JSAE 20159048 SAE 2015-01-1780 A Study on Hybrid Control Method for Improvement of Fuel Economy and Exhaust- *as Emission of Hybrid Trucks Nobunori Okui and Masayuki Kobayashi National Traffic Safety and Environment Laboratory Copyright © 2015 SAE Japan and Copyright © 2015 SAE International ABSTRACT Next-generation vehicles which include Electric Vehicles and Hybrid Electric Vehicles are studied and expected to reduce carbon dioxide emissions. The number of small delivery hybrid trucks has increased in the commercial vehicle class. The engine load of a commercial hybrid truck is reduced by using an electric motor. Fuel economy of the hybrid truck is improved with the assist. On the other hand, exhaust-gas temperature is decreased, and it has a negative effect on the purif ication performance of aftertreatment system. In this report, the fuel performance and emission gas characteristics of marketed small hybrid trucks were surveyed using the chassis dynamometer test system. Next, the relationship between the fuel performance and emission gas characteristics during the traveling of various hybrid trucks was checked and the new hybrid control aiming at both improvement of fuel economy and reduction of the emission gas at a time was reviewed by using the Hy brid powertrain test bed system. INTRODUCTION Recently, climate change due to global warming has been recognized as a major social problem. An increase in the amount of carbon dioxide emitted from vehicles has been highlighted as one of the factors responsible for global warming. In order to reduce carbon dioxide emissions, automobile manufacturers have contributed to and are positive about the research and development of fuel-effective hybrid vehicles with improved engine efficiency [1][2]. For hybrid vehicles, one of the measures to enhance fuel economy is to reduce the workload of the engine. This is accomplished by ut ilizing the braking energy acquired by the electric motor as assistance energy to the driving force during acceleration [3][4]. The proposed measures to increase the amount of braking energy acquired are to control the regenerative brake at an extremely low vehicle speed range and to change the hybrid powertrain layout. On the other hand, a decrease in the workload of the engine causes a drop in the emission temperature. Generally, such a temperature drop has been reported to adversely affect the emission cleaning performance, which affects the catalyst activation temperature of the emission after-treatment system in commercial diesel vehicles [5]-[9]. Note that research on the improvement of the fuel economy of hybrid commercial vehicles, which is found only occasionally, is limited to that based on theoretical calculation [9][10]. Regarding hybrid commercial vehicles that incorporate various measures to improve their fuel economy, the relationship between the actual fuel efficiency and the emission characteristics must be further investigated. Also the research of the improvement of fuel economy and emission characteristics by combining the hybrid control with the actual diesel engine is just a few examples. In this study, the fuel performance and the emission characteristics of small hybrid trucks available on the market were checked using a chassis dynamometer test system. Then, the relationship between the fuel performance and the emission characteristics of driving hybrid trucks were examined and the feasibility of a new hybrid control capable of balancing fuel improvement and exhaust-gas emission was reviewed. A “hybrid powertrain test bed system [11]” was established that is capable of reproducing the actual traveling state of various hybrid vehicles inside the laboratory. Using this te st system, in which the emission after-treatment system was combined with the actual engine, evaluation using an actual road travel pattern specialized for test vehicles was performed, in addition to an e