GB1558711A

GB1558711A - Acceleration fuel supply system

Info

Publication number: GB1558711A
Application number: GB10358/77A
Authority: GB
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1976-03-11
Filing date: 1977-03-11
Publication date: 1980-01-09
Also published as: FR2343898B1; DE2710687A1; FR2343898A1; JPS52110343A; JPS573825B2

Description

(54) AN ACCELERATION FUEL SUPPLY SYSTEM (71) We, NISSAN MOOR COMPANY LIMITED, a corporation organized under the laws of Japan, of No. 2, Takaramachi, Kanagawa-ku, Yokohama City, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : The present invention relates generally to an acceleration fuel supply system for feeding acceleration fuel into an engine during acceleration and particularly to an acceleration fuel supply system of this type which is so improved that acceleration fuel is prevented from being fed into the engine during engine operations other than acceleration, for example, during a gear ratio change of a transmission.

As is well known in the art, a carburetor is provided with an acceleration fuel supply system for increasing the amount of fuel fed from the carburetor to an internal combustion engine during acceleration. The acceleration fuel supply system usually comprises an acceleration fuel pump interlocked with a throttle valve of the engine and operated to feed acceleration fuel into an intake passageway of the carburetor when the degree of opening of the throttle valve is increased.

However, since the acceleration fuel pump is interlocked with the throttle valve, a conventional acceleration fuel supply system has fed acceleration fuel to the intake passageway even during engine operations such as, for example, during a gear ratio change of a transmission other than acceleration.This is because the gear ratio change of the transmission is made by temporarily releasing an accelerator pedal and then by again depressing the accelerator pedal so that the acceleration fuel pump is operated to unnecessarily feed acceleration fuel as if it were during acceleration The acceleration fuel thus excessivelv fed has abruptly increased the amount of burnable components such as hvdrocarbons (HC) and carbon monoxide (CO) produced by -com- bustion in the engine and has increased the fuel consumption of the engine, by unnecessarily reducing the air-fuel ratio of an engine air-ruel mixture formed by the carburetor.

Tt is, therefore, an object of the invention to provide an acceleration fuel supply system which is improved to reduce the amount of acceleration fuel fed into an engine intake passageway by an acceleration fuel pump, for example, to zero so as to reduce the content of burnable components contained in exhaust gas from an engine and the fuel consumption of the engine when it is unnecessary to feed acceleration fuel into the intake passageway as during a gear ratio change of a transmission.

This object is accomplished by providing in inlet passage means providing communication between a fuel source and an acceleration fuel pump flow resisting means for giving a resistance to the flow of fuel drawn by the acceleration fuel pump for causing the acceleration fuel pump to be moved in a direction to effect drawing of fuel with a time delay, by exerting through a damping spring on the acceleration fuel pump the action of operating means for moving the acceleration fuel pump in a direction to effect forcing-out of fuel in response to operation of an engine throttle valve in output increasing direction, and by causing the operating means to return into its rest position in response to operation of the throttle valve into its fully closed position without having an influence upon movement of the acceleration fuel pump in the direction to effect drawing of fuel.

According to the present invention, there is provided an acceleration fuel supply system for an internal combustion engine, comprising an acceleration fuel pump movable in one direction to effect drawing of fuel and in another direction to effect forcing-out of drawn fuel, resilient means for moving the acceleration fuel pump in the one direction, inlet passage means for nro- viding communication between the acceleration fuel pump and a fuel source for-allow ing fuel to be drawn from the fuel source by the acceleration fuel pump, outlet passage means for providing communication between the acceleration fuel pump and an intake passage of the engine for conducting thereinto fuel forced out by the acceleration fuel pump, operating means for moving the acceleration fuel pump in the another direction in response to operation of a throttle valve of the engine in output increasing direction, and flow resistance means located in the inlet passage means for giving a resistance to the flow of fuel drawn by the acceleration fuel pump, whereby movement of said acceleration fuel pump in said one direction is delayed with respect to the time taken for the movement in said one direction under the absence of said flow resistance means.

The invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings in which: Fig. 1 is a graphic representation of the relationship between a gear ratio change of a transmission and the degree of opening of an engine throttle valve and time; Figs. 2 and 3 are schematic views of a first preferred embodiment of an acceleration fuel supply system according to the invention; and Fig. 4 is a graphic representation of the relationship between the diameter of an orifice provided in an inlet passage of the system shown in Figs. 2 and 3 and the returning time of a pump piston forming part of the system; Figs. 5 and 6 are schematic views of a second embodiment of an acceleration fuel supply system according to the invention: Fig. 7 is schematic views of other examples of a plunger forming part of the acceleration fuel supply system shown in Figs. 2 and a3schematic view 3; Fig. 8 is a schematic view of a passage which forms part of each of the acceleration fuel supply systems shown in Figs. 2 and 3 and Figs. 5 and 6 and is provided with a filter and an orifice; and Fig. 9 is a schematic view of a passage which is similar to that shown in Fig. 8 but is provided with a resisting member in lieu of the orifice and the filter.

Referring to Fig. 1, there is shown the relationship between a gear ratio change of a transmission and the degree of opening of a throttle valve of an engine and the time as per the introduction of the present specification. As shown in Fig. 1, during a transmission gear ratio change, shortly after the throttle valve is temporarily and instantly returned into its fully closed position, the throttle valve is abruptly opened again.

Referring to Figs. 2 and 3 of the drawings, there is shown an acceleration fuel supply system according to the invention which is combined with a carburetor for an internal combustion engine (not shown).

The carburetor 10 is shown to include a float chamber 12 having a float 14 therein, and an intake passageway 16 providing communication between the atmosphere and the engine for conducting air thereinto.

The intake passageway 16 has a venturi 18 formed therein and a throttle valve 20 rotatably mounted in the intake passageway 16 downstream of the venturi 18.

The acceleration fuel supply system, generally designated by the reference numeral 22, comprises an acceleration fuel pump 24 comprising means such as a housing or a carburetor body 26 which defines a cylinder 28 therein, and a piston 29 slidably fitted in the cylinder 28 and defining a fuel chamber 30 in the cylinder 28.

The fuel chamber 30 communicates with the float chamber 12 through a passage 31 and with the intake passageway 16 through a passage 32 and an acceleration nozzle 34 which opens into the intake passageway 16 adjacent to or just upstream of the venturi 18. The acceleration fuel pump 24 is operable in one direction to effect drawing of fuel from the float chamber 12 into the fuel chamber 30 and in another direction to effect forcing-out of fuel from the fuel chamber 30 into the intake passageway 16 during acceleration of the engine.

The acceleration pump 24 also comprises a plunger 38 operatively connected to the piston 29 through a damping spring 40 which is interposed between the piston 29 and the plunger 38 to urge same in opposite directions. The plunger 38 is formed of a hollow member such as, for example, a cylinder or conduit which is formed with a bore 42 axially extending therein as shown in Fig. 2, in this embodiment. The plunger 38 is also operatively connected to the piston 29 through a rod 44 which is fixedly secured at one end to the piston 29 and is slidably fitted at the other end in the bore 42 of the plunger 38. A return spring 46 is interposed between the piston 29 and a bottom wall 48 of the cylinder 28 to urge the piston 29 and accordingly the plunger 38 away from the bottom wall 48 or in a direction in which fuel is drawn into the fuel chamber 30. The plunger 38 is formed therethrough with an elongate aperture or slot 50 which extends axially of the plunger 38. Suitable means (not shown) such as a stop is provided for limiting the displacement of each of the piston 29 and the plunger 38 moved by the forces of the springs 40 and 46 to maintain the piston 29 and the plunger 38 at predetermined rest or dormant positions when the throttle valve 20 is in its fully closed position.

A pump lever 52 is operatively connected to the plunger 38 with play of a predetermined value provided therebetween. As is best shown in Fig. 3, the pump levcr 52 is rotatably mounted on a shaft 54 which serves as a fulcrum of the pump lever 52.

The pump lever 52 is connected at one end to the plunger 38 through a pin 56 and at the other end to a pump rod 58. The pin 56 is fixedly secured to the pump lever 52 and is slidably located or loosely fitted in the elongate aperture 50 of the plunger 38.

The pump rod 5S is connected to a throttle valve lever 60 which is securely fixed to the throttle valve 20 through a shaft 62.

The acceleration pump 24 is provided with inlet and outlet check valves 64 and 66 disposed in the passages 31 and 32, respectively. The inlet check valve 64 is opened only when the piston 29 is moved away from the bottom wall 48 for sucking in fuel from the passage 31 into the fuel chamber 30. A spring 68 is provided to urge the outlet check valve 66 into its closed position. The outlet check valve 66 is opened in opposition to the force of the spring 68 only when the piston 29 is moved toward the bottom wall 48 for discharging fuel from the passage 32 into the intake passageway 16.

The acceleration pump 24 is provided with a dash pot for preventing the piston 29 from being abruptly moved in a direction to draw fuel into the fuel chamber 30 when the throttle valve 20 is abruptly moved into its fully closed position as during a gear ratio changing operation for a transmission of a vehicle equipped with the engine. The dash pot comprises an orifice 70 formed in the passage 31 and serving as flow resistance means which gives a resistance to the flow of fuel passing to the fuel chamber 30 through the passage 31 to delay or damp the fuel drawing movement of the acceleration pump 24 and to limit the amount of fuel drawn into the acceleration pump 24. The orifice 70 may be provided in any place in the passage 31, for example, as in a downstream end thereof together with the inlet check valve 64, in lieu of in an upstream end of the passage 31 as shown in Fig. 2.The cross sectional area or diameter of the orifice 70 is decided from the relationship between time required of the pump piston 29 for returning a certain distance or stroke which time is varied in accordance with, for example, the diameter of the orifice 70 as shown in Fig. 4 and time required for completing a gear ratio change of the transmission.Although the time required for the gear ratio change is usually within the range of 0.5 to 1-0 second it is desirable that the returning time of the piston 29 is above 1 second which is two times the minimum of the range of 0 5 to 1-0 second, that is, the diameter of the orifice 70 is below 0 8 millimeter in consideration of the effect of reducing to a certain degree the emission of air pollutants such as hydrocarbons (HC) and carbon monoxide (CO). However, when the returning time of the piston 29 is above 3 second, that is, the diameter of the orifice 70 is below 02 millimeter, this has a bad influence on acceleration. As a result, it is desirable that the diameter of the orifice 70 is within the range of 02 to 0-8 millimeter.When it is desired to reduce the emission of air pollutants below half the above-mentioned degree, the returning time of the piston 29 is above 1 5 second, that is, the diameter of the orifice 70 is below 0 55 millimeter. On the other hand, when the diameter of the orifice 70 is 0'3 millimeter, the emission of air pollutants during the gear ratio change operation is equal to that in the case which the acceleration pump 24 is omitted. In this instance, for surely reducing the emission of air pollutants to such a level, it is desirable that the diameter of the orifice 70 is 0-25 millimeter. As a result, it is also desirable that the diameter of the orifice 70 is within the range of (1-25 to 0 55 millimeter.

The same effect as the orifice 70 is obtained by making the minimum effective cross sectional area of the passage 31 equal to the cross sectional area of the orifice 70, in place of providing the orifice 70. It has been discovered by an experiment that the fuel drawing movement of the acceleration pump 24 can be damped with a desirable time delay by making the cross sectional area of the orifice 70 smaller than the minimum effective cross sectional area of the passage 32 and the acceleration nozzle 34, for example, the cross sectional area of a fuel jet (no numeral) of the acceleration nozzle 34.

It is necessary for preventing acceleration fuel from being fed by the acceleration pump 24 during engine operations other than acceleration that the piston 29 is not moved downward in the drawings until the throttle valve 20 is opened from its fully closed position above a predetermined amount. For this purpose, the relationship between the slot 50 of the plunger 38 and the pin 56 of the pump level 52 is so selected that, when the plunger 38 and the pump lever 52 both are in the rest positions, the pin 56 is located adjacent to the upper end wall in the drawings of the slot 50 or engages the upper end wall, and until the throttle valve 20 is opened from its fully closed position above the predetermined amount, the pin 56 does not engage the lower end wall in the drawings of the slot 50.Alternatively, the force of each of the springs 40 and 46 may be so selected that until the throttle valve 20 is opened from its fully closed position above the predetermined amount, the piston 29 is not moved downward by the plunger 38 moved by the pump lever 52.

The elastic force of the damping spring 40 also determines the fuel forcing-out characteristics of the acceleration fuel pump 24. When the force of the spring 40 is relatively strong, the amount of fuel forced out is increased in the initial stage.

When the force of the spring 40 is relatively weak, the characteristics is such that the amount of fuel forced out is gradually increased and is subsequently gradually reduced. However, since the friction between the piston 29 and the cylinder 28 is varied in accordance with the positions, the elastic force of the spring 40 cannot be weakened below a predetermined value. Also, the gross amount of fuel forced out can not be varied by varying the force of the spring 40.

The acceleration fuel supply system 22 thus described is operated as follows: When an accelerator pedal (not shown) of the vehicle is depressed for starting and accelerating the vehicle, the throttle valve 20 is opened by being rotated counter clockwise as shown in Fig. 3 and concurrently the throttle lever 60 is rotated to move the pump rod 58 upward in the drnw- ing. The pump lever 52 is rotated clockwise in the drawing around the shaft 54 by the upward movement of the pump rod 58. When the degree of opening of the throttle valve 20 is small, the pin 56 of the pump lever 52 is spaced apart from the lower end of the elongate aperture 50 of the plunger 38 so that the plunger 38 is not moved downward by the pump lever 52.When the degree of opening of the throttle valve 20 exceeds a predetermined value, the pin 56 of the pump lever 52 engages the lower end of the slot 50 to move the plunger 38 downward and the piston 29 is moved downward to pressurize fuel in the fuel chamber 30 and to close the check valve 64 by the action of the damper spring 40 due to the downward movement of the plunger 38 and opposed by the action of the spring 46. As a result, fuel is forced out into the passage 32 to open the check valve 66 in opposition to the force of the spring 68 and is then fed through the acceleration nozzle 34 into intake air passing in the intake passageway 16. Thus, the amount of fuel fed into the engine is increased during acceleration.

When the accelerator pedal is temporarily released from a condition in which it is depressed as for a gear ratio change-of the transmission, although the pump rod 58 and the pump lever 52 are abruptly or in stantly returned into the dormant- position by the force of the spring 40 in response to the throttle valve 20 being returned into its fully closed position, the piston 29 can not be instantly returned into the rest position but is gradually returned into the rest position with a time delay in spite of the action of the return spring 46 because of the orifice 7G in the passage 31 resisting fuel being drawn from thé float chamber 12 by and into the acceleration pump 24 so that the pin 56 of the pump lever 52 is located adjacent to or engages the upper end of the slot 50 of the plunger 38.When the accelerator pedal is shortly after depressed to rotate the pump lever 52 clockwise and the pin 56 engages the lower end of the slot 50 of the plunger 38 to move same downward, the piston 29 is prevented from being moved downward by the plunger 38 so that acceleration fuel is prevented from being forced out by the acceleration fuel pump 24 into the intake passageway 16, since the piston 29 is being gradually moved into the rest position by the return spring 46 and is spaced apart from the rest position due to the resistance by the orifice 70 to the flow of fuel passing into the fuel chamber 30.

In this instance, even if the piston 29 is moved downward by the plunger 38, since a small quantity of fuel is drawn by the piston 29 into the acceleration pump 24 after the accelerator pedal has been released, only a small quantity of fuel is discharged into the intake passageway 16.

Thus, unnecessary acceleration fuel is prevented from being fed into the engine to prevent the production of engine exhaust gas containing large quantities of burnable components and an increase in fuel consumption during the gear ratio change of the transmission.

Referring to Figs. 5 and 6 of the drawings, there is shown a second preferred embodiment of an acceleration fuel supply system according to the invention. The acceleration fuel supply system, generally designated by the reference numeral 72, is characterized in that a flexible diaphragm is employed as a portion of an acceleration pump in lieu of the piston 29 shown in Fig.

2. In Fig. 5, like component elements and parts are designated by the same reference numerals as those used in Figs. 2 and 3.

The acceleration fuel supply system 72 comprises a housing 76, and a flexible diaphragm 78 defining a fuel chamber 80 in the housing 76. The fuel chamber 80 communicates with the float chamber 12, the illustration of which is omitted frori Fig. 4, through the passage~31 and with the intake passageway 16 through the pa S- sage 32 and the acceleration nozzle 34. A return spring 82 is providéd to urge the diaphragm i8 in a direction in - Which fuel is drawn into the fuel chamber 80. A pump lever 84 is rotatably mounted about a fulcrum 86 and is operatively connected at one end to the diaphragm 78 through a rod 88 and at the other end to the throttle lever 60 through a pump rod 90.A damping spring 92 is interposed between the pump lever 84 and the pump rod 90 and urges the pump lever 84 and the pump rod 90 in opposite direztions. The damping spring 92 functions so that until the throttle valve 20 is opened from its fully closed position above a predetermined amount, the pump lever 84 is prevented from being rotated to move the diaphragm 78 in a direction to effect forcing-out of fuel from the fuel chamber 80, by the pump rod 90 moved in response to the throttle valve 20 operated in output increasing direction. In this embodiment, the orifice 70 is incorporated in the inlet check valve 64 as shown in Fig. 6 so that the construction of the acceleration fuel supply system 72 is simplified.

The acceleration fuel supply system 72 thus described is operated as follows: When the throttle valve 20 is opened from its fully closed position above the predetermined amount, the diaphragm 78 is moved to increase the pressure of fuel in the fuel chamber 80 by the actions of the throttle lever 60, the pump rod 90, the damping spring 92, the pump lever 84 and the rod 88 which are opposed by the force of the return spring 82. By the increased pressure of fuel in the fuel chamber 80, the inlet check valve 64 is closed and the outlet check valve 66 is opened so that fuel is forced out into intake air passing in the intake passageway 16 through the passage 32 and the acceleration nozzle 34.

When the throttle valve 20 is returned to its fully closed position for deceleration or for stopping, although the pump lever 84 is abruptly disengaged from the diaphragm 78 is response to closing of the throttle valve 20, the diaphragm 78 is gradually moved into a rest position in which it engages the pump lever 84 by the action of the return spring 82 to reduce the pressure of fuel in the fuel chamber 80. By the reduced pressure of fuel in the fuel chamber 80, the outlet check valve 66 is closed and the inlet check valve 64 is opened so that fuel is drawn into the fuel chamber 80.

When the diaphragm 78 is moved by the action of the spring 82 in a direction to effect drawing of fuel into the fuel chamber 80, since the diaphragm 78 is gradually moved with a time lag owing to the resistance of the orifice 70 in the passage 31 to the flow of fuel drawn into the fuel chamber 80, when the throttle valve 20 is opened shortly after it is temporarily returned from an open position into its fully closed position as for a gear ratio changing operation for the transmission, the pump lever 84 is prevented from engaging the diaphragm 78 or engages the diaphragm 78 after is moved toward same a certain amount so that acceleration fuel is prevented from being fed into the intake passageway 16 or acceleration fuel fed into the intake passageway 16 is reduced.

The slot 50 of the plunger 38 can be modified to have an open end as shown in Fig. 7 (1). Alternatively, the slot 50 can be omitted as shown in Fig. 7 (2). In this instance, the pin 56 is located above the plunger 38 as shown in Fig. 7 (2).

A filter 98 can be provided in the passage 31 upstream of the orifice 70 to prevent clogging of the passages 31 and 32, as shown in Fig. 8.

A porous material 100 such as ceramics, sintered alloy, or the like can be employed as fuel flow resisting means in lieu of the orifice 70, as shown in Fig. 9.

It will be thus appreciated that the invention provides an acceleration fuel supply system improved to prevent acceleration fuel from being unnecessarily fed into an engine or to reduce the amount of acceleration fuel fed into the engine when a throttle valve is opened shortly after it is temporarily closed as during a gear ratio change of a transmission so that the production of burnable components by the engine is prevented from being temporarily and abruptly increased and the fuel consumption in the engine is reduced.

WHAT WE CLAIM IS:- 1. An acceleration fuel supply system for an internal combustion engine, comprising an acceleration fuel pump movable in one direction to effect drawing of fuel and in another direction to effect forcing-out of drawn fuel, resilient means for moving said acceleration fuel pump in said one direction, inlet passage means for providing communication between said acceleration fuel pump and a fuel source for allowing fuel to be drawn from said fuel source by said acceleration fuel pump, outlet passage means for providing communication between said acceleration fuel pump and an intake passageway of the engine for conducting thereinto fuel forced out by said acceleration fuel pump, operating means for moving said acceleration fuel pump in said another direction in response to operation of a throttle-valve of the engine in output increasing direction, and flow resistance means located in said inlet passage means for giving a resistance to the flow of fuel drawn by said acceleration

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. lever 84 is rotatably mounted about a fulcrum 86 and is operatively connected at one end to the diaphragm 78 through a rod 88 and at the other end to the throttle lever 60 through a pump rod 90. A damping spring 92 is interposed between the pump lever 84 and the pump rod 90 and urges the pump lever 84 and the pump rod 90 in opposite direztions. The damping spring 92 functions so that until the throttle valve 20 is opened from its fully closed position above a predetermined amount, the pump lever 84 is prevented from being rotated to move the diaphragm 78 in a direction to effect forcing-out of fuel from the fuel chamber 80, by the pump rod 90 moved in response to the throttle valve 20 operated in output increasing direction.In this embodiment, the orifice 70 is incorporated in the inlet check valve 64 as shown in Fig. 6 so that the construction of the acceleration fuel supply system 72 is simplified. The acceleration fuel supply system 72 thus described is operated as follows: When the throttle valve 20 is opened from its fully closed position above the predetermined amount, the diaphragm 78 is moved to increase the pressure of fuel in the fuel chamber 80 by the actions of the throttle lever 60, the pump rod 90, the damping spring 92, the pump lever 84 and the rod 88 which are opposed by the force of the return spring 82. By the increased pressure of fuel in the fuel chamber 80, the inlet check valve 64 is closed and the outlet check valve 66 is opened so that fuel is forced out into intake air passing in the intake passageway 16 through the passage 32 and the acceleration nozzle 34. When the throttle valve 20 is returned to its fully closed position for deceleration or for stopping, although the pump lever 84 is abruptly disengaged from the diaphragm 78 is response to closing of the throttle valve 20, the diaphragm 78 is gradually moved into a rest position in which it engages the pump lever 84 by the action of the return spring 82 to reduce the pressure of fuel in the fuel chamber 80. By the reduced pressure of fuel in the fuel chamber 80, the outlet check valve 66 is closed and the inlet check valve 64 is opened so that fuel is drawn into the fuel chamber 80. When the diaphragm 78 is moved by the action of the spring 82 in a direction to effect drawing of fuel into the fuel chamber 80, since the diaphragm 78 is gradually moved with a time lag owing to the resistance of the orifice 70 in the passage 31 to the flow of fuel drawn into the fuel chamber 80, when the throttle valve 20 is opened shortly after it is temporarily returned from an open position into its fully closed position as for a gear ratio changing operation for the transmission, the pump lever 84 is prevented from engaging the diaphragm 78 or engages the diaphragm 78 after is moved toward same a certain amount so that acceleration fuel is prevented from being fed into the intake passageway 16 or acceleration fuel fed into the intake passageway 16 is reduced. The slot 50 of the plunger 38 can be modified to have an open end as shown in Fig. 7 (1). Alternatively, the slot 50 can be omitted as shown in Fig. 7 (2). In this instance, the pin 56 is located above the plunger 38 as shown in Fig. 7 (2). A filter 98 can be provided in the passage 31 upstream of the orifice 70 to prevent clogging of the passages 31 and 32, as shown in Fig. 8. A porous material 100 such as ceramics, sintered alloy, or the like can be employed as fuel flow resisting means in lieu of the orifice 70, as shown in Fig. 9. It will be thus appreciated that the invention provides an acceleration fuel supply system improved to prevent acceleration fuel from being unnecessarily fed into an engine or to reduce the amount of acceleration fuel fed into the engine when a throttle valve is opened shortly after it is temporarily closed as during a gear ratio change of a transmission so that the production of burnable components by the engine is prevented from being temporarily and abruptly increased and the fuel consumption in the engine is reduced. WHAT WE CLAIM IS:-

1. An acceleration fuel supply system for an internal combustion engine, comprising an acceleration fuel pump movable in one direction to effect drawing of fuel and in another direction to effect forcing-out of drawn fuel, resilient means for moving said acceleration fuel pump in said one direction, inlet passage means for providing communication between said acceleration fuel pump and a fuel source for allowing fuel to be drawn from said fuel source by said acceleration fuel pump, outlet passage means for providing communication between said acceleration fuel pump and an intake passageway of the engine for conducting thereinto fuel forced out by said acceleration fuel pump, operating means for moving said acceleration fuel pump in said another direction in response to operation of a throttle-valve of the engine in output increasing direction, and flow resistance means located in said inlet passage means for giving a resistance to the flow of fuel drawn by said acceleration

fuel pump, whereby movement of said acceleration fuel pump in said one direction is delayed with respect to the time taken for the movement in said one direction under the absence of said flow resistance means.

2. An acceleration fuel supply system as claimed in Claim 1, in which said flow resistance means comprises an orifice formed in said inlet passage means.

3. An acceleration fuel supply system as claimed in Claim 1, in which said opera.

ting means comprises a pump lever rotatably mounted on a fulcrum and having a pin movable in first and second directions in response to operations of said throttle valve in output reducing and increasing directions, respectively, and a plunger engaging said acceleration fuel pump movable toward same by the action of said pin moved in said second direction for moving said acceleration fuel pump in said another direction and movable away from same in response to movement of said pin in said first direction, said plunger being formed with a slot receiving therein said pin for moving said plunger toward said acceleration fuel pump by movement of said pin in said second direction.

4. An acceleration fuel supply system as claimed in Claim 3, in which said acceleration fuel pump comprises means defining a cylinder; a piston slidably fitted in said cylinder and defining therein a fuel chamber communicating with said inlet passage means; and a damping spring interposed between said plunger and said piston and urging said plunger away from said piston and said piston in said another direction.

5. An acceleration fuel supply system as claimed in Claim 1, in which said operating means comprises a pump rod movable in first and second directions in response to operations of said throttle valve in output increasing and reducing directions, respectively, and a pump lever which is rotatably mounted on a fulcrum and engages said acceleration fuel pump for moving same in said another direction in response to movement of said pump rod in said first direction and disengages from said acceleration fuel pump in response to movement of said pump rod in said second direction.

6. An acceleration fuel supply system as claimed in Claim 5, in which said acceleration fuel pump comprises a housing, and a flexible diaphragm engaged and disengaged by said pump lever and defining in said housing a fuel chamber communicating with said inlet passage means.

7. An acceleration fuel supply system as claimed in Claim 2, in which said orifice has a cross sectional area smaller than the minimum cross sectional area or said oLlt- let passage means.

8. An acceleration fuel supply system as claimed in Claim 2, in which said orifice has a minimum effective diameter which is within the range of 0-2 to 0 8 millimeter.

9. An acceleration fuel supply system in combination with a carburetor for an internal combustion engine, said carburetor including a fuel source, an intake passageway for providing communication between the atmosphere and the engine, and a throttle valve rotatably mounted in the intake passageway, said acceleration fuel supply system comprising an acceleration fuel pump movable in one direction to effect drawing of fuel and in another direction to effect forcing-out of drawn fuel, resilient means for moving said acceleration fuel pump in said one direction, inlet passage means providing communication between the fuel source and said acceleration fuel pump for allowing fuel to be drawn from the fuel source by the acceleration fuel pump, outlet passage means providing communication between said acceleration fuel pump and the intake passageway for conducting thereinto fuel forced out by said acceleration fuel pump, operating means operatively connected to the throttle valve for moving said acceleration fuel pump in said another direction in response to operation of the throttle valve in output increasing direction, and flow resisting means located in said inlet passage means for giving a resistance to the flow of fuel drawn by said acceleration fuel pump, whereby movement of said acceleration fuel pump in said one direction is delayed with respect to the time taken for the movement in said one direction under the absence of said flow resistance means.

10. An acceleration fuel supply system as claimed in Claim 9, in which said operating means comprises a pump lever connected to the throttle valve and rotatably mounted on a fulcrum and having a pin movable in first and second directions in response to operations of the throttle valve in output reducing and increasing directions, respectively, and a plunger engaging said acceleration fuel pump movable toward same by the action of said pin moved in said second direction for moving said acceleration fuel pump in said another direction and movable away from same in response to movement of said pin in said first direction, said plunger being formed with a slot receiving therein said pin for moving said plunger toward said acceleration fuel pump by movement of said pin in said second direction.

11. An acceleration fuel supply system as claimed in Claim 9 in which said operating means comprises a pump rod connected to the throttle valve and movable in first and second dil ee-- tions in response to operations of the throttle valve in output increasing and reducing directions, respectively, and a pump lever which is rotatably mounted on a fulcrum and engages said acceleration fuel pump for moving same in said another direction in response to movement of said pump rod in said first direction and disengages from said acceleration fuel pump in response to movement of said pump rod in said second direction.

12. An acceleration fuel supply system as claimed in Claim 2, in which said orifice has a diameter which is within the range of 0-25 to 0 55 millimeter.

13. An acceleration fuel supply system as claimed in Claim 1, in which said fuel flow resisting means comprises a porous material.

14. An acceleration fuel supply system as claimed in Claim 1, further comprising a filter located in said inlet passage means upstream of said fuel flow resisting means for preventing loading of said inlet and outlet passage means.

15. An acceleration fuel supply system constructed and arranged substantially as described herein with reference to and as illustrated in. Figs. 2 and 3, or Figs. 5 and 6, or Fig. 7, or Fig. 8, or Fig 9 of the companying drawings.