Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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AUTOMATIC SHUT-OFF VALVE FOR THE OIL CIRCUIT IN AN AIRPLANE
ENGINE
Subject of the invention
[0001] The present invention concerns an automatic
shut-off and isolation valve for the oil circuit in an
aircraft engine, in particular in a turbojet or a
turboprop.
State of the art
(0002] With certain turbojets, when the aircraft is
stopping, it is interesting to stop or reduce the oil
supply to the bearing housings before the aircraft has
completely stopped, so as to permit a complete drainage of
these housings, whilst the rotation is ceasing. In fact, in
these aircraft, the oil is supplied to the housings by a
pump, the feed pump, and collected at the bottom of these
housings by another pump, the collection pump. Both pumps
being of a volumetric type and driven by the main shaft of
the engine or HP shaft, they continue to work until this
shaft comes to a complete stop.
[0003] In certain cases, an imbalance may occur
between the oil. supplied by the feed pump and the
collection pump or pumps, which may cause an excess of oil
to appear in the housing and cause leaks
(0004] This imbalance may also lead to the
stagnation of oil in the housings during stopping phases of
the engine and may cause the coking of the stagnant oil,
especially in engines with one or several housings which
are particularly hot or particularly sensitive to the
phenomenon known as "soak back", of the temporary heating
of the mechanical parts when the engine is stopped.
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[0005] Document US-A-4,170,873 describes a system
comprising 2 valves, one for safety and the other for
control, allowing to control the oil flow fed to the
bearing housings during running phases at low speed. These
valves are controlled by the pressure in the various
circuits.
[0006] Document US-A-4,245,465 describes a 3-
function valve allowing for one thing to reduce the oil
flow fed to the bearing housings during running phases at
low speed, to cut: the supply of oil to the housings at very
low speed and to control the oil flow at high running
speed. This valve continuously lets oil flow to the oil
tank; it therefore never lets the full flow be fed to the
engine.
(0007] The so-called "anti-siphon" devices provided
for blocking any leak from the tank through the pump to the
bottom areas of the engine during periods of inactivity
occurring during the last turns of the engine may play a
part in reducing the quantity of stagnant oil. They act by
shutting off either the connection from the oil tank to the
feed pump or the outlet of the pump under a certain
pressure.
[0008] Whatever the "anti-siphon" methods used, they
have the common characteristic of acting very late during
the stopping phase, even after the engine has completely
stopped and if this is not the case, of sometimes
significantly slowing down the ignition on restart. The
resumption of the oil supply during restart thus occurs
systematically at a significantly higher speed than that at
which the flow was cut off during stopping. Moreover the
control of such devices to get a cut-off at a significant
speed during stopping, so as to ensure a good drainage,
might lead to make the re-ignition of the pump impossible
on restart. Certain "anti-siphon" devices do not show this
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disadvantage, but then they are based on a more or less
complex control system, which often consumes oil, and which
is useless in many engines.
[0009] None of these systems allows to efficiently
prevent the stagnation of oil in the housings during the
stopping phases of the engine. In particular, none of these
systems describes a device that would prevent the
phenomenon of coking of the stagnant oil.
Aims of the invention
[0010] The present invention aims to provide a
solution to the disadvantages of the state of the art.
[0011] In particular, the invention aims to provide
a simpler and lighter means than the devices known in the
state of the art ("anti-siphon" devices, US-A-4,245,465,
US-A-4,170,873, etc.), which can act at any moment during
the stopping phase of the engine and which allows on
restart to resume the supply at a speed equal or very close
to that at which the flow was cut off during stopping.
[0012] Moreover, the present invention aims to
achieve this objective with a simple and compact valve
without complicated control and scarcely sensitive to
friction and pollution.
Main characteristic features of the invention
[0013] A first aspect of the present invention
concerns a lubrication system in a closed circuit
comprising:
- a feed pump
- an oil tank
- a feed circuit supplying the oil to housings (20)
containing parts to be lubricated;
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a collection circuit returning the oil from the
housings to the tank ;
a bypass circuit returning the oil from the outlet of
the feed pump to the tank or to the inlet of the
feed pump ;
a valve comprising a first position and a second
position as well as an IN inlet , a first BP outlet
and a second M outlet , said IN inlet being connected
to the outlet from the feed pump , the first BP outlet
being connected to the bypass circuit and the second
M outlet being connected to the feed circuit ;
characterized in that, in the first position, the flow
entering via the IN inlet is diverted to the first BP
outlet and, in the second position, the incoming flow
is diverted to the second M outlet , said valve
switching from the first position to the second position
and vice versa, when the incoming flow exceeds a
predetermined threshold upwards and downwards
respectively.
[0014] According to preferred embodiments of the
invention, the lubrication system comprises at least one or
any suitable combination of the following characteristics:
- said valve comprises a valve which slides slightly
loose in a bore machined into a valve body between two
opposite seats , a first seat being connected to the IN
inlet and a second seat being connected to the BP outlet
, the M outlet emerging in the bore in a ring-shaped
cavity surrounding the first seat , so that:
- for a flow rate in the IN inlet lower than the
predetermined threshold, the valve is pushed by a
spring (5) on the first seat controlling the IN
inlet (1) and the connection from the IN inlet (1)
to the ring-shaped cavity (8) is blocked, the
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connection being opened towards the BP outlet via
at least one calibrated opening passing through
the valve and emerging laterally in the bore
upstream from the seat of the BP outlet;
5 - for a flow rate from the IN inlet greater than or
equal to the predetermined threshold, the valve
moves to the second seat in a position where it
rests against the second seat, closing the BP
outlet and where the IN inlet is connected to the
M outlet via the ring-shaped cavity , the first
seat being released. by the movement of the valve
- the valve is made of at least two parts which push
against each other.
- the seal of any outlet or of the two outlets of the
valve is provided by means of a cover principle of the
"sliding type" replacing the seat- valve contact.
- said valve comprises a valve which slides in a bore
between two opposite seats , a first seat being connected
to the M outlet and a second seat being connected to the BP
outlet the IN inlet (1) emerging in the bore in a ring-
shaped cavity surrounding the first seat and the bore or
the valve comprising at least one calibrated channel
between the two seats the parts of said valve being
proportioned in such a way that :
- for a flow rate from the IN inlet (1) lower than
the predetermined threshold, a spring (5) holds
said valve (4) rested against the first seat (23),
closing the M outlet (2), the flow being diverted
towards the BP outlet (3);
-for a flow rate from the IN inlet (1) greater
than or equal to the predetermined threshold, said
valve (4) moves to the second seat (24), opening
the M outlet (2) and closing the BP outlet
- the valve (4) is spherical.
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[0015] A second aspect of the invention concerns an
aircraft engine comprising a lubrication system such as
described above. This engine is for example a turbojet, a
turboprop, a turboshaft or a helicopter engine.
[0016] As an advantage, in such an engine, the
lubrication system and said valve are located in one
casing.
Brief description of the diagrams
[0017] Diagrams 1A and 1B show a valve according to
a first particular embodiment of the invention.
[0018] Diagrams 2A and 2B show a valve according to
a second particular embodiment of the invention.
[0019] Diagrams 3A and 3B show a valve according to
a third particular embodiment of the invention.
[0020] Diagrams 4A and 4B show a valve according to
a fourth particular embodiment of the invention.
[0021] Diagrams 5A and 5B show a valve according to
a fifth particular embodiment of the invention.
[0022] Diagram 6 shows schematically a lubrication
system according to the present invention.
[0023] Diagram 7 shows a scheme of the principle of
an aircraft engine equipped with an automatic shut-off
valve for the oil circuit according to the present
invention.
Detailed description of the invention
[0024] According to the present invention, the flow
from the feed pump to the engine is cut off before the
engine has completely stopped, whilst letting the
collection pumps operate normally. From this moment
onwards, the collection pumps will drain the housings
efficiently, since they continue to suck in the oil flowing
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from the wet components and walls, without any new oil
being fed in.
[0025] In the event of such an interruption in the
flow supply during stopping, it is nevertheless necessary
to ensure that the engine is resupplied early enough on
restart.
[0026] This cutting off of the oil flow supply when
the engine is stopped thus permits to combat the coking in
aircraft engines.
[0027] In the present invention, this function of
stopping the flow supply to the housings is achieved by
means of a shut-off and "bypass" valve. This valve
comprises three ways and two positions. It is placed at the
outlet of the feed pump (IN way) and diverts the flow from
the pump to the tank or the inlet of the pump (BP way,
stands for "bypass") when this flow is weak, whilst closing
the connection to the engine (M way). When the flow from
the pump reaches a predetermined threshold, it diverts this
flow to the engine (M way) and closes the connection to the
tank or the inlet of the pump (BP way) again.
[0028] Particular embodiments of the valve according
to the invention are shown in Diagrams 1A, 1B, 2A, 2B, 3A,
3B, 4A, 4B, 5 A and 5B.
[0029] In a first particular embodiment of the
invention shown in Diagrams 1A and 1B, the valve is
composed of a valve 4, which slides slightly loose in a
bore 7, between two opposite seats 10, 11. One is connected
to the IN way, the other to the BP way. The M way emerges
in a ring-shaped cavity 8 surrounding the IN seat.
[0030] At rest or whilst the flow via the IN way is
lower than a predetermined threshold, the valve 4 is pushed
by a spring 5 towards the seat 10 controlling the IN way
and the connection from the IN inlet to the ring-shaped
outlet 8 emerging in the M way is blocked (Diagram 1A).
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However, the connection is possible to the BP, via the
calibrated opening 9 emerging in the cavity 12 defined by
the bore 7 upstream from the seat 11 of the BP way.
[0031] The pressure of the IN way thus applies to
the surface of the valve resting on the seat 10. Since the
BP way is connected to the tank 16 or the inlet of the
pump, it is considered to be at zero pressure and the
pressure of the IN way is controlled by the flow of the IN
way, controlled by the volumetric feed pump 17 (Diagrams 6
and 7) and passing through the connection channel 9, whose
hydraulic resistance is calibrated. When the force exerted
by this pressure on the valve 4 is less than the load of
the spring 5, the valve presses against the seat 10 of the
IN way and closes the M way (Diagram 1A).
[0032] When, as a result of an increase in the flow
from the pump, this pressure becomes greater than the load
of the spring 5 in this position, the valve moves to the
other seat, creating additional hydraulic resistance to the
flow and increasing the pressure differential applied to
the valve 4. This functioning is verified provided that the
M way offers significant hydraulic resistance (which is
generally the case with aircraft engines) and that the way
from the connecting channel 9 between the two seats 10, 11
is properly suited to it.
[0033] At higher flow rates, the valve 4 comes to
rest against the seat 11 emerging in the BP way, which is
thus completely closed, and the pressure of the engine
circuit applies to the entire surface of the valve 4 on the
side of the M way, which is locked in this position by the
pressure (Diagram 1B). When the flow rate drops, the
resulting decreasing in pressure allows the spring to push
the valve back to its original position (Diagram 1A).
[0034] The fluctuation levels in one direction and
the other, the functional hysteresis and the stability are
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controlled by the ratios of the surface areas of the seats,
the preload, the direction and stiffness of the spring 5
and the ratio of the hydraulic resistance of the connecting
channel 9 relative to that of the M way.
[0035] In other particular embodiments of the
invention:
- the valve may be of any shape, provided that the
hydraulic principles mentioned above are observed;
- the valve might be made in two or more parts that are
more or less fixed and which push against each other;
- the connecting channel may be made in various ways
(see an alternative in Diagrams 2A and 2B).
[0036] The seal of any outlet or of the two oulets
of the valve according to the invention could also be
realized by means of the cover principle of the "sliding
type" 13, instead of a seat-valve-valve piece contact. This
principle is illustrated in Diagrams 3A and 3B.
[0037] In another alternative embodiment shown in
Diagrams 4A, 4B, 5A and 5B, the valve is composed of a
valve 4, which slides in a bore 7 between two seats 23, 24.
Depending on its position and the seat which it is resting
on, it opens or closes the connection to the BP or M ways.
At rest (Diagrams 4A and 5A), the valve 4 is pushed by a
spring 5 to the seat 23 controlling the M way, which it
closes. The valve 4 or the bore 7 is also fitted with one
or more calibrated connections 15 allowing the connection
between the ring-shaped zones located around the seats 23,
24 on both sides of the valve 4. The IN way emerges via the
bore 7, in the ring-shaped space surrounding the seat 23 of
the M way. The pressure of the IN way thus applies to the
ring-shaped surface of the valve around the seat 23. Since
this zone is connected to the BP way, which is open by
means of the calibrated channel 15, the flow moves from the
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IN way to the BP way, the M way being closed by the spring
5. Since the BP way is connected to the tank 16 or the
inlet of the pump 17 (Diagrams 6 and 7), it is considered
to be at zero pressure and the pressure of the ring-shaped
5 zone of the valve 4 around the seat 23 of the M way is
controlled by the flow passing through the connecting
channel 15. When the force exerted by this pressure on the
valve 4 is lower than the load of the spring 5, the valve 4
remains rested against the seat 23 of the M way and keeps
10 it closed (Diagram 4A). When, as a result of an increase in
the flow from the pump 17, this pressure becomes greater
than the load of the spring 5 in this position, the valve
moves to the other seat 24, creating additional hydraulic
resistance to the flow and increasing the pressure
differential applied to the valve 4. At the same time, the
flow begins to move towards the M way and the IN pressure
spreads progressively to a greater surface area of the
valve, increasing the imbalance. This functioning is
verified, provided that the M way offers significant
hydraulic resistance (which is generally the case with
engines) and that the way of the connecting channel 15
between the two seats 23, 24 is properly suited to it. At
higher flow rates, the valve 4 is rested against the seat
24 of the BP way, which is completely closed, and the
pressure of the engine circuit applies to the entire
surface of the valve on the M side, which is locked in this
position by the pressure (Diagram 4B). When the pressure
drops, the decreasing in pressure allows the spring 5 to
push the valve 4 back to its original position (Diagram
4A). The fluctuation levels in one direction and the other,
the functional hysteresis and the stability are controlled
by the ratios of the surface of the seats, the preload, the
direction and stiffness of the spring 5 and the ratio of
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the hydraulic resistance of the connecting channel 15
relative to that of the M way.
[0038] In one embodiment of the invention, the valve
4 is of a spherical shape as shown in Diagrams 4A and 4B.
[0039] In particular embodiments of the present
invention, the calibrated connection between the two sides
may advantageously be realised in the valve itself as shown
in Diagrams 5A and 5B, by grooves in the bore or even via
an external channel.
