This invention relates to choke assemblies for an internal combustion engine. More specifically, the invention relates to an automatic choke assembly having engagement between the choke and throttle.
In small internal combustion engines utilizing a carburetor, such as those engines in a lawnmower, a snowblower, or other outdoor power equipment, the engines typically include a choke assembly that provides a rich fuel-air mixture in the intake manifold upon start-up of the engine to sustain the combustion reaction, and a throttle assembly responsive to the speed of the engine and the load on the engine. In many small engines, the choke assembly is actuated manually.
In engines having an automatic choke assembly, such as those where the choke opening is controlled by a thermally responsive mechanism or where a self-relieving choke is utilized, fluctuating air pressure within the carburetor can case a choke valve in the choke assembly to flutter after the choke has opened. While in certain engine operating conditions some amount of flutter may be desired, uncontrolled flutter in automatic choke devices can adversely affect the operation of the engine, such as by causing engine surging and increased component wear and fatigue within the engine.
The present invention provides an internal combustion engine including a carburetor. The engine also includes a choke valve disposed within the carburetor and a choke lever coupled to the choke valve for movement therewith. The choke valve is movable between an open position and a closed position, and the throttle valve is movable between a wide open throttle position, a high speed no load position, and an idle position. The engine also includes an intermediate lever coupled between the throttle lever and the choke lever for movement with the throttle and choke levers. In one embodiment, the intermediate lever includes a slot for sliding engagement with one of the choke and throttle levers.
In one embodiment, the engine further includes a thermally conductive assembly operable to hold the choke open during warm-engine restarts, the thermally conductive assembly including a mechanism that moves in response to the engine temperature sensed by the thermally conductive assembly.
In another embodiment, the slot includes an enlarged portion to allow the choke valve to flutter within the carburetor. In yet another embodiment, varying the parameters of the intermediate lever, including the length or width of the slot, calibrates operating characteristics within the engine.
The invention also provides for a carburetor having a choke valve and a choke lever coupled for movement therewith, as well as a throttle valve and a throttle lever coupled for movement therewith. The carburetor further includes an intermediate lever coupled to the choke lever via a connecting link. The connecting link translates motion of the choke lever into motion of the intermediate lever.
In one embodiment, the intermediate lever also includes a throttle engagement surface that engages a projection on the throttle lever during operation of the carburetor. At least one of the shape and position of the throttle engagement surface can be varied, which changes operating characteristics of the engine.
In another embodiment, the engine further comprises a thermally conductive assembly operable to hold the choke open during warm-engine restarts, the thermally conductive assembly including a mechanism that moves in response to the engine temperature sensed by the thermally conductive assembly. The mechanism is coupled to a choke retaining lever that is rotatable with movement of the mechanism to hold the choke open.
Further constructions and advantages of the present invention, together with the organization and manner of operation thereof, will become apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings, wherein like elements have like numerals throughout the drawings.
The present invention is further described with reference to the accompanying drawings, which show some embodiments of the present invention. However, it should be noted that the invention as disclosed in the accompanying drawings is illustrated by way of example only. The various elements and combinations of elements described below and illustrated in the drawings can be arranged and organized differently to result in embodiments which are still within the spirit and scope of the present invention.
In the closed position, the choke valve 18 restricts air flow into the engine, increasing the amount of fuel delivered to the engine 10 during engine starting to ensure that the combustion reaction within the engine 10 is sustained when the engine 10 is cold. As the engine 10 warms up, the enriched fuel-air mixture is no longer needed and the choke valve 18 rotates open, allowing more air into the engine 10.
The engine 10 also includes a thermally conductive assembly 22 and an engine muffler (not shown) attached to the exhaust manifold 26 of the engine 10. The thermally conductive assembly 22 is in communication with the exhaust gases produced by the engine 10 to allow the thermally conductive assembly 22 conduct heat from the exhaust gases, indicating the temperature in the engine 10. The thermally conductive assembly 22 includes a mechanism 30 that moves in response to the engine temperature. The mechanism 30 contacts the choke assembly 14, as will be discussed in more detail below, to hold the choke valve 18 open during warm engine restarts and during warm engine operating conditions to prevent an overly-rich fuel-air mixture from causing the engine 10 to sputter, stall, or produce excess emissions. The details of one suitable thermally conductive assembly 22 are described in pending U.S. patent application Ser. No. 10/784,542, filed Feb. 23, 2004, the entire contents of which are incorporated by reference herein. The interaction of the thermally conductive assembly 22 with the choke assembly 14 allows the choke assembly 14 to function as an automatic choke.
Referring now to
The carburetor 34 also includes an intermediate lever 54 disposed between the choke lever 20 and throttle lever 50 for movement with the levers 20 and 50. The intermediate lever 54 allows for interaction between the choke lever 20 and throttle lever 50 during engine operation to hold the choke valve 18 in at least a partially open position when the throttle assembly 42 is in the high speed no load position to prevent excess fluttering of the choke valve 18. The configuration of the intermediate lever 54 controls the rate of choke opening and controls the force of interaction with the throttle to control the speed rise in the engine. The various parameters of the intermediate lever 54 that can be adjusted to calibrate operating conditions within the engine 10 will be discussed in greater detail below.
A biasing member, shown in the illustrated embodiment as a spring 58, is coupled to a spring shaft 62 on the choke lever 20 at one end, and is coupled to a spring anchor shaft 66 on the intermediate lever 54 on the other end. The spring 58 biases the choke valve 18 in the closed position upon engine starting, and also functions to bias the choke valve 18 in the open position after the engine has warmed up.
In the embodiments illustrated in
As best shown in
Many parameters of the intermediate lever 54 can be varied to calibrate or change the operating characteristics within the engine for different application requirements. For example, the shape and position of the tang 86 and lip 96 on the intermediate lever 54, and the shape and position of the first and second protrusions on the throttle lever 50, affects the force between the intermediate lever 54 and the throttle lever 50 (by changing the angle of the force). This force, in turn, controls the speed rise and droop within the engine. In another example, making the slot 70 in the intermediate lever 54 wider allows for more flutter of the choke valve 18, which in turn enriches the fuel-air mixture. Adjusting the width of the slot 70 allows for control of the amount of flutter (providing the desired enrichment during warm-up, but not allowing so much flutter that there are problems with engine surging and engine wear). By controlling these parameters, the engine speed rise during the engine warm-up period can be calibrated (for example, providing more speed rise during cold engine starts), enrichment of the fuel-air mixture during engine starting can be achieved, and the reduced choke flutter results in better reliability of the engine, reduced engine wear, and a wider range of usable spring return.
Referring back to
At engine start-up, the choke valve 18 is in the closed position and the throttle valve 46 is in the wide open throttle position. The influx of air through the intake passage 38 and warm-up of the engine cause the choke valve 18 to move to the open position. The rotation of the choke lever 20 causes the post 74 to slidably engage the intermediate lever 54 within the slot 70, causing rotation of the intermediate lever 54. In circumstances where the engine 10 is already warm upon start-up, the mechanism 30 of the thermally conductive assembly 22 functions to hold the choke valve 18 in at least a partially open position to prevent an overly-rich fuel-air mixture when the engine 10 does not require such a rich mixture to maintain combustion. The mechanism 30 contacts the post 74 on the choke lever 20 to hold the choke open. In the wide open throttle position, the second protrusion 94 engages the lip 96 of the intermediate lever 54.
After the engine starts, the throttle valve 46 moves from the wide open throttle position to the high speed no load position, best shown in
For example, moving the position of the spring anchor shaft 66 as in
Movement of the choke lever 20 is translated into movement of the intermediate lever 134 through the connecting link 138. In the illustrated embodiment, there is a four to one ratio of movement between the choke lever 20 and intermediate lever 134 such that for every four degrees of movement of the choke lever 20, the intermediate lever 134 moves one degree.
The spring 58 is also coupled to the connecting post 142 on the choke lever 20 on one end, and is connected to the spring anchor post 66 on the intermediate lever 134 on the other end. The intermediate lever 134 also includes a throttle engagement surface 148 that engages a projection 150 on the throttle lever 50 as the throttle lever 50 rotates toward the high speed no load position. The shape and position of the throttle engagement surface 148 and the projection 150 can be varied, which also calibrates operating characteristics within the engine, such as changing the angle of the force applied (as discussed in detail above).
As further illustrated in
The spring 58 is coupled on one end to the spring anchor post 66 and on the other end to the connecting post 142. The intermediate lever 134 also includes a throttle engagement surface 148 that engages a projection 150 on the throttle lever 50 as the throttle lever 50 rotates toward the high speed no load position. The shape and position of the throttle engagement surface 148 and the projection 150 can be varied, which also calibrates operating characteristics within the engine, such as changing the angle of the force applied (as discussed in detail above).
The thermally responsive assembly 22 includes a mechanism 174 that contacts a choke retaining lever 178 to hold the choke open during warm engine restarts. The choke retaining lever 178 is pivotable about post 180. The mechanism 174 is coupled to an aperture 182 in the choke retaining lever 178 such that movement of the mechanism 174 due to changes in engine temperatures results in movement of the choke retaining lever 178.
The choke retaining lever 178 includes a cam member 186 that is engageable with the choke lever 20 to hold the choke open. The choke lever 20 includes a cam surface 190 that interacts with the cam member 186 as the choke retaining lever 178 rotates with movement of the mechanism 174.
During operation of the engine 10, the mechanism 174 of the thermally responsive assembly 22 moves with rising temperatures in the engine 10. The movement of the mechanism 174 causes rotation of the choke retaining lever 178. At the same time, the choke valve 18 moves from the closed position (see
Various features of the invention are set forth in the following claims.
This application is a continuation-in-part of U.S. patent application Ser. No. 10/925,111, filed Aug. 24, 2004, the entire contents of which is incorporated by reference herein.
Number | Date | Country | |
---|---|---|---|
Parent | 10925111 | Aug 2004 | US |
Child | 11141657 | May 2005 | US |