Measuring and testing – Vibration – Sensing apparatus
Reexamination Certificate
1998-12-03
2001-01-23
Noori, Max (Department: 2855)
Measuring and testing
Vibration
Sensing apparatus
Reexamination Certificate
active
06176136
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and to a device for determining the state of a vibrating structure of a rotary wing aircraft, particularly a helicopter.
2. Description of the Related Art
More specifically, it is intended to determine whether said vibrating structure, which is subjected to at least one type of vibration, is in a normal state or in an abnormal state (which may be due to a malfunctioning of a component of said structure or of an element of the aircraft that is associated with and/or connected to this structure), while said rotary wing aircraft is operating.
Although not exclusively, the present invention is more particularly applied to determining the state of a system for the suspension of a transmission gearbox of said rotary wing aircraft, such a transmission gearbox being mounted between propulsion means and a lift rotor of said aircraft essentially longitudinally to the axis of said rotor and being suspended with respect to the fuselage of said aircraft. Such a suspension system, which is effective in attenuating vibration in roll, pitch and vertical oscillation, is described in patent FR-2 474 996 and comprises:
struts distributed radially around said transmission gearbox, the upper ends of which are connected to the upper part of the transmission gearbox, and the lower ends of which are articulated to suspension leaves;
a suspension means connecting the lower part of the transmission gearbox to the fuselage of the aircraft and in particular comprising said suspension leaves; and
resonator means associated with said struts respectively.
SUMMARY OF THE INVENTION
To this end, said method for determining the state of a vibrating structure of a rotary wing aircraft, while the latter is operating, is noteworthy, according to the invention, in that:
a) n main vibrational modes of said vibrating structure are defined, n being an integer greater than or equal to 1;
b) p vibrational parameters, for example speeds, displacements, forces, accelerations and/or strains, that can be measured and that will enable the response of said n main vibrational modes to be estimated are defined on said structure, p being an integer greater than or equal to n. To achieve this, and to achieve step c), use is preferably made of a matrix which allows the p vibrational parameters to be estimated from the n fundamental modes and which is determined, either from an identification beforehand, or using known kinematic relationships;
c) estimated values of each of said p vibrational parameters are determined;
d) the values of said p vibrational parameters are measured while said rotary wing aircraft is operating;
e) a correlation coefficient is calculated from said estimated values and said measured values of the p vibrational parameters, preferably complex values;
f) said correlation coefficient is compared with a predefined range of values; and
g) the state of said vibrating structure is deduced from the results of said comparison.
Thus, by virtue of the invention, it is possible to effectively determine the state (normal or abnormal) of said vibrating structure of the rotary wing aircraft while it is operating.
In effect:
if the correlation (defined by said correlation coefficient) is strong, that is to say if said correlation coefficient lies within said predetermined range of values which is formed accordingly, the only vibrations experienced by said vibrating structure are generated from said main vibrational modes defined in the aforementioned operation a). These vibrations are therefore justified and the vibrating structure is in its normal state;
otherwise, other undefined vibrations are generated in addition, and this reveals an abnormal state of said vibrating structure, these additional vibrations being due in particular to poor operation or a defect of the vibrating structure and/or of an element of the aircraft that is connected thereto.
In an advantageous embodiment, operations a) and b) are performed in a preliminary step, as is determining the means needed for determining said estimated values, and the remaining operations, particularly the acquisition of data and the processing, are performed in a subsequent step while said rotary wing aircraft is operating, which makes it possible to simplify and limit the processing performed while said aircraft is operating, particularly while it is in flight.
Furthermore, advantageously, said estimated values of the vibrational parameters are values measured on the vibrating structure while said rotary wing aircraft is operating, for a normal state of said vibrating structure.
Furthermore, said correlation coefficient may be predefined as a function of the state (particularly the setting) of the vibrating structure or alternatively it may be defined during at least one initial flight or an intervention on the vibrating structure.
In a first simplified embodiment, said correlation coefficient corresponds to the difference between a first term obtained from said estimated values and a second term obtained from said measured values.
Furthermore, in a second preferred embodiment:
said correlation coefficient Q is calculated from the expression:
Q
=
[
∑
i
(
Umi
×
Uei
_
)
(
∑
i
Umi
×
Umi
_
)
×
(
∑
i
Uei
×
Uei
_
)
]
in which:
the Umi terms, with i varying from 1 to p, represent the measured values of the vibrational parameters;
the Uei terms, with i varying from 1 to p, represent the estimated values of the vibrational parameters; and
{overscore (Umi)} and {overscore (Uei)} are the complex conjugates of Umi and Uei respectively; and/or
said predefined range of values is preferably between 0.95 and 1.
The present invention is particularly applicable to a vibrating structure that corresponds to a system for the suspension of a transmission gearbox, like the aforementioned one.
In this case, advantageously, at least one of said vibrational parameters is measured on at least one of the following elements of said suspension system: a strut, a suspension leaf, a mass support and an oscillating mass of a resonator means, said resonator means comprising an oscillating mass connected by a mass support to a suspension leaf.
The present invention also relates to a device for implementing the aforementioned method.
According to the invention, said device is noteworthy in that it comprises:
sensors arranged on said vibrating structure and capable of measuring the values of said vibrational parameters; and preferably
means which filter the values measured by said sensors, relative to a frequency b&OHgr;, b being the number of blades of the rotary wing aircraft lift rotor and &OHgr; being its rotational speed; and
a calculation unit receiving the values measured by said sensors and determining, in the aforementioned way, from these and from estimated values of the vibrational parameters, the state of said vibrating structure.
REFERENCES:
patent: 3705516 (1972-12-01), Reis
patent: 3712130 (1973-01-01), Weichbrodt et al.
patent: 4181024 (1980-01-01), Leak et al.
patent: 4751657 (1988-06-01), Imam et al.
patent: 5210704 (1993-05-01), Husseiny
patent: 5333240 (1994-07-01), Matsumoto et al.
patent: 5365787 (1994-11-01), Hernandez et al.
patent: 5724271 (1998-03-01), Bankert et al.
patent: 5845280 (1998-12-01), Treadwell, III et al.
patent: 0490805 (1992-06-01), None
patent: 2474996 (1981-08-01), None
patent: 2692668 (1993-12-01), None
Struzik Alain
Zoppitelli Elio
Eurocopter
Noori Max
Stevens Davis Miller & Mosher L.L.P.
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