2009-01-1337 Study on a High Torque Density Motor for an Electric Traction Vehicle Daiki Tanaka, Takashi Kato, Yuichi Shibukawa, Yuji Naruse and Tadayuki Hatsuda Nissan Motor Co., Ltd. Tomonori Kojima Fujitsu General Limited Copyright © 2009 SAE International ABSTRACT A compact and high performance electric motor, called the 3D motor and designed to achieve output torque density of 100 Nm/L, was developed for use on electric vehicles and hybrid electric vehicles. The motor adopts an axial flux configuration, consisting of a disk-shaped stator sandwiched between two disk-shaped rotors with permanent magnets. It also adopts 9-phase current with a fractional slot combination, both of which increase the torque density. The rated torque output of this high power-density motor is achieved by applying a hybrid cooling system comprising a water jacket on the outer case of the stator and oil dispersion into the air gaps. The mechanical strength of the rotors against centrifugal force and that of the stator against torque exertion were confirmed in mechanical experiments. Several measures such as flux barriers, a chamfered rotor rim, parallel windings, and radially laminated cores were adopted to suppress losses. As a result, the motor achieves maximum efficiency of 97%. INTRODUCTION Global warming and the increasing cost of fossil fuels in recent years have challenged automobile manufacturers to produce low-emission vehicles that reduce the level of carbon dioxide (CO 2) emissions. Electric-powered vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs) ar e considered to be among the possible effective solutions to meet the requirements for reducing emissions and fuel consumption. For the electric motor that is us ed on such electric-powered vehicles, there are multiple demands. Firstly, whether it is installed between the internal-combustion engine and the transmission to function as a traction motor for HEVs or installed inside the wheels to function as an in-wheel motor for EVs, the motor is often required to be thin in its axial direction compared with its radius. Secondly, high torque output is always required to improve the drivability of the vehicle. Thirdly, high efficiency is required to increase the rated power output and decrease the consumption of electricity, thereby directly lowering the operating cost of the vehicle. The 3D motor described here was developed to meet such demands for the traction motor. It is able to generate a high level of torque output from a small motor volume while achieving high efficiency. This paper discusses the technologies employed in the development of the 3D motor with respect to its output performance, mechanical strength and efficiency. OVERVIEW OF 3D MOTOR MOTOR CONFIGURATION Table 1 lists the general specifications of the 3D motor and Figures 1 and 2 show schematic diagrams of its structure. The motor adopts a double-sided configuration with an internal stator. It is constructed of a disk-shaped stator sandwiched between two disk-shaped rotors which are connected to the motor shaft that penetrates the hollow located inside the stator disk. The rotors employ fan-shaped Nd-Fe-B magnets aligned in the SAE Int. J. Passeng. Cars - Electron. Electr. Syst. | Volume 2 | Issue 1 397Downloaded from SAE International by Univ of California Berkeley, Tuesday, July 31, 2018tangential direction with a back core consisting of radially laminated magnetic steel rolled up in a thin layer. The magnets are located in slots formed by the back core that hooks the magnets in the axial direction. The back core is held by a baseplate that holds the back core and magnets against centrifugal force and transmits the torque they generate to the motor shaft. The stator is composed of fan-shaped cores made of radially laminated steel. Each core is wound by rectangular magnetic wires to give the motor its concentrated winding design and is aligned in the