Dynamic Testing and Design Technology for Off-Highway Exhaust Systems

May 12, 2016

Scott Swank

The Tru-Flex bellows design provides a gas tight connection (low or zero leakage) and de-couples movement and vibration including rotation through the long axis of the bellows (torsion), between the engine and the remainder of the exhaust system.

As the industry readies itself for Tier 5 emissions compliance in 2019, it makes sense to look back at recent technological milestones to plot the trajectory of future trends. In the exhaust systems arena, innovations occurring within the last decade, along with new analytical tools, will help shape the way engineers design systems in the future.

Scott Swank, Vice President of Engineering, Tru-Flex, LLC.

2007 EPA emission standards for on-highway vehicles and equipment required that exhaust systems be leak-free from the engine through the treatment system. As a result of the 2007 regulations the heat retention characteristics of the exhaust transmission system became important, because the treatment systems used to meet the emissions standards operate more effectively with higher exhaust stream temperatures.

In the past, the engine outlet and the treatment system were commonly joined using a strip-wound metal hose. However, after new EPA standards were enforced, the nominal leakage rate and lack of thermal insulation associated with the original metal hose approach made it obsolete. Bellows formed from a solid steel tube were found to be the most suitable replacement.

In 2007, Tru-Flex, LLC. introduced its Internally Insulated, Torsional and Non-Torsional Bellows solutions. Several unique features of the Tru-Flex bellows allowed it to manage not only normal displacements between the engine and chassis, but also other major issues such as heat retention, torsion and high-frequency vibration. The combined result of these innovations is an exhaust component that has optimum durability and improves the overall performance of the exhaust system.

The Tru-Flex bellows design de-couples movement and vibration between the engine and the remainder of the exhaust system. This includes rotation through the long axis of the bellows (torsion), which is extremely damaging to all standard type bellows. The design provides a gas tight connection (low or zero leakage).

The de-coupling capability and extensive product array allows an exhaust system engineer complete freedom in designing an exhaust layout in a manner that works best for their particular application.

This Locally Reduced Bellows (LRB) features lower height corrugations centered around the mid-point of the bellows body. The lower height results in a stiffer bellows in this area, which effectively splits any vibrations the bellows experiences into two shorter sections. The main advantage is a reduced magnitude of failure caused by vibrations that are driven into the bellows from a diesel engine or other energy source.

The bellows pictured include an interlock liner and Tru-Flex patented torsional joint. The interlock liner helps to further damp vibrations entering the bellows body and provides a smoother interior flow. The torsional joint is useful when connecting a flexible joint directly to a turbocharger.

The system also allows for some positional tolerance between the engine and aftertreatment device mounting locations (misalignment). The Internally Insulated, Torsional and Non-Torsional Bellows help retain as much heat as possible to support quick light-off and optimum efficiency of the aftertreatment device. A properly designed bellows de-coupler assists with the proper and efficient operation of the engine and aftertreatment system over hundreds of thousands of miles.

Tru-Flex collects measurements via its hexapod measuring unit and can later fully replicate on-vehicle conditions with its 6-axis shaker. Our engineers have developed software that processes all channels of the measurement data into true displacement data in a format that can be provided to the customer quickly.

An ongoing collaboration with a test equipment manufacturer has resulted in a proprietary design for the 6-axis shaker, which has some unique capabilities that allow it to more fully replicate on-vehicle conditions. The equipment was designed to test for longer-term failure modes and allows us to more closely match the real-world lifecycle of its systems.

The test equipment is closely coupled with analysis software that has the capability of significantly reducing and compressing the amount of running time required to meet customers’ durability test goals. Once a customer has designed and built a test truck, Tru-Flex can accurately measure the axial, lateral, angular and torsional dynamics between the engine and treatment system with its hexapod measuring equipment. Once the field data has been gathered, engineers can replicate and accelerate those forces under laboratory conditions with the 6-axis shaker, which guides the design of an optimized, higher functioning, and longer-lasting exhaust system now and in the future.

Scott Swank, Vice President of Engineering, Tru-Flex, LLC, wrote this article for Off-Highway Engineering as part of the annual Executive Viewpoints series appearing in the June 2016 issue.