HSU Charge Prediction and Optimization Software for the EFV

The Marine Corps Expeditionary Fighting Vehicle utilizes 14 hydropneumatic suspension units (HSU) that have variable stiffness controlled by the nitrogen charge (mass) in each. Each HSU consists of a primary spring that contains a nominally 50/50 mixture of nitrogen and oil, and secondary spring that contains nitrogen with a small amount of oil. The vehicle ride height is effected by ambient temperature changes causing the nitrogen to expand or contract. The ride height must be maintained within a 4” operating band in order to achieve acceptable ride quality. The procedure for charging the HSUs currently involves jacking the EFV up and breaking the track in order to put the HSUs in a configuration where the volume is known. The current procedures takes an experienced maintenance crew more than 4 hours to complete. Streamline Automation and the University of Alabama propose to develop an EFV charging procedure that does not require the EFV to be jacked up. This will require the development of a model that accounts for the compressible, polytropic thermodynamic behavior of the nitrogen within the HSU, and the load transfer that takes place between the HSUs as they are charged while supporting the EFV weight.BENEFITS: Streamline Automation will work with the HSU manufacturer and the vehicle integrator during the Phase 1 effort. This will allow the models developed to be validated against existing test data, and to obtain customer concurrence from an early point in the program. This will make it more likely that the HSU charge optimization software will be accepted by these organizations, and used for initial factory adjustments, as well as by Marine Corps maintenance personnel. The EFV is expected to be the first of several vehicles that will use similar HSUs. Other vehicles, such as FCS will need similar charge optimization software.