Fluid coupling device having improved temperature responsiveness

A rotary fluid coupling device is provided of the type including a first rotatable coupling assembly (13) comprising a housing member (15) and a die cast cover member (17). An input coupling member (11) is disposed in a fluid operating chamber (33) and cooperates with an adjacent surface of the cover member (17) to define a viscous shear space therebetween. When the shear space is filled with viscous fluid, torque can be transmitted from the input coupling to the output coupling, such torque transmission resulting in the generation of a substantial amount of heat adjacent the front surface of the cover member. The cover member (17) includes a generally annular portion (36) defining therein a reservoir chamber (35). Disposed within a recessed area defined by the annular portion (36) is a bimetal coil (45) which defines a coil circle C. The annular portion (36) of the cover includes a plurality of blower fin members extending radially inward to a location adjacent the coil circle C, each having an axial height H1 which is a major portion of an axial distance X from the forward surface of the cover member to the bimetal coil. The blower fins (71) generate a radially outward flow of air, thus resulting in an axial flow of air through the bimetal coil, to improve the temperature responsiveness of the coupling device.

BACKGROUND OF THE DISCLOSURE 
The present invention relates to rotary fluid coupling devices, and more 
particularly to such devices wherein heat is generated as a result of the 
torque transmission, and the ability of the coupling device to respond to 
changes in temperature is an important performance criterion. 
Rotary fluid coupling devices of the type which may benefit from the use of 
the present invention have found many uses, one of the most common of 
which is to drive the cooling fan associated with the radiator of a 
vehicle engine. Such coupling devices are frequently referred to as 
"viscous fan drives" because such couplings utilize a high-viscosity fluid 
to transmit torque, by means of viscous shear drag, from an input coupling 
member (clutch) to an output coupling member (housing), to which is bolted 
the cooling fan. 
More specifically, the present invention is especially advantageous when 
used on a relatively high-torque viscous fan drive, i.e., a fan drive 
which is capable of transmitting to the cooling fan in the range of about 
2 horsepower to about 12 horsepower, although it should be understood that 
the invention is not so limited. Typically, such high-torque or 
high-horsepower fan drives include an output coupling assembly comprising 
a cast aluminum housing and a die cast aluminum cover. The input coupling 
member and the die cast cover normally include a plurality of 
interdigitated lands and grooves which define the shear space. When this 
shear space is filled with viscous fluid, torque is transmitted from the 
input coupling member to the output coupling assembly, in response to 
rotation of the input coupling member. 
During torque transmission, substantial heat is generated as a result of 
the shearing of the viscous fluid, and the cast cover is the primary heat 
dissipating element of the device. Therefore, it has been conventional 
practice in such viscous fan drives to have a plurality of cooling fins 
cast integrally with the cover. An example of a fan drive to which the 
present invention may be advantageously applied is shown in U.S. Pat. No. 
4,678,070, assigned to the assignee of the present invention and 
incorporated herein by reference. In such fan drives, the cast cover 
defines a raised, annular, reservoir-defining portion, and disposed within 
the recess defined by this annular portion is the bimetal coil which 
provides temperature responsive operation of the valving within the 
coupling device. 
The air in the recess where the bimetal coil is located is relatively 
stagnant, because the coil and the recess are located on the axis of 
rotation of the coupling device, which is also the center line of the 
natural stream of air flow past the device. Changes in the temperature of 
the water in the radiator, resulting in changes in the temperature of the 
air flowing through the radiator, indicate changes in the need for fan 
drive operation. Heat is transferred from the flowing air to the bimetal 
coil by forced convection, but with relatively little air flow in the 
region of the coil, the fan drive may not respond as quickly as desired to 
changes in coolant temperature. More specifically, when the fan drive has 
been disengaged, and a situation occurs which demands relatively greater 
cooling, the temperature of the coolant rises rapidly, as does the 
temperature of the air being drawn through the radiator. However, the 
bimetal coil does not heat up as rapidly because of the relatively 
stagnant air surrounding the coil, and the engine may overheat before the 
coil has been heated sufficiently to cause the fan drive to engage. 
If the temperature responsiveness of a viscous fan drive can be 
substantially improved, it would then be possible to set the calibration 
at a higher temperature, i.e., the fan drive would engage at a higher 
temperature. A higher calibration temperature would mean that the tan 
clutch would engage less frequently thus reducing the engine horsepower 
consumed by the fan drive, but perhaps more importantly to the customer, 
reducing the amount of time (frequency of engagement) that the fan drive 
spends in the engaged condition. Keeping the fan drive disengaged more of 
the time reduces the amount of undesirable fan noise. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an 
improved rotary fluid coupling device which is capable of generating a 
sufficient flow of air in the region surrounding the bimetal element to 
overcome the problem of stagnant air surrounding the bimetal element. 
The above and other objects of the present invention are accomplished by 
the provision of an improved, relatively high-torque fluid coupling device 
of the type including a first rotatable coupling assembly comprising a 
housing member and a cover member cooperating to define a fluid chamber 
therebetween. A valve means is associated with the first coupling assembly 
and separates the fluid chamber into a fluid operating chamber and a fluid 
reservoir chamber. A second rotatable coupling member is disposed in the 
fluid operating chamber and is rotatable relative to the first coupling 
assembly, a surface of the second coupling member and an adjacent surface 
of the first coupling assembly cooperating to define a viscous shear space 
therebetween. The cover member or the housing member includes a plurality 
of cooling fins disposed generally adjacent the viscous shear space. The 
valve means further comprises a movable valve actuating member supported 
by the cover member, and extending outwardly through the cover member. A 
temperature responsive bimetal element is operatively connected to the 
cover member and to the valve actuating member. The cover member includes 
a generally annular portion disposed generally concentric relative to the 
axis of rotation, the annular portion being configured to define a major 
portion of the fluid reservoir chamber. The bimetal element is disposed 
within the annular portion, and defines an outer periphery. 
The improved coupling device is characterized by the annular portion 
including a plurality of blower fin members oriented generally radially 
relative to the axis of rotation. Each of the blower fin members extends 
radially inwardly from the annular portion to a location disposed adjacent 
the bimetal element periphery. Each of the blower fin members has an axial 
height at its radially inwardmost extent, which comprises a major portion 
of an axial distance X from the forward surface of the cover member to the 
bimetal element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, which are not intended to limit the 
invention, FIG. 1 illustrates one preferred form of a fluid coupling 
device (viscous fan drive) of the type with which the present invention 
may be utilized. The fluid coupling device illustrated in FIG. 1 includes 
an input coupling member, generally designated 11, and an output coupling 
assembly, generally designated 13. The output coupling assembly 13 
includes a die cast housing member 15 and a die cast cover member 17, the 
members 15 and 17 being secured together by a rollover of the outer 
periphery of the cover member 17, as is well known in the art. The fluid 
coupling device is adapted to be driven by a liquid cooled engine and, in 
turn, drives a radiator cooling fan F. The fan F may be attached to the 
housing member 15 by means of a plurality of nuts 19. It will be 
understood, however, that the use of the present invention is not limited 
to any particular configuration of fluid coupling device or any particular 
application thereof, except as specifically noted hereinafter. 
The fluid coupling device includes an input shaft 21 on which the input 
coupling member 11 is mounted. The input shaft 21 is rotatably driven, 
typically by means of a flange 23 which may be bolted to the mating flange 
of an engine water pump. The input shaft 21 functions as a support for the 
inner race of a bearing set 25, which is seated on the inside diameter of 
the housing member 15. The forward end (left end in FIG. 1) of the input 
shaft 21 has an interference fit between a serrated portion 27 and an 
opening defined by a hub portion 29 of the input coupling member 11. As a 
result, rotation of the input shaft 21 causes rotation of the input 
coupling member 11. 
The housing member 15 and the cover member 17 cooperate to define a fluid 
chamber which is separated, by means of a circular valve plate 31, into a 
fluid operating chamber 33 and a fluid reservoir chamber 35. Thus, it may 
be seen that the input coupling member 11 is disposed within the fluid 
operating chamber 33. 
The cover member 17 defines a raised, annular reservoir-defining portion 
36, which is disposed to be generally concentric about an axis of rotation 
A of the device, and further defines a generally cylindrical shaft support 
portion 37, and rotatably disposed within the portion 37 is a valve shaft 
39 extending outwardly (to the left in FIG. 1) through the cover member 
17. Attached to the inner end (right end in FIG. 1) of the valve shaft 39 
is a valve arm 41, the general construction of which forms no part of the 
present invention, but which may be better understood by reference to U.S. 
Pat. No. 3,055,473, assigned to the assignee of the present invention and 
incorporated herein by reference. Movement of the valve arm 41 controls 
the flow of fluid from the reservoir chamber 35 to the operating chamber 
33, through a fill opening 43 formed in the valve plate 31. 
Operatively associated with the outer end of the valve shaft 39 is a 
temperature responsive bimetal element, comprising a coil member 45 which, 
as may best be seen in FIG. 3, includes an inner end portion 45a in 
engagement with the valve shaft 39, and further includes an outer end 
portion 45b, received within a cast enclosure member 46. Preferably, the 
enclosure member 46 is filled with some sort of resilient, elastomeric 
material which cures in such a manner as to grip resiliently the outer end 
45b of the coil. As may also be seen best in FIG. 3, the outer turn of the 
coil 45 defines a coil circle C, having its center disposed approximately 
on the axis of rotation A of the coupling device. The significance of the 
coil circle C will be explained in greater detail subsequently. The manner 
in which the bimetal coil 45 operates to control the movement of the valve 
arm 41, in response to variations in a predetermined temperature 
condition, is well known in the art, is not an essential feature of the 
present invention and will not be described further. 
The cover member 17 defines an axial passage 47 in communication with the 
fluid operating chamber 33, and a generally radial passage 49 which 
provides fluid communication from the axial passage 47 to the fluid 
reservoir chamber 35. Disposed adjacent the axial passage 47 is a pumping 
element (wiper) 51, operable to engage the relatively rotating fluid in 
the operating chamber 33 to generate a localized region of relatively 
higher fluid pressure, and continually pump a small quantity of fluid back 
into the reservoir chamber 35, through the passages 47 and 49, as is well 
known in the art. 
In the subject embodiment of the invention, the input coupling member 11 
includes a forward surface which defines a plurality of annular lands 53. 
The adjacent surface of the housing member 17 forms a plurality of annular 
lands 55. The annular lands 53 and 55 are interdigitated to define a 
serpentine-shaped viscous shear space therebetween, which is shown 
somewhat schematically in FIG. 1. It is believed that in view of 
above-incorporated 4,678,070, those skilled in the art can fully 
understand the construction and operation of the fluid coupling device 
illustrated in FIG. 1, as well as the various flow paths for the viscous 
fluid contained therein. As noted in the background portion of the 
specification, when torque is transmitted from the vehicle engine by means 
of the input shaft 21 to the input coupling member 11, the result is a 
shearing of the viscous fluid contained in the shear space between the 
annular lands 53 and 55. 
Referring now to FIG. 2, it may be seen that the entire finned area of the 
cover member 17 is divided into a plurality of substantially identical 
regions 61. Because each of the regions 61 is substantially identical, 
only one such region 61 will be described hereinafter, it being understood 
that each of the others is the same. Within each of the regions 61 there 
is one generally radially-extending cooling fin 63 which, in the subject 
embodiment, is illustrated as being centrally-disposed within the region 
61. On either side of the radially-extending cooling fin 63 is a pair of 
parallel cooling fins 65. By "parallel" is meant that each of the cooling 
fins 65 is substantially parallel to the radially-extending cooling fin 
63. In addition, each region 61 includes a somewhat shorter cooling fin 67 
which is oriented substantially parallel to the adjacent cooling fin 65, 
and an even shorter cooling fin 69 which is oriented generally radially to 
its adjacent cooling fin 65. The above-described "parallel" cooling fin 
arrangement is not an essential feature of the present invention, is 
described in greater detail in above-incorporated 4,678,070, and therefore 
will not be described in further detail herein. 
Referring now primarily to FIGS. 3 and 4, the present invention will be 
described in some detail. As was explained in the background of the 
present specification, it is desirable in temperature responsive coupling 
devices to maintain a continuous flow of air axially through the bimetal 
coil 45, to avoid the problem of the coil being surrounded by stagnant 
air, and therefore, being less responsive to changing temperature 
conditions. 
In the subject embodiment of the present invention, the cast cover member 
17 includes a plurality of blower fin members, generally designated 71, 
only a few of which are shown in FIG. 3, for ease of illustration. 
Preferably, the fin members 71 are oriented generally radially relative to 
the axis of rotation A. As may best be seen in FIG. 3, each of the blower 
fin members 71 extends radially inwardly from the annular reservoir 
portion 36 to a location disposed adjacent the coil circle C. 
Referring now primarily to FIG. 4, each of the fin members 71 includes, in 
the subject embodiment, a radially inner fin portion 73 and a radially 
outer fin portion 75. The function of the fin members 71 is to provide a 
radially outward flow of the air which is disposed between the coil member 
45 and the adjacent surface of the cover member 17. Such radial movement 
of air will, in turn, draw air axially (see arrows) through the coil 
member 45, and the above-described pattern of air flow has been found to 
alleviate substantially the problem of the bimetal coil 45 being located 
in a recess containing stagnant air. 
In order to perform the above-described function, it is preferred that the 
inner portion 73 of each of the blower fin members 71 extend radially 
inwardly of the coil circle C, but it is believed best to have the inner 
portion 73 terminate under the coil as shown in FIG. 4, rather than 
extending radially all the way to the shaft support portion 37. Therefore, 
references herein, and in the appended claims, to the fin members 71 
extending to a location disposed "adjacent" the coil circle C should be 
clearly understood to mean and include extending to the coil circle C, or 
terminating somewhat radially outward from the coil circle C, or even 
extending a substantial distance radially inward of the coil circle C. 
As may be seen in FIG. 4, the axial distance from the forward surface of 
the cover member 17 to the rear surface of the coil member 45 is 
identified as an axial distance X. The inner fin portion 73 has an axial 
height H1, and preferably, the height H1 comprises a major portion of the 
axial distance X. 
The outer fin portion 75 has an axial height H2 which preferably is greater 
than the axial distance X, i.e., the outer fin portion 75 extends above 
(forwardly of) the underside of the coil member 45. It is believed that 
the configuration of the blower fin members 71 shown in FIG. 4 will 
provide an efficient flow of air through the coil and radially outward. 
However, the present invention is not limited to any particular bimetal 
configuration, except as set forth in the appended claims. 
The invention has been described in great detail sufficient to enable one 
skilled in the art to make and use the same. It is believed that upon a 
reading and understanding of the following specification, various 
alterations and modifications will become apparent to those skilled in the 
art, and it is intended to include all such alterations and modifications, 
insofar as they come within the scope of the appended claims.