Note: Descriptions are shown in the official language in which they were submitted.
Title: "Servo Actuator Contol/Damping Mechanism and Method"
DISCLOSURE
This invention relates generally to servo systems and, more
particularly, to aircraft flight control servo systems. More specifically, the
invention relates t~ a servo actuator control/damping meehanism and
method whieh utilize and combine the functions of an electro-mechanically
driven servo valve to achieve fluid flow and actuator (ram) load control even
after loss of fluid power.
BACKGROUND
Fluid servo systems are used for many purposes, one being to
position the flight control surfaces of high performance aircraft. In such an
application, the servo system desirably should provide for control and
damping of flight control surface displacements or flutter after loss of fluid
power. Otherwise, aircraft damage or loss of control may result. ~~
In conventional electro-hydraulic systems, electro-hydraulic
valves have been used in conjunction with servo valve actuators to effect
position control of the main control servo valve. Typically, the servo
actuators in redundant systems operate on opposite ends of a linearly
movable valve element in the main control valve and are controlled by the
electro-hydraulic valves locsted elsewhere in the system housing. Such
systems also have used bypass/damping valves which oper~te upon loss of
fluid power to bypass flow to and from the main ram or nctuator through
fixed rnetering orifices which damp and control the rate of ram and flight
surface movements. Like the electro-hydraulic valves, such bypass/damping
valves have been located in the system housing remote from the main
control valve. In addition, such systems have utilized electronic differential
pressure sensors to provide dynamic ram load feed-back information to the
aircraft electronic control system which supplies command signals to the
electr~hydraulic valves.
An alternative approach to the electro-hydraulic control system
is an electro-mechanical control system wherein a force motor is coupled
directly and mechanically to the main control servo valve. For an example
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of one form of such systems, reference may be had to (~anadian Patent
Application Serial No. 416,699, filed November 30, 1982, now Canadian
Patent No. 1,182,382, dated February 129 19859 and entitled 'IElectro
Mechanical Direct Drive Valve Servo System with Rotary to Linear Valve
Drive Mechanism~'. These systems also have used remotely located
bypass/damping valves which bypass ram flow through fixed metering
orifices upon loss of fluid power for damping and controlling the rate of ram
and flight surface movements.
In hybrid electro-mechanical systems, the force motor is coupled
directly and mechanically to a pilot valve plunger ~Ivhich controls a hydrauli-
cally powered servo valve actuator for driving the main control servo valve.
As disclosed in Canadian Patent Application Serial Nos. 435,115 and 4~5,533,
respectively filed on August 23,1983 and 3anuary 18,1984, and respectively
entitled "Redundant Control Actuation System -Concentric Direct Drive
Valve" and "Control Actuation System Including Staged Direct Drive Yalve
With Fault Control", a shut~off valve sleeve concentric with the pilot valve
plunger can be used to direct ram flow through fixed metering orifices upon
loss of fluid power for damping and rate control of ram and flight surface
movements.
As indicated, each of the foregoing systems uses added valves or
valve components to aehieve some degree of control over ram and flight
surface movements after loss of fluid power. This results in increased
package size especially in plural redundant systems where redundant valves
or valve components are required for multiple hydraulic actuator systems.
~urthermore, such valves or valve components are shuttled between system
on and off (bypass) positions with the latter serving to direct actuator flow
through the fixed metering orifices. Conseguently, there has been no
provision for active damping or flutter control in response to changing
conditions at the ram or flight control surface. Also ram pressure relief
flow through the fixed metering orifices may under some circumstances be
insufficient to prevent overload of the ram and flight control surface and
resultant damage.
With the foregoing in mind, it would be advantageous and
desirable to provide for active and more precise load and damping control in
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an aircraft flight control servo system. Furthermore, it would be desirable
to provide for such ac~ive or regulated control while minimizing system
package size such as by attributing multiple functions to servo system
components.
SUMMARY OF THE INVENTION
The present invention provides a lluid servo actuator control/
damping mechanism and method which utilize and combine the functions of
an electro~mechanically driven servo valve to achieve ram or actuator fluid
flow and load control even after loss of fluid power as well as the main ram
position control function under normal operating conditions. The mechanism
is particularly useful in an aircraft flight control servo system wherein
reduced package size and weight is desired along with active or regulated
damping control and overload relief functions, and eliminates the need for
separate bypass valves or valve components heretofore utilized to meter
bypass ram flow through fixed orifices.
Briefly, the mechanism comprises a servo valve including a
positionable valve element for selective application of fluid power to a ram,
a sensor connectable to the ram for providing ram load feed-back informa-
tion, and an electro-mechanical drive operable independently of fluid power
for selectively positioning the valve element under normal operating condi-
tions for controlled actuation of the ram and, upon loss of fluid power, for
providillg variable orifices to controllably meter bypass fluid nOw across the
ram by utilizing the existing metering pattern of the servo valve and
modulating the valve element thereof in response to feed-back information
received from the sensor, for actively controlled damping of the ram.
Further stated, a $ervo mechanism according to the ;nvention
comprises a servo valve including a valve element selectively positionable
therein to provide variable orifices for metering fluid flow to and from the
opposed pressure surfaces of the ram, means for connecting a source of high
pressure fluid to the servo valve for metered passage to either ram pressure
surface through the variable orifices, means for directing bypass fluid flow
from either pressure surface to the other through such variable orifices in
the event of a loss of such high pressure fluid, and electro-mechanical drive
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means operat;ve independently of such high pressure fluid to controllably
position the valve element to effect controlled metering of such high
pressure fluid to either pressure surface of the ram for controlled actuation
thereof and, in the event of a loss of such high pressure eluid, to effect
controlled metering of bypass fluid flow across the ram for active or
regulated damping and load control.
To the accomplishment of the foregoing and related ends, the
invention, then, comprises the features hereinafter fully deseribed and
particularly pointed out in the claims, the following descrip$ion and the
annexed drawing setting forth in detail a certain illustrative embodiment of
the invention, this being indicative, however, of but one of the various ways
in which the principles of the invention may be employed.
In accordance with one aspect of the present invention, there is
provided a servo mechanism for use in a fluid servo system -for contrMling a
fluid powered ram actuator having opposed pressure surfaees, comprising a
servo valve including valve means selectively positionable therein to provide
variable fluid pressure and return flow orifices for metering fluid Elow to
and return flow from the opposed pressure surfaces of the ram, means for
connecting a source of high pressure fluid to said servo valve for metered
passage to either pressure surface through said variable fluid pressure
orifices, means for directing bypass fluid flow ~rom either pressure surface
of the ram to the other pressure surface through said variable return flow
orifices in the event of a loss of such high pressure ~luid, and electro-
mechanical means operative independently of such high pressure fluid to
controllably position said valve means to effect controlled metering of such
high pressure fluid through said variable fluid pressure orifices to either
pressure surface of the ram for controlled actuation thereof and, in the
event of a loss of such high pressure fluid, to effect regulated metering of
bypass flow through said variaMe return flow orifices and across the ram for
active damping control thereof.
In accordance with a further aspect of the present invention,
there is provided a servo system comprising a fluid powered ram actua$or
including a cylinder and a piston movable in said cylinder for extension and
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retraction of said ram, a servo valve including positionable valve means for
selective connection of a source of high pressure fluid to either side of said
piston and a return for such fluid from the other side of said piston through
variable fluid pressure and return flow orifices in said servo valve which are
varied by selectively pos;tioning said valve means, thereby to effect
extension and retraction of said ram, sensor means connected to said ram
for providing ram load feedbac~ information, and electro-mechanical means
operable independently of such source of high pressure fluid for selectively
positioning said valve means under normal operating conditions for con-
trolled actuation of said ram and, upon loss of such source of high pressure
fluid, for controllably metering bypass fluid flow across said piston through
said variable return flow orifices in said servo valve by modulating said
valve means in response to feedback information received from said sensor
means, for actively controlled damping of said ram.
In accordance with a further aspect of the present invention,
there is provided a method of controlling a servo system including a fluid
powered ram actuator having opposed pressure surfaces9 a main control
servo valve having valve means positionable therein to provide variable fluid
pressure and return flow orifices for metering flow to and from the opposed
pressure surfaces of the ram, and electro-mechanical means operative
independently of fluid power to effect selective positioning of the val~e
means, said method comprising operating the system in a normal operational
mode by connecting a source of high pressure fluid to the servo valve, and
utili2ing the electro-mechanical means to selectively position the valve
means for metered passage of such high pressure fluid to either pressure
surf~ce of the ram through the variable fluid pressure orifices and from the
opposed pressure surface of the ram through the variable return flow
orif;ces, for contro:lled actuation of the ram; and operating the system in a
damping operational mode upon loss of such source of high pressure fluid by
directing bypass fluid flow from either pressure surface of the ram to the
other pressure surface through the same variable return flow orifices that
are used in such normal operational mode, and utilizing the electro-
mechanical means to selectively modulate the valve means for regulated
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metering of such bypass fluid flow through such variable return flow orifices
and across the ram for active damping control thereof.
BRIEF DESCRIPTION OF THE DRAWING
The invention is illustrated by way of example in the accompany-
ing drawing in which the sole figure thereof is a schematic illustration of a
redundant servo system embodying a preferred form of servo actuator
control/damping mechanism according to the invention.
DETAILED DESCRIPTION
Referring now in detail to the drawing, a dual hydraulic servo
system is designated generally by reference numeral 10 and includes two
similar hydraulic servo actuators 12 and 14. The actuators 12 and 14 are
connected to a common output device such as a dual tandem cylinder
actuator or ram 16 which in turn may be connected to a control member
such as a flight control element of an aircraft. It will be seen below that
the two servo actuators normally are operated simultaneously to effect
position control of the ram 16 and hence the flight control elernent.
However~ each servo actuator preferably is capable of properly effecting
such position control independently of the other so that the control is
maintained even when one of the servo actuators fails or is shut down.
Accordingly, the two servo actuators in the overaLl system provide a
redundancy feature that increases safe operation of the aircraft.
The servo actuators 12 and 14 are similar and for ease in
description, like reference numerals will be used to identify corresponding
like elements of the two servo actuators.
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Each servo aetuator 12, 14 has an inlet port 20 fcsr ~onnection
with a source of high pressure hy~raulic fluid and a return port 22 for
connection with a hydraulic reservoir. Preferably, the respective inlet and
return ports of the servo actuators are connected to separate and inde-
pendent hydraulic system~ in the aircraft, so that in the event one of the
hydraulic systems fails o~- shu~s down, the servo actuator coupled to the
other still functioning hydraulic system may be operated to effect the
position control function.- Hereinafter, the hydraulic systems associated
with the servo actuators 12 and 14 will respectively be referred to as the
forward and aft hydraulic systems~
In each of the servo actuators 12 and 14, an inlet passage 24
connects the inlet port 20 to a common main control servo valve designated
generally by reference numeral 26. Each inlet passage 24 may be provided
with a suitable filter 27 and ~ check valve 28 which blocks reverse flow
through the inlet passage from the servo valve to the inlet port. Each servo
actuator also is provided with a return passage 30 which connects the return
port 22 to the servo valve 26 via a damping mode accumulator or
compensator 32 which serves to maintain pressure in the servo actuator
sufficient to prevent cavitation across damping restrictions during damping
mode operation as described hereafter.
The main control sersro valve 26 includes a plunger or spool 34
longitudinally shiftable in a cylindrical bore 36 which may be formed by a
sleeve (not shown) in an overall system housing. The plunger has two
fluidically isolated valving sections indicated generally at 38 and 40, which
valving sections are associated respectively with the actuators 12 and 14 and
the passages 24 and 30 thereof. The plunger may ~e selectively shifted fro
its illustrated neutral or centered position for selective connection of the
passages 24 and 3û of each servo actuator to passages 42 and d~4 in the same
servo actuator.
The passages 42 and 44 of both servo actuators 12 and 14 are
connected to the ram 16 which includes a pair of cylinders 46 having
respective pistons 48 connected to ram output rod 50 for common movement
therewith. More specifically, the passages 42 and 44 of each servo actuator
96
are connected to a corresponding one of the cylinders of opposite sides of
the piston. The passages 42 and 44 also are connected by respective branch
passages 52 and 54 to a common passage 56 which in turn is connected to
the corresponding return passage 30. As shown, the branch passages 52 and
54 are respectively provided with anti cavitation cheek valves 58 and 60
which block fluid flow from the passages 42 and 44 to the common passage
56 but permit free flow from common passage 56 $o passages 42 and 44.
With particular reference to the main control servo valve 26,
each valving section 38, 4û of the plunger 34 has a pair of longitudinally
(axially) spaced apart lands 60 and 62 which ~e locatable, as when the
plunger is in its neutral position, to block flow through respective metering
ports 64 and 66 that respectively connect the passages 42 and 44 to the
interior of the plunger bore 36. The lands 60 and 62 define therebetween a
supply groove 68 which is in communication with the inlet passage 24 and
outwardly thereof respective return grooves 70 and 72 which are inter-
connected by passage ~4 and in common communication with return passage
30. Accordingly, movement of the plunger to either side of its neutral
position will connect the inlet passage 24 to one of the passages 42 and 44
and the other of such passages to return passage 30 through respective
metering orifices defined by the position of the lands 60 and 62 relative to
respective ports 64 and 66. Moreover, such metering orifices may be varied
in size by selective positioning of the valve plunger in the manner
hereinafter described for controlled metering of flow to and from the
passages 42 and 44.
~ rom the foregoing, it will be apparent that selective movement
of the plunger 34 simultaneously controls both valving sections 38 and 40
whieh selectively connect one side of each piston 48 to a high pressure
hydralllic fluid source and the other side to fluid return for controlled
metering of flow to and from the ram 16 which in turn effects controlled
movement of the output rod 50 either to the right or left. In the event one
cf the servo actuators 12,14 fails or is shut down, the other servo actuator
will maintain control responsive to selective movement of the plunger. -
Controlled selective movement of the valve plunger 34 is de-
sirably effected by an electric force motor 78 which may be located closely
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adjacent one end of the plunger. The Iorce motor may be o~ linear or rotary
type and operative conneetion of the force motor to the valve plunger may
be o~tained by a link member 8~ such as in the manner described in the
a~orementioned Canadian Application 5erial No. 445,533.
The force motor 78 is responsive to command signals received
from an electronic control or command system indicated at 82 which may be
located, for example, in the aircraft coekpit, whereby the force motor
serves as a control input to the valve plunger 34. Also, the force motor
preferably has redundant nnultiple parallel coils so that if one coil or its
associated electronics should fail, its counterpart channel or channels wiU
maintain control. Moreover, suitable failure monitoring circuitry is prefer-
ably provided to detect when and which channel has failed, and to uncouple
or render passive the failed channel.
~ eed-back information to the command system 82 is obtained by
position transducers or sensors 84 and 86 which are desirably operatively
connected to and mlonitor the positions of the valve plunger 34 and ram
output rod 50, respectively. In addition, electronic load sensors 88 or
equivalent devices are desirably operatively connected to respective
cylinders 46 of the ram 16 for monitoring ram load and providing load feed-
back in~ormation to the command system 82 controlling the foree motor 78.
As shown, each load sensor 88 may be in the form of a differential pressure
sensor including a position transducer 92 connected to a longitudinally
shiftable spring centered piston 94. Opposite sides or pressure surfaces of
the piston 94 are respectively connected by passages 96 and 98 to respective
opposite sides or pressure surfaces o~ the piston 48 in the corresponding
cylinder 46 of the ram whereby the position of the piston 94 and corres-
ponding output of the transducer will be indicative of the direction and
magnitude of dif~erential pressure forces acting on the piston 48.
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During normal operation of the servo system 10, high pressure
fluid from the forward and aIt hydraulic systems is supplied via respective
inlet passages 24 to the main control servo valve 26. Through selective
positioning of the valve plunger 34 in response to command signals received
from the command system 82, high pressure fluid from each hydraulic
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system is controllably metered to eith~r side of the respective piston 48 of
the ram 16 to effect controlled movement of the ram output rod 50 with
return flow from the opposite side of the piston beulg simultaneously
directed by the valve plunger to return via the passage 30. Further, each
electronic load sensor 88 may be used during normal operation to provide
dynamic load feed-back information to the command sys~em 82 for imple-
mentation of damping and over-pressure relief functions in conventional
manner. Further, each e1ectronic load sensor 88 may be used during normal
operation to provide surface hinge momen~ cs~ntrol and hinge moment
limiting. This would allow the servo to become a torque or force servo
rather than a positional servo.
Should a loss of hydraulic power occur from both the forward and
aft hydraulic systems, the command system 82 automatically implements
damping mode operation. In the damping mode, the check valves 28 and
compensators 32 serve to maintain positive pressure in the system lO after
such loss of hydraulic power by checking fluid loss through the inlet and
return ports 20 and 22. The compensators' fluid storage volume can be
selected such that damping may be met for a specified minimum period of
time.
With positive pressure maintained in the system, active or
regulated damping control of the ram 16 is effected by modulating the valve
plunger 34 to provide variable orifices which direct snd meter bypass flow
across each ram piston 48. In this regard, it is noted that the electro-
mechanically driven servo valve 26 is not dependent on hydraulic power for
valve plunger positioning whereby the valve plunger will continue to respond
to system commands as long as at least one channel of the motor 78 and
associated electronics survives and remains operative. Further9 the valve
plunger 34 is modulated in response to ram load feed-back information from
the load sensors 88 which monitor the direction and amplitude of differen-
ti~ pressure across the pistons 48.
In asl exemplary situation, over pressure existing or developed on
the extend (left) side of each ram pists)n 48 may be bypassed across the~ram
to the retract (rightj side of each piston ~y moving the valve plunger 34 to
the right of its neutral position to provide a metering orifice connecting
3~
passage 42 to return passage 30. This establishes correspondingly metered
bypass flow across each piston, such flow passing through passage 42 and the
provided orifice to rPturn passage 30 which directs the flow to the retract
side of the piston via bypass passage 56 and branch passage 54. Conversely,
moving the valve plunger to the left of its neutral position will establish and
meter bypass flow in the opposite direction across each piston. Moreover~
the provided orifices~may be controllably varied in size to provide desired
damped bypass flow by selective positioning of the valve plunger in response
to command signals dictated by sensed ram conditions, i.e., ram position
monitored by position sensors 86 and ram load monitored by load sensors 88.
Such active or regulated damping control in response to ram load
feed-back further may have associated therewith an overload relief function
in the damping mode. When excessive load on the ram 16 is sensed by the
load sensors 88, an appropriate command signal may be provided to position
the valve plunger 34 at a locat;on providing a desired orifice size sufficient
to effect rapid relief of such overload condition in order to prevent damage
to the actuator and the controlled element connected thereto.
~ rom the foregoing, it can be seen that bypass flow across the
ram 16 may be controlled by utilizing the existing flow metering pattern of
the main control servo valve 26 and modulating the valve plunger 34 thereof
to provide variable orifices for active damping and overload relief control.
It also is noted that such active control is even more desirable in redundant
systems as shown. If the ram 16 continues to be operated by high pressure
fluid supplied to only one of the servo systems, the other servo system
operates to effect by pass of the inactive portion of the ram 16. Therefore,
the need in such instance for a separate bypass valve is eliminated by such
implementation because the main control valve 26 is operated to permit
fluid transfer across the respective piston 48 as in normal operation.
Although the invention has been shown and described with
respect to a certain preferred embodiment, it is obvious that equiv~lent
alterations and modifications will occur to others skilled in the art upon the
reading and understanding of this specification. The present invention
includes all such equivalent alterations and modifications, and is limited
only by the scope of the following claims.
