How to prevent agricultural tractors from overturning

Tilt sensor, simple and easy to install, can help prevent rollovers on agricultural tractors.

With the advancement of technology and the growth of agriculture in Brazil, farmers have been looking for new, more practical and safe methods to improve the performance of agricultural equipment, in addition to valuing human capital. Consequently, tractors have been purchased to better treat their occupants, offering greater comfort and safety. Currently, it is common to see few workers working in the same area where hundreds of workers were previously needed. New technologies in machines are responsible for such changes and increased production.

However, although Brazilian tractors come with great technological packages, which also provide greater comfort and safety for workers, little exists to detect and warn about the risks that workers run from the machine overturning, if the terrain is too steep. This problem, which is quite important, can be corrected with the implementation of a simple sensor that indicates to the operator the risk of tipping over, providing greater reliability and safety.

Accidents involving agricultural machinery are little publicized and have few statistics, despite occurring in rural areas. There are several risk factors that generate these accidents, such as lack of knowledge, lack of attention, use of machines that do not meet ergonomic principles and outside of safety standards, as well as working in unhealthy conditions, such as heat/cold, sun, dust, noise and vibrations from machines and too much physical exertion. Other factors that also contribute to accidents are operations on inclined terrain, high speed during operations, operator unpreparedness, use of alcoholic beverages, among others.

But let's stay focused on the rollover issue. Although the basic concepts about tractor stability date back to the 20s, only since the 60s has there been a significant increase in the study of tractor dynamics and their stability. Normally the tractor operates on different types of terrain and working conditions. Therefore, publications on tractor dynamics and stability study tractor behavior under various operating conditions.

Tractor rollovers can be classified into two main categories: sideways tipping and rearing, which we will cover below.

SIDE TIP

The tractor's side tipping can also be caused by a sudden movement on level ground at high speed, but it occurs more easily on sloping ground. The lateral tipping of a conventional agricultural tractor occurs in two stages. In the first stage, the tractor begins to tip sideways around the axis that passes through the central pin of the front axle and the point of contact of one of the rear wheels with the ground. Then, the tractor rotates around the axis that connects the points of contact of the two wheels on the same side with the ground. When the line of action of the vertical force relative to the weight, which acts on the gravitational center, passes between the points of contact of the wheels with the ground, the tractor does not tip over. Overturning occurs when this line of action passes outside the points of contact between the wheels and the ground. In Figure 1 it is possible to visualize this line of action of the vertical force acting on the tractor at different inclinations.

In Figure 1 (A), the force-weight line of action passes between the points of contact of the wheels with the ground. Under these conditions the tractor does not tip over. In Figure 1 (B), the line of action of the force-weight passes through the point of contact of one of the wheels with the ground. The tractor is about to tip over. In Figure 1 (C), the line of action of the force-weight passes outside the point of contact of the wheel with the ground and indicates that the tractor is tipping over.

RIGHTING

In the case of rearing, there is a geometric analysis relating to the cases of the tractor rearing, not rearing, or being on the verge of rearing. In Figure 2 it is possible to visualize these actions. 

In Figure 2 (A) it is possible to see that the line of action of the force-weight applied to the CG passes between the points of contact of the wheels with the ground. In this situation, the tractor does not rear up. In Figure 2 (B), the line of action of the force-weight passes through the point of contact of the wheel with the ground, indicating that the tractor is about to rear up. And in Figure 2 (C), the force-weight line of action passes outside the contact points of the wheels with the ground, showing that the tractor is rearing. This occurs as long as the turning moment (clockwise) of the rear wheels is not considered, which makes it difficult to turn them, but because it is small, it can be ignored. According to Promersberger, there are some means available to increase the longitudinal stability of tractors and improve their drivability, such as frontal ballasting of the tractor and increasing, when possible, the distance between the axles, especially in the case where this increase causes a lower elevation of the gravitational center of the set (tractor and implement).

With the aforementioned considerations, researchers from Unesp carried out a test with the aim of verifying the functioning of an inclinometer device, developed by researcher André Luiz Andreoli, through the survey of operational conditions in the field and data, which indicates the danger and imminent tipping over of the agricultural machinery (tractors), in order to provide greater safety for the worker.

The inclinometer test was carried out in the Agricultural Machinery and Bamboo Research Laboratory, belonging to the Department of Mechanical Engineering of the Faculty of Engineering Unesp – Bauru, together with the Department of Electrical Engineering also of the Faculty of Engineering Unesp – Bauru and with the partnership between FCA - Unesp – Botucatu.

To carry out the tests, a specific ramp was built for working with an inclinometer. The purpose of the prototype was to measure the inclination of the tractors, while the lights indicate the risk of tipping over that the tractor runs. Furthermore, a siren was attached to the tractor which served as an audible warning to reinforce the warning of danger to the operator or when the operator is not paying full attention to the panel.

PROTOTYPE

The anti-rollover sensor elucidates and guides the operator in two different ways by reading data on the situation the machine is in. The sensor works simply, indicating as the tractor tilts a change in the color of the lights on the panel. For the stabilized tractor, the sensor is characterized by white light and fixed in the middle. As the machine is tilted, the lights come on and turn yellow, which indicates a controlled tilt angle. When the orange lights come on, it is an indication that the situation the tractor is in is too inclined and the red lights indicate a real danger of the tractor overturning.

As these lights are located close to the tractor's dashboard and the machine operator keeps his eyes fixed most of the time on the field, a sound sensor was also installed on the tractor, so that in a dangerous situation it starts to sound, alerting the risk operator.

During the field test, a Ford tractor, model 6610 4x2, with full ballast, coupled at the front with a Baldan loader, a Massey Fergusson 290 PAVT tractor, ballasted, and an Agrale 1200 4x2 ballasted tractor were used. The inclinometer was carefully leveled and fixed onto the tractor panels, and the sound sensor was also installed at the rear.

The anti-tip sensor, in addition to being a low-cost device, has the ability to analyze and provide a safe response to the operator of different types of agricultural machinery, as each tractor has a tipping limit angle. It is also capable of canceling out the vibrations suffered by the tractor resulting from the environment in which it operates, thus not influencing the reading made by the inclinometer.

The inclinometer is a very useful piece of equipment for operators of agricultural machines, capable of indicating the danger and the imminence of tractors tipping over through light signals placed in front of the operator and the sound signal that helps in perceiving the danger faced, enabling trajectory correction in time to avoid accidents.

Victor M. Schutzer, André Luiz Andreoli, João Eduardo G. dos Santos, José Angelo Cagnon, Unesp; Fabrício Leite, UEM

Article published in issue 152 of Cultivar Máquinas.