Centrifugal clutch

A centrifugal clutch assembly having a resilient restraining means for providing a radially inwardly directed restraining bias to each of a plurality of clutch shoe members is disclosed. The restraining means comprises a coiled spring member circumferentially surrounding and in contact with each clutch shoe member and a rod spring member extending substantially a complete extent of and enclosed within the coil spring member. A coil spring member and the rod spring member each contribute to the radially inwardly directed bias whereby the idle range of the clutch mechanism is increased over the use of either spring member by itself. In this way, overstressing of a spring member is eliminated.

The invention relates generally to centrifugal clutches and in particular, 
to a centrifugal clutch mechanism having a circumferential restraining 
spring assembly. 
BACKGROUND OF THE INVENTION 
Centrifugally actuated clutches are well known for driving many different 
mechanisms. A particularly useful class of centrifugal clutches has an 
idle region in which the clutch shoes are restrained out of contact with a 
driven clutch drum over a desired range of drive motor rotational speed. 
Typically, the major factors determining the idle range are the center of 
gravity and/or mass of the clutch shoes, connection of the clutch shoe to 
the driven supporting structure, and the nature and strength of the 
generally inwardly directed restraining forces. 
Typically, in applications wherein a larger idle range is necessary, either 
the structure or mass of the clutch shoes or the strength (usually the 
spring constant) of the clutch shoe restraining force is changed. Thus by 
either reducing the effective centrifugal mass of the clutch shoes or by 
increasing the restraining force, a larger rotational speed is required to 
effect shoe movement, and a larger idle speed range is obtained. In many 
applications, however, it is impossible or undesirable to alter the 
structure of the clutch shoe assembly and hence it is only the restraining 
force which can be changed. However, the restraining force is generally 
provided by spring materials, which can be used only over certain well 
known ranges, past to top limits of which, they become overstressed and 
hence unreliable. 
A particularly, commercially successful, construction of the centrifugal 
clutch mechanism is one which uses a circumferential coiled spring to 
provide the restraining force. These mechanisms have been the subject of 
many patents and various means have been devised for either improving the 
coiled spring construction or replacing it with, for example, solid 
springs such as those described and claimed in Frederickson, U.S. Pat. No. 
3,768,611, issued Oct. 30, 1973. Although these systems have in general 
proven to be of considerable commercial impact, they too meet serious 
obstacles as the idle range is increased. 
It is therefore a principal object of the invention to provide a 
centrifugal clutch mechanism having an increased idle range without the 
inherent disadvantages of spring material overstressing. Other objects of 
the invention are to provide a centrifugal clutch mechanism which is 
reliable, simple in construction, substantially rattle-free, strong, and 
relatively low in manufacturing cost. 
A further object of the invention is to provide a centrifugal clutch 
mechanism in which the component parts are positionally stable. 
SUMMARY OF THE INVENTION 
The invention features a centrifugal clutch having a driving member, a 
driven member including a clutch drum, a plurality of centrifugally 
responsive clutch shoe members, and a resilient restraining means. The 
centrifugally responsive clutch shoe members are operatively supported by 
the driving member for movement of a frictional surface of the clutch 
members into and out of engagement with the clutch drum. The resilient 
restraining means applies a radially inwardly directed bias to the clutch 
shoe members and comprises a coiled spring member extending around a 
circumference of said drum, inwardly from said clutch drum, and in contact 
with each clutch shoe member, and a rod spring member extending 
substantially a complete extent of and enclosed within the coiled spring 
member. Thereby, the coiled spring member and the rod spring member each 
contribute to the radially inwardly directed bias and the idle range of 
the clutch is increased over the use of either the coil spring or the rod 
spring by itself. 
In preferred embodiments of the invention, the rod spring has an oval-like 
configuration and contacts radially outward portions of the coiled spring 
at at least two spaced apart positions. In a further preferred embodiment, 
the rod spring has a helical configuration and contacts the coiled spring 
further at least at each rod spring end. Each of these variations in the 
rod spring configurations reduces the rattle between the spring member. 
In yet a further aspect of the invention, the rod spring ends define a gap 
in which the ends of the coiled spring are connected; and the ends of the 
rod spring are canted, whereby creeping of the rod spring within the coil 
spring is reduced.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to FIG. 1, the centrifugal clutch assembly 10 has a pair of 
clutch shoe members 12 and 14 slideably mounted and supported on 
protruding portions 16 and 18 respectively of a rotating driving member 
20. Member 20 is secured on a rotating driving member shaft 22, by a 
threaded connection 24 (FIG. 2). Surrounding the clutch shoe and driving 
member is a driven member 28 journalled for rotation about shaft 22 on 
bearings 30. Driven member 28 has a rim portion, clutch drum 32, having an 
inside surface 34 directed parallel to the axis of rotation of shaft 22. 
The radius of curvature of outside surface portions, surfaces 40, 42, of 
shoe members 12 and 14, is the same as the radius of curvature of the 
inside rim surface 34. The shoe members are secured against translation in 
the direction of the axis of rotation of shaft 22 by the protruding 
portions 16, 18 which are securely held by plate members 50, 52 against 
the clutch shoe walls (only wall 54 is shown (FIG. 2)). Members 50, 52 are 
secured against shoes 12 and 14 by fasteners 56, 58 respectively. 
Shoes 12 and 14 are urged in a radially inward direction by a resilient 
restraining means seated in circumferential groove 60 in each clutch shoe 
member. The resilient restraining means comprises a coiled spring 62 (a 
garter spring) connected at its ends to form a continuous circumferential 
spring member and enclosing a rod spring member 66 which extends 
substantially the entire extent of spring member 62. The rod spring member 
66 has spaced apart canted ends 68 and 70 to reduce spring creeping. 
Referring to FIG. 3, the illustrated resilient restraining means comprises 
the coiled spring member 62 which extends completely around and encloses 
the rod spring member 66. The coiled spring, which is preferably a garter 
spring, has at each end hook members 72, 74, respectively, which are 
connected in an operational relationship, in the gap between rod spring 
ends 68,70, to provide a predetermined tensioning of the coiled spring 
member. 
The rod member which is shown without the coiled spring member in FIG. 4 
has a somewhat flattened oval-like shape, so that, referring to FIG. 4, 
its extent in the vertical direction is less than its extent in the 
horizontal direction. As a result, when coiled spring member 62 is 
threaded around rod 66, the right and left hand extreme portions 80, 82 of 
the rod member contact radially outward portions 84, 86 (FIGS. 6 and 7) of 
the spring member 62. As a result, the radial position of the coiled 
spring member relative to the rod member is substantially fixed and rattle 
between the two spring members is significantly reduced. 
To even further reduce rattle, rod spring member 66 has a slightly helical 
configuration, FIG. 5, so that one end 70 of the spring member rises 
slightly above and the other end 68 is slightly below, a plane 88 of 
average mass of the coiled spring member. In this manner, the canted ends 
68, 70 contact and further prevent rattle with the coiled spring member. 
The canted ends also provide easier threading of the coiled spring member 
62 onto the rod spring member and further provide a resistance to creeping 
of rod spring member 66 relative to the coiled spring member 62. 
In operation, the resulting spring effect of having the two substantially 
coaxial spring members is to add their effective spring constants to 
provide a greater restraining force against the radially outward movement 
of clutch shoes 12 and 14. Thus, the centrifugal force developed as the 
clutch shoes are rotated about the axis of rotation of shaft 22 by 
extending members 16, 18 and support member 20 must be increased to 
overcome the restraining forces, and a greater idle range is achieved. 
In addition, the two coaxial spring members combine to provide a 
restraining means having greater capabilities and flexibility than the use 
of the springs in a non-coaxial structure. 
MAJOR ADVANTAGES OF THE INVENTION AND UNOBVIOUSNESS 
The centrifugal clutch according to the invention thus advantageously 
provides a resilient restraining means having a higher effective spring 
constant than available by any of the prior art single spring systems. 
Each of the separate spring restraining members is further not subject to 
overstressing. Additionally, the resilient restraining means 
advantageously prevents creeping of one spring member relative to the 
other. The particular union of a coiled spring and a solid spring member 
advantageously provides strength characteristics and superior stability 
and reliability characteristics unavailable with comparable prior art 
configurations. 
The particular construction described and claimed herein further provides 
the advantage of substantially rattle-free operation which is generally 
unavailable in those configurations wherein a plurality of contiguous coil 
springs or a plurality of contiguous rod spring members are used. Thus, 
the claimed invention uniquely provides advantages and desirable operating 
characteristics unavailable through the use of either of the spring 
members separately and further provides a functional result greater than 
what would be expected by merely combining the spring members. 
The prior art is replete with examples of either circumferential spring 
elements or a plurality of C-shaped spring members used in connection with 
a centrifugal clutch mechanism. Typical examples of systems having a 
circumferential coiled spring, such as a garter spring, with or without a 
retaining means to hold a spring in place, (the retaining means generally 
passing through the interior of the coil spring member but not having 
spring-like qualities itself), are, for example, Moore, et al, U.S. Pat. 
No. 2,947,399, issued Aug. 2, 1960, Brooks, U.S. Pat. No. 3,824,867, 
issued July 23, 1974, Thomas, U.S. Pat. No. 2,180,217, issued Nov. 14, 
1939, Peters, U.S. Pat. No. 3,313,169, issued Apr. 11, 1967, Libby, U.S. 
Pat. No. 1,841,613, issued Jan. 19, 1932 (with a resilient sheet 
material). 
In addition to the prior art references noted above which relate to a 
coiled spring member which circumferentially surrounds the clutch shoe 
members, there are other references, such as Frederickson, U.S. Pat. No. 
3,768,611, issued Oct. 30, 1973 (noted above), which describes a 
centrifugal clutch mechanism having a plurality of C-shaped rings 
circumferentially mounted about the clutch shoes to maintain the shoes in 
a retracted position when the driving member is within an idle range. 
Other references of a related, though different type, are for example 
Kimball et al, U.S. Pat. No. 2,243,565, issued May 27, 1941 (split rings 
54), Savage, U.S. Pat. No. 2,902,128, issued Sept. 1, 1959, Giometti, U.S. 
Pat. No. 3,306,409, issued Feb. 28, 1967 and Selander, U.S. Pat. No. 
2,572,528, issued Oct. 23, 1951. 
There are in addition, a number of references in which a solid, rod shaped, 
retaining member is passed through the coiled spring member in order to 
provide a retaining function. The solid members do not, in these 
references, act as a spring member and do not contribute to the resilient 
restraining function. Typical of these references are Reed, U.S. Pat. No. 
1,889,698, issued Nov. 29, 1932 (FIGS. 9 and 10), Hatcher, U.S. Pat. No. 
1,926,483, issued Sept. 12, 1933, Reed, U.S. Pat. No. 2,028,951, issued 
Jan. 28, 1936, Reed, U.S. Pat. No. 2,029,339, issued Feb. 4, 1936, and 
Armstrong, U.S. Pat. No. 3,628,353, issued Dec. 21, 1971. 
The references thus generally relate to various constructions of spring 
members useful in a clutch mechanism. Most, but not all, relate to 
centrifugal clutch systems. Nevertheless, despite the great proliferation 
of clutch related art, and in particular clutch related art wherein 
circumferential springs are used, the invention claimed herein is not 
suggested or disclosed in any of the cited references, which span a period 
of over forty years. 
Other embodiments of the invention, including additions, subtractions, 
deletions, and modifications of the disclosed preferred embodiment will be 
obvious to those skilled in the art and are within the scope of the 
following claims.