When it come to trends in axles and suspensions, it's all about efficiency. Fleets are constantly looking for ways to become more operationally efficient, whether it's fuel economy, increased payload, lower maintenance costs, longer equipment life, or driver productivity.
At the same time, federal regulations are requiring OEMs and suppliers to develop products that lessen their impact on the environment and keep the driver and public safe.
We asked axle and suspension makers to share with us the trends they're seeing.
1. Losing weight
“'Less weight means more freight’ has been a driving force in suspension design, especially now that trucks have been gaining weight because of emissions equipment, more electronics and more driver creature comforts,” says Reyco Granning Senior Vice President Ray Mueller.
Axle and suspension engineers have responded by using computer-assisted designs to eliminate any material that doesn't contribute to strength and by using high-strength, lower-weight materials.
“However, this chase to be the lightest occasionally over-shoots at the expense of durability,” Mueller warns. “Fleets have to consider the types of loads, the types of road surfaces and the expected life cycle, then choose the product that gives them the best compromise of lower weight and higher durability.”
Steve Slesinski, director, global product planning for Dana's Commercial Vehicle Driveline Technologies, identifies lightweight, more fuel-efficient drivetrains as a major trend. For instance, the Dana Spicer Pro-40 tandem drive axle for on-highway linehaul applications offers up to a 100-pound weight savings versus competitive 40,000-pound tandem axles.
Weight is a bigger issue since more stringent regulations on engine emissions and decreased stopping distances have added significant weight to the vehicle, especially on the front end.
“The trend to help offset the weight increase is to create a complete lineup of products designed with weight optimization in mind,” says David McCleave, director of sales and marketing for Hendrickson Truck Commercial Vehicle Systems. That extends to suspensions.
For example, Hendrickson's HTB LT, a non-torque reactive rear air suspension for tractors, saves up to 275 pounds compared to competitive products, he says.
“One of the most important trends we see is that lightweight components are becoming more popular due to demand for better fuel efficiency and to keep cost of ownership down,” says David Vanette, manager of new business development at Firestone Industrial Products, which is offering lighter-weight primary air spring options.
Some of the ways to do so, he says, are optimizing rubber and fabric construction, and using FEA to optimize steel and plastic components. These next-generation air springs offer weight reductions of up to 3 pounds per spring.
2. Rise of 6x2s
One way to reduce weight and improve fuel economy is the 6x2 axle configuration, in which only one of the two axles in the rear tandem is driven and the other is a non-powered “dead” axle.
“Six-by-two axle configurations can be approximately 300 pounds lighter than 6x4 tandems and can realize about a 2% fuel efficiency improvement through reduced churning and friction by running one drive axle instead of two drive axles,” says Dana's Slesinski.
The Dana bowl tag axle design provides a lightweight tag axle solution while maintaining common fit-up as a standard 6x4 configuration, so many vehicle components and suspension fit-ups can be common, he notes.
Right now, only about 3% of Class 8 trucks have 6x2s, according to Matt Stevenson, general manager for Meritor North American field operations and marketing. But in five years, that should grow to 18%, he says.
Drivers and truck owners have stayed away from 6x2s because traction is inferior, tire wear on the single-powered axle is higher, and resale suffers because subsequent owners can't use trucks or tractors in applications such as construction or agriculture, Stevenson says.
Meritor is trying to educate customers on the 6x2's benefits, and meanwhile has designed products that overcome traditional objections.
For enhanced traction, the FueLite tandem comes with a driver-controlled locking differential on the powered axle. Some customers order it with a manual dump valve for the dead axle's air bags to transfer weight to the drive axle. It also can be bought with an electronically controlled air suspension, or ECAS.