US3780718A

US3780718A - Carburetor for an internal combustion engine

Info

Publication number: US3780718A
Application number: US00265352A
Authority: US
Inventors: S Nambu; Y Etoo
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1971-10-25
Filing date: 1972-06-22
Publication date: 1973-12-25
Anticipated expiration: 1990-12-25
Also published as: JPS5432884B2; JPS4850126A

Abstract

A carburetor for an internal combustion engine having an auxiliary mixture supply control system which is adapted to supply the engine an enriched air-fuel mixture during starting and warm-up operations of the engine to effect satisfactory starting and warm-up operations of the engine, the quantity and air-fuel ratio of the enriched air-fuel mixture being varied in dependence on the variations in engine temperature. The auxiliary mixture supply control system includes an auxiliary fuel supply circuit for admitting additional air into a carburetor induction passage, an auxiliary air supply circuit for admitting additional air into the carburetor induction passage, a needle valve element located in the auxiliary fuel supply circuit to control the quantity of the additional fuel to be introduced into the carburetor induction passage, an air control valve element located in the auxiliary air supply circuit to control the quantity of the additional air to be introduced into the carburetor induction passage, a compression spring for biasing the needle valve element and the air control valve element to a position to decrease the quantities of the additional fuel and air, an actuating device for moving the needle valve element and the air control valve against the compression spring to a position to increase the quantities of the additional fuel and air, and an electronic control circuit responsive to the engine temperatures for varying the magnitude of electric current to be supplied to the actuating device in dependence on the variations in the engine temperature.

Description

United States Patent [1 1 Nambu et al.

[451 Dec. 25, 1973 CARBURETOR FOR AN INTERNAL COMBUSTION ENGINE [75] Inventors: Shyuya Nambu; Yukihiro Etoo, both of Yokohama, Japan [73] Assignee: Nissan Motor Company, Limited,

Kanagawa-ku, Yokohama City, Japan [22] Filed: June 22, 1972 [21] App]. No.: 265,352

3,673,989 7/1972 Aoho et al 123/32 EA Primary Examiner-Laurence M. Goodridge Assistant ExaminerDennis Toth Att0rneyJohn Lezdey (q/ctyt. cyct AMoUNTs OF AIR AND FUEL FOR WAR1V|-UP AMOUNT OF FUEL [57] ABSTRACT A carburetor for an internal combustion engine having an auxiliary mixture supply control system which is adapted to supply the engine an enriched air-fuel mixture during starting and warm-up operations of the engine to effect satisfactory starting and warm-up operations of the engine, the quantity and air-fuel ratio of the enriched air-fuel mixture being varied in dependence on the variations in engine temperature. The auxiliary mixture supply control system includes an auxiliary fuel supply circuit for admitting additional air into a carburetor induction passage, an auxiliary air supply circuit for admitting additional air into the carburetor induction passage, a needle valve element located in the auxiliary fuel supply circuit to control the quantity of the additional fuel to be introduced into the carburetor induction passage, an air control valve element located in the auxiliary air supply circuit to control the quantity of the additional air to be introduced into the carburetor induction passage, a compression spring for biasing the needle valve element and the air control valve element to a position to decrease the quantities of the additional fuel and air, an actuating device for moving the needle valve ele ment and the air control valve against the compression spring to a position to increase the quantities of the additional fuel and air, and an electronic control circuit responsive to the engine temperatures for varying the magnitude of electric current to be supplied to the actuating device in dependence on the variations in the engine temperature.

9 Claims, 8 Drawing Figures AMOUNT OF AiR so-2040 (5162b 3040 5b60 7'0 8U ENGINE TEMPERATURE PATENTEBUECZSIQH 60 7'0 80 ENGINE TEMPERATURE c) wow safl o @2535 EOE E2; dEia E5 E0 5% 5'0-20|O 0 lo 20 30 40 5'0 O O O 0 w w m w m 2 WIN: Qmmnm mzGzw ENGINE TEMPERATURE (C) CARBURETOR FOR AN INTERNAL COMBUSTION ENGINE This invention relates to carburetors for internal combustion engines used in mortor vehicles and more particularly to a carburetor having an auxiliary mixture supply control system for feeding the engine a sufficient amount of air-fuel mixture of proper air-fuel ratio for the initial cold-engine and subsequent warm-up operations.

In the operation of internal combusition engines used in motor vehicles, a large quantity of unburned noxious components contained in engine exhaust gases are emitted to the atmosphere seriously polluting the air especially in urban areas. With a view to minimize such emission of noxious air pollutants, various vehicular air-pollution preventive devices have heretofore been proposed including improvements in the engine and/or carburetor performance.

As is well known in the art, the engine exhaust emission of the noxious air pollutants can be reduced to a minimum only if an air-fuel mixture is completely burned in the combustion chamber of the engine at a proper temperature. It is found, however, quite difficult to accomplish complete combustion in the engine for all the varying operating conditions of the engine. This is because of the fact that it is difficult in existing carburetors to vary the airfuel ratio of an air-fuel mixture to be supplied to the engine to an optimum value so as to meet the varying operating conditions of the engine. For starting and for all other engine operations it is necessary to introduce into'the engine intake air and fuel to form a combustible mixture. When the engine is at a temperature much lower than the normal running temperature, as when starting initially in cold weather, a very much greater proportion of fuel to air is required because, when starting at low temperature, only a part of the fuel introduced into the engine is vaporized. What is introduced into the engine for starting at low temperatures is generally termed a rich or enriched airfuel mixture because of the greater than normal running proportion of fuel to air is supplied.

During the warm-up period, after the engine becomes self-operative, the ratio of fuel to air should be gradually reduced, generally termed as a leaning out of the mixture, as the engine temperature progressively increases until such ratio becomes that of the normal running mixture when the engine attains its normal operating temperature. It has been customary to control the relative proportions of fuel and air introduced into the engine intake for starting and warm-up operation by manual actuation of what is termed a choke valve. it has been found difficult to manually operate such a valve without providing too much or too little fuel relative to the quantity of air supplied, with the result that starting is not only made difficult, but the engine is likely to operate unsatisfactorily and even'stall after it begins to run.

The conditions during starting of an engine, hot or cold, are necessarily different from what they are after the engine is warmed up and is running. Cranking speed is inherently slow, and hence the suction, which the engine can produce, is inherently low. Starting is further dependent upon engine temperature, because the extent of fuel vaporization also depends upon engine temperature. In manual operation of a choke valve, the operator has to depend upon his judgement of conditions to properly position the choke valve to obtain the proper flow of additional fuel into the intake manifold to effect satisfactory starting, and to reposition the choke valve after the engine is running to progressively reduce the quantity of additional fuel supplied, so as to decrease the richness of the mixture. By this method, it is quite difficult to precisely vary the air-fuel ratio of the air-fuel mixture to be supplied to the engine for thereby effecting satisfactory starting of the engine.

To overcome this shortcoming, an automatic choke control mechanism is provided in the carburetor, which mechanism is made responsive to the variations in temperature of engine exhaust gases. With this provision of automatic choke control mechanism, however, it is still difficult to control the relative proportions of fuel and air to be introduced into the engine intake so as to meet all the engine operating requirements.

It is, accordingly, a principal object of the present invention to provide an improved carburetor for an internal combustion engine driving a vehicle which carburetor is capable of automatically controlling the startihg and subsequent operation of the engine, particularly during the warm-up period.

It is another object of the present invention to provide an improved carburetor for an internal combustion engine which is capable of automatically controlling the richness of an air-fuel mixture to be supplied to the internal combustion engine in response to engine temperature so as to eliminate the ordinary hand choke arrangement often used.

It is another object of the present invention to provide a carburetor for an internal combustion engine, which carburetor is provided with an auxiliary mixture supply control system adapted to feed the engine a sufficient quantity of air-fuel mixture of proper air-fuel ratios for starting the initially cold engine and the subsequent warm-up operations.

It is still another object of the present invention to provide a carburetor for an internal combustion engine, which is provided with an auxiliary mixture supply control system adapted to precisely control the relative proportions of fuel and air to be introduced into the engine to meet all the engine operating requirements.

It is still another object of the present invention to provide a carburetor for an internal combustion engine, the carburetor having an auxiliary mixture supply control system which is operative during the initial starting of the cold engine and subsequent warm-up operations for automatically controlling the air-fuel ratio of an air-fuel mixture to be supplied to the engine to appropriate values in response to engine temperature for thereby effecting satisfactory engine operation.

It is a further object of the present invention to provide an auxiliary mixture supply control system for a carburetor of an internal combustion engine, which system is highly reliable in operation and can readily be installed in existing carburetors.

In general, the present invention contemplates to provide a carburetor for an internal combustion engine having a main mixture circuit adapted to supply an airfuel mixture to the carburetor induction passage for high-speed and heavy load operations of the engine, an idling and slow-running mixture circuit adapted to supply an air-fuel mixture to the carburetor induction passage for idling and light load operations of the engine, a throttle valve operatively' disposed in the carburetor induction passage for controlling the quantity and airfuel ratio of the air-fuel mixture to be supplied to the engine, and a'fuel reservoir which supplied fuel to the two circuits. The carburetor is provided with an auxiliary mixture supply control system which is adapted to be operative during starting and warm-up operations of the engine so as to control the quantity and air-fuel ratio of an additional air-fuel mixture to be introduced into the carburetor induction passage in dependence on the variations in engine temperature to thereby effect satisfactory starting and warm-up operations of the engine. In a preferred embodiment, the auxiliary mixture supply control system includes an auxiliary fuel supply circuit having a fuel passage communicating with the fuel reservoir, and an auxiliary fuel supply port located in the carburetor induction passage downstream of the throttle valve, and an auxiliary air supply circuit having passage means leading from an air cleaner and opening into the intake manifold of the engine to admit an additional air thereinto and an air control chamber interposed in the passage means and having a control port to control the quantity of the additional air to be introduced into the intake manifold of the engine. A needle valve means is provided in the auxiliary fuel supply circuit for controlling the effective sectional area of the auxiliary fuel supply port thereby to vary the quantity of the additional fuel to be introduced into the intake manifold of the engine. An air control valve means is operatively disposed in the air control chamber for gradually varying the effective sectional area of the control port so that the additional air and fuel introduced into the intake manifold to form a combustible air-fuel mixture of the optimum air-fuel ratio for starting and warm-up operations of the engine. The needle valve means is operatively connected to the air control valve means, and cooperates therewith. The auxiliary mixture supply control system further includes an actuating device associated with the air control valve means cooperating with the needle valve means, and an electronic control circuit for controlling the actuating device in dependence on the engine temperature so that the movements of the needle valve means and the air control valve means dependent upon the engine temperature to vary the quantity and air-fuel ratio of the additional air-fuel mixture to be introduced into the engine. The actuating device has a movable means which is connected to the air control valve means to which the needle valve means is also connected. The electronic control circuit includes a plurality of input terminals connected to an ignition circuit, a startor circuit and a distributor, and an output terminal connected to the actuating device. The electronic control also includes a first switching transistor connected to the startor circuit, a relay switch connected to the first switching transistor, a second switching transistor for actuating the actuating device and connected to the relay switch, and a thermostatic switch connected between the relay switch and the second switching transistor, the thermostatic switch being closed when the engine temperature is below a first predetermined value to render the second switching transistor conductive thereby to energize the solenoid coil of the actuating device. The electronic control circuit further includes a thermistor mounted on the engine body to respond to the engine temperature to vary the base potential of the second transistor in dependence on the engine temperature so that the quantity and air-fuel ratio of the additional air-fuel mixture to be introduced into the engine is varied in dependence on the engine temperature. A thermostatically controlled time switch is provided which is connected to the second switching transistor for increasing the base potential of the second switching transistor when it is switched on, that is, when the engine temperature is below a second predetermined value which is lower than the first predetermined value so that the needle valve means and the air control valve means are moved to respective positions to provide an enriched air-fuel mixture to the engine during starting of the coldengine.

These and other features and advantages of the present invention will become more apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the accompanying drawings:

FIG. 1 is a graph showing an example of a desired relationship between the air-fuel ratio of air-fuel mixture and the engine temperature during starting condition of an internal combustion engine;

FIG. 2 is a graph showing an example of a desired relationship between the engine speed and the engine temperature during warming-up condition of the engine;

FIG. 3 is a graph showing an example ofa desired relationship between the air-fuel ratio of air-fuel mixture and the engine temperature during the warm-up period;

FIG. 4 is a graph showing an example of a relationship between the friction of the engine and the temperature of lubricating oil used in the engine;

FIG. 5 is a graph showing an example ofa desired relationship between the amounts of air and fuel and the engine temperature during warm-up period, the amounts of air and fuel being suited for each of the cylinders of, for example, a four-cylinder internal combustion engine having a volume of 2,000 cc;

FIG. 6 is a schematic sectional overall view of a preferred embodiment of the carburetor according to the present invention;

FIG. 7 is a view illustrating an example of a circuit diagram of an electronic control part of the carburetor shown in FIG. 6; and

FIG. 8 is a view illustrating an example of operative range of a thermostatic time switch shown in FIG. 7.

Referring now to FIG. 1, there is shown a graph illustrating an example of a desired relationship between the air-fuel ratio of air-fuel mixture and the engine temperature during starting condition of an internal combustion engine. A satisfactory starting of the engine will be obtained and the unburned noxious components of engine exhaust gases produced during engine starting will be reduced to a minimim by controlling the air-fuel ratio of the air-fuel mixture in such a manner as to be within a cross-hatched area A in FIG. 1. As seen from the cross-hatched area A of FIG. 1, if the engine temperature is -30C, it is necessary to restrict the air-fuel ratio fixedly with a certain range, say anywhere between l:l and 4:1 (by weight). Thus, it is apparent. that during starting of a cold engine, it is necessary to supply a mixture having a greater proportion of fuel to air than is required to form the air-fuel mixture for operation of a warmed-up engine. This is because of the fact that when starting at low temperature, only a part of the fuel introduced into the engine is vaporized. When the engine temperature reaches a predetermined value, for example, a value of about 60C, it is necessary to adjust the air-fuel ratio fixedly within a certain range, say anywhere between 12:1 and :1. It should be noted here that during starting of the engine, the engine speed is relatively low, that is, between 150 R.P.M. and 300 R.P.M. and, accordingly, the suction produced by the engine approximates a subatmospheric pressure causing a relatively small amount of air to be drawn into the engine. Thus, the required air-fuel ratio of the air-fuel mixture for starting the engine mainly depends upon the engine temperature because the extent of fuel vaporization depends upon the engine temperature.

During the warm-up period, after the engine becomes self-operative, the ratio of fuel to air should be gradually reduced as the engine temperature progressively increases until such ratio becomes that of the normal running mixture when the engine attains its normal operating temperature. It is a common practice to vary the engine speed in such a manner as to follow the curve B of FIG. 2 with a view to minimize the time period required for warming up the engine and enhancing the operating stability of the engine. As seen in FIG. 2, the engine speed is initially maintained at a relatively high level, that is, at about 1600 R.P.M. when the engine temperature is below +C and subsequently decreased to an ordinary idling speed with the increase in the engine temperature until the same reaches +60C.

FIG. 3 illustrates an example of a desired relationship between the air-fuel ratio of the air-fuel mixture and the engine temperature during the warm-up period. As seen from the graphs of FIGS. 1 and 3, the air-fuel mixture to be supplied to the engine during the warm-up period is leaner than the mixture to be supplied to the engine during starting. This is due to the fact that after the engine becomes self-operative, the engine cylinders are warmed up thereby increasing the degree of fuel vaporization. Since, however, the friction of the piston decreases as the temperature of the lubricating oil used increases as seen from the curve D of FIG. 4, it is required that the amounts of auxiliary fuel and air be increased as the temperature of the lubricating oil is low so as to overcome this friction of the piston for thereby maintaining the engine at its ordinary idling speed. Accordingly, the amounts of air and fuel to be introduced into the engine during warm-up period should be varied in accordance with the curves E and F of FIG. 5 where a four-cylinder internal combustion engine of 2,000 cc is employed.

Referring next to FIG. 6, there is schematically shown a preferred embodiment of a carburetor embodying the present invention, the carburetor being generally indicated by reference numeral 10. The carburetor 10 is provided with a carburetor body 12 which is flanged as at 14 for attachment to an intake manifold 16 of an internal combustion engine (not shown). The carburetor body 12 has formed therein a carburetor induction passage 18 which is opened at its one end to an air cleaner 20 having mounted therein an air cleaner element 22 to supply filtered air and which passage communicates with the intake manifold 16 of the engine. The carburetor 10 is also provided with a throttle valve 24 which is fixedly mounted on a rotatable shaft 26 for rotation in the carburetor induction passage 18, a main venturi 28, a small venturi 30, a main mixture circuit 32, an idling and-slow running mixture circuit 34, and a float chamber 36. Tha main mixture circuit 32, through which an air-fuel mixture is supplied to the carburetor induction passage 18 for relatively heavy load operation such as acceleration or high speed driving of the vehicle, opens into the small venturi 30. The idling and slow running mixture circuit 34 for idle or light load operation opens to the carburetor induction passage 18 downstream of the main venturi 28 through a slow running port 38 and an idling port 40. The slow running port 39 is located at the position closely adjacent to the periphery of the throttle valve 24 when it is substantially closed, while the idling port 40 is located posterior to or downstream of the throttle valve 24. Designated at 42 is an idling adjustment screw for adjusting the flow rate of the mixture through the idling port 40.

As shown in FIG. 6, there is provided in the main mixture circuit 32, a main fuel jet 44, a main fuel and air mixer 46 and a main nozzle 48 in this sequence from the float chamber 36. The main fuel and air mixer 46 has formed at its bottom portion a plurality of restrictors 50 and at its top an air bleed 52 vented from the open air. The sizes of the restriction 50 and the air bleed 52 are designed or selected to provide a desired amount of air-fuel mixture of the proper air-fuel ratio, so that an air-fuel mixture of the optimum air-fuel ratio is produced in the main mixture circuit 32 for delivery to the engine so as to provide a maximum engine performance efficiency. In operation, with the throttle valve 24 substantially fully opened for a relatively heavy load operation, a sufficient amount of suction is established in the small venturi 30 due to the fact that a considerable amount of air is passing through the small venturi 30 during this particular operation. Then, a desired amount of fuel is metered by the main jet 44 and mixed with air in the main mixer 46 to provide an air-fuel mixture, which is drawn through the main nozzle 48 into the small venturi 30 by the suction established therein.

In addition tothe slow running port 38 and the idling port 40 there is provided in the idling and slow running mixture circuit 34 a slow running fuel and air mixer 54 which has formed at its bottom restrictor 56 and an air bleed 58 vented from the ambient atmosphere. The air bleed S8 is designed or selected to admit air from the ambient atmosphere at desired flow rates. While the engine is running under idling or light load conditions with the throttle valve 24 substantially fully closed, the air flow rate delivered into the engine is not large and, therefore, a high vacuum is not established in the small venturi 30. Thus, a metered air-fuel mixture is supplied to the engine through the slow running port 38 and the idling port 40.

According to the present invention, there isfurther provided in the carburetor an auxiliary mixture supply control system which is operative during starting and warm-up operations of the engine so as to control the air-fuel ratio of an additional air-fuel mixture to be introduced into the carburetor induction passage in dependenee on the variations in engine temperature to effect satisfactory starting and warm-up operations. To this end, the auxiliary mixture supply control system, which is generally designated by reference numeral 60, includes an auxiliary fuel supply circuit 62 and an auxiliary air supply circuit 64, through which fuel and air are introduced into the intake manifold of the engine to form an air-fuel mixture of optimum air-fuel ratio specifically suited for the initial starting and subsequent warm-up operations of the engine. The auxiliary fuel supply circuit 62 is provided with a fuel passage 66 communicating with the float chamber 36 through a inainfuel jet chamber 68, an auxiliary fuel chamber 70 communicating with the fuel passage 66, and an auxiliary fuel supply port 72 located in the carburetor induction passage 18 downstream of the throttle valve 24 and communicating with the auxiliary fuel chamber 70. As shown, the auxiliary fuel chamber 70 has formed therein a valve seat 70a for a reason to be described hereinafter. The auxiliary air supply circuit 64 comprises a first conduit 74 communicating with the air cleaner 20, a second conduit 76 communicating-with the intake manifold 16 of the engine, and an air control chamber 78 disposed between the first and

second conduits

74 and 76. Indicated at 80 is a rubber tube which connects the conduit 74 with a conduit 82 leading from the air cleaner 20. The air control chamber 78 is provided with a flow control port 84 which communicates with the second conduit 76 leading to the intake manifold 16. In the illustrated embodiment, the second conduit 76 is shown as opening to the intake manifold 16 but may be arranged to open to the carburetor induction passage 18 downstream of the throttle valve 24.

In order to vary the effective cross-sectional area of the auxiliaryfuel supply port 72 thereby to meter the amount of fuel passing therethrough, a needle valve element 86 is operatively disposed in the auxiliary fuel chamber 70. The needle valve element 86 is provided with a tapered end 88 which projects into the auxiliary fuel supply port 72 for gradually varying the effective cross-sectional area thereof. The needle valve element 86 is also provided with anannular shoulder 90 integral with' the section 88 and functioning like a valve head, and an elongated cylindrical section 92 slidably extending into the air control chamber. Indicated at 94 is a seal member which seals off the fuel chamber 70 from the'air control chamber 78.

The amount of air to be admitted into the intake manifold 16 during starting and warm-up operations of the engine is controlled by an air control valve element 96 which is slidably or movably received in the air chamber 78 for gradually varying the effective sectional area of the air flow control port 84. The air control valve element 96 has a passageway 98 for a purpose to be described hereinafter. As shown, this valve element 96 is interconnected to the needle valve element 86 by suitable connecting means such as a lock nut 100 and cooperates therewith. A compression spring 102 is provided for biasing the air control valve element 96 toward a position to decrease the effective sectional area of the control port 84. The compression spring 102 has one end supported by the air control valve element 96 and the other end supported by an annular retainer plate 104, which is interposed between first and second casings 106 and 108. On both sides of the retainer plate 104 gaskets 1 are provided to serve as seals. As shown, the air control chamber 78 is formed within the first casing 106, which is mounted on the carburetorbody 12 by a suitable connecting means (not shown). The second casing 108 is mounted on the first casing 106.

The sizes of the elements of the auxiliary mixture supply control system 60, including the fuel supply port 70, the tapered end 88 and the air flow control port 84, are selected to ensure provision of an enriched air-fuel mixture having a low air-fuel ratio when the actuating device 110 causes the

ports

72 and 84 to open fully whilst starting the engine at a low engine temperature, but to gradually provide a leaner mixture by closing

ports

72 and 84 at the rate the engine reaches its normal operating temperature, as seen in FIG. 1.

To automatically control the movements of the needle valve element 86 and the air control valve element 96, an actuating device 110 is mounted within the second casing 108. The actuating device 110 includes a movable core 112 slidably accommodated in a guide I ring 114 disposed in'the second casing 108 and in a third casing 116 mounted in the second casing 108. The actuating device also includes a solenoid coil 118 which is wound around a cylindrical portion (not identified) of the movable core 112 in such a manner that the solenoid coil 1 18 and accordingly the movable core 112 are movable within the third casing 116. The actuating device 110 is further provided with a stationary core 120 including an iron core 124 and a permanent magnet 126, which are rigidly secured to the bottom wall of the third casing 116 by means of suitable fastener means such as a bolt 128. Indicated at is an adhesive which seals off the interior of the second casing 116 from the atmosphere. The solenoid coil 118 has one end electrically connected to a lead 132 and the other end electrically connected to a lead 134 which is grounded. The leads 132 and 134 extend through

openings

136 and 138, respectively, which are sealed by a suitable adhesive insulating material.

The movable core 112 is operatively connected to the air control valve element 96, to which the needle valve element 86 is also connected in a manner previously described. More specifically, a connecting rod 140 is provided which has one end screwed into the air control valve element 96 and fixed thereto by a suitable fastner means such as a lock nut 142 and the other end freely disposed in a bore 144 formed in the movable core 112. The connecting rod 140 is provided with an engaging pin 146 at its other end, the engaging pin 146 projecting into an elongated slot 148 formed in the movable core 112 to form a stop motion mechanism to compensate for the axial deflection of the first and second casings 106 and 108, respectively.

As seen in FIG. 6, the guide ring 1 14 is provided with a passageway 150 for providing air communication between the interior of the first casing 106 and the interior of the second casing 108. Moreover, a passageway 152 is provided in the third casing 1 16 which interconnects the interior of the second casing 108 with the interior of the third casing 116. Thus, even when the air control chamber 78 is under vacuum, the air control valve element 96 and the movable core 1 12 are not affected by the vacuum in the air chamber 78 because it is transmitted to the interiors of the first casing 106 and the third casing 116 through passageways 98, 150 and 152.

The auxiliary mixture supply control system 60 operates as follows. During initial cold engine and subsequent warm-up operations, the solenoid coil 118 of the actuating device 110 is energized so that the movable core 112 associated therewith is subjected to an attractive force tending to cause the movable core 112 to move ri-ghtwardly. Consequently, the air control valve element 96 and accordingly the needle valve element 86 are moved rightwardly of the drawing against the force of the compression spring 102. In this instance,

the annular shoulder 90 of the needle valve element 86 leaves the valve seat 70a formed in the auxiliary fuel chamber 70 to admit fuel into the carburetor induction passage through the auxiliary fuel supply port 72, whereas the air control valve element 96 opens the air flow control port 84 to permit air to pass into the intake manifold 16. Thus, the engine is supplied with an airfuel mixture of the air-fuel ratio specifically suited for effecting satisfactory engine operations during starting and warm-up of the engine.

Now, assuming that F represents the attractive force of the solenoid coil 118, 4) represents the magnetic flux density of the solenoid coil 1 18, L represents the length of the solenoid coil 118 and I represents the magnitude of electric current to be applied to the solenoid coil 118, then the following equation holds:

where K represents a constant. It is seen from this equation that the attractive'force F depends upon the magnitude of the electric current applied to the solenoid coil 118 because K, and L are given values. Thus, the extent of movement of the movable core 112 associated with the solenoid coil 1 18 is varied in proportion to the variations in magnitude of the electric current supplied to the solenoid coil 118. Consequently, the amounts of fuel and air supplied to the engine intake manifold during cold engine and subsequent warm-up operations are varied in proportion to the variations in magnitude of the electric current supplied to the solenoid coil 118 of the actuating device 110.

When, however, the engine reaches its normal operating temperature, the solenoid coil 118 of the actuating device 110 is de-energized so that the movable core 112 is not subjected to the attractive force of the solenoid coil 118. In this condition, the air control valve element 96 and accordingly the needle valve element 86 are moved leftwardly of the drawing by the force of the compression spring 102. Consequently, the annular shoulder 90 of the needle valve element 86 is seated on the valve seat 70a formed in the auxiliary fuel chamber 70 to close the auxiliary fuel supply port 72, thereby preventing the fuel in the auxiliary fuel chamber 70 from being introduced into the carburetor induction passage 18 and the intake manifold 16. Concurrently, the air control valve element 96 closes the air flow control port 84 of the air control chamber 78 so that the air in the air control chamber 78 is prevented from being introduced into the intake manifold 16. Thus, after the engine is warmed up to its normal operating temperature, the air-fuel mixture of a required air-fuel ratio is admitted through the main mixture circuit 32 or through the idling and slow running mixture circuit 34 into the intake manifold 16 of the engine.

It is an important feature of the present invention that the magnitude of the electric current to be supplied to the solenoid coil of the actuating device is varied in proportion to the variations in engine temperature so as to control the air-fuel ratio of an air-fuel mixture required for starting and warm-up operations in accordance with the graphs of FIGS. 1 and 3 whereby a satisfactory engine operation is obtained during these particular operations. To this end, the auxiliary mixture supply control system 60 also includes an electronic control circuit which is generally designated by reference numeral 160. The electronic control circuit 160 has a plurality of input terminals electrically connected to a starter circuit 162, an ignition circuit 164, a thermistor 166, a thermostatically controlled time switch 168, a thermostatic switch and a distributor 172, respectively, to receive various input signals therefrom and serves to generate at its output terminal a variable electric signal in response to the input signals for operating the actuating device 110. The starter circuit 162 and ignition circuit 164 are connected to and energized by an ignition switch 174, the ignition switch 174 being connected to a source 176 of dc voltage such as a battery (not shown).

FIG. 7 illustrates in detail the electronic control circuit shown in FIG. 6. In FIG. 7, reference numeral 180 designates an input terminal of the circuit 160 to which terminal is applied an ignition pulse signal generated by the distributor 172 (see FIG. 6), which is driven by the engine, though not shown. The input terminal 180 is connected through a resistor 182 to the base of a transistor 184. The transistor 184 is connected at its collector to a bus line 186 through a resistor 188, the bus line 186 being connected to an input terminal 190 which is connected to the ignition circuit 164 (see FIG. 6) and to which an input voltage is applied when the ignition switch 174 is closed. The collector of the transistor 184 is also connected to a diode 192, which is connected through a resistor 194 to the base of a transistor 196. The emitter of the transistor 184 is grounded through a line 198. A capacitor 200 and a resistor 202 are connected in parallel to between the base of the transistor 196 and the line 198. The collector of the transistor 196 is connected to the bus line 186 and the emitter thereof is connected to the line 198 through

resistors

204 and 206, a point between of which is connected to the base of a transistor 208. The collector of the transistor 208 is connected through a diode 210 to the bus line 186. The collector of the transistor 208 is also connected to a relay circuit 212. The relay circuit 212 includes a relay coil 214 connected between the collector of the transistor 208 and the bus line 186, a stationary contact 216 and a movable contact 218 associated with the solenoid coil 214. The stationary contact 216 is connected to the thermostatic switch 170. The thermostatic switch 170 may be mounted on the engine body so as to respond to the engine temperature such as the temperature of the engine coolant and it is closed until the engine reaches a predetermined temperature, for example, about +60C. The thermostatic switch 170 is connected through a resistor 220 to the base of a tran- Ltr. he s l q f th transisto zlz s c nnected to a bus line 224, to which an input terminal 226 is also connected which in turn is connected to the ignition circuit 164. The emitter of the transistor 222 serves as an output terminal of the electronic control circuit 160 and is connected through the line 132 to the solenoid coil 118 of the actuating device 110 (see FIG. 6). The movable contact 218 of the relay switch 212 is connected to the emitter of a transistor 228. The emitter of the transistor 228 is also connected through a resistor 230 to a line 232 which is grounded. The collector of the transistor 228 is connected to the bus line 224. The base of the transistor 228 is connected to a point between a resistor 234 which is connected to the bus line 224 and the thermistor 166 which is connected to the line 232. The thermistor 166 may be mounted on the engine body to detect the engine temperature such as the temperature of the engine coolant and functions to produce a variable voltage signal dependent upon the engine temperature for varying the electric signal appearing at the output of the electronic control circuit 160 in proportion with the variations in the engine temperature.

The electronic control circuit 160 further includes an input terminal 236, to which the starter circuit 162 is connected. The input terminal 236 is connected to a point 238 between

diodes

240 and 242. The diode 240 is connected to the base of the transistor 208, while the diode 242 is connected to the thermostatically controlled time switch 168, which is connected through a resistor 244 to the base of the transistor 222. The thermostatically controlled time switch 168 includes a bimetallic arm 246 adapted to respond to the engine temperature such as, for example, the temperature of the engine coolant, a movable contact 248 connected to the end of the bimetallic arm 246, and two stationary contacts 250 which are engageable and dis-engageable by the movable contact 248. The thermostatically controlled time switch 168 also includes a heating coil 252 having one end connected through the diode 242 to the point 238 and the other end grounded. The thermostatically controlled time switch 168 serves to engage the stationary contacts 250 when the engine temperature is below +30C to cause the input voltage appearing at the input terminal 236 to be transmitted through the resistor 244 to the base of the transistor 222 thereby to increase the potential at the base of the transistor 222 so that the magnitude of the electric potential current supplied to the solenoid coil 118 of the actuating device 110 is increased thus additionally increasing the amounts of fuel and air introduced into the intake manifold of the engine during starting. After a certain period of time, however, the bimetallic arm 246 is heated by the heating coil 252 to the point where the thermostatically controlled time switch 168 is switched off to discontinue increasing the amounts of fuel and air introduced into the intake manifold.

When, in operation, the ignition key 174a is turned to switch the ignition switch 174 on, the ignition circuit 164 is connected to the source 176 of dc. voltage supply and accordingly the input voltage is supplied to the

input terminals

190 and 226 of the electronic control circuit 160. When, moreover, the ingition key 174 is further turned to switch the starter switch 162 on, the starter circuit 162 is connected to the source 176 of the d.c. voltage supply to that the input voltage is also supplied to the input terminal 236 of the electronic control circuit 160. Under these circumstances, the input voltage appearing at the input terminal 236 is delivered through the diode 240 to the base of the transistor 208 thereby rendering the same conductive. This causes the relay switch 212 to be switched on. On the other hand, the input voltage appearing at the input terminal 226 is supplied through the resistor 234 to the base of the transistor 228 with a result that the transistor 228 is rendered conductive. If, in this instance, the engine temperature is below +60C, the thermostatic switch 170 is closed so that the voltage at the emitter of the transistor 228 is passed through the resistor 220 to the base of the transistor 222. Consequently, the transistor 222 is rendered conductive and accordingly the voltage appearing at the emitter of the transistor 222 is delivered through the line 132 to the solenoid coil 1 18 of the actuating device 110. Thus, the needle valve element 86 and the air control valve 96 are moved to a position against the force of the compression spring 102 to admit additional fuel and air into the intake manifold 16 of the engine (see FIG. 6) in amounts shown in FIG. 5.

if, now, the engine temperature is below +30C, the thermostatically controlled time switch 168 is switched on so that the input voltage appearing at the input terminal 236 is supplied through the diode 242 and the resistor 244 to the base of the transistor 222 to increase the base potential thereof. Consequently, the magnitude of the input signal appearing at the emitter of the transistor 222 energizing the coil 118 is increased, thereby increasing the amount of rich air-fuel mixture introduced into the engine intake manifold to provide an enriched air-fuel mixture for starting the cold engine. After a certain period of time, the bimetallic arm 246 is heated by the heating coil 252 so that the'movable contact 248 disengages the stationary contacts 250. In this instance, the base potential of the transistor 222 depends upon the voltage signal delivered from the transistor 228 and therefore the additional air-fuel supply is discontinued. It will be appreciated that when the engine temperature reaches +30C, the thermostatically controlled switch 168 is switched off to discontinue the additional fuel supply to the engine intake manifold. It will further be noted that when the engine temperature increases to +60C, the thermostatic switch 170 opens to de-energize the actuating device and, accordingly, the auxiliary mixture supply control system is made inoperative.

During the operation of the engine, the distributor 172 is driven from the engine to produce the ignition pulse signal. This ignition pulse signal is supplied through the resistor 182 to the base of the transistor 184 to cause the same to be rendered conductive. Consequently, the input voltage is supplied through the diode 192 and the resistor 194 to the capacitor 200 which commences to charge. This causes the transistor 196 to be rendered conductive for a period of the time constant of the capacitor 200, thereby rendering the transistor 208 conductive for this particular period of time. Thus, the transistor 208 is rendered conductive irrespective of the operating conditions of the starter circuit 162. However, when the distributor 172 is not operated because of the engine being stopped, the transistor 184 is rendered non-conductive. in this condition, the transistor 196 is made non-conductive after the period of the time constant of the capacitor 200 and the resistor 202 has passed so that the relay switch 212 is switched off to de-energize the actuating device 1 10 to discontinue the additional air and fuel introduction into the engine intake manifold.

While the present invention is herein shown and described in connection with a preferred embodiment, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the appended claims.

We claim:

1. In a carburetor for an internal combustion engine having an ignition circuit with an ignition switch, an air cleaner, a main mixture circuit adapted to supply an air-fuel mixture to a carburetor induction passage for high-speed and heavy load operations of the engine, an idling and slow-running mixture circuit adapted to supply an air-fuel mixture to said carburetor induction passage for idling and light load operations of the engine, a throttle valve operatively disposed in said carburetor induction passage for controlling the quantity and airfuel ratio of the mixture to be supplied to said engine, and a fuel supply reservoir which supplies fuel to said two mixture circuits, an auxiliary mixture supply control system which is operative during starting and warm-up operations of the engine to control the quantity and air-fuel ratio of an additional air-fuel mixture to be introduced into said carburetor induction passage in dependence on engine temperature to effect satisfactory starting and warm-up operations of the engine, said auxiliary fuel supply circuit leading from said fuel supply reservoir and communicating with said carburetor induction passage downstream of said throttle valve, and adapted to admit additional fuel thereinto, an auxiliary air supply circuit leading from said air cleaner and communicating with said carburetor induction passage downstream on said throttle valve and adapted to admit additional air thereinto, a needle valve element located in said auxiliary fuel supply circuit for controlling the quantity of said additional fuel to be introduced into said carburetor induction passage, an air control valve element located in said auxiliary air supply circuit for controlling the quantity of said additional air to be introduced into said carburetor induction passage, said needle valve element being operatively connected to said air control valve element and cooperating therewith, an actuating device for simultaneously moving said air control valve element and said needle valve element for thereby controlling the quantities of said additional fuel and said additional air to be introduced into said carburetor induction passage to provide an enriched air-fuel mixture, and an electronic control circuit electrically connected to said actuating means and including a source of dc. voltage supply, a first switching transistor connected to said source of dc. voltage supply and conductive when the ignition switch is switched on, a relay switch connected to said first switching transistor and closed when said first switching transistor is conductive, a thermostatic switch connected to said relay switch and closed when the engine temperature is below a first predetermined value, a second switching transistor connected to said source of dc. voltage supply and to said relay switch and conductive when said ignition switch is switched on, a third switching transistor connected to said second switching transistor through said relay switch and said thermostatic switch, said third switching transistor being also connected to said actuating device, and a thermistor connected to said second transistor for varying the base potential of said third switching transistor in dependence on the engine temperature, whereby said actuating means is energized to a varying degree to correspondingly move said air control valve element and said needle valve element to different positions to control the quantities of said additional fuel and said additional air for thereby varying the air-fuel ratio of said additional air-fuel mixture in dependence on said engine temperature.

2. In a carburetor as claimed in claim 1, wherein said electronic control circuit further includes a starter circuit and thermostatically controlled time switch connected between said starter switch and said third switching transistor, said thermostatically controlled time swtich being closed when the engine temperature is below a second predetermined value lower than said first predetermined value, whereby the base potential of said third switching transistor is increased to energize said actuating device in a degree to cause said needle valve element and said air control valve element to move to a position to provide an enriched air-fuel mixture.

3. In a carburetor as claimed in claim 2, wherein said thermostatically controlled time switch includes a bimetalic arm, a movable contact mounted on the end of said bimetallic arm, a pair of stationary contacts connected to said starter circuit and said third switching transistor respectively, and a heating coil. wound around said bimetallic arm for opening said thermostatically controlled time switch after a certain interval of time.

4. In a carburetor as claimed in claim 1, wherein said auxiliary fuel supply circuit includes a fuel passageway communicating with said fuel supply reservoir, an auxiliary fuel chamber communicating with said fuel passage, and an auxiliary fuel outlet communicating with said auxiliary fuel supply chamber and opening into said carburetor induction passage downstream of said throttle valve.

5. In a carburetor as claimed in claim 4, wherein said needle valve element has a tapered end projecting into said auxiliary fuel outlet for gradually varying the effective cross-sectional area thereof, and an elongated cylindrical section connected to said air control valve element.

6. In a carburetor as claimed in claim 1, wherein said auxiliary air supply circuit includes a first passageway leading from said air cleaner, a second passageway communicating with said carburetor induction passage downstream of said throttle valve, and an air control chamber interposed between said first and second passageway and having a flow control port communicating with said second passageway.

7. In a carburetor as claimed in claim 6, wherein said air control valve element is operatively disposed in said air control chamber for gradually varying the effective sectional area of said flow control port.

8. In a carburetor as claimed in claim 1, wherein said auxiliary mixture supply control system further comprises spring means for biasing said air control valve element and said needle valve element to a position to decrease the quantities of said additional air and fuel to be introduced into said carburetor induction passage.

9. In a carburetor as claimed in claim 1, wherein said actuating device includes a stationary core, a movable core operatively connected to said air control valve element, and a solenoid coil wound around said movable core.

Claims

1. In a carburetor for an internal combustion engine having an ignition circuit with an ignition switch, an air cleaner, a main mixture circuit adapted to supply an air-fuel mixture to a carburetor induction passage for high-speed and heavy load operations of the engine, an idling and slow-running mixture circuit adapted to supply an air-fuel mixture to said carburetor induction passage for idling and light load operations of the engine, a throttle valve operatively disposed in said carburetor induction passage for controlling the quantity and air-fuel ratio of the mixture to be supplied to said engine, and a fuel supply reservoir which supplies fuel to said two mixture circuits, an auxiliary mixture supply control system which is operative during starting and warm-up operations of the engine to control the quantity and air-fuel ratio of an additional air-fuel mixture to be introduced into said carburetor induction passage in dependence on engine temperature to effect satisfactory starting and warm-up operations of the engine, said auxiliary fuel supply circuit leading from said fuel supply reservoir and communicating with said carburetor induction passage downstream of said throttle valve, and adapted to admit additional fuel thereinto, an auxiliary air supply circuit leading from said air cleaner and communicating with said carburetor induction passage downstream on said throttle valve and adapted to admit additional air thereinto, a needle valve element located in said auxiliary fuel supply circuit for controlling the quantity of said additional fuel to be introduced into said carburetor induction passage, an air control valve element located in said auxiliary air supply circuit for controlling the quantity of said additional air to be introduced into said carburetor induction passage, said needle valve element being operatively connected to said air control valve element and cooperating therewith, an actuating device for simultaneously moving said air control valve element and said needle valve element for thereby controlling the quantities of said additional fuel and said additional air to be introduced into said carburetor induction passage to provide an enriched air-fuel mixture, and an electronic control circuit electrically connected to said actuating means and including a source of d.c. voltage supply, a first switching transistor connected to said source of d.c. voltage supply and conductive when the ignition switch is switched on, a relay switch connected to said first switching transistor and closed when said first switching transistor is conductive, a thermostatic switch connected to said relay switch and closed when the engine temperature is below a first predetermined value, a second switching transistor connected to said source of d.c. voltage supply and to said relay switch and conductive when said ignition switch is switched on, a third switching transistor connected to said second switching transistor through said relay switch and said thermostatic switch, said third switching transistor being also connected to said actuating device, and a thermistor connected to said second transistor for varying the base potential of said third switching transistor in dependence on the engine temperature, whereby said actuating means is energized to a varying degree to correspondingly move said air control valve element and said needle valve element to different positions to control the quantities of said additional fuel and said additional air for thereby varying the air-fuel ratio of said additional air-fuel mixture in dependence on said engine temperature.

3. In a carburetor as claimed in claim 2, wherein said thermostatically controlled time switch includes a bimetalic arm, a movable contact mounted on the end of said bimetallic arm, a pair of stationary contacts connected to said starter circuit and said third switching transistor respectively, and a heating coil wound around said bimetallic arm for opening said thermostatically controlled time switch after a certain interval of time.