Vehicle Ride 1
1. Recommended rear sprung mass frequency based on speed & wheelbase at design condition
= 1/[(1/rear sprung mass frequency) -Time lag]
Where,
Time lag = Wheelbase / Speed = 2.7m / 26.82m/s = 0.1s
Rear sprung mass frequency = 1/ (2*Pi) *sqrt(Kride/(Ms)r)
Kride = Kt*Ks/(Kt+Ks) = 245*25/(245+25) = 22.68 N/mm
(Ms)r = 1825*0.45/2 = 410.6 Kg
(Fs)r = 1/ (2*Pi) * sqrt(22.68*1000/410.6) = 1.18 Hz
Recommended rear sprung mass frequency = 1 / [1 / 1.18 – 0.1] = 1.33 Hz.
2. Front sprung mass natural frequency at design:
(Fs)f = 1/ (2*Pi) * sqrt[Kride / (Ms)f]
As Kride = 22.68 N/mm
(Ms)f = 1825 * 0.55 / 2 = 501.8 Kg
(Fs)f = ½ * pi * sqrt(22680/501.8) = 1.07 Hz
3. Front spring rate (Ks)f:
(Fs)f = 1/ (2*Pi) * sqrt(Kride / (Ms)f)
1.15 = 1/ (2*Pi) * sqrt(Kride / 501.8)
Kride = 26.2 N/mm
Kride = Kt*Ks / (Kt+Ks) = 245*Ks / (245+Ks)
Ks = 29.3 N/mm
4. Rear spring rate (Ks)r:
(Fs)r = ½ *Pi * sqrt(Kride / (Ms)r)
(Fs)r = (Fs)f*1.2 = 1.15*1.2 = 1.38
1.38 = 1/ (2*Pi) * sqrt(Kride / 410.6)
Kride = 30.87 N/mm
Kride = Kt*Ks / (Kt+Ks) = 245*Ks / (245+Ks)
Ks = 35.3 N/mm
5. Front sprung mass natural frequency at Curb & GVW:
(Fs)f = 1/ (2*Pi) * sqrt(Kride / (Ms)f)
Kride = 22.68 N/mm
(Ms)f = 1500*0.6 = 900 kg (Curb)
(Ms)f = 2000*0.52 = 1040 Kg (GVW)
(Fs)f = 1/ (2*Pi) * sqrt(22680 / 900) = 0.8 Hz (Curb)
(Fs)f = 1/ (2*Pi) * sqrt(22680 / 1040) = 0.74 Hz (GVW)
6. Rear sprung mass natural frequency at Curb & GVW:
(Fs)r = 1/ (2*Pi) * sqrt(Kride / (Ms)r)
Kride = 22.68 N/mm
(Ms)r = 1500*0.4 = 600 kg (Curb)
(Ms)f = 2000*0.48 = 960 Kg (GVW)
(Fs)f = 1/ (2*Pi) * sqrt(22680 / 600) = 0.98 Hz (Curb)
(Fs)f = 1/ (2*Pi) * sqrt(22680 / 960) = 0.77 Hz (GVW)
7. Front unsprung mass natural frequency at all three load condition:
(Fun)f 1/ (2*Pi) * sqrt(Keq / (Mun)f)
Keq = Kt + Ks = 245 + 25 = 270 N/mm
(Mun)f = 90 Kg at all three load conditions
(Fun)f = 1/ (2*Pi) * sqrt(270000 / 90) = 8.71 Hz
8. Rear unsprung mass natural frequency at all three load condition:
(Fun)r = 1/ (2*Pi) * sqrt(Keq / (Mun)r)
Keq = Kt + Ks = 245 + 25 = 270 N/mm
(Mun)r = 60 Kg at all three load conditions
(Fun)f = 1/ (2*Pi) * sqrt(270000 / 60) = 10.7 Hz
9. Rear to front frequency ratio at all three condition:
10.7/8.71 = 1.2