Navy designs mechanized rear-door assist for MRAP vehicles

By Alan Canfield and Dan Broadstreet, NSWC Panama City Division

Marine Corps Mine Resistant Ambush Protection Buffalo vehicles were designed to protect Marines from improvised explosive devices, and the Navy is improving MRAPs by upgrading them with a new rear-door assist mechanism. This particular MRAP model is managed by Marine Corps Systems Command at Quantico, Va.

Naval Surface Warfare Center Panama City Division Buffalo Systems Deputy Project Engineer Steven “Tate” Carow said the Buffalo MRAP trucks do not have a power system to assist opening its rear door.

“Currently, the vehicle’s rear door requires a manual effort to open, and it weighs about 500 pounds. It is designed so one person can open it on flat ground. However, should there be an emergency situation like a rollover, if the vehicle has to park on uneven terrain or even if the heat of the environment affects the door frame’s shape, the door can bind and become difficult to open,” Carow said.

The Buffalo program office provided specific requirements for the rear-door assist, or RDA, system to meet. With a critical requirement to improve crew survivability, some specific requirements addressed included time to open, reliability and environmental protection. NSWC PCD engineers designed the RDA solution to meet these requirements while using modified commercial-off-the-shelf hardware to reduce cost and production schedule. Key components of the design include a COTS linear electric actuator that unlatches the door and a modified COTS hydraulic cylinder that pushes and holds the door open. The design uses a ruggedized motor controller to activate the linear actuator and hydraulic cylinder.

According to Carow, the linear actuator unlatches the door by pulling on the same latch-bar used to manually open the door. Once the latch is disengaged by the linear actuator, the integrated hydraulic cylinder pushes the door open. The integrated cylinder also holds the door open by pulling on the same latch bar used to manually open the door. Once the latch is disengaged by the linear actuator, the integrated hydraulic cylinder pushes the door open. The integrated cylinder also holds the door fully open for emergency egress, until the controls are reset. The integrated hydraulic cylinder is basically an entire hydraulic circuit driven by a compact motor with no external hoses that can leak or be damaged.

The RDA system can be activated from two locations inside the vehicle and one location outside the vehicle. Multiple internal locations are provided to ensure the crew can open the door in the event of a rollover. The external switch can be activated by first responders if the crew is incapacitated.

Carow said that the COTS cylinders for the RDA required only a minimal modification. “We had the manufacturer increase the cylinder stroke length to fully open the door. Specifying a larger cylinder with standard stroke length would have increased the space claim, power requirements and cost – all factors we were trying to minimize” Carow said.

Another benefit to the team’s modified COTS solution, Carow pointed out, is the system is self-powered.

“The system has its own battery, which is charged from the truck’s alternator. So, even if the truck’s batteries become disabled, the system has enough stored energy to open the door many times,” Carow said.

He explained that should the RDA battery fail, there is a backup to the normal battery-powered activation.

“If all else fails, we have a manual way to crank out the pump’s hydraulic cylinder. A Marine can pull out a handle, which fits into a slot in the integrated hydraulic cylinder, and he or she can then simply use this to jack the door open,” Carow said.

Albert Shaw, Marine Corps Systems Command assistant program manager for the Cat III Buffalo MRAP, said the collaboration with NSWC PCD was a win-win situation because the partnership is producing effective solutions that in many cases can be shared by several Department of Defense entities.