Centrifugal friction mechanism

A centrifugal clutch having at least one input plate and at least one output disk concentric with the plate. At a predetermined speed of input rotation, the plates and disks are forced to move axially into frictional engagement by weights that pivot in response to centrifugal force. Pivoting of the weights is restrained by axially oriented springs, and the speed of engagement can be varied by adjusting the spring force. The springs are accessible for adjustment without diassembling the clutch.

BACKGROUND OF THE INVENTION 
The present invention relates to friction clutches, and more particularly 
to friction clutches in which engagement occurs at a predetermined speed 
in response to centrifugal force. 
Friction clutches that engage at a predetermined speed have been known for 
some time and are particularly useful in combination with motors, such as 
internal combustion engines, that are not capable of starting under load 
conditions. The engine is permitted to accelerate freely with the clutch 
disengaged until it reaches the point on its power curve where it produces 
sufficient torque. At this predetermined speed, the clutch automatically 
engages and applies the load. 
Previously known centrifugal friction clutches have exhibited a number of 
important shortcomings. Many are large and heavy, thus limiting the types 
of equipment on which they can be used. Some engage too abruptly or 
unevenly, causing the engine speed to fall. The engagement speed is 
usually not readily adjustable, and if adjustment is possible, disassembly 
of the mechanism and substitution of parts is often required. Another 
disadvantage of many previously known clutches is a tendency of the 
friction surfaces to remain engaged once engagement is commenced, 
resulting in a speed of disengagement substantially lower than the speed 
of engagement. If stalling on deceleration is to be avoided, the speed of 
engagement must be higher than otherwise desired to compensate for this 
effect. 
An application of centrifugal friction clutches that is particularly 
demanding is the connection of a small displacement internal combustion 
engine to the drive wheel of a go-cart. These vehicles are not equipped 
with transmissions, and it is necessary to continuously engage and 
disengage the clutch as the cart enters straight-aways and turns. The 
clutch must be compact and light-weight, it must engage smoothly and 
always at the same speed, and the speeds of engagement and disengagement 
should be as close to each other as possible. Ease of adjustment of the 
speed of engagement is particularly important since the characteristics of 
different tracks dictate different optimum settings, and the best setting 
for an individual cart and driver must be determined by trial and error. 
The clutches presently used for this purpose must be disassembled for each 
readjustment, and their range of adjustment is relatively small. 
SUMMARY OF THE INVENTION 
The present invention provides an improved centrifugal friction clutch that 
overcomes many of the disadvantages of previously known clutches of this 
type. It employs one or more clutch plates arranged parallel to one or 
more concentric clutch disks. The plates rotate with an input connector 
and a support member, while the disks rotate with an output connector. 
Frictional engagement of the disks with the plates to drive the output 
connector is caused by a pressure mechanism carried by the rotating 
support member. The pressure mechanism includes one or more weights, each 
pivotable about an axis perpendicular to the rotational axis of the 
plates. Upon rotation of the support member, centrifugal force causes the 
weights to pivot, so that cam surfaces on the weights produce the 
necessary axial movement between the plates and disks. 
Preferably, resilient members such as coil springs restrain pivotal 
movement of the weights and insure positive disengagement of the clutch. 
The speed of engagement can be adjusted by varying the spring force. A 
particularly advantageous arrangement utilizes stems that project axially 
from one of the plates and screws projecting through the support member 
are received by the stems. The springs are compressed between the 
screw-heads and the support members to urge the end plate toward the 
support member to loosen the plate-disk stack. 
A clutch housing can be provided with one or more apertures through which 
the position of the screws can be adjusted without disassembly. The 
housing interlocks the plates and rotates with them, and the output 
connector is carried by the housing. 
Other features and advantages of the present invention will become apparent 
from the following detailed description taken in conjunction with the 
accompanying drawings which illustrate, by way of example, the principles 
of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An exemplary centrifugal friction clutch 10 embodying many novel features 
of the present invention is depicted in FIGS. 1 - 8 of the accompanying 
drawings. It is particularly suitable for use in go-cart racing. 
As best seen in FIGS. 2 and 6, the clutch 10 includes a series of three 
concentric clutch plates, 12, 14 and 16 and two concentric clutch disks 18 
interleaved between the plates. Friction linings 20 are attached to both 
faces of each disk 18 to prevent relative rotation when sufficient axial 
pressure is applied to the plate-disk stack 21. One of the end plates 12 
carries a splined hub 22, with the other plates 14 and 16 having centered 
openings 24 and 26, respectively, that are toothed about their peripheries 
to engage the splines 27 so that all of the plates must rotate in unison. 
The disks 18 have central openings 28 of larger diameter than the hub 22 
so that they are free to rotate independently of the plates 12, 14 and 16 
when they are not frictionally engaged. 
A cast aluminum support member 29 having a circular outline and a diameter 
approximately equal to that of the disks 12, 14 and 16 and the plates 18 
has a central opening 30 so that it fits over an unsplined end portion 31 
of the hub 22 that has a reduced diameter. The last disk 16, which is 
adjacent the support member 29, carries four symmetrically spaced, 
integrally formed, stems 32 that extend through apertures 33 in the 
support member, thereby rotationally connecting the support member to the 
disks 12, 14 and 16. The stems 32 are internally threaded to receive 
axially projecting screws 34. Coil springs 36 encircle the screws 34 and 
are compressed between the screw-heads 38 and annular countersunk surfaces 
40 that surround the apertures 33. The springs 36 therefore pull the 
adjacent plate 16 toward the support member 29, urging that plate toward a 
position where there is ample space between the two end plates 12 and 16 
to permit the plates 12, 14 and 16 to rotate independently of the disks 
18. Accordingly, the springs 36 bias the clutch 10 toward a disengaged 
condition. The support member 29 is fixed in position with respect to the 
most distant plate 12 by screws 41 that are threaded into the hub 22, 
thereby limiting the axial travel of the other plates 14 and 16 and the 
disks 18 when the clutch 10 is disengaged. 
Engagement of the clutch 10 in response to centrifugal force is caused by a 
pressure mechanism consisting of four sets of weights 42, each of which is 
disposed within a slot 44 of rectangular outline. The slots 46 are 
radially oriented and symmetrically arranged about the periphery of the 
support member 29, as shown in FIGS. 2 and 3. A pin 46 extends across each 
slot 44 in a direction perpendicular to the rotational axis "A" of the 
disk-plate stack 21, and the corresponding set of weights 42 is pivotable 
on that pin. 
Each set of weights 42 is made up of a plurality of flat parallel stampings 
or leaves 48 perpendicular to the pin 46. When viewed from the side, as 
shown in FIG. 4, each of the weight stampings 48 presents an aperture 50 
in which the pin 46 is received. It has an enlarged drive portion 52 
disposed radially inwardly from the pin 46 and an elongated cam portion 54 
extending radially outwardly from the pin 46. The center of gravity "B" of 
the drive portion 52 is axially spaced outwardly from the pin 46 away from 
the adjacent plates 12, 14 and 16. 
When the disks 12, 14 and 16 and the support member 29 are rotated, 
centrifugal force tends to throw the drive portions 52 radially outwardly, 
as indicated by the arrow "C" in FIG. 4, pivoting the weights 42 so that 
cam surfaces 56 on the portions 54 push the adjacent disk 16 away from the 
support member 29. Thus, the weights move from their rest position, shown 
in FIG. 7, to their pressure applying position, shown in FIG. 8. 
The axial movement of the adjacent disk 16 is restrained by the springs 36, 
but at a predetermined rotational speed the combined force of the four 
sets of weights 42 can compress the springs 36 sufficiently to cause 
frictional engagement between the opposing surfaces of the disk-plate 
stack 21. The resilience of the springs 36 results in smooth engagement 
with minimum loss of engine speed on imposition of a load and 
substantially eliminates random variations in engagement speed that have 
characterized some previously known centrifugal clutches. The springs 36 
also tend to equalize the speed of engagement with the speed of 
disengagement to permit more efficient use of the engine power curve. 
Input power is supplied to the clutch 10 by an engine 58 having a power 
take-off shaft 60, shown in FIG. 1. An input connection for the shaft 60 
is formed by a keyway 62 in an axial bore 64 that extends through the hub 
22. An output connection for the clutch 10 takes the form of a sprocket 65 
for a chain drive, suitable for use with a gocart, attached to the flat 
closed end 66 fo a shallow drum 68. The opposite end 70 of the drum 68 is 
open to slide over the plate-disk stack 21. Generally cylindrical sides 72 
of the drum 68 are provided with axially oriented rectangular slots 74 
which receive a plurality of lugs 76 that project radially from each of 
the disks 18, thereby interlocking the disks with the drum and connecting 
the disks together for joint rotation. The circumferential edges 78 of the 
disks 18 between the lugs 76 are received snugly within the sides 72 of 
the drum 68 to prevent radial movement of the disks. 
On the inner surface of closed end 66 of the drum 68 is a sleeve 80 that is 
separated from the nearest disk 12 by a spacer 84. A cylindrical bearing 
member 82 is affixed to the inner surface of the sleeve 80. A snap ring 
86, followed by another spacer 88, positions the drum 68 on an axial 
projection 90 of the disk 18 that extends through the sleeve 80. 
The drum 68 forms one half of a two-piece housing 92, the second half being 
a shallow cover 94 that fits over the support member 29 and is secured to 
the drum 68 by a plurality of screws 96. Cooling of the clutch 10 is 
effected through round ventilating apertures 98 and 100 arranged in 
circles on the ends of the drum 68 and cover 94, respectively. 
It should be noted that the speed at which the weights 42 overcome the 
restrainng force of the springs 36 can be adjusted by simply turning the 
adjustment screws 34 to vary their axial position. The screws 34 are 
readily accessible through the apertures 100 in the cover 94 without 
disassembling the clutch 10, this accessibility making fine adjustment of 
the engagement speed by trial and error a simple task. Moreover, 
adjustments of greater magnitude can be made by substitution of springs 
having a different spring rate, again utilizing the apertures 100 which 
are of larger diameter than the springs 36. The entire clutch 10 is of 
simple easily disassembled construction which permits the friction linings 
20 to be inspected frequently and replaced with a minimum of time and 
skill when necessary. The number of components is kept to a minimum and 
there is no wasted space within the mechanism. 
The clutch 10 described above is a dry clutch, but many aspects of the 
invention are also embodied in an exemplary wet clutch 110 shown in FIG. 
9. It differs from the dry clutch 10 primarily with respect to the housing 
112 which is sealed against oil leakage by three ring-shaped gaskets 114. 
Its operation and construction are similar to that of the dry clutch 10, 
utilizing four plates 116 and three interleaving disks 118. One of the 
plates 116 carries a spline 120 by which the four plates are locked 
together for joint rotation. The disks 118 interlock with the housing 112 
for rotation therewith. Upon rotation of the plates 116, an interconnected 
weight support 122 causes a plurality of weights 124 to revolve and pivot, 
thereby translating centrifugal force into an axial force that presses the 
plates 116 and the disks 118 together to engage the clutch. 
There are, of course, no ventilation apertures in the oil-tight housing 
112. However, an aperture 126, sealed by a removable plug 128, is provided 
on one end 130 of the housing 112 for access to a plurality of screws 132 
that are used to adjust the tension on a plurality of coil springs 134 
that restrain pivotal movement of the weights 124. Only one such aperture 
126 is required since it can be rotated into alignment with each of the 
screws 132 in succession. 
While two particular forms of the invention have been illustrated and 
described, it will be apparent that various modifications can be made 
without departing from the spirit and scope of the invention.