Effective and environmentally friendly, the new generation of lawnmower tractors

The choice of equipment for landscaping depends on the characteristics and dimensions of the turf. Manufacturers now offer models with mechanical and hydrostatic drive systems, and pay special attention to the introduction of systems to reduce noise and emissions

Mowing lawns is the toughest operation in landscaping. Frequency and cutting height are linked to the type of turf. On the greens of professional golf courses, mowing in the summer is performed practically every day at a height of 3-6 mm; conversely, fairways of the same courses are mowed every 2-3 days to a height of 13-18 mm. In high quality ornamental lawns, mowing is performed at a height of 12-16 mm, on average twice a week; the frequency is weekly for ornamental lawns of lower quality, cutting to a height of 20-25 mm. Recreational lawns in gardens and parks are mowed 20-30 times a year, at a mowing height of 30-40 mm, dropping to less than 10 annual mowings at heights of 40-70 mm for lower quality recreational lawns. For lawns in parks on the outskits, the number of cuttings can fall to 2-3 per year to mow very tall grass.

When the mowing is performed at least weekly at a height of less than 30 mm, you can choose between collecting the mowed grass and mulch cutting. In this second case, the grass is finely chopped within the casing, and is then projected into the sward. The strengths of this approach are that no time is lost emptying the bagger and that you recycle the nutrients and organic matter. The weaknesses consist in the greater frequency of mowings and the fact that, if there are topical fungal infections, these are more quickly propagated.

The quality and the size of the turf come into play in choosing the type of lawn mower, with its cutting apparatus located at the front or underneath. In particular, the position of the driver (on the ground or on board) is determined by the size of the turf, while the type of cutting apparatus (horizontal blades, helical blades, flails) is linked to the height and the quality of cutting.

 

Small tractors

Lawn tractors are machines with driver on board, with the engine placed in front of the driver and horizontal cutting apparatus mounted underneath. They were originally derived from small farming tractors to which they applied garden tyres and the cutting deck underneath. Later, the machine evolved by becoming increasingly responsive to the cut of the lawn.

The power unit is based on a rear axle with drive wheels and a front axle with steerable wheels. They are equipped with Diesel cycle or combustion engines, with powers ranging from 6-10 kW to 20-25 kW depending on the working width. In the version with a bagger for the cut grass, when the basket exceeds certain volumes, a front ballast is also used. For this type of mower, the weight of the machine is almost evenly distributed between the front axle and the rear, so each wheel exerts almost the same pressure on the turf. Furthermore, since the cutting apparatus is underneath, the grass is bent before being cut, causing irregularities to the mowed lawn. The fact of having the engine positioned in the front reduces visibility for the driver, with a possible impact on accuracy. In most cases, the machine is not very manoeuvrable. This is an impediment when one must operate on lawns with irregular layouts of trees, shrubs and flower beds.

There are also models with a small turning radius. Upon turning, the inside rear wheel is disengaged, thus preventing damage to the turf.

In general terms, it could be said that this type of lawnmower is not the most suitable for quality turfs, and it should be taken into account for surfaces exceeding 2000 m2.

 

Types

Depending on the type of transmission, the distinction is between models with mechanical transmission and those with hydrostatic transmission. The first is found primarily on machines with a working width of no more than one metre. Regardless of the transmission, the maximum forward speed does not exceed 9 km/h. The mechanical system can provide 5-7 speed gears, while in the hydrostatic one the speed variation is gradual and continuous, making the driving easier and the work faster. There are two different solutions for the hydrostatic transmission. The one with foot controls is generally preferred, where speed and direction are controlled by separate pedals for forward and reverse. The other solution is the hydrostatic transmission controlled with a lever within reach of the driver.

The system to engage the mowing can be mechanical (pulley-belt system) or hydrostatic. In the hydrostatic version, the engagement can be performed by the operator by pressing the command button of the electromagnetic clutch placed on the dashboard. This system ensures more precise placement of the blades and no kickback. The cutting height is adjustable between 25 and 90 mm, while the working width goes from 60-70 cm to above 130 cm. Depending on the working width, cutting is performed by 1, 2 or 3 cutting blades. The most frequent solution has two asynchronous blades.

The cut grass can be ejected to the side or to the rear. In both cases the grass can be collected in a bagger. A third possibility is mulch cutting, which, as has been mentioned, enables significant advantages in terms of working time. Indicatively it can be said that a lawn tractor with an engine power output of 10-12 kW, with a cutting width of about 1 metre, equipped with a bagger with a capacity of the order of 300-350 litres, taking into account the cutting and grass discharge times, takes about one hour to mow 2500-3000 m2 of turf. By contrast, using the same tractor equipped for mulch cutting, the time is more than halved without doubling the mowing frequency in the course of the year.

One quite frequent solution is to perform a collection mow as the first cut in spring when the grass is tall, then doing mulch mows after that. To allow more versatility of the machine while leaving maximum freedom of choice on the type of cut, many models, both side discharge and rear discharge, include as standard or as an option a kit that allows the machine to perform both collected mowing and mulch mowing. In some models, the change to mulch mowing can be made directly from the driving seat by a lever.

To facilitate cleaning of the cutting deck, there are systems that provide for the connection to a water hose through connectors located on the deck, thus allowing a quick and effective cleaning.

In order to improve the performance of machines, some solutions have been implemented, such as: the inclusion of a system powered by a fan for a better collection of the grass; unloading of the bagger hydrostatically (standard solution over certain bagger capacities) instead of manually with lever actuated by the driver; the pivoting front axle to keep the 4 wheels always in contact with the ground even in conditions of strong irregularities; differential lock; hydrostatic steering; electronic rather than electric motor starter.  Among the solutions to improve the comfort of the driver we find those for the reduction of sound level (below 100 dB) and the containment of vibrations on the steering wheel (about 0.8 to 3.0 m/s 2) and on the seat (0.7-0.8 m/s2). The motor is generally powered by petrol, but diesel cycle engines are increasingly employed. The number of cylinders, depending on the power, can be 2, 3 or 4. The petrol engines have overhead valves (OHP). Several studies and analyses have shown that the environmental impact of these internal combustion engine machines is induced by 10% in the stage of production and distribution, 5% at the end of life and 85% in the utilization stage. For these reasons, many manufacturers have increased their commitment to try and limit the impact during use through targeted interventions to reduce gas emissions and noise levels. Moreover, we are witnessing the introduction of hybrid lawnmowers, together with all-electric ones, even in the professional model range.