Note: Descriptions are shown in the official language in which they were submitted.
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VISCOUS DRIVE WITH VARIABLE PUMP ACTION
BAcxGRouND OF THE INVENTION
This invention relateg to rotary transmissions or
clutches of the viscous fluid type, comprising an outer
rotary casing with an inner rotary element, having closely
spaced surfaces between which the viscous fluid can generate
torque in the well-known manner.
The invention is particularly applicable to
transmissions of the kind in which it is required to reduce
or disconnect the drive at intervals and the invention is
particularly, though not exclusively, applicable to an
automatically controlled transmission or drive between an
internal combustion engine on a vehicle and-an auxiliary
component such as a cooling fan. In the case of cooling
fans in particular it is desirable, particularly in heavy
motor vehicles where the cooling fan absorbs considerable
power, to be able to disconnect the drive when cooling is
not needed. This can be detected, for example, by a thermal
sensor in the coolant circuit, or exposed to the air stream
passing through a radiator, or some other component of the
engine.
There are many existing viscous fluid
transmissions having means for disconnecting the drive but
they tend to be complicated and expensive to produce and for
various reasons their operating life is limited. It is
common practice to provide a pump which continuously
withdraws viscous fluid from an operating zone in which the
fluid provides viscous trnsmission of torque to a reservoir
where the fluid is no longer effective and the drive is
interrupted. In order to control the operation of the drive
it has been proposed to incorporate valves operated
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externally for controlling the flow of fluid towards or
away from tbe reservoir. It has also been proposed to
control the quantity of fluid in the operating zone by
means of an internal displaceable wall or membrane. As
stated above, however, all existing systems suffer from
said disadvantages and it is an object of this
disclosure to provide an improved transmission of this
general type which will be simple to manufacture and
reliable in operation.
Broadly stated, here described is a viscous fluid
transmission including a rotary casing and a rotary
element within the casing, the casing and the rotary
element being connected respectively to two drive
shafts, a quantity of viscous fluid within the casing,
means for pumping the fluid from its normal position in
the casing into a holding reservoir or other displaced
zone so as to reduce the quantity of fluid in contact
with the rotary element and hence the transmitted
torque, and means for varying the pumping action to
modify the quantity of fluid in the casing.
Preferably the pumping means includes cooperating
elements on the casing and the rotary element and the
pumping action may be modified by movement of the rotary
element relative to the casing in an axial direction.
The pumping action may be modified automatically in
response to sensed changes in the temperature of an
external component or medium.
In any case, the transmission preferably includes
means controlling the return of fluid to the casing and
in a particular preferred construction the rotary
element is shifted axially in relation to the rotary
casing by a fluid operated ram having piston and
cylinder elements connected respectively by rotary
thrust bearings, one to the casing and the other to the
rotary element, at least one of the two parts of the ram
being non-rotary.
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More particularly in accordance with a first aspect
of the invention there is provided a viscous fluid
transmission including a rotary casing and a rotary
element within the casing, the casing and the rotary
element being connected respectively to two drive
shafts, a quantity of viscous fluid within the casing,
means for pumping the fluid from its normal position in
the casing into a holding reservoir or other displaced
zone so as to reduce the quantity of fluid in contact
with the rotary element and hence the transmitted
torque, and means for varying the pumping action by
movement of the rotary element relative to the casing in
an axial direction to modify the quantity of fluid in
the casing.
In accordance with a second aspect of the invention
there is provided a viscous fluid transmission including
a rotary casing and a rotary element within the casing,
the casing and the rotary element being connected
respectively to two drive shafts, a quantity of viscous
fluid within the casing, means for pumping the fluid
from its normal position in the casing into a holding
reservoir or other displaced zone so as to reduce the
quantity of fluid in contact with the rotary element and
hence the transmitted torque, means for varying the
pumping action to modify the quantity of fluid in the
casing, said rotary element being shifted axially in
relation to the rotary casing for varying the pumping
action, by a fluid operated ram having piston and
cylinder elements connected respectively by rotary
thrust bearings, one to the casing and the other to the
rotary element, at least one of the two parts of the ram
being non-rotary.
In accordance with a third aspect of the invention
there is provided a viscous fluid transmission including
a rotary casing and a rotary element within the casing,
the casing and the rotary element being connected
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respectively to two drive shafts, a quantity of viscous
fluid within the casing, means for pumping the fluid
from its normal position in the casing into a holding
reservoir or other displaced zone so as to reduce the
quantity of fluid in contact with the rotary element and
hence the transmitted torque, means for varying the
pumping action to modify the quantity of fluid in the
casing, said pumping means including cooperating
elements on the casing and the rotary element; said
pumping action being varied to modify the quantity of
fluid in said casing by shifting said rotary element
relative to said rotary casing.
Embodiments of the invention will now be described
with reference to the accompanying drawings, wherein;
Fig. 1 is a half sectional side elevation through a
rotary fluid transmission embodying the invention;
Figs. 2 and 3 are fragmentary views of component
parts; and
Fig. 4 is an alternative embodiment of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In an automatically operated drive for a cooling
fan on a vehicle engine, the unit comprises a rotary
casing 10 formed from two casing members 11, 12 and an
internal rotary element 13 connected to a short hollow
shaft 14 having an external flange 15 by which it may be
bolted to the drive flange of a shaft, not shown, driven
by the vehicle engine. The fan blades 16 are attached
to a ring 17 secured to the casing shell 11 by bolts 18
with intervening resilient cushioning elements 20.
The two casing shells 11, 12 are formed with
internal annular grooves and ribs 23 and the rotary
element 13 has corresponding grooves and ribs 24 which
lie between and are closely spaced from the grooving and
ribs 23 on the casing. Thus when a viscous fluid is
- present in the casing, a considerable torsional drag or
drive exists between the two parts. To control the
quantity of fluid in this
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1 labyrinth zone, an annular wall 25 is provided within the
casing defining an annular reservoir 26 and a radial passage
27 leads inwards to this reservoir from a pumping port 28
which cooperates with a scoop 29 (Fig. 2) in this outer
annular face of the casing. The ad~acent annular face 30 of
the internal rotary element 13 creates a rotational movement
of the fluid between the two parts and thus causes pumping
action driving the fluid radially inwards. The
effectiveness of the pumping action can be varied by
altering the distance or displacement between the two faces
30, 31 and in this example, the control is effected by
bodily axial movement of the whole rotary element 13
relative to the casing.
In this particular example, the internal element
with the shaft 14 and flange 15 are held fixed axially and
the whole casing is moved. An internal pneumatically
operated ram includes a ram cylinder 35 connected via a
thrust bearing 36 to the shaft 14 and thus held fixed
axially. An annular piston 37 is connected by an internal
hollow spindle 38 and another thrust bearing 39 to the
forward casing part 12. Compressed air to operate the ram
is admitted via a flexible pressure tube 40 and a coupling
41 to an internal passage 42 within the spindle 38, this
communicating via port 43 with the annular space 44 between
the piston and cylinder.
Compressed air is automatically admitted to the
pressure hose 40 under the control of a thermostat sensing
the temperature of the coolant for the engine. When the
coolant temperature rises, the supply of compressed air is
shut off by a valve (not shown) and a compression spring 45
acts in an axlal direction urging the casing 12 bodily to
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the left in Fig. 1 so as to cause axial separation
between the surfaces 30, 31 and thus destroy the pumping
action. Accordingly, fluid is retained in the whole
labyrinth zone and the maximum viscous drive is obtained
hence causing the maximum cooling effect of the fan
blade 16. When the sensed coolant temperature falls,
the thermostat opens the air valve admitting compressed
air to the hose 40 from which it is transmitted to the
front face of the piston 37 generating an axial force
which overcomes the spring 45 and causes the casing to
move bodily to the right thus closing the clearance
between the pumping faces 30 and 31. The resultant
pumping action drives the fluid radially inwards along
the passage 27 into the reservoir 26 where it is
retained and the depletion of fluid in the labyrinth
pumping zone causes the drive to be interrupted. Thus,
without any internal delicate valve mechanisms and
without any rotary seals, other than normal bearing
seals, a simple, reliable control of the pumping action
to vary the quantity of fluid in the operating zone of
the drive unit is provided.
In a modification, there may be added a simple
self-contained means of controlling also the return flow
of fluid from the reservoir to the pumping zone. Thus,
as shown in Fig. 3, the rotary element 13 may be
provided with an additional ring 50 in close contact
with the innermost ring 51 on the casing, and acting as
a valve such that when the element 13 moves to the right
the ring 50 opens a small gap and allows fluid to flow
back to the pumping zone. This again is provided
without any other internal moving parts.
The unit, as described, may be designed for a
positive on/off operation, the internal element 13 having
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1 just two possible positions. Alternatively, however, the
ram cylinder 35 and annular piston 37 may be arranged to
control or adjust the axial position of the rotary element
13 so as to provide either continuous varlation or stepping
positioning so as to modify or modulate the pumplng e~fect
and hence to modulate the guantity of fluid in the
labyrinth, which in turn provides modulation of the speed of
the fan.
In place of the ram 35 and piston 37 as
illustrated, other operating systems may be employed, for
example, an electric solenoid, or a mechanical linkage, or a
mechanical connection to a remote fluid actuator.
In the unit illustrated the control is derived
from a remote thermal sensor, not illustrated, positioned in
the liquid coolant circuit of the engine. Other thermal
controls may be used such as an air sensing unit, for
example in a form of a bi-metal strip positioned in the air
stream flowing over the fan blades 16. This bi-metal
element may be located, for example, at the left-hand front
end of the unit centrally on the rotary axis and arranged to
operate a small pneumatic control valve which admits
compressed air to the ram 35 and piston 37. The air sensing
unit may be used as an alternative or an addition to the
liquid coolant sensor as described.
ALTERNATE EMBODIMENT OF THE INVENTION
In an alternative arrangement of the invention as
illustrated in Fig. 4, the variation in drive can be
achieved automatically as a result of the change in
temperature of a wax capsule which acts between axially
movable parts of the drive comprising an external rotary
casing and an internal rotary element.
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1 In the modified embodiment shown in Fig. 4, the
rotary casing 100 includes a casing member or shell 120
formed with a central cavity 152 housing a compreeslon
spring 153 which reacts against an annular flange 154 on the
end of a spindle 155 mounted with the shaft 14 via the
thrust bearing 136. The spring 153, therefore, normally
acts to cause the casing 100 to be biased to the right to
close the clearance between the faces 130 and 131 with the
resulting interruption of the drive. However, when the
temperature within the unit rises, a wax capsule 156 within
a cavity 157 in the spindle 155 expands and drives out a
piston 158 on a plug 159 secured within the shell 120, thus
overcoming the bias of the spring 153 and causing the casing
100 to move bodily to the left. This opens the clearance
between the pumping faces 130 and 131 to reduce or destroy
the pumping action 80 that the viscous drive between the
casing 100 and the rotary element 130 is restored.
Of course other temperature responsive devices
capable of overcoming the bias of the spring 153 could be
used in place of the wax capsule 156.
