The multi-link suspension derives its name from the fact that it is made up of three or
more links. The MotionView multi-link suspension contains four
links, and it is generally used on cars and off-road vehicles. This suspension offers
flexibility to the designer, since each link’s location can be determined
independently.
Figure 1. Front Multi-link Suspension
In conventional designs, the coil spring (or optionally a torsion bar), shock
absorber, and jounce bumper act between the one lower link and chassis. Hence the lower link
carries most of the load and defines the motion of the lower end of the knuckle. The upper
links carry smaller loads and define the motion of the upper portion of the knuckle. The
steering motion of the knuckle is controlled by the tie rod and the motion of the steering
system. In the vehicle library, the steering systems
contain the tie rod.
Model Use
The front multi-link can be used in either a half car or a full
vehicle analysis. The default geometry and mass is that of a passenger car or light truck,
however the model and data can be revised to reflect any size vehicle, from a large truck to
a scale model car.
Note:
The wheel body represents the mass and inertia of the tire and
the rim.
The wheel hub body represents the mass and inertia of other
rotating bodies such as a brake rotor, but not the half-shafts if the suspension is
driven. The wheel hub and brake rotor have no associated graphics.
The wheel and wheel hub parts use the Wheel CG location as the
center of gravity.
Each body’s Center of Gravity (CG) is estimated from the body’s
geometry. The formulas are coded into the point panel and can be seen via the graphical
user interface. If more accurate CG locations are available they should be used.
The point giving the location of the ball joint between the suspension knuckle and
steering tie rod point resides in the steering system.
Tip:
A wide variety of combinations of suspensions and subsystems can be built using the
Assembly Wizard. You are encouraged to build systems and
understand the resulting model using the graphical user interface.
When building a
new suspension model, build the model with all of the optional systems (stabilizer
bar, etc) included in the model. Immediately turn off the systems using the Project Browser and run an analysis on the base suspension to ensure it
solves properly. As data becomes available for the optional systems; activate those
systems and populate them with data.
Figure 2. Front-Half-Vehicle Model Employing a Multi-link SuspensionThe image below shows the Project Browser view of the systems in a fully populated front suspension model. The Frnt multilink susp system has four “child”
systems. Figure 3. Browser View of a Front-Half-Vehicle Model Systems and Subsystems Employing a
Multi-link Suspension
Points
Points locate the joints and bushings that connect the
suspension bodies to one another. The image below shows the principal points for
the front multi-link suspension: Figure 4. Right Side Principal Points – Front Multi-link Suspension
Note: The image above omits the left side of the suspension, points
locating body centers of mass, and points that locate the optional subsystems (springs,
dampers, bump stops and stabilizer bar) for clarity.
Bodies
The front multi-link suspension is comprised of the bodies shown in the image
below: Figure 5. Right Side Bodies – Front Multi-link Suspension
Note: Optional subsystems may add bodies to the suspension, for example the shock
absorber adds two bodies: a shock rod and shock tube. Any bodies added by optional
subsystems have been omitted from the image above for clarity.
The wheel hub body has no associated graphics and therefore is not
visible in the image above.
Bushings and Joints
The table below describes the bodies, bushings, and joints for the front multi-link:
Note: The table omits the left side joints for clarity.
Label
Type
Body 1
Body 2
Point
Notes
Front Lower Ball Joint
Spherical
Knuckle
Front Lower Control Arm
Front Lower Ball Joint
When the Compliant option is set to No, the compliance for
this joint is turned "Off" and behaves as a pure spherical joint.
Rear Lower Ball Joint
Spherical
Knuckle
Rear Lower Control Arm
Rear Lower Ball Joint
When the Compliant option is set to No, the compliance for
this joint is turned "Off" and behaves as a pure spherical joint.
Front Upper Ball Joint
Spherical
Knuckle
Front Upper Control Arm
Front Upper Ball Joint
When the Compliant option is set to No, the compliance for
this joint is turned "Off" and behaves as a pure spherical joint.
Rear Upper Ball Joint
Spherical
Knuckle
Rear Upper Control Arm
Rear Upper Ball Joint
When the Compliant option is set to No, the compliance for
this joint is turned "Off" and behaves as a pure spherical joint.
Wheel Spindle
Revolute
Wheel Hub
Knuckle
Wheel Center
Wheel Hub
Fix Jt
Fixed Joint
Wheel
Wheel Hub
Wheel Center
When the Spindle compliance option is set to Yes, the joint type changes to
universal.
LCA Front Bush
Universal
Front Lower Control Arm
Subframe, Vehicle Body or Ground
Front Lower Control Arm Bush
When the Compliant option is set to No, this joint compliance is
turned "Off" and behaves as a pure universal joint.
LCA Rear Bush
Universal
Rear Lower Control Arm
Subframe, Vehicle Body or Ground
Rear Lower Control Arm Bush
When the Compliant option is set to No, this joint compliance is
turned "Off" and behaves as a pure universal joint.
UCA Front Bush
Universal
Front Upper Control Arm
Subframe, Vehicle Body or Ground
Front Upper Control Arm Bush
When the Compliant option is set to No, this joint compliance is
turned "Off" and behaves as a pure universal joint.
UCA Rear Bush
Universal
Rear Upper Control Arm
Subframe, Vehicle Body or Ground
Rear Upper Control Arm Bush
When the Compliant option is set to No, this joint compliance is
turned "Off" and behaves as a pure universal joint.
The following image shows the location of the joints and bushings in the
suspension: Figure 6. Right Side Joints and Bushings - Front MacPherson Strut Suspension with Two (2)
Piece Lower Control Arm
