US3147631A

US3147631A - Actuator assembly

Info

Publication number: US3147631A
Application number: US37125A
Authority: US
Inventors: Everett P Larsh
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-06-20
Filing date: 1960-06-20
Publication date: 1964-09-08
Anticipated expiration: 1981-09-08

Description

Sept. 8, 1964v E. P. LARsH 3,147,631

AcTUAToR ASSEMBLY Filed June 2o, 1960 4 sheets-sheet 1 mwENToR EvERl-:TT e LARsH HIS ATTORNEY Sept 8 1964 E. P. LARsH 3,147,631

' AcTuA'roR ASSEMBLY Filed June 2o, 195o 4 sheets-sheet 2 Fm' BY HIS ATTORNEY Sept. 8, 1964 E, P, LARSH 3,147,631.

. ACTUATOR ASSEMBLY Filed June 20. 1960 4 Sheets-Sheet 3 FIGJO INVENTOR EVERETT P. LARSH HIS ATTORNEY sept. s, -1964 l E. p. LARSH 3,147,631;

' ACTUATOR ASSEMBLY Filed June 20, 1960 4 Sheets-SheetA lNvl-:Nron

EVERETT E LARSH HIS ATTORNEY United States Patent O 3,147,631 ACTUA'IUR ASSEli/IBLY Everett I. Larsh, Montgomery County, @hic (124 E. Monument Ave., Dayton 2, Ohio) Filed tune 2t), 1966, Ser. No. 37,125 16 Ciairns. (Cl. 74-89) This invention relates to an actuator assembly. The invention relates more particularly to an actuator assembly in which rotary motion is transformed into linear motion.

An object of this invention is to provide an actuator assembly in which rotary motion is transformed into y linear motion.

Another object of this invention is to provide such an actuator assembly which is capable of transmission of very high amounts of force in consideration of its physical slze.

Another object of this invention is to provide such an actuator assembly which may include means for automatically limiting and/ or indicating the value of the forces transmitted by the assembly.

Another object of this invention is to provide such an actuator assembly which is easily and readily attachable to various types of devices or other apparatus.

Another object of this invention is to provide such an actuator assembly which may be very sturdily built and is long lived. Y

Other objects and advantages reside in the construction of parts, the combination thereof, the method of manufacture, and the mode of operation, as will become more apparent from the following description.

In the drawings:

FIGURE 1 is a side sectional view showing an actuator assembly of this invention.

FIGURE 2 is a side elevational view, with parts broken away, and shown in section disclosing an actuator assembly of this invention with the elements thereof in a position of operation.

FIGURE 3 is a sectional view taken substantially on line 3-3 of FIGURE l.

FIGURE 4 is a sectional View taken substantially on line 4-4 of FIGURE 1.

FIGURE 5 is a sectional view taken substantially on line 5-5 of FIGURE l.

FIGURE 6 is a sectional view taken substantially on line 6-6 of FIGURE l.

FIGURE 7 is a View taken substantially on line 7-7 of FIGURE 6, but showing portions in section.

FIGURE 8 is a View taken substantially on line 88 of FIGURE 6, but showing portions in section.

FIGURE 9 is a side elevational view, with parts broken away, and shown in section showing a modification of an actuator assembly of this invention.

FIGURE l0 is a fragmentary side elevational view, with parts broken away, and shown in section showing another modification of an actuator assembly of this invention.

FIGURE l1 is a fragmentary side elevational view, with parts broken away, and shown in section showing a modification of a portion of an actuator assembly of this invention.

FIGURE l2 is an enlarged sectional view taken substantially on line 12-12 of FIGURE 1l.

FIGURE 13 is a fragmentary sectional view, with parts broken away, and shown in section showing a portion of the apparatus of FIGURES 1l and 12.

FIGURE 14 is a fragmentary sectional view showing a modification of the apparatus of FIGURE 12.

Referring to the drawings in detail, an actuator assembly of this invention, as shown in FIGURES 1-8, may comprise a housing Ztl having an end cover 22 attached Ice thereto. The end cover 22 may be provided with an aperture 24 for attachment thereof.

Within the housing 20 is any suitable reversible motor means herein shown as an electric motor 25 having a stator 26 provided with a rotor 28 which is supported by a shaft 3l). The shaft 30 is journalled at one end thereof in a bearing 32 which is carried in the end cover 22. The other end of the shaft 30 is journalled in a bearing 34 which is carried in a support plate 36 which is secured within the housing 20. The support plate 36 is shown separated from the stator 26 by means of a spacer 38.

Adjacent the plate 36 is an annular gear or internal gear 46 which may be separated from the housing 20 by means of a spacer 42, if desired, or the annular gear may directly engage the housing 20.

The shaft 30 is provided with teeth 44 which may be in the form of a gear attached to the shaft 30 or the teeth 44 may be directly formed in the shaft 30. The teeth 44 are in meshed relation with a plurality of planetary gear Imembers 46. The planetary gear members 46 are also in meshed relation with the annular gear 40, as shown in FIGURES l, 2, and 3. Each of the planetary gear members 46 is rotatably carried upon a bearing 48. Each bearing 48 is rigidly attached to a carrier disc or plate 56. The carrier disc 50 is nonrotatably attached to an output shaft 52 which, of course, rotates at a considerably lesser rate than the motor shaft 30. A thrust plate 54 is rigidly attached to the housing 20 and has an opening `through which the output shaft 52 extends. A plurality of elongate bolt members 56 secure the positions of the end cover 22, the thrust plate 54, the stator 26, and the annular gear 40. Intermediate the thrust plate 54 and the carrier plate 50 is a thrust bearing 60 which may be of any suitable type and is herein shown as comprising a disc 61 provided with a plurality of holes each of which rotatably retains a sphere or ball 62. Thus, the thrust bearing 66 engages the carrier plate 50 and one surface of the bearing plate 54. The other surface of the bearing plate 54 is engaged by a thrust bearing 64, which may be similar to the thrust bearing 60.

The shaft 52.V is shown as having a splined portion 66 which is adapted to receive a nut or cylinder 68 so that the nut or cylinder 68 is rotatable with the shaft 52. A nut 70 is threadedly attached to the end of the shaft 52 and secures the position of the nut or cylinder 68, as shown in FIGURES l and 2.

The outer surface of the nut or cylinder 68 is provided with a helical groove 72. The helical groove 72 has a plurality of convolutions and has ends which terminate adjacent opposite portions of the nut or cylinder 68. These ends of the groove 72 are joined together by means of a passage 74 which is formed within the nut or cylinder 68. l

If desired, the nut or cylinder 68 may be provided with segments 78, as shown in FIGURE 6. The segments 78 are attached to the nut or cylinder 68 by means of screws 80. Each of the segments 78 has formed therein an arcuate portion of the passage 74. There is one segment 7 8 adjacent each end of the groove 72.

Encompassing the housing 20 and the nut or cylinder 68 is a sleeve or shell 81 which is axially slidably movable upon the housing 20. A pin 82 shown in FIGURES 1 and 2 is attached to the sleeve 81 and moves in a suitable guide slot in the housing 20 and prevents rotary movement of the sleeve 81 with respect to the housing 20. The inner surface of the sleeve 81 is cylindrical and is provided with a helical groove 84 which is complementary to the helical groove 72 in the outer surface of the nut or cylinder 68. A multiplicity of rotary members in the form of balls or spheres 86 are disposed Within the groove 84 of the sleeve 81 and within the groove 72 of the nut or cylinder 68 so that the balls 86 join the nut or cylinder 68 to the sleeve 81.

With rotation of the nut 68 the balls or spheres 86 are moved in the

grooves

72 and 84. The passage 74 through the nut or cylinder 68 joins the opposite ends of the helical groove 72 so that the balls 86 never leave engagement with the nut or cylinder 68.

The sleeve 81 may be provided with an end cover 88 which is shown as having an aperture 90 for connection to another element or the like, for transmission of forces thereto.

Thus, it is understood that the sleeve 81 is axially movable with rotation of the nut or cylinder 68 and that the nut or cylinder 68 is rotatable with rotation of the rotor 28. Thus, there is relative axial movement between the housing 20 and the sleeve 81 upon operation of the motor 25. The end covers 22 and 88 serve as means for attachment of the actuator assembly to other elements for transmission of forces thereto by the actuator assembly. However, it is to be understood that other means may be provided for attachment to the sleeve 81 and/or the housing 20.

The thrust bearing 60 carries the thrust load when the nut or cylinder 68 rotates in one direction and the thrust bearing 64 carries the thrust load when the nut or cylinder 68 rotates in the opposite direction.

FIGURE 9 shows a modification in an actuator assembly of this invention in which a housing 100 is rigidly attached to a bracket 102. Rotary motor means 104 of any suitable type are disposed within the housing 100. Planetary gear members 106 are in mesh with a tooth portion 108 at the end of a shaft 110. Each planetary gear 106 is rotatable upon a pin or shaft 112 which is attached to a connector plate 113 which is shown integral with an output shaft 114. The pin or shaft 112 is used to rotatably support each planetary gear 106, rather than the bearing 48 shown in FIGURES 1, 2, and 3. A nut or cylinder 118, similar to the nut or cylinder 68, is attached to the shaft 114 and through ball members 120 is connected to a sleeve 122 in a manner similar to that discussed with respect to the apparatus of FIGURES 1 and 2. Thrust bearing members 124 are disposed on either side of a thrust plate 126. Thus, with rotary movement of the motor 104, the sleeve 122 is axially moved with respect to the housing 100, in a manner discussed above with respect to the apparatus of FIGURES l and 2.

FIGURE shows another modification in an actuator assembly of this invention. Any suitable motor means 130 has an output shaft 134. The rotary motor means 130 may be of a suitable speed or may have suitable speed reduction means therewithin so that the shaft 134 rotates at a desired rate. Thrust bearing members 136 are spaced on either side of a thrust plate 138 in a manner discussed above with respect to the thrust bearing members in FIG- URES 1 and 2. An engagement member 140 is attached to the shaft 134 for rotation therewith and serves as a thrust plate against one of the bearings 136.

Also attached rto the shaft 134 and rotatable therewith is a nut or cylinder 142 which is similar to the nut or cylinder 68 of FIGURES l and 2. The nut or cylinder 142, through ball or sphere members 144, engages a sleeve 146 for axial movement of the sleeve 146, in a manner discussed above.

FIGURES 11, 12, and 13 show another modification in an actuator assembly of this invention. In this modication, means are provided to Iindicate and/or control the forces transmitted from a rotary member to a linearly movable member. In FIGURE 11 any suitable rotary motor means 150 are shown disposed within a housing 152. A shaft 154 of the motor means 150 is journalled in a bearing 156. The bearing 156 is carried by a support plate 158 which is rigidly attached to the housing 152. The plate 158 has a flange 160.

The shaft 154 has a tooth portion 162 which is in meshed relation with planetary gear members 164 each of which is rotatably supported upon a carrier plate 166 by means of a sleeve bearing 168. Also, in meshed relation with the planetary gear members 164 is an annular gear or internal gear 170 which is slidably rotatable within an annular spacer 172. The carrier plate 166 is nonrotatably attached to a shaft 176 upon which is mounted a nut or cylinder 178, similar to the nut or cylinder 68 of FIGURES l and 2. A plurality of lball members 180 connect the nut or cylinder 178 to a sleeve 182 so that the sleeve 182 is axially movable with respect to the housing 152 during rotation of the nut or cylinder 178.

A U-shaped spring has an arm 192 rigidly attached to the plate 158. The plate 158 has a hole or aperture 194 therethrough. The spring 190 has an arm 196 extending through the aperture 194 in the plate 158 and the arm 196 is firmly attached to the annular gear 170. The spring 1?0 thus connects the plate 158 to the annular gear 170 and limits rotational movement of the gear 170 with respect to the housing 152.

All of the forces transmitted from the rotary motor means 150 to the axially movable sleeve 182 are transmitted through the annular gear 170. Also, due to the fact that the spring 190 connects the plate 158 to the annular gear 170, the spring 1510 carries the same loads as does the annular gear 170. The spring 190 is of suicient size that the annular gear 170 does not rotatively move until therotational forces applied to the annular gear 170 exceed a given amount.

Means are provided for indicating when such a given amount is reached. A bracket 200 pivotally supports a lever 202. The lever 202 has a notch 204 through which extends the arm 196 of the spring 190. A switch member 206 is operable by means of the lever 202.

When the rotational forces applied to the annular gear 170 exceed a given amount, the rotational forces cause the arm 196 of the spring 190 to move with respect to the arm 192 of the spring 1%, as shown in dotted lines in FIGURE 12. When the motor 150 is rotating in one direction, the arm 196 is moved in one direction when a given value of torque occurs; when the motor 150 is rotating in the opposite direction, the arm 1% is moved in the opposite direction by the annular gear'170 when a given value of torque occurs. When the arm 196 moves either toward or away from the arm 192, the arm 196 causes the lever 202 to move toward the switch 206. When the lever 202 moves toward the switch 266, the switch 206 is operated.

The switch 206 has connector leads 208 which are electrically joined to any Ysuitable member. The leads 208 may be connected to a suitable control unit which deenergizes the motor means Y150 when the switch 206 is operated by the lever 202. The leads 208 may also be connected to suitable indicator means so that a given value of forces within the actuator assembly may be readily detected.

It is to be understood that a plurality of spring members, such as the spring 190, may be attached to the plate 158 and to the gear 170. Such additional spring members otter greater restraint against movement of the gear 170 with respect to the plate 158.

Therefore, the mechanism shown in FIGURES 11, 12, and 13 may be provided for indicating and/ or controlling the value of the forces transmitted through the actuator assembly of this invention.

FIGURE 14 shows mechanism similar to that of FlG- URES 11, 12,-and 13. However, instead of a switch `such as the switch 206, an adjustable control unit 220 is operated by the lever 202 so that the total resistance of the unit 220 or the voltage across the unit 220 or other conditions in the unit 220 depend directly upon the value of the forces transmitted by the annular gear 170. The unit 220 may comprise an adjustable resistance device such as a carbon pile of any well known type or the unit 220 may be any other electrical unit in which the voltage and/or resistance or other factors may be :allargarsi varied. The unit 220 may also comprise any suitable mechanically operable or fluid operable indicator device. Thus, as the value of the forces transmitted by the annular gear 170 change, conditions in the unit 220 vary in accordance with such changes. Such changes are transmitted to the connector leads. Connector leads 222 extend from the unit 22) for attachment to any suitable control or detector means.

` Thus, it is understood that an actuator assembly of this invention is capable of transforming rotary motion into linear motion. The apparatus is capable of carrying high values of thrust loads in comparison to its physical size. Furthermore, an actuator assembly of this invention may have means for controlling and/or limiting or indicating the amount of forces transmitted by the assembly.

Although the preferred embodiment of the device has been described, it will be understood that within the purview of this invention various changes may be made in the form, details, proportion and arrangement of parts, the combination thereof and mode of operation, which generally stated consist in a device capable of carrying out the objects set forth, as disclosed and defined in the appended claims.

p Having thus described my invention, I claim:

l. Self-contained unitary actuator apparatus comprising a housing, rotary motor means within the housing, gear means within the housing and driven by the motor means, a shaft connected to the gear means and rotatable thereby, a nut attached to the shaft and rotatable therewith, the nut having a helical groove at the periphery thereof, the nut having a passage therethrough which commuuicates with two portions of the. helical groove, a shell encompassing the housing and having a helical groove on the internal Wall surface thereof, and a plurality of spherical members in the helical groove of the shell and in the helical groove of the nut, the spherical members connecting the shell to the nut so that upon rotary motion of the nut there is relative axial movement between the shell and the housing.

2. Apparatus for transforming rotational movement into reciprocal movement comprising support structure, rotary motor means carried by the support structure, a cylindrical nut operatively connected to the rotary motor means for rotation therewith, the nut having a peripheral helical groove with a passage in the nut connecting spacedapart portions of the groove, a shell having a cylindrical internal wall encompassing the nut, the internal wall having a helical groove therein, and roller means disposed Within the groove of the Wall and the groove of the nut connecting the shell to the nut so that upon rotational movement of the nut there is relative movement between the nut and the shell.

3. Force transmission apparatus comprising rotary motor means having an output shaft, a gear attached to the output shaft for rotation therewith, a planetary gear unit in meshed relationship with the gear which is attached to the output shaft, the planetary gear unit including an annular gear, the planetary gear unit also including a carrier, a nut, means connecting the carrier to the nut so that the nut rotates with rotation of the planetary gear unit, the nut having a peripheral surface provided with a helical groove, the nut also having a passage therethrough connecting portions of the helical groove, a sleeve encompassing said nut, the sleeve having an internal Wall provided with a helical groove, a plurality of balls disposed within the grooves and connecting the sleeve to4 the nut so that upon rotation of the nut there is relative movement between the nut and the sleeve.

4. Force transmission apparatus comprising a rotary motor provided with an output shaft, a housing, a plate member joined to the housing and encompassing a portion of the output shaft, bearing means connecting the plate member to the output shaft, the shaft having a portion provided with teeth, an annular gear having internal teeth rotatably supported by the housing, a plurality of planetary gear members in meshed relation with the teeth of the shaft and with the internal gear, a second output shaft, means connecting the planetary gear members to the second output shaft, a resilient member connected to said plate and to said annular gear, electrically operable control means operably connected with a portion of the resilient member for operation with movement of said portion of the resilient member.

5. Force transmission apparatus comprising a rotary motor provided with an output shaft, a housing, a plate member joined to the housing and encompassing a portion of the output shaft, bearing means connecting the plate member to the output shaft, the shaft having a portion provided with teeth, an internal gear rotatably supported by the housing, a plurality of planetary gear members in meshed relation with the teeth of the shaft and with the internal gear, a second output shaft, means connecting the planetary gear members to the second output shaft, a resilient member connected 4to said plate and to said internal gear, electrical control means operably connected with a portion of the resilient member for operation with movement of said portion of the resilient member, a cylinder attached to the second output shaft for rotation therewith, the cylinder having a helical groove in the outer surface thereof, a sleeve encompassing the cylinder, the sleeve having an internal surface provided with a helical groove complementary to the helical groove of the cylinder, rotary means disposed `in the groove of the sleeve and in the groove of the cylinder and connecting the cylinder to the sleeve.

6. Inan actuator assembly, support structure, an annular gear rotatable with respect to the support structure, a resilient member connecting the annular gear to the support structure and limiting movement of the annular gear with respect to the support structure, and electrical means operably connected to lthe resilient member for operation thereby upon movement of a portion of the resilient member.

7. Power transmission apparatus comprising support structure, rotary motor means carried by the support structure, an annular gear rotatably carried by the support structure, planetary gear means in meshed relation with the annular gear and with the rotary motor means, an output shaft connected to the planetary gear means, a U-shaped spring having an arm attached to the support structure and an arm attached to the annular gear, the spring limiting movement of the annular gear with respect to the support structure, a lever carried by the support structure and having a portion engageable by the arm of the spring which is attached to the annular gear, electrically responsive means operably connected with the lever, the lever being movable by said arm of the spring which is attached to the annular gear when the annular gear rotatively moves a given amount with respect to the support structure.

8. Power transmission means comprising a cylinder provided with a surface having a helical groove provided with a plurality of convolutions, the cylinder having a passage therethrough joining two spaced-apart convolutions of the groove, a sleeve encompassing the cylinder and having an internal surface provided with a helical groove complementary to the groove of the cylinder, motor means attached to the cylinder for rotation thereof, rotary means disposed in the groove of the cylinder and in the groove of the sleeve for connection between the cylinder and the sleeve, the rotary means being movable through said passage of the cylinder.

9. Unitary self-contained transmission apparatus comprising a housing, a motor within the housing and having a rotatable shaft, an annular gear carried by the housing, a plurality of planetary gears in meshed relation with the annular gear, a rotatable carrier plate rotatably supporting the planetary gears, gear means carried by the shaft in meshed relation With the planetary gears, a gear output shaft connected to the carrier plate for rotation therewith, a thrust plate carried by the housing adjacent the carrier plate, a thrust bearing intermediate the carrier plate and the thrust plate and in engagement therewith, a cylinder attached to the gear output shaft and rotatable therewith, a thrust bearing disposed intermediate the cylinder and the thrust plate and in engagement therewith, the cylinder having a helical groove provided with a plurality of convolutions, a shell encompassing the cylinder and axially movable with respect thereto, the shell having an internal surface provided with a helical groove complementary to the helical groove of the cylinder, and a plurality of balls within the groove of the cylinder and within the groove of the shell connecting the shell to the cylinder.

10. Unitary self-contained force transmission apparatus comprising housing means, rotary motor means within the housing, a shell encompassing the housing and telescopically movable with respect to the housing, a cylinder within the shell and coaxial therewith, means connecting the cylinder to the rotary motor means, the cylinder having a helical groove at the periphery thereof, the shell having a helical groove which is complementary to the helical groove of the cylinder, the cylinder having a passage connecting portions of the helical groove thereof, a plurality of roller members partially within the groove of the cylinder and partially within the groove of the shell and connecting the shell to the cylinder, the roller members also being movable through the passage of the cylinder.

11. In force transmission apparatus, a irst member,

a second member movable with respect to the rst mem-l ber, restraining means attaching the first member to the second member and restraining said members against relative movement therebetween, and detector means operable upon relative movement between said members.

12. Torque transmission apparatus comprising a support member, a transmission member rotatable with respect to the support member, rest-raining means connecting the transmission member to the support member and restricting movement of the transmission member with respect to the support member, and electrical detector' means operably connected to one of said members and indicating relative movement between said members.

13. Apparatus according to claim 12 in which said electrical detector means comprises a carbon pile.

` 14. Apparatus for transforming rotary forces into linear forces comprising rotary motor means, a rst cylinder, means connnecting the rotary motor means to the lirst cylinder, a second cylinder, a third cylinder, the second 8 and third cylinders being hollow, the rotary motor means being disposed within one of said hollow cylinders, the second and third cylinders being relatively slidably movable, said cylinders being coaxial, the rst cylinder and one of the hollow cylinders having complementary helical grooves, ball means disposed in said grooves and attaching cylinders one to the other so that upon rotary motion of the rst cylinder there is relative axial movement between the second and third cylinders.

15. Unitary self-contained apparatus for transforming rotary forces into linear forces comprising rotary motor means, a irst cylinder, means connecting the rotary motor means to the rst cylinder, a second cylinder, said cylinders being coaxial and having complementary helical grooves, the rotary motor means being disposed within said cylinders, ball means disposed in said grooves and attaching the cylinders one to the other so that upon rotary motion of the first cylinder there is relative axial movement between the cylinders, one of said cylinders having a passage which communicates with spaced portions of the groove of said cylinders, the ball means being movable through said passage.

16. Unitary self-contained actuator apparatus comprising support structure, a rotary motor unit carried by the support structure, an inner cylindrical member, the motor unit being disposed within the inner cylindrical member, the motor unit having an output shaft, a nut attached to the output shaft and rotatable therewith, the nut having an external helical groove provided with a plurality of convolutions, the nut having a passage therethrough joining spaced convolutions of the groove, a shell encompassing the nut and the inner cylindrical member and coaxial therewith, the shell having an internal helical groovecomplementary to the helical groove of the nut, and a plurality of spherical members within the groove and movable within the passage.

References Cited in the tile of this patent UNlTED STATES PATENTS k2,482,082 Wahlberg Sept. 13, 1949 2,616,302 Wahlmarky Nov. 4, 1952 2,820,162 Snell Jan. 14, 1958 2,907,223 y Valenti Oct. 6, 1959 2,917,079 Verbrugge et al. Dec. 15, 1959 v2,936,645' Smith May 17, 1960 2,937,984 Chapellier May 24, 1960 42,946,235 Musser July 26, 1960 2,958,232 Benninghofr" et al. Nov. 1, 1960

Claims

1. SELF-CONTAINED UNITARY ACTUATOR APPARATUS COMPRISING A HOUSING, ROTARY MOTOR MEANS WITHIN THE HOUSING, GEAR MEANS WITHIN THE HOUSING AND DRIVEN BY THE MOTOR MEANS, A SHAFT CONNECTED TO THE GEAR MEANS AND ROTATABLE THEREBY, A NUT ATTACHED TO THE SHAFT AND ROTATABLE THEREWITH, THE NUT HAVING A HELICAL GROOVE AT THE PERIPHERY THEREOF, THE NUT HAVING A PASSAGE THERETHROUGH WHICH COMMUNICATES WITH TWO PORTIONS OF THE HELICAL GROOVE, A SHELL ENCOMPASSING THE HOUSING AND HAVING A HELICAL GROOVE ON THE INTERNAL WALL SURFACE THEREOF, AND A PLURALITY OF SPHERICAL MEMBERS IN THE HELICAL GROOVE OF THE SHELL AND IN THE HELICAL GROOVE OF THE NUT, THE SPEHERICAL MEMBERS CONNECTING THE SHELL TO THE NUT SO THAT UPON ROTARY MOTION OF THE NUT THERE IS RELATIVE AXIAL MOVEMENT BETWEEN THE SHELL AND THE HOUSING.