In the world of automotive engineering, there is (almost) no such thing as good vibrations; they are invariably bad. One of the very few exceptions is the use of vibration as a driver warning aid (typically via the steering wheel rim) of incipient danger, such as the inadvertent crossing of a lane marker.
But generally, vibration and quality do not mix and from the earliest days of motor vehicles, anti-vibration solutions (AVS) have been an essential part of the formula for commercial success: providing end users with the safest, smoothest, and quietest ride while meeting all safety, environmental, and associated legislative requirements, including a contribution to reduction of CO2 emissions levels via weight-saving programs.
Developing effective AVS is a never-ending task, not only because quality targets and expectations of manufacturers/customers rise inexorably, but because evolving designs and technologies bring fresh challenges. Electric vehicles (EVs) may be quieter and smoother than IC engine-powered vehicles, but they change the whole basis on which a car’s overall technology is formulated. The picture is also complicated by the use of alternative materials necessary to achieve weight and cost savings.
A comprehensive range of AVS are used throughout modern vehicles, from the engine and exhaust mounts to the chassis and suspension; the shock absorber’s efficiency and performance are heavily dependent on a number of AVS.
Trelleborg Automotive has developed an extensive portfolio of polymer-based AVS solutions to satisfy specific design challenges. Said the company’s European Engineering Manager Alain Guillaume: “In order to meet the needs of the manufacturer, changing industry requirements and the wide range of environmental and climatic conditions that anti-vibration solutions are exposed to, constant material development and design is critical.
“Improvements in AVS durability, temperature resistance, stiffness, creep, and noise reduction are heavily dependent on compound and polymer design and selection.”
A number of environmental factors must be considered in AVS design to ensure optimal performance in any condition, he explained: “AVS must withstand extreme climatic conditions, ranging from temperatures of -40°C to over +120°C. Vehicles are exposed to a variety of elements: heavy rain, water, snow, and sand, as well as rough terrain. And AVS and the vehicle chassis, in general, must of course withstand constant movement throughout a vehicle’s lifetime, which is generally considered to be at least 10 years.”
Weight reduction—or even keeping it steady as equipment specifications rise—is an enduring problem for all component and OE companies. This need is linked to increased metal prices, so OEMs are looking to source alternative materials and solutions for both reasons.
“Even a small weight reduction can enable significant savings to be made during production, so we are seeing an increasing move from steel to aluminum parts, with growing demand for more plastic components,” said Guillaume.
The use of plastic also allows greater design freedom for inserts supporting elastomer-based parts, an efficient way to increase vehicle durability as plastic components are not susceptible to rust, do not require painting, and are easier to recycle.
As the 2015 deadline for the European Union’s 95% recycling rate for end-of-life vehicles approaches, automakers are looking for more easily recyclable components. New material developments, such as MDI (methylene diphenyl diisocyanate) -based PU (polyurethane), rather than the less environmental NDI (naphthalene diisocyanate) -based materials, have been developed to help OEMs reach these targets.
Environmental and climatic conditions vary dramatically between countries, but it is important for a manufacturer to be able to sell the same vehicle platform right across the globe without incurring the cost of redesigning various components to meet different conditions. It is therefore essential that AVS designs are flexible and robust and that the components can be easily sourced.
“As car technology evolves and we see the increase of more refined and quieter vehicles, especially with the emergence of EVs, anti-vibration solutions must work harder to optimize noise dampening performance,” said Guillaume. “Trelleborg’s top strut mount is designed to prevent sudden excitation of the car body through road input, bumps, obstacles, and potholes. Due to the forces it absorbs, the mount needs to be soft in the axial direction but hard in the radial direction. As well as performing a damping function, the strut mount can also help to isolate tire and spring induced noise and vibration.”
A key driver for innovations in top strut and spring seat technology is the recent pedestrian shock legislation. The legislation requires the reduction in height of the shock-absorber mounts to create increased clearance between the hood and the strut to provide a crumple zone to absorb pedestrian energy in the event of impact and to reduce the possibility of serious injury.
To achieve this, Trelleborg has developed compact strut mounting solutions and retuned surrounding components, such as the bearing, spring seat, spring, bumper, and dust cover.
Guillaume said that the strength of Trelleborg’s bump stop lay in its damping abilities, absorbing and isolating extreme shock, noise, and vibration. The company uses PU materials for bushing and bump-stop applications.
He added that PU elastomers are a useful and cost-effective alternative to rubber in several applications. Elastomeric properties are determined by the material mix, and PU can offer strength, rigidity, softness, and flexibility. “It can also outperform rubber in terms of abrasion resistance, and the injection molding process makes the component easier to shape,” Guillaume said.
Although natural rubber has been—and continues to be—used successfully in a range of AVS, new materials need to be developed to ensure that manufacturers have the optimal solution to their specific requirements. Trelleborg runs an extensive R&D program into the utilization of advanced polymer-based materials in its AVS design, such as thermoplastics, silicon, biomaterials, fiber-reinforced composites, and foams.
“The importance of material development to the industry can be demonstrated through innovations such as the Trelleborg Noise-Free Rubber,” said Guillaume. A self-lubricated, low-friction rubber formulation, it overcomes noise from AVS components such as suspension bushings, engine mounts, and anti-roll bar isolators while the vehicle is in motion. In addition, the material has been engineered to meet stringent fatigue requirements, resulting in an increased durability of some 50%.
Added Guillaume: “Vehicle design has greatly evolved in recent years, yet from the outside it’s easy to forget that the finished product is dependent on the pioneering new design and material developments of integral components, such as AVS, which are critical to the safety, comfort, and durability of the entire vehicle.
“Continued and collaborative design across all vehicle components is essential to meet the evolving needs of the industry, the environment, and the end user.”