Feasibility analysis of electrical variable transmission in off-highway vehicle drivetrains: Fork-lift as a case study

Abstract

Today, the off-highway machinery is driven mainly by high performance diesel engines thanks to its robustness and low costs. Moreover, the off-highway vehicles have a high impact on the world fuel consumption. In a context of reducing emissions and increasing the price of oil, the electrified powertrains for passenger cars have gained a significant in- terest these last years. However, the development of electrified powertrain for off-highway vehicles is slow due to high constraints on the power electronics and the battery. Recently, the strengthening of emission norms pushes the off-highway vehicle manufacturers to elec- trify their technologies. Besides low emissions and noise, the hybrid technology provides a significant lower operational cost and increases the productivity compared to their conven- tional counterparts. Furthermore, a promising hybrid topology could be a series-parallel powertrain equipped with an electric variable transmission (EVT) to achieve a compact powertrain. This configuration allows the internal combustion engine to operate within its optimum operating range in order to reduce fuel consumption, without directly depending on the load conditions. Therefore, this paper proposes a new hybrid drivetrain based on the electric variable transmission for forklift use cases. The goal was to compare in terms of performance this solution with the conventional solution, ie a powertrain equipped with a hydraulic torque converter and an automatic transmission. The results show that the EVT-based solution reduces fuel consumption by 40% and greatly reduces mechanical brake wear improving the maintenance cost. Another challenge of this study was to determine the influence of a gearbox use on the efficiency of the EVT. It has been found that the gearbox allowed to improve the efficiency and the consumption of 5% thanks to intelligent gear shifting strategy.

Date of Award	2 Sept 2019
Original language	English