Effect of input shaft torque control during gear shifting processes in automatic stepped transmissions

Abstract

Introduction (problem statement and relevance).Designing gear shifting algorithms is one of the major problems in development of control systems for automatic gearboxes. Structure and parameters of these algorithms govern such characteristics of shifting processes as torque transients and energy dissipation due to clutch slippage; these, in turn, affect vehicle comfort and lifespan of the gearbox components. In particular, one of the factors defining the said characteristics is engine torque control provided during gear shifts. The functionality of the torque control extends when using the gearbox as a part of a hybrid powertrain with a traction electric machine connected to the gearbox input shaft. Studying gear shifting processes in this aspect is a relevant task aimed at improving control systems of automatic transmissions.The purpose of the studyis to compare different methods of controlling torque at the gearbox input shaft regarding their effect on gear shifting dynamics, clutch energy dissipation, and vehicle comfort.Methodology and research methods.The study was conducted by means of simulations using a mathematical model describing dynamics of a vehicle equipped with an automatic gearbox with an option of having an electric machine installed at the input shaft. Considering straight-line accelerated motion of the vehicle, both upshifts and downshifts were simulated with a correcting torque introduced in inertia phases of the shifts. Analysis of the simulation results allowed calculating key parameters of vehicle dynamics and clutch energy dissipation.Scientific novelty and results.The simulation results show a significant decrease (aver. 40%) of jerks when using an electric machine to correct the input shaft torque in inertia phases of both upshifts and downshifts. It is also shown that correction of the shaft torque allows reducing energy dissipation due to clutch slippage by 16–24% in the case of engine torque control and by 28–34% in the case of torque correction by an electric machine. However, using torque correction by means of an electric machine during downshifts raises the clutch energy dissipation 1.4–2.4 times.The practical significance.The results of the study can be used in designing control systems for automatic gearboxes intended for both conventional and electrified vehicles.