Daimler engines as Wrightbus targets Euro growth

New double deck


Artist’s impressions of the new Wrightbus StreetDeck double decker which is powered by a Mercedes-Benz OM934 5.1-litre engine. The glazed staircase is an option

StreetDeck-Rear Visitors to the NEC will have seen the new Wrightbus Gemini 3 double decker on the B5LH chassis on Volvo’s stand. Christened the ‘dream decker’ it has Volvo’s 5.1-litre, four cylinder D5K engine and ZF Ecolife transmission.

Visually what immediately sets it apart from the earlier generation Gemini is the shallower top deck windows and the thoroughly restyled and far more rounded rear styling. The front is new too, though it is recognisably an evolved Wrightbus product.

Reducing the depth of the windows and their glass thickness from 4mm to 3mm is one of 26 measures that contribute to a weight saving that sees the bus sport an unladen weight figure of only 10,814kg, down from around 12 tonnes previously. Also significant in this respect is the use of lighter Ster seats. The rationale behind the smaller windows is not only weight saving, it also reduces the solar gain from the sun by around 25%.

Inside the driver’s area featured a new assault screen and a fully movable binnacle. The driver’s view to the offside is greatly enhanced by the complete removal of the old B pillar. On the upper deck, the airflow is now more efficient, the old cove units having been replaced with a new simpler system designed in conjunction with Heavac.

Maximum passenger capacity on the bus we inspected was shown as 63 seats plus 38 standees, a total of 101, but this may not be the final figure. Wrightbus will only claim 99 as a definite passenger capacity for the time being but it may be that they will be able to offer a three figure capability. On the upper deck, an additional double seat can be accommodated on the nearside without compromising legroom or infringing TfL stipulations.


Bodily virtually identical to the Volvo mounted ‘Dream Decker’ or Gemini 3, the StreetDeck is the new integral double decker from Wrightbus and has a completely different chassis to that beneath the Volvo. On the past Wrightbus used a VDL DB250 running frame for its own branded deckers but they have now designed their own underframe and build it themselves for incorporation in the product. Of modular construction, it uses front and rear axle modules derived from the New Bus for London, with a new lightweight central wheelbase module and, at the rear, a new Euro6 engine module.

Not quite a first for the UK double deck bus (rather than coach) market, because Nottingham and Greater Manchester had small batches of V6-engined Dennis Falcon Vs in the 1980s, is the fact that it is Mercedes-Benz/Daimler powered using the OM934. This is a 5.1-litre four cylinder unit which develops 228hp (170kW) at 2,200rpm and peak torque of 900Nm at 1,400rpm mounted longitudinally within a demountable skid for ease of maintenance. Features of the engine compared with the Euro5 OM904 it replaces are greater durability, longer maintenance intervals, and reduced engine oil and AdBlue consumption. It weighs 495kg and is 800mm long, with a two stage turbocharger for good low speed torque and a five stage fuel injection system running at 2,400 bar. Apparently, consideration had been given to using the unit’s predecessor in the NBfL but Daimler could not supply at that time.

The engine bay layout has a single leaf radiator on the offside and a single leaf chargecooler on the nearside so that dirt does not get trapped between them. Their electric cooling fans reduce auxiliary power consumption. The ‘offset T’ driveline configuration keeps it simple with a short propshaft driving directly into the portal axle. This layout was chosen because an angle box would have consumed 4% of the torque generated as well as additional fuel. Only 14 bolts have to be unfastened to disconnect the engine cradle or skid, which comes out complete with the cooling pack, aftertreatment unit and gearbox. A further four bolts disconnect the propshaft.

When the DPF regenerates, temperatures in the cassette can reach 700 degrees. To counter this, the fans are programmed to blow across the unit during the regeneration process. Looking at an unbodied chassis, it was interesting to see that separate trays run along the chassis for the airlines, demister pipes, fuel lines and other key functions.

Gearbox options initially are the Voith D854.6 four-speed or ZF 6AP1000B six-speed automatic gearboxes with integral retarders. Subject to successful testing, the Mercedes-Benz G90AMT six-speed automated manual will also be offered. Wrightbus say the latter unit eliminates the parasitic losses associated with an oil pump and torque convertor.

The front axle and suspension unit is the ZF RL75 EC independent suspension, incorporating double wishbones with king post assembly, twin air springs and twin telescopic dampers. It has a 53 degree lock angle. The rear unit is the ZF AV132 drop centre axle with two upper and lower radius rods. Four wide spaced air springs and four telescopic dampers are mounted on bespoke suspension arms. An anti roll bar is also incorporated.

Batteries are 225A/h Varta units, there is a Groeneveld Oilmaster system fitted as standard, the diesel tank holds 245 litres and the AdBlue tanks holds 18-litres.

Measuring 10.469m long, 2.52m wide and 4.395m high, StreetDeck will be offered in both dual and single door formats. To dual door TfL specification, it will seat 73 and accommodate 26 standees, giving it a total capacity of 99.

We were also shown images of a premium version with enhancements including a glazed bodyside section alongside the staircase.

Deliveries are expected to commence around the middle of 2014. No firm orders have been placed yet because, as Group CEO, Mark Nodder, explained, operators want to evaluate the Euro6 models before purchasing. To this end, at least half a dozen seed vehicles will be made available for operators to experience.

Wrightbus anticipate that a fuel saving of at least 10% compared with Euro5 units will be achieved.

Wrightbus Product Director, Geoff Potter, commented, ‘Operators now have the choice of New Bus for London, the Wrightbus Gemini 3 on the Volvo B5TL chassis and StreetDeck, a complete Wrightbus double deck developed here in Northern Ireland. With a full hybrid electric version of StreetDeck a potential future option, we believe that Wrightbus will continue to be a major player in the double deck segment for many years to come.’

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