Suspension Design

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Suspension Design

  1. 1. Electrically assisted human powered vehicle
  2. 2. Configuration Specifications Specification Param. Name Value Unit Number and 2+1 configuration Wheelbase a+b 1.5 m Track t 1.0 m Height h_cg 0.4 m Distance from front a 0.5 m wheels Overall Mass M 200 kg Ground clearance h_ground 0.1 m Wheel size OD D_wheel 0.66 m (all)
  3. 3. Performance Specifications Specification Param. Name Value Unit Maximum lateral a_lat_max 7.8 m/s^2 acceleration Maximum d_max 7.8 m/s^2 deceleration Maximum a_max 3.3 m/s^2 acceleration Deceleration for d_max_tip 8.4 m/s^2 'header' Lateral a_lat_tip 9.3 m/s^2 acceleration at tip over Maximum speed V_max_brake 54 kph for braking Minimum turning R_turn 3.0 m radius
  4. 4. Key Specifications Specification Param. Name Value Unit Ride frequency f_ride 2 Hz Motion ratio (front) MR_front 1 - Motion ratio (rear) MR_rear 0.53 - Suspension K_susp_front 10150 N/m stiffness (front) Suspension K_susp_rear 11012 N/m stiffness (rear) Suspension c_front 404 N-s/m damping (front) Suspension c_rear 417 N-s/m damping (rear) Wheel travel (front) travel_front +/- 50 mm Wheel travel (rear) travel_rear +/- 43 mm
  5. 5. Rear Suspension Details CG height 0.4 m Ground Clearance 0.1 m Pivot radii 0.01905 m Max Acceleration 3.924 m^2/sec Length of swing arm 0.458 m Vehicle mass 200 kg Force accel 784.8 N Pivot Height 0.14 m Moment (Pivot) 109.872 N m Force (wheel- Vertical) 239.8951965 N Stiffness of the wheel (K) 11012 N/m Squat 0.021784889 m Wheel radius 0.33 m Force Lateral 523.2 N Hub width 0.1 m Force (arm) 1726.56 N Axle Diameter 20 mm Motion Ratio Motion Ratio of Rear Suspension 0.53 Wheel Location from Pivot 0.3929 m Shock Location from Pivot 0.208237 m
  6. 6. Decision Matrix Summary Oil/ Helical Air shock Leaf spring spring Satisfaction 452 305 383 Bicycle Motorcycle Car Satisfaction 472 377 318 Twin Shock Single Pivot Multi Link Fork Style Satisfaction 374 348 292
  7. 7. Rear Suspension CAD Models Wheel Rear Swing Arm Rear suspension Assembly Rear Axle
  8. 8. Steering CAD Models Center Pivot Steering Assy. Tie rod
  9. 9. Steering Details Description Specifications Steering bar length 0.6m Grip Length 0.12m Grip Diameter .03m Maximum Steering Bar angle + 45 degree to – 45 degree Steering ratio Hand: Wheel 1.6:1 Steering input force 67 N Maximum aligning torque from tires 125 N-m Wheel angles (inside/outside) 43/28 deg. Track Width 1.0 m Lateral Forces on one corner 522.66N Steering Torque on one corner 62.72N*m Load on Tie Rod 448N Actual Torque on Steering Column 40.32N*m Steering Arm Length 0.14m Steering Pivot length (Base of Column) 0.09m Steering Shaft Dia 0.015m Steering Shaft Length 0.6 to 0.7m Dia of Tie rod 0.00952m Length of Tie rods (Tublar) Chrome Plated light weight 0.177 to 0.60
  10. 10. Schematic Diagram http://www.shakyparts.com/steering_parts.html
  11. 11. Steering Geometry Check
  12. 12. Data for Longitudinal Acceleration and Braking 0.45 LIMITATIONS FOR UPHILL MOTION AT CONSTANT SPEED 0.4 0.35 •Constant Velocity of 19.5 km/h at 3: 0.3 0.25 •Constant Velocity of 11 km/h at 6: 5⁰ Acceleration (g) •Constant Velocity of 4.3 km/h at 15: 0.2 0.15 •Constant Velocity of 2.8 km/h at 20: - Maximum Slope at μ=0.8 0.1 0⁰ Acceleration (g) 0.05 (beyond this slope, vehicle will begin to lose speed) 0 -5⁰ Acceleration 15 6 1.5 2 8 10 0.05 1 3 12 4 Velocity(m/s) (g) ASSUMPTIONS MAXIMUM ACCELERATION ON DIFFERENT SLOPES •Coefficient of friction = 0.8 CONSIDERING AERODYNAMIC DRAG •Wheelbase = 1.5m •Three wheels, (2) in front, (1) drive LIMITATIONS FOR DOWNHILL BRAKING wheel at rear. •CG is located 0.4m above ground and •For 10:1 motor/wheel gear ratio, vehicle speed = 17 m/s 0.47m from front axle or datum •0: - 11.5: slope, minimum stopping distance = 18.4m •Wheels – Standard, 26” dia. X 1 ¼” @0.8g (skidding will occur at steeper slopes unless dec. •Braking discs – 8” front and rear rate is reduced) •Coefficient of Drag – 0.5 (Chassis •0: - 21: slope, minimum stopping distance = 25.5 m @0.6g Team) (skidding will occur at steeper slopes unless dec. rate is •Frontal Area – 0.39 m^2 (Chassis reduced) Team) •For induced velocity of 40 m/s (5: slope), minimum stopping distance = 102 m •Motor Power Rear Wheel = 500W •For induced velocity of 54 m/s (10: slope), minimum stopping distance = 186 m •Motor RPM – 5000 •Human Power = 75 – 200W •N.B: THESE STOPPING DISTANCES ARE ALL BASED ON A DECELERATION OF 0.8g UNLESS STATED OTHERWISE THESE DATA WERE PREPARED BASED ON DATA FROM THE SPREADSHEET ‘Brake Calculation Sheet.xls’
  13. 13. Power and Gearing Requirements Rear Velocity POWER AT CONSTANT SPEED (W) Motor/wheel Pedal/wheel RPM ratio RPM ratio RPM (m/s) 0: 3: 6: 15: 20: Front wheel diameter d_fw 0.66 m Rear wheel diameter d_rw 0.66 m Pedal RPM 50 rpm Motor RPM RPM_m 5000 rpm Gear Ratio 10 GR_10 10/1 1/10 500 17.2783 772 Gear Ratio 9 GR_9 11/1 1/9.1 454.5 15.71 606 Gear Ratio 8 GR_8 16/1 1/6.25 312.5 10.7989 253 Gear Ratio 7 GR_7 20/1 1/5 250 8.63913 160 Gear Ratio 6 GR_6 24/1 1/4.2 208.3 7.19812 114 Gear Ratio 5 GR_5 28/1 1/3.57 178.571 6.1708 89 717 Gear Ratio 4 GR_4 32/1 1/3.13 156.25 5.39945 67 622 1171 Gear Ratio 3 GR_3 56/1 1/1.79 89.2857 3.0854 34 349 662 Gear Ratio 2 GR_2 110/1 1/0.91 45.4545 1.57075 16 176 336 800 1052 Gear Ratio 1 GR_1 220/1 1/0.46 22.7273 0.78538 8 88 168 400 526 RED OUT OF RANGE GREEN HUMAN + ELECTRIC BLACK ELECTRIC ONLY According to the US Road Design Manual, • The maximum slope over an unlimited distance corresponds to 3⁰ •The maximum slope over 150m corresponds to 6⁰ •http://www.dot.state.mn.us/tecsup/rdm/english/3e.pdf (Road Design Manual)
  14. 14. Longitudinal Dimensions  The wheelbase and CG height were selected based on the following limiting conditions:  The maximum deceleration attainable would be 0.8g.  The maximum slope to be encountered would be 20% or 11⁰ on roadways. At these conditions, the vehicle would tend to skid before flipping over the front axle. If the CG height is increased to 0.5m, the vehicle would flip at these conditions. Therefore, considering safety, these parameters were selected. FINAL SPECIFICATIONS 1.Maximum speed on level ground – 56 km/h 2.Maximum speed on 3: uphill (this is the maximum slope over an unlimited distance for access roads) – 19.5 km/h 3.Maximum speed on 6: uphill (this is the maximum slope over 150m for access roads) – 11 km/h 4.Maximum acceleration on level ground – 0.34g 5.Maximum braking deceleration – 0.8g
  15. 15. Vehicle Cornering Stability . X  V cos(   )  . Y  V sin(   ) l f tan  r  l r tan  f   tan ( 1 ) l f  lr  o  i L   2 R Fig. : Kinematics of Lateral Vehicle Motion [Rajmani, R., 2006, “Vehicle Dynamics and Control”
  16. 16. Vehicle Cornering Stability L   f r R 2 L mf mr V x  (  ) R 2Cf 2Cr R L   Kvay R Cornering force F  C *  Cornering stiffness is a function of: • Inflation pressure • Percent of rated load Fig.: Steering Angle for High Speed Cornering • Vertical load [Rajmani, R., 2006, “Vehicle Dynamics and Control” • Size and shape of the tire
  17. 17. Vehicle Cornering Stability t WL t  W ( )  WAY h 2 Fc A W WAY h CG O WA WL   2 t W W WAY h P 1.8 W  WL   M 2 t N C D Assumptions: B Wc 1.25 WB • Wheel base: 1.5m Front • Track width: 1.0m • CG height: 0.4m Fig.: Cornering stability analysis • Coefficient of friction: 0.8 • Two wheels at the front and one at the rear • Front wheels are steered
  18. 18. Vehicle Cornering Stability Track Width for Lateral Stability 800 700 Total Weight Transfer (N) 600 500 400 300 Front Corner Static Load 200 Total Weight Transfer 100 0 25 23 21 19 17 15 13 11 09 07 05 03 01 99 97 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 0. 0. Track Width (m)
  19. 19. Vehicle Cornering Stability CG Height for Lateral Stability 800 Total Weight Transfer (m) 700 600 500 400 Front Corner Static Weight 300 Total Weight Transfer 200 100 0 0.4 0.41 0.42 0.43 0.44 0.45 0.46 0.47 0.48 0.49 0.5 0.51 CG Height (m)
  20. 20. Vehicle Cornering Stability Coefficient of Friction for Lateral Stability 800 700 Total Weight Transfer (N) 600 500 400 Front Corner Static Weight 300 Total Weight Transfer 200 100 0 0.8 0.82 0.84 0.86 0.88 0.9 0.92 0.94 0.96 0.98 1 1.02 Coefficient of Friction
  21. 21. Vehicle Cornering Stability Road Camber for Lateral Stability 660 640 Total Weight Transfer (N) 620 600 580 Front Corner Static Weight 560 Total Weight Transfer 540 520 15 16 17 18 19 20 21 22 23 24 Camber Angle (degree)
  22. 22. Merits and Demerits of Different Braking Methods P ros C ons perform equally well in all c onditions more s tres s on a wheel's s pokes Dis k B rake inc luding water, mud and s now. T he des ign and pos itioning of dis c brakes prec ludes offer better modulation of braking power the us e of mos t types of pannier-rac k s tandard parts and eas y to get c heap, light, and very powerful perform poorly in wet weather when the rims are wet R im B rake mec hanic ally s imple, eas y to maintain wear down quic kly, over longer time and us e, rims bec ome worn heat the rim, bec aus e the brake c onverts kinetic energy into thermal energy us eful for wet or dirty c onditions heavier, more c omplic ated Drum B rake les s maintenanc e and are les s affec ted frequently weaker than rim brakes by road c onditions Intended to s low down the bike on long downhills rather than s top it
  23. 23. Braking Methods Decision Matrix Alternative C riteria Importanc e D is c B rake R im B rake D rum B rake E as y to opetate 10 0.8 0.85 0.8 E as y to maintain 8 0.75 0.8 0.51 E as y to ajus t 6 0.82 0.83 0.62 E as y to as s embly 6 0.8 0.86 0.48 wear 7 0.78 0.52 0.61 W eight 5 0.8 0.85 0.56 F amiliar to c us tomer 9 0.82 0.84 0.65 P erform in all c onditions 12 0.89 0.45 0.51 O verall s afty 15 0.91 0.75 0.65 S atis fac tion 82% 75% 60%
  24. 24. Concept Selection Process and key Specification Braking method: ISO standard (1996):  By comparing Kinetic Energy with mountain  Disk withstands force: 2300 N [1] bike, we decided to select braking method of mountain bike. Key specification::  By comparing typical braking methods of  Force: mountain bike, we thought that disk brake is  The force exerted on front disk: 1870 N feasible for our project.  The force exerted on rear disk: 935 N Disk dimensions:  Torque:  The torque exerted on front disk:367 Nm  Diameter: 8” (200mm)  The torque exerted on rear disk:168 Nm  Thickness: 0.07”(1.8mm)  Material: Stainless Steel Marketing specification:[2] *Hayes Disc Brakes HFX 9 HD V8 Limitations of disk brake: *Rotor: 203mm  Vehicle maximum speed: 40 km/h *Weight: 520g  Total weight: 200 kg *Cable Length Front: 850mm  Kinetic energy distribution: *Cable Length Rear: 1400mm 80%--Front two wheels *Includes: Rotor, Hardware, Pads, 20%--Rear wheel and Pre-Bled Caliper and Lever
  25. 25. CAD Models of Brake Concept 40% Brake 40% Brake Brake Force Force Pad Hydraulic distributor Brake Disc Wheel Handle Bar Parking Brake 20% Brake Force
  26. 26. Isometric View
  27. 27. Side View
  28. 28. Front View
  29. 29. Top View

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