Continuous track
Continuous track or tracked treads are a system of vehicle propulsion used in tracked vehicles, running on a continuous band of treads or track plates driven by two or more wheels. The large surface area of the tracks distributes the weight of the vehicle better than steel or rubber tyres on an equivalent vehicle, enabling continuous tracked vehicles to traverse soft ground with less likelihood of becoming stuck due to sinking.
Modern continuous tracks can be made with soft belts of synthetic rubber, reinforced with steel wires, in the case of lighter agricultural machinery. The more common classical type is a solid chain track made of steel plates, also called caterpillar tread or tank tread, which is preferred for robust and heavy construction vehicles and military vehicles.
The prominent treads of the metal plates are both hard-wearing and damage resistant, especially in comparison to rubber tyres. The aggressive treads of the tracks provide good traction in soft surfaces but can damage paved surfaces, so some metal tracks can have rubber pads installed for use on paved surfaces. Other than soft rubber belts, most chain tracks apply a stiff mechanism to distribute the load equally over the entire space between the wheels for minimal deformation, so that even the heaviest vehicles can move easily, just like a train on its straight tracks.
The stiff mechanism was first given a physical form by Hornsby & Sons in 1904 and then made popular by Caterpillar Tractor Company, with tanks emerging during World War I. Today, they are commonly used on a variety of vehicles, including snowmobiles, tractors, bulldozers, excavators and tanks.
The idea of continuous tracks can be traced back as far as the 1830s.
History
The British polymath Sir George Cayley patented a continuous track, which he called a "universal railway" in 1825. Polish mathematician and inventor Józef Maria Hoene-Wroński designed caterpillar vehicles in the 1830s to compete with the railways. In 1837, Russian army captain Dmitry Andreevich Zagryazhsky designed a "carriage with mobile tracks" which he patented the same year but, due to a lack of funds and interest from manufacturers, he was unable to build a working prototype, and his patent was voided in 1839.Heathcote's Steam Plough
Patented in 1832 by John Heathcoat, M.P. for Tiverton, the Heathcote steam plough was demonstrated in 1837 and press coverage fortunately provided a woodcut of the unusual tracked vehicle. The continuous tracks were made of sections of wood bolted to continuous iron bands which were driven by "drums" at each end. A strong chassis provided the bearings for the drums, and carried the steam engine, fuel and winch. The chassis was supported on "numerous small wheels or rollers" which ran upon the lower iron bands, which "thus form a perfectly portable and smooth road for the platform".The drums were in diameter, apart. The tracks were each wide with a gap in-between giving an overall width of. The twin-cylinder steam engine could be used either to drive the plough winch or to drive the vehicle along, at a speed of up to. Although the machine weighed 30 tons complete with 6 tons of fuel, its ground pressure was only, considerably less than a man.
The successful demonstration was carried out on 20 April 1837, at Red Moss at Bolton-le-Moors. The steam plough was lost when it sank into a swamp by accident and was then abandoned, because the inventor did not have the funds to continue development.
Dreadnaught wheel by Boydell (1846)
Although not a continuous track in the form encountered today, a dreadnaught wheel or "endless railway wheel" was patented by the British Engineer James Boydell in 1846. In Boydell's design, a series of flat feet are attached to the periphery of the wheel, spreading the weight. A number of horse-drawn wagons, carts and gun carriages were successfully deployed in the Crimean War, waged between October 1853 and February 1856, the Royal Arsenal at Woolwich manufacturing dreadnaught wheels. A letter of recommendation was signed by Sir William Codrington, the General commanding the troops at Sebastopol.Boydell patented improvements to his wheel in 1854 – the year his dreadnaught wheel was first applied to a steam engine – and 1858, the latter an impracticable palliative measure involving the lifting one or other of the driving wheels to facilitate turning.
A number of manufacturers including Richard Bach, Richard Garrett & Sons, Charles Burrell & Sons and Clayton & Shuttleworth applied the Boydell patent under licence. The British military were interested in Boydell's invention from an early date. One of the objectives was to transport Mallet's Mortar, a giant 36 inch weapon which was under development, but, by the end of the Crimean War, the mortar was not ready for service. A detailed report of the tests on steam traction, carried out by a select Committee of the Board of Ordnance, was published in June 1856, by which date the Crimean War was over, consequently the mortar and its transportation became irrelevant. In those tests, a Garrett engine was put through its paces on Plumstead Common. The Garrett engine featured in the Lord Mayor's show in London, and in the following month that engine was shipped to Australia. A steam tractor employing dreadnaught wheels was built at Bach's Birmingham works, and was used between 1856 and 1858 for ploughing in Thetford; and the first generation of Burrell/Boydell engines was built at the St. Nicholas works in 1856, again, after the close of the Crimean War.
Between late 1856 and 1862 Burrell manufactured not less than a score of engines fitted with dreadnaught wheels. In April 1858, the journal The Engineer gave a brief description of a Clayton & Shuttleworth engine fitted with dreadnaught wheels, which was supplied not to the Western Allies, but to the Russian government for heavy artillery haulage in Crimea in the post-war period. Steam tractors fitted with dreadnaught wheels had a number of shortcomings and, notwithstanding the creations of the late 1850s, were never used extensively.
Endless Railway by John Fowler (1858)
In August 1858, more than two years after the end of the Crimean War, John Fowler filed British Patent No. 1948 on another form of "Endless Railway". In his illustration of the invention, Fowler used a pair of wheels of equal diameter on each side of his vehicle, around which pair of toothed wheels ran a 'track' of eight jointed segments, with a smaller jockey/drive wheel between each pair of wheels, to support the 'track'. Comprising only eight sections, the 'track' sections are essentially 'longitudinal', as in Boydell's initial design. Fowler's arrangement is a precursor to the multi-section caterpillar track in which a relatively large number of short 'transverse' treads are used, as proposed by Sir George Caley in 1825, rather than a small number of relatively long 'longitudinal' treads.Further to Fowler's patent of 1858, in 1877, a Russian, Fyodor Blinov, created a tracked vehicle called "wagon moved on endless rails". It lacked self-propulsion and was pulled by horses. Blinov received a patent for his "wagon" in 1878. From 1881 to 1888 he developed a steam-powered caterpillar-tractor. This self-propelled crawler was successfully tested and featured at a farmers' exhibition in 1896.
20th century efforts
were used at the end of the 19th century in the Boer Wars. But neither dreadnaught wheels nor continuous tracks were used, rather "roll-out" wooden plank roads were thrown under the wheels as required.In short, whilst the development of the continuous track engaged the attention of a number of inventors in the 18th and 19th centuries, the general use and exploitation of the continuous track belonged to the 20th century, mainly in the United States and England.
A little-known American inventor, Henry Thomas Stith, had developed a continuous track prototype which was, in multiple forms, patented in 1873, 1880, and 1900. The last was for the application of the track to a prototype off-road bicycle built for his son. The 1900 prototype is retained by his surviving family.
Frank Beamond, a less-commonly known but significant British inventor, designed and built caterpillar tracks, and was granted patents for them in a number of countries, in 1900 and 1907.
First commercial success (1901)
An effective continuous track was invented and implemented by Alvin Orlando Lombard for the Lombard Steam Log Hauler. He was granted a patent in 1901 and built the first steam-powered log hauler at the Waterville Iron Works in Waterville, Maine, the same year. In all, 83 Lombard steam log haulers are known to have been built up to 1917, when production switched entirely to internal combustion engine powered machines, ending with a Fairbanks diesel-powered unit in 1934. Alvin Lombard may also have been the first commercial manufacturer of the tractor crawler.At least one of Lombard's steam-powered machines apparently remains in working order. A gasoline-powered Lombard hauler is on display at the Maine State Museum in Augusta. In addition, there may have been up to twice as many Phoenix Centipede versions of the steam log hauler built under license from Lombard, with vertical instead of horizontal cylinders. In 1903, the founder of Holt Manufacturing, Benjamin Holt, paid Lombard $60,000 for the right to produce vehicles under his patent.
The stiff chain by Hornsby & Sons (1904)
At about the same time a British agricultural company, Hornsby in Grantham, developed a continuous track which was patented in 1905. The design differed from modern tracks in that it flexed in only one direction, with the effect that the links locked together to form a solid rail on which the road wheels ran. Hornsby's tracked vehicles were given trials as artillery tractors by the British Army on several occasions between 1905 and 1910, but not adopted.The Hornsby tractors pioneered a track-steer clutch arrangement, which is the basis of the modern crawler operation. The patent was purchased by Holt.