Bosal's Lightweight Exhaust System

Achieving significant weight reduction in automotive parts often requires a complete re-thinking of traditional designs, not just a nip and tuck or a change of materials.

Achieving significant weight reduction in automotive parts often requires a complete re-thinking of traditional designs, not just a nip and tuck or a change of materials. The Bosal Group (Lummen, Belgium), a global developer and manufacturer of exhaust systems and catalytic converters, recognized this when it designed a new prototype exhaust system. “The conventional exhaust system is well overdue for a technical leap forward,” says Dr. Piet Steenackers, technical director of Bosal, “We’ve gone back to first principles to come up with an innovative solution.” That solution is the forthrightly named “Lightweight Exhaust System.”

The underlying principle of Bosal’s system is that each of its components is independently attached to the vehicle structure rather than being hung in one heavy piece, as with conventional assemblies. This utilizes the floorpan to anchor the exhaust and provide mechanical stability, obviating the need for the system to be self-supporting and allowing for the use of lighter weight materials. “Unlike current systems that may use only two or three hangers to support the entire exhaust system, we attach hangers to every major component. This extra support eliminates the need for thick, heavy materials,” says Steenackers. In fact, Bosal uses stainless steel tubing on its prototype that is half the thickness usually specified, reducing weight by almost 33 lb. on an average sedan. “Our attachment system could allow us to reduce pipe thickness even further, but potential damage from gravel and the like might then become a problem,” explains Steenackers. The attachment points between the floorpan and the exhaust are designed to hold the system practically motionless, forgoing the considerable space usually left around the exhaust system for movement from vibration and thermal expansion. (Steenackers says that the movement of Bosal’s system is kept to 1 to 2 mm versus the 1 to 2 cm on exhaust systems on the road today.) This makes the overall package more compact. Consequently, it can be fitted with larger mufflers to reduce noise levels while maintaining the same overall dimensions as a traditional setup.

The chief potential problem presented by Bosal’s system is the transmission of drivetrain vibration to the underside of the car through the numerous stiff mounts. As a countermeasure, the company has fitted flexible joints made of corrugated metal tubes onto the system that isolate engine and transmission vibration. “By using this very flexible decoupling technique we have reduced the vibration of the exhaust system by almost 10dB—by an order of magnitude,” says Steenackers.

On the mufflers, acoustic and thermal insulation are combined to shed more weight. Bosal’s testing results indicate that the integrated insulation is effective enough to, in some cases, eliminate the need for heat shields, saving even more weight and cost.

As for cost, Steenackers says, “Initial costs will be a bit higher because the thinner materials have required us to develop new high-tech handling, assembling and welding techniques. But eventually it should be cheaper to produce than current systems because between 70%-80% of exhaust system costs are in materials, so if you cut that in half you save a lot.” And as stricter emission regulations come into effect over the next few years the premium for weight reduction will no doubt increase, making even costlier light weight solutions more attractive.

Several automakers have conducted long-term durability tests on the system with positive results, according to Steenackers, and he expects that it will be on the road in a production vehicle within three years.