Hybrid technology
Citaro hybrid

Hybrid technology

The base function of the Citaro hybrid is very simple: the disc-shaped and very robustly constructed electric motor is integrated between the combustion engine and automatic transmission. Amongst other things, it works as an alternator during the deceleration of the bus and converts coasting energy into electricity – when braking and when the driver removes their foot from the accelerator. The generated power is stored as electrical energy. Without hybrid technology this energy gained in the recuperation phase would be lost – the Citaro hybrid uses it and therefore saves: as soon as the bus pulls off, the electric motor supports the diesel engine with additional torque – the so-called boost phase. In this way the combustion engine momentarily has to provide less output when pulling away and therefore saves fuel. In addition, the electric motor provides support during idling. This improves the efficiency of the combustion engine and contributes towards a significantly reduced fuel consumption and therefore reduced emissions.

The electric motor does not serve to increase the maximum power. That's why the output and torque of the Citaro hybrid remain unchanged compared to a combustion-engine vehicle of the same type and rating. The engine speed of the combustion engine is not reduced in the boost phase. Only the peak performance is imperceptibly reduced and enhanced by the electric motor.

The interplay of combustion engine for the base load and electric motor for peak loads ensures a high level of energy efficiency of the drive system when driving. The components designed for greatly varying loads are constructed in a very robust manner. Their high durability is comparable with those of conventional combustion-engine powertrains. The electric motor is water-cooled, outputs up to 14 kW and can provide a torque of up to 220 Nm.

The efficiency-optimised lightweight running axle also contributes to increased efficiency in the Citaro hybrid: on the one hand, through fuel savings due to the lower running resistance, and on the other, through less maintenance and a prolonged maintenance interval — from 180,000 to 240,000 km.

Its electronics convert the electrical energy stored as direct current into alternating current for powering the electric motor. Its space-saving water cooling ensures a high level of operating safety.

With its high power-to-size ratio, the innovative supercaps use condenser technology to store the electrical energy from and for the electric motor, saving space and doing so safely. They are designed for the continuous, quick change between charging and discharging in a typical urban bus cycle and have a high level of durability.

In the Citaro hybrid, the intelligent eco steering electrohydraulic steering system also contributes to high energy efficiency. It works in a way that is requirements-optimised, while contributing to reduced fuel consumption in public service applications.

* Not for low entry variants.

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