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Combined PowerHybrid systems will add cost and complication to machines but quarry owners

who embrace the technology could cut their fuel bills. Colin Sowman investigates

After more than 110 years of development,the diesel engine is about as good apower source for mobile plant as it is

possible to get – it is small for the amount ofpower it produces, quiet, reliable, long lasting,needs only a daily supply of fuel and is now veryclean. However, it has two big drawbacks: thecost of diesel and the CO2 emissions thatresult from burning fossil fuels.Miles Watkins, director of sustainable

construction with Aggregate Industries, saysthe fuel consumption of mobile plant is by farthe biggest contributor to the carbon footprintof the company’s quarrying business. Hewould be extremely interested in evaluatingsystems that can reduce carbon emissions butfeels the plant manufacturers have been ‘slowoff the blocks’. ‘We’ve seen telematics anddriver training but very little in the way ofmachine developments,’ he says.Now, however, systems to reduce fuel

consumption arestarting to make theirway through intoproduction machines.Many plantmanufacturers areexploring hybrids –machines with morethan a single source ofpower – as a way tocut fuel consumptionand thereby reduceCO2 emissions andfuel bills.Most hybrids work

on the basis of

harvesting and storing energy when it is notneeded and feeding it back into the drivetrainwhen additional or maximum power isrequired. Traditionally, this energy has beenwasted. For instance, applying the brakesturns the kinetic energy embodied in a movingmachine into heat which is then dissipated tothe atmosphere. But now systems are beingdeveloped to capture and store that energy, andin many cases this involves an electricalsystem and batteries as a storage medium.Unlike the one-solution-fits-all diesel

engine, hybrid systems are good in someconditions and bad in others. For instance, theToyota’s Prius, the world’s most popular hybridcar, is at its best around town where repeatedbraking recharges the batteries which powerthe electric motor to drive the vehicle along oradd to the petrol engine’s power whenaccelerating. However, on a long motorway runthe batteries and electric motor simply add tothe vehicle’s weight, which actually impairs fueleconomy.Hybrids, therefore, need to be tailored to the

machine’s operation: harvesting spare energywhen it will not impair the duty cycle anddelivering it back when it can enhance ‰

Volvo’s prototype hybrid wheel loader was unveiled in 2008 but has not gone into production

Kawasaki schematic showing energy regeneration

26 www.Agg-Net.com November 2011

performance. With that in mind itis not surprising that wheelloaders, with their stop and start,backwards and forwards operation,are the first targets for manymanufacturers’ hybrid systems.Volvo started the charge – albeit

their wheel loader has not yetcome to market – and others havefollowed with their own variationson the technology.Having analysed a typical wheel

loader duty cycle, Volvo’s engineerssandwiched a motor/generatorunit between the engine andtransmission. As the namesuggests, the unit acts as agenerator to charge the batteriesand then switches instantly to amotor when additional power isrequired. In operation the unitwould harvest excess energy fromthe engine, such as when theshovel comes free of the stockpileor when braking, in order to chargebatteries mounted on the side ofthe machine. On the next cycle,when accelerating or penetrating the stockpile,the energy stored in the batteries is fed to thegenerator which instantly switches to motormode and boosts the power available to theoperator.Having installed a large amount of battery

power, other functions such as the air-conditioning can be run from them instead offrom the engine, which means the operatordoes not need to sit with the engine running tokeep cool.While Volvo said the system could

dramatically reduce fuel consumption, they nowsay battery and other technologies have movedon and the machine, as initially exhibited, willnot go into production. However, Volvo’scrusade to reduce fuel consumption continuesand hybrids will play their part, but so will otherinnovations such as the Optishift transmissionwhich is cutting fuel bills by 15% while retainingthe traditional driveline.At this year’s Conexpo exhibition, Kawasaki

exhibited a prototype wheel loader with ahybrid torque converter and a motor/generator.In place of a normal torque converter, Kawasakiare using a ring gear and set of planetary gears.

The engine’s crankshaft is connected to thecentre shaft of the torque converter while thedrive to the transmission is from the centre ofthe planetary gears. A motor/generator isthen used to control the rotation of the ringgear.When the ring gear is free to rotate there is

no drive through the system but as the ringgear is braked, drive starts to be transmittedto the transmission, and at the point where thering gear is stationary, the power is passingstraight through with only minimal losses.However, instead of a simple brake on the ringgear, Kawasaki’s system uses amotor/generator which can take energy fromthe system when the machine is braking orstationary and lifting its bucket clear of thestockpile, and feeds the additional power intothe driveline when accelerating. In stockpileapplications, Kawasaki say up to 35% fuelsavings are possible and it plans to market themachine by 2013.Taking a leaf out of Caterpillar’s book (see

Cat D7E box), John Deere have developed a

diesel-powered electric drive system for wheelloaders. The machine retains its diesel enginebut this is coupled to an alternator (and ahydraulic pump) rather than a mechanicaltransmission. Each wheel is fitted with abrushless oil-cooled electric motor poweredfrom the alternator. This system allows theengine to run at a constant speed and can,therefore, be optimized to be at its most fuelefficient at the set speed. In addition, electricmotors provide maximum torque from zerorevs. This allows the manufacturer to reducethe power and capacity of the installed enginewithout losing any performance in terms ofdriving into stockpiles. According to JohnDeere, their electric-drive wheel loaders canbe up to 25% more fuel efficient in the rightoperation.There are further savings too in terms of

service items as the wheel motors are identical,so at around 20,000h the heavily used frontmotors can be swapped diagonally with thelesser-worked rears. John Deere expect toprice the machine so that the fuel savings will

Kawasaki plan to market their 65Z hybrid wheel loader by 2013

Kawasaki’s hybrid torque converter system

Close-up of John Deere’s electric drive system

Power Systems & Energy Saving

pay back the on-cost within two years.While wheel loaders are an obvious choice

for hybridization, other plant items can benefittoo, and Komatsu have had a hybrid excavatoron the market for a couple of years. During thattime more than one million operating hourshave been clocked up – but only in Japan andChina. However, at Conexpo 2011, Komatsushowed a refined Mk2 version which will beavailable in Europe and the UK.The hybrid HB215LC-1 has a 104kW engine

compared with 116kW in the standard 210machine – and uses a motor/generator in placeof the standard hydraulic slew motor. When theoperator pushes the joystick the electric motorslews the upper structure. As the joystick isreleased the motor instantly switches togenerator mode, which has the effect ofbraking the slewing turret. The energy createdduring this process is stored not in batteries,

but in capacitors, which Komatsu say providefast energy storage and instantaneous powertransmission the next time the operator wantsto slew.Komatsu say the HB215LC-1 saves an

average of 25% fuel compared with its standardexcavator, and they back the hybrid powertrainwith a five-year/7,000h warranty.There could be even bigger fuel savings to

be had with excavators, according to Tana Utley,Caterpillar’s chief technical officer and vice-president of product development. At Conexposhe said: ‘More than 50% of the energy you putinto the fuel tank is lost through losses in thehydraulic system. So our engineers are goingright back and looking at the architecture of thehydraulic system to see if there are differentways to put those components together toreduce metering and parasitic losses.’One potential way to save energy would be

to use individual electric pumps to powereach hydraulic circuit. Not only would the piperuns be shorter (with consequentially lessenergy loss), but electrically controlled pumpscould offer improved controllability andresponsiveness as well as lower fuel bills.At JCB’s recent Waste Day event, group

managing director Tim Burnhope hinted verystrongly that the company was exploringhybrid technology, although he did not identifyany particular machine type.Researchers at Aalto University in Finland

are using hybrid systems based onmotor/generators with storage capacitorsthat can halve the fuel consumption of non-roadmobile machinery. The project has alreadydeveloped hybrid gantry container cranes,although production versions of more mobilemachines may be five years away.In the road transport sector, other forms

hybrids are being evaluated including KERS(Kinetic Energy Recovery System), which is bestknown for its use on Formula 1 racing cars.According to Tobias Knichel of Flybrid Systems,storing the energy mechanically is moreefficient than converting it into electricity andback again.In commercial installations, instead of using

foundation brakes to slow and stop the vehicle,the first application of the brake or retarderengages a constantly variable transmission(CVT) system which uses the excess energy ‰

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John Deere schematic showing the electronic motor/final drive arrangement on each wheel

Komatsu’s hybird HB215LC excavator

Flybrid’s KERS system fitted to a bus transmission

to speed a flywheel up to 65,000 rev/min. Whenadditional power is required, the input/outputratio of the CVT is adjusted so that theenergy stored in the flywheel is fed back intothe driveline.A KERS unit is currently under evaluation in

a city-centre bus and is equally applicable toother stop/start operations, and could bebeneficial to machines such as articulateddumptrucks. However, the backwards/forwardsoperation of wheel loaders would make anyKERS installations more complex, and it is stilltoo early to know what fuel benefits thesystem could achieve.Although hybrid technology is becoming

available, many UK buyers may be reluctantto adopt such innovations as some 80% of theplant in the UK is purchased by plant hirecompanies. This poses a problem becausethe plant hire company may not know whatits machine will be doing from one month tothe next, so the ‘right operation’ cannot beguaranteed.

Furthermore, the additional purchasecost would be borne by the plant hirecompany while the user would accrue thesavings in the form of lower fuel bills. Thegeneral feeling among hire companies is thatthe customer wants to pay as little aspossible and a jump in the rental fee is outof the question. That said, at the smaller endof the market, Speedy have used the fuelsavings available from several items tojustify an increase in hire rates.While these reservations do not hold true

for quarries that own their machines, unlessUK sales reaches a critical volume themanufacturers will not import hybrids. If theydo, but the numbers remain very low, ownersmay be concerned about the service back-up available for their more complicatedmachinery.For instance, if the only criterion was

reducing fuel consumption, then UK buyerswould be queuing up for Caterpillar D7Eelectric-drive bulldozer (see box). During

extensive trials in the waste market, the D7Eused between 10% and 30% less fuel than aD8 – but so far no UK company has placed anorder.‘It’s too early to say yet,’ says Matthew

Hanlon from loader hire specialists JohnHanlon and Co. He believes it is up to themanufacturers to produce a viable machinethat provides fuel savings over the completemix of jobs, rather than just one specifictask.Assuming the machine fits its operation,

Miles Watkins says Aggregate Industrieswould then consider its reliability and whole-life costing. ‘If the initial price is higher thatdoesn’t matter too much providing the whole-life cost is equal or favourable,’ he said.It will take time for hybrid technology to

build up a track record and the manufacturerswill have to make the machine more flexibleif they are to gain wider acceptance. After all,you do not overtake a century of diesel enginedevelopment in a few years. QM

Power Systems & Energy Saving

Perhaps the most widely available hybrid currently on the market is Caterpillar’s D7E electric-drive bulldozer. In place of a complicated hydrostaticsystem or mechanical driveline, the tracks on then D7E are driven by individual electric motors – a move which reduces the number of componentsin the drive chain by up to 60%. Not only does the system cut friction losses and hence fuel consumption, it also reduces maintenance costs.

Caterpillar D7E electric-drive bulldozer

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