Why are tanks tracked? What are the advantages over wheels?

Walking on a track is like laying an infinitely extended track for a tank, so that it can pass through various complicated road conditions smoothly, quickly and safely. Because of the large grounding area, the passing capacity of tanks on soft and muddy roads is increased and the sinking is reduced. Because there are patterns on the track board, pedals can be installed, so you can firmly grasp the ground on roads such as freezing rain, snow or uphill without slipping. Because the length of the track is 4 ~ 6m and the center of the inducer is relatively high, the ability to pass through trenches and vertical walls is strong. Generally, tanks can cross trenches 2 ~ 3m wide and vertical walls 1m high. The reptile also has a special function. When crossing the river, it will dive and walk at the bottom of the river. If the crawler is floating, it can generate propulsion like a propeller to drive the vehicle forward.

Tanks are relatively heavy. If crawler can reduce the pressure per unit area, the requirements on the road surface can be smaller. Moreover, the defense performance and off-road performance are better than those of wheeled vehicles, and the wheeled structure is simpler than that of tracked vehicles. Generally used in light armored vehicles, the highway speed is better than that of tracked vehicles. Maintenance is also much simpler than tracked vehicles. Tightening the track of that damn tank is a big deal.

Wheeled vehicles are mainly used to drive on flat roads, but there are no flat roads on the battlefield, only various road conditions. In order to face all kinds of road conditions, caterpillar vehicles are used. The advantage of this kind of vehicle is its strong grip, which can reduce the pressure of the tank on the road surface and prevent the tank from falling under the road surface. The heavy suspension system is superior to wheeled vehicles, which can make the tank run more smoothly in various road conditions. Because tires have high requirements for air pressure, sometimes they are easy to burst, which has a great impact on the battle. Tires and tracks are easy to get into muddy roads, but they won't get into them. Because its contact area with the ground is much larger than the contact area between the tire and the ground, it will not fall into the muddy road. So for tanks, crawler vehicles should be used instead of wheeled vehicles.

Tanks are known as the "king of land warfare" and can be called the leading force in the land battlefield during the mechanized war. The reason why the tank has such an important position stems from its three major performances: strong firepower, high maneuverability and good protection. Corresponding to the three performances, tanks are generally composed of several systems: weapon system, propulsion system, protection system and communication equipment. Crawler belongs to the action device of tank propulsion system. If the tank is the king of land warfare, then the crawler is the feet of the king of land warfare.

Steel "pavement" for supporting storage tanks

Although the tank is powerful and invulnerable, if there is no crawler, the tank will not be able to move, especially in field conditions. It is with the crawler that tanks can move freely in all kinds of complex terrain. The action device of the tank consists of two parts: crawler and suspension device. Tracks and suspension devices * * * support the tank. Among them, the crawler is responsible for realizing the movement of the tank and ensuring the smooth running of the tank, as well as passing through various complicated and difficult ground and obstacles.

From the point of view of composition, the crawler belt is an endless belt, which is composed of some crawler plates hinged with each other and wraps the wheels of the walking device inside. So the track is like a steel pavement that supports the tank at any time. Because this kind of steel pavement is smoother than ordinary pavement, it can improve riding stability.

From a technical point of view, the function of crawler is to transmit driving torque or braking torque with the help of the driving wheels engaged with it, and to generate traction or braking force with the help of interaction with the ground. The total combat mass supported by the load-bearing wheels is tightly pressed on the lower track, which can increase the contact area between the lower track and the ground, and the pattern on the track can increase its adhesion.

It seems ordinary and hidden.

The crawler looks simple, just a steel belt. But a careful study shows that the structure of reptiles is also quite complicated. If distinguished from the appearance, the crawler can be roughly divided into three forms: integral, combined and belt. The whole track is cast or forged, so the productivity is not high, but the shape of the grounding part is easy to determine. The components of the combined track are simple in shape and high in productivity, and are also suitable for embedding many rubber pads. Therefore, combined track has become the mainstream of modern tank track. Belt crawler has the characteristics of light weight, but its weakness is that its strength lags behind that of integral and combined crawler, and it can only be used for special vehicles such as snowmobiles and lighter vehicles.

Structurally, the tank track is not as simple as it looks. In order to make the tank run, the crawler also needs to work with other accessories to solve all kinds of complicated situations that may be encountered during the running. These devices that work together with the crawler are "accessory devices", which mainly include rubber pads to protect the road surface, snow chains for driving and auxiliary crawler to reduce the grounding pressure when driving in wetlands.

According to the manufacturing materials, tracks can be divided into metal tracks and glued tracks. Track shoes and track pins are made of high-strength wear-resistant alloy steel, which is called metal track. Metal crawler has simple structure, light weight and low cost, but the metal crawler thorn protruding from the ground will damage the road surface, and water and sediment will easily enter the open metal hinge, resulting in rapid wear of pins and lugs, reducing the mobility of tanks, affecting driving efficiency and shortening the service life of the crawler. In order to solve the above problems, the designer installed a rubber block on the ground of the crawler and pressed a rubber bushing between the metal pin and the pin ear of the hinge. The performance and service life of the rubber-covered crawler belt improved in this way are improved, but the structure is complex, the quality is high and the cost is high.

The United States is the first country to improve tank tracks by adding rubber blocks. Rubber track shoes were first used, and later developed into rubber track shoes with replaceable rubber blocks. The latter is to vulcanize the rubber block on the stamped steel bottom plate with sufficient rigidity, and then insert it on the metal track plate body or connect it with the metal plate body by bolts. Some tracks also lay rubber pads on the raceway surface of the bearing wheel to reduce impact and noise, but this increases the driving resistance, increases the heat load of the rubber tire of the bearing wheel, and also increases the weight of the track.

In order to improve the service life of crawler hinges, rubber metal hinges were used in the United States after World War II, and their structures were divided into single pin and double pin. For single-pin articulated crawler shoes, it is necessary to press a rubber sleeve into each ear hole with the same aperture, and the rubber sleeve is directly vulcanized on the outer cylindrical surface of the steel sleeve, with the outer cylindrical surface and the inner equilateral prism. The lugs of adjacent track shoes are alternately arranged along the track width and are penetrated by prismatic steel pins matched with the inner holes of steel sleeves. The double-pin crawler pin is a round steel bar, and both ends are fixedly connected with the end connector. Glue the rubber sleeve on the pin and vulcanize it, then press it into the ear hole of the plate body, and the pin of the adjacent track plate and the end connector are fixedly connected into a whole. The outer diameter of the rubber sleeve is larger than the diameter of the pin ear hole, the relative movement of the contact surface between the rubber sleeve and the ear hole is prevented by interference, and the relative rotation of the pin and the ear hole is realized by the torsional deformation of the rubber sleeve. The bearing area of rubber sleeve of double-pin hinge is larger than that of single-pin hinge, and the corner of rubber sleeve is only half of that of single pin, so the load is small, and the disadvantage is that it is heavy. When the rubber sleeve fails and the wear of the ear hole of the plate body is still small, the replaceable rubber sleeve can continue to be used.

Key factors to improve mobility

Excessive crawler weight will affect the ratio of engine power to vehicle weight, that is, reduce the ton power of the vehicle, resulting in decreased acceleration performance, increased fuel consumption, reduced ride comfort, shortened service life of vehicle suspension devices, and increased maintenance and logistics workload. Early tanks used articulated tracks, which were connected by skeleton metal track shoes and simple track pins. When the tank runs at high speed, the high-speed rotating track ring needs to consume a lot of engine power. According to foreign road tests, the power consumption of crawler belt accounts for about 50% ~ 60% of the power loss between the driving wheel and the ground, and the power required for off-road driving is 270% higher than that for driving on good roads.

In order to reduce the power loss of the track, the effective measure is to reduce the weight of the track metal plate. When designing the track metal plate, in order to ensure the rigidity and strength of the track metal plate within the effective weight range, it is the most effective method to adopt frame structure or connecting rib to strengthen the structure. Among them, longitudinal ribs increase longitudinal stiffness, strength and lateral adhesion, while transverse ribs increase lateral stiffness, strength and longitudinal adhesion.

Tanks are required to adapt to all kinds of roads, and their tracks should not only provide good longitudinal adhesion, but also provide lateral force to prevent vehicles from slipping. Therefore, under the condition of ensuring sufficient longitudinal adhesion, the design of 45 "splayed rib structure can simultaneously solve the problems of effectively controlling weight and providing sufficient lateral longitudinal stiffness and lateral force. Generally speaking, the height of the landing stick is 1/3 track spacing from the hinge axis. Too large will increase the deformation resistance of the ground, and too small will reduce the adhesion of the crawler to the ground. The thickness of the grounding rod ensures that the average pressure in the contact area with the ground is 5 ~ 9 MPa, and the general thickness is 8 ~10 mm. ..

When driving in the wild environment, the grounding rod is very important to ensure the maneuverability of the tank. Because the most critical obstacle to vehicle movement is soil. Because vehicles must travel in soil, including muddy ground, sand, clay and snow, and use it to generate enough propulsion traction. For a specific terrain, only when there is a certain maximum subsidence can the soil support the vehicle, and there is enough shear strength to make the traction force generated by the vehicle greater than the motion resistance, and the vehicle can pass satisfactorily. The shear strength of soil reflects its ability to resist deformation, indicating the ability of the loaded part of soil and its adjacent non-loaded part not to slide.

For different orbital landing shapes, soil deformation and failure forms are different. The soil deformation of track shoes with grounding ribs is larger than that of flat track shoes. Under the condition of the same shear strength between soil particles, most of them provide great adhesion, and the soil is not easy to slip under certain traction conditions. When the traction required by the vehicle is greater than the shear capacity of the soil, the local shear failure of the soil causes the crawler to slide, and at this time, the crawler slides from the front of the vehicle to the rear of the vehicle along the shear plane, resulting in subsidence. For tracked vehicles, the subsidence of the rear part of the vehicle is greater than that of the front part. Because the amount of soil movement at the front end of the orbital landing zone starts from zero and reaches the maximum at the last end of the landing zone. Due to slippage, the amount of soil taken out from under the track changes with the smoothness and slippage of the track. When the crawler skids, the grounding ribs dig away a lot of soil like impeller blades, and some soil adheres to the surface of the crawler due to the compaction of the crawler, which affects the adhesion in the subsequent driving process.

During the rotation of the track, some soil will leave the ground with the rotation of the track. In order to ensure the effective adhesion between the track and the ground, some requirements are put forward for the self-cleaning ability of the track and the convenience of manually removing the deposits on the track plate. When the splay landing pole is arranged in the reverse direction, the compactness of soil can be reduced, the self-cleaning of crawler can be realized, and it is convenient for manual cleaning.