Continuous track

Continuous tracks on a bulldozer
An agricultural tractor with rubber tracks
A Russian tracked vehicle designed to operate on snow and swamps

Continuous track is 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 (with or without rubber pads), also called caterpillar track or tank tread,[1] 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 heaviest vehicles can move easily, just like a train on its straight tracks.

The idea of continuous tracks can be traced back as far as 1770.[citation needed] However, the stiff mechanism was first introduced 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.


Polish mathematician and inventor Józef Maria Hoene-Wroński conceived of the idea in the 1830s.[2] The British polymath Sir George Cayley patented a continuous track, which he called a "universal railway".[3] In 1837, Russian inventor Dmitry 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.

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.[4] 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.[5][6]

Boydell patented improvements to his wheel in 1854 (No. 431) – the year his dreadnaught wheel was first applied to a steam engine – and 1858 (No. 356), 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 in 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,[7] 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.[8]

Between late 1856 and 1862 Burrell manufactured not less than a score of engines fitted with dreadnaught wheels. In April 1858, "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.[9][10] Steam tractors fitted with dreadnaught wheels had a number of shortcomings and, notwithstanding the creations of the late 1850s, were never used extensively.[6][11]

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.[12] 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,[13] 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" (caterpillars).[14] 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.[14]

20th century efforts

Steam traction engines 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.[15] 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 T. 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.[1] 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.[16]

Lombard Steam Log Hauler (Designed, patented 1901)

First commercial success (1901)

A first effective continuous track was not only invented but really 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. Undoubtedly, Alvin Lombard was the first commercial manufacturer of the tractor crawler.

At least one of Lombard's steam-powered machines apparently remains in working order.[17] 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 Centipeed 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.[citation needed]

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.[18] 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 featured a track-steer clutch arrangement, which is the basis of the modern crawler operation. The patent was purchased by Holt.[citation needed]

First Chain Tracked Tractor
(1905, Richard Hornsby & Sons)
Hornsby Chain Tracked Tractor
(1907 enhanced Version)

Holt and the Caterpillar

A modern Caterpillar Inc. D9T bulldozer with High Drive
Caterpillar D9 High Drive
Note the elevated drive sprocket, with advantages for large earth-moving machines[19]

The name Caterpillar came from a soldier during the tests on the Hornsby crawler, "trials began at Aldershot in July 1907. The soldiers immediately christened the 70bhp No.2 machine the 'caterpillar'."[20] Holt adopted that name for his "crawler" tractors. Holt began moving from steam to gasoline-powered designs, and in 1908 brought out the 40 horsepower "Holt Model 40 Caterpillar". Holt incorporated the Holt Caterpillar Company, in early 1910, later that year trademarked the name "Caterpillar" for his continuous tracks.[21]

Caterpillar Tractor Company began in 1925 from a merger of the Holt Manufacturing Company and the C. L. Best Tractor Company, an early successful manufacturer of crawler tractors.

With the Caterpillar D10 in 1977, Caterpillar resurrected a design by Holt and Best, the high-sprocket-drive, since known as the "High Drive",[22] which had the advantage of keeping the main drive shaft away from ground shocks and dirt,[23] and is still used in their larger dozers.

Snow vehicles

In a memorandum of 1908, Antarctic explorer Robert Falcon Scott presented his view that man-hauling to the South Pole was impossible and that motor traction was needed.[24] Snow vehicles did not yet exist however, and so his engineer Reginald Skelton developed the idea of a caterpillar track for snow surfaces.[25] These tracked motors were built by the Wolseley Tool and Motor Car Company in Birmingham, tested in Switzerland and Norway, and can be seen in action in Herbert Ponting's 1911 documentary film of Scott's Antarctic Terra Nova Expedition.[26] Scott died during the expedition in 1912, but expedition member and biographer Apsley Cherry-Garrard credited Scott's "motors" with the inspiration for the British World War I tanks, writing: "Scott never knew their true possibilities; for they were the direct ancestors of the 'tanks' in France."[27]

Military application

Continuous track was first applied to a military vehicle on the British prototype tank Little Willie. British Army officers, Colonel Ernest Swinton and Colonel Maurice Hankey, became convinced that it was possible to develop a fighting vehicle that could provide protection from machine gun fire.[28]

During World War I, Holt tractors were used by the British and Austro-Hungarian armies to tow heavy artillery and stimulated the development of tanks in several countries. The first tanks to go into action, the Mark I, built by Great Britain, were designed from scratch and were inspired by, but not directly based on, the Holt. The slightly later French and German tanks were built on modified Holt running gear.

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