In search of efficiency

Narrow, twisting roads, steep hills and slow-moving traffic in tourist resorts that are always full of visitors during the summer months are all challenges faced by Guernsey’s 42-strong bus fleet. So its vehicles have to be specified accordingly.

Transmission suppliers continue to innovate to squeeze more efficiency and help reduce emissions. Steve Banner reports

The latest batch of buses to be ordered by the States of Guernsey – the island’s government – consists of 22 additional Wrightbus StreetVibes fitted with Allison T 2100 automatic gearboxes.

The 9.04m-long 42-passenger newcomers follow an initial order for 12 StreetVibes delivered in 2017 when the island’s fleet, made up primarily of Euro 3 Dennis Darts, began to be renewed. Fuel economy is up to 20 per cent better than what was on offer from the vehicles they replaced, says States of Guernsey director of traffic and highway services Karl Guille, and the StreetVibes are quieter too.

The Euro 6 newcomers are ideal for the conditions they face, Guille believes.

“You can be in typical rush hour town traffic, with stop-start driving one minute, then need to accelerate smoothly up a steep rural hill the next,” he observes. This is where the T 2100 comes into its own Allison contends, thanks to what it describes as its Continuous Power Technology.

It means that power does not fall away every time the transmission changes gear, Allison says, as can be the case with a manual or automated manual transmission.

The T 2100 boxes are married to Cummins ISB4.5 diesels. They are equipped with a limiter that restricts the StreetVibes to no more than 25mph in line with island speed restrictions that apply to all buses and any vehicle with an unladen weight of over two tons.

The States of Guernsey’s bus fleet is operated on its behalf by HCT Group subsidiary CT Plus Guernsey. It reports that the way in which the Allison box delivers torque has helped to drive down fleet maintenance costs.

Allison believes its boxes can deliver even better fuel economy for its customers than they have hitherto. It is urging operators who have not already done so to consider upgrading their T 2100 transmissions to xFE standard complete with FuelSense 2.0 software.

The package can deliver a fuel economy improvement of up to 7 per cent, says the company, which is carrying out further, real-world, UK trials with the aim of supporting its claim.

Incorporating optimised gear ratios with the FuelSense Max package, xFE transmissions are designed to operate at lower engine speeds in higher ranges with reduced diesel consumption in mind. Add FuelSense 2.0, and a series of software enhancements mean that what Allison refers to as DynActive Shifting will provide the bus with an infinitely-variable combination of shift points.

Rather than rely on fixed points on a shift table, FuelSense 2.0 employs a learning algorithm to keep finding the right balance between fuel economy and performance for the duty cycle. Opt for FuelSense 2.0 Plus and you benefit from an improved version of Neutral at Stop; choose FuelSense 2.0 Max and you benefit from an enhanced version of Acceleration Rate Management as well.

Last autumn’s IAA Hanover Commercial Vehicle Show in Germany saw Allison give its nine-speed automatic transmission its global launch. Developed from the six-speed Allison 2000 Series automatic and designed to utilise the same vehicle manufacturer interfaces, its target audience includes school buses.

There is as yet no indication as to whether it will appear on buses on this side of the Atlantic, alas. Something that will certainly be appearing however, though not immediately, is Voith’s new DIWA NXT box.

Also showcased at last year’s Hanover exhibition, it is still under development. Series production looks set to start in early 2021.

It boasts an additional overdrive gear for buses used on inter-city services, a feature which should appeal to coach operators too, Voith believes.

DIWA NXT also comes with an optional mild hybrid system with a 48v CRU – Central Recuperation Unit. It harvests energy whenever the driver lifts his or her foot off the accelerator pedal and allows the bus to decelerate.

The energy is made available to the vehicle’s electrical system via the battery and a converter as well as for traction.

The CRU is integrated into the flywheel housing between the engine and the transmission. Continuous power is 25kW with peak power of 35kW available.

Retrieving energy that would otherwise be lost improves fuel consumption, shrinks the vehicle’s carbon footprint, and cuts NOx, particulates and other harmful emissions. So does stop/start, on offer as an option on the aforementioned Allison nine-speeder and on other transmissions.

ZF has been making this facility available on its EcoLife six-speed auto box, initially in conjunction with VDL. It shuts off the engine when the bus comes to a standstill at a bus stop, at the lights or in slow-moving traffic but re-starts it immediately when the driver’s foot moves from the brake to the accelerator pedal.

Sounds easy enough, but ZF has had to modify the transmission to make stop/start work effectively. The converter and the lock-up clutch have been reinforced and the hydraulics system has been modified with the aim of providing a rapid response the minute the accelerator pedal dips.

If the bus has been stationary for a while with the engine switched off then the transmission shift elements will need to refill with oil quickly as soon as the driver wants to get going again. However ZF has not had to fit an external oil accumulator thanks to the oil in the primary retarder.

ZF Services has recently made an oil analysis testing kit available in the UK. Draw off a sample and send it to ZF’s laboratory, and within 48 hours of receipt it will tell you if the oil contains contaminants such as dirt or water, if there is evidence of excessive component wear and if oil and filter changes are required.

The results are sent to the operator by email and can also be viewed online.

Says ZF Services UK commercial vehicle business manager Andy Derz: “By helping operators move to a condition-based approach to maintenance, the sampling service can assist in eliminating the risk of premature failure as a result of issues such as contamination, fatigue and incorrect oil selection.”

Such failure can lead to a vehicle coming to a grinding halt while out on the highway causing great inconvenience to passengers, with an expensive repair bill to follow.

ZF Services is now holding a wider stock of remanufactured transmissions at its UK headquarters in Nottingham and a number of independent remanufacturers are widely engaged with the bus and coach market.

With a portfolio of remanufactured products that includes power steering boxes and differentials as well as transmissions, HL Smith of Albrighton near Wolverhampton keeps over 2,000 finished items in stock. Not too far away, Bluestripe ReManufacturing of Stourbridge is celebrating its 30th anniversary this year and is now investing in upgraded test equipment.

Turning to engines, Cummins has been busy developing a close-coupled two-stage emissions control after-treatment system with an eye to satisfying the restrictions that could accompany the advent of Euro VII.

Likely introduction date for the new standard is 2024/25. As yet nothing has been finalised, but a greater emphasis on cutting CO2 seems likely along with an even more rigorous clampdown on harmful pollutants.

“So our new system allows further reductions of NOx and particulate emissions while simultaneously improving fuel efficiency,” contends Cummins executive director of product management and market innovation Tim Proctor. One of the biggest challenges could be to measure the scale of these extra reductions given the degree to which NOx and particulates have already been restricted by Euro 6.

The new system features an extra SCR (Selective Catalytic Reduction) unit along with an updated Holset fixed-geometry turbocharger with an integrated rotary turbine control.

The additional unit is mounted ahead of the main SCR system and the diesel particulate filter and as close as possible to the turbocharger, and gets to work on NOx immediately. It means the main system can be made slightly smaller.

It has one drawback however; two AdBlue dosing units have to be fitted. While the prospect may cause some operators to turn pale, they may have to come to terms with it if emissions legislation evolves in the direction Cummins expects.

While much of the focus today is on pure electric vehicles and diesel has been widely demonised, reports of its death are greatly exaggerated, argues Cummins. It believes diesel-electric hybrid buses still have plenty of potential, and looks set to introduce a 2.8-litre diesel at the Busworld Europe show in Brussels in October which could be used in hybrid configurations.

Continuing technological changes under its ADEPT banner look set to make diesels even more efficient, says the engine giant, realising potential fuel savings of up to 6 per cent.

They include Predictive Cruise Control which uses the vehicle’s GPS to see what is happening on the highway up to a mile-and-a-quarter ahead, and adjusts its speed accordingly. SmartCoast puts the transmission into neutral on downhill gradients using the vehicle’s momentum to save fuel, while SmartTorque2 continually calculates the extra torque needed in line with payload – a bus full of passengers weighs more than an empty one – to minimise downshifting.

Cummins is working on reducing friction and parasitic losses in its diesels, says Proctor.

“Furthermore, the use of enhanced design tools and advanced materials such as composites will bring opportunities to reduce component weight while retaining strength,” he states. “That will further enhance vehicle productivity.”

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