Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ENGINE THERMOSTAT HAVING BYPASS PRESSURE-DAMPENING FLUID
PASSAGE
Field of the Invention
[0001] This invention relates to internal combustion engines, including but
not
limited to control of an engine cooling system flow with a thermostat device.
Background of the Invention
[0002] Internal combustion engines have cooling systems associated therewith
that
transfer heat away from the engine structure. These cooling systems typically
inciude thermally actuated devices, or thermostats, that can route a cooling
fluid flow
either into the engine or into a radiator depending on a temperature of the
cooling
flow.
[0003] Typical engine thermostats are 3-way valves having one inlet and two
outlets. A first port thereof acts as an inlet for the cooling fluid flow. A
second port
thereof acting as a first outlet, when open, directs the cooling fluid flow
directly into
the engine when the cooling flow is at a low temperature. A third port thereof
acting
as a second outlet, when open, allows the cooling fluid flow to bypass the
engine
and pass through a radiator, where it is cooled, before returning to the
engine. A
thermal actuator controls the opening of valves that control the cooling fluid
flow into
the first and/or second outlet. The thermal actuator, typically a material
pushing
onto a rod when heated and expanding, is immersed in the incoming cooling
fluid
flow at the inlet of the thermostat.
[0004] When an engine operates at high engine speed conditions, a cooling
fluid
flow rate is increased. This increased flow rate often creates instabilities
during
transitions periods in a thermostat position. These instabilities are often
the result of
hydrofoil effects onto plates of the thermostat that are used to fluidly block
the
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second and third ports. These instabilities often cause the plates to vibrate
or
"slam" against their valve seats, thus causing damage thereto.
Summary of the Invention
[0005] A thermostat assembly includes an actuator portion having a sealed
container with an arm protruding therefrom. A retainer plate connects the
thermostat assembly to an engine component. A bypass valve plate is arranged
to
sealably engage a bypass valve seat that is formed in the first engine
component.
The bypass valve plate includes a body portion having a central opening and an
outer periphery, an inner rim surrounding the central opening, an outer rim
surrounding the outer periphery, and a plurality of openings formed in the
body
portion. The plurality of openings are disposed adjacent to an interface
between the
body portion and the outer rim, such that a bypass pressure-dampening fluid
passage is defined through the plurality of openings in the bypass valve
plate.
Brief Description of the Drawings
[0006] FIG. 1 is a cross section of a thermostat assembly installed between a
first
and second engine components.
[0007] FIG. 2 and FIG. 3 are cross-section views of one embodiment for a
thermostat assembly having an improved bypass valve plate.
[0008] FIG. 4 and FIG. 5 are outline views from different perspectives of the
improved bypass valve plate of the thermostat assembly shown in FIG. 2.
[0009] FIG. 6 and FIG. 7 are cross-section views of another embodiment for a
thermostat assembly having an improved bypass valve plate and bypass valve
seat
configuration.
[0010] FIG. 8 and FIG. 9 are cross-section views of another embodiment for a
thermostat assembly having an improved bypass valve plate and bypass valve
seat
configuration.
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Description of a Preferred Embodiment
[0011] The following describes an apparatus for and method of reducing an
effect of
instability in cooling fluid flow through a thermostat, especially during a
transitional
phase of operation, by providing an improved bypass fluid flow passage that
has
pressure dampening characteristics.
[0012] A section view of a known thermostat 100 as installed in an internal
combustion engine between a first component 102 and a second component 104
thereof is shown in FIG. 1. The thermostat 100 includes a thermal actuator
assembly 106. The thermal actuator assembly 106 includes an arm 108 that is
capable of extending when heated. The arm 108 passes through a cap 110 that is
sealably and permanently attached to a container 112. The container 112
contains
a "wax pill" 114 that melts and expands under conditions of increased
temperature.
A thermostat plate 115 is non-slidingly engaged with the actuator assembly 106
on
an inner portion thereof, and has a seal 116 over-molded on an outer portion
thereof. A retainer plate 118 surrounds a portion of the actuator assembly 106
and
is disposed in a groove 120 of the second component 104.
[0013] A first spring 122 is disposed between the thermostat plate 115 and the
retainer 118. The first spring 122 pushes the thermostat plate 144 away from
the
retainer 118. In a cold condition, the force of the first spring 122 acts to
maintain a
seated position of the retainer 118 in the groove 120, and to also push the
thermostat plate 115 against an outlet seat 124 that is formed in the second
component 104.
[0014] A bypass valve retainer 126 is connected to the actuator assembly 106
on a
side thereof that is opposite the arm 108. The bypass valve retainer 126 has a
bypass valve plate 128 connected to a distal end thereof. A second spring 130
is
disposed between the bypass valve retainer 126 and the bypass valve plate 128,
acting to push the bypass valve plate 128 away from the actuator assembly 106.
In
the embodiment shown, a groove 132 is formed in the first engine component 102
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opposite the bypass valve plate 128. The groove 132 forms a bypass valve seat
134 that contacts the bypass valve plate 128 under certain conditions,
generally,
warm conditions.
[0015] During operation, a flow of coolant enters the thermostat 100. The flow
of
coolant, or more specifically a coolant supply from the engine, enters the
thermostat
100 through an inlet opening 136. At times when the coolant flow has a lower
temperature, or below about 190 degrees F (88 degrees C), the wax pill 114 in
the
actuator assembly is mostly solid, the arm 108 rests against a support 138
that is
formed in the second component 104, and the bypass valve plate 128 is
suspended
away from the bypass valve seat 134. Thus, the coolant flow entering through
the
inlet opening 136 passes over the bypass valve plate 128 and exits the
thermostat
100 through a bypass passage, or, a coolant return passage 140 that is formed
in
the first component 102 and that routs the coolant flow directly back into the
engine.
[0016] When the coolant flow entering through the inlet opening 136 is warm,
or has
a temperature above about 190 degrees F (88 degrees C), the wax pill 114 melts
and thermally expands within the container 112. The expansion of the wax pill
114
causes the arm 108 to extend away from the container 112, pushing against the
support 138. The extension of the arm 108 causes the thermostat plate 115 to
move away from the outlet seat 124, the first spring 122 to compress, and the
bypass valve plate 128 to move toward the bypass valve seat 134. Continuous
operation under warm conditions will eventually seat the bypass valve plate
128
onto the bypass valve seat 134. In this condition, the flow of coolant
entering the
inlet opening 136 will pass into an actuator chamber 142 of the thermostat
100, and
exit the thermostat through a radiator outlet opening 144. The flow of coolant
passing into the radiator outlet opening 144 will return to the engine after
passing
through a radiator (not shown).
[0017] One embodiment for an improved thermostat 200 is shown in partial cross
section in FIG. 2, and in a detailed expanded cross section view in FIG. 3.
The
thermostat 200 has many similar features and elements with the thermostat 100,
and for the sake of simplicity, common elements are called out using the same
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reference numerals. The thermostat 200 has an inlet opening 136, a bypass
outlet
opening 140, and a radiator outlet opening 144. The thermostat 200 has an
improved bypass valve plate 228. The bypass valve plate 228 is connected to
the
bypass valve retainer 126, and functions substantially similarly to the bypass
valve
plate 128 shown in FIG. 1, but has a plurality of openings 230 formed along an
entire periphery thereof, equidistantly from a central axis 232.
[0018] During operation of the thermostat 200, and especially during a
transition
period of warming coolant flow, the bypass valve plate 228 is pushed toward
the
bypass valve seat 134, as described. In the thermostat 100 of FIG. 1, when the
bypass valve plate 128 has been pushed into the groove 132 but is not yet
seated
onto the bypass valve seat 134, a pressure pulsation effect is created that
causes a
vibration in the bypass valve plate 128. This vibration, over time, may lead
to
various types of failures in the bypass valve plate 128, the retainer 126, and
in
general, to the functionality of the thermostat 100. This vibration may
advantageously be avoided with use of the improved bypass valve plate 228. The
openings 230 act to relieve pressure differentials that cause the vibration
across the
bypass valve plate 228, and effectively eliminate the vibration and increase
the
service life of the thermostat 200 as compared to the service life of the
thermostat
100.
[0019] An outline view from two different perspectives of the improved bypass
valve
plate 228 is shown in FIG. 3 and FIG. 4. The bypass valve plate 228 includes a
body section 402. The body section 402 is substantially flat and has a disk
shape.
An outer rim 404 surrounds the body section 402 along an outer periphery
thereof,
and an inner rim 406 surrounds a central opening 408 of the body section 402.
The
outer rim 404 and the inner rim 406 advantageously provide structural
stiffness to
the body section 402. The plurality of openings 230 is disposed adjacent to
the
outer periphery of the body section 402, close to an interface between the
body
section 402 and the outer rim 404. The body section 402, the inner rim 404,
the
outer rim 406, the central opening 408, and the plurality of openings 230, may
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advantageously be formed simultaneously in a single stamping and cutting
operation of a sheet metal piece.
[0020] During operation of the thermostat 200, a pressure dampening passage is
created between the inlet opening 136, through the plurality of openings 230,
through an area between the bypass valve plate 228 and the bypass valve seat
134,
and out the coolant return passage 140. This pressure dampening passage is
advantageously most effective at dampening pressure pulsations that would
otherwise cause vibrations to the bypass valve plate at times when the bypass
valve
plate 228 is transitioning to a closed position and is close to and. nearly
seated on
the bypass valve seat 134.
[0021] An alternate embodiment for a thermostat 600 having a bypass pressure-
dampening fluid passage is shown in cross section in FIG. 6 and FIG. 7. The
thermostat 600 has many similar features and elements with the thermostat 100,
and for the sake of simplicity, common elements are called out using the same
reference numerals. The thermostat 600 has an inlet opening 136, a bypass
outlet
opening 140, and a radiator outlet opening 144. The thermostat 600 has an
improved bypass valve plate 628, and an improved bypass valve seat 634. The
bypass valve plate 628 is connected to the bypass valve retainer 126, and
functions
substantially similariy to the bypass valve plate 128 shown in FIG. 1. The
bypass
valve plate 628 has an improved lateral surface 630. The lateral surface 630
has a
mostly convex conical profile, and is arranged to mate with the improved
bypass
valve seat 634 that is formed in a first engine component 632 around an
opening of
the coolant return passage 140. In this embodiment, the bypass valve seat 634
has
a substantially concave conical shape that matches the convex conical shape of
the
lateral surface 630 of the bypass valve plate 628.
[0022] During operation of the thermostat 600, and especially during a
transition
period of warming coolant flow, the bypass valve plate 628 is pushed toward
the
bypass valve seat 634, as described. The vibration described above for the
thermostat 100 in FIG. 1 may advantageously be avoided with use of the
improved
bypass valve plate 628. The conical lateral surface 630F acts to relieve
pressure
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differentials that cause the vibration across the bypass valve plate 628, and
effectively eliminate the vibration and increase the service life of the
thermostat 600
as compared to the service life of the thermostat 100.
[0023] In this embodiment, a pressure dampening passage is created between the
inlet opening 136, through a passageway 636 that exists between the bypass
valve
plate 628 and the bypass valve seat 634, and out the coolant return passage
140.
At times when the bypass valve plate 628 is near and approaching the bypass
valve
seat 634, a uniform flow area exists around the entire periphery of the bypass
valve
plate 628 in the passageway 636. The uniform flow area in the passageway 636
acts to promote efficient flow of coolant there through, and is advantageously
most
effective at dampening pressure pulsations that would otherwise cause
vibrations to
the bypass valve plate at times when the bypass valve plate 628 is
transitioning to a
closed position and is close to and nearly seated on the bypass valve seat
634.
[0024] An alternate embodiment for a thermostat 800 having a bypass pressure-
dampening fluid passage is shown in cross section in FIG. 8 and F(G_ 9. The
thermostat 800 has many similar features and elements with the thermostat 100,
and for the sake of simplicity, common elements are called out using the same
reference numerals. The thermostat 800 has an inlet opening 136, a bypass
outlet
opening 140, and a radiator outlet opening 144. The thermostat 800 has an
improved bypass valve plate 828, and an improved bypass valve seat 834. The
bypass valve plate 828 is connected to the bypass valve retainer 126, and
functions
substantially similarly to the bypass valve plate 128 shown in FIG. 1.
[0025] The bypass valve plate 828 has an improved lateral surface 830. The
lateral
surface 830 has a mostly convex conical profile, and is arranged to linearly
contact
the improved bypass valve seat 834 that is formed in a first engine component
832
around an opening of the coolant return passage 140. The bypass valve seat 834
is
formed as a sharp transition, at about 90 degrees, and has little to no
lateral
surfacing that contacts the lateral surface 830 in a flat manner. The bypass
valve
seat 834 can be described as a "sharp" edge surrounding the opening for the
passage 140 that contacts the lateral surface 830 along a line.
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[0026] During operation of the thermostat 800, and especially during a
transition
period of warming coolant flow, the bypass valve plate 828 is pushed toward
the
bypass valve seat 834, as described. The vibration described above for the
thermostat 100 in FIG. 1 may advantageously be avoided with use of the
improved
bypass valve plate 828. The conical lateral surface 830 acts to relieve
pressure
differentials that cause the vibration across the bypass valve plate 828, and
effectively eliminate the vibration and increase the service life of the
thermostat 800
as compared to the service life of the thermostat 100.
[0027] In this embodiment, a pressure dampening passage is created between the
inlet opening 136, through a passageway 836 that exists between the bypass
valve
plate 828 and the bypass valve seat 834, and out the coolant return passage
140.
At times when the bypass valve plate 828 is near and approaching the bypass
valve
seat 834, a high-turbulence flow area exists around the entire periphery of
the
bypass valve plate 828 in the passageway 836. The flow area for fluid passing
through the passageway 836 acts to destroy any pressure differentials that
exist
across the bypass valve plate 828 by disrupting any pressure waves with
turbulence
created by an edge-flow condition near the sharp transition of the seat or
edge 834.
This configuration is advantageously most effective at dampening pressure
pulsations that would otherwise cause vibrations to the bypass valve plate at
times
when the bypass valve plate 828 is transitioning to a closed position and is
close to
and nearly seated on the bypass valve seat 834.
[0028] The present invention may be embodied in other specific forms without
departing from its spirit or essential characteristics. The described
embodiments are
to be considered in all respects only as illustrative and not restrictive. The
scope of
the invention is, therefore, indicated by the appended claims rather than by
the
foregoing description. All changes that come within the meaning and range of
equivalency of the claims are to be embraced within their scope.
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