# Engine Speed Control System for Improving the Fuel Efficiency of Agricultural Tractors for
## 5 Control System Verification
### Fuel-Saving Performance  
In this study, three fuel efficiency parameters were used to evaluate the fuel conservation performance of the system. FCA and SVFC, were calculated from FC using Equations (11) and (12), respectively [13]. \[\mathrm{FCA}=\frac{10\times\mathrm{FC}}{3.6\times v_{a}\times w_{i}} \tag{11}\]  
\[\mathrm{SVFC}=\frac{60000\times\mathrm{FC}}{2\pi\times T_{e}\times N_{e}} \tag{12}\]  
where FCA is fuel consumption per tilled area in L ha\({}^{-1}\); FC is fuel consumption per work hour in L h\({}^{-1}\); SVFC is specific volumetric fuel consumption in L(kWh)\({}^{-1}\); \(w_{i}\) is working width in m.  
Figure 21: Measured and filtered input shaft torque during following operation using the control system. Figure 22: Throttle command of the engine speed controller. For evaluating fuel-saving performance, the fuel efficiency parameters were analyzed through operation with and without the control system. The fuel conservation performance evaluation results are presented as percentage differences between scenarios with and without the system. The results of the fuel efficiency parameters from field experiments with and without the control system are shown in Table 5. A gear step was used from L-4 to M-3 to adjust the operating speed from 2.70 to 6.94 km/h at the rated engine speed. With the control system, FC was reduced from 23.03 to 57.87%, and FCA was reduced from 4.11 to 42.06%. SVFC was reduced from 15.73 to 38.48% in almost all gear steps, but two cases showed increases of 0.66 to 7.24% when the control system was not used. As a result, this system was considered to be more effective at reducing FC. This was attributable to the tendency of the engine speed to be more easily adjusted by the FC than FCA and SVFC [13]. Almost every desired engine speed for the measured input shaft torque corresponded to the maximum torque output speed. The maximum torque output speed was approximately half of the rated engine speed, which was 1300-1400 RPM in this study. Accordingly, a reduction in the operation speed cannot be avoided. In addition, reduction in the work speed also leads to a reduction in tractive resistance and tractive power. Therefore, reduced work speed and tractive power led to lower FCA and SVFC reduction rates than FC, and even increases of SVFC were observed in two cases. As each set of fuel efficiency performance data were obtained under different driving habits, the range of results were significantly widened. The engine operating region during the flowing operations is presented as a set of measured input shaft torques in Figure 23.  
With the control system, the engine operating region was distributed around the optimum operating curve from the desired engine speed determination algorithm. Without the control system, the operating region was more widely distributed. As a result, the engine operating region was maintained under 70% of the rated speed. Consequently, the reduced engine speed attributable to the control system led to improved fuel efficiency. Overall, the developed engine speed control system can be considered an effective system for improving fuel efficiency. Although some experiment results showed less efficiency for reducing SVFC, it could be concluded that the control system may be effective approach towards reducing FC, FCA, and SVFC for common drivers. This system could be useful for developing an integrated control system for engines, automatic transmissions, and instruments for agricultural tractors. Nevertheless, additional research into the development of integrated control systems for tractors with automatic transmission are still required.