INNOVATIVE POWERTRAIN AND ADVANCED ENERGY MANAGEMENT STRATEGY FOR HYBRID HYDRAULIC EXCAVATOR

Abstract

Nowadays, along with the development of industry, the demand for fossil fuels is constantly increasing. Therefore, reducing fossil fuel consumption is one of the most important issues worldwide. This aim has opened up opportunities for the development of new low-emission and energy-efficient vehicles. These include hydraulic excavators (HE) which consume a lot of energy and emit a large amount of harmful emissions. To address this challenge, there are two main directions: reducing energy consumption and/or improving energy recuperation capability in HE. Hybrid powertrain combining an internal combustion engine (ICE) with an electric motor is considered an ideal candidate to reduce energy consumption in HE. Meanwhile, an energy regeneration system (ERS) can be integrated into the HE to recover the potential energy and reuse it in subsequent cycles. Based on the above reasons, an innovative electric hybrid HE named electrical hydraulic continually variable powertrain (EHCVP) which could not only regenerate but also reuse the recovered energy is proposed. In detail, the powertrain includes an ICE and electric motor/generator to drive the main pump. The electric motor/generator can work as a motor or a generator to provide mechanical energy or generate electric energy. The speeds of ICE and motor/generator decide the speed of main pump through planetary gear. Then the ICE’s speed can be controlled to the high-efficiency range by changing the operation mode of the electric motor/generator. A variable displacement pump is installed in system to govern the torque of the engine. Hence, the engine working points can be controlled in the high-efficiency range. Besides, a hydraulic motor is placed at the output port of the boom cylinder. The potential hydraulic energy in the boom cylinder is converted into mechanical energy and drives the electric motor/generator via a function of a double clutch without an additional generator. The generated energy from the motor/generator is stored in a battery and it can be reused in subsequent cycles. However, the maximum displacement of the hydraulic pump limits the controlled range of engine torque in a condition of a large velocity. Hence, the current structure of EHCVP limits the improvement of the energy-saving efficiency in the condition of a large velocity. Finally, the fuel consumption of the total system cannot be improved with varying velocities in real engineering. To enhance energy-saving efficiency, a double clutch with two different gear ratios is installed between the ring gear shaft and hydraulic pump. The ICE’s torque can be governed by both the hydraulic pump and gearbox mainly. Meanwhile, the electric motor/generator governs the speed of the engine. In the condition of a large velocity, the bigger gear ratio is used to decrease the speed and increase the torque of the ICE. So, the ICE can work with its high efficiency in the condition of a large velocity. Compared with the EHCVP without integrating the double clutch, the proposed system could offer improvements in energy saving up to 7%. For developing a new HE with highly efficient and stability, not only a new powertrain but also an energy management strategy should be proposed. In this thesis, an online energy management strategy based on the extremum seeking control (ESC) is used to switch the gear ratio and efficiently distribute the power to the EHCVP. In addition, the conventional penalty function is caused by suddenly changing the power engine and making the unstable of powertrain when the considered parameter such as SOC of battery beyond the allowable range is replaced by a fuzzy logic system. In detail, the fuzzy logic system is constructed based on considering the battery aging with its input parameters are the current, SOC, and temperature of the battery. During the operation, the fuzzy logic system estimates the output penalty value adjusting the power reference of each power source depending on the battery status. To verify the effectiveness of the proposed system, a co-simulation model using Matlab and AMESim has been built with a battery model developed in Matlab, and the powertrain and hydraulic circuit were constructed in AMESim to mimic the motion of the HE. Both simulation and experimental results demonstrated that the working points of the engine could be kept within its high-efficiency region under different working conditions.