Sunghyun Ahn

Shift control of a 2-speed dual clutch transmission for electric vehicle

This paper suggested a shift control algorithm for improving the shift quality(SQ) by modeling a dual clutch transmission(DCT)-type 2-speed transmission system for an electric vehicle(EV). In 2-speed transmission system, the driving comfort decreased when the driveshaft torque of the vehicle fluctuated by shifting gear, unlike with the existing single-gear ratio EV. To improve this, a shift control algorithm was proposed that controlled two units of shift actuators and a unit of a driving motor for the subject DCT. To evaluate the proposed shift control algorithm, a shift performance simulator based on MATLAB/Simulink that consisted of a motor, DCT, actuator, and vehicle model was developed by modeling a DCT-type EV with 2-speed transmission system. The SQ improvement was verified by reducing the overshoot torque of the driveshaft during inertia phase.

Mode shift control for a dual-mode power-split-type hybrid electric vehicle:

This paper presents a mode shift control algorithm for reducing the variation in the driveshaft torque for a dual-mode power-split-type hybrid electric vehicle. To evaluate the shift characteristics of this hybrid electric vehicle, dynamic models for the hybrid electric vehicle powertrain were developed. Using the dynamic models, a mode shift performance simulator was developed, and simulations were performed. To analyse the shift characteristics during the mode shift, bond-graph models for the transient state were constructed, and state equations were derived. From the bond-graph models and state equations, it was found that the transient torque occurs because of the inertia torques of the first motor–generator and the second motor–generator. Based on the transient torque, a mode shift control algorithm was proposed, which compensates for the transient torque. To evaluate the performance of the proposed control algorithm, a test bench for the dual-mode power-split-type hybrid electric vehicle was developed. From the simulations and test results, it was found that the variation in the driveshaft torque was reduced by the proposed control algorithm, which provides improved shift quality.

Development of an integrated engine-hydro-mechanical transmission control algorithm for a tractor

This article presents an integrated engine-hydro-mechanical transmission control algorithm for a tractor considering the engine-hydro-mechanical transmission efficiency. First, the hydro-mechanical transmission efficiency was obtained by network analysis based on the hydrostatic unit efficiency constructed from the test. Using the hydro-mechanical transmission efficiency map and the thermal efficiency of the engine, an engine-hydro-mechanical transmission optimal operating line was obtained, which provides higher total system efficiency. Based on the optimal operating line, an integrated engine-hydro-mechanical transmission control algorithm was proposed, which provides higher total powertrain system efficiency. To evaluate the performance of the proposed control algorithm, an AMESim-MATLAB/Simulink-based co-simulator was developed. From the simulation results for the plow working, it was found that the integrated engine-hydro-mechanical transmission control provides improved fuel economy by 7.5% compared with the existing engine optimal operating line control. The performance of the integrated engine-hydro-mechanical transmission control was also validated using the test bench.

Development of a pressure control algorithm without a pressure sensor for a four-wheel drive unit:

This article proposes a pressure control algorithm without a pressure sensor for a four-wheel-drive unit. To develop the control algorithm, dynamic models of the four-wheel-drive unit were obtained, including the motor, pump, and clutch. For feedback control, a first-order adaptive transfer function of the modified motor speed was proposed to fulfill the transient response characteristics, and the motor input voltage generated the demanded pressure at steady state in the feedforward control. The coefficient α of the adaptive transfer function was obtained with weight factors W 1 and W 2 considering the pressure difference and temperature. The performance of the proposed pressure control algorithm without a pressure sensor was evaluated by experiments at various operating temperatures. It was found that the actual pressure closely followed the demanded pressure with an acceptable error at steady state and within an acceptable rising time in a transient state.

Development of a new sub-shift schedule and control algorithm for a hydro-mechanical transmission

In this study, a new sub-shift schedule was proposed for a hydro-mechanical transmission. To develop the sub-shift schedule, a network analysis was performed by considering the hydrostatic unit loss and mechanical component losses. In the new sub-shift schedule, the sub-shift gear can be selected with respect to the demanded wheel torque and vehicle speed, which provides improved system efficiency for the given vehicle operating condition. Since the sub-shift can only be carried out at a speed ratio where the off-going and on-coming clutch speeds are synchronized in the existing sub-shift control, a sub-shift control algorithm without the clutch speed synchronization was proposed to apply the new sub-shift schedule using the forward clutch pressure and hydrostatic unit stroke control. The performance of the sub-shift control algorithm without the clutch speed synchronization was evaluated by the simulation and experiment. It was found from the simulation and experimental results that the sub-shift can be achieved, showing an acceptable peak-to-peak torque variation in the driveshaft.

Development of a sub-shift control algorithm for an agricultural tractor with hydro-mechanical transmission

A sub-shift control algorithm was proposed for an agricultural tractor with hydro-mechanical transmission. The hydro-mechanical transmission investigated in this study consists of a hydro-static unit and planetary gear sets which provide a continuously variable transmission function and four sub-shift gears. The sub-shift needs to be carried out at the hydro-static unit stroke where the speed of the off-going and on-coming clutches is synchronized. To reduce the hydro-static unit stroke error due to the nonlinear characteristic, the hysteresis characteristic was investigated in the test bench and a hysteresis compensator was developed. Using the compensator in the feedforward loop, a hydro-static unit stroke control algorithm was proposed and validated via experiment. To prevent the torque interruption during the sub-shift, a time delay of the off-going clutch was proposed. In addition, a hydro-static unit stroke duration which maintains the target stroke during the sub-shift was suggested to reduce the speed difference between the clutch plates. The sub-shift control algorithm including the hysteresis compensation, time delay of the off-going clutch, and hydro-static unit stroke duration was evaluated via experiment. It was found from the experimental results that the sub-shift was performed smoothly without the torque interruption, even in the acceleration state when large inertial torque change occurred.

Macroslip detection for a metal V-belt continuously variable transmission using the period difference

In this study, a macroslip detection method is proposed for a metal V-belt continuously variable transmission. The macroslip detection method was developed using the instantaneous periods of the primary pulley’s acceleration and the secondary pulley’s acceleration, which can be obtained from the existing speed sensors. To obtain the instantaneous periods of the accelerations of the pulleys in real time, a signal-processing method was developed on the basis of zero-cross detection. Using the instantaneous periods, the period difference is introduced, and a threshold value b is defined to evaluate the slip state. The characteristics of the period difference and b were investigated by a three-dimensional analysis, in which a three-dimensional model of the continuously variable transmission including the blocks, the bands and the pulleys was constructed, and the velocity of each element and the slip rate were obtained. From the simulation results, it was found that the period difference stays below the threshold value b in the microslip region and begins to increase over the threshold value b in the macroslip region. The macroslip detection method proposed in this study was validated by experiments, which showed that the method is effective for detecting the occurrence of macroslip, independently of the input torque and the speed ratio.

Motor-generator control to improve shift quality for a dual mode power split transmission

In this paper, a motor-generator (MG) control algorithm was proposed to improve the shift quality for a dual mode power split transmission (PST) hybrid electric vehicle (HEV). In order to analyze the shift characteristics during the mode shift, Bondgraph models for transient-state were constructed and state equations were derived. From the state equations, it was found that inertia torque of MG2 causes a transient torque during the mode shift. Based on the transient torque, a MG torque control algorithm which compensates the transient torque was developed to reduce the driveshaft torque variation. To evaluate the performance of the MG2 control algorithm, dynamic models of the dual mode PST HEV were obtained and an AMESim-MATLAB/Simulink based mode shift performance simulator was developed. It was found from the simulation results that the driveshaft torque variation was reduced by the proposed control algorithm which provides improved shift quality.

Development of 2 Stage CVT Shift Control Algorithm to Reduce Torque Variation During 1-2 Upshift of Planetary Gear

In this paper, a 2 stage continuously variable transmission (CVT) shift control algorithm is proposed for the 1–2 upshift of the planetary gear to achieve the shift quality. A fuzzy control algorithm is designed considering the relatively slower response characteristics of CVT. In order to evaluate the performance of the control algorithm, a 2 stage CVT vehicle simulator is developed including a dynamic model of the CVT powertrain. From the simulation results, it is found that CVT gear ratio changes faster in the inertia phase and remains constant after the inertia phase of the planetary gear shift, which provides the reduced torque variation by the proposed control algorithm.Copyright