Fluid-pressure and analogous brake systems – Multiple control
Patent
1982-09-27
1985-01-15
Reger, Duane A.
Fluid-pressure and analogous brake systems
Multiple control
244111, B60T 1110
Patent
active
044935099
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to hydraulic systems for aircraft and the like, such as aircraft ground wheel braking systems. More particularly, it relates to a two-fluid system and method for preventing fire damage and danger caused by the ignition of hydraulic fluid on hot surfaces.
2. Background Art
The Air Force has become increasingly concerned about the danger and dollar loss caused by aircraft hydraulic fires. During the 1965-1979 time period, the Air Force experienced approximately 153 noncombat hydraulic fires with an associated dollar loss of over 179 million. A major cause of these fires is the ignition of hydraulic fluid on hot surfaces. During the 1970 to 1975 time period, about sixty-three percent of the hydraulic fluid fires occurred in the wheel well and/or landing gear area. Most of these fires were related to the ignition of hydraulic fluid on hot brakes.
The hydraulic fluid currently used on most military aircraft is a petroleum-based mineral fluid, per military specification MIL-H-5606, which has a low manifold ignition temperature and high heat of combustion, and burns quite readily. On some recent aircraft, a synthetic hydrocarbon fluid per MIL-H-83282 is being used because of its gunfire resistance and somewhat lower overall flammability characteristics. However, it also has a relatively low hot-surface ignition temperature.
Although these fluids are used throughout such aircraft, the brake, steering, and landing gear hydraulic actuation systems are statistically the most vulnerable. For example, when a hydraulic failure occurs in which these hydrocarbon fluids contact a hot brake, rapid ignition of the fluid occurs creating intense heat which ignites other fuel sources (such as the tire) that sustain the fire after the hydraulic fluid source is depleted.
In an effort to reduce the occurrence of aircraft hydraulic fires, the Air Force initiated a program to develop a nonflammable hydraulic fluid. This effort led to the development of chlorotrifluoroethylene (CTFE) base hydraulic fluids. Although virtually nonflammable, the principal disadvantage of the CTFE hydraulic fluid is its high specific gravity (density) which is 2.11 times that of the MIL-H-5606 fluid. In addition, the CTFE fluid is not compatible with most seal elastomer materials commonly used in MIL-H-5606 fluid hydraulic systems, and CTFE fluid cost for high production quantities is very high compared to aircraft hydraulic fluids presently in use.
The use of CTFE fluid in aircraft hydraulic systems would greatly alleviate fire danger and result in a significant improvement in aircraft safety. However, replacing MIL-H-5606 fluid with CTFE fluid throughout the entire aircraft hydraulic system would result in a significant weight penalty due to the increase in fluid density (e..g., +1700 lbs for the YC-14 advanced medium STOL cargo aircraft). This weight penalty can be reduced to approximately 64 lbs for a cargo/transport aircraft and 30 lbs for a fighter aircraft by employing the two-fluid nonflammable brake hydraulic system of the present invention in which the heavy CTFE fluid is used only in the hydraulic lines to the wheel brakes.
DISCLOSURE OF THE INVENTION
In accordance with the present invention, two different hydraulic fluids are used in a control system. A first hydraulic fluid, which is relatively flammable but otherwise desirable, is used in the system upstream of a piston in a pressure transmitter which serves to mechanically separate the two fluids. A relatively nonflammable second hydraulic fluid, having characteristics making it undesirable as a single fluid in the system, is used in the system between the isolator piston and an actuator which is in use adjacent a load which produces a considerable amount of heat. An example of such a load is the friction surfaces of an aircraft ground wheel brake.
In accordance with an aspect of the invention, makeup nonflammable hydraulic fluid is introduced into the system between the piston and the actuator whenever the quantity of such f
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Kilner Jerome R.
Raymond Eugene T.
Warren Steven M.
Barnard Delbert J.
Reger Duane A.
The Boeing Company
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