Investigation of the Traveling Performance of the Tracked Chassis of a Potato Combine Harvester in Hilly and Mountainous Areas

Abstract

Aiming at the problems of poor passability of a tracked chassis due to small plots, complicated road conditions and steep slopes during mechanized potato harvesting in hilly and mountainous areas. To design a potato combine harvester and take the tracked chassis of the harvester as the research object to study its driving performance under typical road conditions in mountainous areas. Firstly, mechanical analysis and theoretical calculation are carried out on the tracked chassis to obtain the relevant parameters of key components, and secondly, its driving performance is analyzed to obtain the driving limit values of passing performance under different working conditions; RecurDyn software was used to establish the dynamics simulation and analysis model of the whole machine, and the driving limit values of the harvester were determined under five different road conditions through simulation. The results show the following: the driving limit gradient angle is 20° in cross-gradient conditions, 25° in longitudinal up-gradient conditions, 25° in longitudinal down-gradient conditions, the limiting height of the chassis that can be overpassed in obstacle-crossing conditions is 450 mm, and the limiting width of the chassis that can be spanned in trench-crossing conditions is 1200 mm. The simulation results were verified through field tests, and the results of the field tests showed that the harvester met the requirements of stable travelling on longitudinal slopes of 24°, climbed over a 450 mm straight wall and crossed over a 1200 mm trench, which were similar to the simulation results, indicating that the simulation results were accurate and feasible, and met the design requirements for the travelling passage of the crawler potato harvester. This study provides an in-depth understanding of the tracked chassis of the potato combine harvester in hilly mountainous areas, with a view to providing reference for the design of tracked harvesters for other crops in hilly mountainous areas.

1. Introduction

Widely grown in more than 150 countries and regions of the world, the potato is the fourth largest food crop [1,2]. In recent years, China’s potato planting area and total output are located among the world’s first [3]; hilly and mountainous areas are the main terrain of potato cultivation in China [4,5,6]. The terrain has complex road conditions, a low level of mechanization, irregular plot shapes, large slopes, uneven soil quality, and difficulties in steering for mechanized operations [7], which seriously limit the development and application of potato harvesters in the region. At present, there is a lack of a potato combine harvester suitable for hilly and mountainous areas at home and abroad [8,9], and the research and development of a potato combine harvester suitable for hilly and mountainous areas with complex terrain is the urgent demand of local farmers.

Scholars at home and abroad have conducted a lot of research on potato combine harvesters and made some progress. The United States [10], Germany, Belgium, and other developed countries have realized potato integrated joint harvesting, but mostly for the open terrain of the medium and large potato harvester [11], the size of the machine size is large, it is difficult to apply to the hilly and mountainous terrain potato harvesting, and cannot meet the harvesting requirements of the region. China’s level of research, development, and design of small- and medium-sized potato combine harvesting machinery suitable for hilly and mountainous areas is constantly rising. The chassis can be divided into tracked, wheeled, footed, and composite according to the moving mode [12], among which the tracked type has the characteristics of compact structure, strong carrying capacity, etc., which can effectively cope with problems such as the wet soil, sticky and heavy in this terrain, and the complicated and changeable road conditions, which lead to the poor passing performance of the tracked chassis and the difficulty for harvesting machinery to pass through. There is also a lot of research on the tracked chassis in China, such as the omnidirectional position-adjusting tracked chassis for agricultural machinery designed by Lv Fengyu [13], etc.; tracked self-propelled panax pseudoginseng combine harvester developed by Zhang Zhaoguo [14], etc.; tracked self-propelled ginger harvester designed by Wang Ning [15], etc.; and triangular-tracked small-scale maize harvester in hilly and mountainous areas researched and developed by Xiang Wang [16]. In the potato combine harvester chassis research, such as that of Zhao Mingwei [17], Wei Zhongcai [18], Liu Fengshun [19], and Yu Zhenzhen [20], etc., innovations and improvements have been made, but the technology is relatively weak, and the overall situation is one of no machine available and no good machine.

Based on the unique topography of hilly and mountainous areas in China, this study addresses the problems of the existing potato harvester, such as large size, poor passability in complex terrain, and difficulty in applying to hilly and mountainous terrain. Developing a self-propelled potato combine harvester suitable for hilly mountainous areas requires adopting the tracked chassis, focusing on the passing performance of the chassis under typical road conditions in mountainous areas, and evaluating its travelling stability and passing performance under typical road conditions, with a view to providing theoretical bases and references for the design of potato harvesters in hilly mountainous areas.

2. Structure and Working Principle of the Machine

2.1. Structure and Main Technical Parameters of the Machine

Based on the agronomic mode of potato planting in hilly and mountainous areas, a self-propelled potato combine harvester was designed, with the structure of the whole machine shown in Figure 1, which mainly consists of a frame, crawler chassis, digging device, first-class conveying device, second-class sorting and conveying device, and potato collection platform, etc., and it can complete the tasks of digging, conveying, cleaning, and collecting potatoes at one time [21].

According to the agronomic requirements of potato cultivation in hilly and mountainous areas and the norms of mechanized harvesting, Structural calculations of machines in accordance with relevant national standards and local norms to make it clear that the structural dimensions of the whole machine are 5670 mm × 2040 mm × 1800 mm [22], and the design width of the working width is 1200 mm to meet the potato harvesting requirements of planting in different ridge spacings. Potato harvesting requirements, digging shovel digging depth between approximately 150 and 300 mm, the main technical parameters of the machine are shown in

Table 1. Main technical parameters of operating machine.

Parameters	Numerical Values
Machine length × width × height	5670 × 2040 × 1800 (mm)
Engine power	54 kw
Working width	1500 mm
Overall quality	3100 kg
Digging depth (adjustable)	200~300 mm
Suspension mode	Three-point suspension

.

2.2. Working Principle

Upon starting the harvester, the diesel engine provides power to the tracked chassis. The mechanical transmission system, which includes chain drives and a gearbox for speed reduction and torque increase, manages power distribution. The engine’s power output shaft has a rated speed of 720 rpm. The transmission system transfers power to various working components, including the drive wheels of the propulsion system, the digging mechanism, the primary conveyor system, and the secondary sorting conveyor system. The power applied to the drive wheels propels the rubber tracks, enabling the movement of the harvester chassis. In the harvesting operation, the profiling depth-limiting wheel is a part at the front end of the harvester, used to control the working depth of the harvester on the ground, which can adjust the working depth according to the unevenness of the ground to ensure that the digging shovel and other parts work at the proper depth to avoid harming the root system of the crop or miss harvesting; the soil-cutting disc cuts through the soil and the seedling and vine weeds and reduces the impurities in the potato–soil mixture, the digging shovel enters into the soil and excavates the potatoes out of the soil to form a potato–soil mixture, the primary and secondary separation conveyor separates the soil and potatoes in the potato–soil mixture, and sorts the potatoes, and the workers stand on the manual picking platform to pick up and sort the potatoes into the potato collection channel to carry out the collection of potatoes [23].

3. Structural and Mechanical Analysis of Tracked Chassis

3.1. Chassis Structure and Main Parameters

The tracked chassis is mainly composed of the chassis frame, each wheel system, engine, radiator, gearbox, tracked wheelset, connecting mechanism and tensioning device, etc. It has three forward gears: high speed, medium speed, and low speed. The overall size of the tracked chassis is 1800 mm × 950 mm × 380 mm, its three-dimensional structure is shown in Figure 2, and the technical parameters are shown in

Table 2. Main technical parameters of tracked chassis.

Parameters	Numerical Values
Machine length × width × height	1800 × 950 × 380 (mm)
Overall quality	920 kg
Track width	230 mm
Track grounding length/mm	1600 mm
Ground clearance for tracks	250 mm
Track center distance	1190 mm
Drive wheel radius	150 mm
Guide wheel radius	115 mm
Radius of the supporting wheel	85 mm
Bracket wheel radius	70 mm

.

3.2. Mechanical Analysis of Chassis Wheel System

3.2.1. Driving Wheel

The drive wheels are powered by the engine output torque to achieve deceleration and torque increase and power shunt through the mechanical transmission system to provide flexible motion control for the chassis. The drive wheels are mounted on the crawler chassis frame, and bear the frame support force and engine driving force at the same time to ensure the stability and reliability of the vehicle in driving, and its force situation is shown in Figure 3.

Based on the force on the drive wheel, the relationship between the tension at the drive wheel and its torque can be derived:

$$T_{d2}-T_{d1}={\displaystyle \frac{M}{R_d}}$$

(1)

where

• T_d2 is the drive wheel tight side tension, (KN);
• T_d1 is the drive wheel loose edge tension, (KN);
• M is the drive wheel torque, (N·m);
• R_d is drive wheel radius, R_d = 0.15 m;

3.2.2. Guide Wheel

The guide wheel plays the role of positioning, supporting, guiding, distributing force, and reducing resistance in the tracked chassis to ensure the stability and reliability of walking, and its force analysis is shown in Figure 4.

According to Figure 4, the guide wheel is mounted on the tensioning device and is subjected to the support and preload forces applied to it by the tensioning device [24], and based on the forces, the following kinetic equations are derived for the tensioning force at the guide wheel:

$$\left\{\begin{array}{l}{m}_c\ddot{x_c}=F_{ct}+F_C\cos \gamma -T_{c2}-T_{c1}\cos \alpha \\ m_c\ddot{y_c}=G_c+F_C\sin \gamma -F_{cn}+T_{c1}\sin \alpha \\ J_c{\omega }_c=(T_{c1}-T_{c2})R_c\\ F_c=2\rho {\omega }_c^2{R}_c^2\mathit{cos}\gamma \end{array}\right.$$

(2)

where

• m_c is the guide wheel quality;
• F_ct is the pre-tensioning force on the track by the tensioning device;
• F_c is the guide pulley centrifugal force;
• γ is the angle between centrifugal force and horizontal line;
• T_c1, T_c2 is the tensioning force on the loose and tight edges of the guide wheel;
• θ is the front angle of tracked chassis;
• J_c is the guide wheel moment of inertia;
• R_c is the guide wheel radius, R_c = 115 mm;
• ω_c is the guide wheel angular velocity;
• ρ is the crawler unit mass.

3.2.3. Supporting Wheel

The role of the supporting wheel in the track chassis is to support the track system, which can absorb the unevenness and impact of the ground, play the role of vibration damping and buffering, and maintain the correct tension and stable operation of the track. The force analysis of the supporting wheel is shown in Figure 5.

The kinetic equations are as follows:

$$\left\{\begin{array}{c}{m}_1\ddot{x}=T_{L41}+f_{L4}-T_{L41}-F_{L4t}\\ m_1\ddot{y}=G_L+F_{L4n}-N_{L5}-N_{L4}\\ J_l{\omega }_{L5}=R_L·(T_{L41}+f_{L4}-T_{L42})\end{array}\right.$$

(3)

where

• m₁ is the support wheel mass;
• T_Li1, T_Li2 is the tension at the support wheel;
• R_L is the radius of the supporting wheel, R_L = 85 mm;
• J₁ is the moment of inertia of the supporting wheel;
• f_Li is the friction between the supporting wheel and the track;
• F_Lit, F_Lin is the support force in the x and y directions of the supporting wheel;
• ω_Li is the angular velocity of the supporting wheel.

3.3. Crawler Chassis Travelling Resistance Analysis

During travelling, the main resistance that the tracked chassis needs to overcome are slope resistance, steering resistance, soil deformation resistance, and resistance within the travelling device [25,26].

3.3.1. Slope Resistance

Slope resistance refers to the resistance along the longitudinal slope direction that the harvester is subjected to on the slope due to its self-weight during the longitudinal climbing process. When the harvester is travelling on the slope, its self-weight will make the vehicle subjected to a downward force in the longitudinal slope direction, which is directly proportional to the angle of the slope and the harvester’s own weight, so the larger the slope is, the larger the resistance will be, and the calculation formulas are as follows:

$$F_{r1}=mgsin\theta$$

(4)

where

• F_r1 is the gradient resistance, (KN);
• m is the overall quality, (m = 3100 kg);
• g is the gravitational acceleration, (m/s²);
• θ is the road gradient, (°).

3.3.2. Steering Resistance

Steering resistance can be specifically classified into three forms: friction resistance, soil crush and shear resistance, and scraping resistance, which are calculated as follows:

$$F_{r2}={\displaystyle \frac{1}{4}}\beta \mu G{\displaystyle \frac{L}{B}}$$

(5)

where

• F_r2 is the steering resistance, (KN);
• β is the additional drag coefficient when steering, (β = 1.15);
• μ is the friction factor between the track and ground;
• G is the potato harvester deadweight, (m = 3100 kg);
• B is the track center distance, (B = 1.19 m);
• L is the track grounding length, (L = 1.6 m).

3.3.3. Soil Deformation Resistance

Soil deformation resistance refers to the force of deformation of the soil in the contact area between the rubber track and the road surface due to extrusion of the soil by the action of the wheel load during the travelling of the tracked chassis of the harvester, which is calculated by the following formula:

$$F_{r3}={\omega }_1\mathit{mgcos}\theta$$

(6)

where

• ω₁ is the operational specific resistance, (ω₁ = 0.09);
• m is the overall quality, (m = 3100 kg);
• g is the gravitational acceleration, (m/s²);
• θ is the road gradient, (°).

3.3.4. Resistance within the Travelling Unit

The internal resistance of the travelling device when the tracked chassis is travelling mainly consists of the internal friction between the tracked wheelsets, the frictional resistance generated by the track plate engaging with the driving wheel, and the rolling resistance of the track plate.

(1) The friction of the drive wheel is calculated as:

$$F_{r41}=\left(F_A+F_B\right){\mu }_0{\displaystyle \frac{d_0}{D_0}}$$

(7)

• F_A, F_B is the counterforce on drive wheel bearings on both sides, (KN);
• μ₀ is the drive wheel pitch circle diameter, (m);
• d₀ is the drive wheel pin diameter, (m);
• μ₀ is the friction factor between the drive wheel pin and bushing, (μ₀ = 0.1).

(2) The frictional resistance of the guide wheel is calculated as:

$${\mathrm{F}}_{\mathrm{r}42}=2F_T{\mu }_1{\displaystyle \frac{d_1}{D_1}}$$

(8)

where

• F_T is the track loose edge tension, (KN);
• D₁ is the guide wheel outer diameter, ();
• d₁ is the guide wheel pin diameter, (m);
• μ₁ is the friction factor between the guide wheel pin and bushing, (μ₁ = 0.1).

(3) The frictional resistance of the supporting wheel includes the frictional resistance of the supporting wheel journal and the rolling resistance along the track plate, which is calculated by the formula:

$$F_{r43}={\displaystyle \frac{G_0}{D_P}}({\mu }_2{d}_2+2f)$$

(9)

where

• G₀ is the total gravity acting on the track, (KN);
• D_P is the outer diameter of the supporting wheel, (m);
• d₂ is the diameter of the support wheel pin, (m);
• f is the rolling resistance coefficient, (f = 0.03~0.05);
• μ₂ is the friction factor between the support wheel pin and sleeve, (μ₂ = 0.1).

(4) The frictional resistance between the track pins is calculated as:

$$F_{r44}=2{\displaystyle \frac{F_C{\mu }_3{d}_3\pi }{zt}}$$

(10)

where

• F_C is the track tension, (KN);
• μ₃ is the friction factor between the pin and hole;
• d₃ is the track pin diameter, (m);
• z is the number of drive wheel teeth;
• t is the track pitch, (m).

Some minor internal resistance and air resistance are ignored in the calculation, so the internal resistance F_r4 of the travelling device mainly consists of the above four kinds of resistance:

$$F_{r4}=F_{r41}+F_{r42}+F_{r43}+F_{r44}$$

(11)

The total resistance $F_R$ experienced by the tracked chassis during travelling is:

$$F_R=F_{r1}+F_{r2}+F_{r3}+F_{r4}$$

(12)

The calculation of the above driving resistance was carried out to obtain the total resistance under different driving conditions during chassis driving as shown in

Table 3. Resistance values under different driving conditions (unit: KN).

Driving Conditions	Fr1	Fr2	Fr3	Fr4	FR
Straight-line driving on level ground	0	0	14.31	1.61	15.92
Climbing and driving in a straight line	10.36	0	14.31	1.61	26.28
Steering on level ground	0	12.91	14.31	1.61	28.83
Climbing and steering	10.36	12.91	14.31	1.61	39.19

, where climbing driving ($\theta$ = 15°), level steering ($R$ = B/2), climbing steering ($\theta$ = 15°, $R$ = B/2).

4. Crawler Chassis Drivability Analysis

Operating a potato harvester in the hilly and mountainous driving terrain is complex and variable; the requirements of the machine must have strong driving performance, high climbing ability and obstacle passing performance; in order to cope with the situation of steep slopes and uneven ground, based on these requirements, the driving performance of the typical hilly and mountainous road conditions to carry out analyses and calculations [27,28,29].

4.1. Cross-Slope Travelling Stability Analysis and Passability Calculation

In cross-slope travelling, the forces on the whole machine during cross-slope travelling are its own gravity, slope support, ground friction, and track adhesion. Lateral stability can be assessed by the ultimate tipping angle and lateral slip angle to ensure that the vehicle will not tip over or slip under the maximum gradient, and the force analysis of the implements when travelling across the slope is shown in Figure 6.

When the harvester reaches the limit of travelling on a slope, the lateral slope R satisfies the following relationship:

$${\psi }_{h}G\mathit{cos}\gamma =G\mathit{sin}\gamma$$

(13)

where

• ψ_h is the coefficient of lateral attachment of tracks to the ground, (ψ_h = 0.55~0.68);
• G is the gravitational force, (N);
• γ is the horizontal slope, (°).

When the harvester is travelling steadily on the cross slope, the moment is balanced at point A, and the support force satisfies the following relationship:

$$N_2={\displaystyle \frac{G\mathit{cos}\gamma (0.5S+e)-Gh\mathit{sin}\gamma }{S}}$$

(14)

where

• N₂ is the ground support force on the right supporting wheel in the transverse direction;
• S is the distance from the track, (mm);
• e is the center of the mass offset, (mm).

The critical conditions for the harvester to overturn are ${\mathrm{N}}_2$ = 0 and $\mathrm{e}$ = 0. The maximum cross-slope gradient satisfies the following relationship:

$${\gamma }_{max}=\mathit{arctan}{\displaystyle \frac{0.5S+e}{h}}=arc\mathit{tan}{\displaystyle \frac{S}{2h}}$$

(15)

where

• γ_max is the maximum cross slope gradient, (°);
• S is the distance from the track, (mm);
• h is the center of gravity, (mm).

Combined with the structural dimensions of the machine chassis, the relevant parameters are substituted into Equation (15) for calculation to obtain the maximum slope angle that can be passed by cross-slope travelling of the chassis of 20°.

4.2. Longitudinal Slope Travelling Stability Analysis and Passability Calculation

The longitudinal stability of the chassis means that the chassis is able to remain stable and is not prone to slipping and tipping when travelling up and down slopes. The extreme tip-over and longitudinal slip angles are important indicators of the chassis’ stability when travelling up- and downhill. The whole machine in the up and down slope travelling process force situation has its own gravity, slope support force, ground friction, etc., and the machine longitudinal slope travelling force analysis is shown in Figure 7.

When the chassis is driven steadily on a longitudinal slope, the forces on the whole vehicle are balanced, and the moment equation for the supporting wheel C is given by:

$$N_{3}m-Ga\mathit{cos}\beta +Gh\mathit{sin}\beta =0$$

(16)

The forces on the whole vehicle are balanced, so the combined force is zero in the direction perpendicular to the slope, i.e., $N_3=G\cos \beta$, which is obtained by substituting into Equation (17):

$$m={\displaystyle \frac{a\mathit{cos}\beta -h\mathit{sin}\beta }{\mathit{cos}\beta }}$$

(17)

When the slope exceeds the limit, the car body will tip over, so the critical condition for the car body to tip over is m = 0, i.e.,:

$$a\mathit{cos}\beta -h\mathit{sin}\beta =0$$

(18)

The maximum angle of gradient for vertical uphill slopes is:

$${\beta }_{max}=arc\mathit{tan}{\displaystyle \frac{a}{h}}$$

(19)

The maximum slope angle of the vertical down slope is:

$${\beta }_{max}=arc\mathit{tan}{\displaystyle \frac{b}{h}}$$

(20)

Substituting the corresponding values into Equations (19) and (20) for calculation, it can be seen that the lower the tangential height from the center of gravity to the ground, the higher the stability of the chassis, and by lowering the tangential height from the center of gravity to the ground, the ultimate tipping angle of the chassis when going up and down the slope can be increased to improve the stability and safety of the vehicle. The calculated limiting gradient angle for driving on longitudinal uphill gradients is 26° and for driving on longitudinal downhill gradients is 23°, within which the chassis is able to drive smoothly.

The chassis is braked on a longitudinal slope by gravity, support, and friction under the conditions of being braked on a longitudinal slope:

$$F\ge G\mathit{sin}\beta$$

(21)

When the chassis is braked, the friction force consists of ground braking force, vehicle braking force, wind resistance, ground deformation resistance, and transmission system resistance, etc. The friction force calculation formula is:

$$F\le {\phi }_{h}N={\phi }_{h}G\mathit{cos}\beta$$

(22)

From Equations (21) and (22), the longitudinal limit slip angle β_m for chassis travelling longitudinally is:

$${\beta }_m\le arc\mathit{tan}{\phi }_h$$

(23)

The longitudinal slip rate of the chassis is affected by the driving surface conditions and soil environment, and is an indicator of the stability of the chassis on longitudinal slopes.

4.3. Analysis of Stability and Passability Calculation for Crossing Vertical Walls

The process of chassis crossing over vertical obstacles can be summarized in three steps: the front end of the chassis crosses the obstacle, the track support section crosses the obstacle, and the body’s center of mass crosses the obstacle. During the obstacle-crossing process, the position of the body’s center of mass changes with the variation in the chassis angle relative to the ground. The primary influencing factor is the position of the center of mass. The force diagram on the chassis during obstacle crossing is shown in Figure 8.

For the harvester over the vertical wall to reach the limit of the barrier height, the vehicle force balance, the supporting wheel E column moment, the equation is as follows:

$$N_5(L+b-c)-(L+b)G\mathit{cos}\beta +hG\mathit{sin}\beta =0$$

(24)

The pitch angle β reaches a critical value when the line of action of the gravity of the harvester coincides with the edge of the vertical wall, at which point N₅ = 0, i.e.,:

$$hG\mathit{sin}\beta -(L+b)G\mathit{cos}\beta =0$$

(25)

The ultimate chassis deflection angle is:

$${\beta }_{max}=arc\mathit{tan}{\displaystyle \frac{L+b}{h}}$$

(26)

The maximum height over obstacles is:

$$h_{max}=(L+b-c)\mathit{sin}\beta$$

(27)

4.4. Analysis of Stability and Passability Calculation for Crossing Trenches

Crossing trenches involves multiple factors, including the width of the trench, position of the center of mass, length of the track in the support section, size of the supporting wheels, and travel speed. The forces on the chassis when crossing trenches are shown in Figure 9.

The limit width M of the harvester tracked undercarriage across the trench is:

$$M=\sqrt{({{\displaystyle \frac{L}{2}})}^2+r_1^2}+r_2$$

(28)

where

• L is the distance between the drive wheel and guide wheel, (mm);
• r₁ is the guide wheel radius, (r₁ = 115 mm);
• r₂ is the drive wheel radius, (r₂ = 150 mm).

Through the above analysis of the harvesting machine chassis in hilly and mountainous areas under typical road conditions driving critical state of the force analysis, combined with the chassis of the relevant parameters of the chassis, the theoretical analysis of the chassis driving limit value of the typical road conditions for the calculation, we obtain the results as

Table 4. The driving limit values of the chassis under typical road conditions in hilly and mountainous areas.

Parameters	Limit Gradient for Cross-Slope Travelling (°)	Longitudinal Slope Uphill Limiting Gradient Angle (°)	Longitudinal Downhill Limit Slope Angle (°)	Over the Vertical Wall Limit Height (mm)	Crossing the Extreme Width of the Trench (mm)
Numerical Values	20	26	23	450	1150

.

5. Simulation Analysis of the Passability of Tracked Chassis

5.1. Creating Virtual Prototypes

The Track (LM) module in RecurDyn software was used to establish the simulation model of the tracked chassis of the potato combine harvester, as shown in Figure 10a. The component models were assembled with the track system to form a virtual prototype model of the potato harvester, as shown in Figure 10b. The virtual prototype is parameterized to determine the mass, center of mass, etc., and the soil contact parameters are shown in

Table 5. Clayey soil Contact Parameter.

Parameters	Numerical Values
Terrain Stiffness (k_c)	0.42
Terrain Stiffness (k_phi)	2.19 × 10−2
Exponential Number (n)	0.5
Cohesion (c)	4.14 × 10−3
Shearing Deformation Modulus (K)	13
Suspension mode	25
Sinkage Ratio	5 × 10−2

. Carrying out the whole machine assembly and road condition setting, there are three forward gears, the speed is 0.2 m/s, 0.4 m/s, and 0.8 m/s, respectively, add the driving function: STEP(Time, 0, 0, 1, −1.33), STEP(Time, 0, 0, 1, −2.66), STEP(Time, 0, 0, 1, −5.33).

5.2. Analysis of Simulation Results

5.2.1. Simulation Analysis of Transverse Slope Driving Throughput

In order to study the driving ability of the potato combine harvester in the transverse slope, the clay simulation pavement with slope angles of 10°, 15°, 20°, and 25° was established, respectively, with a length of 16 m, a width of 12 m, driving speeds of 0.2, 0.4, and 0.8 m/s, and a driving simulation time of 20 s. Operating the whole machine at three different speeds in four kinds of slope angle of the road surface simulation (Figure 11), three different speeds under the lateral driving track contact force change curve (Figure 12), the whole machine at different speeds under the travelling vertical displacement rule of change (Figure 13), to determine the maximum transverse slope angle of the machine that can be driven [30,31].

The variation curves of the contact force between the track and the ground when the whole machine is travelling at different speeds on a transverse slope are shown in Figure 12.

The analysis shows that, with the speed of travelling, the number of contact times between the track and the ground increases in the same time, and the track is in contact with the ground at all three speeds, the contact force between the track and the ground decreases as the speed becomes faster, the maximum value of the contact force is more than 6000 N when travelling at 0.2 m/s, and the maximum value of the contact force is under 6000 N when travelling at 0.4 m/s and 0.8 m/s, which indicates that, in the case of travelling in the cross-slope, the slow speed can enhance the contact between the track and the ground, and the safety stability is stronger.

The vertical displacement change of the whole machine with different travelling speeds in the transverse slope is shown in Figure 13. From the figure below, it can be seen that in the 10°, 15°, and 20° slopes, the whole machine advances with the speed of 0.2, 0.4, and 0.8 m/s, respectively, the vertical displacement offset is not large, and at the beginning it travels along the straight line, and with the increase in time, the vertical displacement fluctuation appears to be increased by a small magnitude. When the machine is travelling at a speed of 0.2 m/s in a 25° transverse slope, the center of mass vertical displacement decreases to −1210 mm, which indicates that the machine is in contact with the road surface, and the downward offset travelling phenomenon occurs seriously, and the sliding amplitude is large along the slope; when the machine is travelling at a speed of 0.4 m/s and 0.8 m/s in a 25° transverse slope, the drop in the center of mass vertical displacement is also large, and downward. The downward offset travelling phenomenon occurs. The whole machine did not roll over when travelling on a 25° transverse slope, but it was in a non-normal travelling condition and seriously deviated from the set route, so it can be known that the maximum transverse slope angle that the machine can travel is 20°.

5.2.2. Simulation Analysis and Testing of Chassis Passability in Longitudinal Uphill Slopes

In order to study the longitudinal uphill travelling ability of the machine, a clay simulation pavement with longitudinal slope angles of 15°, 20°, 25°, and 30° is set up, with a pavement length of 30 m and a width of 4 m (Figure 14), and a travelling simulation time of 150 s. In the travelling speeds of 0.2, 0.4, and 0.8 m/s, different speeds under the longitudinal climbing pitch angle change curve (Figure 15). The whole machine in different speeds under the travelling vertical displacement change rule (Figure 16) determines the maximum climbing angle of the machine.

As can be seen from Figure 15, when the whole machine is travelling on the longitudinal uphill surface, the three travelling speeds can pass through 15°, 20°, and 25° slopes, but when it comes to 30° slopes, the phenomenon of the tracks slipping and the whole machine stagnating starts to appear, so the chassis should be travelling uphill on longitudinal slopes of less than 30°. The whole machine with 0.2 m/s and 0.4 m/s travelling to the slope angle of 25° pitch angle change is gentler, the vehicle through the slope when the stability is strong; when the whole machine with 0.8 m/s is travelling through the 25° slope angle, the pitch angle fluctuation is violent and the positive and negative difference is large; at this time, the stability of the machine body is poor. Therefore, the maximum climbing angle that the machine can pass is 25°, and the speed control of 0.2 m/s or 0.4 m/s is better.

With vertical displacement changes of the whole machine when travelling uphill in the longitudinal direction with a travelling speed of 0.2, 0.4, and 0.8 m/s, respectively (Figure 16), the whole machine starts to go uphill from the zero point, and the vertical displacement of the center of mass increases linearly with the increase in the climbing height and finally reaches 3900 mm. In this process, there is a small fluctuation in the vertical displacement of the center of mass, but it tends to stabilize soon; the fluctuation mainly occurs in the process of transition between slope and flat, and the slower the speed, the smaller the fluctuation. When the speed is 0.8 m/s, the fluctuation is the most obvious, and the stability of the vehicle body is poor. This shows that the whole machine runs smoothly in the longitudinal uphill process less than or equal to 25° and has good longitudinal uphill performance in the low- and medium-speed states.

5.2.3. Simulation Analysis of Chassis Passability in Longitudinal Downhill Slopes

To study the longitudinal downhill travelling ability of the harvester, the longitudinal downhill travelling ability of the whole machine with different slope angles and different travelling speeds was simulated under the clay road surface (Figure 17). Set the slope gradient in turn angle for 25°, 20°, 15°, road length 18 m, width 3 m, travelling speeds were 0.2, 0.4, and 0.8 m/s, travelling simulation times were 84 s, 42 s, and 21 s. Different speeds under the longitudinal downslope pitch angle change curve (Figure 18). The whole machine in different speeds under the travelling pendant displacement change rule (Figure 19) determines the maximum downhill angle of the machine.

According to Figure 18, it can be seen that when the machine is travelling at 0.8 m/s to a slope angle of 25°, the pitch angle curve fluctuates violently, and the stability of the vehicle body is poor; when travelling at 0.4 m/s to pass the slope angle of 25°, the change in the pitch angle tends to be flat, and it can safely pass the slope angle of 25°, and the vehicle body has a small forward tilt when it is descending a slope; when travelling at 0.2 m/s to pass the slope angle of 25°, the change in the pitch angle is the smallest, and the stability of the whole machine is the highest when going down a slope. The stability of the whole machine is the highest when travelling downhill, indicating that the maximum downhill angle of the machine is 25°, speed control at 0.2 m/s is the safest and smoothest, and do not pass through the slope angle of 25° downhill at 0.8 m/s.

As can be seen from Figure 19, the whole machine starts downhill from the zero point, and with the reduction in height, the center of mass vertical displacement decreases linearly to −3350 mm, during which there are fluctuations in the center of mass vertical displacement, which mainly occurs in the conversion of sloped and flat road surfaces, and tends to stabilize after a certain amount of fluctuation. Among them, the fluctuation is most obvious when passing through the downhill slope with a slope angle of 25° at a speed of 0.8 m/s, and the stability of the vehicle body is poor at this time. When passing the downhill slope of 25° with 0.2 m/s and 0.4 m/s, the curve has no obvious up and down fluctuation, which indicates that the vehicle body has good stability and smoothness at this time.

5.2.4. Simulation Analysis and Test of Chassis Passability in Obstacle Crossing

To study the harvester’s ability to travel over vertical walls, vertical barricades of different heights were set up in the same roadway (Figure 20). The height of the barricade is 250, 300, 350, 400, 450, 500 mm, the length of the road is 32 m, the width is 4 m, the travelling speed is divided into 0.2, 0.4, and 0.8 m/s, and the travelling simulation time is 150 s, 80 s, and 38 s, respectively. The change curve of over-the-obstacle pitch angle under different speeds (Figure 21), the change rule of vertical displacement rule of the whole machine travelling under different speeds (Figure 22), and the determination of the maximum height of crossing vertical obstacles.

As can be seen from Figure 21, the whole machine was respectively over the vertical wall at 0.2 m/s, 0.4 m/s, and 0.8 m/s, the height of the obstacle increased in turn, the pitch angle fluctuation also increased, the pitch angle fluctuation was obvious when passing through the 500 mm vertical wall, and the change was too large, which led to the body of the vehicle tilting back seriously, losing the stability of the machine body, and influencing the normal travelling of the potato harvester, and the maximum height of vertical wall which the machine could overtop was 450 mm. The maximum height of vertical wall that the machine can go over is 450 mm.

From Figure 22, it can be seen that the faster the speed, the earlier the potato harvester reaches the vertical wall, and the volatility is large, and the center of mass vertical displacement curve changes drastically; the slower the speed, the smaller the volatility, and the center of mass vertical displacement curve tends to be more stable. So, in the process of crossing the obstacle, the low-speed travelling over the obstacle through the performance is the best, and it is more secure.

5.2.5. Simulation Analysis and Testing of Chassis Passability in Crossing Trenches

In order to study the ability of the harvester to cross the trenches, different widths of trenches were set up on the clay pavement for simulation (Figure 23). The depth of the trench is 450 mm, the width is 800, 1000, 1200, and 1400 mm, the length of the road surface is 25 m, the width is 4 m, the driving speed is divided into 0.2, 0.4, 0.8 m/s, and the driving simulation time is 120 s, 60 s, and 30 s, respectively. Different speeds can be obtained by crossing the trench pitch angle change curve (Figure 24), and the whole machine travelling at different speeds vertical displacement change rule (Figure 25), determines the maximum width of the machine across the trench.

As can be seen from Figure 24, during the process of the machine crossing the trench, the width of the trench gradually increased, which led to the increase in the pitch angle of the machine, and at the same time, the fluctuation in the pitch angle also became more obvious. When the machine crosses a trench with a width of 1400 mm, the change in pitch angle is too large, resulting in backward tilting and serious instability, which cannot ensure the normal travel of the potato harvester. It is therefore concluded that the maximum width of trench that can be crossed by this potato harvester on clay roads is 1200 mm.

As can be seen from Figure 25, when the width of the trench is from 800 mm to 1200 mm, the faster the speed, the earlier the whole machine passes through the trench; the volatility is small, and the change in the center of mass vertical displacement curve is smooth. The slower the speed, the higher the volatility and the more drastic the vertical displacement curve of the center of mass. Therefore, in the process of crossing the trench not more than 1200 mm in width, the choice of medium- and high-speed forward passability is better, and more safe.

6. Field Experiment

6.1. Test Condition

The performance test of the prototype was carried out at the potato planting base in Dingxi City, Gansu Province, which is a typical hilly and mountainous area with varied terrain, multiple road conditions to meet diversified test requirements, and clayey soil. The test was conducted in the afternoon of 25 October 2023. Before the start of the test, the soil hardness value was measured using a soil hardness tester, which was 48 N·cm⁻³; a small number of soil samples were taken, and the moisture content of the soil was measured to be 23% using the weighing method. The test specimen and the road surface are shown in Figure 26 [32,33].

6.2. Passed Performance Tests

The test is aimed at verifying the passing performance of the prototype in three typical road conditions in hilly and mountainous areas, and the test is carried out in longitudinal slope section, flat and straight road section, and road section with roadblock. The purpose of the test is to check the passing performance of the harvester chassis, assess the driving ability of the prototype in three road conditions, check the authenticity and validity of the theoretical calculations and simulation results, and at the same time, provide a strong basis for further improvement and optimization of the tracked chassis. The purpose of the test is to test the passing ability of the prototype harvester under the three road conditions.

6.2.1. Longitudinal Climb Test

In this test, the longitudinal uphill passability of the harvester was tested. A number of slopes with different gradients were used as the test site, as shown in Figure 27, to comprehensively evaluate the passing performance of the chassis and to find out the optimum range of speeds by conducting the test at different speeds.

The test results are shown in Figure 28. When the climbing angle exceeds 20°, the climbing time starts to become longer, and the phenomenon of climbing strain occurs, but it is able to complete the climbing test. When the climbing angle reaches 24°, the whole machine exists as an obvious climbing strain phenomenon, track chassis, and road surface slippage, thus determining the potato combine harvester in the longitudinal slope travelling the maximum slope angle of 24°. With the theoretical climbing value of 26°, the simulation value of 25° of the error is smaller. The reason for the error is that in the field operation, the soil viscosity is large, and the vehicle in the slope of the road surface is more prone to skidding phenomenon.

6.2.2. Over-the-Barrier Test

The test mainly examines the stability of the chassis when going over the vertical wall; to ensure the accuracy and reliability of the test, the two speeds of 0.2 m/s and 0.4 m/s are selected for the test, and the test site is shown in Figure 29a.

The results of the barrier-crossing test are shown in

Table 6. Over-the-vertical-wall test results.

Velocity/m.s−1	Vertical Wall Height/mm
	250	300	350	400	450	500
0.2	pass	pass	pass	pass	pass	abortive
0.4	pass	pass	pass	pass	pass	abortive

, the actual barrier-crossing ability of the potato combine harvester is basically consistent with the simulation results and theoretical calculations, and the harvester is able to go over the 450 mm straight wall [34,35].

6.2.3. Trench-Crossing Test

Based on the pre-test, two speeds of 0.2 m/s and 0.4 m/s were selected for the test, which can effectively reduce the impact force on the suspension system, lower the risk of body deformation, and guarantee the reliability and accuracy of the test. The test site is shown in Figure 29b.

The results of the trench-crossing test are shown in

Table 7. Trench-crossing test results.

Velocity/m.s−1	Trench Width Height/mm
	800	1000	1100	1200	1300	1400
0.2	pass	pass	pass	pass	abortive	abortive
0.4	pass	pass	pass	pass	abortive	abortive

. The actual trench-crossing capacity of the potato combine harvester is consistent with the simulation results, and the maximum width of the trench that can be crossed on the clay road surface is 1200 mm.

7. Conclusions

This paper presents a dynamic simulation of the performance of a potato harvester equipped with a crawler chassis under five typical hill and mountainous terrain conditions: traversing side slopes, ascending longitudinal slopes, descending longitudinal slopes, overcoming vertical walls, and crossing ditches. Additionally, field tests were conducted on the harvester to determine the performance limits under various operating conditions. Three of these conditions were specifically examined through field experiments to validate the performance of the harvester. The detailed research content is as follows.

(1)

Design of a potato combine harvester, mechanical analysis and theoretical calculations of the tracked chassis, including the four types of resistance, the force relationship of each wheel system, and for the characteristics of hilly and mountainous terrain, analyze the mechanical characteristics of the potato harvester in the process of travelling up and down the transverse and longitudinal slopes, crossing the barriers and crossing the ditches. And according to the theoretical formula to calculate the driving limit values under different working conditions, we find that the limit slope angle is 20° when travelling across the slope, the limit slope angle is 26° when travelling uphill in the longitudinal direction, the limit slope angle is 23° when travelling downhill in the longitudinal direction, the limit height that can be surmount is 450 mm, and the limit width that can be spanned is 1150 mm.

(2)

Simulations of the performance of the potato combine harvester chassis under five typical terrain conditions in hilly and mountainous areas were conducted using RecurDyn and EDEM software. The results from the simulation post-processing reveal the following limits for the chassis: under transverse slope conditions, the maximum slope angle for safe operation is 20°; under longitudinal uphill conditions, the maximum slope angle is 25°; under longitudinal downhill conditions, the maximum slope angle is also 25°; for obstacle crossing, the maximum height the chassis can surmount is 450 mm; and for ditch crossing, the maximum width the chassis can span is 1200 mm.

(3)

The potato combine harvester was tested in the field, and the maximum slope angle of the harvester was measured to be 24° in longitudinal slope travelling, and it was able to climb over the 450 mm high vertical wall and cross the trench with a width of up to 1200 mm. The results of the test were similar to the results of the theoretical calculations and simulation analyses, which showed that the harvester tracked chassis has the ability to pass through the complex terrain.