21 Oct 05
B5-TPH is a crossover-style family wagon with Subaru's new hybrid system, which combines an electric motor and the Subaru flat-four 2.0-litre petrol engine, running on the Miller cycle.
In the Miller cycle, the intake valves stay open at the beginning of the compression stroke. Engines are usually 10-15% more efficient than conventional Otto cycle engines, as they require less energy to overcome friction and take a shorter compression stroke, but there has typically been a loss of power and low-down torque. In this Subaru prototype, this is compensated for by the addition of a turbocharger and the electric motor - the latter, giving 10kW, can add up to 110lb-ft of extra torque. The system also allows for a more compact motor and smaller battery than Subaru's earlier sequential-series hybrids, and is better-suited to the layout of the "boxer" engines.
The first production model to feature this so-called Turbo Parallel Hybrid (TPH) system will be the Legacy Hybrid, due 2007, and Subaru claims that in this car, it will produce around 255bhp yet return over 38mpg. However, the B5-TPH suggests that a hybrid new-generation Impreza wagon isn't too far behind.
