REQUIREMENT FOR THE DEGREE OF. BACHELOR OF SCIENCE. IN. MECHANICAL ENGINEERING. FSAE Chassis and Suspension. Hello forum. I’m fairly new to FSAE and suspension design. One of the overwhelming problems that I’m having is figure out the step by step. This article deals with design of Formula SAE Suspension by considering various loads and their simulation on each component of the system.
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The vehicle presented in this project is the FSAE prototype of the University of Padua, which competed in the season of the series. Fsae is a students suspensipn competition where student teams from around the world design, build, test, and race a small-scale formula style racing car. The cars are judged, by industry specialists, on a number of criteria in different typologies of events, both statics and dynamics.
This event is held to evaluate the steady state cornering capabilities of the cars, thus it has been modeled to find out a basic setup and to evaluate under and oversteering capabilities of the model.
Detail of the CAD front right wheel assembly view from the inside of the car. The model is composed by the 4 wheels rim and tire fixed on the hubs which is connected with the uprights by a rotational joint, the uprights are then connected by two couples of distance constraints representing the a-arms and a single distance constraint representing the toe rod to the chassis.
On the rear the toe rods are connected with the chassis, at the front they are connected with a steering rack which is connected to the frame with a translational joint. An actuator moves the rack causing the front wheels to steer the desired angle.
It has to be taken into account that the model is only considering the roll behavior for the skidpad, consequently the roll stiffness is represented only by springs and the damping is suited for the roll behavior of the car; in the real world you have anti roll bars to get different stiffness in bump and roll, and usually the damping is the same in roll and bump, then it has to be a compromise to suit two different stiffness ie roll and bump.
Analysis of a FSAE suspension system |
The chassis is fixed to the ground for the stiffness test by a supsension joint, which is removed for the other tests. The dynamic response of other inputs will be presented only for the two better configurations on the step input. Below are represented the inputs used to evaluate the dynamic response with different configuration of spring and dampers. The step input has been used to find out the two best configurations amongst the possibilities and to present only the most relevant and suspeension results for the other inputs.
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A kerb or a cone hit at speed is a good approximation of a step input. The sine is used to represent road perturbations, depending on the frequency and the amplitude it could be roughness of the asphalt or a more severe pattern like circuit kerbs, as in our case.
The bracket joint during the dynamic response simulation is removed to have the correct behavior of the suspended and non suspended mass system. Suspensjon are presented the force and displacements graphs for the four tires in each of the six configuration mentioned in the modeling section.
The frequencies for the chassis movement have been calculated with the linearization element and are from 3. The second part of the simulation is about the skid pad, so the car now is no more constrained over four independent patches but trimmed to let it gain the neutral position on a single road and then a torque is applied symmetrically at the two rear wheels following a spline in order to avoid slip on the wuspension phases; the speed is then stabilized via vsae very high rolling resistance given to the tire and the steering rack joint driver positions the rack in order to reach the radius of the typical curve around 18 m.
Here we can see the relative speed and angular speed that stabilizes after some laps, and the results are considered only for the stabilized part of the steady state corner. Here we can see that the relative speeds in red the longitudinal component of the chassis stabilizes in the second part of the simulation.
Comparison of lateral forces and yaw accelerations of the two configurations, soft and then hard:. A test has been made even with a different stiffness distribution: On the other side low chassis movements sometimes are useful to let the driver feel better the behaviour of the car, even if higher stiffness is penalising the grip, moreover the ground clearance required always in racing limits the use of even softer springs.
In the skid pad the difference between the two configurations is very subtle because of the fact that in steady state is the stiffness distribution, which is the same, that gives you some difference. In fact with softer spring on the front the difference is a little higher, but in every skid pad simulation the grip limits of the car are NOT reached, and consequently, as is evident in the suepension acceleration graphs, the car remains neutral.
It would be interesting to investigate further to see how much is the influence of a different stiffness distribution configuration.
Analysis of a FSAE suspension system
All the results of the simulations are valid only for steady state analysis, low stiifness spring and low damping could be bad in transient situations, not only for the driver feeling. The suspenslon right after the Silverstone Event in The tire forces are modeled with a simple tire model with the following parameters: A kerb or a cone hit at speed is a good approximation of a step input Ramp: Note that the input in this case is cyclic.
A1 Suspensuon spring and low damping coefficient: B2 Medium spring and high damping coefficient: C1 Hard spring and low damping coefficient: C2 Hard spring and high damping coefficient: Moreover generally for a driver low chassis movements are better for the feeling.
Eigenvectors and eigenfrequencies calculation: Video of the Eigenmode of the chassis at 3. Soft configuration; normal tire force and displacements of rims and suxpension Hard configuration; normal tire force and displacements of rims and chassis: Response to the sine function: Comparison of lateral forces and yaw accelerations of the two configurations, soft and then hard: Web design by paomedia.