Homework Sourse2 Show how the science of vibrations is applied in vehicle d
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Show how the science of vibrations is applied in vehicle dynamics for determining the perception of ride. relate natural frequency, damping to ride propertiesSolution
SCIENCE OF VIBRATION APPLIED IN VEHICLE DYNAMICS USED FOR DETERMINING PERCEPTION OF RIDE
Ride is normally associated with the level of comfort experienced while travelling in a vehicle.The ride quality normally associated with vehicle\'s response to bumps is a factor of relatively low frequency bounce and rebound movements of suspension system.Ride is perceived as most comfortable when natural frequency is in range of 60 to 90 cycles per minute (CPM) or about 1 to 1.5Hz.A high performance sports car can have a stiffer suspension system with natural frequency of 120 to 150 CPM or 2 to 2.5 Hz.
The amplitude affects human sensitivity to frequency.For Ex:-a frequency range of 30 to 50 CPM will produce motion sickness.The head and neck regions are especially sensitive to vibrations of 18 to 20 Hz which emanate from tires and axle hop.
The perception of ride quality is degraded by virtually any disturbance experienced by occupant.To produce a comfortable ride,high-frequency vibrations of wind and drivetrain noise must be minimised and properly isolatedThe excitation sources like tires ,drivetrain, engine and road roughness and irregularities affect the dynamics of ride.The suspension system must be set in appropriate rubber mountings to isolate high-frequency roadway induced vibrations.However,the natural frequency of a suspension system is still considered a cornerstone of comfortable ride.Example:-Natural frequency of a suspension is determined by the formula:-
fn=188/(deflection)1/2
where fn=Natural frequency in CPM and static deflection is the distance the sprung mass moves downwards in response to weight in inches.
The selection of damping ratio is a sensitive issue when a too small damping may compromise vehicle dynamic performance and a too high damping leads to increase in system damping rigidity.Tires too play a significant role.The forces generated by roadway irregularities must be overcome by springs in order to keep tires in contact with the road.When the tires are firmly in contact with the road,best ride is attained and this is in case of high sprung to unsprung ratio.
Therefore,the science of vibration and natural frequency can determine the perception of ride and its quality.
