The diesel version of the Mercedes-Benz Citaro is covered in this article.
| Mercedes-Benz Citaro hybrid | |
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| Manufacturer | EvoBus GmbH |
| Years in operation | 2020 – 2021 (Trial) |
| Operators | SBS Transit |
| Length | 12 metre |
| Engine | Mercedes-Benz OM 936 h |
| Transmission | TBC |
| Accessibility | Low Floor & Wheelchair-accessible |
| Emission Standard | Euro VI (SCR) |
The Mercedes-Benz Citaro hybrid is a low-floor, twin-axle, diesel-hybrid city bus built by Mercedes-Benz and EvoBus GmbH. First unveiled in 2017, the mild hybrid bus pairs the existing diesel engine with a supercapacitor for reduced fuel consumption.
One unit of the Citaro hybrid was brought into Singapore in 2019, and was registered under a Special Purpose License to SBS Transit as SG4004B. As part of revenue service trials, the bus is authorised for deployment on bus Services 93 and 272 from 9 March 2020 to 8 March 2021 (both dates inclusive).
Singapore Background:
The Citaro hybrid belongs to Mercedes Benz’ popular Citaro range of city buses. Over 45,000 Citaro buses have been built from 1997 to 2015. Excluding the Citaro hybrid, all Citaro buses in Singapore are of the Euro V Diesel version. These buses are manufactured in Germany and shipped completely built-up (CBU) to Singapore. Citaros are also offered with CNG engines, and as diesel-hybrid, CNG-hybrid or full-electric vehicles.
First introduced locally in 2010 by SMRT Buses, and with follow-up orders by SBS Transit, the Citaro is among the most common bus models in Singapore (at around 1000 buses) with deliveries from 2011–2016, later further increased by the Land Transport Authority (LTA). Starting in 2016, these buses were also leased to other operators under the Bus Contracting Model.
Technical Information:
The Citaro hybrid was first unveiled at Busworld Europe 2017. As a mild hybrid vehicle, it was designed to hone the internal combustion engine for maximum efficiency with minimal modifications. The hybrid technology is offered as a piece of optional equipment for its existing Citybus range (both diesel and gas engines). Being lightweight and technically straightforward, the space-efficient design required little modifications to the interior and exterior of the bus.
As the hybrid system assists the combustion engine only during periods of high power demand, output and torque figures for the bus remain unchanged. Supercapacitors serve as the temporary power storage units, which are ideally suited to the continuous quick changeover between charging and discharging that occurs when stopping and pulling away again in typical city bus operation. Braking to a stop from a speed of 50 km/h just once is enough to recharge the power storage units in the Citaro hybrid.
An earlier version of the hybrid drivetrain offered for the Citaro, called the Mercedes-Benz Citaro BlueTec Hybrid, was first introduced in 2007, utilizing a series hybrid drivetrain.
The Citaro hybrid:
The Citaro hybrid employs a mild-hybrid system where the electric motor is mounted in-between the internal combustion engine and transmission. It assists the internal combustion engine during periods of power demand, and acts as a generator to recover energy during braking and coasting. Hence, the engine is less strained during acceleration, reducing fuel consumption by up to 8.5%.
The energy store for the hybrid system consists of roof-mounted supercapacitors, which are well-suited for quick charging and discharging. Unlike full-hybrid vehicles, mild hybrids like the Citaro hybrid are incapable of electric-only propulsion. The hybrid drive adds just 156 kg to the vehicle’s weight, which is a fraction of the weight of other electric drive systems.
The electric motor in the Citaro hybrid does not serve to increase the maximum power, and the output and torque of the new Citaro hybrid remain unchanged compared to a combustion-engine Citaro 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.
A key benefit of the compact and technically straightforward design of the supplementary hybrid drive is that it takes up little space, so the vehicle’s outer contours remain unchanged, as does the interior – there is no loss of passenger seating. The only change is a modified maintenance hatch in the floor area.
The mild-hybrid system thus differs from the series- and parallel-hybrid diesel-electric buses that were previously trialled in Singapore. The Volvo B5LH, of which 50 units were procured by the Land Transport Authority and entered service in 2018, employs a parallel hybrid system similar in drivetrain layout to the Citaro hybrid, but paired with a much more powerful electric motor and chemical battery storage. The Volvo hybrid is also able to move under electric power independently of the diesel engine.
| Citaro hybrid | Volvo B5LH | |
| Engine Output | 220 kW @ 1800 rpm 1,200 Nm @ 1200-1600 rpm |
177 kW @ 2200 rpm 900Nm @ 1200-1600 rpm |
| Motor Output | 14 kN / 220 Nm max | 120 kW / 800 Nm max |
Mercedes-Benz Citaro C2 hybrid
One unit of the Mercedes-Benz Citaro hybrid was spotted in Singapore in late August 2019. With no known further hybrid bus purchases after the Volvo B5LH, the vehicle is believed to be a trial unit.
The bus bears the registration number SG4004B. Under the Road Traffic (Authorisation of Use) Notification 2020, SG4004B is permitted to operate on Bus Services 93 and 272, both of which are operated by SBS Transit. The authorization is valid from 9 March 2020 to 8 March 2021 (both dates inclusive).
| Basic Technical Specifications | |
| Engine | Mercedes-Benz OM 936 h, 7700cc Power/torque rating of 220 kW (299 hp) @ 1800 rpm (80/1269/EEC) Torque rating of 1,200 Nm @ 1200–1600 rpm |
| Emissions control | Euro VI-compliant BlueEFFICIENCY Power, BlueTec® SCR diesel technology (with EGR), common-rail fuel injection system. Requires diesel exhaust fluids such as AdBlue. |
| Motor / Energy Store | Electric Engine rated at 14 kN /220 Nm maximum output Acts as a generator to recharge supercapacitors during braking Two modules of 16 double-layer capacitors; roof-mounted |
| Transmission | TBC |
| Bodywork | EvoBus integral bodywork. Built in Mannheim, Germany. |
| EDS | Gorba |
| PIDS | TBC |
| Passenger Capacity | TBC |
| Additional Specifications | Collision Avoidance System Anti-Fatigue System |
Bus Services 93 and 272 are currently served by Volvo B5LH hybrid buses, which entered service in December 2018. The allocation of SG4004B to these services reflects the possibility that SBS Transit (or LTA) is looking to compare the operational performance of both buses.
The Mercedes-Benz Citaro hybrid is of the second-generation design (also known as Citaro C2) which was launched in 2011. Older Citaro models in Singapore are of the first-generation design (2005/2006-facelift).
Gallery:
Photo Source: MANBSP Facebook (31 Aug 2019)
Photo Source: MANBSP Facebook (31 Aug 2019)
External Links & References:
- World premiere: Mercedes-Benz Citaro hybrid – the hybrid bus that pays for itself – Daimler
- The new Citaro hybrid – Mercedes-Benz
- The Citaro right-hand drives – Technical Information – Mercedes-Benz [PDF]
- Citaro – Technical Information at a glance – Mercedes-Benz
- BlueEFFICIENCY Power Euro VI Engines – Mercedes-Benz
- MANY DAIMLER PREMIERES AT BUSWORLD EUROPE 2017 – Busworld
- Road Traffic (Authorisation of Use) Notification 2020 – Singapore Statuses Online