12-06-2014, 10:13 AM
Vehicle suspension system rigidity analysis and discussion
Vehicle suspension system.docx (Size: 32.48 KB / Downloads: 22)
1->RIDE ANALYSIS-The straight line motion of a vehicle in steady state(only variation in Fz,transverse force)
2->VEHICLE MODELLING-There are 3 types of vehicle modelling.
*FVM(full vehicle model)
*HVM(half vehicle model)
*QVM(quarter vehicle model)
FVM-This model consist of chassis and the 4 tyres of a vehicle.
HVM-This model consist of chassis and two tyres of a vehicle.
QVM-This model consist of chassis and one tyre of a vehicle.
FREQUENCY VS HUMAN COMFORT-
*Human feels comfortable between a frequency range of 1-6 Hz.As we go down the comfort decreases.
*Human cann’t feel the frequency between the range 2-4 Hz.
*We know that ATV track has variation in amplitude.In Atv track taking into consideration of drivers comfort we choose the frequency between 1-2Hz as comfort decreases from 4-6 Hz.
PARAMETERS ON A QUARTER VEHICLE MODEL-
*Ride frequency(wheel center)-f
*Ride rate(wheel center)-k
*damping constant(wheel center)-C
*Motion ratio/position of spring-M/m
*Spring rate-Ks
*Damper damping constant-Cd
*spring travel-x
*Ground clearance-c
ASSUMPTIONS-
*There is variation of amplitude in the road profile.
*Tyre of the vehicle is completly stiff or stiffness of tyre Kt tends to infinity.
*All the analysis and discussion as according to HVM,front half in front view.
CALCULATION-
*Longitudinal mass distribution(Md=55:45)
*If the total weight of our vehicle is 350,as per the longitudinal mass distribution total load on front tyres is 160.Then the load on each tyre is 80 kg.
*The maximum transverse load on tyre is 5g i.e when a 80 kg mass with zero initial velocity traverses a height of 1.5m.
when a vehicle traverse a height of 1.5 m with zero initial velocity then the velocity at the point of impact is (2gh)½.
V=(10*2*1.5)½=5.48 m/sec
change in momentum=mv-0=mv=80*5.48=438.17kgm/sec
*force=change in momentum/t
(t=0.1 sec)
Force=438.17/0.1=4381.78 N
*After getting the value of force we can do the ride analysis parameter iteration.
PURPOSE OF ITERATION-
*As our vehicle will travel in a uneven track we have to select a damper of high damping coefficient(more rigid) and spring of medium stiffness(softer spring) by this iteration process.
*We have to minimize the ground clearance to reduce load transfer.
*Again we have to minimize the ride frequency for drivers comfort.