Automatic choke apparatus and method

An automatic choke apparatus is provided having a choke plate mounted for variable rotation in a carburetor between a closed position and an open position wherein a flow of air entering the carburetor is substantially obstructed in the closed position compared to the open position whereby the flow of fuel entering the engine is increased when in the closed position. The choke plate has a choke shaft arm for rotatably moving the choke plate. The automatic choke apparatus has a throttle plate downstream from the choke plate mounted for variable rotation in the carburetor between an open position wherein a flow of air and fuel mixture exiting the carburetor is at a maximum and a closed position wherein the flow of air and fuel mixture exiting the carburetor is at a minimum. The throttle plate has a throttle lever for rotatably miving the throttle plate. The throttle lever is engagable with the choke shaft arm as the throttle plate is rotated toward the closed position to rotatably move the choke plate toward the open position. The automatic choke apparatus includes engine speed governing structure for moving the throttle plate to limit the maximum speed of the engine. The engine speed governing structure urges the throttle plate toward the closed position after the engine is started such that the throttle lever engages the choke shaft arm to move the choke plate toward the open position.

FIELD OF THE INVENTION 
The present invention relates generally to an automatic choke for an 
internal combustion engine. More particularly, the present invention 
relates to an automatic choke actuated by an engine speed governor 
apparatus. 
BACKGROUND OF THE INVENTION 
When starting an internal combustion engine in cold ambient temperatures, 
it is often necessary to regulate the amount of air entering the 
carburetor. In general, the engine requires a richer fuel to air mixture 
to start the engine when the engine is cold. Once the engine heats up, a 
leaner mixture is required. One method of regulating the amount of air 
entering the carburetor is to control movement of a choke plate rotatably 
mounted in an interior of the carburetor. The choke plate is typically 
movable between a closed position wherein the choke plate sbstantially 
obstructs a flow of air entering the carburetor, and an open position 
wherein the airflow is substantially unobstructed. When the choke plate is 
in the closed position, more fuel is drawn into the engine during starting 
to provide the engine with a richer fuel to air mixture. To start the 
engine in cold ambient temperatures in a system having a rotatable choke 
plate, the choke plate is initially placed in a closed position to 
increase the amount of fuel entering the engine. After the engine is 
started, the engine requires an increased amount of air and a decreased 
amount of fuel to avoid stalling, so the choke plate is moved toward a 
more open position. 
In the past, various apparatus have been employed for starts in cold 
ambient temperatures to automatically move the choke plate to a more 
closed position during the initial starting and then to a more open 
position after the engine is started. Conventional automatic choke 
apparatus and choke pull off devices include apparatus having structure 
which is electrically operated and apparatus having structure which is 
vacuum operated. These apparatus also typically include a temperature 
sensing device which responds to engine temperature sensed and positions 
the choke plate in a closed position for starting when the engine is cold 
and then positions the choke plate in an open position once the engine is 
started and has heated up. However, in those apparatus, the temperature 
sensing devices are slow to react, requiring some additional structure to 
move the choke plate to the partially open position immediately after 
start up before the temperature sensing device has reacted to prevent the 
engine from stalling. In those conventional apparatus, it is the 
electrically or vacuum operated structures that move the choke plate to 
the partially open position immediately after the engine is started to 
prevent stalling. 
As the name suggests, the conventional electrically operated apparatus 
require the presence of an electrical connection to a source of electrical 
power to move the choke plate. Similarly, the conventional vacuum operated 
apparatus require the presence of air pressure differentials to move the 
choke plate. Oftentimes both the electrically operated apparatus and the 
vacuum operated apparatus employ intricate and fragile structure requiring 
a great number of parts to move the choke plate. As a result, both types 
of apparatus are often costly to manufacture and are prone to failure 
especially in the harsh environments surrounding most internal combustion 
engine applications. 
It is clear that there has existed a long and unfilled need in the prior 
art for an automatic choke apparatus and method for automatically 
controlling movement of the choke plate during cold ambient starts while 
addressing the above recited problems, or similar problems. 
SUMMARY OF THE INVENTION 
The present invention relates to a choke pull off device for use on a 
carburetor wherein the carburetor is provided with a choke plate rotatably 
mounted to the carburetor about a choke shaft defining an axis of rotation 
for the choke plate. The carburetor is further provided with a throttle 
plate rotatably mounted to the carburetor about a throttle shaft defining 
an axis of rotation of the throttle plate. The choke pull off device 
includes a choke shaft arm mountable to the choke shaft for rotatably 
moving the choke plate about the axis of rotation of the choke plate. The 
choke pull off device further includes a throttle lever mountable to the 
throttle shaft for rotatably moving the throttle plate about the axis of 
rotation of the throttle plate. The throttle lever includes mechanical 
linkage structure for engaging the choke shaft arm during rotational 
movement of the throttle plate to rotatably move the choke plate. In this 
manner, the choke pull off device provides movement of the choke plate 
through mechanical interaction of the throttle lever and the choke shaft 
arm. 
The present invention also relates to an automatic choke apparatus for use 
in starting an internal combustion engine. The automatic choke apparatus 
includes a carburetor having an air inlet, a fuel inlet, and an air and 
fuel mixture outlet. The apparatus further includes a choke plate mounted 
for variable rotation in an interior of the carburetor adjacent the air 
inlet such that the choke plate is rotatable between a closed position 
wherein a flow of air entering the carburetor is substantially obstructed 
and an open position wherein the flow of air entering the carburetor is 
substantially unobstructed. The choke plate has a choke shaft arm for 
rotatably moving the choke plate. The automatic choke apparatus further 
includes a throttle plate downstream from the choke plate and the fuel 
inlet mounted for variable rotation in the interior of the carburetor such 
that the throttle plate is rotatable between an open position wherein a 
flow of air and fuel mixture exiting the carburetor is at a maximum and a 
closed position wherein the flow of air and fuel mixture exiting the 
carburetor is at a minimum. The throttle plate has a throttle lever for 
rotatably moving the throttle plate. The choke plate is rotatable toward 
the open position and the throttle plate is rotatable toward the closed 
position after the engine is started. The throttle lever is engagable with 
the choke shaft arm as the throttle plate is rotated toward the closed 
position to rotatably move the choke plate toward the open position. 
The present invention further relates to an internal combustion engine 
having an automatic choke. The engine includes a carburetor having a choke 
plate mounted for variable rotation about a choke shaft in an interior of 
an inlet to the carburetor. The choke shaft has a choke shaft arm for 
rotatably moving the choke shaft and the choke plate. The carburetor is 
further provided with structure for supplying air and for supplying fuel 
to the interior of the carburetor for mixing. The carburetor further has a 
throttle plate mounted for variable rotation about a throttle shaft in the 
interior of the carburetor downstream of the choke plate and the structure 
for supplying fuel. The throttle shaft has a throttle lever for rotatably 
moving the throttle shaft and the throttle plate. The throttle lever is 
engagable with the choke shaft arm as the throttle lever rotatably moves 
the throttle plate to rotatably move the choke plate. The carburetor 
further has structure for supplying a mixture of the fuel and the air to 
combustion structure of the engine. 
In addition to the carburetor, the internal combustion engine further 
includes temperature responsive structure for moving the choke plate 
toward an open position as the engine temperature increases. The 
temperature responsive structure moves the choke plate toward a closed 
position as engine temperature sensed decreases. The combustion structure 
is provided for converting the air and fuel mixture supplied by the 
carburetor to rotational movement of an engine output shaft. Governor 
structure is provided for moving the throttle lever and throttle plate to 
limit the maximum rotational speed of the engine output shaft by urging 
the throttle plate from an open position toward a closed position after 
the engine is started. During rotational movement, the throttle lever 
engages the choke shaft arm and rotatably moves the choke shaft arm which 
rotatably moves choke plate toward the open position before the 
temperature responsive structure activates to open the choke plate. In 
this manner, the engine will not be as likely to stall during cold ambient 
starts caused by the choke plate not being sufficiently moved toward the 
open position by the temperature responsive structure. 
This invention also relates to a method for preventing stalling during 
starting of an internal combustion engine in cold ambients. The method 
includes the step of providing a carburetor mountable to the engine having 
a choke plate and a throttle plate rotatably mounted in an interior of the 
carburetor. A choke shaft arm is connected to the choke plate for 
rotatably moving the choke plate. A throttle lever is connected to the 
throttle plate for rotatably moving the throttle plate. The throttle lever 
is mechanically linked with the choke shaft arm during rotational movement 
of the throttle plate to cause rotational movement of the choke plate. The 
method further includes the steps of: positioning the choke plate in a 
closed position wherein a flow of fuel entering the engine during starting 
is greater relative to when the choke plate is in an open position; 
positioning the throttle plate in an open position wherein a flow of air 
and fuel mixture exiting the carburetor is greater than when in a closed 
position; starting the engine; and rotating the throttle plate toward the 
closed position after the engine is started wherein the flow of air and 
fuel mixture exiting the carburetor is decreased, and the rotation of the 
throttle plate causes the throttle lever to move the choke shaft arm 
causing rotation of the choke plate toward the open position wherein the 
flow of fuel entering the engine is decreased.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIGS. 1-7, a preferred embodiment of an automatic choke 
apparatus or automatic choke 10 is shown according to principles of the 
present invention. As shown in FIGS. 1 and 2, the automatic choke 10 is 
mounted to an internal combustion engine 14. In the preferred embodiment, 
the internal combustion engine 14 is part of a generator set where the 
engine has an output shaft 16 which mechanically drives a generator (not 
shown) for generating electrical current. It is anticipated that the 
automatic choke 10 of the present invention could be used with other 
engines for other applications besides in connection with generator sets. 
The automatic choke 10 of the present invention includes a carburetor 20 
for supplying a mixture of air and fuel to an intake manifold 18 of the 
engine 14. As best shown in the partial enlarged views of FIGS. 3-7, a 
flow of air, represented by arrow 30, enters the carburetor 20 at an air 
inlet 22, and a flow of fuel, represented by arrow 32, enters the 
carburetor through a fuel inlet 24. The air and fuel travel through the 
carburetor 20 in an interior passageway 28 during which the air and fuel 
become mixed. The air and fuel mixture, represented by arrow 34, exits the 
carburetor at an outlet 26 and enters the intake manifold 18 of the engine 
14. Combustion structure within the engine converts the air and fuel 
mixture to rotational movement of the engine output shaft 16 during the 
combustion process. 
To control the amount of fuel entering the engine 14 during starting, a 
choke plate 40 is rotatably mounted in the passageway 28 of the carburetor 
20 adjacent the air inlet 22. The choke plate 40 is rotatable between an 
open position, shown in FIGS. 5 and 6, wherein the flow of air entering 
the carburetor 20 is sustantially obstructed, and a closed position, shown 
in FIG. 3, wherein the flow of air entering the carburetor is 
substantially unobstructed. In the closed position, the flow of fuel into 
the carburetor 20 and the engine 14 is greater than when in the open 
position during starting. It should be noted that the choke plate 40 is 
variably positionable in positions between the open position and the 
closed position. The choke plate 40 is rotatably mounted to the carburetor 
20 by a choke shaft 42 which defines an axis of rotation 46 (see FIG. 7) 
of the choke plate 40. The choke shaft 42 extends through the carburetor 
wall to an exterior of the carburetor. A choke shaft arm 44 on the 
exterior of the carburetor is provided to rotatably move the choke plate 
40. A rigid connection between the choke shaft arm 44, the choke shaft 42, 
and the choke plate 40 permits the choke plate to be rotatably moved 
between the open position and the closed position by movement of the choke 
shaft arm. 
A throttle plate 60 is rotatably mounted in the passageway 28 of the 
carburetor 20 downstream from the choke plate 40 and the fuel inlet 24 to 
control the amount of air and fuel mixture which exits the carburetor 20 
at the outlet 26. A throttle shaft 62 mounts the throttle plate 60 to the 
carburetor 20 and defines an axis of rotation 66 (see FIG. 7) of the 
throttle plate. The throttle plate 60 is rotatable between an open 
position, shown in FIG. 3, wherein the air and fuel mixture exiting the 
carburetor 20 at outlet 26 is at a maximum, and a closed position, shown 
in FIG. 5, wherein the air and fuel mixture exiting the carburetor is at a 
minimum. It should be noted that the throttle plate 60 is variably 
positionable between the open position and the closed position. The 
throttle shaft 62 extends through the carburetor wall to the exterior of 
the carburetor where a throttle lever 64 attaches to the throttle shaft. A 
rigid connection exists between the throttle lever 64, the throttle shaft 
62, and the throttle plate 60 which permits the throttle plate to be 
rotatably moved between the open position and the closed position by 
movement of the throttle lever. 
As will be discussed below, the throttle lever 64 and the choke shaft arm 
44 are mechanically linked to each other to interact during operation of 
the engine such that rotational movement of the throttle plate 60 causes 
some rotational movement of the choke plate 40. The preferred structure 
which interacts during operation of the engine includes a cam surface on 
one of the members and an elongate portion on the other member which 
slideably engages the cam surface and follows the cam surface during 
operation. In the preferred embodiment, the throttle lever 64 is provided 
with a cam surface 70 and the choke shaft arm 44 is provided with an 
elongate portion 49 which follows the cam surface 70. The throttle lever 
64 preferably includes a cam plate portion 68 extending from the throttle 
shaft 62 in a general perpendicular direction to the throttle shaft. The 
cam surface 70 forms an edge of the cam plate portion 68. The choke shaft 
arm 44 preferably has a first elongate member 50 extending generally 
perpendicular to the choke shaft 42 and a second elongate member 52 
extending from the first elongated member in a direction generally 
parallel to the choke shaft. During rotational movement of the throttle 
lever 64 to move the throttle plate 60 from the open position toward the 
closed position, the cam surface 70 of the throttle lever 64 slidably 
engages the second elongate member 52 of the choke shaft arm 44 to 
rotatably move the choke plate 40 from the closed position toward the open 
position. It should be noted that the throttle lever 64 and choke shaft 
arm 44 can be mechanically linked in a variety of different manners other 
than the manner shown in the preferred embodiment such that movement of 
the throttle plate is translated to movement of the choke plate. Further, 
even though in the preferred embodiment the throttle lever 64 and choke 
shaft arm 44 interaction takes place on an exterior of the carburetor 20, 
the automatic choke 10 could be configured such that the interaction takes 
place in the interior of the carburetor. 
The cam surface 70 and cam plate portion 68 are shaped to allow for optimum 
choke plate position for various loads and throttle plate settings for the 
engine 14. It is to be appreciated that the cam plate portion 68 and cam 
surface 70 could have various configurations depending upon the 
characteristics and requirements of the engine 14. One method of changing 
the configuration of the cam plate portion 68 without removing the cam 
plate portion is to construct the cam plate portion from a bimetal 
material. The resulting cam plate portion would have a configuration which 
would be changeable with temperature. 
In the preferred embodiment, a temperature responsive device 74 is provided 
for positioning the choke plate 40 based on engine temperature sensed by 
the temperature responsive device. To facilitate starting the engine 14 in 
cold ambients, the temperature responsive device 74 automatically 
positions the choke plate 40 toward a more closed position to obstruct the 
flow of air to increase the flow of fuel entering the engine 14. After the 
engine 14 is started and the engine heats up, the temperature responsive 
device 74 automatically positions the choke plate 40 in the open position 
since an increased flow of fuel is no longer required. 
During operation of the engine 14, choke plate position is sometimes 
determined by the temperature responsive device 74 and other times by the 
choke shaft arm 44/throttle lever 64 interaction. The temperature 
responsive device 74 positions the choke plate 40 at start up of the 
engine, and then after the engine heats up. The choke shaft arm 
44/throttle lever 64 interaction positions the choke plate 40 from a time 
immediately after start up until the engine heats up. As noted above, this 
cooperation is necessary because the temperature responsive device 74 does 
not respond fast enough to move the choke plate 40 to a more open position 
to prevent stalling of the engine. In order to move the choke plate 40 
toward a more open position during the time in which the temperature 
responsive device 74 has yet to react sufficiently, the choke shaft arm 44 
is rotatably moved by the cam surface 70 of the throttle lever 64 
immediately after start up when a more open choke is necessary. 
Referring now to FIGS. 1 and 2, the temperature responsive device 74 
includes a bimetal strip 76 for sensing temperature of the engine 14. The 
bimetal strip 76 is rigidly connected at a first end 94 to the engine 14 
and at a second end 96 to a choke rod 84. The choke rod 84 is linked to a 
choke rod arm 82 which is mounted for rotation about the choke shaft 42. 
In the preferred embodiment, the bimetal strip 76 is in the shape of a 
coil and is exposed to air heated by engine exhaust. A tube 78 provides a 
passageway for air heated by an exhaust manifold 80 to travel to the 
bimetal strip 76. In operation in cold ambients, the bimetal strip exerts 
a pull on the choke rod arm 82 in a direction toward the bimetal strip as 
engine temperature sensed by the bimetal strip 76 increases after the 
engine is started. As best shown in FIG. 5, the choke rod arm 82 engages a 
prong 48 on the choke shaft arm 44 to cause rotational movement of the 
choke shaft arm 44 causing rotational movement of the choke shaft 42 and 
positioning the choke plate 40 in the open position. As the engine 
temperature sensed by the bimetal strip 76 decreases, such as when the 
engine is shut off, the bimetal strip exerts a force on the choke rod 84 
and choke rod arm 82 in a direction away from the bimetal strip. In this 
state, the choke rod arm 82 is no longer acting to engage the prong 48 to 
open the choke plate 40. A spring 92 biases the prong 48 of the choke 
shaft arm 44 against the choke rod arm 82 to rotatably move the choke 
plate 40 to a more closed position to facilitate restarting of the engine 
at a later time. The rigid connection between the bimetal strip 76 and the 
engine 14 is preferably adjustable to permit adjustment of the choke plate 
positioning for a given temperature. 
The automatic choke 10 of the preferred embodiment includes structure for 
automatically moving the throttle lever 64 and throttle plate 60 during 
operation of the engine. In the preferred embodiment, an engine speed 
governing apparatus or governor 86 is provided to move the throttle lever 
64 and throttle plate 60 to limit the maximum speed of the engine 14 and 
output shaft 16. Preferably, the governor 86 is a conventional mechanical 
governor employing spring loaded flyweights (not shown). As best shown in 
FIGS. 1-2, the governor 86 includes a governor arm 88 attached to a 
governor rod 90 which attaches to the throttle lever 64. Typically at 
start up of the engine 14, the throttle plate 60 is in the open position. 
After start up of the engine, the engine speed increases until the 
governor 86 activates. The governor arm 88 and the governor rod 90 then 
move the throttle plate from the open position toward a more closed 
position to limit the maximum speed of the engine. As the throttle lever 
64 rotatably moves the throttle plate 60, the cam surface 70 slidably 
engages the second elongate member 52 of the choke shaft arm 44 to 
rotatably move the choke plate 40. As noted above, this interaction occurs 
during start up to properly position the choke plate 40 at a time when the 
temperature responsive device 74 does not position the choke plate in a 
sufficiently open position. The governor 86 may move the throttle plate 60 
back to a more open position at a later time should the engine be placed 
under an additional load which acts to reduce the speed of the engine 
requiring an increased flow of fuel and air mixture. 
In the preferred embodiment, the choke plate 40 is designed to flutter 
during and for a short period immediately after start up. The fluttering 
occurs between the position determined by the temperature responsive 
device 74 and a more open position. It is believed that fluttering 
provides the engine 14 with additional air so that the engine output 
becomes fast enough to require activation of the engine speed governor 86 
sooner to rotate the throttle plate 60 toward a more closed position which 
rotates the choke plate 40 sooner to a more open position. Without 
fluttering, the engine 14 may be more likely to stall unless the choke 
plate 40 is moved to a more open position immediately after start up. 
Fluttering of the choke plate 40 is accomplished by positioning the choke 
shaft 42 parallel to and offset on a major surface 54 of the choke plate 
40 such that the axis of rotation 46 is offset relative to the choke plate 
40. When an unequal air pressure exists on the exterior of the carburetor 
20 relative to the interior, the choke plate 40 will temporarily move from 
the closed position toward a more open position to increase the air 
entering the carburetor 20. The unequal air pressure is created by 
periodic suction or inhalation from the engine 14 during start up. The 
spring 92 biases the choke plate back to the position determined by the 
temperature responsive device 74. Fluttering occurs while the pressure 
differential is greater than the spring biasing force. 
FIGS. 3-6 illustrate the positions of the choke plate 40 and the throttle 
plate 60 at various times during operation of the engine 14. FIG. 3 
illustrates the automatic choke 10 at start up. During cold ambient 
starts, the temperature device 74 positions the choke plate 40 in the 
closed position to facilitate start up. The throttle plate 60 is initially 
in the open position. It should be noted that the throttle plate 60 may be 
maintained in the open position before start up or, alternatively, the 
throttle plate may be placed in that position at start up. As shown in 
FIG. 3, the throttle lever 64 does not engage the choke shaft arm 44 and 
the choke rod arm 82 engages the prong 48 of the choke shaft arm 44. 
During and immediately after start-up, the choke plate 40 begins to 
flutter as the engine periodically inhales air. The suction of the engine 
14 temporarily creates an unbalanced force on the choke plate 40 which 
overcomes the biasing of the spring force to temporarily rotate the choke 
plate 40 to a more open position. A result of the fluttering is to more 
quickly activate the governor 86 to limit the maximum speed of the engine. 
FIG. 4 illustrates the automatic choke 10 shortly after start up. As noted 
above, the positions of the elements illustrated in FIG. 4 will occur 
sooner because of the fluttering feature described above. The governor 86 
has moved the throttle plate 60 to a more closed position. Movement of the 
throttle lever 64 causes the cam surface 70 to slidably engage the choke 
shaft arm 44 to rotatably move the choke plate 40 to a more open position. 
As shown in FIG. 4, a space exists between the choke rod arm 82 and the 
prong 48, illustrating the necessity of the throttle lever 64/choke shaft 
arm 44 interaction to position the choke plate in a more open position 
that could not be accomplished with the temperature responsive device 74. 
FIG. 5 illustrates the automatic choke 10 once the engine 14 has been 
running for a period of time and is under a light load. The governor 86 
has moved the throttle lever 64 such that the throttle plate 60 is in a 
more closed position than the position shown in FIG. 4. The temperature 
responsive device 74 has sensed an increase in engine temperature and has 
reacted to position the choke plate 40 in the open position. As 
illustrated in FIG. 5, the prong 48 engages the choke rod arm 82 and the 
throttle lever 64 is not engaging the choke shaft arm 44. 
FIG. 6 illustrates the position of the automatic choke 10 when the engine 
14 has been running for a period of time and the engine 14 is under a 
heavy load. As in FIG. 5, the temperature responsive device 74 has sensed 
an increase in engine temperature and has reacted to position the choke 
plate 40 in the open position. Since the engine is under a heavier load 
compared to the load illustrated in FIG. 5, the governor 86 tries to 
maintain a constant maximum engine speed and has moved the throttle plate 
60 to a more open position to increase the flow of air and fuel mixture 
exiting the carburetor. 
The following example illustrates the manner in which the automatic choke 
10 of the present invention may be employed in connection with the engine 
14 used to power a generator as part of a generator set. One type of 
generator set that may be used includes a single cylinder, four-stroke, 
air-cooled engine which drives a generator of the two pole, brush-type 
which generates 4000 watts of power at 3600 rpm governed engine speed. It 
has been found that the engine performs well if the temperature responsive 
device 74 positions the choke plate 40 is in the closed position, shown in 
FIG. 3, at 32 degrees Fahrenheit sensed by the temperature responsive 
device and in the open position, shown in FIGS. 5 and 6, at 120 degrees 
Fahrenheit. 
It is to be understood, that even though numerous characteristics and 
advantages of the invention have been set forth in the foregoing 
description, together with details of the structure and function of the 
invention, the disclosure is illustrative only, and changes may be made in 
detail, especially in matters of shape, size, and arrangement of the parts 
within the principles of the invention to the full extent indicated by the 
broad general meaning of the terms in which the appended claims are 
expressed.