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Target cascading methodology is applied to the optimization problem of the kinematics of a rack and pinion steering mechanism coupled to a double-wishbone suspension system of a hybrid off-road vehicle. This permits the partition of a complex problem into reduced order sub-problems in a hierarchical manner, leading to a more efficient design and optimization process. According to the nature of the problem, it is proposed a four level hierarchy organization. The uppermost level is the general vehicle design problem. The second level consists in various system-level design problems such as frame, powertrain and the set suspension-steering. The steering system design problem is proposed in a third hierarchical level. At the lowest level are the components design problems. The vehicle under study will work mainly under off-road condition at low speed.

Target cascading methodology is proposed as an efficient approach to the design optimization of the geometry of a double-wishbone suspension system of an off-road vehicle. The geometric setting of the suspension plays an important role on its performance, as well as on the interactions with other design domains of the overall system. In order to organize the complexity of this system, two types of hierarchies are established: a system hierarchy and a model hierarchy. For the system-based hierarchical organization, four levels were identified to express the suspension design problem in an overall vehicle design context: a super-system at the top level, two system design levels at the second and third hierarchical levels, and a components level at the lowest level. The model-based hierarchical organization considers four analysis models to investigate the suspension behavior: a steering DOF constrained kinematic model, a longitudinal, a handling and a ride dynamics model.

The target cascading methodology allows dealing with multi-domain coupled design problems. With this methodology, a complex design and optimization problem is decomposed into reduced-order problems in an ordered hierarchical structure, without losing the information about the coupling interactions between them. The order-reduction and partition of the original design problem not only bring computational advantages in the solution process, but also permit the designer to have a deeper insight of the problem nature. This work is centered in the geometric problem related to the design and optimization of a double-wishbone suspension system of an off-road vehicle. Given the nature of this problem, the target cascading methodology is proposed as an efficient solution approach. This methodology recognizes that the suspension system plays an important role in the interactions at different levels of the design problem including system dynamic response and systems physical interactions.