# Development of a Simulation Model for HMT of a 50 kW Class Agricultural Tractor
## 1 Introduction
In another study, a simulation model of HMT for an agricultural tractor was developed and verified using a simulation model, and then the HSU stroke and power transmission efficiency were analyzed [22]. The results showed that the HMT continuously shifted the HSU stroke to perform gear selection and increased the driving speed of the tractor, and the power transmission efficiency of the HMT increased as the driving speed increased for each gear stage, and then decreased again after reaching the maximum point. In previous research, the characteristics for structures and power transmission of the HMT were analyzed using a network model and simulation model. In addition, since the tractor has a heavy load during agricultural operations, unlike a general vehicle, it is necessary to design it in consideration of the workload for agricultural operations [23]. To do this, the performance evaluation through bench tests and field tests under various conditions is necessary. However, the performance evaluation of the transmission using the bench test and the field test is costly and time-consuming [24]. Recently, the performance evaluation of the transmission using the simulation has been actively used [12]. The performance verification using simulation has the advantage of being simple and saving time. In the field of agricultural machinery, the simulation model has been used not only to evaluate the tractor performance but also to improve and optimize the transmission for the tractor. A study on the design of the HMT was performed to present multi-range HMT and to evaluate its performance using a bench test and simulation model [25]. A simulation model was built in the AMESim (version 16, Simens AG, Munich, Germany), and a corresponding test bench was performed to verify the characteristics. The proposed HMT presented a mean efficiency of about 83% in a wide speed range. In another study, the development of a simulation model for tractors was performed to evaluate the fuel efficiency using SimulationX (version 3.6, ESI ITI GmbH, Dresden, Germany) and the simulation results were compared and analyzed with the measured data [26]. The fuel consumption and efficiency between the field test and simulation were 14.04 and 14.19 km/h and 0.30 and 0.33 kg/kWh, respectively, during the rotary tillage, As a result of the t-test, the researchers found that there was no significant difference of fuel consumption and efficiency between the field test and simulation. In another study, a simulation model of the tractor was developed to improve the transmission error and tooth load distribution using KISSsoft (version 2017, KISSsoft AG, Zurich, Switzerland), and the tip and root relief were modified with micro-geometry in the profile direction, and the crowning was modified [27]. As a result of modifying the tip and relief in the profile direction, the transmission error was reduced up to 40.7%, and the tooth load was more evenly distributed than before and decreased the stress on the tooth surface in the case of modifying the crowning in the lead direction. However, the simulation test may be inaccurate in comparison with the performance evaluation using a bench test. Accordingly, it is important to verify the simulation model in comparison with the results of the bench test [28]. Therefore, in this study, the prototype of HMT and the simulation model were developed, and the bench test and simulation were performed. To verify the simulation model, the axle torque, rotational speed, and power transmission efficiency between the measured and simulated according to the gear stages were compared and analyzed. This study is the basic research on the development of an HMT tractor, and the simulation model was developed and verified through a prototype of the HMT platform.