In order for truck manufacturers continue to offer a wide range of truck configurations that their customers require, they must ensure compliance to FMVSS 136 for every new truck tractor that rolls out of the factory. By not performing either simulation or physical testing of everything single configuration that is built and sold, they are not able to self-certify compliance. This exposes the truck companies to significant legal risk due to NHTSA audits and enforcement which can lead to costly recalls. It can also result in significant costs and settlements from legal disputes associated with traffic accidents where the performance of a truck’s ESC system and its compliance with FMVSS regulations may be questioned.
What you Need to Know:
Big changes are coming for truck tractors and buses sold on the US market later this year. Starting August 1st, 2019 new heavy vehicles, such as truck tractors and buses, must be equipped with an Electronic Stability Control (ESC) system. Having been required on cars and light trucks since 2011, an ESC system is used to reduce the number of crashes caused by roll-over or directional loss-of-control of vehicles. The new regulation set by the National Highway Traffic Safety Administration (NHTSA), known as Federal Motor Vehicle Safety Standard Number 136 (FMVSS 136), will prevent upwards of 1,800 crashes and 50 fatalities each year caused by large truck loss-of-control accidents.
FMVSS 136: The Test Requirements
Federal Motor Vehicle Safety Standards are maintained through self-certification, requiring that vehicle manufacturers their products fully comply with all regulations. Compliance to FMVSS 136 is evaluated on the performance of the ESC system through a J-turn maneuver. In this test, the tractor and trailer are driven at speed into a turn. As it enters the turn, the truck tractor must be able to quickly slow down while staying within the boundaries of the lane. This test proves that the system will prevent roll-over while maintaining directional stability as tractor and trailer are decelerating.
Making the J-turn:
A typical failure mode of the J-turn test is the vehicle leaving the lane as a result of excessive oversteer or understeer. Understeer or oversteer are both a result of insufficient tire grip and an improper balance of tire grip between the front and rear axles.
As the truck tractor enters the turn, the tires must generate sufficient lateral force to keep the truck in the lane. However, when the ESC system applies the brakes to slow down the vehicle (to prevent rollover) the tires ability to generate lateral force is reduced which can make it more difficult for the vehicle to stay in the lane. The reduction in lateral force while braking varies between different tires and also depends on how the ESC system distributes braking between individual axles and tires.
FMVSS 136: Vehicle Dynamics:
A vehicle’s ability to comply with FMVSS 136 is influenced by many factors including the vehicles overall mass and mass distribution, the characteristics of the steer and drive axles, the brake system, the implementation of the ESC system, and the tires. Not only are the individual subsystems’ performance of importance, but also the integration between all of them. Given the infinite number of combinations between affecting factors – truck manufacturers will have a lot to consider when developing trucks to meet the standards set by FMVSS 136.
Designing Trucks for the Future: Physical Testing vs. Simulation:
To meet compliance, manufacturers must understand how these systems work together and in conjunction with the ESC system. There are two paths to understanding how a given truck tractor configuration will perform in the J-turn test. The first option is to perform physical testing, where the exact vehicle and tire configuration is evaluated on an automotive proving ground. In the event that a configuration does not pass, costly re-designs or re-fitments must be carried out before it can be sold on the market.
The second path is to use vehicle dynamics simulation to predict vehicle performance. Using mathematical models of the vehicle and its various systems, the J-turn performance can be evaluated long before the truck tractor is built. Using state-of-the-art simulation software, every component of the vehicle is modeled and in some cases, actual physical ESC and brake systems are utilized in real-time Hardware-in-the-loop simulations.
The benefit of using simulations to verify compliance with the regulation is that large numbers of vehicle configurations can be evaluated in an efficient and accurate manner. Being able to collect data on a myriad of configurations is necessary to meet the varying requirements for the different
types of applications for trucks, ranging from long-haul freight transports to regional delivery trucks to off-road trucks running logging operations deep in the forests. By using vehicle dynamics simulation, truck manufacturers are able to test a wide range of configurations, allowing them to continue to offer a large variety of different truck tractor and tire configurations to their customers.
Executing the Most Accurate Simulations:
Simulations are most accurate when they are based on real data collected from physical testing. To accurately represent the tires in these simulations related to FMVSS 136, truck and tire companies are turning to Calspan and their unique capabilities to measure and model tire performance. Using the largest and most powerful flat-track tire test machine in the world, located at Calspan in Buffalo, NY, the indoor lab can measure the tire performance in the exact load conditions they are exposed to during the J-turn. This measurement data is then used by Calspan’s tire modeling experts, to create mathematical tire models (such as Magic Formula/Pacejka). These models are used by truck manufacturers to simulate how a given tire performs when fitted to a given truck configuration. The results from simulations help the truck manufacturers decide what tires are a good match for a truck tractor and allow it to successfully perform the J-turn test. It may also highlight tires which are poorly suited for a given truck configuration, increasing the risk of not passing the J-turn test. From a technical perspective, FMVSS 136 provides an interesting engineering challenge which can be solved using the latest vehicle and tire simulation technologies.
A truck tire being tested at Calspan’s Tire Research Facility. The tire is exposed to the same loads and combined slip which occurs during the FMVSS 136 J-turn maneuver. During these tests, the tires generate cornering and braking forces up to 9,000 lbs/40 kN. Using data collected at Calspan truck manufacturers can predict how any given vehicle configuration will perform in the J-turn maneuver.
Calspan has a long history of helping the automotive industry to evaluate compliance with federal regulations. Calspan’s Tire Research Facility has the capabilities and know-how to help measure the performance of a truck tire and how it will influence J-turn performance. Contact Calspan’s tire experts today to learn how they can help you ensure FMVSS 136 compliance by August 1st.