The long and bumpy road

Every day suspension companies are finding new ways to optimize their products. Whether it’s decreasing weight or creating a new spring design, companies are continually working to improve suspension systems to meet the ever increasing needs of their customers.

Ashley Dudding, Director of Engineering at Hendrickson’s Truck Commercial Vehicle Systems, Woodridge, IL, says there are numerous factors which suspension companies must keep in mind when designing a product. The application of the vehicle is the first factor to consider because it will determine which type of suspension, such as an air versus a spring, should be used. Dudding continues that various performance metrics, including durability and roll stability, are important aspects to consider as well.

Spring vs. rubber vs. air

Depending on the type of application a vehicle will be used in determines whether an air, spring, rubber or other type of suspension will be the best fit. Each type is designed to offer the best ride performance possible, but how they’re able to handle various environments is the key decision maker.

Hutchens Industries (Hutchens), Springfield, MO, designs mechanical steel spring suspensions, often referred to as spring suspensions, for on-highway trailers. Russ Brazeal, Vice President of Engineering at Hutchens, says the company focuses on this type of technology because while it’s an older technology, it’s also a proven one. Spring suspensions offer minimal initial investment and lower long-term maintenance. Brazeal says that as long as the fasteners are maintained, the suspension is basically maintenance-free, whereas an air suspension has air systems and air bags which can be more susceptible to damage.

With a mechanical spring suspension, the springs themselves are the primary energy absorber. Friction between the spring leaves, flat plates of steel shaped and cut to various lengths then bolted together, or in the suspension itself isolates load from the road to keep the vehicle stable and the operator comfortable. This self-damping method eliminates the need for shock absorbers like the kind that are found in air suspensions, says Brazeal.

Dudding notes that spring suspensions offer a more constant spring rate, which means that when the truck is empty the spring rate is similar to when the truck is fully loaded. This requires the spring rate to be high enough to provide good roll stability characteristics when fully loaded, which can be higher than ideal when in the empty state. This can sometimes cause an uncomfortable, stiff ride for vehicle operators, which is why Hendrickson developed its rubber spring suspensions for vehicles that are used both on- and off-road, such as dump trucks.

Rubber springs feature a non-linear, highly variable spring rate, Dudding says. They provide a lower spring rate when a truck is empty to give the vehicle operator a better ride. Once the truck is loaded the spring rate increases to provide higher roll stability, especially important in vehicles with a high center of gravity. This helps ensure a comfortable ride in both loaded and unloaded conditions. Dudding says rubber suspension systems “have a lot of articulation, so they have very good off-road mobility.”

This is important when working in a mining application, for instance, where road surfaces are typically rough and trucks are loaded heavily with material to transport, says Dudding. In this type of application high roll stability is key to avoid tipping over when transported material is being unloaded. “[Rubber suspensions] have a spring rate curve that as you increase load on them they develop very high roll stability,” says Dudding.