Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CONVERSION ACTUATION SYSTEMS AND METHODS FOR TILTROTOR
AIRCRAFT
TECHNICAL FIELD
[0001] The application relates generally to tiltrotor aircraft and, more
particularly, to
actuation systems for tiltrotor aircraft.
BACKGROUND
[0002] Tiltrotor aircraft are hybrids between traditional helicopters and
traditional
propeller driven aircraft. Typical tiltrotor aircraft have rotor systems that
are capable of
articulating relative to the aircraft fuselage. This articulating portion is
referred to as a
pylon or nacelle. Tiltrotor aircraft are capable of converting from a hover
mode, in which
the aircraft can take-off, hover, and land like a helicopter; to an aircraft
mode, in which
the aircraft can fly forward like a fixed-wing airplane.
[0003] The design of tiltrotor aircraft poses unique problems not associated
with either
helicopters or propeller driven aircraft. In particular, the tiltrotor
assemblies must be
articulated between hover mode and aircraft mode. To convert between the hover
mode
and aircraft mode, the pylon must rotate relative to the fuselage.
[0004] Some tiltrotor aircraft use linear actuators, such as screw jacks or
hydraulic
jacks, to rotate the pylon about a rotation point relative to the fuselage.
The actuation
mechanism may experience undesirable effects when the pylons are oriented into
the
aircraft mode.
SUMMARY
[0005] There is provided a method for reducing mechanical backlash on a rod of
an
actuator, the rod drivingly connected to a spindle for displacing rotors of an
aircraft
between a hover mode and a flight mode, the method comprising: displacing the
rod to
displace a component with the spindle until the component abuts against a
downstop of
the aircraft and applies a load against the downstop; and passively
maintaining the
component against the downstop to maintain the load applied against the
downstop.
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[0006] There is provided a method of displacing rotors of an aircraft between
a hover
mode and an aircraft mode, the method comprising: rotating a spindle drivingly
connected to the rotors about a spindle axis to displace the rotors between
the hover
and aircraft modes until a component displaceable with the spindle abuts
against a
downstop of the aircraft and applies a load against the downstop; and
passively
maintaining the component against the downstop to maintain the load applied
against
the downstop.
[0007] There is provided an aircraft, comprising: rotor ducts each having a
rotor, the
rotor ducts and the rotors being displaceable between a hover mode and an
aircraft
mode; a spindle drivingly connected to one of the rotor ducts and rotatable
about a
spindle axis to displace the rotor duct between the hover and aircraft modes;
a
downstop fixedly mounted within the aircraft and defining a contact surface; a
linking
member mountable to the spindle and displaceable therewith about the spindle
axis
toward and away from the contact surface of the downstop; and an actuator with
a rod
displaceable by a drive mechanism, the rod mounted to the linking member such
that
displacement of the rod causes the spindle to rotate about the spindle axis,
the actuator
having a passive friction device engaged with the rod to stop displacement
thereof, the
drive mechanism operable to displace the rod to abut the linking member
against the
contact surface and to apply a load with the linking member against the
downstop, the
drive mechanism disengageable from the rod upon the load being applied against
the
downstop, the passive friction device passively engaging the rod and stopping
displacement thereof upon the load being applied against the downstop.
DESCRIPTION OF THE DRAWINGS
[0008] Reference is now made to the accompanying figures in which:
[0009] Fig. 1A is a perspective view of an aircraft in an aircraft mode;
[0010] Fig. 1B is a perspective view of the aircraft of Fig. 1A in a hover
mode;
[0011] Fig. 1C is a partial cutaway view of the end of a wing of the aircraft
of Fig. 1A
showing a pylon-conversion actuation system;
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[0012] Fig. 2 is an enlarged cutaway view of the pylon-conversion actuation
system of
Fig. 1C;
[0013] Fig. 3 is schematic view of the pylon-conversion actuation system of
Fig. 1C;
[0014] Fig. 4 is a flow chart of displacing rotors of an aircraft between a
hover mode
and an aircraft mode; and
[0015] Fig. 5 is a perspective view of another aircraft in hover mode.
DETAILED DESCRIPTION
[0016] Referring to Fig. 1A, a tiltrotor aircraft 10 is shown in aircraft
mode. The aircraft
in Fig. 1A is an unmanned aerial vehicle (UAV), and therefore has no provision
for
onboard human pilots. The aircraft 10 is not limited to UAVs and may be a
manned
aircraft 10 as well. The aircraft 10 has a fuselage 13 with wings 15 extending
from the
fuselage 13. At the ends of wings 15 are rotor ducts 17, which rotate on the
ends of
wings 15 through a range of from about 90 of rotation up to about 1000 of
rotation. The
rotor ducts 17 are sometimes referred to as pylons or nacelles. The rotor
ducts 17
provide a rotatable support for rotors 19, and the engine used to power rotors
19 may
be located within the fuselage or the corresponding rotor duct 17. When
configured in
the aircraft mode, the rotors 19 rotate in a vertical plane to drive the
aircraft 10 forward
as in a conventional propeller-driven aircraft. Each rotor duct 17 is
generally horizontal,
as shown in Fig. 1A. While the aircraft 10 is shown with rotor ducts 17
located at the
ends of wings 15, other configurations may be used, such as a configuration in
which
the rotor ducts 17 are rotatably connected to the fuselage. In the aircraft
mode, the rotor
ducts 17 and rotors 19 can be converted or pivoted to position the rotors 19
in
essentially a horizontal plane, where they can act as a helicopter rotor and
the aircraft
10 operated as a helicopter for vertical takeoff and landing, as shown in Fig.
1B. The
tiltrotor aircraft 10 is shown in a hover mode in Fig. 1B. In the hover mode,
the plane of
each rotor 19 is generally horizontal and each rotor duct 17 is generally
vertical. The
aircraft 10 may be different from the configuration shown. Another possible
embodiment
of the aircraft 100 is shown in Fig. 5. The aircraft 110 is a manned aircraft,
and has a
fuselage 113 with wings 115 extending from the fuselage 113. Rotor ducts 117
are
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arrange around the fuselage 113 and the wings 115, and rotate relative to the
fuselage
113 from about 90 of rotation up to about 1000 of rotation. The rotor ducts
117 each
have rotors 119 which may be "ducted", and which are rotatable with the rotor
ducts
117. Other configurations for the aircraft 10,110 are also possible.
[0017] Referring to Fig. 1C, the end of one of the wings 15 is shown in
partial cutaway
view. The wing 15 is shown with a pylon-conversion actuation system 21
exposed, and
the rotor duct 17 and corresponding rotor 19 are shown in phantom lines. The
rotor duct
17 in Fig. 1C is in a conversion mode, in other words, between the hover mode
and the
aircraft mode. The wing 15 structurally includes a skin 23 and structural ribs
25. The
pylon-conversion actuation system 21 includes a spindle 27 extending from the
end of
the wing 15 through two ribs 25. Where the spindle 27 passes through the ribs
25,
bearing housings 29 support the spindle 27 and allow for rotation of the
spindle 27
about a spindle axis 31 (see Fig. 2). The spindle axis 31 is transverse to the
axis of
rotation 19A of the corresponding rotor 19, as shown in Fig. 1C. The spindle
axis 31
may intersect the axis of rotation 19A of the rotors 19.
[0018] Referring to Fig. 1C, the spindle 27 is in the form of a spindle duct
which is a
hollow cylindrical body extending along the spindle axis 31. The spindle 27 is
drivingly
connected to the corresponding rotor duct 17 so that rotation of the spindle
27 about the
spindle axis 31 causes the rotor duct 17 to displace between the hover and
aircraft
modes. The connection between the spindle 27 and the rotor duct 17 may take
different
forms. In one possible configuration, and as shown in Fig. 2, the spindle 27
has a distal
spindle flange 27A which is fastened to structure on the rotor duct 17. The
structure of
the rotor duct 17 therefore also rotates about the spindle axis 31, and
through
appropriate gearing in the rotor duct 17, the rotational motion of the
structure about the
spindle axis 31 is converted into rotational motion of the rotor duct 17
between the
hover and aircraft modes. In Fig. 1C, the rotor duct 17 is drivingly connected
to a single
spindle 27. In an alternate embodiment, a single spindle 27 is mechanically
linked to
multiple rotor ducts 17, such that rotation of the spindle 27 drives
displacement of the
rotor ducts 17 between the hover and aircraft modes.
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[0019] Referring to Fig. 2, the pylon-conversion actuation system 21 includes
a linking
member 33. The linking member 33 is mechanically connected to the spindle 27
and is
displaceable with the spindle 27 about the spindle axis 31. The linking member
33
transmits a drive from an actuator 39 of the pylon-conversion actuation system
21 to the
spindle 27, so as to rotate the spindle 27 and drive the rotor duct 17. Many
possible
configurations of the linking member 33 are possible and within the scope of
the present
disclosure.
[0020] One possible configuration of the linking member 33 is shown in Fig. 2.
The
linking member 33 is an assembly of components, and includes a spindle arm 27B
that
is mounted to the duct of the spindle 27 and rotatable about the spindle axis
31. The
spindle arm 27B extends radially outwardly from an outer surface of the duct
of the
spindle 27, and from the spindle axis 31. The linking member 33 also includes
a nut 39A
of the actuator 39. The nut 39A is connected to a distal end of the spindle
arm 27B that
is spaced radially outwardly from the duct of the spindle 27. The nut of 39A
is displaced
by the actuator 39, as explained in greater detail below, and thereby
displaces the spindle
arm 27B and the spindle 27 about the spindle axis 31. In another possible
configuration,
the linking member 33 includes only the nut 39A of the actuator 39.
[0021] Referring to Fig. 2, the actuator 39 of the pylon-conversion actuation
system 21
includes a rod 39B mounted to the linking member 33, for example via the nut
39A. The
rod 39B is displaceable by a drive mechanism 39C of the actuator 39. The drive
mechanism 39C drives the rod 39 in order to effect displacement of the linking
member
33 and the spindle 27 about the spindle axis 31.
[0022] Many configurations of the drive mechanism 39C and of the rod 39B are
possible. For example, in Fig. 2, the drive mechanism 39C is a motor 39C'
powered by
electricity. In an alternate embodiment, the actuator 39 is a hydraulic
actuator, and the
drive mechanism 39C includes a piston and fluid chamber fillable with
hydraulic fluid. The
actuator 39 in Fig. 2 is a linear actuator. In operation, the drive mechanism
39C drives
the rod 39B to linearly displace along a direction D1 parallel to a rod axis
39B' between
an extended position and a retracted position. This linear displacement of the
rod 39B is
converted into rotational displacement of spindle 27 about the spindle axis 31
via the
Date Recue/Date Received 2021-06-17
linking member 33, causing the rotor duct 17 to rotate between the hover and
aircraft
modes.
[0023] In Fig. 2, the actuator 39 includes a ball screw actuator 35. The ball
screw actuator
includes the nut 39A previously described, which has internal threads, and the
rod 39B
is a screw 35A with external threads. A plurality of spherical balls are
captured between
the threads of the nut 39A and the threads of the screw 35A. In the particular
configuration
shown, the motor 39C' drives rotation of the screw 35A about the rod axis
39B', and the
balls help the nut 39A to resist a similar rotational movement. This relative
movement
between the screw 35A and the nut 39A causes the nut 39A to move axially
relative to
the screw 35A along the rod axis 39B', and thereby cause movement of the
linking
member 33 and the spindle 27. It will be appreciated that the ball screw
actuator 35 may
cause the opposite relative movement, e.g., where the nut 39A rotates about
the rod axis
39B', while the screw 35A resists a similar rotation, to cause the screw 35A
to move
axially through the nut 39A. Reference is made to US 5,092,539 for additional
details
about the ball screw actuator 35. A housing of the ball screw actuator 35 is
pivotably
mounted to the aircraft 10. For example, and as shown in Fig. 2, the ball
screw actuator
35 is mounted to the rib 25 at a pivot 35B. This allows the ball screw
actuator 35, and the
nut 39A and the screw 35A, to pivot about a pivot axis 35B' defined by the
pivot 35B to
change the orientation of the screw 35A as the spindle 27 rotates about the
spindle axis
31.
[0024] The actuator 39 has a passive friction device 37 which engages with the
rod 39B.
The passive friction device 37 is in frictional contact with the rod 39B, and
slows or stops
displacement of the rod 39B, and thus stops displacement of the linking member
33, the
spindle 27, and the rotor duct 17. In Fig. 2, the passive friction device 37
is continuously
engaged with the rod 39B and is thus always in frictional engagement with the
rod 39B.
To overcome the frictional engagement of the passive friction device 37, in
Fig. 2 the
motor 39C' is sized to provide a torque output which can exceed the frictional
torque
engagement of the passive friction device 37 with the rod 39B. The excess
torque
provided by the motor 39C' allows for displacement of the rod 39B, and thus
allows for
the rod 39B to drive displacement of the linking member 33, the spindle 27,
and the rotor
duct 17. The passive friction device 37 is passively engaged with the rod 39B
in order to
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Date Recue/Date Received 2021-06-17
allows for the rod 39B to drive displacement of the linking member 33, the
spindle 27,
and the rotor duct 17. The passive friction device 37 is passively engaged
with the rod
39B in order to passively maintain its position when the motor 390' does not
apply the
excess torque. This means that the passive friction device 37 does not require
energy
or activation to engage the rod 39B. The passive friction device 37 operates
differently
from "active" devices, such as brakes, which are activated or provided with
energy to
frictionally engage or lock onto another component. Such active devices are
additional
components which may need to be provided to an existing actuator, and may
require
additional monitoring equipment, such as load sensors. In an embodiment, the
actuator
39 is free of active devices, such as brakes. In an embodiment, the rod 39B is
free of
active devices, such as brakes, for engaging the rod 39B.
[0025] One example of the passive friction device 37 is shown in Fig. 2. The
passive
friction device 37 includes a no-back 37A mounted about the rod 39B. The no-
back 37A
in Fig. 2 is in continuous frictional engagement with the rod 39B. The no-back
37A is a
friction-based device that ensures that when movement of the rod 39B ceases,
such as
by removing current from the motor 39C', the no-back 37A holds or maintains
the
position of the rod 39B. The no-back 37A is a passive device, in contrast to a
brake
which is active because it actively engages/clamps the component whose
movement it
is desired to stop. The no-back 37A in Fig. 2 is a screwed-roller no-back 37A.
The
screwed-roller no-back 37A includes a friction plate with a series of rollers
that provides
a constant level of friction against the rod 39B. The no-back 37A allows for
maintaining
the rod 39B stationary at a specific position of the rod 39B.
[0026] In one possible configuration, the no-back 37A operates bi-
directionally, such
that it operates to prevent rotation of the rod 39B about the rod axis 39B' in
both the
direction of rotation R1 and the opposite direction of rotation R2 when the
motor 39C' is
inactive or when the motor 390' is producing an output torque less than the
frictional
torque engagement of the no-back 37A with the rod 39B. For example, referring
to Fig.
2, when the torque output of the motor 390' in the direction of rotation R1
exceeds the
frictional torque engagement of the no-back 37A with the rod 39B, the no-back
37A
allows the screw 35A to rotate in the direction of rotation R1 about the rod
axis 39B' to
drive the nut 39A in the direction D1, and thereby cause the spindle 27 and
the linking
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with the rod 39B, the no-back 37A allows the screw 35A to rotate in the
direction of
rotation R2 about the rod axis 39B' to drive the nut 39A in a direction
opposite to the
direction D1, and thereby cause the spindle 27 and the linking member 33 to
rotate about
the spindle axis 31 in an opposite direction.
[0027] However, if the motor 39C' is inactive or is producing an output torque
less than
the frictional torque engagement of the no-back 37A with the rod 39B, the
continuous
frictional engagement of the passive no-back 37A will prevent or stop the
rotation of the
screw 35A about the axis 39B' in both directions of rotation RI ,R2, and thus
stop linear
displacement of the screw 35A. The no-back 37A is a component of the actuator
39, and
thus the actuator 39 is able to stop displacement of the rod 39B or hold it in
position
without the use of additional parts, such as a brake. The no-back 37A is able
to hold the
rod 39B in a stationary and desired position without having to continuously
operate the
motor 39C', and thus contributes to reducing the risk of overheating the motor
39C'.
Reference is made to US 6,109,415 for additional details about the no-back
37A. An
alternate configuration of a no-back includes ratchet pawls that allow the
friction elements
to rotate with the screw under opposing load such that the motor does not need
to be
oversized. Other types of passive friction devices 37 may be used.
[0028] When the rotor ducts 17 tilt or are converted from the hover mode to
the aircraft
mode, the actuators 39 may experience mechanical backlash, particularly if the
conversion occurs at higher forward flight speeds. An excessive amount of
mechanical
backlash may contribute to aero-servo-elastic coupling caused by aerodynamic
and other
loads resulting from the conversion of the rotor duct 17 from the hover mode
to the flight
mode, which in turn can lead to an undesired effect at the vehicle level.
[0029] To reduce or eliminate such mechanical backlash on the actuator 39, the
drive
mechanism 39C is operable to "pre-load" the rod 39B. Stated differently, the
drive
mechanism 39C is operable to displace the rod 39B to a position such that a
load will be
exerted on the rod 39B before it experiences mechanical backlash. This load is
capable
of countering or neutering the effects of mechanical backlash that may be
experienced
by the rod 39B.
8
Date Recue/Date Received 2021-06-17
capable of countering or neutering the effects of mechanical backlash that may
be
experienced by the rod 39B.
[0030] Pre-loading the rod 39B may be achieved using different techniques. One
possible technique is now described with reference to Fig. 3. The aircraft 10
has a
downstop 40 fixedly mounted within the aircraft 10 in proximity to the linking
member 33
and the actuator 39. The downstop 40 is a physical object which is fixedly
attached at
an appropriate location within the aircraft 10, and used to arrest or stop
movement of a
component which comes into contact with the downstop 40. In Fig. 3, the
downstop 40
is schematically represented as a block. In an alternate embodiment, the
downstop 40
is an arm fixedly mounted to one of the ribs 25 inwardly of the skin 23, and
rendered
immobile relative to the rib 25. Other configurations for the downstop 40 are
possible.
[0031] Referring to Fig. 3, the downstop 40 is positioned along the path of
movement of
the linking member 33, such that the linking member 33 is displaceable toward
and
away from the downstop 40, depending on the direction of rotation of the
spindle 27.
The downstop 40 is positioned to block further displacement of the linking
member 33,
and thus further displacement of the spindle 27, when the linking member 33
abuts
against a contact surface 42 defined by the downstop 40. The downstop 40 in
Fig. 3
operates to block further movement of the linking member 33 in only one
direction of
movement of the linking member 33. It will be appreciated that additional
downstops 40
may be provided to block further movement of the linking member 33 along all
its
directions of movement.
[0032] The downstop 40 in Fig. 3 is located at a position consistent with the
rotors 19
and the rotor ducts 17 being in the aircraft mode. Stated differently, as the
linking
member 33 moves toward the downstop 40, the rotor duct 17 is converting from
the
hover mode to the aircraft mode. The drive mechanism 39C drives the rod 39B to
displace the linking member 33 toward the downstop 40 in order to abut the
linking
member 33, or some component thereof, against the contact surface 42. The
drive
mechanism 39C continues to drive the rod 39B in this manner until the linking
member
33 is exerting a force or load against the downstop 40. This force or load is
maintained
against the downstop 40, thereby pre-loading the rod 39B, which may help to
reduce or
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eliminate the mechanical backlash that may be experienced by the rod 39B
during
conversion of the rotor ducts 17 from the hover mode to the aircraft mode. The
load is
applied once the spindle 27 has been rotated to displace the rotor ducts 17
and the
rotors 19 from the hover mode to the aircraft mode. The load may also be
applied after
rotating the spindle 27 to displace the rotor ducts 17 and the rotors 19 from
the aircraft
mode to the hover mode, if desired.
[0033] There may be a need or desire to maintain pre-loading on the rod 39B
throughout the duration of the rotor ducts 17 being in the aircraft mode, in
order to
prevent the rotor ducts 17 from beginning to convert to hover mode during
forward flight
of the aircraft 10. When the desired load is applied against the downstop 40,
the drive
mechanism 39C is disengaged from the rod 39B. The drive mechanism 39C is
temporarily made inoperative or ineffective at displacing the rod 39B. The
disengagement of the drive mechanism 39C from the rod 39B may take different
configurations. In one possible configuration, the drive mechanism 39C is
deactivated.
In one possible configuration, the motor 39C' of the drive mechanism 39C is
turned off.
In one possible configuration, the drive mechanism 39C is maintained
activated, and
the gearing that connects the drive mechanism 39C to the rod 39B is configured
such
that the output of the drive mechanism 39C does not cause the rod 39B to
displace.
Other configurations are also possible.
[0034] It will thus be appreciated that when the rod 39B is sufficiently and
initially
preloaded, the drive mechanism 39C is temporarily disengaged from the rod 39B.
When this occurs, the frictional engagement of the passive friction device 37
with the
rod 39B stops displacement of the rod 39B. The pre-load on the rod 39B is thus
maintained by the passive friction device 37 (e.g. the no-back 37A) of the
actuator 39,
to thereby reduce or prevent the effects of mechanical backlash. In contrast,
some
conventional systems use dedicated and active electro-mechanical brakes to
maintain
the actuator at the desired position. The actuator 39 does not require a
dedicated brake
or active device, which may help to reduce weight and cost. Furthermore,
mechanical
brakes are an additional component which may require sensors to detect the
level of
pre-load required. The actuator 39 is able to pre-load the rod 39B and
maintain the pre-
CA 3060742 2019-10-29
load using a passive device, such as the no-back 37A, which is a component
inherent
to the actuator 39, and thus obviates the need to provide additional
components.
[0035] The pylon-conversion actuation system 21 may include suitable
electronics for
controlling the actuator 39 and monitoring displacement of components of the
pylon-
conversion actuation system 21. Referring to Fig. 3, a controller 50
communicates with
the drive mechanism 39C to command the drive mechanism 39C to perform its
various
functions. For instance, the controller 50 commands the drive mechanism 39C to
displace the rod 39B. The position of the rod 39B is related to the position
of the linking
member 33 that is displaced by the rod 39B. The controller 50 may command the
drive
mechanism 39C to displace the rod 39B (and thus the linking member 33) to a
position
which will result in the rod 39B being preloaded when the linking member 33
abuts
against the contact surface 42 of the downstop 40. The controller 50 may set
this
preloading position to correspond to a physical location of the linking member
33 that is
past the known location of the contact surface 42 of the downstop 40. For
example, and
as shown in Fig. 3, the controller 50 may command the drive mechanism 39C to
drive
the rod 39B to displace the linking member 33 to a distance A past the
location of the
contact surface 42 of the downstop 40. The distance A is spaced inwardly from
the
contact surface 42 into the body of the downstop 40. Therefore, as the linking
member
33 is displaced toward the contact surface 42 when converting from hover mode
to
aircraft mode, the linking member 33 travels and closes the distance X shown.
The
controller 50 may command the drive mechanism 39C to continue displacing the
rod
39B to a position that corresponds to the linking member 33 being at the
contact
surface 42 plus the distance A. This helps to ensure that the linking member
33 applies
a load against the downstop 40, so that the rod 39B is preloaded. The
controller 50 in
Fig. 3 is part of the actuator 39, and may be or include Motor Control
Electronics (MCE)
52. In an embodiment, the controller 50 is part of, or controlled by, the
flight control
computer (FCC) 54.
[0036] In Fig. 3, the controller 50 communicates with the drive mechanism 39C
to
command the drive mechanism 39C to regulate a speed of displacement of the rod
39B. For example, when the distance separating the linking member 33 from the
contact surface 42 of the downstop 40 is less than the threshold distance X,
the
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controller 50 communicates with the drive mechanism 39C to command the drive
mechanism 39C to reduce the speed of displacement of the rod 39B to reduce the
speed of impact of the linking member 33 against the contact surface 42.
[0037] The pylon-conversion actuation system 21 may include suitable sensors
for
monitoring displacement of components of the pylon-conversion actuation system
21.
Referring to Fig. 3, a rod position sensor 56 outputs signals indicative of a
position of
the rod 39B of the actuator 39, and a spindle position sensor 58 outputs a
spindle
position signal indicative of a position of the spindle 27. In embodiments
where the
spindle 27 is a cylindrical duct, the displacement of the spindle 27 is
measured in
degrees, and thus the spindle position signal may be a degree value. In Fig.
3, the
spindle 27 has teeth 33A which mesh with teeth of the spindle position sensor
58 to
determine the position of the spindle 27. The teeth 33A are mounted about an
outer
surface of the duct of the spindle 27 and rotatable with the spindle 27 about
the spindle
axis 31. The teeth 33A may be spaced apart from the spindle arm 27B in a
direction
parallel to the spindle axis 31. The spindle arm 27B protrudes radially
outwardly from
the outer surface of the duct of the spindle 27 more than the teeth 33A. Other
position
sensors are possible.
[0038] It will be appreciated that the rod and spindle position sensors 56,58
do not
need to be in direct mechanical engagement with the rod 39B and the spindle
27,
respectively, and that the rod and spindle position sensors 56,58 may include
any
suitable monitor which is capable of directly measuring, or deriving, the
position of the
rod 39B and spindle 27. For example, one or both of the rod and spindle
position
sensors 56,58 may include a monitor on the motor 39C' of the drive mechanism
39C,
which monitors the rotation of the motor 39C' to approximate the position of
the rod 39B
and/or spindle 27 based on the known geometric relationships between the
components of the pylon-conversion actuation system 21. Another example
involves
using variations in the electric current of the motor 39C' to approximate the
position of
the rod 39B and/or spindle 27.
[0039] The controller 50 may communicate with one or both of the rod and
spindle
position sensors 56,58 to receive their output signals. Still referring to
Fig. 3, when the
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load applied against the downstop 40 by the linking member 33 is sufficient,
the rod
position sensor 56 may record the position of the rod 39B, and output a
reference
position signal to the controller 50 that is indicative of a reference
position of the rod
39B. The pylon-conversion actuation system 21 and/or the controller 50 are
operable to
compare the reference position signal to other rod positions signals, in order
to
determine whether the rod 39B has deviated or moved from the reference
position. This
may help to determine if the rod 39B is still sufficiently preloaded to
prevent or reduce
the effects of mechanical backlash, as explained in greater detail below.
[0040] The spindle and rod position sensors 58,56 may be deactivated by the
controller
50 when the desired load is applied against the downstop 40 by the linking
member 33.
This may be done to prevent tripping the spindle and rod position sensors
58,56, which
most of the time may be configured to output warning signals when the
positions of the
rod 39B and the spindle 27 are outside normal parameters or limits. For
example, in the
embodiment where the controller 50 commands the drive mechanism 39C to drive
the
rod 39B to displace the linking member 33 to the distance A past the location
of the
contact surface 42 of the downstop 40, as explained above, the spindle and rod
position
sensors 58,56 may normally be configured to output a warning signal alerting
the
controller 50 of impermissible or undesirable displacements of the rod 39B or
the
spindle 27. Since this displacement of the linking member 33 past the contact
surface
42 is desirable in this situation, the spindle and rod position sensors 58,56
may be
deactivated to prevent them from outputting false or irrelevant warning
signals.
[0041] It can be appreciated that the pylon-conversion actuation system 21
helps to
provide a pre-load on the rod 39B, and to maintain the pre-load using a
component that
is part of the actuator 39, such as the no-back 37A. The pylon-conversion
actuation
system 21 also allows for monitoring the displacement of the rod 39B, to
ensure that the
pre-load is applied when needed, and to detect if movement of the rod 39B has
occurred, which might indicate that the rotor duct 17 is not oriented as it
should be.
[0042] Referring to Fig. 3, there is disclosed a method for loading the
downstop 40 of
the aircraft 40 when displacing the rotors 19 between the hover and aircraft
modes.
There is disclosed a method of displacing the rotors 19 between the hover and
aircraft
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CA 3060742 2019-10-29
modes. The method includes rotating the spindle 27 about the spindle axis 31
to
displace the rotors 19 between the hover and aircraft modes until a component
(e.g.
one or more of the linking member 33, the nut 39A, and the spindle arm 27B)
displaceable with the spindle 27 abuts against the downstop 40 and applies a
load
against the downstop 40. The method includes passively maintaining the
component
against the downstop 40 to maintain the load applied against the downstop 40.
The
method disclosed herein may be considered a method for rotor duct conversion
with
downstop 40 pre-loading.
[0043] Fig. 4 shows an example of the logic 100 that may be applied when
performing
the disclosed methods. At process point 102, the rotor ducts 17 are commanded,
by the
FCC 54, pilot or other authority, to begin converting from the hover mode to
the aircraft
mode. This leads to process point 104, where the pylon-conversion actuation
system 21
is operated to achieve the desired conversion. The actuator 39 and the drive
mechanism 39C are activated to displace the rod 39B in order to rotate the
spindle. The
drive mechanism 39C is commanded to displace the rod 39B to thereby displace
the
component to a position past a position of the downstop 40, such as by
commanding
the rod 39B to displace to a position corresponding to the position of the
downstop 40
plus the distance A past the location of the contact surface 42 of the
downstop 40. This
helps to ensure that the component contacts the downstop 40. Any position
command
may be given in terms of a physical location, a translational distance to
displace, or
degree values of the duct of the spindle 27. At decision node 106, if the
position of the
component from the contact surface 42 is greater than the distance X (the "No"
option
at decision node 106), the drive mechanism 39C continues to drive the rod 39B
to
displace the component toward the contact surface 42. When the distance
separating
the component from the contact surface 42 of the downstop 40 is less than the
distance
X (the "Yes" option at decision node 106), the process point 108 is reached,
and the
controller 50 communicates with the drive mechanism 39C to command the drive
mechanism 39C to reduce the speed of the component displacing toward the
contact
surface 42 to reduce an impact velocity of the component.
[0044] Reducing the speed of the component against the contact surface 42 may
help
to achieve a consistent application of pre-load against the downstop 40. In
the
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CA 3060742 2019-10-29
embodiment where the actuator 39 is a linear actuator with an
electromechanical ball
screw with MCE 52, reducing the speed of the rod 39B to reduce the impact
velocity of
the component may involve the FCC 54 or other suitable authority issuing a
command
for the MCE 52 to reduce its internal current limiter to a predefined value Y
which
corresponds to the desired downstop pre-load value. Commanding the actuator 39
to
reduce the speed of displacement of the rod 39B may also including commanding
the
actuator 39 to reduce a speed of rotation (RPM) of the rod 39B about the rod
axis 3913'.
The speed of displacement of the rod 39B may be correlated with the output
speed of
the motor 39C' in the embodiment where the actuator 39 contains a motor 39C'.
[0045] At the process point 108, position sensors (e.g. the spindle and rod
position
sensors 58,56) are disabled by the controller 50 when the desired load is
applied
against the downstop 40 by the component. This may be done to prevent tripping
the
spindle and rod position sensors 58,56, as explained above. Inhibiting such
velocity and
position continuous monitors may help to prevent nuisance trips during the pre-
load
operation.
[0046] Thus, at process point 109, the rod 39B is displacing at a lower speed
to reduce
the impact velocity of the component. The decision node 112 allows for the rod
39B to
continue displacing at this lower speed (the "No" option at decision node 112)
until the
component abuts against the contact surface 42 to apply the preload, and thus
stops
further displacement of the rod 39B. When the speed of displacement of the rod
39B is
zero for a specified threshold time period, a "yes" response is triggered at
the decision
node 112. When contact with the downstop 40 is made, the actuator 39 is
loaded,
velocity drops, and the MCE 52 may respond by drawing more current to meet the
velocity demand and increase torque applied by the motor 39C'. In an alternate
embodiment, the displacement of the rod 39B is stopped when the distance
separating
the component from the downstop 40 has been less than the threshold distance X
for a
period of time.
[0047] In an embodiment, stopping further displacement of the rod 39B may be
achieved by simply deactivating the motor 39C'. The FCC 54 may disengage the
motor
39C' when its absolute velocity, which may correspond to the speed of
displacement of
CA 3060742 2019-10-29
the rod 39B, is reported to be below a small threshold for a persistent time
period.
Alternatively, the disengagement of the motor 39C' may simply take place
following a
set time after distance X has been reached. The motor 39C' may be disengaged
when
the MCE 52 current saturates to a value Y, and the motor 39C' stops as a
result. When
the motor 39C' is deactivated, the frictional engagement of the passive
friction device
37 with the rod 39B maintains the position of the rod 39B. This allows the
motor 39C' to
avoid having to continuously operate to maintain the pre-load on the downstop
40, and
thus may help to avoid overheating of the motor 39C' or burnout. Thus
passively
maintaining the component against the downstop 40 includes stopping a
displacement
of the rod 39B, such as by stopping a rotation of the rod 39B about the rod
axis 396'.
[0048] After the actuator 39 has been disengaged from the rod 39B or
deactivated, and
the displacement of the rod 39B for preloading has ceased, the controller 50
waits for a
second time period and records a reference position of the stopped rod 39B at
process
point 114. In the embodiment where the actuator 39 has the motor 39C', it may
occur
that the motor 39C' and/or the rod 39B "spring back" to some position after
the motor
39C' has been disengaged, due to the energy stored in the gear train of the
motor 39C'.
The rod 39B will become stationary again after the second time period, and its
position
is then recorded as the reference position. From that point on, the passive
friction
device 37 is maintaining the downstop pre-load value. The FCC 54 may store
this
position of the motor 39C' as the reference position corresponding to the
nominal pre-
load, and the continuous monitors of the pylon-conversion actuation system 21
may be
reactivated to detect any creep or movement from the reference position. The
reference
position may help to determine if there is any creep or motion following
disengagement
of the motor 39C', because it may occur that high vibrations cause the no-back
37A, for
example, to slowly let go of the screw 35A such that the preload is reduced.
These
vibrations may cause the screw 35A to rotate in direction of rotation R2
described
above.
[0049] At decision node 116 in Fig. 4, the FCC 54, pilot or other authority
may
command the rotor ducts 17 to convert from the aircraft mode to the hover
mode. If this
occurs (represented by a "yes" leading from the decision node 116), the
actuator 39 is
reengaged with the rod 39B at process point 118. At process point 118, current
16
CA 3060742 2019-10-29
saturation limits previously imposed by the MCE 52 may be removed. The
actuator 39
is thus able to displace the rod 39B and rotate the spindle 27 about the
spindle axis 31
to move the rotors 19 into the hover mode, as shown in process point 120.
[0050] At decision node 116, when no command is given to the rotor ducts 17 to
convert from the aircraft mode to the hover mode (represented by a "no"
leading from
the decision node 116), the logic 100 arrives at decision node 122, which
governs the
outcome from monitoring displacement of the rod 39B relative to the reference
position.
It may occur that vibration or other loads acting on the actuator 39 affect
the frictional
engagement of the no-back 37A, for example, with the rod 39B, and cause the
screw
35A to slowly backdrive in direction of rotation R2 described above such that
the pre-
load value is proportionally reduced. This may be detected, in one possible
configuration, when the position of the motor 39C' deviates at a slow rate
from the
corresponding reference position by a given threshold. If no deviation of the
rod 39B
has occurred from the reference position or the deviation is less than the
threshold
(represented by a "no" leading from the decision node 122), the logic 100
arrives back
at the decision node 116, to repeat the cycle described above.
[0051] If, however, deviation of the rod 39B has occurred from the reference
position
beyond the threshold value (represented by a "yes" leading from the decision
node
122), the process point 124 is reached, and the actuator 39 is reengaged with
the rod
39B to displace the rod 39B to maintain the pre-load value. Under these
conditions, the
motor 39C' is re-engaged, the creep monitors reset, and the pre-load sequence
of the
logic 100 is re-executed. The method disclosed herein therefore helps to
ensure that
the pre-load remains present under different levels of vibration, including
severe levels.
The use of the passive friction device 37 is thus combined in some embodiments
with
motor 39C'/rod 39B creep detection, and pre-load re-activation. The method may
therefore allow for reducing the downstop 40 impact velocity, ensuring a
consistent
level of pre-load, and ensuring that the pre-load remains present even under
severe
levels of vibration.
[0052] Once the actuator 39 is reengaged, the logic 100 arrives at decision
node 126. It
may occur that the rod 39B deviates from its reference position because of a
failure of
17
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order to displace the rod 39B at lower speed toward the contact surface 42 of
the
downstop 40.
[0053] Other features of the pylon-conversion actuation system 21 disclosed
herein may
be found in US 7,913,947.
[0054] The above description is meant to be exemplary only, and one skilled in
the art
will recognize that changes may be made to the embodiments described without
departing from the scope of the invention disclosed. Still other modifications
which fall
within the scope of the present invention will be apparent to those skilled in
the art, in
light of a review of this disclosure, and such modifications are intended to
fall within the
appended claims.
18
Date Recue/Date Received 2021-06-17
