US3774582A

US3774582A - Idling speed control system for an automotive gasoline powered internal combustion engine

Info

Publication number: US3774582A
Application number: US00305041A
Authority: US
Inventors: K Masaki; H Maruoka
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1971-11-25
Filing date: 1972-11-09
Publication date: 1973-11-27
Anticipated expiration: 1990-11-27
Also published as: DE2257339C2; AU4865372A; FR2163031A5; DE2257339A1; CA959726A; GB1364154A; JPS4858224A; JPS506903B2

Abstract

An idling speed control system for an automotive gasoline powered internal combustion engine which system is adapted to vary the opening condition of a carburetor throttle valve in dependence on the variations in the atmospheric pressure. The idling speed control system includes a throttle opening device which is actuated by intake manifold vacuum for opening slightly the carburetor throttle valve during idling operation of the engine, a solenoid control valve for controlling the supply of intake manifold vacuum to the throttle opening device, and a vacuum level control device which is associated with the solenoid control valve and which is arranged to increase the level of the intake manifold vacuum supplied to the throttle opening device when the atmospheric pressure decreases below a predetermined level whereby the carburetor throttle valve is opened slightly more to provide the engine with an air-fuel mixture of proper air-fuel ratio.

Description

United States Patent 11 1 Masaki et al.

[ Nov. 27, 1973 Filed: Nov. 9, 1972 Appl. No.: 305,041

Foreign Application Priority Data Nov. 25, 1971 Japan 46/94677 US. Cl. 123/103 R, 123/119 R, 123/108, 261/65 R, 261/39 R Int. Cl. F02d 9/00 Field of Search 123/119 R, 103 R, 123/108, 117 A; 261/65 R, 39 R References Cited UNITED STATES PATENTS 3/1973 Shioya et al. 123/103 R 2/1944 Wunsch 123/119R 2,319,595 5 1943 Good 123/119 R Primary ExaminerLaurence M. Goodridge Assistant Examiner-Dennis Toth Attorney-John Lezdey et al.

[5 7] ABSTRACT An idling speed control system for an automotive gasoline powered internal combustion engine which system is adapted to vary the opening condition of a carburetor throttle valve in dependence on the variations in the atmospheric pressure. The idling speed control system includes a throttle opening device which is actuated by intake manifold vacuum for opening slightly the carburetor throttle valve during idling operation of the engine, a solenoid control valve for controlling the supply of intake manifold vacuum to the throttle opening device, and a vacuum level control device which is associated the solenoid control valve and which is arranged to increase the level of the intake manifold vacuum supplied to the throttle opening device when the atmospheric pressure decreases below a predetermined level whereby the carburetor throttle valve is opened slightly more to provide the engine with an air-fuel mixture of proper air-fuel ratio.

5 Claims, 1 Drawing Figure TO INTAKE 4 2 MANIFOL /TO ATMOSPHERE Patented Nov. 27, 1973 KNOB TO INTAKE 42 TO ATMOSPHERE MANIFOLD IDLING SPEED CONTROL SYSTEM FOR AN AUTOMOTIVE GASOLINE POWERED INTERNAL COMBUSTION ENGINE This invention relates in general to idling speed control systems for internal combustion engines and, more particularly, to an idling speed control system which is adapted to maintain the idling speed at an appropriate value irrespective of the variations in atmospheric pressure.

'In an internal combustion engine, it is a common practice to have a throttle valve adjusted so that is is slightly opened during idling operation of the engine. This is advantageous in that the idling speed is constantly maintained at a proper value when an automotive vehicle is operated at an altitude near sea level. However, if the automotive vehicle is at a standstill in a mountainous area or district the attitude of which is well above the sea level, the air density decreases so that the amount of air in weight supplied to the engine is substantially reduced resulting in an air-fuel mixture of improper air-fuel ratio so that it is quite difficult to maintain the idling speed at a proper valuecausing the engine to stall. Moreover, the engine is supplied with an excessively enriched air-fuel mixture with a result that the amounts of noxious and harmful components emitted in engine exhaust gases increase to cause a serious air pollution problem. Furthermore, where a catalytic converter is mounted within the exhaust system of the automotive vehicle, the lift of most catalysts becomes quite short because the unburned compounds contained in the exhaust gases are caused to burn in the catalytic converter producing high temperaturesand frequent replacements of the catalyst are required.

It is, therefore, an object of the present invention to provide a novel idling speed control system for use in an internal combustion engine, which system is capable of maintaining the idling speed at an appropriate value irrespective of the variations in atmospheric pressure.

It is another obejct of the present invention to provide an idling speed control system for an internal combustion engine, which system is arranged to vary the opening degree of a carburetor throttle valve for idling operation of the engine in dependence on the variations in atmospheric pressure thereby to maintain th idling speed at an appropriate value.

It is another object of the present invention to provide an idling speed control system for an internal combustion engine which system is arranged to compensate for the variations in atmospheric pressure by varying the opening degree of a carburetor throttle valve for thereby providing the engine with an air-fuel mixture of a proper air-fuel ratio to provide a satisfactory engine perfonnance efficiency even when an automotive vehicle is operated in a mountainous area the altitude of which is well above sea level.

It is still another object of the present invention to gine in dependence on the variations in the atmospheric pressure.

In a preferred embodiment, the idling speed control system includes a throttle actuating lever fixed to the carburetor throttle valve for opening and closing the carburetor throttle valve during idling operation of the engine. The throttle actuating lever is moved by a throttle opening device having a plunger in abutting engagement with the throttle actuating lever. The throttle opening device includes a diaphragm housing, a diaphragm dividing the diaphragm housing into first and second chambers and connected to the plunger, and a compression spring disposed in the first chamber for biasing the diaphragm in a direction to cause the plunger to move the throttle actuating lever so as to decrease the opening degree of the carburetor throttle valve. The first chamber of the diaphragm housing is connected to a conduit through which intake manifold vacuum is supplied thereto so that thediaphragm and accordingly the plunger connected thereto are moved against the action of the compression spring in a direction to cause the throttle actuating lever to increase the opening degree of the carburetor throttle valve. The idling speed control system also includes a solenoid control valve having an inlet to which intake manifold vacuum is delivered from an intake manifold of the engine, a first outlet communicating with the conduit leading to the first chamber of the throttle opening device, and a second outlet for controlling th level of the intake manifold vacuum delivered through said conduit to the throttle opening device. The solenoid control valve includes a movable core or plunger which controls communication between the inlet and first outlet, and a solenoid coil for controlling the movements of the plunger. The solenoid coil is electrically connected to a barometric switch which is adapted to energize the solenoid coil when the atmospheric pressure is below a predetermined value. This solenoid coil is also electrically connected to an engine temperature responsive switch which serves to energize the solenoid coil of the solenoid control valve when the engine temperature is below a predetermined value in the event the barometric switch is opened when the atmospheric pressure reaches the predetermined value. With this arrangement, if the engine temperature is below the predetermined value or the atmospheric pressure is below the predetermined value during idling operation of the engine, the solenoid coil of the solenoid valve is energized to cause the plunger to move in a position to provide communication between the inlet and the first outlet so that intake manifold vacuum is delivered to the first chamber of the diaphragm housing. In this instance, the

diaphragm and accordingly the plunger are moved against the action of the compression spring to move to slightly open the carburetor throttle valve. A vacuum level control device is provided in the idling speed control system for controlling the level of the intake manifold vacuum supplied to the throttle opening device in dependence on the variations in the atmospheric pressure whereby the degree of opening of the carburetor throttle valve is properly adjusted to maintain the idling speed at an appropriate value. This control device includes a vacuum level control chamber having a control port communicating with the second outlet of the solenoid control valve and an air vent vented to the atmosphere and communicating with the control port,

and a barometric pressure compensating diaphragm assembly having a plunger connected to and movable with a flexible diaphragm responsive to the variations in the atmospheric pressure, the plunger having an end portion extending into the vacuum level control chamber for varying the effective sectional area of the control port thereby to control the level of the intake manifold vacuum to be admitted to the throttle opening device. With this construction, when the atmospheric pressure decreases below a predetermined value, the diaphragm of the barometric pressure compensating diaphragm assembly is moved to a position to cause the plunger to decrease the effective sectional area of the control port of the vacuum level control chamber. Under this circumstance, the degree of communication between the control port and the air vent is decreased so that the level of the intake manifold vacuum is increased. This increased intake manifold vacuum is supplied through the conduit to the first chamber of the throttle opening device and acts on the diaphragm thereof thereby moving the plunger to a position to cause the throttle actuating lever to open slightly more the carburetor throttle valve. Thus, the engine is supplied with an air-fuel mixture of proper air fuel mixture while the engine speed is increased so that a proper idling speed is obtained.

These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawing which shows, in a single FIGURE thereof, one preferred embodiment in accordance with the present invention.

Referring now to the single FIGURE of the drawing which represents a schematic view of one preferred embodiment of an idling'speed control system for an internal combustion engine, the reference numeral 10 designates a part of the conventional internal combustion engine arranged within the automotive vehicle. The internal combustion engine 10 has, as customary, a carburetor 12 through which an air-fuel mixture is supplied to the engine cylinder. The carburetor 12 is shown to have a venturi 14 and a mixture passage 16 leading to an intake manifold (not shown) of the engine. A choke valve 18 is provided in the mixture passage 16 upstream of the venturi 14. This choke valve 18 is fixedly mounted on a shaft 20 and rotatable therewith. A choke actuating lever 22 is also fixedly connected at its one end to the shaft 20.

The choke actuating lever 22 is connected at its other end through a link 24 to one end of a first arm member 26. The first arm member 26 is rotatably mounted on a shaft 28 fastened to a suitable part of the vehicle body (not shown), and serves to control the movement of the choke actuating lever 22. To this end, the first arm member 26 is connected at its other end to a link 30 which is connected to a choke control knob (not shown). As shown, the first arm member 26 has formed thereon a projecting lug 26a which functions in a manner as will be described-in detail.

A throttle valve 32 is provided in the mixture passage 16 for controlling the amount of suction air supplied to the engine cylinder. This throttle valve 32 is fixedly mounted on a shaft 34 which is connected to and rotated by an accelerator pedal, though not shown. One end of a throttle actuating lever 36 is also fixedly mounted on the shaft 34 for controlling the opening degree of the throttle valve 32 during idling operation of the engine. This throttle actuating lever 36 forms a part of the idling speed control system as will be discussed hereinafter in detail. As shown, the, throttle actuating lever 36 is connected through a link 38 to oneend of a second arm member 40, which is rotatably mounted on the shaft 28 at the other end thereof. The second arm member 40 is formed with a projection 40a, which, when the first arm member 26 is rotated counterclockwise to rotate the choke actuating lever 18 in the same direction thereby to close the choke valve 18, is brought into engagement with the projecting lug 260 formed on the first arm member 26 so that the second arm member 40 is caused to rotate counterclockwise to pull the link 38 thereby to rotate the throttle actuating lever 36 counterclockwise whereby the throttle valve 32 is slightly opened during idling operation of the engine.

The present invention contemplates to provide in the internal combustion engine an idling speed control system which is arranged to cooperate with the throttle actuating lever 36 for varying the opening degree of the throttle valve 32 in dependence on the variations in atmospheric pressure during idling operation of the engine so as to supply the engine with an air-fuel mixture of air-fuel ratio appropriate for maintaining the idling speed at a proper value irrespective of the variations in atmospheric pressure.

The idling speed control system, generally designated at 42, includes a throttle opening device 44 which is associated with the throttle actuating lever 36 for controlling the opening degree of the throttle valve 32 during idling operation of the engine 10. In the illustrated embodiment, the throttle opening device 44 is shown to include a plunger 46 having one end in abutting engagement with the other end of the throttle actuating lever 36 and the other end connected to a flexible diaphragm 48 and movable therewith. The diaphragm 48 is disposed within a diaphragm housing 50 and divides the diaphragm housing 50 into first and second diaphragm chambers 50a and 50b. A compression spring 52 is located within the first diaphragm chamber 50a for biasing the diaphragm 48 and accordingly the plunger 46 connected thereto to a position to cause the throttle actuating lever 36 to close the throttle valve 32. The first diaphragm chamber 504 is connected to a conduit 54 which delivers intake manifold vacuum to the first diaphragm chamber 500 to move the diaphragm 48 upwardly, as viewed in the drawing, against the force of the compression spring 52 thereby to open the throttle valve 32.

Indicated at 56 is a three-way solenoid control valve having an inlet 58 communicating through a conduit 60 with the intake manifold (not shown) of the engine and an outlet 62 communicating with the conduit 54 leading to the throttle opening device 44. The solenoid control valve 56 includes a movable core or plunger 64 which is adapted to establish and block communication between the inlet 58 and the outlet 62, and a solenoid coil 66 which, when energized, moves the'plunger 64 downwardly of the drawing thereby providing communication between the inlet 58 and the outlet 62. The solenoid control valve 56 is further provided with an additional outlet 68 which is utilizedfor varying the level of the intake manifold vacuum supplied to the throttle opening device 44 in a manner to be described hereinafter in detail.

The additional outlet 68 formed in the solenoid control valve 56 is connected through a conduit 70 to a vacuum level control device 72 which is adapted to control the level of the intake manifold vacuum delivered to the first chamber 50a of the diaphragm housing 50 in dependence on the variations in atmospheric pressure so that the opening condition of the throttle valve 32 is modified to provide the engine with an airfuel mixture of proper air-fuel ratio. To this end, the vacuum level control device includes a vacuum level control chamber 74 and a barometric pressure compensating diaphragm assembly 76. The vacuum level control chamber 74 has a control port 78 which communicates with the conduit 70 and an air vent 80 vented to the atmosphere. The barometric pressure compensating diaphragm assembly 76 includes a diaphragm housing 82 having first and second chambers 82a and 82b divided by a flexible diaphragm 84. The first chamber 82a has an air vent 86 vented to the atmosphere so that the atmospheric pressure is admitted to the first chamber 820. The second chamber 82b is filled with air or other suitable gas 88 of 760 mmHg at sea level. The barometric pressure compensating diaphragm assembly 76 further includes a control plunger 90 which is fixedly connected to the diaphragm 84 and movable therewith and which has an end portion extending into the vacuum level control chamber 74 to control the effective sectional area of the control port 78, and a compression spring 92 which biases the diaphragm 84 in a direction to cause the control plunger 90 to increase the effective sectional area of the control port 78. It will thus be understood that the diaphragm 84 is movable by a pressure difierence thereacross and that, when the atmospheric pressure prevailing in the first chamber 82a is decreased in mountainous areas, the diaphragm 84 is moved leftwardly of the drawing against the force of the compression spring 92 to cause the plunger 90 to decrease the effective sectional area of the control port 78 for increasing the level of the intake manifold vacuum supplied to the first chamber 50a of the diaphragm housing 50 whereby the diaphragm 48 and accordingly the plunger 46 are moved further upwardly, as viewed in the drawing, thereby rotating the throttle actuating lever 36 counterclockwise to further increase the opening degree of the throttle I valve 32 for increasing the idling speed.

The solenoid control valve 56 is controlled by an electric circuit, which is generally designated by the reference numeral 94. The electric circuit 94 is shown to include a dc. voltage source or battery 96 which is electrically connected to an ignition switch 98, which in turn is electrically connected to a point 100. The point 100 is electrically connected to one terminal of the solenoid coil 66 of the solenoid control valve 56 and also electrically connected to an ignition coil 102. The ignition coil 102 is electrically connected at its primary coil side 1020 to a distributor 104. r

The distributor 104 has an advancing breaker contact assembly 106 and a retarding breaker contact assembly 108. The advancing breaker contact assembly 106 includes a breaker cam 110, a stationary contact point 112 connected to the ground, and a movable contact point 114 carried on a movable contact arm 116. The movable contact arm 1 16 is electrically connected to the primary coil side 102a of the ignition coil 102 and also connected to a condenser 118 having one end grounded. Likewise, the retarding breaker contact assembly 108 includes a breakercam 120, a stationary contact point 122 connected to the ground, and a movable contact point 124 carried on a movable contact arm 126. The movable contact arm 126 is electrically connected to a condenser 128 having one end grounded. This movable contact arm 126 is also electrically connected to the primary coil side 102a of the ignition coil 102 through a timer relay 130.

The timer relay 130 may be of any suitable known construction and in the illustrated embodiment comprises two stationary contacts 132, one of the stationary contacts being electrically connected to the primary coil side 102a of the ignition coil 102 whereas the other contact is electrically connected to the retarding breaker contact assembly 108, a movable contact 134 and a solenoid 136 which, when energized, closes the timer relay 130. The solenoid 136 of the timer relay 130 has one terminal electrically connected to an engine temperature responsive switch 138 and the other end electrically connected to an idling switch 140.

The engine temperature responsive switch 138 may be of any conventional construction and, in the illustrated embodiment, comprises two stationary contacts 138a and a movable contact 138b, one of the stationary contacts being electrically connected to the solenoid 136 of the timer relay 130 and the other being grounded. The movable contact l38b is arranged to close the stationary contacts 138a when the engine temperature represented by such as the temperature of the coolant in the water jacket (not shown) formed in the engine body is low.

The idling switch 140 may be of any known construction as long as it closes when the accelerator pedal is released and opens upon depression of the accelerator pedal. This idling switch 140 is electrically connected when the engine temperature increases and the switch 138 is opened so that the solenoid coil 66 is energized to retract the plunger 64 to provide communication between the inlet 58 and the outlet 62 for thereby supplying intake manifold vacuum to the throttle opening device 44 to open the throttle valve 32.

Assuming that the idling switch 140 is closed, and, in this instance, the engine temperature is low, the engine temperature switch 138 is also closed. Under this condition, the electric path for the solenoid coil 66 is completed so that the solenoid coil 66 of the solenoid control valve 56 is energized to cause the plunger 64 to be retracted for thereby providing communication between the conduit 60 and the conduit 54. At this instant, intake manifold vacuum in the conduit 60'is admitted through the conduit 54 into the first chamber 50a of the diaphragm housing 50 and, consequently, the diaphragm 48 is moved slightly upwardly of the drawing against the action of the compression spring 52 thereby moving the plunger 46 in the same direction. This causes the throttle actuating lever 36 to slightly rotate counterclockwise with a result that the throttle valve 32 is slightly opened for desired idling operation of the engine. At the same time, the timer relay 130 is closed so that'the retarding breaker contact assembly 108 is actuated to retard the ignition timing for thereby effecting faster warm-up of the engine. Retarding of the ignition timing is also reflected by the fact that combustion of the air-fuel mixture admitted into the engine cylinder is delayed to increase the temperature of the engine exhaust gases thereby to reduce the noxious and harmful compounds contained therein by the afterburning effect due to delayed combustion of the airfuel mixture.

As the engine is warmed up, the engine temperature responsive switch 138 is opened due to its inherent construction so that the timer relay 130 is opened. In this instance, the electric current flows through the ignition coil 102 to the advancing breaker contact assembly 106, which is consequently actuated to effect advancing of the ignition timing to increase performance efficiency of the engine for heavy load or acceleration operations of the engine.

If the automotive vehicle is at a standstill in a mountainous area and the atmospheric pressure is below a predetermined level, for example, the level of 600 mml-lg, then the barometric pressure in the first chamber 82a is lower than that of the second chamber 82b of the diaphragm housing 80. Under this circumstance, the diaphragm 84 is moved leftwardly to move the plunger 90 in the same. direction so that the plunger 90 decreases the effective sectional area of the control port 78 of the vacuum level control chamber 74. Accordingly, the level of intake manifold vacuum admitted into the first chamber 50a of the throttle opening device 44 is increased so that the plunger 46 cooperating with the diaphragm 48 is slightly more moved upwardly of the drawing thereby causing the throttle actuating lever 36 to open the throttle valve 32 to a suitable extent. This increased opening condition of the throttle valve is advantageous in that not only the idling speed is increased to a proper value but also the slow-running mixture circuit (not shown) is caused to function to correct the air-fuel mixture to the lean side whereby a satisfactory combustion of the air-fuel mixture is obtained.

It will now be appreciated from the foregoing description that the idling speed control system according to the present invention is capable of varying the opening degree of the carburetor throttle valve in dependence on the variations in the atmospheric pressure 4 whereby an appropriate idling speed is obtained even when the automotive vehicle is at a standstill in an mountainous area and even when the engine is cold when starting.

While only one preferred embodiment of the present invention has been illustrated and described in detail, it is to be expressly understood that the present invention is not limited thereto. Various modifications and changes may also be made in the design and arrangements of the component parts without departing from the scope of the present invention as the same now will be understood by those skilled in the art.

What is claimed is:

1. An idling speed control system for an internal combustion engine having a carburetor throttle valve, comprising, in combination, a throttle actuating lever fixedly connected to said carburetor throttle valve for opening and closing said carburetor throttle valve, a throttle opening means connected with said throttle actuating lever for varying the opening degree of said carburetorthrottle valve during idling operation of said engine in response to an intake manifold vacuum of said engine, a conduit means connected to said throttle opening means for supplying intake manifold vacuum thereto when opened for actuating said throttle opening means, a solenoid control valve means connected to said conduit means for opening said conduit means when energized, a barometric switch means electrically connected to said solenoid control valve means for energizing said solenoid control valve means when the atmospheric pressure is below a predetermined level and a vacuum level control means connected with said solenoid control valve means for controlling the level of the intake manifold vacuumto be supplied through said conduit means to said throttle opening means in dependence on the variations in the atmospheric pressure, said vacuum level control means increasing the level of the intake manifold vacuum to be admitted to said throttle opening means when the atmospheric pressure decreases, whereby said throttle opening means rotates said throttle actuating lever in a direction to increase the opening degree of said carburetor throttle valve during idling operation of said engine.

2. An idling speed control system as claim in claim 1, further comprising an engine temperature responsive means electrically connected to said solenoid control valve means, said engine temperature responsive means energizing said solenoid control valve means when the engine temperature is below a predetermined level.

3. An idling speed control system as claimed in claim 1, wherein said throttle opening means includes a diaphragm housing having first and second chambers, a diaphragm disposed in said diaphragm housing between said first and second chambers, a plunger fixedly connected to said diaphragm and movable therewith, said plunger having an end portion in abutting engagement with said throttle actuating lever, and a compression spring disposed in said first chamber for biasing sa'id diaphragm in a direction to cause said throttle actuating lever to decrease the opening degree of said carburetor throttle valve, said first chamber communicating with said conduit means and being supplied with the intake manifold vacuum, whereby said diaphragm and accordingly said plunger are moved in a direction to cause said throttle actuating lever to increase the opening degree of said carburetor throttle valve.

4. An idling speed control system as claimed in claim 1, wherein said solenoid control valve means includes an inlet to which intake manifold vacuum is supplied, a first outlet communicating with said conduit means, a second outlet for controlling the level of the intake manifold vacuum delivered to said conduit means through said first outlet, a movable core for providing communication between said inlet and said first outlet, and a solenoid coil for moving said movable core to provide communication between said inlet and said first outlet when energized.

5. An idling speed control system as claimed in claim 1, wherein said vacuum level control means includes a vacuum level control chamber having a control port communicating with said second outlet of said solenoid control valve means and an air vent vented to the atmosphere and a barometric pressure compensating diaphragm assembly having means responsive to variations in the atmospheric pressure, said means of said barometric pressure compensating diaphragm assembly decreasing the effective sectional area of said control port of said vacuum level control chamber when the atmospheric pressure is below the predetermined level, whereby the level of the intake manifold vacuum supplied to said throttle opening means is increased.

a: s s a s

Claims

1. An idling speed control system for an internal combustion engine having a carburetor throttle valve, comprising, in combination, a throttle actuating lever fixedly connected to said carburetor throttle valve for opening and closing said carburetor throttle valve, a throttle opening means connected with said throttle actuating lever for varying the opening degree of said carburetor throttle valve during idling operation of said engine in response to an intake manifold vacuum of said engine, a conduit means connected to said throttle opening means for supplying intake manifold vacuum thereto when opened for actuating said throttle opening means, a solenoid control valve means connected to said conduit means for opening said conduit means when energized, a barometric switch means electrically connected to said solenoid control valve means for energizing said solenoid control valve means when the atmospheric pressure is below a predetermined level and a vacuum level control means connected with said solenoid control valve means for controlling the level of the intake manifold vacuum to be supplied through said conduit means to said throttle opening means in dependence on the variations in the atmospheric pressure, said vacuum level control means increasing the level of the intake manifold vacuum to be admitted to said throttle opening means when the atmospheric pressure decreases, whereby said throttle opening means rotates said throttle actuating lever in a direction to increase the opening degree of said carburetor throttle valve during idling operation of said engine.

3. An idling speed control system as claimed in claim 1, wherein said throttle opening means includes a diaphragm housing having first and second chambers, a diaphragm disposed in said diaphragm housing between said first and second chambers, a plunger fixedly connected to said diaphragm and movable therewith, said plunger having an end portion in abutting engagement with said throttle actuating lever, and a compression spring disposed in sAid first chamber for biasing said diaphragm in a direction to cause said throttle actuating lever to decrease the opening degree of said carburetor throttle valve, said first chamber communicating with said conduit means and being supplied with the intake manifold vacuum, whereby said diaphragm and accordingly said plunger are moved in a direction to cause said throttle actuating lever to increase the opening degree of said carburetor throttle valve.

5. An idling speed control system as claimed in claim 1, wherein said vacuum level control means includes a vacuum level control chamber having a control port communicating with said second outlet of said solenoid control valve means and an air vent vented to the atmosphere, and a barometric pressure compensating diaphragm assembly having means responsive to variations in the atmospheric pressure, said means of said barometric pressure compensating diaphragm assembly decreasing the effective sectional area of said control port of said vacuum level control chamber when the atmospheric pressure is below the predetermined level, whereby the level of the intake manifold vacuum supplied to said throttle opening means is increased.