Lubrication – Systems – Gearing
Reexamination Certificate
2000-07-26
2002-09-10
Kim, Chong H. (Department: 3682)
Lubrication
Systems
Gearing
C184S011200, C184S043000, C210S167150
Reexamination Certificate
active
06446755
ABSTRACT:
The present invention relates to a device for lubricating a step-up/down mechanical assembly, particularly a transmission gearbox, especially the main transmission gearbox of a helicopter.
It is known that in step-up/down mechanical assemblies of this type, the oil or lubricating fluid fulfills two functions: on the one hand, it reduces friction at gears, bearings and joints and, on the other hand, it takes away power losses in the form of heat.
The first function, that of reducing the coefficients of friction, does not require a high oil flow rate, the essential thing being that a film of oil be maintained between the various contacting parts. By contrast, its importance to the correct operation of the mechanical assembly is fundamental; in the event of failure, the increase in the coefficients of friction leads to an increase in the heat energy, which may soon manifest itself as surface damage to the contacting parts.
The second function of the oil, which consists in transporting heat energy from the areas in which it is generated (gears, bearings, joints, etc.) to dissipation zones (radiators, walls of casings, etc.), for its part requires a higher oil flow rate.
As far as this second function in particular is concerned, devices arranged locally inside the step-up/down assembly and which are capable of fulfilling an acceptable backup role by causing local recirculation of a reserve of oil between hot and confined zones and cooler zones, such as the walls of casings, are known. In mechanical assemblies which transmit relatively low powers, these devices may even be enough to completely fulfill this second function.
The major benefit of backup devices is, however, that they provide an answer to the problem posed by the loss of lubrication of the moving parts of the step-up/down mechanical assembly in question
Specifically, it is known that in the event of a loss of oil from the lubrication device, for example as a result of a leak in the lubrication circuit or from a seal, the increase in the coefficients of friction and the fact that the thermal energy is practically no longer removed, means that the temperatures of the various parts of the step-up/down assembly increase considerably. This in particular results in damage to the surfaces and degradations in the quality of the materials, which may lead to the destruction of parts such as bearings or teeth.
When said step-up/down assembly is a helicopter transmission gearbox, particularly the main transmission gearbox, the aforementioned consequences entail that, for safety reasons, when oil is lost from said transmission gearbox, the helicopter be set down quickly. This constraint may have very serious consequences when overflying certain zones, such as maritime zones, forests, urbanized zones or enemy territory (in the case of military applications), in which landing or ditching is difficult, or even impossible.
It will be noted that the survivability or operability of the helicopter is lower, the heavier the helicopter, because the powers transmitted by the transmission gearboxes increase out of proportion with their size. In particular, as far as most existing heavyweight helicopters are concerned, the operability following a total loss of lubrication is very low, or even non-existent.
Various backup or survival devices for transmission gearboxes, for the event of the malfunctioning of the transmission-gearbox lubricating system, are known.
In particular, the document FR-2 685 758 discloses a backup lubricating and cooling system for helicopter transmission gearboxes. This lubricating system comes into operation in the event of total failure of the existing lubricating circuit or circuits. For this purpose, this known system has an additional lubricating circuit which is independent of the existing circuit or circuits and which in particular comprises a reservoir, a supply line, pressurizing means or a pump, and a distribution circuit. This known system is therefore bulky, heavy and expensive.
Another source, document FR-1 094 563, discloses a lubricating device for a ball bearing. In this case, the lubricating fluid used for lubrication is accumulated in a rotary casing, which it leaves via a number of stationary tubes which are immersed via an open and elbowed end, in a layer of rotating oil centrifuged out to the periphery of the casing. The lubricating oil flows under the action of the centrifuging pressure.
However, the oil thus collected is simply returned to a specific oil reservoir of the lubricating device.
Furthermore, document FR-2 479 946 discloses a lubricating oil-return circuit for coupling mechanisms. For this purpose, the casing of such a mechanism is rotary and leads to an accumulation of oil in the form of an annular layer, and a collecting tube, the end of which is elbowed, is immersed in this annular layer to collect the oil.
This return circuit needs two pumps, namely a first pump which is mounted in series with the collecting tube, for conveying the fluid to a reservoir, and a second pump for removing the fluid and sending it to the elements that are to be lubricated.
The object of the present invention is to overcome these drawbacks. This invention relates to an effective and not-too-bulky device for lubricating a step-up/down mechanical assembly, which allows said mechanical assembly to continue to operate at least for a given length of time in the event of a leak of lubricating fluid and which, in the case of a helicopter transmission gearbox, allows said helicopter to continue to fly with a transmission of sufficient power for the longest possible determined length of time.
To this end, according to the invention, said device for lubricating a step-up/down mechanical assembly, particularly a transmission gearbox, said lubricating device comprising:
a reservoir for collecting lubricating fluid from said step-up/down mechanical assembly;
a circuit for distributing lubricating fluid;
at least one scoop, a first end of which enters said collection reservoir; and
means capable of creating a relative movement between at least said first end of the scoop and said collection reservoir, which causes lubricating fluid to be made to enter said scoop via said first end,
is noteworthy in that said means create a relative movement which causes, in the lubricating fluid in said collection reservoir, a dynamic effect such that it causes said lubricating fluid to flow through said distribution circuit in such a way as to convey it to at least one element of said step-up/down mechanical assembly that is to be lubricated.
Thus, by virtue of the invention, lubrication is achieved by re-using the oil or lubricating fluid collected (by trickling) in said collection reservoir. In consequence, in the event of a leak or loss of some of the oil, lubrication can be continued using the collected remaining proportion of the oil, which allows said step-up/down mechanical assembly to continue to operate for a certain length of time yet after the incident which caused the loss of oil.
In particular, in the case of a helicopter transmission gearbox, this length of time may be such that it allows said helicopter to land in complete safety at a safe place. According to the invention, as will be seen in greater detail hereinbelow, in order to lengthen this period of operation in the event of an oil leak, the lubrication implemented by the device according to the invention performs the exclusive lubrication of one or more vital parts of said step-up/down assembly, such as the gears.
Furthermore, by virtue of the invention, the lubricating fluid is made to circulate in said distribution circuit by the dynamic effect or force produced by the relative movement of the collecting reservoir and said first end of the scoop. In consequence, the device according to the invention requires no pump or other known means for causing this circulation, thus making it possible to obtain a lightweight, non-bulky and inexpensive device.
Furthermore, the trickling of lubricating fluid along the walls of the step-up/down assembly, which walls are genera
Auricombe Lionel Pierre Jean
Varailhon Christian
Eurocopter
Kim Chong H.
Stevens Davis Miller & Mosher LLP
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