Yamazakii, T., Uchiyama, H., Nakazawa, K., Isomura, T. et al., "The Development of Direct Drive Motors for Solar Cars," SAE Technical Paper 2017-01-1232, 2017, doi:10.4271/2017-01-1232.
Solar car races are held worldwide, aiming to promote vehicles that help reduce environmental loads on the roads. In order to gain superiority in solar car racing, it is essential to develop a high efficiency brushless direct drive motor that optimizes the energy use to the fullest and allows high speed driving when needed.To achieve these goals, two development approaches of solar car motors are proposed: the high efficiency motor which improves electrical characteristics and significantly reduces energy loss; and the variable field magnet motor that offers instant speed boost for a temporary period of time for overtaking opponents.We have developed a high efficiency motor through the application of an amorphous core and laminated magnets. Instead of the standard method of the W-EDM (Wire-Electric Discharge Machining) for amorphous cores, we utilized water jet cutting, through which we succeeded in achieving insulation between laminated cores. In general, a sheet of magnet is used in each slot and its dimension is determined according to the lamination height of the core. In this project, multiple magnet segments shorter in the direction of the shaft are stacked vertically to achieve the desired height, which successfully resulted in the reduction of iron loss. The application of these methods led to the achievement of motor efficiency exceeding 98%.For the instant speed increase, we have developed the optimized design configuration for a variable field magnet module that can change T-N characteristics, utilizing our unique method for varying the effective magnetic flux. The result shows that our variable field magnet motor achieved a 1.57 times higher rotational speed than conventional types.The proposed technologies can contribute to the efficient use of energy in solar car applications, promoting the development of novel solar car systems.