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1. (WO1992009821) AN IMPROVED PAWL AND RATCHET CLUTCH AND METHOD
Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

WHAT IS CLAIMED IS:

1. A pawl and ratchet clutch operably disposed between a driving member and a driven member comprising:
an input member, having a ratchet, secured. to said driving member for rotation therewith;
a hollow output member secured to a hollow output shaft means for coupling to said driven member;
a single, spring member mounted within said output member; and
a plurality of pawls mounted within said output member so as to be responsive to a centrifugal force resulting from rotation of the output member to tend toward disengagement from said ratchet, and mounted within said output member in operative engagement with said spring member to be urged by said spring member into engagement with said ratchet.

2. The pawl and ratchet clutch of claim 1 wherein said contact between said pawls and said spring member is a rolling contact.

3. The pawl and ratchet clutch of claim 1 wherein said spring member comprises a torsion shaft coupled at a first end to a plate member having a plurality of radially extending arms, each of said arms having an end portion with an involute surface.

4. The pawl and ratchet clutch of claim 3 wherein a second end of said torsion shaft is disposed in a recess of said output shaft means so that said second end is easily accessible when said output shaft means is disconnected from said driven member.

5. The pawl and ratchet clutch of claim 3 wherein said plate member is a cam.

6. The pawl and ratchet clutch of Claim 4 wherein said torsion shaft is secured in said recess by a locking member.

7. The pawl and ratchet clutch of claim 1 wherein each of said pawls comprises a substantially cylindrical body having proximate to a first end a head means extending radially therefrom for engaging said ratchet and a tail means, in an opposed orientation to said head means, for counterbalancing said head means, said body having proximate to a second end a member extending radially therefrom, said member having an involute surface portion.

8. The pawl and ratchet clutch of claim 7 wherein said member having an involute surface portion is angularly disposed intermediate said head and tail means .

9. A pawl for use in a pawl and ratchet clutch, comprising:
a rotatable, cylindrical member having a first and second end;
a head portion proximate to said first end and extending radially from said first end;
a tail portion proximate to said first end and extending radially from a said first end, said tail portion being in an opposed orientation to said head portion; and
means, proximate to said second end and extending radially from said second end for receiving a spring force that causes said pawl to rotate.

10. The pawl of claim 9 wherein said receiving means is angularly disposed intermediate said head and tail portions.

11. The pawl of claim 10 wherein said receiving means is a gear tooth.

12. An air turbine starter comprising a housing, said housing defining an inlet, an outlet, and a flow path extending between said inlet and said outlet for communicating a flow of pressurized motive gas therethrough; a turbine member journaled within said housing and disposed within said flow path for rotatably extracting mechanical power from said motive gas, a planetary gear having a high speed gear member drivingly coupled with said turbine member and having a low speed output member; a pawl and ratchet clutch coupling said low speed output member with an output shaft while allowing overrunning of the latter, said pawl and ratchet clutch including a ratchet member drivingly coupled to said low speed output member and a clutch housing circumscribing said ratchet member and drivingly coupled with said output shaft; a plurality of pawls mounted to said clutch housing for radial movement between an inner position engaging said ratchet member, said pawls being moveable outwardly in response to a centrifugal force resulting from rotation of said clutch housing to an outer position free of engagement with said ratchet member; each of said pawls having a gear tooth extending radially therefrom, said gear tooth having an involute surface portion; and a torsion shaft coupled to a cam having a plurality of involute surface portion, said cam mounted within said clutch housing so that said involute portions of said cam comes into rolling contact with said involute surface portions of said pawls, thereby forcing said pawls, simultaneously, to said inner position in the absence of sufficient centrifugal force to overcome the spring force of said torsion shaft.

13. An air turbine starter comprising a housing, said housing defining an inlet, an outlet, and a flow path extending between said inlet and said outlet for communicating a flow of pressurized motive gas therethrough; a turbine member journaled within said housing and disposed within said flow path for rotatably extracting mechanical power from said motive gas, a planetary gear having a high speed gear member drivingly coupled with said turbine member and having a low speed output member; a pawl and ratchet clutch coupling said low speed output member with an output shaft while allowing overrunning of the latter, said pawl and ratchet clutch including a ratchet member drivingly coupled to said low speed output member and a clutch housing circumscribing said ratchet member and drivingly coupled with said output shaft; a plurality of pawls each mounted to said clutch housing for radial movement between an inner position engaging said ratchet member and an outer position free of engagement with said ratchet member, said pawls being moveable toward said outer position in response to a centrifugal force resulting from rotation of said clutch housing; and a single biasing means engaging each of said pawls for exerting substantially equal biasing forces thereon, said biasing forces opposing said centrifugal force to urge each of said pawls toward said inner position.

14. A method for setting the spring force that forces the pawls of a pawl and ratchet clutch into engagement with the ratchet comprising the steps of: mounting a torsion shaft coaxially within said pawl and ratchet clutch;
coupling a first end of said torsion shaft to a cam having a plurality of radially extending arms, each of said arms having an involute surface portion;
twisting said torsion shaft until a preselected twist is achieved;
locking a second end of said twisted torsion shaft within said pawl and ratchet clutch so as to prevent said torsion shaft from untwisting; and
mounting a plurality of pawls, each of said pawls having a head portion, a tail portion and radially extending gear tooth within said pawl and ratchet clutch so that said gear teeth contact said involute surface.

15. A method for adjusting the spring force that forces the pawls of a pawl and ratchet clutch into engagement with the ratchet, wherein said clutch has a pre-twisted torsion shaft coaxially mounted and locked therein and coupled at one end to a cam having a plurality of radially extending arms, each of said arms having an involute surface portion, said cam mounted within said clutch so that its involute surfaces contact at least one of the gear teeth extending from a plurality of pawls mounted within the clutch, comprising the steps of:
unlocking said pre-twisted torsion shaft from said clutch;
adjusting the twist of said torsion shaft by twisting or untwisting said torsion shaft; and
relocking said adjusted torsion shaft in said pawl and ratchet clutch;