One-way pawl clutch with backlash reduction means and without biasing means

• US 20070205069A1
• Filed: 03/02/2007
• Published: 09/06/2007
• Est. Priority Date: 03/06/2006
• Status: Active Grant

• Current Assignee: Hossein Keshtkar
• Original Assignee: Hossein Keshtkar
• Inventors: Keshtkar, Hossein
• Granted Patent: US 8,210,331 B2
• Time in Patent Office: Days
• US Class Current: 192/46
• CPC Class Codes: F16D 41/12 with hinged pawl co-operating with teeth, cogs, or the like F16D41/02, F16D41/24 take precedence

Abstract

One-way clutches primarily employ a driving ring, a driven ring, and a number of identical connectors. The driving ring and the driven ring are rotationally detached, are concentric, and are configured to house the connectors between them. In one rotational direction, the connectors engage the driving and the driven rings, causing them to rotate in unison. In the opposite rotational direction, the connectors disengage the driving and the driven rings, causing them to freewheel. All existing one-way clutches are aided by means that bias the connectors toward engagement, introducing noise, wear, and heat while freewheeling. Additionally, existing one-way clutches that utilize relatively more efficient pawls as connectors, undergo relatively more backlash from freewheeling to engagement, introducing operational imprecision. The one-way clutch in the present invention utilizes pawls for maximum mechanical efficiency. Furthermore, this invention does not require any biasing means, and its backlash can be reduced to any desirable degree.

Claims

1. A one-way clutch mechanism composed of a driving ring, a driven ring, and a pawl ring, where the said three rings are concentric, the driven ring encircles the driving ring, the pawl ring encircles the driven ring, and the driven ring'"'"'s inside radius is larger than the driving ring'"'"'s outside radius;

and furthermore, the driving ring includes a key, resembling a gear tooth, on its outer cylindrical surface, the driven ring includes a notch on its inner cylindrical surface, and the pawl ring includes an axial pivot hole on its mean radius;

and furthermore, the mechanism includes a generally L-shaped pawl having, therefore, an arm, a corner, and a stem, where the arm includes a cutout near one end closest to the corner, the free end of the stem includes a pivot hole normal to the plane of the pawl, and the corner end of the stem overlaps the corner end of the arm;

and furthermore, the pawl arm is disposed tangentially on the outer cylindrical surface of the driving ring in the radial space between the driving ring and the driven ring such that the key on the driving ring is inserted in the pawl arm'"'"'s cutout while the free end of the pawl stem is pivoted to the pawl ring through their respective pivot holes;

and furthermore, when the driving ring rotates in a first rotational direction, the key on the driving ring contacts the pawl arm'"'"'s cutout and rotates the pawl with respect to the pawl ring until the pawl arm touches either the inner cylindrical surface of the driven ring or the surface of the notch on the driven ring, whereupon the pawl arm stays in touch with the driven ring until the pawl arm fully engages with the notch on the driven ring, causing the entire mechanism to rotate in unison in the engaged mode;

but conversely, when the driving ring rotates in a second rotational direction, opposite to the first rotational direction, the key on the driving ring contacts the pawl arm'"'"'s cutout and rotates the pawl with respect to the pawl ring until the pawl arm touches the outer cylindrical surface of the driving ring, whereupon, as the driven ring remains stationary, the driving ring, the pawl, and the pawl ring rotate in unison in the freewheeling mode;

and evidently, while in freewheeling mode, the mechanism does not require the pawl to be biased toward engaging the notch on the driven ring by any means, which eliminates the noise, wear, and heat associated with biasing, and which constitutes a unique feature of the present invention attributed firstly to the ability of the pawl arm to rotate about a pivot centered outside the arm'"'"'s line of thrust and secondly to the said geometrical and kinematical relationships that govern the interplay among the constituent components of the mechanism.

2. The mechanism recited in claim 1 in which the radial positions of the driving ring and the pawl ring are swapped such that the driven ring encircles the pawl ring, the driving ring encircles the driven ring, and the driving ring'"'"'s inside radius is larger than the driven ring'"'"'s outside radius;

and accordingly, the driving ring includes a key, resembling a gear tooth, on its inner cylindrical surface, the driven ring includes a notch on its outer cylindrical surface, and the pawl arm is disposed tangentially on the inner cylindrical surface of the driving ring in the radial space between the driving ring and the driven ring such that the key on the driving ring is inserted in the pawl arm'"'"'s cutout while the free end of the pawl stem is pivoted to the pawl ring through their respective pivot holes.

3. The mechanism recited in claim 1 in which the three concentric rings, instead of being stacked radially, are stacked axially such that the driven ring occupies the axial space between the pawl ring and the driving ring;

and accordingly, the planar surface of the driving ring facing the driven ring includes a key, the planar surface of the driven ring facing the driving ring includes a notch, and the pawl arm is disposed in the axial space between the driving ring and the driven ring in such a way that the pawl stem, while pivoted to the pawl ring, is oriented in the axial direction.

4. The mechanism recited in claim 1 where the three concentric rings are modified to include additional cylindrical features which enable them to support each other both rotationally and axially;

and where, the pawl is modified to conform to the specified modifications for the rings;

and where, the said modifications do not alter the intended fimctions of the rings or the essential geometrical and operational features of the pawl as stipulated in the original claim;

and where, the said modifications add attributes that render the mechanism self-supporting for direct application;

and where, in assembled configuration the three rings have a symmetric radial cross section and the pawl has a symmetric projection as viewed in any direction orthogonal to the axis of the assembled mechanism;

and whereas, the said modifications can take countless interdependent forms that serve the same operational purpose, one form of which includes;

a driving ring with a T radial cross section with its web pointing radially outward;

a driven ring with a radial cross section such that when the driven ring is assembled onto the driving ring, their combine radial cross section is rectangular having a hollow core in the shape of T with the web pointing radially outward;

a pawl ring with a rectangular radial cross section that fits at the free end of the web of the said T-shaped hollow core and has a radial cutout with two coaxial pivot holes for pivoting of the pawl;

and furthermore, to facilitate the assembly of the three concentric rings, the driven ring is cut in half axially to produce a driven ring consisting of two haves that are mirror images of each other and that each half has a radial cross section in the shape of a stair with three steps, where, using stair terminology, the tread of the third step signifies the line of symmetry of the two driven ring halves;

and furthermore, using stair terminology, the riser in the second step of each driven ring half is associated with the cylindrical surface of the driven ring containing a notch, such that the two notches face each other and thus the two driven ring halves remain mirror images of each other;

and corresponding to the twin design of the driven ring, the pawl, still having an L-shaped configuration, is composed of two identical parallel arms in the form of a U, and a stem that is fixed, at one end, to the juncture of the arms while incorporating a pivot hole at the other end;

and furthermore, the pawl'"'"'s arms are disposed tangentially on the outermost cylindrical surface of the driving ring, within the flange of the said T-shaped hollow core;

so that, one arm faces the notched cylindrical surface of the first driven ring half and the other arm faces the notched cylindrical surface of the second driven ring half;

and so that, the pivoted end of the stem extends into the web of the said T-shaped hollow core to be pivoted to the pawl ring that is situated at the free end of the web of the said T-shaped hollow core;

and because of the pawl'"'"'s symmetric twin-arm design, no cutouts at the corner end of the arms is required, but instead the driving ring includes on its outermost cylindrical surface a pair of keys;

one engaging key to sit behind the arms at their connection to the stem, and one disengaging key to sit in between the arms adjacent to the stem.

5. The mechanism recited in claim 4 wherein the pawl employs two identical parallel stems in the form of a U with two coaxial pivot holes at the free end, so that the pawl ring is inserted between the free ends of the stems for pivoting;

and the pawl ring, therefore, has just an axial pivot hole without the radial cutout;

and furthermore, to axially and rotationally support the pawl ring on the driven ring, each driven ring half'"'"'s cross section employs four steps, where, using stair terminology, the tread of the fourth step signifies the line of symmetry of the two driven ring halves, the riser of the fourth steps supports the pawl ring radially, the tread of the third step supports the pawl ring axially, and the riser in the second step of each driven ring half is still associated with the cylindrical surface of the driven ring containing a notch, such that the two notches face each other and thus the two driven ring halves remain mirror images of each other.

6. The mechanism recited in claim 5 where the pawl ring has a T cross section with the web pointing inward, and the web includes an axial pivot hole;

and furthermore, to axially and rotationally support the pawl ring on the driven ring, each driven ring half'"'"'s cross section employs three steps, where, using stair terminology, the tread of the third step signifies the line of symmetry of the two driven ring halves, the riser of the third step supports the flange of the pawl ring radially, the tread of the second step supports the flange of the pawl ring axially, and the riser of the second step of each driven ring half is still associated with the cylindrical surface of the driven ring containing a notch, such that the two notches face each other and thus the two driven ring halves remain mirror images of each other.

7. The mechanism recited in claims 4, or 5, or 6, wherein the driven ring halves include and equal number of a plurality of notches that are uniformly distributed in a circular pattern, in such a way that the two driven ring halves remain mirror images of each other.

8. The mechanism recited in claim 7 wherein a plurality of pawls are pivoted uniformly to the pawl ring, the driving ring includes a plurality of key pairs that are uniformly spaced and are equal in number to the number of pawls, and the number of notches on each driven ring half is a whole multiple of the number of pawls.

9. The mechanism recited in claim 8 wherein, in order to minimize backlash upon activation of the engaging mode, the driven ring comprises a maximum possible number of uniformly spaced notches;

and to minimize the backlash further, M (an integer greater than

     1) pawl assemblies are employed, where a pawl assembly consists of a pawl ring and a set of N (an integer greater than

     0) uniformly spaced pawls;

and furthermore, each pawl ring includes N round pivot holes that are uniformly distributed in a circular pattern with the subtended angle of each pair of consecutive pivot holes equal to 2π

/N;

and furthermore, each pawl ring also includes a plurality N(M−

1) of sectoral slots that are situated at the same radius as that of the round pivot holes, and that divide into equal parts, 2π

/MN, the angle subtended by each two consecutive round pivot holes;

and furthermore, when the M pawl rings are overlaid, each round pivot hole in a given pawl ring aligns with M−

1 sectoral slots in the remaining pawl rings;

and furthermore, it is to the said overlaid arrangement of the pawl rings that the MN pawls are pivoted, so that an individual pawl assembly can rotate with respect to the remaining M−

1 pawl assemblies up to a limit imposed by the sectoral slots;

and furthermore, the number of notches on the driven ring halves is chosen such that the pawls in the same pawl assembly have the same positional alignment with the notches, whereas any two pawls belonging to different pawl assemblies have different positional alignment with the notches;

and consequently, the said alignment differences together with the ability of the pawl rings to have a finite rotational freedom with respect to each other facilitate an engagement mode of operation where only the pawls on one pawl ring undergo engagement, the rest slide to avoid binding with the driven ring;

and furthermore, upon activation of the freewheeling mode, the engaged pawls rotate back, and the non-engaged pawls rotate and slide back to their respective freewheeling configuration.

10. The mechanism recited in claim 9 wherein a single pawl ring and M (an integer greater than 1) set of N (an integer greater than 0) compliant variation of the rigid pawl are employed;

and where, the pawl ring includes a plurality of MN pivot holes that are uniformly distributed;

and where, the pawl arms are connected to the pawl stem by a pin and a rotational spring;

and where, the pawl stem includes two identical cutouts facing the arms so as to provide limits of rotation between the pawl stem and the pawl arms;

and where, by virtue of an initial torque in the said rotational spring, the pawl arms are snugly fitted to the stem within the said cutouts such that in the said snugly fitted configuration the arms cannot rotate toward the stem, but can rotate away from the stem up to the limit imposed by the said cutouts on the stem;

and where, not only the N pawls belonging to each set are uniformly distributed around the pawl ring but also the total number of pawls MN are uniformly distributed around the pawl ring;

and correspondingly, the driving ring includes a plurality of uniformly spaced key pairs that are equal in number to the total number of pawls MN;

and furthermore, the number of notches on the driven ring halves is chosen such that the pawls in the same set have the same positional alignment with the notches, whereas any two pawls belonging to different sets have different positional alignment with the notches;

and consequently, the said alignment differences together with the ability of the pawls to deform facilitate an engagement mode of operation where only the pawls belonging to one set undergo engagement, the rest deform to avoid binding with the driven ring;

and furthermore, upon activation of the freewheeling mode, the engaged pawls rotate back, and the non-engaged pawls rotate and retract to their respective freewheeling configuration.

11. The mechanism recited in claim 10 in which the pawl, instead of a rotationally compliant joint at the corner, utilizes a compliant stem fabricated from sheet spring material;

and where, the compliant stem is rigidly joined to the arms at one end and includes a formed circular feature at the opposite end to accommodate pivoting of the pawl to the pawl ring.