The GEN3 Dynamic Stability Triangle
The Dynamic Stability Triangle is the triangle between the two front support points (tyres or stabilisers) and the centre of the rear axle. When the Centre of Gravity (COG) of the telehandler and load moves past the line between the two front support points, the machine tips forward. If the COG moves past the line between the forward support point and the centre of the rear axle the machine will tip sideways. This point of instability is sudden with no warning.
In the training of telehandler operators, much is made of the movement of the COG and machine stability related to the weight of the load, the angle and extension of the boom, the lateral and longitudinal attitude of the carrier and the points of support. i.e the tyres or stabilisers.
Typically, a manufacturer specifies that the telehandler operate on essentially flat ground (usually with a limit of 5°). The machine, from a practical sense, often operates outside of the manufacturers specifications of lateral slope.
It is difficult for most operators to be mindful of the interaction that boom angle, boom extension, longitudinal and lateral slope can have on the stability of their machine. In addition, the weight of the load has to be known to understand the interaction of moments. Even with a load management system that has all the relevant data, an operator, without a good understanding of moments and their interaction and movement of the COG with load, has trouble understanding at what point the telehandler will tip over.
While on flat ground, the COG moves forward from near the geometric centre of the machine, dependent on the boom extension, boom angle, and load. As the boom is raised, the COG moves back and up. When on a forward rising slope, the COG moves further back, minimising the lateral slope tolerance. With a lateral slope, the load mass moves to the side. Extension of the boom moves the load centre of mass further up and to the side, shifting the overall COG toward the pivot/support line.
In short, with the boom angle at 0°, regardless of the boom extension and load, a lateral slope (side tilt) of 30°+ could be tolerated before tipping the machine over onto it’s side; but at maximum boom angle, and maximum extension, with maximum allowable load and a backward slope of 20°, the telehandler could topple sideways with as little as 0.1° lateral slope.
Until the Dynamic Stability Triangle was incorporated into the EQSS GEN3-LMS, the only available stability feedback was longitudinal, with a cutout to limit increases in operational radius.
With the EQSS GEN3-LMS, the operator is warned when he is close to the edge of the stability triangle, thus enabling him to take timely corrective action.
There are many things that can contribute to the balance between being safe and being compromised. Corrective action could include one or more of the following.
- Lower the boom to move the COG down and forward
- Operate the chassis leveling system to bring the boom vertical
- Retract the boom which moves the COG toward the centre
- Move the steering in a direction to lower the lateral slope
- Reverse the direction that took the machine onto the lateral slope
- Bring the machine to rest and review the work site and re plan the lift
The Dynamic Stability Triangle incorporated into the GEN3-LMS display shows a visual representation of a birds-eye-view of the telehandler with a stability triangle overlay on top and cross hairs to depict the COG. When both stabilisers are lowered the size of the stability triangle on screen increases to demonstrate the greater degree of forward tolerance. When the cross hairs on the stability triangle move into the green/yellow interface a warning is sounded, recommending that corrective action be taken.