Design, analysis and multi-disciplinary optimization of high-performance front leaf springs

• Design and optimization of 7.5 and 8.0 tons front-axle parabolic leaf springs has been performed.
• The kinematic behavior of each leaf spring has been set to follow the steering curve.
• Durability optimization for operational load spectra.
• Verification by testing and evaluating prototypes assembled on test vehicles on test tracks.

The present paper presents the design and optimization procedure for parabolic leaf springs for truck axle payloads of 7.5 and 8.0 tons. The requirements to be met in such a process cover the kinematic behavior of the spring (the conformation of the trajectory of the wheel joint connected to the spring with the trajectory of the steering arm), the spring rates, as well as strength and, most importantly, durability criteria. Therefore, a multi-disciplinary optimization has been performed aiming at the fine tuning between the vehicle’s wheel joint kinematics, the leaf stress response and damage for certain multiaxial load spectra. Optimized kinematics have been calculated using proper design parameters. The springs’ durability has been theoretically assessed based on (a) FEM-calculated stresses at pure vertical loading and braking events, which have been identified to cause the highest stresses in operation, and (b) analytical damage calculations for certain multiaxial load sequences based on the Miner’s elementary linear damage accumulation rule. The vehicle’s kinematics behavior has been verified experimentally by driving prototypes at test tracks. Straight-driving, cornering, comfort and steering behavior have been quantitatively evaluated by 7 different expert drivers. The developed springs were found to perform equivalently to (in case of the 8.0 ton spring) or significantly better (in case of the 7.5 ton spring) than the respective serial springs.