# Engine Speed Control System for Improving the Fuel Efficiency of Agricultural Tractors for
## 1 Introduction  
Agricultural tractors are multi-purpose machines used for performing various types of field operations. Different field operations subject agricultural tractors to varying workloads, which results in varying levels of fuel consumption under different conditions. These conditions include engine speed, soil condition, implementation type, and transmission gear step. Even though the same field operations may be conducted, workload and fuel consumption characteristics change frequently, and improper adjustments to operating conditions decrease tractor fuel efficiency. Engine speed andtransmission gear selection are the most significant factors that affect the fuel efficiency of agricultural tractors [1]. Therefore, in order to improve fuel efficiency, each field operation requires proper adjustment of transmission gear selection and engine speed.  
The fuel efficiency of agricultural tractors can be maximized by operating the engine at full load conditions. To operate under full load conditions, engine speed, transmission gears, and workload should be adjusted appropriately. [PERSON] et al. reported that during field operations in Korea, tractors were operated in the 24% for plowing and 41% for rotary tillage overpowered condition due to the usage of inappropriate transmission gear and engine speed [2]. In order to develop an integrated control system for maximizing fuel consumption efficiency, an engine speed control system should be designed to maintain the maximum economic speed of the diesel engine according to workload. Developing an engine speed control system requires the maximization of fuel efficiency and the incorporation of a method that allows engine speed to be controlled automatically.  
Various methods have been proposed to maximize the fuel efficiency of tractors using engine speed adjustment control. [PERSON] et al. designed a passive eco-driving system in order to assist tractor operators for selecting the optimal operating engine speed and transmission gear depending on the workload. They reported that fuel consumption can be reduced by an average of 69% and 54% in plowing and rotavating operations [2]. [PERSON] and [PERSON] also proposed an automatic system to control the engine speed and transmission gear ratio as optimal conditions using a mechanical instrument for adjusting the governor in five discrete speed ranges. The results showed that the fuel consumption can be reduced by 5-12%, compared to that of a good operator [3]. [PERSON] et al. developed a simple mechanical engine throttle control device for maintaining an optimal engine speed based on the measured power take-off (PTO) load. The operation of this device was based on a specific volumetric fuel consumption map. They reported that more than 8% of specific fuel consumption could be reduced by using the throttle control device [4]. [PERSON] designed a diesel engine speed controller using an optimal gain scheduling proportional-integral-derivative (PID) controller to improve engine performance and reduce fuel consumption. The engine operating region was divided into 15 sections by engine load and speed, and controller gains were determined through experiments. The fuel-saving performance of the system was reported to be better than existing mechanical speed governor [5].  
The objective of this study is to develop a load-sensitive engine speed control system to maximize fuel efficiency. In order to measure workload, torque transducer was attached to input shaft of transmission. This transducer can measure applied load torque to engine in real time not only PTO load but also draft load. Engine speed controller was developed using model-based controller design method. Simple mechanical system was designed for controlling mechanical fuel pump governor to engine speed within optimal engine speed point based on real time input shaft torque. To validate the performance of the system, an experiment was conducted by comparing plowing operations performed with and without the use of the control system.