From the Mercedes-Benz OE 302 to the OE 305

The OE 302 was succeeded ten years later by the OE 305 urban regular-service bus, whose batteries were now accommodated in two compartments running width-wise across the vehicle between the axles. They had a rated voltage of 360 V and a capacity, depending on specification, of between 150 and 275 Ah. Their weight ranged from 2.0 t to 3.5 t. In battery-only operation, they had a range of between 50 and 75 km. The traction motor had the same output as before, namely 115 kW (156 hp) in steady-state operation, with a peak output of 150 kW (204 hp), while the diesel engine was now a six-cylinder unit developing 74 kW (100 hp).

From the hybrid bus to the Duo bus

The hybrid bus was also joined by an electric-only Duo bus, whose traction motor could be powered either from overhead trolley lines or by batteries. A further version of the Duo bus had no batteries and was powered either by overhead lines or a diesel engine. Field trials of the trolley/battery Duo bus began in Esslingen, Germany, in 1975. From 1979, twenty-five O 305 buses with various types of hybrid drive were operating in Stuttgart, Esslingen and Wesel.

Mercedes-Benz O 305 GTD in Esslingen

By 1984, a limited-production Duo articulated hybrid bus, the O 305 GTD, was operating in everyday regular service. In Essen it even used a guided busway and some parts of the tram network. The drive system now comprised an electric traction motor, powered from overhead lines, in combination with a normal diesel engine. The two power sources alternated with each other to drive the third axle.

The O 305 GTD Duo bus and its successor, the O 405 GTD, even carved out some­thing of an international career for themselves. For example, over 200 units were supplied by Mercedes-Benz to the Ecuadorian capital Quito. In Europe, approxi­mately 50 units of the O 405 GTD went into service. In Esslingen, some of these are still operating in regular service today.

O 405 NÜH: the first hybrid bus with wheel hub motors

The mid-1990s marked a new milestone in the development of hybrid-drive buses. For urban operation, Mercedes-Benz began trials of the O 405 GNDE, a diesel/ electric articulated bus with wheel hub motors, but no batteries to store energy. A further landmark in hybrid bus development was the O 405 NÜH low-floor hybrid rural-service bus. This was the first hybrid bus with wheel hub motors, a diesel engine and traction batteries. The two asynchronous wheel hub motors at the rear axle each had an output of 75 kW (103 hp). The low-floor design of the front end of the bus led to the four traction batteries being mounted on the roof, to save space. The powerful sodium-nickel-chloride batteries weighed 800 kg and had a range of 10 km in continuous electric-only regular-service operation. After each such electrically-powered trip through an urban area, the batteries were recharged by the diesel engine.

Mercedes-Benz O 405 NÜH