Vehicle Ride
1. Wheel Rate depends upon the sping rate and Motion ratio^2 that means it depend on both spring stifness and MR where as spring rate depends only on stiifness of spring.
2.Wheel rate or wheel center rate is vertical force acting on the tire per unit vertical displacement at the location along the spindle corresponding to the wheel centerline,measured relative to the chassis.Ride rate is vertical force per unit displacement of the tires' ground contact reference point relative to the chassis.wheel rate is lower than the spring rate due to installation ratio.Wheel spindle vertical travel is larger than corresponding spring displacement. Hence,for infinitely stiff tire,ride rates and wheel center rate are almost EQUAL. For a real tire with finite vertical stiffness the ride rate is always less than wheel rate.
3.i)No - Because of transmissibility Ratio Low frequency high damping and High Frequency Low damping.
ii) No - Because sping stores energy during bound so low damping will be enough and releases energy during rebound so High damping is required.
4. The Rear Ride frequency need to be higher than the front because of the time lag caused due to the wheel base so it need to oscilates faster compared to the front so that the pitch angle can be reduced and it wont have pitching effetct.
5.For improved vibration isolation in the wheel hop region i)lower unsprung mass since frequency=1/m amd ii) Lower damping since lower damping provides higher frequency and better vibration isolation avoiding resonance.
6.i) The air compressor compresses the air and stores it in the reservoir which is directly connectePid to the air springs at each tyre. This makes the system an independent suspension setup. ii)Depending on the intensity of the undulation on the road or tilting of the vehicle around the corner due to high speed, the exact amount of air fills the air springs and the shock is absorbed efficiently. iii) The ride height of the car can be altered according to the need.
7. Sprung Mass 2000Kg Unsprung mass 50kg at each wheel spring Stifness 25N/mm Tire Stifness 250N/mm g =10m/sec^2
fs --> Sprung Mass Natural Frequency = 1/2pi (Kr/Ms)^1/2
fus --> Unsprung Mass Natural Frequency = 1/2pi (Kus/Mus)^1/2
Kr --> Ride rate = Kt*kS/Kt+Ks = 25*250/25+250 = 22.727 N/mm = 22727.27N/m
Kus --> Wheel Hop Rate = Kt+Ks = 275 N/mm = 275000 N/m
fs = 0.89Hz
fus= 10.79 Hz
8. i) front Ride Frequency --> Kfr =1.2 Hz Rear Ride Frequency --> Krr = 0.8hz
WB = 98.42 inches & Speed = 37.42 mph
WB = 98.42 * 0.0254 = 2.48m
Speed = 16.72mps
Tf = 0.83sec & Tr = 1.25
Tf>Tr + dt Not favorable for flat rides
ii) Rear Ride Frequency --> Krr = 1.45hz
Tr = 0.68 Tf = 0.83
Tf = Tr+dt favorable for flat rides