chapter 3
DESCRIPTION
bab 3 vehicle dinamicTRANSCRIPT
CHAPTER 3 : RIDENABILA SULAIMAN JKM PSAS
What is Handling ? Stability measures the time domain response of a
vehicle to disturbance inputs 1.Normal driving 2.Spirited driving 3.Emergency maneuvers Departure from linearity induces anxiety in most drivers
in accident avoidance maneuvers potentially leading to loss of control. Driving pleasure is a subjective evaluation of how easy it
is for drivers to use their car at its handling limit in a variety of situations. Handling is influenced by component design, track and
wheel base, CG height, chassis stiffness, active
What is Ride ? Ride Comfort is a frequency weighted
measure of vertical acceleration together with subjective assessments of harshness over various external road surface induced excitations. Ride is determined by spring, bushing and
damper stiffness, component weights and natural frequencies. The Vehicle Dynamics Engineer is
challenged to strike the best balance between ride and handling to establish the
Introduction Vehicle experience a broad spectrum of vibrations
(due to high speed travel) ride reference to tactile and visual vibrations Aural vibrations noise Ride frequency 0 to 25 Hz Noise frequency 25 to 20,000 Hz Design and construction quality of a car judge
by the vibration environment
Introduction Study of lower-frequency ride vibrations mode
important for vehicle dynamics(determine the magnitude and direction of vibrations imposed on the passenger compartment) RIDE PERCEPTION VEHICLE DYNAMIC RESPONSE
(input to vehicle vibration) EXCITATIONSOURCES Road roughness Tire/wheel
VIBRATIONS
DrivelineEngine
(Vehicle System)
IntroductionMain topics of ride study including,1. 2. 3.
Ride excitation sources Basic mechanics of vehicle vibration response Human perception and tolerance of vibrations
Excitation source Two classes of ride vibrations Road roughness On-board from rotating components
(include the tire/wheel assemblies, driveline and engine)
Excitation sourceEngine/ Transmission Driveline
Road Roughness
Tire/Wheel Assembly
Excitation source road roughnessRoad serve as broad-band random signals Potholes from pavement failure to ever-present road
Road Roughness
Measured using PSM (power Spectral Density) function
Measurement of elevation along wheel tracks (deviation in elevation along a road)
Excitation Sources Road Roughness-Every road section is unique
-Characteristic drop in amplitude with wavenumber (Representing PSD)
-Represent the deviations in the road
Excitation sources Road Roughness
Constant amplitude at low frequency, begins increase rapidly above 1Hz Road roughness presents its largest input to vehicle at high frequency (high frequency ride vibrations) Important to design ride isolation behavior suspension on highway vehicle
Road roughness vertical input to the vehicle that would excite bounce
Excitation sources Tire/Wheel assembly Soft and compliant to absorb road bumps as
part of the ride isolation system
Imperfections in rotating system cause-Mass imbalance -Dimensional variations
Variations in the forces and moment as it rolls
-Stiffness variations
Transmitted to axle (excitation sources for ride vibrations
Forces (vertical, longitudinal and lateral direction
Moments (overturning, aligning torque, rolling resistance) for steering system vibrations
Excitation Sources Tire / Wheel AssemblyDynamics imbalance (nonuniform and asymmetric mass along axis of rotation)
Creates rotating torque on the wheel (tire absorb variations)
Steered wheels steering vibrations due to excitation
Contribution to imbalance effect by tires, wheels, hubs and brake drums
Excitation Sources Tire / Wheel Assembly
Significant effect of the non-uniformities in a
tire/wheel assembly is the generation of excitation forces and displacements at the axle of the vehicle as the wheel rotates.
Excitation Sources-Tire/Wheel Assembly
Radial/vertical force variations may be due to the runout of the hub
and wheel Various harmonics of radial non-uniformities in a tire/wheel assembly :
functionally equivalent to imperfections in shapes 1st harmonic due to the runout Higher harmonic runouts in the wheel are not as closely related to radial
force variations in the overall assembly
Excitation Sources Tire/Wheel Assembly 1st harmonic (eccentricity) tires, wheels and hubs individually may exhibit radial eccentricity Produces both radial and tractive excitation on the axle
2nd harmonic (Ovality) Tires and wheels may have eliptical variations that add or subtract
depending on the mounting positions
Higher-order radial variations Predominantly of importance in the tire only Such variations are substantially absorbed by the tire Effects may arise from construction methods
Radial force variations is relatively independent
of speed
Excitation Sources-Tire/Wheel Assembly Tractive force variations arise from dimensional
and stiffness non-uniformities as a result of two effectsRoll up and down the hill
Longitudinal force is involved and a tractive force variation is observed
Magnitude dependent on the load carried and amount of eccentricity, independent of speed
Excitation Sources- Tire/Wheel Assembly Lateral force variations arise from non-
uniformities in the tire, but cannot be readily related to lateral runnout effects in the wheel or hub components Independent of speed 1st order lateral runnout cause wobble, which
affect the dynamic balance of the assembly Higher order lateral variations predominantly
important in the tire only
Excitation Sources- Driveline ExcitationDriveline
DriveshaftGear reduction Differential in the drive axle Axle shafts to the wheels
Together with spline and universal joints most potential for exciting ride vibrations
Noise could be generate as a result of gear mating reactions Torsional vibration occur along drivetrain
Excitation Sources- Driveline ExcitationAsymmetry of the rotating parts
Mass imbalance
Shaft off-center
Source of driveshaft ride excitations
Elastic member and defect
Not straight Running clearances