Electrically Controlled Automatic Choke Of A Carburetor For An Internal Combustion Engine

Abstract

A coiled bimetal element for rotationally moving a choke valve of an electrically controlled automatic choke is directly heated through an electric current from a battery, and the current flowing through the bimetal is adjusted depending upon the atmospheric temperature and the engine temperature. Further, the current is reduced to a small amount after the choke valve is fully open.

Description

BACKGROUND OF THE INVENTION

This invention relates to an electrically controlled automatic choke for a carburetor for an internal combustion engine, which is particularly suitable to the automatic choke of a carburetor for an engine having an exhaust gas purifier.

A choke valve of an electrically controlled automatic choke closes the air supply passageway to the carburetor for increasing the ratio of the fuel to air mixture during the starting period of the internal combustion engine. The opening operation of the choke valve is conventionally controlled by rotational movement of a coiled bimetal element which is heated indirectly by an electric heater disposed near the bimetal element. Since the bimetal element is heated indirectly in such an arrangement, the rapidity of the movement of the bimetal is limited, particularly, at the normal atmospheric temperature range, that is, in the range of 10.degree. - 30.degree.C., with the result that after the engine is warmed up, the choke valve is often partially closed, that is, overchoked. Consequently, the amount of harmful exhaust gas containing hydrocarbons and nitrogen oxide emitted from the gasoline engine increases undesirably.

Further, in the conventional arrangement the opening speed of the choke valve is independently fixed to the atmospheric temperature and the engine temperature which also increases the amount of harmful exhaust gas emitted by the engine. Furthermore, the current flowing through the heater after the choke valve has been fully open is unchanged, consequently, the electric power consumption for maintaining the choke valve in fall open position in a normal operation of the engine is also unnecessarily large.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an electrically controlled automatic choke for a carburetor for an internal combustion engine having a faster response time to the electric current supplied from the source of current for opening the choke valve.

Another object of the present invention is to provide an electrically controlled automatic choke for a carburetor for an internal combustion engine providing a reduced amount of harmful exhaust gas from the engine during the starting period thereof.

A further object of the present invention is to provide an electrically controlled automatic choke for a carburetor for an internal combustion engine providing variable opening characteristics for the choke valve depending upon the atmospheric temperature and the engine temperature.

Still a further object of the present invention is to provide an electrically controlled automatic choke for a carburetor for an internal combustion engine having reduced electric power consumption during normal engine operation.

An electrically controlled automatic choke of the present invention comprises a directly heated coiled bimetal element, the rotational movement of which is transferred to a choke valve for controlling the opening degree therof, thus regulating the amount of air flow to the carburetor during the starting period of the internal combustion engine.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic diagram of an electric circuit embodying the present invention;

FIG. 2 is a diagram of one example of the electric current flowing through the bimetal element shown in FIG. 1 with respect to the atmospheric temperature near the internal combustion engine;

FIG. 3 is a diagram of the performances of the thermal switches shown in FIG. 1 with respect to the atmospheric temperature near the internal combustion engine; and

FIG. 4 is a diagram of the relationship between the opening degree of the choke valve shown in FIG. 1 and the time after the internal combustion engine is started.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Choke valve 11 is fixed to a rotatable shaft 12. One end of the shaft 12 is fixed to an inner end of a coiled bimetal element 13, the outer end of the coiled bimetal element 13 is electrically and mechanically connected to a stationary portion 14 of a carburetor of an internal combustion engine (not shown). Rotational movement of the bimetal element 13 in response to the temperature therof is transferred to the shaft 12 for rotation. The rotational movement of the shaft 12 changes the opening degree of the choke valve 11 for controlling the amount of air flow to the carburetor during the starting period of the internal combustion engine.

When an ignition key switch 16 is closed for starting the internal combustion engine, first relay switch 17 is closed. In response to the closing operation of the ignition key switch 16 and after detecting that the output voltage of a storage battery 40 is above a predetermined level, a battery charging switch 18 is closed and simultaneously a second relay switch 19 is closed through the closure of the battery charging switch 18.

Thermal switches 20 and 21 are mounted near the internal combustion engine for detecting the atmospheric temperature which is affected in that area by the engine temperature. Performance characteristics of the thermal switches 20 and 21, that is, the on and off states thereof, with respect to the atmospheric temperature near the engine, are shown in FIG. 3. The temperatures T.sub.1 and T.sub.2 are, for instance, 0.degree.C. and 10.degree.C. When the atmospheric temperature is below T.sub.1, both thermal switches 20 and 21 are in the off state, and a first resistance 31 and a second resistance 32 are disconnected from the storage battery or source of current 40. The resistance value R.sub.1 of the first resistance 31 is selected to be larger than R.sub.2 of the second resistance 32. Only the third resistance 33, the resistance value of which is R.sub.3, is connected to the battery 40. As the resistance value of the bimetal element 13 is R.sub.5, under these conditions, the sum of the resistance between the battery terminals is R.sub.3 + R.sub.5. Assuming the output voltage of the storage battery is E, the current I.sub.0 flowing through the bimetal element 13, as shown in FIG. 2, is

I.sub.0 = E/(R.sub.3 + R.sub.5)

The bimetal element 13 is directly heated by the current I.sub.0, thus the inner end of the bimetal element 13 extends spirally and rotates the shaft 12. As a result, the choke valve 11 begins to open following the curve 50 of FIG. 4. When the choke valve 11 is fully open, a switch 22 is closed in response to the full open position of the choke valve 11 and a third relay switch 23 is actuated to disconnect the third resistance 33 from the battery 40 and connect a fourth resistance 34 to the battery 40. The resistance value R.sub.4 of the fourth resistance 34 is selected to be larger than the resistance value R.sub.3 of the third resistance 33, thus the sum of the resistance between the battery terminals changes to R.sub.4 + R.sub.5, and the current I.sub.3, that is the holding current flowing through the bimetal element 13, as shown by a dotted line in FIG. 2, becomes

I.sub.3 = E/(R.sub.4 + R.sub.5)

With the current I.sub.3, the bimetal element 13 is directly heated for maintaining the choke valve 11 in the full open position.

When the atmospheric temperature is between T.sub.1 and T.sub.2, the thermal switch 21 is in the closed position and the thermal switch 20 is still in the open position, as shown in FIG. 3. Consequently, the sum of the resistance between the battery terminals changes to

[R.sub.2 R.sub.3 /(R.sub.2 + R.sub.3)] + R.sub.5

and the current I.sub.1 flowing through the bimetal element 13 is ##SPC1##

as shown in FIG. 2. As a result, the choke valve 11 begins to open following the curve 60 shown in FIG. 4 through rotational movement of the bimetal element 13, which is directly heated by the current I.sub.1. After the choke valve 11 becomes fully open, the second resistance 32 and third resistance 33 are cut out and the fourth resistance 34 is put into the circuit by the operation of the third relay switch 23, as explained previously, and the holding current I.sub.3 begins to flow through the bimetal element 13 for maintaining the choke valve 11 in the full open position.

When the atmospheric temperature is above T.sub.2, for example above 10.degree.C., both of the thermal switches 20 and 21 are in closed position, as shown in FIG. 3; thus, the sum of the outer resistance value is

[R.sub.1 R.sub.2 R.sub.3 /(R.sub.1 R.sub.2 + R.sub.2 R.sub.3 + R.sub.3 R.sub.1)] + R.sub.5

and the current I.sub.2 flowing through the bimetal element 11 is ##SPC2##

as shown in FIG. 2. As a result, the choke valve 11 begins to open quickly following the curve 70 shown in FIG. 4. That is to say, at the normal atmospheric temperature range, for example 10.degree. - 30.degree.C., as the choke valve 11 is designed to open relatively fast, the exhaustion of hydrocarbons (HC) and nitrogen monoxide (NO) from the internal combustion engine is reduced. After the choke valve 11 becomes fully open, the first second, and third resistances 31, 32, and 33 are cut out and the fourth resistance 34 is put into the circuit by the operation of the third relay switch 23 in response to the full open position of the choke valve 11, as explained previously, and the holding circuit I.sub.3 begins to flow in the bimetal element 13 for maintaining the choke valve 11 in the full open position.

The amount of current I.sub.2 flowing through the bimetal element 13, when the atmospheric temperature is above T.sub.2, is, for example, between 2 and 3 amps and the holding current I.sub.0 is designed to be about one fifth, or below, of the current I.sub.2. Consequently, the electric power consumed in the circuit during normal operation of the engine is reduced.

In the embodiment described above, the current controlling means, or first current limiting means, comprises the first, second, and third resistances 31, 32, and 33 and the first and second thermal switches 20 and 21; however, one branch circuit including a thermal switch, for example, the first resistance 31 and the first thermal switch 20, sometimes can be eliminated.

Further, the current controlling means disclosed changes the current therethrough in a step-by-step manner by reason of the thermal switches 20 and 21; however, another current controlling means which changes the current linearly or continuously can also be applied.

Claims

What is claimed is:

1. An electrically controlled automatic choke for a carburetor for an internal combustion engine comprising:

a choke valve controlling the amount of air flow to the carburetor during the starting period of the internal combustion engine;

a rotatable shaft fixed to said choke valve for moving the same;

a coiled bimetal element for rotating said shaft, one end of said bimetal element being fixed to said shaft and the other end thereof being fixed to a stationary member;

and control means for supplying an electric current directly to said bimetal element.

2. An electrically controlled automatic choke for a carburetor for an internal combustion engine as defined in claim 1, in which said control means comprises current controlling means for controlling the current to be supplied to said bimetal element in response to the atmospheric temperature near the internal combustion engine.

3. An electrically controlled automatic choke for a carburetor for an internal combustion engine as defined in claim 2, in which said control means further comprises current limiting means for limiting the current to be supplied to said bimetal element, and switching means for disconnecting said current controlling means from said bimetal element and connecting said current limiting means to said bimetal element when said choke valve is fully open.

4. An electrically controlled automatic choke for a carburetor for an internal combustion engine as defined in claim 3, wherein said current controlling means includes at least one resistor connected in series with a temperature responsive switch and an additional resistor connected across the series combination of said one resistor and switch.

5. An electrically controlled automatic choke for a carburetor for an internal combustion engine as defined in claim 4, wherein said current limiting means includes a control switch operated in response to a fully open condition of said choke valve and a current limiting resistor connected in series with a relay actuated by said control switch to said bimetal element.

6. An electrically controlled automatic choke for a carburetor for an internal combustion engine comprising:

a choke valve for controlling the amount of air flow to the carburetor during the starting period of the internal combustion engine;

a rotatable shaft fixed to said choke valve for moving the same;

a coiled bimetal element for rotating said shaft, one end of which is fixed to said shaft and the other end of which is fixed to a stationary portion of the carburetor;

a source of current for supplying electric current to said bimetal element;

first means for limiting the electric current from said source of current to said bimetal element;

thermal switching means for controlling the resistance value of said first current limiting means in response to the atmospheric temperature near the internal combustion engine;

second means for limiting the electric current from said source of current to said bimetal element;

switching means for disconnecting said first current limiting means from said source of current and connecting said second current limiting means to said source of current when said choke valve is fully open.

7. An electrically controlled automatic choke for a carburetor for an internal combustion engine as defined in claim 6, wherein said first means includes first and second resistors connected in parallel between said source of current and said bimetal element, said thermal switching means including a thermally responsive switch connected in series with said second resistor.

8. An electrically controlled automatic choke for a carburetor for an internal combustion engine as defined in claim 7, wherein said first means further includes a third resistor connected between said source of current and said bimetal element and said thermal switching means further includes a second thermally responsive switch connected in series with said third resistor.

9. An electrically controlled automatic choke for a carburetor for an internal combustion engine as defined in claim 8, wherein said second means includes a control switch operated in response to a fully open condition of said choke valve and a current limiting resistor connected in series with a relay actuated by said control switch to said bimetal element.

10. An electrically controlled automatic choke for a carburetor for an internal combustion engine comprising:

a choke valve for controlling the amount of air flow to the carburetor during the starting period of the internal combustion engine;

a rotatable shaft fixed to said choke valve for moving the same;

a coiled bimetal element for rotating said shaft, one end of which is fixed to said shaft and the other end of which is fixed to a stationary portion of the carburetor;

a source of current for supplying electric current to said bimetal element through the stationary portion of the carburetor;

a first resistance connected to the stationary portion for limiting the current from said source of current to said bimetal element;

a first thermal switch connected to said first resistance in series, said first thermal switch being operable at a first predetermined atmospheric temperature near the internal combustion engine;

a second resistance connected to the stationary portion for limiting the current from said source of current to said bimetal element;

a second thermal switch connected to said second resistance in series, said second thermal switch being operable at a second predetermined atmospheric temperature near the internal combustion engine;

a third resistance connected to the stationary portion for limiting the current from said source of current to said bimetal element;

a fourth resistance connected to the stationary portion for limiting the current from said source of current to said bimetal element;

and switching means for disconnecting said first, second, and third resistances from said source of current and connecting said fourth resistance to the same when said choke valve is fully open.