Fuel supply for a multi-cylinder internal combustion engine

Abstract

In a multi-cylinder internal combustion engine with a single fuel injection valve provided in a manifold entrance, a fuel supply system including a primary and a secondary passage formed by partitioning the manifold entrance is disclosed wherein the portion of the secondary passage located on the outer circumferential surface of the primary passage in the joined portion of each exit of both passages is formed ring-shaped and the exits face the floor surface of a riser portion. Thus, the fuel supply system makes it possible to maintain satisfactory fuel atomizing characteristics during all driving conditions and to obtain uniform mixture distribution characteristics with respect to each engine cylinder.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a fuel supply system for a multi-cylinder internal combustion engine, and more particularly to a fuel supply system designed so as to inject a fuel into a manifold entrance. In a spark ignition-type multi-cylinder internal combustion engine, a SPI method (single point injection method) is employed wherein fuel injection is effected with a single fuel injection valve provided in a manifold entrance. The SPI method makes it possible to remarkably simplify the structure of the fuel supply system and reduce the cost thereof, in comparison with a method in which fuel injection is effected with a plurality of fuel injection valves each provided in the intake port of each cylinder, respectively.

However, the SPI method has drawbacks that it is difficult to obtain satisfactory results in a fuel atomizing characteristic and a mixture distribution characteristic.

To eliminate these drawbacks, an attempt is made to cause the fuel being injected from the fuel injection vave to collide against a diffusion plate, thereby effecting the atomization of the fuel. Another attempt is to effect high-speed fuel injection directed to the clearance between the throttle valve and the bore of the manifold in which the throttle valve is rotatably provided, thereby effecting a fuel atomization by the guideline of a high-speed current of air.

However, with these attempts, the fuel partially sticks to the passage wall surface, so that supply responsibility is apt to be lowered.

Moreover, another method is proposed which injects a fuel onto a riser floor subject to exhaust heat, in place of injecting the fuel onto the inner wall surface of the intake passage, thereby vapourizing the fuel.

However, with this method, the fuel flow has a tendency to be influenced by the amount of the intake air. As a result, according to driving conditions, it is likely that the distribution of the mixture becomes unsatisfactory.

A still further method is proposed which introduces air through a bypass passage whose inlet portion is provided around the nozzle of a fuel injection valve, while whose outlet portion is provided in the downstream side of the throttle valve, thereby effecting the fuel atomization. Although this method is effective at the time of extremely low load operation, the atomizing effect is rapidly reduced in the region of medium and high loads.

SUMMARY OF THE INVENTION

With the above in mind, an object of the present invention is to provide a fuel supply system for a multi-cylinder internal combustion engine which maintains satisfactory fuel atomizing characteristics during the all driving conditions.

Another object of the present invention is to provide a fuel supply system for a multi-cylinder internal combustion engine which makes it possible to obtain uniform mixture distribution characteristics with respect to each engine cylinder.

According to the present invention, in a multi-cylinder internal combustion engine with a single fuel injection valve provided in a manifold entrance, a fuel supply system comprises a primary and a secondary passage formed by partitioning the manifold entrance, each passage having a throttle valve rotatably mounted therein, and a fuel injection valve provided in the primary passage wherein the portion of the secondary passage located on the outer circumferential surface of the primary passage in the joining portion of each exit of both passages is formed ring-shaped and the exits face the floor surface of a riser portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more clearly understood from the accompanying description of a preferred embodiment thereof and from the accompanying drawings. Both the description and drawings, however, are not intended to limit the present invention in any way, but are given for the purposes of illustration and elucidation only. In the drawings:

FIG. 1 is an elevational and cross-sectional view illustrating a fuel supply system for a multi-cylinder internal combustion engine according to the present invention;

FIG. 2 is a cross sectional view taken along the line II--II of FIG. 1;

FIG. 3 is a side view of FIG. 1;

FIG. 4 is a side elevational view illustrating a throttle valve interrelated mechanism employed in the embodiment of the present invention; and

FIG. 5 is a graph illustrating a valve opening characteristic of a primary and a secondary throttle valve of the fuel supply system according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The embodiment of a fuel supply system according to the present invention will be described with reference to accompanying drawings.

FIG. 1 shows a manifold in general comprising a manifold entrance 1, a riser portion 2 disposed perpendicularly to the manifold entrance 1, an exhaust passage 4 provided so as to come in contact with a floor surface of the riser portion 2, and a plurality of branch passages 40a, 40b, . . . each extending through the outside of the riser portion 2 and communicating with each cylinder (not shown), respectively.

As seen from FIG. 2, the manifold entrance 1 comprises a throttle chamber 7 in which two throttle vaves 6a and 6b are provided, and an injection chamber 9 in which a fuel injection valve 8 is provided, which will be described later in more detail. A primary passage 10 and a secondary passage 11 are formed by partitioning a passage consisting of both chambers 7 and 9. The throttle valves 6a and 6b are disposed at the respective entrances 10a and 11a of the passages 10 and 11, respectively.

On the other hand, at the exit portions 10b and 11b, the passages 10 and 11 are formed ring-shaped wherein the secondary passage 11 is concentrically disposed with respect to the outer circumference of the primary passage 10.

It is here noted that the primary passage 10 has a cross-sectional area of the passage sufficient to obtain a predetermined air flow mostly in the region of a low load condition. The secondary passage 11 also has a cross sectional area of the passage sufficient to obtain a predetermined air flow in the region of medium and high loads.

With respect to the primary throttle valve 6a and the secondary throttle valve 6b, it is necessary to present a throttle opening characteristic as shown in FIG. 5.

For this purpose, a lever 13 of the throttle valve 6a and a lever 14 of the throttle valve 6b are associated as shown in FIG. 4, so as to enable a combined operation via a pin 16 and a slot 17. As long as the locus of the pin 16 becomes approximately coincident with the curved central axis of the slot 17, the opening of the throttle valve 6b is small in comparison with that of the throttle valve 6a. When the opening of the throttle valve 6a exceeds, for instance, about 60.degree., the throttle valve 6b is rapidly opened.

Therefore, a relatively small but constant amount of air is introduced into the primary passage 10 from a low load to a high load condition, while a large amount of air is introduced into the secondary passage 11 mainly in the region of medium and high loads.

The exit portion 10b of the primary passage 10 is formed with a venturi 19 as is best shown in FIG. 1, thereby squeezing air flow to step up air flow velocity. The injection nozzle 8 of the fuel injection valve 8 is disposed so that it is directed to the central passage of the venturi 19.

Thus, fuel injection in the direction of the corrugated radiation plate 3 of the riser portion 2 through a venturi throat 19a is made possible.

A flow regulating plate 22 for eliminating the directionability of the primary air flow is provided outside the injection nozzle portion 8a. Also, in order to eliminate the directionability of the secondary air flow, another flow regulating plate 23 is provided at the exit 11b of the secondary passage 11. Thus, these flow regulating plates make it possible to increase the uniformity of the distribution of the mixture with respect to each cylinder.

The fuel which is regulated by a pressure regulator 24 is supplied into the fuel injection valve 8 through a passage 25.

The pressure regulator 24 controls the pressure of the fuel injection so as keep a differential pressure constant between intake vacuum pressure downstream of the throttle valve and the fuel supply pressure.

An air regulator 26 is provided so as to bypass air through the throttle valve 6a of the primary passage 10 and then introduce it upstream of the injection nozzle portion 8a.

The air regulator 26 is provided with a thermo-responsive valve 28 for opening or closing a bypass passage 27, thereby making it possible to open the passage 27 in response to the temperature while the engine is cooling. After a predetermined time passes from the starting of the engine, the air regulator 26 becomes operative to automatically close the passage 27 by responding to the heat by means of, for example, a heater (not shown) assembled therein.

In order to constantly maintain a predetermined air flow at the time of idling, there is provided an idle air guide passage 29 communicating with the upstream side of the valve 28 provided in the bypass passage 27. The passage 29 is provided at the throat portion 19a of the venturi 19 with a plurality of branch openings 30 radially disposed therein.

Thus, it is possible to promote the fuel atomization at the time of idling.

Reference is now made to the operation of the fuel supply system according to the present invention.

When the engine is under a low load condition, that is, the opening of the throttle valve 6a is, for example, less than 30.degree., the opening of the secondary throttle valve 6a is extremely small. Accordingly, air being introduced into the engine passes mostly through the primary passage 10.

The primary air flow has the maximum value in flow speed when passing through the venturi portion 19, and is conducted so as to collide against the corrugated radiation plate 3 of the riser portion 2.

The fuel is injected from the injection nozzle portion 8a of the fuel injection valve 8 in the same direction as the high speed air flow. Accordingly, the fuel is atomized by the high speed air flow and is subject to the heat from the corrugated radiation plate 3, so that fuel evaportion will be effectively promoted. The flow regulating plate 22 prevents the air flow from being partially scattered with respect to the branch passages 40a and 40b communicating with each cylinder, whereby the distribution of the mixture is uniformly effected.

It is to be noted that, even in the region of low-load condition, there is a slight amount of air passing through the secondary passage 11. Therefore, the secondary air flows around the exit of the primary passage 10 perpendicularly projected, thereby moderately preventing the fuel from being attached to the inner wall surface of the passage.

It should be noted that there is an extremely small amount of air flow, such as, for example, in an idling condition even in the region of a low load. In such a case, in comparison with air fuel flowing from the upstream side of the injection nozzle portion 8a, air flow being supplied from the idle air guide passage 29 communicating with the venturi 19 is more than that flowing from the upstream side of the injection nozzle portion 8a. As a result, although the overall air flow is little, it is possible to maintain the atomizing characteristic satisfactory owing to the colliding against the air flow being supplied through the passage 29.

For instance, at the starting time when the engine is cooling, the air necessary for effecting idling operation of the engine is introduced into the primary passage 10. Accordingly, fuel atomization is effectively promoted at the time of not only the idling operation, but also warming-up driving, thereby making it possible to maintain stabilization at the time of the idling operation and reducing the warming-up time.

On the other hand, in the region of medium and high loads on the engine, the ratio of the intake air flow being supplied through the secondary throttle valve 6b in addition to the air flow being supplied through the primary throttle valve 6a gradually increases. Air being supplied from the secondary passage 11 and air being supplied from the primary passage 10 are joined together at their respective exits 10b and 11b. This secondary air flow forms an annular-shaped high speed air layer around the venturi portion 19 in which the primary air flows. As a result, the injection fuel riding on the primary air flow is guided by the annular-shaped high speed air layer in such a manner so as not to become attached to the inner wall of the secondary passage 11 and is effectively atomized, thereby maintaining satisfactory fuel atomization efficiency even in the region of medium and high loads.

Furthermore, in the region of medium and high loads, almost all of the air is conducted into the secondary passage 11 having the cross sectional area of the passage sufficiently larger than that of the primary passage 10, thereby increasing the amount of the mixture with good response during acceleration, without increasing intake passage resistance.

The fuel supply system according to the present invention makes it possible to atomize the fuel in such a manner so as to allow the fuel to ride on a high speed air flow from the region of a low load to that of a high load condition. Further, the fuel supply device according to the present invention is constituted so as to reduce the amount of the fuel attached to the inner wall surface of the passage and so as not to present a specified direction of an air flow mixture. Accordingly, although fuel injection is effected with the SPI method, a very excellent atomizing characteristic and mixture distribution characteristic are obtained.

Furthermore, the fuel supply device according to the present invention also makes it possible to remarkably improve the acceleration responsiveness and exhaust performance.

It is to be understood that modifications and variations of the embodiments of the invention disclosed herein may be resorted to without departing from the spirit of the invention and the scope of the appended claims.

Claims

1. A method for supplying a fuel to a single point fuel injected internal combustion engine comprising:

producing a primary air flow in an air intake manifold;

injecting fuel directly into the primary air flow in a direction substantially parallel to said primary air flow at the point of injection for atomization therein;

producing an auxiliary air flow substantially parallel to said primary air flow around said primary air flow in the vicinity where the fuel injection is effected;

guiding said primary air flow and injected fuel by said auxiliary air flow towards a riser portion of said air intake manifold for evaporating the injected fuel and for creating a uniform air/fuel mixture, said riser portion having a floor surface in contact with an exhaust passage; and

adjusting the auxiliary air flow corresponding to the load condition on the engine for increasing said auxiliary air flow under substantially high load condition.

2. A method for supplying fuel to a single point injection internal combustion engine comprising:

producing an adjustable primary air flow through an intake manifold;

creating an air/fuel mixture by injecting fuel directly into and substantially parallel to the general direction of flow of said primary air flow at the point of injection and in synchronism with engine revolution;

producing an auxiliary air flow which is coaxial with at least a portion of the primary air flow and which flows around the primary air flow;

guiding said air/fuel mixture with said auxiliary coaxial air flow to minimize any tendency of the fuel to attach to inner wall surface of the intake manifold; and

adjusting the ratio of primary to auxiliary air flow so that the amount of auxiliary air flow is substantially smaller than the amount of the primary air flow when the amount of primary air flow is smaller than a predetermined value and so that the amount of auxiliary air flow is rapidly increased when the amount of primary air flow becomes greater than the predetermined value.

3. A method as set forth in claim 2, wherein the primary and auxiliary air flow are directed toward a riser portion provided within the intake manifold.

4. A method as set forth in claim 1 or 2, wherein the auxiliary air flow flows along an internal periphery of the intake manifold.

5. A method as set forth in claim 4, wherein the adjustment of the auxiliary air flow is effected cooperatively with the adjustment of the primary air flow by means of a common adjustment mechanism.