Development of EHPS Motor Speed Map Using HILS System

This paper proposes a systematic method to develop electrohydraulic power steering (EHPS) motor speed maps. To overcome the weaknesses of the existing method, which depends on the test driver's steering feel at a proving ground, this paper utilized theoretical approaches and experimental developments to develop an optimal EHPS motor speed map. Steering torque of the target vehicle according to steering angle and vehicle speed was estimated through theoretical calculations. For the theoretical estimation of steering torque, tire properties of the target vehicle were measured, vehicle dynamics were employed to estimate slip angles, and the steering system was modeled. These estimation results were verified through field tests and then applied to the resistant motor of the EHPS Hardware-In-the-Loop Simulation (HILS) system, which represents the moments generated between the ground and tires. As the experimental development of EHPS motor speed map, an EHPS HILS system was set up, and the concept of desirable steering torque was established to quantify steering feel and catch-up effect. By means of the desirable steering torque, steering feel that was subject to the test driver's hands had criteria at various driving conditions. As the final procedure of this paper, the developed motor speed map was numerically compared with the existing map developed by the existing method, and then, it was verified through field tests with the target vehicle. The developed motor speed map provided sufficient steering assist to the driver and prevented the catch-up effect under all driving conditions. In addition, the steering torque from both maps had the same profiles at all driving conditions, even if the developed map demands lower motor speeds up to 1950 r/min than the existing map at almost all driving conditions.