Rear Semi-Trailing Arm

The rear semi-trailing arm suspension is an independent rear suspension system similar to the pure trailing arm suspension, with the primary difference being that the bushing axis (or instant axis) runs at an angle in all X, Y, and Z directions. The rear semi-trailing arm suspension combines the advantages of the trailing arm and double-pivot swing axle suspension principles, without the associated disadvantages. The semi-trailing arms resemble triangulated wishbones, with the pivots arranged at an angle to the vehicle's transverse axis and either horizontal or slightly towards the vehicle's centerline.

Figure 1. Rear Semi-Trailing Arm Suspension

Model Use

The rear semi-trailing arm 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.

Figure 2. Rear-Half-Vehicle Model Employing a Semi-Trailing Arm Suspension

The image below shows the Project Browser view of the systems in a fully populated rear suspension model. The Rear semitrail arm susp system has five “child” systems.

Figure 3. Browser View of a Rear-Half-Vehicle Model Systems and Subsystems Employing a Semi-Trailing Arm 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 semi-trailing arm suspension:

Figure 4. Right Side Principal Points – Rear Semi-Trailing Arm 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 semi-trailing arm suspension is comprised of the bodies shown in the image below:

Figure 5. Right Side Bodies – Rear Quad-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.

Bushings and Joints

The table below describes the bodies, bushings, and joints for the rear semi-trailing arm suspension:

Note: The table omits the left side joints for clarity.

Label	Type	Body 1	Body 2	Point
Trailing Arm Wheel Revolute Joint	Revolute	Wheel Hub	Semi-Trailing Arm	Wheel Center
Wheel Hub Fix Jt	Fixed	Wheel	Wheel Hub	Wheel Center
Inner Toe Link Bush	Universal	Toe Link	Semi-Trailing Arm	Inner Toe Link
Outer Toe Link Bush	Ball	Toe Link	Semi-Trailing Arm	Outer Toe Link
Trailing Arm Outer Bush	Bush	Semi-Trailing Arm	Vehicle Body	Outer Trail Arm Bushing
Trailing Arm Inner Bush	Bush	Semi-Trailing Arm	Vehicle Body	Inner Trail Arm Bushing

The following image shows the location of the joints and bushings in the suspension:

Figure 6. Right Side Joints and Bushings: Rear Semi-Trailing Arm Suspension