Title of Invention

A REVERSIBLE ONE-WAY CLUTCH HAVING WORM GEAR TRAIN

Abstract One-way clutches use a gear train to drive a worm screw synchronised with teeth on a driven worm gear, when freewheeling. Controlled backlash places the worm in either a contact mode (when engagement occurs), or a non-contact (disengaged) mode when driven in an opposite direction. The backlash can be arranged so that the direction in which the one-way clutch passes power may be reversed.
Full Text FIELD
This invention relates to a reversible one-way clutch having worm gear train and in particular to a mechanical coupling devices known as "free-wheeling clutches" or "one-way clutches"; devices including mechanisms capable of applying a torque between apposed parts in order to transmit rotation in one direction as determined by relative speed of rotation of the parts, but not in the other direction.
BACKGROUND
Free-wheeling clutches comprise internally controlled coupling means for coupling between a pair of co-axial shafts. Usually a number of sets of reversible locking mechanisms are replicated in a circumferential array. A one-way clutch should allow free relative movement (free-wheeling) of a first component in relation to a second component when the relative motion between the components is in a first direction (for example, a positive direction), but should not allow the relative motion to become negative. The clutch should lock the two components as soon as the relative motion tends to become negative. A one-way clutch can be regarded as a mechanical equivalent to an electrical diode - a device for transmitting power in only one direction.
Free-wheeling or one-way clutches are used in many mechanical engineering applications. For example, bicycle chain drives have a ratchet-based one-way clutch which prevents the chain and cranks being turned by the wheel when the rider is coasting. They are used in automatic transmissions in land vehicles. They are used in machines for making electric energy in a dynamo driven by reciprocating motion, such as to-and-fro wave motion.
Existing one-way clutches rely on various locking mechanisms to reversibly lock the first and second shafts. One class of locking mechanism is of the ratchet type, with one or more spring-loaded pawls (also called struts) on a first assembly reversibly engaging with a corresponding number of pockets on a second, apposed assembly. Unless counteractive steps are taken, this class produces a clicking noise during freewheeling and exhibits backlash, but when engaged the pawls provide an effective direct coupling of torque without undue stress to materials. Another class involves a
wedging action between either a strut, sprag, ball, or roller which enters and becomes jammed within a tapered recess when engaged. Usually a number of sets of locking mechanisms are replicated in a circumferential array. While these one-way clutches are relatively noiseless and have little backlash, the wedging action inherently focuses a significant strain on a small surface area where the strut, sprag, ball, or roller makes contact, amplified by the tangent of the taper and by excessive torque. The wedging action (after a little backlash) significantly magnifies the force applied per unit area. It is likely that the material will show permanent distortion at the surface and this type of one-way clutch typically has a short life. Ratchet types of one-way clutches (employing spring-loaded pawls (struts) to reversibly connect between the parts) exhibit a certain amount of reverse motion (also known as backlash) before the parts turn into a co-engagement position and become locked together. By the time positive engagement occurs some momentum may build up and the impulse occurring at the time of contact may be harmful. It may shock the materials to such an extent that fatigue occurs (if only after a number of cycles), hence the clutch parts must be made strong enough to resist failure. In the case of power-generating machines including one-way clutches, the backlash motion may cause considerable forces that may affect many components of the transmission.
It is evident from the above account that known one-way clutches may have to dissipate energy applied to limited volumes of the material of the clutch.
Vibration or noise are other likely problems. If resilient members are used to buffer the impacts, unexpected resonances may occur and the resilient material will fail in time.
PRIOR ART.
Prior Art cited in the PCT examination comprises DE2551003 to Rotzler, which has apparent similarities to the present invention. In order to distinguish the two we shall describe their respective operations without, we hope, introducing any new matter. In the present invention, (see fig 1 A, 1B and 2) there is no separate one-way clutch with sprags or the like. Screw 813 is mounted on bearings fixed to the casing 806. Assume shaft 801 is made to turn in a first direction; then worm wheel 814 which shares the shaft is also made to turn directly. Turning shaft 801 also turns spur gear 806 through
backlash-generating dog clutch 902 / 901, hence causing the screw 813 to be turned at a speed set by a step-up chain of spur and bevel gears. The ratio of the chain was chosen to be the same as the ratio of the worm and screw. At a given angular velocity of shaft 801, screw 813 is made to "chase its tail" around the circumference of worm 814 with little or no friction in the opposite direction to that of the turning of shaft 801. The casing 806 of the mechanism must follow the instantaneous position of screw 813. Since worm 814 is also turning in a synchronous manner, the casing stands still. As a result the shaft 803, which is fixed to the casing 806 at 815, turns at the same angular velocity as that of shaft 801 while the screw and worm are held at a "phase" which minimises friction (814 - Fig IB).
If shaft 801 is made to turn in a second direction, the effect of causing backlash-generating dog clutch 902 in space 901 to turn in the opposite direction is that the screw 813 is in effect displaced axially along its length into contact with the thread of the worm and friction is generated between the screw and the worm. (See Fig IB). The friction has the effect of locking the screw and the worm to each other. As a result the worm 814 is locked to the casing 806, and the mechanism transmits power as rotational movement between shaft 801 and shaft 803. The screw and worm now turn at a "relative phase" which maximises friction (817 or 818 - Fig IB). The different characteristics shown by the mechanism in the two directions illustrate the properties of a one-way clutch.
In comparison, we believe that Rotzler's invention sets out to provide an automatically applied reverse brake for a crane or the like. It has a stationary frame, includes a separate one-way clutch (19; fig 4), and has two separate screws (21, 22) (fig 1) turning against a slow-speed idler worm (23) (fie 2). We shall regard the directly driven screw 21 as a "reference phase" and the screw 22 driven through couplings with backlash as the "variable phase" screw. The presence of dog clutch devices at 9 and at 35 (fig 1) give this device the potential to change the phase between the worm and screw 22 and hence to alternate between a high friction internal state and a low friction internal state dependent on the direction of motion. The worm and screw (having a variable phase power drive capability) serve as a friction-generating device in both cases but the remainder of each mechanism is clearly distinct as are the purposes for which each invention was developed.
OBJECT
It is an object of this invention to provide an improved form of one-way clutch, or at least to provide the public with a useful choice.
STATEMENT OF INVENTION
In a first broad aspect, the invention provides a one-way clutch for providing coupling between a first rotatable shaft having an axis of rotation, and a second, abutting, rotatable shaft having a co-axial axis of rotation, the one-way clutch being capable of coupling the shafts if the first shaft is rotated in an engaging direction relative to the second shaft but of uncoupling the shafts if the first shaft is rotated in a opposite, coastingjhrection relative to the second object, wherein the one-way clutch includes a geared transmission providing reversible coupling and decoupling effected within a gear coupling, including a first gear and a second gear, the coupling being of a type wherein the transmission of power has a positive efficiency when power is transmitted through the gear coupling from the first gear to the second gear, but a negative efficiency when power is transmitted from the second gear to the first gear.
Preferably the direction of coasting is capable of being reversed.
Alternatively the invention provides a mechanism (800) serving as a reversible oneway clutch for providing coupling between a first rotatable shaft (801) having an axis of rotation (804), and a second rotatable shaft (803) having a co-axial axis of rotation; the mechanism being capable of coupling the shafts if the first shaft is rotated in an engaging direction relative to the second shaft but of uncoupling the shafts if the first shaft is rotated in an opposite or coasting direction relative to the second shaft, wherein the mechanism includes a worm wheel (814) driven by a worm screw (813); for which the relative position of the worm screw may be altered during use along an axis of the worm screw so that the worm screw may be turned against the worm wheel in either a first, low-friction mode when the worm screw is in a first position not forced against a surface (815) of the worm wheel teeth and the one-way clutch is in a decoupled state, or in a second, high-friction mode when the worm screw is in a second position forced against the surface of the worm wheel (817) and the one-way clutch is in a coupled state, and the mechanism includes a screw drive portion having
included backlash or dead motion (807) so that the worm screw assumes either the first position when the first shaft is rotated in an engaging direction relative to the second shaft or the second position when the first shaft is rotated in an opposite, coasting direction relative to the second shaft.
Preferably the one-way clutch includes a gear train (806, 808, 809, 810, 811, 812) turned by the first shaft (801) at a fixed rate such that the worm screw (813) terminating the gear train is caused to turn at a rate such that the thread of the worm screw advances at a rate that matches the rate at which the thread of the separately driven worm wheel (814) advances.
Preferably the gear train (806, 808, 809, 810, 811, 812) includes means (807, including 901/902) for including a controlled amount of dead motion or backlash when turned by the first shaft (801) in a first direction but not in a second direction: and the effect of including the backlash is to cause the thread of the worm screw to be displaced from the thread of the separately driven worm wheel so that when backlash is included the worm screw and the worm wheel generate sliding friction that cannot be overcome by rotation of the gear train.
Preferably the gear train (806, 808, 809, 810, 811, 812) and the worm screw (813) are supported on a rotatable frame (806) attached to the second shaft so that rotation of the rotatable frame, relative to rotation of the input shaft (801), is caused by movement of the worm screw over the worm wheel and so that coupling to the mechanism of the one-way clutch is derived from rotational movement of the rotatable frame (806).
Preferably the direction of relative rotation for which the one-way clutch enters an engaged mode may be reversed by changing the orientation of the angular rotation, with respect to the first gear, through which the dog tooth 902 may travel when in use and so that the displacement of the thread of the worm screw (813) may be altered towards one side or the other of the middle of the thread of the worm gear (814).
Preferably the one-way clutch includes a gear train turned by the first shaft; the gear train including a controllable amount of backlash or dead motion, the first gear of the gear train being supported on the incoming drive shaft; the gear train being supported
on a rotatable frame attached to the second shaft and terminating with a worm screw in engagement with a worm wheel, the worm wheel being attached to the first shaft, wherein the gear train has a ratio such that in use the screw of the worm travels at the same speed as the teeth of the worm wheel, and wherein the controllable backlash is predetermined so that when the gear train is turned by the first shaft in a coasting or free-wheeling direction the turning screw of the worm passes in between the teeth of the turning worm wheel with substantially no frictional contact, but when the gear train is turned by the first shaft in an engaging direction the controllable amount of backlash temporarily interrupts the drive to the worm screw, so that afterwards the screw of the worm rubs against the teeth of the worm wheel thereby causing the rotatable frame to rotate and hence causing the second shaft to rotate.
Preferably the controllable amount of backlash or dead motion is determined by controlling the amount of rotational clearance between at least one dog tooth and at least one dog of a loose dog clutch placed between the driving shaft and upon the first gear of the gear train, although optionally the backlash may be provided within the gear train itself.
In a subsidiary aspect, the direction of relative rotation for which the one-way clutch enters an engaged mode may be reversed by changing the orientation of the angular rotation, with respect to the first gear, through which the dog tooth may travel when in use.
PREFERRED EMBODIMENT
The descriptions of the invention to be provided herein are given purely by way of example and are not to be taken in any way as limiting the scope or extent of the invention.
DRAWINGS
Fig 1 A: is a diagram of a "worm clutch"; a one-way clutch making use of a gear train and worm wheel/worm screw inside a frame.
Fig 1B: is a cross-section of the relationship between the worm screw and the worm gear.
Fig 2: is a diagram of the gear train and worm, with drive options.
This invention comprises a novel form of one-way clutch, making use of a lockable gear train for driving a worm screw in one or another phase relationship to a worm wheel, within a frame.
EXAMPLE A
This Example is referred to herein as a "worm clutch". In this version of a one-way clutch, thrust is carried during engagement by the surface of the worm screw, not by colliding sprags, rollers, pawls, or the like. This Example (see Figs 8 and 9) makes use of the negative efficiency that is inherent to some high-ratio gear couplings, such as but not limited to the case of worm wheels driving worm screws, causing the transmission of power to be not effectively reversible. The vector of an applied force at the worm screw face that would cause rotation is too small to overcome friction.
Fig 8A shows the overall structure. First shaft 801 is firmly connected to worm wheel 814 and is connected through a tooth 901 within a cavity providing a type of dog clutch 807 providing a controlled amount of backlash to the concentric first drive pinion 806. (The first pinion may also be a bevel gear). The frame 800 is free to rotate about the first shaft 801 (using bearings 802). The frame 800, which supports the gear train and worm screw (813) mounting is rigidly connected (at 815) to a second shaft 803. The gear train (806, 808, 809, 810) driven by the first shaft 801 includes a right-angle drive and is capable of driving the worm screw 813 in either a first phase (free, without contact) or a second phase (in contact and with static friction) phase relationship to the worm gear 814, but otherwise at the same rate. When the assembly is being driven in a first direction and the clutch is free-wheeling, not driving, the driven gear train makes the worm rotate at a speed (and in a phase) which results in the thread of the turning worm screw 813 passing between the teeth of the worm wheel 814 with substantially no rubbing contact or resulting friction. In effect the worm 813 screws itself around the wheel 814 at exactly the rate of turning of the frame, relative to the input shaft. Synchronisation is determined by the gear train ratio. The proper phase will be set during construction or installation. In this
free-wheeling direction the gears turn freely, the frame is not forced to rotate, and there is no coupling between the input shaft 801 and the output shaft 803.
See Fig 8B, where details of the engagement between the worm screw 813 and worm wheel 814, in a disengaged (815, at left, with no contact) position, engaged for rotation in a first relative sense in 817, and alternatively engaged in a second relative sense in 818 are shown in a longitudinal sectional view. In normal use, the system would either alternate between 815 and 817 or, after being reconfigured, to alternate between 815 and 818.
The controlled backlash has the effect of moving the worm screw slightly along the worm gear - analogous to a change in phase of an AC electrical signal. In the event of contact, the clutch is engaged in that the worm gear 814 is locked to the worm screw 813, whereupon the frame 800 is made to spin by the first (input) shaft 801, thereby driving the second (output) shaft 803. The counterweight 805 serves to balance the mechanism although an alternative version with dual worm wheels is inherently balanced. It should be noted that drive power may instead arrive at the second shaft 803 and be removed from the worm clutch at first shaft 801.
In addition, this worm clutch is reversible in terms of the relative direction which can over-run and which direction is locked. The relative direction which causes engagement may be changed from positive to negative by altering the part responsible for the controlled backlash. In Fig 8 a part of a preferred reversing mechanism is shown; a coaxial central push rod 804 within shaft 801 (which rod may be operated during operation of the transmission) emerges behind pinion 806 as arm 816, which arm is connected to and may advance or retract a wedge 903 into the space used as a dog clutch. (See Fig 9, A, B and C).
When the assembly is being driven in a second (opposite) direction and the clutch is now intended to serve as a coupling between driving and driven shafts, the backlash -conferring means 807 built into the mounting of the spur gear 806 (together with any incidental backlash in the driven gear train) changes the speed of the worm while the backlash is interrupting the drive to the worm, so that when the worm is again driven it will tend to rotate at the same speed but in a phase which results in one side of the thread of the worm coming against the teeth of the worm wheel. Force applied now
tries to have the worm wheel turn the worm screw. In usual conditions, some friction overcomes the small turning moment of the applied force and "negative efficiency" prevails. Specific conditions may be important; for example we consider it useful that the worm screw is dry. As a result the locked pair of gears causes the clutch to transmit power from the driving shaft 801 via the frame 800 to the driven shaft 803. During a change in state, there may be a transfer of momentum from the worm screw to the worm gear. (Please note that the diagrams of Figs 8 and 9 are purely illustrative and do not show correct ratios).
Assuming little backlash in the gear train 806-812, deliberate backlash is provided for as shown in Fig 9. The shaded sector-like tooth 901 is rigidly coupled to the drive shaft 801, and can rotate to a limited degree within a sector-shaped cavity 902, forming a type of a dog clutch, within pinion gear 806. In a first direction (A) the tooth hits the counterclockwise face of the cavity, and in a second direction it turns by a small extent (exaggerated in the drawing) to hit the clockwise face, so that the phase relationship of the worm wheel 814 (rigidly coupled to the input shaft) and the screw 813 is altered. Reversal of operating direction can be imposed by addition of a wedge 903 within the cavity on one side or the other of the tooth, as previously described. This may be done by a mechanic during maintenance, or may be done during operation using the push rod 804. A symmetrical two-tooth version may be preferred.
This apparently complex mechanism has a number of advantages including the purpose of avoiding concentrated loadings (together with impact components), such as those that occur in wedging or pawl-based one-way clutches. Instead, the loading is spread over the larger contact area, the "effective face width" between the worm thread and the worm' gear. The usual lubricated rubbing surfaces should make rubbing contact only during transitional periods.
VARIATIONS
The examples shown here are purely illustrative. One-way clutches may be used in a great variety of applications each of which has a particular set of requirements, such as low noise, high reliability, suited to high or low speeds, and/or coupling or not of high shaft torques. A variety of new applications may be made feasible by improved performance.
COMMERCIAL BENEFITS or ADVANTAGES
The geared system provides the advantages of higher reliability by avoidance of the wedging of parts against each other; a process involving a high amount of locally applied force, so avoiding deterioration of materials and a short service life. The worm clutch provides minimal free-wheeling losses and is positively driven when in the engaged mode. The worm clutch comprises a non-wedging version of one-way clutch.
Finally, it will be understood that the scope of this invention as described and/or illustrated herein is not limited to the specified embodiments. Those of skill will appreciate that various modifications, additions, known equivalents, and substitutions are possible without departing from the scope and spirit of the invention as set forth in the following claims.



We Claim:
1. A reversible one-way clutch having worm gear train for providing coupling
between a first rotatable shaft (801) having an axis of rotation (804), and a second
rotatable shaft (803) having a co-axial axis of rotation; the mechanism being
capable of coupling the shafts if the first shaft is rotated in an engaging direction
relative to the second shaft but of uncoupling the shafts if the first shaft is rotated
in an opposite or coasting direction relative to the second shaft, characterised in
that the mechanism includes a worm wheel (814) driven by a worm screw (813);
for which the relative position of the worm screw may be altered during use along
an axis of the worm screw so that the worm screw may be turned against the worm
wheel in either a first, low-friction mode when the worm screw is in a first position
not forced against a surface (815) of the worm wheel teeth and the one-way clutch
is in a decoupled state, or in a second, high-friction mode when the worm screw is
in a second position forced against the surface of the worm wheel (817) and the
one-way clutch is in a coupled state, and the mechanism includes a screw drive
portion having included backlash or dead motion (807) so that the worm screw
assumes either the first position when the first shaft is rotated in an engaging
direction relative to the second shaft or the second position when the first shaft is
rotated in an opposite, coasting direction relative to the second shaft.
2. A reversible one-way clutch as claimed in claim 1, wherein the one-way clutch includes a gear train (806, 808, 809, 810, 811, 812) turned by the first shaft (801) at a fixed rate such that the worm screw (813) terminating the gear train is caused to turn at a rate such that the thread of the worm screw advances at a rate that matches the rate at which the thread of the separately driven worm wheel (814) advances.
3. A reversible one-way clutch as claimed in claim 2, wherein the gear train (806, 808, 809, 810, 811, 812) includes means (807, including 901/902) for including a controlled amount of dead motion or backlash when turned by the first shaft (801) in a first direction but not in a second direction: and the effect of including the backlash is to cause the thread of the worm screw to be displaced from the thread of the separately driven worm wheel so that when backlash is included the worm
screw and the worm wheel generate sliding friction that cannot be overcome by rotation of the gear train.
4, A reversible one-way clutch as claimed in claim 3, wherein the gear train (806,
808, 809, 810, 811, 812) and the worm screw (813) are supported on a rotatable
frame (806) attached to the second shaft so that rotation of the rotatable frame,
relative to rotation of the input shaft (801), is caused by movement of the worm
screw over the worm wheel and so that coupling to the mechanism of the one-way
clutch is derived from rotational movement of the rotatable frame (806).
5. A mechanism serving as a one-way clutch as claimed in claim 4, wherein the
direction of relative rotation for which the one-way clutch enters an engaged mode
may be reversed by changing the orientation of the angular rotation, with respect to
the first gear, through which the dog tooth 902 may travel when in use and so that the
displacement of the thread of the worm screw (813) may be altered towards one side
or the other of the middle of the thread of the worm gear (814).


Documents:

1964-delnp-2005-abstract.pdf

1964-delnp-2005-assignment.pdf

1964-delnp-2005-claims.pdf

1964-delnp-2005-complete specification (granted).pdf

1964-delnp-2005-correspondence-others.pdf

1964-delnp-2005-correspondence-po.pdf

1964-delnp-2005-description (complete).pdf

1964-delnp-2005-drawings.pdf

1964-delnp-2005-form-1.pdf

1964-delnp-2005-form-18.pdf

1964-delnp-2005-form-2.pdf

1964-delnp-2005-form-26.pdf

1964-delnp-2005-form-3.pdf

1964-delnp-2005-form-5.pdf

1964-delnp-2005-form-6.pdf

1964-delnp-2005-pct-210.pdf

1964-delnp-2005-pct-304.pdf

1964-delnp-2005-petition-137.pdf


Patent Number 246461
Indian Patent Application Number 1964/DELNP/2005
PG Journal Number 09/2011
Publication Date 04-Mar-2011
Grant Date 28-Feb-2011
Date of Filing 09-May-2005
Name of Patentee UNICLUTCH LIMITED
Applicant Address 1/66 CAMPBELL ROAD,GREENLANE, AUCKLAND,1003 NEW ZEALAND.
Inventors:
# Inventor's Name Inventor's Address
1 JEGATHEESON, MUTHUVETPILLAI 1/116 CAMPBELL ROAD, ONE TREE HILL,1003 AUCKLAND (NZ)
PCT International Classification Number F16D 41/07
PCT International Application Number PCT/NZ2003/000251
PCT International Filing date 2003-11-11
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 522552 2002-11-11 New Zealand