Hierarchical control strategy for a hybrid hydro-mechanical transmission (HMT) power-train

A hydraulic hybrid passenger vehicle using a Hydro-mechanical Transmission (HMT) or power-split architecture is being developed as a testbed within the Center for Compact and Efficient Fluid Power. In this paper, the design and experimental implementation of a three-level hierarchical control approach for this vehicle with a second generation hardware are presented. This control strategy segregates the tasks of the drive-train into three layers that respectively 1) manages the accumulator energy storage (high level); 2) performs vehicle level optimization (mid-level); and 3) attains the desired vehicle operating condition (low level). Different high level energy management strategies can be employed without affecting the mid and low level controllers. Two 'high level' energy management strategies have been implemented and experimentally tested initially, a continuously variable transmission (CVT) strategy used as a baseline for comparison, and a rule based hybrid strategy. Results illustrate that the mid and low level power-train control satisfy the driver's demand and the efficiency is dependent on the energy management used.