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Parabolic leaf springs are used as safety parts in heavy/ light commercial vehicles. When designing leaf springs, one must complete the evaluation from the perspectives of fatigue life and durability in order to ensure optimization of the design. After the initial design, rather than trying to establish optimization by producing prototypes by trial and error method, using the virtual prototype process to achieve design optimization, thereby reducing the costs will offer competitive advantage for both suppliers and original equipment manufacturers in the global market. In a reference study carried out in a partnership with Ford Otosan, the finite element methodology was used to verify the design of a 4- layered parabolic leaf spring and a multi-parabolic spring designed as its alternative. The stress distribution on layers during vertical, loaded and windup moment was examined.

In pursuit of offering the best driving comfort, heavy/ light commercial vehicle producers usually need to make serious optimizations on the design of leaf springs and natural frequency calculations in order to decrease the vibration and noise that have negative effects on the human body - especially severe on long road trips. Leaf spring design parameters and natural frequency calculations provide a different approach to minimizing such negative effects on the driver. In this study, design of the leaf spring, boundary conditions of which depend on vehicle, is examined virtually within the triangle of driving comfort by natural frequency, durability and stiffness. Besides the driving comfort, optimization work aimed at decreasing the vibration and noise factors are also determined through finite element methods. Prototypes of leaf springs are produced and their natural frequency measurements, stress levels under maximum load through strain gauges as well as life tests are completed.

Besides the innovative work in the commercial vehicles sector, where there is an ever growing competition, lighter, more comfortable, safer, and more robust products are also being developed through optimization of design parameters of currently available systems. This study explains the possible effects of changing the design parameters of leaf springs on a vehicle's driving dynamics, which has a significant effect on the total weight of the vehicle. These effects include the vehicle's suspension specifications and the suspension system's interaction with the steering system. A virtual vehicle model is analyzed under the loads gathered in road tests, to measure the stress levels on the spring layers and the movement of the leaf spring depending on the limits determined by the vehicle manufacturer. Furthermore, the conformity of the movement of the front axles in connection with the leaf spring with the steering system is also analyzed.

This paper is on the application of electric power assisted steering and yaw stability control to a light commercial vehicle. An active steering system is developed and used for both purposes. Steering system and vehicle dynamics models are derived and built in Simulink and their response is compared to that of a validated Adams/Chassis model of the vehicle. A boost curve type electric power assisted steering controller and a yaw stability control system based on the model regulator steering controller are developed. Their performance is demonstrated through simulation results. A steering test rig built for safely developing steering controllers in a hardware-in-the-loop setting is introduced. Details of the experimental vehicle with active steering, built to test the concepts developed in the paper is also presented.