Electronic choke control

Abstract

An electrical heating means for the bimetallic thermostatic spring controlling a carburetor automatic choke valve is in series with a negative temperature coefficient thermistor which senses engine temperature to open the choke valve in a more efficient manner and improve engine performance during warm-up. A temperature responsive switch is in series with the heater, negative temperature coefficient thermistor and a battery and senses engine block temperature to maintain current flowing in the heater after the engine is shut off and until the entire engine cools down, to provide better warm-engine restarts and reduce pollution.BACKGROUND OF THE INVENTIONThis invention is in the field of automatic choke valves for internal combustion engines and particularly to electrically controlled chokes.It is conventional in internal combustion engines to provide a carburetor having a choke valve therein controlled by a thermostatic spring whereby the choke valve is held closed when the engine is cold. As the engine warms up, heat is directed to the thermostatic spring causing the same to expand and to open the choke valve until, at normal operating temperatures, the choke valve is substantially fully open. Many ambient conditions affect the operation of such metallic springs and they do not normally open the choke valve at a sufficiently high rate to hold emissions and air pollution to a minimum during engine starts and warm-up. Furthermore, after shutting an engine off, the thermostatic spring is normally subject to ambient air temperatures and normally close the choke valve before the engine block is sufficiently cool. Thus, when such a warm engine is restarted, the choke valve is often closed and this results in excessive fuel being fed to the carburetor with the attendant difficulty in starting, excessive emission of polluting materials and often causes "flooding" of the carburetor.Previous attempts have been made to overcome the above-mentioned difficulties, such as by directing warm air or warm engine coolant to the vicinity of the thermostatic spring to thus hold the choke valve open for a longer period of time after engine shut-off. However, such prior devices were capable of holding the choke valve open for only a relatively few minutes after engine shut-off, particularly at fairly low surrounding air temperatures. They were not capable of holding the choke valve open long enough to facilitate easy warm-engine start-ups after the elapse of a few minutes.SUMMARY OF THE INVENTIONIt is a principal object of the present invention to provide means for holding a choke valve open, by electrical means, after engine shut-off until the engine block temperature has been lowered sufficiently to require closed-choke starting conditions.The invention contemplates means for directing battery current through a resistance heater adjacent the thermostatic spring and an engine block temperature-sensing device to terminate operation of the heater only when engine block temperature has reached a predetermined low value.

Description

Claims

1. In an engine having a carburetor choke valve, temperature responsive thermostat means for holding said choke valve closed at low temperatures and for opening said choke valve at higher temperatures, and a source of electric power, the improvement comprising:

electrical heating means in heat conductive relation to said thermostat means for heating the same; and

temperature responsive switching means in series with said source and said electrical heating means, said switching means being mounted in heat conductive relation to a portion of said engine and arranged to be conductive when said portion is above a predetermined temperature and to be non-conductive when said portion cools to a value below said predetermined temperature whereby to maintain current flow from said source through said heating means as long as said portion is above said temperature, irrespective of operation of said engine.

2. The improvement defined in claim 1 including a negative temperature coefficient thermistor in series with said heating means and said source and being in heat conductive relation to a portion of said engine.

3. The improvement defined in claim 1 wherein said electrical heating means is a positive temperature coefficient thermistor.

4. The improvement defined in claim 1 wherein said switching means comprises a temperature responsive switch having relatively movable contacts.

5. The improvement defined in claim 2 including a further temperature responsive switch, closed at elevated temperatures, connected to said electrical heating means to maintain a circuit therethrough in parallel with said negative temperature coefficient thermistor.

6. In a choke system for an internal combustion engine having a carburetor choke valve, temperature responsive means for moving said choke valve between a closed position and an opened position, a source of electrical power, electrical heating means in heat conducting relation to said temperature responsive means for heating said temperature responsive means, the improvement comprising first circuit means including an ignition switch for providing current from said source to said electrical heating means, said ignition switch being operative to open said first circuit means for interrupting the current flow to said electrical heating means when said ignition switch is open, and second circuit means for providing current from said source to said electrical heating means independently of said ignition switch, said second circuit means including a temperature responsive element in heat conductive relation to a portion of the engine and adapted to be conductive when that portion of the engine is above a predetermined temperature and to be non-conductive when that portion of the engine is below the predetermined temperature to maintain current flow from said source through said electrical heating means irrespective of the condition of said ignition switch.

7. A choke system as set forth in claim 6 wherein the first circuit means further includes a negative temperature coefficient thermistor in series with said electrical heating means for controlling the amount of current flowing through said electrical heating means in response to temperature when said ignition switch is closed.

8. A choke system as set forth in claim 6 wherein the electrical heating means is a positive temperature coefficient thermistor.

9. A choke system as set forth in claim 8 wherein the first circuit means further includes a negative temperature coefficient thermistor in series with said electrical heating means for controlling the amount of current flowing through said electrical heating means in response to temperature when said ignition switch is closed.

10. A choke system as set forth in claim 7 further including a temperature responsive switch in parallel circuit with the negative temperature coefficient thermistor and said electrical heating means for shunting said negative temperature coefficient thermistor, said temperature responsive switch being adapted to close at a temperature above a predetermined value for maintaining the current flow through said electrical heating means regardless of the condition of said negative temperature coefficient thermistor.