Energy Efficient and Redundant Steer-by-Wire for Articulated Non-road Mobile Machines

The electrification of on-road vehicles has got momentum in recent years, but for Non-Road Mobile Machines there are still many barriers to cross. In order to completely eliminate the internal combustion engine or reduce its use, the energy loss in machines needs to be minimised at every possible section. One such part is the steering of heavy non-road mobile machines which has been unchanged to a large extent for decades, especially in articulated machines. The major cause of the industry being cautious in replacing the traditional steering system is its safety. As being a safety-critical system, it requires to comply with the highest safety standards. An articulated steered wheel loader has been selected as a case study in this article to first carry out a detailed hazard analysis to assess the machine performance levels required for steering. Two scenarios are selected for hazard analysis: 1. the wheel loader is on work site; 2. the wheel loader is travelling on road. To achieve the required performance level, the requirements of functional safety and safety integrity level of the steering are analysed. Based on corresponding standards and the required performance level for the steering, a new electro-hydrostatic-based steer-by-wire system is proposed. The proposed steering complies with safety standards for articulated steering and has the potential for energy saving. The simulation of the proposed system is carried out from an energy-efficiency point of view in MATLAB/Simulink. The proposed electro-hydrostatic steering system is compared to the traditional steering of a wheel loader in the Mevea digital twin environment and has been found to be substantially more energy efficient in the primary analysis. The simulations show that in conventional steering, 51% of energy is wasted in the steering valve alone, while in EHA (Electro-hydrostatic actuator) steering only 29% is wasted in the entire steering system.