2.4.3. Steering Performance Analysis
When the two tracks perform differential movement driven by the gearbox, one track is braked, resulting in a zero linear speed, and steering is completed relying on the drive of the other track [
12]. The turning radius is related to the track gauge and track width. The steering of the track is directed from the side with a non-zero speed to the side with a zero speed. The radius r of the inner track’s turn is related to the track support surface length L1 through a trigonometric function relationship. R is the turning radius of the entire machine. The schematic diagram of the machine’s differential steering is shown in
Figure 5.
Without considering the external sliding and skidding of the tracked chassis, the trigonometric formula for calculating the turning radius of the entire machine is as follows:
In the formula, B—the track gauge, taken as 2.9 m; b—the track width, taken as 0.35 m; L1—the length of the track support surface, taken as 2.4 m; R—the turning radius of the entire machine.
When the machine makes a stationary turn, the outer track rotates around the inner track, with the inner track’s linear speed being zero. The minimum turning radius of the entire machine, calculated using Formula (2), is 3.8 m.
2.4.4. Engine Calculation and Selection
The selection of the engine is based on the maximum power consumption. Among the various operations, the soil clearing operation is the most power-intensive as it involves earthwork, making it the basis for calculating the overall machine power. During the soil clearing process, the soil must first be loosened and thrown out through a mechanical rotary tilling action, followed by the use of plow blades to excavate the loosened soil and deposit it on both sides of the grapevines. Hence, the machine’s operating power
PS is the sum of the power consumption for soil clearing
Pq and the power required for walking on the maximum slope
Pz. The actual power transmitted by the engine to the output shaft
PA is the ratio of the machine’s operating power
PS to the transmission efficiency
η. The calculation formula is as follows:
In the formula, PA—the actual power transmitted by the engine to the output shaft; PS—the machine’s operating power; Pq—the power consumed by clearing soil; Pz—the required power when walking on the maximum slope; η—transmission efficiency of the track-mounted chassis, η = 0.87.
Power Requirements for Soil Clearing Operations: The gantry track-mounted self-propelled multifunctional operations platform is a dual-sided operational device. According to the “Agricultural Machinery Design Manual”, the power consumption for soil excavation by the dual-sided soil clearing machine’s plow blade is calculated as follows:
In the formula, Pl—power consumption for soil excavation by the plow blade of the soil clearing machine; Px—power consumption of the rotary thrower; n-Number of supporting plows, n = 1, ηT—utilization factor of drawbar pull, ηT = 0.9; a-Design tillage depth, a = 0.25; b-Single plow width, b = 0.5; K-Ploughing specific resistance of soil, K = 35 kpa; umin-Minimum operating speed, umin = 1 km/h; F-force exerted by the thrower on the soil.
Based on measurements, the rotary thrower of the soil-clearing machine has a diameter of 60 cm (radius 30 cm) and a rotational speed of 286 r/min. The soil bulk density in the vineyard is 1.3 g/cm³, with a soil moisture content of 23%, resulting in a unit thrower mass of 21.6 kg and a thrower linear speed of 8.88 m/s. According to the above Formula (4), the force exerted by the thrower on the soil is F = 5835.84 N. The power consumption for soil excavation by the plow blade is Pl = 10KW, and the power required for the rotary thrower is Px = 105 KW, resulting in a total power consumption for soil clearing of Pq = 115 KW.
Power Requirements for Field Transfer: Based on the machine’s full-load speed characteristics, when the maximum slope is 15%, the maximum power required for the machine’s operation is the sum of the power consumption due to rolling resistance on flat ground, air resistance, and maximum slope rolling resistance. The calculation formula is as follows:
In the formula, Pz—the maximum power required for the whole machine operation; Pf—the rolling resistance of the whole machine on flat ground consumes power; Pw—air resistance horsepower; Pi—the maximum climbing rolling resistance consumes power; u—the maximum speed of the whole machine, u = 4 km/h; m—the quality of the whole machine; the quality of the whole machine using SolidWorks quality evaluation module to calculate the quality of the whole machine is about 4500 kg; g—gravity acceleration, g = 9.8 m/s2; f—coefficient of rolling resistance, f = 0.02; Cd—coefficient of air resistance, Cd = 0.9; A—the forward windward area of the whole machine, A = 3.6 m2; α—maximum climbing degree, take 15%, about 8°.
According to the above Formula (5), the power consumption due to rolling resistance on flat ground is Pf = 0.98 KW, air resistance power consumption is Pw = 0.002 KW, and maximum slope rolling resistance power consumption is Pi = 7.35 KW, resulting in a total maximum power requirement for operation Pz = 8.4 KW.
In summary, based on the calculation Formulas (3)–(5), the power required by the machine
PA = 123.4 KW. The actual power transmitted by the engine to the output shaft is calculated to be 141 kW, equivalent to approximately 189 horsepower. To ensure a power reserve, the selected engine power should be slightly greater than the calculated requirement [
13,
14]. Therefore, a Yuchai YCS06200-62 type inline six-cylinder water-cooled diesel engine with 200 horsepower, a maximum torque of 750 N·m, a rated speed of 2100 rpm, and a displacement of 6.2 L was selected. According to the “Handbook of Mechanical Design” [
15]., the corresponding hydraulic pump provides a pressure of approximately 18 MPa.
2.4.5. Selection and Calculation of the Transmission
Due to the compact space layout of the overall power system located at the rear upper part of the multifunctional operation platform, it is necessary to select and calculate the transmission. First, the transmission ratio range must be determined, typically defined by the ratio of the highest gear to the lowest gear. The highest gear is generally the direct gear, with the transfer case input transmission ratio assumed to be 1. At the lowest speed, the transmission ratio is maximum, calculated as follows:
In the formula, umax—the maximum speed of the whole machine; r—the driving wheel pitch circle radius; n—rated engine speed; ig—the transmission ratio of the transfer case; imin—the minimum transmission ratio of the gearbox.
Based on the design of the gantry crawler self-propelled multifunctional grape operation platform, the maximum driving speed should not be less than 4 km/h, with the engine’s rated speed at 2100 r/min, the drive wheel pitch circle radius at 0.12 m, and the transfer case transmission ratio at 1. From the above Formula (6), the lowest gear transmission ratio of the transmission is
imin = 10.6, while the highest gear transmission ratio, which is the transfer case transmission ratio, is
ig = 1, meaning the input speed is directly transferred to the drive shaft. To improve the overall power characteristics and fuel economy and to ensure smoother power transitions, the number of gears selected should be ≥6. The calculation formula for the transmission ratios of each gear is:
Using the Formula (7), the transmission ratios for each gear are shown in
Table 2.
In summary, the theoretical calculation for the lowest gear transmission ratio of the gantry crawler self-propelled multifunctional grape operation platform is 5.7, with the highest gear transmission ratio being 1 and the number of gears being 6. In actual selection, the highest gear transmission ratio is greater than the theoretical calculation. The Fast C6J76TA manual transmission is selected, with the lowest gear transmission ratio at 5.7, the highest gear transmission ratio at 0.8, and the number of gears at 6, with a maximum input torque of 760 N·m, meeting the operational requirements.