# Engine Speed Control System for Improving the Fuel Efficiency of Agricultural Tractors for
## 6 Conclusions  
This study was conducted to develop an engine speed control system to maximize the fuel efficiency of a tractor in plowing operations using simple mechanical devices. The desired engine speed determination algorithm based on measured input shaft torque and PI controller for adjusting the engine speed was designed using a developed computer simulation model. This model was verified by comparing measured operating performance data and simulated data. Finally, an engine throttle control system was constructed using the desired engine speed control algorithm, a PI controller, servo motor, torque and speed measurement instruments, and parameters of fuel conservation performance. A summary of the results of this study are listed below.  
A 1-DOF dynamic tractor simulation model and a fuel consumption prediction map were developed and verified using measured field operation data. Using the simulation model, the mean errors of the simulated engine speed and input shaft torque were 2.03% and 4.87%, respectively, compared with those obtained from the field experiment. It means that 1-DOF dynamic tractor simulation model can predict fuel consumption and work performance and also can be used for model-based controller design methodology.  
Desired engine speed determination algorithm was developed based on workload applied to engine using look-up table method. Fuel consumption prediction map was used to determining the most efficient point of engine speed at measured workload torque. Simple continuous optimal operating line for maximizing fuel efficiency was developed and applied to engine speed control algorithm.  
The parameter gains of the PI controller were tuned using the simulation model by [PERSON] and [PERSON] gain tuning methods, and the applicability of the controller was verified with the tractor model and controller using the measured field experiment data. Main objective of gain tuning is minimizing the engine speed overshooting. After simulation, the average percentage errors and standard deviation between simulated and measured engine speed values were 2.03% and 1.37%. For input shaft torque, the average percentage error and standard deviation were 4.87% and 3.95%, respectively.  
A measuring system was constructed and used for collecting the input shaft torque, fuel consumption, and engine speed data from plowing operations. Hollow type slip ring and strain gage were installed to input shaft of transmission for measuring input shaft torque and engine speed. In order to measure fuel consumption two flow rate sensors were used for inlet flow and drain flow of the fuel supply system.  
Figure 23: Engine operating region of plowing operations.  
The mechanical governor in the experimental tractor was converted into an electrical governor using simple servo motor and throttle potentiometer in order to control the throttle and engine speed control system. This was conducted to maximize the fuel efficiency.  
By plowing field test data, with the engine speed control system in plowing operations can improve FC, FCA, and SVFC about 23.03-57.87%, 4.11-42.06%, and -7.24-38.48%, respectively, over those without using the control system.  
The results of this study can be applied to the development of an optimal engine control algorithm to maximize the fuel efficiency of tractors depending on the workload of different tractor field operations.  
Conceptualization, J.W.L.; methodology, J.W.L. and Y.-J.P.; software, J.W.L.; validation, S.C.K. and J.O.; data curation, W.-J.C., H.-W.H. and J.-T.K.; supervision, Y.-J.P.; writing-original draft preparation, J.W.L.; writing-review & editing, Y.-J.P.  
The author(s) disclose receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Research Foundation of Korea (NRF) Grant funded by the Republic of Korea Government (MOE) (2010-0023058).  
The authors declare no conflict of interest.