Keep on towing

July 1, 2003
TRAILERS have to go where the tractor goes. But what if the tractor has to go up a 60 slope, climb over boulders, or wade across rivers? Stewart & Stevenson's

TRAILERS have to go where the tractor goes. But what if the tractor has to go up a 60° slope, climb over boulders, or wade across rivers?

Stewart & Stevenson's Tactical Vehicles Systems has developed a trailer that does just that, enabling the United States military to effectively double the amount of cargo that a single truck can carry through less-than-friendly terrain.

The trailers have been in production for two years under a United States Army contract that was awarded in 1998. But starting in September 2004, the company will begin producing 3,000 trailers under a competitive rebuy production contract awarded by the Army on April 17. The trailers will complement the Family of Medium Tactical Vehicles (FMTV) A1, an enhanced version of the line of versatile military trucks that Stewart & Stevenson has been producing for a decade.

The new contract, potentially worth more than $2 billion, was issued by the Army's Tank-automotive and Armament Command (TACOM) and includes production that could reach nearly 11,000 FMTV trucks and trailers over five years (8,000 trucks, 3,000 trailers), with an option for 12,000 additional vehicles.

The order includes single- and tandem-axle models. The single-axle trailer is rated at 2.5 tons payload, with the dual-axle trailer at 5 tons. As configured for the US Army, trailers double the payload of the truck, yet the speed of the truck is not limited off-road by the trailer.

“In the US military, off-road mobility is determined by a host of factors — including different terrains and soils,” says Dennis Dellinger, president and COO of TVS. “You can take any one of our trucks cross-country at a certain speed maximum. If you then put a fully loaded trailer behind it and drive them cross-country, the pair will have no problem negotiating the terrain, and the speed loss is less than 1 mph.”

The high-performance off-road trailers can be pulled by any military vehicle the size of the FMTV or larger — compatible with the Army's legacy fleet. The trailers use the Dynamic Analysis Design System (DADS) that accurately predicts the performance of the FMTV and trailer combination.

“One of the military's concerns is that trailers typically don't have the mobility to follow a high-performance off-road vehicle,” says Regis Luther, vice president of engineering and product development for the company's TVS limited partnership. “So we designed a trailer to match the off-road performance of the FMTV.”

Luther adds that some military trucks carry vibration-sensitive loads — rockets, munitions, etc — and the military therefore established a test protocol that determines vibration level and qualifies carriers to carry those payloads. He says the company's trucks and trailers are not excluded from any payloads.

“And that's not true of all military vehicles,” he says.

In addition, all vehicles in the Stewart & Stevenson order — truck and trailer — can be air dropped and lifted by helicopter for rapid deployment. (The five-ton truck can't be dropped but can be lifted by helicopter.)

Improving ride quality

In the trailers' suspension design, four long-leaf parabolics are used per axle minimum, along with lateral sway bars and DADS-modeled suspension geometry to stabilize the trailers.

Stewart & Stevenson is at work, too, on additional ways to improve ride quality and enhance the ability of future trailers to go virtually anywhere the truck goes. Two options the company is developing:

  • Active suspension

    Designed with future combat and tactical systems in mind, this suspension could be used on either a truck, trailer, or fighting vehicle. The system replaces conventional shock absorbers with active struts that power the suspension. Sensors will detect the terrain on which the vehicle is operating, sending electrical impulses to a computer. The computer calculates the action that the strut needs to take in order to maximize ride quality. The active strut, Stewart & Stevenson says, goes beyond the adjustable suspension systems found in some automobiles today. Rather than simply adjust the characteristics of the shock, the active strut delivers power to the suspension to produce the desired ride quality under severe road and off-road conditions.

    The project is a three-way effort between the University of Texas, Northrup Grumman, and Stewart & Stevenson. A preliminary model and prototype system has been developed and built and is currently being evaluated at the University of Texas campus in Austin. Plans then call for the active suspension FMTV to be thoroughly tested at the Stewart & Stevenson test facility adjacent the company's manufacturing facility.

  • Drive axles for trailers

    Stewart & Stevenson is partnering with a United Kingdom company, MultiDrive, for technology to deliver mechanical power to the trailer axle. The idea is to run a driveline from the PTO output of a truck drive axle to a corresponding drive axle mounted on the trailer. The rear axle that drives the trailer is the same one used as the intermediate axle of the 6 × 6 trucks Stewart & Stevenson produces.

The application, however, would require a special driveline in order to accommodate the extreme articulation required for a truck and trailer to travel over rough terrain. Stewart & Stevenson and MultiDrive are working together to apply the MultiDrive system to the FMTV.

The MultiDrive system uses the same basic technology that enables truck-mounted cranes to rotate 360°. By using one of these bearings in the horizontal plane and a linkage in the vertical plane, the Multidrive system allows the drivetrain to deliver constant power to the trailer axle, regardless of the angle between the two.

“The device provides the articulation of a lunette and the drive-through of a transfer case in one unit,” Luther says. “The geometry does not limit the ability of the prime mover and trailer. In an off-road environment, the angles of articulation are higher. This device does not limit the angles of articulation.”

Dellinger says that, in an off-road environment, the trailer has the potential to push the truck out of trouble, as opposed to the truck pulling the trailer out of trouble.

Sharing parts, jobs

More than 80% of the parts that go onto the trailers also are used on the FMTV truck. Commonality of components and features within the family reduces life-cycle cost, enhances reliability, simplifies logistics support, and leads to increased quality.

The trailers are designed to see severe service and are understandably heavier than a similar on-road-only trailer. The single-axle trailer is only 209.5" long, 78" high and 96" wide, yet it weighs 6,860 pounds. Curb weight of the tandem-axle model is 9,520 pounds.

The trucks and trailers also are designed to share jobs. The FMTV can be equipped with cargo bodies, dumps, wreckers, hook lifts, or as tractors. Stewart & Stevenson's enhancements to the FMTV A1 include an EPA 2004 compliant engine, soldier-suggested refinements, and additional reductions in life-cycle costs and logistics burden.

Among the equipment that the FMTV truck and/or trailer will be asked to transport:

  • The High Mobility Artillery Rocket System (HIMARS), produced by Lockheed Martin, which fires a six-pack of MLRS rockets or a single Army Tactical Missile System from a C-130 transportable FMTV chassis; and the FMTV-LHS Load Handling System, an 8.8-ton payload capacity vehicle with companion trailer developed in conjunction with Partek Cargotek, that will self-load and unload ISO containers or flat-racks.

  • The US MEADS Hybrid Electric Launcher, a system developed in conjunction with Lockheed Martin, demonstrates the design and technical capabilities that will be evident on the next generation air defense missile systems. The Permo-Drive Hybrid Hydraulic, an FMTV developed in conjunction with TACOM's National Automotive Center (NAC) and Permo-Drive, has been modified with hybrid hydraulic technologies, reducing fuel consumption significantly, thus reducing the logistics footprint and greenhouse emissions.

Luther says FMTV has been ranked No. 1 in operational readiness (demonstrating over 96%) of all the US Army systems for the past three years.

Sharing a plant

Stewart & Stevenson produces the trucks and trailers at the same 500,000-sq-ft plant in Sealy, Texas, an hour west of Houston.

The trucks and trailers move through the assembly line on powered fixtures that enable the trailers to be rotated for easier assembly. The fixtures are equipped with quick disconnects and can be repositioned easily.

“We can relocate the entire trailer production line in a couple of days if necessary,” says Al Strange, director of operations.

The high degree of parts commonality simplifies the assembly process.

Stewart & Stevenson produces trailers and trucks in the same facility — trucks since 1991, trailers since 2001. That enables the company to send both products through its 13-tank e-coat system, the largest in the South, management says.

A place for everything

Whether it is trailer production or truck manufacturing, the Stewart & Stevenson plant has a place for everything.

Yellow lines painted on the floor mark where items should go. This includes the work carts that contain the components that each station requires. Even the trash cans go in a marked spot on the floor.

“Stations clean their areas throughout the day,” Strange says. “We have a lot of trash cans throughout the plant to make cleanup go quickly.”

Some vendors also have their own spot within the plant. The company's hose vendor, for example, has a fenced bin in which hose inventory is stored. The inventory there is the property of the hose vendor until the time that the component goes onto the production line. Two employees of the vendor work in the area.

Elsewhere, supplied components enter the plant through color-coded receiving doors. Truck drivers are notified which specific door will accept their delivery. When the order is unloaded, engines, transmissions, and other components are within a few feet of where they will be needed on the assembly line.

The color-coded system, combined with signs throughout the property, makes it easier for truck drivers to reach their destination. This is especially important now that Stewart & Stevenson receives shipments around the clock.

“We used to receive only during the day,” Strange says. “This caused a major backup around our plant and the truck stop down the road.”

Reducing defects

An ISO manufacturing facility, Stewart & Stevenson works constantly to make the manufacturing process a little better. TVS recently received certification for the international quality standard ISO/TS 16949-2002. The company is one of the first military vehicle manufacturers in the US to earn this new and stringent certification.

“This is virtually a paperless plant,” Strange says. “The only paper we use is a single sheet that contains the barcode information for each vehicle we produce.”

Touch-screen monitors throughout the plant help workers track what flows through.

“We have infinite control of the assembly process,” Strange says. “We don't have to wait for reports. The system helps us to identify variations from the norm and to fix them right away.

“Every station has the right to reject the work produced by earlier stations. If Station 17 finds something wrong that Station 6 produced, someone from Station 6 fixes the problem and checks all the production in between.”

One of the most effective things Stewart & Stevenson did to reduce defects had nothing to do with sophisticated computer technology. It is a simple marking system that reminds production workers what they were doing at the time they went on break.

“We noticed that most of our defects were simple things — loose or incomplete installations,” Strange says. “We tracked when they were occurring and noticed that most happened right after individuals returned from lunch or a break. The tag system we developed serves as a bookmark that technicians use before they go on break. By having a system that lets people pick up where they left off, we have reduced defects significantly.”

New fabrication shop

Streamlining production and reducing defects has had an unanticipated result — freeing up plant space that Stewart & Stevenson now uses to fabricate many of the components it needs to produce trucks and trailers.

The 90,000-sq-ft facility at one point was a quality-control area. It was there that the company fixed leaks and other imperfections. But as the company's continuous improvement program began to produce results, the company no longer needed the facility.

The area was converted to a warehouse, but Stewart & Stevenson no longer needed much room to store inventory after implementing a just-in-time production system.

The company converted the area into a fabrication shop during the second half of last year. Today the area fabricates approximately 170 different part numbers per day and employs 80 people.

“We saw fabrication as a cost-reduction method,” says Philip Halsey, vice-president of fabrication operations. “Until we opened this shop in October, we had to buy all of our fabricated parts.”

Family of fabrication

The department processes three families of parts — machine forgings and castings, fabricated parts, and frame rails.

A major machine tool in the shop is a Mazak Palletech CNC machining cell that can produce 31 different part numbers simultaneously.

“Instead of 30 smaller machines, we have one big one,” Halsey says. “Instead of 34 operators, we have two.”

A Mitutoyo coordinate measuring machine verifies tolerances of the parts produced.

The fabrication shop also is equipped with a variety of TRUMPF machine tools, including a Trumatic L3030 laser, Trumatic L4030 laser, and a variety of Trumabend V series press brakes with automatic bend angle compensation.

One of the advantages of the CNC equipment is its ability to generate prototypes using software instead of hard tooling.

Pro/E engineering software is the starting point for the prototypes. Data from the engineering stations is transmitted directly to the fab shop via fiber optic cable.

“We can turn around a prototype in hours or days instead of days or weeks that an outside supplier would require,” Halsey says. “And if the first prototype is good, then we are ready to produce as many as production requires.”

Forming frame rails

Stewart & Stevenson produces its own frame rails for the trucks and trailers it manufactures. The same basic shape that is the backbone of the FMTV also is used for the trailer.

Instead of using a press brake, Stewart & Stevenson bought a Yoder roll former to form the frame rails.

“The frame rails are the starting point of the chassis,” Halsey says. “If it isn't right, nothing else fits properly. We are looking for consistent quality, rail after rail.”

The company produces a frame rail in about 15 minutes, including time spent cutting out shapes with a laser. Once the rails have been fabricated, they are loaded onto specially designed racks and taken straight to the e-coat line. They are consumed in the order of fabrication.

Reaching a milestone

In April, Stewart & Stevenson reached a milestone — production of the 20,000th FMTV vehicle. The truck was delivered on time, the 34th consecutive month of perfect performance in delivering trucks to the schedule required by the US Army. Through July, that streak was still alive.

Further, in 26 months of production of 2.5- and 5-ton FMTV trailers, the company has delivered every trailer perfectly on schedule, the company says.

The 20,000 FMTVs designed and produced at Stewart & Stevenson's Sealy facility come in 15 active variations of 2.5-ton cargo and van models and 5-ton cargo, troop carrier, tractor, van, wrecker, tanker, and dump-truck models.

The cargo body is the only one that Stewart & Stevenson produces. Other truck body manufacturers supply the rest.

The U S Army began a tactical wheeled vehicle modernization program to replace its aging fleet of trucks in the late 1980s and awarded Stewart & Stevenson a contract on October 11, 1991, for the manufacture of more than 10,000 US Army 2.5- and 5-ton FMTV trucks.

The company purchased a manufacturing plant near Sealy and modified it into a modern truck assembly plant. Production started in December 1992

Stewart & Stevenson and the U S Army concluded negotiations on October 21, 1996, to extend FMTV production through 1998. Then in late 1998, Stewart & Stevenson was awarded a second multiyear contract.

The Army approved the start of production of the A1 Model FMTV in 1999, after prototypes successfully completed more than 90,000 miles of testing at Aberdeen Proving Ground. The Army's approval of A1 production followed the strenuous but successful government-run Production Verification Test during which the FMTV A1 demonstrated more than 13,000 mean miles between hardware mission failure, well beyond the Army's reliability requirement of 5,500 miles.

The company's test-track facilities, including a looped course, mirror off-road conditions at the US Army's preeminent test facility, the Aberdeen Proving Ground, in Maryland. Features of the TVS track include 30% and 60% slopes/grades; high-frequency, low-amplitude vibration courses, a vertical 24", a frame twister sine wave; half-round bumps; trench obstacles, a return loop with crossover; and a 36" deep mud bath.

About the Author

Bruce Sauer and Rick Weber