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Mack Granite armored and armor-capable dump trucks are scheduled to be delivered to the U.S. Army Corps of Engineers through 2025. (Mack Defense)

Developing for defense

Suppliers to the commercial vehicle segment optimize—read: ruggedize—their product offerings for the tougher terrain encountered by military vehicles.

Engineering drivetrain and propulsion solutions for military vehicles can require a different approach and unique considerations compared with developing for the commercial vehicle (CV) sector.

Building and adapting components and technologies for military vehicles often requires an optimization process to steel them for the more extreme conditions they are projected to experience.

In mid-February, Meritor, Inc. announced it was selected to equip Mack Defense’s new heavy-duty dump trucks for the U.S. Army with a comprehensive drivetrain solution from Meritor.

According to Mark Lyall, Meritor’s Senior Product Manager, the heavy dump truck (HDT) drivetrain platform is “an optimized recipe of commercially off-the-shelf-available components.” Meritor’s products are assembled in the U.S. and backed by its global DriveForce support and service team.

Meritor, whose partnership with Mack traces back to the first half of the 20th century, adapted its technologies developed for on-road CVs to be used on the Mack Defense HDT, Lyall told Truck & Off-Highway Engineering. Meritor Defense optimizes the company’s product based on the vehicle architecture and government performance requirements, as well as duty cycles.

A typical semi- or dump truck that travels daily down an interstate from point A to point B has a completely different duty cycle than a dump truck that would be used in a mine in South Africa. The same applies for a CV dump truck that is used to help build an airfield in Bahrain. The missions and terrain vary greatly around the world—and in many cases, there may be no roads. Lyall explained that the government releases requirements when seeking development of a product, or an array of products, around the operating conditions and missions at hand.

“In this case, the biggest challenge was the relationship between having a commercial dump truck with a significantly high payload, and the performance requirements needed in a military-type duty cycle or application,” Lyall said.
The HDT has larger wheels and tires and significantly tougher performance requirements compared to an everyday CV. The torque loads also are markedly higher in this application than they would be in a commercial truck.

The development process for military differs as well. 

In CV development, Lyall said Meritor would form a program directly with an OEM partner internally; “literally years’ worth of development [would occur] prior to bringing a product to market. That includes the virtual-type testing, on-road testing, leak testing, etc. In the defense world, you typically don’t have two years to develop a product. The timeframes are much shorter. However, the upfront product development and validation requirements remain much the same.”

Testing also reflects the usage and duty cycles of the military vehicle. For an HDT, component-level testing to those duty cycles is performed. “The government does vehicle-level—test-asset-level—testing to those particular duty cycles,” Lyall countered. “There are multiple testing facilities across the United States, as well as in Canada and Alaska. And then there are third-party companies, as well, that have test courses. These courses mimic what a vehicle would see in specific regions of the world.”

Complete drivetrain solution

Meritor’s MX810 front-drive steer-axle family is commercially available for the severe-service construction industry and also has been used on multiple mine-resistant ambush-protected (MRAP) military platforms for the past 20 years. With a weight rating up to 24,000 lb (10,886 kg), the MX810 features a double reduction, which Meritor says aids not only with increased capacity but also enhances ground clearance.

The company’s ProTec Series 50 beam axles are engineered to military specifications with gross axle weight rating (GAWR) up to 30,000 lb (13,608 kg) per axle and are based off Meritor’s P600 solution. It features inter-axle differentials, planetary wheel ends and a weight-optimized architecture. The Meritor MTC-3220-FV high-torque transfer case is compact for ease of maintenance and serviceability while remaining durable enough for the demands of military applications like the HDT. The Meritor Permalube RPL Series drivelines are designed for gear-fast/run-slow drivetrains and high-torque applications that are permanently lubricated and sealed for life to reduce maintenance.

Meritor Defense also is developing high-technology solutions for military applications by leveraging commercially viable global platforms from its Blue Horizon advanced-technology brand. Blue Horizon products center around efficiency, connectivity and electrification; Meritor’s eSuspension, for example, builds on its ProTec lineage with a Scalable Tactical Vehicle Solution that has GAWR ranges from 15,000 to 29,000 lb (6,804 to 13,154 kg) and can be configured for AWD with multiple motor positions.
“We will continue to push the boundaries of performance and durability for the defense sector and do so in a scalable fashion to meet all mission-critical demands,” Lyall said.

The Mack Granite armored and armor-capable dump trucks are scheduled to be delivered to the U.S. Army Corps of Engineers through 2025.

Tailored transmissions

Allison Transmission exhibited in late February at the International Defense Exhibition and Conference in Abu Dhabi, showcasing its 3000- and 4000-series units as well as the 5290 MXR, a future innovation for tracked vehicles. Allison shared the message that it continues to evolve to meet the stringent demands of military fleets worldwide, working with OEMs to design, develop, manufacture and support transmissions for tough conditions.

Dana Pittard, Allison’s VP of Defense Programs, who is also retired from the U.S. Army in the grade of Major General (2-Star), discussed with Truck & Off-Highway Engineering how the company tailors a transmission specifically for fleets that are developing new wheeled or tracked vehicles, and what is involved in the process.

“While Allison’s cross-drive transmissions—unique to tracked vehicles—are specifically designed for either military or heavy-duty tracked vehicles, they still reflect the cutting-edge and innovative technology developed by Allison’s commercial business,” he said. “In fact, one of [our] most significant advantages in the military vehicle market is that Allison is the only tracked-vehicle transmission manufacturer who also can offer wheeled-vehicle transmissions.”

The work, research and development Allison’s engineers bring from the commercial side of the business offers military vehicles “cutting-edge features,” performance and durability that is not available to strictly military transmission developers, according to Pittard. The supplier adapts commercial products and technology to reflect the different environment, conditions and stresses of military duty.

Engineers need to know how to package the transmission in a way that eliminates problems for the power pack integrator and vehicle manufacturer. “We do not want to be [just] transmission salesmen or suppliers,” he said. “Our technical team works closely with the rest of the vehicle team to make the entire platform better.”

Challenges arise when applying these technologies to military vehicles. Additional durability has to be engineered into the military applications, and the vehicles also demand more electronic features to power radios, computer systems, infrared lights, etc.

“These challenges were largely overcome by working closely with our customers to understand requirements, then to develop innovative solutions to these challenges. Solutions range from more robust hardware to software that allows safe operation in a military environment,” he said.

The testing process for military vehicles is somewhat more rigorous than for CVs, and tracked-vehicle applications are more challenging than wheeled-vehicle applications, according to Pittard.

End users specify the conditions under which their military vehicles will operate and Allison Transmission tests to those conditions. “These range from extreme weather conditions and temperatures to nuclear attacks,” he said.

Electrifying drivetrains

Electrified drivetrain technology is an area where Allison’s commercial endeavors inform military product development, Pittard told TOHE. Allison Transmission offers electric hybrid solutions, as well as the ability for the transmission to convert engine power not needed to drive the vehicle into electrical power to operate computers, radars, and other auxiliary systems that require onboard electric vehicle power (OBEVP).

“A unique consideration is the duty cycle of military vehicles and how this differs from the commercial vehicles that can use electrified drivetrains today,” he said. “The bus, garbage truck and other commercial vehicles that start and stop frequently are ideal for electrified drivetrains, as they can [via regenerative braking] recharge their batteries regularly.”

Military vehicles tend to operate differently, because they either drive continuously while “road-marching” great distances or tend to be stationary for extended periods with a need for their engines to be running to power accessories. Pittard explained that neither of those typical operating modes adequately recharge their batteries. Also, many tracked military vehicles operate outside of cities where charging stations are not available.

According to Pittard, Allison is working with various partners to develop electrified drivetrains for future military vehicles. 

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