WO2008056995A2

WO2008056995A2 - Improved pawl for a one-way clutch

Info

Publication number: WO2008056995A2
Application number: PCT/NZ2007/000330
Authority: WO
Inventors: Stephen Daniel Horsfall; Muthuvetpillai Jegatheeson
Original assignee: Uniclutch Limited
Priority date: 2006-11-09
Filing date: 2007-11-09
Publication date: 2008-05-15
Also published as: WO2008056995A3

Abstract

A one-way clutch includes a pawl assembly that has one or both of directional biasing and a forward-projecting pin to ensure that the pawl engages completely with the corresponding detent. The distance between the pin tip and the free end is less than the inter-detent spacing. Before the peg swivels to a position where it might improperly engage with a detent, the non-rigid pin has already engaged with a preceding detent, and swivels the pawl further into engagement, thereby preventing the jam. A small outward biasing spring may assist.

Description

IMPROVED PAWL FOR A ONE-WAY CLUTCH. FIELD

This invention relates to one-way clutches using pawls and pockets, and in particular relates to means to minimise the possibility of the pawl forming an inadequate engagement with the pocket instead of being properly engaged.

BACKGROUND

A one-way clutch operating between two co- axial shafts or a shaft in a housing may be of the type that uses pawls or small pegs extending from axes of rotation housed within a first shaft or part, which can be rotated to extend into engagement with teeth on the second shaft or part and thereby provide positive engagement between the two parts, so that rotation of one part causes rotation of the other if applied in one direction, but not in the other. Rotation of one shaft relative to the other in one direction will push the, or each pawl out of engagement with the teeth, allowing free rotation in that direction, while rotation in the opposite direction will pull the pawl or pawls into engagement with the teeth, preventing further independent rotation in that direction. One-way clutches may use other forms of locking means apart from pawls. One-way clutches are found for example in bicycles, in automatic transmissions, and in machinery.

Prior art

The Applicant's previous PCT application, PCT/NZ2003/044449 revealed some types of pawl-directing means, though not the means described here. For examine a number of patents by Kimes (e.g. JP 2007093022) describes spring members intended to energise each pawl towards the pockets. DE4001137 Walterscheid describes a switchable freewheel clutch having two concentric freewheel parts and two sets of pawls which operate in opposed directions and are swivelled in and out of action as a group by associated control rings which can each rotate relative the first clutch part carrying the pawl sets. Overall control of the pawls is dictated by external requirements and not by relative movements. PROBLEM(S) TO BE SOLVED

Those one-way clutches that rely on spring force to bias the ends of the pawls towards the pockets produce a clicking noise, which may be undesired. The noise indicates wear on the edges of the pawls that will, in time, adversely affect engagement (see below).

Generally an existing pawl and pocket type of one-way clutch will operate successfully and the pawls will engage securely with the second shaft, locking it, whenever the direction of rotation is changed from one way to the other. Occasionally however, depending on the particular position of the teeth on the second shaft at a time when the direction of rotation is reversed, the pawl will catch the tip of a tooth in such a way as to jam there. This provides a tenuous engagement between the shafts, which may subsequently slip, and/or could cause deformation and damage to that pawl or tooth. If the clutch uses a circumferential series of pawls mounted in the first shaft or part, spaced equally around the second shaft to engage with the second shaft simultaneously and thereby share the load, premature and incomplete engagement with one pawl may lock the shafts together before proper contact with other pawls, such that the full strain is borne on only one pawl instead of all of them. This can put undue strain on that pawl and the tooth with which it is engaged.

OBJECT

It is an object of this invention to provide an improved one-way clutch, or an improved mechanism that includes a one-way clutch, or at least to provide the public with a useful choice.

STATEMENT OF INVENTION

In a first broad aspect, this invention provides a one-way pawl clutch suitable for transmitting a torque between two rotatable components sharing a mutual axis of rotation whenever one component tends to overtake the other component in one direction of rotation but not in the other direction; the clutch including at least one separately swivellable elongated pawl spaced at regular intervals around, and housed within a recess within, the pawl-bearing component, each pawl having a length and being swivellable about an axis located near a first or base end of the pawl providing that the pawl may from time to time swivellable either causing a second or peg end to enter and become engaged with one of a plurality of complementary detents or pockets each having an engaging surface and spaced at regular intervals (known as "the pitch") around an adjacent surface of a cylindrical portion of the second or pocket-bearing component in order to lock the rotatable components together and hence be capable of transmitting a force between the peg and and the engaging surface when engaged, or to become disengaged from the pocket-bearing component; wherein each of the pawls includes rotationally dependent biasing means each comprising a sensing beam, attached at a first end to the base of the pawl and extended from the axis of swivel of the pawl towards the pocket-bearing component, and the second end of each sensing beam makes light sliding contact with a surface of the pocket-bearing component so that, when in use, a torque transmitted along the sensing beam when the pawl-bearing component attempts to overtake the pocket-bearing component shall cause positive swivelling of the pawl from a disengaged to an engaged position, or otherwise causes positive counter- swivelling of the pawl from an engaged to a disengaged position whereupon the maintained torque causes the disengaged position to be maintained.

Preferably each sensing beam is comprised of a resilient material that supports a light frictional contact between the sensing beam and the pocket-bearing component of the clutch, so that the torque developed is relatively tolerant of changes in displacement of the pawl-bearing and the pocket-bearing components of the one-way pawl clutch.

More particularly, each sensing beam is comprised of a flat strip of spring steel (the resilient material), having a first end is attached to the base of the pawl and a second end which reaches across a space to make light frictional (sliding) contact with a radially oriented surface of the second component of the clutch.

hi a related aspect, the pocket-bearing component of the clutch is provided with a circumferential or coaxial groove, and the flat strip of spring steel is paired or bifurcated so that both bifurcations enter the groove and each bifurcation is in sliding contact with one or other opposing sides of the groove.

In a second broad aspect, each pawl as previously described in this section is provided with a secondary member or pin having a first end attached to the base of the pawl and a second free end located in a volume placed between the peg of the pawl and in proximity to the teeth of the pocket-bearing component of the clutch, the position of the free end also being closer to the end of the pawl in a radial sense than the length of the pitch of the pocket- bearing component, so that, when in use, the second free end will engage with a tooth of the pocket-bearing component prior to engagement of the end of the pawl with another tooth, thereby applying an outwardly directed torque to the pawl hence causing the pawl to swivel outward and the end of the pawl to enter the intended pocket before making contact with the adjoining tooth.

In a related aspect, the position of the free end is closer to the end of the pawl in a radial sense than an integer multiple of the length of the pitch of the pocket-bearing component, where the integer is at least two.

Preferably the secondary member is comprised of a flat strip of spring steel in order that the member is capable of being temporarily and reversibly deflected during engagement of the pawl with the pocket, so that the force transmitted by the one-way clutch becomes transferred by the one or more pawls.

Preferably the peg projects tangentially with respect to a side wall of the cylindrical body portion of the pawl .

Preferably the flat end of the peg is arranged substantially orthogonally to its axis of projection.

hi a third broad aspect, each pawl of the one-way clutch is further provided with resilient biasing means exerting an engagement torque on the pawl having an effect of pushing the pawl outwards and into an engaged position; wherein the second engagement torque is less than the disengagement torque caused by friction between the sensing beam against the pocket-bearing component so that if the one-way pawl clutch is not engaged the pawls do not contact the pocket-bearing component and there is no clicking sound.

In one form, each resilient biasing means comprises a coiled compression spring.

85 Preferably 8 pawls are housed in the pawl-bearing component.

Preferably 24 projecting teeth each having a substantially radial engagement face and a sloped trailing face comprise the pockets of the pocket-bearing component.

In one aspect, both components of the one-way clutch are generally cylindrical and the pocket-bearing component is housed coaxially within the first component, and the pawls are 90 arranged to swivel inwardly to engage with the second component.

PREFERRED EMBODIMENT

The description of the invention to be provided herein is given purely by way of example 95 and is not to be taken in any way as limiting the scope or extent of the invention.

Throughout this specification unless the text requires otherwise, the word "comprise" and variations such as "comprising" or "comprises" will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. oo DRAWINGS

Fig l : shows an example pawl 102 with both permanent (107) and directional (103) biasing of the pawl. The pawl is in an unintended jammed state.

Fig 2: shows an improved pawl of this invention from the underside. Fig 3 a: shows an improved pawl of this invention just prior to engagement.

105 Fig 3b: shows the improved pawl with the secondary pin engaged.

Fig 3 c: shows the improved pawl nearly fully engaged.

EXAMPLE 1

110 Although this example describes a component for a winch for use on a boat (such as for applying tension to ropes leading to sails) the invention may be applied in those other applications that use one-way clutches. The pawl assembly described in this specification comprises a pawl 100 for a one-way clutch that has two co-axial, mutually rotatable components 300 and 301 respectively, and a mechanism for, from time to time, coupling the

115 two components. In this instance the mechanism is based on a pawl 100 having a "comma" shape (see Figs 1 and 2) comprised of a cylindrical body 101 and a tangentially extending peg 102 which, when the pawl is rotated (swivelled), reaches across a space and ideally will make satisfactory engagement within a pocket 304. Typically there are a number of pawls acting in unison - such as eight or more. According to the invention, the pawl includes

120 fastening means 104 for attaching a spring-steel leg 103 extended perpendicular to the axis of rotation. In use a torque can be applied to the cylindrical body 101 by pressure on the leg 103 that causes the pawl to swivel, causing the peg 102 to be extended accordingly.

Fig 1 shows a portion of a component for a winch; a one-way clutch including pawls of this type, although only one pawl is drawn. The swivellable pawl is housed in an outer body or 125 component 301 , and engages with an inner component, shaft 300. The outer component is in this example a partly-shown pinion gear 301 that forms part of a multi-speed gear box.

The inner shaft 300 is also only partly shown, and is provided with a series of regular and evenly spaced radial teeth 303 and pockets 304 on an outer circumference, each tooth having a substantially radial engagement face 307 and a sloped trailing face 308.

130 The cylindrical body 101 of the pawl is free to swivel within a part-cylindrical aperture 305 in the outer body or component 301. The pawl and the peg 102 can be seated in a recess 306 to be out of contact with the inner shaft 300 when the clutch is disengaged, or, when the one-way clutch should be engaged, a swivelling motion of the pawl 100 brings the peg out of the recess into ideally complete engagement with one of the teeth 303 and pockets 304.

135 When engaged, the radial engagement face 307 of a tooth 303 bears against the end face 102a of the peg 102, such that the inner shaft 300 of the clutch can not rotate further in that direction. Rotation of the shaft 300 in the other direction simply results in the peg 102 being pushed back into the recess 306 by contact with the sloped trailing face 308, and accordingly rotation in that direction is not impeded. One improvement to be described

140 below are intended to hold the peg of the pawl well inside the recess 306 so that it does not collide with teeth 303 during the free-wheeling mode of operation and make a clicking sound.

To assist or cause swivelling of the pawl 100 in moving the peg 102 in and out of the recess 306, the pawl is provided with a spring-steel leg or beam 103, which extends into a

145 circumferential groove 401 (shown as a dotted outline) in the inner shaft 300. The leg serves as a directionally dependent biasing means. The leg 103 is split to form two oppositely-biased leaves 103a and 103b which bear against opposing walls of the groove 401, giving a slight frictional connection. (Two separate leaves of spring steel (for example) comprise one alternative to a split). When the inner shaft is rotated, this frictional contact is

150 sufficient to swivel the pawl 100 one way or the other, hence bringing the peg 102 into or out of engagement. Use of a resilient element for the leg is preferred over a solid, rigid leg since changes in torque caused by dimensional changes, in turn caused by thermal expansion, wear, bearing play, or any other cause are minimised over those expereiced in the case of a rigid leg. The leg 103 could of course bear against a radial end surface rather

155 than within a groove and provide a similar effect, but a groove is often convenient. Each leg may be regarded as "rotationally dependent biasing means" for the corresponding pawl.

A further improvement will now be described; also a form of "swivel control" for a pawl. As shown in Figure 1, a fault condition may happen from time to time with most types of pawl-based one-way clutches. The underlying problem is that occasionally the peg 102 of a

160 single pawl 100 will be swivelled out at such a moment that the end face 102a of the peg

. comes into partial contact with the tip of an engagement face 307 on a tooth, and the friction immediately caused by pressure from the tooth down the length of the peg prevents the pawl from swivelling further. The braking action that is created by this circumstance will prevent the inner shaft 300 from rotating relative to the outer body 301, but inadvertently applies a

165 great deal of pressure to very small areas of the bearing surfaces on both the tooth and the pawl. This pressure can cause deformation or other damage, and usually prevents other pawls around the circumference from contributing to the transfer of torque across the clutch, creating a very uneven distribution of pressure.

Secondary Pin

170 To help prevent the above circumstance, the pawl 100 of this invention is also provided with a secondary pin 106, best seen in Figure 2, and also in Fig 3. The secondary pin 106 is preferably a flat pin formed from spring steel (or some other non-rigid material, otherwise the pin will serve as a pawl), and connected to the cylindrical body 101 of the pawl by the same fastening means 104 as the split leg 103. (104 may comprise a set screw within a

175 threaded shaft that bears down into a slit cut radially and partly through the mass of the pawl. The example of Fig 1 may be fixed to one side of the body of the pawl). As shown, the pin 106 lies alongside the peg 102 on the side closest to the inner shaft 300, projecting in substantially the same direction as the peg 102.

Operation of the pawl having the secondary pin is shown in sequence in Figures 3 a to 3 c. 180 When the peg 102 happens to be in a position relative to the teeth 303 as shown in Figure 3 a where the end of the peg 102a is likely to engage with the tip of an engagement face 307 and accordingly jam, the pin 106 will also be in a position to earlier engage with the engagement face 307' on the preceding tooth 303'.

As shown in Figure 3b, the tip of the pin 106a will engage with the face 307' before the end 185 of the peg 102a engages with the face 307, because the distance from 106a to 102a is, as a part of the invention, made to be less than the distance between engagement faces.

The position of the tip of the pin 106a outside and behind the peg 102 means that any force applied against it by the tooth is not in a radial direction with regard to the axis of rotation of the pawl but causes a rotational torque on the pawl. Accordingly the pressure of tooth 190 307' against the preferably non-rigid pin 106 does not impede turning of the inner shaft 300, but rather causes the pawl 100 to swivel. Had the pawl engaged normally, the pin 106 does not come in contact with any part of the pocket-bearing component of the clutch.

By the time the end of the peg 102a comes into contact with the face 307, pressure on the pin 106 has caused the pawl 100 to swivel further, such that the middle of the engagement 195 face 307 contacts the end of the peg 102a, providing complete and secure engagement as shown in Figure 3c. Note that in the diagram the mating surfaces of the tooth 307 and peg end 102a are not shown parallel. In practice they should be substantially parallel when engaged so that any load is more widely distributed.

The pin 106 is not subjected to strong pressure, because the pawl 100 will swivel as a result

200 of any force applied to the pin until the much stronger peg 102 comes into engagement.

Accordingly the pin 106 can be relatively light. Preferably the pin is somewhat flexible, preferably being made of spring steel strip (or a similar material having resilient, durable properties), such that it is able to flex or bend if put under pressure, allowing that pressure to then be taken up in a normal way by the peg 102. The inventors also believe that the pin 106

205 will at times help to push out an incorrectly engaged pawl end 102a (or one that is about to become mis-engaged) so that it then engages with the next pocket 304, if the pawl is in the wrong position.

Weak Loading Spring.

In order to further attempt to ensure that all engagements of a pawl with a pocket are never

210 incomplete while significant clicking is absent during freewheel, a biasing spring (see 107 in Fig 1) is optionally included in a one-way clutch according to the invention. The effect of this spring is to try to push the pawl 102 into the pocket below against the biasing torque from 103 during freewheel but in unison during engagement, The diagram of Fig 1 shows a compression-type coil spring having both ends (optionally only one end) within recesses,

215 aligned at a constant distance from the axis of swivelling of the pawl 103. Other types of resilient biasing means, such as a V-shaped leaf spring placed in the same general area, may be substituted as will be evident to a person skilled in the art. Another preferable method would be to have a torsion spring concentric with 101 with one leg locked to 101 and the other leg pressing against 100. Biasing springs affecting pawl rotation have been referred to

220 in the literature. Such springs are used alone. The design criterion for this biasing spring, used in conjunction with at least the leaf spring 103, is that it exerts a relatively weak torque on the pawl 102, which should be less than the torque caused by friction at the ends of leaf spring 103 against (or within the groove 401 of) the pocket-bearing component 300. Because the (clockwise) torque exerted by biasing spring 107 is less than the (anticlockwise,

225 during clutch non-engagement) torque exerted by the leaf spring or sensing beam 103, the pawls do not contact the teeth 308 of the component 300 and there is no clicking sound caused by contact between the pawls 102 and the teeth 303 during freewheel operation.

VARIATIONS

230 Alternatively however the pin could be formed as an integral projection formed on the side of the peg itself, or as a flange projecting from the leg 103.

Other variations are also possible within the scope of the invention. While it is preferred for the pawl to use the spring-biased leg 103 to swivel the pawl into and out of engagement with the teeth, other mechanisms could be used. for this purpose.

235 Similarly, while the shape of pawl illustrated is currently preferred, the invention could be applied to pawls of different shapes. In particular, because the leg 103 and pin 106 can be relied upon to swivel the pawl into the correct position before engagement, the peg need not be arranged eccentrically on the cylindrical body of the pawl, but could project directly radially so that a braking force from engagement with a tooth is directed towards the axis of 240 the pawl and distributed evenly across it.

While it is preferred for the peg and the pin to engage with adjacent detents on the inner shaft, it will be appreciated that they could be spaced to engage with two separated detents having one or more other intervening detents between, which neither the peg nor the pin engage with. In this case the distance between the tip of the pin and the end of the peg will 245 be less than the distance between the engaged detents, but might not be less than that between adjacent detents.

While the invention is in the above Example applied to a one-way clutch mechanism in a marine winch, it might equally be applied to a wide variety of other clutch mechanisms using pawls.

250 Finally, it will be understood that the scope of this invention as described by way of example and/or illustrated herein is not limited to the specified embodiments. Where in the foregoing description, reference has been made to specific components or integers of the invention having known equivalents, then such equivalents are included as if individually set forth. Those of skill will appreciate that various modifications, additions, known

255 equivalents, and substitutions are possible without departing from the scope and spirit of the invention as set forth in the following claims.

Claims

We claim:

1. A one-way pawl clutch suitable for transmitting a torque between two rotatable components sharing a mutual axis of rotation when one component tends to overtake

260 the other component in one direction of rotation only; the clutch including at least one separately swivellable elongated pawl spaced at regular intervals around, and housed within a recess within, the pawl-bearing component, each pawl having a length and being swivellable about an axis located near a first or base end of the pawl providing that the pawl may from time to time swivellable either causing a

265 second or peg end to enter and become engaged with one of a plurality of complementary detents or pockets each having an engaging surface and spaced at regular intervals (known as "the pitch") around an adjacent surface of a cylindrical portion of the second or pocket-bearing component in order to lock the rotatable components together and hence be capable of transmitting a force between the peg

270 and and the engaging surface when engaged, or to become disengaged from the pocket-bearing component; characterised in that each of the pawls includes rotationally dependent biasing means each comprising a sensing beam, attached at a first end to the base of the pawl and extended from the axis of swivel of the pawl towards the pocket-bearing component, and the second end of each sensing beam

275 makes light sliding contact with a surface of the pocket-bearing component so that, when in use, an engagement torque transmitted along the sensing beam when the pawl-bearing component attempts to overtake the pocket-bearing component shall cause positive swivelling of the pawl from a disengaged to an engaged position, or otherwise causes positive counter-swivelling of the pawl from an engaged to a

280 disengaged position whereupon the maintained disengagement torque causes the disengaged position to be maintained.

2. A one-way pawl clutch as claimed in claim 1, characterised in that each sensing beam is comprised of a resilient material that supports a light fractional contact between the sensing beam and the pocket-bearing component of the clutch, so that

285 the torque developed is relatively tolerant of changes in displacement of the pawl- bearing and the pocket-bearing components of the one-way pawl clutch.

3. A one-way pawl clutch as claimed in claim 2, characterised in that each sensing beam is comprised of a flat strip of spring steel (the resilient material), having a first end is attached to the base of the pawl and a second end which reaches across a

290 space to make light frictional (sliding) contact with a radially oriented surface of the second component of the clutch.

4. A one-way pawl clutch as claimed in claim 3, characterised in that the pocket- bearing component of the clutch is provided with a circumferential or coaxial groove, and the flat strip of spring steel is paired or bifurcated so that both

295 bifurcations enter the groove and each bifurcation is in sliding contact with one or other opposing sides of the groove.

5. A one-way pawl clutch as claimed in any previous claim, characterised in that each pawl is further provided with a secondary member or pin having a first end attached to the base of the pawl and a second free end located in a volume placed

300 between the peg of the pawl and in proximity to the teeth of the pocket-bearing component of the clutch, so that, when in use, the second free end will engage with a tooth of the pocket-bearing component prior to engagement of the end of the pawl with another tooth, thereby applying an outwardly directed torque to the pawl hence causing the pawl to swivel outward and the end of the pawl to enter the intended

305 pocket before making contact with the adjoining tooth. ^~

6. A one-way pawl clutch as claimed in claim 5, characterised in that the secondary member is comprised of spring steel in order that the member is capable of being temporarily and reversibly deflected during engagement of the pawl with the pocket.

7. A one-way pawl clutch as claimed in claim 5, characterised in that the position of 310 the free end is closer to the end of the pawl in a radial sense than an integer multiple of the length of the pitch of the pocket-bearing component, where the integer is at least two.

8. A one-way pawl clutch as claimed in any previous claim, characterised in that each pawl is further provided with resilient biasing means exerting an engagement

315 torque on the pawl having an effect of pushing the pawl outwards and into an engaged position; wherein the second engagement torque is less than the disengagement torque caused by friction between the sensing beam against the pocket-bearing component so that if, during use, the one-way pawl clutch is not engaged the pawls do not contact the pocket-bearing component, and there is no

320 clicking sound.

9. A one-way pawl clutch as claimed in claim 8, characterised in that each resilient biasing means comprises a coiled compression spring 107, thereby applying an outwardly directed torque to the pawl hence causing the pawl to swivel outward and assisting the end of the pawl to enter the intended pocket before making contact with

325 the adj oining tooth.

10. A one-way pawl clutch as claimed in claim 1 or in claim 5, further characterised in that 8 pawls are housed in the pawl-bearing component.

11. A one-way pawl clutch as claimed in claim 1 or in claim 5, further characterised in that 24 projecting teeth each having a substantially radial engagement face and a

330 sloped trailing face comprise the pockets of the pocket-bearing component.

12. A one-way pawl clutch as claimed in claim 1 or in claim 5, further characterised in that preferably both components are generally cylindrical and the pocket-bearing component is housed coaxially within the first component, and the pawls are arranged to swivel inwardly in order to engage with the second component.