Multilink Suspension#

The multilink suspension is a type of suspension system that uses a series of arms to locate the wheel. This system is widely used in high-performance vehicles because it allows for better control of the wheel’s movement, providing improved handling and comfort. The multilink suspension is complex, as it uses multiple arms to locate the wheel, which allows for precise control of the wheel’s movement.

Key Components#

The multilink suspension can be viewed as a variation of the Double Wishbone Suspension, where the Upper Control Arm and the Lower Control Arm are split into two bars.

Upper Control Arms (UCAs): The upper bars or control arms connect the upper part of the wheel hub to the vehicle chassis. They help control the vertical movement of the wheel and maintain the wheel’s alignment.
Lower Control Arms (LCAs): The lower bars or control arms connect the lower part of the wheel hub to the vehicle chassis. They work in conjunction with the upper control arms to manage the wheel’s movement and alignment.
Knuckle or Upright: This component connects the upper and lower control arms to the wheel hub. It allows the wheel to pivot for steering and supports the wheel bearings.
Tie Rod: In the case of front suspensions, the tie rod connects the steering rack to the wheel hub, allowing for steering input to be transmitted to the wheels.
Spring and Damper: These components are crucial for absorbing shocks and maintaining ride comfort. The position of the spring and damper in the suspension system can be adapted to various configurations, meaning they can be placed in different locations depending on the design requirements.

Configuration: Base#

Note

For an interactive visualization of the suspension, view the CAD example representation: Multilink Base.

The base system of the Double Wishbone suspension is defined using 11 points, as presented in Points Defining the Base Multilink Suspension. Of these, 6 points represent the vehicle chassis and are considered fixed, as the kinematic analysis is relative to these coordinates.

By convention, chassis points (fixed points) are named with letters (UCA FRONT, UCA REAR, LCA FRONT, LCA REAR), while mobile points are named with numbers (uca outer, lca outer, tierod outer, uca outer aux, lca outer aux, wheel center).

Multilink Suspension: Base Configuration

The TIEROD INNER point refers to the steering system (or toe link in the case of rear suspension), which is considered fixed in the analysis. Therefore, the system has a single degree of freedom, requiring a total of 11 constraint equations. To account for the steering behavior, several analyses must be conducted by varying this point’s coordinates.

Points Defining the Base Multilink Suspension#
Points Name	Description	Type
wheel center	Center of the Wheel	mobile
UCA FRONT	Upper Control Arm Front	fixed
UCA REAR	Upper Control Arm Rear	fixed
uca outer	Upper Control Arm Outer	mobile
LCA FRONT	Lower Control Arm Front	fixed
LCA REAR	Lower Control Arm Rear	fixed
lca outer	Lower Control Arm Outer	mobile
TIEROD INNER	Inner Tie Rod	fixed
tierod outer	Outer Tie Rod	mobile
uca outer aux	Upper Control Arm Outer aux	mobile
lca outer aux	Lower Control Arm Outer aux	mobile

The 17 constraint equations necessary to define the system are presented in table Constraint Equations: Base Wishbone Suspension.

Note that all the constraint equations are based on the distance between two points, defined as the square root of the sum of the squares of the differences of the coordinates of the points. With this type of constraint equation, combining several types, it is possible to define the wishbones, tie rod, and all the components. The constraint equations will be represented as explained in Convention for Writing Proposals.

Constraint Equations: Base Wishbone Suspension#
Equation	Initial Point	Final Point
1	uca outer	UCA FRONT
2	uca outer aux	UCA REAR
3	lca outer	LCA FRONT
4	lca outer aux	LCA REAR
5	tierod outer	TIEROD INNER
6	lca outer	uca outer
7	tierod outer	uca outer
8	tierod outer	lca outer
9	uca outer aux	uca outer
10	uca outer aux	lca outer
11	uca outer aux	tierod outer
12	lca outer aux	uca outer
13	lca outer aux	lca outer
14	lca outer aux	tierod outer
15	wheel center	uca outer
16	wheel center	lca outer
17	wheel center	tierod outer

Configuration: 1#

Note

For an interactive visualization of the suspension, view the CAD example representation: Multilink: Configuration 1.

In this configuration, the spring-damper assembly is introduced. The lower point of the suspension (l spring mount) is connected to the knuckle. The other end (U SPRING MOUNT) is connected directly to the vehicle chassis.

The system is defined by adding the equations that define the position of the connection point between the suspension and the knuckle to the base Multilink system equations.

Points Defining the Multilink Suspension Configuration 1#
Points Name	Description	Type
wheel center	Center of the Wheel	mobile
UCA FRONT	Upper Control Arm Front	fixed
UCA REAR	Upper Control Arm Rear	fixed
uca outer	Upper Control Arm Outer	mobile
LCA FRONT	Lower Control Arm Front	fixed
LCA REAR	Lower Control Arm Rear	fixed
lca outer	Lower Control Arm Outer	mobile
TIEROD INNER	Inner Tie Rod	fixed
tierod outer	Outer Tie Rod	mobile
uca outer aux	Upper Control Arm Outer aux	mobile
lca outer aux	Lower Control Arm Outer aux	mobile

Constraint Equations: Configuration 1 Multilink Suspension#
Equation	Initial Point	Final Point
1	uca outer	UCA FRONT
2	uca outer aux	UCA REAR
3	lca outer	LCA FRONT
4	lca outer aux	LCA REAR
5	tierod outer	TIEROD INNER
6	lca outer	uca outer
7	tierod outer	uca outer
8	tierod outer	lca outer
9	uca outer aux	uca outer
10	uca outer aux	lca outer
11	uca outer aux	tierod outer
12	lca outer aux	uca outer
13	lca outer aux	lca outer
14	lca outer aux	tierod outer
15	wheel center	uca outer
16	wheel center	lca outer
17	wheel center	tierod outer
18	Spring/Damper Lower Mount	uca outer
19	Spring/Damper Lower Mount	lca outer
20	Spring/Damper Lower Mount	tierod outer