Extreme loads are no match for properly spec’ed and maintained severe-duty truck models. Vehicle OEMs, in fact, list a range of applications for which they have specific models designed to meet severe-duty needs. Included are dump, concrete, crane, roll-off body, refuse, heavy haul, logging, oil and gas field service, utility, fire and emergency, snow plow and towing and recovery operations.
Behind all these trucks are components and systems designed and packaged for severe-duty operations. “For severe-duty applications, it is critical to completely understand the vocation and how the vehicle is going to be used,” says David G. Gonska, manager, Engineering Applications & Customer Support, North American Axles at Meritor.“ Different uses place different demands and loads on the components, which can have an enormous impact on performance and durability.
“Some fleets want to put the most robust products available in their trucks,” Gonska continues, “but that’s not always necessary and may only increase vehicle weight and cost. A proper understanding of the vocation will allow for optimal product selection.”
Gonska goes on to relate that severe-duty fleets should follow all published application guidelines for selecting the proper driveline, axle or suspension. In any case where there is uncertainty, he advises contacting the manufacturer for assistance in selecting the appropriate components.
Collin Dinsmoor, director, Engineering Suspensions—Powered Vehicle Systems at SAF-Holland recommends the following be considered when selecting severe-duty suspension systems:
• Vehicle type;
• Vehicle weight (loaded and unloaded);
• Vehicle Information;
• Engine configuration;
• Frame type, construction and dimension;
• Drive axle, steer axle and auxiliary axle information;
• Tire, rim and braking systems;
• Engine and/or driveline braking;
• Traction considerations like chains, self in/deflation, ground chain systems
• Vehicle usage and type of application;
• Chassis/body configuration;
• Ride height, axle spacing, wheelbase;
• Articulation and clearance implications;
• Environmental considerations;
• Terrain, operational surfaces;
• Loading and operational duty cycles; and
• Operational regulations.
• On-highway: Operation on Interstate or primary highways with maximum grades of 8%. Operation is subject to legal weight and dimensional limitations.
• On-/off-Highway: Operation on secondary roads with up to 25% of vehicle operation on roads with a maintained sand/gravel, crushed stone or similar road surface. Maximum grades of 12% and frequent grades of 8% can be encountered. Operation is subject to legal weight and/or dimensional limitations or requires special permits.
• Off-highway: Operation on roads with a maintained sand/gravel, crushed rock or similar road surface in excess of 25% of vehicle operation. Maximum grades of 12% and frequent grades of 8% can be encountered. Limited off-road operation, less than 10% of total vehicle operation where grades and surface conditions may vary. Operation may not be subject to legal weight or dimensional limitations.
• Off-road: Operation under minimal or no road conditions for greater than 10% of total vehicle operation. Grades and surface conditions will vary. Operation is not subject to legal weight or dimensional limitations.
“The type of vehicle, including tractor-trailers and trucks with dump bodies, as well as the type of trailers in use, are important factors to consider when spec’ing severe-duty suspension systems,” says Charlie Wells, vice president of sales and marketing at East Manufacturing. “Also take into count the type of cargo and the weight of the heaviest load the vehicle will carry, the conditions faced by the operation such as on-highway, a combination of on- and off-highway or primarily off-highway roads, the typical duty cycle of the vehicle and any ride height requirements. Severe-duty suspensions need to meet demands for tough operating conditions, where maximum strength and durability are required.”
Charles Allen, senior director, Global Service at Meritor, also says it is most important to understand the application and build the right vehicle for the need at hand. “You cannot simply turn a highway axle into a severe service axle,” he states. “Don’t spare the heavier duty specs; if it needs it, buy it.”
Allen, who notes that Meritor offers several drivetrain products that can be spec’ed for severe-duty applications, goes on to recommend that a primary focus when spec’ing axles for severe-duty trucks is startability, since the load will likely be higher than 80,000 lbs. “Know what the components are capable of handling,” he says. “Heavier-duty drive axles come with heavy wall housings, again to handle the tougher hauling demands. Match the driveline to the axle. Don’t be “lightweight” on driveline specs. Match specs for the heavier duty job.”
Designed for demands
Dana’s Spicer 170 and 190 Series Axles, according to the manufacturer, are designed for the demands of severe-duty applications. The axles feature gearing with extra-wide face width for strength and durability, and have larger wheel differential gearing, also for strength and for high power density. Additionally, forged, heat-treated steel differential cases increase gear and bearing life.
Dana’s Spicer heavy-duty steer axles feature larger kingpin bushings and a kingpin sealing system that the company says help ensure long service life and reduced maintenance. In addition, a dual draw key and spring washer kingpin retention system, along with a beam forging design, provide for improved axle durability.
Dana has also expanded its line of Spicer heavy-duty universal joints, including extra heavy-duty versions of the SPL-350 driveshaft and the SPL-250 inter-axle shaft. The heavy-duty driveshaft and inter-axle shaft are designed to withstand the increased stress placed on the driveline by severe-duty applications, the company notes, by being equipped with high power density design features and a higher torque rating.
Hendrickson offers a range of suspensions for severe-duty operations. For trucks there is the PRIMAAX EX rear air suspension, the HAULMAAX rubber suspension that utilizes rubber bolster springs coupled with an auxiliary spring to offer loaded stability and up to 17 in. of diagonal articulation for off-road mobility, as well as the RT/RTE Series steel spring suspension with equalizing beams that distribute load between axles for improved traction.
On trailers in severe-duty applications, Hendrickson offers the INTRAAX Extreme-duty (ED) system in top-mount and low ride height/liftable models. Features of the system include low-pressure air springs with steel pistons and full bottom plate coverage and high-damping, extended-service shock absorbers. Heavy-duty options include rear-mount shock absorbers and chain down-stops for suspension damping and control.
SAF-Holland’s Neway ADZ Series Axle Air-Ride Suspension is designed for severe-duty applications and off-road duty cycles. Offered in single, tandem and tridem axle configurations up to a 78,000-lb. capacity, the axle can be used in high center of gravity applications. The ADZ model’s roll stability for cornering and on uneven terrain, the company notes, is achieved by combining lower control arms and a transverse beam in a one-piece lower module and with a widened design stance. The lower module provides a linear roll rate through the permanent connection of the trailing arms and transverse beam, which the manufacturer says improves handling and steering characteristics.
Once in service, severe-duty components require stringent adherence to maintenance schedules. “Maintenance should be performed in accordance with all equipment manufacturer and industry guidelines, and if there is a discrepancy between different sources, the component manufacturer’s guidelines should be used,” Meritor’s David Gonska advises. “In many severe-duty applications as well, maintenance intervals should be shortened to ensure continued safe operating condition of components. Finally, when replacing components, it is important that components be used that meet the OEM’s original performance requirements.”