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Suspension Design and powertrain integration.pdf

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SUSPENSION DESIGN AND POWERTRAIN INTEGRATION
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III Suspension Design and IV Powertrain IntegrationShock absorbers Shock absorbers Ball joints Ball joints Tires Tires Springs Springs Springs Springs Bushings Bushings Bushings Bushings Steering - Column - Intermediate shaft Steering - Column - Intermediate shaft Shock absorbers Shock absorbers Steering gear Steering gear Stabilizer bar Stabilizer bar Brake rotors Brake rotors Master cylinder Master cylinder Vacuum booster Vacuum booster ABS/TCS/VSES Control module ABS/TCS/VSES Control module Brake calipers Brake calipers Brake pedals Brake pedals Shock mounts Shock mounts Brake rotors Brake rotors Front suspension Front suspension Rear suspension Rear suspension Powertrain mounts Powertrain mounts Chassis Systems ie: FWD, RWD, AWD – Vehicle dynamics characteristics – Package space –M a s s – Cost – Ease of assembly – Tire size capability –E t c . III Suspension DesignFront of Vehicle Upper Ball Joint Lower Ball Joint Kingpin Axis Caster Angle Suspensions - to Control Tire/Unsprung Mass Positions Toe (Rz) Camber (Rx) Caster (Ry) Jounce and Rebound (Z) Lateral (Y) Fore-Aft (X) Side View Toe In Vehicle Centerline Front View Top View Vehicle Centerline Camber Angle (+)Toe Angle, Camber, and Caster change with: ? Wheel position ? Bushing deflection ? Body/Chassis structure deflectionsEffect of Toe on Tire Drag Force 0% 2% 4% 6% 8% 10% 12% 14% 16% 18% 20% 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Toe-in (degrees) % Change in Tire Drag Force 0.150 0.200 0.250 Cornering Coefficient CASTER: No Effect CAMBER: Minor Effect TOE: Most Significant Effect -Due to Lateral Force Component in Direction of Travel F y F x v α Plant Tolerance: ± 0.1°Suspension Layout Procedure C5 Front View Lines Kingpin Layout RollCenter/Control Arm Strut and Spring Control Arm Attachments Side View (Swing Arm) Steering Linkage Tie Rod Key SDFs on DfDr Front View Side View Plan View 3DFront View Lines ?Ground Line ?Spindle Line ?Tire size and Loaded Radius ?Track Width ?Camber ?Body/Wheel Offset and Gap ?Engine/Powertrain ?Other Packaging Constraints Vehicle C L Spindle C L T/2 Tire Loaded Radius γ(+) Hood Line Ground Line Load vs Deflection “Compress to Rim“ 0 20 40 60 80 100 120 0 5000 10000 15000 20000 25000 30000 35000 40000 Applied Load [N] Tire Deflection [mm] 180 kPa 240 kPa Camber Body/Wheel Offset and GapKingpin Layout ?Front View Track width Wheel offset and gap Kingpin Inclination Scrub Radius Upper Strut Mount Spindle Length Hood Line Ground Line C L Scrub Radius (-) Kingpin Inclination Spindle Length Upper Strut Mount Front View Side View Caster Trail Caster Offset Caster Angle ?Side View Caster Angle Caster Trail Kingpin Hood Line Ground Line C Kingpin Inclination Spindle Length Upper Strut Mount MacPherson Strut Suspension?Kingpin, An Imaginary Steering Axis (SA) ?Kingpin Inclination -Incline to have a minimum or negative (outboard) scrub radius -Outer CV joint (FWD) to intersect with Kingpin to avoid torque steer -Can it be outboard (outside of the wheel centerline)? C L Scrub Radius (-) Kingpin Inclination Spindle Length C L Scrub Radius (-) Kingpin Inclination Spindle Length Front View Macpherson Strut SLA (Double Wishbone) SLAScrub Radius -Outboard (negative) scrub radius reduces FWD torque steer (due to uneven tire traction forces) -Balance the split μ braking (Particularly ABS) Pivot Center Fxl Fxr Fxl > Fxr Yaw Moment Steering Moment Top View Deceleration Vehicle Velocity Pivot Center Fxl Fxr Fxl > Fxr Steering Moment Acceleration Yaw Moment Top View?Caster Angle -Once disturbed, Caster trail (moment) force the tire return to the straight position. -As the wheels are turned, both kingpin inclination and caster angles jack up the front of the car. Gravity will lower the car and force the wheels return to the straight position. -Caster provides steering feedback ?Kingpin Offset (Spindle Length) -Minimum Kingpin offset to reduce shake due to the tire&wheel imbalance. Kingpin Kingpin Offset Centrifugal force due to Imbalance Caster Trail(Moment) Caster Angle Pivot Center TopView SideViewHigh Roll Center - Minimum roll moment during cornering - Wheel fight/kick lateral shake. Large lateral force when tire hits a road bump (critical to front wheels) -Excessive tread deviation and lateral movement (equivalent slip angle, force) Low Roll Center - Minimum lateral interference when hit a bump - Large roll moment Inclined Roll Axis At front, use stabilizer bar to compensate the roll High Roll Center Low Roll Center(at ground level) Roll Centers Roll Center/Control ArmInstant Center Front View Swing Arm Roll Center Height (RCH) Lower Ball Joint (LBJ) LCA Bushing Long LCA Roll Center C L Front View C L Front View LBJ Instant Center Kingpin LCA Bushing Strut Mount Roll Center Height Roll Center/Control ArmMore Roll Centers Short Long Arm Hotchkiss/Sold AxleStrut and Spring Strut Length Jounce/Rebound Jounce Bumper Bending at Strut Countered by Spring Friction at Struct (Bending and Side Force) Spring Linkage Ratio and Damper Linkage Ratio Efficiency and Load PackagingLinear Nonlinear Spring and Ride Travel Coil Spring Jounce Bumper Damper (Shock Absorber) Susp. Deflection vs. Load Max Ef f GVW De s ign Cur b Rebound -150 -100 -50 0 50 100 150 0 200 400 600 800 1000 Load (Kg) Susp Deflection (mm) Spring Requirements: 1. Load 2. Travel (at various loads) 3. Ride FrequencyCurb: This groundline condition (also referred to as Min. Curb) represents the most commonly used groundline referenced by Design Staff when styling/developing a vehicle. Curb is a position. Curb represents how a vehicle would look in the showroom, or how potential customers may view a vehicle. Curb is defined as the base equipment with all fluids and fuel. Curb is used by S.A.E. also for publicizing data used for general use. Curb will be maintained, regardless of mass, and wheel centers at curb are agreed upon and locked very early on in a program. GVM: GVM (Gross Vehicle Mass) is used primarily by Truck programs as a styling guide. This is defined as the vehicle loaded with all passengers and the maximum cargo. Trucks are primary users of GVM in that once loaded to GVM, a truck will not go below this level in the rear. GVM is also used for passenger vehicles when evaluating approach, departure, and breakover angles. This condition is evaluated for other things such as Jacking location points. MEJ: (Maximum Effective Jounce) The wheel center location at the upper most point at which a suspension won’t move beyond. MEJ is a position that is not to be exceeded. MEJ is NOT represented by a specific load ( it is different for each vehicle). Various Mass Definitions Base Vehicle Mass Base Curb Mass (Minimum Curb Mass) Base Shipping Mass Powertrain Family Curb Mass EPA Curb Mass Curb Mass Shipping Mass Maximum Curb Mass Normal Curb Mass EPA Certification Mass Gross Vehicle Mass Rating (GVMR) Maximum Passenger Mass Side Impact Mass Design Mass Haul-Away Mass Dynamic Mass Towing Mass EPA Certification Mass 2 Occupants in the Front Seats EPA Curb Mass EPA Option Mass Powertrain Family Curb Mass Powertr ain Family Option Mass Base Curb Mass Base Vehicle Mass Fue l to Ca pac ity Base Powertrai n Mass All Fluids to Capacity Windshiel d Solvent to Capacity Standard Equipmen t Mass Mass Curb+2 CURB+D&EFront Suspension Travel -150 -100 -50 0 50 100 150 1 4 7 10 13 16 19 22 25 28 Suspension Travels Rebound Jounce @2g Jounce@6g Competitive Suspension Travel Benchmark Astra Accord L4 J30-T 90 LS400 95 LS400 LeSabre Accord V6 Millenia C280 Aurora 540i 325is ES300 Prism Omega Camry Regal Jetta Taurus Cirrus Lumina 900SE Cavalier Contour Neon Mustang SL2 Z28 Z24 R 2 = 0.535 72.00 73.00 74.00 75.00 76.00 77.00 78.00 79.00 80.00 81.00 82.00 83.00 73.00 74.00 75.00 76.00 77.00 78.00 79.00 80.00 Predicted Ride Metric Measured Ride Metric Predicted CRI Demerits = 94.9860(Tire Deflection) -0.375 (SQRT(ABS(Rebound Travel*2G Jounce Travel)) -0.5 )SLA Suspension Rear View Suspension Displaced Rear View Rebound Travel Jounce Travel Curb Increased wheel travel dissipates more road induced energy before the suspension travel limiters are engaged Results in lower loads transferred to structure Ride TravelStrut and Damper Shock Lengths mm Wheel Jounce 89 Wheel Rebound 106 Shock Linkage Ratio 1.6 Upper Mount 24 Lower Mount 24 Compressed Jounce Bumper 20 Mount Jounce Compliance 10 Mount Rebound Compliance 10 Shock Travel 121.875 Compliant Shock Travel 101.875 Shock Part Options A B C D Tube Length 218.9 177.2 183.9 206.9 Dead Length 112 70.3 82 100 Shock Collapsed Length 286.9 245.2 251.9 274.9 Shock Extended Length 388.775 347.075 353.775 376.775 Jounce Length 276.9 235.2 241.9 264.9 Rebound Length 398.775 357.075 363.775 386.775 Desgin Length 332.525 290.825 297.525 320.525 Travel Tube Mount Mount Will Damper Bottom-out?Jounce Rebound Damper (Shock Absorber) ?“Glue” that integrates chassis ?Actually, ‘shock’ is absorbed by springs ?Long ride travel = good ride ?Damper is for dissipating the spring restoring energy via ‘heat’ ?On off-road (rough road), dampers may be overheated ?Typical passenger cars with the damper of 30% critical damping ?Why the damping curves are asymmetric in rebound and jounce? ?Significant influence on character -Ride - Handling - Structural integrity and Durability0.01 0.1 1 10 0.1 1 10 100 Frequency (Hz) Max Velocity (m/sec) Rough, Impact Noise &Vib Body Roll Sw ell Dam per Force vs Velocity -1000 -500 0 500 1000 1500 2000 2500 3000 0.0000 0.5000 1.0000 1.5000 2.0000 Velocity (m/s) Damper Force (N) Fr/Reb Rr/Reb Rr/Jounce Fr/Jounce 1995 Mercedez Benz 1996 Lexus LS400 Dam per Force vs Velocity -1000 -500 0 500 1000 1500 2000 0.0000 0.5000 1.0000 1.5000 2.0000 Velocity (m/sec) Damper F orce (N) Fr/Reb Rr/Reb Fr/Jounce Rr/Jounce Damper Synthesis Target % Damping (@various Road Disturbances) Effective DampingRoad Holding (or Wheel Control) ? Low unsprung mass ? High damping ? High ride frequency Rough Road Isolation vs. Travel Control 10% 15% 20% 30% 40% 50% 60% 80% 1.5 1.3 1.4 1.1 1.2 1.0 0.9 0.8 Baseline Study 0.02 0.04 0.06 0.08 0.1 0.12 024681 0 Ramp Bump Suspension Deflection Step Bump Isolation Ride Frequency(Hz) Hop Damping Ratio Better Shake & Impacts Isolation Better Crash Through Control Performance Limit 06/13/200 A Racing Car Designer’s quote, “Only four things left: 1) More power, 2) Less weight, 3) More downforce, and 4) Dampers will do nearly everything else. “Damper Tuning Parameters% Critical Body Damping @0.38m/s 0 10 20 30 40 50 60 70 01 02 03 04 0 %Critical Body Damping Rear Front % Critical Wheel Damping Front@1.5m/s 0 10 20 30 40 50 60 70 80 90 01 02 03 04 0 Total Rebound % Critical Wheel Damping @1.5m/s 0 5 10 15 20 25 30 35 40 01 02 03 04 0 %Critical Wheel Damping Rear Front % Critical Body Damping Front@0.38m/s 0 10 20 30 40 50 60 70 80 90 01 02 03 04 0 Total Rebound Competitive Benchmark Damping Ratios (Effective Damping) Damper Characteristics Verse Temperature 90 o C -30 o C Example Operating Range: -Min -40 o C -Max continuous +90 o C -Peak +120oC -Damper is for dissipating the energy via ‘heat’ -On off-road (rough road), dampers may be overheatedFor 1.0 mm Wheel Displacement Spring and Damper Linkage Ratios Impacts on 1. Loads 2. Spring 3. Damper 4. Mass and Stress Ks = Kw* Ratio 2 ? Front ViewDamping Contribution 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% Shock Ball Joint Stabilizer Bar Bushing Spring Control Arm Bushing Stiffness Contribution 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00% Spring Control Arm Bushing Stabilizer Bar Bushing Shock Others Suspension Friction - An example of damping and stiffness breakdown ?Only ~40% damping is design intend (by shock) ?Columb friction is effectively a high ‘stiffness’ for low amplitude road disturbance ?Or even lock-up the shockControl Arm Attachments ? LCA must clear the wheel envelop ? Wishbone, A arm (pakaging) ? Stabilizer bar attachment (to LCA) ? Tire chains clearance ? Max Road Wheel Steering Angles ? Front and rear LCA bushings(attachments) should be as far as possible ? Wheel Envelop 8 9 10 11 12 13 14 15 16 20 30 40 50 Max Steering Angle (deg) Turning Diameter (m) Max Inside Wheel Sterring Angle Max Outside Wheel Steering Angle Front Bushing Rear Bushing -Handling Bushing (lateral) -Ride Bushing (fore-aft) -Current trend is a L-shaped LCASide View Swing Arm ?Instant center ?Side View Swing Arm ?Side View Swing Arm Angle ?Negative SVSA Angle reduces harshness ?Anti Dive/Anti Lift Side View Kingpin LCA Front Bushing Rear Bushing LBJ Instant center SVSAAnti Dive/Anti Lift Side View Swing Arm 100% Front Anti-Dive tan ρ f = h /( ξ L) 100% Rear Anti-Lift tan ρ r = h /((1- ξ) L) where ξ is the fraction of brake force on the front wheels Side View Instant center ρ f F zf = mgb/L+ m a x (h/L) F xf =ξ(m a x )Bump in Road Forward displacement Wheel in Jounce Larger loads transferred to body when wheel moves forward in bump Vehicle Direction SVSA Suspension Equivalent Link Side View Swing Arm AngleBump in Road Rearward displacement Wheel in Jounce Lower loads transferred to body when wheel moves aft in bump Vehicle Direction Side View Swing Arm Angleρ r Side View Instant center SVSA For Rear Solid Axle SVSA 1.Positive slope is roll oversteer 2.Positive slope is good for ride 3.Short length is bad for power hop Rear Wheel Drive Anti Squat During Acceleration Side View Swing Arm For Solid Axle 100% Rear Anti-Squat tan ρ r = h / L For Independent Suspensions Acceleratrion 100% Rear Anti-Squat tan ρ r = h / L Where the angle ρ r is measured at WC Why? Both arms have the same anti Ackerman Angle ?Ackerman Angle Error Ackerman Angle R= (L/tanδ+t/2) 2 +L 2 ) 0.5 L Turn Center Max δ i Max δ ο t R ?Turning Radius ?Ackerman Steer Angle = tan -1 (L/R) δ i δ ο α o α i Ackerman Angle Ackerman At low speed, max steering angles may be deviated from Ackerman for packaging. Inside and outside wheels’ slip angles cancel out each other. At high speed, turn center moves forward, steering angle is smaller than Ackerman, (parallel steer). L Turn Center δ i δ ο (Top View)Ackerman Geometry Steering System Front Ackermann Geometry Trapezoidal Steering Geometry Steer Arm Steer Arm Angle =tan -1 (t/2/L) Rack/ Tie Rod Forward Rearward At high g cornering, outside wheels do most of the work, is it important to maintain Inside wheel tracks with outside wheel? L Turn Center δ i δ ο t LRack & Pinion Low mass & cost More steering precision Less compliance Less friction Recirculating Ball More packaging flexibility Typical Steering Gear Locations Rear Mount Steering Side View – Front Wheel Transmission or Structure Packaging Conflict Engine Packaging Conflict Tire FWD RWD RWD RWD Good Aligning Torque Steer Good Ackerman Steer Forward
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