| Summary: | Vibrations caused by rough road excitations influence tracked vehicle dynamic performance. Good capabilities of such vehicles like high mobility, manoeuvrability and comfort are guaranteed by optimal suspension systems. The suspension systems of tracked vehicles are exposed to extreme operating conditions. This creates a conflict between ride comfort and handling that is even greater than the conflict between ride comfort and handling for general road vehicles. Tracked vehicles must be able to traverse not only rough roads but also smooth terrains. The challenges in developing an optimized suspension system for tracked vehicles include the high and changeable damping forces required for tracked vehicles crossing rough terrains. The use of active or semi-active suspension systems overcomes the limitations inherent in the conventional passive suspension. However, active suspension systems are expensive, complicated to design and have high power demand. Thus, semi-active suspension systems have emerged as a good compromise between active and passive suspension system. There is considerable current research on the applications of magnetorheological (MR) fluid dampers for semi-active suspensions of executive brand of some cars. However, there is very little research on semi-active devices for tracked vehicle suspension. In fact, currently, there is no commercially available large scale MR dampers in the market that produce the high damping force to suit such applications. In response to these requirements, this research proposes a novel semi-active tracked vehicle suspension system that uses MR dampers to improve the ride comfort and handling characteristics of tracked vehicles. It also assesses the dynamics of the new suspension with various semi-active control methods. This study is conducted in four phases. The first phase provides a numerical investigation on the dynamic performance of a seven-degrees-of-freedom (7-DOF) passive suspension model of the armour personnel carrier (APC) M113 tracked vehicle. The numerical investigation considers the influence of variation of five suspension design parameters on the vehicle dynamic performance. These parameters include number, locations of hydraulic shock absorber, damping coefficient, suspension and wheel stiffnesses. The results indicate that the optimal suspension performance is attained by using two or three dampers. The best locations for these dampers are at the extreme road wheels i.e. the first, second and last road wheel stations. Moreover, the vehicle performance is reduced when the damping coefficient is increased. Additionally, low suspension stiffness offers better vehicle ride while high wheel stiffness degrades the vehicle performance. These results identify the limitations inherent in the conventional passive suspension. For the second phase, the dynamic characteristics of the hydraulic, hydro-gas and MR dampers are experimentally measured and fitted using the Chebyshev orthogonal functions to produce the restoring force surfaces for each damper, which are compared. On one hand, the restoring force surfaces of the hydraulic and hydro-gas dampers show fixed properties at specified frequencies. On the other hand, the restoring force surfaces of the MR dampers show properties that can be controlled at the same specified frequencies by the variation of the applied current levels. Thus, the potential and the effectiveness of the controllable properties of MR dampers for semi-active vibration control is demonstrated. Also, in this phase, the best set of parameters to use in the modified Bouc-Wen model to characterise the MR dampers, has been derived. The third phase of the project is also experimentally based. A new and novel test rig which represents the 7-DOF scaled suspension model of the tracked vehicle is designed and fabricated. The primary purpose of the test rig is to evaluate the performance of the proposed suspension with MR dampers. Furthermore, experiments are conducted on the test rig to evaluate some semi-active control methods and their effectiveness in reducing suspension vibration. The results show that the use of two or three MR dampers at the extreme wheels offers optimal suspension performance. This confirms the numerical results that are derived from the full scale passive suspension system with hydraulic dampers. The experimental results also show that skyhook control and hybrid control (which combines groundhook and skyhook controls) of the semi-active suspension are more effective in reducing the road-induced vibration and improving the suspension dynamic behaviours. Also, validations of the predicted responses of the semi-active scaled MR suspension model with the measured responses have been presented. The fourth and final phase provides a numerical simulation on the development and evaluation of the semi-active control methods for a full scale tracked vehicle suspension with MR dampers using the validated suspension model. Three semi-active control strategies are proposed. The first two controllers are the skyhook and hybrid controls which provide better suspension performance. In addition, the third controller, which is an intelligent fuzzy-hybrid control system, is used to optimize the suspension performance. The results from this intelligent system are compared with the two traditional control methods (skyhook and hybrid controls) under bump, sinusoidal and random excitations. It is shown that the proposed controller can enhance simultaneously the vehicle ride and handling characteristics.
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