Development of a hydraulic variable-diameter threshing drum control system for combine harvester part I: Adaptive monitoring method

Traditional cereal combine harvesters cannot adjust the threshing gap according to the change of feeding rate, leading to large threshing losses. Previous research has developed a hydraulic variable-diameter threshing drum, which adjusts the threshing gap by changing the drum diameter. However, the oil pressure within and without the rod cavity of the hollow hydraulic cylinder for the threshing drum is affected by both the feeding rate and threshing gap in these systems. The correlation model between the independent variables (feeding rate and threshing gap) and the response values (threshing performance and oil pressure) has not yet been studied. Therefore, in this study, the relationship between the independent variables and the response values is studied by using the test method of central composite rotatable design (CCRD). The results showed that under the optimal threshing gap corresponding to different feeding rates, the threshold of oil pressure change within rod cavity was approximately 0.64–0.78 MPa, with a variation of <0.14 MPa. Therefore, an adaptive monitoring method based on constant oil pressure is proposed, which could keep the oil pressure within the rod cavity in the threshold range by adjusting the threshing gap. This minimised the entrainment loss rate under different feeding rates.