The Chassis Challenge for the Humvee Replacement
The U.S. Army and Marine Corps are in the midst of selecting the replacement for the Humvee, which will have a suspension system that eases the severity of traveling over the harshest terrain.
When delivering troops to battle, safety and security is the No. 1 priority, but a certain level of ride performance is necessary to keep the forces fresh as they encounter warzone dangers.
One of the key characteristics that the Army and Marine Corps are looking for in the replacement for the venerable Humvee (derived from the acronym: High Mobility, Multi-Wheeled Vehicle) is an improved suspension. Why? Because they need a suspension system that will elevate the vehicle in areas where bombs may be present and to lower down to fit aboard a ship, all the while ensuring a smooth ride to protect electronic equipment and reduce passenger fatigue.
A little background: The Humvee, introduced in 1985, proved vulnerable to roadside bombs in Afghanistan and Iraq, requiring additional armor to withstand explosions. The Pentagon responded by purchasing heavy-duty, Mine-Resistant Ambush Protected (MRAP) vehicles to withstand these blasts. But these much larger trucks are expensive, and too bulky to provide much maneuverability.
To replace the Humvee, the Army and Marine Corps require a new vehicle that is strong enough to withstand bomb blasts, short enough to fit inside the hull of a transport ship, light enough to be lifted by a helicopter, and agile enough to navigate the most austere off-road terrain.
In 2008, the first initial technology development contracts for this new truck, dubbed the “Joint Light Tactical Vehicle” (JLTV), were awarded; in 2012, the Defense Department selected three companies to build 22 prototype vehicles: AM General (amgeneral.com), Lockheed Martin (lockheedmartin.com) and Oshkosh Corp. (oshkoshdefense.com). This year, the three competitors delivered their prototypes to the military for testing.
The chassis of these rugged vehicles supports the armored protection, powertrain and complex communications systems these vehicles must carry.
The services require the JLTV to weigh no more than 14,000 lb. The trucks will come in two variants: a four-passenger Combat Tactical Vehicle with 3,500-lb. payload and a two-passenger Combat Support Vehicle with a 5,100-lb. payload.
The “concept of operations” document, which outlines the services’ required capabilities, states the vehicle must be able “to leave the local road network and maneuver over cross-country terrain, gravel/dirt secondary roadways, single track trails with no manmade improvements and cross-country terrain with no roads, routes or well-worn trails.” In other words, the JLTV must be able travel pretty much anywhere.
“If you negotiate really rough terrain in the current Humvee, once you get to where you’re going you’re sore all over,” says Dave Marek, vice president of defense engineering at Oshkosh. “You ride in a JLTV and I don’t want to say it’s like riding in a Cadillac, but it isn’t far off.”
Hyperbole aside, Oshkosh’s JLTV design, the Light Combat Tactical All-Terrain Vehicle (L-ATV), leverages an enhanced version of the TAK-4 independent suspension system, which is already deployed in the company’s medium-duty MRAP All-Terrain Vehicle (M-ATV).
The improved “TAK-4i” system provides 20 in. of wheel travel to navigate uneven terrain (a 4-in. improvement over the existing system), a single reduction axle, adjustable suspension height for transportability (to fit aboard transport ships), and high-performance disc brakes to stop in extreme condi-tions as well as to reduce wear.
“The M-ATV is the current benchmark for off-road mobility and protection, performing a mission profile closest to what JLTV would perform,” explains
John Bryant, Oshkosh senior vice president of defense programs. “With JLTV,
the customer needs the protected mobility of an M-ATV in a much smaller, lighter-weight, more transportable package that’s also capable of even greater off-road mobility.”
The M-ATV vehicle weighs (27,500 lb.) about twice as much as the L-ATV (14,000 lb.).
Lockheed Martin also leveraged the suspension of its JTLV offering from an MRAP vehicle. The truck has Meritor’s (meritor.com) ProTec high-mobility independent suspension, used in the Caiman MRAP (built by BAE Systems, a member of Lockheed’s JLTV team). This technology offers a turning radius up to 35°, 21 in. of total independent wheel travel and limited-slip differential, no-spin differential and driver-controlled differential lock.
“This is a proven system, providing us a tremendous level of ride quality, while also facilitating key mobility requirements,” says Kathryn Hasse, director of the Lockheed JLTV effort.
The tricky part was integrating the chassis and its components with other competing requirements such as armor and transportability, Hasse says. To overcome the challenge, she explains her team borrowed a concurrent engineering approach from the commercial automotive world. Design, manufacturing and maintenance all worked in parallel toward developing the JLTV, meeting along the way to chart progress and fix potential problems upfront.
“We did a lot of model development and did weekly model reviews with our entire supply base,” she explains. “From a manufacturing perspective, we did a series of virtual builds working with our component suppliers and our manufacturing supplier, BAE Systems.”
Hasse adds, “We proceeded to build prototype vehicles and put them on essentially a four-post [road simulator] to do an accelerated lifecycle test—assimilating the type of terrain in the durability testing that the vehicles will undergo. And then we built an actual running chassis and put it through reliability and performance testing at our test track facilities.”
So far, the Lockheed JLTV has gone through 180,000 test miles, both virtually and on test tracks.
“We did a tremendous amount of work virtually because frankly it’s expensive to build hardware,” she says. “We took advantage of technology and virtual tools to do the design and assembly before we shelled out the cash to buy the hardware and integrate it.”
This approach helped Lockheed anticipate and fix possible issues before the
prototypes were tested by the government, and long before, if the military selects the Lockheed solution, the vehicles enter full-scale production.
“We’ve always kept in mind we’re not in this for 22 trucks, we’re in this for 50,000 trucks,” Hasse says.
Large volume truck production is a way of life for AM General, the third JLTV
competitor. For the past three decades, the company has built approximately 300,000 Humvees in various configurations. The company is competing for the JLTV contract with its Blast Resistant-Vehicle Off road (BRV-O) with a “Semi-Active Suspension” (SAS), which utilizes an autonomous electronically controlled fluid-strut damping system.
SAS allows the BRV-O vehicle to instantly respond to shifting terrain and load conditions. Throughout 300,000 miles of durability tests, the system had zero failures, explains Chris Vanslager, AM General vice president for business development and program management.
The system works to react promptly to changing terrain to stabilize the vehicle during corners and braking, Vanslager adds. A self-leveling feature on side slopes and grades makes for easier ingress/egress and helps improve weapon sighting.
In June, all three JLTV designs participated in the military’s “severe off-road track” (SORT) demonstration at Marine Corps Base Quantico, VA, allowing service leaders and members of Congress the opportunity to witness these new vehicles maneuver off-road obstacles including steep inclines/declines, log climbs, gravel pits and hairpin turns. All three JLTVs successfully completed the course, proving each suspension capable over rugged terrain.
The Army and Marines will spend up to 14 months evaluating each of the three vehicles, and ultimately select one single JLTV design by 2015. The current plan—subject to change with the whims of government spending priorities—is for the Army to buy 49,909 JLTVs by 2040 and the Marines to buy 5,500 by 2021. No matter which company wins, the ride will be a bit smoother for future troops rolling over rough terrain thanks to the more robust suspensions in all three JLTV offerings.