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.[PAGEBREAK]
The ECAS-equipped tandem automatically dumps air from the non-powered axle's air springs to effect the weight transfer. A FueLite 6x2 also can have electronic traction control added to the standard antilock braking system to augment the mechanical difflock.
Meritor is also preparing an advanced 6x2, called SmarTandem, which has a proprietary controller that automatically handles the diff lock and weight-transfer functions.
3. Faster axle ratios
Officials at both Dana and Meritor believe more truck operators will begin asking for “faster” axle gearing, or lower numeric axle ratios, to save fuel and cut greenhouse gas emissions.
Modern trucks and tractors are electronically speed governed to keep engine revs low, a practice that used to be called “gear fast, run slow.” Fast axles are paired with transmissions with direct-drive top gears, which themselves reduce friction and save fuel.
“The key here is selecting the correct ratio for the application,” says Dana's Slesinski. “Gearing the vehicle too fast may result in having to shift too often on slight grades,” he says. “A good rule of thumb is to gear the vehicle to allow it to pull a 1% grade in top gear at nominal load conditions.”
Meritor's current fastest ratio is 2.47 to 1, and is used by customers who want a tractor to cruise at 60 or 65 mph with the engine turning only 1,300 rpm or so. But truck makers, under new federal mandates to reduce carbon dioxide emissions, have begun offering even slower engine operation, with cruise at 1,100 rpm.
Meritor engineers are looking ahead and preparing ratios in the 2.20 range, according to Allen and Stevenson. Altered metal alloys and gear designs are being explored to make the upcoming gear sets durable as well as economical.
“The North American marketplace will continue to see suspension/ axle suppliers pursue an integration strategy to provide their customer base more complete, engineered solutions system packages that continue to redefine the ‘best’ balance of weight, cost and performance to the end user,” says Bill Hicks, product planning director for SAF Holland Trailer Systems.
The company's SAF CBX integrated suspension/axle systems also include integrated brakes.
Another example is Meritor's new low-mount trailer suspensions, specifically designed as part of a fully integrated system to optimize performance and weight, which are integrated with Meritor trailer axles and Q Plus Cam Brakes.
Reyco Granning also sees continued integration in van trailer air ride slider suspensions.
“Once upon a time, the trailer manufacturer purchased a slider sub-frame from one supplier, suspension components from another, an axle from another, hub, drums, bearings and seals from yet others,” says Mueller. “The trend has been for one supplier to integrate those disparate components into one, ready-to-install unit.”
Another example is Firestone's Air-ide Integrative Air-Damping System, which offers a lighter-weight alternative to cab mount suspension applications, providing the functionality of an air spring and shock absorber in a single part.
5. Less maintenance, longer life
Suspensions have come a long way in reducing maintenance, notes David Clark, corporate warranty manager for Pacific Power Products, which has 10 truck service locations in the Pacific Northwest and is a member of the WheelTime Network.
Clark started out his career as a suspension technician. “When I first started doing suspensions, it wasn't uncommon to do suspension repairs every day, all day long,” replacing pins and bushings and more. Today, he says, suspension repairs are so sporadic, “the suspension specialist like I was is no longer someone who just tears apart trucks. Now they have to do other things. Otherwise it's like the Maytag repairman, they're going to sit there waiting.”
Trailer OEMs, suspension/axle suppliers and component system suppliers are all developing or currently providing several premium wheel end package options delivered direct from the factory that offer longer service life/maintenance intervals with extended warranty coverage.
“While the premium wheel end packages are an upcharge, they offer peace of mind to a fleet knowing they will likely recoup their investment in reduced maintenance, increased uptime and reduced field failures due to bearing issues,” says SAF Holland's Hicks.
Corrosion protection is another trend. SAF Holland's Black Armour solution is standard on SAF-branded trailer suspension systems, and Hal-dex offers a Self Setting Automatic brake adjuster, which encloses the critical moving parts to protect them from corrosive road salts.[PAGEBREAK]
6. Reducing tire wear
The continued demand to reduce costs associated with tires has led suppliers to introduce axles and suspensions to address this need.
For instance, the SAF CBX Self Steering axle suspension addresses tire wear from tire scrub.
Widespread and multi-axle trailers “scrub” the tires laterally on the road surface for every turn the vehicle makes. The higher the loading on the tire, the greater the scrub on the tire, axle, suspension and trailer frame during turns.
The self-steering axle suspension allows the tires to follow the turn of the vehicle as opposed to being pulled laterally through a corner. Thus, when loaded, the SSA carries its share of the designed capacity of the trailer and virtually eliminates tire-scrubbing issues.
The relation between axles, suspensions and tires also becomes a fuel economy issue.
Hendrickson says its SteerTek NXT fabricated axles help maintain better dynamic toe and camber alignment compared to forged I-beam axles, contributing to optimized tire performance. Tires that operate more efficiently decrease the amount of rolling resistance, which contributes to better fuel economy.
Proper inflation is also key to fuel economy as well as tire life, and there is increased use of tire pressure monitoring and inflation systems.
One such product, on the market since 1993, is the Meritor Tire Inflation System by PSI. MTIS goes onto an estimated 36% of all new trailers in the U.S. today, according to Frank Sonzala, PSI executive vice president.
Success comes from results, Sonzala says. A controlled two-year test of the product on trailers showed a 1.4% increase in fuel economy, and there are other benefits.
Sonzala says the apparent cost saving in tires, fuel and the elimination of road service calls means a less-than-eight-month return on investment for many fleets. One is Werner Enterprises, which is retrofitting 24,000 of its trailers at 10 depots nationwide.
Hendrickson, however, says there is a drawback to the typical tire inflation system. It says its TireMaax Pro addresses the problem of tires that are over-inflated or, in the case of duals, mismatched, says Matt Wilson, business unit director for the Controls Business Unit of Hendrickson Trailer Commercial Vehicle Systems.
“A typical tire inflation system cannot actively control the pressure of a tire once it has exceeded the system target pressure,” Wilson contends. Tires that are above the target pressure will not trigger any response from typical tire inflation systems, he says.
“Because tire inflation systems constantly fill tires with air at ambient temperature, over time it is likely that these systems will fill tires with cold dense air. So the inflation system is actually a contributor to tires that are above the target pressure once the outside temperature warms up.”
TireMaax Pro uses special valves in the hubcap and a sophisticated controller to equalize the pressure across all wheel positions and relieve pressure from any over-inflated tires.
MTIS so far has been limited to trailer-axle tires, but engineers are developing an inflation system for drive-axle tires, says PSI's Sonzala. This is more difficult because the more complex drive axles must be made or modified to take internal air lines.[PAGEBREAK]
A power-unit product already on the market is the Spicer Central Tire Inflation System, which Dana acquired from Eaton several years ago. It automatically reduces air pressure to enhance carrying ability off-road, then pumps up the tires when trucks return to pavement. It's more costly, but operators of commercial logging and concrete-mixer trucks have found it can enhance off-road travel without resorting to front-driving axles.
7. Brake changes
Another trend affecting axles and suspensions are changes in new federal stopping distance requirements, which mean higher-torque front brakes or disc brakes being used on the steer axles.
“The additional torque that translates into the steer axle knuckles and beam must be handled effectively,” notes Dana's Slesinski. “The Dana Spicer Steer axles have a strong forged steel I-beam with patented power-rib to handle these increased demands.”
Disc brakes also are being driven by demand for trailers that require less maintenance, says Rick Rickman, vice president of sales for Ridewell. Disc brakes require less frequent maintenance than drum brakes, and when routine maintenance is required it can be accomplished more quickly.
“We have seen the premium cost of disc brakes over drum brakes come down significantly in the past several years, which has resulted in the value of reduced maintenance quickly providing a payback for the higher initial cost,” Rickman says.
Haldex also notes that fleets are demanding spring brakes that are easier to install accurately. That's why it now offers Gold Seal and Life Seal spring brakes with the OEM-specified welded clevis pushrod assembly for truck-tractor and trailer manufacturers. These new models come with the clevis welded to the pushrod and in the exact pre-set position used in new vehicle production.
Vocational market trends
Trends in severe-service markets indicate a continuing move toward air suspensions, says Hendrickson's David McCleave, director of sales and marketing. Hendrickson offers a premium severe-service air suspension, PriMaax EX. In more severe vocations where payload is more of a concern than fuel economy, products like Hendrickson's Haulmaxx rubber suspension can offer up to 900 pounds of weight savings compared to competitive suspensions.
“For instance, for vocations like the refuse industry, weight savings directly translate to route consolidation and optimization, which greatly adds to the bottom line,” McCleave says.
On the other hand, vocational and specialty trucks still use a high percentage of steel spring suspensions, and even van trailers have seen a shift back to more steel spring, mechanical suspensions, notes Reyco Granning Senior Vice President Ray Mueller.
“Initial cost and reduced maintenance are the most common reasons given,” he says. “It's another example of how the trucking industry often values simplicity, durability and low cost over advanced technology.”