While lightweighting has long been a popular option for reducing emissions in the automotive sector, it continues to be less so in the design of off-highway vehicles, and there are many reasons for this. One is that the duty cycles of off-highway vehicles tend to be unpredictable because the applications the owner uses them for are so wide ranging.
One example is telescopic handlers, which are designed for pick and place operations but can be used for many diverse applications from shoveling material to driving in posts. Even if OEMs were able to design for every possible application, the resulting product would be unfeasibly expensive to produce. However, there is a balance to strike.
Farmers need products that meet all of their needs—a Swiss Army knife approach. The key is developing a vehicle that is as capable as efficient design and engineering allows and demonstrating to buyers this range of abilities. In comparison, automotive designers can work to very specific requirements. Drivers understand the limitations of their vehicles and work within them.
Another reason is the unpredictable nature of the loads themselves, due to the range of operations a single machine may be used for in its lifetime. Without predictable loads it is difficult to use simulation to accurately predict stress levels and hence to ensure that the equipment would be able to stand up to all conceivable tasks. The same is true for the unpredictability of the conditions these vehicles work in.
Due to the large variety of applications of off-highway vehicles, in the past there was very little legislative requirement for the performance of this equipment, with the exception of safety regulations in roll-over and falling-object protection systems (ROPS and FOPS). In comparison, automotive design is extensively legislated—for example, crash performance—which leads to an understanding and expectation of the loads on a vehicle structure. This is a benefit as all vehicles have to meet the same standards.
In addition, a lot of attention has been diverted away from reducing weight in off-highway vehicles due to the large amount of investment needed over the last few years in getting engines up to Tier 4 standards. These regulations, phased in over the period of 2008-15, required that PM and NOx emissions be further reduced in new off-highway diesel engines by around 90%. For many companies it is only now that they are able to free up the level of investment needed for researching and developing lightweighting. Since next-stage environmental legislation will be harder to reach, engine manufacturers, OEMs, and other system suppliers must find other ways to differentiate themselves and gain competitive advantages over rivals.
But while the off-highway sector has tended to lag behind, there are a number of ways in which it could learn from the more technologically advanced automotive industry. A tool that has been used in automotive for 20 years and which could offer learning to the off-highway sector is multi-body dynamics, an analysis tool that allows engineers to study the dynamics of moving parts and predict the forces in mechanical systems.
This tool is starting to be used in off-highway, but progress is slow because there isn’t yet a reliable model for one of the key parts of off-highway durability cycles—the soil-bucket interaction model. The modeling of soil is in itself a complicated process. The loading put on the vehicle by cutting through the ground is hard to calculate, and since excavators will be expected to dig a whole range of different materials—from sand to clay to rock—there is also a large disparity between the loads exerted by these materials.
A key focus for the off-highway industry as it strives to meet potentially stricter “Tier 5” emissions targets will be formulating the soil models needed to exploit multi-body dynamics to optimize the vehicle and catch up with advanced automotive models, which take into account both loads and the ride and handling of the vehicle.
This is an excerpt from the article “Lightweighting to improve off-highway emissions” originally published in Off-Highway Engineering Magazine, one of SAE’s award-winning publications, on October 7, 2015. Written for Off-Highway Engineering by Derick Smart, Customer Engineering Manager, Tata Steel.
For further insights into overcoming the engineering, materials choice, and manufacturing challenges of lightweighting to improve off-highway emissions, see the full article.