Input and output members (19), (28) and a clutch disc (32) are coaxially rotatable relative to each other, the clutch disc (32) being frictionally engageable with the input member (19). A coil-would spring (33) is wound around the input member (19) and connected at its ends to the clutch disc (32) and output member (28). An electromagnetic coil (26) may be energized to attract the clutch disc (32) into frictional engagement with the input member (19), causing the coil-wound spring (33) to tightly wind around the input member (19) and drivably connect the input member (19) to the output member (28). A spring (41) quickly and smoothly disengages the clutch disc (32) from the input member (19) when the coil (26) is de-energized. A plurality of pins (36) extending through the clutch disc (32) ensure parallel movement of the clutch disc (32) toward and away from the input member (19). The spring (41) is in the form of an annular plate spring and is resiliently flexed by means of hard rivets (43) projecting from a cover (34). The spring (41) slides on the rivets (43) during engagement and disengagement of the clutch disc (32), thereby minimizing friction and abrasion.

BACKGROUND OF THE INVENTION 
The present invention relates to an improved electromagnetic spring-wound 
clutch which may be advantageously employed to connect an air conditioning 
compressor to an engine of an automotive vehicle. This invention 
constitutes a novel and advantageous improvement to an ELECTROMAGNETIC 
SPRING-WOUND CLUTCH disclosed in copending U.S. patent application Ser. 
Nos. 866,645, filed Jan. 3, 1978 (now U.S. Pat. No. 4,194,607, issued Mar. 
25, 1980), 917,316, filed June 19, 1978 and 942,262, filed Sept. 14, 1978, 
(now U.S. Pat. No. 4,225,027, issued Sept. 30, 1980) which are assigned to 
the same assignee as this application. 
An electromagnetic spring-wound clutch of the general type to which the 
present invention relates is disclosed in U.S. Pat. No. 3,735,847 and 
comprises coaxial input and output members. A clutch plate or disc is 
rotatably provided on the input member. Furthermore, a coil-wound spring 
is wound around the input and output members and connected at its opposite 
ends to the clutch disc and output member. An electromagnetic coil 
attracts the clutch disc into frictional engagement with the input member, 
causing the coil-wound spring to be tightly wound around the input and 
output members and drivably connect the input member to the output member. 
When the coil is de-energized, the clutch disc disengages from the input 
member, and the coil-wound spring releases the input member for rotation 
relative to the output member. 
A major problem in this type of clutch is obtaining fast and smooth 
disengagement of the clutch disc. More specifically, the clutch disc tends 
to vibrate during disengagement, causing noise, and furthermore does not 
disengage completely parallel to the input member. In extreme cases, the 
clutch disc may be deformed or even break. A prior art attempt to overcome 
this problem involves an arrangement in which the coil-wound spring is 
stretched axially by the clutch disc when the coil is energized, and 
disengages the clutch disc when the coil is de-energized due to its 
resilience. However, due to the large spring constant required to drivably 
connect the input member to the output member, the coil must have an 
excessive magnetomotive force to stretch the coil-wound spring. Such a 
large coil cannot be fit into the clutch in a practical manner. 
The problem is basically overcome by the novel improvement disclosed in the 
above mentioned U.S. patent application Ser. No. 866,645 by providing 
spring means and a plurality of pins to quickly and smoothly disengage the 
clutch disc from the input member while maintaining the clutch disc 
parallel to the input member. The spring means in one preferred form of 
the prior disclosure comprises an annular plate spring having axially 
projecting tabs or an annular wave spring. The clutch comprises a cover 
which protectively surrounds the coil-wound spring and has a radially 
outer flange portion which is formed with annular slots through which the 
pins extend. The pins further extend through holes formed through the 
clutch disc and annular spring and are formed with double heads which 
resiliently compress the spring and urge the clutch disc away from 
engagement with the input member and into engagement with the flange 
portion of the cover. 
Although the basic improvement provides a substantial advance over the 
prior art, a problem has been encountered in actual manufacture of such a 
clutch. In order to enable deep drawing of the cover into the required 
shape, the cover must be made of a relatively soft low carbon steel. Due 
to the fact that the clutch disc and therefore the annular spring rotate 
relative to the cover during engagement and disengagement of the clutch, 
the engaging portions of the cover and annular spring rub together. 
Whereas there is but slight abrasion of the annular spring, which is made 
of a high carbon spring steel, frictional contact with the annular spring 
causes substantial abrasion of the cover and the formation of deep groove 
over a period of prolonged use of the clutch. This progressively reduces 
the force of the annular spring exerted on the clutch disc and the 
reliability of smooth disengagement of the clutch. After excessive use the 
clutch may finally fail to disengage. 
Such abrasion of the cover may be eliminated by forming the cover of a high 
carbon steel and hardening the same by a quenching process. However, it is 
impossible to deep draw such a high carbon steel into the required shape 
for the cover. Another unsatisfactory expedient is to form the cover of a 
relatively low carbon steel and surface harden the same after press 
forming. However, practical problems are encountered regarding deformation 
of the cover during surface hardening and the additional manufacturing 
step which increases the production cost. 
SUMMARY OF THE INVENTION 
An electromagnetic spring-wound clutch embodying the present invention 
comprises a rotary input member, a rotary output member coaxial with the 
input member, a rotary clutch disc coaxial with the input member and 
frictionally engageable therewith, a coil-wound spring wound around the 
input member and being connected at its ends to the clutch disc and output 
member respectively, an electromagnetic coil which, when energized, 
attracts the clutch disc into frictional engagement with the input member, 
a cover member fixed to the output member and covering the coil-wound 
spring, the cover member being formed with arcuate slots and the clutch 
disc being formed with circumferentially spaced holes conjugate to the 
slots, double-headed pins extending through the slots and holes 
respectively, a resilient annular plate spring disposed between the cover 
member and heads of the pins which extend external of the cover member and 
a plurality of projecting members fixed to the cover member and engaging 
with the plate spring, the projecting members resiliently flexing the 
plate spring so as to urge the clutch disc to disengage from the input 
member. 
It is an object of the present invention to provide an electromagnetic 
spring-wound clutch featuring greatly reduced frictional abrasion over the 
prior art. 
It is another object of the present invention to provide an electromagnetic 
spring-wound clutch of increased mechanical durability over the prior art. 
It is another object of the present invention to provide an electromagnetic 
spring-wound clutch with a longer service life and reduced maintenance 
requirements over the prior art. 
It is another object of the present invention to provide an electromagnetic 
spring-wound clutch which disengages quickly and smoothly. 
It is another object of the present invention to eliminate a major cause of 
vibration and noise in an electromagnetic spring-wound clutch. 
It is another object of the present invention to eliminate a major cause of 
damage in an electromagnetic spring-wound clutch. 
It is another object of the present invention to provide a generally 
improved electromagnetic spring-wound clutch. 
Other objects, together with the foregoing, are attained in the embodiments 
described in the following description and illustrated in the accompanying 
drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
While the electromagnetic spring-wound clutch of the present invention is 
susceptible of numerous physical embodiments, depending upon the 
environment and requirements of use, substantial numbers of the herein 
shown and described embodiments have been made, tested and used, and all 
have performed in an eminently satisfactory manner. 
Referring now to FIG. 1 of the drawing, an electromagnetic spring-wound 
clutch embodying the present invention is generally designated as 11 and 
comprises a tubular hub 12 which is rigidly mounted to a compressor 13 of 
an air conditioning system for an automotive vehicle (not shown) by means 
of a flange 12a of the hub 12 and bolts 14. An inner race 16a of a ball 
bearing 16 is fitted over the hub 12 and is rigidly held in place by means 
of a nut 17 screwed onto a threaded right end portion of the hub 12 and an 
intervening lock washer 18. A tubular input member 19 is tightly fit onto 
an outer race 16b of the bearing 16 and rigidly held in place by means of 
a reduced diameter right shoulder and a left end of the input member 19, 
the latter being crimped over the left end of the outer race 16b. An 
annular member 21 having a hollow cross-section is press fitted onto the 
input member 19. The left wall of the annular member 21 is cut away, and a 
plurality of circumferentially spaced, arcuate slots 21a are formed 
through the right wall of the annular member 21, although only one slot 
21a is visible in the drawing. A pulley 22 is press fitted onto the 
annular member 21 and connected to an engine of the automotive vehicle 
(not shown) through a V-belt 23. 
Another annular member 24 is welded to the flange 12a of the hub 12 and 
fits inside the hollow of the annular member 21 without touching the same. 
The right wall of the annular member 24 is cut away. Rigidly mounted 
inside the annular member 24 is an electromagnetic coil 26 which may be 
energized through leads which are not shown. 
A generally tubular output member 28 is rotatably supported inside the hub 
12. An output shaft 29 is threaded at its right end and rigidly fixed to 
the output member 28 by means of a nut 31 and conjugate shoulders of the 
shaft 29 and output member 28. The output shaft 29 is constituted by a 
drive shaft of the compressor 13, although the connection is not shown in 
detail. 
An annular clutch disc 32 is rotatably provided around the input member 19. 
A coil-wound spring 33 is wound around the input member 19. One end of the 
spring 33 is connected to the clutch disc 32 by means of a radially 
outwardly extending tab 33a of the spring 33 which fits in a slot 32a 
formed in the inner circumference of the clutch disc 32. The other end of 
the spring 33 is connected to the output member 28 by means of a radially 
inwardly extending tab 33b of the spring 33 which fits in a slot 28a 
formed in the outer circumference of the output member 28. The clutch 11 
further comprises a cover member 34 which is welded or otherwise firmly 
attached to the output member 28. The cover 34 encloses the coil-wound 
spring 33 and extends adjacent to the clutch disc 32. The radially outer 
portion of the generally cup-shaped cover 34 constitutes a flange portion 
(not designated). 
As best seen in FIGS. 2 to 4, a plurality (3 or more) of arcuate slots 34a 
are formed through the outer portion of the cover 34 which faces the 
clutch disc 32. A pin 36 having left and right heads 36a and 36b 
respectively slidably extends through each slot 34a, the diameter of the 
pin 36 being substantially the same as that of the slot 34a. Conjugate to 
the slots 34a, circumferential spaced holes 32b are formed through the 
clutch disc 32. Each hole 32b comprises a small portion 32c having a width 
equal to the diameter of the pin 36 and a large portion 32d having a width 
greater than a diameter of the left head 36a of the pin 36. The clutch 
disc 32 is supported by the pins 36 and guided thereby for axial movement 
in parallelism with the annular member 21. 
As best seen in FIGS. 3 and 4 the clutch 11 further comprises a plurality 
of resilient members or bumpers 42 made of plastic, rubber or the like 
which are press fitted into circumferentially spaced holes 34b in the 
cover 34 so as to face the clutch disc 32. Upon disengagement of the 
clutch disc 32 from the annular member 21 the clutch disc 32 is urged into 
engagement with the bumpers 42 rather than with the facing surface of the 
cover 34 as will become apparent from further description. 
In accordance with an important feature of the present invention, the cover 
34 is made of a relatively soft, low carbon steel to facilitate press 
forming and is formed with a plurality of circumferentially spaced holes 
34c, with each hole 34c being circumferentially spaced between two 
adjacent holes 34b and slots 34a. Projecting members in the form of rivets 
43 are press fitted in the holes 34c and project external of the cover 34 
toward the spring 41. The rivets 43 are made of a material which is harder 
and more abrasion resistant than the cover 34, typically high carbon steel 
or high carbon chromium steel. The ends of the rivets 43 engage with the 
spring 41, thereby preventing the spring 41 from directly engaging with 
the cover 34. In accordance with another important feature of the present 
invention, portions of the spring 41 which engage with the rivets 43 are 
resiliently flexed external of or beyond the heads 36b of the pins 36, or 
rightwardly of the heads 36b as viewed in FIG. 3. This causes the spring 
41 to exert an axial force on the clutch disc 32 through the pins 36 which 
urges the clutch disc 32 rightwardly away from the annular member 21 and 
toward engagement with the bumpers 42. 
In operation, the input member 19, annular member 21 and pulley 22 are 
mutually coaxial and are driven by the V-belt 23 in an integral manner. 
The output member 28, output shaft 29 and cover 34 are also mutually 
coaxial and rotate as a unit. 
With the coil 26 de-energized, the spring 41 urges the clutch disc 32 out 
of engagement with the annular member 21 and into engagement with the 
bumpers 42. The annular member 21 rotates relative to the clutch disc 32, 
which remains stationary. There is no driving connection between the 
pulley 22 and output shaft 29, and the output shaft 29 remains stationary. 
To engage the clutch 11 and drive the compressor 13 from the pulley 22 by 
means of the output shaft 29, the coil 26 is energized with electric 
current. A magnetic circuit is established from the coil 26 through the 
slots 21a of the annular member 21 and the clutch disc 32 indicated by a 
phantom line curve 38 in FIG. 1. This attracts the clutch disc 32 
leftwardly into frictional engagement with the annular member 21 against 
the force of the spring 41. The clutch disc 32 rotates with the annular 
member 21, winding the coil-wound spring 33 tightly around the input 
member 19. Due to the provision of the tabs 33a and 33b and slots 32a and 
28a, the output member 28 is drivingly connected to the input member 19 
through the clutch disc 32 and spring 33. The pulley 22, output shaft 29 
and intervening components rotate as a unit, driving the compressor 13 
from the engine. The rotational movement of the clutch disc 32 relative to 
the cover 34 necessary for winding the coil-wound spring 33 around the 
input member 19 is made possible by the slots 34a in the cover 34. 
To disengage the clutch 11, the coil 26 is de-energized, thereby removing 
the magnetic attractive force from the clutch disc 32. The spring 41 
immediately and smoothly moves the clutch disc 32 away from the annular 
member 21 and into abutting engagement with the bumpers 42. 
It will be noted that the clutch disc 32 is maintained parallel to the 
annular member 21 by the pins 36, and thereby engages and disengages the 
annular member 21 in a completely smooth manner. Vibration, noise and 
damage to the clutch disc 32 are positively prevented by the spring 41 
which immediately disengages the clutch disc 32 from the annular member 21 
upon de-energization of the coil 26. 
Although only one coil-wound spring 33 is shown and illustrated, it will be 
understood by those skilled in the art that two intertwined coil-wound 
springs may be provided. 
It will be noted that the spring 41 needs to exert only a small force on 
the clutch disc 32 since it is necessary only to overcome frictional 
forces of the clutch disc 32 on the pins 36. Where the tabs 33a and 33b of 
the coil-wound spring 33 are axially slidably retained in the slots 32a 
and 28a of the clutch disc 32 and output member 28 respectively, the 
clutch disc 32 may move axially without axial expansion and contraction of 
the spring 33. Thus, the coil 26 does not have to exert a large force on 
the clutch disc 32, and may be of a small size suitable for the overall 
configuration of the clutch 11. 
The bumpers 42 function to prevent impact and vibration of the clutch disc 
32 against the cover 34. The rivets 43 serve the dual function of flexing 
the spring 41 so as to cause the spring 41 to exert an axial force on the 
clutch disc 32 through the pins 36 and to prevent abrasion of the 
relatively soft cover 34 by the relatively hard spring 41. During 
engagement and disengagement of the clutch disc 32, the spring 41 slides 
on the rivets 43 rather than the cover 34. Since both the rivets 43 and 
spring 41 are made of a hard and abrasion resistant material such as high 
carbon steel, abrasion of these elements is minimal even after prolonged 
operation of the clutch 11. Thus, the clutch 11 is smoother and quieter in 
operation, has a longer service life and reduced maintenance requirements 
over the prior art. The present invention further eliminates the 
manufacturing step of forming the annular spring into a wave shape or 
forming tabs on the spring. 
If desired, the rivets 43 may be formed of a relatively soft base or core 
with only the ends which engage with the spring 41 hardened. 
A modification of the rivets 43 is illustrated in FIG. 5. Here, each rivet 
44 is formed with a substantially flat end 44a which engages with the 
spring 41. This arrangement serves to reduce the surface pressure at the 
engaging surfaces of the rivets 44 and spring 41 by distributing the 
pressure over a relatively larger area. 
FIG. 6 shows another modification in which each rivet 46 comprises a metal 
base 46a which is press fitted into the respective hole 34c and a hard, 
low friction material 46b such as rubber or plastic which is thermally 
fused onto the base 46a. At least one annular groove 46c is formed in the 
base 46a to aid in retention of the material 46b to the base 46a. The 
rivets 46 feature yet further reduced vibration and noise due to reduced 
friction between the ends of the rivets 46 and the spring 41 during 
engagement and disengagement of the clutch disc 32. 
In summary, it will be seen that the present invention overcomes the 
problems of the prior art and provides an electromagnetic coil-wound 
clutch which is completely free from vibration, noise and damage upon 
disengagement thereof. Various modifications will become possible for 
those skilled in the art after receiving the teachings of the present 
disclosure without departing from the scope thereof. For example, the 
clutch disc may be formed with arcuate slots and the cover formed with 
conjugate round holes in a manner opposite to that illustrated.