Straightforward drive technology to assist the combustion engine
The basic way in which the Citaro hybrid works could not be simpler: when the bus is decelerating, the electric motor acts as a generator and transforms braking energy into electric power. This power is stored so that it can be used by the electric motor to assist the combustion engine, especially when moving off.
The drive technology behind this has a remarkably straightforward design. One of the hybrid drive's core components is the electric motor. The discshaped unit with integral power electronics is a permanently excited synchronous motor, meaning it is mechanically very robust. The electric motor is fitted between the combustion engine and the automatic transmission. It generates a maximum output of 14 kW and 220 Nm of peak torque.
The electric motor on the Citaro hybrid assists the combustion engine first and foremost when high levels of power are required, particularly when moving off. It does not serve to boost maximum power, however, which is why the output and torque figures for the bus remain unchanged. Instead, the electric motor reduces the burden on the engine while also improving the vehicle's start-off characteristics. This does not involve lowering the engine's speed – the peak output is simply throttled imperceptibly with the electric motor making up the difference.
In addition to this, a slight boost effect from the electric motor at idling speed increases the combustion engine's efficiency. These two functions together translate into a major reduction in fuel consumption.