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Tire inflators provide lesson in green engineering

March 26, 2009

One way mechanical engineering can contribute to a greener future is demonstrated by ASU students in Mechanical Engineering (MAE) Design I & II classes taught by lecturer Mario Gomes.

In the two-semester course, students complete a rigorous, hands-on project to design and build a device that meets a set of performance specifications. One project Gomes devised challenges students to produce a device that automatically maintains optimal automobile tire pressure using the tire's own rotation as a power source.

What does tire maintenance have to do with going green?

According to Pump ‘Em Up (see – a web site that promotes fuel conservation – and the U.S. Department of Energy, properly inflated tires could collectively save American drivers four million gallons of gas per day – saving each driver hundreds of dollars each year – while also extending the life of their vehicles’ tires by as much as 25 percent.

In addition to the economic benefits, reduced gas consumption will help keep the air cleaner and reduce the need to drill for oil in scenic, fragile environments such as the Arctic National Wildlife Refuge.

"Since very few people check their automobile's tire pressure frequently enough, much less actually fill their tires, the need for such a device seemed natural,” Gomes said.

“Also, I was fairly certain that I would be able to mentor the teams of mechanical engineering seniors to create some workable designs,” Gomes says. “I was impressed with the excellent performance of the devices they created. Even more impressive was that by working on this project they developed the ability to make wise design choices based on good engineering analysis."

In the first semester of Gomes' MAE 488 class, four groups – each consisting of 3 to 4 students – develop several conceptual designs.

The fundamental engineering analysis methods they learn in previous courses are then utilized to determine which of their conceptual designs are most promising, using their engineering models to guide their critical thinking and decision-making.

They then refine the preliminary designs in to a single final design and predict the performance of their device.

The goal is to build a device that maintains a minimum inflation rate of one pound per square inch (psi) for every three miles driven.

The design constraints include a budget of not more than $375, having to build a prototype device that can protrude no more than six inches from the tire surface, and designing a system that is easy to mount and dismount – in less than 15 minutes – using standard household tools.

Gomes’ students perfect their design throughout the course’s first semester, progressing from handmade paper sketches to a complete three-dimensional, computer-aided design model, with detailed mathematical models to ensure design guidelines not only meet but exceed project requirements.

The second semester class, MAE 489, challenges students to construct their final designs using the undergraduate MAE machine shop.

Starting with the most crucial component for which the initial analyses demonstrated large uncertainties, students build and test designs based on the outcome of a principal component test.

“The fact that [the design] worked relatively well the first time we put it together was amazing,” says student Soroush Farzin. “It was great to carry a project from the initial design stages all the way to the final testing and delivery phase. Out in the industry, this doesn't happen often.”

Students from each group are trained by shop manager Leonard Bucholz and senior machinist Andre Magdelano to use the shop’s equipment and to machine parts based on the drawings each student group creates.

"The excellent work that Lenny and Andre do teaching the students how to set up and machine parts is an invaluable part of our students' education. The projects would not be possible without all of the experience and skills that they provide." Gomes says.

Three weeks before the end of the semester, the groups test final versions of the devices to see how well they can predict the performance of the instruments and how well they meet overall design goals.

“At first, when I found out that our project was going to be to design a tire inflator I was extremely disappointed,” student Jim Cunningham says. “I wanted to design a battle robot or race car or something cool like that. But looking back, the amount of work and analysis it took to make something as simple as an automatic tire inflator is really astonishing.”

The project “showed both how important and difficult it is to design for manufacturing and cost as well as performance,” Cunningham says. “I think it was a real wake-up call for a lot of students. This experience will make us all more prepared for the real engineering world.”

Said student Mark West: “The most valuable thing I learned from this project was that the design often must change significantly from paper to prototype. Many of the details that were considered inconsequential early on drastically affected the layout and function of the final design near the end.”

Mechanical engineering senior Prateek Sharma says the project was challenging “because it pushes your imagination out of the box. In the end, this keeps it exciting.”

One group came up with a design for an inflator that automatically stopped pumping when a tire had reached optimal pressure – an improvement over other designs that used blow-off valves when tires reached optimal pressure.

See videos of students explaining their design projects, plus a video of a design for the automatic tire inflator that demonstrated the best overall performance.

There’s also a web site that documents work on a series of mechanical engineering and design challenges students have undertaken in Gomes’ classes.

See information on courses offered through the Department of Mechanical and Aerospace Engineering.

Writer: Matt Evans