Sterling Heavies Get A New Chassis And A Fancy New A/C Compressor
Tom Berg
Equipment Editor
Sterling Class 8 trucks will soon sit on a new chassis platform using many parts from Freightliner, its corporate big brother. And the vehicles will use a newly designed air conditioning compressor that promises higher efficiency and better reliability.
That product news came during ceremonies last month marking the 100,000th vehicle built by workers at Sterling's truck manufacturing plant in St. Thomas, Ont., Canada. It took five years to make that many, but the company is increasing its market share and executives promised the next 100,000 will be produced in less time (see Hotline).
Portions of Sterling's existing HN80 heavy duty chassis needed redoing to accommodate higher-capacity cooling required by January '04 diesels, so engineers took the opportunity to completely revamp it, explained Landon Grogran, program manager for the new "HX" chassis. HN80 was the code used by Ford Heavy Truck for the products that became Sterling heavies, and this is their first major redesign since Freightliner LLC bought the series from Ford Motor Co. in 1997.
Higher-capacity cooling comes from bigger cross-flow radiators to be manufactured by Behr. Three sizes - 1,000, 1,200 and 1,400 square inches - are used with various engines from Mercedes-Benz, Detroit, Caterpillar and Cummins, Grogran said. Most of the engines will reject more heat and will have water-to-air coolers whose waste heat will be carried away by engine. The radiators rest on shock-isolating mounts and are braced against the firewall by three rods.
Meanwhile, engineers redesigned the main-frame rails and crossmembers, cab supports and steering gear. The changes add strength and stability, and improve ride quality, said John Merrifield, the company's senior vice president of sales and marketing. Stronger frames will enhance Sterling's position in vocational trucks.
New frame designs include 10- and 11-inch-high rails, plus a new 13-inch-high rail. With insert reinforcement, a main rail's section modulus can be up to 5 million inch-pounds. Full-length inserts can now be ordered on severe-service trucks; the existing HN80 frame uses outserts running only between the cab and rear-axle mounts.
Part of the HX frame is an "OptiLock" chassis grid system, which establishes rows of mounting holes for all chassis components and accessories. There are up to five rows of invisible dots on the rails' sides; holes are spaced 50 millimeters (about 2 inches) apart, vertically and horizontally. Body makers can use OptiLock and Sterling's frame supplier will punch holes to accommodate mounting of most bodies.
More Freightliner Parts
Various parts from Freightliner heavies were incorporated into the HX chassis to save acquisition dollars and wring cost out of manufacturing, Grogran said. These include crossmembers pieces, front suspensions, fuel and air tanks and mounting castings. The extent of commonality among Sterling and Freightliner platforms varies because of the sometimes high amount of customization wanted by customers, Grogran said. But the HX cannot be considered a "Freightliner" chassis.
Proprietary to Sterlings are new cab front supports that are simpler than the current types, and a redesigned Comfort Ride air suspension for the rear of the cab. The cab suspension's air springs and shock absorbers are recalibrated and repositioned for better support and more stability than the current system, and all parts are easier to remove and replace. New TRW power-steering gear uses higher hydraulic pressure, while the steering column uses a lubed-for-life center joint.
Front suspensions will include taper-leaf springs rated up to 20,000 pounds and multi-leaf springs up to 23,000 pounds. There are also maintenance-free suspensions rated up to 14,600 pounds, and new lightweight suspension rated at 12,000 pounds with composite fiberglass springs that save 77 pounds per truck. An AirLiner front suspension will offer improved ride on A-line vehicles. Sterling vocational trucks can be ordered with Hendrickson's PriMaxx air and HaulMaxx walking-beam tandem rear suspensions, and an "enhanced" Freightliner TufTrac suspension with a softer-riding two-stage center bearing.
More Reliable Compressor
The new scroll-type rotary A/C compressor is said to be 35% more efficient than current piston-type compressors, which means the engine works less hard to run it and thus uses less fuel. The compressor's output varies according to need, which also reduces the amount of on-off cycling.
And the new compressor is 50% more durable, so expensive failures will be reduced and maintenance and operating costs cut. Greater durability allows the offering of a two-year warranty, versus one year on current compressor types.
Though the rotary scroll design is the same in principle to those used for some time on automobiles, this unit is engineered and built for use on heavy trucks, executives emphasized. Visteon Corp. designed the unit expressly for Freightliner LLC, and it will be used only on Sterlings for one year; the exclusivity then extends to other Freightliner-family trucks for another year.
The compressor and other accessories will be driven by an easily changed serpentine belt instead of V-belts - another change that's part of the new HX chassis. Accessories will be pad-mounted instead of swivel hung, as was the case with V-belts. Various engine and accessory packages will use one or two serpentine belts with automatic tensioners.
The HX chassis will be phased into production on Sterling's A and L heavy conventionals beginning this month through March '04, Grogran said. Sterling Acterra mediums got a redesigned "MX" chassis in September 2002. The MX is based on Freightliner's Business Class M2 chassis, introduced in February '02; the Acterra, which came out in '00, used chassis parts from the original Business Class.
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