Fault Tolerant Hydraulic Hybrid

This was a one-year add-on project during 2011/2012.

The rates of energy flow through the heavy-vehicle system during accelerations and decelerations are extremely high due to large mass. Therefore, application of hydraulic devices for hybridization of heavy vehicles provides a very competitive option, given their inherent power-density advantage over electric counterparts, and recent technological breakthroughs boosting the conversion efficiency. In particular, hydraulic pump/motors with digitally controlled solenoid valves allow varying the torque via intelligent deactivation of individual elements, rather than reduction of stroke for all elements. This leads to exceptional hydraulic and mechanical efficiency at part load, since the active elements run at their best efficiency, and losses due to “idling” elements are minimal. Added benefit is reduced noise, and very fast response (high bandwidth), as a pump/motor can switch between pumping and motoring in half a shaft revolution.

The initial stage was devoted to generating insight into fault mechanisms in digitally controlled hydraulic pump/motors, and the development of physics-based models capable of simulating such events with sufficient fidelity. Models were based on the Bosch-Rexroth design for Digital Variable Radial pumps. The models were used in simulations to characterize failure modes, including the breaking or leaking of connected lines, aeration, stuck valves, et cetera. The simulations demonstrated fault mechanisms on the virtual platform and were used to explore detection techniques.

It was shown that individual cylinder pressures, and therefore individual valve faults, are unobservable and un-isolable from merely using readily available speed, phase and line pressure sensors. A solution is found by using a sliding mode observer to estimate the lost torque or acceleration from such events and using phase tables to isolate the faulty cylinder/valve.

Finally, system level (hydraulic powertrain, including accumulator and pump) simulations evaluating reconfiguration for faulty scenarios were performed. The detailed model and detection and isolation algorithm itself are incorporated into the full hydraulic hybrid system model to verify mitigation strategies, including reconfiguration of firing sequences.

Publications:

• Wang, C., Ayalew, B., and Filipi, Z., “Fault Diagnosis on a Digital-Displacement Pump/Motor”, Proceedings of ASME Dynamic Systems and Control Conference (DSCC), Paper No. DSCC2013-3967, October 21-23, 2013.
• Johri, R., Salvi, A., and Filipi, Z., “Optimal Energy Management for a Hybrid Vehicle Using Neuro-Dynamic Programming to Consider Transient Engine Operation”, Proceedings of the 4th Annual ASME Dynamic Systems and Control Conference, Arlington, VA, 2011.
• Johri, R., Baseley, S., and Filipi, Z., “Simultaneous Optimization Of Supervisory Control And Gear Shift Logic For A Parallel Hydraulic Hybrid Refuse Truck Using Stochastic Dynamic Programming”, Proceedings of the 4th Annual ASME Dynamic Systems and Control Conference, Arlington, VA, 2011.