Power plants – Combustion products used as motive fluid – Combined with regulation of power output feature
Reexamination Certificate
1998-12-14
2001-01-09
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
Combined with regulation of power output feature
C060S226100, C060S223000
Reexamination Certificate
active
06170252
ABSTRACT:
TECHNICAL FIELD
The present invention relates to gas turbine engines, and more particularly to providing a mounting arrangement for a gearbox of the engine to minimize damage to the gearbox in the event of a high rotor imbalance condition such as a fan blade loss.
BACKGROUND ART
Modem gas turbine aircraft engines have a gearbox that is mounted on their external cases. The gearbox is generally positioned under the engine's core or fan case and uses power from the engine to drive the major accessories needed for engine functions, such as generators for electricity, pumps for circulating fluids and heat exchangers for cooling oil or heating fuel. The accessories are frequently mounted on the gearbox.
The main gearbox of modem turbofan engines such as the Model PW4000, manufactured by the Pratt & Whitney Division of United Technologies Corporation, is mounted within the engine core cowl and is driven by an angle gearbox through a towershaft from the high-pressure compressor. Various components are mounted on the gearbox. The main gearbox drives the fuel pump, scavenge pump, the electrical generator for the electronic engine control, external deoiler, hydraulic pump, and the integrated drive generator (for producing electricity).
Various mounting arrangements are used to mount the gearbox to the external case. The gearbox is often connected to the engine case at two or more locations along the length of the gearbox. For example, a forward V-shaped link may be used to fasten the front of the gearbox to the engine. A plurality of side hanger links may be used on either side of the gearbox housing to stabilize the gearbox. Further, a locator may also be used to provide alignment of the gearbox with respect to the engine case and prevent undesirable movement of the gearbox relative to the engine. Thus, the gearbox may be connected to the engine by a hard mount, that is, a connection which is essentially inflexible and immobile such that case deflections are transmitted to the gearbox. This hard mount arrangement imposes undesirable loads on the mounting hardware and on the gearbox itself.
One problem caused by such arrangements for mounting the gearbox to the engine case is subjecting the gearbox to high loads caused by rotor imbalances. Severe rotor imbalance can occur in an engine, particularly after a fan blade breaks off from the rotor assembly. One cause of fan blade loss is impact with foreign objects, such as birds, hailstones or other objects which, on occasion, are ingested into the engine. The detached fan blade is thrown outwardly and passes through the fan case, but is typically caught by the fabric wraps in the fan containment case assembly. Blade loss produces an imbalance in the rotor and causes the rotor shaft to deflect radially outwardly. The more the rotor deflects, the greater is the radial load on the rotor bearing supports.
The rotor imbalance loads are transmitted from the bearing supports to the engine cases and ultimately to the gearbox fastened to the engine case. The gearbox is forced to move with the engine as the gearbox is fastened to the engine cases. Blade loss loads have been traditionally underestimated with respect to gearbox structural design. If the vibratory loads transmitted to the gearbox are high, the gearbox may not be able to sustain the imbalance loads and this may result in the failure of the gearbox housing itself, and often the liberation of the accessories themselves from the gearbox.
When the gearbox housing breaks, oil from within the gearbox may splash over the hot cases of the engine and immediately ignite, causing a fire. The release of oil from within the gearbox also potentially damages the internal components of the gearbox as they would have to operate without lubrication. If a fuel-bearing accessory breaks off from the gearbox or pulls apart, spilled fuel may cause a fire. If the generator pulls off, a very large component is liberated that can potentially break through the engine cowling itself and ultimately hit an aircraft control surface.
Consequently, gearbox housings have been made thicker, the mount points stronger, and other strength and durability requirements have been increased. However, these prior art solutions have resulted in substantially heavier hardware which in turn has resulted in the gearbox mount loads to increase. In turn, the efficiency of the engines is adversely impacted by such heavier hardware.
It is also known to use a mounting arrangement having some flexibility or mobility to absorb energy and thus prevent the gearbox from engine case deflections and distortions. However, the flexible mounting arrangements of the prior art adversely compromise the life of the hardware as the elastomeric materials used to introduce the desired flexibility harden when cycled in a high temperature environment.
Thus, the challenge for modem gas turbine engines, during fan blade loss events, is the limiting of damage to the gearbox mounts and the gearbox itself.
DISCLOSURE OF THE INVENTION
A primary object of the present invention is to provide a gearbox mounting arrangement that protects the gearbox from the undesirable effects of engine case deflections and distortions experienced during rotor imbalance events such as a fan blade loss condition.
According to the present invention, a locator for a gearbox mount for a gas turbine engine includes a mounting plate having a first stub shaft that extends into a receptacle in the gearbox, a second stub shaft that extends into a receptacle in the engine case, and a load sensitive mechanism in one of the stub shafts such that during a high rotor imbalance condition, the load sensitive mechanism yields to a lower stiffness and restraint level to partially decouple the gearbox from the engine case to minimize damage caused by high deflection loads.
A primary advantage of the present invention is the minimization of damage to the gearbox housing and accessories during large rotor imbalance conditions, such as in the event of a fan blade loss. The locator of the present invention provides acceptable means of controlling loads transmitted to the gearbox. A further advantage of the gearbox mount of the present invention is its ability to provide an appropriate locating structure for the gearbox during normal operating conditions. The locator for a gearbox mount of the present invention provides proper alignment of the gearbox drive systems and minimal relative engine-to-gearbox motion. Another advantage is the ease and cost of manufacturing and incorporating into the gearbox of the prior art the locators of the present invention. The simplicity of the structure of the gearbox locators and the use of economic and readily available materials, allows for cost effective manufacturing processes. Further, gearboxes of the prior art can be retrofitted to include the present invention in a cost-effective manner as the present invention fits into the envelope of prior art gearboxes. The mounting arrangement of the present invention does not require periodic maintenance and is, thus, cost effective to incorporate into prior art engines. The gearbox housing can be made lighter as the strength of the gearbox housing does not have to be increased due to the present invention. As a result, the use of the mounting arrangement of the present invention is beneficial to the efficiency of the engine.
The foregoing and other objects, features and advantages of the present invention will become more apparent in the following detailed description of the best mode for carrying out the invention and from the accompanying drawings which illustrate an embodiment of the invention.
REFERENCES:
patent: 2722391 (1955-11-01), Krieghoff
patent: 2951395 (1960-09-01), Smith et al.
patent: 2978869 (1961-04-01), Hiscock et al.
patent: 3568806 (1971-03-01), Butt
patent: 3710568 (1973-01-01), Rice
patent: 3907220 (1975-09-01), Amelio
patent: 4301989 (1981-11-01), Kallenbach
patent: 4517913 (1985-05-01), Albertini et al.
patent: 5078342 (1992-01-01), Langley et al.
patent: 5277382 (1994-01-01), Seelen et al.
pate
Kim Ted
United Technologies Corporation
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