Abstract
Analysis of rotary tillage process is important for the design of rotary tillers and tractors. As the tillage resistance has complicated characteristics which is related to the soil condition, blade shapes and other reasons, some part of it has not been well understood. The authors selected a Japanese C-shaped blade to study its torque characteristics, particularly from the view point of design technology. Main results are as follows:
1. The torque curve of a C-shaped blade is highly dependent on its boundary condition, which is equivalent to the shape of the upper surface of the soil slice, and is determined by the relative positions of neighbouring rotary blades. Generally the boundary conditions are classified practically into six patterns as shown in Fig. 4.
2. Special attention should be placed on hard soil from the view point of design technology. In the case of hard soil, a quadrilateral model in Fig. 12 might be used to represent torque courves of C-shaped blades.
3. The model is expressed by the maximum torque Tm, the rotational angle θA and θC and the point C′ for the hard soil (cf. Fig. 12).
4. Maximum torque Tm (kg·m) could be expressed by the multiple regression funtions of pa and S as follows:
Tm={2.17pa+0.226S (for pattern I to V) 2.17pa+0.226S+7.1 (for pattern VI)
where, pa=actual tilling pitch (cutting length of straight blade portion cf. Fig. 4)
S=upper surface area of soil slice
5. The angle θA is generally expressed by a linear equation of pa. The equation for the test blade was as follows:
θA=0.32pa+22(deg)
6. The angle θC is approximately 85 degrees for a blade situated at both right and left ends and 62 degrees for the blade situated in the inside positions on a rotary axle.
7. Using location coefficients k1 and k2, the location of the point C′ is expressed by k2Tm and k1θC. The mean values of k1 and k2 were 0.37 and 0.46 respectively.
8. Soil-bin tests showed that the quadrilateral model is effective to estimate a total torque curve of multiple blades on a rotary axle.
