Military Contract Brings Silencer Design Challenges

Silex Inc., Mississauga, Ontario, Canada, recently received a contract from General Motors Defense of London, Ontario, to design and manufacture exhaust systems and insulation blankets for the engine and auxiliary power unit for a new Light Armored Vehicle (LAV III) now in production for the Canadian, U.S., New Zealand, Australian and Saudi Arabian armed forces. General Dynamics Land Systems will use the same system on identical units built in the U.S.

The design parameters of the contract called for a unique product according to Silex. "The acoustic requirements were very tight and the envelope in which the exhaust system was to be placed was extremely small and non-symmetrical," said Mehmood Ahmed, engineering manager for Silex Inc. "This presented quite an engineering challenge and the opportunity to work on an application in which the company had no prior experience."

To design an exhaust system that fit the Kubota diesel application, the company utilized all of its engineering tools and resources. The final system uses a dual silencer design engineered to work in tandem. This design reduces the low and high-frequency noise as per the required specifications.

One tool used by Silex in the design phase of the exhaust system was a three-dimensional boundary element analysis computer program developed in-house by Dr. Zhenlin Ji, who has a Ph.D. in acoustics and noise control. The program was developed to predict noise attenuation of exhaust silencing systems based on proposed designs.

"I really needed all the power in this program to get good results in this application," said Ji. "The program has not only been used in this application, but has also been applied daily in the design of silencers for a variety of other applications."

In the design phase, Silex also used 3D data exchange with GM to enable the capture of previously unutilized volume to improve the performance of the exhaust system. The 3D modeling and acoustic predictive software we use did not eliminate the necessity for a prototype, according to Ahmed. However, it greatly reduced the number of prototypes that would typically be required for this type of development.

The entire exhaust system was designed using the parametric solid modeling program known as Pro/Engineer or Pro/E. "This program allows us to product shop drawings in less than 2 minutes on custom silencers, down from four to eight hours before we had Pro/E," said Ahmed. Pro/E is also used extensively by Silex for the balance of its products including catalytic converter silencers, flexible connectors and the complete line of exhaust system accessories.

During the test phase, Silex employees attended numerous midnight tests of the exhaust system in the LAV III to ensure the product would meet all design parameters and that it would support the troops as required.

Once the design was complete, the project management team took over to ensure all of the Product Part Approval Process (PPAP) procedures were in place. The tooling was ordered and production systems arrived exactly as scheduled at both GM and General Dynamics facilities.

PPAP is used by Silex to ensure all customer engineering design record and specification requirements are properly understood by the supplier and also to make sure that the process has the potential to produce product consistently, meeting these requirements during an actual production run at the quoted production rate.

| back to top |