12/1/1999 | 5 MINUTE READ

A Reflex Is More Than an Involuntary Action

Facebook Share Icon LinkedIn Share Icon Twitter Share Icon Share by EMail icon Print Icon

The car guys at Tenneco Automotive can't help but develop new technology—it's a part of their culture.


Facebook Share Icon LinkedIn Share Icon Twitter Share Icon Share by EMail icon Print Icon

"Find a job that you love doing and you'll never work another day in your life." A cliché, yes, but nevertheless an apt description of the mind-set of many of the product development engineers at Tenneco Automotive's Ride Control Group (Monroe, MI). Their latest effort is the Monroe "Reflex," a new aftermarket shock absorber that should make an immediate impact in the light truck market this winter. While new aftermarket products are often the result of clever marketing, this technology (yes, it is truly technology) is the result of passionate engineers developing new products to satisfy their toughest customers—themselves.

The Team

Product developers at Tenneco Automotive must posses two qualities. First is a love of cars and all things automotive. Second is the ability to communicate and work as part of a team. From a human resources standpoint, this means that you're apt to find people with large garages working at Tenneco. (One engineer states that he currently owns four cars and has never owned less than two since he was in high school.) From an organizational standpoint this means that there are numerous systems in place to ensure that information flows freely throughout the company.

"There's no question that the way that we work in this company gives us a competitive advantage," says Terry Heffelfinger, chief engineer, Engineering Systems Development Aftermarket Engineering. Tenneco's Ride Control Group is divided between OE and aftermarket applications engineering; however a "Core Engineering" team within OE Engineering is where most of the ingenious new ideas come from (like the Reflex design). Everyone at the Monroe facility uses a common materials testing department, as well as sharing NVH and durability labs. This structure creates plenty of opportunities for communication. In addition, every month both engineering staffs get together for "synergy groups" to swap ideas. At these meetings "we don't care whether it's aftermarket or OE, we're just engineers talking about widgets and what we can do to enhance their characteristics or develop more value," explains Heffelfinger.

Other efforts to promote communication among Tenneco's entire engineering community include an annual international symposium where personnel from all of their global facilities (Australia, Belgium, Brazil, Germany, Japan, New Zealand, and the U.S.) congregate, and a global "best practices" program called "NPIS (New Product Introduction System)." NPIS is a project management tool that helps determine feasibility, risk, capital resource deployment, complexity, manufacturability, and potential impact of any new idea. Tenneco maintains a Lotus Notes database containing relevant information concerning research and development of all projects. This, of course, helps prevent anyone from re-inventing the proverbial wheel.

Even more significant than the corporate structure of communication, however, is an implicit "bring your own ideas" engineering policy, where new concepts precede paperwork. People with good ideas are usually free to explore them and the system allows for good ideas to develop. Heffelfinger explains that "the challenge is deploying human resources to projects to come up with a product."

At the Monroe facility, they consider themselves lucky to have a lot of self-described "car guys" who look at their work as a personal challenge. Case in point, Heffelfinger is a weekend SCCA racer who is currently using the Reflex valve technology in the shocks on his racecar. "I've been fortunate enough to be allowed to experiment and play and try and put something into production," he says, "The great joy for me is to take something from concept into production and watch it roll off the line."

Trials and Tribulations

In the case of the Reflex shock, the concept was a patented new valve design by Karl Kazmirski, manager Adjustable Damping and Springs, and senior technician Charles Tyrell. Core Engineering began working on his idea in Spring 1997. They built take-apart shocks with standard components and machined prototype valves in the on-site machine shop. These prototypes were tuned on a shock dynamometer and then given the all-important vehicle dynamics test to determine if the difference could be felt. (Tenneco has its own in-house training program for its ride engineers to develop sensitivity to vehicle dynamics.)

Once this test was passed, Aftermarket Engineering became involved with the project and engineers from all disciplines began six months of design iterations. Over 500 prototypes were built, taking into account such issues as manufacturability, assembly, materials and durability. Of important note here is that engineers at Tenneco change disciplines regularly to broaden their backgrounds.

In what was perhaps the greatest engineering trial for the technology, it was decided that the valve design would go into limited production. In addition to its Monroe brand, Tenneco also sells high performance truck shocks under the "Rancho" name. In Fall 1998, the Reflex valve actually made its debut in the Rancho RSX-Reflex shock. Since they would be produced in much smaller volumes than the full Monroe Reflex line, this gave the engineering team the chance to pilot the manufacturing process. All the manufacturing issues were thereby solved before gearing up for larger production volumes. Tenneco's Cozad, NE, plant was chosen for the pilot because it was already producing light truck shocks. Given that almost every light truck shock uses the same 1 3/8-inch bore, it was possible to use common tooling, thereby saving time and money.

Materials technology was also an important part of the development process. Rather than using a chrome-plated piston rod as they did in the Rancho shock, Tenneco engineers chose to nitro-carbonize the rod for the Monroe model. This process gives the rod a greater corrosion resistance, as well as being more environmentally sound. The valve itself is made from powdered metal and Tenneco employs its proprietary "Fluon" (a fiberglass-Teflon material) band around the piston.

The Technology

Reflex shocks are twin-tube, nitrogen-charged hydraulic shock absorbers. This, in itself, is not really different than most shocks on production vehicles. However, Reflex shocks have a much stiffer compression resistance, giving a firmer ride, which is ideal for good handling. The caveat with this setup is usually that stiff shocks make for a harsh ride on rough roads. Given that Reflex shocks were originally developed for light trucks, this would appear to be a great contradiction of purpose. Welcome to the challenge faced by most ride-control engineers. How do you combine sports car handling with luxury car comfort? Even worse, how do you do this for a truck?

The solution is a new valve in the Reflex shock that opens and closes by way of a small spring. Under smooth-road driving (which mainly generates cornering and braking loads on the shock), the valve stays closed, keeping the shock stiff, which controls body roll and pitch. But when the vehicle hits a bump, the high compression force on the shock (above 1.5 g) causes the spring to compress, opening the valve in 15 milliseconds and providing more oil flow for a lower resistance. The once-stiff shock becomes much softer, hence the elusive comfortable ride.

As further evidence of the usefulness of this new shock design, Nissan is using the technology in the redesigned 2000 Altima. Tenneco also plans to introduce a passenger-car line of Reflex shocks next year.


Impact sensor