In this paper, a direct liquid cooling method is proposed for a radial-flux permanent-magnet motor. To demonstrate the feasibility of the cooling method, a test motor with a rated output of 205 kW was designed, constructed, and tested in an actual vehicle application, an electric city bus. The energy consumption tests were conducted by applying a heavy-duty chassis dynamometer capable of simulating the inertia, weight, and road loads that the buses are subjected to in the normal on-road operation. The electricity consumption on the real bus route of the Espoo line 11 in Finland was 0.61 kWh/km. The test results of the cooling solution show that the motor is capable of meeting the most challenging requirements of the load cycle even with a full payload. The highest winding temperature rise in the test driving cycles was only 26 • C, which proves the effectiveness of direct-liquid-cooled coils in a vehicle motor.INDEX TERMS Electric machines, permanent magnet motors, rotating machines, traction motors, direct liquid cooling.
The city of Tampere in Finland aims to be carbon-neutral in 2030 and wanted to find out how the electrification of public transport would help achieve the climate goal. Research has covered topics related to electric buses, ranging from battery technologies to lifecycle assessment and cost analysis. However, less is known about electric city buses’ performance in cold climatic zones. This study collected and analysed weather and electric city bus data to understand the effects of temperature and weather conditions on the electric buses’ efficiency. Data were collected from four battery-electric buses and one hybrid bus as a reference. The buses were fast-charged at the market and slow-charged at the depot. The test route ran downtown. The study finds that the average energy consumption of the buses during winter was 40–45% higher than in summer (kWh/km). The effect of cabin cooling is minor compared to the cabin heating energy needs. The study also finds that infrastructure needs to have enough safety margins in case of faults and additional energy consumption in harsh weather conditions. In addition, appropriate training for operators, maintenance and other personnel is needed to avoid disturbances caused by charging and excessive energy consumption by driving style.
Electric retrofitting (e-retrofitting) is a viable option for accelerating the renewal of heavy-duty vehicle fleets to reduce the related emissions. We introduce a simulation-based assessment of e-retrofitting strategies for heavy-duty vehicles. Our simulation tool, an electric vehicle fleet simulation toolbox, comprises three modules, namely driving cycles, vehicle dynamics, and vehicle profiles. The first allows for the creation of realistic driving cycles based on GPS data from real routes. The vehicle dynamics and vehicle profiles incorporate, e.g., the modelling of the powertrain and driving conditions. Ten realistic driving cycles were created and used for investigating and comparing three different powertrain alternatives, including the original diesel powertrain, electric with a single-speed transmission and electric with a multi-speed transmission. The vehicles were simulated in two different heavy-load scenarios. First, driving with a cargo load represented by the maximum vehicle weight and second, driving with snow ploughing. We found that the multi-speed transmission in an electric heavy-duty truck significantly improved its traction performance and gradeability. On the other hand, the effect on the electric powertrain efficiency, and thereby on the energy consumption, remained rather minor. Considering the given workload scenarios, our results advocate employing rather than omitting the gearbox in the e-retrofit truck process.
This paper presents a pre-normative roadmap that foresees the developments in the charging of heavy-duty electric vehicles (HD-EVs). It supports and facilitates the future standardization efforts of charging technologies by creating an overview of the popularity of charging technologies and the end users’ needs. The required input for the work was collected using a comprehensive investigation on the available charging technologies and their standardization, reviewing the existing roadmaps and research work, and conducting surveys and interviews of end users and technical stakeholders. According to the findings, a pantograph on the roof of a vehicle and plug-based charging are currently the most used charging interfaces. This trend is likely to continue in the future, since (1) pantographs on vehicle roofs, (2) pantographs on infrastructure, and (3) plugs were graded as charging interfaces with the highest potential by the participants of the technical survey. Static and conductive charging technologies show more potential than dynamic and wireless charging technologies. Nevertheless, inductive charging may be a future charging solution for HD-EVs if the current bottlenecks in the technology can be addressed. These bottlenecks include high prices, slightly lower efficiency, lack of standardization, the maximum achievable power, and safety concerns. Furthermore, interoperability was repeatedly mentioned as the main challenge for today’s charging technologies.
The transportation sector has become the fastest growing source of greenhouse gas (GHG) emissions. One solution to mitigate the impacts is a shift towards electric modes. Where previous studies have only focused on the replacement of individual modes, our study presents a more holistic approach by comparing land-based, water-based and airborne transportation modes. We study the GHG emission reduction potentials of electric cars, buses, trains, ferries and aircraft in comparison to existing modes on 34 routes within Finland and across the Baltic Sea to Sweden and Estonia. By comparing the GHG emissions in carbon dioxide equivalents (CO2-eq) per passenger kilometer for each mode, we also consider the emissions generated from battery production as well as the differences in the energy mix from electricity production of the three studied countries. In addition to CO2-eq emissions per passenger kilometer, we also take real door-to-door travel times into account. Our study found that electric transportation modes possess great potential for emissions reduction. Nevertheless, depending on the energy mix used for electricity production, the emissions of electric transportation modes can exceed those of existing modes significantly. In addition, the emissions generated by battery production can have a significant share of the total emissions and should therefore always be considered. Finally, while also taking into account the door-to-door travel times, our study identified the great potential of electric aircraft to provide a less carbon intensive transportation option paired with short travel times starting on routes beyond 300 km where no high-speed rail exists as well as on routes across the water.
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