192 clutches and power-stop control – Transmission and brake – Torque-responsive brake
Reexamination Certificate
2000-04-24
2001-07-10
Bonck, Rodney H. (Department: 3681)
192 clutches and power-stop control
Transmission and brake
Torque-responsive brake
C188S134000
Reexamination Certificate
active
06257388
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to backstopping clutches and, in particular, to an improved frictional insert for use in such clutches.
2. Disclosure of Related Art
Backstopping clutches are used to prevent transfer of a back drive torque from a driven device to a driving, or torque generating, device. The clutch is typically disposed between the output shaft of the driving device and the input shaft of the driven device. The clutch allows torque to be transferred from the output shaft of the driving device to the input shaft of the driven device in order to rotate the input shaft in either rotational direction. The clutch, however, prevents a back driving torque from being transferred from the input shaft of the driven device to the output shaft of the driving device.
A conventional backstopping clutch includes a hollow outer race having a generally cylindrical inner surface. The clutch also includes an input member disposed within the outer race and coupled to the output shaft of the driving device. A pair of opposed brake shoes are coupled to the input member and rotate with the input member as torque is transferred from the driving device to the driven device. The brake shoes have generally arcuate surfaces that correspond to, and are normally spaced from, the inner surface of the race. The clutch further includes an output member that is connected to the input shaft of the driven device and one or more output pins. Each of the output pins has a first portion disposed between the two brake shoes and a second portion disposed within a corresponding opening in the output member. A lubricant is generally used within the clutch to reduce wear on the components of the clutch.
During normal operation, rotation of the output shaft of the driving device causes a corresponding rotation in the input member of the clutch, and consequently, the brake shoes, output pins and output member of the clutch, to thereby transfer torque to the input shaft of the driven device. In the event that the driven device attempts to generate a back drive torque through the clutch, rotation of the output member causes the output pins to become skewed. As a result, the brake shoes are forced apart from one another and into frictional engagement with the inner surface of the outer race of the clutch.
The above-described clutch often include hardened inserts disposed within slots formed in the arcuate surfaces of the brake shoes. The inserts frictionally engage the inner surface of the race when the brake shoes are forced apart as described above and are provided to reduce wear on the brake shoes. After a period of time, however, the hardened inserts in conventional clutches tend to “hydroplane” or slip relative to the inner surface of the race due to the presence of the lubricant within the clutch. As a result, the inserts do not frictionally engage the race of the clutch and the clutch may fail to prevent transfer of a back driving torque.
There is thus a need for an improved back-stopping clutch that will minimize or eliminate one or more of the above-mentioned deficiencies.
SUMMARY OF THE INVENTION
The present invention provides a backstopping clutch having an improved frictional insert.
A backstopping clutch in accordance with the present invention includes a hollow outer race disposed about a first axis. The outer race includes a radially inner friction surface that may be substantially cylindrical in shape. The clutch also includes an input member rotatably supported within the outer race and first and second brake shoes disposed within the outer race and in engagement with the input member. Each of first and second brake shoes includes one or more arcuate surfaces corresponding to the inner surface of the outer race. Further, at least one of the arcuate surfaces defines a slot that may extend in a direction parallel to the first axis. The clutch further includes at least one output pin and an output member having an opening therein. A first portion of the output pin is disposed between the first and second brake shoes and a second portion of the output pin is disposed within the opening in the output member. Finally, the clutch includes an insert disposed within the slot defined by the arcuate surface of the brake shoe. In accordance with the present invention, the insert includes a groove. The groove may extend in a direction parallel to the axis of the clutch and may include first, second, and third, walls with the second and third walls opposing one another and perpendicular to the first wall.
A backstopping clutch in accordance with the present invention represents a significant improvement as compared to conventional backstopping clutches. When a back driving torque is applied to the clutch and the brake shoes and inserts are urged radially outward into engagement with the inner surface of the race of the clutch, the groove in the insert channels the lubricant within the clutch away from the engagement surfaces. As a result, the insert is less likely to “hydroplane” or slip relative to the inner surface of the race and the clutch is better able to prevent a back driving torque from being transferred to the driving device.
These and other features and objects of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.
REFERENCES:
patent: 3335831 (1967-08-01), Kalns
patent: 3414095 (1968-12-01), Kalns
patent: 4591029 (1986-05-01), Da Foe
patent: 5007511 (1991-04-01), Ostrander
patent: 5104461 (1992-04-01), Ostrander
patent: 5865284 (1999-02-01), Creech
Formsprag Form-Lock Bi-Directional Driving/Backstopping, cover sheet, pp. 2-5, back sheet.
“Formsprag Form-Lock Bi-Directional Driving/Backstopping Clutches”, Bulletin 4601, Jul. 1999, 4 pages.
Bonck Rodney H.
Dykema Gossett PLLC
Rodriguez Saul
Warner Electric Technology, Inc.
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