parameters such as spring constants and damping coefficients. Most of our vehicles are based on passive technologies

A recent trend appeared utilizing active suspension systems, where a force actuator is placed on top of each suspension strut where it reacts to the force exerted by the vehicle due to road irregularities. Such systems are being used by Mercedes (ABC), BMW (active dynamic wheel drive) and Audi.

Another system that has been conceptually developed by Citroen in the late 60s and recently has been implemented once again for these past 10 years is the semi-active suspension. This replaces the passive suspensions damper with a varying damper. These systems come either electrohydraulic (solenoid valve), Electro-rheological where a fluid changes its viscosity when subject to an electric field. And a Magneto-rheological system changes the viscosity by the change in magnetic field

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Scopes and Objectives of WorkResearch of passive & semi-active Suspension SystemsMathematical modelling Data acquisition (real) to be put in the model (20mph)(tyre)Math models generation on SIMULINK Hardware Design StagesSemi-Active Control Study Semi-Active ModelData analysis of both systems and the rig response

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Mathematical Modelling

Sprung MassUnsprung MassRoad

Starting off by generating a mathematical model by using this simple schematic. Incorporating the vehicle body better known as the sprung massSuspension spring and damperThe unsprung mass which brings together the total mass of the suspension system including the wheel.The tyres spring and damper since it acts as an elastic element as wellAnd the road that applies the force on the system being the disturbance5

Mathematical Modelling (Free body Diagram)

Sprung Mass

The dynamic equations will be generated By analysing the sprung mass free body diagramWe have an upward force towards the vehicle body given by my ddThe spring will try to pull back the body by that given force equation and the damping will always be opposing the direction of motion

Summing all forces together in the vertical direction and solving for y dd we get this equation6

Mathematical Modelling (Free body Diagram)

Unsprung Mass

Again for the unsprung mass7

SIMULINK Passive Model

The dynamic equations generated are then modelled on SIMULINK where blocks 2 & 3 represent the dynamic equations and blocks 1 & 4 represent the inputs to the system8

Parametric ValuesModel ValuesM1Sprung Mass287kgM2Unsprung Mass35kgKsSprung Mass Stiffness25500N/mKusTyre Stiffness145000N/mCsSprung Damping2500Ns/mCusTyre Damping0fn sprungSprung Natural Frequency1.5Hzfn unsprungUnsprung Natural Frequency16Hz

To acquire responses, real parametric values of vehicles were required and are as shown on the table.We have an average mass for a quarter modelAnd an unsprung mass ofSpring stiffness and a very high tyre stiffnessTyre Damping is taken as zero as it is insignificant due to the high stiffnessAnd the natural frequencies for the system9

Semi-Active adaptationSkyhook controlON-OFF algorithm

To adopt a semi-active control method, it was researched that the above conditions satisfy the adaptation, where the method of control is the Skyhook control, meaning that the passengers are as if they are hung up to the sky. Where the damping force is given by (1) where the variable is CsadAnd the variable Csad is based on three conditions, which another variable comes into playCa will change according to (3) where it will vary according to the change in relative velocities, and will only be valid if the function is greater than zero10

Semi-Active damping control

SIMULINK Responses: Displacement, Step

Passive0.07115 mSemi-Active0.05778 m

SIMULINK Responses: Displacement, Bump

Passive0.01727 mSemi-Active0.01865 m

SIMULINK Responses: Acceleration, Step

SIMULINK Responses: Acceleration, Bump

SIMULINK Responses: Wheel Deflection, Step

Passive0.006366mSemi-Active0.018m

SIMULINK Responses: Wheel Deflection, Bump

Passive0.0495 mSemi-Active0.02501 m

Rig Design

The idea is to design and manufacture a concept for a Suspension Rig Design, a scale down model having a sprung mass of 5Kg, but due to manufacturing constraints the load was reduced to 0.5Kg. It is used to achieve a response from a step input. Part 1 of 3 thesis study so this thesis will focus on the passive buildup18

Passive Suspension Test Rig

This is the rig.Offering only a 7-10% error from the predicted values of the rig.19

RecommendationsRig improvementCam Actuator, Motor DrivenLVDTAcceleration MeasurementStructure ImprovementFurther Frequency analysis

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Conclusion

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Thank you for your attention!

Thank you all for your attention, and Id like to thank also my tutor for guiding me throughout my work.22

Questions?

Comfort Specs iso2631

Costs

Model Mass AcquisitionModel & SpecsWEIGHTToyota Aygo, 1.0ltr, 5 Speed, 3 Door1240kgFord Fiesta, 4-Dr, sedan1169kgVw Polo1030kgBmw, 1-series, 116i1350kgCitroen C2, 1.4i956kgAverage1149kg

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Spring Selection (Sprung Mass)

Spring Selection (Unsprung Mass)

Rig 5Kg response

SIMULINK Responses: RMS, Bump

Rig 0.5 Kg Response

Rig 0.5 Kg Response

SIMULINK Responses: RMS, Step

Spring-Sprung

Mass (Kg)Natural Freq.=1.5HzStiffness (N/m)Stiffness (N/mm)Static Deflection (m)

19.42588.830.090.1104

29.425177.650.180.1104

39.425266.480.270.1104

49.425355.310.360.1104

59.425444.130.440.1104

Spring Unsprung

Mass (Kg)Natural Freq.=16HzK (N/m)K (N/mm)Static Deflection (m)Body mass

1.125100.53111369.7811.370.00101

2.25100.53122739.5722.740.00102

3.375100.53134109.3534.110.00103

4.5100.53145479.1445.480.00104

5.625100.53156848.9256.850.00105