Hydraulic hybrid transmissions have demonstrated considerable potential in improving the fuel economy of on-road and off-highway vehicles. The authors have previously proposed a novel hydraulic hybrid transmission architecture termed the Blended Hybrid with benefits in efficiency and performance over existing systems. Recently an optimally controlled simulation study found that a blended hybrid power split transmission consumed 16% less energy than an equivalent series hybrid power split transmission over the US standard Urban Dynamometer Driving Schedule. To further explore this novel architecture the authors constructed a hardware-in-the-loop transmission test rig. In this paper the authors detail the construction, control, and measurements results of the blended hybrid on this test rig.

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Hydraulic hybrid transmissions in on-road vehicles have been proven to significantly reduce fuel consumption. Existing hydraulic hybrid transmissions have shown fuel savings of 30-50% [1] with higher savings predicted when using advanced architectures [2]. However while these results are promising there exists room for improvement. Consider the series hybrid architecture which is currently the most common full hydraulic hybrid configuration. This system requires over-center units which increase expense and are relatively uncommon especially for high performance bent axis units. Series hybrids may also possess a synthetic feel due to the high compliance inherent in their accumulators. Further efficiency suffers as the hydraulic units in series hybrids are often forced to operate at high pressures and low displacements. A novel hydraulic hybrid configuration is analyzed in this paper which may reduce costs, improve response, and increase efficiency under certain conditions. An automatic transmission, a series hydraulic hybrid, and the novel blended hybrid architecture were simulated for a class II truck and fuel consumption rates compared. Dynamic programming was used to optimally control all three transmissions thereby removing the effect of controller design of fuel consumption. Simulation results show a 44.8% increase in fuel efficiency for the series hybrid and a 37.0% increase with the proposed system architecture. While the proposed architectures currently lags the series hybrid in fuel economy, there exists sufficient benefits to merit further studies.

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