Parts for fuel saving
By Alex Dahm02 October 2008
Operators of road-going cranes, in particular, have always paid close attention to fuel consumption and, in response, manufacturers are continually updating their equipment.
Liebherr manufactures most of the engines for its mobile and crawler cranes. These are four- and six-cylinder inline and six- and eight-cylinder V-engines, producing 197 to 680 hp (147 to 507 kW). Exceptions include the LTM 1030-2.1 and LTM 1040-2.1 all terrain cranes, which use 278 hp Mercedes engines, while the 1,350 tonne capacity LR 11350 lattice boom crawler crane has a 870 hp Cummins. Transmissions are supplied by ZF.
"Customer demand for more fuel efficient cranes is not new," says Wolfgang Beringer at Liebherr-Werk Ehingen. "An improvement was made by the fully electronic engine control by data-bus systems, which much improves the communication between engine and transmission. A further improvement was the introduction of the ZF AS-Tronic drive with dry clutch, which is more efficient than a torque converter. And, with double the number of gears, 12 instead of six, the cranes require less fuel, as the engine always runs at its optimum revolution speed. So 15 to 20% fuel savings were realised."
Beringer adds that the Liebherr LTF 1035-3.1 and LTF 1045-4.1 telescopic cranes on standard commercial trucks are "excellent alternatives in the taxi crane class," as they use serial truck chassis. Fuel consumption is less than all terrain cranes and they have on-road tyres. "Moreover, the new LTF 1035-3.1 and LTF 1045-4.1 feature a separate superstructure engine, the output of which is matched to the requirements of crane operation. As a consequence, operation of the crane superstructure also results in reduced fuel consumption."
While truck-mounted cranes on serial chassis are the more economical in terms of fuel consumption, Beringer adds that the load capacity of this type of crane is limited to 60 tonnes. "For crane rental companies, the all terrain cranes are and will be number one, due to their diversity of applications."
Beringer adds that although customers naturally demand more economical cranes, "I think they are also aware that there are technical limits."
According to driveline components manufacturer ZF, the advantages of its AS Tronic automated manual transmission come from its intelligent shifting strategy, which lets the engine run at the most economical speed range and reduces fuel consumption, according to the company. "Quickly changing gears reduces engine idling and shorter shifting times means shorter interruptions of tractive power. The AS Tronic shifts each gear reliably and correctly. This conserves the entire driveline and increases the life of the components," says the company.
Overall, the manual transmission adds considerably to the service life of the clutch, adds the company, as does the advantage of having fewer mechanical parts on the inside of the transmission and no mechanical connections to the cab.
The TC Tronic HD (heavy duty) was developed by ZF to meet the requirements of large heavy vehicles with high horsepower engines. It is also aimed at mobile cranes weighing 72 tonnes and more and is designed to handle torque up to 3,500 Newton-metres.
The HD version, which has a clutch and a torque converter, also enables the driver to engage gears in manual mode or automatically. For the HD, ZF engineers have combined the AS Tronic with a further developed torque converter clutch. Unlike the TC Tronic, this transmission has a speed-dependent secondary retarder, the ZF-Intarder, instead of a primary retarder. The latter is particularly suited for brake operations at speeds higher than 25 km/h. In addition, the HD variant does not require an additional external oil tank. As the primary retarder has become obsolete, it was possible to integrate the oil supply required for the hydrodynamic torque converter into the housing. Upon request, this tank can be filled with 26.5 litres of ZF-developed Ecofluid M oil. It makes the final oil fill easier and offers higher mileages and longer oil change intervals, which, in turn, lead to improved economy.
Mike Goatley, ZF sales manager for off highway products in the UK, says the trend will move towards greater communication between all components of the driveline, including the engine, transmission, axles and brakes.
"As a complete driveline supplier, ZF is now working on systems where the entire driveline is operated automatically - transmission shifts, braking functions, diff locks etc. This allows for the driveline to achieve maximum efficiency with no driver input."
Crane manufacturer Manitowoc uses a number of engine builders for different crane models but Mercedes and Cummins predominate. "There are many factors we consider when specifying an engine or driveline component for a crane. These factors include performance, service, availability, and customer preference," says the company.
Despite increased fuel costs in the US, Manitowoc says it is not making any new demands of its suppliers. "Manitowoc maintains good relations with its suppliers and works with them to get the best matched components at the best price." The company adds, "We don't feel that demand for specific cranes is changing based on their fuel efficiency. Cranes are still specified by customers based on their reach and capacity."
Nevertheless, fuel efficiency is on the company's mind and it points out that the design of crane components, other than the driveline, can also reduce fuel consumption. "Improved aerodynamics certainly helps fuel economy in both on-highway and off-highway cranes."
Speaking about the future, the company adds, "It is our view that cranes will at some stage incorporate alternative fuels and power sources, but the component manufacturers must first perfect these technologies before they can be incorporated into our crane designs."
A few years ago biofuels looked like the answer or, at least, part of the answer, to dwindling oil reserves and rising fuel prices. The idea was to grow sugar crops such as sugar beet and sugar cane and starchy plants like corn and maize to produce ethanol by fermentation, or to grow oily crops like soybeans and rapeseed to provide a diesel-like fuel oil.
As a result, many manufacturers now rate their engines to accept a certain proportion of biodiesel. Most will accept fuels that are 5% biodiesel (B5) and many will go further. John Deere, for example, says fuels up to B20 can be used with all of its Stage IIA/Tier 3 engines, while at Perkins the company's aim is to certify all of its engines up to B100.
The reason for this apparent caution is that biodiesel is not a like-for-like substitute for petroleum diesel. With repeated exposure biodiesel can damage seals and gaskets and it can also degrade crankcase oils. It can also degrade, especially if stored incorrectly, and delivers slightly different performance from petroleum diesel.
Just as the industry is adapting to this legislative change, however, the rationale behind biofuels is questionable. One problem is that land previously used for food crops is turned over to cultivate bio fuel crops, which has contributed to the worldwide rise in food prices. Another concern is that forested areas have been cut down to plant bio fuel crops, which is hardly a positive environmental step.
Even without these problems, biofuels are not carbon neutral, because they require machines and chemicals to cultivate, which means extra energy and extra carbon dioxide emitted into the atmosphere. It is a controversial argument, and one that engine manufacturers are quite wisely steering clear of, preferring to fall into line behind government policies.
Whether or not biodiesel becomes a fuel of the future remains to be seen but, as long as oil prices stay high, there are likely to be more hybrid drive systems developed and fitted into construction machines. Hybrid drive systems include electric motors and, usually, batteries plus the diesel engine.
The diesel engine is used to charge the batteries for the electrical system and to drive the machine, according to load and speed. There are also systems that capture the energy used in braking to charge the electrical system - harnessing more ‘free' energy that would otherwise go to waste. These systems are expensive compared to traditional diesel-only powertrains, but persistently high fuel prices have made them more economically viable.