Design and Implementation of Efficient Working Hydraulics of Electrified Non-Road Mobile Machinery for Enhancing Environmental Sustainability

The almost inevitable climate crisis is forcing governments, and industries across all spectrums to make every possible effort to avoid or minimise fossil fuel consumption. One significant contributor to the global carbon emissions is heavy duty mobile machines such as construction, mining, forestry, and agriculture machinery. These machines are essential to the economy but at the same time emits a massive amount of greenhouse gasses in the environment, for example, only construction machines worldwide emit almost same amount of CO2 as of the international aviation. One potential solution to reduce greenhouse gas emissions is the use of electric energy instead of the fossil fuel, like it has been done in passenger cars. The electric cars have been very successful in market and there have been a great progress in that area. But the heavy duty machines such as wheel loader, forest forwarder, excavator and mining machines are much bigger and powerful than the electric cars. These machines not only use more power in moving from one place to another, but they have to perform certain functions like excavation and loading, according to the application. In order to eliminate or reduce the carbon emissions from these heavy power consuming machines, we need to consider these work functions also, as that is the primary goal of the machine.

Should we keep the gas pedal of car fully pressed and control the speed by continuously applying brakes?

The main objective of these machines is to perform these tasks like excavation, and loading; at the same time, some machines have to move continuously to perform the task, such as a wheel loader working at a construction site. This work is usually performed by several linear hydraulic actuators which are implemented at different locations in the machine to perform the task. These actuators are provided hydraulic power using a big centralised hydraulic pump which is usually directly connected to the primary energy source which is typically a diesel engine. Hence the pump always keeps rotating with engine regardless of the hydraulic energy demand that results into unnecessary burning of fossil fuel. In this type of hydraulic system commonly known as conventional hydraulics, the actuators are controlled using hydraulic valves and they designed according to the maximum power requirement at all points in the machine. When maximum hydraulic power is not required the power is wasted in form of throttling and subsequently in the form of heat in the valves.

Electro-Hydraulics and its challenges.

One good alternative to conventional hydraulics is electric motor controlled electro-hydraulic actuators (EHA) where hydraulic power is produced only according to the demand eliminating the throttling losses in valves. The electric motor rotates the small hydraulic pump only according to the power demand. Despite being substantially energy efficient, the EHA technology has certain challenges to fully replace the conventional hydraulic from these machines. The major challenges include reliability, robustness, and safety. For example, in the steering application of these machines which is also performed by linear hydraulic actuators powered by conventional hydraulic system, the safety is of paramount importance as any failure in steering may cause a big accident. In order to replace the steering function in these machines from conventional hydraulics to the EHA, the functional safety of the system must be considered. We cannot directly use EHA in these big machines without being fully confident that they will be at least as safe and reliable as the ones they are replacing. Hence, in order to make the heavy earth moving machines more efficient and electric, we not only have to work on efficiency but also the safety of electro-hydraulic systems and smart ways to implement them.

Vinay Partap Singh received a grant for his doctoral degree at Tampere University in 2022.