Rear MacPherson Strut

A Rear MacPherson Strut suspension is included in the Vehicle Library. The knuckle and wheel are located by a control arm, strut, and toe link. The coil spring is part of the strut and acts between the strut tube and the vehicle body. The spring’s axis typically is not parallel to the strut, but is offset to minimize the bending moment in the strut.

rear_macpherson_strut_1pc_lca_mv

Rear MacPherson Strut Suspension

System Options

The Rear MacPherson Strut suspension offers a standard set of attachments, options, and properties that you can set by selecting the suspension system in the Project Browser to display the System/Assembly panel.

Attachments

Attachments determine how the MacPherson Strut suspension connects to the rest of the vehicle. The Rear MacPherson Strut suspension has attachments for the lower control arm (LCA) and toe link. The strut rod attachment is set in the strut subsystem:

•

The lower control arm attaches to the sub-frame by default, if a subframe is present. When a sub-frame is not present in the model, the Assembly Wizard attaches the lower control arm to the vehicle body. If the vehicle body is not present, for example in a half vehicle model, then the Assembly Wizard will attach the lower control arm (LCA) to ground. You can set the attachment for the lower control arm using the Attachment Wizard from the Model menu, or by selecting the Rear MacPherson Strut suspension system in the Project Browser and revising the attachments within the Attachments tab on the System/Assembly panel.

•

The toe link attaches to the rear sub-frame by default. When a rear sub-frame is not present, then the toe link attaches to the vehicle body. When a vehicle body is not present, for example in a half vehicle model, the Assembly Wizard attaches the toe link to ground. The toe link attachment can be set to any body using the Attachment Wizard, or by selecting the Rear MacPherson Strut suspension in the Project Browser and revising the attachments within the Attachments tab on the System/Assembly panel.

•

The strut-rod attaches to the vehicle body by default. When a vehicle body is not present in the model, for example in a half vehicle model, then the Assembly Wizard will attach the strut-rod to ground. You set the strut-rod attachment as you desire using the Attachment Wizard, or by selecting the strut subsystem in the Project Browser and revising the attachments within the Attachments tab on the System/Assembly panel.

Compliant Option

Like all Vehicle Library suspension systems, the Rear MacPherson Strut (1pc LCA) suspension includes a Compliant option. When you set the Compliant option to No, the suspension bushings are replaced with joints making the suspension kinematic. To set the value of the Compliant option, select the Rear MacPherson Strut suspension in the Project Browser and click the Options tab on the System/Assembly panel.

When the Compliant option is set to No, the lower control arm bushings are replaced with a single revolute joint at the front bushing, with a rotational axis directed along the line from the front LCA bushing to the rear LCA bushing. The toe link inner bushing is replaced with a universal joint, and the toe link outer bushing is replaced with a spherical joint.

Spindle Compliance Option

When you set the Spindle compliance option to Yes, the wheel body connects to the wheel hub via a universal joint and bushing. The universal joint allows camber and toe deflection of the wheel relative to the wheel hub. The wheel hub bushing’s Kx and Ky rates determine the amount of spindle compliance introduced. To set the Spindle compliance option, select the Rear MacPherson Strut (1pc LCA) suspension in the Project Browser and click the Options tab on the System/Assembly panel.

Static Wheel Alignment

The Rear MacPherson Strut (1pc LCA) suspension includes a static alignment dataset and form holding toe and camber variables that determine the orientation of the wheel relative to the knuckle and body in the Global coordinate system. To set the values for toe and camber, select either the static alignment dataset or form and alter the values of the toe and camber variables. It is important to note that you cannot set the toe angle and camber angle independently for the left and right wheels; the toe and camber values must be symmetric.

The toe and camber values that you set will change the location of the spindle align point relative to the wheel center point via parametric expressions. You can view these expressions by selecting the spindle align point and examining its X, Y, and Z locations.

Subsystem Options

The Rear MacPherson Strut suspension requires a strut model, since the strut is a kinematic element in a MacPherson Strut suspension. The strut also includes a coil spring and shock absorber. You can also choose whether your suspension includes strut, stabilizer bar, jounce bumper, or rebound bumper subsystems. The table below shows the optional subsystems available with the Rear MacPherson Strut suspension:

Subsystem

Options

Struts	----	Two (2) Inline Joints	One (1) Cylindrical Joint	Deformable Rod with Two (2) Inline Joints
Stabilizer Bar	None	Stabilizer Bar with Links	Two (2) Piece Bar with Links
Jounce Bumper	None	Internal to Shock	External Jounce Bumper
Rebound Bumper	None	Internal to Shock	External Rebound Bumper

Notes

•	Coil springs act between the strut tube and the vehicle body (attachment).

•	The Rear MacPherson Strut suspension system contains points for the upper and lower spring seats to locate coil springs.

•	Internal jounce and rebound bumpers act between the strut tube and strut rod.

•	External jounce and rebound bumpers act between the lower control arm and the Vehicle Body.

•	You can alter how optional subsystems attach to the suspension by selecting the subsystem in the Project Browser and altering the subsystem’s attachments.

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 MacPherson Strut suspension with a one piece lower control arm:

rear_macpherson_strut_1pc_lca_points_mv

Right Side Principal Points – Rear MacPherson Strut 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 MacPherson Strut suspension is comprised of the bodies shown in the image below:

rear_macpherson_strut_1pc_lca_bodies_mv

Right Side Bodies – Rear MacPherson Strut Suspension (Coil Spring Omitted for Clarity)

Note	Only right side bodies are shown (as the left side bodies are symmetrical), and the coil spring has 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 Rear MacPherson Strut suspension:

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

Label	Type	Body 1	Body 2	Point	Notes
Lower Ball Joint	Spherical	Knuckle	Lower Control Arm	Lower Ball Joint	----
Wheel Spindle	Revolute	Wheel Hub	Knuckle	Wheel Center	----
Wheel Hub Fix Jt	Fixed-Joint	Wheel	Wheel Hub	Wheel Center	When the 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
Inner Toe Link Bush	Universal Joint	Toe Link	Subframe, Vehicle Body or Ground	Inner Toe Link Bush	When the Compliant option is set to Yes, this joint becomes compliant.
Outer Toe Link Bush	Spherical Joint	Toe Link	Knuckle	Outer Toe Link Bush	When the Compliant option is set to Yes, this joint becomes compliant.
Strut Tube Bottom Fixed Joint	Fixed-Joint	Strut Tube	Knuckle	Strut Tube Lower	----
Strut Upper Bush	Universal Joint	Strut Tube	Vehicle Body	Strut Upper	----

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

rear_macpherson_strut_1pc_lca_jnts_bushings_mv

Right Side Joints and Bushings - Rear MacPherson Strut Suspension

Use of this Model

The Rear MacPherson Strut suspension system can be used in either a rear half vehicle or a full vehicle models. The default geometry and mass approximate that of a passenger car or light truck, but the model and data can be revised to reflect any size vehicle, from a large truck to a scale model car.

Notes

•	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 Center location as the center of gravity.

•	The lower control arm bushings are defined so their axes point at each other act like hinges on a door. If the front bushing is moved, both the front and rear bushing realign so they have the same axis of rotation.

•	When the Compliant option is set to No (via the Option menu on the System/Assembly panel in MotionView) the lower control arm bushings are replaced with a single revolute joint located at the front bushing, with its rotational axis directed along the line from the front bushing to the rear bushing.

Tips

•	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 MotionView Project Browser view of the systems in a fully populated rear suspension model. The Rear macpherson susp system has four “child” systems.

rear_macpherson_strut_1pc_lca_browser_mv

Browser view of a Rear-Half-Vehicle Model Systems and Subsystems Employing a Rear MacPherson Strut Suspension

Similar Suspensions:

•	Front MacPherson Strut (1 pc. LCA)

•	Front MacPherson Strut (2 pc. LCA)

•	Rear Quad-Link