Search Results

This paper discusses the evolution of skid steer systems, and takes a new look at the advantages and implications of designing future ground combat vehicles with all non-steerable wheels. The traditional “skid steer” designation of such vehicles is dropped in favor of the more descriptive phrase “differential torque steer” vehicle. The possible advantages of such systems for combat vehicle application are presented along with a synopsis of various past modeling, simulation, and vehicle hardware efforts to evaluate skid steer systems. A comprehensive vehicle modeling effort for a differential torque steer system is then presented. Two independent implementations of the model are presented along with model verification and validation results. Finally the model is used to evaluate potential turning performance for a 4×4 vehicle with differential torque steer.

A theoretical approach is presented to the quantificaiton of potential cross-country performance limits of an active suspension system. A pitch-plane representation of a wheeled vehicle is used along with the assumption of ideal actuators and perfect terrain knowledge. The geometrical constraints on possible chassis motion imposed by the vehicle and terrain geometry are formulated. Algorithms are developed to determine the optimal (in terms of vehicle ride) chassis vertical and pitch motion trajectories as well as vehicle ride limiting speed as a function of both terrain roughness and allowable suspension travel. Finally, possible active suspension implementation schemes for approaching these ideal performance limits are discussed.

The technology thrust to develop an effective electromagnetic actuator for application in an active suspension system has precipitated a fresh look at the active control schemes in an effort to reduce the required force levels of the actuator. The resulting “near constant force” control algorithm is described and its ability to greatly reduce vehicle sprung mass motion is documented through simulation and single wheel station laboratory test stand results. The vehicle power and energy requirements associated with this unwanted vehicle vertical are analyzed and comparisons between the corresponding passive and active systems are presented. The success of the active system leads naturally to the conclusion that a passive suspension equipped vehicle will become power limited at a much lower speed than will this active system when traversing severe cross-country terrain.

This paper discusses the evolution of commercial active suspension systems and the recent adaptation of this potential dual-use technology to military applications. It contrasts the commercial automotive industry's focus on enhancing on-road ride, stability and handling with the military's objective of increasing off-road mobility. The specific adaptation of a commercially developed active suspension system to the Army's High Mobility Multi-purpose Wheeled Vehicle (HMMWV) is described along with changes required to accommodate this 3000 kg, 4x4 all-terrain vehicle. Resulting design and installation are presented, followed by a brief synopsis of the vehicle's performance. The desire for even greater cross-country performance is discussed as the motivation for pursuing the development of more effective off-road control strategies and the progress in this arena is presented.

This paper describes a fuzzy logic (FL) approach to the design, implementation, and tuning of an expert knowledge-based TCS for a four-wheel drive vehicle. Military and commercial mutual interests in TCS technology are highlighted as the underlying motivation for this government, industry, academia cooperative program. Coordinated parallel efforts to model the TCS equipped vehicle and to perform basic on-vehicle TCS experiments provided additional information to augment the knowledge obtained from a study of commercial TCSs and the tire traction literature. The general traction control problem is discussed along with the hardware considerations for a TCS. The design and integration of the resulting FL-based TCS are described along with a representative sample of the test results documenting the system's performance.

The incorporation of semiactive suspension technology into military vehicles is shown to be a win-win proposition. Extensive test results are presented for five comparable pairs of passive and semiactive suspension equipped vehicle configurations. The cross-country ride and platform stability performance for these 19 metric ton tracked vehicles demonstrates the substantial gains achievable with a semiactive suspension. The test results are augmented with simulation results assessing the respective suspension system power losses and evaluating the performance potential achievable by equipping an M2 Bradley Fighting Vehicle with a semiactive suspension system. It is further shown that such a semiactive suspension equipped Bradley will have cross country mobility equivalent to the M1A1 Abrams Main Battle Tank.

This paper describes an investigation of the differences involved in using time domain and frequency domain techniques to analyze the dynamic response of a vehicle traversing nondeformable, off-road terrain. A comparison among the computed results, the computation times, and the costs for each method is made. A comparison showing simulation on both analog and digital computers is also presented.