Rear SLA (1pc LCA)

A Short-Long Arm (SLA) suspension is included in the vehicle library as both a front and rear suspension. This configuration is also known as a Double Wishbone suspension. The coil spring and the shock absorber typically connect to the lower control arm. The SLA name is derived from the length of the control arms. The lower arm is typically long to provide a good spring lever ratio. The upper arm is typically short to provide the proper camber curve. This suspension is widely used on cars, light trucks, and on independent suspension heavy trucks.



Figure 1. Rear SLA Suspension with One (1) Piece Lower Control Arm and Optional Subsystems: External Jounce/Rebound Bumper and Stabilizer Bar Subsystems
In conventional designs the coil spring carries the load of the spring and defines the motion of the lower ball joint location on the knuckle. The upper control arm defines the motion of the upper ball joint location on the knuckle.
  • The wheel is connected to the wheel hub with a fixed joint.
  • The wheel hub is connected to the knuckle with a revolute joint.
  • The knuckle is connected to the upper control arm (UCA) and lower control arm (LCA) with a spherical joint.
  • The upper control arm and lower control arm is connected to a sub frame or the chassis with two bushings.
  • The lower control arm is modeled as a single rigid body (1pc LCA).
  • The suspension in the library is symmetric.

Model Use

The rear SLA (1pc LCA) 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 of the tire and the rim.
  • The wheel hub body represents the mass of the wheel hub and any other components that rotate with the hub, such as a brake rotor. There are no graphic entities for the wheel hub.
  • The upper control arm bushings are defined so their axes are parallel. If the front bushing is moved, both the front and rear bushing realign so that they have the same axis of rotation. The lower control arm bushings’ rotational axes are defined in the same manner.
  • 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 wheel and wheel hub parts use the Wheel CG location as the center of gravity.
  • When the suspension is built as a kinematic suspension, the upper control arm bushings are replaced with a single revolute joint located at the forward bushing location. The lower control arm bushings are replaced with a revolute joint in the same fashion.
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 SLA susp (1 pc LCA) system has five “child” systems.


Figure 2. Browser view of a Rear-Half-Vehicle Model Systems and Subsystems Employing a SLA Suspension with One (1) Piece Lower Control Arm

Attachments

Attachments determine what bodies residing outside the suspension system that the suspension attaches to. The rear SLA (1pc LCA) suspension includes attachments for the lower control arm (LCA), upper control arm (UCA), and toe link:
Entity Attaches To
Lower Control Arm Default: Sub-frame

No subframe: Vehicle body

No vehicle body: Ground

Upper Control Arm Default: Sub-frame

No subframe: Vehicle body

No vehicle body: Ground

Toe Link
Note: The toe link is only found when the SLA suspension is on the rear.
Default: Rear Sub-frame

No subframe: Vehicle body

No vehicle body: Ground

You can also set any attachments using the Attachment Wizard, or by selecting the subsystem in the Project Browser and revising the attachments on the System/Assembly panel.

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 SLA (1pc LCA) suspension:


Figure 3. Right Side Principal Points – Rear SLA Suspension with One (1) Piece Lower Control Arm
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 SLA (1pc LCA) suspension is comprised of the bodies shown in the image below.


Figure 4. Right Side Bodies – Rear SLA Suspension with One (1) Piece Lower Control Arm
Note:

Bushings and Joints

The table below describes the bodies, bushings, and joints for a rear SLA (1pc LCA) suspension:
Note: The shock absorber joints are documented in the shock absorber section.
Label Type Body 1 Body 2 Point Notes
Lower Ball Joint Spherical Knuckle Lower Control Arm Lower Ball Joint  
Upper Ball Joint Spherical Knuckle Upper Control Arm Upper Ball Joint  
Wheel Spindle Revolute Wheel Hub Knuckle Wheel Center  
Wheel Hub

Fix Jt

Fixed-Joint Wheel Wheel Hub Wheel Center When Spindle compliance is set to Yes, the joint type changes to universal and a bushing is superimposed to model the wheel bearing compliance.
LCA Front Bush Bushing Lower Control Arm Subframe, Vehicle Body or Ground LCA Front Bush When the Compliant option is set to No, this bushing becomes a revolute joint.
LCA Rear Bush Bushing Lower Control Arm Subframe, Vehicle Body or Ground LCA Rear Bush When the Compliant option is set to No, this bushing is deactivated.
UCA Front Bush Bushing Upper Control Arm Subframe, Vehicle Body or Ground UCA Front Bush When the Compliant option is set to No, this bushing becomes a revolute joint.
UCA Rear Bush Bushing Upper Control Arm Subframe, Vehicle Body or Ground UCA Rear Bush When the Compliant option is set to No, this bushing is deactivated.
Inner toe Link Bush Universal Joint Toe Link Subframe, Vehicle Body or Ground Inner toe Link Bush  
Outer Toe Link Bush Spherical Joint Toe Link Knuckle Outer Toe Link Bush  
The following image shows the location of the joints and bushings in the suspension:


Figure 5. Right Side Joints and Bushings: Rear SLA Suspension with One (1) Piece Lower Control Arm

External Files

The jounce bumper curve data and the rebound bumper curve data files are stored in the vehicle library and are referred to by this model. A new file should be created and substituted for these files when actual data is available.

Similar Suspensions

Front SLA (2pc LCA)

Rear SLA (1pc LCA)

Rear SLA (2pc LCA)