Vehicle Ride

1. Usually the springs are mounted at a horizontal distance from the wheel centre when viewed from the front. Hence the wheel rate is always related to the spring rate in terms of motion ratio.

2. Wheel rate is measured at the wheel centre and does not take tires into account.

Ride rate on the other hand considers a combination of spring rate and tire rate.

3.No,

• It is desirable to have a high damping ratio in the low-frequency region.
• It is desirable to have a low damping ratio in the high-frequency region.

This is based upon the frequency vs vertical acceleration plot.

• The damping ratio should be set low for the compression region since the spring absorbs a lot of energy in this phase.
• The damping ratio should be set high for the rebound region since the spring releases energy in this phase which must be controlled.

This is based on the force vs velocity plot.

4. To achieve a flat ride.

5.

• A lower unsprung mass improves vibration isolation at wheel hop frequency due to lower transmissibility ratio.
• Low damping is preferred in the wheel hop frequency region due to lower transmissibility ratio.

6. In air suspension, the ride height and stiffness can be easily altered. Hence, the ride frequency can be set as per the load and terrain conditions. This is beneficial for heavy vehicles.

7. Given,

ms = 2000kg,

wf/wr = 50/50,

mus = 50kg,

Ks = 25N/mm,

Kt = 250N/mm,

g = 10 m/s^2.

Assuming motion ratio as 1,

rdie rate Kr = (Ks*Kt)/(Ks+Kt).

Kr = 22.727 N/mm

corner sprung mass mcs = (ms*(wf/wr))-mus

mcs = 450 kg.

Sprung mass frequency fs = (1/2*pi)*sqrt((Kr*1000)/mcs)

fs = 1.131 Hz

Unsprung mass frequency fus = (1/2*pi)*sqrt((Ks+Kt)*1000)/mus)

fus = 11.79 Hz;3

8.Scenario 1

Time lag,

front frequency= 1.2 Hz,

time period = 1/ Ff = 0.833 s

rear frequency = 0.8 Hz,

time period = 1/Fr = 1.25 s

time lag = 1.25-0.833 = 0.417 s

Scenario 2

Time lag,

front frequency = 1.2 Hz,

time period = 1/Ff = 0.833 s,

rear frequency = 1.45 Hz,

time period = 1/1.45 = 0.689 s,

time lag = 0.689-0.833 = -0.144 s

wheelbase = 98.42 in = 2.499 m

speed = 37.4 mph = 16.717 m/s

time lag = wheelbase/speed

=2.499/16.717

time lag = 0.149 seconds.

Due to wheelbase, the lag is 0.149 seconds. Hence, the second set of frequency(Ff = 1.2 Hz, Fr = 1.45 Hz) works best in the flat ride perspective.