Design and Experimental Study of Progressive Spring for Formula Student Race Car

: The purpose of carrying out the present work is to design, manufacture & test the progressive springs on an FS vehicle. This is one type of helical spring with a variable spring rate. The main purpose of designing progressive springs is to avail all the advantages of the variable spring rate over the linear spring rate and better ride quality along with roll control, compared to linear rate springs. We took several factors of vehicle dynamics under consideration before settling on progressive springs. Before starting with the design procedure, we had set objectives and followed the standard methodology of spring design to get the required output. Along with that, we took design philosophy under consideration. We reviewed all the parameters before finalizing the spring material as it is one of the major factors. We carried out all the necessary design calculations to complete the dimensions and stiffness of the spring. The conclusion helped us to achieve better ride quality and roll control accompanying the optimized spring design satisfying all the necessities such as load, stiffness, and deflection of progressive springs.


INTRODUCTION:
FS car's suspension springs compress to absorb impact when tires roll over irregular terrain and keep the car off the ground in correspondence with the damper. The two types of springs used in race cars are linear and progressive. Which one do you think is best for FS cars? On the one hand, progressive-rate springs generally have less total deflection; they also provide the benefits of a lowered car -better handling, reduced nose dive, and decreased body roll, along with better ride quality. This is because the closely wound coils needed to create the dual rates take up deflection space. As a progressive spring compresses, the spring rate will gradually increase. On the other hand, in linear springs, the spring rate is constant, and it is not affected by the load acting on the spring. In this paper, a detailed design procedure and analytical calculation of progressive spring for FS car followed by the experimental study whose results were obtained by spring load testing machine are explained.

Problem Statement
Why choose progressive rate springs over linear rate springs? Progressive springs contribute to the roll control of the vehicle. A progressive spring does not have a constant rate of deflection. For this reason, they are called variable rate springs. Since racetracks have different road surfaces, a suspension that is adaptive to changing with road surfaces is desired. It also means to achieve a compliant suspension in the rough and a tight suspension for high-speed turns. Whereas linear springs allow working easily because the spring rate is constant, this results in quick tuning as many teams avoid risking in terms of suspension settings. Hence progressive springs become a great advantage.
But even after choosing progressive, how will one assure whether it is satisfactory or not? Rather how will one determine the behavior of spring? So that is when the experimental study comes into play which has to go hand in hand with the theoretical research. The load testing setup provides us with estimated results that are further validated with results from testing a car and running it on progressive springs. And then, it leads to the final lock to the tuning.

Objectives
1. To achieve better ride quality and superior handling due to the roll control offered by the springs. 2. To get a lower ride height, increased stiffness through hard cornering, and a more comfortable ride over a stiffer ride. 3. To avail the advantages of the dual stiffness over the different track conditions. 4. To validate the design by correlating design calculations with the testing results data.

Abbreviations
1. FS-formula student 2. k -spring stiffness 3. k1-spring stiffness of softer region of coil 4. k2 -spring stiffness of stiffer region of coil 5. W -load acting on spring 6. W1 -load acting on softer region of coil 7. W2 -load acting on stiffer region of coil 8.

RESULTS:
The designed spring is being tested on an industrial spring testing machine. The results of testing are given in the form of load v/s deflection graph shown in fig.2.

DISCUSSION:
The spring's progressive behavior could be observed from fig.2 Load v/s deflection graph. Initially, the graph is non-linear and then it turns into linear which indicates that at the beginning the load required to deflect the spring up to certain extent is less, and afterward as the deflection goes on increasing the load required increases linearly.

CONCLUSIONS:
In this research paper, part of the discussion is a study about the design of progressive springs for FS cars. This attempt was helpful to get successful results, as we tested the progressive springs on the FS car and an industrial spring testing machine. The stiffness of 29 N/mm at the softer region and 37 N/mm at the stiffer region was being finalized, and the spring with this stiffness fulfilled the aim of both the softer rate at the low load and the stiffer rate for the sharp turns. The stiffness of springs increased with increasing load in parabolic nature. This fascinated the required load transfer at corners. Its starting low stiffness also provided comfort to the driver at small bumps and droops. It provides the required stiffness as well as the maximum strength, which was necessary for our design. At the same time, it also satisfied all the constraints of free length, maximum bump travel, and droop travel. The iteration we performed to achieve the required stiffness within the constraints was successful, and the design gave us the needed results on testing. We validated the spring design with the help of actual testing.