EP0222262A1 - Sealing arrangement for a turbo pump - Google Patents

Abstract

The invention relates to the field of sealing devices. The device according to the invention, for a liquid propellant turbopump, is essentially characterized in that it comprises a housing (4) defining a cavity (C) for a pressurizing gas, delimited on the side of the turbine by a support ring (6) which is integral with it, in contact with a first sealing ring immobilized in rotation (8, 22) and, on the side of the pump, by an attached shell (11) including one face (15 ) is in contact with a second floating sealing ring (12) immobilized in rotation, itself bearing on a friction ring (16) integral with the shaft, said rings being mounted on a concentric bush (17) to said shaft, the shell being further connected to the cavity by a bellows (21). Application to the supply of liquid propellant to rocket engines.

Description

The present invention relates to a turbopump sealing device, more particularly intended to equip the liquid propellant supply assemblies of rocket engines.

We know that modern rocket engines with liquid propellants, usually oxygen and hydrogen, are equipped with distinguished pumps to be transported from the tanks to the combustion chamber with a given pressure and flow rate, the fuel (liquid hydrogen ) and the oxidizer (liquid oxygen). These pumps are driven directly or via a gearbox by a turbine operating from combustion gases supplied by a gas generator or a cumbustion pre-chamber. The shaft common to the pump and the turbine is supported by bearings or bearings usually lubricated by a circulation of hydrogen, all or part of which is evacuated during engine operation towards the turbine compartment.

Whether it is a turbine between two bearings or cantilevered, with a single bearing, it is necessary to incorporate between the bearing and the turbine a sealing means having a double role:

a) Cooling period:

This is the period before starting the engine where the turbo pump is brought into contact with the propellants at very low temperature and under a relatively low pressure, close to that of the tanks, so that during the rotation a thermal regime close to that of operation is already established.

During this phase, the sealing means must, for safety reasons, perfectly isolate the propellants, particularly hydrogen, from the turbine compartment.

If this function is not ensured, hydrogen accumulates in the engine or in the interstage space if it is an engine used in one of the upper stages of the launcher, and there is a high risk explosion when the engine is started.

b) Operation:

During the entire running time of the engine, the sealing means must allow the evacuation of the hydrogen passing through the bearings towards the turbine compartment and it must moreover, in certain lubrication systems, fix the flow of hydrogen at a predetermined value necessary for the proper functioning of the bearings.

From the above, it appears that the turbine sealing means is particularly critical and its design must therefore allow safe and reliable operation.

The sealing means currently used are of several types:
- labyrinths
- contact face seals
- retractable face seals
- floating rings
- segmented joints.

The above-mentioned elementary means are used in simple assembly, or various combinations of two or more of them are used. Some assemblies are pressurized, others use hydrodynamic effects.

The device according to the present invention implements some of the above elementary means, in a new arrangement making it possible to obtain higher performance compared to the existing combinations, in particular:
- no possibility of hydrogen leaking to the turbine during cooling,
- reduced consumption of pressurization gas,
- control of hydrogen flow to the turbine,
- longer service life,
- reduced overall dimensions and mass,
- greater reliability.

According to the invention, and according to a preferred embodiment, the sealing device is mounted in a housing concentric with the rotary shaft between the turbine and the pump itself, said housing defining a cavity for an under gas. pressure, delimited on the side of the turbine by a support ring which is integral with it, in contact with a first floating ring immobilized in rotation and, on the side of the pump, by an attached shell of which one face is in contact with a second floating ring immobilized in rotation, itself bearing on a friction ring secured to the shaft, said rings being mounted on a sleeve concentric with said shaft, the shell being further connected to the cavity by a bellows.

• la figure 1 représente une vue schématique en coupe du dispositif selon l'invention dans sa première forme de réalisation ;
• la figure 2 représente un schéma simplifié du dispositif selon la figure 1 illustrant les diamètres permettant d'obtenir les meilleurs résultats ;
• les figures 3 et 4 représentent des schémas illustrant les conditions de fonctionnement du disposi­tif ; et
• la figure 5 représente une vue schématique en coupe d'une variante du dispositif selon la figure 1.

Other characteristics and advantages of the invention will emerge more clearly from the description which follows. follow of possible embodiments, made with reference to the appended drawings in which:

• Figure 1 shows a schematic sectional view of the device according to the invention in its first embodiment;
• FIG. 2 represents a simplified diagram of the device according to FIG. 1 illustrating the diameters allowing the best results to be obtained;
• Figures 3 and 4 show diagrams illustrating the operating conditions of the device; and
• FIG. 5 represents a schematic sectional view of a variant of the device according to FIG. 1.

In these drawings, the same references designate the same elements.

Referring to FIG. 1, a turbine 1 is mounted for rotation on a shaft 2 of longitudinal axis LL driving a pump (not shown) and comprising a bearing such as a ball bearing 3. The sealing device comprises a housing 4 included in a general casing 5. The housing 4 defines a cavity C for a pressurizing gas through a conduit D, as will be explained below, itself delimited according to the following arrangement:
- on the side of the turbine 1 by a support ring 6 held in the housing, for example by a nut 7, on which a first floating ring 8 is supported with biasing for example by means of a spring 9, said ring 8 consisting of a carbon ring clamped in a metallic hoop immobilized in rotation by engagement of lugs 10 of the hoop in corresponding housings of the housing;
- on the side of the bearing 3 of the pump, by an attached shell 11 in which is disposed a second floating ring 12 of the same type as the previous one tooth and, similarly, immobilized in rotation by engagement of pins 13 of its hoop in corresponding housings of the shell 11; the floating ring 12 is supported by a contact face 14 on the shell 11 and, on the other hand, it can also be supported by a contact surface 15 on a friction ring 16 secured to the shaft 2.

As mentioned above, the two floating rings 8, 12 and the support ring 6 as well as the friction ring 16 are mounted around a bushing 17 concentric with the shaft 2. Advantageously, a vibration damper 18 is interposed between the shell 11 and its housing of the housing 4, in order to prevent any amplification of the vibrations generated during operation. The entire device, that is to say the housing 4, is fixed to the general casing 5 by any suitable means, for example stud-nut assemblies 19, a static seal 20 ensuring the seal with respect to the casing .

The second floating ring 12 being intended to be able to present a play in the longitudinal direction and to be followed along the contact face 14 by the shell 11, as will be better explained below, the latter is made integral with the housing by the through a metal bellows 21 guaranteeing the continuity of the enclosure C and preventing any passage of fluid. The bellows 21 also provides, by its stiffness and precompression during assembly, an initial force of shell / floating ring 12 / friction ring 16 contact.

For the operation of the device as described above, it is necessary to distinguish three phases, namely, the cooling period, a transitional period and the operating period proper.

Referring to Figures 2 to 4, the configuration of the device during cooling is shown in Figure 3.

- ⌀

) > P_A x (⌀

- ⌀

)
expression dans laquelle : ⌀₁, ⌀₃, ⌀₅ sont respective­ment les diamètres de la cavité, de l'arête intérieure de la surface 14 et de l'arête extérieure de la surface 15 ; et P_A est la pression de l'hydrogène au niveau de la pompe. Il y a lieu de noter qu'on a également représenté sur la figure 2 les diamètres ⌀₂0 de l'arête extérieure de la surface 14 et ⌀₄ de l'arête intérieure de la surface 15.The cavity C is pressurized, in the usual way, by gaseous helium (GHe), at a pressure P _c such that the force tending to bring the ring on the bearing side 12 into contact with its friction ring 16 is greater than the force tending to separate it:
P _c x (⌀

- ⌀

)> P _A x (⌀

- ⌀

)
expression in which: ⌀₁, ⌀₃, ⌀₅ are respectively the diameters of the cavity, the internal edge of the surface 14 and the external edge of the surface 15; and P _A is the hydrogen pressure at the pump. It should be noted that FIG. 2 also shows the diameters ⌀₂0 of the outer edge of the surface 14 and ⌀₄ of the inner edge of the surface 15.

If P _c is imposed, one determines ⌀₃ and ⌀₅ so that the above inequality is respected.

In order to maintain the contact between the ring 12 and the shell 11 in all operating cases, it is also necessary to ensure:
⌀₂> ⌀₅

Sealing with the bearing cavity A is ensured by the metal bellows 21 and the contacts (lapped surfaces for example) between the shell 11, the ring 12 and the support ring 16.

In order to avoid any leak, even if only minimal, from level 3 to cavity C, a second condition is imposed on the pressurization (leak from C to level):
P _c > P _A

Thus, the leakage of pressurization gas, and therefore its consumption, is almost zero on the bearing side.

On the turbine side, the ring 8 limits the consumption of pressurization gas (flow rate leakage Q _He towards the turbine cavity B).

During the transient phase, the turbine 2 is rotated until it reaches full operating speed, the turbine pressure P _B increases from partial vacuum (in the case of an engine with upper stages of launchers) or normal atmospheric pressure (in the case of 'a first stage) as well as the bearing pressure.

During the transitional phase, the pressurization is cut and the bellows 21 retracts, canceling the contact between ring 12 and friction ring 16.

The configuration of the device during the operating phase is shown in Figure 4.

The bellows 21 is compressed and the shell 11 bears on the housing, leaving a clearance J between ring and support ring.

The pressurization being cut off and the turbine pressure P _B lower than the bearing pressure P _A , a flow rate Q ′ _{LH2 is} established from the bearing 3 towards the turbine 2.

The sealing device then behaves like a system with two rings in series, the pressure P _{c being} established at a value between P _A and P _B.

It is therefore a contactless system between stationary parts and rotating parts, which has the advantages:
- reduction of the absorbed power
- elimination of friction and therefore wear (longer service life)
- better reliability.

In the case where the system must fix the flow of hydrogen to the turbine, a clearance "e" between ring 12 and bush 17 is determined accordingly.

The consumption of pressurizing gas is particularly critical and must be reduced as much as possible. mum for the following reasons:
- economical: soil consumption
- onboard weight reduction: flight consumption
(after ground / flight pressurization switching)

On the bearing side, pressurization consumption is almost zero as indicated above, so it is on the turbine side that action must be taken if we want to go further in reducing consumption.

For this, it is possible to use, in replacement of the ring 8, a segmented ring 22 (fig. 5) which ensures contact both on the support ring 6 and on the socket 17 during cooling, the order of magnitude the leakage then being ten times lower than that obtained with the ring. As in the case of the ring 8, the segmented ring 22 is biased in contact with the support ring 6 by a spring 23.

In operation, this segmented ring 22 must be cooled. It must therefore have a hydrodynamic effect so that the segments take off from the sleeve under the action of rotation, thus providing a clearance between ring and sleeve which allows a flow of hydrogen. The absence of contact during operation reduces the power absorbed and allows cooling.

The reduction in consumption can also be obtained by using a second ring in series with the first (8).

In order to further increase reliability, one or two labyrinths 24, 25 can be added downstream of the support and friction rings, 6 and 16 which limit the flow of hydrogen during operation in the event of failure of the rings.

The loss of pressurization is also to be considered as a particularly critical failure in the case of an upper stage of a launcher.

The consequences of a loss of pressurization are minimized by defining the bellows 21 so that its initial force F _R caused by its stiffness is greater than the opening force caused by the bearing pressure, according to the expression:

Returning to FIG. 5, it should be noted that among the advantages of the segmented ring 22, one can cite the fact that the latter is permanently in contact with the ring 6 and the sleeve 17, whatever the dimensional variations due to temperature gradients.

It is understood that the present invention has been described and shown for explanatory purposes but in no way limitative and that any useful modification may be made to it, in particular in the field of technical equivalences, without going beyond its ambit.

Claims (7)

1. Turbopump sealing device for liquid propellant, of the type comprising at least one floating ring, mounted in a housing (4) concentric with the rotary shaft (2) between the turbine (1) and the pump (A), characterized by the fact that said housing defines a cavity (C) for a pressurizing gas, delimited on the side of the turbine by a support ring (6) which is integral with it, in contact with a first ring sealing immobilized in rotation (8, 22) and, on the pump side, by an attached shell (11), one face (15) of which is in contact with a second floating sealing ring (12) immobilized in rotation, it -even bearing on a friction ring (16) integral with the shaft, said rings being mounted on a bush (17) concentric with said shaft, the shell being further connected to the cavity by a bellows (21). 2. Device according to claim 1, characterized in that the housing is fixed to a casing (5) by means of a static seal (20). 3. Device according to one of claims 1 or 2, characterized in that a vibration damper (18) is interposed between the shell and the housing. 4. Device according to any one of claims 1 to 3, characterized in that the first sealing ring on the side of the turbine is constituted by a floating ring (8) mounted on the sleeve (17) and urged by a spring (9) in contact with the support ring (6). 5. Device according to any one of claims 1 to 3, characterized in that the first sealing ring on the side of the turbine is constituted by a ring with segments (22) biased by a spring (23) in contact with the support ring (6). 6. Device according to any one of claims 1 to 5, characterized in that at least the shell (11) or the support ring (6) is extended downstream of the pump (A) by a labyrinth ( 24.25). 7. Device according to any one of claims 1 to 6, characterized in that the pumped fluid is hydrogen and that the gas for pressurizing the cavity (C) is helium.

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