Floating wiper for a pump plate of a viscous fluid clutch

A floating wiper assembly mounted on a pump plate of a viscous fluid clutch includes a spring secured at its first end to a pump plate. A wiper formed from a low-friction material is secured to a second end of the spring and received in an opening in the pump plate. During assembly of the clutch, the wiper is urged by the spring into the pumping chamber and accommodates variances in machining and assembly variances. The wiper projects into a pumping chamber to create a fluid pressure rise to enhance the pump-out through an orifice of fluid in the pumping chamber to the reservoir.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a viscous fluid coupling device. 
In particular, the present invention is concerned with a floating wiper 
mounted on a pump plate of a viscous fluid fan clutch. 
2. Statement of the Related Art 
A thermostatically-controlled viscous fluid clutch assembly for driving and 
rotating a vehicle cooling fan is well-known. A multi-bladed fan is 
removably secured to a body of the clutch assembly. The fan and clutch 
assembly are installed between an accessory pulley of a vehicle engine 
(typically the water pump pulley) and a radiator. The clutch assembly 
drives the fan at high speeds close to input speed when cooling is 
required and permits the fan to rotate at low speeds when cooling is not 
required. Thermostatic control of the fan through the clutch assembly 
reduces the load on an engine and the noise caused by fan rotation, 
resulting in horsepower gain and improved fuel economy. 
Generally, a clutch assembly includes a clutch plate having lands and 
grooves mated to the body having complementary lands and grooves. A pump 
plate separates a pair of internally-contained chambers, a collecting 
chamber and a pumping chamber, from a reservoir. Gates in the pump plate 
permit the flow of a viscous fluid from the reservoir to the collecting 
chamber and into a shear zone between the lands and grooves of the body 
and clutch plate. Fluid sheared between the lands and grooves transfers 
input torque from the clutch plate to drive the body and the attached fan. 
Fluid flow through the pump plate gates is controlled by a control arm 
placed adjacent the pump plate. When cooling is not required, the control 
arm is rotated so that the gates are covered and the majority of the fluid 
in the shear zone is pumped into the pumping chamber. Orifices in the pump 
plate permit passage of the fluid from the pumping chamber into the 
reservoir. The removal of a majority of the fluid from the shear zone 
substantially reduces the shear between the clutch plate and the body, 
thereby substantially reducing the rotation of the fan. 
When cooling is required, the control arm is rotated an opposite direction 
to uncover the gates and permit fluid to flow into the shear zone, thereby 
increasing the shearing force between the clutch plate and the body. This 
increase in input torque results in faster rotation of the fan to increase 
the flow of cooling air. 
Oftentimes, a bimetallic element is utilized to actuate the control arm, 
and thus the flow of fluid through the pump plate gates. The bimetallic 
element may be connected to a control shaft which is in turn connected to 
the control arm. As the bimetallic element expands due to the temperature 
of warm ambient air, the shaft rotates, thereby causing the rotation of 
the control arm. As the ambient air cools, the bimetallic element 
contracts, causing the control shaft and the control arm to rotate in an 
opposite direction. 
It is well-known to provide wiper elements on a surface of the pump plate 
in communication with the pumping chamber. A plurality of wipers project 
from the pump plate adjacent each pump plate orifice into the pumping 
chamber. Each wiper can be formed as a thin, flat element secured to the 
pump plate usually by welding. In other embodiments, a wiper may be 
integrally formed with the pump plate by stamping a projection in a pump 
plate adjacent each pump plate orifice. As a fan clutch is rotated, an 
increase in fluid pressure in the pumping chamber occurs as the wiper 
creates a fluid dam. The increase in fluid pressure results in increased 
fluid flow through the pump plate orifices. 
Control of machining and assembly tolerances are important to the function 
of conventional fluid clutch assemblies. A particular area where 
tolerances must be closely checked and controlled involves the wiper and 
the pumping chamber. During formation of a pump plate, the height of a 
stamped or welded wiper must be closely controlled. To maximize the 
pump-out efficiency of a clutch assembly, it is desirable that the wiper 
extend as far as possible into the pumping chamber. Of course, the height 
of a manufactured wiper cannot exceed the allotted design height. 
Furthermore, the distance between the pump plate and the clutch plate must 
be controlled so as to provide adequate space for receiving the wipers. 
The height of wipers and the width of pumping chambers are usually in the 
range of a few thousandths of an inch. Control of these dimensions adds to 
the costs of machining and assembly. In order to reduce costs, 
conventional clutch designs shorten the height of wipers to provide extra 
space and accommodate machining and assembly variances. 
The art continues to seek improvements. It is desirable to provide wipers 
in a pumping chamber to enhance the pump-out of the chamber. Concurrently, 
it is desirable to provide a clutch design wherein the machining and 
assembly costs can be reduced. 
SUMMARY OF THE INVENTION 
The present invention is directed to a viscous fluid drive device 
particularly suitable for a fan clutch assembly of a vehicle. The present 
fan clutch assembly utilizes a floating wiper assembly mounted on a pump 
plate. The wiper is urged into a pumping chamber and into contact with a 
clutch plate by a spring. The spring permits the wiper to position itself 
in a pumping chamber and accommodate variances in the clutch plate 
assembly. The variability of the wiper permits the machining and the 
assembly tolerances of a clutch assembly to be increased, thereby reducing 
the associated costs. 
In a preferred embodiment, the invention includes a floating wiper assembly 
for enhancing the pump-out of fluid from a pumping chamber to a reservoir 
in a viscous fluid clutch. The wiper assembly includes a spring secured at 
its first end to a pump plate. A wiper formed from a low-friction material 
is secured to a second end of the spring and received in an opening in the 
pump plate. During assembly of the clutch, the wiper is urged by the 
spring into the pumping chamber and accommodates variances in machining 
and assembly variances. The wiper projects into a pumping chamber to 
create a fluid pressure rise to enhance the pump-out through an orifice of 
fluid in the pumping chamber to the reservoir.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates a multi-bladed fan and clutch assembly, indicated 
generally at 10, for drawing cooling air through the core of a vehicle 
radiator (not illustrated) through which engine cooling fluid is 
circulated. The fan and clutch assembly 10 is mounted on the outboard end 
of a rotatably driven shaft 12 whose inboard end terminates in a flange 14 
which can be secured to a conventional engine-driven water pump pulley 
(not illustrated). The fan and clutch assembly 10 includes a dished main 
body indicated generally at 16 centrally mounted for rotation on shaft 12 
by a bearing 18. The main body 16 is formed with a plurality of radially 
extending bosses 20 to which a multi-bladed fan 22 (partially illustrated 
in FIG. 1) is attached by threaded fasteners 24. A plurality of fins 26 is 
provided on the outer surface of the main body 16 to dissipate heat 
transferred from a viscous fluid housed by the assembly 10. 
A cover plate indicated generally at 30 is mounted to a front face of and 
cooperates with the main body 16 to form a housing and reservoir as 
described below. The cover plate 30 is a dished member whose annular outer 
edge 32 is secured to the main body 16 by an annular retainer lip 34 spun 
over from the material of the main body 16. An annular seal 36, e.g. a 
formed-in-place gasket, is interposed between the edge 32 and the front 
face of the main body 16 to prevent leakage of the fluid from the interior 
of assembly 10. A plurality of fins 37 is provided on the outer surface of 
the cover plate 30 to dissipate heat transferred from the fluid. 
Disposed behind the cover plate 30 is a disk-like annular pump plate 
indicated generally at 38 whose diameter is slightly less than that of the 
cover plate 30. The pump plate 38 is drivingly secured to the main body 16 
as it is trapped on an annular shoulder 39 (see FIG. 2) of the main body 
16 by the cover plate 30. 
The pump plate 38 has a pair of diametrically opposed passages or gates 40 
provided in its central portion. When uncovered, gates 40 allow the fluid 
to flow into a collecting chamber 41 formed and bounded by the pump plate 
38, a clutch plate 42 and a divider ring 43. The clutch plate 42 is 
mounted (preferably splined or knurled) on shaft 12 at a central opening 
and provides for the hydraulic drive of the main body 16 and attached fan 
22 as described below. Ring 43, preferably formed from TEFLON, is mounted 
in an annular groove 44 in the outer or front face of the clutch plate 42 
and improves pump-out or clutch disengagement as described below. 
As illustrated in FIG. 2, the centrifugal forces of the rotating assembly 
10 force fluid in the collecting chamber 41 to radial fluid flow indicated 
at directional arrow 45. As fluid 45 reaches the lower portion of the 
collecting chamber 41, it is redirected to axial fluid flow indicated at 
directional arrows 46 through well-known passages 47 in the clutch plate 
42 into an annular serpentine fluid shear zone 48 formed by the grooves or 
spaces between interleaved concentric annular ridges or lands 49 formed in 
a rear face of a clutch plate 42 and complementary concentric annular 
ridges or lands 50 formed on an interior surface of the main body 16. 
Fluid sheared in the shear zone 48 transmits input torque from the 
rotatably driven clutch plate 42 to provide for the hydraulic drive of the 
main body 16 and the attached bladed fan 22 for cooling fan operation. Due 
to slippage between the clutch plate 42 and the main body 16, the fan 
speed is always less than the input speed from the shaft 12. 
Fluid indicated at directional arrow 52 is forced radially outwardly by 
centrifugal forces and exits the shear zone 48 into a pumping chamber 54 
formed and bounded by the pump plate 38, the clutch plate 42 and the 
divider ring 43. 
Fluid indicated at directional arrow 56 travels through a discharge orifice 
58 formed in the pump plate 38 back into a fluid reservoir 60 in a manner 
well-known in this art. 
The reservoir 60 formed between the cover plate 30 and the pump plate 38 
contains a specified quantity of viscous fluid. The covering and 
uncovering of the gates 40 to control the supply of the fluid into the 
collecting chamber 41 is provided by a control arm indicated generally at 
62. In the embodiment illustrated, the control arm 62 is a flexible 
longitudinal dished member having a planar central portion 64 and opposite 
planar wings 66 connected by a ramp wall 68 to form a profile 
complementary to the pump plate 38. The control arm 62 is drivingly 
connected to a control shaft indicated generally at 70 as described below. 
The control shaft 70 is rotatably mounted in a tubular hub portion 72 
formed in the central portion of the cover plate 30. An O-ring seal 74 is 
mounted in an annular groove in the control shaft 70 and makes peripheral 
contact with the inner wall of the hub portion 72 to prevent fluid leakage 
to the exterior of the assembly 10. 
A helically-wound bimetallic thermostatic valve control element indicated 
generally at 76 (FIG. 1) includes an inner end portion 78 mounted in a 
slot 79 formed in a forward end of the control shaft 70 and an outer end 
portion 80 mounted in a retaining tab 82 formed in the cover plate 30. 
Preferably, the valve control element 76 is recessed within a cavity 84 
surrounding the hub portion 72. Through this construction, an increase or 
decrease in ambient air temperature causes the winding or unwinding of the 
valve control element 76, resulting in rotation of the control shaft 70 
and the attached control arm 62. The control arm 62 is illustrated in the 
closed position in FIG. 1 wherein the wings 66 cover the gates 40. When 
the valve control element 76 expands due to heat, the control shaft 70 and 
the control arm 62 rotate in one direction so that the wings 66 uncover 
the gates 40 in a well-known manner in this art. When the valve control 
element 76 contracts due to cooling, the control shaft 70 and the control 
arm 62 rotate the opposite direction so that the wings 66 cover the gates 
40. 
A pair of floating wiper assemblies 86 are mounted on the pump plate 38 to 
enhance the pump-out of fluid 56 from the pumping chamber 54 through the 
orifices 58. Each assembly 86 includes a spring 88 and a wiper 90. 
The spring 88 is a thin, longitudinal member constructed from steel or 
other suitable material and is mounted to a front surface 92, i.e. the 
surface in communication with the reservoir 60, of the pump plate 38. A 
first end 94 of the spring is secured to the front surface 92 outbound of 
the control arm 62 by any suitable means. In the embodiment illustrated in 
the figures, the first end 94 is spot welded at 96. Other securing means, 
such as a fastener, can be utilized to secure the first end 94. A second 
end 98 of the spring 88 terminates adjacent a respective orifice 58. 
A wiper 90 is constructed from a low friction material, preferably a 
fiberglass filled polytetrafluoroethylene resin, suitable for contacting 
the clutch plate 42. The wiper 90 is connected to the second end 98 by any 
suitable manner, e.g. a fastener 102. While the wiper 90 illustrated in 
the figures is a solid cylinder, other configurations and shapes are 
within the scope of the invention. 
The wiper 90 is inserted in an opening 104 in the pump plate 38. The 
diameter of the opening 104 is slightly greater than the diameter of wiper 
90, thereby permitting the wiper 90 to freely slide in the opening 104. 
Preferably, the diameter of the opening 104 is not great enough to permit 
the passage of fluid 54 between the wiper 90 and the opening 108. If 
desired, a guiding flange 106 may encircle the opening 104 and protrude 
from a rear surface 108, i.e. the surface in communication with the 
pumping chamber 54, into the pumping chamber 54. The flange 106 acts as a 
guide wall as the wiper 90 slides in the opening 104. The length L of the 
wiper 90 is greater than the distance D between the rear surface 108 and 
the clutch plate 42 as described below. 
In the manufacturing process, each floating wiper assembly 86 is mounted on 
the pump plate 38 as described above. During assembly of the clutch 
assembly 10, pump plate 38 is mounted on the shoulder 39 of the main body 
16. The spring 88 urges the wiper 90 through the pumping chamber 54 and 
into full-time contact with the clutch plate 42. 
Since the length L of the wiper 90 is greater than the distance D between 
the clutch plate 42 and the rear surface 108, the wiper 90 contacts the 
clutch plate 42. The spring 88 allows the stack up tolerances in the 
clutch assembly 10 to be greater than in conventional clutches, thereby 
reducing machining and assembly costs. The tolerances can be increased to 
a sum equal to the length L of the wiper 90 minus the thickness T of the 
pump plate 38 (D=L-T). Therefore, the machining and stack-up variances for 
the assembly 10 prevent the contact of the wiper 90 on the clutch plate 42 
only when D exceeds L-T. The floating feature of the wiper 90 in the 
opening 104 assures contact of the clutch plate 42 by the wiper 90 when 
machining and assembly variances are present in the assembly 10. An 
advantage of this construction is a reduction of machining and assembly 
costs since the machining and assembly tolerances do not have to be as 
closely controlled as in conventional designs. 
In operation, the floating wiper assembly 86 enhances the pump-out of fluid 
54 in the pumping chamber 54. The wiper 90 projects into the pumping 
chamber 54 and creates an increase in fluid pressure, thereby forcing 
fluid 54 through the orifice 58 in a manner well-known in this art. The 
low friction material of the wipers 90 minimizes drag on the clutch plate 
42 by the floating wiper assemblies 86. The present wiper 90 provides 
improved pump-out over conventional wipers since the wiper 90 projects the 
entire distance D of the pumping chamber 54 and engages the clutch plate 
42. 
Although the present invention has been described with reference to a 
preferred embodiment, workers skilled in the art will recognize that 
changes may be made in form and detail without departing from the spirit 
and scope of the invention.