Adjustable stator retainer assembly

A direct drive servovalve having a stator and rotor mounted upon a housing within which a spool valve is reciprocally disposed for engagement with the rotor and movement thereby in response to the application of appropriate electrical signals. The stator assembly is adjustable and after appropriate adjustment there is provided a retainer means secured to the closed end of an isolation tube for clamping the stator assembly in place relative to the rotor assembly of the moored motor. The clamping assembly includes an annular member having a downwardly depending skirt which engages the stator. The annular member is held in place by a retainer ring threadably secured to the outer surface of the isolation tube or alternatively behind fasteners which are threadably received by the closed end of the isolation tube. A separate non load bearing housing cover is positioned over the motor.

FIELD OF THE INVENTION 
This invention relates to direct drive servovalves and more particularly to 
a direct drive servovalve in which rotational motion of a motor rotor is 
converted into linear motion of a spool valve wherein the stator of the 
drive motor is adjustable and the motor includes a retainer assembly to 
secure the stator. 
BACKGROUND OF THE INVENTION 
Torque motor-driven spool valves are well known in the art including such 
valves which operate through the utilization of a rotary torque motor 
having a drive member extending from the rotor thereof into contact with 
the spool valve to directly reciprocate the spool valve within a bore 
provided in the valve housing to thereby control the flow of fluid from a 
source thereof to the load in response to electrical signals applied to 
the drive motor. Typical of such direct drive servovalves is that 
illustrated in U.S. Pat. No. 4,793,377 issued Dec. 27, 1988, to Larry E. 
Haynes et al. The invention described and claimed herein is an improvement 
over the direct drive servovalve disclosed in U.S. Pat. No. 4,793,377 and 
therefore the disclosure of U.S. Pat. No. 4,793,377 is incorporated herein 
by this reference. 
The drive motors of such devices include a rotor and stator disposed within 
a housing in such a manner that the rotor assembly is subjected to the 
high pressure fluid typically used in servo control systems with which the 
device is associated. In such devices, it is desirable to have the ability 
to properly position the rotor to accomplish null centering of the rotor 
assembly and thereafter to position and clamp the stator relative thereto. 
Typical of prior art devices of the type described are U.S. Pat. Nos. 
4,507,634 and 4,641,812. In each of these devices, the motor housing is 
utilized as a load carrying structure to clamp the stator in place 
subsequent to its proper positioning. Furthermore, to retain proper 
positioning between the stator and rotor assemblies, a locking pin and 
structural adhesive is utilized as is shown in U.S. Pat. No. 4,507,634. 
Alternatively, as is shown in U.S. Pat. No. 4,641,812, once the nulling 
process is completed and the motor stator assembly properly located by 
index pins, then the outer housing and the motor stator assembly are 
clamped in place by threading a nut onto a threaded extension of the rotor 
casing. In either structure, the motor housing becomes a load carrying 
member for clamping the stator assembly in place. Obviously, such a 
structure renders it extremely difficult to disassemble such valves for 
repair and/or maintenance and then reassemble them while maintaining the 
desired positioning of the stator and rotor assemblies. 
It would be desirable in such structures to provide a retainer assembly for 
securing the stator of the drive motor while retaining the ability to 
position the stator within a 360.degree. rotational envelope, to securely 
clamp and lock the stator in the desired rotational position and to 
eliminate the motor housing cover as the load carrying structure which 
locks and retains the stator assembly in place. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided a direct drive 
servovalve which includes a valve spool reciprocally mounted within a bore 
in a valve housing along with motor means having a rotor and a stator and 
including a drive member to engage the valve for movement within the bore 
to provide control over the flow of fluid through the valve. A retainer 
means is disposed adjacent a closed end of an isolation tube within which 
the rotor is disposed. The retainer means is secured to the closed end of 
the isolation tube for clamping the stator assembly in place relative to 
the rotor assembly. A separate cover means is then disposed over the motor 
means.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT 
By reference now to FIG. 1, there is shown a direct drive valve 10 
constructed in accordance with the principles of the present invention. As 
is therein shown, a valve housing 12 includes a bore 14 within which there 
is positioned a sleeve 16. A reciprocally movable spool valve 17 is 
mounted within the sleeve 16. A servovalve torque motor 18 is affixed to 
the housing 12 by means of bolts or other fasteners 20 so that a drive 
member 22 engages an opening 24 provided therefor in the spool 17 to move 
the spool 17 in response to electrical signals applied to the motor means 
18 as is well known in the art. 
As is illustrated in FIGS. 1 and 2, the motor means is a rotary motor 
including a stator 26 and a rotor 28 as is well known in the art. 
As is shown particularly in FIG. 1, the direct drive servovalve constructed 
in accordance with the principles of the present invention includes 
appropriate ports for the control of fluid from dual sources thereof under 
pressure P1 and P2 to, for example, a dual tandem actuator (not shown) and 
from the actuator to return through the utilization of dual cylinder 
ports. Such is indicated by the designations P1, R1 and C1 as well as P2, 
R2 and C2. The valve assembly 10 may also include an LVDT 30 as is well 
known in the prior art. The construction of the rotary direct drive 
servovalve as illustrated in FIGS. 1 and 2 and thus far described is well 
known in the prior art and additional detail with regard thereto is not 
believed to be necessary. 
As is shown more particularly in FIG. 2, the valve housing 12 defines a 
first recess 32 which receives the outer surface 34 of a bearing means 36 
mounted upon one end 38 of the rotor shaft 40 to the motor means 18. The 
recess 32 conforms to the outer surface 34 cross-sectional configuration 
of the bearing 36 and has a depth which is substantially less than the 
longitudinal length of the outer surface 34 of the bearing 36. As a result 
and as is clearly illustrated in FIGS. 1 and 2, when the bearing is 
received within the recess 32, a substantial portion of the outer surface 
34 thereof protrudes from the housing 12. 
As a result of the longitudinal dimension of the outer surface 34 of the 
bearing 36, it can be seen from FIGS. 1 and 2 that the bearing is mutually 
received within a second recess 42 defined by the lower portion 44 of the 
isolation tube 46. The isolation tube 46 surrounds the rotor 28 of the 
motor means 18 and isolates hydraulic fluid from the stator portion 26 of 
the motor means 18. 
The isolation tube 46 also includes an upper closed end portion 48 thereof 
which defines a third recess 50 which receives a second bearing means 52. 
The bearing means 36 and 52 are utilized to support the rotor shaft 40 in 
a properly aligned position within the isolation tube 46. Such alignment 
is obtained by inserting the end 54 of the shaft 40 by way of an 
interference fit into the inner race of the bearing means 52. The outer 
race of the bearing means 52 is then inserted by means of a locational 
slip fit between the third recess 50 and the outer race of the bearing 
means 52. The bearing means 36 is then inserted by means of an 
interference fit between the outer surface 34 of the bearing means 36 and 
the second recess 42 inner surface as provided in the lower portion 44 of 
the isolation tube 46. A locational slip fit is provided between the lower 
portion 38 of the shaft 40 and the inner race of the bearing means 36. 
Subsequent to this assembly, which now provides essentially a solid 
structure between the isolation tube 46 and the rotor 28, the assembly is 
inserted into the first recess 32 by a locational slip fit between it and 
the outer surface 34 of the bearing means 36. It can, therefore, be seen 
by those skilled in the art that the outer surface 34 of the bearing means 
36 is utilized as the surface with respect to which the motor assembly 18 
and the housing 12 are aligned. By then appropriately aligning the sleeve 
16 within the housing 12 and positioning the spool 17 therein, it can be 
seen that the longitudinal axis of the rotor shaft 40, the drive member 
22, the opening 24 and the opening 56 through which the drive member 
extends are all axially aligned when viewed in FIG. 1 and when the spool 
17 is in its null position. 
By reference now more particularly to FIGS. 2 through 6, there is 
illustrated and will be described more in detail, one embodiment of a 
retainer assembly for a direct drive servovalve constructed in accordance 
with the principles of the present invention. As is illustrated, the 
stator 26 is secured in position by a retainer assembly which is secured 
to the closed upper end 48 of the isolation tube 46. In accordance with 
this specific embodiment, the retainer assembly is threadably secured to 
the outer upper surface of the isolation tube 46 in such a manner that a 
flange urges an annular member having a downwardly depending cylindrical 
skirt thereon into engagement with the stator for clamping the stator 
between the skirt and an upstanding wall provided as part of the motor 
assembly. 
As is shown, the retainer 60 includes an annular member 62 having a 
downwardly depending skirt 64. A retainer ring 66 is threadably secured to 
the outer surface 68 of the upper closed end 48 of the isolation tube 46. 
As is shown, the retainer ring 66 includes an outwardly extending flange 
70 which overlaps the annular member 62 in such a manner that as the ring 
66 is threaded onto the surface 68, the flange applies downwardly exerted 
clamping pressure against the pole piece 72 of the stator 26. There is 
also provided an upstanding wall 74 which is part of the base 76 of the 
isolation tube 46. The wall 74 defines a shoulder 78 upon which the pole 
piece 72 rests. 
The downwardly depending skirt 64 defines a peripheral edge 80 from which 
depends a key 82. The key 82 engages a key way provided in the pole piece 
72 so that when the retaining member 60 is disposed in place, as 
illustrated in FIG. 2, rotation of the retaining member 60 also rotates 
the stator 26. Such rotation is utilized to accomplish appropriate null 
balance of the direct drive servovalve. 
To accomplish the desired null balance of the direct drive servovalve as 
illustrated in FIGS. 1 and 2, the spool 17 is positioned so that it is at 
the hydraulic null where no fluid flow (other than leakage) is taking 
place between the source and drain for the valve. Thereafter, the stator 
26 is rotated so that a magnetic peak is obtained insofar as positioning 
of the stator and rotor are concerned. After this adjustment, the 
retaining ring 66 is securely tightened thus applying the clamping force 
as above-described to secure the stator in place in its proper adjustment. 
As a security measure, a lock wire 84 is threaded through appropriate 
openings provided in the retaining ring 66 and the top 48 of the isolation 
tube 46 to preclude inadvertently loosening the retaining ring 66. To 
accommodate the locking wire, openings 86 are provided in the flange 70 of 
the locking ring 66 while openings 88 are provided in the upper closed end 
48 of the isolation tube 46. In addition, to secure the locking ring, 
threads are formed on the inner surface 90 thereof which are threadably 
received by the threads formed on the outer surface 68 of the upper 
portion 48 of the isolation tube 46. Openings 92 are provided in the 
locking ring to receive an appropriate tool for properly torquing the 
locking ring in place so that the flange 70 clamps the stator 26 between 
the periphery 80 of the retainer 60 and the shoulder 78 of the wall 74. 
After the drive motor has been thus assembled, it can function adequately 
at this time. However, to preclude contamination of the coils in the 
stator 26 and to otherwise protect the same, a housing 94 is secured in 
place by the fasteners 20 to environmentally protect the motor 18. As will 
be evident to those skilled in the art, the housing 94 does not function 
in any fashion to clamp or otherwise secure the stator or any other 
portion of the drive motor. 
By referring now more particularly to FIGS. 7 through 9, there is 
illustrated an alternative embodiment of a retaining assembly for a motor 
of a direct drive servovalve constructed in accordance with the principles 
of the present invention. The structure of the valve as well as the stator 
and rotor of the drive motor is substantially the same as above-described 
and thus will not be described in detail at this point. As is shown in 
FIGS. 7 through 9, the retainer assembly includes an inverted cup shaped 
member which fits over the top of the isolation tube of the rotor and is 
secured in place by appropriate fasteners to thereby clamp the stator 
between the retainer and the shoulder of an upstanding wall forming part 
of the motor assembly. 
As is shown in detail, the retainer 100 includes a plate member 102 having 
a downwardly depending skirt 104 which defines a periphery 106. A key way 
108 is defined by the periphery 106 and receives a key 110 which is 
affixed to the pole piece 112 of the stator 114. The plate 102 defines a 
plurality of openings 116 therein. Fasteners of a standard threaded nature 
as shown at 118 are inserted through the openings 116 and into threaded 
bores in the closed upper end 120 of the isolation tube 122. The pole 
pieces 112 of the stator rest upon a motor support 124 which is retained 
upon the base 126 of the isolation tube 122 and defines a shoulder 128 
upon which the pole piece 112 rests. 
After assembly of the motor and valve as illustrated in FIG. 7, the 
retainer 100 is rotated to accomplish the appropriate null balance as 
above-described. Thereafter, the fasteners 118 are secured firmly in place 
to thus apply the clamping force to secure the pole pieces 112 of the 
stator between the shoulders 128 and periphery 106 of the support 124 and 
the skirt 104 respectively. Thereafter, for security purposes, the heads 
of the fasteners 118 are safety wired to prevent their becomming loosened 
during use. As is clearly illustrated in FIG. 8, the openings 116 are 
elongated to provide the ability to rotate the retainer 100 through a 
predetermined angular distance to accomplish the desired null balance. 
There has thus been disclosed alternate embodiments of a direct drive 
servovalve having an adjustable stator with a retainer assembly therefor 
which retainer assembly clamps the stator of the drive motor in place 
without reliance upon a motor housing.