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August 20, 2002

6 Min Read
Market pressure, tire pressure, FEA speed design


Replacing a single-piece tire monitoring system, SmarTire's new  two-piece design allows the transmitter (red) to break away from the cradle (gray) under extreme loads, saving money on costly chip replacements and reprogramming of the receiver.

In the highly competitive arena of automotive components, the vast majority of a vehicle's real estate has already been staked out. Entrenched suppliers battle amongst each other for the known inventory of existing assemblies and parts, undercutting each other on prices, whittling lead times to nothing, and striving to optimize production. In a word, the market is cutthroat and the introduction of any new automotive applications, especially ones that have the potential to become standard, is always cause for commotion, as suppliers scramble to lay claim to the latest component.

Following the Firestone tire failure scandal, just such a commotion was raised when the government enacted the Transportation Recall Enhancement Accountability & Documentation (Tread) Act in November 2000. As part of the new law's enforcement, the National Highway Traffic Safety Administration (NHTSA) decided on May 31, 2002 that tire pressure monitoring systems (TPMS) must be installed on new cars to alert drivers to dangerous pressure and temperature levels within their vehicles' tires.

By Oct. 31, 2004, 10 percent of new cars must feature TPMS, with that number increasing to 35 percent in the second year, 65 percent in the third, and 100 percent of new cars by Oct. 31, 2006.

With its work on wireless tire monitoring technology dating back to 1987, SmarTire Systems Inc. (Richmond, BC) had long anticipated the adoption of TPMS by automakers-dubbing them on its website as "the next major breakthrough in vehicle safety following airbags and antilock brakes." Now, by government mandate, its market had emerged, and it would have to act fast to capitalize.

We Need It Yesterday, Please
Kian Sheikh Bahaie, SmarTire's senior mechanical engineer, knew his company was working with a compressed development cycle, and it couldn't afford multiple revisions of the the initial design. With this in mind, and given the enormous stresses the part would be subjected to, Bahaie decided early on to use finite-element analysis (FEA) software to eliminate potential physical defects during the design stage. This task would be difficult, however, given the array of strenuous conditions the product must endure in light of its location and job.

The monitoring system SmarTire developed works by using a wireless transmitter to send real-time updates to a receiver in the car. The receiver alerts the driver to dangerously low or high pressures and temperatures within each tire. Attached by a strap to the wheel's rim or connected to its valve, the transmitter must operate in temperatures ranging from -40 to 125C and under forces of up to 3000G. SmarTire was revising an earlier version with a single-piece design that meant any part failures damaged the transmitter, requiring a new one as well as reprogramming of the receiver at a cost of about $200 to $300. The new two-piece design allowed the transmitter to break away from a cradle piece under extreme loads, salvaging the transmitter and saving costs long-term.

Tough materials were needed to withstand the loads, but the overall part weight had to be kept low since a heavier component would actually be subjected to more G forces. It was decided that a glass-filled nylon would be used, but which one and the percentage of glass were yet to be determined.

SmarTire proceeded with an initial design featuring the transmitter with a top and bottom half that would snapfit together at six locations, and a cradle assembly that would snap together with the transmitter at four positions. SmarTire then subjected this design to linear static, nonlinear, and dynamic/vibration analyses using MSC.visualNastran FEA software from MSC.Software Corp. SmarTire accounted for the FEA results and sent CAD drawings created in SolidWorks to its molder and moldmaker on the project, Manterra Technologies Inc. (Delta, BC).

Manterra president Jerry Presley received the files and a caveat on lead time from SmarTire. "[SmarTire] was on a really tight timetable with this part," Presley says, "but with a lot of our customers, it seems that many of the things we work on are, 'We need it yesterday, please.' I think that's pretty much the way the industry is."


SmarTire's new two-piece design for its tire monitoring system uses six snapfits to connect the top and bottom of the transmitter, and four snapfits to attach the transmitter to the cradle. In this instance, the unit is secured to the rim by a metal strap (see inset for complete assembly).

Getting it Right the First Time
After receiving the design from SmarTire, Manterra took the IGES fields from its SolidWorks files into think3 and used that program's surface data mode to create an STL file for molding simulation in Moldflow and to create SLA prototypes. Manterra ran simulations for 12 different materials in a family mold with three cavities—one cavity each for the top and bottom of the transmitter, and a final cavity for the cradle. With all the simulations done and a prototype tool cut, Manterra began molding with SmarTire's Bahaie on hand for the initial run.

"The first part came out perfectly without any problems," Bahaie says. "We only spent some extra time to try different materials."

Manterra tried other materials, but settled on what the simulations recommended and what ran perfectly on that first run—a 15 percent glass-fiber-filled nylon. The final assembly weighed about 36g, down from 55g, which resulted in an estimated 40 percent savings in materials. Also, after taking just three weeks to cut tooling, the overall program had gone from art to part in only four months. Taking advantage of the quick turnaround, SmarTire has already announced an agreement in principle with Tier One automotive supplier Visteon, and its monitoring system was included in DaimlerChrysler's prototype Jeep Grand Cherokee Concierge at a June 11 exhibition in Stuttgart, Germany.

Meeting strict deadlines with perfect parts on the first run isn't unusual for Manterra, according to Presley, and he says the simulation software tools available to do so are within any molder or moldmaker's reach.

"People who don't use these [software] tools today are nuts," Presley says. "All you need is the computer and the software. It offers the ability to design a mold and get it right the first time, without having to tweak it. How many companies do you know that basically put a mold on a machine and say, 'Well, let's let it tell us where it needs to be'? You don't do that."

Contact information
SmarTire Systems Inc., Richmond, BC
Kian Sheikh Bahaie; (604) 276-9884

Manterra Technologies Inc., Delta, BC
Jerry Presley; (604) 940-9911

MSC.Software Corp.

SolidWorks Corp.

think3 Inc.; www.think3.com

Moldflow Corp.; www.moldflow.com

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