The automotive industry has long sought innovative ways to improve vehicle suspension systems. One such advancement that has gained traction is the use of composite leaf springs. These springs have a rich history, dating back to the days of horse-drawn carriages. However, advancements in materials and manufacturing processes have made composite leaf springs a game-changer in the industry.
The Power of Composite Leaf Springs
Composite leaf springs are designed to absorb vertical vibrations caused by road irregularities. They store potential energy as strain energy and release it gradually over time, resulting in a smoother ride. The use of composites in leaf springs offers several advantages, including high strength-to-weight ratio, fatigue resistance, and natural frequency. Moreover, the internal damping properties of composite materials enhance vibration energy absorption, minimizing noise transmission to neighboring structures.
The Mass Reduction Marvel
The most significant advantage of composite leaf springs is their ability to reduce mass. In the automotive industry, weight reduction is crucial as it directly impacts fuel efficiency and performance. When General Motors (GM) made the switch to a glass-reinforced epoxy composite transverse leaf spring on the 1981 Chevrolet Corvette C4, they achieved remarkable results. The new mono-leaf composite spring weighed only 8 lb/3.7 kg, replacing a ten-leaf steel system that weighed 41 lb/18.6 kg. This reduced unsprung weight by 15 kg/33 lb without compromising spring rates. The transverse mounting of the leaf spring allowed the car to sit lower to the ground, improving handling and overall performance.
GM’s Continued Commitment
GM continues to utilize transverse glass-fiber-reinforced plastic (GFRP) composite leaf springs on their Corvette models, including the 2014 Chevrolet Corvette Coupe. The double-wishbone suspension system, also known as short/long arm (SLA), features a transverse composite leaf spring that spans the width of the car and presses against the lower arm. This design eliminates the need for coil springs and improves tire contact with the road during cornering. The use of composite leaf springs also eliminates the need for standalone rear anti-roll bars, simplifying the suspension system.
Beyond Transverse Springs
While transverse leaf springs have gained popularity, composites also hold potential in longitudinal leaf springs. These springs run parallel to the length of the vehicle and provide crucial suspension as part of the wheel guidance system. Companies like Benteler-SGL are exploring composite solutions for longitudinal leaf springs, aiming to replace steel and save weight. These springs need to excel in torsion and side stiffness, making composites an ideal choice. With advancements in resin transfer molding (RTM), processes are becoming faster and more suitable for high-volume production.
The Polyurethane-Powered Solution
Henkel, a leading adhesive and sealant manufacturer, has developed a polyurethane matrix resin system for fast automotive high-pressure RTM (HP-RTM) processes. This system aims to replicate the performance characteristics of epoxy while increasing processing speed and flexibility. By maximizing the speed of processing, Henkel’s polyurethane-based resin system achieves high-volume manufacturing. The use of polyurethane matrix resins allows for significant weight reduction without compromising strength and durability.
Maximizing Performance with Epoxy
Epoxy resin systems have also seen considerable advancements in recent years. Momentive Specialty Chemicals has developed “snap-cure” epoxy resin systems that retain the properties of traditional epoxy but can be processed in a matter of minutes using HP-RTM. These systems offer a short cure cycle and excellent impregnation of reinforcing fibers. Momentive has collaborated with molders to achieve successful production of epoxy-based leaf springs, such as IFC Composites’ glass-reinforced epoxy leaf springs for light-duty trucks.
The Future of Suspension Systems
The future of leaf springs lies in system integration and multilink solutions. Companies like Benteler-SGL envision a move towards a multilink suspension system with a composite leaf spring covering both jounce and roll functions. This holistic approach to suspension aims to optimize weight reduction without compromising handling or safety. Meanwhile, ZF Friedrichshafen AG is taking suspension systems to the next level with the development of a wheel-guiding transverse leaf spring, combining spring, antiroll, and wheel-control functions.
A Promising Road Ahead
Composite leaf springs have come a long way, transitioning from their humble beginnings in horse-drawn carriages to revolutionizing modern suspension systems. With ongoing advancements in materials, manufacturing processes, and innovative design concepts, these springs offer enhanced performance, significant weight reduction, and improved overall driving experience. As the automotive industry continues to embrace composites, the future looks promising for this technology.