DECEMBER - JANUARYAUTOTECHOUTLOOK.COM19CXO INSIGHTSBy Alexandre Pinto, Innovation and Technical Director, and Stefano Rosta, Managing Director, Business Unit Composite Springs, MubeaLIGHTWEIGHT COMPOSITE LEAF SPRING SUSPENSIONS FOR PLUG-IN HYBRID AND BATTERY ELECTRIC VEHICLESThe demand for increasing battery density vehicles to reach longer distance ranges has driven vehicles to very challenging trade-offs in terms of available suspension design package, high spring rates, and lightweight. The utilization of glass fiber reinforced plastics, in leaf spring constructions as well as new axle concepts offer further lightweight potential and, in addition, better integration of suspension functions and less installation space required for electrificationSuspensions springs play a major role in every aspect. The entire vehicle sprung mass rests on these springs, while their compliance cushions the transmission of shocks to the passenger compartment. For the driver and passengers, the tuning of spring force and spring rate on the front and rear axles ensures a safe and comfortable driving experience.Regardless of efficiency, lightweight design in chassis for electrified vehicle platforms (Battery Electric Vehicles (BEVs) and Plug-in Hybrid Vehicles (PHEV) continues to be of great importance. At the same time, the increasing vehicle weights require higher spring forces and rates and thus, a higher spring mass. Economical, lightweight design succeeds either through the best possible material utilization of the classic steel spring material or through alternative materials such as long fiber reinforced plastics in spring constructions.GFRP SpringsGlass Fiber Reinforced Plastics (GFRPs) offer enormous light weight design potential due to their advantageous ratio of specific tensile strength and specific modulus of elasticity. Particularly when used as a material for leaf springs, these characteristics of an ideal lightweight material can be utilized in the best possible way. This is always possible when the spring is primarily loaded with tension, pressure or bending. This is because a unidirectional layer structure can be used, in which the load is essentially absorbed by the high-modulus fibers.GFRP coil springs potential light weight design is substantially reduced as the spring cross-section is primarily stressed by torsion, which requires an oriented layer structure with different fibers orientation. The limiting factor is the transverse tensile strength of the material, significantly reduced when compared to the fiber-dominated strength. In addition to lower light weight potential, such springs have reduced sag loss resistance and lower durability at high temperatures.Alexandre PintoStefano RostaMost commonly applied on light trucks and commercial vehicles, the longitudinal leaf springs allow high vertical suspension rates required for big vehicle payloads
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