Vehicle Dynamics Engineer · GTU Motorsports, Formula Student · Apr 2019 to Mar 2021

A damper cage that always compresses the roll spring

CAD drawing, front view: pushrods from the wheels to rockers, a heave spring-damper between the rockers, and the roll spring-damper inside its cage — Fig.
1
Title
The heave and roll units with their pushrods, in CAD
Kind
CAD render
Source
GTU Motorsports, Formula Student

Problem

The roll damper sits inclined between the two rockers. In roll one way it compresses; in roll the other way it extends. A damper resists both, but a spring pushes back only when it is compressed, so on its own the roll spring would hold the car in one direction of roll and not the other.

Approach

I designed a cage around the spring-damper: two yokes on four guide rods. However the rockers move the cage, pulling it apart or pushing it together, the yokes compress the spring-damper inside (Fig. 2). The roll spring works in both directions, and the unit fits where a conventional layout did not.

Fig.: 2
Title: Why the cage: the roll spring-damper without and with it
Kind: Schematic, principle only, not to scale
Source: Drawn for this site
Note: Phantom: at rest; solid: displaced; the spring in the accent. The yokes are drawn as plates and rods, not to their shape; the CAD shows the real cage.

What I did

Designed the cage: two end yokes on four guide rods, with the spring-damper and its rod ends held between them (Fig. 3).
Placed it between the rockers, beside the heave spring-damper (Fig. 4).
Designed a later iteration on linear bearings and low-friction joints, for more precise motion.
Took mass out of the cage, one of many small steps on parts that were already light.

CAD render of the damper cage: two end yokes joined by four guide rods, with a spring-damper unit and rod ends held between them — Fig.
3
Title
The damper cage: one spring-damper held between two yokes on four guide rods, loaded in compression whether the rocker pushes or pulls
Kind
CAD render
Source
GTU Motorsports, Formula Student

CAD render of the 2021 design's rear bulkhead assembly: plates carrying the rocker assemblies with two spring-dampers between them, the drive sprocket and brake disc, and the suspension links — Fig.
4
Title
Where the cage sits in the 2021 design: the rear bulkhead assembly, in CAD
Kind
CAD render
Source
GTU Motorsports, Formula Student

Result

Ran on track at Formula Bharat 2020, on the team's first decoupled heave and roll suspension.