Drive hub with curved springs and drive keys for electro-magnetic clutch

An electromagnetic clutch for transmitting driving torque from one rotatable element to another having particular utility for driving a vane-type compressor used in an automotive air conditioning system in a manner to reduce the cost of such clutches as well as the axial length and weight. The clutch includes a rotatably driven pulley assembly connected to a hub affixed to the input drive shaft of the compressor through an armature disk and friction face on the pulley assembly by selectively energizing and deenergizing a magnetic coil with the armature disk being connected to the hub through a plurality of curved leaf springs and a plurality of drive keys received in recesses or notches with the curved springs replacing the normal flat springs which are used to support the armature disk with the curved springs including a linear flexibility and axial flexibility. The flexibility permits the compressor shaft to yield thereby avoiding binding of the compressor rotor and also provides a significantly shorter clutch assembly by eliminating a rubber "sandwich" hub assembly which is especially important in smaller automobiles and reduces the weight of the clutch by a significant amount. With the drive keys and recesses or notches, there is no restriction to radial or axial deflection, but the drive keys and recesses limits the linear deflection of the springs so that they will not deflect beyond a predetermined point which would cause them to take a permanent set during initial clutch engagement when the clutch torque is extremely high.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to an electromagnetic clutch and 
more particularly a clutch using curved flat leaf springs to transmit 
torque and permit axial flexibility of the axially movable component of 
the clutch, together with a key and notch drive connection to enable 
limited relative rotational movement between the inner and outer ends of 
the springs thereby assuring that the springs will not be deflected beyond 
their elastic limit during high torque startup of the compressor of an air 
conditioning unit in an automobile. 
2. Description of the Prior Art 
In the development of electromagnetic clutches for driving air conditioning 
compressors in an automobile, my prior U.S. Pat. No. 3,565,223 issued Feb. 
23, 1971, discloses one structure which has been known for a number of 
years in which flat leaf springs are used to transmit torque and a 
resilient insert is incorporated into the hub to provide flexibility or 
resiliency in the drive connection to the input shaft of the compressor. 
Prior U.S. Pat. No. 3,205,989, issued Sept. 14, 1965, discloses another 
type of electromagnetic clutch using similar straight flat leaf springs 
and a resilient coupling in the drive train. While such devices have 
operated satisfactorily, it is noted that the resilient insert 
arrangements utilizing rubber or some other resilient plastic material 
materially increases the over-all length and other dimensional 
characteristics of the clutch and, of course, increases the weight of the 
clutch as well as the cost thereof, all of which are desired to be 
maintained at a minimum. In both of the prior art patents mentioned above 
and in other similar devices on the market, a pulley is driven from a belt 
connecting with the crank shaft or other rotatable component of an 
internal combustion engine and drives the input shaft of a compressor 
through a magnetic clutch and a resilient coupling. Basically, the 
magnetic clutch includes an axially movable armature disk connected to the 
hub of the clutch through flat leaf springs which enables axial movement 
of the armature disk and transmits torque to the hub which is connected to 
the input shaft. The armature disk is attracted to a friction face on the 
rotatable pulley through an energizable magnetic coil. Also, a resilient 
insert is interposed in the drive coupling between the pulley and input 
shaft of the compressor to prevent binding of the compressor shaft or 
rotor. The previously patented and existing electromagnetic clutches are 
somewhat bulky, include many components, are relatively heavy and have a 
substantial over-all length. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an electromagnetic clutch 
incorporating curved flat leaf springs interconnecting the armature disk 
and hub in an electromagnetic clutch to provide for radial, 
circumferential and axial flexibility and to replace the presently used 
straight flat leaf springs and a rubber "sandwich" type flexible hub in 
which the curved springs serve the dual function of the presently used 
flat leaf springs and the "sandwich" type flexible and resilient rubber 
hub. 
Another object of the invention is to provide an electromagnetic clutch in 
accordance with the preceding object in which the hub includes a 
mechanical driving connection incorporating radially disposed keys or lugs 
received in correspondingly shaped radially disposed recesses or notches 
having a larger circumferential dimension than the keys or lugs to enable 
limited relative rotation between two components of the hub, thereby 
limiting the deflection of the curved springs during high torque 
transmission periods to prevent the springs from being deflected or bent 
beyond their elastic limit, thereby preventing such springs from taking a 
permanent set due to being deflected beyond their elastic limit. 
Still another object of the invention is to provide an electromagnetic 
clutch in accordance with the preceding objects in which the curved 
springs and drive keys and recesses which provides for radial, 
circumferential and axial flexibility which enables driving engagement and 
release of the armature disk of the clutch and limits the deflection or 
linear elongation of the springs to eliminate permanently setting the 
springs also provides for a fewer number of parts, a significantly shorter 
clutch assembly and a weight reduction of the assembly all of which are of 
significant benefit when installing the electromagnetic clutch in an 
automobile to drive the compressor of the air conditioning system from a 
belt or belts driven from the crank shaft or other pulley of an internal 
combustion engine, or the like. 
These together with other objects and advantages which will become 
subsequently apparent reside in the details of construction and operation 
as more fully hereinafter described and claimed, reference being had to 
the accompanying drawings forming a part hereof, wherein like numerals 
refer to like parts throughout.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now specifically to the drawings, a compressor 10 is illustrated 
somewhat schematically in FIG. 2 which may be a vane-type compressor 
utilized in an automobile air conditioning system with the electromagnetic 
clutch 12 of the present invention being associated therewith in a manner 
similar to that disclosed in my prior U.S. Pat. No. 3,565,223 which 
disclosure is incorporated herein by reference thereto with FIG. 2 of the 
drawings in this application being comparable to FIG. 1 of the drawings in 
U.S. Pat. No. 3,565,223. 
The compressor 10 includes a stationary and rigid collar or sleeve 14 
projecting from the compressor housing and a compressor drive shaft or 
input shaft 16 is disposed centrally in the collar 14 with rotation of the 
shaft 16 causing rotation of the rotor of the vane-type compressor in a 
conventional and well-known manner. 
A stationary coil shell 18 is supported fixedly from a shoulder on the 
compressor 10 by suitable brackets 20 and a magnetic coil 22 is positioned 
within the interior of the coil shell 18 in a manner well-known in the 
art. 
Rotatably journaled from the projecting collar 14 is a pulley 24 having one 
or more pulley grooves 26 formed in the outer rim 28 thereof. The pulley 
24 also includes a clutch plate 30 having an axial friction face 32 and 
arcuate slots 34 therein in a conventional manner. The inner edge of the 
plate 30 is provided with a sleeve or rim 36 concentric with the collar 14 
and journaled therefrom by a bearing assembly 38 in the form of a double 
ball bearing arrangement 40 held in place by snap rings 42 and 44 in a 
conventional and well-known manner so that the pulley 24 is rotatably 
supported from the stationary collar 14 while the coil shell and magnetic 
coil are fixedly supported from the compressor 10 by the brackets 20, all 
of which represents conventional electromagnetic clutch structure. 
Attached to the compressor input drive shaft 16 is a hub 46 having a sleeve 
48 telescoped over the shaft 16 and keyed thereto in a conventional manner 
and retained in position thereon by an axial bolt 50. The hub 46 includes 
a hub plate 52 rigid therewith and extending radially outwardly generally 
a distance to cover the inner edge of the annular plate 30 of the pulley 
24. Concentrically arranged with respect to the hub plate 52 is an annular 
armature disk or plate 54 which includes an inner face 56 in opposed 
relation to the face 32 on the pulley plate 30 with energization and 
deenergization of the magnetic coil 22 serving to engage the clutch faces 
32 and 56 or permit disengagement thereof. When the clutch faces are 
engaged, rotational movement of the pulley 24 will be transmitted to the 
armature disk 54. 
Interconnecting the hub plate 52 and the armature disk 54 is a plurality of 
arcuate flat leaf springs 58 each of which are generally U-shaped in 
configuration and includes an elongated arcuate central portion 60 and 
inwardly offset end ears or lugs 62 which have apertures 64 therein for 
receiving anchoring rivets 66 with the outer end of each spring 58 being 
riveted to the armature disk 54 adjacent the outer circumference thereof 
and the inner end being connected to the hub plate 52 for transmitting 
drive torque therebetween with the central portion 60 of the spring 58 
being deflected from its normal curved condition during transmission of 
torque to provide a resilient drive coupling between the armature disk 54 
and the compressor input shaft 16. The flat leaf spring structure also 
provides axial flexibility for movement of the armature disk toward and 
away from the face 32 of the pulley plate 30 so that the springs 58 are 
used to replace both the straight leaf springs and the rubber "sandwich" 
hub employed in the aforementioned prior U.S. Pat. No. 3,565,223 with the 
springs 58 serving the dual purpose of the straight springs and the 
"sandwich" hub. The number of springs 58 may vary depending upon the 
installational load requirements. The curved springs replace the flat 
springs as disclosed in the aforementioned patent and support the armature 
disk and the desired axial tension is attained by increasing the 
pretension slightly on the springs to provide the same axial tension as 
the replaced flat springs. The curvature of the springs and the narrow 
width thereof combine to provide a linear flexibility and resiliency to 
the springs when a torque force is applied between the holes to which the 
ends of the springs are riveted. The depth of the curve provides the same 
radial and axial flexibility when assembled as provided by the replaced 
rubber "sandwich" type flexible hub or coupling and this flexibility is 
needed to permit the compressor shaft to yield thereby avoiding the 
compressor rotor from binding which occurs without a flexible or resilient 
drive coupling. The curved springs also provide an advantage by permitting 
a significantly shorter clutch assembly by elimination of the rubber 
"sandwich" hub assembly which is especially important in smaller 
automobiles and also provides an advantage by reducing the weight of the 
electromagnetic clutch by elimination of a rubber "sandwich" hub assembly. 
As illustrated, the rivet hole centers are angularly offset which permits 
the springs to be in tension when the clutch is engaged and driving. This 
angular component prohibits any backlash due to torsional pumping 
vibrations. Thus even if the rivets were slightly loose, they would not 
turn and work loose, whereas if the rivet holes were lined up radially, 
this could occur. 
FIGS. 3-5 illustrate an arrangement in which the deflection of the springs 
58 is limited by the provision of radially extending keys or lugs 68 on 
the hub plate 52 which are received in corresponding recesses or notches 
70 in the inner edge of the armature disk 54. When observing the armature 
disk 54 from the inner surface as in FIG. 3, the keys or lugs 68 will be 
engaged by and positively driven by the trailing surfaces of the recesses 
or notches 70 thereby limiting the deflection or linear straightening of 
the springs 58, thereby preventing them from being bent or deflected 
beyond their elastic limit thereby preventing the springs 58 from taking a 
permanent set. While three drive keys 68 have been shown, more than three 
can be used if desired. In some installations, up to six drive keys have 
been used successfully. When clutch torque is at a maximum value, such as 
when the clutch is engaged at high speeds, the inertia reaction exerts 
substantial forces on the springs. Such forces, in some instances, tend to 
deflect the springs beyond their designed elastic limit and thus cause the 
springs to take a permanent set. Thus, by adding the drive keys, more 
flexibility in design is permitted in the springs in order to maintain 
them at a desired thickness and desired metallurgical composition without 
restricting the radial, circumferential or axial deflection, yet 
eliminating any problem of the spring bending during the initial 
engagement when the clutch torque may read as high as 80 ft. lbs., whereas 
the driving load of the compressor after initial startup is approximately 
one-third of the startup torque. 
The armature disk 54 is provided with the usual arcuate slots 55 therein 
and the hub plate 52 is provided with the usual cover plate 53 secured in 
position by suitable fasteners and which covers the plate 52 and a portion 
of the armature disk 54 in a conventional manner. 
The foregoing is considered as illustrative only of the principles of the 
invention. Further, since numerous modifications and changes will readily 
occur to those skilled in the art, it is not desired to limit the 
invention to the exact construction and operation shown and described, and 
accordingly, all suitable modifications and equivalents may be resorted 
to, falling within the scope of the invention.