German researchers are looking at new ways to improve the efficiency of rotary mowers. They are developing new designs and approaches based around the rotary cutting systems with the aim of lowering power demands and fuel consumption.

The cutting principle of the rotary mower has not changed since the 1960s when the first systems were patented. For clean cutting, these systems depend on the inertia and stiffness of the grass blades to achieve a clean cut.

The researchers are looking at using what they call an overlaying cutting method in a rotary mower.

This consists of two cutting discs per cutting unit, with one on top of the other. In this design, the top disc blade overlaps over the bottom one on each cutting rotation cycle.

The upper discs rotate independently from the lower discs with various speeds and different directions compared to the lower discs.

Therefore, the mower bar contains two drive chains to drive the separate disc levels.

The cutting blades need to be accelerated up to 80m/s to cut grass even under demanding conditions. Previous power analyses of disc mowers have shown that these high rotational speeds result in high power losses.

The researchers identified from the power analysis of a conventional disc mower where the high power losses take place. The researchers fitted sensors to a cutting disc and a cutting blade to measure the cutting power, the power of one disc and the driving power.

They found that 20% to 45% of the driving power was lost in friction, wind resistance and transport of crop.

This means that, in practice, 40% to 65% of the total driving power are lost.

Based on these results an overlaying cutting method is under investigation.

They developed a new type of cutting unit, which consists of two cutting discs, that were tested on a conventional disc mower. The discs were designed to be rotated in the same direction with a fixed speed ratio.

The cutting power was measured as the difference between the driving and idle power. The tests were carried out on a wheat field in spring 2013 at a driving speed of 12km/h. This would be significantly different from a typical Irish grass field situation with strong permanent pastures.

They found that the number of blades on the lower discs has a stronger influence on cutting quality than the number of blades on the upper discs. The primary factors for the driving power are speeds of the discs.

The total driving power varied between 2.7kW and 6.5kW for the overlaying cutting method. This compares with the power required for a conventional disc mower of about 4.8kW.

They found that the primary factors in terms of power demand and a quality cut are number of blades on the lower discs and the rotational direction. They found that the impact of the number of blades on the upper discs was relatively small.

There is more work to be done on the research this season and, based on the information to date, we can expect to see a change in mower design in the coming years.