Vehicle Ride

1. Wheel rate is product of spring rate and square times motion ratoi. Spring rate depends on spring stiffness alone but wheel rate depends on motion ratio and spring rate.

2. Ride rate is measured by taking contact patch as reference, the vertical deviation from the sprung mass and contact patch. Wheel rate is measured by taking wheel center as reference, The vertical deviation from the sprung mass and wheel centre.

3.

i) Low and high frequency regions

No. To reduce transmissibility ratio for low frequency region high damping and for high frequency region low damping is required.

ii) Compression and rebound region

No. During compression the spring stores energy so low damping is enough whereas during rebound spring releases energy so high damping is required.

4. The rear ride frequency need to be higher than front to avoid pitching effect, otherwise the rear wheel hit the bump after sometime delay from the front wheel hit the bump.

5. For improved vibration isolation lower unsprung mass and lower damping is preferred by avoiding resonance.

6. Air suspension is beneficial in heavy vehicles because depending on the load the air pressure in the suspension varies and hence avoids pitching effect.

7. Ms = 2000 kg, Mus = 50 kg ,Ks =25 N/mm, Kt = 250 N/mm

Sprung mass k = (Ks*kt)/(ks+kt) = (25*250)/(25+250)=22.33 N/mm=22.33*10^3 N/m.

Mass of sprung / wheel = 2000/4=500 kg

Unsprung mass k = ks+kt=50+250=275N/mm = 275+10^3 N/m

Natural frequency

1) for Spring mass = 1/2pi()* sqrt(k/ms)= 1/2*pi() * sqrt(22.73+10^3/500) = 1.073 Hz.

2) For unsprung mass = 1/2*pi() * sqrt(275*10^3/50) = 11.8 Hz

8.

Wheel base = 98.42 inch = 98.42*.0254 =2.49 m

Speed = 37.42miles / hour = 37.42 * 1.609*1000/3600 = 16.73 m /sec

Time lag delta T = wheel base / speed = 2.49/16.73=0.15 sec

1) f(front ) = 1. 2Hz, f(rear) = 0.8 Hz

So time (front) =1/f = 0.83 sec and Time (rear ) = 1/0.8=1.25 sec

Time (front ) < Time (rear)+delta T Implies Flat ride not possible.

2) f(front)=1.2 Hz , f(rear)=1.45 Hz

So Time (front) = 1/1.2=0.83 sec and Time(rear) = 1/1.45=0.69 sec

Time(front) nearly = Time(rear) + delata T Implies Flat ride is possible.

So 2) works bsst for flat ride prespective.