Engine Map and Optimal Operation Path Construction for an Engine-CVT Powertrain System

Abstract

Rising fuel costs increase the importance of CVT powertrains in the automotive industry. Their benefit is that they allow an engine to operate at any condition which motivates development of fuel economy mode control strategies. In this work, an engine map is multiplied by the efficiency of a hydrostatic continuously variable transmission (HCVT). Therefore, the map is pictured in a 3D Cartesian space which is functioned into 3 parameters of indicated engine torque, engine speed, and transmission ratio. Operation of the engine powertrain system can be set to support any required power and speed of the vehicle at the highest efficiency point. The study examines a 900 cc. gasoline engine connected to the HCVT. To generate the operating range of the engine, the engine speed and hydraulic pressure were controlled by an electronic throttle and pump swash plate variation, respectively. The operating range is 3.353 - 10.442 kW. This power corresponds to a vehicle ground speed of 43.065 61.488 km/hr through a gear ratio of 0.5-1.5. Consequently, the system efficiency map was created and then used to construct the best operating path according to the required driving cycle. The points on the path were selected by the concept of the highest overall efficiency in the 3D map. As a result, the optimal operation path was found by connecting each point which is directed to the best solution for vehicle operation.