25 September 2015, 08:00
DLG has been carrying out tractor tests since 1920. Now, its tractor testing facility is gearing up for the future with preparations for a new rolling test bed. Machine Test Manager Andreas Ai discusses the opportunities this new test bed offers and presents the most recent tractor drawbar performance results obtained by the DLG measuring truck.
Tractor tests have a long tradition and date back to the Nebraska Tractor Test Act introduced in Nebraska, USA, in 1919. This law was enacted after an American farmer experienced severe problems with his new tractor. In 1916, Wilmot Crozier bought a Ford Model B from the Minneapolis-based Ford Tractor Company (no connection with the automobile manufacturer). Promoted as an 8-16hp machine and claimed to pull a two-furrow plough (picture 1), this tractor did not live up to the manufacturer's promises. Besides, it did not prove very dependable, with its new owner encountering problems even before receiving the bill. Wilmot Crozier was given a new 1917 model in replacement, which did not last either and was replaced by a Little Bull tractor, which broke down too.
It was only after Wilmot bought what was his fourth tractor in three years – a Rumely OilPull – did the story have a happy ending. When he became senator in 1919, he took the opportunity to draft and enact the Tractor Test Act – which is law still today – which prohibits manufacturers from selling a tractor in Nebraska without obtaining a prior permit. This permit is granted to either a manufacturer or a dealer after a tractor is thoroughly tested and proven to comply fully with all claims made in its brochure and on the condition that a workshop and an extensive parts stock room is operated. The relevant tests have to be carried out by three test engineers who must be present during all test cycles.
Tests started in 1920
The first tractor to pass the test on 31 March 1920 was a Waterloo Boy Model N from John Deere. After that, 65 tractors passed the test in the first year and 172 in the following years up until 1930. All tests were carried out at the Nebraska Tractor Test Laboratory (NTTL), operated by the Agricultural Engineering department of the University of Nebraska. The Nebraska Tractor Test Act was amended in the late 1950s and early 1960s. Today it governs only agricultural truck tractors of more than 20hp.
Tests in Germany
Soon after, German engineers followed the American example. In 1929, the first German drawbar performance measuring truck (picture 2) went into operation at the Institute of Agricultural Machinery at the Berlin Agricultural College, which operated a tractor test field in Potsdam-Bornim near Berlin. This truck had spiked steel wheels, an observation that gives tell-tale evidence that the test ground was not surfaced at the time. Even in those early days, fuel consumption was already recorded along with drawbar power just like in the US.
After World War II and the construction of the Berlin Wall, the German Democratic Republic continued using these test fields for its tractor tests, whereas in West Germany the tractor tests were carried out near Marburg. Later on, they moved to Darmstadt and then, 50 years ago, to the new DLG Test Center in Groß-Umstadt near Frankfurt. This is where the DLG Test Center for Engineering and Farm Inputs still resides today. And from here, the next step was taken. The Organisation for Economic Co-operation and Development (OECD) made the DLG Test Center near Frankfurt the official OECD test station in Germany and NTTL the official OECD test station in the US. The Organisation laid down the OECD Code 2 procedures that stipulate the use of state-of-art testing technology in order to verify the claimed performance and capability of an agricultural or forestry tractor. The fundamental parameters are available at www.oecd.org/tad/tractor. The site also offers a search function and summaries.
The DLG PowerMix test
Like many other test procedures, the OECD Code 2 test procedures have constantly come in for criticism. Notably, farmers have pointed out that power take-off (PTO) output, lift capacity and hydraulic output are measured while the machine is stationary but drawbar power is measured on a moving tractor that is pulling the brake truck. They also argue that the individual engine operating points are specified precisely. Similar criticism were voiced on the statutory private car emission level tests carried out on engine test stands and rolling test beds, the results of which are used to determine a vehicle’s tax rate. These procedures do not require manufacturers to follow consistent procedures. Indeed, they are free to disconnect ancillaries such as generators and the air conditioning system, use a minimum weight model as test candidate, tweak the engine control system or use high tyre inflation pressures for less rolling resistance. In a nutshell, the tests do not reflect field situations.
In response to such criticism, the DLG test engineers developed the so called PowerMix test and introduced it in 2015. This test marks the beginning of a new era in tractor testing and has developed into the 'Gold Standard' for international tractor tests. Simulating a real-life scenario, the DLG brake truck (picture 3) takes off a tractor’s combined drawbar, PTO and hydraulic output. The tests are based on target curves that reflect 14 different work cycles (see tables). The data for these curves were collected in in-field measurements, with the tractor operating a 'real' implement. The fuel consumption rates are converted into specific consumption, i.e. in gram per kilowatt hour (g/KWh), and this figure is used to compare the rates of individual tractors in various power brackets. The consumption rates of today's engines are clearly below the 300g/kWh threshold, a very low level indeed – despite the use of comprehensive emission treatment technology. The results of the last six DLG PowerMix tests are listed in the table below and are also accessible at www.DLG-test.de/powermix.
The future begins now
The new rolling test bed is the most powerful in the world. Currently coming into operation, it will have a major impact on future tractor tests (pictures 4 and 5). When the new test bed is completed towards the end of this year, it will be used to measure the specific fuel and AdBlue consumption of tractors up to 1,000hp/700kW. Here, individual tractor consumption levels are measured in 14 different real-life scenarios, just like the DLG test truck was on the test course and on public roads. With the new test, tractors won't have to travel down test courses any longer. Instead, they will roll on four stationary 2m diameter steel rollers that are driven and braked by electric motors.
The rollers can conveniently be adjusted to individual wheelbases, ranging from 2.05 to 6.00 metres. Each roller, including its electric motor and mounting, tips the scales at about 35 tonnes – heavy enough to cope with tractors up to 30t, which translates into a maximum weight of 60 tonnes. Each wheel can transfer up to 135kN or 13.8t to the roller.
The new test hall features air conditioning that maintains the indoor temperature at 25°C by exchanging 100,000m³ of air every hour. The new rolling test bed will take the DLG PowerMix measurements to another dimension, as it allows the DLG test engineers to carry out tests without having to take the weather into account. This is a new milestone for more efficient testing as many tests have been disrupted by rain, frost and heat in the past.
There are also plans to upgrade the equipment using a device that measures electric drive power of up to 150kW (200hp). Furthermore, it is not only possible to measure outputs and consumption rates indoor but also emission levels while the tractor is working under field conditions. Lastly, from 2017 it will be possible to carry out the transport tests on the stationary test bed as well, which will free test engineers from having to negotiate traffic conditions. This way, a farmer who buys a DLG tested tractor will be given consumption rates as determined under real-life conditions.