Rear Multi-link

The multi-link suspension derives its name from the fact that it is made up of three or more links. The rear Multi-link suspension contains five links, and is generally used on higher end luxury cars. The multi-link suspension is derived from the SLA suspension, in that each wishbone (or A-Arm) is replaced with two links. This suspension offers flexibility to the designer, since each link’s location can be determined independently. In this suspension we use the term “link” and “control arm” interchangeably. Traditionally a link is a rigid body with two connections, and a control arm has three connections.

Figure 1. Rear Multi-link Suspension

In conventional designs, the coil spring, shock absorber, and jounce bumper act between the one lower link and chassis. The chosen lower control arm carries most of the load. Additionally, the rear multi-link suspension consists of a toe link, which provides toe control.

Model Use

The rear multi-link suspension system 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.

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.

The image below shows the Project Browser view of the systems in a fully populated rear suspension model. The rear multi-link suspension system has five “child” systems.

Figure 2. Browser View of a Rear-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 rear multi-link suspension:

Figure 3. Right Side Principal Points – Rear 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 rear multi-link suspension is comprised of the bodies shown in the image below:

Figure 4. Right Side Bodies – Rear Multi-link Suspension

Note:

• The wheel hub body has no associated graphics and therefore is not visible in the image above.
• 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.
• Some suspension designers refer to the control arms as links.

Bushings and Joints

The table below describes the bodies, bushings, and joints for the rear multi-link suspension:

Note: The table omits the joints internal to the strut.

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.
Outer Toe Link Bush	Spherical	Toe Link	Knuckle	Outer Toe Link Bush	When the Compliant option is set to No, the compliance for this joint is turned "Off" and behaves as a pure spherical joint.
Inner Toe Link Bush	Spherical	Toe Link	Subframe, Vehicle Body or Ground	Inner Toe Link 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 5. Right Side Joints and Bushings - Rear MacPherson Strut Suspension