Solid State Controlled Automatic Choke

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 and/or ambient air temperature to open the choke valve in a more efficient manner and thus reduce air pollution and improve engine performance during warm-up. The electrical heating means may be either a conventional resistance heater or a positive temperature coefficient thermistor.

Description

BACKGROUND OF THE INVENTION

This invention is in the field of automatic choke valves for carburetors, and particularly choke valves controlled by solid state devices.

It is conventional in internal combustion engines to provide a carburetor having a choke valve therein controlled by a bimetallic 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 bimetallic springs and they do not normally open the choke valve at a rate to hold emissions and air pollution to a minimum. During the warm-up period, such engines normally cause excessive air pollution due to improper combustion.

SUMMARY OF THE INVENTION

The present invention contemplates solid state control means for a thermostatically controlled choke valve wherein an electrically operated heating means provide heat for the thermostatic spring. The rate of heating the spring is controlled by a negative temperature coefficient (NTC) thermistor. The thermistor is positioned to sense the desired temperature conditions, whether ambient air, engine block temperature or a combination thereof. As the temperature of the thermistor increases, the current through the heating means increases and thus heats the thermostatic spring at the desired rate for smoother warm-up of the engine and to minimize air pollution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view through a portion of an engine embodying one form of the present invention;

FIG. 2 is a perspective view of the thermistor and its mounting as used in the form shown in FIG. 1;

FIG. 3 is a schematic fragmentary sectional view through a modified form of the invention;

FIG. 4 is a perspective view of the thermistor mount of FIG. 3;

FIG. 5 is a vertical sectional view taken on the line 5--5 of FIG. 3;

FIG. 6 is a view similar to FIG. 3 but showing a further modification of the invention;

FIG. 7 is a fragmentary partially sectional view of a still further modification of the invention;

FIG. 8 is a view similar to FIG. 6 but showing another embodiment;

FIG. 9 is a vertical sectional view taken on the line 9--9 of FIG. 8; and

FIGS. 10 and 11 are perspective views of alternative mounting means for thermistors in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the different embodiments to be described, the same reference numerals are employed to designate identical or similar parts.

FIG. 1 schematically shows a portion of an engine block 2 with the automatic choke portion of a carburetor 4 shown. The portion 4 defines a passageway 6 leading to the intake manifolds of the engine and in which a choke valve 8 is pivotally mounted by means of choke shaft 10 journalled in suitable bushings 12. The choke shaft 10 is provided with an arm or link 14 turned outwardly at its end 16. Numeral 18 designates a cover for the automatic choke mechanism, which covers are conventionally formed of suitable plastic material, which also constitutes electrical insulation. Fixedly mounted in the cover 18 is a support shaft 20 having a slot or groove 22 therein. A bimetallic spiral spring 24 is formed with an inner end portion 26 (see FIG. 5) within the slot 22. The outer end of the spring 24 is connected to the end portion 16 of arm 14. The structure thus far described is conventional and, as is well known, when the spring 24 is cold, it assumes a shape and position holding the choke valve 8 substantially closed, that is, extending across the passageway 6. When the spring 24 is heated it expands and, through arm 14, rotates the choke valve 8 to an open position. Conventionally, heat generally originating at the exhaust manifold of the engine is conducted to the interior of the cover 18 to provide the necessary heat for the spring 24 as the engine warms up. However, such heat conducting means are subject to failure and blockage and do not provide reliably efficient and proper response of the spring 24.

As shown in FIG. 1, the support shaft 20 is fixedly secured to a metal cup 28 securely and fixedly mounted in an opening 30 in cover 18. Also fixedly mounted to the cup member 28 is an electrical heating device 32. As will be pointed out, the heating device 32 may be either a conventional electrical resistance element or a positive temperature coefficient thermistor (PTC). As also shown in FIG. 1, a suitable ground conductor 34 is electrically connected to the shaft 10 and electrically connected to the metal portions of the engine, constituting a "ground." Such grounding could be provided by conductive bushings 12, conductive lubricants, or the like.

Numeral 36 designates a negative temperature coefficient thermistor brazed, soldered or otherwise fixedly secured to a pair of contact-support members 38 and 40. The securement is such as to provide good heat conductivity between the thermistor and its supports and good electrical connection therebetween. The assembly of thermistor 36 and its supports is shown in greater detail in FIG. 2. As shown, one end of each element 38 and 40 is provided with an opening 42 by which the assembly is mounted on the engine block 2. As shown in FIG. 1, supports 38 and 40 are held to the engine block by a bolt or the like 44 but are electrically insulated from the engine block by suitable insulating spacers 46. The other ends of the support members 38 and 40 are formed as terminal lugs 48 and 50. The heating means 32 is also provided with a terminal lug member 52 thereon in electrical contact therewith. As shown, the terminal lug 52 is electrically connected to terminal lug 50 and terminal lug 48 is electrically connected to one side of a source of electrical power represented in FIG. 1 by battery 54. The other terminal of the battery is connected to ground (some portion of the engine block or attachments). While a battery 54 is indicated herein, it is to be understood that it represents a suitable source of electrical power, which may include suitable voltage control or regulating devices and/or current limiting resistors. The electrical heating device 32 is shown as being enclosed by a suitable protective material 56, such as an epoxy resin or the like, as is true also of other embodiments.

In operation, assuming that the engine is cold and has just been started, the spring 24 holds the choke valve 8 in its closed position and thermistor 36 is cold so that very little current can flow. However, as soon as the engine is started, voltage is supplied to the electrical circuit just described and a small current flows from battery 24 through thermistor 36, then through heating means 32 to the support shaft 20, spring 24, arm 14 and shaft 10, and conductor 34 to ground, to which the other side of the battery is connected. Thus, a circuit is complete and when the engine or surrounding air is cold, the thermistor 36 presents a relatively high resistance to current flow. However, as current continues to flow, the resistance of thermistor 36 and increasing temperature of its surroundings causes it to warm up somewhat, which results in a reduction in its resistance and increase in current flow. The current flow through heater 32 produces heat which is conducted directly to the spring 24, through support shaft 20, to cause the same to start expanding and to commence opening choke valve 8. Since the thermistor 36 is mounted in close proximity to the engine block, heat from the latter as the engine warms up causes a further reduction in resistance of thermistor 36 and thus more rapidly increases current flow to heater 32 to accelerate opening of the choke valve as engine temperature increases. When the parts reach normal operating temperature, current continues to flow through heating means 32 to thus hold the choke valve open during engine operation.

It is contemplated that the contact between spring 24 and its support shaft 20 and between the spring and arm portion 16 of arm 14 be good electrical contact to conduct current thereacross without arcing. The conductor 34 is provided to ensure good current conduction to ground without arcing. Any arcing present at the aforementioned connections could cause the parts to stick and would present a serious fire hazard, in view of the proximity to the explosive gas-air mixture in the regions of the carburetor.

In the form of the invention thus far described and in the additional modifications to be described, it is to be understood that the total resistance of the circuit through the thermistor and heating means to the battery shall have a value of from 1.0 ohm to 2,000 ohms when the engine is at normal operating temperature. This ensures maintenance of the choke valve in open condition during engine operation. In FIG. 1, the thermistor 36 is electrically insulated from the engine block 2 and current through the heating means 32 passes through spring 24 to ground. In FIG. 3, a modification is shown wherein the choke valve shaft 10 and spring 24 are not used as part of the electrical circuit. As shown in FIG. 3, the heating means 22 is mounted in substantially the same manner as described with reference to FIG. 1. However, the outer end of spring 24 is electrically insulated from the portion 16 of arm 4 by a suitable insulating bushing 58, (best seen in FIG. 5). The thermistor 36 is mounted on a single support bracket 60 serving as a support therefor and as a conductor for electrically connecting the thermistor 36 to engine block 2. Bracket 60 is secured directly to the engine block by means of a bolt 62. A terminal lug 64 on thermistor 36 is electrically connected to the metal cup member 28 on which heating means 32 is mounted and the terminal lug 52 is connected to the battery 52 in the manner shown in FIG. 3. It will be obvious to those skilled in the art that the engine of FIG. 3 operates in identically the same manner as does the form of FIG. 1 but the spring 24 and choke valve shaft 10 are not employed as part of the electrical circuit and the temperature response of thermistor 36 is influenced by engine block temperature more than in the form of FIG. 1.

The modification shown in FIG. 6 is quite similar to that shown in FIG. 3 but differs in the manner of mounting the heating device 32. As shown in FIG. 6, the metal cup 28 is not electrically connected to the heating device 32. It is insulated therefrom by a layer of electrical insulation 66 and a contact plate 68 is positioned against the heating device 32, which contact plate is provided with a terminal lug 70. In this form the current passes through only the heating device 32, then to the thermistor 36. As in the form shown in FIG. 3, insulating means 58 is provided between the spring 24 and the portion 16 of arm 14, but insulation 58 is not required if insulator 66 is used. It may be desirable to omit insulator 66 for better heat conduction to shaft 20.

In FIG. 7, numeral 72 designates a portion of the manifold of the engine, having a well 74 therein and into which a portion of the spring 24 extends. The spring support shaft 20 and heating means 32 are directly connected to a bracket 76. The bracket 76 is electrically insulated from the manifold, by insulating means 78. The contact member 52 is in firm electrical contact with the heating means 32 and connected to the battery while bracket 76 is connected to lug 64. Preferably, this form of the invention also includes electrical insulation between the end of spring 24 and the portion 16 of arm 14 and a housing or cover (not shown) is provided.

In the form shown in FIG. 8, which is similar to those of FIGS. 3, 6 and 7, the cover 18 is provided with a large opening 86 in its side wall and that opening is substantially filled by a plug or wall member 88 formed of electrical resistance material. The spring support shaft 20 is mounted directly in the wall portion 88 to be in good heat conductive contact therewith. A metallic ring 90 is embedded in the outer periphery of the wall portion 88 in good electrical contact therewith and is further provided with a terminal lug 92 connected to one side of the battery 54. The outer end of spring support shaft 20 is provided with a terminal lug 94 electrically connected to the terminal lug 64 of thermistor 36. The manner of operation of this form of the invention will be readily understood from the description of the previous embodiments.

As stated previously, in some instances, it may be desirable to employ a positive temperature coefficient thermistor for the heating device 32 to modify the rate at which heat is produced. It is to be noted that in all forms of the invention the heating device is in direct heat conductive contact with the spring support shaft 20 which in turn is in heat conductive contact with the spring itself to thus enhance heating the same at the desired rate.

FIGS. 3, 6, 7 and 8 all show the thermistor 36 (NTC) mounted on a single bracket electrically connected to the engine block or manifold, employing the latter as a part of the electrical circuit. However, it is to be understood that the thermistor 36 (NTC) of any or all of the embodiments may be mounted in the manner described with reference to FIG. 1 wherein it is not electrically connected to ground. In the forms of FIGS. 3, 6, 7 and 8, when a thermistor is mounted in the manner shown in FIG. 1, the entire electrical circuit will be insulated from the engine block and a complete wire circuit to and from the battery is provided.

FIG. 10 illustrates a further form of thermistor mount wherein two thermistors (NTC) 36 are secured to opposite faces of a bracket 96. The remote end of bracket 96 terminates in a terminal lug 98 and a generally U-shaped yoke 100 embraces the outer faces of the two thermistors 36 and is electrically connected thereto. The yoke 100 is free of contact with the bracket 96 and constitutes a further terminal lug for connection in the electrical circuitry described. In this form two thermistors are arranged in parallel.

FIG. 11 illustrates a still further mounting for a thermistor 36. In this form the thermistor is secured to the outer surface of a threaded plug 102, which may be threaded into a corresponding opening in any desired location on the engine block, water jacket or manifold and provides for good heat conductive contact therewith and electrical connection thereto.

As will be apparent to those skilled in the art the present invention is readily applicable to automobiles presently on the road by a simple alteration of the conventional cover 18 and mounting of the described parts.

The bracket members 38, 40 of FIG. 1, 60 of FIGS. 3, 6, 7 and 8, 96 of FIG. 10 and 102 of FIG. 11 are preferably formed of copper or the like to constitute an efficient heat conductor or "heat sink." In some cases brass may be preferable.

It is understood that NTC 36 could also sense the air stream to the carburetor to control the heater at shaft 20, or other type of actuator for arm 14.

While a limited number of specific embodiments of the invention have been shown and described herein, the same are merely illustrative of the principles involved and other embodiments will be apparent to those skilled in the art, within the scope of the applicant's claims.

Claims

I claim:

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 adjacent said thermostat means for heating said thermostat means;

a negative temperature coefficient first thermistor positioned to be responsive to the temperature at a preselected location relative to said engine; and

circuit means electrically connecting said heating means and said thermistor in series with each other and said source of electric power.

2. The improvement defined in claim 1 wherein said electrical heating means comprises a positive temperature coefficient second thermistor.

3. The improvement defined in claim 2 wherein said thermostat means comprises a bimetallic spring arranged to comprise a portion of said circuit means.

4. The improvement defined in claim 1 including a housing surrounding said thermostat means, a heat conductive support in said housing supporting said thermostat means, said heating means being in heat conductive relation to said support.

5. The improvement defined in claim 4 wherein said heating means is positioned in a recess in a wall of said housing and in supporting relation to said support.

6. The improvement defined in claim 5 wherein said heating means comprises a portion of said wall of said housing, said support being mounted thereon.

7. The improvement defined in claim 1 wherein said first thermistor is mounted on a selected portion of said engine, closely adjacent thereto to be responsive to the temperature thereof.

8. The improvement defined in claim 7 wherein said first thermistor is electrically connected to said portion of said engine and in heat conductive contact therewith, said portion of said engine comprising a portion of said circuit means.

9. The improvement defined in claim 8 wherein said first thermistor is secured in heat conductive and electrical contact with a support member which in turn is secured in heat conductive and electrical contact with said portion of said engine.