Dynamic 4-link Suspension ET 493 Cole Prejean Advisor: Dr. Ho-Hoon Lee

What is a 4-link? A 4-link suspension is a four bar linkage system used in drag racing applications. It is used to connect the rear axel to the chassis, directing the force of acceleration.

4-link directs forces to provide ideal traction

Typical 4-link suspension

4-link suspending rear axel

How it works

Forces Acting on Rear Tire

All About Friction The weight of the rear tires on the track is used to compute the frictional force. The coefficient of friction µ of rubber on concrete is If the weight of the car is 2450 lb. and only rear tires are on track we can assume max Ff. Ff=µN. Ff=2450(.8)

Instant Center

Instant Center (IC) Imaginary point at which bars will intersect. Many different intersect points can be used with existing systems. Different adjustment holes locate linkages.

Analysis of Launch Before the car accelerates, the front to rear weight is about equal (depending on static weight bias) which means the force of the surface is acting almost equally on all tires. Once acceleration is applied to the rear axel, pitch rotation of the car occurs, thus applying more weight to the rear of the car, since the system is suspended by front and rear shocks.

Data Aquisition

High IC A high intersect point directs forces upward, trying to push the car skyward. This reaction forces down the rear axle, providing a higher reaction force against the tire. Extends rear shock absorbers. Less force applied in horizontal direction.

High IC

Low IC A low IC will push the chassis towards the ground. Traction is reduced. Compresses rear suspension.

Low IC

Force of Acceleration

Difference Example High IC creates 300lb. More downward force on rear axle than the low IC. This will create more traction.

Objective Create method to change angle of bottom bar during race, resulting in repositioned IC. Changing IC will redirect forces acting on chassis providing ideal traction at different positions on race track.

The plan To move the bottom bar, instead of adjustment holes, a pivot system will be used. The angle will be controlled by an actuator on each side of the system.

Pivot Groove

Timeline TaskResult 3/12 Approval of project Complete 3/20 Find max acceleration, research of chassis dynamicsComplete 3/28 Calculation of all forces acting on system Complete 4/3 Determine how changing force angles act on rigid body Complete 4/10 Apply forces to 4-link configurations Complete 4/18 Show that difference of IC locations changes force on tires Complete 5/1 Construct draft of pivot bracket Complete