The effect of different types of electric drive unit on energy consumption for heavy commercial vehicle

Abstract

The studies have been started recently in many industries to reduce emissions and increase efficiency in order to prevent environmental pollution. The automotive industry has become the most trend sector for these studies. Because the harmful exhaust gases emitted by the vehicles are too much around the world and the competition in this sector is strong, this situation has become inevitable. For this reason, in order to reduce the emission gases of vehicles, in addition to the size and emission reduction studies of internal combustion engines, the development of environmentally friendly vehicles is becoming widespread with the conversion of vehicles that have become even more popular to electric vehicles. Today, the size of the internal combustion engines have been considerably reduced with emission regulations released by governments. Therefore, it has not been able to meet the performance expectations of the customers. In order to meet customer expectations with the emission regulations introduced, automakers have accelerated studies on electric and hybrid vehicles and they will electrify the majority of the vehicles produced by 2025. The electrification of vehicles is not limited to passenger vehicles, but is also applied to light and heavy commercial vehicles. For this reason, one of the regulations published in Europe is the Vehicle Energy consumption Calculation Tool (VECTO). VECTO is a calculation tool developed by the European Commission for heavy commercial vehicles, calculating fuel consumption and CO2 emissions. In this way, the reference CO2 emission value is determined in 2019, and vehicle manufacturers are requested to keep this reference value below 15% in 2025 and 30% in 2030 in the coming years. As these values cannot be reduced further by conventional vehicles with the internal combustion engines whose emission values have already been improved, the electrification of heavy commercial vehicles has become inevitably. The electrification of vehicles started with hybrid vehicles. The hybrid vehicles are considered as an intermediate type for the transition from traditional vehicles with internal combustion engines to electric vehicles. However, fully electric vehicles are one of the electrified vehicles that automakers have been working on recently. It is foreseen that electric vehicles will dominate the use of hybrid vehicles according to their intended use. The most important feature that distinguishes electric vehicles from traditional vehicles is to use electrical energy instead of using fossil fuels such as gasoline, diesel, natural gas, etc. The electric vehicles are more susceptible to environment both in terms of emission of harmful gases and noise pollution compared to traditional vehicles. Moreover, the accelerating performance of electric vehicle is better and, it is used fewer components in these vehicles. The working principle of purely electric vehicles is to transfer the electrical energy stored in the battery to the wheels with the help of electric motor(s). The basic systems of electric vehicles are the electric motor, the inverter, the gearbox or the electric drive unit where the electric motor, the inverter and the gearbox are in one package, and also the battery. Apart from that, the controller, which provides control of all these components, controls the battery charge status and inverter signal inputs, is one of the basic systems of electric vehicles. As there are many electrical and electronic systems in electric vehicles, many studies are carried out in the field of software and software development to control these systems. In this way, it is ensured that the electric motors operate in more efficient regions, and that the battery management system and the control of the battery are used more efficiently with the software developed. Along with the developed software, the transmission, which is used as a powertrain together with the electric motor and inverter, needs to be developed and, thus the vehicle is provided to operate more efficiently. Pure electrification studies for heavy commercial vehicles started firstly by removing the internal combustion engine and conventional automatic or manual transmission, and attaching the electric motor directly to the rear live axle with the help of a propeller shaft. However, due to the fact that there will be only one ratio, some vehicles could not fulfill their requirements in this case and due to the high starting torque, it was necessary to use very large electric motors. Afterwards, it was accepted to proceed with two configurations for electric heavy commercial vehicles. Those are electric axle (E-axle) for heavy commercial vehicle under 60 tons and electric transmission for over 60 tons. In the vehicle configuration with electric transmissions, a transmission in which electric motors are integrated is formed as a propeller shaft and live back-to-back. The inverter is usually on the vehicle, not on the gearbox. The e-axle is used in the P4 vehicle configuration and is formed as a structure with electric motor, transmission (reducer) and inverter. It is formed by integrating the live rear axle in the vehicle and removing the propeller shaft together with the conventional engine and transmission. E-axle is designed as a single system consisting of electric motor, inverter and gearbox, or only electric motor and gearbox without inverter. When the studies in the literature are examined, it has been observed that the researches on energy consumption for electric vehicles are mostly done for passenger cars with higher annual production volume, and the studies for heavy commercial vehicles are accelerated. Generally, these studies started with hybrid vehicles. A comparison of fuel consumption between conventional vehicles and hybrid vehicles has been performed. Meanwhile, studies continue by examining the energy consumption of electric vehicles. In energy consumption studies, the energy consumption of an entire vehicle is typically investigated. Standard driving cycles were used for energy consumption studies for heavy commercial vehicles, and a comparison of the transmission types used in conventional vehicles was made in terms of energy consumption. The effect of transmissions to be used for electric heavy commercial vehicles, which is the aim of this study, on vehicle energy consumption has been examined. The transmission is formed as an electric drive unit, in a single package, containing the electric motor and the inverter. In addition, it is aimed to obtain the optimum electric drive unit for heavy commercial trucks, taking into account the effects of these drive units on vehicle performance and packaging, as well as the effect of gear number on energy consumption. However, these studies were carried out by not using standard driving cycles, but using driving cycles collected from the real road. In this study, the effect of electric drive units, in which the electric motor, inverter and transmission are in a single system, and the number of gears on energy consumption were investigated. In addition, the effect of electric drive units on vehicle performance characteristics was investigated and compared. Among the electric drive units, multi-speed transmissions have working principles similar to automated manual transmissions (AMT), while multi-mode transmissions are electric drive units that are new to the literature and allow electric motors to operate independently. Therefore, one of the innovative aspects of this study is the introduction of multi-mode transmissions and your analysis in terms of energy consumption. A vehicle model was developed in Matlab/SIMULINK environment to analyze energy consumption and see the effect of electric drive units. In order for these results to reflect more realistic values, real road data were collected for three different routes and driving cycles were created. These routes have been selected as follows in order to investigate their energy consumption in all road conditions. These are municipal, intercity and regional routes. The road data for these routes are collected and processed by using NCODE program, and driving cycles as speed and distance or time are obtained. Then, these cycle drives were integrated into the vehicle model developed in the Matlab/SIMULINK environment, and energy consumption values were obtained for two, three and four-speed electric drive units. In this developed vehicle model, one of the important systems is transmission which is the aim of this study, were developed in two different ways. The difference here is due to different gear shifting algorithms. While the gear shifts in the so-called multi-speed electric drive units have the same logic as the automated manual transmissions (AMTs), the gear shifting algorithm has been created with the aim of making the gear shifting smoother and without torque interruption by active synchronization in the multi-mode electric drive units. On the other hand, when the efficiency maps of electric motors are taken into consideration, the gear increase and decrease processes in the most appropriate speed ranges are created in the electric motor model algorithms. In addition, the energy gain during braking and in the case of going downhill, which contributes greatly to the vehicle's energy consumption, is controlled by the algorithms in the battery and electric motor model, and is added to the system in the form of add energy. In this study, the effects of two different transmission types on energy consumption in different absence conditions and gear numbers were examined and successful results were obtained. When the obtained results are compared, it has been determined that the multi-speed electric drive units are more efficient and the efficiency of the units increases when the number of gears is increased. In the next step of the study, the effect of the increased number of gears on the vehicle package was stated numerically, the analyzes on the vehicle performance were made and the effects were revealed. However, using the same transmission types and road conditions, simulations are also run for conventional vehicles using internal combustion engines to compare the unit energy consumption. When these results are compared, it has been determined that the unit energy consumption of a heavy commercial truck with an internal combustion engine is higher than the unit energy consumption of an electric heavy commercial truck. In the light of all these information, the contribution of the study to the literature is to examine the effect of two different transmission or electric drive units for electric heavy commercial trucks on energy consumption for different road conditions, together with the number of gear changes, and the optimal electric drive unit in terms of efficiency, vehicle performance and design package.