Fluid reaction surfaces (i.e. – impellers) – Articulated – resiliently mounted or self-shifting impeller... – Nonmetallic resilient mounting
Reexamination Certificate
2000-12-15
2002-03-26
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Articulated, resiliently mounted or self-shifting impeller...
Nonmetallic resilient mounting
C416S24400R
Reexamination Certificate
active
06361278
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a coupling membrane for transmitting a rotational moment between a drive shaft hub and a rotor blade holder, especially in a gimbal rotor of a helicopter. The rotor blade holder carries plural rotor blades extending respectively radially relative to the rotation axis so as to thereby form a rotor blade plane. Bearings connecting the rotor blade holder to the drive shaft allow the holder to tilt relative to the shaft, while the center lines of the bearing arrangement between the holder and the hub intersect each other on the axis of the drive shaft.
BACKGROUND INFORMATION
In general, various couplings are used for transmitting rotational moments to or from rotating components including drive shafts. The present application particularly relates to a so-called membrane coupling arranged between a drive shaft and plural rotor blades that are positioned radially about the drive shaft. The membrane coupling uses a membrane as the coupling element, i.e. a so-called coupling membrane. The rotor blades are rotatably arranged in a rotational plane, and the coupling membrane is arranged between the rotor hub of the rotor shaft and the holder structure that holds the rotor blades. Such a coupling membrane is especially applicable in technical structures in which the rotor blade plane must be tiltable relative to the rotational axis of the rotor shaft. Thus, the coupling membrane must be able to allow and follow this tilting motion of the rotor blade plane while still transmitting the rotational moment from the shaft to the rotor blades. A particular application in the field of helicopter technology is the generally known gimbal rotor also called a Cardan rotor.
Such a generally known gimbal rotor is used in a rotary wing aircraft, for example, and particularly in a helicopter. However, other applications for such a gimbal rotor arrangement include machine constructions in which a rotating shaft must be provided with an elastic compensating coupling that transmits a rotational moment while allowing axial relative motion. For example, any application in which a rotating drive shaft drives rotating rotor blades in which tilting of the blade plane is to be enabled can use such a gimbal rotor.
The development of the gimbal rotor was especially motivated and driven in the field of helicopter technology by the on-going need to reduce or avoid the vibrations resulting from various rotor blade movements. First of all, an up and down cyclical or oscillating movement of each rotor blade takes place due to the different relative wind velocities as well as the cyclical blade pitch adjustments as each blade travels around a full circle. Further caused by the change of the rotor radius, the coriolis forces arising in this context in turn lead to a lead-lag pivoting or oscillation of each blade. These horizontal lead-lag motions as well as the known vertical flapping motions of the blades, which are both generally categorized as bending motions, generate vibrations that are conducted through the rotor head into the drive train and the fuselage construction. As a result, these vibrations influence not only the rotor construction itself, but also the entire fuselage construction.
The gimbal rotor provides the advantage in comparison to other rotors, that it significantly reduces or prevents the vibrations that arise due to the flapping and lead-lag oscillating of the rotor blades. This can be achieved because the individual flapping of the rotor blades is prevented and thus the resulting lead-lag oscillation of each blade is reduced or minimized. The gimbal rotor is one step in the direction toward a rotor that enables a tilting motion of the entire rotor blade plane relative to the drive shaft. A component that is necessary for the functioning of the gimbal rotor is the coupling membrane, which is subjected to extreme dynamic loads, which result from the double function of the coupling membrane. On the one hand, the rotational drive moment must be transmitted from the rotor mast to the rotor blades, and this requires a torsionally stiff and torsionally strong and rigid behavior of the coupling membrane. On the other hand, the tilting movements of the rotor must be enabled and followed while still maintaining the power transmitting connection between the mast and the rotor blades. This requires a relatively soft stiffness or flexibility characteristic of the coupling membrane with respect to the tilting movements of the rotor.
The above mentioned dynamic loads arising from the disparate functions, in effect, require diametrically opposed construction requirements for the coupling membrane. The necessary bending softness with respect to tilting movements of the rotor requires the coupling membrane to have a relatively small cross-section with relatively little material, which would, however, negatively influence the torsional stiffness, rigidity and strength that is also required of the coupling membrane. The coupling membranes that are known in the prior art suffer very rapid wear and degradation due to the strong dynamic loads. Especially the loads resulting from the transmission of the rotational moment lead to a relatively rapid material fatigue in the known coupling membrane constructions. Through the use of fiber reinforced composite materials, the operating life of known coupling membranes could be increased in an economical manner, but there is still room for improvement, especially in relation to the structure and configuration of the coupling membrane rather than the material of the coupling membrane.
In known rotor constructions, coupling membranes may have a convex and/or concave configuration and especially a complex dual convex and concave curvature. A disadvantage of such a structural configuration is that the double curvature of the surface of the coupling membrane causes difficulties in the fabrication thereof, and places limits on the use of fiber reinforced composite materials for making such coupling membranes. Moreover, such known concave and/or convex coupling membranes are not constructed in a fault tolerant or damage tolerant manner, so that a fault or damage of the coupling membrane may lead to a complete failure of the coupling arrangement.
It is also known to provide a gimbal rotor using a concave coupling membrane together with elastomeric transverse force or shear force bearings for a four-bladed rotor. The known concave coupling membrane in this context has a form similar to a V-belt pulley with a deep V-groove. The coupling membrane has a massive solid construction in order to achieve a sufficient torsional stiffness, rigidity and strength for transmitting the drive moment. That, however, is not particularly advantageous for achieving a bending softness or flexibility for the purpose of enabling, receiving, and transmitting bending moments arising from the movements of the rotor blades. Moreover, this known coupling membrane is not constructed in a redundant fashion, and does not provide fault or damage tolerance, so that upon the failure of the coupling membrane, no further drive of the rotor is possible.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the invention to improve a gimbal rotor arrangement for transmitting the rotational drive moment from the rotor shaft to the rotor blades while achieving an improved bending elasticity and also providing failure reliability or tolerance. It is a further particular object of the invention to provide a configuration and construction of a coupling membrane that achieves a high torsional stiffness, rigidity and strength, in combination with a high bending flexibility for tilting relative to the rotor axis, with a simple and economical structure and fabrication thereof. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved in an arrangement for transmitting a rotational moment between a drive shaft and plural rotor blade
Eurocopter Deutschland GmbH
Fasse W. F.
Fasse W. G.
Look Edward K.
McAleenan James
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