Editing Shock absorber (section)

==Early history==
In common with carriages and railway locomotives, most early motor vehicles used [[leaf spring]]s. One of the features of these springs was that the friction between the leaves offered a degree of damping, and in a 1912 review of vehicle suspension, the lack of this characteristic in helical springs was the reason it was "impossible" to use them as main springs.<ref>"Springs - A simple study of car suspension", The Automotor Journal, August 10th, 1912, pp936-937</ref> However the amount of damping provided by leaf spring friction was limited and variable according to the conditions of the springs, and whether wet or dry. It also operated in both directions. Motorcycle front suspension adopted coil sprung Druid forks from about 1906, and similar designs later added Friction disk shock absorber rotary friction dampers, which damped both ways - but they were adjustable (e.g. 1924 Webb forks). These [[friction disk shock absorber]] s was also fitted to many cars.

One of the problems with motor cars was the large variation in sprung weight between lightly loaded and fully loaded, especially for the rear springs. When heavily loaded the springs could bottom out, and apart from fitting rubber 'bump stops', there were attempts to use heavy main springs with auxiliary springs to smooth the ride when lightly loaded, which were often called 'shock absorbers'. Realizing that the spring and vehicle combination bounced with a characteristic frequency, these auxiliary springs were designed with a different period, but were not a solution to the problem that the spring rebound after striking a bump could throw you out of your seat. What was called for was damping that operated on the rebound.

Although C.L. Horock came up with a design in 1901 that had hydraulic damping, it worked in one direction only. It does not seem to have gone into production right away, whereas mechanical dampers such as the Gabriel Snubber started being fitted in the late 1900s (also the similar Stromberg Anti-Shox). These used a belt coiled inside a device such that it freely wound in under the action of a coiled spring but met friction when drawn out. Gabriel Snubbers were fitted to an 11.9HP [[Arrol-Johnston]] car which broke the 6 hour Class B record at [[Brooklands]] in late 1912, and the Automator journal noted that this snubber might have a great future for racing due to its light weight and easy fitment.<ref name="AMJ" >"Some accessories to see at Olympia", The Automator Journal, Nov 2nd , 1912, p1284</ref>

French engineers Gaston Dumond and Ernest Mathis patented two different hydraulic shock absorbers with rectilinear motion in 1906–1907, but those were not commercially successful.<ref>{{Cite journal |last=Simionescu |first=P. A. |last2=Norton |first2=Robert L. |date=2024 |editor-last=Okada |editor-first=Masafumi |title=On the History of Early Automobile Suspension Systems |url=https://link.springer.com/chapter/10.1007/978-3-031-45709-8_99 |journal=Advances in Mechanism and Machine Science |language=en |location=Cham |publisher=Springer Nature Switzerland |pages=1012–1022 |doi=10.1007/978-3-031-45709-8_99 |isbn=978-3-031-45709-8}}</ref>

One of the earliest hydraulic dampers to go into production was the Telesco Shock Absorber, exhibited at the 1912 Olympia Motor Show and marketed by Polyrhoe Carburettors Ltd.<ref name="AMJ" /> This contained a spring inside the telescopic unit like the pure spring type 'shock absorbers' mentioned above, but also oil and an internal valve so that the oil damped in the rebound direction. The Telesco unit was fitted at the rear end of the leaf spring, in place of the rear spring to chassis mount, so that it formed part of the springing system, albeit a hydraulically damped part.<ref>"What a Chauffeur Expects to see at Olympia", The Automator Journal, Nov 9th 1912, p1313</ref> This layout was presumably selected as it was easy to apply to existing vehicles, but it meant the hydraulic damping was not applied to the action of the main leaf spring, but only to the action of the auxiliary spring in the unit itself.

The first production hydraulic dampers to act on the main leaf spring movement were probably those based on an original concept by Maurice Houdaille patented in 1908 and 1909. These used a [[lever arm shock absorber|lever arm]] which moved hydraulically damped vanes inside the unit. The main advantage over the friction disk dampers was that it would resist sudden movement but allow slow movement, whereas the rotary friction dampers tended to stick and then offer the same resistance regardless of speed of movement. There appears to have been little progress on commercialising the lever arm shock absorbers until after [[World War I]], after which they came into widespread use, for example as standard equipment on the [[Ford Model A (1927–31)|1927 Ford Model A]] and manufactured by [[Houdaille Industries|Houde Engineering Corporation]] of Buffalo, NY.