JPH06147013A - Bimetal device for automatic choke mechanism of carburetor for general purpose engine - Google Patents

Abstract

PURPOSE:To improve a restarting performance and an exhaust condition by keeping a choke valve at opening corresponding to engine temperature in restarting a engine in a short time after the engine is stopped. CONSTITUTION:A spiral shape bimetal 13, giving opening resistance to a choke valve 4, is nipped between a first heat reserving member 7, to which an electric resistant heating body 9 is attached, and a second heat reserving member 15, joined to the first heat reserving member 7; and a bimetal 13 is thermally insulated by heat radiation from the heat reserving members 7 and 15 after engine stop; reducing the cooling speed of the bimetal 13 so that engine temperature and choke valve opening at the time of warm starting can be made corresponding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bimetal mechanism used for an automatic choke mechanism of a carburetor for a general-purpose engine.

[0002]

2. Description of the Related Art An automatic choke mechanism is known which closes a choke valve at the inlet of a carburetor in order to improve cold startability of an engine and opens the choke valve according to a warm-up state after starting. It is also well known that an automatic choke mechanism that uses a bimetal mechanism that heats the bimetal, which decreases the opening resistance of the choke valve as the temperature rises, with electric resistance heat instead of the engine heat is used in the carburetor for automobiles. is there.

On the other hand, general-purpose engines have come to be subject to exhaust gas regulation in the same manner as automobile engines, and by adopting the automatic choke mechanism of the above structure, it is possible to improve low temperature startability and at the same time reduce pollutants in exhaust gas. Vaporizers have come to be used.

The electric resistance heating element for heating the bimetal of the bimetal mechanism starts to radiate heat when the engine is started, and after reaching a predetermined temperature, the choke valve is opened by the switching action of the positive temperature coefficient semiconductor element (PTC element). It keeps the temperature at full opening and is cut off from the power supply when the engine stops.

However, when the engine is stopped, the engine has a large heat capacity, so that it takes a long time for the temperature to drop. On the other hand, the bimetal mechanism has a small volume and a very small heat capacity, and a general-purpose engine is exposed to the atmosphere. In many cases, the temperature drops in a short time.

For this reason, in a working machine or the like, which is often restarted in a relatively short time after the engine is stopped,
The bimetal mechanism restarts with the choke valve closed even though the engine is warm starting without the need for choking. Will be invited.

This is clear from the fact that the bimetal mechanism is constructed only for the purpose of improving the low-temperature startability and maintaining proper warm-up operation, and does not consider cooling after the power is cut off at all. is there. That is, in order to measure the effective use of electric resistance heat, a heat insulating plate is placed close to the bimetal inside the bimetal case, and the volume around the bimetal is reduced to raise the ambient temperature.
Even with the bimetal mechanism disclosed in Japanese Patent No. 3121, cooling does not occur in a short time after the power is cut off because it has no heat retention capability.

[0008]

SUMMARY OF THE INVENTION The problem to be solved by the present invention is to cool a bimetal mechanism used in an automatic choke mechanism of an automobile engine by heating the bimetal with electric resistance heat in a short time after power-off. Since it works to close the choke valve, it can be restarted in a relatively short time after the engine has stopped, and if it is adopted as it is in a general-purpose engine such as a working machine, it will be difficult to start, and the exhaust condition will deteriorate. The point is that there was no bimetal mechanism with the function to deal with the problem.

[0009]

In order to solve the above problems, the present invention arranges a spirally wound bimetal along a first heat storage member additionally provided with an electric resistance heating element. A second heat storage member is arranged along the side surface on the side opposite to the heat storage member and is coupled to the first heat storage member, and the fixed end of the bimetal is attached to at least one of the two heat storage members, By such means, it is an object of the present invention to provide a bimetal mechanism having an excellent heat retaining ability that delays the operation of the bimetal choke valve in the closing direction due to the temperature decrease after the power is cut off and does not cause deterioration of the unstartable exhaust state when the engine is restarted. I made it happen.

[0010]

When the electric resistance heating element is directly electrified, the two heat storage members are entirely heated, and the bimetal is heated by the radiant heat from them and the conductive heat from the shaft portion to reduce the choke valve opening resistance. When the engine is stopped and the power is shut off, the heat generated by the two heat storage members keeps the bimetal sandwiched between them, preventing the premature movement of the choke valve closing direction against the engine temperature drop and opening the large choke valve. A warm start will be performed at a time.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. A choke valve 4 is attached to a choke valve shaft 3 which is rotatably installed and supported across an inlet portion of an intake passage 2 of a carburetor body 1. The end of the choke valve shaft 3 protruding outside the carburetor body 1 is inserted into a bowl-shaped bimetal case 5. The open end surface of the bimetal case 5 is the carburetor body 1
It is closed by the case cover 6 attached to the side surface of the.

The bimetal case 5 is made of an insulating material such as synthetic resin, and a thick disk-shaped first heat storage member 7 made of a heat conducting material such as aluminum is fixed to the bottom of the bimetal case 5. An electric resistance heating element 9 made of a positive temperature coefficient semiconductor element is inserted into a space 8 provided between the center of the heat storage member 7 and the bottom of the bimetal case 5, and the electric resistance heating element 9 is attached to the back surface of the heat storage member 7. Wire 10 and conductive wire 1 on the ground side
1, the electric current flows through the electric resistance heating element 9.

At the center of the surface of the heat storage member 7, there is an integral shaft portion 1
2, a spiral-shaped bimetal 13 is arranged along this surface, the free end of the outer end of which is connected to the choke valve shaft 3 by a lever 14.

Further, a thick disk-shaped second heat storage member 15 made of a heat conductive material such as aluminum is arranged along the side surface of the bimetal 13 opposite to the first heat storage member 7, The second heat storage member 15 is attached in direct contact with the first heat storage member 7 by fitting the shaft portion 16 of the integrated product protruding in the center into the shaft portion 12 of the first heat storage member 7. .

These two heat storage members 7 and 15 have a diameter substantially equal to that of the bimetal 13 and are configured to heat the entire bimetal 13 substantially uniformly, and the fixed end of the inner end of the bimetal 13 is The two shaft portions 12 and 16 are pierced and attached.

At the same time when the engine is started, the electric resistance heating element 9 is directly electrified and starts to generate heat. The heat is conducted to the two heat storage members 7 and 15 to heat them, and the bimetal 13 has both side surfaces. Radiant heat received from the shafts 12 and 16
It is heated to a high temperature in a short time by the conduction heat from.

That is, since the free end of the bimetal 13 is largely displaced in a short time, the opening speed of the choke valve 4 does not decrease even if it is made small so as to be suitable for a carburetor for a general-purpose engine. The choke valve 4, which was closed at the time of starting, is opened a lot in a short time after starting, and the choke action is released early to thin the air-fuel mixture during warming up and improve the exhaust condition.

After the choke valve 4 is fully opened, the electric resistance heating element 9 interrupts the current due to its switching action, and maintains the temperature at which the bimetal 13 is not displaced in the choke valve closing direction.

When the engine is stopped, the electric current supply to the electric resistance heating element 9 is stopped and the two heat storage members 7 and 15 are no longer heated, but they have a considerably large heat capacity in total and continue to radiate heat for a long time. Therefore, the bimetal 13 sandwiched between them is kept warm and slowly cooled. On the other hand, although the cooling rate of the engine is extremely low, the cooling rate of the bimetal 13 is also low and the choke valve 4 is slowly closed. Then, cool the bimetal 13 at a speed that does not cause an imbalance such that the starting air-fuel mixture is rich between the engine temperature and the choke valve opening, and preferably, the choke valve opening is proportional to the standing time. The heat capacity and the specific heat of the two heat storage members 7 and 15 can be controlled to be appropriately reduced.

Therefore, there is no inconvenience that the choke valve 4 is largely closed at the time of a warm start in which the engine is stopped and restarted after a short time, resulting in inability to start and deterioration of the exhaust state. It is possible to reduce pollutants.

An electric resistance heating element may be attached to the second heat storage member 15, and the fixed end of the bimetal 13 may be fixed by attaching it to either of the two heat storage members 7 and 15.

[0022]

As described above, according to the present invention in which the heat retaining function of the bimetal is improved, in the carburetor for a general-purpose engine which is often restarted in a short time after the engine is stopped, the choke valve opening according to the engine temperature is opened. In this way, the restart can be reliably performed without conflicting with exhaust regulations.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of the present invention.

[Explanation of symbols]

4 choke valve, 7 first heat storage member, 9 electric resistance heating element, 12 shaft part, 13 bimetal, 15
Second heat storage member

Claims (1)

[Claims] 1. A spirally wound bimetal that provides an opening resistance to a choke valve is arranged along a first heat storage member additionally provided with an electric resistance heating element, and a second heat storage member connected to the first heat storage member. Automatic storage choke for a general-purpose engine carburetor, characterized in that the heat storage member is arranged along another side surface of the bimetal, and the fixed end of the bimetal is attached to at least one of the two heat storage members. Bimetal device for mechanism.