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Title:
CARBURETTOR CHOKE MECHANISM
Document Type and Number:
WIPO Patent Application WO/2007/043916
Kind Code:
A1
Abstract:
The present invention relates to a carburettor of an internal combustion engine having a manually activated choke. The carburettor comprises at least a choke valve and a gas valve both located in the carburettor's main air passage which are able to move between an open and a closed position, each valve cooperates with at least one respective lever (10,11). The carburettor further comprises at least one thermally responsive member (14). In the present invention said member (14) influences the air through-flow resistance in said passage when the choke is made active by arranging the member (14) so that it at certain temperatures restricts said movement of said choke valve towards closed position.

Inventors:
ENGMAN THOMAS (SE)
Application Number:
SE2005/001491
Publication Date:
April 19, 2007
Filing Date:
October 07, 2005
Export Citation:
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Assignee:
HUSQVARNA AB (SE)
ENGMAN THOMAS (SE)
International Classes:
F02M1/10; F02D11/02
Domestic Patent References:
WO1996041941A11996-12-27
Foreign References:
US6145487A2000-11-14
EP0691468A21996-01-10
US20050022798A12005-02-03
US4031872A1977-06-28
Attorney, Agent or Firm:
FORNEHEIM, David (Husqvarna AB, Jonsered, SE)
Download PDF:
Claims:
CLAIMS

\ t A carburettor of an internal combustion engine having a manually activated choke, said carburettor comprising at least a choke valve and a gas valve both located in the carburettor's main air passage and is able to move between an open and a closed position, each valve cooperating with at least one respective lever (10,11) ? the carburettor further comprising at least one thermally responsive member (14), characterized in that said member (14) influences the air through-flow resistance in said passage when the choke is made active by arranging the member (14) so that it at certain temperatures restricts said movement of said choke valve towards closed position.

2. A carburettor according to claim 1 wherein the thermally responsive member (14) is made as a bimetal or memory metal member.

3. A carburettor according to any of the preceding claims wherein the thermally responsive member (14) has the shape of a blade of metal.

4. A carburettor according to any of the preceding claims wherein the thermally responsive member (14) has the shape of a coil spring.

5. A carburettor according to any of the preceding claims wherein the thermally responsive member (14) comprises a free end (16) arranged to provide the restriction.

6. A carburettor according to claim 5 wherein the restriction is enabled by a temperature-based movement of the free end (16).

7. A carburettor according to any of the claims 5 - 6 wherein the free end restricts the movement of the choke valve lever (10).

8. A carburettor according to any of claims 5 - 7 wherein supporting means (17-18) is arranged at the free end (16) to partly restrict the movement of said end (16).

9. A carburettor according to claim 8 wherein the supporting means (16-17) is arranged to move together with the gas valve lever (11).

10. A carburettor according to claim 9 wherein said supporting means (17-18) when moving influences the position of the free end (16).

11. A carburettor according to claim 8 wherein the supporting means (17-18) is arranged to move together with the choke valve lever (10).

12. A carburettor according to claim 8 wherein the supporting means (17-18) is arranged on the body of the carburettor.

13. A carburettor according to any of the preceding claim wherein the two levers (10- 11) when the choke is activated cooperates to at least hold the gas valve in a fixed position.

14. A carburettor according to any of claims 8 - 12 and 13 wherein the cooperation is enabled by the cooperation between a lever (10,11) and supporting means (17,18) that is arranged to move together with a lever (10,11).

15. A carburettor according to any of the claims 13 - 14 wherein the cooperation is enabled by the free end (16) of the thermally responsive member cooperating with a valve lever (10,11).

16. A carburettor according to any of the preceding claims wherein the thermally responsive member (14) is arranged on the gas valve lever (11).

17. A carburettor according to any of the preceding claims wherein the thermally responsive member is arranged on the choke valve lever (10).

Description:

CARBURETTOR CHOKE MECHANISM

TECHNICAL FIELD The present invention relates to a carburettor of an internal combustion engine having a manually activated choke. The carburettor comprises at least a choke valve and a gas valve both located in the carburettor's main air passage which are able to move between an open and a closed position, each valve cooperates with at least one respective lever. The carburettor further comprises at least one thermally responsive member.

BACKGROUND

Two-stroke conventional internal combustion engines with carburettors are used in many different areas. One is in chainsaws, which are commonly used outside in forest working characterized by a large variation in climate. The engine therefore has for instance to manage to be run at high speed, in cold climate and at rain. In such use the functionality of the carburettor is very important. It has to provide the right amount of fuel to the engine in relation to different conditions. The fuel/air ratio is important for the operation of the engine, and depends on temperature, pressure, engine speed and load. The carburettor is therefore calibrated at manufacturing to be able to provide, at the engines operating point, the right amount of fuel and air in order for the engine to operate properly.

The operating point is related to operation where the engine has reached its operating temperature. The carburettors calibration is based on such an operating state. On the other hand, when the engine is cold and about to be started, the calibration will not be able provide sufficient conditions for that. Therefore the carburettor is equipped with a choke to increase the fuel ratio in the engine to enable it to start. The fuel/air mixture is enriched. With the choke used the engine will start, go up to a peak in running speed, and then go down and run at a high idle speed. When the worker then pushes the speed control the choke settings will be deactivated and the motor will

operate based on the idle speed settings calibrated at manufacturing. When the engine reaches its operation temperature the engine will run at a predefined idle speed.

One problem with these conventional manual chokes is that its functionality is very much related to the engines temperature at start. During a warmer climate, for instance above zero degrees Celsius, the engine needs less fuel in order to start. The needed fuel/air enrichment for the engine to start goes down when the temperature goes up. Despite the temperature variations at use, the choke is designed to provide a maximum fuel/air ratio that is needed at a very low temperature.

When the worker pulls the starting cord he/she has to recognize that the engine ignites. Every new pull will increase the enrichment in the engine and if the worker do not deactivate the choke after ignition, the enrichment will reach such a high level that the engine cannot start. The higher the temperature, the bigger the risk that this will happen. The object of the present invention is therefore to provide a choke for a carburettor internal combustion engine, which is designed to consider the variations in climate where the engine is used.

SUMMARY OF THE PRESENT INVENTION The present invention relates to a carburettor of an internal combustion engine having a manually activated choke. The carburettor comprises at least a choke valve and a gas valve both located in the carburettor's main air passage which are able to move between an open and a closed position, each valve cooperates with at least one respective lever (10,11). The carburettor further comprises at least one thermally responsive member (14). In the present invention said member influences the air through-flow resistance in said passage when the choke is made active by arranging the member so that it at certain temperatures restricts said movement of said choke valve towards closed position.

DESCRIPTION OF THE DRAWINGS

The invention will now be described further with reference to the accompanying drawings, in which:

Fig. 1 relates to a first embodiment of the present invention in a first state where the thermally responsive member is in a high temperature position, wherein the choke is deactivated.

Fig. 2 also relates to the same state wherein the choke is activated.

Fig. 3 relates to a first embodiment second state where the thermally responsive member is in a low temperature position, wherein the choke is deactivated.

Fig. 4 relates to a second state wherein the choke is made activate.

Fig. 5 relates to a second state wherein the choke is fully activated.

DESCRIPTION OF SOME ILLUSTRATIVE EMBODIMENT

The figures show a first illustrative embodiment of a handle unit in accordance with the invention. Some other illustrative embodiments will be disclosed in the specification below. The illustrative embodiments shall not be interpreted as a limitation of the invention. Their purpose is to illustrate how the invention can be applied and to further illustrate the scope of the invention.

The first embodiment will now be described based on the drawings in which fig. 1 will be used to introduce all the acting parts. In fig. 1 the choke valve lever 10 and the gas valve lever 11 is shown. The gas valve lever is connected via axis 13 to the gas valves located in the internal combustion carburettor. The choke valve lever is spring- loaded and cooperates with a convey arm (not shown) connected via axis 12 to the choke valve. When the choke is made active (anti-clockwise rotation of the axis 12) the convey arm rotates the choke valve lever. The choke valve is then closed. When the choke is deactivated (opening the choke valve), the spring-load will make the choke valve lever to rotate back unless it is not held in place by cooperation with the gas valve lever. Neither the carburettor nor any other parts of the engine is shown is the drawings.

In fig. 1 the thermally responsive member 14 can also be seen. It is formed as a coil spring for instance made as a bimetal or memory metal sheet. It is attached at one end 15 to the gas valve lever 11 and will therefore move together with said lever. The coil springs second free end 16 extends outward from the spring and is arranged between two supporting means 17-18 formed as heels. These means restricts the left-right movement of the free end 16 as shown in fig. 1.

The first edge 19 of the choke valve lever 10 is sloping to cooperate with the leftmost 17 of the two supporting means 17-18. The same lever 10 also comprises a notch 20 to cooperate with the free end 16. The lever also comprises a second notch 21 to cooperate with the rightmost 18 of the supporting means at a second state, see fig. 3 -

5.

The functionality of the first embodiment will now be described in relation to fig. 1 - 5. Fig. 1 - 2 illustrates a first state where the temperature of the engine and the surroundings for instance is about or above -8 degrees Celsius (the degree limit is an example and can be as an alternative be warmer or colder). The basics, as described in the background above, are that the fuel/air enrichment needed for the engine to start is higher at lower temperature, i.e. more fuel is needed. The higher the temperature, the greater the risk that the user pulls the start wire so that the enrichment gets too high. This means that the engine will not be able to start at all. If the user does not deactivate the choke after the first ignition, there is a high likelihood that this will happen.

When the temperature changes the thermally responsive member will reshape. This means that the free end 16, as shown in fig. 1 compared to fig. 3, will extend above the supporting means 17-18. A higher temperature causes the free end to move upwards as shown in fig. 1. When the choke is activated the free end as shown in fig. 2 will restrict the movement of the choke valve lever 10. The free end will fit into the notch 20 and hold the lever 10 is a fixed position that corresponds to a partly open choke valve. Air will therefore flow into the carburettor air passage and decrease the fuel/air enrichment. Moreover, in this position the choke valve lever 10 will cooperate with the gas valve lever 11 and thereby hold the gas valve in a start gas position. When the choke is deactivated, the choke valve will rotate back to open position,

while the choke valve lever can still be held in said fixed position. Finally, when the gas valve lever 11 is activated by the user, the spring loaded choke valve lever 10 will be released and rotate back to its original position.

The result of this partly open choke valve is that there is a lower risk that the engine will get a too high enrichment before it starts. Even if the user misses to deactivate the choke, the engine will probably start before the enrichment gets too high because of the partly open choke valve.

Fig. 3 - 5 illustrates a second state where the temperature of the engine and the surroundings is for instance is about or below -8 degrees Celsius (the degree limit is an example and can be as an alternative be warmer or colder). This means that the free end 16, as shown in fig. 3 compared to fig. 1, will not extend above the supporting means 17-18. When the choke is made active the free end as shown in fig. 4 - 5 will not restrict the movement of the choke valve lever 10. The leftmost notch 21 of the choke valve lever 10 will therefore cooperate with the rightmost 18 of the supporting means to hold the lever 10 is a fixed position that corresponds to a closed choke valve as in conventional carburettors. In this position the choke valve lever 10 will cooperate with the gas valve lever 11 and thereby hold the gas valve in a start gas position. When the choke is deactivated, the choke valve will rotate back to open position, while the choke valve lever can still be held in said fixed position. Finally, when the gas valve lever 11 is activated by the user, the spring loaded choke valve lever 10 will be released and rotate back to its original position.

In a second embodiment the thermally responsive member 14 instead could be attached at one end 15 to the choke valve lever 10 to move together with said lever. The second free end 16 of the coil spring then extends outward from the spring and is arranged between two supporting means for instance formed by providing a passage where the notch 20 is located in the first embodiment. The free end 16 will extend out through said passage when the temperature is at the first state (high temperature), as an example above -8 degrees Celsius. The lever 10 will still have rightmost sloping edge 19 to cooperate with the gas valve lever.

In this embodiment the supporting means 17 - 18 can for instance cooperate with the free end that in the first state extends out through said passage. Thereby it hinders the choke valve lever 10 to rotate further. Instead of the free end 16 cooperating with the notch 20, the free end will cooperate with the space between the supporting means. This will be a mirror solution in relation of the first embodiment. This cooperation means that the choke and gas valves are fixed in same partly open positions as in the first embodiment, fig. 2. When the choke is deactivated, the choke valve will rotate back to open position, while the choke valve lever can still be held in said fixed position. Finally, when the gas valve lever 11 is activated by the user, the spring loaded choke valve lever 10 will be released and rotate back to its original position.

The second state (low temperature) for this second embodiment can preferably be the same as for the first embodiment. Fig. 3 - 5. This means that the free end will not extend through the passage at the choke valve lever. When the choke is made active the choke valve lever 10 can therefore pass the supporting means 17-18. The leftmost notch 21 of the choke valve lever 10 will then cooperate with the rightmost 18 of the supporting means to hold the lever 10 is a fixed position that corresponds to a closed choke valve as in conventional carburettors, see fig. 5. In this position the choke valve lever 10 will cooperate with the gas valve lever 11 and thereby hold the gas valve in a start gas position. When the choke is deactivated, the choke valve will rotate back to open position, while the choke valve lever can still be held in said fixed position. Finally, when the gas valve lever 11 is activated by the user, the spring loaded choke valve lever 10 will be released and rotate back to its original position.

In a third embodiment the coil spring thermally responsive member 14 could be attached at one end 15 to the carburettor body. It will then not move together with any of the levers 10-11. In such an embodiment the free end 16 is still located between the supporting means 17-18. The functionality will be the same as for the first embodiment. There is though a need to redesign the supporting means 17 - 18 so that the free end at said second state does not start to extend above the means when the gas valve lever starts to rotate. Such an effect would hinder the movement of the choke valve lever.

In a forth embodiment the whole thermally responsive member 14 and the supporting means 17- 18 are arranged on the carburettor body. Such an embodiment could be used together with a conventional carburettor. In such a carburettor there are cooperating means (for instance teeth) to enable the cooperation between the tow levers 10 - 11 to hold the choke valve in a closed position and the gas valve in a start gas position. Providing more cooperating means will provide the option to hold the choke valve in a partly open position, see fig. 2. In this embodiment, similar as to the other embodiments, the free end 16 will at the first state extend out and hinder the rotation of the choke valve lever 10. Instead of the cooperation between the notch 20 and the free end 16 as in the first embodiment, the cooperating means on the levers will enable that the levers hold the valves at the position corresponding to fig. 2.

The person skilled in the art should realize that the following solutions are included within the scope of the invention:

As an alternative to the coil spring the thermally responsive member 14 can be formed as a blade of metal. It should however be realized that a certain length of said member is need to enable a movement sufficient enough to provide the restriction.

It is possible to provide a carburettor providing also a third state (or even more states), meaning that the choke valve during activated choke can be set into different positions depending or the temperature. One way of solving that in the first embodiment is to have a second choke valve lever on the same choke axis, which is turned for instance 5 - 10 degrees in relation to the first one, see fig. 1. Moreover, in parallel with the first thermally responsive member 14, a second member is provided intended to cooperate with second choke valve lever. This second member is calibrated to reshape at a different temperature that the first one.