The first high-volume U.S. installations of electronic stability control (ESC) began in the 2003 model year—in about 10% of vehicle sold. With that head start, automakers had the lead time they needed to meet the September 2011 deadline for vehicle ESC system performance requirements of Federal Motor Vehicle Safety Standard (FMVSS) 126. The standard, established by the U.S. NHTSA (National Highway Traffic Safety Administration), covers vehicles under 10,000 lb (4540 kg) Gross Vehicle Weight. However, aftermarket parts are covered by a “do no harm” requirement effective September 2012—i.e., they must not throw a vehicle out of compliance with FMVSS 126. Similar European Community regulations are in effect.
Almost any aftermarket performance part potentially can affect regulatory compliance of the stability system, as John Waraniak, SEMA (Specialty Equipment Market Association) Vice President of Technology, said at a vehicle dynamics symposium during the 2011 SEMA convention in Las Vegas. He pointed to the obvious: steering including ratios and alignment, tires, brakes, and suspension components. But he also included wheels—size, weight, and the cooling airflow they allowed—plus engine modifications that change power and torque, because the stability module may control torque output. Further, the manufacturers must consider the possible effect of different combinations of aftermarket performance parts—parts that do not create an issue by themselves might do so in certain combinations.
The SEMA performance parts customer is looking “to stretch the envelope, to get the chassis tuned for handling, and is willing to sacrifice daily usability and ride/acoustic comfort,” the symposium was told by Paul Venhovens, who holds the BMW-endowed chair at Clemson University’s International Center for Automotive Research (ICAR). He cited a chassis lowering kit as an example of multiple effects, explaining it changes the lower A-arm kinematics, scrub radius, roll center, steering feel, and bump steer, plus joint-bushing forces and elastomeric kinematics. But whatever these effects, the stability system must remain in compliance with FMVSS 126.
Thanks to efforts by SEMA, aftermarket parts makers get until September 2012, a year beyond the OEM deadline, to certify their products. Further, SEMA has put in place a cooperative program to enable its members to test their products.
FMVSS 126 relies on manufacturer self-certification; no forms to file unless perhaps there’s a NHTSA investigation. As with other safety standards, FMVSS 126 itself contains a very well-defined physical test procedure, whereas a manufacturer could choose to use some form of simulation or even an engineering analysis. The standard describes a precise “road test” of hard cornering exercises for the steering, suspension, brakes, and stability control module. Typically, this is performed at proving grounds, using a steering robot and anti-rollover outriggers. Though OEMs do some physical testing at proving grounds, it’s just too time-consuming and expensive even for them to physically test every vehicle variant and every dealer-installed performance parts kit that it markets. So, it’s certainly impractical for comparatively small aftermarket manufacturers, who would have to buy access to proving grounds and obtain the hardware, to perform road testing.
Automakers use simulation for vehicle variants, and because they know what the software in their electronic stability controllers is supposed to do under all conditions, it’s a simpler process than for the SEMA members and others who sell performance parts.
Yes, an aftermarket parts manufacturer could just say, “My product has always worked and it has demonstrated reliability. It meets applicable SAE standards.” But then he has to hope there’s nothing in the stability control system operation with which there’s an unsatisfactory conflict. The risk is there, and in addition, a company’s liability insurer is likely to be looking for stronger evidence.
SEMA’s effort to aid the aftermarket industry is based on CarSim, a program from Mechanical Simulation. With a real-time simulator from dSpace, the program has been running at Clemson University for two years in the ICAR facilities and more recently also at Link Engineering in Dearborn, MI. Although far from free, simulation evaluation for FMVSS 126 is a fraction the cost of a physical road test.
The simulation software for aftermarket parts is designed to replicate the FMVSS 126 test procedure, explained Tom Gillespie, co-founder of Mechanical Simulation. The test uses the vehicle itself, with its OE stability control module in a physical loop with the dSpace simulator, and the operating characteristics of the SEMA member’s parts (along with OE baseline data) plugged into the program. So whatever vehicle stability controller commands are issued will tell the effect, if any, of the aftermarket parts on the stability system performance. An example of the questions it can answer, noted Santhosh Jogi, Director of Engineering of dSpace, is whether or not the vehicle dynamic stability control module will exert the right amount of brake pressure to maintain stability with a modified vehicle.
Last year, Superlift Suspension Systems tested its 6-in (152-mm) lift kit with an American Outlaw 20-in wheel and Pro Comp tires on a Ford F-150 and found it was a combination that demonstrated compliance in a physical road test as well as with the simulation. The test was aided by Ford, which provides data on its OE tires to assist setting up the SEMA-promoted evaluations.
This year, a new Ford Focus was on the simulator, testing Eibach suspension parts and Falken tires, marking the first active participation by a tire maker and Eibach, a German producer of springs and sway bars. Just over a year ago Eibach saw little importance to the testing but kept looking at the SEMA-backed program, explained Greg Cooley, President of Eibach Springs of North America. Eventually, both the German home office CEO Wilfried Eibach and the U.S. subsidiary’s Cooley became enthusiastic supporters.
Two additional suspension parts makers, Hellwig Products and Rancho Suspension, are stepping into the program to test a Ford F-150 and F-250 Super Duty. The two companies will share baseline data on the two vehicles to help them learn about both vehicles’ characteristics, Waraniak told AEI, but actual testing will be separate, with each company’s specific parts.
“We have to figure out what we’re up against to certify our products,” said Mark Hellwig, President of Hellwig Products, at the symposium. “An anti-sway bar is a simple product, but how does it affect electronic stability control?”
He added that the liability insurance was a factor: “We have to be able to tell our insurance company—and show—that we performed due diligence on compliance with FMVSS 126.”
Tires have to meet or exceed the customer’s target for performance and still be safe, Falken Tire’s Richard Smallwood, President and CEO, told attendees at the symposium. “No matter what the brochures say, you can’t have it all. There are trade-offs,” he said. “We have four contact patches about 7-1/2 by 7-1/2 in” to work with for wet vs. dry traction, and several approaches to case designs, such as for off-road, where tires may have to take heavy loads and operate at low pressures.
Simulation testing with product lines of different manufacturers participating will enable the performance parts industry to deal with the questions that multi-sourcing raise. Symposium participants agreed that compatibility charts for components will be needed to list the product mixing that provides assurance of safety as well as maintaining FMVSS 126 compliance.