Fluid shear coupling apparatus

A fluid shear coupling apparatus is disclosed herein which includes a driving member comprising a rotor mounted to a shaft and defining several annular ridges and grooves. The apparatus further includes a driven member including a bearing housing mounted to the shaft, a cover secured about a perimetric flange with the bearing housing, and a plate secured to the cover and defining several annualr ridges and grooves positioned complementary with the ridges and grooves of the rotor. In the preferred embodiment, the plate, cover, bearing housing and rotor are as-formed structures.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: The present invention relates to the field of 
fluid shear couplings, and particularly to a coupling of the type used as 
a vehicle fan drive in which a rotor is received within a driven member. 
2. Description of the Prior Art: A variety of fluid shear couplings, also 
referred to as viscous couplings, have been proposed in the prior art. 
Many of these couplings include a rotor which is connectable with an 
external drive source and is received within a housing that defines a 
fluid shear chamber. Improvements for such couplings have been proposed 
along many lines including bearing structures, fluid valving, temperature 
controls and torque transfer. A purpose behind most improvements in fluid 
shear couplings is the achievement of a coupling which operates 
efficiently with a minimum of cost and weight. The present invention 
satisfies all of these conditions. 
In the preferred embodiment, the present invention provides a fluid shear 
coupling which includes interdigitated ridges and grooves to increase the 
transmission of torque between the rotor and the driven housing. This 
general feature is disclosed in a number of patents, many of which appear 
in class 192, subclass 58. Examples of patents which disclose 
interdigitated ridges and grooves are the following: U.S. Pat. Nos. 
3,856,122, issued to Leichliter on Dec. 24, 1974; 3,323,623, issued to 
Roper on June 6, 1967; and 3,809,197, issued to Clancey on May 7, 1974. 
The present invention also provides a unique sealing structure for a 
temperature-responsive fluid valve. General valving structures are well 
known in the art and typically assume two forms. One type of valve 
structure utilizes a valve which is spring-biased to pivot outwardly from 
a fluid aperture when a control pin is displaced to permit such pivoting. 
Examples of such valve structures are disclosed in U.S. Pat. Nos. 
4,090,596, issued to Blair on May 23, 1978; 4,086,990, issued to Spence on 
May 2, 1978; 4,036,339, issued to Kikuchi on July 19, 1977; and 3,964,582, 
issued to Mitchell on June 22, 1976. In each of these patents, the pin 
slides through a hole in the cover of the coupling. A sealing member is 
inserted into an annular groove on the inside or fluid side of the cover 
to seal the sliding control pin. A second type of fluid control valve is 
one which is rotated to or from the fluid flow aperture, typically in 
correspondence with a coiled, temperature-sensitive spring. Examples of 
other types of such valve structures are contained in U.S. Pat. Nos. 
4,062,432, issued to Evans on Dec. 13, 1977, and 3,191,733, issued to Weir 
on June 29, 1965. 
Another feature of the present invention is contained in the method and 
structure for coupling the cover and bearing housing of the apparatus. One 
of the conventional methods for securing a cover to a bearing housing is 
by simply bolting the members together. The bolts are typically received 
through flanges which extend outwardly from the central portion of the 
coupling at which the shear surfaces are located. This method typically 
requires the inclusion of a substantial outer flange having a width, along 
a diameter, of sufficient distance to accommodate the several bolts. A 
disadvantage of this approach is that the amount and location of such a 
flange significantly increases the weight of the coupling apparatus and 
also places that weight at the outer perimeter at which the moment of 
inertia is the greatest. Also, the method is relatively slow to perform. 
A second alternative in the prior art has been to provide either the 
bearing housing or the cover with a perimetric flange which is then rolled 
over the edge of the other member to join them together. Examples of this 
construction are contained in U.S. Pat. Nos. 3,011,607, issued to 
Englander on Dec. 5, 1961 and 3,007,560, issued to Weir on Nov. 7, 1961. 
This approach is also shown in the Leichliter, Roper and Clancey patents 
previously identified. Disadvantages of this procedure include a resultant 
distortion of the cover faces, and also the slowness of the process. 
A further aspect of the present invention relates to the formation, 
particularly by casting, of certain components of a fluid shear coupling, 
especially using magnesium or a magnesium alloy. Materials which have 
conventionally been used in formation of the cover, bearing housing and 
rotor for prior art devices have included various steel and aluminum 
compositions. Applicant is not aware, however, of the use of a magnesium 
alloy for this purpose. A further aspect of the present invention is the 
inclusion of a plate which defines the several annular ridges and grooves 
for the driven member of a fluid shear coupling, which plate is mounted to 
the cover member of the coupling. In the prior art, for those devices 
which utilize a driven member having annular ridges and grooves, these 
elements are provided as integral portions of the cover. 
SUMMARY OF THE INVENTION 
Briefly, describing one aspect of the present invention, there is provided 
a fluid shear coupling apparatus which includes a driving member including 
a rotor defining several annular ridges and grooves, and a driven member 
defining complementary annular ridges and grooves. The driven member 
includes a bearing housing coupled with a cover, and a plate which defines 
the ridges and grooves of the driven member is secured to the cover. In 
another aspect, the several ridges and grooves constitute as-formed 
structures. In a further aspect, the bearing housing and cover include 
adjacent, outer perimetric flanges which are secured together by means of 
a magneformed band received thereover. An additional aspect of the present 
invention relates to the use of a magnesium alloy for certain components 
of a fluid shear coupling. 
It is an object of the present invention to provide a fluid shear coupling 
apparatus which is relatively light weight and low in cost, but which 
operates efficiently. 
A further object of the present invention is to provide a fluid shear 
coupling apparatus which is readily assembled and calibrated. 
Another object of the present invention is to provide a fluid shear 
coupling apparatus which requires fewer and less expensive manufacturing 
operations. 
Further objects and advantages of the present invention will become 
apparent from the description of the preferred embodiment which follows.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
For the purposes of promoting an understanding of the principles of the 
invention, reference will now be made to the embodiment illustrated in the 
drawings and specific language will be used to describe the same. It will 
nevertheless be understood that no limitation of the scope of the 
invention is thereby intended. Such alterations and further modifications 
in the illustrated device, and such further applications of the principles 
of the invention as illustrated therein, are contemplated as would 
normally occur to one skilled in the art to which the invention relates. 
Referring in particular to the drawings, there is shown a fluid shear 
coupling apparatus 10 constructed in accordance with the present 
invention. In FIG. 1 there is shown a coupling apparatus in assembled 
form, with certain of the components shown more specifically in the 
subsequent figures. 
The preferred embodiment generally comprises a driving member connected 
with an external drive source, and a driven member mounted to the driving 
member for relative rotation about a common axis. The driven member 
includes a bearing housing 15 and a cover 16 secured together by a metal 
band 17. The driving member includes a disc-shaped rotor 11 secured to a 
shaft 12. The shaft includes a mounting portion 13 which is connectable to 
an external drive source, such as by the reception of bolts (not shown) 
through apertures 14. A typical external drive source is a vehicle engine 
for an embodiment in which the apparatus 10 is used as a coupling device 
for driving a plurality of fan blades mounted to the driven member. 
The rotor 11 is shown to have several annular ridges 18 and grooves 19 
facing in a first direction parallel to the central axis 20. The driven 
member includes a plate 21 mounted to the bearing housing 15 and cover 16. 
The plate 21 includes several annular ridges 22 and grooves 23 facing in a 
second axial direction, opposite the first direction. The ridges and 
grooves of the plate 21 are received adjacent respective grooves and 
ridges of the rotor 11. These provide spaced, opposed shear surfaces 
defining a fluid shear chamber therebetween and cooperable with shear 
fluid in the fluid shear chamber to transmit torque between the rotor and 
the plate. The close, spaced-apart positioning of the complementary shaped 
and located ridges and grooves of the rotor and plate provides for varying 
degrees of coupling between the driving member and the driven member in 
relation to the amount of fluid received in the intervening shear chamber, 
as is well understood in the art. 
The driven member and driving member are mounted together to have relative 
rotation about the central axis 20. The rotor 11 includes an outer, 
disc-shaped portion which defines the several annular ridges and grooves. 
The rotor also includes an inner hub portion 24 which is mounted to the 
shaft 12. Particularly, the hub portion 24 includes several 
radially-spaced depressions 25 which are utilized in staking the shaft to 
the rotor, as shown for example in FIG. 1 at 26. 
The bearing housing 15 is bearingly mounted to the shaft 12. The inner race 
27 of ball bearings 28 is received between the hub portion 24 of the rotor 
and a shoulder 29 of the shaft 12. The bearing housing 15 defines a 
central hub portion 30 defining a shoulder 31 against which one side of 
the outer race 32 of the ball bearings is received. The hub portion 
further defines a circumferential recess 33 in which a snap ring 34 is 
received to abut the other side of the outer race 32. 
The cover 16 is secured to the bearing housing 15, preferably by means of a 
magneformed band 17. As shown in FIG. 2, the band 17 has an initial 
configuration in which one of the shoulders 35 is already formed to 
conform with a corresponding surface on the perimeter of the cover 16. The 
main portion 36 of the band is formed at a slight angle, about 2.degree., 
from the central axis to facilitate placement of the band onto the housing 
and cover. The band is positioned on the cover and housing, and the 
magneforming process is then carried out. The forces generated by the 
surrounding magnetic field are sufficient to force the band 17 firmly 
against the outer, perimetric flanges 37 and 38 of the housing 15 and 
cover 16, respectively, to provide a secure clamping together of these 
components. The band is readily and quickly applied by this process, with 
the actual magneforming occurring in a fraction of a second. 
Although the general procedure of magneforming is known, it has not been 
known in the prior art to utilize a magneformed band to join together the 
typical bearing housing and cover for a fluid shear coupling apparatus. 
This construction does, however, have distinct advantages over the prior 
art designs. In particular, it has been the practice to design fluid shear 
couplings with a substantial amount of material radially outward of the 
rotor. The necessity for this material was presented in one approach 
because it was in this region that the bearing housing and cover were 
secured together by means of bolts. In the alternate approach, this 
material has been required in the past to be able to roll over material 
from one component onto the other. The latter method has had the 
additional disadvantage of causing distortion of the components, reducing 
the possibility of later disassembling and reassembling the coupling if 
needed. In the present apparatus, the magneformed band can be readily cut 
away to permit repair of the coupling. 
The use of a magneformed band conversely permits the coupling apparatus to 
have a minimal amount of material positioned radially outward of the fluid 
shear surfaces, and particularly of the rotor. This permits the coupling 
apparatus to be lighter in weight for a given area of shear surfaces, and 
particularly reduces the weight at the outermost location which would have 
the highest moment of inertia. Further, the magneformed band provides a 
simpler and quicker joining of the bearing housing and the cover, reduces 
the number and cost of materials for the fastening process, and simplifies 
the configuration of the bearing housing and cover. As shown, the bearing 
housing and cover include relatively small and simply configured flanges 
37 and 38, respectively, about which the band 17 is received. The bearing 
housing further defines an annular recess in the flange 37 in which an 
O-ring 39 is received to provide a seal between the bearing housing and 
the cover. 
As previously indicated, a typical application for the fluid shear coupling 
apparatus of the present invention is for providing a fan drive in respect 
to a vehicle engine. In this respect, the bearing housing 15 is provided 
with several apertures through which bolts, such as 40, are received. As 
shown particularly in FIG. 3, the bolt 40 preferably comprises a ribbed 
neck screw having a head 41 and a shank 42. The head includes a perimetric 
shoulder which receives a silicone seal ring 43. When the bolt is received 
through the aperture in the bearing housing 15, the seal ring 43 is 
pressed against the surface of the housing and thereby seals the aperture 
to prevent fluid loss. 
The shank 42 preferably includes a ribbed portion 44 adjacent the head of 
the bolt and including several axially directed ribs. These ribs are sized 
to be received in the aperture of the bearing housing and to grip tightly 
against the surface of the aperture to prevent rotation of the bolt when a 
nut is applied to the bolt externally of the housing. A simple and 
reliable technique for mounting a fan blade onto the bearing housing is 
thereby provided. The bolt 40 is inserted through the aperture in the 
bearing housing prior to assembly of the coupling apparatus. The ribbed 
portion 44 holds the bolt within the aperture so that the seal ring 
effectively seals the aperture, even prior to attachment of the fan 
blades. The ribbed portion also grips within the aperture to permit the 
fan blade and fastening nut to be applied on the exposed threaded shank 
after the coupling has been assembled. 
Secured to the cover 16 is a plate 21 which defines the several annular 
ridges and grooves of the driven member. Specific details for the plate 21 
and the cover 16 are provided in FIGS. 4A-4D and 5A-5C, respectively. 
As shown in FIG. 1, the bearing housing 15 includes an annular recess 45 in 
which is received the outer, perimetric edge of the plate 21. The plate is 
thereby clamped between the bearing housing 15 and the cover 16 when those 
components are secured together by means of the band 17. As shown 
particularly in FIG. 4B, the plate 21 is also provided with projections 46 
which are received within corresponding recesses in the bearing housing 
(FIG. 1) to operate as a key to prevent relative rotation of the plate 
with respect to the cover and bearing housing. 
To facilitate assembly and particularly to provide proper alignment of the 
plate with respect to the cover, the plate is provided with three 
projections 47 which are received within three corresponding recesses 48 
in the cover 16. The fit of the projections 47 in the recesses 48 is 
sufficient to provide a preliminary attachment between the plate and the 
cover such that the plate and cover may be assembled together prior to 
fitting with the bearing housing 15. This is advantageous in facilitating 
the assembly in general, and also in the calibration of the valve 
mechanism as described subsequently. As will be apparent from the 
following description, the projections 47 are used to align the plate with 
respect to the cover to assure a proper orientation of the valve and other 
components. 
The plate 21 and cover 16 are provided with cooperating projections to 
carry a valve 49. The plate 21 includes a pair of spaced apart lower pin 
support surfaces 50 and 51, and also a pair of spaced apart upper pin 
support surfaces 52 and 53. These supports are positioned to thereby 
receive a hinge pin 54 (FIG. 1) which in turn supports the valve 49. The 
cover 16 includes a pair of tabs 55 and 56 which are positioned to fall on 
opposite sides of the pin supports and the pin when the cover and plate 
are assembled together. In this fashion, the pin 54 may simply be inserted 
through the several pin supports 50-53 and the valve 49 and it is retained 
in that position by the tabs 55 and 56 upon assembly with the cover. 
The valve 49 is positioned for opening and closing an aperture 57 to 
control the flow of fluid between a fluid reservoir 58 and the working or 
shear chamber 59 defined by the space between the closely positioned 
ridges and grooves of the plate 21 and rotor 11. A spring 60 is received 
at one end in a depression 61 of the plate 21, and at the other end in a 
cavity 62 defined by the valve 49. This spring biases the valve to an open 
position in which the aperture 57 is open and fluid flow is provided 
between the reservoir and the working chamber. A bleed hole 63 extends 
through the plate 21 at the location of the depression 61 to permit a 
slight bleeding of fluid from the reservoir into the working chamber in 
conventional fashion. 
Control of the valve 49 is provided by a suitable control mechanism, a 
variety of which are well known in the prior art. As shown in the 
preferred embodiment, however, a novel control mechanism is provided 
hereby. The cover 16 defines a central recess in which is received a seal 
insert 67 and a seal 68, as shown n FIG. 6A. The seal insert 67 retains 
the seal 68 in position, and includes several ribs 69 (FIG. 6B) which act 
to hold the insert in place within the cavity defined by the cover 16. The 
insert 67 also includes a flange portion 70 which is received within a 
complementary shaped recess of the cover 16. A bracket assembly 71 (FIG. 
1) retains the flange portion 70 of the seal insert in place. The seal 
insert 67 and seal 68 define aligned apertures in which a piston pin 66 is 
slidingly received. The valve 49 carries an adjustable, self-clinching nut 
64 including a portion 65 against which one end of the pin 66 is received. 
The bracket assembly 71 maintains a heat strip 72 in position against the 
other end of the pin 66. 
In accordance with the described construction, the heat strip 72 and dowel 
pin 66 cooperate to control the movement of the valve 49 between open and 
closed positions. The pin 66 has one end engaging the adjustable portion 
65 associated with the nut 64, and the other end abutting the heat strip 
72. A change in position of the heat strip 72, such as with changes in 
ambient temperature, will therefore result in a movement of the pin 66 and 
a corresponding movement of the valve 49. 
The control mechanism is calibrated prior to final assembly of the coupling 
apparatus. This may be readily accomplished by assembling the plate 21 to 
the cover 16 which will be held in that position by the projections 47 
received within the recesses 48. The self-clinching nut 64 is then 
adjusted such that the heat strip 72 maintains the valve in the desired, 
closed position below a certain temperature and permits opening of the 
valve above the desired temperature. Since the valve 49 is provided with a 
self-clinching nut, the calibration of the device is maintained after 
assembly, once it has been determined and set in the appropriate position. 
In contrast, a disadvantage of certain prior art structures has been that 
adjustment was not possible, and calibration had to be accomplished by 
changing the pin 66 until a suitable length was selected. 
As will become more apparent in the following description, the provision of 
the seal insert 67 and seal 68 significantly simplifies the fabrication of 
the cover 16, while providing aligned apertures within which the pin 66 is 
received. The seal 68 is made of a suitable material to provide a 
sufficient seal about its periphery in contact with the recess in the 
cover 16, and also to provide a sliding seal with the pin 66. The seal 
insert 67 is received within the cover, as previously described, and is 
formed of a suitably rigid material to compress the seal within the recess 
to assure a firm, sealed fit. The insert also maintains the positioning of 
the seal 68 to provide a suitable contact with the pin 66. 
As a result of the presence of these two components, a seal is accomplished 
with the cover 16 and the pin 66 without a requirement for special 
treatment of the associated surfaces of the cover 16, other than by the 
original forming procedures such as casting of the cover with the 
indicated recesses. In contrast, the prior art devices have typically 
included a machining of the cover to receive a seal member. It is a 
feature of the present invention that a fluid shear coupling is provided 
that requires a minimal amount of processing of such components as the 
rotor and cover. In the past, it has been typical to first cast the cover, 
then drill and ream a hole for reception of the valve pin, and then to 
trepan a groove on the inside in which a sealing boot was glued. Casting 
of the groove has been difficult because it has been a relatively deep and 
narrow groove in prior art units. The described design for the present 
invention avoids these several steps and minimizes the fabrication of the 
cover. Also, the pin is received in apertures in the seal insert and seal 
which both provide lower coefficients of friction than the reamed hole 
provided in the past, and these components are not subject to corrosion. 
Also, no glue is required by the present construction. 
As is apparent from the description, the plate 21 is an integral and 
substantially closed component. By this it is meant that the plate does 
not have any substantial openings, particularly at the center, which are 
required to be closed by a separate closure element. In contrast, the 
typical prior art couplings have utilized a cover which has the shear 
surfaces, such as the annular ridges and grooves, as an integral portion. 
These prior art units have included a central aperture radially inward of 
the shear surfaces, which aperture is then closed by a separate cover 
plate provided for defining a fluid reservoir in the cover and for 
supporting the valve structures. 
In contrast, the present device includes a plate 21 which cooperates with 
the cover to define the fluid reservoir while also having the shear 
surfaces, preferably the annular ridges and grooves, as an integral 
portion. The present design therefore permits the valve pin supports 
50-53, the fluid aperture 57, the spring depression 61 and the bleed hole 
63 to all be readily formed as integral components of the plate 21 at the 
time of its fabrication. There is no need for providing an additional 
cover plate which in the prior art was typically staked to the cover for 
attachment purposes. 
The provision of the plate 21 also simplifies the formation of the 
recirculation passageways through which fluid moves from the shear chamber 
back to the fluid reservoir. With prior art designs, it has been necessary 
to drill and ball the recirculation holes. However, the present 
construction utilizing the separate cover 16 and plate 21 permits the 
recirculation passageways to be formed at the time of initial fabrication 
for these two components. As shown in FIG. 5B, the cover 16 is formed with 
a pair of radially-extending grooves 73 and 74. The plate 21 includes a 
pair of corresponding holes 75 and 76 extending through the thickness of 
the plate and communicating with the outermost annular grooves 77 and 78. 
The holes 75 and 76 are located to align and communicate with the grooves 
73 and 74 upon assembly of the plate 21 to the cover 16. The channels 73 
and 74 are thereby positioned to define passageways between the plate 21 
and cover 16 which communicate with the respective holes 75 and 76 and 
with the central fluid reservoir 58. The holes are positioned at the end 
of the corresponding grooves 77 and 78 such that fluid within the grooves 
will be forced through the holes 75 and 76 and radially inward along 
channels 73 and 74 to the fluid reservoir. 
A particular feature of the present invention is the provision of major 
components which are utilized in a substantially as-formed condition. By 
this it is meant that the components, such as the cover 16 and plate 21, 
do not undergo any substantial metal working operations after being 
initially fabricated such as by casting. The components may require minor 
treatments such as trimming of a casting, but do not require machining or 
other substantial modifications. Various initial fabrication techniques 
may be used provided that adequate tolerances may be achieved for that 
technique and the material being employed. In the preferred embodiment, 
the as-formed components are cast from a magnesium alloy. Examples of 
alternate methods include molding of the components from a plastic 
material, or preparing a sintered, powdered metal component. Plastic 
components particularly for the plate and rotor are suitable. However, 
appropriate modifications may be necessary in order to deal with the 
physical properties of the plastic, such as its reduced heat transfer 
characteristics. Powdered metal components have been found to work well in 
the described configurations, although in certain applications the cost of 
that fabrication technique is less economical. 
The plate 21 and rotor 11 are preferably provided in an as-cast condition. 
The rotor is press fit upon the shaft 12 and staked thereto as previously 
described. It is important that the central aperture 79 (FIG. 8) be 
accurately sized for fitting upon the shaft 12. It is also important that 
the several annular ridges 18 and grooves 19 be concentric with the axis 
20 of the shaft 12 and be square, i.e. normal to the axis. Centering and 
squaring of the central aperture of the rotor may therefore be 
accomplished after initial casting, as well as trimming of the outer 
diameter. The back of the hub portion of the rotor, which abuts the inner 
bearing race 27, is also closely controlled, preferably within four 
one-thousandths of an inch. This serves as a control on the closeness of 
the rotor to the ridges and grooves of the plate 21, and to the 
recirculation grooves and dams on the plate. 
Control over these and the other various tolerances for the rotor is 
accomplished by utilizing a suitable fabrication technique. The preferred 
technique is to die cast the rotor using a magnesium alloy. This method 
provides highly accurate tolerance control to the degree appropriate for 
formation of this component. 
As shown particularly in FIG. 8, the rotor 11 is formed with several holes 
80 to permit the passage of shear fluid from one side of the rotor to the 
other, as is understood in the art. Also known in the art is the function 
of the secant grooves 81 which preferably extend outwardly from three of 
the holes 80 on the grooved side of the rotor, and also of the secant 
grooves 82 which preferably extend outwardly from the other three holes 80 
on the opposite side of the rotor. 
The plate 21, and particularly the ridges 22 and grooves 23, are similarly 
controlled within desired tolerances. The entire plate 21 is suitably 
fabricated by die casting also from the preferred, magnesium alloy. 
Consequently, the gaps between associated ridges and grooves of the plate 
21 and rotor 11 are readily controlled to provide the desired operating 
characteristics for the fluid shear coupling of the present invention. 
It will be appreciated that the tolerances which may readily be achieved by 
a casting or other molding or forming process are not as precise as may be 
achieved by other techniques such as machining. It may therefore be 
desirable to have larger nominal gaps between the end and side surfaces of 
the associated ridges and grooves of the rotor and plate. It has also been 
found that wider grooves and ridges may be used and are preferred for the 
various reasons cited herein. In prior art couplings which include 
interdigitated ridges and grooves, the ridges and grooves have typically 
been in the range of 0.040 inches in width. In contrast, the present 
device preferably has widths for the ridges and grooves of at least about 
0.080 inches, with the preferred widths being 0.125 inches. 
As a result of widening the gaps between the shear surfaces, a decrease in 
torque transfer is produced. However, the decrease in the amount of torque 
transfer is offset by the fact that the effective viscosity of the fluid 
increases for the widened gaps. The present invention deals with the 
decrease in torque transfer by other means as well. First, the provision 
of an integral plate 21 provides a greater radial distance within which 
the ridges and grooves may be located, thus permitting a greater number of 
ridges and grooves for a given outside diameter. 
Second, it has previously been indicated that the desired coupling 
mechanism for the cover 16 and bearing housing 15 is the use of a 
magneformed band 17. The use of the magneformed band eliminates the need 
for a significant amount of material extending radially outward of the 
shear surfaces as a means for coupling the cover and bearing housing. 
Thus, the shear surfaces may be located more radially outward for a given 
outside diameter of the overall coupling device. As shown for example in 
FIG. 1, the present invention includes fluid shear surfaces which 
preferably extend outwardly to within one-half inch of the periphery of 
the apparatus. Therefore, although the torque factor is reduced in the 
sense that the gaps between shear surfaces are wider, this is offset by 
providing for a greater area of shear surfaces for a given outside 
diameter of the coupling for the reasons described. 
The cover 16 is also provided as an as-formed component, preferably being 
die cast from a magnesium alloy. The cover is fabricated with the various 
features, such as the grooves 73 and 74, being cast as an integral portion 
of the cover. To provide a suitable mating surface with the flange 37 of 
the bearing housing, the cover is cast with a flange 38 that is flat at 
the surface 83. This provides for a proper fit with the bearing housing, 
and also facilitates the sealing of this juncture by means of the O-ring 
seal 39 received therebetween. All of the other various features of the 
cover 16 are also suitably provided in the initial fabrication of the 
cover. These other features, which are preferably cast as an integral 
portion of the cover, include the tabs 55 and 56 for retaining the valve 
pin, the recesses 48 for receiving the aligning projections of the plate, 
and the cooling fins 84, shown particularly in FIG. 5C. 
The present invention thereby provides a cover 16, plate 21 and rotor 11, 
all of which are suitably provided by as-formed components. In prior art 
devices of a comparable nature, the counterparts for these components have 
typically required machining, drilling, reaming, trepaning, staking and 
perhaps other steps to arrive at the required components. The annular 
ridges and grooves, for example, have been machined in the past. 
Particular surfaces of the cover have also required such operations as 
previously indicated. In certain prior art devices, the costs associated 
with the machining of these components may contribute as much as 
one-fourth of the cost of the fluid shear coupling. Eliminating the need 
for these operations is therefore distinctly advantageous both in terms of 
time and expense in preparing the coupling apparatus. 
In accordance with the present invention, the bearing housing 15 is also 
suitably fabricated by die casting from a magnesium alloy. The bearing 
housing does include, however, certain surfaces which are machined. The 
cylindrical surface 85 of the annular recess 45, within which the plate is 
received, is machined to a suitable inside diameter. The outside diameter 
of the plate does not require machining, but is trimmed after casting to 
provide a fit within the machined recess. The bearing housing is also 
balanced and centered. 
Also in contrast to prior art devices, the present coupling does not 
require a two step procedure in finishing the bearing housing. In the 
past, the procedure typically included chucking the inside of the bearing 
housing while a pilot surface was machined on the outside. The outside was 
then chucked and the annular grooves or other surfaces were machined in 
the inside as required. The problem with this approach has been that a 
substantial portion of the mass of the bearing housing was on the 
initially unchucked side. The resulting housing could therefore be 
significantly out of balance after machining. 
In accordance with the present invention, the outer, heavy side of the 
bearing housing is accurately cast. That side may then be chucked, such as 
as the flanges 86, while the inside surfaces are machined. This diminishes 
the amount that the resultant housing may be out of balance, thus 
simplifying any subsequent balancing operation. 
Balancing of the bearing housing of the present invention may be 
accomplished in a variety of fashions, such as by the removal of a portion 
of the fins 87 (FIG. 1). An alternate technique is to remove material by 
drilling several small holes about the perimeter of the bearing housing at 
a location which places the holes under the magneformed band when it is 
applied. Alternatively, holes are cast in the outermost flange 37 of the 
bearing housing and then selected ones are filled to provide balancing 
prior to application of the magneformed band. 
As has been indicated, it is preferred that the components of the present 
invention are formed from a magnesium alloy. As used herein, the term 
magnesium alloy is used to define a metal alloy which includes at least 
about 85 percent magnesium, and may preferably include at least as much as 
about 90 percent magnesium. An example of a magnesium alloy which has been 
found to be particularly well suited to the present invention is the alloy 
known under the designation AZ91B which may include as components 8.5-9.5 
percent aluminum, 0.15 percent minimum manganese, 0.45-0.9 percent zinc 
0.20 percent maximum silicon, 0.25 percent maximum copper, 0.01 percent 
maximum nickel, 0.30 percent maximum other impurities, and the remainder 
as magnesium. 
It has been found that magnesium and magnesium alloys may be utilized to 
form the indicated components for a fluid shear coupling apparatus with 
suitable tolerances and physical parameters. The components have 
substantially the same tolerances as those utilized in the prior art by 
other fabrication techniques, but are able to be achieved by a casting 
process by the use of the magnesium or magnesium alloy. It has been found 
that the die cast magnesium alloy has excellent tolerance control and 
provides three to five times the die life as is achieved with certain 
other metals such as aluminum, which along with steel is the typical metal 
used in prior art coupling devices. 
The use of magnesium components permits the use of thinner walls, resulting 
in better heat transfer and lighter weight. In the field of fluid shear 
couplings, weight is an important factor. An apparatus as described herein 
may have an overall weight of about 4 pounds, whereas a comparable prior 
art device would weigh as much as 51/2 to 81/2 pounds. The use of 
magnesium components has also been found to be advantageous in terms of 
minimized vibration and extended bearing life, due in part to the lighter 
weight of the components. In order to ensure against possible corrosion 
problems for the outer surfaces of the coupling apparatus, the coupling is 
preferably coated with a suitable protective material. 
Magnesium and magnesium alloys have been found to be excellent materials 
for the fabrication of various components for a fluid shear coupling 
apparatus. As described herein, the magnesium alloy is particularly suited 
for the cover, plate, rotor and bearing housing. The advantages achieved 
by use of magnesium and its alloys are applicable to the variety of fluid 
shear couplings described herein and in the prior art, particularly in the 
use of thinner walls, and achievement of better heat transfer and lighter 
weight as a result. 
To the extent that a coupling apparatus requires machining, proper 
precautions should be taken in the removal and disposal of the magnesium 
chips which will burn intensely if not properly handled. However, the 
machining of magnesium and its alloys is practical both physically and 
economically, and will yield not only a superior fluid shear coupling, but 
will also permit longer tool life and the use of reduced horsepower during 
fabrication. 
While the invention has been illustrated and described in detail in the 
drawings and foregoing description, the same is to be considered as 
illustrative and not restrictive in character, it being understood that 
only the preferred embodiment has been shown and described and that all 
changes and modifications that come within the spirit of the invention are 
desired to be protected.