Current Research

Assessment of and Guidelines for Aftermarket Chassis Modifications with Regard to Roll and Yaw Stability 

Principal investigators:

Dr. Paul Venhovens, BMW Endowed Chair in Automotive Systems Integration

Graduate Students:

Mandar A. Hazare

Sponsors:

CU-ICAR (Clemson University International Centre of Automotive Research)

SEMA (Special Equipment Market Association)

Brief abstract: 

The United States National Highway Traffic Safety Administration (NHTSA) has established the Federal Motor Vehicle Safety Standard (FMVSS) 126 that requires all vehicles sold in the USA weighing less than 4,536 kg (10,000 pounds) to include an Electronic Stability Control (ESC) system as standard equipment after September 1st, 2011. FMVSS 126 ensures that a particular vehicle with ESC installed meets the lateral responsiveness and lateral stability criterion and has been found to be highly effective in preventing single-vehicle loss-of-control, run-off-the-road crashes, of which a significant portion are rollover crashes. With this regulation in place there is growing concern among the aftermarket suppliers specialized in development and installation of vehicle performance parts such as suspension and body lift kits, modified sway bars and oversized tires. These chassis modifications may cause the ESC systems to be inoperative or warn the driver through the ESC malfunction telltale or can create unforeseen issues with stability and safety systems.

The chassis modifications also may have a significant impact on the rollover propensity of the vehicle. ESC is a highly effective device to maintain control of the vehicle and will primarily prevent single-vehicle accidents. Both NHTSA and the Insurance Institute for Highway Safety (IIHS) estimated that ESC could prevent 80-88% of all SUV un-tripped rollover crashes. These numbers imply that despite ESC about 12-20% of all un-tripped rollover crashes cannot be avoided. This makes it necessary for the aftermarket industry to completely understand the influence of any modification on the yaw as well as roll stability of the vehicle.

A critical factor for the aftermarket industry is, that the ESC system must be regarded as a 'black-box' since the code and control parameters of the ESC algorithms are of a proprietary nature . ESC algorithms will be unknown for the aftermarket industry and the proper design of chassis modifications and functional assessment of yaw and roll stability becomes even more challenging.

The implementation of Hardware-in-Loop (HIL) simulations as a possible solution to the problem is under development. The simulations will consist of a non-linear vehicle model coupled with an external ESC-ECU in hardware in the loop. The effect of modifications such as lift and suspension kits, new sway bars, and oversized tires can readily be studied through the simulations, and the compliance of the modified vehicle as stipulated in FMVSS 126 can be assessed as well. Furthermore, it would be possible to have more insight on the rollover characteristics of the modified vehicle by additionally simulating NHTSA's fishhook maneuver.

Sensitivity of chassis modifications towards yaw and roll instability will be addressed and the upper threshold for each of these modifications will be established. Based on the results of the sensitivity analysis, guidelines for safe aftermarket modifications will be presented based on the initial baseline design of the vehicle.

Impact:

Altered vehicles must comply with FMVSS 126 after September 1st, 2012. Legally, should an accident occur, the aftermarket parts manufacturer and installer could be targeted, whether the accident was caused by the alterations or not. Therefore, the aftermarket suppliers are in need of best practice tools and processes to assess the impact of chassis modification regarding FMVSS 126 compliance. In order to sustain this business and prevent possible litigation cases, it is of great importance that the chassis design modifications can be assessed and validated during the product development phase before final implementation in a customer's vehicle. 

Project schedule:

January 2010 to December 2010

Preliminary Results:

A non-linear vehicle model that represents a pickup truck has been modeled in CarSim and was validated against actual field test results. The validated CarSim model with a generic ESC modeled in Simulink was then used for the sensitivity simulations. With this preliminary setup, the influence of chassis modifications on the yaw and roll stability was studied in detail. The modified vehicle will be tested for FMVSS 126 as well as NHTSA's fishhook maneuver.