Autocar's Routemaster RMXL in detail
Capoco’s Routemaster design, dubbed RMXL, is 9840mm long, that’s 800mm longer than the old model. The 6540mm wheelbase is just over 700mm longer and the width up 162mm to 2550mm. Although the new Routemaster’s roof is 275mm lower, the lost interior space is easily recovered because the floor is also much lower.RMXL will carry 48 people on the upper deck — eight more than the original — but will accommodate four fewer passengers downstairs because space has repurposed for wheelchairs and pushchairs.
At 8230kg, it will weigh around 400kg more than the old version — a tribute to the original aluminium spaceframe design.
The RMXL is also built around a massive spaceframe of aluminium extrusions. Normal buses are built around a welded steel frame, but this aluminium cage should be lighter and much stiffer.
The skin of the bus is made from rolled aluminium panels, and the floors are made from bonded honeycomb sandwich sheets, the same material used by modern passenger jets.
The frame and floors will be fixed together mechanically, but the windows will be bonded in place. The engine and air suspension are mounted on stainless steel subframes.
The key difference between this Routemaster and the old model lies in the transmission. The engine is still in the nose, but there’s no mechanical connection between the engine and the rear wheels. Instead the engine powers a generator that charges the batteries, which drive the electric motors on each rear wheel.The removal of the huge gearbox, propshaft and rear differential vastly increases the ground floor space. The RMXL’s floor is flat and sits below the centre line of the wheels.
This improves passenger access, for pedestrians and those with wheelchairs and buggies. The air suspension will also lower the bus so that the floor is level with the kerb.
Looked at objectively, one of the most environmentally-unfriendly ways of providing public transport has to be strapping a large diesel engine into a heavy vehicle and then stopping and starting it between five and seven times per mile. The result is that buses can be very ‘dirty’.
While CO2 has become synonymous with ‘pollution’, it‘s Nitrogen Oxides and particulates from inner-cirty diesels that affect human health. Although particulate traps can help, high exhaust temperatures are required to completely burn the soot away, something that can’t be achieved in stop-start traffic. Reducing NoX requires complex in-vehicle treatment, such as the systems used by Mercedes’ Bluetec diesel engines.
Many global cities (including Tokyo, Hong Kong and Delhi) have already addressed this problem by shifting to buses and taxis powered by clean-burning liquid petroleum gas, or compressed natural gas.
However, the next step is to use a hybrid transmission. The RMXL design uses a Ford 2.3-litre ‘hydrogenised’ petrol engine, developing 127bhp. (Boeing is using this engine in a pilotless drone aircraft). Hydrogen fuel is stored in an filament-wound tank, mounted under the staircase.
The engine is designed to run continuously at an optimum speed, driving a 97Kw generator. This charges the Lithium Ion batteries, which are mounted in front of the rear axle. The batteries drive the electric motors on the rear axle.
At a stroke, problems with pavement-side pollution are eliminated and the bus will run quietly – noise pollution is another major problem with heavy buses – and with zero local pollution. A fuel cell stack could be used in place of the engine, but would cost many hundreds of thousands extra.