GB2034823A

GB2034823A - A Constant Depression Carburetor with Increase of Air Throttle Opening and Decrease of Air Bleed at High Mixture Throttle Openings

Info

Publication number: GB2034823A
Application number: GB7937834A
Authority: GB
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1978-11-13
Filing date: 1979-11-01
Publication date: 1980-06-11
Also published as: JPS5566648A; DE2945824A1

Abstract

Actuator (3) drives the air valve (2) to open against a closing biasing force, according to the vacuum between the air venturi valve (2) and the mixture throttle valve (1), bleed air being provided via an air bleed (6), to be mixed into a supply of fuel which is being led into the intake passage, there being link (12) for effectively decreasing relatively the biasing force, at large air throttle openings, and a valve (14) for decreasing the supply of air bleed into the fuel at large throttle openings, so as to enrich the mixture in these circumstances. The arrangement may alternatively comprise solenoid valves to control the vacuum applied to chamber 3 and the air bleed flow in response to throttle position. <IMAGE>

Description

SPECIFICATION A Variable Venturi Carburetor with Increase of Venturi Opening and Decrease of Air Bleed at High Throttle Openings The present invention relates to a variable venturi carburetor, and more particularly to a variable venturi carburetor in which the effective cross-sectional area of the variable venturi is adjusted in proportion to the intake air flow rate.

Variable venturi carburetors are known, in which a variable venturi valve is provided upstream of a throttle valve. A vacuum actuator is provided, which is fed with the vacuum existing between the variable venturi valve and the throttle valve, and which opens the variable venturi valve against a closing biasing force. It is usually arranged that the value of the vacuum is maintained approximately constant, by a feedback control. Such carburetors are effective over a wide range of intake air flow rates, and are widely used. However, in order to maintain the vacuum substantially constant, the venturi valve must not be completely opened. The biasing force to the venturi valve increases in proportion to the amount of opening of the venturi valve. Thus, the variable venturi valve cannot be sufficiently opened at its wide open range.Therefore, if the throttle valve is opened wide, often reduction of torque occurs. This particularly occurs during sudden high-load acceleration of a vehicle in which the engine is mounted.

To overcome this problem, an on-off device has been proposed, which increases the supply of fuel in response to intake vacuum. However, such increase of fuel supply is performed in either fully or not at all, according to its on-off nature, and therefore a properly controlled air/fuel ratio is not obtained. Driving with such a carburetor is rather unsteady.

Therefore, it is an object of the present invention to provide a variable venturi carburetor in which this defect is overcome, and in which, when the throttle valve is opened fully or nearly fully, good intake air flow occurs. It is a further object of the present invention to ensure that in these circumstances the air/fuel ratio remains in the range which provides good operating characteristics of the engine.

According to the present invention, this and other objects are attained by, in an internal combustion engine, a variable venturi carburetor, comprising: an intake passage; a throttle valve in the intake passage; a venturi valve in the intake passage upstream of the throttle valve; a means for injecting fuel into the intake passage; an air bleed which bleeds air into the fuel injected into the intake passage by the fuel injecting means; and an actuator responsive to the vacuum between the throttle valve and the venturi valve, which is fed to it, which opens the venturi valve against a biasing force tending to close the valve, so as to maintain said vacuum substantially constant, and which simultaneously controls the flow of fuel injected by the fuel injecting means according to the degree of opening of the venturi valve; said carburetor comprising a means for effectively decreasing relatively said biasing force at large throttle openings, and means for decreasing the effective cross sectional area of the air bleed at large throttle openings.

In the accompanying drawings: Fig. 1 is a schematic front view, partly cut away, showing a variable venturi carburetor according to an embodiment of the present invention; Fig. 2 is a vertical section taken along the line A-AinFig. 1; Fig. 3 is a schematic vertical section, showing another embodiment of the present invention; Fig. 4 is a part-sectional view taken along the line B-B in Fig. 3, showing also parts at the rear of the section; Fig. 5 is a view similar to Fig. 4, showing the positions of the parts during heavy load operation of the carburetor, when the throttle valve is open wide; and Fig. 6 is a block diagram, illustrating a third embodiment of the present invention.

Referring to Figs. 1 and 2, there is shown therein a first embodiment of the present invention. In a carburetor which is not designated by any reference numeral, there is provided an intake passage which is also not designated by any reference numeral. A throttle valve 1 is provided in the intake passage, and upstream thereof in the intake passage is provided a venturi valve 2. This venturi valve 2 is opened and closed by a diaphragm 3, which acts in response to the vacuum in the intake passage between the throttle valve 1 and the venturi valve 2, in a per se well known way, in order to keep this vacuum at a substantially constant level. Further, a jet needle 5, actuated by the venturi valve 2, is inserted into a fuel nozzle 4, through which fuel is drawn by the intake vacuum into the intake passage.The effective cross-sectional area of the nozzle is increased, by moving this needle, in correspondence to the opening of the venturi, thus controlling the fuel flow in proportion to the air flow so as to obtain a constant air/fuel ratio.

Further, in order to improve atomization the fuel, an air bleed 6 is provided, which injects air into the fuel before it comes out of the nozzle 4, in order to emulsify it. This is all well known in the art.

On the outer end of a shaft 9 on which the throttle valve 1 is mounted, there is fixed a throttle lever 10. On the outer end of a shaft 11 on which the venturi valve 2 is mounted, there is rotatably mounted a power lever 12. The throttle lever 10 and one end of the power lever 12 are connected by a throttle rod 13, so as to form a link mechanism, and so that they rotate together in the same direction. Therefore, when the throttle valve 1 is opened, this power lever 12 is moved in the rotational direction which opens the venturi valve 2.

An air bleed arm 1 5 is supported intermediate its ends by a support 1 7 mounted on the carburetor body 1 6. A needle 14 is fitted at one end of the air bleed arm 1 5 is so arranged that it opens and closes the inlet of the air bleed 6. At the other end of the air bleed arm 1 5 is mounted an air bleed rod 18, which links said end with the end of the power lever remote from the rod 13, thus forming a third link mechanism. Thus, when the throttle valve 1 is opened, i.e., is moved counterclockwise in the figure, then the rod 1 3 ovens downwards, the rod 18 moves upwards, and the air bleed 6 is decreased in its cross sectional area by the needle 14.At heavy load, when the throttle valve 1 is wide open, the air bleed 6 is completely closed. Thereby, the heavier the load on the engine, and the larger the throttle opening, the richer is the mixture, by this closing of the air bleed. It is to be noted that the atomizing action of this air bleed is reduced in its importance at these high engine loads, because atomization is not a problem in, this operational region. 1 8a designates a screw for adjusting the stroke of the needle 14, and 1 8b is a damper spring which absorbs extra movement of the air bleed rod 1 8 after the needle 14 is completely seated against the air bleed 6.

Fig. 2 shows more clearly the arrangement on the valve shaft 11. A lever 21 is connected to this shaft, and, via a pin 20, is connected to the diaphragm rod 13 which leads to the diaphragm device 3. Thus, the diaphragm device 3 drives the venturi valve 2. The le''r 21 is driven in the direction to close the venturi valve 2 by means of a return spring 22 mounted between the lever 21 and the power lever 12, and which is mounted over a collar 23 which fits on the venturi valve shaft 11. That is, one end of the return spring 22 is fixed on the venturi valve lever 21 and the other end of this return.spring 22 is fixed on the power lever 12, thus energizing or biasing the venturi valve 2 in its closing direction.

When the throttle valve 1 is rotated so that it opens, therefore, the power lever 12 is rotated in the opening direction of the venturi valve 2 as stated above, so that the biasing force of the return spring 22 in the closing direction of the venturi valve 2 becomes weaker. Thus, the resistance to opening of the venturi valve 2 becomes less at high throttle opening, and thereby intake air flow resistance is decreased under high load conditions.

It should be particularly noted that in Fig. 1 the radius R of the throttle lever 10, from its pivot point to the point where it joins the rod 13, is larger than the corresponding radius r of the power lever 12. Thus, if the throttle lever 10 is rotated through, say, 800, the power lever 12 is rotated by, 900. In this case, the spring 22 is positively energized in the direction of opening the venturi valve 2. That is to say, the venturi vaiva 2 is positively driven open, so as to ensure sufficient opening thereof under heavy load. And, as herein stated, at this heavy load the air bleed 6 is completely closed, so that the mixture is sufficiently richened to provide good operating performance.This feature of positively opening the venturi valve 2 under conditions of heavy load can also be applied to the second and the third embodiments described hereinafter, although it is not explicitly so stated, Figs. 3, 4, and 5 show the essential parts of the second embodiment of the present invention. The part of the carburetor which is not shown in these figures is the same as in Fig. In these figures, numerals which are the same as corresponding numerals in Figs. 1 and 2 denote corresponding parts.

The venturi valve lever 21, which is fixed to the venturi valve shaft 11, is driven and biased in the direction of closing the venturi valve 2 by the return spring 22, which is attached between the carburetor body and a stop 24. In detail, the return spring 22 is in fact fitted over the outer surface of a cylindrical collar 25, which is fitted on the venturi valve shaft 11, and one of its ends is fixed to a spring seat 26 on the carburetor body 16, while the other end presses against the stop 24, which is attached to the lever 21, and this spring 22 is twisted in such a way that it biases the stop 24 and the lever 21 in the direction of closing the venturi valve 2.As before, the power lever 12 is rotatably fitted over the outer end of the venturi valve shaft 11, by a cylindrical guide collar 27, so as to slidably rotate on the outer surface of this collar, when the throttle valve is actuated and moves the power lever, via the rod 13. A power spring stop 28 is provided between the power lever 12 and the venturi valve lever 21 and this stop 28 is fixed to the venturi valve shaft 11. Further, provided on the shaft 11, between the power spring stop 28 and the air valve lever 21, is a cylindrical collar 29, on the outer cylindrical surface of which a power spring 30 is fitted.

One end of this power spring 30 is fixed to the venturi valve lever 21, and the other free end thereof is, under low load conditions, engaged with the power spring stop 28, as shown in Fig. 4.

At this time, therefore, this power spring has no effect on the rotation of the shaft 11. However, when the engine load increases, the power lever 12 rotates in the direction of opening the venturi valve 2, and at a certain point it picks up the free end of the power spring 30, as shown in Fig. 5, and biases this spring 30 increasingly in the direction of opening the venturi valve 2. Thereby, relatively speaking, the biasing force exerted by the return spring 22, in the direction of closing the venturi valve 2, is reduced. Therefore, as in the first embodiment, the venturi valve is opened more during high load operation of the engine, so that intake passage air flow resistance is decreased. A mechanism for regulating the opening of the air bleed 6, similar to that provided in the first embodiment, is also provided, and functions in the same way, and has the same advantages, as in that embodiment.

Fig. 6 illustrates, in a block-diagrammatical form, the third embodiment of the present invention. Parts which are not shown or designated by any reference numbers are to be understood as being similar to those in the first and/or second embodiments. The vacuum in the inlet passsage between the throttle valve 1 and the venturi valve 2 is communicated with the diaphragm device 3 through a vacuum passage, not shown in any of the drawings, which in this embodiment is branched. The branch leads to a solenoid valve 31, which selectively communicates this branch passage to atmosphere, when energized. Further, a solenoid valve 32 is provided at the inlet of the air bleed 6, and controls the air which flows therethrough.A sensor 33 is provided for detecting the degree of opening of the throttle valve 1, at the end of the throttle valve shaft 9, and the output from this sensor is fed to an electronic control unit 34. This sensor may be an analog sensor of a well known type, and.the electronic control unit 34 may be an integrated circuit also of a well known type, which comprises A/D converters, D/A converters, a microprocessor, fixed and variable stores, and so forth, in a manner which will be well known to one skilled in the art.

The electronic control unit 34, depending on the amount of opening of the throttle valve 1, outputs control signals to change the duty ratios of the solenoid valves 31 and 32. Thus, the amount of vacuum communicated to the diaphragm device 3 is increased during heavy load operation of the engine, so as to increase the amount of opening of the venturi valve. Further, the amount of air allowed to pass through the air bleed 6 is reduced during heavy load operation of the engine. This system of electronic control ensures very precise and quick operation.

Thus, in this embodiment, as in the previous one, the effective cross sectional area of the air bleed is reduced at high load operation of the engine, while the effective biasing force on the venturi valve to close it is reduced (that is, the vacuum supplied to the diaphragm mechanism is increased, thus effectively relatively reducing the biasing force of the spring 22).

Claims

1. A variable venturi carburetor, comprising: an intake passage, a throttle valve in the intake passage; a venturi valve in the intake passage upstream of the throttle valve; means for injecting fuel into the intake passage; an air bleed which bleeds air into the fuel injected into the intake passage by the fuel injecting means; and an actuator responsive to the vacuum between the throttle valve and the venturi valve, which is fed to it, which opens the venturi valve against a biasing force tending to close the valve, so as to maintain said vacuum substantially constant, and which simultaneously controls the flow of fuel injected by the fuel injecting means according to the degree of opening of the ventrui valve; said carburetor comprising: means for effectively decreasing said biasing force at large throttle opening; and means for decreasing the effective cross sectional area of the air bleed at large throttle openings.

2. A carburetor according to claim 1, further comprising a venturi valve shaft rotatable around a first axis on which the venturi valve is mounted, and a return spring wherein said increasing means comprises a link mechanism and a power lever mounted rotatably around said venturi valve shaft; whereby the link mechanism may link the throttle valve to the power lever, and, when the throttle is moved in the opening direction, move the power lever in the direction about the first axis to open the venturi valve; wherein the other end of the return spring bears on the power lever.

3. A carburetor according to claim 1, further comprising a venturi valve shaft rotatable around a first axis on which the venturi valve is mounted, and a return spring which exerts said biasing force, mounted so that one of its ends moves the venturi valve and its other end bears on the carburetor body; wherein said increasing means comprises:: a link mechanism, a power lever mounted rotatably around said venturi valve shaft, the link mechanism linking the throttle valve to the power lever, and, when the throttle is moved in the opening direction, moving the power lever in the direction about the first axis to open the venturi valve, a stop mounted fixedly on the venturi valve shaft, and an adjusting spring mounted about the venturi valve shaft with one of its ends moving the venturi valve and its other end resting against the stop when the throttle is in the closed position and the power lever is in its extreme position in the direction of closing the venturi valve, whereby the power lever, when it moves in the direction of opening the venturi valve, may pick up said end of the adjusting spring and carry it in the direction of opening the venturi valve.

4. A carburetor according to claim 2 or 3, further comprising a throttle shaft rotatable around a second axis on which the throttle valve is mounted, wherein the link mechanism comprises a throttle lever fixedly mounted on the throttle shaft and a link rod which links a point on the throttle lever to a point on the power lever, the distance from the point on the throttle lever to the second axis being longer than the distance from the point on the power lever to the first axis.

5. A carburetor according to claim 2 or 3, wherein said means for decreasing the effective cross sectional area of the air bleed at large throttle openings comprises a needle which co operates with an entry of the air bleed to form a variable orifice; an arm pivoted on the carburetor body, one end of which is attached to the needle; and a linking rod, one end of which is attached to the other end of the arm, and the other end of which is attached to the power lever.

6. A carburetor according to claim 2 or 3, wherein said increasing means decreases the biasing force so much as to reverse it, so that the venturi valve is biased in the opening direction.

7. A carburetor as in claim 1, further comprising a sensor which detects the degree of opening of the throttle, and an electronic controller which receives a signal from said sensor which is representative of said degree of opening; and wherein said increasing means comprises a first electrically controlled solenoid valve whose overall flow resistance is determined by the duty ratio of a signal which it receives from the electronic controller, and which passes a flow of atmospheric air into the vacuum fed to the actuator; and said means for decreasing the effective cross-sectional area of the air bleed at large throttle openings comprises a second electrically controlled solenoid valve whose overall flow resistance is determined by the duty ratio of a signal which it receives from the electronic controller, and which is placed in the air bleed passage.

8. A carburetor substantially as described with reference to, and as illustrated in, Figs. 1 and 2, or Figs. 3 to 5, or Fig. 6 of the accompanying drawings.