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Analysis of passive quarter model suspension system

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We often take suspension systems for granted, but nowadays it is a major concern for manufacturers to offer the best quality to the customer

The aims of a suspension system are

To 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 vehicle’s static weight. Because otherwise would be senseless to have a suspension system

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 suspension’s 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

Incorporating the vehicle body better known as the sprung mass

Suspension spring and damper

The unsprung mass which brings together the total mass of the suspension system including the wheel.

The tyre’s spring and damper since it acts as an elastic element as well

And the road that applies the force on the system being the disturbance

We have an upward force towards the vehicle body given by my dd

The 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 equation

We have an average mass for a quarter model

And an unsprung mass of

Spring stiffness and a very high tyre stiffness

Tyre Damping is taken as zero as it is insignificant due to the high stiffness

And the natural frequencies for the system

And the variable Csad is based on three conditions, which another variable comes into play

Ca 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 zero

Part 1 of 3 thesis study so this thesis will focus on the passive buildup

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

- 1. Analysis of Passive Quarter Model Suspension System; enhanced adaptation to Semi-Active control By: Matthew Fenech Tutor: Ing.Claire Seguna
- 2. Vehicle Suspensions Aims of a Suspension System •Vehicle Isolation from road disturbances •Link between the road and the vehicle •Supporting the vehicle’s static weight
- 3. Types of Suspension Systems •Passive •Active •Semi-Active • EH • ER • MRF
- 4. Scopes and Objectives ofWork • Research of passive & semi-active Suspension Systems • Mathematical modelling • Data acquisition (real) to be put in the model (20mph)(tyre) • Math models generation on SIMULINK® • Hardware Design Stages • Semi-Active Control Study • Semi-Active Model • Data analysis of both systems and the rig response
- 5. Mathematical Modelling Sprung Mass Unsprung Mass Road
- 6. Mathematical Modelling (Free body Diagram) 𝐹𝑠 = 𝑀 𝑦 (Upward Direction) y = 1 M1 [−ksy + ksx − csy + csx] Sprung Mass
- 7. Mathematical Modelling (Free body Diagram) 𝐹𝑠 = 𝑀 𝑦 (Upward Direction) x = 1 M2 [k 𝑠 y − x + C 𝑠 y − x − k 𝑢𝑠 x − r − C 𝑢𝑠 𝑥 − r ] Unsprung Mass
- 8. SIMULINK® Passive Model
- 9. ParametricValues ModelValues M1 Sprung Mass 287kg M2 Unsprung Mass 35kg Ks Sprung Mass Stiffness 25500N/m Kus Tyre Stiffness 145000N/m Cs Sprung Damping 2500Ns/m Cus Tyre Damping 0 fn sprung Sprung Natural Frequency 1.5Hz fn unsprung Unsprung Natural Frequency 16Hz
- 10. Semi-Active adaptation • Skyhook control • ON-OFF algorithm 1. Fa = cSad(y − x) 2. cSad = cmax, if ca > cmax ca, if cmin < ca < cmax cmin, if ca < cmin 3. ca = cskyy y−x , only valid when y y − x > 0 , otherwise ca=cmin
- 11. Semi-Active damping control
- 12. SIMULINK® Responses: Displacement, Step Passive 0.07115 m Semi-Active 0.05778 m
- 13. SIMULINK® Responses: Displacement, Bump Passive 0.01727 m Semi-Active 0.01865 m
- 14. SIMULINK® Responses: Acceleration, Step Passive 14.64 m/s2 Semi-Active 9.417 m/s2.
- 15. SIMULINK® Responses: Acceleration, Bump Passive 13.13m/s2 Semi-Active 7.165m/s2
- 16. SIMULINK® Responses:Wheel Deflection, Step Passive 0.006366m Semi-Active 0.018m
- 17. SIMULINK® Responses:Wheel Deflection, Bump Passive 0.0495 m Semi-Active 0.02501 m
- 18. Rig Design
- 19. Passive SuspensionTest Rig
- 20. Recommendations • Rig improvement • Cam Actuator, Motor Driven • LVDT • Acceleration Measurement • Structure Improvement • Further Frequency analysis
- 21. Conclusion Step Input Displacement (m) Acceleration (𝐦/𝐬 𝟐 ) Wheel Deflection (m) Passive 0.07115 14.64 0.006366 Semi-Active 0.05778 9.417 0.018 % Improvement 18.79% 35.6% -64.3% Bump Input Displacement (m) Acceleration (𝐦/𝐬 𝟐 ) Wheel Deflection (m) Passive 0.01727 13.13 0.0495 Semi-Active 0.01865 7.165 0.02501 % Improvement -7.3% 45.4% 49.47%
- 22. Thank you for your attention!
- 23. Questions?
- 24. Comfort Specs iso2631 Magnitude of OverallVibrationTotalValue Discomfort Response < 0.315ms−2 Not uncomfortable 0.315 ms−2 < 0.03 ms−2 Slightly uncomfortable 0.8 ms−2 < 1.6 ms−2 Fairly uncomfortable 0.5 ms−2< 1 ms−2 Uncomfortable 1.25 ms−2 < 2.5 ms−2 Very uncomfortable 2.0 ms−2 < Extremely uncomfortable
- 25. Costs €118.51 €497.32 €59.46 €6.00 Costs Raw Material Components Literature Services
- 26. Model Mass Acquisition Model & Specs WEIGHT Toyota Aygo, 1.0ltr, 5 Speed, 3 Door 1240kg Ford Fiesta, 4-Dr, sedan 1169kg Vw Polo 1030kg Bmw, 1-series, 116i 1350kg Citroen C2, 1.4i 956kg Average 1149kg
- 27. Spring Selection (Sprung Mass) Spring-Sprung Mass (Kg) Natural Freq.=1.5Hz Stiffness (N/m) Stiffness (N/mm) Static Deflection (m) 1 9.425 88.83 0.09 0.1104 2 9.425 177.65 0.18 0.1104 3 9.425 266.48 0.27 0.1104 4 9.425 355.31 0.36 0.1104 5 9.425 444.13 0.44 0.1104
- 28. Spring Selection (Unsprung Mass) Spring Unsprung Mass (Kg) Natural Freq.=16Hz K (N/m) K (N/mm) Static Deflection (m) Body mass 1.125 100.531 11369.78 11.37 0.0010 1 2.25 100.531 22739.57 22.74 0.0010 2 3.375 100.531 34109.35 34.11 0.0010 3 4.5 100.531 45479.14 45.48 0.0010 4 5.625 100.531 56848.92 56.85 0.0010 5
- 29. Rig 5Kg response
- 30. SIMULINK® Responses: RMS, Bump
- 31. Rig 0.5 Kg Response
- 32. Rig 0.5 Kg Response -20 -10 0 10 20 30 40 50 60 70 80 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Displacement(m) Time (sec) Test 1 Test 2 Test 3
- 33. SIMULINK® Responses: RMS, Step

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