Jack extension tube for a power seat adjuster mechanism for a vehicle

A jack extension tube preferably for vehicles is provided which comprises an elongated tube with a threaded nut securely mounted therein, and a jack screw received in an open end of the tube and threadably received in the threaded nut. The tube has a first flange extending inwardly adjacent an inner end of the threaded nut and a second flange extending inwardly adjacent an outer end of the threaded nut whereby the threaded nut is securely retained within the elongated tube between the first and second flanges. The threads on the threaded nut can be involute threads to reduce noise, wear and chucking between the nut and the screw. The threaded nut can be formed of a rigid synthetic resin material. Further, a stop can be provided on one of the jack screw inner end and the threaded nut inner end whereby the stop prevents the threads on the jack screw from being separated from the threads on the threaded nut during rotation of the jack screw relative to the threaded nut and allowing for a low starting torque when the screw is rotated in a reverse direction.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates to a jack extension tube for use on power seat
 adjuster mechanisms for vehicles and, in particular, to a jack extension
 tube having low-noise operational characteristics and a low-torque
 internal stop-release and which can be mounted to an existing link in the
 seat adjuster mechanism by a fastener such as a rivet.
 2. Description of Related Art Jack extension tubes are used in power seat
 adjuster mechanisms for vehicles to operably connect a vehicle seat track
 or seat back to a powering mechanism to move the seat or any component
 thereof in a desired direction via a link member. By varying the length of
 the tube, jack extension tubes allow a particular seat adjuster mechanism
 to be used with seats on different vehicle models. Further, the tubular
 construction allows cost savings and weight savings over a solid machined
 rod. Two known prior art jack extension tubes are shown in greater detail
 in commonly-assigned U.S. Pat. Nos. 5,312,198 and 5,536,100 issued May 17,
 1994 and July 16, 1996, respectively. Typically, the link member is
 mounted to the extension tube by a fastener such as a shoulder bolt with
 an attached nut, a pin, a rivet and the like.
 However, because these extension tubes are often manufactured solely from
 steel or other metal components, some prior jack extension tubes have been
 known to make excessive amounts of noise during operation--more than is
 aesthetically pleasing while adjusting the seat in the passenger
 compartment of the vehicle. Further, prior extension tubes are often
 subject to "chucking"--looseness between components of the jack extension
 tube which contributes to unacceptable noise and vibration.
 SUMMARY OF THE INVENTION
 The invention generally relates to a jack extension tube for vehicles
 comprising an elongated tube having a first section with an open end and a
 second section spaced from the first section. A threaded nut is mounted in
 the first section and a mounting flange is provided in the second section
 which is adapted to receive a fastener. A jack screw is received in the
 first section open end and is threadably received in the threaded nut. The
 jack screw can include an exposed end defining a gear and an opposite end
 configured so that the jack screw is retained in the threaded nut and
 cannot be fully unscrewed from the threaded nut.
 In one embodiment, the invention relates to the tube having a first flange
 extending inwardly adjacent an inner end of the threaded nut and a second
 flange extending inwardly adjacent an outer end of the threaded nut
 whereby the threaded nut is securely retained within the elongated tube
 between the first and second flanges.
 In another embodiment, the threads on the threaded nut are preferably
 involute shaped threads.
 In an additional embodiment, the threaded nut is preferably formed of a
 rigid synthetic resin material.
 In a further embodiment, a stop is preferably provided on one of the jack
 screw inner end and the threaded nut inner end wherein the stop comprises
 a shoulder on the jack screw inner end and at least one ring received on
 the jack screw between the jack screw inner end and the threaded nut inner
 end in abutment with the shoulder whereby the at least one ring is
 prevented from being removed axially from the jack screw inner end by the
 shoulder. The stop thereby prevents the threads on the jack screw from
 being separated from the threads on the threaded nut during rotation of
 the jack screw relative to the threaded nut.
 The first flange can comprise a circumferential flange. The first flange
 can be integrally formed with the tube. The first and second flanges are
 preferably formed closely adjacent ends of the threaded nut whereby the
 first and second flanges prevent movement of the threaded nut within the
 elongated tube. The second flange is preferably formed at the first
 section open end. The second flange can be integrally formed with the
 first section open end.
 The threaded nut can be formed of a rigid synthetic resin material which
 can be reinforced with fibers and formed of a reinforced nylon material.
 The nut and its associated threads can be injection molded. The threads on
 the threaded nut can be involute shaped threads. The threads on the
 threaded nut and the threads on the jack screw can form a gap
 therebetween. The threads on the threaded nut can have an arcuate surface
 in abutment with the threads on the jack screw whereas the threads on the
 jack screw can have a standard helical thread. The threaded nut and the
 elongated tube can be rectangular in cross section. The threaded nut has
 chamfered portions adjacent each end in abutment with the first and second
 flanges of the tube.
 The stop can comprise a first ring received on the jack screw in abutment
 with the jack screw inner end and a second ring received on the jack screw
 inwardly of the first ring. The first ring and the second ring can be made
 from different materials. At least one of the first ring and the second
 ring is preferably formed from a synthetic resin material. At least one of
 the first ring and the second ring can be made from a self-lubricating
 synthetic resin material. At least one of the first ring and the second
 ring is preferably made from a material selected from the group consisting
 of polyethlyene, polypropylene, and nylon. At least one of the first ring
 and the second ring is preferably formed from the same material as the
 screw.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Referring to the drawings and to FIGS. 1-4 in particular, an improved jack
 extension tube 300 is shown comprising a housing 302, a screw 304 and a
 muffler such as a muffling nut 306.
 The housing 302 comprises an elongated tubular member, preferably having a
 rectangular cross section, with a first end 308 and a second end 310. At
 least one inwardly-extending flange 312 is defined intermediate the first
 and second ends 308 and 310 and preferably more closely adjacent to the
 second end 310.
 The first end 308 of the housing 302 is preferably arranged to pivotally
 receive a link member 314 shown in phantom lines in FIG. 1. To this end,
 the housing 302 has a pair of opposed reinforced openings 317 formed by a
 pair of inwardly-directed extruded annular flanges 318 which are described
 more fully in the commonly assigned U.S. Pat. No. 5,312,198 and is
 incorporated herein by reference. The openings 317 are adapted to receive
 a fastener such as a rivet 316 therein. An elongated slot 320 is also
 formed in the second end 308 of the housing 302 and extends longitudinally
 toward the first end 310 of the housing 302. The elongated slot 320
 defines a receiving area for the link 314. The link member 314 is
 pivotally mounted to the first end 308 of the housing 302 by the rivet 316
 or any other known fastener such as a shoulder bolt, a pin and the like.
 The link member 314 includes an opposite end (not shown) which is
 interconnected within a conventional seat adjuster mechanism which is well
 known in the seat adjuster art. The seat adjuster mechanism can be any
 mechanism used to move, orient, or translate a vehicle seat with respect
 to the passenger compartment of a vehicle, such as adjusters which extend
 or retract a seat longitudinally or vertically within the vehicle
 interior, a recliner mechanism for altering the angular configuration of
 the vehicle seat, and other similar mechanisms.
 The components of the extension tube assembly, such as the housing 302,
 screw 304, and muffling nut 306, are held together more securely than
 prior art jack extension tubes, making failure of the extension tube
 assembly 300 less likely.
 The housing 302 defines an internal longitudinal chamber 322 along the
 length thereof. The housing 302 is preferably formed from a rigid metal,
 such as steel, aluminum, or an alloy thereof, although it is contemplated
 that the housing 302 can also be formed from a synthetic resin material
 which has sufficient rigidity to maintain the stresses encountered by the
 housing 302.
 As shown in FIG. 1 and in greater detail in FIG. 5, the screw 304
 preferably comprises an elongated shaft 324 having a spirally-wound thread
 326 thereon which extends between a first end 328 and a second end 330 of
 the screw 304. The screw 304 is preferably constructed from a rigid metal,
 such as steel or aluminum, and the pitch of the threads 326 is preselected
 to provide a predetermined conversion of rotary-to-linear motion of the
 screw 304 with respect to the housing 302. As shown in FIG. 5, the threads
 326 of the screw 304 are preferably a standard helical thread with
 angularly-configured threads 327 thereon.
 The first end 328 of the screw 304 is provided with a flange 332
 non-rotatably mounted to the first end 328 of the screw 304 in a
 conventional manner. The flange 332 preferably includes any known
 engagement portion, such as a gear 334, adapted to be rotatably driven by
 a conventional seat adjuster motor (not shown). It will be understood that
 the member 334 can comprise other known mechanical engagement elements,
 such as a pulley, a transmission or a gearbox, or any other suitable
 component which can be interconnected to the seat adjuster motor.
 As shown in FIG. 1 and in greater detail in FIG. 3, the second end 330 of
 the screw 304 preferably comprises a head 336 which defines a shoulder 338
 thereon. First and second rings 340 and 342 are rotatably received on the
 shaft 324 of the screw 304 so that the first ring 340 abuts the shoulder
 338 of the head 336, and the second ring 342 is located axially inwardly
 of the first ring 340. The rings 340 and 342 are integral to an inventive
 feature of the extension tube assembly 300 whereby the screw 304 requires
 very little stop-release torque when abutted against the muffling nut 306.
 In the example extension tube assembly 300 shown herein, the first and
 second rings 340 and 342 preferably comprise a synthetic resin bushing and
 a metal washer, respectively.
 As best shown in FIG. 1 and in greater detail in FIG. 2, the muffling nut
 306 comprises an elongated body 344 preferably shaped to coincide with a
 portion of the interior chamber 322 of the housing 302 located between the
 flanges 312 and the second end 310 thereof. In this illustrated
 embodiment, the muffling nut is square in cross section. The muffling nut
 306 also includes a longitudinal threaded bore 346 with internal threads
 348 that correspond in pitch to the threads 326 on the screw 324 so that
 the bore 346 is adapted to receive the screw 304. As needed, the body 344
 of the muffling nut 306 can be formed with chamfered portions 350 on front
 and rear faces 352 and 354 thereof to aid in the retention of the muffling
 nut 306 within the housing 302.
 The muffling nut 306 is preferably made from a polymer composite resin,
 such as Celstran No. N66G40.02.4, and is preferably injection molded to
 the desired shape. The material comprising the muffling nut 306 is
 preferably any type of rigid material which is capable of withstanding at
 least 8.times.10.sup.3 tensile psi. Further, it is preferable that the
 material have a tensile modulus of greater than 0.40.times.10.sup.6 psi.
 It has been found that a nylon material which has been reinforced with at
 least 30% glass fibers produces preferable results in preventing the screw
 304 from being separated from the nut 306 during use. For example, the
 above-identified Celstran material has 40% glass fibers in a nylon base, a
 tensile strength of approximately 33.7.times.10.sup.3 psi and a tensile
 modulus of approximately 1.7.times.10.sup.6 psi. Further, it has also been
 found that a lower-cost material comprising a glass-filled acetal material
 of approximately a 33% ratio can also produce desirable results. An
 example of this material is available under the trade name Zytel 70G33
 HSIL. Each of the above materials can be provided with a lubricant for
 additional beneficial results in the interaction with the screw 304.
 The muffling nut 306 is preferably molded to the desired shape including
 the threads 348 on the internal bore 346 thereof. Although the threads 348
 can be a conventional helical thread aligned with the thread 327 of the
 threads 326 of the screw 304, it has been found that an "involute" screw
 thread such as that shown at 348 in FIG. 5 provides beneficial results. A
 characteristic of the involute screw thread is an arcuate surface 347
 which preferably has a large radius of curvature compared to the overall
 height and pitch of the threads 348 of the nut 306. The configuration of
 the involute screw threads 348 is shown in detail in FIG. 5. A gap 370 is
 preferably defined adjacent to a distal edge of each thread 326 of the
 screw 304 between a proximal edge of each screw thread 348 of the nut 306.
 Further, a gap 372 is defined adjacent a distal edge of each thread 348 of
 the nut 306 and a proximal edge adjacent each thread 326 of the screw 304.
 Further, the involute screw threads on the nut 306 shown by the arcuate
 surface 347 on each thread 348 provide a reduced contact surface of the
 threads 348 on the nut 306 with the threads 326 on the screw 304. The gaps
 370 and 372 cooperate with the involute screw threads 348 on the nut 306
 to provide a reduced contact surface of the nut 306 with the screw 304 at
 the points of interengagement between the threads of each component. This
 configuration proves advantageous in eliminating "chucking" between the
 screw 304 and the nut 306. This reduction in chucking reduces the
 looseness between the screw 304 and nut 306 which thereby reduces noise
 and vibration during operation of a power seat adjusting assembly in which
 the jack extension tube according this invention is incorporated.
 To create a subassembly of the screw 304 and muffling nut 306, the threads
 326 on the screw 304 are mounted within the threaded bore 346 of the
 muffling nut 306 so that the threads 348 of the bore 346 engage the
 threads 326 of the shaft 324. The rings 340 and 342 are located between
 the shoulder 338 of the head 336 of the screw 304 and the rear face 354 of
 the muffling nut 306.
 As shown in FIGS. 1 and 4A, the subassembly can then be mounted to the
 housing 302 by inserting the muffling nut 306 within the open second end
 310 of the housing 302 so that the rear face 354 of the muffling nut 306
 abuts the flanges 312. The muffling nut 306 thereby occupies the portion
 of the internal chamber 322 located between the flanges 312 and the second
 end 310 of the housing 302.
 After insertion of the muffling nut 306 into the portion of the interior
 chamber 322 between the flanges 312 and the second end 310 of the housing
 302, end portions 356 of the second end 310 of the housing 302 are roll
 formed or folded around the chamfered portions 350 on the front face 352
 of the muffling nut 306 as shown in FIG. 1 and in greater detail in FIG.
 4B. Thus, the muffling nut 306 is securely mounted within the portion of
 the interior chamber 322 between the flanges 312 and the end portions 356
 located at the second end 310 of the housing 302.
 This retention of the muffling nut 306 within the housing 302 provides a
 more secure mounting of the muffling nut 306 within the housing 302. The
 screw 304 and muffling nut 306 subassembly are prevented from being
 inadvertently removed from the housing 302 when undue forces are applied
 to the extension tube assembly 300 such as during a vehicle collision.
 It will be understood that the head 336, shoulder 338, and the rings 340
 and 342 cooperate, either alone or in combination, to define a stop for
 the second end 330 of the screw 304 relative to the rear face 354 of the
 muffling nut 306. Specifically, when the second end 330 of the screw 304
 approaches the rear face 354 of the muffling nut 306 (so that the tube 300
 is in the fully extended position) the stop prevents the second end 330 of
 the screw 304 from traversing into the bore 346 of the muffling nut 306
 and along the threads 348 thereof. The abutment of the stop against the
 rear face 354 of the muffling nut 306 thereby prevents the screw 304 from
 becoming separated from the threaded engagement with the muffling nut 306
 due to overtravel of the screw 304 with respect to the muffling nut 306
 which, in turn, prevents the extension tube assembly 300 from becoming
 inoperable if the separation occurs.
 As described above, the link member 314 is pivotally mounted at the first
 end 308 of the housing 302 by a known fastener, such as a rivet 316
 mounted through the link member 314 within the openings 317, so that the
 link member 314 can pivot relative to the slot 320. Further, the gear 334
 located at the first end 328 of the screw 304 is operably interconnected
 with a conventional motor for the seat adjuster mechanism.
 During operation of the seat adjuster mechanism, the motor is selectively
 actuated by a user to perform a particular adjusting operation for a
 vehicle seat. When the motor is actuated by the user, rotation is imparted
 to the gear 334 which, in turn, rotates the screw 304. Due to the
 engagement of the threads 326 of the screw 304 with the threads 348 of the
 muffling nut 306, the muffling nut 306 and the associated housing 302 move
 longitudinally along the screw 304.
 It will be understood that the movement of the housing 302 along the screw
 304 is limited at fully retracted and fully extended positions and can be
 preselected by sizing the housing 302 and screw 304 accordingly and
 mounting the screw 304 to the housing 302 to produce a desired length of
 travel for the tube 300.
 In the fully extended position, the second ring 342 on the second end of
 the screw 304 contacts the rearward face 354 of the muffling nut 306. The
 first ring 340 is retained between the second ring 342 and the shoulder
 338 of the head 336 located at the second end 330 of the screw 304. This
 fully retracted position is shown in greater detail in FIG. 3.
 Preferably, the first and second rings 340 and 342 are formed from
 different materials. The first ring or bushing 340 is preferably formed
 from a self lubricating synthetic resin, such as polyethlyene,
 polypropylene, nylon, or a composite similar to the material of the
 muffling nut 306. The second ring or washer 342 is preferably formed from
 metal such as steel or aluminum or a material having properties similar to
 that of the screw 304. Thus, in the fully extended position, the second
 ring 342 is abutted between the first ring 340 and the muffling nut 306.
 This interengagement of the differing materials of these components
 accomplishes some important functions. First, as the screw 304 approaches
 the fully extended position, the head 336 can be smoothly tightened
 against the muffling nut 306 with one or both of the first and second
 rings 340 and 342 slipping slightly. Second, as the seat adjuster motor is
 actuated in reverse to retract the head 336 of the screw 304 from abutment
 with the muffling nut 306, the rings 340 and 342 smoothly disengage from
 abutment with the rear face 354 of the muffling nut 306 with little torque
 required due to the self-lubricating nature of the second ring 342.
 Thus, the screw 304 smoothly decreases speed and stops when the rings 340
 and 342 abut the rear face 354 of the muffling nut 306 at the fully
 retraced position. Conversely, the head 336 of the screw 304 is easily
 moved out of abutment with the rear face 354 of the muffling nut 306 when
 the screw 304 is extended therefrom. Binding and/or damage to any of the
 components contained in the jack extension tube 300 are substantially
 reduced.
 The muffling nut 306 also provides the important function of reducing noise
 during retraction and extension of the housing 302 with respect to the
 screw 304. The different materials of the screw 304 and the muffling nut
 306 reduce noise generated as the threads 326 of the screw 304 move along
 the threads 348 of the muffling nut 306. Further, the involute thread
 configuration on one or both of the threads 326 and 348 of the screw 304
 and nut 306, respectively, aids this reduction in noise and prevents
 chucking.
 For example, the embodiment described herein has a metal screw 304 and a
 synthetic resin muffling nut 306. The friction, and therefore the noise,
 between the metal screw 304 and the synthetic resin muffling nut 306 is
 substantially less than the friction between a pair of metal components.
 It will be understood that any known sound-deadening materials can be used
 for the muffling nut 306, can be impregnated therein, or can line the
 threads 348 of the muffling nut 306 to provide additional reduction of the
 noise emitted from the extension tube assembly 300 during operation
 thereof due to the rotation of the screw 304 with respect to the housing
 302.
 An alternative embodiment of the extension tube 300 is shown in FIGS. 6-7.
 It will be understood that like reference numbers identify elements common
 to the embodiment shown in FIGS. 6-7 and the previous embodiment shown in
 FIGS. 1-5.
 The alternative embodiment of the extension tube includes a necked-down
 portion 360 located at the first end 308 of the housing 302. The
 necked-down portion 360 has a pair of inwardly-extending flanges 362 which
 are configured to receive a rivet 364 whereby a standard tool or press can
 be used to pivotally mount the link member 314 within the slot 320. The
 remainder of the structure and operation of the extension tube shown in
 FIGS. 6-7 operate the same as that shown in the previous embodiment of
 FIGS. 1-5.
 While particular embodiments of the invention have been shown, it will be
 understood, of course, that the invention is not limited thereto since
 modifications may be made by those skilled in the art, particularly in
 light of the foregoing teachings. Reasonable variation and modification
 are possible within the scope of the foregoing disclosure of the invention
 without departing from the spirit of the invention which is defined by the
 appended claims.