Temperature responsive coupling

A temperature controlled fluid shear coupling adapted to drive a fan for an internal combustion engine. The coupling includes a driven member defining a housing adapted to carry the fan, a drive member adapted to be driven by the engine, a working chamber defined by the driven and drive member and containing viscous fluid, a pump for removing fluid from the working chamber to a reservoir, and temperature control assembly which varies the volume of fluid in the working chamber by controlling fluid flow from the reservoir to the working chamber in response to temperature changes. The temperature control includes a wax filled power element and a valving member. The valving member blocks fluid flow from the reservoir to the working chamber when the wax is solid and allows flow to the working chamber when the wax is a liquid.

FIELD OF THE INVENTION 
This invention relates generally to torque control of fluid shear couplings 
and specifically to control of torque by controlling fluid level in such 
devices. 
DESCRIPTION OF THE PRIOR ART 
Fluid shear couplings are well known in the prior art. These couplings 
employ fluid shear stress to transmit torque between two relatively 
rotatable input and output members. The torque transmitting capacity of 
such couplings may be controlled in many ways. Torque control by varying 
the inventory of the fluid between the input and output members seems to 
be the most successful. Many couplings with inventory control employ a 
bimetallic spring, which is operative to position a valve element or pump 
element in response to temperature changes ambient to the spring. If the 
coupling is to be controlled in response to ambient temperatures exterior 
of the coupling, the spring, by necessity, is positioned on the coupling 
exterior. When so positioned, the spring must also move an intermediate 
mechanism that passes through the wall of the coupling. 
Exterior positioning of the spring, while necessary, creates some control 
problems. Control forces, provided by the bimetallic spring per degree 
temperature change of the spring, are low and at best marginal for moving 
the intermediate mechanism and the valve or pump element. Since the 
control forces are low, the spring is sensitive to centrifugal forces 
generated by rotation of the coupling. The spring is traditionally 
positioned coincident the rotation axis of the coupling to neutralize the 
centrifugal forces. However, there is more air flow at the radial 
extremities of the coupling and positioning of the spring at an extremity 
would provide better temperature response. Further, even with the spring 
positioned at the rotational axis, control may be lost if the intermediate 
mechanism sticks at the point where it passes through the wall of the 
coupling. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide superior torque control for a 
fluid coupling. 
A more specific object of this invention is to provide a fluid coupling 
having a temperature responsive torque regulating means which is 
insensitive to centrifugal forces generated by rotation of the coupling. 
Another object of this invention is to provide a fluid coupling having a 
temperature responsive torque regulating means which is positioned to 
provide improved temperature response. 
The fluid coupling of this invention is of the type including two 
relatively rotatable members which define a fluid working chamber; torque 
is transmitted from one member to the other by fluid shear stress when 
relative rotation occurs between the members; and the amount of torque 
transmitted is controlled by varying the fluid inventory in the working 
chamber. 
According to an important feature of this invention a temperature 
responsive device having a liquid-solid phase change substance controls 
the fluid inventory in response to a phase change of the substance over a 
predetermined temperature range. The use of a liquid-solid phase change 
substance as a control media provides very substantial forces per degree 
temperature change and hence, provides positive operation of the control 
mechanism. 
According to another important feature of this invention a temperature 
responsive device, in thermal communication with the ambient exterior of 
the coupling, is radially disposed with respect to the rotational axis of 
the coupling. This arrangement positions the temperature responsive device 
in an area having an increased air flow and hence, improves temperature 
response of the device.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention is embodied in a viscous fluid coupling 10, shown in 
elevation in FIG. 1. The coupling is adapted to be driven by a liquid 
cooled engine and in turn drive a cooling fan for removing heat from the 
engine coolant. The coupling includes a cast metal housing 11 consisting 
of a front housing member 12 (shown in FIGS. 1 and 2) and a rear housing 
member 14 (shown in FIG. 2). The front housing member is integrally formed 
with six radially disposed bosses 16, a plurality of cooling fins 18, and 
an annular reservoir 20. The reservoir projects axially outward from 
housing member 12 and has secured thereto a temperature control assembly 
22 and a weight 24 to counterbalance the weight of assembly 22. Bosses 16 
are machined and drilled with through holes 26 for securing a fan not 
shown in FIG. 1 to the housing. A ring 28, from which the fan blades 
radiate, is partially shown in FIG. 2. The ring is secured to the housing 
by six bolt and nut sets 30, one set of which is shown in FIG. 2. A raised 
portion 32, cast into housing member 12 contains a drilled passage 32a for 
communicating a fluid to the reservoir from a working chamber within the 
housing 11. Passage 32a is shown only in FIG. 2. For purposes of clarity, 
raised portion 32 in FIG. 2 is shown out of position with respect to the 
position shown in FIG. 1. 
The front and rear housing members are secured together by bolt and nut 
sets 30 and six screws 34 which are circumferentially spaced between bolt 
and nut sets 30. The ends of screws 34 are visable in FIG. 1. One of the 
screws is shown in FIG. 2. Nut and bolt set 30 and screw 34 are shown out 
of position with respect to their positions shown in FIG. 1. 
Referring now to FIG. 2, the coupling per se may be divided into four 
assemblies; a driving assembly which includes a shaft 36 and a drive 
member 38, a driven assembly which includes housing members 12 and 14, a 
bearing assembly which includes a front ball bearing 40 and a rear ball 
bearing 42 for journaling the housing members on shaft 36, and temperature 
control assembly 22. 
Shaft 36 of the driving assembly includes a flange portion 36a and a 
stepped bore portion 36b. Shaft 36 may be supported and rotated in any 
manner desired. Herein, support is provided by a shaft 44 and rotation by 
a pulley 46. Shaft 44 is pressed into stepped bore portion 36b. Shaft 44 
is rotationally supported by an unshown hanger bracket which is adapted to 
be fixed to an engine. Shaft 44 is further secured from axial and 
rotational movement relative to shaft 36 by a cap screw 52 and a pin 54. 
Pulley 46 is secured to flange portion 36a by a plurality of bolts 48, one 
of which is shown. Pulley 46 is driven by a V-belt 50. 
Driven member 38 includes hub portion 38a, an annular ring or rim portion 
38b, and a plurality of L-shaped spokes 38c which secure the rim and hub 
together. Annular rim portion 38b includes a smooth walled portion 38d at 
its outer extent and a ribbed walled portion defined by a plurality 
radially spaced, concentric rings 38e and 38f which project axially from 
both sides of the rim. 
Housing members 12 and 14 of the driven assembly are rotationally supported 
on shaft 36 by the bearings 40 and 42 of the bearing assembly. Rear ball 
bearing 42 includes an inner race 42a, an outer race 42b, and a row of 
ball bearings 42c which are protected by a pair of seals 42d. Inner race 
42a is pressed on shaft 36 and secured from axial movement by a shoulder 
36c formed on the shaft, and hub portion 38a of the drive member 38. Hub 
portion 38a is pressed on shaft 36 and further secured from axial movement 
by a nut 56. Outer race 42b is pressed into a bore 14a defined by an 
axially extending annular flange portion 14b of housing member 14. The 
outer race is further secured from axial movement by a shoulder portion 
14c and metal rolling of the flange portion 14b, as at 14d. 
Bearing assembly 40 includes an inner race 40a, an outer race 40b, and a 
double row of ball bearings 40c which are protected by a pair of seals 
40d. Outer race 40b is pressed into a shouldered bore 20a defined by the 
inner diameter of an inner annular wall portion 20b of reservoir 20. Inner 
race 40a is slide fitted on shaft 36. 
Housing members 12 and 14 of the driven assembly define an annular cavity 
58 having disposed therein drive member 38. Cavity 58 is sealed at its 
radially outer extent by an annular seal 60 and at its radially inner 
extent by seals 40d and 42d. Cavity 58 includes a smooth walled portion 
58a at its radially outer extent and a ribbed walled portion 58b which is 
disposed radially inward and adjacent the smooth walled portion. The ribs 
of ribbed walled portion 58b are defined by a plurality of radially 
spaced, concentric rings 58c and 58d. Rings 58c and 58d project axially 
into the spaces defined by radially spaced, concentric rings 38e and 38f, 
respectively. 
The smooth and ribbed walled portions of rim 38 and cavity 58 are spaced 
apart to define a fluid working chamber 59 which contains a variable 
inventory of viscous fluid such as silicone fluid. The viscous fluid 
transmits rotational forces from drive member 38 to housing members 12 and 
14 via fluid shear stress whenever a rotational speed difference exists 
between drive member 38 and housing members 12 and 14. The amount of 
rotational force transmitted is a function of many variables. Herein, only 
rotational speed differences and fluid level in the working chamber are of 
concern. The amount of rotational force transmitted is directly 
proportional to the speed difference and to the fluid level in the working 
chamber. 
A pump 62 is fixed to housing member 12 at the left end wall of smooth 
walled portion .[.58b.]. .Iadd.58a.Iaddend.. A passage 62a in pump 62 
provides means for passage of fluid through the pump. End 62b of passage 
62a is the pump inlet and end 62c is the pump outlet. Pump 62 is connected 
at its outlet to reservoir 20 via passages 64, 32a and 66. Pump 62 
provides a pumping pressure to remove fluid from working chamber 59 to 
reservoir 20 whenever driven member 38 rotates faster than housing member 
12. Pump 62 is a ramp type pump; such pumps are well known in the art. 
Particulars concerning the structure and operation of ramp pumps may be 
found in U.S. Pat. No. 3,268,041. Fluid flow from reservoir 20 to working 
chamber 59 is provided by an arcuate passage 68 formed in the right end 
wall 20c of reservoir 20. Arcuate passage 68, which is shown only in FIG. 
3, opens into the radially inner part of cavity 58. Spaces between spokes 
38c of drive member 38 allow fluid flow to both sides of working chamber 
59. Fluid flow, radially outward, through the labyrinth defined by the 
ribbed walls of working chamber 59 is enhanced by a plurality of radially 
extending, V-shaped grooves 70 and 72 formed into both faces of rim 
portion 38b. 
When drive member 38 is driving housing members 12 and 14, pump 62 will 
continuously pump fluid from working chamber 59 to reservoir 20 until the 
fluid level falls below inlet 62b. The fluid level in working chamber 59 
may be controlled between a minimum level, as determined by the position 
of passage 62b, and a maximum level by controlling the opening of arcuate 
passage 68. Temperature control assembly 22 controls the amount of opening 
of arcuate passage 68 in response to ambient air temperature changes 
exterior of the coupling housing, thereby controlling the amount of 
driving torque to housing members 12 and 14. 
Referring now to FIGS. 2 and 3, the temperature control assembly includes a 
valve assembly 74 disposed in annular reservoir 20 and a temperature 
sensing assembly 76 mounted on an annular wall portion 20d of reservoir 
20. Annular reservoir 20 is defined by wall portions 20b, 20c, 20d and an 
annular plate 77 which is secured to wall portions 20b and 20d by metal 
rolling. The mating surfaces of walls 20b, 20d and plate 77 are sealed by 
annular seals 77a and 77b. Valve assembly 74 includes an arcuate valving 
member 78, a mounting boss 20e which protrudes from end wall 20c of the 
reservoir, a pin assembly 80 for pivotally securing member 78 to boss 20e, 
a valve boss 20f which protrudes from end wall 20c, and a slotted opening 
78a for connecting the member 78 to temperature sensing assembly 76. 
Bosses 20e and 20f are not visible in FIG. 2. The front face of boss 20f 
has a smooth flat face 20g which provides a sliding-sealing interface with 
arcuate valving member 78. Arcuate passage 68 extends through boss 20f and 
end wall 20c. Passage 68 is sealed from communication with reservoir 20, 
when valving member 78 is in the position shown in FIG. 3. 
Temperature sensing assembly 76 includes a cup-shaped housing 82 having a 
radially extending flange portion 82a and heat transfer fins 82b. Housing 
82 is seated on a thermal insulating, annular ring 90 and is secured to 
wall portion 20d by a plurality of screws 94 which are thermally insulated 
from flange portion 82a by collars 96. A pair of annular seals 97 prevent 
fluid leakage from reservoir 20 and the interior of housing 82. 
Temperature sensing assembly 76 also includes a wax filled power element 
98, a thermal insulating piston 100, and a helical spring 102 for biasing 
piston 100 toward element 98. Piston 100 has a cup-shaped portion 100a 
which embraces one end of element 98, a shaft portion 100b which passes 
through the inside diameter of annular ring 90, and a forked end 
.Iadd.100c .Iaddend.which receives valving member 78. A pin 104 slidably 
secures piston 100 to valving member 78. The annular space defined by the 
outside diameter of shaft portion 100b and the inside diameter of ring 90 
allows enough fluid circulation between reservoir 20 and the interior of 
housing 82 to prevent a hydraulic lock when piston 100 moves. 
Housing 82 and element 98 are thermally insulated from metal contact with 
the coupling housing so that element 98 may respond to ambient 
temperatures exterior of the coupling. The thermal insulating is not 
defeated by the silicone fluid in housing 82, since this fluid is 
relatively stagnant and has a low heat transfer coefficient. The ability 
of the element to respond to ambient temperature exterior of the coupling 
is further enhanced by placing the temperature control radially outward of 
the rotational axis of the coupling and into a position allowing greater 
ambient air flow over the element. 
Wax filled power elements are well known in the art of thermostatic valves 
for engine cooling systems. Element 98 is pressed into housing 82 to 
maximize heat transfer from the housing to the wax in the element. Element 
98 includes a pushrod 98a which extends from the element into contact with 
piston 100. The wax in the element is selected to have a high coefficient 
of expansion at its liquid-solid phase change temperature. The wax volume 
increases when it liquifies and moves the pushrod outward from the 
element, thereby moving piston 100 and causing valving member 78 to 
pivotally move away from arcuate passage 68. The wax volume decreases when 
it solidifies and spring 102 moves the piston toward the element, thereby 
retracting the pushrod and also causing valving member 78 to pivotally 
move over arcuate passage 68. The wax in element 98 may have any 
liquid-solid temperature range desired, for this particular coupling we 
have selected a range of 155.degree. F. to 165.degree. F. 
When the wax is a solid, at temperatures below 155.degree. F., passage 68 
is blocked by valving member 78. When passage 68 is blocked, the fluid 
inventory in working chamber 59 will tend toward a minimum level as 
determined by inlet passage 62b of pump 62. Hence, the position of passage 
62b determines the minimum torque capacity of the coupling. When the wax 
is a liquid, at temperatures above 165.degree. F., passage 68 is 
unblocked; this allows free circulation of the pumped fluid back to the 
working chamber, thereby maintaining the fluid inventory and the coupling 
torque capacity at maximum levels. 
OPERATION 
Operation of the disclosed coupling is believed to be apparent from the 
drawing and the preceding description. When the rotational speed of drive 
member 38 is greater than the rotational speed of housing 11, fluid is 
pumped from the working chamber to the reservoir by pump 62. When passage 
68 is uncovered, the fluid freely returns to the working chamber, thereby 
maintaining the volume of the fluid inventory in the working chamber at a 
maximum and hence, allowing maximum torque transmission from drive member 
38 to housing 11 by fluid shear stress. When passage member 68 is covered, 
the fluid is stored in the reservoir, thereby decreasing the volume of the 
fluid inventory in the working chamber to a minimum and hence, allowing a 
minimum torque transmission from drive member 38 to housing 11. Covering 
and uncovering of passage 68 is controlled by temperature sensing assembly 
76 and valving member 78 of temperature control assembly 22. When the wax 
in element 98 is a solid, valving member 78 is moved to a position 
covering passage 68. When the wax is a liquid, valving member 78 is moved 
to a position uncovering passage 68. 
The preferred embodiment of the invention has been disclosed for 
illustrative purposes. The following claims are intended to cover the 
inventive portion of the preferred embodiment and variations of 
modifications within the spirit of the invention.