*2.3. Design of Critical Components of the DCH* 2.3.1. Reel

A reel is installed at the front of the DCH, which picks up and conveys wheat stalks into the cutting device. In this process, the reel also supports the wheat stalks being cut. The reel can help the cutting device fulfill the cutting operation while pushing harvested wheat stalks into the screw conveyor to avoid cut stalks piling up at the front of the header. As a cam-action reel exerts a strong stalk-lifting force and has a small impact on cropped ear-heads, they are primarily used in rice and WCHs. The structure consists of central spoke wheels, a central rotatable shaft, tine bars, tines, an eccentric spoke wheel, and cranks, as shown in Figure 6. The eccentric spoke wheel, cranks, and central spoke wheel constitute a parallel four-bar linkage mechanism that allows the tines to maintain a well-adjusted dip angle. The diameter of the reel *D*<sup>1</sup> is 1000 mm, and the eccentricity of an eccentric spoke wheel and central spoke wheel *e*<sup>1</sup> is 72 mm.

**Figure 6.** Structural diagram of a cam-action reel. 1. Central spoke wheels; 2. Central rotatable shaft; 3. Tine bar; 4. Tine; 5. Crank; 6. Eccentric spoke wheel.

#### 2.3.2. Screw Conveyor

The structure of the screw conveyor is composed of a cylinder welded with left- and right-handed spiral blades and retractable fingers (Figure 7). The retractable fingers are installed at the screw cylinder, and 16 retractable fingers (with four retractable fingers in each group) are hinged abreast on the retractable finger shaft. The retractable fingers are riveted to a crank and a fixed shaft. The eccentric distance between the center of the retractable fingers and the screw cylinder is *e*2. To avoid the winding of wheat stalks, the perimeter of the screw cylinder must be larger than the length of wheat stalks that have entered the DCH [29]. Generally, the diameter *D*<sup>2</sup> of the screw cylinder is 300 mm. To improve the conveying performance of the spiral conveyor on short wheat stalks, the outer diameter of the spiral blades *D*<sup>3</sup> is 500 mm, and the screw pitch *S* is 460 mm.

The screw cylinder, when rotating, drives the retractable fingers to also rotate. As the screw cylinder and retractable fingers are not concentric, the retractable fingers undergo telescopic motion relative to the screw cylinder surface. When the retractable fingers turn back, they should retract into the screw cylinder, but their protrusion of 10 mm remaining outside the screw cylinder should be ensured to avoid the wear-out of the ends of the retractable fingers. When the retractable fingers turn forward, they should stretch to 40–50 mm outside the spiral blades within the screw cylinder in a bid to ensure their clamping capability [30]. Thus, we obtain,

$$c\_2 = \frac{D\_3 - D\_2}{4} + (15 \sim 20) \tag{2}$$

$$L = \frac{D\_2}{2} + 10 + \epsilon\_2\tag{3}$$

where *e*<sup>2</sup> is set to 70 mm and the length of retractable fingers *L* is 280 mm.

**Figure 7.** Structural diagram of a screw conveyor. (**a**) Overall structure; (**b**) Schematic diagram of retractable fingers. 1. Fixed central axis; 2. Screw cylinder; 3. Spiral blade; 4. Crank; 5. Sleeve; 6. Finger seat; 7. Finger; 8. Finger shaft; 9. Conveyor driving shaft.

#### 2.3.3. Parameters of the Header Triangle

The triangle of the header refers to a particular space composed of three main working parts: a reel, a cutterbar, and a screw conveyor, as shown in Figure 8. Compared with the conventional header, the wheat stalks cut and transported by the DCH are short in length. The triangle is too large, so the crops quickly accumulate between the cutter and the screw conveyor. When the crop is stacked to a certain amount, it will be grabbed by the blades of the screw conveyor, resulting in uneven transportation, feeding, and even blocking; if the triangle area is too small, the harvest loss will increase. The vertical distance *H*<sup>1</sup> between the central rotatable shaft of the reel and the upper cutterbar, the horizontal distance *L*<sup>4</sup> between the screw conveyor center and the upper cutterbar beam, and the forward displacement *b* of the central rotatable shaft (taking the central rotatable shaft directly above the upper cutterbar as the central position) affect the size of the triangle. *L*<sup>4</sup> is usually 350–500 mm. We selected *L*<sup>4</sup> as 450 mm. To make the reel tine shaft have a backward horizontal speed above the cutter, the maximum forward displacement of the reel main shaft *b*max is [30]:

$$b\_{\text{max}} = \frac{D\_1}{2\lambda\sqrt{\lambda^2 - 1}}\tag{4}$$

In Formula (4), *λ* is the ratio of the circumferential speed of the reel to the operating speed of the combine harvester, which is generally 1.5–1.7 [30]. Taking *λ* as 1.5, the *bmax* is 298 mm. The reel can move back correctly to increase its ability to push the stalk, but the distance from the screw conveyor when the reel is adjusted to the final position *δ*<sup>1</sup> should be greater than 25 mm.

**Figure 8.** Diagrammatic sketch of a header triangle. 1. Reel; 2. Screw conveyor; 3. Header triangle; 4. Cutterbar.

Combined with the best straw feed length determined by the bench test, the minimum height of *H*<sup>1</sup> is 753 mm, calculated according to Formula (5) [30].

$$H\_1 \ge \frac{D\_1}{2} + \frac{2(L\_1 - L\_3 - h)}{3} = \frac{D\_1}{2} + \frac{2L\_2}{3} \tag{5}$$

#### 2.3.4. Profiling Mechanism of the Lower Cutterbar

As shown in Figure 1, the support arm, height-limiting connecting rod, swing block, and ground wheels of the profiling mechanism for the lower cutterbar constitute the swing block of the crank. When harvesting, the greater the distance between the upper cutterbar and the ground of the wheat field, the larger the length of the height-limiting connecting rod. However, due to the influences of the DCH's structure and transmission system, the height-limiting connecting rod should be a suitable length.

Statistics indicate that the average plant height of the main wheat varieties in Henan Province, China, is 775 mm. The maximum distance between the ground and upper cutterbar is preliminarily determined to be 400 mm to meet the optimum feed length of stalks. Meanwhile, the lower cutterbar can fluctuate by up to 50 mm with the ground height. The *L*BA was determined using ADAMS software to simulate and study two processes: (1) the motions of the components with the DCH descending and (2) their motions with a change in ground height during harvest. Create a ground with 50 mm bumps and depressions using 3D software, assemble it with a simplified model of the DCH according to actual working conditions, import the model into ADAMS software, merge the upper cutterbars, header frame, and inclined conveyor frame, merge the lower cutterbars and fixed beam, and add motion constraints to the moving parts. During the simulation of header descent, the motion constraints are shown in Table 2. Establish a height sensor between the upper cutterbars and the ground to stop the header from descending after the upper cutterbars reach the set height. The simulation model is shown in Figure 9. During the harvesting simulation, adjust the model to make the ground wheel contact the ground; change constraint 1 in Table 2 to a translational joint; and add a driver to achieve the DCH movement.


**Figure 9.** Simulation model.

#### 2.3.5. Transmission System

The transmission system of DCH is shown in Figure 10. The power of the engine is transmitted to the DCH through the belt and chain drive. Then the driving shaft of the DCH can transfer power through the belt drive transmission to the wobble box of the upper cutterbars. The wobble boxes of the upper and lower cutterbars can transfer power through the belt drive transmission to power both the upper and lower movable cutters. Meanwhile, the driving shaft of the DCH drives the rotation of the screw conveyor by way of a chain drive transmission. The transmission occurs between the driving shaft and the reel to drive the rotation of the reel through the chain and belt drive transmission. The transmission ratio is shown in Table 3.

**Figure 10.** Schematic diagram of the DCH transmission system. 1. Wobble box of the lower cutterbars; 2. Reel; 3. Intermediate shaft of the reel; 4. Screw conveyor; 5. Driving shaft; 6. Wobble box of the upper cutterbars.

**Table 3.** Transmission ratio of the DCH.


*2.4. Field Experiment*

2.4.1. Experimental Arrangement

On 30 May 2022, Xinjiang-9B type WCHs equipped with the newly designed DCH and conventional header were subjected to in-situ operating tests in Xingyang, Henan Province, China. Field surveys were made according to the requirements of relevant standards. The wheat cultivar was Zhoumai 32, with an average plant height of 743 mm and a grain moisture content of 14.5%. The ratio of stalk to grain was 1.18, and testing conditions met the requirements [31]. The suitable field plot should satisfy the criteria, including that the measured zone should be 50 m long, there must be a stable zone 20 m in front of the measured zone, and a harvester parking site no less than 15 m behind the measured zone; the stubble height is 100 to 120 mm [32]. In the experiment, the combine harvesters worked along the lengthwise direction of field plots at a speed of 5 km/h.

#### 2.4.2. Data Collection and Processing

A1m<sup>2</sup> sampling zone was selected in the representative zone along the advancing direction of the combine harvesters at each sampling site. In the sampling zones, all grains and ear-heads were collected; thereafter, once threshed and cleaned, they were weighed. Based on Equations (6) and (7), the harvesting loss rates were calculated, respectively, and then the average value of the harvest loss rates in the five sampling zones was determined [33].

$$F\_{\circ} = \frac{W\_{sh} - W\_z}{W\_{ch}} \times 100\tag{6}$$

$$F = \frac{\sum F\_{\text{j}}}{5} \tag{7}$$

where *Fj* is the loss rate of the sampling point, %; *Wsh* is the mass of grain loss per square meter, g/m2; *Wz* is the mass of grains naturally falling per square meter, g/m2; *Wch* is the mass of grain per square meter, g/m2; and *F* is the average harvest loss rate, %.

The stubble height was measured using the five-point sampling method applied in the experimental field. The stubble heights of three subpoints were determined by measuring at the left, middle, and right sides of the horizontal direction of the harvesting range in each point. The average value of the three subpoints was taken as the stubble height at that point, taking the mean average value of the five points.

Before each experiment, the same amount of diesel oil was added to the fuel tank. After completing the test, the diesel oil remaining in the fuel tank was discharged and weighed. According to Equation (8), the fuel consumption per unit area *Q* could be calculated. Two groups of tests were repeated three times before taking the mean average value.

$$Q = 10,000 \times \frac{q\_1 - q\_2}{B \times L\_4} \tag{8}$$

In the formula, *q*<sup>1</sup> is the weight of fuel in the fuel tank before a test, kg; *q*<sup>2</sup> is the weight of fuel in the fuel tank at the end of a test, kg; *B* is the cutting width of the WCH, m; and *L*<sup>4</sup> is the length of the measured zone, m.
