Diamond Force Engineering

Diamond Force Engineering, a division of Navistar Defense located in Detroit MI, designs Military vehicles for customers worldwide. With the war in Afghanistan in full swing the British Military was seeking a high mobility tactical support vehicle as part of the OUVS program. Navistar’s MTX, a rugged lightweight vehicle meant for border patrol, reconnaissance missions and security details, was suitable starting point but lacked the desired mobility characteristics.

The Expectation

Diamond Force engineers began evaluating suspension options for the MXT with the goal of replacing the solid axle suspension with a modern independent suspension. Packaging concerns along with the desire to change ride height and compensate for changes in vehicle weight led the team to select front and rear independent suspension with air springs and a ride height adjustment system.

The air springs provided a low natural frequency for the suspension which remained relatively constant with vehicle payload changes. The trade off with low natural frequency air suspensions is less control of the sprung mass in low speed handling and transient events. In addition, bottoming and topping of the suspension become more prevalent unless air spring pressures are increased to a point where ride quality suffers. Engineers looked to the damper for help. What was lacking was a damper that adjust damping in real time to changes in terrain, vehicle payload while also providing force authority to prevent bottoming and topping and the control to enhance handling. All this was necessary without having a negative effect on ride quality. It turned out the damper became the critical component in the suspension upgrade project.

The Solution

The Diamond Force team engaged with General Kinetics when they learned of the successful demonstration of the Active Shock semi active damping system on a HMMWV testing program conducted by TACOM. Since the system was designed to be completely scalable the Active Shock engineers, working closely with the Navistar team and the independent suspension supplier, were able to show how adapting the current HMMWV system to the MXT could be done within the tight program schedule. Tuning the system for the vehicle would also be simple without the need to write software code but rather through a simple change of configuration variables in the current software.

The Active Shock system provided the missing pieces in the suspension design. The systems end stop control, whole body control system, real time damping adjustment and the ability to integrate with the selected ride height control system made Active shock the perfect solution to end the compromises present in the suspension system.

Results & Benefits

Test vehicles were built and tested. The vehicles exhibited exceptional ride quality and handling. Active Shock engineers were able to tune the vehicle dampers to meet the test requirement set forth by the customer.

At the end of testing, the Ministry of Defense awarded Navistar a contract to provide 262 Husky vehicles to the UK for urgent operational requirement in Afghanistan. The lighter and more mobile Husky demonstrated the ability to navigate rough terrain like that found in theater while offering added protection from ballistic fire, mines and roadside bombs.

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