192 clutches and power-stop control – Clutches – Automatic
Patent
1994-12-27
1996-06-11
Bonck, Rodney H.
192 clutches and power-stop control
Clutches
Automatic
192 41A, 192104B, F16D 4107, F16D 4314
Patent
active
055247423
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to sprag clutches comprising an inner race and an outer race and sprags located between the races.
This invention is particularly concerned with centrifugal lift off sprag clutches which are well known in the art.
Sprag clutches which use a centrifugal lift off action to effect lift off of the sprags from the outer race are known. The sprags are biased into engagement with both races to effect a wedging action preventing rotation of the races relative to each other in a first direction. Relative rotation of the races in a second direction (overrunning) is permitted. At a certain relative angular velocity in the second direction the centrifugal force acting on the sprags, due to the unbalanced mass created by the asymmetric geometry, increases to a magnitude which causes the sprags to pivot about an axis such that a clearance develops between the sprags and the outer raceway.
The advantage of centrifugal lift off clutches is that the wear of the sprags against the contacting race is reduced during overrunning. However, as the sprags pivot to lift off a race the bias force urging the sprags into the locked position tends to increase. This results in an extended lift off time over a range of angular velocity during which the centrifugal force overcomes the increasing resilient bias force and hence a degree of wear still occurs.
It is an object of the present invention to obviate or mitigate the aforesaid disadvantage.
In accordance with the present invention there is provided a sprag clutch comprising a race, a plurality of sprags held pivotally in a cage concentric with said race, said sprags having a race engaging surface, and resilient means urging said sprags into contact with said race by imparting an urging couple to said sprags at a point of action whereby on attempted rotation of said cage in a first direction relative to said race said sprags move to an engaging position to prevent said rotation and on attempted rotation of said cage and sprags in a second direction relative to said race a centrifugal force acts on each of the sprags imparting a centrifugal couple to pivot it to a disengaged position to allow rotation of said cage and sprags, the centre of gravity of each sprag being so disposed that as each sprag pivots the centrifugal couple increases at a greater rate than the urging couple, wherein the centre of gravity of each sprag is disposed radially inwardly of a fixed pivot centre of the sprag so that the perpendicular distance of the centre of gravity from the pivot centre increases during the pivoting of each sprag causing a corresponding increase in the centrifugal couple, and the perpendicular distance of the point of action of said resilient means from the pivot centre decreases during said pivoting.
Preferably the clutch further comprises inner and outer races between which the sprags and cage are disposed, wherein in said engaged position the sprags are in contact with both said inner and outer races and in said disengage position the sprags pivot out of contact with one of said races.
The inner race may be part of the sprag clutch or may be formed on a shaft or the like on which the clutch is located.
Preferably the resilient means is a garter spring disposed circumferentially around the sprags which is preferably located in a recess in each sprag.
Preferably the garter spring is a tension spring which acts in the recess disposed radially outward of the pivot centre of the sprag.
Preferably the sprags pivot out of contact with the outer race.
A specific embodiment of the present invention will now be described with reference to the accompanying drawings in which:
FIG. 1 is a fragmentary view of a sprag clutch indicating forces acting on each sprag; and
FIG. 2 is an end view of a sprag of FIG. 1 in the direction of arrow Y.
Referring to FIG. 1 there is shown part of a sprag clutch having inner and outer concentric races 1,2 rotatable about a central axis (not shown). In the annular space between the races 1,2 is disposed a plurality of sprags 3 each pivo
REFERENCES:
patent: 2777551 (1957-01-01), Banker
patent: 3019873 (1962-02-01), Ferris et al.
patent: 3498429 (1970-03-01), Frakes
patent: 3702649 (1972-11-01), Giese et al.
patent: 3997041 (1976-12-01), Judd et al.
patent: 5064037 (1991-11-01), Long, Jr.
Bonck Rodney H.
Renold Plc.
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