Connecting rod between a cold part and a hot part

Abstract

Connecting rod between a cold part and a hot part. One aspect of the invention relates to a connecting rod (1) between an accessory housing (10) and a high-pressure compressor (11), said connecting rod (1) extending longitudinally along an axis (X) and comprising at least one convection cooling fin (5) extending longitudinally along the axis (X), each cooling fin (5) having a longitudinal base (7) by which it is connected to the connecting rod (1) and a longitudinal free edge (8) opposite said base (7). Preferably, the connecting rod (1) comprises several cooling fins (5) extending radially outward from their base (7) relative to the axis (X) of the connecting rod (1), these cooling fins (5) being evenly distributed around its periphery (6). Figure to be published with the abstract: Figure 2

Description

Title of the invention: Connecting rod between a cold part and a hot part. TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the general field of mounting a part in a turbojet engine, in particular an accessory housing for driving accessories.

[0002] The present invention relates to a connecting rod between a first part and a second part whose temperature is higher than that of the first part, and in particular a connecting rod between an accessory housing and a high-pressure turbojet compressor. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] In a turbojet engine, accessories such as pumps for hydraulic power generation, fuel supply and lubrication, electric generators for electrical power generation, etc., are grouped within a housing commonly called an accessory gearbox (or AGB). Such a housing generally comprises one or more gear trains that are driven in rotation by power taken from a turbojet shaft and to which the various accessories are coupled.

[0004] The accessory housing is generally mounted in the area of ​​the blower compartment. It is then generally suspended from flanges formed on the retaining housing of this blower compartment.

[0005] In some cases, the accessory housing is mounted in the central compartment of the turbojet engine (also known as the core compartment), and more specifically around the high-pressure compressor (CoHP).

[0006] An example of mounting the accessory box in the central compartment of the turbojet engine is described in document FR2952672B1 on behalf of the company SNECMA.

[0007] The applicant has observed that in some cases where the accessory housing is mounted in the central compartment of the turbojet, some accessories were degraded prematurely, which negatively impacts the overall operation of the turbojet and its performance.

[0008] The main purpose of the present invention is therefore to overcome such drawbacks. Summary of the invention

[0009] In order to find a solution to the problems mentioned above, the applicant first had to study the origins of said problems.

[0010] After extensive research, the applicant found that the accessories were degrading prematurely due to excessive mass heat within the accessory housing, this heat causing a degradation of the properties of the oil contained in said housing.

[0011] When the accessory drive unit is mounted in the central compartment of the turbofan engine, it is attached to the high-pressure section of the turbofan engine, which can have a bulk temperature of approximately 450 °C to 650 °C. This attachment is achieved by means of connecting rods, which notably allow the accessory drive unit to be secured at a distance from these hot parts of the turbofan engine. To ensure isostatic connection, six connecting rods are generally used.

[0012] After numerous studies, the applicant found that, despite their length, these connecting rods transmit a significant amount of heat to the accessory housing. In fact, the applicant observed that the connecting rods are subject to the following three heat transfers: • by conduction between the high-pressure body and the accessory housing; • by convection from the warm air surrounding the accessory housing; and • by radiation the high-pressure body and the accessory housing.

[0013] However, the oil in the accessory drive housing typically degrades at temperatures above 170°C and should preferably be kept below 160°C. The metallic nature of the connecting rods, however, facilitates the conduction of heat accumulated by the connecting rods to the accessory drive housing. Indeed, for reasons of mechanical strength, connecting rods are usually made of steel, superalloy (for example, Inconel®), or titanium. They can have a round or rectangular cross-section and be solid or hollow.

[0014] The applicant therefore sought a solution to address this problem of conduction of a significant amount of heat through the connecting rods between the accessory housing and the high-pressure body on which said housing is fixed.

[0015] Other fastening methods and concepts were evaluated, and following various tests and studies, the applicant decided to retain the connecting rods as the fastening method for the accessory housing. To address the problems mentioned above, the applicant also chose not to modify the material from which these connecting rods are manufactured, particularly due to integration constraints, while seeking to improve heat transfer between the connecting rods and the ambient air by convection in order to make heat transfer by conduction between the high-pressure body and the accessory housing negligible. Indeed, in a turbojet engine, The connecting rods are usually located in an airflow, which is at approximately 135°C when the turbojet is in operation.

[0016] The applicant has conducted a study of heat transfer (excluding radiation) in a connecting rod as a function of different convective heat transfer coefficients (h), which is shown in [Fig. 1]. This study indicates that the more convective heat transfer is favored (by sending more air around the connecting rod or simply by the presence of fins), the lower the temperature at the midpoint of the connecting rod, which tends towards the air temperature (135 °C in the case of this study), thus ensuring the interruption of heat conduction from the high-pressure body to the accessory housing. The applicant concluded that, in order to reduce or eliminate heat transfer by conduction from the high-pressure body to the accessory housing, it is necessary to promote convection and that the minimum temperature at the midpoint of the connecting rod must be substantially equal to that of the accessory housing.This behavior produces a break in the heat transfer from the high-pressure body to the accessory housing, ensuring that no heat is transferred from the high-pressure compressor body to the accessory housing.

[0017] The convection coefficient values ​​h given in [Fig. 1] are not directly related to connecting rod geometries. They correspond to real (h = 10, 20 ... 85 W.m².K*) or hypothetical (h = 0 W.m².K*) engine operating conditions. Thus, h = 0 Wm².K⁻¹ corresponds to engine operation without convection, and h = 10 Wm².K⁻¹ corresponds either to the case of post-engine warming by other components with high thermal inertia (known in English as "oak back") or to the case of natural convection in the central compartment of the turbojet engine just after engine shutdown. The other values ​​(h = 34, 60, 85 Wm².K*) were provided by the applicant's aerothermal department and correspond to other real flight situations, such as takeoff or cruise flight.

[0018] It should be noted that the equation of the convective heat flux <e>(phi) is given by the following formula: <e>= hAAT where phi is the heat flux in Watts, h is the convective heat transfer coefficient in Wm².K*, A is the heat transfer surface area in m², and AT is the temperature difference in Kelvin between the connecting rod surface and the fluid (air in the central compartment of the turbojet). It can be seen that increasing h (which depends on the engine's thermal conditions) or A (which depends on the connecting rod geometry) has the same effect. The invention therefore aims to increase the heat transfer surface area A.

[0019] With a perfectly cylindrical connecting rod without fins, it has been observed that from a convection coefficient h between 10 and 34 Wm 2.K 1 the minimum temperature in the middle of the connecting rod becomes equal to that of the ambient air.

[0020] An objective of the invention is to reach the ambient temperature (infinite temperature) for values ​​of convection coefficient h such that h < 10 Wm"2.K" 1 without using means to increase this convection coefficient h, such for example a fan.

[0021] Thus, the invention offers a solution to the problems mentioned above by structurally modifying the cross-section of the connecting rods so that their convective heat exchange surface A is increased. The parameters of this modification are preferably chosen so that the minimum temperature at the middle of the connecting rod is substantially equal to that of the ambient air.

[0022] One aspect of the invention relates to a connecting rod between an accessory housing and a high-pressure turbomachine compressor, said connecting rod extending longitudinally along an X axis and comprising at least one convection cooling fin extending longitudinally along the X axis, each cooling fin comprising a longitudinal base through which it is connected to the connecting rod and a longitudinal free edge opposite said base.

[0023] Thanks to the invention, in addition to its structural role of mechanical fastening, the connecting rod of the invention also fulfills a thermal protection role for the accessory housing that it connects to a high-pressure body. By extension, such a connecting rod could be used to connect any element negatively sensitive to temperature to another element exhibiting a high temperature, particularly when said connecting rods are usually located in an airflow whose temperature is lower than that of the element exhibiting a high temperature.

[0024] According to one aspect of the invention, at least one cooling fin extends in a middle portion of said connecting rod, over more than half the length of the connecting rod.

[0025] According to another aspect of the invention, at least one cooling fin is one piece with the connecting rod.

[0026] According to a further aspect of the invention, at least one cooling fin is removably fixed to the connecting rod.

[0027] According to one aspect of the invention, the connecting rod comprises several cooling fins extending radially outwards from their base relative to the X axis of the connecting rod.

[0028] According to another aspect of the invention, the connecting rod has several cooling fins distributed regularly around its perimeter.

[0029] According to a further aspect of the invention, the connecting rod comprises 4 to 30 fins, preferably 8 to 20 cooling fins distributed regularly around its circumference.

[0030] According to one aspect of the invention, at least one cooling fin has a constant thickness between its base and its free edge.

[0031] According to another aspect of the invention, this thickness is constant over the entire length of the cooling fin.

[0032] According to a further aspect of the invention, at least one cooling fin is flared at its base.

[0033] According to one aspect of the invention, this flare extends longitudinally along said base.

[0034] According to another aspect of the invention, at least one cooling fin has a bulge at its free edge.

[0035] According to a further aspect of the invention, this bulge extends longitudinally along said free edge.

[0036] According to one aspect of the invention, at least one cooling fin is solid.

[0037] According to another aspect of the invention, at least one cooling fin is hollow.

[0038] According to a further aspect of the invention, the connecting rod comprises a single cooling fin whose base width is substantially equal to the diameter of said connecting rod at the level of this base.

[0039] According to one aspect of the invention, the connecting rod has several cooling fins distributed over the same longitudinal half of the connecting rod.

[0040] According to another aspect of the invention, the cooling fins are all substantially parallel to a radial plane P which is perpendicular to the X axis.

[0041] According to a further aspect of the invention, at least one cooling fin has a perimeter covered with a dark-colored paint or coating, preferably black.

[0042] According to one aspect of the invention, the shape and dimensions of each cooling fin, as well as their number, are such that the convective heat transfer coefficient h of the connecting rod is such that h > 10 W / m2.K.

[0043] According to another aspect of the invention, the shape and dimensions of each cooling fin, as well as their number, are such that the convective exchange surface A of the connecting rod is increased by at least 10% compared to the same connecting rod without cooling fins.

[0044] Another aspect of the invention relates to an assembly comprising a high-pressure compressor body, an accessory housing and a connecting rod linking the high-pressure compressor body to the accessory housing, said connecting rod being a connecting rod according to the invention.

[0045] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0046] The figures are presented for illustrative purposes only and are in no way limiting of the invention.

[0047] [Fig. 1] illustrates the temperature in a connecting rod as a function of its length, for different values ​​of convective heat transfer coefficient h for said connecting rod, the latter having a length of 272 mm and connecting an accessory gearbox (AGB) to a high-pressure compressor body (CoHP) at 450°C in an air environment at 135°C.

[0048] [Fig.2] illustrates an example of the embodiment of a connecting rod according to an example of the invention linking an accessory housing to a high-pressure compressor body.

[0049] [Fig.3] illustrates an example of the realization of a connecting rod according to an example of the invention shown in perspective.

[0050] [Fig.4], [Fig.5], [Fig.6], [Fig.7], [Fig.8], [Fig.9] and [Fig.10] illustrate different alternative and non-exhaustive sections of connecting rods fitted with fins according to an example of the invention. DETAILED DESCRIPTION

[0051] Unless otherwise specified, the same element appearing on different figures has a unique reference.

[0052] The connecting rod 1 according to the invention is a connecting rod intended to link a first part and a second part whose temperature is expected to be higher than that of the first part, preferably in a turbojet engine. The first part is a part to be protected, via connecting rods 1 according to the invention, with a cooler and limited temperature, while the second part is a very hot part whose heat can be transferred to a cooler part according to the laws of thermodynamics.

[0053] The first part is for example an accessory housing 10, for example at a temperature between 160°C and 170°C, while the second is for example a high-pressure compressor body 11, which can for example reach a temperature between 450°C and 650°C during the operation of the turbojet.

[0054] During the operation of the turbojet, the connecting rod 1 according to the invention is preferably located in an airflow whose temperature is lower than the temperatures that can be reached by the accessory housing 10 and the body of the high-pressure compressor 11.

[0055] The connecting rod 1 extends longitudinally along an axis X and comprises two end portions 2, 3, which serve in particular to attach the accessory housing 10 to the high-pressure compressor body 11 of the turbojet engine (see [Fig. 2] and [Fig. 3]). These two end portions 2, 3 are preferably without fins. This is not mandatory, but is recommended to facilitate the mounting of the connecting rods 1 with cooling fins 5 and to limit the risks, particularly of breakage, and in order to to adapt the design of the connecting rods to the need for thermal protection via the addition of cooling fins 5.

[0056] The connecting rod 1 also includes an intermediate part 4, preferably median, located between the two end parts 2, 3 of the connecting rod 1, this intermediate part 4 preferably comprising at least one convection cooling fin 5.

[0057] Thus, the connecting rod 1 according to the invention comprises at least one convection cooling fin 5, which extends longitudinally along the X-axis. This cooling fin 5, preferably all of them, preferably extends over more than half of the total length of the connecting rod 1. The cooling fins 5 project outwards from the periphery 6 of the connecting rod 1, for example radially with respect to the X-axis of the connecting rod, but not necessarily. The connecting rod 1 thus has a larger diameter at the level of the cooling fins 5 compared to a connecting rod without fins.

[0058] By periphery 6 of the connecting rod 1 we mean its external radial surface.

[0059] Each cooling fin 5 has a longitudinal base 7 by which it is connected to the connecting rod 1 and a longitudinal free edge 8 opposite said base 7.

[0060] Each cooling fin 5 is preferably one piece with the connecting rod 1. It can also be removably fixed to the connecting rod 1, for example by screwing, or by any other means of fixing.

[0061] According to one embodiment of the invention, the connecting rod 1 comprises several cooling fins 5 extending radially outwards from their base 7 (see [Fig.4], [Fig.5], [Fig.6] and [Fig.7]).

[0062] In the case where the connecting rod 1 has several cooling fins 5, these can be regularly distributed around its circumference 6 (see [Fig.4], [Fig.5], [Fig.6] and [Fig.7]). Viewed in radial section, such a connecting rod 1 therefore has cooling fins 5 arranged in a star pattern.

[0063] The connecting rod 1 preferably comprises 4 to 30 fins, more preferably 8 to 20 cooling fins.

[0064] The cooling fins 5 can also be distributed on the same longitudinal half of the connecting rod 1, i.e. on the same side of the circumference 6 of the connecting rod 1 (see [Fig. 8]), which notably provides an aerodynamic profile to the connecting rod 1 in its part equipped with cooling fins 5. In this case, the cooling fins 5 are preferably all substantially parallel to a radial plane P which is perpendicular to the X axis. In this case, the connecting rod 1 preferably has from 2 to 15 fins, more preferably from 4 to 8 cooling fins.

[0065] In order to improve the aerodynamic profile of the connecting rod 1, according to another embodiment of the invention, the connecting rod 1 may also include a single cooling fin 5 whose base width 7 is substantially equal to the diameter of said connecting rod 1 at the level of this base 7 (see [Fig. 9] and [Fig. 10]), which notably allows for the improvement of the aerodynamic profile of the connecting rod 1. By base width 7, we mean the thickness of the cooling fin 5 in the part where it is connected to the rest of the connecting rod 1.

[0066] Preferably, the connecting rod 1 according to the invention does not include a single cooling fin 5 extending radially outwards from its base 7, this single cooling fin 5 being such that the width of its base 7 is not substantially equal to the diameter of said connecting rod 1 at the level of this base or being such that it has a substantially constant thickness over the majority of its radial height.

[0067] Preferably, the connecting rod 1 according to the invention does not have longitudinal grooves which locally reduce its average diameter.

[0068] According to one embodiment of the invention, each cooling fin 5 has a constant thickness e between its base 7 and its free edge 8, i.e., the cooling fin 5 has a substantially rectangular cross-section. This thickness is preferably constant along the entire length of the cooling fin 5, i.e., the cooling fin 5 has a substantially parallelepiped shape.

[0069] According to one embodiment of the invention, each cooling fin 5 is flared at its base 7, i.e., the cooling fin 5 has a substantially triangular cross-section. This flare extends preferably longitudinally along the entire length of said base 7.

[0070] According to one aspect of the invention, at least one cooling fin 5 has a bulge 9 at its free edge 8. This bulge 9 extends preferably longitudinally along the entire length of said free edge 8. Its purpose is, in particular, to prevent a protruding edge that could wear down the surrounding fairing elements and / or injure the operator. This bulge 9 could also have a beneficial aerodynamic effect in the event that the airflow in the central compartment of the turbojet engine is not laminar.

[0071] Just like the connecting rod 1 itself, it should be noted that the cooling fins 5 can be solid (see [Fig. 4] to [Fig. 9]) or hollow (see [Fig. 10]), entirely or partially. In [Fig. 3], the connecting rod 1 is solid, while it is hollow in [Fig. 4] to [Fig. 10].

[0072] In order to improve the thermal behavior of the cooling fins 5, these may have a perimeter 6 covered with a paint or a coating of A dark color, preferably black, would optimize the connecting rod's emittance and thus increase radiative heat exchange between connecting rod 1 and the engine. Indeed, their emissivity, which is proportional to the radial flux of radiation, would be improved.

[0073] Luminance, ranging from 0 (black) to 100% (white), indicates whether a color is light or dark. A dark color is defined here as a color whose luminance is less than or equal to 30%, that is, less than or equal to 3 on the Munsell value scale.

[0074] Naturally, the shape, number, and dimensions of each cooling fin 5 are designed to promote convection of the connecting rod 1 and preferably so that the minimum temperature at the middle of the connecting rod 1 is substantially equal to that of the ambient air. The shape, number, and dimensions of each cooling fin 5 depend on numerous parameters such as the length of the connecting rod 1, its diameter, the temperature of the air in which it is used, the temperature of the parts it must connect, etc.

[0075] In general, the shape, number, and dimensions of each cooling fin 5 are such that the convective heat transfer coefficient h of the connecting rod 1 is such that h > 10 W / m².K, which corresponds to the natural convection in the engine compartment. Indeed, the aim is to improve h = 10 W / m².K once the aircraft / engine is landed, so as not to have to use, for example, a blower, by adding fins and increasing / enhancing convection (increasing h beyond the observed natural convection value: h = 10 W / m².K).

[0076] According to another aspect of the invention, the shape and dimensions of each cooling fin 5, as well as their number, are such that the convective heat exchange surface A of the connecting rod 1 is increased by at least 10% compared to the same connecting rod without cooling fins. Indeed, one objective of the invention is to influence the convective heat exchange surface A and not the convective heat exchange coefficient h. For example, for a cylindrical connecting rod of radius R and length L, the heat exchange surface A is given by the following formula: A = 2ir.RL. If we consider a relationship A* = WA, where A is the outer surface, A* is the outer surface of the same connecting rod 1 but with cooling fins 5, and W is the multiplication factor, then according to the invention, W must be greater than 1.1 thanks to the presence of cooling fins 5.

[0077] The invention also relates to an assembly comprising a first part, a second part whose temperature is higher than that of the first part, and a connecting rod 1 according to the invention, linking the first part to the second. Preferably, the first part is an accessory housing 10 (cold part) while the second is a high-pressure compressor body 11 (hot part). whose mass temperature can, for example, reach a value approximately between 450 °C and 650 °C.

[0078] Generally, the temperature of the hot room is approximately 3-4 times the temperature of the cold room, which implies a risk of heat transfer from the hot room to the cold room by conduction. Therefore, convection is promoted (increasing the convective exchange surface area A), through the addition of cooling fins 5, to reduce or even eliminate conduction thanks to sufficient convection (h > 10 W / m².K).

[0079] Although described through a number of examples, variants and embodiments, the connecting rod 1 according to the invention includes various variants, modifications and improvements which will be obvious to a person skilled in the art, it being understood that these variants, modifications and improvements are part of the scope of the invention.< / e> < / e>

Claims

Demands

1. Assembly comprising a high-pressure turbomachine compressor body (11), an accessory housing (10) and a metallic connecting rod (1) linking the high-pressure compressor body (11) to the accessory housing (10), characterized in that said connecting rod (1) extends longitudinally along an axis (X) and comprises at least one convection cooling fin (5) extending longitudinally along the axis (X), each cooling fin (5) comprising a longitudinal base (7) by which it is connected to the connecting rod (1) and a longitudinal free edge (8) opposite said base (7).

2. Assembly according to claim 1, characterized in that the connecting rod (1) has several cooling fins (5) extending radially with respect to the axis (X) of the connecting rod (1) outwards from their base (7).

3. Assembly according to claim 1 or 2, characterized in that the connecting rod (1) has 4 to 30 cooling fins (5), preferably 8 to 20 cooling fins (5), distributed regularly around its circumference (6).

4. Assembly according to any one of the preceding claims, characterized in that at least one cooling fin (5) has a constant thickness (e) between its base (7) and its free edge (8).

5. Assembly according to any one of the preceding claims, characterized in that at least one cooling fin (5) is flared at its base (7).

6. Assembly according to any one of the preceding claims, characterized in that at least one cooling fin (5) has a bulge (9) at its free edge (8).

7. Assembly according to any one of claims 1, 2, 4, 5, or 6, characterized in that the connecting rod (1) comprises a single cooling fin (5) whose base width (7) is substantially equal to the diameter of said connecting rod (1) at the level of this base (7).

8. Assembly according to any one of claims 1 to 6, characterized in that the connecting rod (1) has several cooling fins (5) distributed over the same longitudinal half of the connecting rod (1). 12

9. Assembly according to the preceding claim, characterized in that the cooling fins (5) are all substantially parallel to a radial plane (P) which is perpendicular to the axis (X).

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