*3.2. Longitudinal Rod-Teeth-Type Threshing Drum*

In order to enhance the threshing performance of the threshing device, a longitudinal rod-teeth-type threshing drum was designed (shown in Figure 4), mainly consisting of a top cover, guide plate, spoke disc, feeding section auger, front end cap, main axle, mounting tube, rod teeth, concave sieve, bearing block, rear end cap, etc. The threshing roller is divided into the feeding section, threshing section and grass-discharging section. The total length of the threshing section was 1550 mm, the length of the feeding section was about four-fifths of the total length of the threshing section [17], that is, 315 mm, the length of grass-discharging section was 148 mm, the top cover above the roller and the concave sieve formed a cylindrical threshing chamber and the inner wall of the top cover was equipped with spiral guide plates so that stems of Chinese milk vetch will move along the axis to the grass-discharging section in the joint action of threshing rod teeth and guide plates.

**Figure 4.** Schematic diagram of the longitudinal rod-teeth-type threshing device: (1) top cover; (2) deflector; (3) spoke disc; (4) auger of feeding section; (5) front end cap; (6) main axle; (7) mounting tube; (8) rod teeth; (9) concave sieve; (10) bearing block; (11) rear end cap.

The number of rod teeth on the roller is determined by the productivity of the threshing device [18],

$$z \ge (1 - \beta)q / 0.6q\_d \tag{1}$$

where, *z* is the number of teeth on the roller; *q* is the feed quantity of the thresher, set to 5 kg/s; *β* refers to the weight proportion of crop pods in the feed materials, with the black pod harvest of Chinese milk vetch being 0.4; and *qd* is the threshing ability of each rod tooth (threshing ability is 0.025 kg·s−<sup>1</sup> for the combine harvester). In Equation (1), in the case *<sup>β</sup>* = 0.4, *<sup>q</sup>* = 5 kg·s−<sup>1</sup> and *qd* = 0.025 kg·s<sup>−</sup>1, the number of teeth on the roller is *<sup>z</sup>* ≥ 200. In order to improve the threshing performance, the teeth rows *C*<sup>1</sup> and *C*<sup>2</sup> with different rod-tooth spacing were installed alternately along the circumference of the drum, with the specific parameters designed as follows: rod-tooth spacing of teeth row *C*1, *d*<sup>1</sup> was 30 mm; rod-tooth spacing of teeth row *C*2, *d*<sup>2</sup> was 60 mm; working height of rod teeth, *l,* was 67 mm; diameter of rod teeth, *d,* was 10 mm. Through arrangement calculation, under the condition of ensuring the reliable working state of the threshing drum, the rod-teeth number of teeth row *C*<sup>1</sup> was 53, the rod-teeth number of teeth row *C*<sup>2</sup> was 27 and the total number of rod teeth on the roller was 240, which meets the productivity requirements of the Chinese milk vetch threshing device.

#### *3.3. Air-Sieve-Type Layered Impurity-Controlled Cleaning Device*

The cleaning structure of the Chinese milk vetch seed combine harvester was designed as an air-sieve-type layered impurity-controlled cleaning device. The structure diagram is shown in Figure 5. It is mainly composed of the centrifugal fan and the layered impuritycontrolled cleaning sieve. In the air-sieve cleaning devices of the existing rice or wheat combine harvesters, most of the fans are single-channel centrifugal fans; when the structure and operation parameters are determined, the velocity and direction of air flow produced by single air-duct centrifugal fans cannot meet the different demands of the whole sieve in the process of material screening [19,20]. Referring to the structure characteristics of multiair-duct centrifugal fans both at home and abroad, the number of blades of the centrifugal fan in the cleaning unit of Chinese milk vetch green manure seed combine harvester was designed as three blades, and the impeller diameter was 385 mm. Two adjustable inclined air flow dampers were installed at the air outlet of the fan, forming the upper, middle and lower air ducts, which can meet the cleaning requirements of the front, middle and rear of the layered impurity-controlled cleaning sieve.

**Figure 5.** Three-dimensional and internal structure diagram of the air–sieve-type cleaning device: (1) centrifugal fan; (2) layered impurity-controlled sieve. (**a**) Three-dimensional diagram of the air–sieve-type cleaning device. (**b**) Internal structure diagram of the air–sieve-type cleaning device.
