Pneumatic clutch

An inflatable flexible gland clutch has a gland secured to one of a pair of cooperating clutch elements. The gland mounts friction shoes and includes inflatable chambers which, when subjected to air under pressure, will move the gland to a position where the shoes engage the other clutch element. Other chambers formed in the gland will, when inflated, disengage the clutch by moving the clutch shoes away from engagement with the mating clutch element.

BACKGROUND OF THE INVENTION 
This invention relates to pneumatic clutches, and particularly to a 
pneumatic clutch havng a flexible gland which is actuated to engage and to 
disengage the clutch. 
Pneumatic clutches which have an inflatable rubber or elastomer gland to 
connect rotating parts are commonly used in marine propulsion systems to 
control the fore and astern direction of travel of the ship. In such 
clutches an annular gland is typically permanently connected about the 
outer perimeter of an annual clutch member connected to the prime mover. 
The outer peripheral surface of the gland typically mounts replaceable 
clutch wear elements such as friction shoes. When the gland is inflated 
from a source of air under pressure, the shoes are moved radially 
outwardly to engage the inner periphery of a second annular clutch element 
which is connected through a drive train to the propellers. When the 
clutch is thus engaged, power is transmitted from the prime mover to the 
propellers. To disengage the clutch, the air pressure is removed and the 
gland is allowed to deflate. 
Because of the effect of centrifugal force acting on the gland and the 
friction shoes, there is a tendancy of the shoes to engage the mating 
surface of the outer clutch element even when the gland has not been 
inflated. It is undesirable to allow the shoes to drag across the surface 
of the clutch element when the clutch should be disengaged. Therefore, 
some means for positively disengaging the shoes from the mating element is 
often required. Most typically, positive disengagement is accomplished by 
providing springs which retract the shoes when the air pressure is 
removed. An example of this approach is found in U.S. Pat. No. 2,331,180 
issued Oct. 5, 1943 to Gasser. As the speed of operation of the clutch 
increases heavier springs are needed for disengagement. Thus, when springs 
are used for disengagement it may be necessary to change the springs to 
accommodate different applications of the clutch. 
The purpose of my invention is to provide a pneumatic clutch, and a 
flexible gland for such clutch, in which air pressure is used to prevent 
engagement of the clutch as well as to engage the clutch. 
SUMMARY OF THE INVENTION 
In accordance with the invention there is provided a pneumatic clutch which 
includes a pair of clutch members and an inflatable gland connected to one 
of the clutch members and having friction surfaces engageable with the 
other clutch member, such gland having multiple inflatable chambers which 
are connectable with a source of air under pressure whereby inflation of a 
chamber will engage the clutch and inflation of another chamber will 
disengage the clutch. 
Further in accordance with the invention there is provided such a pneumatic 
clutch in which, when the clutch is engaged, the chamber or chambers used 
for disengagement have an interior dimension in the direction of movement 
towards engagement which is greater than the interior dimension normal 
thereto. 
The invention may further reside in an inflatable annular gland for a 
pneumatic clutch which includes at least three inflatable annular chambers 
arrayed across the width of the gland with a middle chamber being larger 
than the outside chambers, together with pneumatic fittings extending into 
the hollow interior of each compartment. 
It is a principal object of the invention to provide a pneumatic clutch and 
a gland for such a clutch in which air under pressure will both positively 
engage and disengage the clutch. 
It is another object of the invention to provide a pneumatic clutch in 
which positive disengagement of the clutch is accomplished without the 
need for complex mechanical elements. 
It is a further object of the inventin to provide a pneumatic clutch which 
can be held by air pressure in a disengaged position against the 
centrifugal force which would tend to engage the clutch and thereby cause 
wear of the friction surfaces. 
The foregoing and other objects and advantages of the invention will appear 
in the detailed description which follows. In the description reference is 
made to the accompanying drawings which form a part hereof and in which 
preferred embodiments of the invention are illustrated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The clutch includes an annular inner clutch member 10 which is typically 
connected to a source of motive power and is, therefore, the driving 
clutch element. An outer concentric annular clutch element 11 has an inner 
clutch engaging surface 12. An annular gland 13 has its inner peripheral 
surface mounted upon and secured to the outer periphery of the driven 
clutch element 10. The flexible gland 13 is typically constructed of a 
reinforced rubber or other elastomer. It is formed with three hollow 
annular chambers. The middle chamber 14 is connectable to a source of 
compressed air by means of a hollow plug 15 which extends from the 
interior and through a wall of the middle chamber 14 and connects to an 
air pipe 16. The two outer chamber 17 and 18 are similarly connectable to 
a source of air under pressure by means of hollow plugs 19 and 20, 
respectively, connected to air pipes 21 and 22, respectively. 
The outer wall 24 of the gland 13 is thicker than the remaining walls of 
the gland, particularly in the area of the middle chamber 14. This thicker 
wall 24 is used to mount friction shoes which include replaceable wear 
surfaces. Specifically, as shown in FIG. 3 a series of shoes 25 each 
include a base element 26 which has flanges on each side which extend over 
and surround the thickened wall 24 of the gland. The base elements 26 are 
held in position by a series of pins 27 which extend axially of the gland 
through the thickened wall 24. The pins 27 are headed on one end and are 
held in place by cotter pins on the other end. A shoe plate 28 is 
connected to the base element 26 by a series of screws 29. Interposed 
between the shoe plate 28 and the base element 26 is a thin sheet 30 which 
extends axially beyond the limits of the shoe plate 28 and the base 
element 26 and will function to dissipate some of the heat which is 
generated when the clutch is engaged. 
FIG. 1 illustrates the clutch in a disengaged condition in which the 
friction shoes are out of engagement with the outer clutch member 11 so 
that power cannot be transmitted from the driving clutch member 10 to the 
driven clutch member 11. To engage the clutch, air under pressure would be 
admitted into the middle chamber 14 to inflate that chamber. Inflation of 
the middle chamber will continue until the friction shoes 25 engage the 
clutch surface 12 of the driven clutch element 11. The air pressure within 
the middle chamber 14 is maintained as long as it is desired to keep the 
clutch engaged. 
Release of the air pressure in the middle chamber 14 should permit the 
natural reesiliency of the gland 13 to recover its normal shape and 
thereby move to a disengaged position. However, centrifugal forces acting 
on the flexible gland 14 and friction shoes tend to expand the gland so 
that the shoes will drag against the surface 12 of the driven clutch 
elements. Therefore, a mechanism is needed to insure that the friction 
shoes will not engage or drag over the clutch surface of the outer clutch 
member when the clutch is intended to be disengaged. Such a slipping and 
sliding action if is is permitted will shorten the life of the wear 
surfaces and could result in generating considerable heat. 
The pneumatic clutch of this invention provides for the positive 
disengagement by means of the two outer inflatable chambers 17 and 18 of 
the gland 13. To disengage the clutch, air pressure is removed from the 
middle chamber and air under pressure is admitted into the two outer 
chambers 17 and 18 thereby causing those chambers to inflate. This will 
have the effect of collapsing the middle chamber 14 and will pull the 
shoes 25 radialy inwardly of the clutch. 
The outer chambers 17 and 18 of the gland 13 must be so dimensioned that 
when the middle chamber 14 is inflated, the interior dimension of the 
outer chambers 17 and 18 in the direction towards engagement of the clutch 
(i.e., the dimension in the radial direction) is greater than the interior 
dimension at right angles thereto (i.e., the dimension in axial 
direction). This can be accomplished by so shaping the outer chambers that 
when no chamber of the gland is inflated the radial dimension is greater 
than the axial dimension. Alternately, the outer chambers can be so shaped 
that when the gland is uninflated the dimensions are the same. The 
embodiment of FIGS. 1-3 is of the later form and the outer chambers 17 and 
18 are shaped with a circular cross-section which is stretched out of 
shape when the middle chamber 14 is inflated. 
While the preferred form of the flexible gland and its engaging and 
disengaging inflatable chambers is that illustrated in FIGS. 1-3, the 
gland can take several different forms. Specifically, it can be fabricated 
from several separate sections of inflatable tubes such as illustrated in 
FIG. 4. In the embodiment of FIG. 4, an inner tube 35 is mounted within an 
outer tuber 36 and is held in place by rivets 37 which extend through an 
inner plate 38. The interior of the inner tube 35, less the volume 
occupied by the plate 38, defines the middle chamber. The outer chambers 
39 are defined by the spaces between the ends of the inner tube 35 and the 
ends of the outer tube 36. 
In the embodiment in FIG. 5, the middle chamber 40 has bulbous ends 41 and 
the outer chamber 42 are formed as thin pockets within the same flexible 
rubber or elastomer member. 
In the embodiments of FIGS. 6 and 7, a disengaging chamber is disposed in 
the middle of the gland with engaging chambers on either side. 
Specifically, there are three inflatable annular disengaging chambers 50, 
51 and 52 formed at the mid-point and at each lateral side of a gland 53. 
A pair of inflatable engaging chambers 54 and 55 are formed in the gland 
53 in the spaces between the chambers 50 and 51, and 51 and 52, 
respectively. 
Other combinations of arrays of multiple chambers can be employed with 
certain of the chambers functioning when inflated to engage the clutch and 
others being employed when inflated to disengage the clutch. 
In the embodiments of FIGS. 4 through 7, the disengaging chambers are 
elongated in the radial direction in their rest state. 
In all of the embodiments, the chambers may be formed by molding techniques 
which employ fillers with interconnecting voids to form the interior of 
the chambers. When the chambers are described herein as being hollow, that 
term is intended to include an interior formed by a filler with 
interconnecting voids. 
The invention has been illustrated and described in relation to a pneumatic 
clutch of the expandable gland type. That is the type which includes two 
concentric clutch elements with the gland mounted on the inner element and 
inflated to expand to engage the outer element. The invention may also be 
incorporated into a pneumatic clutch using a contracting or constricting 
gland. That is, the gland could be permanently attached to the inner 
periphery of the outer clutch element and would, upon inflation, have its 
opening contracting or constricting to thereby engage the outer periphery 
of the concentric inner clutch element. In such a constricting type clutch 
the friction shoes would obviously be mounted along the inner periphery of 
the gland. Furthermore, the invention may be incorporated into a pneumatic 
clutch in which the two clutch elements are mounted coaxially and have 
contronting surfaces normal to the axis of the clutch. In such an 
arrangement the flexible gland would be mounted on the surface of one 
clutch element and, upon inflation, would expand to engage the opposing 
surface of the other clutch element. 
In all of these arrangements, the multiple chamber pneumatic clutch of the 
present invention can be advantageously employed to ensure positive 
disengagement of the clutch and to maintain the clutch in a disengaged 
condition against the effects of any forces tending to cause engagement.