Taking place in Munich from April 15 to 21, 2013, is bauma, the 30th International Trade Fair for Construction Machinery, Building Material Machines, Mining Machines, Construction Vehicles and Construction Equipment. Among the many innovations at this show, a key focus will be on drive technology for mobile construction machinery. In an interview with Messe München, Professor Günter Kunze, Head of the Department of Construction Machines and Conveying Technology at the Technical University of Dresden, gives an insight into current progress.
Messe München: International emissions standards are a main factor in the push to further develop drive technologies for mobile construction machinery. What are the key areas at present in this field?
Prof. Günter Kunze: Step by step, in Europe and in the United States of America, significantly tighter limit values are being introduced for new machinery, varying according to performance categories. The focus is on the emission of soot particles and nitrogen oxides. Currently for the off-road category in Europe, EU Stage IIIB is the emissions standard, while in the US, the standard is US Tier 4 Interim. In 2014 these will be replaced respectively by EU Stage IV and US Tier 4 Final, both of which require a further drastic reduction in emissions of nitrogen oxide.
Messe München: What technologies and components can be used to adhere to these regulations?
Prof. Günter Kunze: The limit values so far were observed mainly by making adjustments inside the engine. But in doing so, in some cases, the constructors were confronted with the contradiction that a combustion process low on harmful emissions leads to higher fuel consumption. The requirement for ever tighter limit values has emphasized this "ecological conflict." The limit values for off-road vehicles valid from 2014 require in most cases an additional treatment, downstream of the engine, with effective, durable and low-maintenance emissions-reducing components. Depending on the application, a combination of technologies that reduce soot-particle and nitrogen-oxide emissions at the same time can be used to meet the low limits of EU Stage IIIB and US Tier 4 Final. Here, with mobile machinery, attention must be paid to the special conditions in which the machinery is used, to the variable operating cycles and to the performance requirements of the application in question. The enormous variety in off-road machinery makes it impossible to have a standard solution for emissions treatment. For this reason the manufacturers define the operating conditions – for example, temperatures – in order to enable on the one hand filter cleaning in line with soot loading and on the other urea-dosing to reduce nitrogen oxides, depending on engine power. As these operating conditions do not apply in every case with the application profiles in the off-road area, active-regeneration processes are used. Here, emissions systems generate the required temperature themselves. The emissions temperature is achieved either by means of a flame burner or a combination of a flame burner and a catalytic burner. Other developments are aimed at adjusting the engine for the lowest level of fuel consumption in combination with a significant increase in performance of the SCR (Selective Catalytic Reduction) system. With this the future emissions standards are met with only two emissions components – CR and diesel oxidation catalysts (DOC).
Messe München: As well as the drive system, the operating equipment on a mobile construction machine also has to be supplied with sufficient power. What is happening in this area?
Prof. Günter Kunze: Traditionally combustion engines have been installed that can deliver the performance required. In other words the manufacturers work out the peak demand and design and build the engine to match. However there are many ideas and solutions concerned with the "average requirements" of the construction machine as a parameter in the design of the combustion engine. To cover peak loads, suitable storage is then used, which is mechanically, hydraulically or electrically operated. This is known as downsizing the installed engine performance.
Messe München: For years the sector has been working intensively on hybrid drives, but so far there has been no market breakthrough. How do you see the current state of development?
Prof. Günter Kunze: First it must be said that it has taken even the pioneer in hybrid design – Toyota – more than 10 years to gain acceptance and market penetration in the automotive area. In the case of mobile working machinery, the diversity, low production quantities and high lifetimes lead us to assume that developments will be slower still. Basically a hybrid drive means the availability of at least two sources of power. Many different combinations of these sources are thinkable. For example, it could be a combustion engine and an electrically operated machine in combination with a battery to store electricity. Or two independent batteries, for example in ground conveyors. Machines of both these types have already been designed and marketed. Also possible are solutions that recover energy in mechanical or hydraulic form and then store it. Just which solution is best for which machine, is dependent critically on the requirements profile. In hybrid technology in particular the construction machinery sector is working on many innovations, and these will be on show for the first time at the upcoming bauma trade show.