Coupling mechanism for a compressor

A coupling mechanism for a compressor of an automotive air conditioning system which is equipped with a safety mechanism for preventing damage to the engine due to compressor failure or malfunction. A front end plate with a tubular extension which extends in the direction parallel to the axis of rotation of the drive shaft is attached to one end of the compressor housing. A pulley is rotatably supported on said extension by means of a bearing. At its terminal end, the drive shaft is connected to an armature which includes a centrally located hole through which the drive shaft extends. The armature is connected by means of a bolt and a nut and rotates with the drive shaft. The pulley transmits rotational motion from the engine to the drive shaft through an armature plate by means of coupling plate members which are interposed between the pulley and the armature plate. Coupling plate members include breakaway portions which may be easily broken if excessive torque is applied due to compressor failure or malfunction. If the compressor failure or malfunction occurs and the drive shaft stops rotating, damage to the engine is avoided because the excessive torque applied by the pulley causes the breakaway portions of the coupling plate members to break and allows the pulley and coupling members to be disconnected from each other. This allows each to continue to rotate independently without contacting or biting each other.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a coupling mechanism for a refrigerant compressor, 
and more particularly, to a mechanism for disconnecting the drive shaft of 
the compressor from a drive pulley in the event of a compressor failure or 
malfunction. 
2. Description of the Prior Art 
In a standard automotive air conditioning system, an electromagnetic clutch 
is interposed between the automotive engine and the drive shaft of the 
compressor to intermittently transmit the rotational driving force of the 
engine to the drive shaft. The operation of the electromagnetic clutch is 
controlled by a change in the operating conditions of the air conditioning 
system, e.g., a change of temperature in the passenger compartment. 
In the event of a compressor failure or malfunction, the clutch should 
operate to disconnect the engine from the compressor to prevent 
transmission of the rotational driving force from the engine. 
Nevertheless, because the clutch is usually loaded in a compressor which 
has a variable displacement mechanism enabling the compressor to change 
its capacity in direct response to changes in operating conditions, the 
electromagnetic clutch is not necessary to obtain satisfactory control of 
the refrigeration or temperature condition of the air conditioning system. 
It is necessary, however, to provide the compressor with a safety 
mechanism to prevent damage to other parts of the engine or the air 
conditioning system in the event of a compressor failure or malfunction. 
The electromagnetic clutch serves as an expensive solution to this 
problem. 
One example of an automotive air conditioning system compressor which does 
not made use of an electromagnetic clutch is disclosed in U.S. Pat. No. 
3,861,829 to Roberts et al. Moreover, the present invention constitutes a 
novel and advantageous improvement over the coupling mechanism for 
compressors disclosed in U.S. Pat. No. 4,859,156 to Kirkuchi, which is 
incorporated herein by reference. As shown in the compressor of FIG. 1, 
the compressor includes compressor housing 10 and front end plate 11 
attached to an open end of housing 10. Drive shaft 12 is rotatably 
supported within front end plate 11. Tubular extension 1 la extends 
outwardly from front end plate 11 and surrounds drive shaft 12. 
Pulley 14 is rotatably supported on the peripheral outer surface of tubular 
extension 11a through bearing 15. Pulley 14 is securely fitted on the 
peripheral outer surface of bearing 15 by snap ring 26 disposed between 
the inner surface of pulley 14 and the inner end surface, with respect to 
housing 10, of bearing 15. Moreover, snap ring 26 prevents pulley 14 from 
moving parallel to the rotational axis of drive shaft 12. Bearing 15 is 
secured between flange 11b and snap ring 19 which is fixed on the 
peripheral outer surface of tubular extension 11a. 
Armature 13 has a centrally located hole and is secured on the terminal 
outer end portion of drive shaft 12 by a bolt 12a and a nut 33. Armature 
13 is also coupled with drive shaft 12 by the interaction of key 20 on the 
end of drive shaft 12 with key groove 22 in the centrally located hole of 
plate-like element 13. 
A plurality of cylindrical members 28 are disposed between the inner axial 
surface, with respect to housing 10, of armature 13 and the outer axial 
surface, also with respect to housing 10, of pulley 14 to couple armature 
13 to pulley 14. Holes 13a are formed on the inner axial surface of 
armature 13, and one end of each cylindrical member 28 is disposed 
therein. The other end of each cylindrical member 28 is disposed in 
corresponding hole 14a formed on the outer axial surface of pulley 14. 
Cylindrical members 28 may be made of synthetic resins or metals which are 
easily broken if a large torque acts between pulley 14 and armature 13, 
i.e., a sufficiently large force which acts to rotate pulley 14 with 
respect to armature 13. 
In ordinary operation of such a coupling mechanism, the driving force of 
the engine is transmitted to pulley 14 by a belt (not shown) and is then 
transferred to drive shaft 12 of a compressor through cylindrical members 
28 and armature 13. In this manner, drive shaft 12 is rotated. If, during 
the operation of the compressor, a failure or malfunction occurs, and as a 
result of the failure or malfunction the rotation of drive shaft 12 is 
interrupted, the rotation of armature 13 is also interrupted due to the 
coupling of armature 13 with drive shaft 12. Nevertheless, a large 
rotational force is still provided to pulley 14 by the engine, and pulley 
14 consequently provides a large torque to armature 13 through cylindrical 
members 28. This torque is sufficient to break cylindrical members 28 
because cylindrical members 28 are designed to break when such a torque is 
applied. As a result, pulley 14 is disconnected from armature 13 and is 
free to rotate without resistance applied through armature 13 from 
motionless drive shaft 12. The maximum acceptable amount of torque and 
consequently, the size, material, and number of cylindrical members 28 is 
dependent on the air conditioning system and the compressor with which the 
coupling mechanism is used. 
This configuration, however, has certain disadvantages. If the compressor 
should lock or become difficult to rotate due to compressor failure or 
malfunction, pulley 14 is subjected to excessive torque through 
cylindrical members 28. When this torque breaks cylindrical members 28, 
each cylindrical member 28 may be broken at a different location, i.e., 
one cylindrical member 28 may be broken on armature 13 side while another 
is broken on pulley 14 side. As a result, the broken sections of 
cylindrical members 28 contact or bite each other, and pulley 14 cannot be 
sufficiently disconnected from armature 13 to allow it to rotate freely. 
Therefore, the torque applied through these contacts or bites is likely to 
damage the engine and other parts of the driving system, such as the 
alternator, a cooling fan, or a power steering mechanism, which rotate 
together by the belt. 
Further, in this configuration, the diameters of holes 13a of armature 13 
and holes 14a of pulley 14 should be almost the same as the diameter of 
cylindrical member 28 because both ends of each cylindrical member 28 must 
be inserted tightly into holes 13a and holes 14a to securely connect 
armature 6 with pulley 14. Therefore, if these diameters are different 
from each other due to an error in manufacturing, it usually prevents the 
armature 13 from being secured to pulley 14 during assembly. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide an improved coupling mechanism 
for a driven member, e.g., a pulley, which prevents damage to an 
automotive engine in the event of a failure or malfunction of the driven 
member. The driven member may be a compressor for an automotive air 
conditioning system. 
It is another object of this invention to provide an easily assembled 
coupling mechanism for a driven member. 
According to the present invention, a coupling mechanism for a compressor 
comprises a compressor housing having an open end surface. A front end 
plate attaches to the open end surface of the compressor housing. A drive 
shaft is rotatably disposed within the compressor housing. The drive shaft 
has an outer end portion terminating outside of the compressor housing and 
a tubular extension extending outwardly from a front end plate parallel to 
the rotational axis of the drive shaft. A pulley is rotationally supported 
on a bearing fitted on a peripheral outer surface of the tubular 
extension. An armature includes a hub formed at a center of the armature 
and annular armature plate extending outwardly from the hub portion. The 
armature is connected to the outer end portion of the drive shaft. The 
coupling mechanism comprises coupling plate members including a first 
portion located at an inner radial end and a second portion located at an 
outer radial end of each of the plate members and a third portion located 
between each first portion and second portion. The third portion of the 
plate member connects the first portion to the second portion of the plate 
member. 
These plate members are connected with the armature and the pulley at 
regular angular intervals around the circumference of the hub of the 
armature, so that the first portions of these plate members are secured to 
an axial end surface of the armature plate by at least one fastening 
means, and the second portions of the plate members are secured to an 
axial end surface of the pulley by at least one fastening means. Each 
plate member also includes at least one breakaway portion, i.e., a portion 
which fractures or gives way under a predetermined amount of torque or 
other applied mechanical force, formed at the third portion of the plate 
member. In one embodiment, breakaway portions are designed to be easily 
broken in the event that they receive a large torque due to compressor 
failure or malfunction. Further, the first portions of the plate members 
may be located on a first circular plane which is parallel to the axial 
surface of the pulley. The second portions of the plate members may be 
located on a second circular plane which is parallel to the axial surface 
of the pulley. The first portions of the plate members are positioned with 
respect to the second portions of the plate members, so that the material 
of each plate member will be elastically deformed, and the first plane is 
axially offset from the second circular plane. Therefore, if the 
compressor fails or malfunctions and the drive shaft stops rotating, 
damage to engine or the driving system is avoided because the torque 
applied by the pulley causes the breakaway portions to release the plate 
members from the pulley and to disconnect the armature plate from the 
pulley, so that each may rotate without contacting or biting the other. 
Other objects, advantages, and features will be apparent when the detailed 
description of the invention and the drawings are considered.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiments of the present invention share many components 
with the compressor depicted in FIG. 1 except for the construction of 
coupling mechanism between a drive shaft and a pulley. Therefore, similar 
parts are represented by the same reference numerals as in FIG. 1, and the 
detailed description of the similar parts will be omitted in order to 
simplify the following description of the preferred embodiments. 
Referring to FIGS. 3 and 4a-b, a coupling mechanism according to a first 
embodiment of the present invention is depicted. Pulley 14 includes a 
plurality of holes 14a, e.g., four holes 14a, formed in an axial end 
surface of pulley 14 for connecting pulley 14 with coupling plate 7. Holes 
14a of pulley 14 are spaced at regular angular intervals, i.e., 
90.degree., around the circumference of pulley 14 and around the axial 
center of pulley 14. Armature 6 includes hub 6a formed as a cylinder and 
armature plate 6b formed as annular plate extending from the axial end of 
hub 6a. Armature plate 6b includes a plurality of holes, e.g., four pairs 
of holes 6c, formed in armature plate 6b. Four pairs of holes 6c are 
formed at regular angular intervals, i.e., 90.degree., around the 
circumference of armature plate 6b and around hub 6a. Coupling plate 
member 7, which is rectangular in shape, divides plate member 7 into an 
inner plate portion 7a having a plurality of holes 7f, e.g., two holes 7f, 
a center plate portion 7c in the center of plate member 7, and outer plate 
portion 7b having at least one hole 7e. Center plate portion 7c is formed 
between inner plate portion 7a and outer plate portion 7b and includes a 
notched or breakaway portion 7d which is partly cut-out from plate member 
7. Thus, the width of center plate portion 7c is more slender than any 
other portion of plate member 7, so that plate member 7 may be easily 
broken at center plate portion 7c when excessive torque is applied. Four 
plate members 7 may be radially placed on the inner axial surface of 
armature 6 at regular angular intervals of 90.degree. around the 
circumference of armature 6 and around hub 6a and may be connected with 
armature 6 by four pairs of rivets 8, so that four pairs of holes 7f of 
plate members 7 correspond to and are aligned with four pairs of holes 6c 
of armature plate 6b. Further, plate member 7 may be made of an elastic 
material. 
Four plate members 7 are also secured to pulley 14 at regular angular 
intervals of 90.degree. around the circumference of pulley 14 and around a 
radial surface of drive shaft 12, so that bolts 30 pass through washer 9 
and holes 7e of each plate member 7. Bolts 30 screw into holes 14a of 
pulley 14, and outer plate portions 7b are axially offset from inner plate 
portion 7a. Center plate portions 7c are inclined toward pulley 14, 
thereby elastically deforming the material for plate member 7. If a 
distance L extends between the axial inner surface of plate member 7 which 
is secured to armature plate 6b by rivets 8 and the axial outer surface of 
plate member 7 which secured to pulley 14 by bolts 10, distance L must be 
greater than zero. Alternatively, plate member 7 and pulley 14 and 
armature 6 may not be provided with any holes for connecting by bolts 30 
or rivets 8. Instead, armature 6 may be connected to pulley 14 through 
plate member 7 by means of brazing, spot welding, or the like. 
Referring to FIGS. 3 and 5a-b, a coupling mechanism according to a second 
embodiment of the present invention is depicted. Coupling plate member 18 
includes center hole 18a formed in the center of plate member 18 through 
which hub 6a passes and an annular portion 18b extending outward from the 
radial edge of center hole 18a. Plate member 18 includes a plurality of 
holes 18c, e.g., four holes 18c, formed at regular angular intervals, 
e.g., 90.degree., around the circumference of plate member 18 and around 
hub 6a. Projection 17 is rectangular shaped and extends outward from the 
radial edge of annular portion 18b. Projection 17 is divided into inner 
plate portion 17a, center plate portion 17c, and outer plate portion 17b 
which has at least one hole 17e. Center plate portion 17c is formed 
between inner plate portion 17a and outer plate portion 17b and includes 
notched or breakaway portion 17d partly cut out from projection 17. 
Notched portion 17d is more slender than any other portion of plate member 
18, so that it may easily break center plate portion 17c when excessive 
torque is applied. Plate 18 member is connected with armature 6 by a 
plurality of rivets 8, e.g., four rivets 8, at regular angular intervals 
of 90.degree. around the circumference of armature 6 and around hub 6a, so 
that holes 18c correspond to and are aligned with holes 6c of armature 6. 
Further, plate member 18 is secured to pulley 14 through washer 9 with 
bolts 30 at regular angular intervals of 90.degree. around the 
circumference of plate member 18 and around a radial surface of drive 
shaft 12, so that bolts 30 pass through washer 9 and holes 17e of 
projection 17 and screw into holes 14a of pulley 14. Outer plate portions 
17b are axially offset to inner plate portion 17a and center plate 
portions 17c are inclined toward pulley 14, thereby elastically deforming 
the material for coupling plate 18. Alternatively, projection 17 and 
pulley 14 and armature 6 may not be provided with any holes for connecting 
by bolts 30 or rivets 8. Instead, armature 6a-b may be coupled with pulley 
14 through coupling plate 17 by means of brazing, spot welding, or the 
like. 
Referring to FIGS. 3 and 6, a coupling mechanism according to a third 
embodiment of the present invention is depicted. Armature 16 includes 
cylindrical hub 16a and annular armature plate 16b extending outward from 
the axial end of hub 16a. Armature 16 also includes a plurality of 
projections 27, e.g., four projections 27, which are rectangular shaped 
and extend outwardly from the axial edge of armature plate 16b. 
Projections 27 are radially arranged at regular angular intervals, e.g., 
90.degree., around the circumference of armature plate 16b and around hub 
16a of armature 16. Projection 27 includes inner plate portion 27a, center 
plate portion 27c, and outer plate portion 27b which has at least one hole 
27e. Center plate portion 27c is formed between inner plate portion 27a 
and outer plate portion 27b and includes notched portion 27d partly cut 
out from projection 27. Notched portion 27d is more slender than any other 
portion of projection 27, so that it may easily break in center plate 
portion 27c when a large torque is applied. Further, armature 16 and 
projection 27 may be made of an elastic material. 
Projections 27 may be secured to pulley 14 by bolts 30 at regular angular 
intervals, e.g., 90.degree., around the circumference of pulley 14 and 
around a radial surface of drive shaft 12, so that bolts 30 pass through 
washer 9 and holes 27e of projection 27 and screw into hole 14a of pulley 
14. Outer plate portions 27b are axially offset from inner plate portions 
27a, and center plate portions 27c are inclined toward pulley 14, thereby 
elastically deforming the material of armature 16 and 27. 
Referring to FIGS. 4a-b and 7, a coupling mechanism according to a fourth 
embodiment of the present invention is depicted. This embodiment is 
similar to a foregoing embodiment except for the construction of the 
connecting system between coupling plate member 7 and pulley 14. Four 
plate members 7 are secured to pulley 14 at regular angular intervals of 
90.degree. around a circumference of pulley 14 and around a radial surface 
of drive shaft 12, so that bolts 30 pass through washer 9 and holes 7e of 
plate member 7 and screw into holes 14a of pulley 14. Each notched or 
breakaway portion 7d of plate member 7 is formed, such that it is located 
at a predetermined radius from hub 6a of armature 6. Thus, center plate 
portion 7c remain intact without being offset from or inclining toward 
pulley 14. 
During assembly, referring to FIGS. 3 and 4a-b, four coupling plates 7 are 
secured to armature 6 by four pairs of rivets 8, so that holes 6c of 
armature 6 correspond to and are aligned with holes 7f of plate members 7. 
Four plate members 7 are secured to pulley 14, so that four holes 7e of 
plate member 7 correspond to and are aligned with four holes 14a of pulley 
14, and bolts 30 pass through washer 9 and four holes 7e and screw into 
holes 14a of pulley 14. In this embodiment, the diameter of hole 7e is 
designed to be larger than the diameter of hole 14a of pulley 14. 
Therefore, unlike the prior art, if alignment between the center of hole 
7e and the center of hole 14a varies due to the circumferential and radial 
variations in the assembly of the invention, armature plate 6b can be 
easily and quickly secured to pulley 14 by adjusting the center position 
of hole 7e. 
Referring to FIG. 3, if a failure or compressor malfunction occurs during 
the operation, pulley 14 may be subjected to excessive torque through 
coupling plate member 7 and bolts 30. This torque may be sufficient to 
destroy center plate portion 7c of plate member 7 because the center 
portion 7c is designed to breakaway at breakaway portion 7d when such 
excessive torque is experienced. The maximum amount of torque which the 
center portion 7c is designed to withstand and the size, material, and 
number of coupling plate members depends on the air conditioning system 
and the compressor in which the coupling mechanism is used. Therefore, 
when center portion 7c breaks away, pulley 14 is disconnected from plate 
members 7 and is free to rotate without the resistance caused by the 
rotation of drive shaft 12 as applied to pulley 14. When center plate 
portion 7c is broken at breakaway portion 7d, one broken section of center 
plate portion 7c on inner plate side is separated from and radially 
parallel to the other broken section of center plate portion 7c on outer 
plate portion 7b side. The broken sections do not contact each other 
because center plate portion 7b is no longer subject to elastic 
deformation and portions 7a and 7b of plate member may rotate on parallel 
planes. Moreover, the distance L is large enough to prevent contact or 
biting between the broken sections. 
Referring to FIG. 7, if the compressor failure or malfunction of during the 
operation, pulley 14 is subjected excessive torque through coupling plate 
members 7 and bolts 30 due to a compressor failure. Center plate portions 
7c are broken at breakaway portions 7d in this configuration. The broken 
sections of center plate portion 7c remaining on inner plate portion 7a 
are separated from the other broken sections of center plate portion 7c 
remaining on outer plate portion 7b and do not contact each other because 
notched breakaway 7d of plate member 7 are located at a predetermined 
radius from hub 6a of armature 6. 
As a result, if the compressor failure or malfunction occurs, coupling 
plate members 7 are broken at the location of breakaway portions 7d which 
are located at the predetermined radius from hub 6a of armature 6. One 
broken section of plate member 7 remaining attached to armature 6 does not 
contact or bite the other broken section of plate member 7 remaining 
attached to pulley 14. Therefore, unlike the prior art, the invention 
avoids damaging the engine and other parts of the driving system, such as 
an alternator, a cooling fan, a power steering which rotates together by a 
belt. 
Although a detailed description of preferred embodiments of the present 
invention has been provided above, it is to be understood that the scope 
of the invention is not to be limited thereby, but is to be determined by 
the claims which follow.