2103483 Automotive System Design (2022/2)

Suspension

Introduction of Suspension

Suspension refers to the system of components that connect the wheels to the chassis of the vehicle and absorb shocks from the road. The purpose of the suspension system is to provide a smooth and stable ride for the driver while maintaining maximum tire-to-road contact for optimal grip and handling.

In open-wheel race cars, especially FSAE, suspension systems are often designed to be lightweight and compact, with a focus on reducing unsprung weight and maximizing suspension response to improve handling and cornering speed.

Suspension DESIGN GOALS

Our main goals in suspension/steering/brakes system are to:

Make the system as easy to tune or adjust as possible to accommodate changes in racing environments and situations.
Maximizing suspension response to keep contact between tires and track surfaces.
Reduce unsprung mass as much as possible while maintaining a good structural integrity

Suspension Configuration

Double Wishbone suspension

Teams in FSAE competition mostly use Double wishbone suspension configuration due to its good handling, more suspension geometry options, and it's also easier to tune or adjust the suspension setup. Therefore, for these reasons and the time window in the design process, we decide to choose the Double wishbone suspension configuration too.

Spring & Damper layout

There are 2 types of spring & damper layout found in FSAE competitors, push-rod which is easier to tune spring & damper, and pull-rod which provide a lower center of gravity. We decide to choose the push-rod layout. The first reason is that the push-rod layout is way more simple to design and analyze its mechanism so we can make it done in a limited time. The second reason, the spring & damper location in the push-rod layout sits higher in the chassis, which makes the system easier to assemble, and the spring & damper can also be tuned or adjusted easily.

Wheels & Tires

Teams in FSAE competition common wheel sizes are 10-inch diameter wheel and 13-inch diameter wheel, the former is chosen for the following reasons:

Lightweight
Lower CG
Faster acceleration
Faster heat accumulation
OEM tires available

Although larger wheels can attain higher maximum velocities, they suffer from an increased tendency to slip. A larger diameter means a larger contact patch, resulting in more friction acting on the tire and thus a higher tendency to slip. As the data in the table indicates, the average score for the acceleration event for teams using 13-inch diameter wheels is lower, with Budapest TU being the exception.

A lower center of gravity and improved heat accumulation are also beneficial in the endurance event. The many twists and turns make grip, stability, and handling crucial factors. As tires heat up, they gain increased grip, allowing drivers to achieve better lap times as the competition progresses. The smaller 10-inch diameter wheel can accumulate heat faster due to its smaller size, requiring less energy to raise its temperature, and having a smaller surface area to dissipate heat, helping to maintain heat levels.

Refer back to a table in engineering spec benchmark For wheel type, a 3-piece wheel is typically heavier than a 1-piece wheel due to the hardware, such as nuts and bolts, required to join the separate components together. While the 3-piece design offers greater flexibility, the priority in this case is on lightweight performance. Therefore, a 1-piece wheel is preferred as it provides a lighter solution.

The three common materials used for wheel construction are aluminum, magnesium, and carbon, ordered from heaviest to lightest. Our intent is to use magnesium, as it offers a significant improvement over aluminum in terms of weight, being 30-50% lighter, while not much heavier than carbon, with a difference of only 10-15%. Furthermore, magnesium is more readily available in the market.

Refer back to a table in engineering spec benchmark. In the FSAE competition, teams tend to choose smaller tires that are compatible with their selected wheel size in order to reduce unsprung mass. One of the most commonly used tires across teams is the Hoosier 16x7.5-10. According to available data, there are two compound options for this model, but LC0 is more widely used due to its softer nature. The softer the tire, the greater the grip it provides. However, this comes at the cost of reduced durability. Nonetheless, this trade-off is considered to be a worthwhile one due to the benefits it brings.

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