SEMA program to validate performance suspension parts advances

Kinematics and compliance testing, both for FMVSS 126 simulation and product verification, is performed by Morse Measurements on its Anthony Best Dynamics suspension parameter measurement machine.

The aftermarket performance parts industry developed largely on the empirical experience of its entrepreneurs—and then Federal Motor Vehicle Safety Standard (FMVSS) 126 came into the picture, which basically mandated the use of electronic stability control (ESC). Although most cars already were equipped with the technology before the 2011 OE deadline, the makers of suspension performance parts now are faced with “do no harm” compliance.

It isn’t exactly proving a negative, because there is a very specific FMVSS 126 compliance test in the Federal Register. But the seeming complexity and cost directed industry trade group SEMA (Specialty Equipment Market Association) into action. It sought to create ways its members could develop suspension and braking parts, tires, and wheels, and affordably prove their products did not affect the OE systems' operation.

SEMA’s first efforts were to sign up member companies and set up a working relationship some five years ago with the newly formed CU-ICAR (Clemson University International Center for Automotive Research). CU-ICAR leads the SEMA vehicle dynamics program in cooperation with industry test facilities and recently received a $1 million grant from SEMA to perform research to provide its members with guidance in both suspension modification and vehicle emissions.

The current status of the CU-ICAR program was reviewed at a panel forum led by John Waraniak, SEMA Vice President of Vehicle Technology, during the 2013 SEMA Show in Las Vegas.

Roadmap to 2020, then to 2029

CU-ICAR's Prof. Paul Venhovens and graduate students Mandar Hazare and Xianjie Zhou pointed out that FMVSS 126 is just one step along the road to safer cars from the use of electronic controls. They noted that since the LexusLS introduced laser cruise control in 2000 and an advanced parking guidance system in 2006, tire pressure monitoring became an FMVSS (No. 138) in 2007—and that was just the beginning. Now there's a roadmap with projected applications for years to come, including autonomous drive vehicles and connected car technology. Once safety technology gains acceptance on premium cars, it often is turned into federal regulation for the entire fleet.

The performance aftermarket, however, has to learn to walk before it can run. As basic as ESC may seem by comparison with such future technology as self-driving vehicles, the SEMA members have to learn to deal with what's on the road now and coming shortly.

There have been several tests of three possible FMVSS 126 compliance approaches, explained panelist Ed Browalski, SEMA consultant on suspension dynamics: physical testing using a vehicle modified with the SEMA member’s components; “hardware in loop” (HIL) simulation, using the OE electronics and data on the characteristics of the base vehicle and the SEMA member's modified version; and pure simulation.

The physical testing provides precise, comprehensive data, but it requires a test track and instrumentation. It only applies to the modified vehicle’s specific package, so the value is restricted to a high-volume situation (such as the FordF-150). However, cost of this approach has dropped dramatically since the start of the SEMA project. The physical tests have been performed by Link Engineering, a wide-range test company for automotive, commercial vehicle, aviation, and rail that has use of the Ford proving grounds in Romeo, MI.

Two forms of simulation

HIL simulation provides a lot of FMVSS 126 data and is very quick, but it does require baseline and modified vehicle data as well as the HIL setup (obtained by connecting to an actual vehicle). If a SEMA member has data from other simulations, the company can justify the cost by being able to evaluate all of its hardware variations. And there is a substantial cost saving possible by joining with other manufacturers, which has been an approach used by some SEMA members. Mechanical Simulation, developer of CarSim software, anddSpace, maker of the equipment on which it runs, have been working with SEMA on the FMVSS 126 project.

When there’s a lot of data, a potentially low-cost choice is pure simulation, using a generic ESC model and modified vehicle data from the SEMA member. However, although pure simulation is used by OEMs, for aftermarket performance parts makers the accuracy of the generic models is not assured at this time and the methodology is not yet proven, Browalski said.

At some point, Browalski posited, there could be available a lot of high-quality data from the program’s database and more familiarity with the characteristics of other modified vehicles. Then, comparative analysis, another low-cost option, should emerge.

Some of the measuring, simulation, and analytic tools that have been used give the SEMA members the opportunity to go beyond the issue of ensuring regulatory compliance.

Suspension kinematics and compliance measurements (K&C) were brought into the picture by another forum panelist, Bob Simon of Morse Measurement. The company features an Anthony Best Dynamics fixture that can put a vehicle through vertical bounce, pitch, and roll, with cornering, braking, and traction loading at the contact patches of the tires. The equipment's instrumentation provides readouts of dynamic suspension geometry (kinematics) and suspension stiffness (compliance).

Simon said this information can be used to provide proof that design intent had been achieved, and to permit comparative benchmarking of competitive componentry. He cited an example of a sports car with a modified suspension that the company had tested. It showed measurement of lateral g force plotted against roll angle, to indicate the modifications significantly reduced body roll. K&C also is used as an input to the simulation model for FMVSS 126.

Simulation beyond FMVSS 126

CarSim, accepted by many OEMs in their FMVSS 126 programs, is being used in the SEMA program. However, the performance aftermarket should also be looking to simulation for other areas, the SEMA forum was told by Dr. Thomas Gillespie, Director of Product Planning for Mechanical Simulation. He cited acceleration, as in drag racing, as one example, with simulation able to indicate top speed, fuel consumption and emissions, tire traction, suspension squat, and the effects of differential controls and aerodynamics.

He also proposed simulation for braking, to determine effects from aftermarket tires, brake linings, and changes in suspension, including lift and lowering kits that alter vehicle center of gravity.

As vehicles adopt monitoring of lane tracking and controls to maintain alignment, Gillespie said simulation can help development of performance parts for vehicles with trailer-towing controls, adaptive cruise, and other computer-guided systems.

The use of simulation to drive the product design itself was raised during the forum by panelist Rick Darling, Senior Technical Specialist at Altair Product Design. He told the SEMA forum audience that they could use simulation to predict chassis loads, stress in the parts, sensitivities of the suspension to component changes, kinematic and compliance data prior to producing a prototype, and the transfer of wheel loads to vehicle components.

He gave examples of how simulation-predicted loads led to component optimization, so there were fewer prototypes that were stronger, lighter, and lower cost to produce. But even more important, Darling said, the simulations could indicate whether the product design would perform the way the customer expected. They could validate the ride and handling, predict durability, and if there were shortfalls in these areas, provide detailed data that would point to the ways to correct them.