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Suspension system for any vehicle


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The simulation of a vehicles suspension system represents an important part of how the driver experiences ride quality. Without a suspension system, a vehicle acts in a stiff and uncomfortable way. The characteristics of a vehicles performance are dependent on the properties of the suspension. A model of this system would enable a manufacturer to test how certain changes to the properties change the behavior of the vehicle. This way they are able to see how the stiffness of the spring and damper in the suspension system affects the ride experience before building an actual car. This can also reduce the cost of development. The most basic suspension system consists of a spring and shock absorber and also includes the stiffness of the tire being used. More complex suspension systems consist of sensors that take into account and compensate for traction control, engine torque, steering, and braking systems.

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Suspension system for any vehicle

  2. 2. ABSTRACT The simulation of a vehicles suspension system represents an important part of how the driver experiences ride quality. Without a suspension system, a vehicle acts in a stiff and uncomfortable way. The characteristics of a vehicles performance are dependent on the properties of the suspension. A model of this system would enable a manufacturer to test how certain changes to the properties change the behavior of the vehicle. This way they are able to see how the stiffness of the spring and damper in the suspension system affects the ride experience before building an actual car. This can also reduce the cost of development. The most basic suspension system consists of a spring and shock absorber and also includes the stiffness of the tire being used. More complex suspension systems consist of sensors that take into account and compensate for traction control, engine torque, steering, and braking systems.
  3. 3. 1 TABLE OF CONTENTS: LIST OF FIGURES NOMENCLATURE CHAPTER-1 INTRODUCTION 1.1 Suspension systems 1.1.1 Types of Suspension systems according to location 1.1.2 Front Suspension 1.1.3 Rear Suspension 1.1.4 Types of springs used in suspension system 1.1.5 Types of dampers used in suspension system 1.1.6 Types of suspension system according to no of shocks 1.1.7 Objectives of suspension system CHAPTER-2 LITERATURE REVIEW 2.1 Study of FZ Suspension system 2.2 Study of Coil Springs 2.3 Study of damper 2.3.1 Advantages of Mono tube damper over twin tube damper 2.4 Working inside damper 2.5 Conventional spring damper assembly CHAPTER-3 DESIGN PROCESS OF SUSPENSION SYSTEM 3.1 Step 1: Decide the thickness of damper cylinder 3.2 Step 2: Diameter of piston 3.3 Step 3: Piston rod diameter 3.4 Step 4: Estimation of Damping Force according to loading 3.5 Step 5: Estimation of force acting on spring and finding out stiffness of spring 3.6 Step 6: Design of spring 3.7 Step 7: Selection of fluid for damper
  4. 4. 2 CHAPTER-4 MODELLING IN CREO 4.1 Damper Cylinder 4.2 Piston with piston rod 4.3 Floating plate 4.4 Spring: 4.5 Assembly of spring and damper CHAPTER-5 STRESS ANALYSIS IN ANSYS 5.1 Meshing of assembly [Finite Element Analysis] 5.2 Fixed Support 5.3 Damping Force [1260 N] 5.4 External load [2000 N] 5.5 Equivalent stress 5.6 Maximum shear stress CHAPTER-6 CONCLUSION REFERENCES
  5. 5. 3 LIST OF FIGURES:  Figure 1: Dependent suspension  Figure 2: Twin I-Beam independent suspension  Figure 3: Type 1 coil spring  Figure 4: Type 2 coil spring  Figure 5: Torsion bar  Figure 6: Double Wishbone Suspension  Figure 7: Independent rear suspension  Figure 8: Coil Spring  Figure 9: Coil Spring in a bike  Figure 10: Leaf Spring  Figure 11: Leaf spring in truck  Figure 12: Twin tube damper  Figure 13: Mono tube damper  Figure 14: Mono tube damper  Figure 15: Conventional Spring Damper assembly  Figure 16: Damper Cylinder Creo model  Figure 17: Piston with piston rod Creo model  Figure 18: Floating plate  Figure 19: Coil Spring Creo model  Figure 20: Assembly of spring damper in creo  Figure 21: Meshing of assembly Ansys  Figure 22: Fixed Support Ansys  Figure 23: Damping force Ansys  Figure 24: External load Ansys  Figure 25: Equivalent stress Ansys  Figure 26: Maximum shear stress Ansys
  6. 6. 4 NOMENCLATURE: Do : outer diameter of cylinder Di : inner diameter of cylinder T : thickness of cylinder σ : maximum allowable stress Pmax : maximum pressure in cylinder E : energy per stroke m : sprung weight g : acceleration due to gravity h : damping distance s : damping height DCF : damping correction factor ς : Damping ratio Fgas : force due to gas ressure Pgas : pressure of gas Arod : area of piston rod K : stiffness of spring P : load on spring δ : deflection of spring G : shear modulas Nt : no of turns of spring 𝜁 : permissible shear stress
  7. 7. 5 Sut : ultimate stress of spring material Kw : wahl factor C : spring index d : wire diameter Dmean : mean diameter of spring p : pitch of the spring μ : viscosity of damping fluid D : equivalent diameter of flow Vavg : average velocity of piston P1 : pressure above the piston P2 : pressure below the piston
  9. 9. 7 1.1 Suspension systems For many years vehicle dynamics engineers have struggled to achieve a compromise between vehicle handling, ride comfort and stability. Every automotive suspension has two goals: passenger comfort and vehicle control. Comfort is provided by isolating the vehicle’s passengers from road disturbances like bumps or potholes. Control is achieved by keeping the car body from rolling and pitching excessively, and maintaining good contact between the tire and the road Today’s vehicle suspensions use hydraulic dampers (”shock absorbers”) and springs that are charged with the tasks of absorbing bumps, minimizing the automobiles body motions while accelerating, braking and turning and keeping the tires in contact with the road surface. Typically, these goals are somewhat at odds with each other. A typical vehicle suspension is made up of two components: a spring and a damper. The spring is chosen based solely on the weight of the vehicle, while the damper is the component that defines the suspensions placement on the compromise curve. Depending on the type of vehicle, a damper is chosen to make the vehicle perform best in its application. Ideally, the damper should isolate passengers from low-frequency road disturbances and absorb highfrequency road disturbances. Passengers are best isolated from low-frequency disturbances when the damping is high. However, high damping provides poor high frequency absorption. Conversely, when the damping is low, the damper offers sufficient high-frequency absorption, at the expense of low-frequency isolation. The need to reduce the
  10. 10. 8 effects of this compromise has given rise to several new advancements in automotive suspensions. 1.1.1 Types of Suspension systems according to location 1. Front Suspension 2. Rear Suspension 1.1.2 Front Suspension Types of front suspension 1. Dependent Suspension 2. Independent Suspension 1. Dependent Suspension  Dependent front suspension uses a solid axle.  It uses one steel or aluminum beam extending the width of the vehicle. The beam is held in place by leaf springs.  Solid axle is used in truck and off-road vehicles. [figure 1]
  11. 11. 9 2. Independent Front Suspension  It was developed in the 1930's to improve vehicle ride control and riding comfort.  Sprung weight is reduced, creating a smoother ride.  Twin I-Beam, Type 1 Coil Spring, Type 2 Coil Spring, Torsion Bar, Double Wishbone. A. Twin I-Beam  Similar to the solid axle.  Improves ride and handling.  Improves load carrying ability.  Used on pickups, vans and four-wheel drive vehicles. [figure 2]
  12. 12. 10 2. Type 1 Coil Spring  upper control arms  lower control arms  2 steering knuckles  2 spindles  2 upper ball joints  2 lower ball joints  Bushings  Coil springs  Shock Absorbers  Short-arm/long-arm, or the parallel arm design figure 3] 3. Type 2 Coil Spring  Coil spring is mounted on the upper control arm.  Top of the spring is attached to the frame.  Upper ball joint receives the weight of the vehicle and the force of the coil spring.  Makes it the load carrier.
  13. 13. 11 [figure 4] 3. Torsion Bar  No coil or leaf springs.  Supports the vehicle weight and absorbs the road shock.  Performs the same function as a coil spring.  Supports the vehicle's weight. [figure 5] 4. Double Wishbone  Type of strut suspension.  More aerodynamic hood line.  Portion of the strut forms a wishbone shape.
  14. 14. 12  Does not rotate when the wheels turn. [figure 6] 1.1.3 Rear Suspension: 1. Independent rear suspension [figure 7] Some other types of rear suspension are :  Semi-independent rear suspension  Live axle suspension 1.1.4 Types of springs used in suspension systems:
  15. 15. 13 1. Coil spring [figure 8] [figure 9]
  16. 16. 14 2.Leaf Spring [figure 10] [figure 11]
  17. 17. 15 1.1.5 Types of dampers used in suspension 1.Twin tube damper [figure 12] Twin tube damper use an inner and outer tube which separate the oil and gas inside the damper. The smaller inner tube houses the piston shaft assembly, base valve, and oil. The outer tube contains both nitrogen gas and the damper oil. Twin tube dampers are the most commonly used type of dampers by OEM and aftermarket manufacture as they are the cheapest damper to make. However, twin tube dampers do not perform as well as mono tube dampers as the oil heats up and destabilises under extreme usage. 1. Mono tube damper Mono tube dampers use a single outer tube. The oil and nitrogen gas inside are separated by a free piston. Mono tube dampers use much higher gas pressure than twin tube dampers to better stabilise the oil inside under extreme usage.
  18. 18. 16 [figure 13] The advantages of the mono tube design are larger internal parts, which mean greater damping force, increased oil capacity, improved heat dissipation, and the ability to function when inverted. Mono tube dampers are found in some OEM vehicle applications, mainly higher end performance vehicles such as EVO MR, WRX STi, Porsche, etc. 1.1.6 Types of suspension according to number of shocks 1. Dual shock suspension 2. Mono shock suspension 1. Dual shock Suspension The first motorcycle rear suspension was called dual shock suspension. It was created in around 1913. It consisted of two pairs of spring and damper. All the loads acting at the rear of the motorcycle are divided on the two spring damper mechanism.
  19. 19. 17 2. Mono shock Suspension Mono-Shock motorcycle rear suspension was created in the late 80′s and in many applications has more advanced performance than that of the twin-shocks. Single shock rear suspension requires less maintenance and adjustments. In this type all the loads are damped by a single spring damper mechanism. On a motorcycle with a mono-shock rear suspension, a single shock absorber connects the rear swing arm to the motorcycle's frame. Typically this lone shock absorber is in front of the rear wheel, and uses a linkage to connect to the swing arm. Such linkages are frequently designed to give a rising rate of damping for the rear. Mono-shocks are said to eliminate torque to the swing arm and provide more consistent handling and braking. Having only one shock absorber, they tend to be easier to adjust than twin-shock systems. 1.1.7 Objectives of Suspension system 1. Comfort Provide vertical compliance so the wheels can follow the uneven road, isolating the chassis from the roughness of the road. 2. Safety React to the control forces produced by the tires longitudinal, lateral forces, braking and driving torques, in purpose to protect the passengers, the luggage and the suspension system itself. 3. Handling Keep the tires in contact with the road with minimal load variations and resist roll of the chassis.
  21. 21. 19 A detailed literature review was carried for studying the spring-damper system in bikes. Also finding out the specifications required for designing of spring and damper. Mono-suspension system used in various bikes were analysed and studied. 2.1 Study of FZ suspension system: Online data available about suspension system of FZ is as follows: Front suspension: Telescopic fork, Coil spring/Oil damper, 130 mm Rear suspension: Mono cross, Swing arm Coil spring/Oil damper, 120 mm Bore/Stroke: 58 mm * 57.9 mm Weight: 137 kg Rake/Caster angle: 26 degree [Reference: Wikipedia,] 2.2 Study of coil springs: For design of coil springs, standard reference used is V.B. Bhandari. Other references referred for design of helical coil springs are: 1. Design of coil springs-nptel [] 2. Design of springs-elearning [] 3. Wikipedia 4. Coil Springs- Design and Specifications [] 5. Design of Helical Coil Compression Spring A review – IJERA From the literature review, we understood the procedure to design a helical
  22. 22. 20 coil spring. The standard procedure used in design of spring is shown in chapter 3 in details. 2.3 Study of Dampers: Selecting a right damper is crucial part of designing a suspension system. There are two types of dampers used in mono suspension system, i.e. twin tube damper and mono tube damper. In FZ mono suspension system, twin tube damper is used. But in our project we designed the suspension system using mono tube damper. Both the dampers were studied in detail which included its construction and working. Also its advantages and disadvantages were studied. 2.3.1 Advantages of mono tube damper over twin tube damper:  Very wide damping rates can be achieved through bigger diameter pistons and shims designs.  Plush feel and full control over all piston speeds through higher gas and damping rates.  Cools faster and more reliable thought50 the single precision tube shock body.  Bigger diameter piston rods can be used because of bigger internal chambers with sufficient oil.  Can withstand higher pressures and temperatures without aeration or foaming.
  23. 23. 21 References referred for studying damper are: 1. Damper basic equations- KAZ technologies 2. Selecting the right damper- Dictator Technik 3. Damping correction factors by Wanda I. Cameron and Russell A. Green 4. Simple procedure for preliminary design of structural dampers by Wei Liu, Mai Tong and George C. Lee 2.4 Working inside a damper: [figure 14] Dampers also known shock absorbers work on the principle of fluid displacement on both the compression and expansion cycle. The compression cycle controls the motion of a vehicle's unsprung weight, while extension controls the heavier sprung weight. There are two cycles in which shock
  24. 24. 22 absorber works: a. Compression In the compression cycle the piston moves downward and compresses the hydraulic fluid in the chamber which is situated below the piston. In this cycle or downward movement, the fluid flows to upper chamber from down chamber through piston. Some of the fluid also flows into reserve tube through the compression valve. Flow is controlled by valves in the piston and in the compression valve. b. Extension In the extension cycle the piston moves upwards toward the top of the pressure tube. The upward movement results in the compressing of the fluid in the chamber lying above the piston. The extension cycle generally provides more resistance than compression cycle. 2.5 Conventional Spring Damper Assembly: [figure 15]
  26. 26. 24 Step 1: Decide the thickness of damper cylinder: Basic Assumptions: 1. Material: Structural Steel [ductile] 2. Maximum pressure inside cylinder: 53 MPa 3. Outside Cylinder diameter: 53 mm 4. Tensile stress of structural steel: 215 MPa 5. Poisson ratio: 0.29 For finding out inner diameter of cylinder, considering it as pressure vessel, Max pressure > Cavitation pressure 𝐷0 𝐷𝑖 = √ 6+𝑃𝑖(1−2µ) 6+𝑃𝑖(1−2µ) Putting Do = 53 mm, 6 = 215 MPa Pi = 53 MPa μ = 0.29 we get, Di = 44 mm Now, Thickness of the cylinder, T = 𝐷0−𝐷𝑖 2 Putting Do = 53 mm Di = 44 mm We get, T = 4.5 mm
  27. 27. 25 Step 2: Diameter of piston: Piston diameter = Inner cylinder diameter - 2 = 44 -2 = 42 mm Therefore, Diameter of Piston = 42 mm Step 3: Piston rod diameter: From literature survey about piston rod diameter, the usual piston rod diameter for mono tube dampers is 25 mm. Step 4: Estimation of Damping Force according to loading: The reference used for estimating damping force was Dictator Technik – Selecting the right damper. The equation used for finding the damping force was, Damping force = 𝑬𝒏𝒆𝒓𝒈𝒚 𝒑𝒆𝒓 𝒔𝒕𝒓𝒐𝒌𝒆 [ 𝑵.𝒎.] ∗ 𝑪𝒐𝒓𝒓𝒆𝒄𝒕𝒊𝒐𝒏 𝑭𝒂𝒄𝒕𝒐𝒓∗𝟏𝟎𝟎𝟎 𝑺𝒕𝒓𝒐𝒌𝒆[𝒎𝒎] [equ 1] 1. For finding out damping force, first you need to find Energy per stroke in N.m Considering equation for inclined loading, energy per stroke is given by; Energy per stroke, E = m*g*h + m*g*s [equ 2]
  28. 28. 26 m = impact mass [kg] g = acceleration due to gravity [m/s2] = 9.81 s = acceleration height [m] h = damping distance [m] In our case, impact mass, m = 200 kg [designing suspension for 200 kg load] Acceleration height = 0 m Damping distance = 0.04 sin 26º = 0.017 m Putting the above values in equation, we get, Energy per stroke = 34.40 N.m 2. Damper Correction Factor For finding out the damper correction factor, the equation used was the one proposed by Priestley in 2003. The equation is, DCF = [ 10 5+Ɛ ]0.25 For underdamped system, 𝜺 = 0.4 Putting it in above equation, we get DCF = 1.17 3. Stroke From the literature survey about FZ suspension system, we found out the free length, i.e 180 mm. We took the length of outer cylinder as 70 mm. From this we calculated stroke = 40 mm Putting all the values of 1,2 and 3 in equation of damping force, we get
  29. 29. 27 Damping force = 𝟑𝟒.𝟒𝟎∗𝟏.𝟏𝟕∗𝟏𝟎𝟎𝟎 𝟒𝟎 = 1006.2 N Considering 1010 N damping force. Now, finding out the force due to gas pressure, which is given by the equation, Fgas = Pgas * Arod [Reference used is Damper basic calculations by KAZ technologies] In mono tube damper, the gas filled in a gas chamber is nitrogen. The pressure ranges between 50 – 70 psi. Considering 70 psi, i.e. 4.823 bar Arod = 𝜋 4 (𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑜𝑓 𝑝𝑖𝑠𝑡𝑜𝑛 𝑟𝑜𝑑)2 Arod = 0.000491 m2 Putting this in equation of Gas pressure force, Fgas = 236. 62 N Considering 240 N. Therefore, total damping force considered for analysis in ANSYS is, = 1010 + 240 = 1250 N
  30. 30. 28 Step 5: Estimation of force acting on spring and finding out stiffness of spring: Assuming 2000 N load acting on the suspension system and damping force = 1010 N and force of gas = 240 N, Load acting on spring = 2000 – [ 1010 2 + 240] = 1260 N Stiffness of the spring , K = 𝑝 𝛿 Considering displacement of spring = 20 mm, Stiffness of spring = 1260 20 = 63 N/mm Step 6: Design of spring: 1. Free length = 180 mm 2. Compressed length = free length – 𝝳 = 180 – 20 = 160 mm 3. Material: Cold drawn steel wire 4. Permissible Shear stress induced inside spring, 𝜁 = 0.5 S𝑢𝑡
  31. 31. 29 For cold drawn steel wire, Sut = 1050 N/ mm2 Therefore, = 525 N/mm2 5. Spring Index, C = 6 [Assumption] 6. Wahl Factor, Kw = 4𝑐−1 4𝑐−4 + 0.615 𝑐 Therefore, Kw = 1.2525 7. Mean coil diameter, Permissible shear stress induced is also given by, 𝜁 = 𝑘𝑤∗ 8 ∗ 𝑝 ∗ 𝑐 𝛱 𝑑2 Putting values of Kw, P, C and 𝜁, we get mean coil diameter, d = 10 mm 8. Mean diameter of spring Spring Index is given by, C = 𝐷 𝑑 Putting the values of C and d, we get D = 60 mm 9. No. of active coils Deflection,
  32. 32. 30 𝝳 = (8*P*Nt*𝑑3 )/(G 𝑑4 ) Putting the values of 𝝳, P, D, d and G = 81370 N/mm2 for cold drawn wire, we get number of active coils, Nt = 8 (approx) Assuming plane end spring, No. of active coils = Total no of coils Therefore, Inactive coils = 0 10. Solid length Solid length = Nt * d = 80 mm 11. Gap Total gap = compressed length – solid length = 160 – 80 = 80 mm Gap between 2 coils = 𝑻𝒐𝒕𝒂𝒍 𝒈𝒂𝒑 𝑵𝒕−𝟏 = 𝟖𝟎 𝟖−𝟏 = 11.42 mm
  33. 33. 31 12. Pitch Pitch = 𝐹𝑟𝑒𝑒 𝐿𝑒𝑛𝑔𝑡ℎ 𝑁𝑡−1 = 180 7 = 25.71 mm Step 7: Selection of fluid for damper: We are going to select the fluid inside damper based on the viscosity of fluid that is obtained from equation of laminar flow of fluid. [Reference: fluid mechanics] Damping force inside damper is given by, F = (P1 – P2) * A Therefore, (P1 – P2) = 𝐹 𝐴 Equation of pressure difference for laminar flow is given by, P1 – P2 = (32 ∗ µ ∗ 𝑉𝑎𝑣𝑔 ∗ 1)/𝐷2 [eqn 3] D = Equivalent diameter of flow μ = Dynamic viscosity l = length of the flow
  34. 34. 32 Vavg = velocity of piston Equivalent diameter, 4 [ 𝝅 𝟒 𝒅 𝟐 ] = 𝝅 𝟒 𝑫 𝟐 D = 2d Replacing value of D in equation 3, we get P1 – P2 = (32 ∗ µ ∗ 𝑉𝑎𝑣𝑔 ∗ 1)/4𝑑2 Putting F = 1250 N, A = 0.00145 m2, Vavg = 2 m/s, l = 0.04 m , d = 0.01 m in above equation we get viscosity, μ = 0.45 Ns/m2 From this amount of viscosity Sasol oil damper 37 can be selected. [ reference used- Datasheet of sasol oil damper]
  36. 36. 34 1. Damper Cylinder: [figure 16] Thickness = 6 mm, Outer cylinder diameter = 53 mm Height = 70 mm, Inner cylinder diameter = 44.1 mm Diameter of piston rod = 25 mm, Diameter of base plate = 75 mm 2. Piston with piston rod: [figure 17]
  37. 37. 35 Length of the piston rod = 110 mm Diameter of piston rod = 25 mm Diameter of piston = 44 mm Diameter of orifice = 10 mm Length of the orifice = thickness of piston = 5 mm Diameter of base = 75 mm 3. Floating plate: [figure 18] Diameter of plate = 39 mm Spline size = 3*5*5
  38. 38. 36 4. Spring: [figure 19] Free length of spring = 180 mm Stiffness of spring = 60 N/mm Pitch of the spring = 25.7 mm Diameter of coil = 10 mm Mean diameter of spring = 60 mm No of active turns = 8 Plane end spring 5. Assembly of spring and damper [figure 20]
  40. 40. 38 1. Meshing of assembly [Finite Element Analysis] [figure 21] 2. Fixed Support [figure 22]
  41. 41. 39 3. Damping Force [1260 N] [figure 23] 4. External load [2000 N] [figure 24]
  42. 42. 40 5. Equivalent stress [figure 25] Maximum equivalent stress: 14.078 MPa Minimum equivalent stress: 0.0021239 MPa 3. Maximum shear stress [figure 26] Maximum shear stress: 8.1214 MPa Minimum shear stress: 0.0012021 MPa
  44. 44. 42 Conclusion:  Successfully designed spring damper system for 2000 N load acting on spring damper assembly.  Successfully modelled Spring damper assembly in creo as per the specifications obtained during design process.  Obtained maximum and minimum shear stress and equivalent stress values in permissible limits.
  45. 45. 43 REFERENCES :  [Wikipedia and]  Machine Element Design by V.B Bhandari  Selecting the right Damper – Dictator Technik  Understanding your dampers by Jim Kasprzak  Suspension in Bikes Considering Preload, Damping Parameters and Employment of Mono Suspension in Recent Bikes by Prof. D. K. Chavan, Sachin V. Margaje, and Priyanka A. Chinchorkar  Suspension System by Dr. Paul J. Aisopoulos  Datasheet Sasol Damper Oil 37 DAMPER OIL, SYNTHETIC, ANTI-WEAR, VHVI, GRADE 37