Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention relates generally to a low speed, high torque servoactuator
and more particularly to a servoactuator that provides for 360 controlled operation
especially adapted for aircraft nose wheel steering systems and the like.
Conventional aircraft steering systems requiring 360 of motion are either
equipped with a disconnect from the steering motor to the strut assembly, or use high
speed hydraulic motors suitably down geared to develop the proper torque output at
the required low servo speeds. Such systems have been found to be undesirable for
several reasons. With regard to the former, such systems require the undesirabledisconnect feature, and as to the latter, such systems require a plurality of high speed
rotating parts with attendant wear characteristics. In either case, such systems have
been found to have a relatively low power to weight ratio which is undesirable in
modern aircraft in which size and weight are important factors.
Other systems have been known to utilize fluid actuators but have required
complex pressure actuation to achieve desirable performance characteristics, such as
shown and described in U. S. Patent 3,124,043.
SUMMARY OF THE INVENTION
With the foregoing in mind, it is a principal object of this invention to
provide a servoactuator with excellent low speed servo control characteristics.
Another object is to provide such a servoactuator with continuous rotary
output.
Still another object is to provide such a servoactuator with constant power
while operating under constant load and speed conditions.
Yet another object is to provide a light weight servoactuator constructed
of simple and reliable components that provides for improvement in developed power
to weight ratio over eonventional motor-gear approaches.
A further object is to provide such a servoactuator which does not require
high speed rotating parts and attendant wear characteristics, and in which the number
of rotating parts is aLso reduced.
Still a further object is to provide a servoactuator in which the overall
manufacturing cost and complexity is reduced.
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Yet another object is to provide a servoactuator system for an aircraft
nose wheel system with 360 controlled operation and capable of 360 swivelling
without disconnect.
Still yet another object is to provide such a servoactuator system that may
be actuated by electro-hydraulic controls with electrical position feedback, or used
with mechanical input-mechanical feedback eontrol mechanisms.
An additional object is to provide such a servoactuator system including
shimmy damping during tow operations when the system is in a power-off mode.
In accordance with one aspect of the present invention, there is provided a
servoactuator for controlled rotation of a crankshaft and the like comprising a
plurality of angularly disposed actuators, means operatively connecting said actuators
to said crankshaft for effecting rotation of said crankshaft in response to recipro-
cating movements of said actuators, and means for sequencing a source of high
pressure fluid and return to the respective ends of said actuators, said means for
sequencing comprising valve means driven by the rotary motion of said crankshaft,
said valve means comprising a rotatable sleeve having arcuate channels at each end
respectively communicating with a source of high pressure fluid and return, and static
ports adjacent each end of said rotatable sleeve which sequentially communicate with
said arcuate channels as said rotatable sleeve rotates thereby sequencing high pressure
fluid and return to the respective ends of said actuators.
In accordance with a further aspect of the present invention, there is
provided a servoactuator for controlled rotation of a crankshaft and the like
comprising a plurality of angularly disposed actuators, means operatively connecting
said actuators to a shaft for effecting rotation of such shaft in response to
reciprocating movements of said actuators, and means for sequencing a source of high
pressure fluid and return to the respective ends of said actuators so that said actuators
continuously develop output force except for end stroke points, said means for
sequencing comprising valve means driven by the rotary motion of such shaft, said
valve means comprising a rotatable sleeve having arcuate channels at each end
respectively communicating with a source of high pressure fluid and return, and static
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ports adjacent each end of said rotatable sleeve which sequentially communicate with
said arcuate channels as said rotatable sleeve rotates thereby sequencing high pressure
fluid and return to the respective ends of said actuators.
In accordance with a further aspect of the present invention, there is
provided a servoactuator system for providing 360 controlled rotation of an aircraft
nose wheel steering system and the like comprising a pair of angularly disposed
actuators, means operatively connecting said actuators to a shaft for effecting
rotation of said shaft in response to reciprocating movements of said actuators, and
means for sequencing a source of high pressure fluid and return to the respective ends
of said actuators so that said actuators continuously develop output force except for
end stroke points, said means for sequencing comprising valve means driven by the
rotary motion of said shaft, said valve means comprising a rotatable sleeve having a
pair of arcuate channels at each end respectively communicating with a source of high
pressure fluid and return, and a pair of static ports adjacent each end of said rotatable
sleeve, one of said static ports at each end being connected to the extend port of one
of said actuators and the other of said static ports at each end being connected to the
retract port of one of said actuators, said static ports sequentially communicating
with said arcuate channels as said rotatable sleeve rotates thereby sequencing high
pressure fluid and return to the respective ends of said actuators.
In accordance with a further aspect Gf the present invention, there is
provided a servoactuator for controlled rotation of a shaft comprising a housing, a pair
of actuators mounted on said housing and arranged at an angle of appro2dmately 90,
means operatively connecting sQid actuators to a shaft for effecting rotation of such
shaft in response to reciprocating movement of said actuators, and valve means driven
by the rotary motion of such shaft for sequentially simultaneously connecting a source
of high pressure fluid and return with the ends of said actuators so that said actuators
continuously develop output force except for the end stroke points whereby the
required power is essentially constant when driving under a constant load at a constant
rate, said valve means comprising a rotatable sleeve having arcuate channels at each
end respectively communicating with a source of high pressure fluid and return, and
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static ports adjacent each end of said rotatable sleeve which sequentially communi-
cate with said arcuate channels as said rotatable sleeve rotates thereby sequencing
high pressure fluid and return to the respective ends of said actuators.
To the accomplishment of the foregoing and related ends the invention,
then, comprises the features hereinafter fully described and particularly pointed out in
the claims, the following description and the annexed drawings setting forth in detail a
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certain 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.
BRIEF DESCRIPTION OF THE DRAWINGS
In the annexed drawings, Fig. 6 appears on the first drawing sheet before
Fig. ~; Fig. l also appears on the first drawing sheet but follows Fig. 2; and Fig. 5
appears on the last drawing sheet following Fig. 9. A brief description of such
drawings follows:
Fig. l is a side elevat;on view of a preferred form of servoactuator system
in accordance with the present invention;
Fig. 2 is a top plan view of the two actuators included in the servoactuator
system of Fig. l with the manifold and motoring valve removed, as seen from the plane
of the line 2-2 thereof, illustrating the angular relationship and pivoted movement of
such actuators;
Fig. 3 is an enlarged longitudinal section through one of the actuators of
Fig. 2, taken along the line 3-3 thereof;
Fig. 4 is an enlarged longitudinal section through the servoactuator of Fig.
l, taken along the line 4-4 thereof illustrating the relationship between the crankshaft
and motoring valve;
Fig. 5 is a schematic diagram of the servoactuator system of Fig. l to
illustrate more clearly the manner in which the various components of the system are
operatively connected together;
Fig. 6 is an enlarged view of the bypass-damping valve depicited in Fig. 5;
Fig. 7 is an enlarged view of the motoring valve depicted in Fig. 5; and
Figs. 8 and 9 are transverse sections through the motoring valve of Fig. 7
respectively taken along the lines 8-8 and 9-9 thereof illustrating the relationship
between the rotating sleeve arcuate ports and stationary end ports at an instantaneous
position.
DESCRIPTION C)F THE PRE E~RED EMBODIMENT
Referring now in greater detail to the drawings and initia11y to Figs. l
through 4, there is shown a preferred form of servoactuator system l0 constructed in
accordance with the present invention including a housing 12 on which are pivotally
mounted a pair of actuators A and B adapted to drive a crankshaft 14. Rotary motion
of the crackshaft 14 is employed to drive a motoring valve 16 housed in a manifold 17
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mounted on the housing 12. The motoring valve 16 sequences the flow of high pressure
fluid to and from actuators A and B to effect rotation of the crankshaft 14 in a manner
to be subsequently described. Mounted on one end of the crankshaft 14 for rotation
therewith is a pinion gear 18 which drives the torque collar gear 20 of an aircraft nose
wheel strut (not shown). Crankshaft 14 is suitably journaled for rotation between
bearings 21 and 22 in the housing 12, and includes crank or arm 23 to which actuators A
and B are connected as best shown in Figs. 2 and 4. Although the servoactuator system
of the present invention is described and shown in conjunction with an aircraft nose
wheel steering system, it will be appreciated that the system may be used in other
applications where precise low speed, high torque servo-positioned output is required,
for example, in radar antennae drive controls, missile engine gimbal power actuation,
and gun positioning power controls and the like.
Actuators A and B are preferably of identical construction, and accordingly
only one of the actuators A is shown in section in Fig. 3. Each such actuator comprises
an actuator cylinder 24 in which is reciprocally mounted piston 25 and rod 26. A rod
end 28 is secured to the rod 26 and includes a rotatable ball 30 adapted for connection
to the crankshaft 14 (see Fig. 4). The actuators A and B are trunnion mounted for
rotation about a pair of fixed trunnions 32, 34, one of which may contain internal
porting as will be described more fully below. Suitable rod seals 36 and a piston seal
38 may be provided, as well as an end retainer 40 at the outer ends of the cylinders 24
to facilitate removal of the piston for replacement of the various seals when worn
without removing the cylinders from the assembly.
As best seen in Fig. 2, actuators A and B are angularly arranged preferably
at an angle of about 90. During actuation of the actuators, each will pivot about
their respective trunnions 32, 34 as shown in phantom to effect rotation of crank 23.
Connected to the crankshaft 14 as by a universal joint 48 is the valve shaft
50 of the motoring valve 16 which is suitably journalled between bearings 51 and 52
mounted in the manifold 17. The valve shaft 50 has an intermediate gear 53 mounted
thereon which drives a rotary sleeve 54. Surrounding the rotary sleeve 54 is a
stationary sleeve 56 which is received in a bore 58 in manifold 17.
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For a more complete understanding of the details of construction and
operation of the actuator system 10, reference may be had to Fig. 5, which
schematically shows the various components of the system and the manner in whichthey are interconnected together.
Preferably, the porting between the various components is integrally
contained in manifold 17 mounted on housing 12. The system 10 has an inlet filter and
check valve assembly 66 for connection with a source of high pressure hydraulic fluid.
Conduit 68 leads from the inlet valve assembly to pressure ports 70 and 72 of anelectro-hydraulic valve (EH valve) 74 which may be of the dual-coil, dual-stage type
shown. The first stage is an electro-hydraulic preamplifier comprised of a torque
motor 76, jet pipe 78 and receiver 80. The torque motor 76 is conventional and
comprises a rotatably mounted armature 82 which is pivoted in well known manner by
a control signal from an electrical signal-producing means connected to terminal ends
84. The jet pipe 78 is rigidly attached to the armature 82 for rotation therewith. A
very small flow of high pressure fluid is supplied to the jet pipe by a flexible tube 85
which communicates with the conduit 68 via passage 86. Accordingly, high pressure
fluid will exit the jet pipe and impinge upon the face of the receiver 80 which is
provided with two small diameter holes 88 and 90 located side by side in the receiver.
The holes 88 and 90 communicate via passages 92 and 94 respectively with
opposite ends of bore 96 formed in the valve housing 98 in which valve spool 100 is
disposed for axial movement therein. Spool 100 has opposite end lands 102 and 104, and
asso~iated intermediate lands 106 and 108. When in its null position, the lands 106 and
108 block communication between pressure ports 70 and 72 and ports 109 and 110 which
communicate with passages 111 and 112, respectively. However, when the spool is on
either side of null, high pressure fluid will be supplied to one of the passages 111 or 112,
while the other passage will be connected to the system return via central port 115,
passage 116 and return port 114.
When a signal is impressed on the torque motor 76 the resultant torque
causes the jet pipe 78 to rotate off center and a pressure unbalance occurs across the
spool 100 causing it to move. A feedback spring 117 acts on the spool 100 tending to
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retain the spool in its null or centered position. As the spool displaces from null it
deflects the feedback spring 117 developing a force counter to the input torque, causing
the spool to come to rest in a new position whereat the spring force counterbalances
the pressure unbalance created by the jet pipe movement.
Spool displacement is thus proportional to the torque input. For practical
purposes a linear relationship exists between torque and input current and between
spool displacement and flow. Therefore, second stage flow will be proportional to the
input current signal.
The jet pipe design is inherently insensitive to contamination due to
relatively large internal flow passages as compared to nozzle-flapper-type valves.
Moreover, if plugging by contamination were to occur, it would cause a degradation of
performance but not a catastrophic "hardover" failure. The EH valve 74 is also less
sensitive to erosion effects of small, hard particles in the fluid because the height of
the jet pipe over the receiver is not critical.
Conduits 111 and 112 lead from the EH valve 74 to a bypass-damping valve 118
and are connected to annular grooves 120 and 122 in sleeve 124 of valve 118 which in
turn communicate via ports 126 and 128, respectively, with the bore 130 as best seen in
Fig. 6. Longitudinally shiftable within the bore 13D is a spool 132 which has lands 134,
136 and 138, and is spring biased by spring 140 to the left as shown in Fig. 5 or
downwardly as shown in Fig. 6. In this position, passages 142 and 144 which supply flow
to the motoring valve 16 are interconnected via annular grooves 146, 148 and ports 150,
152 by reduced portion 154 between lands 136 and 138. The land 136 underlaps port 156
thus providing a damping orifice 158 communicating with annular groove 146.
The left or lowermost end of the bore 130 is connected to the inlet valve
assembly 66 via conduit 160, whereby when high pressure fluid is supplied to thesystem, the supply pressure overcomes the spring 140 force and shuttles the spool 132
to the right thereby providing communication between ports 126 and 151 (communi-cating with annular groove 146) and 128 and 152, respectively, such communication
previously being blocked by lands 136 and 138.
Passages 142 and 144 supply high pressure fluid and return for the same to
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the inlet ports 170 and 172 in stationary sleeve 56 of motoring valve 16 via annular
grooves 174 and 17~ of the motoring valve as best shown in Fig. 7. Fluid is ported
through ports 170 and 172 to inner annular grooves 180 and 182 providing communication
with longitudinal ports 188 and 190, respectively, in the rotary sleeve 54 via transverse
ports 192 and 194.
~ s best seen in Figs. 8 and 9, the opposite ends 196 and 198 of the rotary
sleeve 54 are provided with arcuate porting channels 200, 201 and 202, 203,
respectively, into which the longitudinal ports 188 and 190 respectively open. Adjacent
each end of the rotary sleeve are porting plates 204 and 206 which include static ports
10 208, 210 and 212, 214, respectively, communicating with respective ends of actuators A
and B. Rotation of the rotary sleeve sequentially directs flow from the longitudinal
ports 188 and 190 into the static ports 208, 210 and 214, 212 for extension and retraction
of the actuators as described below.
Static ports 208 and 210 communicate with extend and retract cavities 216
and 218 of actuator A via annular grooves 220, 222 and passages 224, 226, while static
ports 214 and 212 communicate with extend and retract cavities 228 and 230 of
actuator B via annular grooves 232, 234 and passages 236, 238 as shown in Fig. 5.
Any internal leakage that might occur at each end of the rotary sleeve 54
may be ported to return 114 via annular grooves 240, 242, ports 244, 246, and outer
20 annular grooves 248, 250 which are connected to passage 252 leading to the return 114.
Any fluid between rod seals 36 may also be ported to return 114 via passages 254 and
256 in the actuators. Passage 258 connects passage 256 via annular grooves 260 and
262 to passage 264 which leads to annular groove 250 in the outer sleeve of the
motoring valve as further shown in Fig. 5.
The system is also preferably provided with a conventional fluid compen-
sator 265, shown in Fig. 5, to maintain sufficient fluid head to provide make-up fluid to
the system as needed during contraction of the same due to temperature decrease. In
addition, anti-cavitation valves 266, 267 are provided to ensure against cavitation and
are connected to passages 142 and 144 via passages 268, 269.
There may also be provided pressure relief valves 270 and 271 which direct
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cylinder flow to return during any possible extreme backdriving condition. The valves
270 and 271 are connected to passages 142 and 144 via passages 272 and 273 and annular
grooves 146 and 148 of bypass damping valve 118. Return flow from the pressure relief
valves 270 and 271 is provided by passage 274 connected to passage 116.
A rotary variable differential transformer 278, schematically shown in Fig.
4, may be incorporated to provide electrical feedback position signals proportional to
the angular position of the crankshaft. The feedback transformer may be driven by a
pinion gear 280 secured to the top of the motoring valve shaft 50 which engages an
anti-backlash gear 284 secured to the shaft 286 of the transformer 278. The signals
10 may be fed back to an indicating device and/or connected with the EH valve 74 as
desired.
In operation of the system 10, high pressure fluid is supplied to inlet filter
and check valve assembly B6 in a power-on mode. High pressure fluid acts through
passage 68 and ports 70 and 72 to balance the spool 100 of EH valve 74. Fluid is also
provided via passage 86 to the jet pipe 78 and impinges upon the face of the receiver
80. With the jet pipe centered over the two holes 88, 90 in its null position, equal
pressures are developed on either end of the spool 100.
EH valve 74 may then be energized for rotating the jet pipe 78 off center
toward either of the orifices 88 or 90. Shifting jet pipe to the left as seen in Fig. 5
20 will increase the pressure acting through the passage 92 against the left end of the
spool 100. This will cause the spool to shift to the right opening port 109 to
communication with pressure port 70 between lands 102 and 106. Port 110 will be
opened to communication with return port 115 between lands 106 and 108. High pressure
hydraulic fluid will then flow from pressure port 70 through port 109 to passage 111,
while at the same time hydraulic fluid will be exhausted through passage 112, and ports
110 and 115 through passage 116 to return port )14.
As indicated previously, as the spool lOû displaces from null, it deflects the
feedback spring 117 developing a force on the spool 100 counter ~o the input torque,
causing the spool to come to rest in a new position at which the spring force
30 counterbalances the pressure unbalance created by the jet pipe.
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In the power-on mode, high pressure fluid is also supp]ied to the left end of
bypass damping valve 118 by passage 160, thereby shifting the spool 132 to the right as
shown in Fig. 5 or upwardly as shown in Fig. 6. In such position, fluid communication
exists between passages 111 and 142 and passages 112 and 144. Accordingly, the pressure
differential across inlet ports 170 and 172 of the motoring valve 16 is directly
responsive to the EH valve 74.
~ luid entering the inlet ports 170 and 172 is ported through the stationary
outer sleeve 56 of the motoring valve 16 and into the rotary porting member 54. The
arcuate porting channels 200, 201 and 202, 203 at either end direct the flow into the
10 static ports 208, 210 and 214, 212 which in turn supply fluid to actuators A and B in the
manner previously described.
Clockwise rotation of the servoactuator is accomplished when the load
pressure is greater in passage 142 than in passage 144, which occurs when the spool 100
is shifted to the right as viewed in Fig. 5. The porting member 54 provides properly
sequenced fluid flow through the motoring valve 16 from passages 142 and 144 to the
fixed end port plates 204 and 206 and through internal porting at the actuator swivels
32, 34 to each actuator. As the actuators drive the crankshaft 14, the center porting
member 54 is driven thereby maintaining a constant relationship to output position of
the dual linear motor. The arcuate channels are arranged in angular relationship to the
20 specific position of the linear actuator being driven. The valve porting is overlapped in
the cylinder end switchover region to eliminate a transient cross flow. Valve internal
leakage to return in the overlapped region accornmodates the hydraulic switchover
pressure transient.
It will now be appreciated that the potential maximum developed torque
output of the servoactuator, with a constant pressure drop across the input cylinder
lines is nonlinear with output rotation. However, the required motor flow, or sum of
the actuator displacements is also nonlinear with speed held constant. These
nonlinearities, which are a function of the sinusoidal relationship of each of the linear
actuators displacement, are complementary. Moreover, maximum flow demand is
30 occurring coincident with minimum load pressure demand, whereby when driving under
constant load at a constant rate, the required power is essentially constant.
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In the power off mode, or when no high pressure hydraulic fluid is supplied
to the system such as may occur during towing of the aircraft, there is provided
shimmy damping through bypass damping valve 118. When no pressure is supplied to the
system, bypass damping valve spool 132 is biased to the left thus directing actuator
cylinder flow through the damping orifice 158 of the valve. Accordingly, as the
aircraft is towed with the nose wheel free to swivel, any shimmy that results will be
sufficiently damped. Moreover, it will be appreciated that the bypass damping valve
sleeve 124 may be changed as desired to provide a variety of different damping
characteristi cs .
In either the power on or power off modes, the high pressure relief valves
270 and 271 are connected to the actuators for directing flow to return in the event
that the design pressure differential within the system is exceeded.
Although the invention has been shown and described with respect to a
certain preferred embodiment, it is obvious that equivalent alterations and modifi-
cations will occur to others skilled in the art upon the reading and understanding of the
specification. The present invention includes all such equivalent alterations and
modifications and is limited only by the scope of the claims.
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