A study on quantitative evaluation of drivability in HEVs

Drivability means subjective perception for dynamic performance of a vehicle in response to a driver input. It is an important evaluation of vehicle performance. Generally, drivability evaluation is subjectively evaluated by experienced test drivers in automotive industries. Subjective evaluations are limited in repeatability and require much time and cost. This paper proposed the method for quantification of drivability in Hybrid Electric Vehicles (HEV). Proposed quantitative evaluation method consisted of five evaluation indices which were selected from references having relation to ride comfort and shift quality. We calculated quantitative evaluation of drivability using output data from vehicle test. Based on the proposed method, drivability of HEV was evaluated quantitatively under constant speed and overtaking operation conditions. The results of these evaluations were similar to those of subjective evaluations under the same conditions. In addition, we designed a vehicle dynamic model, including engine, engine clutch, motor, transmission, vehicle and tire to confirm drivability change. Using simulation program, a case study was carried out to estimate drivability caused by modifying system parameters. Through output data of the simulation program, drivability was evaluated based on the proposed method. Consequently, we can improve drivability of HEVs through this process.