Test Drive – Volvo 7900H

Hybrid bus purchases have so far been dominated by double-deckers. But single-decker diesel-electrics are available, and Volvo’s 7900H has found some favour in this sector. Lothian has taken 20 Euro 6 examples, one of which has been driven by Tim Deakin.

Although fully-electric buses look to be the long-term future of the city bus sector, economically and operationally they are still some way off being widely-accepted vehicles. Hybrids meanwhile, although also not yet economically viable stand-alone propositions, have proved themselves up to the most demanding of urban bus operations and also deliver significant fuel savings.

Double-deckers have so far dominated hybrid deliveries, with Volvo’s B5LH one of three such models available. It is in service in several of the UK’s largest cities and has acquired a reputation for reliability, which is why good things should be expected from the 7900H, mechanically a single-deck B5LH.

Among early purchasers of the 7900H was Lothian Buses, which took delivery of 10 Euro 5 examples in April 2013. Evidently successful, a further 20 Euro 6 versions were soon ordered. Prior to them entering service, Engineering Director Bill Devlin kindly made one of the latter available for a routeone Test Drive.

Build

The 7900H is a heavy-duty bus and is built in Poland. Lothian’s are driven across Europe on their delivery run rather than carried by low-loader, says Bill, adding that no problems have been experienced during the over-1,000-mile trip.

Bonded glazing is fitted throughout the bus to give a sleek look, including the windscreen and signalling window, and fibreglass features heavily in body construction.

It is complemented by plastic and aluminium in a bid to keep the unladen weight as low as possible, which at 12,249kg is reasonable for a bus of this type. Volvo also claims a high level of ‘recyclability’.

Engine
Engine mounted longitudinally

The 5.1-litre D5K engine, driving through a 12-speed I-Shift gearbox, is mounted longitudinally at the rear nearside and the radiator is above, giving a ‘shower cubicle’ at the rear of the saloon similar to that seen in some earlier generation diesel single-deckers. The exhaust is to the offside.

Upright radiator leads to a 'shower cubicle' at the rear nearside
Upright radiator leads to a ‘shower cubicle’ at the rear nearside

The 7900H’s parallel hybrid package is shared with the B5LH and allows either the electric motor or the engine, or at times of high demand both, to power the bus. The motor has a maximum rating of 160bhp/800Nm and a continuous rating of 94bhp/400Nm.

Volvo’s I-Start system, made up of two separate battery packs, is fitted as standard.

One set is only ever used to turn the engine over, and so won’t be drained if the interior lights are left on, for example.

The lithium-ion batteries which form part of the hybrid package are roof-mounted, split between the front and rear. They are heated or cooled as appropriate by water, which Volvo says ensures optimum operation regardless of the ambient temperature.

Wisely the manufacturer has elected to position the AdBlue and diesel fillers away from each other. Fuel is added above the offside front wheel and capacity is 205 litres. AdBlue goes in at the extreme rear nearside with the filler tucked behind a small hinged door.

Passenger access

The 7900H’s two-piece inswinging door is 121cm wide. An electrically-operated two-piece ramp is present, and Lothian has specified separate buggy and wheelchair spaces, which are clearly marked on the floor. Mobitec destination equipment is fitted.

The two-bay layout is partially responsible for a low seating capacity of 34, and the rear ‘shower cubicle’ and the first three rows being in a 2+1 layout also restrict seat numbers. Just one tip-up seat is present, at the rear of the buggy bay.

Unusual seating arrangement
Rear ‘shower cubicle’ reduces seating capacity

A comparatively low number of seats is mitigated in continental style by the huge volume of standees which can be carried.

At 49 with no wheelchair user present, it gives Lothian’s 7900Hs a total capacity of 83, dropping by three when a wheelchair user is present. Volvo’s literature notes that 55 standees is the maximum possible.

Of the 34 seats, 15 are accessible before a step is reached, and most of those in the low-floor section are cantilever-mounted, simplifying mopping and sweeping.

Seats
Unusual internal seating arrangements

A centre offside emergency door is present within the low-floor area, with a substantial cable attached to prevent it making contact with the side of the body when open.

Emergency door is mounted amidships
Emergency door is mounted amidships

Initial entry step height is 31cm, rapidly reducing to 23cm when the suspension is knelt. A further step of 25cm is required to access the high-floor area. One pair of seats, those above the engine, is accessed by a third step, of 22cm.

Passenger comfort

The 7900H is most pleasant internally, helped by its large windows. All but four of the seats are finished in a dark red moquette; the exceptions are the first pairs on each side, which are priority positions and stand out by virtue of being covered in a much lighter fabric.

The 2+1 layout at the front of the bus means that the offside priority seats are, unusually, located in the fourth row, adjacent to the emergency door. Nearside priority positions are more conventionally sited immediately behind the wheelchair bay.

11 bell pushes are present and occupants of the priority seats can access the nearest ones to them without standing. Handrails are finished in cream and the forward half of the low-floor area is equipped with a number of straps for standing passengers to hold.

Heating comes from floor-level convection radiators. Thoughtfully, chunky bars in the buggy and wheelchair bays protect the vulnerable radiators from damage, and also give the additional benefit of making it difficult for a child or wheelchair user to touch the hot metal.

No opening windows are present, with ventilation instead coming from forced air at roof level, controlled by the driver. Air-conditioning is available as an option.

Ride quality of the 7900H is very good, and internal noise is low, helped by the engine’s location at the extreme rear. Absent entirely from the Euro 6 model’s noise profile is any clunking associated with the I-Shift’s gear engagement; although not intrusive, it was unquestionably noticeable on earlier Volvo hybrids.

With the Euro 6 model the manufacturer also seems to have smoothed the very obvious transition encountered previously when the engine restarted following a period of electric-only operation.

Driver comfort

By bus standards, the cab is luxurious. It has a high-specification, air suspended Isringhausen seat with armrests on both sides and such a variety of adjustments that it wouldn’t look out of place in a top-line touring coach.

Entry is through a reasonably wide door, and storage for the driver’s bag is adequate. Unusually, the full-length anti-assault screen is made of glass and not the more usual plastic, which should give a better resistance to scratching and fogging when it is cleaned.

Besides the normal holes to reach the ticket machine and cash tray, two additional openings have sensibly been cut in the screen to allow the driver to clearly view the internal mirror and nearside rear-view mirror. The latter in particular is a need which is often overlooked.

The dashboard is black and well laid out, and moves as a complete unit with the steering wheel when a button is pressed. Cab air-conditioning is fitted, as is a comprehensive heating system including a radiator unit.

Dash is typical Volvo and ergonomically good
Dash is typical Volvo and ergonomically good

The external mirrors give a good view and are large, but mounted tightly against the A pillar to minimise blindspots. The standard nearside mirror is complemented by a wide-angle convex addition, which on the test vehicle has been angled downwards and added to the driver’s field of vision, important in cyclist-heavy areas.

Controls and pedals are easy to reach and in typical Volvo style the pedals have an excellent feel. The handbrake lever is situated quite low down to the driver’s right, and would be better located on the dash.

The present location may act as a deterrent to its use for some drivers, increasing the likelihood of it not being used when stationary.

A footrest is provided for the driver’s left leg, and unusually there is also a cup and can holder present. These are common on coaches but less so on buses, and spills are unfortunately inevitable in a vehicle which will have several drivers every day.

Performance

The 7900H uses the same engine installed in Volvo’s Euro 6 double-decker range, which proved itself capable when evaluated in the moderately lighter B5TL (routeone, Test Drive, 25 June).

The 7900H is over a tonne and a half heavier than the B5TL, but with 240bhp on tap, even without the assistance of the electric motor its performance should be on a par with any other single-decker.

Thanks to the parallel hybrid configuration, the motor is able to work in tandem with the engine at times of high power demand. Adding the engine’s 240bhp peak output to the motor’s 160bhp maximum rating gives a theoretical total of 400bhp, and 1,700Nm of torque, under the driver’s right foot, much more than would ever be needed in any urban bus application.

The bus is very smooth and quiet, and a lack of noise from the I-Shift gearbox compared with earlier versions is noticeable from the cab. Gear selection is by standard push buttons.

Low noise is also aided by stop-start functionality, which under normal conditions cuts the engine when the bus is stationary. Predictably this didn’t happen from the beginning of the test, but within a mile of a cold start it began to occur as it should under normal circumstances.

Drivers and passengers unaccustomed to stop-start technology will no doubt find it disconcerting at first, but it is soon forgotten about. Volvo has fitted a hill hold to prevent the bus rolling back when making hill starts without using the handbrake.

The engine doesn’t re-start until around 10mph, and the manufacturer claims that with a careful driver at the helm the 7900H can cover up to a mile with the engine off.

In Edinburgh’s heavy traffic that almost proved possible on one occasion. Fuel savings under such circumstances will be substantial, with Volvo claiming up to a 39% reduction is possible over a non-hybrid single-decker.

The green economy band runs from 1,200-1,600rpm, but I-Shift is not afraid to take engine speed above that. Such is quality of Volvo’s ‘blend’ of diesel and electric power, from the cab it is impossible to detect which is doing most of the work at any given time.

Verdict

Volvo claims the 7900H is the most fuel-efficient and reliable hybrid on the market. When tested in heavy Edinburgh traffic, the Lothian Euro 6 example returned 9.9mpg, and the type’s frugality is backed up by Bill Devlin. He says that the Euro 5 7900Hs in service since April 2013 are returning consumption figures in the region of 35% better than non-hybrid Volvo single-deckers.

Uncluttered panelling will easily accept adverts
Uncluttered panelling will easily accept adverts

It is, he says, not far from being a commercially-viable product in current form, and reliability of the Euro 5 buses has been exceptional.

In Euro 6 form as tested, the 7900H is a fine bus, and the parallel hybrid package shared with the more common B5LH is refined. I-Shift is quieter and the transition between electric and diesel power is less pronounced than previously.

The only real source of criticism is its internal layout. Continental Europe’s fondness of standing passengers means that the seating capacity is lower than it could otherwise be, although turning the three single seats at the front offside into doubles would not be the most challenging task. Equally the arrangement around and above the engine is slightly fussy, albeit by necessity.

But this aside, the 7900H is a very good bus. The fuel-efficient driveline has been comprehensively proven at Euro 5 and Volvo products’ reliability is well established. The bus is sure to please drivers and large windows give an airy saloon.

Combined with a smooth ride, these mean that if you can cover the additional cost of hybrid technology, this bus is well worth the investment.

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