Dimpled bimetal temperature responsive fan drive coupling

A shear liquid fan drive assembly for the radiator cooling system of an internal combustion engine of the type wherein a temperature responsive valve controls the degree of rotary coupling between the engine and a radiator cooling fan by controlling the quantity of shear liquid between a driving disc and a driven housing carrying the fan. The specific improvement relates to a bi-metal strip for the temperature controlled fluid coupling, the strip being so configured that its improper placement on the fluid coupling results in maximum fluid coupling and hence maximum cooling of the engine by the fan.

This invention relates to a viscous liquid fan drive for the radiator 
cooling system of an internal combustion engine. Such fan drives are well 
known and usually include a rotary drive disc which is driven by the 
engine. The drive disc is rotatably mounted within a housing or casing, 
with the casing carrying the blades of a fan. A quantity of viscous 
liquid, often termed a shear liquid, is admitted from a reservoir chamber 
to a drive chamber, the rotary disc being positioned in the drive chamber. 
Depending upon the amount of the shear liquid in the driving chamber the 
degree of rotary coupling between the driving rotor and the fan is varied. 
This variance is usually controlled by a temperature responsive valve 
assembly, the valve opening to admit a larger quantity of fluid when high 
cooling requirements are called for, and closing to limit the degree of 
rotary coupling when lower cooling requirements exist. Such assemblies 
include a passageway for the shear liquid between the radially outermost 
portion of the drive chamber in which the drive rotor is positioned and 
the reservoir chamber. The shear liquid is deflected so as to flow from 
the radially outermost part of the drive chamber through the passageway 
and thence to the reservoir chamber. Such devices are well known, and are 
presently classified in Class 192, Subclass 58 of the United States Patent 
Office classification. Such devices are further described in Society of 
Automotive Engineers publication 740,596 of August 12-16, 1974, by Everett 
G. Blair, hereby incorporated by reference. In general, such devices lower 
the power lost to the radiator cooling fan by correlating the fan power 
requirement with the engine cooling requirement at various engine speeds 
and ambient temperatures. 
The temperature responsive valve assembly usually employs a bi-metal strip 
to determine the position of the valve, such position in turn controlling 
the amount of shear liquid which rotatably couples the engine power to the 
fan. Examples of bi-metal strip constructions of this type are afforded by 
the structures described in U.S. Pat. Nos. 3,179,221 and 3,191,733 to 
Weir, hereby incorporated by reference. The bi-metal strip must be 
properly oriented relative to the valve which it controls. Thus, when the 
bi-metal bows in one direction, it actuates the valve towards one 
position. Bowing of the bi-metal strip in the opposite direction actuates 
the valve toward the opposite position. In the usual valve assembly 
arrangement, lower engine ambient temperatures cause the bi-metal to bow 
in a direction to close the valve, higher engine ambient temperatures 
causing the opposite bowing direction and opposite valve action, i.e., the 
valve is opened. 
In the assembly and in the repair of such temperature controlled fluid 
couplings, it is hence necessary that the bi-metal strip be properly 
oriented with respect to the valve. Thus, if high engine temperatures call 
for maximum shear liquid coupling to thereby effect maximum radiator 
cooling by the fan, improper bi-metal placement may result in engine 
overheating. If, for example, the bi-metal bows to close the valve at high 
engine temperatures, instead of bowing in a direction to open the valve, 
radiator cooling by the fan will be less than required and engine damage 
may occur. 
According to the practice of this invention, a bi-metal strip is so 
configured that an incorrect placement or assembly of the bi-metal strip 
on the housing of the fluid coupling cannot result in overheating of the 
engine due to insufficient cooling action by the fan on the radiator. This 
is accomplished by providing the bi-metal strip with a dimple to thereby 
define a convex zone on one surface of the bi-metal strip and a concave 
zone on the opposite surface of the strip. During normal assembly and 
operation of the apparatus, the convex zone of the bi-metal strip contacts 
an actuating member for the valve. However, should the bi-metal strip be 
incorrectly placed on the fluid coupling, the concave zone will face the 
actuating member, with the construction and relationship of the parts 
being such that the valve will remain in the fully open position to 
thereby provide maximum cooling action by the fan at all times. While the 
bi-metal temperature control action will not be present during such 
mis-assembly (with consequent loss of efficiency otherwise enjoyed by 
proper matching of radiator cooling with engine cooling requirements), the 
coupling will nevertheless preclude engine overheating by virtue of 
constant operation in the maximum coupling condition.

Referring now to FIGS. 1 and 2 of the drawings, the numeral 10 denotes 
generally a typical temperature controlled fluid coupling for coupling the 
engine to the fan. The numeral 12 denotes a shaft adapted to be connected 
to a belt member, such as a pulley, in turn driven by the engine. The 
reader will understand that the radiator is to the left of the illustrated 
coupling 10. The numeral 14 denotes a drive disc coupled to shaft 12, the 
disc rotating in drive chamber 16 of fluid coupling housing 17, the 
housing being of a conventional construction. The housing carries a 
plurality of fan blades, not illustrated. The numeral 18 denotes a 
reservoir chamber which contains a quantity of a shear liquid, such as a 
silicone liquid. The numeral 20 denotes a partition which separates the 
drive chamber 16 (in which the drive rotor 14 rotates) and the reservoir 
chamber 18. The numeral 22 denotes a valve opening in partition 20, the 
opening adapted to be opened or closed by the action of flapper member 24, 
normally biased in the valve open position. Numeral 26 denotes a cover to 
which bracket 28 is attached. The numeral 28 denotes the bracket having 
upstanding ear portions 29 at each end thereof, the ear portions receiving 
the ends of bi-metal strip 30. The numeral 32 denotes an elongated rod for 
actuating the flapper 24. Dimple 36 is centrally provided on the bi-metal 
strip 30, thereby defining a convex zone 38 on one side of the strip and a 
concave zone 40 on the other side. The reader will note that convex zone 
38 contacts one end of elongated rod 32. 
The normal operation of the device shown at FIG. 1 is as follows. When 
engine temperatures are relatively high, maximum radiator cooling is 
required, this in turn requiring maximum liquid coupling between the input 
shaft 12 and the housing 17 which carries the fan blades. Bi-metal 30, in 
response to higher temperatures, bows towards the left as viewed at FIG. 
1, thereby opening aperture 22 of partition 20 and providing a maximum 
quantity of shear liquid in drive chamber 16. In this manner, maximum 
shear liquid coupling between drive rotor 14 and housing 17 is realized. 
Contrariwise, relatively lower engine temperatures permit a lesser turning 
of the fan (with consequent saving of engine power), the bi-metal strip 30 
bowing to the right as viewed at FIG. 1 to thereby close the opening 22. 
Such closure results in less shear liquid in driving chamber 16 with 
relatively greater slippage between input shaft 12 and its attached drive 
disc 14 and the housing 17. 
Referring now to FIG. 3 of the drawings, a reversed position of bi-metal 30 
relative to elongated rod 32 is shown. Such a reversed position might 
occur due to improper assembly of the coupling either at its place of 
initial manufacture or during repair or replacement of the bi-metal strip. 
The reader will observe that in this configuration, bowing of bi-metal 
strip 30 in either direction will not result in contact with elongated rod 
32 and accordingly flapper 24 will remain in its normally biased open 
position. This in turn will result in a maximum of fluid coupling between 
drive shaft 12 and housing 17, in turn causing maximum cooling by the fan 
of the radiator of the engine. While this mode of operation will not be as 
efficient as the mode in the normal position shown at FIG. 1, it will 
nonetheless preclude overheating of the engine due to less than required 
cooling action of the fan under maximum engine temperature conditions.