The History of Car Hydraulics
The study and science of hydraulics is properly called fluid mechanics. In automobiles, hydraulics are used most widely for power steering and power braking, although vehicles with manual transmissions often use a hydraulically actuated clutch. Systems that use hydraulic pressure are particularly useful for delivering an enhanced force in direct proportion to the force exerted by the operator, making -- for instance -- light and heavy braking a reliable and predictable event.
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Hydraulics Defined
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Hydraulics describes the use of fluid transmitted under pressure through a system of pipes and valves to create an effect in a non-fluid system component. In the automobile, this is most commonly achieved by the driver exerting a relatively small pressure on a system component -- most often the steering wheel or brake pedal -- which is then increased by a mechanically operated pump. This increased pressure is delivered to the downstream component, be that the steering rack or the braking pistons, where it either turns the rack or activates the brake pads.
Power Steering
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In essence, the pressurized hydraulic fluid of a power steering system operates a cylinder, which exerts pressure on the steering rack that in turn moves the directional wheels. Although road users in the U.S. are so accustomed to power steering that driving without it seems inconceivable, it was not a common option on many European and Soviet block marques until relatively recently.
Most valuable for low-speed maneuvering and when parking, a hydraulically operated assisted steering system was first patented in 1932 and first used on a production automobile -- the Chrysler Imperial -- in 1951. The next conspicuous improvement came in 1970, when Citroen released its Varipower system. Properly called Direction a rappel asservi, or DIRAVI, this reduced the effect of the hydraulic assist on steering at high speeds, allowing all the convenience of parking and slow-speed maneuvering while eradicating the risk of unintentional oversteer at high speed. Subsequent developments have been little more than evolutions of this principle.
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Hydraulic Braking
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In 1898, one Elmer Ambrose Sperry of Cleveland, Ohio, used electromagnets to press small pads against a rotating disc attached to a wheel to brake that wheel. 20 years later Malcolm Lougheed -- later to become Lockheed -- invented a hydraulic system of fluid-filled cylinders and tubes to deploy brakes, albeit they were shoes in drums, rather than pads and discs. For this reason, although the disc brake much as we know it today was commonplace in most European automobiles by the 1950s, convention did not see it take over as the industry standard for manufacturers in the U.S. until 1973.
Lowriders
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There is a specialist use for car hydraulics that has been gaining adherents since the early 1960s. A "lowrider" uses hydraulics to raise and lower the ground clearance of the vehicle. Drivers of the earliest, non-adjustable lowriders found themselves enthusiastically prosecuted by law enforcement for altering their vehicles, and as a consequence installed hydraulics so that they could return their appearance to stock when necessary to avoid a ticket. This utilitarian function evolved into the bouncing and performance-oriented installations seen today.
X-Sonic
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X-Sonic was a 1956 Chevrolet Corvette designed and built by Ron Aguirre of Rialto, California. It was the first car that ever used hydraulics to raise and lower suspension. Almost immediately upon purchasing the Vette new, Aguirre dropped its body and lowered its appearance with modifications to the suspension and exhaust systems. One year later, California passed a law banning lowered automobiles from road use. To overcome this Aguirre and his father installed hydraulic rams between the springs and the frame, actuated by a hand pump secreted between the seats. The hand pump was soon replaced by a 12-volt motorized unit, and a custom culture was born.
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