Recent Developments in a Novel Blended Hydraulic Hybrid Transmission 2014-01-2399

A novel Blended Hydraulic Hybrid transmission architecture is presented in this paper with benefits over conventional designs. This novel configuration combines elements of a hydrostatic transmission, a parallel hybrid, and a selectively connectable high pressure accumulator using passive and actively controlled logic elements. Losses are reduced compared to existing series hybrid transmissions by enabling the units to operate efficiently at pressures below the current high pressure accumulator's pressure. A selective connection to the high pressure accumulator also allows for higher system precharge which increases regenerative braking torque and energy capture with little determent to system efficiency. Finally operating as a hydrostatic transmission increases transmission stiffness (i.e. driver response) and may improve driver feel in certain situations when compared to a conventional series hybrid transmission.

To explore the novel blended hybrid architecture six transmissions were modeled and simulated. These included baseline manual and automatic transmissions, conventional series hybrid and series hybrid power split transmissions, and the novel blended hybrid and blended hybrid power split transmissions. All six transmissions were then optimally controlled on the UDDS cycle using dynamic programming to remove the influence of controller design on system efficiency. Ultimately the blended hybrid power split transmission improved fuel economy by 17.35% over a baseline automatic transmission while consuming 12.04% less energy than a conventional series hybrid power split transmission.

The blended hybrid architecture was further explored by constructing a hardware-in-the-loop test rig and measuring the transmission over a defined drive cycle.