27-08-2013, 04:27 PM
Suspension systems and components
Suspension systems.pdf (Size: 1.22 MB / Downloads: 255)
Objectives
To provide good ride and handling performance –
– vertical compliance providing chassis isolation
– ensuring that the wheels follow the road profile
– very little tire load fluctuation
To ensure that steering control is maintained during maneuvering –
– wheels to be maintained in the proper position wrt road surface
To ensure that the vehicle responds favorably to control forces produced by the
tires during
longitudinal braking
accelerating forces,
lateral cornering forces and
braking and accelerating torques
this requires the suspension geometry to be designed to resist squat, dive and roll of the
vehicle body
To provide isolation from high frequency vibration from tire excitation
– requires appropriate isolation in the suspension joints
– Prevent transmission of ‘road noise’ to the vehicle body
Vehicle Axis system
• Un-sprung mass
• Right-hand orthogonal axis
system fixed in a vehicle
• x-axis
is
substantially
horizontal, points forward, and
is in the longitudinal plane of
symmetry.
• y-axis points to driver's right
and
• z-axis points downward.
• Rotations:
– A yaw rotation about z-axis.
– A pitch rotation about y-axis.
– A roll rotation about x-axis
Analysis of Suspension Mechanisms
3D mechanisms
Compliant bushes create variable link lengths
2D approximations used for analysis
Requirement
– Guide the wheel along a vertical path
– Without change in camber
• Suspension mechanism has various SDOF
mechanisms
Suspension Types -Dependent
• Motion of a wheel on one side of the vehicle
is dependent on the motion of its partner on
the other side
• Rarely used in modern passenger cars
– Can not give good ride
– Can not control high braking and accelerating
torques
• Used in commercial and off-highway vehicles
Limitations of Roll Centre Analysis
• As roll of the sprung mass takes place, the
suspension geometry changes, symmetry of
the suspension across the vehicle is lost and
the definition of roll centre becomes invalid.
– It relates to the non-rolled vehicle condition and
can therefore only be used for approximations
involving small angles of roll
– Assumes no change in vehicle track as a result of
small angles of roll.