Volvo’s Hybrid surprise
FRANK BEETON reports on important bus news from overseas.
It’s not often that vehicles exceed the expectations of their manufacturers when it comes to actual performance delivery, but Volvo says the latest version of its hybrid bus has turned out to be more economical than originally expected. Volvo commenced field testing of prototype hybrid buses in 2007, and expected them to be about 25 percent better in terms of fuel consumption than conventional diesel models under urban operating conditions.
Two years later, commercially built hybrids entered operation, and increased the margin of improvement by being some 35 percent more economical than the conventional norm. Volvo currently has 260 hybrid buses in operation around the world, so has been in a position to gather substantial data relating to their on-the-road performance, allowing continuous development to result in a second series production hybrid featuring lower masses and an even more impressive margin of improvement at around 37 percent.
The latest evolution Volvo 7900 Hybrid includes an optimised four-cylinder D5F215 diesel engine developing 161 kW (216 hp), a 120 kW (161 hp) I-SAM electric motor/generator, Volvo I-Shift 12-speed automated gearbox, double-reduction portal rear axle with alternative ratio options, beam front axle and electronically-controlled disc brakes. The hybrid system is of the parallel type, which means that the bus can operate exclusively on electric power at lower speeds, bringing the diesel progressively into play as speed increases, or when the batteries need recharging. Energy is recovered during braking, and returned to the batteries under controlled conditions to extend their life, and the bus auxiliary systems are electronically-powered, which eliminates the need for engine idling.
The 12-metre integral body structure makes use of recyclable aluminium, and can be fitted out with two or three double-door entrance/exits. Depending on the operational profile, gross vehicle mass ratings can range between 19 and 29,6 tonnes. Volvo reports a substantial number of repeat orders from operators who have previously purchased its hybrids, and says that future plans for hybrid development include plug-in recharging from the national electrical grid, with the prospect of liquid fuel savings of up to 60 percent when compared to conventional driveline buses.
The progressing delivery of 190 Optare Solo SR midibuses to the City of Cape Town, and Optare Plc’s partnership with Randfontein-based Busmark 2000, has raised the level of local interest in recent developments taking place at the British bodybuilder.
Following the increase in Ashok Leyland’s shareholding in Optare from 26 percent to a controlling 75,1 percent reported in the March 2012 edition of FOCUS, the company has completed its three-year turnaround plan, which included the consolidation of its manufacturing operations at Sherburn in Yorkshire in order to reduce overheads and operating costs. The Sherburn plant opened in August 2011, and this resulted in the progressive closure of the erstwhile Blackburn, Rotherham and Leeds facilities.
The closure of the Blackburn plant ended 80 years of bus and coach manufacturing history at the site. East Lancashire Coachbuilders was established there in 1934, and subsequently produced trolleybuses, trams, and narrow-gauge railway carriages in addition to single and double-deck bodywork for buses and coaches. Export destinations for East Lancs bodywork included Paris, Madrid, Barcelona, Copenhagen and Luxembourg. East Lancs became part of the British Bus Group in the late 1980s, before subsequently passing to Cowies, Arriva Passenger Services and finally the Darwen Group, which had also acquired Optare, through Jamesstan Investments, during 2008. Darwen, through a reverse takeover, then adopted Optare branding for the entire group. As mentioned in March, Optare also has historic roots in another famous Blackburn coachbuilder, Charles H. Roe Limited.
More recently, Optare has delivered 39 Versa hybrid school buses to the City of Manchester. These 57-seaters are equipped with a 130 kW (174 hp) Mercedes-Benz OM904LA diesel engine driving a generator, which feeds current to roof-mounted super capacitors. Twin traction motors and a summation gearbox are coupled to the rear axle, there being no direct mechanical connection between the engine and the drive axle.
During deceleration, the traction motors regenerate energy which is returned to the super capacitors for storage. Optra has also delivered three full-electric Versas to Coventry, while similarly powered Solo SR units have entered service between Dorchester and Poundberry on the English south coast. These latter buses are equipped with US-built Enova P120 full electric drive systems, made up of a 120 kW (161 hp) motor, a 100 kilowatt-hour lithium-ion magnesium phosphate battery pack, and a water-cooled 15,2 kW (20 hp) on-board charger. A self-contained operating range of 144 km is claimed for these units.