## 1 Introduction
AMT systems that use actuators to automatically control MTs benefit from both the high power train efficiency of manual transmissions and the convenience of automatic transmissions [30]. In developing and applying an AMT system, a shifting performance similar to that of a general automatic transmission using a torque converter is required. Therefore, most studies on AMT systems have focused on automatic shift quality, such as fast and smooth clutch engagement [16; 31; 32]. In order to improve the shift quality of AMTs, it is necessary to develop a shift control technology capable of quickly shifting a conventional manual transmission. Research on the AMT shift control technology has mainly been conducted using control algorithms [4; 33; 34], clutch control strategies [35], and performance evaluation [36]. Some researchers have attempted to apply AMT in the field of tractors. [PERSON] et al. [37] proposed a tractor AMT system of the hydraulic shift system type, and conducted a study on the shift control strategy. [PERSON] et al. [38] proposed a control system for clutch engagement of AMT tractors using Matlab/Simulink. They reported that the application of fuzzy control theory can effectively control the clutch engagement process in the AMT tractor. However, the above studies have focused only on simulation, and performance evaluation of the hardware of the actual AMT system was not performed. In order to mount the AMT system onto the tractor transmission, it is needed to perform not only simulation but also single-component experiments and automatic shifting experiments through the development of actual hardware. According to the above studies, most studies on AMTs have been conducted in the automotive field, except for some studies in agricultural tractorsthat used hydraulic actuators. This is because the actuator motor capacity in actuator and control technologies has not yet reached a level applicable to tractors, which have atypical and high load operations. Unlike automobiles, a tractor performs traction by transmitting high driving torque to the wheels, such that it uses high reduction ratios to transmit low rotational speed and high torque from the engine to transmission. Therefore, a shifting system capable of corresponding with high torque compared to an automobile is required for clutch control. From this point of view, the combination of an electric actuator and a reduction gear can provide a good solution to respond to these requirements and provide similar performance without the use of a hydraulic system. Electric actuator-based AMT tractors do not have the problems of low efficiency and complex systems associated with the use of hydraulic transmissions (e.g., power shuttle, power shift, and CVT), and can be easily mounted additionally on a conventional manual transmissions of the tractor, which contributes to providing high convenience. The purpose of this study was to develop an AMT for agricultural tractors by adding electric actuators to conventional manual transmissions, because this system has a higher power transmission efficiency than conventional hydraulic systems and more convenience than manual transmissions. The detailed research objectives are as follows: 1) designing and developing an AMT system by adding actuators and control systems to a conventional manual transmission for shuttle shifting and clutch control; 2) designing a clutch actuator using an electric motor and reduction gear, in consideration of the diaphragm load of the clutch; and 3) evaluating of the shifting performance using an experimental test-bed.