Invented by Ralph Piot in 1930, hydraulic shock absorbers emerged as a development to replace the previous friction discs. Friction discs, at best, could only provide a constant damping force, regardless of the size or speed of the suspension movement. Using the viscous arrangement of hydraulic fluid, the resistance increases with speed, thus providing better damping for larger suspension bumps. Lever-arm shock absorbers were the first hydraulic shock absorbers or dampers used in automotive suspensions. They appeared in the 1930s and were most commonly used in the 1950s and 1960s, but were replaced by telescopic shock absorbers in the 1970s. One of the earliest patents for hydraulic lever-arm shock absorbers was issued in 1925 to Georges de Ram, who was already a well-known manufacturer of friction disc shock absorbers.
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