Irisbus recently launched the Hynovis concept vehicle fitted with a hydraulic hybrid driveline, which has a lower unladen weight than a comparable diesel-electric hybrid bus. Hynovis uses a 5.9-litre six cylinder Tector unit mounted at the rear, reducing fuel consumption and CO2 emissions by 30% and NOx emissions by 50%.
The concept vehicle was developed in cooperation with a number of French suppliers including Poclain Hydraulics who studied and supplied two hydraulic systems. One consists of a stop-start unit that stops the engine while the bus is stationary and restarts it rapidly after pushing the accelerator pedal. The second drives the auxiliary systems while the engine is stopped. The braking energy recovery system relies on hydraulic motor pumps, which are linked to a hydro-pneumatic accumulator. In order to achieve the maximum area of low floor, Hynovis has four small independently suspended steering front wheels. Michelin has developed tyres with an improved rolling co-efficient which contribute towards savings in fuel consumption. Irisbus noted that many operators want a standard passenger flow, with entrance through a front door adjacent to the driver, and exit through double width doors in front of the rear axle, even for passengers in wheelchairs. On Hynovis, the gangway width is around 1,200mm, so that even a large wheelchair can board at the front and depart at the rear.