Why tracked vehicles

Hence, the normal load ladder diagram of the left- and right-side tracks is shown in Figure 3 and calculated as follows: where , , and are the normal loads of the front, rear, and centre point of track, respectively, and the subscripts 1 and 2 indicate the inner and outer track, respectively, the same below. L is the contacted length of the track, and B is the vehicle tread. Figure 4 indicates the lateral resistance ladder diagram, the normal load while the instantaneous centre for the parts of the outer and inner tracks in contact with and sliding on the ground by unit length.

Y is the lateral force acting on centre point C. Sort out when and ,. Steering resistance moment is equivalent to the moment acting on point C to the area of lateral resistance ladder diagram as follows:. With the traverse force, the external moments acting on the tracked vehicle include not only the steering resistance moment but also the simultaneous external moment to the centre generated by lateral force Y ; hence, the integrated lateral external moment is.

Figure 5 shows the external force acting on a tracked vehicle while slope steering. If the tracked vehicle steering moves at a uniform speed, then a longitudinal balanced force and balanced moment acting on the horizontal level centre C are necessary and are related by. The required braking force and traction pull of the inner and outer tracks while vehicle slope steering can be calculated as where and. Figures 6 a and 6 b show comparison graphs of the azimuth angle of traction pull on the outer track and braking force on the inner track, respectively, while slope steering on grades of slope angles.

Based on the theory of terramechanics, after the change rules of traction pull and braking force are calculated, the change rule of the slip rate can be calculated. In terrains such as sand, saturated clay, fresh powder snow, and most disturbed soil, we adopt an exponential function as pointed out by Janosi and Hanamoto [ 18 , 19 ] to describe the corresponding shear force-shear displacement relation as follows: where is shear force, is shear displacement, is soil cohesion, is normal stress, is the internal friction angle of the soil, is the maximum shear strength, and is the shear deformation parameter.

The total shear force generated by the tracks is where and are the width and contacted length, respectively, of the track. Therefore, we obtain where i is the track slip rate, x is the distance between one point on the track and the front end of the contact area, and.

We establish the dynamical model and shear stress-shear displacement relationship of tracked vehicle slope steering using MATLAB.

To correspond the equations 16 to the 12 , the slip rate of both tracks can be resolved. When the slip rate exceeds the maximum, which indicates the terrain cannot provide enough force, it will cause complete slip on the track, finally leading to instability and loss of control. The track slip rate can be taken as an index to judge the performance of vehicle slope steering.

We selected five typical terrains: gault, snow, grit, Petawawa marsh, and LETE sand, with terrain parameters [ 20 , 21 ] as shown in Table 1. Figures 8 a and 8 b show the slip rate changeable curves of inner track steering at different slope angles on snow.

With an increasing slope angle, the slip rate of the inner track gradually increases. As Figures 9 a and 9 b indicate, the vehicle can implement circular steering with a larger gradient on gault terrain than on snow ground. When the angle of the gradient , it will cause a complete slip or skid in the first and fourth quadrant which indicates that the tracked vehicle more easily slips and skids in the upslope phase.

As the angle of gradient increases, the azimuth range related to complete slip and skid becomes larger. The vehicle slope steering properties differ between the snow and gault terrain types. We analyse the track slip and skid conditions of the inner and outer tracks. We selected the above five types of terrain on which to implement a simulation analysis, with the same angle of gradient, steering radius, and steering velocity.

Figures 10 a and 10 b show the slip of the inner and outer tracks on the five types of terrain. Terrain with better cohesion, such as gault, enables vehicle slope steering with a larger angle of the gradient.

For UTVs, terrain condition is necessary to make driving and control strategy. To ignore the impact of terrain conditions will lead to errors in planning and control that can prevent a steering action, or even cause instability and loss of control. When the vehicle steers with a small radius, more power is needed from the terrain. Therefore, slope steering with a small radius can easily cause complete track slip and skid, which can lead to vehicle instability, loss of control, and even rollover.

We indicate the structural parameters of seven typical tracked vehicles in Table 2. We implemented a simulation analysis on slope steering performance, where the terrain type is Petawawa marsh, the angle of gradient , and the steering radius.

Figures 12 a and 12 b compare the slip rate of the inner and outer tracks of seven types of tracked vehicles when slope steering with specified radius. The diagram shows that tracked vehicles with different structural parameters have different inner and outer track slip rates when slope steering with the same gradient angle and steering radius conditions, and it is difficult to judge the exact impact of specified structural parameters on steering performance.

The next, choose AV A as an example, angle of gradient and steering radius , take the control variate method to select five structural parameters to the implement simulated analysis. The five structural parameters of vehicle mass, tread of track, track-ground contact length, height of vehicle centre of gravity, and track width impact the performance of tracked vehicle slope steering. We selected , , , , and for analysis, with simulation results shown in Figures 13 a and 13 b. As Figures 13 a and 13 b show that the vehicle slope steering with heavier mass, the track requires more power corresponding.

For the outer track, the difference mainly exists in the first and fourth quadrants, and for the inner track in the second and third quadrants. Choosing the min and max values to evaluate the variation trend of curves, the increase percentages of the outer track are 1. Obviously, as the mass increases, the increase range decreases. To evaluate the curves quantitatively, the curves are fitted and the slopes of curves are obtained.

Therefore, variation trend of curves can be observed distinctly. Figure 14 shows the curves of slope values of slip rate curves of both tracks, and Table 3 shows the max and min slope values of both tracks at different vehicle mass.

We selected , , , , and for simulated analysis, with results shown in Figure Figures 15 a and 15 b show that as the thread of the track increases, the slip rates of both tracks decrease until the inner and outer tracks cannot achieve slope steering within the specified steering radius. For slope steering performance, when the thread of the track is larger, the steering feature is better. Choose the min and max values to evaluate the variation trend of curves, the increase percentages of the outer track are Obviously, as the thread increases, the decrease range is averaged nearly.

Figure 16 shows the curves of slope values of slip rate curves, and Table 4 shows the max and min slope values of both tracks at different threads of track. Track contact length of , , , , and was selected for simulation analysis, with results shown in Figure Figures 17 a and 17 b indicate that, for the inner track, the slip rate gradually increases in and decreases gradually in , as the track-ground contact length increases.

The turn points are and. For the outer track, the slip rate gradually decreases in and increases gradually in the as the track-ground contact length increases.

The turn points are the same as the inner track. Choose the min and max values to evaluate the variation trend of curves, the increase percentages of the outer track are 9. Obviously, as the length increases, the decrease range decreases. Figure 18 shows the curves of slope values of slip rate curves, and Table 5 shows the max and min slope values of both tracks at different track-ground contact lengths. We selected , , , , and for simulation analysis, with results shown in Figure Figures 19 a and 19 b show that as the height of CG increases, the slip rates of both tracks also increase.

For the outer track, the main difference is obviously in and. For the inner track, it is obviously in. For UTVs, decreasing the height of CG would be beneficial to improve the slope steering performance on the premise of not affecting the trafficability of vehicle.

Choose the min and max values to evaluate the variation trend of curves, the increase percentages of the outer track are 0. Obviously, as the length increases, the increase range is averaged nearly.

Figure 20 shows the curves of slope values of slip rate curves, and Table 6 shows the max and min slope values of both tracks at different heights of CG. As shown in Figures 21 a and 21 b , the slip rate of the outer track increases gradually and the inner slip rate decreases gradually. The track width could increase the contact area, so as to improve vehicle trafficability. However, for the slope steering performance of UTVs, oversize width of track will augment the slip rate of outer track, even lead to totally skid.

Figure 22 shows the curves of slope values of slip rate curves, and Table 7 shows the max and min slope values of both tracks at different track widths. With the augmenting of track width, the slip rate of the outer track gradually increases and the slip rate of the inner track gradually decreases. To enlarge the track width can augment the contact area, so as to improve the maneuverability of a vehicle.

However, on a slope, to overly enlarge the width of the track will increase the slip rate of the outer track, possibly leading to overturning. In this paper, an improved dynamic steering model is proposed when considering the shear stress-shear displacement relation of soil at the track-ground interface to investigate the slope steering performance of a tracked vehicle.

The influence of ground characteristics, slope angle, and radius on the slope steering performance of a tracked vehicle is illustrated. Therefore, to make steering control strategy on the slope for the UTVs must consider about the angle of gradient and terrain conditions so as to plan corresponding steering velocity for both tracks, enabling vehicle get through field gradient terrain as the predetermined route with stability and high effectiveness.

The track slip rate is adopted as an index to evaluate the influence of typical vehicle structure parameters, heavy mass, thread of the track, and track-ground contact length, height of CG, track width, and on the slope steering performance of a tracked vehicle.

Structural parameters must be fully considered when designing a UTV, especially for driving on loose slope terrain. A major project for future research is to measure the characteristics of the ground and the slope angle by the sensors of UTV fusion online. The acquired parameters would be input to the dynamic model of tracked vehicle slope steering and help UTVs make path and motion planning. The numerical data used to support the findings of this study are available from the corresponding author upon request.

The authors declare that there are no conflicts of interest regarding the publication of this article. This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Article of the Year Award: Outstanding research contributions of , as selected by our Chief Editors. Read the winning articles. Journal overview.

Special Issues. Academic Editor: He Chen. Received 06 Jul Revised 19 Nov Accepted 05 Jan Published 31 Jan Abstract A special design is needed for an unmanned tracked vehicle UTV to meet the requirements of off-road environments and complex tasks. Introduction Traditional unmanned vehicle design depends on the assembly of external parts and units to form a vehicle.

Dynamical Model of Tracked Vehicle Slope Steering Figure 1 shows an azimuthal diagram of tracked vehicle slope steering. Figure 1. Figure 2. Force analytical diagram of tracked vehicle slope steering. Though NATO forces were located more closely to Yugoslavia than the Russian forces, the Russians were actually able to occupy key strategic locations throughout the country days in advance of the arrival of NATO units.

Where each NATO tracked vehicle had to be loaded and unloaded onto rail cars for transportation, the nimble Russian wheeled vehicles simply drove at high speed across Europe using the existing road systems. This example made the superior strategic position offered to Russia as a result of their use of wheeled vehicles painfully obvious to the NATO commanders.

Shinseki drove the requirement for wheeled vehicles in the US inventory. These fast and light-weight vehicles, used in conjunction with air transportation assets, provide the US Army the unprecedented ability to respond at a Brigade level to a military situation anywhere in the world within a 96 hour period. A summary of the advantages offered by wheeled combat vehicles is presented below.

Can accommodate heavy armored vehicle designs, with many modern MBTs weighing upward of 70 tons. Current wheeled technologies limit overall vehicle weight to about 35 tons, and therefore are unsuited to heavy systems such as MBTs and self-propelled artillery.

Supporting greater weight tracked vehicles can mount heavier weapon systems and armor systems, offering greater firepower and higher levels of protection. Tracks offer a stable firing platform as compared to wheeled vehicles when employing heavy weapons. Produce a lower ground pressure than most wheeled vehicles, improving performance in demanding terrain such as mud and sand. Average tracked vehicles only produce about half the ground pressure of a wheeled vehicle of equivalent weight.

Offers superior overall tactical mobility, which is to say, the ability to respond quickly and decisively in an active combat situation with hostile forces. Agility pertains to such aspects as speed, acceleration, turning circle and the ability to alter course quickly, which is often critical is taking evasive maneuvers. Wheeled vehicles use far less fuel than tracked vehicles when driving on roads, with this advantage decreasing with the ruggedness of the terrain over which the vehicle is driving.

The consumption rate of other vehicle fluids such as oil is also reduced. Therefore the vehicles can travel farther without having to stop for refueling. Consequently the logistic train i. Logistics provisioning is a major cost for modern armies, largely sets the pace at which forces can advance along a front, and are a huge liability, as unarmed trucks hauling materials to the front are vulnerable to attack.

Valuable combat assets must therefore be stripped from the front line and assigned to protect them. Significantly reduced maintenance requirements compared to tracked vehicles. Wheeled systems do not see the high loads that occur in tracked systems, reducing maintenance down time, frequency of repairs, and need to stock a large supply of replacement parts.

A higher proportion of a fleet is therefore available at any time to engage in combat duties. Also, for a given amount of funding more vehicles can be maintained and kept fielded. Maintenance costs are a major driver of overall military budgetary constraints. Wheeled vehicles are much faster than tracked vehicles, and able to travel for protracted distances using existing road systems without interruption.

Tracked vehicles are not suited to travelling long distances. The wear on the track system is too high, and the vehicles begin to suffer breakdowns en-route.

Engines overheat and the vehicles must be stopped periodically to cool down. Wheeled vehicles actually provide a better mounting system for lighter weapons such as the 25 mm autocannon and ATGM launch systems due to the inherent stabilization offered by the rubber tires.

This improves the performance of these weapons, minimally impacting aiming accuracy when firing while on the move. Though the turning circle of wheeled vehicles is larger than tracked vehicles, wheeled vehicles offer greater overall agility and are much more responsive to being driven that tracked vehicles.

Wheeled vehicles are generally faster, accelerate more rapidly, and can weave and zig-zag better than tracked vehicles, all critical to taking evasive maneuvers to avoid being targeted or impacted by enemy forces.

To exemplify this, consider how quickly you can respond to unforeseen events on the highway when driving your car as compared to operating a bulldozer. Occupants of a wheeled vehicle do not suffer from fatigue as quickly as those in tracked vehicles.

The heavy vibration of tracked vehicles cause their crews to lose focus and transported troops to suffer body aches at a much faster rate than occupants in a tire cushioned vehicle. Passengers in many modern wheeled vehicles are provided the same level of comfort as might be typical for a bus or pick-up truck.

Wheeled vehicles generally have superior survivability against mine strikes. Having a greater ground clearance to accommodate the suspension system, this distance proves critical in reducing the blast wave strength. More complex hull geometries can also be integrated into this increased space claim available under the vehicle, further mitigating blast effects.