SYMPOSIA PAPER Published: 01 January 1960

Automotive Central Hydraulic Systems and their Fluid Requirements


The development of central hydraulic systems will greatly expand the use of hydraulic actuators in automobiles. Tests to date indicate that a properly developed central hydraulic system will offer many customer advantages which can lessen driver fatigue and improve safety and reliability at reduced cost. A central hydraulic system is analogous to the conventional automotive electrical system. With the electrical system, energy is obtained from the generator and stored in the battery. Many accessories are driven by merely hooking onto this system. Items such as headlights, radios, and window lifts are attached without any change to the basic system. However, many other accessories are not so easily added. For example, power steering has its own independent system, which includes pump, actuators, and fluid. Again, power brakes have a completely separate system, utilizing a vacuum booster to assist the operation of the master cylinder, which, in turn, employs a special fluid to actuate the wheel cylinders. Convertible top mechanisms are often a combination of electrical and separate hydraulic systems. It seems that whenever a new actuating mechanism is added, other than an electrical device, it has been necessary to provide a complete system for this one device. The central hydraulic system offers the possibility of operating a multiplicity of devices from one central power source, in much the same manner as from the electrical system. The central hydraulic system consists of a pump, accumulator, and a reservoir. The pump is a generator that charges the accumulator, which in turn, stores energy for use by various mechanisms. Items that can conceivably be actuated from a central hydraulic system are brakes, steering gear, windshield wipers, window lifts, adjustable seats, convertible tops, starters, clutches, fuel pumps, injection equipment, air conditioning, suspensions, and suspension leveling systems. Obviously, connecting of all of these to one power source should reduce complexity and cost. This should mean easier installation, lower maintenance costs, and more trouble-free operation. In addition, items attached to a central hydraulic system can be operated from the accumulator when the engine is off. This permits applications which heretofore were confined to electric battery use because of the requirement for actuation regardless of whether or not the engine was running.

Author Information

Risk, T., H.
Ford Advanced Car Engineering, Ford Motor Co.
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Developed by Committee: D02
Pages: 19–37
DOI: 10.1520/STP46317S
ISBN-EB: 978-0-8031-6779-7
ISBN-13: 978-0-8031-6574-8