Fluid coupling device with improved disengaged operating characteristics

A fluid coupling device, especially a viscous fan drive, of the type including an output coupling member defining a fluid operating chamber. The device includes an input coupling member rotatably disposed in the operating chamber and cooperating with the output member to define a shear space. The output coupling member defines an annular inner surface, at least a major portion of the inner surface cooperating with the axis of rotation to define an included angle between about 20 degrees and about 70 degrees. The input coupling member defines an annular outer surface, a major portion of which conforms generally to the angled inner surface of the output coupling member and is closely spaced apart therefrom. The fluid coupling device of the invention has a substantially reduced idle speed, without a loss of peak speed, as well as a greatly reduced pump-out time.

BACKGROUND OF THE DISCLOSURE 
The present invention relates to torque transmitting fluid couplings, and 
more particularly, to such couplings which utilize internal valving, 
whereby the fluid coupling may be in either an engaged or disengaged 
condition, depending upon the position of the valving. 
Fluid couplings of the type to which the present invention relates are well 
known in the art and may be better understood by reference to U.S. Pat. 
Nos. 3,055,473; 3,174,600; and 3,339,689, all of which are assigned to the 
assignee of the present invention. Briefly, such fluid couplings typically 
include an output coupling member and a cover which cooperate to define a 
fluid chamber, a valve plate dividing the fluid chamber into an operating 
chamber and a reservoir chamber, and an input coupling member disposed 
within the operating chamber and rotatable relative to the output coupling 
member. The input and output coupling members define a shear space such 
that rotation of the input member causes viscous fluid in the shear space 
to exert a viscous drag on the output member, causing it to rotate. The 
valve plate defines a fill orifice, and a valving arrangement controls the 
flow of fluid from the reservoir chamber, through the fill orifice, into 
the operating chamber. Typically, the valving is temperature-responsive, 
as is illustrated in the above-cited patents, such that below a certain 
ambient temperature, the valving is closed, most of the viscous fluid is 
discharged from the operating chamber to the reservoir chamber and the 
fluid coupling is considered to be "disengaged". Above the predetermined 
temperature, the valving gradually opens and viscous fluid is permitted to 
flow from the reservoir into the operating chamber, filling the shear 
space, such that the coupling is "engaged". 
Conventional fluid couplings of the type to which the present invention 
relates have been provided with relatively small clearances between the 
outer periphery of the input member and the inner periphery of the output 
member, partly because the viscous fluid between these adjacent 
peripheries acts as a fluid bearing, and partly to maximize the available 
shear surface and the torque transmitting capacity. Therefore, although 
the present invention may be utilized in fluid coupling devices of many 
different embodiments, it is especially useful in those of the type in 
which the outer periphery of the input member and the inner periphery of 
the output member have been closely spaced apart. It is also especially 
useful in those in which some form of valving is provided to control the 
flow of fluid into the operating chamber, such that the coupling may be 
utilized in either an engaged or a disengaged condition. 
Conventional fluid couplings have generally been of the type referred to as 
"full OD", i.e., the outer surface of the input member and the inner 
surface of the output member are cylindrical and have a maximum diameter 
over the entire axial extent of the respective surfaces. As noted 
previously, a full OD input member provides maximum torque transmission 
when the fluid coupling is engaged. With the coupling disengaged, however, 
several problems arise in connection wth the use of the full OD input 
member. One of these is the "cold-start" condition which arises after the 
coupling has been inoperative for a period of time and fluid has leaked 
from the reservoir into the operating chamber, causing the coupling to 
operate as though it were engaged when it is intended to be disengaged. 
Upon start-up of the coupling under this condition, it typically takes a 
full minute or more for enough of the fluid to be discharged from the 
operating chamber back into the reservoir chamber to reduce the speed of 
the output member to its normal, disengaged level. During this period of 
time, operation of the coupling is normally not desired, e.g., the 
coupling is driving the radiator cooling fan of a vehicle engine and no 
cooling is required upon initial start-up of the vehicle engine. Moreover, 
the continued, engaged operation of the coupling for a period of several 
minutes, typically at speeds well above 1,000 rpm, results in an 
objectionable noise level, especially when the engine is warming up at 
fast idle. A related problem is the output speed level of the coupling in 
the disengaged condition. A relatively higher disengaged output speed 
(referred to as "idle speed") results in a relatively higher horsepower 
consumption by the coupling and the associated cooling fan with no 
resultant benefit. 
As the need for improved fuel efficiency in automobiles has developed, 
production of smaller cars has increased and it has become more common to 
equip such cars with viscous fan drives which, because of their ability to 
be disengaged when engine cooling is not needed, greatly reduce overall 
horsepower consumption. One result of this trend has been greater interest 
in improving the disengaged operating characteristics of viscous fan 
drives, especially the idle speed, which tends to be higher in the smaller 
cars because the proportionately smaller fans can be driven at a 
relatively high speed and consume a substantial amount of input horsepower 
by a small amount of viscous fluid in the shear space. The reduction of 
idle speed toward the ultimate (i.e., the output speed resulting from 
bearing drag alone, with no fluid in the shear space) requires more 
complete pump-out of viscous fluid from the shear space. One aspect of 
maximizing pump-out is the ability to maintain high efficiency of the 
wiper which causes a build-up of pressure within the operating chamber, 
adjacent the discharge orifice, resulting in flow through the discharge 
orifice into the reservoir. 
Those skilled in the art of viscous fan drives who have attempted to reduce 
idle speed recently have been following one general approach, i.e., 
minimizing the occurrence of parallel, closely spaced surfaces on the 
input and output coupling members around their peripheries or, where such 
parallel surfaces do exist, increasing the clearance between them. For 
example, in U.S. Pat. No. 3,990,556, the outer periphery of the input 
coupling member is provided with a series of notches such that adjacent 
notches join to form a line, rather than a surface and the specification 
of the cited patent states that "If there were provided any faces instead 
of a line of notch means ... the residual fluid in the working chamber 
would transmit the torque from the input member to the output member." 
Similarly, in U.S. patent application Ser. No. 764,772, filed Feb. 2, 1977 
in the name of K. R. Streeter, for a "FLUID COUPLING DEVICE WITH IMPROVED 
DISENGAGED OPERATING CHARACTERISTICS", assigned to the assignee of the 
present invention, the inner surface of the output member is cylindrical, 
while the outer surface of the input coupling member is frusto-conical, 
primarily to reduce the peripheral face-to-face engagement and reduce the 
idle speed. 
As a further example, a commercially available viscous fan drive, produced 
by someone other than the assignee of the present invention, is basically 
of the full OD type discussed previously, but with the OD clearance (i.e., 
the radial dimension between the outer surface of the input member and the 
inner surface of the output member) increased to such an extent that, even 
though idle speed is reduced, the pump-out time is increased because of 
reduced wiper efficiency, as will be described in greater detail 
subsequently. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a fluid 
coupling device in which the input and output coupling members are 
configured to improve the disengaged operating characteristics, especially 
idle speed, without adversely affecting the engaged operating 
characteristics, especially peak speed. 
The above and other objects of the invention are accomplished by the 
provision of an improved fluid coupling device including a first rotatable 
member, cover means associated with the first member to define a fluid 
chamber, a valve plate disposed to separate the fluid chamber into an 
operating chamber and a reservoir chamber, and a second rotatable member 
disposed in the operating chamber. The second member has first and second 
wall surfaces oriented generally perpendicular to the axis of rotation, 
defining an axial separation T therebetween, and an annular outer surface 
extending between the first and second wall surfaces. Valve means is 
associated with the valve plate to control the flow of fluid from the 
reservoir chamber into the operating chamber and temperature responsive 
means is associated with the valve means to effect the operation of the 
valve means in response to variations in a predetermined temperature 
condition. The first member defines a generally annular inner surface 
having an axial extent greater than T, at least a major portion of said 
inner surface cooperating with the axis of rotation to define a first 
included angle. At least a major portion of the outer surface of the 
second member cooperates with the axis of rotation to define a second 
included angle, and is closely spaced apart from the major portion of the 
inner surface over at least part of the axial extent thereof. The second 
included angle is approximately equal to, or greater than the first 
included angle.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, which are not intended to limit the present 
invention, FIG. 1 illustrates the preferred form of a fluid coupling 
device with which the present invention may be utilized. The fluid 
coupling device includes an input coupling member 11 and an output 
coupling member 13. The fluid coupling device is shown herein as a drive 
for an automotive engine accessory, and specifically, as a drive for a 
radiator cooling fan. It will be understood, however, that the use of the 
present invention is not limited to any particular fluid coupling 
configuration or application. 
The fluid coupling includes an input shaft 15 on which input member 11 is 
mounted and which is rotatably driven, such as by means of a flange 17 
which, in the subject embodiment, may be bolted to the water pump flange 
(not shown). The input shaft 15 has a reduced shaft portion 19 
intermediate its ends which functions as a support for the inner race of a 
bearing set 21, seated on the inside diameter of the output coupling 
member 13. 
The input coupling member 11 is in the form of a disc having a hub portion 
23 supported by the forward end of the shaft 15. The hub portion 23 has an 
opening therethrough which has an interference fit with a serrated portion 
25 of the shaft 15. The hub portion 23 is pressed onto the shaft 15 until 
it abuts the side of the inner race of the bearing set 21, and the output 
end (left end in FIG. 1) of the shaft 15 is balled over to positively 
retain the input coupling member 11 on the shaft, such that rotation of 
the shaft 15 causes rotation of the input coupling member 11. 
The output coupling member 13 cooperates with a cover assembly, generally 
designated 27, to define a fluid chamber therebetween, the fluid chamber 
being separated by a valve plate 29 into a fluid operating chamber 31 and 
a fluid reservoir chamber 33. Rotatably supported by the cover assembly 27 
is a valve shaft 35 having attached to its inner end (right end in FIG. 
1), a valve arm 37, the general construction and operation of which may be 
better understood by reference to the above-mentioned U.S. Pat. No. 
3,055,473. The cover assembly 27 includes a cover member 39 which, in the 
subject embodiment, is a single-piece metal stamping. Attached, as by 
welding, to the outer surface of the cover member 39 is a bracket member 
41 which supports an outer end 43 of a bimetal coil, generally designated 
45, with an inner end 47 thereof which is positioned in a slot formed in 
the outer end of the valve shaft 35. 
It should be understood that the scope of the present invention is not 
limited to any particular configuration of valving to control the flow of 
fluid from the fluid reservoir chamber 33 into the fluid operating chamber 
31. Nor is the invention limited to any particular type of 
temperature-responsive means to control the valving, it being necessary 
only that the valving be controlled in response to a predetermined 
condition to cause the coupling to be either engaged or disengaged. 
Referring now to FIG. 3, in conjunction with FIG. 1, the input coupling 
member 11 defines a forward surface 49 and a recessed forward surface 51 
adjacent the outer periphery of the coupling member 11. The recessed 
forward surface 51 provides clearance for a wiper portion 53 which may be 
formed integrally during the stamping of the valve plate 29, or may 
comprise a member welded to the valve plate subsequent to stamping. The 
wiper portion 53 operates in a manner well known in the art to generate a 
region of increased fluid pressure adjacent the trailing edge of the wiper 
portion 53, because the input member 11 and the fluid contained in the 
operating chamber 31 are rotating at a faster speed than is the output 
member 13. Adjacent the trailing edge of the wiper portion 53, the valve 
plate 29 defines a discharge orifice (not seen in FIG. 1 or 3), whereby 
the increased fluid pressure within the operating chamber 31 causes a flow 
of fluid through the discharge orifice into the reservoir chamber 33. 
Referring now primarily to FIG. 3, the input coupling member 11 defines a 
rearward wall surface 55, and the output member 13 defines a wall surface 
57, closely spaced apart from the rearward wall surface 55. The wall 
surfaces 55 and 57 cooperate to define a plurality of concentric, 
interdigitated, annular lands and grooves as is well known in the art 
which, in turn, cooperate to define a shear space. It should be 
appreciated that the use of the interdigitated lands and grooves is 
primarily to maximize the available shear area and the torque transmitting 
capability of the coupling, but the scope of the present invention is not 
limited to any particular configuration of shear space. 
The output coupling member 13 defines an annular inner surface, generally 
designated 61, including a cylindrical portion 63 and a frusto-conical 
portion 65. The input coupling member 11 also defines an annular outer 
surface including a cylindrical surface portion 71 and a frusto-conical 
surface portion 73. The forward surface 49 and rearward surface 55 of 
input coupling member 11 define an axial separation T, such that the axial 
extent of the annular inner surface 61 is somewhat greater than T. The 
frusto-conical surface portion 65 should comprise at least a major portion 
of the total inner surface 61 and should have an axial extent equal to at 
least about 0.7T, for reasons which will be described subsequently. 
Similarly, the frusto-conical surface portion 73 should comprise at least 
a major portion of the total annular outer surface of the input member 11 
and should have an axial extent equal to at least about 0.5T, for reasons 
which also will be described subsequently. 
In theory, it may be advantageous for the frusto-conical surface portion 73 
to extend further upward and to the right in FIG. 3 until it meets the 
recessed forward surface 51, eliminating the cylindrical surface 71. 
However, the surface 71 is preferably provided to permit holding of the 
input coupling member 11 during machining thereof. Also, having a sharper 
corner on the outer periphery of the member 11 would probably result in 
damage to the corner during the normal handling incident to the 
manufacturing process. In the subject embodiment, the axial extent of the 
cylindrical surface 71 is approximately 0.050 inches (1.27 mm). 
An essential feature of the present invention is the provision of an angled 
or frusto-conical surface portion on both the input member 11 and the 
output member 13. The frusto-conical surface portion 65 cooperates with 
the axis of rotation of the device to define an included angle A, while 
the frusto-conical surface portion 73 cooperates with the axis of rotation 
to define an included angle B. As used herein the term "included angle" 
will be understood to mean an angle greater than zero degrees, but less 
than ninety degrees. 
During the development of the present invention, it has been found that 
both of the included angles A and B could vary over a substantial range 
without a serious reduction in the performance of the fluid coupling. 
Although the included angle A defined by the inner frusto-conical surface 
portion 65 could be as small as five degrees to ten degrees, it is 
preferably in the range of about twenty degrees to about sixty degrees, 
and in the subject embodiment, the included angle A is illustrated as 
forty-five degrees. The included angle B defined by the outer 
frusto-conical surface portion 73 may, similarly, be as little as five 
degrees to ten degrees, and still result in a fluid coupling having 
improved disengaged operation characteristics. Preferably, however, the 
included angle B is also in the range of about twenty degrees to about 
sixty degrees and in the subject embodiment, is illustrated as forty-five 
degrees. 
From the foregoing description, it will be understood that within the scope 
of the invention, the included angles A and B may vary within the 
specified ranges independently of each other. However, from an operating 
viewpoint, there does not appear to be any advantage in making included 
angle B either larger or smaller than included angle A, and in the 
embodiment of FIG. 3, the frusto-conical surfaces 65 and 73 are 
substantially parallel. Furthermore, contrary to the trend in the recent 
development of the prior art, the surfaces 65 and 73 are closely spaced 
apart to provide a maximum shear area and torque transmitting capability 
during engaged operation. As used herein, the term "closely spaced apart" 
in reference to surfaces 65 and 73 will be understood to mean that the 
surfaces 65 and 73 are sufficiently close together such that viscous fluid 
contained therebetween is able to transmit at least a certain minimum 
amount of torque from the input member 11 to the output member 13. It has 
been found that the present invention operates advantageously with the 
clearance between the surfaces 65 and 73 (outside diameter clearance, 
O.D.CL.) in the range of about 0.020 inches (0.50 mm). 
It will be appreciated that when the included angles A and B are somewhat 
different, the surfaces 65 and 73 are not parallel, the use of the term 
"closely spaced apart" in reference to surfaces 65 and 73 will indicate 
only that the surfaces are close together over a part of the axial extent 
thereof. 
When the fluid coupling of the present invention is operating in the 
disengaged condition, i.e., when the valve arm 37 covers the fill orifice 
and uncovers the discharge orifice, it is desirable, as described 
previously, to pump as much of the viscous fluid as possible out of the 
operating chamber 31. The fluid being pumped from the operating chamber 31 
is primarily that which is being forced radially outward by centrifugal 
force through the shear space defined by rearward wall surface 55 and wall 
surface 57. Referring now to the prior art device illustrated in FIG. 2, 
having a greatly enlarged OD clearance, it may be appreciated that there 
is a tendency for the fluid leaving the shear space and entering the OD 
clearance to form a fluid layer, held by centrifugal force against the 
inner surface of the output member. In an attempt to reduce idle speed, 
the OD clearance was increased until it was greater than the thickness of 
the fluid layer, thus substantially eliminating contact between the fluid 
layer and the outer surface of the input member. However, this greater OD 
clearance (smaller input member diameter) has resulted in a portion of the 
wiper being disposed radially outward from the outer surface of the input 
member, thus reducing wiper efficiency and increasing pump-out time. 
Referring again to FIG. 3, it may be seen that because of the angled 
surfaces 65 and 73, it is impossible to have a layer of viscous fluid of 
the same volume as in FIG. 2 held by centrifugal force against the 
cylindrical surface 63. 
It should be appreciated that although the frusto-conical surfaces 65 and 
73 are shown in FIGS. 1 and 3 as being straight lines (in cross-section), 
it is within the scope of the invention for the surfaces 65 and 73 to vary 
somewhat from the straight configuration shown. For example, the surfaces 
65 and 73 could define a compound angle, i.e., each could comprise two 
surface portions, with each surface portion defining a different included 
angle relative to the axis of rotation. Also, either or both of the 
surfaces 65 and 73 could appear in cross section as slightly curvilinear. 
The essential feature in regard to the surfaces 65 and 73 is the overall 
frusto-conical configuration. 
To illustrate further the improvement is disengaged operating 
characteristics which may be achieved utilizing the present invention, 
test data will be presented hereinafter comparing the invention (as shown 
in FIG. 3) with the prior art device of FIG. 2. At the time of the present 
invention, the prior art device of FIG. 2 was considered by applicant to 
be about the most satisfactory device as far as disengaged operating 
characteristics, especially idle speed. 
For purposes of the test data presented, eleven sample units were prepared, 
Sample Nos. 1-6 being the prior art device of FIG. 2 and Sample Nos. 7-11 
being the invention as in FIG. 3. At the time of assembly of the units, 
measurements were taken of various clearances, which are shown in the 
first portion of the data table and labelled in FIGS. 2 and 3. Wiper 
clearance (W.CL.) is the distance between the wiper portion 53 and 
recessed forward surface 51. Generally, wiper efficiency has been found to 
increase as wiper clearance decreases. Outside diameter clearance 
(O.D.CL.) is measured radially in the prior art device, but in the 
invention, is measured perpencidular to the surfaces 65 and 73. In either 
case, it is the width of the gap between the input and output coupling 
members. Bottom end clearance (B.E.) is the distance between rearward wall 
surface 55 and the wall surface 57. Top end clearance (T.E.) is the 
distance between the valve plate 29 and the forward surface 49. Each of 
these clearances is generally considered relevant to idle speed (i.e., the 
speed of the output coupling member 13 with the unit disengaged). For each 
sample unit, two tests were run; one at 3500 rpm input speed, and the 
other at 4500 rpm input speed. At each input speed, an output speed 
reading was taken for IDLE (disengaged) and PEAK (engaged) and a 
calculation was made of P/I, the ratio of peak speed to idle speed. As is 
well known to those skilled in the art, the P/I ratio is important as an 
indication of the ability of a unit to have reduced idle speed without a 
loss of peak speed. Finally, the last column of data is the time (in 
seconds) required for the unit to pump-out, i.e., go from engaged to 
disengaged, at an input speed of 2000 rpm. It is, of course, desirable for 
pump-out time to be a minimum. Each of the sample units was an Eaton 
Series 140 fan drive, the type used commerically on the Chevrolet 
Chevette, but with OD clearances as shown in the data, for Sample Nos. 
1-6, which are larger than those on the units sold commerically. Each unit 
was equipped with the same 12.6 inch fan and contained the same volume of 
2000 cs. fluid. The bottom line indicates the % of improvement, using the 
invention, for IDLE, P/I ratio and PUMP-OUT time. 
__________________________________________________________________________ 
Sample 
Clearances 3500 rpm Input 
4500 rpm Input 
PUMP- 
No. Wiper 
O.D. 
B.E. 
T.E. 
IDLE 
PEAK 
P/I 
IDLE 
PEAK 
P/I 
OUT 
__________________________________________________________________________ 
1 .019 
.046 
.023 
.041 
1650 
2700 
1.64 
1650 
3050 
1.85 
27 
2 .014 
.047 
.024 
.036 
1650 
2820 
1.71 
1550 
3250 
2.10 
36 
3 .012 
.047 
.023 
.036 
1400 
2800 
2.00 
1500 
3050 
2.03 
27 
4 .014 
.045 
.019 
.039 
1550 
2850 
1.84 
1650 
3150 
1.91 
33 
5 .014 
.050 
.022 
.038 
1350 
2850 
2.11 
1450 
3300 
2.28 
23 
6 .015 
.048 
.020 
.038 
1350 
2730 
2.02 
1530 
3060 
2.00 
30 
AVG. 
.0147 
.0472 
.0218 
.0380 
1492 
2792 
1.87 
1550 
3143 
2.02 
29.3 
7 .014 
.044 
.029 
.034 
1100 
2700 
2.45 
1300 
3000 
2.31 
22 
8 .016 
.040 
.029 
.034 
1150 
2700 
2.35 
1350 
2900 
2.44 
19 
9 .016 
.039 
.029 
.035 
1300 
2750 
2.12 
1350 
3000 
2.22 
24 
10 .016 
.045 
.023 
.038 
1250 
2750 
2.20 
1350 
3100 
2.30 
24 
11 .014 
.040 
.029 
.035 
1200 
2750 
2.29 
1250 
3050 
2.44 
18 
AVG. 
.0152 
.0146 
.0278 
.0352 
1200 
2730 
2.28 
1320 
3010 
2.28 
21.4 
% Improvement 
With Invention 19.6% 21.9% 
15.1% 12.9% 
27.0% 
__________________________________________________________________________ 
In reviewing the above data, and the % improvements for IDLE, it should be 
noted that the effect of bearing drag was not taken into effect. For 
example in the units tested it was found that with absolutely no fluid in 
the unit, the unit would still have an "IDLE" speed of at least about 800 
rpm due to bearing drag (the drag of the bearing set 21 of FIG. 1). 
Therefore, recalculating the % improvement taking bearing drag into 
account, 800 rpm could be used as the "zero" point, or the indication of 
absolute minimum possible idle speed. For example, at 3500 rpm input, the 
prior art devices averaged 692 rpm (1492-800) above "zero" while the 
invention averaged 400 rpm (1200-800) above "zero", an actual improvement 
(decrease) of 292 rpm. This decrease in idle speed toward the minimum 
possible represents an improvement of 42%. A similar recalculation can be 
made for the other percentage figures to yield more meaningful results.