U.S. patent number 3,752,133 [Application Number 05/306,776] was granted by the patent office on 1973-08-14 for multiple heat automatic choke.
This patent grant is currently assigned to Ford Motor Company. Invention is credited to David C. Irish, Richard J. Junttonen.
United States Patent |
3,752,133 |
Irish , et al. |
August 14, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
MULTIPLE HEAT AUTOMATIC CHOKE
Abstract
The carburetor has a conventional automatic choke construction
heating a bimetallic coil by engine exhaust stove heat to slowly
open the choke valve during cold weather starts; supplemental heat
is provided by electrically controlled positive temperature
coefficient heater devices, the smaller of which is operable at all
times concurrent with the stove heat, the larger device being
operable above a predetermined ambient temperature to move the
choke valve open faster, to reduce emissions.
Inventors: |
Irish; David C. (Dearborn,
MI), Junttonen; Richard J. (Farmington, MI) |
Assignee: |
Ford Motor Company (Dearborn,
MI)
|
Family
ID: |
23186784 |
Appl.
No.: |
05/306,776 |
Filed: |
November 15, 1972 |
Current U.S.
Class: |
261/39.3;
261/39.6 |
Current CPC
Class: |
F02M
1/12 (20130101); F02M 1/10 (20130101) |
Current International
Class: |
F02M
1/10 (20060101); F02M 1/00 (20060101); F02M
1/12 (20060101); F02d 011/08 (); F02n 001/10 ();
F02n 023/04 () |
Field of
Search: |
;261/39E,39B,39R
;123/119F |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Burns; Wendell E.
Claims
We claim:
1. An automatic choke system for use with a carburetor having an
air/fuel induction passage,
an unbalance mounted, air movable choke valve mounted for variable
movement across the passage to control airflow through the
passage,
thermostatic spring means operably connected to the choke valve
urging the choke valve towards a closed position with a force
increasing as a function of decreases in the temperature of the
spring means from a predetermined level,
and first and second self-limiting output temperature heater
devices operably associated with the choke valve to effect opening
of the choke valve by varying degrees in response to increases in
temperature of the heater devices up to their individual output
limits, the first heater device being operable at all times, and
control means to render the second heater device operable above a
predetermined ambient temperature level.
2. A choke system as in claim 1, the control means comprising a
thermostatically responsive on-off switch means.
3. A choke system as in claim 1, the heater devices comprising
positive temperature coefficient (PTC)elements characterized by
increasing internal impedance with increasing temperatures up to
their limits limiting further current flow and heat buildup.
4. An automatic choke system for use with a carburetor having an
air/fuel induction passage and
an unbalance mounted, air movable, choke valve mounted for variable
movement across the passage to control airflow through the
passage,
thermostatic spring means operably connected to the choke valve
urging the choke valve towards a closed position with a force
increasing as a function of decreases in the temperature of the
spring means from a predetermined level,
and first normally operable and second intermittently operable
self-limiting output temperature, positive temperature coefficient
(PTC) heater devices located adjacent the spring means operable to
transfer their heat output thereto when operable up to their limit
to reduce the choke valve closing force of the spring means and
permit opening of the choke valve by airflow through the passage
against it, and other means to render the second heater device
operable.
5. A choke system as in claim 4, the other means comprising
temperature sensitive means rendering the second heater device
operable above a predetermined ambient temperature level to begin
transferring its heat output to the spring means.
6. A choke system as in claim 5 including a heat sink secured to
the second heater device for uniformly radiating the heat of the
second heater device to the spring means.
7. A choke system as in claim 5, the heater devices comprising
positive temperature coefficient heater elements characterized by
increasing internal impedance with increases in internal
temperature up to their limits limiting further current flow and
heat buildup.
8. A two phase automatic choke system for use with a carburetor
having an air/fuel induction passage open at one end and adapted to
be connected to an engine intake manifold at the other end for
subjecting the passage to varying manifold vacuum, the passage
having a throttle valve mounted for a variable movement between
positions opening and closing the passage to control air/fuel flow
through it,
the choke system including an unbalance mounted, air movable choke
valve mounted anterior of the throttle valve for variable movement
across the passage to control airflow towards the throttle
valve,
thermostatic spring means operably connected to the choke valve
urging the choke valve towards a closed position with a force
increasing as a function of decreases in the temperature of the
spring means from a predetermined level,
first power means sensitive to engine manifold vacuum for moving
the choke valve towards an open position in opposition to the
spring means,
and means supplemental to the first power means for effecting
subsequent movement of the choke valve towards a position more open
than the position effected by the first power means,
the supplemental means including first and second electrically
energized positive temperature coefficient (PTC) heater devices
located adjacent the bimetallic spring means and operable to
transfer their heat output to the spring means to reduce its choke
valve closing force and permit opening of the choke valve by
airflow through the passage against it, the first heater device
being operable at all times,
and temperature responsive means operable above a predetermined
ambient air temperature to energize the second heater device,
the internal resistance of the PTC heaters above a second
predetermined temperature level restricting current flow and heat
output to thereby eliminate the need for temperature responsive cut
out switch means to deenergize the heater elements above the second
predetermined temperature level.
9. A two phase automatic choke system for use with an internal
combustion engine carburetor having an air/fuel induction passage
open at one end and adapted to be connected to an engine intake
manifold at the other end for subjecting the passage to varying
manifold vacuum, the passage having a throttle valve rotatably
mounted across the passage adjacent the lower end for a variable
movement between positions opening and closing the passage to
control air/fuel flow through it,
the choke system including an unbalance mounted, air movable choke
valve rotatably mounted across the passage adjacent the upper end
for variable opening and closing movements to control airflow
towards the throttle valve,
a thermostatically responsive spring coil operably connected to the
choke valve and normally urging the choke valve towards a closed
position with a force increasing with decreases in the temperature
of the coil from a predetermined level,
first power means operably connected to the choke valve and
sensitive to engine manifold vacuum for moving the choke valve from
an initially closed position towards an open position in opposition
to the coil and in response to operation of the engine from a start
to a running conditon,
the first power means including a vacuum operated movable piston
means, and a first heat source transferring engine heat to the coil
and comprising a hot air containing duct operably connected from
the engine exhaust system to the coil for warming the coil to
reduce its choke valve closing force,
and supplemental second and third electrically controlled,
temperature responsive heat means in a parallel and series flow
arrangement, respectively, with the first power means heat source
and effecting subsequent movement of the choke valve towards a
position more open than the position effected by the first power
means alone,
the supplemental means including a source of electrical energy,
first and second positive temperature coefficient (PTC) heater
device located adjacent the bimetallic spring means and operable to
transfer their heat output to the coil to reduce its choke closing
force and permit opening of the choke valve by airflow through the
passage against it, means connecting the first heater device to the
source at all times for concurrent operation with the first power
means, and temperature responsive switch means operable above a
predetermined ambient air temperature to connect the source to the
second heater device to energize the second heater device, the
internal resistance of the first and second heater devices above a
predetermined heater temperature level increasing to a level
restricting further heat buildup beyond a predetermined level.
10. A choke system as in claim 9 including a heat sink secured to
the second PTC device for uniformly radiating the heat of the
second PTC device to the coil, the second PTC device being larger
than the first device and providing a greater heat output.
11. A choke system as in claim 10, the heat sink comprising a thin
metallic disc secured to the coil mounting means between the second
PTC device and coil.
12. A choke system as in claim 9, including a housing enclosing the
PTC heater devices and coil, an insulating gasket dividing the
housing into a first chamber and a second chamber, the first
chamber having an inlet and outlet for the hot air duct, the second
chamber containing the heater devices and coil and containing an
aperture for flow of hot air through the gasket in a path to
indirectly heat the coil, the PTC heater devices being located in
the housing on the side of the coil opposite to the gasket to
receive heat from a direction opposite to that from the gasket.
Description
This invention relates, in general, to a carburetor for a motor
vehicle engine. More particularly, it relates to an automatic choke
to control the idle speed of the engine during cold weather starts,
while at the same time minimizing the output of undesirable
emissions.
As ambient temperature drops, friction within the engine and the
viscosity of the lubricants increase significantly. Therefore, at
low temperatures, the speeds at which an engine normally would idle
must be increased to prevent stalling. Accordingly, a choke
mechanism is generally provided to lessen the air intake during
cold starting and pre-engine warmup to insure a richer mixture.
Generally, the choke apparatus includes a coiled thermostatic
spring that operatively rotates the choke valve towards a closed or
nearly shut position with decreasing temperatures, and
progressively opens it as the temperature returns towards a chosen
level. A manifold suction responsive device generally cracks open
the choke a predetermined amount when the engine starts. The choke
action provides a rich mixture so that sufficient fuel can be
vaporized to permit smooth starting and running of the engine.
The above construction, while generally satisfactory, is a
compromise between good cold weather running conditions on one hand
and low emission outputs on the other hand. The richer than normal
mixture existing during the choking operation may result in higher
emission output such as, for example, CO.
It is an object of this invention to provide an automatic choke
construction that will provide good cold weather characteristics
and yet reduce to a minimum the output of undesirable smog
producing elements.
It is another object of the invention to provide an automatic choke
construction that provides a leaner than conventional air/fuel
mixture immediately after the engine starts by pulling open the
choke valve faster than would be by conventional choke systems.
It is also an object of the invention to provide an automatic choke
construction including positive temperature coefficient heater
elements operable to shorten the length of time required for the
normal operation of an automatic choke.
Another object of the invention is to provide an automatic choke
construction including a thermostatically controlled bimetal spring
normally urging the choke valve closed with decreasing ambient
temperature changes and opposed by a suction operated motor device
that initially cracks open the choke valve to a predetermined
amount permitting running operation during cold weather; engine
exhaust manifold heat being directed to the spring coil to warm it;
and a first supplemental heat source providing additional heat at
all times to the coil spring in the event the exhaust manifold heat
flow is low; and, a second supplemental heat source providing
further additional heat to the coil at ambient temperatures above a
predetermined level to cause the closing force on the choke valve
to be removed earlier than would be were the supplemental heat
sources not provided; the supplemental heat sources consisting of
positive temperature coefficient semi-conductor heater elements
whose internal resistances increase with increases in the heater
internal temperature and decreases in current flow so as to be
self- limited in temperature output thereby eliminating the need
for thermostatic circuit breakers to prevent bimetal coil
distortion above predetermined temperature levels.
Other objects, features and advantages of the invention will become
more apparent upon reference to the succeeding detailed description
thereof, and to the drawings illustrating a preferred embodiment
thereof; wherein
FIG. 1 is a cross-sectional elevational view of a portion of a
four-barrel carburetor embodying the invention; and,
FIG. 2 is an enlarged view of a portion of the automatic choke
shown in FIG. 1; and,
FIG. 3 is a graph plotting the changes in internal resistance of
the heaters of this invention with changes in internal
temperature.
FIG. 1 is obtained by passing a plane through approximately
one-half of a known type of four-barrel, downdraft type carburetor.
The portion of the carburetor shown includes an upper air horn
section 12, an intermediate main body portion 14, and a throttle
valve flange section 16. The three carburetor sections are secured
together by a suitable means, not shown, over an intake manifold
indicated partially at 18 leading to the engine combustion
chambers.
Main body portion 14 contains the usual air/fuel mixture induction
passages 20 having fresh air intakes at the air horn ends, and
connected to manifold 18 at the opposite ends. The passages are
each formed with a main venturi section 22 containing a booster
venturi 24 suitably mounted for cooperation therewith, by means not
shown.
Airflow through passages 20 is controlled in part by a choke valve
28 unbalance mounted on a shaft 30 rotatably mounted on side
portions of the carburetor air horn, as shown. Flow of fuel and air
through each passage 20 is controlled by a conventional throttle
valve 36 (only one shown) fixed to a shaft 38 rotatably mounted in
flange portion 16. The throttle valves are rotated in a known
manner by depression of the vehicle accelerator pedal, and move
from an idle speed position essentially blocking flow through
passage 20 to a wide open position essentially at right angles to
the position shown.
The rotative position of choke valve 28 is controlled by a
semiautomatically operating choke mechanism 40. The latter includes
a hollow housing portion 42 that is formed as an extension of the
carburetor throttle flange. The housing is apertured for supporting
rotatably one end of a choke lever operating shaft 44, the opposite
end being rotatably supported in a casting 46. A bracket or lever
portion 48 is fixed on the left end portion of shaft 44 for
mounting the end of a rod 52 that is piVoted to choke valve shaft
30. It will be clear that rotation of shaft 44 in either direction
will correspondingly rotate choke valve 28 to open or close the
carburetor air intake, as the case may be.
An essentially L-shaped thermostatic spring lever 54 has one leg 56
fixedly secured to the opposite or righthand end portion of shaft
44. The other leg portion 58 of the lever is secured to the outer
end 59 of a coiled bimetallic thermostatic spring element 60
through an arcuate slot 62 in an insulating gasket 64.
Leg 56 is also pivotally fixed to the rod 76 of a piston 78. The
latter is movably mounted in a bore 79 in housing 42. The under
surface of piston 78 is acted upon by vacuum in a passage 80 that
is connected to carburetor main induction passages 20 by a port 82
located just slightly below throttle valve 36. Piston 78,
therefore, is always subjected to any vacuum existing in the intake
manifold passage portion 18.
The casing 42 is provided with a hot air passage 68 connected to an
exhaust manifold heat stove, for example. The cylinder in which
piston 78 slides is provided with bypass slots, not shown, in a
known manner so that the vacuum acting on the piston will cause a
flow of the hot air from passage 68 to passage 80. More
specifically, hot air will flow into the area around the spring
coil 60 through a hole 83 in gasket 64 and out through slot 62 to
the bypass slots around piston 78.
As thus far described, the construction is conventional. It will be
clear that the thermostatic spring element 60 will contract or
expand as a function of the changes in ambient temperature
conditions of the air entering tube 68; or, if there is no flow,
the temperature of the air within chamber 42. Accordingly, changes
in ambient temperature will rotate the spring lever 54 to rotate
shaft 44 and choke valve 28 in one or the other directions as the
case may be.
As is known, a cold weather start of a motor vehicle requires a
richer mixture than a warmed engine start because considerably less
fuel is vaporized. Therefore, the choke valve is shut or nearly
shut to increase the pressure drop thereacross and draw in more
fuel. Once the engine does start, however, then the choke valve
should be opened slightly to lean the mixture to prevent engine
flooding as a result of an excess of fuel.
The known choke mechanism described automatically accomplishes the
action described. That is, on cold weather starts, the temperature
of the air in chamber 42 will be low so that spring element 60 will
contract and rotate shaft 44 and choke valve 28 to a closed or
nearly closed position, as desired. Upon cranking the engine,
vacuum in passage 80 will not be sufficient to move piston 78 to
open the choke valve. Accordingly, the engine will be started with
a rich mixture. As soon as the engine is running, higher vacuum in
passage 80 moves piston 78 downwardly and rotates shaft 44 a slight
amount so that choke valve 28 is slightly opened so that less fuel
is admitted to induction passage 20. Shortly thereafter, the
exhaust manifold stove air in line 68 will become progressively
warmer and act on choke element 60 to cause it to unwind slowly and
rotate shaft 44 and choke valve 28 to a more open position. It
should be noted that the degree of warmth of the coil will depend
upon the flow of hot air through tube 68, which in turn will vary
as a function of the level of the vacuum in port 82. Further
details of construction and operation are not given since they are
known and believed to be unnecessary for an understanding of the
invention.
As thus far described, the construction is conventional. Turning
now to FIG. 2, it will be seen that the thermostatic spring coil 60
is centrally staked to a metal post 84. The post is formed as an
integral part of a thin metal, aluminum, for example, disc 85 that
is approximately the diameter of coil 60. The disc constitutes a
heat sink or transfer member to evenly radiate heat to the coil
from a pair of heater elements 86 and 87 to which it is
secured.
Heater elements 86 and 87 are positive temperature coefficient
(PTC) semiconductors in the shapes of flat ceramic discs fixed on
disc 85. The element 86 has a central spring-leg type current
carrying contact lug 88 projecting through an insulated cover of
choke cap 90. The heat sink disc is grounded through the cover to
the cast choke housing by extensions and ground terminals 92.
Lug 88 is normally spaced from a contact 93 fixed on a bimetallic
thermal switch 94 that is sensitive to ambient temperature changes.
The switch closes above 65.degree..+-. F, for example, to engage
the contacts and conduct current to the heater from a terminal 96.
The vehicle alternator could serve as a suitable source of
electrical energy to the terminal, when the vehicle is running.
Heater element 87, on the other hand, is connected at all times, to
be energized at all times when the vehicle is running, by an
interconnection 97 to terminal 96. Heater disc 87, as will be seen,
is smaller in size and, therefore, heat output capacity, than
heater disc 86, for a purpose to be described. It is a
characteristic of each of the PTC heaters that its internal
resistance varies directly with the skin temperature of the
element, from a predetermined switch point Ts. The change in the
internal resistance is not a linear function of the elements'
internal temperature but varies in the manner shown more clearly in
FIG. 3. When the PTC heaters are electrically energized, as by
applying line voltage to terminal 96 from the alternator at all
times for heater 87, and for heater 86 when switch 94 closes, the
Joule heat causes rapid self-heating of the PTC elements. The
heater resistance remains almost constant as it heats from room
temperature. It increases as the PTC temperature nears the
switching temperature Ts, or desired upper limit, at which point
the resistance increases sharply, as shown. The electrical
characteristics, of course, can be controlled by the chemical
composition and process of making it.
It will be seen, therefore, that it is an inherent property of this
semiconductor to obtain a very high impedance to current flow at
high internal temperatures, and that the semiconductor has an
ability to maintain a high maximum temperature. The need for a cut
off thermostat to protect against distortion of the bimetallic coil
60, therefore, due to extreme temperature levels is thereby
eliminated.
In this instance, therefore, the PTC device provides heat to coil
60 that is supplemental to that provided by the primary exhaust
manifold hot air system. There may be instances when the manifold
heat flow is so low during cold weather operation due to low
airflow in the carburetor that the coil 60 would not be warmed
enough by primary manifold heat alone to provide the normal slow
progressive heating of the coil 60. The continuous heating of the
smaller heater 87 in this case provides the desired compensatory
primary heat at all times below its output limit to cause the choke
to operate in the desired manner. Subsequently, when the bimetal 94
closes and current passes through the larger PTC element 86, the
internal temperature generated is transferred by conduction to coil
60 through the post 84 and by radiation to the coil from the heat
sink 85, in the same manner as the heat of disc 87.
When the PTC internal temperature reaches the switching temperature
Ts, say 121.degree. C, as seen in FIG. 3, the internal resistance
becomes so high that the current flow is very low and essentially
cut off. It will be seen, therefore, that the heat input to the PTC
elements by the current flow then is essentially balanced by the
heat loss by the PTCs to the environment and to the bimetal post
84. Therefore, for all intents and purposes, the heat of the PTCs
remains at a constant level.
The overall operation is believed to be clear from the above
description and the drawings, and therefore will not be repeated in
detail. In brief, below an ambient temperature level of
65.degree..+-. F, heater 87 is energized to transfer a small heat
output to disc 85 and coil 60, but heater element 86 is not. The
bimetal switch contacts 94, 88 remain open, and the PTC heater 86
remains deenergized. Therefore, the choke hot air system
supplemented by the small output heater 87 provide the only heat
source for choking functions below 65.degree. F. The bimetal coil
60 will unwind, therefore, only as a function of the increased
heating by the hot air from passage 68 and heater 87.
Above 65.degree. F, however, the conventional exhaust manifold
stove heat system and heater 87 constitute the primary heat source,
while the now energized larger PTC heater 86 acts as the
supplemental source to rapidly permit the opening of the choke
valve by airflow faster than were it being controlled by the
primary heat source alone. This leans the fuel/air mixture earlier
than with conventional choke arrangements, and lowers undesirable
emission outputs.
With the above described two phase choke construction, therefore,
it will be seen that it is possible to provide a reliable and
accurate short duration choking effect thereby minimizing vehicle
exhaust emission without jeopardizing the cold weather choking
function.
* * * * *