The present invention relates to an oil circuit in a turbine engine and a turbine engine equipped with such an oil circuit.
As with all internal combustion engines, turbine engines, whether turbojet or turboprop, include moving parts which rub against or other moving parts against the fixed parts.
To not break because of heating due to friction, the parts are anointed with oil that allows one hand to limit (or contain) the heating and, secondly, to lubricate to facilitate sliding parts on each other.

The oil circulates in a circuit 10 provided with heat exchangers, including oil / air exchangers 12, as shown in Fig 1 having a die 14, in the form of a shaped winding pipe so as to perform a heat exchange wherein oil from said parts is introduced and then cooled before being re-injected on said parts.

When starting a turbomachine in cold conditions (e.g. with a temperature below 0 ° C), the oil in the matrix 14 of the air / oil 12 (or interchanges if any) may be jelly making it difficult if not impossible the heat exchange between the oil and the air since the oil can flow through the heat exchanger 14 of the matrix 12. It is then necessary to previously heat the matrix 14 to junction 12 of air / oil heat.

For this, it is known to provide the heat exchanger 12 air / oil from a bypass line 16 serving as a defrosting channel and which surrounds the matrix 14 of heat exchanger 12 air / oil so as to heat the 'frozen oil. This bypass pipe 16 is connected at its upstream end at the inlet 18 of the heat exchanger 12 and outlet 20 of the heat exchanger 12. The oil circuit 10 also includes a

valve 22 for controlling the oil flow in the bypass line 16 in order to authorize the flow of oil in the matrix 14 of heat exchanger 12 when the temperature is below a predetermined threshold. However, the oil passage section of the bypass line 16 is lower than the oil passage section in the heat exchanger air / oil, there is an overpressure in the oil circuit when the matrix 14 of exchanger 12 is frozen. The pressure induces a risk of damage to the oil circuit 10.

In order to reduce this pressure, an obvious solution is to increase the passage section of the bypass line 16 so as to increase the flow rate without changing the operating pressure conditions of the feed pumps. However, for reasons of space, increasing the passage section of the bypass line 16 is not possible.

The invention particularly aims to provide a simple, efficient and economical to this problem.

To this end, the invention proposes an assembly for a turbomachine comprising an oil circuit comprising a heat exchanger air / oil, a primary bypass line connecting an inlet of the heat exchanger air / oil to an output of the exchanger thermal air / oil heat exchanger and surrounding the air / oil so as to exchange heat with the heat exchanger air / oil, and a secondary bypass the primary pipe connecting the upstream of the primary bypass line to downstream of the primary bypass line, the circuit further comprising at least one control valve of the passage of oil flow in the primary and secondary pipes branching and control means of theopening of said at least one valve to a temperature below a threshold temperature.

According to the invention, the addition of a secondary bypass duct allows to derive a portion of the fluid conduit primary shunt, which reduces the fluid pressure in the primary branch pipe in cold operating conditions. The combination of a control valve of the passage of oil flow in the primary and secondary lines and bypass control means of the opening of the valve to a temperature above a threshold temperature, makes it possible to make the operating primary and secondary pass lines only in cold operating conditions, no oil flow not flowing in these conduits when the temperature is higher than the predetermined threshold temperature.

The pressure drop increases with the decrease in temperature due to the increased oil viscosity, it is understood that the addition of a second bypass line is particularly useful. However, this secondary impacts driving the little warming function of the oil of the air / oil by the primary pipe. For example, a bypass 30% of the oil flow from the primary pipe branching into the secondary bypass line keeps the same defrosting time with the heat exchanger.

According to another characteristic of the invention, the assembly comprises a single valve arranged at the outlet of the primary bypass line and downstream of the outlet of the secondary bypass. It would of course be possible to have a valve for each of the primary pipe and bypass conducting secondary bypass. However, this complicates the evidence mounting.

In another embodiment, the single valve could be arranged inlet of the primary bypass duct and upstream of the inlet of the secondary bypass.

The control valve may be a valve which can adopt at least two positions, a first open position allows the oil passage and a second closed position blocks the oil passage. The threshold temperature is for example about 70 ° C.

In another embodiment, the control valve can be a one-way two-way valve that can adopt at least two

positions, a first open position allows the passage of oil through the valve and a second closed position blocks the passage of oil through the valve, but also intermediate positions.

According to another characteristic of the invention, the secondary pipe branch may have a length at least ten times less than the length of the primary bypass. Also, the circuit includes the secondary bypass line which may have a diameter at least three times smaller than the diameter of the primary bypass.

Having a secondary pipe shorter branching and / or having a smaller diameter than the primary bypass line, according to the aforementioned ratios, provides a good distribution of flow between the primary and bypass line secondary branch in order to lower the pressure drop in the primary pipe while ensuring a good defrost the heat exchanger.

In addition, a secondary pipe shorter branching and / or having a small diameter according to the aforementioned ratios, prevents an overpressure in the oil circuit when the matrix of the oil exchanger is frozen without increase the section of the primary bypass. Thus, the size and weight of the primary pipe shunt are reduced.

A second bypass pipe having a shorter length will be preferred because of the induced weight reduction. Moreover, it is very advantageous when the inlet and outlet are arranged close to each other. The diameter of the secondary bypass line is thus adjusted according to the length of the pipe so as to ensure a good distribution of the oil flow in the primary and secondary pipes branching.

The invention also relates to a turbomachine comprising an oil circuit as described above, wherein the heat exchanger

thermal oil / air radially outwardly defines a flow surface of a secondary air flow.

The invention will be better understood and other details, features and advantages of the invention will become apparent from reading the following description given by way of non-limiting example with reference to the accompanying drawings in which:

- Figure 1 is a schematic representation of an oil circuit of the prior art and already described previously;

- Figure 2 is a schematic representation of an oil circuit of the invention, the valve being in an open position;

- Figure 3 is a schematic representation of an oil circuit of the invention, the valve being in a closed position;

- Figure 4 is a schematic perspective view from downstream of a turbomachine comprising a heat exchanger according to the invention;

- Figure 5 is a schematic sectional view of the positioning of a heat exchanger into a vein of the turbomachine;

- Figure 6a is a schematic view of an assembly according to the invention;

- Figure 6b shows a sectional view of the assembly in a radial plane.

- Figure 7 is a schematic perspective view in section on a radial plane of the assembly of Figure 6a.

Referring to Figure 2 which shows an oil circuit 24 according to the invention. In the present description, the term exchanger refers to a medium which is capable of exchanging heat between two entities. Conventionally a structural frame surrounding the heat exchange means, the assembly can therefore be described as heat exchanger without the structural casing is actively involved in heat exchange. Thus, it is well understood that the invention also covers this type product.

As shown in Figure 2, the oil circuit 24 comprises a primary conduit 26 identical to the bypass pipe 16 to bypass the Fig 1 and a secondary conduit 28 bypass that connects the upstream of the primary conduit 26 bypass downstream of the primary conduit 26 bypass. More specifically, the upstream end of the primary pipe 26 and bypass the upstream end of the secondary pipe 28 to bypass are connected to each other at the entrance of the supply line 30 of the exchanger 31 of heat or more specifically of the matrix 33 of the exchanger 31 to heat.

The downstream end of the primary conduit 26 is branch connected to the inlet of a valve 22 whose opening / closing is controlled by control means 35 allowing / blocking the flow of fluid through the valve 22 to a lower oil temperature at a given temperature threshold, for example 70 ° C. In a particular embodiment of the invention, the means of control of the valve are passive and comprise wax adapted to vary in volume depending on the surrounding temperature. The change in volume of the wax in the valve for selectively passing the oil through the valve or blocking the oil flow upstream of the valve. The output of the valve 22 is connected to an outlet pipe 34 of the matrix of the heat exchanger.

In an alternative embodiment (not shown), the valve 22 could be mounted upstream of the upstream end of the primary conduit 26 bypass so as to allow fluid flow in primary conduit 26 to bypass a temperature below the threshold temperature and prohibit the flow of oil to a temperature above the threshold temperature, the oil flow being allowed in the feed pipe 30 of the oil matrix regardless of the temperature. In this configuration, the upstream end of the secondary conduit 28 is branch connected to the outlet of the valve 22 or downstream of the downstream end of the primary conduit 26 bypass.

In yet another embodiment of the invention, it would be possible to use a valve for each drive primary 26 and secondary 28 of derivation, these valves then being controlled simultaneously in opening and closing by the control means.

In the embodiment of Figure 2, the valve 22 is preferably a one-way on-off valve having two positions one of which permits the flow of oil in the primary pipe 26 and secondary branch 28 and the other prohibits travel in said ducts 26, 28. It would be even possible to use a pilot valve with two ports and two positions.

The circulation of oil in the matrix 33 is shown by solid arrows in Figure 2.

According to the invention, when the oil of the matrix 33 is frozen, the oil circulates in the primary pipe 26 and secondary pipe 28 as shown by arrows in dotted lines in Figures 2 and 3.

The dual circulation of oil in the primary conduit 26 and secondary conduit 28 increases the oil flow when the moving die 33 is frozen, thereby reducing the pressure in the oil circuit 24, more particularly in the primary pipe for a given oil flow flowing in the supply line 34.

Preferably, the secondary pipe 28 has a lower oil passage section or equal to the diameter of the oil passage section of the primary conduit 26 so that the oil flows mainly in the primary conduit 26 and thus ensure the thawing of the die 33.

Similarly, we understand that the secondary line must be as short as possible to reduce the loss in the primary pipe while ensuring proper thawing. Thus, by way of example, the secondary duct may be defined by a length at least ten times smaller than the primary pipe and / or a diameter three times less than the first conduit.

Figure 4 shows a turbomachine 36 seen from the downstream thereof (in the direction of the airflow) comprising an impeller 38 and the heat exchanger air / oil 31 carried by an outer annular casing 40 of the secondary air flow stream (arrow A in Figure 5). As best seen in FIG 5, the heat exchanger 31 is carried by the casing 40 and the matrix is ​​arranged so as to form a radially outer surface of flow of the secondary air flow of the turbomachine, c ' is to say the air flow bypassing the low and high pressure compressors, a combustor and high and low pressure turbines.

In practice, it is understood that the heat exchanger 31 to heat air / oil in the form of a ring arranged around the axis 42 of the turbine engine 36.

In the description the term "branch line" should be understood as concerning any fluid passage for circulating oil between the upstream and downstream of the primary pipe.

Thus, in the heat exchanger described above, the secondary conduit may be a simple hole made in a wall separating the oil flowing in the supply pipe 30 and the oil flowing in the downstream portion of the primary conduit 33.

In one embodiment of the invention, the primary conduit to a diameter of about 12 mm and the secondary pipe is a hole as shown in the previous section and has a diameter of 5 mm.

The length of the primary pipe is, in an embodiment, of the order of several meters.

Figure 6a shows an assembly 44 according to the invention comprising a housing formed of a first half-ring 46 and a second half-ring 48 connected to one another by a central portion 50. This assembly 44 comprises , as described above, an oil circuit 24 and a matrix 33 of heat exchange 70 as well as cooling fins arranged on the radially inner side of the oil 33. the matrix core comprises an oil inlet 30 in the matrix 33, an outlet

oil 34 of the die 33 and the one-way valve 22. As described above, the oil inlet 30 also supplies the primary pipe 26 and secondary pipe 28 and the oil outlet 34 is connected to the output of the unidirectional valve 22 or more generally at an output of the valve 22.

The first half-ring 46 comprises a first branch 46a semicircular conduit and one second semicircular 46c branch pipe connected to each other by a connecting leg 46b formed at the circumferential end part opposite to the Central 50 (Figure 6b). The first part 46a is formed upstream of the second branch 46c and the connecting leg 46b of the first half-ring 46 extends substantially axially. The first part 46a, the second branch 46c and the connecting leg 46b together form a first portion 52 of the primary conduit 26 bypass.

The second half-ring 48 includes first semicircular 48a branch line and a second semiconductor circular 48c branch pipe connected to each other by a connecting leg 48b formed at the circumferential end opposite to the central portion 50. the first part 48a is formed upstream of the second branch 48c and 48b connecting limb extends substantially axially. The first part 48a, the second branch 48c and the branch 48b connecting the second half-ring 48 together form a second portion 54 of the primary conduit 26 bypass. The first part 52 of the primary bypass line and the second portion 54 of the primary bypass line integrally together define primary conduit 26 bypass.

More specifically as shown in Figure 7, the central part 50 carries the valve 22 which comprises a tubular body 54 in which is slidably mounted a piston 56 between a first position bearing on a seat 58 closing off the oil flow between the outlet 60 of the primary conduit 26 and the outlet 34 of the die 33 and a second position wherein the piston 56 is away from the seat 58 and allows flow of oil. The piston 56 comprises a first 56a slide radially outer portion sealingly in the body and connected by a rod 56b to 56c a piston head designed to come into bearing on the seat 58 or periphery of the outlet orifice 62. This head comprises a chamfer 64 annular bearing on the periphery of the orifice 62. When the oil flows through the

As shown in Figure 7, the secondary pipe 28 connects the upstream end of the primary pipe 26 to the downstream end of the primary pipe 26. This figure also shows the inlet port 68 of oil in the foreline 26, this port 68 being connected to the oil inlet 30 of the die 33.

The primary line 26 and secondary line 28 are fed by the inlet oil 30 of the matrix 33. The oil in the primary pipe 26 and secondary pipe 28 then flows to the valve 22 which blocks oil at the outlet 60 of the primary conduit 26 and allows the oil to escape through the outlet 34 of the oil matrix 33.

The flow in the primary duct 26 comprises more particularly a flow in the first half-ring 46 then in the second half-ring 48 before joining the valve 22. More specifically, the oil flows in the first branch 46a semicircular, and 46b connecting limb and finally the second 46c semi-circular part of the first half ring 46. once the oil is at the downstream end of the second semi-circular arm 46c of the first half-ring 46, the oil flows thereafter in the second half-ring 48 to the semi-circular region of the second branch 48c and the connecting leg 48b and finally to the first semicircular leg 48a before reaching the exit 34 of the oil matrix 33 through the valve 22.

CLAIMS
1. Assembly (44) for a turbomachine (36) comprising an oil circuit including an air / oil heat exchanger (31), a primary conduit (26) for bypass connecting an inlet of the air / oil heat exchanger (31) an output of the air / oil heat exchanger (31) and surrounding the heat exchanger air / oil (31) so as to exchange heat with the heat exchanger air / oil (31) and a secondary pipe (28) bypass of the primary line (26) connecting the upstream of the primary conduit (26) branching at the downstream of the primary conduit (26) branch, the circuit (24) also comprising at least one valve (22) control the passage of oil flow in the primary ducts (26) and secondary (28) and bypass control means (35) of the

2. The assembly of claim 1, wherein the circuit comprises a single valve (22) arranged at the output of the primary pipe

(26) branching and downstream of the outlet of the secondary conduit (28) branching.

3. An assembly according to one of claims 1 to 2, wherein the valve (22) is a control valve that can assume at least two positions, a first open position allows the oil passage and a second closed position blocks the passage oil through the valve (22).

4. An assembly according to any one of claims 1 to 3, wherein the threshold temperature is 70 ° C.

5. An assembly according to any one of claims 1 to 4, wherein the valve (22) is a control valve (22) unidirectional two-way.

6. An assembly according to any one of claims 1 to 5, wherein the secondary conduit (28) branching has a diameter at least three times smaller than the diameter of the primary conduit (26) branching.

7. A turbomachine comprising an assembly according to any one of claims 1 to 6, wherein the heat exchanger oil / air radially outwardly delimits a flow surface of a secondary air flow.