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Wobble and shimmy vibrations are commonly observed in commercial highway vehicles with solid-beam front axles. These vibrations are typically self-excited and manifest themselves as sustained oscillations about the kingpin and axle tramp. A study was initiated to investigate and quantify wobble and shimmy behaviors, with a primary focus on wobble. A cross functional team including test and simulation engineers evaluated a vehicle exhibiting these behaviors. The team developed an ADAMS model to reproduce the behaviors and developed a DOE to quantify the impact of variables and combinations of variables. The evaluation demonstrated that dynamic imbalance in the rotating masses is a primary source of excitation. Wheel run-out, caster angle, tire brand, tire wear and tire inflation are also significant sources. Future studies will use these findings to mitigate the concern.

The development of commercial vehicles demand a rigorous and relatively expedient integration and validation to be performed in order to have the vehicle delivered to a satisfied customer. In today's market, the end customer often request for vehicles with various customizations and requirements for vocational performance, such as load and fuel economy. These requirements often run into conflict with vehicle dynamics fundamentals such as ride and handling. Examples of such concern are vocation bodies that do not have weight distributed unevenly or even ones that bias the static load distribution of the vehicle such that ride and handling are affected because of change in bounce, roll and pitch natural frequencies. One tool that can be used to develop and evaluate vehicle response to provide guidance for production vehicles is multibody dynamics. Unlike the passenger car industry, no two trucks rolling down the assembly line are necessarily the same.

Recently, the development of various driver assistance systems into today's vehicle have increased due to the availability of affordable advanced electronics. With this increase in electronic content on today's commercial vehicles, various opportunities for sensor fusion are opened up, primarily because the sensors are typically part of the ECU cluster, and always measuring either driver input, vehicle states and potentially the environment around the vehicle. Given the larger variance in vehicle mass and length for commercial vehicles, as opposed to passenger cars, sensor data integrity and robustness is important to assure that all the sensors are reporting the same information, so that safety-critical Driver Assistance Systems can intervene effectively and robustly.

The advancement of computer systems and simulation modeling tools have enabled control systems designers to reduce the development time and bring active safety system products to market faster. Modern tractor-trailers are becoming increasingly equipped with such active safety systems. More often than not, these tractor-trailers are designed to pull either a single trailer or multiple trailers in operation. One of such multiple trailer combinations are the B-Doubles combination, in which the fifth wheel coupling is located at the rear of the lead, trailer, which is mounted on the rear section located immediately above the lead trailer axles. Although this combination is less susceptible to lateral instability compared with an A-Train combination, it can still have exposure to roll instability. Hence, the application of a trailer roll stability system on the combination vehicle may prove beneficial to the roll stability.

Forward collision mitigation systems (FCMS) are becoming standard in passenger car vehicles with the current trend of safety technologies development. Currently, safety systems are on the road towards widespread acceptance in the commercial vehicle industry. Whereas the full Electronic Stability Control (ESC) system attempts to sense the states of the vehicle to assist the driver to maintain directional control of the vehicle, current FCMS attempts to sense the environment around the front of the vehicle and either warns the driver to react or intervenes by slowing down the vehicle autonomously. Some of the latest developments in FCMS for commercial vehicles will be discussed, together with an outlook of future systems. This study will also examine some of the common scenarios that forward collision mitigation systems can be beneficial in, especially for commercial vehicles. The scenarios will be investigated using Hardware-in-loop-simulation, and the results discussed.

Electronic Stability Control (ESC) has presented itself to be a rather significant technological advancement in passenger car safety within the last few years. For the commercial vehicle industry, stability systems have been an option available for tractor-semitrailer within the last few years. However, there are axle weight limits imposed on commercial vehicles, unlike emergency vehicles which are allowed to be loaded to the maximum axle weight ratio. With the fact that fire trucks are carrying high CG loads and may typically be travelling at speeds higher than the normal driving speed for a road, one of the recommendations is that stability systems become available as standard in heavy duty emergency vehicles such as firetrucks. This study will analyze several scenarios commonly encountered by emergency vehicles such as firetrucks and demonstrate the benefits of stability systems for heavy duty emergency vehicles.

The application of stability systems on heavy vehicles clearly has numerous advantages, when the cost of the cargo, the service life of vehicles, and the vehicle potential for damage are taken into account. The primary objective of such systems is to assist the driver to maintain control in the face of uncertain driving conditions. The dynamic effects of such system, however, are not widely tested by the industry. The study presented in this paper will present an evaluation of the effects of full and partial stability systems on tractor-trailers using hardware-in-the-loop simulation. With the advancement of simulation capabilities that enables the repeatability of maneuvers, the study presented attempts to provide various deterministic “what-if” scenarios under various vehicle stability system combinations.