Flexible vane coupling

A slip coupling comprised of a hub with extending flexible vane(s). The vane(s) extend from the hub at an acute angle which allows them to flex when coming in contact with a relatively rotatable friction cylinder. The friction between the vane(s) and the friction cylinder creates resistance to movement. Relative motion between the hub and friction cylinder occurs only when the frictional force between them is overcome.

FIELD OF THE INVENTION
 This invention relates to a device which may be useful as a clutch or
 brake; more specifically, a slip friction clutch or brake with a minimal
 number of parts and long service life.
 BACKGROUND OF PRIOR ART
 Previous friction clutches consist of a multiplicity of small parts in
 order to achieve relatively high torque that is smooth in output. This
 creates a number of problems. Using a large number of parts increases
 manufacturing cost and inherent inaccuracies due to tolerance stack-up.
 The chances for parts not working together properly is also increased.
 Resulting problems can include inconsistent torque, backlash from poorly
 fitted parts; and with more parts, increased chances for failure. Also, it
 is time consuming and costly in terms of labor to assemble a clutch with a
 variety of small pieces. The present high cost of labor makes this type of
 clutch less desirable to produce now than in the past.
 While a variety of inventions exist, many have involved complex designs
 that do not lend themselves to vary low-cost manufacturing and assembly
 procedures. For example, U.S. Pat. No. 3,712,438 is a clutch with radially
 expanding friction surfaces. Specifically, this is a centrifugally
 operated clutch. This type of clutch engage when rotational speeds
 increase sufficiently to force the inner friction surface into the outer
 surface.
 Such clutch designs do not produce torque unless the inner member is
 rotating. Once a critical speed is reached, the inner expanding hub and
 driven member rotate in unison. As a result, this type of design is not
 made for slipping between members except for the brief period while
 engagement occurs.
 Wrap spring type clutches are commonly used when slipping between friction
 surfaces is required. As the friction surfaces wear however, the spring
 must wrap down further to maintain constant torque. Torque output is very
 sensitive to wear due to the limited amount of radial movement of the wrap
 spring that is possible. Wear of 0.002-0.005 inches in the friction
 surfaces will cause the torque to drop off by a relatively large amount.
 This creates a significant limitation to clutch life. To reduce wear,
 expensive coatings or surface hardening of the friction surface must be
 done.
 Furthermore, uneven radial forces result when the spring winds down onto
 the hub. This causes uneven wearing of friction surfaces. The full area of
 the friction element cannot be utilized to its optimum potential.
 Additional manufacturing complexities and costs are required to overcome
 this problem. U.S. Pat. No. 3,405,929 shows one attempt to reduce uneven
 wear of the friction surfaces. Wrap spring clutches typically have only
 one friction surface. With one friction element, torque can be increased
 only by increasing pressure between friction surfaces. Once maximum
 allowable surface pressure between friction surfaces has been reached,
 torque can be increased only by adding additional friction surfaces. U.S.
 Pat. No. 3,242,696 shows two friction surfaces. This increases the
 complexity of the design. With two concentric rings required to support
 friction surfaces, the chances for misalignment are greater.
 Adding a second outer friction surface necessitates reducing the operating
 diameter of the first friction surface. Since torque is a function of
 force and distance from the center of rotation, reducing the diameter of
 the first friction surface reduces the torque it can produce. It also
 limits heat dissipation since heat is generated further away from the
 outer surface where it can be dissipated. Increasing the friction surfaces
 to three or more would compound the previously stated problem even more.
 U.S. Pat. Nos. 5,037,354 and U.S. Pat. No. 5,092,440 are typical small
 clutches of simple design. Both designs require springs and additional
 supporting parts to urge the friction elements together. This increases
 cost and complexity. Both designs show only one friction surface. As
 described with wrap spring clutches, providing only one friction surface
 limits the maximum amount of torque which can be produced. Increasing the
 number of friction surfaces beyond the one shown increases cost and
 complexity still further. If it is even possible at all. The low torque
 output limits commercial applications since many and users require
 relatively high torque.
 U.S. Pat. No. 4,878,880 shows a simple two-piece clutch. Both parts can be
 made as a molded plastic or metal part reducing costs further. There are
 at least two major shortcomings. First, the slipping elements jump from
 radial groove to groove as the clutch is rotated. This is described in
 column 5 lines 2 through 6 of U.S. Pat. No. 4,878,880. As a result, torque
 is not smooth. For current usage in business machines, for example; smooth
 torque is a prime concern. Second, torque is produced by cantilevered
 fingers extending axially from a plate. As the distance from the mounting
 plate increases, a cantilevered beam will have lower resistance to
 deflection. Therefore the outward radial force exerted along the length of
 the fingers is not consistent. Wear will be inconsistent since the part of
 the finger closest to the plate will not deflect as easily. By the very
 nature of the design, the full length of the friction elements cannot be
 fully utilized. As a result, clutch life and torque output will be
 reduced.
 OBJECTS AND ADVANTAGES
 It is among the objects and advantages of this invention to create a
 versatile clutch design which is fully functional with as few as two
 working parts.
 Another object and advantage is the compensation for wear is friction
 surfaces which results in longer clutch life.
 Yet another object and advantage is to have even wear of the friction
 surfaces throughout the life of the clutch.
 Still another object and advantage of the invention is the simplicity in
 adding friction surfaces to increase torque output of the clutch.
 Still another object and advantage of the present invention is to have
 smooth torque output as the friction elements slip against each other.
 Additional objects and advantages include torque that can be different
 depending on whether the clutch is rotated in a clockwise or
 counterclockwise direction. Another additional object and advantage is the
 use of the device as a slip coupling where compliance between the two
 friction elements allows for concentric and angular misalignment between
 the two shafts that it connects.
 Further objects and advantages of the present invention will be apparent
 from consideration of the drawings and ensuing description.

DESCRIPTION OF THE PREFERRED EMBODIMENT--FIGS. 1-3
 A perspective view of a typical embodiment of the clutch is shown in FIG.
 1. The device comprises a housing and shaft assembly 10. The housing
 assembly 10 consists of a cylindrical shell 12 with an outer diameter 12a
 and an inner diameter 12b. Also comprised in the housing and shaft
 assembly 10 is a rear surface 14, a shoulder 16, and a shaft 18. The
 housing assembly 10 is preferentially made from die cast zinc. All
 surfaces have smooth "as cast" finishes. The shaft 18 is formed onto the
 rear surface 14 and extends beyond the cylindrical shell 12. The shaft 18
 is hollow to allow for mounting the clutch to an external drive shaft 20.
 Attaching the housing assembly 10 to the drive shaft 20 can be
 accomplished with a set screw 22, interference press fit, keyway, or
 spline.
 The shaft 18 could also be made from a separate piece of material and
 mounted into the rear surface 14 of the housing and shaft assembly. In
 this case, the material could be carbon steel for additional strength.
 The second part of the device consists of a hub 30. In preferred form, the
 hub 30 consists of a plurality of radially extending vanes 32a-f hereafter
 noted as simply vanes 32. The vanes 32 extend from the hub 30 at an acute
 angle 34 to the surface of the hub 30. In its free state, an outer
 diameter 36 of the vanes 32 is larger than an inner diameter of the
 cylindrical shell 12b. The hub 30 is made from a resilient plastic or
 rubber material which allows for flexing.
 When the hub 30 is assembled into the housing assembly 10 the vanes 32 flex
 inward. This creates pressure and thereby frictional force between the two
 surfaces. As shown in FIG. 1, the vanes 32 are nested inside each other.
 This allows many friction surfaces to be placed radially around a small
 area. The bub 30 is retained inside the housing and shaft assembly 10 by
 means of the shoulder 16 at the edge of the inner surface of cylindrical
 shell 12b.
 The outer surface of shaft 18 supports the hub 30 and acts as a bearing
 surface for hub 30 to spin on the hub 30 can be made to rotate relative to
 the housing assembly by many different methods. Shown in FIG. 1 is a
 timing-belt gear 38 which is molded as part of the hub 30.
 FIG. 2 shows the profile section A--A of FIG. 1. Here, the vanes 32 contact
 the inner surface 12b of the cylindrical shell 12. As shown, the tips of
 the vanes 32 do not contact the inner surface of the cylindrical shell 12.
 This creates a neutral surface interface whereby direction of rotation
 between the cylindrical shell 12 and vanes 32 has a minimal effect on
 torque.
 FIG. 3 shows the axial cross-section view B--B of FIG. 1. The hub 30 is
 retained inside the housing and shaft assembly 10 by means of the inwardly
 projecting lip 16 at the edge of the cylindrical shell 12. Alternately, a
 radial groove 24 could be cut into shaft 18. A snap ring 26 would fit into
 the groove 24 and retain the hub 30 into the housing assembly 10.
 Also shown in FIG. 3 is a space for the timing belt gear 38. This can be
 molded as part of hub 30. Alternately, the gear or pulley 38 can be
 fabricated separately and pressed, bonded, or ultrasonically welded onto
 the hub 30. The set screw 22 is shown as an alternate way to affix the
 housing assembly 10 to the external drive shaft 20.
 In operation, when gear 38 is driven, hub 30 is driven as well. The vanes
 32 frictionally engage the inner surface 12b of the cylinder shell. The
 device of FIG. 1 is set for a predetermined torque in three ways. First is
 the pressure of contact of each vane 32 and cylindrical shell portion 12.
 Second is the number of vanes 32 used. Each vane contributes as equal
 amount of torque. This is the coefficient of friction between the vanes 32
 and cylindrical shell 12. This is determined by the materials used.
 For example, FIG. 4 shows the invention of FIG. 1 but with only a single
 vane 32. One friction surface can be used for applications requiring very
 low torque levels. For vanes 32 or equal dimension, adding a second vane
 32b' will double the torque. Adding a third vane 32c' will increase the
 torque three times that of a single vane and so on. In this way torque can
 be increased with only minor modifications to the basic design. As shows
 vanes 32c' and 32d' that are added do not have to be angled from the hub
 30 in the same direction as vanes 32a' and 32b'.
 Once the predetermined torque level is exceeded, hub 30 will rotate in
 relation to housing assembly 10. This could be a difference in rotational
 velocity of one member may be stopped altogether. As slipping occurs,
 material from housing material 10, they and vanes 32 will gradually wear
 away. Since the vanes 32 were initially flexed inward to fit into housing
 assembly 10, they will expand outward as material is worn away. For a 5/8"
 diameter clutch, the vanes are flexed about 0.015". Material wear after
 1,000,000 revolutions is typically 0.0005". Since material wear is
 considerably less than flexure of the vanes 32, torque will not change
 substantially even though material is being worn away.
 Even with slight variations is concentricity or angularity between housing
 assembly 10 and vanes 32, torque does not change. This is due to the self
 compensating effect of the flexing vanes 32. When one side of the housing
 assembly 10 is closer to the vanes 32 they are compressed more. The
 opposite side is further away so the vanes 32 flex by an equally reduced
 amount. Force vs. deflection of the vanes is fairly linear. The result is
 that higher torque from increased deflection on one side is compensated by
 equally reduced deflection, and torque, on the opposite side.
 FIG. 5 shows another way to mount the device. Here an end housing 50 is
 pressed into each end of a cylindrical shell 52. The inner surface 54 of
 each end housing 50 acts as a bearing surface for a hub 56 to rotate on.
 The cylindrical shell can be made from steel tubing. The end housings 50
 are made from a suitable bearing material such as acetal plastic or oil
 impregnated sintered bronze. The hub 56 is of similar design to hub 30 as
 previously described. The hub 56 slides onto an external drive shaft 58
 and is attached to the drive shaft 58 by means of a set screw 60, keyway,
 or a press-fit.
 The device can be used as a flexible slip coupling between two shafts. This
 is shown in FIG. 6. Here an outer shell 60 is mounted to an external shaft
 62. A mating hub 64 is mounted to a second shaft 66. The materials,
 construction, and operation are the same as previously described. Due to
 the flexing of the vanes, the two shafts can be slightly misaligned and
 torque will not be affected. Misalignment can be concentric, angular, or
 combination of the two. The two shell 60 and hub 64 are attached to their
 respective shafts by means of a set screw 68.
 The housing and hub do not have to be oriented in a radial arrangement.
 FIG. 7 shows the elements oriented axially along a shaft. A housing and
 shaft assembly 70 supports a hub 80 as previously described. Comprised in
 the housing and shaft assembly 70 is an outer cylindrical shell 72, a rear
 surface 74, and a shaft 76. The shaft 76 is formed onto the rear surface
 74 and extends beyond the cylindrical shell 72. The hub 80 is retained on
 the shaft 76 with a retaining ring 78. The shaft 76 is hollow to allow for
 mounting the clutch to an external drive shaft 86. Attaching the housing
 assembly 70 to the drive shaft 86 can be accomplished with a set screw 88,
 interference press fit, keyway, or spline.
 The hub 80 consists of a plurality of axially extending vanes 82a-f. The
 vanes 82 extend from the hub 80 at an acute angle to the face of the hub
 80. The hub 80 is made from a resilient plastic or rubber material which
 allows for flexing. When the hub 80 is assembled into the housing assembly
 70 the vanes 82 flex inward. This creates pressure and thereby frictional
 force between the two surfaces.
 The outer surface of shaft 76 supports the hub 80 and acts as a bearing
 surface for hub 80 to spin on. The hub 80 can be rotated relative to the
 housing assembly by many different methods. Shown in FIG. 7 is a timing
 belt gear 84 which is molded as part of the hub 80.
 Torque can be different depending on direction of rotation. Here the
 surface 74 is serrated. The end of each vane 82 touches the inner serrated
 surface 74 of housing 70. When the hub 80 is rotated counterclockwise, for
 example; the tips of vanes 82 engage the housing 70 for direct lock up
 with no slipping possible between the housing 70 and hub 80. For rotation
 in a clockwise direction, slipping will occur once the limits of the
 frictional force is exceeded. This is because the acute angle of the vanes
 82 allow the vanes to slide over the grooves versus engaging into them.
 As shown in FIG. 8, a housing 90 and a hub 92 do not have to be in fixed
 relation to each other. In this embodiment, a roller wheel 94 which winds
 and unwinds tape as in a videocassette recorder is mounted to the housing
 90. The housing 90 stays generally concentric to hub 92 due to equal
 outward pressure by a plurality of vanes 96. As well as providing
 frictional resistance to rotation, the hub 92 allows for radial deflection
 of the roller wheel 94. Radial deflection can be used to compensate for
 sudden variation in tape speed. The torque limiting feature alone of the
 friction device would not compensate for such variations. The assembly is
 mounted via a cylindrical extension 98 of hub 92.
 Operation of the device is not limited to use as a clutch. FIG. 9 shows the
 device used as a brake with a housing assembly 110 which is directly
 mounted to a stationary plate 112. A hub assembly 114 to which flexing
 vanes 116 are attached is free to rotate. This occurs once the friction
 force between the stationary housing assembly 110 and rotating hub 114 is
 exceeded. The outer dimensions of the housing 110 can be round, square, or
 any other shape most suitable for stationary mounting.
 Thus the reader can se that this device provides improved torque and
 function over what has been previously available. Torque smoothness is
 minimally affected by variations in manufacturing tolerances. With only
 two basic components, assembly is greatly simplified. Automated assembly
 is a practical option with such a design. Flexural compliance of the
 friction elements compensates for dimensional variations so that torque
 loss is minimal as parts wear with use. Tailoring torque to particular
 applications is simplified by merely adjusting deflection or changing the
 number of friction vane elements.
 While the invention has been shown and described with respect to a specific
 embodiment and modification thereof, this is intended for the purpose of
 illustration rather than limitation. Other variations and modifications
 will be apparent to those skilled in the art all within the intended
 spirit and scope of the invention. Accordingly, the patent is not to be
 limited in scope and effect to the specific forms herein shown and
 described nor in any other way that is inconsistent with the extent to
 which the progress in the art has been advanced by the invention.
 Therefore the scope of the flexible vane coupling should be determined by
 the appended claims and their legal equivalents, rather than by the
 examples given above.